Room Temperature Activation of Aromatic CH Bonds by Non‐Classical Ruthenium Hydride Complexes Containing Carbene Ligands

Abstract

Non-classical ruthenium hydride complexes are promising lead structures for the C À H bond activation and functionalization of aromatic compounds. In the present paper, the preparation and crystallographic characterisation of the first organometallic complexes bearing dihydrogen ligands and N-heterocyclic carbene ligands in the same coordination sphere are described. The mixed phosphine/ carbene complex [(IMes)Ru(H) 2 (H 2 ) 2 (PCy 3 )] (IMes 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene; 3a) shows a unique reactivity pattern in the inter-and intramolecular activation of C À H bonds. In particular, complex 3a effects a rapid and remarkably selective intermolecular activation of sp 2 C À H bonds in simple aromatic compounds at room temperature.

Intramolecular Alkyl Phosphine Dehydrogenation in Cationic Rhodium Complexes of Tris(cyclopentylphosphine)

“…] (R= iPr, Cy) [46] and the neutral ruthenium complexes [Ru(L) 2 [13] PiPr 3 , [47] PCyp 3 , [48] N-heterocyclic carbene [49] ). Complex 5 can be prepared more conveniently by direct addition of H 2 (4 atm) to 1.…”

Beryllium‐Induced CN Bond Activation and Ring Opening of an N‐Heterocyclic Carbene

“…[2] A number of groups have observed that N-alkyl and N-aryl-substituted NHCs are prone to both CÀH and CÀN activation of the peripheral organic substituents within the coordination sphere of transition-metal centers. [3,4] Herein we report that the imidazol-2-ylidene ring is prone to reductive ring opening in the presence of reactive hydride compounds; observations that may be of particular relevance to hydride poisoning of NHC-based catalysts.…”

“…Although generally noted for their stability, particularly under catalytic conditions, NHC complexes are susceptible to degradation by a variety of C À H, C À C, and C À N bond-activation reactions at peripheral and/or extracyclic positions. [2][3][4] The reaction to produce compound 3 is unprecedented, however, as it involves complete disruption of the s and p systems of the imidazolylidene framework.…”

The Nature of N‐Heterocyclic Carbenes

“…reacted [MesIRuH 4 PCy 3 ] with toluene -d 8 at ambient temperature and observed a rapid H/D exchange reaction involving the four hydride hydrogen atoms on ruthenium, the methyl protons of the mesityl substituents of the carbene ligand and the deuterium atoms on the meta positions of toluene -d 8 . The ortho -, para -and methyl -deuterium atoms of the solvent did not participate [ 145 ].…”