Reaction of organoelement hydrides R3EH (E = Si, Ge) with metal tert-butylate (M = Al, Ti)-tert-butyl hydroperoxide oxidative systems

Article abstract of DOI:10.1007/s11176-005-0375-y

Trialkyl(aryl)silanes and -germanes effectively react with metal (Al, Ti) tert-butylate-tert-butyl-hydroperoxide under mild conditions (room temperature, benzene or tetrachloromethane) mainly by the element-hydrogen bond. The character of the products depends on the nature of the element, the structure of the radical bound to it, and the solvent. The process is radical in nature. It includes the stages of formation of element-centered radicals and their reaction with the oxygen generated by the system. The intermediate organometallic peroxides can also acts as oxidants for the element (Si, Ge)-hydrogen bonds. 2005 Pleiades Publishing, Inc.

Full text of DOI:10.1007/s11176-005-0375-y

Russian Journal of General Chemistry, Vol. 75, No. 7, 2005, pp. 1098 1107. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 7, 2005,
pp. 1161 1170.
Original Russian Text Copyright
2005 by Stepovik, Gulenova, Martynova, Skvortsov, Cherkasov.
Reaction of Organoelement Hydrides R3EH (E = Si, Ge)
with Metal tert-Butylate (M = Al, Ti) tert-Butyl
Hydroperoxide Oxidative Systems
L. P. Stepovik*, M. V. Gulenova*, I. M. Martynova*,
N. S. Skvortsov*, and V. K. Cherkasov**
* Lobachevskii Nizhny Novgorod State University, Nizhny Novgorod, Russia
** Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, Nizhny Novgorod, Russia
Received February 19, 2004
Abstract Trialkyl(aryl)silanes and -germanes effectively react with metal (Al, Ti) tert-butylate tert-butyl-
hydroperoxide under mild conditions (room temperature, benzene or tetrachloromethane) mainly by the
element hydrogen bond. The character of the products depends on the nature of the element, the structure of
the radical bound to it, and the solvent. The process is radical in nature. It includes the stages of formation of
element-centered radicals and their reaction with the oxygen generated by the system. The intermediate
organometallic peroxides can also acts as oxidants for the element (Si, Ge) hydrogen bonds.
The oxidative activity of organosilicon and organo-
germanium hydrides depends on the structure of the
radicals bound with the heteroatom and the nature of
the oxidant. Potassium permanganate [1], hydrogen
peroxide on a Zeolite catalyst [2], and perbenzoic acid
[3] convert trialkyl(aryl)silanes to corresponding
hydroxy derivatives. Triethylsilane and triethylger-
mane react with mineral acids (H2SO4, HNO3), as
well as with Ag2O at the boiling points of the
hydrides to form siloxane and germanoxane [4].
slowly oxidized by atmospheric oxygen [11, 12], but
tricyclohexylgermane is fast oxidized on exposure to
air to form tricyclohexylgermanol.
Hence, E H can bonds can be oxidized with a
fairly broad range of reagents, and the reactions are
accelerated by radical initiators. There is no informa-
tion in the literature concerning reactions of silicon
and germanium hydrides with oxidative systems com-
prising organoelement compounds or element alcoho-
lates and hydroperoxides, that are known as effective
and selective oxidants for C H bonds in various sub-
strates [13].
Over the past years dimethyldioxirane [5, 6] has
been offered as a mild oxidant that converts trialkyl-
silanes of various structure to hydroxysilanes. The
reaction involves the Si H bond and occurs at tem-
peratures ranging from 70 C to 20 C with a high
conversion and selectivity by the molecular and ra-
dical mechanisms, the first prevailing.
It was previously shown that aluminum and tita-
nium tert-butylates (I and II) react with tert-butyl-
hydroperoxide (III) at a 1:2 ratio under mild condi-
tions (C6H6, CCl4, 20 C) via formation of metal-
containing trioxides [14, 15]. The latter decompose
with evolution of oxygen, including singlet oxygen,
as well as homolytically by the peroxide bonds with
generation of alkoxyl and peroxyl radicals
[scheme (1)].
The reaction of organosilicon hydrides with ozone
at 70 C to 80 C involves formation of hydrotri-
oxides R3SiOOOH [6 9]. At elevated temperatures,
the latter decompose with liberation of singlet oxygen,
hydroxysilane, and, to a smaller degree, siloxane
[6, 8]. The mechanism of the decomposition of silicon
hydrotrioxides is mostly molecular.
(t-BuO)n 1MOOBu-t + t-BuOH,
(t-BuO)nM + t-BuOOH
A
(1)
(t-BuO)n 1MOOBu-t + t-BuOH,
A + t-BuOOH
B
(t-BuO)nM + 1O2,
Silicon and germanium monohydrides are suf-
ficiently stable toward free oxygen. Triphenylsilane
undergoes oxidation to Ph3SiOH, initiated by benzoyl
peroxide (C6H6, 95 C) [10]. However, the ability of
R3GeH to oxidation is much dependent on the struc-
ture of the radical. Triphenylgermane is extremely
O
(t-BuO)n 1M
(t-BuO)n 1MOO + t-BuO,
O
t-BuO
(t-BuO)n 1MO + t-BuOO,
M = Al, n = 3; M = Ti; n = 4.
1070-3632/05/7507-1098 2005 Pleiades Publishing, Inc.

