Synthesis and characterization of trimetallic complexes containing M-Pd-M arrays (M = Mo, W) and their relevance in palladium-catalyzed metal-carbon bond formation

Article abstract of DOI:10.1021/om020043j

The heterobimetallic complexes [MPd(PPh₃)(C≡C-Ph)(CO)₃(η⁵-C₅ -C₅H₂Ph₂(PPh₂)] (5a, M = Mo; 5b, M = W) convert under chromatography to diastereomeric mixtures of the new trimetallic clusters [Pd{M(CO)₃(η⁵-C₅H₂Ph₂ (PPh₂)}₂] (M = Mo, 9a; W, 9b), which contain a linear M-Pd-M array clamped between two (diphenyl)cyclopentadienyl-diphenylphosphino ligands. Diastereomeric pure forms of both trimetallic clusters 9a,b were obtained by fractional crystallization procedures, and the molecular structures of rac-9a and rac-9b were determined by single-crystal X-ray diffraction analyses. The trimetallic complexes 9a,b have been found to be intermediates in coupling reactions between M-I moieties and Bu₃Sn-C≡C-Ph, to form metallacetylides M-C≡C-Ph. Independent high-yield synthetic routes to 9a,b have been developed.

Full text of DOI:10.1021/om020043j

Organometallics 2002, 21, 3001-3008
3001
Syn th esis a n d Ch a r a cter iza tion of Tr im eta llic Com p lexes
Con ta in in g M-P d -M Ar r a ys (M ) Mo, W) a n d Th eir
Releva n ce in P a lla d iu m -Ca ta lyzed Meta l-Ca r bon Bon d
F or m a tion
Francesco Angelucci,† Antonella Ricci,† Claudio Lo Sterzo,*,†,§ Dante Masi,‡
Claudio Bianchini,*,‡ and Gabriele Bocelli
Istituto CNR di Chimica dei Composti Organometallici (ICCOM-CNR), Sezione di Roma,
Dipartimento di Chimica, Box No. 34-Roma 62, Universita´ “La Sapienza”, P.le A. Moro 5,
00185 Roma, Italy, ICCOM-CNR, Via J . Nardi 39, 50132 Firenze, Italy, and Centro CNR di
Studio per la Strutturistica Diffrattometrica, (CSSD-CNR) Palazzo Chimico-Campus,
Parco Area delle Scienze 17/ a, 43100 Parma, Italy
Received J anuary 22, 2002
The heterobimetallic complexes [MPd(PPh3)(CtC-Ph)(CO)3(η5-C5-C5H2Ph2(PPh2)] (5a ,
M ) Mo; 5b, M ) W) convert under chromatography to diastereomeric mixtures of the new
trimetallic clusters [Pd{M(CO)3(η5-C5H2Ph2(PPh2)}2] (M ) Mo, 9a ; W, 9b), which contain a
linear M-Pd-M array clamped between two (diphenyl)cyclopentadienyl-diphenylphosphino
ligands. Diastereomeric pure forms of both trimetallic clusters 9a ,b were obtained by
fractional crystallization procedures, and the molecular structures of rac-9a and rac-9b were
determined by single-crystal X-ray diffraction analyses. The trimetallic complexes 9a ,b have
been found to be intermediates in coupling reactions between M-I moieties and Bu3Sn-
CtC-Ph, to form metallacetylides M-CtC-Ph. Independent high-yield synthetic routes
to 9a ,b have been developed.
In tr od u ction
With the use of properly designed tungsten or mo-
lybdenum models such as [MI(CO)3(η5-C5H2Ph2(PPh2)]
(1a , M ) Mo; 1b, M ) W) (Scheme 1), it has been
possible to establish that the principal steps of this Pd-
catalyzed M-C bond formation process7 are closely
related to the oxidative addition/ transmetalation/ trans-
to-cis isomerization/ reductive elimination sequence,
which is commonly used to describe the Stille reaction,
i.e. the palladium-catalyzed coupling of organic electro-
philes and organostannanes.8
The ability to promote metal-carbon bond formation
by coupling metal halides M-X (M ) Fe, Ru, Mo, W;
X ) I) and trialkyltin acetylide moieties R3Sn-CtC-
R′ (R′ ) H, alkyl, aryl) is a peculiar property of
zerovalent palladium catalysts that has been discovered
by some of us1 and has been successfully applied to form
(i) simple transition metal σ-acetylides (M-CtC-R′);2
(ii) elaborated homo- and hetero-bimetallic µ-acetylene
complexes (M-CtC-Ar-CtC-M′);3 and (iii) highly
ethynylated organometallic oligomers and polymers
[-M-CtC-Ar-CtC-]n.4
In view of the importance of conjugated carbon-rich
materials for advanced technological applications,5 this
Pd-catalyzed coupling reaction has received attention
by other research groups, which have reported success-
ful coupling of the Ru-Cl as well as various M-Br
(M ) Mn, Re) moieties with trialkyltin acetylides.6
The diphenylphosphino sidearm on the cyclopentadi-
enyl ring of complexes 1a ,b efficiently stabilizes and
allows isolation of crucial intermediates such as [MPd-
(PPh3)I(CO)3(η5-C5H2Ph2(PPh2)] 2a ,b and [MPd(PPh3)-
(CtC-Ph)(CO)3(η5-C5H2Ph2(PPh2)] 5a ,b (Scheme 1),
(5) (a) Kingsborough, R. P.; Swager, T. M. Transition Metal in
π-Conjugated Organic Frameworks. In Progress in Inorganic Chem-
istry; Karlin, K. D., Ed.; J ohn Wiley: New York, 1999; Vol. 48, pp 123-
231. (b) Skotheim, T. A.; Elsenbaumer, R. L.; Reynolds, J . R. Handbook
of Conducting Polymers, Second Edition; Marcel Dekker: New York,
1998. (c) Bartik, T.; Bartik, B.; Brady, M.; Dembinski, R.; Gladysz, J .
