Phosphine-pyridonate ligands containing octahedral ruthenium complexes: Access to esters and formic acid

Article abstract of DOI:10.1039/c7cy00932a

The preparation of three well-defined ruthenium complexes arising from phosphine-pyridon-e/-ate ligands is described. Solvent dependent Lewis acidic species formation was observed with these complexes. Selective formation of acetals or esters from primary alcohols was observed in the presence of these catalysts. Preliminary evaluation of these complexes in the base free hydrogenation of carbon dioxide is also reported.

Full text of DOI:10.1039/c7cy00932a

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2017, DOI: 10.1039/C7CY00932A.
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Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
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Phosphine-Pyridonate Ligands Containing Octahedral Ruthenium
Complexes : Access to Esters and Formic Acid
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
b
b
a
a
A. R. Sahoo, F. Jiang, C. Bruneau, G. V. M. Sharma, S. Suresh, T. Roisnel, V. Dorcet and
a
M. Achard *
DOI: 10.1039/x0xx00000x
The preparation of three well-defined ruthenium complexes arising from phosphine-pyridon-e/-ate ligands is described.
Solvent dependant Lewis acidic species formation was observed with these complexes. Selective formation of acetal or
ester from primary alcohols was observed in the presence of these catalysts. Preliminary evaluation of these complexes in
base free hydrogenation of carbon dioxide is also reported.
www.rsc.org/
[9a]
preparation of metal-metal bonded polynuclear complexes.
This latter, lately renamed 6-DPPon has also found wide
Introduction
[9b]
applications in self assembling system for hydroformylation.
Catalytic hydrogen transfer processes ranging from
hydrogenation and dehydrogenation represent an important
research field strengthened by the recent applications related
to biomass transformations, carbon dioxide valorization and
Based on the previous findings of Brunner who demonstrated
that chelating O-alkylated phosphine-pyridones could undergo
[10]
deprotection,
we reported the direct access to the
[1-3]
corresponding phosphine-pyridone for the catalytic
hydrogenation of unfunctionalized ketones and for acetal
liquid organic hydrogen carrier’s development.
Noticeable
breakthroughs were obtained during the last decade on
acceptorless ester formation from alcohols and more recently
[11]
formation from primary alcohols.
Herein we report the preparation of new well-defined
ruthenium complexes featuring proton responsive phosphine-
pyridone ligands. Preliminary evaluation in tunable
acceptorless dehydrogenation of primary alcohols is
investigated for the production of acetals or esters as well as
their evaluation in the base free hydrogenation of carbon
dioxide.
on base free CO hydrogenation, thanks to the use of metal-
2
ligand cooperative catalytic systems based on pincer type or
[4-7]
finely tuned ligands.
While formic acid production still
requires the development of catalysts operating at milder
reaction conditions and low pressure; in dehydrogenation, the
access to tunable catalytic systems allowing the selective
formation of selected dehydrogenated products by simple
modification of the reaction conditions is of great interest. 2-
Pyridone based ranging from bidentate to pincer -containing
ligands have attracted interest of the researchers and found
promising applications in hydrogen transfer processes such as
Results and discussion
Synthesis and characterization of ruthenium(II) complexes
[
8a,b,d,g]
[8c,f,h,i]
dehydrogenation of alcohols,
carbonyl reduction,
[8e]
[8k]
[8l]
β-alkylation of amines, formate production, ester and
Ph
P
R
P
[8k]
carboxylate formation from primary alcohol.
phosphine-pyridon-e/-ate ligand are an interesting class of
hybrid ligands. Among them, non-chelating 6-
diphenylphosphino)-2-pyridon-e/-ate ligand, known as
PyphosH/Pyphos) has found wide applications for the
In turn,
Ph
N
O
O
N
N
O
H
H
H
R = Ph; L2-H
R = t-Bu; L3-H
ref. 11b
L1-H
ref. 11a
(
(
Figure 1 Ligands L1-H, L2-H and L3-H used in this study.
With our reported new ligands in hand (Figure 1), we
investigated the access to the corresponding well-defined
octahedral ruthenium complexes with RuCl (PPh ) as common
2
3 3
metallic precursor (Scheme 1). Among the five possible
isomers, treatment of two equivalents of L1-H with one
equivalent of RuCl (PPh ) in chloroform solution resulted in
2
3 3
the selective formation of the yellow Ru-1 in 60% isolated
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yield. Characterization by NMR spectroscopy and successful
crystallization demonstrated the selective coordination of the
tridentate ligand in a fac mode and selective formation of the
cis (Cl, Cl) isomer. Hydrogen bonding interaction between the
hydroxyl groups and the chloride atoms favoured the selective
formation of this isomer, thus contrasting with the
corresponding ruthenium analogue featuring a phosphine-
[12]
picoline ligand.
