An Iron-Based Dehydration Catalyst for Selective Formation of Styrene

Olaf Nachtigall,* Andrew I. VanderWeide, William W. Brennessel, and William D. Jones *

An Iron-Based Dehydration Catalyst for Selective Formation of

Styrene

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sı Supporting Information

ABSTRACT: We report the synthesis and crystal structure of [Fe(OTf) (FOX)] (A). This

robust iron(II) complex was successfully applied as a homogeneous catalyst for the

dehydration of 1-phenylethanol to styrene. Even at low catalyst loadings and moderate

reaction temperatures, A showed a high catalytic eﬃciency. It was found to selectively activate

the benzylic alcohol group of 1-phenylethanol. This is challenging since the vinyl system of

styrene is highly reactive. In contrast to most of the other dehydration processes, the use of a

Brønsted acid was not necessary. Furthermore, mechanistic insights into this E -type

transformation and its competing S 1-type side reactions are reported. [Fe( HexOH)(OTf)(FOX)][OTf] (B), an alcohol adduct of

A, [Fe(H O) (FOX)][OTf] (C), the completely hydrated derivative of A, and [μ-O{Fe(OTf)(FOX)} ][OTf] (D), a dinuclear

oxidation product of A, were also characterized and are discussed.

KEYWORDS: catalysis, dehydration, iron, industrial chemistry, kinetics, isotopes, reactive intermediates

INTRODUCTION

Scheme 1. Catalytic Dehydration of 1-Phenylethanol (1) to

Styrene (2) with Achiral α-Methylbenzyl Ether (AME) 3,

Chiral AMEs 4 and 4′, and Styrene Dimer 5 as Major

Byproducts

■

Catalytic dehydration processes present an opportunity to

access valuable oleﬁns from abundant alcohols as found in

biomass. Since nucleophilic substitution reactions compete

with the desired elimination of water, ﬁnding oleﬁn-selective

catalysts is still a major challenge. Despite the potential for

higher conversion rates, homogeneous catalytic processes using

Brønsted acids are less common in industrial settings as they

lead to the corrosion of equipment and the production of

aggressive wastes.

Styrene (2) is an important oleﬁn widely used in organic

synthesis and industrial polymerization reactions. The world’s

styrene supplies are commercially produced via the dehydro-

genation of ethylbenzene and, to a lesser extent, the

dehydration of 1-phenylethanol (1). These dehydration

reactions are typically catalyzed by Brønsted acids. It is of

dehydration reactions, including a relatively low-yielding

conversion of 1 to 2.

interest to ﬁnd catalytic conditions under which 1 is converted

to 2 at high rates without oligomerization or polymerization.

This is challenging since the vinyl group of 2 is very reactive. A

simple dimer of 2 is compound 5, which is a common

byproduct along with α-methylbenzyl ether (AME) stereo-

RESULTS AND DISCUSSION

■

Catalyst Design. The aim of this study was to develop an

eﬃcient process for the selective dehydration of 1 that does

not require the use of precious metals or Brønsted acids and

that is based on homogeneous catalysis. Iron(III) chloride and

triﬂate are common Lewis acids that are often applied in

isomers 3, 4, and 4′ (Scheme 1). Under harsher conditions,

heavier oligomers and polymers are formed.

The liquid-phase dehydration of 1 is typically performed at

temperatures around 170 °C with Brønsted-acidic heteroge-

neous catalysts. Klein Gebbink and co-workers showed that

Received: July 6, 2021

Revised: August 3, 2021

suspended Re O is an excellent dehydration catalyst that

selectively converts 1 to 2 in toluene at only 100 °C without

the use of a Brønsted acid. There are few studies on the use of

truly homogeneous, non-Brønsted-acidic catalysts for this

transformation. Espenson and Zhu demonstrated that

methyltrioxorhenium can be used to catalyze various

XXXX American Chemical Society

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selectively convert 1 to 2 . Figure 1 shows the homogeneous

Research Article

catalysis. However, in the presence of water or alcohols,

iron(III) ions tend to aggregate into polyalkoxo/hydroxo/oxo

iron(III) clusters. Such aggregation processes often lead to a

rapid decrease in catalytic activity and cause precipitation. This

is a reason why simple iron(III) salts are typically used in

relatively high loadings in catalysis, ranging from 5 to 15 mol

Since iron(III) ions are also known to activate vinyl

systems, their use in the selective formation of 2 is less

favorable. Iron(II) chloride and triﬂate are less Lewis-acidic

but are also considerably less soluble in organic media.

