Bismuth(III) halides as halide source for preparation of dihaloplatinum(IV) complexes

Article abstract of DOI:10.1016/j.poly.2014.04.006

The complexes [PtMe₂(^tBu₂bpy)], 1a, ^tBu₂bpy = 4,4′-di-tert butyl-2,2′-bipyridine, and [PtMe(ppy)PPh₃], 1b, ppy = deprotonated 2-phenylpyridine, react very easily with BiX₃ (X = C

Full text of DOI:10.1016/j.poly.2014.04.006

Polyhedron 77 (2014) 24–31
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Bismuth(III) halides as halide source for preparation
of dihaloplatinum(IV) complexes
a
a
S. Masoud Nabavizadeh a, , Peyman Hamidizadeh , Farzane Ahmadi Darani ,
⇑
Fatemeh Niroomand Hosseini b, , Arnold L. Rheingold c
⇑
a Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71467-13565, Iran
b Department of Chemistry, Shiraz Branch, Islamic Azad University, Shiraz 71993-37635, Iran
c Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, CA 92093, USA
a r t i c l e i n f o
a b s t r a c t
t
The complexes [PtMe2(tBu2bpy)], 1a, Bu2bpy = 4,40-di-tert butyl-2,20-bipyridine, and [PtMe(ppy)PPh3],
1b, ppy = deprotonated 2-phenylpyridine, react very easily with BiX3 (X = Cl, Br, or I) to give [PtMe2(X)2
(tBu2bpy)] (2a, X = Cl; 3a, X = Br; 4a, X = I) and [PtMe(X)2(ppy)PPh3] (2b, X = Cl; 3b, X = Br; 4b, X = I),
respectively. In these oxidative addition reactions, BiX3 reagent can be used as halide source instead of
hazardous reagents X2. The dihaloplatinum(IV) complexes are characterized using NMR spectroscopy
and the structures of complexes 4a and 3b are further identified by X-ray crystallography. Structures
of Pt(IV) complexes are investigated using DFT calculations at B3LYP level of theory.
Article history:
Received 29 January 2014
Accepted 4 April 2014
Available online 16 April 2014
Keywords:
Platinum
Bismuth halides
Cyclometalated complexes
DFT calculations
Halide source
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
chloride bond at a low-valent metal centre. Limberg et al. have
recently reported a Pt-–Bi donor–acceptor interaction which is
Trivalent bismuth halides BiX3 (X = Cl, Br, I) have been useful in
organic synthesis due to their mild Lewis acidity which allows
them to be easily recover from the reaction media. These com-
pounds have also attracted significant interest because of their
low cost, low toxicity and high abundance in comparison to other
common Lewis acids [1,2]. These compounds and other bismuth
salts have also been implicated as catalysts for many reactions
such as ring-opening reactions of epoxides [3–5], bond-forming
reactions such as Diels–Alder cyclizations [6], aldol and Michael
reactions [7], and the hydroarylation of styrenes and arenes [8,9].
The coordination chemistry of bismuth is dominated by the
Lewis acidic nature of the main-group centre. This behavior is
surprising, considering the presence of a lone pair of electrons cen-
tered on the main group atom, which results in Lewis basicity for
phosphines and arsines. In the case of trivalent bismuth halides,
the observed Lewis acidity is due to the contracted nature of the
bismuth lone pair, which resides in the 6s orbital and so is largely
supported by an ambiphilic PBiP pincer ligand [12].
Oxidative addition reactions have become one of the most pop-
ular types of organometallic reactions. The contribution of Pt(II) d8
organometallic complexes in the activation of organic substrates
and in catalytic cycles is well known [13], for examples in the Shi-
lov, Wacker, and Heck reactions [14–18]. The majority of these
processes involve an initial C–X (X = Cl, Br, I) oxidative addition
and oxidation of Pt(II) to Pt(IV). Furthermore, there has been a
great interest in recent decades to investigate oxidative addition
reactions of square-planar Pt(II) complexes [19–24]. We have also
investigated the oxidative addition of different reagents to
platinum(II) complexes resulting in the octahedral platinum(IV)
compounds [25–31].
