Rhodium(I) Complexes with Hemilabile N-Heterocyclic Carbenes: Efficient Alkyne Hydrosilylation Catalysts

Abstract

A series of alkylammonium-imidazolium chloride salts [RImH(CH2)nNMe2]Cl·HCl (R = Me, t-Bu, Mes; n = 2, 3) have been prepared by alkylation of 1-substituted imidazole compounds with the corresponding chloro-alkyl-dimethylamine hydrochloride. These salts are precursors for the synthesis of a library of rhodium(I) complexes containing amino-alkyl functionalized N-heterocyclic carbene (NHC) ligands with hemilabile character by varying the substituent on the heterocyclic ring and the length of the linker with the dimethylamino moiety. The monodeprotonation of alkylammonium-imidazolium salts with NaH in the presence of [{Rh(μ-Cl)(cod)}2] gave the amino-imidazolium salts [RImH(CH2)nNMe2][RhCl2(cod)]. Further deprotonation with NaH under non anhydrous conditions gave the neutral complexes [RhCl(cod)(RIm(CH2)nNMe2)] in good yields. The abstraction of the chloro ligand by silver salts rendered the cationic complexes [Rh(cod)(κ2C,N-RIm(CH2)3NMe2)][BF4] (R = Me, Mes) by coordination of the NMe2 fragment of the sidear...