The course of oxidative addition reactions of haloalkynes and haloalkenes to dimethyl- and dialkynylaurate(I) anions [RAuR]

The reactions of halo-alkynes Cl-CCH, C-lCC-Cl or PhCC-I with solutions of Li⁺[MeAuMe]⁻ in diethylether containing Ph₃P do not give the expected oxidative addition products Me₂(RCC)Au(PPh₃) with R = H, Cl, Ph. A mixture of other complexes is obtained instead which are generated in secondary reactions involving reductive elimination of ethane and/or dialkyne. However, addition of the halo-alkene H(Cl)CCCl₂ to the same substrate solution affords trans-Me₂[trans-H(Cl)CC(Cl)]Au(PPh₃) in good yield. Its molecular structure with pseudo-C_s symmetry has been determined by the solution NMR spectra and a single-crystal X-ray diffraction study. The reaction of methyl iodide with solutions of Li⁺[RCCAuCCR]⁻ in diethylether containing PPh₃ give the quaternary salts Ph₃PMe⁺ [RCCAuCCR]⁻ as the main products and only small amounts of cis-Me₂(RCC)Au(PPh₃) complexes probably formed in a series of oxidative addition, reductive elimination, and substitution reactions. The structure of Ph₃PMe⁺ [PhCCAuCCPh]⁻ has been determined.     

Synthesis and reactivity of iron carbonyl clusters containing alkynethiolate ligands

The new cluster Li[Fe₃(μ₃,η¹-SCCFc)(CO)₉] reacts with ClAuPPh₃ to afford compound [Fe₃Au(μ₄,η²-CCFc)(CO)₉(PPh₃)], which exhibits an isomeric equilibrium in solution with the cluster [Fe₃Au(μ₃,η²-CCFc)(CO)₉(PPh₃)].The rupture of C-S bonds in the thioethers Me₃SiCCSCCR (R = Fc, SiⁱPr₃) in the presence of Fe₃(CO)₁₂, yields to the clusters [Fe₃(μ-SCCSiⁱPr₃)(μ-CCSiMe₃)(CO)₉] and [Fe₃(μ,η²-(SiⁱPr₃)CCCCSiMe₃)(μ₃-S)(CO)₉] together with the unexpected compounds [Fe₂(μ-SCC(H)R)(CO)₆] (R = SiMe₃, SiⁱPr₃).Additionally, the dinuclear derivatives [Fe₂(μ-SCCR)(μ-CCR′)(CO)₆] (R = Fc, R′ = SiMe₃; R = SiMe₃, R′ = Fc; R = SiMe₃; R′ = SiⁱPr₃) have also been obtained. These compounds have been spectroscopically characterized and the crystal structure of some of them has been solved.     

The synthesis, structure, reactivity and electrochemical properties of ruthenium complexes featuring cyanoacetylide ligands

The complex [Ru(CCCN)(dppe)Cp*] (1) is readily obtained (ca. 70%) from the sequential reaction of [Ru(CCH₂)(dppe)Cp*]PF₆ with ⁿBuLi and phenyl cyanate. The complex behaves as a typical transition metal acetylide upon reaction with tetracyanoethene, affording a metallated pentacyanobutadiene. Complex 1 is a useful metalloligand, and its reactions with [W(thf)(CO)₅], [RuCl(PPh₃)₂Cp], [RuCl(dppe)Cp*] or cis-[RuCl₂(dppe)₂] all afforded products featuring the M-CCCN-M′ motif, for which ground state structures indicate a degree of polarisation. Electrochemical and spectroelectrochemical studies reveal moderate interactions between the metal centres in the 35-electron dications [{Cp*(dppe)Ru}(μ-CCCN){RuL₂Cp′}]²⁺ (RuL₂Cp′ = Ru(PPh₃)₂Cp, Ru(dppe)Cp*).     

Reactivity of alkynyl Pd(II) azido complexes toward organic isocyanides, isothiocyanates, and nitriles

