Bis(phenolato)molybdenum complexes as catalyst precursors for the deoxydehydration of biomass-derived polyols

Article abstract of DOI:10.1016/j.poly.2016.03.053

Bio-based polyols can be converted to olefins and furan derivatives in one step by combined reduction and dehydration (deoxydehydration, DODH). A series of octahedral complexes of hexavalent molybdenum containing an (OSSO)-type bis(phenolate) ligand were prepared and structurally characterized. These complexes were screened as catalyst precursors for the deoxydehydration of anhydroerythritol using 3-octanol as reducing agent. Microwave heating allows a lower reaction temperature.

Full text of DOI:10.1016/j.poly.2016.03.053

Accepted Manuscript
Bis(phenolato)molybdenum Complexes as Catalyst Precursors for the Deoxy-
dehydration of Biomass-Derived Polyols
Klaus Beckerle, Andreas Sauer, Thomas P. Spaniol, Jun Okuda
PII:
S0277-5387(16)30064-X
http://dx.doi.org/10.1016/j.poly.2016.03.053
POLY 11918
DOI:
Reference:
Polyhedron
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Accepted Date:
28 January 2016
25 March 2016
Please cite this article as: K. Beckerle, A. Sauer, T.P. Spaniol, J. Okuda, Bis(phenolato)molybdenum Complexes
as Catalyst Precursors for the Deoxydehydration of Biomass-Derived Polyols, Polyhedron (2016), doi: http://
dx.doi.org/10.1016/j.poly.2016.03.053
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Bis(phenolato)molybdenum Complexes as Catalyst Precursors for the
Deoxydehydration of Biomass-Derived Polyols
Klaus Beckerle, Andreas Sauer, Thomas P. Spaniol, Jun Okuda*
Institute of Inorganic chemistry, RWTH Aachen University,
Landoltweg 1, 52056 Aachen, Germany
The e-mail address of Prof. Jun Okuda is: jun.okuda@ac.rwth-aachen.de
Abstract
Bio-based polyols can be converted to olefins and furan derivatives in one step by combined
reduction and dehydration (deoxydehydration, DODH). A series of octahedral complexes of
hexavalent molybdenum containing an (OSSO)-type bis(phenolate) ligand were prepared and
structurally characterized. These complexes were screened as catalysts for the
deoxydehydration of anhydroerythritol using 3-octanol as reducing agent. Microwave heating
allows a lower reaction temperature.
Keywords
Deoxydehydration • Molybdenum bis(phenolate) complexes • Biomass conversion • Catalysis
1. Introduction
Transformation of biomass into platform chemicals and fuel components requires efficient
methods to reduce the oxygen content.[1] Especially the abundant cellulose and hemicellulose
fractions that are made up from sugar molecules contain a high oxygen to carbon ratio.
Hydrogenation of cellulosic materials has been intensely studied, but sustainable sources for
dihydrogen are still limited. Alternative pathways include deoxydehydration (DODH) that
formally combines dehydration with reduction in one step. This procedure could transform
C6-sugar alcohols directly to furan derivatives or to oxygen-free unsaturated hydrocarbons.
Scheme 1. Catalytic deoxydehydration (DODH).
Until now, the most efficient catalysts for deoxydehydration such as [CH3ReO3]
(methyltrioxorhenium, MTO) contain rhenium.[2] This rare and expensive metal should be
avoided if DODH is performed economically on a large scale. A solution may be found with
more abundant metals such as molybdenum or vanadium which show related properties to
rhenium. Deoxydehydration catalysts based on either of these metals have already been
reported but are generally not as efficient as rhenium based systems.[2c, 3]
High-valent molybdenum compounds supported by phenolate ligands are known to catalyze
oxygen transfer reactions and may be considered as models for oxotransferases.[4] These
compounds are usually based on salen- or salan-type ligands, but sulfur bridged
bis(phenolate)s were also studied.[5] We have now extended our work on bis(phenolate)

