Solution and solid-state photoreductive elimination of chlorine by irradiation of a [PtSb]VII complex

Article abstract of DOI:10.1021/ja5056164

In our search for novel main-group-based redox-active platforms for solar fuel production, we have synthesized Cl₂Sb^IVPt ^IIICl₃(o-dppp)₂ (2, o-dppp = o-(Ph ₂P)C₆H₄)), a complex featuring a highly oxidized [PtSb]^VII core. This thermally stable complex quickly evolves chlorine upon irradiation with a Xe lamp, leading to [Cl ₂Sb^IVPt^ICl(o-dppp)₂] (1) as the photoproduct. This photoreduction is very efficient, with a maximum quantum yield of 13.8% when carried out in a 4.4 M solution of 2,3-dimethyl-1,3- butadiene in CH₂Cl₂. Remarkably, 2 also evolves chlorine when irradiated in the solid state under ambient conditions in the absence of a trap.

Full text of DOI:10.1021/ja5056164

Communication
pubs.acs.org/JACS
Solution and Solid-State Photoreductive Elimination of Chlorine by
Irradiation of a [PtSb]VII Complex
Haifeng Yang and Franco̧ is P. Gabbaï*
Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
S
* Supporting Information
4.4%.4 Although the quantum yield of this reaction is relatively
ABSTRACT: In our search for novel main-group-based
redox-active platforms for solar fuel production, we have
synthesized Cl2SbIVPtIIICl3(o-dppp)2 (2, o-dppp = o-
(Ph2P)C6H4)), a complex featuring a highly oxidized
[PtSb]VII core. This thermally stable complex quickly
evolves chlorine upon irradiation with a Xe lamp, leading
to [Cl2SbIVPtICl(o-dppp)2] (1) as the photoproduct. This
photoreduction is very efficient, with a maximum quantum
yield of 13.8% when carried out in a 4.4 M solution of 2,3-
dimethyl-1,3-butadiene in CH2Cl2. Remarkably, 2 also
evolves chlorine when irradiated in the solid state under
ambient conditions in the absence of a trap.
low, these results suggest that poorly exploited heavy main-
group elements could be considered in lieu of noble metals.5
On the basis of these considerations, we have now chosen to
broaden the scope of our approach by testing the use of
antimony. Our choice of this element was prompted by the
realization that (i) antimony displays a rich III/V redox
chemistry, making it well suited for the targeted application,6
and (ii) the extra valence of tri- or pentavalent antimony when
compared to di- or tetravalent tellurium offers an opportunity
for a greater degree of electronic control through the
incorporation of an extra ligand. This logic led us to consider
[(o-(Ph2P)C6H4)2SbCl], a ligand derived from [(o-(Ph2P)-
C6H4)2Te] by replacement of the Te atom by a less-electron-
releasing SbCl moiety. This ligand could be accessed by
comproportionation of neat SbCl3 and (o-(Ph2P)C6H4)3Sb at
100 °C.6b Reaction of [(o-(Ph2P)C6H4)2SbCl] with
(Et2S)2PtCl2 afforded complex 1 (Scheme 1). This complex
he photoreductive elimination of halogens from transition
T
metal complexes is a thermodynamically difficult process
which necessitates the activation of strong metal−halide bonds.
