Tris(3,5-dimethylpyrazolyl)methane copper(I) complexes featuring one disubstituted cyanamide ligand

Article abstract of DOI:10.1016/j.ica.2018.09.024

The complexes [Cu{HC(3,5-Me₂pz)₃}(NCNR₂)][BF₄] (1–8; R₂ = Me₂ 1, Et₂ 2, C₅H₁₀ 3, C₄H₈O 4, C₄H₈ 5, C₃H

Full text of DOI:10.1016/j.ica.2018.09.024

Accepted Manuscript
Research paper
Tris(3,5-dimethylpyralzoly)methane copper(I) complexes featuring one disub-
stituted cyanamide ligand
Anna A. Melekhova, Alexander S. Novikov, Alexey Yu. Dubovtsev, Andrey A.
Zolotarev, Nadezhda A. Bokach
PII:
S0020-1693(18)30609-1
https://doi.org/10.1016/j.ica.2018.09.024
ICA 18482
DOI:
Reference:
Inorganica Chimica Acta
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Revised Date:
Accepted Date:
23 April 2018
5 August 2018
8 September 2018
Please cite this article as: A.A. Melekhova, A.S. Novikov, A.Y. Dubovtsev, A.A. Zolotarev, N.A. Bokach, Tris(3,5-
dimethylpyralzoly)methane copper(I) complexes featuring one disubstituted cyanamide ligand, Inorganica Chimica
Acta (2018), doi: https://doi.org/10.1016/j.ica.2018.09.024
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Tris(3,5-dimethylpyralzoly)methane copper(I) complexes featuring
one disubstituted cyanamide ligand
Anna A. Melekhova, Alexander S. Novikov, Alexey Yu. Dubovtsev, Andrey A. Zolotarev,
Nadezhda A. Bokach*
Saint Petersburg State University, Universitetskaya Nab. 7/9, 199034 Saint Petersburg, Russian
Federation
Abstract. The complexes [Cu{HC(3,5-Me2pz)3}(NCNR2)][BF4] (1–8; R2 = Me2 1, Et2 2, C5H10 3,
C4H8O 4, C4H8 5, C3H6С6H4 [NC3H6С6H4 is1,2,3,4-dihydroisoquinoline-2-yl] 6, (CH2Ph)2 7,
(Me)Ph 8) were prepared by the reaction of [Cu(NCMe)4][BF4] with HC(3,5-Me2pz)3 and NCNR2
(CH2Cl2, 20–25 °C) and these species were characterized by C, H, N analyses, high resolution
1
mass-spectrometry with electrospray ionization, H, 13C{1H} NMR and FTIR spectroscopic
techniques, molar conductivity measurements, thermogravimetry/differential thermal analysis, and
also by single-crystal X-ray diffraction for 3. The theoretical topological analysis of the electron
density distribution (QTAIM method) together with the NBO analysis were applied to study the
nature of Cu–N and Cu–C coordination bonds in [Cu{HC(3,5-Me2pz)3}(NCNMe2)]+, [Cu{HC(3,5-
Me2pz)3}(NCMe)]+, and [Cu{HC(3,5-Me2pz)3}(CNMe)]+ model species. The nature of Cu–N
coordination bonds in [Cu{HC(3,5-Me2pz)3}(NCNMe2)]+ and [Cu{HC(3,5-Me2pz)3}(NCMe)]+ is
very similar, whereas Cu–C contact in [Cu({HC(3,5-Me2pz)3}(CNMe)]+ is relatively more
1

covalent. The calculated vertical total energies for the Cu–N and Cu–C coordination bonds cleavage
increase in the following row: [Cu{HC(3,5-Me2pz)3}(NCMe)]+ (36 kcal/mol) < [Cu{HC(3,5-
Me2pz)3}(NCNMe2)]+ (41 kcal/mol) < [Cu{HC(3,5-Me2pz)3}(CNMe)]+ (47 kcal/mol), and these
theoretical data are coherent with the experimental observations.
Keywords:
Tris-pyrazolylmethane complexes, copper(I), dialkylcyanamide ligands, QTAIM method, NBO
analysis
Highlights
Eight examples of mononuclear dialkylcyanamide complexes [Cu{HC(3,5-
Me2pz)3}(NCNR2)][BF4]
X-ray diffraction Structure of [Cu{HC(3,5-Me2pz)3}(NCNC5H10)][BF4]
Comparison of the nature of metal-ligand bond in [Cu{HC(3,5-Me2pz)3}(NCNR2)][BF4] and
[Cu{HC(3,5-Me2pz)3}(CNR)][BF4] using QTAIM method and NBO analysis
Graphical Abstract
2

