Synthesis, Structures, and Reactions of Methylplatinum(II) and -palladium(II) Complexes Bearing Diphosphinidenecyclobutene Ligands (DPCB-Y)
journal contributionposted on 15.03.2004, 00:00 by Fumiyuki Ozawa, Seiji Kawagishi, Takeshi Ishiyama, Masaaki Yoshifuji
Dimethylplatinum(II) complexes coordinated with 1,2-diaryl-3,4-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]cyclobutenes (DPCB-Y; aryl = 4-methoxyphenyl, phenyl, 4-trifluoromethylphenyl, 3,5-bis(trifluoromethyl)phenyl] are prepared by ligand displacement of Pt2Me4(μ-SMe2)2 with corresponding DPCB-Y, which is a novel class of ligands having sp2-hybridized phosphorus as coordination atoms. Comparison of the NMR data with those of diimine- and diphosphine-coordinated analogues indicates intermediate magnitude of trans-influence of DPCB-Y ligands. This observation is supported by X-ray structural analysis. On the other hand, structural deviations of the coordinated DPCB-Y from free DPCB-Y suggest the occurrence of strong π-back-donation from the platinum to the ligands. Reflecting the strong π-back-donation, the ethylene protons in [PtMe(η2-C2H4)(DPCB-Y)]OTf appear at δ 5.22−5.02 in the 1H NMR spectra, the chemical shifts of which are significantly lower than those so far reported for platinum(II) complexes (ca. δ 4.0) and comparable to that of free ethylene (δ 5.30). Ethylene polymerization using methylpalladium catalysts bearing DPCB-Y ligands is also reported.