REACTION OF ORGANOELEMENT HYDRIDES R3EH (E = Si, Ge)
1099
The oxygen generated by the systems is a selective
oxidant for methylene and methine C H bonds in al-
kanes, alkylarenes, alkenes [16 19], and some of their
functional derivatives (ethers [20], esters [21], keto-
nes [22], etc.). Oxidation of methylene and methyne
C H bonds leads, depending on the structure of the
starting compounds, to introduction of oxo, hydroxy,
and hydroperoxy groups. Methyl groups are insus-
ceptible to oxidation, except for those in toluene [16]
and -methylethylenes [18]. The conversion of the
starting substrate and the character of the resulting
compounds is strongly dependent on whether the
radicals formed on the initial stage are sufficiently
stable and easy to form. The final stage of the process
most frequently involves destruction of the skeleton
of the starting substrate. The great role in the forma-
tion of secondary products belongs to metal peroxides.
For example, the major products of the oxidation of
triphenylmethane with systems containing alcoholate I
or II and hydroperoxide III were triphenylmethyl
hydroperoxide, phenol and benzophenone [23, 24],
formed by scheme (2).
perature in benzene and tetrachloromethane at the
element hydride metal alcoholate hydroperoxide
ratio of 1:1:2. By special experiments we showed
that in our chosen conditions the substrates react
neither with CCl4 nor with the components of the
oxidative systems.
To find out whether the methylene group of the
ethyl radical bound with an element is susceptible to
oxidation, we reacted Et4Si and Et4Ge with the
Al(OBu-t)3 t-BuOOH system (C6H6, room tempera-
ture, 36 h). It was established that the conversion of
Et4Si is about 5%, and that of Et4Ge is no higher than
10%. Acetaldehyde, acetic acid (0.05 0.08 mol) and
hexaalkylelementoxanes (0.02 0.03 mol) were iden-
tified among the reaction products.
The example of tribenzylsilane was used to show
that replacement of the ethyl radical by benzyl favors
convertion of the methylene group and of the
whole substrate (to 0.35 0.40 mol). Among the reac-
tion products we found (mol/mol tribenzylsilane):
benzaldehyde (0.05 0.10), benzyl alcohol (0.006),
benzoic acid (0.06 0.10), and tribenzylhydroxysilane
(0.12 0.15). The formation of aldehydes on the first
stage is consistent with a radical mechanism of oxida-
tion of the methylene fragment of silanes [14, 18 20].
Presence of tribenzylhydroxysilane implies reaction
of the oxidative system with the Si H bond. Note that
the quantities of benzyl C H and tribenzylsilane Si H
oxidation products are roughly equal, which suggests
almost equal probabilities of formation of R2Si
and R3SiCH Ph (R = PhCH2) radicals.
Ph3COOH + (t-BuO)3Al
Ph3COOAl(OBu-t)2
t-BuOH
PhOC(Ph)2OAl(OBu-t)2
Ph2CO + PhOAl(OBu-t)2.
(2)
As to organoelement compounds, the oxidation of
amines [25] and dialkyl sulfides [26] with the al-
coholate I hydroperoxide III system proceeds mainly
through the attack either on the N H bond, leading to
formation of nitrogen-containing peroxy derivatives,
or on the heteroatom (in R2S) even in the presence of
such readily oxidized groups as benzyl. The oxidants
here are both oxygen and metal-containing trioxides B
[scheme (1)].
Hence, the reaction of the Al(OBu-t)3 t-BuOOH
system with the methylene group is not prevailing
even with benzyl radicals on silicon and is insigni-
ficant with ethyl radicals on silicon or germanium.
Oxidation of element hydrogen bonds with the
I (or II) III system was considered using the
example of silicon and germanium monohydrides
R3EH (R = Et, Ph). The conversions of the starting
element hydrides were close to 100% with phenyl
derivatives, 95% with triethylgermane, and 50 80%
with Et3SiH. At the same time, about 40 50% of
oxygen is evolved in the free state (Table 1).
In the present work we have studied reactions of
oxidative systems consisting of alcoholate I or II and
hydroperoxide III with organosilicon and organo-
germanium, aiming at assessing the effect of carbon
hetero analogs on the regularities of the oxidation and
the nature of its intermediates and final products. It is
known that in the series C H, Si H, and Ge H the
bond length increases (0.109, 0.148, and 0.153 nm,
respectively) and the bond energy decreases (411,
As seen from Table 1, the major transformation
products of Et2SiH, Ph3SiH, and Ph3GeH are either
hydroxy compounds or hexaalkyl(aryl)elementoxanes.
Unlike silicon monohydrides and Ph3GeH, in the case
of triethylgermane significant amounts of (tert-butyl-
peroxy)triethylgermane (0.30 0.50 mol) and small
amounts (0.01 0.02 mol) of tert-butoxytriethylger-
mane were found. The nature of the metal atom in the
alcoholate has no significant effect either the com-
1
326, and 288 kJ mol ) [27].
For the starting substrates we chose both com-
pounds containing reactive element hydrogen bonds
only (triphenylsilane and triphenylgermane) and
containing, along with such bonds, methylene groups
that exibit different reactivity toward the oxidative
systems (triethylsilane, triethylgermane, and tribenzyl-
silane). All reactions were carried out at room tem-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 7 2005

1100
STEPOVIK et al.
