Guanidinate borohydride derivatives of lanthanides: Synthesis and molecular structures of the [(Me3Si)2NC(NCy)2]Gd(BH 4)2DME and [{(Me3Si)2NC(NPr i)2}2

Article abstract of DOI:10.1007/s11172-007-0270-2

Title full: Guanidinate borohydride derivatives of lanthanides: Synthesis and molecular structures of the [(Me₃Si)₂NC(NCy)₂]Gd(BH ₄)₂DME and [{(Me₃Si)₂NC(NPr ⁱ)_2<

Full text of DOI:10.1007/s11172-007-0270-2

Russian Chemical Bulletin, International Edition, Vol. 56, No. 9, pp. 1742—1748, September, 2007
1742
Guanidinate borohydride derivatives of lanthanides: synthesis and
molecular structures of the [(Me3Si)2NC(NCy)2]Gd(BH4)2DME
and [{(Me3Si)2NC(NPri)2}2Sm(BH4)2]–[Li(DME)3]+ complexes. Catalytic
activity of the [(Me3Si)2NC(NCy)2]2Ln(BH4)2Li(THF)2 complexes
(Ln = Nd, Sm, or Yb) in methyl methacrylate polymerization*
G. G. Skvortsov, M. V. Yakovenko, G. K. Fukin, A. V. Cherkasov, and A. A. Trifonovꢀ
G. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
49 ul. Tropinina, 603950 Nizhny Novgorod, Russian Federation.
Fax: +7 (831) 466 1497. Eꢀmail: trif@iomc.ras.ru
The reaction of Gd(BH4)3(THF)2 with two equivalents of sodium N,N´ꢀdicyclohexylꢀ
N″ꢀbis(trimethylsilyl)guanidinate in THF followed by the treatment of the reaction prodꢀ
uct with 1,2ꢀdimethoxyethane produced the monoguanidinate bis(borohydride) complex
[(Me3Si)2NC(NCy)2]Gd(BH4)2DME (1) (Cy is cyclohexyl). The treatment of the heteroꢀ
bimetallic samarium complex {(Me3Si)2NC(NPri)2}2Sm(BH4)2Li(THF)2, in which the lanꢀ
thanide and lithium atoms are linked by two bridging borohydride groups, with 1,2ꢀdimethoxyꢀ
ethane afforded the ionic complex [{(Me3Si)2NC(NPri)2}2Sm(BH4)2]–[Li(DME)3]+ (2).
The structures of complexes
1 and 2 were established by Xꢀray diffraction. The
[(Me3Si)2NC(NCy)2]2Ln(BH4)2Li(THF)2 complexes (Ln = Nd (3), Sm (4), or Yb (5)) were
found to catalyze methyl methacrylate polymerization.
Key words: lanthanides, guanidinate ligand, N,Nꢀligand, borohydride ligand, synthesis,
structure.
Chelate guanidinate ligands have found wide appliꢀ
chloride derivatives with NaBH4 or LiBH4 in tetrahydroꢀ
furan or diethyl ether.10 A convenient procedure for the
synthesis of both bis(borohydride) and monoborohydride
complexes is based on the reactions of lanthanide
tris(borohydrides) Ln(BH4)3(THF)n with alkali metal salts
LM (M = Na or K) of the corresponding ligands.11,14,16,17
The reactions are completed in 8 h and produce the boroꢀ
hydride complexes in high yields. As a rule, the alkali
metal borohydrides MBH4, which are also formed in the
reactions, do not complicate the isolation of the target
products.
Recently,18 we have found that the reacꢀ
tions of the bis(guanidinate) chloride derivatives
[{(Me3Si)2NC(NPri)2}2LnCl]2 (Ln = Nd or Sm) with
NaBH4 are more complex than those of the cyclopentaꢀ
dienyl derivatives. In some cases, the redistribution of
the ligands was observed, producing monoguanidinate
bis(borohydride) derivatives instead of the expected
bis(guanidinate) borohydride complexes regardless of the
ratio of the starting reagents.
cation in coordination and organometallic chemistry
as stabilizing groups and were used in the synthesis
of a wide range of dꢀtransition and mainꢀgroup metal
derivatives.1 Recently, guanidinate ligands have been
successfully used in the chemistry of rare earth metals
for the synthesis of highly reactive alkyl and hydride
derivatives.2—9 Lanthanide borohydride complexes are
of great interest because of their structural diversity10
and high catalytic activity in polymerization of lacꢀ
tones,11,12 methyl methacrylate,13 and isoprene.14 Reꢀ
cently, we have synthesized and characterized a series
of lanthanide bis(guanidinate) borohydride complexes.
