Iminophosphine-palladium(0) complexes as catalysts for the Stille reaction

Article abstract of DOI:10.1016/S0040-4020(02)00733-0

The cross-coupling of iodobenzene with tributylphenylethynylstannane or tributylvinylstannane is efficiently catalysed by iminophosphine-palladium(0)-olefin complexes of the type [Pd(η²-dmf)(P-N)] (dmf, dimethylfumarate; P-N, 1-(PPh₂)-C₆H₄-2-C=NR (R=alkyl, aryl)). The catalytic activity depends on the R substituent of the imino group: the highest reaction rates are obtained using aryl-substituted iminophosphines. Equivalent catalytic systems can be obtained using a palladium source such as Pd(OAc)₂ or Pd(dba)₂ (dibenzylideneacetone, dba) in combination with the iminophosphine ligands. In the coupling of iodobenzene with tributylphenylethynylstannane, the highest reaction rates are obtained using an iminophosphine/palladium molar ratio of 2:1, while in the vinylstannane-iodobenzene coupling the best P-N/Pd ratio is 1:1.

Full text of DOI:10.1016/S0040-4020(02)00733-0

Tetrahedron 58 (2002) 6881–6886
Iminophosphine–palladium(0) complexes as catalysts
for the Stille reaction
a
a
b
b
A. Scrivanti,a U. Matteoli, V. Beghetto, S. Antonaroli and B. Crociani
,
*
a
`
`
Dipartimento di Chimica, Universita ‘Ca Foscari’ di Venezia, Calle Larga S. Marta 2137, Dorsoduro, 30123 Venezia, Italy
`
Dipartimento di Scienze e Tecnologie Chimiche, Universita di Roma ‘Tor Vergata’, Via della Ricerca Scientifica, 00133 Rome, Italy
b
Received 1 May 2002; revised 5 June 2002; accepted 27 June 2002
Abstract—The cross-coupling of iodobenzene with tributylphenylethynylstannane or tributylvinylstannane is efficiently catalysed by
iminophosphine–palladium(0)–olefin complexes of the type [Pd(h2-dmf)(P-N)] (dmf, dimethylfumarate; P-N, 1-(PPh2)-C6H4-2-CvNR
(R¼alkyl, aryl)). The catalytic activity depends on the R substituent of the imino group: the highest reaction rates are obtained using aryl-
substituted iminophosphines. Equivalent catalytic systems can be obtained using a palladium source such as Pd(OAc)2 or Pd(dba)2
(dibenzylideneacetone, dba) in combination with the iminophosphine ligands. In the coupling of iodobenzene with tributylphenylethynyl-
stannane, the highest reaction rates are obtained using an iminophosphine/palladium molar ratio of 2:1, while in the vinylstannane–
iodobenzene coupling the best P-N/Pd ratio is 1:1. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
such as CuI,8 CuCl,9 and diethylamine10 has also been
reported.
The palladium catalysed cross coupling of organostannanes
with alkyl or aryl halides (Stille reaction, Eq. (1)) is one of
the most important reactions leading to the formation of a
new carbon–carbon bond.1–5
More recently, two major breakthroughs have been reported
by Shirakawa,11 – 13 who claimed that allyl complex
[PdCl(h3-C3H5)]2 in combination with the iminophosphine
1-(PPh2)-C6H4-2-CvNCH2CH2Ph is even more efficient
than the Farina system, and by Fu,14 who found that the
coupling reaction can be suitably carried out even with
X¼Cl in the presence of PtBu3. Finally, it is worth noting
that very recently systems catalytic in tin have also been
disclosed.15,16
ð1Þ
Many facets make this reaction a very powerful tool for fine
chemicals synthesis. It is particularly impor0tant to mention
(i) its versatility (a broad range of0 R and R groups can be
coupled), (ii) the fact that the R group, on the organo-
metallic reagent, can tolerate the presence of a wide variety
of functional groups and (iii) its high chemo and
stereoselectivity.
