Organometallic chelates are readily obtained upon coordination of metal species to multidentate ligands. Because of the robust structural nature, chelation frequently serves as a driving force in the molecular assembly and chemical architecture, and they are used also as an efficient catalyst in numerous reactions. Described herein is the development of a Rh(NHC) catalytic system for the hydroarylation of alkenes and alkynes with 2,2'-bipyridines (bipy) and 2,2'-biquinolines; the most representative chelating molecules. Initially generated (bipy)Rh(NHC) chelates become labile because of the strong trans-effect of N-heterocyclic carbenes, thus weakening a rhodium-pyridyl bond, which is trans to the bound NHC. Subsequent rollover cyclometalation leads to the C-H bond activation, eventually giving rise to double functionalization of chelate molecules. Density functional calculations are in good agreement with our mechanistic proposal based on the experimental data. The present study elucidated for the first time the dramatic NHC effects on the rollover cyclometalation pathway enabling highly efficient and selective bisfunctionalization of 2,2'-bipyridines and 2,2'-biquinolines.

The rhodium- or copper-catalyzed intramolecular aromatic carbenoid insertion of biaryldiazoacetates offers a convenient route to fluorene carboxylates with high yields. Whereas, thermal conditions provided a mixture of two regioisomeric products when substituted biaryldiazoacetates were employed as substrates. The developed catalytic conditions displayed an excellent level of regioselectivity, presumably owing to steric effects. The insertion mechanism was assumed to be an electrophilic aromatic substitution, which was supported by preliminary mechanistic studies. A chloro-substituted fluorene derivative was efficiently synthesized and utilized as a base-sensitive protecting group of amines.

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Dirhodium acetates or copper triflate catalyze the highly regioisomeric formation of the fluorenes from appropriately substituted biaryldiazoacetates, whereas under thermal conditions a significantly reduced regioselectivity is observed.