Acid-catalyzed epoxide alcoholysis in the presence of indenyl molybdenum carbonyl complexes

Article abstract of DOI:10.1016/j.jorganchem.2017.12.001

The indenyl molybdenum carbonyl complexes [IndMo(CO)₂(L)_n]BF₄ (L = NCMe with n = 3 (1), 2,2′-bipyridine (2) or 1,4,7-trimethyltriazacyclononane (3) with n = 1) promote epoxide alcoholysis under moderate reaction conditions. Complexes 1 and 2 showed the best performance for the alcoholysis of styrene oxide with different alcohol nucleophiles (acting as both reactant and solvent), leading to the corresponding 2-alkoxy-2-phenylethanol with 100% yield at 10 min and 35 °C. These catalytic results are far superior to those found for previously studied molybdenum carbonyl complexes. An efficient procedure for catalyst recovery and reuse without decrease in reaction rate is described.

Full text of DOI:10.1016/j.jorganchem.2017.12.001

Accepted Manuscript
Acid-catalyzed epoxide alcoholysis in the presence of indenyl molybdenum carbonyl
complexes
Sofia M. Bruno, Isabel S. Gonçalves, Martyn Pillinger, Carlos C. Romão, Anabela A.
Valente
PII:
S0022-328X(17)30680-0
10.1016/j.jorganchem.2017.12.001
JOM 20196
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 21 September 2017
Revised Date: 27 November 2017
Accepted Date: 1 December 2017
Please cite this article as: S.M. Bruno, I.S. Gonçalves, M. Pillinger, C.C. Romão, A.A. Valente, Acid-
catalyzed epoxide alcoholysis in the presence of indenyl molybdenum carbonyl complexes, Journal of
Organometallic Chemistry (2018), doi: 10.1016/j.jorganchem.2017.12.001.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Acid-catalyzed epoxide alcoholysis in the presence of indenyl
molybdenum carbonyl complexes
a
a,
a
b
Sofia M. Bruno , Isabel S. Gonçalves *, Martyn Pillinger , Carlos C. Romão ,
a,
Anabela A. Valente *
a
Department of Chemistry, CICECO - Aveiro Institute of Materials, University of Aveiro,
Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
b
Instituto de Tecnologia Química e Biológica da Universidade Nova de Lisboa, Av. da
República, Estação Agronómica Nacional, 2780-157 Oeiras, Portugal
*
Corresponding authors. Fax: +351 234 401470.
E-mail addresses: atav@ua.pt (A.A. Valente), igoncalves@ua.pt (I.S. Gonçalves).
_
__________________________________________________________________________
Abstract
The indenyl molybdenum carbonyl complexes [IndMo(CO) (L) ]BF (L = NCMe with n = 3
2
n
4
(1), 2,2'-bipyridine (2) or 1,4,7-trimethyltriazacyclononane (3) with n = 1) promote epoxide
alcoholysis under moderate reaction conditions. Complexes 1 and 2 showed the best
performance for the alcoholysis of styrene oxide with different alcohol nucleophiles (acting
as both reactant and solvent), leading to the corresponding 2-alkoxy-2-phenylethanol with
1
00% yield at 10 min and 35 ºC. These catalytic results are far superior to those found for
previously studied molybdenum carbonyl complexes. An efficient procedure for catalyst
recovery and reuse without decrease in reaction rate is described.
1

ACCEPTED MANUSCRIPT
Keywords: Molybdenum carbonyl complexes; Indenyl ligand; Acid catalysis; Epoxide
alcoholysis
_
__________________________________________________________________________
. Introduction
1
In the fine chemicals industry, the use of organometallic complexes to catalyse organic
transformations is widespread due to the high product selectivities that are often reachable
together with the possibility of straightforward catalyst optimization by ligand exchange. In
particular, organometallic Lewis acids (OLAs) are playing an increasingly important role in
modern organic synthesis [1]. Molybdenum-based catalysts are attractive due to the ready
availability and low cost of this element. Several molybdenum(II) carbonyl complexes are
OLAs [2] and have been used as catalysts for numerous reactions [3-6]. Motivated by such
studies, we recently started to explore molybdenum dicarbonyl [7,8], tricarbonyl [8] and
tetracarbonyl [9] complexes for the isomerization of α-pinene oxide to campholenic aldehyde
[
7,8], and the alcoholysis of styrene oxide (StyO) [8,9].
The alcoholysis of epoxides gives β-alkoxy alcohols, which can be employed as
organic solvents, intermediates in organic (e.g. to produce β-alkoxy ketones, β-alkoxy acids
and diols) and inorganic syntheses, and precursors for a broad range of pharmaceuticals [9-
1
3]. Tungsten and molybdenum based complexes may be versatile Lewis acid catalysts for
selective ring-opening reactions of epoxides [14]. The ethanolysis of StyO was tested using
5
3
the cyclopentadienyl molybdenum carbonyl complexes [(η -C H R)Mo(CO) (η -C H )] and
5
4
2
3
5
5
[
[
(η -C H )Mo(CO) (CH R)] (R = H, COOH) [8], and the tetracarbonyl complex cis-
5 5 3 2
Mo(CO) (ppp)] (ppp = 2-(1-pentyl-3-pyrazolyl)pyridine)) [9], as pre-catalysts at 55 ºC,
4
2

