Triketiminate bis(borohydride) complexes of rare-earth metals [(2,6-Me2C6H3N=CMe)2C(2,6-Me2C6H3N=CBut)]Ln(BH4)2(THF)2 (Ln = Y, Nd): sy

Article abstract of DOI:10.1007/s11172-017-1939-9

A new triketimine (2,6-Me₂C₆H₃N=CMe)₂CH(2,6-Me₂C₆H₃N=CBu^t) (1) was synthesized by the reaction of imidoyl chloride 2,6-Me₂C₆H₃N=CClBu<

Full text of DOI:10.1007/s11172-017-1939-9

Russian Chemical Bulletin, International Edition, Vol. 66, No.9, pp. 1665—1674, September, 2017
1665
Triketiminate bis(borohydride) complexes of rareꢀearth metals
[(2,6ꢀMe2C6H3N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]Ln(BH4)2(THF)2
(Ln = Y, Nd): synthesis, structure, and catalytic activity
in polymerization of racꢀlactide, εꢀcaprolactone, and isoprene
G. G. Skvortsov,а A. V. Cherkasov,а and A. A. Trifonovа,b
aG. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
49 ul. Tropinina, 603950 Nizhny Novgorod, Russian Federation.
Fax: +7 (083 12) 66 1497. Eꢀmail: trif@iomc.ras.ru
bA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119334 Moscow, Russian Federation
A new triketimine (2,6ꢀMe2C6H3N=CMe)2CH(2,6ꢀMe2C6H3N=CBut) (1) was syntheꢀ
sized by the reaction of imidoyl chloride 2,6ꢀMe2C6H3N=CClBut with lithium diketiminate
(2,6ꢀMe2C6H3N=CMe)2CHLi. In the crystalline state, compound 1 exists in the diimineꢀ
enamine form; in solution, in the triimine form. The metalation of triketimine 1 with
nꢀbutyllithium in THF at 0 °C produced lithium triketiminate [(2,6ꢀMe2C6H3N=CMe)2C(2,6ꢀ
Me2C6H3N=CBut)]Li(THF)2 (2). The metathesis reactions of Ln(BH4)3(THF)3 (Ln = Y,
Nd) with compound 2 (1 : 1 molar ratio, THF) gave the neutral triketiminate bis(borohydride)
complexes [(2,6ꢀMe2C6H3N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]Ln(BH4)2(THF)2 (Ln = Y (3),
Nd (4)). As opposed to the complexes with neutral triketimine, the monoanionic triketꢀ
iminate ligand is coordinated to Li and Y or Nd cations in a bidentate fashion. Complexes 3
and 4 catalyze the polymerization of racꢀlactide and εꢀcaprolactone; in combination with
[Ph3C][B(C6F5)4] and AlBui3 (1 : 1 : 10 molar ratio), these compounds exhibit catalytic
activity in the polymerization of isoprene.
Key words: rareꢀearth metals, triketiminate ligand, borohydride ligand, synthesis, strucꢀ
ture, catalysis, isoprene, lactide, polymerization.
Due to large ionic radii,1 high electrophilicity, and
Lewis acidity of rareꢀearth ions, the coordinative and sterꢀ
ic saturations of the metal coordination sphere are key
factors responsible for stability and reactivity of such comꢀ
pounds. Therefore, in recent years considerable attention
has been paid to the synthesis of new ligands, which can
be coordinated to rareꢀearth ions and form stable comꢀ
pounds with these elements.2—6 Since rareꢀearth metals
are electropositive7 and the metal—ligand interactions in
their organic derivatives are predominantly ionic, ligands
capable of forming stable anions are preferred in this field
of chemistry. This is the reason why cyclopentadienyl
complexes have long been the most popular organic
derivatives of rareꢀearth metals.8 Polydentate ligand sysꢀ
tems containing rigid Nꢀ and/or Oꢀcoordination sites,
which can sterically and coordinatively saturate the rareꢀ
earth metal ion sphere, thus providing kinetic stability of
the metal complex, are of particular interest. Among these
systems are bulky βꢀdiketiminate ligands, which were synꢀ
thesized for the first time in 1997.9 This type of coordinaꢀ
tion environment has great potential for stabilization of
organolanthanides, as demonstrated by the fact that the
use of βꢀdiketiminate ligands makes it possible to isolate
even very unstable diethyl derivatives,10 which are usually
prone to βꢀhydride elimination. Recently, the synthesis
of a series of new related βꢀtriketimines, as well as
complexes of a number of metals with these ligands, was
reported,11—16 and these compounds were found to exꢀ
hibit interesting properties, including catalytic activity in
the polymerization of isoprene. However, the coordinaꢀ
tion of this type of ligands to rareꢀearth ions is as yet
unknown.
Borohydride complexes of lanthanides are of great inꢀ
terest due to their structural diversity and high catalytic
activity.17 In recent years, a renaissance in the chemistry
of borohydride derivatives of lanthanides has been inꢀ
spired by reports on their high catalytic activity in the
polymerization of lactones,18,19 methyl methacrylate,20
and isoprene.21
* Dedicated to Academician of the Russian Academy of Sciences
G. A. Abakumov on the occasion of his 80th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1665—1674, September, 2017.
1066ꢀ5285/17/6609ꢀ1665 © 2017 Springer Science+Business Media, Inc.

1666
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017
Skvortsov et al.
In the present work, we synthesized a new triketimine
(2,6ꢀMe2C6H3N=CMe)2CH(2,6ꢀMe2C6H3N=CBut) (1)
and investigated possible modes of coordination of its
anion [(2,6ꢀMe2C6H3N=CMe)2C(2,6ꢀMe2C6H3N=Cꢀ
But)]– to lithium and rareꢀearth metal cations. The strucꢀ
tures of the complexes [(2,6ꢀMe2C6H3N=CMe)2C(2,6ꢀ
Me2C6H3N=CBut)]Li(THF)2 (2) and [(2,6ꢀMe2ꢀ
C6H3N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]Ln(BH4)2ꢀ
(THF)2 (Ln = Y (3), Nd (4)) in the crystalline state were
determined and the catalytic activity of the borohydride
complexes in the polymerization of racꢀlactide, εꢀcaproꢀ
lactone, and isoprene was investigated.
N(5)
C(10)
С(6)
O(5)
С(2)
С(1)
N(1)
С(3)
С(19)
N(2)
H(1)
Results and Discussion
С(27)
Synthesis and structures of triketamine 1
and borohydride complexes 2—4
Triketimine 1 was synthesized by the reaction of imiꢀ
doyl chloride 2,6ꢀMe2C6H3N=CClBut with lithium diꢀ
ketiminate (2,6ꢀMe2C6H3N=CMe)2CHLi in toluene and
was isolated as a white powder in 80% yield (Scheme 1).
Triketimine 1 was characterized by elemental analysis,
NMR and IR spectroscopy, and mass spectrometry.
Crystals of triketimine 1 suitable for Xꢀray diffraction
were obtained by slow concentration of a solution of 1 in
acetonitrile. The molecular structure of 1 is shown in
Fig. 1. Selected bond lengths and bond angles are given in
Fig. 1. Molecular structure of compound 1 with displacement
ellipsoids drawn at the 30% probability level. The hydrogen
atoms, except for the H(1) atom, are not shown.
Table 1. In the crystalline state, compound 1 exists in the
diimineꢀenamine tautomeric form, in which the hydroꢀ
gen atom is located on the nitrogen atom of one of the
dimethylaniline moieties rather than on the methine
Scheme 1
Reagents: i. 1) Toluene, 2) pꢀtoluenesulfonic acid, ii. 1) toluene, 2) nBuLi; iii. CH2Cl2; iv. PCl5; v. toluene.

