文摘
Electronic effects in osmylation reactions accelerated by pyridineand quinuclidine derivatives wereinvestigated by varying the substituents on the amine ligand as well ason the alkene substrate. Ligand substituenteffects were gauged by determination of the equilibrium constants forcoordination of the amines to OsO4, evaluationof structural properties and reduction potentials of theamine-OsO4 complexes, and analysis of the kineticsofosmylations in the presence of the amines. Substrate substituenteffects were gauged by kinetic Hammett studiesusing several different amine/alkene combinations. NonlinearHammett relationships resulting from alkene substituenteffects were observed, and the deviation from a linear free energyrelationship was found to depend on the structure,binding capacity, and concentration of the amine. The results wereevaluated in terms of the contending "[3 +2]"and "[2 + 2]" mechanisms currently under consideration.A change in mechanism that depends on the structuraland electronic properties of both alkene and amine isproposed.