The preparation and coordination chemistry of

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7[64[ dH "DMSO!d5# 2[4 "8H\ s\ Me#\ 6[8 1H\ d\ J"HH#. 8[2Hz\ ArŁ\ 7[1 ..... 10Ł Cerrada E\ Jones PG\ Laguna A\ Laguna M[ Inorg Chim Acta. 0885^138]052[.
\ PERGAMON

Polyhedron 07 "0888# 482Ð599

The preparation and coordination chemistry of substituted benzenethiols[ Triphenylphosphine gold"I# complexes of sterically demanding and nondemanding arenethiols[ The absence of gold"I#Ð gold"I# interactions Laila S[ Ahmeda\ William Cleggb\ Dominic A[ Daviesa\ 0\ Jonathan R[ Dilworthc\ Mark R[ J[ Elsegoodb\ D[ Vaughan Gri.thsa\ 1\ Lynne Horsburghb\ John R[ Millera\ Nigel Wheatleya\ a

Department of Biological and Chemical Sciences\ University of Essex\ Central Campus\ Wivenhoe Park\ Colchester CO3 2SQ\ U[K[ b Department of Chemistry\ University of Newcastle!upon!Tyne\ Newcastle!upon!Tyne NE0 6RU\ U[K[ c Inorganic Chemical Laboratory\ University of Oxford\ South Parks Road\ Oxford OX0 2QR\ U[K[ Received 14 May 0887^ accepted 05 September 0887

Abstract Novel substituted benzenethiols can be easily prepared via aryl thiocyanates or aryl bromides[ Reaction of ð"Ph2P#AuClŁ with the sterically!nondemanding benzenethiols HSC5H3NMe1!p and HSC5H3NMe¦ 2!p and with the sterically!demanding benzenethiols HSCMe1H1NMe1!p\ HSC5Me3H!p and in the presence of triethylamine yields the monomeric gold"I# complexes ð"Ph2P#Au"SAr#Ł\ which are analogous to the gold!based antiarthritic drug Aurano_n[ Reaction with the sterically demanding dithiol HSC5Me3SH!p in the presence of NEt2 yields the dimeric complex ð""Ph2P#Au#1"m!SC5Me3S!p#Ł[ Spectrochemical and electrochemical data are reported[ The crystal structures of ð"Ph2P#Au"SC5H3NMe1!p#Ł and ð"Ph2P#Au"SC5H3NMe2!p#ŁPF5 have been solved] both complexes are monomeric in the solid state\ lacking the short goldÐgold interaction which is commonly found in gold"I# complexes of soft ligands\ e[g[\ ð"Ph2P#Au"SPh#Ł1[ Þ 0888 Elsevier Science Ltd[ All rights reserved[ Keywords] Gold^ MetalÐmetal interactions^ Cyclic voltammetry^ Thiols

0[ Introduction The use of copper and gold to combat connective tissue disorders dates back to the Bronze Age^ in more modern times\ gold thiolates are increasingly important in the control and treatment of arthritis\ especially since the introduction of the orally!administered drug Aurano_n ð0\1Ł\ ð"Et2P#Au"SR#Ł "HSRtetraacetylthioglucose#[ The mode of action of gold!based anti!arthritic drugs is still not well understood ð2Ł\ although it is known that gold is transported in the blood stream bound to serum  Corresponding author[ Current address] Laboratoire de Catalyse\ Chimie Fine et Polymeres\ Ecole Nationale Superieure de Chimie de Toulouse\ 007 route de Narbonne\ F!20966 Toulouse cedex 3\ France[ Tel[] ¦22!450!064!581^ fax] ¦22!450!064!599^ e!mail] nwheatleyÝensct[fr 0 Current address] School of Chemical and Life Sciences\ University of Greenwich\ Wellington Street\ London SE07 5PF\ UK[ 1 Current address] Department of Chemistry\ Queen Mary and West! _eld College\ Mile End Road\ London\ E0 3NS\ UK[

