Tunable Electrochemical and Catalytic Features of BIAN- and BIAO-Derived Ruthenium Complexes

Article abstract of DOI:10.1021/acs.inorgchem.5b00615

This article deals with a class of ruthenium-BIAN-derived complexes, [Ru^II(tpm)(R-BIAN)Cl]ClO₄ (tpm = tris(1-pyrazolyl)methane, R-BIAN = bis(arylimino)acenaphthene, R = 4-OMe ([1a]ClO₄), 4-F ([1b]ClO₄), 4-Cl ([1c]ClO₄), 4-NO₂ ([1d]ClO₄)) and [Ru^II(tpm)(OMe-BIAN)H₂O]²⁺ ([3a](ClO₄)₂). The R-BIAN framework with R = H, however, leads to the selective formation of partially hydrolyzed BIAO ([N-(phenyl)imino]acenapthenone)-derived complex [Ru^II(tpm)(BIAO)Cl]ClO₄ ([2]ClO₄). The redox-sensitive bond parameters involving -N=C-C=N- or -Ni=C-C=O of BIAN or BIAO in the crystals of representative [1a]ClO₄, [3a](PF₆)₂, or [2]ClO₄ establish its unreduced form. The chloro derivatives 1a⁺-1d⁺ and 2⁺ exhibit one oxidation and successive reduction processes in CH₃CN within the potential limit of ±2.0 V versus SCE, and the redox potentials follow the order 1a⁺ < 1b⁺ < 1c⁺ < 1d⁺ ≈ 2⁺. The electronic structural aspects of 1aⁿ-1dⁿ and 2ⁿ (n = +2, +1, 0, -1, -2, -3) have been assessed by UV-vis and EPR spectroelectrochemistry, DFT-calculated MO compositions, and Mulliken spin density distributions in paramagnetic intermediate states which reveal metal-based (Ru^II → Ru^III) oxidation and primarily BIAN- or BIAO-based successive reduction processes. The aqua complex 3a²⁺ undergoes two proton-coupled redox processes at 0.56 and 0.85 V versus SCE in phosphate buffer (pH 7) corresponding to {Ru^II-H₂O}/{Ru^III-OH} and {Ru^III-OH}/{Ru^IV=O}, respectively. The chloro (1a⁺-1d⁺) and aqua (3a²⁺) derivatives are found to be equally active in functioning as efficient precatalysts toward the epoxidation of a wide variety of alkenes in the presence of PhI(OAc)₂ as oxidant in CH₂Cl₂ at 298 K, though the analogous 2⁺ remains virtually inactive. The detailed experimental analysis with the representative precatalyst 1a⁺ suggests the involvement of the active {Ru^IV=O} species in the catalytic cycle, and the reaction proceeds through the radical mechanism, as also supported by the DFT calculations.

Full text of DOI:10.1021/acs.inorgchem.5b00615

Article
pubs.acs.org/IC
Tunable Electrochemical and Catalytic Features of BIAN- and BIAO-
Derived Ruthenium Complexes
†
†
†
†
†
‡
Arijit Singha Hazari, Ankita Das, Ritwika Ray, Hemlata Agarwala, Somnath Maji, Shaikh M. Mobin,
,
†
and Goutam Kumar Lahiri*
†
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
‡
Discipline of Chemistry, School of Basic Sciences, Indian Institute of Technology Indore, Indore 452017, India
*
S Supporting Information
ABSTRACT: This article deals with a class of ruthenium−BIAN-derived
II
complexes, [Ru (tpm)(R-BIAN)Cl]ClO (tpm = tris(1-pyrazolyl)methane, R-
4
BIAN = bis(arylimino)acenaphthene, R = 4-OMe ([1a]ClO ), 4-F ([1b]-
4
II
ClO ), 4-Cl ([1c]ClO ), 4-NO ([1d]ClO )) and [Ru (tpm)(OMe-BIAN)-
4
4
2
4
2+
H O] ([3a](ClO ) ). The R-BIAN framework with R = H, however, leads to
2
4 2
the selective formation of partially hydrolyzed BIAO ([N-(phenyl)imino]-
II
acenapthenone)-derived complex [Ru (tpm)(BIAO)Cl]ClO ([2]ClO ). The
4
4
redox-sensitive bond parameters involving NC−CN or NC−
CO of BIAN or BIAO in the crystals of representative [1a]ClO ,
4
[
1
3a](PF ) , or [2]ClO establish its unreduced form. The chloro derivatives
a −1d and 2 exhibit one oxidation and successive reduction processes in
6 2 4
+
+
+
CH CN within the potential limit of ±2.0 V versus SCE, and the redox
3
+
+
+
+
+
potentials follow the order 1a < 1b < 1c < 1d ≈ 2 . The electronic
n
n
n
structural aspects of 1a −1d and 2 (n = +2, +1, 0, −1, −2, −3) have been assessed by UV−vis and EPR
spectroelectrochemistry, DFT-calculated MO compositions, and Mulliken spin density distributions in paramagnetic
II
III
intermediate states which reveal metal-based (Ru → Ru ) oxidation and primarily BIAN- or BIAO-based successive reduction
processes. The aqua complex 3a undergoes two proton-coupled redox processes at 0.56 and 0.85 V versus SCE in phosphate
2
+
II
III
III
IV
+
+
buffer (pH 7) corresponding to {Ru −H O}/{Ru −OH} and {Ru −OH}/{Ru O}, respectively. The chloro (1a −1d )
2
2+
and aqua (3a ) derivatives are found to be equally active in functioning as efficient precatalysts toward the epoxidation of a wide
+
variety of alkenes in the presence of PhI(OAc) as oxidant in CH Cl at 298 K, though the analogous 2 remains virtually
2
2
2
+
IV
inactive. The detailed experimental analysis with the representative precatalyst 1a suggests the involvement of the active {Ru 
O} species in the catalytic cycle, and the reaction proceeds through the radical mechanism, as also supported by the DFT
calculations.
INTRODUCTION
recently been employed in catalysis and to understand other
■
2
fundamental issues. The corresponding ruthenium complexes
The ruthenium complexes of α-diimine (NC−CN)-
derived ligands have drawn significant attention over the
decades primarily due to their diverse applications in dye-
sensitized solar cells, molecular electronics, sensor technology,
homogeneous catalysis, biomedical research, and supramolec-
3
of BIAN are however limited to a few recent reports, dealing
primarily with the structural and electronic aspects as well as
their potential applications in catalysis.
The low-lying unoccupied molecular orbitals of BIAN, π*(α-
diimine) (5b2) and π*(naphthalene) (4a2), facilitate the
successive electron uptake processes particularly on metalation,
which in turn provides a multielectron reservoir platform
1
ular chemistry. In this regard, metal complexes (main group as
well as transition elements) of the robust framework of
bis(arylimino)acenaphthene (BIAN) involving α-diimine frag-
ment conjugated with the naphthalene ring (Chart 1) have
3
b−d,2m
suitable for selective application in catalysis.
The
tetraanionic state of 1,2-bis[(2,6-diisopropylphenyl)imino]-
2n
acenaphthene has also been reported, involving the stepwise
two-electron reductions of the α-diimine group followed by the
addition of two more electrons over the multiple cation (Na )
Chart 1. Representation of R-BIAN and BIAO
+
coordinated naphthalene π system.
The structural rigidity, stereoelectronic tunability based on
the “R” groups (Chart 1), and facile successive electron-
Received: March 18, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Chart 2. Representation of Complexes
accepting feature of BIAN collectively make it an attractive
ligand to design metal complexes suitable for electron-transfer
processes and catalytic application.
perchlorate salts are purified by column chromatography on a
neutral alumina column using 4:1 CH Cl −CH CN mixture as
2
2
3
eluant. To our surprise, under identical reaction conditions the
use of R-BIAN with R = H (Charts 1 and 2) selectively results
In view of the aforestated unique features of BIAN, the
present article is centered around the designing of ruthenium−
in [2]ClO (blue powder) encompassing [N-(phenyl)imino]-
4
II
+
BIAN-based complexes (Chart 2) of [Ru (tpm)(R-BIAN)Cl]
acenapthenone (BIAO) via the hydrolysis of one of the imine
8
+
(
tpm = tris(1-pyrazolyl)methane, R-BIAN = bis(arylimino)-
bonds (CNPh → CO) of BIAN. Complex 2
+
+
+
acenaphthene, R = 4-OMe (1a ), 4-F (1b ), 4-Cl (1c ), 4-NO
2
represents the first example of a ruthenium-coordinated BIAO
+
II
2+
2+
9
10
10
(1d )), [Ru (tpm) (OMe-BIAN)H O] (3a ), as well as
2
ligand; the corresponding mercury, cobalt, copper, and
1
1
partially in-situ-hydrolyzed BIAO for R = H (BIAO: [N-
zinc complexes were however reported recently. The
representative yellow-colored aqua derivative [Ru (tpm)(4-
II
(
phenyl)imino] acenapthenone) derived [Ru (tpm)(BIAO)-
II
+
+
Cl] (2 ) with the broader perspectives of understanding their
electronic structural aspects and catalytic potential.
OMe-BIAN)(H O)](ClO ) [3a](ClO ) (Chart 2) has been
2
4 2
4 2
prepared from the corresponding chloro derivative ([1a]ClO4)
Herein, we report the synthesis and characterization of
in the presence of excess AgClO in refluxing 1:3 acetone−
4
[
1a]ClO −[1d]ClO , [2]ClO , and [3a](ClO ) , molecular
12,13
4
4
4
4 2
water via the Cl/H O exchange process.
2
structures of representative [1a]ClO , [2]ClO , and [3a]-
4
4
The complexes exhibit satisfactory microanalytical data and
(
PF ) , and assessment of electronic structures of the chloro
6 2
molar conductivities in CH CN (Experimental Section). The
n
n
n
3
derivatives 1a −1d and 2 (n = +2, +1, 0, −1, −2, −3) in
accessible redox states via structure, UV−vis, and EPR
spectroelectrochemistry in conjunction with DFT/TD-DFT
calculations. The significant impact of “R” groups in the BIAN
frameworks in 1a −1d and BIAO in 2 on the redox processes
has also been highlighted.
ESI mass spectral data of [1a]ClO -[1d]ClO , [2]ClO , and
4
4
4
[
3a](ClO ) in CH CN and CH OH, respectively, match with
4 2 3 3
their calculated values (Figure S1, Supporting Information and
Experimental Section).
