Oxidation of dimethylplatinum(ii) complexes with a peroxyacid

Article abstract of DOI:10.1039/c3dt50585e

The complexes [PtMe₂(NN)], NN = 2,2′-bipyridine = bipy, 1a; NN = di-2-pyridylamine = dpa, 1b; NN = di-2-pyridyl ketone = dpk, 1c, NN = 4,4′-bis(ethoxycarbonyl)-2,2′-bipyridine, bebipy, react with m-chloroperoxybenzoic acid to give the platinum(iv) complexes [Pt(OH)(O ₂C-3-C₆H₄Cl)Me₂(NN)], NN = bipy, 2, or [Pt(OH)(OH₂...O₂C-3-C₆H ₄Cl)Me₂(NN)], NN = bipy, 3a; dpa, 3b; bebipy, 3d, or [Pt(OH)₂Me₂(dpkOH)]₃[Pt(OH)(OH ₂)Me₂(dpkOH)][H(O₂C-3-C₆H ₄Cl)₂]·2MeOH, 4₃·5·2MeOH. The reactions are proposed to occur by a polar oxidative addition mechanism, followed in most cases by the coordination of water. Complex 3a crystallises as a supramolecular polymer, the compound 4₃·5·2MeOH crystallises as a supramolecular sheet structure, and 3d easily forms a gel, all through strong intermolecular hydrogen bonding.

Full text of DOI:10.1039/c3dt50585e

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Oxidation of dimethylplatinum(II) complexes with a
peroxyacid†
Cite this: Dalton Trans., 2013, 42, 10444
Kyle R. Pellarin, Matthew S. McCready and Richard J. Puddephatt*
The complexes [PtMe2(NN)], NN = 2,2’-bipyridine = bipy, 1a; NN = di-2-pyridylamine = dpa, 1b; NN = di-2-
pyridyl ketone = dpk, 1c, NN = 4,4’-bis(ethoxycarbonyl)-2,2’-bipyridine, bebipy, react with m-chloroperoxy-
benzoic acid to give the platinum(IV) complexes [Pt(OH)(O2C-3-C6H4Cl)Me2(NN)], NN = bipy, 2, or [Pt(OH)-
(OH2⋯O2C-3-C6H4Cl)Me2(NN)], NN = bipy, 3a; dpa, 3b; bebipy, 3d, or [Pt(OH)2Me2(dpkOH)]3[Pt(OH)-(OH2)-
Me2(dpkOH)][H(O2C-3-C6H4Cl)2]·2MeOH, 43·5·2MeOH. The reactions are proposed to occur by a polar
oxidative addition mechanism, followed in most cases by the coordination of water. Complex 3a crystal-
lises as a supramolecular polymer, the compound 43·5·2MeOH crystallises as a supramolecular sheet
structure, and 3d easily forms a gel, all through strong intermolecular hydrogen bonding.
Received 3rd March 2013,
Accepted 21st May 2013
DOI: 10.1039/c3dt50585e
www.rsc.org/dalton
Introduction
The oxidation of methylplatinum(II) complexes with oxygen,
peroxides or other oxygen atom donors can constitute a key
step in potential catalytic cycles for the oxidation of methane
to methanol.1,2 The reactions may involve oxo, peroxo, super-
oxo, hydroperoxo or hydroxo complexes of platinum and these
functional groups are thought to be involved in many other
catalytic oxidation reactions.1–3 A few examples are shown in
Scheme 1. The oxidative addition of hydrogen peroxide to a
dimethylplatinum(II) complex, A, usually occurs with trans
stereochemistry to give B (e.g. NN = 1,10-phenanthroline, 2,2′-
bipyridine, di-2-pyridylamine) and the same product can be
formed by reaction with dioxygen in a moist solvent.1–7 Air oxi-
dation in methanol occurs to give D, and the intermediate
hydroperoxide complex C has been characterised.5 A protic
reagent, water or alcohol, is needed for these reactions but, in
the absence of such reagents, oxygen insertion has been
observed in a few cases, such as in the conversion of E to F
(NP = C5H4N-2-CH2-t-Bu2).7 Oxo complexes have not been
identified in the oxidation of dimethylplatinum(II) complexes,8
but oxygen atom abstraction from a dioxirane by G is reported
to give the oxoplatinum(IV) complex H.9
Scheme 1 Reactions with oxygen or peroxides.
of the cis-chelate complex K (NN = 4,4′-di-t-butyl-2,2′-bipyri-
dine) or oligomers formed by trans oxidative addition.12 The
carboxylate groups in these products are weakly coordinated
and can be displaced by hydrolysis.12
The reaction of A with dimethyldioxirane, dmdo, does not
lead to simple oxygen atom abstraction, but the oxidation is
coupled to proton transfer from water in the solvent to give an
intermediate proposed to be L, which then loses acetone to
give the same product B that is formed by oxidation of A with
hydrogen peroxide (Scheme 3).12
Complexes A (e.g. NN = 1,10-phenanthroline) can undergo
either (or both) cis or trans oxidative addition with dibenzoyl
peroxide to give I and/or J, and the product often seems to be
controlled by thermodynamic rather than kinetic factors
(Scheme 2).6,10,11 Similarly, phthaloyl peroxide can give a mixture
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7.