Given the relevance of such reactions to the photoinduced
splitting of hydrohalic acids,1 a great deal of effort has been
devoted to identifying molecular platforms that support such
transformations.2 Most platforms identified to date contain a
late transition metal such as platinum,2d iridium,2e or gold.2e
These systems can be mononuclear, as in the case of trans-
Pt(PEt3)2(Br)3Ar (A, Ar = o-(CF3)C6H4, Chart 1), which
Scheme 1. Synthesis of 1 and 2
Chart 1
displays a 31P NMR signal at 50.9 ppm and a 195Pt NMR signal
at −5164 ppm. The presence of 195Pt satellites in the 31P NMR
spectrum and the multiplicity of the 195Pt NMR resonance
(triplet, 1JPt−P = 2566 Hz) confirm the expected coordination of
the phosphine arms to the platinum. These spectroscopic
features are close to those observed for the stiboranyl complex
[(o-(Ph2P)C6H4)2SbClPh]PtCl (E, δ(31P) = 53.9 ppm, δ(195Pt)
eliminates bromine with a very high quantum yield (Φ) of
82%.3 Chlorine photoelimination has also been actively pursued
because of its relevance to HCl splitting. Two of the best
platforms reported to date for chlorine elimination are the
AuII−IrII complex B (maximum Φ = 10%, Chart 1)2e and the
= −5019 ppm, JPt−P = 2706 Hz),6c suggesting the possible
1
PtIII−PtIII complex C (maximum Φ = 38%, Chart 1).2d
A
insertion of the antimony atom into one of the Pt−Cl bonds.
This proposal was confirmed by a determination of the crystal
structure of 1, which shows a divalent square-planar platinum
common design element uniting these different systems is the
use of electron-withdrawing ligands which destabilize the high-
valent metal centers, thus favoring reductive elimination.
In a recent paper, we showed that the heterobimetallic TeIII−
PtIII complex D (Chart 1) supports the photoreductive
elimination of chlorine with a maximum quantum yield of
Received: June 4, 2014
Published: July 14, 2014
© 2014 American Chemical Society
10866
dx.doi.org/10.1021/ja5056164 | J. Am. Chem. Soc. 2014, 136, 10866−10869

Journal of the American Chemical Society
Communication
center with a dichlorodiarylstiboranyl ligand positioned trans
from the chloride ligand (Sb−Pt−Cl(3) = 175.25(3)°, P(1)−
Pt−P(2) = 169.86(5)°, Figure 1). The Sb−Pt bond of
Figure 2. (a) Experimental (CH2Cl2, solid line) and calculated
(dashed line) ultraviolet−visible spectra for 2. The calculated spectra
were obtained by TD-DFT calculations using the MPW1PW91
functional and a mixed basis set (peak half-width used for the
simulation: 0.25 eV). The computed excitations are shown as thin lines
with heights proportional to the calculated oscillator strengths. (b)
Plots of the LUMO (−0.120 eV) and LUMO+1 (−0.106 eV) of 2
(0.03 isosurface value). (c) Absorption spectra obtained during the
photolysis of 2 in CH2Cl2 (2.23 × 10−5 M) with monochromatic 320
nm light in the presence of 2,3-dimethyl-1,3-butadiene (7.07 × 10−4
M). The final spectrum is identical to that of 1. The inset shows the
correlation between the quantum yield and the DMBD concentration.
(d) 31P NMR spectra of photolysis of 2 in CH2Cl2 (0.011 M) in the
presence of 2,3-dimethyl-1,3-butadiene (1.77 M).
Figure 1. Solid-state structures of 1 (top left) and 2 (bottom left).
Thermal ellipsoids are drawn at the 50% probability level. Phenyl
groups are drawn in wireframe. Hydrogen atoms are omitted for
clarity. Pertinent metric parameters can be found in the text. NLMO
plots (isovalue = 0.05) of the Sb−Pt bond in 1 (top right) and 2
(bottom right) obtained from the NBO analysis. Hydrogen atoms are
omitted for clarity.
2.4407(5) Å for 1 is notably shorter than that observed in E
(2.5380(8) Å),6c a complex also formed by insertion of the
antimony atom into a Pt−Cl bond. The shorter bond observed
in 1 most likely originates from the geometry adopted by the
pentavalent antimony atom. In E, one of the antimony-bound
chloride ligands is located directly opposite from the platinum
center, thus lengthening the Sb−Pt bond via a trans influence.
