Nitrene Insertion into Aromatic and Benzylic C?H Bonds Catalyzed by Copper Complexes of Fluorinated Bis- and Tris(pyrazolyl)borates

Article abstract of DOI:10.1002/cctc.201901087

Fluorinated bis- and tris(pyrazolyl)boratocopper complexes catalyze the nitrene insertion to C?H bonds of aromatic hydrocarbons efficiently producing amination products in good to excellent yields at room temperature. Imidoiodanes, PhI=NTs (Ts=p-toluenesulfonyl) and PhI=NNs (Ns=p-nitrophenylsulfonyl) serve as the nitrene source. The bis(pyrazolyl)borate catalyst [H₂B(3,5-(CF₃)₂Pz)₂]Cu(NCMe) with PhI=NNs produced the arene C?H functionalized product of mesitylene in 87 % yield with only trace amounts of benzylic C?H insertion. The use of [H₂B(3,5-(CF₃)₂-4-(NO₂)Pz)₂]Cu(NCMe) that has an even weakly donating pyrazolate generated the arene C?H insertion product exclusively. The tris(pyrazolyl)borate complex [HB(3,5-(CF₃)₂Pz)₃]Cu(NCMe), in contrast, generated the benzylic amination product from mesitylene and PhI=NNs in 82 % yield with only very minor amounts of arene C?H functionalization. DFT calculations suggest that Cu-nitrene moiety generated from [HB(3,5-(CF₃)₂Pz)₃]Cu(NCMe) and PhI=NNs activates the benzylic C?H bond of mesitylene via a hydrogen atom abstraction (HAA) followed by a radical rebound (RR) pathway, whereas the functionalization of sp² C?H bonds of mesitylene by [H₂B(3,5-(CF₃)₂Pz)₂]Cu(NNs) ensues possibly via a nitrene addition to the arene core.

Full text of DOI:10.1002/cctc.201901087

Accepted Article
Title: Nitrene Insertion into Aromatic and Benzylic C–H Bonds
Catalyzed by Copper Complexes of Fluorinated Bis- and
Tris(pyrazolyl)borates
Authors: H. V. Rasika Dias, Tharun T. Ponduru, Zhicheng Sun, and
Thomas R. Cundari
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201901087
Link to VoR: http://dx.doi.org/10.1002/cctc.201901087
A Journal of
www.chemcatchem.org

10.1002/cctc.201901087
ChemCatChem
Nitrene Insertion into Aromatic and Benzylic C–H Bonds Catalyzed by
Copper Complexes of Fluorinated Bis- and Tris(pyrazolyl)borates
Tharun T. Ponduru,† Zhicheng Sun,‡ Prof. Dr. Thomas R. Cundari,‡* Prof. Dr. H. V. Rasika
Dias†*
†Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington,
Texas 76019, USA
‡Department of Chemistry, Center for Advanced Scientific Computing and Modeling (CASCaM),
University of North Texas, Denton, Texas 76203, USA.
E-mail: dias@uta.edu; Thomas.Cundari@unt.edu
1
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
Abstract: Fluorinated bis- and tris(pyrazolyl)boratocopper complexes catalyze the nitrene
insertion to C-H bonds of aromatic hydrocarbons efficiently producing amination products in good
to excellent yields at room temperature. Imidoiodanes, PhI=NTs (Ts = p-toluenesulfonyl) and
PhI=NNs (Ns = p-nitrophenylsulfonyl) serve as the nitrene source. The bis(pyrazolyl)borate
catalyst [H2B(3,5-(CF3)2Pz)2]Cu(NCMe) with PhI=NNs produced the arene C–H functionalized
product of mesitylene in 87% yield with only trace amounts of benzylic C–H insertion. The use of
[H2B(3,5-(CF3)2-4-(NO2)Pz)2]Cu(NCMe) that has an even weakly donating pyrazolate generated
the arene C–H insertion product exclusively. The tris(pyrazolyl)borate complex [HB(3,5-
(CF3)2Pz)3]Cu(NCMe), in contrast, generated the benzylic amination product from mesitylene and
PhI=NNs in 82% yield with only very minor amounts of arene C–H functionalization. DFT
calculations suggest that Cu-nitrene moiety generated from [HB(3,5-(CF3)2Pz)3]Cu(NCMe) and
PhI=NNs activates the benzylic C–H bond of mesitylene via a hydrogen atom abstraction (HAA)
followed by a radical rebound (RR) pathway, whereas the functionalization of sp2 C–H bonds of
mesitylene by [H2B(3,5-(CF3)2Pz)2]Cu(NNs) ensues possibly via a nitrene addition to the arene
core.
2
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
Introduction: Arylamine motifs are widespread in natural products, agrochemicals, functional
materials and pharmaceuticals,[1-4] as well as in supporting ligands utilized in metal coordination
chemistry.[5-7] Consequently, efficient methods for the synthesis of arylamines are of significant
value. Classical route to arylamines involves nitration under strongly acidic conditions followed
by a reductive hydrogenation step.[1, 8] Ullmann reported a copper mediated route to arylamines
via a cross coupling of aryl halides with amines in 1903.[9, 10] More efficient, cross-coupling
chemistry catalyzed by palladium leading to C(sp2)-N bond construction was reported by the
Buchwald[11] and Hartwig[12] groups in the early 1990s. These latter cross-coupling methods and
other modifications such as copper mediated Chan-Lam aminations,[13-16] however require pre-
functionalized arenes (typically possessing halide, triflate, boronic acid groups, etc.).
