Synthesis of dinuclear palladium complexes having two parallel isocyanide ligands, and their application as catalysts to pyrrole formation from tert-butylisocyanide and alkynes

Article abstract of DOI:10.1016/j.jorganchem.2008.12.039

Novel dinuclear palladium complexes having two isocyanide ligands were synthesized by using a binucleating ligand, N,N′-bis[2-(diphenylphsphino)phenyl]formamidinate (dpfam). The structure of [Pd₂(μ-dpfam)(tert-BuNC)₂]Cl was confirmed

Full text of DOI:10.1016/j.jorganchem.2008.12.039

Journal of Organometallic Chemistry 694 (2009) 1333–1338
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of dinuclear palladium complexes having two parallel isocyanide
ligands, and their application as catalysts to pyrrole formation from
tert-butylisocyanide and alkynes
*
*
Naofumi Tsukada , Makiko Wada, Naoki Takahashi, Yoshio Inoue
Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel dinuclear palladium complexes having two isocyanide ligands were synthesized by using a binu-
cleating ligand, N,N0-bis[2-(diphenylphsphino)phenyl]formamidinate (dpfam). The structure of [Pd2
Received 21 February 2008
Received in revised form 10 December 2008
Accepted 12 December 2008
Available online 25 December 2008
(l-dpfam)(tert-BuNC)2]Cl was confirmed by X-ray analysis, showing that the Pd–Pd bond length of
2.5824(3) Å falls well within the range of those for known dipalladium complexes having the edge-shar-
ing structure and two isocyanides coordinate to palladium in almost parallel and in close proximity. The
dinuclear complex [Pd2(
butylisocyanide and various alkynes.
l-dpfam)(tert-BuNC)2]PF6 served as catalyst for pyrrole formation from tert-
Keywords:
Palladium
Dinuclear complex
Pyrrole
Ó 2008 Elsevier B.V. All rights reserved.
Isocyanide
Alkyne
1. Introduction
2. Results and discussion
Catalysis using dinuclear transition metal complexes has re-
cently received considerable attention [1]. Cooperation of two me-
tal centers can improve the selectivity and efficiency of
catalyzation, and can promote reactions that are not possible using
a single metal center. Bis(diphenylphosphino)methane (dppm), or
its analogues, is one of the most useful binucleating ligands [2],
particularly for palladium and platinum complexes [3]. Although
those complexes are known to adopt several geometries [2a], as
illustrated in Chart 1A, their application as catalysts has been
rarely reported. In our previous papers [4,5], we focused on the
importance of cis orientation of two reactant ligands (Y in Chart
1B) for catalysis [4,6,7], and reported synthesis of the correspond-
ing A-frame complexes having a new binucleating ligand, N,N0-
bis[2-(diphenylphsphino)phenyl]formamidinate (dpfam) [4] and
their application to catalysis [5]. We report here synthesis of dinu-
clear palladium complexes having the edge-sharing structure,
which have two parallel isocyanide ligands, and their application
as catalysts to pyrrole formation.
2.1. Synthesis of dinuclear palladium complexes
The reaction of dpfamH with PdCl2(tmeda), Pd2(dba)3 ꢀ CHCl3,
and excess tert-butylisocyanide in dichloromethane at room tem-
perature resulted in the formation of the dinuclear palladium com-
plex [Pd2(t-BuNC)2(
with excess NH4PF6 gave [Pd2(t-BuNC)2(
l
-dpfam)]Cl (1a) (Scheme 1). Treatment of 1a
-dpfam)]PF6 (1b) in 81%
l
yield. Crystallization of 1 by slow diffusion of diethyl ether into a
solution of 1,2-dichloroethane afforded a red crystal suitable for
X-ray analysis. The molecular structure of 1a is shown in Fig. 1.
The Pd–Pd bond length of 2.5824(3) Å is shorter than those of
the corresponding A-frame complexes [4] and falls well within
the range of those for known dipalladium complexes having the
edge-sharing structure [2a]. Although the two palladium planes
are slightly twisted (N(1)–Pd(1)–Pd(2)–N(2) 21.19(12)°, C(38)–
Pd(1)–Pd(2)–C(43) 30.26(19)°), two isocyanides coordinate to
palladium in almost parallel and in close proximity. A number of
Pd–Pd bonded complexes having isocyanide ligands have been
reported [8–11]. In most of unbridged complexes, the dihedral
angles between two coordination planes are much larger than that
of 1a, and isocyanide ligands are distant each other [8]. In dipalla-
dium complexes bridged by binucleating ligands such as dppm, the
dihedral angles are smaller, however, two isocyanides coordinate
to palladium centers in trans orientation (Chart 1A) [9]. There are
only a few reports on dipalladium complexes having parallel
isocyanide ligands [10].
* Corresponding authors. Present address: Department of Chemistry, Faculty of
Science, Shizuoka University, Shizuoka 422-8529, Japan. Tel./fax: +81 54 238 4759
(N. Tsukada).