The use of these complexes as initiators for the polyꢀ
merization of lactides allows the reactions to be perꢀ
formed at high rate at room temperature under conꢀ
trolled conditions resulting in the formation of highꢀ
molecularꢀweight polymers with very low polydisperꢀ
sity (1.09).15
Metalloceneꢀtype borohydride complexes are generꢀ
ally synthesized by the reactions of the corresponding
In the present study, we synthesized new
guanidinate borohydride derivatives of lanthanides
and investigated the catalytic activity of the
[(Me3Si)2NC(NCy)2]2Ln(BH4)2Li(THF)2 complexes
* Dedicated to Academician G. A. Abakumov on the occasion
of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1680—1686, September, 2007.
1066ꢀ5285/07/5609ꢀ1742 © 2007 Springer Science+Business Media, Inc.

Lanthanide borohydride complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
1743
(Ln = Nd, Sm, or Yb; Cy is cyclohexyl) in methyl methꢀ
acrylate (MMA) polymerization.
H(2D)
H(2C)
C(14)
C(16)
Si(1)
H(2A)
H(2B)
B(2)
Results and Discussion
H(1D)
H(1A)
C(2)
N(1)
C(1)
For the aboveꢀmentioned reasons, we synthesized
guanidinate borohydride derivatives of lanthanides by the
reactions of tris(borohydrides) Ln(BH4)3(THF)n with soꢀ
dium or lithium guanidinates.
B(1)
C(15)
C(19)
Si(2)
N(3)
H(1B)
H(1C)
O(1)
Gd(1)
N(2)
C(8)
We studied the reaction of gadolinium tris(boroꢀ
hydride) Gd(BH4)3(THF)2 with two equivalents of
{(Me3Si)2NC(NCy)2}Na, which was prepared in situ from
(Me3Si)2NNa and N,Nꢀdicyclohexylcarbodiimide, in
tetrahydrofuran (65 °C). The separation of the precipitate
of NaBH4 that formed, the removal of the solvent
in vacuo, the treatment of the residue with 1,2ꢀdiꢀ
methoxyethane (DME), and the subsequent recrystalliꢀ
zation of the reaction product from toluene were found to
afford the monoguanidinate bis(borohydride) complex
{(Me3Si)2NC(NCy)2}Gd(BH4)2DME (1) instead of the
bis(guanidinate) borohydride derivative. Complex 1 was
isolated in 38% yield (Scheme 1).
O(2)
C(18)
C(17)
Fig. 1. Structure of the monoguanidinate bis(borohydride) comꢀ
plex {(Me3Si)2NC(NCy)2}Gd(BH4)2DME (1). Displacement
ellipsoids are drawn at the 30% probability level.
Table 1. Selected bond lengths (d) and bond angles (ω) in
complex 1
Parameter
Bond
Value
Parameter
Value
d/Å
Bond
d/Å
1.335(2)
1.324(2)
Scheme 1
Gd(1)—N(1) 2.3676(15)
Gd(1)—N(2) 2.3797(15)
Gd(1)—O(1) 2.4894(13)
Gd(1)—O(2) 2.4392(14)
C(1)—N(1)
C(1)—N(2)
Angle
ω/deg
Gd(1)—B(1)
Gd(1)—B(2)
2.596(2)
2.578(2)
N(1)—Gd(1)—N(2)
B(2)—Gd(1)—B(1) 104.79(9)
56.09(5)
linium atom in compound 1 is coordinated by two niꢀ
trogen atoms of the chelate guanidinate ligand, two oxyꢀ
gen atoms of the DME molecule, and two borohydride
groups BH4. The borohydride ligands are µ3ꢀcoordiꢀ
nated to the metal atom through three hydrogen
atoms. The Gd—µ2(H) distances are in the range of
2.27(3)—2.42(3) Å. The Gd—B distances are slightly difꢀ
ferent (2.578(2) and 2.596(2) Å). The tridentate coordiꢀ
nation of the borohydride ligands is confirmed by the
IR spectrum of compound 1, in which these ligands are
observed as four broad bands at 2165, 2227, 2338, and
2438 cm–1 (see Ref. 10). The Gd—N bond lengths are
only slightly different (2.368(2) and 2.380(2) Å). The
C—N distances are 1.335(2) and 1.324(2) Å and characꢀ
terize the negative charge delocalization in the NCN fragꢀ
ment of the guanidinate ligand. The B(1)—Gd—B(2)
bond angle in 1 is 104.79(9)°. The Gd—O bond
lengths are 2.439(1) and 2.489(1) Å. Only two strucꢀ
turally characterized lanthanide bis(borohydride) comꢀ
plexes, (C5Pri4H)Nd(BH4)2THF (see Ref. 14) and
{(Me3Si)2NC(NPri)2}Sm(BH4)2DME,18 were described
in the literature. When developing procedures for the synꢀ
thesis of lanthanide bis(guanidinate) borohydride comꢀ
Transparent colorless crystals of complex 1 were grown
by slow evaporation of its toluene solution at room temꢀ
perature. Complex 1 crystallizes in the space group P–1
with two molecules in the unit cell. The molecular strucꢀ
ture of complex 1 is shown in Fig. 1. The selected bond
lengths and bond angles are given in Table 1.
