Sterically crowded triazenides as novel ancillary ligands in copper chemistry

Article abstract of DOI:10.1016/j.ica.2011.01.079

We have synthesized copper salts MN₃RR′ derived from the biphenyl- or m-terphenyl-substituted triazenes Tph₂N₃H (1a) and Dmp(Tph)N₃H (1b) (Dmp = 2,6-Mes₂C ₆H₃ with Mes = 2,4,6-Me

Full text of DOI:10.1016/j.ica.2011.01.079

Inorganica Chimica Acta 374 (2011) 163–170
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Inorganica Chimica Acta
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Sterically crowded triazenides as novel ancillary ligands in copper chemistry
Hyui Sul Lee a, Mark Niemeyer b,
⇑
a Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
b Institut für Anorganische und Analytische Chemie, Johannes-Gutenberg Universität Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany
a r t i c l e i n f o
a b s t r a c t
We have synthesized copper salts MN3RR0 derived from the biphenyl- or m-terphenyl-substituted triaz-
enes Tph2N3H (1a) and Dmp(Tph)N3H (1b) (Dmp = 2,6-Mes2C6H3 with Mes = 2,4,6-Me3C6H2; Tph = 2-
TripC6H4 with Trip = 2,4,6-i-Pr3C6H2). The homoleptic copper triazenide [CuN3Tph2] (2a) was obtained
in high yield from the metallation of 1a with mesityl copper in n-heptane, while the complex
[CuN3(Dmp)Tph] (2b) was generated by the same method in situ only. Reaction of 2a with triphenylphos-
phane gave the 2:1 adduct [CuN3Tph2(PPh3)2] (3a), regardless of the used complex/donor ratio, while
reaction of 2a or 2b with a stochiometric amount of t-butylisonitrile afforded the 1:1 adducts
[Tph2N3CuCNtBu] (4a) and [Dmp(Tph)N3CuCNtBu] (4b). All new compounds (except 2b) have been char-
acterized by 1H NMR, 13C NMR and IR spectroscopy, elemental analysis, melting point (not 2a), and X-ray
Article history:
Available online 3 February 2011
Dedicated to Prof. Kaim
Keywords:
Copper complexes
Sterically crowded ligands
t-Butylisonitrile
Triazenido ligands
Triphenylphosphane
crystallography. The IR spectroscopic examination of the m(C„N) stretch in the isonitrile adducts 4a and
4b revealed the weaker donor character of the supporting triazenido ligands compared to related b-dike-
timinato ligands.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
Triazenides are weaker donors than the isoelectronic amidi-
nates and the related b-diketiminates, and should induce greater
The design and development of alternative ligand systems capa-
ble of stabilizing monomeric metal complexes while provoking no-
vel reactivity remains one of the most intensely studied areas of
organometallic chemistry [1]. Exploration of this field is driven
by the potential use of these complexes in catalysis and organic
synthesis. Examples of monoanionic chelating N-donor ligands
that have received much recent attention include the b-diketimi-
nate [2] and the amidinate [3] ligand systems. Much less attention
has been given to the closely related triazenides [4]. We recently
succeeded in the preparation of derivatives of aryl-substituted, ste-
rically crowded triazenido ligands, that are bulky enough to pre-
vent undesirable ligand redistribution reactions [5–7]. These
ligands were used to stabilize the first examples of structurally
characterized aryl compounds of the heavier alkaline earth metals
Ca, Sr, and Ba [5] and unsolvated pentafluorophenyl organyls of the
divalent lanthanides Yb and Eu [8]. We have also examined the
unusual ‘‘inverse’’ aggregation behavior of alkali metal triazenides
in their solid-state structures that can be traced back to a different
electrophilicity at a bonded metal atom [5]. In this paper, we de-
scribe the synthesis and characterization of several copper triaze-
nides. Isonitrile adducts have been prepared in order to probe
the donor properties of our triazenide ligands.
2. Experimental
2.1. Materials and methods
All manipulations were performed by using standard Schlenk
techniques under an inert atmosphere of purified argon and sol-
vents freshly distilled from Na wire or LiAlH4. CuMes [10] and
the triazenes Tph2N3H or Dmp(Tph)N3H [5,7] were synthesized
as previously described. NMR spectra were recorded on Bruker
AM200, AC250 or AM400 instruments and referenced to solvent
resonances. IR spectra (Nujol mull, CsBr plates) have been obtained
in the range 4000–200 cmꢁ1 with a Perkin–Elmer paragon 1000 PC
spectrometer. Mass spectra were recorded with a Varian MAT711
or Finnegan MAT95 instrument. Melting points were determined
under Ar atmosphere in sealed glass tubes.
degree of metalꢀꢀꢀ
p-arene interactions to pending aromatic substit-
uents [6]. A series of homologous potassium and thallium com-
plexes crystallizes in isomorphous cells and consists of the first
examples of isostructural molecular species reported for these ele-
ments [9].
2.2. Preparation of [CuN3Tph2] (2a)
A solution of CuMes (0.365 g, 2 mmol) and triazene 1a (1.204 g,
2 mmol) in n-heptane (60 mL) was stirred for 2 h. The volume was
reduced to ca. 30 mL under vacuum and the obtained precipitate
⇑
Corresponding author. Tel.: +49 6131 39 26020; fax: +49 6131 39 25419.
