I. T. Chizhevsky

Carborane complexes of ruthenium with long-chain diphosphine ligands as effective catalysts of controlled radical polymerization

Catalytic systems based on carborane complexes of ruthenium with long-chain diphosphine ligands, such as 1,4-bis(diphenylphosphino)butane and 1,5-bis(diphenylphosphino)pentane, are prepared for the controlled radical polymerization of methyl methacrylate. It is found that the used metallacarboranes can catalyze polymerization initiated by both carbon tetrachloride and 2,2′-azo-bis(isobutyronitrile). It is shown that closo-ruthenacarborane with 1,5-bis(diphenylphosphino)pentane 3,3-[PPh2(CH2)5PPh2]-3-Cl-3,1,2-closo-RuC2B9H11 and its o-phenylenecycloborated derivatives make it possible to conduct polymerization at higher rates than those attained with the use of previously synthesized complexes based on diphosphines with a smaller length of the hydrocarbon fragment. The relationship between the redox potential of the complex and the efficiency of control over molecular-mass characteristics of the polymers is analyzed. Experiments reveal that the addition of small amounts of aliphatic amines causes a considerable increase in the rate of polymerization and leads to a decrease in the concentration of the catalyst with retention of a high degree of control over the process.

Controlled synthesis of poly(methyl methacrylate) catalyzed by 17-electron closo-ruthenacarboranes and aliphatic amines

The radical polymerization of methyl methacrylate catalyzed by systems based on paramagnetic closo-ruthenacarboranes with diphosphine ligands is studied. Effects of the structure of metallocomplex catalysts on the rate of polymerization and the molecular-mass characteristics of the polymers are investigated. It is shown that the addition of amines to the reaction solution makes it possible to reduce the concentration of metallacarborane catalysts to hundredths of a percent, while control over the polymerization process remains at a high level.

Study of paramagnetic iron and ruthenium metallacarboranes using cyclic voltammetry and matrix-activated laser desorption/ionization time-of-flight spectrometry

The complex investigation of paramagnetic (17-electron) iron and ruthenium closo-metallacarboranes with chelate diphosphine ligands 3,3-(Ph2P(CH)nPPh2)-3-Cl-closo-3,1,2-MC2B9H11 (M = Fe, n = 2, 3; Ru, n = 4), o-phenylenecycloboronated 3-Cl-3,3,8- (n = 3, 4; R = H or Me), and bis(o-cycloboronated) (n = 4, 5) was performed using cyclic voltammetry and matrix-activated laser desorption/ionization time-of-flight (MALDI-TOF) spectrometry. Some diamagnetic iron and ruthenium exo-nido- and commo-complexes were studied using the same methods. A relationship between the redox potentials of the metallacarborane complexes and their stability and transformations under the MALDI-TOF conditions was established.

Formation of “three-bridge” cobalt-copper commo-cluster with the (B-H)3...Cu bond in the reaction of [Cs][commo-3,3′-Co(1,2-C2B9H11)2] with copper(i) and copper(ii) compounds

Zwitterionic 4,8,8′-exo-{Ph3PCu}-4,8,8′-(μ-H)3-commo-3,3′-Co(1,2-C2B9H9)-(1′,2′-C2B9H10) and ionic [(PPh3)3Cu][commo-3,3′-Co(1,2-C2B9H11)2 complexes were synthesized in moderate yields by the reaction of anionic commo-complex [Cs][commo-3,3′-Co-(1,2-C2B9H11)2]) in a CH2Cl2 solution with anhydrous CuCl2 or CuCl in the presence of PPh3. The complexes were also synthesized by alternative methods and characterized by NMR and X-ray diffraction methods.

First cupracarborane commo-clusters based on the medium-cage nido-5,6-C2B8H12-carborane and molecular structure of [Ph3PEt][commo-9,9′-Cu(nido-7,8-C2B8H11)2]

A reaction of anhydrous CuCl2 with Na salts of the medium-cage carborane [7-X-nido-5,6-C2B8H10]−(X = H or I) derivatives in THF leads to new cupracarborane commo-clusters, [commo-9,9′-Cu(nido-7,8-C2B8H11)2]− and [commo-9,9′-Cu(11-I-nido-7,8-C2B8H10)2]−, in moderate yields. The clusters were isolated as stable [Ph3PEt]+ salts and characterized by 1H, 31P{1H}, and 11B/11B{1H} NMR spectroscopy and X-ray crystallography (for the unsubstituted derivative). The use in this reaction of the reducing agent Na2SO3 considerably increases the yields of both complexes from 25 and 18% to 74 and 68%, respectively.

Metallacarborane clusters based on the middle-cage carborane [5,6-nido-C2B8H12]. Synthesis and the thermal isonido-to-closo rearrangement of the anionic complex [PPN][commo-1,1′-Rh(7-MeO-isonido-2,4-C2B8H9)-(isonido-2,4-C2B8H10)]

The reaction of the middle-cage carborane 5,6-nido-C2B8H12 with the dimeric rhodium complexes [(η2-C8H14)2RhCl]2 or [(η4-C8H12)RhCl]2 in a MeOH/C6H6 mixture gave the anionic commo-rhodacarborane [PPN][commo-1,1′-Rh(isonido-2,4-C2B8H10)2] (as a mixture of meso and dd/ll isomers) and its 7-B-methoxylated derivative [PPN][commo-1,1′-Rh(7-MeO-isonido-2,4-C2B8H9)(isonido-2,4-C2B8H10)] in moderate yields. The latter was subjected to the thermal isonido-to-closo rearrangement to form the new commo-cluster [PPN][commo-1,1′-Rh(closo-2,3-C2B8H9OMe)(closo-2,3-C2B8H10)]. The newly synthesized compounds were characterized by NMR spectroscopy and X-ray diffraction.