A. Angew. Chem., Int. Ed. Engl. 1996, 35, 414. (d) Steffen, W.; Kohler,
B.; Altmann, M.; Scherf, U.; Stitzer, K.; zur Loye, H.-C.; Bunz, U. H.
F. Chem. Eur. J . 2001, 7, 117.
† ICCOM-CNR, Roma.
§ Address correspondence to: Claudio.Losterzo@uniroma1.it.
‡ ICCOM-CNR, Firenze.
CSSD-CNR.
(1) Lo Sterzo, C. Synlett 1999, 1704.
(6) (a) Chandrasekharam, M.; Chang, S.-T.; Liang, K.-W.; Li, W.-
T.; Liu, R.-S. Tetrahedron Lett. 1998, 39, 647. (b) Cotton, F. A.; Stiriba,
S.-E.; Yokochi, A. J . Organomet. Chem. 2000, 595, 300. (c) Hartbaum,
C.; Roth, G.; Fischer, H. Chem. Ber./ Recl. 1997, 130, 479. (d) Hart-
baum, C.; Fischer, H. Chem. Ber./ Recl. 1997, 130, 1063 (e) Hartbaum,
C.; Fischer, H. J . Organomet. Chem. 1999, 578, 186.
(7) (a) Spadoni, L.; Lo Sterzo, C.; Crescenzi, R.; Frachey, G.
Organometallics 1995, 14, 3149. (b) Cianfriglia, P.; Narducci, V.; Lo
Sterzo, C.; Viola, E.; Bocelli, G.; Kodenkandath, T. A. Organometallics
1996, 15, 5220. (c) Tollis, S.; Narducci, V.; Cianfriglia, P.; Lo Sterzo,
C.; Viola, E. Organometallics 1998, 17, 2388. (d) Ricci, A.; Angelucci,
F.; Bassetti, M.; Lo Sterzo, C. J . Am. Chem. Soc. 2002, 124, 1060.
(2) (a) Crescenzi, R.; Lo Sterzo, C. Organometallics 1992, 11, 4301.
(b) Viola, E.; Lo Sterzo, C.; Crescenzi, R.; Frachey, G. J . Organomet.
Chem. 1995, 493, 55.
(3) (a) Viola, E.; Lo Sterzo, C.; Crescenzi, R.; Frachey, G. J .
Organomet. Chem. 1995, 493 C9. (b) Viola, E.; Lo Sterzo, C.; Trezzi F.
Organometallics 1996, 15, 4352. (c) Buttinelli, A.; Viola, E.; Antonelli,
E.; Lo Sterzo, C. Organometallics 1998, 17, 2574.
(4) (a) Antonelli, E.; Rosi, P.; Lo Sterzo, C.; Viola, E. J . Organomet.
Chem. 1999, 578, 210. (b) Altamura, P.; Giardina, G.; Lo Sterzo, C.;
Russo, M. V. Organometallics 2001, 20, 4360. (c) Caliendo, C.; Fratoddi,
I.; Lo Sterzo, C.; Russo, M. V. Manuscript in preparation.
10.1021/om020043j CCC: $22.00 © 2002 American Chemical Society
Publication on Web 06/13/2002

3002 Organometallics, Vol. 21, No. 14, 2002
Angelucci et al.
Sch em e 1
without depressing further reactivity. Other steps of the
catalytic cycle are therefore amenable to in-depth stud-
ies. For example, on the basis of accurate kinetic and
spectroscopic work7d it has been possible to establish
that the transmetalation process occurs by two different
pathways (paths a and b of Scheme 1), depending on
the initial concentration of the oxidative-addition in-
termediate 2a . In concentrated solutions of [2a ] (= 10-2
M), the transmetalation reaction proceeds via the
formation of the intermediate species [MoPd(PPh3)I-
(CO)3(η5-C5H2Ph2(PPh2)‚Bu3Sn-CtC-Ph] 3a formed
by association between 2a and the organostannane
(path a). When the transmetalation is performed at
lower concentration of 2a (= 10-4 M) (path b), the
reaction proceeds through the highly reactive solvento-
coordinate species [MoPd(S)I(CO)3(η5-C5H2Ph2(PPh2)]
4a (S ) N,N-dimethylformamide).
In this work we report on the characterization of two
new trimetallic complexes, [Pd{M(CO)3(η5-C5H2Ph2-
(PPh2)}2], featuring an unprecedented M-Pd-M array
(M ) Mo, 9a ; W, 9b). Although these compounds have
been originally obtained by degradation under chro-
matographic conditions of the transmetalated interme-
diates 5a ,b, they revealed a surprising reactivity toward
phenyltributyltin acetylides, leading through a unique
pathway to the reductive-elimination products [M(Ct
C-Ph)(CO)3(η5-C5H2Ph2(PPh2)] 7a ,b. Independent high-
yield synthetic routes to 9a ,b have therefore been
developed.
Resu lts a n d Discu ssion
Monitoring the reactions between the oxidative-ad-
dition products 2a ,b and phenyltributyltin acetylide,
Bu3Sn-C≡C-Ph, by 31P{1H} NMR spectroscopy showed
the quantitative formation of the expected transmeta-
lation products 5a ,b (Scheme 1). Isolation of the latter
compounds was troublesome. In fact, the chromato-
graphic separation8a,9 of the reaction mixture yielded
three different products, none of which, surprisingly,
was either 5a or 5b. For simplicity, only the reaction
between 2a and phenyltributyltin acetylide is described
in detail, that of 2b being identical.
