Boron Cations Research Articles

The coordination chemistry of (py) 2BF 2+ and related difluoroboron cations

The substitution and decomposition reactions of the difluorobis(pyridine)boron(III) cation, and of several substituted pyridine and other difluoroboron cations (D) 2BF 2 +, are explored. Donor molecule displacement is greatly accelerated by the presence of electron-withdrawing meta and para pyridine substituents in (substituted pyridine) 2BF 2 + cations, and by electron-donating substituents on pyridine when the substituted pyridine is the attacking species. Increased steric hindrance of D in D 2BF 2 +, and of the attacking base D′, slows or prevents displacement of D by D′. (py) 2BF 2 +·PF 6 − undergoes slow decomposition in acetone, giving initially py·BF 3 and finally py·H +·BF 4 − as the major fluoroboron species. A second decomposition pathway, giving rise to BF 3OH − and several additional fluorine-containing products, is favoured by the presence of strong bases such as amidines and by the presence of NH and OH bonds. Increased susceptibility to ligand displacement facilitates the synthesis of new fluoroboron cations, but also increases the susceptibility to decomposition.

Symmetry breaking localisation of the unpaired electron in spiro-bis(1,9-disubstituted-phenalenyl)boron radicals

We report the crystal structure of a spiro-bis(1,9-disubstituted-phenalenyl)boron cation ( 2 +) and by comparison with the structures of a series of radicals we conclude that the changes in bond lengths in the radicals compared to those of the corresponding cation can be qualitatively predicted by the sign of the partial bond order of the singly occupied molecular orbital (SOMO), which contains the additional electron. By use of this information, we can analyse the structures of the π-dimer radicals 1 and 2 and ascertain the location of the unpaired electron in these compounds. Where these radicals exist as paramagnetic π-dimers (high-temperature regime), the unpaired electrons reside mainly in the phenalenyl units not directly involved in the π-dimer interaction. At low temperatures, where the diamagnetic π-dimers exist, the electrons localise in the phenalenyl units directly involved in the π-dimer, but there still exists some degree of delocalisation of the electrons to the other halves of the molecules. We postulate that the increase in delocalisation of the unpaired electrons is related to the increase of the conductivity by about two orders of magnitude as the electrons spin pair.

Boron Diffusion Mechanism in Silicon Oxide Using AB Initio Methods

AbstractDensity functional theory was employed to explore the diffusion mechanism of boron in amorphous silicon oxide. The oxide was modeled with clusters of various sizes, and both neutral boron atoms and cations were considered. Three stable structures were found where B (or B+) was inserted into oxide: one in which B (or B+) is divalent and two in which B (or B+) is trivalent. Boron diffusion through silicon oxide proceeds as a sequence of B hops from one inserted position to another. For neutral boron the rate limiting step is B hop from one of trivalent structures to a divalent one with activation energies (Ea) in the range of 2.0-3.1 eV, depending on the model cluster. In the case of a cation the rate-limiting step is the B+ hop over the O atom in a divalent structure Si-B+-O-Si with calculated Ea of 2.4-2.8 eV. Experimental activation energies for B diffusion in silicon oxide are in the 2.3 - 4.2 eV range. Our results suggest that both neutral and cation boron can participate in B diffusion in oxide.

Novel Rare Gas Ions BXe+, BKr+, and BAr+ Formed in a Halogen/Rare Gas Exchange Reaction

Singly charged rare gas borynium ions were prepared for the first time by making use of mass-selected ion/molecule reactions in a triple-quadrupole mass spectrometer. Halogen for rare-gas exchange reactions leading to the formation of the novel species BAr+, BKr+, and BXe+ were carried out by allowing the radical cation BBr+• to react with neutral rare gas atoms in the second quadrupole under conditions typically used for collision-induced dissociation (CID) in tandem mass spectrometry experiments. The ions formed contain the bonds B−Ar, B−Kr, and B−Xe, the lengths of which were calculated at the B3-LYP/LANL2DZ level of theory to be 2.590, 2.635, and 2.713 A, respectively. Natural bond orbital (NBO) population analysis revealed that the bond order increases with increasing size of the rare gas atom: Ar < Kr < Xe. The reactions leading to the formation of the singly charged boron cations of Ar, Kr, and Xe are endothermic by 50.1, 45.8, and 38.7 kcal/mol, respectively. The energy required to drive these re...

