Synthesis and Reactivity of Metal-Ligand Cooperative Bifunctional Ruthenium Hydride Complexes: Active Catalysts for β-Alkylation of Secondary Alcohols with Primary Alcohols

Article abstract of DOI:10.1021/acs.organomet.8b00432

Three unsymmetrical NNN ligands with a 2-hydroxypyridyl fragment were used to react with RuHCl(PPh₃)₃(CO), affording the three bidentate ruthenium hydride complexes [(R₁-C₅H₃N-CH₂-C₅H₃N-C₅H₃N-R₂)RuH(PPh₃)₂(CO)][Cl] (R₁ = R₂ = OH, 2a; R₁ = OH, R₂ = H, 2b; R₁ = H, R₂ = OH, 2c), respectively. When 2a,b were treated with t-BuOK, the two tridentate products [(O-C₅H₃N-CH₂-C₅H₃N-C₅H₃N-R₂)RuH(PPh₃)(CO)] (R₂ = OH, 3a; R₂ = H, 3b) were obtained, via selective deprotonation of the -OH group of PyCH₂PyOH moiety, indicating that this -OH group is more acidic than that of the PyPyOH moiety. The reaction of 2c with t-BuOK generated the bidentate product [(C₅H₄N-CH₂-C₅H₃N-C₅H₃N-O)RuH(PPh₃)₂(CO)] (3c) and the tridentate product [(C₅H₄N-CH₂-C₅H₃N-C₅H₃N-O)RuH(PPh₃)(CO)] (3d). 3d could be further transformed to the diruthenium complex [(C₅H₄N-CH-C₅H₃N-C₅H₃N-O)Ru(PPh₃)(CO)]₂ (3e) via C-H activation of the -CH₂- group in boiling toluene. The catalytic activity for β-alkylation of secondary alcohols with primary alcohols of these eight ruthenium complexes was tested, and the bidentate complexes 2c and 3c exhibit the highest activity. Complex 3c can be regarded as the intermediate of 2c. These results are important for developing more efficient bifunctional catalysts for such reactions.

Full text of DOI:10.1021/acs.organomet.8b00432

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Synthesis and Reactivity of Metal−Ligand Cooperative Bifunctional
Ruthenium Hydride Complexes: Active Catalysts for β‑Alkylation of
Secondary Alcohols with Primary Alcohols
Jing Shi,† Bowen Hu,† Peng Ren,‡ Shu Shang,† Xinzheng Yang,*,§,∥ and Dafa Chen*,†
†MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and
Chemical Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
‡School of Science, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, People’s Republic of China
§Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species,
CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, People’s Republic of China
∥University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
S
* Supporting Information
ABSTRACT: Three unsymmetrical NNN ligands with a 2-
hydroxypyridyl fragment were used to react with RuHCl-
(PPh3)3(CO), affording the three bidentate ruthenium hydride
complexes [(R1-C5H3N-CH2-C5H3N-C5H3N-R2)RuH-
(PPh3)2(CO)][Cl] (R1 = R2 = OH, 2a; R1 = OH, R2 = H, 2b;
R1 = H, R2 = OH, 2c), respectively. When 2a,b were treated with
t-BuOK, the two tridentate products [(O-C5H3N-CH2-C5H3N-
C5H3N-R2)RuH(PPh3)(CO)] (R2 = OH, 3a; R2 = H, 3b) were
obtained, via selective deprotonation of the −OH group of PyCH2PyOH moiety, indicating that this −OH group is more acidic
than that of the PyPyOH moiety. The reaction of 2c with t-BuOK generated the bidentate product [(C5H4N-CH2-C5H3N-
C5H3N-O)RuH(PPh3)2(CO)] (3c) and the tridentate product [(C5H4N-CH2-C5H3N-C5H3N-O)RuH(PPh3)(CO)] (3d). 3d
could be further transformed to the diruthenium complex [(C5H4N-CH-C5H3N-C5H3N-O)Ru(PPh3)(CO)]2 (3e) via C−H
activation of the −CH2− group in boiling toluene. The catalytic activity for β-alkylation of secondary alcohols with primary
alcohols of these eight ruthenium complexes was tested, and the bidentate complexes 2c and 3c exhibit the highest activity.
Complex 3c can be regarded as the intermediate of 2c. These results are important for developing more efficient bifunctional
catalysts for such reactions.
two or more proton-responsive sites are rare.19−21 Ikariya and
Kuwata et al. synthesized two ruthenium complexes based on
INTRODUCTION
■
Metal−ligand cooperative bifunctional complexes play crucial
roles in chemical bond activation and catalysis.1−21 A major
NNC tridentate ligands containing a protic pyrazole and a N-
heterocyclic carbene (Figure 1a,b) and studied their reactivity
with bases. In both cases, the protic pyrazole ring was
deprotonated first, indicating that the pyrazole was more acidic
than the N-heterocyclic carbene.20 Recently, the van der Vlugt
strategy of designing metal−ligand cooperative catalysts is by
introducing a proton-responsive ligand to the metal center. In
the presence of a base, the proton-responsive site can be
deprotonated, and the resulting complex might accept a proton
from the substrate. The reversible structural changes of the
ligand are beneficial for substrate activation. For example,
many amido transition-metal complexes can promote H2
activation and H2-related catalytic reactions.2−4 In addition,
Milstein and other groups revealed that lutidine-based PNP-M
and PNN-M complexes, which have slightly acidic methylene
protons, exhibit interesting metal−ligand cooperation based on
an aromatization−dearomatization process and have been
exploited for a series of organic transformations.5−7 Other
types of metal−ligand cooperative complexes are transition-
metal compounds with a 2-hydroxypyridyl group, which can be
deprotonated to a pyridinol form with a CO bond.8−18
Although there are various types of metal−ligand cooper-
ative complexes, systems based on unsymmetric ligands with
Figure 1. Ruthenium complexes a−c based on unsymmetric ligands
with two proton-responsive sites.
Received: June 23, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00432
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group developed a PNN ligand by the combination of 2-
hydroxypyridyl and a PN fragment and introduced it to a
ruthenium center (Figure 1c). Only the 2-hydroxypyridyl
moiety was deprotonated to 2-pyridinol even with excessive
DBU, demonstrating that the −CH2− protons were less
acidic.21c
Recently, we have synthesized the ruthenium dichloride
complexes 1a−c based on the ligands [R1-C5H3N-CH2-
C5H3N-C5H3N-R2] (L1, R1 = OH, R2 = OH; L2, R1 = OH,
R2 = H; L3, R1 = H, R2 = OH) and studied their catalytic
activity on transfer hydrogenation of ketones (Scheme 1).22
hydride, and two pyridyl rings of ligand L1 coordinating with
Ru. However, it was still difficult to confirm its exact
coordination geometry without its single-crystal structure.
Ligand precursors L2 and L3 were then treated with
RuHCl(PPh3)3(CO), and complexes [(HO-C5H3N-CH2-
C5H3N-C5H4N)RuH(PPh3)2(CO)][Cl] (2b) and [(C5H4N-
CH2-C5H3N-C5H3N-OH)RuH(PPh3)2(CO)][Cl] (2c) were
afforded, respectively (Scheme 2).
The 1H NMR spectrum of 2b in CD3OD shows a triplet for
the Ru−H group at −10.90 ppm. The 31P NMR spectrum
shows one singlet for the two PPh3 groups at 45.7 ppm. The IR
spectrum exhibits a strong CO absorption at 1947 cm−1 (in
DCM). Complex 2c displays similar NMR and IR spectra,
indicating their analogous structures.
Scheme 1. Synthesis of Our Previous Ruthenium Complexes
1a−c22
The structure of 2c was further characterized by X-ray
crystallography (Figure 2). The Ru ion is coordinated in an
Complexes 1a−c contain two or three proton-responsive sites
(−OH and −CH2−); however, their reactions with bases did
not give any identified products. Herein, we report the
synthesis of ruthenium hydride complexes supported by L1−L3
and their reactivity with base. Furthermore, these ruthenium
complexes also showed high catalytic activity for β-alkylation of
secondary alcohols with primary alcohols in air, which is
regarded as an environmentally friendly method to synthesize
β-alkylated alcohols and has been catalyzed by other
ruthenium complexes.17b,c,23,24
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Ru(II) Complexes.
Reaction of L1 with RuHCl(PPh3)3(CO) in refluxing methanol
gave the product [(HO-C5H3N-CH2-C5H3N-C5H3N−OH)-
RuH(PPh3)2(CO)][Cl] (2a) (Scheme 2). The 1H NMR
Figure 2. Solid-state structure of complex 2c. The thermal ellipsoids
are displayed at 30% probability. Hydrogen atoms (except Ru−H and
−OH), phenyl rings on PPh3 ligands, and the Cl− anion have been
omitted for clarity. Selected bond distances (Å): Ru(1)−N(1),
2.204(6); Ru(1)−N(2), 2.178(6); Ru(1)−P(1), 2.373(2); Ru(1)−
P(2), 2.379(2); Ru(1)−C(54), 1.816(8); Ru(1)−H(1), 1.657;
C(5)−N(1), 1.367(9); N(1)−C(1), 1.325(9); O(1)−C(1),
1.338(9); C(1)−C(2), 1.382(10); O(1)−H(1A), 0.820.
