The existence and stability of mononuclear and binuclear organopalladium hydroxo complexes, [(R3P)2Pd(R′)(OH)] and [(R3P)2Pd2(R′)2(μ-OH) 2]

Article abstract of DOI:10.1021/om9605544

Adding excess phosphines (Cy₃P, i-Pr₃P) to binuclear hydroxo complexes of palladium, [(Cy₃P)₂-Pd₂(Ph)₂(μ-OH) ₂] and [(i-Pr₃P)₂Pd₂(Ph)₂

Full text of DOI:10.1021/om9605544

5242
Organometallics 1996, 15, 5242-5245
Notes
Th e Existen ce a n d Sta bility of Mon on u clea r a n d
Bin u clea r Or ga n op a lla d iu m Hyd r oxo Com p lexes,
[(R3P )2P d (R′)(OH)] a n d [(R3P )2P d 2(R′)2(µ-OH)2]
Vladimir V. Grushin† and Howard Alper*
Department of Chemistry, University of Ottawa, 10 Marie Curie,
Ottawa, Ontario, Canada K1N 6N5
Received J uly 8, 1996X
Summary: Adding excess phosphines (Cy3P, i-Pr3P) to
binuclear hydroxo complexes of palladium, [(Cy3P)2-
Pd2(Ph)2(µ-OH)2] and [(i-Pr3P)2Pd2(Ph)2(µ-OH)2], in hex-
ane resulted in precipitation of the first mononuclear
σ-phenylpalladium hydroxides, [(Cy3P)2Pd(Ph)(OH)] (1)
and [(i-Pr3P)2Pd(Ph)(OH)] (2), respectively. Both 1 and
2 were isolated, characterized, and found to be stable in
the solid state. In solution, however, they reversibly lost
one of the two phosphine ligands, converting back to the
binuclear hydroxides. Equilibrium between [L2Pd2(R)2(µ-
OH)2] and [L2Pd(R)(OH)] (L ) Ph3P, Cy3P, i-Pr3P, and
R ) Ph, Me) was studied by variable-temperature 31P
NMR spectroscopy, and the corresponding Keq and ∆G
were calculated. The free energy values obtained at
333-235 K were in the range of +19 to -16 kJ / mol.
mononuclear hydroxides, [L2M(R)(OH)], where L )
tertiary phosphine and R ) σ-organic ligand, are com-
mon only when M ) Pt.7 Their palladium congeners,
[L2Pd(R)(OH)], are rare. Twenty years ago, Yoshida et
al.4b described the synthesis of two hydroxo organopal-
ladium complexes having perfluorinated and perchlo-
rinated organic ligands, i.e., [(Ph3P)2Pd(C6F5)(OH)] and
[(Ph3P)2Pd(CCldCCl2)(OH)]. Analogous palladium com-
plexes with conventional σ-organic ligands have not
been reported, although the formation of [(Ph3P)2Pd-
(Ph)(OH)] has been proposed in reactions of [(Ph3P)2-
Pd(Ph)(I)] with KOH,8 [Bu4N]+OH-,9 or AgBF4, followed
by hydrolysis.9 However, this hydroxo complex was not
isolated or reliably characterized in solution.
In this note, we report our preliminary results on the
synthesis, isolation, and characterization of the first
mononuclear σ-phenylpalladium hydroxides stabilized
with bulky, electron-rich tertiary phosphines, [L2Pd(Ph)-
(OH)], where L ) Cy3P and i-Pr3P. We also com-
municate here our studies of the equilibrium between
[L2Pd(R)(OH)] and [L2Pd2(R)2(µ-OH)2], where L ) Ph3P,
Cy3P, i-Pr3P, and R ) Ph, Me.
