Postsynthetic Modification of Half-Sandwich Ruthenium Complexes by Mechanochemical Synthesis

Article abstract of DOI:10.1021/acs.inorgchem.1c00059

A mild and environmentally friendly method to synthesize half-sandwich ruthenium complexes through the Wittig reaction between an aldehyde-tagged half-sandwich ruthenium complex and phosphorus ylide mechanochemically is reported herein. The mechanochemical synthesis of valuable half-sandwich ruthenium complexes resulted in a fast reaction, good yield with simple workup, and the avoidance of harsh reaction conditions and organic solvents. The synthesized half-sandwich ruthenium complexes exhibited high catalytic activity for transfer hydrogenation of ketones using 2-propanol as the hydrogen source and solvent. Density functional theory was carried out to propose a mechanism for the transfer hydrogenation process. The modeling suggests the importance of the labile p-cymene ligand in modulating the reactivity of the catalyst.

Full text of DOI:10.1021/acs.inorgchem.1c00059

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Postsynthetic Modification of Half-Sandwich Ruthenium Complexes
by Mechanochemical Synthesis
Wei-Guo Jia,* Xue-Ting Zhi, Xiao-Dong Li, Jun-Peng Zhou, Rui Zhong, Haibo Yu, and Richmond Lee*
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ABSTRACT: A mild and environmentally friendly method to
synthesize half-sandwich ruthenium complexes through the Wittig
reaction between an aldehyde-tagged half-sandwich ruthenium
complex and phosphorus ylide mechanochemically is reported
herein. The mechanochemical synthesis of valuable half-sandwich
ruthenium complexes resulted in a fast reaction, good yield with
simple workup, and the avoidance of harsh reaction conditions and
organic solvents. The synthesized half-sandwich ruthenium
complexes exhibited high catalytic activity for transfer hydro-
genation of ketones using 2-propanol as the hydrogen source and
solvent. Density functional theory was carried out to propose a mechanism for the transfer hydrogenation process. The modeling
suggests the importance of the labile p-cymene ligand in modulating the reactivity of the catalyst.
reactants).31 Jurca and co-workers reported the mechano-
chemical synthesis of bis(imino)pyridine-MX2 (M = Mn, Fe,
INTRODUCTION
The solvent-free synthesis of transition-metal complexes has
■
Co, Ni, Cu, Zn; X = Cl, Br) complexes via a one-pot, one-step
recently gained considerable attention because it is more
efficient and environmentally friendly.1−5 Various coordination
process from diacetylpyridine, panisidine, and a MX2 precursor
in the presence of MgSO4 and p-toluenesulfonic acid.32
complexes including mononuclear and multinuclear com-
plexes,6−10 metal−organic frameworks,11−13 covalent organic
Following our interest in studying half-sandwich metal
complexes’ catalytic activities with diverse functional li-
frameworks,14 supramolecular compounds,15,16 and coordina-
gands,33−37 we report herein an efficient and more sustainable
method to synthesize a new, previously unreported half-
sandwich ruthenium complex 2, to the best of our knowledge.
Complex 2 bears an aldehyde functional group that can enable
postsynthetic modification, which could be carried out via a
mechanochemical Wittig reaction. The resulting products of 4
(4a and 4b) were obtained efficiently via mortar and pestle
grinding, with the yields comparable to those of their solution-
based methodologies. The ease of implementing such a solid-
state postsynthetic modification of these organometallic
complexes via simple grinding in air, without the need for
expensive or sophisticated ball mills or a specialized
mechanochemical apparatus, further highlights the attractive-
ness and feasibility of this methodology. The catalytic activities
of the complexes were probed in transfer hydrogenation of
ketones using 2-propanol as the hydrogen source and solvent.
In particular, we discovered that complex 4b demonstrated
tion polymers17−19 have been synthesized mechanochemically.
