Synthesis and reactivity of a palladium (I)-palladium (I)-bonded μ-hydroxo complex supported by a bridging butadiene ligand

Article abstract of DOI:10.1021/om020190h

The first Pd-Pd bonded hydroxo-bridged organopalladium dinuclear complex, [Pd₂(μ-OH)(THF)(μ-η²:η²-1,3-C ₄H₆] [PPh₃)₂] [PF₆] (1-THF), was synthesized by a reaction of the sandwich-type complex [Pd₂(μ-η²:η²-1,3-C₄H ₆)₂(PPh₃)₂] [PF₆]₂ with sodium hydroxide in tetrahydrofuran. Reactions of 1-THF with p-toluidine, 3,5-dimethylpyrazole (Hdmpz), benzenethiol, isopropyl alcohol, and p-cresol afforded a series of heteroatom-bridged dinuclear complexes with the general formula [Pd₂(μ-E)(μ-η²:η²-1,3-C₄ H₆)(PPh₃)₂][PF₃] (E = NHC₆H₄Me-p (2), dmpz (3), SPh (4), OCH(CH₃)₂ (5), OC₆H₄Me-p (6)). However, the μ-alkoxo complex 5 was unstable and rapidly decomposed via β-hydrogen elimination by releasing acetone. The complexes 1-THF and 2 were structurally characterized by single-crystal X-ray diffraction analyses. X-ray crystallography of 1-THF revealed that the complex molecule contained a tetrahydrofuran molecule that was associated with the bridging hydroxide through O?H-O hydrogen bonding. The complex 6 was reversibly converted to a hydroxo-bridged complex in the presence of excess water.

Full text of DOI:10.1021/om020190h

Organometallics 2002, 21, 3317-3322
3317
Articles
Syn th esis a n d Rea ctivity of a
P a lla d iu m (I)-P a lla d iu m (I)-Bon d ed µ-Hyd r oxo Com p lex
Su p p or ted by a Br id gin g Bu ta d ien e Liga n d
M. Abdul J alil, Tomoki Nagai, Tetsuro Murahashi,* and Hideo Kurosawa*
Department of Applied Chemistry and Frontier Research Center, Faculty of Engineering,
Osaka University, Suita, Osaka 565-0871, J apan
Received March 7, 2002
The first Pd-Pd bonded hydroxo-bridged organopalladium dinuclear complex, [Pd2(µ-OH)-
(THF)(µ-η2:η2-1,3-C4H6)(PPh3)2][PF6] (1‚THF), was synthesized by a reaction of the sandwich-
type complex [Pd2(µ-η2:η2-1,3-C4H6)2(PPh3)2][PF6]2 with sodium hydroxide in tetrahydrofuran.
Reactions of 1‚THF with p-toluidine, 3,5-dimethylpyrazole (Hdmpz), benzenethiol, isopropyl
alcohol, and p-cresol afforded a series of heteroatom-bridged dinuclear complexes with the
general formula [Pd2(µ-E)(µ-η2:η2-1,3-C4H6)(PPh3)2][PF6] (E ) NHC6H4Me-p (2), dmpz (3),
SPh (4), OCH(CH3)2 (5), OC6H4Me-p (6)). However, the µ-alkoxo complex 5 was unstable
and rapidly decomposed via â-hydrogen elimination by releasing acetone. The complexes
1‚THF and 2 were structurally characterized by single-crystal X-ray diffraction analyses.
X-ray crystallography of 1‚THF revealed that the complex molecule contained a tetra-
hydrofuran molecule that was associated with the bridging hydroxide through O‚‚‚H-O
hydrogen bonding. The complex 6 was reversibly converted to a hydroxo-bridged complex in
the presence of excess water.
In tr od u ction
Until recently several hydroxo-bridged dinuclear or-
ganopalladium(II) complexes have been reported. These
dinuclear structural types are [Pd2R4(µ-OH)2]2- (R )
C6F5,6 C6Cl5,7 C6F3H2-2,4,68), [Pd2R2L2(µ-OH)2] (L )
PPh3; R ) Me,9 Ph,10 C6F5, C6Cl511), and [Pd2(L-L-)2R2-
(µ-X)(µ-OH)] (L-L- ) 2-(dimethylaminomethyl)phenyl,
X ) Br;12 L-L- ) 8-quinolylmethyl, X ) carboxylate13),
having the common PdII(µ-OH)2PdII dinuclear core
without any Pd-Pd interaction. They can react with
various amines, alcohols, nitriles, ketones, and other
protic electrolytes and have been proven as excellent
precursors for preparing related important heteroatom-
bridged dinuclear derivatives.6,7,14-19 Some of these
Late-transition-metal hydroxo, alkoxo, and amido
complexes have attracted recent interest for their
diverse reactivity and relevance to catalytic reactions.1
These species are thought to be involved in many
catalytic processes.2 There has been a common percep-
tion that the late-transition-metal-oxygen or -nitrogen
bonds are unstable, due to a mismatch of the hard basic
ligands with soft metal centers according to the HASB
principle.3 However, a recent study suggests that such
linkages are comparable to those of M-H or M-C bonds
in terms of bond strength4 but reactive enough to
demonstrate interesting reactivities that are usually
absent in metal alkyls or hydrides.5
(5) See, for example: (a) Ritter, J . C. M.; Bergman, R. J . J . Am.
