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有機ホウ素反応剤は高い安定性（保存性）官能基許容性をもつ

What is Boron?

５B

■ Boronhttp://periodictable.com/Elements/005/

■ Boron, atomic No. 5, first isolated in 180８. The isolated form has metallic and non-metallic properties. Mp. ２３００℃. Boron can make stable covalent bonds with various other elements.

■ Flame test

https://www.youtube.com/watch?v=m3mfhquJtjo

What is Boron?

■ RioTinto mine（CA, USA） Open-pit mining for Borax(ホウ砂) 1.8 million tons of Borax was produced in the world every years.

■ Crystals of Borax (ホウ砂） Na2B4O5(OH)4・8H2O

BCl3wikipedia

http://www.larazon.es/riotinto-el-resurgir-de-una-mina-historica-AY8526367#.Ttt1Jsq3GRZZbrphttp://www.gascylinder.co.in/boron-trifoluoride.html

Images:

What is Boron?

■ Borosilicate glassknown for having very low coefficients of thermal expansion, making them resistant to thermal shock, more so than any other common glass.

■ Borazon (立方晶窒化ホウ素)It is one of the hardest known materials, along with various forms of diamond

http://www.eurideastranslation.com/chemistry/laboratory-glassware-2/http://www.okamoto-inc.jp/products/homecare.html

http://www.tagen.tohoku.ac.jp/tech/glass/ware/elements2/index.htmlhttp://www.china-superabrasives.com/products/CBN-Large/AO1.htm

http://www.promasz.eu/brozan.htmlhttp://de.wikipedia.org/wiki/Bornitrid

■ Boronic acid Harmful for many insects.

有機ホウ素反応剤は高い安定性（保存性）官能基許容性をもつ

Electronic Structure of Boron

５B

2p

2s

1s

５B 6C 7N2p

2s

1s

2p

2s

1s

Orbital Hybridization of Boron

2p

2s

1s

５B 6C 7N2p

2s

1s

2p

2s

1s

2sp3C

2sp2

2pCC

2sp3N

2sp2

2p

B

■ empty p orbital

有機ホウ素反応剤は高い安定性（保存性）官能基許容性をもつ

Orbital Hybridization and Structure

2sp2

2p

B

■ empty p orbital

wikipedia

■ Lewis acidityF

■ Planar Structure

F BFF

OB

F FF

CH3H3C2sp3

OCH3H3C

有機ホウ素反

Organoboron Compounds for Synthesis

■ H. C. Brown: organoboron compounds as synthetic reagents.

H. C. Brown (1912-2004) photo: Purdue Univ.H. C. Brown (1961)

BH2 +

H B(ipc)2 H OHoxidation

99% ee

CC

H BHH

BH H

H

HB

HH

CCR

R

BH3

+

Rδ+

δ-

■ BoraneーAlkene Complex

BHH

H

RR

BH2H

■ four membered TS

ROH

H

H2O2

NaOH aq.

■ H2O2 Oxidation ■ anti-Maokovnikov

有機ホウ素反応剤は高い安

R

OHR

H+, H2O

■ Maokovnikov

Basics of Organoboron Compounds

LUMO of BMe3

R BR

R

✔ Weak nucleophilicity and Lewis acidity originated by the vacant 2p orbital.

✔ R3B can react with O2.Not stable in air.

vacant p orbital

■ Trialkylborons：R3B

R B

O

O

■Alkylboronic acid esters：RB(OR)2

Electron donation of oxygen lone pairs to vacant 2p orbital of B: →Lowering Lewis acidity of B.

✔ Lower Lewis acidity and higher covalence of C-B bonds.→ Improvement of the stability

HOMO-2 of MeB(OR)2Electron withdrawing of O→Enhance the covalence of C-B bonds

BO

OR

Basics of Organoboron Compounds■ RB(OR)2 is activated by addition of base

BOR

ORR

ORORB

OR

ORR B

OR

ORR OR

■ Various esters with different reactivity

O

OBR

O

OBR

O

OBR

O

OBR

R

R

R B(pin)R Bpin

OH

OHBR

OB

OBO

B

R R

R

boroxine

–H2O

■ Condensations

■ Protecting groups

R BF3-K+

B NO

O

O

O

MeRN

BN

R

H

H

Burke, 2008 Suginome, 2007R B(dan)MIDA boronate

BO

OOR

M+

Miyaura, 2008

BAr

■ Stabilizations

the anthracene moieties for the cyclization to occur selec-tively at the 1,8-positions and to prevent the strong aggrega-tion of the resulting PAH p skeleton. This anthryl group wasoriginally reported by Anderson and coworkers, and is widelyused for the synthesis of expanded p skeletons.[13]

