[PTR(ETA(2)-OLEFIN)(N-N)](- PREPARATION, STRUCTURAL CHARACTERIZATION,AND OLEFIN STEREOCHEMISTRY() COMPLEXES CONTAINING THE OLEFIN AND THE ALKYL LIGAND IN A CIS ARRANGEMENT )

Cationic Pt(II) complexes containing an alkyl and an olefin in cis pos itions are described, The compounds (1) of general formula [PtR(N-N)(o lefin)]BF4 are obtained either through oxidative addition of the trial kyloxonium 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 pro cess involving the alkene ligand. The rate of alkene exchange is stron gly influenced by the steric hindrance of the N-N ligand above and bel ow the coordination plane, This feature also controls the stereochemis try of alkene coordination. Thus, for type 1 derivatives of alpha-olef ins containing the highly crowded diacetyl bis(di-isopropylphenylimine ), only one enantiomeric couple has been detected in the temperature r ange 203-328 K, and its geometry has been tentatively assigned. Finall y, the X-ray crystal structure of a representative complex has been de termined.