Chem. Soc. 1998, 120, 6826. (b) Ritter, J . C. M.; Bergman, R. J . J .
Am. Chem. Soc. 1997, 119, 2580. (c) Woerpel, K. A.; Bergman, R. J . J .
Am. Chem. Soc. 1993, 115, 7888.
(6) Lo´pez, G.; Ruiz, J .; Garc´ıa, G.; Vicente, C.; Casabo´, J .; Molins,
E.; Miravitlles, C. Inorg. Chem. 1991, 30, 2605.
(7) Lo´pez, G.; Ruiz, J .; Garc´ıa, G.; Mart´ı, J . M.; Sa´nchez, G.; Garc´ıa,
J . J . Organomet. Chem. 1991, 412, 435.
(8) Lo´pez, G.; Garc´ıa, G.; Sa´nchez, G.; Santana, M. D.; Ruiz, J .;
Garc´ıa, J . Inorg. Chim. Acta 1991, 188, 195.
(9) Grushin, V. V.; Bensimon, C.; Alper, H. Organometallics 1995,
14, 3259.
(10) Grushin, V. V.; Alper, H. Organometallics 1993, 12, 1890.
(11) Ruiz, J .; Vicente, C.; Mart´ı, J . M.; Cutillas, N.; Garc´ıa, G.; Lo´pez,
G. J . Organomet. Chem. 1993, 460, 241.
(12) Ruiz, J .; Cutillas, N.; Torregrosa, J .; Garc´ıa, G.; Lo´pez, G.;
Chaloner, P. A.; Hitchcock, P. B.; Harrison, R. M. J . Chem. Soc., Dalton
Trans. 1994, 2353.
(1) Reviews: (a) Fulton, J . R.; Holland, A. W.; Fox, D. J .; Bergman,
R. G. Acc. Chem. Res. 2002, 35, 44. (b) Bryndza, H. E.; Tam, W. Chem.
Rev. 1988, 88, 1163. (c) Fryzuk, M. D.; Montgomery, C. D. Coord. Chem.
Rev. 1989, 95, 1. (d) Roundhill, D. M. Chem. Rev. 1992, 92, 1. (d)
Bergman, R. G. Polyhedron 1995, 14, 3227. (e) Sharp, P. R. J . Chem.
Soc., Dalton Trans. 2000, 2647.
(2) Recent examples: (a) Driver, M. S.; Hartwig, J . F. J . Am. Chem.
Soc. 1996, 118, 7217. (b) Mann, G.; Hartwig, J . F. J . Org. Chem. 1997,
62, 5413. (c) Hartwig, J . F. Synth. Lett. 1997, 3, 329. (d) Louie, J .;
Driver, M. S.; Hamann, B. C.; Hartwig, J . F. J . Org. Chem. 1997, 62,
1268. (e) Wolfe, J . P.; Wagaw, S.; Marcoux, J . F.; Buchwald, S. L. Acc.
Chem. Res. 1998, 31, 805. (f) Marcous, J . F.; Doye, S.; Buchwald, S. L.
J . Am. Chem. Soc. 1997, 119, 10539.
(3) (a) Pearson, R. G. J . Chem. Educ. 1968, 45, 643. (b) Pearson, R.
G. J . Am. Chem. Soc. 1963, 85, 3533.
(4) (a) Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw,
J . E. J . Am. Chem. Soc. 1987, 9, 1444. (b) Bryndza, H. E.; Domaille,
P. J .; Tam, W.; Fong, L. K.; Paciello, R. A.; Bercaw, J . E. Polyhedron
1988, 7, 1441.
(13) Ruiz, J .; Cutillas, N.; Sampedro, J .; Lo´pez, G.; Hermoso, J . A.;
Mart´ınez-Ripoll, M. J . Organomet. Chem. 1996, 526, 67.
(14) Ruiz, J .; Mart´ınez, T.; Vicente, C.; Garc´ıa, G.; Lo´pez, G.;
Chaloner, P. A.; Hitchcock, P. B. Organometallics 1993, 12, 4321.
10.1021/om020190h CCC: $22.00 © 2002 American Chemical Society
Publication on Web 06/18/2002

3318 Organometallics, Vol. 21, No. 16, 2002
J alil et al.
