Synthesis and kinetic studies of new bipyridyl platinum(II) phenoxide complexes by phase transfer catalysis: Crystal structure of [(bipy)Pt(OC6H4-4-OMe)2]

Article abstract of DOI:10.1016/j.ica.2009.11.023

The synthesis of new platinum bipy (bipy = 2,2′-bipyridyl) complexes containing phenoxide ligands is reported, together with kinetic studies of their oxidative addition reactions with MeI to produce phenoxo platinum(IV) complexes. Complexes of the form [(bipy)Pt(OC₆H₄-4-X)₂] (X = OCH₃, CH₃, H, Br, Cl) are prepared by the reaction of the chloro complex [(bipy)PtCl₂] with substituted phenols and KOH in a two phase system of water and chloroform in the presence of benzyl triphenylphosphonium chloride. Platinum(IV) complexes are formed by oxidative addition of MeI to the platinum(II) complexes obtained. The complexes are characterized by elemental analysis, UV-Vis, IR, mass spectrometry and ¹H and ¹³C NMR spectroscopy. The reaction of methyl iodide with [(bipy)Pt(OC₆H₄-4-OMe)₂] to give [(bipy)PtMe(I)(OC₆H₄-4-OMe)₂] follows the rate law rate = k₂[(bipy)Pt(OC₆H₄-4-OMe)₂][MeI]. The values of k₂ increase with increasing polarity of the solvent, suggesting a polar transition state for the reaction.

Full text of DOI:10.1016/j.ica.2009.11.023

Inorganica Chimica Acta 363 (2010) 685–690
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Synthesis and kinetic studies of new bipyridyl platinum(II) phenoxide complexes by phase
transfer catalysis: Crystal structure of [(bipy)Pt(OC6H4-4-OMe)2]
b
b
Ja’afar K. Jawad a, , Harry Adams , Michael J. Morris
*
a Department of Chemistry, College of Science, Sultan Qaboos University, P.O. Box 36, Al-Khod 123, Muscat, Oman
b Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
a r t i c l e i n f o
a b s t r a c t
The synthesis of new platinum bipy (bipy = 2,20-bipyridyl) complexes containing phenoxide ligands is
reported, together with kinetic studies of their oxidative addition reactions with MeI to produce phenoxo
platinum(IV) complexes. Complexes of the form [(bipy)Pt(OC6H4-4-X)2] (X = OCH3, CH3, H, Br, Cl) are pre-
pared by the reaction of the chloro complex [(bipy)PtCl2] with substituted phenols and KOH in a two
phase system of water and chloroform in the presence of benzyl triphenylphosphonium chloride. Plati-
num(IV) complexes are formed by oxidative addition of MeI to the platinum(II) complexes obtained.
The complexes are characterized by elemental analysis, UV–Vis, IR, mass spectrometry and 1H and 13C
NMR spectroscopy.
Article history:
Received 7 October 2009
Received in revised form 12 November 2009
Accepted 13 November 2009
Available online 22 November 2009
Keywords:
Phase-transfer catalysis
Platinum
Phenoxo ligands
Oxidative-addition
N ligands
The reaction of methyl iodide with [(bipy)Pt(OC6H4-4-OMe)2] to give [(bipy)PtMe(I)(OC6H4-4-OMe)2]
follows the rate law rate = k2[(bipy)Pt(OC6H4-4-OMe)2][MeI]. The values of k2 increase with increasing
polarity of the solvent, suggesting a polar transition state for the reaction.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
[7], but more recent works [8,9], including this paper, address
the disparity [10].
An earlier belief that the metal-to-oxygen bond is weak, as a re-
sult of the occurrence of antibonding -interactions between filled
Platinum(II) complexes with phenoxide ligands have been syn-
thesized by many different methods. The phenoxo complexes
[M(OPh)2(PPh3)2] (M = Pd, Pt) have reportedly been prepared by
reaction of [M(PPh3)4] with phenol [11], and monophenoxo com-
plexes of palladium [12,13] and platinum [13,14] have also been
prepared. The preparation of [Pt(OMe)2(dppe)] has been reported
[15], as well as the complex [Pt(OPh)2(dppe)] which exhibits quite
different reactivity [16]. The complexes of the type [M(EPh)2(dppe)]
(M = Pt, Pd; E = O, S, Se) have been prepared previously [16]. The
reaction of [PtMe2(bipy)] with phenol affords the complex
p
metal d-orbitals and oxygen lone pairs [1], may have limited re-
search in this area and reports concerning late transition metal alk-
oxides and aryloxides are still rare, in particular when the other
ligands are mono- or bidentate tertiary amines. It is now recog-
nized, however, that the metal to-oxygen bond may be of compa-
rable strength or even stronger than the metal-to-carbon (sp3)
bond [2].
