Synthesis, structural characterization and catalysis of ruthenium(II) complexes based on 2,5-bis(2′-pyridyl)pyrrole ligand

Article abstract of DOI:10.1039/c6dt03464k

Treatment of the 2,5-bis(2′-pyridyl)pyrrolato (PDP^-) anion with {Ru(COD)Cl₂}_n in THF readily yielded [Ru(PDP)(COD)Cl] (1) in almost quantitative yield. Anion metathesis of 1 in organic solvent by NO₃^- and OTf^- (OTf^- = triflato) gave [Ru(PDP)(COD)(NO₃)] (2) and [Ru(PDP)(COD)(OTf)] (3), and in aqueous solution by BF₄^- and PF₆^- afforded aqueous complexes [Ru(PDP)(COD)(H₂O)](BF₄) (4⁺·BF₄^-) and [Ru(PDP)(COD)(H₂O)](PF₆) (4⁺·PF₆^-), respectively. Treatment of 1 with PhICl₂ in CH₂Cl₂ afforded 5 with halogenated pyrrole. These complexes exhibit similar structure, including one Ru(ii) atom, one 2,5-bis(2′-pyridyl)pyrrole and one monodentate anion or aqua ligand. Each Ru(ii) tightly binds to three adjacent coplanar sites of PDP^- ligand to form a meridional configuration. Complex 1 with NaIO₄ as the oxidant in EtOAc-CH₃CN-H₂O (ratio = 3 : 1 : 2) proved to be highly effective in the catalytic oxidation of olefins to carbonyl products.

Full text of DOI:10.1039/c6dt03464k

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Page 1 of 27
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DOI: 10.1039/C6DT03464K
Synthesis, Structural Characterization and Catalysis of
Ruthenium(II) Complexes Based on 2,5ꢀbis(2’ꢀpyridyl)pyrrole
Ligand
YiꢀQing Zhong, HuiꢀQiong Xiao and XiaoꢀYi Yi *
College of Chemistry and Chemical Engineering, Central South University, Changsha,
Hunan 410083, P. R. China
Fax: 86 731 88879616; Tel: 86 731 88879616;
*To whom correspondence should be addressed. Eꢀmail: xyyi@csu.edu.cn

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Abstract
Treatment of 2,5ꢀbis(2’ꢀpyridyl)pyrrolato (PDPꢀ) anion with {Ru(COD)Cl2}n in
THF readily yielded [Ru(PDP)(COD)Cl] (1) in almost quantitative yield. Anion
ꢀ
metathesis of 1 in organic solvent by NO3 and OTfꢀ (OTfꢀ = triflato) gave
[Ru(PDP)(COD)(NO3)] (2) and [Ru(PDP)(COD)(OTf)] (3) , and in aqueous solution
ꢀ
ꢀ
ꢀ
by BF4 and PF6 afforded aqueous complexes [Ru(PDP)(COD)(H2O)](BF4) (4+·BF4 )
ꢀ
and [Ru(PDP)(COD)(H2O)](PF6) (4+·PF6 ), respectively. Treatment of 1 with PhICl2
in CH2Cl2 afforded 5 with halogenated pyrrole. These complexes exhibits similar
structure, including one Ru(II) atom, one 2,5ꢀbis(2’ꢀpyridyl)pyrrole and one
monodentate anion or aqua ligand. Each Ru(II) tightly binds to three adjacent
coplanar sites of PDPꢀ ligand to form a meridional configuration. Complex 1 with
NaIO4 as the oxidant in EtOAcꢀCH3CNꢀH2O (ratio = 3:1:2) is proved to be highly
effective in the catalytic oxidation of olefins to carbonyl products.

