Rhodium-catalyzed dimerization of terminal alkynes assisted by MeI

Article abstract of DOI:10.1021/om049604s

Dimerization of terminal arylalkynes at ambient temperature catalyzed by Rh(CO)PPh₃)₂-Cl (2) in the presence of MeI leads to formation of enyne with high conversion and high regio- and stereoselectivity. A rhodium intermediate captured from oxidative addition of Mel was used for dimerization of alkyne with selectivity controlled by the use of solvents. In aprotic solvent (such as acetone, CH₂Cl₂, or THF) dimerization of terminal alkynes HC≡C(p-C₆H₄X) (1, X = H, a; NO₂) b; C(O)H, c; Me, d; CN, e; NMe₂, f; CF ₃, g, F, h; Br, i; I, j) leads to the (E)-1,4-disubstituted enynes 6 (a-k) in high selectivity. However, when MeOH is used as a solvent, the dimerization of 1-arylalkynes containing an electron-withdrawing group affords selectively the (Z)-1,4-disubstituted enyne 8. Requirement of the presence of Mel for this conversion indicates that the process presumably involves initially a six-coordinated rhodium methylacetylide intermediate. Oxidative addition of ICH₂CN to 2 yielded the catalytically inactive six-coordinated complex Rh(CO)(PPh₃) ₂(C≡CPh)(I)(CH₂-CN) (5a). The analogous complex 5b with a p-nitro group on the phenyl acetylide ligand is characterized by X-ray diffraction analysis.

Full text of DOI:10.1021/om049604s

136
Organometallics 2005, 24, 136-143
Rhodium-Catalyzed Dimerization of Terminal Alkynes
Assisted by MeI
Chrong-Ching Lee, Ying-Chih Lin,* Yi-Hung Liu, and Yu Wang
Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
Received June 3, 2004
Dimerization of terminal arylalkynes at ambient temperature catalyzed by Rh(CO)(PPh3)2-
Cl (2) in the presence of MeI leads to formation of enyne with high conversion and high
regio- and stereoselectivity. A rhodium intermediate captured from oxidative addition of
MeI was used for dimerization of alkyne with selectivity controlled by the use of solvents.
In aprotic solvent (such as acetone, CH2Cl2, or THF) dimerization of terminal alkynes
HCtC(p-C6H4X) (1, X ) H, a; NO2, b; C(O)H, c; Me, d; CN, e; NMe2, f; CF3, g; F, h; Br, i;
I, j) leads to the (E)-1,4-disubstituted enynes 6 (a-k) in high selectivity. However, when
MeOH is used as a solvent, the dimerization of 1-arylalkynes containing an electron-
withdrawing group affords selectively the (Z)-1,4-disubstituted enyne 8. Requirement of the
presence of MeI for this conversion indicates that the process presumably involves initially
a six-coordinated rhodium methylacetylide intermediate. Oxidative addition of ICH2CN to
2 yielded the catalytically inactive six-coordinated complex Rh(CO)(PPh3)2(CtCPh)(I)(CH2-
CN) (5a). The analogous complex 5b with a p-nitro group on the phenyl acetylide ligand is
characterized by X-ray diffraction analysis.
Introduction
stereoisomeric enynes (E,Z-form and head-to-tail dimers)
is obtained.
Alkyne-coupling reactions catalyzed by transition
metals are of considerable current interest because
these reactions afford unsaturated four-carbon com-
pounds such as conjugated enynes, which are important
building blocks1 for synthetic organic chemistry and key
units found in a variety of biologically active compounds.
Many metal complexes including early, late transition
metals and lanthanide series such as Sc,2 Y,3 Ce,3 La,3
Sm,4 Zr,5 Ti, Cr,6 and Ru,7 Rh,8 Ni,9 Pd,10 and Cu11 have
been used in the dimerization reaction of terminal
alkynes; however, in most cases a mixture of regio- and
The factors that affect regio- and stereoselectivity
depend mainly on the electronic effects and steric
hindrance at the alkyne substituent and at the coordi-
nation sphere of the metal. Methods for selective
construction of head-to-tail enynes in the presence of
the Pd system were developed by Trost.12 The homo-
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10.1021/om049604s CCC: $30.25 © 2005 American Chemical Society
Publication on Web 12/03/2004

Rh-Catalyzed Dimerization of Terminal Alkynes
Organometallics, Vol. 24, No. 1, 2005 137
We are interested in exploring the chemical reactivity
of various metal vinylidene complexes20 commonly
prepared by alkylation21 of metal acetylide complexes.
However, in the reaction of methyliodide with the
rhodium phenylacetylide complex, oxidative addition
takes place preferentially followed by a reductive elimi-
nation to give the 1-phenyl-1-propyne. Surprisingly a
competing dimerization product from the reaction of the
terminal acetylide ligand is also observed. This indicates
that the intermediate generated in the process could be
used to produce a different product. With careful control
of the reaction conditions, the system is developed to
take advantage of the intermediate formed from the
oxidative addition as a catalyst22 to catalyze the dimer-
ization of alkynes. Herein, we describe the catalytic
enyne formation reaction of terminal arylalkynes at
ambient temperature that lead to high conversion and
high regio- and stereoselectivity depending on the
solvent used.
in high yield by using a Pd template.13 Bianchini and
Peruzzini reported the selective coupling of terminal
alkynes to Z-1,4-disubstituted butenynes in a catalytic
manner by using Ru complexes.14 Another complex,
RuTp(py)2Cl (Tp ) trispyazolyborate, py ) pyridine),
was found to be an efficient catalyst for the selective
coupling of HCtCPh and allyl alcohol.15 The catalytic
coupling of HCtCR (R ) Ph, SiMe3, n-Bu, and t-Bu) to
1,4- and 2,4-disubstituted butenynes with the aid of Ru
complexes has been reported.16 Recently, Miyaura re-
ported the iridium-catalyzed dimerization of terminal
alkynes17 to give (E)-enyne, (Z)-enyne, or 1,2,3-bu-
tatriene derivatives in the presence of triethylamine.
The reaction used a triarylphosphine complex selectively
yielding linear (E)-enynes for silylethynes, while the
tripropylphosphine complex provided linear (Z)-enynes
for silylalkynes or 1,2,3-butatrienes for tert-alkyl-
ethynes, and formation of a head-to-tail dimer was not
observed. Gevorgyan and Rubina discovered that a Pd
system in the dimerization of terminal aryl acetylene
produced not only the head-to-tail enyne but also a
head-to-head Z-form enyne.18 They synthesized a series
of different ortho-substituted aryl alkynes and found
that at least one ortho hydrogen in aryl acetylene is
involved for a selective head-to-head dimerization reac-
tion. It was proposed that an agostic interaction between
the transition metal and ortho proton of the aromatic
ring in the substrate is responsible for the observed
unusual regioselectivity of the reaction.
Results and Discussion
Stoichiometric Reactions of Rh Acetylide Com-
plexes. The reaction of HCtCPh (1a) with [Rh]-Cl (2,
[Rh] ) Rh(CO)(PPh3)2) in the presence of MeONa and
CO results in the formation of the rhodium σ-acetylide
complex [Rh]-CtCPh (3a) in high yield. Complex [Rh]-
CtC(p-C6H4NO2) (3b), where the terminal phenyl group
on the acetylide ligand is substituted by a p-nitrophenyl
group, was similarly obtained from HCtC(p-C6H4NO2)
(1b) also in high yield. Addition of MeI to a CH2Cl2
solution of complex 3a affords [Rh]-I (2′) and the organic
compound MeCtCPh (4a) in quantitative yield. Obvi-
ously the reaction proceeds via oxidative addition of
CH3I leading to an unobserved six-coordinated complex
Rh(CO)(PPh3)2(Me)I(CtCPh) followed by reductive elimi-
nation to give [Rh]-I (2′) and 4a. Alkylation at Câ of the
acetylide ligand leading to the vinylidene complex was
not observed.
