Rare-earth dichloro and bis(alkyl) complexes supported by bulky amido-imino ligand. Synthesis, structure, reactivity and catalytic activity in isoprene polymerization

Article abstract of DOI:10.1039/c3dt33108c

A monoanionic amido-imino ligand system [(2,6-iPr₂C ₆H₃)NC(Me)C(CH₂)N(C₆H ₃-2,6-iPr₂)]^- was successfully employed for the synthesis of monomeric dichloro [(2,6-iPr

Full text of DOI:10.1039/c3dt33108c

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Rare-earth dichloro and bis(alkyl) complexes supported
by bulky amido–imino ligand. Synthesis, structure,
reactivity and catalytic activity in isoprene
polymerization†
Cite this: DOI: 10.1039/c3dt33108c
Alexander A. Kissel,a Dmitry M. Lyubov,a Tatyana V. Mahrova,a Georgy K. Fukin,a
Anton V. Cherkasov,a Tatyana A. Glukhova,a Dongmei Cuib and
Alexander A. Trifonov*a
A monoanionic amido–imino ligand system [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-iPr2)]− was suc-
cessfully employed for the synthesis of monomeric dichloro [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-
iPr2)]LnCl2(THF)2 (Ln = Y, 2Y; Lu, 2Lu) and bis(alkyl) [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-iPr2)]Ln-
(CH2SiMe3)2(THF) (Ln = Y, 4Y; Lu, 4Lu) species of yttrium and lutetium. Dichloro complexes 2Y and 2Lu
turned out to be unstable in aromatic solvents. The ligand symmetrization reaction in the case of 2Y
affords the yttrium complex coordinated by dianionic [(2,6-iPr2C6H3)NC(vCH2)C(vCH2)N(C6H3-2,6-iPr2)]2−
ligand, (2,6-iPr2C6H3)NvC(Me)C(Me)vN(C6H3-2,6-iPr2) and YCl3. On the contrary, bis(alkyl) species 4Y
and 4Lu are rather stable and do not undergo such a transformation or thermal decomposition. The
treatment of complex 4Y with DME resulted in C–O bond cleavage and the formation of a dimeric
methoxy-alkyl species {[(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-iPr2)]Y(CH2SiMe3)(μ-OMe)}2 (5). The
ternary systems 4Ln/AliBu3/borate (borate = [HNMe2Ph][B(C6F5)4] and [CPh3][B(C6F5)4]; molar ratio
1 : 10 : 1) performed high catalytic activity in isoprene polymerization and ability to convert into polymer
1000–5000 equivalents of isoprene in 20–120 min with quantitative conversion. The obtained
polyisoprenes possessed high molecular weights (2.9 × 104–4.1 × 104) and moderate polydispersities
(2.14–3.52). Predominant 3,4-regioselectivity (up to 78%) was observed.
Received 29th December 2012,
Accepted 25th February 2013
DOI: 10.1039/c3dt33108c
www.rsc.org/dalton
wide use in coordination chemistry of transition metals since
the early 1960s and continue to attract keen interest due to the
Introduction
The design of new ligand systems suitable for coordination to diversity of their coordination and redox properties.7 In lantha-
rare earth metals and investigation of the structure–reactivity nide chemistry, diazadiene ligands have found use during past
relationships are within the focus of modern organo-rare-earth two decades, and this has stimulated the development of new
chemistry.1 Chelating N-containing ligands provide unique fields of research.8 Several successful attempts to use sterically
scaffolds for the synthesis and isolation of highly reactive rare- hindered diazabutadienes as a platform for construction of
earth species (alkyl, cationic alkyl, hydrido, borohydrido)1,2 new versatile ligand systems have been published so far. We
and have emerged as valuable ancillary ligand systems by employed bulky diazabutadienes as precursors for preparation
virtue of their ability to form strong metal–ligand bonds and of chelating diamido ligands capable of forming geometrically
to allow for an easy tuning of their steric and electronic rigid strained five-membered metallacycles.9 A two-electron
properties.3–6 1,4-Disubstituted diazabutadienes have found reduction of 1,4-bis(2,6-diisopropylphenyl)-2,3-dimethyl-1,4-
diazabuta-1,3-diene (DAD) with alkaline metals allows to
obtain dianionic ene–diamido skeleton,9a while a hydrogen
abstraction from the electrophilic carbon of the imine group
under treatment with two equivalents of a strong nucleophile
(nBuLi) resulted in the formation of a dianionic diamido –N–C-
(vCH2)–C(vCH2)–N framework.9b Lanthanide borohydride
and alkoxide complexes supported by a rigid dianionic
ene–diamido ligand turned out to be efficient catalysts
for the ring opening polymerization of racemic lactide and
aG. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of
Sciences, Nizhny Novgorod Tropinina str.49, Russia. E-mail: trif@iomc.ras.ru;
Fax: +7-831-462-74-97; Tel: +7-831-463-35-32
bState Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, China
†Electronic supplementary information (ESI) available. CCDC 915562–915569.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt33108c
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β-butyrolactone.9a Another approach for derivatization of 1,4-
diazabutadienes was developed by Mashima and co-workers.
Alkylation of 1,4-diazabutadienes by tris(alkyl) rare-earth com-
plexes allowed for the synthesis of mono- or bis(alkyl) species
supported by diamido or amido–imino ligands. The bis(alkyl)
complexes proved to be able to promote intramolecular hydro-
amination of aminoolefins.10 Herein we report on the syn-
thesis, structures and reactivity of dichloro and bis(alkyl)
yttrium and lutetium complexes coordinated by monoanionic
amido–imino ligand derived from bulky 1,4-bis(2,6-diisopro-
pylphenyl)-2,3-dimethyl-1,4-diazabuta-1,3-diene. The catalytic
performance of bis(alkyl) yttrium and lutetium complexes in
isoprene polymerization was explored in detail.
Fig. 1 Molecular structure of complex [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N-
(C6H3-2,6-iPr2)]YCl2(THF)2 (2Y). One of two crystallographically independent
molecules is shown. Thermal ellipsoids are drawn at the 30% probability level.
Hydrogen atoms of 2,6-diisopropylphenyl substitutes and THF molecules are
omitted for clarity. Selected distances (Å) and angles (°): Y(1)–N(1) 2.292(3),
Y(1)–N(2) 2.451(4), Y(1)–Cl(1) 2.5791(12), Y(1)–Cl(2) 2.5659(12), Y(1)–O(1)
2.387(3), Y(1)–O(2) 2.398(2), C(1)–N(1) 1.368(6), N(2)–C(3) 1.295(6), C(1)–C(2)
1.373(6), C(1)–C(3) 1.494(6), C(3)–C(4) 1.489(7); N(1)–Y(1)–N(2) 66.98(12),
Cl(1)–Y(1)–Cl(2) 150.86(4), O(1)–Y(1)–O(2) 110.39(12), N(1)–C(1)–C(2) 126.9(4),
N(1)–C(1)–C(3) 113.7(4), C(2)–C(1)–C(3) 119.4(4), N(2)–C(3)–C(4) 123.3(4), N(2)–
C(3)–C(1) 116.4(4), C(4)–C(3)–C(1) 120.3(4).
Result and discussion
A monoanionic amido–imino ligand system was obtained due
to a single deprotonation of one of the methyl groups by
imino nitrogens of 1,4-bis(2,6-diisopropylphenyl)-2,3-dimethyl-
1,4-diazabuta-1,3-diene (DAD) by one equivalent of LiNiPr2 in
ether–hexane solution at low temperature.11 Salt metathesis
reactions of the amido lithium derivative [(2,6-iPr2C6H3)Nv
C(Me)C(vCH2)N(C6H3-2,6-iPr2)]Li(OEt2) (1) with equimolar
amounts of anhydrous LnCl3 (Ln = Y, Lu) were carried out at
room temperature in THF solution (Scheme 1). Dichloro
complexes [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-iPr2)]-
LnCl2(THF)2 (Ln = Y, 2Y; Lu, 2Lu) were isolated after recrystalli-
zation from THF–hexane mixture as lemon yellow crystals in
78 and 72% yield, respectively. It is worth noting that unlike
the synthesis of the analogous yttrium and lutetium complexes
coordinated by ene–diamido ligand9a which were obtained as
ate-complexes, the similar workup allowed for the isolation of
2Y and 2Lu as salt-free complexes.
Single crystal samples of 2Y and 2Lu suitable for X-ray
analysis were obtained by slow cooling of concentrated THF
solutions from room temperature to −20 °C. The molecular
structure of 2Y is depicted in Fig. 1, for the molecular structure
of 2Lu see ESI;† the crystal and structural refinement data for
2Y and 2Lu are summarized in Table 2. The asymmetric unit
cell of 2Y contains two crystallographically independent mono-
meric molecules. All discussions of structural details refer to
one of the two independent molecules. The coordination
environment of the yttrium atom is set up by two nitrogen
atoms of the chelating amido–imino ligand, two terminal
chloro ligands and two oxygen atoms of coordinated THF
molecules thus resulting in a formal coordination number
of 6. The coordination environment of the yttrium adopts
a structure of a distorted octahedron. The five-membered
metallacycle is nearly planar. The deviation of the yttrium
atom from the mean metallacycle plane is 0.085 Å, and the
dihedral angle between the N(1)Y(1)N(2) and the N(1)C(1)C(3)-
N(2) planes is 14.4°. The chelating N,N-ligand is bound to the
yttrium by two non-equivalent Y–N bonds: 2.292(3) and 2.451(4)
Å. The length of the shorter bond corresponds to the values
of covalent bonds reported for the yttrium complex coordi-
nated by dianionic ene–diamido ligand (2.247(1) and 2.243(1)
Å)9a as well as to those in six-coordinated yttrium–amido com-
plexes.12 The second Y–N bond is slightly shorter compared to
the coordination bond in the six-coordinated bis(amidinate)
yttrium complex (2.539(4) Å)13 but is very close to the values
measured for the tris(pyrazolylborate) complex (2.4288(17)–
2.4918(17) Å).14 The geometry of the planar NCCN fragment in
2Y is similar to that of the parent lithium compound 1.11 The
C–N bonds are non-equivalent: one bond (1.368(6) Å) is close
to a single C–N bond,15 while the second one (1.295(6) Å) per-
forms a double character.15 For comparison, the lengths of the
corresponding bonds in the related lithium compound are:
1.362(12) and 1.257(13) Å.11 The C(1)–C(2) bond length in 2Y
(1.373(6) Å) is characteristic for a double C–C bond15 and
is somewhat shorter than that in the lithium compound
(1.385(13) Å).11
Complexes 2Y and 2Lu are well soluble in THF and toluene
and moderately soluble in hexane. They are air- and moisture-
sensitive but can be stored in the crystalline state in an inert
atmosphere for several months without any evidence of
decomposition. The nature of the solvent turned out to be
crucial for the stability of dichloro complexes 2Y and 2Lu in
solution. Thus, 2Y is stable in THF or hexane solutions at
Scheme 1
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Scheme 2
Scheme 3
60 °C for several hours, but decomposes at ambient temp-
erature in aromatic solvents. The 1H NMR spectrum of 2Y
recorded in benzene-d6 at 293 K immediately after preparation
of the sample shows the expected set of signals attributed to
the unsymmetrical amido–imino ligand. Four doublets (1.03,
3
1.44, 1.50, 1.63 ppm, JHH = 6.7 Hz) and two septets (3.66,
4.20 ppm, 3JHH = 6.7 Hz) are attributed to methyl and methyne
protons of non-equivalent isopropyl groups. The protons of
the methyl group bound by the imino carbon give rise to a
sharp singlet at 1.86 ppm, while the protons of the methylene
group CvCH2 appear as two singlets at 3.98 and 4.59 ppm,
respectively. The complex multiplet in the region
7.00–7.25 ppm can be attributed to six aromatic protons of the
2,6-diisopropylphenyl moieties. The spectrum also contains
two broad singlets at 1.26 and 3.60 ppm due to the β- and
α-methylene protons of the coordinated THF molecules. After
several hours (∼2 h) the 1H NMR spectrum of 2Y indicated the Fig. 2 Molecular structure of complex [(2,6-iPr2C6H3)NC(vCH2)C(vCH2)-
N(C6H3-2,6-iPr2)]Y(μ2-Cl)2Li(THF)2 (3). Thermal ellipsoids are drawn at the 30%
probability level. Hydrogen atoms of 2,6-diisopropylphenyl substitutes and
presence of sets of signals characteristic of the parent diaza-
butadiene and yttrium complex coordinated by dianionic sym-
metric diamido ligand resulting from deprotonation of both
carbon and hydrogen atoms of THF molecules are omitted for clarity. Selected
distances (Å) and angles (°): Y(1)–N(1) 2.2533(15), Y(1)–N(2) 2.2350(16), Y(1)–Cl(1)
methyl groups by imino carbons [(2,6-iPr2C6H3)NC(vCH2)-
C(vCH2)N(C6H3-2,6-iPr2)]2− (Scheme 2).