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Introduction
The oxidative cleavage of olefins to carbonyl products is a synthetically
2
important reaction to introduce oxygen into organic molecules.1,
Transitionꢀmetal complexes as catalysts combined with a variety of coꢀoxidants
t
such as oxone, H2O2, BuOOH, PhI(OAc)2, NaIO4 and etc are used. The
ruthenium complexes are one of the most popular catalysts for olefins oxidation
due to being readily available to form ruthenium intermediates in high
oxidation state.3, 4 Recently, Bera and coꢀworkers reported [Ru(COD)(L)Br2] (L
= imidazo[1,2ꢀa][1,8]naphthyridine) as excellent catalyst toward oxidation of
C=C bond to aldehydes for a wide range of substrates.5 The catalytic reaction
starts from oxidation of COD ligand. The formed rutheniumꢀcisꢀdioxo
intermediate is stabilized by aromatic naphthyridine ligand. Compared with the
ruthenium salt and oxide without application of ligands,6 [Ru(COD)(L)Br2] has
less loading, better selectivity, higher efficiency for olefin oxidation reactions.
The rational design of ligand to stabilize the intermediate can enable the
generation of superior catalysts. We have a longꢀstanding interest in the metal
complexes based on 2,5ꢀbis(2’ꢀpyridyl)pyrrolide (HPDP).7 HPDP ligand
contains a large conjugated backbone, and its central pyrrolato N atom can
behave as
σꢀdonor and πꢀdonor/acceptor corresponding to the metal electron
properties. Thus, PDPꢀ anion is also capable of stabilizing metal center in low
and high oxidation states.8, 9 In some sense, aromatic properties of HPDP are
similar to that of naphthyridine ligand in [Ru(COD)(L)Br2], which forms
favorable to make its ruthenium complex as a potential oxygen transfer catalyst.
The ruthenium complexes containing bispyridylpyrrolide ligand,10, 11 such as
[Ru(PDP)(bipy)]+, [Ru(PDP)(tpy)]+ and [Ru(PDP)2], have been reported
previously, however, these works were focused on the study of their syntheses
and structures. Inspired by Bera’s work, we herein will describe the preparation,
structures of a set of ruthenium COD complexes based on HPDP ligand, and we
also report their catalytic properties for olefin oxidation reactions.

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Experimental Section
1
General Considerations. H NMR spectrum was recorded on a Bruker AVANCE
500M spectrometer operating at 500 MHz, and chemical shifts (δ, ppm) were reported
with reference to SiMe4. Infrared spectra (KBr) were recorded on Nicolet 6700
spectrometer FTꢀIR spectrophotometer. Elemental analyses for C, H and N were
performed on a Perkin Elmer 240C elemental analyzer. GC experiment was
performed on a Kejie 5890F GC system with a FID detector. ESIꢀMS was performed
in a Bruker Daltonik GmbH, Bremen mass spectrometer equipped with an
electrospray ionization (ESI) source, and the experimental parameters were as follows:
capillary temperature, 200 oC; capillary voltage, 4500 V; flow rate, 4 L/min; hexapole,
127 V. Potential measured in CH3CN with 0.1 M [nꢀBu4N]PF6 as supporting
electrolyte; scan rate = 100 mVsꢀ1; E1/2 = 1/2(Epa + Epc); Glassy carbon working
electrode, Pt counter electrode, reference electrode: AgNO3/Ag (0.1 M acetonitrile);
potentials reported in V vs Cp2Fe+/0. GC conditions: Chromatogram column: SEꢀ30;
Injection temperature: 200 oC; Detection temperature: 280 oC. The starting
2,5ꢀbis(2’ꢀpyridyl)pyrrole was prepared according to literature methods.12, 13 All of
other chemicals were obtained from J&K Scientific.
Preparation of [Ru(PDP)(COD)Cl] (1): A mixture of HPDP (718 mg, 3.25 mmol)
and 60% NaH (130 mg, 3.25 mmol) in THF (30 mL) was stirred for about five
minutes. To the resulting yellow solution was added {Ru(COD)Cl2}n (910 mg, 3.25
mmol). The reaction suspension mixture was stirred and kept refluxing overnight. The
solvent was removed by vacuum, and the brown residual was reꢀdissolved in CHCl3.
The precipitate was filtered off. The darkish brown filtrate was layered with ether and
hexane mixture to give brown crystals of 1, which were suitable for Xꢀray diffraction
study. Isolated yield: 1435 mg (95 %). 1H NMR (CDCl3): δ 8.62 (d, J = 4.36 Hz, 2H),
7.65 (t, J = 6.36, 5.86 Hz, 2H), 7.48(d, J = 6.42 Hz, 2H), 7.01(td, J = 5.30, 5.26 Hz,
2H), 6.73(s, 2H), 4.69(m, 2H), 2.95(m, 2H), 2.69(m, 2H), 2.49(m, 2H), 2.09(m, 2H),

