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 d8 Ni(II) ion to be investigated. A trigonal-bipyramidal complex, (BiP2)Ni(PPh) (1), possessing an anionic bismuth donor was prepared via the Bi-C bond cleavage of a BiP3 ligand (BiP3 = Bi(o-PiPr2-C6H4)3) mediated by Ni(0). To remove a PPh moiety, compound 1 was treated with MeI to give a 5-coordinate nickel(II) complex (MeBiP2)Ni(PPh)(I) (2), followed by its exposure to heat or UV irradiation, resulting in the formation of a nickel halide complex, (BiP2)Ni(I) (3). The X-ray crystal structure of 2 revealed that the methyl moiety binds to a bismuth site, providing a neutral MeBiP2 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, (NP2)Ni(Cl) and (PP2)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 (BiP2)Ni(COPPh) (4), which further leads to an analogous methylated product (MeBiP2)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.

Nickel-Catalyzed NO Group Transfer Coupled with NOx Conversion.

Nitrogen oxide (NOx) conversion is an important process for balancing the global nitrogen cycle. Distinct from the biological NOx transformation, we have devised a synthetic approach to this issue by utilizing a bifunctional metal catalyst for producing value-added products from NOx. Here, we present a novel catalysis based on a Ni pincer system, effectively converting Ni-NOx to Ni-NO via deoxygenation with CO(g). This is followed by transfer of the in situ generated nitroso group to organic substrates, which favorably occurs at the flattened Ni(I)-NO site via its nucleophilic reaction. Successful catalytic production of oximes from benzyl halides using NaNO2 is presented with a turnover number of >200 under mild conditions. In a key step of the catalysis, a nickel(I)-•NO species effectively activates alkyl halides, which is carefully evaluated by both experimental and theoretical methods. Our nickel catalyst effectively fulfills a dual purpose, namely, deoxygenating NOx anions and catalyzing C-N coupling.