The Xꢀray diffraction study showed that complex 1
exists as a monomer in the crystalline state. The gadoꢀ

1744
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Skvortsov et al.
Scheme 2
plexes, it was noted18 that the treatment of the products,
which were obtained in the reaction of Ln(BH4)3(THF)2
with (Me3Si)2NC(NR2)M (R = Pri or Cy; M = Li or Na)
in a molar ratio of 1 : 2, with 1,2ꢀdimethoxyethane afꢀ
forded monoguanidinate bis(borohydride) derivatives.
We hypothesized that the ligand redistribution occurs durꢀ
ing the treatment of the complexes with dimethoxyethane
and is provoked by the replacement of monodentate THF
in the coordination sphere of the lanthanide atom by
bidentate DME. To verify this hypothesis, we carried out
the following experiment. The heterobimetallic complex
{(Me3Si)2NC(NPri)2}2Sm(BH4)2Li(THF)2, whose strucꢀ
ture has been determined in our earlier study,19 was disꢀ
solved in DME, and the residue, which was obtained after
evaporation of the solution in vacuo, was recrystalꢀ
lized from hexane. The recrystallization afforded the
[{(Me3Si)2NC(NPri)2}2Sm(BH4)2]–[Li(DME)3]+ comꢀ
plex (2) in 63% yield (Scheme 2).
plex {(Me3Si)2NC(NPri)2}Sm(BH4)2DME (2.607(3) and
2.615(4) Å)18 but are substantially shorter than those in
the dinuclear complex [(1,3ꢀBut ꢀC5H3)2Sm(BH4)]2
2
with the bridging borohydride ligands (2.833(6) and
2.882(6) Å).20 The Sm—N distances are in the range of
2.436(3)—2.474(3) Å. The C—N bond lengths in the NCN
fragments in complex 2 (1.311(4)—1.329(5) Å), like those
in complex 1, are indicative of the electron density deloꢀ
calization in these fragments. The B(1)—Sm—B(2) bond
angle in 2 (94.1(2)°) differs substantially from the correꢀ
Si(1)
N(3)
Si(2)
Transparent yellow crystals of complex 2 suitable for
Xꢀray diffraction were grown by slow evaporation of a
C(1)
N(1)
H(2BA)
H(2BB)
B(2)
H(2BD)
N(2)
hexane solution of the complex at room temperature.
–
Complex 2 crystallizes in the space group P1 with eight
H(2BC)
H(1BD)
molecules in the unit cell. Since the geometric characterꢀ
istics of independent molecules 2 have similar values, the
geometry of only one molecule is discussed below. Acꢀ
cording to the Xꢀray diffraction study, compound 2
exists in the crystalline state as a separated ion pair
(Fig. 2). Complex 2 consists of the complex anion
[{(Me3Si)2NC(NPri)2}2Sm(BH4)2]–, in which the trivaꢀ
lent samarium cation is coordinated by two guanidinate
and two borohydride anions, and the [Li(DME)3]+
cation. The borohydride ligands are coordinated to
the metal atom through the µ2ꢀbridging hydrogen atoms.