[BF4]
H
C
N
N
N
N
N
N
Cu
N
NR2
8 examples
Introduction
Metal-activated cyanamide ligands NCNR2 exhibit enhanced reactivity relatively to nitriles NCR (R
= alkyl, aryl). Thus, disubstituted cyanamides are involved in various types of nucleophilic
additions and 1,3-dipolar cycloadditions (see reviews [1, 2]) that are not feasible for NCR’s. For
example, we demonstrated that copper(I) complexes catalyze the 1,3-dipolar cycloaddition between
ketonitrones and disubstituted cyanamides. Notably, this was the first example of a metal catalyzed
cycloaddition reaction to afford 2,3-dihydro-1,2,4-oxadiazoles [3]. In continuation of that work, we
studied plausible intermediates of the addition and synthesized homoleptic tetrakis-cyanamide
copper(I) complexes [Cu(NCNR2)4][BF4] [4]. It is noteworthy that apart from these [Cu(NCNR2)4]+
species, only one example of mononuclear copper complex featuring disubstituted cyanamide was
known before this work, viz. [Cu(NCNMe2)2(DPEphos)[BF4] (DPEphos is bis[2-
diphenylphosphino)phenyl]-ether) [5], and mononuclear (NCNR2)Cu complexes were not reported.
Hence, information on structural types of copper(I/II) complexes with disubstituted cyanamides is
quite scarce and insufficient for further development of their chemistry.
3

Recently, we reported on the synthesis and structural studies of copper(I) complexes with
one isocyanide ligand CNR, viz. [Cu{HC(3,5-Me2pz)3}(CNR)][BF4] ({HC(3,5-Me2pz)3} = tris(3,5-
dimethylpyrazolyl)methane) and studied their structural features [6]. Species with the {[HC(3,5-
Me2pz)3]Cu} moiety can serve as a convenient model to prepare complexes bearing only one
dialkylcyanamide ligand. It is noteworthy that some mononuclear 6–8 and 10 groups transition
metal complexes bearing one cyanamide ligand (NCNR2)M were synthesized and characterized by
X-ray diffraction study, viz. [Cr(CO)5(NCNEt2)] [7], [Mo{N(3,5-Me2C6H3)(tBu)}3(2-NCNMe2)]
[8],
[Mo(Ph2PC2H4PPh2)2(N2)(NCNEt2)]
[9],
[W(CO)3(PiPr3)2(NCNMe2)]
[10],
[12],
[14],
[MnCp(CO)2(NCNMe2)]
[11],
[13],
[Mn(CO)2{PPh(OEt)2}3(NCNEt2)][BPh4]
i
[ReCl2(PPh2Me)3(NCNEt2)]
[Ru{P(OEt)3}4(NH2 Pr)(NCNEt2)][BPh4]
i
[RuCl2(bpy)(CO)(NCNR2)] (R2 = Me2, Et2) [15], [Os{P(OEt)3}4{NH2 Pr}{NCNEt2}][BPh4] [14],
[PtCl2(Me2SO)(NCNR2)] (R2 = Me2, C5H10) [16], [Pt(Ph)(PPh3)2(NCNMe2)](BPh4)•Et2O [17],
[Pt(CF3)(PPh3)2(NCNEt2)][BF4] [18], and [Ph3PCH2Ph][PtCl3(NCNMe2)] [19]. It is important to
note that not a single example of such monomeric copper complex, bearing one NCNR2, was
reported until our recent work.
The goal of this work was at least two-fold. First, we aimed to synthesize and characterize
mononuclear cationic copper(I) complexes [Cu(L)(NCNR2)][BF4] (L = tridentate ligand, e.g.
tris(3,5-dimethylpyrazolyl)methane abbreviated as {HC(3,5-Me2pz)3}) featuring one disubstituted
cyanamide. These copper species could be interesting for the study of stoichiometric reactions
involving copper(I) center-bound cyanamides. Secondly, we planned to compare the structural
features and chemical properties of these types of complexes with the relevant nitrile [Cu{HC(3,5-
Me2pz)3}(NCMe)]+ [20] and isocyanide analogues [Cu{HC(3,5-Me2pz)3}(CNR)]+ [6].
In this work, we compare the reactivity of conventional nitrile NCR and disubstituted
cyanamide ligands NCNR2. Both disubstituted cyanamides and nitriles coordinate to a metal center
in their neutral form. In contrast, unsubsituted cyanamide NCNH2 and monosubstituted NCNHR
4

tend to be deprotonated upon coordination to a metal centers and form anionic heterocumulene
ligands, e.g. NCNR–,[21] which structure are different from coordinated NCNR2’s.
Results and discussion
The mixed-ligand [Cu{HC(3,5-Me2pz)3}(NCNR2)][BF4] species (1–8; R2 = Me2 1, Et2 2,
C5H10 3, C4H8O 4, C4H8 5, C3H6С6H4 [NC3H6С6H4 is 1,2,3,4-dihydroisoquinoline-2-yl] 6, (CH2Ph)2
7, (Me)Ph 8) were synthesized by two methods (Scheme 1). In the first synthetic route,
CH2Cl2 solutions of HC(3,5-Me2pz)3 and [Cu(NCMe)4][BF4] were combined in a 1:1 ratio,
followed by addition of 1 equivalent of NCNR2 (R2 = Me2, Et2, C5H10, C4H8O, C4H8, C3H6С6H4,
(CH2Ph)2, (Me)Ph). Compounds 1–8 were isolated in good to excellent yields (93–96%; Scheme 1,
A). An alternative method consists of addition of CH2Cl2 solutions of HC(3,5-Me2pz)3 to
CH2Cl2 solutions of [Cu(NCNR2)4][BF4][4] in a 1 : 1 molar ratio (Scheme 1, B) at room
temperature. The former high-yielding method is easier and it is recommended for synthesis of 1–8.
HC(3,5-Me2pz)3,
4NCNR2
NCNR2
[Cu(NCMe)4](BF4)
– 4NCMe
– 4NCMe
A
NR2
N
(BF4)
NR2
N
(BF4)
B
HC(3,5-Me2pz)3
Cu
Cu
N
– 3NCNR2
N
N
N
N
N
R2N
N
N
NR2
N
C
R2N
H
1–8
Scheme 1. Synthesis of (dialkylcyanamide)copper(I) complexes 1–8.
5

