Electrochemical oxidation of methanol with Ru/Pd, Ru/Pt, and Ru/Au heterobimetallic complexes

Article abstract of DOI:10.1021/om010706h

The heterobimetallic complexes CpRu(PPh₃)(μ-Cl)(μ-dppm)PdCl₂ (1) [dppm = bis(diphenylphosphino)methane], CpRu(PPh₃)Cl(μ-dppm)AuCl (2), and CpRu(PPh₃)(μ-Cl)(μ-dppm)PtCl₂ (3) were synthesized by the rea

Full text of DOI:10.1021/om010706h

Organometallics 2002, 21, 711-716
711
Electr och em ica l Oxid a tion of Meth a n ol w ith Ru /P d ,
Ru /P t, a n d Ru /Au Heter obim eta llic Com p lexes
Gilbert J . Matare, Mark E. Tess, Ying Yang, Khalil A. Abboud, and
Lisa McElwee-White*
Department of Chemistry and Center for Catalysis, University of Florida,
Gainesville, Florida 32611
Received August 6, 2001
The heterobimetallic complexes CpRu(PPh3)(µ-Cl)(µ-dppm)PdCl2 (1) [dppm ) bis(diphen-
ylphosphino)methane], CpRu(PPh3)Cl(µ-dppm)AuCl (2), and CpRu(PPh3)(µ-Cl)(µ-dppm)PtCl2
(3) were synthesized by the reaction of CpRu(PPh3)Cl(η1-dppm) (4) with Pd(COD)Cl2,
AuPPh3Cl, and Pt(COD)Cl2, respectively. Compounds 1 and 2 were characterized by X-ray
crystallography. Electrochemical oxidation of CH3OH in the presence of 1, 2, or 3 leads to
considerable enhancement of the oxidative currents and formation of the organic products
CH2(OCH3)2 and HCOOCH3. Addition of water increases both the current and the proportion
of the more highly oxidized product, HCOOCH3. Current efficiencies obtained with
heterobinuclear complexes 1-3 were significantly higher than those obtained using the model
compound CpRuCl(η2-dppm) (5) as catalyst.
In tr od u ction
methanol binding and dehydrogenation. The Ru site is
implicated in the removal of Pt-adsorbed CO, converting
it into CO2 through intermediate Ru oxo species. These
postulates correlate to behavior of discrete species in
homogeneous solution since C-H bond rupture has been
demonstrated in mononuclear organometallic Pt(II)
complexes19-23 and Ru oxo complexes are well-known
oxidants of alcohols.24-29
Recent efforts toward the development of electrooxi-
dation catalysts for direct methanol fuel cells have
included the incorporation of a second metal to improve
the performance of Pt anodes. In addition to the com-
monly utilized Pt/Ru systems,1-7 other electrode ma-
terials including PtSn,8-10 PtRe,10 PtRuOs,11 and
PtRuOsIr12 have been investigated. Binary Pt/Ru alloys
are among the most active, exhibiting lower overpoten-
tials and less surface poisoning than pure Pt anodes.
Many experiments have addressed the mechanism of
oxidation, kinetics, bulk composition, and the nature of
their active sites.1,12-16 Earlier studies from Watanabe17
and others5,18 suggest that the Pt surface is the site of
Homogeneous catalysis with well-defined heterobi-
metallic systems has been a topic of interest due in part
to the potential to explore the cooperative interaction
of the two metals as well as the possibility for each
metal center to perform a separate and distinctive
task.30-38 Recently, we reported the electrochemical
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10.1021/om010706h CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/15/2002

712 Organometallics, Vol. 21, No. 4, 2002
Matare et al.
Sch em e 1
oxidation of methanol catalyzed by the heterobimetallic
complex CpRu(PPh3)(µ-Cl)(µ-dppm)PtCl2 (3).39 In this
work, we report the synthesis, electrochemistry, and
electrocatalytic activity of the related heterobimetallic
complexes CpRu(PPh3)(µ-Cl)(µ-dppm)PdCl2 (1) and
[CpRu(PPh3)Cl(µ-dppm)AuCl (2). Further experiments
on the catalytic behavior of 3 are also reported herein.
