Synthesis and characterization of bis(phosphine)nickel(0) complexes containing nonsymmetrically substituted acetylenes.
Some new nickel p-complexes L2Ni(XC.tplbond.CR)(L = PCy3, PPh3, P(OC6H4Me-o)3; X = Ph, Me; R = Me, Et, CHMe2, CMe3, H, SiMe3, SiPh3) were prepd. by known methods and the influences of various substituents and ligands on the properties of the p-bond, three-membered metalcycle was investigated. With X = Ph kept const., the following substituent variations of R have been tested R = Me, Et, CHMe2, CMe3 (systematic a-Me perturbation on the tetrahedral C atom), H, SiMe3, and SiPh3. The quaternary C atoms of the three-membered metal ring system have very different electron densities (13C NMR anal.) that are caused by nonsym. substitution. The strongest polarization of the acetylene bond between the sp carbon atoms could be obtained with X = Ph, R = SiMe3, and X = Ph, R = 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(PhC.tplbond.CSiMe3) complex:. The electron d. 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 lie P(OC6H4-o)3 caused a decrease in polarization between the two C atoms of the metalacycle.
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