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New organic oxidants (aldehydes and ketones) allowing efficient synthesis of decaborane in a high yield via intermediate alkali metal salt were found. The sodium undecaborate oxidation process was refined, and new reaction stoichiometry was suggested.

Studies of 2,5;6,10;8,10-tri-μ-hydro-nonahydro-nido-nonaborate(1-) - have involved new syntheses, which have led to crystals suitable for the determination of the X-ray crystal and molecular structure, through reactions of B9H13(SMe2) with - or other bases.Crystallographic study of reveals the structure of the anion to be that of a nido-nine-vertex cage, based on the parent bicapped square antiprism with one 5-connected vertex removed.The pentagonal open face is symmetrically bridged by three (μ-H) atoms (two involving the lowest connected boron), conferring effective Cs symmetry upon the polyhedron.Crystals are monoclinic, space group P21/n, with a=26.759(10), b=10.340(4), c=27.044(5) Angtroem, β=103.47(2) deg, and Z=8.Using 6 777 diffracted intensities recorded at 185 K on an Enraf-Nonius CAD4 diffractometer, the structure has been refined to R 0.0847, R' 0.1216.The 11B, two-dimensional 11B(COSY), and 1H n.m.r. parameters all confirm the structural assignment and the n.m.r. spectra have been assigned unambiguously.Cyclic and a.c. voltammetry and coulometry of - in several solvents at Pt led to the electrochemical parameters and to an isomer-specific electrochemical synthesis of anti--.Chemically, the + salt of - reacted with HCl to give -, whereas the n4>+ salt yielded anti-B18H22; reactions with CF3CO2H gave primarily anti--.

Simple iodine oxidation of the B9H12- anion in toluene at room temperature reliably gives excellent yields (～80%) of n-B18H22 (anti-B18H22) and thus provides a convenient, large-scale, safe route to this important polyborane cluster.

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.

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.

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.

Pentaborane(9), B5H9, is shown to be a useful source for the production of higher boron hydride systems. Investigation of the reaction of B5H9 with sodium hydride or potassium hydride in THF or glyme to produce the tetradecahydrononaborate(1-) anion, [B9H14]-, is reported in detail, and evidence is given for reaction pathways. This anion is also obtained from the reaction of NaI with B5H9. When generated in situ from B5H9, [B9H14]- is an intermediate in the syntheses of a number of other higher boron hydride systems: B9H13·L ligand adducts, n-B18H22, B10H14, nido-5,6-C2B8H12, and nido-5,6-(CH3)2-5,6-C2B8H 10. The synthesis of B10H14 reported here is an improved procedure over the earlier reported preparation from B5H9, and the preparations of nido-5,6-(CH3)2-5,6-C2B8H 10 and nido-5,6-C2B8H12 are new syntheses.

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

This study examined the conversions, via oxidative fusion or coupling, of B5H81- to B10H14 and 2,2'-(B5H8)2 in the presence of FeCl2/FeCl3, of B5H81- to B10H14 alone in the presence of RuCl3, and of 1-XB5H71- (X = D and CH3) to 2,4-B10H12D2 and 2,2-(1-CH3B5H7)2 with RuCl3 or FeCl2/FeCl3.The B10H131- ion was shown to form n- and i-B18H22 on treatment with RuCl3 in THF and subsequent exposure to air.The RuCl3-promoted fusions of the square-pyramidal cobaltaboranes 2-(ε5-C5H5)CoB4H71- and 1-(ε5-C5H5)CoB4H71- (both analogues of B5H81- to give nido-(η-C5H5)2Co2B8H12 isomers were also studied.The 2-isomer yields primarily 5,8-, 1,5-, and 1,7-(η-C5H5)2Co2B8H12, while the 1-isomer affords only 2,4-(η5-C5H5)2Co2B8H12.All these observations support a fusion mechanism in which two square-pyramidal substrate molecules, facilitated by coordination to a common metal ion, are initially joined at their basal edges and then complete the fusion process to give a nido 10-vertex cage in which the original apex (1-vertex) atoms become the 2,4-vertexes in the product.The new compounds were characterized via infrared, 11B and 1H NMR, mass spectra, and in some cases by two-dimensional (2D) 11B homonuclear NMR.

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.

The reactions of arachno-6,9-(SMe2)2B10H12 and of arachno-6,9-(MeCN)2B10H12 with the complex cis- give moderate yields of the nido-platinaundecaborane which has been characterised by single-crystal X-ray diffraction analysis.Analogous reactions with the dimeric species 2> (R3 = Me3-nPhn'n = 0,1 or 2), by contrast, give the nido-platinaundecaboranes which have been characterized by single-and multiple-resonance n.m.r. spectroscopy.Additional products of the reactions include the arachno nine-vertex species 4-(MeCN)B9H13 and 4-(SMe2)B9H13.

Full title: Pyrolysis reactions of 1,5-C2B3H5 and 1,6-C2B4H6. Isolation of a new four-carbon carborane, C4B7H11, and the boron-carbon-bonded dimer and trimers of 1,5-C2B3H5. Improved synthesis of the mixed-cage carborane 2′:2-[1′,5′-C2B3H 4][1,6-C2B4H5]. The gas-phase pyrolysis reactions of 1,5-C2B3H5 and 1,6-C2B4H6 in a hot/cold reactor (400/0°C) were studied. In agreement with previous reports, major products of the pyrolysis of 1,5-C2B3H5 were found to be the boron-boron-linked dimer, 2:2′-[1,5-C2B3H4]2, and trimer, 2:2′,3′:2″-[1,5-C2B3H 4][1′,5′-C2B3H 3][1″,5″-C2B3H4]. Also isolated from the reaction were a number of previously unknown compounds, including a boron-carbon-linked dimer 1:2′-[1,5-C2B3H4]2, two boron-boron-, boron-carbon-linked trimers, 2:2′,1′:2″-[1,5-C2B3H 4][1′,5′-C2B3H 3][1″,5″-C2B3H4] and 2:2′,3′:1″-[1,5-C2B3H 4][1′,5′-C2B3H 3][1″,5″-C2B3H4], and a new tetracarbon nido carborane, C4B7H11. The pyrolysis of 1,6-C2B4H6 was found to give only polymerization; however, the copyolysis of 1,5-C2B3H5 and 1,6-C2B4H6 was found to produce the previously reported mixed-cage coupled carborane 2′:2-[1′,5′-C2B3H 4][1,6-C2B4H5] in good yield.

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-.

The synthesis of B11H14- ion from BH4- ion and acids, including BF3·O(C2H5)2, BCl3, SiCl4, or alkyl halides, and the subsequent oxidation of the B11H14- ion to produce B10H14 using Na2Cr2O7, KMnO4, H2O2, or H2O2/FeSO4 is described. An optimum procedure is suggested which can be scaled-up.

Decaborane B10H14 is formed by opening the B10H10(2-) cage in strong acidic medium.The reaction must be carried out in the presence of an inert solvent which dissolves B10H14.The best yields (28percent) are obtained when zinc dust is added to the reaction mixture.The conversions of B10H10(2-) into B10H14 or B10H12(Et2S)2 probably obey the same mechanism. - Keywords: Decaborane, Bis(diethylsulphide)decaborane, Decahydrodecaborate Cage Opening