Sch em e 1
hydroxo complexes and their derivatives are potential
catalysts or intermediates in some organic transforma-
tions.10,20 To expand the scope of applications of the late-
transition-metal hydroxo complexes, it is important to
develop other new systems. In recent years metal-
metal-bonded di- or polynuclear palladium and plati-
num complex systems have attracted a great deal of
interest because they have the potential to promote
homogeneous catalytic reactions due to the cooperative
activation of the coordinated substrate molecule by
multiple metal centers.21 Thus, the chemical behavior
of the hydroxo group on a metal-metal bond of the late
transition metals is of particular interest. As part of our
recent interest in metal-metal-bonded di- and poly-
nuclear organopalladium complexes,22 we report here
the first example of a hydroxo-bridged organopalladium
complex having a Pd(I)-Pd(I) bond and its reactions
with various organic molecules containing N-H, O-H,
and S-H bonds.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of th e µ-Hy-
d r oxo Com p lex 1‚THF . Recently our group reported
a sandwich-type bis(1,3-butadiene)dipalladium(I) com-
plex, [Pd2(µ-η2:η2-1,3-C4H6)2(PPh3)2][PF6]2,23 which we
found as an excellent precursor for preparing a new type
of metal-metal-bonded hydroxo-bridged organopalla-
dium complex. Addition of 1 equiv of sodium hydroxide
to [Pd2(µ-η2:η2-1,3-C4H6)2(PPh3)2][PF6]2 in tetrahydro-
furan at room temperature led to facile release of one
butadiene ligand and formation of the hydroxo-bridged
complex 1‚THF, as outlined in Scheme 1.
Recrystallization from tetrahydrofuran and hexane
gave 1‚THF as an orange crystalline solid in 80% yield.
A
1H NMR monitoring experiment revealed that no
hydroxo addition to the µ-butadiene ligand occurred
during this reaction. The isolated orange crystals were
slowly converted to black within few days when they
were stored at room temperature but were unchanged
for several months in a refrigerator. The 1H NMR
spectrum of 1‚THF in CD2Cl2 showed a singlet at δ 3.92
for the OH proton, whose position was much less
shielded than those in the corresponding Pd-Pd-non-
bonded dinuclear hydroxo-bridged complexes (δ -1.0 to
-3.0).6-12 The proton resonances for 1,3-butadiene were
observed at higher fields (δ 3.39, 3.15, and 2.57) than
(15) Driver, M. S.; Hartwig, J . F. J . Am. Chem. Soc. 1996, 118, 4206.
(16) Driver, M. S.; Hartwig, J . F. Organometallics 1997, 16, 5706.
(17) Ruiz, J .; Rodr´ıguez, V.; Lo´pez, G.; Chaloner, P. A.; Hitchcock,
P. B. J . Chem. Soc., Dalton Trans. 1997, 4271.
(18) Ruiz, J .; Curtillas, N.; Rodr´ıguez, V.; Sampedro, J .; Lo´pez, G.;
Chaloner, P. A.; Hitchcock, P. B. J . Chem. Soc., Dalton Trans. 1999,
2939.
(19) Ruiz, J .; Rodr´ıguez, V.; Curtillas, N.; Pardo, M.; Pe´rez, J .; Lo´pez,
G.; Chaloner, P. A.; Hitchcock, P. B. Organometallics 2001, 20, 1973.
(20) (a) Ruiz, J .; Rodr´ıguez, V.; Lo´pez, G.; Casabo´, J .; Molins, E.;
Miravitlles, C. Organometallics 1999, 18, 1177. (b) Grushin, V. V.;
Alper, H. J . Am. Chem. Soc. 1995, 117, 4305 and references therein.
(21) (a) Catalysis by Di- and Polynuclear Metal Cluster Complexes;
Adams, R. D., Cotton, F. A., Eds.; Wiley-VCH: New York, 1998. (b)
Balch, A. L. In Homogeneous Catalysis with Metal Phosphine Com-
plexes; Pignolet, L. H., Ed.; Plenum Press: New York, 1983; p 167. (c)
Sinfelt, J . H. Bimetallic Catalysis: Discoveries, Concepts and Applica-
tions; Wiley: New York, 1983. (d) Guczi, L. In Metal Clusters in
Catalysis; Gates, B. C., Guczi, L., Knozinger, H., Eds.; Elsevier: New
York, 1986. (e) Murahashi, T.; Kurosawa, H. Coord. Chem. Rev., in
press.
(22) Recent examples: (a) Murahashi, T.; Nagai, T.; Mino, Y.;
Mochizuki, E.; Kai, Y.; Kurosawa, H. J . Am. Chem. Soc. 2001, 123,
6927. (b) Kurosawa, H.; Murahashi, T. Pure Appl. Chem. 2001, 73,
295. (c) Murahashi, T.; Nagai, T.; Okuno, T.; Matsutani, T.; Kurosawa,
H. Chem. Commun. 2000, 1689. (d) Murahashi, T.; Otani, T.; Okuno,
T.; Kurosawa, H. Angew. Chem., Int. Ed. 2000, 39, 537. (e) Murahashi,
T.; Mochizuki, E.; Kai, Y.; Kurosawa, H. J . Am. Chem. Soc. 1999, 121,
10660.
(23) Murahashi, T.; Otani, T.; Mochizuki, E.; Kai, Y.; Kurosawa, H.;
Sasaki, S. J . Am. Chem. Soc. 1998, 120, 4536.

