Reactivity of N-Heterocyclic Carbenes with [Ru₃(CO)₁₂] and [Os₃(CO)₁₂]. Influence of Ligand Volume and Electronic Effects

Abstract

The room-temperature reactions of [Ru 3 (CO) 12 ] and [Os 3 (CO) 12 ] with a variety of N-heterocyclic carbenes (NHCs) have been studied. [Ru 3 (CO) 12 ] reacts easily with N,N′-dimethylimidazol-2-ylidene (Me 2 Im), more slowly with N-methyloxazol-2-ylidene (MeOx), and very slowly with N,N′-dimesitylimidazol-2-ylidene (Mes 2 Im) to give the corresponding CO substitution products [Ru 3 (NHC)(CO) 11 ], but it does not react with the very bulky N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (Dipph 2 Im). DFT calculations have shown that [Ru 3 (Dipph 2 Im)(CO) 11 ] is a minimum in the corresponding potential energy surface; therefore, the absence of reaction between [Ru 3 (CO) 12 ] and Dipph 2 Im has a kinetic origin associated with the large volume of this NHC. [Os 3 (CO) 12 ] reacts with Me 2 Im to give [Os 3 (Me 2 Im)(CO) 11 ]. However, MeOx is not basic enough and Mes 2 Im and Dipph 2 Im are too bulky to react with [Os 3 (CO) 12 ], which is less reactive than [Ru 3 (CO) 12 ]. Therefore, the reactions of [Ru 3 (CO) 12 ] and [Os 3 (CO) 12 ] with NHCs are strongly influenced by the electronic properties and steric demands of the NHCs and also by the intrinsic reactivity of the metal-carbonyls.

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

“…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]. The Ru-Ru bond distances (2.783-3.045 Å ) are comparable to those found in other ruthenium clusters supported by NHC ligands [39]. To minimize the steric interactions between the NHC ligand and the adjacent carbonyl groups, the phenyl ring of the benzyl group is orientated away from the metal center.…”

Beyond ConventionalN-Heterocyclic Carbenes: Abnormal, Remote, and Other Classes of NHC Ligands with Reduced Heteroatom Stabilization

“…49 A marked decrease in catalyst activity was noted, which indicates a mechanism that involves, at least in part, heterogeneous palladium. In this case, the main function of the carbene ligand seems to be the controlled release of palladium from the complex.…”

“…Undoubtedly, exciting further developments may be expected from the interaction of NHC ligands with transition-metal clusters. 49 …”

Synthesis, spectroscopic characterization and DFT study of dinuclear ruthenium sawhorse-type complexes derived from the reaction of trinuclear aggregates and (Z)-5-arylidenerhodanines

“…Other sawhorse type polymers [Ru 2 (CO) 4 (μ-Xpy) 2 ] n 7a-b (figure 2) have been obtained from reaction between [Ru 3 (CO) 12 ] and 2-hydroxy (OHPy) [16] and 2-mercapto-pyridine (SHPy) [17] as yellow and red solids, respectively. Reaction with 2-hydroxypyridine showed the presence of [Ru 4 H 4 (CO) 12 ] and [Ru 2 (CO) 4 (OHPy) 2 (µ-OPy) 2 ] [18] 8a and the reaction with 2-mercaptopyridine presented secondary product, the mononuclear [Ru(CO) 2 (SPy) 2 ].…”

“…Reaction with 2-hydroxypyridine showed the presence of [Ru 4 H 4 (CO) 12 ] and [Ru 2 (CO) 4 (OHPy) 2 (µ-OPy) 2 ] [18] 8a and the reaction with 2-mercaptopyridine presented secondary product, the mononuclear [Ru(CO) 2 (SPy) 2 ]. Therefore, polymeric diruthenium complexes can be obtained not only by using carboxylic acids but also by ligands with particular acid-base properties.…”