Tris(benzhydryl) and Cationic Bis(benzhydryl) Ln(III) Complexes: Exceptional Thermostability and Catalytic Activity in Olefin Hydroarylation and Hydrobenzylation with Substituted Pyridines

Article abstract of DOI:10.1002/adsc.202000782

A series of Ln(III) tris(benzhydryl) complexes [(p-tBu-C₆H₄)₂CH]₃Ln (Ln=La (1), Nd (2), Y (3)) were synthesized by the salt metathesis reactions of LnHal₃(THF)_3.5 (Ln=La, Nd, Hal=Cl; Ln=Y, Hal=I) and [(p-tBu-C₆H₄)₂CH]Na. In 1–3 the benzhydryl ligands are linked with the metal centres in η⁴-coordination mode. For diamagnetic complexes 1 and 3 a fluxional behaviour was detected in solution. Complexes 1–3 proved to be thermally stable: no decomposition was observed even after heating their solutions in toluene-d₈ at 140 °C during 72 h. The reactions of 1 and 2 with B(C₆F₅)₃ allowed for the synthesis of base-free cationic complexes [(p-tBu-C₆H₄)₂CH]₂Ln[(p-tBu-C₆H₄)₂CHB(C₆F₅)₃] (Ln=La (4), Nd (5)) which adopt the structure of a contact ion pair. Combinations of 1–3 and borane ((B(C₆F₅)₃, [Me₂NHPh][B(C₆F₅)₄], [Ph₃C][B(C₆F₅)₄]) as well as 4 and 5 were found to be highly efficient, regio- and chemoselective catalysts for hydroarylation and hydrobenzylation of C=C bonds of a variety of substrates with substituted pyridines. These catalysts enable highly challenging transformations such as hydrobenzylation of 1,1-disubstituted and internal C=C bonds. (Figure presented.).

Full text of DOI:10.1002/adsc.202000782

Title: Tris(benzhydryl) and cationic bis(benzhydryl) Ln(III) complexes:
exceptional thermostability and catalytic activity in olefin
hydroarylation and hydrobenzylation with substituted pyridines
Authors: Alexander Trifonov, Aexander Selikhov, Anton Cherkasov,
Egor Boronin, Georgy Fukin, and Andrey Shavyrin
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.202000782
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10.1002/adsc.202000782
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Tris(benzhydryl) and Cationic Bis(benzhydryl) Ln(III)
Complexes: Exceptional Thermostability and Catalytic Activity
in Olefin Hydroarylation and Hydrobenzylation with
Substituted Pyridines
Alexander N. Selikhov,a,b Egor N. Boronin,a Anton V. Cherkasov,a Georgy K. Fukin,a
Andrey S. Shavyrin,a Alexander A. Trifonov*,b,a
a
G. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences 603137, 49 Tropinina str.,
Nizhny Novgorod Russia GSP-445, Fax: + 007-831-462-74-97 E-mail: trif@iomc.ras.ru
b
A. N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, 28 Vavilova str., 119991,
Moscow, GSP-1, Russia
Received:((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.
Abstract. A series of Ln(III) tris(benzhydryl) complexes [(p- Combinations of
1−3
and borane ((B(C6F5)3,
tBu-C6H4)2CH]3Ln (Ln = La (1), Nd (2), Y (3)) were [Me2NHPh][B(C6F5)4], [Ph3C][B(C6F5)4]) as well as 4 and 5
synthesized by the salt metathesis reactions of were found to be highly efficient, regio- and
LnHal3(THF)3.5 (Ln = La, Nd, Hal = Cl; Ln= Y, Hal = I) and chemoselective
catalysts
for
hydroarylation and
[(p-tBu-C6H4)2CH]Na. In 1-3 the benzhydryl ligands are hydrobenzylation of C=C bonds of a variety of substrates
linked with the metal centres in η4-coordination mode. For with substituted pyridines. These catalysts enable highly
diamagnetic complexes 1 and 3 a fluxional behaviour was challenging transformations such as hydrobenzylation of
detected in solution. Complexes 1−3 proved to be thermally 1,1-disubstituted and internal C=C bonds.
