Inter- and intra-molecular C-H borylation for the formation of PAHs containing triarylborane and indole units

Article abstract of DOI:10.1039/c6dt03526d

Inter-/intra-molecular electrophilic C-H borylation of C4-substituted indoles enables the formation of fused polycyclic aromatic structures containing triarylborane and N-heterocyclic units. These compounds are B-(C)_n-N isosteres of carbocyclic PAHs that do not contain B-N bonds and comparison of one pair of BN/CC isosteres reveals that different resonance structures dominate. These compounds are highly sensitive to protodeboronation, of both the chloroborane intermediates and the mesityl protected products, which results in low isolated yields of the latter. Protodeboronation can be utilised productively for a C-H directed, C-H electrophilic borylation to make a previously unknown pinacol boronate ester by selective protodeboronation of the chloroborane intermediate. Intermolecular and double intramolecular electrophilic C-H borylation of a C4-substituted indole leads to a more highly fused structure containing two boracycles which represents a B-(C)_n-N analogue of the unknown carbon isostere indeno[1,7ab]perylene.

Full text of DOI:10.1039/c6dt03526d

Dalton
Transactions
View Article Online
View Journal
PAPER
Inter- and intra-molecular C–H borylation for the
formation of PAHs containing triarylborane and
indole units†
Cite this: DOI: 10.1039/c6dt03526d
A. Escande, D. L. Crossley, J. Cid, I. A. Cade, I. Vitorica-Yrezabal and M. J. Ingleson*
Inter-/intra-molecular electrophilic C–H borylation of C4-substituted indoles enables the formation of
fused polycyclic aromatic structures containing triarylborane and N-heterocyclic units. These compounds
are B–(C)n–N isosteres of carbocyclic PAHs that do not contain B–N bonds and comparison of one pair
of BN/CC isosteres reveals that different resonance structures dominate. These compounds are highly sen-
sitive to protodeboronation, of both the chloroborane intermediates and the mesityl protected products,
which results in low isolated yields of the latter. Protodeboronation can be utilised productively for a C–H
directed, C–H electrophilic borylation to make a previously unknown pinacol boronate ester by selective
protodeboronation of the chloroborane intermediate. Intermolecular and double intramolecular electro-
philic C–H borylation of a C4-substituted indole leads to a more highly fused structure containing two
boracycles which represents a B–(C)n–N analogue of the unknown carbon isostere indeno[1,7ab]perylene.
Received 9th September 2016,
Accepted 28th September 2016
DOI: 10.1039/c6dt03526d
www.rsc.org/dalton
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are an appealing
domain to explore in the search for novel materials for appli-
cation in organic electronics.1 One challenge in this area is to
tune key properties, and this can be achieved by the incorpo-
ration of heteroatoms.2 Incorporating a 3-coordinate triaryl-
borane moiety into extended π conjugated systems generally
reduces the LUMO energy,3 while the incorporation of an
“electron rich” 5 membered N-heterocycle generally results in
the complementary effect of raising the HOMO energy level.2
However, due to the synthetic challenges associated with incor-
porating a triarylborane and a N-heterocycle into a single com-
pound, PAHs containing both units are extremely rare,3d but
are attractive targets in their own right and for comparison to
isoelectronic carbocyclic analogues. BN/CC isosterism4 is
attracting increasing attention including as a route to access B,
N-PAH analogues of unknown carbocyclic PAHs.5 However, the
majority of B,N-PAHs contain C2B–NC2 moieties,6 with PAHs
containing separated B and N units (C2B–(C)n–NC2 sub-struc-
tures) being less developed.7,8 One rare example is the fused
indolo-borole, A (Fig. 1), whose PAH core is isoelectronic to
Fig. 1 Select previously reported boron containing PAHs.
dibenzopentalene but A is electronically dramatically dif-
ferent.8a Single boracycle containing PAHs such as A, require
kinetic stabilization of the boron center by a bulky exocyclic
group. An alternative approach for stabilising triarylboranes is
to enforce planarity at boron by generating rigid structures
containing two or three boracycles (e.g., B and C).9 While
notable advances have been made in producing boron contain-
ing PAHs,9,10 PAHs containing boracycles, a triarylborane and
a N-heterocycle moiety remain rare.
Pioneering work by Dewar developed double intramolecular
electrophilic C–H borylation as a route to PAHs containing
C2B–NC2 moieties.6,11 To access triarylborane/N-heterocycle
containing PAHs by a related approach requires initial inter-
molecular electrophilic C–H borylation, a more challenging
conversion (than intermolecular N–H borylation utilised by
Dewar) that requires stronger electrophiles than BCl3.12
Electron rich N-heterocycles are particularly well suited to
intermolecular electrophilic C–H borylation using boro-
cations12 and subsequent intramolecular C–H borylation steps
School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL,
UK. E-mail: Michael.ingleson@manchester.ac.uk
†Electronic supplementary information (ESI) available: Detailed experimental
procedures, spectra, computational and crystallographic details. CCDC 1494581.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c6dt03526d
This journal is © The Royal Society of Chemistry 2016
Dalton Trans.

View Article Online
Paper
Dalton Transactions
would enable the incorporation of N-heterocycle and triaryl- 1-BMes and 2-BMes which are confirmed by accurate mass
borane units into a single PAH which would represent B–(C)n–N spectroscopy. However, 1-BMes could not be obtained pure
isosteres of carbocyclic PAHs. Herein we report the develop- and decomposed rapidly during attempts at chromatographic
ment of sequential inter-/intra-molecular electrophilic C–H purification consistent with the propensity of C3 borylated
borylation and the synthesis of triarylborane and N-heterocycle indoles to undergo protodeboronation.13 2-BMes underwent
containing PAHs, including a B–(C)n–N analogue of the slower proto-deboronation during silica gel chromatography,
unknown carbon isostere indeno[1,7ab]perylene.
thus it could be isolated, albeit in only 28% yield due to
deboronation.
