Intermolecular alkynyl ligand transfer in palladium(II) and platinum(II) complexes with -C≡CCOOR and -C≡CPh ligands. Relative stability of the alkynyl complexes and conproportionation of dialkynyl and diiodo complexes of these metals

Article abstract of DOI:10.1021/om9907829

An equimolar reaction of trans-Pd(C≡CCOOMe)₂(PEt₃)₂ with trans-PdI₂(PEt₃)₂ catalyzed by CuI causes conproportionation of the complexes at room temperature, producing trans-PdI(C≡COOMe)(PEt₃)₂ in 88% yield, while the reaction without CuI catalyst gives the monoalkynylpalladium complex in approximately 2% yield after a prolonged period. Similar reactions of trans-Pd(C≡CPh)₂(PEt₃)₂ with trans-PdI₂(PEt₃)₂ with and without CuI catalyst give the alkynyl ligand transfer reaction product trans-PdI(C≡CPh)(PEt₃)₂ in 95% and 33% yields, respectively. CuI-catalyzed conproportionation of trans-Pt(C≡CPh)₂(PEt₃)₂ and trans-PtI₂(PEt₃)₂ occurs more slowly than the corresponding reactions of the Pd complexes; trans-Pt(C≡CCOOMe)₂(PEt₃)₂ does not react with the diiodoplatinum complex even in the presence of CuI. The alkynyl ligand transfer reaction from trans-Pd(C≡CCOOMe)₂(PEt₃)₂ to trans-PtI₂(PEt₃)₂ occurs in the presence of CuI catalyst, affording a mixture of several organopalladium and -platinum complexes. The main Pd complex in the reaction mixture is trans-PdI(C≡CCOOMe)(PEt₃)₂, while the Pt-containing product is composed of trans-Pt (C≡CCOOMe)₂(PEt₃)₂, trans-PtI(C≡CCOOMe)(PEt₃)₂, and trans-PtI₂(PEt₃)₂ in an approximate 1:2:1 molar ratio. Mixing of trans-Pd(C≡CCOOMe)₂(PEt₃)₂, trans-PdI₂(PEt₃)₂, and trans-PtI₂(PEt₃)₂ results in the formation of trans-PdI(C≡CCOOMe)(PEt₃)₂ in a high yield, while the alkynyl ligand transfer from Pd to Pt complexes is almost negligible. trans-PtI₂-(PEt₃)₂ catalyzes the alkynyl ligand transfer between the dialkynyl- and diiodopalladium-(II) complexes and remains unchanged in the reaction mixture.

Full text of DOI:10.1021/om9907829

458
Organometallics 2000, 19, 458-468
In ter m olecu la r Alk yn yl Liga n d Tr a n sfer in P a lla d iu m (II)
a n d P la tin u m (II) Com p lexes w ith -CtCCOOR a n d
-CtCP h Liga n d s. Rela tive Sta bility of th e Alk yn yl
Com p lexes a n d Con p r op or tion a tion of Dia lk yn yl a n d
Diiod o Com p lexes of Th ese Meta ls
Kohtaro Osakada,* Makiko Hamada, and Takakazu Yamamoto
Research Laboratory of Resources Utilization, Tokyo Institute of Technology,
4259 Nagatsuta, Midori-ku, Yokohama 226-8503, J apan
Received October 4, 1999
An equimolar reaction of trans-Pd(CtCCOOMe)2(PEt3)2 with trans-PdI2(PEt3)2 catalyzed
by CuI causes conproportionation of the complexes at room temperature, producing trans-
PdI(CtCOOMe)(PEt3)2 in 88% yield, while the reaction without CuI catalyst gives the
monoalkynylpalladium complex in approximately 2% yield after a prolonged period. Similar
reactions of trans-Pd(CtCPh)2(PEt3)2 with trans-PdI2(PEt3)2 with and without CuI catalyst
give the alkynyl ligand transfer reaction product trans-PdI(CtCPh)(PEt3)2 in 95% and 33%
yields, respectively. CuI-catalyzed conproportionation of trans-Pt(CtCPh)2(PEt3)2 and trans-
PtI2(PEt3)2 occurs more slowly than the corresponding reactions of the Pd complexes; trans-
Pt(CtCCOOMe)2(PEt3)2 does not react with the diiodoplatinum complex even in the presence
of CuI. The alkynyl ligand transfer reaction from trans-Pd(CtCCOOMe)2(PEt3)2 to trans-
PtI2(PEt3)2 occurs in the presence of CuI catalyst, affording a mixture of several organo-
palladium and -platinum complexes. The main Pd complex in the reaction mixture is trans-
PdI(CtCCOOMe)(PEt3)2, while the Pt-containing product is composed of trans-Pt
(CtCCOOMe)2(PEt3)2, trans-PtI(CtCCOOMe)(PEt3)2, and trans-PtI2(PEt3)2 in an ap-
proximate 1:2:1 molar ratio. Mixing of trans-Pd(CtCCOOMe)2(PEt3)2, trans-PdI2(PEt3)2, and
trans-PtI2(PEt3)2 results in the formation of trans-PdI(CtCCOOMe)(PEt3)2 in a high yield,
while the alkynyl ligand transfer from Pd to Pt complexes is almost negligible. trans-PtI2-
(PEt3)2 catalyzes the alkynyl ligand transfer between the dialkynyl- and diiodopalladium-
(II) complexes and remains unchanged in the reaction mixture.
Ch a r t 1
In tr od u ction
Alkynyl complexes of group 10 metals have been
studied extensively and attracted continuous attention
from the viewpoints of synthetic organic chemistry and
material science. Cross-coupling of aryl and vinyl ha-
lides with a terminal alkyne catalyzed by a Pd complex
in the presence of CuI and amine to give aryl alkyne
and enyne, respectively, was first reported in 1975 and
is proposed to involve aryl(alkynyl)- and alkenyl(alkyn-
yl)palladium complexes (Chart 1) as the key intermedi-
ates.1,2 The reaction provides an important method for
forming C(sp)-C(sp2) bonds under mild conditions and
was applied to the preparation of various π-conjugated
polymers composed of alternating arylene and ethyn-
ylene units.3 These polymers exhibit unique luminescent
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In Organometallics in Synthesis. A Manual; Schlosser, M., Ed.; J ohn
Wiley: Chichester, 1994; pp 300-302, and references therein. (c) Heck,
R. F. Palladium Reagents in Organic Synthesis; Academic Press:
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Chem. J ap. 1993, 51, 1053 (in J apanese).
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1975, 4467. (b) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagi-
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Org. Chem. 1983, 48, 5135. (d) Havens, S. J .; Hergenrother, P. M. J .
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Chem. Soc. 1988, 110, 631. (f) Mascarenas, J . L.; Sarandeses, L. A.;
Castedo, L.; Mourino, A. Tetrahedron 1991, 47, 3485. (g) Curtin, M.
L.; Okamura, W. H. J . Am. Chem. Soc. 1991, 113, 6958.
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10.1021/om9907829 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 01/25/2000

Intermolecular Alkynyl Ligand Transfer
Organometallics, Vol. 19, No. 4, 2000 459
with more significant back-donation.11 This implies that
chemical properties alter depending on the substituents
of the alkynyl ligands. Palladium alkoxycarbonylethynyl
complexes, trans-Pd(CtCCOOR)2(PEt3)2 (R ) Me, Et,
t-Bu), were previously prepared from the reaction of
trans-PdCl2(PEt3)2 with Cu(CtCCOOR)(PPh3)n,12 but
their properties have not been investigated in detail.
In this paper we report the structure and properties
of palladium and platinum complexes with -CtCCOOR
ligands and compare them with conventional phenyl-
ethynyl complexes. The study is mainly focused on the
alkynyl ligand transfer among dialkynyl complexes and
diiodo complexes of Pd and Pt, which leads to conpro-
portionation of the Pd complexes or ligand transfer from
Pd to Pt depending on the kind of alkynyl group and
the reaction conditions.