In 1, we observe a very different situation, with the two
antimony-bound chloride ligands projecting in a direction
oblique to the Pt−Sb bond (Pt−Sb−Cl(1) = 99.22(4)°, Pt−
Sb−Cl(2) = 107.51(4)°). The coordination geometry at
antimony is best described as square pyramidal, with the two
chlorine atoms Cl(1) and Cl(2) and the two carbon atoms
C(1) and C(2) defining the base (Cl(1)−Sb−Cl(2) =
153.24(5)°, C(1)−Sb−C(2) = 153.7(2)°).
ligands arranged in a meridional fashion (Figure 1). It is
interesting to note that the bond distance of 2.4405(6) Å
separating the platinum atom and the chlorine atom (Cl(5))
trans from the antimony atom is longer than the Pt−Cl bond
distances involving the chlorine atoms trans from each other
(Pt−Cl(2) = 2.3429(5) Å, Pt−Cl(4) = 2.3231(5) Å). This
noticeable difference suggests that the antimony ligand is a
stronger σ-donor than a chloride ligand. Oxidation of the
platinum center also induced some changes at antimony: (i) an
important shortening of the Sb−Cl bond from 2.494(3) Å (av.)
in 1 to 2.402(2) Å (av.) in 2 and (ii) a contraction of the
Cl(1)−Sb−Cl(2) angle from 153.24(5)° in 1 to 118.67(2)° in
2. As a result, the antimony atom displays a slightly distorted
trigonal-bipyramidal geometry, with Cl(1)−Sb−Pt and Cl(2)−
Sb−Pt angles of 119.99(2)° and 121.33(2)°, respectively.
Finally, the increase in the coordination number of the
platinum center is accompanied by a detectable lengthening
of the Sb−Pt bond from 2.4407(5) Å in 1 to 2.560(2) Å in 2.
A Natural Bond Orbital (NBO) analysis of 1 and 2 carried
out at the DFT-optimized geometry (Gaussian 09 program;
BP86 functional;9 mixed basis sets: Sb/Pt, cc-pVTZ-PP; P/Cl,
6-31g(d′); and C/H, 6-31g)10 shows that the Sb−Pt σ-bond is
largely covalent for both complexes (see NLMO plots in Figure
1). For 1, the orbital contributions from antimony and
platinum (Sb, 49.09%; Pt, 45.12%) are almost identical,
indicating that the bond is essentially nonpolar. Because of
the covalent character of this bond and by analogy with formal
oxidation state assignments11 in complexes with metal−metal
bonds such as B and C,2d,e we describe 1 as a SbIVPtI complex.
In 2, the orbital contributions (Sb, 27.55%; Pt, 43.02%) show
It became important to verify whether 1, with three electron-
withdrawing ligands decorating its core, would be amenable to
oxidation. While no reaction was observed with HCl in
CH2Cl2/Et2O mixtures, 1 quickly reacted with PhICl2 in
CH2Cl2 to afford complex 2 as a deep yellow solid. The 31P
NMR spectrum of 2 displays a signal at 43.3 ppm with 195Pt
satellites (1JPt−P = 1842 Hz) as well as a 195Pt NMR resonance
1
at −3473 ppm. When 2 is compared to 1, its JPt−P coupling
constant is notably reduced and its 195Pt NMR resonance is
shifted downfield, consistent with oxidation of the platinum
center.7 Although tetravalent platinum complexes are known to
thermally eliminate halogens,3,8 31P and 1H NMR spectroscopy
shows that 2 remains intact when heated to 70 °C in the solid
state for 12 h. The UV−vis spectrum of 2 displays an intense
low-energy band centered at 320 nm (ε = 30 005 M−1 cm−1),
which tails into the visible part of the spectrum (Figure 2). X-
ray diffraction confirms Cl2 addition to the platinum center,
which now exhibits an octahedral geometry, with three chloride
