Hydrido complexes of yttrium and lutetium supported by bulky guanidinato ligands [Ln(μ-H){(Me3Si)2NC(NCy)2} 2]2 (Ln = Y, Lu): Synthesis, structure, and reactivity

Article abstract of DOI:10.1002/ejic.200701343

Lewis base free hydrido complexes of yttrium and lutetium supported by bulky cyclohexyl-substituted guanidinato ligands, [Ln(μ-H){(Me ₃Si)₂NC(NCy)₂}₂]₂ (Ln = Y, Lu), were synthesized and characterized. Single-crystal X-ray diffraction studies revealed dimeric structures. ¹H NMR spectroscopy shows that complex [Y(μ-H){(Me₃Si)₂NC(NCy)₂} ₂]₂ retains its dimeric structure in C₆D ₆ solution. Scrambling of the hydrido complexes [Ln(μ-H){(Me ₃Si)₂NC(NCy)₂}₂]₂ (Ln = Y, Lu) in C₆D₆ resulted in an equilibrium mixture containing the heterodimetallic species [{(Me₃Si)₂NC(NCy) ₂}₂Y(μ-H)₂-Lu{(Me₃Si) ₂NC(NCy)₂}₂], indicating the dissociation of dimers and the presence of monomeric species in solution. Both compounds initiate the polymerization of ethylene: the activity of the cyclohexyl-substituted yttrium complex, [Y(μ-H){(Me₃Si) ₂NC(NCy)₂}₂]₂, is much lower than that of the isopropyl-substituted analogue, [Y(μ-H){(Me₃Si) ₂NC(NiPr)₂}₂]₂, while in the case of lutetium the activities of [Ln(μ-H){(Me₃Si)₂-NC(NR) ₂}₂]₂ (R = iPr, Cy) are similar. Complexes [Ln(μ-H){(Me₃Si)₂NC(NR)₂}₂] ₂ (Ln = Y, Lu; R = iPr, Cy) were shown to catalyze efficiently the hydrosilylation of 1-nonene with PhSiH₃ (at a 1:1 substrates mol ratio) to give the terminal silane PhSiH₂(n-C₉H ₁₉) exclusively. If the hydrosilylation reaction is carried out in the presence of a twofold molar excess of 1-nonene, double addition takes place and leads to the formation of tertiary silane PhSiH(n-C₉H ₁₉)₂, which was obtained in 96% yield. The hydrido complexes [Ln(μ-H)-{(Me₃Si)₂NC(NiPr)₂} ₂]₂ (Ln = Y, Lu) efficiently initiate the ring-opening polymerization of ε-caprolactone to give polymers with molar mass up to 80000. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200701343

FULL PAPER
DOI: 10.1002/ejic.200701343
Hydrido Complexes of Yttrium and Lutetium Supported by Bulky Guanidinato
Ligands [Ln(µ-H){(Me3Si)2NC(NCy)2}2]2 (Ln = Y, Lu): Synthesis, Structure,
and Reactivity
Dmitrii M. Lyubov,[a] Alexey M. Bubnov,[a] Georgy K. Fukin,[a] Fedor M. Dolgushin,[b]
Mikhail Yu. Antipin,[b] Olivier Pelcé,[c] Michèle Schappacher,[c] Sophie M. Guillaume,*[c][‡]
and Alexander A. Trifonov*[a]
Keywords: Rare earths / Alkyl complexes / Hydrido complexes / Guanidinato ligands / Polymerization / Hydrosilylation
Lewis base free hydrido complexes of yttrium and lutetium
supported by bulky cyclohexyl-substituted guanidinato li-
gands, [Ln(µ-H){(Me3Si)2NC(NCy)2}2]2 (Ln = Y, Lu), were
synthesized and characterized. Single-crystal X-ray diffrac-
tion studies revealed dimeric structures. 1H NMR spec-
troscopy shows that complex [Y(µ-H){(Me3Si)2NC(NCy)2}2]2
retains its dimeric structure in C6D6 solution. Scrambling of
the hydrido complexes [Ln(µ-H){(Me3Si)2NC(NCy)2}2]2 (Ln =
Y, Lu) in C6D6 resulted in an equilibrium mixture containing
the heterodimetallic species [{(Me3Si)2NC(NCy)2}2Y(µ-H)2-
Lu{(Me3Si)2NC(NCy)2}2], indicating the dissociation of di-
mers and the presence of monomeric species in solution.