Ch a r t 2
and nonlinear optical properties. The intermolecular
transfer of alkynyl ligand between transition metals
plays an important role in the above-mentioned cross-
coupling reactions. Cu(CtCR)L (L ) amine) generated
in situ from a mixture of CuI, terminal alkyne, and
amine undergoes alkynyl ligand transfer to PdAr(X)-
(L′)n (X ) halide, L′ ) phosphine), producing PdAr(Ct
CR)(L′)n, which is responsible for the reductive elimi-
nation of the coupling product. Recently, we reported
the transfer of phenylethynyl ligands between aryl-
palladium and arylplatinum complexes with or without
CuI catalyst.4 CuI promotes the reaction by transporting
the alkynyl ligand between group 10 metals.
A common method for preparing dialkynyl complexes
of Pd and Pt is the reaction of dihalo complexes of these
metals with a terminal alkyne in the presence of CuI
and amine.5,6 The reaction was applied to the synthesis
of not only dialkynylpalladium and -platinum complexes
but also various stable polyyne polymers containing Pd
and Pt which have rigid rodlike structures owing to the
linear -CtC-M-CtC- bond (Chart 2)7-9 and are
regarded as materials with potential optical and liquid
crystalline properties.10 Recently, Louwen et al. sug-
gested that the metal-carbon bonds of di(ethynyl) and
di(phenylethynyl) complexes of Pd and Pt are stabilized
to a small degree by back-donation of d orbitals of the
metal center to π* orbitals of the alkynyl ligand and that
an alkynyl ligand with electron-withdrawing groups
such as CN and COOR may form a coordination bond
Resu lts
P r ep a r a tion a n d Ch a r a cter iza tion of P d a n d P t
Com p lexes w ith -CtCCOOR Liga n d s. Palladium
complexes trans-Pd(CtCCOOR)2(PEt3)2 (1a , R ) Me;
1b, R ) Et), previously obtained by transmetalation of
[Cu(CtCCOOR)(PPh3)m]n and PdCl2(PEt3)2, are pre-
pared more conveniently from the 1:2 reaction of trans-
PdCl2(PEt3)2 with HCtCCOOR in the presence of CuI
catalyst and triethylamine, as shown in eq 1. The NMR
(1H, 31P{1H}, and 13C{1H}) spectra of the complexes
contain the signals of the alkynyl and PEt3 ligands at
expected positions and the relative peak intensities. The
trans coordination of 1a is confirmed from the 13C{1H}
NMR spectrum containing a symmetrical triplet at δ
116.2 (J (PC)) 17 Hz) due to the alkynyl carbon attached
to Pd. An equimolar reaction of trans-PdI2(PEt3)2 with
HCtCCOOMe catalyzed by CuI produces trans-PdI(Ct
CCOOMe)(PEt3)2 (2a ) (eq 2). Although 2a is obtained
(4) (a) Osakada, K.; Sakata, R.; Yamamoto, T. J . Chem. Soc., Dalton
Trans. 1997, 1265. (b) Osakada, K.; Sakata, R.; Yamamoto, T.
Organometallics 1997, 16, 5354.
(5) (a) Sonogashira, K.; Yatake, T.; Tohda, Y.; Takahashi, S.;
Hagihara, N. J . Chem. Soc., Chem. Commun. 1977, 291. (b) Cross, R.
J .: Davidson, M. F. J . Chem. Soc., Dalton Trans. 1986, 1987. (c)
Ogawa, H.; J oh, T.; Takahashi, S.; Sonogashira, K. J . Chem. Soc.,
Chem. Commun. 1988, 561. (d) Onitsuka, K.; Ogawa, H.; J oh, T.;
Takahashi, S.; Yamamoto, Y.; Yamazaki, H. J . Chem. Soc., Dalton
Trans. 1991, 1531.
(6) Similar transmetalation catalyzed by HgCl2: (a) Cross, R. J .;
Gemmill, J . J . Chem. Soc., Dalton Trans. 1984, 199 and 205. (b) Cross,
R. J .; Davidson, M. F. Inorg. Chim. Acta 1985, 97, L35. (c) Anderson,
G. K.; Cross, R. J . Chem. Soc. Rev. 1980, 9, 185.
(7) (a) J ohnson, B. F. G.; Kakkar, A. K.; Khan, M. S.; Lewis, J .; Dray,
A. E.; Wittmann, F.; Friend, R. H. J . Mater. Chem. 1991, 1, 485. (b)
Khan, M. S.; Kakker, A. K.; Long, N. J .; Lewis, J .; Raithby, P.; Nguyen,
P.; Marder, B.; Wittmann, F.; Friend, R. H. J . Mater. Chem. 1994, 4,
1227. (c) Markwell, R. D.; Butler, I. S.; Kakkar, A. K.; Khan, M. S.
Al-Zakwani, Z. H.; Lewis, J . Organometallics 1996, 15, 2331.
(8) Irwin, M. J .; J ia, G.; Vittal, J . J .; Puddephatt, R. J . Organo-
metallics 1996, 15, 5321.
(9) (a) Hagihara, N.; Sonogashira, K.; Takahashi, S. Adv. Polym.
Sci. 1981, 41, 149. (b) Kotani, S.; Shiina, K.; Sonogashira, K. Appl.
Organomet. Chem. 1991, 5, 417. (c) Sonogashira, K.; Fujikura, Y.;
Yatake, T.; Toyoshima, N.; Takahashi, S.; Hagihara, N. J . Organomet.
Chem. 1978, 145, 101. (d) Fujikura, Y.; Sonogashira, K.; Hagihara, N.
Chem. Lett. 1975, 1067. (e) Sonogashiram, K.; Kataoka, S.; Takahashi,
S.; Hagihara, N. J . Organomet. Chem. 1978, 160, 319. (f) Takahashi,
S.; Murata, E.; Sonogashira, K.; Hagihara, N. J . Polym. Sci., Polym.
Chem. Ed. 1980, 18, 661. (g) Ohshiro, N.; Takei, F.; Onituska, K.;
Takahashi, S. Chem. Lett. 1996, 871. (h) Ohshiro, N.; Takei, F.;
Onituska, K.; Takahashi, S. J . Organomet. Chem. 1998, 569, 195.
(10) (a) Takahashi, S.; Takei, Y.; Morimoto, H.; Sonogashira, K. J .
Chem. Soc., Chem. Commun. 1984, 3. (b) Takahashi, S.; Takei, Y.;
Morimoto, H.; Sonogashira, K.; Hagihara, N. Mol. Cryst. Liq. Cryst.
1982, 82, 139.
as a mixture containing much smaller amounts of 1a
and trans-PtI2(PEt3)2 and cannot be obtained in pure
form due to its instability in NEt3 solution at a high
concentration, the 31P{1H} NMR resonance at a different
position from the starting complexes (δ 14.6) and the
1
peak area ratio of the H NMR signals of alkynyl and
(11) Louwen, J . N.; Hengelmolen, R.; Grove, D. M.; Oskam, A.;
DeKock, R. L. Organometallics 1984, 3, 908.
(12) Osakada, K.; Takizawa, T.; Yamamoto, T. Organometallics
1995, 14, 3531. cis-Pt(COOMe)(CtCCOOMe)(PPh3)2 had been pre-
pared from the photoassisted C-C bond cleavage of Pt(MeOOCCt
CCOOMe)(PPh3)2. See: Kubota, M.; Sly, W. G.; Santarsiero, B. D.;
Clifton, M. S.; Kuo, L. Organometallics 1987, 6, 1257.

460 Organometallics, Vol. 19, No. 4, 2000
Osakada et al.
F igu r e 1. ORTEP drawing of 1a with 30% ellipsoidal
levels. Selected bond distances (Å) and angles (deg): Pd-
P1 2.3134(9), Pd-C1 1.999(3), C1-C2 1.193(5), C2-C3
1.445(5), C3-O1 1.190(4), C3-O2 1.326(4), O2-C4
1.445(5), P-Pd-C1 90.1(1) and 89.9(1), Pd-C1-C2
178.9(4), C1-C2-C3 178.3(4).
F igu r e 3. ORTEP drawing of 4b with 30% ellipsoidal
levels. Selected bond distances (Å) and angles (deg): Pt-
P1 2.296(1), Pt-C1 1.994(4), C1-C2 1.197(5), C2-C3
1.432(5), P-Pt-C1 93.2(1) and 86.8(1), Pt-C1-C2
176.8(4), C1-C2-C3 178.7(5).
