Mechanism of the palladium-catalyzed metal-carbon bond formation. Isolation of oxidative addition and transmetalation intermediates

Article abstract of DOI:10.1021/om9601965

To investigate the reaction mechanism of the Pd-catalyzed metal-carbon bond formation, the model compounds [η⁵-1-Ph₂P-2,4-Ph₂C₅H ₂](CO)₃MI (M = Mo, 12; M = W, 13) have been prepared and the

Full text of DOI:10.1021/om9601965

5220
Organometallics 1996, 15, 5220-5230
Mech a n ism of th e P a lla d iu m -Ca ta lyzed Meta l-Ca r bon
Bon d F or m a tion . Isola tion of Oxid a tive Ad d ition a n d
Tr a n sm eta la tion In ter m ed ia tes†
Paola Cianfriglia, Valentina Narducci, Claudio Lo Sterzo,* and Egidio Viola
Centro CNR di Studio sui Meccanismi di Reazione, Dipartimento di Chimica,
Universita` “La Sapienza”, Piazzale Aldo Moro 5, I-00185 Roma, Italy
Gabriele Bocelli and Thomas A. Kodenkandath
Centro di Studio per la Strutturistica Diffrattometrica del CNR, Viale delle Scienze,
I-43100 Parma, Italy
Received March 14, 1996X
To investigate the reaction mechanism of the Pd-catalyzed metal-carbon bond formation,
the model compounds [η5-1-Ph2P-2,4-Ph2C5H2](CO)3MI (M ) Mo, 12; M ) W, 13) have been
prepared and their reactions studied under coupling conditions. Treatment of 12 and 13
with stoichiometric amounts of zerovalent palladium yields the complexes [η5-1-Ph2P-2,4-
Ph2C5H2](CO)3MPd(PPh3)I (M ) Mo, 16; M ) W, 17) by oxidative addition of the M-I
moieties on Pd0. Subsequent reaction of intermediates 16 and 17 with 4-nitro-1-[2-
(tributylstannyl)ethynyl]benzene (Bu3SnCtC(C6H4)p-NO2, 18) leads to the formation of the
transmetalation products [η5-1-Ph2P-2,4-Ph2C5H2](CO)3MPd(PPh3)CtC(C6H4)p-NO2 (M )
Mo, 19; W, 20), which have been isolated and characterized. Complexes 13 and 17 have
been also characterized by X-ray analysis.
In tr od u ction
products are formed only in the presence of zerovalent
palladium. These compounds are models and building
blocks of highly ethynylated organometallic structures,
a subject of relevant interest in material science.4
Because of our interest in the reaction mechanism of
this special catalytic behavior of palladium, we decided
to look for analogies with the mechanism of the pal-
ladium-catalyzed carbon-carbon coupling, which is
outlined in Figure 1.1,5,6 The catalytic cycle consists of
(a) oxidative addition of the electrophile on zerovalent
palladium, (b) transmetalation with an organotin com-
pound, (c) trans to cis isomerization of R ligands, and
(d) reductive elimination to yield the coupled product.
It must be noted that, although single intermediates
and segments of this picture have been independently
studied and characterized in a number of cases,1d,7 no
example has ever been reported of a single reaction that
has allowed the mapping of the overall catalytic cycle.
Moreover, a number of recent reports reveal that a more
The paramount importance of palladium catalysis in
transition metal-mediated organic synthesis has long
been recognized and well-established. In particular, the
coupling between organostannane and nucleophiles in
the presence of palladium, i.e., the Stille conditions,
represents one of the most efficient and useful applica-
tions.1 In this respect, Farina has recently ascertained
that now the great majority of transition metal-medi-
ated cross-coupling reactions reported in the literature
are performed by the Stille reaction.1d In this field, we
have reported the unusual catalytic properties of pal-
ladium in the formation of metal-carbon bond.2 The
exploration of this new reaction has immediately re-
vealed interesting perspectives for the preparation of
organometallic structures. We reported the formation
of a variety of mono and bis transition metal σ-acetylides
complexes by coupling of transition metal halides and
mono and bis trialkyltin acetylides3 (Scheme 1). The
(3) (a) Crescenzi, R.; Lo Sterzo, C. Organometallics 1992, 11, 4301
and references therein. (b) Viola, E.; Lo Sterzo, C.; Crescenzi, R.;
Frachey, G. J . Organomet. Chem. 1995, 493, 55. (c) Viola, E.; Lo Sterzo,
C.; Crescenzi, R.; Frachey, G. J . Organomet. Chem. 1995, 493, C9. (d)
Trezzi, F.; Viola, E.; Lo Sterzo, C. Organometallics, in press.
(4) (a) Bruce D. W.; O’Hare D. Inorganic Materials; J ohn Wiley &
Sons: Chichester, England, 1992. (b) Sun, Y.; Taylor, N. J .; Carty, A.
J . Organometallics 1992, 11, 4293. (c) Lichtenberger, D. L.; Renshaw,
S. K.; Wong, A.; Tagge, C. Organometallics 1993, 12, 3522. (d) Beck,
W.; Niemer, B.; Wieser, M. Angew. Chem. Int. Ed. Engl. 1993, 32, 923.
(e) Lang, H. Angew. Chem., Int. Ed. Engl. 1994, 33, 547.
(5) Morita, D. K.; Stille, J . K.; Norton, J . R. J . Am. Chem. Soc. 1995,
117, 8576 and references therein.
(6) Pereyre, M.; Quintard, J .-P.; Rahm, A. Tin in Organic Synthesis;
Butterworths & Co: London, England, 1987.
(7) (a) Brown, J . M.; Cooley, N. A. Organometallics 1990, 9, 353.
(b) Amatore, C.; J utand, A.; Suarez, A. J . Am. Chem. Soc. 1993, 115,
9531 and references therein. (c) Farina, V.; Krishnan, B. J . Am. Chem.
Soc. 1991, 113, 9585. (d) Stang, P. J .; Kowalski, M. H.; Schiavelli, M.
D.; Longford, D. J . Am. Chem. Soc. 1989, 111, 3347.
† C. Lo Sterzo dedicates this work to the memory of his beloved
brother, Edoardo Lo Sterzo, deceased on April 23, 1995.
* Address correspondence to this author. E-mail: losterzo@netmgr.
ced.rm.cnr.it.
X Abstract published in Advance ACS Abstracts, November 1, 1996.
(1) (a) Heck, R. F. Palladium in Organic Synthesis; Academic
Press: New York, 1985. (b) Stille, J . K. Pure Appl. Chem. 1985, 56,
1771. (c) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (d)
Farina,V.; Krishnan, B.; Marshall, D. R.; Roth, G. P. J . Org. Chem.
1993, 58, 5434. (e) Schlosser, M., Ed. Organometallics in Synthesis;
J ohn Wiley & Sons Ltd.: Chichester, England, 1994. (f) Collman, J .
P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G. Principles and
Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987. (g) Saa’, J . M.; Martorell, G.; Garcia-
Raso, A. J . Org. Chem. 1992, 57, 678. (h) Mitchell, T. N. Synthesis
1992, 803.
(2) (a) Lo Sterzo, C. J . Chem. Soc., Dalton Trans. 1992, 1989. (b)
Crescenzi, R. Tesi di Laurea, Universita` di Roma “La Sapienza”, Roma,
Italy, 1992.