Rhodium complexes19 have also been used to catalyze
the dimerization reaction of terminal alkynes. Rhodium-
(I) triphenylphosphine complexes are most commonly
used as catalysts in these reactions. The selectivity for
enyne formation is 65-75%, but alkyne trimerization
also takes place. In 1990, Vinogradov and co-workers
reported that RhCl(PMe3)3 catalyzed dimerization of
aliphatic terminal alkynes to form enynes.8d However,
the yield of enynes is low and the regio- and stereo-
selectivity of enynes is poor. For arylalkyne, under this
reaction condition no dimer was obtained.
Interestingly, when ICH2CN is used to react with 3a,
the six-coordinated complex Rh(CO)(PPh3)2(CH2CN)I-
(CtCPh) (5a) is obtained in high yield. Namely, the
reductive elimination reaction is obstructed by the
presence of the electron-withdrawing CN group even at
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Bassetti, M.; Falvello, L. R. J. Am. Chem. Soc. 2003, 125, 2386.
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138 Organometallics, Vol. 24, No. 1, 2005
Lee et al.
Scheme 1
Figure 1. ORTEP drawing of 5b.
Table 2. Effect of the Solvent on
Rhodium-Catalyzed Dimerization of 1aa
2
Table 1. Selected Bond Lengths (Å) and Bond
Angles (deg) of 5b
yield
(mol MeI
ratio for time conversion (%)
Rh-I
2.7923(10)
2.3953(24)
1.919(9)
1.428(12)
1.121.(10)
Rh-P1
Rh-C1
Rh-C4
C2-N1
C4-C5
2.3912(23)
2.146(8)
entry solvent %) (equiv) 6a:7a:4a (h)
(%)
for 6a
Rh-P2
Rh-C3
C1-C2
C3-O1
1
2
3
4
5
6
7
MeOH
THF
CH2Cl2
benzene
ether
acetone
MeCN
5
5
1
5
5
5
5
2
0:0:100
78:19:3
81:18:1
79:20:1
71:19:10
79:20:1
5:5:90
2
24
18
18
18
18
18
100
100
100
100
47
100
100
0c
2.010(8)
3
70c
75c
71c
33b
70c
5b
1.143(12)
1.189(11)
0.5
3
I-Rh-C1
I-Rh-C4
I-Rh-P2
Rh-C3-O1
C1-C2-N1
170.36(24)
101.56(22)
89.55(6)
I-Rh-C3
80.65(25)
87.77(6)
112.3(6)
178.3(7)
172.1(9)
1
I-Rh-P1
3
Rh-C1-C2
Rh-C4-C5
C4-C5-C6
1
178.6(7)
a Catalyst: [Rh(CO)(PPh3)2Cl]/K2CO3 (10 equiv). bNMR yield.
cIsolated yield.
177.3(10)
60 °C. Complex Rh(CO)(PPh3)2(CH2CN)I(CtC(p-C6H4-
NO2)) (5b), where the terminal phenyl group is substi-
tuted by a p-nitrophenyl group, is similarly prepared
from 3b and fully characterized by an X-ray diffraction
analysis. An ORTEP drawing of 5b is shown in Figure
1, and selected bond lengths and angles are collected
in Table 1. The coordination sphere of the Rh center
can be described as octahedral with the cyanomethyl
and the acetylide ligands in cis disposition and the
cyanomethyl and iodide ligands in trans disposition.
This kind of cis disposition should also be present in
the reaction of 3a with MeI; it is therefore not surprising
to see rapid formation of 4a via reductive elimination.
Alkylation reaction of terminal acetylenes 1a and 1b
with MeI in MeOH could be carried out catalytically in
the presence of 2′ and the base MeONa at room
temperature. The product 4a is isolated in 88% yield in
6 h and MeCtC(p-C6H4NO2) (4b) in 95% yield in 1 h.
Catalytic Dimerization of Alkyne. When the above-
mentioned procedure was extended to the reaction of
rhodium complexes with other terminal aryl alkynes,
we observed dimerization of alkyne. From the aryl
alkyne HCtC(p-C6H4CHO) (1c), in addition to the
desired alkylation product 4c, the (E)-1,4-disubstituted
enyne 6c (see Scheme 1) was also obtained in high yield.
The stoichiometric reaction of 2 with 1c was first carried
out in the presence of MeI and K2CO3 in MeOH at room
in MeOH. We modified the catalytic reaction by using
THF. Interestingly, the reaction of 1c with MeI in the
presence of 2 and K2CO3/THF at room temperature for
24 h afforded 4c and the dimerization product 6c in a
1:2 ratio, which could be separated by chromatography,
and 6c was identified by 1H and 13C NMR and EI mass
1
spectrum. The H NMR spectrum of 6c displays two
3
doublet signals at δ 7.14 and 6.55 with JH-H ) 16.2
Hz, indicating the presence of two trans olefinic protons.
Two singlet signals at δ 9.99 and 9.98 are assigned to
two aldehyde protons. In the 13C NMR spectrum of 6c,
two singlet resonances at δ 191.43 and 191.33 are
assigned to two carbonyl carbons. The 13C signals of the
CdC group appear at δ 114.6 and 111.1.
(E)-1,4-Disubstituted Enynes from Terminal
Alkynes. In our optimization studies, phenyl-acetylene
was used as the model substrate for the dimerization.
The catalytic system consists of 5 mol % of 2 and 3 equiv
of MeI with 10 equiv of K2CO3 as a base in THF. Most
reactions were complete in 18 h. The ratio of (E)-1,4-
disubstituted enyne 6a, 1,3-disubstituted enyne 7a, and
the alkylation product 4a is 78:19:3 from the reaction
of 1a, showing good chemo-, regio-, and stereoselectivity.
The head-to-head dimeric product (Z)-1,4-disubstituted
enyne was not obtained. The structure of 6a was readily
determined by the coupling constant between two ole-
finic protons (J ) 16.2 Hz) for the (E)-enyne as com-
pared to that (J ) 11.9 Hz) of the (Z)-enyne. Table 2
lists our survey of various solvents for this system
showing nearly complete dimerization and similar
1
temperature. After 5 h, the H NMR spectrum of the
crude reaction mixture revealed the formation of the
alkylation product 4c in low yield possibly due to the
reactive aldehyde group in 1c in the presence of K2CO3

Rh-Catalyzed Dimerization of Terminal Alkynes
Organometallics, Vol. 24, No. 1, 2005 139
Table 3. Dimerization of Terminal Alkynes to Enynes Catalyzed by the [Rh(CO)(PPh3)2Cl]/K2CO3/MeI
Systema
MeI
(equiv)
ratio for
6:7:4
time
(h)
conversion
(%)
yield (%)
for 6
entry
R
2 (mol %)
1e
2
1a, Ph
1
0.5
3
81:18:1
60:15:25
67:0:33
92:0:8
83:3:14
90:8:2
97:0:3
18
48
4
100
100
100
100
84
100
100
75c
52c
60c
90c
54c; 69b
82c
90c
39c
88c
77c
f
1b, p-C6H4NO2
1c, p- C6H4CHO
1d, p-C6H4Me
1e, p-C6H4CN
1f, p-C6H4NMe2
1g, p-C6H4CF3
1h, p-C6H4F
1i, p-C6H4Br
1j, p-C6H4I
5
3
5
3
4d
5
5
3
48
48
40
24
24
24
14
18
1
0.1
0.1
3
6d
7
1
5
8e
9e
10e
11
5
3
1.25
1
0.25
0.1
3
93:3:4
98
100
100
1k, n-Bu
5
10:90:0
a Catalyst: [Rh(CO)(PPh3)2Cl] (2)/K2CO3 (10 equiv)/THF (10 mL). bNMR yield. c Isolated yield. d 5 equiv of NaOMe as base. e 5 mL of
CH2Cl2 as solvent. f 7k in 72% isolated yield.
