Aerobic alcohol oxidation catalyzed by a new, oxygen-bridged heterometallic compound [PPh4][Ru(N)Me2(μ2-O)2Pd((-)-sparteine)]

Article abstract of DOI:10.1016/j.jorganchem.2006.12.014

The reaction between the new hydroxy compound [PPh₄][Ru(N)(OH)₂Me₂] and Pd(OSiMe₃)₂((-)-sparteine) produces (Me₃Si)₂O, H₂O and a new heterobimetallic compound [PPh₄][Ru(N)Me₂(μ₂-O)₂Pd((-)-sparteine)] in good yield. The Ru/Pd bimetallic compound catalyzes the oxidation of aryl and allyl alcohols to the corresponding carbonyl compound in air and the rearrangement of allylic alcohols unsaturated aldehydes. It also oxidizes PPh₃ to O-PPh₃ under O₂.

Full text of DOI:10.1016/j.jorganchem.2006.12.014

Journal of Organometallic Chemistry 692 (2007) 1653–1660
www.elsevier.com/locate/jorganchem
Aerobic alcohol oxidation catalyzed by a new, oxygen-bridged
heterometallic compound [PPh4][Ru(N)Me2(l2-O)2Pd((ꢀ)-sparteine)]
*
Jesse L. Kuiper, Patricia A. Shapley
University of Illinois, Department of Chemistry, 601 S. Goodwin Avenue, Urbana, IL 61801, USA
Received 26 September 2006; received in revised form 15 December 2006; accepted 16 December 2006
Available online 22 December 2006
Abstract
The reaction between the new hydroxy compound [PPh4][Ru(N)(OH)2Me2] and Pd(OSiMe3)2((ꢀ)-sparteine) produces (Me3Si)2O,
H2O and a new heterobimetallic compound [PPh4][Ru(N)Me2(l2-O)2Pd((ꢀ)-sparteine)] in good yield. The Ru/Pd bimetallic compound
catalyzes the oxidation of aryl and allyl alcohols to the corresponding carbonyl compound in air and the rearrangement of allylic alco-
hols unsaturated aldehydes. It also oxidizes PPh3 to O–PPh3 under O2.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Oxidation catalysis; Molecular oxygen; Aerobic oxidation; Heterobimetallic complex; Alcohol
1. Introduction
metal precursors. We have previously prepared heterobi-
metallic and heterotrimetallic with bridging oxo or sulfido
groups through specific bridge-building reactions such as
the reaction of organoosmium(VI) and organoruthe-
nium(VI) chloro compounds [N(n-Bu)4][M(N)R2Cl2] with
Ag2CrO4 [4], AgReO4 [5], or K2WS4 [6]. The ruthenium
compounds [N(n-Bu)4][Ru(N)Me2Cl2] also react with
(trimethylsilyl)sulfido compounds M0(SSiMe3)2L2 (M0 =
Ni, Pd, Pt; L2 = dppe, COD) to form the trimetallic species
{Ru(N)Me2}(l3-S)3{M0L2} [7,8]. These compounds con-
tain coordinately unsaturated metals and some of them
are active for the aerobic oxidation of alcohols.
Although {Ru(N)Me2}(l3-S)3{Pd(dppe)} catalyzes the
oxidation of alcohols with O2, the compound is not stable
under reaction conditions due to the oxidation of the bridg-
ing sulfido groups. In this paper, we report the synthesis of
a new, oxo-bridged Ru(VI)–Pd(II) compound that does not
contain sensitive sulfido or organophosphine ligands.
Because of cooperativity between the metal centers,
compounds containing more than one type of metal center
have the potential to be superior to monometallic catalysts.
This may be especially important for aerobic oxidation cat-
alysts where different metals could selectively coordinate
O2 and the organic substrate. Several enzymes for oxida-
tion reactions demonstrate this with active sites that con-
tain and use multiple metal centers [1], and binuclear
compound of iron and copper can model the oxidation
reactions of enzymes [2]. The interaction between metal
centers can also impede catalysis at a single metal center
as it does in the oxidation of styrene with O2 by trans-
[IrCl(CO)(L-M0)2] [3]. Most synthetic heterometallic inor-
ganic or organometallic compounds are poor catalysts
for oxidation and other reactions because they are either
coordinatively saturated and lack a site for substrate bind-
ing, or because they are not robust to the reaction
conditions.
2. Experimental
There is a need for general methods for the preparation
of reactive heterometallic compounds from a range of
All reactions were conducted under an N2 atmosphere
using standard air-sensitive techniques in a Vacuum Atmo-
spheres drybox unless otherwise stated. NMR spectra were
recorded on Varian Unity-500 and Varian Unity-400 FT
*
Corresponding author. Tel.: +1 217 244 4186.
