Sc and Y Heteroalkyl Complexes with a NCsp3N Pincer-Type Diphenylmethanido Ligand: Synthesis, Structure, and Reactivity

Article abstract of DOI:10.1002/ejic.202000306

New diphenylmethane [4-tBu-2-(C₃H₂N₂Me-1)C₆H₃]₂CH₂ (1) bearing pendant imidazolyl groups in ortho-positions of aromatic rings of diphenylmethane skeleton was synthesized using St

Full text of DOI:10.1002/ejic.202000306

European Journal of Inorganic Chemistry
Accepted Article
Title: Sc and Y Hetero-alkyl Complexes with NCsp3N Pincer Type
Diphenylmethanido Ligand: Synthesis, Structure and Reactivity.
Authors: Ahmad Fayoumi, Dmitry M. Lyubov, Andrey S. Shavyrin,
Anton V. Cherkasov, Anatoly M. Ob’edkov, Alexander
Trifonov, and Alexey O. Tolpygin
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000306
Link to VoR: https://doi.org/10.1002/ejic.202000306
01/2020

10.1002/ejic.202000306
European Journal of Inorganic Chemistry
FULL PAPER
Sc and Y Hetero-alkyl Complexes with NCsp3N Pincer Type
Diphenylmethanido Ligand: Synthesis, Structure and Reactivity.
Ahmad Fayoumi,[a] Dmitry M. Lyubov,[a] Alexey O. Tolpygin,[a] Andrey S. Shavyrin,[a] Anton V.
Cherkasov,[a] Anatoly M. Ob’edkov,[a] Alexander A. Trifonov*[a,b]
[a]
[b]
Mr. Ahmad Fayoumi, Dr. Dmitry M. Lyubov, Dr. Alexey O. Tolpygin, Dr. Andrey S. Shavyrin, Mr. Anton V. Cherkasov, Dr. Anatoly M. Ob’edkov,
Prof. Dr. Alexander A. Trifonov
Institute of Organometallic Chemistry of Russian Academy of Sciences
Tropinina Street 49, GSP-445, 603950, Nizhny Novgorod, Russia
E-mail: trif@iomc.ras.ru
Prof. Dr. Alexander A. Trifonov
Institute of Organoelement Compounds of Russian Academy of Sciences
Vavilova Street 28, 119334, Moscow, Russia
Supporting information for this article is given via a link at the end of the document.
Abstract:
New
diphenylmethane
[4-tBu-2-(C3H2N2Me-
earth metal ions. The Ln−Csp3 pincer complexes are less
1)C6H3]2CH2 (1) bearing pendant imidazolyl groups in ortho-
positions of aromatic rings of diphenylmethane skeleton was
synthesized using Stille cross-coupling reaction between bis(4-(tert-
butyl)-2-iodophenyl)methane and Bu3Sn(C3H2N2Me) in the
presence of Pd(PPh3)4. Potassium diphenylmethanide [{[4-tBu-2-
(C3H2N2Me-1)C6H3]2CH}K(OEt2)]2 (2K) was prepared by treatment
of 1 with an equimolar amount of Lochmann-Schlosser super base.
Rare-earth metal hetero-alkyl complexes {[4-tBu-2-(C3H2N2Me-
1)C6H3]2CH}Ln(CH2SiMe3)2(THF)n (Ln = Sc, n = 0 (2Sc); Y, n = 1
investigated and to date bis(iminophosphorano)methanido
[CH(PPh2NR)2]− (R = SiMe3, iPr, Ad, Ph, C6H2Me3-2,4,6),[8]
[9]
bis(thiophosphinoyl)methanido
bis(pyrazolyl)methanido [CH(C3HN2Me2-3,5)2]−
[CH(PPH2S)2]−
and
[10]
derivatives
are known. Recently tridentate diarylmethanido ligand [2,2’-(4-
MeC6H3NMe2)2CH]− was used for the preparation of Ln(II)
NCsp3N pincer type complexes.[11] Csp3 centred pincer type
ligands were successfully applied for the synthesis of alkylidene
complexes
via
double
deprotonation
of
(2Y)) with NCsp3
N
pincer type diphenylmethanido ligand were
bis(iminophosphorano)methane ligands by amido or alkyl
precursors.[12] Bis(thiophosphinoyl)methane also gives an
opportunity for the preparation of rare-earths alkylidenes.[9,13]
Herein we report on the synthesis of new imidazolyl substituted
diphenylmethane which due to the presence of N-donor centres
proved to be suitable for tridentate coordination with hard Lewis
acids as Ln(III) ions. The synthetic approaches to the
deprotonation of the central methylene fragment as well as the
synthesis of the NCsp3N pincer-type rare earth alkyl complexes
will be considered as well.
synthesized by the selective sp3 CH-bond activation of the central
CH2 group in 1 by Ln(CH2SiMe3)3(THF)2. According to the X-ray
data the diphenylmethanido ligands in 2K and 2Sc perform a
tridentate pincer-type κ3-N,C,N coordination. Complexes 2Ln were
evaluated as catalysts for isoprene polymerization and
hydrosilylation of alkenes and alkynes.
Introduction
Pincer ligands have found a vast application in coordination and
organometallic chemistry of d-transition metals[1] due to their
robust tridentate coordination to the metal centres which
provides high thermal and kinetic stability of their derivatives
along with high activity in a variety of catalytic transformations.[2]
One of the advantages of the pincer ligands is the simplicity of
modification of their electronic and steric properties via variation
of the nature of the central atom, covalently bounding the metal
ion, the nature of the pendant donor groups, and the nature and
size of the linker between the coordination sites of the ligand,
what allows for tailoring geometry and tuning electronic structure
of metal complex, thereby providing control of its reactivity. The
progress in chemistry and catalytic application of d-transition
metals complexes with pincer ligands have been summarized in
several reviews,[3] and books[4] published over recent years.
In contrast pincer-type alkyl complexes of rare-earth metals still
remain poorly explored. To date only few examples of carbon
centred pincer-type rare-earth metal complexes are described
and most of them are derived from 1,3-disubstituted benzenes
and feature covalent Ln−Csp2 bond. Coordination bonds
between Ln ions and donor atoms of the side arms of the pincer
ligands, such as nitrogen,[5] oxygen,[6] sulphur,[6b] or carbon
atoms of NHC pendant[7] provides robust linkage with the rare
Results and Discussion
Bis(4-(tert-butyl)-2-(1-methyl-1H-imidazol-2-yl)phenyl)methane
[4-tBu-2-(C3H2N2Me-1)C6H3]2CH2 (1) was prepared by Stille
cross-coupling
reaction
between
bis(4-(tert-butyl)-2-
iodophenyl)methane[14] and excess (2.5 equiv.) of 1-methyl-2-
(tributylstannyl)-1H-imidazole[15] catalysed by Pd(PPh3)4
in
[16]
toluene solution (Scheme 1). Compound 1 was purified by
column chromatography (silica gel, EtOAc) and was isolated as
amorphous colourless solid in 87% yield. Compound 1 is well
soluble in chloroform, THF, aromatic solvents (toluene,
benzene), moderately soluble in Et2O and almost insoluble in
hexane.
u
tB
u
tB
mo .
l
Pd PPh 2
,
( )
3
4
o uene
l
%
u
tB
u
tB
n
u
B
3
S
T
140 o
C
,
120 h
,
+
.
