Chelating imidazole ligands promote oxidative addition in dimethylplatinum(II) complexes

Article abstract of DOI:10.1016/j.jorganchem.2014.03.014

The oxidative addition chemistry of the complexes [PtMe₂{(mim) ₂CCH₂}], 1, and [PtMe₂{(mim)₂CHMe}], 2, where mim = N-methylimidazol-2-yl, is described. Complex 1 undergoes oxidative addition with alky

Full text of DOI:10.1016/j.jorganchem.2014.03.014

Accepted Manuscript
Chelating Imidazole Ligands Promote Oxidative Addition in Dimethylplatinum(II)
Complexes
Muhieddine Safa, Richard J. Puddephatt
PII:
S0022-328X(14)00136-3
10.1016/j.jorganchem.2014.03.014
JOM 18519
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 31 January 2014
Revised Date: 12 March 2014
Accepted Date: 15 March 2014
Please cite this article as: M. Safa, R.J. Puddephatt, Chelating Imidazole Ligands Promote Oxidative
Addition in Dimethylplatinum(II) Complexes, Journal of Organometallic Chemistry (2014), doi: 10.1016/
j.jorganchem.2014.03.014.
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ACCEPTED MANUSCRIPT
Me
N
N
Me
Me
N
N
H2C
Pt
Me
R-X
Me
Me
N
N
N
N
R
Me
N
N
N
N
Me
R
H2C
H2C
Pt
X
Pt
X
+
Me
Me
Me
Me

ACCEPTED MANUSCRIPT
Highlights
•
•
•
Dimethylplatinum(II) complexes of two bis(imidazolyl) ligands are prepared.
These complexes are highly reactive to oxidative addition.
The stereochemistry of the oxidative addition reaction is established.

ACCEPTED MANUSCRIPT
Chelating Imidazole Ligands Promote Oxidative Addition in
Dimethylplatinum(II) Complexes
Muhieddine Safaa,b and Richard J. Puddephatta,*
aDepartment of Chemistry, University of Western Ontario, London, Canada N6A 5B7.
bPetroleum Research Center, Kuwait Institute for Scientific Research, P.O. Box 24885,
Safat 13109, Kuwait
*Corresponding author. Fax: +519 661 3022. E-mail address: pudd@uwo.ca (R.J.
Puddephatt)
Keywords: Oxidative addition, platinum, imidazole, alkyl halide, iodine, hydrogen
peroxide.
ABSTRACT
The oxidative addition chemistry of the complexes [PtMe2{(mim)2C=CH2}], 1,
and [PtMe2{(mim)2CHMe}], 2, where mim = N-methylimidazol-2-yl, is described.
Complex 1 undergoes oxidative addition with alkyl halides RX to give
[PtXRMe2{(mim)2C=CH2}], X= I, R = Me; X = Br, R = CH2Ph, CH2C6H4-4-CF3,
CH2C6H4-2-CF3, CH2C6H3-3,5-t-Bu2; X = Cl, R = CH2Cl, and with hydrogen peroxide to
give [Pt(OH)2Me2{(mim)2C=CH2}]. Complex 2 undergoes oxidative addition with alkyl
halides RX to give [PtXRMe2{(mim)2CHMe}], X= I, R = Me; X = Br, R = CH2C6H4-4-
CF3, CH2C6H4-2-CF3, and with iodine and hydrogen peroxide to give
[PtX2Me2{(mim)2CHMe}], X = I or OH. The stereochemistry of the reaction has been
determined in each case, and several complexes have been structurally characterized.
The high reactivity of complexes 1 and 2 towards oxidative addition is rationalized in
terms of the strong donating property of the imidazolyl ligands, as supported by
theoretical (DFT) studies.
1.
Introduction
Dimethylplatinum(II) complexes of formula [PtMe2(NN)], where NN is a
chelating nitrogen donor ligand such as 2,2’-bipyridine, are among the most reactive
substrates for oxidative addition and their derivatives [PtMeX(NN)], in which X is a
weakly bound ligand, are important reagents in studies of carbon-hydrogen bond
activation [1,2]. In both reactions, there are significant differences in reactivity between
bis(pyridine) complexes in which there is a 5-membered chelate ring (A, Chart 1) or a 6-
membered chelate ring (B, C, D, Chart 1) [3-10]. The complexes [PtMe2(NN)], such as
A – C, react with alkyl halides, RX, to give platinum(IV) complexes [PtXMe2R(NN)] by
oxidative addition and these reactions have been used to prepare a wide range of
1

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functional organoplatinum(IV) complexes [1,9-17], as well as in fundamental studies of
reactivity and mechanism in oxidative addition reactions [1,18-23].
Chart 1. Dimethylplatinum(II) complexes.
Most of the above studies have used pyridine donors as components of the
bidentate ligands NN (Chart 1) and, in the present work, a comparison is made with the
bidentate ligands (mim)2C=CH2 and (mim)2CHMe, which contain N-methylimidazole
donors, in the dimethylplatinum(II) complexes 1 and 2 (Chart 1) [24]. These ligands
were originally reported to give the palladium(II) complexes [PdMeX(NN)], and
[PdMe2(NN)], and they, and similar ligands, have since been used in forming complexes
with several other transition metals [24-31]. Platinum complexes of these ligands have
not been reported, but several platinum(II) complexes with monodentate imidazole
derivatives are known and they have been shown to exhibit cytostatic activity [32-33].
2. Results and Discussion
The ligands were prepared according to the literature procedure [24], and the
dimethylplatinum(II) complexes were then prepared according to Scheme 1by reaction
with [Pt2Me4(µ-SMe2)2] [34]. The complexes were characterized by their spectroscopic
1
properties. For example, the yellow complex 1 gave, in the H NMR spectrum, a single
2
methylplatinum resonance at δ = 0.53, with coupling constant JPtH = 86 Hz, while the
imidazole protons appeared as two doublets at δ = 7.19, 3JHH = 1 Hz, 3JPtH = 13 Hz, and at
δ = 7.23, 3JHH = 1 Hz. Singlet resonances were observed for the NMe groups at δ = 3.91
and for the =CH2 protons at δ = 6.18. The chemical shifts are similar to those observed
for [PdMe2{(mim)2C=CH2}] [24]. The mass spectrum for complex 1 showed a peak at
m/z = 412 corresponding to [PtMe2{(mim)2C=CH2} - H]+.
2