E-mail address: pshapley@uiuc.edu (P.A. Shapley).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.12.014

1654
J.L. Kuiper, P.A. Shapley / Journal of Organometallic Chemistry 692 (2007) 1653–1660
NMR spectrometers at ambient temperature. IR spectra
were recorded on a Perkin–Elmer 1600 series FTIR. UV–
visible spectra were recorded on a Hewlett–Packard
8452A spectrometer. Elemental analyses were performed
by the University of Illinois microanalytical service. Tolu-
ene, diethyl ether and hexane were distilled from Na/benzo-
phenone under N2. Dichloromethane was distilled from
CaH2 under N2. Acetonitrile was distilled first from P2O5,
then from CaH2 under N2. Sodium trimethylsilanolate
and pyridinium hydrochloride were sublimed under vac-
uum at 210 oC in a temperature controlled oil bath. Sodium
hydroxide was dried under vacuum at 210 ꢁC for 4 days.
HPLC-grade acetonitrile was obtained from Fisher Scien-
tific. The compounds [N(n-Bu4)][Ru(N)Cl2Me2], [PPh4]-
[Ru(N)Cl2Me2] [9], and PdCl2(ꢀ)-sparteine [10], were
prepared according to literature procedure.
C6D6) d 26.5 (s, P(C6H5)4). IR (KBr pellet cmꢀ1) 3607 (s,
mO–H), 3421 (wb, mO–H), 3055 (w, m-arC–H), 2968 (w,
mC–H), 2882 (w, mC–H), 1590 (w, mC@C) 1483 (s, mC@C),
1437 (s, mC@C), 1193 (s, dipO–H), 1119 (s, dipC–H),
1096 (s, mRu„N), 882 (w), 721 (s, doopC–H), 694
(s, doopC–H), 539 (s). UV–visible (e): 212 nm (37 945),
252 nm (70 491), 286 nm (350 727), 378 nm (46 104). Anal.
Calc. for C26H28NO2PRu11/2NaOH: C, 53.98; H, 5.14; N,
2.42. Found: C, 53.47; H, 4.43; N, 2.54.
2.3. Preparation of [PPh4][Ru(N)Me2(l2-O)2Pd((ꢀ)-
sparteine)] (5)
A solution of [PPh4][Ru(N)(OH)2Me2] (0.022 g, 0.042
mmol) in 2 mL of diethyl ether at ꢀ30 ꢁC was added drop-
wise to a solution of Pd(OSiMe3)((ꢀ)-sparteine) (0.022 g,
0.042 mmol) that was also cooled to ꢀ30 ꢁC. The reaction
mixture was stirred for 1 h at room temperature, then fil-
tered, and the solvent was removed from the filtrate under
vacuum. The residue was crystallized from CH2Cl2/ether.
2.1. Preparation of Pd(OSiMe3)2 ((ꢀ)-sparteine) (2)
To a solution of NaOSiMe3 (0.21 g, 1.89 mmol) in 4 mL
of diethyl ether at ꢀ30 ꢁC was added PdCl2((ꢀ)-sparteine)
(0.194 g, 0.472 mmol). The suspension was stirred as the
reaction was warmed to room temperature. After 1 h, the
mixture was filtered and solvent was removed from the fil-
trate under vacuum. The resulting orange solid was crystal-
lized from ether/hexane at ꢀ30 ꢁC. Yield = 0.170 g
1
Yield = 0.033 g (91.7%) red crystals. H NMR (500 MHz,
CDCl3)
d 7.74–6.93 (m, 20H, P(C6H5)4), 3.11–0.52
(m, 26H, (ꢀ)-sparteine), 1.62 (s, 3H, RuCH3), 1.57 (s,
3H, RuCH3). 13C{1H} NMR (125.7 MHz, CDCl3) d
132.4 (P(C6H5)4), 132.3 (P(C6H5)4), 132.1 (P(C6H5)4),
128.8 (P(C6H5)4), 66.8 ((ꢀ)sparteine-C6), 64.7 ((ꢀ)spar-
teine-C11), 62.2 ((ꢀ)sparteine-C10), 56.5 ((ꢀ)sparteine-
C2), 55.6 ((ꢀ)sparteine-C15), 53.8 ((ꢀ)sparteine-C17),
34.9 ((ꢀ)sparteine-C7), 32.1 ((ꢀ)sparteine-C9), 29.5
((ꢀ)sparteine-C5), 26.2 ((ꢀ)sparteine-C8), 26.1 ((ꢀ)sparte-
ine-C14), 25.1 ((ꢀ)sparteine-C3), 25.0 ((ꢀ)sparteine-C4),
24.9 ((ꢀ)sparteine-C12), 22.8 ((ꢀ)sparteine-C13), 2.0
(RuCH3), 1.8 (RuCH3). 31P NMR (500 MHz, CDCl3) d
29.4. IR (KBr pellet; cm ꢀ1) 3056 (w, m-arC–H), 2940 (s,
mC–H), 2885 (s, mC–H), 1438 (s, mC@C), 1239, 1197, 1119
(s), 1070 (m, mRu„N), 1011, 932, 824, 721 (s, doopC–H),
695 (s, doopC–H), 541. UV–visible (e) 266 nm (8 442),
372 nm (1 947): Calcd for C41H52N3O2PPdRu: C, 57.44;
H, 6.11; N, 4.70. Found: C, 57.02; H, 6.39; N, 4.04. ESI-
MS (CH3CN): m/z 860.2 (M++3H).
