PAPER
www.rsc.org/dalton | Dalton Transactions
The d3 /d2 alkyne complexes [MX2 (g-RC∫CR)Tp¢]z (X = halide, z = 0 and 1+): final links in a d6 –d2 redox family tree† Christopher J. Adams,a Kirsty M. Anderson,a Neil G. Connelly,*a David J. Harding,a Owen D. Hayward,a A. Guy Orpen,a Elena Patr´ona and Philip H. Rieger‡b Received 6th August 2008, Accepted 22nd September 2008 First published as an Advance Article on the web 18th November 2008 DOI: 10.1039/b813642d The d4 halide complexes [MX(CO)(h-RC∫CR)Tp¢] {R = Me, M = W, X = F; R = Ph, M = Mo or W, X = F or Cl; Tp¢ = hydrotris(3,5-dimethylpyrazolyl)borate} undergo two-electron oxidation in the presence of a halide source to give the d2 monocations [MX1 X2 (h-PhC∫CPh)Tp¢]+ (R = Me, M = W, X1 = X2 = F; R = Ph, M = Mo, X1 = X2 = F or Cl; M = W, X1 = X2 = F or Cl; X1 = F, X2 = Cl). Each monocation (R = Ph) shows two reversible one-electron reductions (the second process was not detected for R = Me) corresponding to the stepwise formation of the neutral d3 and monoanionic d4 analogues, [MX1 X2 (h-PhC∫CPh)Tp¢] and [MX1 X2 (h-PhC∫CPh)Tp¢]- respectively; the potentials for the two processes can be ‘tuned’ over a range of ca. 1.0 V by varying M and X. Chemical one-electron reduction of [MX2 (h-PhC∫CPh)Tp¢]+ gave [MX2 (h-PhC∫CPh)Tp¢] (M = Mo or W, X = F or Cl). X-Ray structural studies on the redox pairs [WX2 (h-PhC∫CPh)Tp¢]z (X = F and Cl, z = 0 and 1+) show the alkyne to bisect the X–W–X angle in the d2 cations but align more closely with one M–X bond in the neutral d3 molecules, consistent with the anisotropic ESR spectra of the latter; the solution ESR spectrum of [MoF2 (h-PhC∫CPh)Tp¢] showed equivalent fluorine atoms, i.e the alkyne oscillates at room temperature. The successful isolation of [MX2 (h-PhC∫CPh)Tp¢]+ and [MX2 (h-PhC∫CPh)Tp¢] completes a series in which d6 to d2 alkyne complexes are linked in a redox family tree by sequential one-electron transfer and substitution reactions. The implications for such trees in the production of new species and the selective synthesis of paramagnetic complexes acting as synthetically useful ‘alkyne radicals’ are discussed.
Introduction The discovery of the one-electron oxidation of [Cr(CO)2 (hRC∫CR)(h6 -arene)] and the one-electron reduction of [M(CO)2 (hRC∫CR)Tp¢]+ , and the consequent structural characterisation of the redox pairs [Cr(CO)2 (h-PhC∫CPh)(h6 -C6 Me5 H)]z (z = 0, d6 and 1+, d5 )1 and [Mo(CO)2 (h-PhC∫CPh)Tp¢]z (z = 0, d5 and 1+, d4 ),2 enabled us to show that stepwise electron removal from a (formally) d6 complex converted the coordinated alkyne from a two- to a three- to a four-electron donor. Halide substitution of one carbonyl ligand of [M(CO)2 (h-RC∫CR)Tp¢]+ then gave [MX(CO)(h-RC∫CR)Tp¢] (M = Mo or W, X = halide) which was oxidised to the isolable d3 cation [MX(CO)(h-RC∫CR)Tp¢]+ , again structurally characterised (M = W, X = Cl or Br).3 As well as reversible one-electron oxidation to [WX(CO)(h-RC∫CR)Tp¢]+ , the cyclic voltammograms of the neutral tungsten complexes [WX(CO)(h-RC∫CR)Tp¢] showed a second oxidation wave, its irreversibility suggesting that the formation of the d2 dications [WX(CO)(h-RC∫CR)Tp¢]2+ was accompanied by a subsequent chemical reaction. Moreover, preliminary results4 suggested that a School of Chemistry, University of Bristol, Bristol, UK BS8 1TS. E-mail:
[email protected]; Fax: +44 117 929 0509; Tel: +44 117 928 8162 b Department of Chemistry, Brown University, Rhode Island, RI, 02912, USA † Electronic supplementary information (ESI) available: Table S1: Proton, 13 C-{1 H} and 19 F NMR spectroscopic data for 1+ –4+ and 8+ . CCDC reference numbers 697668–697677. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b813642d ‡ Deceased.
530 | Dalton Trans., 2009, 530–543
the product of the second oxidation was the d2 complex [MX2 (hRC∫CR)Tp¢]+ . This paper describes the full characterisation of [MX1 X2 (hRC∫CR)Tp¢]+ (R = Me, M = W, X1 = X2 = F; R = Ph, M = Mo, X1 = X2 = F; M = W, X1 = X2 = F or Cl; X1 = F, X2 = Cl) and the one-electron reduction to the neutral analogues [MX1 X2 (hRC∫CR)Tp¢], completing a redox family tree in which well defined d6 and d2 alkyne complexes are formally connected by a series of ligand substitution and one-electron transfer reactions.
Results and discussion Synthesis of [MX1 X2 (g-RC∫CR)Tp¢]+ (M = Mo or W, X1 X2 = F2 , FCl or Cl2 ) In order to generate [MX(CO)(h-RC∫CR)Tp¢]2+ , the product of the second one-electron oxidation of [MX(CO)(h-RC∫CR)Tp¢] (which occurs at potentials more positive than ca. 1.5 V vs. sce),3 two equivalents of a strong one-electron oxidant were required (cf. [Fe(h-C5 H4 COMe)(h-C5 H5 )]+ used in the formation of [MX(CO)(h-RC∫CR)Tp¢]+ , which occurs at 0.3–0.7 V).3 Our initial studies involved the reaction of [WI(CO)(hMeC∫CMe)Tp¢] with [NO][PF6 ] in CH2 Cl2 , resulting in the slow loss of the carbonyl band in the IR spectrum and, after purification, the isolation of a dark red crystalline product. X-Ray structural studies (see below) revealed this product to be the d2 complex [WF2 (h-MeC∫CMe)Tp¢][I3 ] 1+ [I3 ]- in which the carbonyl This journal is © The Royal Society of Chemistry 2009
and iodide ligands (subsequently forming the triiodide anion) of [WI(CO)(h-MeC∫CMe)Tp¢] had been replaced by two fluoride ions, presumably from the [PF6 ]- anion. We therefore turned our attention to the reaction of the fluoride analogues [WF(CO)(hRC∫CR)Tp¢] (R = Me or Ph) with two equivalents of [NO][BF4 ] where halide exchange would be less complicating. Accordingly, orange crystals of [WF2 (h-RC∫CR)Tp¢][BF4 ] (R = Me, 1+ [BF4 ]or Ph, 2+ [BF4 ]- ) were isolated in moderate yields from the reaction in CH2 Cl2 . In this case, the [BF4 ]- anion is the most likely source of the additional fluoride ligand as similar complexes have been obtained by the abstraction of F- from fluorinated counter anions. For example, [FeF(dppe)(h-C5 Me5 )][PF6 ] is formed in the oxidation of [Fe(dppe)(h-C5 Me5 )][PF6 ] with [Fe(h-C5 H5 )2 ][PF6 ],5 and [MoF(CNxylyl)4 (h-C5 Me5 )][BF4 ]2 results from the reaction of Ag[BF4 ] with [Mo(CNxylyl)4 (h-C5 Me5 )][BF4 ].6 A more rational synthesis of [WF2 (h-PhC∫CPh)Tp¢]+ was then developed using N-fluoropyridinium tetrafluoroborate, [Fpy][BF4 ], as both the strong oxidant and a potential source of the second fluoride ligand. Thus, treatment of [WF(CO)(hPhC∫CPh)Tp¢] with [Fpy][BF4 ] in CH2 Cl2 led to slow loss of the IR carbonyl band and formation of a red-orange solution which was filtered through Celite and then evaporated to dryness in vacuo. The residue was purified using CH2 Cl2 –n-hexane to give [WF2 (hPhC∫CPh)Tp¢][BF4 ] 2+ [BF4 ]- in good yield. The formation of the d2 cation [WF2 (h-PhC∫CPh)Tp¢]+ 2+ from [WF(CO)(h-PhC∫CPh)Tp¢] and [Fpy]+ may involve initial oneelectron transfer followed by rupture of the N–F bond in Fpy and CO substitution in [WX(CO)(h-PhC∫CPh)Tp¢]+ by a fluorine atom, or by fluoride ion substitution of the carbonyl ligand of the dication [WX(CO)(h-PhC∫CPh)Tp¢]2+ . (The possible function of [Fpy]+ as both an oxidant and a source of fluorine is reviewed in ref. 7.) Given the reversibility of the first oxidation wave of [WX(CO)(h-PhC∫CPh)Tp¢] and the irreversibility of the second, substitution in the dication seems more likely (and as might be expected because of the further weakening of the W–CO bond on second oxidation). The reaction of [WCl(CO)(h-PhC∫CPh)Tp¢] with [Fpy]+ gave the mixed halide salt [WFCl(h-PhC∫CPh)Tp¢]+ 3+ contaminated with [WF2 (h-PhC∫CPh)Tp¢]+ 2+ and separation of the two complexes was unsuccessful. However, pure red microcrystals of [WFCl(h-PhC∫CPh)Tp¢][SbCl6 ] 3+ [SbCl6 ]- were isolated from the reaction of SbCl5 (acting as oxidant and source of halide ligand) in CH2 Cl2 with [WF(CO)(h-PhC∫CPh)Tp¢]. The dichloride [WCl2 (h-PhC∫CPh)Tp¢]+ was similarly prepared from [WCl(CO)(h-PhC∫CPh)Tp¢] and 2.5 equivalents of SbCl5 in CH2 Cl2 . On adding the first equivalent of SbCl5 , the colour of the solution changed from green to brown and a new IR carbonyl band appeared at 2083 cm-1 suggesting that [WCl(CO)(hPhC∫CPh)Tp¢] is first oxidised to [WCl(CO)(h-PhC∫CPh)Tp¢]+ .3 Once the rest of the SbCl5 had been added, the carbonyl band slowly disappeared. The dark brown solution was then evaporated to dryness and the residue washed with toluene. Several purifications using CH2 Cl2 –n-hexane yielded the product [WCl2 (hPhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ]- as brown microcrystals. The reaction of [WX(CO)(h-PhC∫CPh)Tp¢] (X = F or Cl) with SbCl5 also occasionally gave small amounts of [WXCl(hPhC∫CPh)L][SbCl6 ] {L = HB(3,5-dimethylpyrazolyl)2 (3,5dimethyl-4-Cl-pyrazolyl), X = F, 5+ [SbCl6 ]- or Cl, 6+ [SbCl6 ]- } in which one pyrazolyl ring of Tp¢ is halogenated at the 4-position, This journal is © The Royal Society of Chemistry 2009
