Synthesis, structure, and reactivity of siloxides and germyloxides of iron(II) and cobalt(II)

Article abstract of DOI:10.1023/A:1023423202997

Iron and cobalt siloxides and germyloxides [(Me₃Si) ₃SiO]₂M (M = Fe (1), Co (2)), (Me₅Si ₂O)₂Fe (3), (Prⁱ₃SiO)₂M (M = Fe (4), Co (5)), (Prⁱ₃GeO)₂Fe (6), (Ph₃SiO)₂Fe (7), (Me₃SiO)₂Fe (8), (Prⁱ₃GeO)₂Fe(bpy) (9), and [(Me ₃Si)₂NFe(μ-OSi₂Me₅) ₂]₂Fe·C₆H₆ (10) were synthesized by the reactions of metal silylamides [(Me₃Si) ₂N]₂M (M = Fe, Co) with the corresponding silanols or triisopropylgermanol. The reaction of pentamethyldisilanol with iron(II) silylamide affords either polymeric complex 3 or coordination oligomer 10, depending on the ratio of the reactants. The structures of complexes 9 and 10 were established by X-ray diffraction analysis. The interaction of the prepared compounds with carbon oxides was studied. Low-coordination cobalt siloxide is the only among all prepared compounds that absorbs CO (2 mol) at room temperature and under 1 atm to form an unstable cluster. Compounds 1, 2, and 4-8 react with CO₂ to form carbonate complexes, and their reactivity decreases with a decrease in the electron-donating ability of the substituents at the central atom: (Me₃Si)₃SiO > Prⁱ ₃GeO ≈ Prⁱ₃SiO > Me₃SiO ? Ph₃SiO.

Full text of DOI:10.1023/A:1023423202997

414
Russian Chemical Bulletin, International Edition, Vol. 52, No. 2, pp. 414—420, February, 2003
Synthesis, structure, and reactivity of siloxides and germyloxides
of iron(II) and cobalt(II)
ꢀ
Ya. V. Fedotova, E. V. Zhezlova, T. G. Mushtina, A. N. Kornev, T. A. Chesnokova,
G. K. Fukin, L. N. Zakharov, and G. A. Domrachev
G. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
49 ul. Tropinina, 603950 Nizhny Novgorod, Russian Federation.
Fax: +7 (831 2) 66 1497. Eꢀmail: akornev@imoc.sinn.ru
Iron and cobalt siloxides and germyloxides [(Me3Si)3SiO]2M (M = Fe (1), Co (2)),
(Me5Si2O)2Fe (3), (Pri3SiO)2M (M = Fe (4), Co (5)), (Pri3GeO)2Fe (6), (Ph3SiO)2Fe (7),
(Me3SiO)2Fe (8), (Pri3GeO)2Fe(bpy) (9), and [(Me3Si)2NFe(µꢀOSi2Me5)2]2Fe•C6H6 (10)
were synthesized by the reactions of metal silylamides [(Me3Si)2N]2M (M = Fe, Co) with the
corresponding silanols or triisopropylgermanol. The reaction of pentamethyldisilanol with
iron(II) silylamide affords either polymeric complex 3 or coordination oligomer 10, depending
on the ratio of the reactants. The structures of complexes 9 and 10 were established by Xꢀray
diffraction analysis. The interaction of the prepared compounds with carbon oxides was studꢀ
ied. Lowꢀcoordination cobalt siloxide is the only among all prepared compounds that absorbs
CO (2 mol) at room temperature and under 1 atm to form an unstable cluster. Compounds 1, 2,
and 4—8 react with CO2 to form carbonate complexes, and their reactivity decreases
with a decrease in the electronꢀdonating ability of the substituents at the central atom:
(Me3Si)3SiO > Pri3GeO ≈ Pri3SiO > Me3SiO >> Ph3SiO.
Key words: transition metals, siliconꢀ and germaniumꢀcontaining organic compounds,
siloxides, Xꢀray diffraction analysis, coordination polymers.
Table 1. Characteristics of compounds 1—10
Progress in the chemistry of individual metalloꢀ
siloxanes1 is due to their potentialities as models of hetꢀ
erogeneous oxide catalysts2 or coꢀcatalysts and their preꢀ
cursors. The structural and magnetic properties of these
compounds are of special interest.3 In this work, we
continue our studies of transition metal siloxides4 and
present the data on the metal siloxides and germyloxides
(R3EO)2M (M = Fe, Co; E = Si, Ge; R = Me, Pri, Ph,
Me3Si; R3Si = Me2(Me3Si)Si).
Comꢀ
pound
ν(MOE)
Appearance
/cm–1
1
2
3
4
5
6
7
960 s
935 s
940 w
950 s
980 s
830 s
950 s
Yellow crystals
Green crystals
Blue powder
Dark green oil
Violet oil
Dark green oil
Gray powder (form hexane),
crystals (from toluene)
White powder
Dark green crystals
Light green crystals
Results and Discussion
Synthesis and structure
8
9
10
950 w
830 s
970 s
Previously described iron and cobalt siloxides
[(Me3Si)3SiO]2Fe (1) and [(Me3Si)3SiO]2Co (2)4 and
newly synthesized homoleptic siloxides and germyloxides
of these metals (Me5Si2O)2Fe (3), (Pri3SiO)2Fe (4),
(Pri3SiO)2Co (5)), (Pri3GeO)2Fe (6), (Ph3SiO)2Fe (7),
and (Me3SiO)2Fe (8) (Table 1) were prepared by the treatꢀ
ment of iron and cobalt silylamides with the correspondꢀ
ing silanols or triisopropylgermanol in aromatic or satuꢀ
rated hydrocarbons.