In tr od u ction
In recent years, there has been considerable interest
in the chemistry of late transition metal hydroxo
complexes, due to their remarkable reactivity and
unusual catalytic and structural properties.1-3 Various
hydroxo compounds of the metals of the nickel triad
have been reported, including organometallic complexes,
which are of special interest because of their relevance
to catalysis. A number of binuclear Ni,4 Pd,5 and Pt6
organometallics with bridging hydroxo ligands have
been synthesized and characterized. At the same time,
Resu lts a n d Discu ssion
Adding tricyclohexylphosphine to solutions of [(Cy3P)2-
Pd2(Ph)2(µ-OH)2]5d,8 in benzene, toluene, or hexane
caused noticeable changes in the 31P NMR spectrum of
the samples. The intensity of the resonances at 38.0
and 36.3 ppm (6:1 due to the trans and cis isomers,
respectively)5d,8 diminished, and two new singlets arose
at 10.2 and 22.2 ppm. The former was obviously due
to the free phosphine, whereas the latter could be
assigned to the new mononuclear hydroxo complex,
[(Cy3P)2Pd(Ph)(OH)]. It was noticed that, as more
phosphine was added, the new resonances at 10.2 and
22.2 ppm intensified in abundance and the peaks of the
dimer became smaller. Similar observations were made
when triisopropylphosphine was added to a hexane
solution of [(i-Pr3P)2Pd2(Ph)2(µ-OH)2]. It is noteworthy
that the triisopropylphosphine palladium hydroxo dimer
is a new compound which was synthesized from [(i-
Pr3P)2PdCl2],10 iodobenzene, and alkali (See Experi-
† Present address: Department of Chemistry, Wilfrid Laurier
University, Waterloo, ON, Canada N2L 3C5.
X Abstract published in Advance ACS Abstracts, October 15, 1996.
(1) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163.
(2) Gilje, J . W.; Roesky, H. W. Chem. Rev. 1994, 94, 895.
(3) Bergman, R. G. Polyhedron 1995, 14, 3227.
(4) (a) Klein, H. F.; Karsch, H. H. Chem. Ber. 1973, 106, 1433. (b)
Yoshida, T.; Okano, T.; Otsuka, S. J . Chem. Soc., Dalton Trans. 1976,
993. (c) Carmona, E.; Marin, J . M.; Paneque, M.; Poveda, L. M.
Organometallics 1987, 6, 1757. (d) Carmona, E.; Marin, J . M.; Palma,
P.; Paneque, M.; Poveda, L. M. Inorg. Chem. 1989, 28, 1985. (e) Lo´pez,
G.; Garcia, G.; Sa´nchez, G.; Garcia, J .; Ruiz, J .; Hermoso, J . A.; Vegas,
A.; Martinez-Ripoll, M. Inorg. Chem. 1991, 30, 2905.
(5) (a) Lo´pez, G.; Ruiz, J .; Garcia, G.; Vicente, C.; Marti, J . M.;
Santana, M. D. J . Organomet. Chem. 1990, 393, C53. (b) Lo´pez, G.;
Ruiz, J .; Garcia, G.; Marti, J . M.; Sa´nchez, G.; Garcia, J . J . Organomet.
Chem. 1991, 412, 435. (c) Ruiz, J .; Vicente, C.; Marti, J . M.; Cutillas,
N.; Garcia, G.; Lo´pez, G. J . Organomet. Chem. 1993, 460, 241. (d)
Grushin, V. V.; Alper, H. Organometallics 1993, 12, 1890. (e) Ruiz, J .;
Cutillas, N.; Torregrosa, J .; Garcia, G.; Lo´pez, G.; Chaloner, P. A.;
Hitchcock, P. B.; Harrison, R. M. J . Chem. Soc., Dalton Trans. 1994,
2353. (f) Grushin, V. V.; Bensimon, C.; Alper, H. Organometallics 1995,
14, 3259.
(7) Bennett, M. A.; Rokicki, A. Inorg. Synth. 1989, 25, 100.
(8) Grushin, V. V.; Alper, H. J . Am. Chem. Soc. 1995, 117, 4305.
(9) Amatore, C.; Carre´, E.; J utand, A.; M’Barki, M. A.; Meyer, G.
Organometallics 1995, 14, 5605.
(6) (a) Lo´pez, G.; Ruiz, J .; Garcia, G.; Vicente, C.; Marti, J . M.;
Hermoso, J . A.; Vegas, A.; Martinez-Ripoll, M. J . Chem. Soc., Dalton
Trans. 1992, 53. (b) Grushin, V. V.; Bensimon, C.; Alper, H. Organo-
metallics 1993, 12, 2737.
