Localized orbital theory and ammonia triborane

In a previous paper [J. Subotnik, Y. Shao and W. Liang, and M. Head-Gordon, J. Chem. Phys., 2004, 121, 9220], we proposed a new and efficient method for computing localized Edmiston-Ruedenberg (ER) orbitals, which are those localized orbitals that maximize self-interaction. In this paper, we improve upon our previous algorithm in two ways. First, we incorporate the resolution of the identity (RI) and atomic resolution of the identity (ARI) approximations when generating the relevant integrals, which allows for a drastic reduction in computational cost. Second, after convergence to a stationary point, we efficiently calculate the lowest mode of the Hessian matrix in order to either (i) confirm that we have found a minimum, or if not, (ii) move us away from the current saddle point. This gives our algorithm added stability. As a chemical example, in this paper, we investigate the electronic structure (including the localized orbitals) of ammonia triborane (NH(3)B(3)H(7)). Though ammonia triborane is a very electron-deficient compound, it forms a stable white powder which is now being investigated as a potential hydrogen storage material. In contrast to previous electronic structure predictions, our calculations show that ammonia triborane has one localized molecular orbital in the center of the electron-deficient triborane ring (much like the single molecular orbital in H(3)(+)), which gives the molecule added energetic stability. Furthermore, we believe that NH(3)B(3)H(7) is the smallest stable molecule supporting such a closed, three-center BBB bond.     

Isomorphic substitution of boron in ZSM-5 type zeolites using TBP as template

A series of B-ZSM-5 samples has been synthesized using ethyl silicate (ES) ester-40, orthoboric acid and tetrabutylphosphonium (TBP) cation template and characterized by XRD, FT-IR, SEM and chemical analysis. It is observed that boron content in the initial reaction mixture influences the crystallization time and the morphology of the crystals. The migration of boron from framework upon calcination is enhanced as the boron content in the framework is increased. The test reaction of 1-hexene is under the profound influence of temperature on conversion and on the formation of primary products trans-2-hexene (t-2H), cis-2-hexene (c-2H) and 3-hexene. The ratios of the selectivity of c-2H to t-2H and 2-hexene to 3-hexene increased with decreasing temperature and decreasing boron content in the framework. Skeletal isomerization products started forming from 250°C as secondary products and increased with further increase of temperature.     

Ammonia triborane: a promising new candidate for amineborane-based chemical hydrogen storage

A convenient and safe method for the synthesis of ammonia triborane is reported along with studies of its hydrolytic reactions that demonstrate ammonia triborane is both soluble and stable in water but that upon the addition of acid or an appropriate transition metal catalyst it rapidly releases hydrogen. These studies indicate that ammonia triborane is a promising material for chemical hydrogen storage applications.     

Reactivity of the dimesityl-1,8-naphthalenediylborate anion: isolation of the borataalkene isomer and synthesis of 1,8-diborylnaphthalenes

The anionic boron peri-bridged naphthalene derivative, namely dimesityl-1,8-naphthalenediylborate (1), undergoes a hydrolysis reaction to afford dimesityl-1-naphthylborane (2) whose structure has been determined. Upon standing at room temperature in toluene for an extended period of time, 1 undergoes a ring expansion reaction to afford 8,10,11a-trimethyl-7-mesityl-11aH-7-boratabenzo[de]anthracene (3). As shown by its crystal structure, compound 3 constitutes a rare example of a borataalkene and features a carbon-boron double bond of 1.475(6) Angstroms incorporated in a conjugated hexa-1-boratatriene system. The reaction of 1 with 9-chloro-9-borafluorene and 5-bromo-10,11-dihydrodibenzo[b,f]borepin results in the formation of diboranes 4 and 5 which bear two different boryl moieties at the peri-positions of naphthalene. These diboranes have been characterized by multinuclear NMR spectroscopy and X-ray single crystal analysis. The boron center of the borafluorenyl moiety is pi-coordinated to the ipso-carbon of a mesityl group with which it forms a contact of 2.730(3) Angstroms. The cyclic voltammogram of 2 in THF shows a quasi-reversible reduction wave at E(1/2)-2.41 V (vs. Fc/Fc+) corresponding to the formation of the radical anion. In the case of diboranes 4, 5 and 1-(dimesitylboryl)-8-(diphenylboryl)naphthalene (6), two distinct waves are observed at E(1/2)-2.14 and -2.56 V for 4, E(1/2)-2.26 and -2.78 V for 5, and E(1/2)-2.41 and -2.84 V for 6. The first reduction wave most likely indicates the formation of a radical anion in which the unpaired electron is sigma-delocalized over the two boron centers.     

