Preparation of dimethyl and chloro/methyl complexes of platinum(II) supported by α-Diimine ligands: Trends in the ease of oxidation to platinum(IV)

Article abstract of DOI:10.1002/1522-2675(20011017)84:10<3247::AID-HLCA3247>3.0.CO;2-W

α-Diimine ligands react with the platinum(II) alkyl complexes [(Me₂S)PtMe₂]₂ and (Me₂S)₂PtClMe to form (RDAB^R′)PtMe₂ and (RDAB^R′)PtClMe (RDAB^R′=RN=CR′-CR′=NR; R=2,6-Me₂Ph, 2,6-(CHMe₂)₂Ph, 3,5-Me₂Ph, 3,5-(CF₃)₂Ph, C₆H₁₁; R′ =Me, H). The oxidation of these complexes with Cl₂, I₂, N-chlorosuccinimide, [PtC1₆]^2- and (TMEDA)PtMe₂I₂ has been investigated. Attempts to determine the oxidation potentials of the Pt¹¹ complexes electrochemically yielded only irreversible one-electron oxidations. However, a qualitative ordering of increasing difficulty of oxidation has been determined for the series (RDAB^R′)PtMe₂ < (RDAB^R′)PtClMe < (RDAB^R′)PtCl₂ ? (RDAB^R′)PtMe(solvent)]⁺. The oxidation proceeds via a two-electron inner-sphere electron transfer from a bridged binuclear intermediate. The oxidation of (RDAB^R′)PtMe₂ by (TMEDA)PtMe₂I₂ exhibits characteristic third-order kinetics, first-order each in [Pt¹¹], [Pt^IV] and [I^-]. Oxidation by a one-electron process in MeCN solution results in a rapid subsequent disproportionation to Pt¹¹Me and Pt^IVMe₃ cations with MeCN occupying the fourth or sixth coordination sites. Single-crystal X-ray structure determinations for [(2,6-Me₂PhDAB^Me)PtMe₃(MeCN)]+[PtCl ₆]_0.5(MeCN) and [(CyDAB^H)PtMe₃(MeCN)]+[PtCl₆] _0.5(MeCN) are reported.

Full text of DOI:10.1002/1522-2675(20011017)84:10<3247::AID-HLCA3247>3.0.CO;2-W

Helvetica Chimica Acta ± Vol. 84 (2001)
3247
Preparation of Dimethyl and Chloro/Methyl Complexes of Platinum(II)
Supported by a-Diimine Ligands: Trends in the Ease of Oxidation
to Platinum(IV)
by John D. Scollard, Mike Day, Jay A. Labinger*, and John E. Bercaw*
Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena,
CA 91125, USA
Dedicated to the memory of Professor Luigi M. Venanzi
a-Diimine ligands react with the platinum(II) alkyl complexes [(Me2S)PtMe2]2 and (Me2S)2PtClMe to
form (RDABR')PtMe2 and (RDABR')PtClMe (RDABR' ˆ RNˆCR' CR'ˆNR; R ˆ 2,6-Me2Ph, 2,6-
(CHMe2)2Ph, 3,5-Me2Ph, 3,5-(CF3)2Ph, C6H11; R' ˆ Me, H). The oxidation of these complexes with Cl2, I2,
N-chlorosuccinimide, [PtCl6]2 and (TMEDA)PtMe2I2 has been investigated. Attempts to determine the
oxidation potentials of the PtII complexes electrochemically yielded only irreversible one-electron oxidations.
However, a qualitative ordering of increasing difficulty of oxidation has been determined for the series
‡
(RDABR')PtMe2 < (RDABR')PtClMe < (RDABR')PtCl2 ꢀ (RDABR')PtMe(solvent)] . The oxidation proceeds
via a two-electron inner-sphere electron transfer from a bridged binuclear intermediate. The oxidation of
(RDABR')PtMe2 by (TMEDA)PtMe2I2 exhibits characteristic third-order kinetics, first-order each in [PtII],
[PtIV] and [I ]. Oxidation by a one-electron process in MeCN solution results in a rapid subsequent
disproportionation to PtIIMe and PtIVMe3 cations with MeCN occupying the fourth or sixth coordination sites.
‡
Single-crystal X-ray structure determinations for [(2,6-Me2PhDABMe)PtMe3(MeCN)] [PtCl6]0.5(MeCN) and
‡
[(CyDABH)PtMe3(MeCN)] [PtCl6]0.5(MeCN) are reported.
Introduction. ± Almost 30 years have passed since Shilov and co-workers first
reported the oxidation of CH4 by mixtures of PtII and PtIV salts in aqueous solution
(Eqn. 1) [1]. Since then, the selective catalytic activation and functionalization of
alkane C H bonds have been the focus of substantial efforts [2 ± 4]. Recently, several
systems have been developed based on late-transition metals (e.g., Pt, Pd, and Hg) [5 ±
9]. These systems promote electrophilic activation and subsequent oxidation of
alkanes. We are currently pursuing new ligand environments for the metal-catalyzed
oxidation of alkanes
2
‰PtCl4Š
R
H ‡ [PtCl6]2 ‡ H2O
R
OH ‡ [PtCl4]2 ‡ 2 HCl
(1)
ƒƒƒƒ!
120ꢁ
Late transition metal complexes supported with a-diimine or diamine ligands
exhibit behavior relevant to catalytic capabilities. For example, Ni and Pd methyl
cations having diimine ancillary ligands have been shown to be highly active catalysts
for the polymerization of ethylene and a-olefins [10 ± 18]. Recently, electrophilic Pt
‡
cations of the type [(N N)PtMe(solvent)] (N N ˆ diimine, diamine), have been
shown to activate C H bonds [19 ± 24], the first step in the catalytic cycle proposed by
Shilov and co-workers for his PtII±IV system (Scheme 1). The next step in the cycle
involves the oxidation of the resulting PtII alkyl complex. Mechanistic details of this
step have been studied for the original Shilov system having only chloro and aquo

3248
Helvetica Chimica Acta ± Vol. 84 (2001)
ligands [26 ± 28]. Oxidation of the PtII alkyl complex must compete with the (rapid)
protonolysis that would reverse the first step. Furthermore, oxidation of the PtII alkyl
complex must be much more efficient than its PtII precursor, otherwise all the PtII will
be oxidized to PtIV, resulting in termination of the catalytic cycle. (In the original Shilov
system, oxidation by PtIV regenerates the PtII catalyst, and this problem does not arise.)
Hence, understanding the oxidation chemistry of PtII a-diimine complexes is crucial for
the design of alkane oxidation catalysts based thereon. In this paper, we report the
synthesis of a number of such complexes and the results of studies aimed at determining
the trends in oxidizability.
Scheme 1
PtII
R-H
RCl
PtII
+ H+
+
R
[PtIVCl6]2–
ROH + H+
Cl–
H2O
[PtIICl4]2–
PtIV
R
Results and Discussion. ± Synthesis and Characterization of Pt Complexes. The
majority of these Pt complexes are new; therefore, the details of their preparation and
characterization will be briefly described. The series of a-diimines, all derivatives of
1,4-diazabutadiene, are generally abbreviated RDABR', where R is the substitutent on
the N-atoms, either a substituted Ph or cyclohexyl, and R' is the ꢀbackboneꢁ substituent,
H or Me. The PtIIMe2 complexes (1a ± g) can be synthesized in 60 ± 95% isolated yield
from the a-diimine and (PtMe2SMe2)2 (Scheme 2). All attempts to prepare complex 1h
resulted in the deposition to metallic Pt. The complexes range in color from forest
green to deep purple. The 1H-NMR spectrum of complexes 1a ± g indicate C2v
1
symmetry, while the H-NMR spectrum of complexes 1c,d also exhibit diastereotopic
isopropyl Me resonances, indicating restricted rotation about the N Cipso bond. The
PtMe resonances show 2J(Pt,H) in the range of 84 ± 87 Hz. In addition, three-bond Pt
coupling to the imine backbone protons in the range of 32 ± 34 Hz is observed for
complexes 1a,1c, and 1g.
The platinum methyl chloride complexes 2a ± h can be synthesized in 70 ± 95% yield
from the corresponding a-diimine and (Me2S)2PtClMe in CH2Cl2 (Scheme 3). This
reaction proceeds slowly and requires 4 days in order to achieve high yields. The
resulting products are insoluble in aromatic solvents and only partially soluble in
CH2Cl2. Interestingly, complex 2h could be synthesized, unlike the dimethyl complex
1
1h. The H-NMR spectra of complexes 2a ± h show Cs symmetry and complexes 2c,d