E-mail address: niemeyer@uni-mainz.de (M. Niemeyer).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.079

164
H.S. Lee, M. Niemeyer / Inorganica Chimica Acta 374 (2011) 163–170
was redissolved by slight warming. Storage at ambient tempera-
ture for two days afforded 2a as yellow crystalline material. Yield:
0.90 g (1.35 mmol, 76%); 1H NMR (250.1 MHz, C6D6): d 0.96 (d,
p-CH(CH3)2), 29.5 (C(CH3)3), 30.9 (o-CH(CH3)2), 34.6 (p-CH(CH3)2),
119.0 (6-C6H4), 120.9 (m-Trip), 122.0 (4-C6H4), 128.4 (5-C6H4),
130.7 (i-Trip), 131.3 (3-C6H4), 147.1 (CNC(CH3)3), 147.3 (o-Trip),
147.3 (p-Trip), 151.0 (1-C6H4); signals for the CNC(CH3)3
CNC(CH3)3 and 2-C6H4 carbon atoms could not be detected. IR (Nu-
3
3JHH = 6.9 Hz, 12H, o-CH(CH3)2), 1.04 (d, JHH = 6.9 Hz, 12H, o-
3
CH(CH3)2), 1.41 (d, JHH = 6.9 Hz, 12H, p-CH(CH3)2), 2.78 (sep,
3
3JHH = 6.9 Hz, 4H, o-CH(CH3)2), 2.98 (sep, JHH = 6.9 Hz, 2H, p-
jol)
= 2198 s (
CN), 1604 m, 1592 m, 1585 sh, 1567 m, 1508 m,
~
v
~
v
CH(CH3)2), 7.27 (s, 4H, m-Trip), 7.13 (t, 2H, 5-C6H4), 6.99 (d,
1484 sh, 1361 s, 1336 s, 1308 s br, 1242 vs br, 1193 s, 1158 ms,
1128 m, 1102 m, 1069 m, 1056 m, 1004 m, 953 w, 938 m, 919 w,
882 sh, 875 ms, 774 m, 756 vs, 727 ms, 693 w, 654 ms, 591 w,
555 w, 484 w. Anal. Calc. for C47H63CuN4: C, 75.51; H, 8.49; N,
7.49. Found: C, 75.42; H, 8.35; N 7.43%.
3
3JHH = 7.9 Hz, 2H, 3-C6H4), 6.93 (t, JHH = 7.3 Hz, 2H, 4-C6H4), 5.99
3
(d, JHH = 8.0 Hz, 2H, 6-C6H4). 13C NMR (100.6 MHz, C6D6): d 23.5
(o-CH(CH3)2), 24.5 (p-CH(CH3)2), 24.7 (o-CH(CH3)2), 30.8 (o-
CH(CH3)2), 35.0 (p-CH(CH3)2), 121.9 (m-Trip), 124.9 (4-C6H4),
125.8 (6-C6H4), 128.2 (5-C6H4), 132.3 (3-C6H4), 132.8 (2-C6H4),
135.3 (i-Trip), 146.8 (o-Trip), 148.1, 148.8 (1-C6H4, p-Trip). IR (Nu-
~
2.5. Preparation of [Dmp(Tph)N3CuCNtBu] (4b) and 4b ꢀ C6H6
jol)
v = 1606 m, 1571 m, 1567 m, 1488 sh, 1361 s, 1338 vs, 1334 vs,
1284 s, 1250 m, 1241 m, 1184 m, 1168 m, 1157 m, 1127 w,
1103 m, 1069 m, 1055 m, 1003 m, 939 m, 877 ms, 780 w, 774 s,
760 vs, 753 vs, 722 m, 670 w, 626 w, 520 w 477 w, 422 m. Anal.
Calc. for C42H54CuN3: C, 75.92; H, 8.19; N, 6.32. Found: C, 76.12;
H, 8.33; N 6.13%.
A solution of the triazene Dmp(Tph)N3H (1.27 g, 2 mmol) and
CuMes (0.365 g, 2 mmol) in 40 mL of n-heptane was stirred for
t
2 h. BuNC (0.23 mL, 2 mmol) was added and stirring was contin-
ued overnight. The volume of the resulting yellow solution was re-
duced to incipient crystallization under reduced pressure. Storage
at ambient temperature for several days afforded 4b as light yellow
crystals. Yield: 0.84 g (0.97 mmol, 49%). mp: 186–194 °C; 1H NMR
(200.1 MHz, C6D6): d 0.86 (s, 9H, C(CH3)3), 1.01 (d, 3JHH = 7.0 Hz, 6H,
2.3. Preparation of [CuN3Tph2(PPh3)2] (3a)
3
PPh3 (1.05 g, 4.00 mmol) was added at ambient temperature to
a stirred solution of 2a (2.00 mmol) in toluene (60 mL). After 2 h
the solvent was removed under reduced pressure and the remain-
ing solid was dissolved in a n-heptane/toluene mixture. Storage at
0 °C for several days afforded 3a C7H8 as pale yellow crystalline
material. The solvent-free complex 3a was obtained by thoroughly
drying under vacuum. Yield: 1.75 g (1.47 mmol, 74%); mp: 185–
o-CH(CH3)2), 1.04 (d, JHH = 6.9 Hz, 6H, o-CH(CH3)2), 1.22 (d,
3JHH = 6.9 Hz, 6H, p-CH(CH3)2), 2.24 (s, 6H, p-CH3), 2.27 (s, 12H,
3
o-CH3), 2.76 (sept, JHH = 6.9 Hz, 2H, o-CH(CH3)2), 2.76 (sept,
3JHH = 6.9 Hz, 1H, p-CH(CH3)2), 6.88 (s, 4H, m-Mes), 6.70–7.25 (m,
7H, Aryl-H), 7.00 (s, 2H, m-Trip). 13C NMR (62.9 MHz, C6D6): d
21.2 (p-CH3), 21.4 (o-CH3), 24.5 (p-CH(CH3)2), 24.5 (o-CH(CH3)2),
25.0 (o-CH(CH3)2), 29.5 (NC(CH3)3), 30.6 (o-CH(CH3)2), 34.6 (p-
CH(CH3)2), 55.9 (NC(CH3)3), 118.0, 120.8, 123.5, 128.0, 130.5 (var-
ious aromatic CH), 120.8 (m-Trip), 128.2 (m-Mes), 129.8 (m-
C6H3), 128.8, 133.9, 134.9, 135.6, 135.8, 140.1, 146.9, 147,2 147,6
149.7 (various aromatic C); one signal for the CNC(CH3)3 carbon
3
190 °C; 1H NMR (250.1 MHz, C6D6): d 0.93 (d, JHH = 6.8 Hz, 12H,
3
o-CH(CH3)2), 1.14 (d, JHH = 6.8 Hz, 12H, o-CH(CH3)2), 1.25 (d,
3
3JHH = 6.8 Hz, 12H, p-CH(CH3)2), 2.86 (sep, JHH = 6.7 Hz, 2H, p-
3
CH(CH3)2), 2.93 (sep, JHH = 6.9 Hz, 4H, o-CH(CH3)2), 6.55 (d,
3JHH = 7.8 Hz, 2H, 6-C6H4), 6.93–7.03 (m, 32H, PPh3 + 3-C6H4),
atom could not be detected. IR (Nujol)
= 2193 s (
CN), 1588 m,
~
v
~
v
3
6.89 (t, JHH = 7.0 Hz, 2H, 4-C6H4), 7.12 (t, 2H, 5-C6H4), 7.14 (s,
1566 m, 1556 sh, 1536 s, 1530 s, 1500 sh, 1461 vs, 1415 m, 1378
vs, 1360 sh, 1306 m, 1275 ms, 1262 s, 1242 m, 1229 m, 1206 m,
1189 ms, 1167 s, 1069 sh, 1030 vw, 1001 w, 938 sh, 978 w,
785 m, 777 w, 754 vs, 739 ms, 724 ms, 695 m, 654 m, 600 w, 591
w, 575 w, 546 w, 515w. Anal. Calc. for C50H61CuN4: C, 76.84; H,
7.87; N, 7.17. Found: C, 76.90; H, 7.65; N 7.06%. Crystals of the
packing complex 4bꢀC6H6 were grown from a saturated benzene
solution.