2.6968(5), Y(1)–Cl(2) 2.6358(5), Y(1)–O(1) 2.4050(13), Y(1)–O(2) 2.3928(13),
Y(1)–Li(1) 3.525(3), N(1)–C(13) 1.392(2), N(2)–C(15) 1.394(2), C(13)–C(14) 1.349(3),
C(13)–C(15) 1.515(3), C(15)–C(16) 1.346(3); N(2)–Y(1)–N(1) 72.60(6), O(2)–Y(1)–
O(1) 91.06(5), Cl(2)–Y(1)–Cl(1) 83.283(16), C(14)–C(13)–N(1) 124.43(18), C(14)–
The 1H NMR spectrum displays a sharp singlet at 2.14 ppm
attributed to two equivalent methyl groups bound to the imino
carbons of DAD. In the 13C{1H}NMR spectrum the related
methyl carbons of DAD appear as a singlet at 16.2 ppm, while
the imino carbon atoms give rise to a singlet at 168.1 ppm.
C(13)–C(15)
121.17(18),
N(1)–C(13)–C(15) 114.38(16),
C(16)–C(15)–N(2)
124.55(19), C(16)–C(15)–C(13) 121.52(18), N(2)–C(15)–C(13) 113.94(16).
Two slightly broadened singlets at 3.34 and 4.82 ppm in the in vacuo, extraction of the solid residue with toluene, and
1H NMR spectrum can be attributed to the diastereotopic recrystallization of the product from a THF–hexane mixture
protons of the two CH2-groups of the [(2,6-iPr2C6H3)NC(vCH2)- afforded the complex [(2,6-iPr2C6H3)NC(vCH2)C(vCH2)-
C(vCH2)N(C6H3-2,6-iPr2)]2− ligand. The methylene carbons in N(C6H3-2,6-iPr2)]Y(THF)2(μ-Cl)2Li(THF)2 (3) in 61% yield as
the 13C{1H} NMR spectrum give rise to a singlet at 86.4 ppm, yellow crystals (Scheme 3). Complex 3 is highly air- and moist-
that is upfield shifted compared to the signal of the appropri- ure-sensitive, soluble in THF and toluene and poorly soluble
ate carbon in the spectrum of 2Y (93.8 ppm). The quaternary in hexane.
carbons of the NCCN-fragment of [(2,6-iPr2C6H3)NC(vCH2)-
Single crystal samples of complex 3 suitable for X-ray dif-
C(vCH2)N(C6H3-2,6-iPr2)]2− are equivalent and give rise to a fraction study were obtained by slow cooling of a saturated
single signal at 161.8 ppm. Moreover, YCl3(THF)2 was isolated solution of 3 in a THF–hexane mixture (1 : 5) from room temp-
from the reaction mixture in 40% yield. Analogous ligand sym- erature to −20 °C. The molecular structure of complex 3 is
metrization reaction was also observed for 2Lu. Unfortunately, depicted in Fig. 2, and the crystal and structural refinement
all our attempts of isolation of the yttrium-containing product data are summarized in Table 2. The X-ray diffraction study
in the crystalline state were unsuccessful.
revealed that complex 3 is an ate-complex. The chelating
In order to get evidence for the formation of yttrium diamido ligand is coordinated to the Y atom resulting in the
complex coordinated by dianionic symmetric diamido ligand formation of the planar five member metallacycle (the average
[(2,6-iPr2C6H3)NC(vCH2)C(vCH2)N(C6H3-2,6-iPr2)]YCl(THF)n deviation of the atoms from the plane is 0.09 Å). In addition,
in the course of the transformation of 2Y in solution, the reac- the yttrium atom is coordinated by two oxygen atoms of two
tion of [(2,6-iPr2C6H3)NC(vCH2)C(vCH2)N(C6H3-2,6-iPr2)]- THF molecules and two chloro ligands, which are μ2-bridging
9b
Li2(OEt2)n with an equimolar amount of YCl3 was carried between the yttrium and lithium atoms. The coordination
out in THF solution at room temperature. The removal of THF number of the yttrium atom is 6 and the geometry of the
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coordination sphere of the metal centre can be described as a
distorted octahedron. The lithium atom is, in turn, coordi-
nated by two THF molecules. The Y–N bonds in 3 have very
similar lengths (2.2350(16) and 2.2533(15) Å) and are slightly
shorter compared to the covalent Y–N bond in 2Y (2.292(3) Å)
but correspond to the values previously found for covalent
bonds in the related metallacyclic yttrium bisamido complex
(2.247(1) and 2.243(1) Å)9a and in six-coordinated yttrium
amides.12,16 The geometry of the diamido ligand in complex 3
substantially differs from that in complex 2Y. The C–C bond
(1.515(3) Å) as well as the C–N bonds within the NCCN frag-
ment in 3 (1.392(2) and 1.394(2) Å) are single bonds.15 The dis-
tances between the imino and methylene carbon atoms
(1.349(3) and 1.346(3) Å) are indicative of a double character of
these bonds.15 It should be noted that the sums of the bond
angles around the C(13) and C(15) atoms are 360.0° which
characterizes the sp2 hybridization of these atoms. Therefore,
the geometry of the diamido ligand can be described by the
structure N–C(vCH2)–C(vCH2)–N.
Scheme 4
In order to synthesize bis(alkyl) lanthanide species, the
alkylation reactions of 2Y and 2Lu with two equivalents of
LiCH2SiMe3 were carried out in hexane at 0 °C. The reaction
mixtures were stirred at this temperature for 2 h, then, yellow
solutions were filtered from the colourless precipitate of LiCl
and were concentrated at reduced pressure. Storing of resul-
tant solutions overnight at −20 °C allowed for isolation of
bright yellow crystals of [(2,6-iPr2C6H3)NvC(Me)C(vCH2)-
N(C6H3-2,6-iPr2)]Ln(CH2SiMe3)2(THF) (Ln = Y, 4Y; Lu, 4Lu) in
65 and 72% yield, respectively (Scheme 4). Decrease of the
yields of 4Y or 4Lu is obviously caused by their high solubility
in common organic solvents. Complexes 4Y and 4Lu are extre-
mely air- and moisture-sensitive, but in the solid state they can
be stored at 0 °C for several months without decomposition.
1
In the H NMR spectrum of complex 3, the diamido ligand
appears as two doublets at 1.21 and 1.29 ppm due to
the methyl groups of the isopropyl fragments and a poorly
resolved septet at 4.07 ppm assigned to the methine protons.
The methylene protons of the NC(vCH2) fragment appear as
two singlets at 3.36 and 4.87 ppm. The methylene carbons are
equivalent and give rise in the 13C{1H} NMR spectrum to a
singlet at 81.4 ppm. The singlet at 161.4 ppm corresponds to
1
According to the H NMR spectra, the dialkyl complexes 4Y
and 4Lu are rather stable. In the case of 4Y, during two weeks
(benzene-d6, 293 K) decomposition does not exceed 10%. The
methylene protons of two equivalent alkyl groups attached to
rare earth metal give rise in the 1H NMR spectra to charac-
teristic high field shifted signals at −0.53 (d, 2JYH = 3.0 Hz; 4Y)
and −0.73 (s, 4Lu) ppm. The trimethylsilyl protons give sharp
singlets at 0.18 (4Y) and 0.19 (4Lu) ppm, respectively. In the
13C{1H} NMR spectra of 4Y, the appropriate methylene and
methyl carbons of alkyl groups give rise to a doublet at 36.4
(1JYC = 40.0 Hz) and a singlet at 3.9 ppm, respectively. The
amido–imino ligands give, in the 1H and 13C{1H} NMR
spectra, the expected sets of signals similar to those observed
for dichloro complexes 2Y and 2Lu. It is noteworthy that
unlike dichloro complexes 2Y and 2Lu, bis(alkyl) species 4Y
and 4Lu turned out to be stable in benzene solution: no
evidence for ligand symmetrization has been found.
1
quaternary carbon atoms. Comparison of the H and 13C{1H}
NMR spectra of 3 and those of 2Y gives unambiguous evidence
of transformation of the amido–imino complex 2Y in benzene-
d6 solution to the dianionic symmetric diamido fragment
[(2,6-iPr2C6H3)NC(vCH2)C(vCH2)N(C6H3-2,6-iPr2)]2−
and
parent DAD (Fig. 3).
Single crystals of 4Y and 4Lu suitable for X-ray diffraction
study were obtained by prolonged cooling of concentrated
solution in THF–hexane mixture at −20 °C. The molecular
structure of 4Ln is depicted in Fig. 4. Complexes 4Y and 4Lu
are isostructural. Crystal and structural refinement data for 4Y
and 4Lu are summarized in Table 2.
