Rearrangement of phosphinohydrazide ligand –NPh-N(PPh2)2 in transition metal coordination sphere: Synthesis and characterization of nickel and cobalt spirocyclic complexes M(NPh-PPh2double bond; length as m-dashN-PPh2)2 and their properties

The reaction of diphosphinohydrazine PhNH-N(PPh2)2 (1) with cobalt(II) silylamide, Co[N(SiMe3)2]2, proceeds via formation of unstable phosphinohydrazide complex Co[NPh-N(PPh2)2]2 followed by rearrangement to a new chelating compound Co(NPh-PPh2double bond; length as m-dashN-PPh2)2 (2). Disproportionation of nickel(I) silylamide, (Ph3P)2Ni-N(SiMe3)2, in the presence of 1, yields Ni(0) and Ni(II) phosphinoamide complexes: Ni[(Ph2P)2N-NPhH]2 (3), Ni(NPh-PPh2double bond; length as m-dashN-PPh2)2 (4). X-ray analysis reveals tetrahedral environment of the cobalt atom in 2 and square-planar environment of the nickel atom in cis-4. In contrast to the crystalline patterns, the solutions of 2 in THF or toluene have EPR signal which is typical to square-planar low-spin d7 cobalt complex. The reactions of 2 with dioxygen, elemental sulfur and diphenyldiazomethane led to the spirocyclic insertion products Co(NPh-PPh2double bond; length as m-dashN-PPh2double bond; length as m-dashX)2 (X = O, S, NNCPh2) while the absorption of carbon monoxide is reversible.