(10) Werner, H.; Bertleff, W Chem. Ber. 1983, 116, 823.
S0276-7333(96)00554-7 CCC: $12.00 © 1996 American Chemical Society

Notes
Organometallics, Vol. 15, No. 24, 1996 5243
mental Section).11 The above NMR experiments sug-
gested that, in solution, the organopalladium hydroxo
dimers were equilibrated with the corresponding mono-
mers upon addition of free phosphine (eq 1).
toluene, dichloromethane, and chloroform, all attempts
to isolate the monomeric hydroxides with triphenylphos-
phine ligands failed. No resonances that could be
assigned to monomeric hydroxo species were observed
in the 31P NMR spectra when PPh3 was added to
solutions of [(Ph3P)2Pd2(R)2(µ-OH)2] (R ) Ph, Me) in
benzene or toluene at room temperature. This observa-
tion was in line with the previously reported8 reaction
between [(Ph3P)2Pd(Ph)(I)] in benzene with aqueous
KOH in the presence of 18-crown-6, which gave [(Ph3P)2-
Pd2(Ph)2(µ-OH)2], free triphenylphosphine, and no de-
tectable mononuclear species. It is believed that the
phase-transfer alkaline hydrolysis of [(Ph3P)2Pd(Ph)(I)]
led to [(Ph3P)2Pd(Ph)(OH)] as the primary product,
which quantitatively converted to the dimer upon facile
elimination of PPh3. Attempts to generate monomeric
hydroxides from the triphenylphosphine hydroxo dimers
and PPh3 in hexane also failed, because of the very poor
solubility of the binuclear complexes in saturated
hydrocarbons. However, when dichloromethane was
used as the solvent, both [(Ph3P)2Pd(Ph)(OH)] (3; δ )
23.1 ppm) and [(Ph3P)2Pd(Me)(OH)] (4; δ ) 30.3 ppm)
were detected by 31P NMR spectroscopy. The 31P NMR
chemical shift of 3 is close to that (23.3 ppm in DMF)
determined by Amatore et.al.9 for the signal that arose
upon addition of water to [(Ph3P)2Pd(Ph)]+ BF4- or when
[(Ph3P)2Pd(Ph)(I)] was treated with [Bu4N]+ OH-.14
For 1 and 2, equilibrium 1 was approached from both
sides, whereas the significantly less stable triphenylphos-
phine derivatives 3 and 4, which could not be isolated,
were generated in situ by adding PPh3 to dichlo-
romethane solutions of the corresponding dimers. For
all complexes 1-4, the equilibrium was monitored by
variable-temperature 31P NMR spectroscopy. At each
temperature, the systems were given enough time to
establish equilibrium 1, so that the integral intensities
measured could be used to compute equilibrium con-
stants, Keq. The 31P NMR data, Keq, and ∆G values
obtained for eq 1 at various temperatures are presented
in Table 1. As can be seen from Table 1, the ∆G values
calculated for the formation of monomers vary in the
range of ca. +20 to -15 kJ /mol, indicating that the
monomeric organopalladium hydroxides are unstable
species which are prone to dimerization via loss of
phosphine. Negative ∆G values were observed for 1 and
2 at ambient and lower temperatures, whereas the
triphenylphosphine complexes 3 and 4 exhibited positive
free energies of formation over the whole range of
temperatures from +18 to -38 °C. It is not surprising
therefore that, unlike the Cy3P and i-Pr3P mononuclear
hydroxides, their triphenylphosphine counterparts can-
not be isolated as individual compounds.
H
O
L
L
R
L
R
L
+ 2L
2
Pd
Pd
Pd
(1)
O
H
R
O
H
1–4
1: L = Cy3P, R = Ph
2: L = i-Pr3P, R = Ph
3: L = Ph3P, R = Ph
4: L = Ph3P, R = Me
An attempt to isolate the new and novel mononuclear
hydroxo complexes was a worthwhile goal. Treatment
of [(Cy3P)2Pd2(Ph)2(µ-OH)2]5d,8 in hexane with excess
Cy3P resulted in the formation and precipitation of
[(Cy3P)2Pd(Ph)(OH)] (1), which was isolated in 72% yield
and found to be analytically and spectroscopically pure.