A Pd(I)-Pd(I)-Bonded µ-Hydroxo Complex
Organometallics, Vol. 21, No. 16, 2002 3319
F igu r e 2. ORTEP view of 2 with 50% probability el-
lipsoids. The counteranion and another set of disordered
carbon atoms (C2, C3) were omitted for clarity.
F igu r e 1. ORTEP view of 1‚THF with 50% probability
ellipsoids. The counteranion and another set of disordered
carbon atoms (C2 and C3) were omitted for clarity.
between phosphines and the coordinated butadiene.
However, two palladium and two phosphorus atoms are
virtually on the same plane. A detailed discussion on
the structural parameters of the 1,3-butadiene ligand
is limited, due to the disorder of its central two carbon
atoms, C2 and C3, with an almost equal occupancy
(51:49).9 However, the geometry is deduced to be η2:η2-
s-trans by the distance (3.8 Å) between the nondisor-
dered terminal atoms C1 and C4. It should be noted
here that structurally well-characterized hydrogen-
bonded late-transition-metal hydroxo complexes are
quite rare.24 On the other hand, hydrogen-bonded alkoxo
or aryloxo complexes are well documented.25 It should
be also mentioned that the proton of the hydroxo ligand
was directly involved in the hydrogen bonding.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 1‚THF
Pd-Pd
2.5854(5)
2.280(1)
2.075(3)
2.101(6)
2.27(2)
Pd2-P2
Pd2-O1
Pd2-C3
Pd2-C4
O1‚‚‚O2
2.282(1)
2.077(3)
2.20(3)
2.112(6)
2.661(7)
Pd1-P1
Pd1-O1
Pd1-C1
Pd1-C2
Pd1-Pd2-P2
Pd2-Pd1-P1
Pd1-O1-Pd2
P1-Pd1-O1
P1-Pd1-C1
159.62(4)
161.97(4)
77.0(1)
110.70(10)
91.7(2)
P2-Pd2-C4
P2-Pd2-O1
C1-C2-C3
C2-C3-C4
92.5(2)
108.21(10)
141.0(7)
138.0(7)
those for the free diene (δ 7.0-5.0). The spectrum also
confirmed the presence of one tetrahydrofuran molecule
in the complex molecule. The 31P signal was observed
at δ 30.61 as a singlet. We also have prepared a
tetrahydrofuran-free hydroxo complex by a heteroge-
neous reaction between the bis(1,3-butadiene) complex
and solid sodium hydroxide in diclhoromethane, but the
yield was very low. The OH proton signal of the
tetrahydrofuran-free complex was observed at the same
position as that of the previous one (δ 3.93), indicating
that in solution the tetrahydrofuran molecule in 1‚THF
was not so strongly associated with the OH group. In
the solid state, however, it was strongly associated with
the OH group through hydrogen bonding, which was
confirmed by a single-crystal X-ray analysis.
Rea ctivity of 1 w ith Va r iou s Or ga n ic Molecu les.
When 1‚THF was stirred with 1 equiv of p-toluidine in
terahydrofuran for 1 h, the air-stable amido-bridged
complex [Pd2(µ-NHC6H4Me-p)(µ-η2:η2-1,3-C4H6)(PPh3)2]-
[PF6] (2) was formed in 84% isolated yield (Scheme 1).
Several Pd-Pd-nonbonded bis(µ-hydroxo)palladium(II)
complexes were also reported to react similarly with
amines; however, in most cases an excess amount of
amine was necessary for shifting the equilibrium toward
palladium amides.10 The 1H NMR spectrum of 2 in CD2-
Cl2 showed that all protons of butadiene are nonequiva-
lent, and the 31P NMR spectrum showed two doublets
at δ 25.30 and 25.34 (J PP ) 55.4 Hz), indicating the
restricted inversion of the configuration at the amido
nitrogen atom, since it has no symmetry element.
The molecular structure of 2 has been confirmed by
a single-crystal X-ray diffraction analysis. An ORTEP
diagram of the complex cation of 2 is shown in Figure
2, and selected bond distances and angles are listed in
Table 2.
An ORTEP diagram of the complex cation of 1‚THF
is provided in Figure 1, and selected bond distances (Å)
and angles (deg) are listed in Table 1.
The X-ray crystallography revealed that the complex
molecule contains a tetrahydrofuran molecule that is
associated with the bridging hydroxo ligand through
O‚‚‚H-O hydrogen bonding (O1‚‚‚O2 ) 2.661(7) Å). The
two palladium ions are doubly bridged by a hydroxo
group and a butadiene ligand, where the Pd-Pd dis-
tance is 2.5854(5) Å. The average Pd-O distance is
2.076(4) Å, which is very similar to those of other
reported bridging PdII-OH bonds.6,8,10 However, the
Pd1-O1-Pd2 angle (77.6(2)°) is significantly smaller
compared to the corresponding angles of Pd-Pd-non-
bonded dipalladium complexes (∼90-100°).6,8,10 The two
phosphine ligands are bent toward the hydroxyl group,
P1-Pd1-Pd2 ) 161.97(4)° and P2-Pd2-Pd1 ) 159.62-
(4)°, presumably as a consequence of steric repulsions
The structural features of 2 are almost similar to
those of 1‚THF, but the µ-amido group is not involved
in any hydrogen bonding. The average Pd-N distance
is 2.105(1) Å, which is slightly longer than the average
Pd-O distance in 1. However, the Pd-Pd distance
(24) Burn, M. J .; Fickes, M. G.; Hartwig, J . F.; Hollander, F. J .;
Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 5875.