Both compounds initiate the polymerization of ethylene: the
activity of the cyclohexyl-substituted yttrium complex, [Y(µ-
H){(Me3Si)2NC(NCy)2}2]2, is much lower than that of the iso-
propyl-substituted analogue, [Y(µ-H){(Me3Si)2NC(NiPr)2}2]2,
whilein thecaseof lutetiumtheactivities of [Ln(µ-H){(Me3Si)2-
NC(NR)2}2]2 (R = iPr, Cy) are similar. Complexes [Ln(µ-
H){(Me3Si)2NC(NR)2}2]2 (Ln = Y, Lu; R = iPr, Cy) were shown
to catalyze efficiently the hydrosilylation of 1-nonene with
PhSiH3 (at a 1:1 substrates mol ratio) to give the terminal
silane PhSiH2(n-C9H19) exclusively. If the hydrosilylation re-
action is carried out in the presence of a twofold molar excess
of 1-nonene, double addition takes place and leads to the
formation of tertiary silane PhSiH(n-C9H19)2, which was ob-
tained in 96% yield. The hydrido complexes [Ln(µ-H)-
{(Me3Si)2NC(NiPr)2}2]2 (Ln = Y, Lu) efficiently initiate the
ring-opening polymerization of ε-caprolactone to give poly-
mers with molar mass up to 80000.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
potential of such species, the study of these compounds has
so far been limited almost to cyclopentadienyl derivatives,[5]
and their analogues in alternative coordination environ-
ments still remain poorly investigated.[6] The large size and
highly positive charge of the LnIII ions, the Lewis acidity of
lanthanides and therefore the high sensitivity of their deriv-
atives to coordination unsaturation of the metal center
make crucial the design of new ligand systems facilitating
the synthesis of stable and isolable complexes. Moreover
tuning the electronic and steric properties of the ancillary
ligation can allow modification and control of the reactivity
of the complexes. Tetrasubstituted guanidinato ligands have
been recently employed for early- and late-transition met-
als[7] and were shown to be the promising ligand system for
Introduction
Organolanthanide sandwich and half-sandwich-type
hydrido complexes have played an important role in the de-
velopment of organolanthanide chemistry[1] since the dis-
covery of the first hydride in the early 1980s.[2] These com-
pounds attract considerable attention due to their catalytic
activity in a variety of olefin transformations[3] and ex-
tremely high reactivity in stoichiometric reactions, which al-
lows even C–F bond activation.[4] However, despite the high
[a] G. A. Razuvaev Institute of Organometallic Chemistry of the
Russian Academy of Sciences,
Tropinina str. 49, 603600 Nizhny Novgorod GSP-445, Russia
Fax: +7-8312-62-74-97
E-mail: trif@iomc.ras.ru
[b] A. N. Nesmeyanov Institute of Organoelement Compounds of the synthesis of lanthanide alkyl complexes.[8] We employed
the Russian Academy of Sciences,
the advantages of the {(Me3Si)2NC(NiPr)2} coordination
Vavilova str. 28, 117813 Moscow, Russia
environment for the stabilization of lanthanide hydrides and
synthesized a novel family of dimeric Lewis base free hydri-
dolanthanide complexes, [Ln(µ-H){(Me3Si)2NC(NiPr)2}2]2
(Ln = Y, Nd, Sm, Gd, Yb, Lu).[9] The samarium and yt-
trium derivatives have shown high catalytic activity in ethyl-
ene polymerization. To date, the number of known mono-
meric hydridolanthanide species is very limited,[4,10] and the
[c] Laboratoire de Chimie des Polymères Organiques, CNRS –
ENSCPB – Université Bordeaux 1, ENSCPB,
16 Avenue Pey-Berland, 33607 Pessac Cedex, France
[‡] Present address: Catalyse et Organométalliques, Sciences Chi-
miques de Rennes – CNRS – Université de Rennes 1 (UMR
6226),
Campus de Beaulieu, 35042 Rennes Cedex, France
Fax: +33-2-2323-6939
E-mail: sophie.guillaume@univ-rennes1.fr
2090
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2090–2098

Hydrido Complexes of Y and Lu Supported by Bulky Guanidinato Ligands
synthesis of structurally defined monomeric hydrido com- highly moisture- and air-sensitive. They are fairly soluble
plexes still remains challenging. The fact that bulky cyclo- in commonly used organic solvents (thf, toluene, hexane,
hexyl-substituted guanidinato ligands allowed the synthesis pentane). Complexes 3 and 4 were characterized by 1H, 13
C
of neutral monomeric bis(guanidinato)lanthanide chlo- NMR and IR spectroscopy. For compound 3, correct mi-
rides[8d] encouraged us to test them for the synthesis of hy- croanalysis data were obtained, while for the lutetium ana-
dride species, in the expectation that the steric repulsion of logue 4 characterization was hampered by the difficulty of
the ligands can enable the existence of monomeric com- sample preparation; nevertheless, the lutetium metal micro-
plexes. We report here on the synthesis and structure of analysis data correspond to the proposed formula. In an
hydridoyttrium and hydridolutetium complexes [Ln(µ- inert atmosphere, complexes 3 and 4 can be stored in the
H){(Me3Si)2NC(NCy)2}2]2 (Ln = Y, Lu) supported by crystalline state at –20 °C without decomposition, while in
bulkier cyclohexyl-substituted guanidinato ligands and the C6D6 solution at 20 °C they slowly decompose with eli-
their catalytic activity in the reactions of olefin polymeriza- mination of Me4Si. The decomposition is complete in three
tion and hydrosilylation.
days. Complexes 3 and 4 do not contain coordinated thf
molecules. In the 1H NMR spectrum of complex 3 at 20 °C,
the hydrogen atoms of the methylene group attached to the
Results and Discussion
yttrium atom appear as a doublet at –0.19 ppm (2JYH
=
3.0 Hz); in the 13C{1H} NMR spectrum the appropriate
carbon atoms give rise to a doublet at δ = 35.1 ppm (2JYC
= 38.3 Hz). In the case of lutetium derivative 4, the singlet
The most efficient synthetic route to hydridolanthanide
complexes is the σ-bond metathesis reaction of the parent
alkyl compounds on treatment with dihydrogen[3c,3d] or
phenylsilane.[11] For the synthesis of the hydridolanthanide
derivatives supported by isopropyl-substituted guanidinato
ligands, [Ln(µ-H){(Me3Si)2NC(NiPr)2}2]2 (Ln = Y, Nd, Sm,
Gd, Yb, Lu),[9] we successfully used the reaction of related
alkyl complexes, [Ln(CH2SiMe3){(Me3Si)2NC(NiPr)2}2],
with PhSiH3 in hexane at room temperature. The same syn-
thetic approach was envisaged for the preparation of yt-
trium and lutetium analogues containing bulkier cyclo-
hexyl-substituted guanidinato ligands. Previously, we
had reported on the attempt to synthesize complex
[Y(CH2SiMe3){(Me3Si)2NC(NCy)2}2] by the alkylation
reaction of chloridobis(guanidinato)yttrium complex
[YCl{(Me3Si)2NC(NCy)2}2]thf with Li(CH2SiMe3), which
afforded an inseparable mixture of the alkyl compound and
its decomposition products.[8d] We have found that the reac-
tions of ate-complexes [{(Me3Si)2NC(NCy)2}2Ln(µ-Cl)2-
1
at δ = –0.49 ppm in the H NMR spectrum and the singlet
at δ = 40.0 ppm in the 13C{1H} NMR spectrum correspond
to the methylene fragment CH2Lu. The guanidinato ligands
give the expected sets of signals in the 1H and 13C{1H}
NMR spectra.
