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The mechanism of carbonate formation from boron hydrides plus allene ([B.sub.4][H.sub.10]{C.sub.3][H.sub.4]) was studied computationally. A new basketlike compound is less stable than the observed basket and the production of arachno carboranes was less favorable due to free energy of activation barrier for loss of [H.sub.2] from [B.sub.4][H.sub.10].

Vinylphosphine-borane complexes are synthesized by palladium-catalyzed C-P cross-coupling of vinyl triflates with secondary phosphine-boranes. The versatility of this method is proved by using many triflates and diaryl-, dialkyl- and alkylarylphosphine-borane precursors and chiral enantiopure phosphine-boranes are synthesized from chiral triflates.

The high-level ab initio electronic structure theory is used to calculate the heats of formation of diphosphene (cis- and trans-[P.sub.2][H.sub.3]), phopshinophosphinidene (singlet and triplet [H.sub.2]PP) and diphosphine ([P.sub.2][H.sub.4]), and those of the [P.sub.2]H and [P.sub.2][H.sub.3] radicals ensuing from PH bond cleavages. The calculated results for the hydrogenation reactions have shown that substitution of an organic substituent for H improves the energetics, suggesting that secondary diphosphines and diphosphenes are potential candidates for use in a chemical hydrogen storage system.

The structure of the long-known protonated iron(II) bis(dicarbollide) assigned to a staggered isomer with a cisoid conformation of the carborane ligands is studied. It is suggested that suitable control of protonation/deprotonation equilibria can induce rotary motion at the molecular level.

The discovery of nonspherical and very oblate deltahedra, conveniently called the oblatocloso deltahedra, in dimetallaboranes among which the dirhenaboranes [Cp.sub.2][Re.sub.2][B.sub.n-2][H.sub.n-2] (8 < n < 12) are the prototypes is reported. The [D.sub.6h] hexagonal bipyramid is the first member of this series (n = 8) with the two metal atoms at the degree 6 vertices in antipodal positions on the [C.sub.6] axis, while the higher members of the series are not bipyramids.

The gas-phase structure of 6,9-CS[B.sub.8][H.sub.12] and 6,9-CN[B.sub.8][H.sub.13] were configured by electron diffraction and ab initio calculations. Results show that the position of the sulfur atom is very close to that of the boron atom occupying the equivalent position in the parent molecule [[B.sub.10][H.sub.14].sup.2-]], reflecting the similarity of sizes of sulfur and boron atoms.

Enatioselective reduction of oxime ethers promoted by chiral spiroborate esters with an O3BN framework is reported for the first time. In the presence of (R,S)-1, 11 arakyloxime ethers are reduced by borane-THF at 0-5 degree Celsius to give (S)-1-aralkylamine in high yield and excellent enantiomeric excess.

The syntheses, properties, and synthetic applications of 13-vertex closo- and nido-carboranes are reported in detail. The results show that the capitation reactions of CAd 12-vertex nido-carborane dianionic salts with dihaloboranes are generally a good method for the preparation of 13-vertex carboranes.

Reactions of the borane carbonyl (CF3)3BCO with selected amines and phosphines are studied. The exclusive attack at the carbonyl C atom is remarkable, although ligand exchange under release of CO is thermodynamically favored, as predicted by density functional theory calculations.

Ab initio and DFT calculations are performed to examine the mechanisms of reduction of alkyl halides and formaldehyde by borane. With alkyl halides, the optimized transition structure geometry resembles diborane, with a pair of hydrogen atoms bridging the boron and carbon atoms by three-center-two-electron bonds.

Selective deboronation of the B6 vertex could be achieved by functionalizing the B3 vertex and the study conducted shows that same results are achieved by sterically masking the B3 vertex from the nucleophile. The compounds provide useful symmetrical intermediates for use as carboracycle and supramolecular precursors.

Intramolecular cycloaddition of novel 1,3-dipoles, N-boranonitrones, was examined. Treatment of O-tert-butyldimethylsilyloximes having olefin moieties with 2 equiv of BF(sub 3).OEt(sub 2) generated N-boranonitrones, which underwent intramolecular cycloaddition to afford N-nonsubstituted cycloadducts.

