Preparation and properties of sandwiched trinuclear palladium(II) complexes with tridentate phosphine and phosphine sulfide ligands

Article abstract of DOI:10.1016/j.jorganchem.2011.03.018

The central phosphino group of tripodal tetradentate tris[2- (diphenylphosphino)ethyl]phosphine (pp₃) was selectively oxidized by the reaction with diethyl disulfide to give tridentate phosphine ligand pOp ₃. The terminal phosphino g

Full text of DOI:10.1016/j.jorganchem.2011.03.018

Journal of Organometallic Chemistry 696 (2011) 2471e2476
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Note
Preparation and properties of sandwiched trinuclear palladium(II) complexes
with tridentate phosphine and phosphine sulfide ligands
,
b
a
a
Sen-ichi Aizawa a , Tatsuya Kawamoto , Suji Nishigaki , Ayano Sasaki
*
a Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
b Department of Chemistry, Faculty of Science, Kanagawa University, Hiratsuka, Kanagawa 259-1293, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The central phosphino group of tripodal tetradentate tris[2-(diphenylphosphino)ethyl]phosphine (pp3)
was selectively oxidized by the reaction with diethyl disulfide to give tridentate phosphine ligand pOp3.
The terminal phosphino groups were reacted with sulfur to give pOp3 trisulfide (pOp3S3). Three palla-
dium(II) ions were sandwiched in the two pOp3 and pOp3S3 ligands to form the trinuclear complexes
with three trans(P) and trans(S) PdX2 (X ¼ Cl, Br, I) moieties, respectively. The tripodal triphosphine,
1,1,1-tris(diphenylphosphinomethyl)ethane (i-p3), and its mono- and tri-sulfide, which have shorter
carbon chains compared with pOp3, form the mononuclear dichloro palladium(II) complexes with cis(P)
and cis(S) geometries. Difference in the catalytic activity for the CeC coupling reaction was discussed in
connection with the coordinated groups and geometries of the complexes.
Received 24 January 2011
Received in revised form
8 March 2011
Accepted 10 March 2011
Keywords:
Tripodal tridentate phosphine
Phosphine sulfide
Sandwiched trinuclear Pd(II) complex
CeC coupling reaction
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
p* orbital of the sulfurephosphorus double bond is moderately low
and can accept electrons from Pd(0) to stabilize the catalytically
Structure, properties, and reaction mechanisms of five-coordi-
nate trigonal-bipyramidal d8 metal complexes have been investi-
gated so far by using the tripodal tetradentate ligands with soft
donors such as tris[2-(diphenylphosphino)ethyl]phosphine (pp3)
[1e12], tris[2-(diphenylphosphino)ethyl]amine (np3) [3e5,13e15],
tris[2-(diphenylarsino)ethyl]amine (nas3) [4,6,13]. On the other
hand, employing tripodal tridentate ligands is of interest because
equivalent coordination of the three donor atoms of the tripodal
ligands does not make usual square-planar or trigonal-bipyramidal
structures of the d8 metal complexes. In this work, we have
attempted selective oxidation of the central phosphino group of
pp3 to give the Pd(II) complex with the tripodal tridentate ligand
considering that the phosphine phosphorus is a good donor for Pd
(II) while the phosphine oxide is scarcely coordinated to Pd(II). The
coordination behavior of the pp3 monooxide ligand (pOp3) was
compared with that of 1,1,1-tris(diphenylphosphinomethyl)ethane
(i-p3), which is a smaller tripodal tridentate ligand with shorter
carbon chains.
active species. On the other hand, the formation of the substrate
adduct and subsequent catalytic reaction on Pd(II) seem not to
be blocked because the phosphine sulfide group is not a strong
s
donor for Pd(II). Therefore, comparison between phosphine
complexes and the corresponding phosphine sulfide ones in the
catalytic reaction is of importance from the viewpoint of coordi-
nation chemistry. Under the circumstances, the syntheses of the Pd
(II) complexes with the phosphine sulfide of the tripodal tridentate
phosphines also have been undertook, and the catalytic activities
for the CeC coupling reaction were compared with those of the
corresponding phosphine complexes.
