Unpredictable Dynamic Behaviour of Ruthenium Chelate Pyrrole Derivatives.

Reaction of [Ru(H) 2 (CO)(PPh 3 ) 3 ] 1 with an equimolar amount of pyrrole-2-carboxylic acid ( H 2 L 1 ) leads to the homoleptic chelate derivative k 2 (O,O)-[RuH(CO)(HL 1 )(PPh 3 ) 2 ] 2 . Prolonged acetonitrile refluxing promotes an unusual k 2 (O,O)- → k 2 (N,O)- dynamic chelate conversion, forming a neutral, stable, air- and moisture- insensitive, solvento-species k 2 (N,O)-[Ru(MeCN)(CO)(L 1 )(PPh 3 ) 2 ] 3 . Analogously, reaction of 1 with the pyrrole-2-carboxyaldehyde ( HL 2 ) affords k 2 (N,O)-[RuH(CO)(HL 2 )(PPh 3 ) 2 ] 4 , 5 , as a couple of functional isomers. Optimized reaction conditions such as temperature and solvent polarity allow the isolation of dominant configurations. Structure 5 is a pyrrolide Ru-carbaldehyde, obtained from cyclization of the pendant CHO function, whereas species 4 can be viewed as an ethanoyl-conjugated Ru-pyrrole. Derivatives 3 - 5 were characterized by single crystal X-ray diffraction, ESI-Ms, IR, and NMR spectroscopy, indicating distinct features for the Ru-bonded pyrrolyl groups. DFT computational results, coplanarity, bond equalization, and electron delocalization along the fused five-membered rings support aromatic features. In accordance with the antisymbiotic trans -influence, both the isolated isomers 4 and 5 disclose CO ligands opposite to N- or O-anionic groups. The quantitative Mayer bond order evidences a stabilizing backbonding effect. Antibacterial and antifungal trials on Gram-positive ( Staphylococcus aureus ), Gram-negative ( Escherichia coli ), and Candida albicans were further carried out.