Complexes of (η6-benzene)ruthenium(ii) with 1,4-bis(phenylthio/seleno-methyl)-1,2,3-triazoles: synthesis, structure and applications in catalytic activation of oxidation and transfer hydrogenation

Article abstract of DOI:10.1039/c5dt02926k

1,4-Bis(phenylthio/seleno methyl)-1,2,3-triazoles (L1-L4) synthesized by a 'Click' reaction react with [{(η⁶-C₆H₆)RuCl(μ-Cl)}]₂ and NH₄PF₆ resulting in complexes [(η⁶-C₆H₆)RuClL]PF₆ (1-4 for L = L1-L4) in which the ligands coordinate in a bidentate mode through S/Se and N of triazole. The CH₂EPh (E = S or Se) attached to nitrogen of triazole remains pendent. Ligands and complexes have been authenticated with multinuclei NMR, IR and HR-MS. Single crystal structures of complexes 1-4 have been solved. The Ru-S and Ru-Se bond lengths (?) are respectively 2.388(2)/2.3902(19) and 2.5007(4)/2.5262(19). The disposition of benzene ring, N, S/Se and Cl around Ru is of a piano stool type. For catalytic oxidation of alcohols [Oppenauer-type and with N-methylmorpholine-N-oxide (NMO)] and transfer hydrogenation (TH) of carbonyl compounds [with 2-propanol and glycerol] all the four complexes have been found efficient. The optimum catalyst loadings (in mol%) are: 0.01 (NMO), 0.1 (Oppenauer), 0.01 (TH with 2-propanol) and 0.5 (TH with glycerol). Interestingly, time profiles (under optimum conditions) of two catalytic oxidations and TH's are almost similar, suggesting that they are competitive on appropriate catalyst loading. DFT calculations are consistent with somewhat low reactivity of 1 in comparison to those of 2-4.

Full text of DOI:10.1039/c5dt02926k

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Dalton Transactions
Complexes of (η6-benzene)ruthenium(II) with 1,4-bis(phenylthio/seleno-
methyl)-1,2,3-triazoles: synthesis, structure and applications in catalytic
activation of oxidation and transfer hydrogenation
Fariha Saleem, Gyandshwar K. Rao, Satyendra Kumar, Mahabir Pratap Singh and Ajai K. Singh*a
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
1,4-Bis(phenylthio/seleno methyl)-1,2,3-triazoles (L1−L4) synthesized by ‘Click’ reaction react with
[{(η6-C6H6)RuCl(µ-Cl)]2 and NH4PF6 resulting in complexes [(η6-C6H6)RuClL]PF6 (1-4 for L= L1−L4)
in which the ligands coordinate in a bidentate mode through S/Se and N of triazole. The CH2EPh (E= S
10 or Se) attached to nitrogen of triazole remains pendent. Ligands and complexes have been authenticated
with multinuclei NMR, IR and HR-MS. Single crystal structures of complexes 1-4 have been solved. The
Ru-S and Ru-Se bond lengths (Å) are respectively 2.388(2) / 2.3902(19) and 2.5007(4)/ 2.5262(19). The
disposition of benzene ring, N, S/Se and Cl around Ru is piano stool type. For catalytic oxidation of
alcohols [Oppenauer-type and with N-methylmorpholine-N-oxide (NMO)] and transfer hydrogenation
15 (TH) of carbonyl compounds [with 2-propanol and glycerol] all the four complexes have been found
efficient. The optimum catalyst loadings (in mol%) are: 0.01 (NMO), 0.1 (Oppenauer), 0.01 (TH with 2-
propanol) and 0.5 (TH with glycerol). Interestingly time profiles (under optimum conditions) of two
catalytic oxidations and TH’s are almost similar, suggesting that they are competitive if appropriate
catalyst loading is made. DFT calculations are consistent with somewhat low reactivity of 1 in
20 comparison to those of 2-4.
substituents on complexes with triazole ligands, it has been
concluded that substituents have only a muted effect on their
55 optical and electrochemical properties. 16
Triazole based organochalcogen ligands have also got
attention. 1,4-Disubstituted-1,2,3-triazoles based multidentate
organochalcogen ligands have been designed via ‘Click’ strategy
Introduction
Triazole attractive as a core of multidentate ligands can be
designed easily using copper(I) catalyzed cycloaddition1 reaction
of azides with terminal alkynes. This simple and mild reaction,
25 developed by Sharpless and Mendel,2 is suitable for a variety of
other synthetic protocols.3 Coordination of triazole based ligands
with metals is interesting4 and has got a lot of attention in areas
ranging from biology/medicine to materials science.6 All the
three nitrogen atoms of triazole are known to coordinate with
30 metal centre. DFT calculations have shown that N3 is a better
donor compared to N2.7 Triazole ligands coordinate with metal
through N3 either as a monodentate ligand or part of a bi-9 or
poly-dentate10 chelator, when there are other donor sites nearby.
When additional donor site is adjacent to N1, coordination
35 through N2 is possible as a part of bi- or poly-dentate chelator.11
Five- or six-membered rings are usually formed in the resulting
metal chelates. In bridging coordination mode two nitrogen atoms
of triazole coordinate with two metals. The C5 coordination of
deprotonated triazoliums results in metal complexes of N-
40 heterocyclic carbenes.12 In 2008, Albrecht and co-workers used
1,3,4-substituted 1,2,3-triazolium salts as precursors of
in recent past and its Pd(II) complexes used to catalyze Heck
17
60 coupling.
Syntheses and structures of divalent Cu, Zn, Cd and
Pd complexes of 1,2,3-triazole based chalcogen ligands have
been reported by Morales-Juárez et al.18 1-(2/4-Picolyl)-4-(2-
(methylthio)pyridine)-1H-1,2,3-triazole prepared by Cu(I) based
‘Click’ reaction gives one-dimensional coordination polymers
65 with CuI, which have [Cu6I6] / [Cu2I2] building blocks. The
ligands and the complexes show photoluminescence and are
catalytically active towards azide–alkyne cycloaddition
reactions.19 Our research group20 has also reported 1,2,3-triazole
based chalcogen ligands prepared by ‘Click’ reaction. Their
70 Ru(II) complexes catalyze transfer hydrogenation (TH) of
carbonyl compounds with 2-pronanol and oxidation of alcohols.
