Non-innocent ligand reservoirs for reducing or oxidizing equivalents in carbonylrhenium(I) complexes: 1,1′-Bis(diphenylphosphino)ferrocene (dppf) and bis-triazinyl-pyridine (BTP)

Article abstract of DOI:10.1016/j.ica.2011.02.005

Organometallic complexes of Re(I) with ligands having opposite redox properties have been synthesized and structurally characterized. X-ray crystal structures of the complexes show typical fac-Re^I(CO)₃ coordination to the redox activ

Full text of DOI:10.1016/j.ica.2011.02.005

Inorganica Chimica Acta 374 (2011) 134–139
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Inorganica Chimica Acta
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Non-innocent ligand reservoirs for reducing or oxidizing equivalents in
carbonylrhenium(I) complexes: 1,10-Bis(diphenylphosphino)ferrocene (dppf)
and bis-triazinyl-pyridine (BTP)
⇑
Sayak Roy, Travis Blane, Alyssia Lilio, Clifford P. Kubiak
Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, 0358, La Jolla, CA 92093-0358, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 13 February 2011
Organometallic complexes of Re(I) with ligands having opposite redox properties have been synthesized
and structurally characterized. X-ray crystal structures of the complexes show typical fac-ReI(CO)3 coor-
dination to the redox active ligands. Complete electrochemical and spectroelectrochemical studies on the
ligands and the metal complexes were performed. The IR-spectroelectrochemical responses were moni-
tored using the fac-Re(CO)3 unit as a probe. The 15–20 cmꢀ1 hypsochromic or bathochromic shift of the
mCO bands upon reduction or oxidation is attributed to ligand-centered processes.
Dedicated to Prof. Wolfgang Kaim on the
occasion of his 60th birthday.
Keywords:
Re(I)–carbonyl complexes
Ferrocene
Ó 2011 Elsevier B.V. All rights reserved.
Electrochemistry
Spectroelectrochemistry
1. Introduction
With this in mind, we carried out a systematic electrochemical
and spectroelectrochemical (SEC) investigation of Re(I)carbonyl
Carbonylrhenium(I) complexes of polypyridyl ligands have
been widely investigated due to their applications in homogeneous
CO2 reduction catalysis, light harvesting systems and intermolecu-
lar electronic communication [1–3]. Drawing inspiration from
Lehn’s catalyst, our lab has recently developed a Re(I)(di-tert-
butyl-bipyridine) complex with greatly enhanced electrochemical
and photoelectrochemical CO2 reduction ability [3,4]. The details
of the electrocatalytic pathway are still under investigation so
new derivatives were synthesized that might offer insight into
the catalytic cycle.
complexes with ligands possessing strong
r-donor abilities like
dppf and strong -accepting abilities like bis-triazinyl pyridines. In
p
this paper, we report four tricarbonylrhenium(I) complexes with
bis-(5,6-dimethyl-[1,2,4]triazinyl) pyridines (dtm), bis-(5,6-diphe-
nyl-[1,2,4]triazinyl)pyridines(dtb)(Fig. 2)and1,10-bis(diphenylphos-
phino)ferrocene (dppf) (Fig. 2). All complexeswere fully characterized
and their complete spectroscopic study is reported here.
2. Experimental
The ligand 1,10-bis(diphenylphosphino)ferrocene (dppf) has
shown widespread utility in organic chemistry, homogeneous
catalysis and materials chemistry (Fig. 1, right) [5]. The use of dppf
as a co-ligand in stabilizing CuI with weakly basic quinones and
azo-carbonyl is now well established [6].
Bis-triazinyl pyridines are currently being examined as possible
ligands for lanthanide and actinide separation in nuclear wastes
(Fig. 1, left) [7]. These ligands have widespread potential in coordi-
2.1. Physical measurements
1H, 31P{1H} and 19F NMR spectra were measured with a
300 MHz Varian spectrometer. UV–Vis–NIR absorption spectra
were recorded with a Shimadzu UV-3600 spectrometer. Electro-
chemistry was performed on a BAS CV-50W in dried deoxygenated
CH2Cl2 or CH3CN using 0.1 M Bu4NPF6 (recrystallized from metha-
nol and dried under vacuum at 80 °C) as supporting electrolyte.
