Bis(phosphanylamino)benzene ligands: a zinc(II) complex and an unusual nickel(I) complex with a Dewar-benzene-type Ni2P2N2 backbone

ZnPr(2) reacts with 1,2-(NHPPh(2))(2)C(6)H(4) (1) to give the bis-amido complex Zn(THF){1-N(PPh(2))-2-N(mu-PPh(2))C(6)H(4)-kappa(3)N,N',P}](2) (3), while monolithiated 1 (prepared in situ from 1 and LiBu(n)) reacts with NiCl(2) with formation of the unusual nickel(I) complex Ni{1-NH(PPh(2))-2-N(micro-PPh(2))C(6)H(4)-kappa(2)N,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-(NHPMes(2))(2)C(6)H(4) (2, Mes = 2,4,6-Me(3)C(6)H(2)) is compared with that of the corresponding phenyl-substituted derivative 1,2-(NHPPh(2))(2)C(6)H(4) (1). B3LYP/LANL2DZ molecular orbital calculations on 4 indicate that a two-electron reduction should convert the Dewar-benzene-like six-membered Ni(2)N(2)P(2) ring 4 in to a benzene-like structure, a structure which is observed for the isoelectronic Zn(II) complex 3.