The catalytic activity is high when N2 of triazole is involved in
coordination with Ru. Ruthenium complexes21 of other
organochalcogen ligands are known to catalyze such
75 transformation. The complexes of some other platinum group
metals with organochalcogen ligands have also been reported to
catalyze these transformations.22 Few 1,2,3-triazole based
tridentate (P,C,S) pincers are known4 but no Se containing pincer
with 1,2,3-trizole core is in our knowledge. Therefore to extend
80 chemistry of 1,2,3-triazole based pincers we report here 1,2,3-
triazole based potentially pincer ligands (L1−L4) having S/Se
donor groups in the arms. The L2 and L3 are examples of
potentially unymmetrical pincers, which are known in much less
number than symmetric ones. Ligands L1−L4 form complexes
85 with (η6-C6H6)Ru(II) (1−4) in which they coordinate in a
complexes of various transition metals with new NHCs.13
A
different coordination mode as anionic triazolate ligand results in
metal complexes from the combination of deprotonated NH
45 (generating triazolate anion) and 4,5-disubstitution. Under basic
conditions, benzotriazoles bind to metal via N1 while 4,5-
disubstituted-1,2,3-triazoles bind to metal via N2. Moreover,
additional metal centers can be coordinated by free neutral
nitrogen atoms of the metal triazolates forming bridged
50 complexes.14 Catalysis by 1,2,3-triazole- and related transition-
metal (Mn, Cu, Fe, Ni, Ru, Rh, Ir, Au Pd and Ni) complexes has
been reviewed recently.15 In an another recent review on effect of
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Page 2 of 12
bidentate mode (Scheme 1). The resulting half sandwich
to record NMR of 1−4. Thus use of different solvents was
complexes have been studied for catalytic oxidation of alcohols 45 considered while drawing inference from NMR data. In 77Se{1H}
(Oppenauer-type and with oxidant NMO) and transfer
hydrogenation (TH) of carbonyl compounds with 2-propanol and
glycerol (hydrogen donors). Use of Ru complex of any 1,2,3-
triazole based ligand for Oppenauer oxidation is not in our
NMR spectrum of L2, signal at 430 ppm, is at higher frequency
(55 ppm) with respect to that of corresponding selenated azide
(375.1 ppm). The signal in 77Se{1H} NMR spectrum of L3 at
362.6 ppm is at 13.2 ppm lower frequency with respect to that of
5
knowledge and present complexes are probably the first 50 corresponding selenated alkyne (375.8 ppm). For L4, two signals
examples. Comparisons of catalytic performance of the different
protocols have been made for the first time. In Oppenauer-type
10 oxidation acetone works as an oxidant cum solvent. Both oxidant
and its byproduct isopropanol are environmental friendly.23
in 77Se{1H} NMR were observed at 429.4 and 362.2 ppm.
The signals of C5 (27.9–35.7 ppm) in 13C{1H} NMR spectra
of 1−4, appear at higher frequencies (up to 7.7 ppm) relative to
those of corresponding free ligands (20.2–28.7 ppm) which
Oppenauer-type oxidation appears to be competitive with NMO 55 coordinate with Ru(II) in a bidentate mode. However, the signals
based one, if optimum mole % of catalyst is used. The use of
non-flammable glycerol for TH, is environmental friendly24-26
15 compared to 2-propanol.21k With present complexes glycerol
appears to be as efficient as 2-propanol provided the required
of H5 in 1H NMR spectra of 1−4 have been found shifted to lower
frequency (up to ~0.2 ppm) relative to those of free ligands. In
77Se{1H}NMR spectra of 3 and 4 signals due to C5-Se appear at
higher frequencies (up to ~85 ppm) compared to those of free L3
amount of catalyst is used. Density functional theory (DFT) 60 and L4. Probably it arises due to coordination of ligand with Ru
calculations support experimental results of catalysis and
structural features of complexes.
through Se. The signals in 77Se{1H}NMR spectra of 2 and 4 due
to C8-Se also show high frequency shift (~17 ppm) with respect
to those of free L2 and L4. This may be due to change in overall
electron density distribution of ligand on its coordination with
20 Results and discussion
1
65 Ru. The signals of η6–benzene in H / 13C{1H} NMR spectra of
Syntheses of L1−L4 and their complexes are summarized in
Scheme 1. All ligands L1−L4 have good solubility in CHCl3,
CH2Cl2, CH3OH and CH3CN while complexes 1−4 are only
moderately soluble in first three of them. They have good
25 solubility in DMSO and CH3CN at room temperature. Ligands
L1−L4 and their complexes 1−4 are stable in air and moisture.
Therefore they can be stored at room temperature for several
months under ambient conditions. The ligands and their
complexes were characterized with 1H, 13C{1H}, 77Se{1H} NMR,
30 HR-MS and IR spectra. The results of elemental analyses (given
below) of complexes 1−4 are consistent with the single crystal
structures (determined with X-ray diffraction).
1−4 appear at lower frequency (up to 0.3/3.4 ppm) with respect to
those of [η6–(C6H6)RuCl2]2 [1H 5.7 ppm; 13C{1H} 84.1 ppm].
This occurs due to substitution of Cl with S or Se, which is less
electronegative and stronger donor than Cl.
High resolution mass spectra (HR-MS) of the ligands and
complexes authenticate them. In the spectra of ligands L1 and L3
peaks appearing at m/z= 336.0600 and 384.0048, respectively
may be ascribed to [L + Na]+. The peaks of ligands L2 and L4 at
m/z = 362.0240 and 409.9665, respectively may be ascribed to [L
75 + H]+. In HR-MS of 1−4 the peaks of cations have been observed
as expected.
70
Crystal structures
In the reactions of [(η6-C6H6)RuCl(μ-Cl)]2 with L1−L4 at room
temperature half-sandwich complexes 1−4 were formed via
80 chloro bridge cleavage which was followed by anion exchange
with NH4PF6. Single crystal structures of all Ru(II) complexes
have been solved by X-ray crystallography, after growing
suitable single crystals by slow diffusion of diethyl ether into
their solutions made in 4 mL of CH3OH-CH3CN mixture (1:4).
85 The crystallographic and refinement data are given in the ESI
(Table S1). The molecular structures of complexes 1−4 with
selected bond lengths and angles are given in Figs. 1−4
respectively. Hydrogen atoms and the PF6¯anion have been
omitted in each case for clarity. More bond angles and distances
90 are given in the ESI (Table S2). Ligands L1−L4 coordinate with
Ru(II) in all complexes 1−4 via nitrogen of triazole and S/Se
forming five-membered chelate ring.
CuSO4 / Na ascorbate
N
N
N
E'
E
N3
+
L1; E = E' = S
Ph
Ph
t-BuOH, RT, 24 h
L2; E = Se, E' = S
L3; E = S, E' = Se
L4; E = E' = Se
E'
E
Ph
Ph
[(η6
-C6H6)RuCl( -Cl)}2]
μ
MeOH / NH4PF6 / RT /
2
3
4
2
3
5
11
6
7
5
1
10
9
8
11
6
7
4
1
10
9
8
S
N
12
Se
Ru
N
N
12
E
N
N
E
Ru
N
Cl
Cl
.PF6
.PF6
1; E = S
2; E = Se
3; E = S
4; E = Se
Scheme 1 Synthesis of Ligands (L1−L4) and their Ruthenium(II)
Complexes (1−4)
35
All the cations of 1−4 have a pseudo-octahedral “piano-stool”
disposition of donor atoms around Ru. Benzene ring occupies one
95 face of octahedron in them. Nitrogen and S/Se atoms form a
chelate ring with the metal center and a chlorine atom completes
the coordination sphere. The Ru–S bond lengths in cations of 1
and 2 are 2.388(2)Å and 2.3902(19) Å respectively. They are
consistent with each other and the values reported for complex
100 [(η6-C6H6)Ru(2-MeSC6H4CH=NCH2-CH2SC6H5)]2+, [2.3921(19)
NMR and mass spectra
1H, 13C{1H} and 77Se{1H} NMR spectra of L1−L4 and
complexes 1−4 were found consistent with the molecular
40 structures (Scheme 1). The scans of all NMR and mass spectra of
ligands L1−L4 and complexes 1−4 are given in the ESI (Figs.
