Synthesis and structure of platinum(II)- and palladium(II)-phosphorin complexes in solid and solution state

Article abstract of DOI:10.1016/j.molstruc.2006.02.010

The novel platinum and palladium complexes with phosphorin, [Pt(dmppn)₂X₂] (X=Cl (1), Br (2), I (3)) and [Pd(dmppn)₂X₂] (X=Cl (4), Br (5)), have been prepared using 4,5-dimethyl-2-phenylphosphorin (dmppn) with M(cod)X₂ or M(PhCN)₂X₂ (M=Pt, Pd). The crystal structure of 3 was determined by single crystal X-ray crystallography and shown a cis configuration in a square planar structure. The chemical shifts for these complexes were observed by ³¹P{¹H} NMR spectroscopy in the solution and they showed significant upfield shifts over 30 ppm relative to that of the free ligand. These upfield shifts indicate that the phosphorin ligand undergoes strong π-back donation from the central metal compared with general phosphine ligands and the difference of these upfield shifts between Pt and Pd is clearly appeared the degree of π-back donation from the central metal. Molecular structure of platinum and palladium complexes in the solution was further estimated to have the cis configuration in the square planar with ³¹P{¹H} and ¹³C{¹H} NMR data.

Full text of DOI:10.1016/j.molstruc.2006.02.010

Journal of Molecular Structure 794 (2006) 215–220
www.elsevier.com/locate/molstruc
Synthesis and structure of platinum(II)– and palladium(II)–phosphorin
complexes in solid and solution state
b
b
b
Michito Shiotsuka a, , Takahiro Tanamachi , Tsuyoshi Urakawa , Yoshihisa Matsuda
*
a Department of Socio Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho,
Showa-ku, Nagoya, Aichi 466-8555, Japan
b Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
Received 11 November 2005; received in revised form 8 February 2006; accepted 9 February 2006
Available online 27 March 2006
Abstract
The novel platinum and palladium complexes with phosphorin, [Pt(dmppn)2X2] (XZCl (1), Br (2), I (3)) and [Pd(dmppn)2X2] (XZCl (4), Br
(5)), have been prepared using 4,5-dimethyl-2-phenylphosphorin (dmppn) with M(cod)X2 or M(PhCN)2X2 (MZPt, Pd). The crystal structure of 3
was determined by single crystal X-ray crystallography and shown a cis configuration in a square planar structure. The chemical shifts for these
complexes were observed by 31P{1H} NMR spectroscopy in the solution and they showed significant upfield shifts over 30 ppm relative to that of
the free ligand. These upfield shifts indicate that the phosphorin ligand undergoes strong p-back donation from the central metal compared with
general phosphine ligands and the difference of these upfield shifts between Pt and Pd is clearly appeared the degree of p-back donation from the
central metal. Molecular structure of platinum and palladium complexes in the solution was further estimated to have the cis configuration in the
square planar with 31P{1H} and 13C{1H} NMR data.
q 2006 Elsevier B.V. All rights reserved.
Keywords: Phosphorin; Platinum; Palladium; X-ray crystal structure; NMR spectroscopy
1. Introduction
phosphorins [4] and developed by the use as the metal catalyst
with a unique coordination mode of phosphorin derivatives in
the field of catalytic chemistry [5]. However, only two
examples of the isolated platinum(II)–phosphorin complexes
have been reported. The first characterized compounds by
NMR measurement have been reported in our previous
communication for platinum(II) and palladium(II) complexes
[M(dmppn)2Cl2] (MZPt and Pd, dmppnZ4,5-dimethyl-2-
phenylphosphorin) which presumed the square planar structure
with a cis configuration in the solution [6]. On second report,
the first X-ray crystal structure of platinum(II)–phosphorin
complex [Pt(2,6-dimethyl-4-phenylphosphorin)2Cl2] has been
revealed a cis configuration by Elschenbroich et al. [7]. This
fact prompted us to attempt the synthesis and the structural
influence of halogeno ligand in platinum(II) and palladium(II)
complexes with phosphorin.