(25) (a) Holland, P. L.; Andersen, R. A.; Bergman, R. G.; Huang, J .;
Nolan, S. P. J . Am. Chem. Soc. 1997, 119, 12800. (b) Kapteijn, G. M.;
Dervisi, A.; Grove, D. M.; Kooijman, H.; Lakin, M. T.; Spek, A. L.; van
Koten, G. J . Am. Chem. Soc. 1995, 117, 10939. (c) Kim, Y. J .; Takenaka,
A.; Yamamoto, A. J . Am. Chem. Soc. 1990, 112, 1096 and references
therein.

3320 Organometallics, Vol. 21, No. 16, 2002
J alil et al.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 2
Sch em e 2
Pd-Pd
2.594(2)
2.292(4)
2.09(1)
2.13(2)
2.31(6)
Pd2-P2
Pd2-N1
Pd2-C3
Pd2-C4
2.273(4)
2.12(1)
2.25(5)
2.17(2)
Pd1-P1
Pd1-N1
Pd1-C1
Pd1-C2
Pd1-Pd2-P2
Pd2-Pd1-P1
Pd1-N1-Pd2
P1-Pd1-N1
P1-Pd1-C1
161.4(1)
161.8(1)
76.0(4)
109.4(4)
91.9(5)
P2-Pd2-C4
P2-Pd2-N1
C1-C2-C3
C2-C3-C4
89.4(6)
110.4(3)
119.0(6)
126.0(7)
Sch em e 3
(2.594(2) Å) and the Pd(1)-N(1)-Pd(2) angle (76.0(4)°)
are almost similar to those of the hydroxo complex
1‚THF. The butadiene ligand is again disordered here
with an unequal occupancy (59:41) and adopts the same
geometry, η2:η2-s-trans, as in 1‚THF.
The azolate-bridged complex [Pd2(µ-dmpz)(µ-η2:η2-1,3-
C4H6)(PPh3)2][PF6] (3) has been obtained in a similar
manner by reacting 1‚THF with 3,5-dimethylpyrazole
(Hdmpz) in tetrahydrofuran (Scheme 1). The complex
precipitated out as a deep orange powder from its
tetrahydrofuran solution upon layering with diethyl
ether. The analytical and spectroscopic data are con-
sistent with the proposed structure. The 1H NMR
spectrum showed two singlets at δ 5.78 and 1.34 for H-4
and the methyl protons of coordinated dmpz, respec-
tively. The 31P resonance was observed at δ 27.42 as a
singlet.
Similar treatment of 1‚THF with benzenethiol in
tetrahydrofuran afforded the air-stable, thiolate-bridged
complex [Pd2(µ-SPh)(µ-η2:η2-1,3-C4H6)(PPh3)2][PF6] (4)
in 74% yield (Scheme 1).26 The NMR spectra and the
analytical data are consistent with the proposed struc-
ture. Three resonances in a ratio of 2:2:1 were observed
for three magnetically different types of aryl protons of
the coordinated thiolate group (one doublet at δ 6.39
for o-H, one triplet at δ 6.75 for m-H, and one triplet at
δ 6.96 for p-H). The spectra showed three peaks for
butadiene protons at δ 3.85, 3.36, and 3.00 and a singlet
31P resonance at δ 30.51, suggesting that the inversion
of the configuration at the sulfur atom was faster than
the NMR time scale at room temperature.
The alkoxo-bridged complex [Pd2(µ-OCH(CH3)2)(µ-
η2:η2-1,3-C4H6)(PPh3)2][PF6] (5) could also be produced
by the same metathesis technique. However, this was
unstable and decomposed through â-hydrogen elimina-
tion. Therefore, an NMR tube reaction was performed
for characterizations of this alkoxo complex and its
decomposition products. Thus, solution of 1‚THF in CD2-
Cl2 was treated with a 5-fold excess of isopropyl alcohol,
and the reaction mixture was subjected to study for
NMR measurements at different intervals. Immediately
after the reaction, the yield of the corresponding alkoxo
complex 5 was about 36%, as estimated by 31P NMR
spectroscopy (δ 29.60 (s)). Coordination of the isopropoxo
group to the palladium atoms was confirmed from its
NMR data. The 1H NMR spectrum showed that two
methyls of the isopropoxo group were magnetically
inequivalent, due to the chiral geometry of the complex
molecule; two diastereotropic methyl peaks appeared at
δ 0.43 and 0.51 as doublets and a complex multiplet for
methyne (CH) proton at δ 1.40. NMR spectra recorded
at different intervals revealed the gradual disappear-
ance of those resonances for the isopropoxo group and
simultaneous appearance of a new peak at δ 2.11, which
can be assigned to free acetone, produced via â-hydrogen
elimination. Unfortunately, we failed to characterize
metal-containing products. Several 31P resonances were
observed after 2 days, indicating the presence of more
than one decomposition product.
