Synthesis and Characterization of Well-Defined s-Block Bis(Carbene) Complexes

Abstract

Although the chemistry of monodentate N-heterocyclic carbenes (NHCs) with s-block metals has been investigated, the coordination chemistry of phenyl dicarbene (CCC=bis(diisopropylphenyl-imidazol-2-ylidenemethyl)phenyl) complexes remains largely underexplored. We report the synthesis and characterization of the free phenyl dicarbene precursors (^BrCCC^Dipp and ^BrCCC^Mes) and the ensuing reactivity with Grignard reagents (3,5-(CF₃)₂-Ph)MgBr and MeMgCl to afford the cyclic dimeric complexes, (^BrCCC^DippMg3,5-(CF₃)₂PhBr)₂, (^BrCCC^MesMg3,5-(CF₃)₂PhBr)₂, and (^BrCCC^DippMgMeCl)₂. Further exploration of various routes to activate the central C−Br bond of the ligands with alkali metals resulted in isolation of the respective NHC adducts of LiN(SiMe₃)₂ and KN(SiMe₃)₂. Notably, these studies imply that flexibility of the pincer framework engenders dimeric complexes of s-block precursors over the monomeric complexes. The identity of the complexes was ascertained using multinuclear NMR spectroscopy and X-ray crystallography.