The spectroscopic characterization of the product
eluted as the first deep-red band is strongly consistent
with formation of the palladium(I) complex [Pd2µ-
I(PPh3)2(η3-C5H2Ph2(PPh2)] (8).10,11 The third band (red)
was due to starting material 2a , whose formation during
the workup accounts for the reverse process between
5a and Bu3SnI.
(9) The isolation of pure transmetalated products 5a ,b was achieved
by precipitation and recrystallization.7b
(10) 1H NMR (CDCl3): δ 7.68 (m), 7.61-7.54 (m), 7.39-6.77 (m),
6.64-6.59 (m), 6.55-6.49 (m), 6.11 (m, Cp). 31P{1H} NMR (CDCl3, 121
MHz): AMX pattern, δA 32.9 (dd, J AM ) 147 Hz, J AX ) 25 Hz),
δM 24.0 (dd, J AM ) 147 Hz, J MX ) 135 Hz), δX -3.3 (dd, J AX ) 25 Hz,
J MX ) 135 Hz). FT-IR (CH2Cl2, cm-1): 3055 (s), 2988 (m), 2306 (m),
1423 (m). MS (15 V, ESP+): 1266 (M + H)+, 1140 (M - I)+, 1003
(M - PPh3 + H)+. Anal. Calcd for C65H42P3IPd2: C, 61.68; H, 4.14.
Found: C, 63.20; H, 4.02. Consistent with the proposed structure, this
product was isolated also by chromatographic separation of the
products of transmetalation obtained by reaction of 2a ,b with different
tin acetylides [Bu3Sn-CtC-C6H4(p-X) (X ) H, Cl, NO2)].
(8) (a) Farina, V.; Krishnamurthy, V.; Scott, W. J . The Stille
Reaction; J ohn Wiley & Sons: New York, 1998. (b) Casado, A. L.;
Espinet, P. J . Am. Chem. Soc. 1998, 120, 8978. (c) Casado, A. L.;
Espinet, P.; Gallego, A. M.; Martinez-Ilarduya, J . M. Chem. Commun.
2001, 339. (d) Casado, A.; Espinet, P.; Gallego, A. M. J . Am. Chem.
Soc. 2000, 122, 11771. (e) Farina, V.; Krishnan, B. J . Am. Chem. Soc.
1991, 113, 9585. (f) Amatore, C.; Carre´, E.; J utand, A.; Tanaka, H.;
Ren, Q.; Torii, S. Chem. Eur. J . 1996, 2, 957. (g) Mateo, C.; Ca´rdenas,
D. J .; Ferna´ndez-Rivas, C.; Echavarren, A. M. Chem. Eur. J . 1996, 2,
1596. (h) Amatore, C.; Broeker, G.; J utand, A.; Khalil, F. J . Am. Chem.
Soc. 1997, 119, 5176. (i) Louie, J .; Hartwig, J . F. J . Am. Chem. Soc.
1995, 117, 11598. (j) Hartwig, J . F. Angew. Chem., Int. Ed. Engl. 1998,
37, 2046.
(11) (a) Kobayashi, Y.; Iitaka, Y.; Yamazaki, H. Acta Crystallogr.,
Sect. B 1972, B28, 899. (b) Felkin, H.; Turner, G. K. J . Organomet.
Chem. 1977, 129, 429. (c) Ducruix, A.; Felkin, H.; Pascard, C.; Turner,
G. K. J . Chem. Soc., Chem. Commun. 1975, 615. (c) Olmstead, M. M.;
Farr, J . P.; Balch, A. L. Inorg. Chim. Acta 1981, 52, 47.

Trimetallic Complexes Containing M-Pd-M Arrays
Organometallics, Vol. 21, No. 14, 2002 3003
F igu r e 1. Sketches and ORTEP drawings of 9a and 9b.
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r a l Refin em en ts
Deta ils for 9a a n d 9b
The red-purple solid isolated from the second band
of the chromatographic column gave a 31P NMR spec-
trum containing two broad signals of slightly different
intensity at δ 35.0 and 34.3 ppm. Initially, the presence
of two noncorrelated 31P NMR signals was interpreted
in terms of the formation of two different products, but
accurately repeated chromatographic separations gave
invariably a single spot elution. Fortunately, well-
shaped crystals of the material eluted as the second
fraction were obtained starting from either 5a or 5b,
which allowed us to carry out single-crystal X-ray
analyses.
X-r a y Str u ctu r e An a lysis of Com p lexes 9a a n d
9b. The molecular structures of complexes rac-9a ,b are
shown in Figure 1 (together with a sketch of the
complexes), while crystal and structural refinement data
are listed in Table 1.
In both compounds, the most relevant feature is a
linear M-Pd-M array in which a palladium center in
a square-planar environment is bound to two trans
molybdenum or tungsten atoms. This trimetallic as-
sembling is framed by two η5-cyclopentadienyl-η1-di-
phenylphosphino chelating ligands. Each cyclopentadi-
enyl moiety coordinates either molybdenum or tungsten
in η5 fashion, while two trans diphenylphosphino groups
complete the square-planar coordination geometry about
palladium. In turn, three terminal carbonyl ligands
complete the piano-stool coordination of each molybde-
num or tungsten center.
