Synthesis and characterization of cerium and yttrium alkoxide complexes supported by ferrocene-based chelating ligands

Article abstract of DOI:10.1021/ic102076g

Two series of Schiff base metal complexes were investigated, where each series was supported by an ancillary ligand incorporating a ferrocene backbone and different N=X functionalities. One ligand is based on an imine, while the other is based on an imino

Full text of DOI:10.1021/ic102076g

ARTICLE
pubs.acs.org/IC
Synthesis and Characterization of Cerium and Yttrium Alkoxide
Complexes Supported by Ferrocene-Based Chelating Ligands
Erin M. Broderick,† Peter S. Thuy-Boun,† Neng Guo,‡ Carola S. Vogel,§ J€org Sutter,§ Jeffrey T. Miller,‡
Karsten Meyer,§ and Paula L. Diaconescu*,†
†Department of Chemistry & Biochemistry, University of California, Los Angeles, California 90095, United States
‡Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
§Department of Chemistry and Pharmacy, Friedrich-Alexander-University Erlangen-Nuremberg, Egerlandstrasse 1, 91058 Erlangen
Germany
S Supporting Information
b
ABSTRACT: Two series of Schiff base metal complexes were investigated, where each series was
supported by an ancillary ligand incorporating a ferrocene backbone and different N=X function-
alities. One ligand is based on an imine, while the other is based on an iminophosphorane group.
Cerium(IV), cerium(III), and yttrium(III) alkoxide complexes supported by the two ligands were
synthesized. All metal complexes were characterized by cyclic voltammetry. Additionally, NMR,
M€ossbauer, X-ray absorption near-edge structure (XANES), and absorption spectroscopies were
used. The experimental data indicate that iron remains in the þ2 oxidation state and that cerium(IV)
does not engage in a redox behavior with the ancillary ligand.
’ INTRODUCTION
examples are still limited.19,25 With a strongly oxidizing metal
center like cerium(IV), there exists the potential for redox events
to occur, effectively changing the ferrocene backbone of the
ancillary ligand into ferrocenium upon complexation. Cerium-
(IV) is a good candidate for this process since it has a redox
potential of 0.88 V in water, while ferrocene has a redox potential
of 0.00 V (both measured versus Cp2Fe/Cp2Feþ).26 It is important
to note that although the structures of Schiff base metal com-
plexes have been thoroughly studied,27 complexes of d0fn metals
have not been the subject of electrochemical investigations,
with the exception of some uranyl complexes.28,29 Several studies of
the electrochemical properties of Schiff base metal complexes
were reported30,31 and, in certain cases, ligand-based oxida-
tions were identified.32-43 Herein, we report the synthesis of
cerium(IV) alkoxides supported by 1 to determine whether
cerium(IV) could oxidize the ferrocene backbone or a differ-
ent functionality of the ancillary ligand. For comparison,
cerium(III) and yttrium(III) alkoxides were also synthesized
(Chart 1). These complexes were characterized by cyclic voltam-
metry and NMR, M€ossbauer, UV-vis-NIR, and X-ray absorp-
tion near-edge structure (XANES) spectroscopies. In addition, a
new ferrocene diphosphazene proligand, 1,10-di(2-tert-butyl-6-
diphenylphosphiniminophenol)ferrocene (2-H2), anditscomplexes
Ancillary ligand design in organometallic chemistry has re-
cently taken on a new dimension as reports of modulated metal
reactivity by direct ligand involvement in reactions are being
demonstrated.1-4 Redox-active ligands have been classified by
Mirkin as follows: (1) substitutionally inert, redox-active ligands,
(2) redox-switchable hemilabile ligands, and (3) redox-active
ligands that are reactive (leaving) fragments in a metal complex.5
We have been pursuing the study of 1,10-disubstituted, ferrocene-
based chelating ligands as versatile frameworks in supporting
group 3 metal and uranium complexes.6,7 Such ligands are
substitutionally inert, redox-active ligands and open avenues in
controlling the reactivity of a metal center by changing the
oxidation state of ferrocene.5,8-14
Metallocene-based chelating ligands offer the possibility to
engage a redox-active metal center in strong electronic commu-
nication, raising the possibility of redox isomerism.15-17 To test
if such a situation occurs between ferrocene and a lanthanide,
cerium, we focused on Schiff bases incorporating ferrocene. 1,10-
Di(2,4-bis-tert-butyl-salicylimino)ferrocene (1-H2, Chart 1) has
already been used to generate various metal complexes; the
Arnold group synthesized and characterized magnesium, tita-
nium, and zirconium complexes,18 while our group reported
yttrium and cerium(IV) complexes.19 The redox properties of
those compounds were not investigated.
While complexes of transition metals have been targeted
Received: October 13, 2010
Published: March 02, 2011
before to study redox isomerism,15,18,20-24 lanthanide and actinide
r
2011 American Chemical Society
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Inorganic Chemistry
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Chart 1. Cerium and Yttrium Alkoxide Complexes Discussed
Scheme 2. Synthesis of the Cerium(III) Alkoxide 1-
Ce(OtBu)(THF)
Scheme 1. Synthesis of 2-H2 and 3-H2
Scheme 3. Syntheses of 2-Ce(OtBu)2 and 3-Ce(OtBu)2
were synthesized and characterized to compare imine-derived
contributions on their electronic properties.
’ RESULTS AND DISCUSSION
Synthesis of 2-H2. The Staudinger reaction of 1,10-diazofer-
rocene, fc(N3)2 (fc = 1,10-ferrocenylene),44 with 2-diphenylpho-
sphino-6-tert-butylphenol45,46 led to the formation of the
bis(phosphazide) 3-H2 as a red solid. The product 3-H2 dis-
played an N-N stretch at 1417 cm-1 in its IR spectrum (CH2-
Cl2, 25 °C) and a 31P chemical shift at 29.7 ppm (121 MHz, C6D6,
25 °C).47-50 Heating 3-H2 under an inert atmosphere in toluene
at 50 °C for 6 h led to N2 elimination to produce 2-H2 (Scheme 1).
The 31P NMR (121 MHz, C6D6, 25 °C) spectrum of 2-H2
revealed a peak at 27.1 ppm.47,48,50,51 Free phosphinimines have
been reported to have 31P chemical shifts ranging from 12.4 ppm to
21.6 ppm, while free phosphazide 31P chemical shifts have been
reported within the range of 25 ppm to 52 ppm.47-49 Phosphi-
nimines tend to display 31P chemical shifts upfield from the
corresponding phosphazide,47,48 a trend that we observed as well.
Cerium Alkoxide Complexes. We previously reported the
isolation of the cerium(IV) bis(t-butyloxide) complex 1-Ce-
(OtBu)2 by the reaction of Ce(OtBu)4(THF)2 with 1-H2.19
The cerium(III) alkoxide complex 1-Ce(OtBu)(THF) was
synthesized by the protonolysis reaction of Ce[N(SiMe3)2]3
with 1-H2 to produce 1-Ce[N(SiMe3)2](THF) (Scheme 2).
The amide ligand was exchanged for tert-butyloxide through the
addition of tBuOH to 1-Ce[N(SiMe3)2](THF), in diethyl ether
at -78 °C, to give 1-Ce(OtBu)(THF) (Scheme 2). The com-
plex 1-Ce(OtBu)(THF) displays a paramagnetic 1H NMR
spectrum with broad peaks (see the Supporting Information):
five characteristic peaks were found that account for the four tert-
butyl groups of the ancillary ligand and the alkoxide group,
indicating a desymmetrized structure in solution, unlike what was
found for the analogous phosphinimine complex (see below).
