Monoanionic triketiminate ligands: Peculiarity of coordination mode to lithium and rare earth ions

Article abstract of DOI:10.1016/j.ica.2020.119623

Deprotonation of β-triketimines (2,6-Me₂C₆H₃N = CMe)₃CH (1), (2,6-Me₂C₆H₃N = CMe)₂CH(2-MeOC₆H₄N = CtBu) (2), (2,6-Me₂C₆H₃N = CMe)₂CH(2,6-Me₂C₆H₃N = CtBu) (3) by equimolar amount of n-BuLi afforded lithium triketiminate complexes [(2,6-Me₂C₆H₃N = CMe)₃C]Li(THF) (4), [(2,6-Me₂C₆H₃N = CMe)₂C(2-MeOC₆H₄N = CtBu)]Li(THF)₂ (5), [(2,6-Me₂C₆H₃N = CMe)₂C(2,6-Me₂C₆H₃N = CtBu)]Li(THF)₂ (6) in 70–80% yields. The salt metathesis reactions of LnCl₃ (Ln = Y, Nd) with 6 lead to the formation of neutral triketiminate dichloro complexes [(2,6-Me₂C₆H₃N = CMe)₂C(2,6-Me₂C₆H₃N = CtBu)]LnCl₂(THF)₂ (Ln = Y (7), Nd (8)) in 78 and 70% yields, while the analogous reaction of YCl₃ with 5 resulted in triketiminate yttrium chloro ate complex [(2,6-Me₂C₆H₃N = CMe)₂C(2-MeOC₆H₄N = CtBu)]Y(THF)Cl(μ²-Cl)₂Li(THF)₂ (9). The reactions of the potassium derivatives of the related triketimines 2, 3 with YbI₂(THF)₂ resulted in the formation of mononuclear triketiminate iodo Yb(II) complexes [(2,6-Me₂C₆H₃N = CMe)₂C(2-MeOC₆H₄N = CtBu)]YbI(THF)₂ (10) and [(2,6-Me₂C₆H₃N = CMe)₂C(2,6-Me₂C₆H₃N = CtBu)]YbI(TMEDA) (11). X-ray analysis revealed that in 4 and rare-earth metals complexes 7–11 the monoanionic β-triketiminate ligands [(2,6-Me₂C₆H₃N = CMe)₃C]^?, [(2,6-Me₂C₆H₃N = CMe)₂C(2-MeOC₆H₄N = CtBu)]^?, [(2,6-Me₂C₆H₃N = CMe)₂C(2,6-Me₂C₆H₃N = CtBu)]^? feature bidentate coordination mode and are coordinated to a metal center only through two nitrogen atoms. The ternary systems 7–9/AliBu₃/[CPh₃][B(C₆F₅)₄] exhibit catalytic activity in isoprene polymerization, allowing to carry out polymerization of 1000 equivalents in 2 h with 91–100% conversion. The obtained polyisoprenes feature high molecular weights (M_n = 12.8 × 10⁴–20.2 × 10⁴) and moderate polydispersities (M_w/M_n = 2.7–3.6), however excellent control of regio- and stereoselectivities (up to 9.9% cis-1,4 units) was observed.

Full text of DOI:10.1016/j.ica.2020.119623

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Research paper
Monoanionic Triketiminate Ligands: Peculiarity of Coordination Mode to
Lithium and Rare Earth Ions
Grigorii G. Skvortsov, Georgy K. Fukin, Anton V. Cherkasov, Tatyana A.
Kovylina, Alexander A. Trifonov
PII:
DOI:
Reference:
S0020-1693(20)30052-9
https://doi.org/10.1016/j.ica.2020.119623
ICA 119623
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Inorganica Chimica Acta
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Revised Date:
Accepted Date:
8 January 2020
21 March 2020
22 March 2020
Please cite this article as: G.G. Skvortsov, G.K. Fukin, A.V. Cherkasov, T.A. Kovylina, A.A. Trifonov,
Monoanionic Triketiminate Ligands: Peculiarity of Coordination Mode to Lithium and Rare Earth Ions,
Inorganica Chimica Acta (2020), doi: https://doi.org/10.1016/j.ica.2020.119623
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Monoanionic Triketiminate Ligands: Peculiarity of Coordination Mode
to Lithium and Rare Earth Ions
a
a
a
a
Grigorii G. Skvortsov, Georgy K. Fukin, Anton V. Cherkasov, Tatyana A. Kovylina and
Alexander A. Trifonova,b,*
aG. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences
Tropinina 49, 603950 Nizhny Novgorod, GSP-445, Russia
Fax: +007 831 462 74 97
b
A. N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, 28 Vavilova str.,
1
19991, Moscow,GSP-1, Russia
ABSTRACT
Deprotonation of β-triketimines (2,6-Me C H N꞊CMe) CH (1), (2,6-Me C H N꞊CMe) CH(2-
2
6
3
3
2
6
3
2
MeOC H N꞊CtBu) (2), (2,6-Me C H N꞊CMe) CH(2,6-Me C H N꞊CtBu) (3) by equimolar
6
4
2
6
3
2
2
6
3
amount of n-BuLi afforded lithium triketiminate complexes [(2,6-Me C H N꞊CMe) C]Li(THF)
2
6
3
3
(4),
[(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)]Li(THF)
(5),
[(2,6-
2
6
3
2
6
4
2
Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)]Li(THF) (6) in 70–80% yields. The salt metathesis
2
6
3
2
2
6
3
2
reactions of LnCl (Ln = Y, Nd) with 6 lead to the formation of neutral triketiminate dichloro
3
complexes [(2,6-Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)]LnCl (THF) (Ln = Y (7), Nd (8))
2
6
3
2
2
6
3
2
2
in 78 and 70% yields, while the analogous reaction of YCl with 5 resulted in triketiminate
3
2
yttrium chloro ate complex [(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)]Y(THF)Cl(µ -
2
6
3
2
6
4
Cl) Li(THF) (9). The reactions of the potassium derivatives of the related triketimines 2, 3 with
2
2
YbI (THF) resulted in the formation of mononuclear triketiminate iodo Yb(II) complexes [(2,6-
2
2
Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)]YbI(THF) (10) and [(2,6-Me C H N꞊CMe) C(2,6-
2
6
3
2
6
4
2
2
6
3
2
Me C H N꞊CtBu)]YbI(TMEDA) (11). X-ray analysis revealed that in 4 and rare-earth metals
2
6
3
-
complexes 7‒11 the monoanionic β-triketiminate ligands [(2,6-Me C H N꞊CMe) C] , [(2,6-
2
6
3
3
-
-
Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)] , [(2,6-Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)]
2
6
3
2
6
4
2
6
3
2
2
6
3
feature bidentate coordination mode and are coordinated to a metal center only through two
nitrogen atoms. The ternary systems 7‒9/AliBu /[CPh ][B(C F ) ] exhibit catalytic activity in
3
3
6 5 4
isoprene polymerization, allowing to carry out polymerization of 1000 equivalents in 2 h with
9
1
1‒100% conversion. The obtained polyisoprenes feature high molecular weights (M =
2.8×10 –20.2×10 ) and moderate polydispersities (M /M = 2.7–3.6), however excellent control
w n
n
4
4
of regio- and stereoselectivities (up to 98.9% cis-1,4 units) was observed.
Keywords: Lanthanides / N ligands / Ligand design / Polymerization / Isoprene
*Corresponding author.
E-mail address: trif@iomc.ras.ru (A.A. Trifonov).
1

1
. Introduction
In the past two decades the development of new supporting ligands allowing to extend the
means of design of metal coordination sphere was in the focus of attention of the numerous
research groups working in the organometallic chemistry of rare-earth metals [1‒6]. An
impressive progress has been made in this field due to application of β-diketiminate lignds
[7‒10]. A key example is the pioneering work that has been undertaken in 1994 to prepare the β-
1
2
diketiminate Ln(III) complexes [11], since, β-diketimines (R N꞊CR ) CH have found a wide use
2
2
in coordination chemistry of transition metals and continue to attract keen interest due to the
diversity of their coordination properties. The fact that β-diketiminate ligands allowed for the
synthesis and isolation of the rare-earth diethyl derivatives [12] usually extremely unstable
because of facile β-hydride elimination illustrates the high potential of this type of coordination
environment in stabilization of organic derivatives of these metals [3, 13]. Actually, the use of β-
diketiminate ligands has made it possible to synthesize a variety of reactive alkyl and
borohydride derivatives of rare-earth metals exhibiting high activity in a number of catalytic
processes [9, 14‒18]. Recently the synthesis of a series of new related β-triketimines and the
cobalt complexes coordinated by triketimines as neutral tridentate N,N,N-ligands, which
performed promising catalytic activity in isoprene polymerization was described [19‒20].
Several examples of transition and non-transition metal complexes coordinated by neutral β-
triketimine ligands have been reported to date [19‒24].
The only example of use of a monoanionic form of a triketiminate ligand in synthesis of β-
triketiminatometal complexes is so far known [25].
Herein we report on the synthesis and structures of a series of triketiminate complexes of
lithium
and
rare-earth
metals
[(2,6-Me C H N꞊CMe) C]Li(THF)
(4),
[(2,6-
2
6
3
3
Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)]Li(THF)
(5),
[(2,6-Me C H N꞊CMe) C(2,6-
2
6
3
2
6
4
2
2
6
3
2
Me C H N꞊CtBu)]LnCl (THF) (Ln = Y (7), Nd (8)), [(2,6-Me C H N꞊CMe) C(2-
2
6
3
2
2
2
6
3
2
MeOC H N꞊CtBu)]Y(THF)Cl(µ-Cl) Li(THF)
(9),
[(2,6-Me C H N꞊CMe) C(2-
2 6 4 2
6
4
2
2
MeOC H N꞊CtBu)]YbI(THF)
(10),
[(2,6-Me C H N꞊CMe) C(2,6-
2 6 3 2
6
4
2
Me C H N꞊CtBu)]YbI(TMEDA) (11). Catalytic activity of rare-earth triketiminate halide
2
6
3
species 7–11 in isoprene polymerization will be considered.
2
. Experimental
2
.1. General Considerations
All experiments were performed in evacuated tubes, using standard Schlenk and glove-box
techniques, with rigorous exclusion of traces of moisture and air. After drying over KOH, THF
2