A method for the preparation of eta(super 5)-metallocarborane complexes of technetium-99m in water was developed. Using this approach [(super 99m)Tc(CO)(sub 3)(H(sub 2)O)(sub 3)](super +) could be prepared directly from (super 99m)TcO(sub 4)(super -) under a range of pH values including neutral pH that affords the opportunity to develop one-pot labeling procedures for base-sensitive targeting vectors.

A series of metallocarboranes were produced by reacting [NEt(sub 4)](sub 2)[Re(CO)(sub 3)Br(sub 3)] or [ReCO)(sub 3)(OH(sub 2))(sub 3)]Br with corresponding carbonates in preaence of aqueous solutions of either alkaline metal or tetraalkylammonium fluoride salts. In the course of the reactions it was discovered that Re metallocarvoranes could be directly prepared from the respective closo-clusters under similar reaction conditions used with nido-carboranes.

Density functional theory (DFT) at the hybrid B3LYP level is applied to the polyhedral boranes BnH(sub n)(super z) (n=8 and 11, z=-2, -4, and -6) for comparison with isoelectronic germanium clusters Ge(sub n)(super z). The energy differences between the global minima and other higher energy borane structures are much larger relative to the case of the corresponding bare germanium clusters.

Immense efforts are made to develop various criteria of aromaticity and these criteria are used not only to explain the available experimental observations but also to design novel aromatics. Extending the aromaticity concept from the classical two dimensional annulenes to spherical species opens a new exciting research area with particular emphasis on fullerenes and closo-boranes.

An efficient 10-step preparation from 4-methoxypyridine of (2R,3R,4R)-2-acetamido-3,4-dihydroxy-piperidine ('XylNAc-isofagomine') in optically active form is described. Key steps include an enantioselective reduction with cateholborane/(S)-2-methyl-CBS-oxazaborolidine, and a stereoselective pseudo-glycosylation of lithium azide by a cyclic sulfite ester.

The conjugation of carbohydrate haptens to protein carriers leading to potential vaccines using traceless Staudinger ligation is reported. The use of a borane-protected phosphane, which is deprotected at the time of the ligation reaction, led to the best results in terms of stability toward oxidation and reactivity.

The N-D stretching region in the infrared spectrum of the ammonia complex of tris-(2-methoxymethyl-phenol)-borane containing one D atom is examined. The N-D bands are hole burned, and the resulting spectra reveal the reorientation kinetics of the ammonia.

The design and self-assembly of five supramolecular complexes, a rectangle, a triangle, a hexagon, and two squares are described. The assemblies and building blocks were characterized with multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and elementary analysis.

The incorporation of multiple p-carborane cages within an aliphatic polyester dendrimer was accomplished through the preparation of a bifuntional carborane synthon. A p-carbonate derivative having an acid and protected alcohol functionality was found to efficiently couple to peripheral hydroxyl groups of low-generation dendrimers under standard esterification conditions.

The synthesis of diborate anions in the hypothesis that the delocalization of the negative charge over more than one boron atom might improve the stability of the anion and provide higher acidity to the ammonium salts of the complex anions is reported. The results of the investigation are presented.

Relevant structural features and corresponding energy penalties easily that allows to estimate the relative stabilities of 11-vertex nido-phospha- and aza-substituted boranes, borates, carbaboranes, and carbaborates are determined. Density functional theory computations at the B3LYP/6-311+G(d,p)/B3LYP/6-31G(d)+ZPE level are conducted to determine the relative energies of 95 phospha- and 46 aza(carba)boranes and -borates.