In continuation of our interest in the oxidative addition reac-
tions with organoplatinum(II) complexes and to better understand
the reactivity of BiX3 (X = Cl, Br, I) toward organometallic com-
pounds, we hereby report the oxidative addition of BiX3 reagents
t
unavailable for mixing with the halide
r
orbitals [10].
to organoplatinum(II) complexes, [PtMe2(tBu2bpy)], 1a, Bu2bpy =
The oxidative addition reaction of [Pt(PCy3)2] with BiCl3 has
been studied resulting in trans-[PtCl(PCy3)2(BiCl2)] [11]. This was
the first reported oxidative addition reaction of the bismuth–
4,40-di-tertbutyl-2,20-bipyridine, and [PtMe(ppy)PPh3], 1b, ppy =
deprotonated 2-phenylpyridine. In these reactions, BiX3 can
replace to X2 reagents acting as halide source for conversion of
Pt(II) to Pt(IV) complexes. It is important, because X2 (i.e. Cl2, Br2
and I2) reagents have high toxicity and their handling is difficult,
in contrast to low toxicity, air stability and ease of handling of
bismuth(III) trihalides. To augment our synthetic experiments, a
⇑
Corresponding authors. Tel.: +98 711 613 7110; fax: +98 711 646 0788.
E-mail addresses: nabavi@chem.susc.ac.ir (S.M. Nabavizadeh), niroomand@
iaushiraz.ac.ir (F.N. Hosseini).
http://dx.doi.org/10.1016/j.poly.2014.04.006
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

S.M. Nabavizadeh et al. / Polyhedron 77 (2014) 24–31
25
series of density functional theory (DFT) calculations were carried
out to investigate the structures of Pt(IV) products.
immediately turned yellow and after a few minutes the yellowish
solution changed to pale yellow. The solution was stirred at room
temperature for 3 h. The solvent was evaporated and a pale-yellow
powder was obtained as a mixture of 2b (major product, 60%) and
[PtCl(ppy)PPh3] (minor product, 40%) and bismuth containing
byproduct, probably BiCl [37]. Due to low solubility, the com-
pounds formed in this reaction could not be separated, therefore
elemental analysis was not useful. NMR data for 2b in CDCl3:
d(1H) 2.14 [d, 3H, 3J(PH) = 3 Hz, 2J(PtH) = 63.8 Hz, 3H, Pt–Me], aro-
matic protons: 9.28 [d, 3J(HH) = 4.9 Hz, 3J(PtH) = 10.4 Hz, 1H, CH
group adjacent to ligating N atom of ppy], 6.50–8.21 [overlapping
2. Experimental
The NMR spectra of the complexes were recorded on a Bruker
Avance DPX 250 or 500 MHz spectrometer. All the chemical shifts
and coupling constants are given in units of ppm and Hz, respec-
tively. Electrospray ion mass spectra (ESI-MS) were recorded on a
Hewlett–Packard Series 1100 spectrometer by using methanol as
solvent. The complexes [PtMe2(tBu2bpy)] [32] and [PtMe(ppy)
PPh3] [33] were prepared as reported. The complexes [Pt(X)2Me2
(tBu2bpy)], X = Cl [34], Br [35] and I [36], were characterized
according to the literature.
multiplets]; d(31P) ꢀ3.22 [s, 1J(PtP) = 2898 Hz, P atom of PPh3]. 31
P
NMR data for [PtCl(ppy)PPh3]: 23.6 [s, 1J(PtP) = 4346 Hz, P atom of
PPh3]. The mixture had not enough solubility in common solvents
for any 13C NMR spectroscopy.
The following reactions were done similarly by using the com-
plex 1b and BiBr3 or BiI3:
2.1. Synthesis of complexes
2.1.1. [Pt(Cl)2Me2(tBu2bpy)], 2a
2.3. Reaction of [PtMe(ppy)PPh3] with BiBr3
This compound had been previously synthesized by the reac-
tion of [PtMe2(tBu2bpy)] with Cl2 [34]. We used BiCl3 instead of
Cl2. To a solution of [PtMe2(tBu2bpy)] (100 mg, 0.2 mmol) in
acetone (15 mL) was added BiCl3 (63.1 mg, 0.2 mmol). The reaction
mixture was stirred for 30 min, after which time a bright yellow
solid was precipitated which was separated and dried under
vacuum. The product complex [Pt(Cl)2Me2(tBu2bpy)], 2a, had 1H
NMR data similar to reported data in acetone-d6 [34]. therefore
no more methods were used for characterization of this compound.
1H NMR data in CDCl3: d1.44 (s, 18 H, tBu), 2.35 (s, 2J(PtH) =
The complex 3b was obtained as pure product in this reaction.
