Half-Sandwich Ruthenium(II) Catalysts for C−C Coupling Reactions between Alkenes and Diazo Compounds

The complex [(η 5 -C 5 H 5 )Ru(PPh 3 ) 2 Cl] ( 1 ) and other readily available ruthenium(II) derivatives of general formula [(η 5 -ligand)Ru(PR 3 ) 2 X] efficiently catalyze the cyclopropanation of styrene and other electron-rich alkenes in the presence of ethyl diazoacetate with a high cis stereoselectivity. When diphenyldiazomethane is employed as carbene source, the reaction with styrene, catalyzed by 1, affords mainly 1,1,3-triphenylpropene, as result of a formal:CPh 2 −:CHCH 2 Ph coupling. Furthermore, appreciable amounts of the metathesis and cyclopropanation products 1,1-diphenylethene and 1,2-diphenylcyclopropanes in a 1:1 molar ratio are observed. The carbene complex [(η 5 -C 5 H 5 )Ru( CPh 2 )(PPh 3 )Cl] ( 13 ), which was detected during the catalytic process, can be readily obtained in 85% isolated yield from 1 and diphenyldiazomethane in a one-pot reaction. With styrene, complex 13 undergoes a stoichiometric carbene transfer reaction, yielding the same organic products observed in the catalytic process with 1 .