Ruthenium nitrosyl complexes containing pyridine-functionalized carbenes - A theoretical insight

The Ru NO bonding situation in a set of ruthenium(II) nitrosyl complexes containing pyridinefunctionalized carbenes as bidentate ligands is presented. Cheng's complex [(L)Ru(NO)Cl-3], where L = 3-tert-butyl-1-(2-pyridyl)imidazol-2-ylidene, la, was used as a model structure and the effect of different families of pyridine-functionalized carbene ligands on the Ru NO bond strength was explored, including imidazolylidenes, triazolylidenes, oxazolylidenes, thiazolylidenes, P-heterocyclic carbenes, imidazolidinone, triazolidinone, among others. The results reveal that the NO group binds more strongly to the Ru(II), than carbene carbon or pyridine nitrogen atoms. The EDA-NOCV results show that the nature of the carbene has a direct influence on the lability of the Ru NO, since it changes the electronic environment around the metallic centre. EDA-NOCV results point out that the nature of the Ru NO interactions (1a-16b) presents a very preponderant covalent character (circa 70%), while the electrostatic character covers circa 30% of the total interaction energy. The energy decomposition still reveals that Ru-NO+ bonds are strengthen in complexes la-16a, than in lb-16c. The weakest Ru NO interactions are observed for complexes containing P-heterocyclic ligands (PHCs), specially for complexes where the NO is coordinated trans to the carbene carbon atoms. The metal, ligand r-back-donation is more intense towards PHC than towards NO+. (C) 2015 Elsevier B.V. All rights reserved.