S0276-7333(96)00196-3 CCC: $12.00 © 1996 American Chemical Society

Pd-Catalyzed Metal-Carbon Bond Formation
Organometallics, Vol. 15, No. 24, 1996 5221
Sch em e 1
palladium-catalyzed metal-carbon coupling and the
oxidative addition step in carbon-carbon coupling
(intermediate a in Figure 1). Unfortunately, 3 and 4
were isolated in low yields, and crystals suitable for
X-ray analysis could not be obtained.
In this article, we report some new examples of this
reaction in which the system is tailored to allow the
isolation of stable oxidative addition products M-Pd-
I. These compounds have also been reacted further with
stannylacetylides in order to study the subsequent step
of the reaction mechanism.
Resu lts
The first attempt to elucidate further the mechanism
of the metal-carbon bond formation was performed by
reacting complexes 3 and 4 with trialkyltin acetylides
R3SnCtCPh (R ) Me, Bu) in DMF. Although starting
materials were rapidly consumed, any attempts to
isolate reaction products failed. However, observation
F igu r e 1. Mechanism of the palladium-catalyzed carbon-
carbon coupling.
1
by H and 31P NMR (Table 1) was consistent with the
complicated mosaic underlies this simplified picture.5
However, these new finding do not rule out this scheme
that still remains a useful model to refer to, in order to
explain key features of the cross-coupling of organotin
compounds with organic electrophiles.
transmetalation reaction indicated in Eq 2. Upon the
We then focused our attention on the isolation of
intermediates from the reactions outlined in Scheme 1.
Attempts to isolate the products that may be formed
upon reacting stoichiometric amounts of simple cyclo-
pentadienyl metal iodides (η5-C5H5)M(CO)nI (M ) Fe,
n ) 2; M ) Mo, n ) 3; M ) W, n ) 3) and zerovalent
palladium were not successful.2b Therefore, we turned
our attention to the (diphenylphosphino)cyclopenta-
dienyl complexes 1 and 2 (eq 1), with the expectation
that the dangling phosphine arm linked to Cp may serve
as a trap for palladium after the insertion into the M-I
moiety.8,9 This was correct, and the M-Pd-I complexes
(2)
addition of 1 equiv of Me3SnCtCPh to a solution of 3
in DMF-d7, the two quartets at 5.79 and 4.67 ppm
relative to the R,R′ and â,â′ Cp ring slightly changed to
5.73 and 4.67 ppm, and two new sets of multiplets
(8) Baker, K. V.; Brown, J . M.; Cooley, N. A.; Huges, G. D.; Taylor,
R. J . J . Organomet. Chem. 1989, 370, 397.
(1)
(9) (a) Bullock, R. M.; Casey, C. P. Acc. Chem. Res. 1987, 20, 167.
Stille, J . K.; Smith, C.; Anderson, O. P.; Miller, M. M. Organometallics
1989, 8, 1040. (b) Brumas, B.; de Caro, D.; Dahan, F.; de Montauzon,
D.; Poliblanc, R. Organometallics 1993, 12, 1503. (c) Ladipo, F. T.;
Anderson, G. K.; Rath, N. P. Organometallics, 1994, 13, 4741.
(10) Spadoni, L.; Lo Sterzo, C.; Crescenzi, R.; Frachey, G. Organo-
metallics 1995, 14, 3149.
3 and 4 were isolated and fully characterized.10 This
result showed the analogy between the first step of the

5222 Organometallics, Vol. 15, No. 24, 1996
Ta ble 1. 1H a n d 31P NMR Da ta for Com p lexes 3 a n d 5
1H NMRa
Cianfriglia et al.
Cp
PPh2
PPh3
-CtCsPh
31P NMRb
5.79, q, 2H,
J ) 2.0 Hz (R-R′)
4.67, q, 2H,
8.32-8.24, m,
4H (ortho)
7.23-7.60, m,
6H (meta, para)
7.98-7.42, br,
6H (ortho)
7.59-7.45, br,
9H (meta, para)
33.55, d,
J ) 456 Hz
17.00, d,
J ) 2.0 Hz (â-â′)
J ) 456 Hz
5.73, q, 2H,
J ) 2.0 Hz (R-R′)
8.62-8.55, m,
4H (ortho)
8.10-7.70, br,
6H (ortho)
6.51-6.47, m,
2H (ortho)
35.80, d,
J ) 454 Hz
4.67, q, 2H,
J ) 2.0 Hz (â-â′)
7.75-7.30, m,
6H, meta, para)
7.60-7.45, br,
9H (meta, para)
6.96-6.94, m,
3H (meta, para)
25.34, d,
J ) 454 Hz
a
Spectra recorded at 300 MHz in DMF-d7 at room temperature. Chemical shifts are reported in ppm downfield of tetramethylsilane
but assigning the residual 1H signal of the deuterated solvent at 7.24 ppm. Spectra recorded at 121 MHz in DMF-d7 at room temperature.
b
Chemical shifts are reported downfield of external 85% H3PO4.
Sch em e 2
appeared at 6.96-6.94 and 6.51-6.47 ppm, due to the
meta and ortho-para protons of the newly entered Ph
group.
introduction of two phenyl groups into the Cp ring could
impart a certain degree of kinetic stabilization to these
otherwise thermodynamically unstable intermediates.
Variations in the {1H}31P NMR spectrum also ac-
counted for the transmetalation process. The two
nonequivalent phosphorus atoms of 3 give rise to two
doublets at 35.55 and 17.00 ppm. The large coupling
constant (J P-P ) 456 Hz) is typical of unequivalent
phosphorus atoms arranged in a trans fashion on a
metal center.10 Upon formation of 5, these two doublets
were shifted to 35.80 and 25.34 ppm. The large value
of the coupling constant (J P-P ) 454 Hz) indicates that
the trans geometry is retained in the new species. The
formation of Me3SnI, detected by GC/MS, confirmed the
occurrence of the transmetalation process.
Because of the clear spectroscopic evidence for the
formation of 5, we were urged to design a more suitable
model that would also allow the isolation of the trans-
metalation product.