NMR data in CDCl3: d(1H) 2.31 [d, 3J(PH) = 3.3 Hz, 2J(PtH) = 65.8 Hz,
3H, Pt–Me], aromatic protons: 9.48 [d, 3J(HH) = 5.8 Hz,
3J(PtH) = 11.3 Hz, 1H, CH group adjacent to ligating N atom of
ppy], 6.65 [d, 3J(HH) = 7.5 Hz, 3J(PtH) = 36.5 Hz, 1H, CH group adja-
cent to ligating C atom of ppy], 6.80–7.75 [overlapping multiplets];
d(31P) ꢀ5.7 [s, 1J(PtP) = 2757 Hz, P atom of PPh3]. Anal. Calc. for C30
H26Br2NPPt: C, 45.8; H, 3.3; N, 1.8. Found: C, 46.3; H, 3.4; N, 2.0%.
The solubility of 3b was not enough in common solvents for any
13C NMR experiment.
t
68.8 Hz, 6H, Me groups trans to N); aromatic protons of Bu2bpy
ligand 7.67 (dd, 3J(H6H5) = 5.8 Hz, 4J(H3H5) = 1.8 Hz, 2H, H5), 8.16
(d, 4J(H3H5) = 1.8 Hz, 2H, H3), 8.84 (d, 3J(H5H6) = 5.8 Hz,
2.4. Reaction of [PtMe(ppy)PPh3] with BiI3
3J(PtH) = 13.4 Hz, 2H, H6). Molar conductance: 2.20
lS/cm.
The following complexes were made similarly using the dim-
ethylplatinum(II) complex, 1a, and BiBr3 or BiI3.
The products were identified as a mixture of 4b (major product,
80%), [PtI(ppy)PPh3] (minor product, 20%) and bismuth containing
byproduct, probably BiI. Because the compounds formed in this
reaction could not be separated, elemental analysis was not useful.
NMR data for 4b in CDCl3: d(1H) 2.53 [d, 3J(PH) = 4.1, 2J(PtH) = 68.5,
3H, Pt–Me], aromatic protons: 9.75 [d, 3J(HH) = 5.5 Hz, 3J(PtH) =
11.8 Hz, 1H, CH group adjacent to ligating N atom of ppy], 6.63
[d, 3J(HH) = 7.9 Hz, 3J(PtH) = 18.2 Hz, 1H, CH group adjacent to
ligating C atom of ppy], 7.00–7.70 [overlapping multiplets]. d(31P)
2.1.2. [Pt(Br)2Me2(tBu2bpy)], 3a
This compound had been previously synthesized by the reac-
tion of [PtMe2(tBu2bpy)] with Br2 and had 1H NMR data similar
to data previously reported,[35] so no more characterization meth-
ods were used. Molar conductance: 2.50 lS/cm. ESI-MS of metha-
nolic solution of 3a shows prominent peak at m/z value of 573.5
corresponding to [PtBrMe2(tBu2bpy)]+ fragment.
ꢀ17.3 [s, 1J(PtP) = 2431 Hz,
P atom of PPh3]. NMR data for
[PtI(ppy)PPh3] in CDCl3: d(31P) 22.7 [s, 1J(PtP) = 4292 Hz, P atom
of PPh3]. The solubility of the mixture was not enough in common
solvents for any 13C NMR experiment.
2.1.3. [Pt(I)2Me2(tBu2bpy)], 4a
This compound had been previously synthesized by the reaction
of [PtMe2(tBu2bpy)] with I2. In the present work, we replace I2 by
BiI3. The first reported 1H NMR chemical shifts of 4a in C6D6 were
incorrect [36] (see Result and discussion for more details). 1H
NMR data in C6D6: d3.13 (s, 2J(PtH) = 73.2 Hz, 6H, Me groups trans
2.5. Reaction of [PtMe(ppy)PPh3] with I2
In a comparative study, to prove that the BiI3 can act as an
t
t
to N), 0.88 (s, 18 H, Bu); aromatic protons of Bu2bpy ligand 8.65
(d, 3J(PtH) = 14.5 Hz, 3J(H5H6) = 5.8 Hz, 2H, H6), 7.69 (d, 4J(H3
H5) = 1.7 Hz, 2H, H3) 6.65 (dd, 3J(H6H5) = 5.8 Hz, 4J(H3H5) = 1.7 Hz,
2H, H5). 1H NMR data in CDCl3: d 2.44 (s, 2J(PtH) = 72.7 Hz, 6H, Me
groups trans to N), 1.45 (s, 18 H, tBu); aromatic protons of tBu2bpy
ligand 8.84 (d, 3J(PtH) = 14.2 Hz, 3J(H5H6) = 5.9 Hz, 2H, H6),
8.16 (d, 4J(H3H5) = 1.7 Hz, 2H, H3), 7.63 (dd, 3J(H6H5) = 5.9 Hz,
iodide source, to
a
solution of [PtMe(ppy)PPh3] (10 mg,
0.016 mmol) in acetone (20 mL) was added I2 (4 mg, 0.016 mmol).