However, using mechanochemistry to synthesize organo-
metallic complexes is uncommon compared to the traditional
solution or homogeneous method.20−26 The synthesis of
organometallic complexes in solution usually needs to be done
under an inert atmosphere and in the absence of water and O2
and requires the addition of pretreated solvents, coupled with a
longer reaction time. The requirement of using dry and
degassed solvents under inert reaction conditions increases the
complexity of the reaction, adding to the cost of the synthesis,
and generates a larger environmental footprint. The recent
renaissance of mechanochemistry as a powerful synthetic tool
can be used to overcome these problems to synthesize high-
value products and organometallic-based catalysts.27−30 Such
solid-state mechanochemical reactions also eliminate the need
to find suitable solvents to dissolve the reagents and other
issues normally associated with solubility, enabling a wider
variety of reagents to be used as molecular precursors. In short,
mechanochemistry removes the need for solvents and also
shortens the reaction time, leading to it being a more efficient
and less polluting process. For example, Bantreil et al. recently
reported the mechanochemical synthesis of half-sandwich
ruthenium complexes with N-heterocyclic carbene (NHC)
and [Ru(p-cymene)(μ-Cl)Cl]2, in situ obtaining the Ag-NHC
complex with only a small amount of water (0.3 μL/mg of
Received: January 8, 2021
Published: March 24, 2021
https://doi.org/10.1021/acs.inorgchem.1c00059
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Scheme 1. Synthesis of Half-Sandwich Ruthenium Complexes with 2-Substituted 8-Hydroxyquinolinate Ligands through
Mechanochemical and Solution Methods
high catalytic activity for transfer hydrogenation of ketones
with a broad range of substrates, forming a library of alcohol
products that have significant synthetic value.
RESULTS AND DISCUSSION
■
Initially, the aldehyde-tagged half-sandwich ruthenium com-
plex 2 was first obtained by the direct reaction between 8-
hydroxyquinoline-2-carbaldehyde (1) and [Ru(p-cymene)(μ-
Cl)Cl]2 in solution using dry acetonitrile (MeCN) in an inert
nitrogen atmosphere (Scheme 1). The ruthenium complex 2
was obtained in 62% yield after 2 h of continuous stirring at 70
°C. Alternatively, complex 2 was also obtained via the
mechanochemical grinding of 1 and [Ru(p-cymene)(μ-Cl)Cl]2
in the solid state. The mechanochemical protocol afforded 2 in
higher yield (83%) and within a fraction of the time (20 min).
The ruthenium complex 2 was fully characterized by Fourier
transform infrared (FTIR), NMR spectroscopy, and mass
spectrometry. As shown in Figure 1, complex 2 exhibits a
strong stretching frequency at 1689 cm−1, characteristic of the
aldehyde ν(CO). The proton signals at 10.70 ppm in the 1H
NMR spectrum can be easily assigned to the hydrogen atom of
the −CHO group in complex 2 (Figure 2). Additionally, the
electrospray ionization mass spectrometry (ESI-MS) spectrum
of [C20H19NO2RuCl]− exhibited peaks at m/z 442.0842 (calcd
Figure 1. FTIR spectra of half-sandwich ruthenium complexes.
for [M − H]−: m/z 441.9995), further confirming the
formation of complex 2. The aldehyde group in the ruthenium
nation of the formation of the product. The CC bond
complex 2 provides a versatile and convenient “ handle” for
postsynthetic modification (Scheme 1).38−41
formation can be readily observed in the FTIR spectrum, as
evidenced by the disappearance of the aldehyde ν(CO)
Next, we attempted to mechanochemically modify the
band and subsequent appearance of two new bands at 1633
and 968 cm−1, which correspond to the ν(CC) and trans
ν(HCCH) stretching frequencies, respectively (Figure 1).
Complete conversion of the aldehyde was also confirmed by
1H NMR data (Figure 2). The proton signal of the −CHO
group observed in 2 at δ = 10.70 ppm was absent, and the
other two new signals appeared as double peaks at δ = 7.69 and
ruthenium complex 2 postsynthetically. Complex 2, in the
presence of excess benzyltriphenylphosphonium chloride,
afforded the desired complex 4a in 62% yield by liquid-
assisted grinding (LAG) in a mortar and pestle in air using two
droplets of CH2Cl2 (approximate value of η = 0.0006 mL/
mg).42 The reaction proceeded readily and afforded complexes
4a in open air without any special precautions. Ex situ FTIR
measurements of the solid mixture allow for easy determi-
1
7.51 ppm in the H NMR spectrum of complex 4a, indicating
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1
Figure 2. H NMR spectra of half-sandwich ruthenium complexes.
CC bond formation. Complex 4a was also obtained by a
mechanochemical ligand-exchange reaction between 3a and
[Ru(p-cymene)(μ-Cl)Cl]2 in 88% yield by LAG (Scheme 1).
Similarly, postsynthetic modification of the ruthenium complex
2 via a Wittig reaction was also successively extended to [(4-
chlorophenyl)methyl]triphenylphosphonium chloride under
the same reaction conditions. Both FTIR and NMR analyses
indicated that the reaction proceeded completely. Of note, the
reaction involving 3b completed within minutes under
mechanochemical conditions, but took 3 h solvothermally to
reach completion. Ex situ FTIR measurements revealed that
the half-sandwich ruthenium complex 4 was immediately
formed when a mixture of the ruthenium complex 2 and
benzyltriphenylphosphonium chloride was ground under LAG
at room temperature (Figure S10).
