Synthesis, structure and catalytic properties of [Ru(dppp) 2(CH3CN)Cl][BPh4] and isolation of catalytically active [Ru(dppp)2Cl][BPh4]: Ruthenium catalysed alkyne homocoupling and tandem alkyne-azide

Article abstract of DOI:10.1039/c4ra01411a

The compound, [Ru(dppp)₂(CH₃CN)Cl][BPh₄] (1) has been synthesised from the precursor complex, [Ru(PPh₃) ₃Cl₂]. The complex has been structurally characterised. The complex has been found to

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Synthesis, structure and catalytic properties of
[Ru(dppp)2(CH3CN)Cl][BPh4] and isolation of
catalytically active [Ru(dppp)2Cl][BPh4]: ruthenium
catalysed alkyne homocoupling and tandem
alkyne–azide cycloaddition†
Cite this: RSC Adv., 2014, 4, 21964
*
Uttam Kumar Das, Rajesh K. Jena and Manish Bhattacharjee
The compound, [Ru(dppp)2(CH3CN)Cl][BPh4] (1) has been synthesised from the precursor complex,
[Ru(PPh3)3Cl2]. The complex has been structurally characterised. The complex has been found to be an
efficient catalyst for the homocoupling of alkynes in the presence of silver salts. The complex can also
catalyse homocoupling of alkynes and subsequent alkyne–azide cycloaddition. The catalytically active
species, [Ru(dppp)2Cl][BPh4] (2) and one of the intermediate complexes, [Ru(dppp)2(CCPh)2] (6), have
been isolated and structurally characterised.
Received 18th February 2014
Accepted 7th May 2014
DOI: 10.1039/c4ra01411a
www.rsc.org/advances
one of the most important factors for producing regio- and
stereoselective products.13–15
Introduction
Diynes are useful starting materials in synthetic organic
chemistry. Number of natural products having anti-bacterial,
anti-cancer and anti-HIV activities contain 1,3-diyne moiety.16
Conjugated diynes afford important functional materials like
non-linear optical materials and organic conducting mate-
rials.17 The coupling of terminal alkynes was rst reported by
Glaser and Hay, independently, which involves copper(I) as
catalyst or reagents.18 Numerous studies performed on this
reaction allowed its further improvements. In all these modied
methods a large amount of bases like pyridine, N,N,N0,N0-tet-
ramethylethylenediamine, piperidine etc. are used.18 This was
followed by reports on palladium catalysed cross coupling of 1-
haloalkynes and terminal alkynes.18,19 Recently complexes of
iron,20a cobalt,20b nickel20c and gold20d have been used for
coupling of terminal alkynes. It may be noted that, the copper
catalysed reactions suffer from the use of large amount of base
and the palladium catalysed reactions are not atom economical.
In iron catalysed reactions extra preparation step of alkynyl
Grignard is required. In nickel catalysed reaction lithium salt of
alkyne is required and the catalyst loading is high. Similarly, in
cobalt and gold catalysed reactions the catalyst loading is high.
Butadiyenes have been used for the synthesis of heterocycles
like thiophene and triazoles and other heterocycles.21 Synthesis
of complex molecules by transition metal catalysed one pot
tandem reactions has gained importance over last few decades.
