Highly Distorted Bismuth-Nickel(II) Complex

Thesynthesis and characterization of a series of nickelcomplexes bearing a bismuth-containing pincer ligand are presented.In particular, a 4-coordinate bismuth-nickel complex revealsa sawhorse geometry, significantly distorted from a square-planarstructure due to bismuth influence. The bimetallic cooperativity ofthe complexes highlights the potential of a bismuth-nickelmoiety as a new type of heterobimetallic sites for the design of bimetalliccomplexes. Thesynthesis and characterization of a series of nickel complexesbearing a bismuth-containing pincer ligand are presented herein. Inparticular, synthesis of a 4-coordinate Bi-Ni-(II) complex allowsthe influence of bismuth on a d(8) Ni-(II) ion to be investigated.A trigonal-bipyramidal complex, (BiP2)-Ni-(PPh) (1), possessing an anionic bismuth donor was prepared via the Bi-Cbond cleavage of a BiP3 ligand (BiP3 = Bi-(o-(PPr2)-Pr- i -C6H4)(3)) mediated by Ni(0). To remove a PPh moiety,compound 1 was treated with MeI to give a 5-coordinatenickel-(II) complex (MeBiP2)-Ni-(PPh)-(I) (2),followed by its exposure to heat or UV irradiation, resulting in theformation of a nickel halide complex, (BiP2)-Ni-(I) (3). The X-ray crystal structure of 2 revealedthat the methyl moiety binds to a bismuth site, providing a neutralMeBiP(2) ligand, while the iodide anion is bound to the nickel-(II)center, displacing one phosphine donor. Because of the methylationon a Bi site, the Bi-Ni bond in 2 is clearly elongatedrelative to that of 1, which indicates that the bondinginteractions between Bi and Ni are substantially different. Interestingly,compound 3 revealing a sawhorse geometry is significantlydistorted away from a square-planar structure compared to the previouslyreported nickel-(II) pincer complexes, (NP2)-Ni-(Cl) and (PP2)-Ni-(I). Such difference indicates that a bismuth donor canbe a structurally influencing cooperative site for a nickel-(II) ion,leading to have a Ni-(I)-Bi-(II) character. Migratory insertionof CO into a Ni-C bond of 1 gives (BiP2)-Ni-(COPPh) (4), which further leads to an analogousmethylated product (MeBiP2)-Ni-(COPPh)-(I) (5) from reaction with MeI. Due to the structural influence of a carbonylgroup in each step, the total reaction time from 1 to 3 was dramatically reduced. The bimetallic cooperativity ofthe complexes and unusual bonding properties presented here highlightthe potential of a bismuth-nickel moiety as a new type of heterobimetallicsite for the design of bimetallic complexes to facilitate a varietyof chemical transformations.