F igu r e 1. Thermal ellipsoids drawing of the molecular
structure of CpRuPPh3(µ-Cl)(µ-dppm)PdCl2 (1). Thermal
ellipsoids are plotted at 50% probability. Phenyl rings and
most hydrogen atoms are omitted for clarity.
Resu lts a n d Discu ssion
Syn t h esis of Het er obim et a llic Com p lexes. The
Ru/Pd complex 1 was prepared as a red air stable
powder in 71% yield from the reaction of CpRu(PPh3)-
Cl(η1-dppm) (4) with (COD)PdCl2 at room temperature
(Scheme 1). Unlike its platinum analogue 3,39,40 solu-
tions of 1 do not show signs of decomposition even when
exposed to air for weeks. The 31P{1H} NMR spectrum
of 1 exhibits the expected three resonances. The Ru-
bound phosphorus signals appear as a doublet of
doublets at 52.2 ppm and a doublet at 37.5 ppm. The
upfield resonance at 19.7 ppm is assigned to the Pd-
bound phosphorus. Treatment of 4 with AuPPh3Cl
affords the orange heterobimetallic complex 2 in 66%
yield. The 31P{1H} NMR data for 2 are consistent with
the resonances observed for the Ru/Pd catalyst 1. The
Ru-bound phosphorus atoms appear at 42.8 and 36.3
ppm as a doublet and a doublet of doublets, respectively.
A doublet at 20.8 ppm is assigned to the Au-bound
F igu r e 2. Thermal ellipsoids drawing of the molecular
structure of CpRuPPh3Cl(µ-dppm)AuCl (2). Thermal el-
lipsoids are plotted at 50% probability. Phenyl rings and
most hydrogen atoms are omitted for clarity.
1
phosphorus atom. In the H NMR spectrum, the meth-
form a distorted six-membered ring, in which the Cp
ligand occupies an apical position. In contrast, as seen
in Figure 2, complex 2 exhibits no interaction between
the Ru and Au centers beyond what could be transmit-
ted via through-bond interactions involving the dppm
ligand. In both complexes, the cyclopentadienyl ligands
are coordinated to the Ru centers in an η5 mode,
resulting in a pseudotetrahedral geometry typical of a
piano stool conformation. The bond lengths and bond
angles of the structures are standard, with the expected
square planar geometry at Pd and linear configuration
at Au.
Cyclic Volta m m etr y of Com p lexes 1-5. Cyclic
voltammetry of the Ru/Pd system 1 in DCE/TBAT (DCE
) 1,2-dichloroethane, TBAT ) tetrabutylammonium
trifluoromethanesulfonate) exhibits irreversible couples
at 1.29 and 1.45 V vs NHE (Figure 3). The wave at 1.29
V is assigned to the Ru(II/III) couple. This wave is
shifted about 160 mV positive compared to that of the
Ru/Pt complex 3, which exhibits a reversible couple at
1.13 V. The shift is consistent with electron donation
through the Cl bridge to the more electron-deficient Pd
ylene protons of the bridging ligands of 1 are observed
as a multiplet at approximately 2.6 ppm as a result of
coupling to the adjacent phosphorus atoms. Similar
coupling is observed in 2, but the chemical shifts of the
diastereotopic methylene protons are significantly dif-
ferent.
X-r a y Cr ysta l Str u ctu r es of Com p lexes 1 a n d 2.
Complex 1 exhibits a bridging chloride (Figure 1), as
does its structurally similar Ru/Pt analogue 3.39 The six
central atoms in 1 (Pd, P1, C6, P2, Ru, and the µ-Cl)
(33) McCollum, D. G.; Bosnich, B. Inorg. Chim. Acta 1998, 270, 13-
19.
(34) Shapley, P. A.; Zhang, N. J .; Allen, J . L.; Pool, D. H.; Liang, H.
C. J . Am. Chem. Soc. 2000, 122, 1079-1091.
(35) Kalck, P.; Wheatley, N. Chem. Rev. 1999, 99, 3379-3419.
(36) Baranger, A. M.; Bergman, R. G. J . Am. Chem. Soc. 1994, 116,
3822-3835.
