Premium
DFT Mechanistic Study on Diene Metathesis Catalyzed by Ru‐Based Grubbs–Hoveyda‐Type Carbenes: The Key Role of π‐Electron Density Delocalization in the Hoveyda Ligand
Author(s) -
SolansMonfort Xavier,
Pleixats Roser,
Sodupe Mariona
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200903525
Subject(s) - carbene , catalysis , chemistry , delocalized electron , ruthenium , transition metal carbene complex , diene , metathesis , density functional theory , ligand (biochemistry) , catalytic cycle , photochemistry , combinatorial chemistry , computational chemistry , organic chemistry , polymerization , polymer , biochemistry , natural rubber , receptor
The catalytic activity and catalyst recovery of two heterogenized ruthenium‐based precatalysts ( H and NO 2 (4) ) in diene ring‐closing metathesis have been studied by means of density functional calculations at the B3LYP level of theory. For comparison and rationalization of the key factors that lead to higher activities and higher catalyst recoveries, four other Grubbs–Hoveyda complexes have also been investigated. The full catalytic cycle (catalyst formation, propagation, and precatalyst regeneration) has been considered. DFT calculations suggest that either for the homogeneous and heterogenized systems the activity of the catalysts mainly depends on the ability of the precursor to generate the propagating carbene. This ability does not correlate with the traditionally identified key factor, the Ru⋅⋅⋅O interaction strength. In contrast, precatalysts with lower alkoxy‐dissociation energy barriers and lower stabilities compared with the propagating carbene also present larger C1C2 bond length (i.e., lower π character of the CC bond that exists between the metal–carbene (RuC) and the phenyl ring of the Hoveyda ligand). Catalyst recovery, regardless of whether a release–return mechanism occurs or not, is also mainly determined by the π delocalization. Therefore, future Grubbs–Hoveyda‐type catalyst development should be based on fine‐tuning the π‐electron density of the phenyl moiety, with the subsequent effect on the metalloaromaticity of the ruthenafurane ring, rather than considering the modification of the Ru⋅⋅⋅O interaction.