Dinuclear ruthenium(I) complexes of the type [Ru 2(CO) 4L 2] 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 3H 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) 2L 2] (L 2 = CH 3OH, PPh 3) ( 6)–( 9) and [Ru 2(CO) 4(CH 3CN) 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.