Cyclotrimerization of phenylethynes to fulvene: Reactivity of cis-dichloro(1, 1′-bis(diphenylphosphino)ferrocene)palladium(II)

Article abstract of DOI:10.1016/S0022-328X(00)00534-9

In the presence of triethylamine (NEt₃) and ethanol (EtOH), phenylethyne (or phenylacetylene, PhC≡CH) underwent cyclotrimerization: cis-dichloro(1,1′-bis(diphenylphosphino)ferrocene)palladiuni(II), [PdCl₂(dppf)] (1), reacted with phenylethyne to give [Pd(dppf)(2,3,5-triphenylfulvene)] (2). Reaction of 2 with dimethyl acetylenedicarboxylate in dichloromethane gave [Pd(dppl)(CH₃O₂CC≡CCO₂CH₃)] (3) and a free 2,3,5-triphenylfulvene. Crystallographic data for 2·H2O: triclinic space group P1?, a = 10.658(2), b = 10.896(2), c = 21.080(3) A?, α = 85.303(9)○, β = 76.556(9)○, γ = 80.447(10)○, Z = 2, R(wR₂) = 0.0487(0.1083).

Full text of DOI:10.1016/S0022-328X(00)00534-9

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 616 (2000) 67–73
Cyclotrimerization of phenylethynes to fulvene: reactivity of
cis-dichloro(1,1%-bis(diphenylphosphino)ferrocene)palladium(II)
Hyo-Jean Kim, Nam-Sun Choi, Soon W. Lee *
Department of Chemistry, Sungkyunkwan Uni6ersity, Natural Science Campus, Suwon 440-746, South Korea
Received 17 May 2000; received in revised form 21 June 2000; accepted 24 June 2000
Abstract
In the presence of triethylamine (NEt3) and ethanol (EtOH), phenylethyne (or phenylacetylene, PhCꢀCH) underwent
cyclotrimerization: cis-dichloro(1,1%-bis(diphenylphosphino)ferrocene)palladium(II), [PdCl2(dppf)] (1), reacted with phenylethyne
to give [Pd(dppf)(2,3,5-triphenylfulvene)] (2). Reaction of 2 with dimethyl acetylenedicarboxylate in dichloromethane gave
(
[Pd(dppf)(CH3O2CCꢀCCO2CH3)] (3) and a free 2,3,5-triphenylfulvene. Crystallographic data for 2·H2O: triclinic space group P1,
,
a=10.658(2), b=10.896(2), c=21.080(3) A, h=85.303(9)°, i=76.556(9)°, k=80.447(10)°, Z=2, R(wR2)=0.0487(0.1083).
© 2000 Elsevier Science B.V. All rights reserved.
Keywords: Cyclotrimerization of phenylethyne; 2,3,5-Triphenylfulvene; Crystallographic data
products [3–7]. Two mechanisms have been proposed:
a metallacyclopentadiene [3–6] route and a metallacy-
clohexadiene route [7]. For example, O’Conner and
co-workers have recently reported the [2+2+1] alkyne
cyclotrimerization to give fulvenes via a metallacy-
clopentadiene route, using chlorobis(phosphine) iria-
cyclopentadiene compounds [3]. Their proposed mecha-
nism involves initial coordination of an alkyne to the Ir
metal, rearrangement of the alkynyl ligand to a vinyli-
dene ligand, and reductive cyclization to the fulvene
products by the coupling of the vinylidene ligand and
the metallacyclopentadiene ring. On the other hand,
Moran and co-workers reported the trmerization of
3,3,-dimethylbut-1-yne, proposing that the reaction
proceeds via a metallacyclobutene intermediate that
reacts with the alkyne by insertion, followed by reduc-
tive elimination from the metallacyclohexadiene to give
the final product (Scheme 1) [7].
1. Introduction
Cyclotrimerization of substituted alkynes in the pres-
ence of transition-metal complexes usually gives 1,3,5-
or 1,2,4-trisubstituted benzene derivatives in high selec-
tivity, which are sometimes difficult to prepare by other
methods. Cobalt, rhodium, nickel, and palladium com-
plexes have been employed for this reaction, and selec-
tivity control to A or B is possible to some extent [1].