The precursor 3 was prepared in 54% yield by thelithiation of 9-bromobis(mesityloxy)anthracene 4[13] withnBuLi, followed by treatment with dibromodiborapentacene5.[14] Compound 3 showed high stability to water and oxygenas a result of the steric protection of the boron atoms by thebulky anthryl groups. The cyclodehydrogenation of 3 with anexcess of FeCl3 proceeded successfully to form 1a in 51%yield as a deep purple solid. As expected, the doubly B-dopednanographene 1a is stable enough to handle in air and wasisolated by column chromatography on silica gel without anyspecial precautions. Compound 1a is sufficiently soluble incommon organic solvents, such as chlorobenzene(4.8 mgmL!1) and ortho-dichlorobenzene (10.8 mg mL!1),thus demonstrating its processability in solution.

The structure of 1 was unambiguously characterized bymass spectrometry, NMR spectroscopy (Figure 1), and finallyX-ray crystallography (Figure 2). These analyses revealed 1ato be a single compound. High-resolution atmospheric

pressure chemical ionization time-of-flight (APCI-TOF) MSshowed a parent ion signal for 1a at m/z 1157.4942 (calcd forC84H63O4B2 [M+H]+, m/z 1157.4931; see the SupportingInformation). Two sets of coupled signals (Ha and Hb, andHc and Hd in Figure 1) were observed at 6.96 and 9.12 ppm,and 7.76 and 9.02 ppm, respectively in the 1H NMR spectrum

of 1a in [D2]tetrachloroethane at 353 K (Figure 1). Therelatively downfield chemical shifts of the Hb and Hd signalsare attributed to the deshielding effect by the ring current ofthe neighboring benzene rings in the cove region. The otherdeshielded singlet signal at 10.85 ppm corresponds to the He

atom, which reflects the close contact with the oxygen atoms(see the Supporting Information).[13] Variable-temperature1H NMR measurements from 193 to 353 K did not show anysignificant change. This temperature independency indicatesa large energy gap between the singlet closed-shell groundstate and a triplet excited state. The gap was calculatedtheoretically to be 34.9 kcalmol!1 for 1a at the B3LYP/6-31G* level, which is far larger than that of the parent undopednanographene 2 (1.5 kcalmol!1) with an open-shell groundstate (see the Supporting Information). The broad 11B NMRsignal of 1a at 58.0 ppm is typical of tricoordinated boroncompounds.

The single crystals were obtained by slow diffusion ofheptane into a solution of 1a in chlorobenzene. The X-raycrystallographic analysis revealed a contorted polycyclicskeleton of the B-doped nanographene 1a composed of 48sp2-hybridized C atoms and two tricoordinated B atoms(Figure 2).[15] Fifteen six-membered rings are fused to formthe nanographene sheet with four cove regions and two zigzagedges. As a consequence of steric overcrowding of the Hb andHd atoms in the cove regions, the p-conjugated core skeletonis distorted away from planarity. Although the distancebetween the most deviated C atoms and the C48B2 meanplane is 1.02 !, the dihedral angles between the mostcontorted benzene rings and the central C4B2 ring is 19.78.The doping positions of the two B atoms were determinedunambiguously, as the B!C bond lengths of 1.507(2), 1.531(2),and 1.535(2) ! are significantly longer than those of the otherC!C bonds (1.37–1.48 !). Notably, these B!C bonds aremuch shorter than those of the nonfused triphenylborane(1.57–1.59 !).[16] This structural characteristic has alreadybeen observed in the other planarized triarylboranes pre-

Scheme 1. Stepwise boron doping of an extended polyaromatic hydro-carbon.

