Synthesis, structures and catalytic activity of 1,3-bis(aryl)triazenide(p-cymene)ruthenium(II) complexes

Article abstract of DOI:10.1016/j.ica.2016.03.004

The synthesis, characterization, crystal structures and catalytic activity of four new 1,3-bis(aryl)triazenide(p-cymene)ruthenium(II) complexes bearing methoxycarbonyl (5), hydroxymethyl (6), acetylphenyl (7) in the ortho position, and methyl in the para position (8) of the bis(aryl)triazenide ligand are reported. These complexes were used as catalysts in the transfer hydrogenation reactions of ketones and alkenone with good to excellent yields of the corresponding alcohol. Remarkable differences in yields were obtained with those complexes with ortho substituents on the aryl group of the triazenide ligand (5-7) compared to that without ortho substituent (8). Good selectivity was also observed in the reduction of the alkenone towards the carbonyl group.

Full text of DOI:10.1016/j.ica.2016.03.004

Accepted Manuscript
Synthesis, structures and catalytic activity of 1,3-bis(aryl)triazenide(p-cym-
ene)ruthenium(II) complexes
Erick Correa-Ayala, Aida Valle-Delgado, Gustavo Ríos-Moreno, Daniel
Chávez, David Morales-Morales, Simón Hernández-Ortega, Juventino García,
Marco Flores-Álamo, Valentín Miranda-Soto, Miguel Parra-Hake
PII:
S0020-1693(16)30096-2
http://dx.doi.org/10.1016/j.ica.2016.03.004
ICA 16939
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
13 January 2016
1 March 2016
3 March 2016
Please cite this article as: E. Correa-Ayala, A. Valle-Delgado, G. Ríos-Moreno, D. Chávez, D. Morales-Morales,
S. Hernández-Ortega, J. García, M. Flores-Álamo, V. Miranda-Soto, M. Parra-Hake, Synthesis, structures and
catalytic activity of 1,3-bis(aryl)triazenide(p-cymene)ruthenium(II) complexes, Inorganica Chimica Acta (2016),
doi: http://dx.doi.org/10.1016/j.ica.2016.03.004
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Synthesis, structures and catalytic activity of 1,3-bis(aryl)triazenide(p-
cymene)ruthenium(II) complexes
Erick Correa-Ayalaa, Aida Valle-Delgadoa, Gustavo Ríos-Morenob, Daniel Cháveza, David
Morales-Moralesc, Simón Hernández-Ortegac, Juventino Garcíad, Marco Flores-Álamod,
Valentín Miranda-Sotoa,*, Miguel Parra-Hakea,*
a Centro de Graduados e Investigación, Instituto Tecnológico de Tijuana, Apartado Postal 1166, Tijuana, B.C. 22000, México
b Unidad Académica de Ciencias Químicas, Universidad Autónoma de Zacatecas, Campus Siglo XXI. Carretera a Guadalajara Km.
6, Ejido La Escondida, Zacatecas 98160, México
cInstituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior.Cd. Universitaria Coyoacán, México D.F.
04510, México
dFacultad de Química, Universidad Nacional Autónoma de México, Circuito Exterior Cd. Universitaria Coyoacán, México D.F.
04510, México
Abstract
The synthesis, characterization, crystal structures and catalytic activity of four new 1,3-
bis(aryl)triazenide(p-cymene)ruthenium(II) complexes bearing methoxycarbonyl (5),
hydroxymethyl (6), acethylphenyl (7) in the ortho position, and methyl in the para position (8)
of the bis(aryl)triazenide ligand are reported. These complexes were used as catalysts in the
transfer hydrogenation reactions of ketones and alkenenone with good to excellent yields of the
corresponding alcohol. Remarkable differences in yields were obtained with those complexes
with ortho substituents on the aryl group of the triazenide ligand (5-7) compared to that without
ortho substituent (8). Good selectivity was also observed in the reduction of the alkenone
towards the carbonyl group.
1. Introduction
For the last decades, coordination and organometallic chemistry have
focused on the design and development of alternative ligands to stabilize metal
complexes and control their reactivity. With this in mind we have directed our
attention to ligands of the type 1,3-bis(aryl)triazenide, since they exhibit a
variety of bonding modes with distinct properties [1,2]. Triazenide ligands can
act as monodentate binding through a terminal [3,4] or central nitrogen [5,6] as
bidentate to form a chelate [7,8], bidentate bridging two metal centers [9,10] or
tricoordinate bridges [11] and tetracoordinate bridges [12] (Fig. 1).

M
N
Ar
N
N
Ar
Ar
N
Ar
Ar
Ar
Ar
Ar
N
N
N
N
N
H
N
N
M
N
Ar
Ar
N
Ar
Ar
N
N
N
N
N
M
M
M
M
M
Figure 1. A generic triazene and binding modes of triazenide ligands.
It can be expected that incorporation of donor groups at the ortho position of the
1,3-bis(aryl)triazenide would produce a markedly different coordination
chemistry. Thus we have turned our attention to the application of 1,3-
bis(aryl)triazenide ligands bearing Lewis basic ortho substituents [13-17],
expecting that they influence the electronic and steric properties of their
complexes, which in turn determine their catalytic activity.
On the other hand, p-cymene complexes of ruthenium with 1,3-
bis(aryl)triazenide as supporting ligands are attracting current interest from the
point of view of their synthesis and structure, as catalysts in hydrogenation of
enones, and anticancer activity. In this context, Strähle and coworkers reported
the synthesis and structure of the first complex of this type, [RuCl(η2-1,3-
ClC6H4NNNC6H4Cl)(η6-p-cymene)] [18]. More recently, Albertin and
coworkers, reported neutral complexes [RuCl(η2-1,3-ArNNNAr)(η6-p-cymene)],
their structures and catalytic activity on hydrogenation of 2-cyclohexen-1-one
and cynamaldehyde under H2 pressure [19]. Košmrlj, Osmak and coworkers
have reported a series of 1,3-bis(aryl)triazenide(p-cymene)ruthenium(II)
complexes with a high in vitro anticancer activity as the first study on the
biological properties of this class of complexes [20].

