Study of aerobic oxidation of phenyl PtII complexes (dpms)PtIIPh(L) (dpms = di(2-pyridyl)methanesulfonate; L = water, methanol, or aniline)

Article abstract of DOI:10.1139/V08-108

Oxidation of phenyl Pt^II complexes K[(dpms)Pt ^IIPh₂], 1, (dpms)Pt^IIPh(MeOH), 2, (dpms)Pt ^IIPh(OH₂), 3, and methyl Pt^II complex (dpms)Pt^IIMe(NH₂Ph), 6, with O₂ in aqueous or methanol solutions under ambient conditions leads to corresponding (dpms)Pt ^IVR(X)OH complexes (R = X = Ph, 7; R = Ph, X = OH, 8; R = Ph, X = OMe, 9; R = Me, X = NHPh; 11; dpms = di(2-pyridyl)methanesulfonate). Complexes 7-9 could be isolated in high yield. Complex 11 as well as its phenyl analogue (dpms)Pt^IVPh(NHPh)OH, 10 can be prepared in high yield by oxidation of corresponding (dpms)Pt^IIR(NH₂Ph) with H ₂O₂ in methanol. Phenyl Pt^II complexes (dpms)Pt^IIPh(HX) derived from HX = aniline and DMSO, 4 and 5, respectively, are inert toward O₂. The rate of oxidation of 1-5 with O₂ decreases in the order 1 > 3 ≈ 2 4, and 5 is unreactive. Methyl analogues are significantly more reactive compared with their phenyl counterparts. Proposed mechanism of oxidation with O₂ includes formation of anionic species (dpms)Pt^IIR(X)- responsible for reaction with dioxygen. Attempts at C-O and C-N reductive elimination from phenyl Pt^IV complexes 7-10 do not lead to phenyl derivatives PhX at 80-100 °C, consistent with the results of the DFT estimates of corresponding activation barriers, ΔG⁰ exceeding 28 kcal/mol.

Full text of DOI:10.1139/V08-108

110
Study of aerobic oxidation of phenyl PtII
complexes (dpms)PtIIPh(L) (dpms = di(2-
pyridyl)methanesulfonate; L = water, methanol, or
aniline)1
Julia R. Khusnutdinova, Peter Y. Zavalij, and Andrei N. Vedernikov
Abstract: Oxidation of phenyl PtII complexes K[(dpms)PtIIPh2], 1, (dpms)PtIIPh(MeOH), 2, (dpms)PtIIPh(OH2), 3, and
methyl PtII complex (dpms)PtIIMe(NH2Ph), 6, with O2 in aqueous or methanol solutions under ambient conditions leads
to corresponding (dpms)PtIVR(X)OH complexes (R = X = Ph, 7; R = Ph, X = OH, 8; R = Ph, X = OMe, 9; R = Me,
X = NHPh; 11; dpms = di(2-pyridyl)methanesulfonate). Complexes 7–9 could be isolated in high yield. Complex 11 as
well as its phenyl analogue (dpms)PtIVPh(NHPh)OH, 10 can be prepared in high yield by oxidation of corresponding
(dpms)PtIIR(NH2Ph) with H2O2 in methanol. Phenyl PtII complexes (dpms)PtIIPh(HX) derived from HX = aniline and
DMSO, 4 and 5, respectively, are inert toward O2. The rate of oxidation of 1–5 with O2 decreases in the order 1 > 3 ≈
2 » 4, and 5 is unreactive. Methyl analogues are significantly more reactive compared with their phenyl counterparts.
Proposed mechanism of oxidation with O2 includes formation of anionic species (dpms)PtIIR(X)– responsible for reac-
tion with dioxygen. Attempts at C–O and C–N reductive elimination from phenyl PtIV complexes 7–10 do not lead to
phenyl derivatives PhX at 80–100 °C, consistent with the results of the DFT estimates of corresponding activation bar-
riers, ∆G0 exceeding 28 kcal/mol.
Key words: platinum phenyl complexes, oxidation, dioxygen, aqueous solution, mechanism.
Résumé : L’oxydation des complexes phénylés du Pt(II), K[(dpms)PtIIPh2], 1, (dpms)PtIIPh(MeOH), 2,
(dpms)PtIIPh(OH2), 3, ainsi que du complexe méthylé du Pt(II), (dpms)PtIIMe(NH2Ph), 6, effectuée avec de l’oxygène
(O2), en solutions aqueuses ou méthanoliques et dans des conditions ambiantes, conduit à la formation des dérivés
(dpms)PtIVR(X)OH correspondants (R = X = Ph, 7; R = Ph, X = OH, 8; R = Ph, X = OMe, 9; R = Me, X = NPh, 11;
dpms = di(2-pyridyl)méthanesulfonate). Les complexes 7–9 ont été isolés avec des rendements élevés. Le complexe 11
ainsi que son analogue phénylé, (dpms)PtIVPh(NHPh)OH, 10, peuvent être préparés avec d’excellents rendements par
oxydation du (dpms)PtIIR(NH2Ph) avec du H2O2 dans le méthanol. Les complexes phénylés du Pt(II), (dpms)PtIIPh(HX),
dans lesquels X représente l’aniline (5) et le DMSO (6) sont inertes vis-à-vis de l’oxygène. Les vitesses d’oxydation
des produits 1-5 par l’oxygène diminuent dans l’ordre 1 > 3 . 2 > 4,5 (inerte). Les analogues méthylés sont sensible-
ment plus réactifs que leurs analogues phénylés. Le mécanisme d’oxydation proposé pour l’action de l’oxygène im-
plique la formation d’espèces anioniques (dpms)PtIIR(X)– qui seraient responsables de la réaction avec le dioxygène.
Les essais réalisés entre 80 et 100EC en vue d’effectuer une élimination réductrice C–O et C–N à partir des complexes
phénylés 7-10 n’ont pas conduit à la formation de dérivés phénylés, PhX; ces résultats sont en accord avec les résultats
d’évaluations, faites à l’aide de la théorie de la densité fonctionnelle (TDF), des barrières d’activation correspondantes,
)G0, qui seraient supérieures à 28 kcal/mol.
Mots-clés : complexes phénylés du platine, oxydation, dioxygène, solution aqueuse, mécanisme.
[Traduit par la Rédaction] Khusnutdinova et al. 120
Introduction
The use of oxygen as the terminal oxidant for selective
transition-metal-mediated functionalization of organic sub-
strates is an important practical goal (1). One of the possible
approaches to selective aerobic CH functionalization may in-
clude a sequence of the following transformations: (i) selec-
tive CH activation with a PtII complex, (ii) aerobic
conversion of resulting hydrocarbyl PtII to a PtIV complex,
and (iii) reductive elimination of organic products from the
PtIV intermediate (Scheme 1).
Received 27 March 2008. Accepted 14 May 2008. Published
on the NRC Research Press Web site at canjchem.nrc.ca on
19 August 2009.
Dedicated to Professor Richard Puddephatt.
J.R. Khusnutdinova, P.Y. Zavalij, and A.N. Vedernikov.2
Department of Chemistry and Biochemistry, University of
Maryland, College Park, MD 20742, USA.
1This article is part of a Special Issue dedicated to Professor
R. Puddephatt.
Recently, we reported facile aerobic dpms-enabled (2)
functionalization of alkyl PtII complexes in water leading to
methanol (3), methyl ether (4), and olefin oxides (5, 6).
2Corresponding author (e-mail: avederni@umd.edu).
Can. J. Chem. 87: 110–120 (2009)
doi:10.1139/V08-108
© 2008 NRC Canada

Khusnutdinova et al.
111
Scheme 1. Aerobic PtII-mediated CH functionalization.
Fig. 1. ORTEP plots (50% probability ellipsoids) for complexes
4 (a) and 11 (b).
Chart 1. dpms Ligand and derived phenyl PtII complexes.
These transformations include selective aerobic conversion
of PtII alkyls to isolable PtIV hydroxo alkyl complexes with
subsequent clean reductive C–O elimination of
a
functionalized alkane product from a PtIV center. A similar
reaction sequence might also be probed for aryl Pt deriva-
tives. Aromatic CH activation with PtII (7, 8) complexes is
well-established, but oxidation of monohydrocarbyl PtIIAr
and diaryl PtIIAr2 complexes with O2 was never observed.
Slow aerobic oxidation of a mixed alkyl aryl (tmeda)-
PtII(Ph)Me complex in methanol was reported but reaction
products were not characterized (9). In this work, we present
first examples of clean aerobic conversion of an anionic di-
phenyl PtII and several neutral monohydrocarbyl PtIIPh(HX)
complexes to corresponding PtIVPh derivatives (Chart 1), all
enabled by dpms ligand. We also report results of attempted
C(sp2)–O and C(sp2)–N reductive elimination from derived
PtIVPh species in water and (or) some organic solvents.
[1]
[2]
(dpms)PtIVPh2H + MeOH
→ (dpms)PtIIPh(MeOH) + PhH
(dpms)PtIIR(MeOH) + HX
→ (dpms)PtIIR(HX) + MeOH
For instance, dissolution of 2 in water or DMSO produces
quantitatively the corresponding aqua or DMSO adducts.
The aniline derivative 4 can be synthesized by reacting 2
with 17 equiv. of aniline in methanol solution. Complexes 2
and 4 were prepared in an analytically pure form.
1
All complexes 2–5 were characterized by H NMR spec-
troscopy and electrospray ionization mass spectrometry
(ESI-MS). Poor solubility of 2–4 in cold methanol or water
prevented us from obtaining high quality 13C NMR spectra.