Similarly to the preparation of 1-Ce(OtBu)2, the complex 2-
Ce(OtBu)2 was obtained from Ce(OtBu)4(THF)2 and 2-H2 in
tetrahydrofuran (THF) at room temperature (Scheme 3). The
complex 2-Ce(OtBu)2 was also independently synthesized from
3-Ce(OtBu)2 by N2 extrusion (Scheme 3). Interestingly, 3-
Ce(OtBu)2 represents the second lanthanide and one of the
few d0fn-metal phosphazide complexes reported.52,53 The com-
1
plex 3-Ce(OtBu)2 is diamagnetic, with a H NMR (300 MHz,
C6D6, 25 °C) spectrum displaying two peaks for the ferrocene
protons, at 4.00 and 4.97 ppm. The tert-butyl peaks of the
phosphinimine ligand and alkoxides were found as two singlets
at 0.83 and 2.00 ppm. The phosphine aryl protons were identified
as multiplets between 6.50 and 7.82 ppm. The 31P NMR spectrum
of 3-Ce(OtBu)2 displayed a peak at 34.6 ppm, comparable to
values reported for analogous complexes.54,55
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Figure 1. Thermal-ellipsoid (50% probability) representation of 2-
Ce(OtBu)2; hydrogen and solvent atoms were removed for clarity.
Selected metrical parameters for 2-Ce(OtBu)2 (distances in Å and
angles in deg): Ce(1)-O(1), 2.0932(11); Ce(1)-O(2), 2.2670(10);
Ce(1)-N(1), 2.5183(12); N(1)-P(1), 1.5982(13); O(1)Ce(1)O(2),
90.03(4); O(1)Ce(1)N(1), 84.72(4).
Figure 2. Thermal-ellipsoid (50% probability) representation of 3-
Ce(OtBu)2; hydrogen and solvent atoms were removed for clarity.
Selected metrical parameters for 3-Ce(OtBu)2 (distances in Å and
angles in deg): Ce(1)-O(1), 2.0691(29); Ce(1)-O(2), 2.0606(29);
Ce(1)-O(3), 2.3237(30); Ce(1)-O(4), 2.3299(30); Ce(1)-N(1),
2.5523(36); Ce(1)-N(2), 2.5355(37); N(1)-P(1), 1.6350(37);
N(1)-N(5), 1.3807(49); N(5)-N(6), 1.2636(47); N(2)-P(2),
1.6290(37); N(2)-N(3), 1.3746(48); N(3)-N(4), 1.2685(48); O-
(1)Ce(1)O(2), 175.24(12); O(1)Ce(1)O(3), 95.64(11); O(2)Ce-
(1)O(4), 98.19(11); O(1)Ce(1)N(1), 86.23(12); O(2)Ce(1)N(2),
88.88(12); N(1)N(5)N(6), 110.34(35); N(2)N(3)N(4), 110.88(35).
In addition to being characterized in solution by 1H, 13C, and
31P NMR spectroscopy, 2-Ce(OtBu)2 (Figure 1) and 3-Ce-
(OtBu)2 (Figure 2) were characterized by single-crystal X-ray
crystallography. Both complexes contain a pseudo-octahedral
cerium ion, with the two t-butoxide ligands coordinated trans in
the axial positions. Metrical parameters for the coordination
environment of cerium in 2-Ce(OtBu)2 and 3-Ce(OtBu)2 are
similar for the two complexes and compare well with those of 1-
Ce(OtBu)2.19 The main difference between the structures of 1-
Ce(OtBu)2 and 2-Ce(OtBu)2 is the NCeOC torsion angles at
the phenoxide oxygen: these values are 4.50(39) and 6.49(40)°
for the nitrogen connected to the phenoxide and 159.56(69) and
139.48(63)° in 1-Ce(OtBu)2, while the corresponding values in
2-Ce(OtBu)2 are 45.05(15)° and 116.47(23)°, respectively,
indicating that there is a larger deviation from the planarity of
the NCeOphenoxide arrangements in the latter compound. It is
likely that this difference is a consequence of the more flexible
PdN than CdN linkage found in 2-Ce(OtBu)2. The structure
of 2-Ce(OtBu)2 contains a mirror plane, indicating that this
symmetry element is maintained in the solid state. The arrange-
ment of the N3 groups in 3-Ce(OtBu)2 is s-trans and they are κ1-
N coordinated to the metal center. This coordination mode is
likely a consequence of the steric properties of the supporting
ligand, since the N3 group is coordinated κ2 and forms a four-
member ring metallocycle in the other lanthanide phosphazide
complex reported.52
Scheme 4. Synthesis of 2-M(OtBu)(THF)x (M = Ce, x = 1; M
= Y, x = 0)
respectively, indicating a Cs-symmetrical species in solution.
Accordingly, the 31P NMR (121 MHz, C6D6, 25 °C) spectrum
of 2-Ce(OtBu)(THF) shows a singlet at 45.1 ppm.
The iminophosphorane cerium(III) alkoxide 2-Ce(OtBu)-
(THF) was synthesized by the salt metathesis of 2-CeCl(THF)
with potassium tert-butoxide, in diethyl ether at -78 °C. The
cerium(III) chloride 2-CeCl(THF) was obtained from the reac-
tion of CeCl3(THF)3 with 2-[Na(THF)]2 in THF, at -78 °C
(Scheme 4). The 1H NMR (300 MHz, C6D6, 25 °C) spectrum of
2-Ce(OtBu)(THF) shows peaks characteristic for a paramag-
netic compound. The tert-butyl protons of the ancillary ligand
and the alkoxide group have chemical shifts of -5.06 and 6.40 ppm,
Yttrium Alkoxide Complexes. The synthesis of 1-Y(OtBu)-
(THF) was previously reported by our group;19 a similar pro-
cedure was followed for the synthesis of 2-Y(OtBu). The salt
metathesis reaction of YCl3(THF)3 and 2-[Na(THF)]2 in THF,
at room temperature, resulted in the formation of 2-YCl, which
reacted with potassium tert-butoxide in THF, at 0 °C, to yield
1
the desired product, 2-Y(OtBu) (Scheme 4). The H NMR
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Table 2. Mo€ssbauer Parameters for the Compounds
Discussed
complex
δ [mm s-1
]
ΔEQ [mm s-1
]
GFWHM [mm s-1
]
1-Y(OtBu)(THF)
2-Y(OtBu)
1-Ce(OtBu)(THF)
2-Ce(OtBu)(THF)
1-Ce(OtBu)2
0.61(1)
0.52(1)
0.53(1)
0.54(1)
0.60(1)
0.53(1)
2.55(1)
2.42(1)
2.42(1)
2.48(1)
2.51(1)
2.48(1)
0.26(1)
0.27(1)
0.28(1)
0.28(1)
0.26(1)
0.28(1)
2-Ce(OtBu)2
complexes based on the iminophosphorane (2) backbone is
more facile than that of the complexes based on imine (1) and
that there is more difficulty in reducing cerium(IV) to cerium-
(III) in 2-Ce(OtBu)2 than in 1-Ce(OtBu)2.