albumin cysteine!23 ð3\4Ł[ The exchange of gold between physiological thiol groups is thought to be important in its biodistribution and pharmacological activity ð5Ð7Ł[ The phenomenon of {{goldÐgold bonding|| ð8\09Ł\ inter! action between two d09 gold"I# centres less than the sum  \ has received both of the van der Waals radii ð00Ł\ 2[21 A theoretical ð01Ð04Ł and experimental attention ð05Ð16Ł[ The reversible formation of gold"I#Ðgold"I# interactions in the solid state by a gold dithiocarbamate complex leads to luminescence in the presence of organic vapours\ o}ering a basis for the detection of volatile organic com! pounds in the atmosphere ð17Ł[ The energy of these interactions has been estimated to  ð18\29Ł\ be 14Ð29 kJ mol−0 for a goldÐgold distance of 2 A of the same order of magnitude as hydrogen bonding[ There has been much debate as to the exact nature of the interaction between the two formally closed!shell centres\ although it is generally agreed that the relativistic con! traction of the ns orbitals due to the extremely high angular momentum of the electrons in the gold atom

9166!4276:88:, ! see front matter Þ 0888 Elsevier Science Ltd[ All rights reserved[ PII] S 9 1 6 6 ! 4 2 7 6 " 8 7 # 9 9 2 2 8 ! 7

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"Z68# is an important element of the phenomenon ð20Ð 23Ł[ Recent ab initio studies ð24\25Ł failed to reproduce an attractive goldÐgold interaction at the HF level\ although inclusion of electron correlation produced a energy mini! mum of ca[ 9[90 au "¼14 kJ mol−0# at the MP1 level[ The energy minimum is quite soft with respect to goldÐgold distance\ in accordance with the large range of goldÐgold distances observed ð8\09Ł[ Much of the recent interest in the coordination chem! istry of sterically!demanding thiols ð26Ł has been directed at the modelling of active sites in proteins such as fer! redoxins ð27Ł[ In such complexes\ both the metal centre and the thiolate anion possess considerable reactivity\ and a degree of steric protection of the sulfur atom is necessary to allow the isolation of stable complexes[ Most sterically hindered thiols studied to date have been sub! stituted with relatively inert carbon! or silicon!based sub! stituents\ partly due to the limitations on synthetic procedures based on the NewmannÐKwart rearrange! ment ð28Ł or chlorosulfonation ð39\30Ł] however\ this has meant that there has been little attempt to separate the electronic e}ects of the sterically!demanding substituents from those caused purely by their size[ In a recent paper ð31Ł\ Schmidbaur et al[ compared the properties of "benzenethiolato#"triphenylphosphine#! gold"I#\ ð"Ph2P#Au"SPh#Ł\ which exists as a goldÐgold bonded dimer in the solid!state\ with analogous com! plexes of sterically!demanding thiols\ which are mono! meric[ In this paper\ we discuss the synthesis of a number of sterically!demanding and !nondemanding ben! zenethiols and their complexation to "triphenyl! phosphine#gold"I# centres in an attempt to separate the e}ects of size and electronic properties on the properties of the complexes\ with particular reference to short gold"I#Ðgold"I# interactions[ 1[ Experimental Chloro"triphenylphosphine#gold"I# ð32Ł\ 3!"dimethyl! amino#benzenethiol ð33Ł and 1\2\4\5!tetramethyl! benzenethiol ð34\35Ł were prepared by literature methods^ solvents were dried by normal methods ð36Ł\ and distilled under dry oxygen!free nitrogen prior to use^ all other chemicals were obtained from normal commercial sour! ces and used as received[ Microanalyses were performed by Mr S[ Hodder "University of Essex#[ NMR spectra were obtained on an JEOL EX!169 spectrometer ð0H 169 MHz\ 02C 56[8 MHz\ standard SiMe3^ 02P 098[2 MHz\ standard 74) H2PO3 "ext[#Ł[ 1[0[ Trimethyl"3!thiocyanatophenyl#ammonium iodide "0# 3!"Dimethylamino#phenyl thiocyanate ð37\38Ł "5[9 g\ 23 mmol# and iodomethane "4[2 ml\ 01[0 g\ 74 mmol# were

re~uxed in methanol for 13 h[ The mixture was allowed to cool and a small amount of diethyl ether added to ensure complete precipitation\ yielding trimethyl"3!thio! cyanatophenyl#ammonium iodide "4[7 g\ 77)# as a yel! low precipitate[ m[p[ 054>C "from EtOH#[ Found C\ 26[1^ H\ 2[8^ N\ 7[5[ C09H02IN1S requires C\ 26[4^ H\ 3[0^ N\ 7[64[ dH "DMSO!d5# 2[4 "8H\ s\ Me#\ 6[8 ð1H\ d\ J"HH# 8[2 Hz\ ArŁ\ 7[1 ð1H\ d\ J"HH# 8[2 Hz\ ArŁ[ dC "DMSO! d5# 54[3 "s\ Me#\ 009[7 "s\ NCS#\ 011[6 "s\ Ar#\ 016[5 "s\ Ar#\ 029[8 "s\ Ar#\ 036[3 "s\ Ar#[ 1[1[ 3!"Trimethylammonio#benzenethiol borate "1#

tetraphenyl!