+
+
+
The molecular identities of the representative complexes
[1a]ClO , [2]ClO , and [3a](PF ) are authenticated by their
+
+
+
2+
4
4
6 2
Further, the potential of 1a −1d /2 or 3a involving the
II
II
single-crystal X-ray structures (Figures 1−3; Tables 1, 2, and
S1, Supporting Information). We failed to generate suitable
labile Ru −Cl or Ru −OH bond, respectively, as precatalyst
for the epoxidation of a wide variety of alkenes has been
2
single crystal for [3a](ClO ) ; however, the corresponding
explored with special references to (i) “R” groups in BIAN, (ii)
4 2
II
II
[3a](PF ) results in a single crystal suitable for its structure
{
Ru −Cl} versus {Ru −H O}, and (iii) BIAN versus BIAO.
6 2
2
The limitation of the traditional method for epoxidation of
alkenes by simple organic peracids involving the narrow
substrate scope and inconvenience in product separation has
4
led to introduction of the metal complex-catalyzed efficient
5
epoxidation process in the presence of suitable oxidants. In
this context, the initial report of Nishiyama et al. of ruthenium
complex/TBHP (tert-butylhydroperoxide) catalyzed epoxida-
6
tion of olefins in 1997 has spurred the subsequent utilization
of varying ruthenium complexes in combination with suitable
7
oxidants for the epoxidation reactions.
RESULTS AND DISCUSSION
■
Synthesis, General Characterization, and Structure.
The 1:1 electrolytic and diamagnetic complexes [Ru (tpm)(R-
II
BIAN)Cl]ClO (red powder) (tpm = tris(1-pyrazolyl)methane
4
and BIAN = bis(arylimino)acenaphthene, R = 4-OMe
[
1a]ClO , 4-F [1b]ClO , 4-Cl [1c]ClO , 4-NO [1d]ClO )
4 4 4 2 4
III
1
4
have been prepared from the metal precursor Ru (tpm)Cl in
combination with respective R-BIAN in refluxing methanol
3
Figure 1. ORTEP diagram of the cationic part of [1a]ClO4·
−
2CH Cl . Ellipsoids are drawn at the 50% probability level. ClO
2
2
4
under a dinitrogen atmosphere (Charts 1 and 2). The isolated
anion, hydrogen atoms, and solvent molecules are omitted for clarity.
B
DOI: 10.1021/acs.inorgchem.5b00615
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Inorganic Chemistry
Article
and [3a](PF ) match fairly well with those of the reported
6
2
analogous systems.
The feasibility of accepting successive two electrons by the
low-lying π* orbitals of the conjugated NC−CN (α-
diimine) or NC−CO (α-ketoimine) fragment of BIAN
or BIAO, respectively, leads to the three redox states, fully
oxidized neutral form (A) to intermediate one-electron reduced
radical state (B) to doubly reduced dianionic form (C)
(
Scheme 1) with distinctive C−N (1.30, 1.35, 1.38 Å), C−O
(
1.25, 1.28, 1.31 Å), and C−C (≥1.47, ∼1.43, ∼1.38 Å) bond
3a−c
distances, respectively.
The experimentally observed single-
bond C−C length [C8−C18 = 1.469(4) ([1a]ClO ) and
4
1
.476(7) Å ([3a](PF ) ), C7−C17 = 1.474(4) Å ([2]ClO )]
6
2
4
and double bond C−N length [C8−N1/C18−N2 = 1.298(4)/
1
.307(3) ([1a]ClO ) and 1.291(6)/1.299(6) Å ([3a](PF ) )
4
6 2
and C7−N1/C17−O1 1.303(3)/1.249(3) Å ([2]ClO )],
4
however, unequivocally establish that the unreduced form of
BIAN or BIAO links to the ruthenium(II) ion in the complexes.
The calculated bond parameters of 1a −1d , 2 , and 3a
1
4
Figure 2. ORTEP diagram of the cationic part of [2]ClO . Ellipsoids
+
+
+
2+
4
−
are drawn at the 40% probability level. ClO4 anion and hydrogen
atoms are omitted for clarity.
based on their DFT-optimized structures (B3LYP-LANL2DZ/
SDD basis set) in the singlet ground state (S = 0) (Table 2 and
Tables S2−S11, Figure S2, Supporting Information) match
fairly well with the X-ray data of representative complexes.
The IR spectra (KBr pellets) of [1a]ClO −[1d]ClO ,
4
4
−
[
2]ClO , and [3a](ClO ) display characteristic strong ClO
4
4 2
4
−1
3a
vibrations at around 1100 and 625 cm , the CO vibration
−1
17
of [2]ClO at 1690 cm , and OH vibration of [3a](ClO )
4
4 2
−1
13a
at 3438 cm
(Experimental Section).
1
+
+
+
H NMR spectra of 1a −1d and 2 in CDCl (Figures 4 and
S3, Supporting Information and Experimental Section) and
a in D O (Figure 4) display partially overlapping calculated
3
2
+
3
2
number of aromatic proton resonances (tpm = 9, BIAN = 14,
BIAO = 11) within the chemical shift range δ 6−9 ppm. The
+
+
+
slightly acidic CH proton resonance of tpm for 1a −1d or 2
appears at a sharp and moderately strong singlet at δ ∼10
13
2+
ppm; however, the same for 3a in D O resolves as a weak
2
but distinct peak at δ 9.7 ppm. The proton resonances
1
4
associated with the six-membered rings of BIAN or BIAO in
Figure 3. ORTEP diagram of the dicationic part of [3a](PF ) ·
6
2
+
+
2+
+
−
C H O. Ellipsoids are drawn at the 40% probability level. PF anions,
hydrogen atoms, and solvent molecule are omitted for clarity.
1a −1d /3a or 2 , respectively, can easily be distinguished
from those of the five-membered rings of tpm, primarily based
on their difference in spin−spin coupling constant (J/Hz)
3
6
6
3
a,13
values (7−8 for BIAN or BIAO and 2−3 for tpm).
The
+
2+
determination. The tridentate tpm ligand is bonded to the
metal ion in [1a]ClO or [2]ClO or [3a](PF ) through its
pyrazolyl nitrogen donors in the usual facial mode, resulting in
two shared six-membered chelates. The N,N or N,O donors
OMe signal for 1a or 3a appears at δ/ppm 3.80 or 3.79,
respectively. The variation of chemical shift values based on the
4
4
6 2
+
+
substituents at the BIAN framework in 1a −1d is rather
13
insignificant.
of BIAN or BIAO in [1a]ClO /[3a](PF ) or [2]ClO4,
Electrochemistry, MO Composition, and Spin Density
4
6 2
+
+
+
respectively, form a five-membered chelate with the metal
ion. The bite angles of the six-membered chelates involving the
tpm ligand, N3−Ru1−N5 (86.37(10)°)/N5−Ru1−N8
Distribution. The chloro derivatives 1a −1c and 2 exhibit
similar electrochemical features with one oxidation (O1) and
two successive reductions (R1 and R2), while complex 1d+
(
(
(
83.87(9)°), N2−Ru1−N4 (85.16(9)°)/N4−Ru1−N7
85.73(9)°), and N3−Ru1−N5 (85.86 (15)°)/N5−Ru1−N8
83.49(17)°), are appreciably larger than those of the
incorporating para-NO
2
-substituted BIAN (Chart 2) possesses
CN
one oxidation (O1) and four reductions (R1−R4) in CH
3
within the potential window of ±2.0 V versus SCE (Figure 5,
corresponding five-membered chelates involving BIAN, N1−
Table 3).
+
+
Ru1−N2 (79.08(10)°) in [1a]ClO , N1−Ru1−N2
The redox potentials of 1a −1d vary systematically
depending on the electron-donating or -withdrawing effect of
the substituents in the BIAN framework, and it follows the
4
(
78.59(16)°) in [3a](PF ) or BIAO, and N1−Ru1−O1
6
2
(
80.14(8)°) in [2]ClO (Table S1, Supporting Information).
4
+
+
+
+
This in conjunction with the smaller average trans angles,
76.60°, 176.91°, and 176.71° in [1a]ClO , [2]ClO , and
order 1a < 1b < 1c < 1d . The impact of the NC−C
+
1
O chromophore of BIAO in 2 with regard to the NC−
4
4
+
+
[
3a](PF ) , respectively (Table S1, Supporting Information),
suggest distorted octahedral geometries.
The Ru −N(tpm), Ru −N(BIAN),
and Ru −O(H O)
CN fragment of BIAN in analogous 1a −1d has been
6
2
reflected in its relatively higher oxidation potential (0.93 V),
II
13
II
3a−c
II
13a,b,15
Ru −Cl,
even comparable to that of the para-NO -substituted BIAN in
2
II
13a,b,16
+
bond lengths in [1a]ClO , [2]ClO ,
1d (0.94 V).
