Oxidation of a dimethylplatinum(II) complex with oxaziridines: A hemiaminal intermediate but no oxo complex

Article abstract of DOI:10.1021/om400079b

The complex [PtMe₂(bipy)] (1; bipy = 2,2′-bipyridine) fails to react with the oxaziridine derivatives RCHON-t-Bu (R = H, Ph, 2-pyridyl) in acetone at room temperature, but an easy reaction occurs in methanol solution to give the platinum(IV) complex [Pt(OH)(OMe)Me ₂(bipy)] and the corresponding imine RCH=N-t-Bu. In the case with R = Ph, the hemiaminal intermediate [Pt(OMe)(OCHPhNH-t-Bu)Me₂(bipy)] was formed and then reacted only slowly to form [Pt(OH)(OMe)Me₂(bipy)] and PhCH=N-t-Bu. Computational studies indicate that the reaction of 1 with oxaziridines occurs to give a charge transfer complex but that further reaction requires assistance from hydrogen bonding and coordination with specific methanol molecules. The work provides strong support for the theory that oxygen atom transfer to 1 from either dioxiranes or oxaziridines must be coupled to proton transfer and does not involve oxoplatinum(IV) intermediates.

Full text of DOI:10.1021/om400079b

Article
pubs.acs.org/Organometallics
Oxidation of a Dimethylplatinum(II) Complex with Oxaziridines: A
Hemiaminal Intermediate but No Oxo Complex
Kyle R. Pellarin and Richard J. Puddephatt*
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7
S
* Supporting Information
ABSTRACT: The complex [PtMe2(bipy)] (1; bipy = 2,2′-bipyridine) fails to react
with the oxaziridine derivatives RCHON-t-Bu (R = H, Ph, 2-pyridyl) in acetone at
room temperature, but an easy reaction occurs in methanol solution to give the
platinum(IV) complex [Pt(OH)(OMe)Me2(bipy)] and the corresponding imine
RCHN-t-Bu. In the case with R = Ph, the hemiaminal intermediate [Pt(OMe)-
(OCHPhNH-t-Bu)Me2(bipy)] was formed and then reacted only slowly to form
[Pt(OH)(OMe)Me2(bipy)] and PhCHN-t-Bu. Computational studies indicate that
the reaction of 1 with oxaziridines occurs to give a charge transfer complex but that
further reaction requires assistance from hydrogen bonding and coordination with
specific methanol molecules. The work provides strong support for the theory that
oxygen atom transfer to 1 from either dioxiranes or oxaziridines must be coupled to
proton transfer and does not involve oxoplatinum(IV) intermediates.
[PtMe2(bipy)] (1; bipy = 2,2′-bipyridine) gave the
dihydroxoplatinum(IV) complex B and not the potential
oxoplatinum(IV) complex C.6,7 The dimethyldioxirane reagent
was prepared as a dilute solution in acetone, and this evidently
contained enough water impurity to give the observed product
B.6 No oxoplatinum complex could be detected, and it was
suggested that the oxygen atom transfer reaction was coupled
to proton transfer from water to give the hydroxo complex
directly.6 The oxo group in C would be highly reactive
according to theory, because there is no suitable orbital on
platinum to form a π bond to the oxo group.6,8 The
oxoplatinum(IV) complex A, for which platinum−oxygen π
bonding is possible,2b reacted only slowly with water to give the
corresponding dihydroxoplatinum(IV) complex.2c
INTRODUCTION
■
The oxygenation of both organic and inorganic compounds
may be catalyzed by platinum or its complexes, and platinum
oxides, hydroxides, peroxides, or alkoxides are often invoked as
reaction intermediates.1 This commercial significance has
naturally stimulated research into the synthesis and properties
of complexes containing these platinum−oxygen-bonded func-
tional groups.1−5 The reagent dimethyldioxirane can act as an
oxygen atom donor, and it has yielded the unique four-
coordinate oxoplatinum(IV) complex A (Scheme 1),2b,c
formulated as containing a PtO double bond, whereas
most known oxoplatinum complexes contain Pt2(μ-O) groups
with Pt−O single bonds.2a However, the reaction of
dimethyldioxirane with the dimethylplatinum(II) complex
This article reports reactions of oxaziridines of the formula
OCHRN-t-Bu (Scheme 2) with complex 1. Oxaziridines are
related to dioxiranes by replacement of one oxygen atom by an
NR group. They are considerably less reactive than dioxiranes
Scheme 1. Reactions of Dimethyldioxirane with
Organoplatinum(II) Complexes
a
Scheme 2. Reactions of Dioxiranes (E = O) or Oxaziridines
(E = NR) To Form Sulfoxides or Epoxides by Oxygen Atom
Transfer
a
Received: January 29, 2013
The oxo complex C is not observed.