There has been a steady development of interest in phenoxide
and aryloxide transition metal complexes because of their impor-
tance in many areas of science, and this area still attracts much
attention. The reason for this continuing interest is that such com-
plexes have been postulated as key intermediates in various tran-
sition metal-catalysed processes [3]. In biology, for example,
metal–phenoxide linkages are formed between a metal and the
phenolic side chain of tyrosine. Metal sequestration units often
have multiple phenoxide donor atoms for chelation such as ente-
robactin [4].
[Pt(Me)(OPh)(bipy)] [17].
A series of complexes of formula
[M(OR)(terpy)]BF4 (M = Pd, Pt; terpy = 2,20:60,200-terpyridine) have
been prepared by reaction of [M(OH)(terpy)]BF4 with ROH [18]. Re-
cently, some late transition metal fluoroaryloxide complexes have
been reported including the platinum complex [(cod)Pt(OC6F5)2]
which was prepared by reaction of [(cod)PtCl2] with KOC6F5 in
THF [9].
As the chemical industry strives to increase efficiency, improve
process safety, and reduce environmental impact, phase transfer
catalysis (PTC) has become recognized as a useful tool for achieving
these goals [19]. Phase transfer catalysis is useful primarily for per-
forming reactions between anions (and certain neutral molecules
and transition metal complexes) and organic substrates. PTC is
needed because many anions (in the form of their salts) and neu-
tral compounds are soluble in water but not in organic solvents,
Metal centres also bind to phenoxide ligands during oxidation
of phenols to ketones as in catecholase [5,6]. Late metal aryloxides
had been less well studied than early transition metal derivatives
* Corresponding author. Tel.: +968 9980 0298; fax: +968 2414 1469.
E-mail address: jawadjk@squ.edu.om (J.K. Jawad).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.11.023

686
J.K. Jawad et al. / Inorganica Chimica Acta 363 (2010) 685–690
whereas the organic reactants are not usually soluble in water. The
catalyst acts as a shuttling agent by extracting the anion or neutral
compound from the aqueous (or solid) phase into the organic reac-
tion phase (or interfacial region) where the anion or neutral com-
pound can freely react with the organic reactant already located in
the organic phase. Reactivity is further enhanced, sometimes by or-
ders of magnitude, because once the anion or neutral compound is
in the organic phase, it has very little (if any) hydration or solvation
associated with it, thereby greatly reducing the energy of activa-
tion [20]. It has been shown [21] that there are several advantages
in using PTC such as an increased reaction rate, a lower reaction
temperature, avoiding the need for expensive anhydrous or aprotic
solvents, and the use of water together with an organic solvent as
reaction medium.
[38] provided the platinum atom acts as a nucleophilic centre dur-
ing the oxidative addition. Jawad et al. [39] also reported solvent
effects on the rate of oxidative addition of MeI to di(4-thiocreso-
late)(2,20-bipyridyl)platinum(II) and they concluded that the most
likely mechanism of reaction of [(bipy)Pt(SC6H4-4-Me)2] with the
methyl iodide involves nucleophilic attack by platinum on the car-
bon atom of MeI to give an intermediate which rapidly rearranges
to the final product.
In this work, we demonstrate an alternative approach, namely
by using phase transfer catalysis (PTC) as a new method to obtain
our new complexes, and we have concentrated on compounds con-
taining the bipy ligand. One reason for this is that aryloxo com-
plexes of this type (containing the bipy ligand) have not, to our
knowledge, previously been reported.