Subsequently, diffraction-quality crystals of 2, 4a, and 4b
were successfully grown and analyzed using single-crystal X-ray
diffraction. The crystallographic data for compounds 2, 4a, and
4b are summarized in Table S1, and selected key bond lengths
and angles are shown in Table S2. The molecular structure of
each complex was determined by X-ray crystallography and is
shown in Figure 3, in which the chlorine atom, a nitrogen
atom, and one oxygen atom each from the ligand and one of
the p-cymene rings form a three-legged piano-stool geometry
with Ru. The Ru−N distances [2.138(4) Å in 2, 2.114(2) Å in
4a, and 2.124(3) Å in 4b] are in the range of typical distances
of half-sandwich ruthenium complexes with a 8-hydroxyquino-
line derivative.43−47 The Ru−Cl distances [2.4087(14) Å in 2,
2.4186(8) Å in 4a, and 2.4112(9) Å in 4b] are consistent with
the Ru−Cl bond length values reported for those of half-
sandwich ruthenium complexes.48−51
Transfer hydrogenation of acetophenone was chosen as the
model reaction to test the catalytic activity of the obtained half-
sandwich ruthenium complexes. The reaction was performed
using 0.5 mol % catalyst loading in the presence of potassium
tert-butoxide as the base under an inert nitrogen atmosphere.
Optimization of the reaction parameters, as shown in Table 1,
revealed that the ruthenium complex 4b gave the best result,
with a 39% yield within 3 h (Table 1, entries 1−3). A higher
91% yield was achieved when the reaction time was increased
to 12 h at 0.25 mol % catalyst loading using 4b (Table 1,
entries 4 and 5). The type of base used was also crucial for the
efficiency of this transformation, and sodium methoxide
(MeONa) was found to be the ideal base for the transfer
hydrogenation reaction of acetophenone (Table 1, entries 5−
10). Lower yields were observed when the other inorganic
bases such as KOAc, K2CO3, and K3PO4 were used. The
reaction also proceeded more sluggishly when a lower reaction
temperature was used (Table 1, entries 11 and 12). As a
control reaction, the desired product was not detected in the
absence of the half-sandwich ruthenium catalyst.
The transfer hydrogenation reaction was further extrapo-
lated to other ketones under the optimized reaction conditions
to evaluate the substrate scope of the catalytic system (Table
2). The reduction of a large variety of substrates, including
aromatic and aryl alkyl/halide groups and aliphatic cyclic
ketones, was efficiently performed. Ketones containing
electron-withdrawing and -donating substituents on their
aromatic backbone also afforded their corresponding products
in excellent yields. Sterically bulky propiophenone and
butyrophenone also afforded their corresponding alcohols in
good yields (Table 2, entries 2 and 3), which means the steric
Figure 3. Molecular structures of complexes 2, 4a, and 4b, with
thermal ellipsoids drawn at the 50% level. All hydrogen atoms are
omitted for clarity.
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is also high in the activation barrier at ΔG⧧ = 34.6 kcal/mol
Table 1. Optimization of Reaction Conditions for Transfer
Hydrogenation of Acetophenone with Half-Sandwich
Ruthenium Complexes
⧧
(ΔGsol = 37.5 kcal/mol) relative to cpxD. An alternative
a
pathway (see Figure 4, Pathway B) whereby the cymene ligand
is substituted with alcohols to give a 16-electron ruthenium(II)
trigonal-bipyramidal complex cpxE is also considered.37 This
cpxE species is endergonic but has a vacant site available for
accepting a hydride, which then sets the stage for β-hydride
elimination through TSE: ΔG⧧ = 20.3 kcal/mol (ΔGsol⧧ = 20.9
kcal/mol). A TSE activation barrier being much lower than
TSC is proposed to be operative. The formed Ru−H species
cpxF is, however, unstable and could undergo ligand
substitution, with the cymene coming back to form stable
cpxD as a resting state, ΔG = −3.7 kcal/mol (ΔGsol = −5.8
kcal/mol). For the next step of transfer hydrogenation to
occur, ligand substitution between the labile cymene of cpxD
and acetophenone forms the precomplex cpxG, which is more
stable compared to cpxF. The reduction of acetophenone from
cpxG through TSG is energetically lower at ΔG⧧ = 18.8 kcal/
loading
(mol %)
time
(h)
temperature
yield
(%)
entry catalyst
base
(°C)
1
2
3
4
5
6
7
8
2
0.5
0.5
0.5
0.5
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
tBuOK
tBuOK
tBuOK
tBuOK
tBuOK
tBuONa
MeONa
KOAc
K2CO3
K3PO4
MeONa
MeONa
3
3
3
80
80
80
80
80
80
80
80
80
80
70
60
24
30
39
92
91
91
95
1
4
2
69
43
4a
4b
4b
4b
4b
4b
4b
4b
4b
4b
4b
12
12
12
12
12
12
12
12
12
9
⧧
10
11
12
mol (ΔGsol = 24.5 kcal/mol) relative to cpxD. The reduced
methylbenzyl alcohol on cpxH is protonated, forming cpxI,
and expulsion of methylbenzyl alcohol and 2-proponal and
coordination with cymene regenerate cpxA, giving an overall
exergonic process.
