Cyclooctene epoxidation with H2O2 and single crystal X-ray determined crystal structures of new molybdenum and tungsten catalysts bearing the hydrophilic ligand hydroxymethyldiphenylphosphine oxide

Article abstract of DOI:10.1016/j.jorganchem.2007.11.018

The dioxo molybdenum and tungsten complexes MoO₂Cl₂(OPPh₂CH₂OH)₂ and WO₂Cl₂(OPPh₂CH₂OH)₂ have been synthesized and characterized by FT-IR, ¹

Full text of DOI:10.1016/j.jorganchem.2007.11.018

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1564–1571
www.elsevier.com/locate/jorganchem
Cyclooctene epoxidation with H O and single crystal X-ray
2
2
determined crystal structures of new molybdenum and
tungsten catalysts bearing the hydrophilic ligand
hydroxymethyldiphenylphosphine oxide
Linsheng Feng, Eugenijus Urnezius, Rudy L. Luck *
Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA
Received 29 September 2007; received in revised form 10 November 2007; accepted 10 November 2007
Available online 21 November 2007
Dedicated to the memory of Professor F.A. Cotton. Labor omnia vincit.
Abstract
The dioxo molybdenum and tungsten complexes MoO
2 2 2 2 2 2 2 2 2 2
Cl (OPPh CH OH) and WO Cl (OPPh CH OH) have been synthesized and
1
31
characterized by FT-IR, H and P NMR. Their structures, as determined by single crystal X-ray diffraction analysis, reveal distorted
octahedral geometries with cis terminal oxygen atoms, trans Cl ligands and that the hydroxymethyldiphenylphosphine oxide ligands
coordinate through the oxygen atom bonded to the P atom. Both of the compounds are studied as catalysts for the epoxidation of
cis-cyclooctene in the presence of hydrogen peroxide as a source of oxygen. Both complexes showed good activity and very high selec-
tivity for the formation of cyclooctene oxide.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Molybdenum oxide; Tungsten oxide; Olefin epoxidation; Hydrogen peroxide; Crystal structures; Catalysis
1
. Introduction
oxides such as MO Cl (OPR ) (M = Mo or W; OPR =
2 2 3 2 3
OPMePh , OPPh ), MO Cl (dppmO ) (M = Mo or W)
2
3
2
2
2
Over the past decades, direct oxidation of olefins using
are good catalysts for the epoxidation of olefins using
tert-butyl hydroperoxide (TBHP) or hydrogen peroxide
as the source for oxygen [4e,4k,4l,4m]. Hydrogen peroxide
is constructive because of its unique features and advanta-
ges such as high atom-efficiency and that the byproduct
oxidants such as hydrogen peroxide, oxygen and alkyl
hydroperoxide in the presence of high-valent transition-
metal catalysts have been used to produce epoxides [1].
Complexes of transition-metals such as rhenium [2], vana-
dium [3], molybdenum [2f,2g,4], manganese [5], tungsten
(H O) is environmentally benign [10]. Consequently,
2
[
4e,6], selenium [7], platinum [8] and titanium [9] have been
metal-catalyzed epoxidation systems have been developed
recently using hydrogen peroxide as oxidant [8,10b,10c,
10d,10e].
Hydroxymethyldiphenylphosphine oxide has been
examined by X-ray crystallography to reveal a hydrogen
bonded dimeric arrangement involving the hydrogen atom
on the hydroxyl group of one molecule interacting with the
P@O group on the adjacent molecule and vice versa [11].
One example of its coordinating capability is displayed in
the crystal structure of the zirconium compound
examined as catalysts for epoxidation. In particular,
molybdenum and tungsten complexes have been widely
investigated because of their demonstrated high activity
for selective oxidation [4,6].
We have previously reported that molybdenum and
tungsten compounds containing a series of phosphine
*
Corresponding author.
E-mail address: rluck@mtu.edu (R.L. Luck).