Triketiminate bis(borohydride) complexes
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017 1667
Table 1. Selected bond lengths (d) and bond angles (ω) in compounds 1, 2, and 4
Bond
d/Å
Angle
ω/deg
Bond
d/Å
Angle
ω/deg
Compound 1
Compound 2
N(1)—C(1) 1.303(2)
N(2)—C(3) 1.349(2)
N(3)—C(5) 1.284(2)
C(3)—C(2)—C(1)
C(1)—C(2)—C(5)
C(3)—C(2)—C(5)
N(2)—C(3)—C(2)
N(1)—C(1)—C(2)
N(3)—C(5)—C(2)
C(3)—N(2)—H(1)
C(27)—N(2)—H(1) 120.0(9)
C(5)—N(3)—C(10) 124.4(2)
C(2)—C(5)—C(6)
121.6(2)
119.6(2)
118.7(2)
122.0(2)
119.8(2)
126.4(2)
115.2(9)
C(2)—C(3)
C(2)—C(5)
1.436(2)
1.516(2)
N(1)—C(1)—C(2)
N(2)—C(3)—C(2)
123.84(9)
123.3(2)
Compound 4
C(1)—C(2)
C(2)—C(3)
C(2)—C(5)
1.454(2)
1.393(2)
1.509(2)
Nd(1)—N(1) 2.434(3)
Nd(1)—N(2) 2.446(3)
Nd(1)—O(1) 2.61(2)
Nd(1)—O(2) 2.74(2)
N(1)—C(1) 1.338(4)
N(1)—C(19) 1.445(4)
N(2)—C(3) 1.341(4)
N(2)—C(27) 1.446(4)
C(1)—C(2)
C(2)—C(3)
C(2)—C(6)
N(3)—C(6) 1.276(4)
Nd(1)—B(1) 2.651(4)*
Nd(1)—B(2) 2.661(4)*
N(1)—Nd(1)—N(2)
B(1)—Nd(1)—B(2)
C(1)—C(2)—C(3)
N(1)—Nd(1)—O(1)
N(1)—Nd(1)—O(2) 166.0(4)
N(2)—Nd(1)—O(2) 95.2(4)
N(2)—Nd(1)—O(1) 167.9(2)
O(1)—Nd(1)—O(2)
O(1)—Nd(1)—B(1)
O(2)—Nd(1)—B(2)
N(3)—C(6)—C(2)
H(1)—Nd(1)—H(2)
H(5)—Nd(1)—H(6)
71.18(8)
163.7(2)
124.5(3)
97.1(2)
N(1)—C(19) 1.414(2)
N(2)—C(27) 1.432(2)
N(3)—C(10) 1.418(2)
N(2)—H(1) 0.92(2)
119.6(2)
Compound 2
96.7(5)
84.6(2)
83.4(4)
125.1(3)
34.8(2)
38.0(2)
Li(1)—N(2) 1.958(2)
Li(1)—N(1) 1.973(2)
Li(1)—O(2) 1.975(2)
Li(1)—O(1) 1.977(2)
N(2)—C(3) 1.314(2)
N(1)—C(1) 1.324(2)
N(3)—C(5) 1.280(2)
N(2)—Li(1)—N(1)
90.47(9
1.418(4)
1.419(4)
1.523(4)
N(2)—Li(1)—O(2) 117.4(2)
N(1)—Li(1)—O(2) 117.6(2)
N(2)—Li(1)—O(1) 110.7(2)
N(1)—Li(1)—O(1) 120.2(2)
O(2)—Li(1)—O(1)
C(1)—C(2)—C(5) 119.47(9)
C(3)—C(2)—C(5) 117.47(9)
101.2(2)
C(1)—N(1)—C(19) 116.2(3)
C(3)—N(2)—C(27) 117.6(3)
Nd(1)—H
2.37(4)—
2.48(4)
C(1)—C(2)
1.428(2)
* The distances between the atoms are given.
carbon. The central C(1)C(2)C(3)C(5) moiety is planar
(the maximum deviation of the atoms from the plane is
0.008(2) Å). Compound 1 adopts the (E,E,Z) conformꢀ
ation (Scheme 2). The central C(1)C(2)C(3)C(5) moiety
is asymmetric because of a considerable difference in the
C—C bond lengths. Thus, the C(1)—C(2) and C(2)—C(5)
bond lengths (1.454(2) and 1.509(2) Å, respectively) corꢀ
respond to the single bond length, whereas the C(2)—C(3)
bond length (1.393(2) Å) is indicative of its doubleꢀbond
character.22 Consequently, the planar structure of the
C(1)C(2)C(3)C(5) moiety is attributed to the presence of
a double bond between the C(2) and C(3) atoms. The
C—N bond lengths in triketimine 1 are also not equivaꢀ
lent. The N(1)—C(1) and N(2)—C(3) bond lengths
(1.303(2) and 1.349(2) Å, respectively) are similar to the
single bond length, whereas the N(3)—C(5) bond length
(1.284(2) Å) is typical of C=N double bonds.22 Thereꢀ
fore, the geometric parameters of compound 1 in the
crystalline state indicate that it exists in the diimineꢀ
enamine form.
In the 1H NMR spectrum of triketimine 1, protons of
But substituents appear as one singlet at δ 1.24. The methyl
protons of three 2,6ꢀdimethylaniline moieties and imino
groups N=CMe are seen as four singlets at δ 1.98, 2.07,
2.08, and 2.11 with equal integrated intensity each correꢀ
sponding to six protons. Aromatic protons appear in
a weak field as two triplets (3JH,H = 7.4 Hz) at δ 6.80 and
6.88, one doublet at δ 6.94 (3JH,H = 7.4 Hz), and a mulꢀ
tiplet at δ 7.01. Based on the NMR spectroscopic data
1
(2D H—13C HSQC) in deuterobenzene, the singlet at
Scheme 2
Crystallization
Dissolution
Triimine
Diimineꢀenamine

1668
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017
Skvortsov et al.
Scheme 3
δ 5.17 was assigned to the methine proton of the central
CHCCC moiety. Therefore, compound 1 exists as triꢀ
imine. It should be noted that the 13C NMR spectrum
also shows a single set of signals corresponding to the
triimine tautomeric form of compound 1. An examinaꢀ
tion of the 1H NMR spectra of compound 1 in a wide
temperature range (C7D8, T = –15—50 °C) revealed no
evidence of the existence of the second prototropic tauꢀ
tomer in solution. The IR spectrum of 1 recorded as Nujol
mulls shows intense absorption bands at 1676 (s), 1662 (s),
and 1595 cm–1 (s) corresponding to asymmetric vibraꢀ
tions of C=N double bonds of the triketiminate ligand
and a broadened absorption band at 3304 cm–1 assigned
to N—H stretching vibrations of the diimineꢀenamine
form. In the IR spectrum of compound 1 in CH2Cl2,
absorption bands characteristic of N—H stretching vibraꢀ
tions are absent.
tons appear in a weak field as a multiplet (at δ 6.85—7.05).
The 7Li NMR spectrum of complex 2 shows a single
signal at δ 1.60.
Therefore, the investigations of the structure of comꢀ
pound 1 by Xꢀray diffraction, 1H and 13C NMR spectroꢀ
scopy, and IR spectroscopy led to the conclusion that
this compound exists in the diimineꢀenamine form in the
crystalline state, while it is transformed into the triimine
form in solution.
