Structural studies of organoboron compounds. XXV ...

Structural studies of organoboron compounds. XXV. Synthesis and structure of CHRISORVIG,STEVENJ. RETTIG,AND JAMESTROTTER

Can. J. Chem. Downloaded from www.nrcresearchpress.com by China University of Science and Technology on 06/05/13 For personal use only.

Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, B.C., Canada V6T lY6 Received July 17, 1986 CHRISORVIG,STEVENJ. RETTIG,and JAMESTROTTER. Can. J. Chem. 65, 590 (1987). The reaction of maltol (3-hydroxy-2-methyl-4-pyrone) with diphenylborinic acid affords a high yield of the title compound. Crystals of (maltolato)diphenylboron are monoclinic, a = 14.3481(6), b = 8.3994(3), c = 12.6657(5)& P = 100.892(4)", Z = 4, space group P21/n. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.041 and R, = 0.052 for 2052 reflections with I 2 3u(l). The molecule contains a five-membered C202Bring having a flattened B-envelope conformation, the B atom being displaced 0.081(2) A from the C202plane. Structural and spectroscopic data are consistent with weak binding of the maltolate oxygen atoms to boron. Bond distances (corrected for libration) are 0-B = 1.533(2) and 1.600(3), B-C = 1.600(3) and 1.605(3) A. CHRISORVIG,STEVEN J. RETTIGet JAMESTROTTER. Can. J. Chem. 65, 590 (1987) La reaction du maltol (hydroxy-3 methyl-2 pyrone-4) avec l'acide diphenylborinique conduit, avec un excellent rendement, au compose mentionnC dans le titre. Les cristaux du (malto1ato)diphCnylbore sont monocliniques avec a = 14,3481(6), b = 8,3994(3) et c = 12,6657(5) A, P = 100,892(4)", Z = 4 et groupe d'espace P21/n. On a rksolu la structure par des mkthodes directes et on a l'a affinCe par la mCthode des moindres carrks jusqu'a des valeurs de R = 0,041 et R,,, = 0,052 pour 2052 rCflexions avec I 2 3u(I). La molCcule conti$nt un anneau a cinq chainons de C202Bqui adopte une conformation enveloppe B aplatie; l'atome de B se trouve 0,081(2) A du plan des C202.Les donnees de structure et spectroscopiques sont en accord avec une liaison faible entre les atomes d'oxygkne du maltolato et le bore. Les longueurs de liaison (corrigees pour la libration) sont : 0-B = 1,533(2) et 1,600(3), B-C = 1,600(3) et 1,605(3) A. [Traduit par la revue]

Introduction (Maltolato)diphenylboron, 1, has been synthesized and its molecular structure determined both as part of a continuing study of the structures of organoboron compounds1 and in parallel with studies of neutral water-soluble aluminum complexes of neurological interest (1) and related gallium analogs (2). The neutral complex tris(maltolato)aluminum has been shown to be a potent neurotoxin (3). The natural product maltol (3-hydroxy-2-methyl-4-pyrone) is commonly used as a food additive. Since ir data indicate weak binding of the maltol oxygen atoms to boron in the title compound relative to that in the tris(malto1ato) complexes of A1 and Ga (2), comparison of the ligand geometries is of interest. Experimental (Malto1ato)diphenylboron ((3-hydroxy-2-methyl-4-pyronato)diphenylboron) A solution of diphenylborinic acid was prepared by the acid hydrolysis (60 rnL 0.10 M HC1) of (2-aminoethano1ato)diphenylboron(1.3 19 g, 5.86 mmol) and extraction with diethylether (4 X 50 mL). To the organic layer was added ethanol (50 mL) followed by a solution of maltol (0.740 g, 5.87 mmol, Aldrich Chemical) in 30 mL ethanol. White flakes appeared within 10 min and the product was isolated after cooling (-20°C) overnight. Yield 1.506 g (90%). Analytically pure flakes were obtained by recrystallization from acetonelwater, mp 195-196.S°C (uncorrected). Anal. calcd. for Cl8HI5Bo3:C 74.52, H 5.21 : found: C 74.95. H 5.28. Ir (KBr. all strone): 1640 cm-' (CO); 1570, 1560 (c=c). 'H nmr (d6-ace'tone, 25"e: 80MHz): 6 2.63 (s, 3H, CH3); 7.25 (m, l I H , 2C6H5 and CHC(0)); 8.62 (d, 5.4 Hz, OCHCH). The ir spectrum was recorded on a Perkin-Elmer 783 from 4000200cm-I and the 'H nmr spectrum on a Bruker WP-80. Crystals suitable for X-ray analysis were obtained by slow evaporation of an acetone solution.

