Eight-membered-ring diaminocarbenes bearing naphthalene moiety in the backbone: DFT studies, synthesis of amidinium salts, generation of free carbene, metal complexes, and solvent-free copper catalyzed azide-alkyne cycloaddition (CuAAC) reaction

Article abstract of DOI:10.1039/c6dt04484k

A new type of eight-membered ring N-heterocyclic carbene (NHC) bearing a rigid naphthalene moiety in the backbone is reported for the first time. Stereoelectronic properties of 4,5-dihydro-1H-naphtho[1,8-ef][1,3]diazocin-3(2H)-ylidene (NaphtDHD) and small

Full text of DOI:10.1039/c6dt04484k

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Page 1 of 37
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EightꢀMemberedꢀRing Diaminocarbenes Bearing Naphthalene Moiety
in the Backbone: DFT Studies, Synthesis of Amidinium Salts,
Generation of Free Carbene, Metal Complexes, and Solventꢀfree
Copper Catalyzed AzideꢀAlkyne cycloaddition (CuAAC) reaction
Gleb A. Chesnokov,[a] Maxim A. Topchiy,[b,c] Pavel B. Dzhevakov,[a,b] Pavel S. Gribanov,[b]
Aleksandr A. Tukov,[b] Victor N. Khrustalev,[c,d] Andrey F. Asachenko,[b] Mikhail S. Nechaev*[a,b]
[a]
M. V. Lomonosov Moscow State University, Leninskie Gory 1 (3), Moscow, 119991, Russia
[b]
A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninsky
Prospect 29, Moscow, 119991, Russia
[c]
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
Vavilov Street 28, Moscow, 119991, Russia
[d]
Department of Inorganic Chemistry, Peoples’ Friendship University of Russia, Miklukhoꢀ
Maklay Street 6, Moscow, 117198, Russia
Eꢀmail: Mikhail S. Nechaev m.nechaev@ips.ac.ru and m.s.nechaev@org.chem.msu.ru

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Abstract
New type of eightꢀmembered ring Nꢀheterocyclic carbenes bearing rigid naphthalene moiety
in the backbone are reported for the first time. Stereoelectronic properties of 4,5ꢀdihydroꢀ1Hꢀ
naphtho[1,8ꢀef][1,3]diazocinꢀ3(2H)ꢀylidene (NaphtDHD) and smaller ring NHCs were theoretically
studied at DFT level. Amidinium salts are prepared from corresponding amidines and dibromides.
Free carbene NaphtDHDꢀDipp (Dipp = 2,6ꢀdiisopropylphenyl) was generated in solution by
treatment of the corresponding salt with LiHMDS. It is stable in solution at low temperatures, while
decompose rapidly at room temperature. Silver(I) and copper(I) complexes were synthesized and
structurally characterized in the solid state. Copper(I) complex [(NaphtDHDꢀMes)CuBr] (Mes =
mesityl, 2,4,6ꢀtrimethylphenyl) exhibits high catalytic activity in alkyneꢀazide cycloaddition
(CuAAC) reaction under solventꢀfree conditions.

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Introduction
Nꢀheterocyclic carbenes (NHC) are widely used as supporting ligands in organometallic
chemistry and catalysis.1 Their steric and electronic properties can be tuned using variation of
substituents, number of nitrogen atoms attached to the ylidene carbon, nature of a backbone of the
heterocycle.2 First stable carbene, isolated by Arduengo and coꢀworkers in the solid state in 1991,
bears imidazolium core (A).3 Later, a wide variety of structural classes of carbenes was reported:
imidazolinium carbenes (B),4 carbenes bearing one nitrogen atom at the ylidene center derived from
aliphatic (C),5 and aromatic (D6 and E7) heterocycles, NHCs stabilized by the remote nitrogen
atoms in the substituents (F)8 or in the aromatic ring (G).9 Many other classes of persistent and
stable carbenes are extensively reviewed in the recent literature.10
Simple and efficient approach for tuning of carbene properties is the variation of a ring size
of the NHC. Sixꢀ (H) and sevenꢀmembered (I) ring diaminocarbenes are commonly referred to as
expandedꢀring carbenes (erꢀNHCs). erꢀNHCs surpass their fiveꢀmembered ring counterparts in
stereoelectronic properties. These ligands are stronger donors and their steric bulk can be tuned in a
wider range. erꢀNHCs were successfully used in a number of catalytic applications.11 To exemplify,
we were able to show that palladium complexes of sixꢀmembered ring carbenes are highly efficient
in Suzuki crossꢀcoupling of heteroaryl halides in water,12 and BuchwaldꢀHartwig arylation of
anilines under solventꢀfree conditions.13 Sevenꢀmembered ring carbenes exhibit steric and
electronic properties sufficient for effective stabilization of cationic gold species, which are highly
active catalysts in addition of nitrogen nucleophiles to aryl acetylenes.14
Recently Cavell et al. reported on the first synthesis of the eightꢀmembered ring carbene
bearing aliphatic backbone (J).15 The key features of the new type diazocanylidenes are high steric
encumbrance around metal atom in the complexes (%Vbur up to 49.1 in Ag complexes),16 and strong
donor properties (νav = 2024.5 cmꢀ1 in [Rh(NHC)(CO)2Cl] complex).2, 17
Following the trend of expansion of the ring size in NHCs and addition of various fragments
in the backbone we performed theoretical and experimental studies of a new type of the eightꢀ

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membered ring carbene bearing rigid naphthalene moiety 4,5ꢀdihydroꢀ1Hꢀnaphtho[1,8ꢀ
ef][1,3]diazocinꢀ3(2H)ꢀylidene (NaphtDHD). In this contribution we report on the comparative
DFT studies of NaphtDHD and smaller ring NHCs, generation of a free carbene, synthesis of
silver(I) and copper(I) complexes, utilization of copper(I) complexes in solventꢀfree alkyneꢀazide
cycloaddition (CuAAC) reaction.

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Results and discussion
DFT calculations
Prior to experimental work, we compared the properties of the eightꢀmembered ring carbene
with smaller ring counterparts using DFT calculations. Recently, we developed a set of calculated
parameters that is useful for characterization of carbenes as ligands in metal complexes.18 This set
includes parameters that characterize donor properties of carbenes, steric properties, stability of free
carbenes and their metal complexes.
Structure optimizations and calculations of electronic parameters of a series of
diaminocarbenes and their rhodium [Rh(NHC)(CO)2Cl] complexes were calculated at DFT level.
Although, silver and copper complexes were prepared experimentally, we have chosen rhodium
carbonyl complexes to calculate Tolman electronic parameter (TEP).19 The calculated parameters
are collected in tables 1 and 2. Here we will discuss the comparison of carbenes’ properties in brief.
A detailed theoretical study will be published elsewhere. It should be noted, that all but one
considered carbenes have aliphatic backbones. Only NaphtDHDꢀMes bears aromatic naphthalene
moiety. Firstly, we will discuss aliphatic carbenes. Then, we will discuss the peculiarities of
NaphtDHDꢀMes.
Table 1
Upon the expansion of the carbene ring from five to eight, the values of NꢀCcarbꢀN valence
angles at the ylidene carbon increase from 106.0° up to 121.9° (Table 1). This leads to changes in
hybridization of the ylidene carbon atom orbitals. The input of pꢀorbital into spx orbital
corresponding to ylidene lone electron pair increases. Thus, the HOMO energies rise from ꢀ4.67 eV
to ꢀ4.21 eV. Simultaneously, HOMOꢀLUMO gap (HLG), singletꢀtriplet energy gap EST, carbene
stabilization energy (CSE) gradually decrease. This means that expanded ring carbenes are softer
ligands, while are more reactive towards insertion into CꢀH bonds, multiple bonds and etc.1a Thus,
isolation of free expanded ring carbenes is more complicated than of fiveꢀmembered ring NHCs.
The calculated measure of NHCs’ basicity is proton affinity (PA). Expansion of the ring
leads to strong increase of the basicity. The difference in calculated PA for fiveꢀ and eightꢀ
membered ring carbenes is 10.8 kcal molꢀ1. This corresponds to the increase of gas phase basicity
by eight orders of magnitude. Indeed, generation of free expanded ring carbenes are only possible
using very strong and nonꢀnucleophilic bases such as LiHMDS. While bases, such as alkoxides and
hydrides, suitable for generation of five membered ring carbenes, are inapplicable.15a, 20
Upon expansion of the ring, substituents at nitrogen atoms are pushed towards the metal in
16
the complexes, thus making carbenes more bulky (Table 2).2 Calculated Vbur
for