The reaction of iron silylamide with triisopropylꢀ
germanol in the presence of an equivalent amount of
2,2´ꢀbipyridyl (bpy) produced the adduct of siloxide 6
with 2,2´ꢀbipyridyl, viz., (Pri3GeO)2Fe(bpy) complex (9).
Compounds 1, 2, and 9 were isolated in the crystalline
form; compounds 3, 7, and 8 are powders; and comꢀ
pounds 4, 5, and 6 are oily liquids.
The degree of association of siloxides [R3SiO]2M deꢀ
pends substantially on the size of the R3Si group. Previꢀ
ously described isostructural iron and cobalt tris(triꢀ
methylsilyl)siloxides 1 and 2 in the crystalline state are
[(Me3Si)2N]2M + 2 R3EOH
(R3EO)2M + 2 (Me3Si)2NH
(1)
1—8
M = Fe, Co; R3E = (Me3Si)3Si, Me5Si2, Me3Si, Pri3Si, Pri3Ge, Ph3Si
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 396—402, February, 2003.
1066ꢀ5285/03/5202ꢀ414 $25.00 © 2003 Plenum Publishing Corporation

FeII and CoII siloxides and germyloxides
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
415
dimers.4 However, judging from the molecular weight deꢀ
termined in benzene by cryoscopy, in a solution these
compounds are monomeric. For example, for siloxide 1
Mcalc = 583, Mcryosc = 556.
The reaction of pentamethyldisilanol with iron silylꢀ
amide affords different products, depending on the ratio
of reactants. When an excess (2.1 : 1) of pentamethylꢀ
disilanol is used, a solution is formed, whose concentratꢀ
ing results in a finely crystalline siloxide (Me5Si2O)2Fe
(3) (reaction (1)), which is a poorly soluble coordination
polymer
of either dimers (in the case of bulky groups, for example,
[(Ph3SiO)2Co(THF)]2)5 or insoluble coordination polyꢀ
mers if the size of the substituents does not prevent assoꢀ
ciation (for example, [(Me3SiO)2M]n, M = Ni, Co).1a In
the latter case, single crystals cannot be prepared, and the
molecular structure of the compounds cannot be studied.
Thus, complex 10 is a unique structurally characterized
example of coordination of the molecular fragments of
silylamide and siloxide at the first steps of formation of
coordination polymer 3.
The crystallographic data for compound 10 are preꢀ
sented in Table 2. The main angles and bond lengths are
presented in Table 3. Three iron atoms in molecule 10 are
in the same line, and the Fe2O2 cycles lie in the relatively
perpendicular planes. The internal O—Fe—O angles at
the central pseudotetrahedral iron atom are 83.74(13)°,
whereas the external angles are 123.68(8)°. The internal
angles at the terminal iron atoms (O—Fe—O) and at the
bridging oxygen atoms (Fe—O—Fe) are closer to orꢀ
thogonal and equal to 87.06(13)° and 94.60(10)°, respecꢀ
tively.
Among
tures of
manganese(II)
[O(Ph2SiO)2]2Mn3[N(SiMe3)2]2(THF)2•1/2THF can be
somewhat analogous to compound 10.7 However, in this
complex the metal atoms are arranged at an angle of
139.5°, which is caused, most likely, by spatial restrictions
for the coordination of the bidentate tetraphenyldisiloxide
ligand simultaneously with three manganese atoms.
a
variety of the known strucꢀ
The precipitate of 3 can again be dissolved only by refluxꢀ
ing for 3 h in THF. However, this results, most likely, in
the complex with THF.
The same compounds taken in the 4 : 3 molar ratio
afford the crystalline trinuclear complex [(Me3Si)2NFe(µꢀ
OSi2Me5)2]2Fe•C6H6 (10) with a rather unusual strucꢀ
ture (Fig. 1). As a rule, bonding of the R3SiO groups (R is
alkyl or aryl) with the metal atom results in the formation
metallosiloxanes,
the
trinuclear
complex
(siloxy)silylamide
C(6C)
C(8C)
C(8A)
C(7C)
Si(3C)
C(5A)
Si(3A)
C(2)
C(8C)
Si(2A)
C(7A)
C(1C)
C(3C)
C(6A)
O(2A)
Si(2C)
C(1)
N(1)
Si(1)
C(4C)
C(3)
Si(1C)
N(1A)
O(2C)
C(5B)
C(5C)
C(2C)
C(3A)
Fe(1)
C(2B)
Fe(2)
Fe(1A)
Si(1A)
O(2B)
O(2)
Si(1B)
C(1B)
C(1A)
C(6)
O(2B)
C(4B)
C(2A)
C(4)
C(3B)
Si(3B)
C(7)
Si(2)
C(5)
Si(3)
C(7B)
C(8B)
C(6B)
C(8)
Fig. 1. Molecular structure of [(Me3Si)2NFe(µꢀOSi2Me5)2]2Fe (10).

416
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
Fedotova et al.
Table 2. Crystallographic data and Xꢀray diffraction parameters
for compounds 9 and 10
Although the structure of iron triphenylsiloxide 7 was
not studied, it can be assumed that compound 7, which is
crystallized from toluene, is a structural analog of dinuclear
cobalt triphenylsiloxide described previously5 because the
atomic radii of cobalt and iron are close.6
Parameter
9
10
Diffractometer
Siemens P3/PC
Smart
Iron trimethylsiloxide 8 is formed on mixing of the
initial reactants as a white powder, whose solubility is very
low even in highꢀpolarity solvents, which is probably
caused by the crossꢀlinked structure of the coordination
polymer that formed.