metal complexes to the coordination chemistry of Mo(VI) compounds and their reactivity in
deoxydehydration catalysis.
2. Results and Discussion
2.1 Synthesis and Characterization
Among the bis(phenolate) ligands, the tetradentate dianionic (OSSO)-type ligand framework
is especially versatile since several parameters allow to adjust the properties of a molecular
catalyst. Substituents in ortho-position are shielding the metal center and influence the
electron density. The length of the linker between the two phenol moieties determines the
molecular fluxionality. We synthesized a range of molybdenum complexes bearing these
tetradentate ligands before testing them in DODH reactions. The SCH2CH2S bridge in
proligands 1a-c previously gave rigid complexes of group 4 metals, provided the ortho-
substituent is larger than isopropyl.[6] The related C3-bridge in ligand 2 is known to give less
rigid complexes.[7] Substituents in ortho- or para-position of the aromatic ring were also
varied. All metal complexes (3a-c, 4) were prepared via a straightforward route by
eliminating HCl using triethylamine (Scheme 2).[8]
Scheme 2. Synthesis of the molybdenum(VI) complexes 3a-c and 4 with an (OSSO)-type
ligand.
The behavior of the complexes in solution was studied by NMR spectroscopy. Complex 3b
with tert-butyl substituents in ortho- as well as in para-position shows two sharp doublets for
the four protons of the 1,2-ethanediyl bridge; two singlets are found for the four tert-butyl
groups (Figure 1). Non-fluxional coordination at 23 °C is clearly indicated. The related
molybdenum complexes 3a and 3c only vary by their smaller substituents at the aromatic ring
(H or Cl instead of the tert-butyl groups). These are fluxional with coalescence temperatures

around 23 °C, as shown by the resonances of the protons of the CH2CH2 bridge that appear as
broad signals due to interconverting helical structures (Scheme 3).[9]
Scheme 3. Interconverting ∆- and Λ-helical species in the C2-bridged complexes.
1
Figure 1. H NMR spectroscopic signals of the protons of the SCH2CH2S bridge in 3a-c (23
°C, thf-d8, the dashed line represents the expected baseline).
1
The H NMR spectrum of 3a (R1, R2 = H) at 23 °C shows a pair of broad signals just below
coalescence, typical for a slow exchange process within a CH2CH2 fragment (Figure 1). In the
dichloro substituted compound 3c, a very broad signal between 2.5 and 3.8 ppm at 23 °C
indicates coalescence and thereby an enhanced exchange rate at this temperature; this signal
1
sharpens upon heating. The H NMR spectrum of 4 at 23 °C shows two multiplets due to the
A2A’2XX’ spin system.[6,7] This agrees with a fluxional C3 bridge. Below −37 °C, the
spectral pattern of 4 indicates that the exchange process is frozen (Figure 2).

Figure 2. Variable temperature 1H NMR spectroscopic signals of the protons of the S(CH2)3S
bridge in complex 4 (23 °C to −77 °C, thf-d8, vertical scales of the two parts differ for better
visibility).
The signal of the central CH2CH2CH2 protons remains broad down to −77 °C. Within the
temperature range studied (−77 - +23 °C), the two signals of the tert-butyl groups remain
distinct showing that the C2-symmetrical trans-O,O configuration is maintained (Scheme 4b).
Scheme 4. a) Conformational change of the 6-membered ring in the C3-bridged complex 4. b)
Interconversion between trans-O,O and cis-O,O-coordination.

The analogous (ONNO)-complex 6 was synthesized to examine the influence of a bridge with
harder N donors that due to the stereogeneity of the amine donors can be expected to be more
1
stereorigid (Scheme 5). H NMR spectroscopic analysis shows two singlets for the tert-butyl
groups confirming C2-symmetry. The ethylene bridge is observed as a multiplet in THF-d8,
while a typical AA’BB’-pattern appears in CD2Cl2.
Scheme 5. Synthesis of the molybdenum(VI) complex 6 with an (ONNO)-type ligand.
Crystals of 3b suitable for structure determination by X-ray diffraction were grown from THF
solution at −30 °C. The molecular structure reveals an octahedrally coordinated metal atom
with trans arranged phenolate oxygen atoms and both oxo ligands as well as thioether donors
in cis position (Figure 3). The cis-α coordinated (OSSO)-type ligand leads to non-
crystallographic molecular C2-symmetry, as found in a related [(SSSS)MoO2] complex.[10]
Figure 3. Molecular structure of 3b. Ellipsoids are drawn at the 50% probability level.
Hydrogen atoms and co-crystallized thf are omitted for clarity. Selected interatomic distances
[Å] and angles [°]: Mo1-O1 1.946(3), Mo1-O2 1.947(3), Mo1-O3 1.697(3), Mo1-O4
1.708(3), Mo-S1 2.6955(13), Mo-S2 2.7348(13), O1-Mo1-O2 150.17(11), O3-Mo-O4
107.48(15), S1-Mo-S2 78.17(4).[11]

