Reactivity of Unsupported Transition Metal-Aluminyl Complexes: A Nucleophilic TM-Al Bond

Despite the long history of research
in transition metal (TM) complexes,
the study of TM-aluminyl complexes is still in its early stage of
development. It is expected that the presence of an electropositive
Al donor atom would open up new possibilities in TM complex reactivity,
and indeed TM-aluminyl has shown an early sign of success in small-molecule
activation. On the other hand, the existing reports on TM-aluminyl
reactivity are often explained to readers with different understanding
on individual cases, and a general picture of TM-aluminyl reactivity
is still not available. In this work, we have attempted to provide
a systematic picture to explain some early explorations in this field,
specifically a series of recently reported heteroallene insertion
reactions involving unsupported TM-aluminyl complexes. Through density
functional theory calculations of a number of TM-aluminyl complexes,
covering both Au and Cu centers, we found that their reactivity against
heteroallenes (including CO2 and carbodiimides) is mostly
based on the strong nucleophilicity of the TM–Al σ-bond.