Rh(III)Cp? and Ir(III)Cp? Complexes of 1-[(4-Methyl)phenyl]-3-[(2-methyl-4′-R)imidazol-1-yl]triazenide (R = t-Bu or H): Synthesis, Structure, and Catalytic Activity

Article abstract of DOI:10.1021/acs.organomet.8b00834

A series of iridium and rhodium complexes have been synthesized using as ligand a triazenide monofunctionalized with an imidazole substituent. Steric hindrance at the imidazole moiety induced differences in the coordination modes as well in the catalytic behavior of complexes 4-7. Complexes 4-7 were tested in the transfer hydrogenation of acetophenone and 5-alken-2-ones. The hydrogenation of either the double bond or the carbonyl group in 5-alken-2-ones, showed to be selective in the presence of 6, 7, and 10 and has a dependence on the presence or absence of base. Control experiments point out that the imidazole moiety in the structure of complexes 4-7 speeds-up the catalysis.

Full text of DOI:10.1021/acs.organomet.8b00834

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Rh(III)Cp* and Ir(III)Cp* Complexes of 1‑[(4-Methyl)phenyl]-3-[(2-
methyl-4′-R)imidazol-1-yl]triazenide (R = t‑Bu or H): Synthesis,
Structure, and Catalytic Activity
†
‡
†
†
§
́
Juan P. Camarena-Díaz, Ana L. Iglesias, Daniel Chavez, Gerardo Aguirre, Douglas B. Grotjahn,
Arnold L. Rheingold,|| Miguel Parra-Hake,*,† and Valentín Miranda-Soto*,†
†
́
́
́
́
Tecnologico Nacional de Mexico/Instituto Tecnologico de Tijuana, Centro de Graduados e Investigacion en Química, Tijuana,
́
Baja California 22000, Mexico
‡
́
Escuela de Ciencias de la Ingeniería y Tecnología, Universidad Autonoma de Baja California, Tijuana, Baja California 21100,
́
Mexico
§Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, California 92182,
United States
||Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, California 92093-0385, United States
S
* Supporting Information
ABSTRACT: A series of iridium and rhodium complexes
have been synthesized using as ligand a triazenide
monofunctionalized with an imidazole substituent. Steric
hindrance at the imidazole moiety induced differences in the
coordination modes as well in the catalytic behavior of
complexes 4−7. Complexes 4−7 were tested in the transfer
hydrogenation of acetophenone and 5-alken-2-ones. The
hydrogenation of either the double bond or the carbonyl
group in 5-alken-2-ones, showed to be selective in the
presence of 6, 7, and 10 and has a dependence on the
presence or absence of base. Control experiments point out
that the imidazole moiety in the structure of complexes 4−7
speeds-up the catalysis.
Chart 1. Classification of Triazenes
INTRODUCTION
■
Triazenes have been described as versatile and very useful
molecules in many areas of chemistry.1 Recently, triazenes
have been classified as linear, cyclic and π-conjugated
molecules.2 Linear triazenes containing the diazoamine
group are important molecules in coordination chemistry
due to their ability to form triazenide anions after
deprotonation with base (Chart 1).3 As ligands, triazenides
are also very versatile due to their ability to coordinate to
alkali metals,3c,d alkaline earth metals,3b and early3e and late
transition metals.3f
Aryl groups have been the most common substituents of
the triazenide system in triazenide complexes of transition
metals.4 In contrast, N-heterocyclic groups have been less
studied as substituents on the triazenide ligand.5 Nevertheless,
there are a few examples of complexes where the triazenide
ligand is mono- or disubstituted with pyridine,5 tetrazol,6
benzothiazole,7 and triazole8 heterocyclic groups. Here we
report on the synthesis and characterization of Ir(III) and
Rh(III) complexes of triazenide ligands monofunctionalized
with sterically hindered or unhindered imidazole moiety as
well as their catalytic properties in transfer hydrogenation of
acetophenone and 5-alken-2-ones.
RESULTS AND DISCUSSION
■
Triazenes 2 and 3 are new compounds, which were
synthesized according to previously reported methodology9
by reaction of 2-lithioimidazoles with 4-azidotoluene, followed
by hydrolysis (eq 1).
Received: November 13, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00834
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described as certain degree of π-delocalization across the
linear triazene moiety.11
Treatment of a solution of 2 or 3 in dry THF with
K[N(SiMe3)2] led to the formation of a potassium triazenide,
which can be directly converted into complexes 4−7 by a
Compounds 2 and 3 were fully characterized by means of
spectroscopic and spectrometric techniques. The H NMR
1
Scheme 1. Synthesis of Triazenide Complexes 4−8
Functionalized with Imidazole
data of both triazenes are consistent with the proposed
structures 2 and 3, wherein the characteristic NH of the
triazene group was observed as a broad singlet at 10.92 and
9.99 ppm, respectively. Moreover, the identity of 2 and 3 in
the solid state was, unambiguously, resolved by X-ray studies
(Figures 1 and 2). Interestingly, the asymmetric unit of 2
transmetalation reaction with [MCp*Cl2]2 (Scheme 1). The
1H and 13C NMR of complexes 4 and 5 showed a very similar
spectrum, as can be expected from their hypothetical
1
structures. The H spectra of 4 showed two resonances at
7.84 and 7.18 ppm (d, J = 8.3 Hz) assigned to the aromatic
hydrogens of the A2B2 system, as well as two doublets at 6.80
and 6.34 ppm (J = 1.8 Hz) due to the imidazole hydrogens. In
addition, the CH3-N, CH3-Ph, and Cp* hydrogens appear as
singlets at 3.49, 2.37, and 1.70 ppm, respectively. However,
the appearance of the aromatic A2B2 system of 6 and 7 is very
different when compared to the A2B2 system observed in
complexes 4 and 5. These resonances are centered at 7.08 and
7.12 ppm, respectively and exhibited a typical second-order
effect with a Δν/J = 1.5 (Figures S26 and S32).