4H, m-Trip). 13C NMR (100.6 MHz, C6D6): d 24.1 (o-CH(CH3)2),
24.5 (p-CH(CH3)2), 25.0 (o-CH(CH3)2), 31.1 (o-CH(CH3)2), 34.6 (p-
CH(CH3)2), 120.9 (m-Trip), 121.0 (4-C6H4), 123.0 (6-C6H4), 127.2
3
4
(5-C6H4), 128.7 (d, JPC = 8.4 Hz, m-PPh3), 129.5 (d, JPC = 0.5 Hz,
2
p-PPh3), 130.7 (2-C6H4), 132.8 (3-C6H4), 134.4 (d, JPC = 16.5 Hz,
1
o-PPh3), 135.0 (d, JPC = 15.2 Hz, i-PPh3), 139.1 (i-Trip), 146.5 (o-
Trip), 146.5 (p-Trip), 150.8 (1-C6H4); 31P NMR (162.0 MHz, C6D6):
~
d
ꢁ1.9; IR (Nujol)
v
= 1604 w, 1556 s, 1530 ms, 1478 ms,
1455 ms, 1359 s, 1339s, 1249 s, 1202 ms, 1156 m, 1093 ms, 1069
s, 1057 w, 1001 m, 968 w, 942 m, 920 w, 895 w, 878 m, 873 m,
850 w, 845 s, 779 w, 784 w, 769 m, 756 s, 743 vs, 729 s, 704 s,
694 vs, 660 m, 649 ms, 590 w, 556 w, 527 ms, 501 vs, 464 m, 439
w. Anal. Calc. for C78H84CuN3P2: C, 78.79; H, 7.12; N, 3.53. Found:
C, 78.62; H, 7.30; N 3.49%.
2.6. X-ray crystallography
X-ray-quality crystals were obtained as described in the exper-
imental section. Crystals were removed from Schlenk tubes and
immediately covered with a layer of viscous hydrocarbon oil (Par-
atone N, Exxon). A suitable crystal was selected, attached to a glass
fiber, and instantly placed in a low-temperature N2-stream [11a].
All data were collected at 100 K (2a, 4b, 4bꢀ(C6H6)) or 173 K (1a,
3a, 4b) using either a Siemens P4 (3a), a rebuild Syntex P21/Sie-
mens P3 (3a, 4b) or a Nonius Kappa CCD (2a, 4b, 4bꢀ(C6H6)) diffrac-
tometer. Crystal data are given in Table 1. Calculations were
performed with the SHELXTL PC 5.03 [11b] and SHELXL-97 [11c] pro-
gram system installed on a local PC. The structures were solved
by direct methods and refined on F2o by full-matrix least-squares
refinement. Absorption corrections were applied by using semiem-
2.4. Preparation of [Tph2N3CuCNtBu] (4a)
tBuNC (0.23 mL, 2 mmol) was added to a stirred solution of 1a
(1.20 g, 2 mmol) in n-heptane (50 mL). The volume of the resulting
yellow solution was reduced to incipient crystallization under re-
duced pressure. Storage at ambient temperature overnight affor-
ded 4a as pale yellow crystals. The workup of the mother liquor
gave another crop of crystalline material. Yield: 1.07 g (1.43 mmol,
72%); mp: 210–214 °C; 1H NMR (400.1 MHz, C6D6): d 0.83 (s, 9H,
pirical
w-scans or a multi-scan refinement. Anisotropic thermal
3
C(CH3)3), 1.17 (d, JHH = 6.8 Hz, 12H, o-CH(CH3)2), 1.19 (d,
parameters were included for all non-hydrogen atoms. In 1a the
methyl carbon atoms of two disordered iso-propyl groups were re-
fined with split positions and side occupation factors of 0.50 for
C242, C243/C244, C245 and C442, C443/C444, C445. The corre-
sponding C241–C242, C241–C243, C241–C244, C241–C245,
C441–C442, C441–C443, C441–C444 and C441–C445 distances
were restrained with DFIX commands. In 3a the ring carbon atoms
3JHH = 6.8 Hz, 12H, o-CH(CH3)2), 1.27 (d, JHH = 6.8 Hz, 12H, p-
3
3
CH(CH3)2), 2.82 (sep, JHH = 6.9 Hz, 2H, p-CH(CH3)2), 3.03 (sep,
3JHH = 6.9 Hz, 2H, o-CH(CH3)2), 6.99 (t, JHH = 7.2 Hz, 2H, 5-C6H4),
3
3
7.10 (d, JHH = 7.5 Hz, 2H, 3-C6H4), 7.13 (s, 4H, m-Trip), 7.30 (t,
3
3JHH = 7.6 Hz, 2H, 4-C6H4), 7.96 (d br, JHH = 7.6 Hz, 2H, 6-C6H4).