Synthesis, characterization, and electronic structure of new type of heterometallic boride clusters

The reaction of [Cp*TaCl(4)], 1 (Cp* = η(5)-C(5)Me(5)), with [LiBH(4)·THF] at -78 °C, followed by thermolysis in the presence of excess [BH(3)·THF], results in the formation of the oxatantalaborane cluster [(Cp*Ta)(2)B(4)H(10)O], 2 in moderate yield. Compound 2 is a notable example of an oxatantalaborane cluster where oxygen is contiguously bound to both the metal and boron. Upon availability of 2, a room temperature reaction was performed with [Fe(2)(CO)(9)], which led to the isolation of [(Cp*Ta)(2)B(2)H(4)O{H(2)Fe(2)(CO)(6)BH}], 3. Compound 3 is an unusual heterometallic boride cluster in which the [Ta(2)Fe(2)] atoms define a butterfly framework with one boron atom lying in a semi-interstitial position. Likewise, the diselenamolybdaborane, [(Cp*Mo)(2)B(4)H(4)Se(2)], 4 was treated with an excess of [Fe(2)(CO)(9)] to afford the heterometallic boride cluster [(Cp*MoSe)(2)Fe(6)(CO)(13)B(2)(BH)(2)], 5. The cluster core of 5 consists of a cubane [Mo(2)Se(2)Fe(2)B(2)] and a tricapped trigonal prism [Fe(6)B(3)] fused together with four atoms held in common between the two subclusters. In the tricapped trigonal prism subunit, one of the boron atoms is completely encapsulated and bonded to six iron and two boron atoms. Compounds 2, 3, and 5 have been characterized by mass spectrometry, IR, (1)H, (11)B, (13)C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis. The density functional theory calculations yielded geometries that are in close agreement with the observed structures. Furthermore, the calculated (11)B NMR chemical shifts also support the structural characterization of the compounds. Natural bond order analysis and Wiberg bond indices are used to gain insight into the bonding patterns of the observed geometries of 2, 3, and 5.     

ortho-Directed electrophilic boronation of a benzyl ketone: the preparation, X-ray crystal structure, and some reactions of 4-ethyl-1-hydroxy-3-(4-hydroxyphenyl)-2-oxa-1-boranaphthalene

4-Ethyl-1-hydroxy-3-(4-hydroxyphenyl)-2-oxa-1-boranaphthalene (4) is formed in 78% yield from the reaction of 1-(4-methoxyphenyl)-2-phenylbutan-1-one with an of excess boron tribromide in dichloromethane followed by treatment with water. Reaction of 4 with iodine in aqueous sodium hydroxide gives a second oxaboracycle, 3-ethyl-1-hydroxy-3-(4-hydroxybenzoyl)-2,1-benzoxaborolane (5). The X-ray crystal structure determinations of both boron heterocycles are reported. Other new compounds reported are 1-(4-hydroxyphenyl)-2-(1-hydroxyphenyl)-butan-1-one (6), formed by reaction of 4 with alkaline hydrogen peroxide, and 1-(4-hydroxyphenyl)-2-(2-biphenyl)-butan-1-one (8), formed by coupling of 4 with bromobenzene in the presence of Pd(PPh₃) ₄.     

Mononuclear Schiff base boron halides: synthesis, characterization, and dealkylation of trimethyl phosphate

A series of mononuclear boron halides of the type LBX(2) [LH = N-phenyl-3,5-di-tert-butylsalicylaldimine, X = Cl (2), Br (3)] and LBX [LH2 = N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (7), Br (8); LH2 = N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (9), Br (10); and LH2 = N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (11), Br (12)] were synthesized from their borate precursors LB(OMe)2 (1) (LH = N-phenyl-3,5-di-tert-butylsalicylaldimine) and LB(OMe) [LH2 = N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine (4), N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine (5), N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine (6)]. The boron halide compounds were air and moisture sensitive, and upon hydrolysis, compound 7 resulted in the oxo-bridged compound 13 that contained two seven-membered boron heterocycles. The boron halide compounds dealkylated trimethyl phosphate in stoichiometric reactions to produce methyl halide and unidentified phosphate materials. Compounds 8 and 12 were found to be the most effective dealkylating agents. On reaction with tert-butyl diphenyl phosphinate, compound 8 produced a unique boron phosphinate compound LB(O)OPPh2 (14) containing a terminal phosphinate group. Compounds 1-14 were characterized by 1H, 13C, 11B, 31P NMR, IR, MS, EA, and MP. Compounds 5, 6, and 11-14 also were characterized by single-crystal X-ray diffraction.     