stable: no decomposition was observed even after heating
their solutions in toluene-d8 at 140 °C during 72 h. The
reactions of 1 and 2 with B(C6F5)3 allowed for the synthesis
of base-free cationic complexes [(p-tBu-C6H4)2CH]2Ln[(p-
tBu-C6H4)2CHB(C6F5)3] (Ln = La (4), Nd (5)) which adopt
the structure of a contact ion pair.
Keywords: lanthanides • benzhydryl complexes • cationic
alkyl complexes • hydroarylation • hydrobenzylation
Kinetic stabilization of homoleptic Ln(III) alkyl
species and the synthesis of isolable and thermally
robust compounds can be achieved owing to
coordination and steric saturation of the coordination
sphere of Ln ion as well as owing to rational selection
of hydrocarbyl ligands. The absence of sites
promoting β-hydride decomposition is a strict
requirement to the hydrocarbon radicals intended to
be used. Currently known homoleptic complexes
typically contain bulky silyl-substituted methanide
fragments (CH2SiMe3,[6] CH(SiMe3)2[7]), neopentyl, [8]
benzyl[9] groups as well as the ligands bearing
pendant Lewis base groups.[10]
Unfortunately, synthetically valuable precursors
with CH2SiMe3 groups are available only for the rare-
earth metals with small or medium ion size (Sc, Y,
Sm, Lu).[6] Application of benzyl complexes of
abundant early lanthanides featuring large ion size is
limited by their relatively short lifetimes at room
temperature and low yields of target compounds.[9,10]
Lately Sadow proposed an original way of
Introduction
Neutral[1] and cationic[2] rare-earth alkyl complexes
have attracted a great deal of attention during past
two decades due to their unique reactivity and
powerful potential in
a
variety of catalytic
applications involving multiple С-С bonds.[3] In
addition, one of the characteristic and extremely
important features of these compounds is their ability
to activate usually inert sp3 and sp2 CH bonds.[4]
Nevertheless, the development of the chemistry of
hydrocarbyl derivatives of rare-earths as well as their
catalytic applications was inhibited to a large extent
by low thermostability. The solution of this problem
is primarily associated with the search for approaches
to stabilization of the coordination sphere of large
and electropositive Ln(III) ions, prone to the
intramolecular reactions of β-hydrogen elimination or
β-hydrogen abstraction of hydrocarbyl ligands.[5]
1
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10.1002/adsc.202000782
Advanced Synthesis & Catalysis
stabilization of Ln(III) tris(alkyl) and cationic alkyl
species via β-SiH agostic interactions between Ln(III)
ion and [C(SiHMe2)3] alkyl groups.[11] This made it
possible to achieve excellent yields and a substantial
increase in the thermal stability of complexes.
Nevertheless, alkyl complexes of the metals of
beginning of the series, from which one would expect
the highest catalytic activity due to the largest values
of ionic radii, still remain hardly accessible.
lanthanides (La, Nd), the reaction of yttrium chloride
with [(p-tBuC6H4)2CH]Na gives tris(benzhydryl)
derivative in a very small yield of 5%, while the
majority of chloride YCl3(THF)3.5 does not react.
However, the use of YI3(THF)3.5 allows to increase
the yield to 75%.
