Ligand Design for Isomer-Selective Oxorhenium(V) Complex Synthesis

Article abstract of DOI:10.1021/acs.inorgchem.6b03076

Recently, N,N-trans Re(O)(L_N-O)₂X (L_N-O = monoanionic N-O chelates; X = Cl or Br prior to being replaced by solvents or alkoxides) complexes have been found to be superior to the corresponding N,N-cis isomers in the cataly

Full text of DOI:10.1021/acs.inorgchem.6b03076

Article
pubs.acs.org/IC
Ligand Design for Isomer-Selective Oxorhenium(V) Complex
Synthesis
,
†,‡
Xiaoge Su, Mengwei Han, Dimao Wu, Danielle L. Gray, John R. Shapley,⊥
§
∥
#
⊥
Jinyong Liu,*
Δ
,‡
Charles J. Werth, and Timothy J. Strathmann*
†
Department of Chemical and Environmental Engineering, University of California, Riverside, California 92521, United States
‡
Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado 80401, United States
§
Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230000, China
∥
⊥
Department of Civil and Environmental Engineering and Department of Chemistry, University of Illinois at Urbana−Champaign,
Urbana, Illinois 61801, United States
#
Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
Δ
Department of Civil, Architectural, and Environmental Engineering, University of Texas at Austin, Austin, Texas 78712, United
States
*
S Supporting Information
ABSTRACT: Recently, N,N-trans Re(O)(LN−O)2X (LN−O
=
monoanionic N−O chelates; X = Cl or Br prior to being
replaced by solvents or alkoxides) complexes have been found
to be superior to the corresponding N,N-cis isomers in the
catalytic reduction of perchlorate via oxygen atom transfer.
However, reported methods for Re(O)(LN−O)2X synthesis
often yield only the N,N-cis complex or a mixture of trans and
cis isomers. This study reports a geometry-inspired ligand
design rationale that selectively yields N,N-trans Re(O)-
(
LN−O)2Cl complexes. Analysis of the crystal structures
revealed that the dihedral angles (DAs) between the two LN−O ligands of N,N-cis Re(O)(LN−O)2Cl complexes are less than
0°, whereas the DAs in most N,N-trans complexes are greater than 90°. Variably sized alkyl groups (−Me, −CH Ph, and
9
−
2
CH Cy) were then introduced to the 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz) ligand to increase steric hindrance in the N,N-
2
cis structure, and it was found that substituents as small as −Me completely eliminate the formation of N,N-cis isomers. The
generality of the relationship between N,N-trans/cis isomerism and DAs is further established from a literature survey of 56
crystal structures of Re(O)(LN−O)2X, Re(O)(LO−N−N−O)X, and Tc(O)(LN−O)2X congeners. Density functional theory
calculations support the general strategy of introducing ligand steric hindrance to favor synthesis of N,N-trans Re(O)(LN−O)2X
and Tc(O)(LN−O)2X complexes. This study demonstrates the promise of applying rational ligand design for isomeric control of
metal complex structures, providing a path forward for innovations in a number of catalytic, environmental, and biomedical
applications.
INTRODUCTION
(hoz)(htz)Cl (N,N-trans 1a, 2a, and 3a in Scheme 1)
■
complexes with high activity for oxygen atom transfer (OAT)
Oxorhenium complexes have been developed for a broad range
39
−
20
1
−10
reactions with perchlorate (ClO ). This unique reactivity
4
of catalytic applications in synthetic chemistry,
biomass
1
1−17
18−24
inspired our research team to develop a biomimetic catalyst
system that integrates these Re complexes and hydrogenation
nanoparticles (e.g., Pd and Rh) on carbon support materials.
conversion,
and environmental remediation.
Non-
radioactive 1 Re/ Re complexes have also been extensively
85
187
186
188
99m
studied as
Re,
Re, and
Tc surrogates for radio-
Since 1996, a number of
2
5−29
30
Under 1 atm of H and ambient temperature, these catalysts
2
pharmaceutical development.
−
V
rapidly and completely reduce the endocrine-disrupting ClO
4
Re (O)(L ) X complexes (LN−O = monoanionic N−O
N−O 2
40,41
−
21−24
in drinking water
into innocuous Cl .
chelates; X = Cl or Br prior to being replaced by solvents or
31
One of the major challenges of developing functional
alkoxides) have been synthesized. Specific LN−O ligands
enable the Re center to exhibit novel catalytic activities,
Re(O)(L ) X complexes is isomer selectivity. Upon the
N−O 2
3
2,33
34
reaction of Re(O)(OPPh )(SMe )X or [NBu ][Re(O)X ]
3
2
3
4
4
including hydrosilylation,
H generation from silanes, C−
2
3
5
36
37
precursor with 2 equiv of HLN−O ligands, most Re(O)-
H activation, aldol condensation, olefin epoxidation, and
38
controlled supramolecular assembly. Of particular note,
oxazolinylphenolato (hoz) and thiazolinylphenolato (htz)
ligands yield Re(O)(hoz) Cl, Re(O)(htz) Cl, and Re(O)-
Received: December 19, 2016
2
2
©
XXXX American Chemical Society
A
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Article
Scheme 1. Previously Developed Isomer Control Strategies (a−c) and the Aim of This Study (d)
(
L
) X products are either N,N-trans or N,N-cis with the
DAs in N,N-cis complexes are significantly smaller than 90°
(Figure 1). Intrigued by this observation, we further
N−O 2
ligand O atom coordinating trans to the oxo group.
Comparison on both isomers of Re(O)(hoz) Cl and Re(O)-
2
(
htz) Cl indicates that the N,N-trans configuration provides
2
significantly higher rates of ancillary ligand dissociation,
intramolecular exchange of the two LN−O, and catalytic activity
20
in OAT reactions. Despite these advantageous properties, the
number of reported N,N-trans Re complexes is much smaller
than that of N,N-cis complexes, and knowledge on controlling
N,N-trans versus N,N-cis structures has been very limited in the
past two decades. In many reports, synthesis yields a mixture of
2
0,42−44
the two isomers,
which are generally difficult to isolate.
20
As pointed out in our previous report, the nonselective
synthesis of Re(O)(LN−O)2X isomers of widely varying
reactivity not only results in a waste of the Re element during
catalyst preparation but also introduces potential artifacts that
can lead to misinterpretation of structure−activity relationships.