(37) Beuken, E.; Feringa, B. L. Tetrahedron 1998, 54, 12985-13011.
(38) Farr, J . P.; Olmstead, M. M.; Wood, F. E.; Balch, A. L. J . Am.
Chem. Soc. 1983, 105, 792-798.
(39) Tess, M. E.; Hill, P. L.; Torraca, K. E.; Kerr, M. E.; Abboud, K.
A.; McElwee-White, L. Inorg. Chem. 2000, 39, 3942-3944.
(40) Orth, S. D.; Terry, M. R.; Abboud, K. A.; Dodson, B.; McElwee-
White, L. Inorg. Chem. 1996, 35, 916-922.

Electrochemical Oxidation of Methanol
Organometallics, Vol. 21, No. 4, 2002 713
the metals via the µ-Cl bridge of 1 is more substantial.
We have also examined the cyclic voltammetric behavior
of the mononuclear Ru model complex CpRuCl(η2-dppm)
(5) (Figure 5). The Ru(II/III) couple of 5 occurs at 0.61
V, while the Ru(III/IV) couple is observed at 1.38 V.
Ca ta lytic Electr ooxid a tion of Meth a n ol By Com -
p lexes 1-3. The cyclic voltammogram of the Ru/Pd
complex CpRu(PPh3)(µ-Cl)(µ-dppm)PdCl2 (1) after ad-
dition of methanol (Figure 3a) shows a minimal current
increase at the Ru(II/III) couple followed by a dramatic
increase at the Pd(II/IV) wave. In contrast, methanol
oxidation with the Ru/Au complex CpRu(PPh3)Cl(µ-
dppm)AuCl (2) occurs at the Ru(III/IV) wave, which is
similar to alcohol oxidation with simple mononuclear
Ru complexes.24,42-45 Cyclic voltammograms of the
model monometallic Ru complex 5 under the same con-
ditions as the bimetallic compounds exhibit considerable
increases in the voltammetric current in the presence
of methanol. However, the onset of oxidation occurs at
potentials far more positive relative to the Ru(III/IV)
wave of the bimetallic complexes. Electrochemical oxi-
dation of methanol in the presence of 1 or 2 leads to
considerable enhancement of the oxidative currents.
Methanol oxidation with 2 occurs at a potential more
positive than with 1. In the absence of methanol, no
anodic activity is observed. Addition of 5 µL of water to
the samples results in further current increases.
Differences among the behavior of 1, 2, and 3 can be
seen in the evolution of product distributions shown in
Tables 5 and 6, which present the average product ratios
of dimethyl acetal to methyl formate formed during bulk
electrolysis of dry and wet methanol. The presence of
water consistently shifts the product ratios toward the
four-electron oxidation product, HCOOCH3. This trend
is reflected by all the complexes and can be seen both
in the initial product ratios for wet vs dry samples and
in the tendency toward production of more methyl
formate in the dry samples as the reaction progresses.
The time evolution of product ratios in the dry samples
presumably arises from water that is generated in situ
during the condensation of formaldehyde46 and formic
acid with excess methanol. This behavior is consistent
with the catalytic performance of complex 3 observed
previously.39
F igu r e 3. Cyclic voltammograms of 1 under nitrogen in
2.5 mL of DCE/0.7 M TBAT; glassy carbon working
electrode; Ag/Ag+ reference electrode; 50 mV/s: (a) solu-
tions as specified in figure; (b) 10 mM 1; 5 mV/s; (s)
switching potential 1.8 V; (- - -) switching potential 1.3 V.
center of 1 (the first oxidation wave of the model
compound PdCl2(η2-dppm) is approximately 200 mV
positive of its Pt analogue). The irreversible wave at 1.45
V is assigned to the Pd(II/IV) oxidation based on
comparisons with the cyclic voltammogram of PdCl2(η2-
dppm). The formal oxidation wave potentials for the
bimetallic complexes 1-3 as well as the mononuclear
Ru complexes 4 and 5 are summarized in Table 4.