Attempts to isolate compounds 4—6 in the crystalline
state were unsuccessful likely due to the disordered isoꢀ
propyl fragments and association of the complexes in conꢀ
centrated solutions. However, we prepared single crystals
of compound 9, the adduct of iron triisopropylgermyloxide
with 2,2´ꢀbipyridyl. Compound 9 is the first structurꢀ
ally characterized molecular complex containing the
Fe—O—Ge fragment (Fig. 2). The Fe—O—Ge bond
angles in complex 9 are 133.9(2)° and 144.6(2)° for the
Ge(1)—O(1)—Fe(1) and Ge(2)—O(2)—Fe(1) fragments,
respectively. The main bond lengths and bond angles in
molecule 9 are presented in Table 4.
Molecular formula C28H50Ge2O2N2Fe C38H102Fe3N2O4Si12
Molecular weight
647.73
1155.83
T/К
110(2)
λ/Å
0.71073
Crystal system
Space group
a/Å
b/Å
c/Å
α/deg
β/deg
Triclinic
P1
Tetragonal
I41/acd
17.409(3)
17.409(3)
45.477(10)
90
90
90
13783(4)
8
1.069
11.49(2)
12.27(2)
12.49(2)
99.85(3)
91.11(3)
116.39(3)
1544(5)
2
γ/deg
V/Å3
Z
dcalc/g cm–3
µ/mm–1
1.392
2.42
0.860
Total number of
measured reflections
Number of independent
16795
75177
8488
4963
reflections (Rint
)
Reactivity
0.0523
5805
0.052
4963
Number of reflections
with I > 2σ(I )
Number of refined
parameters
R1 (I > 2σ(I ))
wR2
All studied compounds are oxygenꢀ and moistureꢀsenꢀ
sitive. The absorption band corresponding to vibrations of
the М—О—Si fragment1 (see Table 1) and observed in
the 900—1000 cm–1 interval disappears because of hyꢀ
drolysis on storage of the compounds for several minutes
in humid air. For individual compounds with a low deꢀ
gree of association (in particular, for dimers and trimers),
this band is rather intense, whereas a lowꢀintensity abꢀ
sorption is observed for coordination polymers 3 and 8. In
addition, hydrolysis of the soluble compounds, which ocꢀ
316
135
0.0608
0.1103
0.0664
0.1048
Triisopropylsiloxide derivatives of iron 4 and cobalt 5
and homoleptic iron triisopropylgermyloxide 6 are oily
substances, which are infinitely soluble in any orꢀ
ganic solvents. Complex 4 is monomeric in a solution:
Mcalc = 402, Mcryosc = 406.
C(22)
C(25)
C(23)
C(26)
Table 3. Main bond lengths and bond angles in compound 10
C(21)
C(20)
Bond
d/Å
Angle
ω/deg
C(27)
C(28)
C(24)
N(2)
Fe(1)—N(1)
Fe(1)—O(2)
1.892(4) N(1)—Fe(1)—O(2)
136.47(7)
1.944(2) O(2)—Fe(1)—O(2A)a 87.06(13)
C(19)
Fe(1)—Fe(2) 2.9039(8) N(1)—Fe(1)—Fe(2)
180.0
N(1)
C(18)
C(16)
Fe(2)—O(2)
2.007(2) O(2)—Fe(1)—Fe(2)
43.53(7)
Fe(2)—Fe(1A)c 2.9039(8) O(2A)a—Fe(2)—O(2) 83.74(13)
Si(1)—N(1) 1.7366(19) O(2A)a—Fe(2)—O(2B)b 123.68(8)
O(1)
Fe(1)
C(2)
C(17)
Si(2)—O(2)
1.662(3) Fe(1A)c—Fe(2)—Fe(1)
180.0
112.66(12)
124.4(2)
117.80(11)
136.91(13)
127.26(13)
94.60(10)
C(1)
C(13)
Si(2)—Si(3) 2.3524(15) O(2)—Si(2)—Si(3)
N(1)—Si(1A)a 1.7366(19) Si(1A)a—N(1)—Si(1)
Si(1)—N(1)—Fe(1)
O(2)
Ge(1)
C(4)
C(14)
C(9)
C(3)
Ge(2)
C(15)
Si(2)—O(2)—Fe(1)
Si(2)—O(2)—Fe(2)
Fe(1)—O(2)—Fe(2)
C(7)
C(5)
C(8)
C(10)
C(11)
C(6)
a—c Atoms found from the basic atoms by the symmetric transꢀ
form: a (–x, –y + 3/2, z), b (–x + 3/4, –z + 1/4), c (x – 3/4,
–x + 3/4, –z + 1/4).
C(12)
Fig. 2. Molecular structure of (Pri3GeO)2Fe(bpy) (9).

FeII and CoII siloxides and germyloxides
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
417
Table 4. Main bond lengths and bond angles in compound 9
The other complexes synthesized by us do not react
with CO at standard temperature and pressure.
