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O2-Generation by Oxidation of Water with Di- and Trinuclear Ruthenium Complexes as Homogeneous and Heterogeneous Catalysts.

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When stored under carbon monoxide, the ruthenacyclopentane 2 decomposes only above 60°C. At this temperature a (formal) insertion of CO['l into a Ru-C bond with
formation of cyclopentanone is observed,"'] the latter being formed from the non-isolable six-membered intermediate [(OC),kuC(0)CH2CH2CH2dH2]
by reductive elimination. The same results upon reaction of 2 with PPh,. In
the absence of CO, 2 already decomposes at -20°C with
cleavage of 1,3-butadiene and trans- and cis-2-butene in
the molar ratio 3 : 3 : 1. Prerequisite for the occurrence of
butadiene is a twofold 0-hydride transfer, which requires a
free coordination site at the metal by elimination of CO.
This explains the unusual stability of 2 in the presence of
carbon monoxide. The elimination of cis- and trans-2-butene from 2 probably takes place via an allylic intermediate."]
Received: June 12, 1986 [Z 1811 IE]
German version: A n g e w Chem. 98 (1986) 1000
CAS Registry numbers:
I . 52621-15~5,2, 104739-34-6: 3, 104739-35-7: (CF,S020CH2)2, 18928-34-2;
(CF,SO2OCH2CH2)?,18934-34-4: cyclo-C,H ,0(CH20S02CF3)Z,
100849-24-9;
Na2[Ru(CO),], 57398-60-4.
[ I ] P. Binger, M. J. Doyl, R. Renn, Chem. Ber. 116 (1983) I : E. Weissberger,
P. Laszlo. Acc. Chem. Res. 9 (1976) 209; R. H. Grubbs, A. Miyashita,
Terruhedron Lert. 22 (1981) 1255.
121 E.Lindner, Adu. Hererocycl. Chem. 39 (1986) 237.
[3] R. Kuwae, K. Kawakami, T. Tanaka, Inorg. Chim. Acru 22 (1977) 39.
[4] E. Lindner, H.-J. Eberle, Angew. Chem. 92 (1980) 70; Angew. Chem. Int.
Ed. Enql 19 (1980) 73: E. Lindner, G. von Au. H.-J. Eberle, Chem. Ber.
114 (1981) 810.
[ S ] E. Lindner, E. Schauss, W. Hiller, R. Fawzi, Angew. Chem. 96 (1984)
727; A n y e x Chem. Int. Ed. Engl. 23 (1984) 711; Chem. Ber. 118 (1985)
3915.
solution of
3 mmol
of (CF3S020CH2)2,
[6] Procedure: A
[7], respectively, in
(CFISO:OCH2CH1)2,or cyclo-C,H II)(CH20S02CFi)2
dimethyl ether (100 mL) was added dropwise within 3 h at -78°C to a
suspension of Na2[Ru(CO),] (3 mmol) in dimethyl ether (50 mL). The
mixture was stirred for I2 h at -78"C, the solvent removed under vacuum at this temperature, and the residue dissolved in IOOmL of nbutane. Upon evaporation of the solution to dryness, the metallacycles
(correct Ru values in atomic absorption spectral analyses) precipitated
as colorless ( 1 ) or pale yellow (2, 3) compounds. Recrystallization from
n-butane at - 78°C; yields 50-60%.
[7] E. Lindner, E. Schauss, Chem. Ber. 118 (1985) 4292.
IS] R. F. G. Johnson, J. Lewis, M. V. Twigg, J. Orgunumer. Chem. 67 (1974)
c'75.
191 M. L. Steigerwald, W. A. Goddard 111, J . A m . Chem. Soc. 107 (1985)
5027
[lo] F. W. Grevels, D. Schulz, E. Koerner von Gustorf, Angew. Chem. 86
(1974) 558; Angew. Chem. Int. Ed. Engl. 13 (1974) 534.
