Functionalization of closo‐Borates via Iodonium Zwitterions

A simple method for the functionalization of closo‐borates [closo‐B₁₀H₁₀]^2? ( 1 ), [closo‐1‐CB₉H₁₀]^? ( 2 ), [closo‐B₁₂H₁₂]^2? ( 3 ), [closo‐1‐CB₁₁H₁₂]^? ( 4 ), and [3,3′‐Co(1,2‐C₂B₉H₁₁)₂]^? ( 5 ) is described. Treatment of the anions and their derivatives with ArI(OAc)₂ gave aryliodonium zwitterions, which were sufficiently stable for chromatographic purification. The reactions of these zwitterions with nucleophiles provided facile access to pyridinium, sulfonium, thiol, carbonitrile, acetoxy, and amino derivatives. The synthetic results are augmented by mechanistic considerations.     

Synthesis of hetero-substituted derivatives of cobalt bis(1,2-dicarbollide)

A new approach to synthesis of hetero-substituted derivatives of cobalt bis(1,2-dicarbollide) was proposed. The approach involves stepwise introduction of functional groups into different dicarbollide ligands. Halogenation of the monohydroxy derivative [8-OH-3,3??-Co-(1,2-C₂B₉H₁₀)(1??,2??-C₂B₉H₁₁)]^? gave the corresponding halogen hydroxy derivatives [8-OH-8??-X-3,3??-Co(1,2-C₂B₉H₁₀)₂]^? (X = Cl, Br, and I). Reactions of 8,8??-??-iodonium-3-commo-cobaltbis(1,2-dicarba-closo-dodecaborate) [8,8??-I-3,3??-Co(1,2-C₂B₉H₁₀)₂] with chloroform and 1,2-dibromoethane yielded the mixed halides [8-Y-8??-I-3,3??-Co(1,2-C₂B₉H₁₀)₂]^? (Y = Cl and Br).     

Carborane Substituents Promote Direct Electrophilic Insertion over Reduction–Metalation Reactions

Two‐electron reduction of 1,1′‐bis(o‐carborane) followed by reaction with [Ru(η‐mes)Cl₂]₂ affords [8‐(1′‐1′,2′‐closo‐C₂B₁₀H₁₁)‐4‐(η‐mes)‐4,1,8‐closo‐RuC₂B₁₀H₁₁]. Subsequent two‐electron reduction of this species and treatment with [Ru(η‐arene)Cl₂]₂ results in the 14‐vertex/12‐vertex species [1‐(η‐mes)‐9‐(1′‐1′,2′‐closo‐C₂B₁₀H₁₁)‐13‐(η‐arene)‐1,13,2,9‐closo‐Ru₂C₂B₁₀H₁₁] by direct electrophilic insertion, promoted by the carborane substituent in the 13‐vertex/12‐vertex precursor. When arene=mesitylene (mes), the diruthenium species is fluxional in solution at room temperature in a process that makes the metal–ligand fragments equivalent. A unique mechanism for this fluxionality is proposed and is shown to be fully consistent with the observed fluxionality or nonfluxionality of a series of previously reported 14‐vertex dicobaltacarboranes.     

Synthesis,characterization, X‐ray crystal structure and in vitro antitumour activity of sodium bis(2‐(3′,6′,9′‐trioxadecyl)‐1,2‐dicarba‐closo‐dodecaborane‐1‐carboxylato)triphenylstannate