We turned our attention to the use of a substituted
η5-Cp ligand that, while maintaining the key presence
of the chelating diphenylphosphino arm, bore bulky
substituents that would make the products more robust
and easier to handle. This idea was pursued by using
the 1-(diphenylphosphino)-2,4-diphenylcyclopentadien-
ide ligand 9, relying on the expectation that, without
altering the reactivity pattern under investigation, the
F or m a tion of ( 5-1-P h 2P -2,4-P h 2C5H2)(CO)3MI (M
) Mo, 12; W, 13). Complexes 12 and 13 were obtained
by the procedure we previously used to form the
corresponding analogs 1 and 2. A much better overall
yield, improved product stability, and simpler synthetic
procedure rewarded the use of the 1-(diphenylphos-
phino)-2,4-diphenylcyclopentadienide ligand with re-
spect to results from the use of the (diphenylphosphino)-
cyclopentadienide. The synthetic route started by
reacting an ethereal suspension of 1,4-diphenyl-1,3-
cyclopentadiene (6) with 1 equiv of TlOEt at room tem-
perature (Scheme 2). Upon mixing reactants, a bright
yellow precipitate of (η5-1,3-diphenylcyclopentadienyl)-
thallium (7) was immediately formed. Once prepared,
the thallium derivative 7 could be either directly used
to form 12 or 13 or isolated and stored in the refrigerator
inside a glovebox for later use, with unchanged ef-
ficiency. In the straightforward preparation, following
filtration, the solid residue was dissolved in THF and
treated with ClPPh2. A tan precipitate of TlCl was
formed and separated from the solution containing the
diphenylphosphino derivative 8. Direct addition at
room temperature of a stoichiometric amount of BuLi
to the THF solution of 8 led to the formation of the

Pd-Catalyzed Metal-Carbon Bond Formation
Organometallics, Vol. 15, No. 24, 1996 5223
Ta ble 2. Cr ysta llogr a p h ic In for m a tion
lithium salt 9, which was then treated with solid (CH3-
CN)3M(CO)3 (M ) Mo, W). In the case of the formation
of 10, the initial slurry turned to a deep yellow-brown
solution, while the formation of 11 was accompanied by
the formation of a red-purple solution. After overnight
stirring at room temperature, followed by a 1 h reflux,
the complete formation of 10 and 11 was checked by
IR.9b,11 After cooling, the addition of 1,2-diiodoethane
to 10 and 11 led to the formation of 12 and 13,
respectively. Chromatographic separation on silica gel
column afforded the pure products in 98% and 79%
overall yields, respectively.
complex
formula
crystal
color
13
17
C
36H30IO4PW
C54H45IO4P2PdW
colorless
prism
colorless
prism
shape
dimensions(mm)
0.31 × 0.43 ×
0.09 × 0.17 ×
0.76
0.28
crystal system
space group
cell constants
a (Å)
b (Å)
c (Å)
orthorhombic
Pbca
monoclinic
P21/n
29.035(2)
12.545(3)
18.640(2)
90
90
90
24.078(3)
16.085(2)
12.289(3)
90
93.31(4)
90
R (deg)
Although, in principle, two different products are
possible from reaction of 7 with ClPPh2, one arising from
the attack of the phosphorus in position 2 of the Cp ring,
and the other from the attack of one of the two
â (deg)
γ (deg)
cell determination
no. of reflections
θ range (deg)
cell volume (Å3)
formula units
42
43
5.6-17.4
6789.51
8
1.70
44.57
5.1-13.2
4730.63
4
1.74
36.14
1
equivalent positions 4 or 5 (eq 3), the H NMR spectrum
of the final products accounted for the exclusive forma-
tion of 12 and 13. This shows that the steric hindrance
D
µ
calc (g cm-3
calc (cm-1
diffractometer
)
)
Philips PW1100 Philips PW1100
radiation, wavelength (Å) Mo KR, 0.710 69 Mo KR, 0.710 69
standard reflection, step
decay of standard
independent reflections
measured
one, every 100
13%
7362
one, every 100
19%
10 312
reflections observed
[I > xσ(I)]
θ range (deg)
indices range: h,k,l
no. of refined
parameters
2725 (x ) 4)
2154 (x ) 4)
3-30
0/37,0/16,0/23
487
3-27
-30/30,0/20,0/15
284
R
0.044
0.043
weights
unitary
-0.96/1.85
0.90/1.31
unitary
-3.44/1.16
0.75/1.99
∆ρmin/max (e/Å-3
)
(3)
min/max absorb
corr factors
by stirring overnight 12 or 13 in the presence of an
equivalent amount of Pd(PPh3)4 (14) or Pd(dba)2 (15).
In the latter case, an equivalent amount of PPh3 was
added to the reaction mixture in order to provide the
ancillary ligand needed to stabilize the palladium center
in products 16 and 17. Isolation of pure products,
performed by chromatographic separation, was much
easier when the combination Pd(dba)2/PPh3 was used,
because of the absence of the troublesome excess of PPh3
present in the reaction mixture when Pd(PPh3)4 was
used. Chromatographic separation on silica gel afforded
air-stable pure 16 and 17 in 92% and 68% yields,
respectively.
of the two phenyl groups disfavors the addition at
carbon C2; consequently, attack can be directed only on
the 4 or 5 position, generating in both cases product 8.
Both 12 and 13 have been characterized by spectros-
copy and microanalysis. Complex 13 has been also
structurally characterized by single-crystal X-ray dif-
fraction (Figure 3).
Rea ction of 12 a n d 13 w ith Zer ova len t P a l-
la d iu m . F or m a tion of th e Oxid a tive Ad d ition
P r od u cts ( 5-1-P h 2P -2,4-P h 2C5H2)(CO)3MP d (P P h 3)I
(M ) Mo, 16; M ) W, 17). Complexes 12 and 13
smoothly undergo oxidative addition on zerovalent
palladium, forming the corresponding products 16 and
17 (eq 4). Reaction occurs at room temperature in THF
To better understand the structural features of these
M-Pd-I complexes, we have investigated the molecular
structure of 17 by single-crystal X-ray analysis. The
results of the single-crystal X-ray diffraction study are
summarized in Table 2, and a plot of 17 with thermal
ellipsoids is displayed in Figure 4.
Rea ction of 16 a n d 17 w ith Sta n n yla cetylid es.
5
F or m a tion of th e Tr a n sm eta la tion P r od u cts (
-
1-P h 2P -2,4-P h 2C5H2)(CO)3MP d (P P h 3)CtC(C6H4)p-
NO2 (M ) Mo, 19; M ) W, 20). Once the oxidative
addition process was clearly assessed with the isolation
of 16 and 17, we took advantage of the easy access to
such important intermediates to further explore the
dynamic of the Pd-catalyzed metal-carbon bond forma-
tion. Referring to Figure 1, the second step occurring
in the Pd-catalyzed carbon-carbon bond formation is
the transmetalation occurring between the oxidatively
(4)
(11) 10: IR (THF, νCO) 1906 (vs), 1816 (vs), 1789 (s), 1733 (s) cm-1
11: IR (THF, νCO) 1924 (vs), 1902 (vs), 1812 (s), 1732 (s) cm-1
.
.

5224 Organometallics, Vol. 15, No. 24, 1996
Cianfriglia et al.
added intermediate and a nucleophile such as an
organostannane.
Both the Mo-Pd and the W-Pd complexes 16 and
17 were then reacted with some representative ethyn-
yltin derivatives. Although we found that several
(phenylethynyl)trialkyltin derivatives which carried dif-
ferent substituents on the phenyl ring successfully
underwent the transmetalation reaction,12 we report
here only the case of the 4-nitro-1-[2-(tributyltin)-
ethynyl]benzene (18), which was the most suitable to
afford stable transmetalation products (eq 5). An
F igu r e 2. 31P{1H} NMR spectra at 121 MHz of complex
20. Upper trace, spectra recorded after dissolution of the
compound in CDCl3 at room temperature. Lower trace,
spectra recorded after addition of an excess of PPh3.
is relative to the R proton adjacent to the phosphorus
atom and is more affected by its deshielding effect,13
while the upfield signal belongs to the â proton. The
31P NMR spectrum of 12 shows a sharp singlet at
-21.31 ppm.