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[Rh(NHC)(CO)2Cl] increase from 23.3% to 28.1%. Since metal fragment is pushed away from the
ylidene carbon, the metalꢀcarbon bond R(CcarbꢀRh) slightly increase from 2.10 Å to 2.15 Å.
Elongation of the metalꢀcarbon bond and increase of HOMO energy are competitive factors
governing the value of metalꢀligand interaction energy. Thus, Eint increase when going from fiveꢀ to
sixꢀ and sevenꢀmembered ring carbenes, while decrease for eightꢀmembered ring carbene. The
decomposition energy D gradually decreases in the row from 55.9 down to 50.9 kcal molꢀ1. This
fact is very important to note. Previously, we claimed that the expansion of the ring in carbene leads
to increase in HOMO and, correspondingly, to increase of metalꢀligand bond energy.18 This turned
out to be true for carbenes bearing small substituents, but false for carbenes bearing bulky aryls. It
is well known that steric properties of ligands are the key for many catalytic applications.21 Thus,
when designing a new carbene ligand one might consider its’ bulkiness since overcrowding the
ylidene carbon might destabilize the resulting metal complex.
Table 2
Tolman electron parameter (TEP) is a commonly accepted yardstick for comparison of the
overall ligand donor properties.19 The lower the value of the average wavenumber νav(CO) for
symmetric and asymmetric CO stretching vibrations, the stronger donor is the ligand attached to the
metal atom. Thus, for fiveꢀmembered ring carbene calculated TEP is 2000 cmꢀ1. It gradually
decreases upon expansion of the ring to 1992 cmꢀ1. Such difference in TEP corresponds to a
significant increase of donor strength of the expanded ring carbenes.2
Since NaphtDHDꢀMes bears naphthalene moiety in the backbone, its properties differs
significantly from those of HHDꢀMes, bearing aliphatic backbone. The valence angle at the ylidene
carbon is smaller by 1.4°. Evidently, this is due to shorter CꢀC bonds of the sp2 hybridized carbon
atoms of the naphthalene moiety and rigid fixation of the benzyl carbons in the plane of the
naphthalene ring. The calculated EHOMO energy in NaphtDHDꢀMes (ꢀ4.21 eV) is significantly lower
than for HHDꢀMes (ꢀ4.09 eV). The value of ꢀ4.21 eV is close to the value, calculated for sixꢀ
membered ring carbene THDꢀMes (ꢀ4.23 eV). It can be supposed, that this is due to two factors:
shrinking of NꢀCcarbꢀN valence angle, and corresponding decrease of the input of the pꢀorbital into
spx orbital corresponding to ylidene lone electron pair, and acceptor properties of benzylic carbon
atoms attached to nitrogens of the NꢀCcarbꢀN moiety.
Calculated HLG for NaphtDHDꢀMes is only 1.93 eV, much lower that for NHCs bearing
aliphatic backbone. Evidently, this due to participation of lowꢀlying πꢀorbitals of the naphthalene
ring in the carbene LUMO (see plots of the frontier orbitals in supplementary information). Thus,
NaphtDHD type carbenes are softer ligands for transition metal complexes, than aliphatic backbone
NHCs. Notably, the EST value is the lowest among all carbenes studied here. Lowest predicted

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values of HLG and EST leads to the assumption that NaphtDHD might lack stability as a free
carbene for isolation in the solid state (see experimental part below) comparing to other NHCs.
However, the calculated carbene stabilization energy (CSE), 97.8 kcal molꢀ1, is higher than for any
of the expanded ring carbenes. The calculated value of PA, 287.7 kcal molꢀ1, lies in between eightꢀ
and sevenꢀmembered ring carbenes.
Ligand properties of NaphtDHDꢀMes are close to its aliphatic eightꢀmembered ring
counterpart HHDꢀMes (Table 2). Although, NaphtDHDꢀMes is less bulky, Vbur = 27.6%, it is a
stronger donor, νav(CO) = 1991 cmꢀ1. Energies D and Eint in the complexes [Rh(NHC)(CO)2Cl] are
virtually the same for both carbenes.
Thus, based on the DFT calculations, one might propose that eightꢀmembered ring carbene
bearing naphthalene moiety in the backbone is a feasible target for synthesis. Combination of
NaphtDHD ligand properties (steric encumbrance, ligand softness, strong donor properties, and the
rigidity of the carbene backbone) promise rich reactivity and interesting catalytic applications.
Synthesis of amidinium salts and generation of carbenes
Eightꢀmembered ring amidinium salts, bearing naphthalene moiety in the backbone, were
synthesized by condensation of formamidines (3) and 1,8ꢀbisꢀ(bromomethyl)ꢀnaphthalene (2)
(Scheme 1). This strategy was initially introduced by Bertrand et al.22 and further developed in our
group for the synthesis if sixꢀ and sevenꢀmembered ring amidinium salts.23 Corresponding
dibromide can be easily prepared starting from commercially available 1,8ꢀnaphthalic anhydride.24
Scheme 1
Preparation of amidinium salts bearing naphthalene moiety in the backbone.
1,8ꢀNaphthalic anhydride can be reduced to 1,8ꢀnaphthalenedimethanol (1) using two
methods: interaction with lithium aluminum hydride in THF,24 and a mixture of sodium
borohydride with bromine in 1,2ꢀdimethoxyethane (1,2ꢀDME).25 Yields of diol are 84% and 61%,
correspondingly. Treatment of the obtained diol with PBr3 in 1,4ꢀdioxane afforded dibromide (2) in
94% yield.26

