Synthesis, structural characterization, and reactivity studies of 5-CF3SO3-B10H13.

In contrast to previous reactions carried out in cyclopentane solvent at room temperature that produced 6-TfO-B10H13 (TfO = CF3SO3), the reaction of closo-B10H10(2-) with a large excess of trifluoromethanesulfonic acid in the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate (bmimOTf) gave exclusively the previously unknown 5-TfO-B10H13 isomer. Experimental and computational studies demonstrated that the difference in the products of the two reactions is a result of 6-TfO-B10H13 isomerizing to 5-TfO-B10H13 above room temperature in bmimOTf solutions. Reactivity studies showed that 5-TfO-B10H13: (1) is deprotonated by reaction with 1,8-bis(dimethylamino)naphthalene to form the 5-TfO-B10H12(1-) anion; (2) reacts with alcohols to produce 6-RO-B10H13 boryl ethers (R = Me and 4-CH3O-C6H4); (3) undergoes olefin-hydroboration reactions to form 5-TfO-6,9-R2-B10H11 derivatives; and (4) forms a 5-TfO-6,9-(Me2S)2-B10H11 adduct at its Lewis acidic 6,9-borons upon reaction with dimethylsulfide. The 5-TfO-6,9-(Me2S)2-B10H11 adduct was also found to undergo alkyne-insertion reactions to form a range of previously unreported triflate-substituted 4-TfO-ortho-carboranes (1-R-4-TfO-1,2-C2B10H10) and reactions with triethylamine or ammonia to form the first TfO-substituted decaborate [R3NH(+)]2[2-TfO-B10H9(2-)], and [R3NH(+)]2[1-TfO-B10H9(2-)] (R = H, Et) salts.

Syntheses and structural characterizations of inorganic ansa-metallocene analogues: ansa-ferratricarbadecaboranes.

New linked cyclopentadienyl-tricarbadecaboranyl and bis-tricarbadecaboranyl dianions have been used to form the first examples of ansa-metallatricarbadecaboranyl complexes. The hybrid cyclopentadienyl-tricarbadecaboranyl dianion, Li2(+)[6-C5H4-(CH2)2-nido-5,6,9-C3B7H9](2-) (1), was produced by an initial carbon-insertion reaction of a nitrile-substituted cyclopentadiene with the arachno-4,6-C2B7H12(-) anion, followed by deprotonation to the dianion with LiH. The linked-cage bis-tricarbadecaboranyl dianion, Li2(+)[6,6'-(CH2)2-nido-(5,6,9-C3B7H9)2](2-) (2), was produced by a similar carbon-insertion route involving the reaction of two equivalents of arachno-4,6-C2B7H12(-) with succinonitrile. The reaction of 1 with an equivalent of FeCl2 produced the hybrid complex, ansa-(2-(CH2)2)-(1-η(5)-C5H4-closo-1,2,3,4-C3B7H9)Fe (3), with a crystallographic determination confirming the formation of a sandwich structure where the ring and cage are linked by the ansa -CH2CH2- group with attachment to the cage at the C2 carbon. The reaction of 2 with FeCl2 produced three isomeric ansa-(CH2)2-ferrabistricarbadecaboranyl sandwich complexes, ansa-(CH2)2-(closo-C3B7H9)2Fe (4, 5 and 6). Crystallographic determinations showed that in 4, the two tricarbadecaboranyl ligands are linked by the ansa-CH2CH2- group at the C2 and C2' cage carbons, whereas in 5 and 6 they are linked at their C2 and C4' carbons, with the structures of 5 and 6 differing in the relative positions of the C4' carbons in the two cages of each complex. The structural determinations also showed that, depending upon the linking position of the ansa-tether, constraints in cage-orientation, such as observed in 4, produce unfavorable intercage steric interactions. However, the cage fragments in these complexes can readily undergo a cage-carbon migration that moves one -carbon and its tether linkage to the more favorable 4-position. This isomerization reduces the cage steric interactions and produces configurations, such as those found for 5 and 6, where the iron cage bonding is enhanced as a result of the binding effect of the tether.