Synthesis and characterisation of luminescent fluorinated organoboron compounds

The reaction of 8-hydroxyquinoline (HQ) with B(C(6)F(5))(3) leads to the formation of the zwitterionic compound (C(6)F(5))(3)BQH (1), involving a proton migration from O to N. Compound 1 can be converted thermally to (C(6)F(5))(2)BQ (2), which can also be prepared from (C(6)F(5))(2)BCl and HQ. The reaction of HQ with (C(6)F(5))B(OC(6)F(5))(2) generates initially (C(6)F(5))(OC(6)F(5))BQ (3), which easily hydrolyses to give the diboron compound ((C(6)F(5))BQ)(2)O (4). Compounds 1, 2 and 4 have been fully characterised, including X-ray analysis. The spectroscopic properties of these compounds, including photoluminescence (PL) have been investigated and compared with the non-fluorinated luminescent boron compound (C(6)H(5))(2)BQ and also with AlQ(3). The changes in luminescent behaviour upon fluorination of these boron quinolinate compounds have been rationalised using computational studies.     

Facile hydrometalation of alkynes by nido-1,2-(CpRuH)(2)B(3)H(7) yielding novel Ru-B edge-bridging alkylidenes. Stepwise conversion of HCtbd1;CC(O)OMe into nido-1,2-(CpRuH)(2)-3-HOB-4-MeC-5-MeOC-BH(3), Cp = eta(5)-C(5)Me(5)

The reaction of the alkyne HCCC(O)OMe with 7 sep 1,2-(Cp*RuH)2B3H7 leads to hydroboration plus hydroruthenation to produce nido-1,3-mu-Me{C(O)OMe}C-1,2-(Cp*Ru)2B3H7, a compound with an exocluster ruthenium-boron mu-alkylidene that exists in two isomeric forms. Both isomers undergo rearrangement with intramolecular chelation of the carbonyl oxygen at a boron site, thereby opening the cluster and generating arachno-2,3,-mu(C)-5-eta1(O)-Me{C(O)OMe}C-1,2-(Cp*Ru)2B3H7. Further heating leads to deoxygenation of the carbonyl fragment by a boron center concurrent with insertion of the carbon atom into the metallaborane cage to give nido-1,2-(Cp*RuH)2-3-HOB-4-MeC-5-MeOC-BH3.     

The C2 selective nucleophilic substitution reactions of 2,3-epoxy alcohols mediated by trialkyl borates: the first endo-mode epoxide-opening reaction through an intramolecular metal chelate

[reaction: see text] Highly efficient C2 selective substitution reactions of 2,3-epoxy alcohols with nucleophiles were developed by using NaN(3)-(CH(3)O)(3)B, NaSPh-(CH(3)O)(3)B, or NaCN-(C(2)H(5)O)(3)B system. The reaction proceeds through novel endo-mode epoxide opening of an intramolecular boron chelate, which was suggested from both experimental and quantum mechanic studies.     

Reaction of 1-alkyl-2-aryl-3-(2-methyl-2,3-epoxypropionyl)aziridines with boron trifluoride etherate in methanol

The reaction of boron trifluoride etherate in methanol with trans-1-methyl(ethyl)-or cis-1-cyclohexyl-2-aryl-3-(2-methyl-2,3-epoxypropionyl)aziridines leads to the formation of the corresponding boron fluoride complexes on the nitrogen atom of the aziridine ring. Reaction with trans-1-cyclohexyl-2-phenyl-3-(2-methyl-2,3-epoxypropionyl)aziridines occurs with stereospecific opening of the aziridine ring to give diastereomeric 2-methyl-5-methoxy-5-phenyl-4-cyclohexylamino-1,2-epoxypen-tan-3-ones, as well as products from the opening of the epoxide and aziridine rings — tetrahydrofuranones and tetrahydropyranones.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 596–600, May, 1986.     