or Part XXIV, see ref. 23.

X-ray crystallographic analysis A crystal bounded by the six faces (followed by their distances in mm from a common origin): (1 0 1},0.12, (1 0 - 1},0.05, (-1 k 1 l ) , 0.11 was mounted in a general orientation. Unit-cell parameters were refined by least-squares on 2 sin 0/h values for 25 reflections (20 = 70-94") measured on a diffractometer with Cu-Ka radiation (h(Ka,) = 1.540562, A(Ka2) = 1.544390 A). Crystal data at 22°C are: C18H15B03 fw = 290.1 Monoclinic, a = 14.3481(6), b = 8.3994(3), c = 12.6657(5) A, P = 100.892(4)", V = 1498.9(1) A3, Z = 4, pc = 1.285Mg m-3, F(000) = 608, ~ ( C U - K a= ) 6.52cm-l. Absent reflections: h01, h + 1 odd, and OkO, k odd, uniquely indicate the space group P2,ln (alternate setting of P21/c, c:,,, No. 14). Intensities were measured with nickel-filtered Cu-Ka radiation on an Enraf-Nonius CAD4-F diffractometer. An w-28 scan at 1.18- 10.06O min-' over a range of (0.60 0.14 tan 0) degrees in w (extended by 25% on both sides for background measurement) was employed. Data were measured to 20 = 150". The intensities of three check reflections, measured every 3600 s throughout the data collection, remained constant to within 4%. After data reduction,' an absorption correction was applied using the analytical method (4, 5). Transmission factors ranged from 0.724 to 0.896. Of the 3067 independent reflections measured, 2052 (66.9%) had intensities greater than or equal to 3u(I) above background where u2(1) = S + 2B + (0.04(S - B ) ) ~with S = scan count and B = normalized background count. The structure was solved by direct methods, all non-hydrogen atoms being positioned from an E-map. Hydrogen atoms were positioned from a subsequent difference map. In the final stages of

+

2 ~ h ecomputer programs used include locally written programs for data processing and locally modified versions of the following: MULTAN 80, multisolution program by P. Main, S. J. Fiske, S. E. Hull, L. Lessinger, G. Germain, J. P. Declercq, and M. M. Woolfson; ORFLS, full-matrix least-squares, and ORFFE, function and errors, by W. R. Busing, K. 0 . Martin and H. A. Levy; FORDAP, Patterson and Fourier syntheses, by A. Zalkin; ORTEP 11, illustrations, by C. K. Johnson.


ORVIG ET AL

FIG. 1. Stereoscopic view of the (malto1ato)diphenylboron molecule; 50% probability thermal ellipsoids are shown for the non-hydrogen atoms. Hydrogen atoms have been assigned arbitrary thermal parameters for the sake of clarity. TABLE1. Final positional (fractional X lo4, H X lo3) and isotropic thermal parameters (U X lo3 A') with estimated standard deviations in parentheses Atom