ACCEPTED MANUSCRIPT
leading to the formation of 2-ethoxy-2-phenylethanol (EPE). The dicarbonyl compounds led
to a faster StyO conversion (100% conversion at 10 min) than the tricarbonyl complexes
(
100% conversion at 1.5-2 h; Mo:StyO = 1:10) [8]. For cis-[Mo(CO) (ppp)], the reaction was
4
performed using a 2-fold decrease in the amount of catalyst (Mo:StyO = 1:20), leading to a
StyO conversion of only 66% at 24 h [9]. These studies reveal a pronounced structure-
activity dependence for StyO ethanolysis promoted by molybdenum carbonyl complexes.
In the present communication, we report on the catalytic performance of cationic
indenyl molybdenum carbonyl complexes of the type [IndMo(CO) (L) ]BF in the
2
n
4
alcoholysis of StyO. Very high activities were found that surpass those of the previously
studied complexes.
2
. Experimental
2
.1. Materials and methods
3
5
The complexes [(η -Ind)Mo(CO) (NCMe) ]BF (1), [(η -Ind)Mo(CO) (2,2'-bipy)]BF
2
3
4
2
4
3
5
(
2), [(η -Ind)Mo(CO) (Me tacn)]BF (3) and [(η -Ind)Mo(CO) (NCMe) ]BF (4) (2,2'-bipy =
2 3 4 2 2 4
2
,2'-bipyridine, Me tacn = 1,4,7-trimethyltriazacyclononane) were synthesized by following
3
1
literature procedures [15-17]. FT-IR and H NMR spectroscopic data for 1-3 have been
discussed in detail in refs. [15-17]. The powder XRD patterns of 1-3 are given in Figure 1; all
compounds exhibit different crystalline structures, and 1 seems the least crystalline. HBF4
(
Fluka, 54% in diethyl ether), 2,2'-bipy (Aldrich), Me tacn (97%, Aldrich), hexane (PA,
3
Sigma-Aldrich), n-pentane (PA, Carlos Erba), methanol (99.9%, Sigma-Aldrich), anhydrous
absolute ethanol (Carlos Erba), 1-butanol (99%, Alfa Aesar), styrene oxide (> 97%, Fluka),
(1R,2R)-phenylpropylene oxide (99%, Aldrich), cyclohexene oxide (98%, Aldrich), 1,2-
3

ACCEPTED MANUSCRIPT
epoxyhexane (97%, Aldrich) were purchased from commercial sources and used as received.
The alcohol solvents were kept over activated molecular sieves prior to use (3 Å for EtOH; 4
Å for MeOH). The ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate
(
[bmim]BF , 99%, Io-li-tec) and N-butyl-3-methylpyridinium tetrafluoroborate ([bmpy]BF ,
4
4
9
9%, Io-li-tec), were dried under vacuum for 2 h at 100 ºC.
FT-IR spectra were recorded using a Unicam-Mattson 7000 spectrophotometer.
Attenuated total reflectance (ATR) FT-IR spectra were recorded on the same instrument
equipped with a Specac Golden Gate Mk II ATR accessory having a diamond top-plate and
–1
KRS-5 focussing lenses, with 4 cm resolution. Powder X-Ray diffraction (XRD) data were
collected at room temperature on an X’pert MPD Philips diffractometer with a curved
graphite monochromator (Cu-K radiation, λ = 1.54060 Å) and a flat-plate sample holder, in
α
a Bragg-Brentano para-focusing optics configuration (45 kV, 50 mA). Samples were step-
scanned in 0.02º 2θ steps with a counting time of 50 s per step.
((Figure 1 here))
2
.2. Catalytic tests
The catalytic reactions were carried out under air in magnetically stirred, closed
borosilicate reaction vessels (10 mL capacity) which were immersed in an oil bath set to 35
ºC or 55 ºC. The reactor was loaded with epoxide substrate (0.82 mmol), solvent (2 mL ROH
(R = Me, Et) or EtOH:IL (180 µL:600 µL)) and molybdenum complex (40 or 80 µmol). Prior
to addition of the substrate, the reactor containing the complex and the solvent was pre-
heated for 10 min at the reaction temperature; then, the epoxide substrate (also pre-heated)
was added to the reactor, which was considered to be the initial instant of the catalytic
4