As Tolman electronic parameters and cone angles for
Cy3P and i-Pr3P are very close,12 it seemed conceivable
that [(i-Pr3P)2Pd(Ph)(OH)] would be of comparable
stability and perhaps isolable as well. When the tri-
isopropylphosphine hydroxo dimer, [(i-Pr3P)2Pd2(Ph)2-
(µ-OH)2], was treated with excess i-Pr3P in hexane and
the resulting solution was kept at -78 °C for a few
hours, the desired complex, [(i-Pr3P)2Pd(Ph)(OH)] (2)
deposited as a crystalline solid which was successfully
isolated. Both 1 and 2 are colorless compounds, which
are quite air-stable in the solid state.13 They were
characterized by elemental analysis and 1H and 31P
1
NMR spectral data. In the H NMR spectra of freshly
prepared samples of 1 and 2 in benzene-d6, the OH
resonances arose as sharp singlets at -3.2 and -3.3
ppm, respectively. Singlet resonances were also ob-
served in the 31P NMR spectra of the mononuclear
organopalladium hydroxides, indicating that the com-
plexes are of trans geometry.
In solution, equilibrium 1 established within minutes.
In fact, the successful isolation of 1 and 2 was due to
the presence of excess free phosphine which shifted
equilibrium 1 toward the mononuclear species. When
samples of 1 and 2 in benzene-d6 or toluene-d8 were
prepared and immediately investigated by ambient-
1
temperature H and 31P NMR, no traces of the dimers
and free phosphines were detected. However, measur-
ing the spectra of the same samples 10-15 min after
they were prepared, revealed the presence of all three
species, i.e., the monomer, the dimer, and the free
ligand. All resonances appeared as sharp lines, sug-
gesting that the direct and reverse processes were slow
on the NMR time scale.
A similar approach was used in an effort to prepare
[(Ph3P)2Pd(R)(OH)] (R ) Ph, Me) from the corresponding
dimers and PPh3. Although various temperatures and
solvents were used, including pentane, hexane, benzene,
From the above and literature4-7 data it is clear that
the equilibrium between [L2M(R)(OH)] and [L2M2(R)2-
(µ-OH)2], where M ) Ni, Pd, Pt, is influenced by a
number of factors, including the nature of M, R, L, and
the solvent. For instance, [(Ph3P)2Pd(C6F5)(OH)] is
stable,4b whereas [(Ph3P)2Pd(C6H5)(OH)] is not, readily
losing triphenylphosphine and forming the dimer. This
difference can be rationalized in terms of the strong
electron-withdrawing effect of the pentafluorophenyl
ligand, as compared to the phenyl. In the pentafluo-
(11) In solution, the triisopropylphosphine binuclear hydroxo dimer,
[(i-Pr3P)2Pd2(Ph)2(µ-OH)2], exists as a 1:7 mixture of cis and trans
isomers (see 1H NMR data in the Experimental Section).
(12) Tolman, C. A. Chem. Rev. 1977, 77, 313.
(13) Even in the crystalline state, complex 2 loses i-Pr3P, converting
slowly to the corresponding dimer. This accounts for the unpleasant
“phosphine odor” of 2 and the lower than anticipated values for both
(14) (a) It is worth noting that many square-planar σ-phenylpalla-
dium(II) complexes, trans-[(Ph3P)2Pd(Ph)(X)], exhibit very similar
chemical shifts in solution 31P NMR spectra.14b (b) Bartik, T.; Himmler,
T. J . Organomet. Chem. 1985, 293, 343.
C
and
H obtained by combustion analysis of the complex (see
Experimental Section).

