PREPARATION AND FLUXIONAL BEHAVIOR OF ETA-3-METHYLBENZYL PLATINUM AND PALLADIUM COMPLEXES

Protonation of the complexes [M(eta2-CH2=CHPh)(L-L)] [M = Pt, L-L = (C6H11)2P(CH2)nP(C6H11)2, n = 2 or 3 (la or lc), But2P(CH2)nPBut2, n = 2 or 3 (lb or ld), and But2PCH2C6H4CHPBut2 (1e); M = Pd, L-L = But2P(CH2)nPBut2, n = 2 or 3 (1f or 19) and But2PCH2C6H4CH2PBut2 (1h)] with HBF4 in diethyl ether affords a series of complexes, [M(eta3-MeCHPh)(L-L)][BF4] (2a-2h), which contain an eta3-methylbenzyl ligand. The complexes 2a-2h were characterized by H-1, C-13 and P-31 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 eta3 half arrow right over half arrow left sigma conversion coupled with single-bond rotation and beta-elimination/hydride migration processes. For 2a-2e, the influence of the chelating diphosphine on the nature of the eta3-benzyl interaction was investigated by P-31-{H-1} NMR spectroscopy and it was found that the largest diphosphines induce the most asymmetric eta3 interaction. Similarly, it was found that the activation barriers to intramolecular rearrangement are lowest for the complexes with the largest diphosphine ligands.