ACCEPTED MANUSCRIPT
reaction. The evolutions of the reactions were monitored using a Varian 3800 GC equipped
with a BR-5 (Bruker) capillary column (30 m × 0.25 mm; 0.25 µm) and a flame ionization
detector (FID), using H as the carrier gas.
2
The concentrations of reactants/products were determined using the internal calibration
method, i.e. based on calibration curves with cyclododecane epoxide as internal standard. The
FID response was linear in the ranges of concentrations used for the calibration curves and
sample analysis. Using the internal calibration method, the determined concentrations of
substrates/products are reliable (experimental range of error of ca. 5%), i.e. the conversion
values account for substrate consumption irrespective of the types of products formed being
detected or not by GC. The products were identified by GC-MS (Trace GC 2000 Series
(Thermo Quest CE Instruments) - DSQ II (Thermo Scientific)), equipped with a capillary
DB-5 type column (30 m × 0.25 mm; 0.25 µm), using He as the carrier gas.
With the aim of studying the stability of the complexes, and checking for the catalytic
contribution of dissolved metal species, contact tests (CT) were performed by mixing the
original complex with EtOH (Mo:StyO = 1:10) at 35 ºC (15 min and 2 h for 1 and 2,
respectively), followed by centrifugation to separate the solid phase. The liquid phase was
filtered through a 0.22 µm PTFE membrane, the solution was transferred to a separate
reactor, and pre-heated at the desired reaction temperature for 10 min. Subsequently, StyO
was added to the solution (the initial StyO:EtOH molar ratio was the same as that used in
normal catalytic tests). Alternatively, the solvent was evaporated from the liquid phases
obtained from CTs, and the resultant dried solids (corresponding to the soluble metal species
for 1 and 2) were characterised. The solid phase of the CT was separated by centrifugation
and dried under reduced pressure for 1 h at 40 ºC, and characterised.
The insoluble molybdenum compound after a typical catalytic batch run was separated
by centrifugation, thoroughly washed with n-pentane, and dried under reduced pressure for 1
5

ACCEPTED MANUSCRIPT
h, at 40 ºC. The amount of dissolved metal species was determined using the equation: (wt%
of dissolved metal species) = 100 × [(initial mass of molybdenum compound) – (mass of
recovered insoluble solid)]/(initial mass of compound).
For catalytic studies using an IL as solvent, the catalyst/IL mixture was reused after the
extraction of the reactant/products using the solvents hexane (5 × 1 mL) and n-pentane (2 × 1
mL); subsequently StyO and EtOH were added to the recovered catalyst/IL mixture in
amounts equivalent to those used for the first batch run.
3
. Results and Discussion
Complexes 1-3 (Scheme 1) were explored for the acid-catalyzed ethanolysis of styrene
oxide (StyO) using EtOH as both reactant and solvent (Mo:StyO molar ratio of 1:10, Table
). For 1 and 2, the epoxide ethanolysis was very fast, leading to 100% conversion at 1 min
reaction in the temperature range of 35-55 ºC (initial turnover frequency (TOF) = 10.3 mol
1
‒1
‒1
molMo min ). The only product formed was 2-ethoxy-2-phenylethanol (EPE, 100%
selectivity). Complex 3 led to slower StyO reaction (100% conversion at 4 h, 55 ºC, TOF =
‒1
‒1
0
.2 mol molMo min ) than 1 and 2, and products with relatively high molar mass were
formed, which were not clearly identified. Without catalyst, the reaction was sluggish (3%
conversion at 4 h, 55 ºC). The performances displayed by 1 and 2 are greatly superior to the
best-performing molybdenum carbonyl complexes studied previously, namely the allyl
5
3
complexes [(η -C H R)Mo(CO) (η -C H )] (R = H, COOH) [8], which led to EPE yields at 1
5
4
2
3
5
‒
1
‒1
min of 60-65% at 35 ºC (TOF = 6.2-6.7 mol molMo min ) and 67-71% at 55 ºC (TOF = 6.9-
‒1
‒1
7
.3 mol molMo min ).
Further catalytic studies were carried out for 1 and 2. Decreasing the amount of
complex (i.e., increasing the Mo:StyO molar ratio from 1:10 to 1:20), at 35 ºC, did not affect
6