Figure 1. Molecular structure of triazene 2. Selected bond distances
(Å): N(2)N(3), 1.276(2); N(3)−N(4), 1.328(2); N(4)···N(10),
2.99. Selected bond angles (deg): N(2)−N(3)−N(4), 111.3(1).
The ability of complexes to be converted into metal
hydrides was examined by reaction of 7 with NaH in 2-
propanol. The single organometallic product was formulated
1
as 8 since its H NMR spectrum exhibited a high-field signal
at −7.72 ppm. Moreover, a metal hydride was also observed
(−14.62 ppm) in the absence of base when 7 was heated to
70 °C for 4 h in 2-propanol (Figure S69). In addition,
compound 10 was synthesized from triazene 912 in the same
manner as complexes 4−7 (eq 2).
Figure 2. Molecular structure of triazene 3. Selected bond distances
(Å): N(2)N(3), 1.260(2); N(1)−N(2), 1.354(2). Selected bond
angles (deg): N(2)−N(3)−N(4), 111.7(2).
showed two triazene molecules connected to each other by
hydrogen bonding, wherein the planes are almost perpendic-
ular to each other. Both triazenes adopt an (E)-configuration
around the NN double bond, which is a common feature in
related 1,3-disubstituted triazenes.4 For compound 2, the
N2N3 bond distance [1.276(2) Å] is longer than the
typical value for a double bond distance (1.222 Å), whereas
the N3−N4 bond distance [1.328(2) Å] is shorter than the
typical value for a single bond (1.420 Å).10 The same behavior
in bond distances is observed for triazene 3 (Figure 2). These
differences in bond distances at the triazene system have been
The purpose of preparing 10, which features a triazenide
ligand 1,3-disubstituted with 4-methylphenyl groups, was to
study the effect of the absence of the imidazole moiety in the
coordination mode as well as its catalytic activity. As a result
1
of the symmetry of 10, its H NMR spectrum showed only
three resonances at 7.11, 2.33, and 1.78 ppm, which were
assigned to the aromatic hydrogens, the methyl groups and
the Cp*, respectively. Interestingly, the aromatic signal
centered at 7.11 ppm exhibits the same second-order effect
B
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Article
(with Δν/J = 1.3), which was observed in 6 and 7 (Figure
S43).
A detailed analysis of the 13C NMR data of triazenes (2−3)
and complexes (4−8) allowed to infer the coordination mode
of the triazenide ligand in complexes 4−8. For example, it was
found that the imidazole-carbon resonance (C4−Im) in
complexes 4 and 5 is shifted upfield (4.4 to 5.5 ppm) in
comparison with the C4−Im resonance in triazene 2.
Furthermore, the signal of C4−Im in 4 has the appearance
of a doublet at 121.9 ppm (2JRh−C4 = 1.7 Hz). These findings
may be considered as direct evidence of imidazole nitrogen
coordination in complexes 4 and 5. In contrast, there is no
evidence for imidazole nitrogen coordination in complexes 6−
8, whose 13C NMR data showed no significant changes in
chemical shifts of the C4−Im resonance (149.6, 149.9, and
149.0 ppm, respectively) in comparison with the same signal
in triazene 3 (149.5 ppm). Additional data that is consistent
with the structure of 6, shown in Scheme 1, is that both ipso
carbons C2−Im and C1−Ph in 6 are coupled with rhodium
and give two doublets at 147.7 (2JRh−C2 = 2.8 Hz) and 144.7
ppm (2JRh−C1 = 2.1 Hz), respectively. Ultimately, a single
crystal of complexes 4, 5, and 10 were analyzed by X-ray
diffraction (Figures 3, S55, and 4).
Figure 4. Molecular structure of complex 10. Selected bond
distances (Å): N(1)−N(2), 1.310(5); N(2)−N(3), 1.319(5);
Ir(1)−N(3), 2.084(3); Ir(1)−N(2), 2.097(3); Ir(1)−Cl(1),
2.387(1). Selected bond angles (deg): N(1)−Ir(1)−N(3), 58.5(1);
N(1)−Ir(1)−Cl(1), 87.1(1); N(3)−Ir(1)−Cl(1), 84.2(1).
the metal through the terminal nitrogens, forming a four-
membered chelate with a bite angle of 58.5(1)°.
Complexes 4−7 were tested as precatalysts in the transfer
hydrogenation of acetophenone to 1-phenylethanol under the
conditions shown in eq 3.