The hydroxo complex 1‚THF has also been reacted
with excess p-cresol. The reaction of 1‚THF with 5 equiv
of p-cresol gave the complex 6 in 82% isolated yield.27
The formation of the cresolate-bridged complex became
directly evident from its 1H spectrum, in which the ortho
and meta aryl protons of the cresolato ligand were
observed at higher field (δ 6.05 and 6.27) compared to
those of the free p-cresol (δ 7.03 and 6.72). The 31P
resonance was observed at δ 28.49 as a singlet. Inter-
estingly, the complex 6 was reversibly converted to a
hydroxo complex in the presence of excess water, which
was confirmed by NMR experiments (Scheme 2). Suc-
cessive addition of water increased the formation of the
hydroxo complex and free cresol. For instance, 72%
hydroxo complex was formed by addition of about 50
equiv of water to the cresolato complex 6 in CD2Cl2
containing a few drops of acetone-d6 for better solubility.
VT NMR Exp er im en ts. As discussed above, the
inversion of configuration at the nitrogen atom in the
µ-amido complex 2 was slower than the NMR time scale
at room temperature, which made all butadiene protons
and two 31P nuclei magnetically nonequivalent. On the
other hand, 1‚THF, 4, and 6 gave only three butadiene
proton peaks and one 31P signal, due to the fast
inversion of the configuration (Scheme 3) compared to
the NMR time scale at room temperature. Therefore,
1‚THF, 4, and 6 were subjected to study for low-
temperature NMR experiments in order to clarify
whether the rate of their configurational changes at the
heteroatom would be slowed or not with respect to the
NMR time scale. The VT NMR studies of 1‚THF and 6
in CD2Cl2 revealed that their configurational changes
remained faster than the NMR time scale even at -90
(27) Some reported Pd-Pd-bonded µ-aryloxo complexes: (a) Som-
movigo, M.; Pasquali, M.; Piero, L.; Dario, B.; Piera, S. Chem. Ber.
1991, 124, 97. (b) Werner, H.; Kraus, H. J .; Thometzek, P. Chem. Ber.
1982, 115, 2914. (c) Yamamoto, T.; Akimoto, M.; Saito, O.; Yamamoto,
A. Organometallics 1986, 5, 1559.
(26) An example of a Pd-Pd-bonded µ-thiolato complex: Osakada,
K.; Chiba, T.; Nakamura, Y.; Yamamoto, T.; Yamamoto, A. Organo-
metallics 1989, 8, 2602.

A Pd(I)-Pd(I)-Bonded µ-Hydroxo Complex
Organometallics, Vol. 21, No. 16, 2002 3321
Ta ble 3. Cr ysta llogr a p h ic Da ta for 1‚THF a n d 2
1‚THF
2
empirical formula
fw
cryst syst
space group
a/Å
Pd2C46H41OP3F6
1025.54
Pd2C47H44NP3F6
1042.58
triclinic
P1h (No. 2)
12.802(2)
18.157(3)
10.550(2)
93.197(6)
91.875(1)
99.219(6)
2219.5(7)
1.560
monoclinic
P21/n (No. 14)
10.0739(2)
22.2119(7)
19.5390(4)
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
91.875(1)
4369.7(2)
1.565
9.93
-50
4
D
calcd/(g/cm3)
µ(Mo KR)/cm-1
9.78
-50
2
T/K
F igu r e 3. VT 1H NMR spectra of complex 4 in the
Z
butadiene region (the asterisks denote solvent peaks).
no. of rflns measd
no. of unique rflns
R
Rw
39763
9893
0.030
0.034
11147
9368
0.086
0.092
°C, the lowest available temperature. In contrast, the
configurational change at the sulfur atom in 4 became
slower than the NMR time scale at -60 °C and the
spectrum showed six different proton signals with an
equal intensity at the butadiene region depicted in
Figure 3. Similarly, the singlet 31P resonance also split
into two AB systems (δ 30.31 and 30.84, J PP ) 74.5 Hz).
(CD2Cl2): δ 67.8 (s, CH2, diene), 91.6 (s, CH, diene), 129.2-
133.9 (m, CH, Ar). 31P NMR (109.4 MHz, external H3PO4, CD2-
Cl2): δ 30.61 (s). Anal. Calcd for Pd2C44H45O2P3F6: C, 51.73;
H, 4.05. Found: C, 51.33; H, 4.42.
