Transformation of NHC·BEt3 into AgCl·NHC: Efficiently preparative method for early–late heterobimetallic complexes using indenyl-functionalized N-heterocyclic carbene as a bridging ligand

Abstract

On treatment of IiPr·BEt3 (3a) (IiPr=1.3-diisopropylimidazol-2-ylidene) with 1.1 equivalents of AgCl in 1,2-dichloroethane (DCE) under refluxing conditions for 1h, AgCl·IiPr complex (4a) was obtained in good yield. AgCl·IMes (IMes=1.3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (4b) was also obtained by the reaction of IMes·BEt3 (3b) with AgCl under DCE-refluxing conditions. This procedure applied to the indenyl-coordinate molybdenum complex dangling the NHC·BEt3 unit (1). The exchange reaction of BEt3 into AgCl cleanly took place to give the molybdenum complex dangling the AgCl·NHC unit (2-Ag). The treatment of 2-Ag with [Pd(η3-allyl)Cl]2 or [RuCl2(η6-p-cymene)]2 afforded Mo–Pd (2-Pd) or Mo–Ru (2-Ru) heterobimetallic complexes in good yields. Conversion of “the protecting group” for NHC from BEt3 into AgCl was an efficient method for the preparation of early–late heterobimetallic complexes using the hybrid-type NHC ligand as a bridging mode.