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1.92(m, 2H). 13C NMR (CDCl3): δ 158.87, 153.27, 139.45, 137.29, 119.76, 118.59,
109.92, 95.38, 89.01, 30.77, 28.98. IR (KBr, cmꢀ1): 2908(w), 2846(w), 1599(s),
1499(s), 1429(w), 1396(s), 1298(m), 1272(w), 1231(w), 1146(m), 1051(w), 999(w),
873(w), 758(s), 509(w), 454(w). Anal. Calc. for RuClN3C22H22: C, 56.83; H, 4.77; N,
9.04%. Found: C, 56.01; H, 4.90; N, 8.95%.
Preparation of [Ru(PDP)(COD)(NO3)] (2): The mixture of 1 (763 mg, 1.64 mmol)
and AgNO3 (288 mg, 1.69 mmol) in THF (20mL) was stirred for 8 h. The resultant
solution was filtered, and the filtrate was layered by ether to give brown crystals of 2,
1
which were suitable for Xꢀray diffraction study. Isolated yield: 739 mg (92 %). H
NMR (CDCl3): δ 8.67 (d, J = 5.40 Hz, 2H), 7.70 (t, J = 7.32, 8.00 Hz, 2H), 7.49 (d, J
= 8.00 Hz, 2H), 7.02 (t, J =6.62, 6.62 Hz, 2H), 6.72 (s, 2H), 5.00 (m,2H), 2.93 (m,
2H), 2.67 (m, 2H), 2.58(m, 2H), 2.10 (m, 2H), 1.93 (m, 2H). 13C NMR (CDCl3): δ
159.52, 153.35, 140.03, 138.06, 119.87, 118.85, 110.36, 96.04, 86.81, 30.92, 30.77,
28.11. IR (KBr, cmꢀ1): 2946(w), 2848(w), 1600(s), 1498(s), 1468(s), 1396(s), 1273(s),
1143(w), 1042(w), 982(m), 881(w), 755(m), 510(w), 453(w). Anal. Calc. for
RuO3C22H22N4·H2O: C, 51.86; H, 4.75; N, 11.00% . Found: C, 51.69; H, 4.53; N,
10.85%.
Preparation of [Ru(PDP)(COD)(OTf)] (3): Complex 3 was synthesized by the
similar procedure with that of 2, only using AgOTf in place of AgNO3. Isolated yield:
1
571 mg (60 %). H NMR (CDCl3): δ 8.73 (t, J = 5.20, 5.24 Hz, 2H), 7.74 (m, 2H),
7.50 (t, J = 7.58, 7.96 Hz, 2H), 7.16 (t, J = 6.62, 6.64 Hz, 1H), 7.08 (td, J = 6.60, 6.66
Hz, 1H), 6.73 (d, J = 4.96 Hz, 2H), 5.08 (m, 2H), 3.01 (m, 1H), 2.93 (m, 1H), 2.68 (m,
13
2H), 2.45 (m, 2H), 2.04 (m, 2H), 1.94 (m, 2H). C NMR (CDCl3): δ 159.57, 158.93,
154.04, 153.55, 138.93, 138.50, 121.10, 120.11, 119.05, 118.95, 110.77, 110.58, 95.90,
95.48, 85.93, 84.23, 30.92, 30.89, 30.69, 27.90, 27.79. IR (KBr, cmꢀ1): 2960(w),
2857(w), 1602(s), 1500(s), 1434(m), 1403(s), 1298(m), 1284(m), 1249(s), 1224(s),

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1169(m), 1150(m), 1029(s), 930(w), 781(m), 752(m), 635(m), 512(m), 454(w). Anal.
Calc. for RuSO3F3C23H22N3·1.5(H2O): C, 45.62; H, 4.16; N, 6.94%. Found: C, 45.52;
H, 4.29; N, 6.92% .
ꢀ
ꢀ
ꢀ
ꢀ
Preparation of [Ru(PDP)(COD)(H2O)](X) X = BF4 (4+·BF4 ); X = PF6 (4+·PF6 ):
The mixture of 1 (188 mg, 0.40 mmol) and AgBF4 (82 mg, 0.42 mmol) in
acetone/water (15mL, v:v=1:1) was stirred for 6 h and filtered under nitrogen. The
filtrate was layered with hexane to give brown single crystals, which was identified as
4+·BF4 by Xꢀray diffraction analysis. The yield of 4+·BF4 is low (ca. 6 %).
Alternatively, the filtrate was added excess NH4PF6 (98 mg, 0.60mmol) and stirring
for 4 h. The acetone was slowly removed by vacuum to give an orange suspension.
After filtered, residual solid was washed with water, redissolved in dichloromethane
and dried with anhydrous sodium sulfate. Recrystallization from CH2Cl2/ether, hexane
ꢀ
ꢀ
ꢀ
1
solvent system obtained crystalline 4+·PF6 . Isolated yield: 197 mg (83 %). H NMR
(acetoneꢀd6): δ 8.97 (t, J = 3.64, 3.68 Hz, 2H), 8.02 (m , 2H), 7.84 (d, J = 6.40 Hz, 1H),
7.78 (d, J = 6.42 Hz, 1H), 7.35 (m, 2H), 6.93 (s, 1H), 6.86 (s, 1H), 5.10 (m, 1H), 5.04
(m, 1H), 3.01 (m, 2H), 2.87 (m, 2H), 2.57 (m, 2H), 2.20 (m, 2H), 2.09 (s, 2H), 2.00
(m, 2H). 13C NMR (CDCl3): δ 158.56, 154.08, 139.49, 138.87, 121.39, 119.14, 110.61,
93.45, 92.98, 29.90, 29.09. IR (KBr, cmꢀ1): 3645(w), 3564(w), 2951(w), 2843(w),
1680(w), 1603(m), 1500(m), 1435(w), 1399(m), 1298(w), 1269(w), 1154(w),
1048(w), 1002(w), 840(s), 752(m), 555(m), 456(w). Anal. Calc. for RuPF6OC22H24N3:
C, 44.60; H, 4.08; N, 7.09%. Found: C, 44.14; H, 4.54; N, 7.17%.
Preparation of [Ru(PDPCl)(COD)Cl] (5): A mixture of 1 (110.5 mg, 0.24 mmol)
and PhICl2 (73.3 mg, 0.26 mmol) in CH2Cl2 (12 mL) was stirred overnight. The
precipitate was filtered off. The filtrate was layered with ether and hexane mixture to
give yellow crystals of 5, which were suitable for Xꢀray diffraction study. Isolated
1
yield: 117.0 mg (91 %). H NMR (CDCl3): δ 8.67 (d, J = 4.40 Hz, 2H), 7.93 (d, J =