as confirmed by X-ray crystallography for 6+ (see below) and observed previously8 for other Tp¢ complexes of Mo and W. It is not known how or when ring substitution occurs to form 5+ and 6+ though it may involve electrophilic attack by Cl+ , generated from SbCl5 .9 No further reaction was observed when a solution of [WCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ]- in CH2 Cl2 was treated with SbCl5 for 18 h, and stirring the salt [WCl(CO)(hPhC∫CPh)Tp¢][BF4 ] with SbCl5 in CH2 Cl2 until no carbonyl band was present in the IR spectrum (ca. 1 day) gave only a mixture of unidentified products. Although the second one-electron oxidation wave was not observed in the CVs of the molybdenum complexes [MoX(CO)(hPhC∫CPh)Tp¢] (X = F, Cl, Br or I) (the potential was probably positive of that of the base electrolyte oxidation wave), [MoF(CO)(h-PhC∫CPh)Tp¢] was also treated with Nfluoropyridinium tetrafluoroborate in an attempt to synthesise [MoF2 (h-PhC∫CPh)Tp¢][BF4 ] 7+ [BF4 ]- . However, after stirring the reaction mixture for ca. four days only the neutral complex [MoF2 (h-PhC∫CPh)Tp¢] 7 was isolated after column chromatography. On the basis of redox potentials (see below) it is possible that the formation of the expected cation [MoF2 (h-PhC∫CPh)Tp¢]+ 7+ is followed by reduction by the pyridine by-product. (However, the complex [MoF2 (h-PhC∫CPh)Tp¢][BF4 ] 7+ [BF4 ]- was subsequently synthesised by oxidising 7 with [Fe(h-C5 H4 COMe)(h-C5 H5 )][BF4 ] in CH2 Cl2 .) In order to prepare the dichloride analogue of 7+ , [MoCl(CO)(h-PhC∫CPh)Tp¢] was treated with one equivalent of SbCl5 in CH2 Cl2 . The resulting brown solution was evaporated to dryness in vacuo and the residue dissolved in toluene. Reducing the volume of the solution gave a precipitate which was removed by filtration and then purified using CH2 Cl2 –n-hexane to give [MoCl2 (hPhC∫CPh)Tp¢][SbCl6 ] 8+ [SbCl6 ]- as brown microcrystals (which slowly decomposed in the solid state, even under nitrogen, so that an acceptable elemental analysis could not be obtained). However, evaporating the toluene filtrate to dryness, and purifying the orange residue using CH2 Cl2 –n-hexane, gave small amounts of a second species which was shown by X-ray diffraction methods (see below) to be the SbCl3 adduct [MoCl(ClSbCl3 )(h-PhC∫CPh)Tp¢] 9. Finally, attempts to synthesise the mixed halide cation [MoFCl(h-PhC∫CPh)Tp¢]+ were unsuccessful. The reaction of [MoCl(CO)(h-PhC∫CPh)Tp¢] with N-fluoropyridinium tetrafluoroborate led to a mixture of unidentified products, although one oxidation wave at 0.78 V and one reduction wave at -1.06 V suggested the presence of a small amount of the neutral complex [MoFCl(h-PhC∫CPh)Tp¢]. When [MoF(CO)(hPhC∫CPh)Tp¢] was treated with SbCl5 , the reaction gave [MoCl2 (h-PhC∫CPh)Tp¢], as indicated by cyclic voltammetry.
Characterisation of [X1 X2 (g-RC∫CR)Tp¢]+ (M = Mo or W, X1 X2 = F2 , FCl or Cl2 ) The complexes 1+ –4+ and 7+ were characterised, as [I3 ]- , [BF4 ]- or [SbCl6 ]- salts, by elemental analysis, cyclic voltammetry (Table 1) and NMR spectroscopy (see ESI†), and the structures of 1+ –4+ and 6+ were determined by X-ray crystallography (see below). The room temperature 1 H NMR spectra of [WF2 (hMeC∫CMe)Tp¢]+ 1+ and [WF2 (h-PhC∫CPh)Tp¢]+ 2+ show four Dalton Trans., 2009, 530–543 | 531
Table 1 Analytical and electrochemical data for [MX1 X2 (h-RC∫CR)Tp¢][Y] E◦ ¢ b /V
Analysis (%)a Complex
Y
M
X1
X2
R
Colour
Yield (%)
C
H
N
+10
0-1
1+ 1+ 2+ 3+ 4+ 7+ 2 4 7 8
[I3 ][BF4 ][BF4 ][SbCl6 ][SbCl6 ][BF4 ]— — — —
W W W W W Mo W W Mo Mo
F F F F Cl F F Cl F Cl
F F F Cl Cl F F Cl F Cl
Me Me Ph Ph Ph Ph Ph Ph Ph Ph
Dark red Orange Red-orange Red Dark brown Dark brown Red Pink Orange Pink
17 35 64 57 62 64 48 47 20 45
26.7 (26.5)c 34.5 (34.5) 44.5 (44.5) 32.4 (32.3)f 32.6 (32.7) 49.5 (50.0) 50.3 (50.0) 47.9 (47.7) 56.9 (57.2) 51.4 (51.5)f
3.5 (3.5) 4.3 (4.2) 4.1 (4.1) 3.0 (3.0) 3.2 (3.0) 4.7 (4.6) 4.9 (4.6) 4.2 (4.4) 5.0 (5.3) 5.3 (4.6)
8.6 (8.4) 12.4 (12.7) 10.7 (10.7) 7.3 (7.4) 7.8 (7.9) 11.6 (12.1) 12.0 (12.1) 11.9 (11.5) 13.6 (13.8) 12.3 (12.4)
d
d
-0.11 -0.04 0.18 0.39 0.55 -0.04 0.41 0.54 0.94
e
-1.61 -1.54 -1.34g -1.22h -1.61 -1.28g -1.24g -0.85
Calculated values in parentheses. b In CH2 Cl2 ; potentials relative to the saturated calomel electrode, calibrated vs. the [Fe(h-C5 H5 )2 ]+ /[Fe(h-C5 H5 )2 ] couple (at 0.47 V) unless stated otherwise. c Calculated for 2 : 1 n-hexane solvate. d Not measured. e Not detected. f Calculated for 1 : 1 CH2 Cl2 solvate. g Calibrated vs. the [Fe(h-C5 H4 COMe)2 ]+ /[Fe(h-C5 H4 COMe)2 ] couple (at 0.97 V). h Calibrated vs. the [Fe(h-C5 H4 COMe)(h-C5 H5 )]+ /[Fe(h-C5 H4 COMe)(h-C5 H5 )] couple (at 0.74 V).
a
singlets (in the ratio 2 : 1 : 1 : 2, between 1.53 and 2.51 ppm) for the six methyl groups at the 3- and 5-positions of the pyrazolyl rings, and two singlets in a 2 : 1 ratio (between 5.96 and 6.10 ppm) for the pyrazolyl protons in the 4-positions. These data are consistent with two equivalent and one inequivalent pyrazolyl rings, i.e. with a plane of symmetry bisecting the angle F–W–F, as are the 19 F NMR spectra of 1+ and 2+ , each of which shows only one signal, with tungsten satellites {J(19 F183 W) = 45 Hz}, at 178.6 and 166.5 ppm respectively, and the 13 C-{1 H} NMR spectra. Coincident 1 H signals lead to the observation of only three methyl peaks for [WCl2 (h-PhC∫CPh)Tp¢]+ 4+ and [MoCl2 (hPhC∫CPh)Tp¢]+ 8+ though their structures in solution are assumed to be similar to those of 1+ and 2. However, for the mixed halide complex [WFCl(h-PhC∫CPh)Tp¢]+ 3+ , the three pyrazolyl rings are necessarily inequivalent and six methyl and three pyrazolyl proton signals are observed. As mentioned above, the ring-chlorinated species [WFCl(hPhC∫CPh)L][SbCl6 ] 5+ [SbCl6 ]- and [WCl2 (h-PhC∫CPh)L][SbCl6 ] 6+ [SbCl6 ]- [L = HB(3,5-dimethylpyrazolyl)2 (3,5-dimethyl-4Cl-pyrazolyl)] were obtained as mixtures with [WFCl(hPhC∫CPh)Tp¢][SbCl6 ] 3+ and [WCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 4+ respectively. In the 1 H NMR spectra of the mixtures, the resonances of the two complexes overlap, complicating assignment. However, the protons at the 4-positions of the pyrazolyl rings in 5+ and 6+ appear as two 1H singlets (5.95 and 6.02 ppm) and one 2H singlet (5.98 ppm), respectively. In the latter case, the observation of only one singlet implies that the two non-chlorinated pyrazolyl rings are equivalent, suggesting that 6+ contains a symmetry plane including the inequivalent pyrazolyl ring of the Tp¢ ligand. The chlorinated pyrazolyl ring is therefore opposite the alkyne. Two sharp alkyne methyl resonances are observed for 1+ in both the 1 H NMR spectrum, at 3.34 and 4.44 ppm, and in the 13 C NMR spectrum, at 27.0 and 24.1 ppm, suggesting that there is no rotation about the metal–alkyne bond at ambient temperature. For the diphenylacetylene analogues 2+ –4+ the acetylenic carbons appear as two deshielded peaks between 217 and 262 ppm, showing that the alkynes act as four-electron donors.10 The phenyl groups of 2+ –4+ give rise to eight 13 C peaks between 129 and 139 ppm. In the 1 H NMR spectra of [WF2 (hPhC∫CPh)Tp¢]+ 2+ , [WFCl(h-PhC∫CPh)Tp¢]+ 3+ , [WCl2 (h532 | Dalton Trans., 2009, 530–543
PhC∫CPh)Tp¢]+ 4+ and [MoCl2 (h-PhC∫CPh)Tp¢]+ 8+ the phenyl groups give rise to five (2+ -4+ ) or four (8+ ) complex multiplets between 6.28 and 8.42 ppm. For 2+ the most shielded multiplet, a, at 6.64 ppm, is relatively sharp [Fig. 1(a)], whereas in 3+ and 4+ [Fig. 1(b)] it is very broad, and for 8+ it is not observed. These spectra are consistent with two inequivalent phenyl groups (and therefore no rotation about the metal–alkyne bond, as noted above), one which freely rotates around the Calk –Cipso bond, giving the three sharp multiplets at lowest field, and one which rotates relatively slowly at room temperature. This was further studied by variable temperature NMR spectroscopy, described for 4+ as a representative example.
