Catalytic etherification of alcohols in Shilov system: C[sbnd]O versus C[sbnd]H bond activation

Article abstract of DOI:10.1016/j.molcata.2016.07.012

A novel catalytic reaction of alcohol etherification in the system ROH ? PtCl₄^2? ‐ PtCl₆^2? was found. Methanol easily transforms into dimethyl ether in the presence of catalytic amounts of Pt^II chloro complexes at 70?°C. Under the same conditions reaction of ethanol affords diethyl ether (catalytic) and π-ethylene Pt^II complex (stoichiometric). The reactions are accompanied by multiple H/D exchange, which is indicative of intermediacy of corresponding alkyl platinum derivatives. The plausible reaction mechanism involves oxidative addition of alcohol forming intermediate alkyl platinum(IV) derivative followed by decomposition of it via reductive elimination step under the action of alcohol giving the ether and regenerating catalyst. In the case of ethyl alcohol reaction, β-hydrogen abstraction from the intermediate Pt-ethyl species yields π-ethylene platinum(II) complex. Although it seems that the reaction does not involve the initial breaking of C[sbnd]H bonds of an alcohol, this system can be regarded as a model for studying of some peculiarities of Shilov chemistry, in particular, of isotope scrambling mechanisms in Shilov alkane activation. In contrast to reactions of dimethyl and diethyl ethers formation, tert-butyl ethers formation in CD₃OH/t-BuOH medium is catalyzed by Pt^IV chloro complexes also and is not accompanied by isotope scrambling. These observations argue against intermediacy of alkyl platinum derivatives suggesting that acid-catalyzed mechanism operates in tert-butyl alcohol etherification.

Full text of DOI:10.1016/j.molcata.2016.07.012

Accepted Manuscript
Title: Catalytic etherification of alcohols in Shilov system:
C-O versus C-H bond activation
Author: Oleg V. Khazipov Denys V. Nykytenko Tatyana V.
Krasnyakova Alexander N. Vdovichenko Dario A.Fuentes
Frias Serge A. Mitchenko
PII:
S1381-1169(16)30263-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2016.07.012
MOLCAA 9946
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
30-3-2016
1-7-2016
6-7-2016
Please cite this article as: Oleg V.Khazipov, Denys V.Nykytenko, Tatyana
V.Krasnyakova, Alexander N.Vdovichenko, Dario A.Fuentes Frias, Serge
A.Mitchenko, Catalytic etherification of alcohols in Shilov system: C-O
versus C-H bond activation, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2016.07.012
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Catalytic etherification of alcohols in Shilov system: C-O versus C-H
bond activation
Oleg V. Khazipova, Denys V. Nykytenkob, Tatyana V. Krasnyakovab,c,
Alexander N. Vdovichenkob, Dario A. Fuentes Friasd, Serge A. Mitchenkoa,b,*
a Platov South-Russian State Polytechnic University (NPI), Prosveshcheniya 132, Novocherkassk,
346428 Russia
b L.M. Litvinenko Institute of Physical Organic and Coal Chemistry; 70 R. Luxemburg Str.,
Donetsk, 83114
с Taras Shevchenko Lugansk State University, 2 Oboronnaya Str., Lugansk, 91011
d Universidad de los Andes, Bogota Colombia
ARTICLE INFO
Article history:
This paper is dedicated to Professor Georgiy Shul’pin, one of the most original and creative
thinkers in the field of catalytic C-H functionalization, on the occasion of his 70th anniversary.
*Corresponding author. E-mail address: samit_RPt@mail.ru (S.A. Mitchenko)
Graphical abstract
Highlights



Catalysis by Na2PtCl4 of methanol and ethanol etherification at 70 C was found.
The reactions of CD3OH (C2D5OH) are accompanied by multiple H/D exchange.
The reactions involve intermediate formation of RPtIV (R=Me, Et) complexes.

2
ABSTRACT
A novel catalytic reaction of alcohol etherification in the system ROH - PtCl42- - PtCl62- was
found. Methanol easily transforms into dimethyl ether in the presence of catalytic amounts of PtII
о
chloro complexes at 70 С. Under the same conditions reaction of ethanol affords diethyl ether
(catalytic) and -ethylene PtII complex (stoichiometric). The reactions are accompanied by
multiple H/D exchange, which is indicative of intermediacy of corresponding alkyl platinum
derivatives. The plausible reaction mechanism involves oxidative addition of alcohol forming
intermediate alkyl platinum(IV) derivative followed by decomposition of it via reductive
elimination step under the action of alcohol giving the ether and regenerating catalyst. In the case
of ethyl alcohol reaction, -hydrogen abstraction from the intermediate Pt-ethyl species yields -
ethylene platinum(II) complex. Although it seems that the reaction does not involve the initial
breaking of CH bonds of an alcohol, this system can be regarded as a model for studying of some
peculiarities of Shilov chemistry, in particular, of isotope scrambling mechanisms in Shilov alkane
activation.
In contrast to reactions of dimethyl and diethyl ethers formation, tert-butyl ethers formation
in CD3OH / t-BuOH medium is catalyzed by PtIV chloro complexes also and is not accompanied
by isotope scrambling. These observations argue against intermediacy of alkyl platinum
derivatives suggesting that acid-catalyzed mechanism operates in tert-butyl alcohol etherification.
Keywords: alcohols; etherification; catalysis; Shilov system; isotope scrambling
1. Introduction
Selective alkane catalytic functionalization under mild conditions to a large extent
determines a progress in areas ranging from natural gas processing and bulk organic synthesis to
fine chemicals and pharmaceutical synthesis [1-4]. The first homogeneous system for alkane C-H
bond activation [5] and catalytic oxidation [6] was discovered by Shilov and co-workers. The
Shilov system exploits a mixture of PtII and PtIV chloro complexes in aqueous solution to convert
alkane into mixtures of corresponding alkyl chloride, alcohol and alkene as primary products:
Although Shilov system is still so far away from commercial application it represents one
of very few examples for selective catalytic alkane functionalization. Due to its uniqueness, that
system is still the subject of intensive study by a number of different scientific groups (see, for
2-
2-
example, reviews [2, 4, 7-11]). Earlier [12, 13] the system СН3СН2ОН – PtCl4 - PtCl6 - D2O

