Chemical Properties of Cationic Phenylplatinum(II) Complexes with a 2,2‘-Bipyridine Ligand. Insertion of CO and Allene into the Pt−C Bond and Oxidative Addition of MeI

Abstract

[PtPh(bpy)(solvent)]BF4 (1-MeCN, solvent = MeCN; 1-acetone, solvent = acetone) are prepared from the reaction of HBF4 with PtPh2(bpy) or from the reaction of AgBF4 with PtI(Ph)(bpy). The MeCN ligand of 1-MeCN in a CD3CN solution undergoes exchange with the solvent in 12 h at room temperature. The coordinated solvent of 1-acetone is replaced with acetone-d6 much more rapidly. 1-acetone reacts easily with H2O and CO to form 1-OH2 and 1-CO, respectively. The reaction of phenylallene with 1-acetone produces the (π-allyl)platinum complex [Pt(η3-CH2CPhCHPh)(bpy)]BF4 (2) as a mixture of syn and anti isomers. One of the isomers, 2-syn, was isolated by recrystallization of the products and characterized by X-ray crystallography and 1H NMR spectroscopy. The complex reacts with CO (1 atm) at room temperature to form a mixture of [Pt((Z)-CH2CPhCHPh)(bpy)(CO)]BF4 (3-Z) and [Pt((E)-CH2CPhCHPh)(bpy)(CO)]BF4 (3-E). The ratio of 3-Z to 3-E decreases gradually during the reaction to afford an equilibrium mixture ([3-Z]:[3-E] = 35:65) after 26 min. First-order rate constants of the reaction under CO and under argon are similar to each other, indicating that the isomerization occurs via a pentacoordinate intermediate with carbonyl and π-allyl ligands bonded to the Pt center. 1-MeCN reacts with MeI at 50 °C to produce a mixture of two isomeric cationic Pt(IV) complexes after 9 days. X-ray crystallography of one of the products, [PtI(Me)(Ph)(NCMe)(bpy)]BF4 (4), revealed an octahedral structure having the methyl, iodo, and bipyridine ligands in the same coordination plane.