S3−S32). NMR spectra of ligands L1−L4 were recorded in
CDCl3. As solubility in CDCl3 was inadequate, CD3CN was used
2
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Dalton Transactions
Å].21d In comparison to value [2.3649(19) Å] reported for [(η6-
Cl(1)−Ru(1)−Se(1) 78.40(9), N(1)−Ru(1)−Cl(1) 88.2(2).
C6H6)RuCl(N-{2-(phenylthio)ethyl}pyrrolidine)]+ complex27 they
are somewhat larger. The Ru–Se bond distance in the cation of 3,
[2.5007(4) Å] is consistent with that of cation of 4
[2.5262(19)Å]. They are somewhat longer, than the values
80 reported for complexes [(η6-C6H6)RuCl(N-{2-(phenylseleno)
ethyl}pyrrolidine)]+, [2.480(11) Å]27 and [(η6-C6H6)Ru(2-
MeSC6H4CH=NCH2CH2SeC6H5)]2+, [2.4848(8) Å].21d The Ru–N
bond lengths of 1−4 vary in a narrow range [2.091(9)–2.100(6)Å]
and are consistent with the values reported for complexes
85 [Ru(2,6-bis(1-benzyl-1,2,3-triazol-4-yl)pyridine)2](PF6)2
[2.050(3)Å],28 and [(η6-C6H6)Ru(2-MeSC6H4CH=N-CH2CH2S-
C6H5)]2+[2.073(6) Å].21d The Ru−C bond lengths [1.66(0)–1.69(1)
Å] and C−Ru−C bond angles of cations of 1−4 are normal.27,29
The PF6− anion is involved in C−H···F secondary interactions
70 in 1−4, resulting in sheet like structures. The secondary
interactions of complexes 1 and 3 are shown in Figs. 5 and 6,
respectively, while for 2 and 4 they are given in the ESI (Figs.S1
and S2). The C−H···F distances (Å) of the complexes have also
been included in the ESI (Table S3).
5
Fig. 1. Molecular structure of 1. Bond distances (Å): Ru(1)─S(1)
2.388(2), Ru(1)−Cl(1) 2.394(3), N(1)−Ru(1) 2.091(9), Ru(1)−C
1.690(1).
Bond
angles
(°):N(1)−Ru(1)−S(1)
80.3(2),
10 N(1)−Ru(1)−Cl(1) 87.2(2), S(1)−Ru(1)−Cl(1) 80.96(9).
Fig. 2. Molecular structure of 2. Bond distances (Å): Ru(1)−S(1)
2.3902(19), N(1)−Ru(1) 2.104(6), Cl(1)−Ru(1) 2.402(2),
15 Ru(1)−C 1.679(1). Bond angles (°):S(1)−Ru(1)−Cl(1) 80.87(7),
N(1)−Ru(1)−Cl(1) 87.18(16), N(1)−Ru(1)−S(1) 80.51(17).
50
Fig. 5. Non-covalent C–H···F interactions in 1
Fig. 6. Non-covalent C–H···F interactions in 3
55
Fig. 3. Molecular structure of 3. Bond distances (Å): Ru(1)−N(1)
20 2.092(2), Ru(1)−Se(1) 2.5007(4), Ru(1)−Cl(1) 2.4032(7)
Ru(1)−C 1.666(1). Bond angles (°): N(1)−Ru(1)−Se(1) 81.03(6),
Cl(1)−Ru(1)−Se(1) 78.18(2), N(1)−Ru(1)−Cl(1) 88.93(6).
Catalytic oxidation of alcohols
The complexes 1−4 have been explored as catalysts for NMO
based and Oppenauer type oxidations of primary and secondary
85 alcohols, summarized in Schemes 2 and 3 respectively. The
protocols of NMO based oxidation are simple to operate and give
the corresponding carbonyl compounds in good to excellent
yield.
O
OH
R'
R = R' = Alkyl/Aryl/H
Catalyst: 1-4 (0.01mol%)
NMO/CH2Cl2/60o/3 h
H2O
+
R
R'
R
65
Fig. 4. Molecular structure of 4. Bond distances (Å): Ru(1)−N(1)
25 2.096(7), Ru(1)−Se(1) 2.5262(19), Ru(1)−Cl(1) 2.419(3),
Ru(1)−C 1.687(1). Bond angles (°): N(1)−Ru(1)−Se(1) 81.5(3),
Scheme 2 Oxidation of alcohol with NMO
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N-Methylmorpholine and water are the by-products of the
oxidation. Dichloromethane is the best solvent for NMO based
oxidation of alcohols under ambient conditions in the presence of
In absence of 1-4 no oxidation was observed. Both of these
catalytic oxidations with catalyst 3 using benzyl alcohol as
substrate have been monitored with 77Se{1H} and 1H NMR
1−4 (0.01 mol %). Other optimum conditions are: temperature 60 45 spectroscopy. In case of NMO based oxidation the signal in
5
°C, time 3 h and base K2CO3. The percent conversions are
summarized in Table 1. The catalytic conversion of benzyl
alcohol with complex 1 is lowest ~88%. This is corroborated by
DFT calculations described below.
77Se{1H} NMR spectrum has been found shifted to higher
frequency (370 ppm), indicating that oxidation occurs via
1
formation of Ru(IV)=O intermediate. The signals in H NMR
spectrum of reaction mixture (ruthenium complex catalyst taken
50 in higher amount than optimum) appear broad, indicating the
formation of paramagnetic species as an intermediate, which is in
agreement with the formation of Ru(IV)=O. Thus with present Ru
complexes the route of NMO based oxidation appears to be via
Ru(IV)=O as reported earlier for other Ru species.20b In
55 Oppenauer-type oxidation of benzyl alcohol, the signal in
77Se{1H} NMR spectrum of reaction mixture, has been found
shifted to higher frequency (~24 ppm) relative to free complex
10 Table 1. Catalytic oxidation of alcohols using complexes 1−4 as
catalysta
Entry no.
Alcohol
Yield(%)
1b
88
85
2c
3c
95
92
4c
97
95
1
2
Benzyl alcohol
4-Methoxybenzyl
alcohol
98
97
3
4
4-Methylbenzyl alcohol
91
87
97
95
95
90
95
92
1
with the progress of reaction, whereas in H NMR spectrum a
4-Chlorobenzyl Alcohol
new signal at δ −9.1 ppm has been noticed in the course of
60 catalysis with 3 (ESI: Fig. S33). These observations may be
attributed to the formation of metal hydride species.30 Thus
catalytic Oppenauer-type oxidation of alcohols with the present
complexes probably proceeds via formation of a ruthenium-
hydride intermediate as reported earlier.20a The time profiles of
65 both these oxidation reactions (under separate optimum
conditions) shown in Figure 7 are almost linear and very close.
This suggests that Oppenauer-type oxidation with 0.1 mole %
loading of present complex catalysts may be a good alternative to
oxidant (NMO) based protocols, as it is economical and more
70 environment friendly.
5
6
1-Phenylethanol
Di(phenyl)ethanol
76
78
85
86
82
82
85
86
aReaction conditions: Catalyst: 1−4 (0.01mol %), alcohol 1 mmol, NMO
3 mmol, solvent DCM, bath temperature 60 °C and reaction time 3 h.
bIsolated yield after column chromatography. cNMR yield.
