Configuration Control in the Synthesis of Homo- and Heteroleptic Bis(oxazolinylphenolato/thiazolinylphenolato) Chelate Ligand Complexes of Oxorhenium(V): Isomer Effect on Ancillary Ligand Exchange Dynamics and Implications for Perchlorate Reduction Catalysis

Article abstract of DOI:10.1021/acs.inorgchem.5b02940

This study develops synthetic strategies for N,N-trans and N,N-cis Re(O)(L_O-N)₂Cl complexes and investigates the effects of the coordination spheres and ligand structures on ancillary ligand exchange dynamics and catalytic perchlorate reduction activities of the corresponding [Re(O)(L_O-N)₂]⁺ cations. The 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz) and 2-(2′-hydroxyphenyl)-2-thiazoline (Hhtz) ligands are used to prepare homoleptic N,N-trans and N,N-cis isomers of both Re(O)(hoz)₂Cl and Re(O)(htz)₂Cl and one heteroleptic N,N-trans Re(O)(hoz)(htz)Cl. Selection of hoz/htz ligands determines the preferred isomeric coordination sphere, and the use of substituted pyridine bases with varying degrees of steric hindrance during complex synthesis controls the rate of isomer interconversion. The five corresponding [Re(O)(L_O-N)₂]⁺ cations exhibit a wide range of solvent exchange rates (1.4 to 24,000 s^-1 at 25°C) and different L_O-N movement patterns, as influenced by the coordination sphere of Re (trans/cis), the noncoordinating heteroatom on L_O-N ligands (O/S), and the combination of the two L_O-N ligands (homoleptic/heteroleptic). Ligand exchange dynamics also correlate with the activity of catalytic reduction of aqueous ClO₄^- by H₂ when the Re(O)(L_O-N)₂Cl complexes are immobilized onto Pd/C. Findings from this study provide novel synthetic strategies and mechanistic insights for innovations in catalytic, environmental, and biomedical research.

Full text of DOI:10.1021/acs.inorgchem.5b02940

Article
pubs.acs.org/IC
Configuration Control in the Synthesis of Homo- and Heteroleptic
Bis(oxazolinylphenolato/thiazolinylphenolato) Chelate Ligand
Complexes of Oxorhenium(V): Isomer Effect on Ancillary Ligand
Exchange Dynamics and Implications for Perchlorate Reduction
Catalysis
,
†,§
∥
⊥
†
†
‡
Jinyong Liu,* Dimao Wu, Xiaoge Su, Mengwei Han, Susana Y. Kimura, Danielle L. Gray,
‡
#
∇
,§
John R. Shapley, Mahdi M. Abu-Omar, Charles J. Werth, and Timothy J. Strathmann*
†
‡
Department of Civil and Environmental Engineering and Department of Chemistry, University of Illinois at Urbana−Champaign,
Urbana, Illinois 61801, United States
§
Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado 80401, United States
Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
∥
⊥
Pure Storage Inc., Mountain View, California 94041, United States
#
Department of Chemistry and School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States
∇Department of Civil, Architectural, and Environmental Engineering, University of Texas at Austin, Austin, Texas 78712, United
States
*
S Supporting Information
ABSTRACT: This study develops synthetic strategies for N,N-trans and N,N-cis Re(O)(LO−N)2Cl complexes and investigates
the effects of the coordination spheres and ligand structures on ancillary ligand exchange dynamics and catalytic perchlorate
reduction activities of the corresponding [Re(O)(LO−N)2]+ cations. The 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz) and 2-(2′-
hydroxyphenyl)-2-thiazoline (Hhtz) ligands are used to prepare homoleptic N,N-trans and N,N-cis isomers of both
Re(O)(hoz) Cl and Re(O)(htz) Cl and one heteroleptic N,N-trans Re(O)(hoz)(htz)Cl. Selection of hoz/htz ligands determines
2
2
the preferred isomeric coordination sphere, and the use of substituted pyridine bases with varying degrees of steric hindrance
+
during complex synthesis controls the rate of isomer interconversion. The five corresponding [Re(O)(L ) ] cations exhibit a
O−N 2
wide range of solvent exchange rates (1.4 to 24,000 s− at 25 °C) and different LO−N movement patterns, as influenced by the
coordination sphere of Re (trans/cis), the noncoordinating heteroatom on LO−N ligands (O/S), and the combination of the two
1
LO−N ligands (homoleptic/heteroleptic). Ligand exchange dynamics also correlate with the activity of catalytic reduction of
−
aqueous ClO4 by H when the Re(O)(L ) Cl complexes are immobilized onto Pd/C. Findings from this study provide novel
2
O−N 2
synthetic strategies and mechanistic insights for innovations in catalytic, environmental, and biomedical research.
INTRODUCTION
salicylimine, 8-hydroxyquinoline, picolinic acid, etc.) and
tetradentate LO−N−N‑O ligands (e.g., salen and salan) with
■
Oxorhenium complexes have been recognized as versatile
catalysts for a series of reactions used in synthetic chemistry as
1
tunable steric and electronic properties have been widely used
5
6
2
to prepare Re(O)(LO−N)2X and Re(O)(L
)X (X = Cl,
well as energy and environmental related applications. The
O−N−N‑O
complexes of 1 Re and Re isotopes have been developed as
86
188
Br, alkyl and alkoxide in neutral complexes, or X = H O,
2
radiopharmaceuticals for tumor imaging and radionuclide
therapy. Fluorescent chemosensing for Re in cells has also
CH CN, etc. in cationic complexes). Of particular note, the
3
3
been developed based on oxorhenium(V) coordination
chemistry. Monoanionic bidentate LO−N ligands (e.g.,
Received: December 22, 2015
4
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b02940
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Article
naturally occurring 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz)
7
structure originally identified in microbial siderophores gives
the Re(O)(hoz) X complex diverse catalytic activities, including
2
8
9
perchlorate reduction, hydrosilylation, H production from
2
1
0
organosilanes, condensation between biomass-derived polyols
1
1
12
and aldehydes, and C−H activation.
Advancement of oxorhenium chemistry has provided insights
that can be applied to address major environmental and energy
−
challenges. Perchlorate (ClO ) is a potent competitive
4
13
inhibitor of the thyroid sodium-iodide symporter. This highly
inert anion has been widely detected in contaminated water
1
4
15
supplies and agricultural products. A nationwide regulation
of ClO4− in drinking water by the U.S. EPA is pending. Our
research team developing innovative water treatment tech-
16
nologies has immobilized Re(O)(hoz) Cl in Pd/C to prepare a
2
17
novel biomimetic heterogeneous catalyst, in which oxorhe-
−
nium single sites reduce ClOx anions via oxygen atom transfer
(
OAT, a two-electron transfer process), and Pd0 nano-
1
8
Figure 2. Possible structures of Re(O)(LO−N
indicates an enantiomer.
)
X isomers. Prime
2
particles transfer electrons from exogenous H to sustain the
2
V
VII
catalytic cycle between Re and Re . At room temperature,
this Re(hoz) −Pd/C catalyst enables rapid reduction of ClO
by H into Cl and H O, exhibiting much higher activity than
−
2
4
(L ) X isomerization, especially for type A and B, remain
O−N 2
−
2
2
largely unexplored despite its importance in mechanistic study
and catalyst design. In practice, synthetic procedures yielding a
mixture of isomers create various difficulties in product
isolation, adding challenges to structural determination and
subsequent investigation on reaction mechanisms and the
structure−activity relationship. Furthermore, failure to control
isomeric structure might yield less active isomers, thus lowering
the cost-effectiveness of catalyst preparation. Therefore, it is
imperative to identify the mechanisms controlling isomer
formation and interconversion, and to establish facile methods
that selectively afford complex products with the desired
coordination sphere.
other reported chemical reduction methods under water
17a
treatment conditions.
Therefore, further development of
oxorhenium complexes and the corresponding transformation
into heterogeneous functional materials show great promise for
addressing environmental, health, and energy challenges.
During our initial efforts synthesizing Re(O)(hoz) Cl
2
following literature methods, we obtained a mixture of two
−
Re(O)(hoz) Cl isomers showing different ClO reduction
2
4
activity. After laborious isolation efforts, we characterized the
two isomers as N,N-trans (2a) and N,N-cis (2b) (Figure 1), the
Herein, we report a systematic investigation of N,N-trans and
N,N-cis Re(O)(LO−N)2Cl isomers covering the following
aspects: formation and interconversion during synthesis, ligand
exchange dynamics, and catalytic ClO4− reduction activities.
First, we identify the formation mechanism of Re(O)(hoz) Cl
2
(
designated OO for the noncoordinating heteroatom on the N-
containing ring) isomers (N,N-trans 2a and N,N-cis 2b). A
novel synthetic strategy is developed, which uses pyridine bases
with varying levels of steric hindrance to control the conversion
of 2b to the desired and thermodynamically favored 2a.
Findings from this work also provide revised structural and
mechanistic interpretations of data presented in previous
Figure 1. Previously reported Re(O)(hoz) Cl isomers.
2
−
former showing much higher ClO reduction activity than the
4
5e,20,23
1
9
20
latter. Recently, Schachner et al. also reported on the
reports.
Next, to generalize the isomerism−property
−
isolation and variable homogeneous ClO4 reduction activities
relationship, we extended the LO−N ligand selection from Hhoz
to Hhtz (2-(2′-hydroxyphenyl)-2-thiazoline). Surprisingly,
ligand modification of the noncoordinating heteroatom from
O to S resulted in a reversed thermodynamic preference of
of 2a and 2b. Isomerism is a frequently encountered
phenomenon during the synthesis of Re(O)(LO−N)2X com-
plexes, which have six possible configurations (Figure 2). The
5b
number of literature reported N,N-trans Re(O)(L ) X
N,N-cis Re(O)(htz) Cl (SS) over the N,N-trans SS isomer.
2
O−N 2
5
a,b,d,e,j
structures (type A)
are much less than N,N-cis structures
Finally, hybridization of hoz and htz in a single Re complex
(OS) led to the selective preparation of N,N-trans Re(O)-
5
b−i
(type B).
No examples of type C or D have been reported,
probably due to the trans influence of the oxo group. Multiple
(hoz)eq(htz)axCl. Comparison among the five Re(O)(LO−N) Cl
2
examples of the C -symmetric structure (type E, X = OMe or
structures identified significantly different behaviors with
2
2
1
OH2) have been documented, while only one example of the
CS-symmetric structure (type F, X = Cl) has been observed.
respect to ligand exchange dynamics, which are correlated
22
−
with catalytic ClO4 reduction activities.