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Scheme 1. Synthesis of platinum(II) complexes 1 and 2.
Some oxidative addition reactions of complex 1 with alkyl halides, which are
expected to occur by the polar, bimolecular SN2 mechanism [1,20,35,36], are shown in
Scheme 2.
Me
Me
N
N
N
N
Me
R
N
N
Me
N
N
Me
Me
H2C
Pt
Br
H2C
+
Pt
Br
Me
R
Me
4b, R = H
4a, R = H
5b, R = 4-CF3
6b, R = 2-CF3
5a, R = 4-CF3
6a, R = 2-CF3
BrCH2C6H4R
Me
Me
N
N
Me
N
N
Me
Me
Me
N
MeI
H2C
Me
Pt
I
H2C
Pt
Me
1
But
N
N
3
N
Me
BrCH2C6H3-tBu2
tBu
Me
Me
N
N
N
Me
tBu
tBu
N
N
Me
N
N
Me
Me
H2C
Pt
Br
+
H2C
Pt
Br
7a
N
Me
Me
7b
Scheme 2. Oxidative addition of alkyl halides to complex 1.
The simplest reaction with methyl iodide gave the complex
1
[PtIMe3{(mim)2C=CH2}], 3. The H NMR spectrum of complex 3 contained two
methylplatinum resonances in 1:2 ratio for the methyl groups trans to iodine and nitrogen
3

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atoms [35,36]. The structure of complex 3 was determined and is shown in Figure 1.
The complex has octahedral coordination geometry and has crystallographic Cs
symmetry, with the mirror plane containing the atoms Pt(1)C(8)I(1)C(5)C(6). The 6-
membered chelate ring adopts the boat conformation, with the vinylidene group oriented
towards the iodide side of the molecule.
Figure 1. The structure of complex 3. Selected bond parameters: Pt(1)-I(1) 2.804(1);
Pt(1)-N(1) 2.155(7); Pt(1)-C(7) 2.062(9); Pt(1)-C(8) 2.046(13) Å; N(1)-Pt(1)-N(1A)
85.7(4)o.
The reaction of benzyl bromide with complex 1 was more complex since it gave
the product [PtBr(CH2C6H5)Me2{(mim)2C=CH2}] as a mixture of isomers 4a and 4b,
formed by trans and cis oxidative addition, respectively. The isomers were formed with
1
ratio 4a:4b ca. 2:1, as determined by integration of the H NMR spectra. Complex 4a
has effective Cs symmetry and, as expected [20], it gave a single methylplatinum
resonance, a single PtCH2 resonance, and only one set of imidazole resonances in the 1H
NMR spectrum. On the other hand, complex 4b has no symmetry (C1) and so it gave two
methylplatinum resonances and two resonances due to the C=CHAHB protons. Similarly,
two peaks were expected for the diastereotopic protons of the PtCH2 group, but only a
single broad peak was observed at room temperature (Figure 2a). However, as the
temperature was lowered, the peak broadened and it then split into two broad resonances
at -60oC (Figure 2b). Rotation about the Pt-CHAHBPh bond cannot make the
diastereotopic protons equivalent, so this observation is unusual. We do not have a
definitive explanation but we suggest that, as a result of rotation of the benzyl group at
higher temperatures, the chemical shifts of the PtCHAHB protons are accidentally
degenerate but that, as rotation is slowed at low temperature, the individual resonances
are partly resolved. The substituted derivatives of benzyl bromide reacted in a similar
way to give complexes 5 – 7, in each case as a mixture of products of trans and cis
1
oxidative addition (Scheme 2) as determined by the H NMR spectra. In these
complexes, the PtCHAHB protons of the substituted benzylplatinum groups of 5b – 7b
were resolved, even at room temperature, in contrast to 4b. The ratio of isomers was ca.
2:1 for 5a:5b but ca. 3:1 for 6a:6b and 7a:7b, suggesting that greater steric bulk of the
substituted benzyl group favors the product of trans oxidative addition.
4

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1
Figure 2. H NMR spectra (600 MHz, CD2Cl2) of complex 4 in the region of the PtCH2
resonances: (a) at 20oC; (b) at -60oC.
The structure of complex 4a was determined and is shown in Figure 3. Again, the
platinum(IV) center has octahedral coordination geometry, with the benzyl and bromo
groups mutually trans. The thermal ellipsoids for the phenyl group carbon atoms are
large, suggesting that there is unresolved librational disorder of this group.
Figure 3. The structure of complex 4a. Selected bond parameters: Pt(1)-Br(1) 2.617(1) ;
Pt(1)-N(1) 2.153(7); Pt(1)-N(4) 2.150(7); Pt(1)-C(11) 2.071(8); Pt(1)-C(12) 2.071(9);
Pt(1)-C(13) 2.095(1) Å; N(1)-Pt(1)-N(4) 87.0(3)°.
The structures of complexes 6a and 7a are similar and are shown in Figures 4 and
5. In each case, the chelate ring adopts the boat conformation with the C=CH2 group syn
to the bromo ligand and anti to the benzyl group. The benzyl group is oriented above one
5