a
Reaction conditions: acetophenone (0.1 mmol), catalyst, base (4
equiv), isopropyl alcohol (1 mL); n-dodecane as an internal standard.
Determined by GC−MS.
On the basis of the calculations, the lability of the cymene
ligand is important in influencing the reactivity of the
ruthenium catalyst, allowing transfer hydrogenation steps to
occur when it is not coordinated to the ruthenium metal
center. However, if the ligand is on the metal center, the
energetics for hydrogen transfer will be unfavorable (see Figure
4, Pathway A). The electron-deficient bipyramidal 16-electron
ruthenium(II) complexes are unstable but reactive, and sterics
play a role in this; the trans-alkene group on the 3b ligand
blocks another ligand from coordinating to the metal,
preventing a full 18-electron ruthenium species. Thus, the
energetically stable 18-electron piano-stool cymene−ruthe-
nium complexes cpxD and cpxA are proposed to be present as
stable intermediates in order to drive the reaction forward.
hindrance of acetophenone did not have an influence on the
catalytic activity of the reaction. While p- and m-methyl
substituents did not hamper the reaction, a lower 72% yield
was obtained for 2-methylacetophenone, even after prolonged
reaction time (Table 2, entries 4−6). However, almost
quantitative yields were observed for 2-acetoanisole (Table 2,
entry 8). The transfer hydrogenation reaction also worked well
for extended aromatic systems such as 2-acetylnaphthalene and
4-acetylbiphenyl and generated the corresponding products in
excellent yields (Table 2, entries 11 and 12). Halide or
trifluoromethyl substituents on the ortho, meta, or para
position of the aromatic ring were also allowed (Table 2,
entries 13−20). The catalyst also tolerated reagents with
hydroxy groups, as shown in 2-hydroxy-2-methylpropiophe-
none, albeit with slightly lower obtained product yield (84%
yield; Table 2, entry 21). Notably, sterically hindered fluoren-
9-one was also efficiently reduced to fluoren-9-ol (Table 2,
entry 22). Also, the heterocycle substrate was tolerated well
(Table 2, entry 23). The aliphatic compound 4-tert-
butylcyclohexanone was also successfully reduced to 4-tert-
butylcyclohexanol in excellent yield (Table 2, entry 24).
Density functional theory (DFT; see the Supporting
Information for computational details) was carried out to
shed light and propose a plausible mechanism for the transfer
hydrogenation process, with 4b catalyst, MeO− base, and
acetophenone chosen for the computational modeling (Figure
4). The facile exchange of Cl− in 4b with MeO− leads to the
methoxyl complex cpxA, and all free energies will be
referenced to cpxA henceforth. The hydrogen-bonded
methoxyl complex with 2-propanol (cpxB) is slightly
exergonic, and further exchange of the methoxide and 2-
propanol leads to cpxC. Both cpxB and cpxC are slightly less
stable compared to cpxA, and β-hydride elimination of the 2-
propanolate in cpxC requires one to overcome a high
CONCLUSION
■
The mechanosynthesis of organometallic half-sandwich
ruthenium complexes 4, including from postsynthetic mod-
ification of the aldehyde-tagged half-sandwich ruthenium
complex 2, has been successfully demonstrated. The
mechanochemical methodology for the synthesis of complex
4 was very efficient, with up to 20% higher isolated yield than
its solution-based counterpart. The molecular structures of all
half-sandwich ruthenium complexes were confirmed by
spectroscopic and X-ray diffraction studies. Complex 4b was
discovered to exhibit high catalytic activity toward transfer
hydrogenation of ketones to alcohols, using 2-propanol as the
hydrogen source and solvent. DFT was used to computation-
ally model and propose a mechanism for this transformation.