Ta ble 1. 13C{1H} NMR P ea k P osition s of Alk yn e
a n d Alk yn yl Com p lexesa
δ
compound
M-Ct or H-Ct tC-Ph or tC-COOR
H-CtC-COOMe
74.6
74.8
1a b
4a b
116.2 (41.8)
111.9 (37.3)
77.8
111.5 (33.7)
108.4 (30.6)
104.4 (29.6)
103.2 (28.2)
83.9
115.8 (31.9)
110.0 (26.1)
H-CtC-Ph
F igu r e 2. ORTEP drawing of 1c with 30% ellipsoidal
levels. Selected bond distances (Å) and angles (deg): Pd-
P1 2.300(2), Pd-C1 2.069(7), C1-C2 1.003(8), C2-C3
1.53(1), P-Pd-C1 92.9(2) and 87.1(2), Pd-C1-C2
176.9(9), C1-C2-C3 175(1).
1cb
4cb
a
b
100 MHz in CD2Cl2 at 25 °C. Low magnetic field shift
referenced to the corresponding peak of the alkyne (ppm) is shown
in parentheses.
phosphine ligands indicate the proposed structure.
Figures 1 and 2 depict the molecular structures of 1a
and trans-Pd(CtCPh)2(PEt3)2 (1c), respectively, the
latter of which was prepared previously12 and has an
isomorphous crystal lattice to its platinum analogue,
trans-Pt(CtCPh)2(PEt3)2 (4c).13 Both molecules have a
crystallographic C2 symmetry around the metal centers
and adopt trans structures in a square-planar coordina-
tion.
than the Pd-CtCPh bond of 1c or higher acidity of
H-CtCCOOMe than H-CtCPh.
Platinum complexes with alkoxycarbonylethynyl
ligands, trans-Pt(CtCCOOMe)2(PEt3)2 (4a ) and trans-
Pt(CtCCOOEt)2(PEt3)2 (4b), are prepared analogously
to 1a and 1b, as shown in eq 4 and characterized by
The reaction of 1c with HCtCCOOMe in a 1:2 molar
ratio for 5 days at room temperature produces phenyl-
acetylene and gives 1a quantitatively (eq 3). The
NMR spectroscopy and X-ray crystallography (Figure
3). The 31P{1H} NMR signals contain a single resonance
flanked by satellite signals. The J (PtP) values (2277 and
2285 Hz) are consistent with the structures having two
PEt3 ligands at mutual trans positions. The 13C{1H}
NMR signals of the alkynyl carbons also exhibit cou-
pling with 195Pt and 31P nuclei. The J (PtC) values of R-
and â-carbons (4a , 976 and 275 Hz; 4b, 989 and 278
Hz) are somewhat larger than those of the phenyleth-
ynyl coordinated analogue 4c (961 and 269 Hz).14 Table
1 summarizes 13C{1H} NMR signal positions of the
alkynyl carbons of the complexes. R-Carbon signals of
mixture after reaction for a shorter period exhibits the
31P{1H} NMR signal of not only 1a but also a single
resonance at δ 18.4, which can be assigned to trans-Pt-
(CtCCPh)(CtCCOOMe)(PEt3)2 (3) based on the 1H
NMR signals of the reaction mixture. On the other hand,
the reaction of 1a with HCtCPh does not cause the
alkynyl ligand exchange. These results can be attributed
to a higher stability of the Pd-CtCCOOMe bond of 1a
(13) Carpenter, J . P.; Lukehart, C. M. Inorg. Chim. Acta 1991, 190,
(14) Sebald, A.; Stader, C.; Wrackmeyer, B.; Bensch, W. J . Orga-
nomet. Chem. 1986, 311, 233.
7.

Intermolecular Alkynyl Ligand Transfer
Organometallics, Vol. 19, No. 4, 2000 461
Ta ble 2. Con p r op or tion a tion of Dia lk yn yl a n d
Diiod o Com p lexes of P d a n d P t
The addition of a catalytic amount of CuI to an
equimolar mixture of 1a and trans-PdI2(PEt3)2 in ben-
zene-d6 results in a decrease in the corresponding 31P-
{1H} NMR signals at δ 18.9 and 7.7, and growth of a
new peak at δ 14.6 assigned to 2a (eq 5). The 31P{1H}
conditionsa
complex
run
catalyst
time
productb
1
2
3
4
5
6
7
8
1a
1a
1c
1c
4a
4a
4c
4c
PdI2(PEt3)2
PdI2(PEt3)2
PdI2(PEt3)2
PdI2(PEt3)2
PtI2(PEt3)2
PtI2(PEt3)2
PtI2(PEt3)2
PtI2(PEt3)2
none
CuI
none
CuI
none
CuI
none
CuI
26 h
<1 h
20 h
3 h
22 h
24 h
26 h
3 h
2a (2%)
2a (88%)
2c (33%)
2c (95%)
no reaction
5a (2%)
no reaction
5c (64%)
a
The reaction was carried out in benzene-d6. [Cu]/[Pd] (or [Pt])
b
and 1H NMR spectra after 1 h at 25 °C contain the
signals of 1a , 2a , and trans-PdI2(PEt3)2 in a molar ratio
of 6:88:6. Further reaction does not cause a variation
in the molar ratio of the three complexes, indicating that
equilibrium was attained. The ratio of the equilibrated
mixture suggests a higher thermodynamic stability of
the iodo(alkynyl)palladium complex 2a than an equi-
molar mixture of trans-PdI2(PEt3)2 and 1a . The reaction
without CuI catalyst occurs much more slowly and gives
2a in approximately 2% yield after 26 h. The bis-
(phenylethylnyl)palladium complex 1c also reacts with
PdI2(PEt3)2 in the presence of CuI catalyst to afford a
mixture of three palladium complexes, 1c, trans-PdI-
(CtCPh)(PEt3)2 (2c), and trans-PdI2(PEt3)2. A yield of
95% is attained for 2c. The phenylethynyl ligand
transfer reaction of 1c to trans-PdI2(PEt3)2 producing
2c takes place slowly even in the absence of CuI catalyst
and affords the prouct in 33% yield.
The reaction of bis(alkynyl)platinum complexes with
trans-PtI2(PEt3)2 was examined to compare the reaction
rate with those of Pd complexes. Complexes 4a and 4c
do not react with trans-PtI2(PEt3)2 at room temperature
in the absence of CuI catalyst. The addition of CuI
catalyst does not enhance conproportionation of 4a and
trans-PtI2(PEt3)2 and produces the iodo(alkynyl)plati-
num complex, trans-PtI(CtCCOOMe)(PEt3)2 (5a ), in 2%
yield after reaction for 24 h. The reaction of 4c and
trans-PtI2(PEt3)2 proceeds smoothly in the presence of
CuI catalyst to afford a mixture of the Pt complexes
containing trans-PtI(CtCPh)(PEt3)2 (5c) in 64% yield
(eq 6).
) approximately 0.01. Yield was calculated based on the peak
area ratio of 31P{1H} NMR signals as follows: Yield) 100[PdI-
(CtCR)(PEt3)2]/([Pd(CtCR)2(PEt3)2] + [PdI(CtCR)(PEt3)2] +
[PdI2(PEt3)2]). No other complexes were found in the 1H and
31P{1H} NMR spectra of the reaction mixture. The relative signal
intensity was calibrated by the comparison of the standard mixture
of the complexes with that of the 1H NMR spectra.
1a and 4a are shifted to lower magnetic field position
from the corresponding signals of H-CtC-COOMe by
41.8 and 37.3 ppm, respectively, whereas the shift of
the R-carbon signals of 1c and 4c is siginificantly
smaller. The difference in the coupling constants and
the chemical shifts is related to a difference in the
strength of the coordination bond depending on the
substituents of the ethynyl groups and may suggest
higher stability of M-C bonds in the methoxycarbon-
ylethynyl complexes than that in the phenylethynyl
complexes.