Recently, the oxidative conversion of 1 to benzaldehyde was

reported to be catalyzed by a molecular iron(II) scorpionate-

type catalyst, which was immobilized on Fe O /TiO core−

shell particles.

intermediate in this oxidation reaction.

We have found that fused oxazolidine (FOX) bicycles are

ideal ligands for iron-based dehydration catalysts that

Styrene (2) was detected to be an

Figure 2. Plots of NMR data recorded during conversion of 1-

phenylethanol (1) to styrene (2) at diﬀerent concentrations of 1 in

deuterated o-dichlorobenzene (ODCB-d ) in a total volume of 0.5 mL

and with 1 mol % [Fe(OTf) (FOX)] (A) at 100 °C. The α-

methylbenzyl ethers (AMEs) 3, 4, and 4′ were the only detected

byproducts.

the consumption of 3 was measured to be faster than the

consumption of 4 and 4′. To our knowledge, this observation

has not been reported in the literature before. The diﬀerent

reactivity of the AME isomers can be explained by the

shielding of the central oxygen atom. While the methyl groups

in meso compound 3 point to the same direction and shield

only one side of the ether bridge, the methyl groups in the

enantiomers 4 and 4′ are staggered and shield both sides.

The selectivity for 2 and the conversion rate of 1 were

maximized at a 164 mM concentration (Scheme 2). 2 was

Figure 1. Depictions of the dehydration catalyst [Fe(OTf) (FOX)]

(

A). (1) Crystal structure of A. Color code: iron, blue; oxygen, red;

Scheme 2. Optimal Conditions for the Selective Conversion

of 1-Phenylethanol (1) to Styrene (2) in o-Dichlorobenzene

nitrogen, green; carbon, gray; sulfur, yellow; ﬂuorine, violet;

hydrogen, white. (2) Simpliﬁed drawing highlighting the coordination

geometry of A.

(ODCB) with [Fe(OTf) (FOX)] (A) as a Homogeneous

Catalyst

catalyst [Fe(OTf) (FOX)] (A). The tetradentate FOX ligand

inhibits the aggregation of the iron ions in the presence of

water and improves their solubility in organic media. It also

favors the formation of octahedral high-spin complexes, such as

A or its previously published chloride and bromide analogs,

with two neighboring reactive sites.

obtained in a 74% yield. Based on the consumption of 1 after

the ﬁrst 2 h, the turnover frequency (TOF) of the catalyst A

Reaction Optimization. NMR experiments showed that

the conversion of 1 catalyzed by A occurs at relatively constant

rates. No induction period was observed, which implies that no

catalytically active nanoparticles had to be formed. Instead, the

smooth kinetic reaction proﬁles are indicative of a homoge-

neous process.

Already 1 mol % of the catalyst A converts 1 to approx. 95%

at only 100 °C (Figure 2). At this temperature, no formation of

dimers or higher oligomers was observed. This means that A

does not activate the vinyl system of 2 but rather selectively

targets the benzylic alcohol 1. However, the amount of the

AMEs 3, 4, and 4′ produced and the reaction rate were found

to depend on the concentration of 1.

−

doubled from approx. 10 to 20 h by decreasing the

concentration of 1 from 1.64 M to 164 mM. This indicates a

substrate inhibition at high concentrations. The selectivity for

2 was even further increased at a 16.4 mM concentration, but

the reaction rate decreased drastically under these highly dilute

−

conditions. The TOF was found to be around 0.4 h . The

decrease implies second-order kinetics for this catalytic

dehydration process.