3
has been exploited as a model for Shilov alkane C-H bonds activation. It was a priori assumed
2-
[12, 13] that hypothetical complex Pt(CH2-CH2OH)Cl3 was a primary product of ethanol
interaction with PtII formed by electrophilic C-H activation. Subsequent conversion of this species
by -abstraction of OH group gave rise to Zeise’s salt anion; the latter one was actually fixed by
NMR-1Н (Eq. 2).
However, a different explanation of the results obtained in [12, 13] is possible. PtII chloro
complexes easily undergo oxidative addition reactions with alkylating agents such as alkyl iodides
and their derivatives, dimethyl sulfate, oxirane, ethyleneimine in acidic solutions, etc. The reaction
occurs either as SN2 process with PtII chloro complexes acting as metal centered nucleophiles, or
according to three-centered concert oxidative addition mechanism [14]. In the latter case PtII
complex acts simultaneously as nucleophile attacking carbon atom and as electrophile bonding a
leaving group. Methyl and other alkyl derivatives of PtIV chloro complexes were synthesized [15-
18] in such a way. These organoplatinum(IV) compounds are stable towards electrophiles, but
easily decompose via reductive elimination step under the action of external [15] or coordinated
[19] nucleophiles. Another reactivity is demonstrated by organoplatinum(II) complexes. These
species decompose via protonolysis liberating appropriate hydrocarbon even at low temperatures
and undergo H/D exchange reaction with a solvent [20].
It could be assumed, that alcohols, in particular ethanol, would be able to react in the same
way as mentioned above alkylating agents involving initial C-ОH (but not С-Н) bond rupture with
intermediate alkyl PtIV complex formation. Subsequent proton -elimination from PtIV-CH2CH3
(or PtII-CH2CH3) could give rise the Zeise’s salt anion. Herein, we report on a new catalytic
2-
reaction of alcohol etherification in the system ROH-PtCl4 , and the data obtained are in
agreement with the above hypothesis.

4
2. Experimental
2.1. Material and methods
All NMR measurements were performed using Bruker AVANCE-II-400 instrument
operating at 400 (1Н) and 100 (13С) MHz. The chemical shifts are reported relatively to residual
protons of the corresponding deuterosolvents or TMS (HMDS) were used as internal standards.
The IR-spectrum of dimethyl ether was obtained on FTIR Perkin Elmer Spectrum BX
instrument using IR gas cuvette with windows made from KBr.
Commercial alcohol СD3CH2OH (All-Union Association "Isotope") was used without
further purification. The CD3OH and СD3CD2OH alcohols were obtained from commercial
deuterated alcohols СD3OD and СD3CD2OD (Merk). Methyl alcohol was diluted with water Н2О
in proportion 1:3, and after that the alcohol was distilled from the resulted mixture on a water bath.
After triple repetition of this procedure the resultant alcohol CD3OH was purified by distillation.
Ethyl alcohol СD3CD2OH was obtained in a similar way, only that commercial alcohol
СD3CD2OD was diluted not with water, but with dry 1,3-propylene glycol HO-CH2CH2CH2-OH.
The purity of the resultant alcohols was controlled by NMR.
The platinum salts Na2PtCl6, Na2PtCl4 and Ziese’s salt were prepared according to
standard techniques [21].
2.2. Etherification of methanol
Platinum salts Na2PtCl4 (0.09 mmol) and Na2PtCl6 (0.09 mmol) were dissolved in 0.6 ml
of methanol. Reactions were carried out at 70 оC in the sealed thick-walled NMR tubes
(CAUTION: the resultant dimethyl ether is a flammable gas creating significant pressure in the
tube at this temperature). To estimate the yield of dimethyl ether the reaction was carried out with
CH3OH for 8 h. To unseal the tube the reaction mass was frozen. The liberated gas at cautious
warming-up was bubbled through CDCl3 (1 ml) containing the internal weight standard HMDS
1
and the resultant solution was analyzed by H NMR. The sample for FTIR spectroscopy was
prepared by a similar manner, only released gas was gathered in a syringe and after that it was
injected into IR gas cuvette. The volume of the collected gas was approximately fitted to the yield
of dimethyl ether estimated from NMR spectra. Isotope scrambling during CD3OH etherification
was monitored by 1H- and 13C{1H}-NMR.
The NMR spectra parameters for dimethyl ether (CD3OD, , ppm): 1Н (s. 3.32); 13C{1H}
(60.6).
The intense band at 1159 sm-1 characteristic [22] for asymmetric stretching of an ether
C-O bond is observed in the IR spectrum.

5
2.3. Reactions of ethanol
Platinum salts Na2PtCl4 (0.09 mmol) and Na2PtCl6 (0.09 mmol) were dissolved in 0.6 ml of
о
ethanol СD3CD2OH and heated at 70 С for 8 h in the sealed NMR tube. Formation of diethyl
1
ether (NMR spectra in CD3OD, , ppm: H (q., 3.46, 2Н, CH2; t., 1.16, 3Н, СН3); 13C{1H}-NMR
(66.5, CH2; 15.4, СН3)) and -ethylene PtII complex (NMR spectra parameters in CD3OD, , ppm:
1H (s. 4.39 accompanied by platinum satellites J(Pt-H) = 65.7 Hz); 13C{1H}-NMR (68.9
accompanied by platinum satellites J(Pt-C) = 193.9 Hz)) were found.
2.4. tert-Butanol etherification reactions
Platinum salts Na2PtCl4 (0.08 mmol) and Na2PtCl6 (0.07 mmol) or only Na2PtCl6
(0.07 mmol) were dissolved in solution of methanol (CD3OH, 0.125 ml, 3.1 mmol) and tert-
о
butanol (0.5 ml, 5.3 mmol) and the reaction mixture was heated at 70 С in the sealed NMR tube.
1
Kinetics of tert-Bu-O-CH3 accumulation was monitored by H NMR using HMDS as internal
weight standard. Accumulation of 1.63 mmol of methyl-tert-butyl ether (yield ~ 2000 % based on
PtII) and 0.04 mmol of di-tert-butyl ether (yield ~ 50 % based on PtII) were determined during 12 h
of the reaction.
NMR spectra parameters for tert-Bu-O-CH3 (, ppm): 1H (s., 3.18, 3Н, ОСН3; s., 1.18, 9Н,
С(СН3)3); 13C{1H} (27.2 С(СН3)3; 48.5 ОСН3; 73.4, OC(CH3)3).
1
13
NMR spectra parameters for di-tert-butyl ether: H-ЯМР (s., 1.59); C{1H} (34.7, СН3;
76.5, C(CH3)3), coincide with the data cited in [23].
2.5. Decomposition of methyl platinum(IV) complex in methanol solution
Soluble in methanol sodium salt of methyl platinum(IV) complex was prepared by
exchange reaction of Rb2Pt(CH3)Cl5 (synthesized by method [16]) with NaClO4 in aqueous
solution. The precipitate of RbClO4 was filtered off and aqueous solution of Na2Pt(CH3)Cl5 was
lyophilized in vacuum. Decomposition of the complex at heating up to 70 C in methanol solution
was accompanied by formation of dimethyl ether (ca. 70 % yield based on the initial
organoplatinum derivative) and methyl chloride. The reaction was monitored by 1H-NMR.
2.6. Reactions of diethyl ether
Saturated aqueous (D2O) solution (0.7 ml) of diethyl ether (~ 6 %), containing Na2PtCl4
о
(30 mg) and Na2PtCl6 (30 mg) was heated at 70 С in the sealed NMR tube for 5 h. The reactions
were monitored by 1H NMR.

