Catalytic hydrogenolysis of silyl triflates to hydrosilanes using iridium pincer complexes
Abstract
Hydrosilanes are convenient reductants for a large variety of organic oxygenated substrates
and they have been successfully applied in the conversion ofbio-based materialsl and C0$_2$
At present, hydrosilanes are produced via energy intensive processes and they generate,
after use, silicon oxides wastes su ch as siloxanes, which are difficult to recycle. These
limitations call for the development of catalytic pro cesses able to transform Si-O bonds in
siloxanes and derivatives (silyl halides and triflates) into Si-H hydrides.
Very recently, the groups of Shimada and Schneider reported for the first time the
hydrogenolysis of sorne silyl halides and triflates with iridium(lII) catalysts and
ruthenium(II). Following these preliminary reports, we studied the catalytic hydrogenolysis
of R$_3$SiOTf (R = Me, Et, Ph) species in the presence of a base, by the dihydride complex
(POCOP)IrH$_2$ (See figure above). Syntheses and crystal structures of sorne isolated Ir(l) and
Ir(III) complexes will be presented as well as their role in the R$_3$SiOTf to R$_3$SiH
transformation.
The new (POCOP)Ir$^I$(TBD) complex, which splits H$_2$ to (POCOP)Ir$^{III}$H$_2$ at a low pressure, is
a pre-catalyst in the hydrogenolysis of Si-OTf linkages. It can be easily obtained from
(POCOP)IrHCI, using the TBD guanidine. To the best of our knowledge, such spontaneous
reductive elimination by a weak base of an iridium(lII) hydro-chloride species is novel.
The kinetic and thermodynamic profiles of the reaction were examined by means of
spectroscopic and DFT studies. The mechanism reveals that rate detennining step is the
hydride transfer from (POCOP)IrH$_2$ to the silyl triflate. The base (e.g. NEt$_3$) is required to
drive the thermodynalnics of the reaction, by promoting the regeneration of iridium hydrides
intennediates, in the presence of H$_2$.
Domains
Material chemistryOrigin | Files produced by the author(s) |
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