E-mail address: sntsuka@ipc.shizuoka.ac.jp (N. Tsukada).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.12.039

1334
N. Tsukada et al. / Journal of Organometallic Chemistry 694 (2009) 1333–1338
reaction was reported by Jautelat and Ley in 1970 [12,13], the yield
was moderate and no further studies have been done. Expectedly,
the reaction of tert-butylisocyanide with phenylacetylene using
1b as catalyst in 1,2-dichloroethane (DCE) at 80 °C afforded pyr-
roles 3a and 3b in high yield, while complex 1a did not serve as cat-
alyst (Eq. (1), Table 1, entries 1 and 2). When the reaction was
conducted at higher and lower temperature or in other solvents
such as THF, toluene, and acetonitrile, pyrroles 3 were obtained in
lower yields (entries 3–8). Although ordinary mononuclear palla-
dium complexes such as Pd(PPh3)4 and Pd(OAc)2 could be used as
a catalyst, the yield of 3 was moderate (entries 10–13). In the reac-
tion using Pd(OAc)2, a significant amount of 5-imino-3-pyrrolin-2-
one 4 was formed (entry 13). The use of proportionate amounts of
reactants decreased the yield of 3 (entries 9 and 12). Higher concen-
tration of tert-butylisocyanide probably prevents coordination of
phenylacetylene to palladium. When a solution of tert-butylisocya-
nide in DCE was added dropwise over 5 h using a syringe pump,
pyrroles 3 were obtained in a satisfactory yield (Eq. (2)).
L
Pd
L
L
Pd
L
L
Pd
L
L
Pd
L
L
Pd
L
L
Pd
L
Y
L
Y
L
Y
Y
Y
Y
Y
A
Y
Y
(trans)
Edge-sharing
A-frame
Face-to-Face
L
Pd
Y
L
Pd
Y
L
Pd
Y
L
Pd
Y
L
Pd
Y
L
Pd
Y
L
L
B
(cis)
L
L
Y
Y
Y
(L = P or N, Y = other ligands)
Chart 1.
N
N
H
+ PdCl2(tmeda) + 1/2 Pd2(dba)3·CHCl3
Ph2P
PPh2
91%
Hdpfam
[Pd]
+
t-BuNC
Ph
excess t-BuNC
dichloromethane
rt
(1)
1:1
Ph
NBut
Ph
NC
+
X–
+
NBut
H
NC
N
N
H
tBu
tBu
N
N
3a
3b
Ph2P
PPh2
Pd
Pd
C
N
C
N
1a (X = Cl)
1b (X = PF6)
81%
tBu tBu
Ph
Scheme 1.
NBut
O
N
H
tBu
4
t-BuNC/DCE
(1.5 mmol)
1b
dropwise over 5 h
(2)
(0.01 mmol)
3a + 3b
Ph
(0.5 mmol)
DCE
80°C, 17 h (total)
78%
(83:17)
Table 1
Palladium-catalyzed pyrrole forming reaction from phenylacetylene and tert-
butylisocyanide.a
Entry Catalyst
Solvent
Temperature Yieldb Ratioc
(°C)
(%)
(3a:3b)
1
2
3
4
5
6
7
8
1a
1b
1b
1b
1b
1b
1b
1b
1b
DCE
DCE
THF
Toluene
Acetonitrile
DMF
DCE
DCE
80
80
80
80
80
80
60
100
80
80
80
80
80
0
92
68
48
32
0
53
76
13
0
–
78:28
53:47
58:42
75:25
–
77:23
80:20
69:31
–
Fig. 1. Molecular structure of the cation of 1a, showing 50% thermal ellipsoids.
Selected bond lengths (Å) and angles (°): Pd(1)–Pd(2) 2.5824(3), Pd(1)–P(1)
2.3417(10), Pd(2)–P(2) 2.3140(10), Pd(1)–N(1) 2.061(2), Pd(2)–N(2) 2.064(2),
Pd(2)–Pd(1)–P(1) 165.64(2), Pd(1)–Pd(2)–P(2) 167.86(2), C(38)–Pd(1)–Pd(2)–
C(43) 30.26(19), N(1)–Pd(1)–Pd(2)–N(2) 21.19(12).
9d
10
11
12d
13
DCE
[Pd2(PhCN)2(PPh3)2](BF4)2 DCE
Pd(PPh3)4
Pd(PPh3)4
2.2. Catalytic pyrrole formation
DCE
DCE
DCE
59
26
24
73:27
65:35
100:0
Since the dinuclear palladium complexes having two parallel
isocyanide ligands were expected to be effective as catalysts in
the reactions oligomerizing more than two isocyanides, we next
investigated the application of the complexes 1 to a pyrrole forming
reaction, in which 2-amino-5-cyanopyrroles are formed from three
molecules of tert-butylisocyanide and one molecule of alkynes (Eq.
(1)). Although the nickel-catalyzed version of this pyrrole forming
e
Pd(OAc)2
a
A mixture of pheylacetylene (0.5 mmol), tert-butylisocyanide (0.5 mmol), cat-
alyst (0.01 mmol, 2 mol%) in solvent (2 ml) were stirred for 16–18 h.
b
GC yields based on tert-butylisocyanide.
Determined by GC.
1.5 mmol of tert-butylisocyanide was used.