13C NMR (100.6 MHz, C6D6): d 24.5, 24.5, 24.9 (2 ꢂ o-CH(CH3)2,

H.S. Lee, M. Niemeyer / Inorganica Chimica Acta 374 (2011) 163–170
165
Table 1
Selected crystallographic data for compounds 1a, (2a)2, 3aꢀC7H8, 4b, and 4bꢀC6H6.a
1a
(2a)2
3aꢀC7H8
4bꢀC6H6
4b (100 K)
4b (173 K)
Formula
C
42H55N3
C84H108Cu2N6
1328.84
pale yellow, plate
0.30 ꢂ 0.20 ꢂ 0.04
tetragonal
P43
15.0461(1)
15.0461(1)
33.6042(4)
90
C85H92CuN3P2
1281.10
C56H67CuN4
859.68
yellow, prism
0.25 ꢂ 0.25 ꢂ 0.20
monoclinic
P21/c
17.6453(2)
12.2230(2)
22.6382(3)
90
94.4469(7)
90
C50H61CuN4
781.57
C50H61CuN4
781.57
yellow, prism
Molecular mass
Color, habit
Crystal size (mm)
Crystal system
Space group
a (Å)
601.89
pale yellow, prism
0.80 ꢂ 0.40 ꢂ 0.40
monoclinic
C2/c
33.037(7)
9.6910(19)
25.009(5)
90
106.99(3)
90
7657(3)
8
pale yellow, plate
0.80 ꢂ 0.50 ꢂ 0.20
triclinic
yellow, prism
0.40 ꢂ 0.35 ꢂ 0.25
triclinic
0.65 ꢂ 0.55 ꢂ 0.45
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
13.601(3)
14.059(3)
19.314(5)
80.956(18)
85.469(17)
89.487(19)
3635.8(14)
2
10.6956(2)
12.2829(2)
19.1514(3)
72.0978(10)
89.1996(11)
70.2091(10)
2241.31(7)
2
10.752(2)
12.311(3)
19.281(4)
71.992(16)
88.779(17)
70.314(16)
2275.5(8)
2
b (Å)
c (Å)
a
(°)
b (°)
90
90
c
(°)
V (Å3)
7607.49(12)
4
1.160
4867.87(12)
4
1.173
Z
Dcalc (g/cm3)
1.044
0.060
1.170
0.390
1.158
0.524
1.141
0.516
l
(mmꢁ1
)
0.605
0.488
2h Range (°)
Collected data
3.4–52.0
7688
6.5–56.6
45 928
4.2–50.0
13 238
6.6–56.5
65 762
7.1–56.6
66 066
3.6–48.0
7581
Unique data/R(int)
Data with I > 2r(I) (No)
7500/0.042
4635
16 606/0.091
14 009
12 656/0.035
7965
11 972/0.090
10 115
11 049/0.158
9314
7145/0.069
4902
Number of parameters (Np)
467
853
825
600
525
525
Number of restraints
8
1
0
0
0
0
R1 (I > 2
r
(I))b
0.070
0.181
1.409
0.38/ꢁ0.26
0.052
0.110
1.234
0.43/ꢁ0.43
0.046
0.113
0.860
0.68/ꢁ0.43
0.050
0.106
1.045
0.31/ꢁ0.40
0.055
0.162
1.682
0.53/ꢁ1.05
0.068
0.187
1.119
0.33/ꢁ0.77
wR2 (all data)c
Goodness-of-fit GOFd
Difference eꢁ density (e Å3)
a
b
c
All data were collected at 173 K (1a, 3aꢀC7H8, 4b) or 100 K (2a, 4b, 4b ꢀ C6H6), using Mo K
a
( = 0.71073 Å) radiation.
R1
=
R
(||Fo| ꢁ |Fc||)/
R(|Fo|.
wR2 = {
R
[w(F2o ꢁ F2c )2]/
R .
[w(F2o)2]}1/2
GOF = {
R
[w(Fo2 ꢁ Fc2)2]/(No ꢁ Np)}1/2
.
d
of a cocrystallized toluene molecule were constrained to a regular
hexagon. In the structure determination of 4b, obtained at 100 K
(173 K), the copper atom was refined with split positions and tem-
perature-dependent side occupation factors of 0.95 (0.88) and 0.05
1,3-disubstituted triazenes [14,15] is prohibited by the sterically
crowded Tph substituents. 1a possesses a trans-conformation
around the central N@N double bond as shown by the torsion an-
gles C11–N1–N2–N3 [ꢁ175.7(2)°] and H3–N3–N2–N1 [0(2)°] and
therefore exists as E-anti isomer according to the nomenclature
of scheme 1. In addition, the torsion angles N2–N1–C11–C16
[ꢁ1.4(3)°] and N2–N3–C31–C36 [ꢁ3.2(3)°] indicate a syn/syn
arrangement of the Tph substituents that point in direction of
the NH hydrogen atom. With interplanar angles of 78.7° and
76.9° the Trip groups are aligned almost orthogonal to the C6H4
arene rings with a staggered conformation of the iso-propyl sub-
stituents (Fig. 1, right).
(0.12) that correspond to different
g g
1-N3 and 2-N1,N3 coordina-
tion modes, respectively (see supporting information). In 4bꢀ(C6H6)
the carbon atoms of the cocrystallized, rotationally disordered ben-
zene ring (sof = 0.5 for C71–C76/C81–C86) were constrained to
regular hexagons. Final R values are listed in Table 1. Important
bond parameters are given in in Table 2. Further details are pro-
vided in the supplementary material.
