Probing the Dynamics and Reactivity of a Stereochemically Nonrigid Cp*Ru(H)(κ²-<i>P</i>,<i>C</i>arbene) Complex

The ability of the coordinatively saturated, 18-electron Cp*(H)RuCHR complex 1 to serve as a masked source of the coordinatively unsaturated Cp*Ru-CH2R species 2 via reversible α-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 1 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 1 with Ph2SiD2 provided evidence in support of a reaction mechanism involving previously undocumented Si−H addition across the RuC unit in 1 in the formation of 3a. Addition of Jutzi’s acid (H(OEt2)2B(C6F5)4) to 1 resulted in the quantitative formation of 4 (the N-C-H cyclometalated variant of [Cp*Ru(κ2-2-NMe2-3-PiPr2-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 1 with mesitylborane (MesBH2) 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.