Here we report on the synthesis of four complexes of formula [RuCl(η2-1,3-
ArNNNAr)(η6-p-cymene)] (Ar = o-COOCH3, o-CH2OH, o-COCH3 and p-tolyl)
and their X-ray molecular structures. The catalytic activity of these complexes in
the transfer hydrogenation of ketones and enones was evaluated with excellent
results.
2. Experimental Section
2.1. General comments
All synthetic work was carried out in air or under argon using standard Schlenk
techniques or an inert atmosphere dry-box where indicated. All solvents were dried over
appropriate drying agents. RuCl3•3H2O (Aldrich) and other reagents are commercially
available and were used as received. [RuCl2(p-cymene)]2 [21], 1,3-bis[2´-
(methoxycarbonyl)phenyl]triazene (1) [22], {1-[2-(hydroxymethyl)phenyl]-3-[4-
methylphenyl]}triazene (2) [17] and 1,3-bis(4'-methylphenyl)triazene (4) [23] were
synthesized according to previously reported procedures. NMR spectra were recorded at
1
400 MHz with Bruker Avance III spectrometer at 30 °C unless otherwise specified. H
and 13C NMR chemical shifts are reported in ppm referenced to residual solvent
resonances (1H NMR: 7.16 for C6HD5 in C6D6, 1.94 for CHD2CN in CD3CN, 2.05 for
acetone-d5 in acetone-d6. 13C NMR: 128.39, 1.39, and 29.92 for benzene-d6,
acetonitrile-d3 and acetone-d6, respectively). Coupling constants J are given in Hertz
(Hz). IR spectra were recorded on a Perkin-Elmer FT-IR 1605 spectrophotometer.
Melting points were measured in an Electrothermal GAC 88629 apparatus. High
Resolution Mass Spectrometry (HRMS) data were obtained in a micrOTOF-Q III MS
instrument with electrospray ionization using sodium formate as calibrant.

2.2. Ligands
2.2.1. 1,3-bis(2´-acethylphenyl)triazene (3)
At −5 °C, 2’-aminoacetophenone (2.22 g, 16.4 mmol) was mixed with an excess of
isoamyl nitrite (1.92 g, 16.4 mmol) in toluene (18 mL), and vigorously stirred for 24 h.
The reaction mixture was dried over MgSO4. The product was purified by
crystallization at −5 °C from a 9:1 toluene/hexane mixture to obtain an amber
crystalline solid (1.55 g, 5.53 mmol, 67%). MP = 118-120 °C; IR (ATR): 3188, 3000,
2950, 1665, 1648, 1576, 1505, 1462, 1429, 1255, 1230, 1186, 1161, 758 cm−1. 1H NMR
[CD3CN, 400 MHz]: δ 13.15 (s, 1H, NH), 8.04 (dd, J = 8.0, 1.2 Hz, 1H, ArB6), 7.90 (d,
J = 8.4 Hz, 1H, ArB3), 7.64 (d, J = 8.0 Hz, 1H, ArA3), 7.61 (td, J = 8.0, 1.6 Hz, 1H,
ArB4), 7.55 (td, J = 8.0, 1.6 Hz, 1H, ArA4), 7.52 (d, J = 8.0 Hz, 1H, ArA6), 7.39 (td, J =
7.0, 1.2 Hz, 1H, ArA5), 7.17 (td, J = 7.8, 1.2 Hz, 1H, ArB5), 2.66 (s, 3H, O=C-CH3(B1)),
2.51 (s, 3H, O=C-CH3(A1)). 13C {1H} NMR [CD3CN, 100 MHz]: δ 203.6 (CB7=O), 203.2
(CA7=O), 148.3 (CA2-N), 143.7 (CB2-N), 137.4 (CA1-C=O), 136.1 (CB4-H), 133.4 (CB6-
H), 132.4 (CA4-H), 128.9 (CA6-H), 128.8 (CA5-H), 122.9 (CB5-H), 120.8 (CA3-H), 120.3
(CB1-C=O), 115.2 (CB3-H), 32.4 (CA8-C=O), 28.8 (CB8-C=O). HRMS (ESI-TOF) m/z:
[M + Na]+ Calcd for C16H15N3O2Na 304.1056; Found 304.1063.
2.3. Synthesis of complexes
2.3.1. [Ru{1,3-bis[2´-(methoxycarbonyl)phenyl]triazenide}(Cl)(p-cymene)] (5)
1,3-bis[2´-(methoxycarbonyl)phenyl]triazene (1) (62.6 mg, 0.2 mmol) was dissolved in
CH2Cl2 (5 mL) and triethylamine (56.8 µL, 0.4 mmol) was added with stirring. Then, a