Inorganic polymers incorporating phosphorus, nitrogen and sul-
fur as well as silicon and oxygen, are being designed to provide the
sophisticated materials of the future [22]. Platinum-containing
polymers [23,24] have been prepared by the interfacial polymeriza-
tion of diamines with potassium tetrachloroplatinate(II) in the
absence of a catalyst. We have synthesized [25] some new
platinum-containing polymers by phase transfer polymerization
between various bisphenolate anions and cis-dichlorobis(dimethyl-
phenylphosphine)platinum(II) in a two phase system of water and
chloroform in the presence of dibenzo-24-crown-8. Recently, inter-
facial polycondensation of bisphenols with alkyl(aryl) phosphonic
dichlorides using PTC has been shown to be the most important
method [26,27] which generates polyphosphonates and polyphos-
phates, and yields linear, solid and high molecular weight polymers
[28]. We have previously reported the synthesis of platinum phos-
2. Results and discussion
In this work bipyridyl platinum(II) phenoxides have been syn-
thesized in two different ways for comparison. Firstly the reaction
of the chloro complex [(bipy)PtCl2] with substituted phenols and
KOH in dichloromethane provides precipitates of red solid com-
plexes that, when washed with Et2O, afford the new platinum(II)
phenoxide complexes in good yield. The new compounds were
characterized in the usual ways.
The same series of the bipyridyl platinum(II) phenoxides have
also been prepared by the reaction of the chloro complex with
substituted phenols and KOH in a two phase system of water
and chloroform in the presence of benzyl triphenylphosphonium
chloride following the general reaction scheme:
phine complexes containing N-(substituted aryl or benzyl)-
c-mer-
captobutyramides using phase transfer catalysis. Complexes of the
form [Pt(PMe2Ph)2{S(CH2)3CONHC6H4-4-X}2], where X = OCH3,
CH3, Cl or benzyl, have been synthesized by the reaction of cis-
dichlorobis(dimethylphenylphosphine)platinum(II) with the corre-
½PtCl2ðbipyÞꢀ þ 2KOH þ 2ð4-X-C6H4OHÞ
Â
Ã
BTPPC
ðbipyÞPtðOC6H4-4-XÞ2 þ 2KCl þ 2H2O
ƒƒƒƒƒƒƒƒ!
CHCl3=H2O; 30ꢁ
C
sponding N-(substituted aryl or benzyl)-c-mercaptobutyramide in
where X = OCH3, CH3, H, Br, Cl; BTPPC = benzyl triphenylphospho-
nium chloride.
a two phase system of water and chloroform in the presence of ben-
zyl triphenylphosphonium chloride [29].
We have found that using phase transfer catalyst (PTC) in-
creased both the reaction rate and the percentage yield, and also
allowed a decrease in the required reaction temperature. Thus,
treatment of yellow recrystallized dichloro(2,20-bipyridyl)plati-
num(II) in chloroform with phenoxides in deionized distilled water
containing potassium hydroxide (N.B. precautions should be taken
with reactions containing chloroform and a base) and benzyl tri-
phenylphosphonium chloride as a PTC agent under an inert atmo-
sphere at 30 °C gave the red phenoxide complexes which are stable
in air and were characterized by elemental analyses, IR, UV–Vis,
and NMR spectra.
The elemental analyses of the new complexes were generally in
good agreement with theoretical values. Table 1 shows the physi-
cal properties of the [(bipy)Pt(OC6H4-4-X)2] complexes, and Table
2 shows the physical properties of the corresponding Pt(IV) com-
plexes [(bipy)PtMe(I)(OC6H4-4-X)2].
The UV–Vis spectra were used mainly to characterize the diphe-
noxo(2,20-bipyridyl)platinum(II) complexes by comparison with
similar samples prepared earlier [30]. As noted earlier, the energies
of the two intense MLCT bands in the UV–Vis spectra of (2,20-bipyr-
idyl)platinum(II) complexes are strongly dependent on the nature
of the ligands bound to platinum and on the solvent. In the diphe-
noxo(2,20-bipyridyl)platinum(II) complexes studied here, the
energy of the MLCT bands was very sensitive to the nature of the
phenoxo group bound to platinum. The lowest energy MLCT band
for the [(bipy)Pt(OC6H4-4-X)2] complexes was observed as follows:
X = OCH3 (525 nm), CH3 (500 nm), H (475 nm), Br (462 nm), Cl
(457 nm). The same band of these complexes (e.g.: X = OCH3) in
acetonitrile solution was at 502 nm and in acetone the band moved
to 516 nm while in dichloromethane it was at 522 nm and in
It has been shown [30] that the UV–Vis spectra of bipyridyl
platinum(II) complexes contain two intense metal to ligand charge
transfer (MLCT) bands, whose energies are strongly dependent on
the nature of the other ligands bound to platinum and also on
the solvent. More electronegative substituents on platinum and
more polar solvents cause the bands to move to higher energy.