E-mail: pudd@uwo.ca
†CCDC 927485 and 927486. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c3dt50585e
Both dmdo and m-chloroperoxybenzoic acid, mcpba, are
used as oxygen atom transfer agents in organic chemistry,
to oxidise sulfides to sulfoxides (Scheme 4), phosphines to
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(NN)]+[m-ClC6H3CO2]−, with hydrogen bonding between
cations and anions, but only a partial structure determination
of the complex with NN = bipy could be obtained and so this
issue was not decided.4 This article reports a further study of
the oxidation reactions of dimethylplatinum(II) complexes A
with mcpba, in comparison to analogous reactions of dmdo
and hydrogen peroxide.
Results and discussion
The reactions of dimethylplatinum(II) complexes [PtMe2(NN)]
with mcpba were studied with four bis(pyridyl) ligands NN.
There were common features, but also significant differences,
so they will be described separately.
Scheme 2 Reactions with dibenzoyl peroxide or phthaloyl peroxide.
Reactions of [PtMe2(bipy)] with mcpba
The reactions of [PtMe2(bipy)], 1a, with mcpba are represented
in Scheme 5. When the reaction was carried out in acetone,
followed by recrystallisation of the white complex formed from
acetone–pentane, the product was characterised as 3a, with
some uncertainty about H-atom positions, as discussed below.
The formation of 3a requires oxidation by mcpba and also the
addition of a molecule of water. However, when the reaction of
1a with mcpba was carried out in acetone-d6 in an NMR tube,
a different complex was formed and tentatively characterised
as 2 (Scheme 5). Recrystallization of complex 2, which was
sparingly soluble in acetone, always led to addition of water
and formation of complex 3a.
Scheme 3 Proposed mechanism of oxidation with dmdo.
The symmetry of the complexes is readily deduced from the
1H NMR spectra. The complex 3a has an effective Cs symmetry
and so it gives only a single methylplatinum resonance
2
[Fig. 1a, δ = 1.85, J(PtH) = 70 Hz] and four resonances for the
bipy protons. On the other hand, complex 2 has only C1 sym-
metry and it gives two methylplatinum resonances (Fig. 1b, δ =
2
2
1.12, J(PtMe) = 75 Hz, MePt trans to O; 1.80, J(PtMe) = 69 Hz,
MePt trans to N) and eight bipy resonances in the 1H NMR
spectrum. However, the data do not distinguish between the
Scheme 4 Comparison of the mechanisms of oxidation of dialkyl sulfides with
mcpba and dmdo.
phosphine oxides, or alkenes to epoxides.13 Peroxyacids differ
from dioxiranes in that they already contain a proton, so the
oxidation of platinum(II) complexes should not require coup-
ling to proton transfer from water, as in the oxidation with
dmdo (Scheme 3). The Tilset group has reported that oxidation
of dimethylplatinum(II) complexes with mcpba gives com-
plexes B (NN = bipy or 4,4′-Me2bipy) with hydrogen bonding
between B and the m-chlorobenzoic acid that is also formed.
The complexes could also be formulated as [PtMe2(OH)(OH2)-
Scheme 5 Reactions of complex 1a with mcpba.
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Fig. 1 Methylplatinum resonances in the 1H NMR spectra (400 MHz) in
acetone-d6 of (a) complex 3a and (b) complex 2. The * indicates 195Pt satellite
spectra and # is an unassigned impurity.
possible isomers 2 and 2* (Scheme 5). The complex 3a also
shows peaks in the 1H NMR spectrum for the 3-chlorobenzoate
group. This complex has previously been reported and, as dis-
cussed then,4 the data do not clearly distinguish between the
formulations [PtMe2(bipy)(OH)(OH⋯HO2CC6H4Cl)], 3a*, or
[PtMe2(bipy)(OH)(OH2⋯O2CC6H4Cl)Me2(bipy)], 3a**, and if
the hydrogen bonding is strong, these structures are effectively
equivalent (Scheme 5). The ESI-MS of complex 2 gives the
highest mass peak centered at m/z = 554.1 g mol−1, as expected
for [2 + H]+, thus supporting the formulation without an extra
water molecule. The cis stereochemistry of this reaction is
unusual.6,14 Complex 2 is expected to be the thermodynami-
cally preferred product because only the cis isomer allows
intramolecular hydrogen bonding, but it also appears to be
the kinetically controlled product. Thus, no trans intermediate
was detected when the reaction was carried out at −20 °C, with
monitoring by 1H NMR spectroscopy.