The Ru/Au complex 2 exhibits a reversible couple at
0.86 V and a quasireversible couple at 1.40 V vs NHE
in DCE/TBAT (Figure 4). The reversibility of the wave
at 0.86 V is not affected by oxidation in the presence of
methanol at potentials up to 1.5 V (Figure 4b). The wave
at 0.86 V is assigned to the Ru(II/III) couple, while the
wave at 1.40 V is assigned to the Au(I/III) oxidation.
This wave is similar to that of the starting material,
Au(PPh3)Cl, which has been reported to oxidize at 1.68
V vs NHE in CH2Cl2.41 The Ru(II/III) wave of the
mononuclear compound CpRu(PPh3)Cl(η1-dppm) (4) is
observed at 0.56 V.40 Overall, the first two redox
potentials of 2 more closely resemble their mononuclear
model compounds than do the first two redox potentials
of 1. This is consistent with the crystal structure data,
which suggest that interactions between the metal
centers of 2 are likely to be minimal, while coupling of
The potential for bulk electrolyses (1.7 V vs NHE) was
chosen during earlier studies on Ru/Pt complex 3, which
exhibits its rise in catalytic current coincident with the
Pt(II/IV) wave at that potential.39 For comparison pur-
poses, bulk electrolyses with complexes 1, 2, and 5 were
performed at the same potential. Thus, oxidations with
Ru/Pd complex 1 were performed between the Pd(II/IV)
and Ru(III/IV) waves, while Ru/Au compound 3 was
electrolyzed between the Au(I/III) and Ru(III/IV) waves.
The Ru complex 5 was oxidized at a potential somewhat
more positive than the Ru(III/IV) couple. Thus, for all
of the bimetallic complexes, oxidation was positive of
both the Ru(II/III) couple and the first oxidative wave
for the second metal. Only in model compound 5 had
(42) Gagne´, R. R.; Marks, D. N. Inorg. Chem. 1984, 23, 65-74.
(43) Navarro, M.; De Giovani, W. F.; Romero, J . R. J . Mol. Catal.
A: Chem. 1998, 135, 249-256.
(44) Lima, E. C.; Fenga, P. G.; Romero, J . R.; De Giovani, W. F.
Polyhedron 1998, 17, 313-318.
(45) Raven, S. J .; Meyer, T. J . Inorg. Chem. 1988, 27, 4478-4483.
(46) Wasmus, S.; Wang, J . T.; Savinell, R. F. J . Electrochem. Soc.
1995, 142, 3825-3833.
(41) Attar, S.; Nelson, J . H.; Bearden, W. H.; Alcock, N. W.; Solujic,
L.; Milosavljevic, E. B. Polyhedron 1991, 10, 1939-1949.

714 Organometallics, Vol. 21, No. 4, 2002
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles (d eg) for Com p lex 1
Matare et al.
Pd-Cl1
Pd-Cl3
Ru-Cl3
2.2842(8)
2.3256(7)
2.4403(7)
Pd-P1
Ru-P2
2.2332(8)
2.2979(7)
Pd-Cl2
Ru-P3
2.3773(8)
2.3347(7)
P1-C6-P2
C13-Pd-Cl2
Pd-Cl3-Ru
119.74(15)
90.11(3)
106.76(3)
P1-Pd-Cl1
Cl1-Pd-Cl3
P2-Ru-Cl3
C6-P1-Pd
91.09(3)
P1-Pd-Cl3
Cl1-Pd-Cl2
P3-Ru-Cl3
86.50(3)
92.44(3)
89.13(2)
174.98(3)
89.36(2)
113.70(9)
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles (d eg) for Com p lex 2
Au-Cl2
Ru-Cl1
2.2860(13)
2.4598(11)
Au-P3
Ru-P2
2.2288(12)
2.2946(11)
Ru-P1
2.3165(12)
P3-C6-P2
P1-Ru-Cl1
118.5(5)
92.65(4)
P1-Ru-P2
C6-P2-Au
98.36(4)
115.32(15)
C6-P2-Ru
P2-Ru-Cl1
P3-Au-Cl2
116.48(14)
88.95(4)
1179.36(5)
Ta ble 3. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for Com p lexes 1 a n d 2
formula
molecular weight
cryst syst
space group
a (Å)
C54H54Cl9P3PdRu
1322.40
monoclinic
P2(1)/n
13.7019(8)
22.763(1)
