Reversible Alkene Binding and Allylic C–H Activation with an Aluminum(I) Complex

Reversible alkene binding to a low-valent main group complex is documented. The reaction involves an aluminium(I) reagent and includes both terminal and strained alkenes. This reversible binding event is just a forerunner to non-reversible C–H activation of the allylic position of the alkene. Mechanistic analysis shows that in contact to common transition metal systems, the C–H activation does not proceed from a metal bound alkene complex. Dissociation of the alkene and reformation of the aluminium(I) fragment is required to liberate the active site and frontier molecular orbitals involved in C–H activation.