"Trimethyl "3!thiocyanatophenyl#ammonium iodide# "1[9 g\ 5[2 mmol# and sodium borohydride "9[36 g\ 02 mmol# were re~uxed in methanol "49 ml# for 13 h under an atmosphere of dry oxygen!free nitrogen[ The mixture was allowed to cool\ and acidi_ed to pH 5 with 09) aq[ hydrochloric acid[ The mixture was _ltered\ and a solution of sodium tetraphenylborate "1[06 g\ 5[2 mmol# in the minimum quantity of methanol was added\ yielding 3!"trimethylammonio#benzenethiol tetraphenylborate "1[1 g\ 61)# as a white precipitate[ m[p[ 062Ð064>C[ Found C\ 79[8^ H\ 5[8^ N\ 1[8[ Calc[ for C22H23BNS C\ 70[2^ H\ 6[9^ N\ 1[8[ dH "DMSO!d5# 2[4 "0OH\ s\ Me#\ 5[6Ð6[2 "19H\ m#\ 6[34 ð1H\ d\ J"HH# 8[0 Hz\ ArŁ\ 6[53 ð1H\ d\ J"HH# 8[0 Hz\ ArŁ[ dC "DMSO!d5# 45[1 "s\ Me#\ 019[8 "s\ Ar#\ 010[5 "s\ BPh3#\ 014[3 "s\ BPh3#\ 017[7 "s\ Ar#\ 024[4 "s\ BPh3#\ 025[1 "s\ Ar#\ 032[7 "s\ Ar#\ 053[3 ðq\ J"CB# 38[5 Hz\ BPh3Ł[ The hexa~uorophosphate salt was "m[p[ 063Ð066>C ð49Ł# was prepared by an analogous method[ 1[2[ 3!Dimethylamino!1\5!dimethylbenzenethiol "2# 3!Dimethylamino!1\5!dimethylphenyl thiocyanate ð40Ł "0[9 g\ 4[3 mmol#\ sodium sul_de nonahydrate "1[9 g\ 15 mmol# and sodium hydroxide "9[14 g\ 5[14 mmol# were re~uxed in ethanol "14 ml# for 3 h under an atmosphere of dry oxygen!free nitrogen[ The mixture was allowed to cool\ and then poured in to a thoroughly degassed 09) aq[ solution of ammonium chloride "49 ml#[ The mixture was extracted with degassed diethyl ether "2×04 ml#[ The ethereal solution was dried over magnesium sulfate and the solvent removed\ yielding 3!dimethylamino!1\5! dimethylbenzenethiol[0 dH "CDCl2# 1[3 "5H\ s\ ArÐCH2#\ 2[9 "5H\ s\ NÐCH2#\ 2[8 "0H\ s\ SH#\ 5[4 "1H\ s\ ArÐH#[ 1[3[ 1\2\4\5!Tetramethylbenzene!0\3!dithiol "4# 0\3!Bis"butylthio#!1\2\4\5!tetramethylbenzene ð40Ł "1[4 g\ 5[5 mmol# was dissolved in liquid ammonia 0 The product was usually found to be contaminated with ca[ 19) bis"3!dimethylamino!1\5!dimethylphenyl#disul_de\ dH "CDCl2# 1[1\ 1[8\ 5[3[

