[3+2] Cycloaddition of ruthenium azido complex with ethyl propiolate and related reactions

Article abstract of DOI:10.1016/j.jorganchem.2018.01.049

The [3+2] cycloaddition reaction of ethyl propiolate with ruthenium azido complex [Ru]?N₃ (1, [Ru] = (η⁵-C₅H₅)(dppe)Ru, dppe = Ph₂PCH₂CH₂PPh₂) has been investigated. The metal-bound heterocyclic complex produced is N(2)-bound triazolate [Ru]N₃CHCO₂Et (2). A regiospecific alkylation happens by treatment of 2 with organic halides and gives a series of cationic N(1)-bound N(3)-alkylated-4-ethoxycarbonyl triazolato complexes {[Ru]N₃(R)C₂HCO₂Et}[X] (3a, R = CH₃, X = I; 3b, R = CH₂Ph, X = Br; 3c, R = CH₂C₆F₅, X = Br; 3d, R = CH₂CN, X = I; 3e, CH₂CO₂CH₃, X = Br) and the following cleavage of the Ru-N bond of 3a and 3b gives ruthenium halides and N(1)-alkylated five-membered-ring organic triazoles N₃(R)C₂HCO₂Et (4a, R = CH₃; 4b, R = CH₂Ph). The structures of 2 and 3c have been determined by single-crystal X-ray diffraction analysis.

Full text of DOI:10.1016/j.jorganchem.2018.01.049

Journal of Organometallic Chemistry 860 (2018) 72e77
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
[3þ2] Cycloaddition of ruthenium azido complex with ethyl
propiolate and related reactions
,
Chao-Wan Chang a *, Ying-Chih Lin b, Gene-Hsiang Lee b, Yu Wang b
a Division of Preparatory Programs for Overseas Chinese Students, National Taiwan Normal University, Linkou, New Taipei City, 24449, Taiwan, ROC
b Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
The [3þ2] cycloaddition reaction of ethyl propiolate with ruthenium azido complex [Ru]ꢀN3 (1, [Ru] ¼
(
h
5-C5H5)(dppe)Ru, dppe ¼ Ph2PCH2CH2PPh2) has been investigated. The metal-bound heterocyclic
Received 13 November 2017
Received in revised form
26 January 2018
Accepted 27 January 2018
Available online 16 February 2018
complex produced is N(2)-bound triazolate [Ru]N3CHCO2Et (2). A regiospecific alkylation happens by
treatment of 2 with organic halides and gives a series of cationic N(1)-bound N(3)-alkylated-4-
ethoxycarbonyl triazolato complexes {[Ru]N3(R)C2HCO2Et}[X] (3a, R ¼ CH3, X ¼ I; 3b, R ¼ CH2Ph,
X ¼ Br; 3c, R ¼ CH2C6F5, X ¼ Br; 3d, R ¼ CH2CN, X ¼ I; 3e, CH2CO2CH3, X ¼ Br) and the following cleavage
of the Ru-N bond of 3a and 3b gives ruthenium halides and N(1)-alkylated five-membered-ring organic
triazoles N3(R)C2HCO2Et (4a, R ¼ CH3; 4b, R ¼ CH2Ph). The structures of 2 and 3c have been determined
by single-crystal X-ray diffraction analysis.
Keywords:
1,3-Dipolar
Ruthenium triazolate
Triazole
© 2018 Elsevier B.V. All rights reserved.
Regiospecific alkylation
[3þ2] cycloaddition
Five-membered ring
1. Introduction
results of detailed synthetic and structural investigations herein.
