19624-22-7

New octahydrotriborates LiB3H8·4Dn (Dn is dioxane), LiB3H8·2Dn, NaB3H 8·Dn, KB3H8·2.5Dn, [Mg(NH 3)6](B3H8)2, [Mg(Dg) 2](B3H8)2 (Dg is diglyme), [Mg(Dg)2](BH4)(B3H8), [Ca(Dg) 2](BH4)(B3H8), [Sr(Dg) 2](B3H8)2, and [C(NH 2)3]B3H8 were synthesized, and solvated salts with the B3H8- anion were prepared. It was shown that LiB3H8 forms hydrazinates of variable composition containing one to four hydrazine moles and the ammoniates LiB3H8·4NH3 and LiB3H 8·3NH3. The properties of the resulting salts and their solvates were studied. The temperature limits of the partial or complete desolvation of the solvates were established. The solubility of NaB 3H8·3Dn and tetraalkylammonium octahydrotriborates in organic solvents was studied over a wide temperature range. The heats of combustion in an oxygen atmosphere were measured, and the enthalpies of formation were calculated: ΔfH0(Me 4NB3H8) = -157.4 kJ/mol, Δy fH0(Et4NB3H8) = -262.5 kJ/mol, and ΔfH0(Bu4NB3H 8) = -443.8 kJ/mol. The destruction of the B3H 8- anion to give the BH4- ion and unstable borane B2H4 was found and confirmed experimentally for the first time. The destruction was studied in reactions of octahydrotriborates with Lewis bases (hydrazine and triphenylphosphine) and Lewis acids (AlCl3 and Al(BH4)3) and also in heat treatment. The B2H4 borane was isolated as the B 2H4·2PPh3 adduct. The reaction NaB 3H8·Dn → NaBH4 + B 5H9 + (H2 + Dn) can be conveniently used to prepare pentaborane(9) under laboratory conditions. The reaction of octahydrotriborate with aluminum chloride Bu4NB3H 8 + AlCl3 → Bu4N[Cl3Al(BH 4)] + B4H10 allows one to prepare tetraborane(10) with a fairly high yield and with a satisfactory degree of purity.

The reactions of the intermetallic compounds CeFe2, CeCo 2, and λ3-ScFe2 with B2H 6 at 4.8 × 103 Pa, 293-573 K, and various contact times were studied. CeFe2 decompose

The reactions between [(C5H5)2MCl2] (where M = Ti, Zr, Hf) and Li[B5H8] in a variety of solvents have been investigated. In the case of Zr, a pale orange solid, μ-(Cp2ClZr)B5H8 (1), is formed in 70% yield. Compound 1 exists as a B5H9 cage with a Cp2ClZr moiety replacing a bridging H atom. The variable temperature NMR spectra of 1 reveal two fluxional processes, one (ΔG? = 54 kJ mol-1) which renders a plane of symmetry in the molecule and a higher temperature one (ΔG? = 48 kJ mol-1) which renders all the basal B atoms equivalent. Dynamic processes are suggested to account for these observations. Passage of a CH2Cl2 solution of 1 through silica gel affords 2, [(Cp2Zr)2B5H8] [B11H14], a yellow, air-stable, crystalline solid, in 14% yield. The cation in 2, [(Cp2Zr)2B5H8]+, consists of a distorted spiro[2.2]pentane-like B5 moiety comprising two B3 triangles sharing a naked boron vertex. The two triangles are twisted 73° with respect to each other, and the two [Cp2Zr] groups bond in a trihapto arrangement to the two opposite B-B-B edges. Each exterior B-Zr edge is H-bridged, and the B atoms possess terminal hydrogens. Reactions of Cp2HfCl2 with Li[B5H8 lead to the formation of the analogue of 2, [(Cp2Hf)2B5H8] [B11H14] (3). The precursor to 3, that is, the Hf analogue of 1, is not observed. Reaction between Li[B5H8] and Cp2TiCl2 afforded no identifiable products, but reaction with CpTiCl3 resulted in cage coupling and the formation of B1OH14.