2. Experimental
2.1. Reagents
Tris[2-(diphenylphosphino)ethyl]phosphine (pp3, Aldrich),
1,1,1-tris (diphenylphosphinomethyl)ethane (i-p3, Aldrich), diethyl
disulfide (Aldrich), sulfur (Wako), potassium tetrachloropalladate
(II) (K2[PdCl4], Aldrich), tetrakis(acetonitrile)palladium(II) tetra-
fluoroborate ([Pd(CH3CN)4](BF4)2, Aldrich), tetra(n-butyl)ammo-
nium bromide (Bu4NBr, Wako), tetra(n-butyl)ammonium iodide
(Bu4NI, Wako), iodobenzene (Kanto Chemical), and styrene (Wako)
were used for preparation or catalytic reaction without further
purification.
Recently, some phosphine sulfides have been employed as the
bound ligands for the palladium catalyst [16e18] instead of phos-
phine. The phosphine sulfide group can act as a good
p acceptor
and a quite weak donor compared with the phosphino group. The
s
* Corresponding author. Tel./fax: þ81 76 445 6980.
E-mail address: saizawa@eng.u-toyama.ac.jp (S.-i. Aizawa).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.03.018

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2.2. Preparation of complexes
single crystals suitable for an X-ray analysis were obtained by
recrystallization from chloroform.
2.2.1. Tris[2-(diphenylphosphino)ethyl]phosphine monoxide (pOp3)
To a solution containing pp3 (0.22 g, 0.33 mmol) in deoxygen-
ated chloroform (ca. 10 cm3) was added diethyl disulfide (0.043 g,
0.35 mol). The solution was stirred at room temperature for 48 h,
and to this was added diethyl ether. The resultant colorless crystals
were recrystallized from deoxygenated chloroform a few times
until the 31P NMR signal for the terminal phosphine oxide groups
was not observed. Yield: 0.12 g (53%). Anal. Found: C, 73.03;
H, 6.08%. Calcd for C42H42OP4: C, 73.46; H, 6.16%. 31P{1H} NMR
2.2.7. [Pd3Br6(pOp3S3)2] (5)
To a solution containing pOp3S3 (0.28 g 0.36 mmol) and Bu4NBr
(0.36 g, 1.12 mmol) in deoxygenated chloroform (ca. 20 cm3) was
added a solution containing [Pd(CH3CN)4](BF4)2 (0.23 g, 0.52 mmol)
in deoxygenated acetonitrile (ca. 20 cm3), and the solution was
stirred at room temperature for 2 h, and then concentrated To this
was added diethyl ether to give red crystals which were recrystal-
lized from chloroform. Yield: 0.20 g (46%). Anal. Found: C, 40.98; H,
3.33%. Calcd for C84H84Br6O2P8Pd3S3$CHCl3: C, 41.10; H, 3.45%. 31P
(CHCl3):
d
ꢀ12.6 (d, terminal), 50.0 (q, central), 3JPeP ¼ 42 Hz.
{1H} NMR (CHCl3):
d 45.4 (q, central), 52.5 (d, terminal),
2.2.2. [Pd3Cl6(pOp3)2] (1)
3JPeP ¼ 60 Hz; 49.6 (d, terminal), 56.1 (q, central), 3JPeP ¼ 64 Hz.
To a solution containing K2[PdCl4] (0.28 g 0.86 mmol) in deox-
ygenated water (ca. 20 cm3) was added a solution containing pOp3
(0.39 g, 0.57 mmol) in deoxygenated chloroform (ca. 10 cm3), and
the mixture was stirred at room temperature for 2 h. The chloro-
form layer was concentrated, and to this was added diethyl ether.
The resultant yellow crystals were collected by filtration and air-
dried. Yield: 0.29 g (51%). Anal. Found: C, 52.13; H, 4.59%. Calcd for
2.2.8. [PdCl2(i-p3)] (6)
To a solution containing K2[PdCl4] (0.20 g 0.61 mmol) in deox-
ygenated water (ca. 20 cm3) was added a solution containing i-p3
(0.38 g, 0.61 mmol) in deoxygenated chloroform (ca. 10 cm3), and
the mixture was stirred at room temperature for 2 h. The chloro-
form layer was concentrated, and the resultant white solid was
collected by filtration and air-dried. Yield: 0.41 g (76%). Anal.