Table 1. Reaction products of trialkyl(aryl)element hydrides R3EH (E = Si, Ge) with oxidative systems
(t-BuO)nM t-BuOOH (M = Al, n = 3; Ti, n = 4, molar ratio 1: 1: 2)a, (mol/mol element hydride, benzene, 20 C)
R = Et, E = Si
R = Et, E = Ge
M = Al M = Ti
Products in the volatile fraction
R = Ph, E = Si
R = Ph, E = Ge
Reaction products
M = Al
M = Ti
3.14
M = Al M = Ti M = Al
M = Ti
3.62
t-BuOH
t-BuOOH
O2
Me2CO
R6E2O
2.39
0.11
2.50
0.06
0.36
0.04
0.04
0.53b
0.06
3.12
2.89
0.05
0.48
0.07
3.03
0.42
2.81
0.38
0.05
Traces
0.41
Traces
0.05
Qualitatively
0.37
0.02
Not determined
Traces
0.04
R3EOOBu-t
R3EH (initial)
0.31b,c
0.20
0.49
Hydrolysis products of the nonvolatile residued
t-BuOH
R3EOH
R6E2O
PhOH
1.88
0.39
0.16
2.69
Traces
0.23
1.23
2.22
1.45
0.96
2.92
0.79
1.87
0.49
2.18
0.15
0.19
0.49e
0.01
0.02f
0.12f
a
b
c
Averaged results. tert-Butoxytriethylgermane (0.01 0.02 mol) was found. About 0.20 mol of an unidentified organogermanium
d
e
peroxy compound was found among the hydrolysis products. About 1 mol of metal in all experiments. R Ge O, 0.44 mol, was
isolated before hydrolysis. Dihydroxydiphenylsilane, 0.06 mol, was found.
6
2
f
position of the products or on their yield. The low
conversion of Et3SiH in the case of titanium al-
coholate can only be noted.
OEPh3
O
+ Ph E
O
O
(4)
3
The formation of the compounds shown in Table 1
can be explained in terms of the radical nature of the
oxidation reactions. It is known that element-centered
radicals R3E are most commonly prepared by reaction
of element hydrides with the tert-butoxyl radicals
generated by photolysis of tert-butyl peroxide [28]. In
the reactions under study, radicals R3E can be formed
by hydrogen abstraction from the starting substrates
by the oxygen-centered radicals generated by the
systems in the course of decomposition of metal-con-
taining trioxides B [scheme (1)].
1, 2
E = Si (1), Ge (2).
when the multiplication product of the steady-state
concentration of oxygen on the rate constant of its
reaction with radicals becomes comparable with the
product of the concentration of the spin trap on the
rate constant of the reaction with the same radicals
[14].
The isotropic ESR spectra of spin adducts 1 and 2
are 1:2:1 triplets characteristic of 2,4,6-substituted
aroxyls. Furthermore, the spectra show additional
superfine structure formed by interaction with 29Si,
73Ge, and 13C magnetic nuclei. The parameters of the
ESR spectrum of adduct 1 of the triphehylsilyl radical,
gi = 2.0048, ai(29Si) = 1.134 mT, and ai(Hm) =
0.116 mT, are close to those reported in the literature
[29]. No data concerning the germanium analog are
available. Our registered parameters of adduct 2 are as
follows: gi = 2.0048, ai(73Ge) = 0.090 mT, ai(Hm) =
0.087 mT, and ai(13C) = 1.030 mT. Evidence for the
identification of the radicals formed by reactions (3)
and (4) was obtained by modeling the formation of
the above-mentioned quinone adducts with Ph3E .
R3EH + XO
R3E + XOH,
(3)
R = Et, Ph; E = Si, Ge; X = t-Bu, t-BuO, (t-BuO)n 1M,
(t-BuO)n 1MO; M = Al, n = 3; M = Ti, n = 4.
We identified the Ph3Si and Ph3Ge radicals in the
reaction of the corresponding hydrides with
Al(OBu-t)3 hydroperoxide III in benzene at 20 C by
means of ESR in the form of spin adducts 1 and 2 with
2,6-di-tert-butyl-p-benzoquinone [29] [scheme (4)].
The formation of radicals 1 and 2 proved only
possible on final stages, when most oxygen has al-
ready been consumed for substrate oxidation and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 7 2005

REACTION OF ORGANOELEMENT HYDRIDES R3EH (E = Si, Ge)
Di-tert-butylperoxalate was used as the source of tert- Ph3SiO + Ph3SiH Ph3Si + Ph3SiOH.
1101
(9)
butoxyl radicals [30]. The ESR spectra of the model
adducts, and their parameters are identical to the
above-listed data.
The formation in our studied reactions of small
amounts of phenol and dihydroxydiphenylsilane
(Table 1) points to formation of hydroperoxides
Ph3EOOH and metal-containing peroxides [sche-
me (2)].
It was previously shown [14, 15] that alcoholate I
(II) hydroperoxide III systems generate oxygen both
in benzene and in CCl4. Using of the latter as the
solvent in the oxidation of element hydrides, we can
assess its effect on the qualitative and quantitative
composition of the reaction products.
The high degree of conversion of element hydrides
R3EH, as well as the fact that the reactions in benzene
give 0.4 0.5 mol of free oxygen suggest intermole-
cular oxidation reactions leading to hydroxy deriva-
tives R3EOH, that probably occur by schemes (7) and
(8). However, in view of the polarity of the E H bond,
we can also suggest that it is oxidized by organo-
metallic peroxides.
