Transformations of phosphazane ligands in the coordination sphere of transition metals. Reactions of phosphinotriazene Ph2P-N(Ph)-N=NPh with Ni0 and NiI complexes

Abstract

3 (Diphenylphosphino) 1,3 diphenyltriazene Ph 2 P-NPh-N=NPh was synthesized. The reactions of this compound with bis(cycloocta 1,5 diene)nickel, (cod) 2 Ni, and nickel(I) bis(triphenylphosphino)bis(trimethylsilyl)amide, (Ph 3 P) 2 Ni-N(SiMe 3 ) 2 , afforded the anionic nickel complex [Ph 4 P] + [Ni(PhNNNPh) 3 ] -in 15 and 78% yields, respectively.The N-N and N-P chemical bonds in phosphazanes are rather weak. 1,2 Since the nitrogen and phosphorus atoms are prone to coordinate to metals, various mo lecular rearrangements and transformations of the phosphazane ligands can occur in the coordination sphere of transition metals. Earlier, 3 we have studied ther mal transformations of the phosphinohydrazine ligands {-NAr-NAr-PPh 2 (Ar = Ph, 4 Bu t C 6 H 4 )} in the coor dination sphere of transition metals. In particular, it has been demonstrated that reactions of the phosphino hydrazine ligand with Co 2+ , Ni 2+ , or Fe 3+ complexes result in isomerization of the former to the amino iminophosphorane ligand {-NPh-PPh 2 =NPh} giv ing rise to the corresponding metal complexes M[NPh-PPh 2 =NPh] n in quantitative yields (Scheme 1). Scheme 1 n = 2, M = Co, Ar = Ph, 4 Bu t C 6 H 4 ; M = Ni, Ar = Ph n = 3, M = Fe, Ar = PhIt is of importance that the character of the process occurring in the metal coordination sphere depends both on the nature of the metal and its oxidation state. Monova lent nickel behaves differently: the reaction of nickel(I) silylamide, (Ph 3 P) 2 Ni-N(SiMe 3 ) 2 , with diphenylphos phino 1,2 diphenylhydrazine (HNPh-NPh-PPh 2 ) is accompanied by the nitrogen-phosphorus bond cleavage to form the nickel azobenzene complex, (Ph 3 P) 2 Ni (PhN=NPh). Other examples of the N-P bond cleavage in phosphazanes, in particular, in the reactions of lithium diphenylphosphinophenylamide with cobalt and nickel halides, 4 were also documented (Scheme 2). Scheme 2 M = Co, NiBased on the results of our earlier studies, 3 the reac tions of phosphinotriazene with nickel complexes are