Syntheses and characterizations of linear triborazanes.

Reaction of the amine boranes NH2(R)BH3, where R = H, Me, and Bz, with 1/3 equiv of sodium hexamethyldisilazane produced the five-membered, linear aminoborane anions Na(+)[BH3N(R)HBH2N(R)HBH3(-)], where R = H (1), Me (1Me), and benzyl (1Bz). Reactions of 1 and 1Me with ammonium chloride and methylammonium chloride, respectively, resulted in elimination of NaCl and H2 to produce the linear triborazanes BH3(RNHBH2)2N(R)H2, where R = H (2) and Me (2Me), with the structure of 2 crystallographically confirmed. The reactions of 1 and 1Me with pyridine-HCl produced the pyridine-capped aminoboranes H3B(RNHBH2)2(NC5H5), where R = H (3) and Me (3Me). 2 and 2Me proved to be stable up to 90 °C but produced a mixture of products when heated above 90 °C. 2 was selectively monochlorinated at the terminal boron when treated with 1 equiv of HCl and dichlorinated when reacted with a second 1 equiv of HCl.

Iridium and ruthenium catalyzed syntheses, hydroborations, and metathesis reactions of alkenyl-decaboranes.

The selective syntheses of new classes of 6,9-dialkenyl- and 6-alkenyl-decaboranes and 6-alkyl-9-alkenyl-decaboranes have been achieved via iridium and ruthenium catalyzed decaborane and 6-alkyl-decaborane alkyne-hydroborations. Reactions employing [Cp*IrCl2]2 and [RuCl2(p-cymene)]2 precatalysts gave ß-E-alkenyl-decaboranes, while the corresponding reactions with [RuI2(p-cymene)]2 gave the α-alkenyl-decaborane isomers, with the differences in product selectivity suggesting quite different mechanistic steps for the catalysts. The alkenyl-decaboranes were easily converted to other useful derivatives, including coupled-cage and functionally substituted compounds, via iridium-catalyzed hydroborations and ruthenium-catalyzed homo and cross olefin-metathesis reactions.

New palladium-catalyzed cross-coupling routes to carbon functionalized metallatricarbadecaboranes.

A general method for the synthesis of cage-carbon-functionalized cyclopentadienyl iron and cyclopentadienyl ruthenium tricarbadecaboranyl complexes has been developed that employs palladium-catalyzed Sonogashira, Heck, and Stille cross-coupling reactions directed at a cage-carbon haloaryl substituent. The key Li(+)[6-(p-XC(6)H(4))-nido-5,6,9-C(3)B(7)H(9)(-)] (X = I (1), Br (2), Cl (3)) haloaryl-tricarbadecaboranyl anionic ligands were synthesized in high yields via the reaction of the arachno-4,6-C(2)B(7)H(12)(-) anion with the corresponding p-halobenzonitriles (p-XC(6)H(4)-CN). The reactions of the salts 1-3 with (η(5)-C(5)H(5))Fe(CO)(2)I and (η(5)-C(5)H(5))Ru(CH(3)CN)(3)PF(6) were then used to produce the haloaryl complexes 1-(η(5)-C(5)H(5))-2-(p-XC(6)H(4))-closo-1,2,3,4-MC(3)B(7)H(9) (M = Fe, X = I (4), Br (5), Cl (6) and M = Ru, X = I (7), Br (8), Cl (9)). The sonication-promoted Sonogashira coupling reactions of 4 with terminal alkynes catalyzed by Pd(dppf)(2)Cl(2)/CuI yielded the alkynyl-linked derivatives 1-(η(5)-C(5)H(5))-2-p-RC(6)H(4)-closo-1,2,3,4-FeC(3)B(7)H(9) (R = (PhC≡C)- (10), (CH(3)CH(2)C(O)OCH(2)C≡C)- (11), ((η(5)-C(5)H(5))Fe(η(5)-C(5)H(4)C≡C))- (12)). Heck reactions of 4 with terminal alkenes catalyzed by Pd(OAc)(2) yielded the alkene-functionalized products 1-(η(5)-C(5)H(5))-2-p-RC(6)H(4)-closo-1,2,3,4-FeC(3)B(7)H(9) (R = (PhCH(2)CH═CH)- (13), (CH(3)(CH(2))(2)CH═CH)- (14)), while the Stille cross-coupling reactions of 4 with organotin compounds catalyzed by Pd(PPh(3))(2)Cl(2) afforded the complexes 1-(η(5)-C(5)H(5))-2-p-RC(6)H(4)-closo-1,2,3,4-FeC(3)B(7)H(9) (R = Ph- (15), (CH(2)═CH)- (16), (CH(2)═CHCH(2))- (17)). These reactions thus provide facile and systematic access to a wide variety of new types of functionalized metallatricarbadecaboranyl complexes with substituents needed for potential metallocene-like biomedical and/or optoelectronic applications.