The Sm—µ2(H) distances are in the range of
2.32(4)—2.52(3) Å. The µ3ꢀcoordination of the BH4
groups is confirmed by the IR spectrum, in which the
BH4 groups are observed as four broad bands at 2235,
Sm(1)
B(1)
H(1BC)
H(1BA)
H(1BB)
N(4)
N(5)
C(14)
Si(4)
N(6)
Si(3)
Fig. 2. Structure of the mononuclear ionic complex
[{(Me3Si)2NC(NPri)2}2Sm(BH4)2]–[Li(DME)3]+ (2). Displaceꢀ
ment ellipsoids are drawn at the 30% probability level. The
isopropyl substituents at the nitrogen atoms and the [Li(DME)3]+
cation are omitted.
2265, 2324, and 2388 cm–1 7
. The Sm—B distances
(2.666(5) and 2.680(5) Å; Table 2) are substantially
longer than those in the neutral bis(borohydride) comꢀ

Lanthanide borohydride complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
1745
Table 2. Selected bond lengths (d) and bond angles (ω) in
complex 2*
It is known that lanthanide borohydride complexes
are catalytically active in the polymerization of both polar
(methyl methacrylate22 and εꢀcaprolactone11) and nonꢀ
polar (isoprene)14 monomers. As expected, the catalytic
properties of metalloceneꢀtype borohydride derivatives
have been studied in most detail, whereas the data on the
catalytic properties of borohydride complexes in the
noncyclopentadienyl ligand environment are still scarce.
Recently,15 we have reported the synthesis and strucꢀ
tures of the {(Me3Si)2NC(NCy)2}2Ln(BH4)2Li(THF)2
complexes (Ln = Nd (3), Sm (4), or Yb(5)), which proved
to be active catalysts for the polymerization of lactides
accompanied by the ring opening. The use of complexes
3—5 as initiators for the polymerization of lactides allows
the reaction to be performed at high rate at room temꢀ
perature under controlled conditions resulting in the forꢀ
mation of highꢀmolecularꢀweight polymers with very low
polydispersity (1.09).15 Hence, it was of interest to study
the catalytic activity of the resulting complexes in the
polymerization of other polar monomers, for example,
of MMA. We investigated the catalytic activity of comꢀ
plexes 3—5 in MMA polymerization. The reaction was
carried out in toluene at (21 0.5) °C under conditions
precluding exposure to atmospheric oxygen and moisture
with the use of different catalystꢀtoꢀmonomer ratios. The
rate of polymerization in the initial step (up to the conꢀ
version of 10%) was measured by the dilatometric method,
and the weighting method was used for studying higher
degrees of conversion. Since the polymerization catalyzed
by samarium complex 4 starts already at negative temꢀ
peratures, the rate of polymerization at 21 °C cannot be
studied by the dilatometric method.
Parameter
Bond
Value
Parameter
Value
d/Å
Bond
d/Å
Sm(1)—N(1) 2.467(3)
Sm(1)—N(2) 2.474(3)
Sm(1)—N(4) 2.444(3)
Sm(1)—N(5) 2.436(3)
Sm(1)—B(1) 2.666(5)
N(5)—C(14)
Sm(1)—B(2)
1.326(4)
2.680(5)
Angle
ω/deg
N(1)—Sm(1)—N(2) 53.86(9)
N(5)—Sm(1)—N(4) 54.38(9)
B(1)—Sm(1)—B(2)
N(1)—C(1)
N(2)—C(1)
1.329(5)
1.311(4)
94.1(2)
N(4)—C(14) 1.323(4)
* The geometric characteristics for one independent molecule
are given.
sponding angle in the neutral bis(borohydride) complex
{(Me3Si)2NC(NPri)2}Sm(BH4)2DME (102.52(13)°).18
It was of interest to consider the differences in
the geometry of mononuclear complexes
2 and
{(Me3Si)2NC(NPri)2}Sm(BH4)2DME in terms of the fillꢀ
ing of the coordination sphere of Sm cations. The calꢀ
culated degree of filling of the coordination sphere of
samarium in 2 is 85.5(2)%,21 which is substantially
larger than that in {(Me3Si)2NC(NPri)2}Sm(BH4)2DME
(81.6(2)%), and, consequently, the nonbonded interꢀ
actions between the ligands in the coordination sphere
of 2 should also be somewhat stronger. Apparently,
due to this fact the Sm—B and Sm—N distances
in 2 (2.436(3)—2.474(3) Å) are longer than those
in {(Me3Si)2NC(NPri)2}Sm(BH4)2DME (Sm—N,
2.374(2)—2.395(2) Å), whereas the BSmB angle
is smaller. In addition, it becomes clear why the
Figures 3 and 4 show the plots of the degree of converꢀ
sion of MMA vs. the reaction time at different concentraꢀ
tions of complexes 3 and 5. It can be seen that the time
dependence of the conversion has a linear character at
lower degrees of conversion.