10867
dx.doi.org/10.1021/ja5056164 | J. Am. Chem. Soc. 2014, 136, 10866−10869

Journal of the American Chemical Society
Communication
that the bonding pair is significantly shifted toward the oxidized
and thus more-electron-demanding platinum center. This shift
of the bonding density shows that oxidation impacts the core
electronic distribution of this heterobimetallic platfom. The
polarization of the Sb−Pt bond in 2 is best reconciled by
invoking the two resonance structures (a and b) shown in
Chart 2. Resonance structure a, which corresponds to a
with 1 as the sole phosphorus-containing species (Figure
2d).2a,c−h This photoreductive elimination of chlorine is
efficient, with a maximum quantum yield of 13.8% measured
at a DMBD concentration of 4.4 M, using potassium
ferrioxalate as a standard actinometer.15 The high quantum
yield of this photoreductive elimination, which exceeds that of
the tellurium complex D,4 is correlated to the destabilizing
effect of the five electron-withdrawing chlorine ligands on the
oxidized core of 2. This situation is reminiscent of that
described for the hexachlorodiplatinum complex C, for which a
maximum quantum efficiency of 38% has been reported.2b It is
also interesting to note that the quantum yield measured for the
photoreduction of 2 is comparable to the value of 19%
measured for the photoaquation of [PtCl6]2− (λ = 313 nm), a
reaction that proceeds through formation of a Pt(III)
intermediate via extrusion of a Cl• radical.16
Chart 2. Relevant Resonance Structures of 2
SbIVPtIII complex, is the most important contributor to the
actual electronic structure of the complex. The second
resonance structure, b, which accounts for the polarization of
the Sb−Pt bonding pair toward platinum, corresponds to a
platinate (PtII) complex stabilized by a Z-type or σ-accepting
stibonium (SbV) ligand.12
To conclude these studies, we decided to test whether 2
would behave like C and evolve chlorine in the solid state.2d To
this end, a sample of 2 was loaded into a quartz cell at
atmospheric pressure, under nitrogen. A small sodium strip,
whose base was covered with Teflon tape in order to prevent
contact with 2, was placed inside the cell. The cell was tightly
closed and irradiated with a Xe lamp for 10 h (Scheme 2). The
temperature of the sample, which was monitored with a
mercury thermometer directly adjoining the cell, was kept
below 32 °C using a high-velocity fan during photolysis. After
10 h, the photolysis was stopped. The solid sample showed
noticeable signs of discoloration, in agreement with the
conversion of deep yellow 2 into pale yellow 1. The surface
of the sodium strip had tarnished significantly, suggesting
Computational methods have also been used to simulate the
UV−vis spectrum of 2 using time-dependent density functional
theory (TD-DFT). A good match with the experimental data is
obtained when the spectrum is simulated using the
MPW1PW91 functional (mixed basis sets: Sb/Pt, cc-pVTZ-
PP; P/Cl, 6-31g(d′); C/H, 6-31g) and the SMD implicit
solvation model with CH2Cl2 as a solvent (Figure 2a).13
According to these calculations, the high oscillator strength
excitations labeled as Ea and Eb contribute to the 320 nm band
and involve the LUMO and LUMO+1 as the accepting orbitals.