Scheme 2. Synthesis of Complexes 2a−c
octahedral geometry. The ligand L3 coordinates with the Ru
atom via its bipyridyl N atoms. The CO ligand is trans to the
middle pyridyl ring, and the hydride is trans to the pyridinol
group. The two PPh3 groups are in trans positions.
Complex 2a was then treated with 2 equiv of t-BuOK, and
the product [(O-C5H3N-CH2-C5H3N-C5H3N-OH)RuH-
(PPh3)(CO)] (3a) was obtained in 98% yield (Scheme 3).
Different from complex 2a, the 1H NMR spectrum of 3a shows
two doublets at 5.19 and 4.15 ppm for the −CH2 group, which
means that the third pyridyl ring also coordinates with Ru. The
doublet at −12.68 ppm for the Ru−H indicates only one PPh3
left. The IR peak at 1935 cm−1 corresponds to a terminal CO.
Its red-shifted phenomenon in comparison to complex 2a is
ascribed to enhanced electron density at the metal center upon
ligand deprotonation, leading to greater donation into the CO
π* orbitals (Δν = −23 cm−1).18a The solid-state structure
reveals its exact geometry (Figure 3). The O(2)−C(16)
spectrum of 2a in CD3OD exhibits several groups of signals
between 8.68 and 6.30 ppm for the pyridyl and PPh3 groups
(39H), one singlet at 3.91 ppm for the −CH2− group (2H),
and one triplet at −11.90 ppm for Ru−H (1H). The 31P NMR
shows one singlet at 45.62 ppm. The IR spectrum displays one
absorption peak at 1958 cm−1 (in DCM) for the terminal CO.
These results indicate there are two trans-PPh3, one CO, one
B
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Complex 2b exhibited reactivity similar to that of 2a with t-
BuOK, and [(O-C5H3N-CH2-C5H3N-C5H4N)RuH(PPh3)-
(CO)] (3b) was afforded within 10 min (Scheme 3). Complex
Scheme 3. Synthesis of Complexes 3a,b
1
3b was identified by H and 31P NMR, IR, elemental analysis,
and X-ray crystallography (Figure 4).
Figure 4. Solid-state structure of complex 3b. The thermal ellipsoids
are displayed at 30% probability. Hydrogen atoms (except Ru−H)
and phenyl rings on the PPh3 ligand have been omitted for clarity.
Selected bond distances (Å): Ru(1)−N(1), 2.186(3); Ru(1)−N(2),
2.125(3); Ru(1)−N(3), 2.156(3); Ru(1)−P(1), 2.2804(9); Ru(1)−
C(35), 1.823(4); Ru(1)-H(1A), 1.580; C(15)−H(16), 1.431(7);
O(1)−C(16), 1.251(6); N(3)−C(16), 1.371(5); N(3)−C(12),
1.354(5); C(12)−C(11), 1.525(7); C(10)−C(11), 1.479(7);
N(2)−C(10), 1.332(6); N(2)−C(6), 1.379(6); C(5)−C(6),
1.438(7); N(1)−C(5), 1.301(6); N(1)−C(1), 1.354(6); C(2)−
C(1), 1.373(7).
Figure 3. Solid-state structure of complex 3a. The thermal ellipsoids
are displayed at 30% probability. Hydrogen atoms (except Ru−H and
−OH) and phenyl rings on PPh3 ligand have been omitted for clarity.
Selected bond distances (Å): Ru(1)−N(1), 2.231(2); Ru(1)−N(2),
2.128(2); Ru(1)−N(3), 2.142(2); Ru(1)−P(1), 2.3051(7); Ru(1)−
C(35), 1.824(3); Ru(1)-H(1A), 1.458; C(15)−H(16), 1.419(5);
O(2)−C(16), 1.291(4); N(3)−C(16), 1.361(4); N(3)−C(12),
1.361(4); C(12)−C(11), 1.521(5); C(10)−C(11), 1.500(5);
N(2)−C(10), 1.349(4); N(2)−C(6), 1.348(4); C(5)−C(6),
1.477(4); N(1)−C(5), 1.361(4); N(1)−C(1), 1.343(4); O(1)−
C(1), 1.309(4); O(1)−H(1), 0.820; C(2)−C(1), 1.410(5).
The reactivity of complex 2c with t-BuOK was slightly
different from that of 2a,b, and the two products [(C5H4N-
CH2-C5H3N-C5H3N-O)RuH(PPh3)2(CO)] (3c) and
[(C5H4N-CH2-C5H3N-C5H3N-O)RuH(PPh3)(CO)] (3d)
were obtained in 56% and 11% yields, respectively, after reflux
in isopropyl alcohol for 24 h. Complex 3c could also be
transformed to 3d with 10% yield without any other additives,
also after reflux in isopropyl alcohol for 24 h. However, in the
presence of 10 equiv of PPh3, complex 3d was completely
converted back to 3c (Scheme 4). It should be noted that
complexes 2c and 3c have the same polarity, and so they might
be mistakenly regarded as the same compound. Significant
distance (1.291(4) Å) is similar to those of a pyridinol
diruthenium complex supported by deprotonated 6,6′-
dihydroxyterpyridine developed by Szymczak’s group, suggest-
ing a CO bond.18a The C−O single distance (O(1)−C(1),
1.309(4) Å) is also comparable to those of Szymczak’s
ruthenium complexes.18a This means that the −OH group of
PyCH2PyOH is more acidic than that of PyPyOH, or else
H(1) would transfer to the pyridinol moiety. The results
suggested complex 3a was formed by the selective deproto-
nation of the −OH group in the uncoordinated 2-
hydroxypyridyl ring of complex 2a, followed by the
substitution of one PPh3. The three pyridyl rings are mutually
cis and are not in the same plane. Even though excess t-BuOK
was used, the other −OH group and the −CH2− group were
unreactive.
1
differences are observed in their H NMR, 31P NMR, and IR
1
spectra. The H NMR spectrum of complex 3c in CD3OD
Scheme 4. Synthesis and Relationship of Complexes 3c,d
C
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a
Table 1. β-Alkylation of 1-Phenylethanol with Benzyl Alcohol Using Ru Complexes 2a−c and 3a−d
b
c
entry
catalyst
conv (%)
A:B ratio
1
2
3
4
5
6
7
2a
2b
2c
3a
3b
3c
3d
51
70
94
26
36
94
70
98:2
98:2
95:5
88:12
90:10
96:4
86:14
a
Reaction conditions: catalyst (0.5 mol %), 1-phenylethanol (2.0 mmol), benzyl alcohol (2.0 mmol), and t-BuOK (1 mmol) at reflux in toluene for
b
c
60 min under an N2 atmosphere. Determined by GC analysis on the basis of secondary alcohol. Determined by GC analysis.
a
Table 2. β-Alkylation of 1-Phenylethanol with Benzyl Alcohol in the Presence of Different Bases
b
entry
base (amt (equiv))
conv (%)
1
2
3
4
5
6
7
8
9
10
Na2CO3 (0.5)
K2CO3 (0.5)
Cs2CO3 (0.5)
KOH (0.5)
NaOH (0.5)
t-BuOK (0.5)
t-BuOK (0.4)
t-BuOK (0.3)
t-BuOK (0.2)
t-BuOK (0.1)
t-BuOK (0.5)
no base
2
4
5
85
91
94
88
78
56
44
94
0
c
11
12
d
13
e
t-BuOK (0.5)
t-BuOK (0.5)
0
52
14
a
Reaction conditions unless specified otherwise: catalyst 2c (0.5 mol %), 1-phenylethanol (2.0 mmol), benzyl alcohol (2.0 mmol), and base at
b
c
reflux in toluene for 60 min. Determined by GC analysis on the basis of secondary alcohol. The reaction was carried out in an air atmosphere.
d
e
No catalyst. The reaction was carried out at 90 °C.
shows no signal between 8.00 and 7.70 ppm, while that of 2c
shows a doublet at 7.88 ppm. Their singlet of the −CH2−
group and the triplet of the Ru−H group are also slightly
different (4.24 and −11.26 ppm for 3c; 4.16 and −11.39 ppm
for 2c). The 31P NMR spectrum of complex 3c shows one
singlet for the two PPh3 groups at 46.2 ppm in CDCl3,
comparable to that of 2c (47.6 ppm). The CO absorptions of
complexes 3c and 2c exhibit a Δν value of 9 cm−1 (1945 cm−1
for 3c and 1954 cm−1 for 2c). Complex 3d was also identified
ypyridyl in 2a is stronger than that of pyridyl in 2c, and as long
as the deprotonated intermediate formed, the pyridinol group
attacked the ruthenium center, accompanied by the loss of one
PPh3. The results further support that it was the −OH group of
the PyCH2PyOH moiety that was deprotonated during the
reaction.
β-Alkylation of Secondary Alcohols with Primary
Alcohols. Initially, the coupling of 1-phenylethanol and benzyl
alcohol was selected as a model reaction to test the catalytic
activity of complexes 2a−c and 3a−d. The reactions were
conducted in toluene at 110 °C for 60 min. Ruthenium
complexes (0.5 mol %) were used as the precatalysts and t-
BuOK (0.5 equiv) as the base under an N2 atmosphere, and
the results are shown in Table 1. It can be seen that complexes
2c and 3c show the highest catalytic activity, giving 94%
conversion within 60 min in both cases (entries 3 and 6). The
tridentate complexes 3a,b,d are not as active as the bidentate
complexes 2a−c, indicating that they are not the reaction
intermediates of those bidentate complexes. The catalytic
1
by H and 31P NMR, IR, and elemental analysis, and the
spectroscopic analysis indicates that it displays a structure
similar to that of 3a,b.