This is because such reactions are considered to be greener.22
Ruthenium complexes have been shown to catalyse head to
head dimerization of alkynes to en–ynes.23 Also ruthenium
complexes have been found to be efficient catalysts for alkyne–
azide cycloaddition reaction.24 It may be noted that, synthesis of
Coordinatively unsaturated ruthenium complexes have
received much attention due to their involvement in ruthe-
nium catalysed organic transformations. Ruthenium can
adopt a wide range of coordination geometries and oxidation
states and because of this ruthenium compounds are found
to be effective catalysts for a variety of organic reactions
including ring closing metathesis,1 C–H activation,2–4 activa-
tion of carbon–carbon multiple bonds2 and C–C bond forma-
tion,2 Oppenauer oxidation5 and transfer hydrogenation.6 It
has been emphasized in the literature that, 16 electron
cationic species are the active catalyst. Thus, in recent years,
some 16 electron cationic stable species have been isolated
and characterised structurally.7–9 Ruthenium(II) phosphine
complexes are widely used as catalysts for various types of
organic transformations. A large number of compounds with
tertiary phosphines of all types, including bi- and tridentate
ones have been synthesised.10,11 Ruthenium complexes with
diphosphine ligands have been shown to be effective catalysts
for various organic transformations.12
The structure of metal complexes plays a pivotal role on their
catalytic properties. Thus, control of ligand orientation on
metal centre determines the efficacy of the complexes as cata-
lysts. Ligand controlled metal catalysis has been shown to be
Department of Chemistry, Indian Institute of Technology, Kharagpur, Kharagpur
721302, India. E-mail: mxb@iitkgp.ac.in
† Electronic supplementary information (ESI) available: Details of the crystal data
and spectral data of the complexes and organic compounds. CCDC 957014,
957015 and 987274. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4ra01411a
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4,5-disubstituted triazoles by alkyne–azide cycloaddition is rare.
There are only two reports in the literature for the synthesis of
alkynyl triazoles and they have been predicted to be important
intermediates in pharmaceutical industries.25,26 Thus we
thought to design a catalytic system for tandem reaction for the
preparation of alkynyl triazole. Herein we report synthesis and
structure of [Ru(dppp)2(CH3CN)Cl][BPh4] (1) and rst example
of ruthenium catalysed Glaser–Hay18 coupling of terminal
alkynes and synthesis and structure of the catalytically active
species, [Ru(dppp)2Cl][BPh4] (2) and isolation and structural
characterization of the reaction intermediate trans-
[Ru(dppp)2(CCPh)2] (6). The ruthenium complex, 1 has also
been utilized for one pot synthesis of 4-substituted-5-alkynyl
1,2,3-trazole.
Fig. 1 ORTEP view of [Ru(dppp)2(CH3CN)Cl]+ cation in 1. Hydrogen
atoms have been omitted for clarity.
ꢁ
˚
Ru1 ¼ 2.003(4) A} (Table S2, ESI†). The BPh4 anion is found
outside the coordination sphere and does not show any
bonding interaction with ruthenium(II) center.
Results and discussion
Synthesis and characterization of [Ru(dppp)2(CH3CN)Cl]
[BPh4] (1) and [Ru(dppp)2Cl][BPh4] (2)
The complex, [Ru(dppp)2Cl][BPh4] (2) crystallizes in mono-
clinic space group P21/a (Table S1, ESI†). The asymmetric unit
consiꢁsts of a complex cation, [Ru(dppp)2Cl]+ and the anion
BPh4 (Fig. 2). The ruthenium center is in a trigonal bypyr-
amidal coordination environment. The basal positions are
occupied by two phosphorus atoms, P1 and P3 {P1–Ru1 ¼
The complex, [Ru(dppp)2(CH3CN)Cl][BPh4] (1) has been syn-
thesised from the reaction of RuCl2(PPh3)3 with diphenylphos-
phinopropane (dppp) in 1 : 2.5 ratio in acetonitrile in the
presence of NaBPh4. This can also be prepared form the reac-
tion of RuCl3$nH2O with excess of dppp in the presence of
NaBPh4. The complex, [Ru(dppp)2Cl][BPh4] (2) has been syn-
thesised by heating a solution of 1 in toluene at 100 ꢀC. The
complexes have been characterised by elemental analyses, IR,
and 1H and 31P NMR spectroscopy. The elemental analyses
agree well with the formulations of the compounds. The 1H
NMR spectrum of 1 shows multiplet in the region 6.87 to 7.85
ppm due to aromatic protons. The signals for P–CH2 protons
appear at 2.75 ppm (broad) and at 2.51 ppm (multiplet). The
signals of –CH3 protons of the acetonitrile ligand and the C–
CH2–C protons appear at 2.09 ppm (broad). The 31P NMR
spectrum of the complex shows a singlet at 36.5 ppm. The
spectral features are similar to those reported for ruthenium
complexes of bidentate phosphine ligands.12 The 1H NMR
spectrum of 2 shows a multiplet in the region 2.57–2.63 (4H)
ppm due to the methylene protons of the P–CH2–CH2–CH2–P
moiety. The signal for methylene protons of the P–CH2 group
appears at, 3.26 ppm (br, 8H) and the signals for aromatic
protons appear at 6.8–7.4 (m, 60H). The 31P NMR spectrum of 2
shows two singlets at, 36.8 and at 47.6 ppm. In addition, a
singlet appears at ꢁ0.1 ppm. This may be due to some impurity.