Table 4. Dimerization of Terminal Alkynes to (Z)-Enynes Catalyzed by the [Rh(CO)(PPh3)2Cl]/K2CO3/CH3I
System in MeOHa
2
MeI
(equiv)
ratio for
6:8:4
time
(h)
conversion
(%)
yield (%)
for 8
entry
R
(mol %)
1
1a, Ph
1
1
1
1
1
1
1
1
1
1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
13:82:5
16
18
18
48
48
40
18
18
18
14
100
82b, 63c
2e
3e
4d,e
5
1b, p-C6H4NO2
1c, p-C6H4CHO
1d, p-C6H4Me
1e, p-C6H4CN
1f, p-C6H4NMe2
1g, p-C6H4CF3
1h, p-C6H4F
0:95:5
96
82c
6d,e
7
8
9
10
0:99.5:0.5
100
91c
25c
90c
35c
1i, p-C6H4Br
1j, p-C6H4I
0:97:3
0:80:20
100
57
a Catalyst: [Rh(CO)(PPh3)2Cl] (1a)/K2CO3 (10 equiv)/MeOH (5 mL). bNMR yield. c Isolated yield. d 5 equiv of MeONa as base. e (Z)-
Enynes were not observed.
product distribution in some aprotic solvents. Dimer-
ization reaction of phenylacetylene was not observed in
MeOH, as shown in entry 1. Low conversion in entry 5
could be due to the low solubility of rhodium complex 2
in ether. Acetonitrile appears to be an inappropriate
solvent in the dimerization of phenylacetylene, presum-
ably because of its coordinating nature (entry 7).
Furthermore, as shown in Table 3, a survey of various
terminal arylacetylenes for this system shows nearly
complete dimerization and similar product distribution
in a variety of solvents such as THF and CH2Cl2. All
disubstituted enynes was not obtained. When MeOH is
used, dimerization reactions of 1-alkynes catalyzed by
2 afforded (Z)-1,4-disubstituted enynes 8 at room tem-
perature in excellent yield with high chemo-, regio-, and
stereoselectivity. The catalytic system consisting of 1
mol % of 2 and 0.1 equiv of MeI with 10 equiv of K2CO3
as a base was tested in MeOH for the catalytic activity
of the dimerization of various 1-alkynes (see Table 4).
For the dimerization of 1a (R ) Ph), the reaction was
complete in 16 h. The product ratio of (E)-1,4-disubsti-
tuted enyne 6a, (Z)-1,4-disubstituted enyne 8a, and the
alkylation product 4a is 13:82:5 (entry 1). The head-to-
tail dimeric product 1,3-disubstituted enyne 7a was not
obtained. The structure of the (Z)-enyne was readily
determined by the coupling constant between two ole-
finic cis-protons (J ) 11.9 Hz). A number of other
terminal arylacetylenes undergo nearly complete dimer-
ization and give a similar product distribution in MeOH
(Table 4). For the dimerization of HCtC(p-C6H4CN)
(1e), the reaction was complete in 48 h. The product
ratio of 8e:4e is 95:5 (entry 3). For 1g, high conversion
(100%) and excellent selectivity (99.5% in Z-isomer) are
found for the catalytic dimerization reaction (entry 7).
Dimerization of 1i reveals similar selectivity and con-
version (entry 9). In the case of 1j (R ) 4-C6H4I), the
dimerization reaction results in lower selectivity and
lower conversion (57%) (entry 10).
1
E-form enyne products 6 are characterized by H and
13C NMR and FAB mass spectroscopic data.
For the catalytic dimerization reaction of arylalkyne
with electron-donating groups such as CH3 (1d) and
NMe2 (1f) on the aryl ring, a stronger base such as
MeONa is required (entries 4, 6). Substrate 1h suffers
from low yield (entry 8). For dimerization of 1j, because
of the low solubility of 6j, the crude dimeric product ratio
was not determined by 1H NMR (entry 10). For alkyne
1c (R ) p-C6H4CHO), the (E)-enyne 6c and alkylation
product 4c are formed in a ratio of 67:33% (6c:4c) with
100% conversion (entry 3). Finally, the aliphatic alkyne
1k produces corresponding head-to-tail dimer 7k as the
major product (entry 11). Dimerization of 1h, 1i, 1j, and
1c to form enynyl products was not reported previously.
This may be due to high affinity of the C-X bond of the
aryl halide to the Pd catalyst.
However, in cases of dimerization reaction of 1-aryl-
alkynes, bearing Me2N, NO2, and Me groups at the para-
position of the aryl group, neither (E)-enynes nor (Z)-
enynes were obtained (Table 4). The reaction of 1b with
MeI in the presence of 2 and K2CO3 in MeOH afforded
only the alkylation product 4b in 10% NMR yield (entry
(Z)-1,4-Disubstituted Enynes from Terminal
Alkynes. The rhodium-catalyzed dimerization reaction
of terminal alkynes in aprotic solvents such as THF,
CH2Cl2, acetone, and benzene gives (E)-1,4-disubstituted
enynes, but the corresponding Z-form isomer of 1,4-

140 Organometallics, Vol. 24, No. 1, 2005
Lee et al.
Scheme 2
2). No dimeric (E)- or (Z)-enyne was obtained. This is
clearly due to the presence of a para-NO2 group at the
phenyl group of 1b. For HCtC(p-C6H4Me) (1d), no
Z-form enyne was observed in MeOH. Under catalytic
conditions, the reaction of 1d with MeI in MeOH affords
the alkylation product 4d, 3d, and a trace amount of
the E-form enyne 6d (entry 4). For 1f, only the alkyla-
tion product 4f was obtained (entry 6). In the dimer-
ization reaction of 1h in MeOH the low yield of (Z)-
enyne8hcouldbeduetoanunstablereactionintermediate
(entry 8). Finally, the reaction of alkyne 1c under
catalytic conditions in MeOH affords a black, insoluble
solid, which was not characterized (entry 3). We pro-
posed that the black solid is derived from polymerization
of 1c in the presence of 2 and K2CO3/MeOH.21 To the
best of our knowledge, the transition metal-catalyzed
dimerization of 1-arylalkyne with high regioselectivity
to the head-to-head (Z)-enynes is rare.
In 1991, Bianchini and co-workers reported that the
selective coupling of terminal alkynes to Z-1,4-disub-
stituted butenynes can be achieved catalytically by
using either the Ru hydrido complex [(PP3)Ru(H)(η2-H2)]-
BPh4 or the η1-dinitrogen derivative [(PP3)Ru(H)(N2)]-
BPh4 (PP3 ) P(CH2CH2PPh2)3).7b When complex [(PP3)-
Ru(CtCSiMe3)]BPh4 is reacted with excess HCtCSiMe3,
catalytic production of (Z)-1,4-bis(trimethylsilyl)but-3-
en-1-yne was observed.
Proposed Mechanism of Rhodium-Catalyzed
Dimerization. There were only a few mechanistic
studies on Rh(I)- and Pd(I)-catalyzed terminal alkyne
dimerization reactions that provided direct evidence. It
is generally accepted that the first step is the addition
of the terminal alkyne to the transition metal catalyst
to yield a metal acetylide complex intermediate (M )
Rh, Pd).13,18,21,23 Indeed, the reaction of 1-alkynes with
2 in the presence of base results in formation of Rh(I)-
acetylide complexes. Further reaction of Rh(I)-acetylide
complex with alkyl halide affords a six-coordinated
Rh(III) complex by oxidative addition. In the absence
of MeI, the reaction of alkyne 1 with 2 and a base affords
only the Rh-acetylide complex. Thererore, formation of
the metal acetylide should be derived from the reaction
of rhodium chloride with the deprotonated terminal
alkyne by base, instead of a direct oxidative addition.
