Bis(arylazo-oximato)palladium(II); synthesis, palladium–nitrogen bond lability, and redox activity

Abstract

The synthesis and characterisation of the title complex, [PdL₂][L = PhNNC(R)NO], and related mixed-ligand complexes including [PdLA](A =ortho-metallated azobenzene) are described. The mass spectrum of [PdL₂] reveals peaks corresponding to loss of oximato-O and NO from the parent ion. Gaseous HCl cleaves the Pd–N(oxime) bond selectively. Triphenylphosphine cleaves one or both Pd–N(azo) linkages giving [PdL₂(PPh₃)] and unstable [PdL₂(PPh₃)₂] which is also produced by oxidative addition of HL to [Pd(PPh₃)₄]. In [PdL₂(PPh₃)] the unidentate and bidentate L groups scramble rapidly at 308 K but slowly at 233 K (¹H n.m.r.). Bidentate phosphine and phosphinoarsine cleave the two Pd–N(azo) bonds simultaneously. Unidentate amines, when present in very large excess, produce unstable [PdL₂(amine)] in which one L is unidentate. Addition of X₂(X = Cl or Br) yields the unstable palladium (IV) complex [PdL₂X₂] which is readily reduced to halogeno-bridged palladium (II) species. A cyclic-voltammetric study of the one-electron quasi-reversible reduction of [PdL₂], [PdL₂(PPh₃)], [PdLA]etc. at a platinum electrode is briefly reported.