2 5
N
N
-
u
n
2 B 3S I
N
N
N
N
I
I
1
8
7
%
( )
Scheme 1. Synthesis of imidazolyl substituted diphenylmethane 1.
1
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10.1002/ejic.202000306
European Journal of Inorganic Chemistry
FULL PAPER
In the 1H NMR spectrum of 1 the central methylene protons
appear as a sharp singlet at 3.97 ppm, while in the 13C{1H}
spectrum the related carbon gives rise to the signal at 36.2 ppm
(CDCl3, 298 K). The protons of t-Bu groups appear as a sharp
singlet at 1.25 ppm and the aromatic protons of the
diphenylmethane fragment give two doublets 6.56 (d, 3JHH = 8.1
one oxygen atom of coordinated Et2O molecule.
Diphenylmethanido fragment in 2K is nearly planar, the dihedral
angle between two phenyl rings is 10.12(9)°. Both imidazolyl
fragments in tridentate diphenylmethanido ligand are nearly
orthogonal to the phenyl rings (the angles between planes of
imidazolyl and aryl rings are 72.92(5) and 74.26(6)°). The K−C
distance in 2K is 3.007(2) Å, what is very close to the related
distances measured in potassium diphenylmethanido complexes
with unsubstituted benzhydryl ligand [(Ph2CH)K(THF)]∞ (K−C:
3.003 Å)[17] and substituted tridentate diphenylmethanide
containing NMe2 groups in ortho-positions of Ph rings {[2,2’-(4-
MeC6H3NMe2)2CH]K(THF)}2 (K−C: 3.044(3) Å).[19] The K−N
distances in 2K (K−N: 2.846(2)–2.899(2) Å) are somewhat
shorter compared to the NMe2-substituted analogue {[2,2’-(4-
MeC6H3NMe2)2CH]K(THF)}2. In the latter compound η5-
pentadienyl type of coordination was realized due to the
interactions between K ion, central benzhydryl and ispo- and
4
Hz), 7.14 (d, JHH = 2.1 Hz) and one doublet of doublets 7.20
3
4
(dd, JHH = 8.1 Hz, JHH = 2.1 Hz). Imidazolyl substituents in
ortho-positions of the diphenylmethane fragment give singlet at
3.05 ppm attributed to methyl group, and two doublets at 6.88
and 7.11 ppm with small coupling constant (3JHH = 1.2 Hz), what
is characteristic for aromatic protons of imidazolyl ring. Long
range 15N−1H correlation allowed to determine the chemical
shifts of 15N atoms in compound 1, where two non-equal
nitrogen atoms appear at 158.2 (NMe) and 256.8 (N) ppm
respectively. 1 was also characterized by IR-spectroscopy, GC-
MS and elemental analysis (See Experimental Section and ESI).
Diphenylmethanido ligand can be bound to rare earth ion by the
salt metathesis protocol starting from anhydrous LnCl3 and alkali
metal diphenylmethanides.[17] It was found that 1 does not react
with n-BuLi, however can be readily deprotonated by Lochmann-
Schlosser super base n-BuLi/t-BuOK affording the potassium
ortho-carbons
of
both
aromatic
rings
(K−CAr:
3.059(3)−3.184(3) Å). In contrast in 2K no K−CAr interactions
were detected. The shortest distances between K ion and
carbon atoms of phenyl and imidazolyl rings are significantly
longer (K−Cipso 3.328(2) Å; K−Cortho 3.520(2) Å; K−CIm
3.299(2) Å). Thus coordination mode of the tridentate
diphenylmethanido ligand varies depending on the substituents
in the phenyl rings: κ3-[N,C,N] in 2K vs μ-η5-pentadienyl:κ3-CNN
in NMe2 substituted analogue. Despite the different coordination
modes of tridentate diphenylmethanido ligands in 2K and {[2,2’-
(4-MeC6H3NMe2)2CH]K(THF)}2 the central benzhydryl carbon
retains sp2-configuration in the solid state with the sum of the
diphenylmethanide
[{[4-tBu-2-(C3H2N2Me-
1)C6H3]2CH}K(OEt2)]2 (2K, Scheme 2). Similarly the phosphino
substituted diphenyl methane [4-tBu-2-(PPh2)C6H3]2CH2 also
was inert toward alkyl lithium reagents but metalation was
successful when n-BuLi/t-BuOK mixture was used.[18] On the
contrary
the
NMe2
substituted
analogue
2,2’-(4-
MeC6H3NMe2)2CH2 readily reacts with both n-BuLi and
Lochmann-Schlosser super bases (n-BuLi/t-BuOM, M = Na,
K).[19]
u
tB
N
N
u
tB
O
Et
2
u
tB
u
tB
n-
Et O
u
u
B
Li/tB OK
,
N
N
r
t
1 h
,
K
2
K
N
N
-
-
C4H10
tB Li
Et2O
u
tB
u
O
N
N
N
N
N
N
2K
7
1
8%
)
(
u
tB
Scheme 2. Synthesis of potassium dihpenylmethanide 2K.
bond angles around 360.0(2)°.
Potassium diphenylmethanide 2K was isolated as bright orange
crystals after crystallization from Et2O solution by slow
concentration at ambient temperature. Complex 2K is well
soluble in THF, moderately soluble in Et2O and almost insoluble
in aromatic (benzene, toluene) and aliphatic (hexane) solvents.
It is extremely air and moister sensitive, but can be stored in
inert atmosphere or vacuum without any traces of decomposition
for several weeks.
Figure
1.
Molecular
structure
of
[{[4-tBu-2-(C3H2N2Me-
1)C6H3]2CH}K(OEt2)]2 (2K). The Et groups of coordinated Et2O molecules,
CH3 groups of tBu substituents and all hydrogen atoms except H(1A) are
omitted for clarity. Bond lengths (Å) and angles (°): K(1)−C(1) 3.007(2),
K(1)−N(1) 2.899(2), K(1)−N(3) 2.860(2), K(1)−N(1A) 2.846(2), K(1)−O(1)
2.700(3); C(1)−K(1)−N(1) 77.57(4), C(1)−K(1)−N(3) 67.42(4), C(1)−K(1)−O(1)
103.66(7),
N(1)−K(1)−N(3)
92.69(4),
K(1)−N(1)−K(1A)
93.91(4),
N(1)−K(1)−O(1) 173.80(7), N(3)−K(1)−O(1) 93.38(7).