x

Y

z

ueq/ulso

defined u2(1), gave uniform average values of w(lFoI - IF,I)' over ranges of both IFoI and sin 0/X and was employed in the final stages of full-matrix refinement of 260 variables. Reflections with I < 3u(I) were not included in the refinement. An isotropic Type I extinction correction (Thornley-Nelmes definition of mosaic anisotropy with a Lorentzian distribution) was applied (8-10). The final value of g was 0.74(13) X lo4. Convergence was reached at R = 0.041 and R,,, = 0.052 for 2052 reflections with I 2 3u(I). For all 3067 reflections R = 0.073. The function minimized was Cw(lFoI - IF,I)', R = CIIFoI - IFcII/CIFoI and R,, = (Cw(lFoI - IF,I)~/CW~F,I')"'. On the final cycle of refinement the mean and maximum parameter shifts corresponded to 0.009 and 0.117u, respectively. The mean error in an observation of unit weight was 2.130. A final difference map showed maximum fluctuations of -0.40 to +0.28 e k 3 , both near 0(2), and was essentially featureless elsewhere. The final positional and thermal parameters appear in Tables 1 and 63, respectively. Measured and calculated structure factors have been placed in the Depository of Unpublished ~ a t a The . ~ ellipsoids of thermal motion for the non-hydrogen atoms are shown in Fig. 1. The thermal motion has been analysed in terms of the rigid-body modes of translation, libration, and screw motion (1 1). The rms standard error in the temperature factors uUij (derived from the least-squares analysis) is 0.0012 A'. 'The subunits PhB and (qalto1ato)B were analysed separately (rms AUij = 0.0016-0.003 l A'). The appropriate bond distances have been corrected for libration ( 11, 12), using shape parameters q 2 of 0.08 for all atoms involved. Corrected bond lengths appear in Table 2 along with the uncorrected values; corrected bond angles do not differ by more than 1u from the uncorrected values given in Table 3. Intra-annular torsion angles defining the conformation of the five-membered chelate ring are listed in Table 4. Bond lengths and angles involving hydrogen and a complete listing of torsion angles (Tables 7-9) are included as supplementary material.

Results and discussion The crystal structure of (maltolato)diphenylboron consists of discrete molecules separated by normal van der Waals distances. The shortest intermole~ularcontact between non-hydrogen atoms is C - . .C = 3.295(4) A. The molecule (Fig. 1) has as its cent@ feature a fused-ring system which is planar to within 0.054(2) A. Each of the three six-membered rings in the molecule is slightly, but significantly, non-planar (maximum deviation from the mean plane = 0.010(3) A), while the five-membered C202B ring has a flattened B-envelope conformation with the boron refinement the non-hydrogen atoms were refined with anisotropic thermal parameters and the hydrogen atoms with isotropic thermal parameters. The scattering factors of ref. 6 were used for non-hydrogen atoms and those of ref. 7 for hydrogen atoms. The weighting scheme w = l / u ' ( ~ ) , where u2(F) is derived from the previously

3The structure factor table, Table 6 (anisotropic thermal parameters) and other material mentioned in the text may be purchased from the Depository of Unpublished Data, CISTI, National Research Council of Canada, Ottawa, Ont., Canada K I A OS2.

CAN. J. CHEM. VOL. 65, 1987

TABLE2. Bond lengths (A) with estimated standard deviations in parentheses Length


Bond

Uncorr.

Length Corr.

Bond

Uncorr.

Corr.

C(7)-B c(8)-c(9) C(9)-C( 10) C(l0)-C(1 I) C(11)-C(12) C(13)-C(14) C(13)-C(18) C(13)-B C(14)-C(15) C(15)-C(16) C(16)-C(17) C(17)-C(18)

1.601(3) 1.386(3) 1.364(4) 1.369(4) 1.381(3) 1.399(3) 1.398(3) 1.596(3) 1.383(3) 1.377(4) 1.369(4) 1.377(3)