The reactivity of alkyl and aryl (2,20-bipyridyl) platinum(II)
complexes towards oxidative addition reactions can be correlated
with the energy of the lowest energy MLCT band [31], suggesting
that it is the energy of the platinum d-orbitals that primarily deter-
mines the reactivity [30,32–34], since in such reactions the metal
centre acts as a nucleophile [35]. We are examining this effect by
studying the oxidative addition of methyl iodide to the complexes
[(bipy)Pt(OC6H4-4-X)2] as a function of the substituent X. Steric ef-
fects due to X should be negligible in these compounds, and it has
already been shown [29] that the energy of the first MLCT band
(and hence the energy of the platinum d-orbitals) correlates well
with Hammett r-values of X.
The ability of the aryl platinum(II) complexes to undergo oxida-
tive addition at all is remarkable since similar complexes stabilized
by tertiary phosphine ligands do not give stable aryl platinum(IV)
complexes [36]. This is probably due to the greater
r-donor and
poorer -acceptor power of bipy compared to tertiary phosphines
p
and to its lower steric requirements. The oxidative addition reac-
tions of methyl iodide to platinum(II) 2,20-bipyridyl and 1,10-phe-
nanthroline complexes has been reported [37]. Solvent effects on
the rate of oxidative addition of methyl iodide to [PtPh2(bipy)]
have been studied [33] and a polar transition state has been sug-
gested for the reaction such as predicted for the SN2 mechanism

J.K. Jawad et al. / Inorganica Chimica Acta 363 (2010) 685–690
687
Table 1
Physical properties of [(bipy)Pt(OC6H4-4-X)2].
Group X
Melting point (°C)
Yield (%)
Colour
CHN
C
% Calc.
H
(Found)
N
H
252–255d
246–248d
236–238d
245–247d
250–252d
78
89
80
82
90
red
red
red
red
red
49.16
(49.18)
43.58
(43.57)
38.00
(38.10)
50.97
(51.07)
48.24
3.38
(3.32)
2.66
(2.67)
2.32
(2.36)
3.92
(3.89)
3.71
5.21
(5.12)
4.62
(4.67)
4.03
(3.96)
4.95
Cl
Br
CH3
OCH3
(5.10)
4.69
(48.09)
(3.69)
(4.65)
d = decomposed.
Table 2
Physical properties of Pt(IV) complexes [(bipy)PtMe(I)(OC6H4-4-X)2].
Group X
Melting point (°C)
Yield (%)
Colour
CHN
C
% Calc.
H
(Found)
N
H
242–244d
236–238d
230–232d
238–240d
240–242d
73
80
81
84
89
yellow
yellow
yellow
yellow
yellow
40.66
(40.76)
36.92
(36.84)
33.00
(32.95)
42.44
(42.22)
40.61
3.12
(3.10)
2.56
(2.54)
2.29
(2.18)
3.56
(3.50)
3.41
4.12
(4.09)
3.74
(3.76)
3.35
(3.10)
3.96
(3.94)
3.79
Cl
Br
CH3
OCH3
(40.58)
(3.36)
(3.72)
characteristic frequencies in the IR spectra of [(bipy)Pt(OC6H4-4-
X)2] which compared with related complexes [40,41].
Table 3
IR spectra of [(bipy)Pt(OC6H4-4-X)2].
Chemical shifts in the 1H NMR spectra of the starting materials
and complexes are tabulated in Table 4, with the corresponding 13C
NMR data given in Table 5. Because of some experimental prob-
lems due to solubility we report the spectral data of the starting
materials and one of the products. Fig. 1 shows the structural for-
mula of the complex [(bipy)Pt(OC6H4-4-OMe)2] with the carbon
atoms numbered to clarify the chemical shifts in Tables 4 and 5.