02-Generation by Oxidation of Water with Di- and
Trinuclear Ruthenium Complexes as Homogeneous
and Heterogeneous Catalysts
By Rarnasarny Rarnaraj, Akira Kira, and Masao Kaneko*
Water-oxidation with generation of molecular oxygen
was first realized only five years ago:"] the strong one-electron oxidizing agent Ru(bpy):@ (bpy = 2,2'-bipyridyl) is
able to bring about the four-electron oxidation of water to
oxygen on the surface of a suitable colloidal or powdered
oxide catalyst such as Ru02.['l These catalysts are far from
ideal, because the reaction is slow and -there are many
problems associated with their use in model systems. The
[*I
Prof. l k M. Kaneko, Dr. R. Ramaraj, Prof. Dr. A. Kira
Solar Energy Science Research Group
The Institute of Physical and Chemical Research
Wako, Saitama, 35 1-01 (Japan)
Anyew Chern. Inr Ed. Engl. 25 (1986)
No. I I
main difficulty of constructing such models lies in the coupling of the one-electron oxidant with the four-electron
formation of oxygen from water. We consider that the design of chemical models and the study of water-oxidation
in non-biological systems are probably the best way of
gaining an insight into the mechanism of the photosynthetic evolution of oxygen. It has already been
that dinuclear ruthenium complexes are capable of oxidizing water by a four-electron process without the addition
of an external catalyst like Ru02. However, the catalyst
turnover number is not high and the total yield of oxygen
obtainable from such systems remains
According to
recent findings, not only homogeneous systems but also
heterogeneous ones may be of importance."] We report
here on the catalytic activity of 0x0-bridged di- and trinuclear ruthenium complexes in the homogeneous and
heterogeneous oxidation of water.
As trinuclear ruthenium complex we used commercially
available ruthenium-red (Wako Chemicals); rutheniumbrown was prepared according to the procedure described
in ref. [6] (with slight modification). The ruthenium-red
cation is oxidized reversibly in acid solution to the ruthenium-brown cation.
[(NH,)~Ru-O-RU(NH,),-O-R~(NH,),ICI,
ruthenium red
a b b r e v i a t i o n for the c a t i o n :
R U ~ ~ ' - O - R U ~ ~ - O - R Uor! ~111,
~ IV,III
[(NH,)~Ru-O-RU(NH~),-O-RU(NH,),]CI,
ruthenium brown
a b b r e v i a t i o n for t h e c a t i o n :
R U ' ~ - O - R U ' ~ ~ - O - R U or
~ ~ IV, I I I , I V
The dinuclear ruthenium complexes "Ru-Ru- H,O" and
"Ru-Ru-NO2" were prepared and characterized according to previously reported ~ r o c e d u r e s . ' ~ . ~ '
The heterogeneous catalysts were prepared by mixing the
di- or trinuclear ruthenium complex with commercially
available kaolin (Nakarai Chemicals Ltd.) in deionized
water and stirring- the mixture until completion of a d s o r p
tion (decolorization of the solution). The product was filtered, washed with deionized water, and dried in air. It has
been reportedL6.'] that the differences in the Mossbauer
and electronic spectra of the cations of ruthenium red and
ruthenium brown are consistent with the charge distribution indicated in Equation (1).
~ ~ z i 1 - 0 -
~ ~ 1 v - 0 -~
~
Ru-red
i
3
i [
R ~ ~ V - O - R ~ I ~ I -RO ~7F
~
V
(1)
Ru-brown
The absorption spectra show that ruthenium-red undergoes thermal and photochemical decomposition in aqueous solution. In contrast, ruthenium-brown does not show
0 VCH Verlugsgesellschafl mbH, 0-6940 Weinheim. 1986
O87O-O833/86/1 Ill-1009 $ 02.80/0
I009
any noticeable thermal or photochemical decomposition in
acidic aqueous solution. The higher thermal and photochemical stability in the latter case may be due to a charge
delocalization in the linearly 0x0-bridged cations of ruthenium-brown.lxl
Cyclovoltammograms of the trinuclear ruthenium complexes were recorded in aqueous solution using a basal
plane pyrrolytic graphite (BPG) working electrode and a
saturated calomel electrode (SCE). The oxidation of water
interferes in the higher potential region. However, a well
defined cyclovoltammogram could be obtained in the
same potential region by using a BPG electrode coated
with poly(styrene sulfonate). The reversible one-electron
reduction of ruthenium-brown [Eq. (l)] and the reduction
of ruthenium-red have already been investigated.l6I In the
present investigation, the cyclovoltammograms of ruthenium-red showed six reduction peaks which are reversible
in the oxidative scan in the potential region -0.5 V to
1.4 V vs. SCE. The wave shapes indicate that five one-electron-transfer processes occur at potentials which are fairly
close to each other. The redox process which occurs at
-0.24 V closely resembles the reactions observed in the
case of the monomeric ammine-ruthenium(II1) complexes.['] The cyclovoltammogram is consistent with a series of one-electron oxidations [Eq. (2)];
'
, ,ce:;
III,III,III
III,IV,III
--024v
Ru-red
IV,V,IV
095v
*
0 72 V
Ru-brown
&
V,IV,V
v
I 08
+
IV,III,IV
(2)
v,v,v
?+
decomposition during the catalytic processes with a maximum turnover number of 62. Variation of the catalyst concentration in the homogeneous and heterogeneous phases
had n o influence on the catalytic activity. This finding suggests that a single molecule of the di- or trinuclear ruthenium complex is involved in the four-electron process of
oxygen evolution. It has also been found that the addition
of 0.1 M H N 0 3 or 0.1 M NaOH does not affect the catalytic activity of the complexes. This shows that the oxidized species is a water molecule rather than a hydroxide
ion. Ruthenium-red was converted into the stable ruthenium-brown in acidic solution. The anodic oxidation of ruthenium-red (t1.3 V vs. SCE) also led to the formation of
ruthenium-brown; no formation of R u 0 2 was observed.