1.605 1.390 1.372 1.379 1.385 1.407 1.405 1.600 1.387 1.384 1.377 1.381

TABLE3. Bond angles (deg) with estimated standard deviations in parentheses Bonds C(2)-O(1)-C(6) C(3)-O(2)-B C(4)-O(3)-B O( 1)-C(2)-C(1) O(1)-C(2)-C(3) C(1)-C(2)-C(3) O(2)-C(3)-C(2) O(2)-C(3)-C(4) C(2)-C(3)-C(4) O(3)-C(4)-C(3) O(3)-C(4)-C(5) C(3)-C(4)-C(5) C(4)-C(5)-C(6) O(1)-C(6)-C(5) C(8)-C(7)-C(l2) C(8)-C(7)-B C(12)-C(7)-B C(7)-C(8)-C(9)

Angle (deg)

Bonds

Angle (deg)

121.4(2) 107.83(14) 108.24(15) 113.5(2) 117.5(2) 129.0(2) 126.6(2) 112.1(2) 121.3(2) 112.1(2) 128.0(2) 119.9(2) 115.7(2) 124.1(2) 116.0(2) 123.7(2) 120.2(2) 122.0(2)

C(8)-C(9)-C( 10) C(9)-C(10)-C( 11) C(l0)-C(l1)-C(l2) C(7)-C(l2)-C(11) C(14)-C(13)-C(18) C(14)-C(13)-B C(18)-C(13)-B C(13)-C(14)-C( 15) C(14)-C(15)-C(16) C(15)-C(16)-C(17) C(16)-C(17)-C(18) C(13)-C(18)-C(17) O(2)-B -0(3) O(2)-B -C(7) -C(13) O(2)-B -C(7) O(3)-B O(3)-B -C(13) C(7)-B -C(13)

120.1(3) 119.7(2) 120.1(2) 122.0(2) 115.9(2) 121.7(2) 122.2(2) 121.6(2) 120.4(2) 119.4(3) 120.2(2) 122.4(2) 99.49(13) 111.0(2) 111.52(15) 109.5(2) 107.0(2) 116.9(2)

atom displaced 0.081(2) A from the C202plane (see Table 4). The conformation of the C202B ring in 1 is intermediate between the essentially planar rings in 2 (13) and 3 (14) and the more folded envelopes observed in 4a and 4 b (15). The 0-B and B-C distances in 1 are relatively long and short, respectively, when compared with those observed in other 0,O-chelates of "Ph2B+" (compounds 2-9, see Table 5), consistent with weak binding of the maltolate oxygen atoms to boron. The O(3)-B distance of 1.600(3) A4 is the longest 0-B bond yet observed for a Ph2B02 compound. Other long 0-B distances occur in 4 a (15), for the pyridinic oxygen atom in 9 (16), and for the aldehyde oxygen atom in 8 (17). In distances in 1-9 ditfer significantly general the two 0-B from one another, by as much as 0.100(6)A in 9. Only in bond lengths equal within compound 3 are the two 0-B experimental error. Despite the sometimes considerable differences between the two 0-B bond lengths, the average 0-B 4Libration corrected bond lengths (esd's assumed equal to those of the uncorrected values) are employed in the discussion of the geometry of the boron atom and are compared with similarly treated distances unless otherwise stated.

TABLE4.

Intra-annular torsion angles (deg) standard deviations in parentheses Atoms

B -0(2) O(2) -C(3) B -0(3) C(4) -0(3) C(3) -0(2)

-C(3)-C(4) -C(4)-O(3) -C(4)-C(3) -B -0(2) -B -0(3)

Torsion angle (deg) 3.2(2) 0.0(2) -3.0(2) 4.5(2) -4.4(2)

distance is a good indicator of the binding strength of the 0,O-chelating ligand to the Ph2B moiety. The B-C distances, which differ by a maximum of 0.020(7) A in 9, also reflect this property. In fact, the sum of all bond lengths involving the boron a t o p is essentially constant for a given chelate ring size: 6.328(7)A for five-membered (1-5') and 6.28(1)A for the six-membered chelates 7-9. Compounds 1-9 fall into three 5Compound 6 with a distance sum of 6.283(6) A is anomalous as a result of 0-B bond shortening to compensate for a sterically lengthened intra-annular N-C bond (18).