2K crystallizes in monoclinic P21/c space group with one
centrosymmetric dimeric molecule lying on the inversion centre
per asymmetric unit. The single crystal X-ray diffraction study
revealed that each potassium ion in 2K is bound with tridentate
diphenylmethanido ligand via central carbon and two nitrogen
atoms of imidazolyl substituents, while the formation of a dimer
realizes due to coordination of one nitrogen atom of imidazolyl
fragment of each diphenylmethanido ligand to both potassium
ions (Figure 1). Moreover, each K ion is additionally bonded with
In the 1H and 13C{1H} NMR spectra of 2K recorded in THF-d8
solution at 298 K the diphenylmethanido ligand gives a single
set of signals. The protons of the central benzhydryl CH
fragment linked with the K ion appear as a sharp singlet at 3.02
ppm. It should be noted that for the previously reported NMe2-
substituted analogue {[2,2’-(4-MeC6H3NMe2)2CH]K(THF)}2 the
chemical shift of the signal corresponding to the
diphenylmethanido protons CH was 4.12 ppm (THF-d8).[19] Such
a shift can be associated with strong shielding of the central
2
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10.1002/ejic.202000306
European Journal of Inorganic Chemistry
FULL PAPER
Scheme 3. Synthesis of heteroleptic Ln3+ alkyl complexes 2Sc and 2Y.
proton by aromatic systems of imidazolyl substituents in the
1
case of 2K. The value of JCH coupling constant is known to
correlate with the type of hybridization of the C−H bonding
orbital.[20] The values are roughly proportional to the contribution
of s-character and can be evaluated from the empirical
Different size of the metal ions (Sc3+ 0.745 Å vs Y3+ 0.900 Å)[24]
lead to the formation of complexes with different coordination
numbers. Thus, 2Sc is a THF-free complex, while yttrium
analogue 2Y was isolated as an adduct with one THF molecule.
The composition of 2Sc and 2Y was proved by NMR
spectroscopy and by microanalysis data.
1
formula JCH = 500*%s (%s = 0.25 for sp3, 0.33 for sp2).[21]
The 1JCH coupling constant measured for 2K (144 Hz; %s = 0.29)
is comparable to the NMe2 substituted analogue {[2,2’-(4-
MeC6H3NMe2)2CH]K(THF)}2
(149 Hz;
%s = 0.30)
and
The structure of 2Sc was also unambiguously established by X-
ray analysis. The molecular structure of 2Sc is depicted in
Figure 2. Complex 2Sc crystallizes in triclinic P-1 space group
with one molecule in the asymmetric unit. The
diphenylmethanido ligand in 2Sc is tridentate and is linked with
the Sc3+ ion by covalent Sc−C and two coordination Sc−N bonds
corresponds to intermediate hybridization between sp2 and sp3
types.
Unfortunately, the attempts of synthesis of rare-earth complexes
applying a salt metathesis approach by the reactions of 2K with
anhydrous LnCl3 (Ln = Sc, Y, Nd) did not allow for the isolation
of the targeted diphenylmethanido complex. The reactions in
THF solution at ambient temperature resulted in KCl
precipitation thus indicating that the reaction took place.
However, the trials to isolate any individual metal containing
product failed.
Alkane elimination reaction between rare-earth metals tris(alkyl)
complexes and ligands is a commonly used simple and efficient
synthetic procedure for preparation of bis- and monoalkyl
complexes.[22] In a number of publication it was demonstrated
that intramolecular activation of sp3 or sp2 CH bonds of the
proligand by alkyl group at the rare-earth metal centre results in
the formation of heteroalkyl complexes containing two different
Ln−C bonds.[23] Recently selective intermolecular CH bond
activation was applied as a straightforward synthetic approach to
resulting in NCsp3
N pincer type bonding. Moreover, two
remaining CH2SiMe3 groups are covalently bound with Sc3+ ion,
thus increasing its coordination number to 5. The geometry of
coordination environment of Sc3+ ion in 2Sc can be described as
a distorted tetragonal pyramid with C(34) carbon atom of the
heteroalky
complexes
containing
CH2SiMe3
and
bis(pyrazolyl)methyl ligands covalently bonded to one yttrium
centre.[10]
In order to prepare rare-earth metal derivatives via CH-bond
activation of the central methylene group of 1 its reactions with
rare-earth metal tris(alkyl) precursors Ln(CH2SiMe3)2(THF)2
and Ln(CH2C6H4NMe2-o)3, (Ln = Sc, Y) were investigated.
Complexes Ln(CH2C6H4NMe2-o)3 proved to be absolutely inert
alkyl CH2SiMe3 group in the apical position.
Figure 2.
Molecular
structure
of
{[4-tBu-2-(C3H2N2Me-
1)C6H3]2CH}Sc(CH2SiMe3)2 (2Sc). The CH3 groups of tBu substituents and
all hydrogen atoms except H(1A) are omitted for clarity. Bond lengths (Å) and
angles (°): Sc(1)−C(1) 2.387(4), Sc(1)−C(30) 2.242(4), Sc(1)−C(34) 2.211(3),
Sc(1)−N(1) 2.250(3), Sc(1)−N(3) 2.266(3); C(34)−Sc(1)−C(30) 103.2(2),
C(34)−Sc(1)−N(1) 101.9(2), C(30)−Sc(1)−N(1) 91.5(2), C(34)−Sc(1)−N(3)
1
toward diphenylmethane 1, no interactions were detected by H
NMR spectroscopy even at high temperature (C6D6, 80 °C). On
the other hand Ln(CH2SiMe3)3(THF)2 (Ln = Sc, Y) complexes
readily activate the central CH2 group of 1 affording heteroleptic
112.9(2),
C(30)−Sc(1)−N(3)
90.7(2),
N(1)−Sc(1)−N(3)
143.7(2),
alkyl
complexes
{[4-tBu-2-(C3H2N2Me-
C(34)−Sc(1)−C(1) 109.9(2), C(30)−Sc(1)−C(1) 146.7(2), N(1)−Sc(1)−C(1)
77.9(2), N(3)−Sc(1)−C(1) 80.5(2).
1)C6H3]2CH}Ln(CH2SiMe3)2 (THF)n (Ln = Sc, n = 0 (2Sc); Y, n =
1 (2Y); Scheme 3) at room temperature. The 1H NMR monitoring
of the reactions (C6D6, 20 °C) indicates quantitative release of
SiMe4 and formation of 2Ln in 2 h. The preparative scale
reactions were performed in toluene solution at ambient
temperature (4 h). Recrystallization of the reaction products by
slow diffusion of hexane into concentrated toluene solutions of
complexes 2Sc and 2Y resulted in the formation of bright orange
microcrystalline solids in 85 and 73% yield respectively.