The σ-bond metathesis reactions of alkyl complexes 3
and 4 with phenylsilane were employed as a synthetic ap-
proach to bis(guanidinato)lanthanide hydrides. The reac-
tions of 3 and 4 with equimolar amounts of PhSiH3 were
carried out in hexane at 0 °C and resulted in the formation
of hydrido complexes [Ln(µ-H){(Me3Si)2NC(NCy)2}2]2 [Ln
= Y (5), Lu (6)]. Concentration of the reaction mixture and
cooling to –18 °C allowed isolation of complexes 5 and 6 as
colorless crystalline solids in 76 and 64% yield, respectively
(Scheme 2).
Hydrido complexes 5 and 6 are extremely air- and moist-
Li(thf)2] (Ln = Y (1), Lu (2)}[8d] with LiCH2SiMe3 occur ure-sensitive colorless crystalline solids. They are sparingly
in hexane at 0 °C cleanly and allow the synthesis of alkyl soluble in aromatic hydrocarbons and in hexane. Com-
complexes [Ln(CH2SiMe3){(Me3Si)2NC(NCy)2}2] [Ln = Y plexes 5 and 6 can be kept in the solid state in an inert
(3), Lu (4)] (Scheme 1).
atmosphere at 0 °C for several weeks without decomposi-
1
Yttrium derivative 3 was isolated as a colorless micro- tion. The H NMR samples of 5 and 6 in C6D6 do not
crystalline solid in 64% yield after separation of LiCl and show any traces of decomposition or solvent metalation for
recrystallization from hexane at –18 °C. Unfortunately in at least one week at 20 °C.
the case of lutetium the same handling procedure afforded
Clear, colorless single crystals of 5 and 6 suitable for
a viscous colorless oil (90% yield), and all attempts to crys- structure determination by single-crystal X-ray diffraction
tallize alkyl complex 4 failed. Compounds 3 and 4 are were obtained by slow cooling of their hexane solutions
Scheme 1.
Eur. J. Inorg. Chem. 2008, 2090–2098
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2091

S. M. Guillaume, A. A. Trifonov et al.
FULL PAPER
Scheme 2.
from 20 to –18 °C. Complex 5 crystallizes as solvate with
one molecule of hexane per asymmetric unit, while crystals
of compound 6 do not contain the solvent molecules. The
molecular structures of complexes 5 and 6 are depicted in
Figure 1 and Figure 2 respectively.
Figure 2. ORTEP diagram (30% probability thermal ellipsoids) of
[Lu(µ-H){(Me3Si)2NC(NCy)2}2]2 (6). Methyl radicals of SiMe
groups and cyclohexyl fragments are omitted for clarity. Selected
bond lengths [Å] and angles [°]: Lu(1)–N(1) 2.348(6), Lu(1)–N(2)
2.265(7), C(1)–N(1) 1.304(12), C(1)–N(2) 1.336(10), C(1)–N(3)
1.444(11), Lu(1)–Lu(1)#2 3.5717(18), Lu(1)–H(1) 2.24, Lu(1)–H(1)
#2 2.2; C(1)#1–Lu(1)–C(1) 119.9(3), N(2)–C(1)–N(1) 115.7(8),
Lu(1)–H(1)–Lu(1)#1 105.0(3).
Figure 1. ORTEP diagram (30% probability thermal ellipsoids) of
[Y(µ-H){(Me3Si)2NC(NCy)2}2]2 (5). Methyl radicals of SiMe3
groups and cyclohexyl fragments are omitted for clarity. Selected
bond lengths [Å] and angles [°]: Y(1)–N(1) 2.332(3), Y(2)–N(4)
2.337(3), Y(1)–N(2) 2.404(3), Y(2)–N(5) 2.406(3), C(1)–N(2)
1.303(4), N(4)–C(20) 1.327(4), C(1)–N(1) 1.340(4), N(5)–C(20)
1.312(4), C(1)–N(3) 1.430(4), N(6)–C(20) 1.447(4), Y(1)–H(1)
2.25(4), Y(2)–H(1) 1.95(4), Y(1)–Y(2) 3.6522(5); C(1)#1–Y(1)–C(1)
in complex 7 [3.6825(5) Å]. The dihedral angle between the
C(1)Y(1)C(1A) and the C(20)Y(2)C(20A) planes in 5 is
90.9(3)°. The coordination mode and geometric parameters
of the guanidinato ligands in complex 5 differ noticeably
from those in compound 7. All four chelating guanidinato
121.53(13), C(20)–Y(2)–C(20)#1 120.76(14), N(2)–C(1)–N(1) ligands in 5 are bonded to the metal atom in a similar
115.3(3), N(5)–C(20)–N(4) 116.1(3), Y(1)–H(1)–Y(2) 120.4(2).
fashion: by one short and one long Y–N bond [5: 2.404(3),
2.332(3) and 2.406(3), 2.337(3) Å; 7: 2.349(2), 2.365(2) Å].
Single-crystal X-ray diffraction analysis has shown that
The bonding situation within the NCN fragments of the
complexes 5 and 6 have similar structures: they do not con-
guanidinato ligands in 5 shows evidence of a localized π
tain coordinated Lewis bases and adopt dimeric structures
system, since one C–N bond is short [1.303(4), 1.312(4) Å],
in which two µ-hydrido ligands bridge two metal atoms
while the second one is long [1.340(4), 1.327(4) Å]. The geo-
(Figure 1 and Figure 2). The coordination sphere of the
metric parameters of the YNCN metallacycles in 5 are dif-
metal centers is determined by the four nitrogen atoms of
ferent from those observed in complex 7 and are consistent
the two guanidinato ligands and by two bridging hydrido
with a localized resonance structure depicted in Figure 3.
ligands. The formal coordination number of the metal atom
is 6.
In the planar tetranuclear Y2H2-core, the Y–H bond
lengths are noticeably different: 1.95(4) and 2.25(4) Å, and
they are surprisingly shorter than the related distances in
the previously reported hydridoyttrium complex containing
isopropyl-substituted guanidinato ligands, [Y(µ-H){(Me3-
[9b]
Si)2NC(NiPr)2}2]2
(7) [2.15(3) and 2.50(4) Å]. The Y···Y
distance in 5 [3.6522(5) Å] is shorter than the Y···Y distance Figure 3. Localized resonance structure of 5.
