Intramolecular insertion of acetylene into a palladium-carbon bond in (iminoacyl)palladium complexes

Article abstract of DOI:10.1021/om9804125

An (iminoacyl)palladium complex (3a) prepared from the reaction of methylpalladium complex 1a with o-((trimethylsilyl)ethynyl)phenyl isocyanide (2) undergoes an intramolecular insertion of acetylene at 45 °C in chloroform to give the ((E)-indolidenemethyl)-palladium complex 4a quantitatively. The treatment of 3 with AgPF₆ followed by Et₄NCl at room temperature causes smooth insertion of acetylene, giving the ((Z)-indolidenemethyl)palladium complex 5 as a main product.

Full text of DOI:10.1021/om9804125

Organometallics 1998, 17, 4335-4337
4335
In tr a m olecu la r In ser tion of Acetylen e in to a
P a lla d iu m -Ca r bon Bon d in (Im in oa cyl)p a lla d iu m
Com p lexes
Kiyotaka Onitsuka, Masaki Segawa, and Shigetoshi Takahashi*
The Institute of Scientific and Industrial Research, Osaka University,
Ibaraki, Osaka 567-0047, J apan
Received May 22, 1998
Summary: An (iminoacyl)palladium complex (3a ) pre-
pared from the reaction of methylpalladium complex 1a
with o-((trimethylsilyl)ethynyl)phenyl isocyanide (2) un-
dergoes an intramolecular insertion of acetylene at 45
°C in chloroform to give the ((E)-indolidenemethyl)-
palladium complex 4a quantitatively. The treatment of
3 with AgPF6 followed by Et4NCl at room temperature
causes smooth insertion of acetylene, giving the ((Z)-
indolidenemethyl)palladium complex 5 as a main prod-
uct.
intramolecular insertion of acetylene into a palladium-
carbon bond of iminoacyl complexes which are produced
by the reaction of organopalladium complexes with
o-ethynylphenyl isocyanide.
The addition of o-((trimethylsilyl)ethynyl)phenyl iso-
cyanide (2) to a dichloromethane solution of 1a at room-
temperature results in the quantitative formation of an
iminoacyl complex (3a ), which was isolated in 83%
yield.5 The IR spectrum of 3a showed absorptions at
The alternative copolymerization of olefins and carbon
monoxide, which proceeds through alternating insertion
of olefins and carbon monoxide into metal-carbon
bonds, is a promising new type of polymerization
catalyzed by transition-metal complexes.1 Since iso-
cyanide is isoelectronic with carbon monoxide and has
a similar reactivity toward organometallic complexes,
i.e., facile insertion into metal-carbon bonds,2 copolym-
erization of isocyanide with unsaturated hydrocarbons
giving polyimines may be possible via transition-metal
catalysts. One of the most remarkable reactivity dif-
ferences of isocyanide compared to carbon monoxide is
the ability of the former to undergo multiple and
successive insertions, leading to the formation of iso-
cyanide homopolymers.3 Therefore, a key step in the
copolymerization of isocyanide with unsaturated hydro-
carbons is insertion into metal-carbon bonds of imi-
noacyl complexes, which are produced by the initial
insertion of isocyanides. However, there are few reports
on the reactions of iminoacylmetal complexes with
unsaturated hydrocarbons.4 We present herein a novel
2153 cm-1 due to ν(CtC) and 1557 cm-1 due to ν(Cd
Ν). In the 13C NMR of 3a a signal assignable to an
imino carbon was observed at δ 194.1 and acetylene
resonances appeared at δ 98.6 and 103.4. These data
strongly suggest that 3a was produced by the insertion
of the isocyano group of 2 into the Pd-C bond of 1a .
The structure of 3a was unequivocally identified by an
X-ray diffraction study, as shown in Figure 1.6 Treat-
ment of the (phenylethynyl)palladium complex 1b with
2 also produced an insertion product (3b), which was
isolated in 80% yield.
(1) For recent reviews and leading references, see: (a) Sen, A. Acc.
Chem. Res. 1993, 26, 303. (b) Drent, E.; Budzelaar, P. H. M. Chem.