Sodium bis[2‐(3′,6′,9′‐trioxadecyl)‐1,2‐dicarba‐closo‐dodecaborane‐1‐carboxylato]triphenylstannate, [(CH₃OCH₂CH₂OCH₂CH₂OCH₂CH₂)‐1,2‐C₂B₁₀H₁₀‐9‐COO)₂SnPh₃]^? Na⁺, compound 1, was synthesized by the 1:1 condensation of triphenyltin(IV) hydroxide with 2‐(3′,6′,9′‐trioxadecyl)‐1,2‐dicarba‐closo‐dodecaborane‐1‐carboxylic acid and crystallized in the presence of sodium bicarbonate. Its structure was determined by spectroscopy, elemental analysis and X‐ray diffraction. The structure of 1 consists of trigonal bipyramidal [Sn(Ph)₃(L)₂]^? anions and Na⁺ cations coordinated by oxygen atoms of polyoxaalkyl chains of different stannate anions, forming cation–anion chains elongated along the c axis. Compound 1 is significantly more active in vitro against seven tumour cell lines of human origin than 5‐fluorouracil, cis‐platin, carboplatin, and previously reported organotin carboranecarboxylates, but is less active than organotin polyoxaalkylcarboxylates. Copyright © 2004 John Wiley & Sons, Ltd.     

Additive Tuning of Redox Potential in Metallacarboranes by Sequential Halogen Substitution

The first artificially made set of electron acceptors is presented that are derived from a unique platform Cs[3,3′‐Co(C₂B₉H₁₁)₂], for which the redox potential of each differs from its predecessor by a fixed amount. The sequence of electron acceptors is made by substituting one, two, or more hydrogen atoms by chlorine atoms, yielding Cs[3,3′‐Co(C₂B₉H_11?yCl_y)(C₂B₉H_11?zCl_z)]. The higher the number of chlorine substituents, the more prone the platform is to be reduced. The effect is completely additive, so if a single substitution implies a reduction of 0.1 V of the redox potential of the parent complex, then ten substitutions imply a reduction of 1 V.     

Versatile reactivity of half-sandwich Ir and Rh complexes toward carboranylamidinates and their derivatives: synthesis, structure, and catalytic activity for norbornene polymerization

Synthesis, structure, and reactivity of carboranylamidinate‐based half‐sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ‐Cl)Cl}₂] (M=Ir, Rh; Cp*=η⁵‐C₅Me₅) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18‐electron complexes [Cp*IrCl(Cab^N‐DIC)] ( 1 a ; Cab^N‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHiPr)]), [Cp*RhCl(Cab^N‐DIC)] ( 1 b ), and [Cp*RhCl(Cab^N‐DCC)] ( 1 c ; Cab^N‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHCy)]). A series of 16‐electron half‐sandwich Ir and Rh complexes [Cp*Ir(Cab^N′‐DIC)] ( 2 a ; Cab^N′‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NiPr)]), [Cp*Ir(Cab^N′‐DCC)] ( 2 b , Cab^N′‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NCy)]), and [Cp*Rh(Cab^N′‐DIC)] ( 2 c ) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab^N,S‐DIC)], [Cp*M(Cab^N,S‐DCC)] (M=Ir 3 a , 3 b ; Rh 3 c , 3 d ), formed through BH activation, are obtained by reaction of [{Cp*MCl₂}₂] with carboranylamidinate sulfides [RN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHR)]S^? (R=iPr, Cy), which can be prepared by inserting sulfur into the C? Li bond of lithium carboranylamidinates. Iridium complex 1 a shows catalytic activities of up to 2.69×10⁶ g_PNB ${{\rm{mol}}_{{\rm{Ir}}}^{ - {\rm{1}}} }Synthesis, structure, and reactivity of carboranylamidinate-based half-sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ-Cl)Cl}(2)] (M = Ir, Rh; Cp* = η(5)-C(5)Me(5)) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18-electron complexes [Cp*IrCl(Cab(N)-DIC)] (1?a; Cab(N)-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NHiPr)]), [Cp*RhCl(Cab(N)-DIC)] (1?b), and [Cp*RhCl(Cab(N)-DCC)] (1?c; Cab(N)-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10))(NHCy)]). A series of 16-electron half-sandwich Ir and Rh complexes [Cp*Ir(Cab(N')-DIC)] (2?a; Cab(N')-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NiPr)]), [Cp*Ir(Cab(N')-DCC)] (2?b, Cab(N')-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10)(NCy)]), and [Cp*Rh(Cab(N')-DIC)] (2?c) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab(N,S)-DIC)], [Cp*M(Cab(N,S)-DCC)] (M = Ir 3?a, 3?b; Rh 3?c, 3?d), formed through BH activation, are obtained by reaction of [{Cp*MCl(2)}(2)] with carboranylamidinate sulfides [RN=C(closo-1,2-C(2)B(10)H(10))(NHR)]S(-) (R = iPr, Cy), which can be prepared by inserting sulfur into the C-Li bond of lithium carboranylamidinates. Iridium complex 1?a shows catalytic activities of up to 2.69×10(6) g(PNB) mol(Ir)(-1) h(-1) for the polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst. Catalytic activities and the molecular weight of polynorbornene (PNB) were investigated under various reaction conditions. All complexes were fully characterized by elemental analysis and IR and NMR spectroscopy; the structures of 1?a-c, 2?a, b; and 3?a, b, d were further confirmed by single crystal X-ray diffraction.     