However, except for the single case of Re(O)(hoz) Cl isomers,
there has been no other study comparing the effects of isomeric
coordination sphere on spectroscopic and catalytic properties
2
RESULTS
■
Controlled Synthesis of N,N-trans and N,N-cis Re(O)-
of Re(O)(L ) X complexes.
(hoz) Cl (OO) Complexes. The Re(O)(hoz) Cl isomers 2a
O−N 2
2
2
Synthetic challenges might be a major factor hindering
isomer-specific investigations. Strategies for controlling Re(O)-
and 2b were initially obtained following a previously reported
method, where a Re(O) (OPPh )(SMe )Cl precursor (1), 2
3 2 3
23a
B
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a
equiv of Hhoz ligand, and a stoichiometric amount of 2,6-
Table 1. Formation of Re(O)(hoz) Cl Isomers 2a and 2b
2
Me Py base (for scavenging HCl) were heated in refluxing
2
1
ethanol for 3 h. As determined by H NMR, the product
contained 2a and 2b at a 63:37 ratio. 2a was purified by three
rounds of recrystallization from CH Cl /pentane. 2b was
2
2
enriched in the mother liquor and isolated by silica gel
chromatography using EtOAc as eluent, while 2a tailed in the
column. ORTEP diagrams and crystal data of 2a and 2b
obtained by our efforts are provided in Figure S1, Table S1, and
Table S2 in Supporting Information. We noted here that we
provide a different 2b crystal structure (crystallized with
toluene) as a higher quality alternative to that recently reported
2
0
by Schachner et al., which contained structural problems with
the model showing poor displacement ellipsoids and high level
20
CIFCheck warnings. In comparison, Schachner et al. followed
8
an earlier synthesis method without using 2,6-Me Py, and
2
obtained a roughly 50:50 mixture of the two isomers regardless
of solvents and Re precursors used during synthesis. In their
report, 2a precipitated out of ethanol, and 2b was collected
from the mother liquor and purified by Soxhlet extraction with
diethyl ether to remove the residual 2a. Because these early
approaches are very laborious, we aimed to develop a
convenient and generalized methodology for isomer-specific
synthesis of Re(O)(LO−N)2Cl complexes, which would benefit a
broad range of oxorhenium chemistry study.
a
Reaction conditions: 1 (20 mg, 0.031 mmol), Hhoz (10.1 mg, 0.062
b
mmol), ethanol (1.2 mL), and reflux (80 °C oil bath). In molar
equivalents relative to Hhoz. Ratio determined with H NMR (500
MHz, CDCl ) from integration area of δ 7.90 (2a) and δ 7.81 (2b)
doublets. Reaction at room temperature. Unknown products besides
The discrepancy of the isomer ratio yielded from our early
c
1
20
approach (63:37) and from the approach by Schachner et al.
50:50) suggested that 2a and 2b might be subject to
3
d
e
(
interconversion. Thus, we monitored product formation at
selected time intervals and found that 1 was quickly converted
to an ∼1:1 mixture of 2a and 2b within 10 min of initiating the
reaction but that prolonged heating slowly converted 2b into 2a
2a and 2b also formed.
A simple method to exclusively yield 2a was thus established
by using an excess amount of 2,4- or 2,6-Me Py and heating for
2
(
Table 1, entries 1 to 4). DFT calculations indicate that 2a has
48 h. Meanwhile, 2b could not be prepared higher than 50%
yield when a base was used. An attempt to exclusively
synthesize 2b without adding base was unsuccessful, but a
new product, [H hoz][Re(O)(hoz)Cl ] (3, Figure 3), was
−1
a lower Gibbs free energy than 2b (ΔG = −0.59 kcal mol at
7
8 °C in ethanol; more detailed results are provided in Table
S3). Since both isomers have limited solubility in ethanol, we
first attempted to accelerate the conversion by dissolution in
chloroform. However, no conversion was observed in chloro-
form, suggesting the need for a polar reaction environment.
Instead, the conversion in ethanol was accelerated by adding
2
3
2
2
obtained. Results agree with Lobmaier et al. who synthesized
Re(O)(L ) Cl complexes from another commonly used
O−N 2
precursor, [NBu ][Re(O)Cl ]; reaction with 2 equiv of
4
4
bis(alkyl/aryl)-(2′-pyridyl)alcoholate ligands without added
−
excess 2,6-Me Py (Table 1, entries 5 to 8). Direct mixing of 1
base resulted in the formation of [Re(O)(L )Cl ] and
O−N 3
2
+
with 2,6-Me Py, which is commonly used as a sterically
[H2LO−N] , and 4 equiv of HL
were necessary to synthesize
2
O−N
hindered noncoordinating base, resulted in a dark brown
product. Therefore, the two methyls do not completely block
Re(O)(L ) Cl, where 2 equiv of HLO−N were sacrificed as a
O−N 2
8,20
base. These findings contrast the earlier reports,
where only
24
coordination with Re (2,6-Me Py coordination with Os and
2 equiv of Hhoz were used without added base to synthesize
2
25
Pt have also been reported), and it appears that this
coordination plays a key role in the isomer interconversion.
Pyridine bases with a variety of substitutions were evaluated
to probe the structural effects on Re isomer interconversion.
Nonsubstituted Py resulted in some uncharacterized products
attributed to its strong binding with Re (Table 1, entries 9 and
the mixture of 2a and 2b. The results also suggest that
−
[Re(O)(hoz)Cl ] is an intermediate that reacts with a second
3
hoz ligand to yield 2a and 2b with equal probability. To verify
this mechanism, we synthesized [HtBu Py][Re(O)(hoz)Cl ]
2
3
(4) from 1 with stepwise and slow addition of 1 equiv of Hhoz
and 1 equiv of 2,6-tBu Py base (Figure 3). Subsequent reaction
2
10). Substitution with one methyl in 2-MePy destabilized the
of 4 with a second equivalent of Hhoz and 2,6-tBu Py afforded
2
Py-Re binding and yielded 2a and 2b but did not promote
2a and 2b in 1:1 ratio. Thus, the highest yield of 2b remains
limited to 50%. The initial 1:1 formation of two isomers is
kinetically controlled since 2a is thermodynamically favored
over 2b, but the exact mechanism remains unclear.
isomer interconversion (entries 11 and 12). The 2,4-Me Py,
2
with a higher electron density on N but the same steric
hindrance of coordination as 2-MePy, achieved even faster
isomer interconversion than 2,6-Me Py (entries 13 and 14).
Thus, both partial steric hindrance and enhanced electron
Synthesis of N,N-trans and N,N-cis Re(O)(htz) Cl (SS)
Isomers with Reversed Formation Preference. Previously,
2
2
density on the coordinating Py are important for catalyzing the
the coordination sphere of Re(O)(htz) Cl was reported as
2
2
6
23b
isomer conversion. As expected, the bulky 2,6-tBu Py showed
N,N-cis. The success on the Re(O)(hoz) Cl isomer synthesis
2
2
no effect on the conversion (entries 15 and 16). A mechanism
for Py-facilitated isomer interconversion from 2b to 2a is
proposed in the Supporting Information (Scheme S1).
motivated us to obtain the corresponding N,N-trans Re(O)-
(htz) Cl structure, which would enable the comparison of
2
ligand effects with the same Re coordination sphere. Thus, we
C
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Figure 4. Formation and conversion of Re(O)(htz) Cl isomers
2
(
structures shown with 35% probability thermal ellipsoid ORTEP
diagrams). DFT-calculated relative Gibbs free energy (in EtOH at 78
C) is provided.
°
preference motivated us to hybridize the two ligands in a single
heteroleptic Re complex. As illustrated in Figure 5, two
intermediates, [Re(O)(hoz)Cl3]− (4) and [Re(O)(htz)Cl3]−
(
6), were first prepared from 1. Both structures have the LO−N
ligand occupying the axial position along the oxo bond. After 4
and 6, respectively, reacted with a second Hhtz or Hhoz, we
were surprised to find that regardless of the hoz/htz addition
sequence the final product was N,N-trans Re(O)-
(
hoz) (htz) Cl (7a). DFT calculations suggest that 7a is
eq ax
Figure 3. Formation and conversion of hoz-coordinated Re complex
products. Structure of 3 is shown with a 35% probability thermal
ellipsoid ORTEP diagram. DFT-calculated relative Gibbs free energy
more stable in comparison with the other three possible
isomeric structures 7b, 7c, and 7d (Figure 5). Notably,
although hoz initially occupied the axial position in 4, it shifted
to the equatorial position when htz was added. This implies
that the mechanism for the initial 1:1 formation of 2a and 2b,
as well as 5a and 5b, could be more complicated than a
previously conceived process, where two equatorial Cl ligands
in 4 and 6 were substituted by the second LO−N while the axial
(
in EtOH at 78 °C) is provided.
targeted the synthesis of N,N-trans Re(O)(htz) Cl (5a)
2
following the method of using excess Me Py that exclusively
2
yielded the N,N-trans 2a and isolation of N,N-cis Re(O)-
(
htz) Cl (5b) from the initial 1:1 isomer mixture by
L
O−N remained static.
With both ligand hybridization sequences for the synthesis,
2
chromatographic separation.
Again, two isomers initially formed in an approximately 1:1
ratio after 15 min (Figure 4). Consistent with the isolation of
7a was already dominant within 15 min after adding the second
O−N equivalent to 4 or 6. A minor product (∼17%) observed
at 15 min gradually disappeared over the following 48 h when
heating with excess Me Py. Because of the low solubility of the
L
2
b, 5b could be selectively eluted with silica gel chromatog-
raphy, and crystallography confirmed the N,N-cis structure.
Surprisingly, ligand shift from hoz to htz reversed the direction
of isomer interconversion during prolonged heating with excess
2
hybrid ligand complex products, the minor species was not
isolated. However, based on the observed preference of htz at
the axial position and the DFT calculation results (Figure 5),
N,N-cis Re(O)(hoz)eq(htz)axCl (7c) is the most probable
structure for this transient product. In addition, another set of
Me Py. After 48 h, the initially formed 5a converted completely
2
to 5b, consistent with the lower Gibbs free energy calculated
for the latter. As a result, isolation of 5a (confirmed by
crystallography to be the N,N-trans structure) from the 1:1
isomer mixture required multiround extraction with chloroform
1
H NMR peaks (see NMR spectra in Supporting Information)
was observed in the CDCl3 solution of recrystallized 7a.