solution of [RuCl2(p-cymene)]2 (61.2 mg, 0.1 mmol) in CH2Cl2 (5 mL) was slowly
added and the mixture stirred for 24 h at room temperature. A dark orange solution was
formed, which was filtered through an alumina column. The solvent was removed under
reduced pressure to obtain a red solid. Recrystallization by vapor diffusion of hexane
into a concentrated solution of the product in THF at room temperature gave red
crystals, suitable for X-ray diffraction analysis (85.6 mg, 0.15 mmol, 73%). MP = 136-
140 °C. IR(ATR): 3062, 2962, 1720, 1593, 1432, 1382, 1294, 1247, 1082, 767, 721
1
cm−1. H NMR [C6D6, 400 MHz]: δ 7.50 (dd, J = 7.6, 1.6 Hz, 2H, ArA3), 7.45 (dd, J =
8.0, 0.8 Hz, 2H, ArA6), 7.12 (td, J = 8.0, 1.6 Hz, 2H, ArA4), 6.80 (td, J = 7.6, 0.8 Hz, 2H,
ArA5), 5.16 (d, J = 6.0 Hz, 2H, p-CymC2,6), 4.83 (d, J = 6.0 Hz, 2H, p-CymC3,5), 3.69 (s,
6H, -OCH3(A8)), 2.68 (sept, J = 6.8 Hz, 1H, p-Cym-CH(C7)-(CH3)2), 1.92 (s, 3H, p-Cym-
13
CH3(C10)), 1.01 (d, J = 6.8 Hz, 6H, CH-CH3(C8,9)). C {1H} NMR [C6D6, 100 MHz]: δ
169.1 (CA7=O), 147.2 (CA2-COOCH3), 131.6 (CA4-H), 130.0 (CA3-H), 125.0 (CA1-N),
125.0 (CA5-H), 124.5 (CA6-H), 103.2 (CC1-CH(CH3)2), 99.3 (CC4-CH3), 82.0 (CC2,6-H),
80.4 (CC3,5-H), 52.4 (-OCH3(A8)), 31.8 (p-Cym-CH(C7)-(CH3)2), 22.8 (CH-CH3(C8,9)), 19.2
(Ar-CH3(C10)). HRMS (ESI-TOF) m/z: [M + Na]+ Calcd for C26H28ClN304RuNa
606.0708; Found 606.0706. Anal. Calcd for C26H28ClN3O4Ru (583.04): C, 53.56; H,
4.84; N, 7.21. Found: C, 53.35; H, 4.77; N, 6.93.
2.3.2. [Ru{1-[2-(hydroxymethyl)phenyl]-3-[4-methylphenyl]triazene}(Cl)(p-cymene)]
(6)

Complex 6 was prepared in the same manner as complex 5, using triazene 2 to obtain a
solid which was crystallized by slow diffusion of hexane in a concentrated solution of
the product in benzene at room temperature to give red crystals suitable for X-ray
diffraction analysis (0.078 g, 0.12 mmol, 74%). MP = 71-74 °C. IR(ATR): 3395, 3026,
2962, 1597, 1503, 1448, 1273, 1032, 814, 755, 637 cm−1. 1H NMR [C6D6, 400 MHz]: δ
7.44 (d, J = 7.2 Hz, 1H, ArA6), 7.40 (d, J = 7.2 Hz, 1H, ArA3), 7.36 (d, J = 8.0 Hz, 2H,
ArB2,6), 7.24 (t, J = 7.2 Hz, 1H, ArA5), 7.03 (t, 3H, ArA4), 7.01 (d, J = 8.0 Hz, 2H,
ArB3,5), 5.02 (d, J = 5.6 Hz, 1H, p-CymC6), 4.90 (m, 1H, p-CymC2), 4.90 (m, 2H, Ar-
CH2(A7)-OH), 4.62 (d, J = 5.6 Hz, 1H, p-CymC3), 4.58 (d, J = 5.6 Hz, 1H, p-CymC5),
3.40 (s, 1H, -OHA8), 2.32 (sept, J = 6.8 Hz, 1H, p-Cym-CH(C7)-(CH3)2), 2.14 (s, 3H, Ar-
CH3(B7)), 1.91 (s, 3H, Ar-CH3(C2)), 0.86 (d, J = 6.8 Hz, 3H, CH-CH3(C8)), 0.84 (d, J = 6.8
1
Hz, 3H, CH-CH3(C9)). H NMR [CD3CN, 400 MHz]: δ 7.42 (dd, J = 7.6, 1.2 Hz, 1H,
Ar), 7.33 (ddd, J = 7.2, 1.6 Hz, 1H, Ar), 7.25 (dd, J = 8, 1.2 Hz, 1H, Ar), 7.16 (m, 5H,
Ar), 5.89 (d, J = 5.2 Hz, 1H, p-Cym), 5.77 (d, J = 6.8 Hz, 1H, p-Cym), 5.42 (d, J = 6.4
2
2
Hz, 2H, p-Cym), 4.68 (dd, JHH = 13.6, 3JHH = 7.2 Hz, 1H, Ar-CH2-OH), 4.58 (dd, JHH
= 13.6, 3JHH = 6 Hz, 1H, Ar-CH2-OH), 3.30 (dd, J = 7.2, 6.4 Hz, 1H, OH), 2.67 (sept, J
= 7.2 Hz, 1H, p-Cym-CH-(CH3)2), 2.33 (s, 3H, Ar-CH3), 2.23 (s, 3H, Ar-CH3), 1.18 (d,
J = 6.9 Hz, 3H, CH-CH3), 1.16 (d, J = 6.9 Hz, 3H, CH-CH3). 13C {1H} NMR [C6D6,
100 MHz]: δ 147.2 (CA1-N), 145.6 (CB1-N), 134.1 (CB4-CH3), 132.9 (CA2-CH2OH),
131.1 (CA3-H), 129.8 (CB3,5-H), 128.4 (CA5-H), 125.1 (CA4-H), 122.5 (CA6-H), 117.7
(CB2,6-H), 102.5 (CC1-CH(CH3)2), 101.7 (CC4-CH3), 81.7 (CC2-H), 81.1 (CC6-H), 79.9
(CC3-H), 79.1 (CC5-H), 62.8 (Ar-CH2(A7)-OH), 31.7 (p-Cym-CH(C7)-(CH3)2), 22.5 (CH-
CH3(C8)), 22.4 (CH-CH3(C9)), 21.0 (Ar-CH3(B7)), 19.0 (p-Cym-CH3(C10)). HRMS (ESI-
TOF) m/z: [M + Na]+ Calcd for C24H28ClN3ORuNa 534.0860; Found 534.0861.