and TMEDA were purified by distillation from sodium/benzophenone ketyl, hexane was dried
by distillation from sodium/triglyme and benzophenone ketyl before use. C D was dried with
6
6
sodium/potassium alloy, C D N was dried with CaH and condensed in vacuum into the NMR
5
5
2
tubes before use. CDCl was purchased from Acros and was used without purification. 2,6-
3
dimethylaniline, o-anisidine were purchased from Acros and were used after the appropriate
purifications. Anhydrous NdCl and YCl [26], YbI (THF) [27], 2,6-Me C H N꞊C(CH )Cl [28],
3
3
2
2
2
6
3
3
(
2,6-Me C H N꞊CMe) CH [29], (2,6-Me C H N꞊CMe) CH(2,6-Me C H N꞊CtBu) [25], (2,6-
2 6 3 2 2 2 6 3 2 2 6 3
Me C H N꞊CMe) CH(2-MeOC H N꞊CtBu)
[20],
[(2,6-Me C H N꞊CMe) C(2,6-
2 6 3 2
2
6
3
2
6
4
Me C H N꞊CtBu)]Li(THF) [25] were prepared according to literature procedures. All other
2
6
3
2
commercially available chemicals were used after the appropriate purifications.
2
.1.1. Instruments and Measurements.
NMR spectra were recorded on Bruker Avance DRX-400 spectrometer in C D , CDCl or
6
6
3
1
13
C D N at 25 °C, unless otherwise stated. Chemical shifts for H and C spectra were referenced
5
5
7
internally using the residual solvent resonances and are reported relative to TMS. Li NMR
chemical shifts were referenced by 1 M LiCl solution in D O at 0 ppm. Infrared spectra were
2
recorded on a Bruker-Vertex 70 spectrophotometer as Nujol mulls. Lanthanide metal analyses
were carried out by complexometric titration [30]. The C, H, N elemental analyses were made in
the microanalytical laboratory of the G. A. Razuvaev Institute of Organometallic Chemistry.
GPC was carried out by using a chromatograph ‘‘Knauer Smartline’’ with Phenogel
4
5
Phenomenex Columns 5u (300 × 7.8 mm) 10 , 10 and a Security Guard Phenogel Column with
RI and UV detectors (254 nm). The mobile phase was THF and the flow rate was 2 mL/min. The
columns were calibrated by Phenomenex medium and High Molecular Weight Polystyrene
Standard Kits with peak molecular weights (M ) from 2700 to 2 570 000 Da. The number
n
average molecular weights (M ) and polydispersity indexes (M /M ) of the polymers were
n
w
n
calculated with reference to a universal calibration vs. polystyrene standards.
.1.2. Synthesis of (2,6-Me C H N꞊CMe) CH (1).
2
2
6
3
3
A solution of 2,6-Me (C H )N=C(CH )Cl (0.89 g, 4.90 mmol) in 20 mL of toluene was
2
6
3
3
added at 0 °C to a suspension of (2,6-Me C H N꞊CMe) CHLi generated in situ from (2,6-
2
6
3
2
Me C H N꞊CMe) CH (1.50 g, 4.89 mmol) and n-BuLi (4.4 mL, 5.10 mmol, 1.16 M hexane) in
2
6
3
2
2
3
0 mL of toluene. The reaction mixture was stirred for 12 h at 25 °C and 3 h at 85 °C. The
solution was decanted from the precipitate and the solvents were removed in vacuum. The solid
residue was washed with cold hexane (35 mL) and dried at ambient temperature in vacuum for 1
h. Triketimine 1 was isolated as pale yellow solid in 74% yield (1.64 g). C H N (451.66): calc.
3
1
37
3
C 82.44, H 8.26, N 9.30; found C 82.79, H 8.40, N 8.95. Diimine-enamine (major tautomer, calc.
1
6
2%) and triimine (calc. 38%) tautomers together, H NMR: (400 MHz, CDCl , 25 °C): δ =
3
3

1
.95, 1.99, 2.10, 2.16, 2.20 (s, 27 H, CH C꞊N, C H (CH ) ), 4.81 (s, 0.38 H, α-CH), 6.88‒7.09
3 6 3 3 2
1
3
(
m, 9 H, C H (CH ) ), 13.72 (br s, 0.62 H, NH) ppm. C NMR: (100 MHz, CDCl , 25 °C): δ =
6 3 3 2 3
1
8.6, 18.7, 18.9, 19.9, 21.1, 25.1 (CH C꞊N, C H (CH ) ), 72.2 (α-CH, triimine tautomer), 108.5
3 6 3 3 2
(
C꞊CCH , diimine-enamine tautomer), 123.0, 123.1, 124.6, 125.8, 126.1, 128.0, 128.1, 128.6,
3
1
32.2, 143.2, 148.7, 149.0, 159.7, 169.0, 171.9 (CH C꞊N, C H (CH ) ) ppm. MS (EI, 70 eV),
3 6 3 3 2
+
m/z (I (%)): 451.65 [M] (20). IR (KBr): ν = 3438 (s), 1637(s), 1606 (s), 1589(s), 1538 (s),
rel
1
361 (s), 1279 (s), 1251 (s), 1211 (s), 1186 (s), 1093 (s), 1039 (s), 986 (s), 930 (s), 890 (m), 811
–
1
(
s), 772 (s), 696 (m), 552 (m), 518 (m) cm .
2
.1.3. Synthesis of [(2,6-Me C H N꞊CMe) C]Li(THF) (4).
2 6 3 3
To a solution of 1 (0.93 g, 2.06 mmol) in 30 mL of THF a solution of n-BuLi (1.86 mL,
.16 mmol, 1.16 M in hexane) was added at 0 °C and the reaction mixture was stirred for 48 h at
5 °C. The solvents were removed in vacuum, and the remaining residue was dissolved in 20 mL
2
2
of warm hexane. Slow cooling of concentrated hexane solution to 25 °C afforded yellow crystals
of 4. The crystals were dried at ambient temperature in vacuum for 30 min. Yield 0.86 g (79%).
1
C H LiN O (529.67): calc. C 79.36, H 8.37, N 7.93; found C 79.03, H 8.59, N 7.68. H NMR:
3
5
44
3
(
400 MHz, C D , 25 °C): δ = 1.07 (m, 4 H, β-CH , THF), 2.19, 2.37 (s, 27 H, CH C꞊N,
6 6 2 3
3
C H (CH ) ), 2.98 (m, 4 H, α-CH , THF), 7.06‒7.12 (m, 3 H, C H (CH ) ), 7.24 (d, 5 H, J =
H,H
6
3
3 2
2
6
3
3 2
1
3
7
1
.5 Hz, C H (CH ) ), 7.32 (s, 1 H, C H (CH ) ) ppm. C NMR: (100 MHz, C D , 25 °C): δ =
6 3 3 2 6 3 3 2 6 6
8.7, 19.0, 19.4, 19.9 (CH C꞊N, C H (CH ) ), 25.1 (β-CH , THF), 67.8 (α-CH , THF), 108.6
3
6
3
3 2
2
2
(
C‒CCH , central), 122.3, 125.0, 127.9, 128.2, 128.5, 128.9, 132.3, 143.8, 151.8, 160.3, 170.1
3
7
(
CH C꞊N, C H (CH ) ) ppm. Li NMR (155.5 MHz, C D , 25 ºC): δ = 1.9 ppm. IR (KBr): ν =
3
6
3
3 2
6
6
1
9
2
606 (s), 1592 (s), 1533 (s), 1304 (s), 1248 (s), 1200 (s), 1183 (s), 1093 (s), 1037 (s), 994 (s),
–
1
15 (s), 890 (s), 842 (s), 789 (s), 772 (s), 690 (s), 651 (s), 617 (m), 552 (s), 498 (m) cm .
.1.4. Synthesis of [(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)]Li(THF) (5).
2
6
3
2
6
4
2
To a solution of 2 (0.99 g, 2.00 mmol) in 30 mL of THF a solution of n-BuLi (1.74 mL,
.02 mmol, 1.16 M in hexane) was added at 0 °C and the reaction mixture was stirred for 12 h at
5 °C. Slow concentration of THF solution afforded yellow crystals of 5. The crystals were dried
2
2
at ambient temperature in vacuum for 20 min. Yield 0.93 g (72%). C H LiN O (645.86): calc.
4
1
56
3
3
1
C 76.25, H 8.74, N 6.51; found C 76.59, H 8.53, N 6.80. H NMR: (400 MHz, C D , 25 °C): δ =
6
6
1
.33 (m, 8 H, β-CH , THF), 1.67 (s, 9 H, C(CH ) ), 1.81, 1.96, 2.19 (s, 18 H, CH C꞊N,
2 3 3 3
C H (CH ) ), 3.41 (s, 3 H, OCH ), 3.43 (m, 8 H, α-CH , THF), 6.81‒7.08 (m, 10 H, C H (CH ) ,
6
3
3 2
3
2
6
3
3 2
1
3
C H OCH ) ppm. C NMR: (100 MHz, C D , 25 °C): δ = 18.5, 18.7, 22.8 (CH C꞊N,
6
4
3
6
6
3
C H (CH ) ), 25.7 (β-CH , THF), 31.3 (C(CH ) ), 43.5 (C(CH ) ), 55.5 (OCH ), 67.8 (α-CH ,
6
3
3 2
2
3 3
3 3
3
2
THF), 103.1 (C꞊CtBu, central), 112.2, 120.4, 120.8, 122.0, 123.4, 128.1, 130.1, 143.7, 152.3,
7
1
61.0, 185.5 (CH C꞊N, tBuC꞊N, C H (CH ) , C H OCH ) ppm. Li NMR (155.5 MHz, C D , 25
3
6
3
3 2
6
4
3
6
6
4