We recently introduced two strategies for selective synthesis
20
of N,N-trans Re(O)(LN−O)2X. First, pyridines with proper
steric hindrance (in excess to the amount for scavenging HX
byproduct) could promote thermodynamically favored isomer
interconversion from the initial mixture of N,N-trans and N,N-
cis isomers (Scheme 1a,b). Second, the direction of isomer
interconversion could be controlled by hybridization of
different LN−O with the opposite isomer preference, such as
incorporating a trans-favoring hoz ligand and a cis-favoring htz
ligand in the complex (Scheme 1c). Despite being effective, the
first strategy requires heating for a prolonged period of time
and using excess base to allow a complete isomer
interconversion, and the direction of interconversion is
controlled by the LN−O ligand structure. The second strategy
Figure 1. Side views of the crystal structures of previously reported
Re(O)(hoz) Cl (1a and 1b) and Re(O)(htz) Cl (2a and 2b) isomers.
The narrow spacing in N,N-cis structures are highlighted with a purple
2
2
sphere.
investigated crystal structures of all previously reported
Re(O)(L ) X complexes and confirmed that this general
N−O 2
trend holds, with a very small number of exceptions (details
presented in Discussion Section). The small DA in N,N-cis
structures indicates a narrow spacing between the two Re-
complexed LN−O ligands. It then follows that introduction of
bulky substituents into the LN−O ligand structure should favor
formation of the N,N-trans isomer by interfering with N,N-cis
arrangement of the two LN−O ligands.
In this contribution, we report on the selective synthesis of
several new N,N-trans Re(O)(LN−O)2Cl complexes. First, we
verified the ligand design rationale by attaching alkyl groups of
varying size to provide steric hindrance on the oxazoline moiety
of hoz and effectively avoid the initial formation of N,N-cis
isomers. The investigation was further generalized by examining
all previously reported Re(O)(LN−O)2X complexes and Tc-
also requires stepwise reactions to ensure a high yield of
heteroleptic Re(O)(LAN−O)(L
B
)X product by minimizing
N−O
A
the formation of homoleptic Re(O)(L
) X or Re(O)-
N−O 2
B
(
L
) X. A key question is thus raised on how to design new
N−O 2
LN−O structures to efficiently yield only N,N-trans products by
minimizing or even eliminating the initial formation of N,N-cis
isomers (Scheme 1d).
Comparing crystal structures of our previously synthesized
N,N-trans and N,N-cis isomers of both Re(O)(hoz) Cl and
2
Re(O)(htz) Cl revealed an interesting trend wherein the
2
dihedral angles (DAs) between the two LN−O ligands in N,N-
trans complexes are apparently larger than 90°, whereas the
(O)(L ) X congeners. DA measurements were provided,
and supporting density functional theory (DFT) calculations
N−O 2
B
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Article
were conducted to extend findings to provide a path forward
for selective synthesis of N,N-trans structures of functional Re
and Tc complexes for catalytic, environmental, and biomedical
applications.
literature. The ligand with −CH Cy (L3, an L2 analogue with
2
phenyl ring saturated) is first reported in this study.
The corresponding Re(O)(LN−O)2Cl complexes were
synthesized from Re(O)(OPPh )(SMe )Cl and 2 equiv of
3
2
3
the HLN−O ligands (L1 to L5) in refluxed ethanol. A
RESULTS
stoichiometric amount of 2,6-di-tert-butylpyridine (tBu Py) or
■
2
Synthesis of Alkyl-Substituted hoz Ligands and N,N-
2,6-dimethylpyridine (Me
byproduct; thus, no excess base was available to promote the
isomer interconversion (Scheme 1). During complex syn-
thesis with L1, the reaction mixture quickly turned from a pale
green suspension to a forest green solution within 6 min, and
2
Py) was added to scavenge HCl
trans Re Complexes. Five HL
ligands were synthesized in
N−O
20
one step by reacting 2-hydroxybenzonitrile and corresponding
amino alcohols in refluxed toluene, with 2 mol % ZnCl as the
catalyst (Scheme 2).
2
45,46
Hhoz derivatives with a small −Me
1
some green solids precipitated by 15 min. H NMR
characterization of the precipitates after 4 h of reaction
indicated a pure species containing 14 individual proton (i.e.,
Scheme 2. Synthesis of HLN−O Ligands
1
H by integration) multiplets and two −CH singlets. Single-
3
crystal analysis identified the N,N-trans Re(O)(Mehoz) Cl
2
structure 4a (Figure 2a). Crystallography data are provided in
Table 1 and Table 2.
In comparison, the previous synthesis of Re(O)(hoz) Cl
2
under the same conditions for 4 h yielded a 60:40 mixture of
N,N-trans and N,N-cis isomers. Thus, we attempted to monitor
the much faster interconversion of N,N-cis Re(O)(Mehoz) Cl,
2
if any, to the N,N-trans isomer at the beginning of synthesis.
While the partially precipitated solids at 15 min exclusively
1
contained N,N-trans complex 4a (Figure 3a), H NMR
characterization of the reaction mixture (i.e., liquid and solid)
indicated that the liquid phase contained two minor impurities,
which disappeared at different rates (Figure 3b−d) and are
probably Re(O)(Mehoz) Cl isomers (vide infra). More solids
2
precipitated with prolonged heating. After 4 h of reaction, the
solid product 4a was in both high isolated yield (92%) and high
purity (like shown in Figure 3a).
As shown in Figure 4, the fixed chirality of the Mehoz ligand
and the enantiomeric Re coordination sphere could generate
two diastereomers of N,N-trans (Type A and Type B; 4a and
4a′) and N,N-cis (Type C and Type D; 4b and 4b′) isomers,
4
7
48
49
(
L1), a large −CH Ph (L2), and a geminal dimethyl (L4)
2
substitution at the 4-position of oxazoline moiety and the Hhox
ligand with a six-member ring dihydrooxazine moiety (L5, a
nonflat ring structure isomer of L1) have been reported in
50
Figure 2. Plain view and side view of (a, b) N,N-trans Re(O)(Mehoz) Cl 4a, (c, d) N,N-trans Re(O)(PhCH hoz) Cl 5a, and (e, f) N,N-cis
2
2
2
Re(O)(hox) Cl 8b (35% probability displacement ellipsoids displayed with H atoms removed for clarity).