Heterocycles are important compounds that can be found in
biomolecules [1e3] and applied widely in agricultural [4e7] and
medicinal [8e13]chemistry. 1,3-Dipolar cycloaddition [14e19] is a
common process to synthesize heterocycles in organic chemistry
while metal catalyzed cycloaddition [20e26] is popular in recent
years. Among various 1,3-dipoles, organic azides [14,16,19] are
particularly important for synthesizing heterocyclic compounds. By
analogy, coordinated azide in metal complexes can also undergo
cycloaddition [27e45]. Azido complexes have been reported to
react with alkynes and alkenes [28,33,37,39,40,46e48] to produce
triazolates. A survey [28] of the azido complexes known to take part
in cycloaddition reactions discloses that the metals involved are
most often palladium(II) [49], platium(II) [36], or cobalt(III) [39,50],
although a whole range of other transition metals [41,51e53] has
been used. In an earlier paper [54] we reported a series of [3þ2]
cycloaddition reactions of alkynes and alkenes with the ruthenium
azido complex. In this paper, a regiospecific alkylation of the 4-
substituted triazolate gives the exclusive N(1)-bound 3,4-
disubstituted triazolates in high yield. We now disclose the
2. Experimental section
2.1. General procedures
All manipulations were performed under nitrogen using
vacuum-line, dry box, and standard Schlenk techniques. CH2Cl2 was
distilled from CaH2 and diethyl ether and THF from sodium
diphenyketyl. All other solvents and reagents were of reagent grade
and were used without further purification. NMR spectra were
recorded on Bruker AM-300WB FT-NMR spectrometers at room
temperature (unless states otherwise) and are reported in units of
d
d
with residual protons in the solvents as an initial standard (CDCl3,
7.24: acetone-d6, 2.04). IR spectra were measured on a Perkin-
d
Elmer 983 instrument and referenced to a polystyrene standard,
using cells equipped with calcium fluoride windows. FAB mass
spectra were recorded on a JEOL SX-102A spectrometer. Complex
Cp(dppe)RuN3 (1) were prepared following the methods reported
in the literature [54]. Elemental analyses and X-ray diffraction
studies were carried out at the Regional Center of Analytical
* Corresponding author.
E-mail address: chang@ntnu.edu.tw (C.-W. Chang).
https://doi.org/10.1016/j.jorganchem.2018.01.049
0022-328X/© 2018 Elsevier B.V. All rights reserved.

C.-W. Chang et al. / Journal of Organometallic Chemistry 860 (2018) 72e77
73
Instrument located at the National Taiwan University.
2.2. Synthesis of N(2)-Bound Cp(dppe)RuN3C2HCO2Et (2)
In a Schlenk flask charged with Cp(dppe)RuN3 (1, 200.2 mg,
MS
(m/z,
Ru102):
886.1
Anal.
(MþꢀBr),
565.1
for
(MþꢀBrCH2C6F5ꢀN3C2HCO2Et).
Calcd.
C
