Gold, isonitrile ligands

When an isonitrile ligand containing a suitable hydroxyl group was reacted with AUCI4, it underwent isomerization (147) via a carbene complex (Scheme 1). With CN(CH2)3OH, in the presence of a noncoordinating anion, the bis(carbene)gold(I) complex [Au tO(CH2)3l(jH 2]+BPhJ was formed. 

The diboration of alkenes has been more challenging to develop. Table 16.5, which is also adapted from the Miyaura review, summarizes a series of diborations of alkenes. These examples show that complexes of group 10 metals lacking phosphine or isonitrile ligands have been most active for diese additions. Gold and rhodium complexes have also been shown to catalyze the diboration of vinylarenes. 

Gold-isonitrile complexes, 18, as a new family of metallomesogens, are prepared and even nonmesomorphic isonitrile ligands have been found to form N and SmA liquid crystals when coordinated to an Au(I)Cl moiety [30 a]. 

The trimeric compounds have been cleaved with a variety of neutral ligands [Eq. (41)] (154). With PPh3 the reaction proceeds smoothly, the rate and extent of reaction being dependent on the nature of R (the process occurs more readily when R is aromatic), but with isonitriles species of indeterminate constitution are obtained in addition to lAu C(OR )=NR (CNR")]. The cyclic complexes also underwent stepwise oxidative addition of bromine or iodine to yield (155) mixed gold(I)-gold(III) species, and finally the analogous gold(III) trimers. 

The complex [AuCl(CO)] undergoes displacement of carbon monoxide with isonitriles to give [AuCl(CNR)] complexes (162, 163), or with other ligands to give species no longer containing a gold-carbon bond. 

Takahashi previously reported some structurally related gold systems, 12a and 12b [21]. Complexes 12a showed Sa phases at elevated temperatures (170-270 °C), while the metal-free ligand showed nematic and Sa phases, depending on the chain length. Addition of an alkoxy chain in the ortho position, relatively to the isonitrile group, 12b, depressed considerably the transition temperatures (90-190 °C), and a nematic phase was observed in addition to the Sa phase. Here, complexation induced mesomorphism since the ligand itself was not liquid crystal. 

The previously mentioned thioether-based precursor complexes are used as starting materials however, instead of a carbene, an isonitrile is first coordinated to the gold atom. After this the resulting isonitrile complex, often still in situ, is further reacted with a secondary amine to form the desired carbene ligand (see Scheme 9.5). 

The binary gold carbonyl complexes are instable, but the family of inorganic 14-electron complexes [Au (Cl)L] is known for its stability with a variety of L ligands (CO, PR3, RNC, pyridine, etc.). These complexes are also prepared from the precursor complex [Au(Cl)(Me2S)] or [Au(Cl)(tmt)], tmt = tetramethylthiophene. The isonitrile complexes undergo the addition of nucleophiles (alcohols, amines) to yield carbene complexes ... 

The processes involved in these adsorptions are related to coordination chemistry in solution, but occur in two dimensions. Metal smfaces can be viewed as planes of metal atoms having vacant coordination sites. Appropriate ligands coordinate (or, in the terms of surface science, adsorb) to a metal surface and form an ensemble that we and others refer to as a self-assembled monolayer. Adsorbates containing polymethylene chains are the most commonly studied b ause they often form oriented, highly ordered SAMs. Some of the presently available systems that yield SAMs include alkanoic acids on oxidized metal surfaces (especially aluminum) (4), alkyl amines on oxidized surfaces of chromium and platinum (5), isonitriles on platinum (6), sulfides (7), disulfides (8-10), and thiols (11,12), on gold, and thiols on silver (ISIS), All of these systems have analogs in classical coordnation chemistry (16). 

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