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

The 'P2N' mixed donor ligand 2-(diphenylphosphino)-N-[2-(diphenylphosphino) benzylidene]aniline (PNCHP) reacted with [Cr(CO)(4)(NBD)] and [M(CO)(4)(C5H 11N)(2)] (M=Mo or W; NBD=norbornadiene; C5H11N=piperidine) to yield cis-[Cr (CO)(4)(PNCHP-kappa(2)N,P)] and cis-[M(CO)(4)(PNCHP-kappa(2)P,P')] respecti vely. PNCHP behaves as a 'P,N' bidentate ligand when M is Cr and a 'P,P' bi dentate ligand when M is Mo or W. Heating cis-[Cr(CO)(4)(PNCHP-kappa(2)N,P) ] or cis-[M(CO)(4)(PNCHP-kappa(2)P,P')] (M=Mo or W) in toluene affords the complexes mer-[M(CO)(3)(PNCHP-kappa(3)P,N,P')] (M=Cr, Mo or W). Reaction of PNCHP with [Mo(CO)(3)(CHT)] (CHT=1,3,5-cycloheptatriene) in cold toluene y ields fac-[Mo(CO)(3)(PNCHP-kappa(3)P,N,P')] which readily isomerises to mer -[Mo(CO)(3)(PNCHP-kappa(3)P,N,P')] in solution. PNCHP reacts with UV-irradi ated tetrahydrofuran solutions of [M(CO)(6)] (M=Cr or W) to yield phosphoru s bound co-ordination isomers of [M(CO)(5)(PNCHP-kappa(1)P)]. The same reac tion when carried out with one half equivalent of PNCHP yields the PNCHP br idged dinuclear species [{M(CO)(5)}(2)(PNCHP-kappa(2)P,P')]. The compounds have been characterised by spectroscopic means and the single crystal struc tures of cis-[Cr(CO)(4)(PNCHP-kappa(2)N,P)], cis-[W(CO)(4)(PNCHP-kappa(2)P, P')], mer-[Mo(CO)(3)(PNCHP-kappa(3)P,N,P')] and [{W(CO)(5)}(2)(PNCHP-kappa( 2)P,P')] determined. In addition, the isomerisation kinetics of fac- to mer -[Mo(CO)(3)(PNCHP-kappa(3)P,N,P')] has been studied to determine rate const ants and thermodynamic activation parameters.