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8.78 Hz, 1H), 7.76 (t, J = 6.16, 6.16 Hz, 2H), 7.13 (t, J = 5.28, 5.30 Hz 2H), 4.71(m,
2H), 2.96(m, 2H), 2.69(m, 2H), 2.48(m, 2H), 2.11(m, 2H), 1.91(m, 2H). 13C NMR
(CDCl3): δ 158.45, 157.71, 153.48, 153.41, 153.34, 153.26, 137.62, 120.44, 120.42,
119.30, 118.79, 109.43, 95.75, 95.70, 89.60, 89.51, 30.75, 30.69, 30.67, 30.61, 28.96,
28.93, 28.90. IR (KBr, cmꢀ1): 2943(w), 2845(w), 1600(s), 1497(s), 1433(w), 1400(w),
1337(w), 1295(m), 1150(m), 1011(w), 977(w),878(w), 775(m), 751(m), 507(w),
458(w). Anal. Calc. for RuCl3C22H20N3·0.5(Et2O): C, 50.49; H, 4.41; N, 7.36% .
Found: C, 50.54; H, 4.54; N, 7.43% .
Oxidation of olefins. Typically, a suspension solution of olefin (0.1 mmol), catalyst
of 1 (3 mol%) and NaIO4 ( 0.25 mmol ) in EtOAcꢀCH3CNꢀH2O (ratio = 3:1:2) was
o
vigorously stirred at 30 C. The color of solution was changed from brownꢀred to
oliveꢀgreen, then to brown during the catalytic reaction proceed. Yield of
corresponding product at suitable interval time were determined by GC analysis using
internal standard.
Xꢀray crystallography Diffraction data of 1ꢀ5 were recorded on a Bruker CCD
diffractometer with monochromatized MoꢀKα radiation (λ = 0.71073 Å). The
collected frames were processed with the software SAINT. The absorption correction
was treated with SADABS.14 Structures were solved by direct methods and refined by
fullꢀmatrix leastꢀsquares on F2 using the SHELXTL software package.15 Atomic
positions of nonꢀhydrogen atoms were refined with anisotropic parameters. All
hydrogen atoms were introduced at their geometric positions and refined as riding
atoms.
Results and Discussion

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Synthesis and characterization of Ru complexes. Treatment of HPDP with NaH
followed by one equiv of {Ru(COD)Cl2}n gave 1 in almost quantitative yield
ꢀ
(Scheme 1). Anion metathesis of 1 in organic solvent by NO3 and OTfꢀ (OTfꢀ =
trifluoromethanesulfonate) gave the complex 2 and 3, respectively, that could be
isolated as crystalline solid in high yield. The BF4 salt of 4+·BF4 was prepared by 1
ꢀ
ꢀ
with AgBF4, unfortunately, isolated yield was poor. Alternatively, excess of NH4PF6
ꢀ
was added into the reaction mixture of 1 and AgBF4, resulting in formation of PF6
salt of 4+·PF6 in high yield. Treatment of 1 with PhICl2 in CH2Cl2 afforded 5 with
ꢀ
halogenated pyrrole. The analogous bispyidylpyrrolide ligand by dithiocyanate
functionalized 3,4ꢀpositions of the pyrrole ring was synthesized by treating the bare
ligand with (SCN)2.8 Complexes 1ꢀ5 are soluble in polar organic solvent, such as
acetone, CH2Cl2, CH3CN, DMSO, but insoluble in water, ether and hexane.
1
These complexes are characterized by ESIꢀMS, IR, H NMR and single crystal
Xꢀray diffraction analysis. ESIꢀMS of 1 displayed a signal at m/z 465.07 (z = 1)
assigned to [1 + H+]. In the IR spectrum of 1, C=C, C=N stretching frequencies of
1
PDPꢀ ligand were determined to be 1599 ꢀ 1396 cmꢀ1. The H NMR shows multiply
peaks at 4.69ꢀ1.93 ppm range for COD ligand, doublet peaks at 8.61, 7.65, 7.47 7.00
ppm for pyridine, and a single peak at 6.73 ppm assigned to the proton resonances of
pyrrole ring. IR spectra of 2ꢀ5 are similar with that of 1. The distinctive signals at
1273 cmꢀ1 for 2 and 1249ꢀ1284 cmꢀ1 for 3 are due to N=O and S=O stretching
frequencies of the coordinated nitrate and triflato ligands in 2 and 3, respectively.
Complex 4+ shows weak bands at 3645 and 3564 cmꢀ1 attributed to the OꢀH bond of
1
the coordinated water. H NMR spectra of 2ꢀ5 closely resemble those in 1, which
clearly reveals the formation of RuꢀNpyrrole bond owing to the absence of the NpyrroleꢀH
resonance. In complex 5, the absence of the CpyrroleꢀH resonance indicates the
formation of CꢀCl bond, which is consistent with the solid state structure.
Description of the crystal structures. The crystallographic data and
experimental details for
1ꢀ5 are shown in table 1. Selected bond distances and
bond angles are listed in table 2. ORTEP diagram of Ru complexes are