Synthesis of 12-vertex mixed ligand closo-cobaltacarborane complexes and molecular structure of [3,3-(Ph2P(CH2)2PPh2)-3-Cl-closo-3,1,2-CoC2B9H11]

A reaction of complexes CoCl₂(dppe) (dppe is the 1,2-bis(diphenylphosphino)ethane) or CoCl₂(dppp) (dppp is the 1,3-bis(diphenylphosphino)propane) with [K][7,8-nido-C₂B₉H₁₂] upon reflux in benzene led to the mixed ligand closo-cobaltacarboranes [3,3-(Ph₂P(CH₂) _n PPh₂)-3-Cl-closo-3,1,2-Co^IIIC₂B₉H₁₁] (n = 2 and 3, respectively) in moderate yields (34 and 16%). The structure of the 18-electron complexes in solution and the solid state was studied by NMR and IR spectroscopy, the structure in the case of the closo-complex with dppe-ligand was confirmed by X-ray crystallography.     

Unique Stereocontrol in Carborane Chemistry: Skeletal Alkylcarbonation (SAC) versus Exoskeletal Alkylmethylation (EAM) Reactions

Reactions between the arachno‐6,9‐C₂B₈H₁₄ ( 1 ) dicarbaborane and acyl chlorides, RCOCl ( 2 ), are subject to stereocontrol that completely changes the nature of the reaction products. While most chlorides produce the 8‐R‐nido‐7,8,9‐C₃B₈H₁₁ ( 3 ) tricarbollides (by skeletal alkylcarbonation=SAC), bulky RCOCls ( 2 ; where R=1‐adamantyl, 2 a ; 1‐mesityl, 2 b ; 9‐anthranyl, 2 c ; 1‐naphthyl, 2 d ) in 1,2‐dichloroethane (DCE) in the presence of triethylamine at 40–60 °C gave a series of entirely different 1‐R‐2‐CH₃‐closo‐1,6‐C₂B₈H₈ ( 4 ) dicarbaboranes upon acidification with conc. H₂SO₄ (by exosleletal alkylmehylation=EAM). Both types of reactions seem to proceed via a common [8‐R‐nido‐7,8,9‐C₃B₈H₁₀]^? ( 3^? ) anion which in the EAM case is unstable because of steric crowd and undergoes rearrangement via the isomeric [R‐nido‐7,8,10‐C₃B₈H₁₀]^? tricarbollide structures which, on protonation, undergo reductive extraction of one CH vertex to generate the 2‐CH₃ substituent in structure 4 .     

A boron-boron linked large metallacarborane cluster: Characterization and X-ray structure of 8,9′-[closo-{3-Co(η-C5H5)-1,2-C2B9H10}]2

The 8,9′-[closo-{3-Co(η⁵-C₅H₅)-1,2-C₂B₉H₁₀}]₂ (1) species, in which two large closo-CoC₂B₉ sub-clusters are connected by a B-B bond, is unexpectedly obtained from the reaction of closo-[3-Co(η⁵-C₅H₅)-1,2-C₂B₉H₁₁] with sulfur in the presence of aluminium chloride under reflux conditions. The solid state conformation of 1 seems to be the result of a pair of intramolecular C-H?H-B dihydrogen bonds between the protonic H atoms of the C₅H₅ fragment of a sub-cluster and the hydridic H atoms of the C₂B₉H₁₁ fragment in the other sub-cluster in 1.     

