Desulfurization of dibenzothiophene and dibenzothiophene sulfone via Suzuki–Miyaura type reaction: Direct access to o-terphenyls and polyphenyl derivatives

Article abstract of DOI:10.1016/j.poly.2018.08.008

The reactivity of dibenzothiophene (DBT) or dibenzothiophene sulfone (DBTO₂) with a variety of phenylboronic acids was mediated by the nickel precursor [Ni(dippe)Cl₂] in the presence of a base. The reaction was performed under relatively mild conditions (70–100 °C), in aqueous media. The study of the reactivity revealed the role of water as a hydrogen source and showed a competition between the desulfurization of the corresponding substrates via a hydrodesulfurization (HDS) or by a hydrodesulfurative cross-coupling (HDSCC) reaction. Furthermore, in the absence of water sulfur-free poly-phenylic compounds were obtained in good yields as a result of a Suzuki–Miyaura type reaction, being the main product in most of the cases the corresponding o-terphenyl derivative, these products are valuable building blocks in the synthesis of more complex materials.

Full text of DOI:10.1016/j.poly.2018.08.008

Accepted Manuscript
Desulfurization of dibenzothiophene and dibenzothiophene sulfone via Suzuki-
Miyaura type reaction: Direct access to o-terphenyls and polyphenyl derivatives
Rubén Gutiérrez-Ordaz, Juventino J. García
PII:
S0277-5387(18)30465-0
https://doi.org/10.1016/j.poly.2018.08.008
POLY 13331
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
13 June 2018
1 August 2018
3 August 2018
Please cite this article as: R. Gutiérrez-Ordaz, J.J. García, Desulfurization of dibenzothiophene and
dibenzothiophene sulfone via Suzuki-Miyaura type reaction: Direct access to o-terphenyls and polyphenyl
derivatives, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.08.008
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Desulfurization of dibenzothiophene and dibenzothiophene sulfone via Suzuki-
Miyaura type reaction: Direct access to o-terphenyls and polyphenyl derivativesϯ
Rubén Gutiérrez-Ordaz and Juventino J. García*
Facultad de Química. Universidad Nacional Autónoma de México. Mexico City 04510.
Mexico.
juvent@unam.mx
Abstract
The reactivity of dibenzothiophene (DBT) or dibenzothiophene sulfone (DBTO2) with a
variety of phenylboronic acids was mediated by the nickel precursor [Ni(dippe)Cl2] in the
presence of a base. The reaction was performed under relatively mild conditions (70 to 100
°C), in aqueous media. The study of the reactivity revealed the role of water as a hydrogen
source and showed a competition between the desulfurization of the corresponding
substrates via a hydrodesulfurization (HDS) or by a hydrodesulfurative cross-coupling
(HDSCC) reaction. Furthermore, in the absence of water sulfur-free poly-phenylic
compounds were obtained in good yields as a result of a Suzuki-Miyaura type reaction,
being the main product in most of the cases the corresponding o-terphenyl derivative, these
products are valuable building blocks in the synthesis of more complex materials.
Key words: Desulfurization; dibenzothiophene; dibenzothiophene sulfone; phenylboronic
acids; cross-coupling; nickel.

Introduction
The removal of organosulfur compounds in crude oil through ‘‘deep desulfurization’’ is a
challenge with relevance in energetic, economic and environmental issues. Unfortunately, a
satisfactory and practical solution has not yet been found. Hydrodesulfurization (HDS) is
the process to remove sulfur from oil; it consists of treating crude oil with high hydrogen
pressures and temperatures (up to 250 atm. and 450°C) in the presence of heterogenous
CoMoS and NiMoS catalysts.[1] However, dibenzothiophene and its methyl-derivatives
(specially with substitutions in positions 4 and 6) are persistent in fuels due to the lack of
reactivity. Alternative technologies to the hydrotreating of petroleum fractions is the
oxidative desulfurization (ODS),[2] which consists in the oxidation of sulfur-containing
compounds with peroxides to produce the corresponding sulfones and sulfoxides. The
resulting products typically exhibit high melting and boiling points, usually a different
solubility, which allows their removal from the petroleum fractions. However, the
sulfoxides and sulfones produced by this process are considered an industrial residue, and
their treatment is limited to confinement, even when these sulfones are a useful raw
material.
The C-S cleavage and further transformation mediated by a transition metal brings a new
perspective in organic synthesis, to obtain valuable chemicals from typically unreactive
molecular motifs. In the case of sulfones traditional methodologies to cleavage the carbon-
sulfur bonds use highly reactive reducing agents, such as sodium amalgam, or
deprotonation of the adjacent positions of the sulfonyl group to incorporate a substituent.[3]
The C-S activation using stoichiometric amounts of a transition metal complex is relatively
more common than the use of catalytic amounts,[4] probably due to the inertness of the