© XXXX American Chemical Society
A
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but give many similar reactions, including oxygen atom transfer
reactions, though with a smaller range of substrates (Scheme
2).9 One complication is that transfer of the NR group, rather
than the O atom transfer, may occur unless R is a bulky group.9
Many of these reactions of oxaziridines and dioxiranes occur by
similar mechanisms.9b,c The oxaziridines have a major
advantage for the present work because they are easily prepared
in pure, anhydrous form, and so the formation of hydrated
product B (Scheme 1) would not be possible. At the outset,
three outcomes appeared possible: formation of the
oxoplatinum(IV) complex C or a product derived from it,6 a
new reaction type, or no reaction at all. This article describes
the chemistry, including the formation and characterization of a
long-lived hemiaminal intermediate in one case.
room temperature, but no evidence for the intermediacy of
complex 4a or 4c (Scheme 3) was obtained. Hence, if these
hemiaminal intermediates are formed at all, they must
decompose more quickly than they are formed.
The final products 55d,7a,14 and 2a−c9,10 are known
compounds and so could be identified easily by their NMR
spectra (Figure 1 and Figure S1 (Supporting Information)).
RESULTS AND DISCUSSION
Synthesis and Characterization. The new chemistry is
shown in Scheme 3. The oxidation of the known imine
■
a
Scheme 3. Oxidation Reactions with Oxaziridines
1
Figure 1. H NMR spectra (400 MHz, CD3OD) of (a, boxed areas)
[Pt(OH)(OMe)Me2(bipy)] (5) and (b) the mixture of [Pt(OD)-
(OCD3)Me2(bipy)] (5-d4) and PhCHN-t-Bu, (2b), formed by
decomposition of complex 4b over a period of 5 days.
For example, complex 5 is characterized by a single
methylplatinum resonance at δ 1.74 (2J(Pt−H) = 71 Hz), a
PtOMe resonance at δ 2.63 (3J(Pt−H) = 39 Hz), and four
bipyridine resonances (Figure 1a). The mixture of products 5*
and 2b from reaction in CD3OD after several days (Figure 1b)
gave resonances essentially identical with those for 5 except
that the methoxyplatinum resonance was absent. A parallel
reaction was carried out in CH3OH, and the product was
isolated and redissolved in CD3OD, to confirm that the
methoxyplatinum group was present. The imine resonances
were identified similarly by comparison with an authentic
sample.9 The singlet imine proton resonance, PhCHaN at δ
8.39 in CD3OD solution, is characteristic (Figure 1b).
a
The potential intermediates 4a,c were not observed.
derivatives t-BuNCHR (2a, R = H; 2b, R = Ph; 2c, R = 2-
pyridyl) with m-chloroperbenzoic acid (MCPBA) gave the
corresponding oxaziridine derivatives 3a−c.10,11 The reactions
of these oxaziridines 3a−c with [PtMe2(2,2′-bipyridine)] (1)12
1
were initially monitored by H NMR spectroscopy in solution
in either acetone-d6 or methanol-d4. In acetone-d6 solution at
room temperature, no reaction was observed over a period of
several days. However, when an oxaziridine was added to a
yellow-orange solution of complex 1 in methanol-d4,13 the color
of the solution was bleached immediately as oxidation to a
platinum(IV) complex occurred. The 1H NMR spectra,
obtained immediately after mixing, showed that the products
from reaction of 1 with 3a or 3c were a 1:1 mixture of
[Pt(OD)(OCD3)Me2(bipy)] (5-d4) and the corresponding
imine 2a or 2c. However, the reaction of 1 with 3b gave a new
complex identified as the hemiaminal derivative [Pt(OCD3)-
(OCHPhND-t-Bu)Me2(bipy)] (4b-d4), which decomposed
only slowly to give 5-d4 and 2b as major products (Scheme
3). Complex 5 was also formed if excess methanol was added to
a solution of 1 in acetone. Details of the characterization are
given below. The reaction of complex 1 with 3a or 3c was
studied by low-temperature 1H NMR spectroscopy, after
mixing the reagents in CD3OD at −80 °C. Spectra were
recorded at 20 °C intervals as the sample was warmed slowly to
The characterization of complex 4b was more challenging
because it is a new compound and it could not be isolated in
pure form. The structure was deduced from the 1H, 1H COSY,
1
1
and H−13C HSQC NMR spectra. The H NMR spectrum of
[Pt(OCD3)(OCHPhND-t-Bu)Me2(bipy)] (4b-d4), prepared
by reaction of complex 1 with oxaziridine 3b, is shown in
Figure 2. The carbon atom PtOC*HaPhN is chiral, and so the
complex has only C1 symmetry and the two pyridyl rings and
two methylplatinum groups are nonequivalent. Two closely
spaced, equal-intensity methylplatinum resonances were
observed at δ 1.82 (2J(PtH) = 66 Hz) and 1.83 (2J(PtH) =
68 Hz). Similarly, two sets of resonances were observed for the
pyridyl group protons, though some were overlapped. The
PtOCH proton appeared as a singlet at δ 4.69 (3J(PtH) = 41
B
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Scheme 4. Potential Reactions of 1 with 3 in the Absence of
Protic Solvent
1
Figure 2. H NMR spectrum of complex 4b-d4 (peaks marked # are
due to impurities, and those marked * are 195Pt satellites). The inset
shows the methoxyplatinum resonance of complex 4b (the peak
marked + is due to the decomposition product 5).