We further calculated the relative free energies of 3c,d using
the DFT method and found that 3d was higher than 3c by 7.4
kcal/mol. This result explains the low yield of 3d, and it is
consistent with the observed conversion of 3d to 3c in the
presence of PPh3.
No bidentate product similar to 3c was detected when
complex 2a was treated with t-BuOK, indicating that the
nucleophilicity of the deprotonated uncoordinated 2-hydrox-
D
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a
Table 3. β-Alkylation of 1-Phenylethanol and Its Derivatives with a Variety of Primary Alcohols
a
Reaction conditions unless specified otherwise: catalyst 2c (0.5 mol %), 1-phenylethanol (2.0 mmol), benzyl alcohol (2.0 mmol), and t-BuOK (1
b
c
mmol) at reflux in toluene for 60 min in an air atmosphere. Determined by GC analysis on the basis of secondary alcohol. 2 h reflux.
activities of complexes 2c and 3c are similar, suggesting 3c is
the catalytic intermediate of 2c.
example, a 94% conversion within 60 min was achieved when
t-BuOK was used. Next, to optimize the base quantity
required, different amounts of t-BuOK were tested, and 0.5
equiv was the best (entries 6−10). Unexpectedly, when the
reaction was carried out in an air atmosphere, the conversion
rate did not decrease (entry 11). This was encouraging because
such reactions usually require an N2 atmosphere.17b,c,23,24
Without a catalyst or base, the reaction failed to take place
(entries 12 and 13). When the reaction was carried at 90 °C,
Subsequently, to optimize the reaction conditions for β-
alkylation of 1-phenylethanol with benzyl alcohol catalyzed by
2c, other bases were tested, and the results are given in Table
2. Weak bases such as Na2CO3, K2CO3, and Cs2CO3 revealed
low conversion in the reaction (entries 1−3). When strong
bases such as KOH, t-BuOK, and NaOH were chosen, the
conversion rate was significantly increased (entries 4−6). For
E
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a
Table 4. β-Alkylation of 1-Phenylethanol with Benzyl Alcohol Using Ru Complexes 3c−e for Different Times
b
entry
catalyst
time (min)
conv (%)
1
2
3
4
5
6
7
8
9
3c
3d
3c
3d
3c
3d
3c
3d
3c
3d
3e
5
5
13
14
28
25
58
39
75
59
94
70
60
10
10
20
20
30
30
60
60
60
10
11
c
a
Reaction conditions unless specified otherwise: catalyst (0.5 mol %), 1-phenylethanol (2.0 mmol), benzyl alcohol (2.0 mmol), and t-BuOK (1
b
c
mmol) at reflux in toluene for 60 min in an air atmosphere. Determined by GC analysis on the basis of secondary alcohol. Catalyst (0.25 mol %).
the conversion was decreased to 52% within 60 min (entry
14).
Scheme 5. Synthesis of 3e
On the basis of the above results, the optimized reaction
conditions were established (entry 3 in Table 1 and entry 11 in
Table 2). β-alkylation of 1-phenylethanol and its derivatives
with a variety of primary alcohols was performed. As shown in
Table 3, most substrates exhibit excellent conversion and
selectivity except for entries 1 and 9. From entries 1−3, it can
be observed that the chloro-substituted benzyl alcohols at a
meta or para position convert to the desired secondary
alcohols with 1-phenylethanol in higher conversion and
selectivity in comparsion to that at an ortho position, probably
due to a steric hindrance effect. In addition, no obvious
substituent effect is observed when either an electron-
withdrawing group or an electron-donating group is intro-
duced to the para position of benzyl alcohol (entries 3−6).
Furthermore, naphthalen-1-ylmethanol also has a good
conversion (95%) and selectivity (100:0) (entry 7). On the
other hand, an electron-withdrawing group at the para position
of 1-phenylethanol does not obviously influence the reaction,
while an electron-donating group decreases the activity and
selectivity dramatically (entries 8 and 9).
As shown in Table 1, complex 3d is not as active as 3c in 60
min. However, at shorter reaction times (5 and 10 min), their
catalytic activities are similar (Table 4, entries 1−4). We
hypothesized this phenomenon might be due to the relative
instability of 3d.
To test our hypothesis, complex 3d was then heated in
refluxing toluene, and the diruthenium complex [(C5H4N-CH-
C5H3N-C5H3N-O)Ru(PPh3)(CO)]2 (3e) was obtained
(Scheme 5). Different from complex 3d, the characteristic
Figure 5. Solid-state structure of complex 3e. The thermal ellipsoids
are displayed at 30% probability. Hydrogen atoms and phenyl rings on
the PPh3 ligand have been omitted for clarity. Selected bond distances
(Å): Ru(1)−N(1), 2.086(3); Ru(1)−N(2), 2.104(3); Ru(1)−N(3),
2.122(3); Ru(1)−P(1), 2.3666(9); Ru(1)−C(35), 1.845(4); Ru(1)−
C(11), 2.296(3); C(1)−C(2), 1.428(5); O(1)−C(1), 1.257(5);
N(1)−C(1), 1.392(4); N(1)−C(5), 1.367(5); C(5)−C(6),
1.477(5); C(6)−N(2), 1.365(4); N(2)−C(10), 1.349(4); C(10)−
C(11), 1.463(5); C(11)−C(12), 1.466(5); N(3)−C(12), 1.364(4).
1
peak for Ru−H disappeares in the H NMR spectrum of 3e.
The IR absorption at 1939 cm−1 corresponds to the terminal
CO groups. The X-ray crystallographic structure shows that 3e
is a diruthenium complex with Ci symmetry, and the Ru(1)−
C(11A) bond is formed via C−H activation of the −CH2−
group (Figure 5). As expected, complex 3e is not as active as
3c,d with the same amount of Ru atoms (Table 4, entry 11),
which explains why 3c is more active than 3d over a longer
period of time (Table 4, entries 5−10).
Reaction Mechanism. On the basis of relevant literature, a
plausible mechanism for this tandem β-alkylation of secondary
F
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Scheme 6. Proposed Reaction Mechanism
alcohols with primary alcohols catalyzed by 2c is shown in
Scheme 6.17b,c In the presence of t-BuOK, precatalyst 2c first
transforms to 3c with a 2-pyridinol ligand via dearomatization
by extrusion of one molecule of HCl. Then, 3c loses one
molecule of PPh3 to form the active intermediate C with an
open site. C further reacts with potassium alkoxide to generate
the alkoxy ruthenium species D. A similar K+-bound alkoxide
intermediate has been confirmed in Szymczak’s system.18a
D
undergoes β-H elimination by releasing one molecule of
carbonyl compounds to afford the dihydride Ru(II) species E.
Next, a base-catalyzed cross-aldol condensation between the
ketones and aldehydes affords α,β-unsaturated ketones. Finally,
the Ru hydride and the K+ in F cooperate to promote the
hydrogenation of a CC bond of the α,β-unsaturated ketones,
resulting in the regeneration of C and the formation of ketone
B. B could be further converted to A following a similar
cooperative process.
In order to further investigate whether dissociation of PPh3
is involved in the catalytic cycle, the β-alkylation of 1-
phenylethanol with benzyl alcohol was performed in the
presence of excess PPh3 (2−8 equiv) (Figure 6).17b,18e It was
Figure 6. Effect of externally added PPh3 on catalyst 2c in β-alkylation
of 1-phenylethanol with benzyl alcohol.
G
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Article
°C (oil bath temperature) for 60 min. After the mixture was cooled to
room temperature, the toluene was evaporated under reduced
pressure and the resulting mixture was purified by silica gel column
chromatography using ethyl acetate and hexane as eluent to afford the
desired product.
observed that the conversion of 1-phenylethanol continuously
decreased with increasing amounts of PPh3. The above
experimental results demonstrated that the elimination of
PPh3 played a vital role in the catalytic cycle. However, as
intermediates C−F have not been isolated, a detailed
mechanistic analysis requires further investigation.
Synthesis of 2a. A solution of L1 (0.18 g, 0.63 mmol) and
RuHCl(PPh3)3(CO) (0.60 g, 0.63 mmol) was heated in refluxing
methanol (200 mL) for 24 h. The mixture was cooled to room
temperature, and the organic phase was evaporated under vacuum.
The crude product was recrystallized with dichloromethane/ether to
give 2a as a yellow powder (0.47 g, 78%). Anal. Calcd for
C53H44ClN3O3P2Ru: C, 65.67; H, 4.57; N, 4.33. Found: C, 65.96;
CONCLUSIONS
■
In summary, the three bidentate ruthenium hydride complexes
2a−c with several proton-responsive sites supported by
unsymmetrical NNN ligands were synthesized. Reactions of
2a,b with t-BuOK gave tridentate products 3a,b, respectively,
via selective deprotonation of the −OH group of the
PyCH2PyOH moiety. The results indicate the −OH group
of the PyCH2PyOH moiety is more acidic than that of
PyPyOH and the −CH2− group. The reactivity with t-BuOK
of 2c was different from that of 2a,b. In addition to the
tridentate product 3d, the bidentate product 3c was also
obtained. It is more difficult for the pyridyl group to replace
PPh3 than the deprotonated pyridinol group, because of their
nucleophilic difference. Although the −CH2− group in 3d is
not reactive with t-BuOK, it can be activated by the other
molecule of 3d to form 3e with H2 release. The
aforementioned eight complexes were tested as catalysts for
β-alkylation of secondary alcohols with primary alcohols, and
the bidentate complexes 2c and 3c showed the highest activity.