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displayed in Figure 1ꢀ5, respectively. Complexes 1ꢀ
4+ have a similar structure,
including one Ru(II) center, one 2,5ꢀbis(2’ꢀpyridyl)pyrrole, one COD and one
monodentated ligands. Ru(II) is best described as pseudoꢀoctahedral with COD
occupying the two coordination sites in a η2
,
η2ꢀfashion, three N atoms of PDPꢀ
, H2O for 4+) occupying the
ligand and X (X = Clꢀ for
1
, NO3 for
2
, OTfꢀ for
3
ꢀ
remaining coordination sites. In these complexes, the RuꢀC bonds have almost
similar bond distances with an average bond length of 2.197 Å, which are well
comparable to those of RuII(COD) complexes.16 Bond distance of RuꢀNpyrrole
(av. 1.964(2) Å) is significantly shorter that of RuꢀNpyridine (av. 2.169(2) Å),
which can be explained by a stronger coordination of the deprotonated pyrrole
nitrogen donor to the metal centre versus the neutral pyridyl group. The RuꢀCl
bond length in
1 is 2.4243(7) Å. The bond distances of RuꢀO in 2ꢀ
4+ are
2.124(2), 2.190(3) and 2.131(4) Å, respectively. The PDPꢀ as pincerꢀtype ligand
coordinates to Ru(II), which is almost planar. The dihedral angles between
pyrrole and pyridine rings are 5.2o and 8.1o for
1 2
, 11.3o and 12.9o for , 8.4o and
8.8o for , 9.4o and 14.1o for +, respectively. That is well comparable to that of
3
4
[Ru(bipy)(PDP)]+, [Ru(tpy)(PDP)]+ [Ru(PDP)2]ꢀtype complexes.11 The bond
angles of NpyrꢀRuꢀNpy and NpyꢀRuꢀNpy’ are about in the range of 74 o and 146 o,
respectively. Complex
chloride atom substituted at the 3ꢀ and 4ꢀposition of the pyrrole ring in
dihedral angles between pyrrole and pyridine rings for
are 5.4o and 10.6o.
5
shares the same geometry as
1. Only difference is
5. The
5
Catalytic olefins oxidation. The formal potentials for the 1ꢀ5 in CH3CN have
been determined by cyclic voltammetry and are listed in S1. The cyclic
voltammograms for these complexes display reversible oxidation couples
assignable to the metalꢀcentered RuIII/RuII couples at range of 0.55ꢀ0.81 V.
One additional wave in more positive direct due to oxidation of the
bispyridylpyrrolide ligand is observed. The catalytic utility and selectivity of
1ꢀ5 was examined by the olefins oxidation. Variations in catalyst loading,
reaction times and solvents are summarized in S3. The yield of carbonyl