2092 Eur. J. Inorg. Chem. 2008, 2090–2098
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Hydrido Complexes of Y and Lu Supported by Bulky Guanidinato Ligands
Unlike the Y···Y distances in complexes 5 and 7, the
Lu···Lu distances in 6 [3.572(2) Å] and [Lu(µ-H){(Me3Si)2-
[9a]
NC(NiPr)2}2]2
(8) [3.5767(3) Å] are similar. The values
of the dihedral angles between two planes defined by the
central carbon atoms of two guanidinato ligands and the
metal atom in complexes 6 and 8 are 90.0(4) and 86.8(3)°,
respectively. The Lu–N distances in 6 [2.265(7), 2.348(6) Å]
and 8 [2.304(2), 2.315(2) and 2.267(2), 2.371(2) Å] are com-
parable and reflect the asymmetric fashion of coordination
of the guanidinato ligands.
The retention of a dimeric structure in complex 5 in
C6D6 solution is proved by NMR spectroscopy. The 1H and
13C{1H} NMR spectra of complex 5 (20 °C, C6D6) are con- Figure 4. 1H NMR spectrum of mixture of 5 and 6 (hydride region,
C6D6, 20 °C) after 24 h. (* - C6D5H).
sistent with a dimeric molecule with an internal mirror
plane. The hydrido ligands appear in the H NMR spec-
1
trum of 5 as a sharp, well-resolved triplet at δ = 8.09 ppm intervals and weighing the quantity of polyethylene pro-
(1JYH = 26.6 Hz), which indicates that each hydrido ligand duced. The ethylene polymerization activity of hydri-
1
couples with two equivalent 89Y nuclei. In the H NMR doyttrium complex 5 (65 gmmol–1 atm–1 h–1) was found
spectrum of complex 6 the hydrido ligands give rise to a to be much lower than that of related complex 7
singlet at δ = 13.31 ppm. For both complexes 5 and 6 the (442 gmmol–1 atm–1 h–1). The catalytic activity of complex
signals corresponding to hydrido ligands are substantially 6 (76 gmmol–1 atm–1 h–1) is comparable to the activity of the
shifted lowfield relative to the respective signals of the other isopropyl-substituted analogue, [Lu(µ-H){(Me3Si)2NC-
1
reported Y and Lu hydrides.[2,3c,3d,6a,6b,11–14] The H NMR (NiPr)2}2]2 (8)[9a] (83 gmmol–1 atm–1 h–1). Both complexes 5
spectrum of complex 5 does not show any evidence of the and 6 are inactive in the polymerization of propylene or
presence of monomeric hydrido species. The dissociation of styrene.
the dimeric hydrido complexes 5 and 6 and the existence of
Hydrosilylation of olefins by rare earth catalysts is a well-
a monomer–dimer equilibrium on the chemical time scale known process, and alkyl and hydrido complexes of the me-
was proved by scrambling these compounds in C6D6 solu- tallocene[15] and post-metallocene[16] type have shown high
tion. In approximately 24 h after mixing the compounds, an activity and selectivity in this reaction. The mechanism and
equilibrium mixture of homometallic complexes 5 and 6 energetics of the hydrosilylation catalytic cycle have been
and heterodimetallic complex [{(Me3Si)2NC(NCy)2}2Y(µ- investigated.[17] We have tested the activity of complexes 5–
H)2Lu{(Me3Si)2NC(NCy)2}2] was observed (Scheme 3).
8 as catalysts of hydrosilylation of olefins with PhSiH3. The
catalytic tests were carried out at a 1:1 olefin/silane mol
ratio in benzene or C6D6 solutions at 20 °C in the presence
of 2 mol-% of complexes 5–8. 1-Nonene was found to react
with PhSiH3 in the presence of complexes 5–8 to give only
the anti-Markovnikov addition product PhSiH2(n-C9H19)
within 4–6 h in quantitative yields. Complexes 5–8 do not
initiate either 1-nonene polymerization or PhSiH3 dehydro-
genative coupling, thus providing clear conversion of 1-
nonene to PhSiH2(n-C9H19). No reaction was observed for
PhSiH3 with cyclohexene, styrene, or norbornene under
similar conditions. The steric bulk of the ligands apparently
limits the reactivity of the catalysts such that only 1-nonene
Scheme 3.
The hydrido ligand of the heterodimetallic complex ap- reacts at a measurable rate. Interestingly, if the reaction of
pears as a diagnostic doublet at δ = 10.81 ppm (1JYH
=
PhSiH3 was carried out with a twofold molar excess of 1-
24.8 Hz) (Figure 4). Formerly, similar behavior was de- nonene in the presence of complexes 5–8 under similar con-
scribed for hydridolanthanide complexes supported by a ditions, the product of a double terminal addition,
linked amido-cyclopentadienyl ligand.[14c]
PhSiH(n-C9H19)2, was isolated in high yields.
The catalytic tests of complexes 5 and 6 in ethylene poly-
Rare earth hydrido complexes used as initiators for the
merization were carried out under rigorously anaerobic ring-opening polymerization of cyclic esters are, to the best
conditions in a sealed glass manometric system (volume of of our knowledge, rather limited.[18] Yasuda has successfully
toluene: 5 mL; catalyst concentration: 5.89ϫ10–6 and used [SmH(C5Me5)2]2 for the homopolymerization of ε-ca-
6.83ϫ10–6 molL–1; temperature: 20 °C; ethylene pressure: prolactone (ε-CL) as well as for the copolymerization of
–0.5 atm), which allows monitoring the polymerization pro- polar monomers such as ε-caprolactone (or methylmethac-
cess by consumption of the monomer. Catalyst efficiencies rylate) with ethylene. By using this highly active samarocene
¯
were estimated both by monomer conversion and by hydride, high molar mass polymers (Mn Ͼ 70 000) with
¯
¯
quenching the polymerization reaction after measured time the lowest molar mass distribution ever reported, (Mw/Mn
Eur. J. Inorg. Chem. 2008, 2090–2098
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2093

S. M. Guillaume, A. A. Trifonov et al.
FULL PAPER
Table 1. Polymerization of ε-CL initiated by 7 or 8 in thf at 23 °C.