Catalytic methods for the direct functionalization of inert arene C–H bonds leading to
C(sp2)-N moieties have advantages over classical nitration/hydrogenation pathways or currently
preferred cross-coupling chemistry in terms of step-efficiency and environmental considerations.[2,
3, 17-19]
Considering their fundamental importance and synthetic value, significant effort has been
devoted to the development of such direct arene C–H amination chemistry resulting in several
important findings.[2, 17, 19-21] Intramolecular C–H amination processes, and those that rely on the
use of directing groups or involve activated C–H bonds are more common.[22-25] In contrast, inter-
molecular, arene C–H functionalization chemistry of simple arenes such as benzene, mesitylene,
etc., is particularly challenging.[17, 26] Nevertheless, advances have been made in recent years to
generate arylamines via the functionalization of C–H bonds of simple arenes.[27-30]
3
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
Table 1. C–H functionalization of benzene and mesitylene at room temperature using PhI=NTs
(Ts = p-toluenesulfonyl) or PhI=NNs (Ns = p-nitrophenylsulfonyl) as the nitrene source
Yield from
eq. 1 with
benzene
C(sp2)-H
40%
Yields from eq. 2 with
mesitylene
Arene substrate/
PhI=NR
Ref
Catalyst
C(sp2)-H
0%
C(sp3)-H
>95%
[31, 32]
[33]
[HB(3,4,5-Br3Pz)3]Cu(NCMe)
AuCl3
substrate used as the
solvent
R = Ts
R = Ts
90%
R = Ts
< 5%
<5%
8:1 in CH2Cl2
R = Ns
45%
R = Ns
81%
R = Ns
<5%
[34]
{[HC(3,5-
20-33 vol%
(Me)2Pz)3]Fe(NCMe)3}(BF4)2
R = Ts
R = Ts
R = Ts
substrate in CH2Cl2
Among the various options for direct C–H aminations, transition-metal-catalyzed formal
nitrene insertion to arene C(sp2)-H bonds represents one of the powerful and attractive strategies
to obtain molecules with C(sp2)-N bonds.[2, 17] Imidoiodanes such as PhI=NTs (Ts = p-
toluenesulfonyl) are the most common nitrene source.[35, 36] In 2003, Perez et al. demonstrated the
functionalization of C(sp2)-H bonds of benzene (used in excess as the solvent) using a copper
tris(pyrazolyl)borate [HB(3,4,5-Br3Pz)3]Cu(NCMe) catalyst and PhI=NTs as the nitrene source
(Table 1).[31, 32] The use of toluene or mesitylene, however, leads to reactions occurring solely at
4
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
the benzylic positions. Sadighi et al. reported the use of copper(I) supported by a 2,9-diaryl-
phenanthroline to catalyze nitrene transfer to the C–H bonds of electron rich arenes such as 1,3-
dimethyoxybenzene, but this catalyst is ineffective for benzene.[37] He and co-workers described
the use of an AuCl3 catalyst and PhI=NNs (Ns = p-nitrophenylsulfonyl) to achieve arene amination
of mesitylene with remarkable arene C–H selectivity (Table 1).[33] Although arene C–H amination
of tri- or more methyl substituted benzenes works well, less substituted benzenes including
benzene itself gave less than 5% of nitrene insertion products while substrates with activated
benzylic C–H bonds have produced varying amounts of C(sp2)-H and C(sp3)-H functionalizations.
The Fe(II) catalyst {[HC(3,5-(Me)2Pz)3]Fe(NCMe)3}(BF4)2 reported by Jensen and Liang displays
notably high aromatic to benzylic C–H amination selectivity (Table 1).[34] Overall, despite these
and other important findings, there is still room for improvements in direct, intermolecular, arene
C–H functionalization via nitrene insertion with respect to substrate scope, chemoselectivity,
product yields, milder conditions, and arene/N-source ratio.
Figure 1. Fluorinated tris- and bis-(pyrazolyl)borate copper complexes
An area of activity in our laboratory concerns nitrene and carbene transfer chemistry of
coinage metal ions supported by highly fluorinated ligands. For example, in 2002 we reported that
5
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
copper(I) adducts such as [HB(3,5-(CF3)2Pz)3]Cu(C2H4) (Figure 1, 1) are competent aziridination
catalysts, readily converting a variety of olefins into the corresponding N-tosyl aziridines with
PhI=NTs.[38] The copper and silver complexes supported by fluorinated tris(pyrazolyl)borates are
also excellent catalysts for functionalizing C–H and C-Cl bonds of alkanes via carbene transfer.[39-
41] Given the current interest and importance, we set out to probe the utility of tris(pyrazolyl)borato
copper complexes such as 2 and related bis(pyrazolyl)borates 3[42] and 4 as catalysts for C–H
aminations of aromatic hydrocarbons. As reported below, we found a remarkable difference in
chemistry between the bis- and tris(pyrazolyl)borate ligand supported catalysts, and notably high
yields of amination products even with low substrate/nitrene source ratios. Results from a
computational study of this process are also presented.