4 mol% of palladium acetate was used.
c
d
e

N. Tsukada et al. / Journal of Organometallic Chemistry 694 (2009) 1333–1338
1335
Table 2
R
R
Palladium-catalyzed pyrrole forming reaction from various alkynes and tert-
O
R
butylisocyanide.a
O
R
O
O
Entry
R1
R2
Product
Yieldb (%)
Ratioc (a:b)
O
(OC)3Co
Co(CO)3
[Rh Rh]
1
2
3
4
5
6
7
8
n-Bu
n-Hex
CO2Me
CH2OMe
Ph
Me
Et
n-Pr
H
H
H
H
5
6
7
8
90
74
24
46
73
42
24
13
79:21
72:28
>95:<5
>95:<5
49:51
>95:<5
–
13
14
CO2Me
CO2Me
Et
9
10
11
12
+
+
N
N
N
R
N
n-Pr
–
P
P
P
P
Pd
a
Pd
Pd
Pd
R
R
A
mixture of an alkyne (0.5 mmol), tert-butylisocyanide (0.5 mmol), 1b
(0.01 mmol, 2 mol%) in DCE (2 ml) were stirred at 80 °C for 16–18 h.
C
N
C
N
C
N
C
N
b
R
Isolated yields based on tert-butylisocyanide.
Determined by GC.
c
tBu
tBu
tBu tBu
1b
15
H
CN
tBuN
Table 2 summarizes the results of reaction of tert-butylisocyanide
with various alkynes. The reactions with aliphatic terminal alkynes
also gave corresponding pyrroles 5 and 6 with moderate regioselec-
tivity (entries 1 and 2). In the reaction with methyl propiolate, one
regioisomer 7a was selectively obtained, although the yield was low
(entry 3). Methoxy group at a propargylic position also controlled
the regioselectivity, giving single isomer 8a in better yield (entry
4). Internal alkynes also reacted with tert-butylisocyanide to afford
highly substituted pyrroles. The reaction of methyl phenylpropio-
late gave 9 in high yield and the reaction of methyl tetrolate pro-
ceeded regioselectively, affording 10a (entries 5 and 6). Although
unactivated internal alkynes were less reactive, pyrroles 11 and
12 were obtained by using 1b as a catalyst. In contrast, the corre-
sponding reactions using Ni(OAc)2 or Pd(PPh3)4 as catalysts gave
no products.
+
tBuN
R
N
N
P
P
R
Pd
Pd
19
tBuN
NBut
R
R
tBuNC
pyrroles
3, 5–12
16
+
+
N
N
N
N
P
P
P
P
Pd
Pd
Pd
Pd
H
R
tBuN
tBuN
tBuN
tBuN
CN
R
R
18
R
17
2 mol% 1a
R1
R2
+
t-BuNC
DCE
80°C, 16–18 h
(3)
R2
R1
R1
NC
R2
NC
tBuNC
+
NBut
H
NBut
H
Scheme 2.
N
N
tBu
tBu
5-12a
5-12b
in adjacent positions by dpfam. A plausible pathway via dipalla-
dium intermediates is shown in Scheme 2. Initially, alkynes
would insert to the Pd–Pd bond of 1b [16], and then isocyanides
would insert to the resulted Pd–C bond on 15. Intramolecular
cyclization of 16 would afford iminopyrrolinyl complex 17. Com-
plex 18 could be formed by cyanation of 17 with a cyanide li-
gand generated by C–N bond cleavage [17] of third tert-
butylisocyanide on palladium. Pyrroles 3 and 5–12 would be ob-
tained by reductive elimination [18] of 19 from 18 and isomer-
ization of 19.
2.3. Mechanistic considerations
To gain insight into the mechanism of the pyrrole formation
by 1b, some stoichiometric reactions of 1b with pheylacetylene
or 3-hexyne in the presence or absence of tert-butylisocyanide
were performed under several reaction conditions. Unfortu-
nately, all reaction gave mixtures of unidentified several com-
plexes. Although details of the reaction mechanism are unclear
at the present time, some considerations have been made based
on the mechanisms for the synthesis of 2(5H)-furanones from al-
kynes, carbon monoxide and water [14]. Joh et al. reported the
furanone formation catalyzed by rhodium carbonyl clusters, for
which they proposed the mechanism via multinuclear rhodium
furanone complex 13 [14c]. Proposal of the intermediate 13
was based on the isolated dicobalt franone complex 14 formed
from Co2(CO)8 and alkynes [15]. Although the authors conclu-
sively proposed a different mechanism via a mononuclear anio-
nic complex for the reaction in their next paper [14d], the
present pyrrole formation could proceed via a dipalladium com-
plex similar to 13 and 14 because two palladium atoms are held
Other reaction pathways via mononuclear intermediates are
also possible [14b,d,e]. At the present time, we cannot determine
which pathway is more suitable for the pyrrole formation using
1b as a catalyst.
3. Conclusion
The dinuclear palladium complexes 1 having the edge-sharing
structure were prepared from Pd(0) and Pd(II) precursors, dpfamH,
and excess of tert-butylisocyanide. Two isocyanides in 1 coordinate
to palladium in almost parallel and in close proximity. The com-
plex 1b was effective as a catalyst in pyrrole formation from three
molecules of tert-butylisocyanide and one molecule of alkyne. The

1336
N. Tsukada et al. / Journal of Organometallic Chemistry 694 (2009) 1333–1338
reaction using 1b gave products in better yields than that using
Pd(PPh3)4. Furthermore, unactivated internal alkynes reacted with
tert-butylisocyanide by using 1b, affording poly-substituted pyr-
roles. The reaction of internal alkynes using Ni(OAc)2 or Pd(PPh3)4
did not give any products. Although the precise mechanism of the
present pyrrole formation has remained unclear, two adjacent pal-
ladium atoms in 1b seems to effectively cooperate each other.