Compound 2-BMes is a substituted B,N isostere of the pre-
viously synthesized compound benzo[l]acephenanthrylene, (D,
Scheme 1 right). Notably 2-BMes does not contain a B–N bond
in contrast to the majority of BN isosteres of carbocyclic
PAHs.6 In our hands crystalline material could not be obtained
for 2-BMes but the calculated structure (at the B3LYP/6-311G
(d,p) level on a model where octyl has been replaced with Me,
termed 2-BMes′) revealed an orthogonal exocyclic mesityl
group and a non planar backbone distorted to minimise inter-
actions in the cove region. Notably, while the solid state struc-
ture of D is planar the calculated structure of D is non-planar
exhibiting a similar distortion to 2-BMes′ (other key metrics
for the calculated and solid state structures of D are compar-
able). Comparison of the calculated structure of 2-BMes′ to the
solid state structure of D revealed that the C2–C3 distance in
2-BMes (1.39 Å) is significantly shorter than the C2–C3 distance
in D (1.46 Å).14 This disparity is attributed to the different
p orbital energies of B, C and N leading a greater contribution
of the R2N–CvC–BR2 resonance form (left, Scheme 2) over the
R2NvC–CvBR2 form (right, Scheme 2) in 2-BMes relative to
that in D where C1vC2–C3vC4 dominates.
The propensity of the indole-boracycles to undergo proto-
deboronation can be used productively to generate pinacol
boronate esters with BPin groups installed at unprecedented
positions. For example, on addition of pinacol/Et3N to 1-BCl
selective protodeboronation occurs at the more electron rich
indole C3 position to form pinacol boronate ester 3 (Scheme 3),
the isolation of 3 also further confirms the formation of 1-BCl.
In the conversion from 1 to 3 a sterically hindered C–H posi-
tion that is not electronically activated has been transformed
Results and discussion
Indoles arylated at C4 were utilized as they are borylated at the
C3 position using boron electrophiles,12 this locates the intro-
duced BCl2 moiety correctly for subsequent formation of a
6 membered boracycle by intramolecular C–H borylation.
Initial studies used N-octyl-4-phenylindole, 1, which can be
borylated using the borylating reagents [LutBCl2][AlCl4] (Lut =
2,6-lutidine) or TBP/BCl3/AlCl3 (TBP = 2,4,6-tBu3-pyridine)12
with in situ NMR spectroscopy consistent with the formation
of 3-BCl2-N-octyl-4-phenylindole. The intramolecular C–H bory-
lation step then proceeds on addition of 2,6-dichloropyridine
(Cl2Py) and AlCl3, forming
a single new indole-product
assigned as 1-BCl (Scheme 1). The addition of Cl2Py and AlCl3
is presumably forming a highly reactive borocation enabling
borylation.12c
A naphthyl substituted congener (compound 2) under iden-
tical one pot, two step electrophilic borylation conditions led
to in situ NMR spectra consistent with the formation of 2-BCl.
The proposed intermediates 1-BCl and 2-BCl are the only
indole containing species observed by in situ 1H NMR spec-
troscopy but they proved extremely sensitive to deboronation.
Therefore the installation of mesityl onto boron was explored
attempting to produce 1-BMes and 2-BMes, respectively. Using
ether-free ZnMes2 or CuMes in >3 equivalents (due to competi-
tive reactions with the protonated base by-products from SEAr
([Lut–H]+ and [Cl2Py–H]+) generating mesitylene and un-
identified zinc/copper species) new boracycles were produced
assigned as 1-BMes and 2-BMes. The 1H and 13C{1H} NMR
resonances are fully consistent with the proposed structures of
Scheme 2 Limiting R2N–CvC–BR2 and R2NvC–CvBR2 resonance
structures.
Scheme 1 Sequential inter-/intra-molecular electrophilic C–H boryla-
tion and subsequent mesityl protection of 4-aryl-N-octyl-indoles.
Scheme 3 Two step “C–H” directed electrophilic C–H borylation.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2016

View Article Online
Dalton Transactions
Paper
into a C-BPin moiety. This site is not selectively accessible via 2,4,6-tri-tert-butylpyridine (TBP) was explored as an alternative
any approach other than sequential inter-/intra-molecular C–H more basic “non-coordinating” pyridine. However, this led to
borylation followed by protodeboronation.15
no intramolecular C–H borylation indicating that Cl2Py is
With sequential inter-/intra-molecular electrophilic C–H essential, possibly for forming a more reactive borocation elec-
borylation conditions developed we sought to modify the struc- trophile.12c The strongly acidic [Cl2Py–H]+ by-product can be
ture of 1 to include an additional aromatic moiety positioned deprotonated in situ using TBP, thus after the formation of the
for a further intramolecular C–H borylation. This would gene- proposed intermediate 6-BCl2 one equiv. of Cl2Py and two
rate a more rigid structure post triple C–H borylation (one equiv. of AlCl3 were introduced along with an excess of TBP
intermolecular and two intramolecular) and thus hopefully (>2 equiv.). Using these conditions the intramolecular C–H
provide enhanced stability towards protic species relative to electrophilic borylation steps are higher yielding and 7 is
2-BMes.10 Therefore 4 (Scheme 4) was synthesised via standard formed as the major indole containing product (by in situ
cross coupling routes and borylated with [LutBCl2][AlCl4].12a NMR spectroscopy). Compound 7 can be isolated in moderate
An equivalent of both Cl2Py and AlCl3 was added to this yield (30% using chromatography during which decompo-
mixture aiming to ring close by C–H borylation at the sition occurs slowly) for a process involving three C–H boryla-
“α-position”. However, borylation appears to proceed at the tion steps in one pot. Isolated 7 resonates at δ11B 45.2 ppm
sterically less hindered “β-position”, with a single new indole which is consistent with other fused triarylboranes.8,9
containing product observed and assigned as 5-BCl based on
X-ray crystallographic analysis on single crystals of 7 con-
the observation of two new singlet resonances (presumably firmed an effectively planar (Fig. 2) triarylborane/N-heterocycle
the indole C2–H and the α C–H) in the aromatic region of containing PAH with the boron center adopting a trigonal
1
in situ H NMR spectra. Attempts to install mesityl and obtain planar geometry (∑C–B–C = 360.0(3)°). The extended packing
a pure product for full characterisation was frustrated by the structure of 7 is notable as it contains head to tail dimers
sensitivity of 5-BCl and putative 5-BMes to protodeboronation (with short face to face contacts, intermolecular centroid
analogous to 1-BCl/1-BMes.