1
(0.287 mmol, 67.3%). H NMR (500 MHz, d6-benzene) d
4.03–0.71 (m, 26H, (ꢀ)-sparteine), 0.66 (s, 9H, OSi(CH3)3),
0.64 (s, 9H, OSi(CH3)3). 13C{1H} NMR (125.7 MHz,
d6-benzene) d 69.0 ((ꢀ)sparteine-C6), 64.0 ((ꢀ)sparteine-
C11), 62.0 ((ꢀ)sparteine-C10), 58.2 ((ꢀ)sparteine-C2),
57.7 ((ꢀ)sparteine-C15), 48.5 ((ꢀ)sparteine-C17), 34.7
((ꢀ)sparteine-C7), 34.3 ((ꢀ)sparteine-C9), 30.1 ((ꢀ)sparte-
ine-C5), 27.4 ((ꢀ)sparteine-C8), 26.0 ((ꢀ)sparteine-C14),
24.5 ((ꢀ)sparteine-C3), 24.2 ((ꢀ)sparteine-C4), 23.2
((ꢀ)sparteine-C12), 19.2 ((ꢀ)sparteine-C13), 5.7 (OSi
(CH3)3(A)), 5.6 (OSi(CH3)3(B)). IR (KBr pellet; cmꢀ1
)
2942, 2885 (mC–H), 1474, 1458, 1438, 1253, 1239, 994,
939, 822, 736, 660, 619. UV–visible (e): 248 nm (3 655),
294 (728), 358 (845). Anal. Calc. for C21H44N2O2PdSi2:
C, 48.58; H, 8.54; N, 5.40. Found: C, 48.64; H, 8.90; N,
5.51.
2.4. Mass spectrometry
2.2. Preparation of [PPh4][Ru(N)(OH)2Me2] (4)
A few crystals of 5 were dissolved in HPLC-grade aceto-
nitrile and directly infused into an LCQ Deca electrospray
ionization-ion trap-mass spectrometer at 3 lL/min. The
concentration of the solution was estimated to be
ꢁ100 lM. In order to obtain the optimal signal, the parent
mass was subjected to an automatic lens optimization using
the AutoTune feature of the Xcalibur software. A capillary
voltage of 3.0 V, a tube lens offset of ꢀ60.0 V, a second
octopole offset of ꢀ14.5 V, a first octopole offset of
ꢀ2.75 V, an inter-octopole lens setting of ꢀ74.0 V and an
entrance lens setting of ꢀ76.0 V were found to be optimal.
Sheath and auxiliary gas flow rates of 60 and 30 units,
respectively, were utilized. Lastly, a spray voltage of
4.3 kV and a capillary temperature of 180 ꢁC were used.
To a solution of [PPh4][Ru(N)Cl2Me2] (0.168 g, 0.293
mmol) in 10 mL of diethyl ether was added excess NaOH
(0.150 g, 3.751 mmol) and the orange suspension was stir-
red for 5 h. White solid precipitated from the yellow solu-
tion and this was separated by filtration. Solvent was
removed from the filtrate under vacuum to yield a yellow
1
solid. Yield = 0.101 g, 66.4%. H NMR (500 MHz, C6D6)
d 7.67-6.99 (m, 20H, P(C6H5)4), 1.64 (s, 2H, Ru(OH)2),
1.52 (s, 6H, Ru(CH3)2). 13C{1H} NMR (125.7 MHz, D8-
toluene) d 132.4 (s, PC6H5), 128.8 (s, PC6H5), 127.9
(s, PC6H5), 127.3 (s, PC6H5), 127.2 (s, PC6H5), 126.8
(d, PC6H5), ꢀ0.1 (s, Ru(CH3)2). 31P NMR (500 MHz,

J.L. Kuiper, P.A. Shapley / Journal of Organometallic Chemistry 692 (2007) 1653–1660
1655
A ZoomScan, high resolution profile experiment was per-
formed, averaging 31 scans for the data presented. Simu-
lated spectra of input elemental formulas were created
using the Isotope Viewer feature of the Xcalibur software.