Fig. 2 Part of the supramolecular polymeric structure of complex 3. Selected
parameters: Pt(1)–O(1) = 2.001(4), Pt(1)–O(2) = 2.037(4), O(3)–C(13) = 1.261(7),
O(4)–C(13) = 1.245(7), O(2)–O(3) = 2.598(5), O(1A)–O(4) = 2.781(3), O(2)–O(1A) =
2.485(6) Å.
The structure of complex 3a is shown in Fig. 2. It confirms
the octahedral stereochemistry at platinum(IV) with the oxygen-
donor groups in mutually trans positions and with the carboxy-
late or carboxylic acid in the outer sphere. The compound
exists as a supramolecular polymer in the solid state with
intermolecular hydrogen bonds indicated by the short dis-
tances O(2)–O(3) = 2.598(5), O(1A)–O(4) = 2.781(3), O(2)–O(1A)
= 2.485(6) Å.15
Chart 1 Possible hydrogen bonding forms in the supramolecular polymer 3a.
structures are shown in Chart 1, in which M and N might re-
The hydrogen atoms in the structure could not be located present 3a** and O and P might represent 3a*. First consider
and refined, so it is interesting to speculate on their positions. the carbonyl distances. In M and N, the carbonyl distances are
The relevant questions are whether the structure is best expected to be roughly equal whereas in O and P they might be
described as a dihydroxoplatinum(IV) complex with H-bonded significantly different. The distance O(4)–C(13) = 1.245(7) is
carboxylic acid, 3a*, or as
a hydroxo(aqua)platinum(IV) slightly shorter than O(3)–C(13) = 1.261(7) Å, which might
complex with H-bonded carboxylate, 3a**, and, if the latter, favour structure O, but the difference is not statistically signifi-
which of the oxygen donors is the hydroxide and which is the cant, which might be argued to favour structure M or N. Next
aqua molecule? Given that the structure is an average over the consider the Pt–O distances, in the context that a Pt–OH dis-
entire crystal, and that there could be easy proton transfer in tance is expected to be slightly shorter than a Pt–OH2 distance.
any O–H⋯O or O⋯H–O unit, it should be recognised that The distance Pt(1)–O(1) = 2.001(4) is slightly shorter than
these questions may not be easily answered. The four possible Pt(1)–O(2) = 2.037(4) Å, which favours structure M over N but
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does not exclude O or P. Of the H-bond distances involving the
carboxylate group, O(2)–O(3) = 2.598(5) is significantly shorter
than O(1A)–O(4) = 2.781(3) Å, which favours M over N (stronger
bond to OH2 over OH−) or O over P (weaker H-bond to CvO).
The shortest H-bond distance is O(2)–O(1A) = 2.485(6) Å, indi-
cating a very strong hydrogen bond between these atoms.15,16
In such a case it is possible that the hydrogen atom is symme-
trically placed between the oxygen atoms,15 and then N and M
or O and P are equivalent. The data do not distinguish unequi-
vocally between the possible structures, but suggest that struc-
ture M may be the most highly populated one of the four.
Several cationic aqua complexes of both platinum(II) and
platinum(IV) are known, usually with weakly coordinating
anions, and they are always acidic and take part in hydrogen
bonding.16
Scheme 6 Oxidation of [PtMe2(dpk)] with mcpba.
indicates the presence of equal amounts of the neutral
complex 4, which is also formed by oxidation of [PtMe2(dpk)]
with hydrogen peroxide,6 and the cationic complex 5, stabil-
ised by the [H(O2CC6H4Cl)2]− anion (Scheme 6). However, a
solution in CD3OD gave a single methylplatinum resonance
[δ = 1.54, 2J(PtH) = 70 Hz] and four pyridyl resonances,
suggesting the presence of a single product of trans oxidative
addition. The ESI-MS from a methanol solution contained a
dominant peak centered at m/z = 444.1, as expected for the ion
[PtMe2(dpkOH)(OH2)]+ present in 5. Clearly, major differences
from the earlier examples include the involvement of the
ketone group of the dpk ligand in the chemistry and the
absence of outer sphere coordination of the carboxylate.
The structure was finally determined using a crystal grown
from chlorobenzene–methanol–pentane and was characterised
as [PtMe2(dpkOH)(OH)]3[PtMe2(dpkOH)(OH2)][H(O2CC6H4Cl)2]·
2MeOH, 43·5·2MeOH. The structure is complex and the
key building blocks are illustrated in Fig. 3. The anions
[H(O2CC6H4Cl)2]− (Fig. 3a) are located at the center of sym-
metry with the distance O(11)⋯O(11A) = 2.373(7) Å. This is
similar to the structure reported for the potassium salt, which
has O⋯O = 2.437(6) Å and which is suggested to contain a
symmetrical O⋯H⋯O linkage.17 Once the anion is character-
ised, the stoichiometry requires that there be one cation for
every four platinum atoms and so indicates the ratio of three
equivalents of neutral [PtMe2(dpkOH)(OH)], 4, to one equi-
valent of cationic [PtMe2(dpkOH)(OH2)]+, 5. All platinum
centers are crystallographically equivalent so, unless the extra
proton lies at a 4-fold symmetry site, there must be disorder of
its position. Fig. 3b shows that there are dimer units formed
by complementary hydrogen bonding between the dpkOH
ligands, with a center of symmetry between the individual
molecules [O(1)⋯O(2A) = O(2)⋯O(1A) = 2.668(3) Å]. The
characterisation of hydrogen bonding between PtOH, PtOH2
and MeOH groups is problematic, as indicated in Fig. 3c.