For example, phenylethyne (or phenylacetylene) can be
converted to 1,2,4-triphenylbenzene by cyclotrimeriza-
tion in the presence of [(CO)3Ni(OiPr)3]. On the con-
trary, it can be converted mainly to 1,3,5-triphenyl-
benzene in the presence of [(h3-allyl)NiCl]2 or
NiBr2(PBu3)2 [2].
Very recently, we reported the preparation and struc-
ture of trans-bis(phenylethynyl)bis(triethylphosphine)-
palladium(II), trans-Pd(CꢀCPh)2(PEt3)2, which was pre-
pared from cis-PdCl2(PEt3)2 and phenylethyne
(HCꢀCPh) in the presence of triethylamine (NEt3) [8].
In order to prepare a cis-bis(phenylethynyl)palladium
derivative, we treated phenylethyne with cis-dichloro-
(1,1% - bis(diphenylphosphino)ferrocene)palladium(II),
There have been only a few reports on the formal
[2+2+1] cyclotrimerization of alkynes to give fulvene
* Corresponding author. Tel.: +82-331-2907066; fax: +82-331-
2907075.
E-mail address: swlee@chem.skku.ac.kr (S.W. Lee).
0022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00534-9

68
H.-J. Kim et al. / Journal of Organometallic Chemistry 616 (2000) 67–73
tetramethylsilane. 31P{1H}-NMR spectra were also
recorded with a Bruker AMX 500 MHz spectrometer
with reference to 85% H3PO4. IR spectra were recorded
with a Nicolet 205 FTIR spectrophotometer. Melting
points were measured with a Thomas Hoover capillary
melting point apparatus without calibration. Elemental
analyses and mass spectrometry were performed by the
Korea Basic Science Center.
2.1. Preparation of [Pd(dppf )(2,3,5-triphenylful6ene)]
(2)
At room temperature (r.t.), NEt3 (0.11 ml, 0.84
mmol) was added to a mixed solvent of EtOH (5 ml)
and CH2Cl2 (7 ml) containing 1 (0.15 g, 0.205 mmol)
and PhCꢀCH (0.21 ml, 2.05 mmol). The mixture was
stirred for 10 h. The resulting solution was concen-
trated under vacuum to about 7 ml to give a yellow
powder. The resulting precipitates were filtered, washed
with Et2O (3×10 ml) and MeOH (1×10 ml), and then
dried under vacuum to give
a yellow solid of
Scheme 1.
[Pd(dppf)(2,3,5-triphenylfulvene)] (2) (0.058 g, 0.060
mmol, 29%). This product conveniently recrystallized
from dichloromethane–hexane.
[PdCl2(dppf)] (1), in the presence of triethylamine and
ethanol, in which case the dppf ligand is a sterically
bulky and chelating ligand. However, an unexpected
product [Pd(dppf)(2,3,5-triphenylfulvene)] (2) was ob-
tained from this reaction. We report here the prepara-
tion, structure, and some properties of 2.
1H-NMR (CDCl3): l 7.494–6.856 (35H, Ph), 6.409
(1H, d, CH in fluvene, J=3 Hz), 4.353–3.896 (8H, m,
Cp), 2.999 (1H, m, diastereotopic, Pd–CH2), 2.934 (1H,
m, diastereotopic, Pd–CH2). 13C{1H}-NMR (CDCl3): l
140.251–122.488 (Ph, fulvene C1–C5), 93.367–71.174
(Cp), 50.057 (fulvene C6). 31P{1H}-NMR (CDCl3): l
21.744 (1P, s), 18.155 (1P, s). Anal. Calc. for
C58H46P2FePd (Mr=967.21): C, 72.03; H, 4.79. Found:
C, 72.42; H, 4.61%. M.p. (decomp.): 165–167°C. IR
(KBr): 3051, 1595, 1479, 1465, 1435, 1365, 1163, 1093,
2. Experimental
Unless otherwise stated, all the reactions have been
performed with standard Schlenk line and cannula
techniques under argon. Air-sensitive solids were ma-
nipulated in a glove box filled with argon. Glassware
was soaked in KOH-saturated 2-propanol for about 24
h and washed with distilled water and acetone before
use. Glassware was either flame- or oven-dried. Hydro-
carbon solvents were stirred over concentrated H2SO4
for about 48 h, neutralized with K2CO3, stirred over
sodium metal, and distilled by vacuum transfer. Diethyl
ether (Et2O) was distilled over sodium metal and
dichloromethane (CH2Cl2) over CaH2. NMR solvent
(CDCl3) was degassed by freeze-pump-thaw cycles be-
fore use and stored over molecular sieves under argon.