Collisionally-induced dissociation (CID) at 35% collisional
energy and a 3.0 m/z isolation width was performed. Com-
parison of the observed fragments in the CID spectrum to
the full mass spectrum showed that in-source fragmenta-
tion was minimal.
32H, (ꢀ)-sparteine and Ru(N)(CH3)2), 0.28 (s, 1H, CH2@
1
CH–CH2OH), 24 h: H NMR (500 MHz, CDCl3) d 9.80
(t (JHH = 1.4 Hz) 0.10H, CH2CH2CHO) 9.58 (d (JHH
=
7.4 Hz), 0.05H, CH2@CH–CHO), 8.00–7.28 (m, 20H,
P(C6H5)4), 6.00 (m, 0.68H, CH2@CH–CH2OH), 5.30 (dd,
JHH = 10.5, 1.8 Hz, 0.78H, CH2@ CH–CH2OH) 5.30 (dd,
JHH = 10.5, 1.8 Hz, 0.71H, CH2@CH–CH2OH), 4.15 (d,
JHH = 4.9 Hz, 2H, CH2@ CH–CH2OH), 3.56–0.56 (m,
32H, (ꢀ)-sparteine and Ru(N)(CH3)2), 0.28 (s, 1H, CH2@
CH–CH2OH).
2.5. Reaction of 5 and O2 with benzyl alcohol
2.8. Reaction of 5 with allyl alcohol
A sample of 5 (0.011 g, 0.013 mmol) was placed in an
NMR tube along with 1 mL of CDCl3 and capped with a
septum. Benzyl alcohol (1.3 lL, 0.013 mmol) was added
A sample of 5 (0.010 g, 0.012 mmol) was added to an
NMR tube along with 1 mL of CDCl3 and the tube was
capped with a septum. Allyl alcohol (0.9 lL, 0.012 mmol)
was added by syringe and a 1H NMR spectrum was
acquired. The NMR tube was heated at 60 ꢁC for 24 h in a
temperature regulated oil bath. A second 1H NMR spectrum
was acquired. 1H NMR (500 MHz, CDCl3), 0 h: d 7.79–6.93
(m, 20H, P(C6H5)4), 5.78 (m, 1H, CH2@CH–CH2OH), 5.19
(dd (JHH = 17.0, 1.9 Hz), 1H, CH2@CH–CH2OH), 4.93 (dd,
JHH = 10.6, 1.9 Hz, 1H, CH2@CH–CH2OH) 3.86 (d,
JHH = 4.9 Hz, 2H, CH2@CH–CH2OH), 3.56–0.56 (m,
32H, (ꢀ)-sparteine and Ru(N)(CH3)2), 0.28 (s, 1H, CH2@
CH–CH2OH), 24 h: 1H NMR (500 MHz, CDCl3) d 9.80 (t
1
and a H NMR spectrum was acquired. The NMR tube
was purged with O2 for 5 min, then heated at 60 ꢁC for
24 h in a temperature regulated oil bath. A second 1H
NMR spectrum was acquired. 1H NMR (500 MHz,
CDCl3), 0 h: d 10.02 (s, 0.01H, C6H5CHO) 7.68–7.64 (m,
8H, P(C6H5)4), 7.56–7.53 (m, 4H, C6H5CH2OH), 7.48–
7.44 (m, 8H, P(C6H5)4), 7.37–7.36 (m, 6H, P(C6H5)4),
7.29 (s, 1H, C6H5CH2OH), 4.70 (s, 2H, C6H5CH2OH)
4.50–1.23 (m, 32H, (ꢀ)-sparteine and Ru(N)(CH3)2),
24 h: 1H NMR (500 MHz, CDCl3) d 10.03 (s, 0.62H,
C6H5CHO) 8.09–7.28 (m, 21.8H, P(C6H5)4, C6H5CH2OH
and C6H5CH2OH), 4.70 (s, 1H, C6H5CH2OH) 4.52–1.00
(m, 32H, (ꢀ)-sparteine and Ru(N)(CH3)2) 1.20 (s, 1H,
H2O).
(JHH = 1.4 Hz) 0.12H, CH2CH2CHO) 9.58 (d (JHH
=
7.5 Hz), 0.04H, CH2@CH–CHO), 7.91–7.33 (m, 20H,
P(C6H5)4), 6.00 (m, 0.68H, CH2@CH–CH2OH), 5.30 (dd,
JHH = 10.4, 1.8 Hz, 0.78H, CH2 @CH–CH2OH) 5.30 (dd
JHH = 10.4, 1.8 Hz, 0.71H, CH2@CH–CH2OH), 4.15 (d,
JHH = 4.9 Hz, 2H, CH2 @CH–CH2OH), 0.28 (s, 0.60H,
CH2@CH–CH2OH).
