MONOALKYLCHROMIUM(III) COMPLEXES OF A TETRADENTATE N4 MACROCYCLE

Chromium(Il) chloride in mixed aqueous solvents forms a strongly reducing complex with the macrocyclic ligand [15]ane N4.Reactions of this complex with organic halides produce the monoalkyl complexes RCr ([15]aneN4)H2O2+ which have been characterized and shown to have a trans configuration. The kinetics of these reactions have been studied, with the result that the reaction follows a second-order rate law. Rate constants have been evaluated for a range of organic halides. These results, together with the stoichiometry, the variation of rate withthe constitution of RX, and related tests, suggest the following mechanism. The chromium(II) complex reacts withalkyl halides in two steps, rate-limiting halogen atom abstraction to generate a carbon-centered free radical followed by rapid coupling of the latter with a second chromium(II) complex. © 1979, American Chemical Society. All rights reserved.