Rev. 1996, 96, 663. (c) Drent, E.; van Broekhoven, J . A. M.; Budzelaar,
P. H. M. Recl. Trav. Chim. Pays-Bas 1996, 115, 263. (d) J iang, Z.; Sen,
A. J . Am. Chem. Soc. 1995, 117, 4455. (e) Markis, B. A.: Kruis, D.;
Rietveld, M. H. P.; Verkerk, K. A.; Boersma, J .; Koojiman, M.; Lakin,
M. T.; Spek, A. L.; van Koten, G. J . Am. Chem. Soc. 1995, 117, 5263.
(f) Sperrle, M.; Consiglio, G. J . Am. Chem. Soc. 1995, 117, 12130. (g)
Rix, F. C.; Brookhart, M.; White, P. S. J . Am. Chem. Soc. 1996, 118,
4746. (h) Brookhart, M.; Wagner, M. I. J . Am. Chem. Soc. 1996, 118,
7219. (i) Ru¨lke, R. E.; Kaasjager, V. E.; Kliphuis, D.; Elsevier, C. J .;
van Leeuwen, P. W. N. M.; Vrieze, K.; Goubitz, K. Organometallics
1996, 15, 668. (j) Nozaki, K.; Sato, N.; Tonomura, Y.; Yasutomi, M.;
Takaya, H.; Hiyama, T.; Matsubara, T.; Koga, N. J . Am. Chem. Soc.
1997, 119, 12779. (k) Safir, A. L.; Novak, B. M. J . Am. Chem. Soc.
1998, 120, 643.
(2) For reviews, see: (a) Yamamoto, Y.; Yamazaki, H. Coord. Chem.
Rev. 1972, 8, 225. (b) Treichel. P. M. Adv. Organomet. Chem. 1973,
11, 21. (c) Shingleton, E.; Oosthuizen, H. E. Adv. Organomet. Chem.
1983, 22, 209.
(3) For reviews, see: (a) Millich, F. Chem. Rev. 1972, 72, 101. (b)
Millich, F. Adv. Polym. Sci. 1975, 19, 117. (c) Drenth, W.; Nolte, R. J .
M. Acc. Chem. Res. 1979, 12, 30. (d) Nolte, R. J . M. Chem. Soc. Rev.
1994, 11.
Heating a chloroform solution of 3a at 45 °C for 19 h
caused the high-yield intramolecular insertion of acety-
(4) Delis, J . G. P.; Aubel, P. G.; Vrieze, K.; van Leeuwen, P. W. N.
M.; Veldman, N.; Spek, A. L. Organometallics 1997, 16, 4150.
(5) The preparation of 3a is as follows. Complex 1a (590 mg, 1.5
mmol) was treated with 2 (299 mg, 1.5 mmol) in 30 mL of dichlo-
romethane for 2 h at room temperature. After it was concentrated
under reduced pressure, the residue was dissolved in about 20 mL of
hexane and cooled to -30 °C to give pale yellow crystals of 3a (742
mg, 83%). 3a : 1H NMR (CDCl3) δ 0.24 (s, 9H), 1.06 (dt, J ) 17.1, 7.7
Hz, 18H), 1.75-1.81 (m, 12H), 2.52 (t, J ) 1.1 Hz, 3H), 7.04 (dt, J )
7.7, 1.4 Hz, 1H), 7.23 (dt, J ) 7.7, 1.4 Hz, 1H), 7.42 (dd, J ) 7.7, 1.4
Hz, 1H), 7.97 (d, J ) 7.7 Hz, 2H); 13C NMR (CDCl3) δ 0.1, 8.3, 15.4 (vt,
N ) 13 Hz), 35.8 (t, J ) 8 Hz), 98.6, 103.4, 116.7, 117.7, 124.0, 128.5,
132.8, 152.5 (t, J ) 2 Hz), 194.1 (t, J ) 5 Hz); 31P NMR (CDCl3) δ
13.9; IR (KBr) 2153 (νC≡C), 1557 (νCdN) cm-1. Anal. Calcd for C25H46
-
ClNP2PdSi: C, 50.68; H, 7.82; N, 2.36. Found: C, 50.74; H, 8.02; N,
2.27.
S0276-7333(98)00412-9 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 09/01/1998

4336 Organometallics, Vol. 17, No. 20, 1998
Communications
F igu r e 1. ORTEP drawing of 3a . Hydrogen atoms and
the solvent molecule are omitted for clarity. Bond distances
and angles are included in the Supporting Information.
F igu r e 2. ORTEP drawing of 4a . Hydrogen atoms are
omitted for clarity. Bond distances and angles are included
in the Supporting Information.
