Synthesis, crystal structure and reactivity of a new pentacoordinated chiral dioxomolybdenum(VI) complex

Article abstract of DOI:10.1016/j.poly.2009.09.022

The novel tridentate chiral ligand 2,6-bis{[(1R,2S,4R)-2-hydroxy-1,3,3-trimethyl-bicyclo[2.2.1]hept-2-yl]}pyridine (1) was readily prepared by reaction of 2,6-dilithiopyridine with (R)-(-)-fenchone. Reaction of 1 with [MoO₂(acac)₂] resulted in the formation of the new metal-oxo five-coordinated complex [MoO₂(ONO)] (2) [ONO = (1 - 2H)]. The reactivity of 2 has been studied and the derivatives [MoS₂(ONO)] (3) and [MoO(O₂)(ONO)] (4) were prepared. The compounds 1-4 have been characterised by ¹H and ¹³C{¹H} NMR, microanalysis and IR spectroscopy. Furthermore, the molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction. The behaviour of 2 as catalyst in oxotransfer and in nucleophilic substitution of propargylic alcohols reactions has been tested.

Full text of DOI:10.1016/j.poly.2009.09.022

Polyhedron 29 (2010) 841–849
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, crystal structure and reactivity of a new pentacoordinated chiral
dioxomolybdenum(VI) complex
*
*
M.R. Pedrosa , J. Escribano, R. Aguado, R. Sanz, V. Díez, F.J. Arnáiz
Departamento de Química, Universidad de Burgos, Pza. Misael Bañuelos s/n, 09001 Burgos, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 April 2009
Accepted 25 September 2009
Available online 29 October 2009
The novel tridentate chiral ligand 2,6-bis{[(1R,2S,4R)-2-hydroxy-1,3,3-trimethyl-bicyclo[2.2.1]hept-2-
yl]}pyridine (1) was readily prepared by reaction of 2,6-dilithiopyridine with (R)-(ꢀ)-fenchone. Reaction
of 1 with [MoO2(acac)2] resulted in the formation of the new metal-oxo five-coordinated complex
[MoO2(ONO)] (2) [ONO = (1 – 2H)]. The reactivity of 2 has been studied and the derivatives [MoS2(ONO)]
(3) and [MoO(O2)(ONO)] (4) were prepared. The compounds 1–4 have been characterised by 1H and
13C{1H} NMR, microanalysis and IR spectroscopy. Furthermore, the molecular structures of 1 and 2 have
been determined by single-crystal X-ray diffraction. The behaviour of 2 as catalyst in oxotransfer and in
nucleophilic substitution of propargylic alcohols reactions has been tested.
Keywords:
Molybdenum
Chiral ligand
Oxo ligands
O,N,O-ligands
Tridentate ligands
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
ars Schiff-bases [7], substituted 1,4-R2-diazabutadienes [8],
oximes, cis-diols and 8-thiomenthols [9], 1,4,7-triazacyclononane
The achievements over the past few decades in developing chi-
ral non-racemic reagents and asymmetric synthetic methodologies
have been remarkable [1]. For example, the synthesis of many chi-
ral non-racemic receptor molecules is now a relatively simple mat-
ter, and optically active ligands are now common place in
enantioselective catalysis with transition metal complexes [2].
One of the difficulties in this area is the development of suitable
chiral ligands that are stable to oxidation and easy to synthesize.
Among the ligands that meet these requirements we found the
20-pyridyl alcohols, which are readily accessible by the reaction
of 2-lithiopyridine with either symmetrical or unsymmetrical ke-
tones, yielding chiral or achiral molecules, respectively [3]. Herr-
mann and coworkers prepared complexes of the type MoO2L2
(L = achiral 20-pyridyl alcoholate) and tested them as catalysts for
the selective oxidation of olefins with molecular oxygen or TBHP
[4]. Another class of chiral chelating ligands that seems to meet
the requirements outlined above are the C2-symmetric bis(oxazo-
lines), which are easily prepared from readily available amino alco-
hols [5]. A wide variety of complexes containing the [MoO2]2+
moiety, ligated either by a tetradentate bis(oxazoline) ligand or
by two bidentate pyridyl alcoholate ligands, was synthesized by
Romão and coworkers and applied to the epoxidation of trans-b-
methylstyrene [6].
[10], as well as anchored on mesoporous MCM-41 for studies on
heterogeneous catalysis [11].
In the last few years, our research group has made a significant
effort to synthesize new dioxomolybdenum(VI) complexes poten-
tially useful as catalysts [12]. Currently our research interest is fo-
cused towards the development of new complexes bearing
hindered chiral ligands as well as controlling the substrates
approaching to the coordination sphere of the molybdenum centre.
Herein we describe the synthesis of the novel tridentate chiral
ligand pyridine-diol (1) and its coordination to molybdenum to
give the new asymmetric oxo-complex [MoO2(ONO)] (2)
[ONO = (1 – 2H)]. The molecular structures of 1 and 2 are pre-
sented. The reactivity from 2 has been studied, and the disulphide
and oxoperoxo derivatives, [MoS2(ONO)] (3) and [MoO(O2)(ONO)]
(4), prepared and characterised. The catalytic potential of complex
2 is discussed for oxotransfer reactions involving the reduction of
sulfoxides and the oxidation of sulphides, as well as for the direct
nucleophilic substitution of propargylic alcohols.
2. Experimental
2.1. General procedures
In the current decade, the [MoO2]2+ moiety has also been re-
ported bearing some other kind of chiral ligands, derived from sug-
Unless otherwise specified all reagents were purchased from
commercial suppliers and used without further purification. All
experiments were carried out using dried solvents and under a
nitrogen atmosphere, using the Schlenk techniques. Diethyl ether
and THF were distilled over Na-benzophenone ketyl prior to use.
* Corresponding authors. Tel.: +34 (9)47 258823; fax: +34 (9)47 258831 (M.R.
Pedrosa).
E-mail addresses: mpedrosa@ubu.es (M.R. Pedrosa), farnaiz@ubu.es (F.J. Arnáiz).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.09.022

842
M.R. Pedrosa et al. / Polyhedron 29 (2010) 841–849
Acetonitrile was distilled over CaH2. Acetone was also distilled
immediately before use from KMnO4. Solvents used in extraction
and purification were distilled prior to use. MoO2(acac)2 was pre-
pared as previously reported [13]. Elemental analyses of C, H, N
and S were performed on a LECO CHNS-932 analyzer. GC–MS
was performed on an Agilent 6890 N/5973 mass spectrometer.
HRMS was carried out on a Micromass AutoSpect spectrometer.