In both isostructural compounds, the chelating cyclo-
pentadienyl-diphenylphosphino ligands cause a severe
deformation of the octahedral and square-planar geom-
etries around the molybdenum (or tungsten) and pal-
ladium centers, respectively. The most relevant defor-
9a
9b
formula
fw
cryst syst
space group
a (Å)
C
64H52Mo2O10P2Pd
C74H72O6P2PdW2
1593.44
monoclinic
P21/n
13.691(7)
21.324(9)
21.714(2)
97.72(2)
6281.9
4
1.67
4.04
8698
1341.35
monoclinic
P21/n
32.413(3)
11.466(2)
16.818(3)
103.01(4)
6089.9
4
b (Å)
c (Å)
â (deg)
V (Å3)
Z
Dx (g/cm3)
1.46
7.89
13216
µ (cm-1
)
no. of reflns collcd
no. of reflns with
6535
8698
Io > 2σ(Io)
no. of variables
735
380
GOF
R
Rw
1.64
0.077
0.154
0.991
0.046
0.1069
mation is experienced by palladium, whose coordination
array deviates remarkably from an ideal square-planar
geometry.
In view of the better quality of the refinement data
for the W-Pd-W derivative, a detailed structural
description is presented only for rac-9b (vide infra).
The axes P4-Pd-P5 and W2-Pd-W3, which should
be orthogonal, are instead heavily bent, with the W2-
Pd-P5 and W3-Pd-P4 angles measuring 75.4° and
76.2°, respectively, while the W3-Pd-P5 and W2-Pd-
P4 angles are 104.6° and 105.7°, respectively (Table 2);
all values diverge remarkably from those of an orthogo-
nal geometry that would require 90° for all angles.
The P4-Pd-P5 and W2-Pd-W3 axes, which, at first
glance, seem to contain the three atoms aligned in a

3004 Organometallics, Vol. 21, No. 14, 2002
Angelucci et al.
Ta ble 2. Su m m a r y of Selected Dista n ces (Å) a n d
An gles (d eg) for Com p lexes 9a a n d 9b
Sch em e 2
9a
9b
M )
Mo
W
Pd-M2
2.941(2)
2.932(2)
2.325(5)
2.333(5)
2.019(4)
1.935(3)
169.2(1)
171.4(3)
104.6(1)
75.8(1)
2.912(1)
2.920(1)
2.326(3)
2.321(3)
2.003(1)
1.992(1)
172.0(3)
166.6(1)
105.7(8)
75.4(8)
Pd-M3
Pd-P4
Pd-P5
M2-Cp1(centrd)
M3-Cp2(centrd)
|M2-Pd-M3|
P4-Pd-P5
M2-Pd-P4
M2-Pd-P5
M3-Pd-P4
75.6(1)
76.2(8)
M3-Pd-P5
105.7(1)
107.2(1)
125.7(2)
127.8(1)
112.5(1)
107.5(2)
123.5(1)
129.1(1)
114.5(1)
104.5(8)
108.3(3)
125.4(3)
126.7(4)
120.5(3)
107.3(5)
127.0(3)
123.4(4)
120.4(4)
Cp1(centrd)-M2-Pd
Cp1(centrd)-M2-C6
Cp1(centrd)-M2-C8
Cp1(centrd)-M2-C10
Cp2(centrd)-M3-Pd
Cp2(centrd)-M3-C41
Cp2(centrd)-M3-C43
Cp2(centrd)-M3-C45
straight line, are significantly bent, forming a broken
line with angles of 166.6° and 172.0°, respectively. In
addition, both tungsten centers suffer a severe distortion
from an ideal octahedral geometry. In the two four-
membered rings Cp1-W2-Pd-P5 and Cp2-W3-Pd-
P4 (each Cp is assumed to act as a single unit of this
ring), the Cp1centroid-W2-Pd angle and Cp2centroid-W3-
Pd angle measure only 108.3° and 107.3°. This heavy
distortion reflects also the deformation of the angles of
the carbonyls trans to the W2-Pd and W3-Pd bonds;
the Cp1centroid-W2-C10 (120.5°) and Cp2centroid-W3-
C45 (120.3°) angles are quite different from the values
found for all the other Cpcentroid-W-CO angles (123.4-
127.0°). Further evidence of the ring strain affecting the
two Cpcentroid-W-Pd-P four-membered rings is seen in
the pronounced out-of-plane bending of both phosphorus
(P4 ) 0.54 Å, P5 ) 0.59 Å) with respect to the
corresponding cyclopentadienyl planes. About the cen-
tral core of the complex not only is the square arrange-
ment heavily deformed, but also the expected planarity
around palladium is not observed. The palladium atom
is in fact found approximately 0.18 Å out of the mean
plane formed by the coordinated W2, W3, P4, and P5
atoms (their out-of-plane deviation is 0.02, 0.02, -0.45,
and 0.46 Å, respectively).
Being unsymmetrically substituted and conforma-
tionally blocked by the chelating action of the diphen-
ylphosphine groups anchored to palladium, the cyclo-
pentadienyl moieties of 9a ,b constitute two elements of
chirality.12 Consequently both complexes 9a ,b exist as
a mixture of two diastereisomers (rac-dl and meso)
(Scheme 2). Therefore, the presence of two distinct
singlets in the 31P NMR spectra of crude 9a ,b as
obtained by in-column degradation of 5a ,b can be
attributed to the formation of both rac (sketches 9a /1-2
of Scheme 2) and meso forms (structure 9a /3) in a 1:1
ratio.13
combinations of early and late transition metals.14
However, any study of the reactivity of 9a ,b requires
the development of a convenient high-yield synthesis,
in contrast to the chromatographic degradation of the
transmetalation products 5a ,b. In search of more ef-
ficient routes to the trimetallic compounds, we have
found that the µ-I binuclear complexes [Pd(µ-I){M(CO)3-
7d
(η5-C5H2Ph2(PPh2)}]2 (10a ,b) shown in Scheme 3 are
excellent starting materials to obtain complexes 9a ,b.