Figure 3. Cyclic voltammograms of 1-Ce(OtBu)2 and 2-Ce(OtBu)2 at
100 mV/s scan rate (1.5 mM in THF, 0.5 M [nPr4N][BArF ], Cp2Fe/
4
Cp2Feþ corrected).
€
Mossbauer Spectroscopy. M€ossbauer spectroscopy was
Table 1. Redox Events for the Compounds Discusseda
used to probe the electronic structure of the ferrocene backbone
in all metal complexes (Table 2). The yttrium complexes were
used as an iron(II) standard, since no electron-transfer processes
were expected to occur between the ferrocene backbone and the
yttrium. All cerium complexes have similar isomer shifts and
quadrupole splittings, indicating that iron is found as iron(II) in
all complexes.
XANES Spectroscopy. To probe whether cerium engaged in
redox events with other parts of the ancillary ligands, X-ray
absorption near-edge structure (XANES) spectroscopic studies
were undertaken. Fe K-edge measurements corroborated the
results of M€ossbauer spectroscopy showing that the data for all
the cerium and yttrium complexes are similar to each other and
ferrocene. Ce L3-edge measurements (Figure 4) indicated that 1-
Ce(OtBu)2 and 2-Ce(OtBu)2 have similar spectra to cerium(IV)
standards, while 1-Ce(OtBu)(THF) and 2-Ce(OtBu)(THF)
have similar characteristics to the cerium(III) standard CeCl3
(the shoulder observed for 1-Ce(OtBu)(THF) is assigned to a
cerium(IV) impurity). The XANES data suggest that cerium(IV)
is not reduced to cerium(III) by the oxidation of iron or any other
functionality of the ancillary ligands.
UV-vis-NIR spectroscopy. The cerium and yttrium alk-
oxide complexes were further characterized by UV-vis-NIR
spectroscopy (see the Supporting Information for spectra). The
metal complexes supported by 1 have molar absorptivities between
20000 and 40000 M-1 cm-1 that consist of two peaks between
290 and 590 nm. The metal complexes supported by 2 have
molar absorptivities between 10000 and 40000 M-1 cm-1 that
consist of one peak between 290 and 590 nm. The f-f transitions
were not observed for the cerium(III) complexes.56
complex
E1/2(Fe2þ/3þ) (V)
E1/2(Ce3þ/4þ) (V)
1-H2
2-H2
1-Y(OtBu)(THF)
2-Y(OtBu)
0.29b
-0.63c
0.09c
-0.29b
1-Ce(OtBu)(THF)
Eox = -0.21c
Ered = -1.05
-0.57b
2-Ce(OtBu)(THF)
1-Ce(OtBu)2
-0.28b
Eox = -1.01b
Ered = -2.07
Eox = -1.70b
Ered = -2.39
2-Ce(OtBu)2
-0.38b
a Numbers are from 250 mV/s scans. b 1.5 mM in THF, 0.5 M
[nPr4N][BArF4], Cp2Fe/Cp2Feþ corrected.
[nPr4N][BArF ], Cp2Fe/Cp2Feþ corrected. 2.0 mM in THF, 0.5 M
c
4
(300 MHz, C6D6, 25 °C) spectrum of 2-Y(OtBu) showed singlets
at 1.61 and 1.55 ppm, which were assigned to the tert-butyl peaks
of the ancillary ligand and the alkoxide, respectively. The ferrocene
protons had chemical shifts at 5.09, 3.81, 3.58, and 3.53 ppm,
while the phosphine aryl protons had chemical shifts between
6.53 and 7.95 ppm. The 31P (121 MHz, C6D6, 25 °C) spectrum
displayed a singlet at 32.6 ppm. The NMR spectroscopic data
indicate that 2-Y(OtBu), like 2-Ce(OtBu)(THF), has pseudo-Cs
symmetry in solution.
Cyclic Voltammetry. Cyclic-voltammetry studies were un-
dertaken to probe the redox activity of cerium(IV) alkoxide
complexes. Experiments were carried out using 1-2 mM THF
Reactivity Studies. To investigate whether redox events
would occur at the ancillary ligands in solution, the reactivity
of the cerium alkoxide complexes toward electron-transfer
reagents was probed. The complexes 1-Ce(OtBu)(THF) and
2-Ce(OtBu)(THF) were converted to 1-Ce(OtBu)I and 2-
Ce(OtBu)I, respectively, by the addition of I2 in toluene
solutions of the compound of interest, with [nPr4N][BArF ] (0.5
4
M, ArF = 3,5-(CF3)2C6H3) serving as the electrolyte (Figure 3
and Table 1). Cyclic voltammograms of the two proligands 1-H2
and 2-H2 revealed one redox event that was assigned to the
Fe2þ/3þ couple (see the Supporting Information). Changing the
imine with a phosphorimine functionality resulted in a more
reducing potential for the Fe2þ/3þ event in 2-H2 (-0.633 V)
than in 1-H2 (0.287 V). All metal complexes show a reversible
(quasi-reversible for 1-Ce(OtBu)(THF)), one-electron event
that was assigned to the Fe2þ/3þ couple. In addition, the cerium
(IV) complexes, 1-Ce(OtBu)2 and 2-Ce(OtBu)2, show an irrever-
sible reduction/oxidation event that was assigned to the Ce4þ/3þ
couple (Figure 3). The oxidation of cerium in 1-Ce(OtBu)(THF)
and 2-Ce(OtBu)(THF) was not observed (see the Supporting
Information for details). Overall, we found that the oxidation of
1
(Scheme 5). After 1 h, H NMR spectroscopy indicated the
formation of diamagnetic species. Salt-metathesis reactions of the
alkoxide-iodide compounds with KOtBu in THF afforded 1-
Ce(OtBu)2 and 2-Ce(OtBu)2.
Cerium(IV) complexes could be converted, in turn, to the
corresponding cerium(III) complexes (eq 1). To reduce the
occurrence of unwanted side products, 1-Ce(OtBu)2 was first
transformed to 1-Ce(OtBu)Cl with 1 equiv of lutidinium
chloride. The complex 1-Ce(OtBu)Cl was reduced by KC8 after
16 h at room temperature in toluene to form 1-Ce(OtBu)(THF),
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Figure 4. Ce L3-edge XANES spectra for cerium(IV) (left) and cerium(III) (right) complexes.
system by the method of Grubbs57 and transferred to the glovebox
without exposure to air. CeCl3 and (NH4)2Ce(NO3)4 were purchased
from Alfa Aesar, and KOtBu and NaN(SiMe3)2 were purchased from
Sigma-Aldrich. All reagents were used as received. Ce(OtBu)4(THF)2,58
Ce[N(SiMe3)2]3,59 1-H2,18 1,10-diazoferrocene,44 2-(diphenyl)phos-
Scheme 5. Transformation of Cerium(III) into Cerium(IV)
Complexes
phino-6-tert-butylphenol,45,46 and [nPr4N][BArF ]60 were synthesized
4
according to published procedures. NMR solvents were obtained from
Cambridge Isotope Laboratories, degassed, and stored over activated
molecular sieves prior to use. 1H NMR spectra were recorded on
Bruker300 or Bruker500 spectrometers at room temperature in C6D6
(the UCLA NMR spectrometers are supported by the NSF Grant CHE-
9974928). Chemical shifts are reported with respect to internal solvent,
7.16 ppm (C6D6) for 1H NMR spectra. For 31P NMR spectra, chemical
shifts are reported with respect to an external standard, 121 ppm (1%
trimethylphosphite in C6D6). UV-vis-NIR spectra were recorded on a
Varian Carey 5000 spectrophotometer from 200 to 1800 nm using
matched, 1-cm quartz cells; all spectra were obtained using a solvent
reference blank in a cuvette fitted with an air-free Teflon adapter. Cyclic
voltammetry data were obtained in an MBraun glovebox system
equipped with binding posts; all data were collected using a Princeton
Applied Research Corp. (PARC) Model 263A potentiostat under
computer control with PARC Model 270 software. XANES experiments
at both Fe K-edge and Ce L3-edge were performed at the Materials
Research Collaborative Access Team (MRCAT) beamline (10-BM) at
the Advanced Photon Source, Argonne National Laboratory. CHN
analyses were performed by Midwest Microlabs, LLC, 7212 N. Shade-
land Ave Suite 110, Indianapolis, IN 46250.