Enantiomeric ratios were determined by chiral HPLC analysis using
a Hewlett Packard Series 1100 with G1315A detector and a Chiral-
cel (OD-H or OJ) column in comparison with the authentic racemic
products. Optical rotations were measured with a digital Perkin–
Elmer 241 polarimeter and the concentrations are given in g/
100 ml. Infrared spectra were measured from samples in KBr pel-
lets on a Nicolet Impact 410 (Software Omnic for Windows) spec-
trometer in the range 4000–400 cmꢀ1. NMR spectra were recorded
on a Varian Unity Inova-400 spectrometer (400 MHz for 1H,
100.6 MHz for 13C and 161.9 MHz for 31P), using CDCl3 as solvent,
at 20 °C. Chemical shifts are expressed relative to tetramethylsil-
overnight. The solvent was then removed under vacuum. Hexane
(15 ml) was added to the resulting solid and the suspension was
stirred for 10 min. The white solid was collected, washed with hex-
ane (2 ꢁ 3 ml), and dried under vacuum.
Yield: 0.469 g (92%). Anal. Calc. for C25H35MoNO4 (509.49): C,
20
58.93; H, 6.98; N, 2.75. Found: C, 58.65; H, 6.85; N, 2.70%. [
a
]
D
:
ꢀ79.0 (c = 1.2 in CHCl3). 1H NMR dH (400 MHz, CDCl3, 20 °C): 0.83
(s, 6 H, H-10), 0.86 (s, 6 H, H-8), 1.16 (s, 6 H, H-9), 1.12–1.21 (m,
2
3
2 H, H-6exo), 1.42 (dd, JH,H = 11.0 Hz, JH,H = 1.4 Hz, 2 H, H-7anti),
1.52 (tt, JH,H = 12.9 Hz, JH,H = 4.9 Hz, 2 H, H-5exo), 1.84–1.87 (m,
2 H, H-4), 1.86–1.93 (m, 2 H, H-5endo), 2.08 (d, JH,H = 11.0 Hz, 2
2
3
2
3
H, H-7syn), 2.29–2.38 (m, 2 H, H-6endo), 7.60 (d, JH,H = 7.9 Hz, 2 H,
3
H-12), 8.02 (t, JH,H = 7.9 Hz,
1
H, H-13). 13C{1H} NMR dC
(100.6 MHz, CDCl3, 20 °C): 17.6 (CH3, C-10), 23.2 (CH3, C-9), 24.7
(CH2, C-5), 29.7 (CH3, C-8), 31.2 (CH2, C-6), 41.7 (CH2, C-7), 48.5
(CH, C-4), 50.1 (C, C-3), 55.8 (C, C-1), 106.0 (C, C-2), 122.4 (CH, C-
12), 139.9 (CH, C-13), 169.0 (C, C-11). IR (cmꢀ1): 936 and 916
m(Mo@O).
ane (1H and 13C) or external 85% H3PO4 31P), with downfield val-
(
ues reported as positive. Coupling constants J are given in Hertz.
2.4. Synthesis of [MoS2(ONO)] (3)
2.2. Synthesis of 2,6-bis{[(1R,2S,4R)-2-hydroxy-1,3,3-trimethyl-
bicyclo[2.2.1]hept-2-yl]}pyridine, (1)
[MoO2(ONO)] (2) (0.100 g, 0.196 mmol) was dissolved in aceto-
nitrile (4 ml) under nitrogen. A suspension of Lawesson’s reagent
(0.048 g, 0.118 mmol) in acetonitrile (4 ml) was added at room
temperature. The mixture was stirred for 1 h, and the resulting
black suspension was filtered under nitrogen. The solvent was re-
moved under vacuum to afford the dithiocomplex (3) as a pale yel-
low microcrystalline product.
To a solution of n-BuLi (17.6 ml, 44 mmol, 2.5 M in hexane) THF
(30 ml) was added under nitrogen. The mixture was cooled to
ꢀ100 °C. A solution of 2,6-dibromopyridine (4.738 g, 20 mmol) in
THF (15 ml) was added dropwise under vigorous stirring and the
solution turned dark-red. After 1 h at ꢀ100 °C, and 2 h at ꢀ78 °C,
a solution of (R)-(ꢀ)-fenchone (7.1 ml, 44 mmol) in THF (8 ml)
was added dropwise. The stirred mixture was then left at room
temperature overnight. Water (10 ml) was then added and the or-
ganic phase was extracted with ethyl acetate (3 ꢁ 20 ml). The col-
lected organic phases were dried over anhydrous sodium sulphate
and the solvents removed under vacuum. The resulting white solid,
was purified by chromatography (SiO2; hexane/ethyl acetate 5/1)
to afford the organic ligand (6.902 g) as a mixture of diastereomers
(ca. 80% d.e.). The desired diastereomer was purified using (R)-(ꢀ)-
fenchone as resolving agent. So, (R)-(ꢀ)-fenchone (1.73 ml,
10.8 mmol) was added to a solution of the product in diethyl ether
(30 ml). The resulting solution was allowed to slowly evaporate at
room temperature to ca. 1 ml. The crystals (96% d.e.) were col-
lected and washed with a 1/1 cool mixture of hexane/diethyl ether
(2 ꢁ 1 ml). Recrystallisation from diethyl ether afforded the ligand
with >99% d.e. The ligand was then purified by chromatography
(SiO2; hexane/ethyl acetate from 20/1 to 5/1) to afford the desired
tridentate chiral ligand 1 as a white solid.
Yield: 0.105 g (99%). Anal. Calc. for C25H35MoNO2S2 (541.62): C,
55.44; H, 6.51; N, 2.59; S, 11.84. Found: C, 55.13; H, 6.32; N, 2.22; S,
11.78%. 1H NMR dH (400 MHz, CDCl3, 20 °C): 0.79 (s, 6 H, H-10),
2
0.95 (s, 6 H, H-8), 1.18 (s, 6 H, H-9), 1.22 (td, JH,H = 12.6 Hz,
2
3
3JH,H = 4.4 Hz, 2 H, H-6exo), 1.42 (dd, JH,H = 11.1 Hz, JH,H = 1.4 Hz,
2
3
2 H, H-7anti), 1.56 (tt, JH,H = 12.7 Hz, JH,H = 4.7 Hz, 2 H, H-5exo),
1.87 (d, JH,H = 4.3 Hz, 2 H, H-4), 1.92–2.00 (m, 2 H, H-5endo), 2.09
(dd, JH,H = 11.0 Hz, JH,H = 1.7 Hz, 2 H, H-7syn), 2.28–2.37 (m, 2 H,
H-6endo), 7.90 (d, JH,H = 7.9 Hz, 2 H, H-12), 8.09 (t, JH,H = 7.9 Hz, 1
H, H-13). 13C{1H} NMR dC (100.6 MHz, CDCl3, 20 °C): 18.1 (CH3,
C-10), 23.6 (CH3, C-9), 24.9 (CH2, C-5), 29.8 (CH3, C-8), 31.5 (CH2,
C-6), 42.1 (CH2, C-7), 48.8 (CH, C-4), 52.8 (C, C-3), 57.1 (C, C-1),
109.7 (C, C-2), 122.1 (CH, C-12), 140.1 (CH, C-13), 168.6 (C, C-11).