2.6. Reaction of 5 and O2 with triphenylphosphine
A sample of 5 (0.008 g, 0.009 mmol) was added to an
NMR tube along with 1 mL of CDCl3 and PPh3 (0.002 g,
0.009 mmol). The tube was capped under N2 and a 31P
NMR spectrum was acquired. The NMR tube was purged
with O2 for 5 min, then heated at 60 ꢁC for 24 h in a tem-
perature regulated oil bath. A second 31P NMR spectrum
was acquired. 31P NMR (500 MHz, CDCl3), 0 h: d 29.4
(s, P(C6H5)4), ꢀ5.4 (s, PPh3), 24 h: 31P NMR (500 MHz,
CDCl3) d 29.5 (s, P(C6H5)4), 23.5 (s, O@PPh3), 17.2 (s,
Ru–PPh3).
2.9. Oxidation of alcohols, Method 1
In the dry box, a sample of 5 (60 mg. 0.070 mmol) was
dissolved in 50 mL of C6D6 (1.4 · 10ꢀ3 M). The solution
was removed from the drybox and anisole (138 lL,
0.350 mmol, 50 equiv) was added as an internal standard.
Next, a reaction tube was equipped with a stir bar and
cap, then charged with 50 equiv of substrate (see
Table 1). A 1 mL aliquot of the solution of 5 was placed
in the reaction tube and a 1H NMR spectrum was acquired.
The reaction mixture was heated to 60 ꢁC with stirring for
24 h, then cooled to room temperature. Another 1H
NMR spectrum was acquired. Results were calculated by
comparison of the integrated values for peaks resulting
from starting materials and products to the integrated val-
ues of peaks resulting from the internal standard, anisole.
2.7. Reaction of 5 and O2 with allyl alcohol
A sample of 5 (0.009 g, 0.010 mmol) was added to an
NMR tube along with 1 mL of CDCl3. The tube was
capped a septum under N2. Allyl alcohol (0.7 lL, 0.010
1
mmol) was added via syringe and a H NMR spectrum
was acquired. The NMR tube was purged with O2 for
5 min, then heated at 60 ꢁC for 24 h in a temperature regu-
1
lated oil bath. A second H NMR spectrum was acquired.
2.10. Oxidation of alcohol and alkene substrates in solution,
Method 2
1H NMR (500 MHz, CDCl3), 0 h: d 7.72–6.94 (m, 20H,
P(C6H5)4), 5.80 (m, 1H, CH2@CH–CH2OH), 5.17 (dd
(JHH = 17.2, 1.8 Hz), 1H, CH2@CH–CH2OH), 4.93 (dd,
JHH = 10.5, 1.8 Hz, 1H, CH2@CH–CH2OH) 3.86 (d,
JHH = 4.9 Hz, 2H, CH2@CH–CH2OH), 3.56–0.56 (m,
A sample of 5 (0.007 g, 8 · 10ꢀ3 mmol) was dissolved in
25 mL chlorobenzene. An aliquot of this solution (2 mL,
6 · 10ꢀ4 mmol catalyst) were added to a mixture of benzyl

1656
J.L. Kuiper, P.A. Shapley / Journal of Organometallic Chemistry 692 (2007) 1653–1660
Table 1
Aerobic oxidations catalyzed by 5, method 1
Substrate
Product
% Conversion
Turnovers
TON (hꢀ1
)
Benzyl alcohol
Benzaldehyde
12.7
12.2
9.1
8.5
7.9
6.4
6.1
4.5
4.3
3.9
3.2
2.3
0.26
0.25
0.19
0.18
0.16
0.13
0.10
4-Methoxybenzyl alcohol
3-Methylbenzyl alcohol
4-Trifluoromethylbenzyl alcohol
4-Methylbenzyl alcohol
4-Chlorobenzyl alcohol
4-Nitrobenzyl alcohol
4-Methoxybenzaldehyde
3-Methylbenzaldehyde
4-Trifluoromethylbenzaldehyde
4-Methylbenzaldehyde
4-Chlorobenzaldehyde
4-Nitrobenzaldehyde
6.5
4.7
Allyl alcohol
Propionaldehyde
Acrolein
2-Octenal
2-Cyclohexanone
Geranial
Cinnamylaldehyde
1-Octen-3-one
30.0
10.5
7.6
15.4
6.3
15.0
5.3
3.8
7.7
3.2
3.3
4.5
0.63
0.22
0.16
0.32
0.13
0.14
0.19
2-Octen-1-ol
2-Cyclohexen-1-ol
Geraniol
Cinnamyl alcohol
1-Octen-3-ol
6.7
9.0
n-Decanol
n-Heptanol
n-Decanal
n-Heptanal
5.8
8.2
2.9
4.1
0.12
0.17
alcohol (50 lL, 0.48 mmol) and anisole (5 lL, 0.018 mmol)
protons and a resonance at 1.5 that integrates to six protons
for the methyl groups. The 13C NMR spectrum of this com-
pound has six resonances between 133 and 128 ppm for the
[PPh4] ion and a single resonance at 4 ppm for the equivalent
methyl carbons. There are absorbances at 3607 and
3421 cmꢀ1 corresponding to the symmetric and asymmetric
O–H stretching vibrations and at 1096 cmꢀ1 for the Ru„N
stretching vibration in the IR spectrum.