The solution was stirred at room temperature for 20 min. The sol-
vent was evaporated and the solid was identified using 1H and 31
P
NMR spectroscopy as 4b as well as small amounts of complex
[PtI(ppy)PPh3].
4J(H3H5) = 1.7 Hz, 2H, H5). Molar conductance: 2.23
lS/cm. ESI-MS
2.6. Crystallography
of methanolic solution of 4a shows prominent peak at m/z value
of 621.7 corresponding to [PtIMe2(tBu2bpy)]+ fragment. Structure
of this complex was also confirmed by single crystal analysis.
Single crystal of [PtMe(Br)2(ppy)PPh3], 3b, was grown from a
concentrated CH2Cl2 solution by slow diffusion of n-pentane. The
single crystal X-ray diffraction study of 3b was carried out on a
2.2. Reaction of [PtMe(ppy)PPh3] with BiCl3
Bruker Platform D8 CCD diffractometer equipped with Mo Ka radi-
ation (k = 0.71073). A 0.24 ꢁ 0.20 ꢁ 0.18 mm3 crystal was mounted
on a Cryo-loop with Paratone-N. The Bruker program packages,
APEX-II and SAINT were used for data collection, integration and
To a solution of [PtMe(ppy)PPh3] (10 mg, 0.016 mmol) in ace-
tone (20 mL) was added BiCl3 (5 mg, 0.016 mmol). The solution

26
S.M. Nabavizadeh et al. / Polyhedron 77 (2014) 24–31
corrections [38]. The structure was solved by direct methods and
refined by full-matrix least squares on F2 for all data using SHELXTL
software [39]. All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were positioned geometrically and refined
with a riding model approximation with their parameters con-
strained to the parent atom with Uiso (H) = 1.2 or 1.5 Ueq (C). At
Pt(IV) centre of complex 3b, there was bromide disorder; the
minority component is designated with a prime. The major config-
uration at Pt is 87.7% occupied. Treatment of disorder resulted in
close contacts between methyl hydrogens and minority portion
of bromide Br1 which registered as methyl hydrogens having more
than unity contact. Attempts to model methyl group C12 as being
disorder and coincident with bromine Br1 positions resulted in
small thermal amplitudes and non-positive definite response for
carbon atom C12. Crystal data, data collection, and structure
refinement details are listed in Table 1.
X
N
N
Me
Me
Me
Me
N
N
+ BiX3
Pt
Pt
X
RT, acetone
1a
2a
3a
4a
+ I2
4a
PPh3
C
Me
Me
X
C
N
+ BiX3
Pt
Pt
X
RT, acetone
PPh3
N
2.7. Theoretical methods
1b
2b
3b
4b
Geometry optimizations were performed with the program
suite Gaussian03 at the DFT/B3LYP level [40]. The effective core
potential of Hay and Wadt with a double-n valence basis set
(LANL2DZ) [41,42] was chosen to describe Pt, Bi, Cl, Br and I. The
6-31G⁄ basis set was used for C, H and N atoms. To evaluate and
ensure the optimized structures of the molecules, frequency calcu-
lations were carried out using analytical second derivatives. In all
cases only real frequencies were obtained for the optimized
structures.
+ I2
4b
Scheme 1. Synthesis of organoplatinum(IV) complexes
those of the previously prepared materials [34–36]. Full data are
collected in the Section 2.
The 1H NMR chemical shifts of Pt–Me and methyl groups of
tBu2bpy ligand for complex 4a in C6D6 were recently reported to
be 2.63 (with 2J(PtH) = 73 Hz) and 1.04 ppm, respectively [36].
When we mixed equimolar amounts of 1a and BiI3 in C6D6 and
3. Results and discussion
recorded the 1H NMR spectrum, Pt–Me and Me of Bu2bpy signals
t
were appeared at d 3.13 (with 2J(PtH) = 73.2 Hz) and 0.88, respec-
tively. We infer that the first reported chemical shifts of 4a in C6D6
were in fact incorrect. To confirm our assignment, we synthesized
the complex 4a using the reaction of complex 1a with iodine,
according to reported method [36] and found that the NMR data
for the product were exactly the same with those obtained for
the resulting complex 4a (from mixing of complex 1a and BiI3).
