Ligand effect in racemization and dynamic kinetic resolution of alcohols: Mechanism on cymene ruthenium complexes

Article abstract of DOI:10.1016/j.jorganchem.2014.10.011

A family of ruthenium complexes with different ligands was utilized in racemization of (R)-1-phenylethanol to investigate the potential influence of the ligands coordinated to the ruthenium center. Kinetic experiments showed that 16-electron cymene ruthenium complex with two chloro-bridge bonds and 18-electron ones with easily dissociative ligands are highly active for catalytic racemization of alcohols. Possible racemization mechanism for cymene ruthenium complexes was then proposed. Computational analysis of dissociation energy barrier, NBO analysis and reaction potential energy surface suggest that ligand-dissociation process is the vital step of the racemization catalyzed by cymene ruthenium complexes. Thereafter, these complexes were applied in the DKR of secondary alcohols to verify their efficiency and applicability.

Full text of DOI:10.1016/j.jorganchem.2014.10.011

Journal of Organometallic Chemistry 775 (2015) 60e66
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ligand effect in racemization and dynamic kinetic resolution of
alcohols: Mechanism on cymene ruthenium complexes
Hui Cao 1, Li-Hua Cai 1, Chen-Xi Wang, Xiao-Han Zhu, Zhi-Ming Li*, Xiu-Feng Hou*
Department of Chemistry, Fudan University, Han Dan Road 220, Shanghai 200433, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A
family of ruthenium complexes with different ligands was utilized in racemization of (R)-1-
Received 30 July 2014
Received in revised form
24 September 2014
Accepted 4 October 2014
Available online 15 October 2014
phenylethanol to investigate the potential influence of the ligands coordinated to the ruthenium cen-
ter. Kinetic experiments showed that 16-electron cymene ruthenium complex with two chloro-bridge
bonds and 18-electron ones with easily dissociative ligands are highly active for catalytic racemization
of alcohols. Possible racemization mechanism for cymene ruthenium complexes was then proposed.
Computational analysis of dissociation energy barrier, NBO analysis and reaction potential energy surface
suggest that ligand-dissociation process is the vital step of the racemization catalyzed by cymene
ruthenium complexes. Thereafter, these complexes were applied in the DKR of secondary alcohols to
verify their efficiency and applicability.
Keywords:
Racemization
Dynamic kinetic resolution
Cymene ruthenium complexes
Density functional theory
sec-Alcohols
© 2014 Elsevier B.V. All rights reserved.
Introduction
for systematical study on the ligand effect during racemization [9].
On the other hand, mechanistic studies of the catalytic racemization
Optically active secondary alcohols are valuable intermediates
in the fine chemical industry [1]. The resolution of racemic mix-
tures is the most convenient way to prepare enantiomerically pure
compounds on an industrial scale [2]. The kinetic resolution (KR) of
racemic secondary alcohols by enzymes such as lipases and ester-
ases is widely used to obtain a range of enantiomerically enriched
alcohols or their esters [3]. However, the theoretical maximum
yield (50%) and the laborious separation of product from the
remaining substrate are major drawbacks of the KR procedure.
Dynamic kinetic resolution (DKR), in which racemization of un-
wanted enantiomers is coupled with KR, is an attractive method to
overcome these drawbacks with theoretical maximum yield up to
100% (Scheme 1).
by cyclopentadienyl ruthenium complexes have attracted extensive
€
attentions in the past few years [8a,10]. Backvall and co-workers
suggested catalytic racemization generally proceeds via reversible
hydrogen transfer reactions [11]. Recently, they revealed the exis-
tence of a CO dissociation process to create a vacant site during the
dehydrogenation step [12]. Nolan and co-workers demonstrated the
importance of the vacant site on the 16-electron ruthenium center
[13]. However, racemization mechanism for ruthenium complexes of
other structures remains to be studied and confirmed.
We report herein our successful effort to utilize a family of
cymene ruthenium complexes to investigate the potential influ-
ence of the ligands coordinated to the metal center on the course of
racemization and DKR. Possible racemization mechanisms for
cymene ruthenium complexes were proposed and verified by ex-
periments along with computational analysis. Two excellent race-
mization catalysts, including 16- and 18-electron cymene
ruthenium complexes, were then investigated in DKR of a variety of
secondary alcohols.
