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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‐(R2P)C6H4}2MeSi]−, PSiP‐R, R=Cy, iPr, or tBu) were synthesized by the reduction of [IrCl(H)(PSiP‐R)] with Me4N⋅BH4 under argon. The same reaction under a nitrogen atmosphere a...

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Published in:Chemistry, an Asian journal an Asian journal, 2011-09, Vol.6 (9), p.2512-2521
Main Authors: Fang, Hongyun, Choe, Yoong-Kee, Li, Yonghua, Shimada, Shigeru
Format: Article
Language:English
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Summary:A series of iridium tetrahydride complexes [Ir(H)4(PSiP‐R)] bearing a tridentate pincer‐type bis(phosphino)silyl ligand ([{2‐(R2P)C6H4}2MeSi]−, PSiP‐R, R=Cy, iPr, or tBu) were synthesized by the reduction of [IrCl(H)(PSiP‐R)] with Me4N⋅BH4 under argon. The same reaction under a nitrogen atmosphere afforded a rare example of thermally stable iridium(III)–dinitrogen complexes, [Ir(H)2(N2)(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(N2)(PSiP‐Cy)] with PMe3 required heating at 150 °C to give the expected [Ir(H)2(PMe3)(PSiP‐Cy)] and a trigonal bipyramidal iridium(I)–dinitrogen complex, [Ir(N2)(PMe3)(PSiP‐Cy)]. The reaction of [Ir(H)4(PSiP‐Cy)] with three equivalents of 2‐norbornene (nbe) in benzene afforded [IrI(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, [IrIII(H)(Ph)(PSiP‐R)], in high yield. The oxidative addition of benzene is reversible; heating [IrIII(H)(Ph)(PSiP‐Cy)] in the presence of PPh3 in benzene resulted in reductive elimination of benzene, coordination of PPh3, and activation of the CH bond of one aromatic ring in PPh3. [IrIII(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. A pincer‐type bis(phosphino)silyl ligand ([{2‐(R2P)C6H4}2MeSi]−, PSiPR) gives unusually stable iridium(III) N2 complexes [IrIII(H)2(N2)(PSiPR)] (see scheme). Substitution of the N2 ligand with PMe3 requires heating at 150 °C. [IrV(H)4(PSiPR)] is a useful source of [IrI(PSiPR)] and reacts with benzene to form [IrIII(H)(Ph)(PSiPR)], which catalyzes a direct borylation reaction of the benzene CH bond.
ISSN:1861-4728
1861-471X
DOI:10.1002/asia.201100085