Palladium(II) carboxylates and palladium(I) carbonyl carboxylate complexes as catalysts for olefin cyclopropanation with ethyl diazoacetate

摘要: Palladium(I) carbonyl carboxylate complexes [Pd(μ-CO)(μ-RCO2)]n (R = Me, n 4; R CMe3, 6) and the corresponding palladium(II) carboxylates (acetate pivalate) catalyze cyclopropanation of olefins with ethyl diazoacetate. The performance these catalysts is similar in terms selectivity cyclopropane yields, regardless oxidation state metal center. However rates reactions are significantly higher for acetate based than pivalate derivatives, which suggests that main catalytic species containing palladium complexes. Kinetic measurements show reaction independent olefin concentration when 1-hexene or styrene, but norbornene exerts an inhibitory effect. In spite this, competition experiments indicate styrene 2.2 times as favorable any four catalysts. These observations while rate-determining formation intermediate carbenoid controlled by catalyst structure, this followed a rapid less specific step not affected nature groups present catalyst. An test using 1:1 benzene/cyclohexane mixture solvents showed transfer ethoxycarbonylcarbene (:C(CO2Et)H) to molecules unselective (relative rate functionalization ≈1.8, catalyst). This result can be interpreted indication involvement free carbene step.