In view of the uniform reaction pathways of oxida-
tive systems containing element hydrides, we con-
sidered the reaction in CCl4 on an example of the
Al(OBu-t)3 hydroperoxide III system. The resulting
data are listed in Table 2.
To find out the role of the latter in the formation
of the final products, we have studied the reaction of
Ph3EH with hydroperoxides Ph3EOOH in the pre-
sence of alcoholates I or II in a 1:1:1 molar ratio in
benzene at room temperature.
The presence of element chlorides among the reac-
tion products provides one more evidence for the
formation of element-centered radicals.
R3E + CCl4
R3ECl + CCl3,
(5)
R= Et, Ph; E = Si, Ge.
Special experiments established that the reactions
of triphenylelement hydroperoxides with alkoholates
I and II in 1:1 or 1:2 molar ratios in benzene at
The highest yield of R3ECl (up to 0.25 0.30 mol)
was obtained with ethyl- and phenylgermanium com-
pounds. Et3SiCl and Et3GeCl were identified by GLC.
The presence of analogous phenyl derivatives was
proved by IR spectroscopy. The IR spectrum of the
nonvolatile residue of Ph3SiH oxidation products
Table 2. Reaction products of trialkyl(aryl)element
hydrides R3EH (E = Si, Ge) with the Al(OBu-t)3
t-BuOOH system (molar ratio 1:1:2)a, (mol/mol element
hydride), CCl4, 20 C
1
contains bands at 510 and 560 cm , characteristic of
Si Cl stretching vibrations, which was confirmed by
the spectrum of an authentic Ph3SiCl. However, in
CCl4, too, the preferred reaction pathway of the
oxidative systems with element hydrides R3EH is the
competing oxidation of element hydrogen bonds.
R = Et
E = Sic E = Ge E = Si E = Ge
Products in the volatile fractiond
R = Ph
Reaction
productsb
t-BuOH
t-BuOOH
O2
Me2CO
R3ECl
2.80
0.08
0.20
0.03
0.10
0.19
2.80
Traces
0.23
0.03
0.30
0.03
0.44
0.08
2.85
0.12
0.37
2.78
In view of the facility of the reaction of the R3E
radicals with oxygen [28, 31], we can propose their
subsequent transformations to trialkyl(aryl)element
hydroperoxides.
0.20
0.03
Traces
R6E2O
R3E + O2
R3EOO ,
(6)
(7)
R3EOOBu-t
R3EOBu-t
R3EOO + R3EH
R3EOOH + R3E .
Hydrolysis products of the nonvolatile residuee
We consider that the latter compounds can also be
formed by direct reaction of metal-containing tri-
oxides B with the starting substrates, similarly to the
oxidation of amines [26]. It is known that in the ini-
tiated oxidation of element hydrides no hydroper-
oxides were found. Hence, the example of the oxida-
tion of Ph3SiH was used to show that triphenylsilyl
hydroperoxide acts as inhibitor [10].
t-BuOH
R3EOH
R6E2O
R3ECl
Cl
1.88
0.41
0.04
1.10
0.06
0.23
1.50
0.85
1.71
0.37
0.20
0.28
0.12
0.40
0.22
a
b
Averaged results. Hexachloroethane, about 0.04 mol, was
c
found directly in the reaction mixture. Unreacted Et SiH,
0.10 mol.
3
d
e
Phosgene was qualitatively identified. About
Ph3SiOOH + Ph3Si
Ph3SiO + Ph3SiOH, (8)
1 mol of aluminum in all experiments.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 7 2005

1102
STEPOVIK et al.
Table 3. Reactiom products of triphenylelement
hydrides Ph3EH with hydroperoxides Ph3EOOH (E = Si,
Ge) in the presence of alcoholates (t-BuO)nM; M = Al,
n = 3: Ti, n = 4) at a 1: 1: 1 molar ratio, C6H6, 20 C
(mol/mol hydroperoxide)
Ph3EH + Ph3EOOM(OBu-t)n 1
PhEO OM(OBu-t)n 1
>
<
H
EPh3
Ph3SiOOH
Ph3GeOOH
(11)
Ph3EOH + Ph3EOM(OBu-t)n 1
,
Reaction
productsb
Ph3SiH, Ph3GeH, Ph3GeH, Ph3SiH,
M = Al M = Al M = Ti M = Ti
E = Si, Ge; M = Al, n = 3; M = Ti, n = 4.
The fact that the peroxide bond in the metal-
containing peroxide can be oxidized with element
hydrides was confirmed by the reactions of a fairly
stable peroxide (t-BuO)2AlOOBu-t [22] with Et3GeH,
as well as with triethyl- and triphenylsilanes (C6H6,
room temperature). The reactions with di-tert-butoxy-
(tert-butylperoxy)aluminum proceed rather slowly.