resulting M-S bond after the C-S cleavage by oxidative addition.[5] In the case of
dibenzothiophene (DBT), the reactivity with metal complexes has been studied during the
last few decades.[6] Albeit most of these studies were performed using late transition metals,
such as rhodium,[7] iridium,[8] palladium,[9] platinum,[10] and nickel.[11,12] Worthy of mention
is the report by Vicic and Jones,[11] where the formation of multiple nickel-sulfur bonds
accounted for the loss of further activity (Scheme 1).
P
P
S
S
Ni
S
P
P
P
P
P
P
"[Ni(dippe)]"
P
P
P
P
H
H
P
P
Ni
Ni
Ni
Ni
Ni
Ni
S
P
P
Ni
Scheme 1. Mechanistic proposal for desulfurization of DBT.[11]
The use of the appropriate nucleophilic organometallic reagent, which can perform the
corresponding transmetalation reaction, is a possible way to regenerate the active species
able to continue with a further C-S cleavage, to yield a C-C bond formation via a cross-
coupling reaction. A variety of transition metals able to perform catalytic C-S activation
systems are known,[4,5] within the nickel-based catalysts, some examples of desulfurization
of aryl and alkyl thioethers via cross-coupling reactions using different catalytic precursors
and transmetalation reagents like organozinc,[13] organo-magnesium.[14] Recent examples of
desulfurization of aryl sulfoxides using organozinc reagents, via the reduction of an
arylthioether, followed by a cross-coupling reaction have also been informed.[15]

Relevant examples regarding cross-coupling desulfurative systems using Suzuki-Miyaura
conditions and triaryl boroxines, with tolerance to a variety of functional groups and low
toxicity have been reported.[16] Also methyl sulfides using rhodium,[17] and aryl sulfones
with nickel catalysts.[18]
In the case of dibenzothiophenes[19] and the corresponding sulfones,[20] our group reported
the catalytic desulfurization of these substrates in high yields using several nickel based
catalytic precursors and a variety of organo-magnesium reagents, which perform a double
purpose: as transmetalation reagent and sulfur scavenger by the formation of MgS (Scheme
2).
R
R
R
R
S
[Ni]cat (1-2 mol%)
Me MgBr
+
Toluene
-MgS, MgBr2
>99%
R= Me, H
O
O
R
R
R
R
S
[Ni]cat (1 mol%)
Me MgBr
+
Toluene
-MgS, MgO, MgBr2
R= Me, H
Yields up to 90%
Scheme 2. Ni-Catalyzed cross-coupling desulfurization for DBTs and sulfones with
Grignard reagents.[19,20]
Since the use of Grignard reagents requires anhydrous reaction conditions we found to be
interesting the use of closely related cross-coupling reaction, tolerant to water or water
containing media to have a desulfurization system under less demanding conditions. Also,
recently our group reported the use of complex [Ni(dippe)Cl2] and KOH in aqueous media
to yield the Ni(0) complex [Ni(dippe)2].[21] This prompted us to prepare low-valent nickel
species in water that could be used in Suzuki-Miyaura type reactions, where the transition-

metal mediated a C–S bond cleavage in DBT and DBTO2 to produce sulfur free
functionalized biphenyls. Our results are disclosed herein.
Results and discussion
Dibenzothiophene reactivity in aqueous media
Using a mixture of THF and water (2:1) the reaction of DBT and phenylboronic acid
(PhB(OH)2) was mediated by a stoichiometric amount of [Ni(dippe)Cl2], using an excess of
KOH to generate a Ni(0) complex in situ.[21] Additionally, tetrabutylammonium bromide
(TBAB) was used as a mass transfer agent as in similar Suzuki-Miyaura reactions.[22] The
optimized conditions are shown in Scheme 3, two main products of desulfurization were
observed: biphenyl as the HDS product and o-terphenyl as a product of hydrodesulfurative
cross-coupling (HDSCC). For all reactions a sample of the aqueous phase was taken and
added with hydrochloric acid to give positive for the presence of sulfides.
The scope of boronic acids were explored to assess the effect of a p-substituent in the
phenylboronic acid in the formation of the cross-coupling product was made. Conversions
and product distribution are shown in Chart 1.
[Ni(dippe)Cl2]
Ar
3
B(OH)2
S
4 KOH, TBAB
+
THF/H2O (2:1)
70°C,92h
R
2a
3a-R
HDS
product
HDSCC
product
R= CF3, H
CH3, OMe
Scheme 3. Reactivity of DBT and phenylboronic acids in aqueous media.