Other catalysis using 1 and synthesis of different types of edge-
sharing dinuclear complexes are under investigation.
preliminary unit cell parameters. The intensity images were also
measured at 0.5° intervals of w. The intensity images were inte-
grated using the CRYSTAL CLEAR program package, and the empirical
absorption correction was applied for the data. The structures
were solved by a direct method (SIR-92). All non-hydrogen atoms
were refined anisotropically by full-matrix least-squares tech-
nique. All hydrogen atoms were placed in idealized positions,
and were included but not refined. All calculations were per-
formed using the CRYSTAL STRUCTURE software package of Rigaku Cor-
poration. Crystal data and refinement details are summarized in
Table 3.
4. Experimental
4.2. Synthesis of [Pd2(tert-BuNC)2(l-dpfam)]PF6 (1b)
All reactions were carried out under a nitrogen atmosphere. Al-
kynes and tert-butylisocyanide were purchased from Aldrich or TCI
and used without further purification. DCE was distilled from CaH2
under a nitrogen atmosphere.
NMR spectra were recorded by using a Bruker DPX-400 or
Bruker DRX-500 spectrometer. 1H NMR chemical shifts were mea-
sured relative to tetramethylsilane in CDCl3. Phosphorus chemical
shifts were determined relative to 85% H3PO4 as an external stan-
dard. IR spectra were recorded by using a JEOL FT/IR-350.
To a solution of 1a (97.8 mg, 0.10 mmol) in dichloromethane
(2.0 mL) and THF (4.0 mL) was added NH4PF6 (163 mg, 1.0 mmol).
After stirring for 2 h, solvents were removed under reduced pres-
sure, and then the residue was dissolved in dichloromethane
(4 mL). White precipitates were removed by filtration and washed
with dichloromethane several times. After the volume of the com-
bined filtrate was reduced to 1 mL under reduced pressure, ether
(10 mL) was added to the solution. Resulted red precipitates were
collected by filtration, washed with ether, and dried. Yield: 88 mg,
81%. 1H NMR (400 MHz, CDCl3) d9.36 (s, 1H), 7.58–7.34 (m, 24H),
7.24–7.16 (m, 2H), 7.11–7.00 (m, 2H), 1.39 (s, 18H); 31P {1H}
4.1. Synthesis of [Pd2(tert-BuNC)2(l-dpfam)]Cl (1a)
To a solution of dpfamH (0.225 g, 0.40 mmol) and Pd2(dba)3 ꢀ
CHCl3 (0.207 g, 0.20 mmol) in dichloromethane (16 mL) were
added tert-butylisocyanide (0.452 mL, 4.0 mmol) and then
PdCl2(tmeda) (0.117 g, 0.40 mmol). After the mixture was stirred
at room temperature for 20 h, Excess tert-butylisocyanide and
dichloromethane were removed under reduced pressure. The resi-
due was redissolved in dichloromethane (4 mL). Ether (40 mL) was
added to the solution. Resulted red precipitates was collected by
filtration, washed with ether, and dried. Yield: 0.36 g, 91%. 1H
NMR (400 MHz, CDCl3) d9.35 (s, 1H), 7.58–7.33 (m, 24H), 7.24–
7.15 (m, 2H), 7.12–7.02 (m, 2H), 1.41 (s, 18H); 31P {1H} NMR
(400 MHz, CDCl3) d 18.49. Anal. Calc. for C47H47ClN4P2Pd2: C,
57.71; H, 4.84; N 5.73; Cl, 3.62. Found: C, 57.08; H, 5.09; N, 5.25;
Cl, 3.36%.
NMR (400 MHz, CDCl3)
C47H47F6N4P3Pd2: C, 51.90; H, 4.36; N 5.15. Found: C, 51.20; H,
4.32; N, 5.15%.
d
17.15, ꢁ143.78. Anal. Calc. for
4.3. General procedure for the reaction of tert-butylisocyanide and
alkynes
To a solution of 1b (10.9 mg, 0.01 mmol) and tert-butylisocya-
nide (57 ml, 0.5 mmol) in DCE (2.0 mL) was added an alkyne
(0.5 mmol) under a nitrogen atmosphere in a pressure vial. After
heating at 80 °C for 16–18 h, the mixture was cooled to room tem-
perature and filtered through a short plug of silica gel using ether
as an eluent. Volatiles were evaporated and the residue was puri-
fied by silica gel column chromatography to give pyrroles.
Recrystallization by slow diffusion of diethyl ether into a solu-
tion of DCE gave a red crystal (1a ꢀ ClCH2CH2Cl ꢀ 1.5H2O). Data col-
lection was carried out on a Rigaku CCD mercury system fitted
with a monochromatic Mo Ka radiation source (l = 0.71069 Å) at
room temperature. Eighteen preliminary data frames were mea-
sured at 0.5° increments of w, to assess the crystal quality and
4.4. 1-tert-Butyl-5-(tert-butylamino)-3-phenyl-1H-pyrrole-2-
carbonitrile (3a) [12]
1H NMR (400 Hz, CDCl3): d 7.62 (m, 2H), 7.39 (m, 2H), 7.30 (m,
1H), 5.78 (s, 1H), 3.88 (s, 1H), 1.83 (s, 9H), 1.34 (s, 9H).