(5)
Formation of 16 was evidenced by an upfield shift of
the two Cp protons, the resonances of which now appear
as triplets at 6.07 ppm for the HR and at 4.54 ppm for
the Hâ. The 31P NMR spectrum of 16 much more
dramatically accounts for the structural variations
taking place with the introduction of the Pd and its
ancillary PPh3 on 12 (eq 4). In 16, the two nonequiva-
lent phosphorus atoms bonded to palladium in trans
configuration give rise to a simple first-order AB split-
ting pattern, which produces two sets of doublets,
centered at 39.23 and 17.49 ppm, respectively, with a
coupling constant of 458 Hz.
On formation of 19, the two Cp protons were only
slightly influenced, while significant variations were
observed for the phenyl protons. In 18, they appear as
two doublets at 8.09 and 7.50 ppm (J ) 9.03 Hz), while
in 19 they were shifted to 7.69 and 6.27 ppm (J ) 8.7
Hz). The 31P NMR spectrum of 19 shows that, with
respect to 16, the two doublets slightly changed their
chemical shift to 39.67 and 26.25 ppm while maintain-
ing a coupling constant of 448 Hz. This accounts for
formation of a new species, still possessing the two
phosphorus group in the trans feature as in 16. By
comparing the 31P NMR data reported in Tables 1 and
3, it is evident that NMR variations occurring with
formation of 16 and 19 (eqs 4 and 5) are similar to those
observed upon formation of 3 and 5 (eqs 1 and 2).
An interesting feature was observed on recording the
31P NMR spectrum of the tungsten complex 20 (Figure
2). Upon dissolving a sample of product in CDCl3, the
31P NMR spectrum showed, along with the expected
pattern for the product (Table 3), two singlets at 25.08
and -6.17 ppm. Observing that the signal at lower field
was characteristic of the free triphenylphosphine ligand,
we attributed the singlet at 25.08 ppm to the trigonal
complex 21 that may be formed by dissociation of PPh3
important effect of the solvent was noticed in this
transformation. In THF, reactions are slow and incom-
plete. Even with the use of a 5-fold excess of the
acetylenic stannane and prolonged reaction time, con-
sistent amounts of starting material remained un-
changed, both in the cases of the Mo-Pd and the W-Pd
complexes. Conversely, reaction of 16 and 17 with a
slight excess of the tin acetylide 18 in DMF goes to
completion within minutes, and following workup,
products 19 and 20 were isolated in 86% and 90% yields,
respectively. Unfortunately, despite several attempts,
no X-ray quality material was obtained.
NMR. Despite some limitations, the NMR technique
was revealed to be a particularly suitable tool for the
study of the phenomenon described in this work (Table
3). In the complexes we studied, limitations resulted
from the presence of a large number of nonequivalent
phenyl groups, in which 1H and 13C NMR resonances
were further complicated by coupling with two non-
equivalent phosphorus groups, resulting in the display
of complicated sets of overlapping signals. Moreover,
the limited solubility of these complexes prevented the
recording of understandable 13C NMR spectra. In spite
of these facts, 1H NMR signals of the sole two cyclopen-
tadienyl protons and 31P NMR spectra allowed a clear
understanding of the transformations under investiga-
tion.
In the following, we shall discuss only some key NMR
features relative to the molybdenum complexes 12, 16,
and 19, those of the corresponding tungsten complexes
being similar.
1
The H NMR spectrum of 12 shows, for the two Cp
protons, two sets of well-separated signals, a quartet
at 6.41 and a doublet at 5.49 ppm. The downfield signal
(13) (a) Mathey, F.; Lampin, J . P. Tetrahedron 1975, 31, 2685. (b)
Casey, C. P.; Bullock, R. M.; Fultz, W. C.; Rheingold, A. L. Organo-
metallics 1982, 1, 1591.
(12) Narducci, V.; Cianfriglia, P.; Lo Sterzo, C. Work in progress.

Pd-Catalyzed Metal-Carbon Bond Formation
Organometallics, Vol. 15, No. 24, 1996 5225

5226 Organometallics, Vol. 15, No. 24, 1996
Cianfriglia et al.
F igu r e 3. Geometry of the complex [η5-1-Ph2P-2,4-
Ph2C5H2](CO)3WI (13) showing the atomic labeling scheme.
The solvent and disordered atoms were omitted for clarity.
The ORTEP diagram is with 30% probability contours of
vibration ellipsoids.
Figu r e 4. Geometry of the complex [η5-1-Ph2P-2,4-Ph2C5H2]-
(CO)3WPd(PPh3)I (17) showing the atomic labelling scheme.
The solvent atoms were omitted to have more evidence.
The ORTEP diagram is with 30% probability contours of
vibration ellipsoids.
from 20 (eq 6). Addition of an excess of PPh3 to the
NMR tube completely suppressed the signal at 25.08
ppm, thus indicating that the new species has com-
pletely reversed to 20.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg)
bond
13
17
angle
13
17
W-Pd
W-Cp
W-C6
W-C7
W-C7′
W-C8
W-I
2.831(1) Cp-W-I
115.5(1)
113.8(1)
2.009(1) 2.003(1) Cp-W-I′
2.072(10) 1.917(12) Cp-W-C6
2.030(25) 1.938(13) Cp-W-C7
122.5(3) 124.7(4)
109.1(6) 124.9(4)
126.5(3) 120.9(4)
80.2(7) 107.5(5)
111.0(4) 83.5(5)
78.8(6) 80.4(5)
137.1(7)
2.044(33)
Cp-W-C8
2.026(11) 1.945(12) C6-W-C7
2.784(2)
2.774(2)
C6-W-C8
C7-W-C8
W-I′
Pd-I
2.665(2) C7-W-I′
2.384(3) C7′-W-I
2.280(3) Pd-W-Cp
Pd-P1
Pd-P2
P-C1
137.2(9)
109.0(1)
71.4(4)
67.0(4)
129.9(4)
166.7(1)
102.7(1)
76.5(1)
89.8(1)
91.1(1)
178.4(1)
123.6(4)
108.8(4)
112.3(4)
105.0(4)
113.2(4)
124.0(4)
1.820(8) 1.782(11) Pd-W-C6
1.874(12) Pd-W-C7
P-C21
P-C31
P-C41
P-C51
P-C61
C6-O9
1.822(11) Pd-W-C8
1.785(13) W-Pd-I
(6)
1.820(9) 1.781(11) W-Pd-P1
1.822(10) 1.856(12) W-Pd-P2
1.013(13) 1.194(14) I-Pd-P1
C7-O10 1.091(44) 1.202(16) I-Pd-P2
C7′-C10′ 1.040(43) P1-Pd-P2
C8-O11 1.092(13) 1.198(16) Pd-P1-C21
C1-C2
C1-C5
C2-C3
C3-C4
C3-C71 1.461(11) 1.489(16) Pd-P2-C61
C4-C5
C5-C81 1.484(12) 1.497(16) C1-P2-C61 128.8(6) 124.8(8)
P2-C1-C5 126.0(6) 122.6(8)
1.387(12) 1.402(15) Pd-P1-C31
1.413(11) 1.502(15) Pd-P1-C41
1.393(12) 1.463(15) Pd-P2-C1
1.436(12) 1.380(15) Pd-P2-C51
X-r a y Str u ctu r es. Drawings of the molecular struc-
tures of complexes 13 and 17 with their respective
labeling schemes are in given Figures 3 and 4. Table 4
reports selected geometrical parameters for the two
complexes. In 13, the tricarbonyl iodine moiety, coor-
dinated by the W atom, shows a disorder consisting of
mutually interchanged positions of the iodine with the
C7dO10 group, having occupancy values of 0.52 and
0.48, respectively.