Bond
d/Å
Angle
ω/deg
Interaction of homoleptic complexes 1, 2, and 4—8 with
CO2. The interaction of CO2 with metal alkoxides occurs,
as a rule, as insertion at the metal—carbon bond to form
the corresponding carbonate complexes.11
Fe(1)—O(2)
Fe(1)—O(1)
Ge(2)—O(2)
Ge(1)—O(1)
Ge(2)—C(10) 1.983(5)
Ge(1)—C(4) 1.966(6)
C(23)—C(24) 1.478(7)
C(21)—C(22) 1.385(7)
Fe(1)—N(2)
Fe(1)—N(1)
1.854(4)
1.887(5)
1.741(4)
1.774(4)
O(2)—Fe(1)—O(1)
Ge(1)—O(1)—Fe(1)
Ge(2)—O(2)—Fe(1)
N(2)—Fe(1)—N(1)
C(13)—Ge(2)—C(16)
C(4)—Ge(1)—C(7)
O(2)—Fe(1)—N(2)
O(1)—Fe(1)—N(2)
O(2)—Ge(2)—C(16)
O(1)—Ge(1)—C(7)
126.84(14)
133.9(2)
144.6(2)
74.70(15)
106.9(2)
114.0(2)
111.91(18)
107.72(17)
109.6(2)
It was assumed4 that the reaction of compound 1 with
CO2 affords the product of insertion of the oxygen atoms
(from CO2) at the silicon—silicon bonds of the polysilyl
fragment, and the Fe—C bond forms. Our experiments
show that the formation of the previously observed siloxꢀ
ane products is due to an oxygen admixture in CO2. The
reaction of compounds 1, 2, and 4—8 with CO2 results in
the insertion of the latter at the M—O bond and formaꢀ
tion of the corresponding carbonates. The reactions occur
in a solution of hydrocarbons at room temperature and
under an atmospheric pressure. The appearance of abꢀ
sorption bands at 1550 and 1380 cm–1 in the IR spectra
indicates the formation of the —OC(O)O— groups. Two
moles of СО2 are readily inserted only in the case of iron
siloxide 1 and cobalt germyloxide 6
2.168(5)
2.177(5)
107.71(19)
curs readily in a polar medium, produces the initial silanol
(germanol) in ∼100% yield and bivalent metal hydroxide.
Complexes 1—3 and 10 containing the polysilyl fragments
are pyrophoric in air.
When the size of substituents at the central atom inꢀ
creases, the ability of the compounds to selfꢀassociation
decreases and a possibility of coordination of small molꢀ
ecules appears.
[(Me3Si)3SiO]2Fe + 2 CO2
Interaction of [(Me3Si)3SiO]2Co (2) with СО. We found
that cobalt tris(trimethylsilyl)siloxide (2) in a toluene soꢀ
lution absorbs ∼2 moles of CO per cobalt atom at room
temperature and atmospheric pressure to form a dark
brown solution. It is of interest that a solution of 2 in THF
does not absorb CO under these conditions. This is probꢀ
ably related to the fact that the coordination sphere of
cobalt is saturated with the donating THF molecules.
After concentrating a toluene solution and storage of
the residue at 0 °С, a minor amount of dark brown crysꢀ
tals is precipitated. The IR spectrum of the new complex
contains intense absorption bands at 840 and 1240 cm–1
corresponding to the SiMe fragments and a set of bands
(2040, 2030, 2000, and 1870 cm–1), which can be asꢀ
signed to the cobaltꢀcarbonyl fragments and bridging CO
groups.8,9 In addition, a new intense siloxane absorption
band is observed at 1050 cm–1, while the absorption at
935 cm–1 (Si—O—Co) disappears, as we suppose, due to
migration of the oxygen atom with insertion to the siliꢀ
con—silicon bond of the polysilanyl fragment.
1
[(Me3Si)3SiOC(O)O]2Fe,
[Pri3GeOC(O)O]2Co.
(2)
(3)
(Pri3GeO)2Co + 2 CO2
6
Conditions: i. 20 °C, 20 min; ii. 20 °C, 30 min.
The resulting carbonates are easily hydrolyzed to
form the initial silanol (germanol), CO2, and bivalent
metal hydroxide. We failed to isolate possible intermediꢀ
ates, carbonic acid derivatives (Me3Si)3SiOC(O)OH and
Pri3GeOC(O)OH, probably because of their instability.
The reactions of cobalt tris(trimethylsilyl)siloxide 2
and triisopropylsiloxides 4 and 5 with carbon dioxide are
sharply slowed down after insertion of one mole of CO2.
[(Me3Si)3SiO]2Co + CO2
2
(Me3Si)3SiOC(O)OCoOSi(SiMe3)3, (4)
It is known that the reaction of cobalt(I) tris(triꢀ
methylsilyl)silyltellurolate Co[TeSi(SiMe3)3](PMe3)3
(Pri3SiO)2M + CO2
Pri3SiOC(O)OMOSiPri3. (5)
4, 5
with
CO
affords
the
dicarbonyl
complex
Co(CO)2[TeSi(SiMe3)3](PMe3)3.10 Thus, CO stabilizes
the lowꢀvalent state of the metal favoring, in our case, the
rearrangement of the more electronegative tris(trimethylꢀ
silyl)siloxide substituent to form the cobaltꢀsilyl complex.
Hydrolysis of the isolated carbonyl complex does not reꢀ
cover the initial tri(trimethylsilyl)silanol. Therefore, we
propose the structure of the silylcobaltcarbonyl cluster
(Me3Si)2(Me3SiO)SiCox(CO)y for the isolated compound.
It was difficult to completely characterize the complex
because of its decomposion already at room temperature.
M = Fe (4), Co (5)
The IR spectrum of the product contains simultaꢀ
neously absorption bands corresponding to the FeOSi and
—OC(O)O— fragments. However, the products of inserꢀ
tion of one mole of CO2 were not isolated in the pure
state.
Iron(II) trimethylsiloxide 8 also absorbs СО2 to form a
carbonate complex (according to the IR spectroscopic
data). However, the reaction rate decreases substantially

418
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
Fedotova et al.
and those of complex 10 were obtained by crystallization from a
hexane—benzene (1 : 1) mixture. A solvate benzene molecule
was revealed in the crystal structure of compound 10.
