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

Abstract

Protonation of the complexes [M(q2-CH,=CHPh) (L-L)] [M = Pt, L-L = (C,H,,),P(CH,),P(C,H,,),, n = 2 or 3 ( l a or lc), But,P(CH,),PBut2, n = 2 or 3 ( l b or I d ) , and Bu',PCH,C,H,CH,PBu', (le); M = Pd, L-L = But,P(CH,),PBut,, n = 2 or 3 ( I f or l g ) and Bu',PCH,C6H,CH,PBut, (1 h)] with HBF, in diethyl ether affords a series of complexes, [M(q3-MeCHPh)(L-L)] [BF,] (2a-2h), which contain an q3-methylbenzyl ligand. The complexes 2a-2h were characterized by 'H, 13C and 31P N M R 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 N M R studies, that involves an q3 e CJ conversion coupled with single-bond rotation and P-elimination/hydride migration processes.For 2a-2e, the influence of the chelating diphosphine o n the nature of t h e q3-benzyl interaction was investigated by 31P-{1H} NMR spectroscopy and it was found that the largest diphosphines induce the most asymmetric q3 interaction. Similarly, it was found that the activation barriers to intramolecular rearrangement are lowest for the complexes with the largest diphosphine ligands.

Catalytic Transformations of Benzylic Carboxylates and Carbonates

“…The variable-temperature NMR studies of many h 3 -benzyl complexes indicate that the h 3 -h 1 -h 3 isomerization through the C 1 -C 2 bond rotation is generally faster than that through the T-Y-T isomerization. In some (h 3 32 [Pd(h 3 -1-phenylethyl)(tmeda)] + (TMEDA = N,N,N¢,N¢-tetramethylethylenediamine), 30 and CpW(h 3 -1-phenylethyl)(CO) 2 , 33 the h 3 -h 1 -h 3 isomerization is slow on the NMR time scale, even at room temperature. The a-methyl groups of their benzyl ligands may retard the isomerization.…”

Ligand driven σ,π-η3 structural rearrangements of organopalladium complexes: their relevance to the CO/styrene copolymerisation reaction

“…A series of Pd-diphosphine complexes containing a benzyl ligand, synthesised on protonation of the corresponding styrene derivatives, shows that, in all cases, the π-benzylic linkage is the preferred coordination mode. 19 On the basis of the above considerations and of the obtained results we propose that the inactivity of P-P ligands towards the CO/aromatic olefins copolymerisation may be due to the inertness of the π-allylic (or π-benzylic) fragment towards CO insertion.|| Therefore, in this case the β-hydrogen elimination becomes the fastest reaction, yielding the compound E-1,5diphenylpent-1-en-3-one, 2 instead of the polyketone.…”

In Situ Powder Diffraction Studies of Electrode Materials in Rechargeable Batteries

“…Spencer and co‐workers synthesized a number of platinum‐benzyl complexes containing varying bisphosphine steric bulk and bite angle and, the dynamic behavior of these complexes was studied by variable temperature NMR 152. Based on their findings, mechanisms of π–σ–π isomerization as well as β‐hydride elimination followed by reinsertion after olefin rotation are operative.…”