Although crystallographic measurement of 1a , 1c,
and 4a confirmed the molecular structures with trans
coordination, comparison of the bond parameters of the
complexes did not provide a clear relationship between
the M-C or CtC bond distances and the substituents
of the alkynyl ligand. Pd-C or Pt-C bond distances of
1a (1.999(3) Å) and 4a (1.994(4) Å) are significantly
shorter than that of 1c (2.069(7) Å). The Pt-C bond of
4c (1.98(1) Å) that has an isomorphous crystal lattice
to 1c is the shortest coordination bond of these com-
plexes. CtC bond distances of 1a , 4a , and 4c (1.193-
(5)-1.21(1) Å) are longer than that of 1c (1.003(8) Å),
which is exceedingly short for a CtC triple bond of the
coordinated alkynyl group, suggesting invalidity of the
position of the alkynyl carbon of 1c in the crystal-
lographic results. Thus, the bond parameters of the
complexes are not suited to discuss stability of the
coordination bond. The crystallographic results of trans-
M(CtCX)2(PR3)2-type complexes (M ) Ni, Pd, Pt)
presented in the review by Manna et al.15 do not appear
to be conclusive regarding the relationship between the
bond parameters and X, whereas trans-M(Y)(CtCX)-
(PR3)2-type complexes show a clear dependence of the
M-C bond distances on the kind of ligand Y.
These results suggest several thermodynamic and
kinetic features of the alkynyl ligand transfer of Pd and
Pt complexes. The CuI-catalyzed reaction of the Pd
complexes in eq 5 indicates higher thermodynamic
stability of the iodo(alkynyl)palladium(II) complex, trans-
PdI(CtCR)(PEt3)2, than the mixture of bis(alkynyl)- and
diiodopalladium(II) complexes. Comparison of the rela-
tive reactivity of 1a and 1c as well as that of 4a and 4c
toward the alkynyl ligand transfer with the respective
diiodopalladium and -platinum complexes has revealed
more facile transfer of the phenylethynyl ligand than
the methoxycarbonylethynyl ligand in the reactions of
both Pd and Pt complexes. The rates of the alkynyl
ligand transfer of 1a and 1c with trans-PdI2(PEt3)2 in
the presence of CuI catalyst are too high to be compared.
Alkyn yl Ligan d Tr an sfer fr om P d(CtCR)2(P Et3)2
(R ) COOMe, P h ) to tr a n s-P d I2(P Et3)2. The bisalk-
ynylpalladium complexes react with trans-PdI2(PEt3)2
with or without CuI catalyst to afford trans-PdI(CtCR)-
(PEt3)2, as summarized in Table 2. Yields of the con-
proportionation reaction vary significantly depending on
the presence of CuI and also on the alkynyl ligand, as
described below.
(15) Manna, J .; J ohn, K. D.; Hopkins, M. D. Adv. Organomet. Chem.
1995, 38, 79, and references therein.

462 Organometallics, Vol. 19, No. 4, 2000
Osakada et al.
Sch em e 1
The reaction of 1c without the addition of CuI proceeds
much faster than that of 1a , which hardly reacts with
trans-PdI2(PEt3)2. Platinum complex 4c reacts smoothly
with trans-PtI2(PEt3)2 in the presence of CuI, but the
reaction of 4a with trans-PtI2(PEt3)2 does not occur
under similar conditions.
phenylethynyl ligand transfer between Pd complexes (ii)
occurs much more slowly than the corresponding reac-
tion involving the alkynylcopper intermediate.
AlkynylLigand Transfer oftra ns-P d(CtCCOOMe)2-
(P Et3)2 to tr a n s-P tI2(P Et3)2. Previously, we reported
the reaction of aryl(phenylethynyl)palladium complex
with aryl(iodo)platinum complexes with PEt3 ligands,
resulting in the selective alkynyl group transfer from
Pd to Pt, as shown in eq 7.4 The alkynyl ligand transfer
The remarkable effect of CuI catalyst in the enhance-
ment of the reaction is ascribed to its smooth transport
of the alkynyl ligand between group 10 metals. Reaction
pathways of the alkynyl ligand transfer are shown in
Scheme 1. The reaction in the presence of CuI probably
involves an alkynylcopper(I) intermediate, as shown in
(i) (Scheme 1). The initial alkynyl ligand transfer from
the bis(alkynyl)palladium complex to Cu gives an
alkynylcopper complex and MI(CtCR)(PEt3)2-type com-
plexes (M ) Pd, Pt). The resulting alkynylcopper(I)
complex easily reacts with diiodo complexes to afford
another molecule of the iodo(alkynyl)palladium (or
-platinum) complex. A higher stability of the alkynyl
complexes of Ni, Pd, and Pt than the alkynylcopper
complexes was suggested on the basis of the results of
the reaction of alkynylcopper complexes with Pd and
Pt complexes with halogeno ligands, producing alkynyl
complexes of group 10 metals as well as structures of
various multinuclear complexes with alkynyl groups
π-bonded to Cu and σ-bonded to Pd and Pt.16,17 Thus,
the second step of (i) in Scheme 1 would proceed rapidly.
On the other hand, alkynyl ligand transfer from Pd to
Cu was recently reported in the reaction of aryl-
(phenylethynyl)palladium complexes with CuI in the
absence or presence of PPh3.4 The alkynyl ligand
transfer from Pd to Cu occurs at a high rate, although
the equilibrium favors the formation of alkynylpalla-
dium complexes. It was also found that the equilibrium
is shifted by the addition of PPh3 ligand, which alters
the stability of the alkynylcopper bond by its ligation
to the Cu center having a labile d10 configuration. Direct
took place at 30-50 °C without catalyst to afford a
quantitative amount of aryl(phenylethynyl)platinum
complex. The addition of CuI catalyst enhanced the
reaction, which is completed within 3 min at room
temperature. The reaction appears to suggest facile
transfer of the alkynyl ligand of the Pd complex and the
thermodynamically much more stable Pt-alkynyl bond
than the Pd-alkynyl bond in these aryl-coordinated
complexes. Thus, we examined the reaction of dialkyn-
ylpalladium complexes with PtI2(PEt3)2 with the expec-
tation of smooth ligand transfer from Pd to Pt com-
plexes, but instead obtained results different from those
expected based on previous observations.
Complex 1a reacts with equimolar trans-PtI2(PEt3)2
in the presence of CuI at room temperature to give a
mixture of Pd and Pt complexes, as shown in eq 8. The
(16) (a) Yamazaki, S.; Deeming, A. J . J . Chem. Soc., Dalton Trans.
1993, 3051. (b) Yamazaki, S.; Deeming, A. J .; Hursthouse, M. B.; Malik,
K. M. A. Inorg. Chim. Acta 1995, 235, 147. (c) Tanaka, S.; Yoshida,
T.; Adachi, T.; Yoshida, T.; Onitsuka, K.; Sonogashira, K. Chem. Lett.
1994, 877.
(17) Similar Pt-Ag multinuclear complexes with bridigng alkynyl
ligands: (a) Espinet, P.; Fornie´s, J .; Martinez, F.; Toma´s, M.; Lalinde,
E.; Teresa Morano, M.; Ruiz, A.; Welch, A. J . J . Chem. Soc., Dalton
Trans. 1990, 791. (b) Espinet, P.; Fornie´s, J .; Mart´ınez, F.; Sotes, M.;
Lalinde, E.; Teresa Moreno, M.; Ruiz, A.; Welch, A. J . J . Organomet.
Chem. 1991, 403, 253. (c) Fornie´s, J .; Lalinde, E. J . Chem. Soc., Dalton
Trans. 1996, 2587. (d) Ara, I.; Berenguer, J .; Fornie´s, J .; Lalinde, E.;
Moreno, M. T. J . Organomet. Chem. 1996, 510, 63.
addition of CuI is essential for smooth alkynyl ligand
transfer from 1a to other complexes in the reaction
mixture. Figure 4 depicts the 31P{1H} NMR spectra after
the reaction for 10 and 235 min. At the beginning of
the reaction, starting complexes 1a and trans-PtI2-

Intermolecular Alkynyl Ligand Transfer
Organometallics, Vol. 19, No. 4, 2000 463
is close to the statistical ratio of 1:2:1. The final ratio of
the complexes 1a , 2a , trans-PdI2(PEt3)2, trans-PtI2-
(PEt3)2, 4a , and 5a is 2:43:5:11:25:14. Remarkably, iodo-
(alkynyl)palladium(II) complex 2a exists as the main
component among the Pd complexes and does not cause
further alkynyl ligand transfer to trans-PtI2(PEt3)2 or
5a .