Syntheses and structural characterizations of anionic borane-capped ammonia borane oligomers: evidence for ammonia borane H2 release via a base-promoted anionic dehydropolymerization mechanism.

Studies of the activating effect of Verkade's base, 2,8,9-triisobutyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane (VB), on the rate and extent of H(2) release from ammonia borane (AB) have led to the syntheses and structural characterizations of three anionic aminoborane chain-growth products that provide direct support for anionic dehydropolymerization mechanistic steps in the initial stages of base-promoted AB H(2) release reactions. The salt VBH(+)[H(3)BNH(2)BH(2)NH(2)BH(3)](-) (1) containing a linear five-membered anionic aminoborane chain was produced in 74% yield via the room-temperature reaction of a 3:1 AB/VB mixture in fluorobenzene solvent, while the branched and linear-chain seven-membered anionic aminoborane oligomers VBH(+)[HB(NH(2)BH(3))(3)](-) (2a) and VBH(+)[H(3)BNH(2)BH(2)NH(2)BH(2)NH(2)BH(3)](-) (2b) were obtained from VB/AB reactions carried out at 50 °C for 5 days when the AB/VB ratio was increased to 4:1. X-ray crystal structure determinations confirmed that these compounds are the isoelectronic and isostructural analogues of the hydrocarbons n-pentane, 3-ethylpentane, and n-heptane, respectively. The structural determinations also revealed significant interionic B-H···H-N dihydrogen-bonding interactions in these anions that could enhance dehydrocoupling chain-growth reactions. Such mechanistic pathways for AB H(2) release, involving the initial formation of the previously known [H(3)BNH(2)BH(3)](-) anion followed by sequential dehydrocoupling of B-H and H-N groups of growing borane-capped aminoborane anions with AB, are supported by the fact that 1 was observed to react with an additional AB equivalent to form 2a and 2b.

Syntheses and surprising regioselectivity of 5- and 6-substituted decaboranyl ethers via the nucleophilic attack of alcohols on 6- and 5-halodecaboranes.

The selective syntheses of new classes of decaboranyl ethers containing a range of functional groups substituted at the B5 or B6 positions were achieved through the reaction of alcohols with halodecaboranes. The surprising regioselectivity of the reaction, where the reaction of the 6-halodecaboranes (6-X-B(10)H(13)) with alcohols yielded the 5-substituted decaboranyl ethers (5-RO-B(10)H(13)) and the reaction with 5-halodecaboranes (5-X-B(10)H(13)) gave the 6-substituted decaboranyl ethers (6-RO-B(10)H(13)), was confirmed by NMR and X-ray crystallographic analyses. The crystallographic determinations also showed that the decaboranyl ethers had shortened B-O bonds and apparent sp(2) hybridization at oxygen indicating significant π-backbonding from oxygen to the cage boron. A possible substitution mechanism was computationally identified involving: (1) initial nucleophilic attack by the alcohol-oxygen at a site adjacent to the 5- or 6-halo-substituted boron, (2) movement of the terminal hydrogen at the point of attack to a bridging position, (3) formation of a 5-membered (B-O-H-Cl-B) cyclic transition state allowing the acidic methanolic-hydrogen to bond to the halogen, (4) release of HX, and finally (5) movement of a bridging hydrogen into the vacated terminal position. Deuterium labeling studies confirmed the movement of hydrogen from a bridging position of the halodecaborane into the halogen-vacated terminal position on the decaboranyl ether product. The relative reaction rates of the 6-X-B(10)H(13) compounds (X = F, Cl, Br, I) with alcohols were likewise found to be consistent with this mechanism.