The benzhydryl anion due to the delocalization of a
negative charge within conjugated π-system, easily
modifiable steric demand, variable and flexible
bonding modes[12] seems to be a promising candidate
for the synthesis of isolable hydrocarbyl lanthanide
complexes. Recently we successfully introduced into
Ln(II) chemistry new bulky benzhydryl ligand [(p-
tBu-C6H4)2CH]−, which proved to be suitable for the
synthesis of isolable thermally stable Yb(II), Sm(II),
and Ca(II) bis(hydrocarbyl) complexes as well as
their half-sandwich alkyl derivatives.[13] In this work
we report on the synthesis of Ln(III) benzhydryl
complexes [(p-tBu-C6H4)2CH]3Ln (Ln = La, Nd, Y),
cationic derivatives [(p-tBu-C6H4)2CH]2Ln[(p-tBu-
C6H4)2CHB(C6F5)3] (Ln = La, Nd), their structure,
stability and catalytic activity in C-C bond formation.
Scheme 1. Synthesis of tris(benzhydryl) complexes 1-3.
It is worth noting that regardless the reagents ratio
the reactions afford only tris(benzhydryl) complexes
[(p-tBu-C6H4)2CH]3Ln, which makes it impossible to
synthesize mixed alkyl halide species.
Complexes 1-3 are extremely air- and moisture-
sensitive. Complexes 1-3 are highly soluble in polar
ether solvents such as THF, DME, Et2O and aromatic
hydrocarbons, but poorly soluble in hexane.
Results and Discussion
Synthesis and characterization of tris(benzhydryl)
and cationic bis(benzhydryl) complexes
The first example of heteroalkyl Ln(III)
benzhydryl complex Lu(CH2SiMe3)2(Ph2CH)(THF)2
was described by Schumann and co-workers in
2006,[14] however all attempts of the synthesis of
The structures of complexes 1−3 were established
by X-ray analysis, which revealed that all complexes
are isomorphous and crystallize in the monoclinic
P21/c space group as a solvate with one molecule of
toluene [(p-tBu-C6H4)2CH]3Ln·(С7H8) (Ln = La, Nd,
Y). Asymmetric unit in 1-3 contains unique molecule
of complex. The molecular structure of 1-3 is
depicted in Figure 1, and the crystal and refinement
data are summarized in Table S1 (see the ESI).
Interestingly, despite high oxophilicity of Ln(III)
centers, their low coordination numbers and the use
of THF-containing halides LnHal3(THF)3.5 as starting
materials in the synthesis, complexes 1-3 do not
contain coordinated THF molecules.
In complexes 1-3 all three benzhydryl ligands
perform the same coordination mode. Similarly to the
related benzhydryl Ln(II) complexes[13] the Ln(III)
ions in 1-3 are not coplanar with the ligands but are
located above the plane. The metal ion is covalently
bound to the benzhydryl ligand via the central
methanide carbon (C1), moreover short distances
between Ln(III) and two ipso- and one ortho- carbons
of the phenyl rings were detected.
homoleptic
unsuccessful. Our approach consisting in the
application of bulky diphenylmethane (p-
Ln(III)
derivatives
remained
tBuC6H4)2CH that provides higher steric demand and
solubility of benzhydryl species proved to be
appropriate for the synthesis of homoleptic tris(alkyl)
complexes. The salt metathesis reactions of
LnHal3(THF)3.5 (Ln = Y, Hal = I; Ln = La, Nd, Hal =
Cl) with [(p-tBuC6H4)2CH]Na in 1:3 molar ratio in
toluene at elevated temperature (60 or 100 °C)
allowed for the preparation of base-free
tris(benzhydryl) complexes [(p-tBu-C6H4)2CH]3Ln
(Ln = La (1), Nd (2), Y (3)) (Scheme 1). Complexes
1-3 were isolated as bright-yellow (1), brown (2) and
orange (3) crystals in 86, 72 and 75% yields
respectively. Application of toluene as a reaction
medium plays a crucial role. When the reactions were
carried out in polar solvents (THF, DME, Et2O) at
ambient temperature only starting materials were
isolated from the reaction mixtures. However, when
the reaction mixtures were heated, intractable oily
products formed. Unlike complexes of large
2
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10.1002/adsc.202000782
Advanced Synthesis & Catalysis
Scheme 2. Synthesis of cationic benzhydryl complexes 4-5.
