title: Metal-ligand synergistic effects in the complex Ni(η(2)-TEMPO)2: synthesis, structures, and reactivity.
abstract: In the current investigation, reactions of the "bow-tie" Ni(η(2)-TEMPO)2 complex with an assortment of donor ligands have been characterized experimentally and computationally. While the Ni(η(2)-TEMPO)2 complex has trans-disposed TEMPO ligands, proton transfer from the C-H bond of alkyne substrates (phenylacetylene, acetylene, trimethylsilyl acetylene, and 1,4-diethynylbenzene) produce cis-disposed ligands of the form Ni(η(2)-TEMPO)(κ(1)-TEMPOH)(κ(1)-R). In the case of 1,4-diethynylbenzene, a two-stage reaction occurs. The initial product Ni(η(2)-TEMPO)(κ(1)-TEMPOH)[κ(1)-CC(C6H4)CCH] is formed first but can react further with another equivalent of Ni(η(2)-TEMPO)2 to form the bridged complex Ni(η(2)-TEMPO)(κ(1)-TEMPOH)[κ(1)-κ(1)-CC(C6H4)CC]Ni(η(2)-TEMPO)(κ(1)-TEMPOH). The corresponding reaction with acetylene, which could conceivably also yield a bridging complex, does not occur. Via density functional theory (DFT), addition mechanisms are proposed in order to rationalize thermodynamic and kinetic selectivity. Computations have also been used to probe the relative thermodynamic stabilities of the cis and trans addition products and are in accord with experimental results. Based upon the computational results and the geometry of the experimentally observed product, a trans-cis isomerization must occur.
authors.affiliation: Department of Chemistry, University of Miami , Coral Gables, Florida 33124, United States.
authors.forename: Derek
authors.initials: D
authors.lastname: Isrow
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: DeYonker
authors.forename: Anjaneyulu
authors.initials: A
authors.lastname: Koppaka
authors.forename: Perry J
authors.initials: PJ
authors.lastname: Pellechia
authors.forename: Charles Edwin
authors.initials: CE
authors.lastname: Webster
authors.forename: Burjor
authors.initials: B
authors.lastname: Captain