Scheme 2. Synthesis of B-doped nanographene 1a. Reagents andconditions: a) 4, nBuLi, Et2O, from 0 8C to 25 8C, then 5, toluene, from0 8C to 25 8C; b) FeCl3, CH3NO2 and CH2Cl2.

Figure 1. 1H NMR spectrum of 1a in [D2]tetrachloroethane at 353 K.

AngewandteChemie

12207Angew. Chem. Int. Ed. 2012, 51, 12206 –12210 ! 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org

Planarization: Yamaguchi, 2012

Steric

the anthracene moieties for the cyclization to occur selec-tively at the 1,8-positions and to prevent the strong aggrega-tion of the resulting PAH p skeleton. This anthryl group wasoriginally reported by Anderson and coworkers, and is widelyused for the synthesis of expanded p skeletons.[13]

The precursor 3 was prepared in 54% yield by thelithiation of 9-bromobis(mesityloxy)anthracene 4[13] withnBuLi, followed by treatment with dibromodiborapentacene5.[14] Compound 3 showed high stability to water and oxygenas a result of the steric protection of the boron atoms by thebulky anthryl groups. The cyclodehydrogenation of 3 with anexcess of FeCl3 proceeded successfully to form 1a in 51%yield as a deep purple solid. As expected, the doubly B-dopednanographene 1a is stable enough to handle in air and wasisolated by column chromatography on silica gel without anyspecial precautions. Compound 1a is sufficiently soluble incommon organic solvents, such as chlorobenzene(4.8 mgmL!1) and ortho-dichlorobenzene (10.8 mg mL!1),thus demonstrating its processability in solution.

The structure of 1 was unambiguously characterized bymass spectrometry, NMR spectroscopy (Figure 1), and finallyX-ray crystallography (Figure 2). These analyses revealed 1ato be a single compound. High-resolution atmospheric

pressure chemical ionization time-of-flight (APCI-TOF) MSshowed a parent ion signal for 1a at m/z 1157.4942 (calcd forC84H63O4B2 [M+H]+, m/z 1157.4931; see the SupportingInformation). Two sets of coupled signals (Ha and Hb, andHc and Hd in Figure 1) were observed at 6.96 and 9.12 ppm,and 7.76 and 9.02 ppm, respectively in the 1H NMR spectrum

of 1a in [D2]tetrachloroethane at 353 K (Figure 1). Therelatively downfield chemical shifts of the Hb and Hd signalsare attributed to the deshielding effect by the ring current ofthe neighboring benzene rings in the cove region. The otherdeshielded singlet signal at 10.85 ppm corresponds to the He

atom, which reflects the close contact with the oxygen atoms(see the Supporting Information).[13] Variable-temperature1H NMR measurements from 193 to 353 K did not show anysignificant change. This temperature independency indicatesa large energy gap between the singlet closed-shell groundstate and a triplet excited state. The gap was calculatedtheoretically to be 34.9 kcalmol!1 for 1a at the B3LYP/6-31G* level, which is far larger than that of the parent undopednanographene 2 (1.5 kcalmol!1) with an open-shell groundstate (see the Supporting Information). The broad 11B NMRsignal of 1a at 58.0 ppm is typical of tricoordinated boroncompounds.

The single crystals were obtained by slow diffusion ofheptane into a solution of 1a in chlorobenzene. The X-raycrystallographic analysis revealed a contorted polycyclicskeleton of the B-doped nanographene 1a composed of 48sp2-hybridized C atoms and two tricoordinated B atoms(Figure 2).[15] Fifteen six-membered rings are fused to formthe nanographene sheet with four cove regions and two zigzagedges. As a consequence of steric overcrowding of the Hb andHd atoms in the cove regions, the p-conjugated core skeletonis distorted away from planarity. Although the distancebetween the most deviated C atoms and the C48B2 meanplane is 1.02 !, the dihedral angles between the mostcontorted benzene rings and the central C4B2 ring is 19.78.The doping positions of the two B atoms were determinedunambiguously, as the B!C bond lengths of 1.507(2), 1.531(2),and 1.535(2) ! are significantly longer than those of the otherC!C bonds (1.37–1.48 !). Notably, these B!C bonds aremuch shorter than those of the nonfused triphenylborane(1.57–1.59 !).[16] This structural characteristic has alreadybeen observed in the other planarized triarylboranes pre-

Scheme 1. Stepwise boron doping of an extended polyaromatic hydro-carbon.