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product is dependent on catalyst, solvent and oxidant. The heterogeneous
solvent system EtOAcꢀCH3CNꢀH2O (ratio = 3:1:2) gave the highest yield. All
complexes
1ꢀ5 have similar catalytic activity. Thus, we chose 1 as a model for
catalytic olefin oxidation. Although 1 mol% of
1
performed very well in the
o
oxidative cleavage of styrene (98 % yield of benzaldehyde after 1 h at 30 C),
this low catalyst loading is not recommended for the cleavage of other olefins
such as cyclooctene since the conversion was only 48 % after 2 h. Thus, 3
mol % of
1 was used throughout the study.
o
A variety of olefins were subjected to this optimized condition at 30 C (Table 3).
Styrene and their derivatives were efficiently converted to the corresponding
aldehydes (entry 1). Better yield have been achieved with the substrates comprising of
electron donating group whereas lower yield is obtained for the substrates containing
electron withdrawing group. For the latter, besides the formation of benzaldehyde,
benzoic acid (~ 10%) was obtained as the side product. cisꢀStilbene and transꢀstilbene
offered quantitative yield to benzaldehyde (entry 2 and 3). In the case of
1,1ꢀdisubstitued styrene (entry 4 and 5), ketone products were gave with 82% and
64% yield, respectively, maybe due to the steric reason. The allkylbenzene, aliphatic
cyclic substrates such as cyclooctene and cyclohexene employed under identical
conditions and afforded medium yield (entry 6ꢀ8), however, longꢀchain olefins offered
the corresponding scission products in poor product yield (entry 9). In the case of
norbornylene, the formation of dialdehyde was facile (entry 10), probably due to the
release of ring strain upon oxidation. To extend to the terminal alkyne such as
phenylacetylene, good conversion is achieved to form benzoic acid (entry 11). When
the reaction time was extended to 24 h for lessꢀreactive substrates, higher yields were
achieved (entry 6ꢀ9 and 11), which suggested that active species from 1 remained
undiminished for a long time.
The mechanism of olefins oxidation catalyzed by ruthenium complexes has been
studied extensively so far. Generally, rutheniumꢀoxo, ꢀperoxo, and/or ꢀhydroperoxo
have been proposed to be active species or intermediates in oxidation reactions.3, 17 As

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mentioned in the introduction section, RuVIꢀcisꢀdioxo is the most active species in
catalytic oxidation olefins by [Ru(COD)(L)Br2] complex. Complex 1 has similar
coordination environment around ruthenium with that in [Ru(COD)(L)Br2], except of
bispyridylpyrrolide instead of naphthyridine ligand in [Ru(COD)(L)Br2]. There is a
similar plausible mechanism in our work, as shown in Scheme 2. It is likely that 1 is
oxidized by NaIO4 to give a RuVIꢀcisꢀdioxo intermediate, subsequently to form a RuIV
cycloadduct by [3+2] cycloaddition reaction. The following twoꢀelectron reduction
and cleavage of CꢀC bond leads to the corresponding carbonyl products. The key
proposed RuVIꢀcisꢀdioxo species from 1 was identified by ESIꢀMS analysis (Fig. S4).
ESIꢀMS of 1 in EtOAcꢀCH3CNꢀH2O (ratio = 3:1:2) exhibits the parent peak [1]+ at
m/z 465.1. Upon addition of 80 equiv of NaIO4 for 10 min, additional peak m/z 389.0
for [Ru(PDP)Cl + 2O]+ together with m/z 354.0 for [Ru(PDP) + 2O]+ appeared . The
signals in the range of m/z 340ꢀ470 changed with time. When the mixture above was
stirred for 1 h, the parent peak disappeared, and a minor peak at m/z 436.1 appeared,
which may be assigned to [Ru(PDP) + 2O + 2CH3CN]+. The observation of peaks
with two additional O atoms may be assigned as two oxo species, indicating of
formation of RuVIꢀcisꢀdioxo intermediate, namely [Ru(PDP)(O)2Cl]. The ESIꢀMS of
the resulting solution of olefins oxidation catalyzed by 1 was measured. The parent
ion peak changed to m/z 451.07 corresponding to [Ru(PDP) + CH3CN + EtOAc]+. It
was indicated that oxygen atom was probably transferred from RuVIꢀcisꢀdioxo species
to organic substrate, and PDPꢀ anion is tightly bound to Ru in the throughout catalytic
cycle.
Conclusions
In summary, a set of ruthenium complexes based on bispyridylpyrrole ligand
have been successfully synthesized. Structural analysis displays the PDPꢀ ligand
binds to ruthenium center with meridional geometry. The 3,4ꢀpositions of the
pyrrole ring was readily halogenated by treating the complex
1 but not the bare