treatment
of
the
heterobimetallic
complex
{(Me3Si)2NC(NPri)2}2Sm(BH4)2Li(THF)2 with diꢀ
methoxyethane affords the separated ion pair (2). The
Li cation is shielded by three DME molecules, and the
degree of filling of its coordination sphere is 89.7(7)%.
Apparently, this is the reason why this cation cannot be
coordinated by BH4– anions.
N (%)
Therefore, it can be concluded that the treatꢀ
ment with dimethoxyethane can lead to the
transformation of the heterobimetallic complexes
{(Me3Si)2NC(NPri)2}2Sm(BH4)2Li(THF)2 into the
2
1
8
6
4
2
ionic
complexes
[{(Me3Si)2NC(NPri)2}2Smꢀ
(BH4)2]–[Li(DME)3]+; however, no disproportionaion of
the complexes was observed.
3
Compounds 1 and 2 are sensitive to atmospheric oxyꢀ
gen and moisture, but they are stable during storage over a
long period of time in vacuo or under an inert atmosphere
at room temperature. Complexes 1 and 2 are readily
soluble in ethers, as well as in aromatic and even aliphatic
hydrocarbons, which substantially hinders their isolation
by recrystallization and decreases the yields of the crystalꢀ
line products.
0
2
4
t/min
Fig. 3. Plot of the conversion (N ) of methyl methacrylate vs. the
time of polymerization in the presence of complex 3 (T =
21 0.5 °C; toluene; C0Cat/mol L–1: 5.70•10–3 (1), 4.66•10–3 (2),
3.00•10–3 (3); C0MMA/mol L–1: 4.67 (1), 4.66 (2), 4.65 (3),
C0MMA/C0cat: 1/820 (1), 1/1000 (2), 1/1550 (3)).

1746
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Skvortsov et al.
with the molecular weight Mw = 88856 g mol–1, Mn
=
N (%)
57979 g mol–1 and the polydispersity factor Mw/Mn = 1.53.
According to the NMR data, the polymerization affords a
heterotactic polymer, with syndiotactic triads predomiꢀ
nating. The percentage of isoꢀ, heteroꢀ, and syndiotactic
triads is 51, 12, and 37%, respectively. The reaction rate
of polymerization in the presence of neodymium comꢀ
plex 4 is substantially lower. The conversion reaches 39.4%
during the same time. The resulting polymer has the
1
3
2
1
2
3
higher molecular weight (Mw = 226139 g mol–1, Mn
=
615045 g mol–1) and a broader molecular weight distribuꢀ
tion (Mw/Mn = 2.72). In the heterotactic polymer, the
percentage of isoꢀ, heteroꢀ, and syndiotactic triads is 31,
34, and 35%, respectively. Ytterbium complex 5 is the
least active in the series of the compounds under considꢀ
eration; the yield of PMMA is 32.1% after 8 h. The reꢀ
0
2
4
t/min
Fig. 4. Plot of the conversion (N ) of methyl methacrylate vs. the
time of polymerization in the presence of complex 5 (T =
21 0.5 °C; toluene; C0Cat/mol L–1: 5.70•10–3 (1), 4.66•10–3 (2),
3.00•10–3 (3); C0MMA: 4.65/mol L–1 (1—3); C0MMA/C0
1/816 (1), 1/1000 (2), 1/1550 (3)).
:
cat
sulting polymerization has the molecular weight Mw
=
94130 g mol–1, Mn = 57726 g mol–1, and the polydisperꢀ
sity factor Mw/Mn = 1.63. In the resulting heterotactic
polymer, the percentage of isoꢀ, heteroꢀ, and syndiotactic
triads is 52, 32, and 16%, respectively. For all three cataꢀ
lysts, the kinetic curves flatten within 6—7 h (see Fig. 5),
and the yield of the polymer changes only slightly with
reaction time. Most likely, this observation is attributed
to the decomposition of the catalyst in the course of polyꢀ
merization.