2.3.3. [Ru{1,3-bis(2´-acethylphenyl)triazenide}(Cl)(p-cymene)] (7)
Complex 7 was prepared in the same manner as complex 5, using triazene 3 to obtain a
solid which was crystallized by slow evaporation of a concentrated solution of the
product in THF at room temperature to give amber crystals suitable for X-ray
diffraction analysis (83.2 mg, 0.15 mmol, 76%). MP = 126-131 °C. IR(ATR): 3060,
2964, 1699, 1593, 1432, 1382, 1294, 1247, 1082, 767, 721 cm−1. 1H NMR [acetone-d6,,
400 MHz]: δ 7.42 (td, J = 6.8, 1.6 Hz, 2H, ArA5), 7.36 (dd, J = 8.0, 1.2 Hz, 2H, ArA6),
7.23 (dd, J = 7.6, 1.6 Hz, 2H, ArA3), 7.17 (td, J = 6.8, 1.6 Hz, 2H, ArA4), 5.99 (d, J = 6.4
Hz, 2H, p-CymC2,6), 5.67 (d, J = 6.4 Hz, 2H, p-CymC3,5), 2.90 (sept, J = 6.8 Hz, 1H, p-
Cym-CH(C7)-(CH3)2), 2.30 (s, 3H, p-Cym-CH3(C10)), 2.30 (s, 6H, O=C-CH3(A8)), 1.29 (d,
J = 6.8 Hz, 6H, CH-CH3(C8,9)). 13C {1H} NMR [acetone-d6, 100 MHz]: δ 202.8 (CA7=O),
145.5 (CA1-N), 133.7 (CA2-COCH3), 131.3 (CA5-H), 128.3 (CA3-N), 125.5 (CA4-H),
124.0 (CA6-H), 104.8 (CC1-CH(CH3)2), 101.5 (CC4-CH3), 82.9 (CC2,6-H), 81.4 (CC3,5-H),
32.6 (p-Cym-CH(C7)-(CH3)2), 30.9 (O=C-CH3(A8)), 23.0 (CH-CH3(C8,9)), 19.5 (Ar-
CH3(C10)). HRMS (ESI-TOF) m/z: [M + Na]+ Calcd for C26H28ClN3O2RuNa 574.0809;
Found 574.0797. Anal. Calcd for C26H28ClN3O2Ru (551.04): C, 56.67; H, 5.12; N, 7.63.
Found: C, 56.49; H, 5.04; N, 7.31.

2.3.4. [Ru{1,3-bis(4´-methylphenyl)triazenide}(Cl)(p-cymene)] (8)
Complex 8 was prepared in the same manner as complex 5, using triazene 4 to obtain a
solid which was crystallized by slow diffusion of pentane in a concentrated solution of
the product in CH2Cl2 at room temperature to give red crystals suitable for X-ray
diffraction analysis (0.064 g, 0.13 mmol, 80%). MP = 187-189 °C. IR(ATR): 3026,
1
2963, 2914, 1603, 1466, 1370, 1276, 1106, 820, 660 cm−1. H NMR [acetone-d6, 400
MHz]: δ 7.24 (d, J = 8.4 Hz, 4H, ArA2,6), 7.10 (d, J = 8.4, Hz, 4H, ArA3,5), 6.02 (d, J =
6.4 Hz, 2H, p-CymC2,6), 5.56 (d, J = 6.4 Hz, 2H, p-CymC3,5), 2.78 (sept, J = 6.8 Hz, 1H,
p-Cym-CH(C7)-(CH3)2), 2.29 (s, 6H, Ar-CH3 (A7)), 2.26 (s, 3H, p-Cym-CH3(C10)), 1.23 (d,
J = 6.8 Hz, 6H, CH-CH3(C8,9)). 13C {1H} NMR [acetone-d6, 100 MHz]: δ 146.3 (CA4-
CH3), 133.9 (CA1-N), 130.0 (CA3,5-H), 117.8 (CA2,6-H), 103.0 (CC4-CH3), 102.9 (CC1-
CH(CH3)2), 82.4 (CC2,6-H), 80.0 (CC3,5-H), 32.6 (p-Cym-CH(C7)-(CH3)2), 22.8 (CH-
CH3(C8,9)), 20.9 (Ar-CH3(A7)), 19.2 (Ar-CH3(C10)). HRMS (ESI-TOF) m/z: [M + Na]+
Calcd for C24H28ClN3RuNa 518.0911; Found 518.0917.
2.4 X-ray crystallography
The crystals of compounds 5 and 7 were mounted on a glass fiber at room temperature,
and then placed on a Bruker SMART APEX CCD-based X-ray diffractometer system
equipped with a Mo-target X-ray tube (λ = 0.71073Å). The detector was placed at a
distance of 5.0 cm from the crystals; in all cases, decay was negligible. A total of 1800

frames were collected with a scan width of 0.3 in x and an exposure time of 10 s/frame.
The frames were integrated with the Bruker SAINT Software package using a narrow-
frame integration algorithm. Systematic absences and intensity statistics were used in
space group determination.
The structures were solved using direct methods using SHELXS-2014/7 program [24].
Anisotropic structure refinements were achieved using full matrix, least-squares
technique on all non-hydrogen atoms. All hydrogen atoms were placed in idealized
positions, based on hybridization, with isotropic thermal parameters fixed at 1.2 times
the value of the attached atom. Structure refinements were performed using SHELXL-
2014/7 [24].
Isopropyl and phenyl group atoms on compound 5 are disordered, and were refined
anisotropically, in two major contributors, using a variable site occupational factor
(SOF). The ratio of SOF was 0.56/0.47 for C24, C25 of isopropyl atoms and 0.63/0.37
for C9-C12.
Crystals of compounds 3, 6 and 8 were mounted under paratone on glass fiber; then, the
crystal was immediately cooled at 130 K using a Cryojet cryostream (Oxford
Cryosystems device). Diffraction data were collected on an Oxford Diffraction Gemini
diffractometer with a CCD-Atlas area detector using a radiation source graphite
monochromator, λMoKα = 0.71073 Å. CrysAlisPro and CrysAlis RED software packages
[25] were used for data collection and data integration. Collected data were corrected
for absorbance using analytical numeric absorption correction [26] with a multifaceted
crystal model based on expressions upon the Laue symmetry using equivalent
reflections.
Structure solution and refinement were carried out with SHELX-2014 [27] and
SHELXL-2014 software, and ORTEP-3 for Windows [28] was used for molecular