The formation and stability of RuVin 0x0-bridged dinuclear ruthenium complexes and its catalytic activity have
been reported on just r e ~ e n t l y . ' ~ . ~In
. ' ' ~the water oxidation
experiment with ruthenium-red and Ce(1v) in the molar ratio 1 : 100, ruthenium-brown was observed spectrophotometrically at the end of the catalytic process. When, however, a molar ratio of 1 :400 was used, the catalyst was found
to undergo decomposition to a monomeric ruthenium
complex at the end of the catalytic process. N o formation
of the black deposit characteristic of RuOz was observed.
From the observed data, it is concluded that the system
ruthenium-redlruthenium-browncatalyzes the water oxidation by Ce(rv). Ruthenium-red is converted into highly
stable ruthenium-brown in acidic solutions as well as in
the presence of anions such as NO:, CI' and SO:'; dinuclear ruthenium complexes, on the other hand, undergo
decomposition to monomeric complexes.
I IbV
From the cyclovoltammetric data it is evident that the trinuclear ruthenium complex exhibits multi-step reversible
electron-transfer behavior and may be called an "electron
sponge."
Oxygen evolution was investigated by adding excess ammonium ceric nitrate to a solution of the trinuclear ruthenium complex in a closed and degassed vessel. Gas bubbles were observed in the solution upon addition of excess
cerium(1v) salt. The gas evolved was identified as oxygen
by gas chromatography. When H,l80 was used, mass spectral analysis resolved the presence of I6O2, 180'60
and
'Q, respectively.
Table I. Water oxidation by ammonium cerium(1v) nitrate in the presence of
di- and trinuclear ruthenium catalysts in 1 h at 25°C under homogeneous
and heterogeneous conditions (on Kaolin). Solution volume 5 mL. Molar ratio catalyst :cerium(lv) I :400.
Catalyst
[moll
Ru-red
Ru-brown
Ru-Ru-HzO
Ru-Ru-N02
1x10-6
IxIO-~
5 x lo-'
5 x lo-'
Homogeneous
O2
turnover
[GL]
number
Heterogeneous
O2
turnover
[pL]
number
Img]
1325
1503
1022
1084
55
18
300
300
250
250
88
30
54.7
62.1
7.3
2.5
42.2
44.8
4.5
1.5
Kaolin
The experimental results are summarized in Table 1 ,
from which it is clear that the trinuclear ruthenium complexes are remarkably better catalysts for water-oxidation
than are the dinuclear ruthenium complexes, both in homogeneous as well as heterogeneous phases. However, the
trinuclear ruthenium complexes were found to undergo
1010
0 VCH Verlugsgeseilschufr mhH, 0-6940 Wernherm. 1986
A trinuclear ruthenium complex in the oxidation state
V,V,V [Eq. (2)] is formed upon addition of excess Ce(1v) to
ruthenium-red IEq. (3)]. Subsequent reaction with water
yields oxygen and ruthenium-brown [Eq. (4)]. This ruthenium-brown is highly stable and catalyzes the oxidation of
water in the presence of excess Ce(rv) in a cyclic process.
In the case of dinuclear ruthenium complexes, the wateroxidation reaction is described by Equation (5).'"]