The results of the catalytic evaluation are summarized in
Table 1. Complexes 4−7 catalyze the reduction of
Table 1. Transfer Hydrogenation of Acetophenone Using
a
4−9 as Precatalysts
b
entry
preCat
subst/preCat/KOH
time (h)
yield (%)
1
2
3
4
5
6
7
8
9
10
4
5
6
7
100/2/10
100/2/10
100/2/10
100/2/10
100/2/-
100/2/10
100/2/10
100/2/-
144
62
89
42
86
42
86
86
4
96
95
93
95
93
57
87
98
83
30
7
Figure 3. Molecular structure of complex 4. Selected bond distances
(Å): N(1)N(2), 1.281(2); N(2)−N(3), 1.29(5); N(2)−Rh(1),
2.103(1); N(5)−Rh(1), 2.070(1); Cl(1)−Rh(1), 2.4051(4). Se-
lected bond angles (deg): N(2)−Rh−N(5), 75.62(5)°; N(2)−
Rh(1)−Cl(1), 87.27(4)°; N(5)−Rh(1)−Cl(1), 90.60(4)°.
10
10
10
8
100/10/-
100/0/10
144
a
b
Reaction conditions: 2-propanol-d8, 70 °C. Yields were determined
1
by H NMR using 1,3,5-trimethybenzene as internal standard.
The crystalline structures of 4 and 5 showed a distorted
octahedral geometry around the metal with a Cp*, chloride,
and triazenide ligand coordinated to the metal atom. In both
complexes, the triazenide ligand is coordinated through the
central nitrogen atom and the imidazole nitrogen (N5).
Moreover, the five-membered chelate [N(2)−Rh−N(5) =
75.62(5)°; N(2)−Ir−N(5) = 74.82(1)°] favored a (Z)-
configuration around the N(1)N(2) double bond in the
triazenide ligand [4: N(1)N(2) = 1.281(2) Å 5: N(1)
N(2) = 1.29(5)]. A similar behavior in the coordination
modes has been observed in copper and cobalt complexes
where the triazenide is substituted with pyridine.5b,c In
contrast, the triazenide ligand in complex 10 coordinates to
acetophenone to afford 1-phenylethanol in 93−96% yield in
the presence of base (42−144 h). In contrast, although a
longer time is required (86 h), no base is needed when
complex 7 is used as precatalyst (entries 4 and 5). With the
aim of evaluating the influence of the imidazole moiety, in a
control experiment using complex 10 with base, a significant
lower yield was observed, suggesting that the imidazole moiety
further assists in the transfer hydrogenation of acetophenone
catalyzed by 7 (entries 4 and 6). Surprisingly, in the absence
of base, complex 10 catalyzed the hydrogenation of
acetophenone in a comparable yield when complex 7 is
C
DOI: 10.1021/acs.organomet.8b00834
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used under the same reaction conditions (entries 5 and 8).
The catalytic behavior of 7 and 10 in the absence of base can
be explained by the ability of the complexes to form metal
hydrides, which are known to be intermediates in the transfer
hydrogenation of carbonyl compounds.13 In this context,
when 7 and 10 were heated in 2-propanol at 70 °C, formation
of the corresponding metal hydrides was observed by 1H
NMR (−14.61 and −16.22 ppm, respectively, Figures S69 and
S70). Interestingly, using metal hydride 8 in the absence of
base, acetophenone was hydrogenated in good yield (83%,
entry 9). Complex 10, although lacking the imidazole
substituent on the triazenide ligand showed 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. Therefore, catalysis may
well operate by a ligand-assisted outersphere mechanism
analogous to that reported by Noyori for transfer hydro-
genation.13 The base alone mediated the transfer hydro-
genation of acetophenone, albeit with lower conversion (entry
10).
5). In addition, the ratio between products A, B, and C
showed to be time dependent and could be controlled by
adjusting the reaction time.
Control experiments showed that the base itself mediated
the hydrogenation of the carbonyl group in substrate 11a in
low yield (entry 7). In addition, the presence of the imidazole
moiety in the structure of precatalysts 6 and 7 accelerate the
catalytic hydrogenation of 11a,b to give species B. Moreover,
species A was not detected in most of the experiments
conducted without base, suggesting that the hydrogenation
follows the order 11a,b → B → C. For instance, when
complex 6 was treated with 1 equiv of 11a in THF-d8 at 70
°C, isomerization of the double bond took place over two
positions to produce 3-hexen-2-one (12), which gives rise to a
1
new set of olefinic signals in the H NMR spectrum at 6.81
and 5.99 ppm (Figures S115 and S116). Under these
reactions conditions, the isomerization of 11a to 12 was
slow (≈16% in 3 h). Further, when 2-propanol was added, an
increase of the concentration of 12 was observed (≈55% in 1
h), which was then hydrogenated to product 13 (B analogue)
and the full reaction sequence completed in 16.5 h (Scheme
2).
Further catalytic studies with 5-alken-2-ones (11a,b), as
substrates, showed that complexes 6, 7, and 10 are selective
precatalysts in the hydrogenation of either the double bond or
the carbonyl group (eq 4.)
Scheme 2. Stoichiometric Hydrogenation Reaction of 11a
with Complex 6
The results summarized in Table 2 show that the selectivity of
transfer hydrogenation is sensitive to the presence of base
In summary, precatalysts 6, 7, and 10 have shown a dual
behavior in the catalytic hydrogenation of 5-alken-2-ones,
which is sensitive to the presence of base. Most importantly,
the hydrogenation of 11a,b to give B in the absence of base is
very selective and the product of the double hydrogenation
(C) is only detected (5−20%) after a longer reaction time (6
h).