The use of the tridentate ligand L2-H with
the same metallic precursor afforded the corresponding yellow
Ru-2 complex where the chloride atom in trans relationship
with the phosphorus atom of L2-H, is interacting with the two
hydroxyl groups of the ligand. Interestingly, NMR spectroscopy
in CDCl
3
demonstrated the formation of the neutral complex
OD highlighted the immediate
whereas the use of CD
3
formation of the resulting red cationic complex. This behaviour
was confirmed with the use of the more basic tridentate ligand
L3-H which led to the square planar pyramidal cationic 16 ē
complex Ru-3 where the methanol molecule acts as proton
2 3 3
Scheme 1 Preparation of the well-defined Ru1-3 from RuCl (PPh ) .
relay. These observations confirm that the formation of Lewis gave the bioester 3j without noticeable isomerized side
acidic species shielded by the two protonated pyridone products whereas undec-10-en-1-ol led to a mixture of
moieties and the concomitant assistance of an alcohol can isomerized esters (not presented). Under our optimal catalytic
[
13,14c]
easily occur from these complexes.
synthesized complexes described above, solid state structures corresponding benzyl benzoate 3a in 100% yield according to a
support the aromatized structure of the pyridone moieties
Figure 2).
For all the conditions, reaction of benzaldehyde 4a afforded the
a
Table 1 Benzyl benzoate from benzyl alcohol 1a
(
Applications in catalytic dehydrogenation and hydrogenation
With these well-defined complexes in hand, we next
investigated their reactivity in dehydrogenation of primary
alcohols (Table 1). Reaction of benzyl alcohol 1a in the absence
of base in THF resulted in the selective formation of the
corresponding acetal 2a albeit in lower yields than with the
Ratio
Yield of
entry
Cat.
Solvent
Base
Conv.
b
2
a/3a/4a
3a
[11,13]
previously described iridium complexes (entries 2-4).
a
1
Ru-2
Ru-1
Ru-2
Ru-3
Ru-2
Ru-1
Ru-2
Ru-3
Ru-2
Ru-2
Ru-2
Ru-2
Toluene
THF
-
12
71
0:0:100
92:0:8
0
0
Interestingly, in a basic environment created by the addition of
sodium hydroxide, the selectivity was completely shifted from
acetal to ester in 50% yield along with benzaldehyde (entry 5).
Replacing THF by toluene led to complete conversion into
benzyl benzoate 3a in 94% isolated yield (entry 7). To the best
of our knowledge, there is only one precedent report in the
literature accounting for the selective formation of acetal or
c
2
-
c
3
THF
-
75
88:0:12
96:0:4
0
c
4
THF
-
56
0
5
THF
NaOH (10)
NaOH (10)
NaOH (10)
NaOH (10)
tBuOK (10)
BnONa (10)
LiOH (10)
KOH (10)
67
0:80:20
0:50:50
0:100:0
0:98:2
50
43
99(94)
73
77
99
39
84
[
13]
a
ester by simple modification of the reaction conditions.
6
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
94
Under similar conditions, the use of Ru-1 lowered selectivity
whereas the use of Ru-3 decreased the conversion (entries 6
and 8). Other hydroxide bases were also evaluated such as
KOH and LiOH. However, the catalytic activities and
selectivities were altered suggesting an effect on the metal
a
7
100
75
a
a
8
9
100
100
41
0:77:21
0:100:0
0:95:5
[8j]
cation on the reaction efficiency (entries 7, 11, 12). As
expected, complete conversion towards the ester was also
observed with the use of a catalytic amount of BnONa
generated by the prior addition of sodium (entry 10). Under
our optimal catalytic conditions, reaction scope was next
d
1
0
1
2
a
a
1
1
85
0:98:2
a
examined with benzylic alcohols affording 63 to 94% isolated Experimental conditions: all reactions were performed under an inert atmosphere of
argon and carried out with benzyl alcohol 1a (0.5 mmol), precatalyst (1 mol%) in a closed
yield (Scheme 2). Notably, no side dehalogenation occurred
b
Schlenk tube in toluene (0.5 mL) at 150 °C for 16 h. Conversions and GC yields were
with halogenated benzylic alcohols 1e and 1f. Aliphatic primary
determined by GC analysis with dodecane (30 µL) as internal standard and the number in
alcohols were selectively converted into the corresponding
parenthesis corresponds to the isolated yield after purification by column
c
d
esters 3g
-i
in up to 85% isolated yields. The use of citronellol
chromatography. Reaction carried out with 0.5 mL of THF at 170 °C for 24 h. BnONa was
generated by the addition of Na to benzyl alcohol 1a.
2
| J. Name., 2012, 00, 1-3
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Ru-2 (1 mol%)
NaOH (10 mol%)
O
+
2 H
2
R
OH
toluene, 150 °C
R
O
3a-i
R
O
1
a-i
O
O
O
O
O
3a : 100%(94%)
3b : 90%(72%)
3c : 75%(63%)
O
O
O
O
O
O
F
F
Br
Br
3d : 99%(89%)
3e : 98%(78%)
3f : 96%(83%)
O
O
Ph
O
O
O
O
Ph
3g : 88%(85%)
3h : 100%(77%)
3i : 90%(78%)
O
Me
O
O
O
3k : 100%(81%)
3j : 100%(82%)
compound : conversion (isolated yield after column chromatography)
Scheme 2 Preparation of various esters from aliphatic and benzylic alcohols
NMR analyses tend to suggest the formation of the hydroxo
complex (C136-O138 = 1.30(2)Å) (Figure 3).