2.2 Deoxydehydration.
Several variants of the mechanism of the deoxydehydration reaction are discussed for
rhenium catalysts.[12] All approaches to describe the metal catalysis involve a mechanism
where a metal compound in high oxidation state reacts with a reductant to a reduced species
that still contains one oxo moiety. This intermediate undergoes condensation with a vicinal
diol to give a five-membered ring, which in turn can eliminate an olefin in a [4+2]
cycloreversion. Reminiscent of the Corey-Winter alkene synthesis,[13] the initial oxidized
species is regenerated. Since a similar mechanism can be expected for Mo(VI) compounds
bearing oxo ligands, the bis(phenolate) complexes were screened for their behavior in the
DODH of 1,4-anhydroerythritol with 3-octanol (Scheme 6).
Scheme 6. DODH of anhydroerythritol.
With all molybdenum complexes, 2,4-dihydrofuran was formed. At the elevated temperatures
required for this reaction to proceed, additional products formed (Scheme 7).

Scheme 7. Formation of byproducts during DODH.
Ketone 10 was formed directly from the alcohol that was used as reducing agent.
Anhydroerythritol subsequently reacted with the ketone to form a high boiling ketal as the
major byproduct. Additionally, dehydration reactions occurred under acidic conditions. A
minor amount of furan was formed by double dehydration of anhydroerythritol in yields
below 5%. Water elimination also led to the formation of octenes from 3-octanol, thus
depleting the reductant in the reaction mixture. To some extent, the yield of 2,4-dihydrofuran
could be optimized by variation of the amount of 3-octanol, but even in the presence of 20
equivalents the reaction needed long reaction times to give high yields. The composition of
the product mixture did not show direct dependence from the starting composition due to
several reactions proceeding simultaneously as well as the variation of octanol availability
with consumption and evaporation (Table 1, runs 5 and 6).
Table 1. Reaction products of DODH of anhydroerythritol.
Yield of
Run
Catalyst
Conv. of
[%]
7
9
[%]
11
[%]
12
[%]
13[a]
[%]
1
3a
3b
3c
4
21
41
35
74
91
81
25
3
4
˂1
˂1
˂1
2
3
2
˂1
3
18
8
6
3
6
4
37
47
57
5
30
17
17
0
14
20
5
5[b]
6[c]
7
4
1
4
4
6
0
23
5 mol% Mo and 10 equiv. of 3-octanol relative to substrate, 200 °C, 18 h reaction time; conversion and
yield determined by NMR spectroscopy’; [a] based on 3-octanol; [b] 5 equiv. of 3-octanol; [c] 20 equiv.
of 3-octanol.
Complex 4 is the most active one among the octahedral Mo(VI) bis(phenolato) complexes.
The rigid complex 3b shows the lowest activity; the 1,4-diazabutanediyl-bridged complex 6
with its (ONNO)-type ligand framework and hard nitrogen donors is also not very active, but
slightly more selective. High temperatures were essential for activity. The reaction rate as
well as the selectivity can be improved by microwave irradiation possibly due to more
homogeneous heat distribution. Reaction times are reduced from 18 h to 1 h and the reaction
occurred even at 160 °C (Table 2). While catalytic activity is clearly inferior to what has been
observed for rhenium catalysts, direct comparison to reported molybdenum and vanadium
systems is difficult due to the variation of substrates as well as reductants. For vanadium
catalysts, lower reaction temperatures (around 160 °C) seem to be sufficient. Reported
activities are in the range of 0.4 turnovers per hour per metal center.[3e] The closest
comparison might be the system consisting of erythritol as substrate, isopropanol as reductant
and ammonium heptamolybdate as catalyst which reaches about 0.4 turnovers per hour per

