Springy Annulene Leads To First Nickel Tetraalkyl

By reacting a nickel(0) complex with a strained cyclic alkene, a team of chemists has prepared the first reported all-alkyl nickel(IV) complex (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200804435). Earlier this year, Columbia University's Matthew Carnes, Colin Nuckolls, Michael Steigerwald, and coworkers reported the synthesis of a unique dibenzocyclooctatetraene (DCOT) molecule that they are exploring as a monomer for ring-opening metathesis polymerization (Angew. Chem. Int. Ed. 2008, 47, 2982). The central eight-membered tetraene ring has one trans double bond, which gives the molecule a spring-loaded helical twist. The researchers have now reacted DCOT with a nickel(0) complex under various conditions. One product is a chiral trimer in which three DCOT molecules surround a nickel atom. Under different conditions, the team ended up with the nickel(IV) tetraalkyl shown. It appears to form when the nickel atom in the trimer "slips" and forms a complex with four DCOT molecules, resulting in four Ni–C bonds. This unique chemistry is driven by DCOT working out the kink in its trans double bond, the researchers believe. The highly stable nickel complexes could be useful as catalyst precursors or as organometallic framework building blocks, they add.