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Amidinium salts (4a, 4b) were obtained by interaction of the dibromide with corresponding
amidines (3a, 3b) in presence of Hünig's base (N,Nꢀdiisopropylethylamine, DIPEA) in DMF.
Corresponding salts were obtained in excellent yields, 87% and 88%, respectively for Mes and Dipp
derivatives.22
We performed the attempts to isolate a free carbene. Previously, Cavell et al. have shown
that deprotonation of amidinium salts is more efficient and high yielding when tetrafluoroborates
are used instead of bromides.20b Presumably, this is due to the fact that in bromides the anion is
bonded to the amidinium proton through a hydrogen bond (see Xꢀray sections below).
Tetrafluoroborate has lower coordination ability, and, thus, does not hinder the deprotonation of
amidinium salt by bulky base. Thus, we converted amidinium bromides into tetrafluoroborates by
treatment of salts with sodium tetrafluoroborate in acetone at room temperature (Scheme 2).
Notably, amidinium bromides are poorly soluble in acetone. Upon addition of sodium
tetrafluoroborate to a suspension of amidinium bromide, the mixture gradually homogenized, and
became a clear solution when reaction finished. Amidinium tetrafluoroborates are white nonꢀ
hygroscopic solids, isolated in virtually quantitative yields, 97% and 98%, correspondingly for Mes
and Dipp derivatives.
Scheme 2
Preparation of amidinium tetrafluoroborates.
We performed generation of a free carbene from [(NaphtDHDꢀDipp)H]BF4 (5b) using bulky
lithium hexamethyldisilazide base (LiHMDS) in dry aprotic solvent.27 To a solution of amidinium
tetrafluoroborate in THF LiHMDS was slowly added. At room temperature, upon addition of a
base, reaction mixture changed its color from transparent into green, then discolored instantly. The
isolated products are a mixture of unidentifiable compounds. There were no signals found in 13C
NMR spectrum in the 220 – 260 ppm region, characteristic for a carbene carbon atom. Typically,
intense coloration is due to the formation of a conjugated πꢀsystem. We supposed that deprotonation
could take place in less hindered benzylic position of a naphthalene moiety, giving rise to the
formation of highly reactive azomethine ylide (Scheme 3).
Scheme 3

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Generation of a free carbene
At ꢀ 80°C, the obtained intense coloring of a solution lasts for a long period of time. To
determine the deprotonation position, we added deuterated water as a scavenger. THF was
evaporated from the reaction mixture, a dichloromethane was added. The mixture was dried over
Na2SO4, solvent was evaporated, and the residues of a solvent were eliminated under high vacuum.
The product was obtained in virtually quantitative yield. 1H NMR of the product contains no signal
13
at 7.48 ppm corresponding to starting [(NaphtDHDꢀDipp)H]BF4 salt (5b). In C{1H} NMR signal
of an amidinium carbon atom at 157.1 ppm disappears. Instead, a multiplet at 154.3 ppm appears
with spinꢀspin coupling constant J(2D, 13C) = 25.4 Hz.
Formation
of
D2ꢀ2,4ꢀbis(2,6ꢀdiisopropylphenyl)ꢀ2,3,4,5ꢀtetrahydroꢀ1Hꢀnaphtho[1,8ꢀ
ef][1,3]diazocinꢀ3ꢀol (6b), bearing deuterium atom in 3ꢀposition corresponds to the formation of the
carbene, rather than the ylide. However, it can be supposed that a carbene and an ylide might be in a
dynamic equilibrium in the reaction mixture. Even small share of an ylide might lead to intense
coloring, while the major share of a carbene leads to the formation of diazocinꢀ3ꢀol in virtually
quantitative yield.
Thus, we obtained solid proofs, that a free carbene bearing eightꢀmembered ring and a
naphthalene moiety in the backbone can be generated from the corresponding amidinium
tetrafluoroborate by treatment with LiHMDS. The carbene is stable in the solution at low
temperatures, while decompose rapidly at room temperature, thus preventing its isolation and
structural characterization. It is worth mentioning, that Cavell and coworkers succeeded to isolate
and structurally characterized first eightꢀmembered ring carbene bearing aliphatic backbone.15a
To rationalize the observed experimental data we went back to the results of DFT
calculations. Lower stability of NaphtDHD than HHD can be attributed to lower HOMOꢀLUMO
gap (HLG, see Table 1). Lower HLG leads to increased reactivity of a carbene towards
intramolecular CꢀH activations and other side reactions.28
It was also of interest to determine the nature of the green coloring of the reaction media
upon generation of the carbene. We optimized the structure of the proposed ylide. To model
absorption spectra of the carbene and the ylide, we performed TDDFT calculations. It was found,
that for the carbene there are only two weak bands at 636 nm and 459 nm in the visible region.

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Thus, calculations support that the free carbene NaphtDHDꢀDipp should be colorless. Oppositely,
for the ylide a number of intense absorption bands were predicted from calculations: 686 nm, 652
nm, 624 nm, 595 nm (red – orange region), and 490 nm (blue region). Exclusion of red and blue
bands from the spectrum should lead to green coloring of the solution bearing ylide. Thus, based on
the simulations of visible spectra of the carbene and the ylide, it can be supposed that the ylide
exists, at least in some ratio, in the equilibrium with the carbene NaphtDHDꢀDipp in the solution at
low temperature.
Calculated total energy of the ylide is 1.9 kcal molꢀ1 lower than for the corresponding
carbene NaphtDHDꢀDipp. Certainly, this calculated energy difference cannot be taken as a
quantitative value of the relative stability of two isomers since calculations were performed in the
gas phase, while the experiment was performed in the solution. However, it can be supposed, that
the energies of both isomers are rather close in the reaction media and both isomers might be in
dynamic equilibrium. It is known from the experiment, that upon scavenging with deuterated water,
only carbene derived product is formed. Thus, we can conclude, that carbene is the major isomer in
the real solution, while ylide is the minor one. Ylide derived product of scavenging with water is
not traced in the NMR spectra, while ylide itself manifests its existence in the solution with the
intense green coloring.
Synthesis of silver and copper complexes
Silver(I) complexes of Nꢀheterocyclic carbenes are synthetically useful. Due to low energy
of a carbeneꢀsilver bond, these complexes can be easily transmetallated to obtain NHC complexes
of other transition metals. The most convenient method of synthesis of silver(I) complexes is
interaction of amidinium salt with silver(I) oxide in CH2Cl2 (Scheme 4).27
Scheme 4
Preparation of silver(I) complexes
In our case, in CH2Cl2 the formation of silver(I) complexes proceeds with moderate yields
(44% for 7a and 40% for 7b). We performed optimization of synthesis of silver(I) complexes
(Table 3). The highest yield for [(NaphtDHDꢀDipp)AgBr] (7b) was obtained in THF at 60°C. The