3
2
3
3
3
IR (cmꢀ1): 523 and 504
m(Mo@S).
2.5. Synthesis of [MoO(O2)(ONO)] (4)
To a solution of [MoO2(ONO)] (2) (0.100 g, 0.196 mmol) in THF
(5 ml), H2O2 (0.5 ml, 4 mmol) was added, and the mixture stirred
for 24 h at room temperature. The resulting solution was dried
over magnesium sulphate (0.4 g) and then filtered. The solvent
was removed under vacuum to afford the oxoperoxo complex (4)
as a deep yellow solid.
Yield: 0.102 g (99%). Anal. Calc. for C25H35MoNO5 (525.49): C,
57.14; H, 6.71; N, 2.67. Found: C, 57.26; H, 6.81; N, 2.72%. 1H
NMR dH (400 MHz, CDCl3, 20 °C): 0.65 (s, 3 H, H-100), 0.87 (s, 3 H,
H-8), 0.96 (s, 3 H, H-80), 0.98 (s, 3 H, H-9), 1.01 (s, 3 H, H-10),
Yield: 5.515 g (72%). M.p.: 62–64 °C. d.e.: 99%. [
a
]
20: ꢀ89.3
D
(c = 1.2 in CHCl3). LRMS (IE, 70 ev): m/z (%): 383 (6) [M+], 286
(100). HRMS (IE): Calculated for C25H37NO2 383.2804, found
383.2810. 1H NMR dH (400 MHz, CDCl3, 20 °C): 0.44 (s, 6 H, H-9),
2
0.98 (s, 6 H, H-10), 1.00 (s, 6 H, H-8), 1.16 (td, JH,H = 12.6 Hz,
2
3JH,H = 4.5 Hz, 2 H, H-6exo), 1.36 (d, JH,H = 10.3 Hz, 2 H, H-7syn),
2
3
1.49 (tt, JH,H = 12.6 Hz, JH,H = 4.5 Hz,
2 H, H-5exo), 1.79 (d,
3JH,H = 4.2 Hz, 2 H, H-4), 1.82 (br s, 2 H, H-5endo), 2.24 (br s, 4 H,
3
2
3
H-7anti and H-6endo), 7.41 (br s, 2 H, H-12), 7.61 (t, JH,H = 7.9 Hz,
1.10 (td, JH,H = 12.7 Hz, JH,H = 4.2 Hz, 1 H, H-60exo), 1.28 (td,
1 H, H-13). 13C{1H} NMR dC (100.6 MHz, CDCl3, 20 °C): 17.1 (CH3,
C-10), 22.1 (CH3, C-8), 24.3 (CH2, C-5), 29.3 (CH3, C-9), 32.5 (CH2,
C-6), 41.9 (CH2, C-7), 46.0 (C, C-3), 48.8 (CH, C-4), 52.1 (C, C-1),
84.0 (C, C-2), 120.4 (CH, C-12), 135.1 (CH, C-13), 160.2 (C, C-11).
2JH,H = 12.6 Hz, JH,H = 4.4 Hz, 1 H, H-6exo), 1.41 (dd, JH,H = 5.0 Hz,
3
2
3JH,H = 1.4 Hz, 1 H, H-7anti), 1.43 (dd, JH,H = 5.1 Hz, JH,H = 1.4 Hz, 1
H, H-70anti), 1.49 (s, 3 H, H-90), 1.50–1.62 (m, 2 H, H-5exo and H-
50exo), 1.83–1.87 (m, 2 H, H-4 and H-40), 1.91–2.05 (m, 2 H, H-5endo
2
3
2
3
and H-50endo), 2.13 (dc, JH,H = 11.0 Hz, JH,H = 1.7 Hz, 1 H, H-70syn),
2
3
2.3. Synthesis of [MoO2(ONO)] (2)
2.20 (dc, JH,H = 11.0 Hz, JH,H = 1.8 Hz, 1 H, H-7syn), 2.46–2.54 (m,
3
1 H, H-60endo), 2.60–2.68 (m, 1 H, H-6endo), 7.71 (d, JH,H = 7.9 Hz,
MoO2(acac)2 (0.326 g, 1 mmol) was dissolved in acetone
(10 ml), then treated at room temperature with a solution of 1
(0.421 g, 1.1 mmol) in acetone (10 ml), and the mixture stirred
1 H, H-12), 7.74 (d, 3JH,H = 7.9 Hz, 1 H, H-120), 8.03 (t, 3JH,H = 7.9 Hz,
1 H, H-13). 13C NMR dC (100.6 MHz, CDCl3, 20 °C): 17.0 (CH3, C-100),
19.1 (CH3, C-10), 21.8 (CH3, C-90), 23.9 (CH3, C-9), 24.9 and 25.0

M.R. Pedrosa et al. / Polyhedron 29 (2010) 841–849
843
(CH2, C-5 and C-50), 29.3 (CH3, C-8), 30.4 (CH3, C-80), 30.5 (CH2, C-
60), 31.2 (CH2, C-6), 41.3 (CH2, C-70), 42.7 (CH2, C-7), 48.3 (CH, C-4),
49.1 (CH, C-40), 49.4 (C, C-3), 49.8 (C, C-30), 56.5 (C, C-10), 58.2 (C, C-
1), 105.8 (C, C-20), 106.2 (C, C-2), 122.7 (CH, C-12 and C-120), 138.8
(CH, C-13), 169.1 (C, C-11), 169.5 (C, C-110). IR (cmꢀ1): 965
and GC–MS. The oxidation of phosphine was followed by measur-
ing the intensity of the phosphorus signals (31P NMR). Solutions of
each pair phosphine and phosphine oxide (molar ratio 1:1) in THF
were used as blanks. Conversion from sulfoxides to sulphides was
measured by GC–MS. The aliquots from the reaction mixture were
treated with 2 M NaOH and extracted with EtOAc. The organic ex-
tracts were dried (Na2SO4) and the filtrate injected in the GC col-
umn. The products were identified by GC–MS.
m(Mo@O), 883 m(O–O).
2.6. X-ray crystallographic studies
2.7.2. Procedure for oxidation of methyl phenyl sulphide catalysed by
complex 2
Crystals of 1 suitable for single-crystal X-ray diffraction were
grown by leaving a diethyl ether solution (using the (R)-(ꢀ)-fench-
one as resolving agent) to slowly evaporate at room temperature.
Crystals of 2 suitable for single-crystal X-ray diffraction were
grown by liquid–liquid diffusion of an acetone solution with hex-
ane. The main crystallographic data for these compounds are sum-
marised in Table 1.