ACCEPTED MANUSCRIPT
the catalytic results for 1 (conversion at 1 min remained 100%), indicating that the intrinsic
activity is very high. For 2, a decrease in conversion at 1 min was observed, although the
‒1
‒1
initial TOF was similar (10.1 mol molMo min ). The catalytic reaction was faster for 1 than
2
, which may be partly due to differences in catalyst solubility since 1 was completely
dissolved under the reaction conditions used, whereas 2 was only partially dissolved; ca. 55
wt% (based on the mass of the recovered insoluble compound; please see the experimental
section for details) of the initial mass was dissolved at 15 min. The lower conversion at 1 min
observed for the higher 2:StyO molar ratio of 1:20 may be associated with the kinetics of
dissolution of the molybdenum compound, affecting the concentration of dissolved active
species with time, and consequently the catalytic reaction kinetics. Decreasing the amount of
2
(Mo:StyO = 1:45) until it was completely soluble (and keeping constant the initial
‒1
‒1
concentration of StyO) led to a TOF of 15 mol molMo min and 98% conversion at 30 min,
5 ºC.
3
((Table 1 and Scheme 1 here))
The reaction mechanism of epoxide alcoholysis generally involves the nucleophilic
attack at one of the carbon atoms of the oxirane ring, giving an alkoxy alcohol product
18,19]. The alcoholysis of StyO using other aliphatic alcohols (MeOH, BuOH), in the
[
presence of 1 or 2 at 35 ºC (Mo:StyO = 1:20), gave the corresponding 2-alkoxy-2-
phenylethanol as the only product. StyO alcoholysis using MeOH or EtOH led to similarly
outstanding catalytic results; quantitative yield of the 2-alkoxy-2-phenylethanol at 1 min for
1
/(MeOH or EtOH) and 10 min for 2/(MeOH or EtOH) (Table 1). With BuOH as
nucleophile, conversion at 1 min was 92% for 1/BuOH and 38% for 2/BuOH (Table 1). The
StyO/BuOH reaction was slower than with MeOH and EtOH, which may be partly due to
7

ACCEPTED MANUSCRIPT
differences in nucleophilicity of BuOH relative to MeOH and EtOH [19]. The use of ethanol
is attractive since it is less toxic and has reached industrial scale production from renewable
biomass [20,21].
Complexes 1 and 2 were further investigated for the ethanolysis of other epoxides at 35
or 55 ºC, namely (1R,2R)-phenylpropylene oxide (MeStyO), cyclohexene oxide (Cy6O) and
1
,2-epoxyhexane (C6O), Table 2. With MeStyO as substrate (Mo:MeStyO = 1:10, 35 ºC), the
two complexes led to 100% conversion at 1 min reaction, and 1-ethoxy-1-phenyl-2-propanol
was the only product formed (100% selectivity). Decreasing the amount of catalyst by 50%
(Mo:MeStyO molar ratio of 1:20) led to slower initial reaction; 100% conversion at 10 min
for 1 and 30 min for 2. These results suggest that MeStyO is less reactive than StyO. The
methyl group in MeStyO may influence the nucleophilic attack of the aliphatic alcohol on the
epoxide, partly due to steric effects [22]. The ethanolysis of Cy6O at 55 ºC (Mo:Cy6O =
1
:10) gave 2-ethoxycyclohexanol in quantitative yield at 1 min for 1, and 85% yield (100%
conversion) at 10 min for 2. These results suggest that the two complexes possess activity for
the alcoholysis of aromatic and aliphatic epoxides. With the linear epoxide substrate C6O,
1
00% conversion was reached at 10 min for 1 and 1 h for 2 (55 ºC). The linear C6 epoxide
substrate was less reactive than the cyclic C6 one. The reaction products were 1-ethoxy-2-
hexanol and 2-ethoxy-1-hexanol, formed in 62%/38% yield for 1, and 59%/29% yield for 2
(unidentified by-products were formed in the presence of 2). Overall, 1 and 2 may possess
activity for the alcoholysis of linear and cyclic epoxides, and, in general, 1 is more active
than 2.
((Table 2 here))
8

ACCEPTED MANUSCRIPT
Compounds 1 and 2 are very active for the aromatic and aliphatic (cyclic and linear)
substrates studied. The trend in the reaction rate for 1 and 2 gives comparable results for the
cyclic substrates (aliphatic and aromatic), while the linear substrate tends to give slower
conversions. This fact can be due to competition effects in the nucleophilic attack of the
aliphatic alcohol, since the formation of isomeric alkoxy alcohols was detected.
In order to study the influence of the indenyl ring hapticity on catalytic performance,
5
5
the
η -Ind congener of complex 1, namely [(η -Ind)Mo(CO) (NCMe) ]BF (4), was tested
2 2 4
under similar homogeneous StyO reaction conditions (Mo:StyO = 1:10; 35 ºC). Complexes 1
and 4 possess different indenyl hapticity modes (the addition of one NCMe ligand to 4 leads
5
3
to η → η ring slippage, Scheme 2). Complex 4 led to fast StyO reaction (95%/100 %
‒1
‒1
conversion at 1 min/10 min) and initial TOF was 9.8 mol molMo min , which is slightly
‒1
‒1
3
lower than for 1 (TOF = 10.3 mol molMo min ). The η -Ind mode for 1 may have
stabilizing effects that lead to slight differences in reactivity compared to 4 [23,24].
((Scheme 2 here))
With the objective of studying the stability of the complexes, contact tests (CT) were
carried out by mixing 1 or 2 with EtOH, at 35 ºC (described in detail in section 2.2). The
catalyst/EtOH mixture of the CT was homogeneous for 1, whereas a suspension was obtained
for 2 (matching the observations for the respective normal catalytic tests). The liquid phases
of CTs were tested for StyO ethanolysis by adding StyO in an amount equivalent to that used
for normal catalytic tests. For 1, the results for the CT were similar to those for the normal
catalytic test (Table 1). For 2, the reaction was initially somewhat slower for the CT than for
the normal catalytic test, although 100% conversion was reached at 30 min (Table 1). These
results indicate that the catalytic reaction occurs in homogeneous phase. Complex 2 and the
9

