Weakly Coordinated Zinc and Aluminum σ‑Complexes of Copper(I)

We
report the synthesis and isolation of three new σ-complexes
of Cu­(I) in which E–H (E = Al, Zn) σ-bonds are coordinated
to copper. The addition of the main group hydride to a toluene-solvated
Cu­(I) complex results in reversible ligand exchange, and the Cu­(I)
σ-complexes have been crystallized. Experimental and computational
data provide a wealth of evidence for weak binding of the E–H
bond to Cu­(I), which can be ascribed to σ-donation from the
E–H bond into the 4s orbital of copper and back-donation from
copper into the E–H σ* orbital.