Highly selective biaryl formation by the cyclooligomerization of arylethynes catalyzed by rhodium and ruthenium porphyrins

Article abstract of DOI:10.1039/b806025h

Rhodium and ruthenium porphyrins catalyze the one-pot formation of biaryl derivatives from arylethynes with high selectivity, giving interesting derivatives not easy to obtain using other different methods; the porphyrin catalysts can be recovered and reu

Full text of DOI:10.1039/b806025h

View Article Online / Journal Homepage / Table of Contents for this issue
LETTER
www.rsc.org/njc | New Journal of Chemistry
Highly selective biaryl formation by the cyclooligomerization
of arylethynes catalyzed by rhodium and ruthenium porphyrinsw
Pietro Tagliatesta,* Elfituri Elakkari, Alessandro Leoni, Angelo Lembo and
Daniel Cicero
Received (in Durham. UK) 9th April 2008, Accepted 3rd June 2008
First published as an Advance Article on the web 12th August 2008
DOI: 10.1039/b806025h
Rhodium and ruthenium porphyrins catalyze the one-pot forma-
tion of biaryl derivatives from arylethynes with high selectivity,
giving interesting derivatives not easy to obtain using other
different methods; the porphyrin catalysts can be recovered
and reused after several experiments with no change of activity.
The rich chemistry of the carbon–carbon triple bond has
been the subject of intense research in the past two decades due
to the well recognized importance that this function shows as a
building block in organic and materials chemistry.1 Among all
the reactions which use the alkyne reactivity to form new
carbon–carbon bonds, the most fascinating one remains the
Scheme 1 The structure of catalysts 1, 2 and 3.
formation of benzene rings, the Reppe cyclotrimerization of
Cp2Co, 3. The structure of the catalysts are reported in
alkynes.2 Such reactions have been deeply studied in the last
Scheme 1. Catalysts 1 and 3 are commercially available while
fifty years because they give functionalized aromatic com-
2 was synthesized by literature methods.7 The structures of the
pounds which are difficult to obtain using the usual methods.3
starting compounds and the biaryl products obtained from the
Moreover, the alkyne scaffolds represent a new source of
cyclodimerization reactions, are reported in Scheme 2.
compounds useful for the synthesis of nanotubes.4
The cyclodimerization reactions were performed in 1,2-di-
Recently we found that the arylethynes can undergo to the
chlorobenzene (DCB) at 160 1C for 48 hz and the reaction
cyclooligomerization reaction in the presence of a catalytic
products were easily separated by preparative medium-pressure
amount of metalloporphyrins, giving trisubstituted benzenes
column chromatography and characterized by EI and/or
and/or arylsubstituted naphthalenes, depending on the nature
1
GC-MS, H and 13C NMR and elemental analysis.
of the catalyst, the reaction conditions and the solvent used.5
The reaction conditions used in this work were optimized on
Biaryl compounds are an important class of organic com-
the basis of those found from our previous studies.5 All the
pounds and are found in several natural products. Furthermore
catalysts were reused at least four times in consecutive experi-
they are extensively used as chiral ligands of catalysts for the
ments, after the stripping of the reaction products.
synthesis of optically active compounds. In this paper we report
on the use of the porphyrin catalysts for obtaining, with high
selectivity, biaryl derivatives starting from 1- or 2-ethynyl-
naphthalene, 4 and 6, and 9-ethynylphenanthrene, 5. The starting
compounds 4 and 6 were available from commercial sources
while compound 5 was synthesised by the Sonogashira reaction.6
The catalysts used for this work were (2,3,7,8,12,13,17,18-
octaethylporphyrinato)ruthenium(II) carbonyl, 1, (5,10,15,20-
tetraphenylporphyrinato)rhodium(III) chloride, 2 and cobaltocene,
Dipartimento di Scienze e Tecnologie Chimiche, Universita’di
Roma-Tor Vergata, Via della Ricerca Scientifica, 00133 Rome, Italy.
E-mail: pietro.tagliatesta@uniroma2.it; Fax: +39 06-72594754;
Tel: +39 06-72594759
w Electronic supplementary information (ESI) available: Spectro-
scopic (1H NMR and EI mass spectra) data for all the compounds
reported in Table 1. 1H NMR and 13C NMR bidimensional experi-
ments for the identification ot biaryl compounds. Experimental con-
ditions for the synthesis of the triarylbenzenes from tribromobenzenes
and boronic acid derivatives and the procedure for obtaining
9-phenanthrene boronic acid. See DOI: 10.1039/b806025h
Scheme 2 Starting compounds and cyclodimerization products.
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008 New J. Chem., 2008, 32, 1847–1849 | 1847