The conversion reached 94% in 60 min with 0.5 mol % of
catalyst in both cases, when 1-phenylethanol and benzyl
alcohol were used as substrates. As an unexpected benefit,
these reactions were not compromised in air. The tridentate
complexes 3a,b,d are less active than the corresponding
bidentate complexes, indicating they are not the intermediates
of 2a−c, and the lower efficiency of 3d in comparison to 3c is
due to its dimerization behavior to form 3e. However, 3c can
be regarded as the intermediate of 2c, confirming that the
catalytic transformation undergoes an aromatization−dearo-
matization process. The results in this paper are important for
developing more efficient bifunctional catalysts for β-alkylation
of secondary alcohols with primary alcohols.
1
H, 4.63; N, 4.26. H NMR (400 MHz, CD3OD, ppm): 8.68 (d, J =
5.2 Hz, 1H), 8.30 (d, J = 8.0 Hz, 1H), 8.23 (d, J = 8.0 Hz, 1H), 7.93−
7.82 (m, 3H), 7.43−7.13 (m, 31H), 6.73 (d, J = 8.0 Hz, 1H), 6.30 (d,
J = 9.2 Hz, 1H), 3.91 (s, 2H), −11.90 (t, J = 18.4 Hz, 1H). 31P NMR
(162 MHz, CD3OD, ppm): 45.6. IR (νCO, in DCM, cm−1): 1958 (s).
Synthesis of 2b. A solution of L2 (0.17 g, 0.63 mmol) and
RuHCl(PPh3)3(CO) (0.60 g, 0.63 mmol) was heated in refluxing
methanol (200 mL) for 24 h. The mixture was cooled to room
temperature, and the organic phase was evaporated under vacuum.
The crude product was recrystallized with dichloromethane/ether to
give 2b as a yellow powder (0.38 g, 63%). Anal. Calcd for
C53H44ClN3O2P2Ru: C, 66.77; H, 4.65; N, 4.41. Found: C, 66.65;
1
H, 4.50; N, 4.46. H NMR (400 MHz, CD3OD, ppm): 8.69 (d, J =
3.2 Hz, 1H), 8.30 (d, J = 5.2 Hz, 1H), 8.23 (d, J = 5.6 Hz, 1H), 7.91
(t, J = 5.6 Hz, 1H), 7.84 (t, J = 5.4 Hz, 1H), 7.43−7.21 (m, 31H),
7.19−7.14 (m, 2H), 6.73 (d, J = 5.2 Hz, 1H), 6.30 (d, J = 6.0 Hz,
1H), 3.91 (s, 2H), −10.90 (t, J = 12.0 Hz, 1H). 31P NMR (162 MHz,
CD3OD, ppm): 45.7. IR (νCO, in DCM, cm−1): 1947 (s).
Synthesis of 2c. A solution of L3 (0.17 g, 0.63 mmol) and
RuHCl(PPh3)3(CO) (0.60 g, 0.63 mmol) was heated in refluxing
methanol (200 mL) for 24 h. The mixture was cooled to room
temperature, and the organic phase was evaporated under vacuum.
The crude product was recrystallized with acetone to give 2c as a
yellow powder (0.38 g, 63%). A crystal suitable for a single-crystal X-
ray diffraction experiment was grown by vapor diffusion of n-hexane
into a dichloromethane solution of 2c at room temperature. Anal.
Calcd for C53H44ClN3O2P2Ru: C, 66.77; H, 4.65; N, 4.41. Found: C,
66.96; H, 4.76; N, 4.40. 1H NMR (400 MHz, CD3OD, ppm): 8.34 (d,
J = 5.6 Hz, 1H), 7.88 (d, J = 8.0 Hz, 1H), 7.65 (t, J = 7.6 Hz, 1H),
7.59 (m, 2H), 7.48 (m, 1H), 7.40−7.18 (m, 30H), 7.17−7.13 (m,
1H), 6.73 (d, J = 8.0 Hz, 1H), 6.37 (d, J = 7.6 Hz, 1H), 6.18 (d, J =
7.6 Hz, 1H), 4.16 (s, 2H), −11.39 (t, J = 19.2 Hz, 1H). 31P NMR
(162 MHz, CD3OD, ppm): 47.6. IR (νCO, in DCM, cm−1): 1954 (s).
Synthesis of 3a. A solution of 2a (1.0 g, 1.0 mmol) and t-BuOK
(0.22 g, 2.0 mmol) was heated in refluxing isopropyl alcohol (300
mL) for 24 h. The mixture was cooled to room temperature, and the
organic phase was evaporated under vacuum. The crude product was
recrystallized with acetone to give 3a as an orange-red powder (0.64 g,
98%). A crystal suitable for a single-crystal X-ray diffraction
experiment was grown by vapor diffusion of n-hexane into a
dichloromethane solution of 3a at room temperature. Anal. Calcd
for C35H28N3O3PRu: C, 62.68; H, 4.21; N, 6.27. Found: C, 62.45; H,
4.40; N, 6.12. 1H NMR (400 MHz, CDCl3, ppm): 16.19 (s, 1H), 7.54
(br s, 1H), 7.33−7.06 (m, 19H), 6.84 (br s, 1H), 6.72 (d, J = 7.6 Hz,
1H), 6.56 (d, J = 7.6 Hz, 1H), 6.45 (br s, 1H), 5.19 (d, J = 13.6 Hz,
1H), 4.15 (d, J = 13.6 Hz, 1H), −12.68 (d, J = 28.8 Hz, 1H). 31P
NMR (162 MHz, CDCl3, ppm): 59.0. IR (νCO, in DCM, cm−1): 1935
(s).
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were carried out
under an inert nitrogen atmosphere using a Schlenk line. Solvents
were distilled from the appropriate drying agents under N2 before use.
All reagents were purchased from commercial sources. Liquid
compounds were degassed by standard freeze−pump−thaw proce-
22a
dures prior to use. RuHCl(PPh3)3(CO)25 and L1−L3
were
prepared as previously described, respectively. The 1H and 31P
NMR spectra were recorded on a Bruker Avance 400 spectrometer.
The H NMR chemical shifts were referenced to residual solvent as
1
determined relative to Me4Si (δ 0 ppm). The 31P{1H} chemical shifts
were reported in ppm relative to external 85% H3PO4. Elemental
analyses were performed on a PerkinElmer 240C analyzer. X-ray
diffraction studies were carried out in a SuperNova X-ray single-
crystal diffractometer. Data collections were performed using four-
circle kappa diffractometers equipped with CCD detectors. Data were
reduced and then corrected for absorption. Solution, refinement, and
geometrical calculations for all crystal structures were performed by
SHELXTL.
Synthesis of 3b. A solution of 2b (1.0 g, 1.0 mmol) and t-BuOK
(0.22 g, 2.0 mmol) was heated in refluxing isopropyl alcohol (300
mL) for 10 min. The mixture was cooled to room temperature, and
the organic phase was evaporated under vacuum. The crude product
was recrystallized with acetone to give 3b as an orange-red powder
(0.60 g, 92%). A crystal suitable for a single-crystal X-ray diffraction
experiment was grown by vapor diffusion of n-hexane into a
dichloromethane solution of 3b at room temperature. Anal. Calcd
for C35H28N3O2PRu: C, 64.21; H, 4.31; N, 6.42. Found: C, 64.12; H,
General Procedure for β-Alkylation of Secondary Alcohols
with Primary Alcohol. The catalytic β-alkylation of secondary
alcohol reaction was carried out in a flask in air. Initially catalyst 2c
(0.5 mol %) and t-BuOK (0.5 equiv) were taken as solids and then in
air a secondary alcohol (1 equiv), primary alcohol (1 equiv), and
toluene (3 mL) were added; the resulting mixture was heated at 110
1
4.45; N, 6.42. H NMR (400 MHz, CDCl3, ppm): 9.49 (br s, 1H),
H
DOI: 10.1021/acs.organomet.8b00432
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Article
7.72−6.99 (m, 23H), 6.22−6.08 (m, 1H), 5.11 (d, J = 13.6 Hz, 1H),
4.13 (d, J = 13.6 Hz, 1H), −12.01 (d, J = 29.0 Hz, 1H). 31P NMR
(162 MHz, CDCl3, ppm): 59.1. IR (νCO, in DCM, cm−1): 1935 (s).