B-centroid C distance = 3.688 Å, Fig. 2). These dimers are
Surmising that “β-site” borylation is precluding the final linked in a slipped face to face arrangement (N1–centroid C
intramolecular C–H borylation an analogue of 4 with this posi- distance = 3.672 Å) resulting in an infinite 1D columnar
tion blocked was targeted. Compound 6 has the “β position” in extended structure. In 7 the B–Cindole (1.527(5) Å) is shorter
4 blocked by a methyl group and was synthesized via standard than the B–Cphenyl (1.557(5) and 1.544(5) Å) bond lengths and
cross coupling routes. The intermolecular C–H borylation of all three are shorter than those in triphenylborane
6 proceeded using [LutBCl2][AlCl4] to form a single new com- (1.57–1.59 Å)17 indicating a degree of multiple B–C bond char-
pound assigned as 6-BCl2 (based on in situ NMR spectroscopy) acter particularly for the B–Cindole bond. This suggests that the
with subsequent double intramolecular C–H borylation using Lewis acidity of the boron center in 7 will be reduced, an effect
Cl2Py/AlCl3 leading to 7. Compound 7 has a greater degree of enhanced by the structural constraint provided by two rigid
fusion (relative to 2-BMes) and thus was more stable (e.g., no boracycles. To probe this further the Lewis acidity of 7 was
decomposition of 7 is observed in “wet” CD2Cl2 after 7 days). examined and found to be extremely low by the modified
However, these reaction conditions only produced 7 in very Gutmann–Beckett method (Δδ31P(Et3PO) = 0 ppm),19 and even
low (<10%) isolated yields with insoluble material also formed after addition of 6 equivalents of Et3PO to 7 there was no indi-
which is attributed to the formation of indole oligomers cation for any Lewis adduct formation (by 1H NMR spectro-
initiated by the strong Brønsted acid [Cl2–pyH]+ by-product scopy). Compound 7 does bind pyridine, with addition of fifty
from SEAr.16 Side reactions appear more prevalent in the for- equivalents of pyridine leading to significant changes in the
mation of 7 than for 2-BCl (by in situ NMR spectroscopy) thus 1H NMR spectrum of 7 (that are reversible on removal of pyri-
dine) consistent with some Lewis adduct formation. However,
in DCM the exposure of 7 to wet pyridine also led to protode-
boronation via cleavage of the B–Cindole bond.
Fig. 2 Left, X-ray crystal structure of 7 with thermal ellipsoids at the
50% level, right extended packing structure (short face to face π inter-
actions are indicated in red between the relevant centroids and the
N atom and centroid). Hydrogen atoms and part of the octyl chains
Scheme 4 Electrophilic C–H borylation of pre-organised indoles.
omitted for clarity.
This journal is © The Royal Society of Chemistry 2016
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Table 1 Electrochemical and photophysical data of 2-BMes and 7
Epa onset (V)
Epc onset [Epc1/2] (V)
HOMOa (eV)
LUMOa (eV)
λonset b (nm)
Optical band gap (eV)
λmax emb (nm)
2-BMes
7
0.57
0.50
−2.68
−1.98 [−2.08]
−5.96
−5.89
−2.71
−3.41
439
491
2.82
2.52
473
492
Cyclic voltammetry performed with NBu4PF6 conc. = 0.1 M in THF. a All scans were calibrated against the ferrocene/ferrocenium (Fc/Fc+) redox
couple, which is taken to be 5.39 eV below vacuum.18 b UV/vis absorption and fluorescence spectra were recorded in CH2Cl2 at 1 × 10−5 M.
The photophysical properties of 2-BMes and 7 in CH2Cl2 state structure of 7 suggesting that packing effects in 7 (e.g.,
revealed that the optical band gap is smaller for 7 (2.52 eV) face to face π stacking) increases the degree of planarization
relative to 2-BMes (2.82 eV, Table 1). The borylated compounds (other metrics for 7 and 7′ are extremely similar). The NICS
emit at 473 nm for 2-BMes, with a Stokes shift of 51 nm, and (1)zz values for the boracycles (A and B) in 7′ indicate they are
at 492 nm for 7 (with an absolute quantum yield of 36%) with effectively non-aromatic (NICS(1)zz for [A] = −3.42 and [B] =
a Stokes shift of 22 nm consistent with a rigid molecule and −2.95) and comparable to that calculated for 8 (−2.94 and
little ICT character. 7 has a less negative cathodic potential −0.77). Whilst the HOMO for 7′ and 8 are of similar energy the
(Epc
= −1.98 V) relative to 2-BMes (Epc
= −2.68 V) LUMO is actually higher in energy for 7′ relative to 8. A related
onset
onset
which was reversible for 7 (centered at −2.08 V), in contrast to trend in LUMO energies is observed on comparing 2-BMes
an irreversible reduction process for 2-BMes. The half- (−2.07 eV) and D (−2.25 eV). For both isosteric pairs the LUMO
reduction potential of compound 7 is significantly less nega- orbitals were found to be similar in character for the BN and
tive than for non-fused triarylboranes (e.g., Mes3B E1/2 = −2.57 CC isosteres (e.g., Fig. 3, right). The relative LUMO energies of
V vs. Fc/Fc+).20 However, it is more negative than reported for B these isoelectronic BN/CC pairs are contrary to the generally
(E1/2 = −1.48 V vs. Fc/Fc+)9c and C (E1/2 = −1.37 V vs. Fc/Fc+),9b observed effect of incorporating triarylboranes into PAHs
this is attributed to greater indole → B π delocalisation increas- which engenders low LUMO energies.3 We tentatively attribute
ing the LUMO energy level (relative to B and C).
these relative LUMO energies to the fact that 2-BMes and 7 are
The fused core of 7 is an isostere of an indenoperylene, a not electron deficient (they are isoelectronic to all carbon
PAH that has attracted recent interest in organic electronics.21a PAHs) and as the LUMO for both 2-BMes and 7 has significant
The synthetically more accessible carbocyclic isomers are boron pz character it will be higher in energy than the LUMO
indeno[1,2,3-cd]perylene21b and indeno[2,1-b]-perylene,21a in the all carbon PAH as a boron pz orbital is intrinsically
whereas 7 represents an isostere of an indeno[1,7-ab]perylene, higher in energy than a carbon pz orbital. In contrast, purely
notably, the carbocyclic PAH analogue is currently unknown to B-doped PAHs are electron deficient and are actually isoelec-
the best of our knowledge. To compare the effects of BN/CC tronic to mono-cationic all carbon PAHs thus the LUMO will
isosterism a model of 7 (where octyl is replaced with methyl, be relatively low in energy in B-doped PAHs. Other notable
termed 7′) and the carbon analogue 8 were investigated. The differences between 7′ and 8 are the disparate dominant reson-
calculated structures of 7′ and 8 (Fig. 3) are both ruffled to a ance structures (N–C2vC3–B vs. C1vC2–C3vC4 analogous to
similar extent which is greater than that observed in the solid that for 2-BMes and D) and distinct charge distributions.