The NMR experiments revealed that the formation rates of

the AMEs 3, 4, and 4′ are aﬀected diﬀerently by the changing

concentration of 1 compared to the formation rate of 2. This

observation opposes the hypothesis that the AMEs are formed

as intermediates of the dehydration of 1 that ﬁnally yields

At a 1.64 M concentration of 1 in o-dichlorobenzene

ODCB), 2 was only obtained in an approx. 20% yield at 95%

8b17

(

Instead, it implies that the AMEs are more likely

conversion. The main products were the chiral AMEs 4 and 4′

as well as the achiral AME 3. Recently, an iron-catalyzed

conversion of styrenes into ketones with 1-arylethanols as

byproducts was reported, and related α-methylbenzyl ethers

were observed as minor byproducts. As the reaction

progressed, 3, 4, and 4′ began to be consumed. Interestingly,

reversibly formed byproducts.

Mechanistic Investigations. To elucidate the reaction

mechanism further, we performed experiments with a mixture

of equal amounts of deuterated 1-phenylethanol (1-d ) and

nondeuterated styrene (2) (Scheme 3). The GC−MS results

in Table 1 show that the AMEs formed after 1 h were almost

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Fe(OTf) (FOX)] (A ) to cyclohexene. Figure 3 shows that

Research Article

Scheme 3. Reaction of Deuterated 1-Phenylethanol (1-d ),

via an activation of 1 by A followed by an attack of 2 at the

activated intermediate.

Nondeuterated Styrene (2), and [Fe(OTf) (FOX)] (A) in

ortho-Dichlorobenzene (ODCB) at 120 °C

Next, we tried to characterize the activated species of 1 in

the presence of the catalyst A. In the NMR spectra, a

broadening of the aromatic and aliphatic signals of 1 was

observed. This can be attributed to a binding of 1 to the

paramagnetic high-spin complex A. Unfortunately, we could

not isolate this adduct. Instead, it was possible to crystallize

and structurally characterize the cyclohexanol ( HexOH)

complex [Fe(OTf)( HexOH)(FOX)][OTf] (B). Cyclohex-

anol is less reactive than 1 but can also be dehydrated by

[

Nondeuterated 1-phenylethanol (1), deuterated styrene (2-d ), the

deuterated α-methylbenzyl ethers (AMEs) 3-d , 4-d , and 4-d , the

partially deuterium-labeled AMEs 3-d , 4-d , and 4-d , traces of the

nondeuterated AMEs 3, 4, and 4′ (faded and in parentheses), and the

nondeuterated, partially deuterated, and deuterated styrene dimers 5,

-d , and 5-d were observed as products.

5 10

exclusively derived from 1-d . Therefore, it does not appear

that these ethers are formed via an addition mechanism from

Figure 3. Depictions of [Fe( HexOH)(OTf)(FOX)][OTf] (B). B is

an adduct of complex I and cyclohexanol. (1) Extract of the crystal

structure of B including relevant hydrogen bond networks. Color

code: iron, blue; oxygen, red; nitrogen, green; carbon, gray; sulfur,

yellow; ﬂuorine, violet; hydrogen, white. (2) Simpliﬁed drawing

highlighting the coordination geometry of B.

-phenylethanol and styrene. However, small amounts of

partially deuterated AMEs (3-d , 4-d , and 4′-d ) and traces

(

<0.1%) of nondeuterated 3, 4, and 4′ were also found in the

reaction mixture. This can be explained by the hydration of 2

to 1, which was observed after the ﬁrst hour of the reaction at

20 °C (≈0.12%). Another possibility is the activation of 2

to a cationic intermediate that connects 1, 2, 5, and the

the equatorial triﬂate ligand is displaced by the alcohol. This

was surprising since the equatorial Fe−OTf bond length of

2.06 Å in A is much shorter than the axial Fe−OTf bond

length of 2.24 Å. A similar diﬀerence was previously reported

b,11,12b,18

AMEs.

This intermediate could react with another

equivalent of either 2 to yield 5, 1 to yield an AME, or with

,18,19

water to yield 1.