+
(where the solubility of 5a is much higher than that of 5b).
However, cationic 7a prepared from the same batch of 7a
Synthesis of N,N-trans Re(O)(hoz)(htz)Cl (OS). The
competition between hoz and htz in determining trans/cis
showed high purity (see below). Thus, an isomerization
occurred in the CDCl solution of 7a, but the structure of
3
D
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Figure 5. Synthesis of Re(O) (hoz)(htz)Cl. Structure of 7a and the anionic part of 4 (the same as 3) and 6 are shown with 35% probability thermal
ellipsoid ORTEP diagrams. Three theoretical isomer structures are shown in the green area. DFT-calculated relative Gibbs free energies (in EtOH at
7
8 °C) are provided.
+
this isomer and related conversion mechanism remain unclear.
The OS hybrid design reversed the N,N-cis isomer preference
encountered during SS complex synthesis.
to Re-coordinated CH CN appeared (δ 2.83 for 2a and δ 3.07
3
+
for 2b , both with an integration area of 0.3 as a result of the
10% probability of CH CN coordination; Figure 7). At room
3
Ligand Exchange Dynamics of Homoleptic [Re(O)-
temperature, presaturation of free CH CN resonance at δ 1.94
3
+
+
(
hoz) ] and [Re(O)(htz) ] Cations. First, 2a and 2b were
caused partial suppression of the Re-coordinated CH CN
2
2
3
+
+
+
converted into cationic [Re(O)(hoz) ] structures (2a and
b , respectively) with AgOTf in CD CN. Compared to
resonance in 2a , supporting the dynamic exchange between
2
+
2
Re-bound and free solvent molecules. At different temperatures
3
Re(O)(hoz) Cl precursors, the cationic species showed darker
(T), the solvent ligand exchange rate constants (k ) were
determined according to eq 2:
2
S
green colors (see Supporting Information for UV−vis spectra).
According to the electronic structure analysis by Machura et
5
h,j,27
kS = π(ω1/2 − ω0)
(2)
al.,
the HOMO of Re(O)(LO−N)2X complexes is a mixture
and X ligands.
of Re d orbitals and the π orbitals of both L
Thus, the exchange of ligand X from Cl to CH CN led to
O−N
where ω1/2 and ω indicate the measured half-height line width
0
−
3
(Hz) for resonances of Re-coordinated and free CH CN,
3
altered energies of charge transfer from HOMO to LUMO (or
higher orbitals) responsible for the visible light adsorption. At
⧧
⧧
respectively. Activation enthalpy (ΔH ) and entropy (ΔS ) of
CH CN exchange with 2a and 2b were obtained via eq 3:
+
+
28
3
1
room temperature, H NMR showed an apparent symmetry for
+
+
ΔH⧧
ΔS⧧
the two hoz ligands in 2a but not in 2b (Figure 6). VT NMR
kS
T
+
log
= 10.32 −
+
showed asymmetric resonances of 2a at lower temperature and
broadened resonances of 2b at elevated temperature,
suggesting that 2a has a much faster intramolecular exchange
19.14T
19.14
(3)
+
⧧
+
As shown in Table 2 (entries 1 and 2), ΔS values are highly
positive for both isomers and consistent with a dissociative
mechanism. The marked difference of ΔH for 2a and 2b
thus derives from the step of solvent ligand dissociation from
+
of the two hoz ligands than 2b . At −12.9 °C, where the
⧧
+
+
+
coalescence of δ 7.87−8.02 resonances of 2a was observed, the
hoz ligand exchange rate constant (k ) was calculated to be 160
L
+
+
−1
[
Re(O)(hoz) (NCCH )] . The estimated k values for 2a and
s
according to eq 1:
2 3 S
+
−1
2
b at 25 °C differ by a factor of 5,300 (24,000 s versus 4.5
−
1
+
−1
πΔν
2
s ). The calculated k for 2a at −12.9 °C is 320 s , twice the
S
kL =
−1
hoz ligand exchange rate k (160 s ) measured with the
(1)
L
coalescence approach (eq 1). This validates the proposed hoz
exchange mechanism involving solvent dissociation (Figure 6);
either retention or exchange of the axial/equatorial position of
the two hoz takes 50% probability. The hoz ligand exchange in
where Δν represents the separation of frequency (Hz) between
28
the two coalescing resonances.
We propose five-coordinate structures, upon solvent
+
+
+
dissociation, as the intermediates (2aI and 2bI in Figure 6)
during the exchange of the two hoz ligands. To quantify the
2a does not alter the Re complex structure, whereas ligand
+
+
exchange in 2b yields the enantiomeric 2b′ . Results shown
here correct a previously interpreted structure for 2a+ in
CD CN as C -symmetric with a H O coordinated trans to the
solvent dissociation rate, 10% (v/v) CH CN was added to the
3
+
+
CD CN solutions of 2a and 2b . A new singlet corresponding
3
3
2
2
E
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1
+
+
Figure 6. VT H NMR (500 MHz, CD CN) spectra and proposed ligand exchange mechanisms for (a) 2a and (b) 2b .
3
2
0,23
+
oxo group,
although such a structure was obtained upon
The preparation of 5a from 5a with AgOTf was rapid at
+
crystallization in water-containing solvent (Figure S2). We also
note that the previously proposed interconversion between two
room temperature, whereas the preparation of 5b required
heating at 80 °C for at least 2 h. Thus, replacement of the
noncoordinating heterocyclic O with S slows Re−Cl dissoci-
ation. VT NMR measurement also showed generally slower
solvent ligand dissociation from htz-coordinated structures than
from the corresponding hoz-coordinated structures. At room
temperature, 5a showed only two broad resonances in the
aliphatic region but gradually resolved into eight resonances as
temperature was lowered (Figure 8). The CH CN dissociation
rate constants at 25 °C for 5a and 5b were measured (Figure
5e,20
N,N-trans cationic enantiomers
is less likely because
enantiomerization of 2a+ into 2a′ requires complicated
+
physical contortions.
+
The varying tendency for ligand dissociation from 2a and
does not only apply to the neutral solvent. When
Re(O)(hoz) ] was prepared from Re(O)(hoz) Cl isomers,
+
+
2
b
+
[
2
2
3
AgCl precipitation was immediately observed upon addition of
AgOTf to the suspension of 2a but was delayed by several
seconds when the silver salt was added to 2b. Density
functional theory (DFT) calculations performed by Schachner
et al. suggested a 3−4 kcal mol higher energy required to
remove Cl from 2b than 2a. This difference in tendency to
dissociate Cl− allowed for convenient chromatographic
isolation of 2b from 2a (5b can be exclusively synthesized, so
the chromatography isolation is not needed). Using pure ethyl
+
+
S3; Table 2, entries 3 and 4) and found to be smaller than those
+
+
for 2a and 2b , respectively. The alteration of O to S led to a
1
⧧
3
−4 kcal mol− increase in ΔH of CH CN dissociation from
2
0
−1
3
Re.
Ligand Exchange Dynamics of Heteroleptic [Re(O)-
hoz)(htz)] Cation. 7a was prepared from 7a in a similar way
+
+
(
+
+
to the preparation of 2a and 5a . VT NMR showed markedly
different behavior of this heteroleptic [Re(O)(hoz)(htz)]+
+
acetate, 2b was readily eluted as a narrow green band (R = 0.7).
f
cation in comparison to that of the homoleptic [Re(O)(hoz) ]
2
−
+
and [Re(O)(htz)2]+ cations. At room temperature, an
In contrast, the facile dissociation of 2a yields Cl and 2a ,
which is electrostatically attracted to the anionic silica gel,
resulting in delayed elution with significant tailing even after
switching the eluent to pure methanol.
asymmetric set of resonances was observed (Figure 9a).
At first glance, N,N-trans 7a seems to behave similarly to the
two N,N-cis 2b and 5b . However, no Re-coordinated CH CN
+
+
+
3
F
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Inorganic Chemistry
Article
+
temperature increased, the ratio of 7b in the equilibrium was
elevated, and the interconversion was accelerated, leading to
the coalescence and slight shifts of the resonances (Figure 9a).
Results also suggest a CH CN dissociation process with
3
reduced LO−N movement around Re. While C -symmetric
2
+
+
square pyramidal intermediates, 2aI and 5aI , are proposed for
OO and SS cations (Figure 6 and Figure 8), the dominant 7aI+
structure might be distorted. First, both experimental
observations and DFT calculations indicate that htz and hoz
have specific location preferences in the OS hybrid complex.
We propose that the square pyramidal five coordinate
+
+
intermediate 7aI* and its further conversion to 7b are not
⧧
favored (Figure 9a). Second, the distinctively low ΔS (Table
) likely originates from the relatively reduced geometry change
occurring upon solvent dissociation. The lowered ΔH may
also be due to the relatively reduced L movement. The
calculated solvent exchange rate constant k for 7a at 25 °C is
correspondingly lowered to 1,400 s .
2
⧧
O−N
+
S
−1
Catalytic Perchlorate Reduction in Homogeneous and
Heterogeneous Systems. The differences in monodentate
ancillary ligand dissociation of N,N-trans and N,N-cis isomers
correlate with differences in rates of homogeneous catalytic
−
ClO4 reduction by Me S, as first demonstrated by the
2
+
+
comparison between 2a and 2b (Figure 10a). The proposed
multistep process is illustrated in Scheme 1. The dominant Re
+
species present in the reaction initiated with 2a was actually
the chloride form 2a (Figures S6 and S7a), suggesting that the
bound Cl− is labile to exchange with ClO4− and ClOx−
intermediates. In contrast, the major Re species observed in
the reaction initiated with 2b+ was first the sulfoxide-
1
Figure 7. VT H NMR (500 MHz, CD CN) spectra (half-height line
+
3
coordinating structure [Re(O)(hoz) (OSR )] , which slowly
+
+
2
2
width shown) of CH CN coordinated in 2a (left) and 2b (right).
Inset plots: model fitting for measured solvent exchange rate (k ) and
temperature (T).