Intense red crystals of [(bipy)Pt(OC6H4-4-OMe)2] suitable for
single crystal X-ray structure determination were grown from
CH2Cl2/Et2O/n-pentane. The molecular structure of the complex
in the crystal is shown in Fig. 2; a summary of the crystallographic
details of the X-ray analysis of is given in Table 6. Selected bond
distances and angles for [(bipy)Pt(OC6H4-4-OMe)2] are compiled
in Table 7. Comparison with related structures such as [(bipy)Pt-
Me(OPh)] [17], [(cod)Pt(OC6F5)2] [9], trans-[Pt(H)(OPh)(PEt3)2]
[14] and trans-[Pt(H)(OPh)(PBz3)2] [13] reveals similar gross fea-
tures e.g. the Pt–O distances of 2.018(3) and 2.019(3) Å in the cur-
rent molecule compared with a range of 2.014–2.130 Å in the
quoted complexes, and the somewhat enlarged Pt–O–C angles of
119.6(2) and 123.0(3)° in the aryloxide ligands.
In addition to the platinum complex, and because the sample
that the crystals were grown from came from the PTC reaction
(i.e., not analytically pure complex) the unit cell contains a water
molecule, and a molecule of 4-methoxyphenol, the phenolic –OH
of which is hydrogen bonded to a second water molecule. This
phenol molecule, which was also identified by mass spectroscopy
(m/z 124), is situated on a crystallographic inversion centre and
is twofold disordered.
Orange solutions of the [(bipy)Pt(OC6H4-4-X)2] complexes in
common organic solvents turned yellow on addition of methyl
iodide and yellow crystals of [(bipy)PtMe(I)(OC6H4-4-X)2] could
be isolated. Once formed, the product was very sparingly soluble
in common organic solvents, but a satisfactory NMR spectrum
Compound
H
Wavenumber (cmꢂ1
)
Intensity
Assignment
810a
1020
814a
1010
814a
1020
760a
1030
752a
1032
m
m
s
m
s
m
s
m
s
Pt–O
C–O
Pt–O
C–O
Pt–O
C–O
Pt–O
C–O
Pt–O
C–O
Cl
Br
CH3
OCH3
s
Where: m = medium, s = strong.
a
peak is split into two.
chloroform at 530 nm. We have thus again confirmed that more
electronegative substituents on platinum and more polar solvents
cause the bands to move to higher energy.
By comparing the IR spectra of diphenoxoplatinum(II) com-
plexes with the starting materials one notices the disappearance
of the weak band at 3640–3600 cmꢂ1, which was attributed to
the OH stretching peak of the free ligand and the two bands at
300–340 cmꢂ1, which were attributed to the Pt–Cl stretch of the
complex [PtCl2(bipy)]. At the same time a new strong band at
752–814 cmꢂ1 appeared, which is attributed to the Pt–O bond
stretch. This confirms the formation of a new square planar com-
plex with, of necessity, a cis-geometry enforced by the bipy ligand.
This is confirmed by the formation of one band (split in two) for the
Pt–O stretch as well as one medium band at 680–714 cmꢂ1 belong-
ing to the Pt–N bond. A strong band at 1010–1032 cmꢂ1 is also evi-
dent in the spectra of the ligand and the new complex, and is
attributed to the C–O vibration, whereas there is no such band in
the spectrum of [PtCl2(bipy)]. Table 3 shows assignments of some

688
J.K. Jawad et al. / Inorganica Chimica Acta 363 (2010) 685–690
Table 4
Assignment of the characteristic chemical shifts in 1H NMR spectra.