TABLE5. Comparison of selected structural parameters (a) Ph2B02moieties (distances in A)*


Compound

0-B

C-B

pMe C. )

*

,

"dB8 PI>'

@ 0CB&@

\Ph

Ph'

'Ph

2

I

Mean 0-B

Me

Mev4Me QBg Ph/

@ M .eA Ph/

'Ph 4 =

1

MeMe 7

"\,Z

0 X B 8

\PI, 3

Sum at B

Mean C-B

Ph/

\Ph 5

Me_$,?_GMe

6, Bg0

PI)/

\Ph

6

R' = ~2 H. b: R' = C6Hl,, R' = Mc)

((,:

( b ) Maltolate ligand and related structures (distances in A, angles in deg)

0(2)-C(3) 0(3)-C(4) o ( 1)--c(2) o ( l)-C(6) c(2)-c(3) c(3)--c(4) c(4)-c(5) C(5)-C(6) O(2)-C(3)-C(2) O(2)-C(3)-C(4) C(2)-C(3)-C(4) O(3)-C(4)-C(3) O(3)-C(4)-C(5) C(3)-C(4)-C(5)

1

Tris(malto1ato)aluminum*

1.343(2) 1.288(2) 1.359(2) 1.344(3) 1.358(3) 1.394(3) 1.410(3) 1.340(3) 126.6(2) 112.1(2) 121.3(2) 112.1(2) 128.0(2) 119.9(2)

1.330(2) 1.271(4) 1.369(13) 1.343(1) 1.350(7) 1.423(9) 1.418(8) 1.313(1) 125.0(6) 115.1(6) 120.0(2) 117.0(6) 124.6(2) 118.4(8)

2,6-Dimethyl-4pyrone HBr H20

4-Pyrone

1.32(2) 1.34 1.39 1.35 1.41 1.39 1.31

1.248 1.355 1.355 1.356 1.440 1.440 1.356

117 126 117

122.9 122.9 115.1

*Average values for the two ordered ligands.

groups. The weakest 0-B binding occurs for compounds 1-4, which all possess unsaturated five-membered chelate rings. The longest mean 0-B distances for this group occur in 1 and 4, which both contain strained ring systems consisting of planar six-membered rings fused to nearly planar five-membered rings. Compounds 5 (19) and 6 (18) contain fully saturated five-membered chelate rings, these particular ligands being among the best donors known for the "Ph,B+" cation. Compounds 7 (13), 8 (17), and 9 (16) all contain less strained six-membered chelate rings. The vco band in the ir spectrum of 1 at 1640 cm-' suggests that O(3) is less strongly bound to the boron atom than are the corresponding oxygen atoms to A1 in tris(malto1ato)aluminum (vco = 1617 cm-') (1). The relative weakness of the O(3)-B

bond with respect to chemically similar bonds has been discussed above. The ratios of the long and short bond distances to the maltolate 0 atoms in the B and A1 complexes (1.044 and 1.029, respectively) further support a stronger interaction of the keto oxygen atom with aluminum. In apparent contradiction to the ir data, the (uncorrected) C(4)-O(3) distance in 1 is 0.016(4) A longer than the corresponding mean (for the two ordered ligands) in tris(maltolato)aluminum. This may result from the greater ring strain in 1 (see below). In general, the bond lengths in the 4-pyrone moieties in 1 and tris(malto1ato)aluminum are similar to one another and to those in 2,6-dimethyl-4-pyrone hydrobromide monohydrate (20) (see Table 5 ) , the C-0 distance involving the protonated keto oxygen atom in the latter structure being slightly longer

