Synthesis, structure, and reactivity of hydridoiridium complexes bearing a pincer-type PSiP ligand

A series of iridium tetrahydride complexes [Ir(H)(4)(PSiP-R)] bearing a tridentate pincer-type bis(phosphino)silyl ligand ([{2-(R(2)P)C(6)H(4)}(2)MeSi](-), PSiP-R, R=Cy, iPr, or tBu) were synthesized by the reduction of [IrCl(H)(PSiP-R)] with Me(4)N·BH(4) under argon. The same reaction under a nitrogen atmosphere afforded a rare example of thermally stable iridium(III)-dinitrogen complexes, [Ir(H)(2)(N(2))(PSiP-R)]. Two isomeric dinitrogen complexes were produced, in which the PSiP ligand coordinated to the iridium center in meridional and facial orientations, respectively. Attempted substitution of the dinitrogen ligand in [Ir(H)(2)(N(2))(PSiP-Cy)] with PMe(3) required heating at 150 °C to give the expected [Ir(H)(2)(PMe(3))(PSiP-Cy)] and a trigonal bipyramidal iridium(I)-dinitrogen complex, [Ir(N(2))(PMe(3))(PSiP-Cy)]. The reaction of [Ir(H)(4)(PSiP-Cy)] with three equivalents of 2-norbornene (nbe) in benzene afforded [Ir(I)(nbe)(PSiP-Cy)] in a high yield, while a similar reaction of [Ir(H)(4)(PSiP-R)] with an excess of 3,3-dimethylbutene (tbe) in benzene gave the C-H bond activation product, [Ir(III)(H)(Ph)(PSiP-R)], in high yield. The oxidative addition of benzene is reversible; heating [Ir(III)(H)(Ph)(PSiP-Cy)] in the presence of PPh(3) in benzene resulted in reductive elimination of benzene, coordination of PPh(3), and activation of the C-H bond of one aromatic ring in PPh(3). [Ir(III)(H)(Ph)(PSiP-R)] catalyzed a direct borylation reaction of the benzene C-H bond with bis(pinacolato)diboron. Molecular structures of most of the new complexes in this study were determined by a single-crystal X-ray analysis.