Half-sandwich ruthenium(II) catalysts for C-C coupling reactions between alkenes and diazo compounds

The complex [(eta(5)-C5H5)Ru(PPh3)(2)Cl] (1) and other readily available ruthenium(II) derivatives of general formula [(eta(5)-ligand)Ru(PR3)(2)X] efficiently catalyze the cyclopropanation of styrene and other electron-rich alkenes in the presence of ethyl diazoacetate with a high cia 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 :CPh2-:CHCH2Ph coupling. Furthermore, appreciable amounts of the metathesis and cyclopropanation products I,1-diphenylethene and 1,2-diphenylcyclopropanes in a I:1 molar ratio are observed. The carbene complex [(eta(5)-C5H5)Ru(=CPh2)(PPh3)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.