Preparation and fluxional behaviour of η³-methylbenzyl platinum and palladium complexes

Abstract

Protonation of the complexes [M(η2-CH2CHPh)(L–L)][M = Pt, L–L =(C6H11)2P(CH2)nP(C6H11)2, n= 2 or 3 (1a or 1c), But2P(CH2)nPBut2, n= 2 or 3 (1b or 1d), and But2PCH2C6H4CH2PBut2(1e); M = Pd, L–L = But2P(CH2)nPBut2, n= 2 or 3 (1f or 1g) and But2PCH2C6H4CH2PBut2(1h)] with HBF4 in diethyl ether affords a series of complexes, [M(η3-MeCHPh)(L–L)][BF4](2a–2h), which contain an η3-methylbenzyl ligand. The complexes 2a–2h were characterized by 1H, 13C and 31P NMR spectroscopy and all except 2a and 2f were found to undergo intramolecular rearrangement in solution at or below room temperature. A mechanism is proposed, on the basis of variable-temperature NMR studies, that involves an η3⇌σ conversion coupled with single-bond rotation and β-elimination/hydride migration processes. For 2a–2e, the influence of the chelating diphosphine on the nature of the η3-benzyl interaction was investigated by 31P-{1H} NMR spectroscopy and it was found that the largest diphosphines induce the most asymmetric η3 interaction. Similarly, it was found that the activation barriers to intramolecular rearrangement are lowest for the complexes with the largest diphosphine ligands.