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ligand with PhICl2.
1 is highly effective in the oxidative cleavage of olefins to
carbonyl products by NaIO4 in an aqueous/organic solvent mixture. The
RuVIꢀcisꢀdioxo intermediate is probably involved.
Acknowledgement
This work was supported by the National Natural Science Foundation of China
(project 21571190), and Grants from the Project of Innovationꢀdriven Plan in
Central South University (2015CXS004).
Notes and references
† Electronic Supplementary Information (ESI) available. CCDC reference numbers
1480593, 1483072ꢀ1483075 for complex 1ꢀ5, respectively. see DOI:
10.1039/b000000x/.
1
(a) H. S. Singh, In Organic Synthesis by Oxidation with Metal Compounds; W. J.
Mijs and C. R. H. I. De Jonge, Eds.; Plenum: New York, 1986; (b) R. A. Sheldon
and J. K. Kochi, Metal-Catalyzed Oxidations of Organic Compounds, Academic
Press, New York, 1981.
2
3
(a) A. Rajagopalan, M. Lara and W. Kroutil, Adv. Synth. Catal., 2013, 355,
3321ꢀ3335; (b) A. E. Kerenkan, F. Beland and T. O. Do, Catal. Sci. Technol.,
2016, 6, 971ꢀ987.
S. L.ꢀF. Chan, Y.ꢀH. Kan, K.ꢀL. Yip, J.ꢀS. Huang and C.ꢀM. Che, Coord. Chem.
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2462ꢀ2466; (b) C.ꢀH. Lee, C.ꢀL. Wu, S.ꢀA. Hua, Y.ꢀH. Liu, S.ꢀM. Peng and S.ꢀT.
Liu, Eur. J. Inorg. Chem., 2015, 2015, 1417ꢀ1423; (c) S. Ohzu, T. Ishizuka, Y.
Hirai, S. Fukuzumi and T. Kojima, Chem. Eur. J., 2013, 19, 1563ꢀ1567.
5
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P. Daw, R. Petakamsetty, A. Sarbajna, S. Laha, R. Ramapanicker and J. K. Bera, J.
Am. Chem. Soc., 2014, 136, 13987ꢀ13990.
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Sharpless, J. Org. Chem., 1981, 46, 3936ꢀ3938; (c) D. Yang and C. Zhang, J. Org.
Chem., 2001, 66, 4814ꢀ4818; (d) A. J. Bailey, W. P. Griffith, A. J. P. White and D.
J. Williams, J. Chem. Soc., Chem. Commun., 1994, 1833ꢀ1834.
7
(a) X.ꢀH. Hu, Y. Liang, C. Li and X.ꢀY. Yi, Dalton Transactions, 2014, 43,
2458ꢀ2464; (b) Y.ꢀP. Wang, J.ꢀJ. Xiao, X.ꢀH. Hu and X.ꢀY. Yi, Inorg. Chim. Acta,
2015, 435, 125ꢀ130; (c) W. Z. Fang, Y. P. Wang, Y. F. Wang, S. C. Zhang and X. Y.
Yi, Rsc Advances, 2015, 5, 8996ꢀ9001; (d) Y.ꢀP. Wang, X.ꢀH. Hu, Y.ꢀF. Wang, J.
Pan and X.ꢀY. Yi, Polyhedron, 2015, 102, 782ꢀ787.
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J. W. Ciszek, Z. K. Keane, L. Cheng, M. P. Stewart, L. H. Yu, D. Natelson and J.
M. Tour, J. Am. Chem. Soc., 2006, 128, 3179ꢀ3189.
G. H. Imler, Z. Lu, K. A. Kistler, P. J. Carroll, B. B. Wayland and M. J. Zdilla,
Inorg. Chem., 2012, 51, 10122ꢀ10128.
10 K. Nomura, H. Sato, K. Kobayashi and M. Kobayashi, WO2014050578ꢀA1;
JP2014082190ꢀA; TW201412887ꢀA; KR2015032894ꢀA; EP2903079ꢀA1.
11 A. McSkimming, V. Diachenko, R. London, K. Olrich, C. J. Onie, M. M.
Bhadbhade, M. P. Bucknall, R. W. Read and S. B. Colbran, Chem. Eur. J., 2014,
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Seaman, A. P. Whitmore and D. J. Williamson, Tetrahedron, 1996, 52,
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Soc., 2010, 132, 713ꢀ724.

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Scheme 1 the preparation of complexes 1ꢀ5.

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Scheme 2 Plausible mechanism for olefins oxidation catalyzed by 1.
Cl
N
O
N
Ru
O
N
RuVI-cis-dioxo intermediate
R1
R2
R3
R4
carbonyl products
NaIO4
NaIO4
Cl
Cl
1
N
N
N
Ru
O
N
Ru
O
O
R3
R4
R4
N
O
N
R3
R2
R1
R1
R2

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Table 1 Xꢀray Crystallographic Data for 1ꢀ5.

