Kinetics and mechanism of dissociation of tris(pyridine-2-carbaldehyde-N-propylimine)- and tris(pyridine-2-carbaldehyde-N-methylimine)-iron(II)

Abstract

The rate of dissociation of tris(pyridine-2-carbaldehyde-N-propylimine)iron(II), [Fe(ppi)₃]²⁺, has been reinvestigated and the studies extended to tris(pyridine-2-carbaldehyde-N-methylimine)iron(II), [Fe(pmi)₃]²⁺. Experimental rate data are in agreement with a mechanism consisting of two simultaneous reaction paths in which the order of bond breaking between the central metal atom and each of the different moieties of the ligand is reversed. Approximate values of rate constants and activation parameters of some of the elementary reaction steps have been obtained for these paths. Comparison with values reported for the complexes of 2.2′-bipyridine. [Fe(bipy)₃]²⁺, and glyoxalbismethylimine. [Fe(gmi)₃]²⁺, suggests that the differences between metal–pyridine and –aliphatic imine bond strengths are significantly reduced on passing from bipy and gmi to the ‘mixed’ ligands pmi and ppi.