Fig. 1 Phenyl region of the 1 H NMR spectra of (a) [WF2 (h-PhC∫CPh)Tp¢]+ 2+ and (b) [WCl2 (h-PhC∫CPh)Tp¢]+ 4+ .
At 20 ◦ C, 4+ shows five multiplets, labelled a, b, c, d and e in Fig. 2, in the ratio 2 : 3 : 1 : 2 : 2. As the temperature is lowered, signals c, d and e are unchanged so are assigned to a phenyl ring which continues to rotate. However, the two most shielded multiplets, a and b, split into two (a1 and a2 ) and three This journal is © The Royal Society of Chemistry 2009
Fig. 2
Variable temperature 1 H NMR spectra of [WCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ]- .
(b1 , b2 and b3 ) resonances. At -80 ◦ C, resonance a1 , corresponding to one ortho-proton, appears at ca 5.2 ppm, very upfield and out of the typical range for phenyl protons.11 Signal a2 , corresponding to the other ortho-proton, overlaps with signal d, at ca 8.2 ppm. Resonances b1 and b3 correspond to the phenyl protons in the meta positions. The former is centred at 7.26 ppm whereas the latter appears more deshielded and overlaps with resonance c at ca. 7.9 ppm. Finally, resonance b2 , at 7.54 ppm, remains invariant between 20 and -80 ◦ C and is assigned to the para proton. The unusual position of ortho-proton resonance a1 suggests that one phenyl ring of the diphenylacetylene is rigidly interleaved between two of the aromatic pyrazolyl rings of the Tp¢ ligand, creating a local magnetic field that would cause the observed upfield shift,10 i.e. phenyl ring b (Fig. 3) is static at low temperature whereas ring a continues to rotate. This suggestion is supported by structural studies on 2+ (see below). This journal is © The Royal Society of Chemistry 2009
Fig. 3 The cation [MX1 X2 (h-PhC∫CPh)Tp¢]+ .
Cyclic voltammetry The cyclic voltammograms (CVs) of [WF2 (h-MeC∫CMe)Tp¢][BF4 ] 1+ , [WF2 (h-PhC∫CPh)Tp¢][BF4 ] 2+ , [WXCl(h-PhC∫CPh)Tp¢][SbCl6 ] (X = F 3+ or Cl 4+ ), [MoF2 (h-PhC∫CPh)Tp¢][BF4 ] 7+ and [MoCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 8+ were recorded in CH2 Cl2 at a platinum disc electrode. Those of 2+ and 7+ show two reversible Dalton Trans., 2009, 530–543 | 533
reduction waves (Table 1), attributable to the stepwise formation of the neutral (formally d3 ) and monoanionic (d2 ) analogues (e.g. [WF2 (h-PhC∫CPh)Tp¢] 2 and [WF2 (h-PhC∫CPh)Tp¢]- 2- ), but the second reduction of the but-2-yne complex 1+ is not observed. (It is probably shifted to a potential negative of the base electrolyte curve.) The CVs of 3+ [SbCl6 ]- , 4+ [SbCl6 ]- and 8+ [SbCl6 ]- are complicated by additional waves due to the redox-active counter anion but the reduction waves of the cations have been assigned by comparison with the CVs of the neutral complexes 3, 4 and 8 (see below). In all cases, the potential for the second reduction is ca. 1.6–1.8 V more negative than the first. The reversibility of the wave for the d3 /d2 couple [MX2 (hRC∫CR)Tp¢]/[MX2 (h-RC∫CR)Tp¢]+ contrasts with the irreversible oxidation of the analogous d3 cyclopentadienyl complexes [MoCl2 (h-RC∫CR¢)(h-C5 H5 )] (R = Me, R¢ = Et or Ph; R = R¢ = Me or Ph),12 a difference also observed for the oxidation of [MX(CO)(h-RC∫CR)Tp¢] (X = halide; M = Mo or W) (reversible oxidation to isolable monocations)3 and [MX(CO)(h-RC∫CR)(hC5 H5 )] (irreversible oxidation).13 In both cases, the bulky Tp¢ ligand seems to impart additional kinetic stability to the oneelectron oxidation products. The alkyne substituent has only a small effect on potential; reduction of the but-2-yne complex [WF2 (h-MeC∫CMe)Tp¢]+ (-0.11 V) is 70 mV more negative than that of [WF2 (hPhC∫CPh)Tp¢]+ . However, for the diphenylacetylene complexes [MF2 (h-PhC∫CPh)Tp¢]+ (M = W 2+ or Mo 7+ ), [WXCl(hPhC∫CPh)Tp¢]+ (X = F 3+ or Cl 4+ ) and [MoCl2 (hPhC∫CPh)Tp¢]+ 8+ the potentials of both reduction waves depend significantly on the metal and the halide such that the potential for a given process can be ‘tuned’ over a range of ca. 1.0 V (as illustrated in Fig. 4). Thus, for example, the potentials for the reduction of [MoF2 (h-PhC∫CPh)Tp¢]+ 7+ and [MoCl2 (hPhC∫CPh)Tp¢]+ 8+ are ca. 0.3–0.6 V more positive than those of the corresponding tungsten complexes (2+ and 4+ ). In addition, the difluoride complexes are ca. 0.3–0.4 V more difficult to reduce than the corresponding dichlorides, i.e. the metal is more electron rich with the more electronegative halide. {This inverse halide order is discussed in more detail elsewhere for [MX(CO)(h-RC∫CR)Tp¢] (X = halide; M = Mo or W, R = Me or Ph).3 } It is noteworthy that the potential for the first reduction of [WFCl(h-PhC∫CPh)Tp¢]+ 3+ is the average of the corresponding potentials for the complexes
[WF2 (h-PhC∫CPh)Tp¢]+ and [WCl2 (h-PhC∫CPh)Tp¢]+ , i.e. the effects of the halide ligands appear additive. It is also noteworthy that replacement of the carbonyl ligand in [MX(CO)(h-RC∫CR)Tp¢]+ by halide, giving [MX2 (hRC∫CR)Tp¢], causes large negative shifts (in excess of 1.5 V) in the potentials associated with the (formal) d4 /d3 and d3 /d2 couples, e.g. compare d4 [WF(CO)(h-PhC∫CPh)Tp¢] {oxidation to [WF(CO)(h-PhC∫CPh)Tp¢]+ (d3 ) at 0.32 and to [WF(CO)(hPhC∫CPh)Tp¢]2+ (d2 ) at 1.50 V}3 with d2 [WF2 (h-PhC∫CPh)Tp¢]+ {reduction to [WF2 (h-PhC∫CPh)Tp¢] (d3 ) at -0.04 and to [WF2 (hPhC∫CPh)Tp¢]- (d4 ) at -1.61 V}. As described elsewhere,3 the product waves observed after the second oxidation of [WX(CO)(h-PhC∫CPh)Tp¢] (X = halide) were tentatively assigned to the formation of the stable dihalides [WX1 X2 (h-PhC∫CPh)Tp¢]+ (X1 = X2 = F or Cl; X1 = F, X2 = Cl). The potentials for the isolated d2 species are indeed identical to those observed for the product waves of [WX(CO)(hPhC∫CPh)Tp¢], shown in Fig. 5 where the CV of [WF2 (hPhC∫CPh)Tp¢]+ (from 0.40 to -1.85 V) is overlaid with the double scan CV (from -0.20 to 1.60 V) of [WF(CO)(h-PhC∫CPh)Tp¢].
Fig. 5 The CV of (a) [WF2 (h-PhC∫CPh)Tp¢]+ 2+ (from 0.40 to -1.85 V) overlaid with the double scan CV of (b) [WF(CO)(h-PhC∫CPh)Tp¢] (from -0.20 to 1.60 V).
As mentioned above, the complex [MoCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 8+ slowly decomposes in the solid state and in CH2 Cl2 , even under a nitrogen atmosphere. The cyclic voltammogram of the product then shows a new oxidation wave at 1.55 V and a reduction wave at 0.43 V, i.e. at potentials similar to those reported for [MoCl3 Tp¢].14 The decomposition pathway is unknown but when [N(PPh3 )2 ]Cl was added to a solution of the partially decomposed sample of [MoCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] in CH2 Cl2 , no appreciable changes were observed in the cyclic voltammogram. Direct chloride displacement of alkyne from 8+ therefore seems unlikely. The synthesis and electrochemistry of [MX2 (g-PhC∫CPh)Tp¢]
Fig. 4 Potentials for the two one-electron reductions of [MX1 X2 (hPhC∫CPh)Tp¢]+ (X1 = X2 = F, M = Mo 7+ or W 2+ ; X1 = X2 = Cl, M = Mo 8+ or W 4+ ; X1 = F, X2 = Cl, M = W 3+ ).
