Well-defined molecular organometallic species are a cornerstone of catalytic methodology, and the activity and selectivity of these complexes can be modulated by judicious choice of metal and surrounding ligands. Catalyst families based on precious metals enjoy high activity and selectivity and require low catalyst loadings. However, precious metals have very limited availability, are rather expensive, and can be quite toxic. Examples of well-defined molecular catalysts based on iron are far fewer in number than their precious metal counterparts. Development of a fundamental structural and mechanistic understanding of Fe-based transfer hydrogenation catalysts represents a critical need for their widespread adoption to replace rare, expensive, and toxic catalyst systems. Owing to this, we have designed, synthesized, isolated, and screened a pair of novel NHC-containing Fe complexes capable of catalyzing the transfer hydrogenation of polar double bonds. Installation of an O-containing NHC wingtip substituent allows these species to behave as bifunctional catalysts that operate in the absence of external base. The pre-catalyst species are activated <i>in situ</i> by visible light irradiation and offer 50-60% yield of various aldehydes and ketones at 1 mol% catalyst loading. Given our experimental data, we have developed a tentative catalytic mechanism. In addition to this, we will present the synthesis and characterization of these catalytic species, as well as results of catalytic screening experiments.

Light-activated iron bifunctional catalysts for transfer hydrogenations of polar double bonds

249th National Meeting (2015)

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