Hz), and the coupling constant is similar to that observed for
the methoxyplatinum group in 5, which gives 3J(PtH) = 39 Hz,
indicating that the alkoxide group is trans to an oxygen donor; a
smaller coupling constant would be expected if the alkoxy
group was trans to carbon or nitrogen.5 Of course, there was no
1H NMR resonance for the PtOCD3 group in 4b-d4; therefore,
the nature of this group was not established. Fortunately, a
sample of 4b was prepared by reaction of 1 with oxaziridine 3b
in methanol, followed immediately by removal of the solvent
under vacuum. Some decomposition to complex 5 occurred
during this procedure, but when the sample was dissolved in
CD3OD, the methoxyplatinum resonance of 4b was observed at
δ 2.51 (3J(PtH) = 40 Hz); the magnitude of the coupling
constant indicates that this methoxy group is trans to oxygen
(Figure 2, inset).5 The 1H−13C NMR HSQC spectrum showed
a correlation of the PtOCHa proton with a 13C resonance at δ
105.9, in the region expected for a hemiaminal derivative.15
Together, these data define the structure of the complex 4b.
The phenyl protons (Figure 2) are significantly more shielded
than in the precursor oxaziridine 3b, probably as a result of π
stacking with the 2.2′-bipyridine ligand.
Figure 3. Calculated structure (left), HOMO (center), and LUMO
(right) for compounds 3b (a−c), 1 (d−f), and 6b (g−i).
Computational Studies. Some insight into the reaction
mechanism was gained by carrying out DFT calculations on
potential products and intermediates of the reactions. These
calculations were carried out on the basis of the BLYP
functional, with double-ζ basis set and first-order scalar
relativistic corrections, and were carried out for the gas phase
and for acetone and methanol solutions, using the conductor
like screening model (COSMO) to treat solvation effects.16
Some potential reactions which do not involve specific
methanol molecules are shown in Scheme 4, with selected
structures, frontier orbitals, and relative energies for the case
with R = Ph shown in Figures 3 and 4 and with selected atomic
and bond parameters in Table 1.
Figure 4. Calculated relative energies (methanol solvent, kJ mol−1)
and structures of compounds in Scheme 4.
This leads to lengthening of the N−O bond of 3b and charge
transfer from platinum to the nitrogen and oxygen atoms of the
oxaziridine (Table 1). We have attempted to detect this
complex by recording low-temperature NMR spectra in
acetone-d6 or a CD2Cl2 solution of a mixture of 1 and 3b,
but no charge transfer complex was detected. Presumably it
does not compete with solvent interactions.17 Nevertheless, 6b
is a likely intermediate and, in the absence of protic solvent, it
could give the metallacycle 7b or 8b, which are calculated to be
The DFT calculations predict that a weak charge transfer
complex 6b may be formed (Figure 3g), with 1 as nucleophile
2
(using the platinum 5dz orbital, Figure 3e) and 3b as the
electrophile (using the σ*(NO) molecular orbital, Figure 3c).
C
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Table 1. Calculated Bond Distances and Hirshfeld Atomic Charges
1
3b (gas)
6b (gas)
6b (Me2CO)
6b (MeOH)
7b (MeOH)
8b (MeOH)
4b (MeOH)
Pt−O/Å
O−N/Å
O−C/Å
N−C/Å
Q(Pt)/e
Q(O)/e
Q(N)/e
2.34
2.29
2.29
2.20
2.10
2.13
1.64
1.51
1.48
2.00
2.06
2.07
2.34
2.31
2.43
1.50
1.50
1.50
1.49
1.52
1.48
1.46
1.46
1.46
1.52
1.48
1.48
0.07
0.30
0.30
0.31
0.43
0.46
0.46
−0.16
−0.04
−0.21
−0.11
−0.21
−0.17
−0.22
−0.18
−0.43
−0.19
−0.32
−0.22
−0.29
−0.17
thermodynamically favorable products, whereas formation of
the oxo complex C is unfavorable (Figure 4). However, no
evidence was found for formation of any of these complexes or
their decomposition products. The high activation energy for
metallacycle formation is attributed to the weak charge transfer
interaction in 6b, the absence of a suitable acceptor orbital on
platinum(II), and the rigididity of the [PtMe2(bipy)] unit to
the distortion needed to form 7b or 8b.18 The calculations for
reactions of 1 with 3a or 3c gave similar results.