Transition metal catalysed ammonia-borane dehydrogenation in ionic liquids.

Significant advantages result from combining the disparate hydrogen release pathways for ammonia-borane (AB) dehydrogenation using ionic liquids (ILs) and transition metal catalysts. With the RuCl(2)(PMe(3))(4) catalyst precursor, AB dehydrogenation selectivity and extent are maximized in an IL with a moderately coordinating ethylsulfate anion.

Ruthenium-catalyzed metathesis reactions of ortho- and meta-dialkenyl-carboranes: efficient ring-closing and acyclic diene polymerization reactions.

The ruthenium-catalyzed metathesis reactions of dialkenyl-substituted ortho- and meta-carboranes provide excellent routes to both cyclic-substituted o-carboranes and new types of main-chain m-carborane polymers. The adjacent positions of the two olefins in the 1,2-(alkenyl)(2)-o-carboranes strongly favor the formation of ring-closed (RCM) products with the reactions of 1,2-(CH(2)=CHCH(2))(2)-1,2-C(2)B(10)H(10) (1), 1,2-(CH(2)=CH(CH(2))(3)CH(2))(2)-1,2-C(2)B(10)H(10) (2), 1,2-(CH(2)=CHSiMe(2))(2)-1,2-C(2)B(10)H(10) (3), 1,2-(CH(2)=CHCH(2)SiMe(2))(2)-1,2-C(2)B(10)H(10) (4), and 1,2-[CH(2)=CH(CH(2))(4)SiMe(2)](2)-1,2-C(2)B(10)H(10) (5) affording 1,2-(-CH(2)CH=CHCH(2)-)-C(2)B(10)H(10) (10), 1,2-[-CH(2)(CH(2))(3)CH=CH(CH(2))(3)CH(2)-]-1,2-C(2)B(10)H(10) (11), 1,2-[-SiMe(2)CH=CHSiMe(2)-]-1,2-C(2)B(10)H(10) (12), 1,2-[-SiMe(2)CH(2)CH=CHCH(2)SMe(2)-]-C(2)B(10)H(10) (13), and 1,2-[-SiMe(2)(CH(2))(4)CH=CH(CH(2))(4)SiMe(2)-]-C(2)B(10)H(10) (14), respectively, in 72-97% yields. On the other hand, the reaction of 1,2-(CH(2)-CHCH(2)OC(=O))(2)-1,2-C(2)B(10)H(10) (6) gave cyclo-[1,2-(1',8'-C(=O)OCH(2)CH=CHCH(2)OC(=O))-1,2-C(2)B(10)H(10)](2) (15a) and polymer 15b resulting from intermolecular metathesis reactions. The nonadjacent positions of the alkenyl groups in the 1,7-(alkenyl)(2)-m-carboranes, 1,7-(CH(2)=CHCH(2))(2)-1,7-C(2)B(10)H(10) (7), 1,7-(CH(2)=CH(CH(2))(3)CH(2))(2)-1,7-C(2)B(10)H(10) (8), and 1,7-(CH(2)=CHCH(2)SiMe(2))(2)-1,7-C(2)B(10)H(10) (9), disfavor the formation of RCM products, and in these cases, acyclic diene metathesis polymerizations (ADMET) produced new types of main chain m-carborane polymers. The structures of 3, 9, 11, 12, 13, and 15a were crystallographically confirmed.

Metal-catalyzed decaborane-alkyne hydroboration reactions: efficient routes to alkenyldecaboranes.