Synthesis of functional polymers based on methacrylic monomers using ruthenium carborane complexes

The radical polymerization of isobornyl acrylate, isobornyl methacrylate, and tert-butyl methacrylate under conditions of catalysis by ruthenium compounds is studied. It is found that the catalytic system based on the carborane complex of ruthenium 3,3-{[1,1-diphenyl-6-phenyl-6-(6,8-(o-phenylene))]-1,6-diphosphahexane}-3-chloro-closo-3,1,2-dicarbollyl ruthenium and isopropylamine makes it possible to conduct the controlled free-radical polymerization of the mentioned monomers via the Atom Tranfer Radical Polymerization mechanism. The molecular weights of the polymers linearly increase, while their polydispersity coefficients linearly decrease during the process. Block copolymers are synthesized on the basis of the above monomers, and the molecular-weight characteristics and glass-transition temperatures of these copolymers are measured.

Ruthenium carborane complexes: a relationship between the structure, electrochemical properties, and reactivity in catalysis of polymerization processes*

The ruthenacarborane complexes of the exo-nido- and closo-structure, namely, diamagnetic exo-nido-5,6,10-[RuCl(PPh3)2]-5,6,10-(μ-H)3-10-H-7,8-(CH3)2-7,8-C2B9H6, 3,3-[Ph2P(CH2)nPPh2]-3-H-3-Cl-closo-3,1,2-RuC2B9H11 (n = 4, 5), paramagnetic 3,3-[Ph2P(CH2)nPPh2]-3-Cl-closo-3,1,2-RuC2B9H11 (n = 2–5), and their some ortho-phenylenecycloboronated derivatives, were studied by cyclic voltammetry. All chelate closo-complexes are characterized by reversible redox transitions, while the exo-nido-complex is liable to irreversible oxidation. Shortening of the methylene link in the diphosphine ligand of closo-ruthenacarboranes and/or the introduction of ortho-phenylenecycloboronated moieties and methyl substituents to the carbon atoms of the {C2B9} ligand lead to a decrease in the redox potential and electron density redistribution to the metal atom. A comparison of the experimental results on methyl methacrylate polymerization in the presence of the catalytic systems based on the studied metallacarboranes with the data on their electrochemical characteristics suggests that the efficiency of using the ruthenium complexes as catalysts is mainly determined by steric factors.

Synthesis of metallacarborane ruthenium(ii) and ruthenium(iii) complexes with chelate 1,3-bis(diphenylphosphino)propane ligand and their mutual transformation in one-electron redox reactions

The first example of 12-vertex metallapolyhedra, namely, tris-phosphorus-containing closo-metallacarborane ruthenium(II) cluster , was synthesized and structurally studied. A principal possibility of the use of aliphatic amines as one-electron reducing agents converting carborane ruthenium(III) complexes to structurally close ruthenium(II) compounds was experimentally demonstrated.

Efficient methods for the preparation of bromine-containing exo-nido- and closo-ruthenacarborane clusters

An efficient method for the synthesis of bromine-containing exo-nido-clusters of a general formula exo-5,6,10-[Br(Ph3P)2Ru]-5,6,10-(μ-H)3-10-H-7,8-R2-nido-7,8-C2B9H6 (R = H, Me) was developed using the reactions of RuBr2(PPh3)3 with [K][7,8-R2-7,8-nido-C2B9H10]. Replacement of the phosphine ligands in the starting exo-nido-cluster (R = H) with the diphosphine ones afforded a series of diamagnetic (18-electron) closo-bromoruthenacarboranes, 3-Br-3,3-[κ2-Ph2P(CH2)nPPh2]-3-H-closo-3,1,2-RuC2B9H11 (n = 3−5). A mild thermal method of the halide ligands exchange (Cl → Br) upon heating of diamagnetic chlorine-containing complexes 3,3-[κ2-Ph2P(CH2)nPPh2]-3-H-3-Cl-closo-3,1,2-RuC2B9H11 (n = 3−5) with excess of CBr4 in benzene (70–80 °C) was suggested for the synthesis of paramagnetic (17-electron) bromine-containing ruthenacarboranes, 3-Br-3,3-[κ2-Ph2P(CH2)nPPh2]-closo-3,1,2-RuC2B9H11 (n = 3, 4) or 3-Br-3,3,8-[κ2-Ph2(CH2)5PPh]-μ-. Paramagnetic chlorine-containing clusters 3-Cl-3,3-[κ2-Ph2P(CH2)nPPh2]-closo-3,1,2-RuC2B9H11 (n = 2−4) were alternatively used as the starting compounds in the exchange reaction. Complexes with dppp and dppb (dppp is 1,3-bis(diphenylphosphino)propane, dppb is 1,4-bis(diphenylphosphino)butane) were used as examples to study the thermal reactions (toluene, 110 °C) leading in the presence of CBr4 to paramagnetic mono(P-o-phenylene)- and bis(P,P-o-phenylene)cycloboronated clusters, 3-Br-3,3,8-[κ2-Ph2(CH2)nPPh]-μ- and 3-Br-3,3,4,8-[κ2-Ph2(CH2)nP]-μ- (n = 3, 4). The compounds obtained were characterized by NMR spectroscopy (in the case of diamagnetic complexes), ESR spectroscopy and mass spectrometry (in the case of paramagnetic compounds). X-ray diffraction experiments were carried out for two cycloboronated paramagnetic complexes.