Probing the Dynamics and Reactivity of a Stereochemically Nonrigid Cp*Ru(H)(κ2-P,Carbene) Complex

The ability of the coordinatively saturated, 18-electron Cp*(H)Ru CHR complex I to serve as a masked source of the coordinatively unsaturated Cp*Ru-CH2R species 2 via reversible cc-hydride elimination was surveyed. The rate constant for this dynamic process (300 K, C6D6) was measured to be 59 +/- 1 s(-1), on the basis of data obtained from selective inversion NMR. experiments. Exposure of I to an atmosphere of CO or to an equivalent of either PMe3 or PH2Ph afforded the corresponding 2 . L adduct (L = CO, 98%; PMe3, 93%; PH2Ph, 67%). Treatment of 1 with Ph2SiH2, PhSiH3, Ph2SiClH, or PhSiClH2 afforded the corresponding net Si-H addition product, 3a-d (82-94%); an NMR spectroscopic investigation of the analogous reaction of I with Ph2SiD2 provided evidence in support of a reaction mechanism involving previously undocumented Si-H addition across the Ru C unit in I in the formation of 3a. Addition of Jutzi's acid (H(OEt2)(2)B(C6F5)(4)) to 1 resulted in the quantitative formation of 4 (the N-C-H cyclometalated variant of [Cp*Ru(kappa(2)-2=NMe2-3-PiPr(2)-indene)]+B(C6F5)(4)(-)). In monitoring the progress of the reaction of 1 with excess catecholborane (HBcat), evidence for the formation of the B-H addition product 5i was obtained en route to the isolable (Bcat)Ru=C species (5, 54%). Conversely, no intermediates were observed in the reaction of I with mesitylborane (MesBH(2),) leading to the Cp*Ru(P,N) complex 6 (81%), which features a tethered borane fragment and a Ru-H-B bridge. Crystallographic characterization data are provided for 2 . PMe3, 3a, 3b, 3d, 5, and 6.