There are six oxygen atoms, comprising four platinum O(3)
atoms and two methanol O(7) atoms arranged in a roughly rec-
tangular fashion about the centre of symmetry. The left and
right sides are related by a mirror plane which contains the
two methanol molecules (the atoms of the anions also lie in
Reaction of [PtMe2(di-2-pyridylamine)] with mcpba
This reaction with [PtMe2(dpa)] is thought to occur according
to eqn (1), to give complex 3b. In this case, the initial reaction
product was sparingly soluble in acetone and precipitated
from solution. After purification, the 1H NMR spectrum in
CD3OD contained only one methylplatinum resonance [δ =
2
1.64, J(Pt–H) = 64 Hz] and four pyridyl resonances, indicating
the formation of a product of trans oxidative addition. Reson-
ances for the m-chlorobenzoate group were also observed. The
presence of an additional water molecule is indicated by
analytical data but is not proved. The most prominent peak in
the ESI-MS was observed at m/z = 413.1, corresponding to
[PtMe2(dpa)(OH)]+. This is consistent with structure 3b, with
loss of water and chlorobenzoate, but also with a complex
[PtMe2(dpa)(OH)(O2CC6H4Cl], with loss of chlorobenzoate, so
the proposed structure is tentative. We have not been able to
grow crystals suitable for X-ray structure determination. For
this product, the potential for intermolecular hydrogen
bonding is very strong because, in addition to the hydrogen
bonding groups present in 3a, the NH group of the dpa ligand
in 3b is also a good hydrogen bond donor and acceptor.6
ð1Þ
Reaction of [PtMe2(di-2-pyridyl ketone)] with mcpba
The reaction of [PtMe2(dpk)] with mcpba in acetone gave a
white precipitate, whose solid state structure after purification
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Fig. 4 Part of the infinite supramolecular sheet structure formed by hydrogen
bonding.
Fig. 3 Structures of key components in complex 43·5·(MeOH)2: (a) the anion
[H(O2CC6H4Cl)2]−, (b) a dimer unit formed by H-bonding between dpkOH
groups, (c) a tetramer unit formed by H-bonding between PtOH, PtOH2 and
MeOH groups. Selected bond parameters: Pt(1)–C(12) = 2.014(11); Pt(1)–C(13) =
2.058(9); Pt(1)–O(3) = 2.022(6); Pt(1)–O(2) = 2.023(5); O(3)⋯O(3B) = 2.584(6);
O(3)⋯O(7A) = 2.631(5); O(1)⋯O(2A) = 2.675(3); O(11)⋯O(11A) = 2.380(7) Å.
Reaction of [PtMe2(4,4′-bis(ethoxycarbonyl)-2,2′-bipyridine)],
1d, with mcpba
The trans oxidative addition of hydrogen peroxide to [PtMe2-
(bebipy)], 1d, occurs easily but the product [Pt(OH)2Me2(be-
bipy)] decomposes easily by loss of the bebipy ligand to give
the insoluble polymeric complex [{Pt(OH)2Me2}n].18,19 Another
potential effect arises from the ability of the carbonyl groups
of bebipy to act as hydrogen bond acceptors,18 so it was of
interest to study the reaction of [PtMe2(bebipy)] with mcpba.
The reaction is thought to occur according to Scheme 7.
The addition of mcpba to a concentrated solution of 1d in
acetone or dichloromethane gave an immediate color change
from purple to pale yellow, but then the mixture became a gel
(Fig. 5). On dilution, a fluid solution could be obtained but it
reformed the gel on concentration. An SEM image showed that
the xerogel contains interwoven worm-like structures (Fig. 5).
This unusual property suggests that 3d forms a highly porous
network structure through intermolecular hydrogen bonding,
and that a large amount of solvent can be trapped in the
pores.20
this plane), while the top and bottom are related by a horizon-
tal rotation axis. There should be one PtOH2, three PtOH and
two MeOH groups, to give seven hydrogen atoms available for
hydrogen bonding. The relevant hydrogen bonding distances
are O(3)⋯O(7A) = O(7A)⋯O(3C) = 2.631(5) Å and O(3)⋯O(3B) =
O(3A)⋯O(3C) = 2.584(6) Å. Only six of the seven OH hydrogen
atoms are required for forming six hydrogen bonds, so one is
expected to be in a non-bridging site (the O(7)⋯O(7D) = 3.65 Å
distance is too long for the extra proton to lie midway between
them at the inversion center). We have not been able to
reliably locate the H-atoms, so they were placed somewhat
arbitrarily and are not shown in Fig. 3c. It should be recog-
nised that there are several possible solutions on how to place
the disordered H-atoms, and it is also possible that some of
the hydrogen bonds may be symmetrical.
