Characterization of a novel binuclear palladium(II) complex formed from the reaction of 2-chloro-3,3-diphenyl-1-(2,4,6-tri-tert-butylphenyl)-1,3- diphosphapropene with tetrakis(triphenylphosphine)palladium(0) including hydrolysis

Article abstract of DOI:10.1002/zaac.200300423

2-Chloro-3,3-diphenyl-1-(2,4,6-tri-tert-butylphenyl)-1,3-diphosphapropene was allowed to react with an equivalent amount of tetrakis(triphenylphosphine) palladium(0) and a novel binuclear palladium(II) complex which includes two P₂O-tridentate ligands [Mes*P(O)CH₂PPh ₂]₂[PdCl]₂ (Mes* = 2,4,6-tBu ₃C₆H₂) was isolated after workup procedure. A tricyclic skeleton of the binuclear complex was characterized by the X-ray crystallography.

Full text of DOI:10.1002/zaac.200300423

Characterization of a Novel Binuclear Palladium(II) Complex Formed from the
Reaction of 2-Chloro-3,3-diphenyl-1-(2,4,6-tri-tert-butylphenyl)-1,3-diphospha-
propene with Tetrakis(triphenylphosphine)palladium(0) Including Hydrolysis
Hongze Liang, Shigekazu Ito, and Masaaki Yoshifuji*
Sendai/Japan, Department of Chemistry, Graduate School of Science, Tohoku University
Received December 9th, 2003.
Dedicated to Professor Reinhard Schmutzler on the Occasion of his 70th Birthday
Abstract. 2-Chloro-3,3-diphenyl-1-(2,4,6-tri-tert-butylphenyl)-1,3-
diphosphapropene was allowed to react with an equivalent amount
of tetrakis(triphenylphosphine)palladium(0) and a novel binuclear
palladium(II) complex which includes two P2O-tridentate ligands
[Mes*P(O)CH2PPh2]2[PdCl]2 (Mes* ϭ 2,4,6-tBu3C6H2) was iso-
lated after workup procedure. A tricyclic skeleton of the binuclear
complex was characterized by the X-ray crystallography.
Keywords: Phosphaalkenes; Steric hindrance; Palladium; Triden-
tate ligands
Charakterisierung eines neuartigen zweikernigen Palladium(II)-Komplexes aus der
Reaktion von 2-Chlor-3,3-diphenyl-1-(2,4,6-tri-tert-butylphenyl)-1,3-diphosphapropen
mit Tetrakis(triphenylphosphan)palladium(0) einschließlich Hydrolyse
Inhaltsübersicht. 2-Chlor-3,3-diphenyl-1-(2,4,6-tri-tert-butylphenyl)-
1,3-diphosphapropen wurde mit einer äquivalenten Menge
Tetrakis(triphenylphosphan)palladium(0) zu einem neuartigen
zweikernigen Palladiumkomplex umgesetzt, der zwei P2O-dreizähn-
ige Liganden enthält [Mes*P(O)CH2PPh2]2[PdCl]2 (Mes* ϭ 2,4,6-
tBu3C6H2). Ein tricyclisches Gerüst des zweikernigen Komplexes
wurde röntgenographisch charakterisiert.
Introduction
chelate dichloropalladium(II) complex without decompo-
sition of 2 [4]. Thus, it has been postulated that the CϪCl
bond in 1 might be reactive toward palladium reagents.
In this paper we report isolation and characterization of
a binuclear palladium(II) complex containing phosphino-
methylphosphinoxy moieties, which construct a tricyclic
skeleton, and the ClϪPd group may indicate the activation
of the CϪCl bond in 1 by palladium.
