C-C bond-forming reactions of Ir(III)-alkenyls and nitriles or aldehydes: generation of reactive hydride- and alkyl-alkylidene compounds and observation of a reversible 1, 2-H shift in stable hydride-Ir(III) alkylidene complexes

Nucleophilic attack of the beta-carbon of an Ir(III)-alkenyl functionality onto the alpha-carbon of a coordinated nitrile- or aldehyde occurs intramoleculary to yield initially iridacyclic structures. Nitriles give rise to isolable complexes that contain delocalized five-membered rings (iridapyrroles, e.g. 3'-8') in a reaction catalyzed by H2O (for some of these syntheses, Ir(III)-eta 3-allyl derivatives may be used as the source of the Ir(III)-alkenyl moiety). In contrast, the alkenyl-to-aldehyde C-C coupling gives transient iridacycles that evolve by a fast alkyl-to-alkylidene migration and beta-H elimination. The end products (13* and 14*) contain an elaborated chelating alkoxide-olefin ligand. Addition of H(OEt2)2]BAr'4] to the iridapyrroles effects stereospecific protonation of the beta-ring carbon. Those iridapyrroles which contain an additional metal-alkyl functionality (e.g. 3a*, alkyl = C2H5) afford highly reactive cationic alkyl-alkylidene intermediates that evolve instantaneously by migratory insertion/beta-H elimination. The end products also contain an elaborated, chelating ligand, although this time with an olefin and imine terminus compared with the previous ligand. Contrary to this result, protonation of the hydride-iridapyrrole complex 8a* in weakly coordinating solvents permits isolation of two unusual cationic cis-hydride-alkylidene compounds 11*, which undergo reversible 1,2-H shifts.