18.517(1)
90
107.398(1)
90
C49.50H45AuCl5P3Ru
1208.05
triclinic
P1h
11.1888(5)
13.5263(6)
15.4678(7)
94.690(1)
90.562(1)
100.561(1)
2292.9(1)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
5511.1(6)
4
T (K)
173(2)
173(2)
λ (Å)
0.71073
1.594
1.160
2664
0.19 × 0.21 × 0.32
1.79 to 27.50
-12 e h e 17,
-29 e k e 29,
-24 e l e 24
39 100
0.71073
1.750
3.956
1190
0.23 × 0.20 × 0.10
1.85 to 27.50
-14 e h e 14,
-17 e k e 17,
-20 e l e 10
15 922
σcalcd (Mg/m3)
µ (mm-1)
F000
cryst size (mm3)
θ range (deg)
hkl limits
no. reflns collected
no. ind reflns
12 610 [R(int) )
0.0279]
10 266 [R(int) )
0.0379]
no data/restraints/ 12 610/0/666
params
10 266/0/551
GOF
1.108
0.0346(F>2σ(F))
0.0839
0.971
0.0375(F>2σ(F))
0.0933
R(Fo)a
wR(Fo
2
b
)
largest diff peak/
0.777/-0.902
1.396/-1.431
hole (e.Å-3
)
a
R1 ) ∑(|Fo| - |Fc|)/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc2)2]/∑w[Fo]2]1/2[F
>2σ(F)].
F igu r e 4. Cyclic voltammograms of 2 under nitrogen in
2.5 mL of DCE/0.7 M TBAT; glassy carbon working elec-
trode; Ag/Ag+ reference electrode: (a) solutions as speci-
fied in figure; 50 mV/s; (b) 10 mM 2 plus 50 µL of meth-
anol; 50 mV/s; (s) switching potential 1.5 V; (- - -)
switching potential 1.3 V.
Ta ble 4. F or m a l P oten tia ls for Com p lexes 1-5
complex
couple
E1/2 (V)a
couple
E1/2 (V)a
1
2
3
4
5
Ru(II/III)
Ru(II/III)
Ru(II/III)
Ru(II/III)
Ru(II/III)
1.29b
0.86
Pd(II/IV)
Au(I/III)
Pt(II/IV)
1.45b
1.40b
1.78b,c
1.13c
0.56c
0.61
(Tables 5 and 6). The Ru/Pd complex 1 begins to yield
more of the four-electron oxidation product as the
reaction progresses, and similar (but more rapid) changes
in behavior are observed for Ru/Au complex 2. In
contrast, Ru complex 5 affords only trace amounts of
dimethyl acetal under dry conditions. Under wet condi-
tions, 5 favors methyl formate formation, but the
reaction is very slow.
During exhaustive bulk electrolysis, oxidative cur-
rents gradually decrease to insignificant amounts as the
solutions develop a brown discoloration. The lifetimes
of the catalysts have not yet been established due to
difficulties with our electrolysis cell, in which bulk
a
All potentials obtained in DCE/TBAT and reported vs NHE.
Irreversible wave, Epa reported. c Performed in CH2Cl2/TBAH as
b
described in ref 40.
Ru reached the Ru(IV) oxidation state. The difference
in the identity and the oxidation state of the second
metal appears to be reflected in the product ratios of
the methanol oxidation products. At early stages of the
reaction, all three bimetallic complexes afford higher
proportions of dimethyl acetal; however, in oxidation of
dry samples with Ru/Pt complex 3 the acetal continues
to predominate even at later stages of the reaction

Electrochemical Oxidation of Methanol
Organometallics, Vol. 21, No. 4, 2002 715
erobinuclear complexes 1-3 were moderately low (19
to 26%), they are significantly higher than the 3.2 and
7.2% current efficiencies obtained from the mononuclear
model compound CpRuCl(η2-dppm) (5) under dry and
wet conditions, respectively. Although the nature of the
metal-metal interaction varies in complexes 1-3, in
each case the presence of the second metal center
apparently results in enhanced catalytic activity.
