Alkenyl-aminoallenylidenes

Group 6 allenylidenes also react with the carbon-carbon triple bond of ynamines to yield similar cyclobutenylidene derivatives 88 along with the corresponding alkenyl-aminoallenylidenes 89 (Scheme 32) [286]. These aminoallenylidene complexes result from a formal [2-1-2] cycloaddition between the ynamine C=C and allenylidene Cp=Cy bonds followed by cycloreversion. A stepwise cyclization initiated by the addition of the nucleophilic R C=CNEt2 carbon at the C or Cy position has been proposed in the formation of these isomeric products. As commented previously, unlike their Cr and W counterparts, the reactions of... 

Allenylidenecomplexes 46 also react with thecarbon-carbon triple bond ofynamines to yield similar mononuclear cydobutenyhdene derivatives 48, although mixtures with the corresponding alkenyl-aminoallenylidene spedes 49 are formed (Scheme 2.20) [ 1 Oc]. The former isomer results from the addition of the C=C bond of y namines across the Co,=Cp unsaturation, while the latter is provided bythe formal [2 + 2] cycloaddition between C=C and Cp=Cy bonds and subsequent cycloreversion. In both processes, stepwise cyclization initiated by the addition of the nucleophilic R C=CNEt2 carbon at the Co, or Cy position, respectively, is proposed. Relative proportions of 49 with respect to 48 increase with the electron-releasing capacity of the para-substituents of the diarylallenylidene skeleton (NMe2 > OMe > Me > H). In contrast, the formation of 48 is favored when the reaction is carried out in low polarity solvents. 

The reactions of the alkenyl-aminoallenylidene complex [Ru =G=G=G(NEt2)GMe=GPh2 (r7 -G9H7)(PPh3)2][PF6] with alkyl carbanions such as Li[GH2R] or allylmagnesium bromide lead to the unusual... 

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