Shvo and co-workers reported the synthesis of a cyclopentadienyl
diruthenium complex, known as Shvo's catalyst, for hydrogen
transfer reactions in 1984 [4]. This catalyst was first introduced to
efficient DKR of alcohols in combination with Candida antarctica
€
lipase B (CALB) by Backvall in 1997 [5]. Afterwards, cyclopentadienyl
ruthenium derivants bearing CO [3c,6], PPh3 [7] and carbene [8] li-
gands have been prepared for successful racemization of secondary
alcohols and DKR in some cases. Now there is an increasing demand
Results and discussion
Ligand effect on catalytic racemization
* Corresponding authors. Tel.: þ86 21 55664878; fax: þ86 21 65641740.
E-mail addresses: zmli@fudan.edu.cn (Z.-M. Li), xfhou@fudan.edu.cn (X.-F. Hou).
These authors contributed equally to this work.
16-Electron cymene ruthenium complexes 1 and 18-electron
ones 2e6 were chosen for our study. Triphenylphosphine,
1
http://dx.doi.org/10.1016/j.jorganchem.2014.10.011
0022-328X/© 2014 Elsevier B.V. All rights reserved.

H. Cao et al. / Journal of Organometallic Chemistry 775 (2015) 60e66
61
Table 1
Catalytic racemization of (R)-7 with complexes 1e6.a
Entry
Catalyst
Base
ee [%]b
1
2
3
4
5
6
7
8
9
1
1
1
1
2
3
4
5
6
tBuOK
K2CO3
K3PO4
KOH
8
30
25
9
17
13
24
97
97
Scheme 1. Schematic DKR of sec-alcohols.
tBuOK
tBuOK
tBuOK
tBuOK
tBuOK
pyridine and N-heterocyclic carbene (NHC) are typical mono-
dentate ligands, while phenanthroline and pentanedione are
representative bidentate chelating ligands (Fig. 1). Complexes 2e6
were synthesized according to the literature procedures [14].
Since catalytic racemization is vital for efficient DKR, these
ruthenium complexes were evaluated using the racemization of
(R)-1-phenylethanol ((R)-7) first as template reaction (Table 1).
a
(R)-1-Phenylethanol (0.25 mmol), catalyst (Ru: 4 mol%), base (5.0 mol%), 60 ꢀC,
toluene (3 mL), 24 h.
b
On the basis of specific rotation results of two runs.
t
With complex 1 as the model catalyst, BuOK is finally chosen as
base for racemization after comparison with K2CO3, K3PO4 and KOH
(Entries 1e4). The racemization efficiency is particularly high with
ee (ee ¼ enantiomeric excess) getting down below 8% after
24 h (Entry 1). For complexes with monodentate ligands (2e4),
complex 3 with a pyridine ligand performs best with a 13% ee after
24 h (Entry 6). However, catalysts with bidentate chelating ligands
(5, 6) racemized less than 20% of (R)-7 after the same time (Entries
8, 9).
Basically, 16-electron complex 1 performs better than 18-
electron ones, while complexes with monodentate ligands
perform better than that with bidentate chelating ligands. Notice-
ably, similar complexes with different ligands can perform
dissimilarly in racemization.
Mechanism of racemization catalyzed by cymene ruthenium
complexes
Based on the mechanism studies on cyclopentadienyl ruthe-
nium complexes [8,10e13] and our experiments, the inner-sphere
pathway for the racemization of cymene ruthenium chloride
complexes was speculated in which the dissociation of ligand is
anticipated to be the key step for 18-electron ruthenium chloride
complexes (Scheme 2). Complex A was first dehalogenated by po-
tassium tert-butoxide (tBuOK), and ruthenium complex C formed
via a ligand exchange process of complex B with alcohol substrate.