Transparent yellow crystals of complex 2 suitable for
Xꢀray diffraction were obtained by slow cooling of a conꢀ
centrated solution of 2 in tetrahydrofuran to –20 °C. The
structure of complex 2 is shown in Fig. 2. Selected bond
lengths and bond angles are given in Table 1. According
to the Xꢀray diffraction data, compound 2 is a monomerꢀ
ic lithium complex, in which the coordination sphere of
the Li+ cation is formed by two nitrogen atoms of the
triketiminate ligand and two oxygen atoms of coordinatꢀ
ed THF molecules. Therefore, the formal coordination
number (CN) of the lithium atom is 4. The nitrogen atom
of the {2,6ꢀMe2C6H3N=CBut} moiety is not involved in
the complexation. In complex 2, the Li—N bond lengths
(1.958(2), 1.973(2) Å) are similar to the Li—N bond
lengths in the related diketiminate complexes [HC(2,6ꢀ
It is known that alkyl derivatives of rareꢀearth metals
are active catalysts (or their precursors) for a number of
transformations of unsaturated substrates.6 In order to
synthesize triketiminate bis(alkyl) complexes of yttrium
and lutetium, we performed the reactions of 1 with the
tris(alkyl) complexes Ln(CH2SiMe3)3(THF)2 (Ln = Y,
Lu)23,24 in C6D6 at 25 °C controlled by 1H NMR spectroꢀ
scopy. It was found that, despite the presence of a labile
proton, compound 1 is inert to Ln(CH2SiMe3)3(THF)2
(Ln = Y, Lu). Besides, triketimine 1 did not react in
THF (25 °C, 12 h) with the alkyl derivatives of yttrium
Y(Me)6Li3(TMEDA)3 and Y(oꢀCH2C6H4NMe2)3 and
with the cationic alkyl complex Y(Me)2(THF)5+[BPh4]–.
After the removal of the solvents and recrystallization of
the solid residues from a THF—hexane mixture, the startꢀ
ing reagents were isolated in quantitative yield.
N(3)
C(5)
The lithiation of triimine 1 with nꢀbutyllithium readiꢀ
ly proceeds at room temperature in THF (Scheme 3).
After the recrystallization from tetrahydrofuran, the
lithium complex [(2,6ꢀMe2C6H3N=CMe)2C(2,6ꢀMe2ꢀ
C6H3N=CBut)]Li(THF)2 (2) was isolated as yellow crysꢀ
tals in 76% yield. Complex 2 is extremely sensitive to
atmospheric moisture and oxygen, readily soluble in THF,
and very poorly soluble in aliphatic hydrocarbons. Comꢀ
pound 2 was characterized by elemental analysis and
NMR and IR spectroscopy.
C(10)
C(2)
C(1)
C(3)
N(1)
C(19)
N(2)
C(27)
Li(1)
In the 1H NMR spectrum (25 °C, C6D6) of complex 2,
protons of But substituents appear as a singlet at δ 1.67.
Protons of eight methyl groups are seen as four singlets
with equal integrated intensity at δ 1.75, 1.93, 2.18, and
2.33. Two multiplets at δ 1.15 and 3.12 belong to methylene
protons of coordinated THF molecules. Aromatic proꢀ
O(1)
O(2)
Fig. 2. Molecular structure of compound 2 with displacement
ellipsoids drawn at the 30% probability level. The hydrogen
atoms and methyl substituents of the tertꢀbutyl group at the
C(5) atom are not shown.

Triketiminate bis(borohydride) complexes
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017 1669
Pri C6H3N=CMe)2]Li(DME) and [HC(2ꢀPriC6H4ꢀ
green (4) crystals in 71 and 80% yield, respectively. Comꢀ
plexes 3 and 4 are sensitive to atmospheric moisture and
oxygen and are readily soluble in aromatic and aliphatic
hydrocarbons, as well as in ethereal solvents.
2
N=CMe)2]Li(THF)2 (see Refs 25 and 26). Thus, the
analysis of the N(1)—C(1) (1.324(2) Å), C(1)—C(2)
(1.428(2) Å), C(2)—C(3) (1.436(2) Å), and C(3)—N(2)
(1.314(2) Å) bond lengths in the planar N(1)C(1)C(2)ꢀ
C(3)N(2) moiety shows that the negative charge is
delocalized within the βꢀdiketiminate skeleton {(2,6ꢀ
Me2C6H3N=CMe)2C}, whereas the moiety of the triꢀ
ketiminate ligand {2,6ꢀMe2C6H3N=CBut} that is not
coordinated to the lithium cation contains the isolated
C—C single bond (1.516(2) Å) and C=N double bond
(1.280(2) Å). The metallocycle Li(1)N(1)C(1)C(2)ꢀ
C(3)N(2) is nonꢀplanar (the average deviation of the
atoms from the plane is 0.172(2) Å). The dihedral angle
between the N(1)Li(1)N(2) and N(1)C(1)C(2)C(3)N(2)
planes is 27.80(8)°.
Scheme 4
Earlier, it was demonstrated that neutral triketimines
3
generally act as κ ꢀNNNꢀchelating ligands in the comꢀ
plexation with transition metal ions.13—15 However,
in the recently synthesized cobalt complexes with triꢀ
ketimine (2,4,6ꢀMe3C6H2N=CMe)2CH(2,4,6ꢀMe3ꢀ
2
C6H2N=CMe), the latter is κ ꢀNNꢀcoordinated to the
metal ion, which is not typical of the neutral ligand.16
The difference in the coordination mode of neutral
triketimines is attributed not only to steric properties
of the ligands but also, apparently, to the nature of the
complexꢀforming agent. Thus, triketimine (2,4,6ꢀMe3ꢀ
C6H2N=CMe)2CH(2,4,6ꢀMe3C6H2N=CMe), which acts
as a bidentate ligand16 in the cobalt complexes (0.58 Å,
Ln = Y (3, 71%), Nd (4, 80%)
The 1H NMR spectrum of diamagnetic complex 3
shows a single set of signals of the triketiminate ligand
[(2,6ꢀMe2C6H3N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]–:
a singlet at δ 1.48 belonging to But groups and four
singlets at δ 1.52, 1.85, 2.08, and 2.17 assigned to methꢀ
yl protons of xylidine and (MeC=N) moieties. Aroꢀ
matic protons appear as a multiplet at δ 6.79—7.14. In
the 1H NMR spectrum of complex 3, BH4 ligands
are seen as four strongly broadened singlets with equal
intensity at δ 1.15, 1.24, 1.36, and 1.57. Two multiplets
at δ 1.29 and 3.62 are assigned to coordinated THF
molecules.
In the 11B NMR spectrum of diamagnetic complex 3,
borohydride ligands give a single singlet at δ –25.1. In the
IR spectra of complexes 3 and 4, borohydride ligands
exhibit five broad absorption bands in the region characꢀ
teristic of stretching vibrations of terminal and bridging
B—H bonds: 2471, 2372, 2288, 2220, 2164 cm–1 for 3
and 2434, 2331, 2289, 2250, 2228 cm–1 for 4.
Crystals of complex 4 suitable for Xꢀray diffraction
were obtained by slow condensation of hexane into a conꢀ
centrated solution of 4 in THF. The molecular structure
of bis(borohydride) complex 4 is shown in Fig. 3. Selectꢀ
ed bond lengths and bond angles are given in Table 1.