PdCl2, phenylethyne (or phenylacetylene, PhCꢀCH),
and dimethyl acetylenedicarboxylate (CH3O2CCꢀ
CCO2CH3) were purchased from Fluka company. Tri-
ethylamine (NEt3) and ethanol (EtOH) were distilled
and stored under argon. cis-PdCl2(dppf) (1) was pre-
pared by the literature method [9].
1029, 744, 696, 633 cm−1
.
2.2. Preparation of [Pd(dppf )(CH3O2CCꢀCCO2CH3)]
(3) and isolation of 2,3,5-triphenylful6ene
To a yellow compound 2 (0.073 g, 0.075 mmol) in
CH2Cl2 (15 ml) was added dimethyl acetylenedicar-
boxylate, CH3O2CCꢀCCO2CH3 (0.019 ml, 0.16 mmol).
After 30 min, the reaction flask was wrapped with an
aluminum foil, and the mixture was stirred at r.t. for 24
h. The color of the solution turned from yellow to red.
Volatile materials were removed under vacuum, and the
resulting red residue was washed with pentane (5 ml).
The remaining solid was dried under vacuum to give a
yellow powder of [Pd(dppf)(CH3O2CCꢀCCO2CH3)] (3)
(0.044 g, 0.055 mmol, 73%).
1H-NMR (CDCl3): l 7.635–7.184 (20H, m, Ph),
4.271 (4H, d, CpH?, J=2 Hz), 4.154 (4H, d, CpHb,
J=2 Hz), 3.367 (6H, s, CH3O2CCꢀCCO2CH3).
13C{1H}-NMR (CDCl3): l 165.844 (CH3O2CCꢀCCO2-
CH3) 136.946–128.017 (Ph), 115.697 (CH3O2CCꢀ
1H- and 13C{1H}-NMR spectra were recorded with a
Bruker AMX 500 MHz spectrometer with reference to
internal solvent resonances and reported relative to

H.-J. Kim et al. / Journal of Organometallic Chemistry 616 (2000) 67–73
69
Table 1
X-ray data collection and structure refinement for 2·H2O
2.3. X-ray structure determination
All X-ray data were collected with use of a Siemens
P4 diffractometer equipped with a Mo X-ray tube and
a graphite crystal monochromator. Details on crystal
data and intensity data are given in Table 1. The
orientation matrix and unit cell parameters were deter-
mined by least-squares analyses of the setting angles of
34 reflections in the range 15.0B2qB25.0°. Three
check reflections were measured every 100 reflections
throughout data collection and showed no significant
variations in intensity. Intensity data were corrected for
Lorenz and polarization effects. Decay corrections were
also made. The intensity data were empirically cor-
rected with psi-scan data. All calculations were carried
out with use of the Siemens SHELXTL programs [10].