Ternary magnesium rhodium boride Mg2Rh1-xB6+2x with a modified Y2ReB6-type crystal structure

The new ternary magnesium rhodium boride Mg2Rh1-xB6+2x has been prepared by the reaction of the mixture of Mg powder, RhB, and crystalline boron in a Ta container sealed under argon. The crystal structure of Mg2Rh0.75(1)B6.50(4) is determined using single-crystal X-ray diffraction, electron diffraction, and high-resolution electron microscopy (space group Pbam, a=8.795(2) A, b=11.060(2) A, c=3.5279(5) A, Z=4, 630 reflections, RF=0.045). It represents a modified Y2ReB6 structure type with an unusual replacement of part of the Rh atoms by boron pairs located in the pentagonal channels parallel to the c axis. The pairs interconnect the neighboring planar boron nets into the 3D framework. The variation of the lattice parameters reveals a homogeneity range Mg2Rh1-xB6+2x. The random distribution of the Rh atoms and boron pairs and the stabilizing effect of the boron pairs on the Y2ReB6 type structure motif are discussed using electronic band structure calculations and chemical bonding analysis with the electron localization function (ELF).     

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.     

298.15K下Li2B4O7-H2O体系水蒸汽分压及渗透系数的等压测定和离子相互作用模型

在已有研究含硼体系的文献中仅考虑了硼酸根B4O7^-2或B(OH)4^-和H3BO3的存在，而对Li2B4O7-H2O体系具有多种硼物种聚合平衡体系的热力学性质的研究尚未见报道．本文用等压法研究了Li2B4O7-H2O体系于298．15K下浓度由稀到过饱和溶液的平衡气相蒸汽压及渗透系数．考虑了水溶液中多种硼物种的存在，以Pitzer方程为基础，建立了可描述该含硼体系的离子相互作用模型。     

Synthesis and spectral properties of cholesterol- and FTY720-containing boron dipyrromethene dyes

Two analogues (1, 2) of free cholesterol and one analogue (3) of the immunosuppressive sphingolipid FTY720 containing a boron dipyrromethene chromophore (BODIPY) were synthesized. The synthetic routes involved preparation of boron dipyrromethene moieties (5, 11), bearing a phenylethynyl group at different positions of the chromophore, and lipids (13, 20) bearing an azido group. The dye was tethered to the lipid via a 1,2,3-triazole in the linker by the click reaction. Analogues derived from 11 [in which an (E)-styrylethynyl moiety is bonded to C-5 of BODIPY] exhibited a marked red shift (approximately 70-80 nm) compared with those derived from 5 (in which a phenylethynyl moiety is bonded to C-8 of BODIPY).     

Unexpected Reduction of Indole Double Bond in Mitragynine Using n-Butylsilane and Catalytic Tris(pentaflorophenyl)borane

An unexpected reduction of indolic double bond of mitragynine was described by using n-butyl silane and tris(pentafluorophenyl)triborane.     

A crossed beam and ab initio investigation on the formation of vinyl boron monoxide (C2H3BO; X1A') via reaction of boron monoxide (11BO; X2Σ+) with ethylene (C2H4; X1A(g))

The reaction dynamics of the boron monoxide radical ((11)BO; X(2)Σ(+)) with ethylene (C(2)H(4); X(1)A(g)) were investigated at a nominal collision energy of 12.2 kJ mol(-1) employing the crossed molecular beam technique and supported by ab initio and statistical (RRKM) calculations. The reaction is governed by indirect scattering dynamics with the boron monoxide radical attacking the carbon-carbon double bond of the ethylene molecule without entrance barrier with the boron atom. This addition leads to a doublet radical intermediate (O(11)BH(2)CCH(2)), which either undergoes unimolecular decomposition through hydrogen atom emission from the C1 atom via a tight transition state located about 13 kJ mol(-1) above the separated products or isomerizes via a hydrogen shift to the O(11)BHCCH(3) radical, which also can lose a hydrogen atom from the C1 atom. Both processes lead eventually to the formation of the vinyl boron monoxide molecule (C(2)H(3)BO; X(1)A'). The overall reaction was determined to be exoergic by about 40 kJ mol(-1). The reaction dynamics are also compared to the isoelectronic ethylene (C(2)H(4); X(1)A(g)) - cyano radical (CN; X(2)Σ(+)) system studied earlier.     