The W-CCp distances are irregular, ranging from
2.295(8) to 2.381(8) Å in 13 and from 2.324(10) to 2.352-
(11) Å in 17. The increased lengths of some bond
distances of the Cp rings may reflect the steric crowding
between the aromatic substituents and the diphen-
ylphosphine moiety, which assumes a different orienta-
tion in 17 for coordination with palladium. When 13
1.433(11) 1.457(16) C1-P2-C51 99.9(4) 103.0(5)
and 17 are compared, the most striking evidence is the
heavy distortion of the general molecular framework
around the tungsten center upon insertion of palladium
and the formation of the four-membered bimetallic ring
Cp-W-Pd-P (assuming the whole Cp participated as
a single unit of this ring). A strong bonding interaction
exists between W and Pd, which are linked at a distance
of 2.831(1) Å, significatively shorter than the sum of the
corresponding covalent radii (2.986 Å).14a The presence
of this Pd-W bond represents the key feature deter-

Pd-Catalyzed Metal-Carbon Bond Formation
Organometallics, Vol. 15, No. 24, 1996 5227
mining the overall arrangement of the entire molecule.
In 13 the P atom is out 0.149(2) Å from the plane of the
η5-Cp ligand. In 17, the coordination with the Pd lowers
this P 0.575(3) Å below the Cp plane. Because of the
short distance between the two metals, the ancillary
triphenylphosphine linked to the palladium exerts a
relevant steric pressure on the W(CO)3 tripod, imposing
a deviation up to 10.7° of the WsCdO groups from
linearity. For the same reason, the P atom linked to
the Cp decreases its distance from C1 from 1.820(8) Å
in 13 to 1.782(11) Å in 17, with a consequent increase
of the steric influence of the diphenylphosphino group
on the nearby phenyl ring linked to the C2. To relieve
this hindrance, the C1-C5 distance is stretched from
1.413(11) Å in 13 to 1.502(15) Å in 17. In 13, the plane
of the phenyl group linked to the C2 because of the
presence of the adjacent diphenylphosphino moiety
shows a dihedral angle of 40.8(3)° with respect to the
Cp plane, while the phenyl ring linked to the C4, free
of any steric influence, is rotated by an angle of only
4.9(4)° with respect to the Cp plane. In 17, the tilt of
the phenyl group in C2 rises to 50.0(4)°, while the
phenyl group in C4 increases to 10.4(4)° its deviation
from the Cp plane. For the phenyl in C2, we relate
these variations with the closer distance of this group
to the diphenylphosphino moiety, while the phenyl in
C4 increases its deviation from the Cp plane because of
the steric pressure exerted by the distorted W(CO)3
tripod.
Relevant variations from ideal geometry are also
observed around the Pd center. The W-Pd-P1 and the
W-Pd-P2 angles deviate to 102.7(1)° and 76.(1)°, far
from the 90° expected for a normal square planar
coordination around Pd. Moreover, the Cp-W-Pd
angle found at 109.0(1)° strongly differs from the values
of the other bond angles observed between the Cp-W
axis and the three W-CO bonds (120-124°). This
strong deformation from regular values occurring at
bond angles and distances of 17 upon formation of the
W-Pd bond accounts for the strong interaction existing
between these two metals. It is important to note that
a computer-assisted literature search revealed that the
Pd-W bond as it is shown in 17 is a very rare feature,
with only few precedents.14 The Pd-I bond length is
longer than that found for other comparable dis-
tances.15,16 This elongation may be ascribed to the steric
hindrance with PPh3 and PPh2 groups and to the trans
effect of the Pd-W and Pd-I. Similar lengthening of
terminal halide-metal bonds, trans to metal-metal
bonds, has been seen before.17
tion, we found that the use of the (diphenylphosphino)-
cyclopentadienyl bidentate ligand enabled the isolation
of the M-Pd-I complexes 3 and 4, formed upon reaction
of M-I moieties (M ) Mo, W) with zerovalent pal-
ladium10 (eq 1). This result, described as an oxidative
addition process, showed an intriguing analogy with the
first step, often crucial, of the mechanism of the Pd-
catalyzed carbon-carbon bond formation.7 Unfortu-
nately, preparation of starting materials required cum-
bersome procedures, and isolation of the product was
difficult and unreliable, because of the instability of the
M-Pd-I complexes 3 and 4.10 Moreover, we could only
obtain spectroscopic evidences of the consequence of
their reaction with (phenylethynyl)trimethyltin. These
results urged the search for a more suitable model to
get insight into the mechanism of the phenomenon we
were investigating.
The replacement of the (diphenylphosphino)cyclopen-
tadienide ligand with the 1-(diphenylphosphino)-2,4-
diphenylcyclopentadienide satisfied this expectation by
improving product stability without depressing reac-
tivity.18a Thus, the starting metal iodides 12 and 13
were straightforwardly obtained by an identical and
simplified synthetic route (Scheme 2), while 1 and 2
required the design of two different synthetic ap-
proaches.10 Moreover, in sharp contrast with the dif-
ficulties encountered with the isolation of 3 and 4, 12
and 13 smoothly formed the products of oxidative
addition 16 and 17, which were easily purified by
chromatographic separation. The improved stability of
both the otherwise labile M-I and M-Pd-I species,
accompanied by the unchanged reactivity, suggested
that the two phenyl groups attached to the Cp ring in
12 and 13 may operate some electronic effect influencing
the electrophilic character of the M-I moiety. In this
respect, although it remains a delicate matter to assess
to what extent the two phenyl groups on the Cp operate
a charge delocalization from the metal through the Cp
ring,18b,c it is important to observe from the X-ray data
of 13 the arrangement of the two phenyl groups bonded
on the Cp (Figure 3). The phenyl in position 2, because
of the presence of the adjacent bulky diphenylphosphino
group, suffers a 40.3(3)° deviation from coplanarity with
the Cp plane, while the phenyl group in position 4, free
from any steric compression, almost aligns its plane to
the Cp ring plane [4.9(4)° of deviation] in the position
for operating electronic conjugation with the Cp ring,
thus influencing charge and electron density on the
metal.
It is important to note that, while the formation of
the M-Pd-I complexes 3, 4, 16, and 17 clearly accounts
for an oxidative addition of M-I moieties on zerovalent
palladium, one can envision this as a peculiar charac-
teristic of the substrate we used without any relevance
to the mechanism of the Pd-catalyzed metal-carbon
bond formation. In this respect, a number of literature
reports account for the formation of M-Pd-X arrays
in which palladium is inserted in a variety of fashions
between a transition metal (M) and a halide (X), and in
some cases their formation has been rationalized as an
oxidative addition of M-X moieties to zerovalent
palladium.3a,10 Moreover, with the formation of the
In the solid state, both molecules are connected by
van der Waals forces.
