Rhodium allenylidenes

Scheme 22 Coupling of an allenylidene ligand with a vinyl group at rhodium...

An intramolecular allenylidene-alkynyl coupling was also observed in the reaction of the mixed alkynyl-allenylidene rhodium(I) complex 73 with carbon monoxide (Scheme 25). In this case, the initially formed thermally unstable allenyl derivative 74 evolved into the metallated cyclobutenone 75 when an excess of CO was present [276]. 

H. Werner, Allenylidenes Their Multifaceted Chemistry at Rhodium, Chem. Comm. 1997, 903-910. 

Although less widespread than the rhodium cognate species, iridium allenylidenes are well documented and have been known since 1997 when the first compounds featuring the allenylidene, Ir=C=C=CRRi, moiety were independently obtained by Oro, " Werner,and their co-workers. While not isolated in the solid state or even detected in solution, the existence of an iridium allenylidene was previously invoked by O Connor et al. to... 

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