The difference between the N@N (1.280(3) Å for N1–N2) and N–
N (1.318(3) Å for N2–N3) bond lenghts is less as one might expect
for localized bonds. Bigger differences of 1.2650(15)/1.3525(15) Å
are observed in the solid state structure of the terphenyl substi-
tuted triazene HN3(Me4Ter)2 (Me4Ter = 3,5,300,500-tetramethyl-
1,10:30,100-terphenyl-20) [7]. The more delocalized bonds in 1a
may be explained in part by the coplanar arrangement of the
3. Results and discussion
3.1. Syntheses and characterization of the triazene HN3Tph2
As we and others have reported before [5–7,9,12], bulky substi-
tuted diaryl triazenes are accessible in high yields by the reaction
of lithium aryls with aryl azides followed by a protolytic workup.
Since we have given only limited information for the bis(biphenyl)
substituted triazene HN3Tph2 in a preliminary communication [6]
some more details including the crystal structure will be provided
in the following section.
(C6H4)N3(C6H4) fragments, since for the triazene HN3(Me4Ter)2
a
bigger torsion for the aryl substituents is found, as shown by the
NNCC dihedral angles of 43.5°/53.8°. However, another part of
the more balanced bonds in 1a may be due to disorder since the
NH positions on N3 and N1 are populated with 75% and 25%,
respectively (see Supporting information).
After crystallization from acetone, triazene 1a is obtained as
pale yellow solid in 75% yield. The air stable but acid labile com-
pound melts with slight decomposition in the range 190–195 °C.
In the IR spectrum the asymmetric N–N@N and N–N@N vibrations
3.2. Syntheses of copper triazenides
at 1510 cmꢁ1 and 1149 cmꢁ1 indicate a mainly localized
p-electron
system. The NH-stretch is observed as a narrow band at 3300 cmꢁ1
.
Donor-free copper triazenides are accessible in n-heptane as the
solvent via metallation of the diaryltriazenes Tph2N3H (1a) or
Dmp(Tph)N3H (1b) (Dmp = 2,6-Mes2C6H3 with Mes = 2,4,6-
Me3C6H2; Tph = 2-TripC6H4 with Trip = 2,4,6-iPr3C6H2) with mesi-
tyl copper (Scheme 2).
The 1H and 13C NMR spectra show only one set of signals and
therefore indicate that only one of several possible isomers
(Scheme 1) dominates in solution.
The triazene crystallizes as a monomer in the space group C2/c
(Fig. 1). Further aggregation involving intermolecular N–HꢀꢀꢀA
hydrogen bridges (A = N, O, and Br) as often observed in other
After crystallization, the pale yellow complex [Cu(N3Tph2)] (2a)
was
isolated
in
76%
yield,
whereas
the
complex

166
H.S. Lee, M. Niemeyer / Inorganica Chimica Acta 374 (2011) 163–170
Table 2
Selected bond distances (Å), angles (°), and dihe-
dral angles (°) for Compounds 1a, 2a, 3aꢀC7H8, 4b,
and 4bꢀC6H6.
1a
N1–N2
N2–N3
N3–H3
1.280(3)
1.319(3)
0.87(3)
N1–C11
N3–C31
N1–N2–N3
N2–N1–C11–C16
N2–N3–C31–C36
1.417(3)
1.398(3)
110.63(19)
ꢁ1.4(3)
Scheme 1. Possible isomers of triazenes according to the nomenclature of
amidinates [13].
ꢁ3.2(3)
(2a)2
Cu1–N1
Cu2–N3
Cu1–N4
[Cu(N3(Dmp)Tph2)] (2b) was generated in situ only. Reaction of 2a
or 2b with a stochiometric amount of t-butylisonitrile afforded the
1:1 adducts [Tph2N3CuCNtBu] (4a) and [Dmp(Tph)N3CuCNtBu]
(4b). However, reaction of 2a with triphenylphosphane gave the
2:1 adduct [CuN3Tph2(PPh3)2] (3a), regardless of the used com-
plex/donor ratio. The donor-free complex 2a is oxygen and air-sen-
sitive whereas the adducts are air-stable in the solid-state for days.
All compounds possess good or moderate solubility in aromatic or
aliphatic hydrocarbons. They show considerable thermal stability
but decompose with N2 evolution at higher temperature (3a:
185–190 °C, 4a: 210–214 °C, 4b: 186–194 °C).
1.878(2)
1.887(2)
1.885(2)
1.878(3)
2.4765(5)
1.311(3)
1.306(3)
1.316(3)
1.302(3)
115.9(2)
115.9(2)
ꢁ140.7(3)
ꢁ141.2(3)
ꢁ55.8(4)
Cu2–N6
Cu1ꢀꢀꢀCu2
N1–N2
N2–N3
N4–N5
N5–N6
N3–N2–N1
N6–N5–N4
N2–N1–C11–C16
N2–N3–C31–C36
N5–N4–C51–C56
3.3. IR spectroscopic characterization of copper triazenides
3aꢀC7H8
Cu–N1
2.220(2)
2.117(2)
2.2706(9)
2.2814(9)
1.315(3)
1.309(3)
1.419(3)
1.418(3)
109.2(2)
59.06(8)
121.61(3)
122.3(5)
114.8(5)
ꢁ31.2(3)
ꢁ165.8(2)
Cu–N3
Cu–P1
Cu–P2
N1–N2
N2–N3
N1–C11
N3–C31
N3–N2–N1
N3–Cu–N1
P1–Cu–P2
P1–CuꢀꢀꢀN2
P2–CuꢀꢀꢀN2
N2–N1–C11–C16
N2–N3–C31–C36
The most important bonding modes in metal triazenides are
shown in Scheme 3. IR spectroscopy should be in principle a valu-
able tool for the assignment of different coordination modes as was
already stated by Moore and Robinson in an older review on the
coordination chemistry of triazenides [4a].
However, due to the lack of structually characterized com-
pounds these assignments have been ambigous for some time. In
the meantime we and others have synthesized numerous metal
triazenides that have been characterized by IR spectroscopy and
X-ray crystallography. Table 3 summarizes characteristic IR vibra-
tions together with the corresponding bonding modes as deter-
mined by X-ray structure determinations in our group.
