Synthesis and reactivity of diphosphine metal complexes bearing peripheral ketenimine functionalities

Abstract

Diphosphinoketenimine ligands (PPh₂)₂CCNR (1a R = ^tBu, 1b R = Ph) were reacted with different Cu(I), Ag(I), Au(I), Pd(II), Ru(II) and Mo(0) metal complexes bearing weakly coordinating ligands yielding a number of mono-, di-, and trimetallic species with the diphosphine acting as either chelate or bridging ligand. The reactivity of some of the new complexes toward water and MeLi was investigated. The mononuclear Pd(II) complex [PdCl₂{(PPh₂)₂CCNPh}] (6b) is transformed into the diphosphinoamide complex [PdCl₂{(PPh₂)₂CHC(O)(NHPh)}] (12) by nucleophilic addition of water. Similarly, treatment of 6b with MeLi yields the diphosphinoenamine complex [PdCl₂{(PPh₂)₂CC(Me)(NHPh)}] (14). A different behaviour is observed in the treatment of diphosphinoketenimine with water in the presence of Cu(I) ion, which leads to hydrolysis of the ligand involving P–C bond cleavage, underscoring the influence of the coordination environment in the reactivity showed by the coordinated ligand. The liberation of the metal assisted synthesized diphosphines from the Pd(II) metal center can be achieved easily and in quantitative yields by treatment with aqueous KCN solution.