[a]
[b]
[c]
[d,e]
[H–]0
[ε-CL]0
[ε-CL]0/[H–]0 Reaction time (Mn)theo
Mw/Mn
¯
¯
(Mn)SEC
¯
¯
Run
Initiator
[mmolL–1]
[mmolL–1]
[min]
[gmol–1]
[gmol–1]
1
2
3
4
5
6
7
8
7
7
7
7
7
7
8
8
8
8
8
21.5
19.1
6.4
20.6
6.5
5.5
0.5
5.4
0.5
7.9
5.3
631
1082
451
1984
1002
1804
25
451
42
1002
1804
29
57
70
96
154
328
50
84
84
15
15
45
15
45
45
15
45
15
45
45
3 300
6 500
8 000
10 950
17 600
37 400
5 700
9 600
9 600
14 500
36 500
7 850
2.5
3.0
4.2
2.2
2.1
2.0
2.6
2.3
3.5
2.4
1.8
11 650
16 600
17 600
37 674
79 000
13 200
18 050
13 100
37 300
69 900
9
10
11
127
320
1
[a] [H–]0 = [1/2]0 = [7 or 8]0. [b] Calculated from H NMR analysis. [c] Calculated for one growing polymer chain per metal atom with
(Mn)theo = ([ε-CL]0/[H–]0 ϫ114ϫconversion). [d] SEC values of precipitated polymer samples corrected with the coefficient 0.56. [e]
¯
Molar mass distribution calculated from SEC chromatogram traces.
Ͻ1.08), for such elevated mass values have been obtained lar mass distribution was obtained over the longest reaction
in a living process.[18c,18d] AB type block copolymerization time of 45 min (Table 1, entry 11); neither do these side re-
of ε-CL with ethylene have also been observed in the pres- actions occur as a result of a highly concentrated reaction
ence of the organolanthanide hydride initiators [Me2Si- medium, as the molar mass distribution increased upon di-
(C5H2-2-Me3Si-4-R)2LnH]2 (Ln = Y, R = tBuMe2Si; Ln = lution of the initiator (Table 1, entries 8–9).
Sm, R = tBu), [Me2Si(C5H2-2-Me3Si)2SmH]2, and [Me2Si-
The 1H NMR spectrum of a precipitated polymer clearly
shows a HO–PCL pattern with typical signals: δ = 4.03 (t,
(C5Me4)2SmH].[18e,18f]
Complexes 7 and 8 do indeed efficiently polymerize ε- CH2O), 3.60 (t, CH2OH), 2.25 [t, C(O)CH2], 1.61 (m,
caprolactone in thf within 15–45 min at room temperature. CH2CH2CH2), 1.34 (m, CH2CH2CH2) ppm. No signal cor-
The reaction is almost immediate: for solutions with a high responding to the expected HO–PCL–C(O)H (δC(O)H
=
concentration of initiator (20 mmolL–1), the polymerization 9.7 ppm), resulting from polymerization by a [(Lu/Y)(µ-
is (visually) instantaneous, and a colorless gel is formed H){(Me3Si)2NC(NiPr)2}2]2 complex along with an oxygen–
within less than 30 s, while lower initiator concentrations acyl bond cleavage of the monomer, was ever observed,
yield much less viscous solutions. In all experiments, quan- which indicates some modification of the initial hydrido
titative monomer conversion is always obtained. Yet, if one complex 7 or 8 prior to initiation and propagation of the
supposes that the hydride species 7 or 8 are the real initiat- reaction. While one chain end could clearly be identified
ing species, the polymerization remains uncontrolled, re- as –CH2OH, the other extremity could not be identified
gardless of the experimental conditions and the metallic hy- without ambiguity. These results indicate that hydrides 7
dride used. Molar masses obtained from size exclusion and 8 lead to highly active initiating species; yet, the poly-
¯
chromatography (SEC), (Mn)SEC, were always greater than merization is not controlled.
the ones calculated from the [monomer]0/[initiator]0 ratio
¯
and monomer conversion, (Mn)theo, suggesting initiation by
species other than 7 or 8. A [{(Me3Si)2NC(NiPr)2}2]Ln–
O(CH2)6–O–Ln[{(Me3Si)2NC(NiPr)2}2] (Ln = Lu, Y) ini-
tiating species, potentially formed upon reduction of the
Conclusions
Contrary to our expectations, replacement of isopropyl-
carbonyl group of the first lactone monomer along with an substituted guanidinato ligands by bulkier cyclohexyl-con-
oxygen–acyl bond cleavage, might well be generated in situ taining analogues in the dimeric hydrido complexes [Ln(µ-
leading to a HO–PCL–O(CH2)6–O–PCL–OH polymer. H){(Me3Si)2NC(NR)2}2]2 (Ln = Y, Lu) does not result in
Such a reduction of the carbonyl group of ε-caprolactone formation of monomeric hydrido species or a lengthening
has been reported in the reaction of [(C5Me5)2SmH]2, from of the Ln–Ln distance. Nevertheless, the dissociation of di-
which the product recovered after hydrolysis was shown to meric hydrido complexes 5 and 6 and the existence of a
be 1,6-hexanediol.[18c] Initiation by such a dimetallic species monomer–dimer equilibrium on the chemical time scale
would reduce by half the calculated molar mass, which was proved by scrambling equimolar amounts of 5 and 6
would then be in agreement with the experimental molar in C6D6 solution, which resulted in the formation of the
¯
¯
mass values. Molar mass distribution values, Mw/Mn, are heterodimetallic complex [{(Me3Si)2NC(NCy)2}2Y(µ-H)2-
quite large, indicating the presence of side reactions such as Lu{(Me3Si)2NC(NCy)2}2]. Complexes 5 and 6 catalyze eth-
transesterifications, the most common in polyester synthe- ylene polymerization under mild conditions with moderate
sis, involving intramolecular back-biting or intermolecular activity. 1-Nonene was found to react with PhSiH3 in a 1:1
reshuffling. Yet these side reactions do not necessarily occur molar ratio in the presence of complexes 5–8 to give only
with a prolonged polymerization time, as the narrowest mo- the anti-Markovnikov addition product, PhSiH2(n-C9H19).