graphics. WinGX [29] software was used to prepare material for publication. Full-
matrix least-squares refinement was carried out by minimizing (Fo2 - Fc2)2. All non-
hydrogen atoms were refined anisotropically.
The H atom of the amine (H–N) and hydroxyl groups (H–O) group were located in the
difference map and refined isotropically with Uiso(H) = 1.2 Ueq (N) and 1.5 Ueq (N). H
atoms attached to C atoms were placed in geometrically idealized positions and refined
as riding on their parent atoms, with C–H = 0.95–1.00 Å and Uiso (H) = 1.2Ueq(C) for
aromatic, methylene and methyne groups, and 1.5 Ueq(C) for methyl group.
2.5 General procedure for transfer hydrogenation studies monitored by 1H NMR.
All measurements were made on a Bruker 400 spectrometer operating at 400 MHz.
Inside a nitrogen glovebox, acetophenone (6 × 10−5 mol), 1,3,5-trimethylbenzene (2 µL)
as internal standard and 0.6 mL of 2-propanol-d8 were transferred into a J-Young NMR
tube. The tube was closed in order to avoid air contamination, and a 1H NMR spectrum
was recorded. Next, the tube was brought back into the glovebox and the ruthenium
precatalyst (1.2 × 10−6 mol) and KOH (6 × 10−6 mol) added. Outside of the glovebox the
tube was placed in an oil bath at 70 °C. At the desired sampling time, the tube was taken
1
out of the oil bath, and a H NMR spectrum was recorded. Percent conversions were
determined by comparing the integration of the aromatic protons at the ortho position of
the alcohol with the aromatic protons at the ortho position of the acetophenone. The
value of the integral for the singlet due to the aromatic protons of 1,3,5-
trimethylbenzene (internal standard) was set equal to 10 units in each case.
2.6 General protocol for catalytic transfer hydrogenation monitored by Gas
Chromatography-Mass Spectrometry (GC-MS).
Complex 6 (1.2 × 10−6 mol), 6-methyl-5-hepten-2-one (6 ×10−5 mol) and 2-propanol
(0.6 mL) were transferred into a 2 mL vial. The resulting solution was heated at 70 ºC

and the reaction progress was monitored by GC-MS analysis in order to calculate the
conversion of the substrate 6-methyl-5-hepten-2-one. After 11 h of reaction, an aliquot
of 0.2 mL was taken and filtered through a short pad of silica gel and diluted to 1.0 mL
with 2-propanol.
The analytical GC/MS system used was an Agilent 7890A GC coupled to 5975C Mass
detector Agilent Technologies, equipped with a HP-5MS capillary column (30 m × 0.25
mm × 0.25 micron) Agilent Technologies, Inc. An Agilent Technologies 7693 auto
sampler was used to inject 1 µL of a solution sample. The ionization energy was 70 eV
with a mass range of 30 to 800 m/z. The initial temperature of the column was set at 80
ºC, held for 2 min, and then a ramp of 10 ºC/min to 250 ºC. The temperature of the
injector was set at 250 ºC and the detector at 230 ºC. The flow rate of the carrier gas
(Helium) was 1.0 mL/min injected with a gas dilution of 1:50. Identification of the
individual components was based on comparison with the mass spectra library
(NIST98).
3. Results and discussion
3.1. Synthesis and general characterization
3.1.1. Ligands
Triazenes 1 [22], 2 [17] and 4 [23] were synthesized according to previously
reported procedures. Triazene 3 was synthesized following modified literature
procedures in a one-step reaction by coupling of o-aminoacetophenone, using isoamyl
nitrite in toluene [30].
The IR spectrum of triazene 3 shows bands at 3188 cm−1 for the N−H group and
1576 cm−1 for the N3 system. The C=O groups appear at 1665 and 1648 cm−1, indicating
1
the asymmetry due to the N=N−N system. The H NMR spectrum of the triazene 3
shows a broad singlet at 13.10 ppm assigned to the triazene N−H group. In the region

8.05-7.15 ppm four doublets and four triplets which integrate for eight hydrogen atoms
on two ortho disustituted non-equivalent aromatic rings. The signal of the acetyl groups
(-COCH3) appears as two singlets at 2.66 and 2.51 ppm, which integrate for the six
hydrogens. The 13C NMR spectrum shows 12 signals for the carbon atoms in the
aromatic region, two carbonyl signals at 203.6 and 203.2, and two methyl signals at
32.4 and 28.8 ppm for the two ortho-acetyl groups. This behavior is a consequence of
an intramolecular hydrogen bond [C(1)=O(1)---HN(1)] in solution, where the carbonyl
group involved in the hydrogen bond is shifted downfield (203.6 ppm) due to electron
density donation. EIMS confirmed the molecular weight (281 uma) for triazene 3 and
its analysis by HRMS gives a peak with m/z = 304.1063which is consistent with the
formation of adduct [M + Na] + in the gas phase.
3.1.2. Ruthenium Complexes
Reaction of 1,3-bis(aryl)triazene ligand precursors (1-4) with half equivalent of
[RuCl(p-cymene)(µ-Cl)]2 in dichloromethane at room temperature and in presence of
trimethylamine, resulted in the formation of new monomeric [RuCl(η2-1,3-
ArNNNAr)(η6-p-cymene)] complexes (5-8) (Equation 1).
Complexes 5-8 were isolated as stable yellow or red solids. Their formulation is
supported by analytical and spectroscopic data (IR, HRMS and NMR spectra), and X-
ray crystal structure determination.