ACCEPTED MANUSCRIPT
solid obtained from the CT with 2, denoted 2-EtOH/35-CT, exhibited matching ATR FT-IR
spectra (Figure 2). Nevertheless, the catalytic reaction occurred in homogeneous phase, and
thus it is important to isolate and characterise the dissolved metal species to ascertain the
structural stability. Attempts to isolate metal species from the liquid phases through
precipitation were not successful. Hence, the solvent was evaporated from the liquid phases
obtained from CTs, and the resultant dried solids (1-EtOH/35-CT-Liq and 2-EtOH/35-CT-
Liq for 1 and 2, respectively) were characterized by ATR FT-IR (Figure 2). The ATR FT-IR
spectrum of 1-EtOH/35-CT-Liq was different from that of the original complex 1, indicating
conversion to an as yet unidentified species. The solid 1-EtOH/35-CT-Liq exhibited no bands
due to stretching vibrations of carbonyl or MeCN ligands, suggesting that complete
dissociation of these ligands occurred. Conversely, 2-EtOH/35-CT-Liq exhibited few spectral
-1
differences from 2 in the range 1000-2000 cm , suggesting that it is somewhat more stable
than 1. Specifically, for 2-EtOH/35-CT-Liq the bands due to stretching vibrations of carbonyl
ligands remained present, albeit with reduced relative intensity. On the other hand, some
noticeable spectral differences between 2 and 2-EtOH/35-CT-Liq for wavenumbers less than
-1
1
000 cm indicate that the isolated solid may comprise a mixture of 2 and an as yet
unidentified species, which may be an oxomolybdenum compound on the basis of the
-1
appearance of a relatively weak band at 957 cm , assignable to a Mo=O stretching vibration.
Further investigation of the catalyst stability for 2/EtOH was carried out by separating
the solid from the reaction mixture obtained from a normal catalytic batch run; the
undissolved solid was separated by centrifugation, thoroughly washed with n-pentane, and
dried under reduced pressure for 1 h, at 40 ºC, giving 2-EtOH/35. The ATR FT-IR spectrum
of the recovered solid 2-EtOH/35 resembled more closely that of 2-EtOH/35-CT-Liq than of
‒
2
. The solid 2-EtOH/35 displayed the bands associated with the ligands Ind (731 and 769 cm
1
‒1
)
and 2,2'-bipy (1600 and 1609 cm ), Figure 2. However, no bands due to stretching
1
0

ACCEPTED MANUSCRIPT
vibrations of carbonyl ligands were observed for the recovered solid, indicating that complete
decarbonylation of 2 had occurred. This was supported by the appearance of relatively weak
-
1
bands at 935 and 957 cm that may be due to stretching vibrations of Mo=O groups. The
spectral differences between 2-EtOH/35-CT and 2-EtOH/35, together with the fact that the
former resembles much more closely the spectrum of 2, suggest that 2 may be more stable
under the conditions of the CT than of the catalytic reaction; the main difference in
conditions used for the two tests is that no substrate was present for the CT (the complex had
no catalytic role, and the colour of the solution remained unchanged), whereas for the
catalytic test the substrate is present from the initial instant. During the course of the catalytic
reaction, 2 may undergo faster structural changes, and the catalytic reaction mechanism may
involve the coordination of the substrate to the metal centre with concomitant changes in the
coordination sphere of the complex, followed by the nucleophilic attack of the alcohol
reactant on StyO, leading to EPE [19,25,26].
The powder XRD patterns of 2 and the recovered solid 2-EtOH/35-CT indicate that the
two compounds are crystalline, exhibiting matching XRD patterns (Figure 3), which is
consistent with the matching ATR FT-IR spectra (Figure 2). On the other hand, the recovered
solid 2-EtOH/35 (possessing a different chemical structure) was essentially amorphous.
((Figures 2 and 3 here))
Catalyst recovery was studied for the systems (1 or 2)/StyO/EtOH using an ionic liquid
(
IL) at 35 ºC (Tables 3 and 4). Commercially available ILs possessing the same anion as the
complexes were chosen, namely [bmim]BF and [bmpy]BF . Homogeneous mixtures were
4
4
obtained for both ILs (1 and 2 were completely soluble). The systems 1/IL led to similar
catalytic results to those without IL, and EPE was formed in quantitative yield at 1 min
1
1

