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The reaction of [Na][C2B8H11] with anhydrous FeCl2 in THF affords a mixture of DD/LL and MESO isomers of anionic paramagnetic commo-ferracarborane [Ph3PR][commo-1,1′-Fe(closo-2,4-C2B8H10)2] (MESO, R = Me: 1a; MESO, Et: 1b; DD/LL, R = Me: 2a; DD/LL, R = Et: 2b) with unusual closo geometry. Both: DD/LL and MESO isomers were successfully isolated and their structures were determined using X-Ray diffraction studies. Paramagnetic properties were confirmed with EPR-spectra as well as oxidative-reductive properties were investigated using cyclic voltammetry. It was shown that facile DD/LL → MESO and MESO → DD/LL transformation leading to equilibrium in CH2Cl2 solution occurs. Quantum chemical calculations of the isomer-to-isomer transformations were performed. Ferra-copper zwitterionic complexes [3,3′,6,7′-exo-{Ph3PCu}-3,3′,6,7′-(µ-H)4-commo-1,1′-Fe(2,4-C2B8H8)2] and [3,3′,6,6′-exo-{Ph3PCu}-3,3′,6,6′-(µ-H)4-commo-1,1′-Fe(2,4-C2B8H8)2] were synthesized and their structures were determined by X-Ray diffraction studies.

The use of improved protocol for the reaction of rhodium acetylacetonate complexes (diene)RhAcac [diene is 1,5-cyclooctadiene or norbornadiene] with exo-nido-ruthenacarboranes 5,6,10-[RuCl(PPh3)2]-5,6,10-(μ-H)3-10-H-7,8-R2-7,8-C2B8H6 (R = H or Me) allowed us to synthesize three new binuclear complexes, wherein the ruthenium atom preserved exo-position and the rhodium-containing moiety coordinated to the open pentagonal face of exo-nido-complex. In addition, one known bimetallacarborane was also prepared for the evaluation of synthetic efficiency of the new procedure.

Treatment of [3-Cl-3,3,8-[Ph2P(CH2)nPPh-µ-(C6H4-ortho)]-1,2-Me2-closo-3,1,2-RuIIIC2B9H8] (1, n = 3; 2, n = 4) with an excess of KOH in a 1:1 benzene/methanol mixture at room temperature in air affords new dioxygen closo-ruthenacarborane complexes [3-(η2-O2)-3,3,8-[Ph2P(CH2)nPPh-µ-(C6H4-ortho)]-1,2-Me2-closo-3,1,2-RuIIIC2B9H8] (3, n = 3) and (4, n = 4) in 42.5% and 45.8% yield respectively. The structures of dioxygen complexes 3 and 4 were established by single-crystal X-ray diffraction. The IR and multinuclear NMR data [1H, 13C{1H}, 31P{1H} and 11B{1H}] along with 2D HSQC correlation spectra for the new dioxygen closo-ruthenacarboranes are discussed.

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-Open image in new window (n = 3, 4; R = H or Me), and bis(o-cycloboronated) Open image in new window (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.

The heating of a mixture of 14-e [Ph2P(CH2)nPPh2]FeCl2 (n = 3 or 2) with the [K]+ salt of the [nido-7,8-C2B9H12]− mono-anion under gentle reflux in benzene affords either the paramagnetic (17-electron) complex [3,3-(dppp)-3-Cl-closo-3,1,2-FeC2B9H11] isolated in 15% yield or a mixture of the paramagnetic complex [3,3-(dppe)-3-Cl-closo-3,1,2-FeC2B9H11] (46% yield) and the diamagnetic complex [commo-8,8′-μ-(Ph2PCH2CH2PPh2)-3,3′-Fe{1,2-C2B9H10}2] (10% yield). All three novel ferracarboranes were characterized by spectroscopic (EPR or NMR) data and single-crystal X-ray diffraction.

Reactions of [ exo -5,6,10-{Cl(Ph 3 P) 2 Ru}-5,6,10-(μ-H) 3 -10-H- nido -7,8-C 2 B 9 H 8 ] ( 1 ) with 1,5-bis(diphenylphosphino)pentane ( 2 ) in benzene either at ambient temperature for ca 2 days or under gently reflux for 30 min in anaerobic conditions both proceed with the replacement of PPh 3 ligands on the ruthenium center with the diphosphine to form diamagnetic (18-electron) closo complex [3,3-{κ 2 -{Ph 2 P(CH 2 ) 5 PPh 2 }}-3-Cl-3-H- closo -3,1,2-RuC 2 B 9 H 11 ] ( 3 ). On heating in benzene, 3 in the presence of a small amount of CCl 4 affords stable paramagnetic (17-electron) species [3,3-{κ 2 -{Ph 2 P(CH 2 ) 5 PPh 2 }}-3-Cl- closo -3,1,2-RuC 2 B 9 H 11 ] ( 5 ) along with traces of ortho -phenylenecycloboronated closo complex, ( 7 ). The latter complex was prepared in higher yields by thermal treatment of either 3 or 5 under more severe conditions in toluene at 110 °C. Thermolysis of 7 in boiling toluene in the presence of a small amount of CCl 4 afforded the new paramagnetic complex ( 8 ), featuring bis( ortho -cycloboronation) of both P-phenyl groups located at the same phosphorus atom of the ruthenium bound dppt ligand; a minor amount of chloro-cage-substituted complex ( 9 ) was also isolated from the latter reaction as the by-product. All new closo -ruthenacarboranes obtained were characterized by a combination of analytical, multinuclear NMR (for even-electron species) or EPR (for odd-electron species) data and, in addition, by single-crystal X-ray diffraction studies of three paramagnetic complexes 5 , 7 and 8 .