Because the complex forms a gel, it could not be crystallised
and, while evaporation of a solvent under vacuum gave a solid,
it was not possible to remove all of the solvent. The solid
product was washed with ether and pentane, dried under
vacuum and then was characterised spectroscopically. The
1H NMR spectrum gave a single methylplatinum resonance
The combination of the two types of platinum building
blocks shown in Fig. 3b and 3c gives rise to an unusual sheet
structure, as shown in Fig. 4. Each tetramer unit in Fig. 3c is
linked to four others through the hydrogen bonding between
the ketal groups (Fig. 3b). The anions are loosely connected in
chains passing through the central cavity of Fig. 4.
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Scheme 7 Reactions of [PtMe2(bebipy)] with H2O2 and mcpba.
Fig. 5 Left, a photograph of the gel from 3d formed in dichloromethane;
right, SEM image of the xerogel.
Fig. 6 Frontier orbitals for the first step in oxidative addition. Potential inter-
mediates were generated by bringing the molecules of 1a and PhCO3H together
with one or both Pt–O distances at 2.4 Å, then searching for an energy
minimum. H-atoms are usually omitted for clarity.
[δ(MePt) = 1.78, 2J(PtH) = 66 Hz] and only one set of resonances
for the ethoxy and pyridyl resonances, indicating trans oxi-
dative addition. EDX analysis showed that the atomic ratio
Pt : Cl = 1 : 1, as expected for 3d, and shows that the m-chloro-
benzoate group is present. The ESI-MS of a dilute solution in
dichloromethane gave a major peak at m/z = 542.1, assigned to
the ion [Pt(OH)Me2(bebipy)]+, and also significant peaks at m/z
= 1119 and 1678, assigned to [{Pt(OH)2Me2(bebipy)}n + H]+,
with n = 2 and 3 respectively. This indicates the presence of oli-
gomers in solution. It is not possible to determine the nature
of the intermolecular hydrogen bonding in 3d but, because
the gel formation was only observed with the product from 1d,
it is reasonable to suggest that it involves the ethoxycarbonyl
groups as additional hydrogen bond acceptors when compared
to 3a.
formation of an intermediate hydrogen-bonded ion pair [Pt-
(OH)Me2(bipy)]+[PhCO2]−. The new HOMO is largely located
on the benzoate group (Fig. 6b). Sideways attack (Fig. 6c) is dis-
favoured by repulsive interactions with “lone-pair” orbitals on
oxygen. Symmetry requires that the nucleophile would be the
lower energy 5dπ orbital of 1a and no easy concerted route to 2
or 2* could be found by the side-on approach of the O–O bond
of perbenzoic acid to platinum. Nucleophilic attack at the ben-
zoate oxygen atom (Fig. 6d) primarily is not favoured, primarily
because hydroxide is a poor leaving group, but also for steric
reasons. As is clear from Fig. 6a and 6b, the angle of end-on
attack Pt⋯O–O can deviate considerably from 180° while still
allowing good overlap of the frontier orbitals in the favoured
line of approach.
Theoretical considerations
The oxidative addition reactions have been modeled by DFT
The likely intermediate and products are shown in
(see the Experimental section for details) for the case with NN Scheme 8, with calculated structures in Fig. 7. Calculated rela-
= bipy, using perbenzoic acid as a model for mcpba. The fron- tive energies are shown in Fig. 8. We use the same labels for
tier orbitals are the 5dz2 orbital (HOMO) of 1a and the σ*(OO) the model benzoate compounds calculated (Fig. 7 and 8) and
orbital of the peroxy acid, as indicated in Fig. 6a.4,6–8 Several the m-chlorobenzoate compounds which were studied experi-
lines of approach were considered. The easiest line of attack is mentally (Scheme 8). The first intermediate is Q, in which the
at the hydroxyl oxygen atom, and this approach leads to very leaving benzoate ion is stabilised by intramolecular hydrogen
easy oxidative addition as illustrated in Fig. 6b, with the bonding [calculated PtO–H = 1.06, CvO⋯H = 1.55] in the
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Fig. 8 Calculated relative energies of proposed intermediates and products.
adjacent hydrogen-bonded carboxylate can coordinate to give
either 2 or 2*. In the gas phase, complex 2 is calculated to be
more stable than 2* by 20 kJ mol−1 (Fig. 8), so this structure 2
is tentatively suggested. The NMR spectrum (Fig. 1) cannot
easily distinguish between 2 and 2*. Complex 2* is calculated
to have a slightly more unsymmetrical, and probably weaker,
hydrogen bond [O–H = 1.01, CvO⋯H = 1.92, O⋯O = 2.83 Å]
than 2 [O–H = 1.02, CvO⋯H = 1.88, O⋯O = 2.82 Å].