The design and synthesis of platinum(II)– and palladium
(II)–phosphine complexes have gained an importance in view
of recent organic synthesis and stereochemistry. An attractive
pursuit in this area is the design of functional supporting ligand
by use of phosphorus ligand with tunable electronic and
structural characteristics [1]. Furthermore, there are particu-
larly successful experimental result [2] and theoretical
interpretations [3] to find out that the stereochemical
configuration around platinum atom on platinum(II) complexes
PtL2X2 (LZphosphine, XZhalide) is fairly dependent on the
steric and electronic factor of the ligand. The reactivity of
catalytic PtL2X2 complexes have been correlated to both s
donation and p back donation from a central metal. On the
other hand, Phosphorin is classified into hetero benzene as
pyridine and has a phosphorus atom in an aromatic ring. Recent
research on the metal complexes with phosphorins and
derivatives has been revealed a strong p-accepting ability of
The present study describes the synthesis and structure of
dihalogenobis(dmppn)platinum(II) complexes Pt(dmppn)2X2
(XZCl (1), Br (2), I (3)) and dihalogenobis(dmppn)
palladium(II) complexes Pd(dmppn)2X2 (XZCl (4), Br(5)).
Single crystal X-ray analysis on 3 has revealed the cis
configuration in the square planar structure and estimated the
steric and electronic factor of phosphorin in the solid state. A
useful information on the configuration of halogeno series was
*
Corresponding author. Tel.: C81 52 735 5172; fax: C81 52 735 5247.
E-mail address: michito@nitech.ac.jp (M. Shiotsuka).
0022-2860/$ - see front matter q 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.02.010

216
M. Shiotsuka et al. / Journal of Molecular Structure 794 (2006) 215–220
obtained the coupling constants between platinum and
phosphorus atom from 31P{1H} NMR spectroscopy.
(ppm)Z137.77 (six, C6), 137.82 (t, Ph–C1), 139.23 (t, C4),
139.63 (t, C3), 149.18 (t, C5), 150.66 (six, C2). 31P{1H} NMR
(CD2Cl2): d (ppm)Z134.1 (J(Pt–P)Z3956 Hz).
2. Experimental
2.2.3. Pt(dmppn)2I2 (3)
2.1. General procedure and materials
Thedmppn(400 mg, 2.0 mmol)inbenzene(5 cm3)wasadded
to the suspension of Pt(cod)I2 (400 mg, 0.72 mmol) in benzene
(20 cm3) and stirred at room temperature. The suspension was
temporarily dissolved and an orange-yellow precipitate appeared
again. The precipitate was filtered, washed with benzene–hexane
(1:3) mixture solution, and dried at 45 8C under reduced pressure.
Recrystallization was performed with dichloromethane. Yield:
532 mg (87%). Anal. Calcd for C26H26I2P2Pt1: C, 36.77; H,
3.09. Found: C, 36.78; H, 3.09. 1H NMR (CDCl3): d (ppm)Z7.45
(d, JZ15 Hz, 1H, C3–H), 7.43 (d, JZ26 Hz, 1H, C6–H), 7.11–
7.26 (m, 5H, phenyl–H), 2.25 (d, JZ8 Hz, 3H, C5–methyl–H),
2.23 (s, 3H, C4–methyl–H). 13C NMR (CD2Cl2): d (ppm)Z
137.41(t, Ph–C1), 139.06(six, C6), 139.19(t, C4), 139.40(t, C3),
148.55 (t, C5), 149.89 (six, C2). 31P{1H} NMR (CD2Cl2): d
(ppm)Z135.4 (J(Pt–P)Z3712 Hz).
All reactions were performed using standard Schlenk
techniques and filtration was carried out in the glove bag
under nitrogen atmosphere. All solvents were purchased from
Nacalai tesque and distilled with CaH2 as drying reagent.
Nitrogen gas was passed into all solvents prior to use.
