Coinage Metals Binding as Main Group Elements: Structure and Bonding of the Carbene Complexes [TM(cAAC)2] and [TM(cAAC)2]+ (TM = Cu, Ag, Au)

• Published in: Journal of the American Chemical Society Vol. 136; no. 49; pp. 17123 - 17135
• Main Authors: Jerabek, Paul, Roesky, Herbert W., Bertrand, Guy, Frenking, Gernot
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 10.12.2014
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja508887s

Quantum chemical calculations using density functional theory have been carried out for the cyclic (alkyl)(amino)carbene (cAAC) complexes of the group 11 atoms [TM(cAAC)2] (TM = Cu, Ag, Au) and their cations [TM(cAAC)2]+. The nature of the metal–ligand bonding was investigated with the charge and energy decomposition analysis EDA-NOCV. The calculations show that the TM–C bonds in the charged adducts [TM(cAAC)2]+ are significantly longer than in the neutral complexes [TM(cAAC)2], but the cations have much higher bond dissociation energies than the neutral molecules. The intrinsic interaction energies ΔE int in [TM(cAAC)2]+ take place between TM+ in the 1S electronic ground state and (cAAC)2. In contrast, the metal–ligand interactions in [TM(cAAC)2] involve the TM atoms in the excited 1P state yielding strong TM p(π) → (cAAC)2 π backdonation, which is absent in the cations. The calculations suggest that the cAAC ligands in [TM(cAAC)2] are stronger π acceptors than σ donors. The trends of the intrinsic interaction energies and the bond dissociation energies of the metal–ligand bonds in [TM(cAAC)2] and [TM(cAAC)2]+ give the order Au > Cu > Ag. Calculations at the nonrelativistic level give weaker TM–C bonds, particularly for the gold complexes. The trend for the bond strength in the neutral and charged adducts without relativistic effects becomes Cu > Ag > Au. The EDA-NOCV calculations suggest that the weaker bonds at the nonrelativistic level are mainly due to stronger Pauli repulsion and weaker orbital interactions. The NBO picture of the C–TM–C bonding situation does not correctly represent the nature of the metal–ligand interactions in [TM(cAAC)2].