Scheme 8 Proposed mechanism of the reaction of 1a with mcpba.
Complex Q may also react with water to give 3a*, which can
then rearrange by carboxylate or proton transfer to give 3a.
Complex 3a is strongly favoured because the carboxylate hydro-
gen bond is much more symmetrical, and stronger, to co-
ordinated water [PtO⋯H = 1.20, CvO⋯H = 1.22, O⋯O =
2.40 Å] compared to hydroxide in 3a* [PtO–H = 1.06, CvO⋯H
= 1.59, O⋯O = 2.65 Å]. The calculated strong, symmetrical
hydrogen bond in 3a is consistent with the observation that a
Pt+OH2 group is almost as acidic as a carboxylic acid.4
Conclusions
The peroxy acid mcpba rapidly oxidises dimethylplatinum(II)
complexes 1a to 1d. The initial step is probably the same in
each case to give an intermediate analogous to Q (Scheme 8,
Fig. 7), by nucleophilic attack by platinum at the peroxide, but
then there are significant differences. Only in the case of 1a
was the primary product of oxidative addition 2a or 2a* charac-
terised, while other complexes formed adducts with water. For
reactions with complexes 1a, 1b and 1d the final complexes
are trans[Pt(OH)(OH2⋯O2C-3-C6H4Cl)Me2(NN)], 3a, 3b and 3d
respectively, in which the m-chlorobenzoate group is strongly
hydrogen bonded in the outer sphere of the complex. The reac-
tion with 1c took place with the participation of the carbonyl
group in forming the product 43·5·(MeOH)2, which contains
fac-tridentate dpkOH ligands. In the crystalline state, complex
Fig. 7 Calculated structures of proposed intermediates and products.
same way as proposed in other oxidation reactions with mcpba 3a forms a supramolecular polymer while 43·5·(MeOH)2 forms
(Scheme 4).13
a novel type of sheet structure, with both structures formed
The 5-coordinate platinum(IV) complex intermediate Q is through strong intermolecular hydrogen bonding. Finally,
expected to undergo easy pseudorotation,21 which can generate complex 3d forms gels in acetone or dichloromethane
an empty coordination site cis to the hydroxide, and then the solutions, and it is suggested that there is additional
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intermolecular hydrogen bonding involving the ester substitu- 8 Hz, H5′), 8.39 (dd, 1H, J(H3H4) = 8 Hz, J(H4H5) = 8 Hz, H4),
ents in this case. Overall, the work has given new insights into 8.46 (dd, 1H, 3J(H3′H4′) = 8 Hz, 3J(H4′H5′) = 8 Hz, H4′), 8.73
the oxidative addition of peroxides, and provided interesting (d, 1H, 3J(H3H4) = 8 Hz, H3), 8.77 (d, 1H, 3J(H3′H4′) = 8 Hz, H3′),
3
3
3
2
examples of polymer, sheet and gel formation by self-assembly 9.05 (d, 1H, J(H5H6) = 6 Hz, J(PtH) = 22 Hz, H6), 9.46 (d, 1H,
of organoplatinum complexes.
3J(H5′H6′) = 6 Hz, H6′). ESI-MS: m/z = 554.1. Calc. for [2 + H]+:
554.07. Anal. Calc. for C19H21ClN2O3Pt·H2O: C, 39.90; H, 3.70;
N, 4.90. Found: C, 39.69; H, 3.49; N, 4.80%.
Experimental
[PtMe2(OH)(OH2)(bipy)]+[3-ClC6H4CO2]−, 3a
Reactions were carried out using standard Schlenk techniques.
NMR spectra were recorded using a Varian Mercury 400 or
Varian INOVA 400 or 600 MHz spectrometer. Mass spectro-
metric analysis was carried out using an electrospray PE-Sciex
Mass Spectrometer (ESI-MS) coupled with a TOF detector. The
ligand bebipy, and the platinum complexes [Pt2Me4(μ-SMe2)2]
and 1a–1d were prepared according to the literature
methods.22
For X-ray structure determinations, a crystal was mounted
on a glass fibre. Data were collected at low temperature 150(2)
K using a Bruker Smart Apex II CCD diffractometer. The unit
cell parameters were calculated and refined from the full data
set. The crystal data and refinement parameters for all com-
plexes are listed in Table 1.23
DFT calculations were carried out by using the Amsterdam
Density Functional program based on the BLYP functional,
with a double-zeta basis set and first-order scalar relativistic
corrections.24 The reported results are from gas phase calcu-
lations. The energy minima were confirmed by vibrational fre-
quency analysis in each case.