According to the Xꢀray diffraction data, compound 4 is
a neutral monomeric neodymium bis(borohydride) comꢀ
plex, in which the triketiminate ligand is coordinated to
the lanthanide metal ions in a bidentate fashion. The
Nd—N distances in complex 4 (2.434(3), 2.446(3) Å) are
slightly different from each other and are comparable with
the corresponding distances in the related neodymium βꢀdiꢀ
3
CN = 4),1 exhibits a κ ꢀNNNꢀcoordination mode in the
complexes with nickel (0.63 Å, CN = 5)1 that has a someꢀ
what larger ionic radius.13 In lithium complex 2 (0.59 Å,
CN = 4),1 unlike compounds with neutral triketimines,
the localization of the negative charge on the central
carbon atom in the monoanionic ligand [(2,6ꢀMe2ꢀ
C6H3N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]–, responsible
for the planar structure of the carbanionic C(1)C(2)ꢀ
C(3)C(5) moiety, virtually excludes the possibility of
binding the third nitrogen atom to the lithium cation Li+
(see Fig. 2).
In order to study the coordination capabilities of the
new potentially tridentate triketiminate ligand [(2,6ꢀ
Me2C6H3N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]– in the
complexation with lanthanide metal ions Ln3+ with large
ionic radii, we performed the reactions of complex 2 with
Ln(BH4)3(THF)3 (Ln = Y, Nd) in a 1 : 1 ratio of
the reagents in THF (Scheme 4). The reaction with
Y(BH4)3(THF)3 was accomplished during 3 h at 65 °C,
while the reaction with Nd(BH4)3(THF)3 was performed
at 25 °C for 48 h and at 60 °C for 3 h (see Scheme 4). After
the extraction of the reaction products with toluene folꢀ
lowed by recrystallization from a THF—hexane mixture,
the bis(borohydride) complexes [(2,6ꢀMe2C6H3ꢀ
N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]Ln(BH4)2(THF)2
(Ln = Y (3), Nd (4) were isolated as colorless (3) and

1670
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017
Skvortsov et al.
ketiminate complexes [HC(2,6ꢀPri2C6H3N=CMe)2]ꢀ
NdCl2(THF)2 (2.459(4), 2.444(4) Å)27 and [HC(2,6ꢀMe2ꢀ
C6H3N=CMe)2]NdCl3Li(THF)3 (2.445(5), 2.422(5) Å).28
The C—N and C—C bond lengths (N(1)—C(1), 1.338(4) Å;
N(2)—C(3), 1.341(4) Å; C(1)—C(2), 1.418(4) Å;
C(2)—C(3), 1.419(4) Å) in the planar N(1)C(1)C(2)ꢀ
C(3)N(2) moiety of complex 4 are in the range of
1.338(3)—1.419(4) Å and are indicative of delocalization
of the negative charge over the βꢀdiketiminate group,
while the third [2,6ꢀMe2C6H3N=CBut] moiety of the
triketiminate ligand, by analogy with complex 2, conꢀ
tains the isolated C—C single bond (1.523(4) Å) and C=N
double bond (1.276(4) Å) and is not involved in the inꢀ
teraction with the metal center. As in complex 2,
the metallocycle Nd(1)N(1)C(1)C(2)C(3)N(2) is nonꢀ
planar (the average deviation of the atoms from the
plane is 0.167(2) Å). The dihedral angle between the
N(1)Nd(1)N(2) and N(1)C(1)C(2)C(3)N(2) planes
is somewhat smaller than the corresponding angle
in 2 (27.80(8)°) and is equal to 22.8(2)°. The Nd—B disꢀ
tances in structure 4 are 2.651(4) and 2.661(4) Å, which
are substantially longer than those in the borohydride
Polymerization of racꢀlactide, εꢀcaprolactone,
and isoprene
We studied the catalytic activity of bis(borohydride)
complexes 3 and 4 in the polymerization of racꢀlactide,
εꢀcaprolactone, and isoprene.
The polymerization of lactide was performed in toluꢀ
ene at monomer/catalyst ratios of 100/1, 250/1, and 500/1
(Table 2, runs 1—6). The complete conversion of 500
equivalents of the monomer catalyzed by complexes 3
and 4 is achieved in 24 h at 25 °C and produces polymers
with an average molecular weight Mw = 20135—59283,
Mn = 13711—23713 and a rather narrow molecular weight
distribution (Mw/Mn = 1.5—2.5). According to the
1H NMR data, the resulting polylactides are atactic.
A comparison of the experimental numberꢀaverage moꢀ
lecular weights evaluated by gelꢀpermeation chromatoꢀ
graphy with the values, which were calculated taking into
account the initial monomer/initiator ratio and the conꢀ
version values, demonstrates that two polymer chains
grow at one metal center, i.e., both borohydride groups of
3 and 4 are involved in the initiation of polymerization.
At low monomer/initiator ratios (100—250), apart from
a good agreement between the experimental and calcuꢀ
lated Mn values, a relatively narrow molecular weight
distribution was observed (Mw/Mn = 1.5—2.3). However,
when the monomer/initiator ratio was increased to
500 equivalents, the experimental Mn values were subꢀ
stantially smaller than the calculated values, which is
indicative of side processes, such as esterification and/or
chain transfer to monomer reactions.
complexes [Nd(C5HPri )(BH4)2(THF)] (2.605(3),
4
2.595(3) Å)21 and [Nd{(Me3Si)2NC(NCy)2}2ꢀ
(BH4)2Li(THF)2] (2.454(3), 2.504(4) Å)29 and are subꢀ
stantially shorter than the corresponding distances in the
dinuclear complex [Nd(COT)(BH4)(THF)]2 (2.875(6),
2.941(6) Å).30 The Nd—B distances in 4 are simiꢀ
lar to those in the amidinate complex [6ꢀMeꢀ
C5H3Nꢀ2ꢀCH2C(NPri)2]Nd(BH4)2(THF)2 (2.676(3),
2.671(3) Å).31
N(3)
C(6)
C(11)
C(2)
C(3)
C(1)
N(1)
C(19)
N(2)
C(27)
B(1)
Nd(1)
B(2)
O(1)
O(2)
Fig. 3. Molecular structure of compound 4 with displacement ellipsoids drawn at the 30% probability level. The hydrogen atoms and
methyl substituents of the tertꢀbutyl group at the C(6) atom are not shown.

Triketiminate bis(borohydride) complexes
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017 1671
Table 2. Polymerization of racꢀlactide initiated by complexes 3
and 4
Complexes 3 and 4 exhibited high catalytic activity in
the polymerization of εꢀcaprolactone. In the polymerizaꢀ
tion catalyzed by yttrium complex 3, the complete conꢀ
version of 1000 equivalents of the monomer was achieved
within 20 min at 25 °C. Neodymium complex 4 is much
more active in the polymerization of εꢀcaprolactone comꢀ
pared to yttrium bis(borohydride) 3 and allows the prepaꢀ
ration of polymer samples characterized by a narrow
molecular weight distribution (Mw/Mn = 1.4—1.7) and
exp
calc
Run Complex
[М]0
[Ln]0
t/h
Mn
•
Mn
•
Mw/Mn
•10–3
•10–3
1
2
3
4
5
6
3
3
3
4
4
4
100
250
500
100
250
500
16
12
24
16
12
24
19.03
15.40
13.71
19.77
13.41
23.71
17.21
18.02
36.04
17.21
18.02
36.04
1.6
1.5
1.5
2.0
2.3
2.5
average molecular weights Mw = 18160—58108, Mn
=
= 12711—37944 within a few seconds (Table 3, runs 5—8).