For 18-electron complexes, a vital ligand-dissociation process took
place to form complex D. Racemization of D was then carried out
With the best catalyst 1 and relative good catalysts 2e4 in hand,
we decided to profile the racemization of (R)-7 with these catalysts
to get details of the racemization process, and the results are pre-
sented in Fig. 2. As shown in Fig. 2, it took about 350 min for catalyst
1 to racemize 80% of (R)-7. Among 18-electron catalysts 2e4,
catalyst 3 with a pyridine ligand was most efficient and it race-
mized 80% of (R)-7 within 220 min. After about 500 min, an ee of
20% was achieved by catalyst 2 with a PPh3 ligand, while catalyst 4
with an NHC ligand is least efficient and only racemized 76% of (R)-
7 even after 800 min. Thus the profile also points out that 1 is the
best catalyst in our studied ruthenium catalysts.
via b-hydride transfer to the vacant site on ruthenium center, and
formed a Ru-hydride intermediate E. The ketone was then hydro-
genated to form a racemic alcohol.
Quantum-chemical calculations based on the density functional
theory (DFT) were used to further prove the mechanism. We
focused on the energy barriers required for the loss of ligands first.
Calculation results of the energy barriers required for the ligand-
dissociation of 18-electron complexes 2e4 are shown in Table 2.
Ligand-dissociation of 3C required lower energy, 18.3 kcal/mol,
than 2C, 20.8 kcal/mol, and 4C, 37.1 kcal/mol in toluene solution.
Besides that, the Natural Bond Orbital (NBO) found that the bond
Fig. 1. Ruthenium complexes utilized in racemization and DKR of sec-alcohols.

62
H. Cao et al. / Journal of Organometallic Chemistry 775 (2015) 60e66
and most effective. Thus, the computational results verified our
anticipation, that ligand-dissociation is the key step of the race-
mization catalyzed by 18-electron cymene ruthenium complexes.
Except that, the RueO distance in 1D is shorter than those in 2C, 3C,
and 4C, which is 1.941, 2.090, 2.066, and 2.088 Å respectively
(Fig. 3). This may be due to the p-donation by the oxygen lone pair,
which would stabilize the 16-electron ruthenium complex 1D
(catalyst 1) and thus enhance its catalytic efficiency [8]. Summa-
rization of the experimental results in Table 1 and the computa-
tional results in Table
2 suggests that 18-electron cymene
ruthenium chloride complex will be an excellent racemization
catalyst when bearing a weak-bonded ligand on ruthenium center.
A computational analysis of the racemization reaction pathway
(1De1D0) was undertaken to get insight into the mechanism
(Fig. 4). Complex 1D is the entrypoint into the racemization cata-
lytic cycle and is set as the zero energy point for the following
discussion. The CbeH bond of 1D engages in a hydrogen bond with
chlorine atom in 1E, and in a
center in 1F. -H elimination from 1F leads to the
ketone Ru-hydride complex 1G. The fact that the energy barriers
between -agostic complex 1F, -coordinated complex 1G and
b
-agostic interaction with the Ru
b
p
-coordinated
Fig. 2. Kinetic profile for racemization of (R)-7 with catalyst 1e4.
b
p
their surrounding transition states are lower than 5 kcal/mol is the
evidence that 1G and 1F are rather unstable intermediates. Via a
orders of metal-ligand bonds in 2C (RueP bond), 3C (RueN bond)
and 4C (RueC bond) are 0.699, 0.499, 0.759, respectively. These
results suggest that the RueN bond in 3C is the weakest and most
easily broken, while the RueC bond in 4C is the strongest and most
difficult to break. Besides, computational analysis of dissociation
energy barriers and bond orders is corresponding with their per-
formance in racemization velocity and efficiency, that, 3C is fastest
barrier of 3.7 kcal/mol, the
dride complex 1G is transformed to the
ruthenium hydride complex 1H, which is 6.8 kcal/mol more stable
than the -coordinated ketone ruthenium hydride complex 1G.
Complex 1H is essentially at the midpoint along the racemization
p-coordinated ketone ruthenium hy-
s
-coordinated ketone
p
Scheme 2. Proposed mechanism for racemization of chiral alcohols by 18-electron cymene ruthenium chloride complexes.

H. Cao et al. / Journal of Organometallic Chemistry 775 (2015) 60e66
63
Table 2
Energy required for ligand-dissociation.