The Ln-Cbenzhydryl bond lengths are almost equal and radius of the metal atom, the more distorted the
vary in the narrow range: 2.597(2)-2.611(2) Å (1), benzhydryl ligand geometry. The calculated solid
[16]
2.534(3)-2.544(3) Å (2), 2.442(2)-2.460(2) Å (3) angles (G2.28
)
of the benzhydryl ligands are
(Table 1). These bond distances are much longer than 33.9(2)-34.9(2)% in 1, 33.6(2)-34.4(2)% in 2 and
those in three-coordinate complexes with 33.2(2)-34.2(2)% in 3. At the same time the
[(Me3Si)2CH] ligands (for comparison see: 2.353(5) percentage of the metal coordination sphere shielded
[7b,c]
Å
in [(Me3Si)2CH]3Y
;
2.515(9)
Å
in by the ligands increases with decrease of the metal
[(Me3Si)2CH]3La [7a]). However, these distances are ionic radius (1: 91.9(2)%; 2: 92.6(2)%; 3: 93.6(2)%).
shorter compared to the homoleptic alkyl complexes Thus, distortion of the ligands geometry allows for
with
Ln{C(SiHMe2)3}3
2.627(4) Å) and Ln{C(SiHMe2)2Ph}3
trisubstituted
methanide
ligands minimizing steric tension in the coordination sphere
[11c]
(Ln-Cav La: 2.687(7) Å, Nd: of the metal atom.
[11a]
(Ln-Cav La:
2.674(3) Å, Nd: 2.61(2) Å). At the same time the Ln-
Cbenzhydryl bond lengths in 1-3 are close to the values
measured in six-coordinate benzyl (4-Me-
C6H4CH2)3La(THF)3 (La-CH2 2.616(2)-2.634(2)
[9b]
Å)[9a], (PhCH2)3Y(THF)3 (2.452(3)-2.463(3) Å),
(PhCHNMe2)3Ln (Ln-CH(average) La: 2.648(3) Å,
Y: 2.516(4) Å, Nd: 2.588(3) Å).[10a,b] and
aminobenzyl derivatives (o-Me2N-C6H4CH2)3Ln (Ln-
CH2(average) La: 2.645(3) Å, Y: 2.472(3) Å, Nd:
2.567(3) Å).[10c,d]
As it was mentioned above in complexes 1−3 short
contacts between Ln(III) ions and two ipso- and one
ortho-phenyl carbons of each ligand were detected (1:
La-Cipso 2.841(2)-2.915(2) Å; La-Cortho 2.948(2)-
2.971(2) Å; 2: Nd-Cipso 2.795(3)-2.867(3) Å; Nd-
Cortho 2.905(3)-2.920(3) Å; 3: Y-Cipso 2.720(2)-
2.844(2) Å; Y-Cortho 2.812(2)-2.814(2) Å) (See below
Table 1). The shortest distances to Cortho atoms not
involved to coordination bonding of ligand with
lanthanide ions in 1-3 are 3.206(2), 3.199(3), and
3.225(2)
Å
correspondingly.
