Alkylidene and Metalacyclic Complexes of Tungsten that Contain a Chiral Biphenoxide Ligand. Synthesis, Asymmetric Ring-Closing Metathesis, and Mechanistic Investigations

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 (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.

Photochemical reaction of W(CO)6 with GeCl4 as a source of germyl and germylene compounds acting as initiators for ring-opening metathesis polymerization of norbornene

“…In our study it was observed that a bimolecular coupling of the tungstanorbornylidene intermediate species led to the formation of bi-(NBE) and regenerated the binuclear compound 1. A similar bimolecular coupling of two carbene ligands has been observed during mild thermolysis of chromium (0) and tungsten(0) pentacarbonylcarbene complexes [33][34][35] and detected by Schrock et al in reaction of alkylidene complexes of tantalum, molybdenum, and tungsten [36][37][38]. For the first time the carbene-carbene coupling reaction was applied in synthesis of bi-(NBE) from NBE in reaction catalyzed by a WASn compound [30].…”

Rhenium(VII) Oxide/Aluminum Oxide: More Experimental Evidence for an Oxametallacyclobutane Intermediate and a Pseudo‐Wittig Initiation Step in Olefin Metathesis

“…shows the formation of (7)- (9). [20] Third, the presence of unlabelled 2-butenes can result from the decomposition of the stable metallacyclobutane or to remaining physisorbed olefins as olefin adsorbs strongly on alumina (80 kJ mol…”

An anionic binuclear complex of tungsten(II), [(μ-Cl)3{W(SnCl3)(CO)3}2]−, and its reactivity towards norbornene

“…The first direct evidence for an alkene-to-alkylidene rearrangement was obtained by Wolczanski et al [19]. A bimolecular coupling of two carbene ligands and the formation of new olefin has been observed during mild thermolysis of chromium(0) and tungsten(0) pentacarbonylcarbene complexes [20][21][22] and detected by Schrock et al in reaction of alkylidene complexes of tantalum, molybdenum and tungsten [23][24][25]. For the first time the carbene-carbene coupling reaction was applied in synthesis of bi-NBE from NBE in reaction catalyzed by the binuclear compound 2 [4].…”