Solid State Isostructural Behavior and Quantified Limiting Substitution Kinetics in Schiff-Base Bidentate Ligand Complexes fac-[Re(O,N-Bid)(CO)3(MeOH)]n
dataset
posted on 2014-12-01, 00:00 authored by Alice Brink, Hendrik G. Visser, Andreas RoodtA range of N,O-donor atom salicylidene complexes of the type fac-[M(O,N-Bid)(CO)3(L)]n (O,N-Bid
= anionic N,O-bidentate ligands;
L = neutral coordinated ligand) have been studied. The unique feature
of the complexes which crystallize in a monoclinic isostructural space
group for complexes containing methanol in the sixth position (L =
MeOH) is highlighted. The reactivity and stability of the complexes
were evaluated by rapid stopped-flow techniques, and the methanol
substitution by a range of pyridine type ligands indicates significant
activation by the N,O-salicylidene type of bidentate
ligands as observed from the variation in the second-order rate constants.
In particular, following the introduction of the sterically demanding
and electron rich cyclohexyl salicylidene moiety on the bidentate
ligand, novel limiting kinetic behavior is displayed by all entering
ligands, thus enabling a systematic probe and manipulation of the
limiting kinetic constants. Clear evidence of an interchange type
of intimate mechanism for the methanol substitution is produced. The
equilibrium and rate constants (25 °C) for the two steps in the
dissociative interchange mechanism for methanol substitution in fac-[Re(Sal-Cy)(CO)3(MeOH)] (5) by the pyridine type ligands 3-chloropyridine, pyridine, 4-picoline,
and DMAP are k3 (s–1), 40 ± 4, 13 ± 2, 10.4 ± 0.7, and 2.11 ± 0.09,
and K2 (M–1), 0.13 ±
0.01, 0.21 ± 0.03, 0.26 ± 0.02, and 1.8 ± 0.1, respectively.