HDSCC
HDS
40
35
30
25
20
15
10
5
5
6
12
35
21
6
31
19
0
-CF3
-CF3
-H
-H
-CH3
-CH3
-OMe
-OMe
Chart 1. Comparative yields for the scope of phenylboronic acids.
As found, in the case of an electron withdrawing group (-CF3) a drop in the global yield
was observed; however, along with a change in selectivity of products, being the HDS
product preferred (biphenyl) compared with the use of electron-donating groups (-CH3 and
-OMe), in the last cases nucleophilicity of organoboronic acid increased, likely improving
the transmetalation step. Thus, this difference in selectivity is indicative of a competition
between HDS and cross-coupling reactions.
To further confirm biphenyl as a HDS product and water as the source of hydrogen, the
same reaction was made using a mixture of THF/D2O. Thus, the expected deuterated
products were observed: 1,1'-biphenyl-2,2'-d2 (biphenyl-d2) and 1,1':2',1''-terphenyl-2-d (o-
terphenyl-d1). (Scheme 4). Noteworthy, a yield variation in comparison with the original
reaction was observed, probably due to a difference in kinetic isotope effect (KIE).

[Ni(dippe)Cl2]
D
S
4KOH, TBAB
B(OH)2
+
+
D
D
D
THF/ 2O
70°C
92h
biphenyl-
4%
d
2
o-terphenyl-d
1
26%
Scheme 4. Isotopic labeling experiment to assess the competition between HDS and
HDSCC.
To shed some light into the reaction intermediates involved in the desulfurization reaction
with DBT, it was monitored by 31P{1H} and 1H NMR using a mixture of THF-d8/H2O, by
24 h intervals for 3 days (Figure 1).
OH
(
)
2
H
O
P
P
P
OH
(
)
Ni
Ni
O
H
P
P
P
P
S
H
P
P
P
P
Ni
Ni
Cl
Cl
Ni
A
Ni
P
B
S
G
t=0 h
t=24 h
t=48 h
t=72 h
101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70
f1 (ppm)
Figure 1. 31P{1H} NMR monitoring for DBT desulfurization
At the beginning the signal assigned to [Ni(dippe)Cl2] (A) was observed, rapidly consumed
to form the dimeric nickel-hydroxo complex [Ni(dippe)(μ-OH)]2(OH)2 (B) at 82.5 ppm,[21]
along with two doublets assigned to the thianickelacycle [Ni(dippe)η2-C,S-C12H8] at 73.1
ppm (d, J = 11.3 Hz) and 71.5 (d, J = 11.3 Hz). A decrease of the signal corresponding to B

was later observed (after 24 hours of reaction), along with the increase of two signals with
multiplicity of doublet of doublets at 100.6 ppm and 91.4 ppm (2JP-P = 14.4, 8.5 Hz),
assigned to [Ni2(dippe)2(μ-H)(μ-S)](OH) (G), the last remains as the final product.
Likewise, the monitoring by 1H NMR showed the expected characteristic signal for a
hydride in G at -11.25 ppm (tt, J = 44, 24 Hz) formed at 24 hours, remaining at the end of
the experiment.
As described in Scheme 1, Vicic and Jones previously reported the formation of a sulfide
bridged nickel dimer in their studies of desulfurization of DBT, also the formation of a
hydride-sulfide bridged nickel dimer, resulting from the protonation of the corresponding
nickel sulfur-bridged dimer by treatment with HPF6 with rather similar 31P{1H} and 1H
NMR signals as a final product.[15] Therefore, we propose a similar reaction occurring with
water as represented in Scheme 5 for the formation of complex G.
(OH)
O
S
P
P
P
P
P
P
P
P
H
H
S
H
Ni
Ni
Ni
Ni
Scheme 5. Formation of [Ni2(dippe)2(μ-H)(μ-S)](OH).
Considering the current results and previous reports regarding DBT desulfurization with
nickel, a mechanistic proposal is presented in Scheme 6. Firstly, the reaction of
[Ni(dippe)Cl2] (A) with KOH takes place to generate the nickel dimer [Ni(dippe)(μ-
OH)]2(OH)2 (B). This type of dimeric nickel dihydroxy species has been reported as highly
reactive in transmetalation reactions with phenylboronic acids by Monfette.[23] Thus, B is
proposed to react with the phenylboronic acid to yield the corresponding biaryl