[8h]
Interestingly,
evaluation of Ru-4 in dehydrogenation of benzyl alcohol 1a
under optimized reaction conditions (Table 1 entry 7) led to an
active dehydrogenation catalyst with 53% yield of 3a
suggesting that the simple introduction of the acetonitrile
Ru-2 (1 mol %)
O
O
NaOH (10 mol%)
Bn
O
toluene 150°C
100 % conv.
4a
3a
O
O
Bn
8 17
C H
O
O
Ru-2 (1 mol %)
O
NaOH (10 mol%)
+
OH
3a (26%)
3l (24%)
toluene 150°C
100 % conv.
O
1g
O
4a
C
8
H
17
Bn
Fig. 2 X-ray structure of Ru1-3. Selected bond lengths, interatomic distances
C
7
H
15
O
C H
7 15
O
(
Å) and angles (°), Ru-1.CH
2
Cl
2
: Ru1-N1 2.170(3); Ru1-N2 2.146(3); Ru1-
3g (24%)
3m (26%)
P1 2.2423(9); Ru1-P2 2.252(1); Ru1-Cl1 2.499(1); Ru1-Cl2 25329(9); O2-
Cl1 2.887; O1-Cl2 2.968; Cl2-Ru1-Cl2 85.15(3); P1-Ru1-P2 95.62(4); N1-
Ru1-N2 177.0(1). Ru-2.CHCl
3
: Ru1-N1 2.160(2); Ru1-N11 2.232(2); Ru1-
O
O
Bn
O
8 17
C H
P1 2.2024(6); Ru1-P2 2.3230(6); Ru1-Cl1 2.5499(6); Ru1-Cl2 2.4126(6);
O3-Cl1 2.941; O13-Cl1 2.960; N1-Ru1-N11 90.35(6); P2-Ru1-Cl2 92.94(2);
Cl1-Ru1-P1 171.44(2). Ru-3.MeOH Ru1-N1 2.107(2); Ru1-N2 2.094(2);
Ru1-P1 2.3334(7); Ru1-P2 2.1786(9); Ru1-Cl1 2.3946(7); N2-Ru1-N1
OBn
O
Ru-2 (1 mol %)
NaOH (10 mol%)
O
+
OH
3a (20%)
3l (50%)
toluene 150°C
100 % conv.
3a
1g
O
O
9
1.36(8); P1-Ru1-Cl1 90.28(2). CCDC 1453001, 1428110, 1515990 contain
C H
8 17
Bn
C H
7 15
O
C
7
H
15
O
the supplementary crystallographic data for Ru-1, Ru-2, Ru-3.
3g (20%)
3m (10%)
[14]
Tishchenko reaction (Scheme 3).
Moreover, equimolar Scheme 3 Competitive experiments
reaction of octan-1-ol 1g with benzaldehyde 4a led to the
ligand has a profound impact on the conversion. Taken into
account the structure of Ru-4 and the effect of the metallic
cation, these results tend to support the formation of an active
formation of the four possible esters with a statistical
[5d,15]
distribution.
During the treatment of benzyl benzoate 3a
with octan-1-ol 1g the four expected esters were observed
along with the major formation of 3l with a 50% yield
[16]
indicating that transesterification also occurred.
Having
established that Ru-2 allowed the formation of ester from
primary alcohol or aldehyde in the presence of hydroxide base,
we focused our attention on its reactivity. Treatment of Ru-2
P
KOH (2.1 eq.)
P
Ph
3
P
Cl
H
Ph3P
N
NCCH
3
Ru
Cl
Ru
N
N
3
CH CN/MeOH
N
H
H
H
O
O
in a MeOH/CH
of potassium hydroxide afforded the Ru-4 complex (Scheme
). Among the possible tautomers, solid state structure and
3
CN mixture in the presence of two equivalent
O
O
O
Ru-2
Ru-4 (75%)
4
Scheme 4 Reactivity of Ru-2 in the presence of hydroxide base.
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[
17]
anionic ruthenium species.
Keeping in mind previous
[11,13]
reports on dehydrogenation, acetalization
and Tishchenko
N
O
[Ru]
O
D
[14]
H
H
N
O
[Ru]
E
reaction, possible mechanisms are depicted in Figure 4. On
the basis of the results obtained during this study, under
neutral conditions, it involves an outer sphere nucleophilic
H
2
H
2
RCH OH
2
RCH OH
R'
H+
R'
N
attack on a coordinated hemiacetal in
C
arising from the
N
[Ru]
O
H
C
acetal pathway
outer sphere
[Ru]
A
transient formation of the Lewis acidic ruthenium
O
H
H
O
O
R
2
OCH R
R
H
2
R'
N
R'
N
H
H+ + RCH
OH
H
[Ru]
[Ru]
2
H
B
or
H
B'
O
O
O
O
R
R
3
R'
N
J
R'
N
H
[Ru]
O
CH
2
R
O
O
[Ru]
R'
R
O
2
RCH OH
I
K
N
O
[Ru] OCH
2
R
H2
Fig. 3 X-ray structure of Ru4.0.5 CH
distances (Å) and angles (°): Ru2-N127 2.23(1); Ru2-N137 2.17(1); Ru2-P11
.217(3); Ru2-P12 2.307(3); Ru2-N111 2.01(1); O138-O101 2.538; O128-
O101 2.524; C126-O128 1.26(1); C136-O138 1.30(2). CCDC 1468966
contains the supplementary crystallographic data for Ru-4
2
Cl
2
Selected bond lengths, interatomic
O=CHR
R'
N
ester pathway
inner sphere
H
2
[Ru]
O
F
2
O
R'
H
H
R
N
[Ru]
2
OCH R
OH
R'
N
H
O=CHR
[
13]
species
formation of a ruthenium monohydride species
the low concentration of aldehyde during these reactions and
basic conditions leading to easy formation of the pyridone Fig. 4 Proposed pathways accounting on acetal and ester formation.