A similar reaction of 1c with trans-PtI2(PEt3)2 takes
place in the presence of CuI catalyst to afford a mixture
of Pd- and Pt-containing products, as shown in eq 9.
Figure 6 depicts the reaction profile, which is quite
different from that of the reaction in eq 8. Consumption
of the bis(phenylethynyl)palladium complex is com-
pleted within the initial 5 min of the reaction. The
resulting iodo(alkynyl)palladium complex 2c is formed
immediately, but is gradually transformed into trans-
PdI2(PEt3)2 through alkynyl ligand transfer with Pt
complexes. The reaction mixture after 6 h contains 2c
and trans-PdI2(PEt3)2 in an approximate 15:85 molar
ratio but no 1c, while the final Pt-containing product is
composed of 5c and 4c in an approximate 32:68 ratio.
Most (>90%) of the phenylethynyl group contained in
the initial 1c is transferred to the Pt complexes by the
reaction to afford a mixture of 4c and 5c as the
Pt-containing species in the reaction mixture. This
contrasts with the reaction 8, producing 2a , which is
inert to further alkynyl ligand transfer with iodoplati-
num complexes. The consumption of 1c and the increase
in the amounts of palladium complexes 2c and trans-
PdI2(PEt3)2 in reaction 9 are faster than the reaction of
1a with trans-PtI2(PEt3)2.
F igu r e 4. 31P{1H} NMR spectra of the reaction mixture
of 1a with PtI2(PEt3)2 catalyzed by CuI in benzene-d6 (a)
after 10 min and (b) after 235 min. The peaks with
asterisks are due to satellite signals of the PEt3 ligand of
the Pt complexes.
(PEt3)2 are present in considerable amounts (Figure 4a).
After reaction for 4 h, Pd complex 2a and Pt complexes
4a , 5a , and trans-PtI2(PEt3)2 are present as the major
complexes in the reaction mixture (Figure 4b). Figure
5 shows the plots of the time-yield curve of the reaction.
Dialkynylpalladium complex 1a decreases rapidly to
about 5% of its original amount during the initial 3 h
of the reaction. The amount of 2a increases at a rate
similar to the decrease of 1a . After 3 h of reaction, the
amount of 2a does not vary further. The amounts of
mono- and dialkynylplatinum complexes 4a and 5a also
increase while keeping their relative approximate 2:1
ratio throughout the reaction. The final ratio of the
dialkynyl-, iodo(alkynyl)-, and diiodoplatinum complexes
F igu r e 5. Time-yield curve of the reaction of 1a with PtI2(PEt3)2 catalyzed by CuI. Change in the amounts of (a) Pd
complexes and (b) Pt complexes.

464 Organometallics, Vol. 19, No. 4, 2000
Osakada et al.
F igu r e 6. Time-yield curve of the reaction of 1c with PtI2(PEt3)2 catalyzed by CuI. Change in the amounts of (a) Pd
complexes and (b) Pt complexes.
Ta ble 3. Rea ction of 1a a n d P d I2(P Et3)2 in th e
P r esen ce of P tI2(P Et3)2
Rea ction of 1a w ith a Mixtu r e of tr a n s-P d I2-
(P Et3)2 a n d tr a n s-P tI2(P Et3)2 To Ca u se Alk yn yl
Liga n d Tr a n sfer . The above reaction 8 suggests either
higher thermodynamic stability of 2a than the other Pd
and Pt complexes in the reaction mixture or an inert
Pd-CtCCOOMe bond of the complex to prevent alky-
nyl ligand transfer to iodoplatinum complexes kineti-
cally. To obtain a more detailed insight into the reac-
tions, the reaction of 1a with a mixture of trans-
PdI2(PEt3)2 and trans-PtI2(PEt3)2 was conducted under
similar conditions. Unexpected alkynyl ligand transfer
reactions took place in the absence of CuI catalyst as
described below.
molar ratio of the complexesb
run time (h)a 1a
2a
PdI2(PEt3)2 4a
5a
0.0 0.0
0.0 0.0
PtI2(PEt3)2
1
0
0.500 0.0
0.500
0.454
0.207
0.085d
0.500
0.497
0.463
0.500
0.500
0.490
0.312
0.050
0.050
0.050
2.5
26
0.419 0.098
0.150 0.642
0.0 0.010
0.0 0.189
0.0 0.0
0.0 0.0
0.0 0.0
(+ CuI)c 0.011 0.905
2
0
0.500 0.0
2
20
0.496 0.006
0.464 0.073
a
Reaction was carried out at 25 °C in benzene-d6. [Cu]/[Pd] (or
b
[Pt]) ) approximately 0.01. The relative signal intensity was
calibrated by the comparison of the standard mixture of the
complex with that of the 1H NMR spectra. c The spectrum was
A mixture of 1a , trans-PdI2(PEt3)2, and trans-PtI2-
(PEt3)2 in a 1:1:1 molar ratio causes a gradual decrease
in the amount of 1a at room temperature accompanied
by an increase in the amount of 2a (eq 10). trans-PtI2-
d
obtained soon after addition of CuI catalyst. Disagreement of the
ratio of the Pd complexes is due to a somewhat disordered baseline
of the spectrum preventing estimation of the precise peak area
ratio.
Sch em e 2
that the alkynyl ligand transfer reaction rate depends
on the concentration of trans-PtI2(PEt3)2.
The addition of CuI to the above-mentioned reaction
mixture (eq 10) causes a rapid decrease in the amount
of the remaining 1a to an almost negligible amount and
the amount of the alkynyl transfer product containing
the Pt metal center increases significantly. Thus, CuI
facilitates the alkynyl ligand transfer from 1a to both
trans-PdI2(PEt3)2 and trans-PtI2(PEt3)2. Even in the
presence of CuI catalyst, the alkynyl ligand transfer
from 2a to trans-PtI2(PEt3)2 is slower than that to trans-
PdI2(PEt3)2. These results indicate that 2a having I and
CtCCOOMe ligands at mutual trans positions is ther-
modynamically more stable than the trans-PtI(Ct
CCOOMe)(PEt3)2 and the other complexes in the reac-
tion mixture.
(PEt3)2 also decreases in amount but at a much slower
rate. Only 2% of trans-PtI2(PEt3)2 is transformed to 5a
after reaction for 26 h at room temperature. Yields of
the complexes during the reaction are summarized in
Table 3. The results clearly indicate that the alkynyl
ligand transfer of 1a to trans-PdI2(PEt3)2 occurs pref-
erentially in the presence of trans-PtI2(PEt3)2, which
does not react directly with 1a under these conditions.
Since reaction 5 (R ) COOMe) does not proceed in the
absence of CuI catalyst, the methoxycarbonylethynyl
ligand transfer between the Pd complexes is attributed
to catalysis by trans-PtI2(PEt3)2. Actually, the reaction
without a decreased amount of trans-PtI2(PEt3)2 ([1a ]:
[trans-PdI2(PEt3)2]:[trans-PtI2(PEt3)2] ) 1.0:1.0:0.1 at t
) 0) occurs more slowly, as shown in Table 3, suggesting
Discu ssion
Alkynyl complexes of transition metals have high
thermodynamic stability among organotransition metal

Intermolecular Alkynyl Ligand Transfer
Organometallics, Vol. 19, No. 4, 2000 465
Sch em e 3
complexes18 but often exhibit high chemical reactivity.
The reactions of bis(alkynyl)palladium and -platinum
complexes described above are influenced by the stabil-
ity of the coordination bond which varies depending on
the metal center and coexisting ligands.
transfer. Our results in the present study indicate that
the reaction proceeds slowly in the absence of these
additives and that CuI enhances the reaction signifi-
cantly. The roles played by HNEt2 used in the above
reaction as well as in many other reactions of alkyne
and aryl halides to form a C(sp)-C(sp2) bond under
these conditions are its coordination to the Cu center
to stabilize alkynylcopper species and/or its facilitation
of abstraction of acidic hydrogen of terminal alkyne. The
conproportionation of dialkynylpalladium and diiodo-
palladium complexes appears to be thermodynamically
favored in both phenylethynyl and methoxycarbonyl-
ethynyl complexes because reaction 5 with CuI catalyst
produces 2a and 2c as the major products in equilibri-
um. The conproportionation of trans-Pd(CtCR)2(PEt3)2
with trans-PdI2(PEt3)2 to produce trans-PdI(CtCR)-
(PEt3)2 is enhanced by the remarkable stability of the
Pd complexes with I and CtCR ligands at the trans
coordination sites.