4bꢀC6H6
A broad intense m
as-N3 absorption in the range 1221–1282 cmꢁ1
as observed for the monomeric complexes [M(N3Tph2)]
Cu–N3
1.8948(12)
1.8337(15)
1.2816(16)
1.3354(16)
1.4189(18)
1.3968(17)
1.147(2)
173.73(5)
110.60(11)
117.30(9)
127.97(9)
176.86(13)
ꢁ42.77(17)
21.64(17)
Cu–C1
N1–N2
N2–N3
N1–C11
N3–C31
C1–N5
C1–Cu–N3
N1–N2–N3
N2–N3–Cu
C31–N3–Cu
N5–C1–Cu
N2–N1–C11–C16
N2–N3–C31–C36
{M = (thf)Li, Na, [17], K [6], Rb [17], Cs [6], Tl [9], Me2Al [18],
(Ph3P)2Cu (4a), (C5H4Me)2Er [17]} indicates an
ing mode of the triazenido ligand. An
1-coordination mode, as
g
2-chelating bond-
g
found in several halogeno mercury triazenides [16], is accompa-
nied by two intense bands in the range 1306–1317 cmꢁ1 and
1163–1178 cmꢁ1. In complexes that have a shallow energy profile
for the coordination of the metal cations as indicated by disorder in
the X-ray structures (e.g. [Cu{N3(Dmp)Tph}(CNtBu)] (4b) and
[ZnR(N3Tph2)] (R = Me, Et [17]) superpositions of the correspond-
ing
g g
1- and 2-typical vibration patterns are observed. The IR
spectroscopic characterization of the complex [Cu(N3Tph2)(CNt-
Bu)] (4a), which could not be structurally authenticated by X-ray
diffraction, shows the population of both g1 and g2 bonding
modes.
4b at ꢁ173 °C
Cu1–N3
Cu1–C1
Cu2–N1
Cu2–N3
N1–N2
N2–N3
N2–N1–C11–C16
N2–N3–C31–C36
1.8934(14)
1.829(2)
1.972(6)
2.073(7)
1.2829(19)
1.3328(19)
ꢁ37.3(2)
12.8(2)
The
symmetrically
l
,
g1g1-bridged
copper
complex
[Cu(N3Tph2)]2 (2a)2 possesses an intense broad
m
as-N3 vibration
at 1334 cmꢁ1. A corresponding, although less intense absorption
at 1336 cmꢁ1 and further bands typical for the other coordination
modes are observed at 1309/1243/1167 cmꢁ1 for the unsymmetri-
4b at ꢁ100 °C
Cu1–N3
Cu1–C1
Cu2–N1
Cu2–N3
N1–N2
N2–N3
N2–N1–C11–C16
N2–N3–C31–C36
cally l,
g1g2-bridged lithium complex [Li(N3Tph2)]2 [6].
1.900(3)
1.834(4)
1.914(5)
2.283(7)
1.285(4)
1.325(4)
ꢁ36.5(5)
12.6(5)
With the prepared isonitrile adducts 4a and 4b it is possible to
examine the donor character of the triazenido ligands experimen-
tally. Thereby, the m(C„N) vibration of the isonitrile ligand is used
as an IR spectroscopic probe. Table 4 shows a comparison of the
corresponding absorption bands in copper complexes with differ-
ent monoanionic N-donor ligands. The observed vibrations of

H.S. Lee, M. Niemeyer / Inorganica Chimica Acta 374 (2011) 163–170
167
Fig. 1. Molecular structure of 1a with thermal ellipsoids set to 30% probability. Hydrogen atoms with exception of the N–H one have been omitted for clarity.
Scheme 2. Synthesis of compounds 2a–4b.
2199 cmꢁ1 (4a) and 2193 cmꢁ1 (4b) are shifted to higher wave
numbers than the corresponding values in copper b-diketiminates
(2121–2148 cmꢁ1) [20a–c,20e] or in a copper tris(pyrazolyl)borate
(2155 cmꢁ1) [20f]. However, a similar high value of 2196 cmꢁ1 is
found for a copper complex with an electron-deficient trifluoro-
methyl-substituted tris(pyrazolyl)borate ligand [20g] while a cop-
per triazapentadienide shows an absorption at 2176 cmꢁ1 [20e]. In
the three-nuclear pyrazolato complex [(CO)3Re(pz)3{Cu(CNc-
Hex)}2] [20h], which possesses two different binding modes, two
vibrations at 2164 cmꢁ1 and 2210 cmꢁ1 are observed that can be
Scheme 3. Important bonding modes in metal triazenides.

168
H.S. Lee, M. Niemeyer / Inorganica Chimica Acta 374 (2011) 163–170
Table 3
Selected IR spectroscopic data for metal triazenides.
b
Formula
Bonding modea
Characteristic NNN vibrations (cmꢁ1
)
References
[Cl–Hg{N3(Dmp)Mph}]
[I–Hg{N3(Dmp)Mph}]
g1
g1
[16]
[16]
1314, 1163
1316 br, 1169 br
1313, 1166 br
1246 br
[I–Hg{N3(Dmp)Tph}]
[Cu(N3Tph2)(PPh3)2] (3a)
[Na(N3Tph2)]
g1
g2
g2
[16]
this work
[17]
1305, 1242–1227 br
[K(N3Tph2)]
g2
[6]
1298, 1236 br
1225 br
1221 br
[Rb(N3Tph2)]
[Cs(N3Tph2)]
[Li(N3Tph2)(thf)]
[Tl(N3Tph2)]
g2
g2
g2
g2
[17]
[6]
[17]
[9]
1243 br
1300, 1248 br
1282 br
1247 br
[AlMe2(N3Tph2)]
g2
[18]
[17]
[19]
this work
[Er(C5H4Me)2N3Tph2]
[Eu{N3(Dmp)Tph}2]
[Cu(N3Tph2)(CNtBu)] (4a)
g2
g2
1283 br
unknown
1317, 1266–1233, 1178
1306, 1262 br, 1167 br
1310–1240 br, 1169
[Cu{N3(Dmp)Tph}(CNtBu)] (4b)
[ZnMe(N3Tph2)]
g1
g1
g1
+
+
+
g2
g2
g2
this work
[17]
[ZnEt(N3Tph2)]
[17]
1306–1260 br, 1168
1334 br
[Cu(N3Tph2)]2 (2a)2
[Li(N3Tph2)]2
l
l
,
,
g1
/
/
g1
this work
[6]
g1
g2
1336, 1309, 1243 br, 1167
a
As verified by X-ray diffraction.