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obtained yield of [(NaphtDHDꢀMes)AgBr] (7a) under optimized conditions is 80%. Previously
only two examples of eightꢀmembered ring NHC silver(I) complexes [(HHDꢀMes)AgBr] and
[(HHDꢀXyl)AgBr] were reported by Cavell et al.15a
Table 3
The obtained complexes are airꢀ and lightꢀstable colorless solids with melting points over
1
300°C. These complexes were characterized by H and 13C NMR. The characteristic signal for the
carbene silver(I) complexes is a doublet of doublets in the 200ꢀ220 ppm region. Appearance of such
signal is due to spinꢀspin interaction of 13C with 107Ag (spin 1/2, 51.84 %) and 109Ag (spin 1/2,
48.16 %). Signals at 210.4 (J(109Ag, 13C) = 267.7 Hz, J(107Ag, 13C) = 226.7 Hz) and 211.8 (J(109Ag,
13C) = 261.3 Hz, J(107Ag, 13C) = 227.2 Hz) were found, correspondingly to Mes and Dipp
substituted complexes.
Previously we have shown that the most convenient way of synthesis of expanded ring NHC
copper(I) complexes is transmetallation of silver(I) complexes with corresponding copper(I) salts.
This approach is high yielding, very simple experimentally and easily reproducible (Scheme 5).23, 29
The obtained yields of copper complexes are high, 84% for 8a and 83% for 8b.
Scheme 5
Synthesis of [(NaphtDHD)CuBr].
Complexes are colorless crystalline solids stable in air. Melting points are over 300°C.
Characteristic for ylidene carbon in NHC copper(I) complex is the signal in 13C NMR in 200ꢀ210
ppm region; 203.6 ppm and 204.7 ppm, respectively for Mes and Dipp derivatives. These
complexes are the first examples of eight membered ring NHCs with copper(I). Moreover, reaction
in scheme 7 is the first example of transmetallation in silver(I) complexes bearing eightꢀmembered
ring carbenes.
Xꢀray structure studies
We were able to obtain Xꢀray quality crystals of Dippꢀsubstituted salt and complexes
[(NaphtDHDꢀDipp)H]Br (4b), [(NaphtDHDꢀDipp)AgBr] (7b), and [(NaphtDHDꢀDipp)CuBr] (8b)
(Figures 1ꢀ3, supporting information).

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Figure 1
Figure 2
Figure 3
Remarkably, all the three investigated compounds are isostructural, apparently, due to the
rigid geometry of the bulk NaphtDHDꢀDipp ligand. The central heterocyclic eightꢀmembered
fragment of this NHC ligand adopts the roofꢀlike conformation with the fold angle on the C1…C5
line of 62.43(7), 61.89(10) and 62.04(8)° for [(NaphtDHDꢀDipp)H]Br (4b), [(NaphtDHDꢀ
Dipp)AgBr] (7b), and [(NaphtDHDꢀDipp)CuBr] (8b), respectively. The idealized Cs (m) symmetry
of these complexes is distorted. The two nitrogen atoms have the trigonalꢀplanar configurations
with the dihedral angle between the corresponding planes of 17.5(1), 17.0(2) and 18.3(1)°,
respectively. Here it is important to note that the previously studied silver complexes [(HHDꢀ
Mes)AgBr] and [(HHDꢀXyl)AgBr] show small values of the spatial twist of the N coordination
planes. The N─Ccarb─N angles (Figures 1ꢀ3) are large, and exceed 120° analogously to previously
reported eightꢀmembered ring carbenes.15a With the attendant Cdipp─N─Ccarb angles
(117.0(2)/118.7(2), 115.1(2)/116.6(2) and 116.3(2)/114.6(2)°, respectively) being small, pushing
the Dipp substituents toward the Ccarb atom. As the result, the Ag and Cu atoms form the short
contacts to the H atom of one of the Dipp ligands (Ag1…H20A 2.81 Å and Cu1…H23A 2.79 Å).
The benzene rings of the Dipp substituents are roughly perpendicular to the carbene plane
(87.74(7)/80.36(8), 84.79(10)/83.28(11) and 82.35(9)/85.72(8)° for [(NaphtDHDꢀDipp)H]Br (4b),
[(NaphtDHDꢀDipp)AgBr] (7b), and [(NaphtDHDꢀDipp)CuBr] (8b), respectively.
As it can be expected, the cation and anion in [(NaphtDHDꢀDipp)H]Br (4b) are linked by the
strong Ccarb─H…Br hydrogen bond (Table 4, Figure 1). The solvate water molecule forms the
hydrogen bonds of two different types – the O1─H1C...Br1 and O1─H1D...π(C27─C28). Further,
the cation, anion and water molecule are bound by the C5─H5A...O1a and C5─H5B...Br1a
intermolecular hydrogen bonds into the layers parallel to (100).
Table 4
The Ag─Ccarb and Cu─Ccarb distances (2.116(3) and 1.907(2) Å, respectively, figures 2 and 3)
for [(NaphtDHDꢀDipp)AgBr] (7b) and [(NaphtDHDꢀDipp)CuBr] (8b) are close to those observed
by us previously in the related complexes with the THPꢀDipp and THDꢀDipp ligands.23 The
Ccarb─Ag─Br and Ccarb─Cu─Br bond angles are practically linear (179.58(9) and 179.22(8)°,
respectively). It is interesting to note that, in contrast to the [(THPꢀDipp)CuBr] and [(THDꢀ
Dipp)CuBr] complexes, the Ccarb─Cu─Br bond angle in [(NaphtDHDꢀDipp)CuBr] (8b) does not
indicate the significant deviation from linearity.

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Catalytic studies
In 2006 Nolan et al. reported on the efficient catalysis of alkyneꢀazide cycloaddition
(CuAAC) reaction under solventꢀfree conditions using [(SIMes)CuBr] complex. A series of 1,4ꢀ
disubstitutedꢀ1,2,3ꢀtriazoles were obtained in high yields under mild reaction conditions.30 In 2010
Nolan et al. reported on utilization of [(IAd)CuI] as catalyst in the same solventꢀfree reaction. 1,2,3ꢀ
Triazoles were obtained at room temperature in higher yields, shorter reaction times, and at low
(down to 0.8 mol%) catalyst loadings.31
In continuation of our studies of metal mediated catalytic transformations under solventꢀfree
conditions we performed tests of activity of a series of NHC copper(I) bromides in the copper(I)ꢀ
catalyzed alkyneꢀazide cycloaddition (CuAAC) reaction.13, 14b, 32 Cycloaddition of benzyl azides
with acetylenes is an efficient, high yielding method of synthesis of 1,2,3ꢀtriazoles. However, aryl
azides33 are more challenging substrates.34 Thus, for comparative tests of the catalysts and
optimization of the reaction conditions we have chosen cycloaddition of phenyl acetylene with pꢀ
tolyl azide (tables 5 and 6).
Table 5
As shown in table 5, Mesꢀsubstituted sixꢀ and eightꢀmembered ring NHC complexes (THPꢀ
Mes)CuBr and (NaphtDHDꢀMes)CuBr (8a) give virtually quantitative yields. NHCs bearing more
bulky Dipp aryl groups give very low yields. We suppose that this is due to the steric overcrowding
of the metal center.
For the most active precatalysts [(THPꢀMes)CuBr] and [(NaphtDHDꢀMes)CuBr] (8a) we
performed a set of experiments to determine precatalysts loading suitable for efficient catalysis
(Table 6). At 1 mol% loading both precatalysts give virtually quantitative yields. Upon decrease of
precatalyst loading to 0.5 and 0.1 mol% the yield drops down only by a few percent. Only at 0.05
mol% loading the yields are below 80%. For [(NaphtDHDꢀMes)CuBr] (8a) at 0.05 mol% loading
we were able to obtain TON value of 1560, which is rather high result if comparing to previously
reported data for solventꢀfree CuAAC reaction with aryl azides.30ꢀ31
Table 6
To determine the scope and limitations of the developed catalytic system we performed
testing of activity of [(NaphtDHDꢀMes)CuBr] (8a) in cycloaddition of pꢀtolyl azide (Table 7) and
benzyl azide (Table 8) with various terminal acetylenes. Utilization of [(NaphtDHDꢀMes)CuBr]
(8a) leads to highly efficient cycloaddition of pꢀtolyl azide and benzyl azide with aliphatic (table 7
entries 1ꢀ5; table 8, entries 1ꢀ5) as well as aromatic (table 7, entries 6ꢀ10; table 8, entries 6ꢀ12)
acetylenes. The catalytic system tolerates functional groups in acetylenes (table 7, entries 2ꢀ4, 7ꢀ9;