Found: C, 56.50; H, 4.60%. Calcd for C41H39Cl2P3Pd$H2O$0.5CHCl3:
C84H84Cl6O2P8Pd3$0.5CHCl3$0.5C4H10O: C, 51.89; H, 4.51%. 31P{1H}
2
NMR (CHCl3):
d
18.8 (terminal), 51.5 (central), JPeP ¼ 300 Hz,
3JPeP ¼ 23 Hz.
C, 56.66; H, 4.75%. 31P{1H} NMR (CHCl3):
d
ꢀ29.6 (s), 16.6 (s).
2.2.3. [Pd3Br6(pOp3)2] (2)
2.2.9. [PdCl2(i-p3S)] (7)
To a solution containing pOp3 (0.23 g 0.33 mmol) and Bu4NBr
A solution containing 6 (0.14 g 0.16 mmol) and sulfur (0.0069 g,
0.22 mmol) in deoxygenated chloroform (ca. 10 cm3) was stirred at
room temperature for 1 h. The reaction solution was concentrated,
and the resultant white solid was collected by filtration and air-
dried. Yield: 0.10 g (73%). Anal. Found: C, 57.39; H, 4.60%. Calcd for
C41H39Cl2P3PdS$H2O: C, 57.79; H, 4.85%. 31P{1H} NMR (CHCl3):
(0.33 g, 1.02 mmol) in deoxygenated chloroform (ca. 10 cm3) was
added
a
solution containing [Pd(CH3CN)4](BF4)2 (0.22 g,
0.50 mmol) in deoxygenated acetonitrile (ca. 20 cm3), and the
solution was stirred at room temperature for 2 h, and then
concentrated. To this was added diethyl ether to give yellow crys-
tals which were recrystallized from chloroform Yield: 0.16 g (42%).
Anal. Found: C, 44.22; H, 3.60%. Calcd for C84H84Br6O2P8Pd3$CHCl3:
d
15.3(s), 33.3(s).
C, 44.55; H, 3.74%. 31P{1H} NMR (CHCl3):
d
17.3 (terminal), 51.6
2.2.10. i-p3 trisulfide (i-p3S3)
(central), 2JPeP ¼ 280 Hz, JPeP ¼ 22 Hz.
A solution containing i-p3 (0.56 g, 0.90 mmol) and sulfur
(0.086 g, 2.7 mmol) in deoxygenated chloroform (ca. 10 cm3) was
stirred at room temperature for 1 h. The reaction solution was
concentrated, and to this was added diethyl ether. The resultant
white crystals were collected by filtration. Yield: 0.51 g (71%). Anal.
Found: C, 64.09; H, 5.26%. Calcd for C41H39P3S3: C, 64.31; H, 5.45%.
3
2.2.4. [Pd3I6(pOp3)2] (3)
The orange iodo complex 3 was prepared by a procedure similar
to that for the bromo complex 2 using Bu4NI instead of Bu4NBr.
Yield: 0.20 g (47%). Anal. Found: C, 39.49; H, 3.30%. Calcd for
C84H84I6O2P8Pd3$CHCl3: C, 39.67; H, 3.33%. 31P{1H} NMR (CHCl3):
31P{1H} NMR (CHCl3):
d 33.4 (s).
2
3
d
10.9 (terminal), 51.7 (central), JPeP ¼ 170 Hz, JPeP ¼ 14 Hz. The
single crystals suitable for an X-ray analysis were obtained by
recrystallization from chloroform.
2.2.11. [PdCl2(i-p3S3)] (8)
To a solution containing K2[PdCl4] (0.14 g 0.43 mmol) in water
(ca. 10 cm3) was added a solution containing i-p3S3 (0.30 g,
0.42 mmol) in chloroform (ca. 50 cm3), and the mixture was stirred
at room temperature for 2 h. The chloroform layer was concen-
trated, and the resultant orange solid was collected by filtration and
air-dried. Yield: 0.19 g (44%). Anal. Found: C, 49.82; H, 4.11%. Calcd
for C41H39Cl2P3PdS3$CHCl3: C, 49.59; H, 3.96%. 31P{1H} NMR
2.2.5. pOp3 trisulfide (pOp3S3)
A solution containing pOp3 (0.33 g, 0.48 mmol) and sulfur
(0.059 g, 1.8 mmol) in deoxygenated chloroform (ca. 25 cm3) was
stirred at room temperature for 1 h. To this was added diethyl ether
to give colorless crystals. Yield: 0.32 g (85%). Anal. Found: C, 64.19;
H, 5.56%. Calcd for C42H42OP4S3: C, 64.63; H, 5.41%. 31P{1H} NMR
(CH3CN): d 33.0(s), 34.8 (s).