Two sets of signals originating from pyridyl protons could
be found in NMR spectra of 2–5, indicating the presence of
two non-equivalent pyridyl fragments and a low C1 molecu-
lar symmetry of these complexes. In particular, two readily
recognizable most downfield-shifted 1H NMR signals of
pyridyl ortho protons integrating as 1H each could be found
in spectra of 2–5 in the range of 8–9 ppm. The signals ap-
pear as virtual doublets with characteristic small H–H cou-
Results and discussion
(dpms)PtII Complexes 2–6
Methanol complex (dpms)PtIIPh(MeOH) (2) can be syn-
thesized by reductive elimination of benzene from diphenyl
PtIV hydride complex (dpms)PtIVPh2H in methanol at 50 °C
(eq. [1]). The latter complex can be prepared by protonation
of anionic diphenyl PtII species K[(dpms)PtIIPh2], 1 (2). Due
to the poor solubility of the hydride, elevated temperatures
and a prolonged time (5 h) are required to bring reaction to
completion. In contrast to (dpms)PtIVPh2H, the methanol
adduct 2 is soluble in warm MeOH. As a result, the reaction
endpoint can be readily recognized when the entire solid dis-
appears. Other solvento complexes studied in this work, 3,
HX = H2O; 4, HX = PhNH2; and 5, HX = Me2SO, can be
prepared most conveniently by a ligand exchange between
methanol complex 2 and an appropriate ligand HX (eq. [2];
R = Ph).
3
pling constant JHH = 5–6 Hz.
Complex 4 was characterized by single-crystal X-ray dif-
fraction. X-ray quality crystals of 4 could be obtained by
slow crystallization from a reaction mixture. Platinum atom
in complex 4 has an idealized square-planar environment
(Fig. 1a). The Pt1–N15 bond, which is trans to aniline
ligand, is 2.024(3) Å long and is shorter than Pt1–N10,
2.102(3) Å, which is trans to phenyl, consistent with a
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112
Can. J. Chem. Vol. 87, 2009
Chart 2. Products of oxidation of complexes 1–4 and 6.
Scheme 2. Plausible mechanism of aerobic oxidation of
(dpms)PtII complexes.
pound, sym-(dpms)PtIVPh2(OH), 7 (Chart 2) is poorly solu-
ble in the reaction medium and can be isolated in an
analytically pure form by filtration from the strongly alka-
line aqueous solution containing KOH (eq. [3]).
stronger trans influence of the phenyl compared with aniline
ligand (10). The Pt1–N21 distance between the metal and
the nitrogen atom of the aniline ligand is 2.066(3) Å. Both
NH bonds of the aniline ligand point away from the
sulfonate group. The shortest Pt1–sulfonate oxygen contact
is non-bonding, 3.186 Å.
[3]
2 K[(dpms)PtIIPh2] + O2 + 2 H2O
→ 2 sym-(dpms)PtIVPh2(OH) + 2 KOH
The mode of coordination of DMSO ligand to the metal in
complex 5 could be established by IR spectroscopy. IR
spectra of 5 exhibit the presence of the ν(S=O) band of
S-coordinated DMSO at 1131 cm–1, typical for S-
coordinated DMSO complexes (11).
Solvento complexes derived from water, 3, and methanol,
2, are air-sensitive, whereas aniline derivative 4 and DMSO
adduct 5 are stable under air. Reactivity of phenyl (dpms)PtII
solvento complexes 2–4 toward O2 will be compared with
that of their methyl analogues (dpms)PtIIMe(HX) (vide in-
fra) whose aerobic oxidation chemistry was reported re-
cently (HX = H2O (3), MeOH (4)). The aniline methyl PtII
complex (dpms)PtIIMe(NH2Ph) (6) was unknown and was
prepared in this work.
1
Complex 7 dissolved in DMSO-d6 exhibits in its H NMR
spectrum a broad singlet at 2.56 ppm with 195Pt satellites
(J = 36 Hz) integrating as 1H and corresponding to the
PtIV(OH) proton. A doublet of doublets at 8.30 ppm (J = 5.5,
1.5 Hz) integrating as 2H, which is seen in the most
downfield region of the spectrum was assigned to the pyridyl
ortho protons. Accordingly, there are nine signals corre-
sponding to two symmetry-related pyridyls and two symme-
try-related phenyl ligands in the aromatic region of the 13C
NMR spectrum of 7, evidencing the mirror symmetry of the
product.
High reactivity of anionic diphenyl PtII complex 1 toward
O2 in aqueous solution and the retention of the planar
arrangement of the four donor atoms at the Pt center upon
oxidation of 1 to mirror symmetric 7 are similar to the
behaviour of the dimethyl analogue K[(dpms)PtIIMe2] in its
reaction with O2 (2). Based on the stereochemical outcome
of these reactions and also reactions including
(dpms)PtIIMe(HX), HX = H2O (3), L = MeOH (4) and
(dpms)PtII(C2H4OH)OH– (5), we suggest that the mecha-
nisms of oxidation of these complexes might be also similar
(Scheme 2; X = Me or Ph, steps b–d only) (5).
For the preparation of 6, a procedure similar to that uti-
lized for its phenyl analogue 4 was used (eq. [2]; R = Me).
Upon mixing of methanolic solutions of (dpms)PtIIMe(MeOH)
(4) with 1.2 equiv. of aniline and removal of the solvent, the
target compound could be isolated as a colourless solid in
87% yield.
1H NMR spectral patterns of 6 in D2O are consistent with
the C1 molecular symmetry. The spectrum shows the pres-
ence of a PtIIMe group resonance at 0.79 ppm (J195PtH
=
The mechanism presented in Scheme 2 was discussed
previously (5) and is based on the idea of the axial attack of
electrophilic O2 at PtII center (9) that allows to account
for the retention of the configuration at the Pt atom in the
course of oxidation reaction. At the same time, we pre-
sume that in the case of neutral monophenyl complexes
(dpms)PtIIPh(HX) only anionic species (dpms)PtIIPh(X)– can
accept such an attack as it was shown previously for some
monoalkyl analogues (5).
72 Hz) integrating as 3H, a singlet of the dpms ligand CH
bridge at 5.91 ppm integrating as 1H, a set of partially
overlapping signals of the aniline phenyl group, and signals
of two non-equivalent pyridyl fragments. Two virtual dou-
blets of ortho H atoms of two pyridyls integrating as 1H
each can be observed at 8.14 ppm (J = 5.5 Hz) and 8.73 ppm
3
(J = 5.9 Hz, J195PtH = 56 Hz). ESI-mass spectrum of
aqueous solution of 6 shows single 195Pt-derived peak with
m/z = 553.1 (calculated for (dpms)195PtIIMe(NH2Ph)·H+,
C18H20N3SO3195Pt, 553.1).
Notably, aerobic oxidation of diphenyl PtII complexes to
form PtIVPh2 products has never been reported. In particular,
(tmeda)PtIIPh2 is unreactive toward O2. In contrast, presum-
ably electron-richer mixed-ligand phenyl methyl analogue
(tmeda)PtII(Ph)Me can be oxidized with O2 (9). Hence, the
presence of the pendant axial sulfonate group (see Fig. 1a,
for example) in anionic (dpms)PtII species is sufficient to
raise energy levels of neutral PtIIPh2 fragment and enable
(dpms)PtIV Complexes — Oxidation of (dpms)PtIIR
complexes with O2 in water or methanol
Diphenyl complex sym-(dpms)PtIVPh2(OH) (7)
Oxidation of K[(dpms)PtIIPh2] (2) with O2 in water is fac-
ile and is complete in about 2 h at 22 °C. The target com-
© 2008 NRC Canada

Khusnutdinova et al.
113
electron transfer between PtII atom present in complex 1 and
dioxygen (Scheme 2, steps b–c) (5).
taining an almost equally acidic but more donating methanol
ligand will be more reactive toward O2. This was proven
correct in the experiments described below.
Phenyl dihydroxo complex unsym-(dpms)PtIVPh(OH)2 (8)
Solutions of aqua complex 3 in water react slowly with O2
at atmospheric pressure and ambient temperature to produce
colourless unsymmetrical phenyl dihydroxo complex unsym-
(dpms)PtIVPh(OH)2, unsym-8 (Chart 2), that can be isolated
in an analytically pure form in 93% yield (eq. [4]):
Phenyl hydroxo methoxo complex (dpms)PtIVPh(OH)(OMe)
(9)
Oxidation of methanol phenyl complex 2 was performed
in methanol at ambient temperature. In the course of the
reaction, solid complex 2 dissolves to produce a more
soluble colourless hydroxo methoxo phenyl complex
(dpms)PtIVPh(OH)(OMe), 9. The product was isolated in an-
alytically pure form in 91% yield (eq. [5]).
[4]
2 (dpms)PtIIPh(OH2) + O2
→ 2 unsym-(dpms)PtIVPh(OH)2
The presence of two non-equivalent pyridyl groups and
hence the C11 molecular symmetry of unsym-8 are evident
from data of H and 13C NMR spectroscopy in aqueous and
DMSO solutions of unsym-8. Interestingly, two hydroxo lig-
ands present in this complex give rise to two individual sig-
nals that integrate as 1H each and appear as broad singlets at
1.45 ppm (no resolved 195Pt satellites) and 2.99 ppm
(2J195PtH = 30 Hz). Based on the analogy with complex 7, the
latter signal might be assigned to the proton of the axial OH
ligand of complex unsym-8, whereas the signal at 1.45 ppm
might be assigned to the proton of the equatorial OH ligand.