There are challenges in modeling the mechanisms of
reactions involving solvent methanol molecules, because of
likely entropic effects and differences in hydrogen bonding. The
energies of potential intermediates and products shown in
Figure 5 are calculated on the basis of the energy of the
perhaps more useful is to consider the changes in bond
distances as the charge transfer complex 6b interacts with
specific methanol molecules (Table 2). Formation of 4b
requires addition of a proton to the oxaziridine nitrogen atom
and a methoxide ion to the platinum center of 6b. The
methanol solvent molecules in 6b·2MeOH-N,Pt (see Table 2
for the nomenclature used to define solvation) cooperate in
aiding this transformation by coordination of the oxygen atom
of one solvent molecule to platinum and by hydrogen bonding
of the second solvent molecule to nitrogen. This push−pull
effect increases the extent of the charge transfer, leading to
oxidation of platinum(II) in 1 or 6b to platinum(IV) in 4b. The
conversion of 4b to 5 formally requires a proton transfer from
nitrogen to oxygen, with loss of the imine PhCHN-t-Bu, but
the reaction is most likely mediated by further methanol solvent
molecules and the reaction is slow in this case. In principle, 5
could be formed directly from a complex such as 6b·2MeOH-
O,Pt or 6b·3MeOH-N,O,Pt, in which a methanol molecule is
hydrogen-bonded to the oxaziridine oxygen atom. This does
not occur to a significant extent in the reaction of 1 with the
oxaziridine 3b, but it might be the dominant route in the
reactions with 3a and 3c in which no intermediate 4a or 4c
could be detected during the formation of 5.
CONCLUSIONS
■
The most striking observation of the present work is that the
oxaziridines 3a−c do not react with complex 1 at room
temperature in acetone solution, whereas they react very rapidly
with 1 in methanol solution. This lends strong support to the
theory that oxygen atom transfer to 1 from either dioxiranes or
oxaziridines to give the oxo complex C (Scheme 1) is
unfavorable.6 It follows that the easy reaction in methanol
solution involves proton coupling, and it is likely that the
slower reaction of 1 with dioxygen in methanol solution also
involves proton coupling.5−7 Similar proton-coupled mecha-
Figure 5. Calculated relative energies (kJ mol−1, methanol solution)
and structures of potential intermediates 6b·xMeOH (in 6b·2MeOH-
N there is a hydrogen bond between the uncoordinated methanol
molecule and the oxaziridine nitrogen atom) and the products 4b and
5. The conversion of 4b to 5 is favored by entropy and by solvation by
individual methanol molecules.
methanol molecules in the hydrogen-bonded cyclic hexamer
(MeOH)6,19 but this is an arbitrary approximation. What is
Table 2. Trends in Calculated Bond Distances and Hirshfeld Atomic Charges with Specific Methanol Solvation in Methanol
a
Solvent for Complexes 6b·xMeOH (x = 1−3)
6b
6b·MeOH-N
6b·MeOH-O
6b·MeOH-Pt
6b·2MeOH-N,O
6b·2MeOH-N,Pt
6b·2MeOH-O,Pt
6b·3MeOH-N,O,Pt
b
Pt−O /Å
2.29
2.07
1.50
1.46
2.24
2.12
1.51
1.45
2.24
2.16
1.52
1.45
2.17
2.24
2.18
1.53
1.44
2.14
2.14
2.11
b
O−N /Å
2.27
2.31
2.35
2.41
b
O−C /Å
1.54
1.55
1.60
1.63
N−C/Å
1.43
1.43
1.41
1.41
c
Pt−O /Å
2.50
2.41
2.40
2.34
Q(Pt)/e
0.31
0.34
0.35
0.41
0.36
0.43
0.43
0.44
Q(N)/e
−0.18
−0.22
−0.11
−0.21
−0.17
−0.18
−0.28
−0.26
−0.10
−0.19
−0.17
−0.26
−0.27
−0.22
−0.17
−0.23
b
Q(O) /e
a
b
c
N or O indicates N···HOMe or O···HOMe hydrogen bonding, and Pt indicates Pt···OHMe bonding. O atom of oxaziridine. O atom of solvent
methanol.
D
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nisms may apply in other important catalytic reactions, such as
in the oxidation of water.1
The reaction of complex 1 with oxaziridine 3b is the best
defined of those studied here because it gives the long-lived
hemiaminal complex 4b. On the basis of the experimental and
computational studies, the formation of 4b is proposed to occur
according to Scheme 5. The easy, reversible formation of the
may be catalyzed by either acid or base and that the reagents or
products may act as base catalysts; thus, this is not
implausible.9,10,15,20 Second, it is possible that complex 5 is
formed without the intermediacy of complex 4a or 4c, as
illustrated in Scheme 6. The nitrogen atom in 6a or 6c is the
Scheme 6
Scheme 5. Proposed Mechanism of Formation of Complex
4b and Its Further Reaction To Give the Imine 2b and
Complex 5
most basic center; therefore, hydrogen bonding of methanol to
nitrogen is expected in preference to hydrogen bonding to the
oxaziridine oxygen atom. Nevertheless, hydrogen bonding can
also occur to the oxygen atom, and this can lead to direct
formation of complex 5 as shown in Scheme 6. The dual
reactivity pattern is analogous to the reaction of oxaziridines
with alkenes, which can give either epoxidation, with loss of an
imine (Scheme 2), or oxyamination of the double bond.22
EXPERIMENTAL SECTION
■
Reactions were carried out using standard Schlenk techniques, unless
otherwise stated. NMR spectra were recorded using a Varian Mercury
400 or Varian INOVA 400 or 600 MHz spectrometer. NMR labeling is
shown in Chart 1. Assignments were confirmed by recording COSY
charge transfer complex 6b is enhanced by the push−pull effect
of methanol molecules coordinating weakly to platinum and by
hydrogen bonding of a second methanol molecule to nitrogen
in 6b·2MeOH-N,Pt. This complex is then proposed to lose
methanol, by loss of a proton from the Pt···OHMe group and
methoxide from the N···HOMe group, to give 4b. This last step
is likely to be promoted by chains or clusters of methanol
molecules, since neither individual step is easy in isolation.