Alkynyl Pd(II) azido complexes of the type [Pd(N₃)(CCR)L₂] (1-3) were obtained by reactions of aqueous NaN₃ with [Pd(Cl)(CCR)L₂] (R = Ph or C(O)OMe). Treating compounds 1-3 with organic isocyanides (R-NC) afforded novel complexes, trans-[Pd(CCPh)(NCNR)(PMe₃)₂] (R = 2,6-Me₂C₆H₃ (4) or 2,6-Et₂C₆H₃ (5)) and trans-[Pd(CCR)(CN₄-t-Bu)L₂] (6: L = PMe₃, R = Ph; 7: L = PEt₃, R = C(O)OMe; 8: L = PMe₃, R = C(O)OMe), which contain either a carbodiimido or a C-coordinated tetrazolato group. Reactions of compounds 1 and 2 with R-NCS (R = 2,6-Me₂C₆H₃ or CH₂CH₃) and 1,4-phenylene diisothiocyanate (C₆H₄(NCS)₂) smoothly proceeded to give tetrazole-thiolato complexes, trans-[Pd(CCPh)(SCN₄-R)L₂] (L = PMe₃, R = Et (9) or 2,6-Me₂C₆H₃ (10); L = PEt₃, R = 2,6-Me₂C₆H₃ (11)), and a phenylene-bridged dinuclear Pd(II) tetrazole-thiolato complex, [(PEt₃)₂(CCPh)Pd(SCN₄-(μ-C₆H₄)-SCN₄)Pd(CCPh)(PEt₃)₂] (12), respectively. Complexes 9-12 contain the Pd-S bond that is formed by the dipolar cycloaddition of the organic isothiocyanate to the Pd-azido bond. In contrast, the corresponding reactions of compounds 1and 2 with C₆F₅CN and Me₃SiCN (organic nitriles, R-CN) gave an N-coordinated Pd(II)-tetrazolato compound {trans-[Pd(CCPh)(N₄C-C₆F₅)(PMe₃)₂] (13)} and a mixture of Pd(II)-cyano complexes {trans-[Pd(CCPh)(CN)(PEt₃)₂] (14) and [Pd(CN)₂(PEt₃)₂] (15)}, respectively. Bis(phosphine) bis(cyano) complexes of Pd and Ni, [M(CN)₂L₂] (L = PEt₃, PMe₃; L₂ = DEPE), could be obtained independently by the reactions of [M(N₃)₂L₂] with excess Me₃SiCN in organic solvents.     

Ferrocenyl-substituted allenylidene complexes of chromium, molybdenum and tungsten: Synthesis, structure and reactivity

Bis(ferrocenyl)-substituted allenylidene complexes, [(CO)₅MCCCFc₂] (1a-c, Fc = (C₅H₄)Fe(C₅H₅), M = Cr (a), Mo (b), W (c)) were obtained by sequential reaction of Fc₂CO with Me₃Si-CCH, KF/MeOH, n-BuLi, and [(CO)₅M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO)₅CrCCC(Fc)R] (R = Ph, NMe₂), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HCCC(Fc)(Ph)OH with [(CO)₅Cr(THF)] followed by desoxygenation with Cl₂CO, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO)₅CrC(OR)CHC(NMe₂)Fc], and (c) replacement of OMe in [(CO)₅CrCCC(OMe)NMe₂] by Fc. Complex 1a was also formed when the mono(ferrocenyl)allenylidene complex [(CO)₅CrCCC(Fc)NMe₂] was treated first with Li[Fc] and the resulting adduct then with SiO₂. The replacement route (c) was also applied to the synthesis of an allenylidene complex (7a) with a CC spacer in between the ferrocenyl unit and C_γ of the allenylidene ligand, [(CO)₅CrCCC(NMe₂)-CCFc]. The related complex containing a CHCH spacer (9a) was prepared by condensation of [(CO)₅CrCCC(Me)NMe₂] with formylferrocene in the presence of NEt₃. The bis(ferrocenyl)-substituted allenylidene complexes 1a-c added HNMe₂ across the C_α-C_β bond to give alkenyl(dimethylamino)carbene complexes and reacted with diethylaminopropyne by regioselective insertion of the CC bond into the C_β-C_γ bond to afford alkenyl(diethylamino)allenylidene complexes, [(CO)₅MCCC(NEt₂)CMeCFc₂]. The structures of 5a, 7a, and 9a were established by X-ray diffraction studies.     

