Stoichiometric aerobic aminohydroxylation of ethylene mediated by dpms-platinum complexes (dmps = di(2-pyridyl)methanesulfonate)

Article abstract of DOI:10.1016/j.ica.2010.09.057

Chloro di(2-pyridyl)methanesulfonate ethylene platinum(II) complex was converted to corresponding N-alkylplatina(II)azetidines by reacting the former with primary amines, MeNH₂ and tert-BuNH₂, to produce 2-ammonioethyl chloro platinum(II) species and their subsequent cyclization in the presence of NaOH in methanol. The N-alkylplatina(II)azetidines are oxidized under air or the atmosphere of pure O₂ to the corresponding N-alkylplatina(IV)azetidines in water or in methanol solution in the presence of one equivalent of a strong acid under ambient pressure at 22 °C. The resulting N-alkylplatina(IV)azetidines undergo C-O reductive elimination in acidic aqueous solutions to produce 2-(N-alkylamino)ethanols.

Full text of DOI:10.1016/j.ica.2010.09.057

Inorganica Chimica Acta 369 (2011) 274–283
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Stoichiometric aerobic aminohydroxylation of ethylene mediated by
dpms–platinum complexes (dmps = di(2-pyridyl)methanesulfonate)
⇑
Julia R. Khusnutdinova, Anthony S. Maiorana, Peter Y. Zavalij, Andrei N. Vedernikov
Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 8 October 2010
Chloro di(2-pyridyl)methanesulfonate ethylene platinum(II) complex was converted to corresponding N-
alkylplatina(II)azetidines by reacting the former with primary amines, MeNH2 and tert-BuNH2, to pro-
duce 2-ammonioethyl chloro platinum(II) species and their subsequent cyclization in the presence of
NaOH in methanol. The N-alkylplatina(II)azetidines are oxidized under air or the atmosphere of pure
O2 to the corresponding N-alkylplatina(IV)azetidines in water or in methanol solution in the presence
of one equivalent of a strong acid under ambient pressure at 22 °C. The resulting N-alkylplatina(IV)-
azetidines undergo C–O reductive elimination in acidic aqueous solutions to produce 2-(N-alkylamino)-
ethanols.
Dedicated to Robert G. Bergman
Keywords:
Ethylene
Aminohydroxylation
Dioxygen
Platina(IV)azetidines
C–O reductive elimination
N-Alkylaminoethanol
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
tionalization of aqua methyl platinum(II) complex (dpms)PtII-
Me(OH2) and a series of platinum(II) hydroxo olefin complexes
Selective 1,2-difunctionalization of alkenes such as 1,2-dihydr-
oxylation and 1,2-aminohydroxylation is of great practical interest
as a synthetic method for preparation of practically important and
biologically relevant molecules [1,2]. A number of selective proto-
cols for olefin aminooxygenation have been developed over the last
few decades. These reactions are catalyzed by osmium [3], palla-
dium [4–6], and platinum [7] complexes. However, most of the
existing methods for catalytic aminooxygenation require the use
of a strong oxidant such as iodobenzene diacetate [4,5] or N-chlo-
roamines [3]. The only example of aerobic Pt-catalyzed 1,2-ami-
nooxygenation of alkenes has recently been reported by Muniz
et al. [7]. However, up to 30 mol.% copper(II) salts are utilized in
this reaction to re-oxidize lower valent platinum species. One of
the possible approaches toward developing selective mediatorless
aminooxygenation of olefins using O2 as the sole oxidant is the
use of ligands that enable selective aerobic oxidation of the cata-
lytic intermediates [8]. The requirement of overall high reaction
selectivity translates into the requirement of high selectivity at
each of the reaction steps, including the step of O2 activation. From
this perspective search for and study of selective reactions of
organotransition metal complexes with O2 is an important goal
[8–10].
leading to MeOH, Me2O [11,12], olefin oxides [13,14] and glycols
[14], respectively (Scheme 1). In the two latter cases organic prod-
ucts with two new C–O bonds are formed. Overall, the reactions in
Scheme 1 include formation of the corresponding platinum(IV) al-
kyls 1a, 2, 3 and the subsequent C–O reductive elimination from
these platinum(IV) species.
In an effort to expand the scope of aerobic functionalization of
olefins in (dpms)Pt-systems and explore the possibility of C–N/
C–O olefin difunctionalization we studied transformations of the
chloro ethylene complex (dpms)PtIICl(C2H4), 4 [14], in the presence
of primary amines RNH2, R = Me, tert-Bu, and dioxygen. In this
work we report selective oxidative coupling of the ethylene ligand
in 4 with RNH2 with O2 as oxidant to produce 2-(N-alkyl-
amino)ethanol-derived salts 8a and 8b (Scheme 2). This transfor-
mation involves several steps. The first step includes facile
external nucleophilic addition of RNH2 to the ethylene ligand in
4 to form 2-ammonioethyl chloro platinum(II) complexes 5a–5b
(Scheme 2a). The latter can be readily converted to platina(II)azeti-
dines (1,2-azaplatinacyclobutanes) 6a–6b in the presence of bases
(Scheme 2b). The azetidines 6a–6b can be oxidized with O2 to pro-
duce the corresponding platina(IV)azetidines 7a–7b in high yield
in acidic media (Scheme 2c). The subsequent C–O reductive elimi-
nation from the platina(IV)azetidines occurs in the presence of
acids and leads to the products of C–N/C–O ethylene difunctional-
ization 8a–8b (Scheme 2c).
Previously we have reported that facially chelating di(2-pyri-
dyl)methanesulfonate ligand, dpms, enables selective aerobic func-
Azametallacyclobutanes can be generated via a number of
routes and have been proposed as intermediates in various
⇑
Corresponding author.
E-mail address: avederni@umd.edu (A.N. Vedernikov).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.09.057

J.R. Khusnutdinova et al. / Inorganica Chimica Acta 369 (2011) 274–283
275
O
O
H+/H2O
-PtII
O
O
75oC
H2O
O2/H2O, 25oC
N
N
OH
OH
N
N
Me
OH2
N
N
Me
OH
PtIV
Me
PtII
MeOH
ref. [6, 7]
PtIV
OH
25oC
1a
1b
80oC
-PtII
O
O2/H2O, 25oC
N
N
N
N
C2H4OH
OH
PtII
PtIV
OH
ref. [9]
+
HOC2H4OH
OH
H2O
O
2
O
O
R
O
O
R
O2/H2O, 25oC
>50oC
-PtII
H
O
R
R
R
O
OH
R
R
N
N
N
N
N
N
PtII
PtIV
PtII
R
H
H
H
H
H
H
OH
3
ref. [8, 9]
R
R
,
-
=
SO3
O
=
N
N
dpms
N
N
Scheme 1.
b)
a)
O
O
O
HR
N
NaOH/MeOH
12h, 50oC
RNH2/MeOH
25oC
N
N
N
N
PtII
N
N
NH2R
PtII
PtII
Cl
Cl
90%
quantitative
6a (R=Me), 6b (R=t-Bu)
4
5a (R=Me), 5b (R=t-Bu)
c)
d)
O
N
O
H+/H2O
1-5d, 100oC
HR
N
O2, H2SO4
1d, 25oC
2+
NH2R
N
OH2
OH2
PtIV
PtII
N
+
HO
N
2-
0.5SO4
OH
73-95%
7a (R=Me), 7b (R=t-Bu)
65%
8a (R=Me), 8b (R=t-Bu)
Scheme 2.
catalytic transformation such as alkene hydroamination [15] and
aziridine isomerization or functionalization [16–18]. Apart from
the external nucleophilic attack of an amine at the coordinated al-
kene, the most important routes leading to azametallacyclobu-
tanes involve [2+2] cycloaddition of alkenes to metal imides
[19,20], cyclometalation of amines first reported by Bergman
[21,22], oxidative addition of aziridines, and intramolecular inser-
tion of alkene into metal-amide bond [23,24]. The presented study
of oxidative transformations of azaplatinacyclobutanes may be
important for developing some alternative routes for metal-medi-
ated functionalization of organic substrates.
methylamine with a suspension of (dpms)Pt(C2H4)Cl, 4, in meth-
anol at room temperature (Scheme 2a). The product 5a was iso-
lated from the cold reaction mixture by filtration as an
analytically pure white fine-crystalline solid in 90% yield. The
complex is stable under air both in the solid state and in aqueous
or methanolic solutions but decomposes slowly in DMSO to pro-
duce ethylene gas among other products. Complex 5a has been
characterized by 1H, 13C NMR spectroscopy as well as by elec-
tro-spray ionization mass spectrometry (ESI-MS). The ESI-MS
spectra of aqueous or methanolic solutions of 5a show the pres-
ence of 5aꢀH+ ion as the only Pt-containing species. Both 1H and
13C NMR spectra contain a full set of signals corresponding to
two non-equivalent pyridyl fragments, consistent with low sym-
metry of 5a. Accordingly, two pairs of diastereotopic hydrogen
atoms present in the ethylene residue produce four signals in
the range of 1.21–3.04 ppm, two of which are accompanied by
discernible platinum-195 satellites with the coupling constant
2JPtH of 72 and 52 Hz. The ethylene proton resonances are
shifted upfield as compared to the ethylene ligand signals in
2. Results and discussion
2.1. Synthesis of (dpms)PtIICl(C2H4NH2R) complexes (R = Me, t-Bu)
(dpms)PtIICl(C2H4NH2Me), 5a
The zwitterionic 2-methylammonioethyl platinum(II) complex
5a was prepared by reacting 5 equ of 40% aqueous solution of

276
J.R. Khusnutdinova et al. / Inorganica Chimica Acta 369 (2011) 274–283
the complex 4, 4.9 and 5.1 ppm. 1H NMR spectra of 5a in DMSO
solutions show a broad singlet at 8.29 ppm integrating as 2H,
consistent with the presence of an ammonium fragment in 5a.