0
022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.11.018

L. Feng et al. / Journal of Organometallic Chemistry 693 (2008) 1564–1571
1565
oxidizing the THF solution of diphenylphosphinyl–metha-
nol with 30% H O at room temperature; the spectroscopic
2
2
data obtained is in agreement with that previously reported
3
1
H
2
C
O
OH
[
13b]. Yield: 97%. M.p.: 138–140 °C. P NMR (CDCl3):
1
d = 31.6 ppm. H NMR (400 MHz, CDCl ): d = 4.40 (s,
2H), d = 5.25 (s, 1H). IR (neat, cm ): 3675 m, 3200 m,
P
3
Cl
ꢀ1
O
2988 s, 2901 m, 1437 m, 1120 m, 1052 s, 851 m, 740 s,
M
O
718 s, 691 s.
O
Cl
P
OH
C
H
2
2.2.2. Synthesis and characterization of
MoO Cl (OPPh CH OH) (1)
2
2
2
2
2
Lead molybdate (0.92 g, 2.5 mmol) was moistened with
.0 ml dichloromethane, and then acetyl chloride (2.3 ml)
1
was added to the suspension. The mixture was stirred for
0 min. A brown solution was obtained after filtration. A
solution of hydroxymethyldiphenylphosphine oxide
5.0 mmol, 0.80 g) in 5 ml dichloromethane was added to
1
(M=Mo), 2 (M=W)
3
Fig. 1. Representation of compounds synthesized.
(
the above brown solution. The resulting gold yellow solu-
tion was stirred overnight at room temperature and then
concentrated under vacuum. An oily product resulted after
diethyl ether was added to the above solution. A yellow
precipitate was subsequently obtained after the addition
of benzene to the oily product. This yellow compound
was separated by filtration and dried under vacuum at
room temperature. Yield: 1.08 g (65%). Anal. Calc. for
C H Cl O P Mo ꢁ 1.5C H : C, 48.37; H, 4.06. Found:
Cp Zr(C(SiMe )CHSiMe )(OCH P(O)Ph ) where the
2
3
3
2
2
ligand coordinates through the hydroxyl oxygen atom
12]. These type of ligands can be described as functional-
[
ized hydrophilic phosphines, for which related derivatives
have been studied during the past decades [13]. They are
expected to be good ligands for organometallic catalysts
since they combine the bonding attributes of phosphine
oxide ligands with the increased solubility in polar solvents
of hydrophilic alcohols [14].
2
6
26
2
6
2
6
6
3
1
C, 48.60; H, 4.03%. M.p.: 113–115 °C. P NMR (CH Cl ):
2
2
Herein, we report on the synthesis, characterization and
catalytic capabilities of molybdenum and tungsten com-
pounds 1 and 2 bearing the hydrophilic phosphine oxide
ligand Ph P(O)CH OH coordinated via the oxygen atom
1
d = 43.8 ppm. H NMR (400 MHz, CDCl ): d = 3.57 (s,
1
3
ꢀ
1
H), d = 4.61 (s, 2H), d = 7.34–7.81 (m, 10H). IR (cm ):
3457 m, 1437 s, 1125 s, 998 m, 941 s (Mo@O), 901 s
2
2
(Mo@O), 739 s, 725 s, 687 s.
bonded to the phosphorus atom as represented in Fig. 1.
2
. Experimental
2.2.3. Synthesis and characterization of
WO Cl (OPPh CH OH) (2)
2
2
2
2
2
2
.1. General method
A solution of (Me Si) O (0.21 g, 1.25 mmol) in 2.5 ml of
3 2
dichloromethane was added to a suspension of WCl6
(0.50 g, 1.25 mmol) in 2.5 ml of dichloromethane. The
resulting suspension was stirred vigorously at ambient tem-
peratures for 1 h. A solution of Ph P(O)CH OH (0.52 g,
Infrared spectra were obtained on a PerkinElmer Spec-
1
31
trum One FT-IR spectrometer. H and P NMR data were
recorded on a Varian XL-400 spectrometer referenced to
CDCl3 or acetone-d6 and 85% H PO , respectively. A
2
2
3.25 mmol) in 2.0 ml dichloromethane was then added to
the above solution and stirred for 30 min; the addition
resulted in an immediate color change from orange to yel-
low. To this yellow solution 0.22 g (Me Si) O in 2.0 ml
3
4
Fisher–Johns melting point apparatus (Fisher Scientific
Company) was used for the melting point determinations.