rutheniuem species , in the case of the ester formation, an
E
for acetal formation followed presumably with the
[Ru]
[11]
G
B/B’
.
Due to
O
O
2
RCH OH
R
K
Increasing the hydrogen pressure had a minimal incidence on
the result whereas increasing the pressure of carbon dioxide
provided better catalytic activity to reach a 205 TON (entry 7
a
inner sphere mechanism involving a coordinated aldehyde and
an alkoxide is more likely. However, at this stage of this
research, the activation of the aldehyde intermediate by the
2
protonated pyridone ring rather than the metallic center via an Table 2 Base free CO hydrogenation
[14c]
outer sphere process cannot totally be ruled out.
Keeping in
Ru1-3 (~ 6 µmol)
mind the recent reports on base free hydrogenation of carbon
dioxide with well-defined ruthenium and iridium complexes
CO
2
HCO H
2
dmso (4 mL), H2
500 rpm
containing
PTA
(1,3,5-triaza-7-phosphaadamantane),
ACRIPHOS (4,5-bis(diphenylphosphino)acridine), azole or
pyridone based ligands, we investigated the activity of our
complexes in the additive-free hydrogenation of carbon
entry
Cat.
Ru-1
Ru-2
Ru-3
Ru-1
Ru-1
Ru-1
Ru-1
Ru-1
Ru-1
Ru-1
pCO
2
/ pH
2
t [h]
16
16
16
72
16
16
16
16
16
16
T (°C)
TON
115-131
33-40
31
2
[HCO H]
1
2
10/50
10/50
10/50
10/60
10/50
10/70
20/50
30/40
10/50
10/50
50
50
50
50
30
50
50
50
70
100
0.19-0.22 M
0.05-0.07 M
0.06 M
[2b,7]
dioxide.
Taking advantage of the recent contributions of
Laurenczy and coworkers highlighting the beneficial influence
of solvent such as dmso acting as hydrogen bond acceptor
toward formic acid production, we next evaluated the catalytic
3
4
355-370
65
0.57-0.60 M
0.11 M
activities of Ru-1, Ru-2 and Ru-3 under these experimental
conditions. Well-defined complexes Ru-2 and Ru-3 featuring
tridentate phosphine-pyridone ligands were found to be active
in the hydrogenation of carbon dioxide at 50 °C leading to a
5
6
137
0.23 M
-1
formic acid concentration up to 0.07 mol.L (Table 2, entries 2
and 3). Astonishingly, under similar reaction conditions,
hydrogenation in the presence of the complex Ru-1 led to a
fourfold more active catalytic system affording around 0.2 M
7
205
0.34 M
8
170
0.30 M
9
80
0.13 M
2 2
[HCO H] at only 10 bar of CO (entry 1). The reaction
temperature was found to be crucial and under similar
pressure, temperature below or above 50 °C altered the
[7a]
catalytic activity (entry 1 compared to 5, 9 and 10).
10
55
0.08 M
a
Experimental conditions: all reactions were performed in a stainless 20 mL reactor under
1
the indicated pressure of CO
2 2
and H . TON were determined by H NMR in the presence
of internal standard (100 µL).
4
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-1
compared to 6 and 1). Finally, up to 0.6 mol.L of formic acid cannulation. Washing the yellow solid with diethyl ether (3×4 mL)
could be achieved after 72h reaction time (entry 4) thus afforded the desired complex with 85% yield (200 mg, 0.26 mmol).
competing with the best reported results which usually require Recrystallization of the complex by slow diffusion of pentane in
[
7,18]
high pressure and longer reaction times.
chloroform furnished crystals suitable for X-ray diffraction studies.
1
The complex becomes cationic when dissolved in methanol.