The crystallographic data for compounds 9 and 10 and the
main details of Xꢀray diffraction experiment and refinement of
the structures are presented in Table 2. Positions of H atoms
were calculated from the geometric conditions and refined in
the rider model. Absorption was applied by the SADABS
program.
likely due to a poor solubility of compound 8. Only
0.5 moles of CO2 are absorbed for 3 days.
Unlike other studied compounds, triphenylsiloxide 7
does not react with СО2. The prolonged storage (5 days)
of its toluene solution under CO2 did not show a noticeꢀ
able absorption of the latter.
The kinetics of this reaction in detail is difficult to
study because the system is heterogeneous (gas—soluꢀ
tion) and the oxygen traces exert a substantial effect. Howꢀ
ever, we can conclude at the qualitative level that the
relative reactivity of the iron and cobalt siloxides and
germyloxides decreases with a decrease in the electronꢀ
donating ability of the substituents at the silicon or gerꢀ
manium atom in the series: (Me3Si)3Si > Pri3Ge ≈ Pri3Si >
> Me3Si >> Ph3Si.* The iron compounds manifest someꢀ
what higher reactivity compared to that of analogous coꢀ
balt derivatives. This agrees with the lower redox potential
of iron ϕ°(Fe2+/Fe0) = –0.44 V; ϕ°(Co2+/Co0) = –0.28 V.
It should be noted for comparison that iron(III) siloxide
[(Me3Si)3SiO]3Fe synthesized previously13 reacts with
CO2 rather slowly and does not react with oxygen. Acꢀ
cepting that the polarities of the M—O bonds in the conꢀ
sidered iron and cobalt compounds are approximately the
same, we can assert that the regularities found by us agree
with the earlier11 data on the decisive influence of the
electronꢀdonating ability of the central metal atom on the
СО2 binding.
Iron(II) pentamethyldisiloxide (Me3SiSiMe2O)2Fe (3). Pentaꢀ
methyldisilanol18 (1.93 g, 13.0 mmol) in hexane (15 mL) was
added to a solution of [(Me3Si)2N]2Fe (2.35 g, 6.25 mmol) in
hexane (25 mL). The mixture was heated for 3 h at 50 °C.
A polycrystalline blue precipitate was formed upon concentratꢀ
ing the solution in vacuo. The mother liquor was decanted, and
the precipitate was washed with hexane (the substance lost its
solubility on crystallization). Solvent residues were removed
in vacuo. Compound 3 was obtained as a light blue powder in
92% yield (2.02 g). Found (%): С, 35.01; Н, 8.69; Fe, 15.70.
C10H30Si4O2Fe. Calculated (%): С, 34.26; Н, 8.63; Fe, 15.93.
IR, ν/cm–1: 1240 s, 1060 w, 940 w (SiOFe), 840 s (SiMe3), 810 s
(SiMe2), 690 m, 620 s.
Iron(II) triisopropylsiloxide (Pri3SiO)2Fe (4). To a solution
of [(Me3Si)2N]2Fe (3.33 g, 8.85 mmol) in hexane (25 mL) was
added Pri3SiOH 19 (3.08 g, 17.7 mmol) in hexane (20 mL). The
mixture was heated at 50 °С for 6 h. The green color of the
solution slowly changed to dark green. The solvent and hexaꢀ
methyldisilazane were removed in vacuo at 80 °С. A dark green
oil was obtained in the residue. The yield was 3.38 g (95%).
Found (%): С, 52.94; Н, 10.39; Fe, 13.50. C18H42Si2O2Fe. Calꢀ
culated (%): С, 53.70; Н, 10.52; Fe, 13.87. IR (liquid film,
KBr), ν/cm–1: 1460 s, 1384 m, 1368 m, 1250 w, 1079 m, 1020 m,
1000 m, 889 w, 845 w, 950 s (Si—O—Fe).
Experimental
Cobalt(II) triisopropylsiloxide (Pri3SiO)2Co (5). To a soluꢀ
tion of [(Me3Si)2N]2Co (2.35 g, 6.2 mmol) in benzene (25 mL)
was added a solution of Pri3SiOH 19 (2.16 g, 12.4 mmol) in
benzene (20 mL). The solution changed its color from green to
violet with pouring together the reactants. The reaction mixture
was stored for 10 h at ∼20 °C. The solvent and hexamethylꢀ
disilazane were removed in vacuo at 80 °С. A dark violet oil was
obtained in the residue. The yield was 2.41 g (96%). Found (%):
С, 51.92; Н, 10.19; Co, 13.80. C18H42Si2O2Co. Calculated (%):
All procedures on synthesis, isolation, and purification of
compounds were carried out in vacuo or under argon. Solvents
were purified using standard methods14: hexane was distilled
over sodium, and benzene and toluene were dehydrated and
distilled with Р2О5. Diethyl ether and THF were refluxed with
NaOH and distilled over Na with addition of benzophenone.
Compounds 1 and 2 4 and silylamides [(Me3Si)2N]2M (M = Co
and Fe)15,16 were synthesized according to previously described
procedures. Triphenylsilanol (98%, Aldrich) was used without
additional purification.
С, 53.30; Н, 10.44; Co, 14.53. IR (liquid film, KBr), ν/cm–1
:
1465 s, 1384 m, 1368 m, 1250 w, 1080 m, 1015 m, 1000 m,
889 w, 845 w, 980 s (Si—O—Co).
NMR spectra were recorded on a Bruker DPXꢀ200 instruꢀ
ment (200 MHz) using Me4Si as internal standard.