Compound 7′ is considerably more polarized than 8, with 7′
having a dipole moment of 3.23 D compared to 0.18 D for 8.
The significant dipole in 7′ (and by analogy 7) is an important
factor directing the intermolecular packing, with head to tail
dimers presumably forming to align the relative dipoles of
adjacent molecules appropriately.
Conclusions
In summary, inter-/intra-molecular electrophilic C–H boryla-
tion leads to fused triarylborane/N-heterocycle containing
PAHs. These compounds are B–N isosteres of carbocyclic PAHs
where the B and N atoms are not directly bonded, in contrast
to the majority of reported BN containing extended PAHs. This
new methodology also enables a B–C2–N isostere of an
unknown carbocyclic PAH to be synthesized. Current work
Fig. 3 DFT calculated structures for 7’ and 8. HOMO and LUMO rep-
resentations at an isovalue of 0.04. Selected calculated bond distances
seeks to extend inter-/intra-molecular C–H borylation to
heterocycles less prone to protodeboronation.
for 7’ (Å) N–C2 = 1.37, C2–C3 = 1.39, C3–B = 1.52 and for 8 (Å) C1–C2 =
1.36, C2–C3 = 1.47, C3–C4 = 1.38.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2016

View Article Online
Dalton Transactions
Paper
pressure. The crude was washed and extracted three times with
H2O/CH2Cl2. The organic layers were collected and concen-
trated. The mixture was purified by silica gel column chrom-
Experimental
General Considerations
Unless otherwise indicated all reagents were purchased from atography with pentane then pentane/CH2Cl2 (80/20) as
commercial sources and were used without further purifi- eluent. A white solid of 4-phenyl-1H-indole was obtained in a
cation. [LutBCl2][AlCl4] was synthesized by
a previously yield of 46% (0.714 g, 3.69 mmol). All NMR spectra are consist-
reported method.12a All appropriate manipulations were per- ent with that previously reported.22
formed using standard Schlenk techniques or in an argon-
Synthesis of 1
filled MBraun glovebox (O2/H2O levels below 0.5 ppm).
Glassware was dried in a hot oven overnight and heated under
1-Octyl-4-phenyl-1H-indole. 4-Phenyl-1H-indole (0.741 g,
vacuum before use. Solvents and amines were distilled from 3.83 mmol) was placed in a round-bottom flask to be solubil-
1
NaK, CaH2, or K and degassed prior to use. H NMR and 13C ised in DMF (6 mL). The sodium hydride (60% dispersed in
NMR spectra were recorded using 400 and 500 MHz spectro- oil) (230 mg, 5.75 mmol) was washed in pentane. The oil-free
meters with chemical shift values being reported in ppm rela- sodium hydride was added portionwise into the solution of
tive to residual protio solvent (e.g. in CHCl3 in CDCl3 δH
=
4-phenyl-1H-indole (caution: exothermic reaction). The
7.27 or δC = 77.2) as internal standards. All coupling constants mixture was stirred for 15 min at ambient temperature. The
(J) are reported in Hertz (Hz). Other NMR spectra were 1-bromooctane was then added. The reaction was followed by
recorded with a 400 MHz Bruker AV-400 spectrometer (11B; TLC and was stopped after 1 h 30 of stirring. The mixture was
162 MHz, 27Al 104.3 MHz). 11B NMR spectra were referenced to washed with water (10 mL) then extracted with CH2Cl2 (3 ×
external BF3: Et2O, and 27Al to Al(NO3)3 in D2O (Al(D2O)63+). 20 mL). The organic layers were concentrated and the crude
Unless otherwise stated all NMR spectra are recorded at 293 K. was purified by silica gel column chromatography with PET
Carbon atoms directly bonded to boron are not always 100% as eluent. A colourless oil of 1-octyl-4-phenyl-1H-indole
observed in the 13C{1H} NMR spectra due to quadrupolar relax- was obtained (0.936 g, 3.06 mmol, 80%). Caution: use DMF
ation leading to signal broadening. All UV-Vis absorption and NaH in small scale and at room temperature!
spectra were recorded on a Varian Cary 5000 UV-Vis-NIR
1H (400 MHz, CD2Cl2): δ 7.76 (d, J = 7.0 Hz, 2H), 7.53 (t, J =
spectrophotometer and the solution emission spectra were 7.8 Hz, 2H), 7.42 (m, 2H), 7.32, (t, J = 7.3 Hz, 1H), 7.22 (m, 2H),
recorded on a Varian Cary Eclipse fluorometer at room temp- 6.70 (d, J = 3.0 Hz, 1H), 4.18 (t, J = 7.3 Hz, 2H), 1.90 (quin, J =
erature in spectroscopic grade solvents exciting at the relative 7.0 Hz, 2H), 1.38 (m, 10H), 0.94 (t, J = 8 Hz, 3H); 13C{1H}
absorbance maxima. Absolute quantum yield values were (101 MHz, CD2Cl2): δ 142.0, 137.1, 134.9, 129.3, 129.1, 128.9,
recorded
on
an
Edinburgh
Instruments
FP920 127.5, 127.3, 122.2, 119.6, 109.3, 100.6, 47.2, 32.4, 30.9, 29.9,
Phosphorescence Lifetime Spectrometer and determined using 29.8, 27.6, 23.3, 14.5; MS (APCI): calc. for [M + H]+ 306.22,
a calibrated Edinburgh Instruments integrating sphere. Cyclic found 306. Accurate mass: calc. for [M + H]+ C22H28N
voltammetry was performed using a CH-Instrument 1110C 306.2216, found 306.2209.
Electrochemical/Analyzer potentiostat under a nitrogen flow.