4.5. 1-tert-Butyl-5-(tert-butylamino)-4-phenyl-1H-pyrrole-2-
carbonitrile (3b) [12]
Table 3
Crystal data and refinement details for 1a.
1H NMR (400 MHz, CDCl3): d 7.41–7.18 (m, 5H), 6.94 (s, 1H),
1a ꢀ ClCH2CH2Cl ꢀ 1.5H2O
Formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
b (°)
C49H54Cl3N4O1.5P2Pd2
1104.10
2.88 (s, 1H), 1.87 (s, 9H), 0.82 (s, 9H).
Monoclinic
P21/c (#14)
13.920(3)
25.632(5)
14.937(3)
104.873(2)
4
5150.8(16)
1.424
2244.00
4.6. 1-tert-Butyl-5-(tert-butylamino)-3-butyl-1H-pyrrole-2-
carbonitrile (5a) [12]
1H NMR (400 MHz, CDCl3): d 5.47 (s, 1H), 3.26 (s, 1H), 2.51 (t,
J = 7.8 Hz, 2H), 1.75 (s, 9H), 1.55 (m, 2H), 1.38 (m, 2H), 1.30 (s,
9H), 0.92 (t, J = 7.3 Hz, 3H).
Z
V (Å3)
Dcalcd (g cmꢁ3
F(100)
)
4.7. 1-tert-Butyl-5-(tert-butylamino)-4-butyl-1H-pyrrole-2-
carbonitrile (5b) [12]
l
(Mo K
a
) (cmꢁ1
)
9.553
39707
No. of data collected
No. of unique data [R(int)
R1 [I > 2r(I)]
wR2
]
11465 (0.041)
0.0471
0.0662
1H NMR (400 MHz, CDCl3): d 6.74 (s, 1H), 2.35–2.30 (m, 3H),
1.78 (s, 9H), 1.53–1.45 (m, 2H), 1.37–1.28 (m, 2H), 0.92 (t,
J = 7.29 Hz, 3H).
Goodness-of-fit indicator
1.011

N. Tsukada et al. / Journal of Organometallic Chemistry 694 (2009) 1333–1338
1337
4.8. 1-tert-Butyl-5-(tert-butylamino)-3-hexyl-1H-pyrrole-2-
carbonitrile (6a)
974, 786, 723, 552 cmꢁ1; MS (EI): m/z 41 (89), 57 (85), 127 (10),
155 (16), 180 (14), 209 (24), 241 (100), 281 (10), 297 (32). Anal.
Calc. for C21H27N3O2: C, 71.39; H, 7.65; N, 11.90. Found: C, 71.32;
H, 7.77; N, 11.74%.
1H NMR (500 MHz, CDCl3): d 5.47 (s, 1H), 3.23 (s, 1H), 2.50 (t,
J = 7.8 Hz, 2H), 1.74 (s, 9H), 1.65–1.50 (m, 2H), 1.40–1.21 (m,
15H), 0.94–0.80 (m, 3H); 13C NMR (125 Hz, CDCl3): d 142.30,
140.06, 118.25, 98.12, 52.20, 32.45, 31.71, 31.31, 30.30, 29.91,
29.85, 29.13, 26.98, 22.67; IR (neat): 3313, 2961, 2928, 2858,
2190, 1653, 1554, 1461, 1367, 1216, 958, 881, 767 cmꢁ1; MS
(EI): m/z 47 (95), 57 (100), 96 (27), 121 (47), 191 (32), 232 (12),
247 (26), 303 (7); HRMS (ESI) calcd for C19H33N3Na [M+Na]+:
326.2567; found: 326.2566.
4.14. Methyl 1-tert-butyl-5-(tert-butylamino)-2-cyano-3-methyl-1H-
pyrrole-4-carboxylate (10a)