Iron(II) triisopropylgermyloxide (Pri3GeO)2Fe (6). Triisoꢀ
propylgermanol20 (0.48 g, 2.2 mmol) in hexane (10 mL) was
added to a solution of [(Me3Si)2N]2Fe (0.41 g, 1.1 mmol) in
hexane (10 mL). During mixing of the reactants the green color
of the solution gained a brown tint. The reaction mixture was
stored for 10 h at ∼20 °C. The solvent and hexamethyldisilazane
were removed in vacuo at 80 °С. A greenꢀbrown oil was obtained
in the residue. The yield was 0.52 g (97%). Found (%): С, 49.35;
Н, 8.80; Fe, 10.94. C18H42Ge2O2Fe. Calculated (%): С, 49.98;
Н, 8.61; Fe, 11.36. IR (liquid film, KBr), ν/cm–1: 2900 v.s,
2840 m, 1445 s, 1370 m, 1355 m, 1235 m, 1010 m, 980 m, 870 m;
IR spectra were recorded on a Perkin—Elmerꢀ577 spectroꢀ
photometer in the region from 4000 to 400 cm–1
.
The content of cobalt and iron was determined by photoꢀ
metric titration; 1ꢀnitrosonaphthol was used for cobalt, and
1,10ꢀphenanthroline was applied for iron.17
The products of hydrolysis of the obtained compounds
were analyzed on a Tsvetꢀ530 gas chromatograph (column
0.3×200 cm, Inerton АW with 5% SEꢀ30, thermalꢀconductivity
detector, helium as carrier gas).
Xꢀray diffraction studies of compounds 9 and 10. Single crysꢀ
tals of complex 9 were prepared by crystallization from hexane,
830 s (Ge—O—Fe); 740 w, 640 m; 565 s, ν (Ge—C); 520 w,
as
ν (Ge—C).
s
* This series was chosen based on the additive contribution of
the substituents and analysis of the available inductive constants
of the siliconꢀ and germaniumꢀcontaining organic substituents.12
Iron(II) triphenylsiloxide (Ph3SiO)2Fe (7). Triphenylsilanol
(0.55 g, 2 mmol) in hexane (10 mL) was added to a solution of
[(Me3Si)2N]2Fe (0.37 g, 1.0 mmol) in hexane (10 mL). The

FeII and CoII siloxides and germyloxides
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
419
mixture was heated for 20 min at 80 °С. During this time, a
green crystalline precipitate formed on the tube walls. The solꢀ
vent and hexamethyldisilazane were removed in vacuo at 80 °С.
The solid residue was recrystallized from hexane. Light green
crystals sensitive to oxygen were obtained in 95% yield (0.57 g).
Found (%): С, 71,75; Н, 4.63; Fe, 9.50. C36H30Si2O2Fe. Calcuꢀ
hexane (15 mL) was connected to a mercury burette filled with
СО2. During 3 min at 20 °С, 22 mL (1 mmol) of СО2 were
absorbed. The second mmole of CO2 reacted within 17 min,
after which gas absorption stopped. The solution changed its
yellowꢀgreen color to brown. Hexane was removed to give a
viscous oil, which solidified with time to afford a fineꢀcrystalline
product. Recrystallization of the latter is difficult due to its high
solubility in hexane. The yield was 0.63 g (95%). Found (%):
С, 36.45; Н, 8.20; Fe, 8.07. [(Me3Si)3SiOC(O)O]2Fe
(C20H54Si8O6Fe). Calculated (%): С, 35.79; Н, 8.11; Fe, 8.32.
IR (Nujol, KBr), ν/cm–1: 1530 m, 1380 m (—OC(O)O—),
1240 s (SiMe), 1050 w, 935 m, 840 s (SiMe), 750 m, 700 w,
620 m (SiC3).
Interaction of complex [(Me3Si)3SiO]2Co (2) with СО2. An
evacuated ampule containing complex 2 (0.59 g, 1.0 mmol) in
hexane (15 mL) was connected to a mercury burette filled with
СО2. The first mmole of СО2 was absorbed rapidly (30 min),
then absorption slowed down, and 0.6 mmoles of СО2 were
additionally absorbed during the next day. The dark green color
of the solution changed to dark blue. The solvent was removed
in vacuo from the reaction mixture, and a dark blue oil reꢀ
mained in the residue. IR (liquid film, KBr), ν/cm–1: 1240 m,
840 s (SiMe); 1550 m, 1370 m (—OC(O)O—), 750 m, 680 w,
620 w (SiC3).
Interaction of complex (Pri3SiO)2Fe (4) with СО2. An evacuꢀ
ated ampule containing siloxide 4 (0.40 g, 1.0 mmol) in hexane
(15 mL) was connected to a mercury burette filled with СО2.
During 30 min at 20 °С, 1 mmole of СО2 was absorbed, and
then absorption ceased. The grayꢀgreen color of the solution
deepened during the reaction. Hexane was removed to give a
viscous oil. IR (liquid film, KBr), ν/cm–1: 1550 m, 1385 m
(—OC(O)O—), 1370 m, 1250 w, 1080 m, 1020 m, 1000 m,
925 w, 889 w, 845 w (Pri3Si), 940 m (Si—O—Fe).
Interaction of complex (Pri3SiO)2Co (5) with СО2. An evacuꢀ
ated ampule containing siloxide 5 (0.41 g, 1.0 mmol) in hexane
(15 mL) was connected to a mercury burette filled with СО2.
