Computational studies of the reactions of B10H13- with alkynes and olefins: pathways for dehydrogenative alkyne-insertion and olefin-hydroboration reactions

Quantum mechanical computational studies of possible mechanistic pathways for B10H13(-) dehydrogenative alkyne-insertion and olefin-hydroboration reactions demonstrate that, depending on the reactant and reaction conditions, B10H13(-) can function as either an electrophile or nucleophile. For reactions with nucleophilic alkynes, such as propyne, the calculations indicate that at the temperatures (approximately 110-120 degrees C) required for these reactions, the ground-state B10H13(-) (1) structure can rearrange to an electrophilic-type cage structure 3 having a LUMO orbital strongly localized on the B6 cage-boron. Alkyne binding at this site followed by subsequent steps involving the formation of additional boron-carbon bonds, hydrogen elimination, protonation, and further hydrogen elimination then lead in a straightforward manner to the experimentally observed ortho-carborane products resulting from alkyne insertion into the decaborane framework. A similar mechanistic sequence was identified for the reaction of propyne with 6-R-B10H12(-) leading to the formation of 1-Me-3-R-1,2-C2B10H11 carboranes. On the other hand, both B10H13(-) and 4,6-C2B7H12(-) have previously been shown to react at much lower temperatures with strongly polarized alkynes, and the DFT and IRC calculations support an alternative mechanism involving initial nucleophilic attack by these polyborane anions at the positive terminal acetylenic carbon to produce terminally substituted olefinic anions. In the case of the B10H13(-) reaction, subsequent cyclization steps were identified that provide a pathway to the experimentally observed arachno-8-(NC)-7,8-C2B10H14(-) carborane. The computational study of B10H13(-) propylene hydroboration also supports a mechanistic pathway involving a cage rearrangement to the electrophilic 3 structure. Olefin-binding at the LUMO orbital localized on the B6 cage-boron, followed by addition of the B6-H group across the olefinic double bond and protonation, then leads to the experimentally observed 6-R-B10H13 products.     

Copper-free Sonogashira reactions of 4-hydroxycoumarins with alkynes

The palladium-catalyzed direct coupling reactions of 4-hydroxycoumarins with various alkynes under copper-free conditions are described. This transformation is highly effective under mild conditions and the desired products are obtained in good yields.     

Deuterium kinetic isotope effects on the gas-phase reactions of C2H with H2(D2) and CH4(CD4)

Kinetics of the ethynyl (C(2)H) radical reactions with H(2), D(2), CH(4) and CD(4) was studied over the temperature range of 295-396 K by a pulsed laser photolysis/chemiluminescence technique. The C(2)H radicals were generated by ArF excimer-laser photolysis of C(2)H(2) or CF(3)C(2)H and were monitored by the chemiluminescence of CH(A(2)Δ) produced by their reaction with O(2) or O((3)P). The measured absolute rate constants for H(2) and CH(4) agreed well with the available literature data. The primary kinetic isotope effects (KIEs) were determined to be k(H(2))/k(D(2)) = 2.48 ± 0.14 and k(CH(4))/k(CD(4)) = 2.45 ± 0.16 at room temperature. Both of the KIEs increased as the temperature was lowered. The KIEs were analyzed by using the variational transition state theory with semiclassical small-curvature tunneling corrections. With anharmonic corrections on the loose transitional vibrational modes of the transition states, the theoretical predictions satisfactorily reproduced the experimental KIEs for both C(2)H + H(2)(D(2)) and C(2)H + CH(4)(CD(4)) reactions.     

Palladium-catalyzed cascade reactions of coumarins with alkynes: synthesis of highly substituted cyclopentadiene fused chromones

The coupling of coumarins with alkynes is described, which proceeds through a palladium-catalyzed cascade sequence. This process provides a new route to the synthesis of highly substituted cyclopentadiene fused chromones.     

Thioether-functionalized ferrocenyl-bis(phosphonite), Fe{(C5H4)P(-OC10H6(micro-S)C10H6O-)}2: synthesis, coordination behavior, and application in Suzuki-Miyaura cross-coupling reactions