Conproportionation of the dialkynyl and dihalo com-
plexes of group 10 metals is related to the transforma-
tion of alkynylpalladium and alkynylplatinum com-
plexes previously reported. Takahashi, Sonogashira, and
their co-workers reported the reaction of trans-Pd-
(CtCH)2(PR3)2 and trans-PdCl2(PR3)2 in the presence
of CuI and amines to produce a dinuclear Pd complex
with a µ-ethynediyl ligand, Cl-Pd(PR3)2-CtC-PdCl-
(PR3)2 (A), as shown in Scheme 2.19 Complex A was
regarded as an important intermediate in polymeriza-
tion of the above two Pd complexes to afford Pd-
containing polyyne polymers, [Pd(PR3)2-CtC-]n. Two
reaction pathways can account for the formation of the
dinuclear Pd complex. One of the pathways shown in
Scheme 3(i) involves the initial disproportionation of the
two starting complexes to afford B, which reacts further
with trans-PdCl2(PR3)2 to afford the dinuclear complex
A. The other pathway (Scheme 3 (ii)) involves the initial
condensation of the two starting complexes to produce
the dinuclear complex C, which undergoes conpropor-
tionation-like transfer of the alkynyl and chloro ligands
with trans-PdCl2(PR3)2 to produce A and C. The result-
ing complex C reacts with trans-PdCl2(PR3)2 to afford
another molecule of A. Smooth intermolecular transfer
of the alkynyl ligand in the above reaction is due to
intermediate alkynylcopper complexes that activate the
Pd-Cl bond to cause rapid and reversible alkynyl ligand
Conversion of 1c into 1a in reaction 3 clearly indicates
that the Pd-CtCPh bond is less stable than the Pd-
CtCCOOMe bond. In agreement with these observa-
tions, the M-CtCPh bond exhibits higher reactivity
toward the alkynyl ligand transfer reaction than the
M-CtCCOOMe bond; the reactions of trans-M(Ct
CCOOMe)2(PEt3)2 with trans-M′I2(PEt3)2 (M, M′ ) Pd,
Pt) are slower than the corresponding reactions of trans-
Pd (CtCPh)2(PEt3)2 in all the combinations of metal
centers M and M′. In particular, the trans-PdI(Ct
CCOOMe)(PEt3)2 complex exhibits a strong coordination
between the Pd center and the alkynyl ligand and
hardly reacts with the trans-PtI2(PEt3)2 under these
conditions. The unique reactivity is probably due to
kinetic factors because the addition of CuI enhances the
reaction to afford some amount of 5a . The remarkable
thermodynamic stability of 2a among the Pd and Pt
complexes described in the present study can be as-
cribed to the balance between the electron-releasing iodo
ligand and electron-withdrawing methoxycarbonyleth-
ynyl ligands at mutual trans positions. On the other
(18) (a) Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw,
J . E. J . Am. Chem. Soc. 1987, 109, 1444. See also: (b) Bruce, M. I.
Chem. Rev. 1991, 91, 197. (c) Bruce, M. I. J . Organomet. Chem. 1990,
400, 321. (d) Doherty, S.; Corrigan, J . F.; Carty, J . A.; Sappa, E. Adv.
Organomet. Chem. 1995, 37, 39.
(19) (a) Takahashi, S.; Ohyama, Y.; Murata, E.; Sonogashira, K.;
Hagihara, N. J . Polym. Sci.: Polym. Chem. Ed. 1980, 18, 349. (b)
Ogawa, H.; J oh, T.; Takahashi, S.; Sonogashira, K. J . Chem. Soc.,
Chem. Commun. 1985, 1220. (c) Ogawa, H.; Onitsuka, K.; J oh, T.;
Takahashi, S. Organometallics 1988, 7, 2257.

466 Organometallics, Vol. 19, No. 4, 2000
Osakada et al.
Sch em e 4
Sch em e 5
hand, the analogous Pt complex 5a does not exhibit
higher stability than the diiodo and dialkynyl complexes
of Pt.
Reactivity of the alkynyl ligand of Pd and Pt com-
plexes toward intermolecular transfer is influenced by
coexisting ligands. The ligand transfer of aryl(phenyl-
ethynyl)palladium-PEt3 complexes with aryl(iodo)pal-
ladium complexes occurs at -30 °C in the absence of
CuI. The reaction with aryl(iodo)platinum complexes
takes place above 30 °C without the addition of CuI and
below room temperature with CuI catalyst. The reaction
of bis(phenylethynyl)palladium complexes with trans-
PdI2(PEt3)2 occurs slowly in the absence of CuI catalyst,
and that with trans-PtI2(PEt3)2 requires a long time
even in the presence of CuI. The electron-releasing aryl
group activates the metal-alkynyl bond to weaken the
coordination more significantly than the alkynyl ligands
in the bis(alkynyl)palladium and platinum complexes.
Another activation of the Pt-alkynyl bond was recently
reported using diplatinate(II) intermediates. The plati-
nate stabilized by electron-withdrawing aryl ligands
such as C6F5 reacts with several transition metal
complexes with the alkynyl ligand to cause switching
of the alkynyl ligand between σ,π- and π,σ-modes.20
Rapid and reversible switching of the coordination of
the alkynyl ligand between σ,π- and π,σ-modes was
observed in many dinuclear transition metal complexes.
A recent report on switching in an A-frame-type di-
nuclear Pt complex indicated the facile activation of the
Pt-alkynyl σ-bond in the bimetallic framework (Scheme
4).21 trans-PtI2(PEt3)2 catalyzes the alkynyl ligand
transfer between 1a and trans-PdI2(PEt3)2, producing
2a , although the performance of the catalyst is lower
than that of CuI. Scheme 5 depicts two possible path-
ways to account for the enhancement of alkynyl ligand
transfer by the Pt complex. One involves abstraction of
a PEt3 ligand of the Pd complex promoted by trans-PtI2-
(PEt3)2 to form unstable tricoordinated Pd species and
PtI2(PEt3)3. The resulting dialkynylpalladium(II) or
diiodopalladium(II) complex with a tricoordinated struc-
ture would easily react with the four-coordinated Pd-
(II) complex to result in the intermolecular ligand
transfer via an associative intermediate. Formation of
tricoordinated complexes was proposed as an intermedi-
ate of various reactions of Pd(II) and Pt(II) complexes.22
Another possible pathway involving abstraction of an
iodo ligand of trans-PdI2(PEt3)2 by trans-PtI2(PEt3)2
leading to a cationic intermediate also accounts for the
catalysis by the Pt complex.23
Recently, transmetalation of the aryl complexes of late
transition metals or the intermolecular aryl ligands of
group 10 metal complexes has been reported using
various aryl ligands and supporting neutral ligands. In
general, the aryl-metal bond is thermodynamically less
stable than the corresponding alkynyl-metal bond,18
and several aryl-nickel and -palladium complexes
have been reported to undergo intermolecular transfer
of the aryl ligand.24 The alkynyl transfer reactions in
the previous and present studies appear to be kinetically
facilitated because the bimetallic intermediate contain-
ing an unsymmetrically bridging alkynyl ligand under-
goes rapid σ-π structural change.
Con clu sion
The Pd(II) and Pt(II) complexes with simple square-
planar coordination exhibit a variety of ligand transfer
reactions depending on the metal center, the substituent
of the alkynyl ligand, and the catalyst added. Elucida-
tion of the detailed mechanism and optimization of the
reaction conditions are important because the alkynyl
(23) The addition of PEt3 ceased the alkynyl ligand transfer reaction
in eq 10, while NaBF4 enhanced the reaction extremely, giving the
products within a few minutes. The results agree with both of the
proposed pathways. The NMR measurement of an equimolar mixture
of trans-PdI2(PEt3)3 and trans-PtI2(PEt3)3 exhibited broadened 31P{1H}
NMR signals. The Pd and Pt complexes undergo ligand transfer,
although the structure of the product is not clear.
