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

Abstract

An asymmetric heterotopic ligand (S-NMeCP) 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-NMeCHP]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-NMeCHP]PF6 with [Cu(MeCN)4]BF4, AgBF4 or Au(THT)Cl gives the bis-ligand complexes [Cu(κ-P-NMeCHP)2(CH3CN)2]BF4·(PF6)2, 1, and [M(κ-P-NMeCHP)2]X·(PF6)2 (3: M = Ag, X = BF4; 6: M = Au, X = Cl) respectively. The 1:1 reaction of [S-NMeCHP]PF6 with AgOTf gave the head-to-tail dimer H,T-[Ag2(μ-N,P-NMeCHP)2(μ-OTf)2](PF6)2, 2, whereas the analogous reaction with Au(THT)Cl gave monomeric [Au(κ-P-NMeCHP)Cl]PF6, 5. Complex 2 was converted to H,T-[Ag2(μ-C,P-NMeCP)2](PF6)2, 4, upon addition of base, while 6 gave [Au(κ-C-NMeCP)2]Cl, 8, when treated likewise. Reaction of [S-NMeCHP]PF6 with Ni(1,5-COD)2 gave the oxidative addition/insertion product [Ni(κ3-N,C,P-NMeCP)(η3-C8H13)]PF6, 9, which converted to [Ni(κ3-N,C,P-NMeCP)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-NMeCP)(CO)]PF6, 14, prepared from the precursor complex [Rh(κ-P-NMeCHP)(acac)(CO)]PF6, 13, upon heating in C6H5Cl. [Pt(κ3-N,C,P-NMeCP)(Cl)]PF6, 12, derived from trans-[Pt(κ-P-NMeCHP)2(Cl)2](PF6)2, 11, was isolated as a single conformer.