Formation of the azetidines 6a–6b can be viewed as a result
of an intramolecular ligand substitution at the PtII center with
the chloro ligand as the leaving group and the nitrogen atom of
the 2-aminoethyl ligand as the nucleophile. An alkali metal
hydroxide additive is required to deprotonate the ammonium
group present in 5a–5b and generate the required nucleophile,
Eqs. (2) and (3):
2.2. (dpms)PtIICl(C2H4NH2t-Bu), 5b
The tert-butyl analog 5b was prepared in a similar fashion as 5a
by adding 5 equ of tert-butylamine to a suspension of complex 4 in
methanol. The mixture produced a clear solution after few min-
utes. Subsequent crystallization overnight at ꢁ20 °C led to the for-
mation of large white crystals of 5b which were separated from the
cold mixture. The yield of an analytically pure product is 89%. The
air-stable complex 5b has been characterized by 1H, 13C NMR spec-
troscopy as well as by ESI-MS and showed the expected spectral
patterns similar to those observed for 5a.
Overall, transformation of 4–5a or 5b presented in Scheme 2a
can be viewed as a result of an outer-sphere attack of nucleophilic
nitrogen atom of an amine RNH2 at one of the carbon atoms of the
coordinated ethylene:
+OH-
-H2O
O
O
(2)
NHR
N
N
N
N
NH2R
PtII
PtII
Cl
Cl
R
O
O
-Cl-
N
N
N
PtII
N
NHR
PtII
N
Cl
H
cis-
O
O
H
N
N
N
N
(1)
Nu
PtII
PtII
O
Nu
Cl
Cl
N
N
N
PtII
+
(3)
This transformation is similar to the chemistry observed for
4 in aqueous alkaline solutions involving nucleophilic attack of
hydroxide at the coordinated ethylene resulting in an anionic
2-hydroxoethyl chloro platinum(II) complex (dpms)PtIICl(C2H4OH)ꢁ
[14].
R
trans-
2.6. Attempted aerobic oxidation of platina(II)azetidines 6a–6b in
methanol in the absence and in the presence of NaOH
2.3. Formation of platina(II)azetidine complexes 6a–6b,
Our previous study of aerobic oxidation of (dpms)PtIIR(HX)
complexes where R = Me, Ph and HX = H2O [11,12,14], MeOH
[12,25] or PhNH2, MeNH2 [25] led us to the hypothesis that the
actual species responsible for dioxygen activation are the corre-
sponding anionic complexes (dpms)PtIIMe(X)ꢁ resulting from
deprotonation of the coordinated HX ligand [14,25]. Accordingly,
in the case of the relatively acidic ligands HX such as H2O and
MeOH the presence of a base additive is beneficial for faster oxida-
tion kinetics of (dpms)PtIIR(HX) complexes.
(dpms)PtII(C2H4NHR-
jC,jN), R = Me, t-Bu
Cyclization of 2-N-alkylaminoethyl chloro platinum(II) com-
plexes 5a–5b to platina(II)azetidines 6a–6b could be achieved in
the presence of methanolic solution of NaOH at 50 °C (Scheme
2b). These complexes were characterized by means of 1H and 13C
NMR spectroscopy and ESI-MS and could be used without further
purification to prepare platina(IV)azetidines 7a–7b.
To test the effect of base additives on the reactivity of 6b to-
wards O2 a solution of 6b in methanol was combined with
0.2 equ of NaOH and stirred under oxygen atmosphere at 22 °C.
According to NMR spectroscopy, the starting material remained
unchanged after 4 days. Similarly, no changes were observed,
according to NMR spectroscopy, in methanolic solution of 6b
which contained no additives and was stirred under O2 atmo-
sphere for 2 days at 22 °C. It is therefore reasonable to assume that
the acidity of the NH group of azetidine 6b is not high enough to
allow for its deprotonation with NaOH in a sufficient extent.
2.4. (dpms)PtII(C2H4NHMe-
jC,jN), 6a
White solid produced from 5a and two equivalents of NaOH
could be separated from the mixture after 24 h by filtration and
washing with water to remove water-soluble inorganic com-
pounds in 76% yield. The reaction is not complete if stoichiometric
amount of NaOH is used. The product was used to prepare corre-
sponding platina(IV)azetidine 7a without further purification. Poor
solubility of 6a in common solvents prevented from obtaining
good quality 1H and 13C NMR spectra for this compound. ESI-MS
spectra of dilute solutions of 5a in aqueous methanol showed the
presence of the cation 6aꢀH+.
2.7. Aerobic oxidation of platina(II)azetidines 6a–6b to
platina(IV)azetidines 7a–7b (R = Me, t-Bu) in the presence of acid
additives
2.5. (dpms)PtII(C2H4NH2t-Bu-
jC,jN), 6b
Interestingly, in contrast to base additives, one equivalent HBF4
or H2SO4 enables aerobic oxidation of platina(II)azetidines to their
platina(IV)azetidine analogs 7a and 7b (Scheme 2c).
Solutions of complexes 6a and 6b in methanol or water contain-
ing one equivalent of a strong acid react under O2 at 22 °C to pro-
duce the platina(IV)azetidines 7a and 7b in 93% and 73% NMR
yield, respectively as the main product. The identity of 7a and 7b
was confirmed by 1H and 13C NMR spectroscopy, ESI mass spec-
trometry and, in the case of 7b, single crystal X-ray diffraction. Oxi-
dation of 6a in the aqueous solution was complete after 2 h under
Heating a stirred suspension of 5b in methanol with 1 equ of
NaOH at 50 °C leads to dissolution of the starting material after
ꢂ30 min. According to 1H NMR spectroscopy, no starting material
was present in the reaction mixture after 12 h. The product 6b
was identified by ESI-MS in the form of the cation 6bꢀH+. Two
sets of signals assigned to two isomers of 6b present in 6:1 ratio
were observed in its 1H NMR spectra. Two isomeric azetidines 6b
may differ by the configuration of the nitrogen atom of the azeti-
dine ring.

J.R. Khusnutdinova et al. / Inorganica Chimica Acta 369 (2011) 274–283
277
O2 atmosphere, whereas a slower reaction was observed under air
with a half life of ca. 2 h. The reaction is complete after 24 h to give
7a in 92% yield. Besides 7a and 7b some unidentified products
formed in 5–27% yield. Complexes 7a and 7b can be prepared more
conveniently if the oxidation of 6a and 6b is performed with
hydrogen peroxide (vide infra).
completion of the oxidation but it grows to 2:1 after 10 h and re-
mains further unchanged. The resulting alkaline solution of
7a(OH) was neutralized with one equivalent H2SO4, evaporated
to dryness to produce white crystalline [(dpms)PtIV(C2H4NMe-
jC,jN)(OH)]2(SO4) quantitatively. The resulting samples of solid
(7a)2(SO4) decompose slowly at room temperature.
The surprising effect of acid additives on the reactivity of pla-
tina(II)azetidines 6a–6b is opposite to what was observed for other
(dpms)PtIIR(HX) complexes [8]. This effect can be accounted for
assuming an acid-promoted reversible conversion of these pla-
tina(II)azetidines to the corresponding solvento 2-ammonioethyl
complexes A (Scheme 3a, HX = H2O or MeOH) that react further
with O2 to form the corresponding acyclic 2-ammonioethyl plati-
num(IV) complexes B (Scheme 3b), according to the mechanism
assumed previously for (dpms)PtIIR(HX) complexes [25]. We pre-
sume that complexes B can subsequently cyclize to form the azeti-
dines 7a–7b (Scheme 3c). The latter reaction may be less efficient
compared to the oxidation step itself so accounting for less than
quantitative yield of the platinum(IV) products, which is observed
normally in aerobic oxidation of (dpms)PtIIR(HX) complexes. A
reversible transformation of acyclic 2-ammonioethyl chloroplati-
num(IV) complexes into the corresponding platina(IV)azetidines
was observed earlier [26].
The product was characterized by ESI-MS, 1H, 13C, COSY and
HSQC NMR spectroscopy. The 1H NMR spectrum of 7a in methanol
exhibits two sets of signals, one for the major and one for the min-
or isomer, each including signals of two non-equivalent pyridyl
fragments of the dpms ligand, four multiplets for the ethylene res-
idue in the range of 2.8–4.5 ppm, two of which have discernible
2
platinum-195 satellites with the coupling constant JPtH of 79 Hz,
and the signal of the methyl group at the azetidine nitrogen with
3
platinum-195 satellites and the coupling constant JPtH of 33 Hz.