2
4
4
C
DOI: 10.1021/acs.inorgchem.5b00615
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Inorganic Chemistry
Article
Table 1. Selected Crystallographic Data for [1a]ClO , [2]ClO , and [3a](PF )
4
4
6 2
[
1a]ClO ·2CH Cl
[2]ClO4
[3a](PF ) ·C H O
6 2 3 6
4
2
2
empirical formula
C H Cl N O Ru
C H Cl N O Ru
C H N O F P Ru
39 38 8 4 12 2
3
8
34
6
8
6
28 21
2
7
5
fw
1012.50
707.49
1073.78
cryst syst
monoclinic
monoclinic
triclinic
space group
a (Å)
P2 /n
P2 /c
P-1
1
1
11.7233 (3)
17.2500 (4)
20.1702 (5)
90
14.48414 (14)
12.64471 (11)
15.76167 (15)
90
11.650 (2)
14.944 (3)
16.267 (3)
71.09 (3)
69.90 (3)
72.02 (3)
2453.3 (9)
2
b (Å)
c (Å)
α (deg)
β (deg)
94.8260 (10)
90
92.8914 (9)
90
γ (deg)
V (Å3)
4064.50 (17)
4
2883.04 (5)
13
Z
μ (mm−1)
0.838
6.554
0.476
T (K)
100 (2)
150 (2)
100 (2)
1.454
Dcalcd (g cm−3)
F(000)
1.655
1.630
2048
1424
1084
θ range (deg)
data/restraints/params
R1, wR2 [I > 2σ(I)]
R1, wR2(all data)
GOF
1.55−29.78
11 546/0/534
0.0520, 0.1223
0.0776, 0.1368
1.048
3.05−72.16
5627/0/388
0.0357, 0.1031
0.0376, 0.1058
1.057
1.48−24.29
7908/1/607
0.0584, 0.1396
0.0864, 0.1508
1.001
largest diff. peak/hole (e Å−3)
1.60/−1.06
0.56/−0.51
1.18/−0.71
Table 2. Experimental and DFT-Calculated Selected Bond Lengths (Angstroms) for [1a]ClO , [2]ClO , and [3a](PF )
4
4
6 2
[1a]ClO4
[2]ClO4
[3a](PF6)2
X-ray
DFT
X-ray
DFT
X-ray
DFT
Ru1−N1
Ru1−N2
Ru1−N3
Ru1−N4
Ru1−N5
Ru1−N7
Ru1−N8
Ru1−O1
Ru1−Cl1
C8−N1
C18−N2
C7−C17
C8−C18
C17−O1
C6−N1
2.021(2)
2.033(2)
2.047(3)
2.088
2.087
2.118
2.020(2)
2.057(2)
2.077
2.112
2.038(4)
2.036(4)
2.023(4)
2.104
2.116
2.070
2.068(2)
2.042(2)
2.095
2.071
2.070(2)
2.083(2)
2.127
2.129
2.075(4)
2.147
2.060(5)
2.126(4)
2.133
2.218
2.0818(19)
2.3690(7)
2.108
2.391
2.3965(8)
1.298(4)
1.307(3)
2.430
1.302
1.302
1.291(6)
1.299(6)
1.303
1.306
1.474(4)
1.490
1.469(4)
1.483
1.476(7)
1.495
1.249(3)
1.443(3)
1.303(3)
1.252
1.428
1.307
C7−N1
C20−N2
1.445(4)
1.430(4)
1.428
1.428
1.446(6)
1.419(6)
1.430
1.431
2
+
2+ 2+
Scheme 1. Varying Redox States of BIAN and BIAO
LUMO of 1a −1d /2 in the S = 1/2 state (>60%) as well as
metal-dominated spin (>0.75) collectively suggest the corre-
II
III
spondences of O1 to a Ru → Ru oxidation process. In
consequence, the redox-sensitive C−C, C−N, and C−O bond
distances of BIAN and BIAO remain virtually invariant on the
oxidation process (O1) (Scheme 1, Tables 6 and S2, S4, S6, S8,
and S10, Supporting Information). The metal-based oxidation
process has been further evidenced by the highly anisotropic
2
+
EPR spectrum of coulometrically oxidized representative 1a
with g = 2.674, g = 2.212, g = 1.769, Δg = 0.905, ⟨g⟩ = 2.248
22
+
+
+
The origin of the redox processes of 1a −1d and 2 (Figure
1
2
3
2
1
2
2
3
1/2
(
Δg = g − g and ⟨g⟩ = {1/3(g + g + g )} ) (Figure 7a).
5
, Table 3) has been ascertained via the DFT-calculated MO
1
3
2
It should be noted that an appreciable contribution of Cl in
compositions (Tables 4 and S12−S34, Supporting Informa-
tion) and Mulliken spin density distributions (Table 5 and
Figure 6) in paramagnetic intermediate states. The metal-based
+
+
+
2+
the HOMO of 1a −1d /2 (>20%) and β-LUMO of 1a −
1d /2 (9−14%) has also been predicted due to the effect of
Ru−Cl covalency. A similar sizable Cl contribution in the DFT-
2+
2+
+
+
+
HOMO of 1a −1d /2 in the S = 0 state (∼60%) and β-
D
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
Figure 4. H NMR spectra of (i) [1a]ClO , (ii) [2]ClO in CDCl ,
4
4
3
and (iii) [3a](ClO ) in D O (t = tpm, b = BIAN or BIAO).
4
2
2
calculated MOs has also been pointed out earlier in analogous
23
Figure 5. Cyclic voltammograms of (i) [1a]ClO , (ii) [1b]ClO , (iii)
4
4
ruthenium complexes.
The presence of two strong π-acceptor ligands, BIAN and
3
[1c]ClO
4
, (iv) [1d]ClO
4
, and (v) [2]ClO
4
in CH
3
CN. (Inset) Cyclic
voltammograms (black) and differential pulse voltammograms (green)
of reversible oxidation (O1) and first reduction (R1) couples.
1
3
tpm, in the complexes raises the pertinent question of their
specific involvements in the successive reduction processes
(
Figure 5). The greater than 80% BIAN/BIAO contribution in
+
+
+
2−
the LUMO of 1a −1d /2 (S = 0) and SOMO of 1a−1d/2 (S
=
SOMO of 1d (S = 1/2) as well as 98% BIAN-dominated spin
2−
1/2) as well as NC−CN (BIAN)/NC−C
in 1d ) and a mixed tpm−BIAN-based situation, respectively
(α-LUMO of 1d2 (S = 1/2) = 88% tpm, SOMO of 1d (S =
− 3−
O (BIAO) dominated spin (>90%) (Table 4), however,
supports the BIAN/BIAO-based first reduction process (R1 in
Figure 5). This has been further supported by the free radical
EPR with g = 2.001 (line width = 25 G) for the
electrogenerated representative 2 (Figure 7b). On the other
hand, the mixed MO compositions of β-LUMO (BIAN/tpm,
3−
1) = 68% tpm/28% BIAN, and spin density of 1d
BIAN(0.998)/tpm(0.951)).
Remarkably, the appreciable positive shift of the redox
potential on selective incorporation of the electron-withdrawing
=
22
+
NO group in the BIAN framework in 1d (Table 3, Figure 5)
2
5
2
8
0−60%/30−40%; BIAO/tpm, 69/25%) in 1a−1c or 2 (S = 1/
facilitates detecting two additional reductions (R3 and R4)
) and HOMO (BIAN/tpm, 61−83%/10−37%; BIAO/tpm,
covering the NO function/naphthalene ring of BIAN as well as
2
−
−
−
1/12%) in 1a −1c or 2 (S = 0) suggest the partial
the reduction of tpm as has been revealed by MO compositions
and spin density plots.
involvement of tpm along with the BIAN- or BIAO-based
orbitals in the second reduction process (R2 in Figure 5). On
the contrary, the β-LUMO of 1d (S = 1/2, BIAN, 96%) and
The representative aqua derivative 3a2+ displays two
successive one-electron oxidation processes, E°298,V (ΔE ,
p
−
HOMO of 1d (S = 0, BIAN 89%) imply solely a BIAN (
mV) at 0.56(60) and 0.85(70) in phosphate buffer versus SCE
at pH 7.0, which undergo anodic shifting with lowering pH
(Figure S4, Table S35, Supporting Information), attributed to
the simultaneous one-electron/one-proton transfer processes,
NC−CN function) based second reduction (R2 in
Figure 5). The involvement of BIAN (NC−CN) or
BIAO (NC−CO) in successive electron uptake
processes (R1 and R2) finds further justification via the
sequential shortening and lengthening of the DFT-calculated
redox-sensitive C−C and C−N/C−O bond distances,
respectively (Scheme 1, Table 6 and S2, S4, S6, S8, and S10,
IV
II
III
leading to the {Ru O} state: Ru −OH /Ru −OH and
2
III
IV
13a,24
Ru −OH/Ru O.
Unfortunately, we failed to check the
shift in potential of 3a2+ with the further change in pH
primarily due to the associated precipitation problem.
The comparison of the oxidation potentials of the chloro
Supporting Information). The subsequent two reductions R3
and R4 of 1d in Figure 5 essentially involve the NO group of
BIAN (∼95% BIAN contribution in LUMO of 1d (S = 0) and
+
+
+
+
2+
(1a −1d , 2 ) and aqua (3a ) derivatives with the reported
analogous {Ru (tpm)(L)Cl} and {Ru (tpm)(L)H O} com-
2
−
II
II
2
E
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 3. Electrochemical Data
b
E°298/V (ΔE /mV)
p
complex
O1
O2
R1
R2
R3
R4
ref
chloro derivatives
−1.12(60)
−1.01(70)
−0.94(70)
−0.77(60)
c
[
[
[
[
[
[
[
[
[
[
[
[
[
1a]ClO4
1b]ClO4
0.77(60)
0.82(60)
0.87(70)
0.94(60)
0.93(90)
0.82
−1.57(120)
−1.54(70)
−1.43(220)
−0.85(60)
−1.32(230)
this work
this work
this work
this work
this work
13a
c
c
1c]ClO4
c
d
1d]ClO4
−1.31(180)
−1.71
c
2]ClO4
II
−0.62(70)
1
c
Ru tpm(L )Cl]ClO
4
II
2
c
Ru tpm(L )Cl]Cl
0.68
18
II
3
e
Ru tpm(L )Cl]Cl
0.65
19
II
4
e
Ru tpm(L )Cl]BF
0.83
20
4
II
5
e
Ru tpm(L )Cl]
0.24
20
II
6
e
Ru tpm(L )Cl]BF
0.79
13b
4
II
7
e
Ru tpm(L )Cl]
0.22
13b
II
8
c
Ru tpm(L )Cl]ClO
1.02
21
4
aqua derivatives
f
[
[
[
[
[
[
[
[
3a](ClO )
0.56(60)
0.44
0.85(70)
0.64
this work
13a
18
4
2
1
II
g
Ru tpm(L )OH ](ClO )
2
4
2
II
2
h
2
Ru tpm(L )OH ](ClO )
0.40
0.71
2
4
II
3
I
Ru tpm(L )OH ](PF )
6 2
1.00
19
2
II
4
j
Ru tpm(L )OH ](BF )
4 2
0.38
20
2
II
5
j
Ru tpm(L )OH ]BF
0.17
0.37
20
2
4
II
6
j
Ru tpm(L )OH ](PF )
6 2
0.38
13b
13b
2
II
7
j
Ru tpm(L )OH ]PF
0.16
2
6
a
1
2
3
4
L : o-benzoquinonediimine. L : 2,2′-bipyridine. L : 4-methyl-4′-(N-phenothiazylmethy1)-2,2′-bipyridine. L : 4,4′-dibenzyl-4,4′,5,5′-tetrahydro-2,2′-
5
6
bioxazole. L : 2-[((1′S)-1′-(hydroxymethyl)-2′-phenyl)ethylcarboxamide]-(4S)-4-benzyl-4,5-dihydrooxazole. L : ((4S,4′S)-(−)-4,4′,5,5′-tetrahydro-
4
7
8
,4′-bis(1-methylethyl)-2,2′-bioxazole. L : N-(1-hydroxy-3-methylbutan-(2S)-(−)-2-yl)-(4S)-(−)-4-isopropyl-4,5-dihydrooxazole-2-carbimidate. L :
b
c
2
-phenylazopyridine. Potential in volts versus SCE; peak potential difference ΔE /mV (in parentheses). In CH CN/0.1 M Et NClO at 100 mV
p
3
4
4
−
1
d
e
−1
f
−1
g
s . Irreversible. In CH CN/0.1 M Bu NPF at 100 mV s . In phosphate buffer, pH 7 at 100 mV s . In H O/0.1 M Et NClO , pH 7 at 100 mV
3
4
6
2
4
4
−
1
h
−1
I
−1
j
−1
s . In H O/0.1 M NaCF SO , pH 6.5 at 50 mV s . In CH CN/0.1 M Bu NPF , pH 7 at 100 mV s . In H O/0.1 M KCl, pH 7 at 100 mV s .