in a reaction vessel. To half of the aliquots was added 0.2 g
˚
of 3 A molecular sieves. The reaction mixtures were heated
to between 95 and 100 ꢁC under 1 atm O2 for 20 h, then
cooled in ice. The product mixture were analyzed by gas
chromatography.
3. Results
The reaction between 3 and 4 in a solution of THF/
diethyl ether at room temperature produces Me3SiOH,
Me3SiOSiMe3, and the heterobimetallic compound [PPh4]
[Ru(N)Me2(l2-O)2Pd((ꢀ)-sparteine)], 5 (Scheme 1). Within
10 min, the yellow solution turns dark red. Filtering the
solution and removing solvent from the filtrate gives the
crude product as a red solid. The crude product crystallizes
slowly crystallizes from CH2Cl2 and diethyl ether at
ꢀ30 ꢁC in 63% yield. It is soluble in CDCl3, CH2Cl2,
THF, benzene, CH3CN and toluene and is insoluble in
diethyl ether and hexane.
The palladium compound, PdCl2((ꢀ)-sparteine) 1, results
from the addition of Na2PdCl4 to a stirring solution of
(ꢀ)-sparteine in CH2Cl2 [10]. It reacts with 2 equiv of NaO-
SiMe3 in diethyl ether to produce Pd(OSiMe3)2((ꢀ)-sparte-
ine), 2, in 65–70% yield. The trimethylsiloxy compound is
very soluble in most organic solvents is insoluble in hexane.
It crystallizes from diethyl ether and hexane at ꢀ30 ꢁC as
dark yellow crystals.
Compound 2 is sensitive to water and acids. It is dia-
magnetic in all solvents. The 13C NMR spectrum includes
17 resonances, 15 between 69.0 ppm and 19.2 ppm for
coordinated sparteine and two at 5.7 and 5.6 for the
inequivalent trimethylsiloxy groups. Along with resonances
Along with fives resonances for the carbons of the
[PPh4]+ ion and 15 resonances for carbons of the (ꢀ)-spar-
teine ligand in the 13C NMR spectrum of 5, there are two
resonances for the inequivalent methyl groups at 2.0 and
1.8 ppm. Electrospray ionization-mass spectrometry of this
compound (Fig. 1) shows a singly-charged molecular ion
peak (+ 3H) at 860.1 m/z and the isotopic ratio matches
with the predicted distribution (Fig. 1). There are no peaks
that do not result from 5 in the mass spectrum. Infrared
spectroscopy has key absorbances for the sparteine ligand
C–H stretch at 2940 cmꢀ1 and the ruthenium-nitrido
1
for coordinated (ꢀ)sparteine in the H NMR spectrum,
there are resonances at 0.66 and 0.64 ppm for the inequiv-
alent trimethylsiloxy groups.
The reaction of [PPh4][Ru(N)Cl2Me2], 3, with excess
sodium hydroxide in diethyl ether at ambient temperature
produces the yellow compound [PPh4][Ru(N)(OH)2Me2],
4. The reaction requires 4 h for completion. After filtering
the reaction mixture to remove the NaCl, the product can
be isolated as a yellow oil by concentrating the solution
and adding hexane. Drying the oil under vacuum forms a
glassy yellow solid. The solid contains some sodium hydrox-
ide and analyzes as [PPh4][Ru(N)(OH)2Me2]11/2 NaOH.
stretch at 1119 cmꢀ1
.