As could be expected for an octahedrally coordinated platinum
species, these two orbitals have eg* character and are
antibonding with respect to the Pt−Cl bonds (Figure 2b). In
agreement with this spectroscopic assignment, irradiation of 2
in CH2Cl2 results in a rapid quenching of the band at 320 nm,
suggesting photoreduction of the complex (Scheme 2, Figure
1
chlorine oxidation. In line with these observations, H and 31P
NMR analysis of the photolyzed solid indicated a 53%
conversion of 2 into 1. The evolution of chlorine was
confirmed by dissolution of the sodium strip in water and
subsequent chloride analysis using ion chromatography. The
latter indicated that 72% of the expected chlorine had been
captured by sodium during the photolysis experiment. We
propose that the rest of the chlorine is incorporated in the
decomposition products observed by 31P NMR spectroscopy in
the 5−25 ppm range (see SI). Using single-point energy
calculations carried out with the B3LYP functional and a mixed
basis set (C/H/P/Cl, 6-311+g(2d,p); Sb/Pt, cc-pVTZ-PP), we
estimate that the photoreduction of 2 into 1 is endothermic by
544 kJ/mol, assuming the formation of two Cl• radicals, or by
300 kJ/mol, assuming the formation of Cl2. These values
provide a measure of the energy-storing potential of this
reaction. Finally, the solid-state photolysis of 2 into 1 can be
carried out with the cell open to air without sodium as a
chemical trap (Figure 3, conversion of 45% after 10 h). The
evolution of chlorine under such conditions shows that the title
SbPt complex is able to evolve chlorine on its own, without the
thermodynamic bias associated with a trap. To our knowledge,
no other bimetallic complexes have been tested under such
conditions. Complex C also evolves chlorine when irradiated in
the solid state, albeit under vacuum, with the chlorine
photoproduct captured in a low-temperature trap.2d
a
Scheme 2. Photoreduction of 2 Using a Xe Lamp (75 W)
a
Conditions: (a) solution photolysis in CH2Cl2 with DMBD (1.77 M)
in a glass NMR tube (complete conversion in 10 min); (b) solid-state
photolysis in a closed quartz cell with Na as a trap (conversion = 53%
in 10 h); (c) solid-state photolysis in an open quartz cell (conversion =
45% in 10 h).
2c). This photoreduction can be monitored by 31P NMR
spectroscopy. When carried out in neat CH2Cl2, the reaction
affords 1 in ∼85% yield, with some decomposition products
detected in the 10−37 ppm range (see SI). The presence of
these decomposition products can be assigned to side reactions
between the ligand and the chlorine generated by photolysis. As
documented in the literature, chlorine atoms can also be
trapped by reaction with the CH2Cl2 solvent.14 Addition of 2,3-
dimethyl-1,3-butadiene (DMBD, 1.77 M) to the solution as a
chlorine scavenger makes the photolysis significantly cleaner,
In summary, we describe a new SbPt platform for the high-
quantum-yield photoevolution of chlorine. The photoreduction
quantum yield of 2 is more than 3 times greater than that
measured for the TePt complex D previously investigated by
our group.4 This increase supports the notion that replacement
of the TeCl unit in D by a less-electron-releasing SbCl2 unit in
2 destabilizes the oxidized complex and facilitates its photo-
10868
dx.doi.org/10.1021/ja5056164 | J. Am. Chem. Soc. 2014, 136, 10866−10869

Journal of the American Chemical Society
Communication
(h) Cook, T. R.; McCarthy, B. D.; Lutterman, D. A.; Nocera, D. G.
Inorg. Chem. 2012, 51, 5152−5163. (i) Powers, D. C.; Chambers, M.
B.; Teets, T. S.; Elgrishi, N.; Anderson, B. L.; Nocera, D. G. Chem. Sci.
2013, 4, 2880−2885. (j) Wickramasinghe, L. A.; Sharp, P. R. Inorg.
Chem. 2014, 53, 1430−1442.
(3) Karikachery, A. R.; Lee, H. B.; Masjedi, M.; Ross, A.; Moody, M.
A.; Cai, X.; Chui, M.; Hoff, C. D.; Sharp, P. R. Inorg. Chem. 2013, 52,
4113−4119.
(4) Lin, T.-P.; Gabbaï, F. P. J. Am. Chem. Soc. 2012, 134, 12230−
12238.
(5) Carrera, E. I.; McCormick, T. M.; Kapp, M. J.; Lough, A. J.;
Seferos, D. S. Inorg. Chem. 2013, 52, 13779−13790.
(6) (a) Wade, C. R.; Gabbaï, F. P. Angew. Chem., Int. Ed. 2011, 50,
7369−7372. (b) Ke, I.-S.; Gabbaï, F. P. Inorg. Chem. 2013, 52, 7145−
7151. (c) Ke, I.-S.; Jones, J. S.; Gabbaï, F. P. Angew. Chem., Int. Ed.