534 | Dalton Trans., 2009, 530–543
In agreement with the electrochemical studies, the cations [MX2 (hPhC∫CPh)Tp¢]+ are easily reduced to the neutral complexes [MX2 (h-PhC∫CPh)Tp¢] using mild reducing agents, e.g. [Co(hC5 H5 )2 ] (-0.86 V) or, in the case of the molybdenum complexes, even [Fe(h-C5 H5 )2 ] (0.47 V). Thus, treatment of [WF2 (hPhC∫CPh)Tp¢][BF4 ] 2+ [BF4 ]- , [WCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] This journal is © The Royal Society of Chemistry 2009
4+ [SbCl6 ]- and [MoCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 8+ [SbCl6 ]- with [Co(h-C5 H5 )2 ] (for 2+ and 4+ ) or [Fe(h-C5 H5 )2 ] (for 8+ ) in toluene gives the neutral complexes [WF2 (h-PhC∫CPh)Tp¢] 2, [WCl2 (hPhC∫CPh)Tp¢] 4 and [MoCl2 (h-PhC∫CPh)Tp¢] 8. In each case, the reaction mixture was filtered through Celite and then dried in vacuo. Purification of the residue using CH2 Cl2 –n-hexane yielded red or pink solids. A similar reaction between [WFCl(hPhC∫CPh)Tp¢][SbCl6 ] 3+ [SbCl6 ]- and [Co(h-C5 H5 )2 ] gave impure [WFCl(h-PhC∫CPh)Tp¢], partially characterised by the FAB mass spectrum (parent ion at m/z = 713) and cyclic voltammetry (oxidation and reduction waves at 0.18 and -1.54 V respectively). As mentioned above, the orange complex [MoF2 (hPhC∫CPh)Tp¢] 7 was isolated directly from the reaction between [MoF(CO)(h-PhC∫CPh)Tp¢] and N-fluoropyridinium tetrafluoroborate. Complexes 2, 4, 7 and 8 were characterised by elemental analysis, cyclic voltammetry (Table 1), ESR spectroscopy (also for 1) and X-ray crystallography. The CVs of [MF2 (h-PhC∫CPh)Tp¢] (M = W 2 or Mo 7) are the same as those of the analogous cationic complexes [MF2 (h-PhC∫CPh)Tp¢]+ except that the wave at the more positive potential is now an oxidation. As noted above, the reduction waves of the cations of the salts 3+ [SbCl6 ]- , 4+ [SbCl6 ]- and 8+ [SbCl6 ]- were partially obscured by waves due to the counter anion [SbCl6 ]- . However, an overlay (Fig. 6) of the CV of [WCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ]- with that of [WCl2 (h-PhC∫CPh)Tp¢] 4, for example, clarifies the assignment of the waves centred at 0.39 and -1.34 V to the couples
[WCl2 (h-PhC∫CPh)Tp¢]+ /[WCl2 (h-PhC∫CPh)Tp¢] and [WCl2 (hPhC∫CPh)Tp¢]/[WCl2 (h-PhC∫CPh)Tp¢]- respectively. ESR spectroscopy The ESR spectra of [WF2 (h-MeC∫CMe)Tp¢] 1 (generated in situ by the reduction of [WF2 (h-MeC∫CMe)Tp¢]+ with [Co(hC5 H5 )2 ]), [WF2 (h-PhC∫CPh)Tp¢] 2, [WCl2 (h-PhC∫CPh)Tp¢] 4, [MoF2 (h-PhC∫CPh)Tp¢] 7 and [MoCl2 (h-PhC∫CPh)Tp¢] 8 were recorded in CH2 Cl2 –thf (1 : 2) between 100 and 290 K. Data are given in Table 2. All of the isotropic spectra are centred at g values that deviate substantially from 2.0023, as expected for metal-based radicals. The values for the tungsten species vary from 1.770 to 1.819, lower than those of the molybdenum compounds 7 and 8, 1.931 and 1.958 respectively. The tungsten spectra are broad, showing no discernible coupling to the metal, but the molybdenum spectra are much sharper, with coupling to 95,97 Mo (I = 5/2, 25.5% combined natural abundance) and to two equivalent fluorine nuclei in the case of 7 (Fig. 7).
Fig. 7 The isotropic ESR spectrum of [MoF2 (h-PhC∫CPh)Tp¢] 7 at 290 K.
The anisotropic ESR spectra are rhombic, with g1 >> g2 and g3 . The low-field g1 feature is generally sharp, and for 4, 7 and 8 all three features show well resolved hyperfine coupling to the spin-active isotope(s) of the metal. In the spectra of 1, 2 (Fig. 8) and 7 (Fig. 9) splitting from the spin 1/2 fluorine nuclei is also apparent.
Fig. 6 The CV of (a) [WCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ]- (from 0.85 to -1.50 to 1.80 to 0.85 V) overlaid with (b) the CV of [WCl2 (h-PhC∫CPh)Tp¢] 4 (from -0.15 to 0.65 to -1.45 to -0.15 V). Table 2 ESR spectroscopic data for [MX2 (h-RC∫CR)Tp¢]a Isotropic parameters
Anisotropic parameters
Complex
M
X
R
giso
AM
AF
T/K
g1
g2
g3
gave
AM
AF
T/K
1
W
F
Me
1.790
—
—
298
1.952
1.752
1.714
1.806
55, —, —
—
110
2
W
F
Ph
1.770
—
—
290
1.934
1.714
1.704
1.784
50, —, —
—
4 7
W Mo
Cl F
Ph Ph
1.819 1.931
— 47
— 20b
240 290
1.974 2.010
1.760 1.897
1.741 1.896
1.825 1.934
51,100, 55 32, 72, 20
69 41
8
Mo
Cl
Ph
1.958
42.25
—
290
2.020
1.934
1.924
1.959
29, 68, 15
37
67, 50, 0 0, 50, 0 65, 90, 0 0, 55, 0 — 52, 0, 69 21, 0, 53 —
a
-4
-1
120 125 120 120
b
Recorded in CH2 Cl2 –thf (1 : 2); hyperfine coupling constants A/10 cm . 1 : 2 : 1 triplet.
This journal is © The Royal Society of Chemistry 2009
Dalton Trans., 2009, 530–543 | 535
observed doublet of doublets. If the metal orbitals contributing to the SOMO were different in each case, this might also account for the changes observed in the couplings on g2 and g3 . X-Ray structural studies
Fig. 8 The simulated (a) and experimental (b) anisotropic ESR spectrum of [WF2 (h-PhC∫CPh)Tp¢] 2 in CH2 Cl2 –thf (1 : 2) at 120 K.
In the light of the NMR and ESR spectroscopic studies of the orientation of the alkynes in [MX1 X2 (h-PhC∫CPh)Tp¢]z (z = 0 or 1+) in solution, the solid state structures of [WF2 (h-MeC∫CMe)Tp¢][I3 ] 1+ [I3 ]- , [WF2 (h-PhC∫CPh)Tp¢][BF4 ] 2+ [BF4 ]- , [WFCl(h-PhC∫CPh)Tp¢][BF4 ] 3+ [BF4 ]- , [WCl2 (hPhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ]- , [WF2 (h-PhC∫CPh)Tp¢] 2, [WCl2 (h-PhC∫CPh)Tp¢] 4, [MoF2 (h-PhC∫CPh)Tp¢] 7, [MoCl2 (hPhC∫CPh)Tp¢] 8 were determined by X-ray crystallography. In addition, the X-ray structures of [WCl2 (h-PhC∫CPh)L][SbCl6 ] 6+ [SbCl6 ]- [L = HB(3,5-dimethylpyrazolyl)2 (3,5-dimethyl-4Cl-pyrazolyl)] and [MoCl(ClSbCl3 )(h-PhC∫CPh)Tp¢]·CH2 Cl2 9·CH2 Cl2 reveal pyrazolyl ring chlorination in the former and unusual Cl ◊ ◊ ◊ SbCl3 adduct formation in the latter. The X-ray structures of the redox pair [WF2 (h-PhC∫CPh)Tp¢]z (z = 1+ 2+ or 0 2), as representative examples, are shown in Fig. 10(a) and (b) respectively. Selected bond lengths and angles for the cations 1+ –4+ and 6+ are given in Table 3; those of the neutral complexes 2, 4 and 7–9 are given in Table 4. All of the structures are similar in that the metal occupies the centre of a pseudooctahedron with the Tp¢ ligand k3 -coordinated and the two halides and the alkyne each occupying one coordination site. Ring chlorination of [WCl2 (h-PhC∫CPh)Tp¢]+ 4+ to give [WCl2 (h-PhC∫CPh)L]+ 6+ [L = HB(3,5-dimethylpyrazolyl)2 (3,5dimethyl-4-Cl-pyrazolyl)] results in little structural change. ˚ ) and angles (◦ ) for [WX1 X2 (hTable 3 Selected bond lengths (A PhC∫CPh)L]+ a
Fig. 9 The simulated (a) and experimental (b) anisotropic ESR spectrum of [MoF2 (h-PhC∫CPh)Tp¢] 7 at 120 K.