Under standard conditions, the solution absorbed 22 mL
(1 mmol) of СО2 for 50 min, after which gas absorption slowed
down. Next 24 h resulted in the additional absorption of
0.1 mmoles of CO2. The color of the solution became dark violet
during the reaction. After the solvent was removed, a viscous oil
was obtained. IR (liquid film, KBr), ν/cm–1: 1560 s, 1390 s
(—OC(O)O—), 1385 m, 1365 m, 1250 w, 1080 m, 1020 m,
1000 m, 925 w, 890 w, 845 w (Pri3Si).
lated (%): С, 71.27; Н, 4.98; Fe, 9.21. IR (Nujol, KBr), ν/cm–1
:
1950 w, 1880 w, 1810 w, 1760 w, 1580 m, 1420 m, 1100 s (Ph),
1010 s, 950 s (Si—O—Fe), 870 s, 730 w, 700 s, 500 s (SiC3).
µ
eff = 3.8µ .
B
Iron(II) trimethylsiloxide (Me3SiO)2Fe (8). To a solution of
[(Me3Si)2N]2Fe (3.02 g, 8.0 mmol) in hexane (15 mL) was
added Me3SiOH 21 (1.44 g, 16.0 mmol) in hexane (10 mL).
A white powder precipitated with pouring together the reactants
was filtered off and washed with hexane. The solvent was reꢀ
moved in vacuo at 50 °С. The yield was 1.83 g (98%). Found (%):
C, 30.31; H, 7.71; Fe 23.59. С6H18Si2O2Fe. Calculated (%):
C, 30.76; H, 7.75; Fe 23.84. IR (Nujol, KBr), ν/cm–1: 1240 s
(SiMe3), 1030 w, 950 w (Fe—O—Si), 870 m, 840 (s) (SiMe3),
750 s, 690 m, 680 m (SiMe3); µeff = 3.5µ .
B
Iron
triisopropylgermyloxide
2,2´ꢀbipyridyl
(Pri3GeO)2Fe(bpy) (9) was synthesized similarly to compound 6
by addition of an equivalent amount (1.1 mmol) of 2,2´ꢀbiꢀ
pyridyl. Dark green crystals were recrystallized from hexane and
obtained in 94% yield (0.67 g). Found (%): С, 51.23; Н, 7.95;
Fe, 8.93. C28H50Ge2O2N2Fe. Calculated (%): С, 51.92; Н, 7.78;
Fe, 8.62. IR (Nujol, KBr), ν/cm–1: 1580 m, 1300 w, 1145 w,
980 m, 870 m, 830 s, 760 m, 745 m, 635 m, 550 s.
Bis[bis(trimethylsilylamino)]tetrakis(µ ꢀpentamethylꢀ
2
disiloxy)]triiron benzenemonosolvate, [(Me3Si)2NFe(µꢀ
OSi2Me5)2]2Fe•C6H6 (10). Pentamethyldisilanol18 (0.59 g,
4.0 mmol) in hexane (5 mL) was added to a solution of
[(Me3Si)2N]2Fe (1.13 g, 3.0 mmol) in hexane (15 mL). The
mixture was heated for 3 h at 50 °C. Compound 10 as a solvate
with a benzene molecule was crystallized from a benzene—hexꢀ
ane (1 : 1) mixture by slow cooling of the warm solution
to ∼20 °C. The mother liquor was decanted. Solvent residues
were removed in an argon flow. Compound 10 (0.88 g, 85%) was
obtained as light green crystals. Found (%): С, 38.87; Н, 9.06;
Fe, 14.11. C38H102Si12O4N2Fe3. Calculated (%): С, 39.48;
Н, 8.90; Fe, 14.50. IR, ν/cm–1: 1400 w, 1250 v.s (SiMe3), 970 s,
890 w, 850 s (SiMe3), 800 m (SiMe2), 770 m, 700 m, 680 m,
620 s, 460 s.
Interaction of complex 2 with CO. An ampule containing
complex 2 (0.59 g, 1.0 mmol) in toluene (5 mL) was connected
to a mercury burette filled with СО and stored for 24 h at 20 °C.
The green color of the solution slowly changed to brown. The
total volume of the absorbed gas was 40 mL (1.8 mmol). The
solution was concentrated in vacuo, and the liquid residue was
stored for 1 h at 0 °C. The mother liquor was decanted, and
blackꢀbrown crystals were analyzed by IR spectroscopy. IR,
ν/cm–1: 2040 s, 2030 s, 2000 s, 1870 m (CO), 1240 s (SiMe3),
1050 s (Si—O—Si), 840 v.s (SiMe3). An attempt to recrystallize
the crystals resulted in resinꢀlike products.
Interaction of complex (Pri3GeO)2Fe (6) with СО2. An evacuꢀ
ated ampule containing germyloxide 6 (0.49 g, 1.0 mmol) in
hexane (15 mL) was connected to a mercury burette filled with
СО2. During 15 min at 20 °С, 22 mL (1 mmol) of СО2 were
absorbed. The second mmole of CO2 reacted within 1 h, after
which gas absorption ceased. The grayꢀgreen solution gained a
violet color. Hexane was removed to produce a viscous oil. The
yield was 0.55 g (95%). Found (%): С, 40.87; Н, 7.55; Fe, 9.58.
[Pri3GeOC(O)O]2Fe (C20H42Ge2O6Fe). Calculated (%):
С, 41.45; Н, 7.30; Fe, 9.64. IR (Nujol, KBr), ν/cm–1: 1540 v.s,
1350 s (—OC(O)O—), 1065 m, 1010 m, 630 m, 565 m (Pri3Ge).