Expansion of iridaborane clusters by addition of monoborane. Novel metallaboranes and mechanistic detail

This work reports the results of a thermally driven cluster expansion of arachno-1-{eta5-C5Me5IrH2}B3H7, 1, with BH3.THF. In addition to the previously reported product, arachno-1-{eta5-C5Me5IrH}B4H9, 2, formed at lower temperatures, reaction at 100 degrees C permits the isolation of four new iridaboranes. Two products, nido-1-(eta5-C5Me5Ir)B5H9, 3, and nido-3-(eta5-C5Me5Ir)B9H13, 4, contain a single Ir atom and five and nine framework boron atoms, respectively. One, nido-3,4-(eta5-C5Me5Ir)2B8H12, 5, contains two Ir atoms and eight framework boron atoms. Their structures are predicted by the electron counting rules to be a nido-iridahexaborane, 3, nido-iridadecaborane, 4, and nido-diiridadecaborane, 5. The accuracy of these predictions in each case is established experimentally by spectroscopic characterization in solution and structure determinations in the solid state. A less stable metallaborane has been identified and the available spectroscopic and crystallographic information are consistent with the formulation nido-3,4-(eta5-C5Me5Ir)2B8H13(eta-BH2), 6, i.e., a species containing an exopolyhedral bridging BH group. These new observations, along with earlier ones on ruthenaborane cluster systems, are used to fully define a general mechanism for a cluster expansion reaction, i.e., addition of borane to form an exopolyhedral adduct followed by cage insertion.     

Reversible dehydrogenation of magnesium borohydride to magnesium triborane in the solid state under moderate conditions

Thermal decomposition of magnesium borohydride, Mg(BH(4))(2), in the solid state was studied by a combination of PCT, TGA/MS and NMR spectroscopy. Dehydrogenation of Mg(BH(4))(2) at 200 °C en vacuo results in the highly selective formation of magnesium triborane, Mg(B(3)H(8))(2). This process is reversible at 250 °C under 120 atm H(2). Dehydrogenation at higher temperature, >300 °C under a constant argon flow of 1 atm, produces a complex mixture of polyborane species. A borohydride condensation mechanism involving metal hydride formation is proposed.     

Novel class of heterometallic cubane and boride clusters containing heavier group 16 elements

Thermolysis of an in situ generated intermediate, produced from the reaction of [Cp*MoCl(4)] (Cp* = η(5)-C(5)Me(5)) and [LiBH(4).THF], with excess Te powder yielded isomeric [(Cp*Mo)(2)B(4)TeH(5)Cl] (2 and 3), [(Cp*Mo)(2)B(4)(μ(3)-OEt)TeH(3)Cl] (4), and [(Cp*Mo)(4)B(4)H(4)(μ(4)-BH)(3)] (5). Cluster 4 is a notable example of a dimolybdaoxatelluraborane cluster where both oxygen and tellurium are contiguously bound to molybdenum and boron. Cluster 5 represents an unprecedented metal-rich metallaborane cluster with a cubane core. The dimolybdaheteroborane 2 was found to be very reactive toward metal carbonyl compounds, and as a result, mild pyrolysis of 2 with [Fe(2)(CO)(9)] yielded distorted cubane cluster [(Cp*Mo)(2)(BH)(4)(μ(3)-Te){Fe(CO)(3)}] (6) and with [Co(2)(CO)(8)] produced the bicapped pentagonal bipyramid [(Cp*MoCo)(2)B(3)H(2)(μ(3)-Te)(μ-CO){Co(3)(CO)(6)}] (7) and pentacapped trigonal prism [(Cp*MoCo)(2)B(3)H(2)(μ(3)-Te)(μ-CO)(4){Co(6)(CO)(8)}] (8). The geometry of 8 is an example of a heterometallic boride cluster in which five Co and one Mo atom define a trigonal prismatic framework. The resultant trigonal prism core is in turn capped by two boron, one Te, and one Co atom. In the pentacapped trigonal prism unit of 8, one of the boron atoms is completely encapsulated and bonded to one molybdenum, one boron, and five cobalt atoms. All the new compounds have been characterized in solution by IR, (1)H, (11)B, and (13)C NMR spectroscopy, and the structural types were unambiguously established by crystallographic analysis of 2 and 4-8.