Cooperative Trimerization of Carbon Monoxide by Lithium and Samarium Boryls

The conversion of
carbon monoxide (CO) to hydrocarbons and oxygenates
on industrial solid catalysts (the Fischer–Tropsch reaction)
largely relies on the cooperation of heteromultimetallic active sites
composed of main group (such as alkali) and transition metals, but
the mechanistic details have not been fully understood at the molecular
level. Here we report the cooperative trimerization of CO by molecular
lithium and samarium boryl complexes. We have found that, in the coexistence
of a samarium boryl complex and a lithium boryl complex, the trimerization
of CO selectively occurred to give a diboryl­allene­triolate
skeleton “BC­(O)­C­(O)­C­(O)­B”, in sharp contrast with the
reaction of CO with either the lithium or the samarium boryl compound
alone. The 13C-labeled experiments and computational studies
have revealed that the CO trimerization reaction took place exclusively
by coupling of a samarium boryl oxycarbene species, which was generated
by insertion of one molecule of CO into the samarium–boryl
bond, with a lithium ketenolate species formed by insertion of two
molecules of CO into the lithium–boryl bond. These results
offer unprecedented insight into CO oligomerization promoted by heteromultimetallic
components and may help better understand the industrial F–T
process and guide designing new catalysts.