5244 Organometallics, Vol. 15, No. 24, 1996
Notes
Ta ble 1. 31P NMR Da ta , Keq, a n d ∆G Va lu es for th e System [L2P d 2(R)2(µ-OH)2] + 2L h 2[L2P d (R)(OH)]
31P NMR chemical shifts, δ
∆G,
kJ /mol
cmpd
L
R
solvent
T, K
dimera
monomer
phosphine
Keq
1
Cy3P
Ph
benzene
toluene
toluene
hexane
hexane
hexane
hexane
hexane
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
291
291
333
245
275
291
313
333
235
255
275
291
235
255
275
38.0; 36.3
38.0; 36.3
37.8; 36.2
49.2
48.9
48.7
22.1
22.2
22.5
32.1
32.2
32.2
32.4
32.6
23.1
23.1
23.2
23.3
30.3
30.1
30.0
10.2
10.2
10.5
19.0
19.4
19.8
20.0
20.3
-7.1
-6.7
-6.0
-5.5
-6.8
-6.0
-5.5
13
-6
-16
+8
8 × 102
5 × 10-2
4 × 102
10
2
3
i-Pr3P
Ph
-12
-5
5 × 10-1
1 × 10-1
8 × 10-3
2 × 10-2
1 × 10-2
2 × 10-3
4 × 10-4
7 × 10-2
2 × 10-2
2 × 10-3
+2
+6
+13
+8
+10
+14
+19
+5
+8
+14
48.5
48.2
Ph3P
Ph3P
Ph
33.6; 33.0
33.6; 33.0
33.6; 33.0
33.6; 33.0
39.6; 39.3
39.6; 39.3
39.5; 39.3
4
Me
a
Two resonances are observed due to the trans and cis isomers. See refs 5d,f and 8.
rophenyl complex the metal center is more electron-
deficient and hence should be more inclined to having
two electron-donating phosphine ligands, rather than
one, in the inner coordination sphere.
Pd2(R)2(µ-OH)2] (R ) Ph, Me) are insoluble in alkanes,
acetone, alcohols, toluene, and ether and only slightly
soluble in benzene at room temperature. On the other
hand, polychlorinated solvents are not always inert
toward basic and nucleophilic tertiary phosphines that
participate in the equilibrium between mononuclear and
binuclear organopalladium hydroxides.
It is also clear that, in general, the tendency for
complexes [L2M(R)(OH)] to dimerize with concomitant
loss of phosphine increases in the order Pt < Pd < Ni.
This is expected, as “softness” increases in going from
Ni2+ to Pd2+ and further to Pt2+ ions and so does the
affinity of the metal for soft ligands. In the dimers, each
metal center has two hard hydroxo ligands and one soft
phosphine, whereas in the monomers, the metal ion is
bound to two soft phosphines and one hard hydroxide.
Therefore, among the nickel triad metals, the hardest
Ni2+ adopts the dimeric structure, whereas mononuclear
It is worth mentioning that an attempt was made to
synthesize a palladacarboxylic acid from the more stable
[(Cy3P)2Pd(Ph)(OH)] and CO in hexane and toluene,
following the successful methodology reported for mono-
nuclear platinum hydroxides.16,17 Unfortunately, unlike
the binuclear Pd hydroxides,8 this mononuclear pal-
ladium hydroxo complex reacted with CO sluggishly at
room temperature; the reaction led to a carbonyl phos-
phine Pd(0) cluster species, presumably [(Cy3P)3Pd3-
(CO)3] (31P NMR).18 Carbonylation did occur, but the
primary products of the reaction were unstable for
isolation and detection, undergoing a series of fast
â-elimination and/or reductive elimination processes.
Similar experiments were conducted in the presence of
excess Cy3P, in hope that extra phosphine would
stabilize primary carbonylation products, preventing
them from decomposition. However, in the presence of
an extra 2 equiv of Cy3P, no reaction with CO was
observed during 24 h at room temperature.
hydroxides are preferably formed by the softest Pt2+
.
The palladium ion is softer than Ni2+ and harder than
Pt2+ and, therefore, capable of forming both binuclear
and mononuclear hydroxides.
Our data suggest that equilibrium 1 is influenced by
the nature of the tertiary phosphine. More studies are
necessary before firm conclusions could be drawn con-
cerning which of the two Tolman parameters (electronic
and steric) governs the equilibrium. We believe that
the relative stability of the mononuclear Cy3P and i-Pr3P
hydroxides may be more due to the large cone angles
rather than enhanced basicity, as compared to those of
triphenylphosphine. Very recently Driver and Hartwig15
reported some reactions of [(Ph3P)2Pd2(Ph)2(µ-OH)2],
which were monitored by 31P NMR spectroscopy, in the
presence of (o-CH3C6H4)3P as the internal standard.
