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Comparative Investigation of Ruthenium‐Based Metathesis Catalysts Bearing N‐Heterocyclic Carbene (NHC) Ligands
Author(s) -
Fürstner Alois,
Ackermann Lutz,
Gabor Barbara,
Goddard Richard,
Lehmann Christian W.,
Mynott Richard,
Stelzer Frank,
Thiel Oliver R.
Publication year - 2001
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 - 10.1002/1521-3765(20010803)7:15<3236::aid-chem3236>3.0.co;2-s
Subject(s) - carbene , reactivity (psychology) , catalysis , ruthenium , metathesis , chemistry , enyne metathesis , combinatorial chemistry , metallacycle , alkene , cycloisomerization , enyne , steric effects , intramolecular force , photochemistry , medicinal chemistry , organic chemistry , stereochemistry , polymerization , physics , medicine , polymer , alternative medicine , x ray crystallography , pathology , diffraction , optics
Exchange of one PCy 3 unit of the classical Grubbs catalyst 1 by N‐heterocyclic carbene (NHC) ligands leads to “second‐generation” metathesis catalysts of superior reactivity and increased stability. Several complexes of this type have been prepared and fully characterized, six of them by X‐ray crystallography. These include the unique chelate complexes 13 and 14 in which the NHC‐ and the Ru=CR entities are tethered to form a metallacycle. A particularly favorable design feature is that the reactivity of such catalysts can be easily adjusted by changing the electronic and steric properties of the NHC ligands. The catalytic activity also strongly depends on the solvent used; NMR investigations provide a tentative explanation of this effect. Applications of the “second‐generation” catalysts to ring closing alkene metathesis and intramolecular enyne cycloisomerization reactions provide insights into their catalytic performance. From these comparative studies it is deduced that no single catalyst is optimal for different types of applications. The search for the most reactive catalyst for a specific transformation is facilitated by IR thermography allowing a rapid and semi‐quantitative ranking among a given set of catalysts.