A Novel Series of CoIII(salen-type) Complexes Containing a Seven-Membered Metallacycle: Synthesis, Structural Characterization and Factors Affecting the Metallacyclization Rate

Abstract

A series of electronically tuned trans-[CoIII(chel)(CH2Cl)]2 complexes, where chel is a salen derivative (salen = 2,2′-ethylenebis(nitrilomethylidene)diphenol) containing either two or four methyl substituents in different positions, has been synthesized and characterized, both in solution and in the solid state. These complexes undergo an intramolecular cyclization reaction in methanolic solution to form the corresponding cis β organometallic derivative containing a seven-membered metallacycle, by replacement of the Cl atom of the axial CH2Cl by the salen phenolate oxygen. The cyclization rate increases on going from two to four methyl substituents in the chelate, in agreement with the electrochemical data that evidence a general shift toward more negative values with an increase in the number of methyl substituents. The cyclization rate is also affected by the substituent position, and both electrochemical and kinetic data evidence a remarkable influence of the methyls on the −C═N– groups of the chelate...