43H37N3P2RuF5Br: C, 53.48; H, 3.86; N, 4.35. Found: C, 54.72; H,
4.01; N, 4.13. Spectroscopic data for 3d are as follows: 1H NMR
(CDCl3): 7.88 (s, 1H, CH), 7.56e7.21 (m, 20H, Ph), 5.05 (s, 2H,
d
0.330 mmol), ethyl propiolate (162 mg, 167
m
L, 1.652 mmol) and
NCH2), 4.79 (Cp), 4.34 (q, 2H, OCH2, JHꢀH ¼ 7.1 Hz), 3.01, 2.60 (2 m,
CH2Cl2 (20 mL) were added. The mixture was stirred at room
temperature for 12 h then the solvent was reduced to 2 mL under
vacuum. To the residue, 20 mL of n-pentane was added and gave
yellow precipitate. After filtration, the precipitate was washed
with 2 ꢁ 10 mL of n-pentane and dried under vacuum to give the
product Cp(dppe)RuN3C2HCO2Et (2) (199.2 mg, 0.283 mmol, 86%
yield). Spectroscopic data for 2 are as follows: IR (KBr, cmꢀ1):
2H, PCH2CH2P), 1.38 (t, 3H, CH3, JHꢀH ¼ 7.1 Hz). 31P NMR (CDCl3):
d
84.67.13C NMR (CDCl3):
d 155.7 (CO2), 145.8 (CH), 139.1e127.7 (Ph
and CCO2), 111.3 (CN), 82.0 (Cp), 63.6 (OCH2), 39.2 (NCH2), 29.0 (t,
PCH2, JC-P ¼ 22.7 Hz), 14.2 (CH3). MS (m/z, Ru102): 745.2 (MþꢀI),
565.1 (MþꢀIꢀtriazolato ring). Anal. Calcd. for C38H37N4P2O2RuI: C,
52.36; H, 4.28; N, 6.43. Found: C, 51.98; H, 4.53; N, 6.21. Spectro-
scopic data for 3e are as follows: 1H NMR (CDCl3):
d 7.86 (s, 1H,
n
(C]O) 1712 (vs),
n
(N]N) 1432 (vs),
n
(CꢀO) 1221 (m). 1H NMR
CH), 7.39e7.10 (m, 20H, Ph), 4.66 (Cp), 4.42 (s, 2H, NCH2), 4.17 (q,
2H, OCH2, JHꢀH ¼ 7.1 Hz), 3.48 (s, 3H, OCH3), 2.84, 2.59 (2 m, 2H,
PCH2CH2P), 1.23 (t, 3H, CH3, JHꢀH ¼ 7.1 Hz). 31P NMR (CDCl3):
(CDCl3):
d
7.44e7.08 (m, 20H, Ph), 7.03 (s, 1H, CH), 4.59 (Cp), 4.06
(q, 2H, OCH2, JHꢀH ¼ 7.1 Hz), 3.30e3.10, 2.70e2.50 (2 m,
PCH2CH2P), 1.18 (t, 3H, CH3, JHꢀH ¼ 7.1 Hz). 31P NMR (CDCl3):
d
84.26.13
C NMR (CDCl3): d 164.7, 156.1 (CO2), 145.0 (CH),
d
88.31.13C NMR (CDCl3):
d
162.1 (CO2), 143.1e127.6 (Ph), 137.9
139.1e127.7 (Ph), 137.4 (CCO2), 81.9 (Cp), 65.7 (NCH2), 62.8 (OCH2),
52.8 (OCH3), 28.7 (t, PCH2, JC-P ¼ 22.6 Hz), 15.1 (CH3). MS (m/z,
Ru102): 778.1 (MþꢀBr), 565.0 (MþꢀBrCH2CO2CH3ꢀN3C2HCO2Et).
Anal. Calcd. for C39H40N3P2O2RuBr: C, 54.62; H, 4.70; N, 4.90.
Found: C, 54.93; H, 4.95; N, 4.74.
(CCO2), 136.0 (CH), 82.0 (Cp), 59.2 (OCH2), 28.9 (t, PCH2, JC-
¼ 22.5 Hz), 14.3 (CH3). MS (m/z, Ru102): 705.1 (Mþ), 565.1
P
(MþꢀN3ꢀCH^CCO2Et). Anal. Calcd. for C36H35N3O2P2Ru: C,
61.36; H, 5.01; N, 5.96 Found: C, 61.67; H, 5.12; N, 5.67.
2.3. Synthesis of N(1)-Bound [Cp(dppe)RuN3(R)C2HCO2Et][X] (3a-
3e)
2.4. Synthesis of organic triazoles N3(CH3)C2HCO2Et (4a) and
N3(CH2Ph)C2HCO2Et (4b)
A Schlenk flask was charged with 2 (100.0 mg, 0.142 mmol) and
ICH3 (100.8 mg, 44.2 mL, 0.710 mmol), CH2Cl2 (20 mL) was added.
To a Schlenk flask charged with 2 (200.0 mg, 0.284 mmol) and
ICH3 (141.9 mg, 88.4 mL, 1.42 mmol), CH2Cl2 (20 mL) was added.
