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 oxygenate d 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 me thyl 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 3 a in the solid state (established by an X-ray structure determination) showed two crystallographically different but structurally similar ce ntrosymmetric dinuclear molecules, each having a TMF eta(6)-bonded to ruthenium(II). Each metal atom is approximately octahedrally coordinat ed by the eta(6)-C(5)Me(4)CH(2) and by three chlorides, two of which b ridge to the other ruthenium and one of which is terminal. The chlorid e bridges are broken on reaction with ligands L to give [(eta(6)-C(5)M e(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 o f 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 (r otamers). One is symmetric (trans), and the other unsymmetric (cis). T he bonding is interpreted in terms of a eta(4),eta(2)-TMF to Ru(II) ra ther 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 o bserved geometries are proposed. The mechanism for the O-2-induced C-H activation is discussed.