Table 2. Transfer Hydrogenation of 5-Hexen-2-one (11a)
a
and 6-Methyl-5-hepten-2-one (11b)
b
entry substrate preCat/KOH time (h) yield (%)
ratio A/B/C
c
1
2
3
4
5
6
7
8
11a
11a
11a
11a
11a
11a
11a
11b
11b
11b
11b
11b
11b
11b
6/KOH
6/-
7/KOH
7/-
10/KOH
10/-
-/KOH
6/KOH
6/-
7/KOH
7/-
10/KOH
10/-
33
1
33
3
22
3
68
38
6
38
6
22
6
33
100
99
96
50
33/0
0/97/3
58/41
CONCLUSIONS
c
■
In summary, we have synthesized iridium(III) and rhodium-
(III) complexes 4−8 bearing a triazenide ligand mono-
functionalized with the imidazole moiety. The coordination
mode of the triazenide ligand is sensitive to the substituents of
the imidazole ring. In this context, the lack of steric hindrance
at the imidazole ring in complexes 4 and 5 has as a
consequence its coordination to the metal ion. However, the
steric hindrance imposed by the tert-butyl group on the
imidazole ring prevents its coordination in complexes 6−8.
These observations were supported by the crystalline
structures of 4 and 5, as well as the NMR data of 4−8. All
complexes were active as precatalysts in the transfer
hydrogenation of acetophenone, with 7 being the most active.
In this sense, the ability of complexes to form metal hydrides
was illustrated by the conversion of 7 into hydride 8.
Complexes 6 and 7 show promising use as precatalyst for
selective hydrogenation of 5-alken-2-ones. The catalytic
behavior of 7 depends on the presence of a base; if a base
is present, then the carbonyl group will be selectively
hydrogenated in the first place. However, in the absence of
base the double bound is preferably hydrogenated, which was
confirmed by stoichiometric studies. Additional reactivity
studies and applications are in progress.
0/96/0
c
46/0
76
0/76/0
10/0/0
70/5/13
2/73/20
83/3/10
0/95/5
11/2/0
0/40/0
d
10
88
95
96
100
13
9
10
11
12
13
14
42
d
-/KOH
68
0
a
b
Reaction conditions: 2-propanol, 70 °C. Yields were determined by
c
d
1
GC-MS. Mixture of A and B. Yields were determined by H NMR
using 1,3,5-trimethybenzene as internal standard.
(KOH). In the absence of KOH, the double bond in 11a-b is
selectively hydrogenated to give B in higher to moderate
yields (entries 2, 4, 6, 11, and 13). In contrast, if KOH is
added, then the carbonyl group is hydrogenated instead
(entries 8 and 10). Interestingly, the hydrogenation of 11a in
the presence of KOH by complexes 6, 7, or 10 is not selective
and gave either a mixture of A/B or A/B/C (entries 1, 3, and
D
DOI: 10.1021/acs.organomet.8b00834
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Synthesis of 1-[(4-Methyl)phenyl]-3-[(4-tert-butyl-2-
EXPERIMENTAL SECTION
■
methyl)imi-dazol-1-yl]triazene (3).
General Procedures. Unless otherwise specified, all manipu-
lations were carried out in an argon-filled glovebox or using Schlenk
techniques. Commercially available reagents were used as received
from Aldrich Chemical Co. and Alfa Aesar. [IrCp*Cl2]2 and
[RhCp*Cl2]2 were prepared by published procedures.14 THF-d8
and C6D6 were purchased from Cambridge Isotope Laboratories
(CIL), dried over calcium hydride, and vacuum transferred prior to
use. CD3CN and CD2Cl2 were used as received from CIL. NMR
spectra were recorded at 400 MHz with a Bruker Avance III
Compound 3 was synthesized in the same manner as 2, using 4-tert-
butyl-1-methylimidazole16 (1.00 g, 7.24 mmol), buthyllitium 2.5 M
(3.2 mL) and 4-azidotoluene (0.964 g, 7.24 mmol) to afford a yellow
solid (1.822 g, yield 92%). Mp 126−128 °C. IR (ATR, cm−1): 3146
spectrometer at 30 °C unless otherwise specified. H and 13C NMR
1
1
ν(N−H) H NMR (400 MHz, CDCl2): δ 10.33−9.17 (br s, 1H,
3
3
chemical shifts are reported in ppm referenced to residual solvent
resonances (1H NMR: 7.24 for CHCl3 in CDCl3, 5.32 for CHDCl2
in CD2Cl2, 7.16 for C6HD5 in C6D6, 1.94 for CHD2CN in CD3CN,
and 3.58 for H2 of THF-d7. 13C {1H} NMR: 77.23, 128.39, and 1.39
for chloroform-d1, benzene-d6, and acetonitrile-d3, respectively).
Coupling constants J are given in Hertz (Hz). IR spectra were
recorded on a PerkinElmer FT-IR 1605 spectrophotometer (ATR
mode). Melting points were measured in an Electrothermal GAC
88629 apparatus. Mass spectra were obtained by direct insertion on
an Agilent Technologies 5975C instrument. High-resolution mass
spectrometry (HRMS) data were obtained in a micrOTOF-Q III MS
instrument with electrospray ionization using sodium formate as
calibrant. Elemental analyses were performed at NuMega Resonance
Laboratories, San Diego, CA. Metal hydride 8 is air-sensitive;
therefore elemental analysis could not be obtained. Although
elemental analysis for 2, 5, and 10 are slightly off the accepted
range, they are provided to illustrate the best values obtained to date.