In the absence of a base, there is no reaction of the
mixture of alkyne 1 and 2 in MeOH, THF, or CH2Cl2.
The dimerization reaction of 1c with 5 mol % of the
Rh(III) complex Rh(CO)(PPh3)2(Cl)I2, prepared by iodi-
nation of 2, under catalytic conditions at room temper-
ature affords the E-form disubstituted enyne 6c in low
yield due to poor catalytic activity of Rh(CO)(PPh3)2-
(Cl)I2.
pathways, ii and iii, respectively.24 Complex A could also
undergo reductive elimination, affording the alkylation
product MeCtCR, 4, via pathway i. To hamper the
reductive elimination pathway, the amount of MeI was
reduced. The reaction favored pathway ii for the alkyne
substrate bearing an aryl group. In this pathway, a
second terminal alkyne coordinates to the Rh atom,
leading to the butenynyl intermediate D. Then further
reaction of D with alkyne affords the product E-enynes
6, regenerating A. However, for aliphatic alkyne such
as 1-hexyne, the head-to-tail dimer 7 is formed more
favorably than the head-to-head E-isomer 6 in the enyne
formation reaction. The reaction may thus proceed
through pathway iii.
Recently, Kirchner and co-workers reported that a
TpRu acetylide complex reacts readily with stoichio-
metric amounts of HCtCPh in benzene to give the
alkyne coupling product featuring an (E)-1,4-enynyl
ligand.25 Head-to-head coupling with E- or Z-selectivity
is, however, more frequently reported. In 1997, Jordan
and Yoshida reported that the dicarbollide methyl
complex (Cp*)(η5-C2B9H11)Hf(µ-η2:η3-C2B9H11)Hf(Cp*)-
Me2 (Cp* ) C5Me5) catalyzed the regioselective dimer-
ization of terminal alkynes HCtCR (R ) Me, nPr, tBu)
to 2,4-disubstituted 1-buten-3-ynes.26
In MeOH the reaction of 1-alkyne with an equal
amount of MeI in the presence of 1-5 mol % of catalyst
2 and base results in alkylation product MeCtCR (4).
However, when the amount of MeI was reduced, the
reaction leads to formation of the (Z)-1,4-disubstituted
enyne 8 in MeOH. The proposed mechanism for the
formation of enyne 8 is shown in Scheme 2 (pathway
iv).27 On the basis of the fact that a small amount of
alkylation product 4 was always obtained in most enyne
formation reactions, we propose that the six-coordinated
complex A is also the intermediate in the dimerization
On the basis of these observations, the proposed
mechanism is depicted in the Schemes 1 and 2. The six-
coordinated methyl acetylide Rh(III) complex (CO)Rh-
(PPh3)2(CtCR)(Me)(I) (A) is considered as the key
intermediate. The catalytic cycle is initiated with for-
mation of A from oxidative addition of MeI to 3. Then
coordination of the second terminal alkyne to the Rh
atom affords two rhodium complexes, B and C, via two
(24) (a) Windmu¨ller, B.; Nu¨rnberg, O.; Wolf, J.; Werner, H. Eur. J.
Inorg. Chem. 1999, 613. (b) Nu¨rnberg, O.; Werner, H. J. Organomet.
Chem. 1993, 460, 163. (c) Tykwinski, R. R.; Stang, P. J. Organo-
metallics 1994, 13, 3203.
(25) (a) Pavlik, S.; Gemel, C.; Slugovc, C.; Mereiter, K.; Schmid, R.;
Kirchner, K. J. Organomet. Chem. 2001, 617-618, 301. (b) Pavlik, S.;
Mereiter, K. Schmid, R.; Kirchner, K. Organometallics 2003, 22, 1771.
(26) (a) Yoshida, M.; Jordan, R. F. Organometallics 1997, 16, 4508.
(b) Crowther, D. J.; Baenziger, N. C.; Jordan, R. F. J. Am. Chem. Soc.
1991, 113, 1455.
(23) (a) Stang, P. J.; Crittell, C. M. Organometallics 1990, 9, 3191.
(b) Huang, L. Y.; Aulwurm, U. R.; Heinemann, F. W.; Kisch, H. Eur.
J. Inorg. Chem. 1998, 1951. (c) Field, L. D.; Ward, A. J.; Turner, P.
Aust. J. Chem. 1999, 52, 1085. (d) Fairlamb, I. J. S.; Ba¨uerlein, P. S.;
Marrison, L. R. Dickinson, J. M. Chem. Commun. 2003, 632.
(27) Gil-Rubio, J.; Laubender, M.; Werner, H. Organometallics 2000,
19, 1365. Bassetti, M.; Marini, S.; D´ıaz, J.; Gamasa, M. P.; Gimeno,
J.; Rodr´ıguez-AÄ lvarez, Y.; Garc´ıa-Granda, S. Organometallics 2002,
21, 4815. Becker, E.; Mereiter, K.; Puchberger, M.; Schmid, R.;
Kirchner, K. Organometallics 2003, 22, 2124.

Rh-Catalyzed Dimerization of Terminal Alkynes
Organometallics, Vol. 24, No. 1, 2005 141
Spectroscopic data of 3a: 1H NMR (d-acetone): δ 7.80, 7.71-
7.49, 7.44 (m, Ph). 31P NMR (d-acetone): δ 28.77 (br). IR (C6H6,
cm-1): 1979 (s, νC≡O), 2122 (w, νC≡C). MS (FAB, NBA, m/z):
757 (M+ + 1), 728 (M+ - CO), 655 (M+ - CtCC6H5), 627 (M+
- CO - CtCC6H5). Anal. Calcd for RhP2C45H35O: C, 71.43;
H, 4.66. Found: C, 71.41; H, 4.77. Complex Rh(CO)(PPh3)2Ct
C(p-C6H4NO2) (3b, 510 mg, 85% yield) was similarly prepared
from 2 (520 mg, 0.75 mmol) and 1b in 4 h under CO.
Spectroscopic data of 3b: 1H NMR (C6D6): δ 7.90 (m, Ph), 7.62
(d, JH-H ) 8.68 Hz, Ph, 2H), 7.05 (m, Ph), 6.33 (d, JH-H ) 8.68
reaction giving 8. Further reaction of 1-alkyne with
complex A in MeOH affords the cationic vinylidene
complex F. Coupling of the σ-acetylide with the vin-
ylidene group results in formation of (Z)-butenynyl
rhodium complex G. Simple σ-bond metathesis of G and
1-alkyne discharges head-to-head (Z)-1,4-disubstituted
enyne 8, regenerating A. No dimerization reaction of
alkyne 1d or 1f was observed in MeOH. Actually, there
are few cases of the reaction of 1-alkyne, which bears
an electron-donating group with the transition metal
to form the vinylidene complex.7b The presence of the
electron-donating group may hinder coupling of the
vinylidene ligand with the acetylide ligand, thus pro-
hibiting formation of the dimer product. The catalytic
system requires the presence of MeI, which is known
to react readily with PPh3 to give phosphonium iodide.