2
3
3
3
4
6
2
7
,13a,24a
plexes, respectively, integrating bidentate ligands (L) with
different electronic properties (Table 3) reveals the significant
variation in potential based on the π-accepting or σ-donating
strength of L.
application in the catalytic epoxidation process+.
In this
+
+
context, the newly designed molecular sets 1a −1d , 2 , and
2+
3a have been tested as possible precatalysts toward the
epoxidation of a wide variety of alkenes. The initial stand+-
ardization process has been monitored with the precatalyst 1a
(chloro derivative) and styrene as the model substrate in
combination with H O , TBHP, IDA, and m-CPBA (H O =
Spectroelectrochemistry and TD-DFT Calculations.
+
+
+
The complexes (1a −1d and 2 ) exhibit a similar spectral
profile in the UV−vis region in CH CN, and the transitions are
assigned based on the TD-DFT calculations (Figure 8, Table
2
2
2
2
3
hydrogen peroxide, TBHP = tert-butyl hydrogen peroxide, IDA
iodobenzene diacetate, m-CPBA = m-chloroperbenzoic acid)
as possible oxidants in CH Cl , CH CN, and C H OH solvents
at 298 K (Table 8). The optimization study reveals that IDA
and CH Cl are the best oxidant and solvent, respectively,
under the catalyst:substrate:oxidant molar ratio of 1:100:200,
which gives maximum conversion of 88% (entry 4, Table 8).
The above optimal condition (eq 1) with styrene as the model
=
7). The moderately intense three visible bands in the range
7
→
00−400 nm are originated via BIAN/BIAO-targeted (dπ)Ru
2
2
3
2
5
25
(π*)BIAN/BIAO MLCT (metal-to-ligand charge transfer)
and (dπ)Ru/(π)BIAN/BIAO → (π*)BIAN/BIAO MLLCT
2
2
2
5
(
metal/ligand-to-ligand charge transfer) transitions. The
2
+
2+
2+
reversible one-electron oxidized species 1a −1d and 2
O1, Figure 5) display two weak bands in the range 800−
00 nm followed by an intense band near 400 nm, which are
(
6
predicted to be originated via (π)BIAN/BIAO → (dπ)Ru
LMCT (ligand-to-metal charge transfer) and (π)BIAN/BIAO/
(
dπ)Ru → (dπ)Ru LMLCT (ligand/metal-to-metal charge
+
+
transfer) transitions. One-electron reversible reduction of 1a −
1
band position as well as intensity of the BIAN-targeted MLCT
or MLLCT band, though an appreciable change is noticed on
moving from 2 to 2. The higher energy UV region bands in all
substrate has therefore been applied for the precatalysts 1a −
+
+
d to 1a−1d (R1, Figure 5) causes the marginal change in
1d , which shows a marginal difference based on the electron-
donating (OMe) or -withdrawing (NO , Cl, F) group at the
para position of the arylimino moieties of BIAN. The
representative aqua derivative 3a extends comparable activity
2
+
2+
+
cases are assigned to ligand-based ((π)BIAN/BIAO→
to that of 1a with selected tested alkenes (Table 9); therefore,
(
π*)BIAN/BIAO) transitions.
the epoxidation reaction of a wide variety of alkenes has been
performed selectively with 1a . It should be noted that under
the above reaction conditions (eq 1) no epoxide formation
takes place in the absence of catalyst.
+
Catalytic Epoxidation. The accessibility of high-valent
IV
ruthenium−oxo {Ru O} species in the selective molecular
frameworks has led to the exploration of their potential
F
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 4. DFT-Calculated Selected MO Compositions of
CH Cl or CH CN or C H OH with the oxidant (IDA or
2
2
3
2
5
n
n
n
1
a −1d and 2
TBHP or H O or m-CPBA).
2 2
Though the metal-catalyzed epoxidation process can also
complex
MO
fragments
% contribution
facilitate oxidative cleavage of the olefinic double bond resulting
a+ (S = 0)
26
1
HOMO
LUMO
Ru/Cl/BIAN/tpm
BIAN/Ru/tpm/Cl
Ru/BIAN/tpm/Cl
BIAN/Ru/tpm/Cl
BIAN/tpm/Ru/Cl
BIAN/tpm/Ru
56/23/11/10
82/11/06/01
61/20/09/09
85/09/05/01
55/40/04/01
61/37/02
+
2+
in aldehyde or ketone or alcohol, the precatalyst 1a or 3a is
found to be chemoselective toward epoxide formation without
1
1
a2+ (S = 1/2)
a (S = 1/2)
β-LUMO
SOMO
1
any trace of carbonyl derivative as ascertained by GC-MS or H
NMR.
β-LUMO
HOMO
HOMO
LUMO
+
The efficiency of the catalyst 1a has also been further tested
−
1
1
a
(S = 0)
by varying the catalyst loading with respect to the substrate
vinyl cyclopentane, which gives an appreciably high TON of
+
b (S = 0)
Ru/Cl/BIAN/tpm
BIAN/Ru/tpm/Cl
Ru/Cl/BIAN/tpm
BIAN/Ru/tpm/Cl
BIAN/tpm/Ru/Cl
BIAN/tpm/Ru/Cl
Ru/Cl/tpm/BIAN
BIAN/Ru/tpm/Cl
Ru/Cl/BIAN/tpm
BIAN/Ru/tpm/Cl
BIAN/tpm/Ru/Cl
BIAN/tpm/Ru/Cl
Ru/Cl/tpm/BIAN
BIAN/Ru/tpm/Cl
Ru/Cl/tpm/BIAN
BIAN/Ru/tpm/Cl
BIAN/Ru/tpm/Cl
BIAN/tpm/Ru/Cl
BIAN/Ru/tpm
59/23/09/09
84/10/04/01
67/13/10/10
85/09/05/01
54/41/04/01
81/12/06/01
60/23/09/09
84/10/04/01
67/13/10/10
85/09/05/01
61/34/04/01
83/10/06/01
59/24/09/09
86/09/03/01
67/13/10/09
86/09/04/01
96/02/01/00
89/06/04/01
95/03/02
2
100 even with 0.001 mol % of the catalyst (Table S36,
2+
1
b (S = 1/2)
b (S = 1/2)
β-LUMO
SOMO
Supporting Information).
1
The individual role of the metal ion, the free ligand (tpm or
BIAN), and the metal ion plus ligand toward the epoxidation
process has been tested with vinyl cyclopentane under the
reaction conditions in eq 1 (Table S37, Supporting
β-LUMO
HOMO
HOMO
LUMO
−
1
1
b
(S = 0)
+
c (S = 0)
Information), which divulges that Ru as RuCl or free ligand
3
1
1
c2+ (S = 1/2)
c (S = 1/2)
β-LUMO
SOMO
(
1:1 tpm-BIAN) or Ru as RuCl + tpm (0.5:1 mol ratio) fails to
3
facilitate the epoxidation process at all. However, Ru as RuCl3
in combination with BIAN (0.5:1 mol ratio) yields slight
conversion (18%) with moderate epoxide formation (30%
selectivity). On the contrary, the infusion of free ligand (tpm +
β-LUMO
HOMO
HOMO
LUMO
1
1
c− (S = 0)
d+ (S = 0)
BIAN) and RuCl in a 1:1 molar ratio (i.e., the in-situ-
d2+ (S = 1/2)
d (S = 1/2)
3
1
1
β-LUMO
SOMO
generated catalyst) enhances the yield up to 66% with 80%
chemoselectivity, which is however less than that achieved by
β-LUMO
HOMO
LUMO
using the corresponding preformed catalyst 1a+ (88%
1
1
d− (S = 0)
conversion, 100% selectivity, Table 9).
+
In general, complex 1a is found to be an effective precatalyst
−
d2 (S = 1/2)
SOMO
BIAN/Ru/tpm
94/03/02
for the oxidation of a wide variety of alkenes to respective
epoxides under the standardized reaction conditions in eq 1,
which gives excellent to good selectivity. It also reveals that
unactivated olefins such as vinyl cyclohexane, 1-phenyl
cyclohexene, vinyl cyclopentane, cyclooctene, cyclooctadiene,
α-LUMO
SOMO1
HOMO
LUMO
tpm/Ru/BIAN
88/06/06
3
−
1
d
(S = 1)
tpm/BIAN/Ru
68/28/04
+
2
(S = 0)
Ru/Cl/tpm/BIAO
BIAO/Ru/tpm/Cl
Ru/Cl/tpm/BIAO
BIAO/Ru/tpm/Cl
BIAO/tpm/Ru/Cl
BIAO/tpm/Ru/Cl
60/24/11/05
80/13/05/02
68/14/11/06
83/11/05/02
69/25/05/01
81/12/06/01
22+
(S = 1/2)
β-LUMO
SOMO
1
-octene, and 1-decene (entries 10−16, Table 9) exhibit
2
(S = 1/2)
comparable to better activity in terms of both % conversion and
selectivity to that of aromatic alkenes. Though cis-stilbene and
trans-stilbene (entries 7 and 8, Table 9) show chemoselective
epoxidation to cis-stilbene oxide and trans-stilbene oxide,
respectively, without any side product, α-methylstyrene (entry
β-LUMO
HOMO
2−
(S = 0)
Table 5. Mulliken Spin Densities for Paramagnetic Forms of
n
n
n
1
a −1d and 2
2
, Table 9) yields overoxidized acetophenone along with the
complex
Ru
BIAN/BIAO
tpm
Cl
desired epoxide as the primary product. The substrate
cyclooctadiene yields the double epoxide as the main product
(76%, entry 14, Table 9) with the partially oxidized
monoepoxide minor product (8%). The controlled experiment
comprising of 1:1 mixture of 1-octene and trans-5-decene as
substrate reveals the preferential formation of terminal oxide
(1,2-epoxyoctane, conversion 80%, selectivity 100%) over the
internal oxide (1,2-epoxydecane, conversion 20%) (entry 17,
Table 9).