Similarly, the slow conversion of 4b to 5, with loss of the imine
2b, is likely to be mediated by one or more methanol
molecules, as indicated in Scheme 5. Organic hemiaminals are
usually detected only as transient intermediates unless
protected in a cavitand or metal−organic framework host, so
it is remarkable that the organoplatinum derivative 4b is so
long-lived.15,20 In addition, complex 4b appears to be the first
example of a platinum(IV) dialkoxide complex, though several
platinum(IV) complexes with one alkoxide group are known.21
Finally, we note that the reactions of 1 with 3a or 3c occur
rapidly to give complex 5 and the corresponding imine 2a or 2c
and that no intermediate hemiaminal complex analogous to 4b
could be detected in these cases. There appear to be two
possible explanations for this. First, it is possible that the
reaction occurs according to Scheme 5 but that the
corresponding hemiaminal complex 4a or 4c is too short-
lived to detect. It is known that imine loss from hemiaminals
Chart 1. NMR Labeling Scheme
and HSQC spectra, but assignments of nonequivalent pyridyl peaks
are arbitrary. Mass spectrometric analysis was carried out using an
electrospray PE-Sciex mass spectrometer (ESI-MS) coupled with a
TOF detector. The complexes [Pt2Me4(μ-SMe2)2], [PtMe2(bipy)]
(1), and an authentic sample of [Pt(OH)(OMe)Me2(bipy)] (5) were
prepared according to the literature.5h,12,14 The imine and oxaziridine
derivatives were prepared by using the known methods.9−11 DFT
calculations were carried out by using the Amsterdam Density
Functional program based on the BLYP functional, with double-ζ basis
set and first-order scalar relativistic corrections.16 General solvation
E
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effects were treated by using the conductor like screening model
(COSMO).16 The energy minima were confirmed by vibrational
frequency analysis in each case.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Figure S1, giving the H NMR spectrum for the reaction of
complex 1 with oxaziridine 3c. This material is available free of
charge via the Internet at http://pubs.acs.org.
[Pt(OCD3)(OCHPhND-t-Bu)Me2(bipy)] (4b-d4). To a solution of
complex 1 (9.0 mg, 0.0236 mmol) in methanol-d4 (0.5 mL) was added
2-tert-butyl-3-phenyloxaziridine (4.2 mg, 0.0236 mmol) dissolved in
the same solvent (0.2 mL). The complex was identified by its
spectroscopic properties. NMR in methanol-d4: δ(1H) 1.82 (s, 3H,
AUTHOR INFORMATION
Corresponding Author
*E-mail for R.J.P.: pudd@uwo.ca.
Notes
■
2
2J(PtH) = 66 Hz, PtMe), 1.83 (s, 3H, J(PtH) = 68 Hz, PtMe), 4.69
3
3
(s, 1H, J(PtH) = 41 Hz, PtOCHa), 6.66 (d, J(HoHm) = 7 Hz, Ho),
6.90 (dd, 3J(HmHo) = 7 Hz, 3J(HmHp) = 7 Hz, Hm), 7.01 (t, 3J(HpHm)
= 7 Hz, Hp), 7.80 (m, 2H, H5/H5′), 8.16 (dd, 1H, J(H4H5) = 8 Hz,
3
The authors declare no competing financial interest.
3J(H4H3) = 8 Hz, H4), 8.37 (d, 1H, J(H3H4) = 8 Hz, H3), 8.22 (dd,
3
1H, 3J(H4′H5c′) = 8 Hz, 3J(H4′H3′) = 8 Hz, H4′), 8.41 (d, 1H,
3J(H3′H4) = 8 Hz, H3′), 9.01 (m, 2H, H6/H6′). δ(13C) 0.1, 0.2 (PtMe),
30.9 (MeC), 44.8 (MeC), 60.1 (OMe), 105.9 (CHO), 125.85 (Co),
127.9 (Cm), 127.6 (Cp), 127.1, 127.2 (C5/C5′), 137.5(Cipso), 140.4
(C4′), 140.0 (C4), 124.0 (C3′), 124.2 (C3), 147.2, 147.3 (C6/C6′). ESI-
MS in methanol-d4: m/z 596 [4b + D]+.