All complexes were characterized by C, H, N analyses, high resolution mass-spectrometry
1
with electrospray ionization, H, 13C{1H} NMR and FTIR spectroscopic techniques, molar
conductivity measurements, thermogravimetry/differential thermal analysis, and also by single-
crystal X-ray diffraction (for 3). Microanalytical data for 1–8 are in good agreement with the
calculated values. High-resolution mass-spectra of 1–8 exhibit sets of peaks corresponding to the
molecular ions [Cu{HC(3,5-Me2pz)3}(NCNR2)]+ with characteristic isotopic pattern. The FTIR
spectra of 1–8 in KBr display two CN absorption bands in the range 2240–2250 cm–1 and 2210–
2225 cm–1, which is apparently due to the decomposition of the complexes in KBr pellet. In Nujol
oil, 1–3 display one broad band of (CN) in the region 2240–2250 cm–1, 5–8 demonstrate one
broad bond with a shoulder at 2240–2260 cm–1, and 4 displays two bands 2250 and 2240 cm–1. All
these bands are moderately high-frequency shifted (20–30 cm–1) from those in the corresponding
uncomplexed dialkylcyanamide (2210–2225 cm–1).
1
The H and 13C{1H} NMR spectra of 1–8 exhibit signals from one HC(3,5-Me2pz)3 and
from two R groups in the NCNR2 ligands. The values of molar conductivities in nitromethane (73–
90 Ohm–1 cm–1 mol–1) for 1–8 agree well with the typical range for 1:1 electrolytes (75–95 Ohm–
1cm–1mol–1) in this solvent [22]. The thermogravimetry/differential thermal analysis data (Figures
S42–S49 and Table S1) demonstrate that mass loss starts in the interval ca. 130–150 °C due to the
extrusion of NCNR2. The mass of the final product (610 °C) corresponds to CuF2 (2–5) or Cu (1),
or does not correspond to any stoichiometry of the proposed final products (6–8).
Single-crystal X-ray diffraction studies were performed for 3 (Figure 1). This species is the
first example of a crystallographically characterized monomeric copper(I) complex of the type
[Cu(L)(NCNR2)][BF4] (L = tris-pyrazolylmethane or tris-pyrazolylborate-based ligand) bearing one
metal center-bound cyanamide. The coordination polyhedron, distorted tetrahedron, of 3 is formed
by one dialkylcyanamide ligand and one {HC(3,5-Me2pz)3}. The 4 parameter 0.69 indicates a
significant deviation from the ideal (4 1.0) [23] tetrahedral geometry. The N–Cu–N angles are
6

restrained by the chelate rings to ca. 88° (from 86.9(3) to 88.9(3)°) and the N–Cu–N angles from
the N atoms of {HC(3,5-Me2pz)3} to the N atom of a dialkylcyanamide span the interval from
116.2(3) to 139.6(3)°. The Cu–N distances (N of {HC(3,5-Me2pz)3} ligand), that range from
2.046(8) to 2.138(7) Å, are close to the Cu–N bond values in [Cu{HC(3,5-Me2pz)3}(NCMe)][BF4]
(2.080(4)–2.0893 Å).[24] The Cu–N(1) bond length (1.883(8) Å) is equal within 3 to those in
[Cu{HC(3,5-Me2pz)3}(NCMe)][BF4] (1.865(4) Å) [24]. The nitrile CN bond length (1.147(13) Å)
in the NCNC5H10 ligand exhibits a value comparable with those in [Cu{HC(3,5-
Me2pz)3}(NCMe)][BF4] (1.137(7)Å) [24], the Cu–N–C angle (167.0(9)°) is non-linear and N–C–N
(177.0(12)°) is close to the linear.
Figure 1. Molecular structure of 3 at 100 K with the atomic numbering scheme. Thermal ellipsoids
are drawn at the 50% probability level.
Nitrile complexes of the type [CuL(NCMe)][X]n (L = tris-pyrazolylmethane, n = 1, or tris-
pyrazolylborate-based ligands, n = 0; X = BF4, PF6) are known. These species were synthesized by
(i) the addition of L (L = tris-pyrazolylmethane or tris-pyrazolylborate-based species) to a solution
of [Cu(NCMe)4]X (X = BF4 or PF6) either at room temperature in CH2Cl2, acetone, or
CH2Cl2/MeCN for 1–24 h under argon or (ii) in MeOH upon reflux for 2 h [25-29]. Typically
complexes of this type are relatively stable in air, and, in particular, the complexes
7