Measurements were made using a 0.001 M analyte solution
Synthesis of 4-(naphthalene-1-yl)-1H indole
with 0.1 M tetrabutylammonium hexafluorophosphate (Fluka To a Schlenk, the 1-naphthylboronic acid (2.06 g, 12 mmol)
≥99.0%) as the supporting electrolyte in THF that had been and the 4-bromo-1H-indole (1 mL, 7.97 mmol) were introduced
degassed and dried prior to use. A glassy carbon electrode and the reagents were degassed. A degassed mixture of DMF
served as the working electrode and a platinum wire as the (40 mL) and aqueous NaOH (0.64 g in 6.5 mL of H2O) was
counter electrode. An Ag/AgNO3 non-aqueous reference elec- transferred via cannula to the reagents. Pd(PPh3)4 (370 mg,
trode was used. All scans were calibrated against the ferrocene/ 0.32 mmol) was then added. The reaction mixture was heated
ferrocenium (Fc/Fc+) redox couple, which in this work is taken for 18 h at 100 °C. The reaction was cooled to room tempera-
to be 5.39 eV below vacuum. The half-wave potential of the ture and the DMF was removed under reduced pressure. The
ferrocene/ferrocenium (Fc/Fc+) redox couple (E1/2
estimated from E1/2, Fc,Fc+ = (Eap + Ecp)/2, where Eap and Ecp are times with CH2Cl2 (3 × 40 mL). The organic layers were col-
, Fc,Fc+) was crude was washed with H2O (40 mL) and then extracted three
the anodic and cathodic peak potentials, respectively.
lected and concentrated. The mixture was purified by silica gel
column chromatography with pentane then pentane/CH2Cl2
(90/10) as eluent. A white powder of 4-(naphthalene-1-yl)-1H
Synthesis of 4-phenyl-1H-indole
To a Schlenk, phenylboronic acid (1.46 g, 12 mmol) and indole was obtained (1.004 g, 4.12 mmol, 52%). All NMR
4-bromoindole (1 mL, 7.97 mmol) were introduced and the spectra are consistent with that previously reported.23
reagents were degassed. A degassed mixture of DMF (40 mL)
Synthesis of 2 4-(naphthalene-1-yl)-1-octyl-1H-indole
and aqueous NaOH (0.64 g in 6.5 mL of H2O) was transferred
via cannula to the reagents. This was followed by the addition The 4-(1-naphthlen-1-yl)-1H-indole (0.991 g, 4.07 mmol) was
of Pd(PPh3)4 (370 mg, 0.32 mmol). The reaction mixture was placed in a round-bottom flask and solubilised in DMF (6 mL).
heated for 18 h at 100 °C. The reaction was cooled to room The sodium hydride (60% dispersed in oil) (245 mg,
temperature and the DMF was removed under reduced 6.13 mmol) was washed in pentane. The oil-free sodium
This journal is © The Royal Society of Chemistry 2016
Dalton Trans.

View Article Online
Paper
Dalton Transactions
hydride was added portionwise into the solution of 4-(1- 6-mesityl-4-octyl-4,6-dihydronaphtho[1′,2′:5,6]borinino[2,3,4-cd]
naphthlen-1-yl)-1H-indole (caution: exothermic reaction). The indole 2-BMes was obtained (15.4 mg, 3.19 × 10−5 mol, 28%).
mixture was stirred for 30 min at ambient temperature. The
1H (400 MHz, in CD2Cl2): δ 9.11 (d, J = 8.3 Hz, 1H), 8.60 (d,
1-bromooctane (0.98 mL, 5.7 mmol) was then added. The reac- J = 7.6 Hz, 1H), 7.94 (dd, J = 7.8 Hz, J = 1.5 Hz, 1H), 7.90 (s,
tion was followed by TLC and was stopped after 1 h 30 of stir- 1H), 7.67–7.58 (m, 6H), 6.95 (s, 2H, Mes), 4.36 (t, J = 7.1 Hz,
ring. The mixture was washed with water (10 mL) then 2H), 2.38 (s, 3H, Mes), 2.04 (s, 6H, Mes), 1.99 (quint, J = 7.1
extracted with CH2Cl2 (3 × 20 mL). The organic layers were con- Hz, 2H), 1.29 (m, 10H), 0.85 (t, J = 7.1 Hz, 3H); 13C{1H}
centrated and the crude was purified by silica gel column (101 MHz, in CD2Cl2): δ 143.2, 140.1, 139.4, 137.2, 136.9,
chromatography with PET 100% as eluent. A colourless oil of 136.8, 133.9, 131.7, 130.6, 129.9, 129.2, 128.9, 127.9, 127.4,
4-(naphthalene-1-yl)-1-octyl-1H-indole was obtained (1.356 g, 127.0, 126.4, 126.2, 125.6, 122.9, 121.4, 111.3, 109.3, 101, 48.3,
3.81 mmol, 94%). Caution: use DMF and NaH in small scale 32.3, 31.1, 30.9, 29.7, 29.6, 27.5, 23.7, 23.2, 22.9, 21.5, 14.4; MS
and at room temperature!
(APCI): calc. for [M + H]+ C35H39NB 484.32, found 484.3.
1H (400 MHz, CD2Cl2): δ 7.95 (dd, J = 8.3 Hz, J = 7.57 Hz, Accurate mass: calc. for [M + H]+ C35H39BN 484.3170, found
2H), 7.82 (d, J = 8.6 Hz, 1H), 7.60 (dd, J = 5.0 Hz, J = 1.0 Hz, 484.3162.
2H), 7.49, (m, 2H), 7.37 (q, J = 7.1 Hz, 2H), 7.20 (d, J = 7.1 Hz,
1H), 7.12 (d, J = 3.0 Hz, 1H), 6.11 (m, 1H), 4.18 (dt, J = 7.1 Hz,
Synthesis of 3
J = 2.0 Hz, 2H), 1.92 (quin, J = 6.8 Hz, 2H), 1.38 (m, 10H), 0.93
1-Octyl-4-(2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)
(m, 3H); 13C{1H} (101 MHz, CD2Cl2): δ 139.8, 136.7, 134.4, phenyl)-1H-indole. A J. Young’s NMR tube was charged with
133.7, 132.6, 129.2, 128.7, 128.6, 128.0, 127.9, 127.1, 126.2, 1 (50 mg, 1.64 × 10−4 mol) and TBP (2,4,6-Tri-tert-butylpyri-
126.1, 126.0, 121.8, 121.4, 109.3, 101.1, 47.2, 32.4, 30.9, 29.9, dine) (41 mg, 1.64 × 10−4 mol). The compound was dissolved
29.8, 27.6, 23.2, 14.5; MS (APCI): calc. for [M + H]+ C26H30N in dry CH2Cl2 (0.7 mL) and BCl3 (1 equiv. 1 M in DCM) and
356.24, found 356.3. Accurate mass: calc. for [M + H]+ C26H30N AlCl3 (27 mg, 1.64 × 10−4 mol) was added to the solution. The
356.2373, found 356.2374.