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"099 ml# under an atmosphere of dry oxygen!free nitro! gen[ Small portions of metallic sodium were added until a blue colour persisted in the solution for one hour[ Solid ammonium chloride was added in small portions until the blue colour was just extinguished[ The ammonia was allowed to evaporated o}\ leaving a white residue which was suspended in chloroform "199 ml#[ An excess of dry hydrogen chloride gas was passed through the suspen! sion[ The remaining solid was _ltered o}\ and the chloro! form removed on a rotary evaporator\ giving 1\2\4\5! tetramethylbenzene!0\3!dithiol "0[2 g\ 87)# as a yellow solid[ dH "CDCl2# 1[3 "01H\ s\ Me#\ 2[9 "1H\ s\ SH#[ dc "CDCl2# 08[6 "s\ Me#\ 017[8 "s\ CÐMe#\ 022[2 "s\ CÐSH#[ 1[4[ Gold"I# complexes ð"Ph2P#AuClŁ "9[1 g\ 399 mmol#\ thiol "399 mmol# and triethylamine "9[93 g\ 309 mmol# were re~uxed in meth! anol "29 ml# for 2 h under an atmosphere of dry oxygen! free nitrogen[ Cooling yielded the "triphenyl! phosphine#gold"I# complex as a white or o}!white pre! cipitate[ Analytical and other data for the complexes are given in Tables 0 and 1[ 1[5[ Cyclic voltammetry Measurements were made using a custom!made glass cell housing the three electrodes and a nitrogen bubbler[ The working and secondary electrode were constructed from platinum wire fused in glass] a silver reference elec! trode was also used[ The cell was powered by a EG and G PAR 251 scanning potentiostat\ and the data recorded on a 275 microcomputer using the ConDecon program[ Test solutions were approximately 099 mM in complex and 0999 mM in Bu3N¦BF!3 "support electrolyte#] solvents and results "quoted relative to Cp1Fe:Cp1Fe¦9 mV# are given in Table 2[ 1[6[ Crystal structure determination Crystal data and experimental details are given in Table 3[ The structures were solved by Patterson methods

followed by normal heavy atom procedures\ and re_ned by the full!matrix least!squares method[ All non!hydro! gen atoms were re_ned anisotropically\ while hydrogens were placed in calculated positions[ Atomic coordinates\ interatomic distances and angles\ anisotropic dis! placement parameters and hydrogen atom positions have been deposited with the Cambridge Crystallographic Data Centre\ Cambridge\ with deposition codes 090578 for 5 and 090582 for 6[ 2[ Results and discussion 2[0[ Preparation of ligands Thiocyanation has previously provided a convenient route to 3!"dimethylamino#benzenethiol ð33\47Ł\ with the thiocyanate being reduced by either LiAlH3 or sodium sul_de[ Quaternisation of the amino group does not appear to interfere with the subsequent reduction\ and so this method can also be used to prepare the unusual\ electron!de_cient trimethylammonio!substituted ben! zenethiols[ However\ the initial thiocyanation step is e}ective only with electron!rich phenyl rings] our attempts to prepare 0\1\3\4!tetramethyl!2\5!dithio! cyanatobenzene "03# by this method were unsuccessful[ We were also unable to prepare 1\2\4\5!tetramethyl! benzene!0\3!disulfonyl dichloride "04# from any of a num! ber of possible precursors[ Hence we used an adaptation of the method of Adams and Ferretti ð48Ð50Ł to prepare 1\2\4\5!tetramethylbenzene!0\3!dithiol "durene dithiol# "4# "see Scheme 0#] this is a signi_cant improvement ð40Ł in terms of simplicity\ cost and safety over the previous six!step synthesis of Raasch ð51Ð53Ł[ 2[1[ Preparation of gold"I# complexes Our gold"I# complexes were stable inde_nitely at room temperature in the solid state\ in line with the _ndings of Schmidbaur et al[ ð31Ł and Fackler et al[ ð54Ł and contrary to the implications of the work of Kowala et al[ ð55\56Ł[ However\ we did notice a small degree of dis!

Table 0 Analyticala and other data for the gold"I# complexes Complex

Yieldb ")#

dPc:ppm

C

H

N

5 ð"Ph2P#Au"SC5H3NMe1!p#Ł 6 ð"Ph2P#Au"SC5H3NMe2!p#ŁPF5 7 ð"Ph2P#Au"SC5Me1H1NMe1!p#Ł 8 ð"Ph2P#Au"SC5Me3H!p#Ł 09 ð""Ph2P#Au#1SC5Me3S!pŁ