Results and discussion:
Details of the synthesis of [HB(3,5-(CF3)2Pz)3]Cu(NCMe) (2)[43] and [H2B(3,5-
(CF3)2Pz)2]Cu(NCMe) (3)[42] catalysts utilized in this work have been reported elsewhere (Figure
1). The related fluorinated bis(pyrazolyl)borate copper complex [H2B(3,5-(CF3)2-4-
(NO2)Pz)2]Cu(NCMe) (4) possessing NO2 groups at the pyrazolyl ring 4-positions was prepared
in an analogous manner to that of 3 using 3,5-(CF3)2-4-(NO2)PzH[44] and KBH4 and CuOTf. X-
ray crystal structure analysis shows that it is a 3-coordinate copper complex (Figure 2) with a
trigonal planar copper site. The bis(pyrazolyl)borate ligand adopts a typical boat conformation.[45,
46]
6
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
Figure 2. Molecular structure of bis(pyrazolyl)borate copper complex [H2B(3,5-(CF3)2-4-
(NO2)Pz)2]Cu(NCMe) (4). Selected distances (Å) and angles (°): Cu-N2 2.040(3), Cu-N5
2.020(3), Cu-N7 1.865(3), N7-C11 1.102(5), N1-B 1.582(5), N4-B 1.586(5), B•••Cu 2.92, N5-Cu-
N2 91.98(11), N7-Cu-N2 129.28(14), N7-Cu-N5 138.72(14), C11-N7-Cu 178.1(4)
In contrast to tris(pyrazolyl)borates, coordination chemistry and in particular, catalytic
properties of bis(pyrazolyl)borato metal complexes have received notably less attention.[41, 46, 47]
We began our work by testing the prowess of bis(pyrazolyl)borato copper(I) adduct, [H2B(3,5-
(CF3)2Pz)2]Cu(NCMe) (3) in C–H amination chemistry using benzene as the substrate and
PhI=NTs as the nitrene source. Dichloromethane was chosen as the solvent. At room temperature,
the reaction involving 5 mol% of catalyst 3 and 1:5 molar ratio of PhI=NTs to benzene produced
the arene C–H amination product in 44% isolated yield (Table 2, entry 1) and the remaining 56%
is TsNH2 and unidentified products. This is comparable to yields observed with [HB(3,4,5-
Br3Pz)3]Cu(NCMe) and {[HC(3,5-(Me)2Pz)3]Fe(NCMe)3}(BF4)2 but involves much lower
7
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
substrate loadings (Table 1). When we changed the nitrene source to PhI=NNs, the benzene
aminated product yield improved significantly to 68% (Table 2, entry 2) and the remaining 32%
is NsNH2 and unidentified products. This result involving benzene substrate indicates that
PhI=NNs is a better nitrene source than PhI=NTs for the arene C-H amination. We also managed
to improve the C–H amination yield further to 76% by using [H2B(3,5-(CF3)2-4-
(NO2)Pz)2]Cu(NCMe) (4) catalyst that has an even more weakly donating supporting ligand (Table
2, entry 3). Comparison of entries 2 and 4 shows that the tris(pyrazolyl)borate complex [HB(3,5-
(CF3)2Pz)3]Cu(NCMe) (2) gives PhNHNs only in 41% yield even with PhI=NNs as the nitrene
source, indicating that the related bis(pyrazolyl)borate complex 3 is a better catalyst for this
reaction. Note also that AuCl3 with this imidoiodane failed to activate benzene (Table 1). The
need for excess substrates to achieve decent yields is a common issue with hydrocarbon amination
chemistry.[2, 29] Entry 5 shows that catalyst 3 can produce reasonable yields (52%) of the nitrene
insertion product even when the aminating agent and benzene is used in an equimolar amounts,
which is very rare.[2]
We then tested the C–H amination chemistry of mesitylene using PhI=NNs as the nitrene
source (room temperature reactions with 5:1 arene:nitrogen source) and catalysts 2-4. The
chemistry mediated by tris(pyrazolyl)borate complex 2 produced benzylic amination product in
82% isolated yield with very minor arene C–H functionalization products (Table 2, entry 4). The
use of PhI=NTs gave slightly lower yield, but still showing high selectivity for benzylic C–H
activation (entry 6). The [HB(3,4,5-Br3Pz)3]Cu(NCMe) catalyst of Perez et al.[32] displayed
similar behavior with mesitylene (Table 1). The bis(pyrazolyl)borate catalyst 3 with PhI=NNs,
in contrast produced the arene C–H functionalized product (87% isolated yield, entry 2) with only
trace amounts of benzylic C–H insertion. The use of 4 instead of 3, generated the arene C–H
8
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
insertion product exclusively and at notable yields of 90% (entry 3). This result is similar to the
outcome reported with AuCl3 but involves a catalyst containing an earth abundant copper.[33] It is
also possible to produce arene C–H insertion products in respectable 72% yield (entry 5) using
equimolar amounts of mesitylene and PhI=NNs. In this case, we also observed benzylic amination
products in about 8% yield.
Table 2. C–H functionalization of benzene and mesitylene at room temperature using PhI=NTs
(Ts = p-toluenesulfonyl) or PhI=NNs (Ns = p-nitrophenylsulfonyl) as the nitrene source and
catalysts [HB(3,5-(CF3)2Pz)3]Cu(NCMe) (2), [H2B(3,5-(CF3)2Pz)2]Cu(NCMe) (3), [H2B(3,5-
(CF3)2-4-(NO2)Pz)2]Cu(NCMe) (4). All the reactions were performed at room temperature and
the yields reported below are isolated yields after separation and purification by column
chromatography. The yields of the minor products (<10% yields) were estimated from NMR data
of the crude reaction mixture.
Entry Catalyst
Yield from
Amination yields from
eq. 2 with mesitylene
Arene
substrate/
PhI=NR
eq. 1 with benzene
C(sp2)-H
C(sp2)-H
C(sp3)-H
[H2B(3,5-
44
5:1
1
(CF3)2Pz)2]Cu(NCMe) (3)
[H2B(3,5-
R = Ts
68
in CH2Cl2
5:1
87%
<3%
2
(CF3)2Pz)2]Cu(NCMe) (3)
R = Ns
R = Ns
R = Ns
in CH2Cl2
9
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
[H2B(3,5-(CF3)2-4-
(NO2)Pz)2]Cu(NCMe) (4)
[HB(3,5-
76
R = Ns
41
90%
R = Ns
< 5%
< 1%
R = Ns
82%
5:1
in CH2Cl2
5:1
3
4
5
6
(CF3)2Pz)3]Cu(NCMe) (2)
[H2B(3,5-
R = Ns
52
R = Ns
72%
R = Ns
8%
in CH2Cl2
1:1
(CF3)2Pz)2]Cu(NCMe) (3)
[HB(3,5-
R = Ns
36
R = Ns
< 5%
R = Ns
75%
in CH2Cl2
5:1
(CF3)2Pz)3]Cu(NCMe) (2)
R = Ts
R = Ts
R = Ts
in CH2Cl2
Encouraged by these results, we have examined the amination of several other aromatic
hydrocarbons using 5 mol% of the bis(pyrazolyl)borato copper catalysts 3 and 4 (Table 3) in
CH2Cl2. Toluene and ethylbenzene substrates used in this work represent less electron rich and
less crowded arenes relative to mesitylene. Ethylbenzene, however, has secondary benzylic C–H
bonds, which are typically relatively more active than primary.[48] Products from the toluene
reaction show that the reaction is less chemoselective, and the nitrene insertions take place at both
arene and benzylic C–H sites, with slight preference for benzylic sites (Table 3, entries 1, 2). The
3 and 4 catalyzed nitrene transfer to ethyl benzene occurs exclusively at benzylic sites with no
detectable arene C–H amination products (Table 3, entries 3, 4). The 1,3,5-triisopropylbenzene
substrate, which contains both active benzylic C–H bonds and electron-rich, yet crowded arene
core, displays reactivity at both arene and benzylic C–H sites, with slightly more preference for
nitrene insertions at benzylic positions. The 1,3,5-triethylbenzene substrate, displays significantly
more selective amination at arene C–H sites and with only minor amounts of benzylic C–H
insertion, which is very different from the outcome involving ethylbenzene substrate noted above.