The thioether-functionalized metalloligand ferrocenyl-bis(phosphonite), Fe(C5H4PR)2 (4, R=-OC10H6(micro-S)C10H6O-) is synthesized in three steps starting from ferrocene, and its coordination behavior toward various transition-metal derivatives is described. The reactions of 4 with [Rh(CO)2Cl]2 or M(COD)Cl2 afforded the chelate complexes, cis-[Rh(CO)Cl{Fe(C5H4PR)2-kappaP,kappaP}] (5) or cis-[MCl2{Fe(C5H4PR)2-kappaP,kappaP}] (6, M=PdII; 7, M=PtII), respectively. However, treatment of 4 with CuX (X=Cl, Br, and I) produces binuclear complexes, [Cu2(micro-X)2(MeCN){Fe(C5H4PR)2-kappaP,kappaP}] (8, X=Cl; 9, X=Br; 10, X=I) where the sulfur atom on one side of the ligand is involved in a weak interaction with the copper center. Reaction of 4 with 1 equiv of Ag(PPh3)OTf gives the mononuclear chelate complex [Ag(OTf)PPh3{Fe(C5H4PR)2-kappaP,kappaP}] (11), whereas treatment with 2 equiv of AuCl(SMe2) produces the dinuclear gold complex [Au(Cl){Fe(C5H4PR)2-kappaP,kappaP}Au(Cl)] (12). The crystal structures of 10 and 12 are reported, where a strong metallophilic interaction is observed between the closed-shell metal centers. The palladium complex 6 catalyzes the Suzuki cross-coupling reactions of aryl bromides with phenylboronic acid with excellent turnover numbers (TON up to 1.36x10(5)).     

Analytical reactions of substituted cyanoferrates: 4. Spectrophotometric determination of beryllium(II), gallium(III), and indium(III) in solution

A new spectrophotometric method for microanalysis of Be²⁺, Ga³⁺, and In³⁺ in solution has been developed. These ions accelerate formation of colored pentacyanoazidoferrate(III) species (absorbing at 555 nm) under alkaline conditions. Ga³⁺ and In⁺ have been quantified in the ranges 0.4–4.0 and 0.4–3.0 ppm, respectively, while for Be²⁺ the range extends to 10 ppm. The reaction is nonselective, but some cations and anions can be tolerated at comparable concentrations.     

Interaction of tetrabutylammonium octahydrotriborate with aluminum chloride. A new method for the preparation of tetraborane(10)

Interaction of Bu₄NB₃H₈ with AlCl₃ at 45–50 °C results in the formation of BH₄ ^– and unstable borane B₂H₄, which is converted into a mixture of B₄H₁₀, B₅H₉, and B₂H₆. This reaction can be used for the preparation of tetraborane(10).     

Quinoxaline-2,3(1H,4H)-dithione: Synthesis and reactions

Quinoxaline-2,3(1H,4H)-dithione can be synthesized efficiently through the thionation of quinoxaline-2,3(1H,4H)-dione with phosphorous pentasulfide. It can also be obtained by reaction of 2,3-dichloroquinoxaline with thiourea or sodium hydrogen sulfide. The most common reactions of quinoxaline-2,3(1H,4H)-dithione involve deprotonation and electrophilic attack at the sulfur atoms to give various substituted derivatives and poly-fused heterocyclic ring systems. The current review aims to provide a survey of the developments in quinoxaline-2,3(1H,4H)-dithione chemistry until 2016.     

A new synthesis of aryl substituted quinazolin-4(1H)-ones

Treatment of a variety of substituted 2-aminobenzonitriles with formic acid under strong acid catalysis provides the corresponding quinazolin-4(1H)-ones in good yield. A potential reaction pathway is described.     

Theoretical study of isoelectronic molecules: B6H10, 2-CB5H9, 2,3-C2B4H8, 2,3,4-C3B3H7, and 2,3,4,5-C4B2H6

Isoelectronic molecules regarding B6H10, 2-CB5H9, 2,3-C2B4H8, 2,3,4-C3B3H7, and 2,3,4,5-C4B2H6 are studied by the density functional B3LYP/6-311G(d,p) method and the electron propagator theory in the partial third-order quasiparticale approximation, as well as the extrapolated calculation with the coupled-cluster CCSD(T) theory. The calculated ionization potentials are in good agreement with the experimental data from photoelectron spectroscopy. Valence structures are characterized with natural orbital bond (NBO) theory, exhibiting the multiple three-center two-electron bonds B-H-B, B-B-B, C-B-B, B-C-B, and C-B-C, and chemical bond rearrangements in the cations.     

Three-component coupling of alkynes, Baylis-Hillman adducts and sodium azide: a new synthesis of substituted triazoles

A three-component coupling was used to prepare a series of 1,4-disubstituted-1,2,3-triazoles from the corresponding acetylated Baylis-Hillman adducts, sodium azide and terminal alkynes. This one-pot reaction further increases the efficacy of ‘Click’ synthesis and diversifies the preparation of multi-functional 1,4-disubstituted-1,2,3-triazoles.     

Thermal transformations of B10H12(NH3)2, B10H12(C5H5N)2, and B10H12(C9H7N)2

Conclusions For B₁₀H₁₂L₂, where L=NH₃, C₅H₅N, or C₉H₇N, features of thermal transformations in the range 25–850°C and the composition of the pyrolysis products are determined. The latter are x-ray amorphous phases, containing nitride, carbide, boron carbide, boron, and carbon.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2481–2484, November, 1988.