title: Gold(I) and Gold(III) Complexes of Cyclic (Alkyl)(amino)carbenes.
abstract: The chemistry of Au(I) complexes with two types of cyclic (alkyl)(amino)carbene (CAAC) ligands has been explored, using the sterically less demanding dimethyl derivativeMe2CAAC and the 2-adamantyl ligandAdCAAC. The conversion of (AdCAAC)AuCl into (AdCAAC)AuOH by treatment with KOH is significantly accelerated by the addition oftBuOH. (AdCAAC)AuOH is a convenient starting material for the high-yield syntheses of (AdCAAC)AuX complexes by acid/base and C-H activation reactions (X = OAryl, CF3CO2, N(Tf)2, C2Ph, C6F5, C6HF4, C6H2F3, CH2C(O)C6H4OMe, CH(Ph)C(O)Ph, CH2SO2Ph), while the cationic complexes [(AdCAAC)AuL]+(L = CO, CNtBu) and (AdCAAC)AuCN were obtained by chloride substitution from (AdCAAC)AuCl. The reactivity toward variously substituted fluoroarenes suggests that (AdCAAC)AuOH is able to react with C-H bonds with pKavalues lower than about 31.5. This, together with the spectroscopic data, confirm the somewhat stronger electron-donor properties of CAAC ligands in comparison to imidazolylidene-type N-heterocyclic carbenes (NHCs). In spite of this, the oxidation ofMe2CAAC andAdCAAC gold compounds is much less facile. Oxidations proceed with C-Au cleavage by halogens unless light is strictly excluded. The oxidation of (AdCAAC)AuCl with PhICl2in the dark gives near-quantitative yields of (AdCAAC)AuCl3, while [Au(Me2CAAC)2]Cl leads totrans-[AuCl2(Me2CAAC)2]Cl. In contrast to the chemistry of imidazolylidene-type gold NHC complexes, oxidation products containing Au-Br or Au-I bonds could not be obtained; whereas the reaction with CsBr3cleaves the Au-C bond to give mixtures of [AdCAAC-Br]+[AuBr2]-and [(AdCAAC-Br)]+[AuBr4]-, the oxidation of (AdCAAC)AuI with I2leads to the adduct (AdCAAC)AuI·I2. Irrespective of the steric demands of the CAAC ligands, their gold complexes proved more resistant to oxidation and more prone to halogen cleavage of the Au-C bonds than gold(I) complexes of imidazole-based NHC ligands.
authors.affiliation: School of Chemistry, University of East Anglia , Norwich NR4 7TJ, U.K.
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Romanov
authors.affiliation: School of Chemistry, University of East Anglia , Norwich NR4 7TJ, U.K.
authors.forename: Manfred
authors.initials: M
authors.lastname: Bochmann