RuV-O-RuV
+2H20
-
Ru"'-O-RU"'
+
0 2
+ 4H@
(5)
Earley and Feuleyl6l studied the kinetics of the reduction
of ruthenium-brown by hydroxide ion. They suggested that
the attack of OH" ion on the central ruthenium atom in
ruthenium-brown would be the most probable step for
which no symmetry restriction is to be anticipated, and
that the reduction leads to the formation of ruthenium-red.
According to Endicott and Tuube["l a spin-paired d 4 ion
(Ru'") can accommodate seven groups in the coordination
sphere; these authors assume that Ru"' also forms seven-
0570-0833/86/1111-1010 $ 02.50/0
Angew. Chem. Int. Ed. Engl. 25 11986) No. I 1
coordinate species as kinetic intermediates.“” From these
results we assume that two water molecules are involved in
the formation of one molecule of oxygen. The first water
molecule attacks the central Ru“ ion in the trinuclear ruthenium complex [Eq. ( 3 ) ] , the second one coordinates at
one of the terminal Ru” atoms. This intermediate may lead
to the formation of an 0-0 bond between the two water
molecules. This is followed by release of oxygen and the
re-formation of ruthenium-brown. The formation of a peroxide intermediate and evolution of oxygen in the wateroxidation process with dinuclear ruthenium complexes has
already been proposed by Meyer et aLLbJAn analogous
model for water-oxidation with manganese complexes in a
heterogeneous environment could facilitate a n understanding of the evolution of oxygen in photosynthe~is.[’~l
Received: July 8, 1986;
revised: September 15, 1986 [Z 1849 IE]
German version: Angew. Chem. 98 (1986) 1012
[I] M. Gratzel (Ed.): Energy Resources Through Photochemistry and Catalysir, Academic Press, New York 1983; J. S. Connolly (Ed.): Photochemical Conoer.sion and Storage of Solar Energy, Academic Press, New York
1981
121 K. Kiwi, M. Gratzel, Angew. Chem. 90 (1978) 900; Angew Chem. Int.
Ed. Enyl. 17(1978) 860; ibid. 91 (1979) and 18(1979) 624; J. M. Lehn, J.
P. Sauvage, R. Ziessel, Noun J. Chim. 3 (1979) 423; M. Kaneko, N.
Awaya. A. Yamada, Chem. Lett. 1982. 619.
[3] J. A. Gilbert, D. S. Eggleston, W. R. Murphy, Jr., D. A. Geselowitz, S.
W. Gersten, D. J Hodgson, T. J. Meyer, J . Am. Chem. SOC.107(1985)
3855.
[4] R. Ramaraj, A. Kira, M. Kaneko, J . Chem. Soc. Foraday Trans. I 82
(1986). in press.
[51 R. Ramaraj, A. Kira, M. Kaneko, Angew. Chem. 98 (1986) 824; Angew.
Chem. Int. Ed. Engl. 25 (1986) 825.
[6] J. E. Earley, T. Fealey, Inorg. Chem. 12 (1973) 323.
[7] 1. M. Fletcher, B. F. Greenfield, C. J. Hardly, D. Scargill, J. L. Woodhead, J . Chem. Soc. 1961. 2000; C. A. Clausen, R. A. Prados, M. Good,
Inory. Nucl. Chem. Lett. 7 (1971) 485.
IS] T. R. Weaver, T. J . Meyer, S. A. Adeyemi, G. M. Brown, R. P. Eckberg,
W. E. Hatfield, E. C. Johnson, R. W. Murray, D. Unterker, J . Am. Chern.
SOC.97 (1975) 3039.
191 H. S. Lim, D. J. Barclay, F. C. Anson, Inorg. Chem. I1 (1972) 1460.
[lo] W. Kutner, J. A. Gilbert, A. Tomaszewski, T. J. Meyer, R. W. Murray, J .
Electroanal. Chem. 20s (1986) 185.
[ I I] J. F. Endicott. H. Taube, Inorg. Chem. 4 (1965) 437.
1121 H. Scheidigger, J. Armor, H. Taube, J. Am. Chem. SOC.90 (1968) 5938.
1131 G. Renger (Ed.): Photosynthetic Water Oxidation, Academic Press, New
York 1978, p. 229; Govindjee, T. Kambara, W. Coleman, Photochem.
Photobiol. 42 (1985) 187.