A series of blank experiments (under identical conditions)
suggest that neither any ruthenium(II) complex from 1−4 nor
15 oxidant NMO alone causes the oxidation. Thus, the role of Ru-
complexes 1-4 as catalyst is crucial in the present NMO based
oxidation. Complexes 1−4 (0.01 mol%) effectively catalyze
oxidation of alcohols without further oxidation to carboxylic acid.
Absence of over oxidation of alcohols to acids was ascertained by
20 preparative experiments, with catalyst 4. Benzyl alcohol (0.108 g,
1 mmol) was subjected to oxidation with NMO (3 mmol) under
optimum conditions. The isolated 0.100 g benzaldehyde was
further treated with NMO (3 mmol) using protocols of oxidation
of alcohols. Even traces of benzoic acid were not detected.
25 Similarly when 4-methylbenzyl alcohol (0.122 g, 1 mmol) was
110
100
90
80
70
60
50
40
30
Oxidation with NMO
Oppenauer-type Oxidation
20
10
0
subjected to oxidation with NMO, 0.110
g of 4-methyl
0
30
60
90
120
150
180
benzaldehyde was obtained. On attempting its conversion to 4 -
methylbenzoic acid by already standardized protocols of
oxidation with NMO the aldehyde was recovered almost
30 quantitatively.
Time (min)
Fig. 7. Time profile of the catalytic oxidation of benzyl alcohol
with complex 3
Oppenauer-type oxidation of alcohols catalyzed with 0.1 mol%
of 1 / 3 using acetone as an oxidant cum solvent has been studied
in detail for optimization20a of reaction conditions. Potassium t-
butoxide has been found to be the best base at 80 °C for the
75
Ru(II) complexes 1-4 as a catalyst for oxidation of alcohols
with NMO (as oxidant) perform better than many other Ru(II)
complexes. For example less catalyst loading (0.01 mol%) is
required in the present case in comparison to Ru(II) complexes of
tetraphenylimidodiphosphinate31(needed at 1 mol% level) for
35 catalytic process. The
% conversions in Oppenauer-type
oxidation of various alcohols have been summarized in Table 2.
The conversion of benzyl alcohol (98%) is somewhat better than
those of other alcohols.
80 good conversions. For such oxidation the required loading of
[(η6-p-cymene)RuCl(L)] (where L = 2-(naphthylazo)phenolato
ligands)32 as a catalyst is 1 mol% and that too with a reaction
time of 8 h. However, half sandwich complexes of Ru(II)21d-f,27
with morpholine based ligands or Schiff bases and related ligands
85 give good conversions at lower loading (0.001 mol% ) than those
of present complexes. For Oppeneauer type oxidation of
alcohols, the present complexes 1 and 3 are somewhat better as
O
OH
R'
R = R' = Alkyl/Aryl/H
Catalyst: 1 / 3 (0.1mol%)
R
R'
R
t-BuOK/Acetone/reflux/3 h
40
Scheme 3. Oppenauer-type oxidation of alcohol
4
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Dalton Transactions
catalyst than heterobimetallic Ru(II) complex [Cp*Rh(µ-
Cl)3RuCl(PPh3)2],33 which gives good conversion with 0.1-0.5
investigated as catalyst in detail. Several aldehydes and ketones
substrates with varying substituents were explored with glycerol
mol% loading but optimum reaction time is longer than 3 h. 45 as well as 2-propanol. The % conversions are given in Tables 3
Ruthenium
complexes
[(PPh3)3RuCl2]
and
and 4 for 2-propanol and glycerol, respectively. For TH with 2-
propanol as well as glycerol most efficient conversion (up to
~100%) was found in the case of benzaldehyde with all the
complex catalysts, while in the case of aliphatic secondary
5
[(C4Ph4COHOCC4Ph4)(µ-H)(CO)4Ru2]34 catalyze Oppeneauer
type oxidation of 1-phenyl ethanol with 0.1 mol% loading,
similar to that of present complex catalysts, but required reaction
time of 22 h is much longer than 3 h found optimum with 1 and 3. 50 ketones the conversions were up to 95% (for cyclopentanone).
10 Table 2. Catalytic Oppenauer-type oxidation of alcohols using
Table 3 Catalytic transfer hydrogenation in 2-propanol using
complexes 1 and 3 as Catalyst a
complexes 1−4 as catalysta
Entry no. Alcohol
Entry no.Carbonyl Compounds
Yield (%)
1
3
Yield (%)
1b
2c
3c
4c
1
2
3
4
5
6
Benzyl alcohol
94
91
82
85
82
80
98
95
90
88
85
86
1
2
Benzaldehyde
4-Methoxy-
benzaldehyde
4-Methyl- benzaldehyde 88
Furfuraldehyde
Acetophenone
4-Chloro-acetophenone 68
4-Methyl-acetophenone 88
Benzophenone
Cyclopentanone
92
90
100
100
97
95
100
100
4-Methoxybenzyl alcohol
4-Methylbenzyl alcohol
4-Chlorobenzyl Alcohol
1-Phenylethanol
3
4
5
6
7
8
9
92
95
88
79
95
96
95
97
94
85
72
92
92
90
98
95
86
75
88
95
95
85
87
Di(phenyl)ethanol
aReaction Conditions: ceatalyst 0.1 mol %, alcohol 1 mmol, 15 ml
acetone, Potassium t-butoxide 1.5 mmol, 80 °C time 3 h, conversion
determined with NMR.
82
88
aReaction conditions: Catalyst: 0.01 mol%, Aldehyde/ ketone 1mmol,
KOH 1mmol, solvent 2-propanol, bath temperature 80 °C and reaction
time 3 h. bIsolated yield after column chromatography, cNMR % yields.
Oxidation of alcohols with NMO catalyzed with all four Ru(II)
complexes, 1−4 is almost similar. Generally catalytic efficiency is
15 somewhat greater for complexes containing Ru-Se bond in
comparison to the corresponding S analogues.20a The higher
electron donating tendency of Se relative to S promotes the
formation of Ru(IV)=O and thus results in better catalytic
activity. Complexes 3 and 4 in which Se is coordinated to
20 ruthenium show better catalytic activity than their S analogs (1).
In 2, Se and S donor sites are one each and therefore its reactivity
is somewhat higher than that of 1, in which both donor atoms are
sulfur. Similarly for Oppenauer oxidation it is observed that 3 is
somewhat more reactive than 1, as the coordination of Se with Ru
25 promotes hydride formation, essential for this type of oxidation
Transfer hydrogenation of carbonyl compounds
Transfer hydrogenation reaction is attractive as it can avoid the
use of molecular hydrogen21k in organic synthesis. Half sandwich
ruthenium(II) complexes 1−4 have been explored to catalyze
30 transfer hydrogenation of carbonyl compounds using 2-propanol /
glycerol as hydrogen donor. Optimum temperature for catalysis
is 80 °C in the presence of KOH (Scheme 4), known to be the
best inorganic base for this reaction.35
55 In absence of 1-4 no TH was observed with either of the two
hydrogen donors. The time profiles of both these TH’s (under
separate optimum conditions) are shown in Fig. 8. Conversion /
yield increases with time almost linearly and similarly, when
catalyst loading and reaction conditions are optimum in each
60 case. Thus, the two hydrogen donors, glycerol and 2-propanol are
efficient and competitive for catalytic TH, except that the latter
donor may be considered better as optimum loading of catalyst is
less.