6
2.7. Methanol reduction into methane
Na2PtCl4 (0.052 g, 0.135 mmol) salt was dissolved in CH3OH (1.5 ml, 37 mmol) and
HClO4 (0.1 ml of 5 M aqueous solution, 0.5 mmol) and the reaction mixture was heated at 70 оС in
the sealed thick-walled tube for 2 h. To unseal the tube the reaction mass was frozen. The liberated
1
gas at cautious warming-up was blown through CDCl3 and analyzed by NMR. The H-NMR
spectrum contains signal at 0.2 ppm, corresponding to СН4.
3. Results
3.1. Reactions of methyl alcohol
о
The catalytic conversion of methanol to dimethyl ether (Eq.3) proceeds at 70 С in the
system МеОН - PtCl42- - PtCl62- (admixtures of PtCl62- were used to prevent PtII disproportionation
[12] and reduction of PtII into Pt0). In the absence of PtII, but in the presence of only PtIV chloro
complexes or platinum black, no conversion of methanol in dimethyl ether was observed.
1
13
The product of the reaction was identified by means of H and C{1H} NMR as well as
FTIR spectroscopy. The methanol conversion of ~ 13 % was achieved during 8 h at Na2PtCl4
initial concentration 0.15 M, and this corresponds to accomplishment of ~ 10 TON based on PtII.
Platinum complexes were gradually reduced under reaction conditions and after 8-10 h they were
precipitated as a platinum black. Besides of dimethyl ether a small amount of methane was formed
when the reaction was carried out in acidic medium.
Reaction of the alcohol with deuterated methyl group CD3OH is accompanied by H/D
exchange: the forming dimethyl ether contains isotopologues CHiD(3-i)OCD3 (i = 1-3) (Fig. 1, 2).
Distribution of the isotopologues does not change in time (Table) indicating multiple character of
the H/D exchange, i.е. isotope scrambling of several atoms simultaneously occurs in the every act
of the substrate interaction with platinum complex.
1
13
The H and C{1H} NMR spectra (Fig. 1, 2) allow us to estimate the relative content of
CD3 and CHiD(3-i) (i = 1-3) groups in the resultant ether. The 13C nuclei of CD3 groups of the
product and of the reactant methanol are in very similar local surroundings and therefore should
13
have very close relaxation times. So, the integration ratio of the C NMR signals for CD3 groups
of the resultant dimethyl ether against the reactant CD3OH should be pretty close to concentration
ratio of these groups.

7
The 13C{1H} NMR signals of CD3 (septet), CD2H (quintet), and CDH2 (triplet) groups of
the resultant ether are partly overlapped (Fig. 2). This makes it difficult to integrate the whole
septet of signals for the CD3 group separately. Therefore we used for integration four upfield
signals of this septet, which do not overlap with relatively intense triplet of the signals for CDH2
group, and neglected the contribution to the resultant integral value of low-intensity signals for
13
CHD2 groups (Fig. 2). The integration ratio of these C{1H} NMR signals for CD3 group of the
resultant dimethyl ether against corresponding four upfield signals of septet for CD3 group of the
reactant CD3OH averages 1:36. The relative concentration of CHiD(3-i) (i = 1-3) groups which are
part of the formed ether can be estimated from integration ratio of theirs against methanol OH-
groups in the 1H-NMR spectrum of the same sample, and this estimation gives value ~ 1:33, which
is pretty close to the mentioned above amount. So, the resultant ether contains CD3 and CHiD(3-i) (i
= 1-3) groups in approximately equal amounts. It agrees with the assumption that the isotopic
composition of the reaction product is CHiD(3-i)OCD3 (i = 1-3), i.e. only one side of the dimethyl
ether product reflects H/D scrambling.
3.2. Reactions of ethanol and diethyl ether
Under the same conditions reaction of ethanol produces diethyl ether and -ethylene PtII
complex (Eq. 4). The latter species are found to be unreactive towards ethanol: the etherification
reaction does not occur with appreciable rate if the Zeise’s salt is used instead of Na2PtCl4. This
result may be a consequence of lower reactivity of the Zeise’s salt anion towards oxidative
addition in comparison with tetrachloroplatinate(II) [24].
The etherification of the deuterated ethanol CD3CD2OH is accompanied by multiple H/D
exchange, but the isotope scrambling occurs predominantly at -position of ethanol, i.e. the
resultant diethyl ether contains isotopologues of a composition CD3CHiD(2-i)OCD2CD3 (i = 1-2)
(Fig. 3). The 1H-NMR spectrum of PtII -ethylene complex formed in the reaction of CD3CD2OH
contains signals corresponding to the two forms (Fig. 4) that can be attributed to the isotopologues
PtII(2-CH2=CD2) and PtII(2-CHD=CD2). It is noteworthy that formation of purely isotopologue
PtII(2-CH2=CD2) was observed in the reaction of ethanol CD3CH2OH under the same conditions.
This is the expected result if mostly methylene group of ethanol is involved in the isotope
exchange in contrast to methyl group.

