Reaction chemistry of [Pd2(μ-OH)2L4]2+ with arylamines

Article abstract of DOI:10.1016/S0020-1693(02)01278-1

The reaction of [Pd₂(μ-OH)₂(PPh₃)₄](BF ₄)₂ (1) with aromatic amines (aniline and p-toluidine) in dichloromethane yields the dinuclear complexes [Pd₂(μ-OH)(μ-NHAr)(PPh₃

Full text of DOI:10.1016/S0020-1693(02)01278-1

Inorganica Chimica Acta 345 (2003) 8Á14
/
www.elsevier.com/locate/ica
Reaction chemistry of [Pd2(m-OH)2L4]2ꢀ with aryl amines.
Structures of [Pd2(m-OH){m-NH(p-tol)}(PPh3)4](BF4)2,
[Pd(h3-CH2C(NH(p-tol)CH2)(PPh3)2](BF4), and
[Pd(PMe2Ph)2(m-PF2O2)]2(PF6)2
S. Kannan, Alan J. James, Paul R. Sharp *
Department of Chemistry, College of Arts and Science, 125 Chemistry, University of Missouri, Columbia, MO 65211, USA
Received 8 April 2002; accepted 6 May 2002
Dedicated in honor of Professor Richard Schrock
Abstract
The reaction of [Pd2(m-OH)2(PPh3)4](BF4)2 (1) with aromatic amines (aniline and p-toluidine) in dichloromethane yields the
dinuclear complexes [Pd2(m-OH)(m-NHAr)(PPh3)4](BF4)2 (2) (ArꢁPh, p-tol). The same reaction in acetone gives the palladium(II)
/
ꢂ
allyl complex, [Pd(h3-CH2C(NHp-tol)CH2)(PPh3)2](BF4) (3). An attempt to prepare the PMe2Ph analog of 1 as the PF6 salt
yielded instead [Pd(PMe2Ph)2(m-PF2O2)]2(PF6)2 (7).The structures of 2 (Arꢁ
/
p-tol), 3, and 7 have been determined by X-ray
diffraction methods.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Palladium; Hydroxo; Amido; Allyl; Phosphine
1. Introduction
[Pd2(m-OH)2(PPh3)4](BF4)2 (1) [9] with aromatic amines
and the unexpected formation of an amido allyl complex
when the reaction is conducted in acetone.
Palladium complexes are important catalysts or
catalyst precursors in organic syntheses [1]. Recently,
they have found use in carbonÃ
/
nitrogen bond formation
[2], in acetalizations [3], in Mannich-type reactions [4]
and in oxidation reactions [5]. Amido, alkoxo, and
hydroxo complexes are proposed as intermediates in
many of these processes. In addition, amido and
hydroxo complexes are useful synthetic precursors
taking advantage of their basicity [6]. They may also
be deprotonated to give oxo and imido complexes [7].
As a continuation of our studies on the chemistry of
hydroxo/oxo and amido/imido complexes of late-transi-
tion metal ions [7,8], we report the reactions of the
triphenylphosphine palladium(II) hydroxo complex
2. Experimental
Reactions were conducted in air. Solvents and
reagents were reagent grade and used as received.
Ethanol was 95%. NMR spectra were recorded at
ambient temperatures on a Bruker AMX-250 spectro-
meter, using internal SiMe4 (1H), external CFCl3 (19F),
and external H3PO4 (31P) as standards and are reported
in ppm with negative shifts upfield of the standard. IR
spectra (cmꢂ1) were recorded on a Nicolet 550 Magna
FTIR spectrometer as mineral oil mulls between NaCl
plates. M-H-W Laboratories, Arizona, carried out the
elemental analyses. [Pd2(m-OH)2(PPh3)4](BF4)2 (1) [9]
and Pd(PMe2Ph)2Cl2 [10] were prepared by reported
methods.
* Corresponding author. Tel.: ꢀ
2754
E-mail address: sharpp@missouri.edu (P.R. Sharp).
/
1-573-882 7715; fax: ꢀ1-573-882-
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 2 7 8 - 1

S. Kannan et al. / Inorganica Chimica Acta 345 (2003) 8Á
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9
2.1. [Pd2(m-OH)(m-NHAr)(PPh3)4](BF4)2 (2)
(ArꢁPh, p-tol)
C2,6), 132.1 (s, tol C3,5), 133.9 (t, JPÃC
C3,5), 135.6 (s, tol C4), 136.1 (s, tol C3,5) 148.8 (t, JPÃC
ꢁ
/
6.5 Hz, PPh3
/
ꢁ
/
5.2 Hz, allyl Cb). Anal. Calc. (Found) for
C46H42BF4N1P2Pd: C, 64.0 (63.9); H, 4.9 (5.0); N, 1.6
(1.6)%.