2014, 53, 2633−2637.
Figure 3. 31P NMR spectra before and after solid-state irradiation of 2
with a Xe lamp (75 W) under ambient conditions in an open quartz
cell. The inset shows a schematic drawing of the experimental setup
used for this open-system solid-state photolysis. The spectral region
marked by an asterisk shows the presence of decomposition products.
(7) (a) Oberhauser, W.; Bachmann, C.; Stampfl, T.; Bruggeller, P.
̈
Inorg. Chim. Acta 1997, 256, 223−234. (b) Oberhauser, W.; Stampfl,
T.; Bachmann, C.; Haid, R.; Langes, C.; Kopacka, H.; Ongania, K.-H.;
Bruggeller, P. Polyhedron 2000, 19, 913−923.
̈
(8) (a) Elding, L. I.; Gustafson, L. Inorg. Chim. Acta 1976, 19, 165−
171. (b) Bondarenko, V. S.; Korniets, E. D.; Sokolenko, V. A.;
Kovrova, N. B.; Kovtonyuk, N. P. Zh. Neorg. Khim. 1989, 34, 1541−
1543. (c) Bryan, S. A.; Dickson, M. K.; Roundhill, D. M. Inorg. Chem.
1987, 26, 3878−3886. (d) Levy, C. J.; Puddephatt, R. J. J. Am. Chem.
Soc. 1997, 119, 10127−10136.
reduction. Another unique feature of the title SbPt platform is
its ability to support this reaction in the solid state, in the
absence of a trap. We propose that such platforms may become
useful for the production of halogens as solar fuels. We are
currently investigating the mechanism of this solid-state
reaction and whether chlorine is evolved as Cl• or Cl2.17
(9) (a) Perdew, J. P. Phys. Rev. B 1986, 33, 8822−8824. (b) Becke, A.
D. Phys. Rev. A 1988, 38, 3098−3100.
(10) (a) Peterson, K. A.; Figgen, D.; Goll, E.; Stoll, H.; Dolg, M. J.
Chem. Phys. 2003, 119, 11113−11123. (b) Figgen, D.; Peterson, K. A.;
Dolg, M.; Stoll, H. J. Chem. Phys. 2009, 130, 164108−164112.
(11) Parkin, G. J. Chem. Educ. 2006, 83, 791−799.
ASSOCIATED CONTENT
* Supporting Information
Additional experimental and computational details; crystallo-
graphic data in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
■
S
(12) (a) Shriver, D. F. Acc. Chem. Res. 1970, 3, 231−238.
(b) Dammann, C. B.; Hughey, J. L.; Jicha, D. C.; Meyer, T. J.;
Rakita, P. E.; Weaver, T. R. Inorg. Chem. 1973, 12, 2206−2209.
(c) Chan, D. M. T.; Marder, T. B. Angew. Chem., Int. Ed. 1988, 27,
442−443. (d) Parkin, G. Organometallics 2006, 25, 4744−4747.
(e) Hill, A. F. Organometallics 2006, 25, 4741−4743. (f) Fontaine, F.-
G.; Boudreau, J.; Thibault, M.-H. Eur. J. Inorg. Chem. 2008, 2008,
5439−5454. (g) Braunschweig, H.; Dewhurst, R. D.; Schneider, A.
Chem. Rev. 2010, 110, 3924−3957. (h) Bouhadir, G.; Amgoune, A.;
Bourissou, D. Adv. Organomet. Chem. 2010, 58, 1−107. (i) Amgoune,
A.; Bourissou, D. Chem. Commun. 2011, 47, 859−871. (j) Braunsch-
weig, H.; Dewhurst, R. D. Dalton Trans. 2011, 40, 549−558.
