Coinage-Metal Bond between [1.1.1]Propellane and M(2)/MCl/MCH(3) (M = Cu, Ag, and Au): Cooperativity and Substituents

A coinage-metal bond has been predicted and characterized in the complexes of [1.1.1]propellane (P) and M(2)/MCl/MCH(3) (M = Cu, Ag, and Au). The interaction energy varies between −16 and −47 kcal/mol, indicating that the bridgehead carbon atom of P has a good affinity for the coinage atom. The coinage-metal bond becomes stronger in the Ag < Cu < Au sequence. Relative to M(2), both MCl and MCH(3) engage in a stronger coinage-metal bond, both -Cl and -CH(3) groups showing an electron-withdrawing property. The formation of coinage-metal bonding is mainly attributed to the donation orbital interactions from the occupied C-C orbital into the empty metal orbitals and a back-donation from the occupied d orbital of metal into the empty C-C anti-bonding orbital. In most complexes, the coinage-metal bond is dominated by electrostatic interaction, with moderate contribution of polarization. When P binds simultaneously with two coinage donors, negative cooperativity is found. Moreover, this cooperativity is prominent for the stronger coinage-metal bond.