Owing to our interest in the chemistry and catalytic activity
of iminophosphine–palladium(0) complexes of the type
[Pd(h2-ol)(P-N)] (ol, activated olefin; P-N, 1-(PPh2)-
C6H4-2-CvNR),17,18 the high reaction rates obtained by
Shirakawa appeared to us very interesting and prompted us
to investigate the catalytic behaviour of the zerovalent
complexes [Pd(h2-ol)(P-N)] shown in Fig. 1. In polar and
coordinating solvents or in the presence of free imino-
phosphine, these compounds containing an alkene of
moderate p-accepting properties such as dimethylfumarate
may undergo olefin dissociation forming highly reactive
palladium(0) intermediates.19 A wide variety of imino-
phosphine ligands have been used in order to highlight the
influence of the imino substituent R on the reaction rate.
Moreover, the use of organostannanes is not a limiting
factor owing to their prompt availability.6
Usually, the reaction is carried out in the presence of 1–2%
of a palladium catalyst. A variety of palladium(II) or palla-
dium(0) phosphine complexes with neutral ligands have
been successfully used as catalyst precursors.1–5 The
catalyst efficiency is determined by the nature of the ligand.
Triphenylphosphine was the ligand commonly used until it
was shown by Farina that enhanced reaction rates can be
achieved employing tri(2-furyl)phosphine or triphenyl-
arsine.7 The rate enhancing effect of a number of promoter
2. Results and discussion
Keywords: palladium; catalysis; iminophosphine; Stille reaction.
*
Complexes 1a–4a were synthesised as described in the
literature.17 The new ligands 5 and 6 were prepared by
Corresponding author. Tel.: þ39-0412348903; fax: þ39-0412348517;
e-mail: scrivant@unive.it
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00733-0

6882
A. Scrivanti et al. / Tetrahedron 58 (2002) 6881–6886
Table 2. Coupling of iodobenzene with tributylphenylethynylstannane:
influence of the solvent
Run
Solvent
Yield (%)
1
2
3
4
5
6
7
Dimethylformamide
Dimethyl sulfoxide
Acetonitrile
Tetrahydrofuran
Dioxane
Toluene
91
87
85
75
68
65
63
Diglyme
T: 508C; t: 2 h; solvent: 5 mL; catalyst: complex 4a; PhI¼
PhCuCSnBu3¼1.30 mmol; stannane/catalyst¼100:1.
Figure 1.
Next, the effect of the ligand/palladium molar ratio on the
catalytic activity was investigated. As a matter of fact, the
iminophosphines can act as bidentate P,N-chelating ligands,
or as monodentate P-ligands,17 and this flexibility could be
advantageous for the catalysis.
reacting 2-(diphenylphosphino)benzaldehyde20 with 4-tri-
fluoromethylaniline or 4-fluoroaniline following a well
established procedure17 (see Section 4).
To evaluate the catalytic efficiency of these complexes in
the Stille reaction, we chose the coupling of iodobenzene
with tributylphenylethynylstannane (Eq. (2)) as a model
reaction.
The results presented in Table 3 indicate that the addition of
1 equiv. of free ligand to complexes 1a–4a has an
indubitable beneficial effect on the reaction rate. On the
contrary, the addition of a second equivalent of imino-
phosphine has very little practical effect. Only in the case of
2a, the addition of 2 equiv. of free ligand depresses the
catalyst activity.
ð2Þ
In preliminary investigations, we used the experimental
conditions typical for the Stille reaction: equimolecular
amounts of the aryl iodide and the organostannane were
reacted in THF in the presence of 1 mol% of palladium(0)
complex. The product yields after 2 h (see Table 1) indicate
that the reaction proceeds at a reasonably good rate and that
it is also highly chemoselective, since no side product was
detected. Interestingly, the catalytic activity appears to be
dependent on both the steric and electronic properties of the
R group on the imino nitrogen. In fact, the conversion
increases on going from a methyl group to the more
sterically demanding t-butyl group and when the alkyl
substituents are replaced by aryl groups.