Synthesis of 3c,d. A solution of 2c (1.0 g, 1.0 mmol) and t-BuOK
(0.22 g, 2.0 mmol) was heated in refluxing isopropyl alcohol (300
mL) for 24 h. The mixture was cooled to room temperature, and the
organic phase was evaporated under vacuum to provide a mixture of
3c and 3d. The mixture was purified by column chromatography on
silica gel (eluent: ethyl acetate/methanol, 5/1 v/v) to give 3c (0.51 g,
56%) as a yellow powder and 3d (0.07 g, 11%) as a brown powder. 3c
could also transform to 3d in 10% yield without any other additives in
refluxing isopropyl alcohol for 24 h. When 3d was added to 10 equiv
of PPh3 in refluxing isopropyl alcohol for 24 h, 3d transformed
completely into 3c. Data for 3c are as follows. Anal. Calcd for
C53H43N3O2P21Ru: C, 69.42; H, 4.73; N, 4.58. Found: C, 69.35; H,
4.62; N, 4.52. H NMR (400 MHz, CD3OD, ppm): 8.34 (d, J = 4.8
Hz, 1H), 7.62 (d, J = 8.0 Hz, 1H), 7.51−7.14 (m, 34H), 6.99 (d, J =
7.2 Hz, 1H), 6.56 (d, J = 8.4 Hz, 1H), 6.33 (d, J = 7.6 Hz, 1H), 6.08
(d, J = 8.0 Hz, 1H), 4.24 (s, 2H), −11.26 (t, J = 19.2 Hz, 1H). 31P
NMR (162 MHz, CDCl3, ppm): 46.2. IR (νCO, in DCM, cm−1): 1945
(s). Data for 3d are as follows. Anal. Calcd for C35H28N3O2PRu: C,
64.21; H, 4.31; N, 6.42. Found: C, 64.13; H, 4.22; N, 6.35. 1H NMR
(400 MHz, CD3OD, ppm): 9.53 (d, J = 5.2 Hz, 1H), 7.75−7.66 (m,
3H), 7.51 (d, J = 7.6 Hz, 1H), 7.45 (d, J = 8.0 Hz, 1H), 7.36−7.13
(m, 17H), 6.84 (d, J = 7.2 Hz, 1H), 6.36 (d, J = 8.4 Hz, 1H), 5.11 (d,
J = 13.6 Hz, 1H), 4.48 (d, J = 14.0 Hz, 1H), −12.16 (d, J = 28.8 Hz,
1H). 31P NMR (162 MHz, CD3OD, ppm): 60.7. IR (νCO, in DCM,
cm−1): 1938 (s).
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 for X.Y.: xyang@iccas.ac.cn.
*E-mail for D.C.: dafachen@hit.edu.cn.
■
ORCID
Xinzheng Yang: 0000-0002-2036-1220
Dafa Chen: 0000-0002-7650-4024
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (Nos. 21672045, 21702038, and
21673250), the National Science and Technology Pillar
Program during the Twelfth Five-Year Plan Period
(2015BAD15B0502), the China Postdoctoral Science Founda-
tion (2016M591519), Shenzhen Fundamental research proj-
e c t s ( J C Y J 2 0 1 6 0 5 2 5 1 6 4 2 2 7 3 5 0 , a n d
JCYJ20170811161344569), and the Heilongjiang Postdoctoral
Foundation (LBH-Z16069).
Synthesis of 3e. A solution of 3d (0.1 g, 0.15 mmol) was heated in
refluxing toluene (50 mL) for 60 min. The yellow precipitate was
collected, washed with copious amounts of ether, and dried under
vacuum to provide 3e as a yellow powder (0.10 g, 54%). A crystal
suitable for a single-crystal X-ray diffraction experiment was grown by
vapor diffusion of ether into a dichloromethane solution of 3e at room
temperature. Anal. Calcd for C70H52N6O4P2Ru2: C, 64.41; H, 4.02; N,
REFERENCES
■
(1) For selected reviews, see: (a) Khusnutdinova, J. R.; Milstein, D.
Metal-Ligand Cooperation. Angew. Chem., Int. Ed. 2015, 54, 12236−
12273. (b) Zell, T.; Milstein, D. Hydrogenation and Dehydrogenation
Iron Pincer Catalysts Capable of Metal-Ligand Cooperation by
Aromatization/Dearomatization. Acc. Chem. Res. 2015, 48, 1979−
1994. (c) Morris, R. H. Exploiting Metal-Ligand Bifunctional
Reactions in the Design of Iron Asymmetric Hydrogenation Catalysts.
Acc. Chem. Res. 2015, 48, 1494−1502. (d) Li, H.; Zheng, B.; Huang,
K. W. A New Class of PN3-Pincer Ligands for Metal-Ligand
Cooperative Catalysis. Coord. Chem. Rev. 2015, 293−294, 116−138.
(e) Younus, H. A.; Su, W.; Ahmad, N.; Chen, S.; Verpoort, F.; et al.
Ruthenium Pincer Complexes: Synthesis and Catalytic Applications.
Adv. Synth. Catal. 2015, 357, 283−330. (f) Werkmeister, S.;
Neumann, J.; Junge, K.; Beller, M.; et al. Pincer-Type Complexes
for Catalytic (De) Hydrogenation and Transfer (De) Hydrogenation
Reactions: Recent Progress. Chem. - Eur. J. 2015, 21, 12226−12250.
(g) Kuwata, S.; Ikariya, T. Metal-Ligand Bifunctional Reactivity and
Catalysis of Protic N-Heterocyclic Carbene and Pyrazole Complexes
Featuring β-NH Units. Chem. Commun. 2014, 50, 14290−14300.
(h) Gunanathan, C.; Milstein, D. Bond Activation and Catalysis by
Ruthenium Pincer Complexes. Chem. Rev. 2014, 114, 12024−12087.
(i) Zhao, B.; Han, Z.; Ding, K. The N-H Functional Group in
Organometallic Catalysis. Angew. Chem., Int. Ed. 2013, 52, 4744−
1
6.44. Found: C, 64.38; H, 4.08; N, 6.42. H NMR (400 MHz, a
mixture of CDCl3 and CD3OD, ppm): 7.41 (d, J = 8.4 Hz, 2H), 7.23
(t, J = 7.6 Hz, 4H), 7.08 (t, J = 6.4 Hz, 8H), 6.96−6.81 (m, 22H),
6.43 (d, J = 8.4 Hz, 2H), 6.37 (d, J = 7.6 Hz, 2H), 6.30 (d, J = 7.2 Hz,
2H), 6.22 (t, J = 7.0 Hz, 2H), 5.74 (d, J = 7.6 Hz, 2H), 5.42−5.36 (m,
4H), 4.50 (s, 2H). 31P NMR (162 MHz, a mixture of CDCl3 and
CD3OD, ppm): 41.2. IR (νCO, in DCM, cm−1): 1939 (s).
Computational Details. All DFT calculations in this study were
performed using the Gaussian 09 suite of programs26 for the M06
functional27 in conjunction with an all-electron 6-31G(d) basis set for
H, C, N, O, and P atoms. The Stuttgart relativistic effective core
potential basis set was used for Ru (ECP28MWB).28 An ultrafine grid
(99,590) was used for numerical integrations. All structures were fully
optimized in toluene with solvent effects corrected by using the
integral equation formalism polarizable continuum model
(IEFPCM)29 and the SMD radii.30 Thermal corrections were
computed within the harmonic potential approximation on optimized
structures at 298.15 K and 1 atm pressure.
ASSOCIATED CONTENT
* Supporting Information
■
̈
4788. (j) Warner, M. C.; Backvall, J.-E. Mechanistic Aspects on
S
Cyclopentadienylruthenium Complexes in Catalytic Racemization of
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00432.
Alcohols. Acc. Chem. Res. 2013, 46, 2545−2555.
(2) For selected examples, see: (a) Chakraborty, S.; Leitus, G.;
Milstein, D. Iron-Catalyzed Mild and Selective Hydrogenative Cross-
Coupling of Nitriles and Amines To Form Secondary Aldimines.
Angew. Chem., Int. Ed. 2017, 56, 2074−2078. (b) Matsunami, A.;
Kuwata, S.; Kayaki, Y. A Bifunctional Iridium Catalyst Modified for
Persistent Hydrogen Generation from Formic Acid: Understanding
Deactivation via Cyclometalation of a 1, 2-Diphenylethylenediamine
Motif. ACS Catal. 2017, 7, 4479−4484. (c) Yuwen, J.; Chakraborty,
S.; Brennessel, W. W.; Jones, W. D. Additive-Free Cobalt-Catalyzed
Hydrogenation of Esters to Alcohols. ACS Catal. 2017, 7, 3735−
Crystallographic details and IR and NMR spectra of the
new compounds (PDF)
Calculated absolute energies and atomic coordinates of
all optimized structures (XYZ)
Accession Codes
CCDC 1433315−1433316, 1433385, and 1837086 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
́
3740. (d) Piehl, P.; Penalopez, M.; Frey, A.; Neumann, H.; Beller, M.
̃
Hydrogen Autotransfer and Related Dehydrogenative Coupling
I
DOI: 10.1021/acs.organomet.8b00432
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Reactions Using a Rhenium (I) Pincer Catalyst. Chem. Commun.
2017, 53, 3265−3268. (e) Nguyen, D. H.; Trivelli, X.; Capet, F.; Paul,
J.-F.; Dumeignil, F.; Gauvin, R. M. Manganese Pincer Complexes for
the Base-Free, Acceptorless Dehydrogenative Coupling of Alcohols to
Esters: Development, Scope, and Understanding. ACS Catal. 2017, 7,
2022−2032. (f) Chen, X.; Jing, Y.; Yang, X. Unexpected Direct
Hydride Transfer Mechanism for the Hydrogenation of Ethyl Acetate
to Ethanol Catalyzed by SNS Pincer Ruthenium Complexes. Chem. -
Eur. J. 2016, 22, 1950−1957. (g) Xu, R.; Chakraborty, S.; Bellows, S.