Discu ssion
During our first approach to the study of the mech-
anism of the Pd-catalyzed metal-carbon bond forma-
(14) (a) Bender, R.; Braunstein, P.; J ud, J .-M.; Dusausoy, Y. Inorg.
Chem. 1983, 22, 3394 and references therein. (b) Howard, K. E.;
Rauchfuss, T. B.; Wilson, S. R. Inorg. Chem. 1988, 27, 3561. (c)
Zhengzhi, Z.; Xukun, W.; Yujun, S.; Xinkan, Y.; Honggen, W. Gaodeng
Xuexiao Huaxue Xuebao (Chem. J . Chin. Univ.) 1990, 11, 255. (d)
Engel, P. F.; Pfeffer, M.; Fischer, J .; Dedieu, A. J . Chem. Soc., Chem.
Commun. 1991, 1274. (e) Engel, P. F.; Pfeffer, M.; Fischer, J . Orga-
nometallics 1994, 13, 4751.
(15) Hirschon, A. S.; Musker, W. K.; Olmstead, M. M.; Dallas, J . L.
Inorg. Chem. 1981, 20, 1702.
(16) Bailey, N. A.; Mason, R. J . Chem. Soc. A 1968, 2594.
(17) Farr, J . P.; Olmstead, M. M.; Balch, A. L. Inorg. Chem. 1983,
22, 1229.
(18) (a) J aniak, C.; Schumann, H. Adv. Organomet. Chem. 1991, 33,
291. (b) Evans, D. A.; Chapman, K. T.; Bisaha, J . J . Am. Chem. Soc.
1984, 106, 4261. (c) Broadley, K.; Lane, G. A.; Connelly, N. G.; Geiger,
W. E. J . Am. Chem. Soc. 1983, 105, 2486.

5228 Organometallics, Vol. 15, No. 24, 1996
Cianfriglia et al.
M-Pd-I complexes, the metal-iodo moiety has cer-
tainly been activated, but other critical key steps need
to be realized in order to complete the catalytic cycle.19
However, convincing evidence that the process we are
studying plays a role in the formation of a metal-carbon
bond promoted by palladium arises from the smooth
reaction occurring between the oxidative addition in-
termediates 16 and 17 and the acetylenic stannane 18,
to form the products of transmetalation, 19 and 20 (eq
5). In reference to the mechanism of the Pd-catalyzed
carbon-carbon bond formation, although the oxidative
addition step is the trigger of the whole catalytic cycle,7
transmetalation is almost invariably the rate-limiting
step, and generally, when the oxidative addition-
transmetalation-reductive elimination sequence fails,
it is this step which warrants attention.1,7,20 In 19 and
20, the metal center M and the acetylide, i.e., the two
partners to be coupled, although joined by the interposi-
tion of palladium, constitute already a single molecular
unit, and the completion of the coupling process through
the trans to cis isomerization and the reductive elimina-
tion steps is expected to be an overall downhill energetic
pathway. In this respect, the behavior of 20 is note-
worthy. During the recording of its 31P NMR spectrum,
it showed a behavior similar to the reversible formation
of the trigonal complex 21 (eq 6), which may be the
precursor to the cis isomer. In the carbon-carbon
coupling reaction, the formation of a similar trigonal
complex has been already invoked as intermediate
during the trans to cis isomerization preceding reductive
elimination.7b,21
aspects of the carbon-carbon coupling itself, for which
important reinterpretations have been proposed.5,7 More-
over, it is also worthy of note that, while the Mo-Pd
bond is quite a common feature, complexes such as 4,
17, and 20 add to the very few existing examples
showing a direct W-Pd bond.14 In our opinion, the
successful isolation of complexes 19 and 20 represents,
indeed, the disclosure of a new scenario in the endless
world of surprises of palladium chemistry.
Exp er im en ta l Section
Rea gen ts a n d Meth od s. Elemental analyses were per-
formed by the Servizio Microanalisi of the Area della Ricerca
di Roma (C.N.R., Montelibretti, Italy).
Solvents, including those used for chromatograpy, and
liquids were thoroughly degassed before use. Flash chroma-
tography was performed with 230-400 mesh silica gel (Merck).
All reactions were carried out under an atmosphere of
prepurified argon using conventional vacuum line and Schlenk
tube techniques22 in oven-dried glassware, or in a nitrogen-
filled Braun glovebox. Liquids were transferred by syringe
or cannula techniques. THF and Et2O were distilled from
sodium-potassium alloy. DMF was distilled from CaH2 under
reduced pressure. Preparation of the 1,3-diphenyl-2,4-cyclo-
pentadiene required modification of the literature report.23 The
crude ethyl 3-benzoylpropionate precursor had to be formed
using an excess of ethyl alcohol and then dissolved in Et2O
and washed to neutrality with an ice-cold solution of NaHCO3
to remove the remaining alcohol and the H2SO4 used to
catalyze its formation. Without these precautions, formation
of the ester was incomplete, and extensive decomposition took
place during distillation. Moreover, the subsequent cyclization
step must be performed by using the minimum amount of
benzene solvent so as to obtain a 1 M solution of EtONa. Bis-
(dibenzylideneacetone)palladium [Pd(dba)2],24 (CH3CN)3Mo-
(CO)3,25 (CH3CN)3W(CO)3,25 Pd[P(C6H5)3]4,26 (CH3)3SnCtCC6-
Preliminary evidence that these complexes further
evolve toward the completion of the catalytic cycle has
already been obtained.12
29
H5,27 HCtC(C6H4)p-NO2,28 and Bu3SnNEt2 were prepared
according to published procedures.
Con clu sion
TlOCH2CH3 (Aldrich), ClP(C6H5)2 (Strem), and ICH2CH2I
(Aldrich) were used as received. The active organometallic
content of the organolithium reagents was checked periodically
by titration with 2,5-dimethoxybenzyl alcohol.30
In conclusion, with the isolation of the oxidative
addition and transmetalation intermediates 16,17, and
19,20, we showed impressive analogies between the Pd-
catalyzed carbon-carbon and metal-carbon bond for-
mation mechanisms, and these results suggest that this
second pathway could disclose the feasibility of a similar
efficient and useful chemistry as that of the former
process. Moreover, the model we engineered in the
present study, by allowing a large degree of systematic
variations, seems particularly suitable to carry out
systematic and quantitative investigations of the pro-
cesses under examination. One can study the depen-
dence of the various steps of these transformations from
steric and electronic factors, by varying the type of
ancillary ligands, both on the metal M and the Pd, and
the number and type of the substituents on the Cp as
well as on the coordinating side arm. The easy isolation
of the oxidative addition intermediate should also allow
its use for systematic screening of the transmetalation
process, taking advantage of the easy availability of a
large variety of organotin partners.6 These studies,
besides clarifying the factors influencing the metal-
carbon formation phenomenon, by reversing the paral-
lelism, might also shed light on many still unclear
(
5-2,4-P h 2C5H3)Tl (7). This compound was prepared by
adopting the method developed by Mathey and Lampin13 for
a similar compound. A 500 mL Schlenk flask was loaded with
17.85 g (81.78 mmol) of 6 and 400 mL of ethyl ether. To this
was added 20.4 g (81.78 mmol) of thallium ethoxide by a
syringe, causing the formation of a yellow precipitate. After
1 h of stirring, the suspension was filtered and the solid
washed with ethyl ether (3 × 20 mL) and then dried under
vacuum to afford 33.44 g (97%) of product.