Cothermolysis reactions of B6H10 with the binary boranes B2H6, B4H10, B5H9, and B5H11 have been studied by a quantitative mass-spectrometric technique to gain insight into the role of B6H10 in borane interconversion reactions. Except in the B6H10-B5H9 system the initial rate of consumption of B6H10 was found to be considerably more rapid than in the thermolysis of B6H10 alone, indicating that interactions were occuring. Detailed kinetic studies of the B6H10-B2H6 and B6H10-B4H10 reactions showed that the rate of consumption of B6H10 was governed in each case by the rate-determining step in the decomposition of the co-reactant, the orders being 3/2 with respect to B2H6 and 1 with respect to B4H10; a considerable increase in the conversion of B6H10 to B10H14 at the expense of polymeric solids was also observed. Added hydrogen was found to have very little effect on the reaction rates and product distributions in the cothermolysis reactions, in marked contrast to its effect on the reactions of B2H6 and B4H10 alone. The kinetic results are entirely consistent with earlier suggestion, based on qualitative observations, that the reactive intermediates {B3H7} and {B4H8} are scavenged by reactions with B6H10, and suggest strongly that this borane, unlike B6H12, plays a pivotal role in the build-up to B10H14 and other higher boranes.

of 2-XB5H8 (X = Br or Cl) with secondary or tertiary silylamines proceed with elimination of hydrogen halides and/or halosilanes and attachment of amino groups to the clusters. Reaction of 2-BrB5H8 with (Me3-Si)2NH produces 2-[(Me3Si)2N]B5H8 in 57% yield. Other bis(silyl)amines react analogously. With (t-Bu)(Me3-Si)NH, 2-BrB5H8 produces 2-[(Me3Si)(t-Bu)N]B5H8 and hypho-2,3-μ-(t-BuNH)B5H10. (t-Bu)(Et3Si)NH reacts analogously. Low temperature analysis of the (t-Bu)(Me3Si)NH reaction in dichloromethane solution via 11B NMR spectroscopy discloses a dual reaction pathway producing a 2-aminopentaborane and a proposed arachno-2,3-μ-(t-BuNH)B5H8 intermediate which subsequently reacts with boranes to form hypho-2,3-μ-(t-BuNH)B5H8. When the above reaction is carried out in B5D9 solution, normal nido-[(t-Bu)(Me3Si)N]B5H8 and partially deuterated hypho-2,3-μ-(t-BuNH)B5H10 is formed. Reaction of 2-[(Me3Si)2N]B5H8 with BCl3 produces 2-[(Me3Si)2N·BCl3]B5H 8, and with (t-Bu)CN produces 2,3-μ-(t-BuCH=N)-2-[(Me3Si)2N]B5H 7.

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The complete spectroscopic characterization of the small phosphorus-bridged pentaborane(9) cluster (μ-diphenylphosphino)pentaborane, [μ-(C6H5)2PB5H8] (1), is reported. The MNDO calculated structure for 1 shows that the B P-B interaction can be best described as consisting of two two-center-two-electron B-P bonding interactions. Indirect support for the involvement of the lone pair of electrons on the phosphorus in cage bonding is obtained from the failure of 1 to react with [(CH3CN)3Mo(CO)3] under forcing conditions. Compound 1 is readily and quantitatively bridge-deprotonated by the action of NaH to produce the corresponding anion, Na[(μ-(C6H5)2P)B5H7] (2). Compound 2 reacts with 1 equiv of [Fe(η5-C5H5)(CO)2I] to yield the iron complex [(μ-(C6H5)2P)B5H 7Fe(η5-C5H5)(CO)2] (3) in high yield as an air-stable, yellow solid. A single-crystal X-ray analysis of 3 shows that the structure consists of a highly distorted square pyramid of boron atoms in which the B(2) H -B(3) bond in B5H9 has been subrogated by a B-P-B bridge and that the [Fe(η5-C5H5)(CO)2] unit is σ-substituted for a terminal proton on B(4). The phosphorus atom exhibits a distorted tetrahedral geometry and is located 0.516 A? below the least-squares basal-B4 plane. The B(2) B(3) atomic distance of the B- P B bridge was found to be 2.68 A?. The structure is formally derived from a two-electron reduction of a nido-pentaborane structure by the three-electron-donating phosphino unit to produce an arachno-pentaborane structure that is directly analogous to arachno-B5H11. Crystallographic data: space group P1/n (No. 14), a = 10.989 (2) A?, b = 13.460 (4) A?, c = 14.454 (5) A?, α = γ = 90 00°, β = 95.42 (2), V = 2128 (1) A?3, Z = 4 molecules/cell.