8
Nevertheless weak isotope exchange in methyl group accompanying etherification of
ethanol CD3CH2OH became evident when the reaction was carried out at 100 C. The methyl
13
group region of the C{1H}-NMR spectrum of ethanol-d3 contains in addition to septet of CD3
also quintet and singlet corresponding to methyl group with residual protons CD2H and CH3
respectively, but does not contain triplet expected for CDH2 group (Fig. 5). However triplet for
isotopologue CH2D became discernible in the 13C{1H}-NMR spectrum of resultant diethyl ether in
contrast to the initial ethanol. Besides of this the relative content of CH3 isotopologue in the
resultant ether is increased in comparison with that in the initial ethanol. Indeed, intensity of CH3
singlet against CD3 septet in the 13C{1H}-NMR spectrum of the resultant ether is obviously greater
than relative intensity of CH3 signal against CD3 septet for the initial ethanol (Fig. 5).
Catalysis of the reverse reaction, i.e. an ether hydrolysis, must occur under the same
conditions. We convinced of it in the example of diethyl ether transformations in aqueous
solutions of PtII. The reverse reaction of ether hydrolysis as well as direct reaction of ethanol
dehydrative etherification is accompanied by -ethylene PtII complex formation. Formation of
these products from dietyl ether in aqueous solutions of K2PtCl4 at 90 oС was earlier reported [25].
But the authors [25] were of opinion that these diethyl ether transformations begin with primary
activation of methyl С-Н bonds of the substrate to yield intermediate Pt-CH2CH2OCH2CH3
derivative and subsequent -elimination of alkoxy group from the last one leads to formation of
alcohol and Zeise’s salt.
It is noteworthy that principal products of the reaction of ethanol in the presence of PtII
chloro complexes are -ethylene complex and diethyl ether. Subsequent reactions of the latter
renew the alcohol and yield -ethylene complex. So, the final product of ethanol reaction with PtII
chloro complexes is -ethylene complex, which was earlier found out [26].
3.3. Reactions in methyl and tert-butyl alcohols mixture
Methyl-tert-butyl ether is the major product when the reaction is carried out under the
same conditions but in the methanol/tert-butanol solution (molar ratio ~ 3:5). The typical kinetics
for methyl-tert-butyl ether accumulation is depicted in Fig. 6. It is noteworthy that platinum
complexes are more stable with respect to precipitation of platinum black in the methanol/tert-
butanol solution than in neat methanol. The catalytic system remains still active after 10 h of the
reaction in the alcohols mixture as opposed to reaction in neat methanol where catalytic activity
was lost because of complete reduction of platinum complexes. The both symmetric (dimethyl and
di-tert-butyl) ethers are also accumulated in trace amounts (Fig. 7, 8).

9
There are two features that distinguish tert-butanol reactions from the reactions (3) and
(4). Isotope scrambling in CD3OH / t-BuOH medium accompanies formation of only dimethyl
ether: isotope content of tert-butyl ethers remains the same as in the starting alcohols (Fig. 7). In
contrast to the reactions of dimethyl or diethyl ether formation, which are catalyzed merely by PtII,
the reactions of tert-butyl ethers formation are catalyzed by PtIV chloro complexes also. It is worth
mentioning that dimethyl ether was not formed in the methanol/tert-butanol solution under
catalysis by PtIV chloro complexes only.
4. Discussion
The C-O coupling is a fundamentally important transformation in organic chemistry that
is being widely used in both industrial and academic laboratory scales for synthesis of
pharmaceuticals [27], fragrance precursors [28] or oxygenates in reformulated gasoline [29].
Dehydrative alcohol etherification is one of the commonly used methods for C-O bond formation.
Although the traditional Williamson ether synthesis has long been used for ethers preparation, this
multi-step procedure presents major problems because of formation of copious amount of waste.
These drawbacks have induced extensive search for novel catalytic systems for etherification of
alcohols. A great number of efficient and broad-scoped catalytic systems for etherification of
alcohols under mild conditions have been recently reported (see, for example, [30-41]) including
those which employ transition metal catalysts [34-41].
Although these catalytic systems based on transition metal catalysts are stable enough and
demonstrate high TON and TOF numbers, molecular mechanisms of catalysis still remain
speculative. It is possible to distinguish two groups of catalytic mechanisms in the literature. These
are acid catalysis and a combination of organometallic and acid catalysis. The first one is believed
to operate, for example, in the catalytic systems based on AuIII [35] and AuI [36], where the gold
complexes act as Lewis acids facilitating generation of the intermediate carbocation from benzyl
alcohol or tertiary alcohol. Therefore, the tertiary alcohols or -activated alcohols (such as
benzylic allylic or propargylic) represent borderline point regarding the capacity of these catalytic
systems to generate carbocation as the electrophilic partner needed to accomplish the etherification
reaction [35].
The second group of catalytic reactions relies on the initial O-H bond activation via
oxidative addition of RCH2OH to organometallic derivatives Mn to form intermediate
H-Mn+2-OCH2R cationic complexes. Cationic H-Mn+2 species acts as Brønsted acid, and activates
the second molecule of an alcohol by electrophilic attack to the oxygen atom with further coupling
of the alkyl group to the alkoxide ligand and liberation of water molecule. Such a mechanism

10
proposed for alcohol etherification catalyzed by cationic complexes of IrIII [37] and RuII [38] is
free from the mentioned above limitations, but obviously would have another. It can be anticipated
that tertiary alcohols could not be involved in etherification reactions because of steric hindrances
either for oxidative addition or for electrophilic attack to the oxygen atom.
Catalytic etherification of alcohols in Shilov system is free from the both of these
restrictions. Platinum chloro complexes are active in etherification of primary as well as tertiary
aliphatic alcohols owing to different mechanisms of these reactions.
4.1. Possible mechanisms for catalytic etherification in Shilov system
The data obtained can be explained assuming of two different mechanisms of catalysis
operating in the observed etherification reactions. They are metal complex catalysis in the cases of
methanol and ethanol etherification reactions and acid catalysis in the case of tert-butyl alcohol
reactions.
We believe that an alcohol oxidative addition to PtII leads to intermediate alkyl PtIV
derivative formation in the case of methanol and ethanol. This is the reverse reaction of hydrolysis
of an alkyl PtIV derivatives giving alcohol, the last step of the Shilov mechanism. Hydroxide is
known to be a poor leaving group. Therefore to involve alcohols into such a transformation they
first need to be converted into species more susceptible to nucleophilic cleavage. Usually it is
achieved in acidic medium: simple protonation of an alcohol OH-group converts it in a good
leaving group. Perhaps, PtII chloro complexes act as a Lewis acid bonding hydroxide as a leaving
group. It could proceed on the same metal center according to concert three-centered oxidative
2-
addition mechanism (Eq. 5) or two different PtII chloro complexes, “nucleophilic” PtCl4 and
-
“electrophilic” Pt(ROH)Cl3 , are involved into the transformation (Eq. 6). It is noteworthy that
activation of C-O bond of an alcohol via oxidative addition to a transition metal complex is not
unprecedented. Such a mechanism, for example, was recently proposed [42] for nickel-catalyzed
cross-coupling reaction of 2-naphthol with aryl Grignard reagents.

