Metal-free alkyne annulation enabling π-extension of boron-doped polycyclic aromatic hydrocarbons.

A C-H functionalizing annulation reaction of boron-doped polycyclic aromatic hydrocarbons (PAHs) with alkynes is described. This metal-free π-extension provides a new synthetic route to fusion atom B-doped polycyclic aromatic hydrocarbons (PAHs) that is demonstrated with the synthesis of a family of new, functionalized, structurally constrained 6a,15a-diborabenzo[]naphtho[2,1-]picenes. These annulation products exhibit deep LUMO energy levels, strong visible-range absorptions, and sterically accessible π-systems that can adopt herringbone or π-stacked solid-state structures based on choice of substituents.

Triple -substitution reactions of B(CF) and [(CF)PF] with P(SiMe).

-Substitution reactions on CF rings of Lewis acids have been exploited to achieve triply substituted derivatives. The reaction of B(CF) with P(SiMe) ultimately affords the Lewis acid B(CFP(SiMe))1. This species binds Lewis bases affording the adducts LB(CFP(SiMe)) (L = MeCN 2, OPEt3, PMe4, PBu5) and reacts with LiMe to give the salt [Li][MeB(CFP(SiMe))]·3THF 6.

Diboraperylene Diborinic Acid Self-Assembly on Ag(111)-Kagome Flat Band Localized States Imaged by Scanning Tunneling Microscopy and Spectroscopy.

Replacement of sp-hybridized carbon in polycyclic aromatic hydrocarbons (PAHs) by boron affords electron-deficient π-scaffolds due to the vacant p-orbital of three-coordinate boron with the potential for pronounced electronic interactions with electron-rich metal surfaces. Using a diboraperylene diborinic acid derivative as precursor and a controlled on-surface non-covalent synthesis approach, we report on a self-assembled chiral supramolecular kagome network on an Ag(111) surface stabilized by intermolecular hydrogen-bonding interactions at low temperature. Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal a flat band at ca.

12b,24b-Diborahexabenzo[a,c,fg,l,n,qr]pentacene: A Low-LUMO Boron-Doped Polycyclic Aromatic Hydrocarbon.

Herein we devise and execute a new synthesis of a pristine boron-doped nanographene. Our target boron-doped nanographene was designed based on DFT calculations to possess a low LUMO energy level and a narrow band gap derived from its precise geometry and B-doping arrangement. Our synthesis of this target, a doubly B-doped hexabenzopentacene (B -HBP), employs six net C-H borylations of an alkene, comprising consecutive hydroboration/electrophilic borylation/dehydrogenation and BBr /AlCl /2,6-dichloropyridine-mediated C-H borylation steps.

Reactions of carbene-stabilized borenium cations.

In this paper we probe the reactivity of the borenium cations [CH(NCHCH)(NCHPh)BH][B(CF)] 2 and [CH(NCHCH)B][B(CF)] 3. The reactions of 2 with cyclohexene or 3,3-dimethyl-1-butene gave the alkyl-aryl borenium salts [PhCH(CHN)CCHCHBR][B(CF)] (R = Cy 4, CHCHtBu 5) while the corresponding reactions with diphenylacetylene, 1-hexyne and 1-phenyl-1-propyne gave the aryl-alkenyl borenium cation salts [PhCH(CHN)CCHCHBC(R)C(H)R][B(CF)] (R = R = Ph 6, R = H, R = CH7, R = Me, R = Ph 8a, R = Ph, R = Me 8b). In contrast, the reaction of 2 with ethynyldiphenylphosphane or 2-vinylpyridine lead to the formation of the adducts, [PhCH(CHN)CCHCHB(H)P(Ph)CCH][B(CF)] 9, [PhCH(CHN)CCHCHB(H)NCHC(H)CH][B(CF)] 10, respectively, while the more bulky donor HC[double bond, length as m-dash]C(Ph)PMes gave 1,2-hydroboration of the phosphinoalkene affording [PhCH(CHN)CCHCHBCHCH(Ph)PMes][B(CF)] 11.

A Highly Warped Heptagon-Containing sp Carbon Scaffold via Vinylnaphthyl π-Extension.

A new strategy is demonstrated for the synthesis of warped, negatively curved, all-sp -carbon π-scaffolds. Multifold C-C coupling reactions are used to transform a polyaromatic borinic acid into a saddle-shaped polyaromatic hydrocarbon (2) bearing two heptagonal rings. Notably, this Schwarzite substructure is synthesized in only two steps from an unfunctionalized alkene.