Compound
Barrier (gas phase)/kcal molꢁ1
Barrier (liquid phase)/kcal molꢁ1
RueP (N or C) bond distance (Å)/bond order
RueO/Å
2C
3C
4C
10.7
10.5
26.4
20.8
18.3
37.1
2.371/0.699
2.118/0.499
2.066/0.759
2.090
2.066
2.088
Fig. 3. Optimized geometries of complexes 2Ce4C, 1D, and transition states of ligand dissociation.
reaction pathway. Then rotation around the RueO bond of the
coordinated ketone, with a barrier 7.7 kcal/mol, leads to another
s
s
-
-
coordinated ketone, 1H0 in Fig. 4, with an opposite orientation of
the phenyl and methyl groups relative to the cymene and chlorine
ligands. 1H0 is converted to the enantiomer of 1D0 following the
reverse passway of 1D to 1H. All in all, the pathway from 1D to 1D0
corresponds to an inversion of configuration at the Cb atom of the
alkoxide. The total energy barrier, regardless of forward or back-
ward direction, is only 14.1 kcal/mol, which can be easily sur-
mounted under experimental conditions.
In short, computational analysis indicated that the dissociation
of ligands to form vacant sites is crucial to racemization of sec-
ondary alcohols catalyzed by 18-electron cymene ruthenium
complexes. And the racemization pathway from 1D to 1D0 sup-
ported the mechanism (Scheme 2), which is consistent with the
study on 16-electron cyclopentadienyl ruthenium complexes [8].
Dynamic kinetic resolution of rac-7 with complexes 1e6
Fig. 4. Schematic reaction pathway for the transformation of (R)-7 into (S)-7 promoted
by complex 1.
The DKR of rac-7 with complexes 1e6 were carried out to gain
insight into the suitability of these complexes to Novozyme-435 and

64
H. Cao et al. / Journal of Organometallic Chemistry 775 (2015) 60e66
Table 4
the results were shown in Table 3. Obviously, the excellent yields
(above 90%) and ee's (above 92%) were obtained with 16-electron
complex 1 (Entry 1) and 18-electron complex 3 with a pyridine
ligand (Entry 3), while low yields (below 70%) were obtained with
bidentate chelating catalysts 5 and 6 (Entries 5e6). The yields of DKR
(Entries 2e4) were consistent with their racemization ability for 18-
electron complexes 2e4. Singularly low enantioselectivity (40%)
gained with catalyst 4 (Entry 4) was probably caused by the esteri-
fication ability [15] of ruthenium complexes with NHC ligands.
The DKR of various sec-alcohols.a
Entry
rac-Alcohol
Catalyst
Temp [ꢀC]
70
Yield [%]b
ee [%]c
1
2
1
3
86
80
98
96
OH
8
3
4
1
3
60
60
92 (85)
95
>99
95
OH
9
Dynamic kinetic resolution of various secondary alcohols
5
6
1
3
93
90
95
95
OH
From template reactions, we screened out 16-electron cymene
ruthenium complex 1 and 18-electron cymene ruthenium complex 3
with a pyridine ligand by yield and ee in the DKR process. A variety of
secondary alcohols 8e16, including electron-deficient and electron-
rich ones, were then selected as substrates for the two catalysts
and the results are summarized in Table 4. No matter the alcohols
were benzylic or aliphatic, these two catalysts almost always gave
good toexcellent yieldsand eevalues, owingtothenaturalvacant site
for catalyst 1 and the easily-dissociative ligand for catalyst 3. The
exception was for alcohol 15 (entry 15 and 16), the yields were rela-
tively low. In addition, for both catalysts, the halogen-substituted
benzylic alcohols seemed to deteriorate the yields to some extent.
On the whole, 16-electron catalyst 1 gave slightly better results than
18-electron cymene ruthenium complex 3 probably due to the co-
ordination competition between alcohol and the leaving ligand.