metal center at 250 °C.[3d] Calculated TOFs of 0.5 (Table 1, entry 5) and 0.6 (Table 1 entry
6) at 200 °C render 3b competitive as precursor for DODH of bio-based substrates.
Table 2. DODH with microwave irradiation.
Yield of
T
[°C]
Equiv.
8
Run
Catalyst
Conv. of
7 a)
[%]
9 a)
[%]
11 a)
[%]
12 a)
[%]
13 a)b)
[%]
8c
200
180
160
10
10
10
89
50
33
49
17
3
12
7
1
10
1
4
4
4
9c
˂1
˂1
10c
3
˂1
5 mol% Mo and 10 equiv. of 3-octanol relative to substrate, 1 h reaction time; conversion and yield determined
by NMR spectroscopy; [a] based on 3-octanol.
3. Conclusions
Octahedral molybdenum(IV) complexes with (OSSO)-type bis(phenolate) are catalyst
precursors for the DODH reaction of diols in the presence of 3-octanol as reductant. High
temperatures are generally required to activate the complexes, but reaction times and
temperatures can be reduced by microwave irradiation.
4. Experimental Section
4.1 General
All manipulations were performed under dry argon atmosphere using Schlenk or glovebox
techniques. NMR spectra were recorded on an Bruker Avance II NMR spectrometer at 400
MHz and 23 °C (1H: 400 MHz; 13C{1H}: 101 MHz).
Reactions with microwave heating were performed in a CEM Discover microwave system in
a 5 mL vial.
Solvents were dried and degassed using an MBraun SPS. Anhydroerythritol, 3-octanol, 1-
butanol, dodecane and DMF were commercially available from Aldrich and used after drying
over molecular sieve (4 Å) and degassing. Molybdenum compounds were purchased from
Aldrich if not stated otherwise and used as received.
Bis(phenols) used as ligand precursors were synthesized according to published
procedures.[6,7,14]
4.2 Crystal Structure Determination.
X-ray diffraction data were collected at -173 °C on a Bruker D8 goniometer with APEX CCD
area-detector in ω-scan mode. Mo-Kα radiation (multi layer optics, λ = 0.71073 Å) from an

Incoatec microsource was used. The programs SAINT+ and Mulabs were used for unit cell
determination and absorption correction.[15] The structure was solved by direct methods and
the refinement was carried out against F2 with SHELXL-2013.[16] The crystal contains co-
crystallized thf molecules in the lattice. The non-hydrogen atoms were refined with
anisotropic displacement parameters, except for those of the disordered THF molecules that
could be refined well with split positions. All hydrogen atoms were placed in calculated
positions.
4.3 Di(oxo){1,4-dithiabutanediyl-2,2‘-bis(phenolato)}molybdenum (3a)
MoO2Cl2 (100 mg, 0.503 mmol) and bis(phenol) 1a (138 mg, 0.503 mmol) were dissolved in
THF (10 mL). Upon addition of triethylamine (102 mg, 1.01 mmol, 0.140 mL) to the green
solution a colorless precipitate formed. The solution was stirred for 19 h and filtered. The
solvent was evaporated under vacuum and upon washing with pentane to remove free
bis(phenol) the product was obtained as a yellow solid in 64% yield (131 mg, 0.232 mmol).
1H NMR (400 MHz, THF-D8, 23 °C) δ (ppm): 2.42 (br. m, 2H, CH2CH2), 3.34 (br. m, 2H,
CH2CH2), 6.88 (m, 4H, CHar), 7.29 (m, 2H, CHar), 7.42 (m, 2H, CHar); 13C {1H} NMR (101
MHz, THF-D8, 23 °C) δ (ppm): 36.9 (CH2CH2), 114.6 (CHar), 118.1 (Car), 121.9 (CHar), 132.5
(CHar), 133.7 (CHar), 169.2 (Car).
Anal. Calcd. for C14H12O4S2Mo (405.92 g·mol-1): C 41.59, H 2.99; Found: C 41.87; H 3.10
4.4 Di(oxo){1,4-dithiabutanediyl-2,2’-bis(4,6-di-tert-butylphenolato)}molybdenum (3b)
MoO2Cl2 (150 mg, 0.770 mmol) and ligand precursor H2-1b (387 mg, 0.770 mmol) were
dissolved in THF (10 mL). Triethylamine (0.22 mL, 156 mg, 1.54 mmol) was added to the
green solution and a colorless precipitate was observed. The yellow solution was stirred for 19
h at ambient temperature. The mixture was filtered and the solvent removed in vacuum to
give compound 3b as yellow powder in 94% yield (453 mg, 0.720 mmol).
1H NMR (400 MHz, THF-D8, 23 °C) δ (ppm): 1.30 (s, 18 H, C(CH3)3), 1.42 (s, 18 H,
C(CH3)3), 2.39 (d, 2H, 3JHH = 10.8 Hz, CH2CH2). 3.37 (d, 2H, 3JHH = 10.8 Hz, CH2CH2), 7.39
4
4
13
(d, 2H, JHH = 2.3 Hz, CHar), 7.44 (d, 2H, JHH = 2.3 Hz, CHar); C{1H} NMR (101 MHz,
THF-D8, 23 °C) δ (ppm): 30.0 (C(CH3)3), 31.9 (C(CH3)3), 35.4 (C(CH3)3), 36.3 (C(CH3)3),
38.0 (CH2CH2), 116.3 (Car), 127.7 (CHar), 128.6 (CHar), 139.9 (Car), 145.5 (Car), 166.7 (Car).
Anal. Calcd. for C30H44O4S2Mo (628.76 g·mol-1): C 57.31, H 7.05; Found: C 57.60; H 7.18
4.5 Di(oxo){1,4-dithiabutandiyl-2,2‘-bis(4,6-dichloro-phenolato)}molybdenum (3c)
MoO2Cl2 (100 mg, 0.503 mmol) and bis(phenol) 1c (210 mg, 0.505 mmol) were dissolved in
THF (10 mL). Upon addition of triethylamine (102 mg, 1.01 mmol, 0.140 mL) to the yellow
solution a colorless precipitate formed. The orange solution was stirred for 19 h and filtered.
The solvent was evaporated under vacuum and upon washing with pentane to remove free
bisphenol the product was obtained as a yellow solid in 92% (194 mg, 0.232 mmol).