˚
˚
2.263(2) A, P3–Ru1 ¼ 2.280(2) A} form two different dppp
˚
ligands and a chloride ion, Cl1 {Cl1–Ru1 ¼ 2.394(2) A}. The axial
positions are occupied by two phosphors atoms, P2 and P4
˚
˚
{P2–Ru1 ¼ 2.429(2) A, P4–Ru1 ¼ 2.416(2) A}. The Ru1–P2 and
Ru1–P4 bond distances as well as P2–Ru1–P4 bond angle {P4–
Ru1–P2 ¼ 173.11(7)ꢀ} (Table S2, ESI†) clearly shows that, the
ruthenium centre is in distorted trigonal bipyramidal coordi-
nation environment.
Studies of catalytic properties of [Ru(dppp)2(CH3CN)Cl][BPh4]
(1)
Ruthenium(II) complexes have been shown to be capable of
activating alkynes via vinylidene complex formation or p-
complex formation towards nucleophilic addition reactions.27
Also it may be noted that, ruthenium complexes of h1 coordi-
nated alkynes have been reported.28 We have been working on
Structural characterization of [Ru(dppp)2(CH3CN)Cl][BPh4]
(1) and [Ru(dppp)2Cl][BPh4] (2)
ꢀ
The complex, 1 crystallizes in triclinic space group P1 (Table S1,
ESI†). The asymmetric unit contains one cationic ruthenium
complex (Fig. 1) and one tetraphenylborate anion. The ruthe-
nium center is in a distorted octahedral coordination environ-
ment. The basal positions are occupied by four phosphorus
from two dppp ligands, P1, P2, P3 and P4 {P1–Ru1 ¼ 2.4025(15)
˚
˚
˚
A; P2–Ru1 ¼ 2.4247(14) A; P3–Ru1 ¼ 2.4750(14) A; P4–Ru1 ¼
˚
Fig. 2 ORTEP view of [Ru(dppp)2Cl]+ cation in 2. Hydrogen atoms
Cl1 {Cl1–Ru1 ¼ 2.4222(13) A} and an acetonitrile nitrogen {N1– have been omitted for clarity.
2.4428(15) A}. The axial positions are occupied by one chloride,
˚
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Table 2 Homocoupling of alkynes catalyzed by 1a
activation of alkyne via vinylidene complex and p-complex
formation towards nucleophilic addition reactions.29 We were
interested in activation of alkynes by ruthenium(II) complexes
via the formation of h1 coordinated alkynes.
Silver salts are known to form acetylide very easily and in
number of catalytic reactions these acetylides have been used.30
Thus it is expected that silver salts will react with phenyl-
acetylene to produce silver acetylide, which in turn react with in
situ generated pentacoordinated cationic ruthenium complex
[Ru(dppp)2Cl]+ to produce ruthenium coordinated h1 alkyne.