The resulting solution was stirred at room temperature for 24 h,
then the solvent was reduced to 2 mL under vacuum. To the res-
idue, 20 mL of n-pentane was added. The yellow precipitate thus
formed was filtered, washed with 2 ꢁ 10 mL of cold n-pentane and
dried under vacuum to give the product [Cp(dppe)RuN3(CH3)
C2HCO2Et][I] (3a) (104.6 mg, 0.124 mmol) in 87% yield. Spectro-
The resulting solution was stirred at room temperature for one
week then the solvent was dried under vacuum. To the residue,
10 mL of cold n-pentane was added. After filtration, the orange
precipitate was washed with 2 ꢁ 10 mL of n-pentane and dried
under vacuum to give the product Cp(dppe)RuI (182.2 mg,
0.264 mmol, 93% yield). The filtrate was dried and extracted with
2 ꢁ 10 mL of cold n-pentane. The extract was filtered and the
filtrate was dried under vacuum to give the colorless liquid
N3(CH3)C2HCO2Et (4a, 29.3 mg, 0.189 mmol, 66.5% yield). Spec-
scopic data for 3a are as follows: 1H NMR (CDCl3):
d 7.95 (s, 1H,
CH), 7.46e7.04 (m, 20H, Ph), 4.73 (Cp), 4.29 (q, 2H, OCH2,
JHꢀH ¼ 7.1 Hz), 3.27 (s, 3H, NCH3), 2.95, 2.65 (2 m, 2H, PCH2CH2P),
1.36 (t, 3H, CH3, JHꢀH ¼ 7.1 Hz). 31P NMR (CDCl3):
d
84.53.13C NMR
troscopic data for 4a are as follows: 1H NMR (CDCl3):
d 8.09 (s, 1H,
(CDCl3): d 156.2 (CO2), 145.1 (CH), 139.0e127.8 (Ph and CCO2), 81.8
CH), 4.36 (q, 2H, OCH2, JHꢀH ¼ 7.2 Hz), 4.30 (s, 3H, NCH3), 1.37 (t,
(Cp), 62.7 (OCH2), 37.6 (NCH3), 28.9 (t, PCH2, JC-P ¼ 22.7 Hz), 14.3
(CH3). MS (m/z, Ru102): 720.2 (MþꢀI), 565.1 (MþꢀIꢀtriazolato
ring). Anal. Calcd. for C37H38N3P2O2RuI: C, 52.49; H, 4.52; N, 4.96.
Found: C, 53.78; H, 4.86; N, 4.69. Complex [Cp(dppe)RuN3(CH2Ph)
C2HCO2Et][Br] (3b) (116.6 mg, 0.121 mmol, 85% yield from
100.1 mg of 2), [Cp(dppe)RuN3(CH2C6F5)C2HCO2Et][Br] (3c)
(106.9 mg, 0.111 mmol, 78% yield from 100.0 mg of 2), [Cp(dppe)
RuN3(CH2CN)C2HCO2Et][I] (3d) (114.1 mg, 0.131 mmol, 92% yield
from 100.2 mg of 2), [Cp(dppe)RuN3(CH2CO2CH3)C2HCO2Et)][Br]
(3e) (111.0 mg, 0.130 mmol, 91% yield from 100.2 mg of 2) were
prepared using the similar procedure as that of 3a. Spectroscopic
3H, CH3, JHꢀH ¼ 7.2 Hz). 13C NMR (CDCl3):
d 158.6 (CO2), 137.8 (CH),
137.2 (CCO2), 61.7 (OCH2), 37.4 (NCH3), 14.2 (CH3). MS (m/z): 156.1
(Mþþ1). Complex N3(CH2Ph)C2HCO2Et (4b) was prepared with
similar procedure as that of 4a to give a mixture of 4b and the
excess BrCH2Ph. Spectroscopic data for 4b are as follows: 1H NMR
(CDCl3):
d 8.13 (s, 1H, CH), 5.91 (s, 2H, NCH2), 4.33 (q, 2H, OCH2,
JHꢀH ¼ 7.1 Hz), 1.33 (t, 3H, CH3, JHꢀH ¼ 7.1 Hz). 13C NMR (CDCl3):
d
155.8 (CO2), 138.1 (CH), 135.3 (CCO2), 129.3e127.9 (Ph), 61.8
(OCH2), 53.3 (NCH2), 14.1 (CH3). MS (m/z): 232.1 (Mþþ1).