lene to give a new complex (4a ) possessing an indole
skeleton. Complex 4a was isolated by alumina column
chromatography followed by recrystallization from dichlo-
romethane-hexane in 61% yield.7 Acetylene insertion
was confirmed by the disappearance of characteristic
acetylene peaks in the IR and 13C NMR spectra of 4a ,
as well as by an X-ray analysis.8 The ORTEP diagram
of 4a is shown in Figure 2. The molecule of 4a sits on
a crystallographic mirror plane defined by Pd(1), Cl(1),
should be noted that the addition of 0.3 equiv of PEt3
inhibited the reaction from 3a to 4a , suggesting that
the insertion of acetylene in 3 proceeds via initial
dissociation of PEt3 to give a vacant site for coordination
of the acetylene.10b,11 (Iminoacyl)palladium complexes
prepared from the reaction of methylpalladium complex
1a with p-tolyl or p-nitrophenyl isocyanide were treated
with unsaturated hydrocarbons such as phenylacetylene
and norbornene under various conditions, but no inter-
molecular insertion products were obtained. This result
suggests that the insertion of acetylene into a Pd-C
bond in (iminoacyl)palladium complexes is only effective
when occurring intramolecularly.10
It has already been reported that cationic palladium
complexes having a weakly coordinated ligand show a
higher reactivity toward insertion of olefins and acety-
(7) The preparation of 4a is as follows. Complex 3a (300 mg, 0.506
mmol) was dissolved in 10 mL of chloroform and warmed to 45 °C for
19 h. The solvent was removed under reduced pressure, and the residue
was purified by column chromatography on alumina using ethyl acetate
as an eluent. A fraction containing the yellow band was collected and
concentrated under reduced pressure. Recrystallization from dichlo-
romethane-hexane gave a yellow powder of 4a (183 mg, 61%). 4a : 1H
NMR (CDCl3) δ 0.65 (s, 9H), 1.07 (dt, J ) 17.1, 7.6 Hz, 18H), 1.48-
1.56 (m, 6H), 1.67-1.75 (m, 6H), 2.56 (s, 3H), 7.16 (dt, J ) 7.4, 1.1 Hz,
1H), 7.32 (dt, J ) 7.4, 1.1 Hz, 1H), 7.39 (d, J ) 7.4 Hz, 1H), 9.39 (d, J
) 7.4 Hz, 2H); 13C NMR (CDCl3) δ 5.1, 8.1, 15.5 (vt, N ) 13 Hz), 20.8,
118.3, 121.9 (t, J ) 2 Hz), 123.4, 127.6, 134.3, 150.3 (t, J ) 3 Hz),
Si(1), and an indolidenemethyl group. The most strik-
ing structural feature of 4a is that the Pd moiety and
the imino group are linked to the olefin, which is
generated by the trans insertion of acetylene.9
When complex 3b was treated under similar condi-
tions, the insertion of acetylene occurred with 12%
conversion to give 4b along with another complex (5b)
in a molar ratio of 4.5:1. Longer reaction time and
higher temperature caused decomposition of 3b to Pd-
(PEt3)2Cl2 and unidentified organic compounds. It
155.3, 161.6, 208.5; 31P NMR (CDCl3) δ 5.5; IR (KBr) 1514 (νCdN) cm-1
.
Anal. Calcd for C25H46ClNP2PdSi: C, 50.68; H, 7.82; N, 2.36. Found:
C, 51.05; H, 7.50; N, 2.39.
(8) Crystallographic data for 4a : fw ) 592.54, orthorhombic, space
group Pnma (No. 62), a ) 15.838(4) Å, b ) 12.923(3) Å, c ) 14.358(3)
Å, V ) 2938.8(10) Å3, Z ) 4, dcalcd ) 1.339 g cm-3, -75 °C, ω-2θ scan,
6° < 2θ < 55°, µ(Mo KR) ) 8.85 cm-1, R (Rw) ) 0.059 (0.093) for 163
parameters against 2152 reflections with I > 3.0σ(I) out of 3790 unique
reflections by full-matrix least-squares method, GOF ) 1.25.
(9) The stereochemistry is cis in the usual acetylene insertion: (a)
Appleton, T. G.; Clark, H. C.; Puddephatt, R. J . Inorg. Chem. 1972,
11, 2074. (b) Tohda, Y.; Sonogashira, K.; Hagihara, N. J . Chem. Soc.,
Chem. Commun. 1975, 54. (c) Tohda, Y.; Sonogashira, K.; Hagihara,
N. J . Organomet. Chem. 1976, 110, C53.
(6) Crystallographic data for 3a ‚CH2Cl2: fw ) 677.47, monoclinic,
space group P21/n (No. 14), a ) 15.705(3) Å, b ) 11.122(3) Å, c )
20.765(3) Å, â ) 108.67(1)°, V ) 3436(1) Å3, Z ) 4, dcalcd ) 1.309 g
cm-3, -75 °C, ω-2θ scan, 6° < 2θ < 55°, µ(Mo KR) ) 9.16 cm-1, R
(Rw) ) 0.045 (0.062) for 307 parameters against 5519 reflections with
I > 3.0 σ(I) out of 8297 unique reflections by full-matrix least-squares
method, GOF ) 1.17.
(10) (a) Murray, T. F.; Norton, J . R. J . Am. Chem. Soc. 1979, 101,
4107. (b) Samsel, E. G.; Norton, J . R. J . Am. Chem. Soc. 1984, 106,
5505.
(11) Brumbaugh, J . S.; Whittle, R. R.; Parvez, M.; Sen, A. Organo-
metallics 1990, 9, 1735.