According to the X-ray analysis, 4Y and 4Lu adopt mono-
meric structures. The metal atoms in 4Y and 4Lu are coordi-
nated by two nitrogen atoms of chelating amido–imino ligand,
by two carbon atoms of the trimethylsilylmethyl groups and by
the oxygen atom of the THF molecule, resulting in a coordi-
nation number of five. Two nitrogen atoms of the amido–
imino ligand, oxygen and yttrium atoms are located in the
same plane (maximum deviation is 0.07 Å), while two carbon
atoms of alkyl groups are situated under and above this plane.
Metal–carbon bond lengths in 4Y (2.374(5) and 2.421(4) Å) and
4Lu (2.320(4) and 2.352(4) Å) fall into the regions of values
Fig. 3 (A) 1H NMR spectrum of 3; (B) 1H NMR spectrum of 2Y (24 h after
sample preparation); # signals attributed to [(2,6-iPr2C6H3)NC(vCH2)C(vCH2)N-
(C6H3-2,6-iPr2)]YCl(THF)n; * signals attributed to (2,6-iPr2C6H3)NvC(Me)C(Me)v
N(C6H3-2,6-iPr2).
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Scheme 5
Fig. 4 Molecular structure of complex [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N-
(C6H3-2,6-iPr2)]Ln(CH2SiMe3)2(THF) (4Ln). Thermal ellipsoids are drawn at the
30% probability level. Hydrogen atoms of 2,6-diisopropylphenyl substitutes, tri-
methylsilylmethyl groups and THF molecule are omitted for clarity. Selected dis-
tances (Å) and angles (°) for 4Y: Y(1)–N(1) 2.476(3), Y(1)–N(2) 2.288(3), Y(1)–
C(29) 2.374(5), Y(1)–C(33) 2.421(4), Y(1)–O(1) 2.356(3), N(1)–C(13) 1.306(5),
N(2)–C(15) 1.376(5), C(13)–C(14) 1.493(6), C(13)–C(15) 1.497(6), C(15)–C(16)
1.363(6); N(1)–Y(1)–N(2) 67.63(12), C(29)–Y(1)–C(33) 109.17(15), N(1)–C(13)–
C(14) 124.1(4), N(1)–C(13)–C(15) 116.4(4), C(14)–C(13)–C(15) 119.4(4), N(2)–
C(15)–C(16) 126.5(4), C(13)–C(15)–C(16) 118.6(4), N(2)–C(15)–C(13) 114.7(4).
Selected distances [Å] and angles [°] for 4Lu: Lu(1)–N(1) 2.436(4), Lu(1)–N(2)
2.246(3), Lu(1)–C(29) 2.320(4), Lu(1)–C(33) 2.352(4), Lu(1)–O(1) 2.307(3), N(1)–
C(13) 1.295(5), N(2)–C(15) 1.372(5), C(13)–C(14) 1.506(6), C(13)–C(15) 1.493(6),
C(15)–C(16) 1.348(6); N(1)–Lu(1)–N(2) 69.10(11), C(29)–Lu(1)–C(33) 109.06(14),
N(1)–C(13)–C(14) 123.4(4), N(1)–C(13)–C(15) 117.6(4), C(14)–C(13)–C(15)
118.9(4), N(2)–C(15)–C(16) 126.6(4), C(13)–C(15)–C(16) 119.0(4), N(2)–C(15)–
C(13) 114.3(4).
Fig. 5 Molecular structure of complex {[(2,6-iPr2C6H3)NvC(Me)C(vCH2)N-
(C6H3-2,6-iPr2)]Y(CH2SiMe3)(μ-OMe)}2 (5). Thermal ellipsoids are drawn at the
30% probability level. Isopropyl groups and hydrogen atoms of the phenyl
rings, trimethylsilylmethyl and methoxy groups are omitted for clarity. Selected
distances (Å) and angles (°): Y(1)–O(1) 2.2246(16), Y(1)–O(1a) 2.2476(14), Y(1)–
C(29) 2.454(6), Y(1)–N(1) 2.3510(18), Y(1)–N(2) 2.4022(19), Y(1)–Y(1a) 3.5737
(5), O(1)–C(33) 1.434(3), C(13)–C(15) 1.415(3), C(13)–C(14) 1.484(3), C(14)–
C(16) 1.439(4), N(1)–C(13) 1.346(3), N(2)–C(14) 1.325(3); O(1)–Y(1)–O(1a) 73.92(6),
N(1)–Y(1)–N(2) 68.12(6), Y(1)–O(1)–Y(1a) 106.08(6), N(1)–C(13)–C(15) 124.6(2),
N(1)–C(13)–C(14) 115.93(19), C(14)–C(13)–C(15) 119.4(2), N(2)–C(14)–C(16)
125.0(2), N(2)–C(14)–C(13) 116.2(2), C(16)–C(14)–C(13) 118.68(19).
previously reported for five-coordinated yttrium and lutetium
bis(alkyl) species.17,26a Similarly to 2Y and 2Lu, the Ln–N
bonds in 4Y and 4Lu are non-equivalent. One Ln–N bond is
short (4Y 2.288(3); 4Lu 2.246(3) Å) and can be considered as a
covalent one. The second one is noticeably longer (4Y 2.476(3),
4Lu 2.436(4) Å) and corresponds to the values characteristic
for coordination Ln–N bonds.14 The bonding situation within
the NCCN fragment in 4Y and 4Lu is similar to that in 2Y and
2Lu: one short (4Y 1.306(5); 4Lu 1.295(5) Å) and one long (4Y
1.376(5); 4Lu 1.376(5) Å) C–N bonds. The distances between
imino carbons C(15) and carbons C(16) (4Y 1.363(6); 4Lu 1.348(6)
Å) are indicative of the double character of these bonds. The
length of the bond C(13)–C(15) (4Y 1.497(6); 4Lu 1.493(6) Å)
gives evidence for the absence of π–π conjugation and negative
charge delocalization in the CvC–CvN fragment.
(μ-OMe)}2 (5) (Scheme 5). The monitoring of this reaction by
1H NMR spectroscopy (benzene-d6, 20 °C) demonstrated that
the reaction is completed in 20 h, affording methoxy-alkyl
yttrium complex 5, SiMe4 and vinyl-methyl ester. The C–O
bond cleavage reactions performed by rare-earth hydrido com-
plexes and the resulting dimeric methoxy-18b and OCH2-
CH2OMe-bridged19 species have been previously documented.
Single crystal samples of 5 suitable for X-ray diffraction
study were obtained at room temperature from hexane solu-
tion. The molecular structure of 5 is depicted in Fig. 5, and the
crystal and structural refinement data are summarized in
Table 2.
Bis(alkyl) complex 4Y was treated with an excess of DME in
hexane solution at room temperature. Surprisingly, this reac-
tion did not lead to the expected substitution of THF by biden-
tate DME molecule in the coordination sphere of yttrium but
resulted in C–O bond cleavage of DME, the loss of one alkyl
group and afforded the methoxy-alkyl yttrium species {[(2,6-
iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-iPr2)]Y(CH2SiMe3)-
Complex 5 proved to be a centrosymmetric dimer in
which two [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-iPr2)]-
Y(CH2SiMe3) fragments are bound by two μ-bridging methoxy-
groups. The coordination environment of yttrium atom in 5 is
set up by two nitrogen atoms of chelating amido–imino
ligand, by two oxygen atoms of μ-bridging methoxy groups and
by a carbon atom of the terminal alkyl ligand (Fig. 5) and
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results in a coordination number of five. The coordination
environment of Y adopts the geometry of a distorted tetra-
gonal-pyramid. The Y2O2-core is absolutely planar with the
Y–O and Y–Y (2.2246(16), Y(1)–O(1a) 2.2476(14), Y(1)–Y(1a)
3.5737(5) Å) distances comparable to those previously
measured in dimeric methoxy-bridged yttrium complexes.19
The Y–C bond distance is 2.454(6). It is worth noting that, in
contrast to the parent alkyl complex 4Y, non-equivalence of
Y–N and C–N bonds in 5 is less pronounced and the geometry
of the YNCCN fragment is more symmetric. The Y–N bond
lengths in 5 are Y(1)–N(1) 2.3510(18) and Y(1)–N(2) 2.4022(19)
Å (compared to Y(1)–N(1) 2.476(3), Y(1)–N(2) 2.288(3) Å in 4Y).
The N–C bond lengths within the NCCN fragment are N(1)–
C(13) 1.346(3) and N(2)–C(14) 1.325(3) Å (compared to N(1)–
C(13) 1.306(5), N(2)–C(15) 1.376(5) Å). Non-equivalence of Y–N
and C–N bonds in complex 5 is less marked compared to 4Y.
Obviously this is a consequence of a disorder of methyl and
methylene groups observed in the crystalline structure of 5.
Complex 5 proved to be rather stable in benzene-d6 solution
at room temperature: no decomposition was observed for one
month. The methylene protons of the alkyl groups attached to
the yttrium appear in the 1H NMR spectrum as two slightly
Scheme 6
Fig. 6 Molecular structure of complex [(2,6-iPr2C6H3)NCHCHN(C6H3-2,6-
iPr2)]˙−YCl2(THF)2 (6). Thermal ellipsoids are drawn at the 30% probability level.
Hydrogen atoms of 2,6-diisopropylphenyl substitutes and THF molecules are
omitted for clarity. Selected distances (Å) and angles (°): Y(1)–O(1) 2.3549(10),
Y(1)–O(2) 2.3563(10), Y(1)–N(1) 2.3739(11), Y(1)–N(2) 2.3741(12), Y(1)–Cl(1)
2.5703(4), Y(1)–Cl(2) 2.5774(4), N(1)–C(2) 1.3307(19), N(2)–C(1) 1.3290(18),
C(1)–C(2) 1.398(2); O(1)–Y(1)–O(2) 105.94(4), N(1)–Y(1)–N(2) 70.22(4), Cl(1)–
Y(1)–Cl(2) 160.779(13), N(2)–C(1)–C(2) 120.09(13), N(1)–C(2)–C(1) 120.03(13).
2
broadened doublets at −0.62 and −0.51 (d, JHH = 11.2 Hz, the
Y–H coupling constant is not resolved) ppm. The appropriate
carbons of the alkyl groups give rise in the 13C{1H} spectra of 5
1
to characteristic doublet at 32.9 ppm (d, JYC = 49.0 Hz). A
sharp singlet at 2.38 ppm in the 1H NMR spectrum corres-
ponds to the protons of μ-bridging methoxy groups and the
related carbon atoms give rise to a singlet at 49.9 ppm in the
13C{1H} NMR spectra. The amido–imino ligand gives, in
the 1H NMR spectra, the expected set of signals. The methyl
group attached to the imino carbon appears as a sharp singlet
at 1.60 ppm, while the methylene group gives two singlets at
3.92 and 4.41 ppm. In the 13C{1H} NMR spectrum of 5, carbon
atoms of the methyl and methylene groups of amido–imino
ligands give singlets at 19.1 and 96.5 ppm, respectively.