Organometallic π-tweezers incorporating pyrazine- and pyridine-based bridging units

Pyrazine- and pyridine-based π-conjugated σ-donor molecules, such as 4,4′-bipyridine, 1,2-di(4-pyridyl)ethylene, 3,5-dipyridyl-1,2,4-triazole, N,N′-bis(4-pyridylmethylidene)benzene-1,4-diamine, 2,5-di(pyridylmethylidene)cyclopentanone, 2,6-di(4-pyridylmethylidene)cyclohexanone (LL, 2a-2g) can successfully be used to span heterobimetallic π-tweezer units of the type [{[Ti](μ-σ,π-CCSiMe₃)₂}M]⁺ ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti; M = Cu, Ag). The thus accessible di-cationic species [{[Ti](μ-σ,π-CCSiMe₃)₂}MLLM{(Me₃SiCC-μ-σ,π)₂[Ti]}]²⁺ (4), which are formed via the formation of [{[Ti](μ-σ,π-CCSiMe₃)₂}MLL]⁺ (3) complexes, can be isolated in yields between 66% and 99%.However, when C₅H₄NCHCHC₆H₄CHCHNC₅H₄ (5a) and C₅H₄NCHNC₆H₄CHCHNC₅H₄ (5b), respectively, are reacted with {[Ti](μ-σ,π-CCSiMe₃)₂}AgBF₄(1c) in a 1:1 molar ratio, then the silver(I) ion is released from the organometallic π-tweezer 1c and coordination polymers [AgBF₄ · 5a]_n (6a) and [AgBF₄ · 5b]_n (6b) along with [Ti](CCSiMe₃)₂ (7) are formed in quantitative yield.     

The crystal structures of NSF3 and (NSF2N(CH3)CH2-)2: How short is the ‘Crystallographic’ NS triple bond?

The synthesis of the first unequivocally characterised bis(difluorothiazyne), [NSF₂N(CH₃)CH₂-]₂ is reported. The crystal structures of this and NSF₃ are also reported. NSF₃ has the same geometrical parameters, within error, as it does in the gas phase. PIXEL calculations show that the principal interactions in its crystal structure are SN?SN dipolar contacts, which form chains with S?N = 3.533(2) Å. These contacts are reminiscent of those observed in the crystal structures of ketones. The exchange of a fluorine by a dialkylamino group has almost no influence on the NS bond distance while the SF bonds are significantly elongated. This behaviour is explained by negative hyperconjugation and confirmed by experimental data (as far as available) and quantum chemical calculations for NSF_n(NMe₂)_3−n and NSF_nPh_3−n (n = 1-3).     

Organometallic complexes for nonlinear optics. Part 36. Quadratic and cubic optical nonlinearities of 4-fluorophenylethynyl- and 4-nitro-(E)-stilbenylethynylruthenium complexes

The complexes trans-[Ru(CC-4-C₆H₄F)X(dppe)₂] [X = Cl (1), CCPh (2), CC-4-C₆H₄NO₂ (3)], trans-[Ru{CC-4-C₆H₄-(E)-CHCH-4-C₆H₄NO₂}X(dppe)₂] [X = CCPh (4), CC-4-C₆H₄CCPh (5)], and [C₆H₃-1,3-{CC-trans-[RuCl(dppe)₂]}₂-5-(CC-4-C₆H₄F)] (6) have been synthesized and the identity of 1 confirmed by a single-crystal X-ray diffraction study. Cyclic voltammetry reveals a metal-centered oxidation, the potential of which is largely invariant on alkynyl ligand replacement across the series 1-5; the diruthenium complex 6 shows two oxidation processes, consistent with weakly interacting metal centers. Hyper-Rayleigh scattering (HRS) studies at 1064 nm using ns pulses suggest quadratic nonlinearities for 3-5 that are amongst the largest thus far for organometallic complexes, a trend maintained with the two-level-corrected data. HRS studies at 800 nm using fs pulses and amplitude modulation to remove multi-photon fluorescence contributions reveal significant fluorescence-free nonlinearities for 3-5; the frequency-independent nonlinearities calculated from the 800 nm results are suggestive of fluorescence contributions to the 1064 nm data. Z-scan studies at 820 nm reveal cubic nonlinearities that increase with the size of the π-system, although error margins are significant.     

Reactions of [Os3(CO)10(MeCN)2] with ethynyl thiophenes: The formation of linked clusters

