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, i Pr, or t Bu) 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 CH 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 CH bond of one aromatic ring in PPh 3 . [Ir III (H)(Ph)(PSiP‐R)] catalyzed a direct borylation reaction of the benzene CH 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.