[Cu{HC(Rpz)3}(NCMe)](PF6) (Rpz = 3-Butpz, 3-Phpz, 3,5-Me2pz; pz - pyrazolyl) are moderately
air stable even in solutions [26]. Bubbling dioxygen into CH2Cl2 solutions of the complexes at –78
°C provides no color change although a faint green solution results upon warming to room
temperature [26]. At the same time, some other authors [29] reported that
[Cu{HC(Rpz)3}(NCMe)][PF6] (Rpz = 3,5-Me2pz, 3,5-Me2-4-Brpz) are rapidly (within a few min)
oxidized by O2 at 7 °C in a CH2Cl2 solution. The complexes [Cu(L)(NCMe)]X (L= tris(3,5-
diisopropyl-1-pyrazolyl)methane; X = ClO4, PF6) are relatively stable toward O2 [27], and
[Cu(HCpz3)(NCMe)][BF4] is a shelf-stable monomeric species [25]. Some works [27, 28] describe
low to moderate stability of these complexes, e.g. [CuL(NCMe)][BF4] (L = tris(3-isopropyl-4,5-
trimethylenepyrazolyl)methane [28] or hydrotris(3,5-diisopropyl-1-pyrazolyl)borate [27]) are very
air-sensitive species.
Complexes 1–8 demonstrated air instability both in solution and in the solid state. For
example, these species start to decompose after 15–30 minutes at room temperature in CDCl3 or
CD2Cl2 to give the known bis-ligated complex, [Cu{HC(3,5-Me2pz)3}2][BF4]2 [30] (identified by
X-ray diffraction study, see Supplementary Materials), free NCNR2 (identified by 1H NMR) and an
unidentified copper species. Moreover, our attempts to crystallize 4 from a CH2Cl2 solution in air
for 1 day led to formation of the crystalline copper(II) dimer [Cu2(-OH)2{HC(3,5-
Me2pz)3}2][BF4]22CH2Cl2 (92CH2Cl2), whose structure was determined by X-ray diffraction
study (see Figure 2 and ESI for the details).
8

–
Figure 2. Molecular structure of 92CH2Cl2 at 100 K with the atomic numbering scheme; BF4 and
the two CH2Cl2 molecules are omitted for clarity. Thermal ellipsoids are drawn at the 50%
probability level.
The facile oxidation of the acetonitrile analog [Cu{HC(3,5-Me2pz)3}(NCMe)][PF6] by O2
to yield the dimeric [Cu2(-OH)2{HC(3,5-Me2pz)3}2][PF6]2 is known [29]. In the solid state, 6–8
gradually turn from colorless to green at room temperature for 1–2 days in air, whereas 1–5
demonstrate less stability and become greenish-beige color immediately after preparation.
Therefore, we can propose that our complexes 1–8, due to the weakness of Cu–N(cyanamide) bond
and kinetic lability, undergo fast NCNR2 ligand dissociation/substitution with formation of some
intermediate complexes that can be easily oxidized in air forming the copper(II) species
[Cu{HC(3,5-Me2pz)3}2][BF4]2 and [Cu2(-OH)2{HC(3,5-Me2pz)3}2][BF4]2. Notably, the isocyanide
analogues [Cu{HC(3,5-Me2pz)3}(CNR)][BF4] demonstrate greater stability and exhibit relatively
strong Cu–C bonds (ca. 50 kcal•mol–1 based on DFT calculations) [6].
Theoretical study of the nature and energies of Cu–N and Cu–C coordination bonds in
[Cu{HC(3,5-Me2pz)3}L]+ (L = NCNMe2, NCMe, CNMe) model species. Additional information
on the binding in metal complexes can be obtained by the theoretical topological analysis of the
electron density distribution (QTAIM method) [31] together with the Natural Bond Orbital (NBO)
9

analysis [32, 33]. This integrated approach has already been successfully used by us [4, 6, 34, 35],
and in the present work we applied these methods to study the nature of Cu–N and Cu–C
coordination bonds in [Cu{HC(3,5-Me2pz)3}(NCNMe2)]+, [Cu{HC(3,5-Me2pz)3}(NCMe)]+, and
[Cu{HC(3,5-Me2pz)3}(CNMe)]+ model species.
The main results of the topological analysis of the electron density distribution and values of
the Wiberg bond indices (bond orders) [36] was computed using the NBO partitioning scheme for
the Cu–N and Cu–C coordination bonds in optimized equilibrium geometries of [Cu({HC(3,5-
Me2pz)3}L]+ (L = NCNMe2, NCMe, CNMe) model species are presented in Table 1. The Poincare-
Hopf relationship (criterion that show that all critical points were determined) was satisfied in all
cases.
10