At 2:1 P-N/Pd, total substrate conversion was achieved in
2 h both using 3a and 4a: this makes it impossible to fully
appreciate the effect of the nature of the aryl group on the
catalysis. However, this finding suggests that substrate/
complex ratios higher than 100:1 can be conveniently
employed with these systems. Accordingly, we have carried
out a set of experiments using 3a at increasingly higher
substrate/catalyst ratios.
The data collected in Table 4 show that the coupling can be
carried out even at substrate/catalyst ratios as high as 1000:1
in reasonable reaction times. Moreover the data in Table 4
highlights a very intriguing aspect of the catalysis. By
comparing the data of runs 5 and 6, it appears that although
higher initial reaction rates are achieved working with
2 equiv. of P-N, at longer reaction times the conversion is
not much higher than that observed when only 1 equiv. of
The Stille reaction can be carried out in a wide range of
solvents.1 To ascertain the effect of the solvent on the
catalytic activity we have carried out a set of isochronous
experiments with complex 4a. The data reported in Table 2
shows an increasing rate in solvents of increasing polarity
and donor properties. The rate enhancement obtained with
highly boiling solvents such as dimethylsulfoxide or
dimethylformamide is of practical interest: in fact their
use allows an increase of reaction temperature, making
possible the coupling of less reactive substrates able to
withstand harsh experimental conditions.
Table 3. Coupling of iodobenzene with tributylphenylethynylstannane:
effect of the addition of free ligand
Run
Catalyst
Added ligand
P-N/Pda
Yield (%)
1
2
3
4
5
6
7
8
1a
1a
1a
2a
2a
2a
3a
3a
3a
4a
4a
4a
–
1
1
–
2
2
–
3
3
–
4
4
1
2
3
1
2
3
1
2
3
1
2
3
40
84
86
60
80
57
79
100
100
75
100
100
Table 1. Coupling of iodobenzene with tributylphenylethynylstannane:
preliminary catalytic data
Run
Catalyst
Stannane/Pda
Yield (%)
9
1
2
3
4
1a
2a
3a
4a
100:1
100:1
100:1
100:1
40
60
79
75
10
11
12
T: 508C; t: 2 h; solvent: THF (5 mL); PhI¼PhCuCSnBu3¼1.30 mmol;
stannane/catalyst¼100:1.
T: 508C; t: 2 h; solvent: THF (5 mL); PhI¼PhCuCSnBu3¼1.30 mmol.
a
a
Molar ratio.
Total ligand/Pd molar ratio.

A. Scrivanti et al. / Tetrahedron 58 (2002) 6881–6886
6883
24 h
Table 4. Coupling of iodobenzene with tributylphenylethynylstannane: catalytic activity of 3a
Run
Catalyst
Added ligand
P-N/Pda
Stannane/Pdb
Yield (%) at different times
1 h
2 h
3 h
4 h
6 h
1
2
3
3a
3a
3a
3a
3a
3a
3
3
3
3
–
3
2:1
3:1
2:1
3:1
1:1
2:1
200:1
200:1
400:1
400:1
1000:1
1000:1
–
–
68
69
20
34
100
100
86
87
28
4
5c
6c
35
63
41
68
51
70
82
85
54
T: 508C; solvent: THF (5 mL); PhI¼PhCuCSnBu3¼1.30 mmol.
a
Total ligand/Pd molar ratio.
Molar ratio.
b
c
Solvent: THF (10 mL); PhI¼PhCuCSnBu3¼2.70 mmol.
