Kinetics and thermodynamics of the template synthesis and of the acidic decomposition of the methylboron-capped iron(II) tris-1,2-dioximates—the clathrochelate derivatives of six (nioxime)- and eight (octoxime)-membered alicyclic ligand synthons—were 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(II) 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.
Reaction of the template synthesis of the methylboron-capped iron(II) tris-heptoximate clathrochelate on Fe 2 + ion as a matrix was found to proceed in the quantitative yield in diluted aqueous-organic solutions. This complex is intensively colored in the visible range, whereas the initial ligand synthons are optically silent, thus allowing to photometric study the kinetics of its synthesis and acidic decomposition reactions. Template condensation of the corresponding chelating and capping ligand synthons gave a solid form of this macrobicyclic complex, which was characterized using modern spectral methods and by the single-crystal X-ray diffraction (XRD) experiment. Kinetic schemes and parameters of the aforemen-tioned reactions for the methylboron-capped clathrochelates, the derivatives of six-(H 2 Nx), seven-(H 2 Gx) and eight(H 2 Ox)membered alicyclic α-dioximes, are dramatically affected by their alicyclic ring size. If the general schemes of their formation persist, those for H 2 Nx and H 2 Gx contain a rate-determining stage, whereas that for H 2 Ox has three initial consecutive stages with close rates. Passing from H 2 Nx to H 2 Gx caused a decrease in the synthesis reaction rates of their macrobicyclic derivatives by approximately three orders of magnitude. These kinetic effects were explained using the XRD data for the initial α-dioximes and for their methylboron-capped macrobicyclic derivatives.
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