Within 20 h, 0.60 0.80 mol of the peroxide, 0.67 mol
of Et3GeH, 0.66 mol of Et3SiH, and 0.61 mol of
Ph3SiH were consumed. No Et3EOBu-t was found. In
the volatile fraction, 0.56 0.73 mol of t-BuOH was
found, and hydrolysis of nonvolatile residues gave
Products in the volatile fraction
t-BuOH
1.63
1.28
1.05
0.98
Hydrolysis products of the nonvolatile residuea
t-BuOH
Ph3SiOH
Ph3GeOH
Ph6Ge2O
PhOH
1.04
1.16
2.20
2.44
0.77
1.69b
0.10
0.82d
0.17
0.03
0.88c
0.10
0.43e
0.14
0.18
0.03
0.23
Ph3EH
(initial)
a
b
About 1 mol of metal in all experiments. Ph Si(OH) , 0.54 mol of Et3SiOH, 0.20 mol of Et6Ge2O, and
2
2
0.05 mol, was found. Ph Ge O isolated before hydrolysis: 0.60 mol of Ph3SiOH. The isolated products are
6
2
c
d
e
0.34 mol, 0.58 mol, and 0.13 mol.
indicative of the preferred coordination of the hydride
hydrogen atom by the oxygen atom of the tert-butoxy
group of the peroxide.
room temperature result in no oxygen evolution. That
means that reactions similar to those involving
t-BuOOH [scheme (1)] fail to occur. Evidence for this
conclusion was obtained by using the readily oxidized
ethylbenzene as solvent instead of benzene. The yield
of acetophenone in this case was no more than 2%. It
(t-BuO)2AlOOBu-t + R3EH
t-BuOH + R3EOAl(OBu-t)2.
(12)
Hence, the Si H and Ge H bonds of trialkyl(aryl)-
was found that hydroperoxides Ph3EOOH fail to react element hydrides can be oxidized both the oxygen
with the corresponding hydrides in benzene at room generated by the Al(OBu-t)3 [or Ti(OBu-t)4] tert-
temperature within a day.
butylhydroperoxide system or by the intermediate
organometallic peroxides of type C.
The reactions of element hydrides with Ph3EOOH
in the presence of alcoholates I and II are complete
Trialkylhydroxysilanes and -germanes, as stronger
within 1.5 2 h. The conversion of Ph3SiH is 77 80%, acids, further react with metal alcoholates, expelling
and that of Ph3GeH is higher than 90% (Table 3). The tert-butanol.
absence of oxygen and alkoxyl radicals in Ph3EOOH
metal alcoholate systems rules out the radical oxida-
R3EOH + (t-BuO)nM
tion pathway in this case.
R3EOM(OBu-t)n 1 + t-BuOH.
(13)
The high yield of t-BuOH and the presence of
phenol point to the possible formation of peroxides C.
Hydrolysis of unsymmetrical alkoxy compounds
gives hexaalkyl(aryl)elementoxanes formed by de-
hydration of hydroxy compounds. However, these
compounds were also found before hydrolysis (Tab-
les 1 and 3). In the oxidation of triphenylgermane
with the Ti(OBu-t)4 t-BuOOH system, almost 90%
of Ph6Ge2O was evolved. Special experiments were
performed to establish that the dehydrating agent for
hydroxytriphenylgermane can be alcoholate II. Hence,
Ph3EOOH + (t-BuO)nM
(t-BuO)n 1MOOEPh3.
t-BuOH
C
(10)
We suggest that the oxidation of triphenylelement
hydrides with peroxides C is favored by electron
density redistribution in the intermediate reaction
complex [scheme (11)].
Evidence for this scheme was provided by the mixing of benzene solutions of Ti(OBu-t)4 and
isolation of hydroxytriphenylsilane in the oxidation Ph3GeH (molar ratio 1:1, 20 C) resulted in precipita-
of Ph3SiH with the Ph3GeOOH Ti(OBu-t)4 system.
tion of about 0.5 mol of hexaphenylgermanoxane
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 7 2005

REACTION OF ORGANOELEMENT HYDRIDES R3EH (E = Si, Ge)
1103
within 5 10 min. Therewith, about 0.1 mol of
t-BuOOH was liberated.
We suggest that the Al Cl bond is formed by the
consecutive transformations of the trichloromethyl
radical, presented in schemes (20) (24). The tri-
chloromethylperoxyl radical either abstracts hydrogen
to give hydroperoxide or undergoes dimerization like
tertiary alkylperoxyl radicals.
Equations (3) and (6) (11) describe formation of
hydroxy derivatives for all the element hydrides R3EH
studied. However, with triethylgermane, one of the
major products of the reactions with the oxidative
systems is (tert-butylperoxy)triethylgermane (IV)
(Tables 1 and 2) whose presence can be explained by
recombination of two peroxyl radicals [31] [sche-
me (14)].
Cl3C + O2
Cl3COO ,
Cl3COOH,
(20)
(21)
R3EH
R3E
Cl3COO
Cl3COO
(22)
2Cl3CO + O2.
Et3GeOO + t-BuOO
Et3GeOOBu-t + O2. (14)
The subsequent reactions of the trichloromethoxyl
radical and trichloromethylhydroperoxide may give
rise to trichloromethanol that decomposes into phos-
gene and hydrogen chloride. One of such pathways is
described by scheme (23).
Alternatively, peroxide IV can be formed by di-
merization of the Et3Ge and t-BuOO radicals. To
obtain evidence for this suggestion, we reacted
Et3GeH with di-tert-butylperoxalate and hydroper-
oxide III at a 1:1:1 ratio in benzene at 50 C. The
reaction in complete within 1 h. The yield of CO2 is
close to quantitative, implying complete conversion of
di-tert-butylperoxalate. Among the reaction products
we identified Et3GeOOBu-t ( 0.90 mol) and
Et3GeOBu-t (0.03 mol), that are probably formed by
schemes (15) (19).
AlOOCCl3
Al OBu-t + HOOCCl3
t-BuOH
R3EH
(23)
Cl2CO + HCl.