3
1H NMR (400 MHz, CDCl3, 23 °C) δ (ppm): 2.52 (d, 2H, JHH = 11.0 Hz, CH2CH2), 3.37 (d,
4
4
2H, 3JHH = 11.0 Hz, CH2CH2), 7.29 (d, 2H, JHH = 2.5 Hz, CHar), 7.42 (d, 2H, JHH = 2.5 Hz,
1
CHar); H NMR (400 MHz, THF-D8, 23 °C) δ (ppm): 3.20 (br. m, 4H, CH2CH2), 7.53 (m,
4H, CHar); 1H NMR (400 MHz, THF-D8, 50 °C) δ (ppm): 3.19 (br. s, 4H, CH2CH2), 7.59 (m,
4H, CHar); 13C {1H} NMR (101 MHz, THF-D8, 23 °C) δ (ppm): 35.8 (CH2CH2), 115.5 (CHar),
122.2 (Car), 124.0 (CHar), 130.0 (CHar), 130.8 (CHar), 161.4 (Car).
Anal. Calcd. for C14H8Cl4MoO4S2 (542.09 g·mol-1): C: 31.02, H: 1.49; Found: C: 31.79, H:
1.73
4.6 Di(oxo){1,5-dithiapentanediyl-2,2’-bis(4,6-di-tert-butylphenolato)}molybdenum (4)
MoO2Cl2 (102 mg, 0.518 mmol) and bis(phenol) 2 (261 mg, 0.505 mmol) were dissolved in
THF (10 mL). Upon addition of triethylamine (100 mg, 0.988 mmol, 0.137 mL) to the dark
green solution a colorless precipitate formed. The red brown solution was stirred for 19 h and
filtered. The solvent was evaporated from the dark red solution under vacuum and upon
washing with pentane to remove free bisphenol the product was obtained as a yellow solid in
84 % (273 mg, 0.232 mmol).
1H NMR (400 MHz, C6D6, 23 °C) δ (ppm): 1.21 (s, 18H, C(CH3)3), 1.55 (s, 18H, C(CH3)3),
2.09 - 2.28 (m, 2H, CH2(CH2)2), 3.48 - 3.62 (m, 4H, SCH2), 7.27 (d, 3H, 4JHH =2.4 Hz, CHar),
7.50 (d, 3H, 4JHH = 2.3 Hz, CHar); 1H NMR (400 MHz, THF-D8, 23 °C) δ (ppm): 1.20 (s, 18H,
3
C(CH3)3), 1.32 (s, 18H, C(CH3)3),1.53 (m, 2H, CH2(CH2)2), 2.84 (t, 4H, JHH = 1.0 Hz,
4
4
1
SCH2), 7.29 (d, 2H, JHH = 1.0 Hz, CHar), 7.32 (d, 2H, JHH = 1.0 Hz, CHar); H NMR (400
MHz, THF-D8, -79 °C) δ (ppm): 1.21 (m, 18H, C(CH3)3), 1.37 (m, 18H, C(CH3)3), 1.57 (m,
4
4
2H, CH2(CH2)2), 2.77 (m, 4H, SCH2), 7.37 (d, 2H, JHH = 1.0 Hz, CHar), 7.54 (d, 2H, JHH
=
2.3 Hz, CHar); 13C {1H}-NMR (101 MHz, THF-D8, 23 °C) δ (ppm): 23.5 (CH2(CH2)2)), 30.0
(C(CH3)3)), 31.8 (C(CH3)3), 35.2 (C(CH3)3), 36.1 (C(CH3)3), 39.0 (SCH2), 121.3 (CHar),
126.3 (Car), 128.0 (CHar), 138.8 (Car), 154.4 (Car), 165.3 (Car).
Anal. Calcd. for C31H46MoO4S2 (642.78 g·mol-1): C 57.92, H 7.21; Found: C 58.10, H 7.48
4.7 Di(oxo){1,4-diazabutanediyl-N,N’-dimethyl-2,2’-bis(4,6-di-tert-butylphenolato)}-
molybdenum (6)
MoO2Cl2 (99 mg, 0.498 mmol) and ligand precursor 5 (248 mg, 0.499 mmol) were dissolved
in THF (10 mL). Triethylamine (111mg, 1.10 mmol) was added to the yellow solution and a
colorless precipitate was observed. The yellow solution was stirred for 19 h. The mixture was
filtered and the solvent removed in vacuum to give compound 6 as yellow powder in 63%
yield (197 mg, 0.316 mmol).
1H NMR (400 MHz, THF-D8, 23 °C) δ (ppm): 1.30 (s, 18 H, C(CH3)3), 1.43 (s, 18 H,
1
C(CH3)3), 2.72-2.79 (m, 4H,CH2CH2). 3.33 (s, NCH3), 7.26 (m, 4H, CHar); H NMR (400
MHz, C6D6, 23 °C) δ (ppm): 1.26 (s, 18 H, C(CH3)3), 1.56 (s, 18 H, C(CH3)3), 2.00 (d, 2H,
3
3JHH = 9.6 Hz, CH2CH2), 2.46 (d, 2H, JHH = 9.6 Hz, CH2CH2), 3.15 (s, NCH3), 6.94 (d, 2H,
4JHH = 2.3 Hz, CHar), 7.43 (d, 2H, 4JHH = 2.3 Hz, CHar); 1H NMR (400 MHz, CD2Cl2, 23 °C)
δ (ppm): 1.30 (s, 18 H, C(CH3)3), 1.43 (s, 18 H, C(CH3)3), 2.65-2.85 (m, 4H,CH2CH2). 3.32
4
4
(s, NCH3), 7.13 (d, 2H, JHH = 2.3 Hz, CHar), 7.28 (d, 2H, JHH = 2.3 Hz, CHar); 13C{1H}

