Rudler carbene

Metal Carbene Catalysts. The first use of isolated single-component car-bene catalysts showed that the Fischer (4) and Casey carbenes (5) polymerize phenylacetylene, ferf-butylacetylene, and cyclooctyne in low yields (130). For example, the bulk polymerization of tert-butylacetylene with (4) gives a high molecular weight (Mn = 260,000) polymer in 28% yield. Polymer-supported Fischer carbene (4) is also active for the polymerization of phenylacetylene under photoirradiation (145). As a catalyst, the Casey carbene (5) is less stable but more active than the Fischer carbene (130). The Rudler carbene (6) readily releases the in-tramolecularly ligated double bond upon the approach of an acetylenic monomer. Thus, it is more active than the Fischer and Casey carbenes (146-148). These carbene complexes are, however, unable to control the polymerization. 

Structural analogues of the /]4-vinylketene E were isolated by Wulff, Rudler and Moser [15]. The enaminoketene complex 11 was obtained from an intramolecular reaction of the chromium pentacarbonyl carbene complex 10. The silyl vinylketene 13 was isolated from the reaction of the methoxy(phenyl)-carbene chromium complex 1 and a silyl-substituted phenylacetylene 12, and -in contrast to alkene carbene complex 7 - gave the benzannulation product 14 after heating to 165 °C in acetonitrile (Scheme 6). The last step of the benzannulation reaction is the tautomerisation of the /]4-cyclohexadienone F to afford the phenol product G. The existence of such an intermediate and its capacity to undergo a subsequent step was validated by Wulff, who synthesised an... 

In 1979, Rudler ef al. reported another example of the presence of a vinylidene complex during the reaction of pentacarbonyl[methoxy(methyl)carbene] tungsten 5 with MeLi followed by acidification with TFA [4]. It was proposed that the vinylidene complex 7 was generated by deprotonation of the a-proton of the carbene complex followed by elimination of methoxide and reaction with the dimethylcarbene complex 8, the addition-elimination product of MeLi with the starting carbene complex, to give the dinuclear complex 6 (Scheme 5.2). 

In a similar manner, Rudler et al. reported in 1986 that treatment of the 4-penten-l-ylidene complex 25 with trimethylsilylacetylene gave the methyl carbene complex 27... 

Scheme 5.8 Formation of a Fischer-carbene complex from vinylidene by Rudler.

The reaction of alkyl-substituted tungsten-carbene complexes of the type (88b) have been reported by Macomber to react with alkynes to give dienes of the type (319). One mechanism that has been proposed to account for this product is a 3-hydride elimination from the metallacyclobutene intermediate (320) and subsequent reductive elimination in the metal hydride species (321). An additional example of this type of reaction has been reported by Rudler, also for an alkyl tungsten carbene complex. Chromium complexes have not been observed to give diene products of this type the reaction of the analogous chromium complex (88a) with diphenylacetylene gives a cyclobutenone as the only reported product (see Scheme 31). Acyclic products are observed for both tungsten and chromium complexes in their reactions with ynamines. These reactions produce amino-stablized carbene complexes that are the result of the formal insertion of the ynamine into the metal-carbene bond. ... 

In a variation of the reactions in Scheme 44, Rudler has reported that the alkene which intercq)ts the vinyl carbene complex leading to cyclopropane products can be tethered onto the starting carbene complex.This was extensively studied for the reaction of the carbene complex (334) with a number of alkynes leading to bicycloheptanones of the type (336). ° This reaction is quite general (14 examples, 44-95%) and is regioselective with terminal alkynes, i.e. it occurs in the same sense that has been observed for the benzannuladon reaction (R = H in 336). Acetylene fails and cyclooctyne gives a reduced... 

J. Levisalles, H. Rudler, and D. Villemin,/. Organomet. Chem., 1980, 193, 235. Mechanism of olefin metathesis IV. Hydrogen and carbene exchange. 

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