M.; Yuan, H.; Cundari, T. R.; Jones, W. D. Iron-Catalyzed
Homogeneous Hydrogenation of Alkenes under Mild Conditions
by a Stepwise, Bifunctional Mechanism. ACS Catal. 2016, 6, 2127−
2135. (h) Zuo, W.; Prokopchuk, D. E.; Lough, A. J.; Morris, R. H.
Details of the Mechanism of the Asymmetric Transfer Hydrogenation
of Acetophenone Using the Amine (imine) diphosphine Iron
Precatalyst: The Base Effect and The Enantiodetermining Step.
ACS Catal. 2016, 6, 301−314. (i) Nielsen, M.; Alberico, E.; Baumann,
W.; Drexler, H.-J.; Junge, H.; Gladiali, S.; Beller, M. Low-Temperature
Aqueous-Phase Methanol Dehydrogenation to Hydrogen and Carbon
Dioxide. Nature 2013, 495, 85−89. (j) Rodríguez-Lugo, R. E.;
Trincado, M.; Vogt, M.; Tewes, F.; Santiso-Quinones, G.;
Ruthenium Complexes Bearing Two Proton-Responsive Pyrazole
Arms. Chem. - Asian J. 2012, 7, 1417−1425. (f) Kashiwame, Y.;
Kuwata, S.; Ikariya, T. Catalytic Intramolecular Hydroamination with
a Bifunctional Iridium Pyrazolato Complex: Substrate Scope and
Mechanistic Elucidation. Organometallics 2012, 31, 8444−8455.
(5) Gunanathan, C.; Milstein, D. Metal-ligand Cooperation by
Aromatization-Dearomatization: a New Paradigm in Bond Activation
and “Green” Catalysis. Acc. Chem. Res. 2011, 44, 588−602.
(6) For recent examples, see: (a) Espinosa-Jalapa, N. A.; Kumar, A.;
Leitus, G.; Diskin-Posner, Y.; Milstein, D. Synthesis of Cyclic Imides
by Acceptorless Dehydrogenative Coupling of Diols and Amines
Catalyzed by a Manganese Pincer Complex. J. Am. Chem. Soc. 2017,
139, 11722−11725. (b) Zeng, R.; Feller, M.; Ben-David, Y.; Milstein,
D. Hydrogenation and Hydrosilylation of Nitrous Oxide Homoge-
neously Catalyzed by a Metal Complex. J. Am. Chem. Soc. 2017, 139,
5720−5723. (c) Xie, Y.; Ben-David, Y.; Shimon, L. J. W.; Milstein, D.
Highly Efficient Process for Production of Biofuel from Ethanol
Catalyzed by Ruthenium Pincer Complexes. J. Am. Chem. Soc. 2016,
138, 9077−9080. (d) Nerush, A.; Vogt, M.; Gellrich, U.; Leitus, G.;
Ben-David, Y.; Milstein, D. Template Catalysis by Metal-Ligand
Cooperation. C-C Bond Formation via Conjugate Addition of Non-
activated Nitriles under Mild, Base-free Conditions Catalyzed by a
Manganese Pincer Complex. J. Am. Chem. Soc. 2016, 138, 6985−
6997. (e) Feller, M.; Gellrich, U.; Anaby, A.; Diskin-Posner, Y.;
Milstein, D. Reductive Cleavage of CO2 by Metal-Ligand-Coopera-
tion Mediated by an Iridium Pincer Complex. J. Am. Chem. Soc. 2016,
138, 6445−6454.
(7) (a) Wen, H.; Zhang, L.; Zhu, S.; Liu, G.; Huang, Z.
Stereoselective Synthesis of Trisubstituted Alkenes via Cobalt-
Catalyzed Double Dehydrogenative Borylations of 1-Alkenes. ACS
Catal. 2017, 7, 6419−6425. (b) Hou, C.; Jiang, J.; Li, Y.; Zhao, C.;
Ke, Z. When Bifunctional Catalyst Encounters Dual MLC Modes:
DFT Study on the Mechanistic Preference in Ru-PNNH Pincer
Complex Catalyzed Dehydrogenative Coupling Reaction. ACS Catal.
2017, 7, 786−795. (c) Jia, X.; Huang, Z. Conversion of Alkanes to
Linear Alkylsilanes Using an Iridium-Iron-Catalysed Tandem
Dehydrogenation-Isomerization-Hydrosilylation. Nat. Chem. 2016,
8, 157−161. (d) Simler, T.; Braunstein, P.; Danopoulos, A. A.
Chromium(II) Pincer Complexes with Dearomatized PNP and PNC
Ligands: A Comparative Study of Their Catalytic Ethylene
Oligomerization Activity. Organometallics 2016, 35, 4044−4049.
(e) Zhang, L.; Zuo, Q.; Leng, X.; Huang, Z. A Cobalt-Catalyzed
Alkene Hydroboration with Pinacolborane. Angew. Chem., Int. Ed.
2014, 53, 2696−2700. (f) Zhang, L.; Peng, D.; Leng, X.; Huang, Z.
Iron-Catalyzed, Atom-Economical, Chemo-and Regioselective Alkene
Hydroboration with Pinacolborane. Angew. Chem., Int. Ed. 2013, 52,
3676−3680.
Grutzmacher, H. A Homogeneous Transition Metal Complex for
̈
Clean Hydrogen Production from Methanol-Water Mixtures. Nat.
Chem. 2013, 5, 342−347. (k) Otsuka, T.; Ishii, A.; Dub, P. A.; Ikariya,
T. Practical Selective Hydrogenation of α-Fluorinated Esters with
Bifunctional Pincer-Type Ruthenium (II) Catalysts Leading to
Fluorinated Alcohols or Fluoral Hemiacetals. J. Am. Chem. Soc.
2013, 135, 9600−9603.
(3) For selected examples, see: (a) Dahl, E. W.; Louisgoff, T.;
Szymczak, N. K. Second Sphere Ligand Modifications Enable a
Recyclable Catalyst for Oxidant-Free Alcohol Oxidation to Carbox-
ylates. Chem. Commun. 2017, 53, 2287−2289. (b) Gorgas, N.; Alves,
̈
L. G.; Stoger, B.; Martins, A. M.; Veiros, L. F.; Kirchner, K. Stable, Yet
Highly Reactive Nonclassical Iron (II) Polyhydride Pincer Com-
plexes: Z-Selective Dimerization and Hydroboration of Terminal
Alkynes. J. Am. Chem. Soc. 2017, 139, 8130−8133. (c) Li, H.; Wang,
Y.; Lai, Z.; Huang, K.-W. Selective Catalytic Hydrogenation of
Arenols by a Well-Defined Complex of Ruthenium and Phosphorus-
Nitrogen PN3-Pincer Ligand Containing a Phenanthroline Backbone.
ACS Catal. 2017, 7, 4446−4450. (d) Deibl, N.; Kempe, R. General
and Mild Cobalt-Catalyzed C-Alkylation of Unactivated Amides and
Esters with Alcohols. J. Am. Chem. Soc. 2016, 138, 10786−10789.
(e) Chai, H.; Liu, T.; Wang, Q.; Yu, Z. Substituent Effect on the
Catalytic Activity of Ruthenium (II) Complexes Bearing a Pyridyl-
Supported Pyrazolyl-Imidazolyl Ligand for Transfer Hydrogenation of
́
Ketones. Organometallics 2015, 34, 5278−5284. (f) Ferrer, I.; Rich, J.;
Fontrodona, X.; Rodríguez, M.; Romero, I. Ru (II) Complexes
Containing Dmso and Pyrazolyl Ligands as Catalysts for Nitrile
Hydration in Environmentally Friendly Media. Dalton Trans. 2013,
(8) Moore, C. M.; Dahl, E. W.; Szymczak, N. K. Beyond H2:
Exploiting 2-Hydroxypyridine as a Design Element from [Fe]-
Hydrogenase for Energy-Relevant Catalysis. Curr. Opin. Chem. Biol.
2015, 25, 9−17.
́
42, 13461−13469. (g) Bellarosa, L.; Díez, J.; Gimeno, J.; Lledos, A.;
́
Suarez, F. J.; Ujaque, G.; Vicent, C. Highly Efficient Redox
(9) (a) Fujita, K.; Tamura, R.; Tanaka, Y.; Yoshida, M.; Onoda, M.;
Yamaguchi, R. Dehydrogenative Oxidation of Alcohols in Aqueous
Media Catalyzed by a Water-Soluble Dicationic Iridium Complex
Bearing a Functional N-Heterocyclic Carbene Ligand without Using
Base. ACS Catal. 2017, 7, 7226−7230. (b) Fujita, K.; Wada, T.;
Shiraishi, T. Reversible Interconversion between 2,5-Dimethylpyr-
azine and 2,5-Dimethylpiperazine by Iridium-Catalyzed Hydro-
genation/Dehydrogenation for Efficient Hydrogen Storage. Angew.
Chem., Int. Ed. 2017, 56, 10886−10889. (c) Fujita, K.; Kawahara, R.;
Aikawa, T.; Yamaguchi, R. Hydrogen Production from a Methanol-
Water Solution Catalyzed by an Anionic Iridium Complex Bearing a
Functional Bipyridonate Ligand under Weakly Basic Conditions.