Low-coordinated phosphorus compounds such as phos-
phaalkenes has greatly developed in the past decades [1] and
we have reported a number of kinetically stabilized organo-
phosphorus compounds by a bulky 2,4,6-tri-tert-butylphe-
nyl (hereafter abbreviated to Mes*) group [2]. Previously we
reported preparation of 2-chloro-3,3-diphenyl-1-(2,4,6-tri-
tert-butylphenyl)-1,3-diphosphapropene (1) which contains
both an sp2-phosphorus atom and a normal sp3-phosphino
group [3]. Since 1 carries two kinds of phosphorus atoms,
1 is expected to function as an unsymmetrical P2-ligand for
transition-metal complex formations. Indeed, 1 was allowed
to react with carbonyltungsten(0) reagents to afford mon-
odentate and chelate tungsten(0) complexes [3]. On the
other hand, attempts to synthesize palladium complexes lig-
ated with 1 were not successful and 1 appeared to have been
decomposed during the reaction, whereas a 2-methyl-1,3-
diphosphapropene derivative 2 afforded the corresponding
Results and Discussion
Structure of 2-Chloro-3,3-diphenyl-1-(2,4,6-tri-tert-
butylphenyl)-1,3-diphosphapropene (1)
Compound 1 was prepared as described in our previous
report [3] and the crystals were obtained by recrystallization
from hexane. The structure of 1 was confirmed by the
X-ray crystallography (Table 1) and Fig. 1 displays an
ORTEP drawing of the molecular structure. Two indepen-
dent molecules were determined and one of them is shown
(Table 2). Although the quality of the data was not
satisfying due to the quality of an employed crystal, the
configuration of the 1,3-diphosphapropene skeleton was
identified. Both of the lone-pair electrons of the sp2-phos-
phorus and the diphenylphosphino group oriented to the
same direction providing a chelate coordination. The differ-
ence in the P(2)ϪC(1) distances might have been caused by
* Prof. Dr. Masaaki Yoshifuji
Department of Chemistry, Graduate School of Science, Tohoku
University
Aoba, Sendai 980-8578/Japan
Fax: ϩ81 22 217 6562
E-mail: yoshifj@mail.tains.tohoku.ac.jp
Z. Anorg. Allg. Chem. 2004, 630, 1177Ϫ1180
DOI: 10.1002/zaac.200300423
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H. Liang, S. Ito, M. Yoshifuji
Table 1 Crystal data of 1 and 3
1
3
Formula
M
C31H39ClP2
509.05
C62H82Cl2O2P4Pd2·3CH2Cl2
1521.73
Crystal dimension
Unit cell dimension:
0.25 x 0.25 x 0.10
0.40 x 0.25 x 0.20
˚
a / A
11.877(2)
11.222(2)
24.221(5)
19.3060(2)
12.7491(2)
28.8991(4)
˚
b / A
˚
c / A
α/ °
β/ °
γ / °
91.375(9)
100.07(1)
89.592(3)
3177(1)
90
94.6405(7)
90
7089.7(2)
4
1.426
0.939
3128
3
˚
Cell volume / A
Z
4
ρcalc / g cmϪ3
µ/ mmϪ1
F000
1.064
0.236
1088
Corrections
Lorentz-polarization Absorption [6]
(trans. factors: 0.561Ϫ0.977)
Lorentz-polarization Absorption [6]
(trans. factors: 0.553Ϫ0.829)
Crystal system
Space group
triclinic
P-1 (#2)
RAXIS-IV
0.7107
monoclinic
P21/c (#14)
RAXIS-IV
0.7107
Measurement device
˚
Wavelength / A
Temperature / K
2θmax / °
Collected reflections
Observed reflections
Measured reflections
Rint
296
55
19149
12039
3682 [I>3σ(I)]
0.058
130
55
47144
16028
11832 [I>4σ(I)]
0.063
Parameters
Solution and Refinement on F
R1
613
730
SIR-92 [7] / teXsan [8]
0.108
SIR-92 [7] / teXsan [8]
0.052
Rw (all data)
Largest difference peak and hole / e A
0.148
ϩ0.36, Ϫ0.40
0.077
ϩ3.44, Ϫ3.10
Ϫ
3
˚
˚
Table 2 Selected bond lengths/A and angles/° for 1
Molecule A
Molecule B
P(1)ϪC(1)
P(2)ϪC(1)
P(1)ϪMes*
P(2)ϪPh
P(2)ϪPh
C(1)ϪCl
1.67(1)
1.78(1)
1.87(2)
1.85(2)
1.88(2)
1.78(1)
1.67(1)
1.86(1)
1.90(1)
1.81(2)
1.86(2)
1.75(1)
C(1)ϪP(1)ϪMes*
P(1)ϪC(1)ϪP(2)
P(1)ϪC(1)ϪCl
P(2)ϪC(1)ϪCl
C(1)ϪP(2)ϪPh
104.8(6)
115.8(7)
122.5(8)
121.4(7)
103.5(6)
100.2(7)
106.2(7)
104.5(6)
114.6(7)
125.6(8)
119.2(8)
102.1(6)
105.3(8)
104.0(7)
PhϪP(2)ϪPh
the effect of the crystalline structure including the motion
of the atoms. Attempted crystallographic analyses of 1 at
low temperatures were not successful probably due to the
conversion of the crystal structure.