A yellow crystal of 2·H2O, shaped as a block of
approximate dimensions 0.32×0.24×0.10 mm3, was
used for crystal and intensity data collection. The unit
cell parameters suggested a triclinic lattice, and success-
ful structural convergence was obtained in the cen-
Formula
C58H48OP2FePd
985.15
297(2)
Formula weight
Temperature (K)
Crystal system
Space group
Triclinic
(
P1
Unit cell dimensions
,
a (A)
10.658(2)
10.896(2)
21.080(3)
85.303(9)
76.556(9)
80.447(10)
2345.5(6)
2
1.395
0.801
0.6874
0.7262
1012
9122
8642
6291
591
3.5–51.0
ꢀ
,
b (A)
,
c (A)
h (°)
i (°)
g (°)
3
,
V (A )
Z
Dcalc (g cm−3
)
v (mm−1
Tmin
)
Tmax
F(000)
No. of reflections measured
No. of reflections unique
No. of reflections with I\2q(I)
No. of parameters refined
2q Range (°)
(
trosymmetric space group P1. The structure was solved
by the direct method and refined by full-matrix least-
squares calculations of F2 values, and all non-hydrogen
atoms were refined anisotropically. The cocrystallized
H2O exhibited a structural disorder. The best fit for the
oxygen was obtained by considering the O atom to be
distributed over two positions with the site occupation
factors of 0.59:0.41. The hydrogen atoms (H351, H352,
and H39) on the fulvene ring were located and refined
with isotropic temperature factors. The hydrogen atoms
of the cocrystallized water molecule were not located.
The other hydrogen atoms were generated in idealized
positions and refined in a riding model. The selected
bond distances and bond angles are shown in Table 2.
Scan type
Scan speed
Variable
1.035
1.052, −0.382
0.0487
0.1083
GoF (goodness-of-fit on F2)
−3
,
Max., min. in Dz (e A
)
R
awR2
a wR2=ꢀ[w(Fo2−Fc2)2]/ꢀ[w(Fo2)2]1/2
.
CCO2CH3), 80.614 (Cp Cipso), 75.481 (Cp Ca), 72.325
(Cp Cb), 52.343 (CH3O2CCꢀCCO2CH3). 31P{1H}-
NMR (CDCl3):
l
26.418 (s). Anal. Calc. for
C40H34O4P2FePd (Mr=802.92): C, 59.84; H, 4.26.
Found: C, 59.76; H, 4.63%. M.p. (decomp.): 160–
162°C. IR (KBr): 2948, 1850 (CꢀC), 1688 (CꢁO), 1433,
1225 (C–O), 1172 (C–O), 1094, 1030, 749, 698, 488
3. Results and discussion
cm−1
.
3.1. Preparation
When the pentane extract was stored at −25°C for 1
day, red crystalline solids were formed. The precipitates
were filtered off and washed with cold pentane to give
red solids of 2,3,5-triphenylfulvene (0.01 g, 0.033 mmol,
44%).
In the presence of triethylamine, [PdCl2(dppf)] (1)
reacts with excess (ten equivalents) phenylethyne
(PhCꢀCH) to give a fulvene complex [Pd(dppf)(2,3,5-
triphenylfulvene)] (2) (Eq. 1). In this reaction, triethy-
lamine acts as a base to remove HCl liberating from the
reaction mixture. When the amount of PhCꢀCH is
reduced down to two equivalents, the reaction does not
go to completion, and at least six equivalents of
PhCꢀCH is required to complete the reaction. How-
ever, using more than ten equivalents of PhCꢀCH does
not improve the yield. Compound 2 must be washed
with methanol in order to remove [NEt3H]Cl from the
reaction mixture in the workup process. Compound 2
appears to be air- and moisture-stable both in solution
and in the solid state.
1H-NMR (CDCl3): l 7.500–7.207 (15H, Ph), 6.910
(1H, d, CH in fluvene, J=1 Hz), 6.121 (1H, d,
diastereotopic, CH2, J=0.5 Hz), 5.939 (1H, d,
diastereotopic, CH2, J=0.5 Hz). 13C{1H}-NMR
(CDCl3): l 153.210 (C1), 141.621–125.117 (Ph, fulvene
C2–C6). Anal. Calc. for C24H18 (Mr=306.41): C, 94.08;
H, 5.92. Found: C, 93.87 H, 6.09%. M.p.: 138–140°C.
MS (EI): 306 (M+, 100), 229 (M+–Ph, 25), 152 (M–
2Ph, 17), 77 (Ph, 9). IR (KBr): 3062, 1655, 1600, 1565,
1485, 1441, 1409, 1373, 1064, 1028, 933, 858, 762, 698
cm−1
.