It is therefore less likely to have free dissociated PPh3
from the catalyst in the reaction mixture. Intermediate
complexes B, C, D, F, and G in Schemes 1 and 2 are
thus proposed to be derived from the dissociation of
iodide from the catalyst consequently bearing cationic
charge.24
Concluding Remarks. A rhodium intermediate
captured from oxidative addition of MeI was used for
selective dimerization of alkyne. Using the rhodium
complex as a catalyst, the dimerization of various
terminal arylalkynes in aprotic solvents (such as CH2-
Cl2, THF, and acetone) resulted in formation of (E)-1,4-
disubstituted enyne 6 in high stereoselectivity. How-
ever, when MeOH is used as a solvent, dimerization of
1-arylalkynes with an electron-withdrawing group gave
the other stereoisomeric product (Z)-1,4-disubstituted
enyne 8 in the presence of 0.1 equiv of MeI. With excess
MeI, a competitive process, namely, oxidative additions
of MeI and alkyne to the Rh metal center followed by
reductive elimination, gave the alkylation product 4 of
the terminal alkyne.
1
Hz, Ph, 2H). 31P NMR (C6D6): δ 33.9 (d, JRh-P ) 134.9 Hz).
13C NMR (C6D6): δ 194.2 (d, 1JRh-C ) 59.1 Hz, CO), 122.07 (d,
2JRh-C ) 11.2 Hz, Câ), 144.9, 135.2, 135.0, 130.8, 130.0, 123.0
(Ph). IR (CH2Cl2, cm-1): 1982 (s, νC≡O), 2089 (w, νC≡C). MS
(FAB+, NBA, m/z): 801 (M+), 773 (M+ - CO), 655 (M+ - Ct
CC6H4 - NO2), 627 (M+ - CO - CtCC6H4NO2). Anal. Calcd
for RhP2C45H34NO3: C, 67.42; H, 4.28; N, 1.75. Found: C,
67.40; H, 4.37; N, 1.79.
Synthesis of [Rh(CO)(PPh3)2(CtCPh)(CH2CN)I] (5a).
To complex 3a (115 mg, 0.15 mmol) in CH2Cl2 (15 mL) was
added dropwise ICH2CN (29 mg, 0.165 mmol) at room tem-
perature under nitrogen. After the reaction mixture was
stirred for 18 h, the color changed from yellow to orange-red,
and the solvent was evaporated under vacuum. Purification
by recrystallization from CH2Cl2/hexane (1:10) gave a pale
orange powder, 5a (115 mg, 83% yield). Spectroscopic data of
5a: 1H NMR (d-acetone): δ 8.30, 8.11, 7.66, 7.37 (m, Ph), 1.91
(m, CH2). 31P NMR (d-acetone): δ 16.8 (d, JRh-P ) 88.4 Hz).
1
2
13C NMR (CDCl3): δ 184.5 (dt, JRh-C ) 47.0 Hz, JP-C ) 8.1
2
3
Hz, CO), 114.3 (dt, JRh-C ) 7.8 Hz, JP-C ) 3.5 Hz, Câ), 95.8
(dt, 1JRh-C ) 35.8 Hz, 2JP-C ) 19.8 Hz, CR), -6.3 (dt, 1JRh-C
)
23.8 Hz, 2JP-C ) 3.78 Hz, CH2), 134.8 (t, J ) 4.9 Hz), 128.1 (t,
J ) 4.9 Hz), 132.1, 131.8, 131.4, 130.6, 130.2, 126.0 (s, CN).
IR (benzene, cm-1): 2206 (w, νC≡N), 2123 (w, νC≡C), 2088 (s,
νC≡O). MS (FAB, NBA, m/z): 924 (M+ + 1), 855 (M+ - CO -
CH2CN), 768 (M+ - I - CO), 627 (M+ - I - CO - CH2CN -
CtCC6H5). Anal. Calcd for RhP2C47H37NOI: C, 61.12; H, 4.04;
N, 1.52. Found: C, 61.20; H, 4.07; N, 1.59. Complex 5b (185
mg) was similarly prepared from the reaction of 3b (175 mg,
0.22 mmol) with ICH2CN (42.5 mg, 0.24 mmol) in 87% yield.
Spectroscopic data of 5b: 1H NMR (CDCl3): δ 8.04, 7.39 (m,
Ph), 7.01 (d, JH-H ) 8.76 Hz, Ph, 2H), 1.85 (m, CH2, 2H). 31P
NMR (CDCl3): δ 17.8 (d, JRh-P ) 88.8 Hz). 13C NMR (CDCl3):
δ 184.38 (dt, JRh-C ) 47 Hz, JP-C ) 8.2 Hz, CO), 145.8, 134.8
(t, J ) 5 Hz), 133.7 (s, CN), 131.7, 131.4, 131.1, 130.9, 130.6,
128.2 (t, J ) 5 Hz) 123.7, 113.5 (dt, JRh-C ) 8 Hz, JP-C ) 3.4
Hz, Câ), 108.5 (dt, JRh-C ) 36.5 Hz, JP-C ) 19.7 Hz, Rh-CR),
-5.98 (dt, JRh-C ) 23.7 Hz, JP-C ) 4.0 Hz CH2). IR (C6H6,
cm-1): 2206 (w, νCN), 2123 (w, νCC), 2088 (s, νCO). MS (FAB,
NBA, m/z): 969 (M+ + 1), 900 (M+ - CO - CH2CN), 813 (M+
- I - CO), 627 (M+ - I - CO - CH2CN - CtCC6H4NO2).
Anal. Calcd for RhP2C47H36N2O3I: C, 58.28; H, 3.75; N, 2.89.
Found: C, 58.30; H, 3.78; N, 2.91. Single crystals of 5b were
grown by slow diffusion of hexane into a dichloromethane
solution, giving yellow crystals suitable for X-ray diffraction
analysis.
Experimental Section
General Procedures. All manipulations were performed
under nitrogen using vacuum-line, drybox, and standard
Schlenk techniques. CH2Cl2 and CH3CN were distilled from
CaH2 and THF and diethyl ether from Na/diphenylketyl. All
other solvents and reagents were of reagent grade and were
used without further purification. The NMR spectra were
recorded on a Bruker AC-200 or a Bruker AM-300WB FT-NMR
spectrometer at room temperature (unless stated otherwise)
and are reported in δ units with residual protons in the solvent
as an internal standard (CDCl3, δ 7.24; CD3CN, δ 1.93; C2D6-
CO, δ 2.04). FAB mass spectra were recorded on a JEOL SX-
102A spectrometer. X-ray diffraction studies and elemental
analyses were carried out at the Regional Center of Analytical
Instrument at National Taiwan University. Complexes Rh-
(CO)(PPh3)2Cl (2) and [Rh(CO)2Cl]2 were prepared from RhCl3
according to the method reported in the literature.28
Synthesis of Rh(CO)(PPh3)2CtCPh (3a). Carbon mon-
oxide was slowly bubbled through a mixture of 2 (500 mg, 0.72
mmol) and HCtCPh (1a, 80 mg, 0.79 mmol) in MeONa/MeOH
(ca. 240 mg of MeONa). After 1.5 h bubbling was ceased and
the reaction was allowed to proceed under a CO atmosphere
for 18 h to yield a yellow powder, which was collected, washed
with methanol, and identified as 3a (45 mg, 82% yield).
Rhodium-Catalyzed Coupling of MeI and Terminal
Alkyne. A flask was charged with 1a (80 mg, 0.79 mmol), 2
(28 mg, 0.04 mmol), MeI (116 mg, 0.82 mmol), and MeOH (15
mL) in the presence of the base MeONa (140 mg). The reaction
mixture was stirred for 10 h, and then the solvent was
evaporated under vacuum. The residue was extracted into 20
mL of CH2Cl2, which was filtered to remove 2, NaCl, excess
MeONa, and other insoluble solids. The solvent was dried
under vacuum and the product purified by column chroma-
tography on silica gel eluted with ether/hexane (1:9), affording
organic compound 4a (81 mg, 88%). Spectroscopic data of 4a:
1H NMR (CDCl3): δ 7.10-6.81 (m, Ph), 2.03 (s, CH3). MS (EI,
m/z): 116.1 (M+).