isolated in a 56% yield. The alkoxide-iodide 2-Ce(OtBu)I reacted
with KC8 in THF at room temperature within minutes to form 2-
Ce(OtBu)(THF), which was isolated in a 68% yield.
Conclusions. Two series of ferrocene-based metal complexes
supported by a Schiff base or an analogue ligand were investi-
gated. The two ancillary ligands differ by the type of the N=X
functionality that they incorporate: one ligand is based on an
imine, whereas the other is based on an iminophosphorane
group. The characterization of the resulting cerium(IV) bis-
(alkoxide) complexes was targeted to determine whether the
presence of a strongly oxidizing metal center will give rise to non-
innocent redox behavior in the supporting ligands. For compar-
ison, the corresponding cerium(III) and yttrium(III) alkoxide
complexes were also synthesized. All the metal complexes were
characterized by cyclic voltammetry and NMR, M€ossbauer, X-ray
absorption near-edge structure (XANES), and absorption spec-
troscopies. The experimental data indicate that iron remains in
the þ2 oxidation state and that cerium(IV) does not engage any
part of the ancillary ligand in redox behavior. The ancillary ligand
containing the iminophosphorane group was more easily oxi-
dized than the ligand with the imine group. Since the ligand does
not engage cerium into a redox behavior, more investigation is
needed to utilize the redox behavior of these complexes to gain
new reactivity.
3-H2. 1,10-diazoferrocene (0.9352 g, 3.49 mmol) dissolved in hex-
anes was added to a stirring solution of 2-(diphenyl)phosphino-6-tert-
butylphenol (2.333 g, 6.97 mmol) in hexanes at room temperature to
yield a red precipitate within minutes. The solid was collected, washed
thoroughly with hexanes, and dried in vacuo producing a bright-red
1
powder. Yield: 2.551 g, 78.1%. H NMR (300 MHz, 25 °C, C6D6), δ
(ppm): 1.59 (s, 18H, CCH3), 3.82 (s, 4H, C5H4), 4.48 (s, 4H, C5H4),
6.56(m, 2H, C6H3), 6.85 (m, 2H, C6H3), 7.01 (m, 12H, P(C6H5)2), 7.37
(d, 2H, C6H3), 7.71 (m, 8H, P(C6H5)2). 13C NMR (75 MHz, 25 °C,
C6D6), δ (ppm): 29.8, 35.7, 63.9, 68.9, 106.5, 118.4, 128.8, 131.5, 131.7,
132.3, 133.7, 139.9, 164.5. 31P NMR (121 MHz, 25 °C, C6D6), δ (ppm):
29.7 (s). The protons for the OH group were not observed in the
spectrum. Elemental analysis could not be performed on this compound
because upon solvation the compound begins to convert to 2-H2.
2-H2. In toluene, 3-H2 was heated at 50 °C for 6 h. The volatiles
were removed, and the product was washed with hexanes and diethyl
ether resulting in a dull-yellow powder. The product was recrystallized
’ EXPERIMENTAL SECTION
All experiments were performed under a dry nitrogen atmosphere
using standard Schlenk techniques or an MBraun inert-gas glovebox.
Solvents were purified using a two-column solid-state purification
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from a concentrated THF solution layered with n-pentane at -36 °C.
Yield: 1.35 g, 43.6%. 1H NMR (300 MHz, 25 °C, C6D6), δ (ppm): 1.77
(s, 18H, CCH3), 3.53 (s, 4H, C5H4), 4.23 (s, 4H, C5H4), 6.50 (m, 2H,
C6H3), 6.86 (m, 12H, P(C6H5)2), 6.98 (m, 2H, C6H3), 7.55 (d, 2H,
C6H3), 7.77 (m, 8H, P(C6H5)2), 13.00 (br s, 2H, OH). 13C NMR
(75 MHz, 25 °C, C6D6), δ (ppm): 29.8, 35.6, 65.3, 131.7, 132.3, 133.1,
140.9. 31P NMR (121 MHz, 25 °C, C6D6), δ (ppm): 27.1 (s). Anal. for
C54FeH54N2O2P2. Calcd: C, 73.63%; H, 6.18%; N, 3.18%. Found: C,
73.58%; H, 6.25%; N, 2.96%.
Method B (from 3-Ce(OtBu)2). 3-Ce(OtBu)2 (0.140 g, 0.115 mmol)
was heated at 85 °C in toluene for 48 h. The volatiles were removed
under reduced pressure, and the product was washed with hexanes and
diethyl ether. The product was extracted with toluene and recrystallized
from a concentrated toluene solution layered with n-pentane at -36 °C.
Yield: 0.061 g, 45.50%. 1H NMR (300 MHz, 25 °C, C6D6), δ (ppm):
1.11 (s, 18H, CCH3), 1.97 (s, 18H, CCH3), 3.88 (s, 4H, C5H4), 4.43 (s,
4H, C5H4), 6.46 (m, 2H, OC6H3), 6.77(m, 2H, OC6H3), 7.02 (m, 12H,
P(C6H5)2), 7.59 (d, 2H, OC6H3), 7.71 (m, 8H, P(C6H5)2). 13C NMR
(75 MHz, 25 °C, C6D6), δ (ppm): 31.6, 33.5, 65.6, 66.8, 127.1, 131.6,
131.8, 134.0. 31P NMR (300 MHz, 25 °C, C6D6), δ (ppm): 30.8 (s).
1-Ce[N(SiMe3)2](THF). A diethyl ether solution of 1-H2 (0.215 g,
0.331 mmol) was added to a diethyl ether solution of Ce[N(SiMe3)2]3
(0.257 g, 0.414 mmol), and the mixture was stirred at room temperature
for 2 h. The volatiles were removed, and the product was washed with
hexanes and then extracted with diethyl ether. The volatiles were
removed again producing a gold powder. The product was recrystallized
from a concentrated toluene solution layered with n-pentane at -36 °C.
Yield: 0.180 g, 57.5%. 1H NMR (300 MHz, 25 °C, C6D6), δ (ppm): -
17.74 (s, 2H, C5H4, OC6H2, or NCH), -5.00 (s, 2H, C5H4 or OC6H2or
NCH), -3.69 (s, 18H, SiCH3 or CCH3), -3.38 (s, 1H, C5H4, OC6H2,
or NCH), -3.07 (s, 2H, C5H4, OC6H2, or NCH), -1.79 (s, 2H, C5H4,
OC6H2, or NCH), 2.08 (s, 18H, SiCH3 or CCH3), 3.60 (s, 18H, SiCH3
or CCH3), 11.14 (s, 2H, C5H4, OC6H2, or NCH), 14.84 (s, 2H, C5H4 or
OC6H2or NCH), 22.06 (s, 2H, C5H4, OC6H2, or NCH). Note: Attempts
were made to acquire elemental analysis data for 1-Ce[N(SiMe3)2]-
(THF). The compound could be shipped, but its static nature prevented
the precise measurement of small amounts required for analysis.