Transition-metal-catalyzed decaborane-alkyne hydroboration reactions have been developed that provide high-yield routes to the previously unknown di- and monoalkenyldecaboranes. These alkenyl derivatives should be easily modified starting materials for many biomedical and/or materials applications. Unusual catalyst product selectivity was observed that suggests quite different mechanistic steps, with the reactions catalyzed by the [RuCl(2)(p-cymene)](2) and [Cp*IrCl(2)](2) complexes giving the beta-E alkenyldecaboranes and the corresponding reactions with the [RuI(2)(p-cymene)](2) complex giving the alpha-alkenyldecaborane isomers.

Efficient syntheses of 5-X-B(10)H(13) Halodecaboranes via the photochemical (X = I) and/or base-catalyzed (X = Cl, Br, I) isomerization reactions of 6-X-B(10)H(13).

High yield syntheses of the 5-X-B(10)H(13) (5X) halodecaboranes have been achieved through the photochemical (X = I) or base-catalyzed (X = Cl, Br, I) isomerization reactions of their 6-X-B(10)H(13) (6X) isomers. 5I was obtained in 80% isolated yield upon the UV photolysis of 6I. Treatment of 6X (X = Cl, Br, I) with catalytic amounts of triethylamine at 60 degrees C led to the formation of 78:22 (Cl), 82:18 (Br), and 86:14 (I) ratio 5X/6X equilibrium mixtures. The 5X isomers were then separated from these mixtures by selective crystallization (Br and I) or column chromatography (Cl), with the supernatant mixtures in each case then subjected to another round of isomerization/separation to harvest a second crop of 5X. The combined isolated yields of pure products after two cycles were 71% 5-Cl-B(10)H(13), 83% 5-Br-B(10)H(13), and 68% 5-I-B(10)H(13). The previously proposed structures of 5-Br-B(10)H(13) and 5-I-B(10)H(13) were crystallographically confirmed. Deprotonation of 6X and 5X with 1,8-bis(dimethylamino)naphthalene (PS) resulted in the formation of [PSH(+)][6X(-)] and [PSH(+)][5X(-)]. Density functional theory-gauge-independent atomic orbital (DFT/GIAO) calculations and crystallographic determinations of [PSH(+)][6Cl(-)] and [PSH(+)][6Cl(-)] confirmed bridge-deprotonation at a site adjacent to the halogen-substituted borons. NMR studies of the 6-Br-B(10)H(13) isomerization induced by stoichiometric amounts of PS showed that following initial deprotonation to form 6-Br-B(10)H(12)(-), isomerization occurred at 60 degrees C to form an equilibrium mixture of 6-Br-B(10)H(12)(-) and 5-Br-B(10)H(12)(-). DFT calculations also showed that the observed 5-X-B(10)H(13)/6-X-B(10)H(13) equilibrium ratios in the triethylamine-catalyzed reactions were consistent with the energetic differences of the 5-X-B(10)H(12)(-) and 6-X-B(10)H(12)(-) anions. These results strongly support a mechanistic pathway for the base-catalyzed 6X to 5X conversions involving the formation and subsequent isomerizations of the 6X(-) anions. While triethylamine did not catalyze the isomerization reactions of either 6-(C(6)H(13))-B(10)H(13) or 6,9-(C(6)H(13))(2)-B(10)H(12), it catalyzed the isomerization of 6-X-9-(C(6)H(13))-B(10)H(12) to 5-X-9-(C(6)H(13))-B(10)H(12) resulting from halo, but not alkyl rearrangement. Comparisons of the chemical shift values found in the temperature-dependent (11)B NMR spectra of 6Cl(-) and 6F(-) with DFT/GIAO chemical shift calculations indicate the fluxional behavior observed for these anions results from a process involving hydrogen migration around the open face that leads to the averaging of some boron resonances at higher temperatures.

Ammonia borane hydrogen release in ionic liquids.