The working electrode was glassy carbon, counter was platinum
wire and a Ag/AgCl wire was used as pseudo-reference. The ferro-
cene/ferrocenium couple served as an internal reference. Infrared
spectra were collected on Bruker Equinox 55 FTIR spectrometer.
IR-spectroelectrochemistry was done with a home-built sixth gen-
eration cell mounted on a specular reflectance unit. A detailed
description of the cell is reported elsewhere [8]. Elemental analysis
nation chemistry because of the small size of the
p system and
availability of much lower energy p⁄ orbitals [7d], but surprisingly
few articles have been published on the redox activity of triazinyl
pyridines in metal complexes.
⇑
Corresponding author.
E-mail address: ckubiak@ucsd.edu (C.P. Kubiak).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.005

S. Roy et al. / Inorganica Chimica Acta 374 (2011) 134–139
135
2.29; N, 16.10. Found: C, 28.90; H, 2.35; N, 16.01%. 1H NMR [CD3CN,
d (ppm)]: 2.16 (s, 6H), 2.33 (s, 6H); IR [CH3CN, mco (cmꢀ1)]: 2031,
1935, 1909; ESI-MS (m/z): 539.66 [M+NH4]+.
2.3.2. Synthesis of [Re(dtb)(CO)3Cl] (2-Cl)
Re(CO)5Cl (145 mg, 0.4 mmol) was dissolved in 50 mL of dry
toluene. An equimolar amount of dtb was added (180 mg,
0.180 mmol) to the solution and the reaction mixture was allowed
to reflux overnight. The solution was evaporated to yield a red res-
idue, which was recrystallized from a mixture of CH2Cl2/hexanes
1:3. Yield: 150 mg (48%), C33H20N6ReO3Cl1 (770.21), Anal. Calc. C,
51.45; H, 2.59; N, 10.90. Found: C, 51.35; H, 2.65; N, 11.06%. 1H
NMR [CD3CN, d (ppm)]: 7.45–7.77 (6 aromatic H); IR [CH3CN, mco
(cmꢀ1)]: 2029, 1938, 1913; ESI-MS (m/z): 787.65 [M+NH4]+.
Fig. 1. 1,10-Bis(diphenylphosphino)ferrocene (dppf), bis-(5,6-dimethyl-[1,2,4]triaz-
inyl) pyridines (dtm) and bis-(5,6-diphenyl-[1,2,4]triazinyl) pyridines (dtb).
2.3.3. Synthesis of [Re(dppf)(CO)3(OTf)] (3-OTf)
[Re(dppf)(CO)3Cl] (31.4 mg, 0.036 mmol) and a small excess of
silver triflate (20 mg, 0.0781 mmol) were stirred at room tempera-
ture under a nitrogen atmosphere for 12 h. The precipitate was fil-
tered out and the solvent was removed under reduced pressure.
The yellow solid was recrystallized from the mixture of CH2Cl2/
pentane 1:3. Yield: 327 mg (92%), C38H28Re1Fe1P2F3S1O6 (942.00),
Anal. Calc. C, 48.44; H, 2.97. Found: C, 48.31; H, 2.94%. 1H NMR
[CD2Cl2, d (ppm)]: 4.44 (s, 4H), 4.50 (s, 2H), 4.56 (s, 2H), 7.43–
7.60 (m, 20H); 31P{1H} NMR [CD2Cl2, d (ppm)]: 12.42; 19F NMR
[CDCl3, d (ppm)]: ꢀ79.5; IR [CH2Cl2, mco (cmꢀ1)]: 1916, 1970,
2048; ESI-MS (m/z): 824.87 (M-OTf).
was performed by Midwest Micro Lab, LLC, Indianapolis, IN. A
ThermoFinnigan LCQdeca mass spectrometer with an electrospray
ionization source was used for mass spectrometry analysis.
2.2. Materials
The 1,10-bis(diphenylphosphino)ferrocene and Re(CO)5Cl were
purchased from Aldrich Chemical Company and used without
further purification. The ligands dtm, dtb and the complex [Re(d-
ppf)(CO)3Cl] were synthesized using reported procedures
[7e,9,10]. All solvents were dried and degassed prior to use by puri-
fication via passage through alumina under argon.
