Indenylidene Ruthenium Complex Bearing a Sterically Demanding NHC Ligand: An Efficient Catalyst for Olefin Metathesis at Room Temperature

Abstract

The synthesis and characterization of a novel indenylidene-containing ruthenium catalyst bearing the N-heterocyclic carbene (NHC) ligand 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) are reported. Comparative reactivity studies with other indenylidene complexes using various substrates show the importance of the sterically demanding SIPr ligand on catalyst reaction profile. The investigation of the reaction scope for ring-closing metathesis transformations establishes the influence of the NHC on catalyst activity especially as a function of substrate steric bulk. The novel catalyst was found very efficient at room temperature for nonsterically hindered substrates. Since the new catalyst was found to be soluble in a variety of solvents, a number of these were examined to gauge the importance of solvent effects.

Imidazol(in)ium‐2‐carboxylates as N‐Heterocyclic Carbene Precursors for the Synthesis of Second Generation Ruthenium Metathesis Catalysts

“…We reasoned that this experimental set-up would help displace carbon dioxide and increase the decarboxylation rate. The ligand exchange was conveniently monitored by 31 P NMR analysis of samples withdrawn from the crude reaction mixture and diluted with a small amount of C 6 D 6 ( Figure 1). Spectra recorded at regular time intervals showed the progressive disappearance of the resonance at 36.8 ppm for the first generation Grubbs catalyst and the simultaneous emergence of two new sharp singlets located at 30.0 ppm and 10.4 ppm for the second generation Grubbs catalyst (2) [29] and free tricyclohexylphosphane (PCy 3 ), respectively (Table 1).…”

“…We also emphasize the usefulness of 31 P NMR spectroscopy as a convenient tool for monitoring the progress of these reactions.…”

Mixed Isobutylphobane/N‐Heterocyclic Carbene Ruthenium‐ Indenylidene Complexes: Synthesis and Catalytic Evaluation in Olefin Metathesis Reactions

“…Bond lengths and angles are similar to those observed in first generation complexes 6 [24] and 8, [32] or in related second generation ruthenium-indenylidene catalysts bearing PCy 3 and the IDip or SIDip ligands. [36,43] It is noteworthy, however, that the 3-phenyl group and the cyclopentene ring of the indenylidene ligand in complex 10 are in the opposite orientation with respect to the other compounds examined. Indeed, the 3-phenyl group lies in front of another terminal phenyl group from an adjacent molecule, whereas in compound 8 and in…”

“…At this point, we prefer not to draw any definite conclusion from these data, although we note that the tendency observed here for mixed phobane/NHC ruthenium-indenylidene complexes is in line with the 31 P chemical shift gap observed between various other second generation ruthenium-alkylidene catalysts, where the IMes or IDip ligands always lead to a more pronounced deshielding of the trans-phosphane than SIMes or SIDip, even if the difference is sometimes less than 1 ppm [IDip is 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIDip is 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene]. [36,[40][41][42][43] It should be noted that the interpretation of 1 H and 13 C NMR spectra was complicated by the presence of many hardly differentiable signals in the aliphatic and aromatic regions due to the phobane and indenylidene ligands, respectively. [44] Yet, elemental analysis confirmed the identity and purity of complexes 10 and 11.…”

Experimental investigation of ruthenium-indenylidene precatalyst for 1-octene metathesis

“…Die ontwikkeling van indenilideenafgeleides (Ind) van die Grubbs-prekatalisator lei tot verbeterde aktiwiteit, termiese stabiliteit en uiteindelike leeftyd (Opstal & Verpoort 2003;Boeda et al 2008;Clavier et al 2009). In die studie is daarop gefokus om die rutenium-indenilideenprekatalisator te optimiseer vir 1-okteenmetatese.…”