Su m m a r y
We have prepared three Ru-containing heterobi-
nuclear complexes which display catalytic activity to-
ward the electrooxidation of methanol. Our results sug-
gest that cooperativity between metal centers in these
well-defined bimetallic systems results in a significant
enhancement of current efficiency for the oxidation of
methanol. Although the efficiency increase is consistent
among the complexes, product ratios of formaldehyde
dimethyl acetal to methyl formate vary with the identity
of the second metal. Addition of water enhances the
oxidative currents and favors the formation of methyl
formate in all complexes. Mechanistic studies and
further investigations of the nature of the metal-metal
interaction during oxidation are currently underway.
F igu r e 5. Cyclic voltammogram of 5 under nitrogen in
2.5 mL of DCE/0.7 M TBAT; glassy carbon working
electrode; Ag/Ag+ reference electrode; 50 mV/s.
Ta ble 5. P r od u ct Distr ibu tion s a n d Cu r r en t
Efficien cies for th e Electr och em ica l Oxid a tion of
Dr y Meth a n ol by 1, 2, a n d 3a
product ratio (µmol of CH2(OCH3)2/HCOOCH3)b
charge/(C)
Ru/Pt (3)
Ru/Pd (1)
Ru/Au (2)
Ru (5)
25
50
75
100
130
efficiency
2.45
2.35
1.51
1.23
1.20
18.6e
3.18
2.41
1.54
0.94
0.87
24.6e
1.44
1.23
0.98
0.59
0.46
25.4e
n.o.c
n.o.c
n.o.c
n.o.c
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Standard Schlenk/vacuum tech-
niques were used throughout. Hexane, methylene chloride, and
1,2-dichloroethane were distilled from CaH2. All NMR solvents
were degassed via freeze-pump-thaw cycles and stored over
molecular sieves. 1H and 31P NMR spectra are referenced to
the residual proton in the deuterated solvent and to 85%
H3PO4, respectively. The 31P NMR spectra were proton-
decoupled. High-resolution mass spectrometry was performed
by the University of Florida analytical service. Cp(PPh3)RuCl-
(η1-dppm) was prepared as previously described.47 AuPPh3Cl
and Pd(COD)Cl2 were purchased from Strem Chemicals and
used as received. RuCl3‚xH2O was purchased from Pressure
Chemicals. All other starting materials were purchased in
reagent grade purity and used without further purification.
Electr och em istr y. Electrochemical experiments were per-
formed under nitrogen using an EG&G PAR model 263A
potentiostat/galvanostat. Cyclic voltammograms (scan rate of
50 mV/s) were recorded in 2.5-3.5 mL of DCE/0.7 M TBAT at
ambient temperature under nitrogen. All potentials are re-
ported vs NHE and referenced to Ag/Ag+. The reference
electrode consisted of a silver wire immersed in an acetonitrile
solution containing freshly prepared 0.01 M AgNO3 and 0.1
M TBAT. The Ag+ solution and silver wire were contained in
a 75 mm glass tube fitted at the bottom with a Vycor tip. All
electrochemical measurements were performed inside a glove-
box. Constant potential electrolysis was performed in a three-
compartment H-cell separated by a medium-porosity sintered
glass frit in 2.5-3.5 mL of DCE/0.7 M TBAT at room temper-
ature under nitrogen using a vitreous carbon working electrode
and platinum foil counter electrode. Cyclic voltammetry was
d
∞
3.2f
a
Electrolyses were performed at 1.7 V vs NHE. A catalyst
concentration of 10 mM was used. Methanol concentration was
0.35 M. b Determined by GC with respect to heptane as an internal
standard. Each ratio is reported as an average of 2-5 experiments.
c No products observed. Only CH2(OCH3)2 observed. e Average
d
current efficiencies after 75-130 C of charge passed. f Current
efficiency after 130 C of charge passed.