3
−
transitioned to the chloro structure 2b as the Cl product built
S
up over a period of 4 h (Figures S7b and S8). In addition, DFT
20
calculations reported previously by Schachner et al. suggests
−
V
−
that, after the OAT from ClO4 to Re , the ClO3 product was
Table 2. Calculated Activation Enthalpy and Entropy, and
Rate Constant at 25 °C for the Solvent Ligand Exchange
between [Re(O)(LO−N)2(NCCH )] and the Free CH CN
much more difficult to dissociate from the oxidized N,N-cis
VII
+
VII
+
+
[Re (O) (hoz) ] than from N,N-trans [Re (O) (hoz) ] .
2 2 2 2
3
3
Although a quantitative model describing the multistep
processes is difficult to establish, findings collectively suggest
Solvent
entry cation ΔH⧧ (kJ mol−1
)
a
ΔS⧧ (J K−1 mol−1
)
a
kS (s−1) at 25 °C
that the generally faster monodentate ligand dissociation from
1
2
3
4
5
2a+
70.8 ± 6.4
94.8 ± 3.3
75.2 ± 0.9
98.1 ± 7.6
62.5 ± 1.4
76.3 ± 26.2
85.4 ± 10.9
78.1 ± 3.6
87.1 ± 23.8
25.1 ± 5.7
2.4 × 104
4.5
5.0 × 103
1.4
1.4 × 103
N,N-trans structures leads to greater reactivity with ClO . The
−
4
+
−
2b
accumulation of Cl in solution effectively prevents 2b from
+
+
−
5a
dissociating into the active 2b such that complete ClO
4
+
5b
reduction could not be achieved within 2 d. In contrast to the
+
20
7a
earlier report where Ph S was used as the reductant (k = 1.1
2
a
−1 −1
VII
+
Errors represent 95% confidence intervals.
M
7
s ), [Re (O) (hoz) ] reduction by Me S and Et S (k =
2 2 2 2
−1
−1
500 and 6900 M s , respectively) is much faster than the
+
−
−
−1 −1
singlet was observed after the 10% CH CN addition (Figure
oxidation of 2a by ClO
4
and ClO
3
(k = 0.45 and 28 M s ,
3
23b
S4), indicating a rapid solvent exchange at room temperature.
At lower temperature, the hoz/htz resonances first broadened
and then turned into sharp peaks with slightly altered chemical
shifts (Figure 9a). Meanwhile, a gradually sharpened Re-
coordinated CH CN singlet at δ 2.75 was also observed (Figure
S4), and the calculated ΔH and ΔS , as well as k at 25 °C
Table 2, entry 5) were the lowest among the three N,N-trans
cations. Comparison of H NMR spectra of the three N,N-trans
cations at the lowest temperature examined (Figure 9b)
suggests that the axial htz and equatorial hoz in the OS hybrid
a have very similar chemical environments to those of the
corresponding htz and hoz ligands in 5a and 2a . Examination
of the H NMR spectrum for 7a at −34.4 °C identified a small
amount of equatorial htz and axial hoz (Figure S5), indicating
respectively). Therefore, throughout the reaction we did not
+
observe [H
hoz] , which is indicative of the accumulation of
2
VII
+
−
[Re (O)
and [H hoz] .
(hoz)
] and subsequent decomposition to ReO
2
2
4
+
17c
2
−
For aqueous heterogeneous ClO4 reduction, 2a and 2b
were immobilized in Pd/C by absorption via transient
dissolution in water, which is more convenient to operate
than the traditional incipient wetness method in terms of
protecting the heterogenized Re species from oxidation by
3
⧧
⧧
S
(
1
17a
Immobilization was accompanied by quantitative Cl−
air.
+
7
release from both isomers. Cationic Re complexes are
immobilized in activated carbon matrix via both hydrophobic
+
+
1
+
17a
and electrostatic interactions. As shown in Figure 10b, the
resulting Re(hoz) −Pd/C catalyst prepared from 2a exhibited a
2
+
+
−
the presence of ∼2% 7b in the solution of 7a . As the
24-fold greater pseudo-first-order rate constant for ClO
4
G
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1
+
+
Figure 8. VT H NMR (500 MHz, CD CN) spectra and proposed ligand exchange mechanism for (a) 5a and (b) 5b . Impurities marked with
3
+
asterisks represent 5a formed during the chloride abstraction from 5b under reflux temperature.
reduction (Table 3) than that prepared from 2b, in line with
the general trend observed for homogeneous reactions and
ligand exchange kinetics.
Re(hoz)(htz)−Pd/C catalyst provided an activity falling
between that observed for the Re(hoz) −Pd/C and Re-
2
(htz)
(Table 3).
−Pd/C catalysts prepared from the N,N-trans complexes
2
−
+
+
Homogeneous ClO4 reduction using 5a and 5b (Figure
+
1
2
1a) was found to be slower than the corresponding 2a and
+
−
b . We note that the small amount of ClO reduction
observed with 5b is actually attributed to the presence of
10% 5a generated during the preparation of 5b under
heating (Figure 8b). Aqueous ClO reduction using Re-
DISCUSSION
4
■
+
Control and Determination of the Re(O)(LO−N)2Cl
+
+
∼
Isomer Structure. The isomer interconversion results for 2a
versus 2b and 5a versus 5b demonstrate that alteration of the
noncoordinating heteroatom in the ligand structure can reverse
the relative stability of competing isomers. Earlier results of
−
4
(
htz) −Pd/C prepared from 5a and 5b (Figure 11b) also
2
shows that heterogenized Re(htz) sites provide lower activity
2
5b
than Re(hoz) . Here, the heterogeneous catalyst prepared from
2
Re(O)(L ) Cl from the Herrmann group and from the
O−N 2
5d
−
the high purity N,N-cis 5b showed no activity, even though Cl
̈
Mosch-Zanetti group suggest that steric hindrance of LO−N
dissociated upon immobilization in Pd/C at room temperature.
ligands favor the formation of the N,N-trans isomer over the
N,N-cis isomer. However, these trends were deduced from a
small number of Re(O)(LO−N)2Cl analogues synthesized in
individual studies. The majority of Re(O)(LO−N)2Cl complexes
prepared with similar or larger sized hoz analogues, including
aryloxides (e.g., phenolates, naphtholates) linked with thiazo-
line, pyrazoles, and benzoheterocycles (e.g., benzoxazole,
These results confirm that N,N-trans structures provid−e
substantially faster ligand dissociation and higher ClO4
reduction activity than N,N-cis structures, demonstrating the
importance of developing effective synthetic strategies to
selectively yield the more reactive N,N-trans isomers for
optimum catalytic properties.
−
+
Homogeneous ClO reduction using 7a showed similar
benzothiazole, benzimidazole and benzotriazole), were re-
4
+
5e−g
activity with 5a (Figure 12), whereas the heterogeneous
ported as N,N-cis.
Therefore, hoz is a relatively unique
H
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Article
1
+
Figure 9. (a) VT H NMR (500 MHz, CD CN) spectra and proposed ligand exchange mechanism for 7a . DFT-calculated relative Gibbs free
3
+
+
energies for 7a and 7b (in CH CN at 25 °C) are provided. Dotted lines indicate the shift of resonances from 23.7 °C to −34.4 °C. (b)
Comparative assignment of H NMR resonances from equatorial hoz and axial htz ligands in the three N,N-trans cations.
3
1
ligand favoring N,N-trans structure. Preparation of the
thermodynamically favored 7a as N,N-trans suggests a
promising strategy for tuning both structure and functionality
via ligand hybridization. In this specific case, hoz contributed to
the metal economy and ease of synthesis of the desired N,N-
cationic [Re(O)(hpz) (NCMe)]+ formed after chloride
2
5e
abstraction was reported as N,N-trans. As another example,
VII
+
the crystal structure obtained for [Re (O) (hoz) ] following
2
2
+
23b
oxidation of 2a was reported as N,N-cis; however, both our
experimental observation and the earlier DFT calculations
20
−
trans OS hybrid structure 7a for ClO4 reduction catalysis. As
suggest that N,N-trans and N,N-cis structures do not
interconvert during ClO4− reduction catalysis. Thus, the most
reasonable explanation for these unexpected isomer “con-
versions” is the presence of an isomeric impurity, which
preferentially formed easy-to-distinguish single crystals that
were selected by investigators for X-ray analysis. Therefore, for
an additional note, attempts at forming 7a by heating a 1:1
mixture of the homoleptic N,N-cis complexes 2b and 5b were
unsuccessful. The lack of conversion of the two starting
complexes suggests no intermolecular LO−N ligand exchange.
Kinetically controlled formation of the 1:1 mixture of N,N-
trans and N,N-cis isomers at the beginning of synthesis and the
thermodynamically controlled isomer interconversion with
prolonged heating suggest that opportunities to identify and
isolate Re(O)(LO−N)2Cl isomers might have been missed in
earlier reports. In the majority of studies, the reaction mixtures
the synthesis of a variety of oxorhenium complexes, Me Py-
2
promoted isomer conversion might serve as a convenient
method to minimize or eliminate other isomers in the raw
product, thus enabling facile product purification and reducing
the possibility of getting incorrect structural and mechanistic
information.
21
were heated for 2 to 48 h. During these times, different
isomers might have converted to the thermodynamically
favorable configuration (N,N-cis in majority of cases). Besides,
crystallization from a mixture of isomers may have created
artifacts in the determination of the targeted compound. This
could further lead to incorrect interpretation during the
subsequent elucidation of reaction mechanisms and struc-
ture−property relationships. For example, the crystal structure
Structure−Activity Relationship and Reaction Mech-
anisms. Results in this contribution demonstrate the critical
role that the Re coordination sphere plays in catalyst activity.
Rates of solvent ligand exchange are 3 orders of magnitude
+
different between two isomers (i.e., 5300-fold for 2a versus
+
+
+
2b ; 3600-fold for 5a versus 5b ). From the data in Table 2,
⧧
the corresponding activation energy differences (ΔΔG ) at 25
−
1
−1
of Re(O)(hpz) Cl (hpz = 3-(2′-hydroxyphenyl)-1-methyl-1H-
°C are 5.1 kcal mol and 4.8 kcal mol , respectively. In
20,23b
2
pyrazole) was reported as N,N-cis; however, the corresponding
previous studies,
this solvent dissociation was assumed as a
I
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Table 3. Summary of 1 mM Aqueous ClO − Reduction
4
Kinetics by Heterogeneous Re−Pd/C Catalysts
pseudo-first-order rate constant (L h− gcat−1)a
1
catalyst precursor
2
2
5
5
7
a
b
a
b
a
5.81 ± 0.17
0.24 ± 0.02
1.03 ± 0.02
no reaction
2.03 ± 0.04
0.047 ± 0.003
−
ReO4
a
Errors represent 95% confidence intervals.