To a solution of complex 2 (2 mol%) in dry solvent (THF, CH2Cl2
or EtOH) (5 ml) at 0 °C, methyl phenyl sulphide (0.124 g, 1.0 mmol)
and tBuOOH (water solution 70%, 1.1 mmol) were added under
nitrogen. The mixture was then stirred at room temperature and
periodically monitored by GC–MS for 3 h. The aliquots from the
reaction mixture were treated with 2 M NaOH and extracted with
EtOAc. The organic extracts were dried (Na2SO4) and the filtrate in-
jected in the GC column. The products were identified by 1H and
13C NMR and GC–MS. Enantiomeric excess were measured by HPLC
with a OD-H chiral column (hexane/i-PrOH:95/5, flow rate 1 ml/
min. k = 254 nm, tR (min) = 18.3 and 19.6); e.e. ꢂ 3%. Yield, 0.125
g, 90% sulfoxide.
Data for both crystals were collected on a Bruker SMART CCD
area-detector diffractometer with Mo
0.71073 Å). Intensities were integrated from several series of expo-
sures [14], each exposure covering 0.3° in , and the total data set
Ka
radiation (k =
x
being a sphere. Absorption corrections were applied, based on mul-
tiple and symmetry-equivalent measurements [15]. The structure
was solved by direct methods and refined by least-squares on
weighted F2 values for all reflections using the SHELXTL program
[16]. All non-hydrogen atoms were assigned anisotropic displace-
ment parameters and refined without positional constraints.
Hydrogen atoms H(2) and H(3) (for structure corresponding to 1)
were located in the electron density difference map, assigned iso-
tropic displacement parameters and refined without positional
constraints. All other hydrogen atoms (from both structures) were
constrained to ideal geometries and refined with fixed isotropic
displacement parameters. Refinement proceeded smoothly to give
the residuals shown in Table 1. Complex neutral-atom scattering
factors were used [17].
2.7.3. General procedure for nucleophilic substitution of propargylic
alcohols catalysed by complex 2
To a solution of 1,3-diphenyl-2-propyn-1-ol (0.208 g, 1 mmol)
in CH2Cl2 (5 ml), the complex 2 (2 mol%) and 2-chloroethanol
(0.242 g, 3 mmol) were added. The mixture was stirred at room
temperature and periodically monitored by GC–MS until the prop-
argylic alcohol was not detected (ca. 12 h). The aliquots from the
reaction mixture were treated with 2 M NaOH and extracted with
EtOAc, the organic extracts were dried (Na2SO4) and the filtrate in-
jected in the GC column. The solvent was removed under vacuum
and the residue was purified by column chromatography (hexane/
ethyl acetate) affording 3-(2-chloro-ethoxy)-1,3-diphenyl-propyne
was identified by 1H and 13C NMR and GC. Enantiomeric excess
was measured by HPLC with a OJ chiral column (hexane/i-
PrOH:80/20, flow rate 1 ml/min, k = 254 nm, tR (min) = 7.4 and
10.2); e.e. ꢂ 3%. Yield, 0.216 g, 80%.
2.7. Catalytic activity
2.7.1. General procedure for catalytic deoxygenation of sulfoxides with
phosphines catalysed by complex 2
To a solution of sulfoxide (3.0 mmol) and phosphine (3.0 mmol)
in THF (5 ml), complex 2 (5 mol%) was added, and the resulting
solution was stirred at reflux. Samples were taken periodically
and the course of the reaction was doubly monitored by 31P NMR
3. Results and discussion
3.1. Diastereoselective synthesis of the chiral 2,6-pyridine-diol ligand
(1)
Table 1
Crystal data and structure refinement for (1)2ꢃfenchone and MoO2(ONO) (2).
For the design of chiral ligands for asymmetric oxidation catal-
ysis, three prerequisites should be met: (a) resistance against oxi-
dation, (b) a straightforward synthetic route and (c) the possibility
to change electronic and steric characteristics by simple variation
of the starting materials [18]. These principles are combined in
the following synthesis. The ligand (1) is a tertiary alcohol, which
resists oxidation. Moreover, this ligand can be made in a simple
two-step synthesis; after halogen–lithium exchange on 2,6-dib-
romopyridine, the nucleophilic attack of the resulting organome-
tallic species at the carbonyl group of fenchone leads to 2,6-
pyridine-diol 1 (Scheme 1).
The reaction product obtained was diastereomerically purified
by crystallization of the main diastereomer, induced by fenchone
as chiral auxiliary. The final product (1) was obtained in a high
yield one-pot procedure, and was fully characterised. The diaste-
reomeric purity was proved by the detection of only one set of sig-
nals in the NMR spectra. The 1H and 13C{1H} NMR signals were
completely assigned by 1D and 2D NMR techniques (see Scheme
2 for the numbering scheme). X-ray crystallography was used to
(1)2ꢃFenchone
MoO2(ONO) (2)
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C60H90N2O5
919.34
C25H35MoNO4
509.48
tetragonal
P41212
13.393(4)
13.393(4)
13.641(4)
2447.0(13)
4
orthorhombic
P212121
11.6149(7)
13.1517(8)
35.352(2)
5400.2(6)
4
b (Å)
c (Å)
V (Å3)
Z
qcalc (g/cm3)
F(0 0 0)
1.131
2016
1.383
1064
h Range (°)
l
2.10–25.00
0.070
2.15–25.00
0.565
(mmꢀ1
)
Reflections collected
52 690
23 393
Independent reflections
5293
2157
Reflections with I > 2
R1, wR2 [I > 2 (I)]
R1, wR2 (all data)
Goodness-of-fit (GOF)
Absolute structure (flack) parameter
r
(I)
4348
2015
r
0.0476, 0.1052
0.0627, 0.1118
1.052
0.0465, 0.0965
0.0507, 0.0982
1.108
10(10)
0.00(9)

844
M.R. Pedrosa et al. / Polyhedron 29 (2010) 841–849
Scheme 1. Diastereoselective synthesis of chiral ligand (1).
confirm the absolute configuration of the ligand 1, using fenchone
as chiral auxiliary for the crystal grown procedure.
Table 2
Hydrogen contacts for (1)2ꢃfenchone (Å and °).
To the best of our knowledge, only three compounds bearing
two chiral fenchyl groups have been crystallographically charac-
terised [19]. The crystal structure here reported, is the first one
showing intermolecular and intramolecular hydrogen bonds, (see
Table 2 and Fig. 1). Two intermolecular hydrogen bonds involve a
hydroxy group of the fenchyl moieties, the first one with the par-
ticipation of a hydroxy group of a neighbour molecule [O(2)–
H(2)ꢃꢃꢃO(3), 2.911 Å] and the second one involving the carbonyl
group of the fenchone unit [O(4)–H(4)ꢃꢃꢃO(5), 2.800 Å]. Also, an-
other two hydrogen bonds, intramolecular interactions, both of
them involving the remaining hydroxy group of the fenchyl moie-
ties and the nitrogen atom from the pyridine ring [O(1)–
H(1)ꢃꢃꢃN(1), 2.539 Å and O(3)–H(3)ꢃꢃꢃN(2), 2.523 Å] are present.