Thereby
the
coordination mode of benzhydryl ligands in
complexes 1-3 formally should be classified rather as
η4. Note that the Ln-C bond lengths are in a good
agreement with metals ionic radii (La 1.216 Å; Nd:
1.163 Å; Y 1.075 Å).[15]
The benzhydryl ligands in 1-3 are coordinated
somewhat non-symmetrically – the shortest and
longest Ln-Cipso distances are 2.841(2), 2.915(2) Å
(1), 2.795(3), 2.867(3) Å (2) and 2.720(2), 2.844(2) Å
(3) correspondingly. Geometry of η4-CCCC fragment
is distorted: the torsion angles CipsoCHCipsoCortho are
25.9(4)-32.8(4)° in 1, 28.1(5)-34.9(5)° in 2, 31.1(2)-
38.0(2)° in 3. It is easy to see that the shorter the ion
Figure 1. Molecular structure of complexes 1-3 (M = La
(1), Nd (2), Y (3)). Thermal ellipsoids are given at 30%
probability level. Methyl groups of tert-butyl substituents
and hydrogen atoms except bonded with methanide
carbons were omitted for clarity. Selected angles [deg]: 1:
C(1)-La(1)-C(43) 116.58(8), C(22)-La(1)-C(43) 116.76(7),
C(1)-La(1)-C(22) 117.57(7). 2: C(1)-Nd(1)-C(43) 116.9(2),
C(22)-Nd(1)-C(43) 116.3(2), C(1)-Nd(1)-C(22) 116.4(2).
3: C(1)-Y(1)-C(43) 114.53(4), C(22)-Y(1)-C(43) 116.12(4),
C(1)-Y(1)-C(22) 114.50(5).
3
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10.1002/adsc.202000782
Advanced Synthesis & Catalysis
Due to delocalization of a negative charge within beginning broaden and then decoalesce affording a
the conjugated π-system of the ligands in complexes series of signals most likely due to the appearance of
1−3 the values of the CH-Cipso bond lengths (1: non-equivalent phenyl rings (4.72, 6.76, 7.22, 7.32,
1.438(3)-1.458(3)Å, 2: 1.436(4)-1.457(5)Å; 3: 7.55 ppm). At 243 K the singlet corresponding to the
1.437(2)-1.457(2) Å) are slightly shortened compared tBu protons clearly splits in two singlets (1.40 and
to the corresponding distances in Ph2CH2 (1.523 and 1.57 ppm) of equal intensities (Figure 2).
1.501 Å).[17] Analogous interactions were previously
Table 1. Ln-C distances (Å) for complexes 1-5.
detected in Ln(II) and Ca(II) benzhydryl
complexes.[13]
Ln-CH
Ln-Cortho
Ln-Cipso
Ln-η6-Caryl
Complexes 1-3 demonstrated unprecedented
thermal stability. The complexes do not undergo
thermal decomposition when their solutions in
2.597(2)
2.610(2)
2.610(2)
2.948(2)
2.958(2)
2.971(2)
2.841(2)
2.863(2)
2.875(2)
2.889(2)
2.897(2)
2.915(2)
1
2
3
4
5
o
toluene-d8 are heated at 140 C during 72 h. For
diamagnetic complexes
1
and
3
thermal
1
decomposition was monitored by H and 13C{1H}
NMR spectroscopy. Interestingly, that the related
tris(benzyl) complexes (C6H5CH2)3Ln(THF)3 (Ln =
La, Nd) start to eliminate the corresponding arenes
even at room temperature, with half-life times of few
hours.[9a, d] Most likely such a unique thermostability
(in the scale applicable to hydrocarbyl rare-earth
derivatives) results from sufficient bulkiness of the
benzhydryl ligands, the absence of β-hydrogen atom
in the ligands, steric and coordination saturation of
the ions spheres due to η4 metal-ligand interaction and
the absence of coordinated O-containing Lewis bases,
prone to cleavage of C-O bonds.[18] It is worthy to
note that complexes 1-3 after isolation do not react
2.535(3)
2.538(3)
2.544(3)
2.905(3)
2.918(3)
2.920(3)
2.795(3)
2.818(3)
2.826(3)
2.844(3)
2.857(3)
2.867(3)
2.442(2)
2.452(2)
2.460(2)
2.812(2)
2.814(2)
2.814(2)
2.720(2)
2.745(2)
2.751(2)
2.765(2)
2.806(2)
2.844(2)
o
with THF or DME even when heated at 70 C. No
complex formation or decomposition was detected.