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of the imidazole rings in 4a, 6a and 7a (Figures 3-5). Unfortunately, we have not been
able to obtain single crystals for X-ray structure determination of the cis isomers 4b – 7b.
Figure 4. The structure of complex 6a. Selected bond parameters: Pt(1)-Br(1)
2.5997(6) ; Pt(1)-N(1) 2.149(4); Pt(1)-N(4) 2.156(4); Pt(1)-C(11) 2.050(5); Pt(1)-C(12)
2.050(5); Pt(1)-C(13) 2.078(6) Å; N(1)-Pt(1)-N(4) 86.1(2)°.
Figure 5. The structure of complex 7a. Selected bond parameters: Pt(1)-Br(1) 2.6364(6);
Pt(1)-N(1) 2.152(4); Pt(1)-N(2) 2.160(4); Pt(1)-C(1) 2.049(5); Pt(1)-C(2) 2.049(5); Pt(1)-
C(3) 2.084(6) Å; N(1)-Pt(1)-N(2) 85.7(2)°.
Complex 1 reacted rapidly with hydrogen peroxide in acetone solution to give the
dihydroxoplatinum(IV) complex [Pt(OH)2Me2{(mim)2C=CH2}], 8, according to Scheme
6

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1
3. The H NMR spectrum showed that 8 was formed by trans oxidative addition of the
HO-OH bond to complex 1. Thus, there was only one methylplatinum resonance and one
set of imidazole peaks. The complex could not be crystallized but it was characterized by
the mass spectrum, which contained a peak at m/z = 430 corresponding to
[Pt(OH)Me2{(mim)2C=CH2}]+, and by comparison to several similar complexes [37-40].
Scheme 3. Oxidative addition of H2O2 and CH2Cl2.
Complex 1 was unstable in chlorinated solvents dichloromethane and chloroform,
and the reaction with dichloromethane was shown to occur by oxidative addition to give
[PtCl(CH2Cl)Me2{(mim)2C=CH2}], 9 (Scheme 3). Complex 9 was isolated as a mixture
1
of the products of trans and cis oxidative addition, 9a and 9b respectively. In the H
NMR spectrum, the trans isomer 9a gave a single methylplatinum resonance and a single
PtCH2Cl resonance. On the other hand, the cis isomer 9b gave two equal intensity
methylplatinum resonances and two resonances for the diastereotopic PtCHaHbCl
protons. The course of the reaction was monitored by recording the 1H NMR spectrum of
a solution of complex 1 in CD2Cl2 over time. The resonances for complex 1 decayed
over a period of one hour at room temperature and were replaced by resonances for 9b-
d2. Over a period of several days, the resonances for 9b-d2 decayed and resonances for
9a-d2 grew in intensity, to finally give an equilibrium mixture with ratio 9a-d2:9b-d2 =
5:2. The reaction occurs more rapidly than with most related dimethylplatinum(II)
complexes [41], and the kinetically controlled product is 9b-d2 but 9a-d2 is slightly more
2
stable thermodynamically. The H NMR spectrum of 9a-d2 gave a single PtCD2Cl
resonance while 9b-d2 gave two resonances. Oxidative addition of dichloromethane
usually occurs by a free radical mechanism [41,42].
Oxidative addition reactions to complex 2 tended to occur with trans
stereochemistry. The simplest examples are with symmetrical reagents iodine and
hydrogen peroxide which gave complexes 10 and 11, respectively, by selective trans
1
oxidative addition (Scheme 4). In the H NMR spectrum, each product gave a single
methylplatinum resonance and a single set of imidazole resonances, as expected for a
complex with effective Cs symmetry. While trans oxidative addition is typical with
hydrogen peroxide, iodine often gives a mixture of products of trans and cis addition
[43].
7

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Scheme 4. Oxidative addition of iodine and hydrogen peroxide to complex 2.
The oxidative addition of methyl iodide to complex
2
gave
[PtIMe3{(mim)2CHMe}], 12, as a mixture of two isomers 12a and 12b. The isomers
arise because the two faces of complex 2 are not equivalent and methyl iodide can
1
approach from either side. The isomers were identified by a correlation in the H
NOESY NMR spectrum between the MeC and axial MePt groups for isomer 12a only.
The ratio of isomers 12a:12b was ca. 4:3 for an isolated sample. Further insight into the
reaction was obtained by carrying out the reaction of complex 2 with CD3I in acetone-d6
1
solution, with monitoring by H NMR spectroscopy as the solution warmed. For this
reaction, there are four possible isomers identified as t-12a-d3 and t-12b-d3, formed by
trans oxidative addition, and c-12a-d3 and c-12b-d3 formed by cis oxidative addition
(Scheme 5). The relative abundance of each isomer can be determined by integration of
the spectra. At the lowest temperature at which reaction was complete, the ratio 12b-
d3:12a-d3 was ca. 3:2 and the ratios t-12b-d3:c-12b-d3 = 1:1 and t-12a-d3:c-12a-d3 = 1:2.
As the solution warmed, the ratios changed to give the equilibrium values 12b-d3:12a-d3
= 3:4 and t-12b-d3:c-12b-d3 = t-12a-d3:c-12a-d3 = 1:2, which is the statistical ratio. The
data are interpreted in terms of the mechanism shown in Scheme 5 [44,45]. The SN2
mechanism can give either 5-coordinate cationic intermediate E or F, on approach from
either side of the square plane of platinum(II), and iodide coordination can then give t-
12a-d3 and t-12b-d3, respectively. The 5-coordinate intermediates can undergo
pseudorotation to give G and H, and iodide coordination can then give c-12a-d3 and c-
12b-d3. Iodide dissociation from any of the octahedral isomers can reform the 5-
coordinate precursor complexes and then further isomerization can occur. The data
suggest that CD3I approach to the less hindered side of complex 2 to give intermediate F
is preferred over formation of G by approach to the more hindered side. However, it is
also clear that pseudorotation of the 5-coordinate intermediates is competitive with iodide
coordination, so the stereoselectivity in the reaction is not high. Complex 12a is likely to
be more thermodynamically stable than 12b because the larger iodo group is syn to the
hydrogen and the smaller methyl group is syn to the methyl substituent of the CHMe
group (Scheme 5). Hence it is possible to rationalize the different selectivities resulting
from kinetic or thermodynamic control.
8