1-Ce(OtBu)(THF). A diethyl ether solution of tBuOH (0.020 g, 0.267
mmol) was added to a diethyl ether solution of 1-Ce[N(SiMe3)2](THF)
(0.253 g, 0.267 mmol) at -78 °C. After stirring for 1 h at -78 °C, the
volatiles were removed, and the solid was extracted into hexanes. The
volatiles were removed yielding an orange powder. The product was
recrystallized from concentrated hexanes. Yield: 0.100 g, 43.3%. 1H
NMR (300 MHz, 25 °C, C6D6), δ (ppm): -12.97 (s, 9H, CCH3 or
OCH3), -7.49 (s, 1H, C5H4, OC6H2, or NCH), -5.06 (s, 1H, C5H4,
OC6H2, or NCH), -2.83 (s, 2H, C5H4, OC6H2, or NCH), -1.29 (s,
9H, CCH3 or OCH3), 1.53 (s, 9H, CCH3 or OCH3), 2.79 (s, 9H, CCH3
or OCH3), 3.20 (s, 1H, C5H4, OC6H2, or NCH), 4.85 (s, 9H, CCH3 or
OCH3), 8.58 (s, 1H, C5H4, OC6H2, or NCH), 9.83 (s, 1H, C5H4,
OC6H2, or NCH), 10.44 (s, 1H, C5H4, OC6H2, or NCH), 12.14 (s, 1H,
C5H4, OC6H2, or NCH), 12.31 (s, 1H, C5H4, OC6H2, or NCH), 13.47
(s, 1H, C5H4, OC6H2, or NCH), 17.81 (s, 1H, C5H4, OC6H2, or NCH).
Anal. for CeC44H59FeN2O3(C6H14). Calcd: C, 63.47%; H, 7.78%; N,
2.96%. Found: C, 63.21%; H, 7.62%; N, 2.79%.
Anal. for C62CeFeH70N2O4P2 C7H8. Calcd: C, 65.91%; H, 6.41%; N,
3
2.23%. Found: C, 65.73%; H, 6.12%; N, 2.11%.
2-CeCl(THF). In THF, at -78 °C, 2-Na2(THF)2 (0.251 g, 0.235
mmol) was added to CeCl3(THF)3 (0.108 g, 0.235 mmol). After 2 h of
stirring at -78 °C, the volatiles were removed. The product was washed
with hexanes, and extracted with diethyl ether. The volatiles were removed,
and the product was recrystallized from a concentrated toluene solution
layered with n-pentane at -36 °C. Yield: 0.183 g, 74.0%. This para-
magnetic complex has no identifiable peaks by 1H or 31P NMR
spectroscopy. Anal. for C58H60FeN2O3P2CeCl. Calcd: C, 61.84%; H,
5.33%; N, 2.49%. Found: C, 62.08%; H, 5.31%; N, 2.24%.
2-Ce(OtBu)(THF). A diethyl ether solution of KOtBu (0.030 g,
0.273 mmol) was added to an ether slurry of 2-CeCl(THF) (0.288 g,
0.273 mmol) at -78 °C. After 1 h of stirring at -78 °C, the volatiles were
removed. The product was extracted with toluene, and the resulting
solution was then concentrated and layered with n-pentane to yield a
yellow precipitate at -36 °C. Yield: 0.135 g, 42.5%. 1H NMR (300 MHz,
25 °C, C6D6), δ (ppm): 13.74 (s, 2H, C5H4), 10.82 (broad s, 3H,
P(C6H5)2 or OC6H3), 10.10 (s, 2H, C5H4), 9.77 (s, 2H, C5H4), 7.44 (s,
5H, P(C6H5)2 or OC6H3), 6.40 (s, 9H, CCH3), 3.60 (s, 12H, P(C6H5)2
or OC6H3), 1.36 (s, 12H, P(C6H5)2 or OC6H3), -4.01 (br s, 2H,
C5H4), -5.06 (s, 18H, CCH3). 31P NMR (121 MHz, 25 °C, C6D6), δ
(ppm): 45.1 (s). Anal. for C62H69FeN2O4P2Ce. Calcd: C, 63.97%; H,
5.97%; N, 2.41%. Found: C, 64.06%; H, 6.09%; N, 2.40%.
1-Ce(OtBu)Cl. Lutidinium chloride (0.017 g, 0.121 mmol) was
added to 1-Ce(OtBu)2 (0.113 g, 0.121 mmol) in THF at room
temperature. After stirring for 1.5 h, the volatiles were removed, and
the product was extracted with hexanes and diethyl ether. The product
was recrystallized from a concentrated diethyl ether solution at -36 °C.
Yield: 0.080 g, 74.0%. 1H NMR (300 MHz, 25 °C, C6D6), δ (ppm): 1.09
(s, 9H, CCH3), 1.29 (s, 18H, CCH3), 1.88 (s, 18H, CCH3), 4.03 (s, 2H,
C5H4), 4.11 (s, 2H, C5H4), 4.22 (s, 2H, C5H4), 4.67 (s, 2H, C5H4), 6.94
(s, 2H, OC6H2), 7.82 (s, 2H, OC6H2), 8.25 (s, 2H, OC6H2). 13C NMR
(75 MHz, 25 °C, C6D6), δ (ppm): 30.6, 31.6, 33.3, 36.1, 64.9, 67.1, 68.7,
69.7, 126.1, 129.9, 131.3, 137.2, 140.0, 167.0, 169.7. Anal. for C44Ce-
FeH59N2O3Cl. Calcd: C, 59.02%; H, 6.64%; N, 3.13%. Found: C,
58.85%; H, 6.44%; N, 3.10%.
3-Ce(OtBu)2. In diethyl ether, 3-H2 (0.391 g, 0.417 mmol) was
added to Ce(OtBu)4(THF)2 (0.240 g, 0.417 mmol). After stirring at
room temperature for 2 h, solvent was removed. The product was washed
with hexanes and extracted with diethyl ether. The product was recrys-
tallized from concentrated toluene layered with pentane at -36 °C.
Yield: 0.293 g, 57.6%. 1H NMR (300 MHz, 25 °C, C6D6), δ (ppm): 0.83
(s, 18H, CCH3), 2.00 (s, 18H, CCH3), 4.00 (s, 4H, C5H4), 4.97 (s, 4H,
C5H4), 6.50 (m, 2H, OC6H3), 6.88 (m, 2H, OC6H3), 7.07 (m, 12H,
P(C6H5)2), 7.63 (d, 2H,OC6H3), 7.82 (m, 8H, P(C6H5)2). 13C NMR
(75 MHz, 25 °C, C6D6), δ (ppm): 31.4, 33.1, 36.3, 64.7, 68.7, 86.9,
108.9, 115.2, 129.6, 130.3, 131.7, 131.8, 132.4, 131.2, 139.5. 31P NMR
(121 MHz, 25 °C, C6D6), δ (ppm): 34.6 (s). Anal. for C54FeH54N6O2P2.
