Latent ruthenium olefin metathesis catalysts featuring a phosphine or an N-heterocyclic carbene ligand |
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Authors: | Joseph S.M. Samec |
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Affiliation: | Division of Chemistry and Chemical Engineering, Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, Ca 91125, USA |
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Abstract: | The synthesis and characterization of latent 18-electron ruthenium benzylidene complexes (PCy3)((κN,O)-picolinate)2RuCHPh (5) and (H2IMes)((κN,O)-picolinate)2RuCHPh (6) are described. Both complexes appear as two isomers. The ratio between the isomers is dependent on l-type ligand. The complexes are inactive in ring-closing metathesis and ring-opening metathesis polymerization reactions even at elevated temperatures in the absence of stimuli. Upon addition of HCl, complexes 5 and 6 become highly active in olefin metathesis reactions. The advantage of the latent catalysts is demonstrated in the ring-opening metathesis polymerization of dicyclopentadiene, where the latency of 6 assures adequate mixing of catalyst and monomer before initiation. Trapping experiments suggests that the acid converts the 18-electron complexes into their corresponding highly olefin metathesis active 14-electron benzylidenes. |
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Keywords: | Olefin metathesis Controlled initiation Acid induced activation |
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