Scheme 2. Synthesis of B-doped nanographene 1a. Reagents andconditions: a) 4, nBuLi, Et2O, from 0 8C to 25 8C, then 5, toluene, from0 8C to 25 8C; b) FeCl3, CH3NO2 and CH2Cl2.

Figure 1. 1H NMR spectrum of 1a in [D2]tetrachloroethane at 353 K.

AngewandteChemie

12207Angew. Chem. Int. Ed. 2012, 51, 12206 –12210 ! 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org

Yamaguchi, 2012

Fig. 9 Left: the structure of compound 17. Middle: A green OLED based on compound 15. Right: An orange OLED based on 17.

4. Devices incorporating 8 wt.% of this material doped intoCBP (4,4¢-bis(9-carbazolyl)biphenyl) showed remarkably highefficiency red phosphorescence, with maximum current, power andexternal quantum efficiencies (EQEs) of 10.31 cd A-1, 5.04 lm W-1

and 9.36%, respectively. It should be noted that, while much higherefficiencies have been achieved with the parent green phosphorIr(ppy)2(acac) using a similar device structure,8a,b the performanceof 4 is still very impressive as it is a red emitter and is expected tohave a much lower efficiency than the parent molecule accordingto the well-known energy gap law.

We have recently examined the impact of functionalization withtriarylboron on the performance of OLEDs containing platinumphosphors.11 Pt(II) complexes present a different challenge thancomplexes of Ir(III), as their square planar geometry increasesthe tendency of these materials for Pt–Pt stacking and exciplexemission. While in some situations this can be advantageous,especially in achieving white OLEDs,28 Pt(II) excimers generallyexhibit lower quantum efficiencies than the parent phosphors.Triarylborane-functionalized Pt(acac) compounds such as 14–16, however, have been found to be much less prone to excimerformation. In addition to 14–16, we have also examined a numberof other BMes2-functionalized NŸC-chelate Pt(acac) complexes.11

In all cases these boron-functionalized complexes were brightlyphosphorescent at room temperature in the solid state andsolution, due to a mixture of LC and MLCT phosphorescence.Furthermore, all of these complexes exhibited significantly higherUP than analogous complexes lacking a boron center.11 Consistentwith earlier studies, the presence of the triarylboron group greatlyincreased the intensity of the MLCT absorption band, and DFTcalculations indicate that the empty orbital on boron was a largecontributor to the LUMO in all cases. Indeed, complex 15 itselfwas found to exhibit an exceptionally high UP of 0.57 in the solidstate, and was evaluated as an emitter for OLEDs alongside theanalogous complex Pt(ppy)(acac), which lacked the boryl group.OLEDs using 15 as an emitter exhibited green emission (CIEcoordinates = 0.35, 0.61), with maximum efficiencies of 34.5 cdA-1, 29.8 lm W-1 and 8.9% EQE compared to 14.1 cd A-1, 11.7 lmW-1 and 6.9% EQE for those using Pt(ppy)(acac). Furthermore,the efficiency of devices containing 15 as the emitter were amongthe highest achieved using Pt(II) to date.29 The improved efficiencyof 15 OLEDs could be attributed to three factors: 1) higher internalquantum efficiency due to the improved UP of the borylatedphosphor itself, 2) reduced low-efficiency exciplex emission due tothe presence of the boryl group, and 3) improved electron injectionand mobility in the emissive layer.

Hole mobilities typically exceed electron mobilities in organicmaterials by 1–2 orders of magnitude,30 leading to charge im-balance in the device and reduced efficiency. For this reason,

improving electron mobility in the emissive layer is one strategythat can be used to achieve better carrier balance in OLEDs.31

To confirm that the BMes2 group indeed improves electrontransport in the device, we fabricated single-carrier devices32

capable of transporting electrons only from thin films of 15or Pt(ppy)(acac). Remarkably, the film of 15 was capable ofsupporting a current density 3–4 orders of magnitude higher thanthat of Pt(ppy)(acac), indicative of markedly improved electronmobility.11a Furthermore, this highlighted the bifunctional natureof the boron-functionalized materials, namely efficient electrontransport and phosphorescence.

