SYNTHESIS, STRUCTURE AND DYNAMIC STUDIES ON BASE-STABILIZED SILYLENE COMPLEXES [(ETA(5)-C(5)ME(5))(PME(3))(2)RUSIX(2)(NCME)(+)]

The silyl complexes Cp*(PMe(3))(2)RuSiX(2)Z (Cp* = eta(5)-C(5)Me(5); 1, SiX(2)Z = Si[S(Tol-p)](3); 2, SIX(2)Z = Si[O(Tol-p)](3); 3, SiX(2)Z = SiMe(2)[S(Tol-p)]), prepared by reaction of the appropriate hydrosilane with Cp* (PMe(3))(2)RuCH(2)SiMe(3), react with Me(3)SiOTf (OTf = OSO2CF3) to afford the triflato(silyl) complexes Cp*(PMe(3))(2)RuSiX(2)OTf (4, X = S(Tol-p); 5, X = O(Tol-p); 6, X = Me) or Cp*(PMe(3))(2)Rusi[S(Tol-p)](OTf)(2) (7). The X-ray crystal structures of the compounds 1, 4, and 7 are described and discussed. Compound 4 reacts with LiBEt(3)H to produce Cp*(PMe(3))(2)RuSiH[S(Tol-p)](2) (8), with water to give Cp*(PMe(3))(2)RuSi[S(Tol-p)](OTf)(OH) (10), and with HCl to afford Cp*(PMe(3))(2) RuSiCl2(OTf) (11). The triflate Cp*(PMe(3))(2)RuSiH[S(Tol-p)](OTf) (9) results from reaction of 8 with Me(3)SiOTf. The base-stabilized silylene complexes [Cp*(PMe(3))2Ru SiX(2)(NCMe)]BPh(4) (13, X = S(Tol-p); 14, X = O(Tol-p); 15, X = Me) are prepared by displacement of triflate from 4-6. The X-ray structures of 13 and 15 are described and compared to the previously reported structure of [Cp*(PMe(3))(2)RuSiPh(2)(NCMe)]BPh(4) (12). The structures are discussed in terms of the amount of incipient silylene character possessed by each. For 12-15, bound acetonitrile exchanges with free acetonitrile in dichloromethane solution via a dissociative mechanism. The rates and activation parameters for these exchange reactions allow an ordering of stabilities for the corresponding base-free silylene complexes, since the reactions involve rate-limiting loss of acetonitrile from the complex. The kinetic data indicate that the stabilizing influences for silylene substituents in this system are ordered according to : S(Tol-p) > O(Tol-p) > Me > Ph. A different ordering is suggested by the X-ray structural data. Apparently conflicting information from the structural and dynamic studies are discussed and rationalized, and it is concluded that the ordering suggested by the kinetic data is more useful.