Ta ble 6. P r od u ct Distr ibu tion s a n d Cu r r en t
Efficien cies for th e Electr och em ica l Oxid a tion of
Wet Meth a n ol by 1, 2, a n d 3a
product ratio (µmol of CH2(OCH3)2/HCOOCH3)b
charge/(C)
Ru/Pt (3)
Ru/Pd (1)
Ru/Au (2)
Ru (5)
25
50
75
100
130
efficiency
1.68
1.34
1.17
0.67
0.41
19.5d
1.38
0.98
0.84
0.70
0.54
20.6d
1.26
1.05
0.97
0.41
0.34
26.1d
n.o.c
n.o.c
n.o.c
n.o.c
0.33
7.2e
a
Conditions the same as in Table 5 except for the addition of 5
µL of water to the cell. b Determined by GC with respect to heptane
as an internal standard. Each ratio is reported as an average of
2-5 experiments. c No products observed. Average current ef-
d
ficiencies after 75-130 C of charge passed. e Current efficiency
after 130 C of charge passed.
electrolysis past 130 C is complicated by the diffusion
of the catalyst between the compartments. Analysis of
the catalyst solutions by 31P NMR after exhaustive bulk
electrolysis indicates the decomposition of the original
bimetallic structures to complex mixtures of other
unidentified phosphorus-containing metal complexes.
Current efficiencies are also summarized in Tables 5
and 6. These values are the ratio of the charge necessary
to produce the observed yields of CH2(OCH3)2 and
HCOOCH3 to the total charge passed during bulk
electrolysis. Although the current efficiencies for het-
performed with
a highly polished glassy-carbon working
electrode (3 mm diameter). Electrolysis products were analyzed
by gas chromatography on an HP5980A chromatograph con-
taining a 15 m × 0.32 mm column of AT-WAX (Alltech, 0.5
µm film) on fused silica. The column was attached to the
injection port with
deactivated guard column. The products produced during
electrolysis were quantitatively determined with the use of a
a
neutral 5 m × 0.32 mm AT-Wax
(47) Bruce, M. I.; Humphrey, M. G.; Patrick, J . M.; White, A. H.
Aust. J . Chem. 1983, 36, 2065-2072.

716 Organometallics, Vol. 21, No. 4, 2002
Matare et al.
known amount of n-heptane as an internal standard. Product
identity was confirmed by comparing retention times of the
oxidation products with authentic samples.
ecules of crystallization were found in the asymmetric unit.
All three were disordered, and each was refined in two parts.
Their site occupation factors were dependently refined to 0.54-
(1), 0.52(1), and 0.67(1) for the major parts and consequently
0.46(1), 0.48(1) and 0.33(1) for the minor parts. A total of 666
parameters were refined in the final cycle of refinement using
10 952 reflections with I > 2σ(I) to yield R1 and wR2 of 3.46%
and 7.76%, respectively. Refinement was done using F2. All
software and sources of the scattering factors are contained
in the SHELXTL program library.48
Cr ysta llogr a p h ic Str u ctu r e Deter m in a tion of 2. Data
were collected at 173 K on a Siemens SMART PLATFORM
equipped with a CCD area detector and a graphite monochro-
mator utilizing Mo KR radiation (λ ) 0.71073 Å). Cell
parameters were refined using up to 8192 reflections. A
hemisphere of data (1381 frames) was collected using the
ω-scan method (0.3° frame width). The first 50 frames were
remeasured at the end of data collection to monitor instrument
and crystal stability (maximum correction on I was <1%).
Absorption corrections by integration were applied based on
measured indexed crystal faces. The structures were solved
by the direct methods in SHELXTL5 and refined using full-
matrix least squares. The asymmetric unit of 2 contained three
molecules, the molecule of interest and two CH2Cl2 solvent
molecules, one of which is located on a center of inversion.