Fig. 1 An ORTEP drawing of the molecular structure of 1 (30 %
probability ellipsoids). Hydrogen atoms are omitted for clarity. One
of the independent molecules is displayed.
Reaction of 1 with Pd(PPh3)4
purification with silica gel column chromatography and
recrystallization from dichloromethane without avoiding
aerial oxygen and moisture, a binuclear palladium(II) com-
plex 3 was obtained as yellow prisms although the isolated
yield was low. Almost the same result was obtained in the
reaction of 1 with Pd(PPh3)4 in benzene as a solvent. The
The 2-chloro-1,3-diphosphapropene (1) was consumed in
the reaction with Pd(PPh3)4 in dichloromethane to give
Cl2Pd(PPh3)2 as precipitates. In the 31P NMR spectrum of
the solution, many unidentified peaks were observed to-
gether with those due to Cl2Pd(PPh3)2 and PPh3. After
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Characterization of a Novel Binuclear Palladium(II) Complex
˚
Table 3 Selected bond lengths/A and angles/° for 3
Pd(1)ϪCl(1)
Pd(1)ϪP(1)
Pd(1)ϪP(2)
Pd(1)ϪO(1)
Pd(2)ϪCl2
Pd(2)ϪP(3)
Pd(2)ϪP(4)
Pd(2)ϪO(2)
P(1)ϪO(2)
P(1)ϪC(1)
P(1)ϪMes*
P(2)ϪC(1)
P(2)ϪPh
2.389(1)
2.274(1)
2.197(2)
2.155(3)
2.380(1)
2.275(1)
2.207(1)
2.161(3)
1.533(3)
1.854(5)
1.852(4)
1.821(4)
1.804(5)
1.813(5)
1.523(3)
1.873(4)
1.840(4)
1.825(4)
1.807(5)
1.821(5)
Cl(1)ϪPd(1)ϪP(1)
Cl(1)ϪPd(1)ϪP(2)
Cl(1)ϪPd(1)ϪO(1)
P(1)ϪPd(1)ϪP(2)
P(1)ϪPd(1)ϪO(1)
P(2)ϪPd(1)ϪO(1)
Cl(2)ϪPd(2)ϪP(3)
Cl(2)ϪPd(2)ϪP(4)
Cl(2)ϪPd(2)ϪO(2)
P(3)ϪPd(2)ϪP(4)
P(3)ϪPd(2)ϪO(2)
P(4)ϪPd(2)ϪO(2)
Pd(1)ϪP(1)ϪO(2)
Pd(1)ϪP(1)ϪC(1)
O(2)ϪP(1)ϪC(1)
Pd(1)ϪP(2)ϪC(1)
Pd(2)ϪP(3)ϪO(1)
Pd(2)ϪP(3)ϪC(2)
O(1)ϪP(3)ϪC(2)
Pd(2)ϪP(4)ϪC(2)
Pd(1)ϪO(1)ϪP(3)
Pd(2)ϪO(2)ϪP(1)
P(1)ϪC(1)ϪP(2)
P(3)ϪC(2)ϪP(4)
168.70(4)
96.93(4)
90.99(9)
73.83(4)
97.69(9)
170.59(9)
168.29(4)
95.71(4)
92.14(9)
74.32(4)
97.19(9)
170.14(8)
109.2(1)
92.1(1)
113.0(2)
95.5(1)
109.2(1)
92.0(1)
112.0(2)
95.6(1)
112.7(2)
112.1(2)
93.9(2)
P(2)ϪPh
P(3)ϪO(1)
P(3)ϪC(2)
P(3)ϪMes*
P(4)ϪC(2)
P(4)ϪPh
Fig. 2 An ORTEP drawing of the molecular structure of 3 (50 %
probability ellipsoids). Hydrogen atoms and the solvent molecules
(dichloromethane) are omitted for clarity.