The Ru/Pd heterometallic compound oxidizes both
benzyl alcohol and triphenylphosphine in 60 ꢁC in the
presence of O2. We monitored the reaction of 5 and
1 equiv of benzyl alcohol in CDCl3 under one atmo-
sphere of oxygen by 1H NMR spectroscopy. After
24 h, the benzyl alcohol had been completely converted
1
The H NMR spectrum of 4 contains resonances between
7.7 and 7.0 ppm that integrate to 20 protons for the PPh4
ion as well as a broad resonance at 1.6 ppm for the hydroxyl

J.L. Kuiper, P.A. Shapley / Journal of Organometallic Chemistry 692 (2007) 1653–1660
1657
Cl
Cl
N
N
N
Pd
Ru
Cl
H3C
H3C
Cl
1
3
- 2 NaCl
2 NaOSiMe3
2 NaOH - 2 NaCl
N
N
Ru
O
- 2 HOSiMe3
O
O
N
N
N
N
Si
+
Pd
Pd
Ru
OH
OH
H3C
H3C
H3C
H3C
O
Si
5
4
2
Scheme 1.
Fig. 1. Electrospray mass spectrum of 5.
to benzaldehyde and water and the concentration of 5
was unchanged from its original concentration. Under
the same reaction conditions, we monitored the conver-
sion of PPh3 to O–PPh3 by 5 in O2 by 31P NMR spec-
troscopy. After 24 h the resonance for PPh3 had
completely disappeared and was replaced by a resonance
for O–PPh3. There was also a very small peak at
17.2 ppm in the spectrum which could correspond to a
tallic compound decomposed to an insoluble black solid in
the presence of allyl alcohol.
We investigated the catalytic oxidation of aryl, allylic,
and primary by O2 in the presence of 5. The standard reac-
tion conditions were 24 h reaction time at 60 ꢁC, in air with
2 mol % catalyst, in C6D6 with anisole as an internal stan-
1
dard. The products were analyzed by H NMR spectros-
copy (Table 1).
metal–phosphine compound as
reaction.
Interestingly, treatment of allyl alcohol with 5 and O2
produced propionaldehyde, a rearrangement product, as
well as acrolein, the oxidation product, in a ratio of 2:1
by 1H NMR spectroscopy. In the absence of air, the bime-
a
byproduct in the
Similar to other Pd-containing aerobic oxidation cata-
lysts, the catalytic oxidation of alcohols is very sensitive
to temperature and the presence of water in the solution.
At 60 ꢁC under O2, compound 5 converts only 6.4 equiv
of benzyl alcohol to benzaldehyde in a 20 h period. At
95 ꢁC, 21 turnovers of benzaldehyde are produced and, in
O
O
+
5 , O2
5 , O2
OH
1:2
PPh3
OH
O=PPh3
5
O
+ H2O
+ 1/2 O2
95 ˚C, 3Å molecular sieves
Scheme 2.

1658
J.L. Kuiper, P.A. Shapley / Journal of Organometallic Chemistry 692 (2007) 1653–1660
˚
the presence of 3 A molecular sieves to scavenge the water
produced in the reaction, 53 turnovers of benzaldehyde are
produced (Scheme 2).
ligands is very soluble in non-polar organic solvents. In
the synthesis, one hydroxyl group from 4 may react with
2 in a concerted fashion, forming the intermediate [PPh4]-
[Ru(N)(OH)Me2(l-O)Pd(OSiMe3)((ꢀ)-sparteine)] and an
equivalent of trimethylsilanol. The new, bridged interme-
diate is set for a second displacement reaction, forming
the l-dioxo heterometallic compound and another mole-
cule of trimethylsilanol. Two molecules of trimethylsilanol
rapidly condense and produce hexamethyldisiloxane and
an equivalent of water (Scheme 4). The bimetallic
[PPh4][Ru(N)Me2(l2-O)2Pd((ꢀ)-sparteine)] is favored over
the trimetallic {Ru(N)Me2}(l3-O)2{Pd((ꢀ)-sparteine)}
even with an excess quantity of the palladium precursor
probably because of the steric bulk of the chelating spar-
teine ligand.
4. Discussion
Because the sulfido ligands groups in {Ru(N)Me2}-
(l3-S)3{Pd(dppe)} were sensitive to oxidizing conditions,
an improved heterometallic oxidation catalyst would have
bridging oxo groups in place of the sulfido groups. Initially,
we tried to synthesize the l-O analog by substituting
Pd(dppe)(OSiMe3)2 for Pd(dppe)(SSiMe3)2 in the reaction
with [PPh4][Ru(N)Me2Cl2] but this was not successful
(Scheme 3).
The formation of the l-sulfido compound is favored
because the more stable Cl–Si bond forms as the S–Si bond
breaks. However the energy difference between the Cl–Si
bond (90 kcal/mol) and the O–Si (110 kcal/mol) bond dis-
favors formation of the l-oxo by this route.