A Shimadzu QP5050 GC–MS was used for the mass spec-
tra determinations and quantitative analysis for the epoxi-
dation reactions. The elemental analysis data were
obtained from Galbraith Laboratories, Inc. Solvents were
used as received from commercial suppliers. Most chemi-
cals were purchased from Aldrich, and all chemicals were
used as received.
3
2
dichloromethane was added and the mixture stirred over-
night at room temperature resulting in a yellow green solu-
tion. The solution was concentrated under vacuum. A light
blue precipitate formed after diethyl ether was added to the
solution slowly. This product was obtained by filtration
and dried under vacuum overnight. Yield: 0.70 g (75%).
Anal. Calc. for C H Cl O P W ꢁ 0.25CH Cl : C, 40.82;
2
6
26
2
6
2
2
2
2
2
.2. Synthesis and characterization
H, 3.46. Found: C, 40.98; H, 3.57%. M.p.: 158–160 °C.
31 1
P NMR (CH Cl ) d = 45.6 ppm. H NMR (400 MHz,
2
2
.2.1. Synthesis and characterization of Ph P(O)CH OH
2
acetone-d ): d = 2.88 (s, 1H), d = 4.80 (s, 2H), d = 7.51–
6
2
ꢀ1
Diphenylphosphinyl–methanol was synthesized accord-
ing to a previously published procedure [15]. Hydroxy-
methyldiphenylphosphine oxide was prepared by
7.98 (m, 10H). IR (cm ): 3372 w, 3278 w, 1437 s, 1123
s, 997 m, 951 s (W@O), 892 s (W@O), 849 m, 736 m, 722
s, 686 s.

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L. Feng et al. / Journal of Organometallic Chemistry 693 (2008) 1564–1571
2
.3. Preparation of single crystals
pounds
triphenylphosphine
bearing
diphenylmethylphosphine
oxide and dppmO2
oxide,
ligands
X-ray quality crystals were obtained by the solvent lay-
[4e,4k,4l,4m,21]. We have now extended this to Mo and
W compounds containing the hydroxymethyldiphenyl-
phosphine oxide ligand. This ligand may afford a higher
catalytic property for olefin epoxidation in polar solvents
which is important if we are to take advantage of using
hydrogen peroxide. It is also noteworthy that in the studies
of the mechanism of olefin epoxidation, of the two mecha-
nisms proposed, i.e., prior binding of the olefin to the metal
followed by oxygen transfer [22] and direct transfer of the
distal oxygen atom in a bonded peroxide group to the ole-
fin [23], recent studies point out that while the latter mech-
anism is favored, intermediates, which involve binding of
the olefin to the metal center, may well be formed, even
though they do not contribute to the epoxidation reaction
directly [24]. With these considerations in mind, a catalyst
which has more solubility in ethanol should be able to
function more effectively irrespective of which mechanism
accomplishes the oxygen transfer.
ering method. Compound 1 was dissolved in dichlorometh-
ane in a crystallizing tube, and a layer of benzene was
added carefully. The tube was sealed and left undisturbed
at room temperature for about a week resulting in X-ray
quality crystals around the boundary layer. Crystals of 2
were prepared in an identical manner except that diethyl
ether was used as the upper solvent.
