Effect of phenyl substitution on bonding in η3-benzyl complexes of platinum

Abstract

Reaction of the platinum(0) styrene complexes [Pt(η²-CH₂CHC₆H₄X){Bu^t₂P(CH₂)₃PBu^t₂}]1a–1f(X = Br-3, Br-4, Me-4, F-4, F-3 or MeO-4) with HBF₄ in diethyl ether afforded the η³-methylbenzyl complexes [Pt(η³-MeCHC₆H₄X){Bu^t₂P(CH₂)₃PBu^t₂}][BF₄]2a–2f. The effect of phenyl substitution on the asymmetry of the η³-methylbenzyl interaction was measured by ³¹P-{¹H} NMR spectroscopy and it was found that, in general, the more electron releasing the substituent, X, the more asymmetric is the bonding. Complexes 2a–2f lose styrene reversibly to form the hydride-bridged dinuclear platinum complex [Pt₂(µ-H)₂{Bu^t₂P(CH₂)₃PBu^t₂}₂][BF₄]₂. Displacement of styrenes from 2a–2f by ethene and bicyclo[2.2.1]hept-2-ene affords known complexes stabilized by a three-centre, two-electron (agostic) bond.