(homocoupling product) along with the formation of the thianickellacycle [Ni(dippe) η2-
C,S-C12H8] (C).
As earlier mentioned (vide supra) the thianickellacycle [Ni(dippe)κ2-C,S-C12H8] can
decompose to form the [Ni2(dippe)2(μ-S)] F and the nickelallycle D, then F can react with
water to yield [Ni2(dippe)2(μ-H)(μ-S)](OH) (G). Likewise, D can react with H2O to yield
E. Here E is a key intermediate; it represents a cross-road between yield biphenyl and o-
terphenyl, this being sensitive to the use of D2O to favor the product of transmetalation (o-
terphenyl) over biphenyl.
P
Cl
3
Ni
A
Cl
P
OH
6 K
OH
6 KCl + Ni(
OH
)
2
(
)
2
H
O
B(OH)2
P
P
P
S
Ni
Ni
2
+
O
H
P
R
B
+ 2 B(OH)
R
R
3
K[B(OH)4] +
P
(OH)
R
S
Ni
P
P
P
P
P
H2O
S
H
Ni Ni
S
Ni
Ni
P
P
P
P
C
OH
K
+
F
G
S
B
R
HO
OH
P
O
P
H
H
Ni
D
Ni
P
P
OH
OH
+ Ni(
)
2
E
+ dippe
O
H
H
Scheme 6. Mechanistic proposal for DBT desulfurization in aqueous media.

The above mechanistic proposal is not an actual catalytic process, due to the continuous
formation of unreactive nickel species such as nickel sulfides and Ni(OH)2. Thus, a
possible way of optimizing the process was the use of anhydrous reaction conditions, to
minimize the production of Ni(OH)2 (vide infra). Likewise, dibenzothiophene sulfone was
evaluated by this methodology, but conversion was poor due to its low solubility (See SI).
Reactivity of Dibenzothiophenes in Anhydrous Media
A cross-coupling desulfurization system under anhydrous conditions was used, using a
rather similar general methodology (including hindered dibenzothiophenes). For instance,
the low KOH solubility in THF restricts its use, thus t-BuOK was used instead. The main
results are summarized in Table 1. The best yields were obtained for DBT, but with a low
selectivity (entries 1-4) in comparison with the previous results in THF/H2O.
Table 1. HDSCC for dibenzothiophenes.
R3
R1
R1
R2
R2
S
[Ni(dippe)Cl2]
+
+
R2
+
R1
R2
R1
6 t-BuOK
3 ArB(OH)2
THF
R1
1a
1b
1c
R1=R2=H
R3
R3
R2
R3
R1= H, R2=Me
R1=R2=Me
2(a-c)
70°C, 92h
3(a-c)R3
5(a-c)R3
4(a-c)R3
R3=H, CF3, CH3, OMe
Yield (%)*
Conv.
R3
B(OH)2
Entry Substrate
5(a-
c)R3
(%)*
2 (a-c) 3(a-c)R3 4(a-c)R3
1
2
3
4
1a
1a
1a
1a
37
47a
66a
56a
-CF3
-H
n.d.
9
17
16
29
42
17
6
3
12
10
5
-CH3
-OMe
1
9
1
5