Synthesis of B- and P-Heterocycles by Reaction of Cyclic Acetals and Ketals with Borinium and Phosphonium Ions.

Tricoordinated cyclic boron cations result from gas-phase ion/molecule reactions of dicoordinated borinium ions with neutral acetals and ketals and thiazolidine. The reaction, which proceeds via initial cationic binding to a heteroatom followed by a consecutive ring-opening and ring-reclosing process, resembles the Eberlin transacetalization of acylium ions (Eberlin, M. N.; Cooks, R. G. Org. Mass Spectrom. 1993, 28, 679). The cyclic structure of the tricoordinated boron cation is demonstrated by tandem mass spectrometry and further confirmed by comparison with authentic cyclic tricoordinated boron cations. The five-membered cyclic boron cations dissociate by ethylene oxide loss to thus reform the reactant-dicoordinated borinium ion; the six-membered boron cations fragment instead by ethylene loss. Consistent with the proposed mechanism, the ion/molecule reaction efficiency falls in the order CH(3)OB(+)C(2)H(5) > CH(3)OB(+)OCH(3) >> CH(3)B(+)CH(3); i.e., the higher the nucleophilicity of the borinium ion, the higher the reaction efficiency. A potential energy surface is calculated for the reaction of CH(3)OB(+)OCH(3) with 2-methyl-1,3-dioxolane, and the reaction is found to be 43.3 kcal/mol exothermic due to initial formation of a strong B-O bond. The analogous reactivity displayed by phosphonium ions is also investigated by both experiment and ab initio calculations. In contrast to the borinium ions, the phosphonium ions exhibit higher regioselectivity for sulfur compared to nitrogen and oxygen. Finally, the present findings indicate that the reaction exothermicity and the regioselectivity are controlled by both the Lewis acidity of the reactant cations and the leaving ability of the released neutrals in the rate-limiting nucleophilic-induced recyclization step.

Hybrid procedure of the ab initio molecular orbital (MO) method and the Monte Carlo samplings; application to cluster B +(H 2O)

The hybrid procedure of the ab initio molecular orbital (MO) method and the Monte Carlo (MC) samplings which we have developed recently is applied to one to one complex of boron cation and water molecule B +(H 2O). In the present ab initio MO-MC samplings, no analytical potential function is assumed, and the ab initio MO method is directly used for energy calculation at each step. As the result of using the new method, the many body interaction is explicitly taken into the assumption, and the chemical reaction involving the rearrangement of arbitrary atoms can be easily treated. In the case of cluster B +(H 2O), no intracluster reaction takes place, but structure under the thermal equilibrium is slightly broken from the optimised geometry. The deformation of structure is attributed to the entropy effect, and it is also considered a symptom of the insertion reaction B +(H 2O) → HBOH +.

Disubstituted Boron Cations Cleave Carbonyl Bonds

The disubstituted boron cations CH3OBOCH3+ and CH3BCH3+ readily cleave CO and C−C bonds in gaseous long-chain aldehydes and ketones in a dual-cell Fourier transform ion cyclotron resonance mass spectrometer. Abstraction of OH by the borocations yields a hydrocarbon product ion that contains the entire carbon skeleton of the aldehyde or ketone. A competing abstraction of part of the carbonyl compound as a small aldehyde results in a borocation product that is indicative of the location of the carbonyl group in the neutral substrate. The mechanisms of these two reactions likely involve common intermediates formed via 1,2-hydride shifts in an initially formed B−OC adduct. Both reactions are highly exothermic. The OH abstraction reaction is the thermodynamically favored pathway while aldehyde abstraction is kinetically favored by the smaller carbonyl compounds. The overall enthalpy change associated with the latter reaction is likely to be relatively insensitive to the size of the carbonyl compound. In contrast, the OH abstraction reaction becomes more exothermic as the size of the substrate increases. This results in a predominant hydrocarbon ion product for the larger aldehydes and ketones.