Table 1. Results of the topological analysis of the electron density distribution and values of the
Wiberg bond indices for the Cu–N and Cu–C coordination bonds in optimized equilibrium
geometries of [Cu{HC(3,5-Me2pz)3}L]+ (L = NCNMe2, NCMe, CNMe) model species.*
(r), e/Å3
2(r),
e/Å5
Model species
Hb,
ε
WI
Hartree/Å3
[Cu{HC(3,5-Me2pz)3}(NCNMe2)]+ 0.611
15.232
15.352
13.773
-0.067
-0.067
-0.161
0.007
0.000
0.001
0.39
0.39
0.69
[Cu{HC(3,5-Me2pz)3}(NCMe)]+
[Cu{HC(3,5-Me2pz)3}(CNMe)]+
0.611
0.719
* (r) – density of all electrons, 2(r) – Laplacian of electron density, Hb – energy density, ε –
ellipticity of electron density, WI – Wiberg bond indices. Results in this table refer to zero Kelvin
temperature.
In all cases, we found the suitable bond critical points (3, –1) for the Cu–N and Cu–C
contacts, where the electron density falls down in two perpendicular directions of space and rises in
the third direction. The values of (r), 2(r), and Hb parameters in these bond critical points (3, –
1) are typical for closed-shell interactions. The ellipticity of electron density (parameter provides a
quantitative measurement of the anisotropy of the electron density and associated to the π character
of bonds) in these bond critical points (3, –1) is low (not exceeding 0.007) confirming the single
bond character of these contacts. It can be concluded that the nature of Cu–N coordination bonds in
[Cu{HC(3,5-Me2pz)3}(NCNMe2)]+ and [Cu{HC(3,5-Me2pz)3}(NCMe)]+ is very similar, whereas
Cu–C contact in [Cu{HC(3,5-Me2pz)3} (CNMe)]+ is relatively more covalent. The calculated
vertical total energies for the Cu–N and Cu–C coordination bonds cleavage, computed as difference
between the total electronic energies of optimized structures of complexes M–L and total electronic
energies of frozen geometries of parts M and L, increase in the following order: [Cu{HC(3,5-
Me2pz)3}(NCMe)]+ (36.10(1) kcal/mol) < [Cu{HC(3,5-Me2pz)3}(NCNMe2)]+ (41.39(1) kcal/mol) <
11

[Cu{HC(3,5-Me2pz)3}(CNMe)]+ (47.05(1) kcal/mol), and these theoretical data are coherent with
the experimental observations, viz. greater stability of isocyanide complexes [Cu{HC(3,5-
Me2pz)3}(CNR)][BF4][6] both in solution and in the solid state compared to the acetonitrile and
dialkylcyanamide analogues [Cu{HC(3,5-Me2pz)3}(NCR)][BF4] (R = Me, NR’2).
Conclusions
In this study, we succeeded in synthesizing a new type of mononuclear (cyanamide)CuI
complex, viz. the cationic monocyanamide [Cu{HC(3,5-Me2pz)3}(NCNR2)] BF4] species. These
complexes demonstrate air instability both in solution and in the solid state and undergo
spontaneous oxidation in air giving [Cu{HC(3,5-Me2pz)3}2][BF4]2 and [Cu2(-OH)2{HC(3,5-
Me2pz)3}2][BF4]2. Similar behavior is demonstrated as with some nitrile complexes of the type
[CuL(NCMe)]X, which can be easily oxidized by O2 [20]. By contrast, results of our previous work
[6] revealed that isocyanide complexes of the same type, [Cu{HC(3,5-Me2pz)3}(CNR)][BF4], are
more stable in solutions and also as solids.
As can be inferred from inspection of the theoretical data, the Cu–N bond in [Cu{HC(3,5-
Me2pz)3}(NCNMe2)]+ and [Cu{HC(3,5-Me2pz)3}(CNMe)]+ demonstrate relatively less covalent
character than the Cu–C bond in [Cu{HC(3,5-Me2pz)3}(CNMe)]+. The calculated vertical total
energies for the Cu–N and Cu–C coordination bonds cleavage increase in the following row:
[Cu{HC(3,5-Me2pz)3}(NCMe)]+
<
[Cu{HC(3,5-Me2pz)3}(NCNMe2)]+
<
[Cu{HC(3,5-
Me2pz)3}(CNMe)]+, suggesting greater stability of the isocyanide complexes [Cu{HC(3,5-
Me2pz)3}(CNR)][BF4] [6] compared to the acetonitrile and dialkylcyanamide analogues
[Cu{HC(3,5-Me2pz)3}(NCR)][BF4] (R = Me, NR’2), which is in accord with the experimental
observations.
Experimental Section
12