Surprisingly despite of pronounced oxophilicity of
rare-earth ions no cleavage of these presumably weak
non-valent interactions takes place in the presence of
O-containing Lewis bases. Apparently, the formation
of M-O coordination bonds in this case does not
compensate for the energy necessary for the cleavage
of the η4 Ln(III)-ligand interactions. The trials to
sublime complexes 1-3 in vacuum 10-4 mm Hg lead
to their decomposition at the temperature above 170
oC. (p-tBu-C6H4)2CH2 was the main decomposition
product (64% yield).
2.570(4)
2.599(4)
2.881(4)
2.892(4)
2.803(4)
2.808(4)
2.852(4)
2.897(4)
2.989(4)
3.005(4)
3.018(4)
3.034(4)
3.116(4)
3.137(4)
2.517(2)
2.529(2)
2.843(2)
2.846(2)
2.774(2)
2.779(2)
2.802(2)
2.865(2)
2.928(2)
2.952(2)
2.961(2)
2.977(2)
3.058(2)
3.088(2)
The room temperature 1H NMR spectra of
diamagnetic complexes 1 (benzene-d6) and
3
(toluene-d8) present the similar sets of signals: the
methanide protons give rise to the singlets with
chemical shifts 2.49 (1) and 2.62 (3) ppm. The signals
corresponding to the protons of tBu groups appear as
singlets with chemical shifts 1.41 (1) and 1.39 (3)
ppm. The o,m-CH aryl protons give rise to a
broadened singlet and a doublet at 6.09 and 7.30 ppm
for complex 1, and at 6.29 and 7.26 ppm for complex
Unsymmetric metal-ligand bonding featuring the
presence of close contact of one of the o-CH protons
with metal similar to that detected by X-ray analysis
in crystalline state becomes evident at 243 K. The
chemical shift of one of the o-CH protons becomes
1
3. The H NMR spectrum of 1 is broadened at room
temperature. In order to detect the presence of an
1
shifted to 4.72 ppm at 203 K (Figure 2). In the H
intramolecular dynamic process
a
variable
1
NMR
spectrum of
the
related
complex
temperature H NMR spectroscopic study of 1 in
toluene-d8 solution was performed in the temperature
(C6H5CHNMe2)3La the o-CH protons appear as a
o
signal with chemical shift 3.10 ppm at -78 C.[10a] For
1
interval 203-303 K. The changes appearing in the H
explanation of this phenomenon the authors[10a]
invoke violation of the aromaticity of the ligand. In
the case of 1 the upfield shift of the signal attributed
to the o-CH proton most likely is caused by the
proximity of the metal center.[13b] The chemical shift
NMR spectrum of 1 during gradual temperature
decrease are related to the signals of aromatic and tBu
protons, while the signal attributed to the methanide
protons remained intact (Figure 2). The signals
corresponding to the aromatic protons at the
4
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10.1002/adsc.202000782
Advanced Synthesis & Catalysis
of the corresponding carbon in the 13C NMR
spectrum (102 ppm) as well as the chemical shifts of
other protons of the Ph ring (6.3-7.6 ppm) indicate the
preservation of aromaticity. The averaged
“symmetric” bonding mode is restored when the
temperature rises to 313 K (see ESI, Figure S4).
Complex 3 demonstrates similar dynamic behavior
however the aromatic signals do not split even at 203
K. The signals corresponding to the protons of tBu
groups at 203 K are also strongly broadened but
decoalescence does not occur.
samples of complexes suitable for X-ray diffraction
were obtained by slow concentration of the solutions
in benzene for 4 and toluene for 5.