Structure of this complex was also confirmed by single crystal
analysis (see Fig. 1) [36].
The cyclometalated platinum(II) complex, 1b, was reacted
cleanly with equimolar amount of BiX3 (X = Cl, Br, I) in acetone at
room temperature to give very pale yellow solutions, from which
air–stable solid products having the general formula [PtMe(X)2
(ppy)PPh3] were obtained. The Pt(IV) products of each reaction
3.1. Synthesis and characterization of the complexes
The reactions studied in this work are summarized in Scheme 1.
As shown in Scheme 1, the dimethylplatinum(II) precursor
[PtMe2(tBu2bpy)], 1a, was reacted very easily and cleanly with
BiX3 at room temperature in acetone, as revealed by the rapid
change of color of the reaction mixture from orange to yellow, to
give the organoplatinum(IV) complexes [Pt(X)2Me2(tBu2bpy)]
(X = Cl, 2a; X = Br, 3a; X = I, 4a). The complexes were characterized
by comparing their NMR spectra and crystal structure (for 4a) with
Table 1
Crystal data, data collection and structure refinement details for complex 3b.
Formula
C30H26Br2NPPt
Formula weight
T (K)
Crystal system
Space group
786.40
100(2)
triclinic
ꢀ
P1
a (Å)
b (Å)
c (Å)
V (Å3)
a
9.0820(4)
10.2644(5)
15.6716(7)
1317.58(10)
77.573(1)
81.719(1)
67.781(1)
2
b
c
Z
Dcalc (Mg mꢀ3
)
1.982
8.438
l
(mmꢀ1
)
Tmin/Tmax
F(000)
0.2366/0.3119
752
No. of reflections
16697
No. of independent reflections Rint
5406 (0.0266)
16.697
1.048
No. of observed reflections [I > 2
r(I)]
Goodness-of-fit (GOF) on F2
R1, wR2 [I > 2
R1, wR2 (all data)
r
(I)]
0.0181, 0.0395
0.0222, 0.0405
Fig. 1. Crystal structure of complex 4a from crystallization of the product obtained
from mixing of complex 1a and BiI3.

S.M. Nabavizadeh et al. / Polyhedron 77 (2014) 24–31
27
Fig. 2. (A) 1H NMR and (B) 31P NMR spectra of complex 3b in CDCl3. Assignments are shown.
contained almost exclusively the complexes 2b–4b. Very small
traces of the complexes [PtX(ppy)PPh3], resulting from Me-X
reductive elimination, were in some cases observed. The
synthesized cyclometalated Pt(IV) complexes were fully character-
ized using 1H and 31P NMR spectroscopy and complex 3b was
further identified by X-ray crystallography (see Experimental Sec-
tion). Typically, in the 1H NMR spectrum of [PtMe(Br)2(ppy)PPh3],
3b, (see Fig. 2A), a doublet at d = 2.31 (with 3J(PH) = 3.3 Hz and
2J(PtH) = 65.8 Hz) assigned to the Me ligand trans to N. The
hydrogen related to the CHAr group adjacent to ligating N and C
atoms of the ppy ligand appeared as doublets at d = 9.48 (with
each other). But in the reaction of complex 1a with BiX3, no isom-
erization is occurred and only isomer from trans addition (i.e. X
groups trans to each other) was observed. This indicates that the
thermodynamic isomers 2b-4b are more stable than the related
kinetic isomers 2b0–4b0 (see Fig. 4). According to our calculations
(see Fig. 4), for the [PtMe(X)2(ppy)PPh3] complexes the cis addition
isomers (i.e. 2b–4b) are predicted to be more stable than the trans
addition isomers (i.e. 2b0–4b0); for example where X = Cl, the com-
plex 2b is 9.9 kcal molꢀ1 more stable than the complex 2b0 in ace-
tone solvent. This interpretation suggested that formation of the
thermodynamic isomer 2b was favoured over the kinetic isomer
2b0 since in isomer 2b the more sterically demanding PPh3 ligand
is situated in the ‘‘axial’’ positions as compared with isomer 2b0
in which it is located in the ‘‘equatorial’’ position. Besides, in con-
trast to the situation in 2b0 in which the two Cl ligands with low
trans influence are located trans to each other, in the thermody-
namic isomer 2b, these ligands are situated trans to the two ligands
PPh3 and C ligating atom of the ppy ligand each having a compar-
atively high trans influence.
