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N‐Heterocyclic Carbene and Phosphine Ruthenium Indenylidene Precatalysts: A Comparative Study in Olefin Metathesis
Author(s) -
Clavier Hervé,
Nolan Steven P.
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700256
Subject(s) - carbene , tricyclohexylphosphine , chemistry , phosphine , ring closing metathesis , ruthenium , enyne metathesis , catalysis , combinatorial chemistry , metathesis , ring opening metathesis polymerisation , organic chemistry , polymerization , polymer
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.