Alkylidene and Metalacyclic Complexes of Tungsten that Contain a Chiral Biphenoxide Ligand. Synthesis, Asymmetric Ring-Closing Metathesis, and Mechanistic Investigations
- 5 February 2003
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 125 (9) , 2652-2666
- https://doi.org/10.1021/ja0210603
Abstract
Two complexes that contain the racemic or enantiomerically pure (S) form of the 3,3‘-di-tert-butyl-5,5‘,6,6‘-tetramethyl-1,1‘-biphenyl-2,2‘-diolate (Biphen2-) ligand, W(NAr)(CHCMe2Ph)(Biphen) (2a) and W(NAr‘)(CHCMe2Ph)(Biphen) (2b) (Ar = 2,6-i-Pr2C6H3; Ar‘ = 2,6-Me2C6H3), were prepared and shown to be viable catalysts for several representative ring-closing reactions to give products in good yields in most cases and high % ee in asymmetric reactions. Exploration of the reaction between 2a and a stoichiometric amount of one desymmetrization substrate allowed two intermediate tungstacyclobutane complexes to be observed, in addition to the final and quite stable tungstacyclobutane complex formed in a reaction between the ring-closed product and a tungsten methylene complex. Reactions involving 13C labeled ethylene allowed for the observation of an unsubstituted tungstacyclobutane complex, an ethylene complex, an unsubstituted tungstacyclopentane complex, and a heterochiral dimeric form of a methylene complex. The tungstacyclopentane complex was found to catalyze the dimerization of ethylene to 1-butene slowly.Keywords
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