The latter feature suggests a metallacyclic structure for both iso-
mers of 7a.
In 13C NMR spectra of the major isomer of 7a, signals of the
azetidine ring carbon atoms appeared at ꢁ2.0 ppm (1JPtC = 414 Hz)
and 80.3 ppm (2JPtC = 115 Hz), which were assigned to the Pt-
bound and N-bound carbon atoms, respectively. The signal of
N–Me group was observed at 56.0 ppm and was accompanied by
platinum satellites (2JPtC = 22 Hz).
2.8.2. (dpms)PtIV(OH)(C2H4NHt-Bu- N)+, 7b
jC,j
2.8. Oxidation of platina(II)azetidines 6a–6b to platina(IV)azetidines
7a–7b with hydrogen peroxide (R = Me, t-Bu)
A solution of complex 6b prepared from 5b and one equiva-
lent NaOH in MeOH was used to synthesize (7b)Cl. Upon
addition of 11 equ of 30% aqueous H2O2 to this solution the reac-
tion mixture turned yellow. According to 1H NMR spectroscopy,
formation of 7b is quantitative after 30 min. The product (7b)Cl
can be isolated from the mixture upon its concentration and
crystallization at ꢁ20 °C. The isolated yield of an analytically
pure (7b)Cl is 64%. The product is a white crystalline solid per-
fectly soluble in methanol, water and DMSO, slightly soluble in
THF. From methanol (7b)Cl crystallizes with one molecule of
the solvent which could not be removed even after drying under
high vacuum (50 mTorr) for several days. The methanol solvate
was fully characterized including 1H and 13C NMR spectroscopy,
ESI-MS, elemental analysis and single crystal X-ray diffraction
The use of a stronger oxidant, hydrogen peroxide, allows for fas-
ter reaction rates and therefore for a more convenient preparation
of complexes 7a–7b.
2.8.1. (dpms)PtIV(OH)(C2H4NHMe- N)+, 7a
jC,j
Complex 6a suspended in methanol reacts with 1.1 equ 30%
aqueous H2O2 at 22 °C to produce in a few minutes a yellow
strongly alkaline solution containing 7a. According to 1H NMR
spectroscopy, formation of 7a is quantitative after 1 h. The product
forms as a mixture of two isomers in 2:1 ratio, presumably with
different configuration at the azetidine nitrogen atom, cis- and
trans-, similar to 6b. Importantly, this ratio is 2:5 after 1 h upon
a)
b)
O
O
O
PtII
H+/HX
O2
HR
N
N
N
N
NH2R
N
N
NH2R
PtIV
OH
PtII
N
X
XH
A
B
6a (R=Me), 6b (R=t-Bu)
- HX
c)
XH = H2O, MeOH
O
HR
N
N
N
PtIV
OH
7a (R=Me), 7b (R=t-Bu)
d)
e)
O
N
O
PtIV
-PtII
HO
N
N
OH
OH
NH2R
PtIV
OH
NH2R
N
OH
NH2R
8a (R=Me), 8b (R=t-Bu)
D
B
H2O
Scheme 3.

278
J.R. Khusnutdinova et al. / Inorganica Chimica Acta 369 (2011) 274–283
+NaBArF
-NaCl
CH2Cl2
O
O
1equ KOtBu
-tBuOH
4
Ht-Bu
Ht-Bu
N
N
N
N
N
N
PtIV
OH
PtIV
OH
THF
Cl-
(7b)BArF
(7b)Cl
4
O
t-Bu
N
N
N
PtIV
(4)
OH
9b
The resulting mixture containing azetidine 9b was character-
ized by 1H NMR spectroscopy in THF-d8 solutions. The most
prominent difference between 1H NMR characteristics of (7b)BArF
and 9b is the absence of the NH group signal at 5.9 ppm, whereas
the OH group singlet was only slightly shifted upfield to 3.23 ppm
as compared to from 3.43 ppm for 7b. Upon dissolution of this
mixture in THF-d8 and heating at 60 °C decomposition was ob-
served with a half-life of 22 h to form some unidentified insoluble
products. Upon completion of the reaction after 4 days the result-
ing solid was dissolved in DMSO and analyzed by means of
ESI-MS and NMR spectroscopy. No free aziridine or its plati-
num(II) complex, the expected C–N reductive elimination prod-
ucts, were detected.
One of the possible reasons for the lack of reactivity of 7b and
9b in C–N reductive elimination might be very slow transformation
of these azetidines into isomer C featuring the alkyl group trans- to
the sulfonate, Eq. (5). Presumably, the slow isomerization cannot
compete with some side reactions which lead to decomposition
of the azetidine.
Fig. 1. ORTEP drawing for the cation (dpms)PtIV 2-N,C–C2H4N–t-Bu)OH]+, 7b, (50%
(j
probability ellipsoids); hydrogen atoms are omitted for clarity. Selected bond
lengths, Å, and angles, °: Pt1–C1, 2.039(3); Pt1–O1, 1.970(2); Pt1–O2, 2.066(2); Pt1–
N3, 2.072(3); Pt1–N10, 2.195(3); Pt1–N20, 2.053(3); Pt1–C1–C2, 94.0(2); C1–C2–
N3, 100.6(3); C2–N3–Pt1, 92.7(2); C1–Pt1–N3, 69.39(13).
(Fig. 1). According to the X-ray diffraction data, chloride counter-
ion is hydrogen-bound to both NH and OH fragments present in
the cation 7b.
The NMR spectral pattern observed for 7b in methanol is similar
to that observed for its methyl analog 7a with one notable differ-
ence: in contrast to 7a, one set of signals was observed in 1H
NMR spectra of 7b. Based on the X-ray diffraction data, we tenta-
tively assign the configuration of 7b present in solutions also as
cis-, which may be expected to be more favorable due to a weaker
steric repulsion between the tert-Bu group and the ortho-pyridyl
hydrogen atoms in cis-7b.
Notably, 1H NMR spectra of 7b in DMSO showed also the pres-
ence of two broad singlets at 4.25 ppm and 7.60 ppm that were as-
signed to the protons of the Pt–OH and Pt–NH fragments,
respectively. The latter signal has discernible platinum satellites
O
O
Rt-Bu
N
N
N
N
N
OH
NRt-Bu
PtIV
PtIV
(5)
2
with the coupling constant JPtH of 58 Hz. Two multiplets of the
OH
C
platinum-bound ethylene
a-CH2 group accompanied by platinum
R = H+ (7b), none (9b)
2
satellites are centered at 2.89 ppm, JPtH = 75 Hz, and 2.94 ppm,
2JPtH = 70 Hz. The multiplets of the N-bound b-CH2 group have plat-
inum-195 satellites as well and are centered at 4.41 ppm,
Similar lack of isomerization reactivity in aprotic organic sol-
vents was also observed previously for (dpms)PtIVR(HNPh)(OH),
R = Me, Ph [25]. At the same time, it has been established that
(dpms)PtIVR complexes with the hydrocarbyl R trans- to the sulfo-
nate leaving group, such as 1b in Scheme 2, are responsible for the
C–O reductive elimination reactivity [11–14].
3JPtH = 35 Hz, and 4.58 ppm, JPtH = 40 Hz, each integrating as one
3
proton relative to the signal of the tert-butyl group whose signal
intensity was assigned to 9H.
The 13C NMR spectra of 7b exhibited two resonances of the car-
bon atoms of the azetidine ring at ꢁ4.1 ppm (Pt-bound) and
54.3 ppm (N-bound). The signals are characterized by 195Pt–C cou-
pling constants of 376 Hz and 114 Hz, respectively. Notably, com-
plex (7b)Cl represents the first example of the structurally
characterized platina(IV)azetidine [26].
2.10. Reductive elimination of N-alkylethanolamines 8a–8b from
platina(IV)azetidines 7a–7b in acidic aqueous solutions
Attempted reductive elimination of N-methyl substituted pla-
tina(IV)azetidine 7a in alkaline and neutral aqueous solutions at
100 °C produced a complex mixture of products. No N-methyl
ethanolamine was detected among the reaction products in alka-
line solutions of 7a, but some trace amount (<5%) of N-methyl
ethanolamine was detected in neutral solutions of 7a(BF4) after
heating it at 100 °C for 3 days, according to 1H NMR spectro-
scopy.
Importantly, in the presence of one equivalent of HBF4 or H2SO4,
clean formation of the corresponding of 2-(N-alkylamino)ethanols
in the form of ammonium salts 8a–8b occurred with a half-life of
about 3 h at 100 °C (Scheme 2d). These products were identified
by 1H NMR spectroscopy and ESI-MS by comparison with authentic
samples. The NMR yield of 8a and 8b is 63–65% after 30 h of reac-
tion. The main platinum-containing products identified by means
of 1H NMR spectroscopy are (dpms)PtII(OH2)2+ and water-insoluble
2.9. Attempted C–N reductive elimination from 7b in THF, benzene and
DCM solutions
One can expect a similar C–X reductive elimination reactivity
for structurally similar platina(IV)oxetanes 3 and platina(IV)azeti-
dines 7a–7b, X = O or N. Holding this consideration in mind we at-
tempted C–N reductive elimination from 7a–7b in the absence and
presence of a base, KOt-Bu, using aprotic solvents, THF, benzene
and dichloromethane. In all the cases decomposition of the starting
material was observed. For instance, (7b)[tetrakis(3,5-bis(trifluo-
romethyl)phenyl)borate], (7b)BArF4, prepared by metathesis of
(7b)Cl and NaBArF4 in dry dichloromethane was deprotonated
upon addition of 1 equ KOt-Bu in THF and removal of the resulting
tert-butanol under vacuum to produce a mixture of KBArF4 and the
neutral azetidine 9b, Eq. (4):

J.R. Khusnutdinova et al. / Inorganica Chimica Acta 369 (2011) 274–283
279
(dpms)2PtII
excess HBF4 [11].