ACKNOWLEDGMENTS
We thank the NSERC (Canada) for financial support.
■
REFERENCES
■
(1) (a) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507.
(b) Goldberg, K. I., Goldman, A. S., Eds. Activation and
Functionalization of C-H Bonds; American Chemical Society:
Washington, DC, 2004; ACS Symposium Series 885. (c) Lersch, M.;
Tilset, M. Chem. Rev. 2005, 105, 2471. (d) Singh, A.; Anandhi, U.;
Cinellu, M. A.; Sharp, P. R. Dalton Trans. 2008, 2314. (e) Vedernikov,
A. N. Chem. Commun. 2009, 4781. (f) Limberg, C. Angew. Chem., Int.
Ed. 2009, 48, 2270. (g) Labinger, J. A.; Bercaw, J. E. Topics Organomet.
Chem. 2011, 35, 29. (h) Piers, W. E. Organometallics 2011, 30, 13.
(i) Boisvert, L.; Goldberg, K. I. Acc. Chem. Res. 2012, 45, 899.
(j) Vedernikov, A. N. Acc. Chem. Res. 2012, 45, 803. (k) Wasylenko, D.
J.; Palmer, R. D.; Berlinguette, C. P. Chem. Commun. 2013, 49, 218.
(2) (a) Weliange, N. M.; Szuromi, E.; Sharp, P. R. J. Am. Chem. Soc.
2009, 131, 8736. (b) Efremenko, I.; Poverenov, E.; Martin, J. M. L.;
Milstein, D. J. Am. Chem. Soc. 2010, 132, 14886. (c) Poverenov, E.;
Efremenko, I.; Frenkel, A. I.; Ben-David, Y.; Shimon, L. J. W.; Leitus,
G.; Konstantinovski, L.; Martin, J. M. L.; Milstein, D. Nature 2008,
455, 1093. (d) Kortz, U.; Lee, U.; Joo, H.-C.; Park, K.-M.; Mal, S. S.;
Dickman, M. H.; Jameson, G. B. Angew. Chem., Int. Ed. 2008, 47, 9383.
(3) (a) Khusnutdinova, J. R.; Zavalij, P. Y.; Vedernikov, A. N. Can. J.
Chem. 2009, 87, 110. (b) Prokopchuk, E. M.; Puddephatt, R. J. Can. J.
Chem. 2003, 81, 476. (c) Lohr, T. L.; Piers, W. E.; Parvez, M. Inorg.
Chem. 2012, 51, 4900. (d) Zhang, F.; Jennings, M. C.; Puddephatt, R.
J. Chem. Commun. 2007, 1496.
(4) (a) Scheuermann, M. L.; Fekl, U.; Kaminsky, W.; Goldberg, K. I.
Organometallics 2010, 29, 4749. (b) Look, J. L.; Wick, D. D.; Mayer, J.
M.; Goldberg, K. I. Inorg. Chem. 2009, 48, 1356. (c) Taylor, R. A.;
Law, D. J.; Sunley, G. J.; White, A. J. P.; Britovsek, G. J. Angew. Chem.,
Int. Ed. 2009, 48, 5900.
(5) (a) Karp, E. M.; Silbaugh, T. L.; Crowe, M. C.; Campbell, C. T. J.
Am. Chem. Soc. 2012, 134, 20388. (b) Figg, T. M.; Cundari, T. R.;
Gunnoe, T. B. Organometallics 2011, 30, 3779. (c) Khusnutdinova, J.
R.; Newman, L. L.; Zavalij, P. Y.; Lam, Y.-F.; Vedernikov, A. N. J. Am.
Chem. Soc. 2008, 130, 2174. (d) Rostovtsev, V. V.; Labinger, J. A.;
Bercaw, J. E.; Lasseter, T. L.; Goldberg, K. I. Organometallics 1998, 17,
4530. (e) Safa, M.; Jennings, M. C.; Puddephatt, R. J. Organometallics
2012, 31, 3539. (f) Wu, J.; Sharp, P. R. Organometallics 2009, 28, 6935.
(g) Weliange, N. M.; Sharp, P. R. Organometallics 2012, 31, 6823.
(h) Rostovtsev, V. V.; Henling, L. M.; Labinger, J. A.; Bercaw, J. E.
Inorg. Chem. 2002, 41, 3608. (i) Safa, M.; Jennings, M. C.; Puddephatt,
R. J. Organometallics 2011, 30, 5625.
A sample of [Pt(OCH3)(OCHPhNH-t-Bu)Me2(bipy)] (4b) was
prepared in the same way, but using methanol solvent. The solvent
was removed immediately under high vacuum (IR: ν(NH) 3340
cm−1), and the product was redissolved in methanol-d4. The 1H NMR
spectrum was as above but with an additional resonance at δ(1H) 2.51
(s, 3H, 3J(PtH) = 40 Hz, PtOMe); about 15% decomposition of 4b to
5 and 2b occurred during the evaporation and redissolution.