Nevertheless, a complete set of NMR and HRMS spectra has been
provided in the Supporting Information, as evidence of bulk purity
and identity. X-ray diffraction data for crystals of compounds 2−5
and 10 were collected on an Agilent Technologies Supernova AtlasS2
and a Bruker APEX II CCD diffractometers.
NH), 7.28 (d, JHH = 8.0 Hz, 2H, ArH), 7.18 (d, JHH = 8.0 Hz, 2H,
ArH), 6.59 (s, 1H, ImH), 3.74 (s, 3H, NCH3), 2.34 (s, 3H, ArCH3),
1.31 [s, 9H, C(CH3)3]. 13C {1H} NMR (100.62 MHz, CD2Cl2): δ
149.5 (C4−Im), 146.8 (C2−Im), 140.0 (C1−Ar), 134.1 (C4−Ar),
130.5 (C3−Ar), 115.9 (C2−Ar), 114.1 (C5−Im), 32.7 (NCH3),
32.3 [C(CH3)3], 30.4 [C(CH3)3], 21.1 (Ar−CH3); EIMS (70 eV)
m/z: M+ 271 (19), 243 (8), 228 (22), 165 (44), 138 (35), 119 (26),
91 (100). HRMS (ESI-TOF) m/z: [M + H]+ calcd for C15H22N5:
272.1870. Found 272.1863. Anal. Calcd for C15H21N5 (271.36): C,
66.39, H, 7.80, N, 25.81. Found: C, 66.35, H, 7.84, N, 26.0%.
Synthesis of Complex 4.
In the glovebox, triazene 2 (0.125 g, 0.5806 mmol) and
K[N(SiMe3)2] (0.116 g, 0.5815 mmol) were dissolved in dry
benzene (10 mL). The yellow reaction mixture was stirred for 10
min. Addition of [RhCl2Cp*]2 (0.18 g, 0.291 mmol) gave an orange
mixture, which was stirred for 2 h at room temperature. After this
time, the reaction mixture was filtrated through a plug of Celite. The
filtrate was collected in a tared flask and the solvent was removed
Synthesis of 1-[(4-Methyl)phenyl]-3-[(2-methyl)imidazol-1-
yl]tria-zene (2).
1
under vacuum to give 4 as an orange powder (0.27 g, 95%). H
NMR (400 MHz, CD2Cl2): δ 7.84 (d, 3JHH = 8.3 Hz, 2H, ArH), 7.18
(d, 3JHH = 8.3 Hz, 2H, ArH), 6.80 (d, 3JHH = 1.8 Hz, 1H, ImH), 6.64
3
(d, JHH = 1.8 Hz, 1H, ImH), 3.49 (s, 3H, NCH3), 2.37 (s, 3H,
ArCH3), 1.70 (s, 15H, Cp*). 13C {1H} NMR (100.62 MHz,
CD2Cl2): δ 160.6 (C2−Im), 148.7 (C1−Ar), 135.6 (C4−Ar), 129.0
(C3−Ar), 125.0 (C2−Ar), 121.9 (d, 2JC−Rh = 1.7 Hz, C4−Im), 118.1
1-Methylimidazole (0.5 g, 0.484 mL, 6.08 mmol) was dissolved in
dry THF (10 mL) and cooled in a dry-ice−acetone bath to −78 °C;
buthyllitium 2.5 M (2.43 mL) was added dropwise and stirred for 2
h. 4-azidotoluene15 (0.8134 g, 6.1 mmol) was added and stirred at
room temperature for 12 h. The reaction was quenched with water
and stirred for 1 h. The product was extracted with ethyl acetate (3 ×
50 mL), and the organic phase was washed with water (3 × 50 mL),
dried over MgSO4, and filtered. The solvent was removed under
vacuum to afford an orange solid (1.180 g, yield 90%). Mp 121−123
°C. IR (ATR, cm−1): 3140 ν(N−H). 1H NMR (400 MHz, CD3CN):
δ 12.0−10.0 (br s, 1H, NH), 7.26 (d, 3JHH = 8.3 Hz, 2H, ArH), 7.18
(d, 3JHH = 8.3 Hz, 2H, ArH), 6.95 (d, 3JHH = 1.2 Hz, 1H, ImH), 6.91
1
(C5−Im), 95.3 (d, JC−Rh = 8.0 Hz, Cp*), 33.5 (NCH3), 21.5
(ArCH3), 9.1 (Cp*−CH3). HRMS (ESI-TOF) m/z: [M + H]+ calcd
for C21H28ClN5Rh 488.1083. Found 488.1078. Anal. Calcd for
C21H27ClN5Rh (487.83): C, 51.70; H, 5.57; N, 14.35. Found: C,
51.78; H, 5.33; N, 14.32%.
Synthesis of Complex 5.
