Decyl(tri- tert -butyl)phosphonium tetrafluoroborate/palladium acetate: An effective catalyst for cross-coupling reaction of arylbromides with phenylacetylene in copper-free conditions

Article abstract of DOI:10.1080/10426507.2012.744013

Abstract The phosphonium salts with sterically hindered cation and noncoordinating anion can be used as phase-transfer reagent in the Sonogashira cross-coupling reaction allowing copper- and amine-free protocol. The reactions proceed under mild conditions

Full text of DOI:10.1080/10426507.2012.744013

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Phosphorus, Sulfur, and Silicon and the
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Decyl(Tri-Tert-Butyl)Phosphonium
Tetrafluoroborate/Palladium Acetate:
An Effective Catalyst for Cross-
Coupling Reaction of Arylbromides
with Phenylacetylene in Copper-Free
Conditions
Vadim Ermolaev a , Vasiliy Miluykov a , Daria Arkhipova a , Elena
Zvereva a & Oleg Sinyashin a
a Institute of Organic and Physical Chemistry A. E. Arbuzov, A.
Arbuzov Str. 8 , Kazan , Russia
Accepted author version posted online: 19 Nov 2012.Published
online: 08 May 2013.
To cite this article: Vadim Ermolaev , Vasiliy Miluykov , Daria Arkhipova , Elena Zvereva & Oleg
Sinyashin (2013) Decyl(Tri-Tert-Butyl)Phosphonium Tetrafluoroborate/Palladium Acetate: An
Effective Catalyst for Cross-Coupling Reaction of Arylbromides with Phenylacetylene in Copper-
Free Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements, 188:1-3, 168-170, DOI:
10.1080/10426507.2012.744013
To link to this article: http://dx.doi.org/10.1080/10426507.2012.744013
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Phosphorus, Sulfur, and Silicon, 188:168–170, 2013
Copyright ꢀC A. E. Arbuzov Institute of Organic and Physical Chemistry
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.744013
DECYL(TRI-TERT-BUTYL)PHOSPHONIUM
TETRAFLUOROBORATE/PALLADIUM ACETATE: AN
EFFECTIVE CATALYST FOR CROSS-COUPLING REACTION
OF ARYLBROMIDES WITH PHENYLACETYLENE IN
COPPER-FREE CONDITIONS
Vadim Ermolaev, Vasiliy Miluykov, Daria Arkhipova,
Elena Zvereva, and Oleg Sinyashin
Institute of Organic and Physical Chemistry A. E. Arbuzov, A. Arbuzov Str. 8,
Kazan, Russia
GRAPHICAL ABSTRACT
Abstract The phosphonium salts with sterically hindered cation and noncoordinating anion
can be used as phase-transfer reagent in the Sonogashira cross-coupling reaction allowing
copper- and amine-free protocol. The reactions proceed under mild conditions with good yields.
Keywords Phosphonium ionic liquid; Sonogashira; copper- and amine-free
Phosphonium salts find extensive application in various fields of organic chemistry.
They are widely used in organocatalysis1 and as anion-transfer catalysts2; they selectively
inhibit the in vitro growth of human pancreatic carcinoma-derived cells (PaCa-2) and
Ehrlich Lettre Ascites cells (ELA)3 and are used to effectively separate cobalt from nickel
by extraction.4 Phosphonium salts are precursors for the synthesis of the Wittig reagent,
which finds broad application in the selective conversion of ketones and aldehydes to
alkenes.5
Phosphonium salts are promising reagents for construction novel ionic liquids pos-
sessing some advantages in comparison to well studied imidazolium and ammonium based
ionic liquids6,7 like high thermal stability, easy functionalization, the absence of CH-
acidic protons and the resistance to superbasic media. Therefore phosphonium ionic liquids
are widely used as the reaction medium in esterification reactions,8 nitration of arenes,9
Received 14 September 2012; accepted 23 October 2012.
The authors would like to acknowledge FASIE (r/16815) and IVF RT for financial support.
Address correspondence to Vadim Ermolaev, Institute of Organic and Physical Chemistry A. E. Arbuzov,
A. Arbuzov Str. 8, Kazan 420088, Russia. E-mail: ermolaewadim@gmail.com
168