The reaction of the side-on, end-on ditantalum dinitrogen complex [([NPN]Ta).sub.2]([micro]-[[eta].sup.1]-[N.sub.2])[([micro]-H).sub.2] (where NPN = PhP(C[H.sub.2]Si[Me.sub.2]NPh)2) with a variety of secondary and primary boranes is reported. With 9-BBN, hydroboration of the Ta2[N.sub.2] unit occurs via B-H addition, which in turn triggers a cascade of reactions that result in N--N bond cleavage, ancillary ligand rearrangement involving silicon group migration, and finally elimination of be[N.sub.2]ene from the N-Ph group and a B-H moiety to generate the imide--nitride derivative. In the presence of excess 9-BBN, the Lewis acid--base adduct of the imide--nitride ([NP[micro]-N]Ta(=NB[C.sub.8][H.sub.14])([micro]-NB(H)[C.sub.8] [H.sub.14])Ta[NPN]) is formed. A similar set of reactions is observed for dicyclohexylborane ([Cy.sub.2]BH), which hydroborates the dinitrogen complex to generate [NPN]Ta(H)([micro]-[[eta].sup.1]: [[eta].sup.2]-NNB[Cy.sub.2])[([micro]-H).sub.2]Ta[NPN], followed by loss of [H.sub.2] and silicon group migration to yield the imidenitride [NP[micro]-N]Ta(=NB[Cy.sub.2])([micro]-N)(Ta[NPN]. With thexyl borane ([H.sub.2]BC[Me.sub.2]CH[Me.sub.2]), a similar sequence of reactions is suggested starting with hydroboration to generate [NPN]Ta(H)[[micro]-[[eta].sup.1]:[[eta].sup.2]-NNB(H)[C.sub.6][H.sub.13]) [([micro]-H).sub.2]Ta[NPN], followed by loss of [H.sub.2] and ancillary ligand rearrangement. When bis(pentafluorophenyl)borane (HB[([C.sub.6] [F.sub.5]).sub.2]) is used, no hydroboration of coordinated [N.sub.2] is observed, rather simple adduct formation to give [([NPN]Ta).sub.2] ([micro]-[[eta].sub.1]:[[eta].sub.2]-NN-B(H) [([C.sub.6][F.sub.5]).sub.2])[([micro]-H).sub.2] occurs. Key words: dinitrogen, tantalum, hydroboration, N--N bond cleavage. Resume : On rapporte les resultats de la reaction du complexe de diazote ditantale [([NPN]Ta).sub.2]([micro]-[[eta].sub.1]: [[eta].sub.2]-[N.sub.2])[([micro]-H).sub.2] (dans lequel NPN = PhP[(C[Hs.sub.2]Si[Me.sub.2]NPh).sub.2]) avec une variete de boranes secondaires et primaires. Avec le 9-BBN, l'hydroboration de l'unite [Ta.sub.2][N.sub.2] se produit par une addition B-H, qui provoque a son tour une cascade de reactions conduisant a une rupture de la liaison N--N, un rearrangement du ligand impliquant une migration du groupe du silicium et finalement l'e1imination du be[N.sub.2]ene du groupe N-Ph et une portion B-H pour generer la formation du derive imide--nitrure ([NP[micro]-N]Ta(=NB[C.sub.8][H.sub.14])([micro]-NB(H) [C.sub.8][H.sub.14])Ta[NPN]). On observe un ensemble de reactions semblables avec le dicyclohexylborane ([Cy.sub.2]BH) qui provoque une hydroboration du complexe de diazote pour generer le [NPN]Ta(H)([micro][[eta].sub.1]:[[eta].sub.2]-NNB[Cy.sub.2]) [([micro]-H).sub.2]Ta[NPN], suivie d'une perte de [H.sub.2] et de la migration du groupe du silicium pour conduire h la formation de l'imide nitrure [NP[micro]-N]Ta(=NB[Cy.sub.2])([micro]-N)Ta[NPN]. Avec le thesylborane ([H.sub.2]BC[Me.sub.2]CH[Me.sub.2]), la reaction suivrait un cours semblable qui debuterait avec une hydroboration pour generer le [NPN]Ta(H)([micro]-[[eta].sub.1]: [[eta].sub.2]-NNB(H)[C.sub.6][H.sub.13])[([micro]-H).sub.2]Ta[NPN], suivie d'une perte de [H.sub.2] et d'un rearrangement de ligand. Avec le bis(pentafluorophenyl)borane (HB[([C.sub.6][F.sub.5]).sub.2]), on n'observe pas l'hydroboration du [N.sub.2] coordine, uniquement la formation d'un adduit simple qui genere le [([NPN]Ta).sub.2] ([micro]-[[eta].sub.1]:[[eta].sub.2]-NN-B (H)[([C.sub.6] [e.sub.5]).sub.2][([micro]-H).sub.2]. Mots cles : diazote, tantale, hydroboration, scission de la liaison N--N. [Traduit par la Redaction]

