Diboron Compounds Research Articles

ChemInform Abstract: Regio‐ and Stereoselective Copper‐Catalyzed β‐Borylation of Allenoates by a Preactivated Diboron.

AbstractMild and efficient copper‐catalyzed borylation of electron‐deficient allenoates (I) using the sp2‐sp3 mixed hybridized diboron compound (II) regioselectively installs a boron moiety on the β‐position with complete stereocontrol.

ChemInform Abstract: Cyclopalladated Ferrocenylimine as Efficient Catalyst for the Syntheses of Arylboronate Esters.

AbstractBoth aryl/heteroaryl bromides and chlorides undergo the coupling reaction with diboron compound (III) in the presence of PCy3 catalyst (Ia) and biphenylphosphino catalyst (Ib), respectively, under optimized conditions.

Selective CH Borylation of Alkenes by Palladium Pincer Complex Catalyzed Oxidative Functionalization

The CH borylation of simple alkenes catalyzed by palladium pincer complex 1 was performed in the presence of hypervalent iodine and bis(pinacolato)diboron compounds. The borylation reaction probably occurs by a PdII→PdIV oxidation–diboronate transmetalation sequence. TFA=trifluoroacetate.

Reversible Intramolecular C−C Bond Formation/Breaking and Color Switching Mediated by a N,C-Chelate in (2-ph-py)BMes2 and (5-BMes2-2-ph-py)BMes2

A diboron compound with both 3-coordinate boron and 4-coordinate boron centers, (5-BMes2-2-ph-py)BMes2 (1) and its monoboron analogue, (2-ph-py)BMes2 (2) have been synthesized. Both compounds are luminescent but have a high sensitivity toward light. UV and ambient light cause both compounds to isomerize to 1a and 2a, respectively, via the formation of a C-C bond between a mesityl and the phenyl group, accompanied by a drastic color change from yellow or colorless to dark olive green or dark blue. The structures of 1a and 2a were established by 2D NMR experiments and geometry optimization by DFT calculations. Both 1a and 2a can thermally reverse back to 1 and 2 via the breaking of a C-C bond, with the activation barrier being 107 and 110 kJ/mol, respectively. The N,C-chelate ligands in 1 and 2 were found to play a key role in promoting this unusual and reversible photo-thermal isomerization process on a tetrahedral boron center. Reactions with oxygen molecules convert 1a and 2a to 5-BMes2-2-[(2-Mes)-ph]-pyridine (1b) and 2-(2-Mes)-ph-pyridine (2b), respectively.

Polyborylated reagents for modern organic synthesis.

Diverse kinds of gem- and vic-diborylated compounds are now readily available thanks to advances in gem-diborylation of lithium carbenoids as well as vic-diborylation of carbon–carbon multiple bonds with diboron compounds. These diborylated reagents lead to invention of polyborylated reagents and many novel and useful synthetic methods for supreme stereocontrol. This review summarizes preparative methods and synthetic reactions of di- and polyborylated reagents with the emphasis on multiple bond formation.

Enhancing Electron Accepting Ability of Triarylboron via π-Conjugation with 2,2‘-Bipy and Metal Chelation: 5,5‘-Bis(BMes2)-2,2‘-bipy and Its Metal Complexes

The synthesis of a new diboron compound, 5,5‘-bis(BMes2)-2,2‘-bipy (B2bipy, 1), has been accomplished. The conjugation of the 2,2‘-bipy unit with the two BMes2 groups in 1 has been found to greatly enhance the electron-accepting ability of the boron centers, compared to the biphenyl analogue. 1 is an effective chelate ligand for metal ions and three metal complexes; namely, [CuI(B2bipy)(PPh3)2][BF4], 2, PtII(B2bipy)Ph2, 3a, and PtII(B2bipy)Me2, 3b, have been synthesized. The binding of metal ions to B2bipy was found to further significantly increase the electron-accepting ability/Lewis acidity of the boron centers. Cyclic voltammetry diagrams revealed that the free ligand and all three complexes display two reversible reduction peaks that are separated by 0.31−0.40 V. The first reduction potential (E1/2) for 1, 2, 3a, and 3b was found to be −1.69, −1.36, −1.34, and −1.38 V, respectively, versus FeCp2+/0 in DMF, which supports that the electron-accepting ability of the metal complexes is much greater than ...

Chemistry of the Diboron Compounds

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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.