In TH using glycerol as hydrogen source, glycerol is
1
65 dehydrogenated to dihydroxyacetone (DHA; H NMR δ 4.4 and
3.5 ppm) and other products,36 but they all are obtained in low
yield and difficult to separate. The low yield of dihydroxyacetone
is not of much concern because glycerol is very cheap and high
recovery of this main byproduct is not going to cut the cost of the
70 process very significantly.
110
100
90
80
Catalyst: 1-4 (0.01-0.5 mol%)
O
OH
R'
70
H-source/KOH/80oC/2-3 h
60
R
R'
R
50
TH in 2- propanol
40
TH in Glycerol
R = R' = Alkyl/Aryl/H
H source = 2-propanol /
glycerol
30
20
10
0
35
Scheme 4. Transfer Hydrogenation of Carbonyl Compounds
0
30
60
90
120
150
180
Time (min)
The optimum catalyst loading is 0.01 and 0.5 mol % with 2-
propanol and glycerol respectively. Maximum conversion has
40 been obtained in 3 h for both hydrogen sources. For TH reactions
using 2-propanol as hydrogen source all the complexes 1−4 were
studied as catalyst. With glycerol only complexes 1 and 3 were
Fig. 8. Time profile of catalytic TH of benzaldehyde using
complex 3.
The comparison of catalytic performance of present Ru(II)
75 complexes for TH with 2-propanol and glycerol, with the
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Dalton Transactions
Page 6 of 12
catalysts reported in literature reveals a mixed bag. For TH in 2-
Homogeneous vs heterogeneous catalysis. To understand
propanol, the optimum catalyst loading has been reported as 0.2 90 whether the catalytic reactions (i.e. Oxidation of alcohols and
mol
%
for Ru(II) complex37 bearing bis(trifluoromethyl)
transfer hydrogenation of carbonyls) are homogeneous or
heterogeneous, mercury and PPh3 poisoning tests47 have been
executed with benzyl alcohol / benzaldehyde substrate. The
reactions were carried out under the optimum conditions using
pyrazolylpyridyl-NNN ligands and [RuCl2(PPh3)3]ethylene-
diamine system38. The optimum loading of complex of
[RuCl2(arene)]2 with ImEt−CH2CH2OEt for TH was found to be
0.05−0.5 mol %.39 The performance of the present complexes 95 complexes 4 / 1 as catalysts. No significant inhibition of
appears to be better than that of [RuCl2(p-cymene)]2 as its
required loading (0.5 mol %) for good conversion is higher than
5
40
conversion was noticed. Thus, the present catalysis appears to be
homogeneous in nature.
10 those of the present complexes. Conversion in TH with 2-
propanol catalyzed with Ru(II) carbonyl complexes of (CCC)-
DFT calculations
pincer bis(carbene) ligands41 is good at 0.01 mol% loading, 100 Density functional theory (DFT) calculations were executed on
which is comparable with those of 1−4 but required reaction time
(6 h) is higher than those of the present complexes.
With glycerol as a hydrogen source for TH, 5 mol% of
[RuCl2(η6-C6H6)(DAPTA)]42 and 1 mol % of the RuCl2(TPPS)3
all Ru(II) complexes 1−4. HOMOs of all complexes are
essentially similar and positioned primarily on Ru and benzene
ring. The d-orbital of Ru(II) interacting with π orbital of benzene
ring, p-orbitals of one N (triazole ring) and S/Se atom constitute
15
(TPPS: tris(3-sulfophenyl)phosphine trisodium salt) and 105 HOMO of the complex. The contribution of orbitals of S or Se
RuCl2(TPP)3 (triphenylphosphine),43 are needed, to get the
desired products in reasonable yield. Further, the reaction time
20 with them for good conversion is of the order of 24−48 h,
whereas with 0.5 mol % of 1 and 3 good conversion occurs in 3 h
which is comparable with the optimum time observed with Ru(II) 120 energy gap of a complex and its chemical reactivity.48−50 The
and Cl coordinated with Ru to these HOMO’s, is only small.
Interestingly to HOMO’s of complexes 2 and 4, the p orbitals of
uncoordinated Se also contribute somewhat.
There is a possible correlation between the HOMO−LUMO
complexes of 1-benzyl-3-phenylchalcogenylmethyl-1,3-dihydro-
benzo-imidazole-2-chalcogenones.44 Thus the present complexes
25 may be considered efficient as yields are good in a short time.
large HOMO−LUMO energy gap reflects low reactivity.49b. The
HOMO−LUMO energy gaps of complexes 2−4 (Figure 9) are
almost same. The energy gap for complex 1 is slightly higher
than rest of other three Ru(II) complexes. Thus relatively higher
Table 4 Catalytic transfer hydrogenation in glycerol using 125 reactivity of complexes 2−4, in comparison to 1 (observed
complexes 1 and 3 as catalysta
experimentally) may be at least partly ascribed to their low
Entry no.
Carbonyl Compounds
1
3
energy gaps relative to that of 1. The DFT-based calculated
values of bonding parameters are consistent with experimental
ones (Table S4).
Yield (%)
1
2
3
4
5
6
7
8
9
Benzaldehyde
4-Methoxy- benzaldehyde
4-Methyl- benzaldehyde
Furfuraldehyde
95
92
88
85
82
82
88
78
88
100
97
92
88
85
86
91
82
95
80
Acetophenone
4-Chloro-acetophenone
4-Methyl-acetophenone
Benzophenone
Cyclopentanone
aReaction Conditions: catalyst 0.5 mol %, Aldehyde/ketone 1 mmol, KOH 1
mmol, Glycerol 5 mL, bath temperature 80 °C and reaction time 3 h,
conversion determined by NMR.
1
30 The TH reactions catalyzed with 3 have been monitored with H
NMR and 77Se{1H} NMR spectroscopy. A new broad singlet
1
was noticed around δ –10.0 ppm in H NMR spectrum (ESI: Fig.
S34) whereas the signal in 77Se{1H} NMR spectrum was found
1
shifted to higher frequency by 23 ppm. The new signal in H
Fig. 9. Frontier molecular orbitals of Ru(II) complexes 1−4
35 NMR is characteristic of metal-hydride formation which probably
occurs due to M–Cl bond cleavage or its very considerable
weakening to make available on metal centre a coordination site
for the formation of M–H bond containing intermediate.45
Therefore catalytic TH reactions with present Ru(II) species
40 probably progress via formation of alkoxide and metal-hydride
intermediates.46 Like oxidation of alcohol, TH reactions catalyzed
with all four Ru(II) complexes, 1−4 are almost similar, which is
corroborated by DFT calculation.
Conclusions
105 1,2,3-Triazole based potentially pincer ligands (L1−L4) with
S/Se donor sites have been synthesized by ‘Click’ reaction
between sulfated/selenated azide and sulfated/selenated alkyne.
They react with [(η6-benzene)Ru(II)Cl2]2 and NH4PF6 giving four
half-sandwich complexes (1−4). Multinuclear NMR and mass
6
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Dalton Transactions
spectrometry authenticate the ligands and their complexes.