Polyol-Metall-Komplexe. 27. Bis-diolato-antimonate(III) mit Guanosin als Diol

Polyol Metal Complexes. 27. Bis-Diolato Antimonates(III ) with Guanosine as the Diol The complex anions of K₃[Sb^III(Guo1,2′,3′H_?3)₂] · 10 H₂O ( 1 ) and [Co(NH₃)₆][Sb^III(Guo1,2′,3′H_?3)₂] · 9 H₂O ( 2 ) are four-coordinate homoleptic bis(diolato)antimonate(III ) species. The guanosine trianions act as carbohydrate ligands through their cis-furanoidic ribosyl moiety, thus forming no nucleobase–metal bonds.     

Synthesis of new charge-compensated cobalt bis(1,2-dicarbollide) derivatives

New hetero-substituted charge-compensated cobalt bis(1,2-dicarbollide) derivatives were synthesized by the reaction of 8,8′-μ-iodo-3-commo-3-cobalta-bis(1,2-dicarba-closo-dodecaborane) [8,8′-μ-I-3,3′-Co(1,2-C₂B₉H₁₀)₂] with 1,4-thioxane, pyridine N-oxide, and tetrahydropyran. X-ray diffraction studies showed that the 8′-iodo-8-(pyridiniumoxy)eucosahydro-1,1′,2,2′-tetracarba-3-commo-cobalta-closo-tricosaborate molecule has the gauche-conformation (the substituents are turned with respect to each other by 69.2°). The positive charge is predominantly localized on the N(Py) atom.     

Synthesis and characterization of three dinuclear copper(I) complexes of 1,2‐bis(diphenylphosphino)‐1,2‐dicarba‐closo‐dodecaborane

Three dinuclear copper(I) complexes, [Cu₂(µ‐Cl)₂(1,2‐(PPh₂)₂‐1,2‐C₂B₁₀H₁₀)₂]·2CH₂Cl₂ ( 1 ), [Cu₂(µ‐Br)₂(1,2‐(PPh₂)₂‐1,2‐C₂B₁₀H₁₀)₂]·2THF ( 2 ) and {Cu₂(µ‐I)₂[1,2‐(PPh₂)₂‐1,2‐C₂B₁₀H₁₀]₂} ( 3 ) have been synthesized by the reactions of CuX (X = Cl, Br and I) with the closo ligand 1,2‐(PPh₂)₂‐1,2‐C₂B₁₀H₁₀. All these complexes were characterized by elemental analysis, FT‐IR, ¹H and ¹³C NMR spectroscopy and X‐ray structure determination. Single crystal X‐ray structure determinations show that every complex contained di‐µ‐X‐bridged structure involving a crossed parallelogram plane formed by two Cu atoms and two X atoms (X = Cl, Br, I). The geometry at the Cu atom was a distorted tetrahedron, in which two positions were occupied by two P atoms of the PPh₂ groups connected to the two C atoms of carborane (Cc), and the other two resulted from two X atoms which bridged the other Cu atom at the same time. To the best of our knowledge, this is the first example of copper(I) complexes with 1,2‐diphenylphosphino‐1,2‐dicarba‐closo‐dodecaborane as ligand characterized by X‐ray diffraction. The catalytic property of the complex 3 for the amination of iodobenzene with aniline was also investigated. Copyright © 2005 John Wiley & Sons, Ltd.     