Thus, the ratio of complex 2 to solvent is 1:1.5. The non-H
atoms were treated anisotropically, whereas the methyl hy-
drogen atoms were calculated in ideal positions and were
riding on their respective carbon atoms. A total of 552
parameters were refined in the final cycle of refinement using
8794 reflections with I > 2σ(I) to yield R1 and wR2 of 3.84%
and 4.26%, respectively. Refinement was done using F2. All
software and sources of the scattering factors are contained
in the SHELXTL program library.48
Cp (P P h 3)Ru (µ-Cl)(µ-P P h 2CH2P P h 2)P d Cl2 (1). In a 100
mL flask, Cp(PPh3)RuCl(η1-dppm) (0.227 g, 0.268 mmol) and
PdCl2(COD) (0.077 g, 0.27 mmol) were dissolved in 50 mL of
CH2Cl2. The red-orange solution was stirred at room temper-
ature for 24 h. The solution was concentrated to a small
volume, and hexane was vacuum transferred to precipitate a
red solid. The solid was filtered with a swivel medium frit,
washed with hexanes, and dried under vacuum. The product
was further recrystallized from CH2Cl2/hexane to yield 0.195
g (71%) of 1. Single crystals suitable for X-ray diffraction were
grown by slow solvent diffusion of hexane into a solution of
the red product in 1,2-dichloroethane. 1H NMR (CDCl3): δ
8.14-6.04 (m, 35H, Ph2PCH2PPh2 + PPh3), 4.72 (s, 5H, Cp),
2.71-2.63 (m, 2H, Ph2PCH2PPh2). 31P NMR (CDCl3): δ 52.2
(dd, Ru-PPh2-CH2PPh2, J PP ) 28 Hz, 35 Hz), 37.5 (d, Ru-PPh3,
J PP ) 35 Hz), 19.7 (d, PPh2CH2PPh2-Pd, J PP ) 28 Hz). HRMS
(FAB): calcd for C48H42Cl3PdP3Ru 990.0026 (MH+-Cl), found
990.0073. Anal. Calcd for C48H42Cl3PdP3Ru: C, 56.21; H, 4.12.
Found: C, 55.98; H, 4.00.
Cp (P P h 3)Ru Cl(µ-P P h 2CH2P P h 2)Au Cl (2). The reaction
was performed similarly as for 1 starting from CpRu(PPh3)-
Cl(η1-dppm) (0.300 g, 0.354 mmol) and PPh3AuCl (0.175
g, 0.354 mmol). Yield: 0.251 g (66%). Single crystals suitable
for X-ray diffraction were obtained by recrystallization from
1
CH2Cl2/hexane. H NMR (CDCl3): δ 7.91-6.83 (m, 35H, Ph2-
PCH2PPh2 + PPh3), 4.74 (m, 1H, Ph2PCHHPPh2), 4.09 (s, 5H,
Cp), 1.33 (m, 1H, Ph2PCHHPPh2). 31P NMR (CDCl3): δ 42.8
(d, Ru-PPh3, J PP ) 43 Hz), 36.3 (dd, Ru-PPh2-CH2PPh2, J PP
)
28 Hz, 43 Hz), 20.8 (d, AuPPh2CH2PPh2, 28 Hz). HRMS
(FAB): calcd for C48H42Cl2P3AuRu 1080.0585 (M+), found
1080.0585. Anal. Calcd for C48H42Cl2P3AuRu: C, 53.35; H, 3.92.
Found: C, 53.62; H, 3.83.
Cr ysta llogr a p h ic Str u ctu r e Deter m in a tion of 1. Data
were collected at 173 K on a Siemens SMART PLATFORM
equipped with a CCD area detector and a graphite monochro-
mator utilizing Mo KR radiation (λ ) 0.71073 Å). Cell
parameters were refined using up to 8192 reflections. A
hemisphere of data (1381 frames) was collected using the
ω-scan method (0.3° frame width). The first 50 frames were
remeasured at the end of data collection to monitor instrument
and crystal stability (maximum correction on I was < 1%).
Absorption corrections by integration were applied based on
measured indexed crystal faces. The structure was solved by
the direct methods in SHELXTL5 and refined using full-matrix
least squares. The non-H atoms were treated anisotropically,
whereas the hydrogen atoms were calculated in ideal positions
and were riding on their respective carbon atoms. The C6
protons were refined freely. Three 1,2-dichloroethane mol-
Ack n ow led gm en t. The Division of Chemical Sci-
ences, Office of Basic Energy Sciences, U.S. Department
of Energy, provided funding for this work. K.A.A. wishes
to acknowledge the National Science Foundation and
the University of Florida for funding of the purchase of
the X-ray equipment.
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
distances, bond angles, positional parameters, and anisotropic
displacement parameters for 1 and 2. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
OM010706H
(48) Sheldrick, G. M. SHELXTL program library; Bruker-AXS:
Madison, WI, 1998.