NMR (400 MHz, CDCl ): δ 12.24 (s, 1H), 11.9 (s, 1H), 7.68-7.58 (m,
H), 7.47-7.05 (m, 11H), 6.95-6.92 (m, 5H), 6.66-6.57 (m, 3H), 6.09
d, J = 8.1 Hz, 1H), 4.02 (dd, J = 16.8 Hz, J = 11.6 Hz, 1H), 3.63-3.57
m, 2H), 3.29 (dd, J = 16.8 Hz, J = 12.5 Hz, 1H); P { H} NMR (162
): δ 68.0 (d, J = 35.9 Hz), 44.9 (d, J = 36.0 Hz); H NMR
400 MHz, CD OD): δ 7.74-7.66 (m, 3H), 7.45 (t, J = 7.6 Hz, 1H), 7.38-
.33 (m, 6H), 7.29-7.25 (m, 5H), 7.21-7.12 (m, 8H), 6.78 (d, J = 7.5
H
3
Conclusions
6
In conclusion, we have reported the synthesis of three new
well-defined ruthenium complexes featuring proton
responsive phosphine-pyridone ligands. Solvent dependent
formation of the neutral and cationic complexes was
demonstrated. Selective formation of acetal or ester was
observed by simple modification of the reaction conditions.
Competitive experiments highlighted the catalytic activity of
such system in dehydrogenation of primary alcohols and
Tishchenko reactions. Whereas tridentate ligands afforded
better results in dehydrogenation, an opposite trend was
observed in the seminal base and additive-free hydrogenation
(
(
1
2
3
1
1
1
2
1
MHz, CDCl
3
(
3
7
1
Hz, 1H), 6.72 (d, J = 8.3 Hz, 1H), 6.02 (d, J = 8.3 Hz, 1H), 4.23 (dd, J =
1
=
7.7 Hz, J
2
= 11.4 Hz, 1H), 3.95-3.87 (m, 2H), 3.70 (dd, J
1
= 18.9 Hz, J
OD): δ 98.6 (br), 45.3 (d,
OD): δ 167.4 (quat-C),
66.6 (quat-C), 160.0 (quat-C), 157.3 (quat-C), 141.6 (CH), 139.2
CH), 134.9 (d, JP-C = 10.3 Hz, CH), 134.5 (quat-C), 134.1 (quat-C),
2
3
1
1
13.6 Hz, 1H); P { H} NMR (162 MHz, CD
3
13
1
J = 33.8 Hz); C { H} NMR (101 MHz, CD
1
(
3
of carbon dioxide leading up to 0.6
concentration in dimethyl sulfoxide.
M formic acid
1
1
1
3
32.6 (CH), 132.4 (CH), 130.8 (d, JP-C = 2.4 Hz, CH), 130.3 (d, JP-C
1.6 Hz, CH), 128.9 (d, JP-C = 9.6 Hz, CH), 116.1 (d, JP-C = 11.6 Hz, CH),
15.8 (d, JP-C = 12.6 Hz, CH), 109.6 (CH), 108.2 (CH), 47.1 (d, JP-C
1.9 Hz, CH ), 40.6 (d, JP-C = 34.0 Hz, CH ); HRMS(ESI-TOF): calc’d for
=
=
2
2
Experimental section
+
C H N O P Cl Ru [M] 758.0354; found 758.0356. Anal. Calcd for
C
3
6
32
2
2
2
2
2
36
H
32
N
2
O
2
P
Cl
2
Ru.H
2
O: C, 55.68; H, 4.41; N, 3.61. Found: C, 55.47;
Synthesis of the complex Ru-1
H, 4.37; N, 3.54.
A 25 mL Schlenk tube with magnetic stirrer was charged with the
ligand L1-H (100 mg, 0.34 mmol) in degassed chloroform (5 mL)
Synthesis of Ru-3
under argon atmosphere. After 5 minutes of stirring, [RuCl
2 3 3
(PPh ) ]
A 25 mL Schlenk tube with magnetic stirrer was charged with the
ligand L3-H (50 mg, 0.16 mmol) in degassed chloroform (3 mL)
(163 mg, 0.17 mmol) was added to the solution. The resulting clear
red solution was allowed stir at room temperature under an inert
atmosphere for 6 hours. The completion of the reaction was
under argon atmosphere. After 5 minutes of stirring, [RuCl
2 3 3
(PPh ) ]
(
158 mg, 0.16 mmol) was added to the solution. The resulting clear
3
1
confirmed by the disappearance of the peak at -11 ppm in P NMR.
Then solvent was evaporated to minimum volume (~1 mL) under
vacuum. Subsequent addition of diethyl ether (4 mL) furnished
bright yellow coloured solid. Washing the above solid with diethyl
ether (3*4 mL) afforded the desired complex with 60% yield (77mg,
red solution was allowed stir at room temperature under an inert
atmosphere for 2 hours. The completion of the reaction was
confirmed by the disappearance of the peak at 6 ppm in P NMR.