The fact that nondeuterated 1-

phenolethanol and the partially deuterated AMEs were only

observed in low concentrations shows that catalyst A is

selective for alcohol substrates even if the concentration of 2 is

high and the reaction temperature is elevated.

After a total reaction time of 4 h, 1-phenylethanol was

completely consumed. Interestingly, the nondeuterated species

for the axial and equatorial M−X bonds in [M(X) (FOX)]

(M(X) = Mn(Br) , Fe(Cl) , Fe(Br) , or Co(Br) ).

Methanol was found to preferentially occupy the axial positions

in the complexes [Co(Cl)(CH OH)(FOX)][Cl] and [Ni-

(Cl)(CH OH)(FOX)][Cl]. Since the axial position is

sterically less shielded, it should also provide more space for

the relatively bulky cyclohexyl moiety. However, the equatorial

displacement appears to be thermodynamically favored in

was the least abundant styrene dimer. Also, the completely

deuterium-labeled compound 5-d₁₀was considerably less

abundant than the partially deuterated dimer 5-d . This

implies that the dimer is neither exclusively formed from 2 nor

[Fe(OTf) (FOX)] as the Fe−O bond strength is increased in

this position. In addition, the crystal structure of complex B

shows strong hydrogen bonding. The coordinated cyclo-

hexanol is hydrogen-bridged to the displaced triﬂate ion. The

same triﬂate ion is connected via an uncoordinated cyclo-

from 1-d . Consequently, 5 cannot simply be considered as the

product of a dimerization of styrene. Since the selectivity of A

for 2 as a substrate is low, it is most likely that 5 is produced

Table 1. Composition of the Reaction Mixture Shown in Scheme 3 Determined via GC−MS at Diﬀerent Time Points

time

compound (isotope ratio)

0 h

1 h

4 h

+ 1-d (1:1-d )

51.5% (0:1)

48.5% (1:0)

3.7% (1:29)

70.7% (27:10)

8.4% (1:42)

17.2% (1:50)

+ 2-d (2:2-d )

89.9% (11:10)

0.6% (1:5)

1.6% (1:10)

7.9% (1:8:3)

-d + 3-d (3-d :3-d )

-d + 4′-d + 4-d + 4′-d₁₀({4-d + 4′-d }:{4-d + 4′-d })

+ 5-d + 5-d (5:5-d :5-d )

Total amounts of deuterated, partially deuterated, and nondeuterated species of the same compound are given in percent. Ratios between

deuterated, partially deuterated, and nondeuterated species are in parentheses. The trace amounts of 3, 4, and 4′ are not included in the AME

ratios.

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Research Article

hexanol molecule to the hydroxy group of the FOX ligand.

This hydrogen bond network could be another reason for the

equatorial displacement. Halide analogs of A, namely,

No rearrangement of the disubstituted oleﬁn 5 was observed

during step (VI). This indicates that the cationic intermediate

formed after the nucleophilic attack of 2 is short-lived. In

similar reactions, the positive charge can migrate via a [1,3]-

hydride shift from a secondary carbon to a tertiary carbon.

Since the cationic intermediate is converted into an alkene by

proton elimination, Brønsted acid conditions extend the

lifetime of such intermediates and favor this rearrangement

process. However, the NMR data indicates that no [1,3]-

[

M(X) (FOX)] (M(X) = Mn(Br) , Fe(Cl) , Fe(Br) , or

2 2 2 2 2

Co(Br)₂), did not catalyze the dehydration of 1.

The reaction mechanism depicted in Scheme 4 summarizes

the ﬁndings of the NMR, GC−MS, and crystallographic

Scheme 4. Proposed Mechanism of the Conversion of 1-

Phenylethanol (1) by the Catalyst [Fe(OTf) (FOX)] (A)

hydride shift occurred during the formation of 5. This

conﬁrms that the reaction conditions are not Brønsted-acidic.

The complete mechanism shown in Scheme 4 was tentatively

formulated before but was not supported with the substantial

amount of evidence gained during this study.