11
Decomposition of the resultant alkyl platinum(IV) derivative via reductive elimination
step under the action of alcohol as a nucleophilic reagent yields the final product and regenerates
the catalyst.
The intermediacy of PtIV alkyl derivatives in the reactions of methanol (ethanol) with
2-
PtCl4 is confirmed by the following experimental observations. Synthesized by method [16]
methyl PtIV complex decomposes at heating in methanol solution with dimethyl ether formation.
The reaction obviously occurs as reductive elimination under the action of methanol as
nucleophilic reagent (Eq. 7).
Alkyl PtIV complexes are known [15] to be complementary reduced into corresponding
organoplatinum(II) derivatives (Eq. 8).
Although the equilibrium (8) is shifted to the left, it could be expected of corresponding alkyl PtII
2-
2-
complexes generation in the system ROH (R = CH3, CH3CH2) – PtCl4 – PtCl6 . The following
effects could evince the intermediate formation of the latter species: i) protonolysis of methyl
platinum(II) derivatives would lead to methane liberation [20] and ii) alkyl PtII complexes
2-
generating in the system CD3OH (CD3CD2OH) – PtCl42- – PtCl6 , are known to be involved [20]
in H/D exchange with labile protons (deuterons) of a medium, and finally this would result in
isotope scrambling in the products of reactions (3) and (4).
Both of these effects were actually observed. If the reaction (3) was carried out in acidic
medium methane was liberated in addition to the ether. Dimethyl and diethyl ethers formed in the
reactions of deuterated alcohols CD3OH and C2D5OH contained isotopologues CHiD(3-i)OCD3 and
CD3CHiD(2-i)OCD2CD3. It is essential that ethyl alcohol etherification reaction is accompanied by
isotope scrambling mainly at -position. It agrees with intermediacy of ethyl platinum derivative
(Eq. 9), but not of hypothetical complex PtII(CH2-CH2OH) supposed in [12, 13]. The latter
confirms the initial activation of C-O bond (but not of C-H bonds) of an alcohol (step 1) in the
systems under consideration. Decomposition of the primary formed ethyl platinum(IV) derivative
by reductive elimination (step 2) leads to diethyl ether. Zeise’s salt anion formation apparently

12
occurs as a result of decomposition at this temperature of the intermediate ethyl PtIV complex1
(or rather of ethyl PtII derivative formed by equilibrium reaction 8, step 3) through -elimination
(step 5). Stabilization of the resultant ethylene by -coordinaton to PtII complex facilitates progress
1
of the reaction. Monitoring (at least by H-NMR) of intermediate formation of an alkyl PtIV
complex would be the direct evidence for stepwise mechanism (9), but it is hardly possible:
accumulation of these species in detectable amounts is unfeasible at high temperature used.
Dissimilar etherification mechanism evidently operates in the system CD3OH – tert-BuOH
– PtII and/or PtIV. Firstly, the tert-butyl ethers formation is catalyzed not only by PtII but by PtIV
chloro complexes also. Secondly, isotope scrambling is not observed for the resultant tert-butyl
ethers. Both these observations argue against the mechanism, which involves intermediate
formation of alkyl platinum derivatives. One could assume that acid catalysis mechanism operates
in this case as well as in mentioned above catalytic system based on AuIII [35].
The proposed mechanism (Eq. 9) for the observed catalytic etherification of ethanol allows
a different interpretation of some results of earlier works [12, 13], in which the reaction of PtII
chloro complexes with ethyl alcohol was believed to proceed through initial C-H bond activation.
It could be supposed that ethyl PtIV complex is the primary product of alcohol interaction with PtII
under conditions used in [12, 13]. This species in aqueous solutions used in [12, 13] clearly
undergo fast hydrolysis regenerating ethanol or -elimination yielding Zeise’s salt anion. Ethylene
glycol, which is one of the products of ethanol and diethyl ether oxidation in the Shilov system
[12, 13, 25], could arise from the intermediate PtII -ethylene complex through the sequence of
1 The fraction of -elimination in ethyl platinum(IV) complex decomposition does not exceed 1 %
at ambient temperature in aqueous solutions [43], but high activation barrier is typical for this
reaction [44].

13
transformations: oxidation of Zeise’s salt anion by PtIV [15] followed by fast hydrolysis of the
resultant hydroxyethyl PtIV intermediate (Eq. 10-11).
It should be noted, however, the present work was done at essentially lower temperature
than previous works [12-13, 25] (70 C vs. 90-120 °C). Besides of temperature, the main
distinction in the reaction conditions in the case under consideration and in the works [12, 13] is an
alcohol concentration: we use alcohols as a medium, while in the works [12-13, 25] reactions were
carried out in aqueous solutions. Both of these factors, i.e. different media and different
temperatures, could be account for different mechanisms of ethanol interaction with PtII chloro
complexes in the system under consideration and in the previous works. But irrespective of the
mechanism of ethanol etherification, the earlier results [12-13, 25] may need re-interpretation in
view of the possibility of reactions (4) under conditions used in those studies.
4.2. Isotope scrambling reactions
Alkanes activation in Shilov system is accompanied by H/D exchange between H-atoms
of a substrate and a deuterated solvent. Actually, Shilov system was found out owing to
observation of such an exchange [5] of H-atoms of hydrocarbons with movable deuterium atoms
of a medium. Two mechanisms were proposed for explanation of the observed isotope scrambling
reactions. The first one, “alkyl-carbene” mechanism, assumes H/D exchange occurring in
reversible transformations of alkyl platinum(II) complex2 into carbene one through -elimination
(Eq. 12) or deprotonation under the action of a base (Eq. 13) [20].
2 We do not consider the possibility of H/D exchange in alkyl platinum(IV) complexes, because it
is known [15, 20] that such a reaction is not typical for organoplatinum(IV) derivatives.

