(ETA-6-NAPHTHALENE)(ETA-4-1,5-CYCLOOCTADIENE)RUTHENIUM(0) - EFFICIENT SYNTHESIS, CHEMISTRY, AND CATALYTIC PROPERTIES

The ruthenium(0) complex (eta-4-1,5-cyclooctadiene)(eta-6-naphthalene)ruthenium(0), Ru(eta-6-C10H8)(eta-4-C8H12) (2), is conveniently synthesized in 55-64% yield on a gram scale by treatment of Ru(acac)2(eta-4-C8H12) (acac = acetylacetonate) with sodium naphthalide. A preliminary H-1 NMR study of the rate of replacement of naphthalene by arenes in the presence of acetonitrile at room temperature has been made. The reaction is first order in 2 and approximately first order in acetonitrile up to [CH3CN]/[2] ca. 3, but a higher order for the latter cannot be excluded. Benzene, toluene, and xylene (8 mol per mol of 2) in THF-d8 replace naphthalene at almost the same rate, but the reaction is slower when there are more than two methyl groups in the entering arene, the order being p-xylene > 1,2,4-trimethylbenzene > 1,2,3,4-tetramethylbenzene >> mesitylene. The results are consistent with the initial formation of labile intermediate eta-4- or eta-2-naphthalene complexes that are stabilized by acetonitrile, e.g., Ru(eta-4-C10H8)(eta-4-C8H12)(NCMe). Solutions of 2 in acetonitrile lose naphthalene to form a dinuclear mu-naphthalene complex Ru2(eta-4-C8H12)2(mu-C10H8) (5). The new eta-6-arene complexes Ru(eta-6-arene)(eta-4-C8H12) (arene = C6H5CN (4), 1,2,4-C6H3Me3 (6), 1,2,3,4-C6H2Me4 (7), C6H5CH = CH2 (9), 1-Me-4-CH2 = CMeC6H4 (10), (E)-C6H5CH = CHC6H5 (11), (C6H5)3As (14), and (2-MeC6H4)3p (15) have been obtained from 2, and the new ruthenium(II) complexes [RUCl2(eta-6-arene)]2 (12) and Ru(O2CMe)2(eta-6-arene) (13) (arene = 1-Me-4-CH2 = CMeC6H4) have been prepared from 10. Protonation of 2 with HPF6 gives the hydridoruthenium(II) complex [RuH(eta-6-C10H8)(eta-4-C8H12)]PF6 (16), from which naphthalene is readily displaced by p-xylene or mesitylene to give [RuH(eta-6-arene)(eta-4-C8H12)]PF6. In the presence of acetonitrile and hydrogen (1-20 atm), 2 catalyzes the hydrogenation of olefins. It is much more active than Ru(eta-6-arene)(eta-4-C8H12) (arene = C6H6, 1-Me-4-Me2CHC6H4) under the same conditions, probably as a consequence of the ease of eta-6 --> eta-4 conversion for naphthalene.