data for 3b are as follows: 1H NMR (CDCl3):
d
8.30 (s, 1H, CH),
2.5. X-ray analysis
7.52e6.41 (m, 25H, Ph), 4.86 (s, 2H, NCH2), 4.79 (Cp), 4.33 (q, 2H,
OCH2, JHꢀH ¼ 7.1 Hz), 2.80, 2.60 (2 m, 2H, PCH2CH2P), 1.40 (t, 3H,
Single crystals suitable for X-ray diffraction study were grown as
mentioned above. The chosen single crystal was glued to a glass
fiber and mounted on a SMART CCD or a CAD4 diffractometer. The
CH3, JHꢀH ¼ 7.1 Hz). 31P NMR (CDCl3):
d
85.80.13C NMR (CDCl3):
d
156.5 (CO2), 145.8 (CH), 139.3e127.8 (Ph and CCO2), 82.2 (Cp),
62.8 (OCH2), 53.6 (NCH2), 28.7 (t, PCH2, JC-P ¼ 22.5 Hz), 13.9 (CH3).
data were collected using 3 kW sealed-tube molybdenum K
a ra-
MS
(m/z,
Ru102):
796.1
(MþꢀBr),
565.1
diation (
l
¼ 0.7107 Å). Intensity was intergrated and absorption
(MþꢀBrCH2PhꢀN3C2HCO2Et). Anal. Calcd. for C43H42N3P2O2RuBr:
corrections were applied using SADABS [57]. Data were processed
and refined by using SHELXTL [58] program. Hydrogen atoms were
placed geometrically using the riding model with thermal param-
eters set to 1.2 times that for the atoms to which the hydrogen is
attached and 1.5 times that for the methyl hydrogens. Crystal data
of 2 and 3c are listed in Table 1. Final values of all refined atomic
positional parameters (with esd's) and tables of thermal parame-
ters are given in the Supporting Information.
C, 58.98; H, 4.83; N, 4.80. Found: C, 59.35; H, 4.98; N, 4.65.
Spectroscopic data for 3c are as follows: 1H NMR (CDCl3):
d 8.43 (s,
1H, CH), 7.36e7.06 (m, 20H, Ph), 5.01 (s, 2H, NCH2), 4.76 (Cp), 4.43
(q, 2H, OCH2, JHꢀH ¼ 7.1 Hz), 2.77, 2.72 (2 m, 2H, PCH2CH2P), 1.48 (t,
3H, CH3, JHꢀH ¼ 7.1 Hz). 31P NMR (CDCl3):
d
86.12.13C NMR (CDCl3):
156.4 (CO2), 145.4 (CH), 139.9e128.2 (Ph and CCO2), 82.4 (Cp),
d
63.2 (OCH2), 39.6 (NCH2), 28.8 (t, PCH2, JC-P ¼ 22.5 Hz), 13.7 (CH3).

74
C.-W. Chang et al. / Journal of Organometallic Chemistry 860 (2018) 72e77
Table 1
Crystal and intensity collection data for complexes 2 and 3c.
Identification code
2
3c
Emperical formula
Formula weight
Temperature, K
Wavelength, Å
Crystal system
Space group
a, Å
C36H35N3O2P2Ru
704.68
295(2)
0.71073
monoclinic
P21/C
11.32500(10)
17.3080(2)
16.4280(2)
90
97.1970(10)
90
3202.35(6)
4
1.462
0.627
C43H37F11N3O2P3Ru
1030.74
150(1)
0.71073
monoclinic
Cc
18.1148(2)
15.2868(2)
17.5414(2)
90
118.0954(5)
90
4285.13(9)
4
1.598
0.567
2080
b, Å
c, Å
a
b
g
, deg
, deg
, deg
V, Å3
Z
Density (calcd), Mg/m3
Absorption coeff, mmꢀ1
F(000)
1448
Crystal size
0.30 ꢁ 0.25 ꢁ 0.10 mm 0.35 ꢁ 0.24 ꢁ 0.20 mm
q
Range, deg
3.13 to 27.48
ꢀ14ꢃ h ꢃ 14
ꢀ20 ꢃ k ꢃ 22
ꢀ21 ꢃ l ꢃ 21
23095
1.84 to 27.50
ꢀ23ꢃ h ꢃ 22
ꢀ19 ꢃ k ꢃ 19
ꢀ19 ꢃ l ꢃ 22
23175
Limiting indices
Reflections collected
Independent reflections
GOFa on F2
7302(R(int) ¼ 0.0414)
8314(R(int) ¼ 0.0572)
1.018
1.051
Fig. 1. ORTEP drawing of 2; thermal ellipsoids are drawn at the 30% probability level.