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Me
Me
N
N
N
I
Me
Me
Me
Me
Me
N
N
N
N
Me
H
Me
H
+
Pt
Pt
I
Me
N
N
Me
Me
12a
Me
Me
12b
MeI
N
+
CD3
CD3
N
N
N
Me
Me
-
-
Me
Me
Me
H
Me
H
I
Pt
I
Pt
N
E
CD3I
N
N
N
N
t-12a-d3
Me
Me
Me
Me
-
- I
Me
N
N
+
Me
Me
Me
Me
N
N
N
N
N
N
CD3
Me
Me
H
Me
H
Me
H
CD3
Me
I
Pt
Pt
I
Pt
G
N
N
N
N
2
c-12a-d3
Me
Me
Me
Me
Me
+
+
I
N
N
N
N
CD3
Me
-
-
Me
H
CD3
Me
H
CD3I
I
Pt
Pt
Me
-
Me
c-12b-d3
- I
Me
H
N
N
N
N
Me
Me
Me
Me
I
N
N
N
N
Me
Me
H
Me
H
Me
I
Pt
Pt
Me
Me
CD3
CD3
N
N
F
Me
Me
t-12b-d3
Scheme 5. Proposed mechanism of oxidative addition of CD3I to complex 2.
The oxidative addition of the derivatives of benzyl bromide occurred more
selectively to give only the isomer 13 from 1,4-C6H4(CF3)(CH2Br) and 14 from 1,2-
C6H4(CF3)(CH2Br) (Scheme 6). For example, complex 13 gave only one methylplatinum
resonance, one PtCH2 resonance, and one set of imidazole resonances. In these reactions,
the benzyl group is larger than the bromo group, so the isomer with benzyl group syn to
the hydrogen atom and bromo group syn to the methyl substituent of the CHMe group is
favored by both kinetic and thermodynamic control.
9

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Scheme 6. Oxidative addition of benzyl bromide derivatives to complex 2.
The structure of complex 14 was determined and is shown in Figure 6. It
confirms the structure deduced from the 1H NMR spectrum, with the complex formed by
selective trans oxidative addition to complex 2. The six-membered chelate ring is in the
boat conformation with the C-Me group syn to the bromo ligand. The bite angle of the
chelate ligand, N(1)-Pt(1)-N(3) 86.6(1)°, is similar to that in complex 6a (86.1(2)°,
Figure 4).
Figure 6. The structure of [PtBrMe2(CH2-2-C6H4CF3){(mim)2CHMe}], 14. Selected
bond parameters: Pt(1)-Br(1) 2.5951(6); Pt(1)-N(1) 2.152(4); Pt(1)-N(3) 2.152(4) ; Pt(1)-
C(11) 2.086(5); Pt(1)-C(19) 2.044(4); Pt(1)-C(20) 2.051(4) Å; N(1)-Pt(1)-N(3) 86.6(1)o.
3. Computational Studies and Conclusions
The dimethylplatinum(II) complexes [PtMe2{(mim)2C=CH2}], 1, and
[PtMe2{(mim)2CHMe}], 2, are very reactive towards oxidative addition chemistry. The
10

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reactivity towards dichloromethane and also to oxidation by air is higher than for
[PtMe2(bipy)] [41], consistent with the greater donor power of the imidazolyl compared
to pyridyl subsituents [24]. In most oxidative addition reactions, the platinum(II) center
is the nucleophile using its 5dz orbital (Figure 7). The calculated energy of the HOMO
2
and the calculated Hirshfeld charge on platinum for related complexes are shown in
Table 1. It can be seen that the calculated energy of the HOMO is higher and the
calculated positive charge on platinum is lower for complexes 1 and 2 than for pyridyl
analogs, consistent with the high reactivity of complexes 1 and 2 [24]. We note that the
methyl substituent in 2 is close to platinum, and can hinder reaction at that face, but this
close proximity does not lead to C-H or C-C bond activation analogous to the known
reactions of ligands such as D [4,38,46].
Figure 7. (a) The DFT calculated structure of complex 2 and (b) the calculated HOMO
(mostly Pt 5dz ) of complex 2.
2
Table 1. Calculated energies (eV) of the HOMO and Hirshfeld charges, Q(Pt), on
platinum [47].
Complex 1 Complex 2 [PtMe2(bipy)] [PtMe2(2-py2CHMe)]
E(HOMO) -3.93
Q(Pt) 0.139
-3.78
0.136
-4.88
0.186
-4.59
0.191
The ligand (mim)2C=CH2 forms platinum(IV) complexes in which the PtN2C3
chelate ring is in the boat conformation with the =CH2 group syn to the halide ligand in
complexes 3, 4a, 6a and 7a (Figures 1,3,4,5). DFT calculations were carried on complex
3 in different conformations, as illustrated in Figure 8. The experimentally observed
conformation 3-syn was calculated to be more stable than 3-anti by 5 kJ mol-1, and they
could interconvert by way of the conformation 3-planar (Fig. 8), with a significant barrier
of 49 kJ mol-1 predicted.
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Figure 8. The calculated structures and relative energies of complex 3 in different
conformations.
In contrast, the interconversion of isomeric complexes 12a and 12b requires
dissociation of the iodide ligand at an intermediate stage (Scheme 5). The DFT
calculation predicts that 12a and 12b have almost equal energy (Figure 9), consistent
with the observation of both isomers at equilibrium, as established by NMR
spectroscopy.
Figure 9. The calculated structures and relative energies of complexes 12a and 12b.
The calculated structures and energies of the most stable trans and cis isomers of
[PtBrMe2(CH2Ph){(mim)2C=CH2}], 4a and 4b, are shown in Figure 10. The illustrated
conformers with the bromo ligand syn to the C=CH2 group are preferred in each case.
Several conformations of the benzyl ligand were tested, and the preferred orientation in
4a was close to that observed crystallographically (Figure 3), with the benzyl group
above one of the imidazole rings. The preferred conformation of the benzyl group in 4b
was found to be towards an imidazole group, and this conformer of 4b was calculated to
be only 3 kJ mol-1 higher in energy than 4a, consistent with the observation of both
isomers in equilibrium.
12

