Isonitrile-gold complexes

Kaharu, T., Ishii, R. and Takahashi, S. (1994) Liquid-crystalline gold—isonitrile complexes. Journal of the Chemical Society, Chemical Communications, (11), 1349-1350. 

The first starts from common NHC precursor compounds, such as imidazolium salts, in contrast to the other route in which the NHC unit is formed via template synthesis starting from a gold isonitrile complex. 

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]. 

Schneider, W., Sladek, A., Bauer, A., Angermaier, K. and Schmidbaur, H. (1997) Structural Investigation of Bis(isonitrile) gold(I) Complexes. Zeitschriftfur Naturforschung B. A Journal of Chemical Sciences, 52, 53-56. 

Gold(I) isonitrile complexes were first reported (131) in 1956, when it was found that they were generally less stable than the isonitrile complexes of other transition metals. This was attributed to the low tendency of gold to form bonds with double bond character. A number of isonitrile complexes have been made, however, and they have been used extensively in the preparation of carbene and imino complexes of gold(I). 

Reactions of tetrachloroaurates with isonitriles and amines constitutes a convenient in situ preparation of bis(carbene)gold(I) complexes (143,... 

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. 

Other gold(III) complexes containing one gold-carbon bond include the isonitrile complexes [AuX3(CNR)] (131) and the trimeric imino compounds [Au3 C(OR)=NR 3X6] (X = Br or I), which have been prepared (155) by oxidative addition of halogen to the gold(I) species. 

Espinet has also studied gold(I) isonitrile complexes [55]. In the substituted complexes (Figure 27) it is seen that the alkoxy chain length produces little variation in the transition temperatures and the Sa phase dominated. However, for the chlorogold(I) complexes, then the crystal and Sa phase are stabilized in the 3-fluorinated complexes (i. e. = F) compared to the unfluorinated complexes in the... 

Figure 26 Isomers of gold carbene complexes obtained from coordinated isonitriles.

Gold and silver isonitriles complexes were investigated recently ((168) M = Au, Ag X = N03, PFg, BF4 = 4, 8, 12). Overall, the phenyl and biphenyl gold derivatives showed an SmA phase, whereas the analogous silver complexes displayed an additional SmC phase (Figure 74). Electrostatic interactions thus seem to favor and stabilize lamellar arrangements, since phenyl isocyanides... 

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 ... 

As a versatile alternative to the generation of free carbenes, Hashmi and co-workers developed a methodology for the synthesis of abnormal NHCs where the carbene is constructed directly at the metal center. Thus, a [3 + 2] dipolar cycloaddition of azomethine ylides and gold isonitriles afforded the abnormal saturated imidazolinylidene gold eomplexes 9 [eqn (3.3)]. This methodology circumvents the regioseleetivity issue of C4 vs. C5 eoordination because the carbenic carbon is pre-coordinated to the metal center in the isonitrile precursor. Moreover, this procedure provided aeeess to a new subclass of abnormal carbenes and yielded the first abnormal earbene complexes featuring a saturated heteroeyele, unlike all previous abnormal imidazolylidene complexes, derived from unsaturated heteroeyeles. 

Isonitrile)gold(I) acetylide complexes. Journal of Materials Chemistry, 5,... 

Direct reaction of the bis(isonitrile)gold(I) cations with alcohols or amines also gave the biscarbene complexes [Eq. (38)] (132, 141, 142). With bulky C6HnNC, only one carbene moiety was formed (141, 142) under the conditions employed in the preparation of the other biscarbene compounds. 

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. 

The isonitrile gold(I) nitrate ([AuI(N03)(CN-But)]) has been used to prepare Au/Fe203 89 the complex was added to a slurry of freshly precipitated ferric hydroxide in acetone. After removal of solvent and calcination (673 K), small gold particles (<4nm) were obtained with a loading of 3wt.% Au. 

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