The structures and the properties of polyaminoborane oligomers by using ab initio computational tools including dynamic electron correlation effects are investigated. The variations of the properties upon conformation changes are studied.

The synthesis of novel intramolecularly base-stabilized borane derivatives with six- and seven-membered chelate rings is described. The crystal structures and characterization of these compounds are discussed.

The changes in molecular structure associated with the crystalline of the donor-acceptor complex HCN-BF3 are studied using density functional theory. Short-range dipole-dipole interactions are attributed to be one of the main causes of the 0.84 angstrom shortening the B-N bond in the crystal phase compared to the gas phase.

The influence of the electronic effects on the enantioselectivity of the oxazaborolidine-catalyzed asymmetric borane reduction of ketones is examined and the utility of the robust catalyst is extended for the preparation of secondary alcohols with a variety of functional groups. Experimental findings disclosed that soluble coordinateable anions in the reductive system greatly affect the enantioselectivity especially for the beta-methoxy catalyst because of their coordination with the boron atom in the catalysts.

Comparative studies on the catalytic dehydricoupling of the amine-borane adduct Me(sub 2)NH.BH(sub 3) with a variety of [MeN-BH(sub 2)](sub2)) and the phosphine-borane adduct Ph2Ph.Bh3 with a variety of Rh (pre) catalysts such. Results suggest that the catalytic dehydrocoupling of Me(sub 2)NH.BH(sub 3) is heterogenous in nature involving Rh(O) collids, while that of Ph(sub 2)PH.BH(sub 3) proceeds by a homogeneous mechanism even when starting with Rh(O) precursors such as Rh/Al(sub 2)O(sub 3).

A systematic investigation and comprehensive comparisons of the potential energy reactions of the BH(sub 2)(super +) with H2, methane, ethylene and acetylene in the gas phase is discussed. The remarkable electrophilic properties of BH(sub 2)(super +) are discussed, and the details on the bonding structure of the three-center two-electron bonds characteristic of these compounds are presented.

A metal-free catalytic intramolecular hydrosilylation reaction is reported. The key intermediates in the catalytic cycle are silyl cationic species. The reaction is used to produce 2-silanorbornanes 2 from 3-cyclopentenemethylsilanes 1 under mild conditions and in high isolated yields. Key words: hydrosilylation, catalysis, silaheterocycles, silyl cations.

Structures of B2H2n(super 2+) dications (n = 1-4) are investigated at the QCISD(T)/6-311G level of theory. Although deprotonations of the dications are exothermic, they show considerable kinetic barriers.

The syntheses and structural characterization of a wide variety of new types of metallaphosphamonocarbaborane complexes formally derived from anions in which metals adopt an unprecedented array of coordination geometrics is described. The 10 vertex phosphamonocarbaborane anions are unique in their abilities to stabilize transition metals in a variety of environments because of their unusual range of readily accessible formal charges and coordination geometrics.

Systematic studies of the reactions of the exo-G-R-arachno-6, 7-PCB(sub 8)H(sub 11-) anion with Lewis acids are reported. The results revealed the development of rational high-yield routes of 10-vertex arachno- and nido-phosphamonocarboranes, exo-6-R-arachno-6,7-PCB(sub 8)H(sub 12) and 6-R-nido-6,9-PCB(sub 8)H(sub 9-).