Materials and Instrumentations. The diakylcyanamides NCNR2 (R2 = Me2, Et2, C5H10,
C4H8O, C4H8; Aldrich) and solvents were obtained from commercial source and used as received.
The cyanamides NCN(CH2Ph)2, NCN(Me)Ph, NCNC3H6С6H4 [1,2,3,4-dihydroisoquinoline-2-
ylcarboxamide]],[37] the copper(I) complex [Cu(NCMe)4][BF4],[38] and HC(3,5-Me2pz)3 [39] were
synthesized in accord with the published procedures. The high resolution mass-spectra were
obtained on a Bruker micrOTOF spectrometer equipped with an electrospray ionization source
(HRESI+ MS) and MeOH was employed as the solvent. The instrument was operated in positive ion
mode using an m/z range of 50–3000. The capillary voltage of the ion source was set at –4500 V
(positive mode mass-spectrometry) and the capillary exit ±(70–150) V. In the isotopic pattern, the
most intense peak is reported. Infrared spectra were recorded using a Bruker FTIR TENSOR 27
1
13
instrument in KBr pellets. H and C{1H} NMR spectra were measured on a Bruker Avance III
400 spectrometer at ambient temperature. Residual solvent signals were used as the internal
standard. Microanalyses (C, H, N) were carried out on a Euro EA3028-HT instrument. Molar
conductivities were measured with a Mettler Toledo meter FE30/FG3 in a solution of nitromethane
(molar
concentrations
were
2.0–5.5•10–4
mol/L)
at
room
temperature.
The
thermogravimetry/differential thermal analysis (Figures S42–S49) were performed with a
NETZSCH TG 209 F1 Libra thermoanalyzer and MnO2 powder was used as a standard. The initial
weights of the samples were in the range 1.1–2.3 mg. The experiments were run in an open
aluminum crucible in a stream of argon at a heating rate of 10 K/min. The final temperature was
610 °C. Processing of the thermal data was performed with Proteus analysis software [40].
X-ray structure determinations. Suitable crystals of 3 and 9 were measured at Agilent
Technologies SuperNova and Xcalibur Eos diffractometers at a temperature of 100K using
monochromated CuKα radiation. All structures have been solved by the direct methods by means of
the SHELX program [41] incorporated in the OLEX2 program package [42]. For crystallographic
data and refinement parameters see ESI. The carbon-bound H atoms were placed in calculated
13

positions and were included in the refinement in the ‘riding’ model approximation, with Uiso(H) set
to 1.5Ueq(C) and C–H 0.98 Å for CH3 groups, with Uiso(H) set to 1.2Ueq(C) and C–H 0.97 Å for
CH2 groups, with Uiso(H) set to 1.2Ueq(C) and C–H 0.95 Å for CH groups and with Uiso(H) set to
1.5Ueq(O) and O–H 0.98 Å for OH-groups. Empirical absorption correction was applied in
CrysAlisPro [43] program complex using spherical harmonics, implemented in SCALE3
ABSPACK scaling algorithm. The crystal structure of 9 contained disordered molecules of solvent
that have been treated as a diffuse contribution to the overall scattering without specific atom
positions by SQUEEZE/PLATON program [44]. The high values of the some refinement
parameters of structures (large R-values for all structures; large values of anisotropic displacement
parameters for 9) and relatively low bonds precision in the structural model (for 3) are because of
insufficient quality of the studied crystals. Although some refinement parameters are not perfect,
the structural models in their principal features are correct. The following refinement restraints were
used: for 3 Uanis(N7) = Uanis(N5); for 9 restrained some distances (O1_$1–H1_$1, O1A–H1A,
Cu1–H1 Cu1A–H1A, Cu1A_$2–H1A, where 1 is 1-X,1-Y,2-Z and 2 is 2-X,2-Y,1-Z).
Supplementary crystallographic data for this paper have been deposited at Cambridge
Crystallographic Data Centre (1442806 for 3, 1817364 for 9) and can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif.
Computational details. The full geometry optimization of [Cu({HC(3,5-Me2pz)3}L]+ (L =
NCNMe2, NCMe, CNMe) model species has been carried out at the M06/LanL2DZ level of theory
with the help of Gaussian-09 program package [45]. No symmetry restrictions have been applied
during the geometry optimization procedure. In all cases the Hessian matrix was calculated
analytically in order to prove the location of correct minima (no imaginary frequencies). The
topological analysis of the electron density distribution with the help of the atoms in molecules
method (QTAIM) has been carried out by using the Multiwfn program [46]. The Cartesian atomic
coordinates for optimized equilibrium geometries of all model species are presented in Table S5
(ESI).
14