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ꢀ
1
2
3
4+·BF4
5
Formula
fw
C22H22ClN3Ru
464.95
Monoclinic
P21/c
C22H22N4O3Ru
491.50
C23H22F3N3O3RuS
1157.13
Monoclinic
P21/c
C22H24BF4N3ORu
534.32
C22H20Cl3N3Ru
533.83
Orthorhombic
ꢀP2ac2ab
16.7129(5)
7.7974(2)
31.1102(8)
90
crystal system
Space group
a, Å
Monoclinic
P21/c
Triclinic
—
P1
13.7766(4)
8.1417(3)
16.7532(6)
90
16.181(2)
9.1454(15)
13.653(2)
90.00
11.2980(6)
27.7584(14)
15.1162(7)
90.00
7.9945(2)
11.5727(2)
12.2086(2)
98.6740(10)
105.5400(10)
90.7500(10)
1074.08(4)
2
b, Å
c, Å
α, deg
β, deg
γ, deg
104.071(2)
90
102.043(6)
90.00
108.956(3)
90.00
90
90
V, Å3
1822.74(11)
4
1975.9(5)
4
4483.6(4)
4
4054.19(19)
8
Z
ρcalc, g cmꢀ3
1.694
1.652
1.714
1.652
1.749
T, K
120(2)
293(2)
296(2)
296(2)
296(2)
ꢁ, mmꢀ1
F(000)
1.019
0.826
0.850
0.784
1.184
944
1000
2336
540
2144
No. of reflection
16332
10716
29573
37556
25005
No. of independent reflection
4020
4476
10072
4947
4643

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Rint
0.0503
1.017
0.0370
1.018
0.0446
1.024
0.0226
1.026
0.0283
1.019
Goodnessꢀofꢀfit (GOF)a
R1, b wR2 c [I > 2σ(I)]
0.0295, 0.0583
0.0578, 0.0680
0.0367, 0.0884
0.0669, 0.1044
0.0508, 0.1048
0.1111, 0.1325
0.0538, 0.1776
0.0667, 0.2031
0.0489, 0.1071
0.0400, 0.1010
R1, wR2 (all data)
½
aGoF = [Σw(|Fo| − |Fc|)2/(Nobs − Nparam)] . bR1 = Σ||Fo| − |Fc||/Σ|Fo|. cwR2 [(Σw|Fo| − |Fc|)2/Σw2|Fo|2]½

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Table 2 Selected bond distances (Å) and bond angles (o) of 1ꢀ5.
Bond distances (Å)
Bond angles (o)
NpyꢀRuꢀNpy
Complex RuꢀNpyr RuꢀNpy
2.169(2)
RuꢀCCOD
RuꢀX
NpyrꢀRuꢀNpy
’
2.189(3)
2.218(3)
RuꢀCl
74.27(9)
74.25(9)
1.964(2)
1.963(3)
1.960(4)
146.38(9)
1
2
3
2.185(2)
2.184(3)
2.185(3)
2.186(4)
2.187(4)
2.189(5)
2.192(5)
2.189(5)
2.188(3)
2.4243(7)
RuꢀO(NO3)
2.124(2)
RuꢀO(OTf)
2.190(3)
RuꢀO(H2O)
2.131(4)
RuꢀCl
2.171(4)
2.208(3)
74.81(11)
74.02(11)
145.96(11)
146.09(16)
146.0(2)
2.158(5)
2.234(5)
2.162(6)
2.204(6)
2.201(3)
2.212(3)
74.32(17)
74.42(17)
73.9(2)
4+·BF4 1.960(5)
ꢀ
74.8(2)
74.20(11)
74.44(11)
1.971(3)
146.74(10)
5
2.4139(9)

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a
Table 3. Oxidative cleavage of olefins by
1
with NaIO4
Entry
1
Substrate
Product
Time (h)
1
Yield (%)
95, 95, 85, 90
O
R
R
1
97
(R=H, OMe, F, Br)
2
Ph
O
Ph
O
3
4
Ph
Ph
1
2
99
82
O
O
5
6
2
64
O
2
24
2
32
56
O
O
O
38
O
7
8
24
2
69
O
n
n
80
(n=1, 3,5)
OHC
CHO
24
2
90
O
3, 22, 10
13, 21, 27
OH
9
24
10
1
100
2
63
86
11b
24
a Reaction conditions: 0.1 mmol of substrate, 3 mol% catalyst 1, 0.25 mmol of NaIO4,
EtOAcꢀCH3CNꢀH2O (ratio = 3:1:2) solvent system, 30 oC, yield determined by GC.
b two drops of con. H2SO4 was added.

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Figure 1 ORTEP diagram of 1 with ellipsoids shown at the 50% probability level. The
hydrogen atoms are omitted for clarity.

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Figure 2 ORTEP diagram of 2 with ellipsoids shown at the 30% probability level. The
hydrogen atoms are omitted for clarity.

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Figure 3 ORTEP diagram of 3 with ellipsoids shown at the 50% probability level. The
hydrogen atoms are omitted for clarity.

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ꢀ
Figure 4 ORTEP diagram of 4+·BF4 with ellipsoids shown at the 50% probability
level. The hydrogen atoms are omitted for clarity.

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Figure 5 ORTEP diagram of 5 with ellipsoids shown at the 50% probability level. The
hydrogen atoms are omitted for clarity.