Synthesis and characterization of complexes of PdII and PtII containing the iminophosphorane ligand Ph3PNCN

Abstract

The chemistry of the iminophosphorane Ph₃PNCN towards different palladium(II) and platinum(II) subtrates has been investigated. This ligand shows a high selectivity for co-ordination through the terminal N atom (that of the cyanide group), while the phosphoiminic N atom shows very poor nucleophilic ability. The reaction of [PdCl₂(NCPh)₂] with Ph₃PNCN (1∶2 molar ratio) gives trans-[PdCl₂(NCNPPh₃)₂] 1. The crystal structure of 1 has been determined and shows the iminophosphorane co-ordinated selectively through the nitrilic N atom. The reaction of the cationic derivatives [M(C–P)(NCMe)₂][ClO₄] [M = Pd or Pt; C–P = o-CH₂C₆H₄P(C₆H₄Me-o)₂] with Ph₃PNCN (1∶2 molar ratio) resulted in the formation of [M(C–P)(NCNPPh₃)₂][ClO₄] (M = Pd 2 or Pt 3), for which the same terminal N-co-ordination has been observed. The reaction of [Pd(dmba)(NCMe)₂][ClO₄] (dmba = C₆H₄CH₂NMe₂-2) with Ph₃PNCN (1∶1 molar ratio) gave the dinuclear derivative [{Pd(µ-NCNPPh₃)(dmba)}₂][ClO₄]₂ 4 in which the iminophosphorane acts as an N,N-bridging ligand, while reaction in 1∶2 molar ratio gave [Pd(dmba)(NCNPPh₃)₂][ClO₄] 5 which possess N-terminal co-ordination. The reaction of this iminophosphorane with monosolvate complexes [Pd(dmba)(PPh₃)(THF)][ClO₄] or [Pt(C–P)(PPh₃)(NCMe)][ClO₄] (1∶1 molar ratio) resulted in the formation of [Pd(dmba)(PPh₃)(NCNPPh₃)][ClO₄] 6 or [Pt(C–P)(PPh₃)(NCNPPh₃)][ClO₄] 7, and the reaction with the halide bridging derivatives [{Pd(µ-Cl)(dmba)}₂] or [{Pt(µ-Cl)(C–P)}₂] (2∶1 molar ratio) produced cleavage of the bridging system and formation of [PdCl(dmba)(NCNPPh₃)] 8 and [PtCl(C–P)(NCNPPh₃)] 9. The same N-terminal co-ordination mode is observed in complexes 6–9.