−
Figure 10. (a) Homogeneous ClO4 reduction (as indicated by sulfide
+
+
oxidation) catalyzed with 2a and 2b . Reaction conditions: Re (4
mM), LiClO4 (100 mM), and Me S (400 mM) in 95/5 (v/v)
2
−
CD CN/D O at 25 °C. (b) Heterogeneous aqueous ClO reduction
3
2
4
by 1 atm H catalyzed with Re(hoz) −Pd/C prepared from 2a and 2b.
2
2
−1
Reaction conditions: catalyst (5 wt % Re and 5 wt % Pd, 500 mg L )
and NaClO (1 mM) in pH 3 water at 25 °C.
4
−
Scheme 1. Proposed Mechanism of Re-Catalyzed ClO
Reduction
4
a
−
+
Figure 11. (a) Homogeneous ClO reduction catalyzed with 5a and
4
+
−
5
b and (b) heterogeneous ClO4 reduction catalyzed with Re(htz) −
Pd/C prepared from 5a and 5b. Reaction conditions are the same as
2
those described in Figure 10.
−
+
Figure 12. (a) Homogeneous ClO4 reduction catalyzed with 7a and
(
−
b) heterogeneous ClO4 reduction catalyzed with Re(hoz)(htz)−Pd/
C prepared from 7a. Reaction conditions are the same as those
a
The blue area indicates the heterogeneous catalysis pathway; the
described in Figure 10.
orange area indicates the decomposition pathway.
steps (Scheme 1) determine the overall reaction rate. Also, we
fast step, and the rate-determining step (RDS) was proposed to
observed markedly different rates of sulfoxide dissociation (i.e.,
+
+
+
be the reaction between five-coordinate [Re(O)(hoz) ] and
much slower from 2b than from 2a ) and chloride dissociation
(i.e., 5b requires a high temperature to react with AgOTf) from
these isomers. Re−Cl bond distances in N,N-cis structures are
generally shorter than those in N,N-trans structures (Table S2),
but a quantitative correlation for the five complexes was not
observed between Re−Cl distances and ligand dissociation
2
−
⧧
ClO . DFT-calculated ΔΔG on this simplified reaction
model was 9.9 kcal mol . Direct comparison between the
DFT-calculated ΔΔG and measured ΔΔG for two different
steps is not meaningful; however, the values are the same order
of magnitude and imply a possible scenario where multiple
4
−1
20
⧧
⧧
J
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Inorganic Chemistry
Article
3
c,e
kinetics. A deeper mechanistic understanding in future efforts
might necessitate examination of energy levels and electronic
structures of transition states and intermediates involved in
multiple reaction steps, as well as an upgraded reaction model
for the overall catalytic cycle.
for biomedical design.
Thus, rationally tuned ligand
exchange kinetics and patterns might influence the activity
and stability of functional oxorhenium complexes in both
catalysis and biomedical applications. The fundamental
coordination chemistry acquired from oxorhenium might also
33
32
Heterogenization in the activated carbon matrix facilitated
activity evaluation of individual Re complexes. During
be transferred to develop oxomolybdynum and oxotungsten
complexes. Tunable functionalities of these complexes are
anticipated to inspire innovation in a broad range of
environmental, energy, and healthcare technologies.
−
homogeneous ClO4 reduction (TON = 100 upon comple-
+
tion) using presynthesized N,N-trans [Re(O)(LO−N)2] , the
dominant Re species in solution after the reaction started was
Re(O)(L ) Cl. Except for 2a, all Re complexes were severely
CONCLUSIONS
O−N 2
■
−
−
inhibited by the Cl product before 50% ClO was reduced. In
4
Three N,N-trans Re(O)(L ) Cl complexes (2a, 5a, and 7a)
O−N 2
contrast, during the immobilization of Re(O)(LO−N)2Cl
and two N,N-cis Re(O)(LO−N)2Cl complexes (2b and 5b) were
synthesized. For OO and SS complexes, a 1:1 mixture of N,N-
trans and N,N-cis isomers were initially obtained, and the
mixtures fully converted to thermodynamically favored 2a and
−
precursors in Pd/C, 0.134 mM Re-bound Cl was quantita-
tively released in water that already contained 1 mM HCl. For
all OO−, SS−, and OS−Pd/C catalysts, pseudo-first-order
kinetics were consistent during the complete reduction of 1−4
mM ClO4− (TON = 30−120). It appears that immobilized Re
species on carbon surface have substantially lowered affinity
5
b upon heating in ethanol with excess Me Py base. The hybrid
2
OS complex synthesized with two opposite LO−N addition
sequences afforded the same product 7a as N,N-trans
Re(O)(hoz) (htz) Cl. Cationic N,N-trans complexes ex-
−
−
with aqueous Cl . Except for H O (and OH ), the aqueous
2
eq
ax
phase does not contain other ligands, such as acetonitrile,
hibited 3 orders of magnitude faster solvent ligand dissociation
and intramolecular LO−N exchange than the corresponding
N,N-cis isomers. With the same Re coordination sphere, htz
sulfide, and sulfoxide involved in homogeneous catalysis.
−
Therefore, as reflected by heterogeneous ClO4 reduction
kinetics (Table 3), the intrinsic activity order for the five
complexes is 2a > 7a > 5a > 2b > 5b. The ligand effect on the
overall catalytic activity with the same N,N-trans or N,N-cis
coordination sphere is thus OO > OS > SS.
resulted in a slower ligand exchange than hoz. The ax/eq
+
preference of htz and hoz in the hybrid 7a reduced L
O−N
⧧
movement and ΔS for solvent dissociation, thus leading to a
+
+
slower ligand exchange than both 2a and 5a . The order of
ligand exchange rates of the five complexes roughly correlated
with the order of overall ClO4− reduction rates at the
heterogeneous Re(LO−N)2−Pd/C catalyst surface. Selective
synthesis of N,N-trans structures significantly contribute to
the application of catalytic ClO4− treatment in water. The
mechanistic insights benefit the development of functional
coordination complexes of Re and other metals for a wide range
of applications.
Significance in Water Technology Innovation. Per-
chlorate contamination of drinking water supplies is a serious
problem that recently caused several incidents of water supply
29
interruption in California. A life cycle assessment (LCA)
3
0
−
study for drinking water treatment of ClO4 indicated that
20-fold activity improvement of the first generation bimetallic
>
ReO −Pd/C catalyst (prepared from reductive immobilization
x
−
31
of ReO ) is necessary for catalytic treatment to be
4
competitive with conventional water treatment technologies
(
ion exchange and biological reduction). Therefore, improving
EXPERIMENTAL SECTION
reactivity of the immobilized Re component is vital for reducing
the loadings of immobilized Re and Pd. The activities of
■
General information. All chemicals and solvents were purchased
from Alfa-Aesar, Sigma-Aldrich, and Cambridge Isotope Laboratories,
and used as received. NMR (Varian Unity INOVA, operating at a
spectral frequency of 499.432 MHz), X-ray structure determination,
and elemental analysis were conducted in the NMR Laboratory,
George L. Clark X-ray Facility and 3M Materials Laboratory, and the
Microanalysis Laboratory in the University of Illinois School of
Chemical Sciences, respectively. Temperatures for VT−NMR were
calibrated with methanol (<25 °C) and ethylene glycol (>25 °C).
Half-height line width values were determined automatically using
Vnmr 6.1c. Aqueous solutions were prepared using deionized (DI)
water (Barnstead Nanopure system; resistivity >17.5MΩ cm). UV−vis
measurements were conducted on a Shimadzu 2550 spectropho-
tometer with solvent as background. Unless specified, all procedures
were conducted under air.
Re(O)(L ) −Pd/C catalyst prepared from 2a, 5a, and 7a are
O−N 2
approximately 110, 20, and 40 times more active than ReO −
x
Pd/C. In contrast, the catalyst prepared from 2b is merely 4
times more active than ReO −Pd/C, and the one prepared
x
from 5b shows no activity. Therefore, developing effective
strategies for isomer control contributes both fundamental
understanding of oxorhenium chemistry and supports the
development of innovative and practical water treatment
technologies. Further ligand structure modification is feasible
to continue the fine-tuning of Re complex reactivity, provided
that these ligands favor the formation of desired isomeric
structures. The successful immobilization of five different
complexes in Pd/C matrix also demonstrates that the
organometallic Re complex module in the biomimetic catalyst
can be flexibly replaced with a wider selection of structures.
Implications in Ligand Exchange Dynamics. Findings
in this study highlight a collection of strategies for controlling
ligand exchange dynamics. As summarized in Table 2, coarse
adjustment (i.e., orders of magnitude range) can be realized by
coordination sphere design, and fine-tuning (i.e., 3−5 times)
can be realized by ligand structure design. As suggested by VT
NMR observation, complexes with homoleptic and heteroleptic
ligand coordination exhibited different ligand movement
patterns, which impact the molecular shape that is important
Preparation of 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz). A
mixture of 2-hydroxybenzonitrile (1.19 g, 10 mmol), ethanolamine
(0.73 g, 12 mmol), ZnCl (68 mg, 0.5 mmol), and toluene (10 mL)
2
was refluxed in a 25 mL flask for 24 h. Then, the solvent was removed
in vacuo, and the residue was extracted with five portions of 5 mL of
Et O. The combined organic phase was dried, and the residue was
2
dissolved in EtOAc and purified by silica gel flash chromatography
(
hexanes/EtOAc = 4/1) to provide the product as a colorless oil,
which turned into a slightly orange-pink solid after being placed at −20
°
C overnight. Yield: 1.20 g (74%). Characterization data matched
34
those in the previous report.