Then solvent was evaporated to minimum volume (~1 mL) under
vacuum. Subsequent addition of diethyl ether (4 mL) furnished brick
red coloured solids. Washing the above solid with diethyl ether (3×4
mL) afforded the desired complex with 88% yield (103 mg, 0.14
mmol). Recrystallization of the complex by slow diffusion of diethyl
31
0.10 mmol). Recrystallization of the complex by slow diffusion of
diethylether in methanol furnished crystals suitable for X-ray
1
diffraction studies. H NMR (400 MHz, CD Cl ): δ 12.33 (s, 2H), 7.69
2
2
(t, J = 7.8 Hz, 2H), 7.32-7.29 (m, 3H), 7.19 (t, J = 7.2 Hz, 4H), 7.15-
ether in methanol furnished crystals suitable for X-ray diffraction
7
.11 (m, 4H), 7.03-6.99 (m, 4H), 6.80 (q, J = 7.3 Hz, 5H), 6.49 (t, J =
1
studies. H NMR (400 MHz, CD
3
OD): δ 7.90 (br, 3H), 7.67 (t, J = 7.9
3
1
8.5 Hz, 4H), 4.53-4.46 (m, 2H), 3.89-3.82 (m, 2H); P {1H} NMR (162
Hz, 1H), 7.31 (br, 9H), 7.18 (d, J = 7.4 Hz, 2H), 7.09 (t, J = 7.9 Hz, 2H),
1
3
MHz, CD Cl ): δ 57.52; C {1H} NMR (101 MHz, CD Cl ): δ 170.6
2
2
2
2
6
1
3
.74 (d, J = 7.4 Hz, 1H), 6.66 (d, J = 8.2 Hz, 1H), 5.82 (d, J = 8.2 Hz,
H), 4.09 (dd, J = 17.6 Hz, J = 9.1 Hz, 1H), 3.76-3.61 (m, 2H), 3.43-
.31 (m, 1H), 1.09 (d, J = 16.2 Hz, 9H); P { H} NMR (162 MHz,
(quat-C), 161.3 (quat-C), 140.0 (CH), 135.9 (quat-C), 135.5 (quat-C),
1
2
1
34.6 (quat-C), 134.2 (quat-C), 132.4 (t, JP-C = 4.3 Hz, CH), 130.8 (t, JP-
= 4.3 Hz, CH), 130.0 (CH), 129.7 (CH), 128.8 (t, JP-C = 4.7 Hz, CH),
28.1 (t, JP-C = 4.8 Hz, CH), 114.5 (t, JP-C = 5.3 Hz, CH), 111.1 (CH),
31
1
C
13
1
CD
3
OD): δ 118.4 (d, J = 30.6 Hz), 38.7 (d, J = 30.4 Hz); C { H} NMR
OD): δ 167.0 (quat-C), 166.4 (d, JP-C = 1.2 Hz, quat-C),
60.7 (quat-C), 158.0 (d, JP-C = 1.2 Hz, quat-C), 141.5 (CH), 139.0
CH), 135.8 (br, quat-C), 131.0 (br, CH), 129.0 (d, JP-C = 9.4 Hz, CH),
1
(
101 MHz, CD
3
4
2 2
4.6 (d, JP-C = 18.2 Hz, CH ), 44.4 (d, JP-C = 18.2 Hz, CH ); HRMS(ESI-
1
(
+
TOF): calc’d for C H N O P Cl Ru [M] 758.0354; found 758.0358.
3
6
32
2
2
2
2
Anal. Calcd for C36
H
32
N
2
O
2
P
2
Cl
2
2 2
Ru.CH Cl : C, 52.69; H, 4.06; N, 3.32.
1
1
3
16.0 (d, JP-C = 11.4 Hz, CH), 115.5 (d, JP-C = 11.2 Hz, CH), 109.2 (CH),
07.9 (CH), 41.8 (d, JP-C = 28.8 Hz, CH ), 39.8 (d, JP-C = 26.2 Hz, CH ),
3.2 (d, JP-C = 32.7 Hz, quat-C), 26.4 (d, JP-C = 2.7 Hz, CH ); HRMS(ESI-
ClNaRu [M-H+Na] 725.0798; found
Cl Ru: C, 55.29; H, 4.91; N,
Found: C, 52.99; H, 4.07; N, 3.30.
2
2
Synthesis of Ru-2
3
+
+
35 2 2 2
TOF): calc’d for C34H N O P
7
3
A 25 mL Schlenk tube with magnetic stirrer was charged with the
ligand L2-H (100 mg, 0.31 mmol) in degassed chloroform (5 mL)
25.0801. Anal. Calcd for C34
H
36
N
2
O
2
P
2
2
.79. Found: C, 54.50; H, 4.99; N, 3.80.
under argon atmosphere. After 5 minutes of stirring, [RuCl
2 3 3
(PPh ) ]
(
297 mg, 0.31 mmol) was added to the solution. The colour of the Synthesis of Ru-4
solution changed from dark brown to opaque pale yellow after 10
minutes of vigorous stirring. The resulting solution was allowed stir
at room temperature under an inert atmosphere for 2 hours. The
completion of the reaction was confirmed by the disappearance of
A 25 mL Schlenk tube with magnetic stirrer was charged with the
complex Ru-1 (50 mg, 0.066 mmol) in a mixture of methanol (1 mL)
and acetonitrile (4 mL) under argon atmosphere. After 5 minutes of
stirring, KOH (8 mg, 0.14 mmol) was added to the solution. The
resulting clear yellow solution was allowed stir at room
3
1
the peak at -14 ppm in P NMR. Then solvent was removed by
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DOI: 10.1039/C7CY00932A
ARTICLE
Journal Name
temperature under an inert atmosphere for 6 hours. Then solvent Organomet. Chem. 1985, 282, C7; (d) S. Murahashi, T. Naota, K.
was removed under vacuum. Solubilizing the complex with i. Ito, Y. Maeda and H. Taki, J. Org. Chem., 1987, 52, 4319.