Diphenylmethanido moiety in 2Sc is not planar. The dihedral
angle between two phenyl rings of the diphenylmethanido
skeleton is 57.21(6)°. Imidazolyl fragments are also twisted with
respect to the phenyl rings of dihpenylmethanido fragment
(angles between planes of imidazolyl and phenyl rings are
43.76(5) and 46.11(5)°). It should be noted that, in contrast to 2K,
the imidazolyl fragments in 2Sc are oriented in the opposite
directions relative to each other. The geometry of the central
diphenylmethanido carbon in 2Sc is indicative of its intermediate
hybridization state between sp2 and sp3: the sum of the bond
tBu
tBu
Toluene
4h
rt,
SiMe
1
Ln(CH2
3)3(THF)2
-
N
N
SiMe4
angles
C(2)−C(1)−C(16),
C(2)−C(1)−H(1A)
and
N
N
Ln
C(16)−C(1)−H(1A) is 351(2)° and is noticeably larger compared
to the related heteroalkyl complex containing a σ-bonded
(THF)
85%
n
Me3Si
SiMe3
2Sc
2Y
=
diphenylmethanido
ligand
[Ph2CH]Lu(CH2SiMe3)2(THF)2
(n 0),
(338.5°).[17] The measured value is close to the sum of the
angles around benzhydryl carbon atom in the parent potassium
=
73%
(n 1),
3
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10.1002/ejic.202000306
European Journal of Inorganic Chemistry
FULL PAPER
complex 2K and for recently published Ln(II) complexes with
bulky benzhydryl ligands.[25]
accompanied by SiMe4 elimination along with the formation of
complex mixture of the metal containing products.
The Sc−C bonds bond lengths in 2Sc are slightly different
(2.211(3) and 2.242(4) Å), while the Sc−CH bond is significantly
Stereospecific diene polymerization is perhaps an area of
catalysis where organolanthanides have largely been employed
with success demonstrating all their inherent potentialities.[34] In
this regard, heteroleptic alkyl complexes 2Sc and 2Y have been
used as catalyst precursors for the isoprene (IP) polymerization
under variable reaction conditions. The choice of metal ion and
the catalyst activator(s) play a fundamental role in the control of
the ultimate catalyst performance. Catalytic activity of complexes
longer (2.378(4) Å). The Sc−CH2SiMe3 bond lengths are close
[26]
to those in pentacoordinated Sc3+ tris(alkyl)
as well as in
mono- and bis(alkyl) complexes coordinated by dianionic
(N−,N,N−)[27] and monoanionic (N,N−,N),[28] (N,N,N−),[29]
(O,N−,O),[30] and (P,N−,P)[31] pincer type ligands. The distance
between Sc3+ ion and diphenylmethanido carbon is so long that
can be compared with coordination Sc−C bonds in the
pentacoordinated complex with N-heterocyclic carbene ligand
2
Ln in isoprene polymerization was evaluated in toluene at room
temperature. The results of the catalytic tests are summarized in
Table 1.
{[Me-NHC-CH2CH(n-Bu)OSc(CH2SiMe3)2]2
(Sc−C
2.385(2) Å).[32] The Sc−N bond distances in 2Sc (2.250(3) and
2.266(3) Å) are slightly shorter than the values measured in Sc
complexes with coordinated imidazolyl fragments (2.270–2.303
Å).[33]
Complexes 2Ln as well as the binary systems 2Ln/borate (Borate
= [Ph3C][B(C6F5)4] (TB) or [PhNHMe2][B(C6F5)4] (HNB)) or
2Ln/AliBu3 did not perform any appreciable activity in the process
(Table 1, entries 1–6). On the other hand, ternary systems
2Ln/Borate/AliBu3 (1:1:10 molar ratio) trigger isoprene
polymerization with moderate catalytic activity. Complex
2Y demonstrated higher activity in comparison with scandium
analogue 2Sc. in the combination with TB and AliBu3, it allowed
to achieve 98% polymer yield ([IP]/[Cat] = 1000) in 6 h at
ambient temperature (Table 1, Entry 3). Activity of the catalytic
At ambient temperature in the 1H NMR spectrum of 2Sc the
central diphenylmethanido protons appear as a singlet at 4.09
ppm, while the appropriate carbons in the 13C NMR spectrum
give rise to a singlet at 69.5 ppm. Two alkyl CH2SiMe3 groups in
case of 2Sc are non-equivalent and give rise to two sets of
signals both in 1H (ScCH2: δH = 0.03 and 0.45 ppm; SiMe3: δH
=
−0.09 and 0.05 ppm) and 13C (ScCH2: δC = 39.3 and 46.2 ppm;
SiMe3: δC = 3.5 and 3.8 ppm) spectra. The methyl protons of the
imidazolyl fragments in the 1H NMR spectrum of 2Sc are also not
equivalent and are presented by two very broad singlets at 2.87
and 3.08 ppm, while only one signal at 1.26 ppm is attributed to
the protons of tBu-groups. Cooling the solution of 2Sc to 243 K
resulted in sharpening of all signals in 1H and 13C NMR spectra.
More over at this temperature the tBu and aromatic protons of
two parts of diphenylmethanido skeleton become non-equivalent
system based on scandium complex 2
Sc/TB/AliBu3 was
somewhat lower and under similar conditions ([IP]/[Cat] = 1000)
the polymer yield was 75%. It was found that the nature of
activator (TB vs HNB) affects the molecular weights and PDI of
the resulted polymers. Thus, the polymers obtained in the
presence of TB were characterized by moderate molecular
masses (36.3·103 and 22.8·103) and rather broadened
monomodal PDI (1.95 and 2.90). In the case of HNB the
polymer samples were characterized by bimodal molecular
mass distribution with predominant content of rather high
molecular weights fractions (93.3·103 (94.4%) for 2Sc and
135.9·103 (93.5%) for 2Y). This effect can be rationalized by the
difference in pathways of the reactions of TB and HNB with alkyl
complexes as well as by the different nature of the reaction
products. Thus, the reaction of TB results in an alkyl group
abstraction, the formation of cationic alkyl species and
Ph3CCH2SiMe3. The protonolysis of Ln−CH2SiMe3 bond by
HNB along with the formation of cationic alkyl species affords
PhNMe2. PhNMe2 is able to coordinate to the rare-earth ions
during the catalytic reaction and most likely this leads to the
appearance of two types of catalytically active species.[35]
Despite these differences in Mn and PDI of the resulted
polymers in all cases the catalytic systems 2Ln/TB/AliBu3
demonstrated similar stereoselectivities affording predominantly
1,4-cis polyisoprenes (68.5–83.4%) with close content of 1,4-
trans (9.2–13.6%) and 3,4 (3.9–19.2%) units.
1
both in H and 13C NMR spectra (See ESI Fig. S10 and S11).
For the imidazolyl substituents also two sets of signals appear.
1
At high temperature (333 K) in the H NMR spectrum of 2Sc
a
single set of signals corresponding to the protons of tBu-
substituents (1.25 ppm) and imidazolyl fragments (3.08 ppm)
appears, while two CH2SiMe3 groups remain non-equivalent.
Such a behaviour of 2Sc in solution at various temperatures can
be associated with dynamic processes in the metal coordination
sphere probably due to fast in NMR time-scale
formation/dissociation of Sc−N coordination bonds.