The rate and extent of H(2)-release from ammonia borane (AB), a promising, high-capacity hydrogen storage material, was found to be enhanced in ionic-liquid solutions. For example, AB reactions in 1-butyl-3-methylimidazolium chloride (bmimCl) (50:50-wt %) exhibited no induction period and released 1.0 H(2)-equiv in 67 min and 2.2 H(2)-equiv in 330 min at 85 degrees C, whereas comparable solid-state AB reactions at 85 degrees C had a 180 min induction period and required 360 min to release approximately 0.8 H(2)-equiv, with the release of only another approximately 0.1 H(2)-equiv at longer times. Significant rate enhancements for the ionic-liquid mixtures were obtained with only moderate increases in temperature, with, for example, a 50:50-wt % AB/bmimCl mixture releasing 1.0 H(2)-equiv in 5 min and 2.2 H(2)-equiv in only 20 min at 110 degrees C. Increasing the AB/bmimCl ratio to 80:20 still gave enhanced H(2)-release rates compared to the solid-state, and produced a system that achieved 11.4 materials-weight percent H(2)-release. Solid-state and solution (11)B NMR studies of AB H(2)-release reactions in progress support a mechanistic pathway involving: (1) ionic-liquid promoted conversion of AB into its more reactive ionic diammoniate of diborane (DADB) form, (2) further intermolecular dehydrocoupling reactions between hydridic B-H hydrogens and protonic N-H hydrogens on DADB and/or AB to form neutral polyaminoborane polymers, and (3) polyaminoborane dehydrogenation to unsaturated cross-linked polyborazylene materials.

Base-promoted ammonia borane hydrogen-release.

The strong non-nucleophilic base bis(dimethylamino)naphthalene (Proton Sponge, PS) has been found to promote the rate and extent of H(2)-release from ammonia borane (AB) either in the solid state or in ionic-liquid and tetraglyme solutions. For example, AB reactions in 1-butyl-3-methylimidazolium chloride (bmimCl) containing 5.3 mol % PS released 2 equiv of H(2) in 171 min at 85 degrees C and only 9 min at 110 degrees C, whereas comparable reactions without PS required 316 min at 85 degrees C and 20 min at 110 degrees C. Ionic-liquid solvents proved more favorable than tetraglyme since they reduced the formation of undesirable products such as borazine. Solid-state and solution (11)B NMR studies of PS-promoted reactions in progress support a reaction pathway involving initial AB deprotonation to form the H(3)BNH(2)(-) anion. This anion can then initiate AB dehydropolymerization to form branched-chain polyaminoborane polymers. Subsequent chain-branching and dehydrogenation reactions lead ultimately to a cross-linked polyborazylene-type product. AB dehydrogenation by lithium and potassium triethylborohydride was found to produce the stabilized Et(3)BNH(2)BH(3)(-) anion, with the crystallographically determined structure of the [Et(3)BNH(2)BH(3)](-)K(+).18-crown-6 complex showing that, following AB nitrogen-deprotonation by the triethylborohydride, the Lewis-acidic triethylborane group coordinated at the nitrogen. Model studies of the reactions of [Et(3)BNH(2)BH(3)](-)Li(+) with AB show evidence of chain-growth, providing additional support for a PS-promoted AB anionic dehydropolymerization H(2)-release process.

Ammonia triborane: a new synthesis, structural determinations, and hydrolytic hydrogen-release properties.

Iodine oxidation of B(3)H(8)(-) in glyme solution to produce (glyme)B(3)H(7), followed by displacement of the coordinated glyme by reaction with anhydrous ammonia provides a safe and convenient preparation of ammonia triborane, NH(3)B(3)H(7) (1). X-ray crystallographic determinations and DFT computational studies of both NH(3)B(3)H(7) and the NH(3)B(3)H(7) x 18-crown-6 adduct demonstrate that while computations predict a symmetric single bridging-hydrogen conformation, NH(3)B(3)H(7) has a highly asymmetric structure in the solid-state that results from intermolecular N-H(+)...H(-)-B dihydrogen bonding interactions. Studies of its hydrolytic reactions have shown that upon the addition of acid or an appropriate transition metal catalyst, aqueous solutions of 1 rapidly release hydrogen, with 6.1 materials wt % H(2)-release being achieved from a 22.7 wt % aqueous solution of 1 at room temperature in the presence of 5 wt % Rh/Al(2)O(3) (1.1 mol% Rh). The rate of H(2)-release was controlled by both the catalyst loadings and temperature.

