Synthesis, Structure, and Reactivity of Hydridoiridium Complexes Bearing a Pincer‐Type PSiP Ligand

Abstract

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.

Cationic, Neutral, and Anionic Hydrides of Iridium with PSiP Pincers

“…22 This analogue was reported to readily form a κO,P,P P(SiOH)P dihydride complex after cleaving a water molecule and inserting the OH fragment into the Si−Ir bond. Instead of such an irreversible transformation, the treatment of 2 with water in a NMR tube in CD 2 Cl 2 was observed to provoke just small shifts in most of the NMR signals, including the diagnostic singlets in the 31 P{ 1 H} and 19 F spectra, at δ 69.60 and −77.49 respectively, and the triplet corresponding to the hydride ligand in the 1 H high-field region, at δ −29.52 (J HP = 14.9 Hz). Decreasing the temperature provoked decoalescence of each of these shifted signals into two, whose relative intensity depended on the amount of added water.…”

“…17 Aimed at extending this chemistry to compound types that can fulfill the requirements of different catalytic transformations, we describe here the preparations and structures of a variety of iridium PSiP hydrides, including dihydrogen and anionic derivatives, still unknown in the chemistry of these pincers. 18 The work starts from the five-coordinate precursor [IrClH{κP,P,Si-Si(Me)(C 6 H 4 -2-PiPr 2 ) 2 }] (1), previously reported by Shimada et al 19 and, besides the new complexes, also describes in detail the dynamic behavior in solution of the known tetrahydride [IrH 4 {κP,P,Si-Si(Me)(C 6 H 4 -2-PiPr 2 ) 2 }] (10).…”

Arene and Hydride Complexes of Ruthenium with fac PSiP Pincer Ligands

“…Synthesis and Characterization: The starting complexes RuCl 2 (PPh 3 ) 3 ,10 [Ru(μ‐Cl){κ P, P,Si ‐Si(Me)(C 6 H 4 ‐2‐P i Pr 2 ) 2 }] 2 ( 1 )5a and the diphosphane HSi(Me)(C 6 H 4 ‐2‐P i Pr 2 ) 2 ,6a were prepared as previously reported. All other reagents were commercially available and used as received.…”

High-Turnover Aromatic C–H Borylation Catalyzed by POCOP-Type Pincer Complexes of Iridium

“…Hartwig and co-workers used pendant Si-H groups in substrates and propose the intermediacy of a silyl/diboryl Ir(III) complex (IV, Scheme 1). Shimada et al 21 determined that (PSiP)Ir catalysts gave 5-80 turnovers in the borylation of benzene with B 2 pin 2 after 1 d at 120 °C. 19 Li et al demonstrated that a combination of two pyridine/boryl bidentate ligands on Ir gave rise to a potent catalyst, again with an implied Ir(III) triboryl intermediate (VI).…”