Max. and min. transmission 0.934, 0.769
0.896, 0.808
R1 ¼ 0.0402
wR2 ¼ 0.0866
R1 ¼ 0.0621,
wR2 ¼ 0.1006
0.634, ꢀ0.773
R (I > 2
s
(I))
R1 ¼ 0.0328,
wR2 ¼ 0.0686
R1 ¼ 0.0505,
wR2 ¼ 0.0764
0.308, ꢀ0.406
pattern resonances appearing at
d
4.06 (q, 2H, OCH2, JH-H ¼ 7.1 Hz)
R (all data)
and
d
1.18 (t, 3H, CH3, JH-H ¼ 7.1 Hz) attributed to ethoxycarbonyl
peak, hole, e Åꢀ3
group. The FAB mass spectrum displays parent peak at m/z 705.1.
Complex 2 was recrystallized from a mixture of CHCl3 and hexane
(1:5) at 5 ꢂC, and the molecular structure was determined by an X-
ray diffraction study; an ORTEP drawing of 2 is shown in Fig. 1 and
selected bond distances and bond angles are given in Table 2. The
triazolato ligand is N(2)-bound to ruthenium. The bond distance of
Ru-N(2) (2.091(2) Å) is typical of a Ru-N single bond. The N(1)-N(2),
N(2)-N(3), N(3)-C(1), N(1)-C(2) and C(1)-C(2) bond lengths of
1.343(3), 1.330(3), 1.357(3), 1.330(3) and 1.372(3) Å, respectively, all
displaying partial double-bond character, are indicative of several
resonance contributions and the five-membered triazolato ring is
essentially planar. The N(1)-N(2)-N(3), N(2)-N(3)-C(1), N(2)-N(1)-
C(2), N(3)-C(1)-C(2) and N(1)-C(2)-C(1) bond angles of 112.7(2)ꢂ,
105.1(2)ꢂ,105.1(2)ꢂ,107.8(2)ꢂ and 109.3(2)ꢂ, respectively, indicate the
irregular pentagonal structure of the five-membered triazolato ring.
a
GOF ¼ [S[w(F2o-F2c)2]/(n-p)]1/2, where n and p denote the number of data and
parameters. R1
¼
(SjjFojꢀjFcjj)/SjFoj, wR2 ¼ [S[w(F2o-Fc2)2]/S[w(Fo2)2]]1/2 where
w ¼ 1/[sqꢄꢃ (F2o)þ (0.0639P)2 þ 1.2129P] and P ¼ (Fo2 þ 2F2c)/3.
2
3. Results and discussion
3.1. Reaction of 1 with ethyl propiolate
Treatment of [Ru]-N3 (1) [54] with a 5-fold excess of ethyl pro-
piolate in CH2Cl2 at room temperature for 8 h affords the [3þ2]
cycloaddition product, the N(2)-bound 4-ethoxycarbonyl-1,2,3-
triazolato complex [Ru]N3C2HCO2Et (2), with 83% isolated yield
(Scheme 1). By monitoring the reaction with 31P NMR spectroscopy,
two singlet resonances at d 88.2 and 88.3 attributed to the N(1)- and
N(2)-bound isomers, respectively, were observed at the initial stage
of the reaction. The N(1)-bound isomer converted to the N(2)-bound
isomer in 12 h at room temperature. The 1H NMR spectrum of 2
3.2. Reactions of 2 with electrophiles
displays a characteristic singlet resonance at
d 7.03 assigned to CH, a
Treatment of 2 with a 5-fold excess of BrCH2C6F5 in CH2Cl2 at
room temperature for 24 h yields exclusively an N(1)-bound N(3)-
singlet resonance at 4.59 attributed to Cp and two sets of AX
d
Scheme 1.