ACCEPTED MANUSCRIPT
reaction (Table 3). Comparably, 2/[bmim]BF led to similar catalytic results to those for the
4
system without IL, and EPE was formed in quantitative yield at 10 min reaction (Table 4).
For 2/[bmpy]BF , quantitative yield of EPE was reached at 30 min. The catalytic systems
4
were reused after separating the reaction product by solvent extraction, and subsequently
adding StyO and EtOH in amounts equivalent to those used in the first batch run. Hexane and
n-pentane were used as the extractants, since (i) they are immiscible with the ILs, (ii) 2 was
insoluble in these organic solvents, and (iii) the substrate/product may be efficiently extracted
from the IL/catalyst mixture (monitored by GC). For three consecutive batch runs no
significant drop in StyO conversion was observed for 1/[bmim]BF , 1/[bmpy]BF (Table 3),
4
4
and 2/[bmim]BF (Table 4). For 2/[bmpy]BF , the performance improved such that
4
4
nd
rd
quantitative yield of EPE was reached at 10 min for the 2 and 3 batch runs. Hence, catalyst
recovery and reuse mediated through use of an appropriate IL seems to be an effective way of
enhancing the productivity of these homogeneous catalysts.
((Tables 3 and 4 here))
4
. Conclusions
In conclusion, a simple highly efficient method for the preparation of β-alkoxy alcohols
is presented via ring opening of epoxides (styrene oxide, (1R,2R)-phenylpropylene oxide,
cyclohexene oxide, 1,2-epoxyhexane) by using an indenyl complex of the type
[
IndMo(CO) (L) ]BF as a catalyst precursor under moderate reaction conditions. Similar
2 n 4
catalytic results were obtained using methanol or ethanol as reacting solvents, although the
latter is eco-friendlier; n-butanol was also an effective nucleophile, although the alcoholysis
reaction was slower. Selective and very fast ethanolysis reaction at 35 ºC was verified for the
1
2

ACCEPTED MANUSCRIPT
compounds possessing L=NCMe (1) or 2,2'-bipyridine (2); 2-ethoxy-2-phenylethanol was
formed in up to 100% yield within 1 min reaction. Steady performances were observed for
the two compounds in consecutive catalytic runs performed using an ionic liquid as solvent.
Characterization studies suggested that 2 is more stable than 1. These types of complexes
may be promising candidates for other acid-catalyzed reactions, and future work will center
on identifying the nature of the active species formed under the catalytic conditions,
performing kinetic studies, and preparing heterogeneous catalysts based on these indenyl
complexes.
Acknowledgments
This work was developed in the scope of the project CICECO – Aveiro Institute of
Materials (POCI-01-0145-FEDER-007679) financed by national funds through the Fundação
para a Ciência e a Tecnologia (FCT) (ref. UID/CTM/50011/2013) and Ministério da
Educação e Ciência (MEC) and when applicable, cofinanced by Fundo Europeu de
Desenvolvimento Regional (FEDER) under the PT2020 Partnership Agreement. The FCT
and the European Union are acknowledged for a post-doctoral grant to S. M. B.
(SFRH/BPD/108845/2015), cofunded by Ministério da Ciência, Tecnologia e Ensino
Superior (MCTES) and the European Social Fund through the program Programa
Operacional Potencial Humano (POPH) of Quadro de Referência Estratégica Nacional
(QREN).
References
[
1] R. Qiu, Y. Chen, S.-F. Yin, X. Xu, C.-T. Au, RSC Adv. 2 (2012) 10774.
1
3