In case of 2Y the central diphenylmethanido protons appear in
1
the H NMR spectrum (C6D6, 293 K) as a singlet at 4.03 (2Y),
while the appropriate carbon in the 13C NMR spectrum gives rise
to a doublet at 67.2 ppm (1JYC = 8.2 Hz) due to splitting with 89
Y
1
nuclei (I = ½, 100%). Unlike 2Sc in the H and 13C NMR spectra
of 2Y two alkyl CH2SiMe3 groups are equivalent and give a
single set of signals (YCH2: δH = –0.28 ppm; δC = 34.1 ppm;
SiMe3: δH = 0.30 ppm; δC = 4.6 ppm). Both of them are rather
broad and no 89Y−1H or 89Y−13C coupling was observed. tBu and
Me groups of the diphenylmethanido ligand in the case of 2Y are
also equivalent and give a sharp singlet at 1.26 ppm (tBu) and a
broad singlet at 2.82 ppm (CH3). The values of 13C−1H coupling
constants of the central diphenylmethanido CH groups for 2Sc
(133.6 Hz) and 2Y (135.8 Hz) are indicative of the hybridization
state intermediate between sp3 and sp2.
It should be noted that incorporation of the tridentate [NCsp3N]
pincer type ligand in the rare-earth metals coordination sphere in
complexes 2Ln does not allow to achieve high activity and
selectivity of the catalytic system in isoprene polymerization. For
example, ternary catalytic systems [Ln]/borate/AliBu3 (1:1:10
molar
ratio)
based
on
tris(alkyl)
complexes
Ln(CH2SiMe3)3(THF)2 in identical conditions proved to be more
active compared to 2Ln and complete conversion of 1000
equivalents of monomer was achieved in few seconds (Table 1,
Entries 5–8). At the same time the ternary catalytic systems
Ln(CH2SiMe3)3(THF)2/borate/AliBu3 demonstrated selectivity
Both heteroleptic alkyl complexes 2Ln turned out to be rather
stable. No decomposition was detected after heating in solution
at 80 °C (C7D8, 3 days); noticeable decomposition of 2Ln starts
only after heating at 100 °C for
6 h. Decomposition is
4
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10.1002/ejic.202000306
European Journal of Inorganic Chemistry
FULL PAPER
similar to that of 2Ln yielding the polyisoprenes featuring the
content of 1,4-cis units from 69.1% up to 81.1%. On the other
Table 1. Isoprene polymerization initiated by systems 2Ln/borate/AliBu3 (borate: [Ph3C][B(C6F5)4] (TB), [PhNHMe2][B(C6F5)4] (HNB), [Ln]/[borate]/[AliBu3] =
1:1:10).
Microstructure, %[c]
[d]
Entry[a]
Cat.
Activ./AliBu3 (eq.)
t
Yield, %[b]
Mn [10−3 [d]
]
Mw/Mn
cis-1,4
trans-1,4
3,4
3.9
1
2
3
4
2Sc
2Sc
2Y
TB / (10)
HNB / (10)
TB / (10)
6 h
6 h
6 h
6 h
75
68
98
86
82.5
13.6
36.3
1.95
93.3 (94.4%)
20.3 (5.6%)
3.11
1.66
68.5
79.9
83.4
12.3
10.5
9.2
19.2
9.6
22.8
2.90
135.9 (93.5%)
5.1 (6.5%)
2.01
1.17
2Y
HNB / (10)
7.4
2.7 (83.7%)
588.7 (16.3%)
5.84
2.26
5
6
Sc(CH2SiMe3)3(THF)2
Sc(CH2SiMe3)3(THF)2
TB / (10)
30 s
45 s
>99
>99
69.1
69.6
7.8
23.1
7.5
19.6 (93.3%)
926.9 (6.7%)
4.15
1.83
HNB / (10)
22.9
7
8
Y(CH2SiMe3)3(THF)2
Y(CH2SiMe3)3(THF)2
TB / (10)
10 s
10 s
>99
>99
81.1
79.7
1.0
3.5
17.9
16.8
71.8
36.3
1.50
1.99
HNB / (10)
[a] Polymerization conditions: temp = rt (20−22 °C); toluene (3.5 mL); 10 mmol of IP [IP]; 10 μmol of catalyst [cat.] (2Ln or Ln(CH2SiMe3)3(THF)2); [cat.]:[IP] =
1:1000; activators: TB, [Ph3C][B(C6F5)4]; HNB, [PhNHMe2][B(C6F5)4]; [cat.]:[activator] = 1:1.05. [b] Average value calculated over three independent runs. [c]
Determined by 1H NMR and 13C NMR spectroscopy in CDCl3 at rt. [d] Determined by GPC in THF at 40 °C against a polystyrene standard.
hand the related rare-earth metal complexes coordinated by
[NCsp2N],[5a,d,36] [NCsp2O],[6b] [NCsp2S],[6b] and [CCsp2C][37] pincer
type ligands derived from 1,3-disubstituted benzene in the
combination with borates (HNB, TB or B(C6F5)4) and AlR3
(AliBu3, AlEt3, AlMe3) provided comparable or higher activities,
but significantly higher 1,4-cis selectivity.
ambient temperature in 12 h 2Ln allowed to achieve 97 and 90%
conversions affording exclusively linier anti-Markovnikov addition
product CH3(CH2)8SiH2Ph (Table 2, Entries 1 and 2). Activity of
2Y in styrene hydrosilylation was significantly lower than for
nonene-1, at ambient temperature it allows to achieve 43%
conversion only in 48 h giving predominantly Markovnikov
Such differences in selectivity of catalytic systems based on 2Ln
and rare-earth metal [NCsp2N], [NCsp2O], [NCsp2S], and [CCsp2C]
pincer type complexes most likely results from the different
metal-ligand bonding and the structure of the real catalytically
active species. Thus in 2Ln the [NCsp3N] pincer ligand is strongly
distorted while in the [NCsp2N], [NCsp2O] and [CCsp2C] pincer
complexes derived from 1,3-disubstituted benzene metal-ligand
fragments adopt nearly planar configuration.
Table 2. Alkene and acetylene hydrosililation catalyzed by 2Ln
Markovnikov /
anti-Markovnikov
In order to elucidate the nature of the catalytically active species
the reactivity of 2Ln towards TB and HNB in THF-d8 was
investigated. According to the NMR spectroscopy the reaction of
1
2
3
4
5
6
2Sc
2Y
97
90
<2
43
15
95
- / >99
- / >99
- / -
Ln with TB expectedly affords Ph3CCH2SiMe3 while in the case
Nonene-1
Styrene
Styrene
20
20
70
12
48
24
2
of HNB SiMe4 and PhNMe2 were formed. No evidences for the
abstraction of diphenylmethanido ligand by trityl cation or its
release due to protonolysis of the metal-ligand bond were
detected. Unfortunately, the 1H NMR spectra of the cationic alkyl
species generated in-situ from 2Ln and TB or HNB in THF-d8
solution were rather broad and do not allow to get additional
information about their structure. Moreover, the cationic alkyl
species proved to be unstable in THF-d8 solution and
decomposed within 2 h affording SiMe4 and a complex mixture
of metal containing products.