The amine (0.400 mmol) was slowly added to a stirred
CH2Cl2 (5 ml) suspension of [Pd2(m-OH)2(PPh3)4](BF4)2
1 (250 mg, 0.170 mmol) and the mixture was stirred
overnight. The resulting clear red solution was evapo-
rated to dryness in vacuo. The residue was extracted
with CH2Cl2 (2 ml) and filtered. THF (3 ml) addition to
2.3. [Pd(PMe2Ph)2(m-PF2O2)]2(PF6)2 (7)
An acetone solution of AgPF6 (250 mg, 0.990 mmol)
was added to a stirred suspension of PdCl2(PMe2Ph)2
(220 mg, 0.486 mmol) in acetone containing few drops
of water. The mixture was stirred for 2 h and then
filtered to remove AgCl. The volatiles were removed in
vacuo and the residue was extracted with CH2Cl2. The
extract was filtered and the volume of the filtrate was
reduced to 2 ml and layered with C6H5CH3. Slow
evaporation yielded yellow crystals of the product
the filtrate followed by cooling at ꢂ
gave a redÁorange solid, which was filtered-off, washed
with ether and dried in vacuo. Recrystallization from
CH2Cl2/diglyme (diglymeꢁ2-methoxyethyl ether) gave
red crystals suitable for X-ray diffraction (Arꢁp-tol).
ArꢁPh. Yield: 210 mg (80%). IR: 3574 (OH), 3292
(NH). 1H NMR (CD2Cl2): ꢂ
OH), 1.30 (br, NH), 7.1Á7.4 (m, PPh3 and NHPh).
31P{1H} NMR (CD2Cl2): 29.3, 29.9 (AB quartet, 2JPP
19.5 Hz). 19F NMR (CD2Cl2): ꢂ
151.3 (s). Anal. Calc.
(Found) for C78H67B2F8OP4Pd2N×diglyme: C, 60.1
(60.0); H, 4.8 (4.5); N, 0.8 (1.0)%.
Arꢁp-tol. Yield: 180 mg (68%). IR: 3582 (OH), 3301
(NH). 1H NMR (CD2Cl2): ꢂ
OH), 1.28 (br s, NH), 2.41 (s, tol), 7.2Á
tol). 31P{1H} NMR (CD2Cl2): 29.0, 29.8 (AB quartet,
2JPP 20.0 Hz). 19F{1H} NMR (CD2Cl2): ꢂ
151.4 (s).
Anal. Calc. (Found) for C79H69B2F8NOP4Pd2×0.5di-
glyme: C, 60.6 (60.5); H, 4.7 (4.8); N, 0.9 (0.9)%.
/
10 8C overnight
/
/
/
/
3
/
3.20 (t, JPH
ꢁ2.5 Hz,
/
/
ꢁ
/
suitable for X-ray analysis. Yield: 210 mg (69%).
1H NMR (d6-acetone): 1.91 (d, 24H, JPH
2
/
ꢁ11.6 Hz,
/
/
PMe2), 7.50Á
tone): 19.8 (s, PMe2Ph), ꢂ
/
7.72 (m, 20H, PPh). 31P NMR (d6-ace-
1
/
13.5 (t, JPÃF
ꢁ960 Hz,
/
1
/
PF2O2), 142.6 (sept, JPÃF
(d6-acetone): ꢂ
71.6 (d, 1JFÃP
1JFÃP
960 Hz, PF2O2).
ꢁ
/
708 Hz, PF6). 19F NMR
708 Hz, PF6), ꢂ80.6 (d,
3
/
3.27 (t, JPH
ꢁ/2.5 Hz,
/
ꢁ
/
/
/7.4 (m, PPh3 and
ꢁ
/
ꢁ
/
/
2.4. X-ray structure determinations
/
Crystals of the complexes were obtained as described
above and were taken from the mother liquor and
placed in an N2 cold stream on a SMART CCD system.
A summary of crystal data and data collection and
processing is given in Table 1. Data collection and
processing followed routine procedures. Details may be
found in the supporting information.
