Half-Sandwich Ruthenium(II) Catalysts for C−C Coupling Reactions between Alkenes and Diazo Compounds
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Abstract
The complex [(η5-C5H5)Ru(PPh3)2Cl] (1) and other readily available ruthenium(II) derivatives of general formula [(η5-ligand)Ru(PR3)2X] 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 :CPh2−:CHCH2Ph 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 [(η5-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.
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