A comparison of the catalytic activities of complexes 3
and 5 at the catalystꢀtoꢀmonomer ratios under study shows
that neodymium complex 3 is more active in MMA polyꢀ
merization. For example, the conversion with the use
of complex 3 as the catalyst ([MMA]0/[3]0 = 1/820)
reaches 8% during 3 min, whereas the conversion in the
presence of ytterbium complex 5 during this time is lower
than 4%. The investigation of the catalytic activity of
complexes 3—5 in MMA polymerization at higher deꢀ
To
new
summarize,
guanidinate
we
synthesized
the
grees of conversion was performed by the weighting
bis(borohydride)
complex
Cat
method (T = 21 0.5 °C; C0
= 0.3•10–2 mol L–1
;
[(Me3Si)2NC(NCy)2]Gd(BH4)2DME (1). The treatꢀ
[MMA]0/[Cat]0 = 1/1550). The catalytic activity of the
lanthanide bis(guanidinate) borohydride complexes in the
methyl methacrylate polymerization decreases in the seꢀ
ries Sm > Nd > Yb (Fig. 5). Therefore, no correlation
between the catalytic activity of complexes 3—5 in MMA
polymerization and the ionic radius of lanthanides
was observed (ionic radii: Nd, 0.983 Å; Sm, 0.958 Å;
Yb, 0.868 Å).23
ment
of
the
heterobimetallic
complex
{(Me3Si)2NC(NPri)2}2Sm(BH4)2Li(THF)2, which conꢀ
tains two bridging borohydride anions between
the
samarium
and
affords
lithium
the
atoms,
ionic
with
complex
dimethoxyethane
[{(Me3Si)2NC(NPri)2}2Sm(BH4)2]–[Li(DME)3]+ (2).
However, no disproportionation of the complexes was
observed. The {(Me3Si)2NC(NCy)2}2Ln(BH4)2Li(THF)2
complexes (Ln = Nd (3), Sm (4), or Yb (5)) catalyze
MMA polymerization at room temperature, the cataꢀ
lytic activity of the complexes decreasing in the series
Sm > Nd > Yb.
In the methyl methacrylate polymerization in the
presence of samarium complex 4, the conversion
reaches 62.3% during 8 h. The reaction affords a polymer
N (%)
1
Experimental
60
The complexes were synthesized under conditions precludꢀ
ing exposure to atmospheric oxygen and moisture with the use of
the standard Schlenk technique. Tetrahydrofuran, hexane, and
toluene were dried over sodium benzophenone ketyl, thoroughly
degassed, and condensed in vacuo into a reaction tube immediꢀ
ately before use. The IR spectra were recorded on a Specord
M80 instrument as degassed Nujol mulls. The 1H, 7Li, 11B,
and 13C NMR spectra were measured on a Bruker DPX 200
instrument. Anhydrous LnCl3,24 (Me3Si)2NLi(Et2O), and
(Me3Si)2NNa,25 as well as Ln(BH4)3(THF)n,26 were syntheꢀ
sized according to known procedures. N,N´ꢀDiisopropylcarboꢀ
diimide, N,N´ꢀdicyclohexylcarbodiimide, and NaBH4 were
2
40
3
20
0
2
4
6
t/h
Fig. 5. Plot of the conversion of MMA vs. the time of polymerꢀ
ization in the presence of complexes 3 (1), 4 (2), and 5 (3)
Cat
MMA
(C0
=
3.00•10–3 mol L–1
;
C0
= ;
4.65 mol L–1
C0MMA/C0 = 1/1550, toluene, T = 21 0.5 °C).
cat

Lanthanide borohydride complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
1747
commercial reagents (Acros). N,N´ꢀDiisopropylcarbodiimide
was used after drying with A4 molecular sieves and condensation
in vacuo; NaBH4 was used without additional purification. The
chemical shifts are given in ppm relative to the known shifts of
the residual protons of the deuterated solvents. The molecular
weight distribution was determined on a Waters gel permeation
chromatograph equipped with a Rꢀ403 differential refractomeꢀ
ter (Waters) as the detector with the use of tetrahydrofuran as
the eluent. The calibration was performed with narrowꢀdisperse
polystyrene standards.