2
C
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Table 1. Crystal Data and Refinement Details
N,N-trans Re(O)(Mehoz) Cl (4a)
N,N-trans Re(O)(PhCH hoz) Cl (5a)
N,N-cis Re(O)(hox) Cl (8b)
2
2
2
2
formula
C H ClN O Re
C H ClN O Re
C H ClN O Re
2
0
20
2
5
32 28
2
5
20 20
2
5
formula weight
temperature (K)
wavelength (Å)
crystal system
space group
a (Å)
590.03
742.21
590.03
100(2)
100(2)
193(2)
0.71073
hexagonal
P61
0.71073
monoclinic
P21
0.71073
orthorhombic
P2 2 2
1 1
1
11.2324(4)
11.2324(4)
13.9014(7)
6.8299(3)
15.2612(8)
90
7.9530(6)
15.1091(12)
16.3803(12)
90
b (Å)
c (Å)
27.4564(12)
90
α (deg)
β (deg)
90
91.4735(18)
90
γ (deg)
120
90
90
V (Å3)
3000.0(3)
6
1448.50(12)
1968.3(3)
4
Z
2
ρcalc (g cm−3)
absorption coefficient (mm−1)
F(000)
1.960
6.244
1716
1.702
4.331
732
1.991
6.345
1144
3
crystal size (mm )
0.176 × 0.115 × 0.05
2.221−29.573
−15 ≤ h ≤ 15
0.35 × 0.109 × 0.089
1.957−28.334
−18 ≤ h ≤ 18
−9 ≤ k ≤ 9
−20 ≤ l ≤ 20
38 153
0.226 × 0.214 × 0.136
1.83−27.29
−10 ≤ h ≤ 10
−19 ≤ k ≤ 19
−21 ≤ l ≤ 20
24 754
θ range (deg)
index ranges
−
−
14 ≤ k ≤ 15
38 ≤ l ≤ 38
No. of reflections collected
No. of independent rflns, Rint
completeness to θ = 25.69°
absorption correction
107 510
5600, 0.0658
99.9%
7190, 0.0280
99.9%
4412, 0.0571
99.6%
integration
0.78222 and 0.55895
full-matrix least-squares on F2
integration
integration
max. and min transmission
refinement method
0.7697 and 0.2964
0.5401 and 0.3485
full-matrix least-squares on F2
4412/0/262
full-matrix least-squares on F2
7190/15/389
1.212
data/restraints/parameters
goodness-of-fit on F2
5600/15/283
1.209
1.033
R1/wR2 (I > 2σ(I))
0.0214/0.0470
0.0236/0.0476
−0.012(2)
0.0232/0.0546
0.0250/0.0557
−0.016(4)
3.006 and −2.197
A
0.0258/0.0574
0.0289/0.0588
0.007(9)
R1/wR2 (all data)
absolute structure parameter
largest diff. peak/hole (e Å−3)
instrument
1.627 and −2.163
0.810 and −0.675
a
b
A
B
a
b
Burker D8 Venture equipped with a Photon 100 detector using multilayer optics to monochromatize Mo Kα radiation. Siemens Platform
diffractometer equipped with an Apex II CCD detector using graphite-monochromatized Mo Kα radiation.
Table 2. Selected Bond Distances (Å) for Five Re(O)(LO−N)2Cl Complexes
a
a
1
a
4a
5a
1b
8b
Re(1)−O(1)
Re(1)−O(4)
Re(1)−O(2)
Re(1)−N(1)
Re(1)−N(2)
Re(1)−Cl(1)
1.671(4)
1.977(4)
1.990(4)
2.038(4)
2.090(4)
2.3824(14)
1.725(5)/1.727(9)
2.006(4)
1.724(12)/1.736(6)
1.986(4)
1.6902(18)
1.9863(17)
2.0006(16)
2.099(2)
1.695(3)
1.981(3)
1.978(3)
2.124(3)
2.142(3)
2.3728(11)
1.998(4)
2.001(4)
2.098(4)
2.081(4)
2.069(4)
2.103(4)
2.113(2)
2.3853(15)/2.376(7)
2.331(6)/2.398(2)
2.3700(6)
a
Data from ref 20 for comparison.
respectively. DFT calculations suggest that 4a is the most
group of the Re(O)(Mehoz) Cl product suggest a stereo-
2
thermodynamically favored structure among the four isomers.
selective formation of the Re coordination sphere. In
comparison, the space groups of the previously reported
1
The high-purity H NMR spectrum and the P6 crystal space
1
D
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1
Figure 3. Synthesis of Re(O)(Mehoz) Cl and partial H NMR (400 MHz, CDCl ) spectra of products. Symbols *, +, and @, respectively, indicate
2
3
protonated tBu Py, OPPh , and excess HMehoz ligand in the reaction mixture. Symbols & and # indicate two probable isomers gradually
2
3
disappearing in the reaction mixture at different rates.
Figure 4. Calculated structure and relative Gibbs free energy of the four Re(O)(Mehoz) Cl isomers.
2
5
1
crystals of Re(O)(OPPh )(SMe )Cl precursor (Pcmn) and
ing a small methyl group to oxazoline moiety of the original hoz
ligand.
The isomer control strategy was further examined with the
3
2
3
Re(O)(L ) Cl complexes with achiral hoz and htz ligands
P2 /c or P2 /n) indicate a racemic mixture of Re
1 1
coordination enantiomers. Since the Re(O)(OPPh )(SMe )Cl
3
precursor is racemic, the selective formation of 4a suggests that
a chiral LN−O ligand could induce the interconversion between
Re(O)(Mehoz) Cl diastereomers 4a and 4a′. On the basis of
the calculated Gibbs energy, one of the two impurities observed
during the Re(O)(Mehoz) Cl synthesis (resonances labeled
with # symbols in Figure 3b) might be 4a′. The other impurity
labeled with & symbols) that appeared to have symmetry is
probably a μ-oxo dimer. Enantioselective synthesis of
oxorhenium complexes with other types of multidentate ligands
have been reported, but the mechanism remains unclear.
N−O 2
2
0
(
large benzyl-substituted L2. Similar to the synthesis of
3
2
Re(O)(Mehoz) Cl, solid products complexing with L2 quickly
2
precipitated. While the product during the first 2 h contained
some impurities, heating the mixture for more than 8 h yielded
a high-purity product, and its crystal structure was also type A
N,N-trans Re(O)(PhCH hoz) Cl (5a, Figure 2c). The space
2
2
2
2
group P2 also indicates the absence of mirror planes in the
1
1
crystal unit cell. The H NMR spectrum of 5a showed
(
significant differences with other N,N-trans Re(O)(R-hoz) Cl
5
2
2
complexes such as 1a and 4a (e.g., δ 3.8, δ 5.6, and δ 6.7−7.0;
Figure 5c vs 5a,b). For comparison, Re(O)(CyCH hoz) Cl
2
2
53,54
with the even bulkier L3 was synthesized following the same
1
Further investigation is needed to elucidate the interconversion
mechanism that alters the chirality of the Re coordination
sphere. Nevertheless, results demonstrate that N,N-trans
structured complex can be selectively synthesized by introduc-
procedure for 5a; the product has a very similar H NMR
spectrum to that of 4a (Figure 5d vs 5b), suggesting that the
1
product (6a) is also N,N-trans. Thus, the unique H NMR
spectrum of 5a might be attributed to the influence of the ring
E
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1
Figure 5. Partial H NMR spectra of five Re(O)(R-hoz) Cl complexes.