Dihalogeno(cyclooctadiene) platinum [Pt(cod)X2] (XZBr, I)
were purchased. Bis(benzonitrile)dichloro platinum(II)
[Pt(PhCN)2Cl2] and bis(benzonitrile)dihalogeno palladium(II)
[Pd(PhCN)2X2] (XZCl, Br) were prepared by literature
methods [8]. The ligand 4,5-dimethyl-2-phenylphosphorin
(dmppn) was prepared by the method of Alcaraz et al. [9].
The 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded on
a JEOL JNM-GX 400 FT-NMR spectrometer. Proton and
carbon chemical shifts were recorded relative to internal
SiMe4, while the phosphorus chemical shifts were relative to
external 85% H3PO4. Elemental analyses for C and H were
carried out at Elemental Analysis Service Center, Kyushu
University.
2.3. Preparation of Pd(dmppn)2X2
2.3.1. Pd(dmppn)2Cl2 (4)
Ligand dmppn (400 mg, 2.0 mmol) in benzene (5 cm3) was
added to solution of Pd(PhCN)2Cl2 (307 mg, 0.80 mmol) in
benzene (20 cm3) and stirred at room temperature. After 5 min,
the solution was suspended and an orange-yellow precipitate
appeared. The precipitate was filtered, washed with benzene–
hexane (1:3) mixture solution, and dried at 45 8C under reduced
pressure. Yield: 325 mg (70%). Anal. Calcd for
C26H26Cl2P2Pd1 1.0 C6H6: C, 58.68; H, 4.96. Found: C,
58.60; H, 4.92. 1H NMR (CDCl3): d (ppm)Z7.64 (d, JZ7 Hz,
1H, C6–H), 7.47 (d, JZ27 Hz, 1H, C3–H), 7.16–7.26 (m, 5H,
phenyl–H), 2.28 (d, 3H, C5–methyl–H), 2.27 (s, 3H, C4–
methyl–H). 13C NMR (CD2Cl2): d (ppm)Z139.3 (t, JZ5 Hz,
C4), 139.4 (t, JZ6 Hz, C3), 139.4 (t, JZ16 Hz, Ph–C1), 141.4
(six, JZ34 Hz, C6), 149.1 (t, JZ11 Hz, C5), 155.7 (q, JZ42,
13 Hz, C2). 31P{1H} NMR (CD2Cl2): d (ppm)Z148.7.
2.2. Preparation of Pt(dmppn)2X2
2.2.1. Pt(dmppn)2Cl2 (1)
The round-bottomed flask was charged with the solution of
Pt(PhCN)2Cl2 (300 mg, 0.80 mmol) and dmppn (400 mg,
2.0 mmol) in benzene (20 cm3). After stirred for 1 h, the
mixture solution was added to 40 cm3 of hexane and a pale
yellow adduct was precipitated. The precipitate was filtered,
washed with benzene–hexane (1:3) mixture solution, and dried
at 45 8C under reduced pressure. Yield: 363 mg (68%). Anal.
Calcd for C26H26Cl2P2Pt1 1.0 C6H6: C, 51.62; H, 4.34.
Found: C, 51.12; H, 4.35. 1H NMR (CDCl3): d (ppm)Z7.53 (d,
JZ11 Hz, 1H, C3–H), 7.50 (d, JZ23 Hz, 1H, C6–H), 7.16–
7.26 (m, 5H, phenyl–H), 2.30 (s, 3H, C4–methyl–H), 2.25 (d,
JZ7 Hz, 3H, C5–methyl–H). 13C NMR (CD2Cl2): d (ppm)Z
137.04 (six, C6), 138.00 (t, Ph–C1), 139.11 (t, C4), 139.84 (t,
C3), 149.41 (t, C5), 151.07 (six, C2). 31P{1H} NMR (CD2Cl2):
d (ppm)Z134.3 (J(Pt–P)Z4052 Hz).