Diboron and Triboron Compounds Based on Linear and Star-Shaped Conjugated Ligands with 8-Hydroxyquinolate Functionality: Impact of Intermolecular Interaction and Boron Coordination on Luminescence

New 8-R-quinoline functionalized linear and star-shaped conjugated molecules have been synthesized using Suzuki-Miyaura coupling methods (R = MeO, L1-L5; R = CH3OCH2O, L1'-L5'). When treated with HCl, L1'-L5' are converted readily to the corresponding 8-hydroxyquinoline compounds L(OH)1-L(OH)5 which react readily with BPh3 in refluxing THF to produce the corresponding polyboron chelate compounds B1-B5 in good yields. L1-L5 and B1-B5 display similar thermal stability with Td at approximately 300 degrees C. Experimental and molecular orbital calculation results showed that the chelation by boron stabilizes the LUMO level of the ligand and narrows the HOMO-LUMO gap, resulting in the blue emission of the ligands and the green or orange emission of the boron compounds. Crystal structures of L1, L3, and L5 showed that these molecules have layered arrangements in the solid state with significant intermolecular pi-pi interactions. The linear diboron B5 displays concentration and temperature-dependent emission in solution, attributable to intermolecular interactions. The properties of a monoboron compound BPh2(5-Ph-8-MeO-q) (B0) and its corresponding free ligand L0 were investigated and compared to the closely related diboron compound B1 and the ligand L1, which revealed that the increase of the number of chromophores linked by an aromatic group has a significant impact on thermal stability and the HOMO and LUMO energy levels.

Efficient Homogeneous Catalysis in the Reduction of CO2 to CO

The well-defined copper(I) boryl complex [(IPr)Cu(Bpin)] [where IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, and pin = pinacolate: 2,3-dimethyl-2,3-butanediolate] deoxygenates CO2 rapidly and quantitatively, affording CO and the borate complex [(IPr)Cu(OBpin)]. The boryl may be regenerated by treatment with the diboron compound pinB-Bpin, giving the stable byproduct pinB-O-Bpin. The use of a copper(I) alkoxide precatalyst and stoichiometric diboron reagent results in catalytic reduction of CO2, with high turnover numbers (1000 per Cu) and frequencies (100 per Cu in 1 h) depending on supporting ligand and reaction conditions.

A Gentle and Efficient Route for the Deoxygenation of Sulfoxides Using Catecholborane (HBcat; cat = 1,2‐O2C6H4).

AbstractFor Abstract see ChemInform Abstract in Full Text.

A gentle and efficient route for the deoxygenation of sulfoxides using catecholborane (HBcat; cat = 1,2-O 2C 6H 4)

The addition of catecholborane (HBcat; cat = 1,2-O 2C 6H 4) to a wide range of sulfoxides affords the corresponding sulfides, dihydrogen, and catBOBcat. The diboron compound catBOBcat acts like a Lewis acid and will coordinate one molecule of the starting sulfoxide. Although deoxygenations with bulky or electron withdrawing sulfoxides are slow, these reactions can be greatly accelerated with the use of excess HBcat or by employing a rhodium catalyst.

Recent Chemistry of the Diboron Compounds

AbstractFor Abstract see ChemInform Abstract in Full Text.

Linear and Nonlinear Optical Properties of Three-Coordinate Organoboron Compounds

Three-coordinate boron, isoelectronic with a trigonal planar carbonium ion, possesses a vacant p orbital which can conjugate with an organic π system and thus serve as a π acceptor. We and others have prepared a series of symmetric compounds of the general form (mes)2 B⇐X⇒B(mes)2 [mes=mesityl=2,4,6 Me3C6H2; ⇐X⇒=conjugated organic π system such as –(p-C6H4)n– or trans–trans–CH=CH–(p-C6H4)n–CH=CH–] as well as donor–acceptor compounds of the general form D⇒X⇒B(mes)2 [D=π donor such as MeO, MeS, H2N, Me2N, Ph2P, ferrocenyl; ⇒X⇒=conjugated organic π system such as –C6H4–, –C6H4–CH=CH–, –C6H4–C≡C–, –C6H4–CH=CH–C6H4–] and examined representative single-crystal structures as well as linear (UV–vis absorption and fluorescence) and second- and third-order nonlinear optical properties (by electric field-induced second harmonic generation (EFISH) and third harmonic generation (THG)). The bulky mesityl groups protect the boron centers from hydrolysis. Many of the compounds are highly fluorescent, with the unsymmetric ones displaying limited solvatochromic behavior in absorption spectra but significant solvatochromic effects in their emission spectra consistent with small dipole moments in the ground state and large dipole moments in the excited states. Results from other groups on the use of related boron compounds as either electron-transport materials or emitting agents in electroluminescent devices, and on the preparation and optical properties of three-coordinate boron-containing conjugated polymers are presented. Preliminary results of extended Hückel (EH) and density functional (DF) molecular-orbital calculations on representative symmetric diboron compounds and extended Hückel tight-binding (EHTB) calculations on a model boron-containing polymer are reported. The B(mes)2 group is a good π acceptor, and three-coordinate boron moieties show significant promise for use in molecular and polymeric optical materials.