1H NMR (DMSO-d6): δ 5.39 (d, 2H, J ) 2.2 Hz), 5.89 (t,
1H, J ) 2.2 Hz), 6.17 (t, 2H, J ) 7.7 Hz), 6.41 (t, 4H, J ) 7.7
Hz), 6.59 (d, 4H, J ) 7.7 Hz). 13C NMR (DMSO-d6): δ 71.08,
75.21, 90.90, 91.67, 92.99, 96.49, 107.56. IR (Nujol, KBr): 1595
(m), 1519 (m), 897 (w), 794 (w), 756 (m), 691 (m) cm-1. Anal.
Calcd for C17H13Tl: C, 48.42; H, 3.10. Found: C, 48.50; H,
3.15.
(22) Shriver, D. F., Dredzon, M. A. The Manipulation of Air-Sensitive
Compounds, 2nd ed.; Wiley-Interscience: New York, 1986.
(23) (a) Kugel, M. Liebigs Ann. Chem. 1898, 299, 50. (b) Drake, N.
L.; Adams, J . R., J r. J . Am. Chem. Soc. 1939, 61, 1326.
(24) Ukay, T.; Kawazawa, H.; Ishii, Y.; Bonnett, J . J .; Ibers, J . A. J .
Organomet. Chem. 1974, 65, 253.
(25) Tate, D. P.; Knipple, W. R.; Augl, J . M. Inorg. Chem. 1962, 1,
433.
(26) Coulson, D. R. Inorg. Synth. 1972, 13, 121.
(27) Lorberth, J . J . Organomet. Chem. 1969, 16, 327.
(28) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627.
(19) Grushin, V. V.; Alper, H. Chem. Rev. 1994, 94, 1047.
(20) Negishi, E.; Takahashi, T.; Baba, S.; Van Horn, D. E.; Okukado,
N. J . Am. Chem. Soc. 1987, 109, 2393.
(21) (a) Stang, P. J .; Kowalski, M. H. J . Am. Chem. Soc. 1989, 111,
3356. (b) Portnoy, M.; Milstein, D. Organometallics 1993, 12, 1655.
(29) J ones, K.; Lappert, M. F. J . Chem. Soc. 1965, 1944.
(30) Winkle, M. R.; Lansinger, J . M.; Ronald, R. C. J . Chem. Soc.,
Chem. Commun. 1980, 87.

Pd-Catalyzed Metal-Carbon Bond Formation
5-1-P h 2P -2,4-P h 2C5H 2)(CO)3MoI (12). Compound
Organometallics, Vol. 15, No. 24, 1996 5229
(
7
lization from THF/pentane (vapor diffusion) at room temper-
ature; mp dec above 204 °C.
(9.77g, 39.16 mmol) was dissolved in THF (60 mL) and then
treated with 8.38 g (7.04 mL, 37.98 mmol) of chlorodiphen-
ylphosphine. A white precipitate of thallium chloride was
formed while the stirring was continued for 1 h. The mixture
was then filtered, and the residue on the filter was washed
three times with 20 mL portions of THF. BuLi (1.6 M solution
in hexanes) (23.7 mL, 37.98 mmol) was then added to the
filtrate, forming a pale orange solution of 9. After 15 min,
11.51 g (37.98 mmol) of (CH3CN)3Mo(CO)3 was added as solid.
After overnight stirring, an intense orange solution was
formed, and following a 1 h reflux and cooling at room
temperature, 10.70 g (37.98 mmol) of solid 1,2-diiodoethane
was added. A deep red solution was formed. After 2 h of
stirring, approximately 20 g of Celite was added, and the
solvent was removed under reduced pressure. The resulting
residue was placed on a silica column (50 cm × 5 cm). Elution
with hexane/dichloromethane (7/3) produced first a little yellow
band, which was discarded, and then a second red band, which
was collected. The latter, after removal of the solvent under
vacuum left 26.63 g (98%) of 12 as red solid. The compound
can be further purified by recrystallization from THF/pentane
(vapor diffusion) at room temperature, forming the stoichio-
metrically bound THF complex 12‚THF; mp dec above 100 °C.
Anal. Calcd for C36H30O4IMoP: C, 55.4; H, 3.87. Found:
C, 55.47; H, 3.77.
Anal. Calcd for
Found: C, 52.58; H, 3.30.
C54H45O4IP2PdW: C, 52.43; H, 3.67.
P r ep a r a tion of Bu 3Sn CtC(C6H4)p-NO2 (18). A mixture
of 7.26 g (20.06 mmol) of (diethylamino)tributylstannane and
2.46 g (16.72 mmol) of (p-nitrophenyl)acetylene was stirred
at room temperature for 3 h. Following removal under vacuum
of the diethylamine formed during the reaction, pure product
(5.68 g, 78%) was isolated by Kugelrohr distillation at 200 °C/
10-2 mm Hg.
1H NMR (CDCl3): δ 0.90 (t, 9H, J ) 7.5 Hz, CH3CH2CH2-
CH2Sn), 1.06 (t, 6H, J ) 7.5 Hz, CH3CH2CH2CH2Sn), 1.33 (p,
6H, J ) 7.5 Hz, CH3CH2CH2CH2Sn), 1.58 (ses, 6H, J ) 7.5
Hz, CH3CH2CH2CH2Sn), 7.53 (d, 2H, J ) 8.9 Hz, o-Ph), 8.12
(d, 2H, J ) 8.9 Hz, m-Ph). 13C NMR (CDCl3): δ 11.23, 13.65,
26.93, 28.85 (CH3CH2CH2CH2Sn), 101.36, 107.81 (-CtC-),
123.43, 130.87, 132.53, 146.62 (Ph). IR (neat, KBr): 2956-
2881 (br), 2447 (w), 1923 (w), 1794 (w), 1736 (w), 1678 (w),
1592 (s), 1517 (s), 1488 (m), 1460 (s), 1419 (w), 1337 (m), 1344
(s) cm-1. MS: m/z 380 (M+ - Bu), 324 (M+ - 2Bu), 266 (M+
- 3Bu). The oily nature of the product does not allow
elemental analyses to be accurately obtained.
(
5-1-P h 2P -2,4-P h 2C5H2)(CO)3MoP d (P P h 3)CtC(C6H4)p-
NO2 (19). A 100 mL Schlenk flask was loaded with 2.54 g
(2.21 mmol) of 16‚THF and then evacuated/nitrogen filled
three times. With the addition of 100 mL of DMF, a bright
red solution was obtained. Following dropwise addition of
4-nitro-1-[2-(tributyltin)ethynyl]benzene (1.73 g, 3.97 mmol),
the color changed to brown-orange, and the mixture was
stirred for 1 h. The contents of the flask were then transferred
to a separatory funnel, diluted with 100 mL of THF, and
extracted with 6 × 100 mL portions of brine. The organic
phase was then dried over magnesium sulfate, filtered, and
concentrated. Pentane was then added until the solution
became cloudy; the flask was stored in a freezer (-28 °C)
overnight, producing an orange precipitate. The mother liquor
was decanted and the product washed with pentane and dried
under high vacuum, yielding 2.41 g (86%) of 19‚THF as a dark
orange solid. An analytical sample was obtained upon recrys-
tallization from THF/pentane (vapor diffusion) at room tem-
perature; mp dec above 160 °C.