2.3.2. Pd(dmppn)2Br2 (5)
This compound was prepared by similar procedures of
complex 4. Yield: 321 mg (60%). Anal. Calcd for
C26H26Br2P2Pd1 2/3 C6H6: C, 50.13; H, 4.21. Found: C,
1
50.47; H, 4.27. H NMR (CDCl3): d (ppm)Z7.546 (d, JZ
2.2.2. Pt(dmppn)2Br2 (2)
18.1 Hz, 1H, C6–H), 7.498 (d, JZ20.8 Hz, 1H, C3–H), 7.12–
7.33 (m, 5H, phenyl–H), 2.285 (d, JZ8.1 Hz, 3H, C5–methyl–
H), 2.262 (d, JZ1.5 Hz, 3H, C4–methyl–H). 13C NMR
(CD2Cl2): d (ppm)Z139.2 (d, JZ31 Hz, Ph–C1), 139.3 (d,
JZ14 Hz, C3), 139.5 (d, JZ11 Hz, C4), 142.4 (d, JZ34 Hz,
C6), 148.9 (d, JZ20 Hz, C5), 155.5 (dd, JZ34, 6 Hz, C2).
31P{1H} NMR (CD2Cl2): d (ppm)Z147.7.
The dmppn (400 mg, 2.0 mmol) in dichloromethane (20 cm3)
was added to the solution of Pt(cod)Br2 (394 mg, 0.85 mmol) in
benzene (10 cm3). After stirred for 10 min, the dichloromethane
was distilled off under reduced pressure and a yellow adduct was
precipitated. The precipitate was filtered, washed with benzene–
hexane (1:3) mixture solution, and dried under reduced pressure.
Yield: 456 mg (71%). Anal. Calcd for C26H26Br2P2Pt1: C,
41.34; H, 3.47. Found: C, 41.79; H, 3.44. 1H NMR (CDCl3): d
(ppm)Z7.51 (d, JZ12 Hz, 1H, C3–H), 7.45 (d, JZ25 Hz, 1H,
C6–H), 7.11–7.26 (m, 5H, phenyl–H), 2.27 (s, 3H, C4–methyl–
H), 2.24 (d, JZ8 Hz, 3H, C5–methyl–H). 13C NMR (CD2Cl2): d
2.4. Crystallography of Pt(dmppn)2I2 (3)
An orange prismatic crystals suitable for X-ray diffraction
study of Pt(dmppn)2I2 (3) were isolated from CH2Cl2

M. Shiotsuka et al. / Journal of Molecular Structure 794 (2006) 215–220
217
Table 1
complexes Pd(dmppn)2X2 (XZCl (4), Br(5)) were prepared
using 4,5-dimethyl-2-phenylphosphorin (dmppn) with M(cod)X2
or M(PhCN)2X2 (MZPt, Pd) by the ligand exchange reaction.
The elemental analysis of present five complexes was identified
asthe composition of M(dmppn)2X2, respectively. These isolated
complexes were stable against air and moisture in a dichloro-
methane solution although free dmppn ligand in the solution was
gradually received the oxidation by the air or moisture. Attempts
to obtain the palladium(II) and platinum(II) complexes through
direct reactions of MCl2 (MZPd, Pt) with dmppn in methanol
were unsuccessful because of the decomposition of p system of
phosphorin; the decomposition of p system in phosphorin ring
was presumed the disappearance of the signals assignable to the
Crystallographic data for complex 3
Formula
C26H26PtI2P2
849.34
Fw
Crystal system
Space group
˚
a (A)
Orthorhombic
Pbcn
19.10(1)
9.423(7)
14.797(6)
2667(2)
4
˚
b (A)
˚
c (A)
3
˚
V (A )
Z
D
calc (mg mK3
)
1.584
Crystal size (mm3)
0.20!0.10!0.20
0.71069
76.98
Radiation Mo Ka (l)
m (Mo Ka) (cmK1
T (K)
)
1
293
aromatic protons in phosphorin ring by H NMR spectroscopy
and the appearance of the characteristic n(PaO) stretching band
by IR spectroscopy.
