ALKYNE ACTIVATION BY ELECTROPHILIC [(ETA-C-5ME(5))RU(NO)(R)]+ (R=ME, PH, P-TOLYL) FRAGMENTS - BETA-MIGRATORY INSERTION, ISOMERIZATION, AND METALLACYCLE FORMATION

Treatment of Cp(*)Ru(NO)R(2) complexes 1-3 with 1 equiv of triflic acid (HOTf) leads to the formation of the triflato complexes Cp(*)Ru(NO)(R)(OTf) (4-6) (R = CH3 (1, 4), C6H5 (2, 5), p-tolyl (3, 6); Cp(*) - eta 5-C(5)Me(5)). X-ray data for 5 (C17H20NO4SF3Ru): monoclinic space group P2(1)/n, a = 10.041(2) Angstrom, b = 13.797(4) Angstrom, c = 15.113(3) Angstrom, beta = 106.68(2)degrees, Z = 4, R/R(W) = 4.50/3.37%. The dissociation of the triflate ligands in 4-6 in solution is detectable by NMR spectroscopy. The Delta H/Delta S values for equilibrium between bound and free triflate in THF are (-2.1(1) kcal/mol)/(-9(1) eu) for 4 and (-2.3(2) kcal/mol)/(-9(1) eu) for 5. Triflate dissociation from complexes 4-6 in CH2Cl2 is trapped by the binding of PhC=CPh, leading to the eventual formation of neutral ruthenacyclopentadiene products 8-10 by beta-migratory insertion followed by orthometallation of a beta-aryl group. X-ray data for 8 (C25H27NORu): monoclinic space group P2(1)/c, a = 16.724(7) Angstrom, b = 7.274(2) Angstrom, c = 17.904(7) Angstrom, beta = 102.26(3)degrees, Z = 4, R/R(W) = 4.40/3.89%. X-ray data for 10 (C31H31NORu): monoclinic space group P2(1)/n, a = 9.597(2) Angstrom, b = 22.577(4) Angstrom, c = 12.094(2) Angstrom, beta = 101.34(2)degrees, Z = 4, R/R(W) = 4.84/4.57%. Formation of 8 requires a cis-trans isomerization in the intermediate sigma-vinyl complex formed by methyl beta-migratory insertion to the alkyne. A proposed mechanism for the cis-trans-sigma-vinyl isomerization invokes resonance stabilization through back-donation into the NO-pi(*) levels of the [Cp(*)Ru(NO)] fragment. Exclusive formation of 10 when 6 is treated with PhC=CPh shows orthometallation is rapid in comparison to cia-trans isomerization of the intermediate a-vinyl ligand. Protonation experiments using DOTf show the metallacycle to open first at the Ru-C-aryl bond; treatment of 8 with excess HOTf results in the generation of (E)-alpha-methylstilbene and Cp(*)Ru(NO)(OTf)(2) (7).