Syn t h esis of [P d 2(µ-NH C6H 4Me-p )(µ-η2:η2-1,3-C4H 6)-
(P P h 3)2][P F 6] (2). To a solution of 1‚THF (200 mg, 0.195
mmol) in THF (20 mL) was added p-toluidine (21 mg, 0.196
mmol), and the mixture was stirred at room temperature for
1 h. After removal of all volatiles by a rotary evaporator, the
residual solid was dissolved in THF (10 mL) and the solution
filtered. Orange-red crystals of 2 were obtained from the
filtrate upon layering hexane, collecting by decantation, and
drying under vacuum. Yield: 170 mg (84%). 1H NMR (270
MHz, CD2Cl2): δ 7.50-7.20 (m, 30H, Ph), 6.48 (d, 2H, J ) 8.1
Hz, p-tol), 5.81 (d, 2H, J ) 8.1 Hz, p-tol), 3.65 (br d, 1H, diene),
3.48 (br d, 1H, diene), 3.34 (br m, 1H, diene), 3.28 (br m, 1H,
diene), 2.69 (br d, 1H, diene), 2.51 (br d, 1H, diene), 2.07 (s,
3H, CH3). 13C NMR (CDCl3): δ 20.8 (s, CH3), 54.3, 56.6 (s, CH2,
diene), 90.4, 92.2 (s, CH, diene), 121.7 (s, CH, p-tol), 128.9-
133.4 (m, CH, Ar and p-tol), 152.1 (s, CH, p-tol). 31P NMR
(109.4 MHz, external H3PO4, CD2Cl2): δ 25.30 and 25.34 (d, J
) 55.4 Hz). Anal. Calcd for Pd2C47H44NP3F6: C, 54.14; H, 4.28;
N, 1.21. Found: C, 54.11; H, 4.36; N, 1.37.
Con clu sion
We have synthesized and characterized the first
stable Pd-Pd-bonded hydroxo-bridged organopalladium
complex and demonstrated its reactivity with several
organic compounds having N-H, S-H, and O-H bonds.
The study revealed that this novel hydroxide-bridged
complex 1‚THF reacted with the organic molecules in a
manner similar to that reported for Pd-Pd-nonbonded
bis(µ-hydroxo) complexes. In the present metathesis
reaction the Pd-Pd bond remains intact in the resultant
complexes, which allowed us to prepare a new family
of dinuclear complexes. This new system will be par-
ticularly useful in view of our present objectives to
examine the behavior of various active bridging func-
tional groups, including hydroxo, amido, and alkoxo,
coordinated to metal-metal fragments.
Syn t h esis of [P d 2(µ-d m p z)(µ-η2:η2-1,3-C4H 6)(P P h 3)2]-
[P F 6] (3). Through the same procedure described for the
synthesis of 2, 3 was obtained as an orange-red solid from the
reaction of 1‚THF (200 mg, 0.195 mmol) with 3,5-dimeth-
ylpyrazole (18.75 mg, 0.195 mmol) in THF (20 mL). Yield: 156
mg (78%). 1H NMR (270 MHz, CD2Cl2): δ 7.56-7.28 (m, 30H,
Ph), 5.78 (s, 1H, dmpz), 3.32 (br m, 2H, diene) 3.18 (br m, 2H,
diene), 3.28 (br m, 1H, diene), 2.32 (br d, 2H, diene), 1.34 (s,
6H, Me). 13C NMR (CD2Cl2): δ 13.1 (s, CH3) 57.7 (s, CH2,
diene), 92.4 (s, CH, diene), 109.2 (s, CH, dmpz), 129.0-134.0
(m, CH, Ar), 152.2 (s, CH, dmpz). 31P NMR (109.4 MHz,
Exp er im en ta l Section
All reactions were carried out under a nitrogen atmosphere
with standard Schlenk techniques. Solvents were dried and
freshly distilled prior to use. Other chemicals were of reagent
grade and used as received. The sandwich 1,3-butadiene
complex [Pd2(µ-η2:η2-1,3-C4H6)2(PPh3)2][PF6]2 was prepared by
the method already reported by us.23
NMR spectra were recorded on a J EOL GSX-270 spectrom-
external H3PO4, CD2Cl2): δ 27.42 (s). Anal. Calcd for Pd2C45
43N2P3F6: C, 52.39; H, 4.20; N, 2.72. Found: C, 51.97; H,
4.43; N, 3.07.
-
1
eter operating at 270 MHz for H and 109.4 MHz for 31P nuclei.
H
13C and VT NMR studies were conducted on a J EOL J MTC
400 MHz spectrometer. The elemental analyses were per-
formed by the microanalytical service within our department.