3
(CHCl3):
d
44.6 (d, terminal), 51.1 (q, central), JPeP ¼ 54 Hz.
2.3. Crystal structure determination
2.2.6. [Pd3Cl6(pOp3S3)2] (4)
To a solution containing K2[PdCl4] (0.24 g 0.74 mmol) in water
(ca. 20 cm3) was added a solution containing pOp3S3 (0.38 g,
0.49 mmol) in deoxygenated chloroform (ca. 10 cm3), and the
mixture was stirred at room temperature for 2 h. The chloroform
layer was concentrated, and to this was added diethyl ether. The
resultant reddish brown crystals were collected by filtration and
air-dried. Yield: 0.32 g (60%). Anal. Found: C, 47.40; H, 4.23%. Calcd
for C84H84Cl6O2P8Pd3S6$0.5CHCl3$0.5C4H10O: C, 47.34; H, 4.11%.
The measurements of 3$4CHCl3 and 4$4CHCl3 were made on
a Rigaku Mercury CCD X-ray diffractometer using graphite-mono-
chromated Mo K
a
(l
¼ 0.71073 Å) radiation at 200 K. Cell Param-
eters were refined using the program CrystalClear (Rigaku and
MSC, version 1.3, 2001) and the collected data were reduced using
the program CrystalStructure (Rigaku and MSC, version 3.8, 2006).
Empirical absorption corrections were applied. The structures were
solved by direct methods using SIR 92 [19] and refined by full-
matrix least-squares techniques using SHELXL-97 [20]. All non-
hydrogen atoms for 3 and 4 were refined anisotropically and
31P{1H} NMR (CHCl3):
d 45.5 (q, central), 53.1 (d, terminal),
3JPeP ¼ 60 Hz; 51.1 (d, terminal), 56.8 (q, central), 3JPeP ¼ 64 Hz. The

S.-i. Aizawa et al. / Journal of Organometallic Chemistry 696 (2011) 2471e2476
2473
hydrogen atoms were included in calculated positions. The iodine
atom (I4) in 3$4CHCl3 was found to be disordered over two sites in
a ratio of 0.5:0.5. The structure of 4$4CHCl3 contains voids
comprised of a disordered solvent molecule.
ethylene protons of bis(2-butoxyethyl) ether contained as an
internal reference and followed as a function of time.
3. Results and discussion
Crystal data for 3$4CHCl3: C88H88Cl12I6O2P8Pd3, M ¼ 2931.34,
ꢀ
ꢀ
triclinic, space group P-1, a ¼ 15.151(9) A, b ¼ 17.622(13) A, c ¼ 21.49
The molecular structures of 3 and 4 obtained by X-ray analyses
were shown in Figs. 1 and 2, respectively. Both complexes take the
trinuclear structure in which the three Pd(II) ions are sandwiched
between two pOp3 or pOp3S3 ligands by coordination of phosphine
phosphorus or phosphine sulfide sulfur atoms, respectively. All the
Pd(II) ions have the square-planar trans geometry, and the Pd(II)eP
and Pd(II)eS bond distances are in the range of those reported for
trans(P) [21,22] and trans(S) [17] geometries with multidentate
phosphine and phosphine sulfide ligands, respectively. The clear
difference in molecular structures of 3 and 4 is that both central
phosphine oxide oxygen atoms are directed outside in the trinu-
clear structure of 3 while one oxygen atom is inversed to be
directed inside for 4 as shown in the 31P NMR spectra below.