The synthetic strategy involves the selective removal
of a PdI2 group from 10a ,b by a chelating diphosphine
ligand such as dppe (dppe ) 1,2-diphenylphosphinoeth-
ane) (Scheme 3). Using this procedure both complexes
9a ,b were obtained as a mixture of the 9a ,b/1-3
stereoisomers.
Rea ctivity of 9a tow a r d Or ga n osta n n a n es. In
previous mechanistic studies of the palladium-catalyzed
M-C bond formation reaction, the transmetalation
complexes 5a ,b have been shown to be crucial interme-
diates in the catalytic cycle leading to the cross-coupling
products 7a ,b (Scheme 1). Indeed, both the metal center
M and the acetylide moiety in complexes 5a ,b join in a
single molecular unit, and completion of the coupling
process only needs the trans-to-cis isomerization and the
reductive elimination steps. It was found that the
(13) From a comparison of the X-ray structures of 9a reported in
Figure 1 with the sketches 9a /1-3 (Scheme 2), it is evident that the
crystalline material obtained upon recrystallization of chromatographi-
cally pure 9a is the rac mixture 9a /1-2. Consequently, the mother
liquor from which these crystals were obtained should result enriched
in the meso form 9a -3. According to this, the 31P NMR spectra of a
sample of the crystalline material (9a /1-2) used for the X-ray analysis
show a single peak at 34.3 ppm, while that of the material recovered
from the mother liquor shows a major peak at 35.0 ppm, due to the
meso form 9a -3, accompanied by a little signal due to a residual amount
of the rac form. An identical NMR behavior was displayed by the
W-Pd-W derivatives rac-9b and meso-9b (see the Experimental
Section).
Alter n a tive Syn th esis of th e Tr im eta llic Com -
p lexes 9a ,b . Complexes 9a ,b with their unusual
M-Pd-M array represent unique structures with po-
tential applications in catalytic processes promoted by
(14) (a) Bianchini, C.; Meli, A. Acc. Chem. Res. 1998, 31, 109. (b)
Bianchini, C.; Meli, A.; Vizza, F. Eur. J . Inorg. Chem. 2001, 43, 43. (c)
Wheatley, N.; Kalck, P. Chem. Rev. 1999, 99, 3379.
(12) Haltermann, R. L. Chem. Rev. 1992, 92, 965.

Trimetallic Complexes Containing M-Pd-M Arrays
Organometallics, Vol. 21, No. 14, 2002 3005
Sch em e 3
Sch em e 4
transmetalation reaction proceeds under dilute condi-
tions ([2a ] = 10-4 M) with the intermediacy of the
solvento complex 4a generated by substitution of PPh3
with DMF (path b of Scheme 1).7d Unambiguous iden-
tification of the solvento complex 4a was obtained from
its independent synthesis by reaction of 1a with a
phosphine-free zerovalent palladium complex, Pd2(dba)3
(dba ) dibenzylideneacetone) (Scheme 4). Although all
our attempts to isolate 4a invariably ended with the
isolation of the binuclear µ-I complex [Pd(µ-I){Mo(CO)3-
(η5-C5H2Ph2(PPh2)}]2 (10a ), the latter dissolved in DMF
converted immediately and quantitatively into 4a ,
which was studied in the reaction toward organostan-
nanes.
ppm (trace b in Figure 2). Immediately, the two peaks
disappeared and were replaced by a doublet of doublets
with J (PP) ) 454 Hz, which was attributed to the
formation of complex 5a bearing trans PPh3 and Cp-
PPh2 groups.7b Therefore, it is likely that the precursor
PPh3-deficient complex is the DMF adduct [Pd(CtC-
Ph)-(DMF){Mo(CO)3(η5-C5H2Ph2(PPh2)}] quoted as 11a
in Figure 2. This figure incorporates all the experimen-
tal evidence obtained and summarizes the stepwise
transformation of 10a into 7a , as well as the reaction
with PPh3 used to intercept the reactive solvento
intermediate 11a .
Con clu sion s
The solvento complex 4a , generated in DMF from 10a ,
was treated with Bu3Sn-CtC-Ph in a 5 mm NMR
tube, and the reaction was followed by 31P NMR
spectroscopy (Figure 2). Upon addition of a 10-fold
excess of the tin acetylide at room temperature, the
singlet of 4a at 51.9 ppm (trace a) disappeared im-
mediately to give two signals at 1.2 and 2.2 ppm. A
signal at -20.2 ppm appeared later (trace b taken after
15 min), which was attributed to the reductive-elimina-
tion product 7a . On warming the sample at 60 °C, the
concentration of 7a increased and two new signals at
34.7 and 34.1 ppm due to 9a /1-3 (meso/rac) appeared
in the spectrum (trace c). After 20 h at 60 °C, while the
signals at 1.2 and 2.2 ppm had disappeared, the main
product 7a was accompanied by a residual amount of
9a (trace d). Further in time only 7a was visible in the
spectrum.
The complexes of transmetalation 5a ,b, which are key
intermediates in the Pd-catalyzed coupling of a metal
halide with trialkyltin acetylide moieties, are unstable
under chromatographic separation and degrade to two
new products: a trimetallic cluster containing a linear
M-Pd-M array (9a , M ) Mo; 9b, M ) W) and a dimeric
palladium(I) complex 8 with a Pd-Pd bond.11 In this
formally Pd(I) complex, the two metal centers are
bridged by an iodide atom and by a η3-pseudoallylic
cyclopentadienyl ligand. The formation of both products
is difficoult to explain given the complexity of the intra-
and intermolecular rearrangements involved as well as
the absence of detected intermediates.