The 1H NMR spectrum of the methanol-d4 solution of complex 4b
(prepared in methanol as above) was monitored for several days. After
2 days, conversion to complex 5 and imine 2b was complete. NMR in
CD2Cl2: complex 5, δ(1H) 1.62 (s, 6H, 2J(PtH) = 73 Hz, PtMe), 2.68
3
3
(s, 3H, J(PtH) = 41 Hz, OMe), 7.71 (m, 2H, J(H5H6) = 6 Hz,
3J(H5H4) = 8 Hz, J(H5H3) = 1 Hz, H5), 8.11 (m, 2H, J(H4H5) = 8
4
3
Hz, 3J(H4H3) = 8 Hz, 4J(H4H6) = 2 Hz, H4), 8.30 (d, 2H, 3J(H3H4) =
8 Hz, H3), 8.99 (dd, 2H, J(H6H5) = 6 Hz, J(H6H4) = 2 Hz, H6);
3
4
compound 2b, δ(1H) 1.32 (s, 9H, Bu), 7.45 (m, 3H, Hm/Hp), 7.76
t
(m, 2H, Ho), 8.38 (s, 1H, NCH).
Complex 1 with Aziridine 3c. To a solution of [PtMe2(bipy)]
(1; 10.2 mg, 0.0267 mmol) in methanol-d4 (0.5 mL) was added 2-tert-
butyl-3-pyridinyloxaziridine (3c; 4.8 mg, 0.0267 mmol) dissolved in
the same solvent (0.2 mL). The reaction mixture showed the
formation of complex 5 and the parent imine 2c. NMR in methanol-
d4: complex 5-d4, δ(1H) 1.74 (s, 6H, 2J(Pt−H) = 71 Hz, Pt-Me), 7.86
(dd, 2H, J(H5H6) = 5 Hz, J(H5H4) = 8 Hz, H5), 8.30 (dd, 2H,
3
3
3J(H4H5) = 8 Hz, J(H4H3) = 8 Hz, H4), 8.68 (d, 2H, J(H3H4) = 8
3
3
Hz, H3), 9.05 (d, 2H, J(H6H5) = 5 Hz, H6); compound 2c, δ(1H)
3
1.34 (s, 9H, tBu), 7.47 (dd, 1H, (H5′H6′) = 5 Hz, 3J(H5′H4′) = 7 Hz,
H5′), 7.91 (m, 1H, J(H4′H5′) = 7 Hz, J(H4′H3′) = 7 Hz, H4′), 8.05
3
3
3
(d, 1H, J(H3′H4′) = 7 Hz, H3′), 8.38 (s, 1H, NCH), 8.60 (d, 1H,
3J(H6′H5′) = 5 Hz, H6′). A similar reaction, at lower concentration,
was carried out at −80 °C, with NMR monitoring at 20° intervals as
the solution was warmed to room temperature, but only resonances
for starting materials and the above products were observed. A similar
reaction was carried out in methanol solvent, and the product 5 was
1
isolated and characterized by comparison of its H NMR spectrum
with that of an authentic sample. In particular, the methoxyplatinum
resonance was observed at δ 2.68 (s, 3H, 3J(PtH) = 41 Hz, OMe). The
isolated yield of 5 was 86%.
Complex 1 with Oxaziridine 3a. To a solution of complex 1
(12.3 mg, 0.0322 mmol) in methanol-d4 (0.5 mL) was added 2-tert-
butyloxaziridine (3a; 3.3 mg, 0.0267 mmol) dissolved in the same
(6) Pellarin, K. R.; McCready, M. S.; Puddephatt, R. J. Organo-
metallics 2012, 31, 6388.
1
solvent (0.2 mL). The H NMR spectrum of the reaction mixture
(7) (a) Thorshaug, K.; Fjeldahl, I.; Romming, C.; Tilset, M. Dalton
Trans. 2003, 4051. (b) Rashidi, M.; Nabavizadeh, M.; Hakimelahi, R.;
Jamali, S. Dalton Trans. 2001, 3430.
(8) (a) Winkler, J. R.; Gray, H. B. Struct. Bonding (Berlin) 2011, 142,
17. (b) O’Halloran, K. P.; Zhao, C.; Ando, N. S.; Schultz, A. J.;
Koetzle, T. F.; Piccoli, P. M. B.; Hedman, B.; Hodgson, K. O.; Bobyr,
E.; Kirk, M. L.; Knottenbelt, S.; Depperman, E. C.; Stein, B.;
Anderson, T. M.; Cao, R.; Geletii, Y. V.; Hardcastle, K. I.; Musaev, D.
showed the formation of complex 5* (spectrum as above) and the
parent imine 2a. NMR in methanol-d4: compound 2a, δ(1H) 1.16 (s,
2
9H, t-Bu), 7.25 and 7.44 (AB multiplet, each 1H, J(HaHb) = 16 Hz,
CHaHb). Over several days, the resonances for 2a decayed as a
further reaction to give the trimer occurred, but resonances of complex
5 remained unchanged. A similar reaction was carried out in methanol,
and the product 5 was isolated and characterized as above. Yield: 79%.