70
H.-J. Kim et al. / Journal of Organometallic Chemistry 616 (2000) 67–73
phenylethynes. Unfortunately, we cannot give a clear-
cut explanation about the mechanism for the formation
of the fulvene ligand in this reaction. The known
mechanisms involving
a metallacyclohexadiene or
metallacyclopentadiene intermediate do not seem to be
appropriate for our case, because they cannot clearly
explain the relative orientation of the three phenyl
groups on the fulvene ring. In other words, the cy-
clotrimerization of alkynes generally gives, except one
example, the fulvenes with a substituent at the exocyclic
double bond, as shown in Scheme 1. Very recently,
Yamamoto and co-workers have reported the cy-
clotrimerization of aliphatic akynes (1-pentyne, 1-
hexyne, 1-octyne, 1-dodecyne, and 3-cyclopentyl-
propyne), in which the catalyst is a mixture of [(h3-al-
lyl)PdCl]2 (5 mol%) and dppf (10 mol%), to give the
fulvenes with no substituent at the exocyclic double
bond (Eq. 2) [13]. They observed that, under their
reaction conditions, phenylethyne undergoes the reac-
tion to give several unidentified products and the com-
pound 2,3,5-triphenylfulvene can be detected by GC.
(1)
In the preparation of 2, a mixed solvent of EtOH and
CH2Cl2 is used. In the absence of EtOH, the reaction
does not proceed at all. In addition, the reaction with
methanol (MeOH) in place of EtOH also proceeds well,
but the following workup gives a lower yield. We have
carried out this reaction in N,N-dimethylformamide
(HCONMe2, DMF), a polar solvent with no ionizable
hydrogen atoms, to check the possibility that the alco-
hol in this reaction acts as a proton donor. The reaction
with DMF in place of EtOH does not occur at all.
These experimental results suggest that EtOH maybe
acts as a proton donor and is preferable to MeOH in
terms of workup although both have almost the same
acid strength (pKa=16.00 for EtOH; pKa=15.54 for
MeOH). However, we cannot rule out the possibility
that EtOH acts as a reducing agent and consequently
reduces the Pd metal.
The presence of bidentate coligands in metal com-
plexes allows the isolation cis-dialkynyl Pd complexes
[11,12]. However, in our reaction, the expected cis-di-
alkynyl complex cis-[Pd(CꢀCPh)2(dppf)] is not ob-
tained, but the reaction proceeds to give the unexpected
product [Pd(dppf)(2,3,5-triphenylfulvene)] (2). The pal-
ladium metal appears to have been formally reduced
form +2 (in 1) to 0 (in 2) during the reaction, but its
actual oxidation state is not clear (see below). Com-
pound 2 has a 2,3,5-triphenylfulvene ligand, which has
probably been formed by the cyclotrimerization of
(2)
When this reaction is carried out in neat NEt3, which
is expected to act as a base as well as a solvent to
promote deprotonation, the product gives a mixture of
the starting material (1), the compound 2, and a new
product. No matter how hard we have tried to com-
pletely remove NEt3, it has always remained in the
product mixture. Moreover, the separation of the mix-
ture has not been successful, and therefore we have
given up further reactions.
