Bis(phosphanylamino)benzeneligands: a zinc(ii) complex and an unusual nickel(i) complex with a Dewar-benzene-type Ni2P2N2 backbone

Abstract

ZnPr₂ reacts with 1,2-(NHPPh₂)₂C₆H₄ (1) to give the bis-amido complex [Zn(THF){1-N(PPh₂)-2-N(μ-PPh₂)C₆H₄-κ³N,N′,P}]₂ (3), while monolithiated 1 (prepared in situ from 1 and LiBuⁿ) reacts with NiCl₂ with formation of the unusual nickel(I) complex [Ni{1-NH(PPh₂)-2-N(μ-PPh₂)C₆H₄-κ²N,P}]₂ (4), which has a Ni–Ni bond. Complexes 3 and 4 were structurally characterised. Furthermore, the structure of the sterically demanding bis-aminophosphine 1,2-(NHPMes₂)₂C₆H₄ (2, Mes = 2,4,6-Me₃C₆H₂) is compared with that of the corresponding phenyl-substituted derivative 1,2-(NHPPh₂)₂C₆H₄ (1). B3LYP/LANL2DZ molecular orbital calculations on 4 indicate that a two-electron reduction should convert the Dewar-benzene-like six-membered Ni₂N₂P₂ ring in 4 to a benzene-like structure, a structure which is observed for the isoelectronic Zn^II complex 3.