[{(Me3Si)2NC(NꢀPri)2}2Sm(BH4)2]–[Li(DME)3]+ (2). The
{(Me3Si)2NC(NꢀPri)2}2Sm(BH4)2Li(THF)2 complex (0.17 g,
0.19 mmol) was dissolved in DME. Then DME was removed
in vacuo at room temperature. The solid residue was dissolved in
hexane (20 mL). The hexane solution was slowly concentrated
at room temperature, and yellow crystals of complex 2 were
obtained in a yield of 0.124 g (0.12 mmol, 63%). Found (%):
C, 43.82; H, 10.15; Sm, 14.22. C38H102B2LiN6O6Si4Sm. Calcuꢀ
lated (%): C, 44.29; H, 9.98; Sm, 14.59. IR (Nujol mulls),
ν/cm–1: 2388, 2324, 2265, 2235, 1638, 1327, 1257, 1116, 1081,
1049, 956, 920, 842, 760, 686, 662.
[N,N´ꢀDicyclohexylꢀN´ꢀbis(trimethylsilyl)guanidinate]ꢀ
bis(borohydride)gadolinium(III)
dimethoxyethanate,
(1). The
Methyl methacrylate polymerization catalyzed by complexes
3, 4, and 5 (general procedure). Methyl methacrylate (1.81 g,
18.1 mmol) was added to a solution of complex 3 (0.0128 g,
0.012 mmol) in toluene (1.94 mL), and the mixture was placed
in a thermostat at 21 0.5 °C. After 8 h, the reaction tube was
opened, air was admitted into the tube, and one drop of methaꢀ
nol was added. The solution was filtered to separate the hydrolyꢀ
sis products of the catalyst. Then the polymer was precipitated
from the toluene solution with hexane, filtered off, washed with
methanol and hexane, and dried to constant weight in vacuo at
room temperature. Poly(methyl methacrylate) was isolated in a
yield of 1.13 g.
Xꢀray diffraction study. Experimental Xꢀray intensities were
measured on an automated Smart APEX diffractometer (graphite
monochromator, MoKα radiation, ω—ϕꢀscanning technique)
at 100 K. All structures were solved by direct methods and reꢀ
fined by the leastꢀsquares method based on F 2hkl with anisotroꢀ
pic displacement parameters for all nonhydrogen atoms. All
H atoms (except for the hydrogen atoms of the BH4 groups)
were positioned geometrically and refined using a riding model.
The hydrogen atoms of the BH4 groups were located in differꢀ
{(Me3Si)2NC(NꢀCy)2}Gd(µ3–BH4)2DME
Gd(BH4)3(THF)2 compound (0.73 g, 2.11 mmol) was added to
a solution of sodium guanidinate, which was prepared by the
reaction of (Me3Si)2NNa (0.76 g, 4.15 mmol) with N,N´ꢀdiꢀ
cyclohexylcarbodiimide (0.86 g, 4.17 mmol), in THF (50 mL).
The reaction mixture was stirred at 65 °C for 14 h. Tetrahydroꢀ
furan was removed by vacuum condensation, and the solid resiꢀ
due was extracted with toluene to separate NaBH4 that formed.
The toluene extract was filtered, and toluene was removed
in vacuo at room temperature. The solid residue was dissolved in
DME (15 mL), and the solvent was removed in vacuo at room
temperature. After recrystallization of the residue from toluene,
colorless crystals of 1 were obtained in a yield of 0.25 g
(0.39 mmol, 38%). Found (%): C, 42.35; H, 9.33; Gd, 24.17.
C23H58B2GdN3O2Si2. Calculated (%): C, 42.91; H, 9.08;
Gd, 24.43. IR (Nujol mulls), ν/cm–1: 2438, 2338, 2227, 2165,
1638, 1304, 1254, 1180, 1050, 1008, 942, 865, 842, 757, 723,
680, 642.