Compound
Chemical shifts of aromatic protons, d (ppm)
Chemical shifts of non-aromatic protons, d (ppm)
[(bipy)PtCl2] in DMSO-d6
8.61 (d, H(3), J = 8.0 Hz), 8.41 (t, H(4), J = 7.8 Hz), 7.89
(t, H(5), J = 6.8 Hz), 9.54 (d, H(6), J = 5.6 Hz)
6.77 (d, 2H), 6.76 (d, 2H)
9.30 (d, 2H, C6), 8.20 (t, 2H, C9), 7.57 (t, 2H, C8), 7.12
(t, 2H, C7), 6.62 (t, 2H, C1), 6.60 (t, 2H, C2)
4-Methoxyphenol in CDCl3 solution
Complexes in CDCl3 solution:
e.g., [(bipy)Pt(OC6H4-4-OMe)2]
3.75 (s, 3H, OCH3), 5.39 (s, 1H, OH)
3.73 (s, 3H, OCH3)
Table 5
Assignment of the characteristic chemical shifts in 13C NMR spectra.
Compound
Chemical shifts of aromatic carbons, d (ppm)
Chemical shifts of non-aromatic
carbons, d (ppm)
[(bipy)PtCl2] in CDCl3 solution
4-Methoxyphenol (CDCl3 solution)
Complexes in CDCl3 solution: e.g.,
[(bipy)Pt(OC6H4-4-OMe)2]
157.66, 149.25, 141.42, 128.57, 125.02
154.07 (C–OH), 149.98 (C–OCH3), 116.54, 115.39
161.77 (C5, C10), 151.13 (C3), 150.10 (C6), 138.42 (C8), 122.42 (C9),
120.12 (C7), 115.21 (C1), 114.6 (C2)
56.30 (OCH3)
56.17 (C4)
Table 6
Experimental details for the single crystal structure of [(bipy)Pt(OC6H4-4-OMe)2]ꢃ
7
0.5HOC6H4-4-OMeꢃ1.5H2O.
8
9
6
1
2
Empirical formula
Formula weight
T (K)
C55H58N4O13Pt2
1373.23
150(2)
4
3
3
N
N
O
O
O
O
Wavelength (Å)
Crystal system
Space group
0.71073
monoclinic
P21/c
5
5
10
10
1
1
2
2
Pt
Unit cell dimensions
a (Å)
b (Å)
c (Å)
12.956(2)
16.309(3)
11.940(2)
9
8
4
a
(°)
90
b (°)
90.381(3)
90
2522.9(7)
2
1.808
5.610
1352
2
1
6
c
(°)
Volume (Å3)
7
Z
Density (calculated) (Mg/m3)
Absorption coefficient (mmꢂ1
F(0 0 0)
Fig. 1. The structure of the complex [(bipy)Pt(OC6H4-4-OMe)2] with numbered
carbon atoms.
)
Crystal size (mm3)
0.23 ꢄ 0.21 ꢄ 0.21
h Range for data collection (°)
1.57–25.00
Index ranges
ꢂ15 6 h 6 15, ꢂ19 6 k 6 19,
ꢂ14 6 l 6 14
Reflections collected
23 993
Independent reflections
Completeness to h = 25.00°
Absorption correction
Maximum and minimum
transmission
4445 [Rint = 0.0491]
100.0%
semi-empirical from equivalents
0.3854 and 0.3586
Refinement method
full-matrix least-squares on F2
4445/184/338
0.997
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
Largest difference in peak and hole
r
(I)]
R1 = 0.0255, wR2 = 0.0543
R1 = 0.0368, wR2 = 0.0573
0.789 and ꢂ0.725 (e Åꢂ3
)
was obtained by adding one drop of methyl iodide to a suspension
of [(bipy)Pt(OC6H4-4-X)2] in chloroform in an NMR tube and
recording the spectrum before the product began to crystallize
from the resulting solution.
In the case of X = OMe, the methyl of the 4-methoxy phenol was
a singlet at 3.9 ppm and the methyl platinum resonance appeared
as a singlet at 2.1 ppm with satellites due to the coupling to 195Pt
with 2J(PtH) = 68 Hz. The magnitude of the coupling constant in
such complexes is usually sufficient to determine the stereochem-
istry [42], but because the trans-influence of 2,20-bipyridyl and
iodide are very similar, either stereochemistry I or II is possible.
Fig. 2. ORTEP diagram of [(bipy)Pt(OC6H4-4-OMe)2] in the crystal.