ºC): δ = 1.8 ppm. IR (KBr): ν = 1602 (s), 1587 (s), 1536 (s), 1246 (s), 1191 (s), 1146 (s), 1113
(s), 1092 (s), 1067 (s), 1049 (s), 1016 (s), 959 (s), 916 (s), 892 (s), 829 (s), 787 (s), 762 (s), 738
–
1
(
s), 681 (s), 654 (s), 572 (s), 506 (s), 493 (s), 475 (s) cm .
.1.5. Synthesis of [(2,6-Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)]YCl (THF) (7).
2
2
6
3
2
2
6
3
2
2
To a suspension of YCl (0.67 g, 3.43 mmol) in THF (20 mL) a solution of 6 (2.20 g, 3.42
3
mmol) in THF (30 mL) was added and the reaction mixture was stirred for 12 h at 25 °C and 4 h
at 70 °C. The solvent was removed in vacuum, the remaining solid was extracted with toluene
(50 mL) at 50 °C and the extract was filtered. Toluene was evaporated in vacuum, and the
remaining solid residue was recrystallized by slow condensation of hexane into a concentrated
THF solution. Pale yellow crystals of 7 were washed with cold hexane and dried at ambient
temperature in vacuum for 30 min. Yield 2.13 g (78%). C H Cl N O Y (796.75): calc. C 63.31,
4
2
58
2
3
2
1
H 7.34, N 5.27, Y 11.16; found C 63.60, H 7.52, N 5.41, Y 11.05. H NMR: (400 MHz, C D , 25
6
6
°
C): δ = 1.38 (m, 8 H, β-CH , THF), 1.47 (s, 9 H, C(CH ) ), 1.52, 1.85, 2.07, 2.16 (s, 24 H,
2 3 3
1
3
CH C꞊N, C H (CH ) ), 3.86 (m, 8 H, α-CH , THF), 6.85‒6.99 (m, 9 H, C H (CH ) ) ppm. C
3
6
3
3 2
2
6
3
3 2
NMR: (100 MHz, C D , 25 °C): δ = 18.2, 18.4, 20.1, 21.3 (CH C꞊N, C H (CH ) ), 25.6 (β-CH ,
6
6
3
6
3
3 2
2
THF), 31.5 (C(CH ) ), 43.7 (C(CH ) ), 69.2 (α-CH , THF), 104.5 (C‒CtBu, central), 123.3,
3
3
3 3
2
1
25.0, 128.5, 128.6, 131.6, 132.3, 143.5, 148.7, 160.6, 187.4 (CH C꞊N, tBuC꞊N, C H (CH ) )
3 6 3 3 2
ppm. IR (KBr): ν = 1603 (s), 1592 (s), 1518 (s), 1338 (s), 1276 (s), 1231 (s), 1178 (s), 1135 (s),
1
6
2
093 (s), 1042 (s), 1017 (s), 946 (s), 915 (s), 887 (s), 859 (s), 837 (s), 769 (s), 755 (s), 676 (s),
–
1
08 (m), 575 (m), 501 (m) cm .
.1.6. Synthesis of [(2,6-Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)]NdCl (THF) (8).
2
6
3
2
2
6
3
2
To a suspension of NdCl (0.76 g, 3.03 mmol) in THF (20 mL) a solution of 6 (1.96 g, 3.04
3
mmol) in THF (30 mL) was added and the reaction mixture was stirred for 12 h at 25 °C and 6 h
at 65 °C. The solvent was removed in vacuum, the remaining solid was extracted with toluene
(50 mL) at 50 °C, and the extract was filtered. Toluene was evaporated in vacuum, and the
remaining solid residue was recrystallized by slow condensation of hexane into a concentrated
THF solution. Green crystals of 8 were washed with cold hexane and dried at ambient
temperature in vacuum for 30 min. Yield 1.81 g (70%). C H Cl N O Nd (852.09): calc. C
4
2
58
2
3
2
5
9.20, H 6.86, N 4.93, Nd 16.93; found C 59.46, H 7.05, N 4.71, Nd 16.78. IR (KBr): ν = 1606
(
(
s), 1589 (s), 1524 (s), 1335 (s), 1290 (s), 1231 (s), 1183 (s), 1138 (s), 1093 (s), 1070 (s), 1017
–
1
s), 949 (s), 918 (s), 868 (s), 834 (s), 769 (s), 744 (s), 668 (s), 608 (s), 575 (m), 498 (m) cm .
.1.7. Synthesis of [(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)]Y(THF)Cl(µ-Cl) Li(THF)
2
2
2
6
3
2
6
4
2
(9).
To a suspension of YCl (0.37 g, 1.89 mmol) in THF (20 mL) a solution of 5 (1.22 g, 1.89
3
mmol) in THF (30 mL) was added and the reaction mixture was stirred for 72 h at 25 °C. The
5

solvent was removed in vacuum, the remaining solid was extracted with toluene (50 mL), and
the extract was filtered. Toluene was evaporated in vacuum, and the remaining solid residue was
recrystallized by slow condensation of hexane into a concentrated THF solution. Light yellow
crystals of 9 were washed with cold hexane and dried at ambient temperature in vacuum for 30
min. Yield 1.33 g (77%). C H Cl LiN O Y (913.19): calc. C 59.19, H 7.06, N 4.60, Y 9.74;
4
5
64
3
3
4
1
found C 59.47, H 7.20, N 4.31, Y 9.85. H NMR: (400 MHz, C D , 25 °C): δ = 1.40 (m, 12 H, β-
6
6
CH , THF), 1.50 (s, 9 H, C(CH ) ), 1.63, 1.84, 2.11 (s, 18 H, CH C꞊N, C H (CH ) ), 3.29 (s, 3
2
3 3
3
6
3
3 2
1
3
H, OCH ), 3.62 (m, 12 H, α-CH , THF), 6.81‒7.04 (m, 10 H, C H (CH ) , C H OCH ) ppm. C
3
2
6
3
3 2
6
4
3
NMR: (100 MHz, C D , 25 °C): δ = 18.1, 18.4, 20.4 (CH C꞊N, C H (CH ) ), 25.7 (β-CH ,
6
6
3
6
3
3 2
2
THF), 30.8 (C(CH ) ), 42.5 (C(CH ) ), 55.3 (OCH ), 68.3 (α-CH , THF), 103.1 (C‒CtBu,
3
3
3 3
3
2
central), 112.2, 120.0, 120.7, 124.0, 124.9, 128.4, 132.1, 142.3, 143.8, 151.0, 159.7, 181.6
7
(
CH C꞊N, tBuC꞊N, C H (CH ) , C H OCH ) ppm. Li NMR (155.5 MHz, C D N, 25 ºC): δ =
3
6
3
3 2
6
4
3
5
5
5
.1 ppm. IR (KBr): ν = 1609 (s), 1589 (s), 1516 (s), 1338 (s), 1273 (s), 1245 (s), 1180 (s), 1141
(s), 1116 (s), 1093 (s), 1048 (s), 1017 (s), 963 (s), 915 (s), 870 (s), 842 (s), 769 (s), 744 (s), 682
–
1
(
s), 606 (s), 566 (m), 498 (s) cm .
.1.8. Synthesis of [(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)]YbI(THF) (10).
2
2
6
3
2
6
4
2
A solution of potassium derivative [K{(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)}] in
2
6
3
2
6
4
situ prepared from 2 (0.38 g, 0.77 mmol) and metallic K (0.033 g, 0.84 mmol, 9% molar excess)
in THF (35 mL) was added to a solution of YbI (THF) (0.44 g, 0.77 mmol) in THF (25 mL) and
2
2
the reaction mixture was stirred for 3 d at 25 °C. The solvent was removed in vacuum, the
remaining solid was extracted with toluene (50 mL), and the extract was filtered. The solvent
was removed in vacuum and the remaining solid was dissolved in THF (10 mL). Slow
condensation of hexane into a concentrated THF solution afforded brown crystals of 10. Yield
0
.54 g (75%). C H IN O Yb (938.82): calc. C 52.45, H 6.01, N 4.48, Yb 18.43; found C 52.18,
41 56 3 3
1
H 6.28, N 4.13, Yb 18.27. H NMR: (400 MHz, C D N, 25 °C): δ = 1.48 (s, 9 H, C(CH ) ), 1.59
5
5
3 3
(
m, 8 H, β-CH , THF), 1.71, 1.88, 2.18 (s, 18 H, CH C꞊N, C H (CH ) ), 3.62 (s, 3 H, OCH ),
2 3 6 3 3 2 3
3
3
.63 (m, 8 H, α-CH , THF), 6.75 (d, 1 H, J = 7.6 Hz, C H (CH ) ), 6.90‒7.29 (m, 9 H,
2
H,H
6
3
3 2
1
3
C H (CH ) ) ppm. C NMR: (100 MHz, C D N, 25 °C): δ = 18.4, 18.8, 20.8 (CH C꞊N,
6
3
3 2
5
5
3
C H (CH ) ), 26.3 (β-CH , THF), 31.1 (C(CH ) ), 42.8 (C(CH ) ), 55.9 (OCH ), 68.3 (α-CH ,
6
3
3 2
2
3 3
3 3
3
2
THF), 103.4 (C‒CtBu, central), 112.5, 120.4, 121.1, 124.7, 125.5, 128.8, 128.9, 129.1, 129.9,
32.4, 132.5, 142.5, 144.0, 151.3, 160.2, 182.4 (CH C꞊N, tBuC꞊N, C H (CH ) ) ppm. IR (KBr):
1
3
6
3
3 2
ν = 1609 (s), 1589 (s), 1521 (s), 1242 (s), 1186 (s), 1141 (s), 1093 (s), 1034 (s), 1006 (s), 958 (s),
–
1
9
15 (s), 879 (s), 828 (s), 808 (s), 775 (s), 749 (s), 670 (m), 603 (m), 572 (m), 501 (s) cm .
2
.1.9. Synthesis of [(2,6-Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)]YbI(TMEDA) (11).
2
6
3
2
2
6
3
6