Calcd: C, 64.32%; H, 6.09%; N, 7.26%. Found: C, 64.58%; H, 6.14%;
N, 6.90%.
1-Ce(OtBu)I. Iodine (0.018 g, 0.071 mmol) was added to a THF
solution of 1-Ce(OtBu)(THF) (0.122 g, 0.141 mmol) at room tem-
perature. After stirring for 1 h, the volatiles were removed, and the
product was extracted with hexanes and diethyl ether at -36 °C. The
product was recrystallized from a concentrated diethyl ether solution.
Yield: 0.090 g, 65.0%. 1H NMR (300 MHz, 25 °C, C6D6), δ (ppm): 1.01
(s, 9H, CCH3), 1.27 (s, 18H, CCH3), 1.91 (s, 18H, CCH3), 4.02 (s, 2H,
C5H4), 4.07 (s, 2H, C5H4), 4.13 (s, 2H, C5H4), 4.80 (s, 2H, C5H4), 6.96
(s, 2H, OC6H2), 7.85 (s, 2H, OC6H2), 8.44 (s, 2H, OC6H2). 13C NMR
(75 MHz, 25 °C, C6D6), δ (ppm): 30.7, 31.6, 33.3, 34.1, 36.1, 65.0, 68.5,
68.8, 70.1, 126.9, 129.9, 131.5, 167.5, 170.2. Anal. for C44CeFeH59-
N2O3I. Calcd: C, 53.55%; H, 6.03%; N, 2.84%. Found: C, 53.23%; H,
5.91%; N, 2.99%.
2-Ce(OtBu)2. Method A (from 2-H2). A diethyl ether solution of
2-H2 (0.423 g, 0.417 mmol) was added to Ce(OtBu)4(THF)2 (0.240 g,
0.417 mmol) at -78 °C. The reaction was stirred for 0.5 h at room
temperature then the volatiles were removed. The product was washed
with hexanes, ether, and a small amount of toluene to yield a brown
powder. The product was recrystallized from concentrated toluene
layered with pentane at -36 °C. Yield: 0.375 g, 84.8%.
2-Ce(OtBu)I. Iodine (0.013 g, 0.053 mmol) was added to a THF
solution of 2-Ce(OtBu)(THF) (0.115 g, 0.105 mmol) at room tem-
perature. After stirring for 1 h, the volatiles were removed, and the
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Inorganic Chemistry
ARTICLE
product was extracted with hexanes and diethyl ether. The product was
recrystallized from a toluene solution layered with hexanes at -36 °C.
Yield: 0.093 g, 90.3%. 1H NMR (300 MHz, 25 °C, C6D6), δ (ppm):
1.19 (s, 9H, CCH3), 1.93 (s, 18H, CCH3), 3.79 (s, 4H, C5H4), 4.26 (s,
4H, C5H4), 6.49 (m, 2H, P(C6H5)2), 6.87(m, 2H, P(C6H5)2), 7.00 (m,
Cyclic Voltammetry. Solutions were contained in PARC Model
K0264 microcells consisting of a glassy carbon working electrode, a 1
mm diameter Pt wire counter electrode, and a silver-wire quasi-reference
electrode. Scan rates from 50 to 1000 mV/s were employed to assess the
chemical and electrochemical reversibility of the observed redox trans-
formations. Potential calibrations were performed in situ for all samples
at the end of each data collection cycle by addition of 1 equiv of ferrocene
per complex and the use of the ferrocenium/ferrocene couple as an
internal potential standard.
12H, P(C6H5)2), 7.60 (m, 6H, OC6H3), 8.06 (m, 4H, P(C6H5)2). 31
P
NMR (121 MHz, 25 °C, C6D6), δ (ppm): 33.1 (m). A 13C NMR
spectrum for 2-Ce(OtBu)I could not be obtained because of its low
solubility in regular deuterated solvents. Anal. for C58CeFeH61N2O3P2
I. Calcd: C, 57.15%; H, 5.04%; N, 2.29%. Found: C, 57.45%; H, 5.15%;
N, 2.01%.
X-ray Crystal Structures. X-ray quality crystals were obtained from
various concentrated solutions placed in a -35 °C freezer in the glovebox.
Inside the glovebox, the crystals were coated with oil (STP Oil Treatment) on
a microscope slide, which was brought outside the glovebox. The X-ray data
collections were carried out on a Bruker AXS single crystal X-ray diffract-
ometer using MoKR radiation and a SMART APEX CCD detector. The data
was reduced by SAINTPLUS and an empirical absorption correction was
applied using the package SADABS. The structures were solved and refined
using SHELXTL (Bruker 1998, SMART, SAINT, XPREP, AND SHELXTL,
Bruker AXS Inc., Madison, Wisconsin, U.S.A.). All atoms were refined
anisotropically and hydrogen atoms were placed in calculated positions
unless specified otherwise. Tables with atomic coordinates and equiva-
lent isotropic displacement parameters, with all the bond lengths and
angles, and with anisotropic displacement parameters are listed in the cifs.
X-ray Crystal Structure of 2-Ce(OtBu)2. X-ray quality crystals
were obtained from a concentrated toluene solution layered with n-
pentane. A total of 9462 reflections (-40 e h e 39, -21 e k e 20, -24
e l e 23) were collected at T = 100(2) K with 2θmax = 61.57°, of which
8218 were unique (Rint = 0.0301). The residual peak and hole electron
density were 0.69 and -0.36 e A-3. The least-squares refinement
converged normally with residuals of R1 = 0.0257 and GOF = 1.012.
Crystal and refinement data for 2-Ce(OtBu)2: formula C62H70N6O4P2-
FeCe, triclinic, space group C2/c, a = 28.326(3) Å, b = 14.7583 Å, c =
16.8906(16) Å, β = 114.249(1)°, V = 6438.1(10) Å3, Z = 4, μ = 1.351
mm-1, F(000) = 2728, R1 = 0.0327, wR2 = 0.0623 (for all data).
X-ray Crystal Structure of 3-Ce(OtBu)2. X-ray quality crystals
were obtained from a concentrated toluene solution layered with n-
pentane. A total of 19129 reflections (-18 e h e 18, -18 e k e 18, -
29 e l e 29) was collected at T = 100(2) K with 2θmax = 61.01°, of which
13408 were unique (Rint = 0.0501). The unit cell contains two molecules
of toluene, of which one was disordered. That disorder was not modeled;
instead the aromatic carbons were constrained to fit a benzene ring and
to have the same value thermal ellipsoids. Because of these constraints
and disorder, the CCC angle made by the methyl group and the ring is
different than the expected value and one of its hydrogen atoms is too
close to one of the aromatic hydrogens. This disorder was not solved.
2-YCl. In THF, at room temperature, 2-Na2(THF)2 (0.223 g, 0.209
mmol) was added to YCl3(THF)3 (0.086 g, 0.209 mmol). The reaction
was stirred for 1 h, then the volatiles were removed. The product was
washed with hexanes and ether, then extracted with toluene. The
volatiles were removed from the resulting solution yielding a yellow
powder, which was recrystallized from a concentrated toluene solution
layered with n-pentane at -36 °C. Yield: 0.160 g, 76.0%. 1H NMR (300
MHz, 25 °C, C6D6), δ (ppm): 1.51 (s, 18H, CCH3),3.42 (s, 2H, C5H4),
3.54 (s, 2H, C5H4), 3.71 (s, 2H, C5H4), 4.98 (s, 2H, C5H4), 6.54 (m, 2H,
OC6H3), 6.84 (m, 2H, OC6H3), 6.98 (m, 12H, P(C6H5)2), 7.47 (d, 2H,
OC6H3), 7.68 (m, 8H, P(C6H5)2). 31P NMR (121 MHz, 25 °C, C6D6),
δ (ppm): 30.7 (s). A 13C NMR spectrum for 2-YCl could not be
obtained because of its low solubility in regular deuterated solvents.