solution was stirred for 20 min at room temperature. After a
near quantitative formation of the indoleBCl2 intermediate (by
in situ NMR spectroscopy), 2,6-dichloropyridine (24 mg, 1.64 ×
Synthesis of 2-BMes (using ZnMes2)
A J. Young’s NMR tube was charged with 2 (0.007 mL, 2.05 × 10−4 mol) and AlCl3 (27 mg 1.64 × 10−4 mol) were introduced
10−5 mol). The compound was solubilised in dry CH2Cl2 to the solution. The reaction was stirred for 6 h at room temp-
(0.7 mL) and [LutBCl2][AlCl4] (9 mg, 2.52 × 10−5 mol) was erature to obtain a new compound assigned as 1-BCl (by in situ
added. The solution was stirred for 1 h at room temperature. NMR spectroscopy). A solution of pinacol (1 M in NEt3)
After a near quantitative formation of the intermediate (1.3 mL, 1.3 × 10−3 mol) was then added to the reaction
assigned as indole-BCl2 (by NMR spectroscopy), 2,6-dichloro- mixture. The volatile compounds/solvent were removed under
pyridine (4 mg, 2.70 × 10−5 mol) and AlCl3 (3 mg, 2.25 × 10−5 reduced pressure, the residue was dissolved in DCM (∼3 mL)
mol) were introduced to the solution. The reaction was stirred and passed through a short plug of base treated (5% NEt3 in
for 18 h at room temperature to obtain 2-BCl. Then excess hexane) silica gel. The crude reaction mixture was then puri-
Zn(Mes)2 was added (28 mg, 9.22 × 10−5 mol) to the solution fied by preparative silica gel TLC with PET/CH2Cl2 (70/30) as
and the reaction mixture was stirred for 18 h at room tempera- eluent. The desired product was isolated as a colourless oil
ture. The solution was filtered via
Compound 2-BMes was extracted with dry toluene. The
a
cannula transfer. (27 mg, 6.26 × 10−5 mol, 38%).
1H (500 MHz, CDCl3): δ 7.80–7.76 (m, 1H), 7.55–7.60 (m,
mixture was purified by rapid silica gel plug chromatography 1H), 7.55–7.51 (m, 1H), 7.40 (td, J = 7.3, 1.4 Hz, 1H), 7.37–7.34
with PET then PET/CH2Cl2 (90/10) as eluent. A yellow oil of (m, 1H), 7.32–7.28 (m, 1H), 7.13–7.09 (m, 2H), 6.42 (dd, J = 3.2,
6-mesityl-4-octyl-4,6-dihydronaphtho[1′,2′:5,6]borinino[2,3,4-cd] 0.6 Hz, 1H), 4.17 (t, J = 7.2 Hz, 2H), 1.89 (quin, J = 7.2 Hz, 2H),
indole, 2-BMes was obtained.
1.44–1.26 (m, 10H), 1.06 (s, 12 H), 0.94 (t, 7.0 Hz, 3H); 13C{1H}
2-BMes (using CuMes). An ampoule with a J. Young’s tap (126 MHz, CDCl3): δ 146.3, 136.4, 135.8, 133.9, 129.9, 129.3,
was charged with 2 (40 mg, 1.13 × 10−4 mol). The compound 128.2, 127.4, 126.0, 121.2, 119.7, 108.0, 100.8, 83.3, 46.5, 31.8,
was solubilised in dry CH2Cl2 (4.5 mL) and [LutBCl2][AlCl4] 30.4, 29.2, 29.2, 27.0, 24.4, 22.6, 14.1; 11B (128 MHz, CD2Cl2):
(40 mg, 1.13 × 10−4 mol) was added. The solution was stirred δ 32.0 (br); MS (APCI) calc. for C28H38BNO2 = 431.29, found
for 1 h at room temperature. Then 2,6-dichloropyridine 431.3. Accurate mass: calc. for [M + H]+ C28H39BNO2 432.3068,
(17 mg, 1.15 × 10−4 mol) and AlCl3 (15 mg, 1.13 × 10−4 mol) found 432.3068.
were introduced to the solution. The reaction was stirred for
Synthesis of 4
18 h at room temperature. Then excess CuMes was added
(82 mg, 4.52 × 10−4 mol) to the solution and the reaction
4-(3-(Naphthalen-1-yl)phenyl)-1-octyl-1H-indole.
4-(3-
mixture was stirred in the dark for 18 h at room temperature. (Naphthalen-1-yl)phenyl)-1H-indole (0.167 g, 0.52 mmol) was
The solution was filtered from the copper salts via a cannula placed in a round-bottom flask and solubilised in DMF (3 mL).
transfer. Compound 2-BMes was extracted with dry toluene. Sodium hydride (60% dispersed in oil) (32 mg, 0.79 mmol)
The mixture was further purified by rapid preparative silica gel was washed in pentane and added portionwise into the solu-
TLC with PET/CH2Cl2 (95/15) as eluent. A yellow oil of tion of 4-(3-(naphthyl)phenyl-1H-indole (caution: exothermic
Dalton Trans.
This journal is © The Royal Society of Chemistry 2016

View Article Online
Dalton Transactions
Paper
reaction). The mixture was stirred for 30 min at ambient temp- dry CH2Cl2 (10 mL) and BCl3 (V = 0.2 mL, C = 1 mol L−1 in
erature and 1-bromooctane (0.13 mL, 0.73 mmol) was then CH2Cl2), 2,4,6-Tri-tert-butylpyridine (146 mg, 5.9 × 10−4 mol)
added. The reaction was followed by TLC and was stopped and AlCl3 (26.5 mg, 1.97 × 10−4 mol) were added. The solution
after 1 h 30 of stirring. The mixture was washed with water was stirred for 1 h at room temperature. After a near quantitat-
(5 mL) then extracted with CH2Cl2 (3 × 10 mL). The organic ive formation of a new species assigned as 6-BCl2 (by in situ
layers were dried over MgSO4, then concentrated and the crude NMR spectroscopy), 2,4,6-Tri-tert-butylpyridine (49 mg, 1.98 ×
was purified by silica gel column chromatography with PET 10−4 mol) and 2,6-dichloropyridine (29 mg, 1.97 × 10−4 mol)
then PET/CH2Cl2 (99/1 → 95/5) as eluent. A colourless oil was and AlCl3 (53 mg, 3.94 × 10−4 mol) were introduced to the solu-
obtained
(4-(3-(naphthalen-1-yl)phenyl)-1-octyl-1H-indole, tion. The reaction was stirred for 18 h at room temperature to
0.194 g, 0.45 mmol, 86%). Caution: use DMF and NaH in obtain 7. The mixture was purified by preparative alumina
small scale and at room temperature!
gel TLC with PET/CH2Cl2 (95/15) as eluent. A yellow oil
1H (400 MHz, CD2Cl2): δ 8.02 (dd, J = 8.3 Hz, J = 0.8 Hz, of
6-methyl-2-octyl-2H-2-aza-14b-boraindeno[1,7-ab]perylene
1H), 7.92 (dd, J = 8.1 Hz, J = 0.8 Hz, 1H), 7.88 (d, J = 7.8 Hz, 7 was obtained (27 mg, 5.95 × 10−5 mol, 30%).