A solution of potassium derivative [K{(2,6-Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)}]
2
6
3
2
2
6
3
in situ prepared from 3 (0.58 g, 1.17 mmol) and metallic K (0.050 g, 1.28 mmol, 9% molar
excess) in THF (35 mL) was added to a solution of YbI (THF) (0.67 g, 1.17 mmol) in THF (25
2
2
mL) and the reaction mixture was stirred for 12 h at 25 °C. The solvent was removed in vacuum,
the remaining solid was extracted with toluene (50 mL), and the extract was filtered. The solvent
was removed in vacuum and the remaining solid was dissolved in TMEDA (10 mL). Slow
condensation of hexane into a concentrated TMEDA solution afforded brown crystals of 11.
Yield 0.58 g (54%). C H IN Yb (908.90): calc. C 52.86, H 6.43, N 7.71, Yb 19.04; found C
4
0
58
5
1
5
3.21, H 6.50, N 7.44, Yb 19.17. H NMR: (400 MHz, C D N, 25 °C): δ = 1.49 (s, 9 H,
5 5
C(CH ) ), 1.61, 1.88 (s, 12 H, CH C꞊N, C H (CH ) ), 2.15 (s, 18 H, CH C꞊N, C H (CH ) , CH
3
3
3
3
6
3
3 2
3
6
3
3 2
TMEDA), 2.19 (s, 6 H, CH C꞊N, C H (CH ) ), 2.36 (s, 4 H, CH TMEDA), 6.91‒7.15 (m, 9 H,
3
6
3
3 2
2
1
3
C H (CH ) ) ppm. C NMR: (100 MHz, C D N, 25 °C): δ = 18.5, 18.7, 20.4, 21.7 (CH C꞊N,
6
3
3 2
5
5
3
C H (CH ) ), 31.9 (C(CH ) ), 44.1 (C(CH ) ), 46.4 (TMEDA), 58.6 (TMEDA), 104.9 (C‒CtBu,
6
3
3 2
3 3
3 3
central), 125.5, 128.1, 128.9, 129.0, 132.1, 132.6, 143.8, 149.0, 161.0, 180.2 (CH C꞊N, tBuC꞊N,
3
C H (CH ) ) ppm. IR (KBr): ν = 1600 (s), 1589 (s), 1513 (s), 1347 (s), 1287 (s), 1231 (s), 1180
6
3
3 2
(s), 1130 (s), 1093 (s), 1042 (s), 1028 (s), 1014 (s), 977 (s), 946 (s), 831 (s), 792 (s), 761 (s), 741
–
1
(
s), 676 (s), 597 (s), 575 (m), 498 (m) cm .
2
.1.10. Polymerization of isoprene (general procedure).
Under a nitrogen atmosphere at 25 °C borate (0.01 mmol) was added to a solution of (7‒9)
(
0.01 mmol) in toluene (1 mL) and then 10 equivalents of AliBu or AlEt (0.1 mmol) were
3 3
added. After which to the reaction mixture isoprene (1000 equiv.) was added. Polymerization
was initiated and carried out for 2‒4 hours. The reaction mixture was quenched by the addition
of ethanol, and then poured into a large amount of ethanol to precipitate the polymer, which was
dried under vacuum at 60 ° C to a constant weight. Then, 1,4- 3,4-regioselectivity was
1
13
1
determined by H and C { H} NMR spectroscopy. GPC of polyisoprenes was performed in
THF at 20 °C. The number average molecular masses (M ) and polydispersity indexes (M /M )
n
w
n
of the polymers were calculated with reference to a universal calibration against polystyrene
standards.
2
.2. X-ray crystallography
The X-ray data for 4, 7, 9 and 10 were collected with Bruker D8 Quest diffractometer (MoKα-
radiation, ω-scans technique, λꢀ=ꢀ0.71073ꢀÅ) using APEX2 [31] software package. The structures
2
were solved by direct methods and were refined by full-matrix least squares on F for all data
using SHELX [32]. SADABS [33] was used to perform absorption corrections. All non-hydrogen
atoms in 4, 7, 9 and 10 were found from Fourier syntheses of electron density and were refined
7

anisotropically. All hydrogen atoms were placed in calculated positions and were refined in the
“
riding” model with U(H) ꢀ=ꢀ1.2U of their parent atoms (U(H) ꢀ=ꢀ1.5U for methyl groups).
iso eq iso eq
The crystallographic data and structures refinement details are given in Table 1. CCDC-
1
967977 (4), 1967978 (7), 1967979 (9) and 1967980 (10) contain the supplementary
crystallographic data for this paper (the corresponding CIF files are available in the Supporting
Information). These data are provided free of charge by The Cambridge Crystallographic Data
Centre: ccdc.cam.ac.uk/structures.
Table 1. Crystallographic data and structure refinement details for 4, 7, 9 and 10.
Compound
4
7
9
10
Empirical formula
C
35
H
44LiN
3
O
C
42
H
58Cl
2
N
3
O
2
Y,
C
45
H
64Cl
3
LiN
3
O
4
Y
41 3 3
C H56I N O Yb
½
C
7
H
8
Formula weight
T, K
529.67
100(2)
842.79
100(2)
913.19
100(2)
938.82
298(2)
Crystal system
Space group
a, Å
b, Å
c, Å
Monoclinic
P2 /n
10.5491(2)
12.9255(3)
23.2034(5)
90
Monoclinic
P2 /c
10.9044(18)
10.4131(17)
37.838(5)
90
Monoclinic
P2
10.9553(6)
19.7656(11)
11.4358(6)
90
Monoclinic
P2
11.8982(4)
12.2653(5)
14.4785(5)
90
1
1
1
1
α, deg.
β, deg.
101.8870(10)
90
3095.99(11)
4
1.136
90.882(3)
90
4295.9(11)
4
113.7310(10)
90
2266.9(2)
2
110.5882(16)
90
1977.97(13)
2
1.576
γ, deg.
3
V, Å
Z
d
calc., g/cm3
1.303
1.338
Absorption coefficient,
mm
0.068
1.522
1.507
3.184
-1
F
000
1144
1780
960
940
Crystal size, mm
θ range for data
collection, deg.
Index ranges
0.29 × 0.26 × 0.20 0.58 × 0.36 × 0.14 0.68 × 0.23 × 0.17 0.15 × 0.14 × 0.03
2.33-30.07
2.71-29.87
2.18-30.02
2.24-26.19
-14  h  14
-15  h  15
-14  k  14
-52  l  52
58444
-15  h  15
-27  k  27
-16  l  16
33061
-14  h  14
-15  k  15
-17  l  17
18182
-
-
18  k  18
32  l  32
Reflections collected
Independent reflections
Rint
43551
9070
12261
13250
7817
0.0467
99.9
0.0735
99.9
0.0394
99.9
0.0374
99.8
Completeness to θ, %
Data/restraints/parameters 9070 / 105 / 425
12261 / 2 / 533
1.034
13250 / 136 / 564
0.994
7817 / 531 / 480
1.026
2
S(F )
Final R indices
1.029
= 0.0543
wR = 0.1237
= 0.0806
wR = 0.1368
0.36 / -0.28
R
1
R
1
= 0.0414
wR = 0.0854
= 0.0647
wR = 0.0928
R
1
= 0.0376
wR = 0.0820
= 0.0464
wR = 0.0851
0.60 / -0.41
R
1
= 0.0465
wR = 0.0977
= 0.0502
wR = 0.0994
1.30 / -2.25
(
I > 2σ(I))
Final R indices
all data)
2
2
2
2
R
1
R
1
R
1
R
1
(
2
2
2
2
Largest diff. peak and
0.76 / -0.57
3
hole, e/Å
3
. Results and discussion
3
.1. Synthesis and characterization
8