2094
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2090–2098

Hydrido Complexes of Y and Lu Supported by Bulky Guanidinato Ligands
0 °C, and the reaction mixture was stirred for 1 h. The colorless
The reaction of PhSiH3 with a twofold molar excess of 1-
nonene catalyzed by complexes 5–8 results in a double ter-
minal addition PhSiH(n-C9H19)2. Complexes 7 and 8 ef-
ficiently polymerize ε-caprolactone in thf; however, the po-
lymerization remains uncontrolled.
solution was filtered. After removing all volatiles, complex 3 was
isolated as a colorless viscous liquid (0.750 g, 90%). 1H NMR
(200 MHz, C6D6): δ = 3.55 (m, 4 H, CH, Cy), 1.96–1.21 (m, 40 H,
CH2, Cy), 0.42 [s, 9 H, CH2Si(CH3)3], 0.27 [s, 36 H, NSi(CH3)3],
–0.49 (s, 2 H, LuCH2) ppm. 13C{1H} NMR (50 MHz, C6D6): δ =
169.3 (CN3), 55.2 (CH, Cy), 40.0 (LuCH2), 37.9, 32.0, 26.4, 26.2,
23.1 (CH2, Cy), 5.2 [CH2Si(CH3)3], 2.6 [NSi(CH3)3]2 ppm. IR (nu-
jol, KBr): ν = 1630 (s), 1300 (w), 1250 (s), 1200 (s), 1210 (m), 950
˜
(s), 930 (m), 820 (s) cm–1.
Experimental Section
Synthesis of [Y(µ-H){(Me3Si)2NC(NCy)2}2]2 (5): To a hexane solu-
tion of 3 (40 mL) in situ obtained from 1 (1.530 g, 1.46 mmol) and
Me3SiCH2Li (0.138 g, 1.46 mmol) was added a solution of PhSiH3
(0.158 g, 1.46 mmol) in hexane (5 mL) at 0 °C. The reaction mix-
ture was stirred for 30 min at 0 °C and then concentrated in vacuo
to approximately 1/4 of its initial volume. When crystallization
started, the solution was cooled to –18 °C and kept at that tempera-
ture overnight. The mother liquor was decanted, the colorless solid
was washed with cold hexane and dried in vacuo at room tempera-
ture for 45 min to give 5 as a colorless microcrystalline solid
(0.914 g, 76%). C76H162N12Si8Y2 (1646.68): calcd. C 55.43, H 9.91,
Y 10.79; found C 55.07, H 10.32, Y 10.43. 1H NMR (200 MHz,
All experiments were performed in evacuated tubes by using stan-
dard Schlenk techniques with rigorous exclusion of traces of moist-
ure and air. The solvents thf, benzene, toluene, and hexane were
purified by distillation from sodium/benzophenone ketyl and were
condensed in vacuo prior to use. N,NЈ-diisopropylcarbodiimide and
1-nonene were purchased from Acros, dried with molecular sieves,
and purified by distillation. N,NЈ-dicyclohexylcarbodiimide was
purchased from Acros and used without any purification. Phenylsi-
lane was dried with calcium hydride and condensed in vacuo prior
to use. Anhydrous LnCl3 and [Li(Et2O)N(SiMe3)2][20] were pre-
[19]
pared according to literature procedures. ε-Caprolactone (ε-CL,
Lancaster) was dried first with CaH2 (one week) and then over
4,4Ј-ε-caprolactone (ε-CL, Lancaster). All other commercially
available chemicals were used after the appropriate purification. IR
spectra were recorded as Nujol mulls with a FSM 1201 spectropho-
tometer. NMR spectra were recorded with Bruker DPX 200 and
Bruker Avance DPX 400 spectrometers. Deuteriated benzene was
dried with sodium benzophenone ketyl and vacuum-transferred.
1
C6D6): δ = 8.09 [t, JY-H = 26.6 Hz, 2 H, Y(µ-H)2Y], 3.23 (m, 8 H,
CH, Cy), 2.09–1.30 (m, 80 H, CH2, Cy), 0.31, 0.21 (s, together 72
H, SiMe3) ppm. 13C{1H} NMR (50 MHz, C6D6): δ = 168.8 (CN3),
55.0 (CH, Cy), 37.5, 36.9, 31.6, 26.1, 25.4, 25.0 (CH2, Cy), 2.7, 2.3
{N[Si(CH ) ] } ppm. IR (Nujol, KBr): ν = 1630 (s), 1605 (m), 1320
˜
3 3 2
(s), 1250 (s), 1205 (s), 1050 (s), 950 (s), 820 (s) cm–1.
1
Chemical shifts for H and 13C NMR spectra were referenced in-
Synthesis of [Lu(µ-H){(Me3Si)2NC(NCy)2}2]2 (6): A solution of
PhSiH3 (0.110 g, 1.02 mmol) in hexane (5 mL) was added at room
temperature to a solution of 4 obtained in situ from 2 (1.153 g,
1.02 mmol) and Me3SiCH2Li (0.096 g, 1.02 mmol) in hexane
(40 mL) at 0 °C. The reaction mixture was stirred for 45 min and
then concentrated in vacuo to approximately 1/4 of its initial vol-
ume. When crystallization started, the solution was cooled to
–18 °C and kept at that temperature overnight. The mother liquor
was decanted, the solid was washed with cold hexane and dried
in vacuo at room temperature for 45 min to give 6 as a colorless
microcrystalline solid (0.594 g, 64%). C76H162Lu2N12Si8 (1818.70):
calcd. C 50.19, H 8.98, Lu 19.24; found C 49.86, H 8.57, Lu 18.93.
1H NMR (200 MHz, C6D6): δ = 13.31 [s, 2 H, Lu(µ-H)2Lu], 3.70
(m, 8 H, CH, Cy), 2.12–1.21 (m, 80 H, CH2, Cy), 0.37, 0.36 (s,
together 72 H, SiMe3) ppm. 13C{1H} NMR (50 MHz, C6D6): δ =
168.9 (CN3), 55.3 (CH, Cy), 37.6, 36.7, 31.6, 26.3, 25.5, 25.4 (CH2,
ternally to the residual solvent resonances and reported relative to
tetramethylsilane. Lanthanide metal analyses were carried out by
¯
complexometric titration. Molar mass (Mn) and molar mass distri-
¯
¯
bution (Mw/Mn) determinations were performed by size exclusion
chromatography (SEC) in thf at 20 °C (flow rate 1.0 mLmin–1) with
a Jasco apparatus equipped with a refractive index detector and
one Polymer Laboratory column with 5 µm particle size. The poly-
mer samples were dissolved in thf (2 mgmL–1). Average molar mass
values were calculated from the linear polystyrene calibration curve
¯
by using the correction coefficient previously reported [(Mn)exp
=
0.56(Mn)SEC].[21] The monomer conversion was calculated from the
¯
1H NMR spectrum of the crude polymer sample by the integration
(Int.) ratio Int.P(CL)/[Int.P(CL)
+ Int.(CL)] by using the
CH2OC(O) methylene triplet (δ = 4.04 ppm) peak.
