Probing Dynamic Equilibria between Platinum(II)−η2-Benzene Adducts and Unobserved Five-Coordinate Platinum(IV) C−H Oxidative Addition Intermediates

Low-temperature addition of nitrile ligands to platinum(II) η2-benzene reagents, [(κ2-HTp‘)Pt(η2-C6H6)(R)][BAr‘4] (R = H, Ph), results in reversible trapping of the postulated five-coordinate C−H oxidative addition product to give cationic platinum(IV) nitrile adducts, [(κ2-HTp‘)Pt(C6H5)(H)(R)(NCR‘)][BAr‘4] (R = Ph, H, R‘ = Me, CMe3, p-XC6H4). At higher temperatures, irreversible loss of benzene from the Pt(II) η2-benzene reagents occurs to form cationic Pt(II) nitrile products.