η5‐(3)‐1‐Methyl‐1,2‐dicarbollyl‐η5‐2′,5′‐dimethylpyrrolylcobalt(III)

In the title compound, (η⁵‐2,5‐di­methyl­pyrrolyl)[(7,8,9,10,11‐η)‐7‐methyl‐7,8‐dicarba‐nido‐undecaborato]­cobalt(III), [3‐Co{η⁵‐[2,5‐(CH₃)₂‐NC₄H₂]}‐1‐CH₃‐1,2‐C₂B₉H₁₀] or [Co(C₃H₁₃B₉)(C₆H₈N)], the Co^III atom is sandwiched between the pentagonal faces of the pyrrolyl and dicarbollide ligands, resulting in a neutral mol­ecule. The C—C distance in the dicarbollide cage is 1.649 (3) Å.     

The Versatile Coordination Modes of Monophosphine‐o‐Carborane in the Formation of Iridium and Rhodium Complexes: Synthesis,Reactivity, and Characterization

Monophosphine‐o‐carborane has four competitive coordination modes when it coordinates to metal centers. To explore the structural transitions driven by these competitive coordination modes, a series of monophosphine‐o‐carborane Ir,Rh complexes were synthesized and characterized. [Cp*M(Cl)₂{1‐(PPh₂)‐1,2‐C₂B₁₀H₁₁}] (M=Ir ( 1 a ), Rh ( 1 b ); Cp*=η⁵‐C₅Me₅), [Cp*Ir(H){7‐(PPh₂)‐7,8‐C₂B₉H₁₁}] ( 2 a ), and [1‐(PPh₂)‐3‐(η⁵‐Cp*)‐3,1,2‐MC₂B₉H₁₀] (M=Ir ( 3 a ), Rh ( 3 b )) can be all prepared directly by the reaction of 1‐(PPh₂)‐1,2‐C₂B₁₀H₁₁ with dimeric complexes [(Cp*MCl₂)₂] (M=Ir, Rh) under different conditions. Compound 3 b was treated with AgOTf (OTf=CF₃SO₃^?) to afford the tetranuclear metallacarborane [Ag₂(thf)₂(OTf)₂{1‐(PPh₂)‐3‐(η⁵‐Cp*)‐3,1,2‐RhC₂B₉H₁₀}₂] ( 4 b ). The arylphosphine group in 3 a and 3 b was functionalized by elemental sulfur (1 equiv) in the presence of Et₃N to afford [1‐{(S)PPh₂}‐3‐(η⁵‐Cp*)‐3,1,2‐MC₂B₉H₁₀] (M=Ir ( 5 a ), Rh ( 5 b )). Additionally, the 1‐(PPh₂)‐1,2‐C₂B₁₀H₁₁ ligand was functionalized by elemental sulfur (2 equiv) and then treated with [(Cp*IrCl₂)₂], thus resulting in two 16‐electron complexes [Cp*Ir(7‐{(S)PPh₂}‐8‐S‐7,8‐C₂B₉H₉)] ( 6 a ) and [Cp*Ir(7‐{(S)PPh₂}‐8‐S‐9‐OCH₃‐7,8‐C₂B₉H₉)] ( 7 a ). Compound 6 a further reacted with nBuPPh₂, thereby leading to 18‐electron complex [Cp*Ir(nBuPPh₂)(7‐{(S)PPh₂}‐8‐S‐7,8‐C₂B₉H₁₀)] ( 8 a ). The influences of other factors on structural transitions or the formation of targeted compounds, including reaction temperature and solvent, were also explored.     