(
5-1-P h 2P -2,4-P h 2C5H2)(CO)3WI (13). This compound
was prepared as described for 12, by reacting 7.21 g (18.4
mmol) of (CH3CN)3W(CO)3 and an equimolar amount of 9 to
form 11 and subsequent treatment with 5.18 g (18.4 mmol) of
1,2-diiodoethane. The crude mixture was adsorbed on Celite
and chromatographed on silica gel, using a gradient elution
with a mixture of hexane/dichloromethane, and 11.57 g (79%)
of product was recovered as red solid. Recrystallization from
THF/pentane (vapor diffusion) at room temperature formed
the stoichiometrically bound THF complex 13‚THF; mp 122-
124 °C.
Anal. Calcd for C36H30O4IPW: C, 49.79; H, 3.48. Found:
C, 49.66; H, 3.47.
(
5-1-P h 2P -2,4-P h 2C5H2)(CO)3MoP d (P P h 3)I (16). A 100
mL Schlenk flask was loaded with 1.25 g (1.60 mmol) of 12‚
THF, 1.21 g (2.11 mmol) of bis(dibenzylideneacetone)palla-
dium, and 0.55 g (2.11 mmol) of triphenylphosphine. Follow-
ing three cycles of evacuation/nitrogen filling, 20 mL of THF
was added to the flask, causing the formation of a dark slurry,
which only after several minutes of vigorous stirring turned
to a deep red solution. After 1 h, approximately 20 g of Celite
was added to the reaction mixture, and the solvent was
removed under vacuum. The resulting residue was placed on
Anal. Calcd for C62H49O6MoNP2Pd: C, 63.74; H, 4.23.
Found: C, 63.89; H, 4.5.
(
5-(1-P h 2P -2,4-P h 2)C5H2)(CO)3WP d (P P h 3)CtC(C6H4)p-
NO2 (20). This compound was prepared as described for 19
by reacting 2.0 g (1.61 mmol) of 17‚THF and 1.7 mL (1.26 g,
2.89 mmol) of 4-nitro-1-[2-(tributyltin)ethynyl]benzene in 80
mL of DMF as solvent. Following cold (-28 °C) precipitation
with pentane from a concentrated THF solution, 1.70 g (90%)
of the product was recovered as a dark solid. An analytical
sample was obtained by recrystallization from THF/pentane
(vapor diffusion) at room temperature; mp dec above 90 °C.
a
silica column (45 cm × 3 cm). Elution with hexane/
dichloromethane (6/4) produced a rapidly moving pale yellow
band, which was discarded. Elution was continued with a
hexane/dichloromethane (4/6) mixture, and a red band devel-
oped, which was concentrated under vacuum and added to 50
mL of THF before being evaporated to complete dryness. In
this way, 1.69 g (92%) of the THF bound complex 16‚THF was
isolated as red solid. An analytical sample was obtained by
recrystallization from THF/pentane (vapor diffusion) at room
temperature; mp dec above 186 °C.
Anal. Calcd for
Found: C, 60.03; H, 4.02.
C
62H49O6NP2PdW: C, 59.28; H, 3.93.
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t for Com p lexes 13 a n d 17. Red-purple crystals
of 13 and red-orange crystals of 17 were grown at room
temperature by vapor diffusion of pentane into the respective
concentrated solution of the compound in THF. Both crystals
were mounted on a Philips PW1100 single-crystal diffracto-
meter; the symmetry and appropriate unit cell parameters
were refined from least-squares calculations using the angular
values of computer-centered reflections. Details are sum-
marized in Table 3. Unfortunately, both crystals decomposed
during the data collection procedures, resulting in low-quality
experimental data. The corrections for the Lorentz and
polarization effects and for the intensity decay were performed
during the data reduction procedure.31 The data of 13 were
corrected for absorption with the ψ scan method,32 and that
Anal. Calcd for
C
54H45O4MoIP2Pd: C, 56.44; H, 3.95.
Found: C, 56.33; H, 3.46.
(
5-1-P h 2P -2,4-P h 2C5H2)(CO)3WP d(P P h 3)I (17). This com-
pound was prepared from 2.89 g (3.33 mmol) of 13‚THF, 2.50
g (4.35 mmol) of bis(dibenzylideneacetone)palladium, and 1.16
g (4.44 mmol) of triphenylphosphine in 50 mL of THF solvent
as described for 16. The crude mixture was adsorbed on Celite
and chromatographed on silica column (5 cm × 55 cm).
Elution with a hexane/dichloromethane (4/6) mixture produced
a red band that, upon concentration, addition of THF (50 mL),
and evaporation to dryness, afforded 3.34 g (81%) of 17‚THF
as red solid. An analytical sample was obtained by recrystal-

5230 Organometallics, Vol. 15, No. 24, 1996
Cianfriglia et al.
of Walker and Stuart33 with the DIFABS34 program was used
to correct those of complex 17. The structures were solved by
direct methods,35 and the refinement procedures were per-
formed by full-matrix least-squares techniques with SHELX93.36
The anisotropic thermal parameter of heavy atoms (the
disordered atoms were kept isotropic) was used for complex
13, while in complex 17, all atoms were isotropic but tungsten,
palladium, iodine, and phosphorus. Most of the H atoms of
complex 13 were found in a ∆F map, and the remaining H
atoms were put in their calculated positions and all refined
isotropically. In complex 17, the hydrogens were fixed with
idealized C-H ) 0.80 Å. In both complexes, the solvent atoms
were refined isotropically.
Some THF solvation was also present in both complexes.
In complex 17, the THF molecule was found with one carbon
atom disordered in two different positions, while the exact
disorder situation present in 13 could not be determined, and
the molecule was found to be statistically distributed over
many positions. Some constrains were applied to distances
within the THF molecules. The H atoms associated with the
disordered THF molecules were ignored. All calculations were
performed on a DELL 486 personal computer with the Crys-
ruler package.37
(31) Belletti, D. A new hardware and software system for controlling
the Philips PW1100 single crystal diffractometer with
computer; Internal Report 1/94; Centro di Studio per la Strutturistica
Diffrattometrica del C.N.R., Parma, Italy, 1994.
(32) North, A. C. T.; Phillips, D. C.; Mattews, F. S. Acta Crystallogr.
1968. A24, 351.
(33) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(34) Gluzinski, P. XRAY, Set of programs for X-ray structural
calculations; Polish Academy of Sciences, Warszawa, Poland, 1989.
(35) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, C.; Camalli, M. J . Appl. Crystallogr. 1994, 27,
435.
a personal
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic parameters, positional and thermal parameters, and
complete interatomic distances and angles for complexes 13
and 17 and figures containing 1H and 31P NMR spectra (16
pages). Ordering information is given on any current mast-
head page.
OM9601965
(36) Sheldrick, G. M. SHELX93. Program for the Refinement of
Crystal Structures; University of Go¨ttingen, Germany, 1993.
(37) Rizzoli, C.; Sangermano, V.; Calestani, G.; Andreetti, G. D. J .
Appl. Crystallogr. 1987, 20, 436.