Bioinformatics and Computational Biology, Department of
Chemistry, IIT Delhi using Gaussian 09 software. The B3LYP53
functional implemented in Gaussian 0954 software was used for
calculations. LANL2DZ (having ECP for core electrons) basis set
Single-crystal X-ray structures of all four complexes are solved.
The ligands L1−L4 coordinate with Ru in a bidentate mode. The
disposition of donor atoms around Ru is a pseudo-octahedral
5
“piano-stool” type. These half-sandwich complexes of 60 for Ru and 6-311G** basis set for the rest of the elements were
ruthenium(II) have been explored for oxidation of alcohols
(NMO based and Oppenauer-type) and transfer hydrogenation of
carbonyl compounds (2-propanol and glycerol, as hydrogen
source). The 0.1 and 0.01 mol % of each of the present
used. Coordinates obtained from single crystal X-ray diffraction
studies, were directly used for geometry optimization. The
frequency calculations at the end of the geometry optimization
were carried out for all the four complexes, to characterize the
10 complexes is efficient for Oppenauer-type and NMO based 65 stationary points as minima. Molecular orbital calculations were
oxidation respectively. In TH with glycerol optimum catalyst
loading (0.5 mol%) is more than that of 2-propanol (0.01 mol%).
However, their time profiles under respective optimum conditions
are similar, making glycerol competitive with 2-propanol as a
15 hydrogen source. The time profile of NMO based oxidation
matches with that of Oppenauer-type oxidation when optimum
conditions specific to each are used. Thus later can be a good
alternative to NMO oxidant based protocols, if catalyst loading at
a level of 0.1 mole% is made. Both catalytic oxidations and TH’s
carried out with optimized coordinates using same level of theory
and basis set. Chemcraft software (http://www.chemcraftprog.
com) was used for visualization of molecular orbitals.
70 Chemicals and reagents
The reported methods were used for the synthesis of [{(η6-
C6H6)RuCl(μ-Cl)}2],55
azidomethyl
phenyl
sulfide,17a
azidomethyl phenyl selenide,56 propargyl phenyl sulfide57 and
propargyl phenyl selenide. Thiophenol, diphenyl diselenide,
20 appear to be homogeneous in nature as revealed by Hg and PPh3 75 NaBH4, propargyl bromide, benzyl bromide, and NH4PF6 were
poisoning tests. The Se coordinated complexes are found to be
somewhat better catalytic activators than their S analogs, which is
corroborated by DFT studies in terms of HOMO–LUMO energy
gaps. The bond lengths/angles of all four Ru(II) complexes are
25 consistent with DFT calculations.
procured from Sigma-Aldrich (USA) and used as received.
Common reagents, solvents and substrates were procured locally.
All the solvents were dried and distilled before use by standard
procedures.58
80
Synthesis of L1 and L2. Azidomethyl phenyl sulfide (0.330 g, 2
mmol) / azidomethyl phenyl selenide (0.424 g, 2 mmol) was
taken in 3 mL of t-BuOH in a round bottom reaction flask.
Propargyl phenyl sulphide(0.296 g, 2 mmol) was added to it.
Experimental section
Physical measurement
85 Each of CuSO4.5H2O (10 mol%, 0.050 g) and sodium ascorbate
(20 mol%, 0.078 g) was dissolved separately in 2 mL of distilled
water in two separate test tubes. Both the solutions were mixed
and the resulting dark brown mixture was quickly added to the
reaction flask. The resulting reaction mixture in the flask was
90 stirred at room temperature for 12 h. It was poured into water (30
mL). The resulting aqueous phase was extracted with CHCl3 (4 ×
25 mL). The organic extracts were combined and thereafter
washed with water (20 mL), 20% ammonia solution (50 mL) and
brine (20 mL). The extract was dried with anhydrous Na2SO4 and
95 its solvent was evaporated off under reduced pressure on a rotary
evaporator to get ligands L1and L2 as off white solids.
L1: Yield: 0.594 g (95%). Mp. 55 °C.Anal. Found: C, 61.30; H,
4.80; N, 13.44%. Calcd for C16H15N3S2: C, 61.31; H, 4.82; N,
13.41%. IR (cm−1): 478 (m), 688 (s), 739 [s; νC−H (aromatic)], 893
100 (b), 1048 (m), 1123 (m), 1226 (m), 1331 (m), 1439 [b; νC−C
(aromatic)], 1475 [ m; νC=N], 1578 [m; νN=N], 2101 (s), 2362 (m),
2923 [m; νC−H (aliphatic)], 3064 [m; νC−H (aromatic)], 3114 (m).
1H, 13C{1H}, and 77Se{1H} NMR spectra were recorded on a
30 Bruker Spectrospin DPX-300 NMR spectrometer at 300.13,
75.47, and 57.24 MHz, respectively. The chemical shifts (in ppm)
are reported relative to appropriate standards. The glass wares
dried in oven, under ambient conditions were used. Before use,
commercial nitrogen gas was passed successively through traps
35 containing solutions of alkaline anthraquinone, sodium-dithionite,
alkaline pyrogallol, concentrated H2SO4 and KOH pellets.
Schlenk techniques were used to create nitrogen atmosphere. IR
spectra (4000−400 cm−1) were recorded on a Nicolet Protége 460
FT-IR spectrometer as KBr pellets. The C, H and N analyses
40 were carried out with a with a Perkin-Elmer 2400 Series II C, H
and N analyzer. Single crystal structure data were collected at
298(2) K on a Bruker AXS SMART Apex CCD diffractometer
using Mo-Kα (0.71073 Å) radiation. The software SADABS51
was used for absorption correction SHELXTL and OLEX 2 for
45 space group, structure determination and refinements.52 All
hydrogen atoms were included in idealized positions with
isotropic thermal parameters set at 1.2 times that of the carbon
atom to which they were attached. The least-squares refinement
cycles on F2 were performed until the model converged. High
50 Resolution Mass Spectral (HR-MS) measurements were
performed with an instrument Bruker Micro TOF-Q II, based on
electron spray ionization (10 eV, source temperature: 180 °C and
calibrant: sodium formate) taking sample in CH3CN. The melting
points determined in an open capillary are reported as such. All
55 DFT calculations were carried out at Supercomputing Facility for
L2: Yield: 0.669 g (93%). Mp. 60 °C. Anal. Found: C, 53.30; H,
4.21; N, 11.60%. Calcd for C16H15N3SSe: C, 53.33; H, 4.20; N,
105 11.66%.IR (cm−1): 462 (m), 690 (s), 738 [s;νC−H (aromatic)], 1042
(m), 1098 (m), 1226 (m), 1339 (m), 1438 [b; νC−C (aromatic)], 1475 [
m; νC=N], 1578 [m; νN=N], 2364 (b), 2923 [s; νC−H (aliphatic)], 3058
[m; νC−H (aromatic)], 3140 (m).