Table 2
,
Selected bond distances (A) and bond angles (°) for 2·H2O
Pd1–C35
Pd1–P2
C36–C37
C39–C40
C39–H39
2.113(4)
2.334(1)
1.469(6)
1.372(6)
0.94(5)
Pd1–C36
C35–C36
C37–C38
C35–H351
Fe1–Ct(1)a
2.218(4)
1.425(6)
1.390(6)
0.93(5)
1.645
Pd1–P1
2.308(1)
1.461(6)
1.439(7)
1.00(5)
1.647
C36–C40
C38–C39
C35–H352
Fe1–Ct(2)
a
C35–Pd1–C36
C36–Pd1–P1
C36–Pd1–P2
38.3(2)
138.1(1)
117.9(1)
121.5(1)
74.8(2)
113(3)
C35–Pd1–P1
C35–Pd1–P2
P1–Pd1–P2
C6–P2–Pd1
C36–C35–H351
C36–C35–H352
H351–C35–H352
C35–C36–C37
C35–C36–Pd1
C37–C36–Pd1
C37–C38–C39
C40–C39–H39
C39–C40–C36
99.9(1)
156.1(1)
103.62(4)
113.2(1)
117(3)
C1–P1–Pd1
C36–C35–Pd1
Pd1–C35–H351
Pd1–C35–H352
C35–C36–C40
C40–C36–C37
C40–C36–Pd1
C38–C37–C36
C40–C39–C38
C38–C39–H39
Ct(1)–Fe1–Ct(2)
120(3)
117(4)
106(2)
126.2(4)
106.7(4)
104.3(3)
107.2(4)
109.9(4)
120(3)
125.8(4)
66.9(2)
114.1(3)
108.6(4)
130(3)
107.5(4)
178.37
a Ct(1) and Ct(2) refer to the computed centroids of the ring carbons C1–C5 and C6–C10, respectively.

H.-J. Kim et al. / Journal of Organometallic Chemistry 616 (2000) 67–73
71
31P{1H}-NMR, 13C{1H}-NMR, and IR. The yellow
compound 3 is stable both in solution and in the solid
state. The NMR spectra of 3 became so simple com-
pared with those of 2, probably due to the enhanced
1
symmetry. For example, H-NMR spectra of 3 exhibit
two sharp doublets at l 4.154 and 4.271 ppm with the
coupling constant J=2 Hz for the Cp protons, and its
31P{1H}-NMR spectra exhibit only one singlet at l
26.468 ppm to indicate the two phosphorus nuclei of
the dppf ligand to be equivalent. In the IR spectra of 3,
the band at 1850 cm−1 can be assigned to the CꢀC
stretching and that at 1688 cm−1 to the CꢁO stretching.
Scheme 2.
In compound 2, the exocyclic double bond of the
(3)
fulvene ligand appears to be a neutral CH2 group
bonded to Pd in the h2-type. In H-NMR spectra of 2,
1
The 2,3,5–triphenylfulvene, which has been liberated
from the reaction of 2 with dimethyl acetylenedicar-
boxylate, can be isolated from the pentane extract when
the reaction mixture is washed with pentane in prepar-
ing 3. The free fulvene has been characterized by spec-
troscopy (1H-NMR, 13C{1H}-NMR, and IR),
high-resolution mass spectrometry, and elemental anal-
the vinyl protons of the exocyclic double bond exhibit
two multiplets at l 2.999 and 2.934 ppm, which indi-
cates that these protons are diastereotopic and the
resonance structure II is a major contributor in which
the five-membered ring has an aromatic character. In
the free fulvene, which has been isolated from the
substitution reaction of 2 and dimethyl acetylenedicar-
boxylate (CH3O2CCꢀCCO2CH3), the corresponding
protons appear as two doublets at l 6.121 and 5.939
ppm with the coupling constant J=0.5 Hz. The high-
field shift of the exocyclic CH2 protons on bonding to
the Pd metal is consistent with a well-known fact that
the chemical shifts of protons alpha to a metal are often
considerably shifted to high field of those in the parent
(or free) ligand [14]. We speculate the hybridzation of
the terminal carbon of the exocyclic double bond (C6)
to be intermediate between sp2 and sp3, and therefore
the oxidation state of Pd might be intermediate between
0 and +2. The C-6 atom appears at an extremely high
field of l 50.057 ppm in the 13C{1H}-NMR spectra,
which might further support the structure of II as a
1
ysis. H-NMR spectra of the fulvene exhibit two dou-
blets at l 5.939 and 6.121 ppm for the vinyl protons of
the exocyclic double bond, and one doublet at l 6.910
ppm for the proton on the fulvene ring. Very recently,
Bazan and co-workers have reported that transition-
metal complexes containing cyclopentadienyl-based lig-
ands can be obtained from fulvene and a suitable
homoleptic complex of the type ML4 (M=Zr or Hf;
L=CH2Ph or NMe2) [15]. In their study, (h6-fulvene)-
metal species has been proposed as an intermediate,
which undergoes intramolecular nucleophilc substitu-
tion to give the desired product.