2
Figure 6. Illustration of the DA measurement. Atoms involved in the plane of coordination “arch” are highlighted.
current of benzyl Ph onto the hoz backbone protons. The
verification of N,N-trans configuration for 5a and 6a further
demonstrates that the ligand design strategy could be applied to
alkyl groups of a variety of sizes.
In contrast to the alkyl-substituted R-hoz ligands, the
expansion of the ring size from five-member to six-member
in Hhox (L5) yielded a 60:40 mixture of N,N-trans and N,N-cis
Re(O)(hox) Cl isomers (8a and 8b, respectively) within 10
2
The achiral HMe hoz (L4) led to the exclusive formation of
one species 7a, which was characterized as N,N-trans by H
min of synthesis (Figure S1 of the Supporting Information),
and prolonged heating led to the undesired interconversion of
8a to 8b (like that shown in Scheme 1b). Both isomers of
2
1
NMR spectra comparison (Figure 5) and crystallography
44
(
refined structure unavailable due to high-level disorders).
Compared with 4a, the increased number of methyl groups in
a enhanced its dissolution in the OPPh -containing ethanol,
Re(O)(hox) Cl exhibited low solubility in commonly used
2
solvents (e.g., CH Cl or CHCl ), such that isolation of 8a
2
2
3
7
from the mixture was challenging. 8b was purified by silica
3
2
0
such that no solids precipitated even after 24 h of heating.
Nevertheless, the recovered solid after only 15 min of reaction
was high-purity 7a, further demonstrating that the alkyl
substitution as small as methyl groups could be introduced to
eliminate the formation of the N,N-cis isomer.
chromatography, and its structure was confirmed by
crystallography (Figure 2e). Thus, unlike the side-protruding
methyl group in Mehoz, the slight bulkiness of the chair-shaped
dihydrooxazine moiety in hox does not favor the formation of
N,N-trans structure. The new crystal structures of 4a, 5a, and
F
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8
b follow the DA trend of greater than 90° for N,N-trans
results of DFT calculations conducted with solvent effects (in
ethanol) support this speculation. The calculated structures are
reported in a separate .xyz file in the Supporting Information.
Although DAs of the calculated structures do not closely match
the DAs in crystal structures, there are only two exceptions to
the greater than 90° or less than 90° trend (vide infra). Because
Re generally does not locate on the plane of the coordination
“arch”, the DAs are actually determined by the spatial
orientation of the Re−O−C and Re−N−C linkages. Interest-
(Figure 2b,d) and less than 90° for N,N-cis (Figure 2f).
DISCUSSION
■
Characteristic Dihedral Angles in N,N-trans and N,N-
cis Re(O)(L ) X. To generalize the DA trend initially
N−O 2
observed from complexes prepared in our lab, we extended
the comparison to other Re(O)(LN−O)2Cl complexes reported
in literature. Because some ligands are not planar, the DAs were
measured based on the approximated planes of O−C−C−C−
N coordination “arch” (Figure 6). As summarized in Table 3,
ingly, an extended survey on all reported non-C
N,N-cis and O,O-cis Re(O)(LO−N−N−O X crystal struc-
(i.e., the same Re coordination sphere as in N,N-
-symmetric,
s
)
2
63−66
tures
cis Re(O)(L ) X, but the two LN−O ligands are linked by two
Table 3. Summary of Dihedral Angles of Re(O)(LN−O)2X
and Tc(O)(LN−O)2X Crystal Structures
N−O 2
to four carbons) found that all DAs are greater than 90° (Table
S4). Therefore, it appears that the spatial orientation of the
Re−O−C and Re−N−C linkages are influenced by both the
N,N-trans/cis coordination pattern and the presence/absence of
the linker between the two LN−O ligands. The spatial
orientations then determine the relative position of the two
LN−O ligands.
atom
number of
the chelation
ring
number of
total
examples/
DA trend
exception
DA
DA range
average
detailed
(
including
Re)
(excluding (excluding information
exception) exception)
entry
collection
N,N-trans Re(O)(LN−O)2Cl
Implications for N,N-trans/cis Configuration Control
for Re(O)(LN−O)2Cl Complexes. Results suggest that the less
than 90° DA trend is an intrinsic property of N,N-cis
1
2
six
13/1
92.5°−
34.4°
85.6°
105.9°
85.6°
Table S1
Table S1
1
five
1/a
Re(O)(L ) X complexes. Hence, bulky substitutions such
N,N-cis Re(O)(LN−O)2Cl
N−O 2
as on the 4-position of hoz oxazoline moiety will significantly
increase the energy of N,N-cis isomer. Thus, its formation can
be suppressed, or its interconversion to the less strained N,N-
trans can be promoted. We further examined the effect of Me
substitution on htz, which has been found to favor the N,N-cis
isomer (Table 4, entry 3). DFT calculation suggests that, like
Mehoz, Mehtz also favors type A N,N-trans isomer (Table 4,
entry 4). In the calculated structure of the two N,N-cis
3
4
six
18/0
32.5°−
1.0°
47.5°
78.6°
Table S2
Table S3
8
five
9/0
62.3°−
9.9°
8
N,N-cis Tc(O)(LN−O)2Cl
5
6
six
3/0
38.7°−
9.7°
47.3°
61.2°
Table S5
Table S5
5
five
4/1
55.6°−
2.1°
7
a
Re(O)(Mehtz) Cl isomers (Figure 7), the small DA between
With only one example, the general DA trend for five-member
chelated N,N-trans Re(O)(LN−O)2X remains uncertain.
2
the two Mehtz ligands results in close vicinity of Me with the
other Me (Type C) or with the other thiazoline ring (Type D),
there have been 14 examples of N,N-trans Re(O)(L ) X
corresponding to the enhanced Gibbs energy elevation (e.g.,
N−O 2
20,30,35,42−44,55−57
−1
crystal structures reported to date
(X = Cl, Br,
6.48 kcal mol ) in comparison to Re(O)(htz)
2
Cl isomers
−1
or CH CN for cationic form, including the new complexes
(0.53 kcal mol ). Specifically in the type D structure, bonding
orientation around the Me-substituted carbon atom of the
equatorial thiazoline moiety has distorted, such that the methyl
group can avoid pointing into the narrow spacing (Figure 7,
also see the .xyz file in Supporting Information). We note that
the relatively low Gibbs energy for type D N,N-cis Re(O)-
3
reported in this work; see Table S1 for details). With only one
exception (74.7°), the DAs of all other 12 N,N-trans
Re(O)(L ) X with a variety of six-member ring chelating
N−O 2
ligands range from 92.5° to 134.4°. There has been only one
example of N,N-trans Re(O)(L ) X with a five-member ring
N−O 2
5
7
chelate ligand showing a DA of 85.6°. Thus, DA trend for this
specific category is still uncertain; more crystal structure
examples are needed.