110 Synthesis of L3 and L4. The solution of propargyl phenyl
selenide (0.390 g, 2 mmol) made in 3 mL of t-BuOH was added
to azidomethyl phenyl sulfide (0.330 g, 2 mmol) / azidomethyl
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phenyl selenide (0.424 g, 2 mmol) taken in a reaction flask. The
CuSO4.5H2O (10 mol%, 0.050 g) and sodium ascorbate (20
mol%, 0.078 g) were dissolved in 2 mL of distilled water
νC−C (aromatic)], 1573 [b; νN=N], 2361 (m), 2928 [m; νC−H (aliphatic)],
3085 [m; νC−H (aromatic)].
separately in two test tubes. Both the solutions were mixed 60 The NMR and HR-MS data of L1-L4 and 1-4 is given in Table 5
5
together and the resulting dark brown mixture was quickly added
to the reaction flask. The reaction mixture was stirred at room
temperature for 12 h. The L3 and L4 were obtained after a work
up similar to the one used for L1 and L2.
General procedure for catalytic oxidation of alcohols with
NMO. To a 20 mL aliquot of CH2Cl2, alcohol substrate (1
mmol), K2CO3 (1.2 mmol) and solid NMO (3 mmol) were added.
L3: Yield: 0.684 g (95%). Mp. 65 °C. Anal. Found: C, 55.31; H, 65 One of the complexes 1−4 taken in CH3CN was added with
10 4.21; N, 11.61%. Calcd for C16H15N3SSe: C, 55.33; H, 4.20; N,
11.66%. IR (cm−1): 471 (m), 684 (s), 738 [s;νC−H (aromatic)], 1034
(m), 1108 (m), 1219 (m), 1368 (m), 1444 [b; νC−C (aromatic)], 1470 [
m; νC=N], 1549 [m; νN=N], 1735 (s), 2354 (b),2927 [s; νC−H
(aliphatic)], 3060 [m; νC−H (aromatic)], 3134 (m).
15 L4: Yield: 0.765 g (94%). Mp. 70 °C.Anal. Found: C, 47.17; H,
3.72; N, 10.31%. Calcd for C16H15N3Se2: C, 47.19; H, 3.71; N,
10.32. IR (cm−1): 464 (m), 689 (s), 737 [s;νC−H (aromatic)], 1042
(m), 1104 (s), 1220 (m), 1444 [b; νC−C (aromatic)], 1470 [ m; νC=N],
syringe so that its amount was 0.01 mol%. The mixture was
refluxed for 3 h. The reaction was followed by 1H NMR
spectroscopy. On completion of reaction the mixture was cooled
to room temperature and its solvent evaporated off with a rotary
70 evaporator. Water (30 mL) was added to the concentrate having
oxidized product. It was extracted with 20 mL of diethyl ether.
The solvent from the extract was evaporated off and the residual
liquid was analyzed with 1H and 13C{1H} NMR spectroscopy.
General procedure for Oppenauer type oxidation of alcohols.
1577 [m; νN=N], 1744 (s), 2855 [s; νC−H (aliphatic)], 2924 [s; νC−H 75 To an aliquot of acetone (15 mL), 1 mmol of alcohol substrate
20 (aliphatic)],3057 [m; νC−H (aromatic)].
and potassium t-butoxide (0.1 mmol) were added. An appropriate
volume of solution of catalyst complex 1 or 3 (1 mmol) made in
acetonotrile was added via syringe so that final concentration of
Synthesis of complexes 1−4. To
C6H6)RuCl(µ-Cl)}2] (0.050 g, 0.1 mmol) made in CH3OH (5 mL)
was added a solution of L1(0.0626 g, 0.2 mmol) / L2 (0.0720 g, 80 for 3 h. The reaction was monitored by H NMR spectroscopy.
a
solution of [{(η6-
the catalyst became 0.1 mol%. The mixture was refluxed at 80 oC
1
25 0.2 mmol) / L3 (0.0720 g, 0.2 mmol) / L4 (0.0814 g, 0.2 mmol)
made in CH3OH (5 mL) and the mixture was stirred for 8 h at
room temperature. The resulting orange solution was filtered, and
the volume of the filtrate was reduced (~7 mL) with a rotary
After completion of reaction the mixture was allowed to cool at
room temperature and its solvent was evaporated off with a rotary
evaporator. Water (30 mL) was added to the concentrate having
oxidized product. It was extracted with 20 mL of petroleum ether.
evaporator. It was mixed with solid NH4PF6 (0.032 g, 0.2 mmol), 85 The solvent from the extract was evaporated off and oxidized
1
30 and the resulting orange coloured microcrystalline solid was
filtered, washed with 5 mL of ice-cold CH3OH, and dried in
vacuo. Single crystals of each of 1−4 were obtained by diffusion
of diethyl ether into solution of complex made in a mixture (1: 4)
of CH3OH and CH3CN.
35 1: Yield: 0.107 g (80%). Mp. 220 °C (d). Anal. Found: C, 39.25;
H, 3.16; N, 6.21%. Calcd for C22H21N3ClRuS2[PF6]: C, 39.26; H,
3.14; N, 6.24%. IR (cm−1): 491 (b), 557(s), 749 [m; νC−H (aromatic)],
850 [s; νP−F], 1089 (b), 1136 (b), 1255 (b), 1440 [m; νC−C (aromatic)],
product present as a liquid or solid was analyzed with H NMR
spectroscopy.
General procedure for transfer hydrogenation of carbonyl
compounds with 2-propanol. The solution of a carbonyl
90 compound (1 mmol) made in 2-propanol (10 mL), KOH (1
mmol) and one of the complexes 1−4 dissolved in CH3CN (added
with syringe so that it had a concentration level of 0.01 mol%)
were mixed. The mixture was heated at 80 °C for 3 h with
stirring. Thereafter 2-propanol was removed with a rotary
1575 [b; νN=N], 2361 (m), 2919 [m; νC−H (aliphatic)], 3086 [m; νC−H 95 evaporator and water (30 mL) was added to the concentrate. The
40 (aromatic)].
hydrogenated product was extracted with diethyl ether (20 mL).
The solvent from the extract was evaporated off resulting in
2: Yield: 0.117 g (82%). Mp. 200 °C (d).Anal. Found: C, 36.71;
1
H, 2.90; N, 5.81%. Calcd for C22H21N3ClRuSSe[PF6]: C, 36.70;
H, 2.94; N, 5.84%. IR (cm−1): 558 (b), 690 (m), 745 [s;νC−H
(aromatic)], 848 [s; νP−F], 1088 (m), 1133 (m), 1246 (b), 1403 [m;
45 νC−C (aromatic)], 1574[b; νN=N], 2361 (m), 2918 [m; νC−H (aliphatic)],
3087 [m; νC−H (aromatic)].
3: Yield: 0.119 g (83%). Mp. 210 °C (d). Anal. Found: C, 36.72;
H, 2.91; N, 5.80%. Calcd for C22H21N3ClRuSSe[PF6]: C, 36.70;
H, 2.94; N, 5.84%. IR (cm−1): 558 (b), 692 (m), 745 [s;νC−H
50 (aromatic)], 838 [s; νP−F], 1088 (m), 1140 (m), 1246 (b), 1439 [m;
νC−C (aromatic)], 1574 [b; νN=N], 2361 (m), 2929 [m; νC−H (aliphatic)],
3088 [m; νC−H (aromatic)].
liquid or solid which was analyzed with H and 13C{1H} NMR
spectroscopy.