The reaction of the ruthenacarborane exo - nido -5,6,10-[Cl(Ph 3 P) 2 Ru]-5,6,10-(m-H) 3 -10-H-7,8-(Ph) 2 -7,8-C 2 B 9 H 6 with phenylacetylene in dichloromethane in the presence of triethylamine at ambient temperature affords exo - nido -5,6,10-[(Ph 3 P) 2 Ru]-5,6-(μ-H) 2 -10-[μ-(PhC=CH)]-10-H-7,8-(Ph) 2 -7,8-C 2 B 9 H 6 containing vinylene bridge group between carborane framework and ruthenium atom. Structure of the complex has been determined by X-ray diffraction study.

Reactions of [3,3-(PPh3)2-3-Cl-3-H-3,1,2-closo-RuC2B9H11] (1) and its exo-nido isomer [exo-5,6,10-{Ru(Ph3P)2Cl}-5,6,10-(μ-H)3-10-H-7,8-nido-C2B9H8] (2) with NH4PF6 in methanol or ethanol solution followed by heating in the presence of an excess of phenylacetylene (3) affords a mixture of two isomeric closo species [3,3-{(1′-3′-η3):(5′,6′-η2)-ortho-C6H4PPh2CHC(Ph)CHCHPh}-8-(σ–CH CHPh)-3,1,2-closo-RuC2B9H10] (4) and [3,3-{(1′-3′-η3):(5′,6′-η2)-ortho-C6H4PPh2CHC(Ph)CHCHPh}-4-(σ–CH CHPh)-3,1,2-closo-RuC2B9H10] (5) in which boron vertexes in β- and α-sites with respect to the cage carbons bear the (E)–CH CHPh group. The X-ray diffraction study of 4 together with the multinuclear NMR data for 4 and 5 revealed that such an unusual η3:η2-phosphacarbocyclic ligand in both isomeric complexes is formed by specific insertion of the initially metal-bound PPh3 group into the chain of two alkyne molecules coupled in a “head-to-tail” fashion around the metal vertex.

The heating of the 18-electron complex [3,3-(dppb)-3-H-3-Cl-closo-3,1,2-RuC(2)B(9)H(11)] (3) in benzene at 80 °C in the presence of a small amount of CCl(4) as initiator afforded paramagnetic 17-electron species [3,3-(dppb)-3-Cl-closo-3,1,2-RuC(2)B(9)H(11)] (4) along with minor amounts of two P-phenylene ortho-cycloboronated derivatives [3-Cl-3,3,8-{Ph(2)P(CH(2))(4)PPh-μ-(C(6)H(4)-ortho)}-closo-3,1,2-RuC(2)B(9)H(10)] (5) and [3,7-Cl(2)-3,3,8-{Ph(2)P(CH(2))(4)PPh-μ-(C(6)H(4)-ortho)}-closo-3,1,2-RuC(2)B(9)H(10)] (6) in total yield of ca. 80%. The heating of either 3 or 4 in toluene at 95 °C in the absence of CCl(4) led to the selective formation of 5, which was isolated in 64% and 46% yield, respectively. Thermolysis of 3 at higher temperatures (boiling toluene, 110 °C) gives novel paramagnetic species [3-Cl-3,3,7,8-{Ph(2)P(CH(2))(4)P-μ-(C(6)H(4)-ortho)(2)}-closo-3,1,2-RuC(2)B(9)H(9)] (7) featuring bis(ortho-cycloboronation) of both P-phenyl groups at the same phosphorus atom of the ruthenium-bound dppb ligand. All new paramagnetic complexes 4-7, as well as starting diamagnetic species 3, were characterized by single-crystal X-ray diffraction and, in addition, by EPR spectroscopic studies of odd-electron complexes. Ruthenacarboranes 3-5 and 7 all display high efficiency as catalysts for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). Complex 5 gave the best catalyst performance in terms of polydispersity; the PDI (M(w)/M(n)) of the polymer samples is as low as 1.15.