1H NMR (500 MHz, CDCl3): d 4.18 (s,1H), 3.79 (s, 3H), 2.35 (s,
3H), 1.79 (s, 9H), 1.09 (s, 9H); 13C NMR (125 MHz, CDCl3): d
165.71, 147.71, 135.18, 116.21, 110.70, 100.25, 62.02, 58.87,
50.83, 31.69, 29.46, 12.49; IR (KBr): 3302, 2975, 2204, 1692,
1548, 1516, 1440, 1368, 1270, 1193, 1110, 1041, 951, 797,
678 cmꢁ1; MS (EI): m/z 41 (47), 57 (59), 147 (100), 179 (49), 235
(25), 281 (6). Anal. Calc. for C16H25N3O2: C, 65.98; H, 8.59; N,
14.43. Found: C, 65.89; H, 8.59; N, 14.27%.
4.9. 1-tert-Butyl-5-(tert-butylamino)-3-hexyl-1H-pyrrole-2-
carbonitrile (6b)
1H NMR (500 MHz, CDCl3): d 6.73 (s, 1H), 2.44–2.53 (m, 2H),
2.27–2.35 (m, 3H), 1.78 (s, 9H), 1.24–1.37 (m, 6H), 1,14 (s, 9H),
0.83–0.94 (m, 3H); 13C NMR (125 Hz, CDCl3): d 138.58, 122.43,
121.02, 117.91, 98.68, 60.24, 55.12, 32.00, 31.70, 30.63, 30.42,
29.27, 26.75, 22.60, 14.05; IR (neat): 3330, 2960, 2926, 2857,
4.15. 1-tert-Butyl-5-(tert-butylamino)-3,4-diethyl-1H-pyrrole-2-
carbonitrile (11)
1H NMR (500 MHz, CDCl3): d 2.58 (q, J = 7.6 Hz, 2H), 2.40 (q,
J = 7.6 Hz, 2H), 2.31 (s, 1H), 1.76 (s, 9H), 1.17 (t, J = 7.6 Hz, 3H),
1.14 (s, 9H), 1.08 (t, J = 7.6 Hz, 3H); 13C NMR (125 MHz, CDCl3): d
138.77, 138.25, 120.42, 117.68, 97.52, 59.93, 54.86, 32.09, 30.60,
19.02, 18.05, 15.41, 15.24; IR (KBr): 3329, 2972, 2933, 2874,
2187, 1547, 1444, 1368, 1310, 1264, 1218, 1062, 980, 938,
809 cmꢁ1; MS (EI): m/z 41 (87), 57 (79), 148 (56), 163 (100), 219
(27), 275 (4); HRMS (ESI) calcd for C17H29N3Na [M+Na]+:
298.2254; found: 298.2252.
2202, 1658, 1556, 1458, 1366, 1221, 1154, 1030, 940, 815 cmꢁ1
;
MS (EI): m/z 47 (85), 57 (100), 120 (75), 191 (41), 232 (14), 247
(27), 303 (3); HRMS (ESI) calcd for C19H33N3Na [M+Na]+:
326.2567; found: 326.2567.
4.10. Methyl 1-tert-butyl-5-(tert-butylamino)-2-cyano-1H-pyrrole-3-
carboxylate (7a)
1H NMR (400 MHz, CDCl3): d 6.10 (s, 1H), 3.87 (s, 3H), 3.29 (s,
1H), 1.83 (s, 9H), 1.32 (s, 9H); 13C NMR (100 MHz, CDCl3): d
163.28, 141.90, 125.82, 115.71, 115.16, 100.16, 60.78, 52.50,
51.65, 31.27, 29.70; IR (KBr): 3443, 2976, 2208, 1720, 1564,
1506, 1200, 1118 cmꢁ1; MS (EI): m/z 41 (71), 57 (100), 133 (53),
165 (86), 174 (22), 189 (14), 206 (24), 221 (39), 277 (9);
HRMS (ESI) calcd for C15H23N3NaO2 [M+Na]+: 300.1682; found:
300.1683.
4.16. 1-tert-Butyl-5-(tert-butylamino)-3,4-dipropyl-1H-pyrrole-2-
carbonitrile (12)
1H NMR (400 MHz, CDCl3): d 2.51 (t, J = 7.6 Hz, 2H), 2.32 (t,
J = 7.6Hz, 2H), 2.32 (s, 1H), 1.75 (s, 9H), 1.55 (tt, J = 6.1, 7.4 Hz,
2H), 1.43 (tt, J = 6.1, 7.4 Hz, 2H), 1.13 (s, 9H), 0.93 (t, J = 6.1 Hz,
9H), 0.87 (t, J = 6.1 Hz, 3H); 13C NMR (100 MHz, CDCl3): d 138.93,
137.20, 119.23, 117.70, 98.20, 59.95, 55.08, 32.07, 30.60, 27.70,
23.69, 14.08, 13.88; IR (KBr): 3332, 2963, 2871, 2192, 1659,
1548, 1503, 1445, 1366, 1319, 1228, 957, 778, 695 cmꢁ1; MS
(EI): m/z 41 (100), 57 (92), 162 (94), 176 (26), 191 (48), 247 (34),
303 (4); HRMS (ESI) calcd for C19H33N3 [M+Na]+: 326.2567; found:
326.2566.
4.11. 1-tert-Butyl-5-(tert-butylamino)-3-methoxymethyl-1H-pyrrole-
2-carbonitrile (8a) [12]
1H NMR (500 MHz, CDCl3): d 5.69 (s, 1H), 4.38 (s, 2H), 3.40 (s,
3H), 3.26 (s, 1H), 1.76 (s, 9H), 1.31 (s, 9H).
4.12. Methyl 1-tert-butyl-5-(tert-butylamino)-2-cyano-3-phenyl-1H-
pyrrole-4-carboxylate (9a)
4.17. Synthesis of pyrroles 3 using slow addition of tert-
butylisocyanide
1H NMR (400 MHz, CDCl3): d 7.31–7.43 (m, 5H), 4.11 (s, 1H),
3.59 (s, 3H), 1.86 (s, 9H), 1.12 (s, 9H); 13C NMR (100 MHz, CDCl3):
d 165.54, 146.68, 138.16, 132.23, 129.41, 127.75, 116.24, 110.59,
100.03, 62.67, 56.87, 50.91, 31.81, 29.47. IR (KBr): 3320, 2974,
2208, 1726, 1689, 1516, 1451, 1368, 1279, 1189, 1127, 1035,
822, 709, 662 cmꢁ1; MS (EI): m/z 41 (82), 57 (66), 128 (18), 154
(8), 180 (15), 209 (100), 241 (34), 297 (25). Anal. Calc. for
C21H27N3O2: C, 71.39; H, 7.65; N 11.90. Found: C, 71.29; H, 7.84;
N, 11.69%.