This certainly suggests that neither monomeric nor
dimeric organopalladium hydroxo complexes with tri-
o-tolylphosphine ligand (Θ > 190°), if formed at all, were
sufficiently stable to be observed by 31P NMR tech-
niques. Therefore, in order to stabilize mononuclear
organopalladium hydroxides, [L2Pd(R)(OH)], where L )
tertiary phosphine, optimal steric and electronic pa-
rameters for the L are required. The position of
equilibrium 1 seems to be dependent on solvent. More
experiments are needed to understand which solvents
stabilize the mononuclear hydroxides. Unfortunately,
a number of obstacles emerge making these studies
difficult, if not impossible, in many cases. Some orga-
nopalladium hydroxo dimers are insufficiently soluble
for NMR studies. For instance, the complexes [(Ph3P)2-
Exp er im en ta l Section
A Varian XL 300 NMR spectrometer equipped with a
temperature controller was used for measuring 1H and 31P
NMR spectra. Combustion microanalysis was performed with
a Perkin-Elmer 2400 Series II instrument. All chemicals were
purchased from Aldrich Chemical Co. and Organometallics and
were used as received. The organopalladium hydroxo dimers
were synthesized as described in the literature.5d,f,8
[(Cy3P )2P d (P h )(OH)] (1). Tricyclohexylphosphine (200
mg, 0.71 mmol) was added to a mixture of [(Cy3P)2Pd2(Ph)2-
(µ-OH)2]8 (90 mg, 0.09 mmol) and oxygen-free hexane (6 mL),
and the mixture was stirred under N2 at 60 °C for 10 min.
During that time, the dimer dissolved and the mononuclear
hydroxo complex concomitantly precipitated. The mixture was
stirred for 2 h at room temperature; the white solid was
separated, washed with O2-free hexane (3 × 2 mL), and dried
(16) Bennett, M. A. J . Mol. Catal. 1987, 41, 1.
(17) Bennett, M. A.; Robertson, G. B.; Rokicki, A.; Wickramasinghe,
W. A. J . Am. Chem. Soc. 1988, 110, 7098.
(18) (a) Yoshida, T.; Otsuka, S. J . Am. Chem. Soc. 1977, 99, 2134.
(b) Di Bugno, C.; Pasquali, M.; Leoni, P.; Sabatino, P.; Braga, D. Inorg.
Chem. 1989, 28, 1390.
(15) Driver, M. S.; Hartwig, J . F. J . Am. Chem. Soc. 1996, 118, 4206.

Notes
Organometallics, Vol. 15, No. 24, 1996 5245
under vacuum. The yield was 103 mg (72%). Anal. Calcd
for C42H72OP2Pd: C, 66.2; H, 9.5. Found: C, 65.9; H, 9.2. H
2.2 (m, 6 H, CH), 6.9-7.2 (m, 6H, 3,4,5-C6H5), 7.6-7.9 (m, 4H,
2,6-C6H5). 31P NMR (C6D6, 20 °C) δ: 48.7 (s).
1
NMR (C6D6, 20 °C) δ: -3.2 (s, 1H, OH), 1.0-2.2 (m, 66H,
C6H11), 6.9 (m, 1H, 4-C6H5), 7.1 (m, 2H, 3,5-C6H5), 7.7 (m, 2H,
2,6-C6H5). 31P NMR (C6D6, 20 °C) δ: 22.2 (s).
[(i-P r 3P )2P d (P h )(OH)] (2). Triisopropylphosphine (50 µL,
0.26 mmol) was added under N2 to an O2-free solution of [(i-
Pr3P)2Pd2(Ph)2(µ-OH)2] (72 mg, 0.1 mmol) in hexane (3 mL).