CAN. J. CHEM. VOL. 65. 1987


594

than the corresponding distances in the maltolate complexes. Although the structure of malt01 itself has not been determined, the related structures of 4-pyrone (21) and 2,6-dimethyl4-thiopyrone (22) indicate that upon coordination the keto C-0 distance increases relative to that in 4-pyrone while the adjacent ring C-C distances decrease slightly. The remaining bond lengths are essentially unchanged. There are some significant differences between the maltolate ligands of 1 and tris(maltolato)aluminum. The most prominent of these is the difference in the ligand bite (O(2). . .0(3)) which is reduced from an average value of 2.562(8) A in the A1 complex to 2.384(2) A in 1. The 0...0distance in the free ligand would be expected to be approximately 2.75 A. This change is achieved primarily by angular deformations about the ring junction atoms C(3) and C(4); angles in the chelate ring decrease with compensatory increases in the exocyclic 0-C-C and (to a lesser extent) the C-C-C angles in the six-membered heterocycle. Both C-0 distances in the chelate ring of 1 are longer, and the C(3)-C(4) bond shorter than the corresponding mean values in tris(maltolato)aluminum. This could result from partial electron delocalization and/or the increased ring strain in 1.

Acknowledgments We thank the Natural Sciences and Engineering Research Council of Canada for financial support and the University of British Columbia Computing Centre for assistance. We also thank Mr. P. Borda for the C , H analysis. 1. M. M. FINNEGAN, S. J. RETTIG,and C. ORVIG.J. Am. Chem. SOC.108, 5033 (1986). T. G. LUTZ,W. 0. NELSON, A. SMITH,and 2. M. M. FINNEGAN,

C. ORVIG.TObe published.

3. D. R. MCLACHLAN and C. ORVIG. In preparation. 4. P. COPPENS, L. LEISEROWITZ, and D. RABINOVICH. Acta Crystallogr. 18, 1035 (1965). and H. TOMPA.Acta Crystallogr. 19, 1014 5. J. D. MEULENAER (1965). and J. B. MANN.Acta CrystalIogr. Sect. A, 24, 6. D. T. CROMER 321 (1968). E. R. DAVIDSON, and W. T. SIMPSON. J . Chem. 7. R. F. STEWART, Phys. 42, 3175 (1965). and P. COPPENS. Acta Crystallogr. Sect. A, 30, 8. P. J. BECKER 129 (1974); 30, 148 (1974); 31, 417 (1975). and W. C. HAMILTON. Acta Crystallogr. Sect. A, 9. P. COPPENS 26, 71 (1970). 10. F. R. THORNLEY and R. J . NELMES. Acta Crystallogr. Sect. A, 30, 748 (1974). and K. N. TRUEBLOOD. Acta Crystallogr. Sect. 11. V. SCHOMAKER B, 24, 63 (1968). Acta Crystallogr. 9, 747 (1956); 9, 754 12. D. W. J. CRUICKSHANK. (1956); 14, 896 (1961). Can. J . Chem. 60, 2957 (1982). 13. S. J. RETTIGand J. TROTTER. W. KLIEGEL, and D. NANNINGA. 14. S. J. RETTIG,J. TROTTER, Can. J . Chem. 56, 1676 (1978). D. NANNINGA, S. J. RETTIG,and J. TROTTER. 15. W. KLIEGEL, Can. J. Chem. 61, 2493 (1983). H.-W. MOTZKUS, D. NANNINGA, S. J. RETTIG, 16. W. KLIEGEL, and J. TROTTER. Can. J . Chem. 64, 507 (1986). and J. TROTTER. Can. J . Chem. 54, 1168 (1976). 17. S. J. RETTIG H.-W. MOTZKUS, S. J. RETTIG,and J. TROTTER. 18. W. KLIEGEL, Can. J . Chem. 62, 838 (1984). and W. KLIEGEL. Can. J. Chern. 52, 19. S. J. RETTIG,J . TROTTER, 2531 (1974). 20. H. HOPE.Acta Chem. Scand. 19, 217 (1965). R. C. BENSON, P. BEAK,and W. H. FLYGARE. J. 21. C. L. NORRIS, Am. Chem. Soc. 95, 2766 (1973). Bull. Soc. Chim. Belg. 65, 213 (1956). 22. J. TOUSSAINT. 23. W. KLIEGEL, L. PREU,S. J. RETTIG,and J. TROTTER. Can. J. Chem. 64, 1855 (1986).