The intramolecular interactions involving nitrogen and oxygen
are shorter than intermolecular ones involving only oxygen atoms.
The ligand 1 is air-stable as well as thermally stable, and can be
stored for months, at room temperature without the need for spe-
cial care.
The deprotonated diol can be described as a chelating, dianion-
ic, tridentate ligand. It complexes a metal centre with a coordina-
tive bond by the nitrogen of the pyridine ring and two covalent
single bonds by the alcoholate oxygens of the former hydroxy
groups. An additional advantage of this ligand is the number of
the ring atoms in the corresponding complex. Five-membered
rings are generally thermodynamically more stable than the six-
membered rings.
A–HꢃꢃꢃB
d(A–H)
d(HꢃꢃꢃB)
d(AꢃꢃꢃB)
<(AHꢃꢃꢃB)
Intramolecular hydrogen bonds
O(1)–H(1A)ꢃꢃꢃN(1)
O(3)–H(3A)ꢃꢃꢃN(2)
0.820
0.907
2.000
1.900
2.539
2.523
122.686
124.053
Intermolecular hydrogen bonds
O(2)–H(2A)ꢃꢃꢃO(3)
0.829
0.821
2.132
1.998
2.911
2.800
156.467
165.463
O(4)–H(4A)ꢃꢃꢃO(5)
gands can very easily be replaced by 20-pyridinyl alkoxides [4,20]
(Scheme 3).
MoO2(acac)2 reacts with 1.1 equivalent of 1, to form the com-
plex 2 that could be isolated in nearly quantitative yield. The driv-
ing force for the ligand exchange reaction is very probably the
superior chelating potential of 1 with respect to acetylacetone [21].
The dioxomolybdenum(VI) complex 2 was obtained as a micro-
crystalline white solid, and was fully characterised; it is air and
moisture stable, soluble in common solvents, and can be stored
for months at room temperature without special care.
The infrared spectrum of 2 exhibits two very strong m(Mo@O)
bands at 916 and 936 cmꢀ1, characteristic of the symmetric and
asymmetric stretching vibrations of the cis-[MoO2]2+ fragment
[19–21]. The other bands in the I.R. spectrum are attributable to
the bound ligand.
The 1H and 13C{1H} NMR spectra for complex 2 have been re-
corded, and all H and C signals were completely assigned by 1D
and 2D NMR techniques (see Scheme 2). It should be noted that
the 1H and 13C{1H} NMR spectra of 2 showed, as expected, only
one set of resonances for the two fenchyl groups suggesting the
formation of a C2-symmetric five-coordinate dioxomolybdenum
complex. The 1H NMR spectrum of complex 2 shows the signals
corresponding to the chiral ligand shifted, as usual, to lower fields
upon coordination. It is noteworthy that compared to the free li-
gand the signal corresponding to the H-7syn is shifted upfield (from
2.24 to 2.08 ppm), that can be interpreted as an increase of shield-
ing as a result of the proximity of this proton to protons from C-8
methyl group and H-12, as evidenced by the observed NOE interac-
tions. Similarly, two other systems of NOE interactions can be used
to full assignment of signals. The first one formed by the protons H-
5exo, H-6exo and H-7anti, and the second one H-5endo, H-6endo and
protons from C-9 methyl group. Finally, the signal corresponding
to protons from C-10 methyl group is slightly shifted upfield (from
0.98 to 0.83 ppm), possibly induced by the electron density associ-
ated to the metal centre. The 13C{1H} NMR spectra demonstrate
that the ligand is bound to the dioxomolybdenum core, and show
the striking shift of the signal of the quaternary carbon atom re-
lated to the hydroxy function (C-2) and the pyridine ring (C-11).
3.2. Synthesis and characterisation of [MoO2(ONO)] (2)
As a consequence of our interest in chiral molybdenum com-
plexes, we have evaluated the potential utility of 1 as chiral ligand.
In this work, MoO2(acac)2 was chosen as the precursor compound,
since previous results reported showed that the acetylacetonato li-
Scheme 2. The numbering scheme for 1 in NMR.

M.R. Pedrosa et al. / Polyhedron 29 (2010) 841–849
845
Fig. 1. A view of the hydrogen-bonding in the crystal structure for (1)2ꢃfenchone with thermal ellipsoids at the 50% probability level. The hydrogen atoms (except those
involved in the hydrogen bonds) are omitted for clarity.
Scheme 3.
Thus, when the ligand is bound to the dioxomolybdenum core, the
signal corresponding to C-2 is shifted downfield from 84.0 in 1 to
106.0 ppm in 2, and the signal of C-11 is found at 160.2 ppm for
the free ligand (1) but at 169.0 ppm for the metal complex (2). Both
effects can be explained by a shift of electron density towards the
molybdenum centre.
The X-ray crystal structure of compound 2 was determined. Se-
lected bond distances and angles are given in Table 4 and an ORTEP
presentation shown in Fig. 2.
The crystallographic analysis of a suitable crystal of 2 revealed a
five-coordinate mononuclear complex, one structural type quite
uncommon for dioxomolybdenum(VI) complexes, that are gener-
ally six-coordinate showing a distorted octahedral coordination
sphere. For related dioxomolybdenum(VI) species bearing a triden-
tate ligand, the sixth position is typically occupied by a donor ligand
as observed in [MoO2(C5H3N-2,6-(CH2–CPh2–O)2)(L)] (L = Me2SO)
[22,23] or [MoO2(C5H3N-2,6-(CH2–S)2)(L)] (L = (CH2)4SO) [24]. In
some cases, the supposed five-coordinate mononuclear complexes
are weakly associated by unsymmetrical Mo@OꢃꢃꢃMo interactions
to give an essentially ‘‘binuclear” structure [20] or a ‘‘linear poly-
meric” structure such as [MoO2(C5H3N-2,6-(CH2O)2)n] [24].
To the best of our knowledge, molecular structures correspond-
ing strictly to five-coordinate mononuclear complexes of dioxomo-
lybdenum(VI) with trigonal bipyramidal arrangement are limited
to the Holm’s pyridinedithiol complex [MoO2(C5H3N-2,6-(CH2–
CPh2–S)2)] [22,23], and the pyridine-diol complex reported by
Sharpless, [MoO2(C5H3N-2,6-(HCtBu–O)2)] [25].
The molecular structure for complex 2 (Fig. 2) reveals that the
geometry of the [MoO4N] coordination unit is best approximated
by a distorted trigonal bipyramid around the molybdenum atom,
with axial O(1) (alkoxy groups) and equatorial O(2) (oxo groups)
and N(1) atoms.