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table 8, entries 4, 5, 10ꢀ12). Only for bulky Mes substituted acetylene (table 7, entry 10; table 8,
entry 9) the isolated yields were 78% and 80%, respectively for pꢀtolyl and benzyl azides.
Table 7
Table 8
Table 9 exemplifies the broad spectrum of utilization of [(NaphtDHDꢀMes)CuBr] (8a) in
cycloadditions of various acetylenes and organic azides. Volatile acetylenes bearing propyl, tertꢀ
butyl, trimethylsilyl groups are efficiently added to azides at room temperature (entries 1ꢀ9). High
yields over 80% were obtained in the reactions of various aryl (entries 2, 4, 5, 7, 9, 11, 12) and
benzyl azides (entries 1, 3, 6, 8, 10).
Table 9

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Conclusions
In conclusion, we developed a new type of expanded ring NHC NaphtDHD bearing eightꢀ
membered ring and a naphtyl moiety in the backbone.
Properties of a new type of carbenes were compared to smaller ring (5, 6, and 7) NHCs.
According to DFT calculations, NaphtDHDꢀMes is a bulky carbene bearing a rigid backbone. It
exhibits strong donor properties as ligand in transition metal complexes.
A free NaphtDHDꢀDipp carbene was generated in solution from the corresponding
amidinium salt under treatment of a strong base LiHMDS. It is stable at low temperatures, while
decompose rapidly at room temperature. Formation of a free carbene was confirmed by scavenging
with deuterated water.
Silver(I) complexes of NaphtDHDꢀMes and NaphtDHDꢀDipp were synthesized by treatment
of corresponding amidinium salts with Ag2O. Copper(I) complexes were obtained via
transmetallation of silver(I) complexes with copper(I) salts. Structures of amidinium salts and metal
complexes in the solid state were determined by Xꢀray crystallography.
We performed comparative study of catalytic activity of 5ꢀ, 6ꢀ, 7ꢀ, and 8ꢀmembered ring
NHC copper(I) complexes in Huisgen cycloaddition of organic azides with terminal acetylenes
under solventꢀfree conditions. A highly efficient catalytic system based on [(NaphtDHDꢀ
Mes)CuBr] (8a) complex was developed. Cycloaddition of various aryl and benzyl azides with
various aliphatic and aromatic terminal acetylenes proceeds in high to quantitative yields. The
developed catalytic system is suitable for substrates bearing functional groups.
This report is another successful example of utilization of expanded ring carbenes in
synthesis of transition metal complexes and catalysis of important organic transformations. erꢀ
NHCs and their complexes are synthetically accessible. Variation of the ring size gives simple
access for tuning of stereoelectronic properties of NHCs in a wide range. This enabled us to develop
a new type of catalyst operative under solventꢀfree conditions.
Acknowledgements
The reported study was partially supported by the Russian Foundation for Basic Research
(RFBR), research project number 16ꢀ29ꢀ10706 ofi_m.

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Experimental
Calculation procedures
All calculations were conducted at the DFT level using the PBE functional.35 Valence
electrons were treated using a TZ2P basis set. Innermost electrons of Rh, Cl, C, N, O atoms were
emulated using effective core potentials ECPꢀSBKJC.36 All stationary points, except those
corresponding to complex fragments, were characterized as minima by calculations of normal
modes of vibrations. All calculations were made using PRIRODA program.37 Graphical
representation of molecular orbitals were made using MOLEKEL 4.3.38 For detailed explanation of
the meaning of calculated parameters EST, CSE, PA, D, Eint, Vbur see reference.18
General procedure for preparation of amidinium salts.
N,NꢀDiisopropylethylamine (0.142 g, 1.1 mmol, 1.1 eq) was added to mixture of appropriate
N,N’ꢀdiarylformamidine (1 mmol,
1
eq) and 0.314
g
(1 mmol,
1
eq) of 1,8ꢀ
bis(bromomethyl)naphthalene (2) in 5 ml of dry DMF. Reaction mixture was heated at 125°C for 3
h. After cooling to r.t., water (50 ml) was added and resulting mixture was extracted with CH2Cl2
(3x25 ml), organic phase was washed with saturated solution of K2CO3 and dried over anhydrous
MgSO4. The solvent was removed under reduced pressure, and the crude solid was recrystallized
from toluene or hexaneꢀdichloromethane mixture, filtered and dried in vacuum.
2,4-dimesityl-4,5-dihydro-1H-naphtho[1,8-ef][1,3]diazocinium bromide (4a)
Yield 87%. White microcrystalline solid. Mp = 275ꢀ276°C
1H NMR (600 MHz, Chloroformꢀd) δ 8.10 (d, J = 16.5 Hz, 2H), 7.94 (d, J = 7.0 Hz, 2H),
7.39 (dd, J = 8.2, 7.0 Hz, 2H), 7.33 (s, 1H), 7.19 (d, J = 7.0 Hz, 2H), 6.99 (s, 2H), 6.76 (s, 2H), 4.48
(d, J = 16.3 Hz, 2H), 2.65 (s, 6H), 2.24 (s, 6H), 1.39 (s, 6H).
13C{1H} NMR (151 MHz, Chloroformꢀd) δ 154.9, 140.5, 140.2, 135.9, 135.7, 132.9, 132.3,
132.0, 131.5, 130.9, 130.7, 129.7, 126.0, 60.0, 21.0, 19.4, 17.8.
E.A. found (calcd.), %: C 72.60 (72.51), H 6.42 (6.48), N 5.37 (5.46).