The observation of inequivalent fluorines at low temperature (as seen in the solid state structures, see below) but equivalent fluorines in the isotropic spectrum of 7 suggests that alkyne motion, probably oscillation, occurs at room temperature. Such fluxional behaviour was observed for the d5 complexes [Mo{P(OMe)3 }2 (hRC∫CR)(h-C5 H5 )] (R = Me or Ph), variable temperature ESR spectroscopy giving the rates and activation parameters for alkyne oscillation.15 The pattern of 19 F coupling constants in the low temperature spectra varies between the two sets of compounds. In the tungsten compounds, g1 apparently shows coupling to only one fluorine nucleus, whereas g2 is best modelled assuming coupling to both fluorine nuclei, but with different coupling constants, and g3 shows no coupling. Conversely, for the molybdenum compounds g1 and g3 both show different couplings to both fluorine nuclei, whereas g2 does not apparently show any. The implication is that the SOMO is different in the two cases, which might be caused by the position of the alkyne. If it were to align very much with one metal–fluorine bond in the tungsten case (although this is not suggested by the crystal structures), the SOMO would only have a significant contribution from one fluorine atom, hence leading to a doublet on g1 . However, in the molybdenum case, if the alkyne much more nearly bisected the F–M–F unit, the SOMO would contain contributions from both fluorine atoms, giving the 536 | Dalton Trans., 2009, 530–543
1+
2+
3+
4+
6+
C(16)–C(17) C(16)–W(1) C(17)–W(1) X(1)–W(1) X(2)–W(1) N(1)–W(1) N(3)–W(1) N(5)–W(1)
1.295(6) 2.042(5) 2.027(5) 1.900(3) 1.929(3) 2.193(4) 2.149(4) 2.120(4)
1.338(6) 2.060(4) 2.037(5) 1.886(2) 1.893(2) 2.196(3) 2.121(4) 2.117(4)
1.308(4) 2.038(3) 2.035(3) 2.312(1)d 1.916(2)d 2.206(3) 2.144(2) 2.107(3)
1.308(6) 2.033(5) 2.037(5) 2.308(1) 2.336(1) 2.224(4) 2.139(4) 2.114(4)
1.305(5) 2.033(4) 2.037(4) 2.310(1) 2.330(1) 2.237(3) 2.155(3) 2.123(3)
C(16)–C(17)–C(18) C(24)–C(16)–C(17) X(1)–W(1)–X(2) N(1)–W(1)–N(3) N(1)–W(1)–N(5) N(3)–W(1)–N(5) C(16)–W(1)–C(17) X(1)–W(1)–C(17) X(1)–W(1)–C(16) X(2)–W(1)–C(17) X(2)–W(1)–C(16)
148.6(5) 146.9(5)c 101.9(1) 82.49(14) 82.10(13) 84.60(15) 37.10(18) 82.92(16) 108.73(16) 87.40(16) 107.07(15)
149.3(4) 146.3(4) 101.6(1) 82.2(1) 82.6(1) 85.3(1) 38.1(2) 87.1(1) 108.2(1) 84.4(1) 110.1(1)
149.2(3) 144.2(3) 102.0(1)d 81.0(1) 86.4(1) 83.0(1) 37.5(1) 81.9(1)d 109.6(1)d 87.1(1)d 105.1(1)d
149.2(5) 146.8(5) 102.1(1) 83.7(2) 84.1(2) 82.8(2) 37.5(2) 83.2(2) 106.9(2) 83.0(2) 105.7(2)
148.8(4) 146.1(4) 101.8(1) 83.6(1) 83.9(1) 82.7(1) 37.4(2) 83.2(1) 107.9(1) 83.8(1) 105.4(1)
bX(1) e bX(2) e Dbf
48.4 61.0 12.6
59.7 50.5 9.2
44.8 64.1 19.3
53.1 55.1 2.0
51.1 57.0 5.9
L = Tp¢ for 1+ –4+ and HB(3,5-dimethylpyrazolyl)2 (3,5-dimethyl-4-Cl˚ . c Actually C(19)–C(16)– pyrazolyl)] for 6+ . b C(3)–Cl(3) = 1.710(4) A C(17), but equivalent. d X(1) = Cl, X(2) = F. e bX(1) or bX(2) = dihedral angle formed by X(1)–M or X(2)–M and C(16)–C(17) bonds. f Db = |bX(1) bX(2) |.
a
This journal is © The Royal Society of Chemistry 2009
Fig. 10 X-Ray structures of (a) [WF2 (h-PhC∫CPh)Tp¢]+ 2+ and (b) [WF2 (h-PhC∫CPh)Tp¢] 2 (hydrogen atoms have been omitted for clarity), and (c) a space filling diagram for 2+ ˚ ) and angles (◦ ) for [MX1 X2 (hTable 4 Selected bond lengths (A PhC∫CPh)Tp¢] 2
4
7
8
9
C(16)–C(17) C(16)–M(1) C(17)–M(1) X(1)–M(1) X(2)–M(1) N(1)–M(1) N(3)–M(1) N(5)–M(1) Sb(1)–Cl(3) Sb(1)–Cl(4) Sb(1)–Cl(5) Sb(1) ◊ ◊ ◊ Cl(1)
1.319(5) 2.049(4) 2.024(4) 1.939(2) 1.982(2) 2.252(3) 2.175(3) 2.155(4) — — — —
1.300(9) 2.050(6) 2.032(6) 2.401 (2) 2.428(2) 2.234(5) 2.199(6) 2.157(5) — — — —
1.288(5) 2.057(4) 2.026(4) 1.974(2) 1.914(2) 2.250(3) 2.181(3) 2.180(3) — — — —
1.297(7) 2.021(6) 2.047(6) 2.417(2) 2.408(2) 2.299(5) 2.171(5) 2.165(4) — — — —
1.301(3) 2.038(2) 2.039(2) 2.450(1) 2.392(1) 2.268(2) 2.182(2) 2.156(2) 2.358(1) 2.349(1) 2.394(1) 3.115(1)
C(16)–C(17)–C(18) C(24)–C(16)–C(17) X(1)–M(1)–X(2) N(1)–M(1)–N(3) N(1)–M(1)–N(5) N(3)–M(1)–N(5) C(16)–M(1)–C(17) X(1)–M(1)–C(17) X(1)–M (1)–C(16) X(2)–M(1)–C(17) X(2)–M(1)–C(16) Cl(1)–Sb(1)–Cl(5) Cl(3)–Sb(1)–Cl(4) Cl(4)–Sb(1)–Cl(5) Cl(3)–Sb(1)–Cl(5)
145.8(4) 143.4(4) 90.1(1) 78.4(1) 79.5(1) 89.8(1) 37.8(2) 94.8(1) 108.7(1) 84.1(1) 118.3(1) — — — —
141.3(7) 140.7(6) 96.1(1) 81.2(2) 82.2(2) 85.9(2) 37.1(3) 87.8(2) 104.9(2) 81.9(2) 112.2(2) — — — —
147.9(4) 144.9(4) 93.2(1) 79.0(1) 79.6(1) 88.5(1) 36.8(1) 83.2(1) 115.5(1) 93.7(1) 107.8(1) — — — —
145.6(6) 144.4(5) 93.5(1) 81.5(2) 81.2(2) 86.6(2) 37.2(2) 81.8(2) 111.1(2) 89.8(2) 109.7(2) — — — —
146.4(2) 143.5(2) 96.8(1) 83.2(1) 81.8(1) 85.4(1) 37.2(1) 80.4(1) 109.2(1) 89.2(1) 108.2(1) 173.5(1) 93.7(1) 94.1(1) 95.4(1)
bX(1) a bX(2) a Dbb
73.1 27.5 45.6
65.4 37.6 27.8
30.8 71.7 40.9
40.6 61.4 20.8
41.5 62.8 21.3
bX(1) or bX(2) = dihedral angle formed by X(1)–M or X(2)–M and C(16)– C(17) bonds. b Db = |bX(1) - bX(2) |.
a
In all cases the alkyne is orientated so that one substituent lies towards the Tp¢ ligand while the other points towards the This journal is © The Royal Society of Chemistry 2009
halogen atoms. For the diphenylacetylene complexes, one phenyl ring is interleaved between two pyrazole rings, as illustrated by the space filling diagram for 2+ (Fig. 10(c)). This interleaving results in phenyl ring b being static with the position of one ortho proton resulting in the unusual upfield shift observed in the 1 H NMR spectrum (see above). The ‘orthogonal’ alkyne orientation differs from that in the cyclopentadienyl analogue [MoCl2 (h-PhC∫CPh)(h-C5 H5 )] where the C∫C bond is more nearly parallel to the C5 ring.12 Theoretical studies on [NbCl2 (h-RC∫CR)Tp¢],16 with the orthogonal arrangement,17 and [NbCl2 (h-HC∫CH)(h-C5 H5 )]12,18 and [MoCl2 (h-HC∫CH)(h-C5 H5 )]12 (both with the alkyne parallel to the C5 ring), suggested that such geometrical preferences result from steric rather than electronic effects. The precise orientation of the alkyne in [MX1 X2 (hPhC∫CPh)Tp¢]z (z = 0 or 1+) depends on the electronic configuration of the metal centre. The dihedral angles bX(1) and bX(2) {formed by the C(16)–C(17) and X(1)–M(1) or X(2)–M(1) bonds respectively} of the cations [MX2 (h-PhC∫CPh)Tp¢]+ (X = F or Cl) are similar. The difference, Db = |bX(1) - bX(2) |, of 12.6, 9.2, 2.0 and 5.9◦ for [WF2 (h-MeC∫CMe)Tp¢]+ 1+ , [WF2 (hPhC∫CPh)Tp¢]+ 2+ , [WCl2 (h-PhC∫CPh)Tp¢]+ 4+ and [WCl2 (hPhC∫CPh)L]+ 6+ [L = HB(3,5-dimethylpyrazolyl)2 (3,5-dimethyl4-Cl-pyrazolyl)] respectively shows that the alkyne approximately bisects the X(1)–W(1)–X(2) angle, as observed in solution by NMR spectroscopy (and in the solid state for the isoelectronic complex [NbCl2 (h-PhC∫CMe)Tp¢]17 ). A larger difference, Db = 19.3◦ , for the mixed halide complex [WFCl(h-PhC∫CPh)Tp¢]+ 3+ , where the alkyne C(16)–C(17) bond is more closely aligned with the W–Cl bond, is consistent with chloride acting as a worse pdonor than fluoride, i.e. with the inverse halide order observed by cyclic voltammetry. For the redox pairs [WX2 (h-PhC∫CPh)Tp¢]z (z = 0 or 1+, X = F or Cl) Db increases on reduction, with the alkyne aligned more closely with bond X(2)–W(1), by 18.2 and 12.9◦ for X = F and Cl Dalton Trans., 2009, 530–543 | 537