(24) Intermolecular aryl ligand transfer of group 10 metal com-
plexes: (a) Scott, J . D.; Puddephatt, R. J . Organometallics 1983, 2,
1643. (b) Ozawa, F.; Kurihara, K.; Fujimori, M.; Hidaka, T.; Toyoshima,
T.; Yamamoto, A. Organometallics 1989, 8, 180. (c) Ozawa, F.; Hidaka,
T.; Yamamoto, T.; Yamamoto, A. J . Organomet. Chem. 1987, 330, 253.
(d) Yamamoto, T.; Wakabayashi, S.; Osakada, K. J . Organomet. Chem.
1992, 428, 223. (e) Osakada, K.; Sato, R.; Yamamoto, T. Organome-
tallics 1994, 13, 4645. (f) Casado, A. L.; Casares, J . A.; Espinet, P.
Organometallics 1997, 16, 5730. (g) Casado, A. L.; Espinet, P. Orga-
nometallics 1998, 17, 3677. (h) Casado, A. L.; Espinet, P. J . Am. Chem.
Soc. 1998, 120, 8978.
(20) (a) Berenguer, J . R.; Fornie´s, J .; Lalinde, E.; Martinez, F. J .
Chem. Soc., Chem. Commun. 1995, 1227. (b) Berenguer, J . R.; Fornie´s,
J .; Lalinde, E.; Mart´ınez, F. Organometallics 1996, 15, 4537. (c)
Berenguer, J . R.; Fornie´s, J .; Lalinde, E.; Mart´ınez, F.; Sa´nchez, L.;
Serrano, B. Organometallics 1998, 17, 1640.
(21) Yam, V. W.-W.; Yeung, P. K.-Y.; Chan, L.-P.; Kwok, W.-M.;
Phillips, D. L.; Yu, K.-L.; Wong, R. W.-K.; Yan, H.; Meng, Q.-J .
Organometallics 1998, 17, 2590.
(22) (a) Ozawa, F.; Ito, T.; Yamamoto, A. J . Am. Chem. Soc., 1980,
102, 6457. (b) Tatsumi, K.; Hoffmann, R.; Yamamoto, A.; Stille, J . K.
Bull. Chem. Soc. J pn. 1981, 54, 1857. (c) Alibrandi, G.; Scolaro, L. M.;
Romeo, R. Inorg. Chem. 1991, 30, 4007. (d) Minniti, D. Inorg. Chem.
1994, 33, 2631.

Intermolecular Alkynyl Ligand Transfer
Organometallics, Vol. 19, No. 4, 2000 467
with that obtained from the 31P{1H} NMR spectrum. The
signals of 3 were as follows. 1H NMR (benzene-d6): δ 1.02 (m,
18H, P(CH2CH3)3), 1.80 (m, 12H, P(CH2CH3)3), 3.48 (s, 3H,
OCH3), 7.06 (t, 1H, para), 7.52 (d, 2H, ortho); meta hydrogens
were overlapped with those of other products.
ligand transfer reaction is involved in various synthetic
organic reactions such as metal-catalyzed cross-coupling
of alkynes and haloarenes and homocoupling of alkynes.
Extension of study to many other transition metal
complexes would serve to clarify the thermodynamics
of the alkynyl complexes of transition metals and to
determine new aspects of their chemical properties.
P r ep a r a tion of tr a n s-P t(CtCCOOMe)2(P Et3)2 (4a ) a n d
tr a n s-P t(CtCCOOEt)2(P Et3)2 (4b). To PtI2(PEt3)2 (462 mg,
0.56 mmol) dispersed in NEt3 (15 mL) were added HCt
CCOOEt (130 mg, 1.3 mmol) and CuI (approximately 0.1 mg)
together at room temperature. The mixture was stirred for 2
h at room temperature, resulting in precipitation of a colorless
solid. The solid was removed by filtration. The solvent was
evaporated to dryness, and the resulting solid was extracted
with hexane several times. Recrystallization of the extract
from Et2O yielded trans-Pt(CtCCOOMe)2(PEt3)2 (4a ) as color-
Exp er im en ta l Section
Gen er a l, Mea su r em en t, a n d Ma ter ia ls. Manipulations
of the metal complexes were carried out under nitrogen or
argon using standard Schlenk techniques. NMR spectra (1H,
13C, and 31P) were recorded on a J EOL EX-400 spectrometer.
31P{1H} NMR peak positions were referenced to external 85%
H3PO4. Elemental analyses were carried out by Yanaco type
MT-5 CHN autocorder.
1
less crystals (243 mg, 60%). H NMR (benzene-d6) δ 0.91 (m,
18H, P(CH2CH3)3), 1.86 (m, 12H, P(CH2CH3)3), 3.44 (m, 4H,
OCH3). 31P{1H} NMR (benzene-d6): δ 11.2 (s, J (PPt) ) 2277
Hz). 13C{1H} NMR (benzene-d6): δ 155.1 (CO), 111.9 (t, Pt-
C, J (PtC) ) 976 Hz, J (PC) ) 15 Hz), 103.2 (PtCtC, J (PtC) )
275 Hz), 51.1 (OCH3), 16.5 (apparent triplet due to virtual
coupling, P(CH2CH3)3, J (PtC) ) 37 Hz, 17 Hz), 8.3 (s,
P(CH2CH3)3). Anal. Calcd for C20H36O4P2Pt: C, 40.20; H, 6.10.
Found: C, 39.96; H, 5.88.
Complex 4b was obtained analogously (322 mg, 91%). 1H
NMR (benzene-d6): δ 0.92 (m, 18H, P(CH2CH3)3), 1.00 (m, 6H,
OCH2CH3), 1.87 (m, 12H, P(CH2CH3)3), 4.07 (m, 4H, OCH2-
CH3). 31P{1H} NMR (benzene-d6): δ 11.2 (s J (PtP) ) 2285 Hz).
13C{1H} NMR (benzene-d6): δ 154.8 (CO), 111.5 (t, Pt-C,
J (PtC) ) 989 Hz, J (PC) ) 13 Hz), 103.7 (PtCtC, J (PtC) )
278 Hz), 60.2 (OCH2), 16.5 (apparent triplet due to virtual
coupling, P(CH2CH3)3, J (PtC) ) 37 Hz, 17 Hz), 14.4 (OCH2CH3),
8.3 (s, P(CH2CH3)3). Anal. Calcd for C22H40O4P2Pt: C, 42.23;
H, 6.44. Found: C, 41.91; H, 6.22.
P r ep a r a tion of tr a n s-P d (CtCCOOMe)2(P Et3)2 (1a ) a n d
tr a n s-P d (CtCCOOEt)2(P Et3)2 (1b). To PdCl2(PEt3)2 (434
mg, 1.1 mmol) dispersed in NEt3 (20 mL) were added HCt
CCOOMe (178 mg, 2.1 mmol) and CuI (10 mg, 5.3 µmol)
together at room temperature. The initial yellow solution
became colorless and was accompanied by the formation of a
colorless solid on stirring at room temperature. The solid was
separated by filtration. The solvent was evaporated to dryness,
and the resulting solid was extracted with hexane several
times. Recrystallization of the extract from Et2O yielded trans-
Pd(CtCCOOMe)2(PEt3)2 (1a ) as colorless crystals (489 mg,
92%). 1H NMR (benzene-d6): δ 0.94 (m, 18H, P(CH2CH3)3), 1.74
(m, 12H, P(CH2CH3)3), 3.43 (s, 6H, OCH3). 31P{1H} NMR
(benzene-d6): δ 18.9 (s). 13C{1H} NMR (benzene-d6): δ 154.5
(CO), 116.2 (t, Pd-C, J (PC) ) 17 Hz), 104.4 (PdCtC), 51.1
(OCH3), 17.1 (apparent triplet due to virtual coupling, P(CH2-
CH3)3, 14 Hz), 8.5 (s, P(CH2CH3)3). Anal. Calcd for C20H36O4P2-
Pd: C, 47.20; H, 7.13. Found: C, 46.96; H, 6.85.
trans-Pd(CtCCOOEt)2(PEt3)2 (1b) was prepared analo-
gously. 1H NMR (benzene-d6): δ 0.96 (m, 24H, P(CH2CH3)3
and OCH2CH3), 1.75 (m, 12H, P(CH2CH3)3), 4.04 (dd, 4H,
OCH2, J ) 7 Hz). 31P{1H} NMR (benzene-d6): δ 18.6 (s). 13C-
{1H} NMR (benzene-d6): δ 154.2 (CO), 115.8 (t, Pd-C, J (PC)
) 17 Hz), 104.8 (PdCtC), 60.3 (OCH2), 17.2 (apparent triplet
due to virtual coupling, P(CH2CH3)3, 15 Hz), 14.3 (OCH2CH3),
8.5 (s, P(CH2CH3)3). Anal. Calcd for C22H40O4P2Pd: C, 49.21;
H, 7.51. Found: C, 49.46; H, 7.62.
