Highly Distorted Bismuth-Nickel(II) Complex.

The synthesis and characterization of a series of nickel complexes bearing a bismuth-containing pincer ligand are presented herein. In particular, synthesis of a 4-coordinate Bi-Ni(II) complex allows the influence of bismuth on a d 8 Ni(II) ion to be investigated. A trigonal-bipyramidal complex, (BiP 2 )Ni(PPh) ( 1 ), possessing an anionic bismuth donor was prepared via the Bi-C bond cleavage of a BiP 3 ligand (BiP 3 = Bi( o -P i Pr 2 -C 6 H 4 ) 3 ) mediated by Ni(0). To remove a PPh moiety, compound 1 was treated with MeI to give a 5-coordinate nickel(II) complex (MeBiP 2 )Ni(PPh)(I) ( 2 ), followed by its exposure to heat or UV irradiation, resulting in the formation of a nickel halide complex, (BiP 2 )Ni(I) ( 3 ). The X-ray crystal structure of 2 revealed that the methyl moiety binds to a bismuth site, providing a neutral MeBiP 2 ligand, while the iodide anion is bound to the nickel(II) center, displacing one phosphine donor. Because of the methylation on a Bi site, the Bi-Ni bond in 2 is clearly elongated relative to that of 1 , which indicates that the bonding interactions between Bi and Ni are substantially different. Interestingly, compound 3 revealing a sawhorse geometry is significantly distorted away from a square-planar structure compared to the previously reported nickel(II) pincer complexes, (NP 2 )Ni(Cl) and (PP 2 )Ni(I). Such difference indicates that a bismuth donor can be a structurally influencing cooperative site for a nickel(II) ion, leading to have a Ni(I)-Bi(II) character. Migratory insertion of CO into a Ni-C bond of 1 gives (BiP 2 )Ni(COPPh) ( 4 ), which further leads to an analogous methylated product (MeBiP 2 )Ni(COPPh)(I) ( 5 ) from reaction with MeI. Due to the structural influence of a carbonyl group in each step, the total reaction time from 1 to 3 was dramatically reduced. The bimetallic cooperativity of the complexes and unusual bonding properties presented here highlight the potential of a bismuth-nickel moiety as a new type of heterobimetallic site for the design of bimetallic complexes to facilitate a variety of chemical transformations.