AlOER3 + [Cl3COH]
Phosgene was qualitatively identified among the
reaction products. Hydrogen chloride reacts with the
alkoxy group on aluminum.
[C(O)OOBu-t]2
t-BuO + t-BuOOH
t-BuO + Et3GeH
t-BuOO + Et3Ge
t-BuO + Et3Ge
2CO2 + 2t-BuO ,
(15)
(24)
t-BuOH +
Al Cl.
Al OBu-t + HCl
t-BuOO + t-BuOH, (16)
Et3Ge + t-BuOH,
Et3GeOOBu-t,
Et3GeOBu-t.
(17)
(18)
(19)
Note that schemes (20) (24) describe not all the
processes that occur in CCl4, since the
quantity of element chlorides is always smaller than
the amount of chlorine bound with metal.
The above results led us to conclude that alcoholate
I (II) hydroperoxide III systems effectively oxidize
trialkyl(aryl)silanes and -germanes. The reactions
proceed mainly by the element hydrogen bond and
involves the R3E radicals. The nature of the resulting
products depends primarily on the structure of the
radical and the nature of the element (Si, Ge). The
specific character of the reaction of triethylgermane
with the oxidative systems can be explained by the
fact that the spin density in R3Ge is concentrated on
the element [32], as well as by the higher stability of
the germanium-containing peroxyl radicals R3GeOO
as compared to their silicon analogs [28]. Comparing
the reactions of the systems with identical compounds
of carbon, silicon, and germanium one can see that
the degree of conversion significantly increases in
going from Ph3CH ( 30%) [23] to Ph3SiH and
Ph3GeH ( 100%). Moreover, unlike the reaction with
triphenylmethane, that resulted in isolation of (tri-
phenylmethyl)hydroperoxide and its rearramgement
and decomposition products [23, 24, 33], in the case
of element hydrides alcohols R3EOH were found. We
Equations (15) and (16) model generation of tert-
butylperoxyl radicals. The insignificant yield of
Et3GeOBu-t suggests that t-BuO radicals are mostly
consumed for formation of triethylgermyl and tert-
butylperoxyl radicals.
Together the above data provide evidence for the
homolytic formation of peroxide IV and for the for-
mation of tert-butylperoxyl radicals in the reaction of
alcoholates
I
and II with hydroperoxide III
[scheme (1)].
Note that the amount of free oxygen in the reac-
tions carried out in CCl4 is always smaller than in
benzene (Table 2). Among the hydrolysis products
we always found the chloride anion. The IR spectrum
of the nonvolatile products contains a strong band at
1
1621 cm , assignable to Al Cl stretching vibrations
[comparison with the spectrum of an authentic
(PhCH2O)2AlCl]. It was previously shown that Ph3ECl
(E = Si, Ge) do not change under the hydrolysis
conditions.
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1104
STEPOVIK et al.
explain this result by the high oxidative activity of
the intermediate organometallic peroxides toward the
more polar and weaker E H bonds.
(PhCH2)3SiH, Et3SiH, Ph3SiH, Et4Si, Ph4Ge, and
Et4Ge were prepared by treatment of SiHCl3 or SiCl4
with Grignard reagents by published procedures.
Ph3GeBr and Et3GeBr were prepared by bromination
of Ph4Ge and Et4Ge in 1,2-dibromoethane. Their
melting and boiling points and refractive indices agree
with published data. Ph3GeH and Et3GeH were syn-
thesized by reduction of the corresponding bromine
derivatives of germanium with lithium alumohydride
[39]. Ph3SiOOH was prepared from Ph3SiCl and 96%
hydrogen peroxide, mp 110 111 C [40]. Ph3GeOOH
was synthesized by an analogous procedure from
Ph3GeBr, mp 136 C [41]. Et3GeOOBu-t was obtained
by reaction of Et3GeCl with t-BuOOH, bp 79 C
(14 mm Hg), n2D0 1.3458 [42]. The activity of the
peroxides was no less than 98%. The concentration of
tert-butylhydroperoxide was no less than 99.6 99.8%.
EXPERIMENTAL
The IR spectra were recorded on Specord IR-75
and Specord-1000 IR instruments (liquid film
between KBr windows). The ESR spectra were regis-
tered on a Bruker ER-200D-SRC spectrometer equip-
ped with an ER 4105 DR double resonator (working
frequency 9.5 GHz) and an ER4111VT temperature
control unit. The g factors were determined using di-
phenylpicrylhydrazyl as reference. Chromatographic
analysis of the reaction products in the liquid phase
was carried out on a Tsvet-2-65 gas chromatograph
with a flame ionization detector and argon as carrier
gas. High-boiling products (benzyl alcohol, benzal-
dehyde, phenol, Et6Si2O, Et6Ge2O, Et3GeOOBu-t,
Et3GeCl, Ph3SiH, PhCH2SiH, etc.) were analyzed us-
ing a 3000 3 mm column packed with 5% SE-30 on
Inerton-AW, oven temperature 100 230 C. Hexachlo-
roethane was analyzed on a 2400 3 mm column
packed with 15% of Apieson-L on Chromaton-N-AW-
DMCS, oven temperature 140 C. Acetone, tert-butyl-
hydroperoxide, tetraethylgermane, and tetraethylsilane
were analyzed on an LKhM-80 gas chromatograph
using a 1200 3 mm column packed with 15% of
dinonyl phthalate on Chromaton N-AW-DMCS,
carrier gas helium, oven temperature 40 80 C. The
chromatograms were treated by the external calibra-
tion technique. All manipulations with metal-contain-
ing compounds were carried out under oxygen-free
dry argon.