2.3.4. Synthesis of [Re(dppf)(CO)3(CH3CN)](OTf) (4-OTf)
2.3. Synthesis
[Re(CO)3(dppf)(OTf)] (32 mg, 0.0328 mmol) was dissolved in
dry CH3CN and refluxed in a nitrogen atmosphere for 6 h. The sol-
vent was removed under vacuum leaving a yellow solid. The com-
pound was recrystallized from CH2Cl2/pentane 1:3. Yield: 309 mg
(93%), C40H31N1Re1Fe1P2F3S1O6 (1015.00), Anal. Calc. C, 47.33; H,
3.05; N, 1.37. Found: C, 47.26; H, 3.15; N, 1.22%. 1H NMR [CD2Cl2,
d (ppm)]: 31P{1H} NMR [CDCl3, d (ppm)]: 9.96; 19F NMR [CDCl3, d
(ppm)]; IR [CH2Cl2, mco (cmꢀ1)]: 1946, 1971, 2050; ESI-MS (m/z):
865.69 (M-OTf).
2.3.1. Synthesis of [Re(dtm)(CO)3Cl] (1-Cl)
Re(CO)5Cl (145 mg, 0.4 mmol) was dissolved in 50 mL of dry
toluene. An equimolar amount of dtm (100 mg, 0.4 mmol) was
added to the solution and the reaction mixture was stirred and re-
fluxed overnight. The orange precipitate was collected and
recrystallized from
138 mg (66%), C13H12N6ReO3Cl1 (521.93), Anal. Calc. C, 29.91; H,
a mixture of CH2Cl2/hexanes 1:3. Yield:
Fig. 2. Complexes 1-Cl, 2-Cl, 3-OTf and 4-OTf.

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S. Roy et al. / Inorganica Chimica Acta 374 (2011) 134–139
Table 1
refinement details are presented in Table 1 for all complexes and
selected bond lengths and bond angles are tabulated in Table 2.
Crystal data and structure refinement of 1-Cl and 4-OTf.
The structure of 4-OTf contains a disordered triflate anion.
Complex
[Re(dtm)(CO)3Cl] [Re(dppf)(CO)3(CH3CN)](OTf)
Formula
Molecular weight
T (K)
C
13H12ClN6O3Re
ReFeF3P2SNO6C40H30
1082.36
100 (2)
0.71073
monoclinic
Cc
521.94
3. Results and discussion
100 (2)
0.71073
monoclinic
P2l/n
k (Å)
Crystal system
Space group
Unit cell
a (Å)
b (Å)
c (Å)
3.1. Synthesis and characterization
The complexes 1-Cl and 2-Cl were synthesized by refluxing
commercially available Re(CO)5Cl with the ligands, dtm and dtb,
respectively. Three recrystallizations from CH3CN/Et2O 1:3 re-
sulted in pure crystalline compounds. A typical three-band (E
and A) pattern was observed in the IR spectrum, confirming a
fac-[Re(CO)3] group. Stirring of the reported complex [Re(d-
ppf)(CO)3Cl] (3-Cl) [10] with AgOTf in CH2Cl2 followed by filtration
of insoluble AgCl, afforded 3-OTf. The complex 4-OTf was synthe-
sized by refluxing 3-OTf in CH3CN. The IR spectrum of 3-OTf shows
three well-separated CO bands at 2050, 1970 and 1915 cmꢀ1
where as 4-OTf exhibits relatively coalescenced E bands (1947
and 1972 cmꢀ1) attributed to solvent coordination, along with a
sharp A band (2050 cmꢀ1).
9.3227(5)
18.5627(10)
9.9428(6)
90
108.8210(10)
90
1628.64(16)
4
2.129
36.937(3)
41.370(3)
26.280(2)
90
131.3720(10)
90
30 137(4)
30
1.789
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢀ3
)
Number of reflection/Rint
Reflection/constraints/
parameters
202 921/0.0747
67 043/27/1984
3751/0/231
R1,wR2 [I > 2r(I)]
0.027, 0.0521
0.0361, 0.0551
0.0593, 0.1136
0.1292, 0.1136
1.007
1.688 and ꢀ1.551
R1,wR2 (all)
Goodness-of-fit (GOF)
Largest difference in peak 1.303 and
and hole (e Åꢀ3
ꢀ1.010
)
3.2. Crystallography
The IR, NMR and mass spectroscopic results were confirmed by
determination of X-ray crystal structure of 1-Cl (Fig. 3). Crystallo-
graphic data, bond lengths and bond angles are listed in Tables 1
and 2. There is no reported structure for the crystal structure of
the free ligand and we were unable to grow crystals so we could
not compare the bond lengths in free ligand with the lengths in
1-Cl. The structure 1-Cl shows typical facial binding of the
Re(CO)3Cl unit by the dtm ligand leading to a neutral coordination
sphere. Significant contraction along the N1–Re–N2 bond angle re-
sults in a distortion of the octahedral geometry. The triazinyl rings
are slightly displaced from the coordination plane created by the
Re–N1–C6–C7–N2 atoms. The coordination of Re(I) by the 6,60-
nitrogens of dtm is sterically hindered relative to the 2,20-nitrogens
due to substituted methyl groups at the 5,50 positions. The crystal
structure shows axial disorder along Cl–Re–CO. A shorter axial CO
bond length in comparison to equatorial CO indicates better Re(I)
to p⁄ back donation in the equatorial direction.