1H), 7.84 (t, J = 1.8 Hz, 1H), 7.79 (dt, J = 7.8 Hz, J = 1.8 Hz, 1H),
1H (400 MHz, in CD2Cl2): δ 9.01 (dd, J = 7.0 Hz, J = 1.5 Hz,
7.62 (t, J = 7.3 Hz, 1H), 7.52 (m, 5H), 7.37 (d, J = 7.8 Hz, 1H), 1H), 8.60 (d, J = 7.0 Hz, 1H), 8.52 (s, 1H), 8.39 (dd, J = 9.0 Hz,
7.24 (m, 3H), 6.70 (dd, J = 3.3 Hz, J = 0.8 Hz, 1H), 4.16 (t, J = J = 8.5 Hz, 2H), 8.15 (dd, J = 8.0 Hz, J = 1.0 Hz, 1H), 7.95 (d, J =
7.1 Hz, 2H), 1.85 (quint, J = 7.1 Hz, 2H), 1.29 (m, 10H), 0.87 (t, 7.5 Hz, 1H), 7.78 (dd, J = 8.0 Hz, 1H), 7.68 (m, 2H), 7.60 (d, J =
J = 7.1 Hz, 3H); 13C{1H} (101 MHz, CD2Cl2): δ 141.9, 141.5, 7.3 Hz, 1H), 7.50 (t, J = 8.03 Hz, 1H), 4.43 (t, J = 7.3 Hz, 2H),
140.9, 137.0, 134.6, 134.4, 132.2, 130.9, 129.1, 129.0, 128.9, 3.08 (s, 3H), 2.06 (quint, J = 7.28 Hz, 2H), 1.49–1.25 (m, 10 H),
128.8, 128.2, 128.1, 127.6, 127.2, 126.6, 126.5, 126.3, 126.0, 0.86 (t, J = 7.0 Hz, 3H); 7 13C{1H} (101 MHz, in CD2Cl2):
122.1, 119.7, 109.4, 100.6, 47.2, 32.3, 30.8, 29.8, 29.7, 27.5, δ 140.9, 139.9, 139.6, 137.9, 137.0, 136.4, 136.1, 134.8, 133.8,
23.2, 14.4; MS (APCI): calc. for [M + H]+ C32H34N 432.27, found 133.6, 132.6, 132.3, 131.3, 129.7, 126.6, 126.5, 124.9, 123.7,
432.3. Accurate mass: calc. for [M + H]+ C32H34N 432.2686, 123.1, 122.7, 110.5, 48.2, 32.4, 31.2, 29.8, 29.7, 27.6, 27.3, 23.2,
found 432.2683.
14.4; Cipso–B are not observed. 7 11B (128 MHz, CD2Cl2): δ 45.2
(br); MS (APCI): calc. for [M + H]+ C33H33NB 454.27, found
454.6. Accurate mass: calc. for [M + H]+ C35H39BN 454.2712,
Synthesis of 6
4-(2-Methyl-5-(naphthalen-1-yl)phenyl)-1-octyl-1H-indole. In found 454.2691.
a Schlenk, 1-(3-bromo-4-methylphenyl)naphthalene (0.546 g,
1.84 mmol), N-octylindole-4-boronic ester (0.653 g,
Theoretical calculations
1.84 mmol), Pd(PPh3)4 (0.213 g, 1.84 × 10−4 mol), NaOHaq
(0.15 g in 1.5 mL of H2O) and DMF (10 mL) were degassed.
The reaction mixture was heated for 2 d at 100 °C. The reaction
was cooled to room temperature and the DMF was removed
under reduced pressure. The crude was washed and extracted
three times with H2O/CH2Cl2. The organic layers were col-
lected, dried over MgSO4 and concentrated. The mixture was
purified by silica gel column chromatography with PET then
PET/CH2Cl2 (90/10) as eluent. Compound 6 was obtained as a
colourless oil in a yield of 46% (0.380 g, 0.85 mmol).
Calculations were performed using the Gaussian09 suite of
programmes.24 Calculations were performed at the B3LYP/6-
311G(d,p) level.25 In all cases, structures were confirmed as
minima by frequency analysis and the absence of imaginary
frequencies. NICS calculations were performed using two func-
tionals (with a 6-311G(d,p) basis set) with and without a PCM
(DCM) for the model compound 1-BMes′. Only minor differ-
ences were observed thus all calculations were performed at
the B3LYP/6-311G(d,p) level.
1H (400 MHz, CDCl3): δ 8.14 (d, J = 7.82 Hz, 1H), 7.94 (d, J =
7.6 Hz, 1H), 7.87 (m, 1H), 7.61 (s, 1H), 7.58–7.47 (m, 6H), 7.39
(d, J = 8.1 Hz, 1H), 7.33 (m, 1H), 7.15 (m, 2H), 6.38 (d, J = 2.8
Hz, 1H), 4.18 (t, J = 6.81 Hz, 2H), 2.39 (s, 3H), 1.91 (quint, J =
6.3 Hz, 2H), 1.31 (m, 10H), 0.93 (t, J = 6.8 Hz, 3H); 13C{1H}
(101 MHz, CDCl3): δ 140.8, 140.2, 137.8, 135.9, 135.2, 134.4,
133.8, 131.8, 130.0, 128.7, 128.2, 127.8, 127.3, 127.0, 126.2,
125.9, 125.4, 121.1, 120.1, 108.3, 100.7, 46.6, 31.8, 30.2, 29.2,
29.2, 27.0, 22.6, 20.1, 14.1; MS (APCI): calc. for [M + H]+
C33H36N 446.28, found 446.27. Accurate mass: calc. for
[M + H]+ C33H36N 446.2842, found 446.2839.
Acknowledgements
We acknowledge the ERC (Grant number 305868), the Royal
Society and the EPSRC (EP/K039547/1) for financial support.
We also acknowledge the use of the EPSRC UK National
Service for Computational Chemistry Software and Dr Jennifer
Jones for quantum yield measurements. Additional research
data supporting this publication are available as ESI† accom-
panying this publication.
