Application of the allylboration reaction of terminal acetylenes with allyldihaloboranes for the preparation of capping agents for the synthesis of precursors of polymeric iron(II) clathrochelates

Template condensation on the iron(II) ion matrix of three cyclohexanedione-1,2-dioxime molecules with esters of 1,4-pentadienylboronic acids afforded apically functionalized bis(diolefin)-containing clathrochelates, which are new potential monomers for the preparation of functionalized carbochain polymers. The complexes were characterized by the data of elemental analysis, UV-Vis spectroscopy, ¹H, ¹¹B, and ¹³C NMR spectroscopy, ⁵⁷Fe Mössbauer spectroscopy, IR spectroscopy, and MALDI-TOF mass spectrometry. The molecular and crystal structures of the clathrochelates synthesized and the electron density distribution on a molecule of one of them were determined by X-ray diffraction analysis.     

Allylboranes and the synthesis of diamond molecules

The review summarizes our data on the synthesis of selected allylic, bicyclic, and highly strained cage boranes, investigations of their physicochemical properties, and applications of these compounds. Procedures for the construction of boron polyhedral systems, transformations of 1-boraadamantane compounds into 1-hydroxyadamantanes and 1-azaadamantanes, and the synthesis of chiral derivatives of 1-boraadamantane and 3-borabicyclo[3.3.1]nonane are considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 788–800, April, 2008.     

An unusual mechanism of polymerization of MMA initiated by ammonia-triisobutyl borane and atmospheric oxygen

The kinetics of polymerization of methyl methacrylate in vacuum initiated by ammonia-triisobutyl borane (iso-Bu₃B · NH₃) oxidized in air is studied. It is shown that the rate of reaction shows the first order with respect to the monomer concentration and a variable order with respect to the initiator concentration; the process is characterized by a low activation energy. It is demonstrated that polymerization proceeds according to a two-step mechanism. The mechanism of polymerization initiation and reinitiation is investigated via ESR spectroscopy, and it is found that one primary radical generated during initiation can form up to 200 substantial chains during the subsequent chain-transfer process.     

Structure and Bonding Nature of the Strained Lewis Acid 3-Methyl-1-boraadamantane: A Case Study Employing a New Data-Analysis Procedure in Gas Electron Diffraction

Base-free 3-methyl-1-boraadamantane was synthesized by starting from its known THF adduct, transforming it to a butylate-complex with n-butyllithium, cleaving the cage with acetyl chloride to give 3-n-butyl-5-methyl-7-methylene-3-borabicyclo[3.3.1]nonane and closing the cage again by reacting the latter with dicyclohexylborane. The identity of 3-methyl-1-boraadamantane was proven by (1) H, (11) B and (13) C?NMR spectroscopy and elemental analysis. The experimental equilibrium structure of the free 3-methyl-1-boraadamantane molecules has been determined at 100?°C by using gas-phase electron diffraction. For this structure determination, an improved method for data analysis has been introduced and tested: the structural refinement versus gas-phase electron diffraction data (in terms of Cartesian coordinates) with a set of quantum-chemically derived regularization constraints for the complete structure under optimization of a regularization constant, which maximizes the contribution of experimental data while retaining a stable refinement. The detailed analysis of parameter errors shows that the new approach allows obtaining more reliable results. The most important structural parameters are: r(e) (B-C)(av) =1.556(5)??, ${\angle }$(e) (C-B-C)(av) =116.5(2)°. The configuration of the boron atom is pyramidal with ${\sum \angle }$(C-B-C)=349.4(4)°. The nature of bonding was analyzed further by applying the natural bond orbital (NBO) and atoms in molecules (AIM) approaches. The experimentally observed shortening of the B?C bonds and elongation of the adjacent C?C bonds can be explained by the σ(C-C)→p(B) hyperconjugation model. Both NBO and AIM analyses predict that the B?C bonds are significantly bent in the direction out of the cage.     

New efficient boron-containing initiators of methyl methacrylate radical polymerization

An efficient method for methyl methacrylate radical polymerization by tri-n-propyl-, triisopropyl-, and triisobutylborane ammonia complexes, including the addition of a boron-containing initiating agent into the monomer in air, was developed. An advantage of this method is that the reaction occurs at room temperature, requires no peroxide components, and leads to polymers with enhanced thermal stability.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2120–2125, October, 2004.     

Macrocyclization of the semiclathrochelate o -carboranylboronate and n -butylboronate iron(II ) oximehydrazonates: synthesis and structure of clathrochelate products and unexpected allosteric effect of the apical substituent

The template condensation of diacetylmonooxime hydrazone (HDXO) with n-butylboronic acid and dimethyl ester of o-carboranyldiboronic acid on the iron(II) ion matrix afforded the [Fe(DXO)₃(BBu)](BF₄) and [Fe(DXO)₃(Bo-carb)](BF₄) semiclathrochelates. The H⁺-ion-catalyzed macrocyclization of these precursors with an excess of formaldehyde and triethyl orthoformate (TOF) resulted in the corresponding macrobicyclic complexes. In the case of o-carboranylboronate semiclathrochelate, the macrocyclization with TOF gave the clathrochelate with the previously unknown syn,syn,anti-orientation of the ethoxy substituents relative to the 1,3,5-triazacyclohexane capping fragment. The complexes obtained were characterized using elemental analysis, IR, UV-Vis, MALDI-TOF mass, ¹H, ¹¹B, and ¹³C NMR, and ⁵⁷Fe M?ssbauer spectroscopies and X-ray crystallography. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1724–1731, September, 2007.