Helvetica Chimica Acta ± Vol. 84 (2001)
3249
Scheme 2
Me
Pt
R
toluene
RDABR'
0.5 [Me2Pt(SMe2)]2
+
N
Me
– SMe2
R'
a: R = 2,6-Me2Ph, R' = H
b: R = 2,6-Me2Ph, R' = Me
c: R = 2,6-(CHMe2)2Ph, R' = H
d: R = 2,6-(CHMe2)2Ph, R' = Me
e: R = 3,5-Me2Ph, R' = Me
f: R = 3,5-(CF3)2Ph, R' = Me
g: R = C6H11, R' = H
N
R
R'
1a–h
h: R = C6H11, R' = Me
also exhibit diastereotopic Me resonances. 13C{1H}- and 195Pt{1H}-NMR spectra could
2
not be obtained for complexes 2b, 2e, and 2f due to their insolubility. The J(Pt,H)
coupling constants of the PtMe groups range from 79 ± 82 Hz, slightly lower than for the
corresponding PtMe2 complexes. The 3J(Pt,H) coupling constants for the imine proton
trans to Me in complexes 2a, 2c, and 2g range from 35 ± 38 Hz, while the imine proton
trans to Cl has 3J(Pt,H) coupling constants in the range of 105 ± 107 Hz. This difference
in coupling constants for the imine protons may be attributed to the trans influence of
the respective ligands. Since Me is a better s-donor than Cl, it exerts a stronger trans
influence: the Me group pulls s character from the Pt center, resulting in a weakening of
the Pt N bond trans to the Me group and a hence-smaller coupling constant.
UV/VIS Spectroscopy. Complexes containing electron-rich metal centers and p-
acceptor ligands such as a-diimines often exhibit low-energy solvent-dependent metal-
to-ligand charge transfer (MLCT) absorptions. Fig. 1 illustrates a typical UV/VIS
spectrum of a PtII Me2 a-diimine and its PtIV oxidation product. All PtII spectra exhibit a
diimine-centered LL transition, 1(p ! p*) near 370 ± 400 nm. The vibronic structure of
this transition is not well-resolved as a result of overlapping charge-transfer transitions.
Similar features have been observed in the spectra of Pt(bpy)Cl2 [29] and Pt(bpy)(pz)2
[30]. A second solvent-insensitive band occurs near 215 nm in the spectrum of each
1
complex. This band is assigned to a higher energy spin-allowed LL transition, (p !
p2*), centered on the a-diimine ligand.
At longer wavelengths (500 ± 644 nm), there are two bands that undergo a distinct
bathochromic shift with decreasing solvent polarity. In some cases, a shoulder of
considerably weaker intensity is observed on the lower-energy band. By analogy to
Scheme 3
Me
R
CH4Cl2
– SMe2
RDABR'
(SMe2)2PtClMe
+
Pt
N
N
Cl
R'
R
R'
2a–h

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Table 1. NMR Spectroscopic Data for New Complexes
1H-NMRa)
13C-NMRa)
195Pt-NMRb)
Complex
PtMe (2J(Pt,H))
Diimine Me (3J(Pt,H))
PtMe (2J(Pt,H))
1a
2a
1b
2b
1c
1.44 (87)
1.20 (81)
0.79 (87)
0.72 (79)
1.52 (86)
1.30 (84)
1.80 (86)
0.87 (79)
0.90 (87)
0.87 (80)
1.14 (87)
0.98 (80)
2.37 (85)
1.34 (79)
1.18 (77)
9.40 (33)
8.74 (36), 9.38 (107)
1.24
13.9 (802)
11.2 (704)
14.9 (799)
1452
1320
1079
c
c
1.25,1.66
)
)
9.40 (32)
8.72 (35), 9.40 (105)
50
1.29, 1.69
1.43
1.41, 1.83
1.35
1.33, 1.88
8.17 (34)
8.45 (38), 8.89 (107)
1.84, 1.96
13.7 (805)
10.6 (722)
12.5 (811)
11.7 (730)
13.4d)
1344
1199
1309
1403
1435
2c
1d
2d
1e
2e
1f [23]
2f
1g
2g
2h
c
c
)
)
)
)
12.1d)
c
c
c
)
12.7 (800)
1304
1111
1225
13.4d)
12.4 (717)
a) Chemical shifts d in ppm relative to TMS; coupling constants J in Hz. b) Chemical shifts d in ppm relative to
K2PtCl4. c) Complex not sufficiently soluble. d) Unresolved.
Fig. 1. UV/VIS Spectra of Complexes 1a and 3b
literature assignments for related halo/polypyridine PtII systems [29][31][32], we
attribute the lower-energy band to 1MLCT [d(Pt) ! p*] excitation and the shoulder to
the corresponding triplet state. The shift of the lower-energy band ranges from
1
1
1190 cm to 1580 cm when moving from MeCN to toluene for complexes 1a ± g.
Quantitative analysis of the long-wavelength absorption band was performed for the
complex 1b. Correlation of the energies at the absorption maxima with the empirical

Helvetica Chimica Acta ± Vol. 84 (2001)
3251
solvent parameter E*MLCT of Manuta and Lees [33] led to the graph shown in Fig. 2. The
solvatochromism of the a-diimine complexes is comparatively strong and quite obvious
from color changes between blue and purple, depending on the solvent. The band shifts
dramatically to lower energy in less-polar solvents, suggesting considerable charge-
transfer character. The negative solvatochromism indicates a polar ground state and a
less-polar excited state. Methyl substituents on the a-diimine also result in a small blue
shift for these two bands (see Table 2). This feature is also consistent with a MLCT
transition and has previously been observed in related complexes [30].
Fig. 2. Correlation between long-wavelength absorption maxima of complex 1b in different solvents and the
solvent parameter EM* LCT
Table 2. UV/VIS Data for Complexes 1a ± ga)
MeCN
Toluene
Complex
1(p ! p2*)
1(p ! p*)
1MLCT
1(p ! p*)
1MLCT
1a
1b
1c
1d
1e
1f [23]
1g
210 (31.5)
234 (12.7)
216 (22.6)
202 (79.8)
390 (4.4)
376 (4.8)
392 (4.2)
382 (3.2)
584 (2.2)
514 (2.7), 544 (2.9)
598 (2.1)
404 (3.1)
396 (5.2)
410 (4.9)
398 (5.0)
584 (1.9), 632 (2.8)
546 (2.5), 592 (3.3)
592 (1.8), 644 (2.5)
552 (2.4), 598 (3.2)
522 (1.7), 558 (1.9)
b
b
)
)
)
b
200 (52.7)
228 (9.6)
386 (4.1)
374 (3.2)
560 (2.6)
528 (2.2)
400 (4.1)
540 (2.1), 576 (2.8)
a) lmax, nm (103 e, m 1 cm 1). b) Insufficiently soluble.

