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

Dinuclear ruthenium(I,I) carboxylate complexes [Ru2(CO)4(μ-OOCR)2]n (R = CH3 (1a), C3H7 (1b), H (1c), CF3 (1d)) and 2-pyridonate complex [Ru2(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 [Ru2(CO)4(μ-L1)2]2 (4) and (5), [Ru2(CO)4(μ-L1)2L2] (L2 = CH3OH, PPh3) (6)–(9) and [Ru2(CO)4(CH3CN)2(μ-L1)2] (10) and (11), where L1 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.