2
.4. X-ray crystallography
Suitable crystals were selected, rolled in epoxy resin and
mounted on glass fibers. An Enraf Nonius CAD-4 X-ray dif-
fractometer was used to collect the data. Final cell constants
and orientation matrix were obtained by collecting appropri-
ate preliminary data, selecting 25 reflections, centering and
refinement by a least squares fit. Mo Ka radiation
˚
(
k = 0.71073 A) was used for data collection. The proce-
dures used to collect the data, solve and refine the structure
were as detailed previously for other complexes [16]. The
Windows program WINGX was used as the interface for the
solution and refinement of the models [17]. The data were
solved using the program SIR97 [18]. The models, with H
atoms at calculated positions with their thermal parameters
constrained to be 1.2 or 1.5 times the isotropic equivalent of
the C or O atoms respectively to which they are bonded, were
refined to convergence using SHELXL97 [19]. Complex 1 con-
tained disorder in the position of the hydroxy oxygen atom
for one of the OPPh CH OH ligands and in the occupancy
The dioxomolybdenum compound 1 was synthesized by
slight modifications to the procedure for the synthesis of
the related complex MoO Cl (OPPh Me) [21]. Complex
2
2
2
2
1 can be isolated as a yellow precipitate if the sticky prod-
uct obtained upon removal of reaction solvent is stirred in
benzene at room temperature. We also attempted to make
the dioxotungsten compound 2 using the published proce-
dure [21] for WO Cl (OPPh Me) but this was not success-
2
2
2
2
ful. A mixture of products believed to consist of
WO Cl (OPPh CH OH) and WO(O) Cl (OPPh
CH OH) was obtained in low yields. The dioxotungsten
2
2
2
2
2
2
2
2-
2
2
2
2
and position of a benzene molecule of solvation. This was
accounted for using standard refinement procedures [20].
Complex 2 was ordered.
compound 2 was made by modification to the procedure
for WO Cl (DME) [25]. A pale light blue precipitate was
2
2
obtained upon the addition of diethyl ether to the reaction
mixture in dichloromethane which was further purified into
white crystals after filtration and recrystallization from a
dichloromethane/ether solvent mixture.
2
.5. Catalytic reactions using H O as oxidant
2 2
The reactions were carried out under an open atmosphere
The spectroscopic data for compounds 1 and 2 were
assessed by FT-IR and NMR spectroscopy ( H, P). Com-
1
31
using a two-necked 25 ml round bottom flask equipped with
a reflux condenser and a magnetic stirrer. In a typical exper-
iment, 0.200 g (1.82 mmol) of cis-cyclooctene, 1 mol% cata-
pound 1 contained two strong m(Mo@O) absorption bands
ꢀ
1
ꢀ1
at 941 cm and 901 cm . The equivalent to this for com-
ꢀ2
ꢀ1
ꢀ1
lyst (1.82 ꢂ 10 mmol) in 2.0 mL ethanol, 0.28 ml of 30%
plex 2 was shifted to 951 cm
and 892 cm . These
H O (2.72 mmol, 1.5 equiv) and 0.100 g n-decane
absorptions are in the same range for related compounds
of the form MO Cl (OPR ) , M = Mo or W [4e], and sim-
2
2
(
0.703 mmol) as internal standard were added to initiate
2
2
3 2
the reaction. The reaction was then heated to 70 °C for a spe-
cific time. Samples were taken periodically and analyzed by a
Shimadzu QP5050 GC–MS. The conversion of cyclooctene
and the selectivity to cyclooctene oxide were calculated using
calibration curves recorded prior to the reaction.
ilarly located strong absorptions were previously assigned
to the symmetric and asymmetric stretching vibrations
for the metal oxygen double bonds [26]. The m(P@O)
absorption bands shifts to higher frequencies at
ꢀ1
ꢀ1
1125 cm and 1123 cm for the compounds 1 and 2,
ꢀ
1
respectively compared to 1120 cm for the free ligand.
3
. Results and discussion
Interestingly, complexes containing the OPPh Me ligand
2
ꢀ
1
revealed a shift to lower frequencies, i.e., 1171 cm in
ꢀ
1
3.1. Synthesis and spectroscopic characterization of
dioxomolybdenum and dioxotungsten compounds
the free ligand compared to 1155–1152 cm in the Mo
and W analogues [4e]. The difference in the initial shifts
of the free ligands, i.e., m(P@O) in O@PPh CH OH at
2
2
ꢀ
1
We have previously reported on the syntheses and char-
acterization of dioxomolybdenum and dioxotungsten com-
1120 cm
compared to m(PO) in O@PPh CH at
2
3
ꢀ1
1171 cm , is due to the existence of O@PPh CH OH as
2
2

L. Feng et al. / Journal of Organometallic Chemistry 693 (2008) 1564–1571
1567
a hydrogen bonded dimer [11] which would lower the
Table 1
Details of the structural refinement for 1 and 2
stretching frequency of the P@O bond.