Synthesis of [Y(CH2SiMe3){(Me3Si)2NC(NCy)2}2] (3): To a solu-
tion of 1 (1.090 g, 1.04 mmol) in hexane (20 mL) was added a solu-
tion of Me3SiCH2Li (0.098 g, 1.04 mmol) in hexane (10 mL) at
0 °C, and the reaction mixture was stirred for 1 h. The colorless
solution was filtered and concentrated in vacuo to approximately
1/10 of its initial volume. Complex 3 was isolated as a colorless
microcrystalline solid (0.70 g, 64%) from hexane by cooling.
C42H91N6Si5Y (909.52): calcd. C 55.46, H 10.08, Y 9.77; found C
55.33, H 10.31, Y 9.58. 1H NMR (200 MHz, C6D6, 20 °C ): δ =
Cy), 3.2, 2.9 {N[Si(CH ) ] } ppm. IR (Nujol, KBr): ν = 1635 (s),
˜
3 3 2
1610 (m), 1305 (s), 1250 (s), 1070 (s), 955 (s), 835 (s) cm–1.
Typical Ethylene Polymerization Procedure: Catalytic tests with eth-
ylene (volume of toluene: 5 mL, catalyst concentration: 5.9ϫ10–6
and 6.8ϫ10–6 molL–1, temperature: 20 °C, monomer pressure:
–0.5 atm) and propylene (volume of toluene: 5 mL, catalyst concen-
tration: 5.9ϫ10–6 and 6.1ϫ10–6 molL–1, temperature: 0 °C, mono-
mer pressure: –0.5 atm) were carried out under rigorously anaero-
bic conditions in a sealed glass manometric system. The reactions
were monitored by monomer consumption. Catalyst efficiencies
were estimated by both monomer absorption and by quenching the
polymerization reaction after measured time intervals and weighing
the quantity of polymer produced. The polymers were washed with
dilute HCl and methanol and dried in vacuo to constant weight.
3.37 (br.m, 4 H, CH, Cy), 1.15–1.91 (m, 40 H, CH2, Cy), 0.45 [s,
2
9 H, CH2Si(CH3)3], 0.30 [s, 36 H, NSi(CH3)3], –0.19 (d, JY-H
=
3.0 Hz, 2 H, YCH2) ppm. 13C{1H} NMR (50 MHz, C6D6, 20 °C ):
δ = 168.3 (CN3), 55.2 (CH, Cy), 35.1 (d, JY-C = 38.3 Hz, YCH2),
1
36.8, 33.2, 26.4, 26.1, 22.7 (CH2, Cy), 4.7 [CH2Si(CH3)3], 2.4
[NSi(CH ) ] ppm. IR (Nujol, KBr): ν = 1635 (s), 1310 (w), 1254
˜
3 3 2
(s), 1195 (s), 1060 (m), 955 (s), 845 (s), 740 (s) cm–1.
Typical ε-CL Polymerization Procedure: Compound 7 (9.6 mg,
6.41 µmol) or 8 was initially dissolved in thf (1.9 mL) before ad-
dition of ε-CL (0.1 mL, 0.9 mmol). The clear solution was then
stirred over 15–45 min at 23 °C. The reaction was then quenched
Synthesis of [Lu(CH2SiMe3){(Me3Si)2NC(NCy)2}2] (4): To a solu-
tion of 2 (0.950 g, 0.84 mmol) in hexane (20 mL) was added a solu-
tion of Me3SiCH2Li (0.079 g, 0.84 mmol) in hexane (10 mL) at
Eur. J. Inorg. Chem. 2008, 2090–2098
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2095

S. M. Guillaume, A. A. Trifonov et al.
FULL PAPER
with an acetic acid solution (0.1 mL, 1.45 mol, 14.5ϫ103 mol L–1).
The resulting mixture was dried, and the conversion determined by
1H NMR spectroscopic analysis of the crude polymer sample. This
nonfractionated polymer was dissolved in CH2Cl2, purified upon
precipitation in a large amount of cold pentane, and finally dried
under dynamic vacuum. The recovered polymers were then charac-
Typical Hydrosilylation Procedure (PhSiH3/1-Nonene = 1:2): To a
solution of 5 (0.0418 g, 0.032 mmol) in hexane (3 mL) were added
phenylsilane (0.200 g, 1.85 mmol) and 1-nonene (0.470 g,
3.70 mmol) (PhSiH3/1-nonene = 1:2). The reaction mixture was
stirred for 24 h and then treated with methanol (1 mL). A pale-
yellow solution was filtered and concentrated in vacuo. The viscous
liquid residue was dried in vacuo at 80 °C for 2 h. After Kugelrohr
distillation (180–210 °C, 10–2 bar) PhSiH(n-C9H19)2 was obtained
as a colorless liquid (0.610 g, 91%). C24H44Si (360.69): calcd. C
1
terized by H and 13C NMR spectroscopy and SEC.
