(Cyclopentadienone)iron complexes (CICs) are interesting complexes due to their intrinsic properties, including low cost, stability of the pre-catalyst, chemoselectivity, relatively simple preparation and low toxicity. They have been shown to be able to promote reactions involving hydrogen transfer (HT), such as C=O and C=N reductions, alcohol oxidations and ‘‘hydrogen borrowing’’ processes. We recently developed a protocol to synthesise primary alcohols, compounds that are useful in bulk/fine chemical and pharmaceutical industries, via CIC-promoted reductive opening of epoxide. CICs proved to be an alternative to the currently employed catalysts for the catalytic reductive opening of epoxides, in which several issues are still present, such as use of noble metals, poor selectivity to primary alcohols and by-products formation as well as the need for expensive and oxygen-sensitive ligands. The cyclooctene-derived complex shown in the scheme, proved to be effective in the reductive opening of epoxides, with high selectivity and under mild conditions. To prevent the undesired oligomerization side reactions, a low concentration of substrate was chosen. Aliphatic epoxides turned out to be particularly challenging compared to the aromatic ones, demanding the presence of an additional co-catalyst. A range of Lewis acids was tested, allowing us to steer the selectivity to both primary and secondary alcohols. In particular, Group IV isopropoxides (i.e. Ti, Hf, Zr) give preferentially the branched alcohol while Lewis acids such as Al(OTf)3 and BF3.OEt2 are selective for the linear alcohol.

Catalytic hydrogenation promoted by (cyclopentadienone)iron complexes for the reductive opening of epoxides

ACS Spring Meeting 2021

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