1
In the H NMR spectra of complexes 5, 7 and 8, the p-cymene aromatic protons
are observed as two doublets in the range of 6.0-4.8 ppm, while the isopropyl methyl
protons appear as doublets in the range of 1.30-1.02 ppm. These results are in
agreement with the (p-cymene)Ru(triazenide)(L) complexes previously reported [18-
20]. In contrast, in complex 6 the p-cymene aromatic protons are observed as four
doublets (one of them is overlapped with the methylene signal) and the isopropyl
methyl protons are also inequivalent, appearing as two doublets at 0.86 and 0.84 ppm. It
has been suggested that this is a consequence of the chirality of the Ru center due to the
coordination of the asymmetric triazenide ligand from 2. This behavior has been
observed in related asymmetric (p-cymene)Ru(N^N) complexes [36-38]. On the other
hand, all the complexes show a septet in the range of 2.90-2.32 ppm for the isopropyl
CH protons. The same behavior can be seen in the 13C NMR spectra. For example,
signals for the isopropyl methyl carbons appear in the range of 23-22 ppm in complexes
5, 7 and 8, while in complex 6 two signals at 22.5 and 22.4 ppm are observed.
The aromatic rings in the 1,3-diaryltriazenide ligands give signals and
integration for equivalent ortho-disubstituted aromatic rings (5 and 7), para-
disubstituted (8) and the presence of both systems in complex 6. Additional equivalent
methyl signals are observed as singlets at 2.30 and 2.29 ppm for complexes 7 and 8,
respectively. The equivalent methoxy groups of complex 5 are observed as a singlet at
3.64 ppm. Interestingly, when complex 6 is analyzed in C6D6 the signal of the
methylene group (-CH2OH) is overlapped with the resonance of one p-cymene
hydrogen ortho to the isopropyl group [H(16)], and the OH appears as a broad
multiplet. In contrast, if 6 is analyzed in CD3CN the hydrogens of the methylene
becomes diastereotopic and are observed as a set of two doublet of doublets at 4.68 and
2
3
2
3
4.58 ppm with JHH = 13.6, JHH = 7.2 Hz and JHH = 13.6, JHH = 6 Hz, respectively.

Moreover, the OH hydrogen appears as a doublet of doublets at 3.30 ppm with 3JHH
=
7.2 and, 3JHH = 6.4 Hz. In the 13C NMR spectra it is of relevance the carbonyl signals of
the ortho-methoxycarbonyl (169.1 ppm) and ortho-acetyl (202.8 ppm) groups in
complexes 5 and 7, respectively; in both cases the carbonyl signals are equivalent,
unlike those in the free triazene 3. The methylene carbon in the ortho-
hydroxymethylene group in complex 6 appears at 62.8 ppm. The NMR assignments
were confirmed by gCOSY, gHSQC and gHMBC experiments (see Supporting
Information). Complexes 5-8 were analyzed by HRMS (ESI-TOF) and their spectra
showed the formation of adducts of the type [M + Na]+, which may be a consequence of
using sodium formate as calibrant.
3.2. Description of the crystal structures
Amber crystals of triazene 3 suitable for X-ray diffraction were obtained from a
toluene/hexane mixture. Compound 3 crystallized in the orthorhombic crystalline
system with the space group P bca. The molecular structure of triazene 3 is shown in
Figure 2 with bond distances and angles, while crystal data is given in Table 2. Triazene
3 adopts a trans configuration about the N=N double bond and is quasi planar with the
dihedral angle between the two aromatic rings at 2.39˚. The N(1)-N(2)=N(3) bond angle
is 112.1(11)˚. Also, the N(1)-N(2) and N(2)=N(3) bond distances are 1.333(15) Å and
1.259(16) Å, respectively, which indicates the presence of single and double bond. The
bond distances and angles are in agreement with those reported for most related
triazenes with ortho-substituents [31-35]. A distinct intramolecular hydrogen bond
C(1)=O(1)---HN(1) is present, with a distance of 1.937(18) Å, while the C(6)=O(2) of
the other o-acetyl group presents an interaction with the methyl hydrogen of the o-
acetyl group of another molecule [C(6)=O(2)---H(16)'C(16)'] with a distance of 2.64(4)
Å.

Figure 2. ORTEP picture of the molecular structure of compound 3 with thermal
ellipsoids drawn at 50% probability level. Bond distances (Å): N(1)-N(2), 1.333(15);
N(2)=N(3), 1.2590(16); N(1)-H(1D), 0.907(15); C(1)=O(1), 1.2245(18); C(6)=O(2),
1.2203(18). Bond angles (º): N(3)-N(2)-N(1), 112.09(11); N(2)-N(1)-H(1D), 119.9(13).
Crystals of the series of triazenide ruthenium complexes suitable for X-ray diffraction
studies were obtained. Compounds 5, 7 and 8 crystallized in the monoclinic crystalline
system while 6 in the orthorhombic system, with different space groups (Pn for 5, P21
21 21 for 6, P21/c for 7 and Cc for 8). Relevant crystallographic data are included in
Table 1.
Table 1. Crystallographic data and refinement parameters for triazene 3, and complexes
5-8.
3
5
6
7
8
Empirical
formula
fw
T(K)
λ(Å)
C16 H15 N3 O2 C26 H28 Cl C30 H34 Cl N3 C26 H28 Cl
C24 H28 Cl
N3 Ru
495.01
130 (2) K
0.71073 Å
N3 O4 Ru
583.03
298
O Ru
589.12
173(2) K
0.71073 Å
N3 O2 Ru
551.03
298
281.31
173(2) K
0.71073 Å
0.71073
0.71073
Cryst syst
Space
group
Unit cell
dimensions
a(Å)
Orthorhombic Monoclinic Orthorhombic Monoclinic Monoclinic
P b c a
Pn
P 21 21 21
P 21/c
C c
15.7858(11) 11.8640(12)
8.1374(5) 9.3238(9)
8.2430(4)
15.7074(8)
9.8554(9)
13.8618(13) 24.6543(13)
12.0989(8)
b(Å)
c(Å)
21.7015(13) 11.8597(12) 21.2161(10) 18.8855(18) 7.6486(5)
α(deg)
β(deg)
γ(deg)
V(Å3)
Z
90
90
90
90
90.537(2)
90
1311.8(2)
2
90
90
90
90
90
101.289(2)º 109.497(8)
90
2530.1(4)
4
90
2150.7(3)
4
2787.7(3)
8
2747.0(2)
4
F(000)
1184
596
1216
1128
568