respectively. This alkyne alignment is also observed in the neutral molybdenum complexes 7 and 8 (Db = 40.9 and 20.8◦ respectively). For both Mo and W, Db is greater for fluoride than chloride, i.e. the alkyne aligns more closely with one fluoride in [WF2 (hPhC∫CPh)Tp¢] than with one chloride in [WCl2 (h-PhC∫CPh)Tp¢]. This might be expected to lead to a lower barrier to alkyne oscillation in the dichloride though this has not been quantified. Although the asymmetry in the MX2 (h-PhC∫CPh) unit might be due to crystal packing effects, the anisotropic ESR spectra of [WF2 (h-PhC∫CPh)Tp¢] 2 and [MoF2 (h-PhC∫CPh)Tp¢] 7, in a CH2 Cl2 –thf glass, also show inequivalent halides. ˚ , consistent The M–Calk distances are in the range 2.024–2.060 A with the alkynes acting as four-electron donors10 in both the d2 cations and d3 neutral species. There is, perhaps, a small decrease of ˚ on reduction for the redox pairs [WF2 (h-PhC∫CPh)Tp¢]z ca. 0.01 A (z = 0 2 or 1+ 2+ ) and [WCl2 (h-PhC∫CPh)Tp¢]z (z = 0 4 or 1+ 4+ ). For those pairs, the average W–X distance is lengthened by ca. ˚ on reduction. The d3 cations [WX(CO)(h-PhC∫CPh)Tp¢]+ 0.07 A ˚) (X = Cl or Br) show shorter W–X distances (by ca. 0.09 A than those of their, d4 , neutral analogues,3 consistent with the HOMO of [WX(CO)(h-PhC∫CPh)Tp¢] being p-antibonding with respect to the W–X bond. Theoretical studies showed that the SOMO of [MoCl2 (h-HC2 H)(h-C5 H5 )] is also partly Mo–Cl p* in character.12 The angle X(1)–W(1)–X(2) in the cations 1+ –4+ and 6+ is very similar to that of the isoelectronic d2 complex [NbCl2 (hPhC∫CMe)Tp¢] (102◦ ), whereas in the neutral species 2, 4, 7 and 8 that angle is narrower (90–97◦ ). The obtuse angle in [NbCl2 (hPhC∫CMe)Tp¢] was ascribed17 to the alleviation of a destabilising interaction between a filled dxz orbital on the metal and a linear combination of p pCl orbitals. ˚ upon oxidation in The W–N bond lengths decrease by ca. 0.05 A the redox pairs [WX2 (h-PhC∫CPh)Tp¢]z (z = 0 or 1+, X = F or Cl), presumably simply because of the increased positive charge on the metal. For all complexes the strong trans influence of the alkyne is reflected in the M(1)–N(5) bond which is longer than M(1)–N(1) or M(1)–N(3), as found in [NbCl2 (h-PhC∫CMe)Tp¢].17 The X-ray structure of [MoCl(ClSbCl3 )(h-PhC∫CPh)Tp¢] 9, shown in Fig. 11 with selected bond lengths and angles in Table 4, is very similar to that of [MoCl2 (h-PhC∫CPh)Tp¢] but for the attachment of an SbCl3 unit to Cl(1). As seen for the other neutral complexes, the C(16)–C(17) alkyne bond in [MoCl(ClSbCl3 )(hPhC∫CPh)Tp¢] 9 is aligned with one of the M–X bonds, although in this case X is the chloride bonded to Sb. The Cl–Sb–Cl angles and the Cl–Sb bond lengths of the SbCl3 unit in [MoCl(ClSbCl3 )(h-PhC∫CPh)Tp¢] are similar to ˚ ).19 Chlorine atom Cl(1) those of pure SbCl3 (ca. 95◦ and 2.36 A is trans to Cl(5) with the Cl(1)–Sb–Cl(5) angle 173.5(1)◦ . The ClSbCl3 unit therefore has approximately octahedral geometry with two vertices unoccupied. A similar structural feature was observed for [Cl ◊ ◊ ◊ BiClPh2 ]- , in which chloride, acting as a Lewis base towards BiClPh2 , donates a lone pair into a Bi–Cl s* orbital, forming a 3c-4e interaction also described as a secondary bond.20 ˚ ] is the longest of the The Sb(1)–Cl(5) bond length [2.394(1) A SbCl3 unit [cf. 2.358(1) and 2.349(1) for Sb(1)–Cl(3) and Sb(1)– Cl(4) respectively], as also observed in other SbCl3 adducts such as SbCl3 ·NH2 Ph which has a long range contact between antimony and the aniline N atom.21 538 | Dalton Trans., 2009, 530–543
Fig. 11 Molecular structure of [MoCl(ClSbCl3 )(h-PhC∫CPh)Tp¢] 9 (hydrogen atoms have been omitted for clarity).
A redox family tree for metal alkyne complexes The successful synthesis of [MX2 (h-RC∫CR)Tp¢]z (M = Mo or W, X = halide, z = 0 and 1+) completes a series of metal alkyne complexes in which [M(CO)2 (h-RC∫CR)Tp¢] is linked to [MX2 (h-RC∫CR)Tp¢]+ by a sequence of one-electron transfer and carbonyl substitution reactions. These links are illustrated in the ‘redox family tree’ shown in Fig. 12 where the alkyne complexes are also related to [M(CO)3 Tp¢]- and [MX3 Tp¢], thereby extending the family to link the d6 anion (low formal oxidation state stabilised by the p-accepting carbonyl ligands) and the d2 trihalide (high formal oxidation state stabilised by pdonor ligands). {A similar, though somewhat less extended, tree can be constructed for related alkyne complexes of chromium (Fig. 13) which includes the (formal) d6 cyclobutadiene complex [Cr(CO)2 (h-PhC∫CPh)(h-C4 Ph4 )] and its sequential reduction to the d7 monoanion [Cr(CO)2 (h-PhC∫CPh)(h-C4 Ph4 )]- and the d8 dianion [Cr(CO)2 (h-PhC∫CPh)(h-C4 Ph4 )]2- .22 } While useful in simply showing the relationship between known species, other such trees may be constructed in order to predict the existence of new species, for example from adjacent groups in the periodic table. Thus, one would anticipate that the known complexes [Re(CO)2 (h-PhC∫CPh)(hC5 H5 )]23 and [Re(dppe)(h-MeC∫CPh)(h-C5 H5 )]2+ ,24 isoelectronic with d4 [M(CO)2 (h-RC∫CR)Tp¢]+ and d2 [MX2 (h-RC∫CR)Tp¢]+ (M = Mo or W, X = halide) respectively, would undergo two reversible one-electron oxidation and reduction reactions respectively. Accordingly, a preliminary electrochemical study25 of [Re(dppe)(h-MeC∫CPh)(h-C5 H5 )]2+ in MeCN showed two reversible reduction waves, at -0.08 and -0.75 V (vs. the oneelectron oxidation of [Fe(h-C5 H5 )2 ] at 0.39 V), and treatment of the dication with [Co(h-C5 H5 )2 ] in CH2 Cl2 gave a six-line isotropic ESR spectrum (giso = 2.053, ARe = 237.5 G) in agreement with the formation of the paramagnetic monocation [Re(dppe)(hMeC∫CPh)(h-C5 H5 )]+ . One might also be able to estimate the This journal is © The Royal Society of Chemistry 2009
Fig. 12 A redox family tree for molybdenum and tungsten alkyne complexes (X = halide). Species in braces have been detected by cyclic voltammetry but not fully characterised.
potentials of unknown processes, given the observed effects of the ancillary ligands and metals described above. Selectivity in the synthetic application of paramagnetic alkyne complexes (‘alkyne radicals’) Given the evidence for unpaired electron density on the alkyne ligands of [Cr(CO)2 (h-RC∫CR)(h-arene)]+ ,1 [M(CO)2 (hRC∫CR)Tp¢]+ , (M = Mo or W)2 and [Mo{P(OMe)3 }2 (hRC∫CR)(h-C5 H5 )],15 one might expect unusual and useful synthetic applications for these and other paramagnetic (formally d3 and d5 ) members of the family trees. Given the variation in potentials with the metal and ancillary ligands, control of redox potential to allow, for example, nucleophilic attack rather than one-electron reduction is possible. For selectivity (regioand stereo-specificity), one would also need to control alkyne orientation. Asymmetric alignment of the alkyne relative to the X–M–X group is observed for [MX2 (h-RC∫CR)Tp¢] in the solid state but not in solution because of fluxional processes, e.g. alkyne oscillation or rotation. However, selectivity may be possible in species such as [MX(CO)(h-RC∫CR)Tp¢]+ given the preferential alkyne alignment with the better p-acceptor ligand (i.e. CO). Summary Two-electron oxidation of [MX(CO)(h-RC∫CR)Tp¢], using a strong oxidant and a source of halide, e.g. the N-fluoropyridinium This journal is © The Royal Society of Chemistry 2009
cation or SbCl5 , gave the d2 cations [MX2 (h-RC∫CR)Tp¢]+ (M = Mo or W, X = F or Cl). The reaction of [WX(CO)(h-PhC∫CPh)Tp¢] (X = F or Cl) with SbCl5 also occasionally gave [WXCl(h-PhC∫CPh)L][SbCl6 ] [L = HB(3,5dimethylpyrazolyl)2 (3,5-dimethyl-4-Cl-pyrazolyl)] with the 4chlorinated ring opposite the alkyne. Treatment of [MoCl(CO)(hPhC∫CPh)Tp¢] with SbCl5 also gave the structurally characterised SbCl3 adduct [Mo(ClSbCl3 )Cl(h-PhC∫CPh)Tp¢]. Both phenyl rings of [WF2 (h-PhC∫CPh)Tp¢]+ 2+ , [WFCl(hPhC∫CPh)Tp¢]+ 3+ and [MCl2 (h-PhC∫CPh)Tp¢]+ (M = W 4+ or Mo 8+ ) rotate around their Cipso –Calkyne bonds at room temperature. However, at low temperature the phenyl ring interleaved between two pyrazole groups becomes static with one ortho proton giving rise to a 1 H NMR signal significantly shifted upfield. The potentials for the two one-electron reductions of [MX1 X2 (hPhC∫CPh)Tp¢]+ depend on the metal and the halide; each process can be ‘tuned’ over ca. 1.0 V by varying M and X. The paramagnetic complexes [MX1 X2 (h-PhC∫CPh)Tp¢] were synthesised by reducing the corresponding cations with [Co(h-C5 H5 )2 ] or [Fe(hC5 H5 )2 ]. The solution ESR spectrum of [MoF2 (h-PhC∫CPh)Tp¢] at 290 K shows coupling of the unpaired electron to two equivalent fluorine atoms. However, its anisotropic spectrum, and that of [WF2 (h-PhC∫CPh)Tp¢], shows inequivalent fluorines, i.e. the alkyne is more closely aligned with one of the M–F bonds at low temperature (although the alkyne undergoes oscillation in solution). Dalton Trans., 2009, 530–543 | 539
Fig. 13 A redox family tree for chromium alkyne complexes {L = P(OMe)3 , R = aryl}. Species in braces have been detected by cyclic voltammetry but not fully characterised.
