8 research outputs found
Dramatic Effect of A Ring Size of Alicyclic α-Dioximate Ligand Synthons on Kinetics of the Template Synthesis and of the Acidic Decomposition of the Methylboron-Capped Iron(II) Clathrochelates
Kinetics and thermodynamics of the template synthesis and of the acidic decomposition of the methylboron-capped iron(II) tris-1,2-dioximatesâthe clathrochelate derivatives of six (nioxime)- and eight (octoxime)-membered alicyclic ligand synthonsâwere compared. In the case of a macrobicyclic iron(II) tris-nioximate, the plausible pathway of its formation contains a rate-determining stage and includes a reversible formation of an almost trigonal-antiprismatic (TAP) protonated tris-complex, followed by its monodeprotonation and addition of CH3B(OH)2. Thus, the formed TAP intermediate undergoes a multistep rate-determining stage of double cyclization with the elimination of two water molecules accompanied by a structural rearrangement, thus giving an almost trigonal-prismatic (TP) iron(FII) semiclathrochelate. It easily undergoes a cross-linking with CH3B(OH)2, resulting in the elimination of H+ ion and in the formation of a macrobicyclic structure. In contrast, the analogous scheme for its macrobicyclic tris-octoximate analog was found to contain up to three initial stages affecting the overall synthesis reaction rate. The rates of acidic decomposition of the above clathrochelates were found to be also affected by the nature of their ribbed substituents. Therefore, the single crystal XRD experiments were performed in order to explain these results. The difference in the kinetic schemes of a formation of the boron-capped iron(II) tris-nioximates and tris-octoximates is explained by necessity of the substantial changes in a geometry of the latter ligand synthon, caused by its coordination to the iron(II) ion, due to both the higher distortion of the FeN6-coordination polyhedra, and the intramolecular sterical clashes in the molecules of the macrobicyclic iron(II) tris-octoximates
Binuclear iron(II) cage complexes as electrocatalysts of hydrogen evolution reaction in different hydrogen-producing systems
A New Series of Cobalt and Iron Clathrochelates with Perfluorinated Ribbed Substituents
The study tackles one of the challenges
in developing platinum-free
molecular electrocatalysts for hydrogen evolution, which is to seek
for new possibilities to ensure large turnover numbers by stabilizing
electrocatalytic intermediates. These species are often much more
reactive than the initial electrocatalysts, and if not properly
stabilized by a suitable choice of functionalizing substituents, they
have a limited long-time activity. Here, we describe new iron and
cobaltÂ(II) cage complexes (clathrochelates) that in contrast to many
previously reported complexes of this type do not act as electrocatalysts
for hydrogen evolution. We argue that the most probable reason for
this behavior is an excessive stabilization of the metalÂ(I) species
by perfluoroaryl ribbed groups, resulting in an unprecedented long-term
stability of the metalÂ(I) complexes even in acidic solutions