The H atoms on the OH and CH groups in the free
1
2
2
ligand appear as broad singlets at 5.25 and 4.40 ppm,
respectively. The resonance for the H atom in the OH moi-
ety for compound 1 and 2 was observed shifted upfield
greatly to 3.57 and 2.88 ppm, respectively. This increased
shielding is probably due to the removal of the H-bonded
interactions as the free ligand may also exist in solution
Formula
(C13H13O P) O Cl - (C13H13O P) -
2
2
2
2
2
2
Mo0.5C
702.3
6
H
6
O
751.16
2
Cl
2
W
Formula weight
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
P21/c
˚
Radiation (Mo) (A)
0.71069
9.248(3)
15.562(4)
21.490(6)
90
0.71069
9.494(3)
14.467(2)
20.805(8)
90
˚
a (A)
˚
as a dimer. In contrast, the resonance for the CH group
b (A)
2
˚
c (A)
in compounds 1 and 2 shifted downfield only slightly to
a (°)
b (°)
c (°)
4
.61 and 4.81 ppm, respectively.
96.66(2)
90
99.22(3)
90
3
1
P NMR spectroscopy is very useful in assessing the
˚
3
composition and purity of compounds bearing phosphorus
V (A )
3071.9(15)
4
2820.6(15)
4
atoms [27]. Similar to OPPh Me at 30 ppm [4e], the reso-
Z
2
Reflections collected/unique
[R ]
int
Data/restraints/parameters
Completeness to
4664/3995 [0.0159]
3939/3677 [0.0108]
nance for the
P
atom in the free ligand, i.e.,
O@PPh CH OH, was found at 31.6 ppm (relative to 85%
2
2
3995/0/395
100.0
3677/0/334
100.0
H PO ). This resonance for the P atom in compounds 1
3
4
and 2 shifts downfield to 43.8 and 45.6 ppm, respectively
due to coordination via the O atom (bonded to the P atom)
to the metal. A similar downfield shift was also observed
for the related MO Cl (OPPh Me) , M = Mo or W com-
pounds [4e]. The single resonance suggests that the P atoms
are magnetically equivalent in these compounds at least in
solution.
theta = 22.47 (%)
a
a
Absorption correction
w-scan
1.519
0.745
w-scan
1.769
4.437
3
d
calc (g/cm )
ꢀ
1
l (mm
h (°)
k (A)
)
2
2
2
2
1.62–22.48
0.71073
293(2)
1.054
1.72–22.47
0.71073
293(2)
1.050
˚
T (K)
Goodness-of-fit
b
c
d
e
R
1
,
wR
2
(I > 2r(I))
0.0262, 0.0687
0.0204, 0.0437
a
b
c
3
.2. X-ray crystallographic data
Ref. [28].
P
P
R1 ¼
kF oj ꢀ jF ck= jF oj.
P
P
2
o
2
c
2
2
2 1=2
o
wR2 ¼ ½ ½wðF ꢀ F Þ ꢃ= ½wðF Þ ꢃꢃ
.
Crystals were grown as described in the experimental
2
d
e
2
2
2
2
w ¼ 1=½ ðF Þ þ ð0:0338PÞ þ 2:5648Pꢃ; where P ¼ ðF þ 2F Þ=3.
o
o
c
section. Crystal data and details of structural refinement
are listed in Table 1. Selected bond lengths and angles of
compound 1 and 2 are given in Table 2.
2
2
o
2
2
o
2
c
w ¼ 1=½ ðF Þ þ ð0:0212PÞ þ 2:6767Pꢃ; where P ¼ ðF þ 2F Þ=3.