In the solid state, the alkyne bisects the X–M–X angle in the cations [WX2 (h-PhC∫CPh)Tp¢]+ (X = F or Cl); the mixed halide cation [WFCl(h-PhC∫CPh)Tp¢]+ has the alkyne more closely aligned with the W–Cl bond, consistent with chloride as a worse net donor than fluoride. In the neutral molecules [MX2 (hPhC∫CPh)Tp¢] (M = Mo or W; X = F or Cl) the alkyne is more aligned with one of the M–X bonds, in agreement with the anisotropic ESR spectra. The synthesis of the redox pairs [MX2 (h-RC∫CR)Tp¢]z completes a redox family tree in which a series of d2 to d6 alkyne complexes is linked by stepwise one-electron redox and substitution reactions. Such trees can be used to predict the existence of new species and possibly the potentials at which they will oxidise or reduce. They also provide a means by which one might design stable (to reduction or oxidation) paramagnetic alkyne complexes, formally ‘alkyne radicals’, with potential in selective synthesis.
Experimental General The preparation, purification and reactions of the complexes described were carried out under an atmosphere of dry nitrogen using dried and deoxygenated solvents purified either by distillation or by using Anhydrous Engineering double alumina or alumina/copper catalyst drying columns. Reactions were 540 | Dalton Trans., 2009, 530–543
monitored by IR spectroscopy where necessary. Unless stated otherwise, complexes were purified using a mixture of two solvents. The impure solid was dissolved in the more polar solvent, the resulting solution was filtered and then treated with the second solvent, and the mixture was reduced in volume in vacuo to induce precipitation. Unless stated otherwise, complexes are stable under nitrogen and dissolve in polar solvents such as CH2 Cl2 to give moderately air-stable solutions. The compounds [Co(h-C5 H5 )2 ],26 [MX(CO)(h-RC∫CR)Tp¢] (M = Mo or W; X = F, Cl, Br or I; R = Me or Ph),3 [Fe(h-C5 H5 )2 ][PF6 ] and [Fe(h-C5 H4 COMe)(h-C5 H5 )][BF4 ]27 were prepared by published methods. The compounds SbCl5 (as a 1.0 mol dm-3 solution in CH2 Cl2 ) and N-fluoropyridinium tetrafluoroborate were purchased from Aldrich. Solution IR spectra were recorded in CH2 Cl2 using CaF2 cells, on a Perkin Elmer Spectrum One FT-IR spectrometer over the range 2200 to 1600 cm-1 . Proton, 13 C-{1 H} and 19 F NMR spectra were recorded on JEOL GX270, Eclipse 300 or GX400 spectrometers with SiMe4 or CCl3 F (for 19 F) as internal standards. X-Band ESR spectra were recorded on a Bruker ESP300E spectrometer equipped with a Bruker variable temperature accessory and a Hewlett-Packard 5350B microwave frequency counter. The field calibration was checked by measuring the resonance of the diphenylpicrylhydrazyl (dpph) radical before each series of spectra. FAB mass spectra were recorded using a VG Analytical Autospec instrument. This journal is © The Royal Society of Chemistry 2009
Electrochemical studies were carried out using an EG & G Model 273A potentiostat linked to a computer using EG & G Model 270 Research Electrochemistry software in conjunction with a three-electrode cell. The auxiliary electrode was a platinum wire and the working electrode a platinum disc (1.6 mm diameter). The reference was an aqueous saturated calomel electrode separated from the test solution by a fine porosity frit and an agar bridge saturated with KCl. Solutions were 1.0 ¥ 10-3 mol dm-3 in the test compound and 0.1 mol dm-3 in [NBun 4 ][PF6 ] as the supporting electrolyte with CH2 Cl2 as the solvent. Under the conditions used, E◦ ¢ for the one-electron oxidation of [Fe(h-C5 H4 COMe)2 ], [Fe(h-C5 H4 COMe)(h-C5 H5 )] or [Fe(h-C5 H5 )2 ], added to the test solutions as an internal calibrant, is 0.97, 0.74 and 0.47 V respectively. Microanalyses were carried out by the staff of the Microanalysis Service of the School of Chemistry, University of Bristol. Syntheses [WF2 (g-MeC∫CMe)Tp¢][I3 ] 1+ [I3 ]- . To a solution of [WI(CO)(h-MeC∫CMe)Tp¢] (303 mg, 0.439 mmol) in CH2 Cl2 (30 cm3 ) was added solid [NO][PF6 ] (41 mg, 0.917 mmol). The mixture was stirred for 2.5 h and the resulting purple solution filtered through Celite. Addition of n-hexane (30 cm3 ) and reduction of the volume in vacuo gave a dark red solid which was purified twice by allowing n-hexane (80 cm3 ) to diffuse into a concentrated solution in CH2 Cl2 (15 cm3 ) at -20 ◦ C. This gave the product as a dark red, crystalline 2 : 1 n-hexane solvate, yield 71 mg (17%, based on tungsten). [WF2 (g-MeC∫CMe)Tp¢][BF4 ] 1+ [BF4 ]- . To a solution of [WF(CO)(h-MeC∫CMe)Tp¢] (102 mg, 0.175 mmol) in CH2 Cl2 (30 cm3 ) was added solid [NO][BF4 ] (41 mg, 0.351 mmol). The mixture was stirred for 2.5 h and then the resulting dark brown solution was filtered through Celite. Addition of n-hexane (30 cm3 ) and reduction of the volume in vacuo gave an orange-brown solid which was redissolved in CH2 Cl2 (5 cm3 ). Addition of diethyl ether (10 cm3 ) and cooling the mixture to -20 ◦ C for 1 h gave an orange solid. Repetition of the purification process gave the product as orange crystals, yield 40 mg (35%). [WF2 (g-PhC∫CPh)Tp¢][BF4 ] 2+ [BF4 ]- . To a stirred solution of [WF(CO)(h-PhC∫CPh)Tp¢] (205 mg, 0.290 mmol) in CH2 Cl2 (80 cm3 ) was added N-fluoropyridinium tetrafluoroborate (71 mg, 0.385 mmol). After 6 h the orange-red solution was filtered through Celite and evaporated to dryness in vacuo. Purification of the residue using CH2 Cl2 –n-hexane gave the product as an orangered solid, yield 145 mg (64%). 3+ [SbCl6 ]- ·CH2 Cl2 . [WFCl(g-PhC∫CPh)Tp¢][SbCl6 ]·CH2 Cl2 To a stirred solution of [WF(CO)(h-PhC∫CPh)Tp¢] (350 mg, 0.496 mmol) in CH2 Cl2 (120 cm3 ) was added dropwise SbCl5 (1.0 cm3 of a 1.0 mol dm-3 solution in CH2 Cl2 , 1.00 mmol). After stirring the mixture for 5 h, the red solution was filtered through Celite and evaporated to dryness in vacuo. The red residue was washed twice with toluene (15 cm3 ) and the solid obtained was purified using CH2 Cl2 –n-hexane, yield 313 mg (57%). [WCl2 (g-PhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ]- . To a stirred solution of [WCl(CO)(h-PhC∫CPh)Tp¢] (407 mg, 0.564 mmol) in CH2 Cl2 (150 cm3 ) was added dropwise SbCl5 (1.41 cm3 of a This journal is © The Royal Society of Chemistry 2009
1.0 mol dm-3 solution in CH2 Cl2 , 1.41 mmol). When no carbonyl band remained in the IR spectrum (ca. 1 h), the brown solution was evaporated to dryness in vacuo and the residue washed with toluene (15 cm3 ). Several purifications using CH2 Cl2 –n-hexane gave the product as brown crystals, yield 385 mg (62%). [MoF2 (g-PhC∫CPh)Tp¢][BF4 ] 7+ [BF4 ]- . To a stirred solution of [MoF2 (h-PhC∫CPh)Tp¢] (69 mg, 0.113 mmol) in CH2 Cl2 (30 cm3 ) was added [Fe(h-C5 H4 COMe)(h-C5 H5 )][BF4 ] (32 mg, 0.102 mmol). After 3 min the brown solution was filtered through Celite, n-hexane was added (50 cm3 ) and the volume of the solution reduced in vacuo to give brown crystals which were washed with diethyl ether (3 ¥ 20 cm3 ), yield 51 mg (64%). [MoCl2 (g-PhC∫CPh)Tp¢][SbCl6 ] 8+ [SbCl6 ]- . To a stirred solution of [MoCl(CO)(h-PhC∫CPh)Tp¢] (482 mg, 0.76 mmol) in CH2 Cl2 (120 cm3 ) was added SbCl5 (0.76 cm3 of a 1.0 mol dm-3 solution in CH2 Cl2 , 0.76 mmol). After 5 min, the brown solution was dried in vacuo and the residue redissolved in toluene (40 cm3 ). Reduction of the volume to ca. 10 cm3 gave brown crystals which were purified using CH2 Cl2 –n-hexane and then washed with nhexane (2 ¥ 10 cm3 ), yield 318 mg (43%). [WF2 (g-PhC∫CPh)Tp¢] 2. To a stirred suspension of [WF2 (hPhC∫CPh)Tp¢][BF4 ] (125 mg, 0.159 mmol) in toluene (35 cm3 ) was added [Co(h-C5 H5 )2 ] (34 mg, 0.175 mmol). After stirring the mixture for 15 min, the dark red solution was filtered through Celite and the filtrate evaporated to dryness in vacuo. Purification of the residue using CH2 Cl2 –n-hexane gave the product as a pale red solid, yield 59 mg (53%). The complexes [WFCl(h-PhC∫CPh)Tp¢] 3 and [WCl2 (hPhC∫CPh)Tp¢] 4 were prepared similarly, from [WFCl(hPhC∫CPh)Tp¢][SbCl6 ] and [WCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] respectively. [MoF2 (g-PhC∫CPh)Tp¢] 7. To a stirred solution of [MoF(CO)(h-PhC∫CPh)Tp¢] (385 mg, 0.620 mmol) in CH2 Cl2 (110 cm3 ) was added N-fluoropyridinium tetrafluoroborate (231 mg, 1.25 mmol). After 4 d, the volume of the orange solution was reduced in vacuo to ca. 10 cm3 , silica was added and the mixture dried in vacuo. The residue was placed on a silica–toluene chromatography column. Elution with toluene–diethyl ether (1 : 1) gave an orange band which was collected and evaporated to dryness in vacuo. Purification using CH2 Cl2 –n-hexane gave the product as an orange solid, yield 74 mg (20%). [MoCl2 (g-PhC∫CPh)Tp¢]·CH2 Cl2 8·CH2 Cl2 . To a stirred suspension of crude [MoCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] (273 mg, 0.28 mmol) in toluene (30 cm3 ) was added [Fe(h-C5 H5 )2 ] (53 mg, 0.28 mmol). After 10 min, the light brown solution was filtered through Celite and the filtrate evaporated to dryness in vacuo. The orange residue was washed with diethyl ether (20 cm3 ) and then purified using CH2 Cl2 –n-hexane to give a pink solid, yield 96 mg (45%). Structure determinations Crystals of 1+ [I3 ]- , 3+ [SbCl6 ]- , 4+ [SbCl6 ]- , 4 and 7–9 were grown by allowing n-hexane to diffuse into a concentrated solution of the complex in CH2 Cl2 at -20 ◦ C. The same method was used to grow crystals of 2+ [BF4 ]- (from CH2 Cl2 –diethyl ether), 6+ [SbCl6 ]- and 2 (from thf–n-hexane). Dalton Trans., 2009, 530–543 | 541
0.0281, 0.0671 0.0639, 0.1194 0.0337, 0.0666 0.0358, 0.0720 0.0294, 0.0567
Formula M Crystal system Space group (no.) ˚ a/A ˚ b/A ˚ c/A ◦ a/ b/◦ g /◦ T/K ˚3 U/A Z m/mm-1 Reflections collected Independent reflections (Rint ) Final R indices [I > 2s(I)]: R1,wR2
0.0368, 0.0622 0.0305, 0.0634 0.0271, 0.0555 0.0290, 0.0602
0.0304, 0.0643
C30 H34 BCl7 MoN6 Sb 955.29 Triclinic P1¯ (2) 9.922(1) 10.448(1) 18.807(1) 75.94(1) 83.24(1) 79.43(1) 173(2) 1853.6(3) 2 1.603 19763 8425 (0.0262) C29 H32 BCl2 MoN6 642.26 Monoclinic P21 /c (14) 16.483(5) 12.527(4) 17.014(5) 90 113.12(1) 90 173(2) 3231.1(17) 4 0.598 20476 7417 (0.1700) C29 H32 BF2 MoN6 609.36 Monoclinic P21 /c (14) 9.718(3) 32.315(11) 9.779(3) 90 113.27(1) 90 173(2) 2821.1(16) 4 0.508 29496 6472 (0.0932) C29 H32 BCl2 N6 W 730.17 Monoclinic P21 /c (14) 17.400(2) 9.493(2) 18.149(3) 90 109.29(1) 90 100 (2) 2829.5(7) 4 4.302 24031 5523 (0.0695) C29 H32 BF2 N6 W 697.27 Monoclinic P21 /c (14) 9.643(2) 32.628(7) 9.823(2) 90 113.99(1) 90 173(2) 2823.6(9) 4 4.134 29564 6494 (0.0562) C29 H31.91 BCl8.09 N6 SbW 1067.63 Monoclinic P21 /c (14) 10.210(2) 16.872(2) 22.063(3) 90 96.64(1) 90 173(2) 3775.4(8) 4 4.363 24085 8670 (0.0612) C29 H32 BCl7 FN6 SbW 1048.17 Monoclinic P21 /c (14) 13.507(2) 16.179(2) 19.124(2) 90 102.37(1) 90 173(2) 4082.2(7) 4 3.968 45157 9360 (0.0341) C29 H32 B2 F6 N6 W 784.08 Monoclinic P21 /c (14) 12.263(2) 12.517(2) 20.124(3) 90 99.57(1) 90 173(2) 3045.9(7) 4 3.860 15983 5366 (0.0426) C19 H28 N6 BF2 I3 W 953.83 Monoclinic P21 /c (14) 11.791(2) 16.443(3) 14.028(2) 90 95.49(2) 90 173(2) 2707.3(7) 4 7.720 17474 6206 (0.0363)
C29 H31 BCl9 N6 SbW 1099.06 Monoclinic P21 /c (14) 10.437(1) 16.998(1) 21.716(2) 90 95.08(1) 90 173(2) 3837.4(7) 4 4.357 24624 8797 (0.0372)
[MoCl(ClSbCl3 )(hPhC∫CPh)Tp¢]· CH2 Cl2 9·CH2 Cl2 [MoCl2 (hPhC∫CPh)Tp¢] 8 [MoF2 (hPhC∫CPh)Tp¢] 7 [WCl2 (hPhC∫CPh)Tp¢] 4 [WF2 (h[WCl2 (h-PhC∫CPh)- PhC∫CPh)+ L][SbCl6 ] 6 [SbCl6 ] Tp¢] 2 [WCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ][WF2 (h-PhC∫CPh)- [WFCl(h-PhC∫CPh)Tp¢][BF4 ] 2+ [BF4 ]Tp¢][SbCl6 ] 3+ [SbCl6 ][WF2 (h-MeC∫CMe)Tp¢][I3 ] 1+ [I3 ]-
Table 5 Crystal and refinement data for [WF2 (h-MeC∫CMe)Tp¢][I3 ] 1+ [I3 ]- , [WF2 (h-PhC∫CPh)Tp¢][BF4 ] 2+ [BF4 ]- , [WFCl(h-PhC∫CPh)Tp¢][SbCl6 ] 3+ [SbCl6 ]- , [WCl2 (h-PhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ]- , [WCl2 (h-PhC∫CPh)L][SbCl6 ] 6+ [SbCl6 ]- {L = HB(3,5-dimethylpyrazolyl)2 (3,5-dimethyl-4-Cl-pyrazolyl}, [WF2 (h-PhC∫CPh)Tp¢] 2, [WCl2 (h-PhC∫CPh)Tp¢] 4, [MoF2 (h-PhC∫CPh)Tp¢] 7, [MoCl2 (h-PhC∫CPh)Tp¢] 8 and [MoCl(ClSbCl3 )(h-PhC∫CPh)Tp¢]·CH2 Cl2 9·CH2 Cl2
542 | Dalton Trans., 2009, 530–543
Many of the details of the structure analyses of [WF2 (h-MeC∫CMe)Tp¢][I3 ] 1+ [I3 ]- , [WF2 (h-PhC∫CPh)Tp¢][BF4 ] 2+ [BF4 ]- , [WFCl(h-PhC∫CPh)Tp¢][SbCl6 ] 3+ [SbCl6 ]- , [WCl2 (hPhC∫CPh)Tp¢][SbCl6 ] 4+ [SbCl6 ]- , [WCl2 (h-PhC∫CPh)L][SbCl6 ] 6+ [SbCl6 ]- [L = HB(3,5-dimethylpyrazolyl)2 (3,5-dimethyl-4-Clpyrazolyl)], [WF2 (h-PhC∫CPh)Tp¢] 2, [WCl2 (h-PhC∫CPh)Tp¢] 4, [MoF2 (h-PhC∫CPh)Tp¢] 7, [MoCl2 (h-PhC∫CPh)Tp¢] 8, and [MoCl(ClSbCl3 )(h-PhC∫CPh)Tp¢]·CH2 Cl2 9·CH2 Cl2 are listed in Table 5. Diffraction intensities were collected on a Bruker SMART CCD diffractometer, with graphite-monochromated Mo-Ka ˚ ) radiation. The structures were solved by SHELXS(0.71073 A 97, expanded by Fourier-difference syntheses, and refined with the SHELXL-97 package incorporated into the SHELXTL crystallographic package.28 The positions of the hydrogen atoms were calculated by assuming ideal geometries but not refined. All nonhydrogen atoms were refined with anisotropic thermal parameters by full-matrix least-squares procedures on F 2 . The structure of 1+ [I3 ]- was refined with one of the terminal iodine atoms of the anion disordered over two different positions, in an approximately 56 : 44 ratio. The structures of 2 and 2+ [BF4 ]- have been re-refined from those reported in our initial communication (CSD refcodes YODDUQ and YOCYAQ respectively).4 In the case of 2, the new refinement allowed freely rotating methyl groups (AFIX 137) rather than the fixed model used previously (AFIX 33), and in the case of 2+ [BF4 ]- the new model includes an apical proton attached to the boron atom of the Tp¢ ligand (which was missing from the previous structure). The structure of 4+ [SbCl6 ]- was best refined with a chlorine atom replacing the central hydrogen atom H(3A) of a pyrazolyl ring with an approximately 9% occupancy. The structures of 3+ [SbCl6 ]and 8 both contained disordered solvent molecules, which were apparently CH2 Cl2 but which could not be satisfactorily modelled. In both cases this disorder was removed using the SQUEEZE function of the PLATON crystallographic programme.29 In the case of 3+ [SbCl6 ]- this revealed two voids per unit cell, each containing approximately 98 electrons (i.e. about two molecules of CH2 Cl2 ), and for 8 two voids per unit cell each containing approximately 50 electrons (i.e. about one molecule of CH2 Cl2 ). In the cases of 7 and 8, poor crystal quality resulted in relatively weak data being collected, with correspondingly low ratios of observed to unique reflections and high values of Rint . CCDC reference numbers 697668–697677.
Acknowledgements We thank Professor Eric McInnes (University of Manchester) for helpful discussions of the ESR spectroscopic data, EPSRC for Studentships (D.J.H. and O.D.H.) and the University of Bristol for Postgraduate Scholarships (K.M.A and E.P.)
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