ACCEPTED MANUSCRIPT
[
[
(
[
(
[
(
[
[
2] W. Beck, K. Sunkel, Chem. Rev. 88 (1988) 1405.
3] P.V. Bonnesen, C.L. Puckett, R.V. Honeychuck, W.H. Hersh, J. Am. Chem. Soc. 111
1989) 6070.
4] A.V. Malkov, I.R. Baxendale, D. Dvorak, D.J. Mansfield, P. Kocovsky, J. Org. Chem. 64
1999) 2737.
5] A.V. Malkov, S.L. Davis, I.R. Baxendale, W.L. Mitchell, P. Kocovsky, J. Org. Chem. 64
1999) 2751.
6] P. Kocovsky, G. Ahmed, J. Srogl, A.V. Malkov, J. Steele, J. Org. Chem. 64 (1999) 2765.
7] S.M. Bruno, C.A. Gamelas, A.C. Gomes, A.A. Valente, M. Pillinger, C.C. Romão, I.S.
Gonçalves, Catal. Commun. 23 (2012) 58.
8] S.M. Bruno, A.C. Gomes, M. Abrantes, A.A. Valente, M. Pillinger, I.S. Gonçalves, J.
Organomet. Chem. 799-800 (2015) 179.
9] L.S. Nogueira, P. Neves, A.C. Gomes, A.A. Valente, M. Pillinger, I.S. Gonçalves, J.
Organomet. Chem. 846 (2017) 185.
[
[
[
[
[
10] J.G. Smith, Synthesis-Stuttgart, (1984) 629.
11] N. Iranpoor, I.M. Baltork, Synth. Commun. 20 (1990) 2789.
12] P. Silva, F. Vieira, A.C. Gomes, D. Ananias, J.A. Fernandes, S.M. Bruno, R. Soares,
A.A. Valente, J. Rocha, F.A.A. Paz, J. Am. Chem. Soc. 133 (2011) 15120.
[
(
[
[
13] Y.-X. Zhou, Y.-Z. Chen, Y. Hu, G. Huang, S.-H. Yu, H.-L. Jiang, Chem. Eur. J. 20
2014) 14976.
14] C. Wang, L. Luo, H. Yamamoto, Acc. Chem. Res. 49 (2016) 193.
15] J.R. Ascenso, C.G. de Azevedo, I.S. Gonçalves, E. Herdtweck, D.S. Moreno, C.C.
Romão, J. Zühlke, Organometallics 13 (1994) 429.
16] J.R. Ascenso, C.G. de Azevedo, I.S. Gonçalves, E. Herdtweck, D.S. Moreno, M.
Pessanha, C.C. Romão, Organometallics 14 (1995) 3901.
[
1
4

ACCEPTED MANUSCRIPT
[
(
[
(
[
17] J.R. Ascenso, I.S. Gonçalves, E. Herdtweck, C.C. Romão, J. Organomet. Chem. 508
1996) 169.
18] R.F. Mendes, P. Silva, M.M. Antunes, A.A. Valente, F.A.A. Paz, Chem. Commun., 51
2015) 10807.
19] L. Zhang, C. Hu, W. Mei, J. Zhang, L. Cheng, N. Xue, W. Ding, J. Chen, W. Hou, Appl.
Surf. Sci. 357 (2015) 1951.
[
[
(
[
20] D.M. Alonso, J.Q. Bonda, J.A. Dumesic, Green Chem 12 (2010) 1493.
21] M. Vohra, J. Manwar, R. Manmode, S. Padgilwar, S. Patil, J. Environ. Chem. Eng. 2
2014) 573.
22] S.M. Bruno, A.C. Gomes, T.S.M. Oliveira, M.M. Antunes, A.D. Lopes, A.A. Valente,
M. Pillinger, I.S. Gonçalves, Org. Bio. Chem. 14 (2016) 3873.
23] M.J. Calhorda, C.A. Gamelas, I.S. Gonçalves, E. Herdtweck, C. C. Romão, L. F. Veiros,
Organometallics 17 (1998) 2597.
24] C.A. Gamelas, N.A.G. Bandeira, C.C.L. Pereira, M.J. Calhorda, E. Herdtweck, M.
Machuqueiro, C.C. Romão, L.F. Veiros, Dalton Trans. 40 (2011) 10513.
[
[
[
[
25] M.L. Kantam, K. Aziz, K. Jeyalakshmi, P.R. Likhar, Catal. Lett. 89 (2003) 95.
26] L. Zhang, C. Hu, J. Zhang, L. Cheng, Z. Zhai, J. Chen, W. Ding, W. Hou, Chem.
Commun. 49 (2013) 7507.
1
5

ACCEPTED MANUSCRIPT
Figure Captions
Scheme 1. Cationic molybdenum carbonyl complexes in 1-3.
Scheme 2. Indenyl ring slippage upon addition of one NCMe ligand to 4.
Figure 1. Powder XRD patterns of (a) 1, (b) 2 and (c) 3.
Figure 2. ATR FT-IR spectra of (a) 1, (b) 1-EtOH/35-CT-Liq, (c) 2, (d) 2-EtOH/35-CT, (e)
2
-EtOH/35-CT-Liq, and (f) 2-EtOH/35.
Figure 3. Powder XRD patterns of (a) 2 and the corresponding recovered solids (b) 2-
EtOH/35-CT and (c) 2-EtOH/35.
1
6