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Helvetica Chimica Acta ± Vol. 84 (2001)
The bleaching of the UV/VIS spectrum upon oxidation from PtII to PtIV is also
consistent with these assignments. The much higher oxidation potential for PtIV vis-a-
vis PtII blue-shifts the MLCT bands into the UV for the PtIV complexes.
Oxidation by Halogens. Complexes 1a ± h are oxidized by Cl2 or I2 to the
dihalodimethylplatinum(IV) complexes 3 and 4 (Scheme 4). Care must be taken to
thoroughly dry the Cl2 gas, as any moisture present creates HCl, which can protonate
the Me groups on platinum to give the PtIVCl4 concomitant with the release of CH4. The
addition of halogens always occurs in a trans fashion, indicating a stepwise process.
Likewise, the chloro(methyl)complexes 2 undergo facile oxidation by Cl2 or I2 to form
the PtIV complexes 5 and 6 (Scheme 5). Complexes 3 and 5 are microcrystalline yellow
solids while the diiodo complexes 4 and 6 are orange solids.
Scheme 4
X
Me
Pt
Me
R
R
CH2Cl2
Pt
N
Me
+ X2
N
Me
R'
N
R'
X
R
N
R
R'
R'
X = Cl; 3a–h
X = I; 4a–h
1a–h
X = Cl, I
Scheme 5
X
Me
Pt
Me
R
R
CH2Cl2
Pt
N
Cl
+ X2
N
Cl
R'
N
R'
X
R
N
R
R'
R'
X = Cl; 5a–h
X = I; 6a–h
X = Cl, I
2a–h
Oxidation by N-Chlorosuccinimide. Addition of excess N-chlorosuccinimide to
MeOH solutions of complexes 1 and 2 results in oxidation to the octahedral PtIV
chloro(methoxy)(methyl)complexes 7 and 8, as evidenced by the rapid bleaching of
deeply colored solutions (Scheme 6).
In MeCN, cationic PtIVCl(MeCN) complexes are formed. Complexes 7 and 8 are
yellow powders, and, while attempts to grow single crystals for X-ray-analysis proved
impossible, single crystals of 9b and 9g were obtained as the [PtCl6]2 salts (vide infra).
Oxidation by PtIV. The oxidation of complexes 1e ± h and 2e ± h in MeOH by excess
hexachloroplatinate, comparable to the oxidation step in the Shilov cycle, results in the
formation of complexes 7e ± h and 8e ± h (Scheme 7).
Interestingly, [PtCl6]2 is unable to oxidize the PtII complexes supported by a-
diimine ligands with 2,6-dimethylphenyl or 2,6-diisopropylphenyl substituents. We
believe that the inability of the 2,6-disubstituted aryl group to rotate into the Pt square
plane is responsible for the lack of oxidation of complexes 1a ± d and 2a ± d. Indeed, the

Helvetica Chimica Acta ± Vol. 84 (2001)
3253
Scheme 6
Cl
N
Cl
Pt
O
O
Me
Pt
Me
R
R
N
X
N
X
R'
MeOH
R'
N
N
OMe
R
R
R'
R'
1a–h
2a–h
X = Me; 7a–h
X = Cl; 8a–h
Scheme 7
Cl
Me
Me
R
[PtCl6]2–
MeOH
R
Pt
N
N
X
Pt
N
X
R'
R'
N
OMe
R
R
R'
R'
1e–h
2e–h
X = Me; 7e–h
X = Cl; 8e–h
3,5-dimethylphenyl-substituted a-diimine complex 1e is oxidized cleanly while com-
plex 1a is not. The cyclohexyl-substituted a-diimine complexes 1g, 2g, 2h are also
cleanly oxidized. The oxidation by [PtCl6]2 can also be carried out in MeCN and
results in the formation of the cationic PtIV complexes 9e ± h and 10e ± h (Scheme 8).
2
The counter ion in these complexes is 0.5 equivalents of PtCl6
.
Scheme 8
+
Cl
Me
Pt
Me
[PtCl6]2–
MeCN
R
R
N
X
N
X
[PtCl6]2–
Pt
R'
0.5
R'
N
N
NCMe
R
R
R'
R'
X = Me; 9e–h
X = Cl; 10e–h
1e–h
2e–h
Oxidation by (TMEDA)PtI2Me2. a-Diimines are modest p-acceptor ligands and are
expected to be excellent at stabilizing PtII complexes. Tetramethylethylenediamine, on
the other hand, is a good s-donor and not a p-acceptor; therefore, tetramethyleth-
ylenediamine should be better at stabilizing PtIV than a-diimines. Nevertheless,
compelxes 1e ± h are oxidized cleanly by (TMEDA)PtI2Me2 to form the complexes 4e ±
h (Scheme 9).

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Helvetica Chimica Acta ± Vol. 84 (2001)
Scheme 9
I
Me
Me
R
R
Pt
N
N
Me
Pt
N
Me
R'
R'
N
I
R
R
R'
+
R'
1e–h
4e–h
+
I
CH2Cl2
Me
Me
Me2
N
Me2
N
Pt
I
Me
Pt
Me
N
N
Me2
Me2
It has been suggested that the Me groups of TMEDA have a significant steric effect
on the stability of PdIV compounds, as they appear to promote the dissociation of I
from (TMEDA)PdIMe3 [34]. In an attempt to probe the steric effects of the [NR2]
groups, (TMEDA)PtMe2 was treated with (TEEDA)PtI2Me2 (TEEDA ˆ tetraethyl-
ethylenediamine). Unfortunately, there is no reaction, likely a consequence of
excessive steric bulk that blocks approach of the two complexes. Attempts to prepare
[NH2CH2CH2NH2]PtMe2 and [NH2CH2CH2NH2]PtI2Me2 to further investigate the
importance of steric repulsion between the N-substituents and I ligands were
unsuccessful.
In contrast, (TMEDA)PtI2Me2 is incapable of oxidizing the chloro(methyl)
complexes 2a ± h (Scheme 10). The replacement of a Me by a Cl has resulted in a
complex that is more difficult to oxidize than the dimethyl complexes. Since a Cl group
is about the same size as a Me group, this is probably not a steric effect; rather, the
reduction potentials of complexes 2e ± h are likely greater than the reduction potentials
of the dimethyl complexes 1e ± h.
Scheme 10
I
Me
Pt
Me
R
Me2
N
CH2Cl2
+
N
Cl
Pt
I
no reaction
Me
R'
N
Me2
N
R
R'
2a–h
Oxidation Kinetics of Complex 1g. The rate of the oxidation of complex 1g by
(TMEDA)PtI2Me2 was determined (Scheme 11). With a large excess of PtIV, pseudo-
first-order rate constants (kobs) were obtained by fitting to a nonlinear least-squares
equation 40 ± 60 data points collected over 4 ± 6 half-lives. A typical graph of
absorbance vs. time for the reaction is shown in Fig. 3. The rates are slow (hours) for
the reaction at room temperature with no added halide. A summary of the kinetics data
appears in Table 3.

Helvetica Chimica Acta ± Vol. 84 (2001)
3255
Scheme 11
I
Me
H11C6
Me
H
11C6
Pt
I
N
Me
Pt
N
N
Me
N
C6H11
C6H11
CH2Cl2
4g
1g
+
+
298 K
kobs
I
Me
Me
Me2
N
Me2
N
Pt
I
Me
Pt
Me
N
N
Me2
Me2
>10x excess
Fig. 3. Decay of the MLCT band in (CyDABH)PtMe2 (1g) during reaction with (TMEDA)PtI2Me2
The dependence on [PtIV] for the reaction was determined by varying the
concentration of (TMEDA)PtI2Me2. The plot of kobs vs. [PtIV] is shown in Fig. 4. The
reaction was carried out at constant ionic strength by the addition of 50 equivalents of
tetrabutylammonium tetrafluoroborate ((TBA)BF4). A first-order dependence in
[PtIV] is observed for the reaction.
Addition of I is found to accelerate the oxidation of complex 1g. The dependence
on I was determined by varying [I ] while keeping the ionic strength of the solution

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Helvetica Chimica Acta ± Vol. 84 (2001)
Table 3. Kinetic Data for the Oxidation of Complex 1g
[1g]/mma)
[(TMEDA)PtI2Me2]/mma)
[I ]/mma)
T/K
kobs/s
)
1b
0.898
8.98
18.0
26.9
35.9
44.9
8.98
44.9
296.15
0.00366
0.00782
0.0126
0.0166
0.0231
0.00366
0.00309
0.00230
0.00170
0.000186
0.00537
0.00772
0.0127
0.898
44.9
35.9
26.9
18.0
0
296.15
0.898c)
8.98c)
44.9c)
288.15
298.15
308.15
318.15
0.0180
b
a) In CH2Cl2. ) A542 ˆ m1 ‡ (m1 m2) exp( kobs(t)). c) In CH2Cl2/THF 2 : 3.
Fig. 4. Plot of kobs vs. [(TMEDA)PtI2Me2]
constant with (TBA)BF4. A first-order dependence on [I ] was determined by plotting
kobs vs. [I ] (Fig. 5).
Thus, the oxidation of (CyDABH)PtMe2 by (TMEDA)PtI2Me2 exhibits character-
istic third-order kinetics, first-order each in PtII, PtIV, and iodide (Eqn. 2):
d‰ꢂCyDABH†PtMe2Š
ˆ k[(CyDABH)PtMe2][(TMEDA)PtI2Me2][I ]
(2)
dt