View Article Online
Scheme 3 Proposed mechanism for the cyclodimerization.
In a previous paper5b we proposed a mechanism for the
cyclodimerization of phenylacetylene to give the 1-phenyl-
naphthalene, catalyzed by ruthenium porphyrins, in terms of
the formation of a vinylidene intermediate of the metal complex
by a Z2-1-alkyne - Z1-vinylidene rearrangement.8 Such an
intermediate could then undergo the concerted attack of a
second molecule of alkyne in a (formal) Diels–Alder reaction
(see Scheme 3) to give the final dimeric product while triphenyl-
benzenes probably derive from an open intermediate.
The yield of the dimeric products is also related to the use of
solvent in the reaction with the best results obtained in
dichlorobenzene.
Investigating our proposed reaction mechanism, the next
application of the metalloporphyrins catalysis should be
directed to the possibility of obtaining other more complicated
biaryl derivatives. The approach simply consisted in the use of
ethynyl derivatives of naphthalene and phenanthrene. 1- and
2-ethynylnaphthalene and 9-ethynylphenanthrene could be
good candidates for obtaining the dimerization reaction and
in fact in the presence of catalyst 1 or 2, substrates 4 and 5,
afford the biaryls 7 and 8, respectively, while substrate 6,
which has two possibilities of attack at C1 and C3, gives
mainly compound 10 while 9 was obtained in trace amount.
This last result probably derives from the slightly different
stability of the anthracene and phenanthrene polynuclear
aromatics (DDGf E 6 kcal molꢁ1).9 In Table 1 the reaction
yields for all the substrates, compared with those obtained
using cobaltocene catalyst are reported.
Scheme 4 Cyclotrimerization products.
clear that the ruthenium and rhodium porphyrins, used for
this work, afford biaryl compounds with moderate to high
yield and good selectivity while cobaltocene, a classic catalyst
used in the cyclooligomerization of ethynes3 gives mainly a
mixture of 1,3,5- and 1,2,4-triarylbenzenes with small amount
of the cyclodimers. The structures of the final cyclotrimeriza-
tion compounds are reported in Scheme 4.
All the triarylbenzene final products were also synthesi-
zed, for comparison, by the Suzuki coupling of the
1,3,5- or 1,2,4-tribromobenzene with the suitable boronic acid
derivatives.10
The substrate conversion was always higher than 95% for
all the experiments. From the data reported in Table 1, it is
In the case of substrate 5 the yield in biaryl compounds, for
both the porphyrin catalysts, was lower than those obtained
for the ethynylnaphthalenes due to the presence of polymeric
material in the final mixture. Such result, in our opinion,
derives from the presence of a steric hindrance effect in the
reaction intermediate which does not allow a good cyclization
rate compared with that for polymer formation. Moreover all
the isolated dimers show interesting properties as new materi-
als for OLED building.
Table 1 Cyclooligomerization of arylethynes, 4, 5 and 6 in DCBa by
Ru(OEP)CO, 1b, RhTPPCl, 2b and Cp2Co, 3c
Yieldd (%)
Biaryl 1,3,5-Triaryl 1,2,4-Triaryl
Entry Catalyst Substrate
1
2
3
4
5
6
7
8
9
a
1
1
1
2
2
2
3
3
3
4
5
6
4
5
6
4
5
6
73.4
33.2
62.2e
86.0
35.7
89.7e
1.2
5.7
Trace
5.9
1.3
1.4
Trace
27.0
25.2
21.8
13.8
1.6
13.6
3.0
2.9
7.2
66.3
60.1
75.8
In fact they all present a strong fluorescence band in the blue
region as has been reported by other authors for similar
compounds.11
The catalytic properties of the metalloporphyrins in the one-
pot formation of asymmetric biaryls make this reaction a good
alternative to the well known methods. The possibility to
recycle the metalloporphyrins several times compared with
the other cyclotrimerization catalysts can be considered as of
high significance.
1.2
1.7
b
Volume ratio DCB : substrate = 3 : 1. Reactions carried out at 160 1C
c
with a molar ratio substrate : porphyrin = 5700 : 1. Reactions carried
out at 150 1C with a molar ratio substrate : cobaltocene = 5700 : 1.
The financial support of Italian MIUR is gratefully
acknowledged. The authors thanks Mr G. D’Arcangelo for
recording the mass spectra.
d
Yields determined by GC or flash chromatography analysis. e Two
isomers.
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008
1848 | New J. Chem., 2008, 32, 1847–1849