F
dx.doi.org/10.1021/om400079b | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
G.; Neiwert, W. A.; Fang, X.; Morokuma, K.; Wu, S.; Kogerler, P.; Hill,
C. L. Inorg. Chem. 2012, 51, 7025.
(9) (a) Emmons, W. D. J. Am. Chem. Soc. 1957, 79, 5739. (b) Davis,
F. A.; Sheppard, A. C. Tetrahedron 1989, 45, 5703. (c) Bach, R. D.;
Coddens, B. A.; McDouall, J. J. W.; Schlegl, H. B.; Davis, F. A. J. Org.
Chem. 1990, 55, 3325. (d) Petrov, V. A.; Resnati, G. Chem. Rev. 1996,
96, 1809. (e) Bohe, L.; Lusinchi, M.; Lusinchi, X. Tetrahedron 1999,
55, 155. (f) Toullec, P. Y.; Bonaccorsi, C.; Mezzetti, A.; Togni, A. Proc.
Natl. Acad. Sci. U.S.A. 2004, 101, 5810. (g) Hirschi, J. S.; Takeya, T.;
Hang, C.; Singleton, D. A. J. Am. Chem. Soc. 2009, 131, 2397.
(h) Camerano, J. A.; Samann, C.; Wadepohl, H.; Gade, L. H.
Organometallics 2011, 30, 379.
(10) (a) Franchi, P.; Casati, C.; Mezzina, E.; Lucarini, M. Org. Biomol.
Chem. 2011, 9, 6396. (b) Boudou, C.; Berges
̀
, M.; Sagnes, C.;
Sopkova-de Oliveira Santos, J.; Perrio, S.; Metzner, P. J. Org. Chem.
́
2007, 72, 5403.
(11) Pews, R. G. J. Org. Chem. 1967, 32, 1628.
(12) (a) Hill, G. S.; Irwin, M. J.; Levy, C. J.; Rendina, L. M.;
Puddephatt, R. J. Inorg. Synth. 1998, 32, 149. (b) Scott, J. D.;
Puddephatt, R. J. Organometallics 1983, 2, 1643.
(13) Chaudhury, N.; Puddephatt, R. J. J. Organomet. Chem. 1975, 84,
105.
(14) Monaghan, P. K.; Puddephatt, R. J. Organometallics 1984, 3,
444.
(15) (a) Chudek, J. A.; Foster, R.; Young, D. J. Chem. Soc., Perkin
Trans. 2 1985, 1285. (b) Morris, W.; Doonan, C. J.; Yaghi, O. M.
Inorg. Chem. 2011, 50, 6853. (c) Garralda, M. A.; Hernandez, R.;
Ibarlucea, L.; Pinella, E.; Torres, M. R.; Zarandona, M. Organometallics
2007, 26, 5369.
(16) (a) Te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; van
Gisbergen, S.; Guerra, C. F.; Snijders, J. G.; Ziegler, T. J. Comput.
Chem. 2001, 22, 931. (b) Becke, A. Phys. Rev. A 1988, 38, 3098.
(17) An analogous but stronger charge transfer complex is formed
between 1 and iodine, and this can be detected by low-temperature
NMR monitoring: Nabavizadeh, S. M.; Amini, H.; Rashidi, M.;
Pellarin, K. R.; McCready, M. S.; Cooper, B. F. T.; Puddephatt, R. J. J.
Organomet. Chem. 2012, 713, 60.
(18) (a) Grice, K. A.; Scheuermann, M. L.; Goldberg, K. I. Top.
Organomet. Chem. 2011, 35, 1. (b) Puddephatt, R. J. Angew. Chem., Int.
Ed. 2002, 41, 261.
(19) Boyd, S. L.; Boyd, R. J. J. Chem. Theory Comput. 2007, 3, 54.
(20) (a) Kawamichi, T.; Haneda, T.; Kawano, M.; Fujita, M. Nature
2009, 461, 633. (b) Hooley, R. J.; Iwasawa, T.; Rebek, J., Jr. J. Am.
Chem. Soc. 2007, 129, 15330.
(21) (a) Pal, S.; Vedernikov, A. N. Dalton Trans. 2012, 41, 8116.
(b) Smythe, N. A.; Grice, K. A.; Williams, B. S.; Goldberg, K. I.
Organometallics 2009, 28, 277. (c) Hadi, S.; Appleton, T. G.; Ayoko,
G. A. Inorg. Chim. Acta 2003, 352, 201.
(22) (a) Mithani, S.; Drew, D. M.; Rydberg, E. H.; Taylor, N. J.;
Mooibroek, S.; Dmitrienko, G. I. J. Am. Chem. Soc. 1997, 119, 1159.
(b) Donohoe, T. J.; Callens, C. K. A.; Flores, A.; Lacy, A. R.; Rathi, A.
H. Chem. Eur. J. 2011, 17, 58.
G
dx.doi.org/10.1021/om400079b | Organometallics XXXX, XXX, XXX−XXX