Following the success of this system, we later extended thisconcept to a trifunctional material11b 17 (Fig. 9) designed asa phosphorescent successor to the highly fluorescent molecule7, which had been incorporated into efficient blue fluorescentOLEDs.7d Similar to 16 in structure, this material further containsthe N-phenyl-1-naphthyl group as a strong electron donor. Thismoiety, taken from the widely used hole transport materialNPB (N,N¢-di-[(1-naphthalenyl)-N,N¢-diphenyl]-(1,10-biphenyl)-4,4¢-diamine), should thus be able to efficiently support oxidationand hole-transport. Furthermore, incorporation of the NPBmoiety leads to bright ligand-centerd charge transfer phosphores-cence, facilitated by Pt(II). When used in a doped emissive layer inOLEDs, devices exhibiting bright orange electrophosphorescence(lEL = 581 nm, CIE = 0.52, 0.47) with efficiencies of 35.0 cd A-1,36.6 lm W-1 and 10.1% EQE have been achieved. This is quiteremarkable since the emission of 17 is much red-shifted, comparedto that of 15. Though to date only three reports on the subject havebeen published,11,16 these results give a promising outlook for theuse of triarylboron-containing metal complexes as phosphorescentmaterials in OLEDs.

5. Triarylboron-containing metal complexes as anion sensors

Many reports to date have focused on the use of triarylboroncompounds as chemical sensors for fluoride and cyanide, due to thehigh selectivity with which the BMes2 group binds these anions andthe unique colorimetric and luminescent color changes that resultfrom the anion binding event. Several excellent reviews have beenpublished recently on the use of triarylboranes as anion sensors,in which the reader will find further information on strategies foranion detection and improving the sensitivity of the chemosensorin organic and protic media.5b,c

Transition metal-containing triarylboranes offer the advantageof long lived phosphorescence that minimizes interference frombackground fluorescence or scattering in sensing applications. Inaddition, transition metal compounds offer new possibilities forredox-active sensors, in which the analyte binding event triggers

7810 | Dalton Trans., 2011, 40, 7805–7816 This journal is © The Royal Society of Chemistry 2011

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Fig. 9 Left: the structure of compound 17. Middle: A green OLED based on compound 15. Right: An orange OLED based on 17.

4. Devices incorporating 8 wt.% of this material doped intoCBP (4,4¢-bis(9-carbazolyl)biphenyl) showed remarkably highefficiency red phosphorescence, with maximum current, power andexternal quantum efficiencies (EQEs) of 10.31 cd A-1, 5.04 lm W-1

and 9.36%, respectively. It should be noted that, while much higherefficiencies have been achieved with the parent green phosphorIr(ppy)2(acac) using a similar device structure,8a,b the performanceof 4 is still very impressive as it is a red emitter and is expected tohave a much lower efficiency than the parent molecule accordingto the well-known energy gap law.

We have recently examined the impact of functionalization withtriarylboron on the performance of OLEDs containing platinumphosphors.11 Pt(II) complexes present a different challenge thancomplexes of Ir(III), as their square planar geometry increasesthe tendency of these materials for Pt–Pt stacking and exciplexemission. While in some situations this can be advantageous,especially in achieving white OLEDs,28 Pt(II) excimers generallyexhibit lower quantum efficiencies than the parent phosphors.Triarylborane-functionalized Pt(acac) compounds such as 14–16, however, have been found to be much less prone to excimerformation. In addition to 14–16, we have also examined a numberof other BMes2-functionalized NŸC-chelate Pt(acac) complexes.11