To a solution of 1b (10.9 mg, 0.01 mmol) in DCE (1.0 mL) was
added phenylacetylene (55 ml, 0.50 mmol) under a nitrogen atmo-
sphere in a Schlenk tube with a rubber septum. The flask was
placed in an 80 °C oil bath. A solution of tert-butylisocyanide
(170 ml, 1.5 mmol) in DCE (2.0 mL) was added to the reaction mix-
ture in the flask over 5 h using a syringe pump. After the addition
was completed, the reaction mixture was stirred at 80 °C for an-
other 12 h. The mixture was cooled to room temperature and fil-
tered through a short plug of silica gel using ether as an eluent.
The yield and the isomer ratio were determined by GC using n-
dodecane as an internal standard.
4.13. Methyl 1-tert-butyl-5-(tert-butylamino)-2-cyano-4-phenyl-1H-
pyrrole-3-carboxylate (9b)
1H NMR (400 MHz, CDCl3): d 7.37–7.34 (m, 2H), 7.32–7.28 (m,
Acknowledgments
1H), 7.23–7.20 (m, 2H), 3.73 (s, 3H), 2.81 (s, 1H), 1.91 (s, 9H),
0.75 (s, 9H); 13C NMR (100 MHz, CDCl3):
134.40, 128.02, 127.19, 123.81, 123.79, 115.37, 102.64, 62.60,
55.61, 51.47, 32.14, 30.00; IR (KBr): 3370, 2971, 2210, 1709,
1604, 1510, 1479, 1431, 1362, 1320, 1263, 1181, 1112, 1027,
d 163.29, 139.60,
This work was supported by Grants-in-Aid for Scientific
Research [No. 17750081] from MEXT, and partially carried out
using instruments at the Center for Instrumental Analysis of Shi-
zuoka University.

1338
N. Tsukada et al. / Journal of Organometallic Chemistry 694 (2009) 1333–1338
(c) N.D. Jones, S.J.L. Foo, B.O. Patrick, B.R. James, Inorg. Chem. 43 (2004) 4056;
Appendix A. Supplementary material
(d) J.N.L. Dennett, M. Bierenstiel, M.J. Ferguson, R. McDonald, M. Cowie, Inorg.
Chem. 45 (2006) 3705.
CCDC 705109 contains the supplementary crystallographic
data for 1a ꢀ ClCH2CH2Cl ꢀ 1.5H2O. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.12.039.
[7] (a) P. Nair, G.K. Anderson, N.P. Rath, Inorg. Chem. Commun. 5 (2002) 653;
(b) P. Nair, G.K. Anderson, N.P. Rath, Organometallics 22 (2003) 1494;
(c) P. Nair, G.K. Anderson, N.P. Rath, Inorg. Chem. Commun. 6 (2003) 1307.
[8] (a) N.M. Rutherford, M.M. Olmstead, A.L. Balch, Inorg. Chem. 23 (1984)
2833;
(b) Y. Yamamoto, H. Yamazaki, Bull. Chem. Soc. Jpn. 58 (1985) 1843;
(c) T. Tanase, K. Kawahara, H. Ukaji, K. Kobayashi, H. Yamazaki, Y. Yamamoto,
Inorg. Chem. 32 (1993) 3682;
(d) T. Tanase, H. Ukaji, Y. Yamamoto, J. Chem. Soc., Dalton Trans. (1996) 3059;
(e) Y. Yamamoto, F. Arima, J. Chem. Soc., Dalton Trans. (1996) 1815;
(f) T. Tanase, J. Matsuo, T. Onaka, R.A. Begum, M. Hamaguchi, S. Yano, Y.
Yamamoto, J. Organomet. Chem. 592 (1999) 103;
(g) J. Vicente, J.-A. Abad, A.D. Frankland, J. López-Serrano, P.G. Jones,
Organometallics 21 (2002) 272.
References
[1] (a) R.M. Bullock, C.P. Casey, Acc. Chem. Res. 20 (1987) 167;
(b) H. Steimhagen, G. Helmchen, Angew. Chem., Int. Ed. 35 (1996) 2339;
(c) E.K. van den Beuken, B.L. Feringa, Tetrahedron Lett. 54 (1998) 12985;
(d) G.J. Rowlands, Tetrahedron 57 (2001) 1865;
(e) M. Shibasaki, Y. Yamamoto (Eds.), Multimetallic Catalysis in Organic
Synthesis, Wiley-VCH, Weinheim, 2004.
[2] (a) A.L. Balch, Homogeneous Catalysis with Metal Phosphine Complexes,
Plenum Press, New York, 1983;
[9] (a) Y. Yamamoto, H. Yamazaki, Organometallics 12 (1993) 933;;
(b) M. Rashidi, J.J. Vittal, R.J. Puddephatt, J. Chem. Soc., Dalton Trans. (1994)
1283;
(c) J.-F. Bérubé, K. Gagnon, D. Fortin, A. Decken, P.D. Harvey, Inorg. Chem. 45
(2006) 2812.