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2,4-bis(2,6-diisopropylphenyl)-4,5-dihydro-1H-naphtho[1,8-ef][1,3]diazocinium bromide (4b)
N+
N
Br-
Yield 88%. White microcrystalline solid. Mp = 333ꢀ335°C
1H NMR (600 MHz, DMSOꢀd6) δ 8.94 (s, 1H), 8.16 (dd, J = 8.1, 1.5 Hz, 2H), 7.61 (dd, J =
7.1, 1.5 Hz, 2H), 7.57 (dd, J = 8.1, 6.9 Hz, 2H), 7.49 – 7.43 (m, 4H), 7.25 (dd, J = 7.5, 1.7 Hz, 2H),
7.20 (d, J = 16.5 Hz, 2H), 4.67 (d, J = 16.2 Hz, 2H), 2.26 – 3.30 (m, J = 6.8 Hz, 2H), 2.01 (p, J = 6.7
Hz, 2H), 1.49 (d, J = 6.7 Hz, 6H), 1.28 (d, J = 6.7 Hz, 6H), 0.83 (d, J = 6.8 Hz, 6H), 0.71 (d, J = 6.6
Hz, 6H).
13C{1H} NMR (151 MHz, DMSOꢀd6) δ 157.1, 145.1, 144.1, 139.3, 135.2, 133.0, 131.4,
130.4, 130.2, 130.2, 125.9, 125.3, 124.8, 58.8, 28.6, 28.0, 25.2, 24.7, 24.2, 23.7.
E.A. found (calcd.), %: C 73.97 (74.35), H 7.52 (7.59), N 4.51 (4.69).
2,4-dimesityl-4,5-dihydro-1H-naphtho[1,8-ef][1,3]diazocinium tetrafluroborate (5a)
Solution of sodium tetrafluoroborate (0.367 g, 3.3 mmol) in 50 ml of water was added to
solution of 1.69 g (3.3 mmol) 2,4ꢀdimesitylꢀ4,5ꢀdihydroꢀ1Hꢀnaphtho[1,8ꢀef][1,3]diazocinium
bromide (4a) in 40 ml of acetone. Acetone was slowly evaporated in vacuum from homogenous
solution; precipitate was filtered and dried in vacuum over P4O10. Yield 1.67 g (97%).
1H NMR (600 MHz, Chloroformꢀd) δ 7.99 (d, J = 7.9 Hz, 2H), 7.45 (t, J = 7.9 Hz, 2H), 7.36
(s, 1H), 7.28 – 7.21 (m, 4H), 7.05 (s, 2H), 6.81 (s, 2H), 4.55 (d, J = 16.4 Hz, 2H), 2.60 (s, 6H), 2.29
(s, 6H), 1.43 (s, 6H).
13C{1H} NMR (151 MHz, Chloroformꢀd) δ 155.7, 140.6, 136.0, 133.0, 132.6, 131.7, 131.8,
131.1, 130.0, 126.3, 59.0, 21.0, 18.3, 17.8.
IR (υ/cm–1): 2954 (w), 2919 (w), 2859 (w), 2360 (vw), 1652 (vs), 1506 (w), 1477 (m), 1452
(m), 1386 (m), 1359 (m), 1315 (w), 1189 (m), 1135 (m), 1049 (vs), 1024 (vs), 985 (m), 950 (m),
906 (m), 860 (m), 812 (m), 773 (m), 681 (m).

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2,4-bis(2,6-diisopropylphenyl)-4,5-dihydro-1H-naphtho[1,8-ef][1,3]diazocinium tetrafluroborate
(5b)
Solution of sodium tetrafluoroborate (0.367 g, 3.3 mmol) in 50 ml of water was added to
solution of 2.0 g (3.3 mmol) 2,4ꢀbis(2,6ꢀdiisopropylphenyl)ꢀ4,5ꢀdihydroꢀ1Hꢀnaphtho[1,8ꢀ
ef][1,3]diazocinium bromide (4b) in 50 ml of acetone. Acetone was slowly evaporated in vacuum
from homogenous solution; precipitate was filtered and dried in vacuum over P4O10. Yield 1.98 g
(98%).
1H NMR (600 MHz, Chloroformꢀd) δ 8.00 (d, J = 7.0 Hz, 2H), 7.49 – 7.40 (m, 5H), 7.34
(dd, J = 7.8, 1.5 Hz, 2H), 7.31 (dd, J = 7.0, 1.3 Hz, 2H), 7.25 (d, J = 16.0 Hz, 2H), 7.12 (dd, J = 7.8,
1.5 Hz, 2H), 4.57 (d, J = 16.4 Hz, 2H), 3.50 (p, J = 6.6 Hz, 2H), 2.07 (p, J = 6.7 Hz, 2H), 1.52 (d, J
= 6.6 Hz, 6H), 1.29 (d, J = 6.7 Hz, 6H), 0.85 (d, J = 6.9 Hz, 6H), 0.76 (d, J = 6.6 Hz, 6H).
13C{1H} NMR (151 MHz, Chloroformꢀd) δ 154.8, 146.7, 144.3, 139.3, 133.0, 132.0, 131.2,
130.3, 126.2, 126.0, 125.2, 60.3, 29.1, 28.4, 26.1, 25.2, 24.7, 24.4.
D2-2,4-bis(2,6-diisopropylphenyl)-2,3,4,5-tetrahydro-1H-naphtho[1,8-ef][1,3]diazocin-3-ol (6b)
To a solution of 200 mg (0.3 mmol) of (E)ꢀ2,4ꢀbis(2,6ꢀdiisopropylphenyl)ꢀ4,5ꢀdihydroꢀ1Hꢀ
naphtho[1,8ꢀef][1,3]diazocinium tetrafluroborate (5b) in 15 ml of dry, degassed THF was added a
solution of 55 mg (0.3 mmol) of LiHMDS in 15 ml THF at ꢀ80°C. Reaction mixture color changed
from transparent to dark green. Reaction mixture was stirred for 30 min at ꢀ80°C, 2 ml of D2O was
added in one portion and reaction mixture was allowed to warm to room temperature. All volatiles
were removed on rotary evaporator and the residue was dissolved in 20 ml of CH2Cl2, dried over
anhydrous Na2SO4 and evaporated to dryness. Drying in vacuum to constant weight gave 168 mg
(95%) of white solid.

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1H NMR (600 MHz, Chloroformꢀd) δ 7.99 (dd, J = 8.3, 1.3 Hz, 2H), 7.44 (d, J = 8.3 Hz,
1H), 7.41 (d, J = 8.1 Hz, 2H), 7.33 (dd, J = 7.8, 1.6 Hz, 2H), 7.29 (dd, J = 7.1, 1.3 Hz, 2H), 7.22 (d,
J = 16.7 Hz, 2H), 7.12 (dd, J = 7.8, 1.5 Hz, 2H), 4.55 (d, J = 16.3 Hz, 2H), 3.48 (p, J = 6.7 Hz, 2H),
2.05 (p, J = 6.8 Hz, 2H), 1.50 (d, J = 6.7 Hz, 6H), 1.27 (d, J = 6.7 Hz, 6H), 0.84 (d, J = 6.9 Hz, 6H),
0.75 (d, J = 6.5 Hz, 6H).
13C{1H} NMR (151 MHz, Chloroformꢀd) δ 154.3 (td, J = 30.0, 3.8 Hz), 146.5, 144.3, 139.2,
132.9, 132.0, 131.1, 130.5, 130.1, 126.1, 125.9, 125.2, 67.8, 67.8, 60.2, 29.0, 28.4, 26.0, 25.6, 25.1,
24.6, 24.3.
General procedure for preparation of silver complexes
A screwꢀcap vial equipped with a magnetic stir bar was charged with 0.232 g (1 mmol, 1 eq)
of Ag2O, 2 ml of solvent followed by 1 mmol of corresponding amidinium salt. Reaction mixture
was stirred for 24 h at room temperature or at 60°C, filtered through celite and carefully diluted
with equal volume of methanol. Precipitate was filtered and dried in vacuum.
(2,4-dimesityl-4,5-dihydro-1H-naphtho[1,8-ef][1,3]diazocin-3(2H)-ylidene)silver(I) bromide (7a)
Reaction of 45.1 mg (0.195 mmol) of Ag2O and 100 mg (0.195 mmol) of 2,4ꢀdimesitylꢀ4,5ꢀ
dihydroꢀ1Hꢀnaphtho[1,8ꢀef][1,3]diazocinium bromide (4a) in 2 ml of dry CH2Cl2 gave 53 mg
(44%) of product as colorless needles.
Reaction of 45.1 mg (0.195 mmol) of Ag2O and 100 mg (0.195 mmol) of 2,4ꢀdimesitylꢀ4,5ꢀ
dihydroꢀ1Hꢀnaphtho[1,8ꢀef][1,3]diazocinium bromide (4a) in 2 ml of dry THF gave 96 mg (80 %)
of product as colorless needles. Mp = 220ꢀ221°C
1H NMR (600 MHz, Chloroformꢀd) δ 7.95 (d, J = 8.2 Hz, 2H), 7.44 (t, J = 7.6 Hz, 2H), 7.21
(d, J = 7.0 Hz, 2H), 6.98 (s, 2H), 6.79 (s, 2H), 6.44 (d, J = 16.0 Hz, 2H), 4.45 (d, J = 15.9 Hz, 2H),
2.42 (s, 6H), 2.26 (s, 6H), 1.44 (s, 6H).
13C{1H} NMR (151 MHz, Chloroformꢀd) δ 210.4 (dd, J(109Ag, 13C) = 267.7 Hz, J(107Ag,
13C) = 226.7 Hz), 146.5, 137.9, 135.4, 134.1, 133.8, 133.0, 131.4, 130.7, 130.2, 130.2, 126.0, 57.2,
57.1, 21.1, 18.6, 18.3.