The synthetic approaches to β-triketimines developed in the past decade allow for the
modification of both electronic and steric properties of these ligands in a wide range due to
variation of the radicals attached to the nitrogen atoms [19‒24]. A new β-triketimine (2,6-
Me C H N꞊CMe) CH (1) was synthesized by the treatment of lithium diketiminate [(2,6-
2
6
3
3
Me C H N꞊CMe) CHLi] with equimolar amount of imidoyl chloride 2,6-Me C H N꞊CClMe
2
6
3
2
2
6
3
[
28] in toluene (Scheme 1). [(2,6-Me C H N꞊CMe) CHLi] was prepared in situ by the reaction
2 6 3 2
of (2,6-Me C H N꞊CMe) CH [29] with n-BuLi in 1:1 molar ratio. Triketimines (2,6-
2
6
3
2
2
Me C H N꞊CMe) CH(2-MeOC H N꞊CtBu)
(2),
(2,6-Me C H N꞊CMe) CH(2,6-
2 6 3 2
2
6
3
2
6
4
Me C H N꞊CtBu) (3) were prepared according to literature procedures [20, 25].
2
6
3
H
NH2
C
i
iii
ii
N
N
N
N
2
-2 H O
- n-BuH
- LiCl
2
Li
N
N
N
i. CH C(O)CH C(O)CH toluene, 100 C, p-toluenesulfonic acid;
3
2
3,
ii. n-BuLi, hexane;
iii. 2,6-Me C H N=CClMe, toluene.
2
6 3
1, 74%
Scheme 1. Synthesis of β-triketimine 1.
Triketimine 1 was isolated as pale yellow powder in 74% yield. Triketimine 1 is soluble in
THF, toluene, CH CN, CHCl and slightly soluble in hexane.
3
3
The tautomerism of triketimines 2 and 3 was previously described [20, 25]. Triketimine 2
in solution of CDCl exists in diimine-enamine tautomeric form. 3 adopts a triimine tautomeric
3
form, in which the hydrogen atom is located on the methine carbon. In contrast to 2 and 3
prototropic triimine/diimine-enamine tautomers of triketimine 1 exist together in equilibrium
(38:62) in solution (Scheme 2). Prototropic rearrangement is investigated using HSQC
1
13
(
Heteronuclear Single Quantum Correlation) H– C NMR experiment and the ratio of diimine-
enamine (major isomer) and triimine (minor isomer) were determined from the integral
1
intensities of the corresponding NH (diimine-enamine) and α-CH (triimine) signals in the H
1
NMR spectrum of 1 recorded in CDCl at 25 °C (Figure 1S). Thus, the H NMR spectrum of 1
3
shows two peaks at δ = 4.81 and 13.72 ppm, corresponding to α-CH and NH protons
respectively. The protons of Me groups of both tautomers give rise to five well-resolved singlets
in the region 1.94‒2.21 ppm and a multiplet in a weak field at 6.88‒7.09 ppm is due to aromatic
1
3
protons. In the C NMR spectrum of 1 the signals at 72.2 ppm and 108.5 ppm belong to methine
minor isomer) and alkenyl carbon atoms of major isomer (Figure 2S). The carbon atoms of
xylidine (C H (CH ) ) and (CH C꞊N) fragments give rise to as a set of signals in the region
(
6
3
3 2
3
1
23.0‒171.9 ppm. The IR spectrum (Nujol, KBr) of 1 exhibits strong absorption bands at 1637,
–
1
1
606, 1589, 1538 cm corresponding to asymmetric vibrations of the C꞊N multiple bonds, as
9

–
1
well as broadened absorption band at 3438 cm related to the N‒H group of diimine-enamine
tautomer.
H
C
NH
N
N
Equilibrium
N
N
N
Triimine, 38%
Diimine-enamine, 62%
Scheme 2. Prototropic tautomerism of 1.
Triketimines 1–3 can be easily deprotonated by the treatment with an equimolar amount of
n-BuLi in THF at 0 °C (Scheme 3). After recrystallization of the reaction products from
THF/hexane or THF solutions, complexes 4, 5 were obtained as yellow crystals in 79 and 72%
yields. The synthesis and structure of [(2,6-Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)]Li(THF)
2
6
3
2
2
6
3
2
(6) were previously described [25]. Complexes 4 and 5 are very air- and moisture-sensitive,
soluble in ethers and aromatic solvents and virtually insoluble in aliphatic hydrocarbons.
H
C
R3
R1
R1
R2
R3
THF
N
N
N
N
N
+ n-BuLi
-
n-BuH
(THF)n
Li
N
R2
1
2
3
13
4, 79% (R = Me, R = Me, R = Me, n = 1)
1
2
3
5
, 72% (R = tBu, R = H, R = OMe, n = 2)
1
2
3
6
, 76% (R = tBu, R = Me, R = Me, n = 2)
Scheme 3. Synthesis of lithium triketiminates 4–6.
The H NMR spectrum of complex 4 recorded in C D at 25 °C exhibits a single set of
1
6
6
-
signals corresponding to equivalent triketiminate ligands [(2,6-Me C H N꞊CMe) C] . The methyl
2
6
3
3
protons of xylidine and (CH C꞊N) fragments appear as two singlets at δ = 2.19 and 2.37 ppm.
3
The signals at δ = 7.06‒7.12 ppm, one doublet at 7.24 (3JH,H = 7.5 Hz) and one singlet at 7.32
ppm can be ascribed to the aromatic protons. The methylene groups of coordinated THF
7
molecule appear as two multiplets at δ = 1.07 and 2.98 ppm. In the Li NMR spectrum of
complex 4 one signal at δ = 1.9 ppm was detected. The 13C NMR spectrum of 4 includes
characteristic signals of xylidine and (CH C꞊N) fragments and coordinated THF molecule.
3
1
The H NMR spectrum of complex 5 (C D , 25 °C) consists of a sharp singlet at δ = 1.67
6
6
ppm corresponding to 9 protons of the tBu group and three singlets of equal integral intensity at
δ = 1.81, 1.96 and 2.19 ppm assigned to the protons of the methyl groups of xylidine and
(
CH C꞊N) fragments. The protons of methoxy groups appear as a singlet at δ = 3.41 ppm. Two
3
1
0

broad singlets at δ = 1.33 and 3.43 ppm are due to methylene protons of THF molecules, and a
1
3
multiplet in the range 6.82‒7.07 ppm is associated with ten aromatic protons. The C NMR
spectrum of 5 in C D at 25 °C displays the expected set of resonances of the triketiminate ligand
6
6
-
7
[
(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)] and coordinated THF molecules. The Li NMR
2 6 3 2 6 4
spectrum of 5 contains a single resonance at δ = 1.8 ppm.
Clear yellow crystals of 4 suitable for X–ray diffraction study were obtained by slow
condensation of hexane into the concentrated solution of the complex in THF. Molecular
structure of complex 4 is shown in Fig. 1. The crystallographic data and structural refinement
details for 4 and other reported in this paper complexes 7, 9 and 10 are listed in Table 1. Selected
bond lengths and bond angles for 4, 7, 9, 10 are presented in Table 2.
Table 2. Selected bond lengths (d) and angles (ω) in compounds 4, 7, 9 and 10.
Compound
Bond
d/Å
Angle
/deg
4
Li(1)–N(1)
Li(1)–N(2)
N(1)–C(1)
N(2)–C(3)
C(1)–C(2)
C(2)–C(3)
C(1)–C(4)
C(2)–C(5)
N(3)–C(5)
C(3)–C(15)
Li(1)–O(1)
Y(1)–N(1)
Y(1)–N(2)
N(1)–C(1)
N(2)–C(3)
C(1)–C(2)
C(2)–C(3)
C(1)–C(4)
C(2)–C(5)
N(3)–C(5)
C(3)–C(18)
Y(1)–Cl(1)
Y(1)–Cl(2)
Y(1)–O(1)
Y(1)–O(2)
1.875(3)
1.897(3)
1.321(2)
1.310(2)
1.434(2)
1.437(2)
1.514(2)
1.485(2)
1.282(2)
1.525(2)
1.860(3)
2.324(2)
2.326(2)
1.322(2)
1.336(2)
1.420(3)
1.415(3)
1.510(3)
1.522(3)
1.274(3)
1.511(3)
2.5682(6)
2.5767(6)
2.405(2)
2.375(2)
O(1)–Li(1)–N(1)
O(1)–Li(1)–N(2)
N(1)–Li(1)–N(2)
C(1)–N(1)–C(16)
C(1)–N(1)–Li(1)
C(16)–N(1)–Li(1)
C(3)–N(2)–C(24)
C(3)–N(2)–Li(1)
C(24)–N(2)–Li(1)
127.5(2)
133.2(2)
96.0(2)
120.3(2)
125.2(2)
114.2(2)
121.4(3)
124.3(2)
110.5(3)
7
Cl(1)–Y(1)–N(1)
Cl(1)–Y(1)–N(2)
Cl(2)–Y(1)–N(1)
Cl(2)–Y(1)–N(2)
Cl(1)–Y(1)–Cl(2)
N(1)–Y(1)–N(2)
C(1)–N(1)–C(19)
C(1)–N(1)–Y(1)
C(19)–N(1)–Y(1)
C(3)–N(2)–C(27)
C(3)–N(2)–Y(1)
C(27)–N(2)–Y(1)
C(2)–C(5)–N(3)
C(5)–N(3)–C(10)
O(1)–Y(1)–O(2)
Cl(1)–Y(1)–N(1)
Cl(1)–Y(1)–N(2)
Cl(1)–Y(1)–Cl(2)
Cl(1)–Y(1)–Cl(3)
Cl(2)–Y(1)–Cl(3)
N(1)–Y(1)–N(2)
C(1)–N(1)–C(18)
C(1)–N(1)–Y(1)
C(18)–N(1)–Y(1)
C(3)–N(2)–C(26)
C(3)–N(2)–Y(1)
C(26)–N(2)–Y(1)
C(2)–C(5)–N(3)
C(5)–N(3)–C(10)
94.74(4)
97.30(4)
96.62(4)
95.35(4)
162.75(2)
75.01(5)
117.7(2)
133.1(2)
109.0(2)
117.0(2)
130.7(2)
112.0(2)
124.2(2)
124.4(2)
88.12(5)
92.18(7)
90.72(7)
92.66(3)
170.97(3)
82.00(3)
75.91(9)
118.0(2)
130.2(2)
111.1(2)
117.9(3)
129.5(2)
112.5(2)
125.4(3)
121.8(3)
9
Y(1)–N(1)
Y(1)–N(2)
N(1)–C(1)
N(2)–C(3)
C(1)–C(2)
C(2)–C(3)
C(1)–C(4)
C(2)–C(5)
N(3)–C(5)
C(3)–C(17)
Y(1)–Cl(1)
Y(1)–Cl(2)
Y(1)–Cl(3)
Y(1)–O(2)
2.305(3)
2.346(3)
1.326(4)
1.321(4)
1.417(4)
1.431(4)
1.520(4)
1.507(4)
1.283(4)
1.515(4)
2.5764(8)
2.6641(8)
2.6633(8)
2.370(2)
1
1