(k) Bauer, J.; Braunschweig, H.; Dewhurst, R. D. Chem. Rev. 2012,
112, 4329−4346. (l) Owen, G. R. Chem. Soc. Rev. 2012, 41, 3535−
3546. (m) Kameo, H.; Nakazawa, H. Chem.Asian J. 2013, 8, 1720−
1734. (n) Mingos, D. M. P. J. Organomet. Chem. 2014, 751, 153−173.
(13) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B
2009, 113, 6378−6396.
(14) Alfassi, Z. B.; Mosseri, S.; Neta, P. J. Phys. Chem. 1989, 93,
1380−1385.
(15) (a) Hatchard, C. G.; Parker, C. A. Proc. R. Soc. London, Ser. A
1956, 235, 518−536. (b) Parker, C. A. Proc. R. Soc. London, Ser. A
1953, 220, 104−116. (c) Kuhn, H. J.; Braslavsky, S. E.; Schmidt, R.
Pure Appl. Chem. 2004, 76, 2105−2146.
(16) Znakovskaya, I. V.; Sosedova, Y. A.; Glebov, E. M.; Grivin, V. P.;
Plyusnin, V. F. Photochem. Photobiol. Sci. 2005, 4, 897−902.
(17) Perera, T. A.; Masjedi, M.; Sharp, P. R. Inorg. Chem. 2014, 53,
7608−7621.
AUTHOR INFORMATION
Corresponding Author
francois@tamu.edu
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Science Foundation
(CHE-1300371), the Welch Foundation (A-1423), and Texas
A&M University (Arthur E. Martell Chair of Chemistry).
REFERENCES
■
(1) (a) Mann, K. R.; Lewis, N. S.; Miskowski, V. M.; Erwin, D. K.;
Hammond, G. S.; Gray, H. B. J. Am. Chem. Soc. 1977, 99, 5525−5526.
(b) Mann, K. R.; Bell, R. A.; Gray, H. B. Inorg. Chem. 1979, 18, 2671−
2673. (c) Maverick, A. W.; Gray, H. B. Pure Appl. Chem. 1980, 52,
2339−2348. (d) Sigal, I. S.; Mann, K. R.; Gray, H. B. J. Am. Chem. Soc.
1980, 102, 7252−7256. (e) Mann, K. R.; Dipierro, M. J.; Gill, T. P. J.
Am. Chem. Soc. 1980, 102, 3965−3967. (f) Gray, H. B.; Maverick, A.
W. Science 1981, 214, 1201−1205. (g) Eidem, P. K.; Maverick, A. W.;
Gray, H. B. Inorg. Chim. Acta 1981, 50, 59−64. (h) Heyduk, A. F.;
Nocera, D. G. Science 2001, 293, 1639−1641. (i) Esswein, A. J.;
Nocera, D. G. Chem. Rev. 2007, 107, 4022−4047.
(2) (a) Heyduk, A. F.; Macintosh, A. M.; Nocera, D. G. J. Am. Chem.
Soc. 1999, 121, 5023−5032. (b) Cook, T. R.; Esswein, A. J.; Nocera,
D. G. J. Am. Chem. Soc. 2007, 129, 10094−10095. (c) Teets, T. S.;
Nocera, D. G. J. Am. Chem. Soc. 2009, 131, 7411−7420. (d) Cook, T.
R.; Surendranath, Y.; Nocera, D. G. J. Am. Chem. Soc. 2009, 131, 28−
29. (e) Teets, T. S.; Lutterman, D. A.; Nocera, D. G. Inorg. Chem.
2010, 49, 3035−3043. (f) Teets, T. S.; Neumann, M. P.; Nocera, D. G.
Chem. Commun. 2011, 47, 1485−1487. (g) Teets, T. S.; Cook, T. R.;
McCarthy, B. D.; Nocera, D. G. Inorg. Chem. 2011, 50, 5223−5233.
10869
dx.doi.org/10.1021/ja5056164 | J. Am. Chem. Soc. 2014, 136, 10866−10869