Table 5. Coupling of iodobenzene with tributylphenylethynylstannane:
activity of different catalyst precursors
Table 7. Coupling of iodobenzene with tributylphenylethynylstannane:
effect of the nature of the ligand
Run
Catalyst
Added liganda
Stannane/Pdb
Yield (%)
Run
Catalyst
Added ligand Ligand/Pda
Yield (%) at different
times
1
2
3
4
5
6
7c
8c
9c
1a
1
1
1
3
3
3
3
3
3
100:1
100:1
100:1
400:1
400:1
400:1
1000:1
1000:1
1000:1
84
92
86
86
89
88
54
53
55
1 h 2 h 4 h 24 h
Pd(dba)2
Pd(OAc)2
3a
Pd(dba)2
Pd(OAc)2
3a
1
2
3
4
5
6
7
8
9
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
1
3
4
5
6
7
2:1
2:1
2:1
2:1
2:1
2:1
2:1
4:1
2:1
6
11
55
58
26
27
5
58
65
53
15
69
67
59
51
10
67
74
62
64
85
93
90
87
69
80
81
82
36
34
16
19
3
44
49
38
Pd(dba)2
Pd(OAc)2
P(fur)3
P(fur)3
3
T: 508C; t: 2 h; solvent: THF (5 mL); PhI¼PhCuCSnBu3¼1.30 mmol.
a
Total ligand/Pd molar ratio¼2:1.
b
Molar ratio.
Solvent: THF (10 mL); PhI¼PhCuCSnBu3¼2.70 mmol.
c
T: 508C; solvent: THF (10 mL); PhI¼PhCuCSnBu3¼2.70 mmol;
stannane/Pd¼1000:1.
a
Total ligand/Pd molar ratio.
the ligand is used. The slowing down of the reaction rate at
high substrate conversions is a quite general feature in
Stille’s coupling, and it is attributed to poorly understood
processes leading to partial decomposition of the catalyst.7
higher substrate/catalyst ratios using different P-N/Pd ratios
and reaction times (Table 6). Therefore, it is likely that all
three catalytic systems give rise to a unique catalytic species
under reaction conditions.
Although the synthesis of complexes 1a–4a is not
particularly laborious, the possibility to employ some
commercially available palladium(0) species as catalyst
precursors could add further interest to the excellent results
reported here. Thus, we have investigated the activity of the
systems prepared by mixing in situ iminophosphines 1–7
with some commercially available palladium derivatives
such as Pd(dba)2 (dba, dibenzylideneacetone)20,21 or
Pd(OAc)2 widely used as catalyst precursors (Table 5).
Unquestionably, among the systems tested here, Pd(OAc)2
emerges as the most convenient catalyst precursor owing to
its commercial availability, its price and shelf durability.
Therefore we chose this species to fully investigate the
effect of the nature of the iminophosphine ligand (Table 7).
The data in Table 7 demonstrates that the highest catalytic
efficiency is achieved when the R substituent is an aryl
group. Particularly good results are obtained with R¼Ph and
4-MeOPh (runs 2 and 3). With aryl groups bearing electron-
withdrawing para substituents, such as –F or –CF3, the
initial reaction rates are somewhat lower (runs 4 and 5),
however the final product yields are similar to those
obtained with 3 and 4. On the contrary, when R is an
According to the data presented in Table 5, the tested
systems show a catalytic activity almost identical: the small
differences observed appear to be within the experimental
error in the determination of the product yield. This
similarity is further confirmed by the data obtained at
Table 6. Coupling of iodobenzene with tributylphenylethynylstannane at various P-N/Pd ratios and reaction times
Run
Catalyst
Added ligand
P-N/Pda
Yield (%) at different times
1 h
2 h
3 h
4 h
6 h
24 h
1
2
3
4
3a
3
3
3
3
1:1
1:1
2:1
2:1
20
21
34
36
28
29
54
55
35
37
63
63
41
41
68
69
51
51
70
71
82
83
85
85
Pd(OAc)2
3a
Pd(OAc)2
T: 508C; solvent: THF (10 mL); PhI¼PhCuCSnBu3¼2.70 mmol; stannane/Pd¼1000:1.
a
Total ligand/Pd molar ratio.