2.2. [Pd(CH2C{NH(p-tol)}CH2)(PPh3)2](BF4) (3)
(a) From [Pd2(m-OH)2(PPh3)4](BF4)2. p-Toluidine (45
mg, 0.42 mmol) was slowly added to a stirred acetone (5
ml) suspension of dihydroxo complex 1 (250 mg, 0.170
mmol). The mixture was stirred for 24 h after which time
the clear yellow solution was filtered. The filtrate was
concentrated to approximately 1 ml, layered with 2 ml
3. Results and discussion
of C6H14 and cooled at ꢂ10 8C for 12 h. The resulting
/
white solid was filtered-off, washed with C6H14 and
dried. Yield: 220 mg (75%). (b) From [Pd2(m-OH)(m-
NHp-tol)(PPh3)4](BF4)2. p-Toluidine (10 mg, 0.093
mmol) was slowly added to a stirred acetone (2 ml)
3.1. [Pd2(m-OH)(m-NHAr)(PPh3)4](BF4)2 (2, Arꢁ
Ph, p-tol)
/
Many Pt and Pd bridging amido complexes have been
prepared by aminolysis of bridging hydroxo complexes
[11,12]. Although this process has been applied to
solution of 2 (Arꢁ
solution was stirred for 2 h, layered with C6H14 (4 ml),
and cooled at ꢂ10 8C overnight. The white crystalline
/p-tol) (120 mg, 0.077 mmol). The
/
platinum complexes of the type [Pt(m-OH)L2]22ꢀ (Lꢁ
/
product was filtered-off, washed with C6H14 and ether,
and dried. Yield: 115 mg (91%). Crystals for the X-ray
analysis were obtained from acetone/C7H16.
a phosphine, L2ꢁa diphosphine), aminolysis reactions
/
with the analogous Pd complexes have not been
reported. As we previously reported with the Pt analog
[12], the dihydroxo bridged palladium(II) compound
[Pd(m-OH)(Ph3P)2]2(BF4)2 (1) with aryl amines (Scheme
1) readily yields the hydroxo-amido bridged dinuclear
palladium(II) complexes [Pd2(m-OH)(m-NHAr)(PPh3)4]-
1
IR: 3348 (NH). H NMR (CD2Cl2): 1.65 (br s, 1H,
NH), 2.36 (s, 3H, tol), 2.64 (m, 2H, allyl syn-H), 3.24 (br
2
d, JHH
ꢁ
/
2.5 Hz, 2H, allyl anti-H), 7.04Á7.40 (m, 34H,
/
PPh3 and tol). 31P{1H} NMR (CD2Cl2): 26.1 (s). 19F
NMR (CD2Cl2): ꢂ
151.8 (s). 13C {1H} NMR (CD2Cl2):
21.0 (s, tol CH3), 55.1 (dd, JPÃC 19.9 and 39.8 Hz, allyl
Ca), 123.6 (s, PPh3 C1), 129.15 (t, JPÃC 5.1 Hz, PPh3
C2,6), 131.23 (s, PPh3 C4), 131.5 (s, tol C1), 131.9 (s, tol
/
(BF4)2 (2, ArꢁPh, p-tol). The spectroscopic properties
/
ꢁ
/
of 2 closely resemble those reported for the Pt analogs
with the exception that 195Pt coupling in the NMR
spectra is absent in 2. The 31P NMR spectra of 2 show a
ꢁ
/

10
S. Kannan et al. / Inorganica Chimica Acta 345 (2003) 8Á
/14
Table 1
Crystallographic and data collection parameters at 173 K
a
Complex
[Pd2(m-OH)(m-NHp-tol)(PPh3)4](BF4)2 (2)
[Pd(h3-CH2C(NHp-tol)CH2)(PPh3)2](BF4) [Pd(PMe2Ph)2(m-PF2O2)]2(PF6)2
(3)
(7)
d
Formula
C79H69B2F8NOP4Pd2×2.5CH2Cl2×0.5C6H14O3
C46H42BF4N1P2Pd
colorless/rod
triclinic
C32H44F16O4P8Pd2
yellow/prism
triclinic
Color/habit
Crystal system
Space group
red/prism
monoclinic
P21/c
¯
P1/
¯
P1/
/
/
˚
a (A)
16.8842(8)
23.4920(12)
21.6947(11)
11.1017(7)
13.9591(8)
14.6092(9)
86.586(1)
71.638(1)
70.093(1)
2
8.8701(4)
16.6431(8)
16.8285(8)
72.812(1)
85.223(1)
84.191(1)
2
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
Z
96.102(1)
4
Crystal size (mm) 0.3ꢃ0.3ꢃ0.2
0.3ꢃ0.2ꢃ0.1
0.3ꢃ0.3ꢃ0.2
Trans range (%)
Observed
100Á
/
78.64
100Á
7184
/
81.84
100Á
8348
/
83.05
9901
(ꢀ2s(I))
Total/unique/Rint 45 520/18 077/0.0620
19 983/8743/0.0329
27.12/98.1
14 400/9931/0.0173
27.14/94.9
u max/% mea-
sured
R1 b/wR2 c/S
27.22/94.7
0.0679/0.1953/0.997
0.0366/0.0788/1.023
0.0337/0.0875/1.030
a
Siemens CCD system (omega scans), SADABS absorption correction.