Synthesis of compound 7
6-Methyl-2-octyl-2H-2-aza-14b-boraindeno[1,7-ab]perylene. A
Schlenk tube fitted with a J. Young’s valve was charged with
Notes and references
4-(2-methyl-5-(naphthalen-1-yl)phenyl)-1-octyl-1H-indole,
6
1 For a recent review see: Q. Ye and C. Chi, Chem. Mater.,
2014, 26, 4046.
(88 mg, 1.97 × 10−4 mol). The compound was solubilised in
This journal is © The Royal Society of Chemistry 2016
Dalton Trans.

View Article Online
Paper
Dalton Transactions
2 For a review see: M. Stępień, E. Gońka, M. Żyła and
N. Sprutta, Chem. Rev., 2016, DOI: 10.1021/acs.
chemrev.6b00076.
3 See: (a) C. D. Entwistle and T. B. Marder, Chem. Mater.,
2004, 16, 4574; (b) F. Jäkle, Chem. Rev., 2010, 110, 3985;
12459; (b) V. Bagutski, A. Del Grosso, J. Ayuso Carrillo,
I. A. Cade, M. D. Helm, J. R. Lawson, P. J. Singleton,
S. A. Solomon, T. Marcelli and M. J. Ingleson, J. Am. Chem.
Soc., 2013, 135, 474; (c) A. Del Grosso, J. Ayuso Carrillo and
M. J. Ingleson, Chem. Commun., 2015, 51, 2878.
(c) A. Lorbach, A. Hübner and M. Wagner, Dalton Trans., 13 P. A. Cox, A. G. Leach, A. D. Campbell and G. C. Lloyd-
2012, 41, 6048; (d) A. Escande and M. J. Ingleson, Chem.
Commun., 2015, 51, 6257.
Jones, J. Am. Chem. Soc., 2016, 138, 9145; and references
therein.
4 For select reviews on BN/CC isosterism: (a) M. M. Morgan 14 P. F. Thomson, D. Parrish, P. Pradhan and
and W. E. Piers, Dalton Trans., 2016, 45, 5920; M. K. Lakshman, J. Org. Chem., 2015, 80, 7435.
(b) P. G. Campbell, A. J. V. Marwitz and S.-Y. Liu, Angew. 15 Boronic Acids: Preparation and Applications, ed. D. Hall,
Chem., Int. Ed., 2012, 51, 6074; (c) Z. Liu and T. B. Marder,
Angew. Chem., Int. Ed., 2008, 47, 242.
5 B. Neue, J. F. Araneda, W. E. Piers and M. Parvez, Angew.
Chem., Int. Ed., 2013, 52, 9966.
6 X.-Y. Wang, J.-Y. Wang and J. Pei, Chem. – Eur. J., 2015, 21,
3528.
7 B–(C)n–N PAHs containing arylamine and arylborane units
Wiley-VCH, 2011.
16 W. E. Noland and C. F. Hammer, J. Org. Chem., 1960, 25,
1525.
17 F. Zettler, H. D. Hausen and H. Hess, J. Organomet. Chem.,
1974, 72, 157.
18 C. M. Cardona, W. Li, A. E. Kaifer, D. Stockdale and
G. C. Bazan, Adv. Mater., 2011, 23, 2367.
have been reported see: (a) T. Agou, M. Sekine, J. Kobayashi 19 M. A. Beckett, D. S. Brassington, S. J. Coles and
and T. Kawashima, Chem. Commun., 2009, 1894; as have M. B. Hursthouse, Inorg. Chem. Commun., 2000, 3, 530.
1,4 azaborines, for a recent example see: (b) X. Liu, 20 C.-W. Chiu, Y. Kim and F. P. Gabbai, J. Am. Chem. Soc.,
Y. Zhang, B. Li, L. N. Zakharov, M. Vasiliu, D. A. Dixon and
S.-Y. Liu, Angew. Chem., Int. Ed., 2016, 55, 8333.
8 (a) A. Iida, A. Sekioka and S. Yamaguchi, Chem. Sci., 2012,
3, 1461. During the reviewing process the following paper
2009, 131, 60.
21 (a) Z. Yao, M. Zhang, H. Wu, L. Yang, R. Li and P. Wang,
J. Am. Chem. Soc., 2015, 137, 3799; (b) Y. Avlasevich, C. Kohl
and K. Müllen, J. Mater. Chem., 2006, 16, 1053.
was published containing a B–(C)n–N PAH: (b) V. M. Hertz, 22 J. F. P. Andrews, P. M. Jackson and C. J. Moody,
J. G. Massoth, M. Bolte, H.-W. Lerner and M. Wagner,
Tetrahedron, 1993, 49, 7353.
Chem. – Eur. J., 2016, 22, 13181.
23 H. Muratake and M. Natsume, Heterocycles, 1990, 31, 683.
9 For pioneering studies see: (a) Z. Zhou, A. Wakamiya, 24 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
T. Kushida and S. Yamaguchi, J. Am. Chem. Soc., 2012, 134,
4529; (b) S. Saito, K. Matsuo and S. Yamaguchi, J. Am.
Chem. Soc., 2012, 134, 9130; (c) K. Matsuo, S. Saito and
S. Yamaguchi, J. Am. Chem. Soc., 2014, 136, 12580.
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
Gaussian 09, Revision C1, Gaussian, Inc., Wallingford CT,
2009.
10 For select recent examples see: (a) V. M. Hertz, M. Bolte,
H.-W. Lerner and M. Wagner, Angew. Chem., Int. Ed., 2015,
54, 8800; (b) H. Hirai, K. Nakajima, S. Natatsuka, K. Shiren,
J. Ni, S. Nomura, T. Ikuta and T. Hatakeyama, Angew.
Chem., Int. Ed., 2015, 54, 13581; (c) F. Miyamoto,
S. Nakatsuka, K. Yamada, K.-I. Nakayama and
T.
Hatakeyama,
Org.
Lett.,
2015,
17,
6158;
(d) K. Schickedanz, T. Trageser, M. Bolte, H.-W. Lerner and
M. Wagner, Chem. Commun., 2015, 51, 15808;
(e) K. Fujimoto, J. Oh, H. Yorimitsu, D. Kim and A. Osuka,
Angew. Chem., Int. Ed., 2016, 55, 3196.
11 M. J. S. Dewar, V. P. Kubba and R. Pettit, J. Chem. Soc.,
1958, 3073.
12 (a) A. Del Grosso, M. D. Helm, S. A. Solomon, D. Caras-
Quintero and M. J. Ingleson, Chem. Commun., 2011, 47, 25 http://comp.chem.umn.edu/info/DFT.htm.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2016