COPPER-FREE SONOGASHIRA REACTION
169
Table 1 The degree of conversion of bromoarenes in Sonogashira reaction using a catalyst system Pd(OAc)2/(1)∗
No
Bromoarene
Product
Conversion (%)
1
2
3
6
7
4-Me-C6H4-Br
3-Me-C6H4-Br
2-Me-C6H4-Br
1, 3-Br2-C6H4
1, 4-Br2-C6H4
69
79
69
61
21
44
72
77
60
8
9
10
2, 3, 4-F3-C6H2-Br
2, 4- (CF3)2 -C6H3-Br
2, 6-Me2-C6H3-Br
∗Reaction conditions: 2 mmol aryl bromide, 2.3 mmol (15% excess) phenyl-acetylene, 2.3 mmol Cs2CO3,
5 mL toluene, 0.02 mmol (1 mol%) Pd(OAc)2, 1 mmol phosphonium salt, time 12 h at 30 ◦С, conversion degree
determined by GC-MS.
synthesis of isoindoline-1-one,10 reductive carbonylation of nitrobenzenes11 and thiocar-
bonylation.12 Catalytic reactions as Suzuki13 and Sonogashira14 cross-coupling, Buchwald-
Hartwig amination15 and carbonylation reactions16 were also successfully carried out in
phosphonium ionic liquids. Typically phosphonium ionic liquids based on linear phos-
phines (as tri-n-hexylphosphine and tri-n-butylphosphine) and phosphine complexes of
palladium or palladacycles were employed. The use of phosphonium ionic liquids based on
sterically hindered tri(tert-butyl)phosphine and commercially available palladium acetate
might allow to realize cross-coupling reactions under mild reaction conditions with high
yields. Here we report the results of our investigations on simple and convenient catalysts
for the cross-coupling of bromoarenes and phenylacetylene—Sonogashira reaction.
Sonogashira reaction is an important cross-coupling reaction involving haloarenes
allowing selectively the synthesis of terminal and disubstituted acetylenes. The Sonogashira
reaction is basically the interaction of a halogenoarene (usually arene iodide) with terminal
acetylene in the presence of palladium(0), a base, a copper salt and an amine.17 It is consid-
ered that the copper compound reacts with the acetylene giving a copper acetylide, which
acts as a nucleophilic reagent.18 However, subsequent separation of the reaction products
from the impurities of copper compounds is generally a difficult experimental problem due
to the high tendency of formation of complexes of copper(I) with acetylenes—the reaction
products. In the presence of copper compounds some side-reactions (like Hay/Glaser reac-
tion) leading to a decrease of yield of the desired product take place.19 Only one publication
is devoted to copper-free Sonogashira reaction of bromobenzene with phenylacetylene,
which is carried out in phosphonium ionic liquid at elevated temperatures in presence of
phosphine ligand, however.20
We have found that the catalytic system based on palladium acetate and decyl(tri-tert-
butyl)phosphonium tetrafluoroborate (1)21 will effectively implement Sonogashira reaction
in the absence of any compounds of copper(I) under mild reaction conditions at 30 ◦C. The
results are presented in Table 1.
The catalyst shows good activity regardless of the nature of the substituents in the
arene ring. It should be noted that the phosphonium salt plays an important role in the
catalysis (Table 2).
Thus in the absence of phosphonium salts 1 the conversion was only 15%. Use of
an equimolar mixture of palladium acetate and phosphonium salt 1 causes an increase of

170
V. ERMOLAEV ET AL.
Table 2 The conversion degree of 4-bromotoluene in Sonogashira reaction with respect to the ratio of the
phosphonium salt 1/palladium acetate. Reaction conditions are presented in the footnote of Table 1
Ratio of the phosphonium salt / palladium acetate
Conversion degree
1 : 1
44
2 : 1
55
6 : 1
69
10 : 1
69
the conversion of 4-bromotoluene up to 44%. The highest conversion of 4-bromotoluene
to (4-metyldiphenylacetylene was achieved at a ratio phosphonium salt / palladium acetate
of 10:1. A further increase of the concentration of phosphonium salt 1 does not affect the
increase of conversion of 4-bromotoluene.
Thus, it can be concluded that the catalyst based on palladium acetate and decyl(tri-
tert-butyl)phosphonium tetrafluoroborate, can effectively implement the Sonogashira reac-
tion involving bromoarenes not depending on the substituentes in the arene ring.
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