138877-22-2Relevant academic research and scientific papers
Synthesis and characterization of bis(phosphine)nickel(0) complexes containing nonsymmetrically substituted acetylenes
Bartik, Tamás,Happ, Berit,Iglewsky, Marek,Bandmann, Heinz,Boese, Roland,Heimbach, Paul,Hoffmann, Thomas,Wenschuh, Eberhard
, p. 1235 - 1241 (2008/10/08)
Some new nickel π-complexes of the general formula L2Ni(XC≡CY) (L = PCy3, PPh3, P(O-o-Tol)3; X = Ph, Me; Y = Me, Et, i-Pr, t-Bu, H, SiMe3, SiPh3) were prepared, and the influence of various substituents and ligands on the properties of the π-bond, three-membered metallacycle was investigated. With X = Ph kept constant, the following substituent variations of Y have been tested Y = Me, Et, i-Pr, t-Bu (systematic α-methyl perturbation on the tetrahedral C atom), H, SiMe3, and SiPh3. It could be established that the quaternary C atoms of the three-membered metal ring system have very different electron densities (13C NMR analysis) that are caused by nonsymmetrical substitution. The strongest polarization of the acetylene bond between the sp carbon atoms could be obtained with X = Ph, Y = SiMe3 and X = Ph, Y = SiPh3 substituted acetylenes. The differences between the interaction of these C atoms with the metal center have been confirmed by an X-ray diffraction study of the (PPh3)2Ni(PhC1≡C2SiMe 3) complex: monoclinic, space group P21/c; a = 12.200 (2) A?, b = 12.564 (2) A?, c = 26.607 (4) A?, α = 90°, β = 98.37 (1)°, γ = 90°, V = 4034.8 (1.1) A?3, Z = 4, R = 0.0477; Ni-C1 and Ni-C2 bond lengths 1.884 (6) and 1.926 (6) A?; bend-back angles 31.8 (5)° (on C1) and 41.3 (5)° (on C2). The electron density of the complexed acetylene carbon atoms is influenced also by the properties of phosphine ligands on the transition metal. Donor phosphine ligands like PCy3 caused an increase, while acceptor ones like P(O-o-Tol)3 caused a decrease in polarization between the two C atoms of the metallacycle.