Aqueous solutions of 8 acidified with HBF4 show the pres-
ence of monoprotonated species 8·H+, m/z = 556.1 (calcu-
lated for (dpms)195PtPh(OH)2·H+, C17H17N2SO5195Pt, 556.1).
The rate of reaction in eq. [4] is much slower than that for
K[(dpms)PtIIPh2] (eq. [3]); an estimated half-life of 3 is
8.8 h. This fact may be related to the neutral character of 3
in contrast to anionic complex 1, and therefore, a much
lower fraction of anionic hydrocarbyl (dpms)PtII species is
available for attack with O2 in the case of 3.
[5]
2 (dpms)PtIIPh(MeOH) + O2
→ 2 (dpms)PtIVPh(OH)(OMe)
According to 1H NMR spectroscopy, complex 9 in
DMSO-d6 exhibits a broad singlet of the PtIV(OH) proton at
2.52 ppm integrating as 1H and a singlet of the methoxo
ligand at 2.94 ppm with discernible 195Pt satellites (3J195PtH
=
33 Hz) integrating as 3H. An ESI-mass spectrum of solution
of 9 in MeOH acidified with HBF4 shows the presence of a
peak with m/z = 570.1 that corresponds to a monoprotonated
species (dpms)195PtPh(OCH3)(OH)·H+, (calculated for
C18H19N2SO5195Pt, 570.1).
Assuming that oxidation of methanol adducts
(dpms)PtIIR(MeOH) proceeds via similar mechanisms for R =
Me and Ph and implies retention of the configuration of both
R and MeO ligands at the Pt center, complex 9 was
tentatively assigned the same configuration (see Chart 2) as
the product of aerobic oxidation of the methyl analogue.
In the latter case, as established by a single-crystal X-ray
As in the case of bishydrocarbyl complexes
K[(dpms)PtIIR2], R = Me or Ph, aerobic oxidation of
monohydrocarbyl species (dpms)PtIIR(OH2) leads to PtIV
hydroxo derivatives unsym-(dpms)PtIVR(OH)2 for both R =
Me (3, 5) and Ph. Based on available estimates of half-life
of (dpms)PtIIR(OH2) measured under identical conditions in
neutral aqueous solutions at 22 °C, the reactivity of com-
diffraction
analysis
of
the
reaction
product,
(dpms)PtIVMe(OMe)OH methyl and methoxo fragments re-
tain their positions in the equatorial plane of the product (4).
Half-life of complex 2 (eq. [5]) determined at 22 °C and 1
atm (1 atm = 101.325 kPa) partial pressure of O2 was esti-
mated to be 5.5 h. This result means that the reactivity of
methanolic solutions of 2 is slightly higher than that of
aqueous solutions of its aqua-analogue 3.
A comparison of reactivity of analogous methanol com-
plexes (dpms)PtIIR(HX), HX = MeOH, R = Me and Ph
shows that the methanol phenyl complex 2 is less reactive
compared with the electron-richer methanol methyl com-
plex: Me (τ1/2 < 1 h) (4) > Ph (τ1/2 ≈ 5.5 h). The same trend
was observed for aqua complexes, HX = H2O, R = Me and
Ph.
Considering oxidation of the aniline derivatives 4 and 6
with O2, one can expect poor reactivity because the acidity
of aniline is many orders of magnitude lower than that of
H2O or MeOH that serve as ligands in species 2 and 3 (12).
Hence, anionic intermediates (dpms)PtIIR(NHPh)– required
for oxidation may be available in exceedingly low concen-
trations only. Similarly, dimethylsulfoxide ligand present in
adduct 5 is even less acidic than aniline. Therefore, complex
5 may be even less reactive toward O2. Reactivity of aniline
adducts 4 and 6 as well as that of DMSO adduct 5 toward
O2 was tested in the following experiments.
plexes (dpms)PtIIR(OH2) decreases in the order Me (τ1/2
≈
15min) (5) > Ph (τ1/2 ≈ 8.8 h). Assuming that mechanisms of
these aerobic oxidation reactions are also similar (Scheme 2,
steps a–d), this difference can be related to the electron-
poorer character of the phenyl complex 3. On one hand,
electron-poorer complex 3 is more acidic than its methyl
analogue. That increases the fraction of anionic
(dpms)PtIIR(OH)– species available for reaction with O2 (5)
and makes complex 3 more reactive. On the other hand, an
electron-poorer PtII center in anionic intermediate
(dpms)PtIIPh(OH)– is more difficult to oxidize that leads to
an overall lower reactivity of the phenyl aqua complex 3.
Notably, no monophenyl PtII complexes were known that
are able to react with O2 to produce PtIVPh derivatives. As in
the case of complex 1, we assume that the anionic pendant
sulfonate tail present in dpms ligand allows to raise energy
levels of neutral PtIIPh(OH) fragment to an extent, which is
sufficient to enable electron transfer from PtII atom present
in this species to O2.
Taking these considerations into account, one can suggest
that methanol analogue of aqua adduct 3, complex 2 con-
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Can. J. Chem. Vol. 87, 2009
Phenylamido complexes (dpms)PtIVPh(NHPh)(OH) (10)
and (dpms)PtIVMe(NHPh)(OH) (11)
structure of complex 11 reveals the presence of a Pt atom in
a slightly distorted octahedral environment (Fig. 1b). As in
the case of the PtIIPh aniline adduct 4, the Pt1–N2 bond
trans to hydrocarbyl is longer than the Pt1–N1 bond trans to
phenylamido ligand, 2.189(3) Å vs. 2.089(3) Å, respec-
tively. The Pt1–N3 bond with formally anionic phenylamido
ligand is about 0.05 Å shorter than the Pt–N bond in the PtII
adduct 4 with neutral aniline ligand, 2.018(3) Å. One of the
sulfonate oxygen atoms in the PtIV complex 11 is bound to
the metal with a short Pt1–O3 distance of 2.102(3) Å.
The configuration of complex 11 shows that the methyl
and phenylamido fragments retain their equatorial positions
in the course of oxidation of the PtII precursor 6 with H2O2.
Different ability of aniline-derived methyl and phenyl
(dpms)PtII complexes 4 and 6 to react with O2 in water is re-
markable. Though the acidity of coordinated aniline may be
expected to be many orders of magnitude lower compared
with that of PtII-bound water or methanol ligands, corre-
sponding anionic phenylamido PtII species (dpms)PtIIR(NHPh)–
required for reaction with O2 (Scheme 2, steps b–c) may still
be available in sufficient concentration in the case of R =
Me. At the same time, the electron-poorer nature of phenyl
ligand might be responsible for precluding a facile electron
transfer between the PtII center in (dpms)PtIIR(NHPh)– and
dioxygen.
Methanolic solutions of complexes 4 and 5 are inert to-
1
ward O2. No changes were observed by H NMR spectros-
copy as well as no new species were detected by ESI-MS
after 7 days of exposure of the above solutions to O2 (1 atm)
at ambient temperature.
To be able to test reductive elimination chemistry of an
amido phenyl (dpms)PtIV(OH) complex, which can be de-
rived from the aniline adduct 4, oxidation of 4 was per-
formed with hydrogen peroxide (eq. [6]).
[6]
(dpms)PtIIPh(PhNH2) + H2O2
→ (dpms)PtIVPh(NHPh)(OH) + H2O
Treatment of complex 4 dissolved in methanol with
2.5 equiv. of 30% H2O2 1produced complex 10 in a quantita-
tive yield, according to H NMR spectroscopy. The colour-
less product could be precipitated with diethyl ether and
isolated in an analytically pure form in 90% yield.
Phenylamido phenyl PtIV complex 10 was fully character-
1
ized by H and 13C NMR spectroscopy and ESI-mass spec-
1
trometry. H NMR spectrum of 10 in DMSO-d6 solutions
shows two broad singlets, one at 3.01 ppm and another at
4.36 ppm integrating as 1H each that can be attributed to OH
and NH protons, respectively. Both 1H and 13C NMR spectra
reveal a low C1 molecular symmetry of 10. ESI-mass spectra
of 10 dissolved in methanol exhibit single 195Pt-derived peak at
m/z = 631.1 that corresponds to (dpms)195PtPh(NHPh)(OH)H+
(calculated for C23H22N3O4195Pt S, 631.1).
Finally, the inertness of complex 5 toward O2 is consistent
with its virtual inability to produce an anionic phenyl PtII
complex required for aerobic reaction (Scheme 2, step a).
Attempted reductive elimination from (dpms)PtIVPh
complexes
Based on presumed common mechanism of oxidation of
(dpms)PtIIR(HX) species, R = Me and Ph, the configuration
of complex 10 at the Pt atom was assumed to be the same as
for its methyl analogue 11 (Chart 2; vide infra).
It is assumed that C–X reductive elimination from PtIV
center (X = O, N, C, H) is most facile if it proceeds via five-
coordinate intermediates with a coordination vacancy trans
to the hydrocarbyl being eliminated (13, 14). The ability of a
d6 metal complex to produce low-coordinate transients and
therefore the presence of a good leaving group may be criti-
cal for fast reductive elimination chemistry at a PtIV center.
The best leaving group available in (dpms)PtIV complexes 7–
11 is the sulfonate but it is cis to hydrocarbyl ligands in all
of the complexes. As a result, reductive elimination from 7–
11 might be expected to be preceded by their isomerization.