˚
tance of 2.358(3) A. This interaction may be responsible for
the significantly longer bond length in Mo1–O2 of
1.764(2) A as compared to a Mo1–O1 bond distance of
1.732(2) A. The second intramolecular H-bond consists of
the OH group on the adjacent phosphine oxide ligand
and one of the terminal Cl ligands resulting in an O5–Cl2
˚
distance of 3.157(3) A and a H5–Cl2 distance of
2.378(1) A, see Fig. 2. This interaction may also be respon-
sible for the significantly longer Mo1–Cl2 distance of
2.4263(11) A compared to the Mo1–Cl1 distance of
2.3875(11) A. An inspection of the crystal packing does
3
.2.1. Crystal structure of MoO Cl (OPPh CH OH) (1)
2 2 2 2 2
An ORTEP-3 [29] drawing of 1 is shown as Fig. 2. This
˚
˚
crystal contains a disordered benzene molecule of crystalli-
zation that was slowly evaporating out of the crystal lattice
as evident by the reduction in the intensity standards to
9
5%. The geometry about the molybdenum atom is dis-
˚
torted octahedral with two Cl-atoms trans to each other
(
Cl1–Mo1–Cl2 = 166.43(3)°) and the two oxo-oxygen
˚
˚
atoms (O1, O2 or Ooxo) cis to each other. The two oxygen
atoms of the hydroxymethyldiphenylphosphine oxide
ligands (O ) are thus also cis to each other with an O3–
not reveal any intermolecular bonding interactions. It is
possible that the presence of the benzene molecules of sol-
vation within the crystal hinder this development as these
interactions were observed in the structure of the related
compound 2, see below.
lig
Mo1–O4 angle of 78.58(8)°. These four oxygen atoms are
located in a distorted equatorial plane. The bond distance
˚
for Mo@Ooxo is within the expected range of 1.66–1.76 A
[
30]. The P–O bond lengths and P–O–Mo angles are also
similar to that measured for other phosphine oxide ligands
binding to Mo atoms [4e,4k,4m].
3.2.2. Crystal structure of WO Cl (OPPh CH OH) (2)
2
2
2
2
2
The molecule also contained disorder in the position of
one OH group on one ligand which refined to a 50:50 ratio
and P1–C11–O6 and P1–C11–O61 angles of 116.8(3)° and
An ORTEP-3 [29] representation of 2 is shown in Fig. 3.
The tungsten atom is in a distorted octahedral environment
in which the two chlorides are in trans positions and the
two terminal oxygen atoms are cis to each other. The inner
core arrangement of 2 is similar to 1 except that there is no
disorder in the structure of 2 and the phosphine oxide
ligand exhibits a slightly different rotational conformation.
1
10.6(4)°, see Fig. 2. There appeared to be two intramolec-
ular H-bonds within the molecule. One of these involves
the disordered O atom O61 and the terminal oxo O2 atom
˚
with a O61–O2 distance of 3.140(7) A and an H61–O2 dis-

1568
L. Feng et al. / Journal of Organometallic Chemistry 693 (2008) 1564–1571
Table 2
˚
Selected bond length (A) and angles (°) for 1 and 2
1
2
M1–Cl1
M1–Cl2
M1–O1
M1–O2
M1–O3
M1–O4
P1–O3
P1–C11
P1–C111
P1–C121
P2–O4
P2–C21
P2–C211
P2–C221
O5–C21
O6–C11
O61–C11
2.3875(11)
2.4263(11)
1.732(2)
1.764(2)
2.198(2)
2.154(2)
1.505(2)
1.847(3)
1.794(3)
1.799(3)
1.508(2)
1.816(4)
1.795(3)
1.795(3)
1.411(4)
1.317(5)
1.288(7)
2.3646(12)
2.3661(12)
1.698(3)
1.724(3)
2.230(3)
2.118(3)
1.503(3)
1.821(5)
1.790(5)
1.793(5)
1.503(3)
1.819(4)
1.788(4)
1.794(4)
1.418(5)
1.408(6)
Fig. 3. ORTEP-3 [29] representation of 2 with selected atom numbering.
Thermal ellipsoids are drawn at the 50% probability level and hydrogen
atoms are represented by circles of arbitrary radii. The H-bonded
interaction is illustrated by dashed lines.