4J(HP) = 5.8 Hz
and
3J(PtH) = 11.3 Hz)
and
6.64
(with
4J(HP) = 7.5 Hz and 3J(PtH) = 36.5 Hz), respectively. In the 31P
NMR spectrum of the Pt(IV) complex 3b (see Fig. 2B), a singlet
signal at d = ꢀ5.7 appeared with a 1J(PtP) value of 2757 Hz.
Although the data would well establish the relative disposition of
the different ligands on the Pt center of complex 3b as indicated
in Fig. 2 (with chirality at Pt center), the formation of a 1:1 mixture
of two enantiomers that are not distinguishable by NMR spectros-
copy is possible.
Note that in the reaction of complex 1a with BiX3, no isomeriza-
tion is occurred and only isomer from trans addition was observed.
Complex 3b was also characterized by single-crystal X-ray dif-
fraction analysis as illustrated in Fig. 3. It confirms the character-
ization of 3b as an octahedral platinum(IV) complex formed by
oxidative addition of BiBr3 to complex 1b. The coordination geom-
etry around platinum centre contains the Me group, the nitrogen
atom and the ortho C of the ppy ligand, two bromides and P atom
of PPh3. The bond distances between platinum and carbon atoms
are 2.048(3) and 2.1047(10) Å for Pt(1)–C(7) (trans to Br) and
Pt(1)–C(12) (trans to N), respectively. These values are consistent
with trans influence of Br and N. The bromide atoms are located
trans to the C atom of the ppy and PPh3 ligands with the bond dis-
tances of Pt(1)–Br(1) = 2.5853(3) and Pt(1)–Br(2) = 2.5244(3) Å,
respectively, which is consistent with higher trans influence of C
atom compared to P atom. The two bromide atoms are cis disposed
to one another (Br(2)–Pt(1)–Br(1) 87.268(10)), indicating that the
angles around the Pt centre are rather close to the ideal angle of
90°. The aromatic N atom is coordinated to platinum centre, which
is in accord to the usual preference of the ppy ligand to form cyclo-
metalated complexes, and is positioned trans to Me group.
Fig. 3. (a) The molecular structure of complex [PtMe(Br)2(ppy)PPh3], 3b. Selected
bond distances (Å) and angles (°): Pt(1)–C(7) 2.048(3); Pt(1)–C(12) 2.1047(10);
Pt(1)–N(1) 2.140(2); Pt(1)–P(1) 2.3070(7); Pt(1)–Br(2) 2.5244(3); Pt(1)–Br(1)
2.5853(3); C(7)–Pt(1)–C(12) 93.58(13); C(7)–Pt(1)–N(1) 80.02(10); C(12)–Pt(1)–
N(1) 173.53(12); C(7)–Pt(1)–P(1) 92.62(8); C(12)–Pt(1)–P(1) 89.06(10); N(1)–
Pt(1)–P(1) 92.18(6); C(7)–Pt(1)–Br(2) 85.04(7); C(12)–Pt(1)–Br(2) 89.89(10);
N(1)–Pt(1)–Br(2) 88.59(6); P(1)–Pt(1)–Br(2) 177.373(18); C(7)–Pt(1)–Br(1)
170.47(8); C(12)–Pt(1)–Br(1) 92.02(10); N(1)–Pt(1)–Br(1) 94.19(6); P(1)–Pt(1)–
Br(1) 95.177(19); Br(2)–Pt(1)–Br(1) 87.268(10).
3.2. Stereochemistry of Pt(IV) complexes based on DFT calculated
energies
The Pt(IV) products of the reaction of complex 1b with BiX3 con-
tained only the thermodynamic 2b–4b isomers (X groups cis to

28
S.M. Nabavizadeh et al. / Polyhedron 77 (2014) 24–31
Fig. 4. Possible isomers of complexes [PtMe(X)2(ppy)PPh3] and their relative energies in acetone.
Our DFT calculations showed that alternative isomers, (2a0 and 2a00
Me
Pt
Me
Pt
Cl
Pt
in Fig. 5) were ruled out, because the energies for the isomers 2a0
(both methyls in a trans arrangement) and 2a00 were 140 and
119 kcal/mol higher than that for 2a, respectively.