According to the standard procedure, a mixture of
a metal alcoholate and a substrate in a solvent was
treated with the hydroperoxide. The reactions were
complete within 1.5 2 h, as judged from the disap-
pearance of the oxidized substance or hydroperoxide.
Increase of the reaction time to 1 day did not affect
the conversion of the substrate and the yield of the
oxidation products. The solvent and volatile products
were condensed in a trap cooled with liquid nitrogen.
Nonvolatile residues were hydrolyzed in ether with
10% sulfuric acid and thoroughly extracted with ether.
The volatile fractions and ethereal hydrolyzates were
analyzed by GLC. The aqueous acidic hydrolyzates
were analyzed for t-BuOH [34]. Metals were preci-
pitated as hydroxides and then calcined to oxides.
Oxidation
of
tribenzylsilane
with
the
(t-BuO)3Al t-BuOOH system (1:1:2) in benzene.
A mixture of 1.61 g of (t-BuOH)3Al, 1.18 g of t-
BuOOH, and 1.98 g of (PhCH2)3SiH in 20 ml of
benzene was kept at room temperature for a day.
Hydrogen evolution was observed. The reaction solu-
tion was dark orange. The volatile fraction contained
1.40 g of tert-butanol, 0.02 g of acetone, and 0.07 g
of benzaldehyde. The residue was a brown dry ma-
terial. During hydrolysis, a solid material insoluble in
ether or aqueous acids formed on the phase interface.
The quantities of unreacted Ph3SiH and Ph3GeH,
apart from GLC, were determined by the volume of
hydrogen evolved after treatment of the samples with
a solution of KOH in tert-butanol [10]. Analysis for
tert-butoxy groups was performed by the Deniges
method [34] and analysis for acetic acid, by the pro-
cedure in [35]. Carbonyl compounds were identified
as 2,4-dinitrophenylhydrazones by the melting points
and by TLC on Silufol UV-254 plates in benzene or
9:1 benzene diethyl ether. The quantity of oxygen
evolved during the reactions was determined by the
weigh of benzoic acid formed by the reaction of
oxygen with benzaldehyde [16].
1
According to the IR spectrum [ , cm : 1060 (Al O),
1590 (COO ), and 3340 (OH)] and the Al content it
was aluminum dihydroxybenzoate. Found Al, %:
14.48. C7H7AlO4. Calculated Al, %: 14.83. The
residue was hydrolysed by boiling with dilute sulfuric
acid. Benzoic acid, 0.05 g, was isolated from the
hydrolyzate, mp 121 C.
Titanium tetra(tert-butylate) was prepared by
treatment of TiCl4 with tert-butanol in the presence
of NH3 [36], bp 82 83 C (2 mm Hg), n2D0 1.4420 [37].
Aluminum tri(tert-butylate) was obtained by the reac-
tion of aluminum with tert-butanol [38] and purified
by sublimation at 160-170 C (1 mm Hg). Found Al,
%: 11.08. C12H27AlO3. Calculated, %: Al 10.98.
The ethereal extract contained 0.02 g of tert-butyl-
hydroperoxide, 1.00 g of tert-butanol, 1.08 g of tri-
benzylsilane, 0.03 g of benzyl alcohol, 0.04 g of
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REACTION OF ORGANOELEMENT HYDRIDES R3EH (E = Si, Ge)
1105
benzoic acid (analyzed as methyl ether after treatment
with diazomethane), and 0.27 g of tribenzylhydroxy-
silane.
0.07 g of hexaethylgermanoxane, 0.10 g of aluminum,
and 0.027 g of the chloride anion.
Phosgene was identified by qualitative reaction
with benzidine and by the formation of 1,2-diphenyl-
urea upon treatment of the volatile fraction with
aqueous aniline [43].
For quantitative analysis for (PhCH2)3SiH, an
aliquot of the ethereal solution was evaporated. The
dry residue was dissolved in boiling hexane. After
cooling, crystals of (PhCH2)3SiH, mp 85 86 C,
formed and were filtered off. The filtrate was spiked
with a small crystal of (PhCH2)3SiH. After 1 h, was
filtered off, mp 102-103 C. Mixed sample gave no
melting point depression.
Reaction of triphenylsilane with the (t-BuO)3Al
t-BuOOH system (1:1:2) in CCl4. A mixture of
1.47 g of (t-BuO)3Al, 1.56 g of Ph3SiH, and 1.08 g
of t-BuOOH in 20 ml of carbon tetrachloride was kept
at room temperature for 5 h. Over this period of time,
48 ml of O2 evolved. The reaction solution got dark
yellow. C2Cl6, 0.07 g, was chromatographically
determined directly in the reaction mixture. The vo-
latile fraction contained 1.31 g of tert-butanol, 0.05 g
of tertbutyl hydroperoxide, and 0.01 g of acetone.
Hydrolysis of the nonvolatile residue (light brown dry
material) gave 0.67 g of tert-butanol, 1.40 g of hydr-
oxytriphenylsilane, 0.17 g of Ph3SiCl, 0.155 g of
aluminum, and 0.082 g of the chloride anion.