6
(a) J. Zhang, G. Leitus, Y. Ben-David and D. Milstein, J. Am.
dichloromethane and cannula filtration after removed the insoluble
KCl. Removal of solvent from the filtrate afforded the desired faint
yellow complex with 75% yield (37mg, 0.05 mmol). Recrystallization
of the complex by slow diffusion of pentane in dichloromethane
Chem. Soc., 2005, 127, 10840; (b) A. Solvhoj and R. Madsen,
Organometallics, 2011, 30, 6044; (c) D. Spasyuk and D. Gusev,
Organometallics, 2012, 31, 5239; (d) M. Nielsen, H. Junge, A.
Kammer and M. Beller, Angew. Chem. Int. Ed., 2012, 51, 5711.
1
furnished crystals suitable for X-ray diffraction studies. H NMR (400
7
Selected recent reports on base free hydrogenation of CO
a) S. Moret, P. J. Dyson and G. Laurenczy, Nat. Commun., 2014,
, 4017 ; (b) K. Sordakis, A. Tsurusaki, M. Iguchi, H. Kawanami, Y.
Himeda and G. Laurenczy, Chem. Eur. J., 2016, 22, 15605; (c) S.-
5.8 Hz, J = 8.8 Hz, 1H), 2.02 (s, 3H); P { H} NMR (162 MHz, M. Lu, Z. Wang, J. Li, J. Xiao and C. Li, Green Chem., 2016, 18
2
:
MHz, CD
.30-7.23 (m, 5H), 7.17-7.05 (m, 13H), 6.99-6.95 (m, 1H), 6.13-6.06
m, 3H), 5.83 (d, J = 8.5 Hz, 1H), 3.46-3.23 (m, 3H), 2.75 (dd, J
2 2
Cl ): δ 12.22 (br, 2H), 7.53-7.50 (m, 1H), 7.42-7.38 (m, 2H),
(
5
7
(
1
1
=
3
1
1
,
2
CD
TOF): calc’d for C H N O P Ru [M+H+H O] 728.1164; found
2 2
Cl
): δ 67.08 (d, J = 28.5 Hz), 48.95 (d, J = 29.2 Hz); HRMS(ESI- 4553; (d) K. Rohmann, J. Kothe, M. W. Haenel, U. Englert, M.
+
Hölscher and W. Leitner, Angew. Chem. Int. Ed., 2016, 55, 8966.
Selected references on 2-pyridone ligands : (a) K.-i. Fujita, N.
Tanino and R. Yamaguchi, Org. Lett., 2007, , 109; (b) A. M.
Royer, T. B. Rauchfuss and D. L. Gray, Organometallics, 2010, 29
763; (c) I. Nieto, M. S. Livings, J. B. Sacci III, L. E. Reuthers, M.
A clean and dry Schlenk tube (5mL) was charged with complex Ru-2 Zeller and E. T. Papish, Organometallics, 2011, 30, 6339; (d) R.
0.005 mmol, 1 mol%) in degassed toluene (0.5 mL). NaOH (0.05 Kawahara, K.-i. Fujita and R. Yamaguchi, Angew. Chem. Int. Ed.,
3
8
34
3
2
2
2
8
728.1172.
9
General procedure for the dehydrogenation
,
6
(
mmol, 10 mol%) was added to this opaque yellow solution. After 2012, 51, 12790; (e) S. Zeyneb, B. Sundararaju, M. Achard and C.
stirring for 5 minutes, the appropriate alcohol (0.5 mmol) was Bruneau, Green Chem, 2013, 15, 775; (f) C. M. Moore and N. K.
Szymczak, Chem. Commun., 2013, 49, 400; (g) S. Chakraborty, P.
E. Piszel, W. B. Brennessel and W. D. Jones, Organometallics,
mixed. This reaction mixture was stirred in a preheated oil bath at
150 °C. The reaction was monitored by TLC and GC. After the
2
ACS Catal., 2016, , 1981; (i) J. Shi, B. Hu, D. Gong, S. Shang, G.
015, 34, 5203; (h) C. M. Moore, B. Bark and N. K. Szymczack,
6
completion of the reaction, the reaction mixture was cooled to
room temperature and solvent was evaporated. The crude reaction
mixture was purified by silica gel column chromatography using
petroleum ether and ethyl acetate mixture as eluent to get the
desired ester.
Hou and D. Chen, Dalton Trans., 2016, 45, 4828; (j) E. W. Dahl, T.
Louis-Goff and N. Szymczack, Chem. Commun., 2017, 53, 2287;
(
k) L. Wang, N. Onishi, K. Murata, T. Hirose, J. T. Muckerman, E.
Fujita and Y. Himeda, ChemSusChem, 2017, 10 , 1071; (l) S. Y. de
Boer, T. J. Korstanje, S. R. La Rooij, R. Kox, J. N. H. Reek and J. I.
van der Vlugt, Organometallics, 2017, 36, 1541.