Equ iom ola r Rea ction of tr a n s-P d I2(P Et3)2 w ith HCt
CCOOMe. To PdI2(PEt3)2 (220 mg, 0.37 mmol) dispersed in a
mixture of NEt3 (3 mL) and THF (12 mL) were added HCt
CCOOMe (31 mg, 0.37 mmol) and CuI (1 mg, 0.53 µmol)
together at room temperature. A colorless solid was formed
from the yellow solution on stirring at room temperature. The
solid was separated out by filtration. The product obtained
after evaporation of most of the solvents exhibits NMR signals
due to 1a and 2a in an approximate 1:5 molar ratio. Removal
of the NEt3 in high vacuum caused the deposition of Pd metal
and prevented the isolation of 2a from the reaction mixture.
1H NMR data of 2a (benzene-d6): δ 0.93 (m, 18H, P(CH2CH3)3),
1.91 (m, 12H, P(CH2CH3)3), 3.42 (s, 3H, OCH3). 31P{1H} NMR
(benzene-d6): δ 14.6 (s).
Rea ction of 1c w ith HCtCCOOMe. To an NMR sample
tube was charged a benzene-d6 (0.5 mL) solution of 1c (11 mg,
0.020 mmol) under nitrogen. After capping the tube by a
rubber septum, HCtCCOOMe (3.3 mg, 0.039 mmol) was
added to the solution by a syringe through the septum. The
1H and 31P{1H} NMR spectra were recorded periodically. After
the reaction for 5.5 h, the 31P{1H} NMR spectrum showed the
signals due to 3 (δ 18.4) and 1c in an approximate 8:1 peak
area ratio. After the reaction for 5 days, the 31P{1H} NMR
spectrum contained the signals of 1a , 3, and 1c in approximate
7:3:0.3 ratio. The 1H NMR signals of 3 observed in the mixture
after the reaction for 5 days show a reasonable peak area ratio
Rea ction s of th e Com p lexes. Complexes 1a and 1c used
in the reactions with diiodo complexes of Pd and Pt were
purified by repeated recrystallization and their purities con-
firmed. Time-yield curves of the Pd complexes before and after
final recrystallization did not show any difference, indicating
that CuI is not contaminated in the Pd complexes.
Rea ction of 1a a n d of 1c w ith tr a n s- P d I2(P Et3)2.
Complexes 1a (19.3 mg, 0.038 mmol), trans-PdI2(PEt3)2 (22.6
mg, 0.038 mmol), and CuI (0.1 mg, 0.53 µmol) were charged
to an NMR sample tube. After addition of benzene-d6 (0.5 mL)
to the mixture, the tube was capped with a rubber septum
under argon. The Pd complexes were soon dissolved, while a
part of CuI remained undissolved. The 31P{1H} NMR spectra
1
were recorded at 25 °C periodically, and the H NMR spectra
were checked occasionally.
Rea ction s of 1a a n d of 1c w ith tr a n s-P tI2(P Et3)2.
Complexes 1a (33.0 mg, 0.065 mmol), trans-PtI2(PEt3)2 (42.7
mg, 0.062 mmol), and CuI (0.1 mg, 0.53 µmol) were charged
to an NMR sample tube. After addition of benzene-d6 (0.5 mL)
to the mixture, the tube was capped with a rubber septum
under argon. The 31P{1H} NMR spectra were recorded at 25
°C periodically, and the 1H NMR spectra were checked
occasionally.
Rea ction s of 1a w ith P d I2(P Et3)2 in th e P r esen ce of
tr a n s-P tI2(P Et3)2. Complexes 1a (9.2 mg, 0.018 mmol), trans-
PdI2(PEt3)2 (10.9 mg, 0.018 mmol), and trans-PtI2(PEt3)2 (12.4
mg, 0.018 mmol) were charged to an NMR sample tube. After
addition of benzene-d6 (0.5 mL) to the mixture, the tube was
capped with a rubber septum under argon. The complexes were
dissolved immediately. The 31P{1H} NMR spectra were re-
corded at 25 °C periodically, and the 1H NMR spectra were
checked occasionally.
Cr ysta l Str u ctu r e Deter m in a tion . Crystals of 1a , 1c, and
4b suitable for crystallography were obtained by recrystalli-
zation from hexane. Crystals were mounted in glass capillary
tubes under argon. The unit cell parameters were obtained
by least-squares refinement of 2θ values of 20 reflections with

468 Organometallics, Vol. 19, No. 4, 2000
Osakada et al.
Ta ble 4. Da ta a n d Deta ils of Str u ctu r e Refin em en t
monochromated Mo KR radiation (λ ) 0.710 69 Å) and the
ω-2θ method. An empirical absorption correction (ψ scan
method) of the collected data was applied. Table 4 summarizes
crystal data and details of data refinement.
1a
1c
4b
formula
molecular wt
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C
20H36O4P2Pd C28H40P2Pd
C22H40O4P2Pt
625.59
triclinic
508.84
triclinic
P1h (No. 2)
9.085(2)
10.665(2)
7.028(2)
98.52(2)
102.77(2)
106.72(2)
619.5
544.98
monoclinic
P21/c (No. 14) P1h (No. 2)
9.179(2)
10.963(2)
14.844(3)
Calculations were carried out by using the program package
teXsan on a VAX-II computer. Atomic scattering factors were
taken from the literature.25 A full-matrix least-squares refine-
ment was used for non-hydrogen atoms with anisotropic
thermal parameters. Hydrogen atoms were located by assum-
ing ideal positions and were included in the structure calcula-
tion without further refinement of the parameters.
9.323(1)
11.125(2)
7.498(2)
104.36(1)
98.08(2)
111.75(1)
676.0
105.14(2)
1442
2
0.767
568
Z
1
1
Ack n ow led gm en t. This work was financially sup-
ported by a Grant-in-Aid for Scientific Research from
the Ministry of Education, Science, Sports, and Culture,
J apan (No. 09940229). The authors are grateful to
Nihon Kagaku Kogyo Co. for the generous donation of
PEt3.
µ (mm-1
F(000)
)
0.898
264
1.364
5.380
312
1.537
Dcalcd (g cm-3
)
1.255
cryst size (mm) 0.4 × 0.5 × 0.5 0.4× 0.5 × 0.6 0.2× 0.3 × 0.3
2θ range (deg) 5.0-55.0
5.0-45.0
1760
5.0-55.0
2546
no. of unique
reflns
2838
no. of reflns
used
2357
1099
2387
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data of complexes 1a , 1c, and 4b. This material is available
free of charge via the Internet at http://pubs.acs.org.
no. of variables 124
142
214
R (Rw)a
GOF
0.034 (0.036)
0.043 (0.032)
2.44
0.020 (0.023)
1.29
0.89
weighting
scheme
[σ(Fo)2]-1
[σ(Fo)2]-1
[σ(Fo)2]-1
OM9907829
20° e 2θ e 22°. Intensities were collected on a Rigaku AFC-
5R automated four-cycle diffractometer by using graphite-
(25) International Tables for X-ray Crystallography; Kynoch: Bir-
mingham, England, 1974; Vol. IV.