The 31P NMR spectra of the single crystals of 3 in chloroform
showed two signals for the terminal phosphino groups at 10.9 ppm
and the central phosphine sulfide groups at 51.7 ppm. Since the
AA0XX0 spin systems are made up of the three sets of two chemi-
cally equivalent coordinated terminal phosphorus atoms trans to
each other (A and A0) and the two central phosphorus atoms (X and
3
ꢀ
ꢁ
ꢀ
(4) A,
a
¼ 85.14(9)ꢁ,
b
¼ 81.51(9)ꢁ,
g
¼ 70.09(8) , V ¼ 5331(11) A ,
Z ¼ 2, rcalcd ¼ 1.826 g cmꢀ3
,
m
¼ 2.701 mmꢀ1, F(000) ¼ 2824, T ¼ 200
(2) K, R1 ¼ 0.1264, wR2 ¼ 0.3195 for 19347 (I > 2
s(I)).
Crystal data for 4$4CHCl3: C88H88Cl18O2P8Pd3S6, M ¼ 2575.00,
ꢀ
ꢀ
trigonal, space group R-3, a ¼ 26.86(4) A, c ¼ 25.68(3) A, V ¼ 16046
(36) A , Z ¼ 6, rcalcd ¼ 1.599 g cmꢀ3
,
m
¼ 1.230 mmꢀ1, F(000) ¼ 7752,
3
ꢀ
T ¼ 200(2) K, R1 ¼ 0.0820, wR2 ¼ 0.2209 for 6532 (I > 2
s(I)).
2.4. Measurements
31P and 1H NMR spectra were recorded on a JEOL JNM-A400
FT-NMR spectrometer operating at 160.70 and 399.65 MHz. In
order to determine the chemical shifts of 31P NMR signals, a 3 mm
o.d. NMR tube containing the sample solution was coaxially
mounted in a 5 mm o.d. NMR tube containing deuterated water as
a lock solvent and phosphoric acid as a reference.
2
2.5. General procedure for the CeC coupling reaction
X0), virtual JPeP coupling through the Pd(II) ions should be
observed for the sandwiched trinuclear structure of 3. The 31P NMR
2
Reactions of iodobenzene (5.7 g, 28 mmol) with styrene (3.2 g,
30 mmol) in DMF (10 cm3) were carried out under nitrogen at
120 ꢁC in the presence of tributylamine (14 g, 76 mmol) as a base
and trinuclear complexes 1 or 4 (3.8 ꢂ 10ꢀ3 mmol) or mononuclear
complexes 6, 7, 8, or [PdCl(pp3)]Cl (1.1 ꢂ 10ꢀ2 mmol) as a catalysts.
The yields were calculated by the 1H NMR intensity of the ortho
protons of stilbene formed on the basis of the intensity of the
spectral simulation [23] actually gave a large JPeP value (170 Hz)
characteristic of the trans(P) geometry (Fig. 3) [21,24], and this fact
indicates that the complex 3 maintains the sandwiched trinuclear
structure in solution. The 31P NMR simulation also revealed that the
complex 1 and 2 have a similar sandwiched trinuclear structure
2
with trans(P) geometry showing the large virtual JPeP coupling
(300 Hz for 1 and 280 Hz for 2).
Fig. 1. ORTEP diagram of 3.

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Fig. 2. ORTEP diagram of 4. The peripheral phenyl rings are omitted for clarity.
The 31P NMR spectrum for crystals of 4 dissolved in chloroform
tetrasulfide (pp3S4) ligand in the solid state (Fig. S1), the former
pOp3S3 ligand can be assigned to the ligand with phosphine oxide
groups directed outside, and consequently, the latter to that with
phosphine oxide group directed inside. The bromo complex 5 dis-
solved in chloroform showed the 31P NMR spectra with two set of
signals for pOp3S3 quite similar to that for 4 indicating that 5 takes
the sandwiched trinuclear structure with two kinds of pOp3S3
conformation.
While the i-p3 ligand is a tripodal tridentate ligand with
equivalent three diphenylphosphino groups, the 31P NMR spectrum
of 6 in chloroform showed signals for coordinated phosphino
groups at 16.6 ppm and relatively small free phosphino group
at ꢀ29.6 ppm (Fig. 5(a)) indicating that 6 takes the square-planar
geometry with two coordinated phosphino groups at the cis posi-
tion and one pendent free phosphino group in which i-p3 acts as
exhibits two sets of signals for the pOp3S3 ligand with different
3JPeP values between the terminal and central phosphorus atoms,
64 Hz and 60 Hz (Fig. 4). The former pOp3S3 ligand shows the signal
for the central phosphine oxide group at lower field than that for
the terminal phosphine sulfide groups as observed for the free
pOp3S3 ligand (see Experimental Section), while the latter pOp3S3
ligand shows the reverse order of chemical shifts (Fig. 4). Consid-
ering that the natural conformation of the free pOp3S3 ligand may
correspond to that for the ligand with phosphine oxide group (P2]
O1) directed outside in 4 of which the conformation is also
observed for the free tris[2-(diphenylphosphino)ethyl]phosphine
Fig. 3. Simulated (a) and observed (b) 31P NMR spectral of 3. The simulated spectrum
is depicted by using JPeP ¼ 170 Hz and JPeP ¼ 14 Hz.