Hydrolysis of compounds 1—8. Tetrahydrofuran (3 mL) was
condensed to a degassed weighted sample (∼0.05—0.1 g) of the
analyzed compound, and then a tenfold molar excess of water
was added. The mixture was stored until metal hydroxide comꢀ
pletely precipitated (∼20—30 min) and then was centrifuged.
The precipitate was dried in vacuo and dissolved in a minimal
Interaction of compounds 1, 2, and 4—7 with СО2. The reacꢀ
tions were carried out under similar conditions (1 atm, 20 °С),
and the blank experiment was conducted without the complexes.
Before use, carbon dioxide was purified by twice freezing in
liquid nitrogen followed by passing through P2O5.
Interaction of complex [(Me3Si)3SiO]2Fe (1) with СО2. An
evacuated ampule containing compound 1 (0.58 g, 1.0 mmol) in

420
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
Fedotova et al.
amount of 0.1 N HCl. The metal content was determined by
photometric titration17 and by burning of a weighted sample in
an HClO4—H2SO4 mixture followed by microanalysis.17 The
corresponding silanols and triisopropylgermanol were found in
the centrifugate by GLC.
6. S. S. Batsanov, Zh. Neorg. Khim., 1991, 36, 3015 [J. Inorg.
Chem. USSR, 1991, 36 (Engl. Transl.)].
7. H.ꢀG. Gosink, H. W. Roesky, H.ꢀG. Schmidt,
M. Noltemeyer, E. Irmer, and R. H. Irmer, Organometallics,
1994, 13, 3420.
Hydrolysis of carbonates was performed similarly to the hyꢀ
drolysis of compounds 1—8, and CO2 evolved was determined
chromatographically using Silipor 600 GC as sorbent and voluꢀ
metrically using a mercury burette. The corresponding silanols
or triisopropylgermanol were found in the liquid phase by GLC.
8. O. Vohler, Chem. Ber., 1958, 91, 1161.
9. K. M. Abraham and G. Urry, Inorg. Chem., 1973, 12, 2850.
10. D. E. Gindelberger and J. Arnold, Inorg. Chem., 1993,
32, 5813.
11. X. Yin and J. R. Moss, Coord. Chem. Rev., 1999, 181, 27.
12. A. N. Egorochkin and M. G. Voronkov, Elektronnoe stroenie
organicheskikh soedinenii kremniya, germaniya i olova [Elecꢀ
tronic Structure of Organic Silicon, Germanium, and Tin Comꢀ
pounds], Izdꢀvo SO RAN, Novosibirsk, 2000, 614 pp. (in
Russian).
13. A. N. Kornev, T. A. Chesnokova, V. V. Semenov, E. V.
Zhezlova, L. N. Zakharov, L. G. Klapshina, G. A.
Domrachev, and V. S. Rusakov, J. Organomet. Chem., 1997,
547, 113.
Xꢀray diffraction studies were performed on a
diffractometer kindly presented by the Center of Strucꢀ
tural Studies of the Division of General and Technical
Chemistry of the Russian Academy of Sciences.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos. 00ꢀ15ꢀ97439
and 00ꢀ03ꢀ42004).
14. C. Reichardt, Solvents and Solvent Effects in Organic Chemisꢀ
try, VCH, Weinheim, 1988.
References
15. R. A. Andersen, K. Faegri, J. C. Green, A. Haaland, M. F.
Lappert, W.ꢀP. Leung, and K. Rypdal, Inorg. Chem., 1988,
27, 1782.
16. H. Burger and U. Wannagat, Monatsh. Chem., 1963, 94, 1007.
17. Z. Marczenko, Kolorymetryszne oznaczanie pierwiastkow,
Wydawnictwa NaukowoꢀTechniszne, Warszawa, 1968,
501 pp. (in Polish).
1. (a) M. G. Voronkov, E. A. Maletina, and V. K. Roman,
Geterosiloksany [Heterosiloxanes], Nauka, Novosibirsk,
1984 (in Russian); (b) R. Murugavel, A. Voight, M. G.
Walawalkar, and H. W. Roesky, Chem. Rev., 1996, 96, 2205.
2. F. J. Feher and R. L. Blanski, J. Am. Chem. Soc., 1992,
114, 5886.
18. U. G. Stolberg, Chem. Ber., 1963, 96, 2798.
19. C. Eaborn, J. Chem. Soc., 1952, 2840.
20. H. H. Anderson, J. Am. Chem. Soc., 1953, 75, 814.
21. M. F. Shostakovskii, I. A. Shikhiev, D. A. Kochkin, and
V. I. Belyaev, Zh. Obshch. Khim., 1954, 24, 2202 [J. Gen.
Chem. USSR, 1954, 24 (Engl. Transl.)].
3. (а) A. L. Buchachenko, Usp. Khim., 1990, 59, 529 [Russ.
Chem. Rev., 1990, 59 (Engl. Transl.)]; (b) A. Cornia, A. C.
Fabretti, D. Gatteschi, G. Palyi, E. Rentschler, O. I.
Shchegolikhina, and A. A. Zhdanov, Inorg. Chem., 1995,
34, 5383.
4. A. N. Kornev, T. A. Chesnokova, E. V. Zhezlova, G. K.
Fukin, L. N. Zakharov, and G. A. Domrachev, Dokl. Akad.
Nauk, 1999, 369, 203 [Dokl. Chem., 1999 (Engl. Transl.)].
5. G. A. Sigel, R. A. Bartlett, D. Decker, M. M. Olmstead, and
P. P. Power, Inorg. Chem., 1987, 26, 1773.
Received July 19, 2001;
in revised form September 18, 2002