An independent high-yield synthesis of 9a ,b has been
developed. It will allow us to study in depth the
chemistry of these unique compounds in which the
bridging palladium atom still mediates the formation
of M-CtC-R moieties from trialkyltin acetylenes. It
is very likely that other reactions at molybdenum or
tungsten may be assisted by the bridging palladium
center that may behave as either a leaving group or an
active promoter. One of the many possible reactions is
the hydrodesulfurization (HDS) of thiophenes, carried
out in the industrial practice with catalysts containing
either molybdenum or tungsten in conjunction with late
transition metals (like palladium) as activators.14,15
The intermediacy of 9a along the way from 4a to 7a
was initially quite surprising. In fact, it was hard to
conceive that this trimetallic complex, previously iso-
lated after chromatographic degradation of 5a , could
still be reactive toward an organostannane yielding 7a .
This is indeed what happened, as shown by an inde-
pendent NMR experiment in which pure 9a in DMF
reacted with a 10-fold excess of phenyltributyltin acetyl-
ide to selectively give 7a after 20 h at 60 °C.
31P NMR spectroscopy gave valuable information on
the structure of the intermediate along the conversion
of 4a to 9a . PPh3 was added into the NMR tube when
the spectrum contained the two singlets at 1.2 and 2.2
(15) (a) Kabe, T.; Ishihara, A.; Qian, W. Hydrodesulfurization and
Hydrodenitrogenation; Wiley-VCH: Weinheim, 1999. (b) Vasudevan,
P. T.; Fierro, J . L. G. Catal. Rev. Sci. Eng. 1996, 38, 161.

3006 Organometallics, Vol. 21, No. 14, 2002
Angelucci et al.
F igu r e 2. In situ 31P{1H} NMR study of the reaction between 4a and Bu3SnCtC-Ph in DMF-d7.
Legend for 13C NMR assignments:
Exp er im en ta l Section
Gen er a l P r oced u r es. Elemental analyses were performed
by the Servizio Microanalisi of the Dipartimento di Chimica,
Universita` di Roma “La Sapienza”. FT-IR spectra were re-
corded on a Nicolet 510 instrument in the solvent subtraction
mode, using a 0.1 mm CaF2 cell. 1H, 13C, and 31P NMR spectra
were recorded on a Bruker AC300P spectrometer at 300, 75,
[P d {Mo(CO)3(η5-C5-C5H2P h 2(P P h 2)}2] (9a ). This com-
pound was isolated as a product of decomposition, under
chromatographic conditions (n-hexane/dichloromethane, 7:3),
of the product of transmetalation 5a . Subsequently, the
following direct synthesis has been developed. In a Schlenk
tube 10a (0.195 g, 0.12 mmol) and dppe (0.049 g, 0.12 mmol)
were dissolved in THF (20 mL) to give a deep brown solution.
Upon warming to 50 °C for 16 h, the reaction mixture turned
deep purple. After cooling at room temperature, deep yellow
crystals of PdI2(dppe)16 separated from the solution, which
were filtered off, washed with THF, and dried under vacuum.
Celite was added to the filtered solution and the solvent
removed under vacuum. The coated residue was chromato-
graphed on a silica column (30 cm × 2 cm). Elution with
n-hexane/dichloromethane, 7:3, produced a purple band, which
and 121 MHz, respectively. Chemical shifts (ppm) are reported
in δ values relative to Me4Si; for 1H NMR, CHCl3 (δ 7.24) or
DMF (δ 2.90) and for 13C NMR CDCl3 (δ 77.0) or DMF-d7 (δ
161.7) were used as internal standards. The 31P NMR chemical
shifts are relative to 85% H3PO4. Mass spectra were obtained
on a Fisons Instruments VG-Platform Benchtop LC-MS (posi-
tive ion electrospray, ESP+) spectrometer. Solvents, including
those used for chromatography, were thoroughly degassed
before use. Chromatographic separations were performed
using 70-230 mesh silica gel (Merck). All manipulations were
carried out under an atmosphere of argon with Schlenk type
equipment on a dual manifold/argon vacuum system. Liquids
were transferred by syringe or cannula. THF was distilled from
sodium-potassium alloy. [W(I)(CO)3(η5-C5-C5H2Ph2(PPh2)]
(1b)7b and [Pd(µ-I){Mo(CO)3(η5-C5-C5H2Ph2(PPh2)}]2 (10a )7d
were prepared according to published procedures. Ph2PCH2-
CH2PPh2 (dppe), Pd2(dba)3, Bu3Sn-CtC-Ph, and PPh3 (Al-
drich) were used as received.
(16) (a) Ito, T.; Tsuchiya, H.; Yamamoto, A. Bull. Chem. Soc. J pn.
1977, 50 (5), 1319. (b) Oberhauser, W.; Bachmann, C.; Stampfl, T.;
Haid, R.; Bru¨ggeller, P. Polyhedron 1997, 16, 2827.

Trimetallic Complexes Containing M-Pd-M Arrays
Organometallics, Vol. 21, No. 14, 2002 3007
was eluted and collected to give, after removal of the solvent,
contaminated by a residual amount of the rac form. Anal.
1
0.097 g (64%) of 9a . H, 13C, and 31P NMR spectroscopic data
Calcd for C64
H, 3.28.