66 61 57 69 54

¦28[8 ¦28[8d ¦27[6 ¦27[8 ¦28[9

49[8 "40[0# 31[9 "31[9# 42[6 "42[4# 42[4 "42[7# 38[2 "38[5#

3[04 "3[0# 2[5 "2[6# 3[4 "3[2# 3[6 "3[4# 2[7 "2[7#

1[2 "1[2# 0[7 "0[7# 1[3 "1[1#

a

Required values are given in parentheses[ Based on ð"Ph2P#AuClŁ[ c 098[2 MHz\ standard 74) aq[ H2PO3 "ext[#\ solvent CDCl2 unless otherwise stated[ d Solvent acetone!d5[ b

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L[S[ Ahmed et al[ : Polyhedron 07 "0888# 482Ð599 Table 1 H and 02C"0H#!NMRa data for the gold"I# complexes

0

Com! pound 5 6 7 8 09

NMR!data

dH 1[8 "5H\ s\ NÐCH2#\ 5[04 ð1H\ d\ J"HH# 7[5 Hz\ ArŁ\ 6[4 "06Hb\ m\ Ar#[ dC 30[1 "s\ NÐCH2#\ 002[5 "s\ C2ÐH#\ 018[2 "s\ C1ÐH#\ 022[4 "s\ CÐS#\ 037[9 "s\ CÐNMe1#[ c dH 2[7 "8H\ s\ NÐCH2#\ 6[5 "08Hb\ m\ Ar#[ dcC 46[6 "s\ NÐCH2#\ 019[8 "s\ C1ÐH#\ 029[6 "s\ C2ÐH#\ 022[2 "s\ CÐS#\ 028[3 "s\ CÐNMe2#[ dH 1[6 "5H\ s\ ArÐCH2#\ 1[8 "5H\ s\ NÐCH2#\ 5[5 "0H\ s\ Ar#[ dC 24[0 "s\ ArÐCH2#\ 30[0 "s\ NÐCH2#\ 001[7 "s\ CÐH#\ 028[4 "s\ CÐCH2#\ 033[4 "s\ CÐS#\ 036[7 "s\ CÐNMe1#[ dH 1[2 "5H\ s\ C1ÐCH2#\ 1[6 "5H\ s\ C2ÐCH2#\ 5[64 "0H\ s\ Ar#[ dC 19[1 "s\ C1ÐCH2#\ 10[2 "s\ C2ÐCH2#\ 017[1 "s\ CÐH#\ 021[7 "s\ C2ÐCH2#\ 025[8 "s\ C1ÐCH2#\ 028[4 "s\ CÐS#[ dH 1[7 "01H\ s\ ArÐCH2#[ dC 11[2 "s\ ArÐCH2#\ 024[5 "s\ CÐS#\ 025[4 "s\ CÐCH2#[

a0

H\ 169 MHz^ 02C\ 56[8 MHz^ standard SiMe3\ solvent CDCl2 unless otherwise speci_ed^ peaks assigned to triphenylphosphine are not recorded unless otherwise speci_ed[ b Includes 04H corresponding to PPh2[ c Solvent acetone!d5[

Table 2 Electrochemical dataa for the gold"I# complexes Solvent 5

CHCl2

6 7

DMSO!d5 CH1Cl1

8 09

CH1Cl1 CH1Cl1

Eox 069 0122 −003 341 163

a Potentials in mV relative to "Cp1Fe:Cp1Fe¦¦439 mV vs SCE in THF#[

E0:1

DE

297 480

066 040

−204 286 843 695

134 192 055 105

Cp1Fe:Cp1Fe¦9 mV

proportionation of the complexes of sterically!demand! ing thiols on attempted recrystallisation\ leading to deposition of metallic gold[ 2[2[ Electrochemistry The _ve gold complexes showed a complex elec! trochemistry when studied by cyclic voltammetry[ On the _rst sweep\ the complexes showed a broad oxidation peak at −003 to ¦482 mV "see Table 2#\ with the more elec! tron!rich thiols "e[g[\ 5 and 7# giving the lower values for the oxidation potential[ No corresponding reduction peak could be observed\ even on increasing the sweep speed to 1999 mV s−0 and reducing the temperature to 199 K and the oxidation peak was substantially reduced in height or even absent in immediately subsequent scans\ indicating an EC!type process\ where an electrochemical oxidation is immediately followed by a chemical rearrangement[ This can be explained by an initial trans! fer of an electron from the complex\ followed by dis! sociation of a thiyl radical\ which may then dimerise to form a disul_de or react with the solvent or adventitious