Preparation of N,N-trans Re(O)(hoz) Cl (2a). A mixture of Re(O)
2
(OPPh )(SMe )Cl (500 mg, 0.770 mmol), Hhoz (277 mg, 1.70
3
2
3
K
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Inorganic Chemistry
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mmol), 2,6-lutidine (490 μL, 454 mg, 4.24 mmol), and EtOH (30 mL)
was refluxed in a 50 mL flask. The mixture turned gray-brown in the
first 5 min and then gradually turned forest green over the following
in [H hoz][Re(O)(hoz)Cl ]. Elemental analysis (C H N O Cl Re)
2
3
22 30
2
3
3
calculated: C, 39.85%; H, 4.56%; N, 4.22%; Cl, 16.04%; Re, 28.08%.
Found: C, 39.32%; H, 4.32%; N, 4.16%; Cl, 13.89%; Re, 28.34%.
Preparation of 2-(2′-hydroxyphenyl)-2-thiazoline (Hhtz). A
mixture of 2-hydroxybenzonitrile (1.19 g, 10 mmol), cysteamine
1
0 min. The green suspension was refluxed for 48 h. After cooling
down and filtering off the liquid phase through a glass frit, the solid
phase was sequentially washed with 3 × 2 mL of EtOH and 3 × 1 mL
(0.85 g, 11 mmol), ZnCl (27 mg, 0.2 mmol), and MeOH (10 mL)
2
1
of Et O to afford a green powder. Yield: 383 mg (88%). H NMR (500
was refluxed in a 25 mL flask under N for 5 h. Then, the solvent was
2
2
MHz, CDCl ) δ 7.90 (dd, J = 8.1, 1.8 Hz, 1H), 7.66 (dd, J = 7.9, 1.8
Hz, 1H), 7.41 (ddd, J = 8.7, 7.0, 1.8 Hz, 1H), 7.20 (ddd, J = 8.6, 7.3,
removed in vacuo, and the residue was extracted with five portions of 5
mL of diethyl ether. The combined organic phase was dried, and the
residue was dissolved in EtOAc and purified by silica gel flash
chromatography (hexanes/EtOAc = 4/1) to provide the product as a
yellow oil, which turned into a yellow solid after being placed at −20
°C overnight. Yield: 1.53 g (85%). Characterization data matched
3
1
.8 Hz, 1H), 6.93 (ddd, J = 8.2, 7.2, 1.1 Hz, 1H), 6.85 (dd, J = 8.6, 1.2
Hz, 1H), 6.80−6.75 (m, 2H), 5.09−4.74 (m, 6H), 4.32−4.21 (m, 2H).
Elemental analysis (C H N O ClRe) calculated: C, 38.47%; H,
18
16
2
5
2
.87%; N, 4.98%; Cl, 6.31%; Re, 33.13%. Found: C, 38.34%; H, 2.56%;
5
a
N, 4.90%; Cl, 6.14%; Re, 32.10%. UV−vis spectra in CH Cl solution
are shown in Figure S9a and b. Single crystals suitable for X-ray
those in previous reports.
2
2
Preparation of N,N-trans Re(O)(htz) Cl (5a). A mixture of Re(O)
2
diffraction were grown by diffusion of pentane into the CH Cl2
(OPPh )(SMe )Cl (200 mg, 0.308 mmol), Hhtz (116 mg, 0.647
2
3
2
3
solution of the product.
Preparation of N,N-cis Re(O)(hoz) Cl (2b). A mixture of Re(O)
mmol), 2,6-di-tert-butylpyridine (160 μL, 136 mg, 0.712 mmol), and
EtOH (18 mL) was refluxed in a 25 mL flask for 15 min. The product
2
(
OPPh )(SMe )Cl (100 mg, 0.154 mmol), Hhoz (55 mg, 0.337
was filtered and washed with 2 × 2 mL of EtOH and 2 × 1 mL of Et O
3
2
3
2
mmol), 2,6-di-tert-butylpyridine (84 μL, 72 mg, 0.374 mmol), and
EtOH (6 mL) was refluxed in a 10 mL flask for 15 min. The mixture
turned forest green in the first 5 min. After cooling down and filtering,
the solid phase was washed with 2 × 1 mL of EtOH and dissolved in
CH Cl for silica gel flash chromatography (EtOAc). The product (R
f
as an ∼1:1 mixture of N,N-trans and N,N-cis isomers. The mixture was
collected in a 20 mL vial and extracted with 3 times of 5 mL of CHCl .
3
Each extraction used sonication for 15 s and occasional shaking during
the following 30 min. Clarified CHCl solution was combined and
3
dried. The green solid residue rich in the N,N-trans isomer was further
purified by three rounds of recrystallization with CH Cl /pentane
2
2
0
.7) was isolated from the N,N-trans isomer (tailed) as a green powder
2
2
1
1
after solvent removal in vacuo. Yield: 41 mg (47%). H NMR (500
followed by quick CHCl extraction. Yield: 84 mg (46%). H NMR
3
MHz, CDCl ) δ 7.81 (dd, J = 8.1, 1.8 Hz, H), 7.56−7.60 (m, 2H), 7.46
(500 MHz, CDCl ) δ 7.68 (dd, J = 8.1, 1.6 Hz, 1H), 7.55 (dd, J = 7.9,
3
3
(
(
dd, J = 8.6, 1.1 Hz, 1H), 7.19 (ddd, J = 8.6, 7.2, 1.8 Hz, 1H), 6.94
ddd, J = 8.0, 7.3, 1.0 Hz, 1H), 6.88 (ddd, J = 8.1, 7.1, 1.1 Hz, 1H),
1.6 Hz, 1H), 7.38 (ddd, J = 8.6, 7.1, 1.6 Hz, 1H), 7.17 (ddd, J = 8.5,
7.3, 1.6 Hz, 1H), 6.95 (ddd, J = 8.1, 7.3, 1.1 Hz, 1H), 6.78 (dd, J = 8.3,
0.9 Hz, 1H), 6.75−6.70 (m, 2H), 5.53 (ddd, J = 14.8, 9.1, 5.7 Hz, 1H),
5.09 (ddd, J = 14.8, 10.4, 9.2 Hz, 1H), 4.59 (ddd, J = 14.5, 9.2, 5.4 Hz,
1H), 4.41 (ddd, J = 14.5, 10.4, 9.1 Hz, 1H), 3.86 (td, J = 10.6, 9.3 Hz,
1H), 3.71 (m, 2H), 3.60 (td, J = 10.6, 9.2 Hz, 1H). Elemental analysis
(C H N O S ClRe) calculated: C, 36.39%; H, 2.71%; N, 4.72%; S,
6.73 (dd, J = 8.4, 1.1 Hz, 1H), 5.01 (ddd, J = 10.9, 8.6, 7.7 Hz, 1H),
4.87 (ddd, J = 10.5, 9.5, 8.6 Hz, 1H), 4.63 (dt, J = 10.6, 8.7 Hz, 1H),
4.52 (dt, J = 10.6, 8.5 Hz, 1H), 4.43 (ddd, J = 13.6, 10.8, 9.6 Hz, 1H),
4.13 (ddd, J = 13.6, 10.4, 7.8 Hz, 1H), 4.01 (ddd, J = 12.3, 10.6, 8.4
Hz, 1H), 3.71 (ddd, J = 12.3, 10.6, 8.6 Hz, 1H). Elemental analysis
18
16
2
3 2
(
6
C H N O ClRe) calculated: C, 38.47%; H, 2.87%; N, 4.98%; Cl,
.31%; Re, 33.13%. Found: C, 38.41%; H, 2.71%; N, 4.82%; Cl, 6.37%;
10.79%; Cl, 5.97%; Re, 31.34%. Found: C, 36.28%; H, 2.68%; N,
1
8
16
2
5
4.63%; S, 10.67%; Cl, 5.70%; Re, 30.95%. UV−vis spectra in CH Cl
2
2
Re, 35.70%. UV−vis spectra in CH Cl solution are shown in Figure
S9a and b. Single crystals suitable for X-ray diffraction were grown by
diffusion of toluene into the CH Cl solution of the product.
solution are shown in Figure S9c and d. Single crystals suitable for X-
2
2
ray diffraction were grown by diffusion of toluene into the CH Cl
2
2
solution of the product.
2
2
Preparation of [H hoz][Re(O)(hoz)Cl ] (3). A mixture of Re(O)
Preparation of N,N-cis Re(O)(htz) Cl (5b). A mixture of Re(O)
2
3
2
(
OPPh )(SMe )Cl (81 mg, 0.125 mmol), Hhoz (43 mg, 0.264
(OPPh )(SMe )Cl (167 mg, 0.257 mmol), Hhtz (102 mg, 0.566
3
2
3
3
2
3
mmol), and EtOH (5 mL) was refluxed in a 10 mL flask for 15 min.
After solvent removal in vacuo, the addition of chloroform (2 mL)
converted the residual green oil into a solid phase. The liquid phase
mmol), 2,6-lutidine (164 μL, 151 mg, 1.407 mmol), and EtOH (10
mL) was refluxed in a 25 mL flask for 48 h. The product was filtered
and washed with 3 × 2 mL of EtOH and 3 × 1 mL of Et O to afford a
2
1
was then filtered off to afford a light green powder. Yield: 30 mg
green powder. Yield: 140 mg (92%). H NMR (500 MHz, CDCl ) δ
3
1
(
38%). H NMR (500 MHz, CD CN) δ 10.17 (br, 2H), 7.90 (dd, J =
7.56 (ddd, J = 8.6, 7.0, 1.7 Hz, 1H), 7.52 (dd, J = 8.0, 1.7 Hz, 1H),
7.46−7.43 (m, 2H), 7.16 (ddd, J = 8.6, 7.2, 1.7 Hz, 1H), 6.94 (ddd, J =
8.2, 7.3, 1.2 Hz, 1H), 6.82 (ddd, J = 8.1, 7.0, 1.2 Hz, 1H), 6.51 (dd, J =
8.4, 1.1 Hz, 1H), 4.73 (dt, J = 14.9, 9.9 Hz, 1H), 4.61 (ddd, J = 14.7,
8.0, 6.4 Hz, 1H), 4.11 (ddd, J = 13.8, 11.5, 8.3 Hz, 1H), 3.89 (ddd, J =
13.5, 8.5, 4.6 Hz, 1H), 3.87−3.79 (m, 2H), 3.19 (ddd, J = 10.9, 8.4, 4.5
Hz, 1H), 2.51 (td, J = 11.2, 8.5 Hz, 1H). Elemental analysis
(C H N O S ClRe) calculated: C, 36.39%; H, 2.71%; N, 4.72%; S,
3
8.1, 1.7 Hz, 1H), 7.74 (ddd, J = 8.9, 7.3, 1.7 Hz, 1H), 7.60 (dd, J = 7.9,
1.8 Hz, 1H), 7.29 (d, J = 8.4 Hz, 1H), 7.23 (ddd, J = 8.8, 7.3, 1.8 Hz,
1H), 7.16 (ddd, J = 8.1, 7.4, 1.0 Hz, 1H), 7.00 (ddd, J = 7.9, 7.2, 0.8
Hz, 1H), 6.80 (d, J = 8.3 Hz, 1H), 5.03 (t, J = 9.8 Hz, 2H), 4.92 (t, J =
.6 Hz, 2H), 4.22 (t, J = 9.8 Hz, 2H), 3.83 (t, J = 9.6 Hz, 2H).