Anal. for C54ClFeH52N2O2P2Y. Calcd: C, 64.66%; H, 5.29%; N, 2.79%.
Found: C, 64.83%; H, 5.68%; N, 2.50%.
2-Y(OtBu). A diethyl ether solution of KOtBu (0.020 g, 0.182
mmol) was added to a diethyl ether slurry of 2-YCl (0.183 g, 0.182
mmol) at 0 °C. After stirring for 1 h at 0 °C, solvent was removed, and
the product was washed with hexanes then extracted with toluene. The
product was recrystallized from a concentrated toluene solution layered
with n-pentane at -36 °C. Yield: 0.180 g, 95.0%. 1H NMR (300 MHz,
25 °C, C6D6), δ (ppm): 1.51 (s, 9H, CCH3), 1.60 (s, 18H, CCH3), 3.53
(s, 2H, C5H4), 3.58 (s, 2H, C5H4), 3.81 (s, 2H, C5H4), 5.09 (s, 2H,
C5H4), 6.53 (m, 2H, OC6H3), 6.73 (m, 2H, OC6H3), 6.94 (m, 12H,
P(C6H5)2), 7.31 (m, 3H, P(C6H5)2), 7.59 (d, 2H, P(C6H5)2), 7.9 5 (m,
3H, P(C6H5)2). 13C NMR (75 MHz, 25 °C, C6D6), δ (ppm): 25.8, 30.6,
34.8, 35.6, 64.7, 66.4, 67.7, 67.8, 71.5, 105.1, 114.2, 131.6, 131.9, 133.8,
140.9, 170.3. 31P NMR (121 MHz, 25 °C, C6D6), δ (ppm): 32.6 (s).
Anal. for C58FeH61N2O3P2Y. Calcd: C, 66.93%; H, 5.90%, N, 2.69%.
Found: C, 66.53%, H, 5.84%, N, 2.63%.
XANES Measurements. The setup used was similar to that
outlined by Castagnola et al.61 In an argon-filled Vacuum Atmospheres
glovebox with a large-capacity recirculator (0.25 ppm of O2 and 0.5
ppm of H2O), a predetermined amount of each sample was loaded as a
self-supporting wafer without binder in the channels (i.d. = 4 mm) of a
stainless steel multisample holder. The sample holder was then placed in
the center of a quartz tube, which was equipped with gas and thermo-
couple ports and Kapton windows. After the whole setup was purged
with dry He, it was transferred into the experiment hutch. The quartz
tube was mounted on a positioning platform. The beam was set to scan
the sample cell holder by manipulating the position of the platform.
Once the sample positions were fine-tuned, the XAS spectra were
recorded in transmission mode at room temperature. The energy
calibration and background removal were performed with Athena.
The residual peak and hole electron density were 2.58 and -1.80 e A-3
.
The least-squares refinement converged normally with residuals of R1 =
0.0621 and GOF = 1.051. Crystal and refinement data for 3-Ce(OtBu)2:
formula C62H70N6O4P2FeCe, triclinic, space group P1, a = 13.104(4) Å,
b = 13.120(4) Å, c = 21.294(7) Å, R = 93.180(3)°, β = 103.069(3)°, γ =
103.040(3)°, V = 3452(2) Å3, Z = 2, μ = 0.961 mm-1, F(000) = 1460, R1
= 0.0962, wR2 = 0.1606 (for all data).
’ ASSOCIATED CONTENT
Mossbauer Spectroscopy. 57Fe M€ossbauer spectra were re-
€
S
Supporting Information. Experimental details for com-
b
corded on a WissEl M€ossbauer spectrometer (MRG-500) at 77 K in
constant acceleration mode. 57Co/Rh was used as the radiation source.
WinNormos for Igor Pro software has been used for the quantitative
evaluation of the spectral parameters (least-squares fitting to Lorentzian
peaks). The minimum experimental line widths were 0.21 mm s-1. The
temperature of the samples was controlled by an MBBC-HE0106
pound characterizations and full crystallographic descriptions (as
cif). This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
€
Corresponding Author
*E-mail: pld@chem.ucla.edu.
MOSSBAUER He/N2 cryostat within an accuracy of (0.3 K. Isomer
shifts were determined relative to R-iron at 298 K.
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dx.doi.org/10.1021/ic102076g |Inorg. Chem. 2011, 50, 2870–2877

Inorganic Chemistry
ARTICLE
(33) De Castro, B.; Freire, C. Inorg. Chem. 1990, 29, 5113.
’ ACKNOWLEDGMENT
(34) Vilas-Boas, M.; Freire, C.; de Castro, B.; Christensen, P. A.;
Hillman, A. R. Inorg. Chem. 1997, 36, 4919.
(35) de Castro, B.; Freire, C.; Pereira, E. J. Chem. Soc., Dalton Trans.
This work was supported by the UCLA, DOE (Grant
ER15984), Sloan Foundation, the University of Erlangen-Nur-
emburg, DFG, and the Bavarian California Technology Center
(BaCaTec). The use of the Advanced Photon Source was
supported by the U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences, under Contract No. DE-AC02-
06CH11357. MRCAT (Sector 10) operations are supported by
the Department of Energy and the MRCAT member institutions.
1994, 571.
(36) Freire, C.; de Castro, B. J. Chem. Soc., Dalton Trans. 1998, 1491.
(37) de C.T. Carrondo, M. A. A. F.; de Castro, B.; Coelho, A. M.;
Domingues, D.; Freire, C.; Morais, J. Inorg. Chim. Acta 1993, 205, 157.
(38) Goldsby, K. A.; Blaho, J. K.; Hoferkamp, L. A. Polyhedron 1989,
8, 113.
(39) Azevedo, F.; de C. T. Carrondo, M. A. A. F.; de Castro, B.;
Convery, M.; Domingues, D.; Freire, C.; Duarte, M. T.; Nielsen, K.;
Santos, I. C. Inorg. Chim. Acta 1994, 219, 43.
’ REFERENCES
(40) Shimazaki, Y.; Tani, F.; Fukui, K.i.; Naruta, Y.; Yamauchi, O.
J. Am. Chem. Soc. 2003, 125, 10512.
(1) Chirik, P. J.; Wieghardt, K. Science 2010, 327, 794.
(2) van der Vlugt, J. I.; Reek, J. N. H. Angew. Chem., Int. Ed. 2009,
48, 8832.
(3) Ray, K.; Petrenko, T.; Wieghardt, K.; Neese, F. Dalton Trans.
2007, 1552.
(4) Kohl, S. W.; Weiner, L.; Schwartsburd, L.; Konstantinovski, L.;
Shimon, L. J. W.; Ben-David, Y.; Iron, M. A.; Milstein, D. Science 2009,
324, 74.
(5) Allgeier, A. M.; Mirkin, C. A. Angew. Chem., Int. Ed. 1998, 37, 894.