Ligand Transfer Reactions between Schiff Base Divalent Group 14 Element Species and Titanium, Nickel, Boron, and Phosphorus Halides

Reactions of the inorganic complexes TiCl4, NiCl2, BF3, PCl3, and (Y)PCl3 (Y = O, S), Cp2TiCl2, and t-BuPCl2 with the Schiff base divalent group 14 element species (L2)M (1−3: L2 = N,N‘-bis(salicylidene)ethylenediamine (Salen), M = Ge (1), Sn (2); L2 = (R,R)-(−)-N,N‘-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, M = Pb (3)) have been investigated. TiCl4 and Cp2TiCl2 afforded the ionic [ClTi(L2)]+[MCl3]- (4) and the neutral Cp(Cl)Ti(L2) (5) complexes, respectively. With NiCl2·DPPE (DPPE = 1,2-bis(diphenylphosphino)ethane) and (Salen)Sn as starting materials, substitution of tin led to the complex (Salen)Ni·SnCl2 (7). The linear diboron compound F2B(Salen)BF2 (9) together with the complex (Salen)Sn·SnF2 (10) were produced on reaction of BF3·Me2O with (Salen)Sn. With t-BuPCl2 and PCl3, the phosphite t-BuP(L2) (11) and the phosphocation [(L2)P]+ (12) together with the anion [MCl3]- (9) were obtained, respectively. The phosphoryl and thiophosphoryl chlorides (Y)PCl3 (Y = O, S) yielded the dinucle...

Lewis Base Adducts of Diboron Compounds: Molecular Structures of [B2(cat)2(4-picoline)] and [B2(cat)2(4-picoline)2] (cat = 1,2-O2C6H4)

Lewis Base Adducts of Diboron Compounds: Molecular Structures of [B2(cat)2(4-picoline)] and [B2(cat)2(4-picoline)2] (cat = 1,2-O2C6H4)

Unprecedented stereoselectivity in a reaction of a novel diboron compound ? 1,6-bis(dialkylboryl)-2,4-hexadiene with carbonyl compounds

Arylboration of carbonyl compounds with a novel diboron reagent — 1,6-bis(dipropylboryl)-2,4-hexadiene — proceeds in a regio- and stereospecific way to give exclusivelyd,l-diastereomers of the corresponding 2,3-divinylsubstituted 1,4-diols. Their iodocyclization allowed preparation of 3,7-dioxabicyclo[3.3.0]octane derivatives withcis-junction of the tetrahydrofuran rings.

ChemInform Abstract: Facile Synthesis of Functional Mono‐ and Di(tert‐butyl)boron Compounds.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Beiträge zur chemie des bors: CLXXVII. Dithiadiboretane und trithiatriborane (borthiine): kinetische und thermodynamische produkt-kontrolle

Thermal decomposition of μ-(aminoborondithiolato)bis(tricarbonyliron) compounds gives the 2,4-diamino-1,3,2,4-dithiadiboretanes (R 2NBS) 2 (R 2N  NMe 2, N iPr 2, tmp) at ∼ 200°C. (Me 2NBS) 2 thus obtained reacts with itself in solution to give (Me 2NBS) 3. Therefore, the B 2S 2 compounds are the kinetically controlled products while the B 3S 3 ring systems represent the thermodynamic products. This is further substantiated by the thermolysis of PhBS 2Fe 2(CO) 6 at 200°C which yields a mixture of (PhBS) 2 with (PhBS) 3, while pure (PhBS) 2 is readily obtained from PhBCl 2 and (Me 3Si) 2S under mild conditions. Pyrolysis of the diboron compound (Me 2N) 2B 2S 2Fe 2(CO) 6 proceeds with disproportionation leading to (Me 2NBS) 2 as the volatile products, while the spirocyclic iron cluster μ-(2,5,7,10-tetramethyl-2,10-diaza-5,7-diazonia-1,6-diboratotricyclo-[5.3.0.0 1,5]decane-6,6-dithiolato)bis(tricarbonyliron) yields bis(1,3-dimethyl-1,3,2-diazaborolidin-2-yl)sulfide. Silthiane cleavage of (Me 2Si) 2S with aminoboron halides R 2NBX 2 and (Me 2N) 2BCl require reflux conditions in toluene to give (R 2NBS) 2,3 heterocycles.

Assignment of vibrational spectra of some dialkylamido-derivatives of boron

A number of inconsistencies and errors in previous vibrational assignments for molecules containing B–NR2 groups have been corrected. This was achieved by studying the i.r. and Raman spectra of B(NR2)3, B[N(CH2)4]3, B(NR2)2Br, and B2(NR2)4, where R = Me or Et. The antisymmetric BN stretches were always above 1 500 cm–1, with the symmetric BN stretches near 1 350 cm–1. The value of ν(B–B) in the diboron compounds was ca. 1 230 cm–1. In B(NR2)3 there is extensive vibrational coupling between the NR2 groups.