We were interested in studying its catalytic properties towards
Glaser–Hay coupling and subsequent alkyne–azide cycloaddi-
tion reaction. Thus, coupling of phenylacetylene (3a) was
chosen as a model reaction. The coupling reaction of 3a was
carried out in the presence of a catalytic amount of 1 (1 mol%)
in the presence of silver salts (3 mol%) and air at various
solvents at different temperature for the optimization of the
reaction (Table 1). It has been found that, DMF is the best
solvent and Ag(NO3) is the ideal co-catalyst and the optimum
ꢀ
temperature was found to be 90 C. It may be noted that, the
a
reaction carried out in degassed DMF under argon atmosphere
failed to afford the desired product. Similarly, in the absence of
silver salts no product formation could be detected. Also, we
could not get any product from the reaction of phenylacetylene
in the absence of 1 but in the presence of only Ag(NO3).
However, reaction carried out only in the presence of 1 gives
corresponding ene–yene. Thus it is clear that, presence of 1 as
well as silver(I) and air is essential for the reaction.
Reaction conditions: alkyne (1.0 mmol), 1 (0.01 mmol), AgNO3 (0.03
mmol), DMF (5.0 cm3), temp. (90 ꢀC). b Yields are isolated.
and the coupling products were isolated in good to excellent
yield (Table 2).
As mentioned we were interested in tandem reaction of
homocoupling of alkynes and subsequent cycloaddition reac-
tion with azide. Accordingly, in a separate reaction rst phe-
nylacetylene was taken in DMF and to this complex 1 (2 mol%)
and Ag(NO3) (5 mol%) was added and the reaction mixture was
heated for 30 min. To this was then added NaN3 and the reac-
tion mixture was heated for 8 h. The reaction mixture on usual
workup afforded, 4-phenyl-5-phenylethylyne-1H-[1,2,3]triazole
(5a) in 85% yield. In order to check the involvement of Ag(I) in
the reaction, a separate reaction was done using isolated
coupled product and NaN3 in the presence of only 1 and the
corresponding triazole could be isolated in good yield. In
another reaction the preformed coupled product was reacted
with NaN3 only in the presence of Ag(NO3). In this case no tri-
azole formation could be detected. Similarly, reaction between
preformed diyene with NaN3 in the absence of 1 failed to give
any product under the employed reaction condition. Thus, it is
clear that, the cycloaddition reaction is catalysed by the ruthe-
nium complex, 1. The reaction was generalized using number of
alkynes and triazoles were isolated in good yields (Table 3). It
may be noted that, when alkyl azide was used instead of sodium
azide, we could not detect any triazole formation. Thus it is clear
that, polarity of azide is very important in this case.
Having established the optimum condition, we were
interested in studying the scope of the reaction. Thus, a
number of alkynes were subjected to the coupling reaction
Table 1 Optimization of coupling of phenyl acetylene catalyzed by 1
and Ag(I)a
Entry
Solvent
Temp. (ꢀC)
T (h)
Yieldb (%)
Ag(1)
1
2
3
4
5
6
7
8
Toluene
Toluene
DMSO
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
DMF
DMF
DMF
90
90
90
90
90
60
90
70
90
25
90
90
90
90
90
24
5
5
5
2
1
0.5
1
0.75
24
0.5
2
24
24
0.5
—
75
65
87
93
38
90
80
95
—
95
75
—
—
95
—
Ag2(CO3)
Ag2(CO3)
Ag2(CO3)
Ag(OAc)
Ag(OAc)
Ag(OAc)
Ag(NO3)
Ag(NO3)
Ag(NO3)
Ag(NO3)
Ag(NO3)
Ag(NO3)c
Ag(NO3)d
Ag(NO3)e
9
10
11
12
13
14
15
Mechanistic investigation
We next proceeded to examine the mechanism of the coupling
reaction. As it has been mentioned, in solution, the complex
looses the hemilabile acetonitrile ligand and forms catalytically
active trigonal bipyramidal complex, [Ru(dppp)2Cl]+. A model
reaction was carried out with phenyl acetylene in the presence
a
Reaction conditions: phenylacetylene (1.0 mmol), 1 (1 mol%) Ag(I) (3
mol%) in solvent (5.0 cm3). Isolated. In the absence of 1. Under
argon atmosphere. Complex 2 as catalyst instead of complex 1.
b
c
d
e
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Table 3 Alkyne–azide cyclization catalyzed by 1a
during reaction the diacetylide complexes can undergo
isomerization.