N
N
Cl
N
N
Cl
Cl
N
N
Me
Me
Me
The oxidative addition of Ph2ECl2 (E = Te or Se) to complex 1a
was reported in 2003 (see Scheme 2) [43]. It has been suggested
that the nucleophilic Pt(II) center of complex 1a could attack
Ph2ECl2 at either E (E = Te) or at Cl (E = Se) to give [PtClMe2(TePh2
Cl)(tBu2bpy)] or [PtCl2Me2(tBu2bpy)], respectively. Very recently
[44] we reported the reaction of [PtMe2(dppm)], dppm = 1,1-bis
(diphenylphosphino)methane, with BiCl3 and suggested to give a
Pt(IV)–Bi(III) complex, [PtCl(BiCl2)Me2(dppm)], followed by
Cl
Me
Cl
2a
0
2a'
2a''
+119
+140
Fig. 5. Possible isomers of complex [Pt(Cl)2Me2(bpy)] and their relative energies in
kcal molꢀ1 in acetone.
X
Bi
X
N
N
Me
Me
Pt
X
Ph2
Cl
Te
Cl
P
N
N
Me
Me
Me
Me
Cl
Se
Ph
Ph
Ph
Ph
H2C
Pt
Stronger base
towards BiX3
Pt
P
Stronger acid
Ph2
towards Pt(II)
Cl
- Ph2Se
- BiX
+
+
+
+
Cl
TeClPh2
BiX2
Me
X
Me
Me
N
Me
Me
Me
Pt
N
N
N
N
P
Pt
Pt
Pt
N
Me
P
Me
Cl
X
Cl
X
X
TeClPh2
BiX2
Me
Pt
Cl
N
N
Me
Me
Me
Me
N
N
Me
Pt
N
P
Pt
X
Pt
Cl
Me
N
P
Me
Cl
X
Scheme 2. The oxidative addition of Pt(II) complexes (1a and [PtMe2(dppm)]) with Ph2ECl2 (E = Te or Se) and BiX3 (X = Cl, Br or I).

S.M. Nabavizadeh et al. / Polyhedron 77 (2014) 24–31
29
Fig. 6. DFT optimized structures of the cyclometalated platinum(IV) complexes, 2b–4b. H atoms are omitted for clarity of presentation.
reductive elimination of Cl2Bi–Me giving [PtMeCl(dppm)]. It seems
that reactions of complex 1a with BiCl3 and Ph2SeCl2 proceed via a
same mechanism in which Pt center attacks at Cl atom of BiCl3 or
Ph2SeCl2 to give dichloroplatinum(IV) complex. However, the
products of the reactions of complex 1a and [PtMe2(dppm)] with
BiCl3 or Ph2TeCl2, respectively, are different and as suggested for
Ph2TeCl2 [43], the mechanism contains Pt(II) attack to metal center
of BiCl3 or Ph2TeCl2 to form Pt–Bi or Pt–Te bonds. We suggest in the
reaction of complex 1a with Ph2ECl2 (E = Te or Se), the electron rich
Pt(II) center attacks at Te center of Ph2TeCl2, compared with Cl
atom in Ph2SeCl2, because Te center has more Lewis acidity than
Se center. The same behavior is suggested for the reactions of BiCl3
with complexes 1a and [PtMe2(dppm)]. According to DFT calcula-
tion, Pt charge in complex [PtMe2(dppm)] is negative (dPt = ꢀ0.43)
compared with positive charge on Pt atom of 1a (dPt = +0.17).
Therefore the dppm complex is weaker Lewis base than complex
1a and should attack at Cl atom of BiCl3, instead of Bi center, giving
dichloroplatinum(IV) complex 2a.
Table 2
Selected calculated bond distances (Å) and angles (°) for complexes 2b–4b compared
to the experimental data of complex 3b.
Bond distance (Å)
and angle (°)
2b
3b
3b (exp.)