Stereoelectronic Effects and Gas-phase Affinities of Dicoordinated Borinium Cations

The relative affinities of the borinium cations (CH 3 O) 2 B + and CH 3 OB + H towards pyridines were determined by the kinetic method using a pentaquadrupole mass spectrometer and the absolute affinities of these ions towards pyridine itself were estimated with the aid of ab initio calculations at the MP2/6-31G(d,p)//6-31G(d,p) level to be 75.7 and 82.2 kcal mol -l , respectively (1 kcal = 4.184 kJ). The affinities were found to correlate linearly with the proton affinities of the meta- and para-substituted pyridines, but steric effects decrease the affinities for ortho-substituted pyridines. A set of gas-phase stereoelectronic parameters (s k ) for these isomers was measured from the deviation of the value of the logarithm of the experimentally measured ion abundance ratio from the regression line established for meta- and para-substituted pyridines. The S k value of 2,6-dimethylpyridine with (CH 3 O) 2 B + is smaller than that for other dimethylpyridines, owing to the stabilizing effects of auxiliary hydrogen bonding interactions between one hydrogen of each of the ortho-methyl substituents and the two oxygens of the (CH 3 0) 2 B + ion. The dimethoxy boron cation (CH 3 O) 2 B + is shown to have smaller steric effects than CH 3 OB + H, even though the former ion has two bulky methoxy groups. This is ascribed to the relatively longer B-N bond in (CH 3 O) 2 B + -Py as a result of reduced charge density on the boron atom due to resonance stabilization within the dimethoxy boron cation.

Stereoelectronic Effects and Gasphase Affinities of Dicoordinated Borinium Cations

The relative affinities of the borinium cations (CH3O)2B+ and CH3OB+H towards pyridines were determined by the kinetic method using a pentaquadrupole mass spectrometer and the absolute affinities of these ions towards pyridine itself were estimated with the aid of ab initio calculations at the MP2/6–31G(d,p)//6–31G(d,p) level to be 75.7 and 82.2 kcal mol-1, respectively (1 kcal=4.184 kJ). The affinities were found to correlate linearly with the proton affinities of the meta- and para-substituted pyridines, but steric effects decrease the affinities for ortho-substituted pyridines. A set of gas-phase stereoelectronic parameters (Sk) for these isomers was measured from the deviation of the value of the logarithm of the experimentally measured ion abundance ratio from the regression line established for meta- and para-substituted pyridines. The Sk value of 2,6-dimethylpyridine with (CH3O)2B+ is smaller than that for other dimethylpyridines, owing to the stabilizing effects of auxiliary hydrogen bonding interactions between one hydrogen of each of the ortho-methyl substituents and the two oxygens of the (CH3O)2B+ ion. The dimethoxy boron cation (CH3O)2B+ is shown to have smaller steric effects than CH3OB+H, even though the former ion has two bulky methoxy groups. This is ascribed to the relatively longer B—N bond in (CH3O)2B+—Py as a result of reduced charge density on the boron atom due to resonance stabilization within the dimethoxy boron cation. © 1997 by John Wiley & Sons, Ltd.

ChemInform Abstract: Gas‐Phase Reactions of Dicoordinated Boron Cations with Alcohols.

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.

Gas-Phase Reactions of Dicoordinated Boron Cations with Alcohols

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGas-Phase Reactions of Dicoordinated Boron Cations with AlcoholsThilini D. Ranatunga and Hilkka I. KenttaemaaCite this: Inorg. Chem. 1995, 34, 1, 18–27Publication Date (Print):January 1, 1995Publication History Published online1 May 2002Published inissue 1 January 1995https://doi.org/10.1021/ic00105a008RIGHTS & PERMISSIONSArticle Views81Altmetric-Citations29LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (810 KB) Get e-Alerts Get e-Alerts

ChemInform Abstract: Dicoordinated Boron Cations Dehydrate Organic Ethers in the Gas Phase.

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.

Dicoordinated boron cations dehydrate organic ethers in the gas phase

Condensed-phase studies of two-coordinated boron cations are limited to ions with conjugatively stabilizing substituents the reactions of these ions are dominated by simple addition. We have investigated the gas-phase reactions of two simple, dicoordinated boron cations, CH 3 OBOCH 3 + and CH 3 BCH 3 + , in a dual-cell Fourier-transform ion cyclotron resonance device

Structure and bonding trends in two- and three-coordinate boron cations

Structure and bonding trends in two- and three-coordinate boron cations

ChemInform Abstract: Synthesis and Characterization of the First Borane Adducts and Boron Cations of Some N‐Alkyl and N‐Aminotriphenylphosphoranimines.