To the best of our knowledge, rare-earths alkyl and hydrido
species coordinated by radical-anionic ancillary ligands still
remain unknown. Redox-active 1,4-diazabutadienes which are
able to receive one electron and to be reduced to a radical-
anion represent good candidates for the synthesis of related
derivatives. The reaction of in situ generated radical-anionic
lithium salt [(2,6-iPr2C6H3)NCHCHN(C6H3-2,6-iPr2)]˙−Li+-
(THF)n with anhydrous YCl3 was carried out at room temp-
erature in THF solution and afforded a related yttrium
dichloro complex [2,6-iPr2C6H3)NCHCHN(C6H3-2,6-iPr2]˙−YCl2-
(THF)2 (6) (Scheme 6). Complex 6 was isolated by slow layering
of hexane into THF solution as bright red-orange crystals in
84% yield. Complex 6 is extremely air- and moisture-sensitive
but can be stored in vacuum or under inert atmosphere
for several months without any evidence of decomposition.
Dichloro complex 6 is well soluble in THF and DME, less
soluble in aromatics and insoluble in hexane.
complex 6 recorded at room temperature in toluene solution
demonstrated a sharp characteristic signal attributed to the
uncoupled electron which interacts with two equivalent N, two
H and one Y nuclei (gi = 2.0022, AN(214N) = AH(21H) = 5.3 G,
AY(89Y) 2.1 G).
The X-ray study revealed that complex 6 is monomeric. The
molecular structure of 6 is depicted in Fig. 6, and the crystal
and structural refinement data are summarized in Table 2.
The coordination environment of the yttrium atom is set up by
two nitrogen atoms of chelating 1,4-diazabutadiene ligand, by
two terminal chloro ligands and by two oxygen atoms of co-
ordinated THF molecules, thus resulting in a formal coordi-
nation number of 6. The metal centre adopts a slightly
distorted octahedral geometry: yttrium, two nitrogen atoms of
chelating ligand and two oxygen atoms are situated in the
equatorial plane (maximum deviation is 0.04 Å), while two
chloro ligands occupy the apical positions. The diazabutadiene
ligand is symmetrically coordinated to the yttrium centre. The
yttrium–nitrogen distances in 6 (2.3739(11), 2.3741(12) Å) have
similar values, they are somewhat longer compared to the
covalent Y–N bonds in the six-coordinated yttrium amido com-
plexes12 or in complexes 2Y and 3, but shorter than Y–N
coordination bonds.13,14 These bond lengths correspond well
to the values reported for the related eight-coordinated yttrium
complex containing radical-anionic diazabutadiene ligand
(2.362(6) Å).20 The C–N bond lengths within the NCCN
fragment (1.3307(19) and 1.3290(18) Å) are longer, while the
C–C bond is shorter (1.398(2) Å) compared to those in parent
The radical-anionic character of the diazabutadiene ligand
in complex 6 in both solution and the crystalline state was
proved by EPR-spectroscopy. The EPR spectrum of dichloro
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diazabutadiene (2,6-iPr2C6H3)NvCHCHvN(C6H3-2,6-iPr2).21
The bonding situation within the NCCN fragment of 6 is
indicative of its radical-anionic state.20,22
In order to prepare related bis(alkyl) yttrium species the
reactions of dichloro complex 6 with alkyl lithium reagents
(LiCH2SiMe3, LiCH2C6H4-o-NMe2, MeLi) were carried out. The
reaction of 6 with two molar equivalents of LiCH2SiMe3 was
carried out in hexane at 0 °C. The reaction mixture was stirred
at this temperature for 2 h. Formation of a colourless precipi-
tate of LiCl indicated that the salt metathesis reaction took
place. Separation of LiCl from the reaction mixture and
removal of volatiles in vacuum afforded a deep-red viscous oil.
Unfortunately, all our attempts to isolate the reaction products
failed. The reaction of 6 with LiCH2C6H4-o-NMe2 in 1 : 2 molar
ratio was carried out in toluene at 0 °C. However, instead of
the expected yttrium bis(alkyl) complex, Y[CH2C6H4-o-NMe2]3
(7)23 and [(2,6-iPr2C6H3)NCHCHN(C6H3-2,6-iPr2)]˙−Li(THF)2
(8) were isolated in 32 and 43% yields, respectively (Scheme 7).
Complex 7 was authenticated by 1H and 13C NMR spectroscopy
and microanalysis, and 8 by EPR and microanalysis.
The process of 1,4-diazabutadiene ligand transfer from
yttrium to lithium was also observed in the reaction of 6 with
four molar equivalents of MeLi in the presence of TMEDA
(Et2O, 0 °C). The reaction afforded a mixture of [Li(TMEDA)]3-
[YMe6]24 (9) and [(2,6-iPr2C6H3)NCHCHN(C6H3-2,6-iPr2)]˙−Li-
(TMEDA) (10) (Scheme 8). Complexes 9 and 10 were isolated in
45 and 37% yield, respectively.
Fig. 7 Molecular structure of complex [(2,6-iPr2C6H3)NCHCHN(C6H3-2,6-
iPr2)]˙−Li(TMEDA) (10). Thermal ellipsoids are drawn at the 30% probability
level. Hydrogen atoms of 2,6-diisopropylphenyl substitutes and TMEDA mole-
cule are omitted for clarity. Selected distances (Å) and angles (°): Li(1)–N(2)
2.031(3), Li(1)–N(1) 2.043(3), Li(1)–N(4) 2.098(3), Li(1)–N(3) 2.184(3), N(1)–C(13)
1.3284(19), N(2)–C(14) 1.3289(19), C(13)–C(14) 1.403(2); N(2)–Li(1)–N(1)
85.73(11), N(4)–Li(1)–N(3) 83.61(10), N(1)–C(13)–C(14) 121.10(14), N(2)–C(14)–
C(13) 120.85(14).
deviation is 0.234(4) Å). The geometry of the NCCN fragment
in 10 is characteristic of the radical-anionic state.
Isoprene polymerization
Single crystals of 10 suitable for X-ray analysis were
obtained by cooling of a concentrated hexane solution at Bis(alkyl) rare earth species established a reputation as suit-
−20 °C. Complex 10 adopts a monomeric structure. The able precursors for catalytic systems performing controlled
coordination sphere of the lithium atom is formed by two diene polymerization with high activities and selectivities.
nitrogen atoms of the chelating radical-anion of diazabuta- Most of these catalytic systems are efficient for the production
diene and by two nitrogen atoms of the coordinated TMEDA of 1,4-polyisoprenes25 while the catalysts for the synthesis of
molecule (Fig. 7). The coordination environment of the 3,4-polyisoprenes are less numerous.17e,26 The binary catalytic
lithium atom in 10 can be described as a distorted tetrahedral systems LLnCl2/AlR3 (LLnCl2 = 2Y, 2Lu, 6; R = Et, iBu;
geometry. The dihedral angle between the LiNCCN and LiNN [LLnCl2] : [AlR3] molar ratio 1 : 10) were tested in isoprene
(TMEDA) planes is 66.6(4)°. The Li–N(NCCN) bonds in 10 are polymerization in toluene at room temperature and showed no
very similar (2.031(3) and 2.043(3) Å) and are somewhat catalytic activity, neither did the ternary systems LLnCl2/AlR3/
shorter than the coordination bond distances to the nitrogen borate (borate B(C6F5)3, [HNEt3][BPh4], [HNMe2Ph][B(C6F5)4]
atoms of TMEDA molecule (2.098(3) and 2.184(3) Å). Five or [CPh3][B(C6F5)4]; [LLnCl2] : [AlR3] : [borate] molar ratio
membered metallacycle LiNCCN is nearly planar (maximum 1 : 10 : 1). The catalytic activity of complexes 4Ln in isoprene
polymerization was explored in toluene under different con-
ditions at room temperature. The results of the catalytic tests
are summarized in Table 1. Complexes 4Ln alone turned out
to be inactive in isoprene polymerization. When complexes
4Ln were activated with an equimolar amount of borate
(B(C6F5)3, [HNEt3][BPh4], [HNMe2Ph][B(C6F5)4] or [CPh3]-
[B(C6F5)4]) no polymerization occurred (Table 1, entries 1–4).
Scheme 7
Also, organoaluminium reagents (AlEt3, AliBu3) were not suit-
able as activators (Table 1, entries 5, 6). The catalytic activities
of the ternary systems 4Ln/AlR3/borate proved to be dramati-
cally influenced by the nature of both AlR3 and borate com-
ponents. When AlEt3 was used, no catalytic activity was
detected (Table 1, entries 7–10), while the employment of
AliBu3 allowed for preparation of highly active catalytic systems
Scheme 8
4Ln/(AliBu3)/[HNMe2Ph][B(C6F5)4] and 4Ln/(AliBu3/[CPh3]-
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Table 1 Catalytic tests in isoprene polymerization by systems based on bis(alkyl) complexes 4Y and 4Lua
Boraneb
AlR3
t (min)
Conv. (%)
Mn c × 10−4
Mw/Mn
1,4-cisd (%)
1,4-transd (%)
3,4d (%)
c
Entry
Cat
[Ln]/[IP]
1
2
3
4
5
6
7
8
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Y
4Lu
4Lu
4Lu
1/1000
1/1000
1/1000
1/1000
1/1000
1/1000
1/1000
1/1000
1/1000
1/1000
1/1000
1/1000
1/1000
1/2500
1/4000
1/5000
1/5000e
1/5000f
1/1000
1/1000g
1/1000h
1/1000
1/1000
1/2500
A
B
C
D
—
—
A
—
—
—
—
360
360
360
360
360
360
360
360
360
360
360
360
20
50
70
80
100
120
20
20
360
20
0
0
0
0
0
0
0
0
0
—
—
—
—
—
—
—
—
—
—
—
—
—
2.14
2.39
2.54
3.52
2.64
3.39
8.71
2.97
—
2.47
8.63
2.51
1.42
2.40
1.68
—
—
—
—
—
—
—
—
—
—
—
—
15.0
15.8
16.4
14.3
17.1
16.9
27.0
7.4
—
—
—
—
—
—
—
—
—
—
—
—
—
25.0
6.2
12.3
13.5
17.9
18.7
7.0
17.6
—
—
—
—
—
—
—
—
—
—
—
—
—
60.0
78.0
71.3
72.2
65.0
64.4
66.0
75.0
—
—
—
—
—
—
—
—
—
—
AlEt3
AliBu3
AlEt3
AlEt3
AlEt3
AlEt3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
B
9
C
D
A
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
0
0
0
B
—
C
C
C
C
C
C
D
D
D
C
D
D
100
100
98
98
95
96
100
100
0
2.9
7.4
10.2
13.2
8.2
10.0
14.1
8.4
—
3.5
5.9
128.3
4.7
108.6
3.9
100
100
100
21.8
41.5
45.0
6.6
7.5
7.8
71.6
51.0
47.2
20
35
25
4Lu
1/5000
D
AliBu3
50
97
63.3
4.8
31.9
a Molar ratio of components of catalytic system precatalyst/AliBu3/borane = 1 : 10 : 1. b Borane: A = B(C6F5)3, B = [HNEt3][BPh4], C = [HNMe2Ph]-
[B(C6F5)4], D = [CPh3][B(C6F5)4]. c Mn and Mw/Mn were determined by GPC. d Polyisoprene microstructure was determined by 1H and 13C NMR
spectroscopy. e Polymerization was carried out at constant temperature (20 °C). f Polymerization was carried out in dilute solution (toluene
15 mL). g Polymerization was carried out in presence of 1 molar equivalent of Me2NPh. h Polymerization was carried out in presence of 10 molar
equivalents of Me2NPh.