The chlorotriborane(7) (B3H6Cl) adduct of N(CH3)3 was formed by the reaction of B4H8·N(CH3)3 with HCl in dichloromethane or with HgCl2 in chloroform. The reaction of B3H7·N(CH3)3 with BCl3 in dichloromethane was found to be a better preparative method for B3H6Cl·N(CH3)3. The BCl3 treatment was employed to convert the N(CH3)2H, N(CH3)H2, NH3, and S(CH3)2 adducts of B3H7 into the corresponding adducts of B3H6Cl. In contrast, B3H7·P(CH3)3 and B3H7·PH3 are inert to BCl3. The B3H6Cl adducts of P(CH3)3 and PH3 could be obtained by treating the B3H7 adducts with a mixture of HCl and BCl3 in dichloromethane. The 11B and 1H NMR spectra of these B3H6Cl adducts showed that their structures were described as 1-(Lewis base)-2-chlorotriborane(7).

The interaction of BCl3 with excess CFCl3 has been examined by 11B and 19F NMR. Although small amounts of BFCl2 and BF2Cl, 9% each, are observed after 283 h at 65°C, BF3 is not a major product. At 130°C, however, BF3 is formed in 89% yield after 33 h. Boron trifluoride is isolated in 98 and 97% yields from the reactions of BCl3 and BBr3, respectively, with CFBr3 at 130 °C. At ambient temperature, Hg(CF3)2 reacts with BCl3 and BBr3, generating BF3 in 99 and 98% yields, respectively. The reaction of B2Cl4 with excess CFCl3 was followed spectroscopically at 65, 90, and 130°C, and the 19F chemical shifts of the partially fluorinated diboron tetrahalides have been assigned. Diboron tetrafluoride was isolated from the reaction between B2Cl4 and CFBr3 in 89% yield, from B2Br4 and CFBr3 in 78% yield, and from B2Cl4 and Hg(CF3)2 in 89% yield. Within 45 min the reaction between 1-BCl2B5H8 and Hg(CF3)2 produces the new compound 1-BF2B5H8 in 96% yield. Tetraboron tetrachloride is by far the least reactive of the boron chlorides examined.

The effects of added hydrogen on the kinetics of the first-order thermal decomposition of the two arachno species tetraborane(10) and pentaborane(11) have been studied in detail by a mass-spectrometric method.In the case of B4H10, the order and activation energy were unaltered, but the reaction rate was retarded and there was a marked change in product distribution: the percentage yield of B5H11 remained the same, but B2H6 was formed in preference to B5H9, B6H12, B10H14, and involatile solids.These results provide cogent new evidence that B4H10 decomposes via the single rate-determining step (i), but raise doubts about the validity of subsequent steps in the B4H10+H2 (i) previously proposed mechanism.In the thermolysis of B5H11 there was a dramatic change in product distribution, but the order, activation energy, and initial rate of disappearance of B5H11 were all unaffected by the presence of the added H2.These results establish for the first time that the so-called 'equilibrium' (ii) proceeds in the forward direction via the rate-determining B5H11+H2B4H10+1/2B2H6 (ii) dissociation (iii), followed by the rapid reactions (-i) and (iv).They also imply that in the thermolysis B5H11->+ (iii) 2->B2H6 (iv) of B5H11 in the absence of added H2 the reactive intermediate reacts subsequently with itself and is not consumed by reaction with B5H11.

The kinetics of thermal decomposition of pentaborane(11) have been investigated by a mass-spectrometric technique in the pressure range 1.75-10.50 mmHg and temperature range 40-150 deg C.In conditioned Pyrex vessels the reaction was shown to occur by a homogeneous gas-phase process according to the first-order initial-rate low -d/dt=1.3*107 exp(-72600/RT).The main volatile products are H2 and B2H6, the latter appearing at the rate of ca. 0.5 mol per mol of B5H11 consumed.Pentaborane (9) is also produced, at less than half the rate of B2H6, together with even smaller amounts of hexaboranes and B10H14, and traces of B4H10; some 40-45percent of the boron is converted into involatile solid hydride BHx, where x varies from ca. 2.0 at 40 deg C to ca. 1.1 at 150 deg C.No obvious dependence on temperature was detected in the overall distribution of boron between volatiles and solid, but the production of B5H9 was favoured at higher temperatures.Mechanistic implications of these results are discussed.

