Synthesis, structure and kinetics of Group 6 metal carbonyl complexes containing a new ‘P2N’ mixed donor multidentate ligand

Abstract

The ‘P₂N’ mixed donor ligand 2-(diphenylphosphino)-N-[2-(diphenylphosphino)benzylidene]aniline (PNCHP) reacted with [Cr(CO)₄(NBD)] and [M(CO)₄(C₅H₁₁N)₂] (M = Mo or W; NBD = norbornadiene; C₅H₁₁N = piperidine) to yield cis-[Cr(CO)₄(PNCHP-κ²N,P)] and cis-[M(CO)₄(PNCHP-κ²P,P′)] respectively. PNCHP behaves as a ‘P,N’ bidentate ligand when M is Cr and a ‘P,P’ bidentate ligand when M is Mo or W. Heating cis-[Cr(CO)₄(PNCHP-κ²N,P)] or cis-[M(CO)₄(PNCHP-κ²P,P′)] (M = Mo or W) in toluene affords the complexes mer-[M(CO)₃(PNCHP-κ³P,N,P′)] (M = Cr, Mo or W). Reaction of PNCHP with [Mo(CO)₃(CHT)] (CHT = 1,3,5-cycloheptatriene) in cold toluene yields fac-[Mo(CO)₃(PNCHP-κ³P,N,P′)] which readily isomerises to mer-[Mo(CO)₃(PNCHP-κ³P,N,P′)] in solution. PNCHP reacts with UV-irradiated tetrahydrofuran solutions of [M(CO)₆] (M = Cr or W) to yield phosphorus bound co-ordination isomers of [M(CO)₅(PNCHP-κ¹P)]. The same reaction when carried out with one half equivalent of PNCHP yields the PNCHP bridged dinuclear species [{M(CO)₅}₂(PNCHP-κ²P,P′)]. The compounds have been characterised by spectroscopic means and the single crystal structures of cis-[Cr(CO)₄(PNCHP-κ²N,P)], cis-[W(CO)₄(PNCHP-κ²P,P′)], mer-[Mo(CO)₃(PNCHP-κ³P,N,P′)] and [{W(CO)₅}₂(PNCHP-κ²P,P′)] determined. In addition, the isomerisation kinetics of fac- to mer-[Mo(CO)₃(PNCHP-κ³P,N,P′)] has been studied to determine rate constants and thermodynamic activation parameters.