P(4)ϪPh
94.1(2)
Pd(1)ϪP(1)ϪC(1)ϪP(2)
Pd(1)ϪP(2)ϪC(1)ϪP(1)
Pd(2)ϪP(3)ϪC(2)ϪP(4)
Pd(2)ϪP(4)ϪC(2)ϪP(3)
O(1)ϪPd(1)ϪP(1)ϪO(2)
O(1)ϪP(3)ϪPd(2)ϪO(2)
Cl(1)ϪPd(1)ϪP(1)ϪC(1)
O(1)ϪPd(1)ϪP(1)ϪC(1)
Cl(2)ϪPd(2)ϪP(3)ϪC(2)
O(2)ϪPd(2)ϪP(3)ϪC(2)
17.3(2)
18.0(2)
16.0(2)
16.6(2)
45.8(2)
46.9(2)
21.1(3)
161.0(2)
18.7(2)
161.2(2)
was eliminated and hydrolysis seemed to have occurred to
give a PϪCH2ϪPϪO framework in the ligand. Thus, the
1,3-diphosphapropene 1 afforded a novel P2O-tridentate li-
gand [Mes*P(OϪ)CH2PPh2] from the reaction with
Pd(PPh3)4. Three solvent molecules (dichloromethane) were
included in the crystalline state and the single crystals were
maintained in dichloromethane. Indeed, the single crystals
of 3 changed slowly from transparent to opaque in air prob-
ably due to release of the solvent molecules.
chlorine atom on the palladium seemed to come from the
sp2-carbon atoms. The 31P NMR signals due to 3 were not
observed in the reaction mixture before workup procedure,
indicating that the oxygen atom might have been incorpor-
ated by addition of water during the process of the chroma-
tography or recrystallization.
The structure of 3 was confirmed by X-ray crystallogra-
phy (Table 1). As displayed in Fig. 2, 3 includes a tricyclic
skeleton which contains almost planar four-membered rings
(Table 3). The geometries around the palladium atoms are
almost planar. Two phosphorus atoms in each ligand coor-
dinate on the palladium atom with a chelating fashion while
the oxygen atom coordinates on the other palladium atom.
The shorter (O)PϪPd distances compared to the corre-
sponding (Ph2)PϪPd distances might indicate lower trans
effect of the oxygen atoms than that of the chlorine atoms.
The P(1)ϪC(1) and P(3)ϪC(2) distances clearly indicate re-
duction of the PϭC double bonds. The chlorine atom in 1
It is plausible that formation mechanism of 3 might
include oxidative insertion of the palladium(0) metal into
the CϪCl bond in 1 and hydrolysis of the phosphorus-car-
bon double bond. The oxidative insertions of such kind
were reported in the reaction of similarly bulky 2-halo-
1-phosphaethenes with palladium reagents [5]. Recently we
reported isolation and structural elucidation of a dichloro-
palladium(II) complex
4
containing the ligated
[1-(diphenylphosphino)ethyl](2,4,6-tri-tert-butylphenyl)-
phosphine starting from 2, [4] but we did not observe such
dimerization of 4 to the corresponding product like 3. It
might indicate that the C(sp2)ϪX (X ϭ Cl, Br) part in the
phosphaalkene derivatives behaves as a reacting site pro-
moted by palladium, suggesting its utility as a material for
palladium-catalyzed reactions, whereas the C(sp2)ϪMe part
is inactive. The hydrolysis of 1 did not occur, indicating that
the hydrolysis might be facilitated by the effect of pal-
ladium.
