title: Rollover cyclometalation pathway in rhodium catalysis: dramatic NHC effects in the C-H bond functionalization.
abstract: 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.
authors.affiliation: Molecular-Level Interface Research Center and Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.
authors.forename: Jaesung
authors.initials: J
authors.lastname: Kwak
authors.forename: Youhwa
authors.initials: Y
authors.lastname: Ohk
authors.forename: Yousung
authors.initials: Y
authors.lastname: Jung
authors.forename: Sukbok
authors.initials: S
authors.lastname: Chang
mesh_terms: D015082:2,2'-Dipyridyl / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D011804:Quinolines / Q000138:chemical synthesis* / Q000737:chemistry; D012238:Rhodium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D006571:Heterocyclic Compounds; D009942:Organometallic Compounds; D011804:Quinolines; C030011:carbene; D015082:2,2'-Dipyridyl; D012238:Rhodium; D008697:Methane