Ring-methyl activation in pentamethylcyclopentadienyl complexes .5. Syntheses and structures of tetramethylfulvene complexes of ruthenium(II)

As previously reported, [{(eta(5)-C(5)Me(5))RuCl2}2], 1a, is oxygenated to the mu-oxo complex, [{(eta(5)-C(5)Me(5))RuCl2}O-2], 2a (Angelici, R. J.; et al Organometallics 1992, 11, 2303). It is now shown that 2a spontaneously decomposes in chloroform solution by activation of a methyl C-H bond, to give the dinuclear tetramethylfulvene (TMF) complex [{(eta(6)-C(5)Me(4)CH(2))RuCl2}(2)], 3a, and water. The structure of 3a in the solid state (established by an X-ray structure determination) showed two crystallographically different but structurally similar centrosymmetric dinuclear molecules, each having a TMF eta(6)-bonded to ruthenium(II). Each metal atom is approximately octahedrally coordinated by the eta(6)-C(5)Me(4)CH(2) and by three chlorides, two of which bridge to the other ruthenium and one of which is terminal. The chloride bridges are broken on reaction with ligands L to give [(eta(6)-C(5)Me(4)CH(2))RuCl2(L)], 4a (L=py), or 5a (L=Me(2)SO). All the complexes 2-5 are diamagnetic. NMR spectra of solutions of 3a show the presence of several structural isomers; these do not interconvert rapidly on the NMR time scale below 70 degrees C. The adducts 4a and 5a also show an unexpected rigidity; thus, 4a shows two noninterconverting isomers (rotamers). One is symmetric (trans), and the other unsymmetric (cis). The bonding is interpreted in terms of a eta(4),eta(2)-TMF to Ru(II) rather than the alternative eta(5),eta(1)-TMF to Ru(TV), by analysis of the details of the crystal structure determination of 3a and the (1)J(C-H) of the exocyclic =CH2 in the C-13 NMR spectrum. Reasons for the observed geometries are proposed. The mechanism for the O-2-induced C-H activation is discussed.