All four substrates listed on Table 3 generate higher amination product yields with the catalyst 4
relative to that of 3.
The bis(pyrazolyl)borate copper catalysts 3 and 4 show a unique reactivity profile
compared to the previously utilized
[HB(3,4,5-Br3Pz)3]Cu(NCMe),[32] {[HC(3,5-
10
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
(Me)2Pz)3]Fe(NCMe)3}(BF4)2.[34] and AuCl3 catalysts in arene hydrocarbon amination.[33] For
comparison, with toluene, [HB(3,4,5-Br3Pz)3]Cu(NCMe) catalyst[32] produces exclusive benzylic
aminations while {[HC(3,5-(Me)2Pz)3]Fe(NCMe)3}(BF4)2 shows a large preference for arene C–
H amination.[34] Catalysts 3 and 4 functionalize both arene and benzylic C–H sites of tolunene,
with slight preference for benzylic sites. The nitrene transfer to ethylbenzene catalyzed by 3 and
4 occurs exclusively at benzylic sites with no detectable arene C–H amination products while
{[HC(3,5-(Me)2Pz)3]Fe(NCMe)3}(BF4)2 in contrast, produces near equal amounts of arene and
benzylic C–H amination products. The results from the 3 or 4 catalyzed reactions involving 1,3,5-
triethyl or triisopropylbenzene are similar to the outcome reported with AuCl3 catalyst.[33]
However, AuCl3 does not show any significant arene C–H bond functionalization with benzene or
less substituted benzenes. Catalysts 3 and 4 are also effective at significantly lower substrate
loadings
compared
to
[HB(3,4,5-Br3Pz)3]Cu(NCMe)[32]
and
{[HC(3,5-
(Me)2Pz)3]Fe(NCMe)3}(BF4)2.[34] For example, the substrate (arene) has been used as the reaction
medium or at 20-30 vol% in CH2Cl2 with the latter two catalysts (Table 1), whereas the catalyst 3
afforded high yields of the nitrene insertion products at 5:1 substrate:nitrene source ratio (Tables
2 and 3).
11
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
Table 3. C–H functionalization of aromatic hydrocarbons at room temperature using PhI=NNs
(Ns = p-nitrophenylsulfonyl) as the nitrene source and catalysts [H2B(3,5-(CF3)2Pz)2]Cu(NCMe)
(3), [H2B(3,5-(CF3)2-4-(NO2)Pz)2]Cu(NCMe) (4) (using 5:1 molar ratio of arene:PhI=NNs and 5%
catalysts in CH2Cl2). All the reactions were performed at room temperature and the yields reported
below are isolated yields after separation and purification by column chromatography. The yield
of the minor products of <10% yields were estimated from NMR data of the crude reaction
mixture.
Entry
Substrate/
catalyst
Product/
isolated yield
1
2
[H2B(3,5-(CF3)2Pz)2]Cu(NCMe) (3)
26%
32%
47%
51%
[H2B(3,5-(CF3)2-4-(NO2)Pz)2]Cu(NCMe) (4)
3
4
[H2B(3,5-(CF3)2Pz)2]Cu(NCMe) (3)
60%
68%
[H2B(3,5-(CF3)2-4-(NO2)Pz)2]Cu(NCMe) (4)
5
6
[H2B(3,5-(CF3)2Pz)2]Cu(NCMe) (3)
25%
30%
41%
48%
[H2B(3,5-(CF3)2-4-(NO2)Pz)2]Cu(NCMe) (4)
12
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
7
8
[H2B(3,5-(CF3)2Pz)2]Cu(NCMe) (3)
68%
75%
10%
<5%
[H2B(3,5-(CF3)2-4-(NO2)Pz)2]Cu(NCMe) (4)
The results summarized in Tables 2 and 3 suggest several important steric and electronic
factors in play in terms of the selectivity of nitrene insertions mediated by 2, 3 and 4 to aromatic
hydrocarbons that relies on a delicate balance between supporting ligand, C–H bond energy,
electron density at the arene core, and steric crowding at nitrene insertion sites. The difference in
selectivity displayed by tris(pyrazolyl)borate 2 and bis(pyrazolyl)borate 3 is particularly
interesting. In order to better understand the nitrene insertion process, a computational study was
undertaken to further elucidate the mechanism, especially the selectivity of C–H amination. Many
of the results of the present work parallel the study by Hou et al.,[49] so the points most salient to
the present experiments are summarized herein, with additional details in the Supporting
Information.