Cl1–M1–Cl2
Cl1–M1–O1
Cl1–M1–O2
Cl1–M1–O3
Cl1–M1–O4
Cl2–M1–O1
Cl2–M1–O2
Cl2–M1–O3
Cl2–M1–O4
O1–M1–O2
O1–M1–O3
O1–M1–O4
O2–M1–O3
O2–M1–O4
O3–M1–O4
M1–O3–P1
M1–O4–P2
P1–C11–O6
P1–C11–O61
O61–C11–O6
P2–C21–O5
166.43(3)
95.08(10)
94.85(9)
84.42(6)
85.04(6)
94.49(10)
92.66(9)
84.37(6)
162.83(4)
96.53(11)
94.36(11)
84.61(8)
The bond distances for W@O, W–Cl and W–O atoms are
similar to those reported previously for related complexes
82.73(8)
94.97(11)
95.89(11)
82.30(8)
[
4e,4k,25,30,31].
Complex 2 exhibits one intramolecular H-bonded inter-
action between one OH moiety (i.e., O6) and the terminal
85.26(6)
83.60(8)
˚
oxo O2 with an O6–O2 distance of 2.755(5) A and an
101.46(12)
169.12(10)
90.55(10)
89.40(10)
167.94(10)
78.58(8)
147.19(13)
157.56(13)
116.8(3)
101.09(16)
172.17(13)
95.05(13)
86.52(13)
163.83(13)
77.39(10)
141.74(16)
163.37(18)
110.8(3)
˚
H6–O2 distance of 1.982(3) A, see Fig. 3. As was the case
with complex 1, this interaction also results in a signifi-
˚
cantly longer W1–O2 distance of 1.724(3) A compared to
˚
W1–O1 of 1.698(3) A. The absence of any H-bonded inter-
actions with the terminal Cl atoms affords W–Cl distances
˚
of W1–Cl1 = 2.3646(12) and W1–Cl2 = 2.3661(12) A that
are not significantly different. The other hydroxy ligand is
involved in an intermolecular H-bond to the O atom in
the hydroxy group of an adjacent molecule that is linked
up intramolecularly to the terminal oxo ligand with O5–
110.6(4)
86.6(4)
111.4(2)
110.4(3)
0
˚
0
O6 distances of 2.788(4) A and an H5–O6 distance of
2
˚
.177(3) A. This results in long parallel chains within the
crystal lattice with the more hydrophobic part of the
chains, i.e., the phenyl ligands on adjacent chains, oriented
towards one another, see Fig. 4.
3.3. Application in epoxidation catalysis
Dioxotungsten compounds such as WO Cl (OPPh -
2
2
2
Me) , WO Cl dppmO have been previously assessed as
2
2
2
2
catalysts for the epoxidation of olefins and they have dis-
played high activity and selectivity [4e]. An oxo-tungsten
cluster was also reported to show very good activity for
olefin epoxidation using H O as oxidant [6c,10e,32]. The
2
2
catalytic reaction was believed to have proceeded through
an oxo-peroxo-tungsten active species [33]; however, the
active oxygen transfer specie has not so far been clarified
Fig. 2. ORTEP-3 [29] representation of 1 with selected atom numbering.
Thermal ellipsoids are drawn at the 50% probability level and hydrogen
atoms are represented by circles of arbitrary radii. H-bonded interactions
are illustrated by dashed lines and both disordered OH atoms (O6 and
O61) are illustrated. The benzene molecule of solvation is not included.
[
6c]. We examined the ability of compounds 1 and 2 to
effect the epoxidation of cis-cyclooctene, and, in order to
compare the catalytic attributes of these new dioxomolyb-
denum and dioxotungsten compounds with that of related

L. Feng et al. / Journal of Organometallic Chemistry 693 (2008) 1564–1571
1569
Fig. 4. Packing diagram depicting intra- and intermolecular H-bonding (dashed lines) and the orientation of the phenyl ligands on adjacent chains in 2.