Nuclear magnetic resonance spectra show that the chiral
(ꢀ)-sparteine ligand on palladium influences the symmetry
of the heterometallic compound. The methyl groups on the
1
ruthenium in 5 are inequivalent in the H and 13C NMR
spectra. Because of the asymmetry of the Pd(ꢀ)-sparteine
compound 2, the reaction between 2 with 4 could form
two diastereomers but we observe only one of them by
13C NMR spectroscopy.
Better precursors to a new heterometallic oxygen-
bridged compound are [PPh4][Ru(N)(OH)2Me2] and Pd-
(OSiMe3)2((ꢀ)-sparteine) which react cleanly to form 5.
This compound with large, organic diamine and alkyl
N
CH3
Ru
N
CH3
S
L
- 2 ClSSiMe3
Me3Si
+
+
Pd
Pd
Ru
S
Cl
Cl
L
H3C
H3C
L
L
S
Pd
S
Cl
N
Me3Si
Ru
N
H3C CH3
O
O
L
Me3Si
Ru
NO REACTION
L
H3C
H3C
Cl
Me3Si
Scheme 3.
Me3SiO
Me3SiO
N
N
Me3SiO
Me3SiO
N
Pd
HO
Pd
N
Me3SiO
N
N
Pd
HO
O
HO
O
O
H
H
N
Ru
Me
Me
N
Ru
+ HOSiMe3
Ru
N
Me
Me
Me
Me
N
N
N
N
O
N
=
Ru
Pd
+ HOSiMe3
Me
Me
N
O
N
2 HOSiMe3
H2O + Me3SiOSiMe3
Scheme 4.

J.L. Kuiper, P.A. Shapley / Journal of Organometallic Chemistry 692 (2007) 1653–1660
1659
Electrospray ionization-mass spectrometry data for
compound 5 confirms its composition. The ESI-MS spec-
trum shows an envelope of singly-charged peaks with an
average mass of 860.1 m/z, closely matching the predicted
isotopic distribution for C41H55N3O2PPdRu + 3H as seen
in Fig. 1. The nearly identical appearance of the isotopic
distribution between the observed and predicted compound
both in terms of the intensity distribution and mass match
provide exceptionally strong evidence that the compound
of interest formed. Also, the full mass spectrum from 75
to 2000 m/z demonstrates that the compound is very pure
relative to volatile material with a mass greater than
75 Da. Other peaks in the spectrum correspond to the
counter-ion, [PPh4] (e.g. m/z 339.4) and in-source frag-
ments (e.g. m/z 795.3, 706.5).
In-source fragments were identified through analysis of
a collisionally-induced dissociation, or MS/MS, spectrum
of the molecular ion using 35% collisional energy and an
isolation width of 3 m/z. Collectively, this data illustrates
the power of mass spectrometric techniques for assessing
the identity of organometallic compounds as well as rela-
tive purity of the compound solution. Even when mass
spectrometry is not coupled a with separation technique,
can be a measure of purity [11]. However, non-volatile
impurities (i.e. silica, glass) may not be ionized. Even
though mass spectrometry is an information-rich analytical
technique, few research groups currently use mass spec-
trometry as a method for identification of inorganic and
organometallic compounds [12].
Compound 5 oxidizes alcohols, with a preference for
benzylic and allylic alcohols. The turnover number for
the oxidation of benzyl alcohol is much higher when molec-
ular sieves are added to remove water as it is formed. The
competition between rearrangement and oxidation of allyl
alcohol suggests that oxidation reactions of alcohols occur
with alcohol binding to the ruthenium center. Compound 5
includes both ruthenium(VI) and palladium(II) centers that
are each capable of oxidizing an alcohol [13]. Coordination
of the hydroxy group of allyl alcohol to the ruthenium cen-
ter allows the C–C double bond to interact with the neigh-
boring palladium(II) center and rearrange through a
palladium-allyl intermediate [14]. If the alcohol initially
coordinated to the palladium, a rearrangement of the
alkene at the ruthenium(VI) center would be unlikely.
preferentially oxidizes allyl and aryl alcohols. Likely, coor-
dination occurs at the ruthenium center as indicated by the
allylic rearrangement.
Acknowledgements
We gratefully acknowledge the financial support of the
Donors of The Petroleum Research Fund, administered
by the American Chemical Society (ACS-PRF 36240-
AC). NMR spectra were obtained in the Varian Oxford
Instrument Center for Excellence in NMR Laboratory.
Funding for this instrumentation was provided in part
from the W. M. Keck Foundation, the National Institutes
of Health (PHS 1 S10 RR10444-01), and the National
Science Foundation (NSF CHE 96-10502). Purchase of
the Siemens Platform/CCD diffractometer by the School
of Chemical Sciences was supported by National Science
Foundation grant CHE 9503145.
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1660
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