Manganese-Catalyzed Upgrading of Ethanol into 1‑Butanol

Biomass-derived
ethanol is an important renewable feedstock. Its
conversion into high-quality biofuels is a promising route to replace
fossil resources. Herein, an efficient manganese-catalyzed Guerbet-type
condensation reaction of ethanol to form 1-butanol was explored. This
is the first example of upgrading ethanol into higher alcohols using
a homogeneous non-noble-metal catalyst. This process proceeded selectively
in the presence of a well-defined manganese pincer complex at the
parts per million (ppm) level. The developed reaction represents a
sustainable synthesis of 1-butanol with excellent turnover number
(>110 000) and turnover frequency (>3000 h–1). Moreover, mechanistic studies including control experiments, NMR
spectroscopy, and X-ray crystallography identified the essential role
of the “N–H moiety” of the manganese catalysts
and the major reaction intermediates related to the catalytic cycle.