(l
2
-OH)2 which dissolves in water in the presence of
for the success of this transformation. The acid is presumed to pro-
mote the azetidine ring opening to produce an aqua 2-ammonio-
ethyl platinum(II) intermediate which is expected to be reactive
towards O2, similar to other (dpms)PtIIR(OH2) complexes studied
previously. All attempts at direct C–N reductive elimination of azir-
idines from the platina(IV)azetidines in either aprotic or protic sol-
vents were unsuccessful presumably because of unavailability of
the isomer required for facile C–X reductive elimination. The final
step of the platinum-mediated aerobic oxidative coupling of ethyl-
ene and a primary amine to 2-(N-alkylamino)ethanols is the C–O
reductive elimination of platina(IV)azetidines that also requires
the presence of one equivalent of a strong acid in aqueous solution.
This reaction, most likely, includes acyclic 2-ammonioethyl plati-
num(IV) intermediates resulting from the azetidine ring opening
and protonation of the basic amino group. Overall, the current
work may be useful for mechanistic analysis and development of
new systems for aerobic platinum-catalyzed aminooxygenation
of olefins.
The ability of platina(IV)azetidines to undergo the acid-assisted
C–O reductive elimination in water can be accounted for by assum-
ing an initial azetidine ring opening to form dihydroxo alkyl plati-
num(IV) species B (Scheme 3c, X = OH). The resulting acyclic alkyl
species might isomerize into D featuring the 2-ammonioalkyl
trans- to the sulfonate group (Scheme 3d). This isomerization step
is presumed to be much slower for the platina(IV)azetidines 7a–7b
rendering them unreactive in C–N reductive elimination. The iso-
mer D can be attacked by nucleophilic water molecules to form
the organic products 8a–8b, following the nucleophilic substitu-
tion mechanisms discussed previously for 1a [11,12] and 2 [14].
To gain evidence in favor of the proposed mechanism for the for-
mation of 8a–8b, the reaction mixtures containing 7a and one
equivalent of HBF4 in water at 100 °C were monitored using 1H
NMR spectroscopy. A new species was detected in the course of
the reaction whose fraction never exceeded 20% of the initial con-
centration of 7a. Signals of the observed intermediate grew in the
initial period of reaction, reached the maximum at about 6 h and
disappeared after 30 h. This species was characterized by the mul-
tiplets at 3.86–4.06 ppm and a singlet at 2.48 ppm, integrating as
2H and 3H, respectively, which could be assigned to the resonances
of the N-bound b-CH2 group, and the N–Me group, respectively.
The absence of platinum-195 satellites for the signal of the N–Me
group at 2.48 ppm argues against the coordination of the N–Me
group to the Pt center in the observed intermediate, consistent
with the structure proposed for B (Scheme 3). Two matching peaks
of the ortho-protons of the pyridyl groups of the dpms ligand were
observed in the aromatic region as well, indicative of the low C1
symmetry of the observed intermediate. Therefore, 1H NMR
characteristics of the observed species are consistent with those
expected for B and not D. In contrast to B, the latter is expected
to be very reactive in SN2-type C–O reductive elimination
[11,12,14]. Finally, according to ESI-MS, a new signal appeared
and grew in aqueous solutions of 7a containing H2SO4 during its
heating. The peak is characterized by m/z 537.1 which matches
the value expected for an acyclic species [(dpms)PtIV(CH2CH2-
NH2Me)(OH)2]+.
4. Experimental section
General. All manipulations were carried out under purified ar-
gon atmosphere using standard Schlenk and glove box techniques
if not indicated otherwise. All reagents for which synthesis is not
given are commercially available from Aldrich, Acros, Alfa-Aesar
or Pressure Chemicals and were used as received without further
purification. Potassium di(2-pyridyl)methanesulfonate and com-
plex 4, (dpms)Pt(CH2@CH2)Cl, were synthesizes as described previ-
ously [14,28]. DMSO-d6, CD2Cl2 and CD3OD from Cambridge
Isotope Laboratories were dried over CaH2, vacuum-transferred
and stored in Teflon-sealed flasks in an argon-filled glove box.
Water was deaerated by repeating freezing–pumping cycles and
stored under argon in a Teflon-sealed Schlenk flask in a glove
box. 1H (400 MHz, 500 MHz or 600 MHz) and 13C NMR (100 MHz
or 125 MHz) spectra were recorded on a Bruker AVANCE 400, Bru-
ker DRX-500 or Bruker AVANCE-600 spectrometers. Chemical
shifts are reported in ppm and referenced to residual solvent reso-
nance peaks. IR spectra were recorded on a JASCO FT/IR 4100 spec-
trometer. ESI-MS experiments were performed using
a JEOL
No b-hydride elimination or hydroamination products which
are typically observed for platina(II)azetidines [15] have been de-
tected in acidic solutions of the platina(IV)azetidines 7a or 7b upon
heating. Thus, formation of high-valent platina(IV)azetidine com-
plexes leads to preferential 1,2-difunctionalization of olefins in
contrast to ‘‘monofunctionalization” observed for hydroamination
or ‘‘aza-Wacker-process” mediated by PtII and PdII species
[15,27]. Further investigation of aminohydroxylation of the substi-
tuted alkenes is required to elucidate the mechanism of the C–O
reductive elimination from platina(IV)azetidines 7a–7b.
AccuTOF-CS instrument. GC–MS experiments were performed
using a JEOL JMS-SX 102A instrument. Elemental analyses were
carried out by Chemisar Laboratories, Inc., Guelph, Canada.
4.1. Preparation of (dpms)PtII(C2H4NH2Me)Cl, 5a
To a stirred suspension of (dpms)Pt(C2H4)Cl (98 mg, 193
in 26 mL MeOH was added 40% aqueous solution of MeNH2 (85
973 mol, 5 equ). Stirring continued for 3 h at room temperature.
lmol)
lL,
l
The resulting suspension was left at ꢁ20 °C for 4 h. White fine-
crystalline solid was filtered off from the cold mixture, washed
with cold methanol and dried under vacuum to give 68.9 mg of
the product. The volume of the filtrate was reduced to 1 mL, the
resulting suspension was cooled down to ꢁ20 °C, filtered. The solid
was washed with cold methanol to give an additional 24.7 mg of
3. Summary and conclusions
Overall,
a mediatorless aerobic coupling of an ethylene
chloro platinum(II) complex and primary alkylamines enabled by
di(2-pyridyl)methanesulfonate ligand to form 2-(N-alkylamino)
ethanols has been demonstrated in protic media. This multistep
reaction includes nucleophilic attack of an amine at the ethylene
chloro platinum(II) complex and subsequent cyclization of the
resulting 2-ammonioethyl platinum(II) intermediates in basic
media to form platina(II)azetidines. An important finding of this
work is the discovery of the ability of platina(II)azetidines sup-
ported by di(2-pyridyl)methanesulfonate ligand to react with O2
in acidic aqueous solutions at ambient temperature and pressure.
The corresponding platina(IV)azetidines can be prepared in high
yield. Interestingly, the presence of a strong acid additive is critical
the product. Combined yield of 5a is 93.6 mg (174 lmol), 90%.
White crystalline solid, air-stable, poorly soluble in water and
methanol, soluble in DMSO. Solutions of 5a in dmso-d6 decompose
with a half-life of ꢂ7 h at 20 °C to produce (dpms)PtCl(dmso-d6),
free ethylene (a singlet at 5.29 ppm) along with unidentified
products.
2
1H NMR (dmso-d6, 22 °C, 400 MHz), d: 1.02–1.41 (m, JPtH
=
=
3
62 Hz, 1H), 2.10–2.41 (m, 2H), 2.33 (s, 3H), 2.59–2.84 (m, JPtH
40 Hz, 1H), 6.00 (s, 1H), 7.41 (ddd, J = 7.8, 6.0, 1.5 Hz, 1H), 7.51
(ddd, J = 7.8, 5.6, 1.5 Hz, 1H), 7.76 (d, J = 7.8 Hz, 1H), 7.82 (dd,
J = 7.8, 1.5 Hz, 1H), 8.06 (td, J = 7.8, 1.5 Hz, 1H), 8.12 (td, J = 7.8,

280
J.R. Khusnutdinova et al. / Inorganica Chimica Acta 369 (2011) 274–283
1.5 Hz, 1H), 8.29 (br s, 2H, NH2), 8.87 (d, J = 6.0 Hz, 1H), 9.03 (dd,
J = 5.6, 1.5 Hz, 1H). 13C NMR (dmso-d6, 22 °C, 500 MHz), d: ꢁ0.7
(Pt–CH2), 31.6 (N–CH3), 53.6 (N–CH2), 75.9 (CHSO3), 124.1, 125.6,
128.0, 129.6, 137.9, 138.1, 150.5 (CH, py), 150.8 (C quat, py),
151.8 (CH, py), 154.0 (C quat, py) (signal assignments are from
to room temperature and the white precipitate was filtered off,
washed with methanol until a neutral pH of the filtrate and dried
under vacuum to give 56.0 mg of 6a. Volume of the filtrate was re-
duced to 2 mL under vacuum and the crude product was filtered
off, washed with cold methanol and dried to give 8.8 mg of 6a.