5
6
1b
1b
1b
1b
1c
1c
1c
1c
10
35
54
45
--
-CF3
-H
n.d.
2
7
21
40
35
n.d.
1
3
n.d.
5
7
6
7
-CH3
-OMe
-CF3
-H
2
6
8
3
1
6
9
n.d.
2
n.d.
Trace
1
n.d.
1
10
11
12
5
12
14
-CH3
-OMe
5
5
Trace
Trace
6
6
1
All reactions were carried out in a Schlenk flask (50 or 25 mL) equipped with a Rotaflo valve stirred and
heated at 70°C during 92 hours in 3 mL of THF. n.d.= Not detected. Reaction conditions:
[Ni(dippe)Cl2]:[DBT]:ArB(OH)2:t-BuOK molar ratio 1:1:3:6, respectively. *All conversions and yields were
determined by CG-MS. a) Additional C-S cross-coupling products were detected vide infra.
As mentioned above a variety of cross-coupling products was obtained: o-terphenyls (3a-
R3), o-tetraphenyls (5a-R3), and the cross-coupling/C-H activation triphenylenes (4a-R3),
but in low yields. Surprisingly, for entries 2-4 low yields of an additional C-S cross-
coupling product 6a-R3 was observed (Scheme 7). The formation of these products may be
explained by a nucleophilic attack into the corresponding M-S bond of thianickelacycle C,
by a phenylboronic species.
H
CH3
O
H
S
H3C
S
O
S
4%
3%
17%
6a-CH3
6a-H
6a-OMe
Scheme 7. Additional C-S coupling products produced in anhydrous media.

Reactivity of Dibenzothiophene Sulfones (DBTO2s) in Anhydrous Media.
To assess the reactivity of sulfones derived from DBTs under anhydrous conditions, the
study was limited to the more reactive phenylboronic acids, i.e., the ones with electron
donor substituents, in dioxane, these results are summarized in Table 2. In contrast with
DBTs, the use of the corresponding sulfones gave superior yields, including the methyl-
substituted ones (entries 5-11).
Table 2. Reactivity of sulfones
R3
R1
O
O
R1
R2
R2
S
[Ni(dippe)Cl2]
+
+
+
R2
R1
R2
R1
6 t-BuOK
3 ArB(OH)2
1,4-Dioxane
100°C, 92h
R1
1
2
1d
1e
1f
R =R =H
R3
R3
R2
R3
1
2
R = H, R =Me
2(a-c)
1
2
3(a-c)R3
5(a-c)R3
R =R =Me
4(a-c)R3
R3=H, CF3, CH3, OMe
Yield (%)*
2(a-c) 3(a-c)R3 4(a-c)R3
Conv.
R3
B(OH)2
Entry Substrate
(%)*
5(a-c)R3
1
2
3
1d
1d
1d
92
100
89
-H
17
18
5
42
68
80
13
4
20
10
-CH3
-OMe
3
n.d
No phenylboronic
acid
4a
1d
81
42
n.d.
n.d.
n.d.
5b
6
1d
1e
1e
1e
1f
97
73
98
81
77
-CH3
-H
5
5
62
43c
67c
64c
n.d.
14
20
14
6
9
5
7
-CH3
-OMe
-H
9
8
8
5
6
9
16
n.d.
n.d.

10
11
1f
1f
54
57
-CH3
3
6
15
12
18
14
Traces
n.d.
-OMe
All reactions were carried out in a Schlenk flask (50 or 25 mL) equipped with a Rotaflo valve stirred and
heated at 100°C during 92 hours in 3 mL of 1,4-dioxane. Reaction conditions:
[Ni(dippe)Cl2]:[DBTO2]:ArB(OH)2:t-BuOK molar ratio 1:1:3:6, respectively. *All conversions and yields
were determined by CG-MS. nd = not detected. a) Control experiment, other products were detected vide
infra. b) Mercury-drop test using the same reaction conditions resulted in no inhibition, tetraphenylene (2%),
9-fluorenone (2%), DBT (3%) detected. c) Regio-isomeric mixtures of the corresponding terphenyl products
were detected.
Here the main products were o-terphenyls in fair to very good yields (entry 3), consistent
with a transmetalation step at intermediate (D) in Scheme 9. An interesting issue is that
despite the use of anhydrous reaction media, the formation of HDS and HDSCC products
was observed. To explain this, we propose that a dehydration process of the phenylboronic
acids is taking place to produce water in situ, reports on this are already well known.[24,25]
A control experiment in absence of phenylboronic acid (entry 4), revealed the formation of
biphenyl (42%) probably from the quenching of intermediate D during work up instead of
tetraphenylene (2%) from a dimerization reaction.[26,27] Also DBT (13%) was detected as
reduction of DBTO2. Unexpectedly, 9-fluorenone was detected as an additional major
product (24%), confirmed by GC-MS using a commercial standard (see SI); it can be
produced by carbonylation of biphenylene.[28] Considering the reaction conditions of the
current reaction, we found that commercially available t-BuOK usually contains variable
amounts of potassium carbonate as an impurity[29] and it could be the source of carbonyl.
In the case of 4-MeDBTO2 (entries 6 to 8) the conversion was rather similar to DBTO2, but
in this case a variety of isomeric terphenyls were detected with substitution at the biaryl
moiety. Products distribution is shown in Scheme 8.