It was found that complexes 3 and 4 and the twoꢀ
component systems 3 or 4/[Ph3C][B(C6F5)4] (1 : 1) and
3 or 4/AlBui3 (1 : 10) cannot initiate the polymerization
of isoprene in toluene at room temperature. However,
the threeꢀcomponent catalytic systems 3 or 4/AlBui3/
[Ph3C][B(C6F5)4] (1 : 10 : 1) exhibit moderate activity in
the polymerization of isoprene and can provide ~60%
conversion of 1000 equivalents of the monomer in 48 h
under mild conditions giving polymers composed mainly
of cisꢀ1,4 units (62.7—66.1% of 1,4ꢀcis units) (Table 4,
runs 3 and 6). The resulting polymers are characterized
by a rather broad molecular weight distribution (Mw/Mn =
= 3.2—3.3) and low molecular weights (Mn = 6.1—6.3•103).
In summary, the lithium triketiminate complex
[(2,6ꢀMe2C6H3N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]Liꢀ
(THF)2 (2) was synthesized by the reaction of triketimine
1 with nꢀbutyllithium. First rareꢀearth metal complexes
with the anionic triketiminate ligand were prepared and
structurally characterized. The bis(borohydride) complexꢀ
es of rareꢀearth metals [(2,6ꢀMe2C6H3N=CMe)2C(2,6ꢀ
Me2C6H3N=CBut)]Ln(BH4)2THF2 (Ln = Y (3), Nd (4))
were synthesized by the metathesis reactions of
Ln(BH4)3(THF)3 (Ln = Y, Nd) with lithium triketꢀ
iminate 2. According to the Xꢀray diffraction data, both
in lithium complex 2 (the ionic radius of Li+ is 0.59 Å,
CN = 4)1 and the complex of neodymium having a much
larger ionic radius (1.11 Å, CN = 8),1 the monoanionic
triketiminate ligand is coordinated to the metal ion in
Note. Conditions: toluene, [M] = 1.0 mol L–1, T = 25 °C. The
conversion of the monomer M was determined by Н NMR
1
spectroscopy and was equal to 100% in all experiments. The
exp
molecular weights Mn
of the polymers were determined by
gelꢀpermeation chromatography using polystyrene standards.
calc
Mn
were calculated by the equation 144.14Y•0.5[M]/[Ln]
(Y is the yield).
Table 3. Polymerization of εꢀcaprolactone initiated by comꢀ
plexes 3 and 4
exp
calc
Run Complex
[М]0
[Ln]0
t/s
Mn
•
Mn
•
Mw/Mn
•10–3
•10–3
1
2
3
4
5
6
7
8
3
3
3
3
4
4
4
4
1100
1250
1500
1000
1100
1250
1500
1000
1240
1300
1480
1200
1110
1115
1125
1150
21.38
33.22
39.94
27.90
12.97
12.71
21.78
37.94
15.71
14.27
28.54
57.07
15.71
14.27
28.54
57.07
2.6
2.7
1.8
1.4
1.7
1.4
1.4
1.5
Note. Conditions: toluene, [M] = 1.0 mol L–1, T = 25 °C. The
conversion of the monomer M was determined by 1Н NMR
spectroscopy and was equal to 100% in all experiments. The
exp
molecular weights Mn
of the polymers were determined by
gelꢀpermeation chromatography using polystyrene standards.
calc
Mn
were calculated by the equation 114.14Y•0.5[M]/[Ln]
(Y is the yield).
Table 4. Polymerization of isoprene initiated by the catalytic systems 3— or 4—AlBui3—[Ph3C][B(C6F5)4] (1 : 10 : 1)
Run Complex
Borate
AlR3
t/h
Y (%)
Positions of units
Mn•10–3
Mw/Mn
cisꢀ1,4
transꢀ1,4
3,4
1
2
3
4
5
6
3
3
3
4
4
4
—
AlBui3
—
24
24
48
24
24
48
10
10
56
10
10
59
—
—
62.7
—
—
66.1
—
—
34.2
—
—
32.0
—
—
3.1
—
—
1.9
—
—
6.1
—
—
6.3
—
—
3.2
—
—
3.3
TB
TB
—
TB
TB
AlBui3
AlBui3
—
AlBui3
Conditions of polymerization: the complex (a solution of 10 μmol of complexes 3 or 4 in toluene), [AlR3] : [Ln] : [TB] =
= 10 : 1 : 1, T = 25 °C, where TB = [Ph3C][B(C6F5)4]; t is the polymerization time; the ratio [IP]/[Ln] = 1000, where
IP is isoprene, Ln = Y (3), Nd (4). The molecular weights of the polymers were determined by gelꢀpermeation
chromatography using polystyrene standards.

1672
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017
Skvortsov et al.
2,6ꢀDimethylꢀNꢀ[4ꢀ(2,6ꢀdimethylphenyl)iminoꢀ3ꢀ{1ꢀ[(2,6ꢀ
a bidentate fashion only through two nitrogen atoms,
while the third nitrogen atom is not involved in the
metal—ligand interaction and delocalization of the negaꢀ
tive charge. The observed coordination mode differs from
dimethylphenyl)imino]ethyl}ꢀ5,5ꢀdimethylhexꢀ2ꢀenꢀ2ꢀyl]aniline,
(2,6ꢀMe2C6H3N=CMe)2CH(2,6ꢀMe2C6H3N=CBut)
(1).
nꢀButyllithium (37.00 mL, 42.9 mmol, 1.16 M solution in hexꢀ
ane) was added to a solution of (2,6ꢀMe2C6H3N=CMe)2CH2
(12.78 g, 41.7 mmol) in toluene (50 mL) at 0 °C. The reaction
mixture was stirred at 0 °C for 1 h, and then a solution of
2,6ꢀMe2(C6H3)N=C(But)Cl (9.55 g, 42.70 mmol) in toluene
(20 mL) was added. The resulting reaction mixture was stirred
for 48 h, the solution was decanted from the precipitate of
LiCl, and the solvents were removed in vacuo. The solid resiꢀ
due was washed with hexane (2×35 mL) and dried in vacuo for
1 h. Triketimine 1 was isolated as a white powder in a yield
of 80% (16.49 g). Found (%): C, 83.07; H, 8.69; N, 8.12.
C34H43N3. Calculated (%): C, 82.71; H, 8.78; N, 8.51.
M.p. 133 °C. MS (EI, 70 eV), m/z (Irel (%)): 493.71 [M]+ (10).
1H NMR (400 MHz, 25 °C, CDCl3), δ: 1.24 (s, 9 H, C(CH3)3);
1.98, 2.07, 2.08, 2.11 (all s, 24 H, CH3C=N, C6H3(CH3)2);
5.17 (s, 1 H, CH); 6.80 and 6.88 (both d, 3 H, C6H3(CH3)2,
3JH,H = 7.4 Hz); 6.94 (d, 2 H, C6H3(CH3)2, 3JH,H = 7.4 Hz);
7.01 (m, 4 H, C6H3(CH3)2). 13C NMR (100 MHz, 25 °C,
CDCl3), δ: 18.6, 18.9, 20.0, 20.8 (CH3C=N, C6H3(CH3)2);
28.8 (C(CH3)3); 44.9 (C(CH3)3); 67.7 (CH, C(1)C(2)C(3)ꢀ
C(5)); 121.6, 122.9, 123.3, 125.7, 126.2, 127.8, 128.0, 128.2,
148.8, 170.3 (C6H3(CH3)2, CH3C=N, ButC=N,). IR (Nujol
mulls), ν/cm–1: 3304 (m), 1676 (s), 1662 (s), 1595 (s), 1307 (s),
1287 (s), 1214 (s), 1169 (s), 1096 (s), 1070 (s), 1031 (s), 986 (s),
921 (s), 868 (m), 806 (s), 769 (s), 761 (s), 684 (m), 628 (m),
529 (m), 518 (m), 498 (m).