Total reflections
Ra
b,c
2692
0.048
Rw
0.060
a
RZS[jF0jKjFcj]/SjF0j.
3.2. Crystallography of Pt(dmppn)2I2 (3)
b
c
2 1/2
RwZ[Sw(jF0jKjFcj)2/SwjF0j ]
.
wZ1/s2(F0).
The single crystal of Pt(dmppn)2I2 (3) appropriate for X-ray
crystallography was obtained as orange prismatic crystals by
recrystallization from CH2Cl2 solution. The crystal structure of
3 is shown in Fig. 1 and this complex crystallizes as a
monomeric square planar structure. This is the first example of
diiodobis(phosphorin)platinum(II) complex that has been
established the molecular structure by X-ray crystallography
although only one example for the crystal structure of dichloro
complex [Pt(2,6-dimethyl-4-phenylphosphorin)2Cl2] (6) has
been reported by Elschenbroich et al. [7]. Selected bond
lengths and angles are listed in Table 2 and the atom numbering
is shown in Fig. 1. The coordination geometry of two
phosphorus and two iodine atoms bound to platinum atom is
a cis configuration and the angles of P–Pt–I (88.88) and P–Pt–
P* (91.78) are slightly distorted from the angle of ideal square
planar geometry.
solution. The crystal was mounted on a glass fiber. All
measurements were made on a Rigaku AFC7R diffracto-
meter with graphite monochromated Mo Ka radiation (lZ
˚
0.71069 A) and a 12 kW rotating anode generator. Cell
constants and an orientation matrix were obtained from a
least-squares refinement using 23 reflections in the range
27.798!2q!29.998. For the intensity data collection, the
uK2q scan mode was used at the scan rate 16 minK1 and
scan width was (1.00C0.30 tan q)8. The intensities of three
standard reflections were monitored after every 150
reflections. Over the course of data collection, the standards
increased by 1.2% and, therefore, a linear correction factor
was applied to the data to account for this phenomenon. An
empirical absorption and Lorentz-polarization absorption
correction were applied. Crystallographic data are given in
Table 1.
The coordination geometry of complexes is favorable for
trans isomer according to more hindered ligand and the iodo
ligand acts as a sterically more hindered ligand than chloro and
bromo on the current stereochemical study with
All the calculations were performed by using teXsan
crystallographic software package of the Molecular Structure
Corporation. The structure was solved by heavy atom
Patterson methods and expanded using Fourier techniques
[10]. The non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included in idealized positions (d(C–
˚
H)Z0.95 A) but not refined. The final cycle of full-matrix
least-squares refinement with scattering factors was based on
1866 observed reflections (IO3.00s(I)) and 142 variable
parameters. Neutral atom scattering factors were taken from
Cromer and Waber [11] and anomalous dispersion effects
were included in Fcalc [12]; the values of Df0 and Df00 were
those of Cregh and McAuley [13].
3. Results and discussion
3.1. Synthesis
Dihalogenobis(dmppn)platinum(II)complexesPt(dmppn)2X2
(XZCl (1), Br (2), I (3)) and dihalogenobis(dmppn)palladium(II)
Fig. 1. A view of Pt(dmppn)2I2 (3), with displacement ellipsoids drawn at the
50% probability level. H atoms have been omitted.

218
M. Shiotsuka et al. / Journal of Molecular Structure 794 (2006) 215–220
Table 2
difference of bond length between cis and trans isomer and
almost all phosphines have been classified as the ligand
contributed strongly trans influence relative to iodo ligand. The
shortness of Pt–I length on 3 can be explained that phosphorin
is classified as the ligand of weaker trans influence than
phosphines. Trans influence mainly results from s effect in a
recent theory [17]. In fact, Pt–I lengths on cis-platinum
complexes with phosphine ligands came longer than those on
trans-complexes, while Pt–P lengths were contrary shorter.