Tunable Low-LUMO Boron-Doped Polycyclic Aromatic Hydrocarbons by General One-Pot C-H Borylations.

Boron-doping has long been recognized as a promising LUMO energy-lowering modification of graphene and related polycyclic aromatic hydrocarbons (PAHs). Unfortunately, synthetic difficulties have been a significant bottleneck for the understanding, optimization, and application of precisely boron-doped PAHs for optoelectronic purposes. Herein, a facile one-pot hydroboration electrophilic borylation cascade/dehydrogenation approach from simple alkene precursors is coupled with postsynthetic B-substitution to give access to ten ambient-stable core- and periphery-tuned boron-doped PAHs.

Synthesis of a Doubly Boron-Doped Perylene through NHC-Borenium Hydroboration/C-H Borylation/Dehydrogenation.

Reaction of an N-heterocyclic carbene (NHC)-borenium ion with 9,10-distyrylanthracene forms four B-C bonds through two selective, tandem hydroboration-electrophilic C-H borylations to yield an isolable, crystallographically characterizable polycyclic diborenium ion as its [NTf ] salt (1). Dehydrogenation of 1 with TEMPO radical followed by acidic workup yields a 3,9-diboraperylene as its corresponding borinic acid (2). This sequence can be performed in one pot to allow the facile, metal-free conversion of an alkene into a small molecule containing a boron-doped graphene substructure.

Chiral carbene-borane adducts: precursors for borenium catalysts for asymmetric FLP hydrogenations.

The carbene derived from (1R,3S)-camphoric acid was used to prepare the borane adduct with Piers' borane 7. Subsequent hydride abstraction gave the borenium cation 8. Adducts with 9-BBN and the corresponding (1R,3S)-camphoric acid-derived carbene bearing increasingly sterically demanding N-substituents (R = Me 9, Et 10, i-Pr 11) and the corresponding borenium cations 12-14 were also prepared.

Synthesis of a diboryl-N-heterocycle and its conversion to a bidentate cationic Lewis acid.

Sequential reaction of 2-lithio-1-methylimidazole with 9-borabicyclo[3.3.1]nonane (9-BBN) dimer and 9-Cl-9-BBN yields diboryl-N-heterocycle C4H5N2(H)(BC8H14)2 (1).

Planar N-heterocyclic carbene diarylborenium ions: synthesis by cationic borylation and reactivity with Lewis bases.

The NHC-borane adduct (IBn)BH3 (1) (NHC= N-heterocyclic carbene; IBn=1,3-dibenzylimidazol-2ylidene) reacts with [Ph3 C][B(C6 F5 )4 ] through sequential hydride abstraction and dehydrogenative cationic borylation(s) to give singly or doubly ring closed NHC-borenium salts 2 and 3. The planar doubly ring closed product [C3 H2 (NCH2 C6 H4 )2 B][B(C6 F5 )4 ] is resistant to quaternization at boron by Et2 O coordination, but forms classical Lewis acid-base adducts with the stronger donors Ph3 P, Et3 PO, or 1,4-diazabicyclo[2.2.

A family of N-heterocyclic carbene-stabilized borenium ions for metal-free imine hydrogenation catalysis.

This manuscript probes the steric and electronic attributes that lead to "frustrated Lewis pair" (FLP)-type catalysis of imine hydrogenation by borenium ions. Hydride abstraction from (IBu)HB(CF) prompts intramolecular C-H bond activation to give (CHN)(Bu) (CMeCH)CB(CF), defining an upper limit of Lewis acidity for FLP hydrogenation catalysis. A series of seven N-heterocyclic carbene-borane (NHC-borane) adducts ((R'CNR)C)(HBCH) (R' = H, R = dipp , Mes , Me ; R = Me R' = Me , Cl, ) and ((HC)(NMe)(NR)C)(HBCH) (R = Bu, , Ph ) are prepared and converted to corresponding borenium salts.

Activation of hydrogen and hydrogenation catalysis by a borenium cation.

The readily prepared borenium salt [(IiPr(2))(BC(8)H(14))][B(C(6)F(5))(4)] (2) [IiPr(2) = C(3)H(2)(NiPr)(2)] is shown to activate H(2) heterolytically in the presence of tBu(3)P. Compound 2 also acts as a catalyst for the metal-free hydrogenation of imines and enamines at room temperature.

Metal-free catalytic hydrogenation of polar substrates by frustrated Lewis pairs.

In 2006, our group reported the first metal-free systems that reversibly activate hydrogen. This finding was extended to the discovery of "frustrated Lewis pair" (FLP) catalysts for hydrogenation. It is this catalysis that is the focal point of this article.