DEPT). IR (KBr),
m
: 3468 (w br), 3135 (w), 3014 (w), 2945 (w),
Yield 64.8 mg (129
uble in methanol.
l
mol), 76%. White crystalline solid, poorly sol-
2907 (w), 1601 (w), 1478 (w), 1433 (w), 1407 (w), 1314 (w),
1240 (s), 1170 (s), 1034 (s), 902 (w), 860 (w), 805 (w), 758 (s)
cmꢁ1. ESI-MS of solution of 5a in MeOH/H2O (50:50 v/v): m/z
539.0; calc. MꢀH+ C14H19N3SO3195Pt35Cl 539.0. Anal. Calc. for
1H NMR (dmso-d6, 22 °C, 400 MHz), d: 0.98–1.12 (m, JPtH
=
2
2
60 Hz, 1H), 1.18–1.34 (m, JPtH = 55 Hz, 1H), 2.30 (d, J = 5.5 Hz,
3JPtH ꢂ 20 Hz, 3H), 4.03–4.24 (m, JPtH ꢂ 50 Hz, 1H), 4.97–5.33 (m,
3
C14H18ClN3O3PtS: C, 31.20; H, 3.37; N, 7.80. Found: C, 30.98; H,
2H), 5.81 (s, 1H), 7.30 (ddd, J = 7.7, 5.6, 1.5 Hz, 1H), 7.53 (ddd,
J = 7.7, 5.6, 1.5 Hz, 1H), 7.75 (d, J = 7.7 Hz, 1H), 7.78 (d, J = 7.7 Hz,
1H), 8.05 (td, J = 7.7, 1.5 Hz, 1H), 8.09 (td, J = 7.7, 1.5 Hz, 1H), 8.63
3.63; N, 7.58%.
Complex (dpms)PtCl(dmso-d6) was obtained independently by
dissolving LPt(CH2@CH2)Cl in dmso-d6. 1H NMR of (dpms)PtCl-
(dmso-d6) (dmso-d6, 22 °C, 400 MHz), d: 6.28 (s, 1H), 7.54 (ddd,
J = 7.9, 5.9, 1.5 Hz, 1H), 7.64 (ddd, J = 7.9, 5.9, 1.5 Hz, 1H), 7.87 (d,
J = 7.9 Hz, 1H), 7.94 (d, J = 7.9 Hz, 1H), 8.18 (td, J = 7.9, 1.5 Hz,
1H), 8.22 (td, J = 7.9, 1.5 Hz, 1H), 8.83 (dd, J = 5.9, 1.5 Hz, 1H),
9.06 (dd, J = 5.9, 1.5 Hz, 1H).
(dd, J = 5.6, 1.5 Hz, 1H), 8.72 (dd, J = 5.6, 1.5 Hz, 1H). IR (KBr), m:
3480 (w), 3159 (w), 2935 (w), 2884 (w), 2817 (w), 1603 (w),
1475 (w), 1455 (w), 1433 (w), 1254 (m), 1202 (m), 1154 (m),
1031 (s), 810 (w), 762 (w) cmꢁ1. ESI-MS of solution of 6a in
MeOH/H2O (50:50 v/v): m/z 503.1; calc. C14H18N3SO3195Pt, 503.0.
4.4. Preparation of (dpms)PtII(C2H4NHtBu-
jC,jN), 6b
4.2. Preparation of (dpms)PtII(C2H4NH2t-Bu)Cl, 5b
A 25 mL Schlenk flask equipped with a magnetic stirring bar
was charged with 48.9 mg (84 mol) of 5b, and 5 mL of 16.9 mM
solution of NaOH in degassed MeOH (84 mol, 1 equ NaOH) under
an argon atmosphere. The Schlenk tube was Teflon-sealed under
argon, and the stirred suspension was heated at 50 °C. The starting
material dissolved after ꢂ30 min. Heating continued for 12 h to
complete the reaction. The product was identified by ESI-MS as
azetidine complex 6b. Two isomers, cis- and trans-6b, were de-
tected in a 6:1 ratio. The crude product contaminated with NaCl
was used in oxidation experiments.
l
A
100 mL round-bottom flask was charged with (dpms)-
Pt(C2H4)Cl (151 mg, 297 mol) and 40 mL of methanol. Tert-butyl-
amine (150 L, 1.42 mmol, 5 equ) was added dropwise to the stir-
l
l
l
red suspension at room temperature. After a few minutes all
starting material dissolved. Stirring continued for 1 h, and the
resulting solution was left to crystallize overnight at ꢁ20 °C. White
large crystals of the product were filtered off from the cold mix-
ture, washed with several milliliters of cold methanol and dried
under vacuum to give 115.7 mg of the product. An additional frac-
tion of the product was obtained by reducing volume of the filtrate
to 5 mL under vacuum. The resulting suspension was cooled down
to ꢁ20 °C and filtered. The resulting solid was washed with 1 mL of
cold methanol and vacuum-dried to give 38.4 mg of the pure prod-
1H NMR (CD3OD, 22 °C, 400 MHz), d: cis-6b: 1.00 (vtd, J = 9.2,
2.9 Hz, JPtH = 78 Hz, 1H), 1.15 (s, 9H), 1.25–1.62 (m, 1H; JPtH could
not be determined due to overlap with multiplets of the minor iso-
mer), 4.36–4.56 (m, 1H; JPtH could not be determined reliably), 5.09
(ddd, J = 13.0, 9.2, 2.9 Hz, JPtH = 88 Hz, 1H), 5.86 (s, 1H), 7.30 (ddd,
J = 7.8, 5.8, 1.6 Hz, 1H), 7.46 (ddd, J = 7.8, 5.8, 1.6 Hz, 1H), 7.81
(vd, J = 7.8 Hz, 1H), 7.84 (vd, J = 7.8 Hz, 1H), 8.04 (td, J = 7.8,
1.6 Hz, 1H), 8.05 (td, J = 7.8, 1.6 Hz, 1H), 8.92 (dd, J = 5.8, 1.6 Hz,
1H), 8.97 (d, J = 5.8 Hz, 1H). trans-6b: 1.18 (s, 9H), 1.19–1.60 (m,
2H), 4.59–4.75 (m, 1H), 4.94–5.04 (m, 1H), 7.30–7.37 (m, 1H),
7.47–7.52 (m, 1H), 8.49–8.56 (m, 2H), 8.76 (d, J = 6.0 Hz, 1H),
8.86 (d, J = 5.6 Hz, 1H), other peaks of a minor isomer and 195Pt-
H coupling constants could not be determined. ESI-MS of solution
of 6b in methanol, m/z 545.1; calc. for MꢀH+, C17H24N3SO3195Pt
545.1.
uct. Combined yield of 5b is 154.1 mg (265 lmol), 89%. White crys-
talline solid, air-stable, poorly soluble in water in methanol;
soluble in DMSO.
1H NMR 1H (dmso-d6, 22 °C, 400 MHz), d: 0.91–1.23 (m, 1H, 2JPtH
could not be determined), 1.18 (s, 9H), 2.16–2.49 (m, 2H), 2.92–
2
3.13 (m, JPtH = 50 Hz, 1H), 5.95 (s, 1H), 7.41 (ddd, J = 7.8, 5.7,
1.5 Hz, 1H), 7.50 (ddd, J = 7.8, 5.5, 1.3 Hz, 1H), 7.77 (d, J = 7.8,
1H), 7.80 (d, J = 7.8 Hz, 1H), 7.92 (br s, 2H, NH2), 8.05 (td, J = 7.8,
1.7 Hz, 1H), 8.09 (td, J = 7.8, 1.5 Hz, 1H), 8.71 (d, J = 5.7 Hz, 1H),
9.05 (dd, J = 5.5, 1.3 Hz, 1H). 13C NMR (dmso-d6, 22 °C, 500 MHz),
d: ꢁ0.77 (1JPtC = 760 Hz), 25.33, 45.87, 55.34, 75.74, 124.15,
125.55, 128.22, 129.49, 137.75, 138.05, 150.46, 151.03, 152.46,
4.5. Oxidation of 6a with H2O2 to 7a in methanolic solution
154.01. IR (KBr), m: 3474 (w br), 3414 (w br), 3057 (w), 2974 (w),
2835 (w), 1604 (w), 1476 (w), 1457 (w), 1430 (w), 1376 (w),
A suspension of 6a (20.0 mg, 4.0
placed into a 10 mL vial equipped with a magnetic stirring bar. A
30% aqueous H2O2 solution (4.5 L, 4.4 mol, 1.1 equ) was added
to the stirred suspension. After a few minutes the starting material
completely dissolved and the solution turned yellow. Stirring con-
lmol) in 0.8 mL of CD3OD was
1304 (w), 1247 (m), 1236 (m), 1211 (s), 1178 (s), 1159 (m), 1039
(s), 854 (w), 808 (w), 763 (m) cmꢁ1. ESI-MS for solution of 5b in
l
l
MeOH/H2O (50:50 v/v), m/z 581.1, calc. MꢀH+, C17H25N3SO3
-
195
Pt35Cl 581.1. Anal. Calc. for C17H24ClN3O3PtS: C, 35.14; H, 4.16; N,
7.23. Found: C, 34.84; H, 4.28; N, 6.86%.
tinued for 1 h at rt. 1,4-dioxane (10 lL) was added as an internal
Complex 5b decomposes in dmso-d6 solutions at 20 °C with a
half-life of 22 h to produce (dpms)PtCl(dmso-d6), ethylene (a sin-
glet at 5.29 ppm) and unidentified products.