Electrochemical behaviour of cobalta-dicarbollide sandwich complexes with different capping units

The redox aptitude of a series of cobalt(III) or cobalt(I) sandwich complexes bearing a charge compensated dicarbollide ligand ([9-L-7,8-C₂B₉H₁₀]⁻) as a constant unit and different counterparts (varying from classical [7,8-C₂B₉H₁₁]²⁻ to charge-compensated [9-L-7,8-C₂B₉H₁₀]⁻ dicarbollides, from cyclopentadienyl [C₅R₅]⁻ (R = Me, H) to cyclobutadiene [C₄Me₄]⁰ ligands) has been studied. All the Co(III) complexes display the reversible sequence Co(III)/Co(II)/Co(I). In contrast, the Co(I) complexes (namely, those capped by tetramethylcyclobutadiene) accede reversibly only to the Co(II) oxidation state, the passage to Co(III) being irreversible. When possible, the Co(II) intermediates have been characterized by EPR spectroscopy. The molecular structures of the monocation [Co(η-9-SMe₂-7,8-C₂B₉H₁₀)₂]⁺ in its DD/LL and meso diastereomeric forms as well as that of heteroleptic (η-7,8-C₂B₉H₁₁)Co(η-9-SMe₂-7,8-C₂B₉H₁₀) have been obtained by single-crystal diffraction. Presented at the 3rd Chianti Electrochemistry Meetings July 3−9, 2004, Certosa di Pontignano, Italy     

Syntheses of C-substituted icosahedral dicarbaboranes bearing the 8-dioxane-cobalt bisdicarbollide moiety

The treatment of 1,2-, 1,7- and 1,12-carbaborane lithiated isomers with [3,3′-Co-8-(CH₂CH₂O)₂-(1,2-C₂B₉H₁₀)-(1′,2′-C₂B₉H₁₁)] (1) at molar ratios 1:1 or 1:2 at room temperature in THF leads generally to the formation of a series of orange double-cluster mono and dianions. These were characterized by NMR and MS methods as [1′′-X-1′′,2′′-closo-C₂B₁₀H₁₁]⁻, [2]⁻; [1′′-X-1′′,7′′-closo-C₂B₁₀H₁₁]⁻, [3]⁻ and [1′′-X-1′′,12′′-closo-C₂B₁₀H₁₁], [4]⁻ for the monoanions, whereas [1′′,2′′-X₂-1′′,2′′-closo-C₂B₁₀H₁₀]²⁻, [2]²⁻; [1′′,7′′-X₂-1′′,7′′-closo-C₂B₁₀H₁₀]²⁻, [3]²⁻; and [1′′,12′′-X₂-1′′,12′′-closo-C₂B₁₀H₁₀]²⁻, [4]²⁻ for the dianions (where X = 3,3′-Co-8-(CH₂CH₂O)₂-(1,2-C₂B₉H₁₀)-1′,2′-(C₂B₉H₁₁)). Moreover, these borane-cage subunits can be easily modified via attaching variable substituents onto cage carbon and boron vertices, which makes these compounds structurally flexible potential candidates for BNCT of cancer and HIV-PR inhibition.     

Iodinated ortho‐Carboranes as Versatile Building Blocks to Design Intermolecular Interactions in Crystal Lattices

The crystal structures of numerous iodinated ortho‐carboranes have been studied, which has revealed the diversity of intermolecular interactions that these substances can adopt in the solid state. The nature—mostly as it relates to hydrogen and/or halogen bonds—and relative strength of such interactions can be adjusted by selectively introducing substituents onto the cluster, thus enabling the rational design of crystal lattices. In this work we present the newly determined crystal structures of the following iodinated ortho‐carboranes: 9‐I‐1,2‐closo‐C₂B₁₀H₁₁, 4,5,7,8,9,10,11,12‐I₈‐1,2‐closo‐C₂B₁₀H₄, 3,4,5,6,7,8,9,10,11,12‐I₁₀‐1,2‐closo‐C₂B₁₀H₂, 1‐Me‐8,9,10,12‐I₄‐1,2‐closo‐C₂B₁₀H₇, 1,2‐Me₂‐8,9,10,12‐I₄‐1,2‐closo‐C₂B₁₀H₆, and 1,2‐Ph₂‐8,9,10,12‐I₄‐1,2‐closo‐C₂B₁₀H₆. Their 3D supramolecular organization has been thoroughly investigated and compared to similar previously published crystal structures. Such a systematic survey has allowed us to draw some general trends. C_c? H???I? B hydrogen bonds (C_c= cluster carbon atoms) appear to be significant in the growth of the crystal lattices of these compounds, given the acidity of hydrogen atoms bonded to C_c, and the polarization of B? I bonds. These hydrogen bonds can be disrupted by selectively blocking the positions next to C_c, that is, B(3) and B(6), with bulky substituents that prevent iodine atoms from approaching as hydrogen acceptors. Halogen bonds of the type B? I???I? B are frequently observed in most cases, thus suggesting that these interactions could be attractive in boron clusters. In addition, different substituents can be grafted onto the ortho‐carborane surface, thereby providing further possibilities for homomeric or heteromeric molecular assembly.     