(28) (a) Colton, R.; Farthing, R. H.; Knapp, J. E. Aust. J. Chem. 1970,
23, 1. (b) Schneider, R. L.; Watters, K. L. J. Catal. 1981, 72, 172. (c)
Evans, D.; Osborn, J. A.; Wilkinson, G. Inorg. Synth. 1990, 28, 79. (d)
Serron, S.; Nolan, S. P.; Moloy, K. G. Organometallics 1996, 15, 4301.
Typical Procedure for Dimerization of Arylacetylene.
To a flask charged with 2 (20 mg, 0.029 mmol), K2CO3 (4.0 g,

142 Organometallics, Vol. 24, No. 1, 2005
Lee et al.
29 mmol), and MeI (208 mg, 1.49 mmol) in CH2Cl2 (15 mL)
was added 1a (302 mg, 2.9 mmol) by a syringe. The reaction
mixture was stirred for 18 h at room temperature, and the
solvent was removed under vacuum. The residue was extracted
into 20 mL of CH2Cl2, which was filtered to remove organo-
metallic compounds, salt, and K2CO3. The solution was dried
under vacuum and the residue purified by column chroma-
tography eluted by ether/hexane (1:9). The solution was dried
under vacuum, and the major product was identified as 6a
(226 mg, 75% yield). Minor products 7a and 4a are identified
by NMR and are not isolated. Spectroscopic data for 6a: 1H
NMR (CDCl3): δ 7.45-7.38, 7.35-7.29 (m, Ph, 10H), 7.05 (d,
127.1, 126.8, 125.8 (q, JFC ) 3.7 Hz), 125.4 (q, JFC ) 3.7 Hz).
MS (FAB, m/z): 340.0 (M+).
Compound 6h (55 mg) was synthesized from 2 (40 mg, 0.058
mmol), K2CO3 (1.6 g, 11.6 mmol), CH2Cl2 (5 mL), MeI (492
mg, 3.48 mmol), and 1h (142 mg, 1.16 mmol) in 39% yield.
Spectroscopic data for 6h: 1H NMR (CDCl3): δ 7.44-7.34 (m,
3
Ph, 4H), 7.04∼6.94 (m, Ph, 4H), 7.00 (d, dCH, JH-H ) 16.2
Hz), 6.28 (d, dCH, 3JH-H ) 16.2 Hz). 13C NMR (CDCl3): δ 140.0
(s, -CdC-Ar), 107.7 (s, -CdC-Ar), 90.1 (s, Ar-CtC-), 88.3
1
1
(s, Ar-CtC-), 164.6 (d, JF-C ) 36.6 Hz), 161.3 (d, JF-C
)
3
37.6 Hz), 133.4 (d, JF-C ) 8.3 Hz), 132.5 (d, JF-C ) 3.3 Hz),
3
128.0 (d, JF-C ) 8.2 Hz), 119.5 (d, JF-C ) 3.5 Hz), 115.9 (d,
2JF-C ) 21.8 Hz), 115.8 (d, JF-C ) 22.0 Hz). MS (FAB, m/z):
2
3
3
dCH, JH-H ) 16.2 Hz), 6.39 (d, dCH, JH-H ) 16.2 Hz). 13C
NMR (CDCl3): δ 141.2 (s, C-Ar), 108.1 (s, -CdC-Ar), 91.7
(s, Ar-CtC-), 88.9 (s, Ar-CtC-), 136.3, 131.5, 128.7, 128.6,
128.3, 128.1, 126.3, 123.4 (all singlet, phenyl). MS (FAB,
m/z): 204.1 (M+).
240.0 (M+).
Compound 6i (369.2 mg) was prepared from 2 (20 mg, 0.029
mmol), K2CO3 (3.2 g, 23.2 mmol), CH2Cl2 (10 mL), 1i (420 mg,
2.32 mmol), and MeI (83 mg, 0.58 mmol) in 88% yield.
3
Spectroscopic data for 6i: 1H NMR (CDCl3): δ 7.47 (d, JH-H
Dimerization of 1b to 6b. A similar reaction using 2 (20
mg, 0.029 mmol), K2CO3 (800 mg, 5.8 mmol), THF (10 mL),
HCtC(p-C6H4NO2) (1b, 85 mg, 0.58 mmol), and MeI (246 mg,
1.74 mmol) gave a mixture of 6b, 7b, and 4b in a 60:15:25
ratio. Compound 6b (44.2 mg) was obtained in 52% isolated
yield. Spectroscopic data for 6b: 1H NMR (CDCl3): δ 8.23 (d,
3JH-H ) 8.7 Hz), 8.22 (d, 3JH-H ) 8.7 Hz), 7.62 (d, 3JH-H ) 8.7
Hz), 7.58 (d, 3JH-H ) 8.7 Hz), 7.17 (d, dCH, 3JH-H ) 16.2 Hz),
6.56 (d, dCH, 3JH-H ) 16.2 Hz). 13C NMR (CDCl3): δ 142.5 (s,
-CdC-Ar), 112.5 (s, -CdC-Ar), 93.5 (s, Ar-CtC-), 92.7 (s,
Ar-CtC-), 148.4, 147.8 141.1, 132.9, 130.2, 127.6, 124.8,
124.3 (all singlet, phenyl). MS (FAB, m/z): 294.0 (M+).
3
3
) 8.5 Hz), 7.46 (d, JH-H ) 8.5 Hz), 7.32 (d, JH-H ) 8.0 Hz),
7.28 (d, 3JH-H ) 8.0 Hz), 6.99 (d, dCH, 3JH-H ) 16.2 Hz), 6.36
(d, dCH, JH-H ) 16.2 Hz). 13C NMR (CDCl3): δ 140.3 (s,
3
-CdC-Ar), 108.6 (s, -CdC-Ar), 91.2 (s, Ar-CtC-), 89.7 (s,
Ar-CtC-), 135.1, 132.9, 131.9, 131.6, 127.7, 122.7, 122.6,
122.2 (all singlet, phenyl). MS (FAB, m/z): 362.9 (M+ + 1).
Compound 6j (254 mg) was prepared from 2 (10 mg, 0.0145
mmol), K2CO3 (2 g, 14.5 mmol), CH2Cl2 (5 mL), HCtC(p-C6H4I)
1j (330 mg, 1.45 mmol), and MeI (20 mg, 0.145 mmol) in 77%
yield. Spectroscopic data for 6j: 1H NMR (CDCl3): δ 7.67 (d,
3JH-H ) 8.4 Hz), 7.66 (d, 3JH-H ) 8.4 Hz), 7.17 (d, 3JH-H ) 8.4
Hz), 7.14 (d, 3JH-H ) 8.4 Hz), 6.96 (d, dCH, 3JH-H ) 16.2 Hz),
6.36 (d, dCH, 3JH-H ) 16.2 Hz). 13C NMR (CDCl3): δ 140.5 (s,
-CdC-Ar), 108.7 (s, -CdC-Ar), 91.5 (s, Ar-CtC-), 90.0 (s,
Ar-CtC-), 137.9, 137.6, 135.6, 132.9, 127.9, 122.7, 94.3, 94.2
(all singlet, phenyl). MS (FAB, m/z): 455.8 (M+).
A similar reaction using 2 (10 mg, 0.0145 mmol), K2CO3 (2.0
g, 14.5 mmol), CH2Cl2 (5 mL), 1e (184 mg, 1.45 mmol), and
MeI (20 mg, 0.145 mmol) gave 6e (99 mg) in 54% yield.