In a 2015 computational study, Hou et al. reported that C–H amination of benzene via
nitrene addition is more favored than sp2 C–H bond activation by hydrogen atom abstraction
(HAA) followed by radical rebound (RR) when studying a tris(pyrazolyl)borate Cu(I) catalyst
[HB(3,4,5-Br3Pz)3]Cu(NCMe) utilized by Pérez and co-workers.[31, 32, 49] Herein, the free barriers
calculated for nitrene addition to functionalize an sp2 C–H bond of mesitylene are similar in
comparison to the HAA/RR pathway for benzylic amination of mesitylene by [H2B(3,5-
(CF3)2Pz)2]Cu(NNs) and [HB(3,5-(CF3)2Pz)3]Cu(NNs) active species. The DFT calculations with
the B3LYP functional indicate a triplet ground state for both of these nitrenes. The calculated
singlet-triplet splitting is ~13 kcal mol-1 for both the bis(pyrazolyl)borate and tris(pyrazolyl)borate
models. Note also that the generation of copper-nitrenes in these processes have been proposed,[50]
and observed experimentally with related bis(pyrazolyl)methane systems with pendent
13
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
heteroarenes.[51] Significant spin density is found on both the nitrene nitrogen and the copper,
suggesting a mix of Cu(II)-imidyl and Cu(I)-nitrene character. For [HB(3,5-(CF3)2Pz)3]Cu(NNs),
the spin density (via Mulliken population analyses) is 1.4 e- on nitrene N and 0.31 e- on Cu, whereas
for [H2B(3,5-(CF3)2Pz)2]Cu(NNs), the spin densities are 0.91 e- on nitrene N and 0.36 e- on Cu,
with the rest of the spin density located on the two oxygens of the Ns group. The Cu-N(Ns) bond
length in [HB(3,5-(CF3)2Pz)3]Cu(NNs) is 1.78 Å and in [H2B(3,5-(CF3)2Pz)2]Cu(NNs) is 1.77 Å.
Figure 3. Calculated Gibbs free energy map of arene H-atom abstraction (HAA), blue, and nitrene
addition, black, by [H2B(3,5-(CF3)2Pz)2]Cu(NNs). Reported free energies are in kcal mol-1.
14
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
Arene and benzylic C–H activation of mesitylene was investigated. The HAA/RR
mechanism was evaluated for both [HB(3,5-(CF3)2Pz)3]Cu(NNs) and [H2B(3,5-
(CF3)2Pz)2]Cu(NNs) catalyzed C–H amination, Figure 3. The optimized HAA TS structures show
an elongated benzylic C–H bond and arene C–H bond. With [HB(3,5-(CF3)2Pz)3]Cu(NNs), the C–
H bond is stretched from 1.09 to 1.38 Å for arene HAA (N···H···C angle = 175˚) and from 1.10
to 1.28 Å for benzylic HAA (N···H···C angle = 168˚). With [H2B(3,5-(CF3)2Pz)2]Cu(NNs), the
C–H bond is stretched from 1.10 to 1.37 Å for arene HAA (N···H···C angle = 178˚) and from 1.09
to 1.24 Å for benzylic HAA (N···H···C angle = 175˚). For the HAA C–H activation step,
calculated free energy barriers show that benzylic C–H activation is more favored than arene C–
H activation for both tris- and bis(pyrazolyl)borato-Cu(NNs): 22.8 kcal mol-1 vs. 35.5 kcal mol-1
for [HB(3,5-(CF3)2Pz)3]Cu(NNs) and 13.5 kcal mol-1 vs. 27.0 kcal mol-1 for [H2B(3,5-
(CF3)2Pz)2]Cu(NNs) (see Supporting Information). This difference is expected due to the breaking
of the stronger arene C–H bond[48] and the unfavorable formation of arene radical upon the loss of
aromaticity. Additionally, for mesitylene, one expects an additional steric advantage for activation
at a benzylic versus an arene C–H bond. The formation of the organic radical and Cu[NH(Ns)]
after the arene HAA transition state is endergonic by 18 - 20 kcal mol-1 for both tris- and
bis(pyrazolyl)borato-Cu(NNs), while it is only marginally exergonic (4 - 6 kcal mol-1) for benzylic
HAA. These calculations suggest that this Cu-nitrene moiety is more likely to activate the benzylic
than arene C–H bond of mesitylene if operating via an HAA/RR pathway due to the sterically
more accessible and weaker benzylic C–H bond, which clearly contrasts experimental selectivity
observed in the case of bis(pyrazolyl)borate systems. Inspired by the work of Hou et al. the direct
C-N bond formation or nitrene addition pathway for [H2B(3,5-(CF3)2Pz)2]Cu(NNs) was examined
next due to the observed high arene C–H selectivity. The optimized transition state suggests a step-
15
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
wise nitrene addition followed by proton transfer rather than a concerted nitrene insertion, as was
proposed by Hou et al.[49] This result agrees with previous experiment-theory research on nitrene
two-step aziridination using substituted styrenes as substrate studies.[52, 53] The nitrene addition
pathway has a lower barrier than arene sp2 HAA (17.0 vs. 27.0 kcal mol-1), suggesting it is the
preferred route for functionalization of the mesitylene sp2 C–H bonds. NBO analysis shows that
nitrene addition leads to an amido-copper intermediate as illustrated in Figure 3, with a Cu(I) –
N(Ns)(Mes+) configuration. The barrier of nitrene addition TS for the [HB(3,5-(CF3)2Pz)3]Cu is
calculated to be 35.1 kcal mol-1 higher than the reactants. It is surmised that the steric bulk of the
3-[HB(3,5-(CF3)2Pz)3]Cu coordination and the energetic expense of a reduced coordination to 2-
[HB(3,5-(CF3)2Pz)3]Cu linkage isomer thwart this pathway. The optimized structure of the nitrene
addition TS shows that geometry distortion of the complex is required for the mesitylene to fit into
the activation site, which could cause the high barrier. One of the Cu-NPz is elongated from 2.01
to 2.72 Å, hence moving from 3 towards 2 coordination of the tris(pyrazolyl)borate supporting
ligand. Benzylic HAA may not be the favored pathway in the experiments with [H2B(3,5-
(CF3)2Pz)2]Cu(NNs) even though it has a slightly lower calculated barrier than that of nitrene
addition (13.5 vs. 17.0 kcal mol-1) perhaps because the benzylic HAA is reversible or that the
mesitylene radical might be trapped in the solvent cage. In both cases, the rate of HAA could be
greatly limited and make RR the rate limiting step even though benzylic C–H bond is weaker.
We have also performed an isotope labelling experiment using a 1:1 mesitylene and
mesitylene-d12 mixture with PhI=NNs using [H2B(3,5-(CF3)2Pz)2]Cu(NCMe) (3) catalyst, as
described by He et al for a similar AuCl3 mediated process.[33] Product analysis indicated the
formation of MesNHNs and d11-MesNHNs in a 1:1 ratio, suggesting that the C-H functionlization
step might not be the rate determining step.