ACCEPTED MANUSCRIPT
Table 1
Alcoholysis of styrene oxide in the presence of complexes 1-3.
a
Complex Solv./Temp. (ºC)
Mo:StyO
Time
(min)
Conv. Initial TOF
b
‒
1
-1
molar ratio
(%)
(
mol molMo min )
1
1
1
1
EtOH/55
1:10
1:10
1:20
-
1
1
1
1
100
100
100
99
10.3
EtOH/35
10.3
EtOH/35
20.5
c
EtOH/35-CT
-
1
1
1
1
1
1
1
1
1
1
3
1
1
1
1
3
1
1
3
6
1
1
3
1
2
0
100
100
92
-
1
1
MeOH/35
BuOH/35
1:20
1:20
20.5
18.8
0
100
100
100
49
-
2
2
2
EtOH/55
EtOH/35
EtOH/35
1:10
1:10
1:20
10.3
10.3
10.1
0
100
32
-
c
2
EtOH/35-CT
-
-
0
0
78
-
100
43
-
2
2
MeOH/35
BuOH/35
1:20
1:20
8.8
0
100
38
-
7.8
0
89
-
00
100
33
-
2
3
EtOH/35
EtOH/55
1:45
1:10
15.0
0
0
0
89
-
98
-
100
2
-
0.2
0
22
-
-
-
-
0
49
80
40
91
100
a
b
Reaction conditions: [StyO] = 0.39 M. StyO conversion. The only product was the
0
corresponding 2-alkoxy-2-phenylethanol (100% selectivity), excluding complex 3 which

ACCEPTED MANUSCRIPT
c
led to higher molar mass products. Liquid phase obtained from the contact test (CT;
StyO and EtOH in amounts equivalent to those used in a typical batch run using
Mo:StyO molar ration of 1:10).

ACCEPTED MANUSCRIPT
Table 2
Ethanolysis of different epoxides, in the presence of complexes 1 and 2.
a
b
c
Complex Substrate/ Mo:StyO Time Conv. Select.
Reaction product
T (ºC)
molar ratio (min) (%)
(%)
1
2
1
MeStyO/35 1:10
MeStyO/35 1:10
MeStyO/35 1:20
1
1
1
1
1
1
3
100
100
98
100
100
100
100
100
100
100
1
-ethoxy-1-phenyl-2-
0
100
79
propanol
2
MeStyO/35 1:20
0
0
98
100
1
2
Cy6O/55 1:10
Cy6O/55 1:10
1
1
1
100
94
100
82
0
100
85
2-ethoxycyclohexanol
d
1
2
C6O/55
C6O/55
1:10
1:10
1
1
1
3
6
100
14
62; 38
58; 25
68; 28
63; 28
59; 29
d
d
d
d
1
2
-ethoxy-2-hexanol
0
0
0
73
96
100
-ethoxy-1-hexanol
a
b
c
Reaction conditions: [Substrate] = 0.39 M. Substrate conversion. Product
0
d
selectivity. Selectivity to 1-ethoxy-2-hexanol and 2-ethoxy-1-hexanol

ACCEPTED MANUSCRIPT
Table 3
a
Ethanolysis of styrene oxide using 1/IL systems at 35 ºC.
b
IL
Run Reaction time (min) Conv. (%)
[
bmim]BF4
1
2
3
1
2
2
3
3
1
1
1
1
1
10
1
100
100
100
100
98
100
98
100
[
bmpy]BF4
10
a
Reaction conditions: 40 µmol of Mo, 0.82 mmol StyO,
80 µL EtOH and 0.6 mL IL. StyO conversion. The only
b
1
product was 2-ethoxy-2-phenylethanol (100% selectivity).

ACCEPTED MANUSCRIPT
Table 4
Ethanolysis of styrene oxide using 2/IL systems at 35 ºC.
a
b
IL
[bmim]BF4
Run Reaction time (min) Conv. (%)
1
1
2
2
2
3
3
3
1
1
1
2
2
3
3
1
10
1
10
30
1
10
30
1
10
30
1
10
1
47
100
53
98
100
25
98
100
52
90
100
71
[
bmpy]BF4
100
77
100
10
a
Reaction conditions: 40 µmol of Mo, 0.82 mmol StyO,
80 µL EtOH and 0.6 mL IL. StyO conversion. The only
b
1
product was 2-ethoxy-2-phenylethanol (100% selectivity).

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Highlights
+
1
2
3
4
5
) Cationic [IndMo(CO) (L) ] complexes as (pre)catalysts for styrene oxide alcoholysis.
2
n
) MeOH, EtOH or BuOH as solvent and reactant to give 2-alkoxy-2-phenylethanol (APE).
) Quantitative yield of APE within 1 min at 35 ºC and 5 mol% (pre)catalyst.
) Catalytic performance surpasses that of previously studied Mo carbonyl complexes.
) Recycling of homogeneous catalyst/ionic-liquid system with retention of performance.