[B(C6F5)4] (molar ratio 1 : 10 : 1, toluene, r.t.) able to convert
It was noted that at [IP]/[Ln] = 5000 : 1 ratio polymerization
into polymer 1000–5000 equivalents of isoprene in 20–120 min reaction was strongly exothermic. In order to decrease polydis-
with quantitative conversion (Table 1, entries 13–18 and persity of polyisoprenes, the catalytic tests ([IP]/[Ln] = 5000 : 1)
22–25) and to obtain polyisoprenes with high molecular were performed at controlled temperature (20 °C) and in more
weights and moderate polydispersities (2.14–3.52). The nature diluted solution (toluene, 15 mL). Control of temperature
of borate was found to play a crucial role as well: when (thermostat, 20 °C) allowed for a slight decrease of PDI from
B(C6F5)3 or [HNEt3][BPh4] were used instead of [HNMe2Ph]- 3.52 to 2.64 (Table 1, entries 16, 17). Dilution of the reaction
[B(C6F5)4] or [CPh3][B(C6F5)4], only trace amounts of polymer mixture did not influence the polydispersity (Table 1, entries
were obtained (Table 1, entries 7, 8 and 11, 12). With an 18). The system 4Lu/(AliBu3)/[HNMe2Ph][B(C6F5)4] ([IP]/[Ln] =
increase of the [IP]/[Ln] ratio, molecular weights of the 1000 : 1, Table 1, entry 12) showed similar activity and slightly
polymer samples obtained with catalytic system 4Y/(AliBu3)/ higher 3,4-selectivity (71.6 vs. 60.0%). It is noteworthy that the
[HNMe2Ph][B(C6F5)4] increase linearly (Table 1, entries 13–16) systems 4Ln/(AliBu3)/[CPh3][B(C6F5)4] performed activity
(Fig. 8). The polydispersities also increase gradually with an similar to those of the systems containing [HNMe2Ph]-
increase of monomer/catalyst ratio (Table 1, entries 13–16) [B(C6F5)4] ([IP]/[Ln] = 1000 : 1, Table 1, entries 13 and 19, 22
(Fig. 9).
and 23), however the molecular weights and the polydispersi-
It is noteworthy that the values of experimental molecular ties of the polymer samples obtained in the presence of
weights amount to only a half of the calculated ones ([IP]/[Ln] [CPh3][B(C6F5)4] were noticeably higher (4Y: Mn × 10−4 2.9 and
= 1000 : 1, experimental Mn × 10−4 = 2.9, calculated Mn × 10−4
=
14.1; Mw/Mn 2.14 and 8.71; 4Lu: Mn × 10−4 3.5 and 5.9; Mw/Mn
6.81; [IP]/[Ln] = 2500 : 1, experimental Mn × 10−4 = 7.4, calcu- 2.47 and 8.63). Regioselectivity was also proved to be influ-
lated Mn × 10−4 = 17.03). The decrease of molecular weights of enced by the nature of borane: for 4Y both systems possessed
the polymer samples may result from the enhanced instability similar 3,4-selectivities (60.0 and 66.0%), while for 4Lu, selec-
of the initiator at catalyst-preformation and polymerization tivity in the presence of [HNMe2Ph][B(C6F5)4] was noticeably
conditions as well as Al-mediated chain transfer.27 The system higher (71.6 vs. 51.0%). Such a different behavior of catalytic
4Y/(AliBu3)/[HNMe2Ph][B(C6F5)4] showed moderate regioselec- systems is obviously caused by the presence of Me2NPh in the
tivity with predominant 3,4-regularity (up to 78%) (Table 1, reaction mixture which forms as a by-product in the reaction
entries 13–20).
of 4Ln with [HNMe2Ph][B(C6F5)4]. In order to prove the effect
Dalton Trans.
This journal is © The Royal Society of Chemistry 2013

Table 2 Crystallographic data and structure refinement details for 2Y–10
Compound
2Y
2Lu
3
4Y
Chemical formula
Molecular weight
C36H55Cl2N2O2Y
707.63
C36H55Cl2LuN2O2
793.69
C44H70Cl2LiN2O4Y
857.77
C40H69N2OSi2Y
739.06
Crystal system
Space group
a (Å)
Monoclinic
P2(1)
13.6998(7)
17.3673(9
Monoclinic
P2(1)/n
10.22474(15)
19.8935(2)
Monoclinic
P2(1)/c
10.7796(4)
21.4931(8)
Orthorhombic
Pbca
12.8921(16)
17.167(2)
b (Å)
c (Å)
α (°)
15.5199(8)
90
18.6553(2)
90
20.0970(7)
90
39.247(5)
90
β (°)
90.2480(10)
90
3692.6(3)
4
1.273
1.756
102.4496(13)
90
3705.37(8)
4
1.423
2.840
103.8840(10)
90
4520.2(3)
2
1.260
1.449
90
90
γ (°)
V (Å3)
Z
8685.9(18)
8
1.130
1.427
DC (g cm−3
)
μ (mm−1
)
θ Range for data collection (°)
Reflections collected/unique
Data/restraints/parameters
Final R indices [I > 2σ(I)]
R indices (all data)
1.17–27.00
23 765/15 419 [R(int) = 0.0356]
15 419/7/786
R1 = 0.0513, wR2 = 0.1150
R1 = 0.0750, wR2 = 0.1250
0.923
2.89–30.00
75 908/10 778 [R(int) = 0.0843]
10 778/0/391
R1 = 0.0332, wR2 = 0.0497
R1 = 0.0595, wR2 = 0.0533
0.965
1.89–29.25
47 770/12 187 [R(int) = 0.0515
12 187/0/503
R1 = 0.0402, wR2 = 0.0863
R1 = 0.0657, wR2 = 0.0943
1.016
2.08–26.00
70 096/8525 [R(int) = 0.2178]
8525/14/440
R1 = 0.0684, wR2 = 0.1229
R1 = 0.1396, wR2 = 0.1377
0.997
Goodness-of-fit on F2
Compound
4Lu
5
6
10
Chemical formula
Molecular weight
C40H69N2OSi2Lu
825.12
C66H106N4O2Si2Y2
1221.55
C34H52Cl2N2O2Y
680.59
C32H52LiN4
499.72
Crystal system
Space group
a (Å)
Orthorhombic
Pbca
12.8244(10)
17.1331(14)
Monoclinic
P2(1)/n
12.8326(6)
20.5123(10)
Monoclinic
P2(1)/n
10.1030(6)
19.7166(12)
Monoclinic
P2(1)/c
13.6221(13)
12.2902(12)
b (Å)
c (Å)
α (°)
39.156(3)
90
13.8751(7)
90
18.5131(11)
90
19.4681(19)
90
β (°)
90
90
8603.4
8
1.274
2.380
109.9730(10)
90
3432.6(3)
2
1.182
1.795
105.3320(10)
90
3556.5(4)
4
1.271
1.820
100.295(2)
90
3206.8(5)
4
1.035
0.060
γ (°)
V (Å3)
Z
DC (g cm−3
)
μ (mm−1
)
θ Range for data collection (°)
Reflections collected/unique
Data/restraints/parameters
Final R indices [I > 2σ(I)]
R indices (all data)
2.05–26.00
68 189/8394 [R(int) = 0.0917]
8394/16/448
R1 = 0.0525, wR2 = 0.0827
R1 = 0.0813, wR2 = 0.0878
1.074
1.85–26.00
29 248/6722 [R(int) = 0.0386]
6722/73/376
R1 = 0.0465, wR2 = 0.1160
R1 = 0.0687, wR2 = 0.1247
1.045
2.10–26.00
30 475/6974 [R(int) = 0.0320]
6974/0/378
R1 = 0.0292, wR2 = 0.0670
R1 = 0.0402, wR2 = 0.0703
1.039
1.97–26.00
26 863/6300 [R(int) = 0.0453]
6300/0/354
R1 = 0.0492, wR2 = 0.1095
R1 = 0.0764, wR2 = 0.1187
1.033
Goodness-of-fit on F2

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Dalton Transactions
(C6H3-2,6-iPr2)]˙− ligand systems proved to be suitable coordi-
nation environment for the synthesis and isolation of mono-
meric salt-free yttrium and lutetium dichloro complexes
LLnCl2(THF)2. Complex [(2,6-iPr2C6H3)NvC(Me)C(vCH2)-
N(C6H3-2,6-iPr2)]YCl2(THF)2 is stable in THF and hexane
whereas in solutions of aromatic solvents undergoes the
ligand symmetrization reaction which afforded the yttrium
species coordinated by dianionic [(2,6-iPr2C6H3)NC(vCH2)-
C(vCH2)N(C6H3-2,6-iPr2)]2− ligand, DAD and YCl3(THF)n.
Dichloro complexes [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-
2,6-iPr2)]LnCl2(THF)2 coordinated by amido–imino ligand can
be easily alkylated with LiCH2SiMe3 to afford the related bis-
(alkyl) species [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-
iPr2)]Ln(CH2SiMe3)2(THF). On the contrary, all attempts to syn-
thesize bis(alkyl) yttrium complexes supported by radical-
anionic ligand failed. The alkylation reactions of [(2,6-
iPr2C6H3)NCHCHN(C6H3-2,6-iPr2)]YCl2(THF)2 with LiCH2C6H4-
o-NMe2 or MeLi resulted in transfer of radical-anionic ligand
from yttrium to lithium. Bis(alkyl) complex [(2,6-iPr2C6H3)-
NvC(Me)C(vCH2)N(C6H3-2,6-iPr2)]Y(CH2SiMe3)2(THF) despite
of its thermal stability demonstrated high reactivity in
cleavage of C–O bonds of DME. The reaction afforded a rare
example of alkoxy-alkyl species – {[(2,6-iPr2C6H3)NvC(Me)-
C(vCH2)N(C6H3-2,6-iPr2)]Y(CH2SiMe3)(μ-OMe)}2.
