Catalysts for Regio- And Stereoselective C(sp³)-H Deuteration of Tricyclohexylphosphine with Benzene-d₆Generated via Dehydrochlorination of Chlorido(dihydrido)iridium Complexes Containing a Xanthene-Based Bis(silyl) Chelate Ligand

The catalytic C(sp³)-H deuteration of tricyclohexylphosphine (PCy₃) with excess benzene-d₆at 60 °C was achieved using the iridium catalyst precursor Ir(κ²Si,Si-xantsil)(H)₂(PCy₃)Cl ( 1 ), in the presence of (Me₃Al)₂·DABCO (xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl), DABCO = 1,4-diazabicyclo[2.2.2]octane). In this reaction, the 3,5-equatorial and 4-axial C-Hs of PCy₃were selectively deuterated, chiefly affording P(Cy-d₃)₃. To gain insight into the reaction mechanism, iridium complexes bearing an asymmetric and bulkier bis(silyl)-xanthene chelate ligand with SiMe₂and Si(p-Tol)₂coordinating moieties, namely, Ir(κ²Si,Si-xantSi^MeSi^p-Tol)(H)₂(L)Cl (L = pyridine ( 2-py ) or PCy₃( 2-PCy )), were synthesized, and similar reactions using them were examined under stoichiometric and catalytic conditions. The stoichiometric reaction of 2-py with (Me₃Al)₂·DABCO at 60 °C resulted in dehydrochlorination to give the dinuclear complex [Ir(μ-κ¹Si:η⁶,κ¹Si-xantSi^MeSi^p-Tol)(H)]₂( 3 ). On the other hand, the analogous reaction of 2-PCy in benzene at 60 °C afforded the thermally unstable Ir(xantSi^MeSi^p-Tol)(H)(PCy₃) ( 4 ). When this reaction was performed in benzene-d₆, the partially deuterated analogue Ir(xantSi^MeSi^p-Tol)(D)(PCy₃-d_n) ( 4-D ) was formed due to the deuteration of Ir-H and some C(sp³)-Hs of PCy₃of 4 via H/D exchange with benzene-d₆. Moreover, 2-PCy showed catalytic activity similar to that of 1 .