Spectroscopic data for 6e: 1H NMR (CDCl3): δ 7.63 (d, 3JH-H
3
3
) 6.2 Hz), 7.62 (d, JH-H ) 6.2 Hz), 7.54 (d, JH-H ) 8.5 Hz),
Compound 6c (44 mg) was prepared from 2a (20 mg, 0.029
mmol), K2CO3 (800 mg, 5.8 mmol), THF (10 mL), 1c (74 mg,
0.585 mmol), and MeI (166 mg, 1.16 mmol) in 60% yield.
Spectroscopic data for 6c: 1H NMR (CDCl3): δ 10.0 (s, COH,
1H), 9.99 (s, COH, 1 H), 7.87 (d, 3JH-H ) 8.1 Hz), 7.86 (d, 3JH-H
7.51 (d, 3JH-H ) 8.5 Hz), 7.08 (d, dCH, 3JH-H ) 16.2 Hz), 6.50
(d, dCH, JH-H ) 16.2 Hz). 13C NMR (CDCl3): δ 140.7 (s,
3
-CdC-Ar), 111.1 (s, -CdC-Ar), 92.2 (s, Ar-CtC-), 92.0 (s,
Ar-CtC-), 118.5 (CN), 118.3 (CN), 140.1, 133.0, 132.6, 132.2,
132.1, 132.0, 127.2, 126.8, 112.1, 111.8 (all singlet, phenyl).
MS (FAB, m/z): 255.2 (M+ + 1).
3
3
) 8.1 Hz), 7.62 (d, JH-H ) 8.4 Hz), 7.58 (d, JH-H ) 8.4 Hz),
3
3
7.14 (d, dCH, JH-H ) 16.2 Hz), 6.56 (d, dCH, JH-H ) 16.2
Hz). 13C NMR (CDCl3): δ 141.7 (s, -CdC-Ar), 111.3 (s, -Cd
C-Ar), 92.7 (s, Ar-CtC),92.3 (s, Ar-CtC-), 191.4 (s, COH),
191.3 (s, COH), 141.1, 136.3, 135.6, 132.1, 130.2, 129.8, 129.6,
126.9 (all singlet, phenyl). MS (FAB, m/z): 261.1 (M+ + 1).
Compound 7k (176 mg) was prepared in 72% yield from 2
(20 mg, 0.029 mmol), K2CO3 (1.6 g, 11.6 mmol), CH2Cl2 (5 mL),
1k (245 mg, 2.9 mmol), and MeI (1.23 g, 8.7 mmol). Spectro-
Compound 6d (63 mg) was obtained from 2 (20 mg, 0.029
mmol), MeONa (156 mg, 2.9 mmol), THF (10 mL), MeI (250
mg, 1.74 mmol), and 1d (70 mg, 0.58 mmol) in 90% yield.
Spectroscopic data for 6d: 1H NMR (CDCl3): δ 7.36 (d, 3JH-H
) 8.0 Hz), 7.32 (d, 3JH-H ) 8.0 Hz), 7.15 (d, 3JH-H ) 7.75 Hz),
3
3
7.13 (d, JH-H ) 7.75 Hz), 7.00 (d, dCH, JH-H ) 16.2 Hz),
6.33 (d, dCH, JH-H ) 16.2 Hz), 2.34 (s, CH3, 6H). 13C NMR
3
(CDCl3): δ 140.9 (s, -CdC-Ar), 107.2 (s, -CdC-Ar), 91.6
(s, Ar-CtC-), 88.4 (s, Ar-CtC-), 21.5 (s, CH3), 21.3 (s, CH3),
138.6, 138.2, 133.7, 131.6, 129.4, 129.1, 126.2, 120.4, 119.4 (all
singlet, phenyl). MS (FAB, m/z): 232.1 (M+).
2
scopic data for 7k: 1H NMR (CDCl3): δ 5.18 (d, JH-H ) 2.06
2
3
Hz), 5.01 (d, JH-H ) 2.06 Hz), 2.28 (d, JH-H ) 6.72 Hz, 2H),
3
2.09 (d, JH-H ) 7.44 Hz, 2H), 1.50-1.27 (m, 8H), 0.93-0.84
(m, 6H). MS (FAB, m/z): 164.0 (M+).
Compound 6f (172 mg) was obtained from 2 (10 mg, 0.0145
mmol), MeONa (391 mg, 7.25 mmol), CH2Cl2 (5 mL), 1f (210
mg, 1.45 mmol), and MeI (20 mg, 0.145 mmol) in 82% yield.
Preparation of 8a. A flask was charged with 2 (20 mg,
0.029 mmol), K2CO3 (4.0 g, 29 mmol), and MeOH (10 mL), and
then MeI (40 mg, 0.29 mmol) and 1a (302 mg, 2.9 mmol) were
added by a syringe. The reaction mixture was stirred at room
temperature, and the solvent was removed under vacuum. The
residue was extracted into 20 mL of CH2Cl2, which was filtered
to remove organometallic compounds, salt, and K2CO3. The
solution was dried under vacuum and the residue purified by
column chromatography eluted by ether/hexane (1:9). The
solution was dried under vacuum, and the major product was
identified as 8a (190 mg) in 63% yield. Spectroscopic data for
3
Spectroscopic data for 6f: 1H NMR (CDCl3): δ 7.33 (d, JH-H
3
3
) 9.2 Hz), 7.30 (d, JH-H ) 9.2 Hz), 6.67 (d, JH-H ) 9.1 Hz),
3
3
6.64 (d, JH-H ) 9.1 Hz), 6.90 (d, JH-H ) 16.2 Hz), 6.18 (d,
3JH-H ) 16.2 Hz). 13C NMR (CDCl3): δ 139.8 (s, -CdC-Ar),
103.8 (s, -CdC-Ar), 91.5 (s, Ar-CtC-), 87.8 (s, Ar-
CtC-), 40.3 (NMe2), 40.2 (NMe2), 150.4, 149.8, 139.8, 132.4,
127.3, 112.2, 111.9, 110.8 (all singlet, phenyl). MS (FAB,
m/z): 290.1 (M+).
3
8a: 1H NMR (CDCl3): δ 7.93 (d, JH-H ) 8.7 Hz, 2 H), 7.48
Compound 6g (182.7 mg) was prepared from 2 (40 mg, 0.058
mmol), K2CO3 (1.6 g, 11.6 mmol), THF (10 mL), MeI (492 mg,
3.48 mmol), and 1g (203 mg, 1.16 mmol) in 90% yield.
Spectroscopic data for 6g: 1H NMR (CDCl3): δ 7.68-7.46 (m,
3
(m, Ph, 2 H), 7.46-7.00 (m, Ph, 5 H), 6.71 (d, JH-H ) 12.0
Hz, dCH), 5.93 (d, 3JH-H ) 12.0 Hz, dCH). 13C NMR (CDCl3):
δ 141.8 (s, CdCAr), 108.0 (s, CdCAr), 96.4 (s, ArCtC), 88.8
(s, ArCtC), 139.3, 137.1, 132.0, 129.4, 129.0, 129.0, 128.9,
128.8 (all singlet, phenyl). MS (FAB, m/z): 204.0 (M+).
