Novel ruthenium( ii ) and ( iii ) carborane complexes with diphosphine ligands and their application in radical polymeri
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Russian Chemical Bulletin, International Edition, Vol. 69, No. 8, pp. 1520—1529, August, 2020
Novel ruthenium(II) and (III) carborane complexes with diphosphine ligands and their application in radical polymerization* I. D. Grishin, N. A. Knyazeva, and A. M. Penkal´ N. I. Lobachevsky National Reseach State University of Nizhny Novgorod, 23 prosp. Gagarina, 603950 Nizhny Novgorod, Russian Federation. Fax: +7 (831) 462 3550. E-mail: [email protected] Ruthenium(II) and (III) carborane complexes containing XantPhos as a ligand were synthesized for the first time. It was shown that the reaction of the known complex exo-5,6,10[Cl(Ph3P)2Ru]-5,6,10-(-H)3-10-H-nido-7,8-C2B9H8 with a 10% molar excess of XantPhos in benzene at 80 C leads to a new closo-ruthenacarborane 3-Cl-3,3-[κ2-XantPhos]-closo-3,1,2RuC2B9H11, which can be easily converted to the corresponding acetonitrile complex 3-CH3CN3,3-[κ2-XantPhos]-closo-3,1,2-RuC2B9H11 by the reaction with isopropylamine in a dichloromethane—acetonitrile solvent mixture at 40 C. These compounds, as well as previously synthesized ruthenium(II) carborane complexes, were used as a basis for new catalyst systems allowing to conduct controlled radical polymerization at high rates even at low catalyst loading. The specific features of methyl methacrylate polymerization under the action of the indicated catalyst systems were considered and the mechanism of the process was investigated. Key words: methyl methacrylate, XantPhos, ruthenacarboranes, amines, controlled radical polymerization, MALDI mass spectrometry.
Atom transfer radical polymerization (ATRP) is a powerful tool for preparing homo- and copolymers with specified molecular weight characteristics, architecture, and properties.1—8 This process is based on the reversible transfer of a halogen atom between a polymer chain and a transition metal complex, which is accompanied by single electron transfer and a change in the oxidation state of the metal (Scheme 1). Scheme 1
The ATRP is distinguished by the procedural simplicity of implementation, as well as by a large library of monomers and initiators, which can be used to obtain macromolecules with a desired architecture. In contrast to two other known methods of controlled radical poly* Based on the materials of the International Conference "Chemistry of Organoelement Compounds and Polymers 2019" (November 18—22, 2019, Moscow, Russia).
merization, namely, stable free-radical polymerization9—12 and RAFT,13,14 which require the introduction of stoichiometric amounts of regulating agents with respect to the initiator, ATRP in some cases allows the synthesis of macromolecules using metal complex catalysts at concentrations at the level of parts per million (ppm), thereby significantly reducing the cost of polymer production.1 Despite the fact that by now quite a number of catalyst systems for carrying out ATRP have been proposed, the development of new catalysts characterized by higher efficiency and stability under conditions of the process remains an important issue. According
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