Indeed, when alkyl (dpms)PtIV(OH) complexes with an alkyl
group cis to the sulfonate are submitted to reductive elimina-
tion experiments, intermediates with the alkyl trans to the
sulfonate are actual reactive species involved in C–O
reductive elimination reactions. These species can be de-
tected by NMR spectroscopy in reaction mixtures and, in a
number of cases, isolated in analytically pure form (3–6).
Whereas C(sp3)–X elimination from PtIV can operate an SN2
(X = O, N) (15, 16) or a recently discovered direct C(sp3)–O
elimination mechanism (6), in the case of aryl PtIV deriva-
tives, a direct C(sp2)–X elimination was observed only (17).
Hence, a direct C(sp2)–X reductive elimination from com-
plexes 7–10 might be expected.
Reactivity of an analogous methyl PtII aniline adduct 6 to-
ward O2 was also tested. Notably, upon stirring of aqueous
solution of 6 under O2 atmosphere (1 atm) at an ambient
temperature, slow oxidation leading to complex
1
(dpms)PtIVMe(NHPh)(OH), 11, (Chart 2) was evident by H
NMR spectroscopy and ESI-mass spectrometry (eq. [7]).
The reaction half-life was estimated to be 30 h.
[7]
2 (dpms)PtIIMe(PhNH2) + O2
→ 2 (dpms)PtIVMe(NHPh)(OH)
Similar to 10, complex 11 could be prepared by oxidation
of methanolic solution of 6 with 1.1 equiv. of H2O2. The re-
action is quantitative by NMR spectroscopy.
Aqueous solutions of 11 are weakly basic (pH ≈ 9) pre-
sumably due to reversible protonation on the nitrogen atom
of the phenylamido ligand.
1
As in the case of phenyl PtII complex 10, the H NMR
spectrum of 11 in DMSO-d6 shows the presence of two
broad singlets at 2.22 ppm and 4.17 ppm, corresponding to
1
OH and NH fragments, respectively. Both H and 13C NMR
spectroscopy suggests a low C1 molecular symmetry of com-
plex 11. ESI-mass spectra of aqueous solutions 11 exhibit
single 195Pt-derived peak with m/z = 569.1 (calculates for
(dpms)195PtMe(NHPh)(OH)·H+, C18H20N3SO4195Pt, 569.1).
X-ray quality crystals of 11 could be obtained by slow dif-
fusion of ether vapours into solution of 11 in methanol. The
Heating complex 7 in DMSO at 100 °C for 6 days re-
sulted in clean isomerization to unsym-7 featuring one of the
phenyl groups in the axial position. No other products were
detected in the solution.
Similarly, unsymmetrical phenyl dihydroxo complex 8
dissolved in water and exposed to 100 °C for 3 days cleanly
© 2008 NRC Canada

Khusnutdinova et al.
115
produced the more stable isomer sym-8 with the aryl in the
axial position (half-life ≈ 12.5 h). No other products were
the results of DFT modeling are qualitatively consistent with
our experimental observations.
1
found. The latter complex is Cs symmetric, according to H
and 13C NMR spectroscopy and produces the same signal in
ESI-mass spectra as its unsymmetrical precursor.
Summary
Though none of the PtIV phenyl complexes
(dpms)PtIVPh(X)OH exhibited C–X reductive elimination
chemistry in the temperature range of 20–100 °C, results of
this study may be important for understanding of factors af-
fecting reactivity of hydrocarbyl PtII complexes toward O2.
When observed, aerobic oxidation of dipyridylmethane-
sulfonate monohydrocarbyl PtII complexes (dpms)PtIIR(HX)
derived from water, methanol, and aniline (HX) leads to PtIV
hydroxo complexes (dpms)PtIVPh(X)OH. This reactivity de-
pends both on the solvento ligand HX and the donicity of
the hydrocarbyl R. Among phenyl PtII species, the anionic
diphenyl complex is the most reactive, whereas aniline and
DMSO adducts are inert: X = Ph > MeO ≈ HO » PhNH,
DMSO. In turn, methyl derivatives are more reactive than
their phenyl counterparts, R = Me > Ph; even the aniline
adduct can be oxidized with O2 when R = Me.
To probe the effects of solvent and pH on reactivity of
sym-8, its samples were submitted to C–O reductive elimina-
tion in DMSO and also acidic and alkaline aqueous solu-
tions at 100 °C. No changes were detected in these solutions
1
by H NMR spectroscopy after 5 days, suggesting that the
Gibbs activation energy for direct C–O elimination from PtIV
exceeds 30 kcal/mol in all these cases.
Reductive elimination reactions from complexes 9 and 10
were probed in aprotic DMSO-d6, CD3CN, and DMF-d7.
In the case of 9 in DMSO-d6 solution slow formation of a
1
single PtII complex 5-d6 and methanol was detected by H
NMR spectroscopy and ESI-MS at 100 °C. No anisole or
phenol was detected. The reaction was clean and involved
presumably the solvent as a reductant (eq. [8]).
[8]
(dpms)PtIVPh(OMe)OH + 2 Me2SO
→ (dpms)PtIIPh(dmso) + MeOH + Me2SO2
Experimental section
A complex mixture of unidentified products formed in
General
DMF-d7 and CD3CN solutions of 9 at 100 °C already after
All manipulations were carried out under purified argon
using standard Schlenk and glovebox techniques. All re-
agents for which synthesis is not given are commercially
available from Sigma-Aldrich, Acros, Alfa Aesar, or Pres-
sure Chemicals and were used as received without further
purification. Potassium di(2-pyridyl)methanesulfonate was
synthesized as described previously (2). DMSO-d6, CD3CN,
DMF-d7, and CD3OD from Cambridge Isotope Laboratories
were dried over CaH2, vacuum-transferred, and stored in
Teflon-sealed flasks in an argon-filled glovebox. Water was
deaerated by repeating freezing-pumping cycles and stored
under argon in a Teflon-sealed Schlenk flask in a glovebox.
1H (400 MHz) and 13C NMR (125 MHz) spectra were re-
corded on a Bruker AVANCE 400 or Bruker DRX-500 spec-
trometers. Chemical shifts are reported in ppm and
referenced to residual solvent resonance peaks. IR spectra
were recorded on a JASCO FT/IR 4100 spectrometer. ESI-
MS experiments were performed using a JEOL AccuTOF-
CS instrument. Elemental analyses were carried out by
Chemisar Laboratories Inc., Guelph, Canada.3
1
several hours, but no anisole or phenol was detected by H
NMR spectroscopy either.
Phenylamido complex 10 in CD3CN solution produced a
soluble PtII complex (dpms)PtIIPh(CD3CN) along with a
complex mixture of solids of unknown composition after 5 h
at 80 °C. No diphenylamine or phenol was detected by H
NMR spectroscopy.
1
Similarly, a complex mixture of products not containing
diphenylamine formed when a solution of complex 10 in
DMF-d7 was heated at 80 °C for 24 h. ESI-MS spectra of
acidified reaction mixtures diluted with methanol exhibited a
peak of unreacted starting material, m/z 631.1, and two
new peaks with m/z = 1225.2 and m/z = 613.1 that might be
assigned to a mono- and doubly-protonated dinuclear
species
C46H39N6O6195Pt2S2 1225.1)
NHPh)2]2+ (calcd. 613.1), respectively.
[(dpms)2PtIV2Ph2(µ-NPh)(µ-NHPh)]+
(calcd.
and
[(dpms)2PtIV2Ph2(µ-
Therefore, none of complexes 7–10 reacted via PtIV–Ph
bond cleavage, and none can be used for arene CH
functionalization such as the one shown in Scheme 1. Oxida-
tion of a solvent (complex 9 in DMSO) or, presumably
phenylamido ligand (complex 10 in MeCN), or formation of
insoluble polynuclear complexes (complex 10 in DMF) was
seen instead.
Computational details
Theoretical calculations in this work have been performed
using density functional theory (DFT) method (18), specifi-
cally functional PBE (19), implemented in an original pro-
gram package “Priroda” (20). In PBE calculations,
relativistic Stevens–Basch–Krauss (SBK) effective core po-
tentials (ECP) (21), optimized for DFT calculations, have
been used. Basis set was 311-split for main-group elements
with one additional polarization p-function for hydrogen and
additional two polarization d-functions for elements of
higher periods. Full geometry optimization has been per-
formed without constraints on symmetry. For all species un-
der investigation, frequency analysis has been carried out.
Our DFT estimates of the Gibbs activation energy for the
“direct” C–O or C–N elimination from (dpms)PtIVPh phenyl
complexes 8–10 provided high barriers for these reactions.
In particular, the Gibbs activation energy for PhOH elimina-
tion from sym-8 is 29.4 kcal/mol. The same value was found
for PhOMe elimination from an isomer of complex 9 with
phenyl ligand in the axial position. Finally, the Gibbs activa-
tion energy for Ph2NH elimination from an isomer of com-
plex 10 with the axial PtIVPh group is 28.7 kcal/mol. Hence,
3 Caution: methanol flash point is 12 °C and is lower under pure O2 atmosphere.
© 2008 NRC Canada

116
Can. J. Chem. Vol. 87, 2009
All minima have been checked for the absence of imaginary
frequencies. All transition states possessed just one imagi-
nary frequency. Using method of intrinsic reaction coordi-
nate, reactants, products, and the corresponding transition
states were proven to be connected by a single minimal en-
ergy reaction path.
added, and
a
white suspension was stirred at RT.