R1ꢁ(a jjFojꢂjFcjj)/a jFoj.
b
c
wR2ꢁ[(a w(Fo2ꢂFc2)2)/a w(Fc2)2]1/2
The half occupancy solvent molecules were disordered about an inversion center.
.
d
Scheme 1.
Fig. 1. Drawing of the cationic portion of [Pd2(m-OH)(m-
NHAr)(PPh3)4](BF4)2 (2) (Arꢁp-tol). Aryl group hydrogen atoms
are omitted for clarity. Arbitrary spheres represent hydrogen atoms
and aryl group carbon atoms; all other atoms are represented by 50%
probability thermal ellipsoids.
doublet of doublets with JPÃP of about 20 Hz indicating
inequivalent phosphine ligands in a cis configuration. IR
/
spectra show the presence of both hydroxo (nOH
3582 cmꢂ1) and amido groups (nNH
3292, 3301
cmꢂ1). The 1H NMR spectrum shows the expected
aromatic peaks and the tol methyl peak for 2, Arꢁp-
tol. The OH proton triplet (JPH 2.5 Hz) shows that the
ꢁ
/
3574,
ꢁ
/
/
Table 2
ꢁ
/
˚
Selected distances (A) and angles (8) for [Pd2(m-OH)(m-NH(p-
OH group is coupled to only two of the phosphine
ligands, presumably to one on each Pd center in a trans
position to the OH group. The NH group signal could
not be positively assigned.
tol))(PPh3)4](BF4) (2) (Arꢁp-tol)
Bond distances
Pd1ÃO1
Pd1ÃN1
Pd1ÃP3
Pd1ÃP4
Pd2ÃO1
2.122(4)
2.134(4)
Pd2ÃN1
Pd2ÃP1
Pd2ÃP2
Pd1ÃPd2
N1ÃC51
2.104(4)
2.2556(15)
2.3042(15)
3.1985(6)
1.443(7)
An X-ray crystal structure determination confirms the
2.2530(15)
2.3134(15)
2.119(4)
identity of 2 (Arꢁp-tol). A drawing of the cationic
/
portion is given in Fig. 1. A summary of crystal and data
collection parameters is given in Table 1. Selected
distances and angles are listed in Table 2. Although
the crystals of 2 are not isomorphous with those of the
reported Pt analog [12], the structures of the cationic
portions are nearly isostructural. The most notable
Bond angles
Pd2ÃO1ÃPd1
Pd2ÃN1ÃPd1
O1ÃPd1ÃN1
P3ÃPd1ÃP4
97.93(16)
98.01(17)
80.89(16)
94.36(6)
N1ÃPd2ÃO1
P1ÃPd2ÃP2
C51ÃN1ÃPd2
C51ÃN1ÃPd1
81.65(16)
95.02(6)
111.0(3)
109.1(3)

S. Kannan et al. / Inorganica Chimica Acta 345 (2003) 8Á
/14
11
difference is the near planarity of the Pd complex
O edge
of the two Pd square-planar coordination spheres is only
Table 3
Selected distances (A) and angles (8) for [Pd(h3-CH2C(NH(p-
tol))CH2)(PPh3)2](BF4) (3)
˚
reported here. The fold along the common NÃ
/
10.58 whereas that for the Pt analog is 31.18. As a result,
Bond distances
˚
Pd distance (3.1985(6) A) in 2 is longer than that
the PdÃ
/
Pd1ÃC1
Pd1ÃC2
Pd1ÃC3
Pd1ÃP1
Pd1ÃP2
2.141(3)
2.159(3)
2.273(2)
2.3049(7)
2.3229(7)
N1ÃC3
N1ÃC71
C1ÃC3
C2ÃC3
1.368(3)
1.420(3)
1.415(4)
1.419(4)
˚
in the Pt complex (3.159(1) A). Bond distances in 2 are
longer than in the Pt complex or equal despite the
˚
greater covalent radius of Pt (1.28 vs. 1.30 A). The
greatest difference is in the MÃO distances, which are
significantly longer in 2 (2.119(4) and 2.124(4) A) than
/
Bond angles
C1ÃPd1ÃC2
C1ÃPd1ÃC3
C2ÃPd1ÃC3
C1ÃPd1ÃP1