3
κ ꢀNNN coordination typical of neutral triketiminate
ligands in dꢀtransition metal complexes.13—15 The differꢀ
ence in the coordination mode is apparently associated
with the electronic state of the ligand rather than with the
ionic radius of the metal atom. The localization of the
negative charge in the monoanionic ligand on the central
carbon atom is responsible for the planar structure of the
carbanionic moiety C(1)C(2)C(3)C(5), as opposed to the
neutral form, thus excluding the possibility of coordinatꢀ
ing the third nitrogen atom to the metal ion. Borohydride
complexes 3 and 4 proved to be active catalysts for polyꢀ
merization of racꢀlactide and can be used to prepare atacꢀ
tic polylactides with a narrow molecular weight distribuꢀ
tion. Complexes 3 and 4 exhibited high catalytic activity
in the polymerization of εꢀcaprolactone giving polyꢀ
lactones with a narrow molecular weight distribution. It
was demonstrated that triketiminate bis(borohydride)
complexes 3 and 4 included as components in threeꢀcomꢀ
ponent (3 or 4/[Ph3C][B(C6F5)4]/AlBui3, (1 : 1 : 10))
catalytic systems can be employed to perform polymerꢀ
ization of isoprene with low rate and low stereoselectivity.
Lithium {2,6ꢀdimethylꢀNꢀ[4ꢀ(2,6ꢀdimethylphenyl)iminoꢀ3ꢀ
{1ꢀ[(2,6ꢀdimethylphenyl)imino]ethyl}ꢀ5,5ꢀdimethylhexꢀ2ꢀenꢀ2ꢀ
yl]anilide}ditetrahydrofuranate, [(2,6ꢀMe2C6H3N=CMe)2Cꢀ
(2,6ꢀMe2C6H3N=CBut)]Li(THF)2 (2). nꢀButyllithium (3.58 mL,
4.15 mmol, 1.16 M solution in hexane) was added to a solution
of triketimine 1 (2.04 g, 4.13 mmol) in THF (30 mL) at 0 °C,
and the reaction mixture was stirred at 25 °C for 12 h. Yellow
crystals of 2 were obtained by slow concentration of a solution
of complex 2 in THF at 25 °C. The crystals were washed with
cold hexane and dried in vacuo at 25 °C for 30 min. Yellow
crystals of complex 2 were isolated in a yield of 2.02 g (76%).
Found (%): C, 77.94; H, 9.23; N, 6.70. C42H58LiN3O2. Calcuꢀ
lated (%): C, 78.35; H, 9.08; N, 6.53. 1H NMR (400 MHz, 25 °C,
benzeneꢀd6), δ: 1.15 (m, 8 H, βꢀCH2, THF); 1.67 (s, 9 H,
C(CH3)3); 1.75, 1.93, 2.18, 2.33 (all s, 24 H, CH3C=N,
C6H3(CH3)2); 3.12 (m, 8 H, αꢀCH2, THF); 6.85—7.05 (m, 9 H,
C6H3(CH3)2). 13C NMR (100 MHz, 25 °C, benzeneꢀd6),
δ: 18.5, 18.7, 20.4, 23.8 (CH3C=N, C6H3(CH3)2); 25.4 (βꢀCH2,
THF); 32.3 (C(CH3)3); 44.3 (C(CH3)3); 67.7 (αꢀCH2, THF);
104.2 (C=CBut, C(1)C(2)C(3)C(5)); 122.1, 122.4, 128.2, 128.4,
129.9, 130.3, 149.8, 152.1, 161.7, 183.6 (CH3C=N, ButC=N,
C6H3(CH3)2). 7Li NMR (155.5 MHz, 25 °C, benzeneꢀd6), δ:
1.6. IR (Nujol mulls), ν/cm–1: 1606 (s), 1592 (s), 1535 (s), 1287
(s), 1251 (s), 1234 (s), 1194 (s), 1135 (s), 1090 (s), 1048 (s),
1014 (s), 941 (s), 915 (s), 890 (s), 828 (s), 780 (s), 761 (s), 741 (s),
721 (s), 670 (s), 639 (m), 597 (m), 572 (s), 518 (s), 496 (s).
Yttrium(III) bis(borohydride) {2,6ꢀdimethylꢀNꢀ[4ꢀ(2,6ꢀdiꢀ
methylphenyl)iminoꢀ3ꢀ{1ꢀ[(2,6ꢀdimethylphenyl)imino]ethyl}ꢀ
5,5ꢀdimethylhexꢀ2ꢀenꢀ2ꢀyl]anilide}ditetrahydrofuranate, [(2,6ꢀ
Me2C6H3N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]Y(BH4)2(THF)2
(3). A solution of 2 (0.31 g, 0.48 mmol) in THF (35 mL) was
added to a solution of Y(BH4)3(THF)3 (0.17 g, 0.49 mmol) in
Experimental
All operations during the synthesis and isolation of the prodꢀ
ucts were carried out in evacuated equipment using the stanꢀ
dard Schlenk technique. Tetrahydrofuran was dried with poꢀ
tassium hydroxide and distilled over sodium benzophenone
ketyl. Hexane and toluene were dried by heating to reflux and
distillation over sodium metal. Benzeneꢀd6 was dried with soꢀ
dium metal, degassed, and condensed in vacuo. The compounds
(2,6ꢀMe2C6H3N=CMe)2CH2,11 2,6ꢀMe2C6H3N=C(But)Cl,32
and Ln(BH4)3(THF)3 (Ln = Y,33 Nd34) were synthesized acꢀ
cording to procedures published earlier. Sodium borohydride,
racꢀlactide, ∑ꢀcaprolactone, benzeneꢀd6, CDCl3, and isoprene
are commercial reagents (Acros). Isoprene and εꢀcaprolactone
were dried with potassium hydride followed by distillation
in vacuo and stored in evacuated containers. racꢀLactide was
crystallized from dry THF, dried in vacuo, and stored in a dry
nitrogen atmosphere. The IR spectra were recorded on a Brukerꢀ
Vertex 70 spectrometer. The samples were prepared under
a dry argon atmosphere as Nujol mulls. The 1H, 13C, 7Li, and
11B NMR spectra were measured on a Bruker Avance III
spectrometer (400 MHz, 25 °C, benzeneꢀd6, CDCl3). The
chemical shifts are given in ppm relative to known shifts of
residual protons of deuterated solvents. The molecular weight
characteristics of the polymer samples were determined on
a Knauer Smartline chromatograph equipped with Phenogel
Phenomenex 5u columns (300×7.8 mm); the average pore diꢀ
ameter was 104 and 105 Å; a refractometer detector; THF was
used as the mobile phase; the flow rate was 2 mL min–1, T = 40 °C.
The calibration was performed using polystyrene standards with
molecular weights varying from 2700 to 2570000.