1
1
1
1
1
1
1
1
1
1
2
2
a2+ (S = 1/2)
a (S = 1/2)
b2+ (S = 1/2)
b (S = 1/2)
c2+ (S = 1/2)
c (S = 1/2)
d2+ (S = 1/2)
d (S = 1/2)
d2 (S = 1/2)
0.755
0.047
0.782
0.048
0.781
0.049
0.777
0.051
0.024
0.053
0.805
0.040
0.098
0.941
0.032
0.943
0.037
1.001
0.035
0.937
0.98
0.028
0.010
0.062
0.005
0.043
0.010
0.036
0.006
−0.001
0.951
0.039
0.008
0.118
0.004
0.147
0.004
0.147
0.005
0.152
0.007
−0.001
−0.002
0.155
0.005
24
−
As proposed earlier, the ruthenium-catalyzed epoxidation
reaction of alkene proceeds through the in situ formation of
3−
d
(S = 1)
(S = 1/2)
(S = 1/2)
0.998
0.006
0.946
2+
III
IV
{Ru −OH} or {Ru O} active intermediate. The use of
hydroxyl or radical scavenger specific for each intermediate,
however, can distinguish between the nature of the active
27
species. The extent of variation in % conversion of the
representative substrate 1-octene to its corresponding oxide in
the presence of specific hydroxyl (N,N′-dimethylthiourea,
DMTU) or radical (TEMPO, 2,2,6,6-tetramethylpiperidinyloxy
radical) scavenger has thus been tested under similar reaction
conditions (eq 1). Though the % conversion of 1-octene to its
corresponding epoxide remains virtually unaltered in the
presence of DMTU (Table S38, Supporting Information), the
Surprisingly, under identical reaction conditions (eq 1) the
+
precatalyst 2 (chloro derivative) involving partially hydrolyzed
BIAN ligand (i.e., BIAO) has failed to deliver any reasonable
catalytic activities with any of the tested alkenes (Table 9). The
+
observed inertness of 2 could possibly be attributed to its
IV
inability to form the necessary {Ru O} intermediate species
+
(
see below), as revealed by the independent reaction of 2 in
G
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
n
n
n
Figure 6. DFT-calculated Mulliken spin density plots of 1a −1d and 2 .
Table 6. DFT(B3LYP/LANL2DZ/SDD)-Calculated Selected
n
n
Bond Distances of Coordinated BIAN or BIAO in 1a −1d
or 2n
C8−
C7−
N1−
N1−
N2−
N2−
O1−
complex
C18
C17
C8
C7
C18
C17
C17
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
a2+
a+
a
1.496
1.483
1.431
1.396
1.301
1.302
1.339
1.381
1.301
1.302
1.340
1.381
−
a
2
+
b
b
b
b
1.496
1.484
1.431
1.395
1.496
1.484
1.431
1.395
1.499
1.485
1.434
1.402
1.420
1.420
1.508
1.490
1.433
1.395
1.304
1.301
1.340
1.382
1.304
1.301
1.340
1.382
1.301
1.301
1.340
1.374
1.370
1.383
1.303
1.307
1.341
1.396
1.304
1.301
1.340
1.382
1.304
1.301
1.341
1.382
1.301
1.301
1.339
1.374
1.372
1.383
+
−
2
+
c
+
c
c
−
c
Figure 7. EPR spectra of electrogenerated (a) 1a2+ and (b) 2 in
2+
d
d
d
d
d
d
+
CH CN/0.1 M Et NClO at 77 K.
3
4
4
+
−
(1) Addition of IDA to a solution of precatalyst 1a in
2−
CH Cl immediately changes the color of the solution
2
2
3−
from red-brown to yellow due to the formation of
IV
2
+
{
Ru O} species which causes the disappearance of the
1.257
1.252
1.287
1.314
+
+
visible transitions of 1a at 565 and 688 nm with the
concomitant growth of two higher energy new bands at
482 and 430 nm (Figures S5 and S6, Supporting
−
13a,24a,b
Information).
This has also been supported by the
complete inertness of alkene toward the epoxide formation on
mass spectrometry which shows the peaks at m/z =
IV
IV
addition of TEMPO suggests the involvement of {Ru O} as
823.06 and 838.06 corresponding to {Ru (tpm)(BIAN)-
+
2+
II
an active intermediate (Scheme 2).
O]ClO } (calcd 823.20) (4 ) and {Ru (tpm)(BIAN)-
4
IV
+
The formation of active {Ru O} intermediate has also
OCH3} (calcd 838.23), respectively (Figure S7,
been justified by the following controlled steps.
Supporting Information). The identification of the
H
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure S9, Supporting Information), however, reveals the
involvement of a radical intermediate step (b in Scheme 3) as it
results in the lengthening of the C −C bond of styrene from
α
β
1
.32 to1.50 Å in [5] with a simultaneous stretching of the Ru−
2+
O bond of 1.77 Å in 4 to 1.93 Å in [5]. The formation of a
C −O single bond (1.43 Å) in [5] leads to a radical center at
β
C as has been corroborated by the Mulliken spin density of
α
0
.76 on C . Moreover, the almost identical calculated Mulliken
α
2+
charge of 1.00 and 0.92 on Ru in optimized 4 and [5],
respectively, favors the radical mechanism (Schemes 2−4). The
DFT-supported radical pathway can also be substantiated by
the fact of no epoxide formation from 1-octene as a model
substrate in the presence of radical scavenger TEMPO under
the experimental conditions stated in eq 1.
CONCLUSION
In conclusion, the salient features of the article as well as the
outlook are stated below.
■
•
The newer classes of Ru−BIAN-derived chloro
II +
[
Ru (tpm)(R-BIAN)(Cl)] (R = 4-OMe, 4-F, 4-Cl, 4-
+
+
II
NO , 1a −1d ) and aqua [Ru (tpm)(OMe-BIAN)-
2
2
+
2+
(
H O)] (3a ) derivatives are reported. The BIAN
2
framework with R = H, however, results in a partially
hydrolyzed BIAO ([N-(phenyl)imino]acenapthenone)-
II
derived first ruthenium complex [Ru (tpm)(BIAO)-
+
+
(
Cl)] (2 ) (Chart 2).
•
•
Appreciable variation in the redox potential based on the
+
+
electronic nature of the “R” group of BIAN in 1a −1d
+
or BIAO in 2 has been evident which in effect leads to
the experimental observation of four successive reduc-
+
tions particularly in 1d encompassing R = NO group.
2
The sensitivity of the NC−CN or NC−
CO bond parameters of BIAN or BIAO in accessible
n
n
n
redox states of 1a −1d or 2 (n = +2, +1, 0, −1, −2,
−3), respectively, has been reflected in experimental and
DFT-optimized structures.
Figure 8. UV−vis spectroelectrochemical plots in CH CN/0.1 M
3
NEt ClO .
4
4
II
+
IV
IV
solvated species ({Ru (tpm)(BIAN)OCH } ) implies
• The formation of the {Ru O} state ([Ru (tpm)(R-
3
IV
2+
2+
the reactive feature of the intermediate {Ru O}
BIAN)(O)] , 4 ) for the BIAN-derived precursor
2+
+
+
2+
species (4 ).
chloro (1a −1d ) or aqua (3a ) derivative makes it an
2
+
(
2) The yellow solution of the intermediate 4 reverts back
efficient precatalyst for the epoxidation of a wide variety
+
IV
to its original red-brown color (1a ) upon addition of
of alkenes. The inaccessibility of the {Ru O} state of
+
Me S, which is attributed to the oxidation of dimethyl
the analogous BIAO-derived 2 , however, makes it
2
sulfide to dimethyl sulfoxide (GC) with the concomitant
reduction of Ru(IV) to Ru(II) (Figure S5, Supporting
Information).
virtually ineffective for the epoxidation process.
The present article thus demonstrates enormous potential of
the suitably designed BIAN-derived newer molecular frame-
works toward the tunable electrochemical and catalytic
applications.
2
+
(
3) Addition of PPh to the freshly prepared 4 in CDCl in
3
3
a 1:1 ratio results in Ph PO as evidenced by its
3
3
1
characteristic P NMR resonance at δ 30 ppm (Figure
S8, Supporting Information).
24a
EXPERIMENTAL SECTION
■
The olefin approaches the metal−oxo species either via side-
30
Materials. The ligands tris(1-pyrazolyl)methane (tpm) and
28
3
1
on fashion or end-on fashion. However, the observed
substituted bis(arylimino)acenaphthene (BIAN) and the precursor
3
2
appreciably higher % conversion in case of trans-stilbene
76%) as compared to cis-stilbene (66%) (entries 7 and 8,
complex Ru(tpm)Cl ·1.5H O were prepared as reported previously
3 2
(
in the literature. The starting material pyrazole was purchased from
Sigma-Aldrich. Other solvents and reagents were of reagent grade and
used as received. For spectroscopic and electrochemical studies,
HPLC-grade solvents were employed.
Table 9) suggests that the less hindered side-on approach is
preferred. The probable five intermediates involving the
transfer of oxygen of {MO} to the olefinic double bond
are (a) concerted transition state, (b) radical, (c) carbocation,
Physical Measurements. The electrical conductivities of the
1
3a,24a,29
complexes in CH CN were checked by using a Systronic 305
3
(
3
d) π-radical cation, and (e) metallaoxetene
).