To a solution of [PtMe2(bipy)] (20.0 mg, 0.0526 mmol) in
acetone (5 mL) was added meta-chloroperbenzoic acid (9.0 mg,
0.0526 mmol). The solution was stirred for 30 min, and then
layered with pentane to precipitate a white solid, which was
separated, washed with pentane and dried in vacuo. Yield:
2
23.5 mg, 81%. NMR in CD3OD: δ(1H) = 1.85 (s, 6H, J(PtH) =
3
3
70 Hz, PtMe), 7.42 (t, 1H, J(H4′H5′) = 8 Hz, J(H5′H6′) = 8 Hz,
H5′), 7.47 (d, 1H, J(H5′H6′) = 8 Hz, H6′), 7.86 (dd, 2H, J(H5H6)
3
3
= 6 Hz, 3J(H5H4) = 8 Hz, H5), 7.90 (d, 1H, 3J(H4′H5′) = 8 Hz, H4′),
7.97 (s, 1H, H2′), 8.29 (t, 2H, J(H4H3) = 8 Hz, J(H4H5) = 8 Hz,
3
3
H4), 8.67 (d, 2H, J(H3H4) = 8 Hz, H3), 9.00 (d, 2H, J(H6H5) =
6 Hz, H6). ESI-MS: m/z = 416.1. Calc. for [3a − ClC6H4CO2]+:
416.09. Anal. Calc. for C19H21ClN2O4Pt·H2O: C, 38.68; H, 3.93;
N, 4.75. Found: C, 38.16; H, 3.20; N, 4.65%.
3
3
[PtMe2(dpa)(OH)(OH2)]+[3-ClC6H4CO2]−, 3b
This was prepared similarly from [PtMe2(dpa)] (20.1 mg,
0.0507 mmol) and m-chloroperbenzoic acid (13.0 mg,
0.0527 mmol). Yield: 65%. NMR in CD3OD: δ(1H) = 1.65 (s,
6H, 2J(PtH) = 66 Hz, PtMe), 7.28 (dd, 2H, 3J(H5H6) = 6 Hz,
3J(H5H4) = 8 Hz, H5), 7.36–7.39 (m, 2H, H3), 7.37 (m, 1H, H5′),
cis-[PtMe2(OH)(O2C-3-C6H4Cl)(bipy)], 2
2
2
7.46 (d, 1H, J(H4′H5′) = 8 Hz, H4′), 7.88 (d, 1H, J(H5′H6′) = 8
Hz, H6′), 7.95 (s, 1H, H2′), 7.97 (ddd, 2H, 3J(H4H5) = 8 Hz,
3J(H4H3) = 9 Hz, 4J(H4H6) = 2 Hz), 8.45 (d, 2H, 3J(H6H5) = 6 Hz,
H6). ESI-MS: m/z = 413.1. Calc for [PtMe2(dpa)OH)]+: 413.09.
Anal. Calc. for C19H22ClN3O4Pt: C, 39.33; H, 3.42; N, 7.40.
Found: C, 38.88; H, 3.78; N, 7.16%.
To a solution of [PtMe2(bipy)] (4.00 mg, 0.0105 mmol) in
acetone-d6 (1 mL) in an NMR tube was added m-chloroperben-
zoic acid (1.80 mg, 0.0105 mmol). Upon addition, the color of
the solution changed from red to colorless. NMR in acetone-
d6: δ(1H) = 1.12 (s, 3H, 2J(PtH) = 75 Hz, PtMe), 1.80 (s, 3H,
3
3
2J(PtH) = 69 Hz, PtMe), 7.19 (m, J(H4′′H5′′) = 8 Hz, J(H5′′H6′′) =
8 Hz, H5′′), 7.29 (d, 3J(H4′′H5′′) = 8 Hz, H4′′), 7.57 (d, 3J(H5′′H6′′) =
[Pt(OH)Me2(dpkOH)]3[PtMe2(OH2)(dpkOH)]+[H(O2C-3-
C6H4Cl)2]−, 4.5·[H(O2C-3-C6H4Cl)2]
8 Hz, H6′′), 7.96 (dd, 1H, J(H5H6) = 6 Hz, J(H4H5) = 8 Hz, H5),
3
3
7.97 (s, 1H, H2′′), 8.00 (dd, 1H, 3J(H5′H6′) = 6 Hz, 3J(H4′H5′) =
To a solution of [PtMe2(dpk)] (5.40 mg, 0.0131 mmol) in
acetone (5 mL) was added mcpba (3.3 mg, 0.0131 mmol). The
color changed from red to colorless. The solution was layered
with pentane (3 mL) to precipitate the product as a white
powder, which was washed with pentane (3 × 2 mL) and ether
(3 × 2 mL) and dried in vacuo. Yield: 73%. NMR in CD3OD:
δ(1H) = 1.54 (s, 6H, 2J(PtH) = 70 Hz, PtMe), 7.56 (ddd, 2H,
3J(H5H6) = 6 Hz, 3J(H5H4) = 8 Hz, 4J(H5H3) = 1 Hz, H5), 7.92
Table 1 Crystal and structure refinement data
Complex
3a
43·5·(MeOH)2
Formula
Fw
C19H21ClN2O4Pt
571.92
C68H81Cl2N8O18Pt4
2149.65
0.71073
Monoclinic
C2/m
23.271(6)
20.831(4)
7.896(2)
90
104.39(3)
90
3707.7(14)
2
λ/Å
Cryst. syst.