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Figure 10. Calculated structures and relative energies of 4a and 4b.
The
calculated
structures
and
energies
of
isomers
of
[PtBrMe2(CH2Ph){(mim)2CHMe}], as a model for complexes 13 and 14, are shown in
Figure 11. The trans-syn isomer, analogous to the observed structures of the derivatives
13 and 14, is predicted to be most stable. The next in energy is the cis-syn isomer
(Figure 11), which is calculated to be 9 kJ mol-1 higher in energy than the trans-syn
isomer. Although the difference is not huge, if other factors such as solvation effects are
equal, it would lead to an equilibrium constant of ca. 5 x 10-3, whereas the analogous
value for 4 (Figure 10) would be 0.2. Thus, the predictions of the DFT calculations are
consistent with the experimental observations. For reasons outlined above, the trans-syn
isomer (Figure 11) is also expected to be the product of kinetic control, so it is not
surprising that it is the only isomer detected in formation of complexes 13 and 14.
Figure 11.
Calculated structures of isomers of the model complex
[PtBrMe2(CH2Ph){(mim)2CHMe}].
In conclusion, both the high reactivity of the complexes 1 and 2 towards oxidative
addition, and differences in selectivity of the stereochemistry of oxidative addition
between complexes 1 and 2, can be understood in terms of a combination of electronic
and differential steric effects.
4. Experimental
13

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All reactions were carried out under nitrogen, either using Schlenk techniques or in
a dry box, unless otherwise specified. NMR spectra were recorded using an Inova 400,
Inova 600 or Mercury 400 spectrometer. Mass spectrometry studies were carried out
using an electrospray PE-Sciex Mass Spectrometer (ESI MS), and a high resolution
Finnigan MAT 8200 instrument. The complex [Pt2Me4(µ-SMe2)2] and ligands were
prepared according to the literature [24,34]. DFT calculations were carried out using the
ADF software, with the Becke-Perdew gradient-corrected exchange-correlation
functional, double zeta basis set, and scalar relativistic correction. The calculations refer
to the gas phase only, with no symmetry constraints used [47].
Chart 2. NMR labeling scheme
[PtMe2{(mim)2C=CH2}], 1. [Pt2Me4(µ-SMe2)2] (0.4 g, 0.70 mmol) was added to a
stirring solution of (mim)2C=CH2 (0.262 g, 1.40 mmol) in ether (15 mL). The product
precipitated from solution as a light yellow solid. After 12 h. at 0oC, the mixture was
filtered, and the product was washed with ether (6 mL) and pentane ( 6 mL), and then
dried under high vacuum. It was purified by dissolution in the minimum volume of
acetone, followed immediately by precipitation with pentane, then the product was
separated and dried as above. Yield 81%. NMR in acetone-d6: δ(1H) = 0.53 (s, 6H, 2JPtH
= 86 Hz, PtMe), 3.91 (s, 6H, NMe), 6.18 (s, 2H, =CH2), 7.19 (d, 2H, 3JHH = 1 Hz, 3JPtH
=
3
13 Hz, H5), 7.23 (d, 2H, JHH = 1 Hz, H4). Anal. Calcd. for C12H18N4Pt: C, 34.87; H,
4.39; N, 13.55. Found: C, 34.51; H 4.46; N, 13.19%.
[PtMe2{(mim)2CHMe}], 2. This was prepared similarly, and isolated as a yellow solid.
Yield 83%. NMR in acetone-d6: δ(1H) = 0.49 (s, 6H, 2JPtH = 88 Hz, PtMe), 1.66 (d, 3H,
3JHH = 7 Hz, CMe), 3.82 (s, 6H, NMe), 4.64 (q, 1H, 3JHH = 7 Hz, CH), 7.03 (d, 2H, 3JHH
=
2 Hz, H4), 7.08 (d, 2H, 3JHH = 2 Hz, 3JPtH = 14 Hz, H5). Anal. Calcd. for C12H20N4Pt: C,
34.70; H, 4.85; N, 13.49. Found: C, 34.48; H, 5.02; N, 13.29%.
[PtIMe3{(mim)2C=CH2}], 3. To a solution of [PtMe2{(mim)2C=CH2}], 1, (0.1 g, 0.24
mmol) in ether (10 mL) was added MeI (0.015 mL, 0.24 mmol). There was an
immediate color change from yellow to white. The mixture was stirred for 4 h., then the
white solid product which precipitated was separated, washed with pentane (3 x 1 mL)
and ether (3 x 1 mL) and dried under high vacuum. Yield 65 %. NMR in CD2Cl2: δ(1H)
= 0.89 (s, 3H, 2JPtH = 74 Hz, PtMe), 1.30 (s, 6H, 2JPtH = 71 Hz, PtMe), 3.83 (s, 6H, NMe),
6.08 (s, 2H, =CH2), 7.09 (d, 2H, 3JHH = 1 Hz, H4), 7.41 (d, 2H, 3JHH = 1 Hz, 3JPtH = 9 Hz,
H5). Anal. Calcd. for C13H21IN4Pt: C, 28.12; H, 3.81; N, 10.09. Found: C, 28.19; H,
4.15; N, 9.44%.
[PtBr(CH2Ph)Me2{(mim)2C=CH2}], 4. To a solution of complex 1 (0.1 g, 0.24 mmol)
in acetone (15 mL) was added benzyl bromide (0.04 g, 0.24 mmol). The mixture was
stirred for 3 h., then the volume was reduced to 1 mL, and pentane (5 mL) was added to
14