Me
Me
Me
Me
Me
Me
Me
Me
OMe
OMe
3b'-Me
17%
3b-Me
50%
3b'-H
18%
3b-H
25%
3b-OMe
45%
3b'-OMe
19%
Scheme 8. Isomers of terphenyls obtained after 4-MeDBTO2 desulfurization.
On using 4,6-Me2DBTO2 low conversion to the cross-coupling products was observed
(entries 9-11), in all the cases the reduction of the sulfone to 4,6-Me2DBT was detected
59% (entry 9), 18% (entry 10) and 25% (entry 11) (see SI), particularly when using
phenylboronic acid (entry 9). For entries 10 and 11 major cross-coupling products were
observed, probably due to a favorable nucleophilic addition of the aryl fragment.
These results represent an alternative way to synthetize a variety of polyaromatic products,
o-terphenyls and tetraphenyls are building blocks for the construction of specific
polyaromatic hydrocarbons (PAHs),[30] for fabrication of organic light-emitting diodes
(OLEDs)[31] and pharmaceuticals.[32] On the other hand, triphenylenes are considered
among the most important polycyclic aromatic compounds, for their utility as
polyphenylenes precursors which could be post functionalized in graphene segments,[33]
and as building blocks of liquid crystals and OLEDs.[34] Even when triphenylenes are not a
major product in this work, they can be prepared from o-terphenyls by the Scholl
reaction.[35] Current methodologies for the preparation of triphenylenes are scarce, and
require further innovation.[36]
As previously described for DBTs (vide supra) a monitoring for the sulfone reaction was
performed by 31P{1H} NMR (see SI), the formation of intermediate D (s, 69 ppm) (Scheme

9) was identified after the first 24 hours of reaction along with [Ni(dippe)2] (s, 56 ppm),
these signals were constantly observed. Also, two low abundance signals assigned to
[Ni(dippe)μ-S]2 (s, δ 79 ppm) and [Ni(dippe)μ-SO2]2 (s, δ 74 ppm). At the end of the
experiment two doublet of doublets with characteristic P-P coupling constants for nickel-
zero complexes were observed.[37,38] For these we propose the formation of Ni(0)
compounds containing a π- arene moiety derived from the corresponding cross-coupling
products 3a-H (d, δ 76.8, 70.1 ppm, 2JP-P = 52 Hz) and 4a-H (d, δ 76.3, 67.8 ppm, 2JP-P
=
55 Hz).[39]
Thus, considering the experimental evidence obtained with sulfones and Scheme 6 for
DBTs, a mechanistic proposal for sulfones is presented in Scheme 9. Initially the formation
of a Ni(0) intermediate,[40] with coordination of DBTO2 (A-SO2), then the oxidative
addition complex (C-SO2). Followed by a nucleophilic attack promoted by tert-butoxide
anion[41] into sulfur atom giving the adduct C’-SO2, which can better react with a second
equivalent of tert-butoxide to form the nickelacycle D and release of a sulphate. After that,
the proposal is similar to Scheme 6; a hydrolysis of D can take place from dehydration of
phenylboronic acids, followed by a transmetalation step to yield H, and then by a reductive
elimination of the corresponding o-terphenyl.

P
P
Cl
Cl
Ni
A
O
O
B(OH)2
S
+
2
2 t-BuOK
2KCl
R
R
R
R
+
2 B(OH)2Ot-Bu
P
O
O
H
Ni
S
O
O
P
S
A-SO2
O
S
P
P
P
O
H
Ni
Ni
P
Ar
H
R2
Ot-Bu
O
B
B
O
B
O
OH
+ K
C-SO2
R2
O
R2 = Ar or t-BuO
t-BuOK
Hydrolysis &
Transmetalation
P
Ni
O
S
P
O
O
P
+
H O
2
(ArBO)3
3
Ni
P
Dehydration
C'-SO2
D
HO
O
-
3
B
HO
R
Ar
2
O
O
tBu
S
tBu
O
O
Scheme 9. Mechanistic proposal for dibenzothiophene sulfone desulfurization.
CONCLUSIONS

