Kinetics of the dirhodium tetraacetate catalyzed decomposition of ethyl diazoacetate in 1,4-dioxane. Is nitrogen involved in the transition state?

Abstract

The rate of decomposition of ethyl diazoacetate (EDA) in 1,4-dioxane under bis-(hexafluoroacetoacetonato)copper(II) (HFAC) and of dirhodium tetraacetate (DRTA) has been measured in the temperature range 332–352 ° K. While the copper catalyst promoted irregular and irreproducible decomposition of EDA in formal kinetic terms, DRTA promoted a smooth reaction that was first order in EDA. Apparent rate constants were in the range 3.0 - 12 × 10(−4)s(−1) within the indicated temperatures. The only product detected was the C-H insertion adduct of the putative EDA-derived rhodium carbene into a methylene group of dioxane. Activation parameters for the first order EDA transfiguration under DRTA catalysis were: ΔH ≠ = 16.4 ± 1.4 Kcal mol(−1),and ΔS ≠ = −25 ± 4 eu. The highly negative entropy of activation was deemed compatible with the coupling of EDA and DRTA without the exclusion of nitrogen during the rate determining step en route to the metal carbene.