J.K. Jawad et al. / Inorganica Chimica Acta 363 (2010) 685–690
689
Table 7
Thus the reactions are first order in both platinum complex and
methyl iodide. The resulting second order rate constants are given
in Table 8, which also includes the second order rate constants for
oxidative addition of methyl iodide to [(bipy)PtPh2] [33] and [(bi-
py)Pt(SC6H4-4-Me)2] [39] in various solvents together with the
polarity parameter ET [43] for each solvent. This may confirm that
there is a simple correlation and simple kinetics between the oxi-
dative addition and these different metal bonds.
In each case there is an increase in rate by a factor of about 10–15
between the least polar and most polar solvents, suggesting a com-
mon mechanism with a polar transition state. Activation energies
and entropies of activation have been measured, and it was found
that the entropy of activation has a large negative value typical of
oxidative addition reactions of methyl iodide [44,45]. The mecha-
nism of the reaction of diaryl(2,20-bipyridyl)platinum(II) complexes
with methyl iodide has already been shown [33,34] to involve
nucleophilic attack by platinum on the carbon atom of MeI to give
[PtMePh2(bipy)]+Iꢂ, which rapidly rearranges to [PtIMePh2(bipy)].
Thus by analogy, the most likely mechanism of reaction of [(bipy)P-
t(OC6H4-4-X)2] with methyl iodide involves nucleophilic attack by
platinum on the carbon atom of MeI to give a similar intermediate,
which rapidly rearranges to the final product.
Selected bond lengths [Å] and angles [°] for [(bipy)Pt(OC6H4-4-OMe)2].
Pt(1)–N(1)
Pt(1)–N(2)
Pt(1)–O(1)
Pt(1)–O(2)
O(1)–C(11)
O(2)–C(18)
O(3)–C(14)
O(3)–C(17)
O(4)–C(21)
O(4)–C(24)
1.994(3)
2.000(3)
2.019(3)
2.018(3)
1.347(5)
1.353(5)
1.379(5)
1.421(6)
1.383(5)
1.413(6)
N(1)–Pt(1)–N(2)
N(1)–Pt(1)–O(1)
N(2)–Pt(1)–O(1)
N(1)–Pt(1)–O(2)
N(2)–Pt(1)–O(2)
O(1)–Pt(1)–O(2)
C(11)–O(1)–Pt(1)
C(18)–O(2)–Pt(1)
80.96(14)
173.48(12)
93.23(13)
94.00(13)
174.95(12)
91.82(12)
123.0(3)
119.6(2)
Table 8
Solvent effects on the second order rate constants for reactions with methyl iodide.
Solvent
ET
(bipy)Pt(SC6H4- (bipy)Pt(OC6H4- (bipy)PtPh2
4-Me)2
4-OMe)2
3. Experimental
k2 (30 °C)
k2 (30 °C)
k2 (40 °C)
(l molꢂ1 minꢂ1
)
(l molꢂ1 minꢂ1
)
(l molꢂ1 minꢂ1
)
3.1. General information
Benzene
Ethyl acetate
Chloroform
Dichloromethane 41.1 0.71
Acetone
34.5
38.1
39.1 0.14
6.5
11.3
0.68
2.08
4.12
8.36
Unless otherwise stated, all of the starting materials were ob-
tained at the highest levels of purity possible from commercial
sources and used as received. All reactions were performed in an
atmosphere of nitrogen. The complex [PtCl2(bipy)] was prepared
according to a literature procedure [30]. Its 1H NMR spectrum
was checked with a recent Ref. [46].
21
40.5
89
42.2 0.88
46.0 1.40
46.3
Acetonitrile
Nitromethane
Mass spectra were recorded on a Quattro Ultima Pt Mass Spec-
trometer (Waters Corp, Milford, USA). Infrared spectra of the com-
plexes were obtained utilizing CsI window (200–4000 cmꢂ1) using
a Perkin Elmer 1300 IR spectrophotometer. Electronic absorption
spectra were measured using an HP8453 UV–Visible spectropho-
tometer in the range 200–1100 nm. Microanalyses were performed
by the Centre National de la Recherche Scientifique, Service Central
D’Analyse, Vernaison, France, or were obtained from the Chemistry
Department, University College London, UK. The 1H and 13C NMR
spectra were recorded on a Bruker 400 MHz NMR spectrometer.
TMS was used as standard.