Rare-earth alkyl complexes are known to be efficient catalysts
for hydrosilylation of multiple C−C bonds.[38] Complexes 2Ln were
evaluated as catalyst for hydrosilylation of alkenes and alkynes
with PhSiH3. Catalytic tests were carried out in benzene-d6
under NMR control in the presence of 2 mol % of catalyst
([Alkene]:[PhSiH3]:[Cat] = 50:50:1). Complexes 2Ln demonstrate
high activity in catalysis of PhSiH3 addition to nonene-1. At
2Sc
2Y
83 / 17
95 / 5
72 / 28
E / Z
2Sc
2Y
7
2Sc
2Y
84
92
71
90
58 / 42
55 / 45
56 / 44
53 / 47
Hexyne-1
70
70
24
24
8
9
2Sc
2Y
PhC≡CH
10
5
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10.1002/ejic.202000306
European Journal of Inorganic Chemistry
FULL PAPER
shifts for 1H, 13C{1H} NMR spectra were referenced internally to the
residual solvent resonances and are reported relative to SiMe4.
Lanthanide metal analyses were carried out by complexometric
titration.[42] The C, H, and N elemental analyses were performed in the
microanalytical laboratory of the G. A. Razuvaev Institute of
Organometallic Chemistry.
[a] Reaction conditions: C6D6 (0.6 mL); 10 μmol of 2Ln (2% mol);
[alkene]:[Cat.] = 50:1; [PhSiH3]:[Cat.] = 50:1; [b] Determined by 1H NMR
and 29Si{1H} NMR spectroscopy and by GC-MS according to previously
published data.[38f,39]
addition product PhCH(Me)SiH2Ph with 83% selectivity (Table 2,
Entry 4). Increasing the reaction temperature up to 70 °C
allowed to achieve almost quantitative conversion (95%) in 24 h
(Table 2, Entry 4), but as it could be expected at this
temperature the selectivity decreases giving Markovnikov
addition product in 72% (Table 2, Entry 6). Surprisingly,
scandium analogue 2Sc was found to be almost inactive in
styrene hydrosilylation at ambient temperature giving only traces
of hydrosilylation products (<2%; Table 2, Entry 3). However,
when temperature was increased to 70 °C in 24 h the product
yield was 15%. Internal alkenes (cyclo-hexene, cis- or trans-
stilbenes) were absolutely inactive even at high temperature
(70 °C, 24 h) in the presence of 2Ln.
Synthesis of [4-tBu-2-(C3H2N2Me-1)C6H3]2CH2 (1). In a glove-box to
a solution of bis(4-(tert-butyl)-2-iodophenyl)methane (1.50 g, 2.87 mmol)
and 1-methyl-2-(tributylstannyl)-1H-imidazole (2.62 g, 7.05 mmol) in
toluene (50 mL) Pd(PPh3)4 (0.065 g, 0.06 mmol; 2% mol) was added.
The reaction mixture was heated in oil bath at 140 °C for 120 h,
hydrolysed with water and organic compounds were extracted with ethyl
acetate. 1 was purified by column chromatography (silicagel, EtOAc) and
was isolated as amorphous solid in 87% yield (1.08 g, 2.45
mmol). 1H NMR (400 MHz, CDCl3, 293 K): 1.26 (s, 18H, CH3tBu), 3.06
5
(s, 6H, NCH3), 3.98 (s, 2H, CH2), 6.57 (d, 3JHH
=
6
u
u
tB
tB
4
8.1 Hz, 2H, H6), 6.89 (d, 3JHH = 1.2 Hz, 2H, H8,9),
1
3
2
7.12 (d, 3JHH = 1.2 Hz, 2H, H8,9), 7.15 (d, 4JHH
=
=
7
N
9
N
8
N
N
3
4
2.1 Hz, 2H, H3), 7.21 (dd, JHH = 8.1 Hz, JHH
Complexes 2Ln also enable PhSiH3 addition to terminal triple
C≡C bonds of hexyne-1 and phenylacetylene at 70 °C, while at
20 °C no reaction takes place. After 24 h at 70 °C hydrosilylation
of hexyne-1 and phenylacetylene in the presence of 2 mol % of
2Ln resulted in the formation of hydrosilylation products in 71–
92% yield respectively (Table 2, Entries 7–10). In all cases the
formation of mixtures of E- and Z-isomers almost in equal
amounts was observed. In contrast to terminal triple C≡C bonds
complexes 2Ln were inactive in hydrosilylation of internal
phenylmethyl and diphenyl acetylenes even in harsh conditions
(70 °C, 24 h).
2.1 Hz, 2H, H5) ppm. 13C{1H} (100 MHz, CDCl3,
293 K): 31.3 (s, CH3 tBu), 32.9 (s, NCH3), 34.4 (s, C tBu), 36.2 (s, CH2),
120.3 (s, CH, C8,9), 126.0 (s, CH, C5), 127.4 (s, CH, C3), 127.7 (s, CH,
C
8,9), 129.5 (s, C2), 129.9 (s, CH, C6), 138.6 (s, C1), 147.7 (s, C7), 148.8
(s, C4) ppm. 15N−1H correlation: 158.2 (NMe), 256.8 (N). 1H NMR of 1
(400 MHz, C6D6, 293 K): 1.11 (s, 18H, CH3 tBu), 2.64 (s, 6H, NCH3),
4.30 (s, 2H, CH2), 6.47 (d, 3JHH = 1.0 Hz, 2H, H8,9), 7.08 (dd, 3JHH = 8.2
Hz, 4JHH = 2.1 Hz, 2H, H5), 7.12 (d, 3JHH = 8.2 Hz, 2H, H6), 7.21 (d, 4JHH
3
= 2.1 Hz, 2H, H3), 7.33 (d, JHH = 1.0 Hz, 2H, H8,9) ppm. 13C{1H} NMR
(100 MHz, C6D6, 293 K): 31.0 (s, CH3 tBu), 32.2 (s, NCH3), 34.0 (s, C
tBu), 35.4 (s, CH2), 120.0 (s, CH, C8,9), 125.8 (s, CH, C5), 127.1 (s, CH,
C3), 128.4 (s, CH, C8,9), 130.5 (s, C2), 130.7 (s, CH, C6), 139.5 (s, C1),
148.0 (s, C7), 148.1 (s, C4) ppm. Elemental analysis calculated for
C29H36N4 (440.62 g/mol): C, 79.05; H, 8.24; N, 12.72. Found: C, 79.15;
H, 8.08; N, 12.77. MS: [M+] 440.2. IR (Nujol, KBr): 1740 (w), 1650 (m),
1610 (m), 1570 (m), 1525 (m), 1485 (s), 1405 (s), 1360 (s), 1340 (m),
1280 (s), 1260 (s), 1230 (w), 1200 (m), 1130 (s), 1105 (m), 1080 (m),
1050 (w), 1030 (s), 920 (m), 895 (m), 870 (w), 850 (w) 835 (m), 810 (s),
Conclusion
New
diphenylmethane
[4-tBu-2-(C3H2N2Me-1)C6H3]2CH2
bearing pendant imidazolyl groups was synthesized and
successfully employed as a tridentate pincer type NCsp3N alkyl
ligand for the synthesis of heteroleptic rare-earth alkyl
complexes containing two different types of Ln−C bond. It was
demonstrated that tridentate diphenylmethanido ligand allows to
provide high thermal stability of heteroleptic rare-earth metal
alkyl species. Heteroalkyl Sc and Y complexes demonstrate
moderate activity in intermolecular hydrosilylation of terminal
alkenes and acetylenes. Combined with borates and AliBu3
complexes 2Ln catalyse isoprene polymerization. Further
investigation of reactivity of heteroleptic rare-earth metal alkyl
complexes containing simultaneously two different Ln−C bonds
is in progress.