(dpms)PtPh(MeOH) dissolved after 10 min, and the target
complex (dpms)PtPh(NH2Ph) formed as large crystals. The
reaction mixture was placed into a freezer at –20 °C for 4 h.
White precipitate of 4 was filtered off, washed with 0.5 mL
of cold methanol, and dried under vacuum for 12 h. Yield:
60 mg (97.6 µmol), 83%. White solid, poorly soluble in
methanol and water.
Preparation of (dpms)PtIIPh(MeOH) (2)
IR (KBr) ν: 3494 (w, br), 3056 (w), 2828 (w), 1603 (w),
1573 (w), 1494 (w), 1436 (w), 1252 (m), 1222 (m) 1166
(m), 1031 (s), 757 (m), 686 (m) cm–1. 1H NMR (D2O,
22 °C) δ: 6.00 (s, 1H), 6.94–7.00 (m, 1H), 7.01–7.16 (m,
(dpms)PtPh2H (184 mg, 306 µmol), prepared according to
the literature procedure (2), in MeOH (30 mL) was placed
into a 100 mL Schlenk tube equipped with a stirring bar un-
der an argon atmosphere, and the reaction mixture was
stirred at 50 °C. Colourless solution formed after 5 h. The
solution was filtered under argon, reduced in volume to 2–
3 mL under vacuum, and the resulting suspension was
cooled down to –20 °C. White precipitate of 2 was filtered,
washed with cold methanol, and dried under vacuum for
12 h. Yield: 127 mg, 75%. White solid, oxidizes in air,
poorly soluble in methanol, dissolves in water and DMSO
with the loss of methanol ligand and formation of
(dpms)PtPh(OH2) and (dpms)PtPh(DMSO), respectively.
IR (KBr) ν: 3394 (w, br), 3046 (w), 2949 (w), 2764 (w),
1602 (w), 1572 (w), 1480 (w), 1438 (w), 1252 (m), 1168
3
6H), 7.20–7.27 (m, 3H), 7.31 (d, J = 7.1 Hz, JPtH = 40 Hz,
2H), 7.77 (vd, J = 7.8 Hz, 2H), 7.89 (td, J = 7.8, 1.4 Hz,
1H), 7.98 (td, J = 7.8, 1.6 Hz, 1H), 8.34 (dd, J = 6.0, 1.4 Hz,
1H), 8.43 (dd, J = 5.6, 1.6 Hz, 1H). 13C spectrum of
(dpms)PtPh(MeOH) could not be obtained due to its low
solubility. ESI of solution in MeOH/H2O (1:1 v/v), m/z
615.1. Calculated for (dpms)PtPh(NH2Ph)·H+, C23H22N3O3195PtS:
615.1. Anal. found: C, 44.63; H, 3.27; N, 6.61. Calcd. for
C23H21N3O3PtS: C, 44.95; H, 3.44; N, 6.84.
Preparation of (dpms)PtIIPh(dmso) (5)
1
(m), 1033 (s), 767 (m), 742 (m), 702 (m), 687 (m) cm–1. H
(dpms)PtPh(MeOH) (55.6 mg, 100 µmol) and 5 mL of dry
degassed DMSO were placed into a 25 mL Schlenk tube un-
der an argon atmosphere. The reaction mixture was stirred
for 1 h at RT to produce a clear solution. The solvent was re-
moved by vacuum distillation. The resulting solid was
washed with cold methanol and ether and dried under vac-
uum for 24 h at 65 °C. Yield: 51.1 mg, 85%. White solid,
soluble in methanol and DMSO. The complex is stable in
MeOH solutions at RT for several days; ligand exchange oc-
curs in DMSO-d6 solutions to give (dpms)PtPh(DMSO-d6)
(τ1/2 = 1.2 h at RT).
NMR (CD3OD, 22 °C) δ: 6.02 (s, 1H), 6.86–6.92 (m, 1H),
6.98 (vt, J = 7.5 Hz,), 7.04 (ddd, J = 7.8, 5.7, 1.5 Hz, 1H),
3
7.43 (dd, J = 7.5, 1.1 Hz, JPtH = 32 Hz, 2H), 7.62 (ddd, J =
7.9, 5.4, 1.6 Hz, 1H), 7.80 (dd, J = 7.9, 1.5 Hz, 1H), 7.94 (d,
J = 7.8 Hz, 1H), 7.98 (td, J = 7.8, 1.6 Hz, 1H), 8.11 (td, J =
7.9, 1.7 Hz, 1H), 8.43 (dd, J = 5.7, 1.7 Hz, 1H), 8.81 (d, J =
5.4 Hz, 1H). 13C spectrum of (dpms)PtPh(MeOH) could not
be obtained due to its low solubility in methanol. ESI of di-
lute solution in methanol, m/z 554.1. Calculated for
(dpms)PtIIPh(MeOH)·H+, C23H21N3O3195PtS: 554.1. Anal.
found: C, 39.36; H, 3.47; N, 5.19. Calcd. for
C18H19N2O4PtS: C, 39.06; H, 3.28; N, 5.06.
IR (KBr) ν: 3048 (w), 2924 (w), 1606 (w), 1574 (w),
1483 (w), 1435 (w), 1231 (m), 1167 (m), 1131 (m), 1031
(s), 765 (m), 685 (m) cm–1. The ν(S=O) band of S-
coordinated dimethylsulfoxide at 1131 cm–1 is missing in IR
spectra of other PtII sulfonate complexes reported here. The
frequency is typical for Me2SO ligand coordinated to a metal
through the sulfur atom (11) and similar to S=O frequency
of (dpms)Pt(dmso)(OH) (1127 cm–1) (6).
Preparation of (dpms)PtIIPh(OH2) (3)
(dpms)PtPh(MeOH) (20 mg, 36 µmol) and 20 mL of
deaerated water were placed into a 50 mL round-bottomed
flask and stirred at room temperature until complete dissolu-
1
tion of the starting material. H NMR spectrum of the sam-
3
1H NMR (CD3OD, 22 °C) δ: 3.07 (s, J195PtH = 36 Hz,
ple diluted with D2O recorded after 20 min showed complete
conversion of 2 into (dpms)PtPh(OH2) and 1 equiv. of meth-
anol. The mixture was evaporated to dryness, and the result-
ing solid was dried under vacuum for 8 h. Yield: 19 mg,
97%. White solid, oxidizes in air, poorly soluble in water.
1H NMR (D2O, 22 °C) δ: 6.08 (s, 1H), 6.98–7.12 (m, 4H),
7.23 (d, J = 7.5 Hz, 2H), 7.63 (ddd, J = 7.7, 5.5, 1.3 Hz,
1H), 7.77 (dd, J = 7.7, 1.5 Hz, 1H), 7.89 (d, J = 7.9 Hz, 1H),
8.01 (td, J = 7.7, 1.6 Hz, 1H), 8.10 (td, J = 7.7, 1.5 Hz, 1H),
3
3H), 3.19 (s, J195PtH = 30 Hz, 3H), 6.17 (s, 1H), 6.90 (td,
J = 7.3, 1.3 Hz, 1H), 7.01 (t, J = 7.3, 1.3 Hz, 1H), 7.17–7.27
3
(m, 2H), 7.39 (d, J = 7.3, J195PtH = 40 Hz, 1H), 7.58 (ddd,
3
J = 7.9, 5.5, 1.3 Hz, 1H), 7.70 (d, J = 7.3 Hz, J195PtH
=
35 Hz, 1H), 7.95 (d, J = 7.9 Hz, 1H), 7.98 (d, J = 7.9 Hz,
1H), 8.04 (td, J = 7.9, 1.5 Hz, 1H), 8.12 (td, J = 7.9, 1.5 Hz,
3
1H), 8.30 (dd, J = 5.5, 1.5 Hz, J195PtH = 55 Hz, 1H), 9.11
3
(dd, J = 5.5, 1.5 Hz, J195PtH = 23 Hz, 1H). 1H NMR
8.31 (dd, J = 6.0, 1.5 Hz, 1H), 8.74 (vd, J = 5.5 Hz, 1H). 13
C
3
(DMSO-d6, 22 °C) δ: 3.06 (s, J195PtH = 30 Hz, 3H), 3.09 (s,
3J195PtH = 30 Hz, 3H), 6.20 (s, 1H), 6.86 (td, J = 7.4, 1.5 Hz,
1H), 6.97 (t, J = 7.4, 1H), 7.16 (td, J = 7.4, 1.5 Hz, 1H),
7.28 (ddd, J = 7.9, 5.5, 1.1 Hz, 1H), 7.35 (d, J = 7.4,
3J195PtH = 30 Hz, 1H), 7.58 (ddd, J = 7.9, 5.5, 1.1 Hz, 1H),
spectrum of (dpms)PtPh(OH2) could not be obtained due to
its low solubility in water. ESI of aqueous solution, acidified
with HBF4, m/z 540.1. Calculated for (dpms)PtPh(OH2)·H+,
C17H17N2O4195PtS: 540.1.
3
7.62 (d, J = 7.4, J195PtH = 30 Hz, 1H), 7.90 (d, J = 7.9 Hz,
Preparation of (dpms)PtIIPh(NH2Ph) (4)
(dpms)PtPh(MeOH) (65 mg, 117 µmol) was placed into a
10 mL vial equipped with a stirring bar. Deaerated methanol
(2 mL) and 185 mg of aniline (2 mmol, 17 equiv.) were
1H), 7.93 (d, J = 7.9 Hz, 1H), 8.06 (td, J = 7.9, 1.4 Hz, 1H),
8.10–8.17 (m, 2H), 8.98 (dd, J = 5.5, 1.4 Hz, 1H). 13C NMR
(DMSO-d6, 22 °C) δ: 43.8 (CH3), 44.4 (CH3), 75.4, 124.1,
124.4, 127.3, 128.1 (Cq), 128.2, 129.3, 136.3, 137.3, 140.1,
© 2008 NRC Canada

Khusnutdinova et al.