The boron hydride B4H10 is prepared in high yields (90 percent) through hydride-ion abstraction reactions when a mixture of BH4(-)/B3H8(-) is treated with CH3I or I2, respectively.A high yield (96 percent) method for the conversion of B3H8(-) to B4H10 is the reaction of B3H8(-) with AlCl3 in solvents which do not have any Lewis base character.The solvents are assumed to react as electron acceptors with the intermediate to form B4H10, R(-) and H2 (R-H = solvent).A 1:1 mixture of B4H10 and B5H9 is obtained when B3H8(-) is treated with CH3I or I2.The reaction can be viewed to involve an initial step in which unstable B3H7 is generated which immediately undergoes decomposition to give B4H10, B5H9 and H2.Treatment of B4H10 with (n-Bu)4NBr results in the formation of B3H-Br(-) which decomposes slowly at 0 deg C to form B5H9.An alternative synthesis of B5H9 via hydride-ion abstraction is possible through the reaction of (n-Bu)2O-BF3 with B3H8(-) in ether solvents. - Keywords: Syntheses of B4H10 and B5H9

The gas-phase thermolysis of arachno-B6H12 produces predominantly B5H9 and B2H6 in a molar ratio of 2:1 via a first-order reaction having Arrhenius parameters which are essentially identical to those reported for the decomposition of the structurally related B5H11; these results imply a mechanism involving elimination of BH3 as the rate-determining initial step in both reactions.

The mechanisms by which gaseous boron hydrides so readily interconvert and build up into larger clusters has excited considerable academic and industrial interest for several decades. This paper describes recent progress that has been made in unravelling this complex series of interconversion reactions. Initial reaction rates have been studied mass spectrometrically to obtain rate equations, orders of reaction and energies of activation. Detailed and continuous product analysis for H//2 and all the volatile boranes formed, coupled with a study of cothermolysis reactions of selected pairs of boranes gives further insight into the processes occurring. Crucial aspects of the thermolysis of B//2H// 6, B//4H//1//0, B//5H//1//1, and B//6H//1//0 are discussed, as are the effects of the added H//2 and the cothermolysis of B//6H//1//0 with alkenes. The final section presents data on the UV absorption spectra and photolytic stability of eight volatile boranes and the reaction kinetics of B//6H//1//0 photolysis.

Halopentaboranes(9) are converted to the parent pentaborane(9) in high yields with tributyltin hydride as the halogen reducing agent. Tributyltin hydride also reduces several other haloboranes and halometalloboranes. Deuterium-labeled pentaboranes(9) are produced from halopentaboranes(9) and tributyltin deuteride.

The gas-phase thermolysis of B6H10 has been studied kinetically by mass spectrometry for pressures in the range 1 - 7 mmHg, and at temperatures between 75 and 165 deg C (348 - 438 K).Hexaborane (10) was found to decompose by a second-order process with an

An improved synthesis of the nido-manganahexaborane 2,2,2-(CO)3-2-MnB5H10 has been developed that utilizes H2 pressures of ca. 100 atm and certain heterogeneous catalysts. Yields up to 41% have been obtained by using 5% Ru/C as catalyst. The new rhenahexaborane 2,2,2-(CO)3-2-ReB5H10 has been obtained in a similar manner and has been characterized spectroscopically. Possible mechanisms of formation of these metallaboranes in the catalyzed and uncatalyzed reactions are discussed.

Platinum dibromide has been found to promote cage growth and dehydrocoupling reactions between diborane and small, polyhedral carboranes and boranes, yieldind either larger single-cage compounds or bridge-substituted diborane-polyhedral carborane/borane complexes.For the catalyzed reaction of diborane with 1,5-C2B3H5, a cage growth reaction accurs to give the new arachno carborane, 5,6-C2B6H12.For 1,6-C2B4H6 and B5H9, cage growth reactions do not take place but instead the coupled diborane-polyhedral cage species 2:1',2'- and 2:1',2'- are obtained.

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Various derivatives of 1,2′-(B5H8)2 and 2,2′-(B5H8)2 were produced via halogenation and deprotonation reactions. The rearrangement of the parent compounds and some of their derivatives was studied in the presence of Lewis bases. Cleavage of the intercage σ bond in 1,2′-(B5H8)2 was observed in the presence of halogens and hydrogen halides, while boron-boron σ-bond cleavage was not observed in 2,2′-(B5H8)2.