3
(d, JHH = 1.2 Hz, 1H, ImH), 3.69 (s, 3H, NCH3), 2.31 (s, 3H,
ArCH3). 13C {1H} NMR (100.62 MHz, CD3CN): δ 151.1 (C2−Im),
141.3 (C1−Ar), 134.5 (C4−Ar), 130.9 (C3−Ar), 126.1 (C4−Im),
1
121.3 (C5−Im), 116.6 (C2−Ar), 32.9 (NCH3), 20.9 (ArCH3). H
Complex 5 was synthesized in the same manner as 4, using 2 (0.108
g, 0.5017 mmol), K[N(SiMe3)2] (0.100 g, 0.5013 mmol) and
[IrCl2Cp*]2 (0.200 g, 0.251 mmol) in dry benzene. After filtration,
the solvent was removed under vacuum to give 5 as yellow powder
NMR (400 MHz, CD2Cl2): δ 11.93.0−9.55 (br s, 1H, NH), 7.28 (d,
3
3JHH = 8.2 Hz, 2H, ArH), 7.16 (d, JHH = 8.2 Hz, 2H, ArH), 7.01 (s,
3
1H, ImH), 6.87 (d, JHH = 1.2 Hz, 1H, ImH), 3.75 (s, 3H, NCH3),
2.33 (s, 3H, ArCH3). 13C {1H} NMR (100.62 MHz, CD2Cl2): δ
150.4 (C2−Im), 139.9 (C1−Ar), 134.3 (C4−Ar), 130.4 (C3−Ar),
126.3 (C4−Im), 120.4 (C5−Im), 116.1 (C2−Ar), 32.9 (NCH3),
21.1 (ArCH3). EIMS (70 eV) m/z: M+ 215 (41), 187 (28), 172 (4),
119 (85), 109 (90), 91 (100). HRMS (ESI-TOF) m/z: [M + H]+
calcd for C11H14N5: 216.1244. Found 216.1240. Anal. Calcd for
C11H13N5 (215.26): C, 61.38; H, 6.09; N, 32.54. Found: C, 61.33;
H, 6.51; N, 33.0%.
1
3
(0.27 g, 93%). H NMR (400 MHz, CD2Cl2): δ 7.80 (d, JHH = 8.4
Hz, 2H, ArH), 7.18 (d, 3JH3H = 8.4 Hz, 2H, ArH), 6.76 (d, JHH = 1.8
3
Hz, 1H, ImH), 6.65 (d, JHH = 1.8 Hz, 1H, ImH), 3.56 (s, 3H,
NCH3), 2.38 (s, 3H, ArCH3), 1.71 (s, 15H, Cp*). 13C {1H} NMR
(100.62 MHz, CD2Cl2): δ 165.3 (C2−Im), 149.1 (C1−Ar), 135.9
(C4−Ar), 129 (C3−Ar), 125.4 (C2−Ar), 120.8 (C4−Im), 117.9
(C5−Im), 87.5 (Cp*), 33.7 (NCH3), 21.5 (ArCH3), 8.9 (Cp*−
CH3). HRMS (ESI-TOF) m/z: [M + H]+ calcd for C21H28ClN5Ir:
E
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Article
578.1649. Found 578.1641. Anal. Calcd for C21H27ClN5Ir (577.14):
C, 43.70; H, 4.72; N, 12.13. Found: C, 42.48; H, 4.80; N, 11.33%.
Synthesis of Complex 6.
113.3 (C5−Im), 87.3 (Cp*), 34.4 (NCH3), 32.3 [C(CH3)3], 30.6
[C(CH3)3], 21.0 (ArCH3), 11.0 (Cp*−CH3). HRMS (ESI-TOF) m/
z: [M − H]+ calcd for C25H35N5Ir: 598.2517. Found 598.2535.
Synthesis of Complex 10.
Complex 6 was synthesized in the same manner as 4, using 3 (0.160
g, 0.5896 mmol), K[N(SiMe3)2] (0.118 g, 0.5915 mmol), and
[RhCl2Cp*]2 (0.185 g, 0.2931 mmol) in dry benzene. After filtration,
the solvent was removed under vacuum to give 6 as an orange
powder (0.30 g, 94%). 1H NMR (400 MHz, CDCl3): δ 7.11 (d, 3JHH
Complex 10 was synthesized in the same manner as 4, using 9 (0.100
g, 0.4438 mmol), K[N(SiMe3)2] (0.097 g, 0.486 mmol), and
[IrCl2Cp*]2 (0.1761 g, 0.221 mmol) in dry benzene. After filtration,
the solvent was removed under vacuum to give 10 as yellow solid
(0.21 g, 81%). H NMR (400 MHz, CD2Cl2): δ 7.13 (d, JHH = 8
Hz, 4H, ArH), 7.10 (d, 3JHH = 8 Hz, 4H, ArH), 2.33 (s, 6H, ArCH3),
1.78 (s, 15H, Cp*). 13C {1H} NMR (100.62 MHz, CD2Cl2): δ 144.2
(C1−Ar), 134.5 (C4−Ar), 129.9 (C3−Ar), 117.6 (C2−Ar), 86.7
(Cp*), 21.2 (ArCH3), 10.3 (Cp*−CH3). HRMS (ESI-TOF) m/z:
[M + Na]+ calcd for C24H29ClN3IrNa: 610.1564. Found 610.1571.
Anal. Calcd for C24H29ClN3Ir (587.18): C, 49.09; H, 4.98; N, 7.16.
Found: C, 48.56; H, 4.70; N, 6.96%.