water "see Scheme 1#[ The irreversibility of this process and the breadth of the peaks in the voltammagrams pre! vented a quantitative measurement of electron stoi! chiometry\ although the results are consistent with a two electron transfer in the case of the dimeric complex 09[ In all the complexes except 6\ there are additional oxi! dation processes at more positive potentials\ one for 8 and 09 and two for 5 and 7[ These all have coupled reduction peaks\ although these are much smaller than the oxidation peaks[ The interpeak spacings and the observed variation of peak potential with sweep speed both indicate that the electron transfer in these processes is very slow\ which may also explain the disparity in peak currents[ 2[3[ Crystal structures of 5 and 6 Both 5 and 6 crystallise in the triclinic P0¹ space group\ with two molecules per unit cell\ related by a centre of symmetry[ The molecular structures are shown in Figs 0 and 1\ and signi_cant interatomic distances and angles are given in Tables 4 and 5[ The geometry around the gold atom is approximately linear\ with PÐAuÐS being 065[42"4#> for 5 and 064[41"3#> for 6[ Perhaps surpris! ingly\ given the very di}erent electronic properties of the two thiol phenyl rings\ there is no signi_cant di}erence  for 5 and between the two AuÐS distances^ 1[187"1# A  1[182"2# A for 6[ These distances are within the range of AuÐS distances observed to date for "tri!  phenylphosphine#gold"I# thiolates\ 1[173Ð1[209 A ð2\8\09\31\54\57Ð68Ł] the angles at sulfur\ 093[0"1#> for 5  and 092[5"1#> for 6 and the AuÐP distances\ 1[148"0# A  for 5 and 1[148"2# A for 6\ are also typical for this type of complex[ The most striking feature of these crystal structures is the absence of any short gold"I#Ðgold"I# interaction\ with

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486

Table 3 Crystal data and experimental details of the structure determinations for 5 and 6

Colour and habit Crystal dimensions "mm# Formula Space group # a "A # b "A # c "A a "># b "># g ">#  2# U "A Z Di}ractometer Radiation Re~ections measured Unique re~ections Observed re~ections Transmission factors Re_nement Weighting scheme "w−0#

5 orangeÐbrown tablets 9[4×9[5×0[9 C15H14AuNPS P0¹ "No[ 1# 8[6493"6# 09[823"1# 02[2761"8# 68[429"7# 57[823"5# 54[257"8# 0198[7"1# 1 Enraf!Nonius CAD3 MoÐKa 3139 "0[4²u²14# 3139 2891 ðF×2s"F#Ł max 0[9\ min 9[68 F s1"Fo#¦9[9993Fo1

Agreement analysis "S# Final R Final R? Program

0[75 9[920 9[934 Molen ð45Ł

Scheme 0[

 for 5 and minimum Au = = = Au distances of 5[070 A  4[516 A for 6[ The possibility that a goldÐgold interaction might be overtaken by a stacking interaction between

6 pale blue tablets 9[31×9[02×9[09 C16H17AuNPS = PF5 P0¹ "No[ 1# 7[541"8# 09[533"01# 04[607"06# 76[41"8# 76[56"6# 63[11"01# 0280"2# 1 StoeÐSiemens ð44Ł MoÐKa 4064 "1[5²u²14# 3781 3536 ðF×1s"F#Ł max 9[349\ min 9[117 F1 s1"Fo1#¦1[5282P¦9[9911P1 ðP"Fo1¦1F1c#:2Ł 0[960 9[9145 9[9619 SHELXTL ð46Ł

the thiolate rings of 5 was investigated\ as the rings are parallel^ however\ the closest approach is [ C"01# = = = C"01?#2[49"0# A Short goldÐgold interactions have been observed in a wide range of gold"I# compounds ð8\09Ł\ including ð"Ph2P#Au"SPh#Ł1 "05# ð31\68Ł and ð"Ph2P#Au"C2CPh#Ł1 ð79Ł[ It has been proposed that the tendency to form goldÐgold bonds increases with the softness of the ligand ð8\09\70\71Ł\ and hence we would de_nitely expect 5 to show such a short contact\ as the 3!"dimethyl! amino#benzenethiolato ligand is softer than the ben! zenethiolato ligand in 05[ However\ many gold"I# complexes of the type ðLAuXŁ\ where X is a soft anionic ligand such as iodide\ exist as chains or clusters of distinct anions and cations\ ðL1AuŁðAuX1Ł\ in the solid state ð8\09\72Ð76Ł[ It would be expected that any goldÐgold interactions in these com! pounds would be enhanced by the Coulombic attraction between the ions\ although recent ab initio studies indicate that the electron populations on the gold centres in the two isomeric forms\ ðLAuXŁ1 and ðL1AuŁ¦ðAuX1Ł−\ as well as their total energies\ are very similar ð77Ł[ Schmidbaur et al[ ð31Ł have postulated that the steric demands of the thiol ligand prevent goldÐgold inter!