Helvetica Chimica Acta ± Vol. 84 (2001)
3257
Fig. 5. Plot of kobs vs. [I ]
The mechanism for the oxidation of complex 1g by (TMEDA)PtI2Me2 is shown in
Scheme 12. The initial step involves a rapidly established equilibrium (K) with I ,
which lies far to the left, to form a five-coordinate PtII complex. The bimolecular second
step (k1) is assumed to be rate-determining and results in the formation of an iodide-
bridged intermediate, which then undergoes a rapid inner-sphere electron transfer
followed by dissociation to give the products. Both steric and inductive electronic
effects are expected to be important. The former is a direct consequence of the
geometry of the bridged complex; bulky in-plane ligands are expected to hinder the
bridge formation. If the ligands are bulky enough to prevent the formation of this
bridge, no oxidation can occur.
The activation parameters were determined by plotting ln (kobs/T) vs. 1/T for Tover
1
a 308 range (Fig. 6). The activation parameters (DH=ˆ 6.9 kcal ´ mol , DS=ˆ 45 e.u.)
show that the reaction is characterized by negative entropies of activation and
relatively small enthalpies of activation. This behavior is characteristic of an inner-
sphere process involving a bridged transition state [35], in agreement with the
proposed mechanism and within the range of the activation parameters reported for the
ligand exchange at PtIV catalyzed by PtII [36].
Electrochemistry. Transition-metal complexes containing a-diimine ligands typi-
cally undergo ligand-centered reductions to form species that may be formulated as
metal complexes of a-diimine anion radicals. Electrochemical studies of the new
complexes were carried out in MeCN/0.1m tetrabutylammonium hexafluorophosphate
((TBA)PF6) in order to minimize interaction of the coordinatively unsaturated species

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Helvetica Chimica Acta ± Vol. 84 (2001)
Scheme 12
Me
Me
H
11C6
H11C6
K
+ I–
Pt
N
Me
Pt
I
N
Me
N
N
C6H11
C6H11
1g
I
Me
Me
Me2
N
I
Pt
I
Me
Me
Me
Me
H11C6
Me2
N
k1
N
Pt
I
Pt
I
N
Me
Me
+
Me2
H11C6
k-1
N
N
Pt
N
Me2
C6H11
N
I
C6H11
fast
– I–
I
Pt
I
Me
Pt
Me
H11C6
Me2
N
+
N
Me
Me
N
N
Me2
C6H11
4g
with the electrolyte. Fig. 7 illustrates a typical cyclic voltammogram, in which there is a
reversible one-electron reductive wave, but oxidation gives highly irreversible one-
electron waves with strongly solvent-dependent peak potentials, suggesting rapid
reaction of the resulting PtIII species. The oxidations remain irreversible even at scan
rates as high as 300 V/s. The electrochemical data of complexes supported with a-
diimine 2,6-(CHMe2)2PhDABMe (d) are summarized in Table 4.
The single-electron oxidation of PtII to PtIII was probed chemically. Oxidation of
(pen)PtMe2 by ferrocenium hexafluorophosphate results in the formation of a PtIII
species followed by rapid disproportionation to cationic PtII and PtIV Me species
Table 4. Comparison of the Irreversible Oxidation Potentials for Pt Complexes Supported with a-Diimine (2,6-
(CHMe2)2PhDABMe
)
Complex
PtII/PtIIIa)b)
1 e reda)
(2,6-(CHMe2)2PhDABMe)PtMe2(1d)
(2,6-(CHMe2)2PhDABMe)PtClMe (2d)
(2,6-(CHMe2)2PhDABMe)PtCl2
611
1833
1827
1821
1825
1140
1560
> 2500
‡
[(2,6-(CHMe2)2PhDABMe)PtMe(MeCN)]
a
) All values in mV and referenced to the Fc/Fc couple. b) Irreversible.
‡

Helvetica Chimica Acta ± Vol. 84 (2001)
3259
Fig. 6. Plot of ln (kobs/T) vs. 1/T
‡
Fig. 7. Cyclic voltammogram of (2,6-Me2PhDABMe)PtMe2 (1d; in MeCN/0.1m Bu4N PF6 at 10 V/s, internally
‡
referenced to Fc/Fc couple)
(Scheme 13). Ferrocenium hexafluorophosphate is not a strong enough oxidant to
oxidize complexes 1a ± h, but bulk electrolysis of MeCN solutions of 1a ± h leads to the
formation of the cationic PtII and PtIV Me complexes (Scheme 14). This reactivity
pattern was previously established for (RDABR')PtMe2 by Tilset and co-workers [22].
X-Ray Crystallographic Structural Determination of Complexes 9b and 9g. The
molecular structures of complexes 9b and 9g were determined crystallographically, and

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Helvetica Chimica Acta ± Vol. 84 (2001)
Scheme 13
+
Me
Me
Pt
N
Me
N
Me
Pt
NCMe
+
MeCN
+ 2 [(C5H5)2Fe]+
N
Me
2
– 2 (C5H5)2Fe
+
Me
N
N
Pt
N
N
NCMe
=
N
N
N
Scheme 14
Me
Me
+
R
Pt
N
Me
R'
N
+
NCMe
R
Me
R
– 2 e–
R'
Pt
N
N
Me
2
MeCN
+
R'
Me
Me2
N
R
Pt
NCMe
R'
1a–h
N
Me2
Table 5 contains the experimental and crystallographic data. ORTEP Views of the
cations are shown in Figs. 8 and 9, and selected bond distances and angles are listed in
Table 6.
The molecular structure of complex 9b consists of discrete platinum cationic units of
‡
[C24H33ClN3Pt] , sitting at a general position, and the counterion, [PtCl6]2 , sitting at a
center of symmetry. The Pt-atom of the cation displays predominately octahedral
geometry. The N(1) Pt(1) N(2) angle is constrained to 75.38 as a consequence of the
a-diimine ligandꢁs two-C-atom bridge. The sum of the angles around the Pt-atom in the
[N2PtC2] plane is 359.98. The average Pt C bond length of 2.059 Š and Pt N bond
length of 2.21 Š are comparable to the bond lengths of similar complexes reported by
Tilset and co-workers [22] and others [37 ± 39]. The Pt MeCN bond distance is
noticeably shorter in complex 9b due to a smaller trans-influence exerted from the Cl
ligand relative to Me. The planes of the arene rings are rotated relative to the [N2PtC2]
plane by an average of 988 and are within 3.28 of being coplanar. This feature is similar
to other a-diimine Pt [40][41] and Pd [42][43] complexes, but is unlike the complex of
Tilset and co-workers, where the arene rings are oriented 81.88 from each other. The
hexachloroplatinate anion is unexceptional, and the structure exhibits no unusual
intermolecular contacts.

