Rhodium-Catalyzed Activation and Functionalization of the C−C Bond of Biphenylene

Biphenylene reacts with the rhodium(I) dimer [(dtbpm)RhCl] 2 ( 1 ) (dtbpm = bis(di- tert -butylphosphino)methane) to yield (dtbpm)Rh(2,2‘-biphenyl)Cl ( 2 ). Lewis bases react with compound 2 at room temperature, displacing the chelating phosphine. A new five-coordinate complex, (PPh 3 ) 2 Rh(2,2‘-biphenyl)Cl ( 3 ), is formed when the base is triphenylphosphine. Fluorenone and fluorenimine are formed when the base used is carbon monoxide and isonitrile, respectively. The dimer 1 and compound 2 are catalysts for coupling reactions of biphenylene with unsaturated organic substrates. Substituted phenanthrenes and benzenes are formed using alkynes with simple alkyl or aryl substituents. Substituted phenanthrenes and fluorenes are produced using alkynes with trimethylsilyl substituents. Olefinic substrates yield vinylbiphenyls. The production of vinylbiphenyls is hindered by steric substitution on the olefin. α-Olefins with substituents that block double-bond migration yield the cleanest product ratios.