Dimethylamino allenylidene

The behavior of tra s-[RuCl(=C=C=C=CH2)(dppm)2][PF6] towards the tertiary amine allyldimethylamine merits to be highlighted since the reaction led to the dimethylamino-allenylidene complex 32 through an Aza-Cope (or Claisen) rearrangement of the initially generated quaternary vinyl-allyl-ammonium salt [RuCl C=CC(NMe2CH2CH=CH2)=CH2 (dppm)2][PF6] (31) (Scheme 8) [47]. 

Scheme 3.24 Ferrocenylethyl(dimethylamino)allenylidene ruthenium by nucleophilic addition of ferrocenylmethylamine to C3 of 10 and subsequent rearrangement.

In sharp contrast with the remaining transition metals, Group 6 allenylidenes [M (=C=C=CR R )(C0)5] (M = Cr, Mo, W) containing non-donnor substituents at Cy are in general thermally unstable [11-15]. For this reason, most of the reported examples are substituted derivatives bearing heteroatomic Ti-donor groups [9]. In this sense, the first stable Group 6 allenylidenes reported in the literature were the amino-allenylidene complexes 2, prepared by E. O. Fischer and coworkers by a Lewis-acid induced elimination of ethanol from the 3-dimethylamino-l-ethoxy-3-... 

Scheme 15 Synthesis of dimethylamino(organyl)allenylidene complexes 53...

The related reaction of 10 with ferrocenylmethylamine affords, in addition to the C3 adduct (as the minor product), a 2-ferrocenylethyl(dimethylamino)allenyli-dene complex as the major product, formed by migration of the resonance-stabilized [FcCH2] carbenium ion to the terminal carbon atom of the chain (Scheme 3.24) [46], The formation of pyrrolyl- and indolyl-substituted allenylidene complexes by reaction of complex 10 with various pyrroles and N-methylindole [47] has also been rationalized as involving initial attack of the electron-rich heterocyde on C3 of 10 followed by proton migration to the terminal =CH2 entity of the intermediate butenynyl-substituted a-complex (Scheme 3.25). 

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