New ligands for gold : bonding mode and structural complex characterisation
Date
2008-12
Authors
Strasser, Christoph Erik
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
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)AuCl
or (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 diffraction
revealed linear complexes in part associating by Au…Au and/or Au…S contacts, two polymorphs
of one compound associating by either Au…S interactions or p-stacking was also
obtained. (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 the
electronic influence tris(azol-2-yl)phosphanes exert upon gold(I) by substituting the chloride
with various thiolates. In contrast to Ph3PAuCl, only NCS– and PhC(O)S– afforded stable
compounds 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 an
exceptional seven. Among the solid-state structures of A the rare instance of a polymorph and
a thf solvate not exhibiting aurophilic interactions as opposed to the original structure were
observed. Complex B was shown to crystallise in polymorphs where dimers are associated
either by Au…Au or Au…Cl interactions but otherwise exhibit similar arrangements of the
ligand, this set of polymorphs is unprecedented amongst gold complexes. An NMR
experiment proved that tris(thiazolyl)phosphane complexes are subject to hydrolysis under
alkaline 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 the
gold atoms with other metal centres such as Me3CNCAuCl or AgNO3. A second solvate
obtained additionally exhibits Au…Au interactions. The scope of uncommon bis-imine coordination
to 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 porous
crystal structure of gold and the co-crystallised solvent could be partially removed by
evacuation at elevated temperatures. Utilising a ditopic phosphite ligand instead of the
commonly 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 deprotonated
at C-5 of the thiazole ring, Fischer-type pentacarbonyltungsten carbeniate complexes were
prepared and structurally characterised. Starting from these complexes, the analogous Fischertype
methoxycarbene as well as carbyne complexes could be obtained by alkylation and
formal oxide abstraction, respectively. The latter products readily formed dinuclear adducts
with 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…H
interaction which was examined by low-temperature 1H NMR measurements. Transfer of the
carbeniate ligand derived from 1-(thiazol-2-yl)piperidine to Ph3PAu+ afforded an aurated
thiazole product (by an unprecedented loss of CO) which may be represented as a pseudoabnormal
azolylidene complex owing to W(CO)5-coordination at a distant nitrogen. The
carbeniate 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 from
chromium and tungsten to gold(I) affording a novel class of complexes, all of which were
structurally characterised. This work bridges the unnatural divide created between Fischer and
N-heterocyclic carbene complexes.
Description
Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008.
Keywords
Gold complexes, Heterocycles, Carbene, Tungsten, Azole, Ligands, Porous crystal, rNHC, Polymorph, Dissertations -- Chemistry, Theses -- Chemistry, Gold compounds, Ligands, Complex compounds