Fig. 8 Plot Mn vs. [IP]/[Ln] (catalytic system 4Y/[HNMe2Ph][B(C6F5)4]/AliBu3).
Bis(alkyl) yttrium and lutetium complexes 4Ln activated by
AliBu3 and borate (borate = [HNMe2Ph][B(C6F5)4] and [CPh3]-
[B(C6F5)4]; molar ratio 1 : 10 : 1) performed high catalytic
activity in isoprene polymerization affording polyisoprenes
with predominant 3,4-selectivity (up to 78%) and moderate
polydispersities (2.14–3.52). The nature of borate was found to
affect polyisoprene molecular weight and the 3,4-selectivity of
the polymerization reaction, but not the catalytic activity of the
ternary catalytic systems.
Fig. 9 Plot Mw/Mn vs. [IP]/[Ln] (catalytic system 4Y/[HNMe2Ph][B(C6F5)4]/
AliBu3).
of tertiary amine on Mn and Mw/Mn of polymers, the polymeri-
zation tests were carried out in the presence of 1 or 10 molar
equivalents of Me2NPh (Table 1, entries 20, 21). Polydispersity
of the polyisoprene obtained with the system 4Y/(AliBu3)/
[CPh3][B(C6F5)4] in the presence of one equivalent of Me2NPh
was found to be much lower compared to that in its absence
(Table 1, entries 19 and 20; 2.97 vs. 8.71) and just slightly
higher than that of the polymer produced by the system
4Y/(AliBu3)/[HNMe2Ph][B(C6F5)4] (Table 1, entries 13 and 4;
Mw/Mn 2.97 and 2.14). The Mn value and 3,4-regularity in the
case of the system 4Y/(AliBu3)/[CPh3][B(C6F5)4]/Me2NPh were
higher than those for 4Y/(AliBu3)/[HNMe2Ph][B(C6F5)4] (Mn:
8.4 × 104 vs. 2.9 × 104; 3,4-regularity: 75 vs. 60%). When ten
molar equivalents of Me2NPh were added, polymerization was
completely inhibited. The polyisoprenes obtained with 4Y at
different [IP]/[Ln] ratios showed monomodal distributions,
as revealed by GPC analysis. For the polymerization tests
catalyzed by 4Lu, the monomer loadings were increased up to
1 : 2500 and 1 : 5000, and the molecular weight distribution
became bimodal (Table 1, entries 24, 25).
Experimental
All experiments were performed in evacuated tubes by using
standard Schlenk techniques, with rigorous exclusion of traces
of moisture and air. After being dried over KOH, THF was puri-
fied by distillation from sodium/benzophenone ketyl; hexane
and toluene were dried by distillation from sodium/triglyme
and benzophenone ketyl prior to use. C6D6 was dried with
sodium and condensed in vacuo into NMR tubes prior to use.
CDCl3 was used without additional purification. 2,6-Diiso-
propylaniline, isopropylamine and Me2NC6H4-o-Me were pur-
chased from Acros and were dried over CaH2. 2,3-Butanedione
was purchased from Acros and was used without additional
purification. Methyl lithium solution (1.5 M in Et2O) and
Me3SiCH2Li (1.0 M in pentane) were purchased from Acros.
Anhydrous
YCl3,28
(2,6-iPr2C6H3)NvCHCHvN(C6H3iPr2-
2,6),21 (2,6-iPr2C6H3)NC(Me)CH(Me)(C6H3-2,6iPr2),29 and [(2,6-
iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-iPr2)]Li(OEt2)11 were
prepared according to published procedures. All other com-
Conclusions
Monoanionic amido–imino [(2,6-iPr2C6H3)NvC(Me)C(vCH2)- mercially available chemicals were used after the appropriate
N(C6H3-2,6-iPr2)]- and radical-anionic [(2,6-iPr2C6H3)NCHCHN- purifications. NMR spectra were recorded with and Bruker
Dalton Trans.
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Dalton Transactions
Paper
3
DPX 200 or Bruker Avance II 400 MHz spectrometers in CDCl3, iPr), 1.61 (d, JHH = 6.7 Hz, 6H, CH3 iPr), 1.86 (s, 3H, C–CH3),
3
C6D6 at 293 K, unless otherwise stated. Chemical shifts for 1H, 3.66 (br s, 8H, α-CH2 THF), 3.70 (sept, JHH = 6.7 Hz, 2H,
3
13C, 29Si, 7Li and 89Y NMR spectra were referenced internally to CH iPr), 4.00 (s, 1H, CvCH2), 4.21 (sept, JHH = 6.7 Hz, 2H,
the residual solvent resonances and are reported relative to CH iPr), 4.62 (s, 1H, CvCH2), 7.00–7.26 (complex m, together
TMS, 1 M LiCl or 1 M YCl3 in D2O. IR spectra were recorded as 6H, CH C6H3) ppm. 13C{1H} NMR (100 MHz, C6D6, 293 K): 19.6
Nujol mulls with a “Bruker-Vertex 70” instrument. Lanthanide (s, C–CH3), 24.5 (s, CH3 iPr), 24.7 (s, CH3 iPr), 24.9 (s, CH3 iPr),
metal analyses were carried out by complexometric titration. 25.0 (s, β-CH2 THF), 27.1 (s, CH3 iPr), 27.8 (s, CH iPr), 28.1 (s,
The C, H, N elemental analyses were performed in the micro- CH iPr), 70.1 (s, α-CH2 THF), 95.0 (s, CvCH2), 124.0 (s, CH
analytical laboratory of the G. A. Razuvaev Institute of Organo- m-C6H3), 124.2 (s, CH m-C6H3), 124.8 (s, CH p-C6H3), 126.6 (s,
metallic Chemistry.
CH p-C6H3), 141.2 (s, C o-C6H3), 146.9 (s, C o-C6H3), 147.1 (s, C
ipso-C6H3), 147.3 (s, C ipso-C6H3), 156.1 (s, CvCH2), 181.7 (s,
C–CH3) ppm. IR (Nujol, KBr, cm−1): 1640 (s), 1355 (m), 1335
(s), 1255 (m), 1135 (m), 1120 (m), 1110 (m), 990 (m), 965 (s),
Synthesis of [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-
iPr2)]YCl2(THF)2 (2Y)
A solution of 0.595 g (1.23 mmol) 1 in THF (10 mL) was added 855 (s), 785 (m), 640 (w). Elemental analysis: Calc. for
to a suspension of YCl3 (0.24 g, 1.23 mmol) in THF (15 mL) C36H55Cl2LuN2O2: C, 54.48; H, 6.98; N, 3.53; Lu, 22.04. Found:
and the reaction mixture was stirred for 3 h. The solvent was C, 54.31; H, 6.72; N, 3.27; Lu, 22.13.
removed in vacuum and the solid residue was extracted with
Synthesis of [(2,6-iPr2C6H3)NC(vCH2)C(vCH2)N(C6H3-2,6-
iPr2)]Y(THF)2(μ-Cl)2Li(THF)2 (3)
toluene (25 mL) and the toluene extracts were filtered for sep-
aration of LiCl. The solvent was removed in vacuum and the
solid residue was dissolved in THF–hexane mixture (1 : 4) and A of solution of nBuLi (4.94 mL, 1.0 M, 4.94 mmol) in hexane
kept overnight at −20 °C. The mother liquor was decanted was added to a solution of DAD (1.000 g, 2.47 mmol) in diethyl
from the yellow crystals. The crystals of 2Y were washed with ether (30 mL) at 0 °C. The reaction mixture was stirred for 1 h.
cold hexane and dried in vacuum for 10 min. Complex 2Y was The solvents were removed in vacuum and the solid residue
isolated in 78% yield (0.678 g, 0.96 mmol). 1H NMR (400 MHz, was dissolved in THF. The resulted solution was added to a
3
C6D6, 293 K): 1.03 (d, JHH = 6.7 Hz, 6H, CH3 iPr), 1.26 (br s, suspension of YCl3 (0.483 g, 2.47 mmol) in THF (10 mL) and
3
8H, β-CH2 THF), 1.44 (d, JHH = 6.7 Hz, 6H, CH3 iPr), 1.50 (d, the reaction mixture was stirred for 2 h. The solvent was
3
3JHH = 6.7 Hz, 6H, CH3 iPr), 1.63 (d, JHH = 6.7 Hz, 6H, CH3 removed in vacuum, and the solid residue was extracted with
iPr), 1.86 (s, 3H, C–CH3), 3.60 (br s, 8H, α-CH2 THF), 3.66 (sept, toluene (30 mL). The toluene extracts were filtered for sepa-
3JHH = 6.7 Hz, 2H, CH iPr), 3.98 (s, 1H, CvCH2), 4.20 (sept, ration of the precipitate of LiCl, and toluene was removed in
3JHH = 6.7 Hz, 2H, CH iPr), 4.59 (s, 1H, CvCH2), 7.00–7.25 vacuum. Recrystallization of the solid residue from a THF–
(complex m, together 6H, CH C6H3) ppm. 13C{1H} NMR hexane mixture (1 : 5) afforded yellow-orange crystals of
(100 MHz, C6D6, 293 K): 19.3 (s, C–CH3), 24.4 (s, CH3 iPr), 24.7 complex 3 in 61% yield (1.293 g, 1.51 mmol). 1H NMR
3
(s, CH3 iPr), 25.0 (s, CH3 iPr), 25.1 (s, β-CH2 THF), 27.1 (s, CH3 (400 MHz, C6D6, 293 K): 1.21 (d, JHH = 6.7 Hz, 12H, CH3 iPr),
3
iPr), 27.9 (s, CH iPr), 28.2 (s, CH iPr), 69.3 (s, α-CH2 THF), 93.8 1.29 (d, JHH = 6.7 Hz, 12H, CH3 iPr), 1.39 (br s, 16H, β-CH2
(s, CvCH2), 124.0 (s, CH m-C6H3), 124.2 (s, CH m-C6H3), 124.9 THF), 3.36 (s, 2H, CvCH2), 3.57 (br s, 16H, α-CH2 THF), 4.07
3
(s, CH p-C6H3), 126.6 (s, CH p-C6H3), 141.1 (s, C o-C6H3), 146.4 (sept, JHH = 6.7 Hz, 4H, CH iPr), 4.87 (s, 2H, CvCH2),
(s, C o-C6H3), 147.0 (s, C ipso-C6H3), 147.3 (s, C ipso-C6H3), 7.18–7.34 (complex m, together 6H, CH C6H3) ppm. 13C{1H}
156.1 (d, 2JYC = 2.0 Hz, CvCH2), 181.3 (s, C–CH3) ppm. The 2D NMR (100 MHz, C6D6, 293 K): 23.0 (s, CH3 iPr), 24.5 (s, CH3
Y–H g-HMQC NMR spectrum was set with hsqcetgp pulse iPr), 25.3 (s, β-CH2 THF), 27.7 (s, CH iPr), 67.7 (s, α-CH2 THF),
program, delay D1 = 1.5 s, cnst2 = 200, GPZ2 = 14% (400; 81.4 (s, CvCH2), 124.2 (s, CH m-C6H3), 124.9 (s, CH p-C6H3),
19.6 MHz, C6D6, 293 K): 1.86; 400.5 (Y⋯NC–CH3), 3.98; 400.5 141.1 (s, C o-C6H3), 147.0 (s, C ipso-C6H3), 161.2 (s, CvCH2)
(Y⋯NCvCH2), 4.59; 400.5 (Y⋯NCvCH2) ppm. IR (Nujol, KBr, ppm. 7Li NMR (155.5 MHz, C6D6, 293 K): 2.1 (br s) ppm.