(Mehoz) Cl (Table 4, entry 2) is due to a > 90° DA in the
2
calculated structure. This is one of the two DA trend exceptions
obtained in our calculated structures. The other one is the Tc
congener of the same structure (vide infra).
The previously reported N,N-cis Re(O)(LN−O)2X crystal
structures are more abundant than N,N-trans. There are 17
Literature reviews also suggest that reported Re(O)(LN−O) X
2
1
9,42−44,56,58,59
structures with six-member ring chelation
(in-
complexes with plane-extended LN−O ligands (e.g., containing
benzo-fused heterocycles or naphthanolate) are mostly N,N-cis
(Table S2, entries 5−8 and 12−13). DFT calculations show
that N,N-cis isomers are strongly favored by the benzo analogs
of hoz and htz (Table 4, entries 5 and 6). Replacing the hoz
phenolate with naphthalate could also invert the trans/cis
preference (Table 4, entries 7−8 versus 1). However, as
VII
cluding a dioxo Re (O) (hoz) complex, Table S2) and 9
2
2
58,60−62
structures with five-member ring chelation
(Table S3),
all of which show less than 90° DAs. The DAs for six-member
ring chelation structures are generally smaller than that for five-
member ring counterparts (Table 3, entry 3 vs 4), suggesting
the influence of different ring strains by six- and five-member
ring chelations.
Although the DA values appear to be also influenced by
other factors such as cocrystallized solvent molecules (e.g.,
Table S2, entry 1 vs 2), crystal system (e.g., Table S2, entry 15
vs 16) and ligand X (e.g., Table S1, entry 1 vs 2), the lack of
exception going across the 90° DA dividing line implies that the
characteristic DA trend in N,N-trans and N,N-cis crystal
structures might also apply to structures in solution. Indeed,
55
supported by both the actual crystal structures and calculated
energies (Table 4, entries 9 and 10), methyl substitutions
strongly favor N,N-trans. Therefore, we propose that
introducing steric effects into the LN−O structure could be an
effective strategy to selectively prepare a variety of N,N-trans
Re(O)(L ) X complexes.
N−O 2
Implications for Tc(O)(LN−O)2Cl complexes. The results
for Re complexes motivated us to further examine, with a
G
DOI: 10.1021/acs.inorgchem.6b03076
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 4. DFT-calculated relative Gibbs free energy (in kcal
Table 5. DFT-calculated relative Gibbs free energy (in kcal
−1
−1
mol ) for Re(O)(L ) Cl isomers (in EtOH at 78 °C)
mol ) for Tc(O)(L ) Cl isomers (in EtOH at 78 °C)
N−O 2
N−O 2
that excess lutidine and prolonged heating might be helpful in
promoting Tc complex isomer interconversion. Calculation
results for Tc(O) (Mehoz) Cl and Tc(O) (Mehtz) Cl (Table
2
2
5
4
, entries 2 and 4) are similar to those of Re congeners (Table
, entries 2 and 4), suggesting that the alkyl substitution
strategy might also be effective for selective synthesis of N,N-
trans Tc(O)(LN−O)2X complexes, which have not been
characterized to date. Since coordination sphere (e.g., trans/
cis) as well as ligand structure (e.g., hoz and htz) control ligand
20
exchange dynamics and catalytic activity for Re complexes,
systematic investigation of Tc congeners is anticipated to
promote innovation in both Tc coordination chemistry and
radiopharmaceutical development.
CONCLUSIONS
Inspired from the characteristic DAs between the two L
ligands in N,N-trans and N,N-cis Re(O)(L ) X complexes,
■
N−O
N−O 2
a
20 b
Data from ref. A to D refer to diastereoisomers as shown in Figure
.
we successfully synthesized four N,N-trans Re(O)(LN−O)2Cl
4
complexes (LN−O = Mehoz, PhCH hoz, CyCH hoz, and
2
2
Me hoz) without observing the formation of N,N-cis isomers.
2
Literature review, experimental results, and DFT calculations
collectively demonstrate that introducing steric hindrance to
LN−O destabilizes N,N-cis isomers. DFT calculations also
suggest that Tc complex congeners follow the similar trend
of Re complexes. Hence, results from this study provide
guidance for preparation of a wide range of N,N-trans
Re(O)(L ) X and new N,N-trans Tc(O)(LN−O)2X com-
N−O 2
plexes for catalytic and biomedical innovations.
EXPERIMENTAL SECTION
■
General Information. All chemicals and solvents were purchased
from Alfa-Aesar, Sigma-Aldrich, and Cambridge Isotope Laboratories
and were used as received. NMR, X-ray structure determination,
elemental analysis and electrospray ionization high-resolution mass
spectrometry (ESI−HRMS) were conducted in the NMR Lab, George
L. Clark X-ray Facility & 3M Materials Lab, Microanalysis Lab, and
Mass Spectrometry Lab in the School of Chemical Sciences, University
of Illinois. NMR spectra for all ligands and complexes are provided in
Supporting Information. Unless specified, all procedures were
conducted under air. DA measurement was conducted with Mercury
(v3.5.1, The Cambridge Crystallographic Data Centre) on CIF files.
General Procedures of Ligand Preparation. In a 15 mL flask,
the mixture of 2-hydroxybenzonitrile (358 mg, 3 mmol), substituted
Figure 7. Calculated structure of the two N,N-cis Re(O)(Mehtz) Cl
2
isomers (hydrogens shown).
calculation approach, whether or not the DA trend and isomer
control strategy could be applied to radioactive Tc(O)-
(
L
) X congeners. To the best of our knowledge, there
N−O 2
3
0,67−70
have been 7 crystal structures reported to date,
all of
which are N,N-cis with only a single exception to the <90° DA
trend (Table 3 and Table S5). DFT calculations suggest that
N,N-trans is the favored configuration for both Tc(O)(hoz) Cl
2
and Tc(O)(htz) Cl (Table 5, entries 1 and 3). However, the
2
30
ethanolamine (3.3 mmol), ZnCl (8 mg, 0.06 mmol), and toluene (5
mL) was refluxed for 24 h. The solvent was removed in vacuo, and the
2
reported crystal structure of Tc(O)(htz) Cl was N,N-cis. The
2
1
H NMR spectra for these complexes were reported to be of
residue was extracted with Et O (3 mL × 5). The combined organic
2
poor quality, and we propose that the most probable reason is
the formation of a trans/cis mixture, from which a N,N-cis single
crystal was picked for X-ray diffraction analysis. We speculate
phase was dried, and the residue was redissolved in minimal amount of
EtOAc or CH Cl and purified by silica gel flash chromatography
2
2
(hexanes/EtOAc = 4/1). All products after solvent removal appeared
H
DOI: 10.1021/acs.inorgchem.6b03076
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
as an oil, but some solidified after being placed at −20 °C overnight
and remained solid at room temperature.