100 General procedure for catalytic transfer hydrogenation of
carbonyl compounds with glycerol. A solution of a carbonyl
compound (1 mmol) made in glycerol (5 mL), KOH (1.5 mmol),
and solution of a complex from 1 and 3 in CH3CN (added with
syringe to make its overall concentration 0.5 mol% ) were mixed
1
105 and heated at 80 °C for 3h. The reaction was followed by H
NMR spectroscopy. After completion of the reaction, the mixture
was cooled to room temperature and mixed with 30 mL of water.
The resulting hydrogenated product was extracted with diethyl
ether (20 mL). The solvent from the extract was evaporated off,
110 giving a liquid or solid which was analyzed with 1H NMR
spectroscopy.
4: Yield: 0.132 g (85%). Mp. 200 °C (d). Anal. Found: C, 34.45;
H, 2.77; N, 5.46%. Calcd for C22H21N3ClRuSe2[PF6]: C, 34.46;
55 H, 2.76; N, 5.48%. IR (cm−1): 557 (b), 689 (m), 740 [s;νC−H
(aromatic)], 838 [s; νP−F], 1088 (m), 1132 (m), 1241 (b), 1438 [s;
8
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Dalton Transactions
Table 5 NMR Chemical Shift (δ, ppm) at 25 °C in CDCl3 (L1-L4) / CD3CN(1-4) and HR-MS data in CH3CN
Ligand/Complex
1H NMR
(vs TMS)
13C{1H} NMR
( vs TMS)
77Se{1H}
( vs Me2Se )
HR-MS
4.20 (s, 2H, H5), 5.53 (s, 28.7, 53.9, 121.6, 127.2,
2H, H8), 7.16−7.32 (m, 127.4, 128.7, 129.0, 129.1
10H, H1−H3, H10− H12), 129.4, 129.5, 132.4, 145.7
7.43 (s, 1H, H7)
[M + Na]+ (m/z) =
336.0600; calcd. value for
C16H15N3NaS2 = 336.060
(δ: 0.0 ppm)
L1
4.21 (s, 2H, H5), 5.55 (s, 28.7, 44.7, 121.8, 126.4,
[M + H]+ (m/z) =
2H, H8), 7.18−7.51(m,
11H, H1−H3, H7, H10−H12)128.3, 129.5, 134.7, 145.7
127.3, 128.9, 128.9,
430.4
362.6
362.0240; calcd. value for
C16H16N3NaSSe =
362.0224 (δ:1.6 ppm)
L2
L3
L4
4.12 (s, 2H, H5), 5.50 (s, 20.2, 53.4, 121.2, 127.1,
2H, H8), 7.16−7.27 (m, 128.2, 128.8, 129.1,
9H, H1,H2, H7, H10−H12) 129.4, 131.5, 131.8,
[M + Na]+ (m/z) =
384.0048; calcd. value for
C16H15N3NaSSe =
7.41−7.49 (m, 2H, H3)
132.6, 145.8
384.0044 (δ: 0.3 ppm)
4.12 (s, 2H, H5), 5.58 (s, 20.5, 44.6, 121.6, 127.4,
2H, H8), 7.18−7.61 (m, 128.9, 129.1, 129.5,
429.5, 362.5
[M + H]+ (m/z) =
11H, H1−H3, H7,
H10−H12).
129.8, 133.0, 133.2,
134.6, 146.2
409.9665; calcd. value for
C16H16N3Se2 = 409.9672
(δ: 7ppm)
3.83−4.01 (m, 2H,H5),
5.69−5.84 (m, 2H, H5), 35.8, 55.4, 86.9,122.5,
5.44 (s, 6H,Ru−ArH),
7.21−7.52 (m, 10H,
H1−H3, H10−H12), 7.94 (s, 132.8, 134.6, 146.8
[M]+ (m/z) = 527.9905;
calcd. value for
C22H21ClN3RuS2 =
527.9905 (δ: 0.0 ppm)
1
2
3
4
128.9, 129.1, 129.3,
129.9, 130.6, 131.2,
1H, H7)
3.92−4.11 (m, 2H,
H5),5.54 (s, 6H,
Ru−ArH), 5.85−6.00 (m, 129.1, 129.4, 129.9,
2H, H8), 7.33−7.64 (m, 131.2, 134.8, 146.8
10H, H1−H3, H10−H12),
35.9, 46.0, 87.0, 122.7,
126.5, 128.9, 129.0,
[M]+ (m/z) = 575.9358;
calcd. value for
C22H21ClN3RuSSe =
575.9352 (δ: -0.6 ppm)
447.5
447.9
8.01 (s, 1H, H7)
3.69−3.86 (m, 2H,H5),
27.9, 55.2, 86.4, 122.9,
[M]+ (m/z) = 575.9346;
calcd. value for
C22H21ClN3RuSSe =
575.9352 (δ: 0.6 ppm)
5.49 (m, 6H, Ru−ArH), 128.8, 129.0, 129.9,
5.67−5.83 (m, 2H, H8), 130.4, 130.5, 130.6,
7.20−7.23(m, 2H, H10), 130.7, 132.7, 147.6
7.34−7.48 (m, 8H, H1−H3,
H11,H12), 7.92 (s, 1H, H7)
3.79−3.95 (m, 2H,H5),
5.58 (s, 6H, Ru–ArH),
5.83−5.93 (m, 2H, H8), 129.3, 129.9, 130.3,
7.33−7.63 (m, 10H, H1– 130.6, 130.7, 134.7, 147.6
H3, H10−H12), 7.98 (s, 1H,
28.1, 45.9, 86.4, 123.1,
126.4, 128.8, 129.3,
[M]+ (m/z) = 623.8793;
calcd. value for
C22H21ClN3RuSe2 =
623.8800 (δ: 0.8 ppm).
447.6, 447.5
H7)
5
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DOI: 10.1039/C5DPT0a2g92e6K10 of 12
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wascarried out. The conversion was ~ 97%. Similarly transfer
hydrogenation reaction of benzaldehyde (1.0 mmol) with 2-
propanol (15 ml) / glycerol (5 mL) using 1 (0.01 / 0.5 mol%) as a
catalyst was carried out in a flask, having 400-time excess of Hg
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equivalents of PPh3 in place of Hg. After 3 h of reaction ~ 95%
15 conversion was observed in case of oxidation as well as TH.
Acknowledgments
A.K.S thanks Council of Scientific and Industrial Research
(CSIR), and Department of Atomic Energy (BRNS), India for
financial support. F.S, S.K and M.P.S thank University Grants
20 Commission (UGC) for Senior Research Fellowship. G.K.R.
thanks CSIR for Research Associateship. Authors also thank
Prof. B. Jayaram (Coordinator, SCFBio) and Dr. Goutam
Mukherjee for providing access to the computational facilities of
‘Supercomputing Facility of Bioinformatics and Computational
25 Biology’ (SCFBio), Department of Chemistry, IIT Delhi.
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Notes and references
Department of Chemistry, Indian Institute of Technology Delhi,
New Delhi 110016, India.
*Corresponding author. Fax: +91-01- 26581102; Tel: +91-011-
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DOI: 10.1039/C5DT02926K
Complexes of (η6-benzene)ruthenium(II) with 1,4-bis(phenylthio/seleno-
methyl)-1,2,3-triazoles: synthesis, structure and applications in catalytic
activation of oxidation and transfer hydrogenation
Fariha Saleem, Gyandshwar K. Rao, Satyendra Kumar, Mahabir Pratap Singh and Ajai K. Singh*