(12) Clark, H. C.; Milne, C. R. C.; Wong, C. S. J . Organomet. Chem.
1977, 136, 265.

Communications
Organometallics, Vol. 17, No. 20, 1998 4337
lenes into their Pd-C bonds than neutral analogues.1,11,12
We converted 3a into a cationic complex by treatment
with AgPF6 in the expectation that acetylene insertion
would be facilitated. The resulting cationic complex,
however, proved too unstable for characterization. The
addition of Et4NCl to the reaction mixture after 30 min
gave neutral products that could be characterized. The
31P NMR spectrum of the reaction mixture indicated the
formation of 4a and a new complex (5a ) in a 1:7 molar
ratio. Isolation by column chromatography on alumina
followed by recrystallization from dichloromethane-
hexane afforded a pure sample of 5a in 66% yield.13 The
molecular structure of 5a is shown in Figure 3.14 The
molecule of 5a sits on a crystallographic mirror plane
F igu r e 3. ORTEP drawing of 5a . Hydrogen atoms are
omitted for clarity. Bond distances and angles are included
in the Supporting Information.
defined by Pd(1), Cl(1), Si(1), and an indolidenemethyl
group. Although complex 5a is also derived from the
intramolecular acetylene insertion of 3a , it can be that,
in contrast to 4a , the stereochemistry in the acetylene
insertion is cis.9 Similar treatment of 3b with AgPF6,
followed by Et4NCl, also gave 4b and 5b in a 1:8 molar
ratio. No isomerization of 5a into 4a was observed after
heating a chloroform solution of 5a at 45 °C overnight,
suggesting that 5a is not an intermediate in the
formation of 4a from 3a .
The reaction presented herein may be regarded as an
elementary process in the alternative copolymerization
of isocyanide with acetylene. We are trying to extend
the present finding into a cyclopolymerization system
to give poly(indolidenemethyl)s.
(13) The preparation of 5a is as follows. To a solution of complex
3a (660 mg, 1.11 mmol) in 30 mL of acetone was added silver
hexafluorophosphate (338 mg, 1.34 mmol). After the mixture was
stirred for 30 min at room temperature, the precipitates were filtered
off. The filtrate was treated with tetraethylammonium chloride (740
mg, 4.47 mmol) for 30 min at room temperature. About 10 mL of water
was added to the reaction mixture, followed by extraction with
dichloromethane. After the extract was dried over sodium sulfate, the
solvent was removed under reduced pressure and the residue was
purified by alumina column chromatography with dichloromethane.
Concentration of the yellow fraction followed by recrystallization from
dichloromethane-hexane gave a yellow powder of 5a (613 mg, 66%).
5a : 1H NMR (CDCl3) δ 0.63 (br, 9H), 1.07 (dt, J ) 17.1, 7.6 Hz, 18H),
1.48-1.56 (m, 6H), 1.67-1.75 (m, 6H), 2.56 (s, 3H), 7.16 (dt, J ) 7.4,
1.1 Hz, 1H), 7.32 (dt, J ) 7.4, 1.1 Hz, 1H), 7.39 (d, J ) 7.4 Hz, 1H),
9.39 (d, J ) 7.4 Hz, 2H); 13C NMR (CDCl3) δ -0.1, 8.1, 15.8 (vt, N )
13 Hz), 19.6, 118.8, 123.3, 123.4, 126.0, 127.4, 150.1, 155.1, 168.2, 208.7;
31P NMR (CDCl3) δ 4.0. Anal. Calcd for C25H46ClNP2PdSi: C, 50.68;
H, 7.82; N, 2.36. Found: C, 50.92; H, 7.53; N, 2.15.
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research on Priority Areas,
“New Polymers and Their Nano-Organized Systems”
(No. 277/08246103), from the Ministry of Education,
Science, Sports and Culture. We thank The Materiel
Analysis Center, ISIR, Osaka University, for the sup-
port of spectroscopic measurements, X-ray crystal-
lography, and microanalyses.
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental details and full characterization data for all new
complexes and tables of X-ray crystallographic data for
complexes 3a , 4a , and 5a (20 pages). Ordering information
is given on any current masthead page.
(14) Crystallographic data for 5a : fw ) 592.54, hexagonal, space
group P63/m (No. 176), a ) 20.811(4) Å, c ) 12.970(3) Å, V ) 4864(2)
Å3, Z ) 6, dcalcd ) 1.213 g cm-3, -75 °C, ω-2θ scan, 6° < 2θ < 55°,
µ(Mo KR) ) 8.02 cm-1, R (Rw) ) 0.040 (0.060) for 163 parameters
against 2252 reflections with I > 3.0σ(I) out of 3890 unique reflections
by full-matrix least-squares method, GOF ) 1.13.
OM9804125