14
The other mechanism, “alkyl-alkane” one, supposes that exchange occurs in mutual
reversible conversions of alkyl PtII derivative into -adduct of an alkane and PtII [20, 45]:
2-
We found that methane in the system CD3OH – PtCl42—PtCl6 is formed only in the
presence of an acid and is not liberated in detectable amounts in neutral solutions. But nevertheless
etherification reaction is accompanied by H/D exchange in neutral solutions as well: isotopologues
CHiD(3-i)OCD3 (i = 1-3) are present in the resultant dimethyl ether. Reasoning from these, “alkyl-
carbene” mechanism for H/D exchange seems to be more probable.
If it is so, the observed regiospecific isotope scrambling occurring mainly in the
methylene positions of diethyl ether argues for reversibility of -elimination from intermediate
ethyl platinum derivative in contrast to -elimination. Indeed, i) reversible -elimination should
lead to extensive isotope scrambling in methyl position of diethyl ether as well, and ii)
transformation of platinum(II) -ethylene complex backwards into ethyl platinum derivative under
these conditions was not observed. The ascending shape of dimethyl ether isotopomers
CHiD(3-i)OCD3 distribution, d3 > d2 > d1 (Table), can be explained by more fast reaction (12) (or
13) in comparison with complementary oxidation of methyl platinum(II) into methyl platinum(IV)
derivative (Eq. 8).
One more feature of H/D exchange accompanying reactions of CD3CD2OH alcohol is
noteworthy, namely formation of isotopologues of -ethylene complex. The fact of their formation
means that -elimination from the intermediate ethyl platinum derivative occurs faster than -
elimination.
5. Conclusions
We have demonstrated the facile catalytic etherification of alcohols in Shilov system.
Reactions of methanol (CD3OH) and ethanol (CD3CD2OH) are catalyzed by PtII (PtIV being
inactive) and are accompanied by multiple H/D exchange, which is indicative of intermediacy of
corresponding alkyl platinum derivatives. The data obtained can be rationalized assuming that
reaction involves an alcohol oxidative addition forming alkyl platinum(IV) derivative followed by
decomposition of the latter via reductive elimination step under the action of alcohol as a
nucleophilic reagent.

15
Although the reaction does not probably involve the initial breaking of CH bonds of an
alcohol, this system can be regarded as a model for studying of some peculiarities of Shilov
chemistry, for example, of isotope scrambling mechanisms in Shilov alkane activation.
In contrast to formation of dimethyl and diethyl ethers, tert-butyl ethers formation in
CD3OH / t-BuOH medium is catalyzed by platinum(IV) chloro complexes also and is not
accompanied by isotope scrambling. These observations argue against intermediacy of alkyl
platinum derivatives suggesting that acid-catalyzed mechanism operates in tert-butyl alcohol
etherification.
Acknowledgments
This work was financially supported by Russian Science Foundation through grant No.
14-23-00078. We are very grateful to Prof. Jay A. Labinger (California Institute of Technology,
U.S.A.) for the helpful discussion and essential remarks.
References:
[1] A.E. Shilov, G.B. Shul'pin. Activation and catalytic reactions of saturated hydrocarbons in the
presence of metal complexes. Kluver: Boston. (2000).
[2] J.A. Labinger, J.E. Bercaw. Nature. 417 (2002) 507.
[3] R.H. Crabtree. J. Chem. Soc., Dalton Trans. (2001) 2437.
[4] J.A. Labinger. J. Molec. Catalysis A: Chemical. 20 (2004) 27.
[5] N.F. Goldshleger, M.B. Tyabin, A.E. Shilov, A.A. Shteinman. Russ. J. Phys. Chem. 43 (1969)
1222.
[6] N.F. Goldshleger, V.V. Eskova, A.E. Shilov, A.A. Shteinman. Russ. J. Phys. Chem. 46 (1972)
785.
[7] A. Sen. Acc. Chem. Res. 31 (1998) 550.
[8] E.S. Rudakov, G.B. Shul’pin. J. Organomet. Chem. 793 (2015) 4.
[9] J.A. Labinger, J.E. Bercaw. J. Organomet. Chem. 793 (2015) 47.
[10] A.F. Shestakov, N.F. Goldshleger. J. Organomet. Chem. 793 (2015) 17.

16
[11] A.F. Shteinman. J. Organomet. Chem. 793 (2015) 34.
[12] A.C. Hutson, M. Lin, N. Basickes, A. Sen. J. Organomet. Chem. 504 (1995) 69.
[13] J.A. Labinger, A.M. Herring, D.K. Lyon, G.A. Luinstra, J.E. Bercaw, I.T. Horvath, K. Eller.
Organometallics. 12 (1993) 895.
[14] S.L. Litvinenko, V.V. Zamashchikov, V.I. Shologon, Z.Z. Rozhkova, Metallorg. Khim.
(Russian: Organometal. Chem.) 2 (1989) 553.
[15] G.A. Luinstra, L. Wang, S.S. Stahl, J.A. Labinger, J.E. Bercaw, J. Organometal. Chem., 504
(1995) 75.
[16] V.V. Zamashchikov, E.S. Rudakov, V.S. Garkusha-Bozhko, S.A. Mitchenko, S.L.
Litvinenko, V.S. Chuprina, Koord. Khim. (Russian: Coordin. Chem.) 12 (1986) 822.
[17] S.A. Mitchenko, V.V. Zamashchikov, S.M. Slinkin, V.N. Voshchula, Zh. Obsh. Khim.
(Russian: J. Gen. Chem.) 61 (1991) 2127.
[18] V.I. Shologon, S.L. Litvinenko, V.V. Zamashchikov, Metallorg. Khim. (Russian:
Organometal. Chem.) 4 (1991) 471.
[19] S.A. Mitchenko, E.V. Khomutov, A.N. Vdovichenko, I.V. Zhikharev, A.F. Popov, I.P.
Beletskaya. Inorg. Chim. Acta. 320 (2001) 38.
[20] S.S. Stahl; J.A. Labinger; J.E. Bercaw. J. Am. Chem. Soc. 118 (1996) 5961.
[21] I.N. Chernyaev (Ed.), Sintez Kompleksnykh Soedineniy Metallov Platinovoy Gruppy
(Synthesis of Platinum Metal Complex Compounds), Handbook, Nauka, Moscow, 1964.
[22] L.J. Bellamy. The Infrared Spectra of Complex Molecules, London: Champman & Hall,
(1975).
[23] R. West, D.L. Powell, M.K.T. Lee, L.S. Whatley. J. Am. Chem. Soc. 86 (1964) 3227.
[24] V.V. Zamashchikov, S.L. Litvinenko, O.N. Uzhik, V.F. Galat. Koord. Khim. (Russian:
Coordin. Chem.) 12 (1986) 972.
[25] A. Sen, M. Lin, Kao L.-Ch., A.C. Hutson. J. Am. Chem. Soc., 114 (1992) 6385.
[26] R.F. Hartley. Inorg. Chim. Acta. 5 (1971) 197.
[27] J. Blacker, M.T. Williams. Pharmaceutical process development: current chemical and
engineering challenges. Royal Soc. of Chem. 2011.
[28] W.H. Miles, K.B. Connell. J. Chem. Educ. 83 (2006) 285.
[29] M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi, C. Della Pina. Angew. Chem. Int. Ed. 46
(2007) 4434
[30] H.A. Kalviri, C.F. Petten, F.M. Kerton. Chem. Commun. (2009) 5171.
[31] H.A. Kalviri, F.M. Kerton. Adv. Synth. Catal. 353 (2011) 3178.
[32] M. Roze, V. Kampars, K. Teivena, R. Kampare, E. Liepins. Material Science and Applied
Chem. 28 (2013) 67. DOI: 10.7250/msac.2013.011.