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A. Scrivanti et al. / Tetrahedron 58 (2002) 6881–6886
Table 8. Coupling of iodobenzene with tributylphenylethynylstannane:
relative reactivity of halobenzenes
Table 9. Coupling of iodobenzene with tributylvinylstannane
Run
Catalyst
Added ligand Ligand/Pda
Yield (%) at different
times
Run
Catalyst
Aryl halide
Yield (%) at different
times
1 h 2 h 4 h 24 h
2 h
4 h
24 h
1
2
3
4
5
6
7
8
3a
3a
–
3
3
4
4
1
5
6
7
1:1
2:1
1:1
1:1
2:1
1:1
1:1
1:1
1:1
1:1
2:1
4:1
42
3
45
47
5
16
34
36
20
39
66
84
57
7
55
59
8
33
41
46
29
50
69
86
71
21
64
64
30
47
55
54
39
56
76
91
89
80
79
80
83
70
76
73
67
62
86
94
1
2
3
Pd(OAc)2/3
Pd(OAc)2/3
Pd(OAc)2/3
PhI
PhBr
PhCl
100
30
0
40
0
78
3
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2 P(fur)3
Pd(OAc)2 P(fur)3
Pd(OAc)2 P(fur)3
T: 908C; t: 24 h; solvent: dioxane (5 mL); PhX¼PhCuCSnBu3¼1.30
mmol; stannane/Pd¼200:1; ligand/Pd¼2:1.
alkyl group, such as Me or CH2CH2Ph, much lower
catalytic activities are observed (runs 1 and 6).
9
10
11
12
To further assess the catalytic efficiency of the systems with
iminophosphines 3–7, their activity was compared with
that of Farina’s system (Pd(dba)2/P(2-furyl)3) in a set of
experiments carried out under the same conditions. The
relevant data collected in runs 7 and 8 of Table 7 show that
while Farina’s system affords slightly higher initial reaction
rates, the systems with aryl substituted P-N ligands, such as
3 or 4, provide higher final yields. Thus, it is evident that the
iminophosphines are able to give more robust catalytic
species.
T: 908C; solvent: dioxane (5 mL); PhI¼CH2uCHSnBu3¼1.30 mmol;
stannane/Pd¼200:1.
a
Total ligand/Pd molar ratio.
P-N/Pd 2:1 (Table 9); however, after an initial period in
which the catalyst activity is very high, the reaction rate
decreases. Accordingly, the product yields obtained after
24 h using 1 or 2 equiv. of iminophosphine are similar. The
experiments also showed that the use of the preformed Pd(0)
catalyst 3a is equivalent to the use of Pd(OAc)2 in
combination with 1 or 2 equiv. of ligand 3.
A challenging aspect of the Stille reaction is to get
reasonable coupling rates even with aryl bromides or aryl
chlorides. When the catalytic system 3a/3 is used in THF at
508C, the coupling of PhX with PhCuCSnBu3 proceeds
only for X¼I, no reaction being observed when X¼Br or Cl.
The use of dioxane as solvent allows to increase the reaction
temperature at 908C. Under these conditions, the coupling of
PhBr with the alkynylstannane proceeds at a moderately
good rate, while chlorobenzene is almost unreactive. The
relevant data is collected in Table 8, and shows that, as
usual, the relative reactivity of PhX decreases in the series
X¼I.Br.Cl.
As far as the effect of the imino-nitrogen substituent R on
the catalyst activity is concerned, it appears that the same
factors observed with tributylphenylethynylstannane are
also operative with tributylvinylstannane. As a matter of
fact, the higher reaction rates are observed when R is phenyl
(run 3) or p-methoxyphenyl groups (run 4), while the lowest
product yields are obtained when R is an alkyl group (runs
6 and 9). However, it should be noted that the difference
in reactivity observed with the various substituents R
appears to be less wide than in the case of tributyl-
phenylethynylstannane.
The reaction of phenyl iodide with tributylphenylethynyl-
stannane is a model reaction useful to investigate the effects
due to the catalyst composition and the reaction conditions.
However from the synthetic point of view the most useful
application of the Stille reaction is the coupling of aryl
halides with vinylstannanes. Therefore, we have also
studied the coupling of iodobenzene with tributylvinylstan-
nane (Eq. (3)) in order to better characterise the efficiency of
the P-N/Pd catalytic systems.