Triketiminate bis(borohydride) complexes
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017 1673
THF (25 mL), and the reaction mixture was stirred at 65 °C for
3 h. The reaction product was extracted with toluene (50 mL)
and separated from the precipitate of LiBH4. The toluene was
removed in vacuo, and the solid residue was dissolved in THF
(3 mL). Colorless crystals of complex 3 were obtained by slow
condensation of hexane into a concentrated solution of comꢀ
plex 3 in THF at 25 °C. The crystals were washed with cold
hexane and dried in vacuo at 25 °C. Colorless crystals of 3 were
isolated in a yield of 0.26 g (0.34 mmol, 71%). Found (%):
C, 66.32; H, 9.05; N, 5.74; Y, 11.68. C42H66B2N3O2Y. Calculatꢀ
ed (%): C, 66.77; H, 8.81; N, 5.56; Y, 11.77. 1H NMR (400 MHz,
25 °C, benzeneꢀd6), δ: 1.15 (br.s, 2 H, BH4); 1.24 (br.s, 2 H,
BH4); 1.29 (m, 8 H, βꢀCH2, THF); 1.36 (br.s, 2 H, BH4); 1.48
(s, 9 H, C(CH3)3); 1.52 (s, 6 H, CH3C=N, C6H3(CH3)2); 1.57
(br.s, 2 H, BH4); 1.85, 2.08, 2.17 (all s, 18 H, CH3C=N,
C6H3(CH3)2); 3.62 (m, 8 H, αꢀCH2, THF); 6.79—7.14 (m, 9 H,
C6H3(CH3)2). 13C NMR (100 MHz, 25 °C, benzeneꢀd6), δ:
18.2, 18.4, 20.1, 21.3 (CH3C=N, C6H3(CH3)2); 25.5 (βꢀCH2,
THF); 31.5 (C(CH3)3); 43.7 (C(CH3)3); 69.5 (αꢀCH2, THF);
100.4 (C=CBut, C(1)C(2)C(3)C(6)); 121.6, 123.2, 124.9, 128.6,
129.0, 129.4, 131.6, 143.5, 160.6, 180.1 (CH3C=N, ButC=N,
C6H3(CH3)2). 11B NMR (128 MHz, 25 °C, benzeneꢀd6), δ:
–25.1. IR (Nujol mulls), ν/cm–1: 2471 (s), 2372 (s), 2288 (s),
2220 (s), 2164 (s), 1609 (s), 1595 (s), 1513 (s), 1335 (s), 1245 (s),
1192 (s), 1085 (s), 1028 (s), 944 (s), 918 (s), 868 (s), 837(s),
763 (s), 676 (s), 603 (s), 575 (s), 515 (m).
in THF (25 mL), and the reaction mixture was stirred at 25 °C
for 48 h and at 60 °C for 3 h. The reaction product was extractꢀ
ed with toluene (50 mL) and separated from the precipitate of
LiBH4. The toluene was removed in vacuo, and the solid resiꢀ
due was dissolved in THF (3 mL). Green crystals of complex 4
were obtained by slow condensation of hexane into a concenꢀ
trated solution of complex 4 in THF at 25 °C. The crystals were
washed with cold hexane and dried in vacuo at 25 °C for 30 min.
Green crystals of complex 4 were isolated in a yield of 0.554 g
(0.68 mmol, 80%). Found (%): C, 61.89; H, 8.54; N, 5.43;
Nd, 17.50. C42H66B2N3O2Nd. Calculated (%): C, 62.21;
H, 8.20; N, 5.18; Nd, 17.79. IR (Nujol mulls), ν/cm–1: 2434 (s),
2331 (s), 2289 (s), 2250 (s), 2228 (s), 1606 (s), 1589 (s), 1513 (s),
1327 (s), 1231 (s), 1178 (s), 1096 (s), 1023 (s), 946 (s), 918 (s),
876 (s), 834(s), 766 (s), 665 (s), 606 (s), 577 (s), 498 (m).
Polymerization of isoprene (general procedure). One equivꢀ
alent of borate [Ph3C][B(C6F5)4]) (10 μmol) and AlBui3
(0.1 mmol, 10 equiv.) were successively added to a solution of
complex 3 or 4 (10 μmol) in toluene (1 mL). Then isoprene
(10 μmol, 1 mL, 1000 equiv.) was added with stirring to the
resulting solution. The reaction mixture was stirred for 48 h and
then ethanol (10 mL) was added. The polymer that precipitatꢀ
ed was washed with ethanol (5×10 mL) and dried in vacuo at
60 °C to constant weight. The molecular weight characteristics
of the polymers were determined by gelꢀpermeation chromatoꢀ
graphy. The numberꢀaverage molecular weights (Mn) and the
polydispersity indices (Mn/Mw) were calculated using polyꢀ
styrene standards. The content of cisꢀ1,4, transꢀ1,4, and
3,4 units in the polymer samples was determined by 1H and
13C NMR spectroscopy.
Neodymium(III) bis(borohydride) {2,6ꢀdimethylꢀNꢀ[4ꢀ(2,6ꢀ
dimethylphenyl)iminoꢀ3ꢀ{1ꢀ[(2,6ꢀdimethylphenyl)imino]ethyl}ꢀ
5,5ꢀdimethylhexꢀ2ꢀenꢀ2ꢀyl]anilide}ditetrahydrofuranate, [(2,6ꢀ
Me2C6H3N=CMe)2C(2,6ꢀMe2C6H3N=CBut)]Nd(BH4)2ꢀ
(THF)2 (4). A solution of 2 (0.55 g, 0.85 mmol) in THF (35 mL)
was added to a solution of Nd(BH4)3(THF)3 (0.35 g, 0.86 mmol)
Polymerization of racꢀlactide (general procedure). Complex 3
(7.6 mg, 0.010 mmol) and racꢀlactide (0.360 g, 2.50 mmol)
Table 5. Crystallographic data and the Xꢀray data collection and structure refinement statistics for compounds 1, 2, and 4
Parameter
1
2
4
Formula
Molecular weight
C34H43N3
493.71
C42H58LiN3O2
643.85
C42H66B2N3NdO2
810.83
Space group
P21/n
P21
P21/c
a/Å
b/Å
c/Å
α/deg
12.3957(12)
16.5709(15)
14.7696(11)
90
10.1224(2)
17.1888(2)
11.8855(2)
90
20.1153(5)
16.9059(5)
12.2731(2)
90
β/deg
103.942(3)
90
2944.4(4)
4
1.114
0.065
113.731(2)
90
1893.12(6)
2
1.129
0.068
91.918(2)
90
4171.34(17)
4
γ/deg
V/Å3
Z
dcalc/g cm–3
1.291
1.281
μ/mm–1
θꢀScan range/deg
Number of measured reflections
Number of reflections with I > 2σ(I)
Rint
1.88—27.00
19188
6414
0.0229
3.02—30.51
40921
11542
0.0221
2.84—26.00
62572
8184
0.0537
Number of refined parameters
GOOF (F2)
349
1.034
444
1.035
518
1.036
R1 (I > 2σ(I))
0.0448
0.1269
0.289/–0.186
0.0359
0.0945
0.273/–0.156
0.0363
0.0771
1.374/–1.833
wR2 (based on all reflections)
Residual electron density
(max/min)/e Å–3

1674
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 9, September, 2017
Skvortsov et al.
were dissolved in toluene (2.5 mL). The mixture was stirred at
25 °C for 12 h and then ethanol (5 mL) was added. The solvents
were removed, and the residue was dried in vacuo to constant
weight. The degree of conversion of the monomer and the
microstructure of the polymer were determined by NMR
spectroscopy. The yield was determined by the weight method.