Table 2
Important bond lengths and bond angles.
1-Cl
4-OTf
Bond lengths
Bond lengths
C1–O1: 1.135(5); Re1–C3: 1.894(6)
C2–O2: 1.153(5); Re1–C3B: 1.87(4)
C3–O3: 1.157(8); Re1–C1: 1.936(4)
C3B–O3B: 1.14(5); Re1–C2: 1.919(4)
Re1–Cl(1B): 2.436(1); Re1–Cl1:
2.472(2)
Re1–N1: 2.143(3); Re1–N2: 2.160(3)
N1–C6: 1.327(5); N1–N3: 1.350(4)
N2–C7: 1.332(5); N2–N6: 1.357(4)
N3–C4: 1.316(5); N4–C6: 1.332(5)
N5–C8: 1.329(5); N5–C7: 1.339(5)
N6–C9: 1.324(5); C4–C5: 1.426(6)
C6–C7: 1.494(5); C8–C9: 1.421(6)
N4–C5: 1.332(5)
C1–O1: 1.142(2); Re1–C1: 1.910(2)
C2–O2: 1.11(2); Re1–C2: 1.950(2)
C3–O3: 1.15(2); Re1–C3: 1.98(2)
C4–N1: 1.08(2); Re1–N1: 2.183(2)
Re1–P1: 2.527(6); Re1–P2:
2.511(6)
In spite of disorder in the phenyl rings and an unusually high
unit cell parameter (Z = 30) for the crystal of 4-OTf (Fig. 3), the
coordination sphere around Re(I) is clear. Re(I) shows distorted
octahedral geometry due to the considerably smaller bite angle
of the dppf ligand (ca. 100°). The solvent molecule CH3CN coordi-
nates the metal in an axial position. Re(I) to ligand back donation
results in the elongation of the C–O and C–N bond lengths of coor-
dinated CO and CH3CN.
Bond angles
N2–Re1–N1: 73.84(12)
C1–Re1–N1: 170.78(15)
C3B–Re1–Cl1B: 176.7(11)
C1–Re1–N2: 97.22(15)
C2–Re1–N1: 98.46(14)
C2–Re1–N2: 172.16(15)
C3–Re1–N1: 96.09(19)
C3–Re1–Cl1: 177.49(18)
Bond angles
P1–Re1–P2: 100.83(2)
C1–Re1–C3: 93.0(7)
C1–Re1–C2: 85.9(7)
C3–Re1–C2: 87.5(8)
C1–Re1–N1: 175.5(6)
C3–Re1–N1: 91.2(7)
C2–Re1–N1: 92.5(7)
C3–Re1–P2: 82.5(5)
N1–Re1–P2: 89.6(4)
C1–Re1–P1: 94.7(5)
C2–Re1–C1: 90.53(18)
C3B–Re1–N2: 93.3(11)
3.3. Optical spectra
2.4. Crystallography
The UV–Vis spectra of the ligands dtm and dtb, and the com-
pounds 1-Cl and 2-Cl were measured in CH3CN. The complexes
show a higher energy band (415 nm in 1-Cl and 460 nm in 2-Cl)
Slow diffusion of hexane into the solution of 1-Cl in CH3CN re-
sulted in needle and plate shaped crystals. Yellow needles of 4-OTf
were obtained by diffusion of pentane into CH2Cl2 solution at room
temperature. Single-crystal X-ray structure determinations are
carried out at 100(2) K on either a Bruker P4 or Platform diffrac-
due to electronic transition from d of Re(I) to the p⁄ of the bis-
p
triazyl pyridine ligand. The lower energy bands (240, 270 and
330 nm for 1-Cl and 235, 290 and 340 nm for 2-Cl) in the complexes
are attributed to intra-ligand (p–
p⁄) transitions (Fig. 4). The spectra
tometer using Mo K
a
radiation (k = 0.71073 Å) in conjunction with
of the free ligands have the intra-ligand transition bands in the
same region (230–310 nm). The bathochromic shift of these bands
in the complexes is of the result of coordination to Re(I).