Helvetica Chimica Acta ± Vol. 84 (2001)
3261
Table 5. Crystal Data and Structure Refinement for Complexes 9b and 9g
9b
9g
Empirical formula
[C24H33ClN3Pt]2]PtCl6] ´ 2 MeCN
[C18H33ClN3Pt]2[PtCl6] ´ 2 MeCN)
T [K]
Formula weight [g mol
85
1678.06
85
1533.92
1
]
Unit-cell dimensions
a [Š]
b [Š]
c [Š]
a [8]
b [8]
g [8]
V [Š3]
Z
33.152(26)
9.561(4)
20.226(17)
9.609(4)
10.918(5)
13.468(5)
94.04(3)
105.34(3)
101.43(4)
1324.2(10)
1
113.54(6)
5877(6)
8
Crystal system
Space group
Monoclinic
C2/c
Triclinic
P1
Å
Data/Restraints/Parameters
Goodness-of-fit (obs. data)
Final R indices (obs. data)
R indices (all data)
5178/0/321
2.296
4631/0/268
1.357
R1 ˆ 0.0403, wR2 ˆ 0.0791
R1 ˆ 0.0272, wR2 ˆ 0.0520
R1 ˆ 0.0365, wR2 ˆ 0.0546
R1 ˆ 0.0508, wR2 ˆ 0.0804
Fig. 8. Labeled ORTEP-3 [51] view of the 9b cation. Thermal ellipsoids drawn at 60% probability; H-atoms
omitted for clarity.
The molecular structure of complex 9g is similar to that of 9b. The asymmetric unit
‡
consists of the discrete Pt cation [C18H33ClN3Pt] , sitting at a general position, and a
2
[PtCl6] anion, sitting at a center of symmetry. The geometry of the Pt cation is
essentially octahedral with the (N1) Pt N(2) angle restricted to 76.18. The bond
distances and angles are very close to those for complex 9b. The cyclohexyl groups are
oriented pseudo orthogonal to each other, similar to the related complex (Cy-
DABH)PtMe4 [37]. The cyclohexyl groups, being less sterically demanding than the 2,6-

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Helvetica Chimica Acta ± Vol. 84 (2001)
Fig. 9. Labeled ORTEP-3 [51] view of the 9g cation. Thermal ellipsoids drawn at 60% probability; H-atoms
omitted for clarity.
Table 6. Selected Bond Lengths [Š] and Angles [8]
9b
9g
Pt C(1)
Pt C(2)
Pt N(1)
Pt N(2)
Pt Cl(1)
Pt N(3)
N(1) C(3)
N(2) C(4)
C(3) C(4)
2.061(7)
2.057(7)
2.196(6)
2.221(6)
2.290(2)
1.982(7)
1.278(9)
1.281(9)
1.521(10)
1.453(9)
1.462(9)
2.051(6)
2.057(5)
2.176(4)
2.172(4)
2.2854(17)
1.976(5)
1.272(7)
1.268(6)
1.464(7)
1.469(7)
1.479(7)
N(1) C(7)
N(2) C(13)
N(1) Pt N(2)
N(1) Pt C(1)
C(1) Pt C(2)
N(2) Pt C(2)
Cl(1) Pt N(3)
Pt N(1) C(7)
Pt N(2) C(13)
C(1) Pt N(2)
C(1) Pt N(1)
75.3(2)
98.4(3)
87.1(3)
76.14(16)
100.2(2)
85.2(2)
99.2(3)
98.5(2)
173.46(17)
123.6(4)
124.4(3)
176.26(19)
174.6(2)
178.28(14)
125.2(3)
126.3(4)
173.7(3)
174.5(3)
dimethylphenyl groups of complex 9b, can rotate freely into the [N2PtC2] plane to
reduce steric congestion, while, in complex 9b, the Ph groups are both locked in
positions orthogonal to the [N2PtC2] plane. The hexachloroplatinate anion exhibits no
unusual intermolecular contacts.
Conclusions. ± Platinum(II) alkyl complexes supported by a-diimine ligands,
(RDABR')PtMe2 and (RDABR')PtClMe, have been prepared, and the relative ease of
oxidation has been investigated. Oxidation by halogens to the corresponding trans-

Helvetica Chimica Acta ± Vol. 84 (2001)
3263
dihalo PtIV complexes proceeds rapidly for all complexes examined, whereas, with N-
chlorosuccinimide, the chloro/solvento PtIV complexes are generated. With hexachlor-
oplatinate, only the less-crowded members of the series are oxidized. Interestingly, and
counter to our expectations based on ligand electronic effects, the less-crowded
(RDABR')PtMe2 complexes react, essentially completely, with (TMEDA)PtI2Me2 to
form (RDABR')PtI2Me2 and (TMEDA)PtMe2. Unfavorable steric interactions be-
tween the TMEDA Me groups and the iodide ligands for (TMEDA)PtI2Me2 appear to
be responsible, favoring the less-crowded PtII and PtIV products. Studies of the
mechanism for this reaction with (CyDABH)PtMe2 indicate a two-electron inner-
sphere electron transfer with the usual third-order kinetics, consistent with generation
of the reactive iodide-bridged {(TMEDA)Me2IPt ´´´ I ´´´ Pt(CyDABH)Me2I}-activated
complex. Attempts to determine the oxidation potentials of the PtII complexes
electrochemically yielded only irreversible one-electron oxidations, so that
thermodynamic potentials for the PtII/PtIV couples could not be obtained via
electrochemistry. However, a qualitative ordering of oxidation potentials has been
determined for the series (RDABR')PtMe2 < (RDABR')PtMeCl < (RDABR')PtCl2 ꢀ
‡
(RDABR')PtMe(solv)] . Oxidation by one-electron processes in MeCN solution
results in a rapid subsequent disproportionation to PtII Me and PtIV Me3 trimethyl
cations with MeCN occupying the fourth or sixth coordination sites. Single-crystal X-
‡
ray structure determinations for [(2,6-Me2PhDABMe)PtMe3(MeCN)] [PtCl6]0.5(-
‡
MeCN) and [(CyDABH)PtMe3(MeCN)] [PtCl6]0.5(MeCN) have been determined.
Experimental Part
General. All experiments were performed under dry Ar with standard Schlenk techniques unless otherwise
noted. THF, petroleum ether (p.e.), Et2O, and benzene were distilled from Na/benzophenone ketyl under N2.
Toluene was distilled from molten Na, MeOH from Mg turnings, MeCN and CH2Cl2 from CaH2 under Ar and
stored over activated 4 Š molecular sieves. K2PtCl4 and K2PtCl6 were obtained from Pressure Chemical. All
other reagents were obtained from Aldrich and used as received except as noted. N,N,N',N'-Tetramethyleth-
ylenediamine (TMEDA), 2,6-diisopropylaniline, and 2,6-dimethylaniline were distilled prior to use. a-Diimines
[44][45], Pt(SMe2)2MeCl, and [Me2Pt(SMe2)]2 [46] were synthesized according to lit. procedures. 1H-
(500.168 MHz), 13C- (125.781 MHz), and 195Pt- (107.25 MHz) NMR spectra were recorded in CD2Cl2, C6D6, or
(D6)acetone at approximately 208 on a Varian Unity-500 spectrometer. The chemical shifts (d) in ppm were
referenced to internal CDHCl2 (5.32), C6D5H (7.15) or CD3COCD2H (2.04 for 1H) and to CD2Cl2 (54.0), C6D6,
(128.0) or CD3COCD3 (29.9) for 13C; 195Pt signals were referenced externally to K2PtCl4
( 1935); coupling
constants (J) in Hz. Electrochemical experiments were carried out on a BAS100 instrument with (TBA)PF6
electrolyte and a Pt electrode. Elemental analyses were performed by Mr. Fenton Harvey at the California
Institute of Technology or by Midwest Microlab (Indianapolis, IN).
Kinetics. Stock solns. of the reactants were prepared by weighing samples and dissolving in CH2Cl2 or
CH2Cl2/THF 2 :3 as indicated in Table 3. A constant ionic strength of 44.9 mm was maintained by the addition
Bu4NI and/or Bu4NBF4. The reactions were started by mixing appropriate volumes of freshly prepared stock
solns. of the reactants in a 1 cm quartz cell maintained in the thermostat-controlled cell compartment of a
Hewlett-Packard HP8452A diode-array spectrophotometer. The progress of the reaction was monitored at
appropriate time intervals by recording the absorbance at 542 nm. Under kinetics conditions, the starting [PtII]
was always < 0.9 mm and at least 10 Â lower than the [PtIV]. It was found that the reactions obey a pseudo-first-
order rate law over the entire course of the reaction. Pseudo-first-order rate constants, kobs, were evaluated by
fitting a nonlinear least-squares equation to the plots of (At A1) against time, where At and A1 are the
absorbance of the reacting mixture at time t and at the end of the reaction, resp. The activation parameters were
calculated from the gradient and intercept of the plot of ln (kobs/T) vs. 1/T over a 308 temp. range.
General Procedure for the Synthesis of (RDABR')PtMe2 (1a ± h). [Me2Pt(SMe2)]2 (250 mg, 0.435 mmol) was
dissolved in toluene (20 ml). a-Diimine a ± h (0.870 mmol) was added as a solid. The soln. became deep purple