The O(1)–Mo(1)–O(1) angle is 145.1(2)°; all other bond angles
at the molybdenum atom are <126°. Furthermore, the O(1)–
Mo(1)–N(1) and O(2)–Mo(1)–O(1) angles are 72.55(10)° and
101.0(2)°, respectively, while angles involving only equatorial li-
gands are larger, 109.9(2)° and 125.04(11)°. Consideration of dihe-
dral parameters substantiates the assignment of
a trigonal
bipyrimid geometry, which is, however, considerably distorted.
The coordination unit has a C2-symmetry, with a twofold axis coin-
cident with the Mo–N bond vector that relates the two halves of
the molecule. The Mo(1)–O(1) vector makes an angle of 17.45°
with the threefold axis of an idealized trigonal bipyramid. The
planes defined by Mo(1)–O(2)–O(2)#–N(1) and Mo(1)–O(1)–
O(1)#–N(1) are related by a dihedral angle of 88.9°, close to the
ideal angle of 90°.
The plane of the pyridine unit is nearly perpendicular to the
O(2)–Mo(1)–O(2)# plane [dihedral angle = 88.9°] and this plane,
together with the projection of the N ? Mo vector, bisects the
O(2)–Mo(1)–O(2)# angle. This dihedral angle is very different from
the 61.9° found for the Holm’s molecule [17,18]. In our structure,
the metallocyclic chelate arms of the ligand (five-membered)
adopt a plane conformation, in the same plane that the pyridinic
ring, while in the Holm’s pyridinedithiol complex the metallocyclic

846
M.R. Pedrosa et al. / Polyhedron 29 (2010) 841–849
Fig. 2. Molecular structure and atom-labelling scheme for MoO2(ONO) (2) with thermal ellipsoids at the 50% probability level. The hydrogen atoms (except those involved in
the intramolecular hydrogen bonds) are omitted for clarity.
chelate arms (six-membered) adopt a boat conformations. For 2
the torsion angle O(1)–O(1)#–C(11)–C(11)# is only 4° compared
with the angle of 8.5° in the Sharpless derivative [25]. In fact, car-
bon atoms from pyridinic ring lie approximately in the plane of the
O(1)–O(1)#–Mo(1)–N(1) skeleton to which is bound, with maxi-
mum displacements from the least-squares plane of 0.038 Å for
C-12 (0.119 and 0.188 Å for Sharpless derivative) and 0.083 Å for
C-11 (0.136 and 0.188 Å for Sharpless structure).
[2.402 and 2.442 Å] [25]. However, for 2 significant intermolecular
interactions through hydrogen bonds can also be observed be-
tween the two C–H (meta) from pyridinic ring of the ligand and
two Mo@O groups from two different neighbouring molecules.
The conformational arrangement is controlled by the presence of
these intermolecular hydrogen bonds, giving rise to the association
to form the 3D supramolecular framework. A view of the crystal
structure of 2 is shown in Fig. 3 (see Table 3).
The molecular structure for complex 2 (Fig. 2, Table 3) also re-
veals two intramolecular hydrogen bonds involving oxygen atoms
from alkoxy groups and protons H-6endo [C(6)–H(6endo)ꢃꢃꢃO(1),
2.268 Å], shorter than those in the structure reported by Sharpless
3.3. Reactivity of complex 2
We have unsuccessfully tried to increase the coordination num-
ber of molybdenum in complex 2 in order to obtain hexacoordinat-
ed species. Thus, all attempts of reaction of 2 with a wide range of
O- and N-donors strong bases (sulfoxides, phosphine oxides and
Table 3
Hydrogen contacts for MoO2(ONO) (2) (Å and °).
A–HꢃꢃꢃB
d(A–H)
d(HꢃꢃꢃB)
d(AꢃꢃꢃB)
<(AHꢃꢃꢃB)
Intramolecular hydrogen bonds
C(6)–H(6endo)ꢃꢃꢃO(1)
0.990
0.990
2.268
2.268
2.726
2.726
106.917
106.917
C(6)#1–H(6endo)#1ꢃꢃꢃO(1)#1
Intermolecular hydrogen bonds
C(12)–H(12)ꢃꢃꢃO(20)
0.950
0.950
2.394
2.394
3.267
3.267
152.485
152.485
C(12)#1–H(12)#1ꢃꢃꢃO(200)
Symmetry transformations used to generate equivalent atoms: #1 y, x, ꢀz.
Table 4
Selected bond lengths (Å) and angles (°) for MoO2(ONO) (2).
Bond lengths
Mo(1)–O(2)
Mo(1)–O(1)
Mo(1)–N(1)
1.695(3)
1.907(4)
2.190(5)
O(1)–C(2)
C(2)–C(11)
N(1)–C(11)
1.414(6)
1.531(8)
1.344(5)
Bond angles
O(2)–Mo(1)–O(2)#1
O(2)–Mo(1)–O(1)
O(2)–Mo(1)–O(1)#1
N(1)–Mo(1)–O(2)
N(1)–Mo(1)–O(1)
Mo(1)–N(1)–C(11)
109.9(2)
98.81(19)
101.0(2)
125.04(11)
72.55(10)
117.6(3)
O(1)–Mo(1)–O(1)#1
O(2)#1–Mo(1)–O(1)#1
O(2)#1–Mo(1)–O(1)
N(1)–Mo(1)–O(2)#1
N(1)–Mo(1)–O(1)#1
Mo(1)–O(1)–C(2)
145.1(2)
98.81(19)
101.0(2)
125.04(11)
72.55(10)
130.1(3)
Fig. 3. 3D supramolecular framework for MoO2(ONO) (2) showing the intermolec-
ular hydrogen-bonding pattern. The hydrogen and carbon atoms corresponding to
the fenchyl moieties, have been omitted for clarity.
Symmetry transformations used to generate equivalent atoms: #1 y, x, ꢀz.

M.R. Pedrosa et al. / Polyhedron 29 (2010) 841–849
847
pyridines) led consistently to the isolation of the unchanged
complex.
3.3.2. Synthesis and characterisation of [MoO(O2)(ONO)] (4)
The relevance of molybdenum(VI) complexes as catalysts for
processes such as oxidation of olefins, has prompted us to study
the replacement of oxo by peroxo in the complex 2 [29].
Treatment of [MoO2(ONO)] (2) with H2O2 at room temperature
resulted in a solution which afforded the deep yellow oxoperoxo
complex [Mo(O)(O2)(ONO)] (4) (99%). The complex 4 is a solid sol-
uble in common solvents, that decomposes by action of the light,
so that it must be stored in the dark, but it can be handled in air
for brief periods of time.