The DFT calculations on the optimized adduct of
(Scheme
1
31
conductivity bridge. H NMR and P NMR spectra were recorded
using Bruker Avance III 400 MHz. FT-IR spectra were recorded on a
Nicolet spectrophotometer with samples prepared as KBr pellets.
Cyclic voltammetry measurements were performed on a PAR model
273A electrochemistry system. Glassy carbon working electrode,
2
+
ruthenium−oxo species (4 , ΔE(S = 0)−(S = 1) = 7506
cm ) with styrene as a model substrate i.e., [5] (Scheme 4 and
−1
I
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
n
n
n
Table 7. TD-DFT(B3LYP/CPCM/CH CN)-Calculated Electronic Transitions for 1a −1d and 2
3
ε/M− cm−1 (f)
1
transitions
a2+ (S = 1/2)
character
λ/nm expt (DFT)
1
822(817)
660(614)
435(452)
330(329)
277(284)
810(0.039)
HOMO−2 → LUMO(98)
BIAN(π) → Ru(dπ)
BIAN(π) → Ru(dπ)
BIAN(π) → Ru(dπ)
1170(0.004)
17 150(0.052)
11 890(0.073)
30 670(0.004)
HOMO−4(β) → LUMO+1(β)(95)
HOMO−10(β) → LUMO(β) (91)
HOMO−2(β) → LUMO+2 (β) (64)
BIAN(π)/Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
HOMO−6(β) → LUMO+2 (β)(64)
+
1
a (S = 0)
658(597)
552(474)
478(448)
379(370)
328(318)
288(261)
2710(0.016)
9200(0.139)
15 600(0.041)
7360(0.022)
13 350(0.231)
21 170(0.018)
HOMO → LUMO(61)
Ru(dπ) → BIAN(π*)
HOMO−3 → LUMO(69)
HOMO−3 → LUMO(51)
HOMO−3 → LUMO+1(69)
HOMO−5 → LUMO+1(66)
HOMO−4 → LUMO+4(61)
Ru(dπ)/BIAN(π) → BIAN(π*)
Ru(dπ)/BIAN(π) → BIAN(π*)
BIAN(π)/Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
1
a (S = 1/2)
658(648)
575(562)
485(462)
379(378)
332(329)
288(289)
740(0.004)
HOMO(β) → LUMO(β)(98)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
Ru(dπ)/BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
6840(0.003)
15 680(0.223)
7470(0.040)
13 360(0.002)
20 820(0.013)
HOMO−1(α) → LUMO(α)(58)
HOMO−1(α) → LUMO(α)(69)
HOMO−4(β) → LUMO(β)(61)
HOMO−4(β) → LUMO+1(β)(75)
HOMO−3(β) → LUMO+3(β)(83)
BIAN(π) → BIAN(π*)/tpm(π*)
2+
1
b
(S = 1/2)
793(743)
517(484)
442(439)
328(319)
283(281)
950(0.017)
HOMO−2(β) → LUMO(β)(97)
HOMO−3(β) → LUMO+1(β)(62)
HOMO−2(β) → LUMO+1(β)(74)
HOMO(α) → LUMO+2(α)(64)
BIAN(π) → Ru(dπ)
Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
3190(0.014)
11 210(0.050)
11 560(0.004)
20 070(0.013)
HOMO−6(β) → LUMO+2(β)(84)
+
1
b (S = 0)
662(590)
556(503)
476(441)
328(311)
314(307)
289(273)
2140(0.022)
7670(0.079)
11 920(0.252)
13 660(0.006)
15 100(0.031)
16 120(0.005)
HOMO−1 → LUMO(55)
HOMO−2 → LUMO(51)
HOMO → LUMO+1(62)
HOMO−4 → LUMO+1(52)
HOMO−4 → LUMO+1(56)
HOMO−6 → LUMO+1(69)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π)/Cl(π) → BIAN(π*)
BIAN(π)/Cl(π) → BIAN(π*)
1
b (S = 1/2)
590(559)
558(543)
498(493)
331(352)
316(306)
291(294)
6730(0.007)
9370(0.020)
13 360(0.004)
11 720(0.038)
13 840(0.006)
15 400(0.010)
HOMO−1(α) → LUMO(α)(52)
HOMO−1(β) → LUMO(β)(82)
HOMO−2(β) → LUMO(β)(85)
HOMO−5(β) → LUMO(β)(82)
HOMO−4(β) → LUMO+1(β)(68)
HOMO−6(β) → LUMO(β)(68)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
2+
1
c
(S = 1/2)
796(741)
576(563)
521(515)
445(438)
329(323)
286(266)
1050(0.014)
1390(0.004)
3840(0.022)
12 700(0.063)
13 130(0.006)
23 110(0.009)
HOMO−2(β) → LUMO(β)(98)
HOMO−6(β) → LUMO(β)(82)
HOMO−8(β) → LUMO(β)(95)
HOMO−2(β) → LUMO+1(β)(74)
HOMO−1(β) → LUMO+1(β)(91)
BIAN(π) → Ru(dπ)
BIAN(π) → Ru(dπ)
BIAN(π) → Ru(dπ)
BIAN(π)/Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π)/Cl(π) → BIAN(π*)
HOMO−7(β) → LUMO+2(β)(87)
+
1
c (S = 0)
664(593)
561(506)
477(441)
329(318)
315(307)
290(264)
2250(0.024)
8810(0.085)
13 570(0.241)
16 340(0.039)
17 680(0.009)
19 270(0.001)
HOMO−1 → LUMO(55)
HOMO−2 → LUMO(51)
HOMO → LUMO+1(51)
HOMO−9 → LUMO(67)
HOMO−5 → LUMO+1(63)
HOMO−7 → LUMO+1 (59)
Ru(dπ)/BIAN(π) → BIAN(π*)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
1
c (S = 1/2)
590(567)
564(504)
497(461)
330(330)
317(311)
291(279)
9440(0.049)
HOMO−1(β) → LUMO(β)(72)
HOMO−1(β) → LUMO(β)(79)
HOMO−1(α) → LUMO(α)(79)
HOMO(β) → LUMO(β)(81)
HOMO−5(α) → LUMO(α)(61)
HOMO−4(α) → LUMO+2(α)(79)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
Ru(dπ)/Cl(π) → BIAN(π*)
Ru(dπ)/BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
11 290(0.007)
14 410(0.051)
13 990(0.008)
15 200(0.006)
15 400(0.001)
BIAN(π) → BIAN(π*)/tpm(π*)
J
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Table 7. continued
λ/nm expt (DFT)
Article
ε/M− cm−1 (f)
1
transitions
d2+ (S = 1/2)
character
1
827(879)
657(594)
434(417)
330(331)
277(274)
810(0.046)
HOMO(β) → LUMO(β) (98)
BIAN(π) → Ru(dπ)
BIAN(π) → Ru(dπ)
Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
1140(0.001)
17 200(0.030)
11 950(0.002)
30 680(0.150)
HOMO−6(β) → LUMO(β)(74)
HOMO−3(β) → LUMO+1 (β)(74)
HOMO−9(β) → LUMO+1 (β)(51)
HOMO−6(α) → LUMO+3 (α)(61)
+
1
d (S = 0)
652(595)
552(507)
478(454)
330(301)
287(281)
2780(0.028)
9230(0.049)
15 570(0.028)
13 230(0.099)
21 180(0.021)
HOMO−1 → LUMO(50)
HOMO → LUMO+1(54)
HOMO−1 → LUMO+1(66)
HOMO−4 → LUMO+1(52)
HOMO−6 → LUMO+2(53)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π)/Cl(π) → BIAN(π*)
1
d (S = 1/2)
801(836)
578(578)
488(455)
316(314)
283(295)
1310(0.010)
HOMO(β) → LUMO(β) (96)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
Ru(dπ) → BIAN(π*)
BIAN(π) → BIAN(π*)
BIAN(π) → BIAN(π*)
10 260(0.002)
16 010(0.009)
30 580(0.005)
36 740(0.009)
HOMO → 1(α)→LUMO+1(α)(77)
HOMO → 1(α)→LUMO+2(α)(59)
HOMO → 7(α)→LUMO(α)(58)
HOMO−6(β) → LUMO(β)(62)
2+
2
(S = 1/2)
397(442)
354(347)
255(326)
6120(0.067)
11 270(0.048)
17 860(0.001)
HOMO−7(β) → LUMO (β)(88)
HOMO(α) → LUMO+1(α)(57)
BIAO(π*) → Ru(dπ)
BIAO(π) → BIAO(π*)
BIAO(π) → BIAO(π*)
HOMO−2(α) → LUMO+1(α)(56)
+
2
(S = 0)
638(566)
493(439)
378(372)
314(337)
301(305)
10 550(0.170)
6620(0.016)
3630(0.006)
16 090(0.013)
16 700(0.022)
HOMO−2 → LUMO(47)
HOMO−1 → LUMO+1(67)
HOMO−5 → LUMO(68)
HOMO → LUMO+2(48)
HOMO−4 → LUMO+1(66)
Ru(dπ) → BIAO(π*)
Ru(dπ) → BIAO(π*)
Cl(π)/BIAO(π) → BIAO(π*)
Ru(dπ) → BIAO(π*)
BIAO(π)/Cl(π) → BIAO(π*)
2
(S = 1/2)
483(459)
362(365)
337(326)
249(317)
13 700(0.001)
16 480(0.008)
17 000(0.060)
21 740(0.019)
HOMO−2(α) → LUMO(α)(79)
HOMO−4(β) → LUMO(β)(62)
HOMO−4(α) → LUMO(α)(54)
HOMO−5(α) → LUMO(α)(38)
HOMO−9(β) → LUMO(β)(37)
Ru(dπ) → BIAO(π*)
BIAO(π) → BIAO(π*)
BIAO(π) → BIAO(π*)
BIAO(π)/Cl(π) → BIAO(π*)
Cl(π)/BIAO(π) → BIAO(π*)
a
Table 8. Optimization of the Critical Reaction Parameters
cell. A platinum wire-gauze working electrode was used for the
constant potential coulometry experiment. UV−vis spectral studies
were performed on a PerkinElmer Lambda 950 spectrophotometer.
