[PtR(η2-olefin)(N-N)]+ complexes containing the olefin and the alkyl ligand in a cis arrangement.: Preparation, structural characterization, and olefin stereochemistry

Cationic Pt(II) complexes containing an alkyl and an olefin in cis positions are described, The compounds (1) of general formula [PtR(N-N)(olefin)]BF4 are obtained either through oxidative addition of the trialkyloxonium salt R3O+BF4- to the appropriate three-coordinate precursor [Pt(N-N)(olefin)] or by substitution of an alkene for the chloride in [PtR(Cl)(N-N)] complexes. The complexes are involved in a dynamic process involving the alkene ligand. The rate of alkene exchange is strongly influenced by the steric hindrance of the N-N ligand above and below the coordination plane, This feature also controls the stereochemistry of alkene coordination. Thus, for type 1 derivatives of alpha-olefins containing the highly crowded diacetyl bis(di-isopropylphenylimine), only one enantiomeric couple has been detected in the temperature range 203-328 K, and its geometry has been tentatively assigned. Finally, the X-ray crystal structure of a representative complex has been determined.