The 31P NMR spectrum of the complex shows a singlet at 38.3
ppm, In addition to this a singlet appear at 0.1 ppm. This may
be due to some impurity (Fig. S5, ESI†).
The complex, trans-[Ru(dppp)2(CCPh)2] (6) crystallizes in
ꢀ
triclinic space group P1 (Table S1, ESI†). The Ruthenium center
is in a distorted octahedral coordination environment. The
basal positions are occupied by four phosphorus atoms, P1, P2,
˚
˚
P3, P4 {P1–Ru1 ¼ 2.394(2) A, P2–Ru1 ¼ 2.3826(19) A, P3–Ru1 ¼
˚
˚
2.405(2) A, P4–Ru1 ¼ 2.4096(19) A} (Table 2). The axial positions
are occupied by two carbon atoms, C55 and C63, of coordinated
˚
˚
phenyl acetylene {C55–Ru1 ¼ 2.041(7) A, C63–Ru1 ¼ 2.037(7) A}.
In a separate reaction, 1 was treated with phenyl acetylene
and Ag(NO3) in DMF in 1 : 2 : 2 ratio and was heated for 5 min
and the reaction was quenched by the addition of water and the
product was extracted by ethyl acetate. The ethyl acetate extract
was evaporated and 31P NMR spectrum of the isolated products
was recorded in CDCl3 (Fig. S6, ESI†). The 31P NMR spectrum of
the solution shows two singlets at 25.2 and at 23.0 ppm, along
with two singlets at 47.6 and 36.5 ppm due to 2. The singlets at
25.2 and at 23.0 ppm can be assigned to the species, cis-
[Ru(dppp)2(CCR)2]. In addition to these signals, three singlets
were observed at 1.5, 0.2, ꢁ1.2 ppm. These signals are due to
some decomposed product. We could not observed any signal
due to trans-[Ru(dppp)2(CCR)2].
Based upon these observations it is suggested that, in solu-
tion complex 1 looses acetonitrile ligand to produce the pen-
tacoordinated complex [Ru(dppp)2Cl]+. The complex rst reacts
with two equivalent of Ag(CCR) to produce the comparatively
less stable cis-[Ru(dppp)2(CCR)2] complex and a very small
amount of trans-[Ru(dppp)2(CCR)2]. The reactive cis-
[Ru(dppp)2(CCR)2] undergoes reductive elimination to give the
a
Reaction conditions: alkyne (1.0 mmol), NaN3 (2.0 mmol), DMF (5.0
cm3), temp. (90 ꢀC). b Yields are isolated.
of catalytic amount of [Ru(dppp)2Cl][BPh4] and we could isolate
the coupled product in high yield (Table 1, entry 15). No
appreciable difference between the catalytic activity of 1 and 2
could be observed. This is expected, as 1 looses CH3CN very
easily in solution to produce 2. Thus it is clear that,
[Ru(dppp)2Cl]+ is the active species.