UV−vis spectroelectrochemical studies were performed on a BAS
SEC2000 spectrometer system. The supporting electrolyte was
+
b
entry
solvent
catalyst 1a (mmol %)
oxidant
H O
% conversion
1
2
3
4
5
6
7
8
9
CH Cl2
1
22
39
27
88
75
88
27
32
19
62
23
28
24
68
2
2
2
CH Cl2
1
TBHP
m-CPBA
IDA
2
−
3
Et NClO , and the solute concentration was ∼10
M. All
CH Cl2
1
4
4
2
electrochemical experiments were carried out under a dinitrogen
CH Cl2
1
2
atmosphere at 298 K. The half-wave potential E° was set equal to
CH Cl2
0.5
2
IDA
2
0
.5(Epa + E ), where E and Epc are anodic and cathodic cyclic
pc pa
CH Cl2
IDA
2
voltammetry peak potentials, respectively. The elemental analyses were
carried out on a Thermoquest (EA 1112) microanalyzer. Electrospray
mass spectra (ESI-MS) were recorded on a Bruker’s Maxis Impact
C H OH
1
H O
2
2
5
2
C H OH
1
TBHP
m-CPBA
IDA
2
5
C H OH
1
2
5
(282001.00081). The EPR measurements were made with a JEOL
10
11
12
13
14
C H OH
1
2
5
model FA200 electron spin resonance spectrometer. GC analysis was
done by a Shimadzu GC-2014 gas chromatograph with a FID detector
using a capillary column (112−2562 CYCLODEXB, from J&W
Scientific, length 60 m, inner diameter 0.25 mm, film 0.25 μm), and
GC-MS analysis was performed on an Agilent Technologies 7890A
GC system coupled with a 5975C inert XL EI/CI Mass Selective
Detector (GCMSD) with its triple-axis detector.
CH CN
1
H O
2
3
2
CH CN
1
TBHP
m-CPBA
IDA
3
CH CN
1
3
CH CN
1
3
a
1
mmol of styrene, solvent = 3 mL, oxidant = 2 equiv,
catalyst:substrate:oxidant = 1:100:200, 298 K, 6 h under aerobic
conditions. Percent (%) conversions were calculated by GC with n-
decane as an internal standard as well as by GC-MS. TBHP: tert-butyl
hydrogen peroxide. IDA: iodobenzene diacetate. m-CPBA: m-
chloroperbenzoic acid. H O : hydrogen peroxide.
b
Crystallography. Single crystals of [1a]ClO and [2]ClO were
4
4
grown by slow evaporation of their 1:2 dichloromethane-n-hexane
solutions, while those of [3a](PF ) were obtained from 1:1 acetone-
6
2
n-hexane solution. X-ray crystal data for [1a]ClO , [2]ClO , and
4
4
2
2
[
3a](PF6)2 were collected on RIGAKU SATURN-724+, Agilent
Technologies (Oxford Diffraction) SUPER NOVA, and Bruker
SMART APEX-II, CCD diffractometers, respectively. The data
collection for [1a]ClO4 and [2]ClO4 were evaluated using the
platinum wire auxiliary electrode, and a saturated calomel reference
electrode (SCE) were used in a standard three-electrode configuration
K
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 9. Catalytic Epoxidation of Olefins
a
1
mmol of styrene, solvent = 3 mL, oxidant = 2 equiv, catalyst:substrate:oxidant = 1:100:200, 298 K, 6 h under aerobic conditions. Products are
b
analyzed by GC with n-decane as an internal standard as well as by GC-MS. Selectivity in terms of epoxide formation. NC = Not determined.
CrysAlisPro CCD and CrystalClear-SM Expert software, respectively.
Except H1A and H1B (protons of aqua molecule in [3a](PF ) ), the
6 2
The data for [1a]ClO were collected by the standard ϕ−ω scan
other hydrogen atoms were added in the refinement process as per the
4
techniques, scaled and reduced using CrysAlisPro RED software, and
riding model. The disordered solvent molecules in [1a]ClO and
4
3
4
by the ω scan technique for [2]ClO . The cell refinement and data
[3a](PF ) were SQUEEZED by the PLATON program. CCDC
6 2
4
reduction in [3a](PF ) were performed with SAINT V7.68A. The
1052730 ([1a]ClO ), 1052731 ([2]ClO ), and 1052732 ([3a](PF ) )
4 4 6 2
6
2
structures were solved by direct method using SHELXS-97 and refined
contain supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallographic
Data Center via www.ccdc.cam.ac.uk/data_request/cis.
Computational Details. Full geometry optimizations were carried
out by using the density functional theory method at the (R)B3LYP
2
33
by full matrix least-squares with SHELXL-97, refining on F . All non-
hydrogen atoms were refined anisotropically. The hydrogen atoms
were placed in geometrically constrained positions and refined with
isotropic temperature factors, generally 1.2Ueq of their parent atoms.
L
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Preparation of the Complexes. The complexes [1a]ClO −
Scheme 2. Proposed Mechanistic Pathway
4
[
1d]ClO4 and [2]ClO4 were synthesized by following a general
procedure using respective R-BIAN. For [2]ClO R-BIAN with R = H
4
was used. The details are given below for [1a]ClO4.
Synthesis of [Ru(tpm)(OMe-BIAN)Cl]ClO , [1a]ClO . Ru(tpm)-
4
4
Cl ·1.5 H O (101 mg, 0.24 mmol) and the ligand R-BIAN (R =
3
2
OCH , Chart 2) (106 mg, 0.27 mmol) were taken in 40 mL of
3
methanol. The reaction mixture was heated at reflux with stirring
under a dinitrogen atmosphere for 8 h, and the color of the solution
turned to reddish brown. The solvent was then evaporated under
reduced pressure. The solid mass thus obtained was dissolved in 2 mL
of acetonitrile followed by addition of a saturated aqueous solution of
NaClO . The solution was then refrigerated for 6 h, and the resulting
4
solid was filtered through a Buchner funnel and dried under vacuum. It
was then purified on a neutral alumina column by using 4:1 CH Cl −
2
2
CH CN as eluant. Evaporation of the solvent under reduced pressure
3
yielded the solid product of [1a]ClO .
4
1
[
1a]ClO : Yield 114 mg (57%). H NMR in CDCl [δ/ppm (J/
4
3
Hz)]: 9.82 (s, 1H), 8.77 (d, 2.6, 1H), 8.36 (d, 2.4, 2H), 8.03 (d, 8.2,
2
2
3
H), 7.70 (d, 7.2, 2H), 7.49 (t, 7.4, 2H), 7.24 (m,4H), 7.14 (d, 7.2,
Scheme 3. Probable Intermediates in Metal-Catalyzed
Oxygen Transfer Reaction from Metal−Oxo to Olefins
H), 6.99 (d, 2.1, 2H), 6.71 (d, 7.5, 2H), 6.47 (d, 2.6, 1H), 6.19 (t, 2.5,
+
H), 3.80 (s, 6H). MS (ESI+, CH CN): m/z {1a } calcd 743.122;
3
−
−1
found 743.128. IR (KBr): ν(ClO , cm ): 1093, 622. Molar
conductivity (ΛM (Ω cm M ), CH CN): 118. Anal. Calcd for
C H N Cl O Ru: C, 51.31; H, 3.59; N, 13.30. Found: C, 51.31; H,
4
−1
2
−1
3
36
30
8
2
6
3
.50; N, 13.18.
1b]ClO : Yield 112 mg (58%). H NMR in CDCl [δ/ppm (J/
1
[
4
3
Hz)]: 9.89 (s, 1H), 8.80 (d, 2.6, 1H), 8.38 (d, 2.6, 2H), 8.07 (d, 8.2,
2
7
H), 7.78 (m, 2H), 7.52 (d, 7.8, 2H), 7.36 (m, 2H), 7.24 (m, 1H),
.17 (d, 7.2, 2H), 7.00 (d, 1.6, 2H), 6.94 (m, 2H), 6.50 (t, 2.4, 1H),
+
Scheme 4. Proposed Radical Intermediate During
Epoxidation
6.30 (m, 2H), 6.23 (t, 2.4, 2H). MS (ESI+, CH CN): m/z {1b } calcd
719.082; found 719.104. IR (KBr): ν(ClO , cm ): 1089, 622. Molar
conductivity (ΛM (Ω cm M ), CH CN): 114. Anal. Calcd for
C H N Cl F O Ru: C, 49.89; H, 2.96; N, 13.69. Found: C, 49.74; H,
3
−
−1
4
−1
2
−1
3
34
24
8
2
2
4
2
.82; N, 13.23.
1c]ClO : Yield 105 mg (52%). H NMR in CDCl [δ/ppm (J/
1
[
4
3
Hz)]: 9.87 (s, 1H), 8.79 (d, 2.7, 1H), 8.37 (d, 2.6, 2H), 8.08 (d, 8.2,
2
5
3
H), 7.74 (d, 6.6, 2H), 7.64 (d, 7.1, 2H), 7.52 (t, 8.1, 2H), 7.20 (m,
H), 7.01 (d, 2.2, 2H), 6.51 (t, 2.6, 1H), 6.26 (d, 8.9, 1H), 6.24 (m,
+
H). MS (ESI+, CH CN): m/z {1c } calcd 751.023; found 751.060.
3
−
−1
−1
IR (KBr): ν(ClO , cm ): 1086, 622. Molar conductivity (Λ (Ω
cm M ), CH
4
M
+
+
−
−
+
−
2+
35
2
−1
level for 1a −1d , 1a −1d , 2 , 2 , and 3a and (U)B3LYP level
3
CN): 122. Anal. Calcd for C34H N Cl O Ru: C,
24 8 4 4
2+
2+
2−
3−
2+
for 1a −1d , 1a−1d, 1d , 1d , and 2 , and 2 used the Gaussian 09
program package. Except ruthenium all other elements were assigned
the 6-31G* basis set. The SDD (in 2 , 2 , 2, 2 ) and LANL2DZ (in
a −1d , 1a −1d , 1a−1d, 1a −1d , 3a ) basis sets with effective
47.96; H, 2.84; N, 13.16. Found: C, 48.12; H, 2.87; N, 13.04.