DCalc
1.341
1.476
1.424
1.447
1.437
(Mg/m3 )
µ(mm-1)
R1(%)a
wR2(%)b
0.091
0.0844
0.1320
0.735
0.0335
0.0796
0.695
0.0411
0.0686
0.752
0.0619
0.0752
0.869
0.1241
0.1958
a R1 = R||Fo| _ |Fc||/R|Fo|.
b wR2 = [R[w(Fo _ Fc ) ]/R[w(Fo ) ]]1/2.
2
2 2
2 2
The ORTEP diagrams of complexes 5-8 are given in Figures 3-6 with selected bond
lengths and angles. In all compounds the ruthenium atom is surrounded by the η6-
bonded p-cymene ring, a chelating η2-triazenide ligand and one chloro ligand, attaining
a pseudo-octahedral “three legged piano stool” geometry. The small-bite of the
triazenide [N(1)-Ru-N(2), in the range of 58.84(12) to 59.28(8)] conditions the bond
angles around the metal, but only those affecting this ligand, in such a way that the N-
Ru-Cl angles are all close to the expected 90˚. The Ru-N distances are in the range of
2.054(3)-2.132(3) Å, while the N-N bond lengths in the triazenide ligands are around
1.307 Å, a value which is between a single (N-N) and a double bond (N=N). The
distances Ru-C and Ru-CT of the p-cymene ligand in the complexes have values
between 2.151(4)-2.225(3) Å, and 1.6659(17)-1.676(2) Å, respectively. All these values
are in the range found for the reported structures of (p-cymene)Ru-(triazenide)
complexes [18-20] and are comparable to other Ru-triazenide complexes [39-45]
(without the p-cymene ligand). Those values are also comparable with a p-cymene-Ru-
triarylguanidinate complex [46] with an o-methoxy substituent of similar structure, the
bite angle being slightly larger. As in the previously mentioned complex, 7 has a syn
conformation with respect to the two o-acetyl substituent found as far away from the p-
cymene ring, while 5 adopts an anti-conformation as a result of the steric hindrance
exerted between the two o-methoxycarbonyl substituent. The lengths and angles of the
o-substituent in complex 5 (o-methoxycarbonyl), 6 (o-hidroxymethyl), and 7 (o-acetyl)
are in agreement with related structures [16], and in the case of 5 and 7, this values are
comparable to the o-substituent in triazene 1 [13] and 3, respectively.

Figure 3. Structure of the asymmetric unit of 5 with thermal ellipsoids drawn at 20%
probability level. Bond distances (Å): Ru-N1, 2.054(3); Ru-N3, 2.132(3); N(1)-N(2),
1.304(4); N(2)-N(3), 1.311(4); N(1)-C(1), 1.393(5); Ru-Cl1, 2.3927(11); Ru-CT, 1.670;
Ru-C17, 2.226(6); Ru-C20, 2.176(5); C(13)=O(1), 1.211(5); C(15)=O(3), 1.192(5).
Bond angles (°): N(1)-N(2)-N(3), 103.8(3); N1-Ru-N3, 58.85(12); Cl-Ru-N1,
85.04(10); Cl-Ru-N3, 84.59(10); O(2)-C(13)=O(1), 124.27.
Figure 4. Structure of the asymmetric unit of 6 with thermal ellipsoids drawn at 50%
probability level. Bond distances (Å): Ru-N1, 2.067(3); Ru-N3, 2.086(3); N(1)-N(2),
1.307(5); N(2)-N(3), 1.318(4); N(1)-C(1), 1.411(5); Ru-Cl, 2.3963(8); Ru-CT, 1.676;
Ru-C17, 2.190(3); Ru-C20, 2.226(4); C(13)-O(1), 1.432(6); O(1)-H(1), 0.819(4). Bond
angles (°): N(1)-N(2)-N(3), 102.9(3); N1-Ru-N3, 59.22(13); Cl-Ru-N1, 84.43(9); Cl-
Ru-N3, 86.00(10); C(13)-O(1)-H(1), 109.6(6).

Figure 5. Structure of the asymmetric unit of 7 with thermal ellipsoids drawn at 10%
probability level. Bond distances (Å): Ru-N1, 2.094(3); Ru-N3, 2.052(3); N(1)-N(2),
1.313(4); N(2)-N(3), 1.306(4); N(1)-C(1), 1.411(4); Ru-Cl1, 2.3890(11); Ru-CT, 1.666;
Ru-C17, 2.185(4); Ru-C20, 2.190(4); C(13)=O(1), 1.208(5); C(15)=O(3), 1.211(5).
Bond angles (°): N(1)-N(2)-N(3), 102.9(3); N1-Ru-N3, 59.16(12); Cl-Ru-N1,
85.63(10); Cl-Ru-N3, 85.89(8); C(14)-C(13)=O(1), 120.94(5); C(16)-C(15)=O(3),
120.9(6).
Figure 6. Structure of compound 8 with thermal ellipsoids drawn at 70% probability
level. Bond distances (Å): Ru-N1, 2.057(4); Ru-N3, 2.083(4); N(1)-N(2), 1.323(5);
N(2)-N(3), 1.301(5); N(1)-C(1), 1.395(5); Ru-Cl, 2.3936(7); Ru-CT, 1.676; Ru-C17,
2.207(5); Ru-C20, 2.228(5). Bond angles (°): N(1)-N(2)-N(3), 102.6(3); N1-Ru-N3,
59.29(14); Cl-Ru-N1, 85.93(11); Cl-Ru-N3, 85.22(10).
In all the complexes the crystal arrangement exhibits intermolecular C-H···Cl
hydrogen bonds; complexes 5 and 7 exhibit intermolecular C-H···O hydrogen bonds;
the crystal of complex 6 is stabilized by a benzene molecule, and complex 8 presents
one π-π interaction between the phenyl rings of the triazenide ligand. For example in
complex 7 the C-H···O interactions generate a 2D layer in the plane ac (Figure 7); these
are formed by the interactions of the two C=O3 producing a bifurcated hydrogen bond
[C8-H8···O3, 2.70 Å; C6-H6···O3, 2.61 Å] (Figure 7). The interactions C21-H21···Cl1