The single crystal X-ray diffraction studies of 4
and 5 revealed that both complexes are isostructural
and crystallize in the monoclinic P21/c space group as
solvates with one molecule of benzene (4) or toluene
(5). Asymmetric unit of 4 and 5 contains unique
molecule of complex. Molecular structures of 4 and 5
are depicted in Figure 3. The complexes adopt a
structure of a contact ion pair.[11d-e] Two benzhydryl
ligands are bound with Ln(III) centers in a fashion
similar to that in 1 and 2. The distances between
Ln(III) and CHbenzhydryl are slightly shorter compared
to the parent tris(alkyl) complexes (4: 2.570(4,
2.599(4) Å; 5: 2.517(2), 2.529(2) Å) (Table 1) due to
more electrophilic nature of the metal center. The
distances to Сipso and Cortho atoms are also slightly
shortened (4: La-Cipso 2.803(4)-2.897(4) Å, La-Cortho
2.881(4), 2.892(4) Å; 5: Nd-Cipso 2.774(2)-2.865(2) Å,
Nd-Cortho 2.843(2), 2.846(2) Å). The distortion of the
benzhydryl ligands in 4 and 5 is more pronounced
compared to the parent 1 and 2. The torsion angles
CipsoCHCipsoCortho in η4-coordinated benzhydryl
ligands are 24.3(6)-35.3(6)° in 4 and 27.4(3)-37.9(3)°
in 5. At the same time, the coordination sphere of the
Ln3+ cations in 4 and 5 is sterically more loaded
compared to complexes 1-3. The percentage of the
metal coordination sphere shielded by the ligands is
94.6(2)% in 4 and 95.1(2)% in 5.
1
Figure 2. Fragment of the H NMR spectrum of 1 in
toluene-d8 at variable temperatures.
Catalytic activity of cationic complexes bearing
nucleophilic alkyl groups at an extremely Lewis
acidic rare-earth metal center[2a-c] in a variety of
transformations of unsaturated substrates[2a-d, 3a-d, 11d,e]
4]
as well as in C-H bond activation[2i, prompted
The third benzhydryl ligand becomes covalently
bonded with the boron via methanide carbon but at
the same time it remains connected to the Ln3+ cation
via η6-coordination of one Ph ring. The Ln-CAr
permanent interest to this class of compounds. The
synthesis of cationic species derived from 1 and 2
was attempted. Complexes 1 and 2 readily react with
B(C6F5)3 in benzene solution at RT affording the
distances are 2.989(4)-3.137(4)
Å
(Ln-Arcentre
2.717(2) Å) in 4 and 2.928(2)-3.088(2) Å (Ln-Arcentre
2.647(2) Å) in 5. Two of Ln-CAr distances (4:
3.116(4), 3.137(4) Å; 5: 3.058(2), 3.088(2) Å) are
noticeably longer than others (4: 2.989(4)-3.034(4) Å;
5: 2.928(2)-2.977(2) Å). The minimal distance from
Ln atoms to the CH group associated with boron is
4.208(4) Å and 4.151(2) Å for 4 and 5 respectively.
The B-C bond lengths are 1.659(6)-1.717(6) Å (4)
and 1.659(3)-1.714(3) Å (5). The distances B-
corresponding
cationic
complexes
[(p-tBu-
C6H4)2CH]2Ln[(p-tBu-C6H4)2CHB(C6F5)3] as red (4)
and black (5) crystals in 89 and 94 % yields (Scheme
2). When [NHMe2Ph][B(C6F5)4] was used, a
quantitative formation of
1
equivalent of
diphenylmethane was observed by 1H NMR
spectroscopy, however the attempts to isolate
monocationic complex in individual state failed. The
reactions of 1 and 2 with [Ph3C][B(C6F5]4 did not CHbenzhydryl (1.717(6) (4) and 1.714(3) (5)) are slightly
longer than B-C(Ar) distances in 4 and 5 (1.659(6)-
1.684(6) Å). Thus, the complexes 4 and 5 are rather
rare examples of base-free cationic alkyl species of
large lanthanides.[19]
allow for the preparation of isolable cationic
complexes. In the case of Y complex 3 no tractable
products were obtained in the reactions with B(C6F5)3,
[Ph3C][B(C6F5]4 and [NHMe2Ph][B(C6F5)4]. Unlike
Ln[C(SiHMe2)3]3, which easily form dicationic
complexes [11d] the treatment of 1 and 2 with 2 equiv.