standard. According to 1H NMR spectroscopy, quantitative oxida-
tion occurred. The resulting solution was strongly alkaline. The ra-
tio of two isomers characterized by the signals of the N–Me groups
at 2.87 ppm and 2.11 ppm, was 2:5 after 1 h after preparation. The
ratio increased slowly to 2:1 after 10 h, which remained un-
changed after 1 day.
4.3. Preparation of (dpms)PtII(C2H4NHMe-
jC,jN), 6a
A 100 mL Schlenk tube equipped with a magnetic stirring bar
was charged with 91.2 mg of 5a (169 mol) and 18 mL of
18.8 mM NaOH solution in degassed MeOH (338 mol, 2 equ
NaOH). The Schlenk tube was Teflon-sealed under argon and
heated at 50 °C for 24 h. The resulting suspension was cooled down
The NOE experiments exhibited weak positive NOE’s between
N–Me group and ortho-protons of pyridyl of the dpms ligand in
l
l
both isomers of 7a.
3
1H NMR (CD3OD, 22 °C, 400 MHz), d: cis-7a: 2.87 (s, JPtH
=
2
27 Hz, 3H), 2.83–2.93 (m, 1H; JPtH could not be determined),

J.R. Khusnutdinova et al. / Inorganica Chimica Acta 369 (2011) 274–283
281
2
2
2
3.07–3.27 (m, JPtH = 64 Hz, 1H), 4.62–4.73 (m, JPtH ꢂ 64, 1H),
4.86–4.98 (m, 1H), 6.61 (s, 1H), 7.75 (ddd, J = 7.7, 5.6, 1.4 Hz, 1H),
7.88 (ddd, J = 7.7, 5.4, 1.4 Hz, 1H), 8.07 (d, J = 7.7 Hz, 1H), 8.11 (d,
J = 7.7 Hz, 1H), 8.26–8.32 (m, 2H), 8.76 (dd, J = 5.6, 1.4 Hz,
1H), 7.60 (br s, JPtH = 58 Hz, 1H, NH), 7.85 (ddd, J = 7.9, 5.9,
1.3 Hz, 1H), 7.91 (ddd, J = 7.9, 5.5, 1.0 Hz, 1H), 8.09 (d, J = 7.9 Hz,
1H), 8.10 (d, J = 7.9 Hz, 1H), 8.33 (td, J = 7.9, 1.4 Hz, 1H), 8.39 (td,
J = 7.9, 1.2 Hz, 1H), 8.83 (d, J = 5.9 Hz, 1H), 9.48 (d, J = 5.5 Hz, 1H).
13C NMR (dmso-d6, 22 °C, 500 MHz), d: ꢁ4.1 (1JPtC = 376 Hz, Pt-
CH2), 25.2 (C–CH3), 48.5 (CH3, MeOH), 54.3 (2JPtC = 114 Hz, N–
CH2), 60.2 (C quat, t-Bu), 69.3 (CHSO3), 126.1, 127.3, 127.4, 128.5,
142.6, 143.8 (CH, py), 149.9 (C quat, py), 150.2, 150.3 (CH, py),
3JPtH = 26 Hz, 1H), 9.02 (d, J = 5.4 Hz, JPtH = 13 Hz, 1H). trans-7a:
2.11 (s, JPtH = 33 Hz, 3H), 2.64–2.89 (m, 1H; JPtH could not be
determined), 2.97–3.31 (m, 1H; JPtH could not be determined),
3
3
2
2
4.02–4.28 (br m, 1H), 4.57–4.77 (br m, 1H), 6.70 (s, 1H), 7.79
(ddd, J = 7.7, 5.6, 1.5 Hz, 1H), 7.91 (ddd, J = 7.7, 5.6, 1.1 Hz, 1H),
8.05–8.11 (m, 2H), 8.25–8.34 (m, 2H), 8.69 (d, J = 5.6 Hz,
150.4 (C quat, py). IR (KBr), m: 3550 (w br), 3267 (w br), 3018
(w), 2971 (w), 2923 (w), 2813 (w), 1607 (w), 1477 (w), 1441 (w),
1308 (m), 1299 (m), 1204 (w), 1144 (s), 1068 (w), 1029 (w), 959
(m), 768 (m), 697 (m) cmꢁ1. ESI-MS of solution of (7b)Cl in MeOH:
m/z 561.1; calc. for cationic 7b, C17H24N3SO4195Pt, 561.1. X-ray
quality crystals were obtained by slow crystallization from concen-
trated methanolic solution at ꢁ20 °C.
3JPtH = 27 Hz, 1H), 8.92 (d, J = 5.6 Hz, JPtH = 14 Hz, 1H). 13C NMR
3
(CD3OD, 22 °C, 500 MHz), d: cis-7a: ꢁ2.0 (1JPtC = 414 Hz, Pt–CH2),
56.0 (2JPtC = 22 Hz, NMe), 72.3 (m, CDSO3), 80.3 (2JPtC = 115 Hz, N–
CH2), 128.0, 128.4, 129.2, 130.3, 143.6, 144.4, 149.8, 151.2, 152.6,
152.9 (py). trans-7a: ꢁ5.0 (Pt-CH2), 39.7 (NMe), 63.8 (N-CH2),
72.3 (m, CDSO3), 128.6, 128.8, 129.4, 130.1, 144.1, 145.1, 149.7,
151.1, 151.9, 152.5 (py). (JPtC could not be determined). ESI-MS of
solution of 7a in MeOH: m/z 519.1; calc. MꢀH+, C14H18N3SO4195Pt
519.1.
Anal. Calc. for C18H28ClN3O5PtS: C, 34.37; H, 4.49; N, 6.68.
Found: C, 34.45; H, 4.73; N, 6.36%.
Table 1 lists the key parameters of the single crystal X-ray struc-
ture determination for (7b)ClꢀMeOH.
4.6. Preparation of (7a)2(SO4)
4.8. Preparation of (7b)BArF
4
A sample of 6a (53.3 mg, 105
solution (12 L, 116 mol) were used as described above. After 1 h
the resulting alkaline solution was neutralized with 1 equ of 1.00 N
H2SO4 (105 L). The resulting neutral solution of was evaporated
under vacuum to produce white crystalline [(dpms)PtIV(C2H4-
NMe- C, C, N)-
N)(OH)]2(SO4). Solid [(dpms)PtIV(C2H4NMe-
lmol), 10 mL of H2O and 30% H2O2
A 50 mL flask equipped with a magnetic stirring bar was
l
l
charged with (7b)ClꢀMeOH (39.0 mg, 62
l
mol), NaBArF (54.5 mg,
4
61 mol) and 10 mL of CH2Cl2. The reaction mixture was stirred
l
l
under for 1 h at room temperature. Initially insoluble starting
*
material (7b)Cl MeOH dissolved after 1 h and NaCl precipitated
j
j
j j
from solution. The reaction mixture was filtered from NaCl through
Celite, washed with small amount of CH2Cl2 and dried under vac-
uum for 1 day. The product was isolated as white solid, perfectly
(OH)]2(SO4) was used for reductive elimination experiments
immediately after preparation. According to 1H NMR spectroscopy,
two isomers were present in solution in D2O, presumably cis- and
trans-(7a)2(SO4), in 6:1 ratio. 1H NMR (D2O, 22 °C, 400 MHz), d: cis-
soluble in CH2Cl2 and THF. Yield 63.4 mg (44.5 lmol), 72%.