Dibenzothiophene and dibenzothiophene sulfone were desulfurized by a metal mediated
protocol using nickel and Suzuki-Miyaura type coupling, both in aqueous media and
anhydrous conditions. The use of D2O revealed a competition between HDS and cross-
coupling reaction. The desulfurization under anhydrous conditions in organic solvents gave
high conversions and yielded a variety of poly-phenyl compounds of interest, in a one-pot
reaction. The products distribution revealed the key role of water in the system to yield o-
terphenyls.
EXPERIMENTAL SECTION
General Considerations
Unless otherwise noted, all manipulations were performed using standard Schlenk
techniques in an inert-gas/vacuum double manifold or under high purity argon atmosphere
(Praxair 99.998) in an MBraun UniLab glovebox (<1 ppm H2O and O2). All reagents and 9-
fluorenone standard were purchased from Aldrich and Merck and were dried or degassed
before use. [Ni(dippe)Cl2] was synthetized according with the reported procedure.[42]
Water was distilled and deoxygenated under argon flow. The solvents were dried using
standard techniques and stored in the glovebox before use. Deuterated solvents (D2O, THF-
d8, 1,4-dioxane-d8) were purchased from Cambridge Isotope Laboratories and were stored
under 4 Å molecular sieves for 24 h before use. NMR spectra were acquired at room
temperature on a 400 MHz Varian Unity spectrometer. Chemical shifts for 1H NMR spectra
(δ parts per million) are reported relative to the residual protio-solvent. 31P{1H} NMR
chemical shifts (δ parts per million) are reported relative to external 85% H3PO4. Coupling
constants (J values) are given in Hz. The following abbreviations were used for the NMR

data: s = singlet; d = doublet; dd = doublet doubleted and tt = triplet tripleted. GC–MS
determinations were performed using an Agilent Technologies G3171A equipped with a
column: 5% phenylmethylsilicone, 30 m x 0.25 mm x 0.25μm.
Desulfurization experiments in aqueous media
Unless otherwise noted, all reactions were performed using Schlenk flask (50 and 25 mL)
fitted with Rotaflo valve. [Ni(dippe)Cl2] (0.04 g, 0.1021 mmol) was slowly added into a
KOH (0.0232 g, 0.4084 mmol) solution in H2O (2 mL), then THF (2 mL) was added. After
5 min. solution turned deep orange. Then, phenylboronic acid (0.0373 g, 0.3063 mmol),
dibenzothiophene (0.0188 g, 0.1021 mmol) (in case of dibenzothiophene sulfone
experiments 0.0221g, 0.1021 mmol) and TBAB (0.0387 g, 0.1021 mmol) were added with
constant stirring. Finally, additional THF (2 mL) was added. Then, the flask was heated in a
silicon oil bath at 70°C. The formation of a small amount of a green solid was detected
during the reaction, identified as Ni(OH)2. After, the reaction mixture was cooled to RT,
exposed to air, extracted 3 times with CH2Cl2 (5 mL), dried over Na2SO4 and concentrated.
The concentrate was analyzed by using GCMS chromatography. A sample from the
residual aqueous phase was added with a drop of concentrated HCl to yield a gas identified
as H2S.
Influence in substituents of phenylboronic acids
For experiments showed in Scheme 3, Chart 1, the procedure was the same that described
above but using the following amounts of phenylboronic acids: 4-
(Trifluoromethyl)phenylboronic acid (0.0582 g, 0.3063 mmol), 4-(Methyl)phenylboronic