ACCEPTED MANUSCRIPT
precipitate the product as a white solid, which was separated, washed with ether and
pentane (1 x 2 mL), and dried under high vacuum. Yield 82%. NMR in CD2Cl2: 4a;
2
2
δ(1H) = 1.19 (s, 6H, JPtH = 71 Hz, PtMe), 2.99 (s, 2H, JPtH = 99 Hz, PtCH2), 3.79 (s,
6H, NMe), 5.98 (s, 2H, =CH2), 6.56 (d, 2H, 3JHH = 7 Hz, 4JPtH = 11 Hz, Ho), 6.81 (t, 2H,
3JHH = 7 Hz, Hm), 6.92 (t, 1H, 3JHH = 7 Hz, Hp), 6.94 (d, 2H, 3JHH = 2 Hz, H4), 7.04 (d, 2H,
3JHH = 2 Hz, 3JPtH = 9 Hz, H5); 4b; δ = 0.79 (s, 3H, 2JPtH = 76 Hz, PtMe), 1.05 (s, 3H, 2JPtH
2
= 71 Hz, PtMe), 3.61 (br, 2H, JPtH = 104 Hz, PtCH2), 3.76 (s, 3H, NMe), 3.78 (s, 3H,
NMe), 6.05, 6.06 (m, each 1H, =CH2), 6.90-6.92 (m, 2H, H4 and H4’), 7.06-7.07 (m, 2H,
H5 and H5’), 7.08 (d, 2H, JHH = 8 Hz, JPtH = 11 Hz, Ho), 7.30 (m, 3H, Hm, Hp). Anal.
Calcd. for C19H25BrN4Pt: C, 39.05; H, 4.31; N, 9.59. Found: C, 39.27; H, 4.37; N,
9.49%.
3
4
[PtBr(CH2C6H4-4-CF3)Me2{(mim)2C=CH2}], 5. This was prepared similarly and
isolated as a white solid. Yield 80%. NMR in CD2Cl2: 5a; δ(1H) = 1.22 (s, 6H, 2JPtH = 70
2
Hz, PtMe), 3.03 (s, 2H, JPtH = 100 Hz, PtCH2), 3.80 (s, 6H, NMe), 5.99 (s, 2H, =CH2),
4
3
6.62 (d, 2H, 3JHH = 8 Hz, JPt-H = 11 Hz, Ho), 6.95 (d, 2H, JHH = 1 Hz, H4), 7.02 (d, 2H,
3JHH = 1 Hz, 3JPt-H = 8 Hz, H5), 7.07 (d, 2H, 3JHH = 8 Hz, Hm); 5b; δ = 0.79 (s, 3H, 2JPtH
=
74 Hz, PtMe), 1.00 (s, 3H, 2JPtH = 70 Hz, PtMe), 3.59 (d, 1H, 2JHH = 9 Hz, 2JPtH = 100 Hz,
PtCH2), 3.86 (d, 1H, 2JHH = 9 Hz, 2JPtH = 84 Hz, PtCH2), 3.78 (s, 3H, NMe), 3.82 (s, 3H,
NMe), 6.08, 6.09 (m, each 1H, =CH2), 6.94-6.98 (m, 2H, H4, H4’), 7.04-7.07 (m, 2H, H5,
H5’), 7.34 (d, 2H, JHH = 8 Hz, Hm), 7.43 (d, 2H, JHH = 8 Hz, JPtH = 11 Hz, Ho). Anal.
Calcd. for C20H24BrF3N4Pt: C, 36.82; H, 3.71; N, 8.59. Found: C, 36.59; H, 3.60; N,
8.78%.
3
3
4
[PtBr(CH2C6H4-2-CF3)Me2{(mim)2C=CH2}], 6. This was prepared similarly and
isolated as a white solid. Yield 81%. NMR in CD2Cl2: 6a; δ(1H) = 1.28 (s, 6H, 2JPtH = 70
2
Hz, PtMe), 3.25 (s, 2H, JPtH = 108 Hz, PtCH2), 3.77 (s, 6H, NMe), 5.79 (s, 2H, =CH2),
3
4
3
6.96 (d, 1H, JHH = 6 Hz, JPtH = 13 Hz, Ho), 6.99 (d, 2H, JHH = 1 Hz, H4), 7.11 (d, 2H,
3JHH = 1 Hz, 3JPtH = 8 Hz, H5), 7.15-7.18 (m, 3H, Hm, Hp); 6b; δ = 0.76 (s, 3H, 2JPtH = 74
2
Hz, PtMe), 1.15 (s, 3H, JPtH = 70 Hz, PtMe), 3.69-3.70 (m, 2H, PtCH2), 3.78 (s, 3H,
NMe), 3.80 (s, 3H, NMe), 6.08, 6.10 (m, each 1H, =CH2), 7.05-7.08 (m, 4H, H4, H4’, H5,
H5’), 7.19-7.43 (m, 4H, C6H4). Anal. Calcd. for C20H24BrF3N4Pt: C, 36.82; H, 3.71; N,
8.59. Found: C, 36.93; H, 3.74; N, 8.55%.
[PtBr(CH2C6H3-3,5-t-Bu2)Me2{(mim)2C=CH2}], 7. This was prepared similarly and
isolated as a white solid. Yield 83%. NMR in CD2Cl2: 7a; δ(1H) = 1.07 (s, 18H, t-Bu),
1.26 (s, 6H, 2JPtH = 71 Hz, PtMe), 2.99 (s, 2H, 2JPtH = 93 Hz, PtCH2), 3.75 (s, 6H, NMe),
6.01 (s, 2H, =CH2), 6.26 (d, 2H, 4JHH = 2 Hz, 4JPtH = 10 Hz, Ho), 6.87 (d, 2H, 3JHH = 2 Hz,
4
3
3
H4), 6.90 (t, 1H, JHH = 2 Hz, Hp), 6.95 (d, 2H, JHH = 2 Hz, JPtH = 7 Hz, H5); 7b; δ =
0.80 (s, 3H, 2JPtH = 76 Hz, PtMe), 1.06 (s, 18H, t-Bu), 1.14 (s, 3H, 2JPtH = 71 Hz, PtMe),
3.67 (b, 2H, Pt-CH2), 3.74 (s, 3H, NMe), 3.79 (s, 3H, NMe), 6.03, 6.05 (m, each 1H,
=CH2), 7.04-7.11 (m, 4H, H4, H4’, H5, H5’), 7.18 (s, 2H, JPtH = 11 Hz, Ho), 7.29 (m, 1H,
4
Hp). Anal. Calcd. for C27H41BrN4Pt: C, 46.55; H, 5.93; N, 8.04. Found: C, 46.79; H,
5.71; N, 7.85%.
[Pt(OH)2Me2{(mim)2C=CH2}], 8. To a solution of complex 1 (0.01 g, 0.02 mmol) in
acetone (2 mL) was added excess H2O2 (0.1 mL). The product was isolated as a white
solid by evaporation of the solvent, and was purified by precipitation from solution in
minimum CH2Cl2 by addition of pentane. Yield: 45%. NMR in acetone-d6: δ(1H) = 1.36
2
(s, 6H, JPtH = 73 Hz, PtMe), 2.99 (br, 2H, OH), 3.98 (s, 6H, NMe), 6.21 (s, 2H, =CH2),
15