Double-walled boron nitride nanotubes grown by floating catalyst chemical vapor deposition.

One-dimensional nanostructures exhibit quantum confinement which leads to unique electronic properties, making them attractive as the active elements for nanoscale electronic devices. Boron nitride nanotubes are of particular interest since, unlike carbon nanotubes, all chiralities are semiconducting. Here, we report a synthesis based on the use of low pressures of the molecular precursor borazine in conjunction with a floating nickelocene catalyst that resulted in the formation of double-walled boron nitride nanotubes. As has been shown for carbon nanotube production, the floating catalyst chemical vapor deposition method has the potential for creating high quality boron nitride nanostructures with high production volumes.

Computational studies of the reactions of B10H13- with alkynes and olefins: pathways for dehydrogenative alkyne-insertion and olefin-hydroboration reactions.

Quantum mechanical computational studies of possible mechanistic pathways for B10H13(-) dehydrogenative alkyne-insertion and olefin-hydroboration reactions demonstrate that, depending on the reactant and reaction conditions, B10H13(-) can function as either an electrophile or nucleophile. For reactions with nucleophilic alkynes, such as propyne, the calculations indicate that at the temperatures (approximately 110-120 degrees C) required for these reactions, the ground-state B10H13(-) (1) structure can rearrange to an electrophilic-type cage structure 3 having a LUMO orbital strongly localized on the B6 cage-boron. Alkyne binding at this site followed by subsequent steps involving the formation of additional boron-carbon bonds, hydrogen elimination, protonation, and further hydrogen elimination then lead in a straightforward manner to the experimentally observed ortho-carborane products resulting from alkyne insertion into the decaborane framework. A similar mechanistic sequence was identified for the reaction of propyne with 6-R-B10H12(-) leading to the formation of 1-Me-3-R-1,2-C2B10H11 carboranes. On the other hand, both B10H13(-) and 4,6-C2B7H12(-) have previously been shown to react at much lower temperatures with strongly polarized alkynes, and the DFT and IRC calculations support an alternative mechanism involving initial nucleophilic attack by these polyborane anions at the positive terminal acetylenic carbon to produce terminally substituted olefinic anions. In the case of the B10H13(-) reaction, subsequent cyclization steps were identified that provide a pathway to the experimentally observed arachno-8-(NC)-7,8-C2B10H14(-) carborane. The computational study of B10H13(-) propylene hydroboration also supports a mechanistic pathway involving a cage rearrangement to the electrophilic 3 structure. Olefin-binding at the LUMO orbital localized on the B6 cage-boron, followed by addition of the B6-H group across the olefinic double bond and protonation, then leads to the experimentally observed 6-R-B10H13 products.

Ionic-liquid-promoted decaborane dehydrogenative alkyne-insertion reactions: a new route to o-carboranes.

Unlike in conventional organic solvents, where Lewis base catalysts are required, decaborane dehydrogenative alkyne-insertion reactions proceed rapidly in biphasic ionic-liquid/toluene mixtures with a wide variety of terminal and internal alkynes, thus providing efficient, one-step routes to functional o-carborane 1-R-1,2-C2B10H11 and 1-R-2-R'-1,2-C2B10H10 derivatives, including R = C6H5- (1), C6H13- (2), HC[triple bond]C-(CH2)5- (3), (1-C2B10H11)-(CH2)5- (4), CH3CH2C(O)OCH2- (5), (C2H5)2NCH2- (6), NC-(CH2)3- (7), 3-HC[triple bond]C-C6H4- (8), (1-C2B10H11)-1,3-C6H4- (9), HC[triple bond]C-CH2-O-CH2- (10); R,R' = C2H5- (11); R = HOCH2-, R' = CH3- (12); R = BrCH2-; R' = CH3- (13); R = H2C=C(CH3)-, R' = C2H5- (14). The best results were obtained from reactions with only catalytic amounts of bmimCl (1-butyl-3-methylimidazolium chloride), where in many cases reaction times of less than 20 min were required. The experimental data for these reactions, the results observed for the reactions of B10H13(-) salts with alkynes, and the computational studies reported in the third paper in this series all support a reaction sequence involving (1) the initial ionic liquid promoted formation of the B10H13(-) anion, (2) addition of B10H13(-) to the alkyne to form an arachno-R,R'-C2B10H13(-) anion, and (3) protonation of arachno-R,R'-C2B10H13(-) to form the final neutral 1-R-2-R'-1,2-C2B10H10 product with loss of hydrogen.