3.2. Property
1
major contributor. H-NMR spectra of 2 exhibit four
When
1
is treated with propargyl chloride
peaks assigned to the Cp protons, indicating a low
symmetry of 2. In 31P{1H}-NMR spectra of 2, two
broad singlets appear at l 21.744 and 18.155 ppm,
indicating that two phosphorus nuclei of the dppf
ligand are inequivalent.
(HCꢀCCH2Cl) in the presence of NEt3, no sign of
reaction can be observed. In the presence of
phenylethyne and triethylamine, 3 can be directly ob-
tained by treating 1 with excess dimethylacetylene di-
carboxylate (Scheme 2). However, the free fulvene
cannot be isolated in this reaction. In addition, in the
presence of sodium borohydride, 1 reacts with dimethy-
lacetylene dicarboxylate to also give 3.
Compound 2 has been treated with excess tri-
ethylphosphine (PEt3) to check whether substitution
reaction for the fulvene or dppf ligand occurs, but no
sign of reaction has been observed. Compound 2 has
also been treated with iodomethane (MeI) to check
whether oxdative addition occurs, but the reaction has
not occurred, either. Moreover, 2 does not react with
[Pd(dppf)(CH3O2CCꢀCCO2CH3)] (3) has been pre-
pared by the reaction of compound 2 with dimethyl
acetylenedicarboxylate (2.2 equivalents) in CH2Cl2 (Eq.
1
3). Compound 3 has been characterized by H-NMR,

72
H.-J. Kim et al. / Journal of Organometallic Chemistry 616 (2000) 67–73
unsaturated organic compounds such as a tetrasubsti-
tuted alkene (2,3-dimethyl-2-butene), ethylene
square planar palladium complexes in which the dppf
fragment acts as a ligand [16]. The distance of Pd1···Fe1
,
(H2CꢁCH2), and carbon monoxide (CꢀO).
is 4.242(1) A, which clearly rules out direct bonding
interaction between the two metals.
,
The bond distances of Pd–C35 (2.113(4) A) and
3.3. Structure
2
,
Pd–C36 (2.218(4) A) are fairly typical of Pd–h -alkene
,
(H2CꢁCR2; 2.187–2.107 A) [17]. The C35–C36 bond
distance of 1.425(6) A is somewhat shorter than that of
C(sp )–C(sp ) (1.54 A) but longer than that of C(sp )–
C(sp ) (1.33 A). This distance, therefore, indicates that
The structure of 2 with the atomic numbering scheme
is shown in Fig. 1, in which the cocrystallized H2O
molecule is omitted for clarity. Compound 2 has one
bidentate dppf ligand and one h2-fulvene ligand. The
coordination sphere of the Pd metal can be described as
a distorted square plane. The equatorial plane, which is
defined by C35, C36, P1, and P2, is relatively planar
with an average atomic displacement of 0.0083 A. The
Pd metal lies below the equatorial plane by 0.077(7) A.
The Pd–P1 and Pd–P2 bond distances of 2.308(1) and
,
3
3
2
,
2
,
C35–C36 bond has a partial double bond character.
However, the sums of bond angles around C35 {354°:
C36–C35–H351 (117(3)°); C36–C35–H352 (120(3)°);
H351–C35–H352 (117(4)°)} and C36 {358.7°: C35–
C36–C40 (126.2(4)°); C35–C36–C37 (125.8(4)°); C37–
C36–C40 (106.7(4)°)} are very close to 360°, suggesting
that both carbon atoms are sp2-hybridized. The ideal
value for the sum of the corresponding three bond
angles around the sp3-hybridized carbon is 328.5°
(109.5°×3). The fulvene ring plane, defined by C35–
C40, is relatively planar with an average atomic dis-
,
,
,
2.334(1) A in compound 2 are longer than the Pd–P
,
bond distances of 2.283(1) and 2.301(1) A found for the
parent compound 1 [9]. The P–Pd–P angle in 2 also
becomes larger from 99.07° in 1 to 103.62(4)°.