ACCEPTED MANUSCRIPT
7.25 (d, 2H, 3JHH = 1 Hz, H4), 7.30 (d, 2H, 3JHH = 1 Hz, 3JPtH = 14 Hz, H5). Anal. Calcd.
for C12H20N4O2Pt: C, 32.22; H, 4.51; N, 12.52. Found: C, 32.07; H, 4.72; N, 12.28%.
[PtCl(CH2Cl)Me2{(mim)2C=CH2}], 9. A solution of [PtMe2{(mim)2C=CH2}], 1 (0.05
g, 0.12 mmol) in CH2Cl2 (2 mL) was stirred for 2 days. The white product was obtained
by precipitation with pentane, then separated, washed with pentane, and dried under high
2
vacuum. Yield 78 %. NMR in CD2Cl2: 9a; δ(1H) = 1.12 (s, 6H, JPtH = 70 Hz, PtMe),
3.72 (s, 2H, 2JPtH = 56 Hz, PtCH2), 3.84 (s, 6H, NMe), 6.11 (s, 2H, =CH2), 7.15 (d, 2H,
3JHH = 2 Hz, 3JPtH = 9 Hz, H5), 7.20 (d, 2H, 3JHH = 2 Hz, H4); 9b; δ = 0.89 (s, 3H, 2JPtH
=
74 Hz, PtMe), 1.13 (s, 3H, 2JPtH = 69 Hz, PtMe), 3.80 (s, 3H, NMe), 3.81 (s, 3H, NMe),
2
2
4.13 (m, 1H, JPtH = 45 Hz, PtCH2Cl), 4.60 (m, 1H, JPtH = 88 Hz, PtCH2Cl), 6.09, 6.10
(m, each 1H, =CH2), 7.07 (br, 2H, H4, H4’), 7.27 (d, 1H, 3JHH = 2 Hz, 3JPtH = 12 Hz, H5),
7.50 (d, 1H, 3JHH = 2 Hz, 3JPtH = 6 Hz, H5’). Anal. Calcd. for C13H20Cl2N4Pt: C, 29.25; H,
3.90; N, 10.25. Found: C, 29.24; H, 3.86; N, 10.23%.
[PtI2Me2{(mim)2CHMe}], 10. To a solution of [PtMe2{(mim)2CHMe}], (0.14 g, 3.3
mmol) in acetone (10 mL) was added iodine (0.085 g) dissolved in acetone (5 mL). After
30 min., the solvent was removed and the orange product was purified by precipitation
from minimum CH2Cl2 by addition of pentane, then separated, washed with pentane, and
3
dried under vacuum. Yield 63%. NMR in CD2Cl2: δ(1H) = 1.89 (d, 3H, JHH = 7 Hz,
2
3
CMe), 2.32 (s, 6H, JPtH = 71 Hz, PtMe), 3.87 (s, 6H, NMe), 4.64 (q, 1H, JHH = 7 Hz,
CH), 7.08 (d, 2H, JHH = 2 Hz, H4), 7.26 (d, 2H, JHH = 2 Hz, JPtH = 9 Hz, H5). Anal.
Calcd. for C12H20I2N4Pt: C, 21.54; H, 3.01; N, 8.37. Found: C, 21.21; H, 2.96; N, 8.05%.
[Pt(OH)2Me2{(mim)2CHMe}], 11. This was prepared in a similar way as complex 8,
3
3
3
but using complex 2. Yield 55%. NMR in acetone-d6: δ(1H) = 1.37 (s, 6H, JPtH = 73
2
Hz, PtMe), 1.80 (d, 3H, 3JHH = 7 Hz, CMe), 3.92 (s, 6H, NMe), 4.80 (q, 1H, 3JHH = 7 Hz,
CH), 7.17 (d, 2H, JHH = 2 Hz, JPtH = 10 Hz, H5), 7.19 (d, 2H, JHH = 2 Hz, H4). Anal.
Calcd. for C12H22N4O2Pt: C, 32.07; H, 4.93; N, 12.47. Found: C, 32.28; H, 4.69; N,
12.25%.
3
3
3
[PtIMe3{(mim)2CHMe}], 12, This was prepared similarly to complex 3 but using
1
complex 2, and isolated as a white solid. Yield 79%. H-NMR in CD2Cl2: (4.13a) δ =
0.93 (s, 3H, 2JPt-H = 75 Hz, Pt-CH3), 1.32 (s, 6H, 2JPt-H = 70 Hz, Pt-CH3), 1.55 (d, 3H, 3JH-
H = 8 Hz, CCH3), 3.75 (s, 6H, N-CH3), 4.45 (q, 1H, 3JH-H = 8 Hz, C-H), 7.01 (d, 2H, 3JH-H
3
3
= 2 Hz, Im{H2 and H2’}), 7.38 (d, 2H, JH-H = 2 Hz, JPt-H = 10 Hz, Im{H1 and H1’});
(4.13b) δ = 0.70 (s, 3H, 2JPt-H = 74 Hz, Pt-CH3), 1.37 (s, 6H, 2JPt-H = 70 Hz, Pt-CH3), 1.94
3
3
(d, 3H, JH-H = 7 Hz, CCH3), 3.74 (s, 6H, N-CH3), 4.49 (q, 1H, JH-H = 7 Hz, C-H), 6.99
(d, 2H, JH-H = 2 Hz, Im{H2 and H2’}), 7.20 (d, 2H, JH-H = 2 Hz, JPt-H = 11 Hz, Im{H1
and H1’}). Anal. Calcd. for C13H23IN4Pt (%): C, 28.02; H, 4.16; N, 10.05. Found: C,
28.29; H, 3.97; N, 9.77%.
3
3
3
[PtBr(CH2C6H4-4-CF3)Me2{(mim)2CHMe}], 13. This was prepared similarly to
complex 5 but using complex 2, and isolated as a white solid. Yield 79 %. NMR CD2Cl2:
2
3
δ(1H) = 1.34 (s, 6H, JPtH = 69 Hz, PtMe), 1.73 (d, 3H, JHH = 8 Hz, CMe), 2.87 (s, 2H,
2JPtH = 97 Hz, Pt-CH2), 3.66 (s, 6H, NMe), 4.18 (q, 1H, JHH = 8 Hz, CH), 6.36 (d, 2H,
3
3JHH = 8 Hz, JPtH = 11 Hz, Ho), 6.84 (d, 2H, JHH = 2 Hz, H4), 6.93 (d, 2H, 3JHH = 8 Hz,
4
3
Hm), 7.02 (d, 2H, JHH = 2 Hz, JPtH = 7 Hz, H5). Anal. Calcd. for C20H26BrF3N4Pt: C,
3
3
36.71; H, 4.00; N, 8.56. Found: C, 36.65; H, 3.84; N, 8.31%.
[PtBr(CH2C6H4-2-CF3)Me2{(mim)2CHMe}], 14. This was prepared similarly to
complex 6 but using complex 2, and isolated as a white solid. Yield 81%. NMR in
16