16
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
In summary, we have described efficient nitrene insertion into aromatic and benzylic C–H
bonds catalyzed by highly fluorinated bis- and tris(pyrazolyl)boratocopper complexes, producing
amination products in good to excellent yields. We have also found that bis(pyrazolyl)borate
ligand supported catalyst 3 is a better catalyst than the tris(pyrazolyl) version 2 for the arene C-H
amination reaction. We have also shown that PhI=NNs acts as a better nitrene source than its
analog PhI=NTs for the arene C-H amination. The tris- and bis(pyrazolyl)borate ligand supported
catalysts 2 and 3 show remarkable difference in, and opposite selectivity towards benzylic vs
aromatic C–H aminations with mesitylene. We have also demonstrated that it is possible to
achieve reasonable yields of nitrene insertion products using equimolar amounts of aminating
agent and the aromatic substrate. This work also highlight the value of less explored
bis(pyrazolyl)borate ligand support in the Scorpionate family.[46]
Experimental Section:
General Considerations. All manipulations were conducted in a N2 atmosphere using standard
Schlenk techniques, unless noted otherwise. Toluene was freshly distilled from sodium and
benzophenone prior to use. The CH3CN and CH2Cl2 were freshly distilled over CaH2. Glassware
was oven-dried at 150°C overnight. All reagents were purchased from commercial vendors. N-
tosyl phenyliodinane (PhI=NTs)[54] and N-nosyl phenyliodinane (PhI=NNs) were synthesized
according to known methods.[55] Temperatures mentioned refer to the external oil bath
temperature. All additions and manipulations were done under a dry N2 atmosphere. Column
chromatography was done using 230-400 mesh silica gel in open air. Preparative TLC was done
using commercial silica plates with UV absorbance. NMR spectra were recorded at 25°C on a
13
19
JEOL Eclipse 500 spectrometer (1H, 500.16 MHz; C, 125.77 MHz; F, 470.62 MHz). Proton
17
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
and carbon chemical shifts are reported in parts per million versus Me4Si. 19F NMR chemical shifts
were referenced relative to external CFCl3. Elemental analyses were performed using a Perkin-
Elmer Model 2400 CHN analyzer. The 4-nitro-3,5-bis(trifluoromethyl)pyrazole,[44], [HB(3,5-
(CF3)2Pz)3]Cu(NCMe) (2)[43] and [H2B(3,5-(CF3)2Pz)2]Cu(NCMe) (3)[42] were prepared by
published methods.
Synthesis of [H2B(3,5-(CF3)2-4-(NO2)Pz)2]K. 4-nitro-3,5-bis(trifluoromethyl)pyrazole (500 mg,
2.0 mmol) in toluene (10 mL) was added at room temperature to KBH4 (60 mg, 0.96 mmol) in 10
mL of toluene. The reaction mixture was heated to ca. 115-120 °C with stirring and kept at that
temperature for 20 h. After cooling, the mixture was filtered through Celite and the toluene was
removed under reduced pressure to obtain [H2B(3,5-(CF3)2-4-(NO2)Pz)2]K as a white solid, 90%
yield. 1H NMR (acetone-d6): δ 3.66 (v br, B-H, 2H) ppm. 13C{1H}NMR (acetone-d6): δ 118.8 (q,
1JCF = 269 Hz, CF3), 120.1 (q, 1JCF = 268 Hz, CF3), 132.5 (q, 2JCF = 38 Hz, CCF3), 135.2 (q, 2JCF
= 36 Hz, CCF3) ppm; 19F NMR (acetone-d6): δ -58.9, -62.7 ppm. Anal. Calcd for
C10H2BF12KN6O4: C, 21.92; H, 0.37; N, 15.33. Found: C, 21.87; H, 0.38; N, 15.32.
Synthesis of [H2B(3,5-(CF3)2-4-(NO2)Pz)2]Cu(NCMe) (4):
Bis(copper(I) trifluoromethanesulfonate) benzene (147 mg, 0.29 mmol) and [H2B(3,5-(CF3)2-4-
(NO2)Pz)2]K (321 mg, 0.58 mmol) were combined in toluene (15 mL) and stirred for 15 min at
room temperature. Dry acetonitrile (0.5 mL) was added to this mixture and the solution was heated
to 80 °C. This temperature was maintained for 1 h. The mixture was filtered through Celite and
the toluene removed under reduced pressure to obtain [H2B(3,5-(CF3)2-4-(NO2)Pz)2]Cu(NCMe)
1
as a white solid, 76% yield. H NMR (CDCl3): δ 2.33 (s, CH3, 3H), 3.86 (v br, B-H, 2H) ppm.
18
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
13C{1H} NMR (CDCl3): δ 2.72 (s, CH3), 115.2 (s, CN), 118.0 (q, 1JCF = 270 Hz, CF3), 121.0 (q,
1JCF = 269 Hz, CF3), 132.1 (br s, CNO2), 133.3 (q, 2JCF = 42 Hz, CCF3), 135.3 (q, 2JCF = 39 Hz,
CCF3) ppm. 19F NMR (CDCl3): δ -58.0, -61.2 ppm. Anal. Calc. for C12H5BCuF12N7O4: C, 23.49;
H, 0.82; N, 15.98. Found: C, 23.41; H, 0.85; N, 15.90.
General Procedure for C–H Amination:
Benzene (0.2 ml, 2.47 mmol, 5.0 equiv.) and N-tosyl phenyliodinane (200 mg, 0.49 mmol, 1.0
equiv.) and 4 Å molecular sieves (100 mg) were dissolved in dry CH2Cl2 (5 mL). Catalyst
[H2B(3,5-(CF3)2Pz)2]Cu(NCMe) (3, 5 mol%) was added, and the resulting mixture was stirred at
room temperature under N2 for 12 h. The greenish solution, was diluted with CH2Cl2 and the
products were separated using silica gel column chromatography (7:3/hexanes:EtOAc). Yield
44% based on the nitrene source used. Note: The yield of product did not change much when we
have used acetonitrile as the solvent. Other experiments were performed via a similar procedure
using the applicable catalyst and the arene in a CH2Cl2 medium.
