SiNN-pincer iridium complexes were synthesised and demonstrated to catalyse deuteration of trialkylsilanes with benzene-d6 through H/D exchange at room temperature.
The catalytic C(sp 3 )−H deuteration of tricyclohexylphosphine (PCy 3 ) with excess benzene-d 6 at 60 °C was achieved using the iridium catalyst precursor Ir(κ 2 Si,Si-xantsil)(H) 2 (PCy 3 )Cl (1), in the presence of (Me 3 Al) 2 •DABCO (xantsil = (9,9-dimethylxanthene-4,5diyl)bis(dimethylsilyl), DABCO = 1,4-diazabicyclo[2.2.2]octane). In this reaction, the 3,5-equatorial and 4-axial C−Hs of PCy 3 were selectively deuterated, chiefly affording P(Cy-d 3 ) 3 . To gain insight into the reaction mechanism, iridium complexes bearing an asymmetric and bulkier bis(silyl)−xanthene chelate ligand with SiMe 2 and Si(p-Tol) 2 coordinating moieties, namely, Ir(κ 2 Si,Si-xantSi Me Si p-Tol )(H) 2 (L)Cl (L = pyridine (2-py) or PCy 3 (2-PCy)), were synthesized, and similar reactions using them were examined under stoichiometric and catalytic conditions. The stoichiometric reaction of 2-py with (Me 3 Al) 2 •DABCO at 60 °C resulted in dehydrochlorination to give the dinuclear complex [Ir(μ-κ 1 Si:η 6 ,κ 1 Si-xantSi Me Si 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 Me Si p-Tol )(H)(PCy 3 ) (4). When this reaction was performed in benzene-d 6 , the partially deuterated analogue Ir(xantSi Me Si p-Tol )(D)(PCy 3 -d n ) (4-D) was formed due to the deuteration of Ir−H and some C(sp 3 )−Hs of PCy 3 of 4 via H/D exchange with benzene-d 6 . Moreover, 2-PCy showed catalytic activity similar to that of 1. On the basis of these results, it is suggested that 4 and 4-D functioned as active species for the catalytic deuteration of PCy 3 using 2-PCy.
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