C2ÃPd1ÃP1
C3ÃPd1ÃP1
C1ÃPd1ÃP2
C2ÃPd1ÃP2
C3ÃPd1ÃP2
P1ÃPd1ÃP2
˚
66.82(11)
37.24(10)
37.23(10)
95.35(8)
C3ÃN1ÃC71
C3ÃC1ÃPd1
C3ÃC2ÃPd1
N1ÃC3ÃC1
N1ÃC3ÃC2
C1ÃC3ÃC2
N1ÃC3ÃPd1
C1ÃC3ÃPd1
C2ÃC3ÃPd1
127.9(2)
76.45(15)
75.74(15)
125.2(3)
119.8(3)
113.4(2)
124.08(17)
66.32(14)
67.03(14)
˚
in the Pt analog (2.059(6) and 2.066(6) A).
In some dihydroxo complexes related to 1, it is
possible to exchange both hydroxo groups for amido
groups [12]. Attempts to do this and obtain the bis-
amido compound [Pd2(m-NHAr)2(PPh3)4](BF4)2 failed.
Excess aryl amine in a variety of solvents (CH2Cl2,
ClCH2CH2Cl, THF, toluene) at room temperature gives
only the amido-hydroxo complex 2. Refluxing the
mixtures gives palladium metal and triphenylphosphine
oxide. The Pt analog of 2 also failed to give a diamido
complex. This was attributed to steric factors, which
also must apply here for Pd. An entirely different
product is obtained when the reaction of 1 with aryl
amines is conducted in acetone.
162.08(9)
127.36(7)
161.94(8)
95.45(8)
128.02(7)
102.21(2)
Scheme 2.
3.2. [Pd(CH2C{NH(p-tol)}CH2)(PPh3)2](BF4) (3)
The reaction of [Pd(m-OH)(Ph3P)2]2(BF4)2 1 with p-
toluidine in acetone gives white crystalline [Pd(h3-
CH2C{NH(p-tol)}CH2)(PPh3)2](BF4) (3). The 31P
NMR spectrum of 3 shows a single resonance at 26.1
ppm. The IR spectrum shows the presence of an NH
group but no OH group. The 1H NMR spectrum shows
the presence of aryl ring protons, a tol methyl group (d
2.36, 3H) and two resonances at d 2.65 (m, Jꢁ
/
3 Hz,
2H) and 3.24 (d, Jꢁ2.5 Hz, 2H). The resonances at d
/
1
2.65 and 3.24 could not be assigned from the H NMR
spectrum alone. The 13C NMR spectrum shows the
expected peaks for the PPh3 and the tol group and two
additional carbon peaks (d 55.1 and 148.8), which are
coupled to the phosphorus atoms. The identity of 3 as
the mononuclear allyl complex [Pd(h3-CH2C{NH(p-
tol)}CH2)(PPh3)2](BF4) was revealed by an X-ray crys-
tal structure determination (Scheme 1, Tables 1 and 3,
Fig. 2). The unidentified resonances in the NMR spectra
are assigned to the allyl group. An examination of the
literature reveals that the analog of 3 has been pre-
viously prepared from the reaction of amines with the
allenyl/propargyl complex [Pd(h3-CHCCH2)(PPh3)2]-
(BF4) (4) (Scheme 2) [13]. This and related complexes
have attracted attention for resonance contributions
from metallacycle and heteroatom substituted trimethy-
Fig. 2. Drawing of the cationic portion of [Pd(h3-CH2C(NHp-
tol)CH2)(PPh3)2](BF4) (3). Aryl group hydrogen atoms are omitted
for clarity. Arbitrary spheres represent hydrogen atoms and aryl group
carbon atoms; all other atoms are represented by 50% probability
Complex 3 is also obtained when the hydroxo amido
complex 2 is treated with 1 equiv. of amine in acetone.
Without the added amine, both 1 and 2 are stable in
acetone for several days.