View Article Online
Maitlis, J. Organomet. Chem., 1980, 200, 161; (e) N. E. Shore, Chem.
Rev., 1988, 88, 1081; (f) M. Lautens, W. Klute and W. Tam, Chem.
Rev., 1996, 96, 49; (g) V. O. Reikhsfel and K. L. Makovetskii, Russ.
Chem. Rev. (Engl. Transl.), 1966, 35, 510; (h) P. M. Maitlis, Acc.
Chem. Res., 1976, 9, 93.
References
z Typical procedure for the reaction catalyzed by metalloporphyrin 1:
1.8 mg of catalyst 1 (2.4 ꢂ 10ꢁ3 mmol), were dissolved in 3 ml of
1,2-dichlorobenzene and 1 g of arylethyne was added. The resulting
solution was warmed at 160 1C for 48 h, under nitrogen. The crude
product was purified by flash chromatography (SiO2, hexane–diethyl
ether). The fractions containing the desired cyclodimerization pro-
ducts were collected, recrystallized and identified by 1H and 13C mono-
and bi-dimensional NMR and EI mass spectra. The yields were
between 33 and 90% depending on the substrates and the catalyst.
For the reactions catalyzed by cobaltocene 2, a similar procedure was
used.
1 Acetylene Chemistry, Chemistry, Biology and Material Science, ed.
F. Diederich, P. J. Stang and R. R. Tykwinski, Wiley-VCH,
Weinheim, 2005.
2 W. Reppe, N. Kutepow and A. Magin, Angew. Chem., Int. Ed.
Engl., 1969, 8, 727.
4 V. S. Iyer, K. P. C. Vollhardt and R. Wilhelm, Angew. Chem., Int.
Ed., 2003, 42, 4379.
5 (a) P. Tagliatesta, B. Floris, P. Galloni, A. Leoni and G. D’Arcangelo,
Inorg. Chem., 2003, 42, 7701; (b) E. Elakkari, B. Floris, P. Galloni and
P. Tagliatesta, Eur. J. Org. Chem., 2005, 889; (c) V. Conte, E.
Elakkari, B. Floris, V. Mirruzzo and P. Tagliatesta, Chem. Commun.,
2005, 1587.
6 K. Sonogashira, Y. Tohda and N. Hagihara, Tetrahedron Lett.,
1975, 4467.
7 I. A. Cohen and B. C. Chow, Inorg. Chem., 1974, 13, 488.
8 C. Bruneau and P. H. Dixneuf, Acc. Chem. Res., 1999, 32, 311.
9 A. Streitwieser, Jr and C. H. Heathcock, Organic Chemistry,
Macmillan Publishing Co., New York, 1998.
10 B. E. Huff, T. M. Koenig, D. Mitchell and M. A. Staszak, Org.
Synth., 1998, 75, 53.
11 B.-B. Jang, S. H. Lee and Z. H. Kafafi, Chem. Mater., 2006, 18, 450.
3 (a) L. P. Yur’eva, Russ. Chem. Rev. (Engl. Transl.), 1974, 43, 48;
(b) K. P. C. Vollhardt, Acc. Chem. Res., 1977, 10, 1; (c) K. P. C.
Vollhardt, Angew. Chem., Int. Ed. Engl., 1984, 23, 539; (d) P. M.
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008 New J. Chem., 2008, 32, 1847–1849 | 1849