Synthesis of [Cu{HC(3,5-Me2pz)3}(NCNR2)][BF4] (1–8). Method A: A solution of
HC(3,5-Me2pz)3 (47.4 mg, 0.159 mmol) in CH2Cl2 (1 mL) was added under vigorous stirring to a
solution of [Cu(NCMe)4][BF4] (50 mg, 0.159 mmol) in CH2Cl2 (5 mL). The resulting transparent
yellow reaction mixture was stirred for 30 min at room temperature, whereupon any one of NCNR2
(R2 = Me2, Et2, C5H10, C4H8O, C4H8, C3H6С6H4, (CH2Ph)2, (Me)Ph; 0.159 mmol) was added to the
solution, stirred for 30 min and then the solvent was evaporated at room temperature in vacuum to
dryness and washed with Et2O (2 mL) to give in each case a pale greenish-beige crystalline solid.
Method B: A solution of HC(3,5-Me2pz)3 (15 mg, 0.051 mmol) in CH2Cl2 (1 mL) was added to a
solution of [Cu(NCNMe2)4][BF4] (30 mg, 0.051 mmol) in CH2Cl2 (5 mL) under vigorous stirring.
The resulting transparent reaction mixture was stirred for 1 h at room temperature and then the
solvent was evaporated at room temperature in vacuum to dryness, washed with diethyl ether (2
mL) to give a pale beige crystalline solid.
[Cu{HC(3,5-Me2pz)3}(NCNMe2)][BF4] (1). Yield 79 mg, 96%. Anal. Calcd for
C19H28N8BCuF4: C, 43.98; H, 5.44; N, 21.60%. Found: C, 43.85; H, 5.23; N, 21.56%. HRESI+-MS,
m/z: 431.1711 ([M]+, calcd 431.1722). IR spectrum in KBr, selected bands, cm−1: 2215, 2252 s
ν(NC). 1H NMR in CD2Cl2, δ: 2.32 (s, 9H, Me), 2.54 (s, 9H, Me), 3.04 (s, 6H, NMe2), 6.01 (s, 3H,
CHpyrazolyl), 7.74 (s, 1H, CH). 13C{1H} NMR in CD2Cl2, δ: 10.7 (Me), 13.3 (Me), 40.09 (NMe2),
67.6 (CH), 106.6 (CHpyrazolyl), 139.8, 150.7 (Cpyrazolyl), NCN was not detected. Λm = 82 Ohm–1 cm–1
mol–1.
[Cu{HC(3,5-Me2pz)3}(NCNEt2)][BF4] (2). Yield 82 mg, 94%. Anal. Calcd for
C21H32N8BCuF4: C, 46.12; H, 5.90; N, 20.49%. Found: C, 45.95; H, 5.72; N, 20.20 %. HRESI+-
MS, m/z: 459.2036 ([M]+, calcd 459.2035). IR spectrum in KBr, selected bands, cm−1: 2209, 2251 s
1
ν(NC). H NMR in CD2Cl2, δ: 1.39 (t, 6H, Et), 2.32 (s, 9H, Me), 2.54 (s, 9H, Me), 3.25 (q, 4H,
13
Et), 6.01 (s, 3H, CHpyrazolyl), 7.75 (s, 1H, CHpyrazolyl). C{1H} NMR in CD2Cl2, δ: 10.7 (Me), 12.7
(Et), 13.32 (Me), 46.1 (Et), 67.6 (CH), 106.6 (CHpyrazolyl), 139.8, 150.6 (Cpyrazolyl), NCN was not
detected. Λm = 90 Ohm–1 cm–1 mol–1.
15

[Cu{HC(3,5-Me2pz)3}(NCNC5H10)][BF4] (3). Yield 85 mg, 96%. Anal. Calcd for
C22H32N8BCuF4: C, 47.28; H, 5.77; N, 20.05%. Found: C, 47.40; H, 5.69; N, 20.01%. HRESI+-MS,
m/z: 471.2037 ([M]+, calcd 471.2035). IR spectrum in KBr, selected bands, cm−1: 2209, 2242 s
ν(NC). 1H NMR in CD2Cl2 δ: 1.67 (m, 2H, C5H10), 1.74 (m, 4H, C5H10), 2.32 (s, 9H, Me), 2.54 (s,
13
9H, Me), 3.34 (q, 4H, C5H10), 6.01 (s, 3H, CHpyrazolyl), 7.74 (s, 1H, CH). C{1H} NMR in CD2Cl2,
δ: 10.7 (Me), 13.3 (Me), 22.8 (C5H10), 24.7 (C5H10), 50.1 (C5H10), 67.6 (CH), 106.56 (CHpyrazolyl),
139.8, 150.6 (Cpyrazolyl), NCN was not detected. Λm = 87 Ohm–1 cm–1 mol–1. Crystals of 3 suitable
for X-ray diffraction analysis were obtained by slow evaporation of the reaction mixture at room
temperature.
[Cu{HC(3,5-Me2pz)3}(NCNC4H8O)][BF4] (4). Yield 85 mg, 96%. Anal. Calcd for
C21H30N8OBCuF4: C, 44.97; H, 5.39; N, 19.98%. Found: C, 44.79; H, 5.46; N, 19.81%. HRESI+-
MS, m/z: 473.1823 ([M]+, calcd 473.1828). IR spectrum in KBr, selected bands, cm−1: 2216, 2248 s
1
ν(NC). H NMR in CDCl3, δ: 2.28 (s, 9H, Me), 2.57 (s, 9H, Me), 3.30 (q, 4H, C4H8O), 3.83 (q,
13
4H, C4H8O), 5.91 (s, 3H, CHpyrazolyl), 7.82 (s, 1H, CH). C{1H} NMR in CDCl3, 10.9 (Me), 13.7
(Me), 48.5 (C4H8O), 65.6 (C4H8O), 67.8 (CH), 106.6 (CHpyrazolyl), 140.4, 150.4 (Cpyrazolyl), NCN was
not detected. Λm = 73 Ohm–1 cm–1 mol–1.
[Cu{HC(3,5-Me2pz)3}(NCNC4H8)][BF4] (5). Yield 83 mg, 96%. Anal. Calcd for
C21H30N8BCuF4: C, 46.29; H, 5.55; N, 20.57%. Found: C, 46.20; H, 5.72; N, 20.53%. HRESI+-MS,
m/z: 457.1876 ([M]+, calcd 457.1879). IR spectrum in KBr, selected bands, cm−1: 2208, 2242 s
ν(NC). 1H NMR in CDCl3, δ: 2.02 (v, 4H, C4H8), 2.28 (s, 9H, Me), 2.58 (s, 9H, Me), 3.60 (q, 4H,
C4H8), 5.91 (s, 3H, CHpyrazolyl), 7.84 (s, 1H, CH). 13C{1H} NMR in CDCl3, δ: 10.9 (Me), 13.7 (Me),
25.9 (C4H8), 67.8 (CH), 106.6 (CHpyrazolyl), 140.5, 150.4 (Cpyrazolyl), NCN was not detected. Λm = 85
Ohm–1 cm–1 mol–1.
[Cu{HC(3,5-Me2pz)3}(NCNC3H6С6H4)][BF4] (6). Yield 90 mg, 93%. Anal. Calcd for
C26H32N8BCuF4: C, 51.45; H, 5.31; N, 18.46%. Found: C, 51.51; H, 5.38; N, 18.29%. HRESI+-MS,
m/z: 519.2034 ([M]+, calcd 519.2035). IR spectrum in KBr, selected bands, cm−1: 2214, 2248 s
16

