Tungsten neopentylidene complex

As regards the metathesis polymerisation of cyclic trienes, it has been carried out in an attempt to find alternative routes for preparing soluble and meltable precursors of polyacetylene [149, 150], Hence, several substituted or unsubstituted tricyclic or other polycyclic trienes were subjected to polymerisation in the presence of metathesis catalysts such as WCl6-SnMe4 [151-154] and the tungsten neopentylidene complex [Me(F3C)2CO]2W(=NAr)(=CHCMe3) [155]. A successful solution of the problem is outlined below [125,150] ... 

Imido alkylidene complexes were first prepared by a reaction analogous to that shown In equation 6. Recently they have been prepared from imido alkyl complexes by well-behaved a-hydrogen abstraction reactions (16) Imido neopentylidene complexes seem to be more stable than oxo neopentylidene complexes, possibly because the oxo ligand is sterically more accessible to Lewis acids, including another tungsten center. 

Osborn s discovery (14) that aluminum halides bimTto oxo ligands in tungsten oxo neopentyl complexes, and that these complexes decompose to give systems which will efficiently metathesize olefins, raised more questions concerning the role of the Lewis acid. A subsequent communication (20) answered some of the questions the aluminum halide removes We oxo ligand and replaces it with two halides to yield neopentylidene complexes (equation 8). 

Other complexes have been reported to activate alkanes, including thermally generated tungsten neopentylidene analogs (Equation (3)).11... 

Scheme 1.2 The synthesis of HMTO and HIPTO tungsten oxo-neopentylidene complexes.

S. J. Holmes, D. N. Clark, H. W. Turner, and R. R. Schrock, o-Hydride Elimination from Methylene and Neopentylidene Ligands. Preparation and Protonation of Tungsten(IV) Methylidyne and Neopentylidyne Complexes, J. Am. Chem. Soc. 104, 6322-6329 (1982). 

Scheme 5.2 Synthesis of a ROMP-active cyclometallated aryl-oxy(chloro)neopentylidene tungsten complex [50].

Scheme 2. Sjmthesis of a ROMP-Active Cyclometidated Arylojgf(chloro)neopentylidene Tungsten Complex...

ABSTRACT. Cyclometalated aryloxy(chloro)neopentylidene-tungsten complexes can be synthesized starting from WCl4(OAr)2 (OAr = 2,6-disubstituted phenoxide), but also starting from the neopentylidyne complex W(CCMe3)Cl3(dme) (by reaction with LiOAr). Some of these cyclometalated neopentylidenes are probably among the most active and stereoselective one-component metathesis catalysts. In particular, they are fairly active in the metathesis of an olefinic ester such as ethyl oleate and they have been successfully used in the metathesis of olefinic sulfides. 

A general mediod for the synthesis of aryloxy(chloro)neopentylidene-tungsten complexes involves the reaction of WCl4(OAr)2 (OAr = 2,6-disubstituted phenoxide) [20] with 1 equiv or 1.5 equiv of MgNp2(dioxane) (Np=CH2C(CH3)3) [11, 21] (Scheme 1). The reaction proceeds via a double (or triple) kylation of tungsten followed by an a-H abstraction and elimination of neopentane [22]. In the particular case of the 2,6-diphenyl-phenoxide complexes, the activation of m ortho C-H bond in one of the phenyl substituents of the aryloxide ligands leads to the elimination of HCl with the formation of a cyclometalated compound (Scheme 2) [23, 24]. 

Interestingly, this type of cyclometalated complex can be obtained via an other route starting from the Schrock s neopentylidyne complex W(CCMe3)Cl3(dme) (dme = dimethoxyethane) [25, 26]. The purpose of this paper is to report the main features of this new way of synAesis and to give some examples of the catalytic properties of these cyclometalated aryloxy(chloro)neopentylidene-tungsten complexes in olefin metathesis. 

CATALYTIC PROPERTIES OF CYCLOMETALATED ARYLOXY(CHLORO)-NEOPENTYLIDENE-TUNGSTEN COMPLEXES IN OLEFIN METATHESIS... 

We have found that metathesis of olefmic sulfides can be successfully achieved by using, as homogeneous catalyst, the aryloxy(chloro)neopentylidene-tungsten complex 1. Thus, the self-metathesis of allyl methyl sulfide (4) and of 5-dkylthiocycloooctenes (5) (or their cometathesis with various acyclic or cyclic olefins without functional groups) can lead to a family of new olefins, dienes, or unsaturated polymers containing one or more thioether groups. 

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