If more than one characteristic NNN vibration is present the most intense is underlined.
b
assigned to the three- and two-coordinate copper atoms, respec-
tively. Therefore, these results clearly support the predicted weak-
er donor character of triazenides compared to b-diketiminates.
Unfortunately, comparable data for copper amidinates have not
been reported yet.
169.18(11)) may be attributed to the presence of small-bite ligands
that causes Pauli repulsion between the metal centers. A nearly
realized C2-symmetry with a twofold axis perpendicular to the
Cu2N3 plane is broken by small but significant differences in the
conformation of the Tph substituents. The central Cu2N6 fragment
is not planar and both N3 planes are tilted by 29.8° to each other
(Fig. 2, right). The copper atoms Cu1/Cu2 are displaced by
0.213 Å/ꢁ0.395 Å and ꢁ0.411 Å/0.185 Å from the planes defined
by the nitrogen atoms N1N2N3 and N4N5N6 and the Tph substit-
uents alternately point above and below the central eight-mem-
bered ring. Therefore, a syn/anti-conformation of the respective
triazenido ligands with torsion angles N–N–Cn1–Cn6 of approxi-
mately ꢁ55° and ꢁ141° is observed. Within the Tph- substituents
the arene rings of the C6H4 and Trip fragments possess an almost
orthogonal alignment with interplanar angles of 63.9° (C1n/C2n),
75.8° (C3n/C4n), 76.2° (C5n/C6n) and 68.8° (C7n/C8n).
The small variance of the Cu–N and N–N bond lengths with val-
ues in the range 1.878(2)–1.887(2) Å and 1.302(3)–1.315(3) Å indi-
cates a symmetric bonding situation. With 1.882 Å the average Cu–
N distance is almost identical to the corresponding values in the
two other structurally characterized copper(I) triazenides
[CuN3Ph2]2 (1.898(3) Å) [21] and [CuN3Dip2]2 (1.8818(16) Å) [22].
The observed Cu1ꢀꢀꢀCu2 contact distance of 2.4765(5) Å is typical
for dimeric copper complexes [23].
3.4. Structural studies of copper triazenides
Crystals suitable for X-ray diffraction experiments could be ob-
tained from n-heptane or n-heptane/toluene mixtures with excep-
tion of the isonitrile adduct 4a. For 5a co-crystallization of the used
solvent was observed. Since the structure refinement of complex
4b gave only poor results due to disorder of the copper atom, the
compound was recrystallized from benzene to give the packing
complex 4bꢀC6H6. Figs. 2–5 show the molecular structures of the
examined complexes, important bond parameters are summarized
in Table 3.
3.4.1. Molecular structure of the homoleptic copper triazenide
[CuN3Tph2] (2a)
The complex crystallizes as dimers without additional imposed
symmetry in the tetragonal space group P43 (Fig. 2). In the dimeric
units both two-coordinate metal atoms are bridged by two triazen-
ido ligands in a
l,
g1g1-fashion. The slight deviation from an al-
most linear coordination (N1–Cu1–N4: 169.36(11), N3–Cu2–N6:
3.4.2. Molecular structures of the isonitrile adducts
[Cu{N3(Dmp)Tph}(CNtBu)] (4b) and 4bꢀC6H6
Since the structural analysis of the solvent-free complex 4b is
hampered by disorder of the copper atom the following discussion
focusses on the molecular structure of the packing complex
4bꢀC6H6. The complex crystallizes with monomeric units in the
monoclinic space group P21/c (Fig. 3). The copper atom shows a lin-
ear coordination (C1–Cu–N3 = 173.73(5)°) by the Tph-substituted
nitrogen atom N3 and the carbon atom C1 of the isonitrile donor.
Table 4
m
(C„N)-vibrations in isonitrile adducts of copper complexes with different mono-
anionic N-donor ligands.
m
(C„N) (cmꢁ1
)
Compounds
References
2121
2126
2128
2138
2148
2155
2176
2193
[C{C(Me)N(Mes)}2]Cu(CNXyl)
[C{C(Me)N(Dip)}2]Cu(CNXyl)
[ClC{C(Me)N(Xyl)}2]Cu(CNXyl)
tBuNC
[C{C(Me)N(Mes)}2]Cu(CNtBu)
[HB(Pz)3]Cu(CNtBu)
[N{(C3F7)C(Dipp)N}2]Cu(CNtBu
4b
[20a]
[20b]
[20c]
[20d]
[20e]
[20f]
[20e]
this work
[20g]
The
g
1-coordination of the triazenido ligand is remarkable since
similiar isonitrile adducts of copper b-diketiminate always possess
an N,N-chelating binding mode [20a,b,c,e].
The higher nucleophilic character of N3 compared to the Dpp-
substituted nitrogen atom N1 may be explained by the stronger
2196
2199
2164/2210
[HB(3,5-(CF3)2Pz)3]Cu(CNtBu)
4a
[(CO)3Re(pz)3{M(CNcHex)}2]
this work
[20h]
overlap of the NNN and (C31 ? C36)-p-systems as indicated by
the different torsion angles N2–N1–C11–C16 [ꢁ42.77(17)°] and

H.S. Lee, M. Niemeyer / Inorganica Chimica Acta 374 (2011) 163–170
169
Fig. 2. Molecular structure of dimeric copper triazenide (2a)2 with thermal ellipsoids set to 50% probability. For clarity carbon atoms of iso-propyl groups are reduced in size
(left) and carbon atoms of Tph substituents have been omitted (right).
corresponding values in the three-nuclear complex [(CO)3Re(pz)3
{Cu(CNcHex)}2] (1.881(5), 1.834(7) and 1.151(8) Å) [20h] with a
structurally related N–Cu–C„N–R fragment. The copper b-diketi-
minate [(C{C(Me)N(Mes)}2)Cu(CNtBu)][20e] shows comparable
Cu–C and C„N bond distances of 1.8273(18) Å and 1.154(2) Å
but notably longer Cu–N distances of 1.9232(13) Å and 1.9604
(14) Å that may be attributed to the chelating coordination mode
of the b-diketiminato ligand.