Theoretical insights suggest the importance of the lability of
the cymene ligand toward modulation of the reactivity of the
catalyst. A large library of synthetically valuable alcohol
products were generated using the optimal catalyst. The
success of adopting mechanochemistry in our synthetic
protocols has given us the confidence to explore further
other reactions involving analogous organometallic com-
pounds, and we hope that this work will further encourage
more organometallic chemists to consider using mechano-
chemistry as part of their toolbox of synthetic methodologies.
activation barrier of ΔG⧧ = 31.1 kcal/mol (ΔGsol = 28.9
⧧
kcal/mol) relative to cpxA (see Figure 4, Pathway A). An
energetically stable Ru−H species cpxD is formed. The
subsequent reduction of acetophenone from cpxD via TSD
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a
Table 2. Screening of Substrates for Transfer Hydrogenation of Ketone Compounds Catalyzed by Complex 4b
a
Reaction conditions: ketones (0.1 mmol), catalyst (0.25 mol %), MeONa (4 equiv), isopropyl alcohol (1 mL), 80 °C, 12 h; n-dodecane as an
b
c
internal standard. The yields were determined by GC−MS. 24 h.
Bruker micrOTOF-Q II 10280 and Bruker micrOTOF II 10257 mass
spectrometers.
EXPERIMENTAL SECTION
■
Materials and measurements. All operations were carried out
under an inert nitrogen atmosphere using standard Schlenk
techniques. All solvents were purified and degassed by standard
procedures. The compounds 8-hydroxyquinoline-2-carbaldehyde
(1),52 2-styryl-8-hydroxyquinoline (3a),53,54 2-(4-chlorostyryl)-
quinolin-8-ol (3b),5 5 , 5 6 [(4-chlorophenyl)methyl]-
triphenylphosphonium chloride,57 and benzyltriphenylphosphonium
Synthesis of the Half-Sandwich Ruthenium Complex 2. Method
A (mechanochemical synthesis method): [Ru(p-cymene)(μ-Cl)Cl]2
(61.2 mg, 0.10 mmol), 1 (0.2 mmol), and K2CO3 (27.6 mg, 0.2
mmol) were manually ground in a mortar with a pestle for 20 min in
the presence of 5 droplets of CH2Cl2. The resulting products was
poured into a CH2Cl2 solution, and any precipitate that formed was
removed by filtration. The solvent in the resulting filtrate was
removed in vacuo. The mixture was passed through a short pad of
silica gel with hexane and isopropyl alcohol to give the ruthenium
complex 2 (73.6 mg, 83%). Method B (solution method): A solution
of [Ru(p-cymene)(μ-Cl)Cl]2 (61.2 mg, 0.10 mmol), 1 (0.22 mmol),
and K2CO3 (35.4 mg, 0.22 mmol) in MeCN (5 mL) was purged with
nitrogen and then stirred at 70 °C for 2 h. After the solution was
cooled to room temperature, the solvent was removed under vacuum
(rotary evaporator). The mixture was passed through a short pad of
silica gel with ethyl acetate and petroleum ether (2:1) to give the
characteristic dark-red half-sandwich ruthenium complex 2 (55.0 mg,
chloride58 were synthesized according to the literature. H and 13C
1
NMR were recorded on a Bruker AV 400/500 spectrometer at room
temperature. Chemical shifts (δ) are given as parts per million (ppm)
and refer to the shift of the hydrogen or carbon atoms in the solvents
used (CDCl3). The following abbreviations were used for assignment
of the signals and their multiplicities: s, singlet; d, doublet; t, triplet; q,
quartet; m, multiplet. The given coupling constants J are listed as the
average of the experimental findings. The FTIR (KBr pellet) spectrum
was recorded (400−4000 cm−1 region) on a Bruker TENSOR 27
FTIR spectrometer. Elemental analyses were performed on a
PerkinElmer 2400 CHN analyzer. ESI-MS spectra were recorded on
1
62%). H NMR (500 MHz, CDCl3): δ 10.67 (s, 1H), 8.14 (d, 1H),
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Figure 4. Top: Computational modeling of the reaction mechanism for transfer hydrogenation catalyzed by 4b. Values are gas-phase free energies
at the M11-L/def2TZVP+QZVP level of theory on optimized minimum or transition-state structures at M11-L/6-31G(d,p)+SDD [solution free
energy calculation with implicit 2-propanol solvation in square brackets]. Bottom: Transition-state structures TSE and TSG and bond distances for
hydrogen transfer.