X-ray crystallographic data. A suitable crystal covered with a layer of hydrocarbon/Paratone-N
oil was selected and mounted on a Cryo-loop. The X-ray intensity data were measured at the room
temperature on a Bruker D8 Quest with a Photon 100 CMOS detector equipped with an Oxford
Cryosystems 700 series cooler, a Triumph monochromator, and a Mo K fine-focus sealed tube
(λ = 0.71073 Å). Intensity data were processed using the Bruker Apex3 program suite. Absorption
corrections were applied by using SADABS. Initial atomic positions were located by direct
methods using XT, and the structures of the compounds were refined by the least-squares method
57]
using SHELXL[56,
within Olex2[58] GUI. All the non-hydrogen atoms were refined
19
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
anisotropically. Hydrogen atoms on acetonitrile CH3 group were included at calculated positions
and refined riding on corresponding carbon. The BH2 hydrogen atoms were located in a Fourier
difference synthesis and refined satisfactorily. Oxygen atoms of one of the nitro groups show
positional disorder, which was resolved satisfactorily. X-ray structural figures were generated
using Olex2. CCDC 1917595 file contains the supplementary crystallographic data. Further
details are given in the CIF.
Computational Details: DFT calculations were carried out using Gaussian 16, Revision A.03
package.[59] Geometry optimization and frequency calculations were performed with B3LYP
functional and 6-31+G(d) basis set, which have been proven accurate in previous study of nitrene
aziridination catalysts.[52, 53] The calculated Gibbs free energies are computed in the gas-phase, at
298.15 K and 1.0 atm.
Acknowledgments. This work was supported by the Robert A. Welch Foundation (Grant Y-
1289 to HVRD). Z. S. and T. R. C. thank the support of the U.S. Department of Energy, Office
of Science, Basic Energy Science, Catalysis Science Program under award DE-FG02-
03ER15387. Z. S. and T. R. C. also acknowledge the National Science Foundation for their
support of the UNT Chemistry CASCaM high performance computing facility through Grant
CHE-1531468.
Supporting Information Available: Tables of selected structural and spectroscopic and
computational data, additional figures and details.
Keywords: Catalysis, C-H functionalization, Copper, Nitrene, Pyrazolyl borates
20
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
References.
[1]
Z. Rappoport, The Chemistry of Anilines, Parts 1 and 2, John Wiley & Sons, Chichester,
2007.
[2]
[3]
[4]
[5]
J. Jiao, K. Murakami, K. Itami, ACS Catal. 2016, 6, 610-633.
R. K. Rit, M. Shankar, A. K. Sahoo, Org. Biomol. Chem. 2017, 15, 1282-1293.
Y. Shirota, H. Kageyama, Chem. Rev. 2007, 107, 953-1010.
J. A. McCleverty, T. J. Meyer, Comprehensive Coordination Chemistry II, 2nd ed.,
Elsevier, Amsterdam, 2003.
[6]
[7]
[8]
[9]
M. N. Hopkinson, C. Richter, M. Schedler, F. Glorius, Nature 2014, 510, 485.
R. L. Webster, Dalton Trans. 2017, 46, 4483-4498.
H.-U. Blaser, H. Steiner, M. Studer, ChemCatChem 2009, 1, 210-221.
F. Ullmann, Ber. Dtsch. Chem. Ges. 1903, 36, 2382-2384.
[10] K. Kunz, U. Scholz, D. Ganzer, Synlett 2003, 2428-2439.
[11] A. S. Guram, S. L. Buchwald, J. Am. Chem. Soc. 1994, 116, 7901-7902.
[12] F. Paul, J. Patt, J. F. Hartwig, J. Am. Chem. Soc. 1994, 116, 5969-5970.
[13] D. M. T. Chan, K. L. Monaco, R.-P. Wang, M. P. Winters, Tetrahedron Lett. 1998, 39,
2933-2936.
[14] P. Y. S. Lam, C. G. Clark, S. Saubern, J. Adams, M. P. Winters, D. M. T. Chan, A.
Combs, Tetrahedron Lett. 1998, 39, 2941-2944.
[15] J. Bariwal, E. Van der Eycken, Chem. Soc. Rev. 2013, 42, 9283-9303.
[16] K. Masanori, K. Masayuki, M. Toshihiko, Chem. Lett. 1983, 12, 927-928.
[17] Y. Park, Y. Kim, S. Chang, Chem. Rev. 2017, 117, 9247-9301.
[18] P. Ruiz-Castillo, S. L. Buchwald, Chem. Rev. 2016, 116, 12564-12649.
[19] P. Stavropoulos, Comment. Inorg. Chem. 2017, 37, 1-57.
[20] F. Roudesly, J. Oble, G. Poli, J. Mol. Catal. A: Chem. 2017, 426, 275-296.
[21] P. Gandeepan, T. Müller, D. Zell, G. Cera, S. Warratz, L. Ackermann, Chem. Rev. 2019,
119, 2192-2452.
[22] B. J. Stokes, H. Dong, B. E. Leslie, A. L. Pumphrey, T. G. Driver, J. Am. Chem. Soc.
2007, 129, 7500-7501.
[23] J. A. Jordan-Hore, C. C. C. Johansson, M. Gulias, E. M. Beck, M. J. Gaunt, J. Am. Chem.
Soc. 2008, 130, 16184-16186.
[24] R. Singh, K. Nagesh, M. Parameshwar, ACS Catal. 2016, 6, 6520-6524.
[25] A. V. G. Prasanthi, S. Begum, H. K. Srivastava, S. K. Tiwari, R. Singh, ACS Catal. 2018,
8, 8369-8375.
[26] P. Wedi, M. van Gemmeren, Angew. Chem. Int. Ed. 2018, 57, 13016-13027.
