HYDROGEN MIGRATION TO ACYCLIC PENTADIENYL LIGANDS - THE REACTIONS OF (ETA-5-2,4-DIMETHYLPENTADIENYL) (ETA-4-2,4-DIMETHYLPENTA-1,3-DIENE)(L)RUTHENIUM(II) TETRAFLUOROBORATES (L = TBUNC, CO, P(OME)3) WITH DIENES

Diene-for-diene substitutions occur on reaction of the title complexes [Ru(eta5-C7H11)(eta4-C7H12)L]BF4 (L = tBuNC (2), CO (3), P(OMe)3 (4)) with an excess of butadiene 2,3-dimethylbutadiene. cyclohexa-1,3-diene or cycloocta-1,5-diene giving complexes of the type [Ru(eta5-C7H11)(diene)L]BF4 (5-16). Apparent pentadienyl-for-pentadienyl substitutions occur on reaction of 2 with the cyclopentadienes C5H6 or C5Me5H giving [Ru(eta5-C5R5)(eta4-C7H12)(CNtBu)]BF4 (R = H (17), Me (18)), on reaction of 2 or 3 with cyclohexa-1,4-diene to give [Ru(eta5-C6H7)(eta4-C7H12)L]BF4 (L = tBuNC (19), CO (20)), and on reaction of 2, 3 or 4 with cycloocta-1,3-diene to give [Ru(eta5-C8H11)(eta4-C7H12)L]BF4 (L = tBuNC (21), CO (22), P(OMe)3 (23)). The (eta4-C7H12) ligand is readily displaced from 19 and 20 by an excess of a cyclohexadiene (1,3- or 1,4-) to give [Ru(eta5-C6H7)(eta4-C6H8)L]BF4 (L = tBuNC (24), CO (25)) and from 21 by an excess of cycloocta-1,5-diene giving [Ru(eta5-C8H11)(eta2 : eta2-C8H12)(CNtBu)]BF4 (26). All the apparent pentadienyl-for-pentadienyl substitutions are suggested to occur via initial displacement of the (eta4-C7H12) ligand from 2-4, with subsequent C-H activation and inter-ligand hydrogen migration from the incoming diene to the (eta5-C7H11) ligand leading to the observed products.