In order to probe the role of silver, complex 1 was treated
with phenylacetylene and Ag(NO3) in 1 : 2 : 2 ratio in DMF and
the mixture was heated for 5 min. The reaction solution on
standing afforded a few crystals of trans-[Ru(dppp)2(CCPh)2] (6),
which has been characterised by spectroscopic techniques and
single crystal X-ray crystallography (Fig. 3). In this reaction
probably both trans- and cis-complexes are produced and the
trans-product being more stable crystallizes out. Number of
trans-bis acetylide complexes containing diphosphine ligands
have been synthesised starting form trans-dichloro and dihy-
drido complexes of ruthenium.28 However, in one of the reports
it has been shown that, cis-Ru(PMe3)4Me2 reacts with terminal
alkynes to afford both cis- and trans-[Ru(PMe3)(CCR)2], the
trans-product being the minor product.28a Thus it is clear that,
Fig. 3 ORTEP view of [Ru(dppp)2(CCPh)2] (6). Hydrogens have been Scheme 1 Suggested mechanism of alkyne homocoupling catalyzed
omitted for clarity.
by 1.
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coupled product and Ru(0). The Ru(0) complex is oxidized by CDCl3, ppm): d ¼ ꢁ0.08, 36.8 and 47.6 ppm; IR (KBr): n (cmꢁ1) ¼
aerial oxygen to produce Ru(II) back (Cycle A, Scheme 1). It is 507, 697, 738, 1088, 1433, 1479, 1575, 2860, 2924, 3054.
also possible that, Ag+ oxidizes Ru(0) to Ru(II) and metallic silver
is produced, which undergoes aerial oxidation (Cycle B, Scheme
1). It may be noted that, in couple of occasions we could see the
formation of silver mirror aer prolonged heating. In the
complex 6, the two phenyl acetylides are trans to each other and
that is why no reductive elimination takes place when the
complex 6 is heated.
It is suggested that, the cycloaddition reaction proceeds by
the mechanism suggested in the literature for [Cp*RuCl(PPh3)2]
catalysed azide–alkyne cycloaddition reaction.24c The source of
proton is the water generated in coupling reaction of alkyne.
Homo coupling of alkyne catalysed by 1
In a round bottomed ask 1 (1 mol% with respect to alkyne),
alkyne (1 mmol), AgNO3 (3–5 mol%) and DMF (5 mL) was taken.
The reaction mixture was stirred at 90 ꢀC under air for required
time. The solvent was removed under vacuum and the product
was isolated by column chromatography on silica gel using n-
hexane as an eluent, giving 80–98% yield (99% purity by 1H
NMR). Spectral data of the compounds are given in ESI.†
Homo coupling of alkyne followed by alkyne–azide
cycloaddition catalysed by 1
Experimental
Aer the completion of homo-coupling reaction, in this round
bottomed ask 1 mmol of NaN3 was added and stirred at 90 ꢀC
for 6–8 h. The conversion of 1,3-dialkyne was monitored by TLC.
The solvent was removed under vacuum and the product was
isolated by column chromatography on silica gel using n-hexane
and ethylacetate mixture as an eluent, giving 70–85% yield.
Spectral data of the compounds are given in ESI.†
Solvents and reagents used were reagent grade products. 1H
NMR spectra were recorded on Bruker Avance II (400 and 200
MHz) spectrometers. The 31P (161.98 MHz) NMR spectra were
recorded on Bruker Avance II spectrometer (1H frequency: 400
MHz). HRMS of the newly synthesised compounds were recor-
ded on Waters TOF MS in ESI+ mode in methanol water
mixture.
