The N-heterocyclic carbene chemistry of transition-metal carbonyl clusters

Abstract

In the last decade, chemists have dedicated many efforts to investigate the coordination chemistry of N-heterocyclic carbenes (NHCs). Although most of that research activity has been devoted to mononuclear complexes, transition-metal carbonyl clusters have not escaped from these investigations. This critical review, which is focussed on the reactivity of NHCs (or their precursors) with transition-metal carbonyl clusters (mostly are of ruthenium and osmium) and on the transformations underwent by the NHC-containing species initially formed in those reactions, shows that the polynuclear character of these metallic compounds or, more precisely, the close proximity of one or more metal atoms to that which is or can be attached to the NHC ligand, is responsible for reactivity patterns that have no parallel in the NHC chemistry of mononuclear complexes (74 references).

Synthesis and catalytic activity of N-heterocyclic carbene metal carbonyl complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole

“…The NHC ligand coordinates to only one ruthenium atom in a j 2 -C,N chelating fashion. The Ru-C carbene bond distance is 2.067(9) Å , similar to the corresponding values reported for other ruthenium carbonyl clusters with NHC ligands [38]. The Ru-N bond distance is 2.148(6) Å , shorter than that in LRu 3 (CO) 8 (l-H)(l-Cl) (2.301(2) Å , L = 1-{2-[bis(3,5-dimethylpyrazol-1-yl)methyl]phenyl}-3-benzylimidazol-2-ylidene) [26].…”

Murai Reaction on Furfural Derivatives Enabled by Removable N,N′‐Bidentate Directing Groups

“…The generally accepted mechanism for the Murai reaction involves a mononuclear Ru 0 complex as the first active species . We thus anticipated the conversion of the Ru 3 (CO) 12 pre‐catalyst into a mononuclear Ru carbonyl by breaking of the Ru−Ru bond and release of CO . Accordingly, two free‐energy profiles were calculated, one involving Ru(CO) 3 and the other Ru(CO) 2 .…”

Synthesis and reactivity of bis(3,5-dimethylpyrazol-1-yl)methanes functionalized by 2-halophenyl groups on the methine carbon

“…Recently, the coordination chemistry of polydentate NHCs toward transition metal carbonyl clusters has received increasing attention [35]. Remarkable CeH bond activation processes were often observed in the reactions of polydentate NHCs with transition metal carbonyl clusters, especially triruthenium and triosmium clusters [36,37].…”