C.-W. Chang et al. / Journal of Organometallic Chemistry 860 (2018) 72e77
75
Table 2
Selected bond distances (Å) and angles (deg) of 2.
RuꢀN2
N1ꢀN2
N2ꢀN3
N3ꢀC1
N1ꢀC2
C1ꢀC2
2.091(2)
1.343(3)
1.330(3)
1.357(3)
1.330(3)
1.372(3)
C1ꢀC3
C3ꢀO1
C3ꢀO2
O2ꢀC4
C4ꢀC5
1.462(3)
1.198(3)
1.351(3)
1.453(3)
1.465(5)
P1ꢀRuꢀP2
N2ꢀRuꢀP1
N2ꢀRuꢀP2
RuꢀN2ꢀN1
RuꢀN2ꢀN3
N2ꢀN3ꢀC1
N1ꢀN2ꢀN3
N2ꢀN1ꢀC2
83.58(2)
90.26(5)
89.46(5)
124.7(2)
122.51(14)
105.1(2)
112.7(2)
105.1(2)
N3ꢀC1ꢀC2
N1ꢀC2ꢀC1
C1ꢀC3ꢀO1
C1ꢀC3ꢀO2
O1ꢀC3ꢀO2
C3ꢀO2ꢀC4
O2ꢀC4ꢀC5
107.8(2)
109.3(2)
126.5(3)
110.0(2)
123.5(3)
116.7(2)
109.6(3)
Scheme 2.
alkylated-4-ethoxycarbonyl triazolato complex {[Ru]N3(CH2C6F5)
C2HCO2Et}[Br] (3c) with 78% isolated yield (Scheme 2). For the
N(2)-bound triazolato complex 2, the alkylation might have
occurred at one of the two nitrogens, the N(1) nitrogen eith less
steric hindrance or the N(3) nitrogen with the more nucleophi-
licity. From the NMR spectra it is hard to determine the absolute
structure of 3c. To make crystals suitable for single-crystal X-ray
diffraction analysis, we changed the counterion Brꢀ to PF6ꢀ. Finally,
the structure of 3c was confirmed to be a N(1)-bound N(3)-alky-
lated-4-ethoxycarbonyl triazolate by
a single-crystal X-ray
diffraction study; An ORTEP diagram is shown in Fig. 2 and
selected bond distances and bond angles are given in Table 3. The
planar five-membered triazolato ring is coordinated to the Ru
center via the N(1) atom. The RuꢀN(1) distance of 2.093(4) Å is
typical of a RuꢀN single bond. The N(1)ꢀN(2), N(2)ꢀN(3) dis-
tances of 1.321(5) Å and 1.347(5) Å, respectively, are both between
NꢀN double bond and single bond. The bond distances N(3)ꢀC(1),
N(1)ꢀC(2) and C(1)ꢀC(2) of 1.358(6), 1.351(5) and 1.364(6) Å,
respectively, show partial double bond character, suggesting the
delocalized
p bonding mode of the triazolato ring and indicating
the ring is essentially planar. The N(1)-N(2)-N(3), N(2)-N(3)-C(1),
C(2)-N(1)-N(2), N(3)-C(1)-C(2) and N(1)ꢀC(2)ꢀC(1) bond angles
of 106.3(3)ꢂ, 110.9(4)ꢂ, 109.7(4)ꢂ, 104.7(4)ꢂ and 108.4(4)ꢂ, respec-
tively, all in a reasonable range, indicating a irregular pentagonal
structure of the five-membered triazolato ring. From the ORTEP
drawing we found that the alkylation occurred at the more
nucleophilic N(3) nitrogen atom and transformed to a less hin-
dered N(1)-bound structure, the same result as that we found
before [54]. Some regiospecific alkylations of triazoles and tetra-
zoles were reported [39,55,56], but to our knowledge, such an
alkylation of triazolates was not ever seen until we did it. Similar
reactions of 2 with other organic halides also give exclusively
cationic N(1)-bound N(3)-alkylated-4-ethoxycarbonyl triazolato
complexes {[Ru]N3(R)C2HCO2Et}[X] (3a, R ¼ CH3, X ¼ I; 3b,
R ¼ CH2Ph, X ¼ Br; 3d, R ¼ CH2CN, X ¼ I; 3e, R ¼ CH2CO2CH3,
X ¼ Br) with high yields (Scheme 2).