680 (s), 635 (m) cm−1
.
Synthesis of [{[4-tBu-2-(C3H2N2Me-1)C6H3]2CH}K(OEt2)}2 (2K). To a
mixture of 1 (0.400 g, 0.91 mmol) and tBuOK (0.100 g, 0.91 mmol) in
Et2O (20 mL) a hexane solution of n-BuLi (1.5 M, 0.6 mL, 0.91 mmol)
was added. The solution immediately became bright orange and the
orange precipitate formed. The reaction mixture was stirred at ambient
temperature for 1 h, then the solvent was removed in vacuum and the
solid residue was washed 3 times with hexane (15 mL) to remove LiOtBu.
Crystallization of the reaction product by slow concentration of the
solution in Et2O at ambient temperature resulted in the formation of
bright orange crystals of 2K. Complex 2K was isolated in 78% yield (0.390
g, 0.35 mmol). 1H NMR (400 MHz, THF-D8, 293 K): 1.13 (t, 3JHH = 7.0 Hz,
12H, CH3 Et2O), 1.19 (s, 36H, CH3 tBu), 3.02 (s, 2H, KCH), 3.31 (s, 12H,
3
4
NCH3), 3.40 (q, JHH = 7.0 Hz, 8H, CH2 Et2O), 6.55 (d, JHH = 2.5 Hz,
4H, H3), 6.72 (d, 3JHH = 1.2 Hz, 4H, H8,9), 6.77 (d, 3JHH = 1.2 Hz, 4H, H8,9),
6.85 (dd, 3JHH = 8.8 Hz, 4JHH = 2.5 Hz, 4H, H5),7.18 (d, 3JHH = 8.8 Hz, 4H,
H6) ppm. 13C{1H} NMR (100 MHz, THF-D8, 293 K): 14.7 (s, CH3 Et2O),
31.2 (s, CH3 tBu), 31.9 (s, NCH3), 65.3 (s, CH2 Et2O), 72.7 (s, KCH),
114.4 (s, CH, C6), 118.9 (s, CH, C8,9), 125.7 (s, CH, C5), 126.3 (s, CH,
C8,9), 126.6 (s, CH, C3),126.9 (s, C4), 128.1 (s, C1), 142.4 (s, C2), 152.1 (s,
C7) ppm. Elemental analysis calculated for C66H90K2N8O2 (1105.67
g/mol): C, 71.69; H, 8.20; N, 10.13. Found: C, 71.50; H, 8.15; N, 10.30.
Experimental Section
All experiments were performed by using standard Schlenk or glove-box
techniques, with rigorous exclusion of traces of moisture and air. After
being dried over CaH2 THF was purified by distillation from
sodium/benzophenoneketyl; hexane and toluene were dried by distillation
from sodium/triglyme and benzophenoneketyl prior to use. Benzene-d6,
toluene-d8 and THF-d8 were dried with sodium and were condensed in
vacuum into NMR tubes prior to use. CDCl3 was used without additional
Synthesis of {[4-tBu-2-(C3H2N2Me-1)C6H3]2CH}Sc(CH2SiMe3)2 (2Sc).
A toluene solution (10 mL) of 1 (0.410 g, 0.94 mmol) was added to a
solution of Sc(CH2SiMe3)3(THF)2 (0.425 g, 0.94 mmol) in toluene (10
mL). The orange reaction mixture was stirred at ambient temperature for
4 h and the volatiles were removed in vacuum. The solid residue was
dissolved in small amount of fresh toluene (3 mL) and to the resulted
purification.
Bis(4-(tert-butyl)-2-iodophenyl)methane,[14]
1-methyl-2-
Pd(PPh3)4,[16]
were prepared
(tributylstannyl)-1H-imidazole,[15]
[41]
Ln(CH2SiMe3)3(THF)2,[40] and Ln(CH2C6H4NMe2-2)3
according to literature procedures. NMR spectra were recorded using a
Bruker DPX 200 or Bruker Avance III 400 MHz spectrometer. Chemical
6
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10.1002/ejic.202000306
European Journal of Inorganic Chemistry
FULL PAPER
solution hexane was layered to give bright orange crystals of 2Sc. The
mother liquid was decanted and the crystals were washed with hexane
and dried in vacuum. Complex 2Sc was isolated in 85% yield (0.525 g,
0.80 mmol). 1H NMR (400 MHz, toluene-d8, 293 K): −0.09 (s, 9H, SiMe3),
0.03 (s, 2H, ScCH2), 0.05 (s, 9H, SiMe3), 0.49 (brs, 1H, ScCH2),0.58 (br
s, 1H, ScCH2), 1.26 (s, 18H, CH3 tBu), 2.87 (br s, 3H, NCH3), 3.08(br s,
3H, NCH3), 4.09 (s, 1H, ScCH), 6.12 (br s, 2H, CH), 6.33 (br s, 1H,
CH),6.84 (br s, 3H, CH), 7.26 (br s, 2H, CH) ppm. 13C{1H} NMR
(100 MHz, toluene-d8, 293 K): 3.5 (s, SiMe3), 3.8 (s, SiMe3), 31.5 (s,
CH3 tBu), 34.0 (s, C tBu), 34.3 (br s, NCH3), 39.3 (br s, ScCH2), 46.2(br
s, ScCH2), 69.5(s, ScCH), 117.2 (very br, CH Ar), 120.6 (br s, CH Ar),
125.7 (s, CH Ar),126.5 (s, CH Ar), 129.2 (s, CH Ar), 130.4 (s, CH Ar),
139.2 (s, C Ar), 142.5 (br s, C Ar), 144.5 (br s, C Ar), 148.4 (br s, C Ar)
ppm. 1H NMR (400 MHz, toluene-d8, 243 K): −0.04 (s, 9H, SiMe3), 0.03
(0.5 mmol) and alkene or acetylene (0.5 mmol). The reaction course was
controlled by 1H NMR spectroscopy. Conversion and selectivity were
determined by integrating the remaining substrates and the newly formed
hydrosilylation products in the 1H, 13C{1H} and 29Si{1H} NMR spectra
according to previously known data.
