Mono- and dimeric complexes of an asymmetric heterotopic P,CNHC,pyr ligand

Abstract

An asymmetric heterotopic ligand (S-N^MeCP) containing a central bicyclic, expanded-ring NHC with one pyridyl and one phosphine exo-substituent has been synthesised and its coordination chemistry with selected late transition metals investigated. The amidinium precursor [S-N^MeCHP]PF₆ shows variable coordination modes with Ag(I), Cu(I) and Au(I) depending on the L : M ratio. The reaction of two mols of [S-N^MeCHP]PF₆ with [Cu(MeCN)₄]BF₄, AgBF₄ or Au(THT)Cl gives the bis-ligand complexes [Cu(κ-P-N^MeCHP)₂(CH₃CN)₂]BF₄·(PF₆)₂, 1, and [M(κ-P-N^MeCHP)₂]X·(PF₆)₂ (3: M = Ag, X = BF₄; 6: M = Au, X = Cl) respectively. The 1 : 1 reaction of [S-N^MeCHP]PF₆ with AgOTf gave the head-to-tail dimer H,T-[Ag₂(μ-N,P-N^MeCHP)₂(μ-OTf)₂](PF₆)₂, 2, whereas the analogous reaction with Au(THT)Cl gave monomeric [Au(κ-P-N^MeCHP)Cl]PF₆, 5. Complex 2 was converted to H,T-[Ag₂(μ-C,P-N^MeCP)₂](PF₆)₂, 4, upon addition of base, while 6 gave [Au(κ-C-N^MeCP)₂]Cl, 8, when treated likewise. Reaction of [S-N^MeCHP]PF₆ with Ni(1,5-COD)₂ gave the oxidative addition/insertion product [Ni(κ³-N,C,P-N^MeCP)(η³-C₈H₁₃)]PF₆, 9, which converted to [Ni(κ³-N,C,P-N^MeCP)Cl]PF₆, 10, upon exposure of a CHCl₃ solution to air. Complex 10 showed conformational isomerism that was also present in [Rh(κ³-N,C,P-N^MeCP)(CO)]PF₆, 14, prepared from the precursor complex [Rh(κ-P-N^MeCHP)(acac)(CO)]PF₆, 13, upon heating in C₆H₅Cl. [Pt(κ³-N,C,P-N^MeCP)(Cl)]PF₆, 12, derived from trans-[Pt(κ-P-N^MeCHP)₂(Cl)₂](PF₆)₂, 11, was isolated as a single conformer.