7.91 (d, 1H), 7.44 (t, 1H), 7.09 (d, 2H), 6.86 (d, 2H), 5.69 (d, 1H),
5.57 (d, 1H), 5.26 (q, 2H), 2.51 (m, 1H), 2.31 (s, 3H), 1.00 (d, J = 9
Hz, 3H), 0.92 (d, J = 15 Hz, 3H). 13C NMR (125 MHz, CDCl3): δ
192.7, 169.6, 150.0, 145.1, 138.4, 133.4, 131.6, 120.2, 116.7, 111.0,
103.0, 101.0, 85.7, 81.7, 81.5, 80.4, 31.3, 22.4, 19.1. IR (KBr cm−1):
3434 (m), 3057 (w), 2965 (w), 2924 (vw), 2873 (w), 1733 (vw),
1687 (s), 1589 (m), 1549 (s), 1499 (m), 1453 (s), 1368 (s), 1342
(s), 1313 (m), 1280 (m), 1229 (m), 1169 (m), 1108 (s), 872 (m),
832 (m), 739 (m), 598 (m), 509 (m). Anal. Calcd for
C20H20NO2RuCl: C, 54.24; H, 4.55; N, 3.16. Found: C, 54.28; H,
4.47; N, 3.10. ESI-MS. Calcd for [C20H19NO2RuCl]− ([M − H]−):
m/z 441.9995. Found: m/z 442.0842.
Synthesis of the Half-Sandwich Ruthenium Complex 4a.
Method A (mechanochemical synthesis method): Benzyltriphenyl-
phosphonium chloride (77.6 mg, 0.2 mmol) and potassium tert-
butoxide (33.7 mg, 0.3 mmol) were manually ground in a mortar with
a pestle for 1 min, until a yellow solid was obtained. Then, 2 (42.7 mg,
0.1 mmol) was added to the solid mixture and subsequently ground
for 1 h in the presence of 2 droplets of CH2Cl2. The resulting
products were poured into a CH2Cl2 solution, the unsolved
precipitate was removed by filtration, and the solvent in the filtrate
was removed in vacuo. The mixture was passed through a short pad of
silica gel with hexane and isopropyl alcohol to give the ruthenium
complex 4a (30.1 mg, 62%). Method A (mechanochemical synthesis
method): [Ru(p-cymene)(μ-Cl)Cl]2 (61.2 mg, 0.10 mmol), 3a (0.2
mmol), and K2CO3 (27.6 mg, 0.2 mmol) were manually ground in a
mortar with a pestle for 20 min in the presence of 5 droplets of
CH2Cl2. The resulting products were poured into a CH2Cl2 solution,
the unsolved precipitate was removed by filtration, and the solvent
was removed in vacuo. The mixture was passed through a short pad of
silica gel with hexane and isopropyl alcohol to give the ruthenium
complex 2 (91.6 mg, 88%). Method B (solution method): A solution
of [Ru(p-cymene)(μ-Cl)Cl]2 (61.2 mg, 0.10 mmol), 3a (0.22 mmol),
and K2CO3 (35.4 mg, 0.22 mmol) in methanol (5 mL) was purged
with nitrogen and then stirred at 70 °C for 2 h. After it was cooled to
room temperature, the solvent was removed under vacuum (rotary
evaporator). The mixture was passed through a short pad of silica gel
with ethyl acetate and petroleum ether (2:1) to give the dark-red half-
sandwich ruthenium complex 4a (70.9 mg, 69%). 1H NMR (400
MHz, CDCl3): δ 8.13 (d, J = 20 Hz, 1 H), 8.02 (d, J = 8 Hz, 1 H),
7.69 (d, J = 8 Hz, 3 H), 7.51 (t, J = 16 Hz, 2 H), 7.42 (t, J = 12 Hz, 1
H), 7.36 (d, J = 16 Hz, 1 H), 7.29 (t, J = 16 Hz, 1 H), 7.02 (d, J = 12
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Hz, 1 H), 6.78 (d, J = 8 Hz, 1 H), 5.62 (d, J = 4 Hz, 1 H), 5.51 (d, J =
4 Hz, 1 H), 5.39 (d, J = 8 Hz, 1 H), 5.14 (d, J = 4 Hz, 1 H), 2.57 (m,
1 H), 2.33 (s, 3 H), 1.03 (d, J = 8 Hz, 3 H), 0.94 (d, J = 4 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ 168.6, 155.8, 144.3, 137.5, 135.9,
134.0, 131.0, 129.7, 129.2, 128.6, 127.4, 119.9, 115.7, 110.5, 101.4,
100.2, 85.6, 81.0, 80.9, 80.3, 30.8, 22.2, 22.0, 18.9. IR (KBr cm−1):
3432 (m), 3063 (vw), 2958 (m), 2923 (s), 2854 (m), 1632 (w), 1549
(m), 1493 (w), 1457 (w), 1436 (m), 1370 (m), 1195 (vw), 1105 (w),
1082 (w), 969 (vw), 852 (w), 823 (w), 741 (w), 691 (w), 512 (w).