Reaction Scale-Up. Since the formation rates of all

byproducts are increased at high concentrations of 1, we

decided to feed 1 slowly to a larger-scale reaction at a constant

addition rate (Scheme 5). 2 was continuously distilled from the

Scheme 5. Conversion of 1 to 2 via Reactive Distillation

reaction mixture. Such reactive distillation setups are common

for liquid-phase transformation processes in industrial

productions. The solvent, o-dichlorobenzene (ODCB), and

the starting material 1 have higher boiling points than the

product 2. The challenge is to distill 2 from the reaction

mixture before it reacts with the cationic intermediate to form

or before it polymerizes at the relatively high reaction

temperature. The high-temperature polymerization of 2 can

occur independently of a catalyst and involves free radicals.

(

I) Displacement of the equatorial triﬂate ligand of A by 1. (II)

The optimization of such distillation processes is complex

and involves sophisticated equipment and engineering skills.

Our experiment was aimed to demonstrate the potential for

the chemical optimization of this process. After only 1 h of

operation, common Brønsted-acidic catalysts, such as zeolites

Formation of a cationic intermediate. (III) Elimination of a proton

from a cationic intermediate yielding styrene (2). (IV) Recovery of A

via water elimination. (V) Nucleophilic attack of 1 at a cationic

intermediate resulting in formation of α-methylbenzyl ethers 3, 4, and

′. (VI) Formation of a styrene dimer (5) caused by nucleophilic

,24

attack of 2 at a cationic intermediate. (III), (V), and (VI) are

competing reaction pathways. Water formed in the dehydration

process may displace triﬂate ligands at iron centers in the catalytic

cycle.

and silica-aluminas, show signs of signiﬁcant deactivation.

In contrast, A was proven to be very robust. The turnover

number of 310 is high for a homogeneous iron catalyst. Also,

the reaction rate did not notably decrease over the course of

the reaction, and even higher turnover numbers could have

been achieved. This is possible because the FOX ligand

inhibits the aggregation of the iron catalyst. After the

completion of the distillation, [Fe(H O) (FOX)][OTf] (C)

experiments. In step (I), the equatorial triﬂate ligand of A is

displaced by the alcohol 1. The activation of 1 by the Lewis

acid A leads to the formation of a cationic intermediate

was crystallized from the reaction mixture (Figure 4). In this

(

Scheme 4, step (II)). This benzylic carbocation can undergo

an elimination of a proton yielding styrene (2) (Scheme 4, step

III)). The E -type conversion of 1 to 2 competes with the

oﬀ-white compound, the two triﬂate ligands of A are displaced

by water molecules. The equatorial Fe−OH bond length

(

(2.06 Å) is signiﬁcantly shorter than the axial Fe−OH bond

S 1-type transformation of 1 to 3, 4, 4′, or 5. Another

length (2.13 Å). The water did not induce oxidation or

oligomerization, and the catalytic activity was retained. It is

likely that water completely displaces the triﬂate ligands at A in

the catalytic cycle depicted in Scheme 4 as the water content in

the reaction mixtures increases during the dehydration of 1-

phenylethanol (1). Therefore, complex C could replace

complex A in Scheme 4.

molecule of 1 can attack the cation to form the α-methylbenzyl

ethers (AMEs) 3, 4, or 4′ (Scheme 4, step (V)). The side

reaction yielding the styrene dimer (5) likely proceeds via a

nucleophilic attack of a styrene molecule (2) at the cationic

intermediate (Scheme 4, step (VI)). While the formation of 5

was only observed at a temperature of at least 120 °C, 2, 3, 4,

and 4′ were already obtained at 100 °C. This is probably due

to the lower nucleophilicity of 2 than that of 1.

At high temperatures, A was found to react with air to form

the dinuclear iron(III) complex [μ-O{Fe(OTf)(FOX)} ]-

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catalyst [μ -O{FeCl(FOX)} ][Cl] , which was recently used for

Research Article

EXPERIMENTAL METHODS

■

Elemental compositions were determined on a PerkinElmer

400 Series II analyzer. Nuclear magnetic resonance data was

recorded on a Bruker Avance 400 spectrometer. GC−MS data

was recorded on a Hewlett-Packard 5890 GC Series II

equipped with a Hewlett-Packard 5970 Series mass selective

detector. NMR spectra, chromatograms, and selected MS data

are provided in the Supporting Information.