Scheme 1[

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Fig[ 0[ The molecular structure of ð"Ph2P#Au"SC5H3NMe1!p#Ł[

Fig[ 1[ The molecular structure of the ð"Ph2P#Au"SC5H3NMe2!p#Ł¦ cation[

actions in ð"Ph2P#Au"SC5R2H1#Ł "RMe\ Et\ Pri#\ despite the bending of the phenyl ring away from any obstacle "AuÐSÐC 090[6Ð009[7># and the softer nature of the thiol ligands compared to the benzenethiolato ligand[ This explanation for the absence of short goldÐgold contacts has been applied in other systems ð54\78\89Ł[ However\ in neither 5 nor 6 is the arenethiolate ligand signi_cantly more sterically demanding than that in 05[

The long Au [ [ [ Au distances in 5 and 6 cannot be explained in terms of ligand softness or steric demands[ Hence we are forced to conclude that explanations of the existence or absence of short gold"I#Ðgold"I# contacts which are based on the softness or steric demands of the anionic ligand are at best incomplete\ and that such contacts should be viewed as just one of the many inter! molecular interactions which occur to stabilise a crystal[

L[S[ Ahmed et al[ : Polyhedron 07 "0888# 482Ð599 Table 4  # and angles "># for ð"Ph2P#Au! Signi_cant interatomic distances "A "SC5H3NMe1!p#Ł "5#] _gures in parentheses indicate the estimated stan! dard deviation in the least signi_cant digit Complex

Distance or  or ># angle "A

Complex

Distance or  or ># angle "A

AuÐP PÐC"10# PÐC"20#

1[148"0# 0[705"4# 0[707"4#

AuÐS SÐC"00# PÐC"30#

1[187"1# 0[652"5# 0[797"4#

PÐAuÐS C"10#ÐPÐAu C"30#ÐPÐAu C"10#ÐPÐC"30#

065[42"4# 004[3"1# 002[2"1# 094[2"1#

C"00#ÐSÐAu C"20#ÐPÐAu C"10#ÐPÐC"20# C"20#ÐPÐC"30#

093[0"1# 009[4"1# 095[1"1# 094[3"1#

Table 5  # and angles "># for ð"Ph2P#Au! Signi_cant interatomic distances "A "SC5H3NMe2!p#ŁPF5 "6#] _gures in parentheses indicate the estimated standard deviation in the least signi_cant digit Complex

Distance or  or ># angle "A

Complex

Distance or  or ># angle "A

AuÐP"0# P"0#ÐC"6# P"0#ÐC"0#

1[148"2# 0[703"3# 0[703"4#

AuÐS SÐC"08# PÐC"02#

1[182"2# 0[667"4# 0[710"4#

P"0#ÐAuÐS C"0#ÐP"0#ÐAu C"6#ÐP"0#ÐAu C"6#ÐP"0#ÐC"0#

064[41"3# 004[7"1# 003[7"1# 093[7"1#

C"08#ÐSÐAu C"02#ÐP"0#ÐAu C"0#ÐP"0#ÐC"02# C"6#ÐP"0#ÐC"02#

092[5"1# 096[2"1# 096[4"1# 095[0"1#

Acknowledgements The authors would like to thank Mr[ N[ L[ Barnard "University of Essex# for his help in conducting the elec! trochemical experiments\ Johnson Matthey for their gift of sodium tetrachloroaurate\ and the following for stu! dentships during the period of this work] European Social Fund "LSA#\ London Borough of Bromley "DAD#\ B[ P[ Chemicals Ltd[ "NW#[ The authors also thank Professor Pekka Pyykko "University of Helsinki#\ as well as one of the reviewers of the original submission\ for bringing to our attention certain published articles[

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