cm−1): 1640 (s), 1355 (m), 1335 (s), 1250 (m), 1130 (m), 1125 Elemental analysis: Calc. for C44H70Cl2LiN2O4Y: C, 61.61; H,
(m), 1110 (m), 985 (m), 965 (s), 855 (s), 785 (m), 640 (w). 8.23; N, 3.27; Y, 10.36. Found: C, 61.39; H, 8.35; N, 3.16; Y,
Elemental analysis: Calc. for C36H55Cl2N2O2Y: C, 61.10; H, 10.41.
7.83; N, 3.96; Y, 12.56. Found: C, 60.1; H, 8.13; N, 4.16; Y,
12.67.
Synthesis of [(2,6-iPrC6H3)NvC(Me)C(vCH2)N(C6H3-2,6-iPr2)]-
Y(CH2SiMe3)2(THF) (4Y)
Synthesis of [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-
iPr2)]LuCl2(THF)2 (2Lu)
A
solution of Me3SiCH2Li (1
M in pentane, 2.0 mL,
2.00 mmol) was added to a suspension of 2Y (0.71 g,
A synthetic procedure similar to that of 2Y was used. LuCl3 1.00 mmol) in hexane (10 mL) at 0 °C. The reaction mixture
(0.36 g, 1.33 mmol) in THF (15 mL), 1 (0.643 g, 1.33 mmol) in was stirred for 1 h at 0 °C, then was filtered from LiCl and was
THF (10 mL). Yellow crystals of 2Lu were isolated in 72% yield concentrated under reduced pressure to one quarter of its
(0.758 g, 0.96 mmol). 1H NMR (400 MHz, C6D6, 293 K): 1.03 (d, initial volume. The resulting solution was stored at −20 °C for
3JHH = 6.7 Hz, 6H, CH3 iPr), 1.25 (br s, 8H, β-CH2 THF), 1.44 (d, 24 h. The mother liquor was decanted from yellow crystals, the
3
3JHH = 6.7 Hz, 6H, CH3 iPr), 1.50 (d, JHH = 6.7 Hz, 6H, CH3 crystals were washed with small amount of hexane and then
This journal is © The Royal Society of Chemistry 2013
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Dalton Transactions
dried in vacuum for 10 min. Complex 4Y was isolated in 65% stirred overnight at room temperature. Storing of the reaction
yield (0.482 g, 0.65 mmol). Single crystals of 4Y suitable for mixture overnight at −5 °C resulted in formation of bright
X-ray analysis were obtained by cooling of concentrated solution yellow cubic crystals. The mother liquor was decanted, crystals
1
in THF–hexane mixture (1 : 10, 2 mL) at −20 °C for 7 days. H were washed with cold hexane and dried in vacuum for
2
NMR (400 MHz, C6D6, 293 K): −0.53 (d, JYH = 3.0 Hz, 4H, 10 min. Complex 5 was isolated in 57% yield (0.232 g,
3
1
2
CH2SiMe3), 0.18 (s, 18H, CH2Si(CH3)3), 1.03 (d, JHH = 6.7 Hz, 0.19 mmol). H NMR (400 MHz, C6D6, 293 K): −0.62 (d, JHH
=
3
6H, CH3 iPr), 1.10 (m, 4H, β-CH2 THF), 1.32 (d, JHH = 6.7 Hz, 11.2 Hz, 2H, YCH2SiMe3, YH coupling constant is not
3
2
12H, CH3 iPr), 1.52 (d, JHH = 6.7 Hz, 6H, CH3 iPr), 1.78 (s, 3H, resolved), −0.51 (d, JHH = 11.2 Hz, 2H, YCH2SiMe3, YH coup-
C–CH3), 3.21 (sept, JHH = 6.7 Hz, 2H, CH iPr), 3.35 (br s, 4H, ling constant is not resolved), 0.34 (s, 18H, CH2Si(CH3)3), 0.97
α-CH2 THF), 3.47 (sept, JHH = 6.7 Hz, 2H, CH iPr), 3.89 (s, 1H, (d, JHH = 6.8 Hz, 6H, CH3 iPr), 1.05 (d, JHH = 6.8 Hz, 6H, CH3
3
3
3
3
3
CvCH2), 4.45 (s, 1H, CvCH2), 7.08–7.20 (complex m, together iPr), 1.21 (d, JHH = 6.8 Hz, 12H, CH3 iPr), 1.32–1.42 (complex
6H, CH C6H3) ppm. 13C{1H} NMR (100 MHz, C6D6, 293 K): 3.9 m, together 24 H, CH3 iPr), 1.60 (s, 6H, C–CH3), 2.38 (s, 6H,
(s, CH2Si(CH3)3), 19.8 (s, C–CH3), 24.5 (s, CH3 iPr), 24.6 (s, OCH3), 2.75 (sept, 3JHH = 6.8 Hz, 2H, CH iPr), 3.10 (sept, 3JHH
=
β-CH2 THF), 24.9 (s, CH3 iPr), 25.0 (s, CH3 iPr), 25.8 (s, CH3 6.8 Hz, 4H, CH iPr), 3.90 (sept, 3JHH = 6.8 Hz, 2H, CH iPr), 3.92
1
iPr), 28.4 (s, CH iPr), 28.7 (s, CH iPr), 36.4 (d, JYC = 40.0 Hz, (s, 2H, CvCH2), 4.41 (s, 2H, CvCH2), 6.84–7.22 (complex m,
YCH2SiMe3), 69.8 (s, α-CH2 THF), 93.9 (s, CvCH2), 123.9 (s, together 12H, CH C6H3) ppm. 13C{1H} NMR (100 MHz, C6D6,
CH m-C6H3), 124.3 (s, CH p-C6H3), 124.5 (s, CH m-C6H3), 126.8 293 K): 4.1 (s, CH2Si(CH3)3), 19.1 (s, C–CH3), 23.1 (s, CH3 iPr),
(s, CH p-C6H3), 139.8 (s, C p-C6H3), 143.4 (s, C ipso-C6H3), 23.8 (s, CH3 iPr), 24.5 (s, CH3 iPr), 24.6 (s, CH3 iPr), 24.9 (s,
2
145.2 (s, C p-C6H3), 146.8 (s, C ipso-C6H3), 156.9 (d, JYC
=
CH3 iPr), 25.1 (s, CH3 iPr), 26.1 (s, CH3 iPr), 26.6 (s, CH3 iPr),
2.0 Hz, CvCH2), 181.1 (d, JYC = 1.0 Hz, C–CH3) ppm. The 2D 28.1 (s, CH iPr), 28.5 (s, CH iPr), 28.6 (s, CH iPr), 32.9 (d, 1JYC
=
2
Y–H g-HMQC NMR spectrum was set with hsqcetgp pulse 49.0 Hz, YCH2SiMe3), 49.9 (s, OCH3), 96.5 (s, CvCH2), 123.6
program, delay D1 = 1.5 s, cnst2 = 200, GPZ2 = 14% (400; (s, CH C6H3), 123.7 (s, CH C6H3), 124.2 (s, CH C6H3), 124.4 (s,
19.6 MHz, C6D6, 293 K): −0.53; 940.6 (Y⋯CH2SiMe3), 0.18; CH C6H3), 124.7 (s, CH C6H3), 126.9 (s, CH C6H3), 139.2 (s, C
940.6 (Y⋯CH2Si(CH3)3), 1.78; 940.6 (Y⋯C–CH3), 3.47; C6H3), 139.5 (s, C C6H3), 142.7 (s, C C6H3), 144.4 (s, C C6H3),
2
940.6 (Y⋯CH(CH3)2), 3.86; 940.6 (Y⋯NCvCH2), 4.45; 940.6 145.1 (s, C C6H3), 146.3 (s, C C6H3), 156.8 (d, JYC = 1.0 Hz,
2
(Y⋯NCvCH2)
ppm.
Elemental
analysis:
Calc.
for CvCH2), 182.8 (d, JYC = 1.0 Hz, C–CH3) ppm. 29Si{1H} NMR
2
C40H69N2OSi2Y: C, 65.00; H, 9.41; N, 3.79; Y, 12.03. Found: (79.5 MHz, C6D6, 293 K): −2.8 (d, JYSi = 4.1 Hz, YCH2SiMe3)
C, 64.57; H, 9.14; N, 4.11; Y, 12.15.
ppm. The 2D Y–H g-HMQC NMR spectrum was set with
hsqcetgp pulse program, delay D1 = 1.5 s, cnst2 = 200, GPZ2 =
14% (400; 19.6 MHz, C6D6, 293 K): −0.62; 635.9
(Y⋯CH2SiMe3), −0.51; 635.9 (Y⋯CH2SiMe3), 0.34; 635.9
(Y⋯CH2Si(CH3)3), 2.38; 635.9 (Y⋯O–CH3), 4.41; 635.9
(Y⋯NCvCH2) ppm. Elemental analysis: Calc. for C66H106N4O2-
Si2Y2: C, 64.89; H, 8.75; N, 4.59; Y, 14.56. Found: C, 65.12; H,
8.14; N, 5.12; Y, 14.49.
