Group nine metals ligated by tridentate “pincer” ligands have attracted substantial attention as potential catalysts for carbon-carbon and carbon-heteroatom coupling. Recently, while investigating rhodium and iridium complexes supported by the SiNN pincer architecture as catalysts for the dehydrogenative borylation of terminal alkynes, our group showed that the silyl functionality could bind on a gradient between silyl hydride and traditional L type sigma donation. However, it was unclear if this interaction affected the catalytic cycle. We sought to further investigate pincer complexes featuring SiH donors. Herein we report the synthesis and preliminary reactivity studies of the PNSi ligated complex (PNSi)Rh(COE) (COE=cyclooctene), where PNSi is an analogue of the bisphosphinodiarylamido PNP ligand with one phosphine donor replaced by a silyl group. Carbon monoxide displaces both the olefin and the SiH resulting in a dicarbonyl product that converts to a monocarbonyl pincer complex when exposed to vacuum. Unlike (PNP)Rh(L) species, which undergo oxidative addition with phenyl halides to form five coordinate Rh(III) species, the PNSi complex releases the SiH from the pincer with concomitant generation of benzene. In an attempt to produce a stable six coordinate oxidative addition product (PNSi)Rh(COE) was reacted with o-bromonitrobenzene. Complexes containing a non-olefin L type ligand could be accessed, with varying degrees of success, by substitution of COE for sulfide and phosphite. Using a variety of NMR techniques, we have been able to observe the SiH interaction with the metal.

Synthesis and reactivity studies of rhodium complexes supported by a PNSi pincer ligand

253rd National Meeting (2017)

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