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IR (υ/cm–1): 3029 (w), 2969 (w), 2914 (w), 1740 (m), 1498 (vs), 1471 (s), 1358 (m), 1306
(m), 1284 (w), 1190 (w), 1031 (w), 993 (w), 854 (w), 820 (m), 773 (m), 678 (w).
E.A. found (calcd.), %: C 59.77 (60.02), H 5.17 (5.20), N 4.43 (4.52).
(2,4-bis(2,6-diisopropylphenyl)-4,5-dihydro-1H-naphtho[1,8-ef][1,3]diazocin-3(2H)-
ylidene)silver(I) bromide (7b)
Reaction of 38.8 mg (0.167 mmol) of Ag2O and 100 mg (0.167 mmol) of 2,4ꢀbis(2,6ꢀ
diisopropylphenyl)ꢀ4,5ꢀdihydroꢀ1Hꢀnaphtho[1,8ꢀef][1,3]diazocinium bromide (4b) in 2 ml of dry
dichloromethane gave 47.1 mg (40%) of product as white solid.
Reaction of 38.8 mg (0.167 mmol) of Ag2O and 100 mg (0.167 mmol) of 2,4ꢀbis(2,6ꢀ
diisopropylphenyl)ꢀ4,5ꢀdihydroꢀ1Hꢀnaphtho[1,8ꢀef][1,3]diazocinium bromide (4b) in 2 ml of dry
THF gave 100 mg (85%) of product as white solid. Mp = 290°C
1H NMR (600 MHz, Chloroformꢀd) δ 7.97 (dd, J = 8.3, 1.3 Hz, 2H), 7.46 (dd, J = 8.2, 6.9
Hz, 2H), 7.35 (t, J = 7.7 Hz, 2H), 7.31 (dd, J = 7.0, 1.3 Hz, 2H), 7.26 (d, J = 7.8 Hz, 2H), 7.10 (dd, J
= 7.7, 1.5 Hz, 2H), 6.44 (d, J = 15.9 Hz, 2H), 4.58 (d, J = 15.9 Hz, 2H), 3.30 (hept, J = 6.9 Hz, 2H),
2.30 (hept, J = 6.7 Hz, 2H), 1.47 (d, J = 6.9 Hz, 6H), 1.41 (d, J = 6.8 Hz, 6H), 1.02 (d, J = 6.8 Hz,
6H), 0.68 (d, J = 6.7 Hz, 6H).
13C{1H} NMR (151 MHz, Chloroformꢀd) δ 211.8 (dd, J(109Ag, 13C) = 261.3 Hz, J(107Ag,
13C) = 227.2 Hz), 145.3, 145.2, 145.1, 131.8, 131.0, 129.5, 125.9, 125.4, 125.3, 58.9, 58.8, 29.4,
28.1, 26.3, 25.4, 25.0, 24.1.
IR (υ/cm–1): 2962 (vs), 2923 (m), 2863 (m), 1589 (w), 1496 (s), 1456 (m), 1381 (m), 1356
(m), 1300 (m), 1178 (m), 1051 (m), 812 (m), 796 (m), 765 (m).
E.A. found (calcd.), %: C 63.26 (63.08), H 6.35 (6.29), N 3.70 (3.98).
General procedure for preparation of copper complexes.
A screwꢀcap vial equipped with a magnetic stir bar was charged with 1 mmol (1 eq) of
corresponding silver complex, 1 mmol of copper halide and 2 ml of dichloromethane. Reaction
mixture was stirred for 24 h at room temperature, filtered through celite and evaporated to dryness.
Resulting solid was recrystallized from dichloromethaneꢀdiethyl ether mixture.

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(2,4-dimesityl-4,5-dihydro-1H-naphtho[1,8-ef][1,3]diazocin-3(2H)-ylidene)copper(I) bromide (8a)
Yield 84%. White microcrystalline solid. Mp = 295°C.
1H NMR (600 MHz, Chloroformꢀd) δ 7.95 (dd, J = 8.3, 1.3 Hz, 2H), 7.43 (dd, J = 8.2, 7.0
Hz, 2H), 7.20 (dd, J = 7.0, 1.3 Hz, 2H), 6.98 (s, 2H), 6.80 (s, 2H), 6.43 (d, J = 15.9 Hz, 2H), 4.39 (d,
J = 15.9 Hz, 2H), 2.44 (s, 6H), 2.27 (s, 6H), 1.50 (s, 6H).
13C{1H} NMR (151 MHz, Chloroformꢀd) δ 203.6, 145.3, 137.8, 135.5, 134.3, 134.0, 133.3,
131.4, 131.3, 130.7, 130.1, 130.1, 125.9, 57.3, 21.1, 18.7, 18.5.
IR (υ/cm–1): 3025 (w), 2979 (m), 2946 (w), 2913 (w), 1740 (w), 1600 (w), 1504 (vs), 1471
(s), 1432 (m), 1351 (m), 1303 (s), 1187 (m), 1031 (m), 1002 (m), 852 (m), 819 (m), 771 (s), 682
(m).
E.A. found (calcd.), %: C 62.71 (63.08), H 6.13 (6.29), N 3.71 (3.98).
(2,4-bis(2,6-diisopropylphenyl)-4,5-dihydro-1H-naphtho[1,8-ef][1,3]diazocin-3(2H)-
ylidene)copper(I) bromide (8b)
Yield 83%. White microcrystalline solid. Mp = 312°C.
1H NMR (600 MHz, Chloroformꢀd) δ 7.96 (dd, J = 8.3, 1.3 Hz, 2H), 7.45 (dd, J = 8.2, 6.9
Hz, 2H), 7.36 (t, J = 7.7 Hz, 2H), 7.31 (dd, J = 7.0, 1.3 Hz, 2H), 7.27 (d, J = 7.8 Hz, 2H), 7.10 (dd, J
= 7.7, 1.5 Hz, 2H), 6.43 (d, J = 15.9 Hz, 2H), 4.52 (d, J = 15.9 Hz, 2H), 3.31 (p, J = 6.8 Hz, 2H),
2.31 (p, J = 6.8 Hz, 2H), 1.47 (d, J = 6.9 Hz, 6H), 1.43 (d, J = 6.8 Hz, 6H), 1.04 (d, J = 6.9 Hz, 6H),
0.69 (d, J = 6.7 Hz, 6H).
13C{1H} NMR (151 MHz, Chloroformꢀd) δ 204.7, 145.5, 145.3, 144.0, 135.4, 132.1, 131.7,
131.5, 130.9, 129.3, 125.9, 125.2, 125.1, 59.0, 29.4, 28.2, 26.2, 25.2, 25.0, 24.1.