ACCEPTED MANUSCRIPT
CD2Cl2: δ(1H) = 1.34 (s, 6H, 2JPtH = 69 Hz, PtMe), 1.86 (d, 3H, 3JHH = 7 Hz, CMe), 3.11
2
3
(s, 2H, JPtH = 104 Hz, PtCH2), 3.69 (s, 6H, NMe), 4.32 (q, 1H, JHH = 7 Hz, CH), 6.71
(m, 1H, Ho), 6.78 (d, 2H, JHH = 1 Hz, H4), 6.81 (d, 2H, JHH = 1 Hz, JPtH = 7 Hz, H5),
7.01-7.08 (m, 3H, HmHp). Anal. Calcd. for C20H26BrF3N4Pt: C, 36.71; H, 4.00; N, 8.56.
Found: C, 36.54; H, 3.73; N, 8.81%.
3
3
3
X-ray Structure Determinations: In a typical experiment, a sample was mounted on a
Mitegen polyimide micromount with Paratone N oil. All X-ray measurements were made
using a Bruker Kappa Axis Apex2 diffractometer at a temperature of 150 K. The
structure was solved by direct methods. The hydrogen atoms for the main molecule were
introduced at idealized positions and were allowed to refine isotropically. The structural
model was fit to the data using full matrix least-squares based on F2. The structure was
refined using SHELXL [48]. Data are given in Table 2 and in the CIF files (CCDC
984275-984279). Complex 3 contained a dichloromethane solvate molecule which
appeared to be disordered, but this disorder could not be resolved. Complex 7 contained
a solvent accessible void of 487 Å3, but the solvent molecules were poorly defined, and
the electron density was modelled by using SQUEEZE; there was also some unresolved
disorder of the benzyl substituents.
Table 2. Crystal and refinement data for the complexes.
Complex
Formula
fw
32.CH2Cl2
4.0.5CH2Cl2
6
7
14
C27H44Cl2I2N8Pt2 C19.5H26BrClN4Pt C20H24BrF3N4Pt C27H41BrN4Pt C20H26BrF3N4Pt
1195.58
0.71073
150
626.89
0.71073
150
652.43
0.71073
150
696.62
0.71073
150
654.45
0.71073
150
λ /
Å
T / K
Cryst.syst.
Sp.gp.
monoclinic
P21/m
monoclinic
C2/c
monoclinic
P21/c
orthorhombic monoclinic
Pbcn
P21/c
16.424(1)
13.052(1)
16.649(1)
90
21.034(1)
16.738(1)
12.754(1)
90
10.8308(4)
16.8547(5)
12.5852(4)
90
30.038(2)
16.554(1)
12.574(1)
90
10.6274(7)
16.5446(1)
12.9666(9)
90
a /
b /
c /
Å
Å
Å
α /°
96.088(2)
90
3548.9(3)
4
2.238
9.796
110.303(3)
90
4211.2(4)
8
1.978
8.700
105.87(1)
90
2209.9(1)
4
1.961
8.196
90
90
105.737(2)
90
2194.4(3)
4
1.981
8.254
β /°
γ /°
V / Å3
Z
6252.4(8)
8
1.585
5.802
0.0514
0.0867
dc. /Mg m-3
µ / mm-1
R1(I>2σI)
wR2(all)
0.0504
0.1154
0.0499
0.1241
0.0350
0.0900
0.0310
0.0579
Supporting Materials
X-ray data in electronic CIF format (CCDC 984275-984279).
Acknowledgments
We thank the NSERC (Canada) for financial support.
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ACCEPTED MANUSCRIPT
Synopsis
The bis(N-methylimidazol-2-yl) ligands, (mim)2C=CH2 or (mim)2CHMe, promote
oxidative addition chemistry in their dimethylplatinum(II) complexes.
1