Tetraglymes as Prochiral Host Reagents for Ammonia Borane

The molecular structure of the complex of ammonia borane (AB) with acyclic ether tetraglyme Me(OCH₂CH₂)₄OMe ( 1 ), 1· (AB)₂ was determined by single‐crystal X‐ray structure analysis for the first time. The crystal structure features two AB molecules, bonded by dihydrogen bonds, per one tetraglyme unit. The intermolecular BH ··· HN distances of 1.94 Å are shorter than those in the solid ammonia borane (2.02–2.32 Å). A comparison of the hydrogen and dihydrogen bonds in 1· (AB)₂ and in the complexes of AB with crown‐ethers (CE) was carried out. The complex formation with both the CE and the acyclic polyether 1 activates the B–H bond in AB via N–H ··· O hydrogen bonds and therefore increases the reducing activity of AB. Supposedly, the structure of 1· (AB)₂ is related to the initial steps of the AB activation in a polyether solution. The effect of the substituents on the complexation of the substituted derivatives of 1 comes down to a structural adjustment minimizing steric repulsion. Computations reveal that the complexation of diastereomeric disubstituted glymes with AB leads to the formation of diastereomeric complexes that differ noticeably in stability. This is a prerequisite for inducing stereoselectivity, which makes such complexes attractive for potential synthetic applications.     

Quantum-Chemical Study of the Adducts of Silicon Halides with Nitrogen-containing Donors: II.1 Calculation of a Donor-Acceptor Bond Energy. Complex trans-SiH4·2NH3

Structural and thermodynamic characteristics of the trans-SiH₄·2NH₃ adduct were obtained by ab initio and DFT (RHF and B3LYP) calculations. Scanning the potential energy surface (PES) of the com plex showed that its structure corresponds to a local minimum, whereas the global minimum corresponds to the free fragments. The energy of the silicon-nitrogen chemical bond was calculated with inclusion of fragment rearrangement energies and basis set superposition error. The procedure offered for calculating the Si-N bond energy was extended to adducts of silicon halides with ammonia. It was found that the energy of SiX₄ rearrangement contributes most to the energies of donor-acceptor bonds in mono- and diammoniates of silicon tetrahalides.     

On the Brink of Decomposition: Controlled Oxidation of a Substituted Arsanylborane as a Way to Labile Group 13-15-16 Compounds

The reactivity of the organic-substituted arsanylborane tBuAsHBH₂NMe₃ ( 1 ) towards different elemental chalcogenes as well as organic oxidants such as O-NMe_3, Me₃Si−O−O-SiMe₃, MesCNO and cyclohexenesulfide is reported. By the reaction of 1 with grey selenium, the selenium oxidation product tBuAs(Se)HBH₂NMe₃ ( 2 ) was obtained. For the oxidation with sulfur, the two products tBuAs(S)HBH₂NMe₃ ( 3 a ) and tBuAs(S)SHBH₂NMe₃ ( 3 b ) could be isolated as oils. The structural characterization of As(tBuAs(S)SHBH₂NMe₃)₃ ( 4 ) as well as corresponding DFT computations allow insights into the decomposition behavior of 3 a and 3 b in solution. For the reaction of MesCNO with 1 , the formation of an unusual As−H activation product Mes-C(NOH)-AstBu-BH₂NMe₃ ( 5 ) is observed. In the reaction with Me₃N−O, the first isolatable oxo-arsanylboranes tBuAs(O)HBH₂NMe₃ ( 6 a ) and tBuAs(O)OHBH₂NMe₃ ( 6 b ) are obtained, with 6 b also being accessible via the controlled reaction of 1 with air.     

"True" inorganic heterocycles: structures and stability of group 13-15 analogues of benzene and their dimers