17
[33] C.F. Petten, H.A. Kalviri, F.M. Kerton. Sustain. Chem. Process. (2015) DOI:
10.1186/s40508-015-0043-4.
[34] Yi Lin, Ruimao Hua, Hang-Bin Sun, Xianquing Qiu. Organometallics, 24 (2005) 2819.
[35] A.B. Cuenca, G. Mancha, G. Asensio, M. Medio-Simon. Chem. Eur. J. 14 (2008) 1518.
[36] R.M.P. Veenboer, S.P. Nolan. Green Chem. 17 (2015) 3819.
[37] A. Prades, R. Corberan, M. Poyatos, E. Peris. Chem. Eur. J. 14 (2008) 11474.
[38] J. Kim, D.-H. Lee, N. Kalutharage, Ch. S. Yi. ACS Catal. 4 (2014) 3881.
[39] M. Murai, K. Origuchi, K. Takai. Org. Lett. 16 (2014) 3828.
[40] E. Emer, R. Sinisi, M.G. Capdevila, D. Petruzziello, F. De Vincentiis, P.G. Cozzi. Eur. J. Org.
Chem. 2011 (2011) 647
[41] Y. Miyake, S. Uemura, Y. Nishibayashi. ChemCatChem. 1 (2009) 342.
[42] D.-G. Yu, B.-J. Li, S.-F. Zheng, B.-T. Guan, B.-Q. Wang, Z.-J. Shi. Angew. Chem. Int. Ed.
49 (2010) 4566.
[43] V.V. Zamashchikov, Е.S. Rudakov, S.A. Mitchenko, A.N. Kitaigorodskiy, G.V. Nizova,
G.B. Shul’pin. Russ. Chem. Bull. (1986) 192.
[44] H.E. Bryndza. J. Chem. Soc. Chem. Commun. (1985) 1696.
[45] E.S. Rudakov, V.P. Tretyakov, S.A. Mitchenko, A.V. Bogdanov. Dokl. AN SSSR (Russian:
Proceedings of Acad. Sci. of the U.S.S.R.) 259 (1981) 899.

18
1
Fig. 1. H-NMR spectrum of dimethyl ether isotopologues observed under the following reaction
conditions: Na2PtCl4 (0.09 mmol), Na2PtCl6 (0.09 mmol), CD3OH (0.6 ml), 70 C, 20 min.
Fig. 2. 13C{1H}-NMR spectrum of the reaction (3) mixture observed under the following reaction
conditions: Na2PtCl4 (0.09 mmol), Na2PtCl6 (0.09 mmol), CD3OH (0.6 ml), 70 C, 490 min.

19
Fig. 3. 13C{1H}-NMR spectrum of the reaction (4) mixture observed under the following reaction
conditions: Na2PtCl4 (0.09 mmol), Na2PtCl6 (0.09 mmol), CD3CD2OH (0.6 ml), 70 C, 180 min.
Fig. 4. 1H-NMR spectrum of the Zeise’s salt observed under the following reaction conditions:
Na2PtCl4 (0.09 mmol), Na2PtCl6 (0.09 mmol), CD3CD2OH (0.6 ml), 70 C, 180 min.

20
Fig. 5. Methyl group region in the 13C{1H}-NMR spectrum of the reaction (4) mixture
observed under the following reaction conditions: Na2PtCl4 (0.09 mmol), Na2PtCl6 (0.09 mmol),
CD3CH2OH (0.6 ml), 100 C, 60 min.

21
Fig. 6. Typical kinetics for methyl-tert-butyl ether accumulation under the following
reaction conditions: Na2PtCl4 (0.08 mmol), Na2PtCl6 (0.07 mmol), CD3OH (0.125 ml), tert-BuOH
(0.5 ml), 70 C.

22
1
Fig. 7. H-NMR spectrum of the methanol and tert-butanol reaction mixture observed under the
following reaction conditions: Na2PtCl4 (0.08 mmol), Na2PtCl6 (0.07 mmol), CD3OH (0.125 ml),
tert-BuOH (0.5 ml), 70 C, 600 min.

23
Fig. 8. 13C{1H}-NMR spectrum of the methanol and tert-butanol reaction mixture observed under
the following reaction conditions: Na2PtCl4 (0.08 mmol), Na2PtCl6 (0.07 mmol), CD3OH (0.125
ml), tert-BuOH (0.5 ml), 70 C, 600 min.

24
Table. Distribution of dimethyl ether isotopologues CHiD(3-i)OCD3 (i = 1-3) obtained under the
following reaction conditions: Na2PtCl4 (0.09 mmol), Na2PtCl6 (0.09 mmol), CD3OH (0.6 ml),
70 C.
[CHiD(3-i )OCD3 ]
i3
di 
[CHiD(3-i )OCD3 ]
t, min

