Carbon–Hydrogen Bond Activation C–NBond Coupling and Cycloaddition Reactivity of a Three-CoordinateNickel Complex Featuring a Terminal Imido Ligand

摘要

The three-coordinate imidos (dtbpe)Ni=NR (dtbpe = ^tBu2PCH2CH2P^tBu2, R = 2,6-ⁱPr2C6H3, 2,4,6-Me3C6H2 (Mes), and 1-adamantyl (Ad)), which contain a legitimate Ni–N double bond as well as basic imido nitrogen based on theoretical analysis, readily deprotonate HC≡CPh to form the amide acetylide species (dtbpe)Ni{NH(Ar)}(C≡CPh). In the case of R = 2,6-ⁱPr2C6H3, reductive carbonylation results in formation of the (dtbpe)Ni(CO)2 along with the N–C coupled product keteneimine PhCH=C=N(2,6- ⁱPr2C6H₃). Given the ability of the Ni=N bond to have biradical character as suggested by theoretical analysis, H atom abstraction can also occur in (dtbpe)Ni=N{2,6-ⁱPr₂C₆H₃} when this species is treated with HSn(ⁿBu)₃. Likewise, the microscopic reverse reaction—conversion of the Ni(I) anilide (dtbpe)Ni{NH(2,6-ⁱPr₂C₆H₃)} to the imido (dtbpe)Ni=N{2,6-ⁱPr₂C₆H₃}—is promoted when using the radical Mes*O^• (Mes* = 2,4,6-^tBu₃C₆H₂). Reactivity studies involving the imido complexes, in particular (dtbpe)Ni=N{2,6-ⁱPr₂C₆H₃}, are also reported with small, unsaturated molecules such as diphenylketene, benzylisocyanate, benzaldehyde, and carbon dioxide, including the formation of C–N and N–N bonds by coupling reactions.In addition to NMR spectroscopic data and combustion analysis, wealso report structural studies for all the cycloaddition reactionsinvolving the imido (dtbpe)Ni=N{2,6-ⁱPr₂C₆H₃}.