The resulting solution was kept first at -17 °C for 3 h and
then at -78 °C for 5 h. The cold mother liquor was quickly
removed by pipet from the precipitated well-shaped crystals
which were washed with cold (-78 °C) pentane (2 × 1 mL),
and dried under vacuum, first at -78 °C, and then at room
temperature. The yield was 60 mg (58%). Anal. Calcd for
[(i-P r 3P )2P d Cl2]. An O2-free solution of triisopropylphos-
phine (2 mL, 1.64 g, 1 mmol) in EtOH (100 mL) was added
dropwise to a vigorously stirred O2-free solution of Na2[PdCl4]
obtained by dissolving PdCl2 (0.6 g, 0.34 mmol) and NaCl (0.6
g, 1.03 mmol) in water (15 mL). The reaction mixture was
worked up in air. Water (50 mL) was added, and the pale-
yellow precipitate was filtered, washed with EtOH (50 mL),
water (100 mL), and acetone (10 mL), and dried under vacuum.
The yield was 1.62 g (96%). 1H NMR (CDCl3, 20 °C) δ: 1.4
(dd, 36H, J H-H ) 7.1 Hz; J P-H ) 14.1 Hz, CH3), 2.8 (m, 6H,
CH). 31P NMR (CDCl3, 20 °C) δ: 36.4 (s). This complex was
originally prepared by the reaction between [(i-Pr3P)3Pd] and
HCl.10
[(i-P r 3P )2P d 2(P h )2(µ-OH)2]. A mixture of [(i-Pr3P)2PdCl2]
(0.4 g, 0.8 mmol), iodobenzene (0.35 g, 1.3 mmol), benzene (6
mL), and a solution of KOH (2 g) in water (4 mL) was
vigorously stirred under reflux (N2) for 4 h. Benzene (5 mL)
was added, the organic layer was separated and evaporated,
and the residual oil was stirred with CH2Cl2 (4 mL) and 50%
KOH (4 g) under N2 for 3 h. The mixture was worked up in
air. The organic layer was separated, filtered through cotton,
and evaporated. The oily residue was dissolved in hexane (2
mL), and the solution was kept at -17 °C overnight. The
colorless crystals were separated, washed with cold hexane,
and dried under vacuum. The yield was 0.12 g (41%). Anal.
Calcd for C30H54O2P2Pd2: C, 49.9; H, 7.55. Found: C, 49.8;
H, 7.45. 1H NMR (C6D6, 20 °C) δ: -3.4 (br s, 0.12H, OH-cis),
-1.8 (d, 1.76H, J P-H ) 2.7 Hz, OH-trans), -0.6 (br t, 0.12H,
OH-cis), 1.0 (dd, 31.5H, J H-H ) 7.2 Hz, J P-H ) 13.9 Hz, CH3-
trans), 1.1 (dd, 4.5H, J H-H ) 7.2 Hz, J P-H ) 13.8 Hz, CH3-cis),
C
24H48OP2Pd: C, 55.3; H, 9.3. Found: C, 54.4; H, 9.1.13 1H
NMR (C
6D6, 20 °C) δ: -3.3 (s, 1H, OH), 1.2 (dd, 36H, J H-H
)
7.1 Hz, J H-P ) 13.4 Hz, CH3), 2.2 (m, 6H, CH), 6.9 (m, 1H,
4-C6H5), 7.1 (m, 2H, 3,5-C6H5), 7.6 (m, 2H, 2,6-C6H5). 31P NMR
(C6D6, 20 °C) δ: 32.1 (s).
Va r ia ble-Tem p er a tu r e 31P NMR Stu d ies. The samples
were prepared and run under nitrogen; 85% H3PO4 was used
as an external standard (20 °C). A standard 5-mm NMR tube
was charged with an oxygen-free solvent (See Table 1 for
specifics; 0.7 mL), a hydroxo complex (1, 2, or one of the dimers;
10-15 mg), and tertiary phosphine (if a dimer was used; ca. 2
mol equiv/equiv of the dimer). At each temperature, the
samples were run several times with D1 ) 1 s, at intervals of
10-45 min, until identical integration ratios (within experi-
mental reproducibility) were obtained for three measurements
in a row. Once equilibrium 1 established, two more spectra
were obtained with D1 ) 3 and 5 s. No changes in the
integration ratio were noticed.
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada (NSERC)
for support of this research.
OM9605544