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H. Liang, S. Ito, M. Yoshifuji
[Mes*P(O)CH2PPh2]2[PdCl]2 (3). Yellow crystals, 185Ϫ186 °C
(decomp). Elemental analysis for C62H82Cl2O2P4Pd2 (1266.97 g/
mol): found (calc.) C 58.52 (58.78), H 6.23 (6.52) %.
1H NMR (CDCl3): δ ϭ 1.22 (s, 18H, tBu), 1.57 (s, 18H, tBu), 1.75 (s, 18H,
tBu), 3.50 (m, 2H, CHH), 5.42 (m, CHH), 6.84 (m, 2H, Ph), 6.99 (m, 2H,
Ph), 7.23Ϫ7.35 (m, 8H, Ph), 7.44Ϫ7.49 (m, 8H, Ph), 7.65 (d, 4J(H,H) ϭ
7.6 Hz, 2H, m-Mes*), 7.69 (d, 4J(H,H) ϭ 7.6 Hz, 2H, m-Mes*).
31P{1H} NMR (CDCl3): δ ϭ 1.89 (2J(P,P) ϭ 40 Hz), Ϫ36.5 (2J(P,P) ϭ
40 Hz).
Concluding Remarks
We have succeeded in isolation of a product starting from
the reaction of 1 with Pd(PPh3)4 and a novel binuclear pal-
ladium complex 3 was characterized. Complex 3 might have
been obtained from the oxidative insertion of the pal-
ladium(0) species into the CϪCl bond in 1. Our previous
study established that a bulky 1,3-diphosphapropene with-
out halogen atom functioned as a ligand for palladium
complexes, whereas 1 did not afford any palladium complex
but decomposed. This paper suggests an approach to design
ligands including low-coordinated phosphorus atoms. Ad-
ditionally, this finding would be helpful to understand the
properties of metal complexes including 1,3-diphosphapro-
pane (diphosphinomethane) derivatives.
This work was supported in part by Grants-in-Aid for Scientific
Research (No. 13304049 and 14044012) from the Ministry of Edu-
cation, Culture, Sports, Science and Technology, Japan. H. Liang
is grateful to the Japan Society for the Promotion of Science for
the Postdoctoral Fellowships for Foreign Researchers.
References
[1] a) M. Regitz, O. J. Scherer, Multiple Bonds and Low Coordi-
nation in Phosphorus Chemistry; Georg Thieme Verlag:
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2003, 44, 8297.
Experimental Section
Compound 1 was prepared according to the literature [3] and crys-
tallized from hexane. A single crystal was employed for the X-ray
crystallography. Crystallographic data for the structural analyses
have been deposited with the Cambridge Crystallographic Data
Centre (1: CCDC-225901, 3: CCDC-225900). Copies of this infor-
mation can be obtained from the Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK, Fax ϩ44-1223-336033; E-mail:
deposit@ccdc.cam.ac.uk, or www: http://www.ccdc.cam.ac.uk.
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Preparation and isolation of 3. A mixture of 1 (0.30 g, 0.59 mmol)
and Pd(PPh3)4 (0.68 g, 0.59 mmol) in dichloromethane (15 mL)
was stirred for
2 days and several compounds including
Cl2Pd(PPh3)2 and small amount of triphenylphosphine oxide (ca.
0.2 g) were precipitated out. The solution was concentrated in va-
cuo and was treated by silica-gel column chromatography (hexane-
AcOEt) to afford triphenylphosphine (0.27 g, 1.24 mmol) and
26 mg of yellow solid which displayed many peaks including
Cl2Pd(PPh3)2 in the 31P NMR spectrum. The yellow solid was dis-
solved in dichloromethane and 1 mg of crystals were formed at
0 °C after 1 week out of the solution (0.3 % isolated yield from 1).
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