The source of the C3 unit for the allyl must be
acetone. Two possible pathways for the reaction are
considered in Scheme 3. In path A, the reaction of
acetone with the dihydroxo complex gives the hydroxo
allyl complex 5 by hydroxo group deprotonation of
acetone and tautomerization of the resulting enolate.
Hydroxo complexes are effective deprotonating agents
and Pd and Pt enolate complexes have been formed by
lenemethane complexes [13Á17]. The phenyl analog of 3
/
has been structurally characterized and the metrical
parameters are identical to those of 3 [13].

12
S. Kannan et al. / Inorganica Chimica Acta 345 (2003) 8Á14
/
hydroxo complex [Pd(PPh3)2(MeCN)(OH)]ꢀ has been
reported [18a].
In path B of Scheme 3, the absence of acetone
reactivity with 1 and 2 is accommodated by prior
reaction of aniline with acetone to form the imine. The
imine, or its eneamine tautomer, then reacts with the
dihydroxo complex 1 (or 2) cleaving the bridge with loss
of a proton to the hydroxo group. This reaction is
essentially equivalent to the reported reactions of the
carbonate and dioxygen complexes L2Pd(CO3) and
L2Pd(O2) with AcCH2C(O)CH2Ac except that there is
one less base equivalent per metal with the bridging
dihydroxo complex. As a result the protonated form, 3,
is isolated.
3.3. [Pd(PMe2Ph)2(m-PF2O2)]2(PF6)2 (7)
Scheme 3.
In an attempt to prepare the PMe2Ph analog of 1 as
ꢂ
the PF6 salt, Pd(PMe2Ph)2Cl2 was treated with AgPF6
reactions with acetone [4,18]. Pd carbonate and dioxy-
gen complexes, L2Pd(CO3) and L2Pd(O2), are also
deprotonating agents and their reaction with the acidic
in wet acetone. The 31P NMR spectrum of the isolated
product is too complex for [Pd(PMe2Ph)2(m-
OH)]2(PF6)2 and an X-ray diffraction study reveals the
product to be [Pd(PMe2Ph)2(m-PF2O2)]2(PF6)2 (7), evi-
dently formed by partial hydrolysis of half of the PF6
anions (Scheme 5). Similar hydrolysis products have
been previously reported [19]. A drawing of the cationic
portion is given in Fig. 3. A summary of crystal and data
collection parameters is given in Table 1. Selected
distances and angles are listed in Table 4.
ketone
AcCH2C(O)CH2Ac
yields
L2M(h3-Ac-
CHC(O)CHAc), a deprotonated analog of 5 [17a,17b].
(Deprotonated 5, (Ph3P)2Pd(h3-CH2C(O)CH2) is
known [15b].) This reaction is essentially equivalent to
the first reaction of path A except that there are 2 equiv.
of base per metal with the carbonate and dioxygen
complexes. As a result the deprotonated analog of 5 is
isolated.
The second reaction of path A requires aminolysis of
5. The Pt analog of 5 [14b] has been isolated (from the
hydrolysis of the Pt analog of 4) and, although reactions
with amines have not been reported, the analogous
alkoxo allyl complex 6 does react with amines to give Pt
analogs of 3 (Scheme 4) [14c].
An obvious problem with path A is that the dihy-
droxo complex 1 and the hydroxo amido complex 2 are
stable in acetone in the absence of added amine.
(Complex 1 is prepared in an acetone/CH2Cl2 mixture.)
Path A could still be followed if the reaction is amine
catalyzed, probably by cleavage of the m-hydroxo bridge
[11e]. Deprotonation of acetone by the Pd terminal
4. Conclusions
The dihydroxo bridged palladium complex behaves
similarly to the Pt analog and reacts with 1 equiv. or
excess aromatic amine in dichloromethane to yield only
a single amido-hydroxo exchange giving the mixed
bridge hydroxo amido complex. In acetone, the solvent
participates in the reaction chemistry, most likely via
amine catalyzed acetone deprotonation, and yields the
amido allyl complex 3. The isolation of 7 indicates that
ꢂ
PF6 is susceptible to hydrolysis under conditions
commonly used in the synthesis of bridged Pt and Pd
ꢂ
hydroxo complexes. The hydrolysis product (F2PO2
)
may interfere with the formation of the hydroxo
complex and should be avoided when a hydroxo
complex is desired.
Scheme 4.
Scheme 5.

S. Kannan et al. / Inorganica Chimica Acta 345 (2003) 8Á
/14
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