2
3
Fig. 4. 31P NMR spectrum of 4.

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2475
Fig. 5. 31P NMR spectra of 6 (a), 7 (b), and 8 (c). Ref denotes the signal for D3PO4 in the outer D2O.
the bidentate ligand with six-membered chelate ring. The pendent
free phosphino group of 6 changed to phosphine sulfide (33.3 ppm)
by the reaction of 6 with sulfur to give 7 keeping the cis(P) geom-
etry (Fig. 5(b)). The 31P NMR for 8 showed two kinds of signals for
phosphine sulfide groups (Fig. 5(c)). The large and small signals
were assigned to the two coordinated and one free phosphine
sulfide groups indicating the cis(S) geometry of 8.
solutions with metal:ligand ratio of 1:1 only gave the respective
trinuclear complexes and free ligands. These facts indicate that the
pOp3 and pOp3S3 trinuclear complexes are thermodynamically
much more stable than the corresponding 1:1 mononuclear
complexes having a eight-membered chelate ring and one terminal
pendent phosphino group for the pOp3 ligand and a ten-membered
chelate ring and one pendent phosphine sulfide group for the
pOp3S3 ligand, respectively, to maintain the square-planar geom-
etry. Contrarily, the carbon chains of the i-p3 and i-p3S3 ligands are
too short to form the trinuclear structure and consequently, gave
the mononuclear complexes.
The reaction solutions of 1 or 2 with 6 equiv. of Bu4NI in chlo-
roform gave the 31P NMR spectrum of 3. On the other hand, the
sulfide complex was not formed by the reactions of 1 or 2 with
excess sulfur in chloroform at 50 ꢁC for 5 h. These facts indicate that
the sandwiched trinuclear structure was maintained during the
substitution reaction of halide ions and the pOp3 ligand was not
dynamically dissociated in solution. Considering that 31P NMR
signals for the free pOp3S3 ligand was observed by the reaction of 4
The 31P NMR spectrum of the reaction solution of pp3 with
diethyl disulfide showed that the central phosphino group was
selectively oxidized and the most of the terminal phosphino groups
remained unoxidized. A small amount of the phosphine dioxide
with the oxidized terminal phosphino group was completely
removed by repeated recrystallizations from deoxygenated chlo-
roform. The pure phosphine trisulfide, pOp3S3, was prepared from
the pure phosphine monoxide, pOp3, with excess of sulfur.
The 31P NMR spectra of the reaction solutions of K2[PdCl4] with
pOp3 and with pOp3S3 in which the metal:ligand molar ratio was
3:2, showed that the trinuclear complexes, 1 and 4, were formed
almost quantitatively, respectively. Furthermore, the reaction

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structure. It is probable that the trans(P) geometry of 1 is relatively
thermodynamically unstable to facilitate the formation of the
catalytically active species.
Appendix A. Supplementary data
CCDC 800188 and 800189 contain the supplementary crystal-
lographic data for 3 and 4, respectively. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Appendix. Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.03.018.
Fig. 6. Changes in the yield of stilbene with time in MizorokieHeck reaction catalyzed
by 1 (B), 4 (C), 6 (-), 7 (,),8 (:), and [PdCl(pp3)]Cl (A).
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concentration of the catalytically active Pd(0) species compared
with the phosphino groups. Furthermore, the weaker
s donation of
the phosphine sulfide to Pd(II) is of great advantage to the migra-
tory insertion of Pd(II) to give the acceleration of the catalytic cycle.
The catalytic activity of 1 appears to be higher than the other
phosphine complexes 6 and 7 with square-planar cis(P) geometry
and [PdCl(pp3)]Cl with five-coordinate trigonal-bipyramidal