This observation reveals that tertiary phosphines are highly s
donor and p acceptor ligand relative to iodo ligand. However,
the bond lengths of both Pt–P and Pt–I on 3 are short as
mentioned above and, therefore, phosphorin can be regarded
lower s donor ligand but higher p acceptor ligand than tertiary
phosphines. This interpretation is in fair agreement with
current reports of phosphorin research [4].
Selected bond lengths and angles on complex 3
˚
Bond length (A)
Pt–I
2.631(2)
2.236(4)
1.72(2)
1.38(2)
1.41(2)
1.36(2)
1.41(2)
1.75(2)
1.43(2)
C6–C7
1.35(2)
1.40(3)
1.37(2)
1.40(2)
1.37(2)
1.38(2)
1.51(2)
1.49(2)
Pt–P
C7–C8
P–C1
C8–C9
C1–C2
C9–C10
C10–C11
C11–C6
C12–C2
C13–C3
C2–C3
C3–C4
C4–C5
C5–P
C5–C6
Bond angles (8)
I–Pt–P
88.8(1)
92.00(7)
91.7(2)
171.2(1)
129.6(6)
123.9(6)
122(1)
C2–C3–C13
C3–C2–C12
C3–C4–C5
C4–C3–C13
C4–C5–C6
C5–C6–C7
C5–C6–C11
C6–C7–C8
C6–C11–C10
C7–C6–C11
C7–C8–C9
C8–C9–C10
C9–C10–C11
119(1)
121(1)
127(1)
116(1)
122(1)
120(1)
120(1)
118(1)
122(1)
118(1)
123(1)
116(1)
119(1)
I–Pt–I*
P–Pt–P*
P–Pt–I*
Pt–P–C1
Pt–P–C5
P–C1–C2
P–C5–C4
P–C5–C6
C1–P–C5
C1–C2–C3
C1–C2–C12
C2–C3–C4
˚
The P–C bond lengths (1.72(2) and 1.75(2) A) on 3 were
˚
almost same as those (1.712(4) and 1.719(4) A) on 6. The most
116(1)
120(1)
of P–C lengths on Pt(PR3)2X2 (XZhalides) are situated in the
˚
range of 1.80–1.89 A and those on cis-Pt(PEt3)((C6H2Me3)-
106.5(8)
122(1)
˚
116(1)
PZCPh2)Cl2 (7) were reported 1.66(1) A (PaC bond) and
124(1)
˚
1.79(1) A (P–C bond) by Kroto et al. [18]. These differences of
bond lengths obviously show that phosphorus atom of dmppn
are included in an aromatic p system because P–C lengths of 3
are intermediate between those of tertiary phosphines (sp3
hybridization) and phospha–alkene (sp2 hybridization).
dihalogenobis(PR3)platinum(II) complexes (PR3Ztertiary
phosphines). Indeed, the crystal structure of cis-
diiodobis(PR3)platinum(II) complexes were few reported as
compared with the cis-dichrolobis(PR3)platinum(II)
complexes [14]. These results demonstrate that phosphorin
acts as a less hindered ligand than many kinds of phosphines
because 3 isolates as a cis isomer.
The phosphorin ring of one ligand in 3 appeared to be
piled up the phenyl ring of another ligand as shown in
Fig. 2. The intramolecular distances between atoms of
phosphorin ring and ones of phenyl ring between two
ligands were calculated and it was turned out that the
distances between most neighboring atoms were in the range
The bond lengths of Pt–I and Pt–P are showed about cis-
diiodobis(PR3)platinum(II) and trans-platinum(II) complexes
revealed that phosphorus atom was situated in trans position of
iodine atom by X-ray crystallography in Table 3 [14–16]. The
˚
˚
of 3.58–4.05 A (P1–C7* 3.58(2) A, C1–C8* 3.63(2) A, C2–
˚
˚
˚
C9* 3.75(3) A, C3–C9* 3.99(2) A, C4–C10* 4.05(2) A, C5–
˚
˚
Pt–P length (2.236(4) A) on 3 is included in the range of the
˚
C6* 3.95(2) A). These distances are sufficiently considered
˚
lengths on the collated cis-complexes (2.219(3)–2.271(4) A)
and shorter than that on trans-complexes (2.292(6)–
that p–p interaction exist between p system of phosphorin
and phenyl ring on two dmppn ligands in 3. Additionally,
the six atoms in the phosphorin ring are approximately
located on the least square plane and the C–C lengths in
phosphorin ring are reasonable as the bond distances on
˚
2.371(2) A). On the other hand, The Pt–I length (2.631(2) A)
˚
on 3 is rather closed to the region of the lengths on trans-
˚
complexes (2.599(2)–2.626(2) A) and appreciably shorter than
˚
that on cis-complexes (2.629(1)–2.672(2) A) in spite of the cis
configuration. Trans influence is employed to interpret the
Table 3
Bond lengths of Pt–I and Pt–P in the complexes of Pt(PR3)2I2
˚
Pt–I (A)
˚
Pt–P (A)
Complexes
Refs.