Abstract The first borane adducts of N-alkyl and N-aminotriphenylphosphoranimines, Ph3P[dbnd]N—R, were prepared by two different general synthetic methods. The first method involved displacement of THF (tetrahydofuran) from THF-borane by the free imines, and the second employed the reaction of LiBH4 with iminium bromides, Ph3P[dbnd]N(R)HBr, in diethyl ether. Imine boranes, Ph3P[dbnd]N(R)BH3, were synthesized where R [dbnd] methyl, ethyl, n-propyl, isopropyl, isobutyl, t-butyl. dimethylamino, phenylamino, and methyl, phenylamino as the nitrogen attached groups. Symmetrical boron cations, (Ph3P[dbnd]NR)2, BH2 +, where R = methyl, ethyl, and n-propyl, were synthesized by displacement of iodide from in-situ generated iodoborane adducts, Ph3P[dbnd]N(R)BH2I, by the free imines. An attempt to form an unsymmetrical boron cation from (CH3)3 NBH2I and Ph, P[dbnd]N(n-C3H7) resulted only in a mixture of the corresponding symmetrical boron cations. Physical, chemical and spectral properties of the borane adducts and b...

SYNTHESIS AND CHARACTERIZATION OF THE FIRST BORANE ADDUCTS AND BORON CATIONS OF SOME N-ALKYL AND N-AMINOTRIPHENYLPHOSPHORANIMINES

Abstract The first borane adducts of N-alkyl and N-aminotriphenylphosphoranimines, Ph3P[dbnd]N—R, were prepared by two different general synthetic methods. The first method involved displacement of THF (tetrahydofuran) from THF-borane by the free imines, and the second employed the reaction of LiBH4 with iminium bromides, Ph3P[dbnd]N(R)HBr, in diethyl ether. Imine boranes, Ph3P[dbnd]N(R)BH3, were synthesized where R [dbnd] methyl, ethyl, n-propyl, isopropyl, isobutyl, t-butyl. dimethylamino, phenylamino, and methyl, phenylamino as the nitrogen attached groups. Symmetrical boron cations, (Ph3P[dbnd]NR)2, BH2 +, where R = methyl, ethyl, and n-propyl, were synthesized by displacement of iodide from in-situ generated iodoborane adducts, Ph3P[dbnd]N(R)BH2I, by the free imines. An attempt to form an unsymmetrical boron cation from (CH3)3 NBH2I and Ph, P[dbnd]N(n-C3H7) resulted only in a mixture of the corresponding symmetrical boron cations. Physical, chemical and spectral properties of the borane adducts and b...

ChemInform Abstract: Main Group Metallocenes: Recent Developments

Synthesis, structure, and chemistry of some trimethylsilylated and permethylated dyclopentadienyl compounds of s- and p-block elements are described. Bent-sandwich structures are found for the magnesium complex ((Me3Si)3C5H2)2Mg, for the calcium compound ((Me3Si)2CsH3)2Ca'THF and for the metallocenes of germanium, tin and lead, (Me5C5)2EI. Half-sandwich structures could be proved for adducts of silylated cyclopenta- dienyllithium compounds with nitrogen- and oxygen- donors, for a new class of boron cations, Me5C5BR +, and for the group 14 cations MesCsEI' (El = Ge,Sn,Pb). - A bent-po- lydecker sandwich is the structural basis of the potassium compound (Me3Si)C5H4KS - De- camethylsilicocene, (MesC5)2Si, the first stable silicon(l1) compound, could be synthesized from a silicon(lV) precursor, (Me5C5)2SiCl2. The properties of this .ii-complex are compa- red with those of the heavier homologues.

Main-group metallocenes: Recent developments

Abstract

ChemInform Abstract: Chemistry of Boron. Part 173. Salts of the Bis(diisopropylamino)boron(1+) Cation.

AbstractThe reaction of (I) with aluminum and gallium tribromide produces stable salts(II) of the title boron cation.

Beiträge zur Chemie des Bors, 154. Addition von Trimethylsily‐Verbindungen und von anderen Elektrophilen an ( tert ‐Butylimino) (tetramethylpiperidino)boran

Contributions to the Chemistry of Boron, 154. Addition of Trimethylsilyl Compounds and Some Other Electrophiles to (tert-Butylimino)-(tetramethylpiperidino)borane The amino-imino borane 3 adds methyl triflate and triflic acid to form tricoordinated borane derivatives (1, 4). In contrast, trimethylsilyl triflate and trimethylsilyl iodide yield salts (2, 5) of the [tert-butyl(trimethylsiyl)amino](tetramethylpiperidino)boron(1+) cation containing a dicoordinated boron atom.