In all cases these boron-functionalized complexes were brightlyphosphorescent at room temperature in the solid state andsolution, due to a mixture of LC and MLCT phosphorescence.Furthermore, all of these complexes exhibited significantly higherUP than analogous complexes lacking a boron center.11 Consistentwith earlier studies, the presence of the triarylboron group greatlyincreased the intensity of the MLCT absorption band, and DFTcalculations indicate that the empty orbital on boron was a largecontributor to the LUMO in all cases. Indeed, complex 15 itselfwas found to exhibit an exceptionally high UP of 0.57 in the solidstate, and was evaluated as an emitter for OLEDs alongside theanalogous complex Pt(ppy)(acac), which lacked the boryl group.OLEDs using 15 as an emitter exhibited green emission (CIEcoordinates = 0.35, 0.61), with maximum efficiencies of 34.5 cdA-1, 29.8 lm W-1 and 8.9% EQE compared to 14.1 cd A-1, 11.7 lmW-1 and 6.9% EQE for those using Pt(ppy)(acac). Furthermore,the efficiency of devices containing 15 as the emitter were amongthe highest achieved using Pt(II) to date.29 The improved efficiencyof 15 OLEDs could be attributed to three factors: 1) higher internalquantum efficiency due to the improved UP of the borylatedphosphor itself, 2) reduced low-efficiency exciplex emission due tothe presence of the boryl group, and 3) improved electron injectionand mobility in the emissive layer.

Hole mobilities typically exceed electron mobilities in organicmaterials by 1–2 orders of magnitude,30 leading to charge im-balance in the device and reduced efficiency. For this reason,

improving electron mobility in the emissive layer is one strategythat can be used to achieve better carrier balance in OLEDs.31

To confirm that the BMes2 group indeed improves electrontransport in the device, we fabricated single-carrier devices32

capable of transporting electrons only from thin films of 15or Pt(ppy)(acac). Remarkably, the film of 15 was capable ofsupporting a current density 3–4 orders of magnitude higher thanthat of Pt(ppy)(acac), indicative of markedly improved electronmobility.11a Furthermore, this highlighted the bifunctional natureof the boron-functionalized materials, namely efficient electrontransport and phosphorescence.

Following the success of this system, we later extended thisconcept to a trifunctional material11b 17 (Fig. 9) designed asa phosphorescent successor to the highly fluorescent molecule7, which had been incorporated into efficient blue fluorescentOLEDs.7d Similar to 16 in structure, this material further containsthe N-phenyl-1-naphthyl group as a strong electron donor. Thismoiety, taken from the widely used hole transport materialNPB (N,N¢-di-[(1-naphthalenyl)-N,N¢-diphenyl]-(1,10-biphenyl)-4,4¢-diamine), should thus be able to efficiently support oxidationand hole-transport. Furthermore, incorporation of the NPBmoiety leads to bright ligand-centerd charge transfer phosphores-cence, facilitated by Pt(II). When used in a doped emissive layer inOLEDs, devices exhibiting bright orange electrophosphorescence(lEL = 581 nm, CIE = 0.52, 0.47) with efficiencies of 35.0 cd A-1,36.6 lm W-1 and 10.1% EQE have been achieved. This is quiteremarkable since the emission of 17 is much red-shifted, comparedto that of 15. Though to date only three reports on the subject havebeen published,11,16 these results give a promising outlook for theuse of triarylboron-containing metal complexes as phosphorescentmaterials in OLEDs.

5. Triarylboron-containing metal complexes as anion sensors

Many reports to date have focused on the use of triarylboroncompounds as chemical sensors for fluoride and cyanide, due to thehigh selectivity with which the BMes2 group binds these anions andthe unique colorimetric and luminescent color changes that resultfrom the anion binding event. Several excellent reviews have beenpublished recently on the use of triarylboranes as anion sensors,in which the reader will find further information on strategies foranion detection and improving the sensitivity of the chemosensorin organic and protic media.5b,c

Transition metal-containing triarylboranes offer the advantageof long lived phosphorescence that minimizes interference frombackground fluorescence or scattering in sensing applications. Inaddition, transition metal compounds offer new possibilities forredox-active sensors, in which the analyte binding event triggers

7810 | Dalton Trans., 2011, 40, 7805–7816 This journal is © The Royal Society of Chemistry 2011

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■ Organoboron Pharmaceuticals

New Directions of Organoborons

NH

HN B

ON

N

Ph

OOH

OH

OB

F

OH

Bortezomib, 悪性リンパ腫治療薬 the first therapeutic proteasome inhibitor, for treating relapsed multiple myeloma and mantle cell lymphoma.

Tavaborole, 抗真菌剤 topical antifungal medication for the treatment of onychomycosis

■ Organoborons for Materials

OEL