3
cis-Pt{P(CH3)3}2I2
2.631(2)
2.665(2)
2.672(2)
2.658(2)
2.662(2)
2.629(1)
2.648(1)
2.622(1)
2.612(1)
2.626(2)
2.599(2)
2.236(4)
2.244(4)
2.271(4)
2.219(3)
2.247(3)
2.257(2)
2.266(2)
2.348(2)
2.371(2)
2.292(6)
2.315(4)
[7a]
[7b]
[8]
cis-Pt(biphosphole)I2
cis-Pt(PPh2ChCPh)2I2
trans-Pt{P(CH3C6H5)3}2I2
trans-Pt{P(C6H11)3}2I2
trans-Pt{P(C6F5)3}2I2
trans-Pt{P(CH3)3}2I2
[9a]
[9b]
[9c]
[9d]
Fig. 2. Another view of complex 3, with displacement ellipsoids drawn at the
50% probability level. H atoms have been omitted.

M. Shiotsuka et al. / Journal of Molecular Structure 794 (2006) 215–220
219
aromatic compounds as shown in Table 2. The least square
plane of both the phosphorin and phenyl ring is pitched at a
dihedral angle of 56.158. This angle is larger than those of
Iodocopper(I) complex with dmppn [19] and possessed to
the effects of not only a steric repulsion between the
hydrogen atoms, the one is bound to C4 in the phosphorin
ring and another one to C11 in the phenyl ring, but also
p–p stacking between phosphorin and phenyl ring of each
dmppn ligands.
The 31P{1H} NMR spectra on present platinum complexes
were observed only three signals in both CDCl3 and CD2Cl2,
respectively. Then, these three complexes are speculated to
exist one isomer without the cis–trans isomerization in the
1
solution. The coupling constant J(31P–195Pt) is determined
with the separated width of two outside signals in pseudo
triplet. The 1J(31P–195Pt) for complexes 1, 2, and 3 were
respectively determined to be 4052, 3976, and 3712 Hz. The
1J(31P–195Pt) is most informative for the determination
between the cis and trans configurations in the solution. The
1J(31P–195Pt) for platinum(II) complexes Pt(PR3)2X2 are
typically greater than 3000 Hz on the cis configuration of
two phosphorus atoms and smaller than 3000 Hz on the trans
configuration according to previous studies [22]. Indeed, it was
reported that the cis-complexes 6 and 7 were observed the
1J(31P–195Pt) of 3907 and 4294 Hz; two phosphorus atoms
occupied mutually a cis position as determined by X-ray
crystallography. While trans-complex 7 was measured the
1J(31P–195Pt) of 2590 Hz; this complex was observed in the
solution and not isolated [6,18]. These observations support
that these platinum complexes have the cis configuration in the
solution and this interpretation is consistent with result that 3
revealed the cis configuration in the solid state by X-ray
crystallography.
3.3. NMR studies
The 31P{1H} NMR spectra on platinum complexes 1–3
showed signals near 135 ppm while those on palladium
complexes 4 and 5 did near 148 ppm as shown in Table 4.