The stereochemistry of oxidative addition of methyl iodide to
cis-[PtMe2(PMe2Ph)2] has previously been shown to be trans by
deuterium labelling studies [38]. The NMR spectrum indicates that
the complex has structure I, corresponding to trans-oxidative addi-
tion. Thus for the 4-methoxy group of the 4-methoxy phenol only
one resonance was observed for the methyl protons. The only other
likely structure is II, formed by cis-oxidative addition, but this con-
tains non-equivalent aryl groups and so is not consistent with the
NMR spectrum.
OCH3
Single-crystal X-ray diffraction data collection and analyses
were performed on a Bruker SMART 1 K CCD area detector diffrac-
tometer equipped with Mo Ka radiation (k = 0.71073 Å). The crys-
=2,2'-bipyridyl
N
N
tallographic measurements were carried out at 150 K. Data
H3CO
processing was carried out using SHELX software [47].
O
Pt
I
Me
Pt
I
O
N
N
H3CO
H3CO
O
O
N
N
3.2. Synthesis of the [(bipy)Pt(OC6H4-4-X)2] complexes
Me
The Pt(II) complexes were all prepared in a manner similar to
the example given here.
(I)
(II)
3.2.1. Preparation of [(bipy)Pt(OC6H4-4-Cl)2]
Since the platinum(IV) product has no MLCT band in the UV–Vis
spectrum, the kinetics of the reaction could be followed conve-
niently by monitoring the decay of the MLCT band due to the plat-
inum(II) complexes by UV–Vis spectrophotometry.
Graphs of log(At ꢂ A1) versus time gave good straight lines,
indicating a first order dependence of the rate on the concentration
of the platinum(II) complexes, and the pseudo-first order rate con-
stants obtained were proportional to the concentration of methyl
iodide for a given solvent.
Recrystallized dichloro(2,20-bipyridyl)platinum(II) (0.422 g,
1.0 mmol) in chloroform (15 ml) was added to a magnetically stir-
red solution of 4-chlorophenol (0.256 g, 2.0 mmol) in deionized
distilled water (15 ml) containing potassium hydroxide (0.127 g,
2.2 mmol) and benzyl triphenylphosphonium chloride (0.039 g,
0.1 mmol) at 30 °C in a 100 ml flask, equipped with an N2 inlet,
water-cooled condenser and thermometer. After stirring for 1 h
under N2, the organic layer was separated and the aqueous layer
extracted (three times) with chloroform. The chloroform fractions

690
J.K. Jawad et al. / Inorganica Chimica Acta 363 (2010) 685–690
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were dried over anhydrous magnesium sulfate. The solution was
filtered and the chloroform evaporated under vacuum, to give a
red solid. Yield: 89%. MS m/z 606.4 [M+H]+.
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3.3. Synthesis of the [(bipy)PtMe(I)(OC6H4-4-X)2] complexes
The Pt(IV) complexes were all prepared in a manner similar to
the example given here.
3.3.1. Preparation of [(bipy)PtMe(I)(OC6H4-4-Cl)2]
To a suspension of [(bipy)Pt(OC6H4-4-Cl)2] (0.606 g, 1 mmol) in
dichloromethane (10 ml) was added an excess of methyl iodide.
After stirring the mixture for 10 min a yellow solution was
obtained. Diethyl ether was added dropwise until the solution be-
came cloudy and the mixture was set aside in the refrigerator,
when yellow crystals of the product crystallized. Yield 80%. MS
m/z: 748.3 [M+H]+.
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3.4. Kinetic studies
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Standard solutions of [Pt(OC6H4-4-OMe)2(bipy)] and MeI in the
required solvent were prepared. They were then mixed in the
required proportions, and the resulting solution transferred to a
1 cm quartz UV cell, which was held in the cell compartment of
the UV–Visible spectrophotometer. Spectra were then recorded
as the reaction proceeded. The concentration of platinum(II) com-
plex was about 10ꢂ4 M at the start of each reaction.
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Acknowledgment
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Financial support of this work was provided by Sultan Qaboos
University (Grant IG/SCI/CHEM/06/02).
Appendix A. Supplementary material
CCDC 696237 contains the supplementary crystallographic data
for [(bipy)Pt(OC6H4-4-OMe)2]. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2009.11.023.
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