Anal. Calcd for C27H26NORuCl: C, 62.72; H, 5.07; N, 2.71. Found:
C, 62.77; H, 5.09; N, 2.78. ESI-MS. Calcd for [C27H26NORu]+ ([M
− Cl]+): m/z 482.1060. Found: m/z 482.1072.
the structures were solved by direct methods and subsequently refined
on F2 by using full-matrix least-squares techniques (SHELXL).59
SADABS60 absorption corrections were applied to the data, all non-
hydrogen atoms were refined anisotropically, and hydrogen atoms
were located at calculated positions. All calculations were performed
using the Bruker SMART program.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c00059.
■
sı
Synthesis of the Half-Sandwich Ruthenium Complex 4b.
NMR data and IR spectra of the half-sandwich
ruthenium complexes and computational details (PDF)
Method
A (mechanochemical synthesis method): [(4-
Chlorophenyl)methyl]triphenylphosphonium (84.7 mg, 0.2 mmol)
and potassium tert-butoxide (33.7 mg, 0.3 mmol) were manually
ground in a mortar with a pestle for 1 min until a yellow solid was
obtained. Then, 2 (42.7 mg, 0.1 mmol) was added to the solid
mixture and grinding was continued for 1 h in the presence of 2
droplets of CH2Cl2. The resulting products was poured into a CH2Cl2
solution, the unsolved precipitate was removed by filtration, and the
solvent was removed under vacuum. The mixture was passed through
a short pad of silica gel with hexane and isopropyl alcohol to give the
ruthenium complex 4b (33.7 mg, 61%). Method A (mechanochem-
ical synthesis method): [Ru(p-cymene)(μ-Cl)Cl]2 (61.2 mg, 0.10
mmol), 3b (0.2 mmol), and K2CO3 (27.6 mg, 0.2 mmol) were
manually ground in a mortar with a pestle for 20 min in the presence
of 5 droplets of CH2Cl2. The resulting products were poured into a
CH2Cl2 solution, the unsolved precipitate was removed by filtration,
and the solvent was removed in vacuo. The mixture was passed
through a short pad of silica gel with hexane and isopropyl alcohol to
give the ruthenium complex 4b (102.9 mg, 93%). Method B (solution
method): A solution of [Ru(p-cymene)(μ-Cl)Cl]2 (61.2 mg, 0.10
mmol), 3b (0.22 mmol), and K2CO3 (35.4 mg, 0.22 mmol) in
methanol (5 mL) was purged with nitrogen and then stirred at 70 °C
for 2 h. After it was cooled to room temperature, the solvent was
removed under vacuum (rotary evaporator). The mixture was passed
through a short pad of silica gel with ethyl acetate and petroleum
ether (2:1) to give the dark-red half-sandwich ruthenium complex 4b
(64.0 mg, 58%). 1H NMR (500 MHz, CDCl3): δ 8.10 (d, J = 16 Hz, 1
H), 8.03 (d, J = 12 Hz, 1 H), 7.68 (d, J = 8 Hz, 1 H), 7.62 (d, J = 8
Hz, 2 H), 7.48 (d, J = 8 Hz, 2 H), 7.33 (d, J = 8 Hz, 1 H), 7.29 (d, J =
8 Hz, 1 H), 7.02 (d, J = 8 Hz, 1 H), 6.79 (d, J = 8 Hz, 1 H), 5.62 (d, J
= 4 Hz, 1 H), 5.52 (d, J = 4 Hz, 1 H), 5.36 (d, J = 8 Hz, 1 H), 5.09 (d,
J = 8 Hz, 1 H), 2.56 (m, 1 H), 2.32 (s, 3 H), 1.03 (d, J = 8 Hz, 3 H),
0.94 (d, J = 4 Hz, 3 H). 13C NMR (125 MHz, CDCl3): δ 168.9,
155.9, 144.8, 137.9, 135.4, 134.8, 132.9, 131.9, 130.2, 129.9, 129.0,
128.9, 120.2, 116.2, 111.0, 101.9, 100.5, 85.9, 81.4, 81.2, 80.8, 31.2,
22.6, 22.4, 19.3. IR (KBr cm−1): 3435 (m), 3045 (w), 2961 (m), 2921
(m), 2851 (w), 1737 (vw), 1625 (w), 1593 (w), 1550 (s), 1490 (m),
1439 (s), 1403 (m), 1372 (s), 1330 (m), 1296 (m), 1260 (m), 1105
(s), 1035 (m), 1012 (m), 975 (w), 869 (w), 831 (s), 808 (m), 736
(w), 540 (w). Anal. Calcd for C27H25NORuCl2: C, 58.81; H, 4.57; N,
2.54. Found: C, 58.84; H, 4.52; N, 2.59. ESI-MS. Calcd for
[C27H25ClNORu]+ ([M − Cl]+): m/z 516.0667. Found: m/z
516.0703.