Synthesis of [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-iPr)]-
Lu(CH2SiMe3)2(THF) (4Lu)
The synthetic procedure similar to that of 4Y was used. 2Lu
(0.632 g, 0.79 mmol) in hexane (10 mL), 1.59 mL (1.0 M,
1.59 mmol) Me3SiCH2Li. Complex 4Lu was isolated as yellow
1
crystals in 72% yield (0.482 g, 0.57 mmol). H NMR (400 MHz,
C6D6, 293 K): −0.73 (s, 4H, CH2SiMe3), 0.19 (s, 18H, CH2Si-
3
(CH3)3), 1.04 (d, JHH = 6.7 Hz, 6H, CH3 iPr), 1.32 (complex m,
3
together 16H, CH3 iPr and β-CH2 THF), 1.55 (d, JHH = 6.7 Hz,
6H, CH3 iPr), 1.75 (s, 3H, C–CH3), 3.24 (sept, 3JHH = 6.7 Hz, 2H,
CH iPr), 3.46 (complex m, together 6H, α-CH2 THF and CH
iPr), 3.89 (s, 1H, CvCH2), 4.47 (s, 1H, CvCH2), 7.08–7.20
(complex m, together 6H, CH C6H3) ppm. 13C{1H} NMR
(100 MHz, C6D6, 293 K): 4.1 (s, CH2Si(CH3)3), 20.1 (s, C–CH3),
24.5 (s, CH3 iPr), 24.6 (s, CH3 iPr), 25.1 (s, CH3 iPr), 25.2 (s,
β-CH2 THF), 26.0 (s, CH3 iPr), 28.3 (s, CH iPr), 28.6 (s, CH iPr),
42.6 (s, LuCH2SiMe3), 70.5 (s, α-CH2 THF), 95.5 (s, CvCH2),
123.9 (s, CH m-C6H3), 124.3 (s, CH p-C6H3), 124.6 (s, CH
m-C6H3), 126.9 (s, CH p-C6H3), 140.1 (s, C o-C6H3), 143.5 (s, C
ipso-C6H3), 145.0 (s, C o-C6H3), 148.2 (s, C ipso-C6H3), 157.2 (s,
CvCH2), 181.5 (s, C–CH3) ppm. Elemental analysis: Calc. for
C40H69LuN2OSi2: C, 58.22; H, 8.43; N, 3.40; Lu, 21.20. Found:
C, 58.39; H, 8.55; N, 3.26; Lu, 21.17.
Synthesis of [(2,6-iPr2C6H3)NCHCHN(C6H3-2,6-
iPr2)]˙−YCl2(THF)2 (6)
Li (0.018 g, 2.66 mmol) and (iPr2C6H3)NvC(H)C(H)v
N(C6H3iPr2) (1.000 g, 2.66 mmol) in THF (25 mL) were stirred
at room temperature until complete disappearance of Li metal.
The resulted red-orange solution was added to a suspension of
anhydrous YCl3 (0.520 g, 2.66 mmol) in THF (10 mL) and the
reaction mixture was stirred for 2 h. The solvent was removed
in vacuum, and the resulted solid residue was extracted with
toluene. The toluene extract was evaporated to dryness. The
resulted solid was recrystallized from a mixture of THF–hexane
(1 : 4) at 0 °C to give 1.52 g of 6 (84%, 2.23 mmol). EPR spec-
trum (9.644 GHz, THF, 293 K): gi = 2.0022, AN(214N) = AH(21H)
= 5.3 G, AY(89Y) = 2.1 G. IR (Nujol, KBr, cm−1): 1638 (s), 1345
(s), 1309 (s), 1243 (s), 1184 (m), 1135 (m), 1058 (m), 971 (m),
952 (s), 844 (s), 788 (m), 639 (w). Elemental analysis: Calc. for
Synthesis of [(2,6-iPr2C6H3)NvC(Me)C(vCH2)N(C6H3-2,6-
iPr2)]Y(CH2SiMe3)(μ-OMe)]2 (5)
DME (0.3 mL) was added to a solution of complex 4Y (0.493 g, C34H52Cl2N2O2Y: C, 60.00; H, 7.70; N, 4.12; Y, 13.06. Found: C,
0.67 mmol) in hexane (15 mL) and the reaction mixture was 60.10; H, 7.82; N, 4.09; Y, 13.14.
Dalton Trans.
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Paper
Reaction of 6 with LiCH2SiMe3
Polymerization of isoprene
A
solution of LiCH2SiMe3 (1.38 mL, 1 M in pentane, A typical polymerization procedure was carried out as follow-
1.38 mmol) was added to a suspension of 6 (0.470 g, ing. Under a nitrogen atmosphere and room temperature,
0.69 mmol) in hexane (15 mL) at 0 °C and the reaction mixture a toluene solution (2 mL) of 10 mmol of borate was added to a
was stirred for 2 h. The precipitate of LiCl was separated by fil- toluene solution (3 mL) of complex 4Y (7.4 mg, 10 mmol) in a
tration. Hexane was removed in vacuum to give a deep-red oil.
25 mL flask. Then 10 equiv. of AliBu3 (0.1 mL, 100 mmol,
1.0 M in toluene) were added under stirring over the course of
a few min. Upon the addition of 1000–5000 equiv. of isoprene
(1–5 mL, 0.01–0.05 mol), polymerization was initiated and
carried out for 20–360 min. The reaction mixture was poured
into methanol and then dried under vacuum at ambient temp-
erature to a constant weight. Then, 1,4- 3,4-regioselectivity was
determined by 1H and 13C{1H} NMR spectroscopy. GPC of poly-
isoprenes was performed in THF at 20 °C. The number average
molecular masses (Mn) and polydispersity indexes (Mw/Mn) of
the polymers were calculated with reference to a universal cali-
bration against polystyrene standards.
Reaction of 6 with LiCH2C6H4-o-NMe2, formation of
[(2,6-iPr2C6H3)NCHCHN(C6H3-2,6-iPr2)]˙−Li(THF)2 (8)
A suspension of LiCH2C6H4-o-NMe2 (0.271 g, 1.92 mmol) in
toluene (15 mL) was added to a solution of 6 (0.653 g,
0.96 mmol) in toluene (15 mL) at 0 °C and the reaction
mixture was stirred for 2 h. The resulting solution was filtered
from LiCl and concentrated in vacuum to approximately 0.1 of
its initial volume. Storing of concentrated solution at −20 °C
for 3 d resulted in the formation of pale yellow crystals of
Y[CH2C6H4-o-NMe2]3 (7) (0.151 g, 0.31 mmol, 32%). 1H NMR
of 7 (400 MHz, C6D6, 293 K): 1.62 (s, 6H, YCH2), 2.05 (s, 18H, N
(CH3)2), 6.67 (t, 3JHH = 7.0 Hz, 3H, CH C6H4), 6.80 (d, 3JHH = 7.5
X-Ray crystallography
The X-ray data for 2Y-10 were collected on a Agilent Xcalibur E
diffractometer (2Y) and SMART APEX diffractometer (2Lu-10)
(graphite-monochromated, MoKα-radiation, ω-scan technique,
λ = 0.71073 Å, T = 100(2) K). The structures were solved by
direct methods and were refined on F2 using CrysAlis Pro [X2]
(2Y) and SHELXTL30 (2Lu-10) package. All non-hydrogen atoms
and HC14,C16 in 3, HC16 in 4Lu and HC13,C14 in 10 were found
from Fourier syntheses of electron density and were refined
anisotropically. All other hydrogen atoms in 2Y-10 were placed
in calculated positions and were refined in the riding model.
ABSPACK (CrysAlis Pro)31 (2Y) and SADABS32 (2Lu-10) was used
to perform area-detector scaling and absorption corrections.
The details of crystallographic, collection and refinement data
are shown in Table 2 and the corresponding cif files are avail-
able as ESI.† CCDC-915562–915569 contain the supplementary
crystallographic data for this paper.
3
Hz, 3H, CH C6H4), 7.00 (t, JHH = 6.8 Hz, 3H, CH C6H4), 7.11
(d, 3JHH = 6.5 Hz, 3H, CH C6H4). Elemental analysis: Calc. for 7
C27H36N3Y: C, 65.98; H, 7.38; N, 8.55; Y, 18.09. Found: C,
66.12; H, 7.57; N, 8.33; Y, 17.92. The volatiles of the mother
liquor were removed in vacuum and the solid residue was
dried for 30 min. The resulting solid residue was dissolved in
THF–hexane mixture (1 : 4, 5 mL). Slow concentration of the
resulted solution at room temperature afforded red crystals of
(8) (0.228 g, 0.43 mmol, 43%). EPR spectrum (9.644 GHz, THF,
293 K): gi = 2.0030, AN(214N) = AH(21H) = 5.65 G, ALi(7Li) = 0.85
G. Elemental analysis: Calc. for 8 C34H52LiN2O2: C, 77.30; H,
9.93; N, 5.31. Found: C, 77.43; H, 9.98; N, 5.33.
Reaction of 6 with MeLi, formation of [(2,6-iPr2C6H3)-
NCHCHN(C6H3-2,6-iPr2)]˙−Li(TMEDA) (10)
A solution MeLi (1.60 mL, 1.5 M in Et2O, 2.40 mmol) and
TMEDA (0.3 g, 2.6 mmol) was added to a solution of complex
6 (0.411 g, 0.60 mmol) in Et2O (15 mL) at 0 °C. The reaction
mixture was stirred for 1 h. The volatiles were removed in
vacuum and the solid residue was extracted with toluene. The
toluene extracts were filtered. Slow concentration of the
toluene solution at room temperature resulted in formation of
colorless crystals of [Li(TMEDA)]3[YMe6] (9) (0.148 g,
0.27 mmol, 45%). 1H NMR for 9 (400 MHz, C6D6, 293 K): −0.54
(s, 18H, YCH3), 1.90 (s, 12H, CH2 TMEDA), 2.19 (s, 36H, CH3
TMEDA). Elemental analysis: Calc. for 9 C27H36N3Y: C, 65.98;
H, 7.38; N, 8.55; Y, 18.09. Found: C, 66.12; H, 7.57; N, 8.33; Y,
17.92. The mother liquor was separated and the volatiles were
removed in vacuum. The solid residue was dissolved in hexane
(5 mL) and stored at −20 °C overnight. Red cubic crystals of
complex 10 were isolated in 37% yield (0.110 g, 0.22 mmol).
EPR spectrum (9.644 GHz, toluene, 293 K): gi = 2.0030,
AN(214N) = AH(21H) = 5.7 G. Elemental analysis: Calc. for
C32H52LiN4: C, 76.91; H, 10.49; N, 11.21. Found: C, 76.83; H,
10.67; N, 11.35.
Acknowledgements
This work has been supported by the Russian Foundation for
Basic Research (grant number 11-03-91163-ΓΦEH; 12-03-
31493-
-a), Program of the Presidium of the Russian
Academy of Science (RAS), and RAS Chemistry and Material
Science Division. We thank Dr A. Poddel’sky for recording the
EPR spectra.
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