X-ray crystallography. The X-ray data for 2K and 2Sc were collected with
Bruker D8 Quest and Rigaku OD Xcalibur diffractometers (MoKα
-
radiation, ω-scans technique, λꢀ=ꢀ0.71073ꢀÅ, T = 100 K) using APEX3[43]
and CrysAlis Pro[44] software packages. SADABS[45] and CrysAlis Pro
was used to perform absorption corrections. The structures were solved
by direct methods and were refined by full-matrix least squares on F2 for
all data using SHELX.[46] All non-hydrogen atoms and H(1A) atoms in 2K
and 2Sc were found from Fourier syntheses of electron density (all non-
hydrogen atoms were refined anisotropically). All other hydrogen atoms
were placed in calculated positions and were refined in the “riding” model
with U(H)isoꢀ=ꢀ1.2Ueq of their parent atoms (U(H)isoꢀ=ꢀ1.5Ueq for methyl
groups). The crystallographic data and structures refinement details are
2
2
(d, JHH = 10.4 Hz, 1H, ScCH2), 0.05 (d, JHH = 10.4 Hz, 1H, ScCH2),
0.15 (s, 9H, SiMe3), 0.54 (d, 2JHH = 11.0 Hz, 1H, ScCH2), 0.79 (d, 2JHH
=
11.0 Hz, 1H, ScCH2), 1.28 (s, 9H, CH3 tBu), 1.29 (s, 9H, CH3 tBu), 2.67
(s, 3H, NCH3), 2.95 (s, 3H, NCH3), 4.22 (s, 1H, ScCH), 5.94 (s, 1H, H8,9),
6.08 (s, 1H, H8,9), 6.36 (d,3JHH = 8.5 Hz, 1H, H6), 6.88 (dd,3JHH = 8.5
Hz, 4JHH = 1.5 Hz, 1H, H5), 6.94 (d, 4JHH = 1.5 Hz, 1H, H3), 7.00 (d, 4JHH
= 1.5 Hz, 1H, H3), 7.14 (m, 3H, H5,6,8,9), 7.35 (s, 1H, H8,9) ppm. 13C{1H}
NMR (100 MHz, toluene-d8, 243 K): 3.3 (s, SiMe3), 3.6 (s, SiMe3), 31.2
(s, CH3 tBu), 31.3 (s, CH3 tBu), 33.1 (s, NCH3), 33.7 (s, C tBu), 34.0 (s,
NCH3), 34.1 (s, C tBu), 39.0 (br s, ScCH2), 45.3 (br s, ScCH2), 69.3 (s,
ScCH), 116.5 (s, CH, C6), 118.4 (s, CH, C6), 120.1 (s, CH, C8,9), 120.9 (s,
CH, C8,9), 122.3 (s, CH, C5), 126.1 (s, CH, C3), 126.4 (s, CH, C3), 127.4
(s, CH, C5), 128.2 (s, CH, C8,9), 130.0 (s, CH, C8,9), 135.0 (s, C4), 135.8
(s, C1), 138.6 (s, C4), 141.9 (s, C2), 142.6 (s, C1), 144.1 (s, C2), 147.8 (s,
C7), 150.8 (s, C7) ppm. Elemental analysis calculated for C37H57N4ScSi2
(659.00 g/mol): C, 67.43; H, 8.72; N, 8.50; Sc, 6.82. Found: C, 67.24; H,
8.92; N, 8.33; Sc, 6.75.
given in Table S1 (See ESI). CCDC–1980060 (2K) and 1980061 (2Sc
)
contains the supplementary crystallographic data for this paper. These
data are provided free of charge by The Cambridge Crystallographic
Data Centre: ccdc.cam.ac.uk/structures. The corresponding CIF files are
also available in the Supporting Information.
Acknowledgements
This work was financially supported by the Russian Science
Foundation (grant 17-73-20262). The X-ray study of 2K and 2Sc
has been carried out using the equipment of The Analytical
Center of G. A. Razuvaev IOMC RAS.
Synthesis of {[4-tBu-2-(C3H2N2Me-1)C6H3]2CH}Y(CH2SiMe3)2(THF)
(2Y). Complex 2Y was synthesized and isolated similarly to 2Sc starting
from Y(CH2SiMe3)3(THF)2 (0.640 g, 1.29 mmol) and 1 (0.560 g, 1.29
mmol). Complex 2Y was isolated as bright orange microcrystalline solid in
73% yield (0.730 g, 0.94 mmol). 1H NMR (400 MHz, C6D6, 298 K): –0.28
(br s, 4H, YCH2), 0.30 (s, 18H, SiMe3), 1.26 (s, 18H, CH3 tBu), 1.39 (br s,
4H, β-CH2 THF), 2.82 (br s, 6H, NCH3), 3.57 (br s, 4H, α-CH2 THF),
4.03 (br s, 1H, YCH), 6.11 (s, 2H, CH Ar), 6.82 (s, 2H, CH Ar), 6.96 (br m,
4H, CH Ar), 7.26 (br m, 2H, CH Ar) ppm. 13C{1H} NMR (100 MHz, C6D6,
293 K): 4.6 (s, SiMe3), 25.7 (s, β-CH2 THF), 31.6 (s, CH3 tBu), 33.6 (s,
NCH3), 33.9 (s, C tBu), 34.1 (br s, YCH2), 67.2 (d, 1JYC = 8.1 Hz, YCH),
68.4 (s, α-CH2 THF), 117.6 (very br, CH Ar), 120.5 (br s, CH, CH Ar),
126.8 (s, CH Ar), 127.2 (s, CH Ar), 127.5 (s, CH Ar), 128.6 (s, CH Ar),
139.9 (br s, C Ar), 143.9 (br s, C Ar), 150.5 (br s, C Ar) ppm. Y-HMBC
(400 MHz, C6D6, 293 K): {–0.28;832}, {4.03;832}. Elemental analysis
calculated for C41H65N4OSi2Y (775.06 g/mol): C, 63.54; H, 8.45; N, 7.23;
Y, 11.47. Found: C, 63.70; H, 8.58; N, 7.20; Y, 11.39.
Keywords: rare earth metals • alkyl complexes •
diphenylmethanides • pincer ligands
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European Journal of Inorganic Chemistry
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Table of Contents
[NCsp3N] pincer alkyls
u
tB
u
tB
H
n
C
N
N
N
N
L
THF n
(
)
e
M
i
3S
e
iM
S
3
Ln = Sc3+, Y3+
Thermally stable heteroleptic tri(alkyl) rare-earth metal complexes [NCsp3N]Ln(CH2SiMe3)2(THF)n (Ln = Sc, Y) containing NCsp3
N
pincer dyphenylmethanido ligand were synthesized through selective Csp3−H bond activation of the central CH2 group of imidazolyl
substituted diphenylmethane. Incorporation of NCsp3N pincer dyphenylmethanido ligand provides stability and at the same time
maintains high reactivity of these heteroleptic tri(alkyl)s.
10
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