Angew. Chem., Int. Ed. 2015, 54, 9057−9060. (d) Zeng, G.; Sakaki, S.;
Fujita, K.; Sano, H.; Yamaguchi, R. Efficient Catalyst for Acceptorless
Alcohol Dehydrogenation: Interplay of Theoretical and Experimental
Studies. ACS Catal. 2014, 4, 1010−1020. (e) Fujita, K.; Tanaka, Y.;
Kobayashi, M.; Yamaguchi, R. Homogeneous Perdehydrogenation
and Perhydrogenation of Fused Bicyclic N-Heterocycles Catalyzed by
Isomerisation of Allylic Alcohols Catalysed by Pyrazole-Based
Ruthenium (IV) Complexes in Water: Mechanisms of Bifunctional
Catalysis in Water. Chem. - Eur. J. 2012, 18, 7749−7765.
(4) (a) Toda, T.; Saitoh, K.; Yoshinari, A.; Ikariya, T.; Kuwata, S.
Synthesis and Structures of NCN Pincer-Type Ruthenium and
Iridium Complexes Bearing Protic Pyrazole Arms. Organometallics
2017, 36, 1188−1195. (b) Touge, T.; Nara, H.; Fujiwhara, M.;
Kayaki, Y.; Ikariya, T. Efficient Access to Chiral Benzhydrols via
Asymmetric Transfer Hydrogenation of Unsymmetrical Benzophe-
nones with Bifunctional Oxo-Tethered Ruthenium Catalysts. J. Am.
Chem. Soc. 2016, 138, 10084−10087. (c) Umehara, K.; Kuwata, S.;
Ikariya, T. Synthesis, Structures, and Reactivities of Iron, Cobalt, and
Manganese Complexes Bearing a Pincer Ligand with Two Protic
Pyrazole Arms. Inorg. Chim. Acta 2014, 413, 136−142. (d) Umehara,
K.; Kuwata, S.; Ikariya, T. N-N Bond Cleavage of Hydrazines with a
Multiproton-Responsive Pincer-Type Iron Complex. J. Am. Chem. Soc.
2013, 135, 6754−6757. (e) Yoshinari, A.; Tazawa, A.; Kuwata, P. S.;
Ikariya, P. T. Synthesis, Structures, and Reactivities of Pincer-Type
J
DOI: 10.1021/acs.organomet.8b00432
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Iridium Complexes Bearing a Functional Bipyridonate Ligand. J. Am.
Chem. Soc. 2014, 136, 4829−4832. (f) Kawahara, R.; Fujita, K.;
Yamaguchi, R. Cooperative Catalysis by Iridium Complexes with a
Bipyridonate Ligand: Versatile Dehydrogenative Oxidation of
Alcohols and Reversible Dehydrogenation-Hydrogenation between
2-Propanol and Acetone. Angew. Chem., Int. Ed. 2012, 51, 12790−
12794.
Formation: Efficient and Atom Economical Strategy for the
Utilisation of Alcohols as Alkylating. Agents. Chem. - Eur. J. 2016,
22, 18147−18155. (c) Chakrabarti, K.; Paul, B.; Maji, M.; Roy, B. C.;
Shee, S.; Kundu, S. Bifunctional Ru(II) complex catalysed carbon-
carbon bond formation: an eco-friendly hydrogen borrowing strategy.
Org. Biomol. Chem. 2016, 14, 10988−10997. (d) Paul, B.;
Chakrabarti, K.; Kundu, S. Optimum Bifunctionality in a 2-(2-
Pyridyl-2-ol)-1,10-Phenanthroline Based Ruthenium Complex for
Transfer Hydrogenation of Ketones and Nitriles: Impact of the
Number of 2-Hydroxypyridine Fragments. Dalton Trans. 2016, 45,
11162−11171.
(18) (a) Moore, C. M.; Bark, B.; Szymczak, N. K. Simple Ligand
Modifications with Pendent OH Groups Dramatically Impact the
Activity and Selectivity of Ruthenium Catalysts for Transfer
Hydrogenation: The Importance of Alkali Metals. ACS Catal. 2016,
6, 1981−1990. (b) Tseng, K.-N. T.; Lin, S.; Kampf, J. W.; Szymczak,
N. K. Upgrading Ethanol to 1-Butanol with a Homogeneous Air-
Stable Ruthenium Catalyst. Chem. Commun. 2016, 52, 2901−2904.
(c) Geri, J. B.; Szymczak, N. K. A Proton-Switchable Bifunctional
Ruthenium Complex That Catalyzes Nitrile Hydroboration. J. Am.
Chem. Soc. 2015, 137, 12808−12814. (d) Moore, C. M.; Szymczak,
N. K. Nitrite Reduction by Copper through Ligand-Mediated Proton
and Electron Transfer. Chem. Sci. 2015, 6, 3373−3377. (e) Moore, C.
M.; Szymczak, N. K. 6,6′-Dihydroxy Terpyridine: a Proton-
Responsive Bifunctional Ligand and Its Application in Catalytic
Transfer Hydrogenation of Ketones. Chem. Commun. 2013, 49, 400−
402.
(19) (a) Fogler, E.; Garg, J. A.; Hu, P.; Leitus, G.; Shimon, L. J. W.;
Milstein, D. System with Potential Dual Modes of Metal-Ligand
Cooperation: Highly Catalytically Active Pyridine-Based PNNH-Ru
Pincer Complexes. Chem. - Eur. J. 2014, 20, 15727−15731.
(b) Langer, R.; Fuchs, I.; Vogt, M.; Balaraman, E.; Diskin-Posner,
Y.; Shimon, L. J. W.; Ben-David, Y.; Milstein, D. Stepwise Metal-
Ligand Cooperation by a Reversible Aromatization/Deconjugation
Sequence in Ruthenium Complexes with a Tetradentate Phenanthro-
line-Based Ligand. Chem. - Eur. J. 2013, 19, 3407−3414.
(20) (a) Toda, T.; Yoshinari, A.; Ikariya, T.; Kuwata, S. Protic N-
Heterocyclic Carbene Versus Pyrazole: Rigorous Comparison of
Proton- and Electron-Donating Abilities in a Pincer-Type Framework.
Chem. - Eur. J. 2016, 22, 16675−16683. (b) Toda, T.; Kuwata, S.;
Ikariya, T. Unsymmetrical Pincer-Type Ruthenium Complex
Containing β-Protic Pyrazole and N-Heterocyclic Carbene Arms:
Comparison of Brønsted Acidity of NH Groups in Second
Coordination Sphere. Chem. - Eur. J. 2014, 20, 9539−9542.
(21) (a) Tang, Z.; Otten, E.; Reek, J. N. H.; van der Vlugt, J. I.; de
Bruin, B. Dynamic Ligand Reactivity in a Rhodium Pincer Complex.
Chem. - Eur. J. 2015, 21, 12683−12693. (b) Tang, Z.; Mandal, S.;
Paul, N. D.; Lutz, M.; Li, P.; van der Vlugt, J. I.; de Bruin, B. Rhodium
Catalysed Conversion of Carbenes into Ketenes and Ketene Imines
Using PNN Pincer Complexes. Org. Chem. Front. 2015, 2, 1561−
1577. (c) de Boer, S. Y.; Korstanje, T. J.; La Rooij, S. R.; Kox, R.;
Reek, J. N.; van der Vlugt, J. I. Ruthenium PNN(O) Complexes:
Cooperative Reactivity and Application as Catalysts for Acceptorless
Dehydrogenative Coupling Reaction. Organometallics 2017, 36,
1541−1549.
(10) (a) Duan, L.; Manbeck, G. F.; Kowalczyk, M.; Szalda, D. J.;
Muckerman, J. T.; Himeda, Y.; Fujita, E. Noninnocent Proton-
Responsive Ligand Facilitates Reductive Deprotonation and Hinders
CO2 Reduction Catalysis in [Ru(tpy)(6DHBP)(NCCH3)]2+
(6DHBP = 6,6′-(OH)2bpy). Inorg. Chem. 2016, 55, 4582−4594.
(b) Wang, W.-H.; Ertem, M. Z.; Xu, S.; Onishi, N.; Manaka, Y.; Suna,
Y.; Kambayashi, H.; Muckerman, J. T.; Fujita, E.; Himeda, Y. Highly
Robust Hydrogen Generation by Bioinspired Ir Complexes for
Dehydrogenation of Formic Acid in Water: Experimental and
Theoretical Mechanistic Investigations at Different pH. ACS Catal.
2015, 5, 5496−5504. (c) Onishi, N.; Xu, S.; Manaka, Y.; Suna, Y.;
Wang, W.-H.; Muckerman, J. T.; Fujita, E.; Himeda, Y. CO2
Hydrogenation Catalyzed by Iridium Complexes with a Proton-
Responsive Ligand. Inorg. Chem. 2015, 54, 5114−5123. (d) Wang,
W.-H.; Muckerman, J. T.; Fujita, E.; Himeda, Y. Mechanistic Insight
through Factors Controlling Effective Hydrogenation of CO2
Catalyzed by Bioinspired Proton-Responsive Iridium(III) Complexes.
