Thiophene versus aryl coordination in tricarbonylmanganese complexes with interesting non-linear optical properties

Molecular orbital calculations performed with the B3LYP HF/DFT hybrid functional are used to study the bonding and coordination geometry of a π ligand containing a large delocalised system (X=1-(thiophenyl),2-(aryl)ethene) to tricarbonylmanganese(I) in complexes [(ηn-X)Mn(CO)3]+. The coordination mode of X depends on the nature of the substituent on the para aryl carbon with respect to the ethene position. A hydroxyl group (R=OH) favours the η5 coordination through the thiophene ring, while an amino substituent (R=NH2) yields a slightly more stable η6-X, coordinated through the aryl ring in good accordance with the experimental results. The difference is due to the electronic characteristics of the R substituents. The higher donating amino group creates an electron richer aryl with increased coordination ability, shifting the balance between the two possible coordination geometries. The small energy differences obtained for the relative stability of the two isomers of each complex (≤10 kJ mol−1), however, suggest that the isolation of these species should be strongly dependent on experimental conditions such as the choice of the solvent.