When compared with Farina’s system (runs 10–12), the
iminophosphines appear to be less active being unable to
furnish the same initial reaction rates; however, while the
activity of the P(2-furyl)3 decreases rapidly with the time,
the iminophosphine based systems appear more robust and
provide higher final yields.
3. Conclusions
ð3Þ
The data presented here demonstrates that iminophos-
phine–palladium complexes are very active catalytic
systems for the Stille reaction. In particular, these systems
provide reaction rates comparable or superior to those
attainable with the trifurylphosphine–palladium(0) system,
one of the most efficient catalysts known.
Usually, the reactivity of stannanes in Stille coupling
decreases in the order alkynylqvinyl.aryl.alkyl5 and
indeed, the coupling of tributylvinylstannane with iodo-
benzene proceeds very sluggishly at 508C in THF. Suitable
reaction rates were obtained working with a stannane/Pd
ratio of 200:1 in dioxane at 908C.
Two features of the catalysis appear particularly significant:
(i) the reaction rate is markedly dependent on the imino-
nitrogen substituent R, and (ii) the best ligand to palladium
ratio is 2:1 with alkynylstannanes, while it is 1:1 with
vinylstannanes.
First, we checked the best P-N/Pd molar ratio for the
reaction. Experiments carried out with the iminophosphines
3 and 4 revealed that using a molar ratio P-N/Pd 1:1 the
initial reaction rates are much higher than those obtained at

A. Scrivanti et al. / Tetrahedron 58 (2002) 6881–6886
6885
These systems are particularly robust allowing very high
product yields even at stannane/palladium ratios as high as
1000:1 with acetylenic substrates and 200:1 with vinyl ones.
Anal. data: calcd for C31H28NO4PPd: C, 60.45; H, 4.58; N,
2.27. Found: C, 60.5; H, 4.5; N, 2.3.
4.1.2. 2-(PPh2)-C6H4-1-CHvNC6H4F-4 (5). 2-(Diphenyl-
phosphino)benzaldehyde (1.00 g, 3.44 mmol) and the
4-fluoroaniline (1.25 g, 11.3 mmol) were dissolved in
80 mL of a MeOH/CH2Cl2 mixture (3/1 v/v) under nitrogen.
The solution was stirred at room temperature, and the
reaction progress was monitored by TLC. When the
condensation was complete (ca. 20 h), the solvents were
removed under reduced pressure and the residue purified by
chromatography (silica gel, 20% ethyl ether in n-hexane
(v/v)), followed by recrystallization in cold methanol
The catalysts formed by adding 1 or 2 equiv. of imino-
phosphine to Pd(OAc)2 appear particularly convenient for
their prompt availability and stability.
As far as the mechanism of the reaction is concerned,
Shirikawa has proposed a catalytic cycle involving the
initial oxidative addition of the organostannane to a
palladium(0)–iminophosphine species generated in situ.13
We are currently investigating the mechanistic details in
order to rationalise the effects on the reaction rate brought
about by the presence of an activated olefin such as
dimethylfumarate, the nature of the imino-nitrogen sub-
stituent and the change in the P-N/Pd molar ratio, and also to
explain the lasting catalytic activity of these systems.
1
(2208C). Pale yellow solid (yield: 0.93 g, 70%). H NMR
(CDCl3, ppm), d: 6.85–7.00 (m, 11H), 7.25–7.40 (m, 5H),
7.43–7.50 (m, 1H), 8.15–8.20 (m, 1H), 9.03 (d, J¼5.1 Hz,
1H); 31P NMR (CDCl3, ppm), d: 210.2; nmax (Nujol) 1623
(CvN), 1232 (C–F) cm21
; Anal. data: calcd for
C25H19FNP: C, 78.32; H, 4.99; N, 3.65. Found: C, 78.5;
H, 5.0; N, 3.6.