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IR (υ/cm–1): 2958 (s), 2925 (m), 2865 (w), 1654 (vs), 1504 (w), 1462 (m), 1446 (m), 1388
(m), 1365 (m), 1321 (m), 1267 (m), 1184 (m), 1166 (m), 1056 (m), 813 (s), 790 (m), 771 (m), 727
(s).
E.A. found (calcd.), %: C 62.61 (63.08), H 6.13 (6.29), N 3.71 (3.98).
General procedure for solvent free cycloaddition
A screwꢀcap vial equipped with a magnetic stir bar was charged with organic azide (1.0
mmol, 1 eq), terminal acetylene (1.03 mmol, 1.03 eq) and 1 mol% of (NHC)CuBr. The reaction
mixture was stirred at ambient temperature overnight (unoptimized). The reaction mixture was
dissolved in 10 ml of dichloromethane and filtered through a pad (4.5 cm) of silica gel.
Concentration of containing product fractions in vacuum afforded 1,4ꢀdisubstitued 1,2,3ꢀtriazole.
Isolated yields are average of two runs.

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DOI: 10.1039/C6DT04484K
Tables
Table 1
Calculated parameters of free carbenes: valence angle at the ylidene carbon atom (∠NꢀCcarbꢀN),
HOMO energy (EHOMO), HOMO–LUMO gap (HLG), singlet–triplet energy gap (EST), carbene
stabilization energy (CSE), proton affinity (PA). (Valence angle in °, EHOMO, HLG in eV; EST, CSE,
PA in kcal molꢀ1)a,b
NHC
∠NꢀCcarbꢀN
EHOMO
HLG
EST
CSE
PA
SIMes
THPꢀMes
106.0
115.6
118.2
121.9
120.5
ꢀ4.67
ꢀ4.23
ꢀ4.07
ꢀ4.09
ꢀ4.21
3.55
3.27
3.12
3.09
1.93
78.3
73.2
67.5
67.7
61.3
102.2
97.3
95.2
96.1
97.8
277.2
285.6
287.2
288.0
287.7
THDꢀMes
HHDꢀMes
NaphtDHDꢀMes
a
Here and below: Mes – mesityl, 2,4,6ꢀtrimethylphenyl, Dipp – 2,6ꢀdiisopropylphenyl, SI –
saturated imidazolinꢀ2ꢀylidene, THP
–
tetrahydropyrimidinꢀ2ꢀylidene, THD
–
–
tetrahydrodiazepinꢀ2ꢀylidene, HHD
dihydronaphtodiazocinꢀ2ꢀylidene.
–
hexahydrodiazocinꢀ2ꢀylidene, NaphtDHD
b
Detailed explanation of the calculation parameters are given in the supplementary
information.

Dalton Transactions
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Table 2
Calculated parameters of the complexes [Rh(NHC)(CO)2Cl] (interatomic distances R(C–Rh) in Å,
ligand dissociation energies D and carbene–metal interaction energies Eint in kcal molꢀ1, CO average
stretching frequencies νav(CO) in cmꢀ1, buried volume Vbur in %).
NHC
R(CcarbꢀRh)
D
Eint
νav(CO)
Vbur
SIMes
THPꢀMes
2.10
2.13
2.13
2.15
2.14
55.9
55.4
53.9
50.9
49.9
64.7
65.7
65.9
63.2
63.2
2000
1994
1993
1992
1991
23.3
25.8
26.9
28.7
27.6
THDꢀMes
HHDꢀMes
NaphtDHDꢀMes

Page 25 of 37
Dalton Transactions
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Table 3
Optimization of the synthesis of (NaphtDHDꢀDipp)AgBr (7b)
Entry
Solvent
Yield, %
1
2
3
4
5
6
DMSO
СH3CN
1,2ꢀDCE
THF
СH3OH
1,2ꢀDME
No reaction
57
67
85
Decomposed
Decomposed

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Table 4
Hydrogen bonds for [(Naphꢀ8ꢀDipp)H]Br (4b) [Å and °].
D*ꢀH...A*
d(DꢀH)
d(H...A)
d(D...A)
∠(DꢀH...A)
C3─H3...Br1
C5─H5A...O1a
C5─H5B...Br1a
O1─H1C...Br1
O1─H1D...C27
O1─H1D...C28
1.00
0.99
0.99
0.96
0.94
0.94
2.65
2.52
2.78
2.41
2.89
2.63
3.645(2)
3.292(4)
3.680(2)
3.362(3)
3.772(4)
3.534(4)
178.5
134.4
150.6
172.2
156.4
161.4
* D – proton donor; A – proton acceptor;
Symmetry transformations used to generate equivalent atoms: a x, ꢀy+½, zꢀ½

Page 27 of 37
Dalton Transactions
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Table 5
Catalytic activity of (NHC)CuBr complexes.a
N3
Ph
(NHC)CuX
1 % mol
25oC
+
N
N
N
Ph
9a
Complex
Yield (%)
Complex
Yield (%)
[(SIMes)CuBr]
90
>99
33
[(SIPr)CuBr]
4
5
1
2
[(THPꢀMes)CuBr]
[(THDꢀMes)CuBr]
[(THPꢀDipp)CuBr]
[(THDꢀDipp)CuBr]
[(NaphtDHDꢀMes)CuBr] (8a)
>99
[(NaphtDHDꢀDipp)CuBr] (8b)
a
pꢀTolyl azide (1.0 mmol, 1 eq), phenyl acetylene (1.03 mmol, 1.03 eq), 1 mol%
(NHC)CuBr.

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Table 6
Optimization of the catalyst loading.a
N3
Ph
8a
)
(Naph-8-Mes)CuBr (
x % mol
+
N
N
25oC
N
Ph
9a
Precatalyst, mol%
Yield, %
(THPꢀMes)CuBr
(NaphtDHDꢀMes)CuBr (8a)
1
>99
98
95
>99
97
94
0,5
0,1
0,05
70
78
a
pꢀTolyl azide (1.0 mmol, 1 eq), phenyl acetylene (1.03 mmol, 1.03 eq), n mol%
(NHC)CuBr.

Page 29 of 37
Dalton Transactions
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Table 7
Cycloaddition of pꢀtolyl azide with various acetylenes mediated by (NaphtDHDꢀMes)CuBr (8a).a
(NaphtDHD-Mes)CuBr (8a)
R
1 mol%
+
N
N
N
R
25oC
N3
9b-9k
Entry
Product
Yield, % Entry
Product
Yield, %
N
N
N
1
95
96
6
7
95
N
N
N
9b
9g
MeO2C
OH
2
88
N
N
N
N
N
N
9c
9h
NC
HO
N
N
3
4
96
92
98
8
9
94
>99
78
N
N
N
N
9d
9i
HO
N
N
N
N
N
N
N
9e
9j
N
N
5
10
N
N
N
N
9f
9k
a
pꢀTolyl azide (1.0 mmol, 1 eq), acetylene (1.03 mmol, 1.03 eq), 1 mol% (NaphtDHDꢀ
Mes)CuBr (8a).