Accession Codes
CCDC 2036546−2036548 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
■
Wei-Guo Jia − The Key Laboratory of Functional Molecular
Solids, Ministry of Education, Anhui Laboratory of
Molecular-Based Materials (State Key Laboratory
Cultivation Base), College of Chemistry and Materials
Science, Anhui Normal University, Wuhu 241002, China;
State Key Laboratory of Structural Chemistry, Fujian
Institute of Research on the Structure of Matter, Chinese
Academy of Science, Fuzhou 350002, China; orcid.org/
0000-0001-7976-7543; Email: wgjiasy@mail.ahnu.edu.cn
Richmond Lee − School of Chemistry and Molecular
Bioscience and Molecular Horizons, University of
Wollongong, Wollongong, New South Wales 2522, Australia;
orcid.org/0000-0003-1264-4914;
Email: richmond_lee@uow.edu.au
Authors
Xue-Ting Zhi − The Key Laboratory of Functional Molecular
Solids, Ministry of Education, Anhui Laboratory of
Molecular-Based Materials (State Key Laboratory
Cultivation Base), College of Chemistry and Materials
Science, Anhui Normal University, Wuhu 241002, China
Xiao-Dong Li − The Key Laboratory of Functional Molecular
Solids, Ministry of Education, Anhui Laboratory of
Molecular-Based Materials (State Key Laboratory
Cultivation Base), College of Chemistry and Materials
Science, Anhui Normal University, Wuhu 241002, China
Jun-Peng Zhou − The Key Laboratory of Functional
Molecular Solids, Ministry of Education, Anhui Laboratory of
Molecular-Based Materials (State Key Laboratory
Cultivation Base), College of Chemistry and Materials
Science, Anhui Normal University, Wuhu 241002, China
Rui Zhong − The Key Laboratory of Functional Molecular
Solids, Ministry of Education, Anhui Laboratory of
Molecular-Based Materials (State Key Laboratory
Cultivation Base), College of Chemistry and Materials
Science, Anhui Normal University, Wuhu 241002, China
Haibo Yu − School of Chemistry and Molecular Bioscience and
Molecular Horizons, University of Wollongong, Wollongong,
New South Wales 2522, Australia; orcid.org/0000-0002-
1099-2803
General Procedure for Transfer Hydrogenation of Ketone
Compounds with a Half-Sandwich Ruthenium Complex. A
mixture of ketone compounds (0.1 mmol), MeONa (0.4 mmol, 4
equiv), and a half-sandwich ruthenium complex (0.25 mol %) in 2-
propanol (1.0 mL) was heated to 80 °C for 12 h. After the reaction
had completed (monitored by thin-layer chromatography), the
reaction mixture was cooled to room temperature. Then, the solvent
was removed under reduced pressure and extracted with ethyl acetate
and water (3× 5 mL). The organic layers were analyzed by GC−MS
using n-dodecane as an internal standard.
X-ray Structure Determination. The diffraction data of 2, 4a,
and 4b were collected on a Bruker AXS SMART APEX
diffractometer, equipped with a CCD area detector using Mo Kα
radiation (λ = 0.71073 Å). All of the data were collected at 298 K, and
4319
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Inorg. Chem. 2021, 60, 4313−4321

Inorganic Chemistry
pubs.acs.org/IC
Featured Article
zene To Organize the Solid State To Achieve a [2 + 2] Cycloaddition
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.1c00059
Reaction. Cryst. Growth Des. 2019, 19 (6), 3092−3096.
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MacGillivray, L. R. Supramolecular Catalysis in the Organic Solid
State through Dry Grinding. Angew. Chem., Int. Ed. 2010, 49 (25),
4273−4277.
Notes
The authors declare no competing financial interest.
(17) Yuan, S.; Liu, S.-S.; Sun, D. Two isomeric [Cu4I4]
luminophores: solvothermal/mechanochemical syntheses, structures
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Phosphorescence of Luminescent Coordination Polymers Composed
of Dinuclear Copper(I) Iodide Rhombic Cores. Chem. - Eur. J. 2018,
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ACKNOWLEDGMENTS
■
We acknowledge financial support from the National Natural
Science Foundation of China (Grant 21102004), Australian
Research Council (DECRA Award DE210100053), University
of Wollongong (VC Fellowship), and National Computing
Infrastructure (Australia) for computing resources. We also
thank Dr. Davin Tan for helpful discussions and suggestions.
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Diana, E.; Turci, F. Solvent-Free Synthesis of Luminescent Copper(I)
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