TY - JOUR
T1 - Mechanistic insights into the cis-trans isomerization of ruthenium complexes relevant to catalysis of olefin metathesis
AU - Poater, Albert
AU - Ragone, Francesco
AU - Correa, Andrea
AU - Szadkowska, Anna
AU - Barbasiewicz, Michał
AU - Grela, Karol
AU - Cavallo, Luigi
PY - 2010/12/27
Y1 - 2010/12/27
N2 - The mechanism of the trans to cis isomerization in Ru complexes with a chelating alkylidene group has been investigated by using a combined theoretical and experimental approach. Static DFT calculations suggest that a concerted single-step mechanism is slightly favored over a multistep mechanism, which would require dissociation of one of the ligands from the Ru center. This hypothesis is supported by analysis of the experimental kinetics of isomerization, as followed by 1HNMR spectroscopy. DFT molecular dynamics simulations revealed that the variation of geometrical parameters around the Ru center in the concerted mechanism is highly uncorrelated; the mechanism actually begins with the transformation of the square-pyramidal trans isomer, with the Ruï£CHR bond in the apical position, into a transition state that resembles a metastable square pyramidal complex with a Cl atom in the apical position. This high-energy structure collapses into the cis isomer. Then, the influence of the N-heterocyclic carbene ligand, the halogen, and the chelating alkylidene group on the relative stability of the cis and trans isomers, as well as on the energy barrier separating them, was investigated with static calculations. Finally, we investigated the interconversion between cis and trans isomers of the species involved in the catalytic cycle of olefin metathesis; we characterized an unprecedented square-pyramidal metallacycle with the N-heterocyclic carbene ligand in the apical position. Our analysis, which is relevant to the exchange of equatorial ligands in other square pyramidal complexes, presents evidence for a remarkable flexibility well beyond the simple cis-trans isomerization of these Ru complexes. All change! The mechanism of cis to trans isomerizations in Ru complexes (see figure) relevant to olefin metathesis is investigated with a combined experimental and theoretical approach.
AB - The mechanism of the trans to cis isomerization in Ru complexes with a chelating alkylidene group has been investigated by using a combined theoretical and experimental approach. Static DFT calculations suggest that a concerted single-step mechanism is slightly favored over a multistep mechanism, which would require dissociation of one of the ligands from the Ru center. This hypothesis is supported by analysis of the experimental kinetics of isomerization, as followed by 1HNMR spectroscopy. DFT molecular dynamics simulations revealed that the variation of geometrical parameters around the Ru center in the concerted mechanism is highly uncorrelated; the mechanism actually begins with the transformation of the square-pyramidal trans isomer, with the Ruï£CHR bond in the apical position, into a transition state that resembles a metastable square pyramidal complex with a Cl atom in the apical position. This high-energy structure collapses into the cis isomer. Then, the influence of the N-heterocyclic carbene ligand, the halogen, and the chelating alkylidene group on the relative stability of the cis and trans isomers, as well as on the energy barrier separating them, was investigated with static calculations. Finally, we investigated the interconversion between cis and trans isomers of the species involved in the catalytic cycle of olefin metathesis; we characterized an unprecedented square-pyramidal metallacycle with the N-heterocyclic carbene ligand in the apical position. Our analysis, which is relevant to the exchange of equatorial ligands in other square pyramidal complexes, presents evidence for a remarkable flexibility well beyond the simple cis-trans isomerization of these Ru complexes. All change! The mechanism of cis to trans isomerizations in Ru complexes (see figure) relevant to olefin metathesis is investigated with a combined experimental and theoretical approach.
KW - density functional calculations
KW - homogeneous catalysis
KW - isomerization
KW - olefin metathesis
KW - ruthenium
UR - http://www.scopus.com/inward/record.url?scp=78651263085&partnerID=8YFLogxK
U2 - 10.1002/chem.201001849
DO - 10.1002/chem.201001849
M3 - Article
C2 - 21053211
AN - SCOPUS:78651263085
VL - 16
SP - 14354
EP - 14364
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
SN - 0947-6539
IS - 48
ER -