New ligands for gold : bonding mode and structural complex characterisation

[摘要] Novel gold(I) trithiophosphite complexes were synthesised by utilising the ligands P(SR)3 (R= Me, Ph) and 1,2-bis(1,3,2-dithiaphospholan-2-ylthio)ethane (2L). Reaction with (tht)AuClor (tht)AuC6F5 readily yielded the corresponding complexes (RS)3PAuX and 2L(AuX)2 (X =Cl, C6F5) as well as {Au[P(SMe)3]2}CF3SO3. Structural characterisation by X-ray diffractionrevealed linear complexes in part associating by Au…Au and/or Au…S contacts, two polymorphsof one compound associating by either Au…S interactions or p-stacking was alsoobtained. (MeS)3PAuCl and (MeO)3PAuCl were found to be isostructural in the solid state.The complex chloro[tris(4-methylthiazol-2-yl)phosphane]gold, A, was used to probe theelectronic influence tris(azol-2-yl)phosphanes exert upon gold(I) by substituting the chloridewith various thiolates. In contrast to Ph3PAuCl, only NCS– and PhC(O)S– afforded stablecompounds which could be attributed to a weaker donating capability of the tris-(azolyl)phosphane ligand class. The compounds A and chloro[tris(thiazol-2-yl)phosphane]-gold, B, were shown to crystallise in 4 new polymorphs and solvates bringing the total to anexceptional seven. Among the solid-state structures of A the rare instance of a polymorph anda thf solvate not exhibiting aurophilic interactions as opposed to the original structure wereobserved. Complex B was shown to crystallise in polymorphs where dimers are associatedeither by Au…Au or Au…Cl interactions but otherwise exhibit similar arrangements of theligand, this set of polymorphs is unprecedented amongst gold complexes. An NMRexperiment proved that tris(thiazolyl)phosphane complexes are subject to hydrolysis underalkaline conditions.A trimeric gold(I) heterometallacycle, obtained by reacting (tht)AuCl with 4,4-dimethyl-2-(2-thienyl)oxazoline deprotonated at C-5 of the thiophene ring, was structurally characterised.Intramolecular Au…S interactions were found to be present which precluded interaction of thegold atoms with other metal centres such as Me3CNCAuCl or AgNO3. A second solvateobtained additionally exhibits Au…Au interactions. The scope of uncommon bis-imine coordinationto AuI was expanded by utilising 1,2-bis(1-imidazolylmethyl)-2,4,6-trimethylbenzene(2L) to synthesise the [Au2(μ-2L)2]2+ cation. The triflate salt forms the first porouscrystal structure of gold and the co-crystallised solvent could be partially removed byevacuation at elevated temperatures. Utilising a ditopic phosphite ligand instead of thecommonly used ditopic phosphane ligands, a new cationic species of the type [Au2(μ-2L)3]2+was characterised in the solid state for the first time. Finally, employing 2-phenylthiazole and 1-(thiazol-2-yl)piperidine which can be deprotonatedat C-5 of the thiazole ring, Fischer-type pentacarbonyltungsten carbeniate complexes wereprepared and structurally characterised. Starting from these complexes, the analogous Fischertypemethoxycarbene as well as carbyne complexes could be obtained by alkylation andformal oxide abstraction, respectively. The latter products readily formed dinuclear adductswith AuCl.A Fischer-type methoxycarbene could be transferred to AuI affording the first such gold(I)complex exhibiting Au…Au interactions in the solid state as well as a rare agostic Au…Hinteraction which was examined by low-temperature 1H NMR measurements. Transfer of thecarbeniate ligand derived from 1-(thiazol-2-yl)piperidine to Ph3PAu+ afforded an auratedthiazole product (by an unprecedented loss of CO) which may be represented as a pseudoabnormalazolylidene complex owing to W(CO)5-coordination at a distant nitrogen. Thecarbeniate originating from 2-phenylthiazole, on the other hand, afforded, by rare W(CO)5-trapping and without CO-loss, a pseudo Fischer-type carbene complex.Carbene transfer to gold was complemented by the first transfers of rNHC ligands fromchromium and tungsten to gold(I) affording a novel class of complexes, all of which werestructurally characterised. This work bridges the unnatural divide created between Fischer andN-heterocyclic carbene complexes.

[发布机构] Stellenbosch University