ν(NC). 1H NMR in CDCl3, δ: 2.28 (s, 9H, Me), 2.58 (s, 9H, Me), 3.06 (m, 2H, CH2), 3.67 (m, 2H,
CH2), 4.59 (m, 2H, CH2), 5.92 (s ,3H, CHpyrazolyl), 7.13–7.35 (m, 4H, С6H4 ), 7.84 (s, 1H,
CHpyrazolyl). 13C{1H} NMR in CDCl3, δ: 10.9 (Me), 13.7 (Me), 27.7 (CH2), 67.8 (CH), 106.6
(CHpyrazolyl), 126.0, 127.0, 127.6, 129.3, 132.4 (C6H4), 140.5, 150.4 (Cpyrazolyl), NCN was not
detected. Λm = 80 Ohm–1 cm–1 mol–1.
[Cu{HC(3,5-Me2pz)3{NCN(CH2Ph)2}][BF4] (7). Yield 101 mg, 95%. Anal. Calcd for
C31H36N8BCuF4: C, 55.49; H, 5.41; N, 16.70%. Found: C, 55.47; H, 5.35; N, 16.61%. HRESI+-MS,
m/z: 583.2347 ([M]+, calcd 583.2348). IR spectrum in KBr, selected bands, cm−1: 2210, 2239 s
ν(NC). 1H NMR in CDCl3 δ: 2.14 (s, 9H, Me), 2.57 (s, 9H, Me), 4.36 (m, 4H, CH2), 5.89 (s, 3H,
CHpyrazolyl), 7.29–7.41 (m, 10H, Ph), 7.81 (s, 1H, CHpyrazolyl). 13C{1H} NMR in CDCl3, δ: 10.9 (Me),
13.6 (Me), 67.8 (CH), 106.5 (CHpyrazolyl), 128.8, 129.1, 133.6 (C6H4), 140.5, 150.3 (Cpyrazolyl), CH2
and NCN were not detected. Λm = 86 Ohm–1 cm–1 mol–1.
[Cu{HC(3,5-Me2pz)3}(NCNMePh)][BF4] (8). Yield 74 mg, 94%. Anal. Calcd for
C24H30N8BCuF4: C, 49.62; H, 5.21; N, 19.29%. Found: C, 49.55 ; H, 5.31; N, 19.18 %. HRESI+-
MS, m/z: 493.1899 ([M]+, calcd 493.1879). IR spectrum in KBr, selected bands, cm−1: 2214, 2251 s
1
ν(NC). H NMR in CDCl3, δ: 2.32 (s, 9H, Me), 2.60 (s, 9H, Me), 3.52 (3H, NMe), 5.95 (s, 3H,
13
CHpyrazolyl), 7.16 (m, 3H, Ph), 7.45 (m, 2H, Ph), 7.86 (s, 1H, CHpyrazolyl). C{1H} NMR in CDCl3,
10.9 (Me), 13.8 (Me), 47.6 (MeN), 67.8 (CH), 106.6 (CHpyrazolyl), 115.3, 124.3, 129.9, (Ph), 140.6,
150.5 (Cpyrazolyl), NCN was not detected. Λm = 79 Ohm–1 cm–1 mol–1.
The thermogravimetry/differential thermal analysis data for 1–8 (Figures S42–S49)
demonstrate that mass loss starts in the interval ca. 130–150 °C; differential thermal analysis curves
exhibit first endothermic peak in the region 165–245 °C due to the loss of NCNR2. Complex 6
displays several differential thermal analysis peaks at the 130–310 °C interval from NCNR2 loss
accompanied with decomposition of the complex. Complexes 1–5 and 7–8 undergo further
decomposition in the range 220–610 °C with one endothermic peak at 320–330 °C (1–5, and 8) or
17

several peaks at 360–380 °C (7). The mass of final product corresponds to CuF2 (2–5) or Cu (1), or
does not correspond to any stoichiometry of the proposed final products (6–8).
Acknowledgements. The work was supported by the Russian Science Foundation (grant
14-13-00060). AYD is grateful to Saint Petersburg State University for his postdoctoral grant.
Physicochemical measurements were performed at the Center for Magnetic Resonance, X-ray
Diffraction Center, Center for Chemical Analysis and Materials Research, and Center for
Thermogravimetric and Calorimetric Research (all belong to Saint Petersburg State University).
18

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