Typical Hydrosilylation Procedure (PhSiH3/1-Nonene = 1:1): To a
solution of 7 (0.0418 g, 0.033 mmol) in hexane (3 mL), were added
phenylsilane (0.280 g, 0.260 mol) and 1-nonene (0.330 g,
0.260 mmol) (PhSiH3/1-nonene = 1:1). The reaction mixture was
stirred for 24 h and then treated with methanol (1 mL). The pale-
yellow solution was filtered and concentrated in vacuo. The viscous
liquid residue was dried in vacuo at 100 °C for 1 h. The product of
reaction was purified by Kugelrohr distillation (180–210 °C,
10–2 bar). PhSiH2(n-C9H19) (0.550 g) was isolated as a colorless li-
quid in 91% yield. C15H26Si (234.45): calcd. C 76.84, H 11.18, Si
11.98; found C 76.92, H 11.30, Si 11.79. 1H NMR (200 MHz,
1
79.92, H 12.29, Si 7.79; found C 79.49, H 12.30, Si 7.74. H NMR
(200 MHz, CDCl3): δ = 7.51 (m, 2 H, Ph), 7.36 (d, 3JH-H = 2.3 Hz,
3
1
2 H, Ph), 7.32 (d, JH-H = 1.5 Hz, 1 H, Ph), 4.23 (quint, JSi-H
=
3.3 Hz, 1 H, SiH), 1.24 (br.m, 28 H, CH2), 0.87 (br.m, 10 H, CH3,
SiCH2) ppm. 13C{1H} NMR (50 MHz, CDCl3): δ = 136.2 (Ph),
134.7 (Ph), 129.1 (Ph), 127.8 (Ph), 33.3, 31.9, 29.5, 29.4, 29.3, 24.5,
22.7 (CH ), 14.1 (CH ), 11.9 (SiCH ) ppm. IR (Nujol, KBr): ν =
˜
2
3
2
3070 (m), 3049 (m), 3015 (s), 2109 (s), 1949 (w), 1876 (w), 1813
(w), 1759 (w) 1734 (w), 1589 (w), 1465 (s), 1425 (m), 1408 (m),
1378 (m), 1300 (m), 1260 (s), 1169 (s), 1115 (s), 1013 (m), 940 (m),
822 (s), 732 (s), 695 (s), 466 (m) cm–1.
3
CDCl3): δ = 7.61 (m, 2 H, Ph), 7.42 (d, JH-H = 1.8 Hz, 2 H, Ph),
3
1
7.39 (d, JH-H = 1.5 Hz, 1 H, Ph), 4.34 (t, JSi-H = 3.8 Hz, 2 H,
SiH2), 1.31 (br.m, 14 H, CH2), 0.93 (br.m, 5 H, CH3, SiCH2) ppm. X-ray Crystallography: Low-temperature diffraction data were col-
13C{1H} NMR (50 MHz, CDCl3): δ = 135.3 (Ph), 132.9 (Ph), 129.5 lected with Bruker-AXS Smart Apex I (for 5) and Apex II (for 6)
(Ph), 127.9 (Ph), 32.9, 31.9, 29.6, 29.4, 29.3, 25.2, 22.8 (CH2), 14.2
(CH ), 10.8 (SiCH ) ppm. IR (Nujol, KBr): ν = 3070 (m), 3050
diffractometers with graphite-monochromated Mo-Kα radiation (λ
= 0.71073 Å). All structures were solved by direct methods and
refined against F2 on all data by full-matrix least-squares with
˜
3
2
(m), 3015 (s), 2130 (s), 1950 (w), 1880 (w), 1813 (w), 1638 (w), 1589
(w), 1378 (m), 1300 (m), 1250 (s), 1169 (s), 1115 (s), 940 (m), 840 SHELXTL.[22] Absorption correction in 5 was applied by using
(s), 699 (m), 635 (s), 505 (w), 455 (m) cm–1.
SADABS.[23] The crystals of complex 6 are twins. A double set of
Table 2. Crystallographic data and structure refinement details for 5 and 6.
5
6
Empirical formula
Formula weight
C82H175N12Si8Y2
1731.88
C76H162Lu2N12Si8
1818.84
T [K]
Space group
100(2)
Fdd2
100(2)
I42d
¯
Crystal system
orthorhombic
tetragonal
Unit cell dimensions
a [Å]
b [Å]
c [Å]
37.7477(18)
38.30371(8)
14.9435(7)
90
26.656(9)
26.656(9)
14.905(7)
90
α [°]
β [°]
90
90
90
90
10590(7)
4
1.141
1.983
3824
γ [°]
Volume [Å3]
21606.5(18)
8
1.065
1.198
7528
Z
Density (calculated), [gcm–3]
Absorption coefficient [mm–1]
F(000)
Crystal size [mm]
θ range for data collection, deg
Index ranges
0.10ϫ0.10ϫ0.10
26.00
–46ՅhՅ46
–47ՅkՅ47
–18ՅlՅ18
10487, Rint = 0.0668
0.22ϫ0.14ϫ0.10
27.00
–23ՅhՅ24
0ՅkՅ33
0ՅlՅ19
5840
Independent reflections
Observed reflections [IϾ2σ(I)]
Completeness to θ
3280
98.9
99.7
Data/restraints/parameters
10487/86/501
0.993
5840/0/223
0.877
Goodness-of-fit on F2
Final R indices [IϾ2σ(I)]
R1 = 0.0550
wR2 = 0.1339
R1 = 0.0832
wR2 = 0.1445
0.648/–0.282
R1 = 0.0490
wR2 = 0.0926
R1 = 0.1133
wR2 = 0.1080
1.645/–2.568
R indices (all data)
Largest diff. peak and hole [eÅ–3]
2096
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2090–2098

Hydrido Complexes of Y and Lu Supported by Bulky Guanidinato Ligands
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program incorporated in the APEX II software.[24] The frames were
integrated separately for each component and then reflections of
two components were separately included in the refinement by
HKLF 5 format [BASF = 0.116(9)]. All non-hydrogen atoms were
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rido H atoms) were included in idealized positions, and their Uiso
values were set to ride on the Ueq values of the parent carbon atoms
[Uiso(H) = 1.5Ueq for methyl carbon atoms and 1.2Ueq for other
carbon atoms]. Hydrido hydrogen atoms in 5 and 6 were located
from Fourier synthesis and refined isotropically in 5 and in riding
motion approximation for 6. Crystallographic data and structure
refinement details are given in Table 2. CCDC-675002 and -675003
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
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Acknowledgments
This work has been supported by the Russian Foundation for Basic
Research (Grant Nos. 08–03–00391-a, 06–03–32728-a, 07–03–
12164-ofi), Program of the Presidium of the Russian Academy of
Science (RAS), and RAS Chemistry and Material Science Division.
A. T. thanks the Russian Foundation for Science Support.
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