117
140.8, 151.5, 152.5 (Cq), 153.2, 154.0 (Cq). Carbon
assignments were made from DEPT experiments. ESI of
solution in methanol acidified with HBF4, m/z 600.1. Calcu-
lated for (dpms)PtPh(Me2SO)·H+, C19H21N2S2O4195Pt:
600.1. (dpms)PtPh(DMSO-d6): ESI of solution in methanol
acidified with HBF4, m/z 606.1. Calculated for
(dpms)PtPh((CD3)2SO)·H+, C19H15D6N2S2O4195Pt: 606.1.
Resulting clear solution was stirred under O2 at room tem-
perature. After 48 h, the solution was reduced in volume to
1 mL under vacuum. Resulting suspension was left at 5 °C
for 1 h. White precipitate was filtered off, washed with
0.5 mL of cold water, and dried under vacuum for 8 h.
Yield: 92.3 mg, 93%. White solid, very soluble in water,
methanol, and DMSO.
IR (KBr) ν: 3548 (w, br), 3070 (w), 2928 (w), 1607 (w),
1574 (w), 1481 (w), 1445 (w), 1301 (m), 1210 (w), 1142 (s),
Preparation of (dpms)PtIIMe(NH2Ph) (6)
1
1027 (w), 966 (s), 737 (m), 698 (s) cm–1. H NMR (DMSO-
Solution of (dpms)PtMe(MeOH) (192 µmol) in deaerated
methanol (10 mL), prepared from isomeric hydrides
(dpms)PtMe2H (91.4 mg, 192 µmol) (5), was placed in a
50 mL Schlenk tube and combined with distilled aniline
(18.1 mg; 194 µmol, 1.01 equiv.). The mixture was stirred at
2
d6, 22 °C) δ: 1.45 (br s, 1H), 2.99 (br s, J195PtH = 30 Hz,
1H), 6.93 (s. 1H), 7.03–7.23 (m, 5H), 7.60 (ddd, J = 7.8,
5.5, 1.3 Hz, 1H), 7.88–8.00 (m, 2H), 8.06 (dd, J = 7.8,
1.3 Hz, 1H), 8.09 (d, J = 7.8 Hz, 1H), 8.26 (td, J = 7.8,
1.5 Hz, 1H), 8.33 (td, J = 7.8, 1.5 Hz, 1H), 8.96 (dd, J = 5.5,
1
room temperature for 15 min. According to H NMR, ligand
1
1.5 Hz, 1H). H NMR (D2O, 22 °C) δ: 6.84 (s, 1H), 7.03 (d,
exchange was complete in 15 min. The reaction mixture was
evaporated to dryness; the resulting colourless solid was
washed with ether and dried under vacuum for 6 h. Yield:
92.9 mg, 87%. White solid, soluble in methanol and water,
slowly oxidizes in air.
3
J = 8.0 Hz, J195PtH = 20 Hz, 2H), 7.22–7.35 (m, 3H), 7.58
(ddd, J = 7.9, 5.9, 1.3 Hz, 1H), 7.97 (ddd, J = 7.9, 5.5,
1.2 Hz, 1H), 8.03 (dd, J = 5.9, 1.4 Hz, 1H), 8.10 (dd, J =
7.9, 1.3 Hz, 1H), 8.16 (d, J = 7.9 Hz, 1H), 8.29 (td, J = 7.9,
1.4 Hz, 1H), 8.35 (td, J = 7.9, 1.4 Hz, 1H), 8.95 (dd, J = 5.5,
1.4 Hz, 1H). 13C NMR (DMSO-d6, 22 °C) δ: 70.7, 125.6,
126.2, 126.5, 126.8, 127.1, 127.3 (Cq), 127.6, 132.2, 141.9,
142.7, 148.3, 149.5 (Cq), 151.1, 152.7 (Cq). Quaternary car-
bon assignments are from DEPT experiment. ESI of solution
in MeOH/H2O (1:1 v/v) acidified with HBF4, m/z 556.1. Cal-
culated for (dpms)PtPh(OH)2·H+, C17H17N2SO5195Pt: 556.1.
Anal. found: C, 36.48; H, 3.29; N, 4.74. Calcd. for
C17H16N2O5PtS: C, 36.76; H, 2.90; N, 5.04.
1H NMR (D2O, 22 °C) δ: 0.79 (2J195PtH = 72 Hz, 3H),
5.91 (s, 1H), 7.05–7.33 (m, 6H), 7.38 (m, 1H), 7.74 (vd, J =
7.8 Hz, 2H), 7.88 (vt, J = 7.8 Hz, 1H), 8.03 (vt, J = 7.8 Hz,
1H), 8.14 (d, J = 5.5 Hz, 1H), 8.73 (d, J = 5.9 Hz, J195PtH
56 Hz, 1H). ESI-MS of aqueous solution of
(dpms)PtMe(NH2Ph), m/z observed: 553.1. Calcd. for
(dpms)PtMe(NH2Ph)qH+, C18H20N3SO3195Pt: 553.1.
3
=
Preparation of sym-(dpms)PtIVPh2OH (7) by oxidation
of K(dpms)PtIIPh2 (1) with O2
Preparation of (dpms)PtIVPh(OMe)(OH) (9) by
oxidation of (dpms)PtIIPh(MeOH) with O2
K[(dpms)PtPh2] (55.9 mg, 88 µmol) (2) was dissolved in
2 mL of deaerated water and placed into a 10 mL vial
equipped with a magnetic stirring bar. The vial was filled
with O2, and the solution was stirred at room temperature for
2 h. No K(dpms)PtPh2 was detected in solution after that
time; the solution pH was ~12. White precipitate was filtered
off and washed with water until neutral reaction of the fil-
trate. The product was dried under vacuum for 6 h. Yield:
47.0 mg, 87%. White solid, soluble in dichloromethane and
DMSO, insoluble in water.
(dpms)PtPh(MeOH) (98.2 mg, 177 µmol) in 75 mL of dry
methanol was placed into a 250 mL round-bottomed flask
equipped with a magnetic stirring bar. The flask was filled
with O2, and the reaction mixture was stirred vigorously at
RT. After 40 h, the clear solution was reduced in volume to
~0.3 mL under vacuum. Resulting suspension was left at
–20 °C for 1 h. White precipitate was filtered off, washed
with small amount of cold methanol, and dried under vac-
uum for 12 h. Yield: 91.8 mg, 91%. White solid, soluble in
methanol and DMSO.
IR (KBr) ν: 3583 (w, br), 3055 (w), 2981 (w), 1604 (w),
1574 (w), 1472 (w), 1449 (w), 1294 (m), 1203 (w), 1143 (s),
1025 (m), 981 (s), 736 (m), 695 (m) cm–1. 1H NMR
IR (KBr) ν: 3318 (w, br), 3031 (w), 2976 (w), 2817 (w),
1606 (w), 1573 (w), 1483 (w), 1446 (w), 1298 (s), 1210 (m),
2
(DMSO-d6, 22 °C) δ: 2.56 (br s, J195PtH = 36 Hz, 1H), 6.89
1
1147 (s), 1027 (m), 974 (s), 742 (s), 696 (s) cm–1. H NMR
(s, 1H), 6.92–7.04 (m, 6H), 7.34 (dd, J = 8.0, 1.7 Hz,
3J195PtH = 30 Hz, 4H), 7.65 (ddd, J = 7.8, 5.5, 1.2 Hz, 2H),
8.08 (d, J = 7.8 Hz, 2H), 8.23 (td, J = 7.8, 1.5 Hz, 2H), 8.30
(dd, J = 5.5, 1.5 Hz, 2H). 13C NMR (DMSO-d6, 22 °C) δ:
70.7, 124.9, 125.9, 126.4 (Cq), 126.5, 127.3, 130.9, 141.8,
149.6, 151.4 (Cq). Quaternary carbon assignments are from
DEPT experiment. ESI of solution in MeOH/CH2Cl2 (1:1
v/v) acidified with HBF4, m/z 616.1. Calculated for
(dpms)PtPh2(OH)·H+, C23H21N2SO4195Pt: 616.1. Anal.
found: C, 44.81; H, 3.45; N, 4.24. Calcd. for
C23H20N2O4PtS: C, 44.88; H, 3.27; N, 4.55.
3
(DMSO-d6, 22 °C) δ: 2.52 (br s, 1H), 2.94 (s, J195PtH
=
33 Hz, 3H), 6.95 (s, 1H), 7.04–7.31 (m, 5H), 7.60 (ddd, J =
7.9, 5.8, 1.5 Hz, 1H), 7.92 (dd, J = 5.8, 1.5 Hz, 1H), 7.96
(ddd, J = 7.9, 5.5, 1.2 Hz, 1H), 8.07 (dd, J = 7.9, 1.2 Hz,
1H), 8.09 (d, J = 7.9 Hz, 1H), 8.27 (td, J = 7.9, 1.5 Hz, 1H),
8.34 (td, J = 7.9, 1.5 Hz, 1H), 8.95 (dd, J = 5.5, 1.5 Hz, 1H).