S-0 bond, whereas CH31 approaches from the opposite
side (Scheme 1).l2l On the basis of these, and other observations, an ion-pair structure (Scheme 1 ) was inferred for
“a-lithiosulfoxides”~2b~‘~q
and the diastereofacial differentiation was attributed to the attractive interaction of the
electrophile E with Lie.
CH31
Scheme 1. lon-pair structure model for a-sulfinylalkyllithium compounds
[2b, e, 0-E = H > O , D20, C 0 2 , RCHO, R2C0, (CH,O),PO.
We report here on the X-ray structure analysis of
a-(phenylsulfinyl)-~-methylbenzyllithium-tetramethylethylenediamine l a (Fig. l).[31The diastereomer l a is formed
from a ca. 1 : 1 mixture of the two diastereomeric u-methylbenzylphenyl sulfoxides 2 upon reaction with n-butyllithium in ether/TMEDA.‘41
PhCHMe-S(0)Ph
TM::z>L,her [PhCMe-S(0)PhJQLi@
2
la
l a crystallizes as a dimer, with bonding occurring via a
Li202 four-membered ring. Two further coordination sites
on each Li@ are occupied by the TMEDA N-atoms. The
la-(Phenylsulfiny1)-a-methylbenzyllithiumtetramethylethylenediamine]z :
Crystal Structure of an a-Sulfinyl “Carbanion”**
By Michael Marsch, Werner Massa, Klaus Harms,
Gerhard Baum, and Gernot Boche*
a-Sulfinyl “carbanions” [R’R’C-S(0)R3]o are important synthetic building blocks.”] Thus, in reactions with
electrophiles the chiral sulfoxide group determines the
diastereofacial differentiation: oxygen-containing electrophiles E attack the anionic C-atom from the side of the
[*] Prof. Dr. G. Boche, M. Marsch, Priv.-Doz. Dr. W. Massa, G. Baum
Fachbereich Chemie der Universitat
Hans-Meerwein-Strasse. D-3550 Marburg (FRG)
Dr. K Harms
lnstitut fur Anorganische Chemie der Universitat
Tammannstrasse 4, D-3400 Gottingen (FRG)
[**I This work was supported by the Fonds der Chemischen lndustrie and
the Ikutsche Forschungsgemeinschaft.
Anqew. Chem. i n t . Ed Engl. 2S 11986) No. 11
Fig. I . Crystal structure of the dimer la (H atoms omitted) at -65°C. Space
group CZ/c, a=3855(2), b= 1201.5(6), c = 1813(1) pm, 8=96.59(5)”, 2 = 8
(dimer). CAD4 (Enraf-Nonius) four-circle diffractometer, MoK,, radiation,
graphite monochromator, w-scans, @= 2-20”. Because of the small crystals,
with broad reflection profile (Am= Zo)--larger crystals were always deformed-only 1865 of 4050 observed independent reflections measured: 3 17
parameters (only S, phenyi residues bound to S, a n d methyl C-atoms of
TMEDA molecules with anisotropic temperature factors; H atoms placed at
calculated sites). R, =0.083. The two crystallographically independent molecules are bound perpendicularly to the slightly folded L i 2 0 2four-membered
ring via a pseudo C,-axis to give the dimer.-Important bond lengths [pm]
and angles [“J (mean values of both molecules): LiO 192(2), Li-N 213(2). LiLi(A) 265(4), S - 0 158(1), S-C(1) 163(1), S-C(9) 181(1), C(I)-C(2) 144(2), C(1)C(8) 154(2): 0 - L i - 0 91(1), Li-0-Li 87(1), Li-0-S 148(l), Li(A)-0-S 123(1),
0-S-C(1) 117(1), O-S-C(9) 101(1), C(1)-S-C(9) 104(1), S-C(1)-C(2) 120(1), SC(l)-C(8) I19(1), C(2)-C(I)-C(8) 118(1). Further details of the crystal structure investigation are available on request from the Fachinformationszentrum Energie, Physik, Mathematik GmbH, D-75 14 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-52096, the names of
the authors, and the full citation of the journal.
0 VCH Verlag.~gesellschajim h f f , 0-6940 Weinheim. 1986
0 5 7 0 - ~ 8 3 3 / 8 6 / 1 1 1 I - i 0 1 102.50/0
~
10 I 1
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water, oxidation, heterogeneous, generation, homogeneous, trinuclear, complexes, ruthenium, catalyst
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