1H NMR (THF-d8, 22 °C, 400 MHz), d: 1.26 (s, 9H), 2.87 (m,
3
2
7a: 2.30 (s, JPtH = 33 Hz, 3H), 2.91 (m, JPtH = 62 Hz, 1H), 3.27 (m,
2JPtH = 80 Hz, 1H), 4.03 (m, 1H), 5.09 (m, 1H), 6.78 (s, 1H), 7.80
(ddd, J = 7.8, 5.7, 1.4 Hz, 1H), 7.92 (ddd, J = 7.8, 5.4, 1.1 Hz, 1H),
8.09 (d, J = 7.8 Hz, 1H), 8.13 (d, J = 7.8 Hz, 1H), 8.30–8.37 (m, 2H),
2
2
2JPtH = 68 Hz, 1H), 3.15 (m, JPtH = 81 Hz, 1H), 3.44 (s, JPtH = 27 Hz,
2
1H, OH), 4.56–4.78 (m, 2H), 5.92 (br s, JPtH = 74 Hz, 1H, NH),
6.49 (s, 1H), 7.57 (s, 4H), 7.72–7.85 (m, 10H), 7.98–8.06 (m, 2H),
3
3
8.62 (d, J = 5.7 Hz, JPtH = 26 Hz, 1H), 8.85 (d, J = 5.4 Hz, JPtH
=
3
13 Hz, 1H); trans-7a: 2.46 (s, JPtH = 33 Hz, 3H), 2.94–3.44 (m,
2H), 4.42–4.51 (m, 1H), 6.76 (s, 1H), 7.85–7.99 (m, 2H), 8.15–
8.24 (m, 2H), 8.28–8.37 (m, 2H), 8.64 (d, J = 5.4 Hz, 1H), 8.90 (d,
J = 5.4 Hz, 1H).
Table 1
Crystal structure data and structure refinement for (7b)ClꢀMeOH.
Empirical formula
C18H28ClN3O5PtS
Formula weight
Crystal size (mm3)
Crystal habit
Crystal system
Space group
a (Å)
629.03
4.7. Preparation of (7b)Cl
0.32 ꢃ 0.15 ꢃ 0.10
colorless prism
triclinic
The solution of crude 6b containing 1 equ of NaCl in MeOH was
prepared by heating 5b (126 mg, 217 lmol) and 1 equivalent of
ꢀ
P1
9.5764(6)
10.0716(6)
12.8674(8)
92.272(1)
102.071(1)
114.844(1)
1089.87(12)
2
NaOH in 13 mL of MeOH at 50 °C for 14 h as described above and
was used without isolation of 6b. A 30% aqueous solution of
H2O2 (282 mg, 2.49 mmol, 11 equ) was added to the stirred solu-
tion of 6b. The reaction mixture turns immediately bright yellow;
stirring continued for 30 min. According to 1H NMR spectroscopy,
(7b)Cl formed quantitatively as the only product. The resulting
solution was reduced in volume to 1 mL under vacuum and was
left to crystallize at ꢁ20 °C overnight. Large colorless crystals were
filtered off, washed with cold methanol and dried under vacuum to
give 53.3 mg of the product. The filtrate was evaporated to a vol-
ume of 0.2–0.3 mL and left at ꢁ20 °C for overnight. The crystalline
product, (7b)ClꢀMeOH, was filtered off and washed with small
amount of cold methanol to give an additional fraction of white
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
Density (
q
calc) (g/cm3)
1.917
6.690
616
Absorbtion coefficient (
l
) (mmꢁ1
)
ꢀ
F(0 0 0) (e)
h Range for data collection (°)
Index ranges
2.25–27.50
ꢁ12 6 h 6 11, ꢁ13 6 k 6 13,
0 6 l 6 16
23101
4988
4904
Number of reflections collected
Number of independent reflections
Number of observed reflections
[I > 2r(I)]
Coverage of independent reflections
crystals, 34.0 mg. Combined yield 87.3 mg (139 lmol), 64%. Color-
less crystalline solid, perfectly soluble in methanol, water and
99.6
DMSO, slightly soluble in THF.
(%)
1H NMR (dmso-d6, 22 °C, 400 MHz), d: 1.15 (s, 9H), 2.89 (m,
Final R indices
R1, I > 2r(I) 0.0213
wR2, all data 0.0529
Rint 0.0288
Rsig 0.0256
2JPtH = 75 Hz, 1H), 2.94 (m, JPtH = 70 Hz, 1H), 3.16 (d, J = 5.3 Hz,
2
3H, MeOH), 4.10 (q, J = 5.3 Hz, 1H, MeOH), 4.25 (br s, 1H, OH),
3
3
4.41 (m, JPtH = 35 Hz, 1H), 4.58 (m, JPtH = 40 Hz, 1H), 7.01 (s,

282
J.R. Khusnutdinova et al. / Inorganica Chimica Acta 369 (2011) 274–283
8.27 (td, J = 7.8, 1.4 Hz, 1H), 8.31 (td, J = 7.7, 1.4 Hz, 1H), 8.79 (dd,
J = 6.0, 1.4 Hz, JPtH = 34 Hz, 1H), 9.16 (d, J = 5.4 Hz, 1H).
acidified methanolic solution of the decomposition products re-
vealed the presence of a strong signal, characterized by m/z
545.1, corresponding to 6bꢀH+ (calc. C17H24N3SO3195Pt 545.1).
Low intensity peaks were detected by ESI-MS, characterized by
m/z 561.1 and 480.0.
3
4.9. Oxidation of 6a and 6b with O2 in neutral, basic, and acidic
solutions
Solid samples of crude isolated complexes 6a or 6b were dis-
4.11.2. Reaction in CD2Cl2 and C6D6
solved in D2O or CD3OD to generate 9–9.4 mM solutions. The
resulting solutions were combined with 10 lL 1,4-dioxane used
A solution of 15 mg of 9b in 0.7 mL CD2Cl2 ([9b] = 15 mM) is
stable after 3 days of heating at 60 °C in a sealed Young tube.
as an internal standard and an additive of an acid (1 M H2SO4 or
50 wt.% HBF4) or a base (as 0.1 M NaOH solution) or were used
without additives. The resulting solutions were placed into 10 mL
flasks equipped with a magnetic stirring bar. The air was replaced
with O2 and vigorous stirring continued at room temperature. For
aerobic oxidation experiments, the reaction mixtures were stirred
vigorously under air.
The suspension of partially soluble 9b (8 mg, 5 lmol) in C6D6
was heated in a sealed Young tube at 60 °C for 25 h. The resulting
reaction mixture was evaporated to dryness, re-dissolved in dmso-
d6 and analyzed by 1H NMR. The presence of complex mixture of
unidentified products along with 6b (in 18% yield) and unreacted
9b (31%) was observed by 1H NMR spectroscopy. The yields of 6b
and 9b were estimated by integration of CHSO3 singlets at
No changes were observed in 1H NMR spectra of the neutral
reaction mixtures in D2O or CD3OD containing 6a or 6b after 2–
24 h under O2 or in the presence of 0.2 equivalents of NaOH after
4 days of stirring under O2 atmosphere.
5.82 ppm and 6.99 ppm, respectively, using BArF peaks as an
4
internal standard.
4.12. Reductive elimination from (7a)2(SO4) in acidic D2O solutions
Oxidation of 6a to form 7a was observed in D2O solution in the
presence of 1 equivalent of HBF4 or H2SO4 as an acid source. The
yield of 7a after 2 h was 93 2%. Slower oxidation was seen under
air to give 7a in 92 2% yield (an average of 2 runs) after 24 h.
Oxidation of 6b to 7b was observed in CD3OD solution with a
half-live of ꢂ2 h at 20 °C. After 24 h 7b formed in 73 2% yield,
according to 1H NMR spectroscopy.
Oxidation of 6b in the presence of 1 equ. HBF4 in D2O solution
under 1 atm O2 occurred with a half life of 2.4 h at 20 °C; yield of
7b after 24 h is 80%.
A sample of (7a)2(SO4) (10.8 mg, 17
6:1 ratio) was dissolved in 0.8 mL of D2O and acidified with 1
equivalent of HBF4 (4 L of 50% wt. aq. HBF4, 17 mol). The result-
lmol, cis-/trans- mixture in
l
l
ing solution was placed into an NMR Young tube and 1H NMR spec-
tra of the reaction solution were recorded before reaction and then
in regular intervals during heating at 100 °C. Formation of proton-
ated N-methyl ethanolamine, HOC2H4NH2Me+ (8a), was detected
by 1H NMR, identified by comparison of 1H NMR spectrum with
an authentic sample. Another product, (dpms)PtII(OH2)2+, de-
scribed earlier [11], was detected by 1H NMR spectroscopy as the
main Pt-containing species after 33 h at 100 °C. Small amounts of
4.10. Preparation of (dpms)PtIV(C2H4NHt-Bu-
jC,jN)(OH), 9b
solid (dpms)2PtII
(l-OH)2 formed after 33 h. The product dissolves
2
A 25 mL round-bottom flask equipped with a magnetic stirring
bar was charged with (7b)BArF (63.4 mg, 44
mol), 5.2 mg of t-
mol, 1 equ) and 5–6 mL of dry degassed THF. The
in 0.8 mL of D2O in the presence of 20 lL of 50 wt.% HBF4 at 100 °C
to give (dpms)PtII(OH2)2 as the sole product, detected by 1H NMR
spectroscopy.
+
l
4
BuOK (44
l
resulting solution turned yellow immediately after addition of t-
BuOK; stirring continued for 1 h. After 1 h solvents were removed
and the yellow solid was dried under vacuum for 1 day. The prod-
uct was obtained as yellow crystalline solid, 62.1 mg. The product
4.12.1. HOCH2CH2NH2Me+ꢀ(8a)
1H NMR (D2O/HBF4, 22 °C, 400 MHz): 2.74 (s, 3H), 3.16 (m,
AA0XX0, 2H), 3.83 (m, AA0XX0, 2H).
was used as a mixture with 1 equ of KBArF without separation.