The reaction of 2 equiv. of [Os₃(CO)₁₀(MeCN)₂] with R-CC-L-CC-R (R = H, L = (C₄H₂S); R = SiMe₃, L = (C₄H₂S-C₄H₂S), (C₄H₂S-C₄H₂S-C₄H₂S), (C₄H₂S)-(C₁₄H₈)-(C₄H₂S)) affords the series of linked clusters [{Os₃(CO)₁₀}(HCC(C₄H₂S)CCH){Os₃(CO)₁₀}] (1), [{Os₃(CO)₁₀}(Me₃SiCC(C₄H₂S-C₄H₂S)CCSiMe₃){Os₃(CO)₁₀}] (2), [{Os₃(CO)₁₀}(Me₃SiCC(C₄H₂S-C₄H₂S-C₄H₂S)CCSiMe₃){Os₃(CO)₁₀}] (4) and [{Os₃(CO)₁₀}(Me₃SiCC(C₄H₂S)-(C₁₄H₈)-(C₄H₂S)CCSiMe₃){Os₃(CO)₁₀}] (6) as the major products. The complexes have been characterised by a range of spectroscopic methods and, in the case of 1 and 2 by single crystal X-ray crystallography. The alkyne groups cap the osmium triangles in the expected μ₃-η²-||-bonding mode and each triangle is coordinated by nine terminal and one μ₂-carbonyl group. Solution UV-Vis spectra of the complexes were similar to those observed for the free ligands consistent with there being little delocalisation between the cluster units and the thiophene groups.     

Benzene and heterocyclic rings formation in cycloaddition reactions catalyzed by RuCp derivatives: DFT studies

The mechanism of the RuCp(COD)Cl catalyzed cyclotrimerization of acetylene, as well as the cyclocotrimerization of two alkynes with one molecule of ethylene, R-CN (R = H, Me, Cl, COOMe), CX₂ (X = O, S, Se), and HNCX (X = O, S) investigated by means of high level DFT/B3LYP calculations, has been reviewed. The key reaction step is in all cases the oxidative coupling of two alkyne ligands to give a metallacyclopentatriene intermediate (or metallacyclopentadiene in other systems). This metallacycle adds unsaturated molecules, containing CC, CC and CX bonds, or RCN, CX₂, and HNCX, in a concerted fashion, directly to the RuC bond, forming bicyclic carbenes. The cycle is completed by a rearrangement followed by an exothermic displacement of the arene or pyridine, by two acetylene molecules regenerating the catalytically active species. Small differences are found depending on the molecules and bonds involved. These reactions are reviewed and the proposed mechanisms compared with other available studies.     

Alkoxy-substituted group 6 allenylidene complexes - Synthesis and properties

Bis(alkoxy)allenylidene complexes, [(CO)₅MCCC(OR′)OR], as well as mono(alkoxy)allenylidene complexes, [(CO)₅MCCC(OR′)Ph], of chromium and tungsten are accessible from propynones [HCCC(O)Ph] or propynoic acid esters [HCCC(O)OR; R = Et, (−)-menthyl, endo-bornyl] by the following reaction sequence: (a) deprotonation of the alkynes, (b) reaction with [(CO)₅M-THF] (M = Cr, W), and (c) alkylation of the resulting alkynyl metallate, [(CO)₅MCCC(O)R], with Meerwein salts. Vinylidene complexes, [(CO)₅MCC(R′)C(O)OR], are formed as a by-product by C_β-alkylation of the alkynyl metallate. Dimethylamine displaces one alkoxy substituent of the bis(alkoxy)allenylidene complexes to give dimethylamino(alkoxy)allenylidene complexes, [(CO)₅MCCC(OR)NMe₂]. The analogous reaction of dimethylamine with a mono(alkoxy)-substituted allenylidene complex affords the aminoallenylidene complex [(CO)₅CrCCC(NMe₂)Ph]. When the amine is used in large excess, the α,β-unsaturated aminocarbene complex [(CO)₅CrC(NMe₂)C(H)C(NMe₂)Ph] is additionally formed by addition of the amine across the C_αC_β-bond of the allenylidene ligand. The reaction of [(CO)₅MCCC(OEt)₂] with dimethyl ethylenediamine offers access to bis(amino)allenylidene complexes, in which C_γ is part of a five-membered heterocycle. Photolysis of bis(alkoxy)allenylidene complexes in the presence of triphenylphosphine yields tetracarbonyl- and tricarbonyl{bis(phosphine)}allenylidene complexes. Diethylaminopropyne inserts into the C_βC_γ bond of [(CO)₅MCCC(OEt)OMethyl] to give alkenylallenylidene complexes. Subsequent acid-catalyzed intramolecular cyclization affords a pyranylidene complex.     

Layered (2-D) structure of [Ru2(O2CMe)4]2[Ni(CN)4] determined via Rietveld refinement of synchrotron powder diffraction data

Reaction of [Ru₂(O₂CMe)₄]Cl and K₂[Ni(CN)₄] forms [Ru₂(O₂CMe)₄]₂[Ni(CN)₄] with the targeted layered structure possessing Ru-NCNi linkages, albeit strained, with Ru-NC and Ni-CN angles in the range of 147-167°. The magnetic properties of [Ru₂(O₂CMe)₄]₂[Ni(CN)₄] can be fit to a zero-field splitting model with D/k_B = 95 K (66 cm⁻¹).     