1
3
3
= 8.6 Hz, 2H, ArH), 7.08 (d, JHH = 8.6 Hz, 2H, ArH), 6.35 (s, 1H,
ImH), 3.50 (s, 3H, NCH3), 2.31 (s, 3H, ArCH3), 1.85 (s, 15H,
Cp*), 1.27 [s, 9H, C(CH3)3]. 13C {1H} NMR (100.62 MHz,
2
CDCl3): δ 149.6 (C4−Im), 147.7 (d, JC−Rh = 2.8 Hz, C2−Im),
144.7 (d, 2JC−Rh = 2.1 Hz, C1−Ar), 134.1 (C4−Ar), 129.6 (C3−Ar),
1
117.8 (C2−Ar), 113.4 (C5−Im), 94.0 (d, JC−Rh = 8.2 Hz, Cp*),
34.3 (NCH3), 31.9 [C(CH3)3], 30.2 [C(CH3)3], 21.1 (ArCH3), 9.8
(Cp*−CH3). HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C25H36ClN5Rh: 544.1709. Found 544.1711. Anal. Calcd for
C25H35ClN5Rh (543.93): C, 55.20; H, 6.48; N, 12.87. Found: C,
55.41; H, 6.61; N, 12.47%.
General Procedure for Transfer Hydrogenation Studies
Monitored by 1H NMR. Acetophenone (0.06 mmol), 1,3,5-
trimethylbenzene (2 μL) as internal standard and 0.6 mL of 2-
1
propanol-d8 were transferred into a J. Young NMR tube, and a H
Synthesis of Complex 7.
NMR spectrum was recorded. Then, the precatalyst (2 mol %) and
KOH (10 mol %) were added. No base was added in the case of
entries 5 and 7 (Table 1). The reaction mixture was heated at 70 °C
according to the time shown in Table 1. The conversions were
1
quantified by the integration of the H NMR signals of the alcohol
and acetophenone. The value of the integral for the singlet due to the
aromatic protons of 1,3,5-trimethylbenzene (internal standard) was
set to 10 units in each case.
Complex 7 was synthesized in the same manner as 4, using 3 (0.135
g, 0.4975 mmol), K[N(SiMe3)2] (0.100 g, 0.5013 mmol) and
[IrCl2Cp*]2 (0.200 g, 0.251 mmol) in dry benzene. After filtration
the solvent was removed under vacuum to give 7 as an orange solid
General Procedure for Transfer Hydrogenation Studies
Monitored by Gas Chromatography−Mass Spectrometry
(GC-MS). 6-Methyl-5-hepten-2-one or 5-hexen-2-one (0.1 mmol),
precatalyst (2 mol %), and KOH (10% mol) were stirred in 2-
propanol (1 mL) in a 2 mL vial at 70 °C. No base was added in the
case of entries 2, 4, 7, and 9 (Table 2). The reaction was monitored
at different times by sampling aliquots of 0.05 mL diluted in 1 mL of
methylene chloride.
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 μm)
Agilent Technologies, Inc. An Agilent Technologies 7693 auto
sampler was used to inject 1 μL of a sample solution. The ionization
energy was 70 eV with a mass range of 30 to 800 m/z. The injector
temperature was set at 250 °C and the detector to 230 °C. 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
done by comparison with the mass spectra library (NIST98). For the
substrate 5-hexen-2-one, the initial temperature of the column was
set at 60 °C, held for 2 min, and then a ramp of 10 °C/min to 250
°C. For the substrate 6-methyl-5-hepten-2-one, the initial temper-
ature of the column was set at 70 °C, held for 2 min and then a ramp
of 10 °C/min to 250 °C.
1
3
(0.29 g, 92%). H NMR (400 MHz, CD2Cl2): δ 7.14 (d, JHH = 8.5
Hz, 2H, ArH), 7.10 (d, 3JHH = 8.5 Hz, 2H, ArH), 6.43 (s, 1H, ImH),
3.58 (s, 3H, NCH3), 2.33 (s, 3H, ArCH3), 1.82 (s, 15H, Cp*), 1.28
[s, 9H, C(CH3)3]. 13C {1H} NMR (100.62 MHz, CD2Cl2): δ 149.9
(C4−Im), 146.6 (C2−Im), 144.0 (C1−Ar), 135.1 (C4−Ar), 130.0
(C3−Ar), 117.7 (C2−Ar), 114.2 (C5−Im), 87.0 (Cp*), 34.8
(NCH3), 32.3 [C(CH3)3], 30.4 [C(CH3)3], 21.2 (ArCH3), 10.1
(Cp*−CH3). HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C25H36ClN5Ir: 634.2275. Found 634.2280. Anal. Calcd for
C25H35ClN5Ir (633.25): C, 47.41; H, 5.57; N, 11.05. Found: C,
47.13; H, 5.83; N, 10.66%.
Synthesis of Complex 8.
To a solution of 7 (0.080 g, 0.126 mmol) in 2-propanol (10 mL),
was added solid NaH (0.009 g, 0.375 mmol) at room temperature
and stirred overnight. The solvent was evaporated under vacuum to
give a dark brown residue, which was redissolved in dry benzene and
filtered through a short plug of Celite. The filtrate was collected in a
tared flask, and the solvent was removed under vacuum to give a
solid, which was washed with hexane (3 × 5 mL) and dried in vacuo
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00834.