O
10
7
8
1
3
60
60
88
82
>99
95
OH
11
9
10
1
3
82 (73)
76
>99
96
OH
Cl
12
13
11
12
1
3
70
70
81
75
94
97
OH
Br
13
14
1
3
95
88
86
90
OH
Conclusions
F3C
14
In summary, the DFTcalculations indicate that, the dissociation of
ligands to form vacant sites is the key step for racemization of sec-
ondary alcohols catalyzed by cymene ruthenium complexes, and the
complex with weak ligand such as pyridine shows excellent race-
mization efficiencies, which was proved by kinetic experiments.
Computational analysis also demonstrates that the mechanism for
interconversion between R- and S- alcohols catalyzed by the 16-
electron cymene ruthenium species involves ruthenium hydride
intermediates, which is consistent with former report on cyclo-
pentadienyl ruthenium complexes. Application of 16-electron cym-
ene ruthenium complex 1 and 18-electron 3 with easily-dissociative
pyridine ligand in DKR process of various rac-alcohols demonstrates
that both complexes are efficient and applicable catalysts.
15
16
1
3
70
60
68
63
98
73
OH
15
17
18
1
3
93
92
94
71
OH
16
a
rac-Alcohol (0.5 mmol), catalyst (Ru complex: 2 mol%), Novozyme-435 (10 mg),
Na2CO3 (0.5 mmol), tBuOK (8 mol%), toluene (5 mL), p-chlorophenyl acetate
(1.5 mmol), 48 h.
On the basis of 1H NMR analysis [16]. The yields given in parentheses are using
b
isopropenyl acetate as acyl donor.
c
Determined by HPLC or GC with a chiral column.
Experimental section
General
Anhydrous solvents were distilled under nitrogen from sodium
(hexane, toluene) or calcium hydride (dichloromethane), and
methanol was distilled over magnesium and iodine. Complexes 1,
alcohols, acylating agents and other chemical reagents were ob-
tained from commercial sources and used without further purifi-
cation. 1H and 13C NMR spectra were recorded on a Bruker VAVCE-
DMX 400 MHz instrument relative to TMS. Enantiomeric excesses
were determined by specific rotation, HPLC or GC. Specific rotation
was measured by a Rudolph IV-589 Automatic Polarimeter. HPLC
was equipped with a capillary column Daicel OD-H. GC was
equipped with a capillary column Varian CP 7502.
All manipulations were carried out under a nitrogen atmo-
sphere using standard Schlenk techniques unless otherwise stated.
Table 3
The DKR of rac-7 with complexes 1e6.a
Entry
Catalyst
Yield [%]b
ee [%]c
1
2
3
4
5
6
1
2
3
4
5
6
91
83
90
70
59
69
99
98
99
40
96
97
Synthesis of complexes 2e6
a
[Ru(p-cymene)Cl2(triphenylphosphine)] (2)14a
To a suspension of [Ru(p-cymene)Cl2]2 (100 mg, 0.163 mmol) in
toluene (5 mL), triphenylphosphine (0.36 mmol, 2.2 equiv) was
added at room temperature. The resulting mixture was heated to
rac-1-Phenylethanol (0.5 mmol), Novozyme-435 (10 mg), Na2CO3 (0.5 mmol),
tBuOK (5 mol%), catalyst (Ru complex: 4 mol%), 60 ꢀC, toluene (5 mL), p-chlor-
ophenyl acetate (1.5 mmol), 48 h.
b
On the basis of 1H NMR analysis [16].
c
On the basis of specific rotation results of two runs.

H. Cao et al. / Journal of Organometallic Chemistry 775 (2015) 60e66
65
reflux for 1 h. After the mixture was cooled, the precipitate was
General procedure for the racemization of (R)-1-phenylethanol
filtered, washed with hexane (3 ꢂ 5 mL), and dried in vacuum,
affording an orange solid (155.6 mg, 84%). 1H NMR (400 MHz,
To a 25 mL Schlenk tube containing 5 mL toluene, Ru or Ir
complex (0.01 mmol, 4.0 mol%) and base (5.0 mol%) were added
and stirred for 10 min before (R)-1-phenylethanol (>97% ee,
0.25 mmol) was added. The reaction mixture was stirred at 60 ꢀC
for 24 h. Toluene was then removed by evaporation under reduced
pressure, and the residue was extracted with petroleum ether, and
evaporated under reduced to give an oily mixture. The yield was
directly determined by 1H NMR. Enantiomeric excesses were
CD3Cl):
d
¼ 1.10 (d, J ¼ 6.1 Hz, 6H), 1.80 (s, 3H), 2.80 (m, 1H), 4.92 (d,
J ¼ 5.8 Hz, 2H), 5.12 (d, J ¼ 5.8 Hz, 2H), 7.20, 7.30, 7.76 (m, 15H); 13
C
NMR (400 MHz, CDCl3):
110.78, 127.54, 129.85, 134.03.