Li(1)–Cl(2)
Li(1)–Cl(3)
Li(1)–O(3)
Li(1)–O(4)
2.311(7)
2.356(7)
1.932(7)
1.903(7)
Cl(2)–Li(1)–Cl(3)
O(3)–Li(1)–O(4)
97.0(2)
101.0(3)
1
0
Yb(1)–N(1)
Yb(1)–N(2)
N(1)–C(1)
N(2)–C(3)
C(1)–C(2)
C(2)–C(3)
C(1)–C(4)
C(2)–C(5)
N(3)–C(5)
C(3)–C(17)
Yb(1)–I(1)
Yb(1)–O(2)
Yb(1)–O(3)
2.395(8)
2.40(2)
1.34(2)
1.33(2)
1.39(2)
1.43(2)
1.52(2)
1.55(2)
1.27(2)
1.52(2)
3.0316(9)
2.40(2)
2.408(9)
I(1)–Yb(1)–N(1)
I(1)–Yb(1)–N(2)
I(1)–Yb(1)–O(2)
I(1)–Yb(1)–O(3)
N(1)–Yb(1)–N(2)
C(1)–N(1)–C(18)
C(1)–N(1)–Yb(1)
C(18)–N(1)–Yb(1)
C(3)–N(2)–C(26)
C(3)–N(2)–Yb(1)
C(26)–N(2)–Yb(1)
C(2)–C(5)–N(3)
C(5)–N(3)–C(10)
O(2)–Yb(1)–O(3)
117.1(2)
113.0(2)
93.6(2)
101.0(2)
73.8(4)
117.3(9)
132.7(9)
109.6(8)
117.1(9)
133.4(8)
109.5(7)
126.0(9)
122.7(9)
77.2(3)
Figure 1. Molecular structure of 4, showing the atom numbering scheme. Thermal ellipsoids are
given at 30% probability level. All hydrogen atoms are omitted for clarity.
According to the X-ray diffraction study compound 4 is monomeric lithium complex,
crystallizes in the monoclinic space group P2 /n with one molecule of complex in the
1
asymmetric part of the unit cell. The monoanionic triketiminate ligand in 4 performs a bidentate
coordination mode via two nitrogen atoms while the third imino group remains non-involved
into the metal‒ligand bonding. The Li ion in 4 is three-coordinate and adopts planar geometry,
but metallocycle LiNCCCN is slightly distorted (the average deviation of atoms from the plane
is 0.10 Å). The Li–N (1.875(3), 1.897(3) Å) and Li–O (1.860(3) Å) bond lengths in 4 are slightly
shorter than the previously reported values for the related three-coordinate lithium diketiminate
1
2

complexes [HC(2,6-iPr C H N꞊CtBu) ]Li(THF) (Li–N 1.927(6) Å; Li–O 1.910(6) Å), [HC(2,6-
2
6
3
2
Et C H N꞊CMe) ]Li(THF)
(Li–N
1.908(4)
Å;
Li–O
1.887(6)
Å),
[HC(2,6-
2
6
3
2
iPr C H N꞊CMe) ]Li(THF) (Li–N 1.917(4), 1.912(4) Å; Li–O 1.911(4) Å) [34‒36]. The analysis
2
6
3
2
of the bond lengths within NCCCN fragment of the ligand (N‒C: 1.321(2) Å, 1.310(2) Å; C‒C:
.434(2) Å, 1.437(2) Å) confirms delocalization of negative charge within the β-diketiminate
framework {(2,6-Me C H N꞊CMe) C}. The third {2,6-Me C H N꞊CMe} fragment which is not
1
2
6
3
2
2
6
3
connected with the lithium cation features distinguishable single C‒C (1.485(2) Å) and double
C꞊N (1.282(2) Å) bonds.
-
Thereby in 4 the monoanionic β-triketiminate ligand [(2,6-Me C H N꞊CMe) C] features
2
6
3
3
2
3
bidentate κ -NN-coordination mode. The observed type of coordination differs from κ -NNN-
cordination mode typical for neutral triketimine complexes of d-transition metals [19‒21].
Apparently, the distinction of types of coordination is caused by the electronic state of the ligand.
-
The localization of negative charge in monoanionic ligand [(2,6-Me C H N꞊CMe) C] on the
2
6
3
3
central carbon atom in 4, causing flattening of the carbanionic C(1)C(2)C(3)C(5) fragment
(Figure 1), actually excludes any possibility for chemical bonding of the third nitrogen atom with
+
lithium cation Li (I.R. (ionic radius) = 0.59 Å, C.N. = 4) [37].
A number of studies have shown that neutral triketimines typically interact with ions of
3
transition metals as tridentate κ -NNN-ligands [19, 20]. Only two Co(II) complexes containing
2
neutral triketimines (2,4,6-Me C H N꞊CMe) CH(2,4,6-Me C H N꞊CMe) featuring bidentate κ -
3
6
2
2
3
6
2
NN-coordination are known [22]. Distinction in types of coordination of neutral triketimines is
caused not only by steric properties of ligands, but also, apparently, by the nature of
metalocentre. Thus, triketimine (2,4,6-Me C H N꞊CMe) CH(2,4,6-Me C H N꞊CMe) acting as a
3
6
2
2
3
6
2
3
bidentate ligand [22] in cobalt complexes (I.R. = 0.58 Å, C.N. = 4) [37], forms κ -NNN-
coordination compounds [21] with nickel (I.R. = 0.63 Å, C.N. = 5) [37], having a slightly larger
ionic radius. To study a coordination of the monoanionic potentially tridentate triketiminate
-
3+
ligand [(2,6-Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)] with rare-earth metal ions Ln having
2
6
3
2
2
6
3
large ionic radius, reactions of complex 6 with anhydrous LnCl (Ln = Y, Nd) were carried out in
3
THF. The salt metathesis reaction of anhydrous LnCl with 6 (1:1 molar ratio, THF) afforded the
3
triketiminate dichloro yttrium and neodymium complexes [(2,6-Me C H N꞊CMe) C(2,6-
2
6
3
2
Me C H N꞊CtBu)]LnCl (THF) (Ln = Y (7), Nd (8)) in 78 and 70% yields (Scheme 4). The
2
6
3
2
2
analogous reaction of YCl with 5 resulted in the formation of triketiminate yttrium chloro ate
3
complex [(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)]Y(THF)Cl(µ-Cl) Li(THF) (9). 9 was
2
6
3
2
6
4
2
2
isolated as light yellow crystals in 77% yield (Scheme 4).
1
3

tBu
tBu
N
N
N
N
Cl
O
O
THF
O
Li
+ LnCl3
Ln
Cl
N
- LiCl
N
O
6
Ln = Y (7, 78%), Nd (8, 70%)
O
O
tBu
tBu
O
O
Li
N
N
Cl
Cl
N
N
O
O
THF
Li
Y
N
N
O
Cl
+
YCl3
5
9, 77%
Scheme 4. Synthesis of lanthanide complexes 7–9.
The H and C NMR spectra of diamagnetic yttrium complexes 7 and 9 (C D , 25 °C)
1
13
6
6
demonstrate the expected sets of signals due to triketiminate ligands and coordinated THF
1
13
molecules and are in a good agreement with the H, C spectra recorded for the Li complexes 6
7
[
25] and 5. The Li NMR spectrum of 9 contains a single resonance at δ = 5.1 ppm.
Transparent crystals of complexes 7 and 8 suitable for X-ray diffraction studies were
obtained by slow concentration of toluene solution. The molecular structures of 7 and 8 are
shown in Figures 2a and 2b respectively. Complex 7 crystallizes in the monoclinic space group
P2 /c. The asymmetric part of the unit cell in 7 contains one molecule of complex and one
1
solvate molecule of toluene located at the symmetry element. Complex 7 crystallizes as a solvate
7
·(C H ) . Complex 8 crystallizes as a solvate 8·THF in triclinic space group P–1 with two
7 8 0.5
crystallographically independent molecules of complex in the asymmetric part of the unit cell.
Unfortunately, the poor quality of crystalline samples of 8 makes it impossible to study the
structure in detail and allow to obtain only the data on connectivity of atoms. Therefore,
geometric parameters and details of the molecular structure are given for complex 7 only.
3
+
The coordination sphere of the Y ion is composed of two terminal chloro ligands, two
2
nitrogen atoms of the chelating κ -N,N-triketiminate ligand and two oxygen atoms of THF
3
+
molecules. The coordination polyhedron of the Y can be described as a distorted tetragonal
bipyramid: the N and O atoms are located in the base, and Cl atoms occupy the apical positions.
Thus, the formal coordination number of Y cation is six. The Y–Cl, Y–N and Y–O distances in
complex 7 are similar with those measured for the related six-coordinate β-diketiminate yttrium
compounds [HC(2,6-iPr C H N꞊CMe) ]YCl (THF) , [PhC(2,6-iPr C H N꞊CH) ]YCl (THF) ,
2
6
3
2
2
2
2
6
3
2
2
2
[
HC(2-tBuC H N꞊CMe) ]YCl (THF) , [HC(2,6-Me C H N꞊CMe) ]YCl (THF) [18, 38]. The
6 4 2 2 2 2 6 3 2 2 2
Y–Cl bond lengths (2.5682(6), 2.5767(6) Å) in 7 are very similar to those reported for the related
1
4