4b
Pt–C(Me)
Pt–C(ppy)
Pt–N
Pt–P
Pt–X(trans to C)
Pt–X(trans to P)
C(Me)–Pt–C(ppy)
C(Me)–Pt–N
2.083
2.032
2.208
2.399
2.539
2.465
2.087
2.039
2.219
2.416
2.709
2.620
2.1047(10)
2.048(3)
2.140(2)
2.092
2.046
2.228
2.446
2.915
2.794
2.3070(7)
2.5853(3)
2.5244(3)
93.58(13)
173.53(12)
89.06(10)
92.02(10)
89.89(10)
80.02(10)
92.62(8)
170.47(8)
85.04(7)
92.18(6)
94.19(6)
88.59(6)
95.1
94.4
93.7
172.1
91.1
92.1
87.7
79.5
95.9
171.5
86.0
95.1
92.9
86.3
177.8
89.7
172.0
90.9
92.3
88.0
79.3
90.9
171.3
85.7
94.5
93.5
86.6
178.4
89.1
171.6
91.1
92.1
88.3
79.1
94.6
171.9
85.7
93.8
94.7
86.8
179.3
88.8
C(Me)–Pt–P
C(Me)–Pt–X(trans to C)
C(Me)–Pt–X(trans to P)
C(ppy)–Pt–N
C(ppy)–Pt–P
C(ppy)–Pt–X(trans to C)
C(ppy)–Pt–X(trans to P)
N–Pt–P
N–Pt–X(trans to C)
N–Pt–X(trans to P)
P–Pt–X(trans to P)
X–Pt–X
3.3. DFT Investigation of cyclometalated Pt(IV) complexes
177.373(18)
87.268(10)
To analyze the structure of the newly synthesized cycloplatinat-
ed complexes, 2b–4b, DFT method was used. Complex 3b was
Fig. 7. Qualitative frontier molecular orbitals for complexes 2b–4b.

30
S.M. Nabavizadeh et al. / Polyhedron 77 (2014) 24–31
Table 3
Acknowledgments
Energies (eV) of the relevant frontier orbitals of platinum complexes.
Orbital
E (eV)
We thank the Iran National Science Foundation (Grant No.
90004861), the Shiraz University Research Council and the Islamic
Azad University, Shiraz Branch for financial support. We gratefully
acknowledge Professor Mehdi Rashidi for his valuable suggestions
and continuous support.
2b
3b
4b
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
ꢀ5.886
ꢀ1.904
ꢀ5.470
ꢀ2.052
ꢀ5.079
ꢀ2.201
Appendix A. Supplementary data
CCDC-961300 contains the supplementary crystallographic
data for complex 3b. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
structurally characterized by X-ray diffraction analysis and was
used as standard example to estimate the reliability of the DFT/
B3LYP level of calculations associated with the geometrical param-
eters. The structures of 2b–4b are schematically presented in Fig. 6.
Selected calculated bond lengths of optimized geometries of com-
plexes at B3LYP/6-31G(d) level (LANL2DZ potential for Pt, Cl, Br
and I) and the corresponding experimental crystallographic data
for complex 3b are given in Table 2. The computed structural
details are in reasonable agreement with the experimental param-
eters and error in some cases is due to comparison of the geomet-
rical parameters calculated in gas phase with those obtained
experimentally in solid state.
As can be seen from Table 2, typically for complex 2b, the
Pt–CH3 bond length (2.083 Å) is within the expected range for a
Pt(IV)–Me moiety. Bond lengths of the ppy ligand with Pt, i.e. Pt–
C trans to the Cl and Pt-N trans to Me, are 2.032 and 2.208 Å,
respectively. Also, as expected, the calculated Pt–P bond in 2b is
shorter (2.399 Å) than those in 3b and 4b (2.416 and 2.446 Å,
respectively), complying with the larger 1JPtP value for the complex
2b (2898 Hz) as compared with those of the complexes 3b
(2757 Hz) and 4b (2431 Hz). This is due to the greater trans influ-
ence of the iodide ligand as compared with bromide and chloride.
Qualitative representations of the highest occupied and lowest
unoccupied molecular orbitals in complexes 2b–4b are presented
in Fig. 7. The energies of the relevant frontier orbitals of complexes
2b–4b are also shown in Table 3. The HOMO–LUMO gap of 2b is
equal to 3.982 eV. The highest occupied MO of 2b is mainly p orbi-
tals of two chloride ligands with small contribution of ppy ligand
(see Fig. 7). The LUMO is localized on the d orbitals of Pt atom with
significant contribution of the orbitals of the PPh3 ligand. The value
of the energy separations between the HOMO and LUMO of 3b and
4b are smaller than that of 2b and equals to 3.418 and 2.878 eV,
respectively. The highest occupied molecular orbitals of 3b and
4b are essentially the orbitals of two halide ligands as expected
for a Pt(IV) complex (see Fig. 7). The LUMO of these cyclometalated
platinum(IV) complexes can be ascribed as combination of Pt atom,
PPh3 and halide ligands.
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