d
¼ 17.38, 21.52, 29.88, 86.78, 88.70, 95.62,
[Ru(p-cymene)Cl2(pyridine)] (3)14b
To a suspension of [Ru(p-cymene)Cl2]2 (100 mg, 0.163 mmol) in
toluene (5 mL), pyridine (28 L, 0.36 mmol, 2.2 equiv) was added at
m
calculated using the equation e.e ¼
a/a0 where a and a0 was the
optical rotation of the product and (R)-1-phenylethanol
room temperature. The resulting mixture was heated to reflux for
3 h. After the mixture was cooled, the precipitate was filtered,
washed with hexane (3 ꢂ 5 mL), and dried in vacuum, affording a
respectively.
yellow solid (99.2 mg, 79%). 1H NMR (400 MHz, CD3Cl):
d
¼ 1.31 (d,
J ¼ 6.9 Hz, 6H), 2.10 (s, 3H), 3.00 (sept, 1H), 5.22 (d, J ¼ 5.9 Hz, 2H),
General procedure for dynamic kinetic resolution of rac-alcohols
5.44 (d, J ¼ 5.7 Hz, 2H), 7.31 (m, 2H), 7.74 (m, 1H), 9.04 (d, J ¼ 4.8 Hz,
2H); 13C NMR (400 MHz, CDCl3):
82.82, 97.03, 103.58, 124.5, 137.5, 154.9.
d
¼ 18.22, 22.31, 30.67, 82.27,
To a 25 mL Schlenk tube containing 5 mL toluene, Ru or Ir
complex (0.01 mmol, 2.0 mol%) and potassium tert-butoxide
(0.04 mmol, 5.0 mol%) were added and stirred for 10 min. Sodium
carbonate (0.5 mmol), alcohol (0.5 mmol), acylating agents
(1.5 mmol) and Novozym-435 (10 mg) were then added. The sol-
vent was then stirred for 24 h at 60 ꢀC or 70 ꢀC. After evaporation to
dryness, the mixture was loaded to a 10 ꢂ 3 cm silica column.
Elution with petroleum ether removed any alcohol. The product
was eluted with 3:50 ethyl acetate/petroleum ether, and the sol-
vent removed to give an oily mixture. The yield was directly
determined by 1H NMR. Enantiomeric excesses were determined
by specific rotation, HPLC or GC.
[Ru(p-cymene)Cl2(NHC)] (NHC ¼ 1,3-dicyclohexylimidazole-2-
ylidene) (4)14c
0.55 equiv of silver oxide (0.11 mmol) was added to a suspension
of 1,3-dicyclohexylimidazole salt (0.2 mmol) in dichloromethane
(5 mL). The mixture was stirred for 6 h at room temperature and in
dark environment. [(p-cymene)RuCl2]2 (0.11 mmol) was then
added to the mixture and reacted overnight. The solution was
loaded directly onto a 10 ꢂ 3 cm silica column. Elution with
dichloromethane removed remaining [(p-cymene)RuCl2]2. The or-
ange band was eluted carefully with 1:150 methanol/dichloro-
methane, and the solvent removed to give an orange solid (76.4 mg,
71%). 1H NMR (400 MHz, CDCl3):
d
¼ 1.18e1.26 (m, cyclohexyl), 1.37
Computational methods
(d, J ¼ 4.8 Hz, 2H), 1.47e1.89 (m, cyclohexyl), 2.14 (s, 3H), 2.3e2.4
(m, cyclohexyl), 2.86 (sept, 1H), 4.84 (m, 2H), 5.14 (d, J ¼ 5.8 Hz, 2H),
5.42 (d, J ¼ 5.8 Hz, 2H), 7.06 (s, 2H). 13C NMR (400 MHz, CDCl3):
All theoretical calculations were performed with Gaussian 09
quantum chemistry software at BP86/SVP level for C, H, O, P, N, Cl.
