Disentanglement of Donation and Back-Donation Effects on Experimental Observables: A Case Study of Gold-Ethyne Complexes

摘要

The Dewar-Chatt-Duncanson (DCD) model was introduced more than 60 years ago to describe the if coordination of ethene to a coinage-metal atom. It gives a formally simple picture of the bond between an unsaturated substrate (S) and a transition metal (M), which involves the donation of π electrons from the substrate to empty do orbitals of the metal (S→M) and the back donation from filled dπ orbitals of the metal to empty substrate orbitals of the proper symmetry (M→S). In unsaturated organic systems, these empty orbitals have typically a π* anti-bonding character and their population tends to weaken the C-C bond, but a reverse effect may also be observed if the empty orbitals have a bonding character, as recently observed.The DCD model enjoys enormous popularity among chemists, as it represents the standard framework in which to analyze the electronic properties of ligands and metal fragments, especially with a view of rationalizing and controlling the activation of substrates in catalyzed chemical reactions. It appears also appropriate for the captodative description of the carbon bond.