3
6
1
[1d]ClO : Yield 118 mg (57%). H NMR in CDCl [δ/ppm (J/
4
3
2+
+
−
Hz)]: 9.98 (s, 1H), 8.86 (d, 2.8, 1H), 8.57 (d, 8.3, 2H), 8.42 (d, 2.7,
2H), 8.15 (d, 8.2, 4H), 8.01 (d, 7.5, 2H), 7.56 (t, 7.8, 2H), 7.28 (d, 3.9,
2
+
2+
+
+
−
−
2+
1
37
core potential were employed for the ruthenium atom. The
vibrational frequency calculations were performed to ensure that the
optimized geometries represent the local minima and there are only
positive eigenvalues. All calculations were performed with the
Gaussian09 program package. Vertical electronic excitations based
on (R)B3LYP/(U)B3LYP-optimized geometries were computed for
1H), 7.12 (d, 7.2, 2H), 7.00 (d, 2.1, 2H), 6.57 (m, 1H), 6.50 (m, 2H),
+
6.23 (t, 2.6, 2H). MS (ESI+, CH CN): m/z {1d } calcd 773.071;
3
−
−1
found 773.080. IR (KBr): ν(ClO , cm ): 1091, 622. Molar
conductivity (ΛM (Ω cm M ), CH CN): 108. Anal. Calcd for
C H N Cl O Ru: C, 46.80; H, 2.77; N, 16.05. Found: C, 46.95; H,
4
−1
2
−1
3
34
24 10
2
8
2.80; N, 15.92.
[2]ClO : Yield 74 mg (44%). H NMR in CDCl [δ/ppm (J/Hz)]:
n
n
n
1
1
a −1d (n = +2, +1, 0) and 2 (n = +2, +1, 0) using the time-
4
3
38
dependent density functional theory (TD-DFT) formalism in
9.96 (s, 1H), 8.72 (d, 2.7, 1H), 8.56 (d, 2.1, 1H), 8.53 (d, 2.7, 1H),
8.42 (m, 1H), 8.41 (d, 1.8, 1H), 8.36 (d, 8.1, 1H), 8.18 (d, 8.2, 1H),
7.87 (t, 7.2, 2H), 7.53 (m, 6H), 6.97 (d, 2.1, 1H), 6.82 (d, 2.2, 1H),
acetonitrile using a conductor-like polarizable continuum model
39
40
(
CPCM). Chemissian 1.7 was used to calculate the fractional
contributions of various groups to each molecular orbital. All
calculated structures were visualized with ChemCraft.
General Procedure for Catalytic Epoxidation Studies. The
6.68 (t, 2.5, 1H), 6.44 (t, 2.6, 1H), 6.14 (t, 2.6, 1H). MS (ESI+,
41
+
CH CN): m/z {2 } calcd 608.053; found 608.037. IR (KBr):
3
−
−1
−1
ν(ClO4 , cm ): 1090, 623; ν(CO, cm ): 1690. Molar
−1
2
−1
catalyst [1a]ClO (4.13 mg, 0.0049 mmol, 1 mol %) in 3 mL of
conductivity (ΛM (Ω cm M ), CH CN): 92. Anal. Calcd for
4
3
CH Cl was taken in a vial and stirred for ∼15 min at 298 K. The
C H Cl N O Ru: C, 47.54; H, 2.99; N, 13.86. Found: C, 47.68; H,
2
2
28 21
2
7
5
olefin (0.50 mmol) was then added to it with simultaneous stirring
followed by the addition of iodobenzene diacetate (2 equivalents with
respect to olefin) as the oxidant. The mixture was stirred at 298 K for 6
h. The reaction mixture was then diluted with water and extracted with
ethyl acetate (10 mL) three times. The combined organic extracts
were dried over Na SO and concentrated under reduced pressure,
2.80; N, 13.90.
Preparation of [Ru(tpm)(OMe-BIAN)(H O)](ClO ) ([3a]-
2
4 2
(ClO
AgClO
) ). The mixture of [1a]ClO (100 mg, 0.12 mmol) and
4
2
4
(100 mg, 0.48 mmol) in 1:3 acetone−water (25 mL) was
4
heated at reflux under stirring for 6 h. The initial reddish brown
solution turned to yellow with the precipitation of AgCl. It was then
cooled to room temperature and filtered through a sintered glass
crucible (G4). The filtrate was concentrated to 5 mL under reduced
pressure, and excess NaClO was added to it. The solid [3a](ClO )
4 2
2
4
and the yields were determined by gas chromatography with respect to
the internal standard, n-decane (1 mmol). A 2.0 μL aliquot was
subjected for analysis by GC-FID in each case.
4
M
DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
thus obtained was filtered off and washed with a few drops of chilled
Kru
̈
ger, H.-J. Angew. Chem., Int. Ed. 2014, 53, 5988−5992. (d) Tao,
Milli-Q water followed by drying in vacuo over P O .
W.-J.; Li, J.-F.; Peng, A.-Q.; Sun, X. -L; Yang, X.-H.; Tang, Y. Chem.
Eur. J. 2013, 19, 13956−13961. (e) Fedushkin, I. L.; Sokolov, V. G.;
Piskunov, A. V.; Makarov, V. M.; Baranov, E. V.; Abakumav, G. A.
Chem. Commun. 2014, 50, 10108−10111. (f) Wen, C.; Yuan, S.; Shi,
Q.; Yue, E.; Liu, D.; Sun, W.-H. Organometallics 2014, 33, 7223−7231.
(g) Bridges, C. R.; McCormick, T. M.; Gibson, G. L.; Hollinger, J.;
Seferos, D. S. J. Am. Chem. Soc. 2013, 135, 13212−13219.
(h) Fedushkin, I. L.; Markina, O. V.; Lukoyanov, A. N.; Morozov,
A. G.; Baranov, E. V.; Maslov, M. O.; Ketkov, S. Y. Dalton Trans. 2013,
4
10
1
[
3a](ClO ) : Yield 80 mg (73%). H NMR in D O [δ/ppm (J/
4
2
2
Hz)]: 9.70 (s, 1H), 8.56 (d, 8.0, 1H), 8.46 (d, 3.0, 1H), 8.35 (d, 2.7,
1
2
6
H), 8.19 (d, 6.0, 1H), 8.13 (d, 7.0, 1H), 7.89 (d, 2.1, 1H), 7.84 (d,
.2, 1H), 7.53 (m, 2H), 7.16 (m, 8H), 6.70 (m, 1H), 6.61 (d, 3.0, 1H),
.34 (m, 4H) 3.79 (s, 6H). MS (ESI+, CH OH): m/z {3a(ClO ) −
3
4 2
+
−1
ClO −H O} calcd 807.102; found 807.092. IR (KBr): ν(OH, cm ):
3
M ), H O): 195. Anal. Calcd for C H N Cl O Ru: C, 46.76; H,
4
2
−
−1
−1
2
438; ν(ClO , cm ): 1092, 623. Molar conductivity (Λ (Ω cm
−1
4
M
2
36 32
8
2
11
3
.49; N, 12.12. Found: C, 46.54; H, 3.21; N, 12.32.
Caution! Perchlorate salts of metal complexes with organic ligands are
4
2, 7952−7961. (i) Papanikolaou, P. A.; Gdaniec, M.; Wicher, B.;
Akrivos, P. D.; Tkachenko, N. V. Eur. J. Inorg. Chem. 2013, 5196−
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Demeshko, S.; Meyer, F. Angew. Chem., Int. Ed. 2012, 51, 10584−
0587. (k) Li, L.; Lopes, P. S.; Rosa, V.; Figueira, C. A.; Lemos, M. A.
N. D. A.; Duarte, M. T.; Aviles, T.; Gomes, P. T. Dalton Trans. 2012,
potentially explosive. Heating of dried samples must be avoided; handling
of even a small amount has to proceed with great caution.
5
1
ASSOCIATED CONTENT
Supporting Information
X-ray crystallographic files in CIF format for [1a]ClO ,
■
́
*
S
41, 5144−5154. (l) Clark, K. M.; Bendix, J.; Heyduk, A. F.; Ziller, J. W.
Inorg. Chem. 2012, 51, 7457−7459. (m) Hill, N. J.; Vargas-Baca, I.;
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[
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4 6 2
1
pulse voltammograms of [3a](PF ) , electronic spectra, H
6
2
NMR, 3 P NMR spectra, DFT-optimized structures, bond
1
parameters, MO compositions, and energies of DFT optimized
states. The Supporting Information is available free of charge
on the ACS Publications website at DOI: 10.1021/
acs.inorgchem.5b00615.
(
3) (a) Mondal, P.; Agarwala, H.; Jana, R. D.; Plebst, S.; Grupp, A.;
Ehret, F.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2014, 53,
M.; Gallo,
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389−7403. (b) Ragaini, F.; Cenini, S.; Borsani, E.; Dompe,
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K.; Pandey, R.; Mishra, L.; Zou, R.-Q; Xu, Q.; Pandey, D. K.
AUTHOR INFORMATION
Corresponding Author
E-mail: lahiri@chem.iitb.ac.in.
■
́
Polyhedron 2008, 27, 2877−2882. (d) Vigano, M.; Ragaini, F.;
Buonomenna, M. G.; Lariccia, R.; Caselli, A.; Gallo, E.; Cenini, S.;
*
Jansen, J. C.; Drioli, E. ChemCatChem 2010, 2, 1150−1164.
(4) (a) Crawford, K.; Rautenstrauch, V.; Uijttewaal, A. Synlett 2001,
Notes
1
127−1128. (b) Wahren, U.; Sprung, I.; Schulze, K.; Findeisen, M.;
The authors declare no competing financial interest.
Buchbauer, G. Tetrahedron Lett. 1999, 40, 5991−5992. (c) Kelly, D.
R.; Nally, J. Tetrahedron Lett. 1999, 40, 3251−3254.
ACKNOWLEDGMENTS
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2003, 5, 1−7. (b) Lane, B. S.; Burgess, K. Chem. Rev. 2003, 103,
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(d) Legros, J.; Bolm, C. Chem.Eur. J. 2005, 11, 1086−1092.
(e) Bregeault, J. M. Dalton Trans. 2003, 3289−3302. (f) Herrmann,
W. A.; Fischer, R. W.; Marz, D. W. Angew. Chem., Int. Ed. 1991, 30,
Financial support received from the Department of Science and
Technology, University Grants Commission (fellowship to
A.H. and R.R.), Council of Scientific and Industrial Research
(
fellowship to A.D., H.A. and S.M.), New Delhi (India) is
gratefully acknowledged.
1
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J. Am. Chem. Soc. 1997, 119, 6189−6190. (h) Hermann, W. A.;
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DOI: 10.1021/acs.inorgchem.5b00615
Inorg. Chem. XXXX, XXX, XXX−XXX