On the other hand, we attempted the reduction of 2 with
phosphines and phosphites. In the case of phosphites and bulky
phosphines (PPh3, PBu3) no reaction was observed, even after
refluxing in toluene or xylene for 2 h under nitrogen. The solution
remained colourless and 2 was recovered without evidence of
alteration. However, with PMe3 and PEt3, a colour change to dark
brown was observed at room temperature suggesting the reduc-
tion of 2. It was not possible to ascertain and identify undoubt-
edly well defined products. Taking into account some
experimental results it seems likely that the dioxomolybde-
num(VI) would be reduced to oxomolybdenum(IV) instead of
the ubiquitous comproportion dinuclear species containing the
{Mo2O3}4+ core. Thus, when one equivalent of phosphine (PMe3
or PEt3) was used (molar ratio Mo/P = 1), it was fully transformed
to the corresponding phosphine oxide, but when using only a half
equivalent of phosphine 50% of 2 remained unaltered. Comple-
mentarily, we failed to obtain the dinuclear complex of Mo(V) de-
The infrared spectrum of 4 shows a very strong m(Mo@O) band
at 965 cmꢀ1 characteristic of the oxo terminal group, as well as an-
other band at 883 cmꢀ1 corresponding to the peroxo group [30].
The most relevant feature in the NMR of this complex is the
presence of two sets of resonances for the two fenchyl groups on
the chiral pyridine-diol ligand, because of the change of one oxo
group by a peroxo group results in the lost of the C2-symmetry
making both fenchyl groups no-equivalents. The NOESY experi-
ment shows NOE contacts that allow the full assignment of signals.
The 13C NMR spectra demonstrate, as well as in the case of com-
plexes 2 and 3, that the ligand is bound to the molybdenum core.
rived from
2
by treating [Mo2VO3(acac)4] [26], with two
equivalents of ligand 1. Only complex 2 could be recovered in
variable yields.
Thus, one can speculate that the steric encumbrance of the
coordinated chiral ligand is responsible for the unusual chemical
stability of 2, since the molybdenum centre became inaccessible
for most of reactants. However, others interesting ways of reaction
were observed for 2 as shown below.
3.4. Catalytic tests involving complex 2
Considering the well-known efficiency of many dioxomolybde-
num(VI) complexes as catalysts in oxygen atom transfer reactions
[31], we decided to examine the ability of complex 2 to accomplish
the catalytic oxotransfer reaction from sulfoxide to phosphine and
from tert-butylhydroperoxide to sulphide.
On the other hand, the direct catalytic nucleophilic substitution
of propargylic alcohols is an interesting process in organic synthe-
sis that has been recently developed using a variety of reagents as
catalysts including MoO2(acac)2 [32] and MoO2Cl2(L)2 (L = DMSO,
DMF) [33].
3.3.1. Synthesis and characterisation of [MoS2(ONO)] (3)
The replacement of oxo by sulphide in compound 2 has been
examined, bearing in mind the relevance of terminal sulphide in
the active site of some molybdenum enzymes [27].
Treatment of complex [MoO2(ONO)] (2) with Lawesson’s re-
agent at room temperature afforded the pale yellow disulphide
complex [MoS2(ONO)] (3) in high yield. An interesting feature ob-
served is that only the dithiocomplex was formed when different
molar ratio Lawesson’s reagent/dioxomolybdenum complex were
tested. With defect of the Lawesson’s reagent a mixture of
[MoO2(ONO)] (2) and [MoS2(ONO)] (3) was formed, and no analyt-
ical or spectroscopical evidences of formation of [MoOS(ONO)]
were found.
3.4.1. Catalytic reduction of sulfoxides
The catalytic reduction was tested using (p-Tol)2SO, MePhSO or
DMSO as sulfoxides and PPh3, PEtPh2 or PMe3 as oxoacceptors. In
all cases, the results were compared with the corresponding reac-
tions in the absence of catalyst.
When the least hindered phosphine (PMe3) was used in combi-
nation with the least hindered sulfoxide (DMSO), the catalysed
oxotransfer reaction took place as usually known. For all other
phosphine and sulfoxide combinations, no reaction was observed
after 1 h, in THF at reflux under nitrogen. However a small amount
of phosphine oxide (3–5%) was formed in all cases when PMe3 was
used. This amount corresponds to the reaction between the cata-
lyst (3–5 mol%) and the phosphine.
The complex 3 is soluble in common solvents, but it is air sen-
sitive, so that it must be stored under nitrogen, in order to avoid
decomposition with liberation of sulphur.
The infrared spectrum for 3 shows two strong m(Mo@S) bands at
523 and 504 cmꢀ1, characteristic of the symmetric and asymmetric
stretching vibrations of the cis-[MoS2]2+ fragment, analogous to the
previously reported [27,28].
It should be noted that the 1H and 13C{1H} NMR spectra of 3
showed only one set of resonances for the two fenchyl groups on
the chiral pyridine-diol ligand consistent with the full oxo-for-sul-
phide exchange that allows to keep the C2-symmetry from the ori-
ginal dioxoderivative (2). The 1H NMR spectrum of 3 only shows
the signals corresponding to the chiral ligand shifted due to coor-
dination. Compared to the free ligand the signals corresponding
to H-8, H-12 and H-13 are shifted ca. 0.5 ppm downfield. In general
all the other signals are shifted a little bit more than in complex 2
but in the same direction. In the NOESY experiment, several sys-
tems of NOE contacts could be found, which allowed the full
assignment of signals. Among them the most interesting ones are
those involving, (i) the H-7syn, H-12 and protons from C-8 methyl
These results are consistent with the idea that the sterically
demanding tridentate ligand prevents that the phosphine, when
it acquires a certain size, removes the oxygen from the molybde-
num centre and the approach of the sulfoxide to reoxidize the
metal.
3.4.2. Catalytic oxidation of sulphides
For the catalytic oxidation reaction we chose methyl phenyl sul-
phide (PhSMe) as substrate and tert-butylhydroperoxide as oxi-
dant. In a typical catalytic run one equivalent of substrate was
treated with 2 mol% catalyst and one equivalent of oxidant in dif-
ferent solvents (THF, CH2Cl2 or EtOH). In all cases, the same exper-
imental results have been obtained, 10% sulphide and 90%
sulfoxide. The control experiments confirmed that substrate oxida-
tion in the absence of catalyst was unsuccessful. We attempted to
determine the enantioselectivity of the oxotransfer process by
HPLC, and found that the complex 2 is unable to produce a signif-
icant enantiomeric excess for the methyl phenyl sulfoxide formed.
group, (ii) the protons H-5exo, H-6exo and H-7anti, and (iii) H-5endo
,
H-6endo and protons from C-9 methyl group. 13C{1H} NMR spectra
demonstrate, as in complex 2, that the ligand is bound to molybde-
num, and show the striking shift downfield of the signal of the qua-
ternary carbon atoms C-2 (22 ppm) and C-11(9 ppm).

848
M.R. Pedrosa et al. / Polyhedron 29 (2010) 841–849
(b) R.S. Atkinson, Stereoselective Synthesis, Wiley, Chichester, 1995;
These results are encouraging but also leave the question why
(c) G. Proctor, Asymmetric Synthesis, Oxford University Press, Oxford England,
1996.