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Helvetica Chimica Acta ± Vol. 84 (2001)
or deep green (depending on the a-diimine) after a few minutes. The mixture was stirred overnight at r.t. The
solvent was reduced, and the resulting product was precipitated by the addn. of p.e. Products were collected by
filtration in 60% ± 95% yields.
General Procedure for the Synthesis of (RDABR')PtCl (2a ± h). Pt(SMe2)2ClMe (250 mg, 0.676 mmol) was
dissolved in CH2Cl2 (10 ml). a-Diimine a ± h (0.676 mmol) was added as a solid. The soln. turned reddish purple
after a few min. The mixture was stirred 4 d at r.t. The solvent was reduced, and p.e. was added to precipitate the
product. The product was collected by filtration and washed with cold p.e. Yields ranged from 70 ± 95%.
Alternative Procedure for the Synthesis of 2a ± h. Complex 1a (100 mg, 0.204 mmol) was dissolved in
toluene, and HCl in Et2O (0.1m, 2.20 ml, 0.22 mmol) was added via syringe. The soln. became cloudy with a
yellow precipitate after a few min. The mixture was stirred overnight at r.t., the solvent was reduced, and the
resulting product was collected by filtration and washed with cold p.e. Yields ranged from 75 ± 90%.
Typical Procedure for [(RDABR')PtCl2Me2 (3a). Complex 1a (50 mg, 0.102 mmol) was dissolved in CH2Cl2
(15 ml). Gaseous Cl2, filtered through activated basic alumina, was introduced into the reaction. The soln.
became light yellow almost immediately. The solvent was reduced and the resulting product was precipitated by
the addn. of p.e. Products were collected by filtration in 80% ± 95% yields.
Typical Procedure for [(RDABR')PtI2Me2 (4g). Complex 1g (50 mg, 0.11 mmol) was dissolved in CH2Cl2
(10 ml). Excess I2 was added as a solid. The soln. became light yellow after a few min, then purple as the excess I2
dissolved. The mixture was stirred 1 h at r.t. The excess I2 was reduced by addn. of a sat. aq. soln. of Na2S2O3
(10 ml). The org. layer was separated and the aq. layer extracted with CH2Cl2 (3 Â 10 ml). The solvent was dried
over anh. Na2SO4, reduced in volume, and the resulting product was precipitated by the addn. of p.e. Products
were collected by filtration in 80% ± 95% yields.
Typical Procedure for [(RDABR')PtCl(OMe)Me2 (7a). Complex 1a (50 mg, 0.102 mmol) was dissolved in
MeOH (15 ml). N-Chlorosuccinimide (15 mg, 0.11 mmol) was added as a solid. The soln. turned pale yellow
after a few min. The mixture was stirred 3 h at r.t. The solvent was reduced and the resulting product was
precipitated by the addn. of p.e. Products were collected by filtration in 60% ± 95% yields.
Typical Procedure for [(RDABR')PtClMe2(MeCN)]2(PtCl6) (9g). Complex 1g (50 mg, 0.11 mmol) was
dissolved in MeCN (15 ml). K2PtCl6 (121 mg, 0.25 mmol) was added as a solid. The soln. turned pale yellow and
cloudy after ca. 1 h. The mixture was stirred overnight at r.t. The solvent was replaced with toluene and filtered
through Celite. The resulting product was recrystallized from a mixture of toluene and p.e. Products were
collected by filtration in 42% ± 60% yields.
Data of (2,6-Me2DABH)PtMe2 (1a). Deep green solid. Yield 362 mg (0.74 mmol, 85%). 1H-NMR (C6D6):
9.40 (s, 2 H CˆN, 3J(Pt,H) ˆ 33); 7.20 (m, 6 arom. H); 2.24 (s, 12 H, PhMe2); 1.4 (s, PtMe2, 2J(Pt,H) ˆ 87).
13C{1H}-NMR (CD2Cl2): 163.5; 149.0; 129.7; 127.1; 126.9; 17.7; 13.9 (1J(Pt,C) ˆ 802). 195Pt{1H]-NMR (CD2Cl2):
1452. Anal. calc. for C20H26N2Pt: C 49.07, H 5.35, N 5.72; found: C 49.49, H 5.17, N 5.56.
Data of (2,6-Me2PhDABMe)PtMe2 (1b). Deep purple solid. Yield 356 mg (0.69 mmol, 79%). 1H-NMR
(CD2Cl2): 7.20 (m, 4 arom. H); 7.13 (m, 2 arom. H); 2.16 (s, 12 H, PhMe2); 1.24 (s, 2 Me CˆN); 0.79 (s, PtMe2,
2J(Pt,H) ˆ 87). 13C{1H}-NMR (CD2Cl2): 170.6; 146.2; 129.2; 128.2; 126.3; 20.2; 17.5; 14.9 (1J(Pt,C) ˆ 799).
195Pt{1H}-NMR (C6D6) 1079. Anal. calc. for C22H30N2Pt: C 51.05, H 5.84, N 5.41; found: C 50.88, H 5.55,
N 5.38.
Data of (2,6-(CHMe2)2PhDABH)PtMe2 (1c). Deep green solid. Yield 366 mg (0.61 mmol, 70%). 1H-NMR
(CD2Cl2): 9.40 (s, 3J(Pt,H) ˆ 32, 2 H CˆN); 7.32 (m, 6 arom. H); 3.24 (septet, 4 CHMe2); 1.52 (s, 2J(Pt,H) ˆ 86,
PtMe2); 1.30 (d, 12 H, CHMe2); 1.13 (d, 12 H, CHMe2). 13C{1H}-NMR (CD2Cl2): 163.4; 146.5; 140.4; 127.7;
123.4; 28.1; 24.9; 23.1; 13.7 (1J(Pt,C) ˆ 805). 195Pt{1H}-NMR (CD2Cl2): 1344. Anal. calc. for C28H42N2Pt:
C 55.89, H 7.04, N 4.66; found: C 55.64, H 6.64, N 4.50.
Data of (2,6-(CHMe2)2PhDABMe)PtMe2 (1d). Deep purple solid. Yield 329 mg (0.52 mmol, 0.60%).
1H-NMR (C6D6): 7.19 (m, 6 arom. H); 3.18 (septet, 4 CHMe2); 1.80 (s, 2J(Pt,H) ˆ 86, PtMe2); 1.36 (d, 12 H,
CHMe); 1.01 (d, 12 H, CHMe); 0.50 (s, 2 Me CˆN). 13C{1H}-NMR (C6D6): 169.8; 144.3; 139.6; 128.2; 124.0;
28.4; 24.1; 24.0; 21.3; 12.5 (1J(Pt,C) ˆ 811 Hz). 195Pt{1H}-NMR (C6D6): 1309. Anal. calc. for C30H46N2Pt:
C 57.21, H 7.36, N 4.45; found: C 56.99, H 6.85, N 4.36.
Data of (3,5-Me2PhDABMe)PtMe2 (1e). Purple solid (428 mg, 0.83 mmol, 95%). 1H-NMR (C6D6): 6.92
2
(s, 2 arom. H); 6.61 (s, 4 arom. H); 2.36 (s, 12 H, PhMe2), 1.43 (s, 2 Me CˆN); 0.90 (s, J(Pt H)ˆ 87, PtMe2).
13C{1H}-NMR (CD2Cl2): 171.0; 148.2; 139.0; 128.0; 119.8; 21.7; 21.2; 13.4 (1J(Pt,C) unresolved). 195Pt{1H}-
NMR (CD2Cl2): 1435. Anal. calc. for C22H30N2Pt: C 51.05, H 5.84, N 5.41; found: C 50.88, H 5.87, N 5.25.
Data of (CyDABH)PtMe2 (1g). Deep purple solid. Yield 322 mg (0.72 mmol, 83%). 1H-NMR (C6D6): 8.17
(s, 3J(Pt,H) ˆ 34, 2 CH); 4.24 (m, 2 H CˆN); 2.37 (s, 2J(Pt,H) ˆ 85, PtMe2); 2.08 (m, 2 CH2); 1.55 (m, 2 CH2);
1.46 (m, CH2); 1.23 (m, 2 CH2); 1.03 (m, 2 CH2); 0.91 (m, CH2). 13C{1H}-NMR (C6D6): 157.6; 65.4; 34.3; 26.4;