β-diketiminate yttrium complexes (2.549(2)–2.560(2) Å) [18, 38]. The Y–N bond lengths in 7
2.324(2), 2.326(2) Å) are close to each other and comparable to the values (2.334(2)–2.380(3)
Å) measured in the related yttrium complexes [18, 38]. The C‒N and C‒C bond lengths (C–N:
.322(2), 1.336(2) Å; C–C: 1.415(3), 1.420(3) Å) in planar fragment of NCCCN in complex 7 lie
(
1
in the narrow range of values 1.322(2)‒1.420(3) Å and demonstrate delocalization of the
negative charge over the conjugated system of β-diketiminate group. The third fragment {2,6-
Me C H N꞊CtBu} of the triketiminate ligand similarly to 6 [25], features distinguishable single
2
6
3
C‒C (1.522(3) Å) and double C꞊N (1.274(3) Å) bonds and remains non-coordinated.
a
b
Figure 2. Molecular structures of 7 (a) and 8 (b), showing the atom numbering schemes. Thermal
ellipsoids of 7 are given at 30% probability level. All hydrogen atoms are omitted for clarity.
Colorless transparent crystals of 9 suitable for single crystal X-ray diffraction were grown
by slow condensation of hexane into a concentrated THF solution at room temperature. The
molecular structure of 9 is depicted in Figure 3. The X-ray diffractions study revealed that 9 is a
heterobimetallic yttrium ate complex containing one equivalent of LiCl. 9 crystallizes in the
monoclinic space group P2 with one molecule in the asymmetric part of the unit cell. The
1
coordination sphere of the yttrium atom in 9 is set up by two N atoms of the triketiminate ligand,
2
two μ -bridging chloro ligands, one terminal chloro anion, and one oxygen atom of coordinated
THF molecule which results in Y3+ formal coordination number of six. The Y–N (2.305(3),
2
2
.346(3) Å) and Y–O (2.370(2) Å) bond lengths in 9 are comparable with those in 7 (Y–N:
.324(2), 2.326(2) Å; Y–O: 2.375(2), 2.405(2) Å) and yttrium complexes
1
5

3
1
2
1
2
[
R C(R N꞊CR ) ]YCl (THF) (2.343(2)–2.380(3) Å; R = 2,6-iPr C H , 2-tBuC H ; R = Me, H;
2 2 2 2 6 3 6 4
3
R = Ph, H) [38], [HC(2,4,6-Me C H N꞊CMe) ]YCl (THF) (2.356(3), 2.342(3) Å) [39]. The
3
6
2
2
2
2
C‒N, C–C bond lengths in complex 9 (N–C: 1.321(4), 1.326(4) Å; C–C: 1.417(4), 1.431(4) Å)
are indicative of a delocalization of the negative charge over the β-diketiminate fragment.
Complex 9 contains three chloro ligands: one is terminal, while two others are μ-bridging
between yttrium and lithium atoms and thus participate in the formation of the dinuclear
structure. The terminal Y–Cl distance (2.5764(8) Å) is predictably shorter than the bridging ones
(2.6633(8), 2.6641(8) Å), and the lengths of both types of bond are in a good agreement with the
corresponding values previously reported for yttrium diketiminate complexes [38‒40].
Figure 3. Molecular structure of 9, showing the atom numbering scheme. Thermal ellipsoids are
given at 30% probability level. All hydrogen atoms and CH groups of THF molecules are
2
omitted for clarity.
It is noteworthy that for monoanionic triketiminate ligands, when the ionic radius of the
+
3+
metal increases (from Li to Ln ), the type of coordination remains unchanged. Thus, we
attempted the synthesis of Yb2+ complexes (I.R. = 1.02 Å) [37] in which such a bidentate
coordination mode of monoanionic triketiminate ligands is preserved. The reactions of equimolar
amounts of the potassium derivatives of triketimines 2 and 3 (prepared in situ by metallation of
1
6

the corresponding triketimine with K in THF) and YbI (THF) afforded mononuclear iodo
2
2
triketiminate Yb2+ complexes [(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)]YbI(THF) (10)
2
6
3
2
6
4
2
and [(2,6-Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)]YbI(TMEDA) (11) (Scheme 5).
2
6
3
2
2
6
3
R3
R1
1
2
) K
R2
N
N
2
) YbI (THF)2
(X)n
2; 3
Yb
-
-
0.5 H2
KI
N
I
1
2
3
1
0, 75% (R = tBu; R = OMe; R = H; X = THF; n = 2)
1
2
3
1
1, 54% (R = tBu; R = Me; R = Me; X = TMEDA; n = 1)
2
+
Scheme 5. Synthesis of Yb complexes 10 and 11.
Complexes 10 and 11 were isolated as brown air- and moisture-sensitive crystals and were
1
13
authenticated by microanalysis, H and C NMR and IR spectroscopic methods. The complexes
are soluble in THF, 1,2-dimethoxyethane, TMEDA and toluene, but insoluble in hexane.
1
The H NMR spectrum of diamagnetic complex 10 recorded in C D N exhibits a single set
5
5
of signals corresponding to equivalent triketiminate ligands. One doublet (3JH,H = 7.6 Hz) and a
1
multiplet (at 6.75 and 6.90‒7.29 ppm, respectively) in the H NMR spectrum of 10 can be
ascribed to aromatic protons. Nine protons of the tBu group appear as a sharp singlet at 1.48
ppm. Three singlets at 1.71, 1.88 and 2.18 ppm are assigned to the protons of the methyl groups
of xylidine and (CH C꞊N) fragments, while a singlet at 3.62 ppm corresponds to methoxy group.
3
Coordinated THF molecules appear as two multiplets at 1.59 and 3.63 ppm.
1
The H NMR spectrum of ytterbium complex 11 (C D N, 25 °C) has the following set of
5
5
signals: one singlet at 1.49 ppm corresponding to nine protons of the tBu substituents and four
singlets with the chemical shifts 1.61, 1.88, 2.15, 2.19 ppm attributed to the 36 protons of the
methyl groups of TMEDA, xylidine and (CH C꞊N) fragments. Four protons of the methylene
3
group of coordinated TMEDA molecule appear as a singlet at 2.36 ppm. The aromatic protons
appear as a multiplet in low field (6.91–7.15 ppm).
The IR spectra of complexes 7‒11 exhibit three strong absorption bands in the region
1
513‒1609 cm–1 corresponding to asymmetric vibrations of the C꞊N multiple bonds in the
triketiminate ligands.
1
7

a
b
Figure 4. Molecular structures of 10 (a) and 11 (b), showing the atom numbering schemes.
Thermal ellipsoids of 10 are given at 30% probability level. All hydrogen atoms are omitted for
clarity.
Clear brown crystals of complexes 10 and 11 suitable for X-ray diffraction were obtained
by slow condensation of hexane into the concentrated solutions of compounds in THF or
TMEDA. Molecular structures of complexes 10 and 11 are shown in Fig. 4. According to the X-
ray diffraction study compounds 10 and 11 unlike the related dimeric iodo diketiminates
1
2
1
2
{
[HC(R N꞊CR ) ]YbITHF} (R = 2,6-iPr C H , SiMe ; R = Me, Ph, tBu) adopt monomeric
2 2 2 6 3 3
structures [7, 41]. Complex 10 crystallizes in the monoclinic space group P2 with one molecule
1
located in the asymmetric part of the unit cell. As in the case of complex 8, the quality of the
data collected for 11 is sufficient only to obtain the atomic connectivity. Therefore, details on the
molecular structure of complex 10 only are discussed below.
2
+
The Yb cation in 10 is bonded to two N atoms of the triketiminate ligand, the terminal I
2
+
atom, and two O atoms of the THF molecules. Thus, the formal coordination number of Yb is
. As in 4, 7 and 9, the third nitrogen atom of the triketiminate ligand is not involved into the
5
metal–ligand interaction. The Yb–N bond lengths in complex 10 are similar (2.395(8), 2.40(2)
Å) and comparable with the bond distances published earlier for related diketiminate derivatives
{
[HC(2,6-iPr C H N꞊CMe) ]YbITHF} (2.414(4), 2.398(4) Å), {[HC(Me SiN꞊CPh) ]YbITHF}
2 6 3 2 2 3 2 2
1
8