[2] (a) H.B. Kagan, in: G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.), Comprehensive
Organometallic Chemistry, vol. 8, Pergamon, Oxford, 1982;
(b) G.W. Parshall, S.D. Ittel, Homogeneous Catalysis, second ed., Wiley, New
York, 1992.
[3] (a) G. Chelucci, F. Soccolini, Tetrahedron: Asymmetry 3 (1992) 1235;
(b) M. Genov, K. Kostova, V. Dimitrov, Tetrahedron: Asymmetry 8 (1997)
1869;
the optical selectivity for this molybdenum system is so poor com-
pared to others. At this point we suggest two possible interpreta-
tions, (i) the loss of selectivity along the reaction evolution could
be attributed to the opening of the chelate ring by protonation of
one Mo–O bond from the fenchylpyridine ligand [4,8,9], (ii) it has
previously been noted that dioxomolybdenum(VI) complexes,
bearing bidentate pyridyl alcoholate ligands containing a bulky
(c) B. Koning, J. Buter, R. Hulst, R. Stroetinga, R.M. Kellogg, Eur. J. Org. Chem.
(2000) 2735.
group at
a-position to the connecting oxygen atom, are signifi-
cantly less enantiomerically selective than those with only methyl
groups at this position [34]. Both interpretations are consistent
with the results observed, but given the extremely rugged and ro-
bust catalyst, it seems difficult that the opening of the chelating
ring takes place.
[4] (a) W.A. Herrmann, J.J. Haider, J. Fridgen, G.M. Lobmaier, M. Spiegler, J.
Organomet. Chem. 603 (2000) 69;
(b) J. Fridgen, W.A. Herrmann, G. Eickerling, A.M. Santos, F.E. Kuhn, J.
Organomet. Chem. 689 (2004) 2752.
[5] (a) M. Gomez, S. Jansat, G. Muller, G. Noguera, H. Teruel, V. Moliner, E. Cerrada,
M. Hursthouse, Eur. J. Inorg. Chem. (2001) 1071;
(b) K. Kandasamy, H.B. Singh, R.J. Butcher, J.P. Jasinski, Inorg. Chem. 43 (2004)
5704;
3.4.3. Catalytic nucleophilic substitution of propargylic alcohols
The catalytic experiment was carried out using 1,3-diphenyl-2-
propyn-1-ol as propargylic alcohol, 2-chloroethanol as nucleophile
and 5 mol% of complex 2 as catalyst. The reaction led, in mild con-
ditions, to the quantitative formation of the corresponding ether,
3-(2-chloro-ethoxy)-1,3-diphenyl-propyne, but in a racemic form.
(c) S.M. Bruno, B. Monteiro, M.S. Balula, F.M. Pedro, M. Abrantes, A.A. Valente,
M. Pillinger, P. Ribeiro-Claro, F.E. Kuhn, I.S. Gonçalves, J. Mol. Catal. A: Chem.
260 (2006) 11.
[6] (a) F.E. Kuhn, A.M. Santos, A.D. Lopes, I.S. Gonçalves, J.E. Rodriguez-Borges, M.
Pillinger, C.C. Romão, J. Organomet. Chem. 621 (2001) 207;
(b) F.E. Kuhn, J. Zhao, W.A. Herrmann, Tetrahedron: Asymmetry 16 (2005)
3469.
[7] (a) A.K. Sah, C.P. Rao, P.K. Saarenketo, E.K. Wegelius, E. Kohlemainen, K.
Rissanen, Eur. J. Inorg. Chem. (2001) 2773;
(b) J. Zhao, X. Zhou, A.M. Santos, E. Herdtweck, C.C. Romão, F.E. Kuhn, Dalton
Trans. (2003) 3736;
4. Conclusion
(c) X. Zhou, J. Zhao, A.M. Santos, F.E. Kuhn, Z. Naturforsch. B 59 (2004) 1223;
(d) X.-Y. Wang, H.-C. Shi, C. Sun, Z.-G. Zhang, Tetrahedron 60 (2004) 10993.
[8] S. Gago, J.E. Rodriguez-Borges, C. Teixeira, A.M. Santos, J. Zhao, M. Pillinger, C.D.
Nunes, Z. Petrovski, T.M. Santos, F.E. Kuhn, C.C. Romão, I.S. Gonçalves, J. Mol.
Catal. A: Chem. 236 (2005) 1.
[9] I.S. Gonçalves, A.M. Santos, C.C. Romão, A.D. Lopes, J.E. Rodriguez-Borges, M.
Pillinger, P. Ferreira, J. Rocha, F.E. Kuhn, J. Organomet. Chem. 626 (2001) 1.
[10] Z. Petrovski, A.A. Valente, M. Pillinger, A.S. Dias, S.S. Rodrigues, C.C. Romão, I.S.
Gonçalves, J. Mol. Catal. A: Chem. 249 (2006) 166.
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(2004) 227;
(b) M. Abrantes, A. Sakthivel, C.C. Romão, F.E. Kuhn, J. Organomet. Chem. 691
(2006) 3137.
[12] (a) F.J. Arnáiz, R. Aguado, M.R. Pedrosa, A. De Cian, J. Fischer, Polyhedron 19
(2000) 2141;
We have developed a one-pot procedure that allows the prepa-
ration of a new chiral C2-symmetrical pyridine-diol ligand (1) in
high yield. A new dioxomolybdenum(VI) complex MoO2(ONO)
(2) bearing the ligand 1 can be obtained in good yield by a straight-
forward synthesis. The complex 2 is a five-coordinated monomer,
showing a distorted trigonal bipyramidal disposition, an unusual
geometry in the dioxomolybdenum(VI) chemistry. We found that
reactions of 2 with O- or N-donors ligands do not lead to the for-
mation of the corresponding addition compounds. However the
sulphide and peroxo derivatives, [MoS2(ONO)] (3) and
[MoO(O2)(ONO)] (4), were also readily prepared from 2.
We have proved that 2 is a rare catalyst in oxygen atom transfer
reactions from sulfoxides to phophines since only PMe3 is able to
reduce 2 and DMSO to oxidise the reduction product in mild con-
ditions. Moreover, we have developed a method for the selective
oxidation of sulphides to the corresponding sulfoxides using tert-
butylhydroperoxide catalysed by 2. Also, we have found that com-
plex 2 works as an efficient catalyst in nucleophilic substitution
reactions of propargylic alcohols. Finally, we have proved that
complex 2, in the tested conditions, leads to no significant enantio-
selective processes.
(b) F.J. Arnáiz, R. Aguado, M.R. Pedrosa, J. Mahía, M.A. Maestro, Polyhedron 20
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[14] SAINT Integration Software, Siemens Analytical X-ray Instruments Inc., Madison,
Supplementary data
WI, 2000.
CCDC 706392 and 706391 contain the supplementary crystallo-
graphic data for (1) and (2). These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
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We would like to thank Junta de Castilla y León (BU033A06 and
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61436/BQU) for financial support. J. Escribano thanks Junta de
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