HMehoz (L1). The starting ethanolamine is (S)-(+)-2-amino-1-
the CH Cl2 solution of the product. Elemental analysis
2
(C H ClN O Re) calculated: C, 40.71%; H, 3.42%; N, 4.75%; Cl,
20
20
2
5
6.01%; Re, 31.56%, found: C, 40.99%; H, 3.23%; N, 4.59%; Cl, 7.01%;
propanol (L-alaninol, 248 mg). The final product is a slightly orange-
Re, 29.37%. ESI−HRMS: m/z calculated for C H N O Re (the
20
20
2
5
1
+
pink solid. Yield: 423 mg (80%). H NMR (500 MHz, CDCl ) δ 12.23
dominant [M−Cl] ): 555.0930, found: 555.0923.
3
(
br, 1H), 7.64 (dd, J = 7.8, 1.7 Hz, 1H), 7.36 (ddd, J = 8.2, 7.3, 1.7 Hz,
Preparation of N,N-trans Re(O)(Ph(CH )hoz) Cl (5a). A mixture of
2 2
1H), 7.01 (dd, J = 8.3, 1.0 Hz, 1H), 6.86 (ddd, J = 7.7, 7.4, 1.0 Hz,
Re(O)(OPPh )(SMe )Cl (100 mg, 0.154 mmol), HPh(CH )hoz (82
3 2 3 2
1
H), 4.51 (dd, J = 9.2, 7.8 Hz, 1H), 4.48−4.41 (m, 1H), 3.95 (t, J = 7.6
mg, 0.324 mmol), 2,6-lutidine (38 μL, 35 mg, 0.324 mmol) and EtOH
(6 mL) was refluxed in a 15 mL flask. Green solid gradually
precipitated from the solution. After it was heated for 48 h, the
suspension was cooled, and the liquid phase was filtered through a
glass frit. The solid phase was sequentially washed with EtOH (1 mL ×
13
Hz, 1H), 1.37 (d, J = 6.5 Hz, 3H). C NMR (126 MHz, CDCl ) δ
1
3
65.1, 160.1, 133.5, 128.2, 118.8, 116.9, 111.0, 73.5, 61.1, 21.7.
HPh(CH )hoz (L2). The starting ethanolamine is (S)-(−)-2-amino-
2
3
-phenyl-1-propanol (L-phenylalaninol, 499 mg). The final product is a
1
red oil. Yield: 478 mg (62%). H NMR (400 MHz, CDCl ) δ 12.05
3) and Et O (1 mL × 3) to afford a green powder. Yield: 99 mg
3
2
1
(
1
br, 1H), 7.63 (dd, J = 7.8, 1.7 Hz, 1H), 7.38 (ddd, J = 8.4, 7.2, 1.7 Hz,
H), 7.35−7.31 (m, 2H), 7.27−7.24 (m, 3H), 7.02 (dd, J = 8.3, 1.1
Hz, 1H), 6.87 (ddd, J = 7.9, 7.2, 1.1 Hz, 1H), 4.67−4.59 (m, 1H), 4.40
dd, J = 9.4, 8.5 Hz, 1H), 4.14 (dd, J = 8.5, 7.3 Hz, 1H), 3.12 (dd, J =
3.7, 6.3 Hz, 1H), 2.82 (dd, J = 13.7, 7.6 Hz, 1H). 13C NMR (101
(87%). H NMR (400 MHz, CDCl ) δ 7.84 (dd, J = 8.1, 1.4 Hz, 1H),
3
7.62 (dd, J = 8.0, 1.1 Hz, 1H), 7.45−7.15 (m, 12H), 6.93−6.88 (m,
2H), 6.76−6.73 (m, 2H), 5.58−5.52 (m, 1H), 4.88 (dd, J = 9.1, 3.0
Hz, 1H), 4.83−4.74 (m, 2H), 4.65−4.62 (m, 1H), 4.53 (t, J = 8.9 Hz,
1H), 3.86−3.77 (m, 2H), 3.27 (dd, J = 14.1, 8.9 Hz, 1H), 3.02 (dd, J =
13.5, 9.5 Hz, 1H). Single crystals suitable for X-ray diffraction were
(
1
MHz, CDCl ) δ 165.7, 160.1, 137.8, 133.6, 129.5 (C × 2), 128.9 (C ×
2
3
), 128.2, 126.9, 118.9, 117.0, 110.8, 71.4, 67.0, 42.1.
grown by diffusion of pentane into the CH Cl2 solution of the
2
HCy(CH )hoz (L3). The starting ethanolamine, (S)-(+)-2-amino-3-
cyclohexyl-1-propanol (3-cyclohexyl-L-alaninol), was prepared from its
hydrochloride salt. The salt (1.07 g, 5.5 mmol) was dissolved in water
product. Elemental analysis (C H ClN O Re) calculated: C, 51.78%;
H, 3.80%; N, 3.77%; Cl, 4.78%; Re, 25.09%, found: C, 51.54%; H,
2
32 28
2
5
3.48%; N, 3.73%; Cl, 5.13%; Re, 23.44%. ESI−HRMS: m/z calculated
+
(
5 mL), and the solution was added dropwise with another water
for C H N O Re (the dominant [M−Cl] ): 707.1556, found:
3
2
28
2
5
solution (3 mL) containing NaOH (232 mg, 5.8 mmol). A brown oil
gradually formed over the water layer. After NaOH addition, the
mixture was extracted with EtOAc (5 mL × 3). The combined organic
phase was dried with Na SO , and the solvent was removed in vacuo
707.1550.