4. Experimental
4.1.3. 2-(PPh2)-C6H4-1-CHvNC6H4CF3-4 (6). This com-
pound was prepared following the same procedure used for
5. Pale yellow solid (yield: 1.23 g, 83%). 1H NMR (CDCl3,
ppm), d: 6.85–6.90 (m, 2H), 6.90–6.98 (m, 1H), 7.25–7.40
(m, 11H), 7.43–7.50 (m, 1H), 7.50–7.55 (m, 2H), 8.15–
8.20 (m, 1H), 9.00 (d, J¼5.1 Hz, 1H); 31P NMR (CDCl3,
ppm), d: 29.9; nmax (Nujol) 1621 (CvN), 1320 (C–F)
cm21; Anal. data: calcd for C26H19F3NP: C, 72.05; H, 4.42;
N, 3.23. Found: C, 72.3; H, 4.4; N, 3.3.
4.1. Materials and instrumentation
1H and 31P NMR spectra were recorded on a Bruker AM 400
NMR spectrometer operating at 400.13 and 161.98 MHz,
respectively. 85% phosphoric acid was used as external
standard for 31P NMR. GLC analyses were performed on a
HP 5890 series II gas chromatograph, GC–MS analyses
were obtained on a HP 5890 series II gas chromatograph
interfaced to a HP 5971 mass-detector using the same type
of column.
4.2. Catalytic experiments
The reactions were carried out in a jacketed glass reactor
(volume ca. 30 mL) equipped with a reflux condenser, a
side arm with stopcock for freeze-thaw cycles and with a
threaded side port with rubber septum and cap for syringe
sampling. The details for run 1 of Table 1 are reported as an
example.
All the reactions, unless otherwise stated, were carried out
under an inert atmosphere (argon).
The product yields reported in Tables were determined by
GLC.
Aryl halides (Aldrich) and other commercial solvents
(Aldrich or Fluka) were purified before the use following
literature procedures.22 Pd(OAc)2 (Engelhard Industries),
dibenzylideneacetone (Fluka), dimethylfumarate (Fluka),
4-trifluoromethylaniline (Aldrich), 4-fluoroaniline (Aldrich)
and tributylvinylstannane (Fluka) were commercial products
and used as received.
The reactor was charged under argon with 5 mL of THF,
510 mg (1.3 mmol) of tributylphenylethynylstannane,
150 mL (270 mg, 1.3 mmol) of iodobenzene, and
7.2 mg (0.013 mmol) of [Pd(dimethylfumarate)(Ph2P-
(C6H4CHvNCH3)]. Then the reactor was heated at 508C
by circulating a thermostatic fluid through the outer jacket.
After 2 h, the reaction mixture was cooled to rt and the crude
reaction mixture analysed by GLC to determine substrate
conversion and product yield.
Tributylphenylethynylstannane,23 tri(2-furyl)phosphines,24
and Pd(dba)225 were prepared as described in the literature.
The iminophosphines 2-(PPh2)-C6H4-1-CHvNR (R¼Ph
(3), CH2CH2Ph (7)) were prepared by published methods.20
The iminophosphines 2-(PPh2)-C6H4-1-CHvNR (R¼CH3
(1), CMe3 (2), C6H4OMe-4 (4)) as well as the corresponding
complexes [Pd(h2-dmf){2-(PPh2)-(C6H4-1-CHvNR}] (1a,
2a, 4a) were synthesised as described in Ref. 17.
Acknowledgments
Financial support by Ministero Italiano dell’Istruzione,
`
dell’Universita e della Ricerca Scientifica (MIUR) is
gratefully acknowledged.
4.1.1. Pd(h2-dmf){2-(PPh2)-C6H4-1-CHvNPh}] (3a).
The synthetic procedure of Ref. 17 was used: the new
complex was obtained as a yellow-orange solid in 73%
yield. 1H NMR (CDCl3, d): 3.14 (s, 3H), 3.25 (s, 3H), 3.51
(dd, J¼10.0 Hz, 1H), 4.24 (dd, J¼10.0 Hz, 1H), 7.1–7.6
(m, 19H), 8.12 (d, J¼3.4 Hz, 1H); 31P NMR (CDCl3) d:
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