Elemental analysis (C H N O Cl Re) calculated: C, 34.05%; H,
9
18
18
2
5
3
2
.86%; N, 4.41%; Cl, 16.75%; Re, 29.30%. Found: C, 33.72%; H,
18
16
2
3 2
2
.65%; N, 4.28%; Cl, 15.11%; Re, 30.03%. Single crystals suitable for
10.79%; Cl, 5.97%; Re, 31.34%. Found: C, 35.68%; H, 2.67%; N,
X-ray diffraction were grown from the chloroform of the product.
Preparation of [H-tBu Py][Re(O)(hoz)Cl ] (4). In a 25 mL flask,
4.56%; S, 10.50%; Cl, 5.32%; Re, 30.83%. UV−vis spectra in CH Cl
2
2
solution are shown in Figure S9c and d. Single crystals suitable for X-
2
3
Re(O) (OPPh )(SMe )Cl (300 mg, 0.462 mmol) was stirred in 10
ray diffraction were grown by diffusion of pentane into the CH Cl
3
2
3
2
2
mL of boiling ethanol as a pale green suspension. Hhoz (76 mg, 0.467
mmol) dissolved in 2 mL of ethanol was slowly added into the flask
over 45 min via a 1 mL syringe. The solution gradually turned bright
green. Then, 2,6-di-tert-butylpyridine (114 μL, 97 mg, 0.509 mmol) in
solution of the product.
Preparation of [H-tBu Py][Re(O)(htz)Cl ] (6). Hhtz (42 mg, 0.233
2
3
mmol) dissolved in 1 mL of ethanol was slowly added, via a 1 mL
syringe over 15 min, into the 15 mL flask with Re(O) (OPPh )-
3
1
mL of ethanol was slowly added in the same way. After heating for
(SMe )Cl (150 mg, 0.231 mmol) suspension in 5 mL of boiling
2
3
another 15 min, the solvent was removed in vacuo. The solid residue
was washed with 3 × 1 mL ethanol and 3 × 1 mL diethyl ether to
ethanol. The solution gradually turned dark green. Then, 2,6-di-tert-
butylpyridine (57 μL, 49 mg, 0.254 mmol) in 1 mL of ethanol was
slowly added in the same way. Deep green powders precipitated out
when about a half of 2,6-di-tert-butylpyridine was added. After cooling
down and filtration, the solid was washed with 3 × 1 mL of ethanol
1
afford a light green powder. Yield: 233 mg (76%). H NMR (500
MHz, CD CN) δ 11.21 (br, 1H), 8.47 (t, J = 8.2 Hz, 1H), 7.91 (d, J =
3
8
.2 Hz, 2H), 7.60 (dd, J = 7.9, 1.8 Hz, 1H), 7.23 (ddd, J = 8.4, 7.3, 1.8
Hz, 1H), 7.00 (ddd, J = 8.1, 7.2, 1.1 Hz, 1H), 6.80 (dd, J = 8.3, 1.1 Hz,
H), 4.92 (t, J = 9.6 Hz, 2H), 3.83 (t, J = 9.6 Hz, 2H), 1.54 (s, 18H).
The resonances corresponding to the Re-coordinated hoz match those
and 3 × 1 mL of diethyl ether to afford a deep green powder. Yield:
1
1
122 mg (78%). H NMR (500 MHz, CD CN) δ 11.18 (br, 1H), 8.46
3
(br, 1H), 7.90 (br, 2H), 7.50 (dd, J = 7.9, 1.7 Hz, 1H), 7.20 (ddd, J =
L
DOI: 10.1021/acs.inorgchem.5b02940
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
8
8
.7, 7.2, 1.7 Hz, 1H), 7.02 (ddd, J = 8.2, 7.2, 1.2 Hz, 1H), 6.82 (dd, J =
.3, 1.2 Hz, 1H), 4.18 (t, J = 8.5 Hz, 2H), 3.75 (t, J = 8.5 Hz, 2H), 1.54
X-ray Crystallography. Single crystal X-ray diffraction data were
collected on different instruments summarized in Table S1.
Combinations of 0.5° φ and ω scans were used to collect the data.
The collections, cell refinements, and integrations of intensity data
(
s, 18H). Elemental analysis (C H N O SCl Re) calculated: C,
22 30 2 2 3
3
8.91%; H, 4.45%; N, 4.12%; Cl, 15.66%; Re, 27.42%; S, 4.72%.
3
5
Found: C, 38.06%; H, 4.20%; N, 4.08%; Cl, 14.43%; Re, 28.35%; S,
.14%. Single crystals suitable for X-ray diffraction were grown by
diffusion of pentane into the CH Cl solution of the product.
were carried out with the APEX2 software package. Face-indexed
absorption corrections were performed numerically with the program
5
3
6
37
XPREP. SADABS was used to make incident beam and decay
corrections. The structures were solved with the direct methods
39
2
2
Preparation of N,N-trans Re(O)(hoz) (htz) Cl (7a). A mixture of
eq
ax
3
8
[
H-di-tBu-Py][Re(O)(hoz)Cl ] (230 mg, 0.347 mmol), Hhtz (63 mg,
program and refined with the full-matrix least-squares SHELXL
3
0
.353 mmol), 2,6-lutidine (42 μL, 39 mg, 0.364 mmol), and EtOH (15
program. Additional refinement details and metrical parameters are
mL) was refluxed in a 25 mL flask for 15 min. Then, another portion
of excess 2,6-lutidine (121 μL, 112 mg, 1.05 mmol) was added, and the
mixture was kept under reflux for 48 h. The product was filtered and
provided in Table S1.
Computational Details. DFT was applied to structures 2a, 2b,
4
0
+
+
41
5a, 5b, 7a, 7b, 7c, 7d, 7a , and 7b at the B3LYP level. The basis set
used for rhenium was effective-core-potential (ECP) based LANL2DZ
washed with 3 × 2 mL of EtOH and 3 × 1 mL of Et O to afford a
2
4
2
43
green powder. Yield: 163 mg (81%). Further purification was
basis, with reoptimized functions of Couty and Hall and a set of
44 45
1
conducted by slow crystallization from saturated CHCl solution. H
polarization f function. The 6-31G** basis sets were used for all H,
46
3
NMR (500 MHz, CDCl ) δ 7.92 (dd, J = 8.1, 1.8 Hz, 1H), 7.57 (dd, J
C, N, O, and Cl atoms. The 6-311G* basis sets was used for S atoms.
3
=
7.9, 1.6 Hz, 1H), 7.43 (ddd, J = 8.6, 7.0, 1.8 Hz, 1H), 7.20 (ddd, J =
Solvation energies were obtained by applying the SMD solvation
4
7
8
.3, 7.2, 1.6 Hz, 1H), 6.96 (t, J = 7.6 Hz, 1H), 6.84 (d, J = 8.5 Hz, 1H),
model with default radii and nonelectrostatic terms. For 2a, 2b, 5a,
+
+
6
.82−6.78 (m, 2H), 5.10−5.04 (m, 1H), 4.93−4.78 (m, 3H), 4.69
5b, 7a, 7b, 7c, and 7d, the solvent was ethanol; for 7a and 7b , the
solvent was acetonitrile. Previous publications
2
0,48
(ddd, J = 14.4, 9.1, 5.3 Hz, 1H), 4.51 (dt, J = 14.4, 9.8 Hz, 1H), 3.87
q, J = 10.6, 9.1 Hz, 1H), 3.74 (ddd, J = 10.9, 9.0, 5.3 Hz, 1H).
have shown that
(
this protocol yielded data matching experimental results for related
complexes. All of the geometry optimization and thermochemistry
results were gained using the Gaussian09 (Rev. D01) package of
Elemental analysis (C H N O SClRe) calculated: C, 37.40%; H,
18
16
2
4
2
.79%; N, 4.85%; Cl, 6.13%; Re, 32.21%; S, 5.55%. Found: C, 36.63%;
4
9
H, 2.65%; N, 4.70%; Cl, 6.67%; Re, 32.32%; S, 4.97%. UV−vis spectra
programs.
Perchlorate Reduction Catalysis in Homogeneous Solution.
Stock solutions of [Re(O)(L) ][OTf] (20 mM in CD CN), Me S (0.5
M in CD CN), and LiClO (2 M in D O) were sequentially mixed in a
5 mm NMR tube to yield a 0.5 mL of solution containing 0.1 M of
in CH Cl solution are shown in Figure S9e and f. Single crystals
2
2
suitable for X-ray diffraction were grown by diffusion of pentane into
2
3
2
the CH Cl solution of the product.
3
4
2
2
2
Preparation of [Re(O)(L) ][OTf] in CD CN. In general, Re(O)-
2
3
−
(
L) Cl reacted with 1.05 equiv of AgOTf in CD CN (1 mL for every
ClO
4
, 0.4 M of Me
2
S, and 4 mM of Re (TON = 100) with an ∼95/5
O. Conversion of Me S to Me SO, which is
reduction, was monitored by H NMR.
4
2
3
1
0 mg of Re complex) at room temperature for 30 min. For N,N-cis
(v/v) ratio of CD
coupled to ClO
Alternatively, 0.1 M of ClO , 0.4 M of Et S, and 16 mM of Re
4 2
3
CN/D
2
2
2
−
1
Re(O)(htz) Cl, reflux for 2 h was necessary. The white AgCl
2
−
precipitate was filtered off through a glass pipet filled with glass wool.
The resulting dark green solutions were stored at −20 °C until
(TON = 25) were used in order to effectively monitor the
transformation of Re complexes during the reaction.