Polymerization of εꢀcaprolactone (general procedure). Comꢀ
plex 3 (7.6 mg, 0.010 mmol) and εꢀcaprolactone (0.285 g,
2.50 mmol) were dissolved in toluene (2.5 mL). The mixture
was stirred at 25 °C for 5 min and then ethanol (5 mL) was
added. The solvents were removed, and the residue was dried
in vacuo to constant weight. The degree of conversion of the
monomer was determined by NMR spectroscopy. The yield
was determined by the weight method.
Xꢀray diffraction study of compounds 1, 2, and 4 was perꢀ
formed on Bruker Smart Apex (1) and Agilent Xcalibur E (2, 4)
diffractometers (ωꢀscanning technique, MoꢀKα radiation,
λ = 0.71073 Å, T = 100 K). The structures were solved by direct
methods and refined by the fullꢀmatrix leastꢀsquares method
based on F2hkl with anisotropic displacement parameters for all
nonhydrogen atoms. The hydrogen atom H(1) in 1 and the
hydrogen atoms of the bis(borohydride) groups, H(1)—H(8),
in 4 were located in difference electron density maps and reꢀ
fined isotropically. The other hydrogen atoms in compounds 1,
2, and 4 were positioned geometrically and refined isotropically
11. P. H. M. Budzelaar, R. Gelder, A. W. Gal, Organometallics,
1998, 17, 4121.
12. D. Barnes, G. L. Brown, M. Brownhill, I. German, C. J.
Herbert, A. Jolleys, A. R. Kennedy, B. Liu, K. McBride,
F. S. Mair, R. G. Pritchard, A. Sanders, J. E. Warren, Eur.
J. Inorg. Chem., 2009, 1219.
13. N. G. Hamedani, H. Arabi, G. H. Zohuri, F. S. Mair,
A. Jolleys, J. Polym. Sci., Part A: Polym. Chem., 2013,
51, 1520.
14. M. N. Alnajrani, F. S. Mair, Dalton Trans., 2014, 43, 15727.
15. M. N. Alnajrani, F. S. Mair, RSC Adv., 2015, 5, 46372.
16. M. N. Alnajrani, F. S. Mair, Dalton Trans., 2016, 45, 10435.
17. M. Ephritikhine, Chem. Rev., 1997, 97, 2193.
18. I. Pallard, A. Soum, S. M. Guillaume, Chem. Eur. J., 2004,
10, 4054.
19. F. Bonnet, A. R. Cowley, P. Mountford, Inorg. Chem., 2005,
44, 9046.
20. F. Bonnet, A. C. Hilier, A. Collins, S. R. Dubberley,
P. Monutford, Dalton Trans., 2005, 421.
21. D. BarbierꢀBaudry, O. Blacque, A. Hafid, A. Nyassi,
H. Sitzmann, M. Visseaux, Eur. J. Inorg. Chem., 2000, 2333.
22. F. A. Allen, O. Connard, D. G. Watson, L. Brammer,
G. Orpen, R. Taylor, J. Chem. Soc., Perkin Trans., 1987, 1.
23. M. F. Lappert, R. J. Pearce, J. Chem. Soc., Chem. Comꢀ
mun., 1973, 126.
with fixed thermal parameters U(H)iso = 1.2U(C)eq (U(H)iso
=
24. S. Arndt, P. Voth, T. P. Spaniol, J. Okuda, Organometallics,
2000, 19, 4690.
25. D. T. Carey, E. K. CopeꢀEatough, E. VilaplanaꢀMafe, F. S.
Mair, R. G. Pritchard, J. E. Warren, R. J. Woods, Dalton
Trans., 2003, 1083.
26. P. Jutzi, K. Leszczynska, A. Mix, B. Neumann, W. W.
Schoeller, H.ꢀG. Stammler, Organometallics, 2009, 28, 1985.
27. M. Xue, R. Jiao, Y. Zhang, Y. Yao, Q. Shen, Eur. J. Inorg.
Chem., 2009, 4110.
28. Z.ꢀQ. Zhang, Y.ꢀM. Yao, Y. Zhang, Q. Shen, W.ꢀT. Wong,
Inorg. Chim. Acta, 2004, 357, 3173.
= 1.5U(C)eq for methyl groups). The Xꢀray data integration was
performed, absorption corrections were applied, and the strucꢀ
tures were refined using the APEX2,35 SADABS,36 SHELX,37
and CrysAlis PRO program packages.38 The crystallographic
data and the Xꢀray data collection and structure refinement
statistics are given in Table 5. The structures were deposited
with the Cambridge Crystallographic Data Centre (CCDC
1558092 (1), 1558093 (2), and 1558094 (4)) and are available at
ccdc.cam.ac.uk/getstructures.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 17ꢀ03ꢀ00253 A).
29. G. G. Skvortsov, M. V. Yakovenko, P. M. Castro, G. K.
Fukin, A. V. Cherkasov, J.ꢀF. Carpentier, A. A. Trifonov,
Eur. J. Inorg. Chem., 2007, 3260.
30. S. M. CendrowskiꢀGuillaume, M. Nierlich, M. Lance,
M. Ephritikhine, Organometallics, 1998, 17, 786.
31. G. G. Skvortsov, A. O. Tolpygin, D. M. Lyubov, N. M.
Khamaletdinova, A. V. Cherkasov, K. A. Lyssenko, A. A.
Trifonov, Russ. Chem. Bull. (Int. Ed.), 2016, 65, 2832.
32. J. E. Steves, M. D. Kennedy, K. P. Chiang, W. S. Kassel,
W. G. Dougherty, T. J. Dudley, D. L. Zubris, Dalton Trans.,
2009, 1214.
33. B. G. Segal, S. J. Lippord, Inorg. Chem., 1978, 17, 844.
34. U. Mirsaidov, I. B. Shaimuradov, M. Khikmatov, J. Inorg.
Chem. USSR (Engl. Transl.), 1986, 31, 753.
35. Bruker (2012). APEX2. Bruker AXS Inc., Madison, Wisꢀ
consin, USA.
References
1. R. D. Shannon, Acta Cryst., 1976, A32, 751.
2. F. T. Edelmann, D. M. M. Freckmann, H. Schumann,
Chem. Rev., 2002, 102, 1851.
3. W. E. Piers, D. J. H. Emslie, Coord. Chem. Rev., 2002,
233—234, 131.
4. A. A. Trifonov, Rus. Chem. Rev., 2007, 76, 1049.
5. A. A. Trifonov, Coord. Chem. Rev., 2010, 254, 1327.
6. A. A. Trifonov, D. M. Lyubov, Coord. Chem. Rev., 2017,
340, 10.
7. L. R. Morss, Chem. Rev., 1976, 76, 827.
8. H. Schumann, J. A. MeeseꢀMarktscheffel, L. Esser, Chem.
Rev., 1995, 95, 865.
36. Bruker (2001). SADABS. Bruker AXS Inc., Madison, Wisꢀ
consin, USA.
9. J. Feldman, S. J. McLaine, A. Parthasarathy, W. J. Marꢀ
shall, J. C. Calabrese, S. D. Arthur, Organometallics, 1997,
16, 1514.
37. G.M. Sheldrick, Acta Cryst., 2015, C71, 3.
38. Agilent. CrysAlis PRO. Agilent Technologies Ltd, Yarnton,
Oxfordshire, England, 2014.
10. P. G. Hayes, W. E. Piers, L. W. M. Lee, L. K. Knight,
M. Parvez, M. R. J. Elsegood, W. Clegg, Organometallics,
2001, 20, 2533.
Received June 28, 2017