For Ru, we use the standard SDD basis set in Gaussian 09 [17e20].
The geometries of reactants, intermediates, products and transition
states were fully optimized and characterized by the number of
imaginary frequencies. Furthermore, all the extrema were
confirmed by calculation of the intrinsic reaction paths [21]. The
natural bond orbital (NBO) program in Gaussian 09, Version 3.1
[22], was used to obtain more information about some special
bonds. The effect of solvation on reaction energetics was deter-
mined by means of single-point self-consistent reaction field
(SCRF) calculations using the polarized continuum model (PCM)
[23]. Gas-phase optimized structures were used in the single point
calculations in toluene as solvent with a relative permittivity of 2.4.
Free energies in solution with all non-electrostatic effects are dis-
cussed in the text. Computational details are provided in the Sup-
porting Information.
d
¼ 18.87, 23.17, 31.27, 25.48, 26.07, 35.37, 35.88, 59.33, 83.72, 85.32,
97.36, 105.13, 119.38, 171.33.
[Ru(p-cymene)Cl(phen)]Cl (5)14d
2 equiv (0.326 mmol) of phenanthroline were added to a sus-
pension of [(p-cymene)RuCl2]2 (100 mg, 0.163 mmol) in dichloro-
methane (10 mL). The mixture was stirred for 3 h at room
temperature, during this time the colour changed from orange to
yellow. After evaporation to dryness, the residue was dissolved in
water; the solution was filtered and evaporated to dryness giving
the product in quantitative yield. 1H NMR (400 MHz, D2O):
d
¼ 0.83
(d, J ¼ 6.7 Hz, 6H), 2.11 (s, 3H), 2.50 (hept, 1H), 5.90 (d, J ¼ 6.6 Hz,
2H), 6.13 (d, J ¼ 6.6 Hz, 2H), 7.87 (s, 2H), 7.97 (dd, J ¼ 6.8 Hz,
J ¼ 7.9 Hz, 2H), 8.58 (d, J ¼ 8.3 Hz, 2H), 9.659 (d, J ¼ 5.6 Hz, 2H). 13
C
NMR (400 MHz, D2O):
104.27, 126.42, 127.36, 130.63, 139.02, 145.45, 155.13.
d
¼ 18.00, 20.93, 30.58, 83.98, 86.17, 103.16,
[Ru(p-cymene)Cl(acac)]Cl (6)14e
Acknowledgements
A suspension of [(p-cymene)RuCl2]2 (100 mg, 0.163 mmol) and
Na(acac)$H2O (59 mg, 0.425 mmol) in acetone (AR) (10 mL) was
stirred for 40 min. The solvent was vacuum-evaporated until dry-
ness and the residue was extracted with dichloromethane
(4 ꢂ 5 mL). The solvent was then removed in vacuum and the
residue dissolved in acetone. The resulting solution was partially
concentrated under reduced pressure and an orange solid precip-
Financial support from the National Natural Science Foundation
of China (Grant No. 20871032, 20971026, 21271047 and 21102019),
Shanghai Leading Academic Discipline Project, Project Number:
B108, and Shanghai Key Laboratory Green Chemistry and Chemical
Process is gratefully acknowledged.
itated in quantitative yield. 1H NMR (400 MHz, CDCl3):
d
¼ 1.31 (d,
J ¼ 6.8 Hz, 6H), 1.985 (s, 6H), 2.27 (s, 3H), 2.89 (m, 1H), 5.15 (s, 1H),
Appendix A. Supplementary data
5.21 (d, J ¼ 5.9 Hz, 2H), 5.45 (d, J ¼ 6.1 Hz, 2H). 13C NMR (400 MHz,
CDCl3):
186.47.
d
¼ 18.11, 22.30, 27.30, 30.76, 78.88, 82.43, 98.80, 99.62,
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.10.011.

66
H. Cao et al. / Journal of Organometallic Chemistry 775 (2015) 60e66
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