Table 3
a
Epoxidation of cis-cyclooctene with catalysts in the presence of H
2
O
2
in ethanol solvent
b
c
Catalysts
Conversion (%)
Selectivity (%)
6
h
24 h
6 h
24 h
MoO
WO Cl
MoO Cl
WO Cl
MoO
2
Cl
2
(OPPh
CH
(OPPh CH
CH
CH
CH
2
CH
2
OH)
2
(1)
(2)
36.5 ± 0.7
82.0 ± 1.4
67.7 ± 1.3
>99
>99
Ref. [4e]
Ref. [4e]
Ref. [4e]
Ref. [4e]
>99
>99
2
2
(OPPh
2
2
OH)
2
83.7 ± 0.7
d
2
2
2
3
)
2
2
35
70
d
2
2
(OPPh
2
3
)
2
e
2
Cl
2
(OPPh
2
3
)
43
e
f
2
WO Cl
2
(OPPh
2
3
)
2
90
100
a
2 2
Experiment condition: catalyst/cis-cyclooctene/H O mole ratio equals 1:100:150. T = 70 °C. GC–MS quantitative analysis using decane as internal
standard.
P
b
c
d
e
f
Conversion = {1 ꢀ [remaining mole of olefin]/ [initial mole of olefin]} ꢂ 100%.
P
Selectivity = {[mole of olefin epoxide]/ [mole of oxo products]} ꢂ 100%. All of these data are based on at least three trials.
2 2 3
H O and CH CN as solvent.
Identical experimental conditions, H
8 °C, 24 h.
2
O
2
in ethanol.
7
3
1
compounds made before, the reactions were carried out
using conditions identical to those utilized previously [4e].
The results for the epoxidation of cis-cyclooctene with
the ethanol/H O system and complexes 1 and 2 and previ-
is the only product detected. P NMR measurements after
24 h of reaction indicate the presence of the unattached
phosphine oxide ligand suggesting that the starting cata-
lytic material had decomposed in both cases.
2
2
ously published selected data are summarized in Table 3. It
is clear from the data in Table 3 that both of the catalysts
display good activity and very high selectivity to form
cyclooctene oxide. Within a 6 h reaction time period, the
tungsten compound 2 displayed much better conversion
than the molybdenum analogue 1, which is comparable
with what was found for related compounds [4e] as listed
in Table 3. This may be related to the increased stability
of complex 2 under these catalytic conditions [4e]. These
catalysts show better activity than their related OPPh CH
4. Conclusion
Two new molybdenum and tungsten complexes contain-
ing hydrophilic phosphine oxide ligands have been synthe-
sized and characterized using FT-IR and NMR
spectroscopic methods. Their structures were assessed by
single crystal X-ray diffraction methods and both displayed
intramolecular H-bonded interactions. The tungsten com-
pound also contained intermolecular H-bonds resulting in
long polymeric stacked chains. The catalytic property of
these compounds for the epoxidation of cis-cyclooctene
was assessed using H O as the source of oxygen. Both of
2
3
analogs when the solvent used was acetonitrile, Table 3.
However, in ethanol, the OPPh CH derived catalysts
2
3
appear more functional which may be reflective of the fact
that a less polar catalyst may interact better with the cyclo-
octene substrate as suggested in the Sharpless et al. pro-
posed mechanism for epoxidation [23].
Extending the time of reaction to 24 h revealed that
while 2 did not complete further epoxidation of remaining
substrate, 1 still displayed activity and almost achieved
double the conversion. Interestingly, the transformation
with both catalysts was very selective as cyclooctene oxide
2
2
them showed very high selectivity for the cyclooctene oxide
with the tungsten compound 2 displaying an initial higher
catalytic activity than the molybdenum complex 1. The pres-
ence of the more polar OPPh CH OH ligand did not confer
2
2
any advantage (over related complexes containing
OPPh CH ) in the epoxidation reaction under the condi-
2
3
tions of our experiment with ethanol as the solvent. Reac-
tions with 1 and 2 using more polar substrates are envisaged.

1
570
L. Feng et al. / Journal of Organometallic Chemistry 693 (2008) 1564–1571
(b) V.B. Romakh, B. Therrien, G. Suess-Fink, G.B. Shul’pin, Inorg.
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crystallographic data for compounds 1 and 2. These data
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