acid (0.0518 g, 0.3063 mmol) and 4-(Methoxy)phenylboronic acid (0.0587 g, 0.3063
mmol).
Isotopic labeling using D2O
A NMR tube with J. Young´s valve was charged in a run with a solution of [Ni(dippe)Cl2]
(0.02g, 0.0511 mmol), phenylboronic acid (0.0187 g, 0.1531 mmol), dibenzothiophene
(0.0094 g, 0.0511 mmol) and TBAB (0.019 g, 0.0511 mmol), then added into a KOH
(0.0116 g, 0.2042 mmol) solution made with D2O (1 mL) and THF (2 mL). After 5 min.
color solution turned to deep orange. Then the reaction was heated in a silicon oil bath at
70°C for 92 hours. After this time, the tube was opened to air. The reaction mixture was
centrifugated at 5000 cycles/min to remove Ni(OH)2 and then was extracted 3 times with
CH2Cl2 (3 mL), concentrated, and then analyzed by GCMS.
Desulfurization of dibenzothiophenes and sulfones in anhydrous media
Using [Ni(dippe)Cl2] (0.02g, 0.0511 mmol), added into a t-BuOK (0.0344 g, 0.3066 mmol)
solution in THF (2 mL), the color turned dark amber after 5 min. Then, phenylboronic acid
(0.1531 mmol) and dibenzothiophene (0.0094 g, 0.0511 mmol), 4-MeDBT (0.0101 g,
0.0511 mmol) or 4,6-Me2DBT (0.0108 g, 0.0511 mmol) were added with constant stirring
corresponding dissolved in THF (1 mL). Then, the flask was heated in a silicon oil bath at
70°C for 92 hours. Formation of dark particles was observed during the reaction, identified
as metallic nickel. After this time, the reaction mixture was cooled to RT, exposed to air,
the mixture was centrifugated at 5000 cycles/min to remove solids identified as metallic
nickel and KCl. The organic layer was analyzed by GC-MS.
For dibenzothiophene sulfones: [Ni(dippe)Cl2] (0.02 g, 0.0511 mmol) was added into a t-
BuOK (0.0344 g, 0.3066 mmol) solution in 1,4-dioxane (2 mL), After 5 min. color solution

turned to amber dark. Then, with constant stirring corresponding phenylboronic acid
(0.1531 mmol) and dibenzothiophene sulfone (0.0110 g, 0.0511 mmol), 4-MeDBTO2
(0.0118 g, 0.0511 mmol) or 4,6-Me2DBTO2 (0.0125 g, 0.0511 mmol) were added dissolved
in 1,4-dioxane (1 mL). Heated in a silicon oil bath at 100°C for 92 hours. Formation of a
small amount of dark particles was noticed during the reaction, identified as nickel native.
After this time, the reaction mixture was cooled to room temperature, exposed to air,
mixture was centrifugated at 5000 cycles/min to remove solids (metallic nickel and KCl).
Then the organic layer was analyzed by GC-MS.
Use of different phenylboronic acids
For experiments showed in Table 1 ad 2, the procedure was made following the previous
procedure but using the following amounts of phenylboronic acids: 4-(Trifluoromethyl)-
phenylboronic acid (0.0291 g, 0.1532 mmol), phenylboronic acid (0.0187 g, 0.1532 mmol),
4-(Methyl)phenylboronic acid (0.0259 g, 0.1532 mmol) and 4-(Methoxy)phenylboronic
acid (0.0293 g, 0.1532 mmol).
Mercury drop test
Following the procedure described above, the very same reaction was performed with the
addition of one drop of elemental Hg into the reaction mixture. At the end of run, the
reaction mixture was cooled to room temperature, air exposed, centrifugated at 5000
cycles/min and filtered through celite and analyzed by GC–MS.
Monitoring by NMR

Using [Ni(dippe)Cl2] (0.02 g, 0.0511 mmol) it was slowly added into a KOH (0.0132g,
0.2042 mmol) solution in H2O (1 mL), then THF-d8 (1 mL) was added. A color change to
deep orange was observed after 5min. Then, with constant stirring phenylboronic acid
(0.0187 g, 0.1531 mmol), dibenzothiophene (0.0094 g, 0.0511 mmol) and TBAB (0.019 g,
0.0511 mmol) were added. Finally, an additional mL THF-d8 was added. Then the mixture
was transferred into a NMR tube with J. Young´s valve and heated 70°C for 72 hours,
monitored every 24 hours.
Alternatively, [Ni(dippe)Cl2] (0.02g, 0.0511 mmol) was added into a t-BuOK (0.0344g,
0.3066 mmol) solution in 1,4-dioxane-d8 (2 mL). A color change to amber was observed
after 5 min. Then added with phenylboronic acid (0.0187 g, 0.1531 mmol),
dibenzothiophene sulfone (0.0115 g, 0.0511 mmol). The reaction was transferred into a
NMR tube with J. Young´s valve and heated in a silicon oil bath at 100°C. The NMR tube
was heated for 96 hours and monitored every 24 hours.
Conflicts of interest
The authors declare no conflicts of interest.
Acknowledgements
We thank CONACYT 178265 and PAPIIT-DGAPA-UNAM 202516 for their financial
support of this work. R.G.-O. thanks to CONACYT (595860) for a graduate studies grant.
We also thank Dr. Alma Arévalo for her technical assistance.
ϯ Dedicated to Prof. William D. Jones on his 65th birthday.

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