In the molecular structure of the solvate-free isonitrile adduct
4b disorder of the copper atom is observed. Although refinement
with two split positions is possible, the anisotropic displacement
parameters indicate a shallow energy profile for the coordination
of the metal atom and a high mobility parallel to an imaginary axis
through the nitrogen atoms N1 and N3 (Fig. 4). The side occupation
factor of the minor site depends on the data collection temperature
and increases from 5% at ꢁ173 °C to 12% at ꢁ100 °C. Contrary to
the well ordered structure of 4bꢀC6H6 the disorder in 4b probably
arises from small conformational differences due to the cocrystal-
lized solvent. Apparently, the different NNCC torsion angles of
ꢁ37.3(2)° in 4b versus ꢁ42.77(17)° in 4bꢀC6H6 lead to a small
Fig. 3. Molecular structure of the isonitrile adduct 4bꢀC6H6 with thermal ellipsoids
set to 50% probability. Hydrogen atoms and the cocrystallized solvent have been
omitted.
but significant increase of the nucleophilicity of nitrogen atom N1.
3.4.3. Molecular structure of the triphenylphosphane adduct
[Cu{N3(Dmp)Tph}(PPh3)2]ꢀC7H8 (5aꢀtoluene)
N2–N3–C31–C36 [21.64(17)°]. A smaller torsion angle allows high-
The monomeric compound crystallizes as packing complex with
ꢀ
er transfer of electron density from the
p
-system of the C6H4 ring
toluene in the triclinic space group P1 (Fig. 5). The copper atom
to the adjacent nitrogen atom. The
g
1-coordination of the triazen-
possesses a severely distorted tetrahedral coordination with inter-
ido ligand accounts for significantly different N–N distances of
1.2816(16) Å (N1–N2) and 1.3354(16) Å (N2–N3). With bond leng-
hts of 1.8948(12) Å, 1.8337(15) Å, and 1.147(2) Å, respectively, the
Cu–N, Cu–C and C„N distances are almost identical to the
ligand angles in the range 59.06(8)–123.01(6)° by the two g
2-coor-
dinated nitrogen atoms N1 and N3 of the triazenido ligand and the
phosphorous atoms P1 and P2 of the two triphenylphosphane
donors. In an alternative description that assigns only one
Fig. 4. Molecular structures of the solvate-free isonitrile adduct 4b at ꢁ173 °C (left, ellipsoids with 50% probability) and ꢁ100 °C (right, ellipsoids with 30% probability).
Hydrogen atoms have been omitted. Side occupation factors for Cu2: 0.05 (ꢁ173 °C), 0.12 (ꢁ100 °C).

170
H.S. Lee, M. Niemeyer / Inorganica Chimica Acta 374 (2011) 163–170
Appendix A. Supplementary material
CCDC 800783, 800784, 800785, 800786, 800787 and 800788
contain the supplementary crystallographic data for compounds
1a, (2a)2, 3aꢀC7H8, 4b (at 100 K), 4b (at 173 K) and 4bꢀC6H6, respec-
tively. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.ica.2011.01.079.
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[11] (a) H. Hope, Progr. Inorg. Chem. 41 (1995) 1;
Fig. 5. Molecular structure of the bis(triphenylphosphane) adduct 3a with thermal
ellipsoids set to 30% probability. For clarity carbon atoms of iso-propyl groups and
PPh3 ligands are reduced in size and hydrogen atoms have been omitted.
(b) SHELXTL PC 5.03, Siemens Analytical X-Ray Instruments Inc., Madison, WI,
1994.;
coordination site, represented by N2, to the small-bite triazenido
ligand the copper atom shows a trigonal planar coordination with
interligand angles in the range 114.8(5)–122.3(5)°. According to
the torsion angles N2–N1–C11–C16 and N2–N3–C31–C36 of
ꢁ31.2(3)°, respectively ꢁ165.8(2)° a syn/anti-conformation of both
Tph substituents is realized.
(c) G.M. Sheldrick, SHELXL
, Program for Crystal Structure Solution and
Refinement, Universität Göttingen, 1997.
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(2009) 2326.
[13] S. Patai, Z. Rappoport, The Chemistry of Amidines and Imidates, Wiley,
Chichester, 1991.
The different Cu–N distances (Cu–N1 2.220(2) Å, Cu–N3
2.117(2) Å) indicate an asymmetric coordination of the triazenido
ligand while the coordination of the two triphenylphosphane do-
nors is rather symmetrical (Cu–P1 2.2706(9) Å, Cu–P2
2.2814(9) Å). The average Cu–N distances of 2.169 Å is widened
[14] A.G.M. Barrett, M.R. Crimmin, M.S. Hill, P.B. Hitchcock, G. Kociok-Köhn, P.A.
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(c) M. Hörner, L. Bresolin, J. Bordinhao, E. Hartmann, J. Strähle, Acta
Crystallogr., Sect. C 59 (2003) o426;
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Sect. C 61 (2005) o303.
by 0.28 Å compared to the corresponding distances in the
g
1-coor-
dinated complexes 2a and 4b. In some related PPh3 complexes, the
b-dialdiminate [{PhC(C(H)N(Ph))2}Cu(PPh3)2] [24] and the bi-nu-
clear oxalimidinate [(Ph3P)2Cu{(Tol)N}2CC{N(Tol)}2Cu(PPh3)2]
[25] Cu–N and Cu–P bond lengths of 2.053(3) Å and 2.292(1) Å,
respectively 2.063(5) Å and 2.291(2) Å are observed.
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In summary, we have used sterically crowded, triazenido li-
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adducts allowed for the first time to experimentally probe the do-
nor character of the triazenido ligands, which are as expected
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We thank the Deutsche Forschungsgemeinschaft (SPP 1166) for
financial support and Dr. Falk Lissner for the collection of three X-
ray data sets.