Ligand redox non-innocent behaviour in ruthenium complexes of ethynyl tolans

A small series of half-sandwich bis(phosphine) ruthenium acetylide complexes [Ru(CCC₆H₄CCSiMe₃)(L₂)Cp′] and [Ru(CCC₆H₄CCC₆H₄R-4)(L₂)Cp′] (R = OMe, Me, CO₂Me, NO₂; L₂ = (PPh₃)₂, Cp′ = Cp; L₂ = dppe; Cp′ = Cp^∗) have been synthesised. One-electron oxidations of these complexes gave the corresponding radical cations, which were significantly more chemically stable in the case of the Ru(dppe)Cp^∗ derivatives. The representative complex [Ru(CCC₆H₄CCC₆H₄OMe-4)(dppe)Cp^∗] was further examined by spectroelectrochemical (IR and UV-Vis-NIR) methods. The results of the spectroelectrochemical studies, supported by DFT calculations, indicate that the hole is largely supported by the ‘RuCCC₆H₄’ moiety in a manner similar to that described previously for simple aryl ethynyl complexes, rather than being more extensively delocalized along the entire conjugated ligand.     

Reactivity of the N-heterocyclic carbene complexes [Ru(IMes)2(CO)HX] (X = OH, Cl) with alkynes

Treatment of the 16-electron hydroxy hydride complex [Ru(IMes)₂(CO)H(OH)] (1, IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene) with HCCR affords the alkynyl species [Ru(IMes)₂(CO)H(CCR)] (R = Ph 3, SiMe₃, 4) and [Ru(IMes)₂(CO)(CCR)₂] (R = Ph, 5). Deuterium labelling studies show that the mono-alkynyl complexes are formed via hydrogen transfer from a coordinated alkyne ligand to Ru-OH, while bis-alkynyl formation is proposed to take place through hydrogen transfer to Ru-H. Both 3 and 5 readily coordinate CO to give the corresponding dicarbonyl species 6 and 7. Addition of HCCPh to the hydride chloride precursor [Ru(IMes)₂(CO)HCl] (2) results in a different reaction pathway involving alkyne insertion into the Ru-H bond to yield the alkenyl chloride complex [Ru(IMes)₂(CO)(CHCHPh)Cl] 8. Complexes 3-8 have been structurally characterised by X-ray crystallography.     

Gold(I) alkynyl complexes derived from ethynylanilines: crystal structure of [Au(CC-4-C6H4NH2){P(3-tolyl)3}] a polymer in the solid state via NH?Au contacts

Reaction of [AuCl(SMe₂)] with para-ethynylaniline and para-ethynyl-ortho-toluidine affords oligomers, [Au(CC-4-C₆H₃RNH₂)]_n (R = H, Me), which in turn react with tertiary phosphines or 2,5-dimethylphenylisocyanide to give monomeric adducts, [Au(CC-4-C₆H₃RNH₂)L]. One of these, [Au(CC-4-C₆H₄NH₂){P(3-tolyl)₃}], has been crystallographically characterised and is a polymer in the solid state, being held together via NH?Au contacts.     

Novel stable five-coordinate diorgano cobalt(III) complexes: Formation, structure, and reaction with carbon monoxide

A series of new five-coordinate acyl vinyl cobalt(III) complexes Co{η¹-C(CCPh)CHPh}[C(O)CCO] L₂(L = PMe₃) (6-10) were prepared via formal insertion of diphenylbutadiyne into Co-H function of mer-octahedral hydrido-acyl(phenolato)-cobalt(III) complexes. The complexes are diamagnetic. One square pyramidal structure of complex 6 was confirmed by X-ray diffraction analysis. These complexes are stable in solid state. In solution, six-coordinate acyl vinyl carbonyl cobalt(III) complex 11 is approved through the reaction of complex 7 with CO and the structure of complex 11 was determined by X-ray method.     

Group 8 and 10 metal acetylide naphthalimide dyads

[M]-CC-naphthalimide derivatives {[M] = CpNi(PPh₃), CpFe(dppe), CpRu(dppe) and Cp*Ru(dppe)} have been prepared and their X-ray structures determined. The structures show significant non-linearity of the acetylide link, with concomitant ν_CC at low energy and high intensity. Other properties confirm the strong-donor/strong-naphthalimide acceptor nature of the compounds. All the compounds exhibit an intense MLCT band in the visible spectrum that resolves into two bands in non-polar solvents. Spectroelectrochemistry of the CpFe species shows that the MLCT band disappears upon oxidation, and the appearance of a LMCT band at lower energy.     