Helvetica Chimica Acta ± Vol. 84 (2001)
3265
26.1; 12.7 (1J(Pt,C) ˆ 800). 195Pt{1H}-NMR (C6D6): 1304. Anal. calc. for C16H30N2Pt: C 43.14, H 6.79, N 6.29;
found: C 43.06, H 6.24, N 6.29.
1
Data of (2,6-Me2PhDABH)PtClMe (2a): Purple solid. Yield 296 mg (0.58 mmol, 86%). H-NMR (C6D6):
9.38 (s, 3J(Pt,H) ˆ 107, H CˆN); 8.74 (s, 3J(Pt,H) ˆ 36, H CˆN); 7.24 (s, 3 arom. H); 7.19 (s, 3 arom. H); 2.30
(s, PhMe2); 2.27 (s, PhMe2); 1.20 (s, J(Pt,H) ˆ 81, PtMe2). 13C{1H}-NMR (CD2Cl2): 165.5; 164.5; 148.2; 147.7;
2
131.0; 129.5; 128.5; 128.4; 128.2; 127.7; 18.3; 17.5; 11.2 (1J(Pt,C) ˆ 704).195Pt{1H}-NMR (CD2Cl2): 1320.
Anal. calc. for C19H25ClN2Pt: C 44.75, H 4.55, N 5.49; found: C 44.21, H 4.20, N 5.22.
Data of (2,6-Me2PhDABMe)PtClMe (2b). Purple solid. Yield 345 mg (0.64 mmol, 95%). 1H-NMR (C6D6):
7.25 ± 7.14 (m, 6 arom. H); 2.22 (s, PhMe2); 2.20 (s, PhMe2); 1.66 (s, Me CˆN); 1.25 (s, Me CˆN); 0.72 (s,
2J(Pt,H) ˆ 79, PtMe). Anal. calc. for C19H25ClN2Pt: C 46.88, H 5.06, N 5.21; found: C 46.88, H 4.69, N 5.11.
Data of (2,6-(CHMe2)2PhDABH)PtClMe (2c). Purple solid. Yield 345 mg (0.55 mmol, 82%). 1H-NMR
(CD2Cl2): 9.40 (s, 3J(Pt,H) ˆ 105, H CˆN); 8.72 (s, 3J(Pt,H) ˆ 35, H CˆN); 7.35 (m, 4 arom. H); 7.28
(m, 2 arom. H); 3.22 (m, 4 CHMe2); 1.35 (d, 6 H, CHMe); 1.34 (d, 6 H, CHMe); 1.30 (s, 2J(Pt,H) ˆ 84, PtMe);
1.16 (d, 6 H, CHMe); 1.16 (d, 6 H, CHMe). 13C{1H}-NMR (CD2Cl2): 165.1; 164.1; 145.7; 144.9; 141.5; 140.1;
129.2; 128.4; 124.0; 123.5; 28.8; 28.2; 24.9; 24.6; 23.4; 23.0; 10.6 (1J(Pt,C) ˆ 722). 195Pt{1H}-NMR (CD2Cl2):
1199. Anal. calc. for C27H39ClN2Pt: C 52.12, H 6.32, N 4.50; found: C 52.19, H 6.19, N 4.26.
Data of (2,6-(CHMe2)2PhDABMe)PtClMe (2d). Orange-red solid. Yield 308 mg (0.47 mmol, 70%).
1H-NMR (C6D6): 7.34 (m, 3 arom. H); 7.29 (m, 3 arom. H); 3.03 (septet, 2 CHMe2); 3.02 (septet, 2 CHMe2); 1.69
(s, Me CˆN); 1.35 (d, 6 H, CHMe); 1.33 (d, 6 H, CHMe); 1.29 (s, Me CˆN); 1.16 (d, 6 H, CHMe); 1.15
2
(d, 6 H, CHMe); 0.87 (s, J(Pt,H) ˆ 79, PtMe). 13C{1H}-NMR (C6D6): 174.4; 172.5; 142.6; 140.5; 139.6; 128.7;
127.8; 124.4; 123.7; 28.9; 28.3; 24.1; 24.0; 23.9; 23.6; 22.3; 20.5; 11.7 (1J(Pt,C) ˆ 730). 195Pt{1H}-NMR (C6D6):
1403. Anal. calc. for C29H45ClN2Pt: C 53.57, H 6.67, N 4.31; found: C 53.19, H 6.53, N 4.15.
Data of (3,5-Me2PhDABMe)PtClMe (2e). Purple solid. Yield 335 mg (0.62 mmol, 92%). 1H-NMR (C6D6):
6.98 (s, 1 arom. H); 6.97 (s, 1 arom. H); 6.70 (s, 2 arom. H); 6.64 (s, 2 arom. H); 2.38 (s, PhMe2); 2.38
(s, PhMe2); 1.83 (s, Me CˆN); 1.41 (s, Me CˆN); 0.87 (s, 2J(Pt,H) ˆ 80, PtMe). Anal. calc. for C21H27ClN2Pt:
C 46.88, H 5.06, N 5.21; found: C 46.82, H 4.67, N 4.92.
Data of 3,5-(CF3)2 PhDABMe)PtClMe (2f). Purple solid. Yield 377 mg (0.50 mmol, 74%). 1H-NMR
(C6D6): 7.96 (s, 1 arom. H); 7.92 (s, 1 arom. H); 7.65 (s, 2 arom. H); 7.61 (s, 2 arom. H); 1.88 (s, Me CˆN); 1.33
(s, Me CˆN); 0.98 (s, 2J(Pt,H) ˆ 80, PtMe). Anal. calc. for C21H27ClN2Pt: C 33.46, H 2.01, N 3.72; found:
C 33.15, H 1.75, N 3.44.
Data of (CyDABH)PtClMe (2g). Yellow solid. Yield 271 mg (0.58 mmol, 86%). 1H-NMR (CD2Cl2): 8.89
(s, CH, 3J(Pt,H) ˆ 107); 8.45 (s, CH, 3J(Pt,H) ˆ 38); 4.34 (m, H CˆN); 4.21 (m, H CˆN); 2.21 (m, 4 H,
2
CH2); 1.87 (m, 4 H, CH2); 1.75 (m, 2 H, CH2); 1.45 (m, 6 H, CH2); 1.21 (m, 4 H, CH2); 1.34 (s, J(Pt,H) ˆ 79,
PtMe). 13C{1H}-NMR (CD2Cl2): 161.6; 159.2; 67.1; 65.9; 35.0; 33.7; 26.2; 26.1; 26.1; 26.0; 13.4 (1J(Pt,H)
unresolved). 195Pt{1H}-NMR (CD2Cl2): 1111. Anal. calc. for C15H27ClN2Pt: C 38.67, H 5.84, N 6.01; found:
C 38.36, H 5.74, N 5.95.
1
Data of (CyDABMe)PtClMe (2h). Yellow solid. Yield 294 mg (0.59 mmol, 88%). H-NMR (CD2Cl2): 4.37
(m, H CˆN); 4.14 (m, H CˆN); 2.86 (m, CH2); 2.03 (m, CH2); 1.96 (s, Me CˆN); 1.84 (s, Me CˆN); 1.84
2
(m,CH2); 1.67 (m, CH2); 1.54 (m, 2 CH2); 1.42 ± 1.22 (m, 4 CH2); 1.18 (s, J(Pt,H) ˆ 77, PtMe). 13C{1H}-NMR
(CD2Cl2): 174.9; 171.5; 67.8; 66.1; 30.6; 30.2; 26.0; 25.8; 25.7; 25.3; 22.7; 18.8; 12.4 (1J(Pt,C) ˆ 717). 195Pt{1H}-
NMR (CD2Cl2): 1225. Anal. calc. for C17H31ClN2Pt: C 41.33, H 6.33, N 5.67; found: C 41.10, H 6.25, N 5.22.
Data of (CyDABH)PtI2Me2 (4g). Orange-yellow solid. Yield 62 mg (0.088 mmol, 80%). 1H-NMR (CD2Cl2):
8.54 (s, 3J(Pt,H) ˆ 32, 2 CH); 4.13 (m, 2 H CˆN); 2.31 (m, 2 CH2); 2.16 (s, 2J(Pt,H) ˆ 85, PtMe2); 1.90
(m, 2 CH2); 1.74 (m, CH2); 1.45 (m, 4 CH2); 1.22 (m, CH2). 13C{1H}-NMR (CD2Cl2): 161.7; 66.6; 34.9; 26.1; 26.0;
13.9 (1J(Pt,C) ˆ 506). 195Pt{1H}-NMR (CD2Cl2): 1150. Anal. calc. for C16H30I2N2Pt: C 27.48, H 4.32, N 4.01;
found: C 27.01, H 4.27, N 3.73.
Data of (CyDABH)PtICl(OMe)Me2 (7g). Yellow solid. Yield 50 mg (0.10 mmol, 95%). 1H-NMR (CD2Cl2):
8.61 (s, 3J(Pt,H) ˆ 26, 2 CH); 4.05 (m, 2 H CˆN); 2.76 (m, 3J(Pt,H) ˆ 61, MeO); 2.26 (m, CH2); 2.10
(m, CH2); 1.90 (m, 2 CH2); 1.74 (m, CH2); 1.61 (s, 2J(Pt,H) ˆ 72, PtMe2); 1.45 (m, 3 CH2); 1.33 (m, CH2); 1.22
(m, CH2). 13C{1H}-NMR (CD2Cl2): 160.8; 65.4; 33.8; 32.9; 26.0; 25.9; 0.98 (1J(Pt,C) ˆ 639). 195Pt{1H}-NMR
(CD2Cl2): 1206. Anal. calc. for C17H33I2N2OPt: C 39.88, H 6.50, N 5.74; found: C 40.31, H 6.40, N 5.84.
‡
Data of [(CyDABH)PtClMe2MeCN)] 2[PtCl6]2 (9g). Yellow solid. Yield 96 mg (0.066 mmol, 60%).
3
1H-NMR (CD2Cl2): 9.55 (s, J(Pt,H) ˆ 29, CH); 3.90 (m, 2 H CˆN); 2.71 (m, MeCN); 2.17 (m, 2 CH2); 1.93
(m, 3 CH2); 1.76 (s, 2J(Pt,H) obscured, PtMe2); 1.74 (m, CH2); 1.43 (m, 2 CH2); 1.28 (m, 2 CH2). 13C{1H}-NMR
(CD2Cl2): 166.5; 66.9; 32.7; 32.7; 26.0; 25.9; 25.9; 25.8; 6.5;
C36H70Cl8N6Pt3: C 29.70, H 4.85, N 5.77; found: C 29.52, H 4.44, N 4.41.
0.32 (1J(Pt,C) ˆ 488). Anal. calc. for