Ionic-liquid-promoted decaborane olefin-hydroboration: a new efficient route to 6-R-B10H13 derivatives.

Unlike in conventional organic solvents where transition metal catalysts are required, decaborane olefin-hydroboration reactions have been found to proceed in biphasic ionic-liquid/toluene mixtures with a wide variety of olefins, including alkyl, alkenyl, halo, phenyl, ether, ester, pinacolborane, ketone, and alcohol-substituted olefins, and these reactions now provide simple high-yield routes to 6-R-B10H13 derivatives. Best results were observed for reactions with bmimX (1-butyl-3-methylimidazolium, X = Cl(-) or BF4(-)) and bmpyX (1-butyl-4-methylpyridinium, X = Cl(-) or BF4(-)). Both the experimental data for these reactions and separate studies of the reactions of B10H13(-) salts with olefins indicate a reaction sequence involving (1) the ionic-liquid-promoted formation of the B10H13(-) anion as the essential initial step, (2) the addition of the B10H13(-) anion to the olefin to form a 6-R-B10H12(-) anion, and finally, (3) protonation of 6-R-B10H12(-) to form the final neutral 6-R-B10H13 product. The 6-R-B10H13 derivatives also undergo ionic-liquid-mediated dehydrogenative alkyne-insertion reactions in biphasic bmimCl/toluene mixtures, and these reactions provide high yield routes to 3-R-1,2-R' 2-1,2-C2B10H9 ortho-carborane derivatives.

Crystallographic characterizations and new high-yield synthetic routes for the complete series of 6-X-B10H13 halodecaboranes (X = F, Cl, Br, I) via superacid-induced cage-opening reactions of closo-B10H10(2-).

The high-yield syntheses of 6-X-B 10H 13 [X = Cl (88%), Br (96%), I (84%)] resulted from the cage-opening reactions of the (NH 4 (+)) 2B 10H 10 (2-) salt with ionic-liquid-based superacidic hydrogen halides, while both the previously unknown 6-F-B 10H 13 (77%) derivative and 6-Cl-B 10H 13 (90%) were synthesized in high yields via the reactions of (NH 4 (+)) 2B 10H 10 (2-) with triflic acid in the presence of 1-fluoropentane and dichloromethane, respectively. Structural characterizations of 1- 4 confirm the predicted structures and indicate strong halogen back-bonding interactions with the B6 boron. The reaction of 6-Br-B 10H 13 with Bu 3SnH produced the parent B 10H 14 in 70% yield, and thus, this reaction, in conjunction with the haloacid-induced closo-B 10H 10 (2-) cage-opening reactions, has the potential to provide an alternative to the traditional diborane pyrolysis route to decaborane.

Synthesis, characterization, and computational studies of 6-(RR'N)-nido-5,7-C2B8H11: a polyborane cluster with a cage-boron having an exopolyhedral dative boron-nitrogen double bond.

The reactions of the arachno-4,6-C 2B 7H 13 carborane with the secondary and primary amines, Me 2NHBH 3 and ( t )BuNH 2BH 3, in ionic liquid media result in both boron-insertion into the cage at a position across the two cage-carbons and additional hydrogen-elimination via the reaction of a hydridic B-H with a protonic amine N-H hydrogen to produce the 6-(RR'N)- nido-5,7-C 2B 8H 11 carboranes. Computational characterizations of these compounds and the previously reported 6-ClC 6H 4-9-(RR'N)- nido-6-NB 9H 10 azaboranes indicate that the amine-nitrogens form unique exopolyhedral dative BN double bonds with a cage-boron.