3.3. Formation of free organic triazoles
Fig. 2. ORTEP drawing of 3c; thermal ellipsoids are drawn at the 50% probability level.
Complexes 3a-3e are stable in air but unstable in solutions.

76
C.-W. Chang et al. / Journal of Organometallic Chemistry 860 (2018) 72e77
Table 3
Selected bond distances (Å) and angles (deg) of 3c.
RuꢀP1
RuꢀN1
N1ꢀN2
N1ꢀC2
C1ꢀC3
O2ꢀC3
C6-C7
2.2905(12)
2.093(4)
1.321(5)
1.351(5)
1.485(6)
1.326(6)
1.504(7)
RuꢀP2
N2ꢀN3
N3ꢀC1
C1ꢀC2
O1ꢀC3
N3ꢀC6
2.2967(14)
1.347(5)
1.358(6)
1.364(6)
1.195(6)
1.463(6)
P1ꢀRuꢀP2
N1ꢀRuꢀP2
RuꢀN1ꢀC2
N2ꢀN3ꢀC1
N3ꢀC1ꢀC2
C2ꢀC1ꢀC3
O1ꢀC3ꢀO2
O2ꢀC3ꢀC1
83.44(5)
88.34(10)
128.1(3)
110.9(4)
104.7(4)
131.6(4)
126.0(4)
108.7(4)
N1ꢀRuꢀP1
RuꢀN1ꢀN2
N1ꢀN2ꢀN3
C2ꢀN1ꢀN2
N3ꢀC1ꢀC3
N1ꢀC2ꢀC1
O1ꢀC3ꢀC1
N3ꢀC6ꢀC7
93.75(11)
122.1(3)
106.3(3)
109.7(4)
123.7(4)
108.4(4)
125.2(5)
109.2(4)
3.4. Conclusion
The reaction of ruthenium azido complex [Ru]ꢀN3 (1, [Ru] ¼ (h5
-
C5H5)(dppe)Ru, dppe ¼ Ph2PCH2CH2PPh2) with ethyl propiolate
yields a [3þ2] cycloaddition product [Ru]N3C2HCO2Et (2). A regio-
specific alkylation of 2 with organic halides yields a series of
cationic N(1)-bound N(3)-alkylated-4-ethoxycarbonyl triazolato
complexes {[Ru]N3(R)C2HCO2Et}[X] (3a, R ¼ CH3, X ¼ I; 3b,
R ¼ CH2Ph, X ¼ Br; 3c, R ¼ CH2C6F5, X ¼ Br; 3d, R ¼ CH2CN, X ¼ I; 3e,
CH2CO2CH3, X ¼ Br) exclusively with high yields and the following
Ru-N bond-breaking produces free five-membered-ring organic
triazoles N3(R)C2HCO2Et (4a, R ¼ CH3; 4b, R ¼ CH2Ph). A new
method of synthesis is proceeding by removing the heterocyclic
five-membered-ring triazolato ligands of ruthenium complexes,
thus form a reaction cycle (Scheme 3).
Acknowledgment
We are grateful for support of this work by the National Science
Council, Taiwan, Republic of China.
Scheme 3.
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