Isolation of [Ru(dppp)2(CCPh)2] (6)
The complex [Ru(dppp)2(CH3CN)Cl][BPh4] (0.33 g; 0.25 mmol)
was treated with phenylacetylene and AgNO3 in 1 : 2 : 2 ratio in
DMF and the mixture was heated for 5 min. The reaction
Synthesis of [Ru(dppp)2(CH3CN)Cl][BPh4] (1) {dppp ¼ 1,3-bis
(diphenylphosphino)propane}
A sample of RuCl2(PPh3)3 (1.03 g; 1.2 mmol) and 1,3-bis(di-
phenylphosphino)propane (1.03 g; 2.5 mmol) were dissolved in
distilled acetonitrile (10 mL) and the reaction solution was
reuxed for about 5 h. The colour of the reaction solution
turned brown to light yellow. The reaction solution was then
ltered and NaBPh4 (0.41 g; 1.2 mmol) was added. The solution
was concentrated over a water bath. A yellow, crystalline solid
separated out. The separated solid was ltered and washed with
hexane (3–4 times) and dried in vacuum. The compound was
nally recrystallised from acetonitrile. Yield: 1.0 g (76%): 1H
NMR (400 MHz, CDCl3, ppm): 1.99 (br, 3H), 2.08 (s, 4H), 2.24
(qt, J ¼ 7.6, 9.2 Hz, 4H), 2.6 (br doublet, J ¼ 17.8 Hz, 4H), 6.89–
7.84 (m, 60H); 31P NMR (161.98 MHz, CDCl3, ppm): d ¼ 34.033
ppm; IR (KBr): n (cmꢁ1) ¼ 522, 697, 747, 1090, 1381, 1608, 2369,
solution on standing afforded
a few crystals of trans-
[Ru(dppp)2(CCPh)2], which has been structurally characterised
by single crystal X-ray crystallography. Yield: 0.03 g (10%).
Single crystal data collection and renements
Single crystal X-ray data of 1, 2 and 6 were collected on Bruker
Smart APEX system that uses graphite monochromated Mo Ka
˚
radiation (l ¼ 0.71073 A). The structure was solved by direct
method and rened by least square method on F2 employing
WinGx31 package and the relevant programs (SHELX-97 (ref. 32)
and ORTEP-3 (ref. 33)) implemented therein. Non-hydrogen
atoms were rened anisotropically and hydrogen atoms on C-
atoms were xed at calculated positions and rened using a
riding model. For 6 PLATON SQUEEZE was used for removing
disordered solvent molecule.
2958,
3057
cmꢁ1
;
elemental
analysis:
calcd
for
C
80H75BClNP4Ru: C 72.70, H 5.72, N 1.06; found: C 72.75, H
5.92, N 1.09.
Conclusions
Synthesis of [Ru(dppp)2Cl][BPh4] (2)
In conclusion, we have successfully synthesised and charac-
A sample of [Ru(dppp)2(CH3CN)Cl][BPh4] (0.66 g; 0.5 mmol) was terised
a
new simple cationic ruthenium complex,
ꢀ
dissolved in 3 mL of toluene and heated for 1 hour at 100 C. [Ru(dppp)2(CH3CN)Cl][BPh4]. The complex can efficiently
The yellow solutions turned brown. On standing for 2–3 h, at catalyse homocoupling of alkyne in the presence of silver(I) salts
room temperature a dark brown power separated out. The and air. This is the rst report on ruthenium(II) catalysed
powder was ltered and washed with hexane. The compound oxidative coupling of alkynes. The catalytically active species,
was nally crystallised from dichloromethane–diethyl ether [Ru(dppp)2Cl][BPh4] has been isolated and structurally charac-
layer. Yield: 0.5 g; 79%. Elemental analysis calculated for terised. One of the intermediate complex, [Ru(dppp)2(CCPh)2]
C
78H72BClP4Ru (mol. wt. ¼ 1280.63): C, 73.15; H, 5.67; found: C, has been isolated and structurally characterised. This complex
1
73.20; H, 5.75; H NMR (400 MHz, CDCl3, ppm): d ¼ 2.57–2.63 can also catalyse cycloaddition reaction between sodium azide
(m, 4H), 3.26 (br, 8H), 6.8–7.4 (m, 60H); 31P NMR (161.98 MHz, and alkynes and thus it has been used for tandem synthesis of
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4-substituted-5-alkynyl-1,2,3-triazoles. The catalyst loading is 14 (a) R. Kumareswaran, M. Nandi and T. V. RajanBabu, Org.
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We thank Department of Science & Technology, Government of
India, New Delhi for single crystal X-ray and NMR facilities
and nancial assistance. UKD thanks Council of Scientic &
Industrial Research, New Delhi for fellowship.
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