Syn th esis of [P d 2(µ-OH)(THF)(µ-η2:η2-1,3-C4H6)(P P h 3)2]-
[P F 6] (1‚THF ). To a stirred solution of Pd2(µ-η2:η2-1,3-C4H6)2-
(PPh3)2][PF6]2 (400 mg, 0.352 mmol) in THF (60 mL) was added
0.1 M NaOH (aqueous; 3.5 mL, 0.350 mmol) by a syringe, and
the mixture was allowed to stand for 1 h. After removal of all
volatiles by a rotary evaporator, the residual solid was
dissolved in THF (10 mL) and the solution filtered. Orange
crystals of 1‚THF were obtained from the THF solution upon
layering hexane, collecting by decantation, and drying under
vacuum. Yield: 290 mg (80%). 1H NMR (270 MHz, CD2Cl2):
δ 7.59-7.48 (m, 30H, Ph), 3.92 (s, 1H, OH), 3.39 (br m, 2H,
diene), 3.15 (br m, 2H, diene), 2.57 (br d, 2H, diene). 13C NMR
Syn th esis of [P d 2(µ-SP h )(µ-η2:η2-1,3-C4H6)(P P h 3)2][P F 6]
(4). Following the same procedure described for the synthesis
of 2, 4 was obtained as a red solid from the reaction of 1‚THF
(200 mg, 0.195 mmol) with benzenethiol (20 µL, 0.195 mmol)
in THF (20 mL). Yield: 150 mg (74%). 1H NMR (270 MHz,
CD2Cl2, 25 °C): δ 7.46-7.33 (m, 30H, Ph), 6.96 (br t, 1H, SPh),
6.75 (br t, 2H, SPh), 6.39 (br d, 2H, SPh), 3.85 (br m, 2H,
diene), 3.36 (br m, 2H, diene), 3.00 (br d, 2H, diene). 13C NMR
(CD2Cl2): δ 62.9 (s, CH2, diene), 93.2 (s, CH, diene), 128.9-
133.5 (m, CH, Ar). 31P NMR (109.4 MHz, external H3PO4, CD2-
Cl2, 25 °C): δ 30.51 (s). Anal. Calcd for Pd2C46H41SP3F6: C,
52.84; H, 3.95. Found: C, 52.81; H, 4.10.
NMR Tu be Rea ction s of 1 w ith Isop r op yl Alcoh ol To
F or m 5. To 1‚THF (7 mg, 6.8 × 10-3 mmol) in 0.6 mL of CD2-

3322 Organometallics, Vol. 21, No. 16, 2002
J alil et al.
Cl2 in an NMR tube was added isopropyl alcohol (2.6 µL, 0.034
mmol), and NMR spectra were recorded at different intervals.
Immediately after the reaction the conversion of 1‚THF into
5 was estimated to be 36%. 5: 1H NMR (270 MHz, CD2Cl2) δ
7.65-7.47 (m, 30H, Ph), 3.38 (br m, 2H, diene) 3.12 (br m,
2H, diene), 2.58 (br m, 2H, diene), 1.40 (m, 1H, CH), 0.52 (d,
mated Mo KR radiation at -50 °C. Indexing was performed
from two oscillation images, which were exposed for 4.2 and
3.3 min for 1‚THF and 2, respectively. Data for both crystals
were processed by the PROCESS-AUTO program package and
corrected for Lorentz and polarization effects. Symmetry-
related absorption corrections were applied using the program
ABSCOR. Both structures were solved by heavy-atom Patter-
son methods and expanded using Fourier techniques.
3H, J HH ) 5.9 Hz, Me), 0.43(d, 3H, J HH ) 6.2 Hz, Me); 31P
NMR (109.4 MHz, external H3PO4, CD2Cl2): δ 29.60 (s).
Syn th esis of [P d2(µ-OC6H4Me-p)(µ-η2:η2-1,3-C4H6)(P P h 3)2]-
[P F 6] (6). To a solution of 1‚THF (300 mg, 0.29 mmol) in
dichloromethane (20 mL) was added p-cresol (156 mg, 1.45
mmol), and the mixture was stirred at room temperature for
3 h. The volume of the reaction mixture was reduced to about
5 mL, and hexane was added to afford a red powder of 6.
Yield: 258 mg (82%). 1H NMR (270 MHz, CD2Cl2): δ 7.59-
7.33 (m, 30H, Ph), 6.27 (d, 2H, 2J HH ) 8.1 Hz, OC6H4Me), 6.05
2
2
Ack n ow led gm en t. Partial support of this work
through Grants-in-Aid for Scientific Research from the
Ministry of Education, Science and Culture, CREST of
J apan Science and Technology Corporation, and the
J apanese Government Special Coordination Fund for
Promotion of Science and Technology is gratefully
acknowledged. Thanks are also due to the J apan Society
for the Promotion of Science (J SPS) for a postdoctoral
fellowship to M.A.J .
2
(d, 2H, J HH ) 8.1 Hz, OC6H4Me), 3.39 (br m, 4H, diene), 2.68
(br d, 2H, diene), 1.99 (s, 3H, Me). 31P NMR (109 MHz, external
H3PO4, CD2Cl2): δ 28.49 (s). Anal. Calcd for Pd2C47H43
-
OP3F6‚0.5CH2Cl2: C, 52.53; H, 4.08. Found: C, 52.26; H, 4.09.
X-r a y Cr ysta llogr a p h ic Stu d ies. The crystallographic
data are summarized in Table 3. Crystals of 1‚THF were grown
from a solution of the complex in tetrahydrofuran/hexane.
Crystals of 2 were grown by slow evaporation of its methanol
solution. All measurements were made on a Rigaku RAXIS-
RAPID imaging plate diffractometer with graphite-monochro-
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, bond lengths and angles, and anisotropic thermal
parameters for 1‚THF and 2. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM020190H