i1
i = 3
0.5
0.6
0.7
0.6
0.5
i = 2
0.3
0.2
0.2
0.2
0.3
i = 1
0.2
0.2
0.1
0.2
0.2
20
30
40
50
490
Mean
value
0.58
0.24
0.18
A.E. Shilov, G.B. Shul'pin. Activation and catalytic reactions of saturated hydrocarbons in the presence of
J.A. Labinger, J.E. Bercaw. Nature. 2002. V.417. P. 507-514.
metal complexes. Kluver: Boston. 2000.
R.H.Crabtree //
J. Chem. Soc., Dalton Trans. 2001. P. 2437-2450.
J.A.Labinger // J. Molec. Catalysis A: Chemical. 2004. V. 220. P. 27-35.
N.F. Goldshleger, M.B. Tyabin, A.E. Shilov, A.A. Shteinman. Russ. J. Phys. Chem.
1969, 43, 1222.
N.F. Goldshleger, V.V. Eskova, A.E. Shilov, A.A. Shteinman. Russ. J. Phys. Chem.
1972, 46, 785.
A. Sen. Acc. Chem
E.S. Ruda ov, G.B. Shul’pin. J. Organomet. Chem
J.A. Labinger, J.E. Bercaw. J. Organomet. Chem 2015. V.
A.F. Shesta ov, .F. oldshleger. J. Organomet. Chem 2015. V. 793. P. 17-33.
A.F. Shteinman. J. Organomet. Chem 2015. V. 793 P. 34-40.
A.C. Hutson, M. Lin, N. Basickes, A. Sen. J. Organomet. Chem
Labinger J.A., Herring A.M. Lyon D.K., Luinstra G.A., Bercaw J.E., Horvath I.T., Eller K. Organometallics.
S.L. Litvinenko, V.V. Zamashi ov, .I. Shologon Z.Z. Rozh ova, Russian: Organometall. Chem.) (1989) 553.
G.A. Luinstra, L. Wang, S.S. Stahl, J.A. Labinger, J.E. Bercaw, J. Organometal. Chem., 14 (1995) 75.
V.V. Zamashik v, E.S. Rudakov, V.S. Gar usha-Bozhko, S.A Mitchen o, S.L. Litvinen o, V.S. Chuprina, Koord. Khim
S.A. itchen o, V.V. Zamashikov, S.M. Sli in, .N. Voshula, Z. Obsh. Khim (Russian: J. Gen. Chem.) 61 (1991) 2127.
V.I. Shologon, S.L. itvinen o, V.V. Zamashi ov (Russian: Organometall. Chem.) (1991) 471.
Mitchen S.A., Khomutov E.V., dovichen .N.,.Zhikharev I.V, Popov A.F., Belets ay I.P. Inorganica Chimica Acta, 2001, V. 320,
S.S. Stahl; J.A Labinger; J.E. Bercaw. J. Am Chem Soc. 11 (1996) 5961.
Sintez Kompleksnykh Soedineniy Metallov latinovoy Gruppy (Synthesi of Platinum Metal Complex Compounds), Handboo
L.J. The of London: Champman Hall, (1975).
R. West, D.L. Powell, M.K.T. Lee, L.S. Whatley J. Am
V.F. Galat, Koord. Khim
Chem Soc., 11 (1992) 6385.
. Res. 1998. V. 31. P. 550-557.
k
.
2015. V. 793. P. 4-16.
93. P. 47-53.
.
7
k
N
G
.
.
.
.
1995. V. 504. P. 69-74
,
– 1993. – V.12. N o.3. – P.895-905.
k
V
,
k
.
.
(
2
o
k
.
k
k
. (Russian: Coordin. Chem.) 12 (1986) 822.
M
k
n
k
V
.
L
k
k
,
.
.
4
k
o
V
ko
A
k
a
N o.1-2, Р. 38-46.
.
.
.
8
P
s
kEditor I.N. Chernyaev, Moscow, Nauka, 1964, p. 239.
.
,
&
.
.
Chem
.
Soc. 1964. V. 86. No. 16. P. 3227.
(Russian: Coordin. Chem.) 12 (1986) 972.
V.V. Zamashchikov
A. Sen, M. Lin, Kao L.- Ch., A.C. Hutson.
R.F. Hartley Inorg. Chim Acta
27 J. Blac er, M.T. illiams. Pharmaceutical process development: current chemical and engineering challenges. Royal Soc. of Chem
28 W.H. Miles, K.B. Connell. J. Chem Educ. 83 (2006) 85.
29 M. Pagliaro, R. Ciriminna, H. imura, M. Rossi, C. Della Pina. Angew. Chem
H.A. Kalviri, C.F. Petten, F.M. Kerton. Chem Com un. (2009) 5171
31 H.A. Kalviri, F.M. Kerton. Adv. Synth. Catal 353 (2011) 3178.
32 M. Roze, V. Kampars, K. Teivena, R. Kampare, E. Liepins. Material Science and Applied Chem
33 C.F. Petten, H.A. Kalviri F.M. Kerton. Sustain. Chem Process. (2015) DOI: 10.1186/s40508-015-0043-4.
Yi Lin, Ruimao Hua, Hang-Bi Sun, Xianquing Qiu. Organometallics, 24 (2005) 2819
35 A.B. Cuenca, G. Mancha, G. Asensio, M. Medio-Simon. Chem Eur. J. (2008) 1518.
36 R.M.P. Veenboer, S.P. Nolan. Green Chem 17 (2015) 3819.
37 A. Prades, R. Corberan, M. Poyatos, E. Peris. Chem Eur. J. 14 (2008)
38 J. Kim D.-H. Lee, N. Kalutharage, Ch. S. Yi. CS Catal. (2014) 3881.
39 M. Murai, K. Origuchi, K. Ta ai. Org. Lett. (2014) 3828.
40 E. Emer, R. Sinisi, M.G. Capdevila, D. Petruzziello, F. De Vincentiis, P.G. Cozzi. Eur. J. Org. Chem
41 Y. Miyake, S. Uemura, Y. Nishibayashi. ChemCatChem (2009) 342.
uan, B.-Q. Wang, Z.-J. Shi. Angew. Chem
o, A.N. itaigorod iy G.V. Nizova, G.B. Shul’pin. Russ. Chem
un. (1985) 1696.
,
S.L. Litvinen
ko, O.N
.
Uzh
i
k
,
.
J
.
Am
.
.
4
.
.
5 (1971) 197.
k
W
. 2011.
.
2
K
. Int. Ed. 46 (2007) 4434
.
m
.
.
.
28 (2013) 67. DOI:
1
0.7250/msac.2013.011.
,
.
n
.
.
14
.
.
11474.
,
A
4
k
16
.
2011 (2011) 647
.
1
42 D.-G. Yu, B.-J.
V.V. Zamashchikov
H.E. Bryndza J. Chem
E.S. Ruda ov, V.P. Tretyakov
L
i, S.-F. Zheng
,
B.-T.
G
m
. Int. Ed. 49 (2010) 4566.
,
Е.S. Ruda kov, S.A. Mitchen
k
K
s
k
,
.
Bull. 1986. 192.
.
Soc. Chem. Com
k
,
S.A. Mitchenko, A.V. Bogdanov, Do
k
l. AN SSSR (Russian
:
Proceedings of Acad. Sci. of
t
he U.S.S.R.) 259 (1981)
8
99.