Oxidation of triethylsilane with the (t-BuO)4Ti
t-BuOOH system (1:1:2) in benzene. During the
reaction of 1.33 g of (t-BuO)4)Ti, 0.70 g of t-BuOOH,
and 0.45 g of Et3SiH in 13 ml of benzene, 36 ml of
oxygen evolved (under normal conditions). The reac-
tion mixture was orange. The condensate of the vo-
latile fraction contained 0.91 g of tert-butanol, 0.22 g
of triethylsilane, 0.05 g of hexaethylsiloxane, and
traces of acetone. The residue was a viscous yellowish
oil. The ethereal solution after hydrolysis contained
0.55 g of tert-butanol, 0.22 g of hexaethylsiloxane,
and traces of triethylhydroxysilane. In the aqueous
acidic solution, 0.23 g of t-BuOH and 0.18 g of ti-
tanium were found.
Special experiments showed that Ph3SiCl is not
hydrolyzed by 10% H2SO4 in ether. For quantitative
evaluation of this compound, an aliquot of the ethereal
extract of the hydrolysis products, containing a mix-
ture of Ph3SiCl and Ph3SiOH, was taken, the solvent
was removed at reduced pressure, and the residue was
refluxed for 5 h with 10% NaOH. After acidification
of the aqueous phase, 0.022 g of the chloride anion
was found, which corresponds to 0.17 g of Ph3SiCl.
The weight of the isolated hydroxytriphenylsilane was
1.56 g (mp 149 C) of which 0.16 g was formed from
Ph3SiCl and 1.40 g by hydrolysis of Ph3SiO Al
bonds.
Reaction
of
triethylgermane
with
the
(t-BuO)3Al t-BuOOH system (1:1:2) in CCl4. To
a solution of 0.93 g of (t-BuO)3Al and 0.60 g of
Et3GeH in 15 ml of CCl4, 0.68 g of t-BuOOH was
added. After 30 min, oxygen evolution commenced
(19 ml under normal conditions). The reaction solu-
tion got pink. In the condensed solvent, 0.77 g of tert-
butanol, 0.40 g of (tert-butylperoxy)triethylgermane,
0.21 g of chlorotriethylgermane, 0.06 g of (tert-but-
oxy)triethylgermane, 0.04 g of hexaethylgermanoxane,
and 0.01 g of acetone were found. No t-BuOOH was
detected. The conversion of Et3GeH was about 100%.
Indirect evidence for the formation of Et3GeCl was
provided by the hydrolysis of the latter. After boiling
of the condensate of the volatile products with a 5%
NaOH solution for 30 min, hexaethylgermanoxane
was found instead of chlorotriethylgermane. (tert-
Butylperoxy)triethylgermane was determined by
chromatography and iodometric titration. For qualita-
tive identification of Et3GeOOBu-t, an aliquot of the
volatile fraction was treated with aqueous sulfuric
acid; as a result, Et6Ge2O and t-BuOOH were found.
It is known that (tert-butylperoxy)triethylgermane is
easily hydrolyzed with regeneration of tert-butyl-
hydroperoxide. The residue after removal of volatile
products was a light pink solid. After treatment by the
above-described procedure, the ethereal and aqueous
acidic solutions contained 0.30 g of tert-butanol,
The reactions of the other element hydrides with
alcoholate I (II) hydroperoxide III systems and the
analysis of the resulting products were carried out in
a similar way.
Reaction of Ph3SiH with Ph3GeOOH and
Ti(OBu-t)4
(1:1:1)
in
benzene.
To
a
solution of 0.31 g of Ph3SiH and 0.42 g of Ph3
GeOOH in 15 ml of benzene, 0.42 g of Ti(OBu-t)4
was added. Three min after component mixing, the
reaction mixture got yellow and after 20 min, brown.
Therewith, KJ test revealed no peroxide compounds.
Simultaneously, a crystalline precipitate formed. After
20 h, the crystals were filtered off. Hexaphenylger-
manoxane, 0.10 g, was isolated before hydrolysis. The
melting points of the sample and mixed sample were
184 C. The volatile fraction contained 0.08 g of
t-BuOH.
The residue was a solid yellow material. It was
treated by the above-described procedure. tert-Butanol,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 7 2005

1106
STEPOVIK et al.
0.17 g, and 0.02 g of phenol were determined chro-
matographically in the ethereal solution. It also con-
tained a mixture of Ph3SiH, Ph3SiOH, and Ph6Ge2O.
For determination of unreacted Ph3SiH, an aliquot of
the ethereal hydrolyzate was evaporated. The residue
was treated with a solution of KOH in n-butanol. The
quantity of the evolved hydrogen was 7.07 ml under
normal conditions, which corresponds to 0.08 g of
triphenylsilane. From the rest ethereal solution, the
solvent was removed, and the solid residue was
treated with 5 ml of petroleum ether. Undissolved
crystals of Ph3SiOH (0.26 g, mp 149 C) were filtered
off. Petroleum ether was evaporated, and triphenyl-
silane was dissolved in 10 ml of diethyl ether. The
insoluble residue was Ph6Ge2O, 0.25 g, mp 185 C.
The mixed sample of the isolated and authentic
Ph3SiOH and Ph6Ge2O gave no melting point depres-
sion. t-BuOH, 0.05 g, was found in the aqueous acidic
hydrolyzate.
13. Spirina, I.V., Maslennikov, V.P., and Aleksan-
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