3
1H NMR (CD3OD, 22 °C) δ: 2.66 (s, J195PtH = 27 Hz, 3H),
6.67 (s, 1H), 7.10–7.28 (m, 5H), 7.53 (ddd, J = 7.8, 5.5,
1.5 Hz, 1H), 7.92 (ddd, J = 7.8, 5.5, 1.2 Hz, 1H), 8.02–8.14
(m, 3H), 8.24 (td, J = 7.8, 1.5 Hz, 1H), 8.30 (td, J = 7.8,
1.5 Hz, 1H), 9.01 (dd, J = 5.5, 1.5 Hz, 1H). 13C NMR
(DMSO-d6, 22 °C) δ: 57.3 (CH3), 70.7, 125.6, 126.1, 126.3,
126.7, 127.0, 127.8, 129.3 (Cq), 131.4, 141.9, 142.7, 148.0,
149.6 (Cq), 151.5, 152.4 (Cq). Assignments of carbon peaks
are made from DEPT experiments. ESI of solution in MeOH
acidified with HBF4, m/z 570.1. Calculated for
Preparation of unsym-(dpms)PtIVPh(OH)2 (8) by
oxidation of (dpms)PtIIPh(OH2) with O2
(dpms)PtPh(MeOH) (99.1 mg, 179 µmol) and 100 mL of
deaerated water were placed into 250 mL round-bottomed
flask. This suspension was stirred for 30 min under argon.
© 2008 NRC Canada

118
Can. J. Chem. Vol. 87, 2009
(dpms)PtPh(OCH3)(OH)·H+, C18H19N2SO5195Pt: 570.1.
Anal. found: C, 37.79; H, 3.41; N, 4.77. Calcd. for
C18H18N2O5PtS: C, 37.96; H, 3.19; N, 4.92.
Preparation of (dpms)PtIVMe(NHPh)(OH) (11)
Distilled aniline (33.3 mg, 358 µmol, 1.2 equiv.) was
added to a solution of (dpms)PtMe(MeOH) prepared
from 140.1 mg (295 µmol) isomeric hydrides
1
(dpms)PtMe2H and 15 mL MeOH (5). According to H
Attempted oxidation of (dpms)PtIIPh(NH2Ph) (4) and
(dpms)PtIIPh(dmso) (5) with O2
NMR, the ligand exchange was complete in 15 min to give
(dpms)PtMe(NH2Ph), which was used in the next step
without isolation. The mixture was placed into an ice bath;
35 mg of 30% H2O2 (~308 µmol) were slowly added to
the stirred reaction mixture. Mixture turned yellow immedi-
Solution of (dpms)PtPh(NH2Ph) (2 mg, 3 µmol) in 2 mL
of CD3OD was placed into a 10 mL round-bottomed flask
equipped with a magnetic stirring bar. The flask was filled
with oxygen, and the solution was stirred vigorously at room
1
ately after addition of H2O2. According to H NMR, oxida-
1
temperature. According to H NMR, the starting material
tion was complete in less than 15 min to give
(dpms)PtMe(NHPh)(OH) quantitatively. The resulting solu-
tion was reduced in volume to 2 mL; the product was precip-
itated with 6 mL of ether, filtered off, and dried under
vacuum for 3 h. Yield: 106.2 mg, 63%. The product is solu-
ble in methanol, DMSO, and water; aqueous solutions have
weakly basic reaction (pH ~9).
remained unchanged after
7
days. No traces of
(dpms)PtIVPh(NHPh)(OH) or other products were detected
in the solution by ESI-MS; no precipitate formed.
An analogous procedure was used for attempted oxidation
of (dpms)PtPh(dmso) (2 mg, 3 µmol) in CD3OD (1 mL) with
1
O2. According to H NMR, after 7 days of stirring under O2
at RT, only starting material (dpms)PtIIPh(dmso) was present
in solution; no other products were detected in the amounts
exceeding 2%; no precipitate formed.
IR (KBr) ν: 3548 (w, br), 3087 (w), 2973 (w), 1592 (w),
1489 (w), 1448 (w), 1296 (m), 1212 (m), 1154 (s), 980 (m),
1
750 (m), 688 (m) cm–1. H NMR (DMSO-d6, 22 °C) δ: 2.22
(br s, 1H), 4.17 (br s, 1H), 6.40–6.87 (m, 5H), 7.26 (s, 1H),
7.68–7.77 (m, 1H), 7.80 (ddd, J = 7.9, 5.7, 1.2 Hz, 1H), 8.02
(d, J = 7.9 Hz, 1H), 8.06 (d, J = 7.9 Hz, 1H), 8.23 (td, J =
7.9, 1.9 Hz, 1H), 8.30 (td, J = 7.9, 1.2 Hz, 1H), 8.63 (dd, J =
Preparation of (dpms)PtIVPh(NHPh)(OH) (10)
(dpms)PtPh(NH2Ph) (53.8 mg, 87.5 µmol) and 2 mL of
MeOH were placed into a 10 mL vial equipped with a stir-
ring bar, and 25 µL of 30% aq. H2O2 were added slowly
upon stirring. Stirring continued for 1 h at RT. Solid
(dpms)PtPh(NH2Ph) dissolved, and reddish solution formed.
1
5.7, 1.2 Hz, 1H), 8.67–8.77 (m, 1H). H NMR (CD3OD,
22 °C) δ: 2.19 (2J195PtH = 68 Hz, 3H), 6.49 (s, 1H), 6.82 (m,
1H), 6.90 (m, 2H), 7.07 (d, J = 7.7 Hz, 2H), 7.41 (ddd, J =
7.7, 5.8, 1.1 Hz, 1H), 7.77 (ddd, J = 8.0, 5.8, 1.2 Hz, 1H),
7.96 (d, J = 7.7 Hz, 1H), 8.02 (d, J = 7.7 Hz, 1H), 8.07 (td,
J = 7.7, 1.5 Hz, 1H), 8.23 (td, J = 7.7, 1.5 Hz, 1H), 8.33 (d,
J = 5.8 Hz, 1H), 8.67 (d, J = 5.8 Hz, 1H). 13C NMR
(DMSO-d6, 22 °C) δ: 2.2 (1J195PtC = 606 Hz), 70.4, 116.0,
119.4, 125.8, 126.7, 126.9, 128.0, 128.2, 141.5, 142.4,
148.3, 149.7, 150.0, 152.2, 155.8. ESI-MS of aqueous solu-
tion of (dpms)PtMe(NHPh)(OH), m/z observed: 569.1.
Calcd. for (dpms)PtMe(NHPh)(OH)·H+, C18H20N3SO4195Pt:
569.1. Anal. found: H, 3.24; C, 38.18; N, 6.97; S, 5.50.
Calcd. for C18H19O4N3PtS, H, 3.37; C, 38.03; N, 7.39; S,
5.64.
1
The yield of 10 is quantitative according to H NMR spec-
troscopy. Ether (2 mL) was slowly added to the solution, and
the resulting mixture was stored for 1 day at RT. Crystalline
precipitate of (dpms)PtPh(NHPh)(OH) was filtered off,
washed with ether and pentane; yield: 36 mg. An additional
fraction of the product was obtained by evaporation of the
filtrate. Dry solid was washed with water (10 mL), ether
(5 mL), and pentane (5 mL) and dried under vacuum for
10 h; yield: 13.9 mg. Combined yield: 50 mg (79 µmol),
90%.
IR (KBr) ν: 3555 (w, br), 3050 (w), 2970 (w), 1592 (w),
1574 (w), 1489 (w), 1298 (m), 1207 (w), 1145 (s), 1026 (m),
1
980 (s), 760 (s), 695 (s) cm–1. H NMR (DMSO-d6, 22 °C)
Oxidation of (dpms)PtIIMe(NH2Ph) (6) with O2
δ: 3.01 (br s, 1H), 4.36 (br s, 1H), 6.28–6.40 (m, 1H), 6.44–
6.70 (m, 4H), 6.95 (s, 1H), 6.97–7.06 (m, 3H), 7.07–7.27
(m, 2H), 7.59 (ddd, J = 7.8, 5.5, 1.1 Hz, 1H), 7.78–7.84 (m,
1H), 7.97 (d, J = 5.5 Hz, 1H), 8.08 (d, J = 7.8 Hz, 1H), 8.10
(d, J = 7.8 Hz, 1H), 8.25 (td, J = 7.8, 1.3 Hz, 1H), 8.29 (td,
(dpms)PtIIMe(PhNH2) (40 mg, 72 µmol) and 10 mL of
water were placed into a 50 mL round-bottomed flask
equipped with a magnetic stirring bar. The flask was filled
with O2, and the solution was stirred vigorously under O2
atmosphere at room temperature. According to 1H NMR
1
J = 7.8, 1.3 Hz, 1H), 8.90 (d, J = 4.3 Hz, 1H). H NMR
spectroscopy,
slow
oxidation
occurred
to
give
(CD3OD, 22 °C) δ: 6.57 (s, 1H), 6.65–6.79 (m, 3H), 6.92 (d,
(dpms)PtMe(NHPh)(OH) as the only PtIV product. The reac-
tion half-life is ~30 h at RT. Signals corresponding to
protonated starting material (m/z 553.1) and oxidation prod-
uct (dpms)PtIVMe(NHPh)(OH) (m/z 569.1) were detected by
ESI-MS.