(
2.342(4), 2.385(4) Å), {[HC(2,6-iPr C H N꞊CtBu) ]YbITHF} (2.397(3), 2.438(3) Å) [7, 41].
2 6 3 2 2
The C–N (1.33(2), 1.34(2) Å) and C–C (1.39(2), 1.43(2) Å) bond lengths in 10 within the six–
membered metallacycle YbNCCCN give evidence for delocalization of the negative charge in
the diketiminate fragment. The terminal Yb–I bond in complex 10 (3.0316(9) Å) is predictably
shorter than the bridging ones (3.100(2)–3.228(2) Å) in relared iodo diketiminate ytterbium
1
2
1
2
complexes {[HC(R N꞊CR ) ]YbITHF} (R = 2,6-iPr C H , SiMe ; R = Me, Ph, tBu) [7, 41].
2
2
2
6
3
3
3
.2. Isoprene polymerization.
Catalytic activity of the halide complexes 7–11 in isoprene polymerization was explored in
toluene at 25 °C. The polymerization results are summarized in Table 3. It was established that
neither complexes 7–11, nor binary systems (7–11)/[Ph C][B(C F ) ] (1 : 1), (7–11)/AliBu (1 :
3
6
5 4
3
1
0) perform catalytic activity in toluene solution at room temperature. However, three-
component systems (7–9)/AliBu /[Ph C][B(C F ) ] (1 : 10 : 1) exhibit catalytic activity in
3
3
6 5 4
isoprene polymerization and provide total conversion of 1000 equivalents of the monomer within
h under mild conditions (Table 3). A series of tests revealed a strong influence of the
2
composition of the catalytic systems based on complexes 7–9 on the molecular-weight
characteristics and morphology of the polymer samples. It was found that initiation of isoprene
polymerization with ternary catalytic systems (7–9)/AlEt /[Ph C][B(C F ) ] (1 : 10 : 1) leads to
3
3
6 5 4
polyisoprene samples containing 92.4–94.3% of cis-1,4-units (see Table 3, entries 2, 6, 10),
whereas the use of ternary catalytic systems (7–9)/AliBu /[Ph C][B(C F ) ] (1 : 10 : 1) allows
3
3
6 5 4
for obtaining polyisoprenes with very high content (96.0–99.0%) of 1,4-cis units (see Table 3,
entries 1, 5, 9). The complexes 7–9 based systems containing AliBu performed higher activities
3
than those with AlEt (Table 3, entries 1, 2, 5, 6, 9, 10). The catalytic tests performed with AlEt
3
3
4
afforded the polymers with low molecular weights M (3.0×10 ) and broad molecular weight
n
distribution (M /M = 3.6‒4.6). The polyisoprene samples produced by the ternary systems (7–
w
n
9
)/AliBu /[Ph C][B(C F ) ] (1 : 10 : 1) feature monomodal GPC traces with high M (12.0–
3 3 6 5 4 n
4
2
0.2×10 ) and rather broad molecular weight distribution (M /M = 2.7–4.5). For the yttrium and
w n
neodymium systems containing [Ph C][B(C F ) ] activator the observed activities at monomer
3
6 5 4
loading 1000 equivalents have similar values, however when [PhNHMe ][B(C F ) ] was used
2
6 5 4
the activity of ternary system 8/AliBu /HNB (1 : 10 : 1) dropped (in 2 h conversion for 8 is
3
9
2%). The PIP sample obtained with ternary system 8/AliBu /HNB showed monomodal GPC
3
trace with polydispersity value M /M = 2.5 (Table 3, entry 13). When the ternary system based
w
n
on complex 8 activated by [Et NH][BPh ] was employed no catalytic activity was detected
3
4
(
Table 3, entry 14). Yttrium ate complex 9 in the presence of AliBu was slightly less active than
3
7
in combination with TB borate (91% vs 100% for [Ph C][B(C F ) ]). However, when AliBu
3 6 5 4 3
1
9

was used the similar cis-1,4 selectivity for both complexes 7 and 9 was achieved (Table 3,
entries 1, 9).
Few reports concerning catalytic activity of Sm(II) complexes in diene polymerization
[42- 45] were published so far, while nearly nothing is known about performance of Yb(II)
compounds in this transformation. In order to explore the effect of the nature and of rare-earth
metal on the activity and selectivity in isoprene polymerization, we performed a series of tests
catalyzed by the binary 10, 11/AliBu3 (1
:
10) and ternary systems 10,
1
1/AliBu /[Ph C][B(C F ) ] (molar ratio, (1 : 10 : 1)) in toluene. It was found that neither binary
3
3
6 5 4
nor ternary systems based on Yb(II) complexes enable isoprene polymerization.
Table 3. Catalytic tests in isoprene polymerization initiated by systems 7–9/(AliBu3,
AlEt )/[Ph C][B(C F ) ].
3
3
6 5 4
Entry Cat [Ln]/[IP] Borate AlR
3
t (h) Conv. (%) M
n
×10-4
M /M
w n
1,4-cis
%)
1,4-trans 3,4
(
(%)
(%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
7
7
7
7
8
8
8
8
9
9
9
9
8
8
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
1/1000
TB
TB
―
AliBu
3
3
3
3
3
3
2
100
82
20.2
3.0
―
3.7
3.9
―
97.0
93.8
―
2.6
0.4
AlEt
3
4
1.6
―
4.6
―
AliBu
―
24
24
2
0.0
0.0
100
85
TB
TB
TB
―
―
―
―
―
―
AliBu
12.8
3.0
―
2.7
3.6
―
99.0
94.3
―
0.0
1.2
―
1.0
4.5
―
AlEt
3
4
AliBu
―
24
24
2
0.0
0.0
91
TB
TB
TB
―
―
―
―
―
―
AliBu
12.0
3.0
―
4.5
4.6
―
96.0
92.4
―
3.0
2.7
―
1.0
4.9
―
0
1
2
3
4
AlEt
3
4
80
AliBu
24
24
2
0.0
0.0
92
TB
―
―
―
―
―
―
HNB AliBu
3
3
17.9
―
2.5
―
87.8
―
0.0
―
12.2
―
3
Et NB AliBu
24
0.0
Conditions: complex (10 μmol in toluene, [Ln] : [AlR
C][B(C ], HNB = [PhNHMe ][B(C ], Et NB = [Et
polystyrene standard.
3
] : [Borate] = 1/10/1, (T = 25 °C); TB =
NH][BPh ]. M determined by GPC against
[Ph
3
6
F
5
)
4
2
6
F
5
)
4
3
3
4
n
Formerly the ternary catalytic systems for isoprene polymerization based on the related
rare-earth dichloro complexes coordinated by “classic” diketiminate ligand {CH[C(Me)N(2,6-
Me C H )] }LnCl (THF) were described by Cui and co-workers [18]. The comparison of the
2
6
3
2
2
2
catalytic performance of systems 8-[PhNHMe ][B(C F ) ]-AliBu and {CH[C(Me)N(2,6-
2
6
5 4
3
Me C H )] }NdCl (THF) -[PhNHMe ][B(C F ) ]-AliBu (1:1:10) in isoprene polymerization
2
6
3
2
2
2
2
6
5 4
3
(1000 equiv.) demonstrates that the complex derived from the diketiminate ligand provides
higher activity, stereoselectivity and control over molecular mass distribution.
2
0

4
. Conclusions
Coordination of monoanionic triketiminate ligands to metal ions having various radii (Li+,
3
+
2+
+
Ln , Ln ) was explored on a series of triketiminate complexes of Li (4‒6), neural (Ln = Y (7),
3
+
Nd (8)) and ate (Ln = Y (9)) triketiminate dichloro Ln complexes as well as mononuclear
2
+
triketiminate Yb iodides (10, 11). X-ray analysis revealed that in complexes 4, 7, 8, 9, 10, 11
having considerably different radii of the metal ions the monoanionic β-triketiminate ligands
-
-
[
(2,6-Me C H N꞊CMe) C] ,
[(2,6-Me C H N꞊CMe) C(2-MeOC H N꞊CtBu)] ,
[(2,6-
2
6
3
3
2
6
3
2
6
4
-
Me C H N꞊CMe) C(2,6-Me C H N꞊CtBu)] feature bidentate coordination mode and are
2
6
3
2
2
6
3
coordinated to the metal centers only through two nitrogen atoms, whereas the third nitrogen is
3
drifted away. The observed type of coordination differs from κ -NNN-cordination mode typical
for neutral triketimine complexes of d-transition metals [19‒21]. It should be noted that the
distinction of types of coordination is caused by electronic state of the ligand. The localization of
negative charge on the central carbon atom causes flattening of the central CCCC fragment and
3
excludes a possibility of κ -NNN-cordination. Complexes 7–9 activated by borate
(
[Ph C][B(C F ) ]) and alkylaluminium compounds (AliBu , AlEt ) enable isoprene
3 6 5 4 3 3
polymerization. Catalytic activity of the ternary systems was found to depend strongly on the
nature of the metal atom, borate and alkyl aluminium components. The binary and ternary
2
+
catalytic systems based on Yb complexes 10 and 11 complexes proved to be inert in isoprene
polymerization.
Acknowledgments
This work was financially supported by the Russian Foundation for Basic Research (Project 18-
4
3-520036). The X-ray study of 4, 7, 9, 10 has been carried out in the framework of the Russian
state assignment using the equipment of The Analytical Center of IOMC RAS.
1
13
Supporting Information (see footnote on the first page of this article): The H and C NMR
7
spectra of 1 and complexes 4, 5, 7, 9‒11, the Li NMR of 4, 5, 9 and IR spectra of 1, 4, 5, 7–11
are presented.
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Graphical Abstract
Declaration of interests
VThe authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐
The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests:
2
6

Highlights
Monoanionic β-triketiminate ligands feature bidentate coordination mode and are coordinated to
a metal center only through two nitrogen atoms.
The ternary systems based on these complexes exhibit catalytic activity in isoprene
polymerization
The ternary systems provide very high content of cis-1,4 units (98.9%)
2
7