Crystallography. A Rigaku Synergy-S diﬀractometer with

dual PhotonJet-S microfocus X-ray sources (Cu Kα and Mo

Kα) and a HyPix-6000HE HPC detector was used for

crystallographic experiments. CCDC 2086601−2086604 con-

tain the supplementary crystallographic data. These data can

be obtained free of charge from The Cambridge Crystallo-

graphic Data Centre. Bond lengths and angles as well as

additional plots of the crystal structures are also provided in

the Supporting Information.

Figure 4. Depictions of [Fe(H O) (FOX)][OTf] (C). (1) Extract of

the crystal structure of C. Color code: iron, blue; oxygen, red;

nitrogen, green; carbon, gray; sulfur, yellow; ﬂuorine, violet;

hydrogen, white. (2) Simpliﬁed drawing highlighting the coordination

geometry of C.

[

OTf] (D) (Figure 5). D is similar to the dinuclear iron(III)

Synthesis. All commercial reagents were used as received

without further puriﬁcation. Diethyl ether was distilled from

sodium metal and benzophenone ketal. Acetonitrile was

distilled from phosphorus pentoxide. Reactions requiring

anhydrous conditions were performed in a Vacuum Atmos-

pheres nitrogen-ﬁlled glovebox or under an argon atmosphere

using Schlenk techniques.

[

Fe(OTf) (FOX)] (A). [Fe(Cl )(FOX)] (1.00 g, 2.35

mmol) was charged in a 20 mL scintillation vial with a Teﬂon

stir bar and suspended in anhydrous acetonitrile (2 mL) under

a nitrogen atmosphere. A solution of silver triﬂate (1.21 g, 4.71

mmol) in anhydrous acetonitrile (2 mL) was added to the

stirred suspension. Silver chloride precipitated immediately

from the reaction mixture. After the suspension was stirred for

min at room temperature, the precipitate was ﬁltered oﬀ.

Figure 5. Depictions of [μ-O{Fe(OTf)(FOX)} ][OTf] (D). (1)

Extract of the crystal structure of D not including two noncoordinated

triﬂate counteranions. Color code: iron, blue; oxygen, red; nitrogen,

green; carbon, gray; sulfur, yellow; ﬂuorine, violet; hydrogen, white.

Anhydrous diethyl ether (10 mL) was added to the clear

solution. Colorless crystals of A, suitable for X-ray crystallog-

raphy, were collected by ﬁltration after 30 min. The crystals

were rinsed with diethyl ether. Anhydrous n-hexane (5 mL)

was added to the mother liquor, and more crystals of A were

collected after 1 day and washed with diethyl ether. The

combined crystal batches were dried in vacuo to yield A as a

colorless solid (1.24 g, 1.90 mmol, 81%). C, H, and N (%) =

(

2) Simpliﬁed drawing highlighting the coordination geometry of D.

5,25

water oxidation.

However, as found in the alcohol adduct

B, the equatorial triﬂate of A was displaced to form the

dinuclear complex D, while its chloride analog is oxide-bridged

via the axial positions. To minimize the formation of complex

D, reactive distillation was performed under a constant stream

of inert gas.

3.10, 2.61, and 6.48 (calc. 33.09, 2.62, and 6.43 for

C H F Fe N O S ). The eﬀective magnetic moment (μ )

eff

of 5.05 was determined by NMR using the Evans method and

indicates a high-spin electronic conﬁguration.