J = 7.8 Hz, 2H), 7.02–7.13 (m, 3H), 7.19 (dd, J = 7.7,
3
1.9 Hz, J195PtH = 23 Hz, 2H), 7.45–7.54 (m, 2H), 8.03 (d,
J = 7.8 Hz, 1H), 8.04 (d, J = 7.6 Hz, 1H), 8.08 (d, J =
5.8 Hz, 1H), 8.13 (td, J = 7.8, 1.5 Hz, 1H), 8.17 (td, J = 7.6,
1.5 Hz, 1H), 8.60 (d, J = 5.6 Hz, 1H). 13C NMR (DMSO-d6,
22 °C) δ: 70.4, 115.6, 118.7, 125.4, 125.8, 126.3, 126.8,
127.2, 127.7, 127.8, 128.2 (Cq), 131.6, 141.8, 142.6, 149.0,
150.0 (Cq), 150.9, 152.1 (Cq), 155.4 (Cq). Quaternary car-
bon assignments were made based on DEPT experiment.
ESI of solution in methanol, m/z 631.1. Calculated for
(dpms)PtPh(NHPh)(OH)·H+, C23H22N3O4195PtS: 631.1.
Anal. found: C, 43.52; H, 3.26; N, 6.33. Calcd. for
C23H21N3O4PtS: C, 43.81; H, 3.36; N, 6.66.
Isomerization of unsym-(dpms)PtIVPh(OH)2 (unsym-8)
into sym-(dpms)PtIVPh(OH)2 (sym-8)
Solution of unsym-(dpms)PtPh(OH)2 (103 mg, 180 µmol)
in water (30 mL) was placed into a 50 mL round-bottomed
flask equipped with a magnetic stirring bar and a condenser.
The mixture was heated at 100 °C. After 70 h, the reaction
mixture was reduced in volume to ~1 mL under vacuum and
© 2008 NRC Canada

Khusnutdinova et al.
119
Table 1. X-ray data for the complexes 4 and 11.
Compound
Formula
4
11
C23H21N3O3PtS·2CH3OH
C18H19N3O4PtS
FW
678.66
568.51
Crystal system
Space group
Monoclinic
P2/n
Monoclinic
P21/c
a (Å)
b (Å)
c (Å)
9.9681(6)
8.7798(5)
28.8445(16)
90
90.6590(10)
90
2524.2(3)
4
1.786
8.530(2)
11.102(3)
19.457(5)
90
90.916(4)
90
1842.4(8)
4
2.050
α (°)
β (°)
γ (°)
Volume (Å3)
Z
D(calcd.) (Mg/m3)
Abs. coeff. (mm–1)
F(000)
5.682
1336
7.759
1096
No. of reflns./ind.reflns.
Abs. corr.
No. of data/restr./params.
R1, wR2 (I > 2σ(I))
47802/5791
Semi-empirical
5791/31/336
0.0244, 0.0583
22924/4408
Semi-empirical
4408/1/267
0.0231, 0.0588
left at 5 °C for 1 h. White precipitate was filtered off and
dried under vacuum for 6 h. Yield: 94 mg, 91%.
Attempted reductive elimination from sym-
(dpms)PtIVPh(OH)2 (sym-8)
Four samples of sym-(dpms)PtPh(OH)2 (2.5 mg each,
4.5 µmol) were dissolved in neutral D2O (0.8 mL),
50 mmol/L solution of HBF4 in D2O (0.8 mL), 11 mmol/L
NaOD/D2O solution (0.8 mL), and DMSO-d6 (0.8 mL) un-
der argon. The solutions were placed into NMR Young tubes
and Teflon-sealed. Residual solvent peaks were used as in-
ternal standards. The solutions were heated at 100 °C. Ac-
cording to 1H NMR spectroscopy, concentration of sym-
(dpms)PtPh(OH)2 remained unchanged after 5 days; no
IR (KBr) ν: 3500 (w, br), 3062 (w), 2964 (w), 1607 (w),
1574 (w), 1475 (w), 1441 (w), 1267 (m), 1205 (m), 1146 (s),
996 (m), 736 (m), 691 (m) cm–1. 1H NMR (DMSO-d6,
2
22 °C) δ: 2.32 (br s, J195PtH = 26 Hz, 2H), 6.38 (d, J =
3
7.3 Hz, J195PtH = 35 Hz, 2H), 6.74 (s, 1H), 6.87 (vt, J =
7.3 Hz, 2H), 7.04 (vt, J = 7.3 Hz, 1H), 7.65 (ddd, J = 7.8,
5.8, 1.3 Hz, 2H), 8.06 (d, J = 5.8 Hz, 2H), 8.08 (d, J =
1
7.8 Hz, 2H), 8.31 (td, J = 7.8, 1.3 Hz, 2H). H NMR (D2O,
22 °C) δ: 6.72 (s, 1H), 6.85–7.22 (m, 4H), 7.26 (vt, J =
7.3 Hz, 1H), 7.63 (ddd, J = 8.0, 5.9, 1.3 Hz, 2H), 8.09 (dd,
J = 5.9, 1.4 Hz, 2H), 8.14 (dd, J = 8.0, 1.3 Hz, 2H), 8.33 (td,
J = 8.0, 1.4 Hz, 2H). 13C NMR (DMSO-d6, 22 °C) δ: 72.1,
125.9, 126.3, 127.2, 127.4, 128.0, 132.5, 142.3, 149.8, 150.9.
1
products were detected by H NMR.
Attempted reductive elimination from
(dpms)PtIVPh(OH)(OMe) (9)
Reaction in DMSO-d6
Attempted reductive elimination from sym-
A sample of (dpms)PtPh(OMe)(OH) (2 mg, 3.5 µmol) was
dissolved in 0.7 mL of DMSO-d6. The solution was placed
into an NMR Young tube and Teflon-sealed under argon.
The solution was heated at 80–100 °C, periodically cooled
(dpms)PtIVPh2(OH) (sym-7) in DMSO-d6 solution
A sample of sym-(dpms)PtPh2(OH) (2 mg, 3.2 µmol) was
dissolved in dry DMSO-d6 (0.7 mL), and solution was
placed into an NMR Young tube under an argon atmosphere.
The Young tube was heated at 100 °C in a silicon-oil bath.
The only reaction observed was isomerization of 7 into cor-
responding unsymmetrical isomer (half-life is 26 h). After
6 days, the isomerization was complete, yield of unsym-7 >
1
down to room temperature and analyzed by H NMR. Slow
reaction occurred at 80 °C with a half-life of ~47 h. The re-
action continued at 100 °C with a half-life of 4.5 h; quantita-
tive formation of only one platinum-containing product,
(dpms)PtPh(DMSO-d6), was observed. 1H NMR of the prod-
uct was identical to that of (dpms)PtPh(DMSO-d6) obtained
by dissolving (dpms)Pt(MeOH) in DMSO-d6; ESI of acidi-
fied solution diluted with methanol showed the presence of a
signal with m/z = 606.1 (calcd. For (dpms)PtPh(C2D6SO)H+,
C19H15D6N2S2O4195Pt, m/z 606.1). One equivalent of metha-
1
97% by H NMR spectroscopy. No biphenyl or phenol were
detected.
1H NMR (DMSO-d6, 22 °C) δ: 1.37 (br s, 1H), 6.65 (d,
3
J = 8.2 Hz, J195PtH = 44 Hz, 2H), 6.78 (s, 1H), 6.88–7.12
(m, 6H), 7.20–7.39 (m, 2H), 7.59 (ddd, J = 7.9, 5.9, 1.5 Hz,
1H), 7.65 (ddd, J = 7.9, 5.7, 1.3 Hz, 1H), 8.00 (dd, J = 5.7,
1.5 Hz, 1H), 8.08 (d, J = 7.9 Hz, 1H), 8.14 (dd, J = 7.9,
1.5 Hz, 1H), 8.20 (dd, J = 5.9, 1.5 Hz, 1H), 8.25 (td, J = 7.9,
1.5 Hz, 1H), 8.34 (td, J = 7.9, 1.5 Hz, 1H). 13C NMR
(DMSO-d6, 22 °C), δ: 71.9, 124.3, 125.1, 125.5, 125.8,
126.9, 127.1, 127.3, 127.4, 128.4, 128.7, 132.7, 133.8,
141.6, 142.6, 148.7, 150.3, 152.7, 152.9.
1
nol was released into solution, according to H NMR spec-
troscopy.
Reactions in DMF-d7 and CD3CN
Analogous procedure was applied to reactions in DMF-d7
and CD3CN as solvents. NMR Young tubes with the samples
1
were heated at 100 °C and periodically monitored by H
© 2008 NRC Canada

120
Can. J. Chem. Vol. 87, 2009
NMR. Formation of a complex mixture of unidentified prod-
ucts was evident by H NMR spectroscopy.
(PRF#42307-AC3), and the NSF (CHE-0614798) for the fi-
nancial support of this work.
1
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3
4H), 7.24 (dd, J = 7.5, 1.5 Hz, J195PtH = 45 Hz, 2H), 7.52
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3J195PtH = 63 Hz, 1H), 8.85 (dd, J = 5.5, 1.5 Hz, 1H). ESI of
acidified solution diluted with methanol exhibited only one
peak, m/z 566.1 (Calcd. for (dpms)195PtPh(CD3CN)H+,
C19H15D3N3O3195PtS: 566.1).
The precipitate formed in the reaction mixture was dis-
1
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Acknowledgements
We thank the University of Maryland, the Donors of the
American Chemical Society Petroleum Research Fund
4 Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of
Unpublished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 3796. For more
information on obtaining material, refer to cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml. CCDC 683095 and 683096 contain the crystallo-
graphic data for this manuscript. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (Or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2008 NRC Canada