H44W2O6P2Pd: C, 53.19; H, 3.07. Found: C, 54.17;
showed this product to be a ca. 1:1 mixture of the rac and meso
diastereoisomers. Anal. Calcd for C64H44Mo2O6P2Pd: C, 60.56;
H, 3.49. Found: C, 60.87; H, 3.47.
Ch a r a cter iza tion of 9b/1-2 (m eso d ia ster eoisom er ,
insoluble in acetone). 1H NMR (CDCl3): δ 7.68 (br), 7.45-7.06
(m), 6.97-6.85 (m), 6.23 (m, Cp). 31P{1H} NMR (CDCl3): δ 28.1
(bs). 13C NMR (CDCl3): δ 227.6, 222.6, 213.9 (CO), 134.6-125.6
(Ph), 113.9 (s, C2), 106.0 (br, C4), 88.4 (s, C3), 91.2 (s, C5), 58.7
(s, C1). FT-IR (CH2Cl2, cm-1): 1932 (s), 1862 (s) (νCO).
Ch ar acter ization of 9b/3 (r a c-dl diaster eoisom er , soluble
in acetone). 1H NMR (CDCl3): δ 7.61 (br), 7.26-7.01 (m), 6.86-
6.63 (m), 6.18 (m, Cp). 31P{1H} NMR (CDCl3): δ 28.4 (bs). 13C
NMR (CDCl3): δ 227.0, 223.1, 214.0 (CO), 134.6-126.0 (Ph),
113.5 (s, C2), 88.1 (s, C3), 90.7 (s, C5), 59.0 (br, C1). FT-IR (CH2-
Cl2, cm-1): 1926 (s), 1859 (s) (νCO).
X-r a y Diffr a ction Stu d ies. A summary of crystal and
intensity data is presented in Table 2 for both compounds.
Com p lex 9a . A prismatic specimen of the complex, with
dimensions 0.3 × 0.6 × 0.9 mm, was mounted on a Philips
PW1100 single-crystal diffractometer.17 Data collection was
carried out at room temperature with Mo KR radiation (λ )
0.71069 Å) in the θ range 3-25° (-41 e h e 40, 0 e k e 14,
0 e l e 21). Cell parameters were obtained from least-squares
of 32 reflections (θ range 4.9-13.0°) automatically well cen-
tered on the diffractometer.
One check reflection was monitored every 100: a decompo-
sition of about 21% was observed during the data collection
time. A total of 6535 reflections were with I g 2σ(I) out of a
total of 13216 independent measured (Rint ) 0.043). Only 3831
are those with I g 3σ(I); however corrections for the decay and
for Lorentz and polarization effects were applied. The absorp-
tion correction was performed with the program DIFABS.18
The structure was obtained with the SIR9719 program using
all the measured reflections and was refined with the CRYS-
RULER package20 using SHELX97.21 Four water molecules
were detected in the lattice structure and successfully refined.
The low quality of the experimental data stopped the refine-
ment to R ) 0.154.
Com p lex 9b. A parallelepiped crystal with dimension
0.55 × 0.125 × 0.175 mm was used for the data collection.
Experimental data were recorded at room temperature (20 °C)
on an Enraf-Nonius CAD4. A set of 25 carefully centered
reflections in the range 7° e θ g 9.5° was used for determining
the lattice constants. As a general procedure, the intensities
of three standard reflections were measured periodically every
200 reflections for orientation and intensity control. This
procedure did not reveal decay of intensities. The data were
corrected for Lorentz and polarization effects. Atomic scatter-
ing factors were those tabulated by Cromer and Waber22 with
anomalous dispersion corrections taken from ref 23. An
empirical absorption correction was applied via Ψ scan with
correction factors in the range 0.996-0.863. The computational
work was carried out by using the program SHELX97.21 Final
atomic coordinates of all atoms and structure factors are
available on request from the authors and are provided as
Supporting Information. The structure was solved by direct
methods using the SIR92 program.19 The refinement was done
Subsequent recrystallization of this mixture (CH2Cl2/n-
pentane, vapor diffusion) at -20 °C afforded a crystalline
material, whose X-ray structural determination showed it to
be the rac diastereoisomer (9a /1-2). By evaporation of the
solvent from the mother liquor a residue consisting in the meso
diastereoisomer (9a /3), slightly contaminated by a residual
amount of the rac diastereoisomer, was obtained.
1
Ch a r a cter iza tion of 9a /1-2 (r a c d ia ster eoisom er ). H
NMR (CDCl3): δ 7.67 (br), 7.46-7.07 (m), 6.99-6.85 (m), 6.30
(m, Cp). 31P {1H} NMR (CDCl3): δ 34.3 (bs). 13C NMR
(CDCl3): δ 234.5, 222.4, 213.7 (CO), 134.5-125.7 (Ph), 116.1
(s, C2), 111.0 (br, C4), 93.0 (s, C3), 90.1 (s, C5), 57.8 (d, J C-P
)
