Dinuclear ruthenium(I) complexes of the type [Ru2(CO)4L2] with carboxylate or 2-pyridonate ligands : Evaluation as catalysts for olefin cyclopropanation with diazoacetates

Abstract Dinuclear ruthenium(I,I) carboxylate complexes [Ru 2 (CO) 4 (μ-OOCR) 2 ] n (R = CH 3 ( 1a ), C 3 H 7 ( 1b ), H ( 1c ), CF 3 ( 1d )) and 2-pyridonate complex [Ru 2 (CO) 4 (μ-2-pyridonate) 2 ] n ( 3 ) catalyze efficiently the cyclopropanation of alkenes with methyl diazoacetate. High yields are obtained with terminal nucleophilic alkenes (styrene, ethyl vinyl ether, α-methylstyrene), medium yields with 1-hexene, cyclohexene, 4,5-dihydrofuran and 2-methyl-2-butene. The E -selectivity of the cyclopropanes obtained from the monosubstituted alkenes and the cycloalkenes decreases in the order 1b  >  1a  >  1d  >  1c . The cyclopropanation of 2-methyl-2-butene is highly syn -selective. Several complexes of the type [Ru 2 (CO) 4 (μ-L 1 ) 2 ] 2 ( 4 ) and ( 5 ), [Ru 2 (CO) 4 (μ-L 1 ) 2 L 2 ] (L 2  = CH 3 OH, PPh 3 ) ( 6 )–( 9 ) and [Ru 2 (CO) 4 (CH 3 CN) 2 (μ-L 1 ) 2 ] ( 10 ) and ( 11 ), where L 1 is a 6-chloro- or 6-bromo-2-pyridonate ligand, are also efficient catalysts. Compared with catalyst 3 , a halogen substituent at the pyridonate ligand affects the diastereoselectivity of cyclopropanation only slightly.