−
characterization and homogeneous ClO4 reduction catalysis. UV−vis
Perchlorate Reduction Catalysis in Heterogeneous Re(L) −
spectra in CH CN solution are shown in Figure S10.
2
3
+
+
1
Pd/C Material. A 50 mL pear-shaped flask was sequentially loaded
N,N-trans [Re(O)(hoz) ] (2a ). H NMR (500 MHz, CD CN) δ
2
3
with Re(O)(LO−N)2Cl (containing 1.25 mg Re), 25 mg of Pd/C, a
magnetic stir bar, and 50 mL of water (pH 3.0, prepared by addition of
7
2
5
.97 (d, J = 7.8 Hz, 2H), 7.62 (t, J = 7.7 Hz, 2H), 7.14 (t, J = 7.7 Hz,
H), 7.06 (d, J = 8.5 Hz, 2H), 5.18 (ddd, J = 10.9, 8.6, 7.0 Hz, 2H),
.06 (dt, J = 10.3, 8.7 Hz, 2H), 4.71−4.59 (m, 2H), 4.37 (br, 2H) (at
1
2
mM HCl). The flask was sealed with a rubber stopper, sonicated for
min with occasional shaking, and then placed in a 25 °C water bath.
room temperature).
+
+
1
The suspension was stirred at 1100 rpm under 1 atm H (supplied
N,N-cis [Re(O)(hoz) ] (2b ). H NMR (500 MHz, CD CN) δ 7.99
2
2
3
through two stainless steel needles as gas inlet and outlet to the
fumehood atmosphere) for 4 h to allow an adequate immobilization of
the Re(O)(LO−N)2Cl precursor into Pd/C matrix.
solution (0.2 M in H O) was then introduced in the catalyst
suspension to initiate the reaction. Aqueous samples were periodically
collected from the H2 outlet and immediately filtered (0.45-μm
cellulose membrane) to quench the reaction. ClO4 concentration was
(
dd, J = 8.1, 1.8 Hz, 1H), 7.85 (dd, J = 7.9, 1.8 Hz, 1H), 7.74 (ddd, J =
8
2
1
.7, 7.1, 1.8 Hz, 1H), 7.47 (ddd, J = 8.5, 7.3, 1.8 Hz, 1H), 7.23 (m,
H), 7.07 (ddd, J = 8.1, 7.1, 1.2 Hz, 1H), 6.90 (dd, J = 8.4, 1.1 Hz,
H), 5.06 (ddd, J = 10.7, 8.7, 7.8 Hz, 1H), 4.98 (ddd, J = 10.5, 9.5, 8.6
1
7a
NaClO stock
4
2
Hz, 1H), 4.82 (dd, J = 10.2, 9.0 Hz, 2H), 4.36 (ddd, J = 13.3, 10.8, 9.4
Hz, 1H), 4.23 (ddd, J = 13.4, 10.5, 7.9 Hz, 1H), 4.12 (dt, J = 12.0, 9.3
Hz, 1H), 3.95 (dt, J = 12.1, 9.7 Hz, 1H) (at room temperature).
−
+
+
1
measured by ion chromatography (Dionex ICS-3000, IonPac AS16
N,N-trans [Re(O)(htz) ] (5a ). H NMR (500 MHz, CD CN) δ
2
3
−1
column, 1.0 mL min flow rate, 65 mM KOH eluent, 30 °C column
7
2
4
.89 (d, J = 7.8 Hz, 2H), 7.65 (t, J = 7.2 Hz, 2H), 7.14 (d, J = 7.0 Hz,
H), 7.11 (dd, J = 8.4, 0.9 Hz, 2H), 4.91 (br, 4H), 3.90 (t, J = 8.6 Hz,
H) (at room temperature).
−
temperature). Cl concentration was measured with an IonPac AS19
−1
column (1.0 mL min flow rate, 10 mM KOH eluent, and 30 °C
column temperature) on the same system.
+
+
1
N,N-cis [Re(O)(htz) ] (5b ). H NMR (500 MHz, CD CN) δ 7.84
2
3
(
8
=
8
1
1
1
dd, J = 8.1, 1.5 Hz, 1H), 7.77 (dd, J = 8.0, 1.4 Hz, 1H), 7.74 (ddd, J =
.5, 7.3, 1.6 Hz, 1H), 7.46 (ddd, J = 8.4, 7.4, 1.5 Hz, 1H), 7.25 (ddd, J
8.2, 7.6, 0.9 Hz, 1H), 7.21 (dd, J = 8.4, 0.9 Hz, 1H), 7.01 (ddd, J =
.2, 7.2, 1.0 Hz, 1H), 6.84 (dd, J = 8.4, 0.9 Hz, 1H), 4.78 (ddd, J =
4.9, 7.8, 6.9 Hz, 1H), 4.63 (dt, J = 14.9, 9.7 Hz, 1H), 4.40 (ddd, J =
3.9, 9.3, 7.4 Hz, 1H), 4.11 (dt, J = 13.8, 9.2 Hz, 1H), 3.88−3.85 (m,
H), 3.57 (q, J = 7.2 Hz, 1H), 3.52 (dt, J = 11.2, 9.0 Hz, 1H), 3.34
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.5b02940. CCDC 1440558 (structure 2a), 1440571
■
*
S
(
2b), 1440485 (3), 1440486 (5a), 1440487 (5b), 1440488
(6), 1440489 (7a), and 1440490 (the C -symmetric aqua
(
ddd, J = 11.2, 9.3, 7.4 Hz, 1H) (at room temperature).
+
+
1
N,N-trans [Re(O)(hoz)(htz)] (7a ). H NMR (500 MHz, CD CN)
2
3
δ 8.06 (dd, J = 8.3, 1.6 Hz, 1H), 7.84 (dd, J = 8.0, 1.5 Hz, 1H), 7.70
ddd, J = 8.7, 7.4, 1.7 Hz, 1H), 7.58 (ddd, J = 8.7, 7.3, 1.5 Hz, 1H),
.23−7.17 (m, 1H), 7.14−7.07 (m, 3H), 5.19 (ddd, J = 10.9, 8.6, 7.1
Hz, 1H), 5.03 (td, J = 10.2, 8.8 Hz, 1H), 4.81 (ddd, J = 14.2, 11.6, 9.5
Hz, 1H), 4.77−4.68 (m, 2H), 4.53 (td, J = 11.1, 7.4 Hz, 1H), 4.00 (td,
J = 11.3, 9.3 Hz, 1H), 3.91 (ddd, J = 11.1, 9.2, 4.3 Hz, 1H) (at room
temperature).
complex) contain the supplementary crystallographic data for
this paper. The data can be obtained free of charge from the
Cambridge Crystallographic Data Centre at www.ccdc.cam.ac.
uk/getstructures.
(
7
Experimental sections and additional materials as noted
in the text (PDF)
M
DOI: 10.1021/acs.inorgchem.5b02940
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Crystallographic data (CIF)
Article
Schachner, J. A.; Mo
3
(
̈
sch-Zanetti, N. C. Eur. J. Inorg. Chem. 2012, 2012,
764−3773. (h) Machura, B.; Kusz, J. Polyhedron 2008, 27, 187−195.
i) Machura, B.; Wolff, M.; Benoist, E.; Schachner, J. A.; Mosch-
̈
AUTHOR INFORMATION
Corresponding Authors
(J.L.) E-mail: jyliu@mines.edu; jinyong.liu101@gmail.com.
(T.J.S.) E-mail: strthmnn@mines.edu.
■
Zanetti, N. C. Dalton Trans. 2013, 42, 8827−8837. (j) Machura, B.;
Kruszynski, R. Polyhedron 2007, 26, 2957−2963.
*
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*
Present Addresses
D.W.: Room B-901, Hong Ta Xiao Qu, Anhai, Jinjiang, Fujian
4
3
62261, P.R. China.
S.K.: Department of Chemistry and Biochemistry, University of
South Carolina, Columbia, South Carolina 29208, United
States.
(7) Bergeron, R. J. Chem. Rev. 1984, 84, 587−602.
́
(8) Abu-Omar, M. M.; McPherson, L. D.; Arias, J.; Bereau, V. M.
Angew. Chem., Int. Ed. 2000, 39, 4310−4313.
(
Notes
9) (a) Ison, E. A.; Trivedi, E. R.; Corbin, R. A.; Abu-Omar, M. M. J.
Am. Chem. Soc. 2005, 127, 15374−15375. (b) Du, G.; Abu-Omar, M.
The authors declare no competing financial interest.
M. Organometallics 2006, 25, 4920−4923.
ACKNOWLEDGMENTS
■
(10) Ison, E. A.; Corbin, R. A.; Abu-Omar, M. M. J. Am. Chem. Soc.
2005, 127, 11938−11939.
(11) Wegenhart, B. L.; Abu-Omar, M. M. Inorg. Chem. 2010, 49,
741−4743.
12) Lin, A.; Peng, H.; Abdukader, A.; Zhu, C. Eur. J. Org. Chem.
013, 2013, 7286−7290.
13) (a) Greer, M. A.; Goodman, G.; Pleus, R. C.; Greer, S. E.
Environ. Health Perspect. 2002, 110, 927−937. (b) Braverman, L. E.;
He, X.; Pino, S.; Cross, M.; Magnani, B.; Lamm, S. H.; Kruse, M. B.;
Engel, A.; Crump, K. S.; Gibbs, J. P. J. Clin. Endocrinol. Metab. 2005,
Financial support was provided by the National Science
Foundation (CBET-1555549) and the U.S. EPA Science to
Achieve Results Program (Grant #RD83517401). Professor
Kenneth Suslick, Professor Gregory Girolami (UIUC), and Dr.
Zhenggang Xu (Texas A&M University) are acknowledged for
helpful discussions. Dr. Dean Olson and Dr. Mike Hallock
4
(
2
(
(
UIUC) are, respectively, acknowledged for assistance with
NMR measurements and DFT calculations. Dr. Jeffery Bertke,
Dr. Amy Fuller, and Ms. Hyunjin Lee (UIUC) conducted the
crystallography analysis.
9
0, 700−706.
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Morrow, J. C.; Jackson, W. A. Environ. Sci. Technol. 2010, 44, 9564−
9570. (b) Parker, D. R.; Seyfferth, A. L.; Reese, B. K. Environ. Sci.
Technol. 2008, 42, 1465−1471.
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