A study indicating that silane and its derivatives, SiH(sub 4-n)X(sub n) (n= 0-3, X = F and Cl), form hydrogen bridged complex with borane (BH3) at gas phase is presented. The SiH(sub 4-n)Xn-BH3 complexes are considered as analogues of B2H6 with one monomer BH3 substituted by SiH(sub 4 - n)Xn.

The titanium-catalyzed hydroboration reactions of decaborane are carried out with variety of terminal olefins. The composition of all products was established by elemental analysis and exact mass determinations.

The formation of (Cp(super *)ReH2)2B4H4(2) from Cp(super *)ReCl4 and its reaction with BH3.thf, CO and Co2(CO)8 are described. The characterizations of intermediates reveal mechanistic details.

A study showing that N,N-dialkyl-tert-alkylamines are convenient borane carriers for hydroboration is demonstrated. The alkylboranes obtained after hydroboration were oxidized with hydrogen perodixe/sodium hydroxide and the product alcohols were obtained in quantitative yields.

The first example of a binuclear ruthenium complex involving the p-carborane framework in the bridging ligand is reported. It is found that the electrochemical and spectroscopic behavior of p-carborane-bridged [Ru.sup.II] binuclear species indicate little delocalization through this bridge.

A new and efficient method for the selective synthesis of secondary alkyl anilines and heterocyclic anilines including tetrahydroquinolines, benzazepines and benzoxazines in good yield by a BF3-Et2O/BH3 reductive rearrangement of O-silylated oximes is described. The bulk of the substitutents on the silicon atom, the size of the aliphatic ring and the presence of alkoxy substituents on the aryl group all play an important role in the aniline.

Propargylic boranes generated by lithiation of optically active N-proparglyoxazolidinones undergo reaction with a range of aldehydes to produce gamma,gamma-disubstituted allenamides with good diastereoselectivity. A new method for the diastereoselective synthesis of allenylcarbinols through propargylic boranes is developed.

The Bcl-X(sub L)/BH3 domain interactions are considered to explore the possibility that unnatural oligomers with discrete folding properties might provide a general basis for development of molecules that block protein-protein interactions. The path from beta-to alpha/beta- to (alpha/beta+alpha)- peptide ligands leads to conclude that foldamer-based strategies for disrupting protein-protein interactions would grow in efficacy as number of foldamer scaffolds with distinct shapes is increased.

The borane reduction of ether-protected aromatic lactams that provides a novel process for reduction of amide and N-protected groups is examined. It is shown that the reaction takes place through two consecutive elimination and reductions to form the foresaid products through two C-O bond cleavages.

Crystalline Diphenylchloroborante.Tetrahydrofuran is unexpectedly stable complex containing an intact THF ligand in the presence of a boron halide bond. Using Gillespie's ligand close-packing arguments, the short B - O and long B - Cl bonds of this ether cleavage precursor complex are rationalized.

A versatile new method for the preparation of NHC boranes starting from two stable, readily available reactants, a heterocyclic salt and an amine or phosphine-borane, is reported. The method uses a Lewis base exchange at boron and provides easy access to new NHC boranes, in particular B-substituted borane ones.

A study was conducted to gain insight into variety of insertion reactions on treatment of Piers' borane, HB[([C.sub.6][F.sub.5]).sub.2] with either tert-butyl or isopropyl carbodiimide which yield the boron amidinates HC[(RN).sub.2]B[([C.sub.6][F.sub.5]).sub.2] [where R = iPr, tBu]. The data obtained for the isolated product of thermolysis of iPr species provide further support for the concept of existence of the transient 'open-chain' form of these amidinates in solution.

Brookhart's Ir(III) pincer complex Ir[H.sub.2]POCOP is used as catalyst to perform the catalytic dehydrocoupling/dehydrogenation of N-methylamine-borane, MeN[H.sub.2]*B[H.sub.3] and synthesize high molecular weight poly(N-methylaminoborane) [[MeNH-B[H.sub.2]].sub.n] ([M.sub.W] > 20 000). The synthetic strategy could be applied to obtain broad range of amine-borane precursors by using variety of catalysts to prepare polyaminoboranes and could find potential use for development of new class of inorganic polymers.