Alkylidene and metalacyclic complexes of tungsten that contain a chiral biphenoxide ligand. synthesis, asymmetric ring-closing metathesis, and mechanistic investigations.
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 (Biphen(2-)) ligand, W(NAr)(CHCMe(2)Ph)(Biphen) (2a) and W(NAr')(CHCMe(2)Ph)(Biphen) (2b) (Ar = 2,6-i-Pr(2)C(6)H(3); Ar' = 2,6-Me(2)C(6)H(3)), 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 (13)C 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.
Tsang
W C Peter
WC
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Hultzsch
Kai C
KC
Alexander
John B
JB
Bonitatebus
Peter J
PJ
Schrock
Richard R
RR
Hoveyda
Amir H
AH
D000475:Alkenes / Q000138:chemical synthesis / Q000737:chemistry*; D001713:Biphenyl Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003500:Cyclization; D003503:Cyclobutanes / Q000737:chemistry; D005030:Ethylenes / Q000737:chemistry; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism; D014414:Tungsten / Q000737:chemistry*
D000475:Alkenes; D001713:Biphenyl Compounds; D003503:Cyclobutanes; D005030:Ethylenes; D008024:Ligands; D009942:Organometallic Compounds; C036216:ethylene; D014414:Tungsten