[27] N. A. Romero, K. A. Margrey, N. E. Tay, D. A. Nicewicz, Science 2015, 349, 1326-
1330.
[28] T. Kawakami, K. Murakami, K. Itami, J. Am. Chem. Soc. 2015, 137, 2460-2463.
[29] M. P. Paudyal, A. M. Adebesin, S. R. Burt, D. H. Ess, Z. Ma, L. Kürti, J. R. Falck,
Science 2016, 353, 1144-1147.
[30] A. John, J. Byun, K. M. Nicholas, Chem. Commun. 2013, 49, 10965-10967.
[31] M. M. Díaz-Requejo, T. R. Belderraín, M. C. Nicasio, S. Trofimenko, P. J. Pérez, J. Am.
Chem. Soc. 2003, 125, 12078-12079.
[32] M. R. Fructos, S. Trofimenko, M. M. Díaz-Requejo, P. J. Pérez, J. Am. Chem. Soc. 2006,
128, 11784-11791.
21
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
[33] Z. Li, D. A. Capretto, R. O. Rahaman, C. He, J. Am. Chem. Soc. 2007, 129, 12058-
12059.
[34] S. Liang, M. P. Jensen, Organometallics 2012, 31, 8055-8058.
[35] P. Müller, C. Fruit, Chem. Rev. 2003, 103, 2905-2920.
[36] B. Darses, R. Rodrigues, L. Neuville, M. Mazurais, P. Dauban, Chem. Commun. 2017,
53, 493-508.
[37] C. W. Hamilton, D. S. Laitar, J. P. Sadighi, Chem. Commun. 2004, 1628-1629.
[38] H. V. R. Dias, H.-L. Lu, H.-J. Kim, S. A. Polach, T. K. H. H. Goh, R. G. Browning, C. J.
Lovely, Organometallics 2002, 21, 1466-1473.
[39] H. V. R. Dias, R. G. Browning, S. A. Richey, C. J. Lovely, Organometallics 2004, 23,
1200-1202; H. V. R. Dias, R. G. Browning, S. A. Richey, C. J. Lovely, Organometallics
2005, 24, 5784.
[40] H. V. R. Dias, R. G. Browning, S. A. Polach, H. V. K. Diyabalanage, C. J. Lovely, J. Am.
Chem. Soc. 2003, 125, 9270-9271.
[41] H. V. R. Dias, C. J. Lovely, Chem. Rev. 2008, 108, 3223-3238.
[42] H. V. R. Dias, S. A. Richey, H. V. K. Diyabalanage, J. Thankamani, J. Organomet.
Chem. 2005, 690, 1913-1922.
[43] H. V. R. Dias, H.-J. Kim, H.-L. Lu, K. Rajeshwar, N. R. de Tacconi, A. Derecskei-
Kovacs, D. S. Marynick, Organometallics 1996, 15, 2994-3003.
[44] A. Maspero, G. B. Giovenzana, D. Monticelli, S. Tagliapietra, G. Palmisano, A. Penoni,
J. Fluor. Chem. 2012, 139, 53-57.
[45] C. Pettinari, Scorpionates II: Chelating Borate Ligands, Imperial College Press, London,
2008.
[46] C. Pettinari, C. Santini, in Comprehensive Coordination Chemistry II, Vol. 1 (Eds.: J. A.
McCleverty, T. J. Meyer), Pergamon, Oxford, 2003, pp. 159-210.
[47] M. M. Díaz-Requejo, P. J. Pérez, Chem. Rev. 2008, 108, 3379-3394.
[48] X.-S. Xue, P. Ji, B. Zhou, J.-P. Cheng, Chem. Rev. 2017, 117, 8622-8648.
[49] K. Hou, D. A. Hrovat, X. Bao, Chem. Commun. 2015, 51, 15414-15417.
[50] R. T. Gephart, T. H. Warren, Organometallics 2012, 31, 7728-7752.
[51] J. Moegling, A. Hoffmann, F. Thomas, N. Orth, P. Liebhäuser, U. Herber, R.
Rampmaier, J. Stanek, G. Fink, I. Ivanović-Burmazović, S. Herres-Pawlis, Angew. Chem.
Int. Ed. 2018, 57, 9154-9159.
[52] V. Bagchi, P. Paraskevopoulou, P. Das, L. Chi, Q. Wang, A. Choudhury, J. S. Mathieson,
L. Cronin, D. B. Pardue, T. R. Cundari, G. Mitrikas, Y. Sanakis, P. Stavropoulos, J. Am.
Chem. Soc. 2014, 136, 11362-11381.
[53] V. Bagchi, A. Kalra, P. Das, P. Paraskevopoulou, S. Gorla, L. Ai, Q. Wang, S.
Mohapatra, A. Choudhury, Z. Sun, T. R. Cundari, P. Stavropoulos, ACS Catal. 2018, 8,
9183-9206.
[54] G. Besenyei, S. Németh, L. I. Simándi, Tetrahedron Lett. 1993, 34, 6105-6106, also see:
DOI: 6110.1039/SP6123.
[55] P. Dauban, R. H. Dodd, Synlett 2003, 2003, 1571-1586.
[56] G. Sheldrick, Acta Crystallogr. Sect. A: Found. Adv. 2015, 71, 3-8.
[57] G. Sheldrick, Acta Crystallogr. Sect. C: Struct. Chem. 2015, 71, 3-8.
[58] O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H. Puschmann, J. Appl.
Crystallogr. 2009, 42, 339-341.
22
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901087
ChemCatChem
[59] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman,
G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V.
Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V.
Ortiz, A. F. Izmaylov, J. L. Sonnenberg, Williams, F. Ding, F. Lipparini, F. Egidi, J.
Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N.
Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M.
Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A.
Montgomery Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd, E. N. Brothers, K.
N. Kudin, V. N. Staroverov, T. A. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A.
P. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C.
Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B.
Foresman, D. J. Fox, Wallingford, CT, 2016.
23
This article is protected by copyright. All rights reserved.