NMR (101 MHz, CD2Cl2, 23 °C) δ (ppm): 29.9 (C(CH3)3), 39.9 (C(CH3)3), 35.3 (C(CH3)3),
35.5 (C(CH3)3), 49.0 (NCH3), 60.1 (CH2CH2), 115.7 (Car), 123.7 (CHar), 138.0 (CHar), 138.8
(Car), 144.5 (Car), 185.1 (Car);
Anal. Calcd. for C32H50MoN2O4 (624.28 g·mol-1): C 61.72, H 8.09, N 4.50; Found: C 62.35;
H 7.99, N 4.92
4.8 General procedure for deoxydehydration reactions
A thick-walled glass tube with a screw cap was charged in the glovebox sequentially with the
catalyst (10 µmol), anhydroerythritol and 3-octanol in the given ratio. If applicable, the given
amount of an additional solvent was added. A magnetic stirring bar was added and the
mixture was stirred for 10 minutes at ambient temperature before being inserted into a
preheated oil bath. After the given reaction time, the glass tube was taken from the heating
bath and cooled down rapidly with cold water. Mesitylene (23 µL) was added as an internal
standard and the mixture was vigorously shaken. Upon homogenization, an aliquot (roughly
1
0.05 mL) of the mixture was taken up in 0.5 mL of CDCl3 and analyzed by H NMR
spectroscopy.
Reactions with microwave heating were conducted in an analogous manner in a sealed 5 mL
tube suitable for CEM microwaves.
Appendix A. Supplementary data
CCDC 1057638 contains the supplementary crystallographic data for 3b. 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.
Acknowledgements
We gratefully acknowledge financial support by the Cluster of Excellence at RWTH Aachen
EXC 236 “Tailor-Made Fuels from Biomass”. K. B. thanks Sophia Knecht for her assistance.
This work is dedicated to Professor Malcolm L. H. Green on the occasion of his 80th birthday.
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Graphical Abstract - Pictogram

Graphical Abstract - Synopsis
Octahedral complexes of hexavalent molybdenum containing an (OSSO)-type bis(phenolate)
ligand were prepared and structurally characterized. These complexes were screened as
catalysts for the deoxydehydration of anhydroerythritol using 3-octanol as reducing agent.