44.9 Hz, C1). FT-IR (CH2Cl2, cm-1): 1939 (s), 1875 (s) (νCO).
Ch a r a cter iza tion of 9a /3 (m eso d ia ster eoisom er ). 1H
NMR (CDCl3): δ 7.60 (br), 7.29-7.01 (m), 6.81-6.63 (m), 6.26
(m, Cp). 31P{1H} NMR (CDCl3): δ 35.0 (bs). 13C NMR
(CDCl3): δ 237.8, 226.6, 213.7 (CO), 134.5-125.4 (Ph), 116.2
(s, C2), 110.9 (br, C4), 94.0 (s, C3), 90.8 (s, C5), 58.1 (d, J C-P
48.5 Hz, C1). FT-IR (CH2Cl2, cm-1): 1938 (s), 1873 (s) (νCO).
Ch a r a cter iza tion of P d I2(d p p e). 1H NMR (CDCl3):
)
δ
7.84-7.74 (m), 7.55-7.43 (m), 2.35 (s), 2.23 (s). 31P{1H} NMR
(DMF-d7): δ 66.7 (s). Anal. Calcd for C26H24I2P2Pd: C, 41.2;
H, 3.2. Found: C, 41.3; H, 3.4. MS (15 V, ESP+): 781 (M +
Na)+, 633 (M - I)+. Analytical and spectroscopic properties
are in agreement with reported data.16
[P d (µ-I){W(CO)3(η5-C5H2P h 2(P P h 2)}]2 (10b). A Schlenk
flask was loaded with [W(I)(CO)3{η5-(1-Ph2P-2,4-Ph2)C5H2}]
(1b)7b (0.58 g 0.73 mmol) and Pd2(dba)3 (0.33 g, 0.36 mmol).
After three cycles of vacuum/argon, 15 mL of THF was added
to the flask and the resulting dark solution was stirred for 30
min at room temperature. Upon addition of n-pentane, a brown
powder precipitated, which was collected by filtration, washed
repeatedly with pentane to eliminate the residual dba ligand,
and dried under vacuum. Then 0.42 g (64%) of pure 10b was
1
obtained. H NMR (CDCl3): δ 8.49 (m), 7.75-7.51 (m), 7.30-
7.15 (m), 7.00-6.75 (m), 6.00 (m, 1H, Cp-H), 4.68 (m, 1H, Cp-
H). 31P{1H} NMR (CDCl3): δ 39.0. 13C NMR (CDCl3): δ 228.4,
214.4, 212.5 (CO), 136.8-125.4 (Ph), 116.7 (d, J C-P ) 7.2 Hz,
C2), 108.0 (d, J C-P ) 7.2 Hz, C4), 92.6 (d, J C-P ) 7.2 Hz, C3),
87.0 (d, J C-P ) 12.6 Hz, C5), 58.7 (d, J C-P ) 46.7 Hz, C1). FT-
IR (CH2Cl2, cm-1): 1965 (s), 1889 (s), 1869 (sh) (νCO). Anal.
Calcd for C32H22IMoO3PPd: C, 47.17; H, 2.72. Found: C, 46.97;
H, 2.74.
[P d {W(CO)3(η5-C5-C5H2P h 2(P P h 2)}2] (9b). Like 9a , this
compound was first isolated as a product of decomposition,
under chromatographic conditions (silica gel, n-hexane/dichlo-
romethane, 1:1), of the product of transmetalation 5b. Sub-
sequently, the direct synthesis was accomplished with a
procedure similar to that used for 9a . In a Schlenk tube 10b
(0.257 g, 0.14 mmol) and dppe (0.063 g, 0.15 mmol) were
dissolved in THF (10 mL), and the resulting deep brown
solution was warmed at 70 °C for 17 h. After cooling at room
temperature, Celite was added to the crude mixture and the
solvent was removed under vacuum. The coated residue was
then chromatographed on a silica column (30 cm × 2 cm).
Elution with n-hexane/dichloromethane, 1:1, produced a dark
purple band, which was eluted and collected to give, after
removal of the solvent, 0.097 g (63%) of 9b as a bordeaux
crystalline solid. 1H, 13C, and 31P NMR spectroscopic data
showed this product to be a 1:1 mixture of the rac and meso
diastereoisomers. These were easily separated due to their
different solubility in acetone. Treating the mixture with
acetone, a solution of the rac diastereoisomer was obtained,
while the solid residue was the meso diastereoisomer, slightly
(17) Belletti, D. Gestione on line di diffrattometro a cristallo singolo
Philips PW1100 con PC. Centro di Studio per la Strutturistica
Diffrattometrica del CNR di Parma. Internal report; 1993; 1/93.
(18) Gluzinski, P. XRay set of programs for X-ray structural calcula-
tions; Polish Academy of Sciences: Waeszawa, Poland, 1989.
(19) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Moliterni, A. G. G.; Burla, M. C.; Polidori, G.; Camalli, M.; Spagna, R.
SIR97, A package for crystal structure solution by direct methods and
refinement, 1997.
(20) Rizzoli, C.; Sangermano, V.; Calestani, G.; Andreetti, G. D. J .
Appl. Crystallogr. 1987, 20, 436.
(21) Sheldrick, G. M. SHELX97, Program for Crystal Structure
Determination; University of Go¨ttingen: Germany, 1997.
(22) Cromer, D. T.; Waber, J . T. Acta Crystallogr. 1965, 18, 104.
(23) International Tables of Crystallography; Kynoch Press: Bir-
mingham, UK, 1974; Vol. IV.

3008 Organometallics, Vol. 21, No. 14, 2002
Angelucci et al.
by full-matrix least-squares calculations, initially with isotro-
pic thermal parameters, then with anisotropic thermal pa-
rameters for Pd, W, O, P, and all C atoms but the phenyls.
The phenyl rings were treated as rigid bodies with D6h
symmetry, and the hydrogen atoms were allowed to ride on
the attached carbon atoms. Two solvent crystallization mol-
ecules, pentane and cyclopentadiene, were detected and suc-
cessfully refined.
Su p p or tin g In for m a tion Ava ila ble: Figures showing 1H,
31P NMR and MS spectra of 8. Full tables of crystal data,
atomic coordinates, thermal parameters, and bond lengths and
angles for 9a and 9b. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM020043J