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Helvetica Chimica Acta ± Vol. 84 (2001)
Data of (TMEDA)PtI2Me2. Yellow solid. Yield (52 mg, 0.088 mmol, 80%). 1H-NMR (CD2Cl2): 3.10 (s,
3J(Pt,H) ˆ 15, 12 H, NMe2); 2.84 (s, 3J(Pt,H) ˆ 7.5, 2 NCH2); 2.40 (s, 2J(Pt,H) ˆ 73, PtMe2). 13C{1H}-NMR
(CD2Cl2): 62.2; 54.0; 19.8 (1J(Pt,C) ˆ 493). 195Pt{1H}-NMR (CD2Cl2): 1559. Anal. calc. for C8H22I2N2Pt:
C 16.14, H 3.73, N 4.71; found: C 16.20, H 3.82, N 4.67.
X-Ray Crystallographic Analysis. Data were collected on an Enraf-Nonius CAD-4 diffractometer with the
CAD-4 software package [47] and graphite monochromated MoKa radiation at 85 K. Table 5 summarizes the
crystallographic data1). The data processing, solution and refinement were done with SHELXS-93 [48] and
SHELXL-97 [49] programs.
A suitable crystal of complex 9b was grown from a sat. soln. of MeCN containing excess K2PtCl6. The cell
constants were obtained by centering 25 reflections (15.08 < 2q < 24.68). The Laue symmetry of 2/m was
determined by merging symmetry-equivalent positions. The data were collected in the q range of 1.38 to 25.08
(
39 ꢃ h ꢃ 36, 11 ꢃ k ꢃ 11, 24 ꢃ 1 ꢃ 24) in the w scan mode. Three standard reflections were measured
every 60 min and showed negligible decay of the crystal. No attempt was made to locate the H-atoms. For space
group C2/c, there are 8 general positions, i.e., 8 molecules in the unit cell. The unit-cell contains 4 molecules of
PtCl6, each sitting on a special position. Therefore, the list of atomic coordinates contains only one-half of a
PtCl6. The monocation lies on a general position; the dianion on a center of symmetry. For each cation, there is a
disordered MeCN molecule. There are also 8 molecules of MeCN as a solvent of crystallization in the unit cell.
This molecule of MeCN is disordered between two sites (51.4 :48.6; constrained to a total population of 1) and
forms a V pointing toward the cation and sharing a common Me group. The Me groups are not exactly at the
same site, resulting in a fairly large displacement ellipsoid and shortened Me C bond lengths. The six half-H-
atoms were ignored; the Me C-atom was refined anisotropically and the other four partial solvent atoms were
refined isotropically. Therefore, the list of atomic coordinates contains the positions of two MeCN moieties.
During data collection, the crystal fell off. As a result, y-scans were not made and the crystal size was not
measured. No absorption correction could be made due to lack of y-scan data. Consequently, the residual
3
3
electron excursions are rather large (2.96 e Š at 1.13 Š from Pt(1), 2.89 e Š at 1.08 Š from Pt(1),
3
3
2.88 e Š at 1.09 Š from Pt(2), 2.06 e Š at 0.86 Š from Pt(1) as well as ca. 18 other peaks greater than
3
1 e Š in magnitude).
A suitable crystal of complex 9g was grown from a sat. soln. of MeCN/p.e. The cell constants were obtained
Å
by centering 25 reflections (27.28 < 2q < 28.08). The Laue symmetry of 1 was determined by merging symmetry-
equivalent positions. The data were collected in the q range of 1.58 to 25.08 ( 11 ꢃ h ꢃ 11, 12 ꢃ k ꢃ 12,
16 ꢃ l ꢃ 15) in the w scan mode. Three standard reflections were measured every 75 min and showed no decay
of the crystal. An empirical absorption correction was applied to the data based on the y scans data
(8.343 mm 1) with CRYM50. H-Atoms were refined anisotropically and all H-atoms placed at calculated
positions with Uiso at 120% of the Ueq of the attached atom. During least-squares refinement, the H-atoms on the
MeCN of solvation were restrained to geometric positions with the C H distances free to refine as a unit and
with the torsion angle free to optimize the fit to electron density. The asymmetric unit contains the principal
compound (C18H33ClN3Pt) solvated by one molecule of MeCN and half a molecule of PtCl6 (which sits on a
center of symmetry). Therefore, the unit-cell contents appear to be A2B with two MeCN solvates of
crystallization. In the final difference Fourier synthesis, the electron density fluctuates in the range of ‡ 1.26 to
3
0.90 e Š
.
This work was supported by the Department of Energy, Office of Industrial Technology, Akzo-Nobel
Petrochemicals, and BP.
1
)
Crystallographic data (excluding structure factors) for the structure(s) reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as deposition No. CCDC-111741 for 9b and
No. CCDC-102762 for 9g. Copies of the data can be obtained, free of charge, on application to the CCDC,
12 Union Road, Cambridge CB21EZ, UK (fax: ‡ 44(1223)336033; e-mail: deposit@ccdc.cam.ac.uk).
Structure factors are available from the authors via e-mail: xray@caltech.edu.

Helvetica Chimica Acta ± Vol. 84 (2001)
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Received July 10, 2001