The yellow colored complexes 3-OTf and 4-OTf exhibit spectral
features very similar to those of 3-Cl. All the complexes show a
a Bruker APEX detector. All structures were solved by direct meth-
ods using SHELXS-97 and refined with full-matrix least-squares pro-
cedures using SHELXL-97 [11]. The non-hydrogen atoms were refined
with anisotropic thermal parameters. The crystal data and

S. Roy et al. / Inorganica Chimica Acta 374 (2011) 134–139
137
Fig. 3. Molecular structures of 1-Cl and 4-OTf with ellipsoids at 50%. The H atoms for both structures and the OTf in 4-OTf are removed for clarity.
3.4. Electrochemistry
Cyclic voltammetry experiments on the ligands, dtm and dtb,
and the complexes 1-Cl and 2-Cl were compared. The electrochem-
istry of the free ligands was performed in 0.1 M Bu4NPF6/CH2Cl2
due to poor solubility in CH3CN. As a result of the electron donating
effects of the methyl substituents in dtm, the ligand is reduced at a
more negative potential than dtb (supporting information, S1).
Complexes of 1-Cl and 2-Cl exhibit almost identical electrochemi-
cal features with one reversible reduction leading to occupancy in
the p⁄ orbitals of ligands. Ligand coordination to the metal causes
the ligand-centered reductions to shift anodically due to charge
transfer from ligand nitrogens to the metal. The first reduction is
followed by a quasi-reversible and an irreversible step. This kind
of behavior is generally due to chloride loss and reduction of chlo-
ride-free Re species [13]. The complexes each show a comparable
third reduction step, confirmed by SEC as ligand centered process
(Fig. 5, left and supporting information S2).
Fig. 4. Optical spectra of 1-Cl (black) and 2-Cl (red, inset) in CH3CN. (For
interpretation of the references in color in this figure legend, the reader is referred
to the web version of this article.)
The electrochemical responses of the triflate complexes 3-OTf
and 4-OTf are comparable in CH2Cl2. Both complexes have the re-
dox active ferrocenyl phosphine as coligand, which shows a revers-
ible oxidation. Oxidation of 4-OTf occurs at a higher positive
potential compared to 3-Cl and 3-OTf because of overall accumula-
tion of positive charge (supporting information S4) [13]. The
weak absorption band at 430–440 nm due to an intra-ligand tran-
sition in the coordinating dppf [10,12].
Fig. 5. Electrochemistry of 1-Cl (left) and 3-OTf (right) in 0.1 M Bu4NPF6/CH3CN and 0.1 M Bu4NPF6/CH2Cl2, respectively (At RT, 100 and 50 mV/s scan rate, respectively).

138
S. Roy et al. / Inorganica Chimica Acta 374 (2011) 134–139
Table 3
Oxidation and reduction potentials from cyclic voltammetry.a
Compound
E1 (Ox)
E2 (1st red)
E3 (2nd red)
E4 (3rd red)
dtmb
1-Cla
dtbb
2-Cla
3-Cl
–
–
–
–
ꢀ2.23e
ꢀ1.30d
ꢀ1.84d
ꢀ1.05d
-
–
–
ꢀ1.80e
ꢀ2.42e
ꢀ2.14e
ꢀ2.29e
ꢀ1.52e
ꢀ2.04e
0.67c
0.43b
0.39d
0.60d
-
-
ꢀ1.58e
–
–
–
–
–
–
–
3-OTfb
4-OTfb
ꢀ1.69e
a
b
c
In 0.1 M Bu4NPF6/CH3CN at RT.
In 0.1 M Bu4NPF6/CH2Cl2.
In 0.1 M Bu4NClO4/CH2Cl2 at RT, Ag/Ag+ as reference.
Half wave potential corresponding to a reversible wave.