Crystal and molecular structures of {Cu(μ-CCPh)(triphos)}2 [triphos = (PPh2CH2)3CMe]

The binuclear complex {Cu(μ-CCPh)(triphos)}₂ [triphos = (PPh₂CH₂)₃CMe] has been obtained from a reaction between {Cu(CCPh)}_n and triphos. The two copper atoms are bridged unsymmetrically by two CCPh groups, each attached through one carbon only [Cu-C, 2.016(4) Å], the separation between the two coppers being 2.4663(8) Å. Only two of the three phosphorus atoms in each ligand are coordinated to copper [Cu-P(1,2) 2.281, 2.273(1) Å]. The observed structure may be rationalised using a recent theoretical study [C. Mealli, S.S.M.C. Godinho, M.J. Calhorda, Organometallics 20 (2001) 1734] and differs from that assumed for the rationalisation of its luminescence properties [V. Pawlowski, G. Knör, C. Lennartz, A. Vogler, Eur. J. Inorg. Chem. (2005) 3167].     

Platinum allenylidene complexes and formation of platinum and palladium acetonitrile alkynyl complexes

The platinum(0) complex [Pt(PPh₃)₄] reacts with brominated propargylic amides and esters in benzene by oxidative addition to give trans-[Br(PPh₃)₂Pt-CC-C(O)R] complexes whereas no reaction occurs when halogenated solvents (CH₂Cl₂, CHCl₃) are used. The cis-ligands PPh₃ can be replaced by P(ⁱPr)₃ and the bromide by trifluoroacetate. O-Alkylation of those trans-[X(PR′₃)₂Pt-CC-C(O)R] complexes (X = Br, CF₃COO; R′ = Ph, ⁱPr) derived from propargylic amides with MeOTf or [Me₃O]BF₄ in CH₂Cl₂ gives the first cationic monoallenylidene complexes of platinum, trans-[X(PR′₃)₂PtCCC(OMe)NR₂]⁺Y⁻ (Y = OTf, BF₄). In contrast, trans-[Br(PPh₃)₂Pt-CC-C(O)OMenthyl] derived from a propargylic ester does not react with MeOTf in CH₂Cl₂. However, in acetonitrile instead of O-methylation the substitution of acetonitrile for the bromide ligand to yield the cationic acetonitrile alkynyl platinum complex trans-[MeCN(PPh₃)₂Pt-CC-C(O)OMenthyl]⁺OTf⁻ is observed. The related palladium complexes trans-[X(PR′₃)₂Pd-CC-C(O)OR] (X = Br, CF₃COO; R′ = Ph, ⁱPr, R = menthyl, Et) react with MeOTf or [Et₃O]BF₄ analogously affording trans-[MeCN(PR′₃)₂Pd-CC-C(O)OR]⁺Y⁻ (Y = OTf, BF₄).     

Preparation, structure and decomposition of gold(I) and gold(III) acetylide complexes

1-Alkynyl-dimethyl(triorganophosphine)gold(III) complexes of the type cis-Me₂(Ph₃P)Au-CC-R with R = H, Me, Ph (1-3) have been prepared from the cis-Me₂(Ph₃P)AuX (X = Cl, I) complexes and lithium alkynyls. The crystal structures of 1 and 2 have been determined together with those of the reference compounds cis-Me₂(Ph₃P)AuX (X = Cl, I) and cis-Me₂(Me₃P)AuI. The molecules have a standard square planar geometry and are not associated into oligomers. Due to the different hybridization of the carbon orbitals, the Au-C(CR) bonds are found significantly shorter than the Au-CH₃ bonds. Compounds 1-3 are stable colourless, crystalline solids at 20 °C but decompose on heating with selective (cis) reductive elimination of ethane and formation of the gold(I) alkynyls (Ph₃P)Au-CC-R thus retaining the stronger gold-alkynyl bonds. Two complexes of this type have also been prepared by conventional routes from (R₃P)AuX complexes and the crystal structures of (Me₃P)Au-CC-Ph and [(p-Tol)₃P]Au-CC-H have been determined. The former with the small Me₃P ligand is associated into two different trimers via aurophilic bonding and further aggregated into chains via weak inter-trimer contacts, while the latter is a monomer owing to the steric bulk of the (p-Tol)₃P ligand.