[PtR(η²-olefin)(N-N)]⁺ Complexes Containing the Olefin and the Alkyl Ligand in a <i>cis</i> Arrangement. Preparation, Structural Characterization, and Olefin Stereochemistry

Abstract

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 α-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.