These observations are typical for the h1 coordination of metal
complexes with phosphorin; phosphorus resonances of phos-
phorin in the case of h6 coordination have been observed upper
field than 50 ppm [20]. It is noticeable that both platinum and
palladium complexes showed significant upfield shifts of the
phosphorus resonance by over 48 and 35 ppm relative to that of
the free dmppn, respectively. The degrees of the upfield shifts
in platinum complexes were greater than those of palladium
complexes. Such coordination shifts were reported in previous
studies [21] and this difference has been considered to attribute
to different dsp2 hybrid orbitals of each complexes as treated in
VB theory; platinum complex is expressed as 5d6s6p2 while
palladium as 4d5s5p2.
The 31P{1H} NMR spectra for palladium complexes 4
and 5 were observed as a slightly broad singlet (half-line
width 49 Hz), respectively. The trans isomers of palladiu-
m(II) complexes Pd(PR3)2Cl2 generally have greater coup-
Furthermore, chemical shifts of adjacent carbon atoms to
phosphorus (C2 and C6) also showed upfield shifts in the range
of 13–18 ppm and those of C3 and C5 observed downfield
shifts in the range of 3–7 ppm in present complexes as shown
in Table 4. These assignments were performed by 13C-DEPT
and 13C–1H COSY measurement for present complexes. These
changes in the direction of the shifts indicate the alteration of
p-system of the phosphorin due to p-back donation because
these changes of carbon resonance in phosphorin are consistent
with the changes on an aromatic compound introduced to an
electron donor group. Therefore, the main factor of these
upfield shifts in the phosphorin is plausibly attributed to p-back
donation from the central metal to stabilize the metal–
phosphorus bonding.
2
ling constants J(31P–31P) than 150 Hz while the cis isomers
have smaller ones than 20 Hz [23]. Additionally, the 13C
signal patterns of adjacent carbon atoms to phosphorus (C2
and C6) in 4 were observed as multiplets while those in 5 as
doublet of doublets and doublet. These signal patterns of 4
and 5 suggests to possesses the cis configuration in the
solution. Because the signal patterns of the carbon atoms
bonded to phosphorus between the cis and trans isomers
showed distinct multiplicities on the previous 13C NMR
studies of Pd(PR3)2Cl2. The patterns on the cis isomers have
been observed as multiplets or doublet of doublets or
doublet, while those on the trans isomers have appeared as
1:2:1 triplet [23].
Table 4
31P- and 13C-NMR data for free ligand, Pt(dmppn)2X2 (XZCl (1), Br (2), I (3)), and Pd(dmppn)2X2 (XZCl (4), Br(5)) in CD2Cl2
Sample
d
31Pa (Dd)c
d
13Cb (Dd)c
C2
C6
C3
C5
C4
dmppn
183.8
168.5
154.8
136.1
142.0
139.5
1
2
3
4
5
134.3 (49.5)
134.1 (49.7)
135.4 (48.4)
148.7 (35.1)
147.7 (36.1)
151.1 (17.4)
150.7 (17.8)
149.9 (18.6)
155.7 (12.8)
155.5 (13.0)
137.0 (17.8)
137.8 (17.0)
139.1 (15.7)
141.4 (13.4)
142.4 (12.4)
139.8 (K3.7)
139.6 (K3.5)
139.4 (K3.3)
139.4 (K3.3)
139.3 (K3.2)
149.4 (K7.4)
149.2 (K7.2)
148.6 (K6.6)
149.1 (K7.1)
148.9 (K6.9)
139.1 (0.4)
139.2 (0.3)
139.2 (0.3)
139.3 (0.2)
139.5 (0.0)
a
Chemical shifts in ppm relative to H3PO4 (85% aqueous solution).
Chemical shifts in ppm relative to TMS.
b
c
DdZd(dmppn)Kd(complex).

220
M. Shiotsuka et al. / Journal of Molecular Structure 794 (2006) 215–220
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010. Crystallographic data for the structural analysis have been
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CCDC 231727 for compound 3. Copies of this information
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