Bis[N,N´ꢀdiisopropylꢀN´´ꢀbis(trimethylsilyl)guanidinate]ꢀ
di(tetrahydroborato)tris(dimethoxyethane)lithiumsamarium(III),
Table 3. Crystallographic parameters and the Xꢀray diffraction data collection and refinement
statistics for complexes 1 and 2
Parameter
1
2
Molecular formula
Molecular weight
Space group
a/Å
b/Å
C23H58B2GdN3O2Si2
643–.77
C38H102B2LiN6O6Si4Sm
1030.52
–
P1
P1
8.3942(5)
10.3568(6)
19.740 (1)
98.293(1)
97.319(1)
101.776(1)
1640.6(2)
2
23.3000(8)
23.6675(8)
24.1504(8)
98.184(1)
97.248(1)
112.722(1)
11917.4(7)
8
c/Å
α/deg
β/deg
γ/deg
V/A3
Z
ρ
calc/g cm–3
1.303
2.116
1.149
1.106
µ/mm–1
θꢀScan range/deg
2.04 – 29.18
17095
8561 (Rint = 0.0157)
330
1.61 – 25.00
94273
41805 (Rint = 0.0764)
2268
Number of measured reflections
Number of reflections with I > 2σ
Number of variables
Goodnessꢀofꢀfit
1.084
0.922
R1/wR2 (I > 2σ(I ))
R1/wR2 (based on all reflections)
Residual electron
density, max/min, е Å–3
0.0219/0.0552
0.0236/0.0563
1.153/–0.765
0.0513/0.0950
0.1061/0.1070
1.537/–0.616

1748
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Skvortsov et al.
ence electron density maps and refined isotropically. All calcuꢀ
lations were carried out with the use of the SHELXTL v. 6.10
program package.27 Absorption corrections were applied using
the SADABS program.28 Principal crystallographic parameters
and the Xꢀray diffraction data collection and refinement statisꢀ
tics are given in Table 3. The atomic coordinates were deposꢀ
ited with the Cambridge Structural Database (CCDC 649132
and 649133 for complexes 1 and 2, respectively). The spectroꢀ
scopic and Xꢀray diffraction studies were carried out at the
Analytical Center of the G. A. Razuvaev Institute of Organomeꢀ
tallic Chemistry of the Russian Academy of Sciences.
10. M. Ephritikhine, Chem. Rev., 1997, 97, 2193.
11. I. Pallard, A. Soum, and S. M. Guillaume, Chem. Eur. J.,
2004, 10, 4054.
12. F. Bonnet, A. R. Cowley, and P. Mountford, Inorg. Chem.,
2005, 44, 9046.
13. F. Bonnet, A. C. Hilier, A. Collins, S. R. Dubberley, and
P. Monutford, Dalton Trans., 2005, 421.
14. D. BarbierꢀBaudry, O. Blacque, A. Hafid, A. Nyassi,
H. Sitzmann, and M. Visseaux, Eur. J. Inorg. Chem.,
2000, 2333.
15. G. G. Skvortsov, M. V. Yakovenko, P. M. Castro, G. K.
Fukin, A. V. Cherkasov, J.ꢀF. Carpentier, and A. A. Trifonov,
Eur. J. Inorg. Chem., 2007, 3260.
16. M. Visseaux, T. Chenal, P. Roussel, and A. Mortreux,
J. Organomet. Chem., 2006, 691, 86.
17. F. Yuan, Y. Zhu, and L. Xiong, J. Organomet. Chem., 2006,
691, 3377.
18. A. A. Trifonov, G. G. Skvortsov, D. M. Lyubov, G. K.
Fukin, E. A. Fedorova, and M. N. Bochkarev, Izv. Akad.
Nauk, Ser. Khim., 2005, 2433 [Russ. Chem. Bull., Int. Ed.,
2005, 54, 2511].
19. G. G. Skvortsov, M. V. Yakovenko, G. K. Fukin, E. V.
Baranov, Yu. A. Kurskii, and A. A. Trifonov, Izv. Akad.
Nauk, Ser. Khim., 2007, 441 [Russ. Chem. Bull., Int. Ed.,
2007, 56, 456].
20. Y. K. Gun´ko, B. M. Bulychev, G. L. Soloveichik, and V. K.
Belsky, J. Organomet. Chem., 1992, 424, 289.
21. I. A. Guzei and M. Wendt, Dalton Trans., 2006, 33, 3991.
22. F. Bonnet, A. C. Hillier, A. Collins, S. R. Duberley, and
P. Mountford, Chem. Commun., 2005, 421.
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 05ꢀ03ꢀ32390
and 06ꢀ03ꢀ32728ꢀa) and the Council on Grants of the
President of the Russian Federation (Program for State
Support of Leading Scientific Schools of the Russian Fedꢀ
eration, Grants NShꢀ4947.2006.3 and NShꢀ8017.2006.3,
and the Program for State Support of Young Scientists,
Grant MKꢀ8752.2006.3).
A. A. Trifonov thanks the Russian Science Support
Foundation for financial support.
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Received May 31, 2007