When tetraborane(10) was treated with trimethylphosphine in a 1:1 molar ratio in tetrahydrofuran at -90 to -70°C, (CH3)3P·BH3, THF·B3H7, and H2B(THF)2+B3H8 - were produced. The formation of (CH3)3P·B3H7 was minimal. The same reaction was performed in dimethyl ether, diethyl ether, and dichloromethane, and the patterns of product distribution were compared with each other. The previously proposed mechanism for the B4H10 cleavage reactions was used to explain the observed results by taking the effects of concentrations and strength of the reacting bases into consideration. This mechanistic model explained also the results of the reactions of B4H10 with trimethylamine and phosphine in tetrahydrofuran. The values of 4 ± 1 and 0.41 ± 0.02 were obtained as the equilibrium constants for (CH3)3P·BH3 + THF·B3H7 ? THF·BH3 + (CH3)3P·B3H7 at 25°C and H3P·BH3 + THF·B3H7 ? THF·BH3 + H3P·B3H7 at 0°C, respectively.

Two new 1-(dichloroboryl)pentaborane(9) derivatives, 1-(Cl2B)B5H8 and 1-(Cl2B)-2-ClB5H7, have been produced via the reaction of BCl3 with B5H9 and 2-ClB5H8, respectively, in the presence of Friedel-Crafts catalysts. These compounds are the first examples of σ bonding between borane cluster atoms and external trigonal boron atoms. The boron-boron bonds undergo cleavage at elevated temperature in the presence of diethyl ether and insert ethylene at ambient temperature to form 1-[2-(dichloroboryl)ethyl]pentaborane(9) derivatives.

The boron hydrides B2H6, B4H10, B5H11, and B10H14 are prepared in good yields through hydride ion abstraction reactions when the borane anions BH4-, B3H8-, B4H9-, and B9H14- respectively are treated with 1 molar equiv of a Lewis acid BX3 (X = F, Cl, or Br), generally in the absence of a solvent, for reaction periods of 1-4 h. A high-yield (85-90%) method for the conversion of B5H9 to B9H14- is presented as the precursor to the practical conversion of B5H9 to B10H14 (45-50%). Additionally, treatment of the anion BrB3H7- with BBr3 results in the formation of 2-BrB4H9 in low yield (15%). The hydride ion abstraction reactions by BBr3 and BCl3 lead to the new anions HBBr3- and HBCl3-.

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Reaction of (η5-C5H5)BeCl with KB5H8 results in formation of the title compound, which forms crystals in the monoclinic space group P21/c with a = 10.266 (8) A?, b = 5.616 (4) A?, c = 16.187 (7) A?, β = 98.50 (5)°, V = 923.0 (5) A?3, and Z = 4. The low-temperature X-ray structure was solved by direct methods, using anisotropic refinement of positional and temperature factors for nonhydrogen atoms and isotropic refinement for hydrogen atoms, which converged to R1 = 0.0551 and R2 = 0.0831 for 1294 independent observed reflections. The structure of [μ-(η5-C5H5)Be]B5H 8 is like that of B5H9, but with a bridge hydrogen replaced by the (η-C5H5)Be moiety. Selected chemical properties of the title compound are described.

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Thermally induced flash reactions of tetraborane(10) and pentaborane(11) with acetylene, methylacetylene, and dimethylacetylene have been studied, and the volatile products, consisting almost exclusively of parent or alkyl closed-cage carboranes and hydrocarbons, have been individually isolated and characterized. Both the total carborane yield and the relative yields of B3 and B4 carboranes are largest in reactions of dimethylacetylene and least in those of acetylene. Derivatives of 1,2-C2B3H5 are formed in significant amounts from alkylacetylenes but not from acetylene. The results are compared with previous work on borane-alkyne systems, particularly the electric-discharge and flash reactions of diborane with acetylene, and implications in regard to reaction pathways are discussed. The pentaborane(11)-dimethylacetylene system is exceptional; flash reactions are not observed in 1:1 mixtures, but a 2:1 alkyne:borane ratio results in flash reaction below room temperature in which largely noncarborane products are obtained.

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