ACS Catal. 2013, 3, 856−860. (e) Wang, W.-H.; Hull, J. F.;
Muckerman, J. T.; Fujita, E.; Himeda, Y. Second-Coordination-
Sphere and Electronic Effects Enhance Iridium(III)-Catalyzed
Homogeneous Hydrogenation of Carbon Dioxide in Water Near
Ambient Temperature and Pressure. Energy Environ. Sci. 2012, 5,
7923−7926. (f) Hull, J. F.; Himeda, Y.; Wang, W.-H.; Hashiguchi, B.;
Periana, R.; Szalda, D. J.; Muckerman, J. T.; Fujita, E. Reversible
Hydrogen Storage Using CO2 and a Proton-Switchable Iridium
Catalyst in Aqueous Media under Mild Temperatures and Pressures.
Nat. Chem. 2012, 4, 383−388.
(11) Siek, S.; Burks, D. B.; Gerlach, D. L.; Liang, G.; Tesh, J. M.;
Thompson, C. R.; Qu, F.; Shankwitz, J. E.; Vasquez, R. M.; Chambers,
N.; Szulczewski, G. J.; Grotjahn, D. B.; Webster, C. E.; Papish, E. T.
Iridium and Ruthenium Complexes of N-Heterocyclic Carbene- and
Pyridinol-Derived Chelates as Catalysts for Aqueous Carbon Dioxide
Hydrogenation and Formic Acid Dehydrogenation: The Role of the
Alkali Metal. Organometallics 2017, 36, 1091−1106.
(12) (a) Chakraborty, S.; Piszel, P. E.; Hayes, C. E.; Baker, R. T.;
Jones, W. D. Highly Selective Formation of n-Butanol from Ethanol
through the Guerbet Process: A Tandem Catalytic Approach. J. Am.
Chem. Soc. 2015, 137, 14264−14267. (b) Chakraborty, S.; Piszel, P.
E.; Brennessel, W. W.; Jones, W. D. A Single Nickel Catalyst for the
Acceptorless Dehydrogenation of Alcohols and Hydrogenation of
Carbonyl Compounds. Organometallics 2015, 34, 5203−5206.
(13) Sahoo, A. R.; Jiang, F.; Bruneau, C.; Sharma, G. V. M; Suresh,
S.; Roisnel, T.; Dorcet, V.; Achard, M. Phosphine-Pyridonate Ligands
Containing Octahedral Ruthenium Complexes: Access to Esters and
Formic Acid. Catal. Sci. Technol. 2017, 7 (7), 3492−3498.
(14) Wang, R.; Ma, J.; Li, F. Synthesis of α-Alkylated Ketones via
Tandem Acceptorless Dehydrogenation/α-Alkylation from Secondary
and Primary Alcohols Catalyzed by Metal-Ligand Bifunctional Iridium
Complex [Cp*Ir(2,2′-bpyO)(H2O)]. J. Org. Chem. 2015, 80, 10769−
10776.
(15) Nieto, I.; Livings, M. S.; Sacci, J. B.; Reuther, L. E.; Zeller, M.;
Papish, E. T. Transfer Hydrogenation in Water via a Ruthenium
Catalyst with OH Groups near the Metal Center on a bipy Scaffold.
Organometallics 2011, 30, 6339−6342.
(16) Royer, A. M.; Rauchfuss, T. B.; Gray, D. L. Organoiridium
Pyridonates and Their Role in the Dehydrogenation of Alcohols.
Organometallics 2010, 29, 6763−6768.
(22) (a) Shi, J.; Hu, B.; Chen, X.; Shang, S.; Deng, D.; Sun, Y.; Shi,
W.; Yang, X.; Chen, D. Synthesis, Reactivity, and Catalytic Transfer
Hydrogenation Activity of Ruthenium Complexes Bearing NNN
Tridentate Ligands: Influence of the Secondary Coordination Sphere.
ACS Omega 2017, 2, 3406−3416. (b) Shi, J.; Hu, B.; Gong, D.;
Shang, S.; Hou, G.; Chen, D. Ruthenium Complexes Bearing an
Unsymmetrical Pincer Ligand with a 2-Hydroxypyridylmethylene
Fragment: Active Catalysts for Transfer Hydrogenation of Ketones.
Dalton Trans. 2016, 45, 4828−4834.
(17) (a) Chakrabarti, K.; Maji, M.; Panja, D.; Paul, B.; Shee, S.; Das,
G. K.; Kundu, S. Utilization of MeOH as a C1 Building Block in
Tandem Three-Component Coupling Reaction. Org. Lett. 2017, 19,
4750−4753. (b) Roy, B. C.; Chakrabarti, K.; Shee, S.; Paul, S.;
Kundu, S. Bifunctional RuII-Complex-Catalysed Tandem C-C Bond
(23) For selected reviews, see: (a) Huang, F.; Liu, Z.; Yu, Z. C-
Alkylation of Ketones and Related Compounds by Alcohols:
Transition-Metal-Catalyzed Dehydrogenation. Angew. Chem., Int. Ed.
2016, 55, 862−875. (b) Dobereiner, G. E.; Crabtree, R. H.
Dehydrogenation as a Substrate-Activating Strategy in Homogeneous
K
DOI: 10.1021/acs.organomet.8b00432
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Transition-Metal Catalysis. Chem. Rev. 2010, 110, 681−703.
(c) Nixon, T. D.; Whittlesey, M. K.; Williams, J. M. J. Transition
Metal Catalysed Reactions of Alcohols Using Borrowing Hydrogen
Methodology. Dalton Trans. 2009, 753−762. (d) Guillena, G.;
Constant and Atomic Surface Tensions. J. Phys. Chem. B 2009, 113,
6378−6396.
́
Ramon, D. J.; Yus, M. Alcohols as Electrophiles in C-C Bond-Forming
Reactions: The Hydrogen Autotransfer Process. Angew. Chem., Int. Ed.
2007, 46, 2358−2364.
(24) (a) Chang, W.; Gong, X.; Wang, S.; Xiao, L. P.; Song, G.
Acceptorless Dehydrogenation and Dehydrogenative Coupling of
Alcohols Catalysed by Protic NHC Ruthenium Complexes. Org.
Biomol. Chem. 2017, 15, 3466−3471. (b) Wang, Q.; Wu, K.; Yu, Z.
Ruthenium(III)-Catalyzed β-Alkylation of Secondary Alcohols with
Primary Alcohols. Organometallics 2016, 35, 1251−1256. (c) Chang,
X.; Chuan, L. W.; Li, Y.; Pullarkat, S. A. One-Pot β-Alkylation of
Secondary Alcohols with Primary Alcohols Catalyzed by Ruthena-
cycles. Tetrahedron Lett. 2012, 53, 1450−1455. (d) Gnanamgari, D.;
Sauer, E. L. O.; Schley, N. D.; Butler, C.; Incarvito, C. D.; Crabtree, R.
H. Iridium and Ruthenium Complexes with Chelating N-Heterocyclic
Carbenes: Efficient Catalysts for Transfer Hydrogenation, β-
Alkylation of Alcohols, and N-Alkylation of Amines. Organometallics
2009, 28, 321−325. (e) Cheung, H. W.; Lee, T. Y.; Lui, H. Y.; Yeung,
C. H.; Laua, C. P. Ruthenium-Catalyzed β-Alkylation of Secondary
Alcohols with Primary Alcohols. Adv. Synth. Catal. 2008, 350, 2975−
́
2983. (f) Prades, A.; Viciano, M.; Sanau, M.; Peris, E. Preparation of a
Series of “Ru(p-cymene)” Complexes with Different N-Heterocyclic
Carbene Ligands for the Catalytic β-Alkylation of Secondary Alcohols
and Dimerization of Phenylacetylene. Organometallics 2008, 27,
́
4254−4259. (g) Viciano, M.; Sanau, M.; Peris, E. Ruthenium Janus-
Head Complexes with a Triazolediylidene Ligand. Structural Features
and Catalytic Applications. Organometallics 2007, 26, 6050−6054.
́
(h) Martínez, R.; Ramon, D. J.; Yus, M. RuCl (DMSO)4, Catalyzes
the β-Alkylation of Secondary Alcohols with Primary Alcohols
2
through a Hydrogen Autotransfer Process. Tetrahedron 2006, 62,
8982−8987.
(25) Jasimuddin, S.; Thakurata, D. G. Synthesis and Character-
ization of Stable Thiazolylazo Anion Radical Complexes of
Ruthenium(II). Transition Met. Chem. 2009, 34, 937−942.
(26) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Hratchian, X. L., H,
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.;
Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J.
C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.;
Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo,
J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; J. Austin, A.; Cammi,
R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.;
Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian 09, revision C.01; Gaussian, Inc.,
Wallingford, CT, 2010.
(27) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. Theor. Chem. Acc.
2008, 120, 215−241.
(28) (a) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss,
H. Energy-Adjusted ab initio, Pseudopotentials for the Second and
Third Row Transition Elements. Theor. Chim. Acta 1990, 77, 123−
141. (b) Martin, J. M. L.; Sundermann, A. Correlation Consistent
Valence Basis Sets for Use with the Stuttgart-Dresden-Bonn
Relativistic Effective Core Potentials: the Atoms Ga-Kr and In-Xe.
J. Chem. Phys. 2001, 114, 3408−3420.
(29) Tomasi, J.; Mennucci, B.; Cammi, R. Quantum Mechanical
Continuum Solvation Models. Chem. Rev. 2005, 105, 2999−3093.
(30) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. Universal
Solvation Model Based on Solute Electron Density and on a
Continuum Model of the Solvent Defined by the Bulk Dielectric
L
DOI: 10.1021/acs.organomet.8b00432
Organometallics XXXX, XXX, XXX−XXX