Group 13-15 inorganic analogues of benzene, [HMYH](3) (M = B, Al, Ga; Y = N, P, As), mixed heterocycles of the type [BAlGaNPAs]H(6) and their dimers have been theoretically examined at the B3LYP/TZVP level of theory. Six different isomers have been structurally characterized for the mixed compounds [BAlGaNPAs]H(6). B-N bonding strongly (about approximately 90-100 kJ mol(-)(1)) stabilizes the mixed heterocycles, followed by the preference of the Al-N bonded structures over Ga-N bonded ( approximately 30-40 kJ mol(-1)), while B-P bonding is slightly (5-10 kJ mol(-1)) more favorable compared to B-As. Thus, the bonding pattern is predicted to be the most stable, followed by the core. Processes of [HMYH](3) formation from donor-acceptor complexes H(3)MYH(3) are predicted to be thermodynamically favorable for all MY combinations. Dimerization reactions of the coordinationally unsaturated [HMYH](3) heterocycles yielding hexamer clusters [HMYH](6) are found to be exothermic, with the exception of borazine, for which, as for benzene, dimerization is strongly endothermic due to the aromaticity of C(6)H(6) and [HBNH](3). Despite the high endothermicity of [HBNH](3) dimerization, the B-N bond formation is the driving force of the dimerization of mixed species [BAlGaNPAs]H(6). The dimerization enthalpies of [BAlGaNPAs]H(6) may be both exo- and endothermic, depending on the bonding pattern of the isomers. A complete set of mean MY bond energies in four- and six-membered cycles of [HMYH](6) was derived. The MY energies were found to be transferable quantities and may serve for a qualitative prediction of the relative stability of different isomers of mixed cluster compounds. [BAlGaNPAs](2)H(12) clusters are promising synthetic targets, they are expected to serve as single-source precursors for the stoichiometry-controlled CVD processes of the group 13-15 composites. A strategy of their synthesis and the most suitable starting systems have been also predicted.     

Structural and Thermodynamic Characteristics of Compounds X2MYH2 (M = Al,Ga, In; X = F,Cl, Br,I; Y = N,P, As) Formed by Hydrogen Halide Elimination from Donor-Acceptor Complexes X3MYH3

Geometry and thermodynamic characteristics of complexes X₂MYH₂ (M = Al, Ga, In; X = F, Cl, Br, I; Y = N, P, As) and their components were found by the B3LYP density functional method with the LANL2DZ(d,p) basic set. The nitrogen complexes X2MNH2 have a planar structure, whereas the phosphorus and arsenic complexes are pyramidal. Upon HX elimination, the dissociation energy of the M-Y bonds considerably increases (by 150-270 kJ mol^{- 1}), which makes the dissociation of X2MYH2 into components thermodynamically unfeasible even at temperatures about 1000°C. A linear correlation between the dissociation enthalpies of M-Y bonds in the X₃MYH₃ and X₂MYH₂ complexes was found for each central atom M, which makes it possible to estimate the dissociation enthalpies of coordination-unsaturated compounds of the Group IIIa elements from the dissociation enthalpies of their coordination-saturated analogs. The enthalpies of dimerization of X₂MYH₂ fall in the range from 40 (Y = P, As) to 260 kJ mol^{- 1} (Y = N), which makes the process X₃MNH₃ = [X₂MNH₂]₂ + HX with the retention of the metal-nitrogen bond more favorable than the dissociation of the initial complex into the components. Thus, dimers [X₂MNH₂]₂ can be intermediates in chemical deposition of nitrides from the gas phase of donor-acceptor complexes.     

Structure and stability of oligomeric anions [M n X3 n + 1]? (M = Al, Ga, In; X = F, Cl, Br, I; n = 2–4): A quantum-chemical study

The structural and thermodynamic properties of oligomeric anions [M _n X_{3n+ 1}]⁻ (M = Al, Ga, In; X = F, Cl, Br, I; n = 2, 3, 4) have been obtained by the density functional theory B3LYP method with the LAN2DZ(d) and LAN2DZ(d)+ basis sets. A wide diversity of structural isomers was found for trimeric fluoride anions M₃F₁₀⁻. Among the trimers, except In₃F₁₀⁻, the most stable is a linear isomer composed of two MX₃ molecules coordinated to the MX₄⁻ anion. The formation of tetrameric anions M₄X₁₃⁻ was demonstrated to be thermodynamically allowed at low temperatures at MX₃: X⁻ > 4: 1. The existence of higher oligomers is less probable. The affinity of oligomer halides (MX₃) _n for halide ions increases with an increase in n. The propensity to form oligomeric anions decreases in the series F > Cl ≥ Br > I. The fluoride systems show a tendency to form structures with CN = 5 and 6, these structures for In being the most stable. Original Russian Text ? A.Yu. Timoshkin, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 1, pp. 87–100.