Methylidene-rhodium complex

In the gas phase reaction of Rh with c-CaH, among other processes, elimination of C2H4 has been observed and the resulting metal ion was shown to have the structure of a methylidene-rhodium complex (238) instead of a hydrido-methylidene species (239) . RhCHa (238) reacts readily with H2 and CH4 and represents the first example of methane activation by a cationic mononuclear transition-metal complex in the gas phase. Reactions of both Rh = CH2 and its analogues Fe-CH2 and C0-CH2 with cyclic hydrocarbons were studied, and it is assumed that in the initial step metallacycloalkanes are generated (Scheme 35). 

The bis( -methylene)rhodium complex (Structure 8) undergoes thermal decomposition at 300-350 °C to yield mainly propene and methane H-labeling experiments showed that the propene originates rather selectively (>75 %) from two CH2 groups and one CH3 unit a //-methylidene (CH) intermediate 9 (from H abstraction) with consecutive isomerizations is assumed to yield the propene (Scheme 3). 

In the presence of rhodium [RhX(cod)]2 (where X = Cl, OSiMe3) and also RuHCl(CO)(i-PPr3)2 complexes, intramolecular condensation of divinylsubstituted silicon derivatives proceeds to open an original route for synthesizing organosilicon compounds containing organocyclotrienes, cyclodienes or cycloalkenes with jco-cyclic methylidenes. 

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