The two Cp rings are not perfectly parallel but
twisted from each other with a dihedral angle of 1.8(2)°.
The torsion angle of P1···C1···C6···P2 is 30.4(2)°, indi-
cating that the two Cp rings adopt a gauche (or stag-
gered) conformation. For comparison, the ideal torsion
angle for the gauche conformation is 36°. The Fe1–Ct
(Ct: a centroid of the Cp ring) distances are 1.645 and
,
placement of 0.048 A. The dihedral angle between the
equatorial plane and the fulvene ring is 83.6(2)°.
In summary, we have observed the cyclotrimerization
of phenylethynes to fulvene from the reaction of cis-
[PdCl2(dppf)] (1) with excess PhCꢀCH in the presence
of NEt3 and EtOH. We have isolated and characterized
the free fulvene. The Pd–fulvene complex,
[Pd(dppf)(2,3,5-triphenylfulvene)] (2), undergoes substi-
,
1.647 A, and the angle of the Ct(1)–Fe–Ct(2) (Ct(1):
C1–C5; Ct(2): C6–C10) is 178.37°. The bite angle of
P1···Fe1···P2 is 64.32(3)°, and the distance of P1···P2 is
tution
with
dimethyl
acetylenedicarboxylate
,
3.648(2) A. The above bonding parameters within a
ferrocene moiety are consistent with those found in
(CH3O2CCꢀCCO2CH3) to give a corresponding Pd–
alkyne p-complex.
Fig. 1. ORTEP drawing of 2 showing the atom-labeling scheme and 50% probability thermal ellipsoids.

H.-J. Kim et al. / Journal of Organometallic Chemistry 616 (2000) 67–73
73
[3] J.M. O’Connor, K. Hibner, R. Merwin, P.K. Gantzel, B.S.
Fong, J. Am. Chem. Soc. 119 (1997) 3631.
4. Supplementary material
[4] E. Johnson, G.J. Balaich, P.E. Fanwick, I.P. Rothwell, J. Am.
Chem. Soc. 119 (1997) 11086.
[5] L.S. Liebeskind, R. Chidambaram, J. Am. Chem. Soc. 109
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[6] J. Moreto, K.-I. Maruya, P.M Bailey, P.M. Maitilis, J. Chem.
Soc. Dalton Trans. (1982) 1341.
[7] G. Moran, M. Green, A.G. Orpen, J. Organomet. Chem. 250
(1983) C15.
Crystallographic data for the structure reported in
this paper have been deposited with the Cambridge
Crystallographic Data Centre, CCDC no. 144172 for 2.
Copies of this information may be obtained free of
charge from the Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44-1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.
cam.ac.uk).
[8] H.-J. Kim, S.W. Lee, Bull. Korean Chem. Soc. 20 (1999) 1089.
[9] T. Hayashi, M. Konishi, Y. Kobori, M. Kumada, G. Higuchi, T.
Hirotsu, J. Am. Chem. Soc. 106 (1984) 158.
[10] Bruker, SHELXTL, Structure Determination Software Programs,
Bruker Analytical X-ray Instruments Inc., Madison, WI, USA,
1997.
Acknowledgements
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[12] C. Stader, B. Wrackmeyer, J. Organomet. Chem. 295 (1985)
C11.
This work was supported by the Brain Korea 21
Project.
[13] U. Radhakrishnan, V. Vladimir, Y. Yamamoto, Tetrahedron
Lett. 41 (2000) 1971.
[14] R.H. Crabtree, The Organometallic Chemistry of the Transition
Metals, 2nd edn, John Wiley & Sons, Oxford, 1994, pp. 53–54.
[15] J.S. Rogers, R.J. Lachiocotte, G.C. Bazan, Organometallics 18
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[16] K.-S. Gan, T.S.A. Hor, in: A. Tongni, T. Hayashi (Eds.),
Ferrocenes, VCH, New York, 1995, pp. 3–104.
[17] A.G. Orpen, L. Brammer, F.H. Allen, O. Kennard, D.G. Wat-
son, J. Chem. Soc. Dalton Trans. (1989) S16.
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