General procedure for the formic acid generation
9
(a) K. Mashima, H. Nakano and A. Nakamura, J. Am. Chem.
Degassed dimethyl sulfoxide (4 mL) and Ru-1 (5 mg, 6.59 µmol)
were added in a 20 mL autoclave. The reactor was sealed, applied
vacuum, then filled with argon (ten cycles) and then ended with
vacuum. Carbon dioxide was introduced at 10 bar and the mixture
was stirred at this pressure for 5 minutes. Then, molecular
hydrogen was introduced under stirring at an initial pressure of 20
Soc., 1993, 115, 11632; (b) B. Breit and W. Seiche, J. Am. Chem.
Soc., 2003, 125, 6608.
1
0 H. Brunner, A. Köllnberger, A. Mehmood, T. Tsuno and M.
Zabel, J. Organomet. Chem., 2004, 689, 4244.
1 (a) F. Jiang, M. Achard, V. Dorcet, T. Roisnel and C. Bruneau,
1
Eur. J. Inorg. Chem., 2015, 4312; (b) A. R. Sahoo, F. Jiang, C.
Bruneau, G. V. M. Sharma, S. Suresh and M. Achard, RSC Adv.,
bar and slowly increased to reach a total pressure of 60 bar (pH
2
~
5
0 bar). The resulting mixture was then stirred at 50 °C for 16h. 2016, 6, 100554.
After, the autoclave was cooled down to room temperature. Then 12 T. Miura, I. E. Held, S. Oishi, M. Naruto and S. Saito,
Tetrahedron Lett., 2013, 54, 2674.
1
the unreacted hydrogen and CO were carefully released. Addition
2
3 (a) C. Gunanathan, L. J. W. Shimon and D. Milstein, J. Am.
Chem. Soc., 2009, 131, 3146; (b) E. Kossoy, Y. Diskin-Posner, G.
Leitus and D. Milstein, Adv. Synth. Catal., 2012, 354, 497.
of 100 µL of dimethylformamide followed by stirring for three
1
minutes and analysis by H NMR (within 30 mins) allowed the
determination of the turnover number and formic acid
concentration.
1
4 (a) T. Ito, H. Horino, Y. Koshiro and A. Yamamoto, Bull. Chem.
Soc. Jpn., 1982, 55, 504.;(b) M.-O. Simon and S. Darses, Adv.
Synth. Catal.¸2010, 352, 305; (c) S. A. Morris and D. Gusev,
Angew. Chem. Int. Ed., 2017, 56, 6228.
Aknowledgments
CEFIPRA/IFCPAR N° 5105-4 is acknowledged for a fellowship to
A.R.S. and the funding of this project.
1
5 J. Cheng, M. Zhu, C. Wang, J. Li, X. Jiang, Y. Wei, W. Tang, D.
Xue and J. Xiao, Chem. Sci., 2016, , 4428.
6 A. Dubey and E. Khaskin, ACS Catal., 2016,
7
1
6, 3998.
Notes and references
17 For an anionic iridium species involving pyridone ligand see:
K.-i. Fujita, R. Kawahara, T. Aikawa and R. Yamaguchi, Angew.
Chem. Int. Ed., 2015, 54, 9057.
1
(a) M. Trincado, D. Banerjee and H. Grützmacher, Energy
Environ. Sci., 2014, , 2464; (b) R. H. Crabtree, Chem. Rev., 2017,
DOI : 10.1021/acs.chemrev.6b00556.
7
1
8 For comparison with previously reported complexes under
base and additive free conditions, ref. 7a: [HCO H]= 1.93 M p
tot= 100 bar, 120h; ref. 7b: [HCO H]= 0.1 M p tot= 50 bar, 50h,
ref. 7c [HCO H]= 0.12 M p tot= 50 bar, 30mins ; ref. 7d :
HCO H]= 0.33 M ptot= 120 bar, 16h
2
2
1
(a) J. Eppinger and K. -W. Huang, ACS Energy Lett., 2017,
88; (b) J. Klankermayer, S. Wesselbaum, K. Beydoun and W.
2,
2
2
Leitner, Angew. Chem. Int. Ed. 2016, 55, 7296.
[
2
3
3
4
2
5
2
M. Aresta, A. Dibenedetto and E. Quaranta, J. Catal., 2016,
43, 2.
J. R. Khusnutdinova and D. Milstein, Angew. Chem. Int. Ed.,
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(a) Y. Blum, D. Reshef and Y. Shvo, Tetrahedron Lett., 1981,
2
, 1541; (b) S. -I. Murahashi, K. -i. Ito, T. Naota and Y. Maeda,
Tetrahedron Lett., 1981, 22, 5327; (c) Blum, Y.; Shvo, Y. J.
6
| J. Name., 2012, 00, 1-3
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Catalysis Science & Technology
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DOI: 10.1039/C7CY00932A
Selective formation of esters from primary alcohols or formic acid from carbon dioxide was achieved in
the presence of phosphinepyridone containing ruthenium catalysts