and C21-H21···πC17-C22 complete the interactions leading to the formation of the 3D
framework. The secondary interactions for the other complexes and triazene 3 are given
in the Supporting Information, Figures S1-S3.
Figure 7. Representation of the bifurcated hydrogen bond in compound 7. The
hydrogen atoms not involved have been omitted for clarity.
Figure 8. Representation of the 2D arrangement in compound 7. Only the hydrogen
atoms involved in the non covalent interactions have been drawn.
3.3 Transfer Hydrogenation Catalysis

Complexes 5-8 were tested in the catalytic reduction of acetophenone to 1-
phenylethanol under the conditions showed in Equation 2.
Table 1. Transfer hydrogenation of acetophenone using 5-8 as precatalysts.a
Catalyst
Entry
Substrate/Catalyst/KOH
100/2/10
Time (h)
Yield (%)b
5
5
6
6
7
8
8
1
2
3
4
5
6
7
12
24
5
94
86
96
42
78
9
100/2
100/2/10
100/2
24
12
12
24
100/2/10
100/2/10
100/2
15
aReaction conditions: 2-propanol-d8, 70 °C, with or without KOH as base. bYields were
determined by 1H NMR.
The results of the catalytic evaluation are summarized in Table 1. After 12 h yields of 1-
phenylethanol were 94 and 78% for 5 and 7, respectively (entry 1 and 5). However,
greater success was achieved by using 6 as precatalyst since a higher yield was obtained
in less time (96% in 5 h, entry 3). Interestingly, complex 8, lacking any ortho-
substituent group at the triazenide ligand was almost ineffective in catalyzing transfer
hydrogenation under the same conditions (9% after 12 h, entry 6). This result shows that
the presence of an ortho-substituent with donating properties in the structure of the
triazenide ligand enhance the activity of the catalysts. Moreover, it can be expected that
the ortho-substituents can acts as a Lewis base accepting a proton or participating in a
hydrogen bond as acceptor. With this assumption in mind, the ability of complexes (5, 6
and 8) to hydrogenate acetophenone was also tested in absence of base. Interestingly,
acetophenone was hydrogenated to 1-phenylethanol without using KOH, although the
catalysis is not as fast when is compared with the system using KOH. Thus, 6 is the
fastest catalyst but only when KOH is used. In the absence of base the

hydroximethylene substituent may be able to participate in hydrogen bonding and this
may affect its activity (42% in 24 h) whereas 5 is the most active when no base is used
(86% in 24 h). Further studies would be needed to explain the role of the ortho-
substituent in the catalysis.
Under the same conditions of Equation 2, hydrogenation of benzophenone using 5 and 6
was also studied finding similar results, with yields of 94 and 98% after 12 and 5h,
respectively. On the other hand, a more promising result was obtained when 6 was used
to perform the chemoselective reduction of 6-methyl-5-hepten-2-one to 6-methyl-5-
hepten-2-ol (Equation 3).
After 11 h of reaction, analysis of an aliquot by GC-MS showed a 96% yield of the
unsaturated alcohol. This is an important result because there are several possibilities in
the hydrogenation of this substrate because the C=C bond could also be hydrogenated or
isomerized.
4. Conclusions
A series of four Ru(II) complexes of triazenide ligands (prepared from precursors 1-
4) have been synthesized and characterized by IR, HRMS, NMR and X ray
diffraction. We have found that functional groups at the ortho position in triazenide
ligands of complexes 5-7 do not participate as metal coordinating sites. However,
comparing transfer hydrogenation using 5-7 and 8, these ortho substituents clearly
have an influence in the catalytic properties of complexes 5-7. Complex 8, although
lacking ortho substituents on the bis(aryl)triazenide ligand showed some catalytic
activity, probably due to the deprotonated triazene nitrogen, which may act as a
Lewis base accepting one proton, thus forming a Noyori’s type of hydride complex.
However, we cannot discard the possibility that the ortho groups behave in the same
manner. Therefore, catalysis may as well operate by a ligand assisted outer sphere

mechanism [47] analogous to that reported by Noyori for transfer hydrogenation.
On the other hand, it seems that the nature of the functional group at the ortho
position in the 1,3-aryl-triazenide ligands can be tuned in order to modulate the
catalytic properties of their complexes. In addition, the chemoselective reduction of
6-methyl-5-hepten-2-one to 6-methyl-5-hepten-2-ol by complex 6 shows a
promising area of opportunity to explore the catalytic properties of triazenide
complexes on the selective transformation of other substrates containing two or
more different functional groups.
Acknowledgements
This work was supported by Consejo Nacional de Ciencia y Tecnología
(CONACyT) Grant 60467 and Dirección General de Educación Tecnológica (DGEST)
Grant 5150.13-P. ECA thanks CONACyT for graduate fellowship. We thank
CONACyT for ITT NMR and HRMS facilities (Grants INFR-2011-3-173395 and
INFR-2012-01-187686).
Supplementary information
Supplementary NMR and RX Tables. Crystallographic data have been deposited
at the Cambridge Crystallographic Data Center as supplementary material number
CCDC 1438682 (3), 1437505 (5), 1438681 (6), 1437504 (7), 1439216 (8). Copies of the
data can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK. E-mail:deposit@ccdc.cam.ac.uk.
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Highlights
Ruthenium triazenide complexes as selective catalysts for hydrogenation of alkenones.
Intramolecular hydrogen bonding in triazenes and ruthenium triazenide complexes.
Base free transfer hydrogenation by ruthenium triazenide complexes.