Cathodic peak potential corresponding to an irreversible wave.
d
e
Fig. 7. IR spectroelectrochemical oxidation of 3-OTf to (3-OTf)+ in 0.1 M Bu4NPF6/
CH2Cl2.
irreversible reduction step of 4-OTf at very negative potential is
attributed to a Re(I) centered reduction (Table 3 and Fig. 5, right).
Table 4
3.5. IR-spectroelectrochemistry
IR-spectroelectrochemical data.a
Compounds mco [cmꢀ1
]
Additional information on the effects and location of electrons
was obtained from IR-spectroelectrochemical (IR-SEC) studies.
The IR-SEC measurements on compounds l-Cl and 2-Cl were per-
formed in CH3CN at RT. Both l-Cl and 2-Cl show typical three band
spectrum due to the fac-Re(CO)3Cl moiety. Upon the first one elec-
tron reversible reduction, a shift in the bands of about 20 cmꢀ1 to
lower energy is observed (Fig. 6, left). The shift of the bands is ex-
pected due to electron uptake into the p⁄ level of bis-triazyl pyri-
dine ligands, which in turn increases metal to CO back donation
1-Clb
(1-Cl)Åꢀb
1Åb
2030, 1935, 1910
2010, 1905, 1877
2005, 1890, 1865
(sh)
1990, 1865 (br)
2028, 1937, 1907
2010, 1907, 1880
1995, 1980, 1880,
1965 (sh)
1985, 1960 (br)
2035, 1953, 1900
2047, 1972, 1920
2050, 1970, 1915
2065, 1990, 1940
2050, 1972, 1947
2062, 1990, 1960
1ꢀb
2ꢀClb
(2-Cl)Åꢀb
2Åb
2ꢀb
(metal dp
to p⁄ of CO). As the more negative potentials are applied,
3-Clc,d
(3-Cl)+d
3-OTfc
(3-OTf)+c
4-OTfc
(4-OTf)+c
a further shift to lower energy is observed. The amount of the shift
is much less than the shift in the first reduction. This feature is ex-
plained by chloride loss and formation of the neutral solvated com-
plex [Re(L-L)(CO)3(CH3CN)]. There is also the appearance of a small
peak, which is tentatively assigned to the formation of a very small
quantity of dinuclear species, common among bipyridine com-
plexes of Re(CO)3 (see supporting information, S3). The input of
the 2nd electron into the compounds results in a considerable blue
shift in the mCO stretch. Upon applying more voltage, the com-
pounds show signs of decomposition (Fig. 6, right).
a
b
c
0.1 M Bu4NPF6 at RT.
In CH3CN.
In CH2Cl2.
d
0.1 M Bu4NClO4.
The compounds 3-OTf and 4-OTf show identical spectroelectro-
chemical behavior in 0.1 M Bu4NPF6/CH2Cl2. Because of the ferro-
cene backbone, dppf ligand can be oxidized reversibly. Upon
oxidation, a uniform blue shift of the mCO bands reflects decreased
back donation from Re(I) to the CO p⁄ orbitals (Fig. 7, Table 4, and
supporting information S5).
4. Summary
The present work describes the synthesis and complete charac-
terization of the set of complexes, 1-Cl, 2-Cl, 3-OTf and 4-OTf, bear-
ing diverse redox active ligands. The solution behavior of the
complexes was monitored by NMR, IR and UV–Vis spectroscopy,
Fig. 6. IR spectroelectrochemical reduction of 2-Cl to (2-Cl)Åꢀ (left) and 2Å to 2ꢀ (right) in 0.1 M Bu4NPF6/CH3CN.

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139
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and redox properties were investigated by IR-spectroelectrochem-
istry. In spite of disorder in the X-ray crystal structure for 1-Cl, the
facial binding of the Re(CO)3Cl unit to the ligand is clear. The struc-
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trile solvent molecule to the Re(I) unit.
Acknowledgements
The authors thank Starla D. Glover, and John C. Goeltz for their
insightful discussions. Jim Golen and Curtis Moore are greatly
appreciated for their help and guidance with crystallography.
Authors also gratefully acknowledge Helios Solar Energy Research
Center, which is supported by the Director, Office of Science, Office
of Basic Energy Sciences of the US Department of Energy, under the
contract no. DE-AC02-05CH11231.
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Appendix A. Supplementary material
CCDC 798826 and 798827 contain the supplementary crystallo-
graphic data for 1-Cl and 4-OTf, respectively. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2011.02.005.
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