Preparation of N,N-trans Re(O)(Cy(CH )hoz) Cl (6a). A mixture of
2
2
Re(O)(OPPh )(SMe )Cl (100 mg, 0.154 mmol), HCy(CH )hoz (84
3
2
3
2
mg, 0.324 mmol), 2,6-lutidine (38 μL, 35 mg, 0.324 mmol), and EtOH
(6 mL) was refluxed in a 15 mL flask. Green solid gradually
precipitated from the solution. After it was heated for 48 h, the
suspension was cooled, and the liquid phase was filtered through a
glass frit. The solid phase was sequentially washed with EtOH (1 mL ×
2
4
to afford a slightly orange oil. A portion of the oil (519 mg) was used
to synthesize the HCy(CH )hoz ligand. The final product is an orange
2
1
oil. Yield: 649 mg (83%). H NMR (400 MHz, CDCl ) δ 12.30 (br,
3
1
1
1
3
1
H), 7.63 (dd, J = 7.8, 1.8 Hz, 1H), 7.36 (ddd, J = 8.4, 7.2, 1.8 Hz,
H), 7.00 (dd, J = 8.3, 1.1 Hz, 1H), 6.86 (ddd, J = 8.0, 7.3, 1.1 Hz,
H), 4.49 (dd, J = 9.4, 7.7 Hz, 1H), 4.41 (dtd, J = 9.4, 7.5, 6.2 Hz, 1H),
.96 (t, J = 7.6 Hz, 1H), 1.85−1.60 (m, 6H), 1.57−1.47 (m, 1H),
2) and Et O (1 mL × 3) to afford a green powder. Yield: 72 mg
2
1
(62%). H NMR (400 MHz, CDCl ) δ 7.92 (dd, J = 8.2, 1.7 Hz, 1H),
3
7.68 (dd, J = 7.9, 1.7 Hz, 1H), 7.45 (ddd, J = 8.7, 7.1, 1.8 Hz, 1H), 7.25
(ddd, J = 8.0, 7.4, 1.7 Hz, 1H, partially overlaps with the CHCl3
residue peak), 6.94 (ddd, J = 8.0, 7.2, 0.9 Hz, 1H), 6.87 (dd, J = 8.5,
0.8 Hz, 1H), 6.77 (ddd, J = 8.0, 7.1, 0.9 Hz, 1H), 6.75 (dd, J = 8.2, 0.8
Hz, 1H), 5.31−5.24 (m, 1H), 4.99 (t, J = 8.7 Hz, 1H), 4.86 (dd, J =
8.7, 3.5 Hz, 1H), 4.67 (t, J = 8.7 Hz, 1H), 4.57 (dd, J = 8.3, 6.1 Hz,
1H), 4.53−4.45 (m, 1H), 2.64−2.55 (m, 2H), 1.83−0.88 (m, 24H).
Elemental analysis (C H ClN O Re) calculated: C, 50.95%; H,
1
3
.45−1.38 (m, 1H), 1.33−1.11 (m, 3H), 1.03−0.91 (m, 2H).
C
NMR (101 MHz, CDCl ) δ 165.1, 160.0, 133.4, 128.1, 118.8, 116.9,
3
1
11.0, 72.7, 63.5, 44.4, 35.3, 33.8, 33.4, 26.7, 26.5 (C × 2).
HMe hoz (L4). The starting ethanolamine is 2-amino-2-methyl-1-
2
propanol (294 mg). The final product is a slightly yellow-green solid.
1
Yield: 360 mg (63%). H NMR (500 MHz, CDCl ) δ 12.21 (br, 1H),
3
7
.63 (dd, J = 7.8, 1.7 Hz, 1H), 7.36 (ddd, J = 8.6, 7.4, 1.6 Hz, 1H), 7.01
32
40
2
5
(
2
1
dd, J = 8.4, 1.0 Hz, 1H), 6.86 (ddd, J = 7.7, 7.4, 0.9 Hz, 1H), 4.10 (s,
5.35%; N, 3.71%; Cl, 4.70%; Re, 24.68%, found: C, 50.63%; H, 4.97%;
H), 1.40 (s, 6H). 13C NMR (126 MHz, CDCl ) δ 163.7, 160.1,
N, 3.73%; Cl, 4.83%; Re, 24.60%. ESI−HRMS: m/z calculated for
3
+
33.4, 128.1, 118.8, 116.9, 111.1, 78.6, 67.3, 28.7 (C × 2).
Hhox (L5). The starting ethanolamine is 3-amino-1-propanol (248
C H N O Re (the dominant [M−Cl] ): 719.2495, found: 719.2480.
32
40
2
5
Preparation of N,N-trans Re(O)(Me hoz) Cl (7a). A mixture of
2 2
Re(O)(OPPh )(SMe )Cl (150 mg, 0.231 mmol), H-4,4-Me hoz (93
3 2 3 2
1
mg, 0.485 mmol), 2,6-lutidine (59 μL, 55 mg, 0.509 mmol), and EtOH
(8 mL) was refluxed in a 15 mL flask. After it was heated for 15 min in
total, the green solution was cooled, and the solvent was evaporated in
the fume hood overnight. The solid residue was redissolved in ∼0.5
mL of EtOH, and this liquid was added dropwise in 10 mL of Et O to
2
4
1.1, 21.9.
precipitate both the green product and white OPPh . After the liquid
phase was filtered through a glass frit, the solid was quickly washed
3
Preparation of N,N-trans Re(O)(Mehoz) Cl (4a). A mixture of
2
Re(O)(OPPh )(SMe )Cl (100 mg, 0.154 mmol), HMehoz (57 mg,
with EtOH (0.5 mL × 2) and Et O (0.5 mL × 3) to afford a green
3
2
3
2
1
0.324 mmol), 2,6-lutidine (38 μL, 35 mg, 0.324 mmol), and EtOH (6
powder. Yield: 87 mg (61%). H NMR (500 MHz, CDCl ) δ 7.94 (dd,
3
mL) was refluxed in a 15 mL flask. Green solid gradually precipitated
from the solution. After it was heated for 15 min in total, the
suspension was cooled, and the liquid phase was filtered through a
glass frit. The solid phase was sequentially washed with EtOH (1 mL ×
J = 8.2, 1.2 Hz, 1H), 7.73 (dd, J = 8.0, 1.0 Hz, 1H), 7.39 (ddd, J = 8.4,
7.0, 1.4 Hz, 1H), 7.21 (ddd, J = 8.6, 7.1, 1.4 Hz, 1H), 6.93 (ddd, J =
8.1, 7.1, 0.8 Hz, 1H), 6.83 (dd, J = 8.4, 0.8 Hz, 1H), 6.76 (ddd, J = 8.0,
7.2, 1.0 Hz, 1H), 6.74 (dd, J = 7.1, 0.7 Hz, 1H), 4.66−4.53 (m, 4H),
1.96 (s, 3H), 1.94 (s, 3H), 1.85 (s, 3H), 1.65 (s, 3H). Elemental
analysis (C H ClN O Re) calculated: C, 42.75%; H, 3.91%; N,
3
) and Et O (1 mL × 3) to afford a green powder. Yield: 84 mg
2
1
(
92%). H NMR (400 MHz, CDCl ) δ 7.93 (dd, J = 8.1, 1.7 Hz, 1H),
3
22 24
2
5
7
.70 (dd, J = 8.0, 1.6 Hz, 1H), 7.45 (ddd, J = 8.6, 7.1, 1.8 Hz, 1H), 7.24
4.53%; Cl, 5.74%; Re, 30.13%, found: C, 42.14%; H, 3.57%; N, 4.45%;
(
ddd, J = 8.2, 7.4, 1.7 Hz, 1H, partially overlaps with the CHCl peak),
Cl, 6.94%; Re, 29.40%. ESI−HRMS: m/z calculated for
3
+
6
.95 (ddd, J = 8.0, 7.0, 0.9 Hz, 1H), 6.89 (dd, J = 8.5, 0.8 Hz, 1H), 6.78
ddd, J = 8.0, 7.0, 0.9 Hz, 1H), 6.76 (dd, J = 8.4, 0.7 Hz, 1H), 5.39−
.31 (m, 1H), 5.03 (t, J = 8.6 Hz, 1H), 4.78 (t, J = 8.6 Hz, 1H), 4.72
dd, J = 8.6, 3.8 Hz, 1H), 4.60−4.51 (m, 1H), 4.48 (dd, J = 8.1, 6.0 Hz,
H), 1.75 (d, J = 6.5 Hz, 3H), 1.72 (d, J = 6.6 Hz, 3H). Single crystals
suitable for X-ray diffraction were grown by diffusion of pentane into
C H N O Re (the dominant [M−Cl] ): 583.1243, found: 583.1243.