Using the same procedure compound 8e (151 mg) was
obtained in 82% yield from 1e (184 mg, 1.45 mmol). Spectro-
3
3
phenyl, 8H), 7.11 (d, JH-H ) 16.2 Hz), 6.47 (d, JH-H ) 16.2
Hz). 13C NMR (CDCl3): δ 140.1 (s, -CdC-Ar), 110.2 (s,
-CdC-Ar), 91.5 (s, Ar-CtC-), 90.5 (s, Ar-CtC-), 139.4,
137.0, 134.2, 132.0, 131.8, 130.8, 130.3, 129.9, 129.7, 128.4,

Rh-Catalyzed Dimerization of Terminal Alkynes
Organometallics, Vol. 24, No. 1, 2005 143
3
scopic data for 8e: 1H NMR (CDCl3): δ 7.94 (d, JH-H ) 8.46
Table 5. Crystal Data and Structure Refinement
for 5b
Hz), 7.67 (d, 3JH-H ) 8.06 Hz), 7.65 (d, 3JH-H ) 8.06 Hz), 7.53
(d, 3JH-H ) 8.46 Hz), 6.80 (d, dCH, 3JH-H ) 12.0 Hz), 6.10 (d,
empirical formula
fw
temperature
wavelength
cryst syst
space group
unit cell dimens
C49H40Cl4IN2O3P2Rh
dCH, JH-H ) 12.0 Hz). 13C NMR (CDCl3): δ 140.3 (s,
3
1138.38
CdCAr), 112.0 (s, CdCAr), 95.5 (s, ArCtC), 91.2 (s, ArCtC),
118.6 (CN), 118.2 (CN), 138.2, 132.2, 132.1, 132.0, 129.1, 127.5,
112.2, 111.9, 110.3 (all singlet, Ph). MS (FAB, m/z): 254.0 (M+).
Compound 8g (224 mg) was similarly obtained in 91% yield
from 1g (246.7 mg, 1.45 mmol). Spectroscopic data for 8g: 1H
NMR (CDCl3): δ 7.99 (d, JH-H ) 8.2 Hz), 7.65-7.54 (m, Ph,
6H), 6.80 (d, dCH, JH-H ) 11.9 Hz), 6.06 (d, dCH, JH-H
295(2) K
0.71073 Å
triclinic
P1h
a ) 12.915(2) Å
b ) 13.210(3) Å
c ) 15.975(3) Å
2363.9(7) Å3, 2
1.599 Mg/m3
1.352 mm-1
1136
R ) 77.06(2)°
â ) 71.678(13)°
γ ) 66.88(2)°
3
3
3
)
volume, Z
11.9 Hz). 13C NMR (CDCl3): δ 139.5 (s, -CdC-Ar), 109.4 (s,
-CdC-Ar), 95.2 (s, Ar-CtC-), 89.6 (s, Ar-CtC-), 138.1,
131.7, 130.6 (d, JF-C ) 6.18 Hz), 130.1 (d, JF-C ) 6.18 Hz),
128.8, 127.7, 125.6 (m), 125.3, 122.2 (d, JF-C ) 12.7 Hz). MS
(FAB, m/z): 340.0 (M+). Compound 8h (44.3 mg) was similarly
obtained in 25% yield from 1h (177.5 mg, 1.45 mmol).
Spectroscopic data for 8h: 1H NMR (CDCl3): δ 7.89 (m, phenyl,
density (calcd)
absorp coeff
F(000)
cryst size
0.35 × 0.30 × 0.20 mm
θ range for data
collection
1.69 to 24.97°
limiting indices
-13 < h < 15,
0 < k < 15,
-18 < l < 18
8309 [I>2σ(I): 5787]
3
2H), 7.41 (m, Ph, 2H), 7.05 (m, Ph, 4H), 6.66 (d, dCH, JH-H
3
) 11.9 Hz), 5.87 (d, dCH, JH-H ) 11.9 Hz). MS (FAB, m/z):
no. of independent
reflns
max. and min. transmn 0.7785 and 0.6829
refinement method
240.0 (M+). Compound 8i (235.8 mg) was similarly obtained
in 90% yield from 1i (262 mg, 1.45 mmol). Spectroscopic data
for 8i: 1H NMR (CDCl3): δ 7.76 (d, JH-H ) 8.5 Hz), 7.51 (d,
3
full-matrix least-
squares on F2
8309/0/522
3JH-H ) 8.6 Hz), 7.49 (d, 3JH-H ) 8.6 Hz), 7.32 (d, 3JH-H ) 8.5
3
3
no. of data/restraints/
params
Hz), 6.67 (d, dCH, JH-H ) 11.9 Hz), 5.93 (d, dCH, JH-H
)
11.9 Hz). 13C NMR (CDCl3): δ 137.7 (s, -CdC-Ar), 107.9 (s,
-CdC-Ar), 95.3 (s, Ar-CtC-), 88.9 (s, Ar-CtC-), 135.3,
132.8, 131.7, 131.5, 130.2, 122.8, 122.5, 122.1 (all singlet,
phenyl). MS (FAB, m/z): 361.8 (M+). Compound 8j (115 mg)
was similarly obtained in 35% yield from 1j (330 mg, 1.45
mmol). Spectroscopic data for 8j: 1H NMR (CDCl3): δ 7.71 (d,
goodness-of-fit on F2
0.943
final R indices [I>2σ(I)] R1 ) 0.0454,
wR2 ) 0.1301
R indices (all data)
R1 ) 0.0738,
wR2 ) 0.1475
largest diff peak and
hole
1.065 and -0.809 e/Å3
3JH-H ) 8.14 Hz), 7.69 (d, JH-H ) 8.35 Hz), 7.61 (d, JH-H
)
3
3
8.35 Hz), 7.17 (d, 3JH-H ) 8.14 Hz), 6.63 (d, 3JH-H ) 11.9 Hz),
5.91 (d, 3JH-H ) 11.9 Hz). 13C NMR (CDCl3): δ 137.8 (s, -Cd
C-Ar), 108.1 (s, -CdC-Ar), 95.7 (s, Ar-CtC-), 89.3 (s, Ar-
CtC-), 137.6, 137.4, 135.8, 132.8, 130.3, 122.6, 94.6, 94.3 (all
singlet, phenyl). MS (FAB, m/z): 455.8 (M+).
gave a total of 8309 unique measured data in which 5787 were
considered observed, I > 2σ(I). The structure was first solved
by using the heavy atom method (Patterson synthesis), which
revealed the positions of metal atoms. The remaining atoms
were found in a series of alternating difference Fourier maps
and least-squares refinements. The quantity minimized by the
least-squares program was w(|Fo| - |Fc|)2, where w is the
weight of a given operation. The analytical forms of the
scattering factor tables for the neutral atoms were used. The
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were included in the structure factor calculations in
their expected positions on the basis of idealized bonding
geometry but were not refined in least squares.
X-ray Analysis of 5b. Single crystals of 5b suitable for an
X-ray diffraction study were grown by the methods described
in the previous section. The diffraction data were collected on
an Enraf-Nonius CAD4 diffractometer equipped with graphite-
monochromated Mo KR (λ ) 0.71037 Å) radiation. Crystal-
lographic computations were carried out using the NRCC-SDP-
VAX structure determination package.29 A suitable single
crystal of 5b was mounted on the top of a glass fiber with glue.
Initial lattice parameters were determined from 25 accurately
centered reflections in the range from 15.70° to 23.74°. Cell
constants and other pertinent data are collected in Table 5.
Data were collected using the θ-2θ scan method. The final
scan speed for each reflection was determined from the net
intensity gathered during an initial prescan and ranged from
2 to 8 deg min-1. Merging equivalent and duplicate reflections
Acknowledgment. Financial support from the Na-
tional Science Council, Taiwan, is gratefully acknowl-
edged.
Supporting Information Available: Tables of crystal
data collection, refinement parameters, atomic coordinates,
bond lengths and angles, anisotropic displacement parameters,
and hydrogen coordinates for 5b. This material is available
free of charge via the Internet at http://pubs.acs.org.
(29) (a) Gabe, E. J.; Lee, F. L.; Lepage, Y. In Crystallographic
Computing 3; Shelldrick, G. M., Kruger, C., Goddard, R., Eds.;
Clarendon Press: Oxford, England, 1985; p 167. (b) International
Tables for X-ray Crystallography; D. D. Reidel Pub. Co.: Dordrecht,
1974; Vol. IV. (c) LePage, Y.; Gabe, E. J. Appl. Crystallogr. 1990, 23,
406.
OM049604S