Intermediate B was characterized by the following set of signals
in 1H NMR spectrum in D2O: 2.48 (s, 3H), 2.55–2.70 (m, 1H), 3.04–
3.15 (m, 1H), 3.86–3.94 (m, 1H), 3.96–4.06 (m, 1H), 8.71 (d,
J = 6.0 Hz, ortho-H of py), 8.94 (d, J = 6.0 Hz, ortho-H of py). Other
peaks could not be seen due to overlap with resonances of 7a
and other reaction products. ESI-MS analysis of an analogous reac-
tion mixture after heating at 100 °C for 5 h in H2O/H2SO4 solution
exhibited new signals at m/z 537.1 that match the calculated pat-
tern expected for [(dpms)PtIV(CH2CH2NH2Me)(OH)2]+ (calc. m/z
537.1 for C14H20N3O5S195Pt).
4
Complex 9b decomposes slowly in THF-d8 solution at room tem-
perature with a half-life of ꢂ17 h.
1H NMR (THF-d8, 22 °C, 400 MHz), d: 1.12 (s, 9H), 2.54 (m,
2
2JPtH = 67 Hz, 1H), 2.92 (m, JPtH = 84 Hz, 1H), 3.23 (br s, 1H, OH),
3
3
4.17 (m, JPtH= 43 Hz, 1H), 4.35 (m, JPtH = 40 Hz, 1H), 6.32 (s, 1H),
7.62–7.71 (m, 2H), 7.91 (d, J = 7.7 Hz, 1H), 7.93 (d, J = 7.7 Hz, 1H),
8.13 (td, J = 7.7, 1.3 Hz, 1H), 8.15 (vt, J = 7.7 Hz, 1H), 8.78 (d,
3
J = 5.6 Hz, JPtH = 23 Hz, 1H), 9.02 (d, J = 4.7 Hz, 1H). KBArF4: 7.57
(s, 4H), 7.79 (br s, 8H).
The graphs of concentration of 7a (filled circles), B (empty
rhombs) and 8a (filled triangles) vs. time and the graph in coordi-
nates ln ([7a]initial/[7a]) versus time are given in the Supporting
Information, Fig. 11. Concentrations of 7a, B, and 8a were calcu-
lated by integration of N–Me group of isomeric complexes 7a at
2.46 ppm and 2.30 ppm, CH2-multiplet of B at 3.86–4.06 ppm
and a multiplet of 8a at 3.83 ppm, using residual HDO peak as an
internal standard. The estimated 1st order rate constant of disap-
4.11. Attempted reductive elimination from 9b in aprotic solvents
4.11.1. Reaction in THF-d8
A sample of 9b (10 mg, 6.8 lmol, as a mixture with 1 equivalent
of KBArF4) was dissolved in 0.7 mL of dry degassed THF-d8, and the
resulting yellow solution was placed into an NMR Young tube;
[9b] = 9.8 mM. The reaction mixture was heated at 60 °C under
an argon atmosphere and periodically analyzed by 1H NMR. The
signals of starting material disappear with a half-life of 22 h at
60 °C to produce insoluble products. After 4 days at 60 °C no 9b re-
mained in solution, and insoluble reaction products were dissolved
in MeOH or dmso-d6.
pearance of 7a at 100 °C is (6.0 0.3) 10ꢁ5 sꢁ1
.
4.12.2. Reductive elimination from (7b)Cl in neutral and acidic D2O
solutions
A solution of 3.7 mg of (7b)Cl (3.7 mg, 6 mol) in 0.7 mL D2O was
placed into an NMR Young tube and was heated at 100 °C. The
reaction was monitored by 1H NMR spectroscopy. The complex
(7b)Cl disappeared with a half-life 21 h. An intermediate species
In dmso-d6 solution of decomposition products, the complex 6b
was detected by 1H NMR spectroscopy and identified by compari-
son with 1H NMR spectrum of authentic sample of 6b. ESI-MS of

J.R. Khusnutdinova et al. / Inorganica Chimica Acta 369 (2011) 274–283
283
appeared in the beginning of reaction and eventually disappeared
References
after prolonged heating, characterized by a multiplet at 3.87–
3.97 ppm. After 5 days at 100 °C (7b)Cl has completely disap-
peared. The organic product of the reaction was identified as 8b
by comparison of its 1H NMR spectrum with an authentic sample.
The yield of 8b is 65% based on integration of a multiplet at
3.83 ppm and using residual solvent peak as a standard. Insoluble
[1] S.C. Bergmeier, Tetrahedron 56 (2000) 2561.
[2] D.J.P. Ager, I. Prakash, D.R. Shaad, Chem. Rev. 96 (1996) 835.
[3] K. Muniz, Chem. Soc. Rev. 33 (2004) 166.
[4] E.J. Alexanian, C. Lee, E.J. Sorensen, J. Am. Chem. Soc. 127 (2005) 7690.
[5] G.S. Liu, S.S. Stahl, J. Am. Chem. Soc. 128 (2006) 7179.
[6] L.V. Desai, M.S. Sanford, Angew. Chem., Int. Ed. 46 (2007) 5737.
[7] K. Muniz, A. Iglesias, Y.W. Fang, Chem. Commun. (2009) 5591.
[8] A. Vedernikov, Chem. Commun. (2009) 4781–4790.
[9] J. Zhang, E. Khaskin, N.P. Anderson, P.Y. Zavalij, A.N. Vedernikov, Chem.
Commun. (2008) 3625.
[10] K.A. Grice, K.I. Goldberg, Organometallics 28 (2009) 953.
[11] A.N. Vedernikov, S.A. Binfield, P.Y. Zavalij, J.R. Khusnutdinova, J. Am. Chem. Soc.
128 (2006) 82.
[12] J.R. Khusnutdinova, P.Y. Zavalij, A.N. Vedernikov, Organometallics 26 (2007)
3466.
[13] J.R. Khusnutdinova, L.L. Newman, P.Y. Zavalij, Y.F. Lam, A.N. Vedernikov, J. Am.
Chem. Soc. 130 (2008) 2174.
(dpms)2Pt2(l-OH)2 was another reaction product. The solid dis-
solved upon heating in the presence of a large excess HBF4 to form
[(dpms)Pt(H2O)2]2+ [11].
4.12.3. HOCH2CH2NH2t-Bu+ (8b)
1H NMR (D2O, 22 °C, 400 MHz): 1.38 (s, 9H), 3.16 (m, AA’XX’,
2H), 3.83 (m, AA’XX’, 2H).
[14] J.R. Khusnutdinova, P.Y. Zavalij, A.N. Vedernikov, Organometallics 26 (2007)
2402.
Acknowledgments
[15] C.F. Bender, R.A. Widenhoefer, J. Am. Chem. Soc. 127 (2005) 1070.
[16] H. Alper, F. Urso, D.J.H. Smith, J. Am. Chem. Soc. 105 (1983) 6737.
[17] S. Calet, F. Urso, H. Alper, J. Am. Chem. Soc. 111 (1989) 931.
[18] J.P. Wolfe, J.E. Ney, Org. Lett. 5 (2003) 4607.
[19] P.J. Walsh, F.J. Hollander, R.G. Bergman, Organometallics 12 (1993) 3705.
[20] S.A. Blum, V.A. Rivera, R.T. Ruck, F.E. Michael, R.G. Bergman, Organometallics
24 (2005) 1647.
[21] D.P. Klein, J.C. Hayes, R.G. Bergman, J. Am. Chem. Soc. 110 (1988) 3704.
[22] E. Teuma, F. Malbosc, V. Pons, C. Serra-Le Berre, J. Jaud, M. Etienne, P. Kalck, J.
Chem. Soc., Dalton Trans. (2001) 2225.
[23] P.S. Hanley, D. Markovic, J.F. Hartwig, J. Am. Chem. Soc. 132 (2010) 6302.
[24] A.L. Casalnuovo, J.C. Calabrese, D. Milstein, J. Am. Chem. Soc. 110 (1988) 6738.
[25] J.R. Khusnutdinova, P.Y. Zavalij, A.N. Vedernikov, Can. J. Chem.-Revue
Canadienne De Chimie 87 (2009) 110.
We thank the National Science Foundation (CHE-0614798) and
the US–Israel Binational Science Foundation for the financial sup-
port of this work.
Appendix A. Supplementary material
CCDC 797450 contains the supplementary crystallographic data
for (7b)Cl MeOH. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. 1H and 13C NMR spectra of compounds 6a,
6b and 7b and kinetic characterization for the C–O reductive elim-
ination from 7a in acidic aqueous solutions can be found, in the on-
line version, at doi:10.1016/j.ica.2010.09.057.
[26] S.A. Mitchenko, V.V. Zamashchikov, S.M. Slinkin, Zh. Obshch. Khim. 63 (1993)
956.
[27] V. Kotov, C.C. Scarborough, S.S. Stahl, Inorg. Chem. 46 (2007) 1910.
[28] A.N. Vedernikov, J.C. Fettinger, F. Mohr, J. Am. Chem. Soc. 126 (2004) 11160.