N-Heterocyclic Carbene and Phosphine Ruthenium Indenylidene Precatalysts: A Comparative Study in Olefin Metathesis

• Published in: Chemistry : a European journal Vol. 13; no. 28; pp. 8029 - 8036
• Main Authors: Clavier, Hervé, Nolan, Steven P.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.01.2007; WILEY‐VCH Verlag; Wiley
• Subjects: Chemistry; Chemistry, Multidisciplinary; indenylidenes; metathesis; N-heterocyclic carbenes; phosphanes; Physical Sciences; ruthenium; Science & Technology; SUBSTITUTION; MECHANISM; COMPLEXES; phosphanes; ruthenium; ENYNE METATHESIS; ETHYLENE; metathesis; RING-CLOSING METATHESIS; CONSTRUCTION; indenylidenes; EFFICIENT; CATALYSTS; CYCLIZATION; N-heterocyclic carbenes
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200700256

Kinetic studies on ring‐closing metathesis of unhindered and hindered substrates using phosphine and N‐heterocyclic carbene (NHC)‐containing ruthenium‐indenylidene complexes (first and second generation precatalysts, respectively) have been carried out. These studies reveal an appealing difference, between the phosphine and NHC‐containing catalysts, associated with a distinctive rate‐determining step in the reaction mechanism. These catalysts have been compared with the benzylidene generation catalysts and their respective representative substrates. Finally, the reaction scope of the two most interesting precatalysts, complexes that contain tricyclohexylphosphine and 1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene (SIMes), has been investigated for the ring‐closing and enyne metathesis for a large range of olefins. Owing to their high thermal stability, the SIMes‐based indenylidene complexes were more efficient than their benzylidene analogues in the ring‐closing metathesis of tetrasubstituted dienes. Importantly, none of the indenylidene precatalysts were found to be the most efficient for all of the substrates, indeed, a complementary complex‐to‐substrate activity relationship was observed. Complementary catalysts: A thorough evaluation of the catalytic performance of phosphine‐ and N‐heterocyclic carbene‐containing ruthenium catalysts is the subject of the present study (see figure). Examination of a number of substrates revealed that catalyst generation is complementary to the type of substrate.