[10] (a) D. Perreault, M. Drouin, A. Michel, P.D. Harvey, Inorg. Chem. 31 (1992)
2740;
(b) P.D. Harvey, Z. Murtaza, Inorg. Chem. 32 (1993) 4721;
(c) R. Provencher, P.D. Harvey, Inorg. Chem. 35 (1996) 2113.
[11] (a) Y. Yamamoto, H. Yamazaki, Inorg. Chem. 25 (1986) 3327;
(b) T. Tanase, T. Fukushima, T. Nomura, Y. Yamamoto, Inorg. Chem. 33 (1994)
32.
[12] M. Jautelat, K. Ley, Synthesis (1970) 593.
[13] (a) For related reactions using TMSCN, see: N. Chatani, T. Hanafusa,
Tetrahedron Lett. 27 (1986) 4201;
(b) R.J. Puddephatt, Chem. Soc. Rev. 12 (1983) 99;
(c) B. Chaudret, B. Delavaux, R. Poilblanc, Coord. Chem. Rev. 86 (1988) 191;
(d) R.J. Puddephatt, L. Manojlovic-Muir, K.W. Muir, Polyhedron 9 (1990) 2767;
(e) G.K. Anderson, Adv. Organomet. Chem. 35 (1993) 1.
[3] (a) For recent examples, see D. Evrard, M. Drouin, Y. Mugnier, P.D. Harvey,
Inorg. Chim. Acta 350 (2003) 442;
(b) R.U. Kirss, D.A. Forsyth, M.A. Plante, J. Organomet. Chem. 688 (2003) 206;
(c) C.B. Pamplin, S.J. Rettig, B.O. Patrick, B.R. James, Inorg. Chem. 42 (2003)
4117;
(d) G. Besenyei, L. Párkányi, G. Szalontai, S. Holly, I. Pápai, G. Keresztury, A.
Nagy, Dalton Trans. (2004) 2041;
(e) G. Szalontai, G. Besenyei, Inorg. Chim. Acta 357 (2004) 4413;
(f) J.H.K. Yip, J. Wu, K.-Y. Wong, K.P. Ho, L.L. Koh, J.J. Vittel, Eur. J. Inorg. Chem.
(2004) 1056;
(g) T. Braun, A. Steffen, V. Schorlemer, B. Neumann, H.-G. Stammler, Dalton
Trans. (2005) 3331;
(b) T. Kusumoto, T. Hiyama, K. Ogata, Tetrahedron Lett. 27 (1986) 4197.
[14] (a) J. Tsuji, T. Nogi, J. Am. Chem. Soc. 88 (1966) 1289;;
(b) E.M. Campi, G.D. Fallon, W.R. Jackson, Y. Nilsson, Aust. J. Chem. 45 (1992)
1167;
(c) T. Joh, K. Doyama, K. Onitsuka, T. Shiohara, S. Takahashi, Organometallics
10 (1991) 2493;
(d) T. Joh, H. Nagata, S. Takahashi, Inorg. Chim. Acta 220 (1994) 45;
(e) K. Fuji, T. Morimoto, K. Tsutsumi, K. Kakiuchi, Chem. Commun. (2005)
3295.
(h) D. Evrard, S. Clément, D. Lucas, B. Hanquet, M. Knorr, C. Strohmann, A.
Decken, Y. Mugnier, P.D. Harvey, Inorg. Chem. 45 (2006) 1305;
(i) D. Evrard, K. Groison, A. Decken, Y. Mugnier, P.D. Harvey, Inorg. Chim. Acta
359 (2006) 2608.
[15] (a) H.W. Sternberg, J.G. Shukys, C.D. Donne, R. Markby, R.A. Friedel, I. Wender,
J. Am. Chem. Soc. 81 (1959) 2339;
(b) O.S. Mills, G. Robinson, Inorg. Chim. Acta 1 (1967) 61.
[16] (a) R.J. Puddephatt, M.A. Thomson, Inorg. Chem. 21 (1982) 725;
(b) M.J. Irwin, G. Jia, J.J. Vittal, R.J. Puddephatt, Organometallics 15 (1996)
5321.
[17] W.D. Jones, W.P. Kosar, Organometallics 5 (1986) 1823.
[18] R.A. Stockland, G.K. Anderson, N.P. Rath, J. Am. Chem. Soc. 121 (1999)
7945.
[4] N. Tsukada, O. Tamura, Y. Inoue, Organometallics 21 (2002) 2521.
[5] (a) N. Tsukada, T. Mitsuboshi, H. Setoguchi, Y. Inoue, J. Am. Chem. Soc. 125
(2003) 12102;
(b) N. Tsukada, K. Murata, Y. Inoue, Tetrahedron Lett. 46 (2005) 7515;
(c) N. Tsukada, H. Setoguchi, T. Mitsuboshi, Y. Inoue, Chem. Lett. 35 (2006)
1164.
[6] (a) N.D. Jones, B.R. James, Adv. Synth. Catal. 344 (2002) 1126;
(b) S.J.L. Foo, N.D. Jones, B.O. Patrick, B.R. James, Chem. Commun. (2003) 988;