22
24
2
5
(
5
(
1
Preparation of N,N-cis Re(O)(hox) Cl (8b). A mixture of Re(O)-
2
(OPPh )(SMe )Cl (150 mg, 0.231 mmol), Hhox (86 mg, 0.485
3 2 3
mmol), 2,6-lutidine (59 μL, 55 mg, 0.509 mmol), and EtOH (9 mL)
was refluxed in a 15 mL flask for 48 h. After it was cooled and filtered,
the solid phase was washed with EtOH and then redissolved in
I
DOI: 10.1021/acs.inorgchem.6b03076
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
2
2
Present Address
Xiamen Intellectual Property Office, Room 1301 (West Bldg.),
91 Changqing Rd, Xiamen, Fujian, 361012, P. R. China.
1
Notes
Hz, 1H), 7.16 (ddd, J = 8.7, 6.8, 1.7 Hz, 1H), 6.85 (t, J = 7.6 Hz, 1H),
The authors declare no competing financial interest.
CCDC 1492182 (structure 4a), 1492183 (5a), and 1492184
6
2
4
3
2
.75 (t, J = 7.6 Hz, 1H), 6.29 (d, J = 8.3 Hz, 1H), 4.82 (t, J = 5.5 Hz,
H), 4.54 (dt, J = 15.9, 5.3 Hz, 1H), 4.32 (dt, J = 9.9, 4.7 Hz, 1H),
.00 (dt, J = 15.0, 4.7 Hz, 1H), 3.67 (ddd, J = 15.8, 8.3, 4.7 Hz, 1H),
.51 (td, J = 9.7, 3.1 Hz, 1H), 3.21 (ddd, J = 14.9, 9.3, 5.2 Hz, 1H),
.42 (dp, J = 13.4, 6.0 Hz, 1H), 2.27 (dp, J = 15.3, 5.1 Hz, 1H), 1.93
(
8b) 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.
(
dtt, J = 13.9, 9.1, 4.5 Hz, 1H), 1.55−1.52 (m, 1H, partially overlaps
with the water peak). Single crystals suitable for X-ray diffraction were
grown by diffusion of pentane into the CH Cl2 solution of the
ACKNOWLEDGMENTS
2
■
product. Elemental analysis (C H ClN O Re) calculated: C, 40.71%;
20
20
2
5
Financial support was provided by the National Science
Foundation (CBET-1555549) and the U.S. Environmental
Protection Agency Science to Achieve Results Program (Grant
No. RD83517401). Dr. D. Olson and Dr. M. Hallock (UIUC)
are, respectively, acknowledged for assistance with NMR
measurements and DFT calculations. Dr. J. Bertke (UIUC)
conducted the crystallography analysis.
H, 3.42%; N, 4.75%; Cl, 6.01%; Re, 31.56%, found: C, 40.70%; H,
3
.02%; N, 4.65%; Cl, 6.23%; Re, 30.56%. ESI−HRMS: m/z calculated
+
for C H N O Re (the dominant [M−Cl] ): 555.0930, found:
20
20
2
5
555.0938.
X-ray Crystallography. Single-crystal X-ray diffraction data were
collected on a Bruker D8 Venture diffractometer equipped with a
Photon 100 detector using multilayer optics to monochromatize Mo
Kα radiation (for 4a and 7a) and a Siemens Platform diffractometer
equipped with an Apex II CCD detector using graphite-monochrom-
atized Mo Kα radiation (for 8b). Combinations of 0.5° φ and ω scans
were used to collect the data. The collections, cell refinements, and
integrations of intensity data were performed with the APEX2 software
REFERENCES
■
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package. Face-indexed absorption corrections were performed
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72
SADABS. The structures were solved with the direct methods
73
74
program and refined with the full-matrix least-squares SHELXL
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Computational Details. DFT
structures at the B3LYP level.
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7
5,76
was applied to all Re complex
The basis set used for rhenium was
77−79
80
8
1
mized functions of Couty and Hall and a set of polarization f
82
83,84
function. The 6-31G (d, p) basis sets
were used for all H, C, N,
8
5,86
O, and Cl atoms. The 6-311G(d) basis sets
were used for S atoms.
̈
2
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8
7
energies were obtained by applying SMD solvation model with
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optimization and thermochemistry results were gained using
8
8
Gaussian09 (Revision D01) package of programs. Calculated
energies and optimized structure coordinate files (.xyz format) are
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́
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ASSOCIATED CONTENT
■
*
S
Supporting Information
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The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
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AUTHOR INFORMATION
■
*
*
(11) Kasner, G. R.; Boucher-Jacobs, C.; McClain, J. M.; Nicholas, K.
Corresponding Authors
E-mail: jyliu@engr.ucr.edu. (J.L.)
E-mail: strthmnn@mines.edu. (T.J.S.)
M. Oxo-Rhenium Catalyzed Reductive Coupling and Deoxygenation
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ORCID
Jinyong Liu: 0000-0003-1473-5377
Danielle L. Gray: 0000-0003-0059-2096
(13) Raju, S.; Moret, M. E.; Klein Gebbink, R. J. Rhenium-Catalyzed
Dehydration and Deoxydehydration of Alcohols and Polyols:
J
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DOI: 10.1021/acs.inorgchem.6b03076
Inorg. Chem. XXXX, XXX, XXX−XXX