Transition Metal−Carbon Complexes. A Theoretical Study

Abstract

The equilibrium geometries and bond dissociation energies of 16VE and 18VE complexes of ruthenium and iron with a naked carbon ligand are reported using density functional theory at the BP86/TZ2P level. Bond energies were also calculated at CCSD(T) using TZ2P quality basis sets. The calculations of [Cl2(PMe3)2Ru(C)] (1Ru), [Cl2(PMe3)2Fe(C)] (1Fe), [(CO)2(PMe3)2Ru(C)] (2Ru), [(CO)2(PMe3)2Fe(C)] (2Fe), [(CO)4Ru(C)] (3Ru), and [(CO)4Fe(C)] (3Fe) show that 1Ru has a very strong Ru-C bond which is stronger than the Fe-C bond in 1Fe. The metal-carbon bonds in the 18VE complexes 2Ru-3Fe are weaker than those in the 16VE species. Calculations of the related carbonyl complexes [(PMe3)2Cl2Ru(CO)] (4Ru), [(PMe3)2Cl2Fe(CO)] (4Fe), [(PMe3)2Ru(CO)3] (5Ru), [(PMe3)2Fe(CO)3] (5Fe), [Ru(CO)5] (6Ru), and [Fe(CO)5] (6Fe) show that the metal-CO bonds are much weaker than the metal-C bonds. The 18VE iron complexes have a larger BDE than the 18VE ruthenium complexes, while the opposite trend is calculated for the 16VE compounds. Charge and energy decomposition analyses (EDA) have been carried out for the calculated compounds. The Ru-C and Fe-C bonds in 1Ru and 1Fe are best described in terms of two electron-sharing bonds with sigma and pi symmetry and one donor-acceptor pi bond. The bonding situation in the 18 VE complexes 2Ru-3Fe is better described in terms of closed shell donor-acceptor interactions in accordance with the Dewar-Chatt-Duncanson model. The bonding analysis clearly shows that the 16VE carbon complexes 1Ru and 1Fe are much more strongly stabilized by metal-C sigma interactions than the 18VE complexes which is probably the reason why the substituted homologue of 1Ru could become isolated. The EDA calculations show that the nature of the TM-C and TM-CO binding interactions resembles each other. The absolute values for the energy terms which contribute to Delta(Eint) are much larger for the carbon complexes than for the carbonyl complexes, but the relative strengths of the energy terms are not very different from each other. The pi bonding contribution to the orbital interactions in the carbon complexes is always stronger than sigma bonding. There is no particular bonding component which is responsible for the reversal of the relative bond dissociation energies of the Ru and Fe complexes when one goes from the 16VE complexes to the 18VE species. That the 18 VE compounds have longer and weaker TM-C and TM-CO bonds than the respective 16 VE compounds holds for all complexes. This is because the LUMO in the 16 VE species is a sigma-antibonding orbital which becomes occupied in the 18 VE species.

Assignment of pre-edge features in the Ru K-edge X-ray absorption spectra of organometallic ruthenium complexes

“…Most notably, the success of Ru carbene species as efficient catalysts in olefin metathesis has attracted significant attention over the last decade. Theoretical studies have investigated the nature of ruthenium catalysts [11][12][13], but somewhat surprisingly only sparing attention has been given to using spectroscopic approaches to provide detailed electronic structure insight into these key catalytic centres; a situation which has only recently been addressed [14][15][16]. In light of this, it is important to explore the information content that might be available through the investigation of Ru K-edge XAS.…”

Recent advances in the field of multicarbene and multimetal carbene complexes of the Fischer-type

“…Some attention is given to spectral data in support of the carbene ligand character, while specific structural aspects are emphasized. Theoretical calculations in the past have focused mainly on the donor/acceptor nature of the carbene substituents of simple monocarbene complexes [12][13][14][15][16][17] or the steric and electronic effects of the heteroatom on the carbene ligand [18].…”

“…11 shows two older examples of biscarbene complexes incorporated into systems containing metal-metal bonds (small clusters). The reaction of dirheniun decacarbonyl with two equivalents organolithium reagent afforded a dirhenium biscarbene complex (14). As a result of steric strain the carbene ligands are found in different electronic environments with one ligand being in an axial and the other in an equatorial position [48].…”

Reply to Réplique: A New Concept for Bonding in Carbodiphosphoranes?

“…Insight into the electronic structure of CDPs gave us [6] where again a single carbon atom is engaged in donor-acceptor interactions. [7] Finally, we are grateful to Professor Schmidbaur for pointing out that the bidirectional arrow in our Scheme 1 which is shown in ref. [24] in his rplique [1] should be omitted.…”