Kinetic Study. Under a nitrogen atmosphere, a stock

solution of A (16.0 mg, 24.5 μmol) in 1-phenylethanol (300

mg, 2.46 mmol) was prepared at room temperature and

quickly transferred to NMR tubes with J. Young valves

CONCLUSIONS

■

In summary, we have developed a homogeneous dehydration

catalyst that is stabilized and solubilized by a fused oxazolidine

containing deuterated o-dichlorobenzene (ODCB-d ). The

following concentrations were used: 1.64 M, 100 μL of stock

(

FOX) ligand. While previous catalysts were based on

solution in 400 μL of ODCB-d ; 164 mM, 10 μL of stock

Brønsted acids or precious metals, our iron-based catalyst

operates without additives. It selectively converts 1-phenyl-

ethanol to styrene in good yields at moderate temperatures,

and only low catalyst loadings are needed. Furthermore, the

catalyst allowed us to study the diﬀerent reaction pathways of

this industrially relevant dehydration process. The results

presented in this study partially revise prevalent mechanistic

assumptions and provide more detailed insights into the

styrene production. Since selective alcohol-to-oleﬁn trans-

formations are also important for the conversion of biomass to

ﬁne chemicals, these ﬁndings are potentially of broad

relevance.

solution in 490 μL of ODCB-d

solution in 499 μL of ODCB-d . The H NMR spectra of all

; 16.4 mM, 1 μL of stock

solutions were recorded before the reaction mixtures were

heated to 100 °C. The progress of the reaction mixtures was

followed by H NMR, and no lock signal was used.

Mechanistic Study. In a nitrogen-ﬁlled glovebox, A (22.4

mg, 34.3 μmol) was charged into a 2 mL Schlenk tube, along

with a Teﬂon stir bar. The ﬂask was sealed, removed from the

glovebox, and attached to a Schlenk line. Under a stream of

nitrogen, o-dichlorobenzene (0.97 mL), which had previously

been purged with nitrogen, 1-phenylethanol-d (106 mg, 833

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μmol), and styrene (85 mg, 816 μmol) were added. A 50 μL

aliquot of the reaction mixture was taken, and then the ﬂask

was sealed and heated under stirring to 120 °C. Two more 50

μL aliquots were taken after reaction times of 1 and 4 h. All

aliquots were analyzed by GC−MS.

Energy, Basic Energy Sciences (BES) Chemical Sciences,

Geosciences, & Biosciences (CSGB) Division, for ﬁnancial

support (DE-SC0020230). The NSF MRI program is

acknowledged for the purchase of an X-ray diﬀractometer

(CHE-1725028).

Reactive Distillation/Catalytic Reaction. Under a

constant stream of argon, A (1.61 g, 2.46 mmol) and 1-

phenylethanol (1.00 mL, 8.28 mmol) were dissolved in ODCB

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ASSOCIATED CONTENT

sı Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acscatal.1c03037 .

■

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AUTHOR INFORMATION

Corresponding Authors

Olaf Nachtigall − Department of Chemistry, University of

Rochester, Rochester, New York 14627, United States;

Present Address: Department of Chemistry, University of

California, Irvine, California 92697, United States

■

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and S-Centered Nucleophiles to Generate Heterocycles. ACS Catal.

(

O.N.); orcid.org/0000-0001-7247-8781 ;

Email: olaf.nachtigall@fu-berlin.de

William D. Jones − Department of Chemistry, University of

Rochester, Rochester, New York 14627, United States;

orcid.org/0000-0003-1932-0963; Email: jones@

chem.rochester.edu

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Andrew I. VanderWeide − Department of Chemistry,

University of Rochester, Rochester, New York 14627, United

States; orcid.org/0000-0001-9486-3170

William W. Brennessel − Department of Chemistry,

University of Rochester, Rochester, New York 14627, United

States; orcid.org/0000-0001-5461-1825

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Complete contact information is available at:

https://pubs.acs.org/10.1021/acscatal.1c03037

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Author Contributions

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The manuscript was written through contributions of all

authors. All authors have given approval to the ﬁnal version of

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Notes

The authors declare no competing ﬁnancial interest.

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Catalyzed Dehydrative Coupling/Friedel −Crafts Cyclization of Two

ACKNOWLEDGMENTS

O.N. thanks the Alexander von Humboldt Foundation for a

Feodor Lynen Fellowship. We thank the U.S. Department of

■

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