1
to give 8 as red solid (0.060 g, 80%). H NMR (400 MHz, C6D6): δ
7.38 (d, 3JHH = 8.3 Hz, 2H, ArH), 7.06 (d, 3JHH = 8.4 Hz, 2H, ArH),
5.96 (s, 1H, ImH), 3.05 (s, 3H, NCH3), 2.18 (s, 3H, ArCH3), 1.92
(s, 15H, Cp*), 1.52 [s, 9H, C(CH3)3], −7.73 (s, 1H, IrH). 13C {1H}
NMR (100.62 MHz, CDCl3): δ 149.0 (C4−Im), 147.7 (C2−Im),
147.1 (C1−Ar), 133.3 (C4−Ar), 129.5 (C3−Ar), 117.4 (C2−Ar),
Additional experimental information, Nuclear magnetic
resonance spectra for all complexes, GC-MS analysis,
HRMS spectra, and crystallographic data for complexes
2−5 and 10 (PDF)
F
DOI: 10.1021/acs.organomet.8b00834
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3450−3451. (e) Manssen, M.; Weimer, I.; Adler, C.; Fischer, M.;
Schmidtmann, M.; Beckhaus, R. From organic azides through
titanium triazenido complexes to titanium imides. Eur. J. Inorg.
Chem. 2018, 2018, 131−136. (f) Carlton, L.; Nyoni, M. S.;
Fernandes, M. A. Triazenide complexes of iridium. Evidence for
[Ir(η1-N3Ph2)(HN3Ph2) (1,5-cod)], structures of [Ir2(μ-OMe)2(1,5-
cod)2], [Ir2(μ-N3Ph2)2 (1,5-cod)2], [Ir(η2-N3Ph2)(H)(SiPh3)(1,5-
cod)], [Ir(η2-N3Ph2)(H)(SnPh3) (1,5-cod)] and [Ir(η2-N3Ph2)-
(SC6F5)2(1,5-cod)]. Polyhedron 2016, 119, 194−201.
Accession Codes
CCDC 1877017−1877021 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: mparra@tectijuana.mx (M.P.H.).
*E-mail: vmiranda@tectijuana.mx (V.M.S.).
́
(4) (a) Correa-Ayala, E.; Campos-Alvarado, C.; Chavez, D.;
■
́
Morales-Morales, D.; Hernandez-Ortega, S.; García, J. J.; Flores-
Alamo, M.; Miranda-Soto, V.; Parra-Hake, M. Ruthenium (p-
II
́
cymene) complexes bearing ligands of the type 1-[2′-
(methoxycarbonyl)phenyl]-3-[4′-X-phenyl]triazenide (X = F, Cl,
Br, I): Synthesis, structure and catalytic activity. Inorg. Chim. Acta
2017, 466, 510−519. (b) Correa-Ayala, E.; Valle-Delgado, A.; Ríos-
ORCID
Douglas B. Grotjahn: 0000-0002-2481-7889
Valentín Miranda-Soto: 0000-0002-7495-6772
Notes
́
́
Moreno, G.; Chavez, D.; Morales-Morales, D.; Hernandez-Ortega, S.;
García, J. J.; Flores-Alamo, M.; Miranda-Soto, V.; Parra-Hake, M.
́
Synthesis, structures and catalytic activity of 1,3-bis(aryl)triazenide(p-
cymene)ruthenium(II) complexes. Inorg. Chim. Acta 2016, 446,
The authors declare no competing financial interest.
́
161−168. (c) Ibarra-Vazquez, M. F.; Cortes-Llamas, S. A.; Peregrina-
ACKNOWLEDGMENTS
Dedicated to the memory of Professor Pascual Royo. This
́
Lucano, A. A.; Alvarado-Rodríguez, J. G.; Manríquez-Gonzalez, R.;
■
́
Lopez-Dellamary, F. A.; Moreno-Brambila, M. I.; Rangel-Salas, I. I.
Iridium (III) 1,3-bis(aryl)triazenide complexes: Synthesis, character-
ization and structure. Inorg. Chim. Acta 2016, 451, 209−215.
(d) Vajs, J.; Steiner, I.; Brozovic, A.; Pevec, A.; Ambriovic-Ristov, A.;
Matkovic, M.; Piantanida, I.; Urankar, D.; Osmak, M.; Kosmrlj, J.
The 1,3-diaryltriazenido(p-cymene)ruthenium(II) complexes with a
́
́
research was supported by Tecnologico Nacional de Mexico
(TecNM, grant 6185.17-P) and Consejo Nacional de Ciencia
́
y Tecnologia (CONACyT, grant 162005). JPCD thanks
́
CONACyT for graduate fellowship. We thank CONACyT for
ITT NMR, HRMS, and X ray facilities (Grants INFR-2011-3-
173395, INFR-2012-01-187686 and INFR-2014-224405).
high in vitro anticancer activity. J. Inorg. Biochem. 2015, 153, 42−48.
́
̃
ez, S.; Oresmaa, L.; Estevan, F.; Hirva, P.; Sanau, M.; Ubeda,
́
(e) Iban
M. A. Triazenides as suitable ligands in the synthesis of palladium
compounds in three different oxidation states: I, II and III.
Organometallics 2014, 33, 5378−5391.
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