Proton‐Assisted Hydrogen Activation on Polyhedral Cations

The treatment of [1,1‐(PR₃)₂‐3‐(Py)‐closo‐1,2‐RhSB₉H₈] (PR₃=PMe₃ ( 2 ) or PPh₃ and PMe₃ ( 3 ); Py=pyridine) with triflic acid (TfOH) affords [1,3‐μ‐(H)‐1,1‐(PR₃)₂‐3‐(Py)‐1,2‐RhSB₉H₈]⁺ (PR₃=PMe₃ ( 4 ) or PMe₃ and PPh₃ ( 5 )). These products result from the protonation of the 11‐vertex closo‐cages along the Rh(1)? B(3) edge. These unusual cationic rhodathiaboranes are stable in solution and in the solid state and they have been fully characterized by multinuclear NMR spectroscopy. In addition, compound 5 was characterized by single‐crystal X‐ray diffraction. One remarkable feature in these structures is the presence of three {Rh(PPh₃)(PMe₃)}‐to‐{ηⁿ‐SB₉H₈(Py)} (n=4 or 5) conformers in the unit cell, thus giving an uncommon case of conformational isomerism. [1,1‐(PPh₃)₂‐3‐(Py)‐closo‐1,2‐RhSB₉H₈] ( 1 ), that is, the bis‐PPh₃‐ligated analogue of compounds 2 and 3 , is also protonated by TfOH, but, in marked contrast, the resulting cation, [1,3‐μ‐(H)‐1,1‐(PPh₃)₂‐3‐(Py)‐1,2‐RhSB₉H₈]⁺ ( 6 ), is attacked by a triflate anion with the release of a PPh₃ ligand and the formation of [8,8‐(OTf)(PPh₃)‐9‐(Py)‐nido‐8,7‐RhSB₉H₉] ( 9 ). The result is an equilibrium that involves cationic species 6 , neutral OTf‐ligated compound 9 , and [HPPh₃]⁺, which is formed upon protonation of the released PPh₃ ligand. The resulting ionic system reacts readily with H₂ to give cationic species [8,8,8‐(H)(PPh₃)₂‐9‐(Py)‐nido‐8,7‐RhSB₉H₉]⁺ ( 7 ). This reactivity is markedly higher than that previously found for compound 1 and it introduces a new example of proton‐assisted H₂ activation that occurs on a polyhedral boron‐containing compound.     

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) _n PPh₂]-3-H-3-Cl-closo-3,1,2-RuC₂B₉H₁₁ (n = 4, 5), paramagnetic 3,3-[Ph₂P(CH₂) _n PPh₂]-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.     

1,2‐Bis­(methylsulfanyl)‐1,2‐dicarba‐closo‐dodecaborane(12)

In the title compound, 1,2‐(SCH₃)₂‐1,2‐closo‐C₂B₁₀H₁₀ or C₄H₁₆B₁₀S₂, the methylsulfanyl groups are bonded to the C atoms of the 1,2‐dicarba‐closo‐dodecaborane cage. The C_cage—C_cage distance is 1.8033 (18) Å and the S—C_cage—C_cage—S torsion angle is 1.07 (13)°. The C_cage—C_cage distance is compared with those in other 1,2‐dicarba‐closo‐dodecaborane derivatives.