(6) Diaconescu, P. L. Acc. Chem. Res. 2010, 43, 1352.
(7) Diaconescu, P. L. Comments Inorg. Chem. 2010, 31, 196.
(8) Gregson, C. K. A.; Gibson, V. C.; Long, N. J.; Marshall, E. L.;
Oxford, P. J.; White, A. J. P. J. Am. Chem. Soc. 2006, 128, 7410.
(9) S€uss;ner, M.; Plenio, H. Angew. Chem., Int. Ed. 2005, 44, 6885.
(10) Liu, G.; He, H.; Wang, J. Adv. Synth. Catal. 2009, 351, 1610.
(11) Ringenberg, M. R.; Kokatam, S. L.; Heiden, Z. M.; Rauchfuss,
T. B. J. Am. Chem. Soc. 2007, 130, 788.
(41) Shimazaki, Y.; Yajima, T.; Tani, F.; Karasawa, S.; Fukui, K.;
Naruta, Y.; Yamauchi, O. J. Am. Chem. Soc. 2007, 129, 2559.
(42) Orio, M.; Jarjayes, O.; Kanso, H.; Philouze, C.; Neese, F.;
Thomas, F. Angew. Chem., Int. Ed. 2010, 49, 4989.
(43) Meleshonkova, N. N.; Shpakovsky, D. B.; Fionov, A. V.;
Dolganov, A. V.; Magdesieva, T. V.; Milaeva, E. R. J. Organomet. Chem.
2007, 692, 5339.
(44) Shafir, A.; Power, M. P.; Whitener, G. D.; Arnold, J. Organo-
metallics 2000, 19, 3978.
(45) Pearson, D. E.; Wysong, R. D.; Breder, C. V. J. Org. Chem. 1967,
32, 2358.
(46) Willoughby, C. A.; Duff, R. R.; Davis, W. M.; Buchwald, S. L.
Organometallics 1996, 19, 472.
(47) Shalev, D. E.; Chiacchiera, S. M.; Radkowsky, A. E.; Kosower,
E. M. J. Org. Chem. 1996, 61, 1689.
(48) Molina, P.; Lꢀopez-Leonardo, C.; Llamas-Botía, J.; Foces-Foces,
C.; Fernꢀandez-Casta~no, C. Tetrahedron 1996, 52, 9629.
(49) Goerlich, J. R.; Farkens, M.; Fischer, A.; Jones, P. G.; Schmut-
zler, R. Z. Anorg. Allg. Chem. 1994, 620, 707.
(50) Liu, X.; Thirupathi, N.; Guzei, I. A.; Verkade, J. G. Inorg. Chem.
2004, 43, 7431.
(51) Liu, C.-Y.; Chen, D.-Y.; Cheng, M.-C.; Peng, S.-M.; Liu, S.-T.
Organometallics 1995, 14, 1983.
(52) Liu, B.; Cui, D. Dalton Trans. 2009, 550.
(53) Bebbington, M. W. P.; Bourissou, D. Coord. Chem. Rev. 2009,
253, 1248.
(54) Hillhouse, G. L.; Goeden, G. V.; Haymore, B. L. Inorg. Chem.
(12) Slone, C. S.; Mirkin, C. A.; Yap, G. P. A.; Guzei, I. A.; Rheingold,
A. L. J. Am. Chem. Soc. 1997, 119, 10743.
(13) Tennyson, A. G.; Lynch, V. M.; Bielawski, C. W. J. Am. Chem.
Soc. 2010, 132, 9420.
(14) Ringenberg, M. R.; Nilges, M. J.; Rauchfuss, T. B.; Wilson, S. R.
Organometallics 2010, 29, 1956.
(15) Sixt, T.; Sieger, M.; Krafft, M. J.; Bubrin, D.; Fiedler, J.; Kaim,
W. Organometallics 2010, 29, 5511.
(16) Kaim, W.; Lahiri, G. K. Angew. Chem., Int. Ed. 2007, 46, 1778.
(17) Poneti, G.; Mannini, M.; Sorace, L.; Sainctavit, P.; Arrio, M.-A.;
Otero, E.; Criginski Cezar, J.; Dei, A. Angew. Chem., Int. Ed. 2010,
49, 1954.
(18) Shafir, A.; Fiedler, D.; Arnold, J. J. Chem. Soc., Dalton Trans.
2002, 555.
(19) Broderick, E. M.; Diaconescu, P. L. Inorg. Chem. 2009, 48, 4701.
(20) Kaim, W.; Sixt, T.; Weber, M.; Fiedler, J. J. Organomet. Chem.
2001, 637-639, 167.
(21) Sixt, T.; Fiedler, J.; Kaim, W. Inorg. Chem. Commun. 2000, 3, 80.
(22) Shaw, A. P.; Norton, J. R.; Buccella, D.; Sites, L. A.; Kleinbach,
S. S.; Jarem, D. A.; Bocage, K. M.; Nataro, C. Organometallics 2009,
28, 3804.
(23) Paim, L.; Batista, A.; Dias, F.; Golfeto, C.; Ellena, J.; Siebald, H.;
Ardisson, J. Transition Met. Chem. 2009, 34, 949.
(24) Gibson, V. C.; Gregson, C. K. A.; Halliwell, C. M.; Long, N. J.;
Oxford, P. J.; White, A. J. P.; Williams, D. J. J. Organomet. Chem. 2005,
690, 6271.
1982, 21, 2064.
(55) Cadierno, V.; Zablocka, M.; Donnadieu, B.; Igau, A.; Majoral,
J. P.; Skowronska, A. Chem.—Eur. J. 2000, 6, 345.
(56) Buchler, J. W.; Dippell, T. Eur. J. Inorg. Chem. 1998, 1998, 445.
(57) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(58) Evans, W. J.; Deming, T. J.; Olofson, J. M.; Ziller, J. W. Inorg.
Chem. 1989, 28, 4027.
(59) Bradley, D. C.; Ghotra, J. S.; Hart, F. A. J. Chem. Soc., Dalton
Trans. 1973, 1021.
(60) Thomson, R. K.; Scott, B. L.; Morris, D. E.; Kiplinger, J. L.
Compt. Rend. Chim. 2010, 13, 790.
(61) Castagnola, N. B.; Kropf, A. J.; Marshall, C. L. Appl. Catal., A
2005, 290, 110.
(25) Monreal, M. J.; Carver, C. T.; Diaconescu, P. L. Inorg. Chem.
2007, 46, 7226.
(26) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877.
(27) Holm, R. H.; Everett, J., G. W.; Chakravorty, A. In Progress in
Inorganic Chemisrty; Cotton, F. A., Ed.; Wiley: New York, 2007; p 83.
(28) Mizuoka, K.; Kim, S.-Y.; Hasegawa, M.; Hoshi, T.; Uchiyama,
G.; Ikeda, Y. Inorg. Chem. 2003, 42, 1031.
(29) Mizuoka, K.; Ikeda, Y. Inorg. Chem. 2003, 42, 3396.
(30) Kapturkiewicz, A.; Behr, B. Inorg. Chim. Acta 1983, 69, 247.
(31) Zanello, P.; Cinquantini, A. Trans. Met. Chem. 1985, 10, 370.
(32) Roy, N.; Sproules, S.; Weyherm€uller, T.; Wieghardt, K. Inorg.
Chem. 2009, 48, 3783.
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