Sp. gp.
0.71073
Monoclinic
P21/c
3
4
(dd, 2H, J(H3H4) = 8 Hz, J(H3H5) = 1 Hz, H3), 8.07 (ddd, 2H,
a/Å
b/Å
c/Å
α/°
12.8754(7)
10.0368(5)
15.0169(8)
90
3J(H4H5) = 8 Hz, 3J(H4H3) = 8 Hz, 4J(H4H6) = 1 Hz, H4), 8.45
3
4
(dd, 2H, J(H6H5) = 6 Hz, J(H6H4) = 1 Hz, H6), 7.40 (dd, 1H,
2J(H5′H6′) = 8 Hz, 2J(H4′H5′) = 8 Hz, H5′), 7.48 (d, 1H, 2J(H5′H6′) =
β/°
93.153(8)
90
1937.66(18)
4
2
γ/°
8 Hz, H6′), 7.90 (d, 1H, J(H4′H5′) = 8 Hz, H4′), 7.96 (s, 1H, H2′).
V/Å3
Anal. Calc. for C66H74Cl2N8O16Pt4: C, 37.99; H, 3.57; N, 5.37.
Found: C, 37.68; H, 3.81; N, 5.21%. ESI-MS: m/z = 444.1. Calc.
for [4 + H]+: 444.1.
Z
R1, I > 2σ(I)
wR2, all data
0.032
0.077
0.052
0.138
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Dalton Transactions
[PtMe2(OH)(bebipy)(OH2)]+[3-ClC6H4CO2]−, 3d
R. J. Puddephatt, Chem. Commun., 2009, 1487; M. Safa,
M. C. Jennings and R. J. Puddephatt, Organometallics, 2012,
31, 3539; F. Zhang, M. C. Jennings and R. J. Puddephatt,
Chem. Commun., 2007, 1496; R. A. Taylor, D. J. Law,
G. J. Sunley, A. J. P. White and G. J. P. Britovsek, Chem.
Commun., 2008, 2800.
7 K. A. Grice and K. I. Goldberg, Organometallics, 2009, 28,
953; R. A. Taylor, D. J. Law, G. J. Sunley, A. J. P. White and
G. J. P. Britovsek, Angew. Chem., Int. Ed., 2009, 48, 5900.
8 K. R. Pellarin, M. S. McCready and R. J. Puddephatt,
Organometallics, 2012, 31, 6388.
9 E. Poverenov, I. Efremenko, A. I. Frenkel, Y. Ben-David,
L. J. W. Shimon, G. Leitus, L. Konstantinovski, J. M. L. Martin
and D. Milstein, Nature, 2008, 455, 1093; I. Efremenko,
E. Poverenov, J. M. L. Martin and D. Milstein, J. Am. Chem.
Soc., 2010, 132, 14886.
To a solution of [PtMe2(bebipy)] (39.3 mg, 0.0747 mmol) in
acetone (5 mL) was added mcpba (18.4 mg, 0.0747 mmol).
Upon addition, the solution color changed from purple to pale
yellow and then formed a gel. The solvent was removed under
vacuum, and the remaining solid was washed with ether and
pentane, and dried in vacuo. Yield: 83%. NMR in CD2Cl2: δ(1H)
3
2
= 1.44 (t, 6H, J(HH) = 7 Hz, CH3), 1.78 (s, 6H, J(PtH) = 66 Hz,
PtMe), 3.39 (br, OH), 4.45 (q, 4H, 3J(HH) = 7 Hz, CH2), 8.09
(dd, 2H, 3J(H5H6) = 5 Hz, 4J(H5H3) = 1 Hz, H5), 8.73 (d, 2H,
4J(H5H3) = 1 Hz, H3), 9.04 (d, 2H, 3J(H6H5) = 5 Hz, H6), 7.23
(dd, 1H, 3J(H5′H6′) = 8 Hz, 3J(H5′H4′) = 8 Hz, H5′), 7.37 (d,
3
3J(H6′H5′) = 8 Hz, H6′), 7.45 (d, 1H, J(H4′H5′) = 8 Hz, H4′), 7.84
(s, 1H, H2′). ESI-MS: m/z = 542.1, 1119.3, 1677.4. Calc. for
[PtMe2(bebipy)(OH)]+, 542.1; Calc. for {[PtMe2(bebipy)(OH)2]n +
H}+, 1119.3 when n = 2, 1678.4 when n = 3. EDX atom anal.:
Cl : Pt = 1.09 : 1.
10 A. J. Canty, M. C. Denney, G. van Koten, B. W. Skelton and
A. H. White, Organometallics, 2004, 23, 5432.
11 A. J. Canty, H. Jin, B. W. Skelton and A. H. White, Inorg.
Chem., 1998, 37, 3975.
Acknowledgements
12 K. R. Pellarin, M. S. McCready, T. I. Sutherland and
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We thank the NSERC (Canada) for financial support.
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