of B(C6F5)3 in benzene does not allow for the
1
In the H NMR spectrum of diamagnetic complex
4 recorded in toluene-d8 two sets of signals attributed
to two nonequivalent benzhydryl ligands are
presented in a 2:1 ratio of integral intensities. The
signals, corresponding to the protons of methanide
CH-La group appear as a singlet with chemical shift
synthesis
of
dicationic
species
[(p-tBu-
C6H4)2CH]Ln[(p-tBu-C6H4)2CHB(C6F5)3]2.
The
reactions afford monocationic complexes while the 3.15 ppm, while the protons of CHB(C6F5)3 fragments
give rise to a broadened singlet at 3.84 ppm. The
signals corresponding to the tBu protons appear at
1.31 and 1.15 ppm in a 2:1 ratio and are also strongly
broadened. In the aromatic region, the protons of the
benzhydryl ligand associated with boron appear as
strongly broadened singlets at 7.42 and 6.29 ppm,
second equivalent of B(C6F5)3 remains unreacted and
was isolated from the reaction mixture. Complexes 4
and 5 are highly air- and moisture-sensitive. They are
highly soluble in THF, sparingly soluble in aromatic
hydrocarbons and insoluble in hexane. Single-crystal
5
This article is protected by copyright. All rights reserved.

10.1002/adsc.202000782
Advanced Synthesis & Catalysis
while the signals corresponding to other two
benzhydryl fragments are less broadened and give
rise to a doublet at 6.82 and a singlet at 5.72 ppm. In
demonstrated a powerful potential of half-sandwich
cationic rare-earth alkyl complexes (mainly of Sc and
Y) in o-aryl C(sp2)-H and benzylic C(sp3)-H bonds
alkylation[24] and established possible pathways and
mechanisms of these reactions. However, nothing
was known about catalytic activity of cationic alkyl
species of larger rare-earth metals in olefin
hydroarylation and hydrobenzylation.
Complexes 1-5 were evaluated as precatalysts for
addition of C(sp2)-H and C(sp3)-H bonds of
alkylpyridines to olefins. Alkylations of α-picoline
and 2,6-lutidine with styrene were explored as
benchmark reactions (Table 2). The catalytic tests
were performed in neat substrates ([styrene]:[α-
picoline] = 0.85:1, [styrene]:[2,6-lutidine] = 0.85:1) at
80 oC in the presence of 2 mol % of [Ln]-precatalyst.
11
the B NMR spectrum a sole singlet at -10.7 ppm is
observed. Three signals were observed at –126.1 ppm
(6 F, o-C6F5), –163.9 ppm (3 F, p- C6F5), and –166.8
ppm (6 F, m-C6F5) in the 19F spectrum. Unfortunately,
the 13С{1H} NMR spectrum could not be recorded
due to low solubility of the complex in aromatic
solvents, while attempts to record the spectrum in
THF-d8 lead to a rapid degradation of the complex
with the formation of unidentifiable products.
1
The reason for signals broadening in H NMR
spectrum of complex 4 is most likely a dynamic
process. The variable T experiments were carried out
in the 213-303 K region. The temperature decrease
leads to a strong signal broadening, however no
splitting was observed even at 213 K.
Table 2. Addition of C(sp2)-H and C(sp3)-H bonds of α-
picoline and 2,6-lutidine to styrene catalysed by 1-5.a)
№
Ln
[B]b)
Pyridine
t,
h
Yield 10b/
c)[%]
Figure 3. Molecular structure of complexes 4 and 5. (M =
La (4), Nd (5)). Thermal ellipsoids are given at 30%
probability level. Methyl groups of tert-butyl substituents
and hydrogen atoms except bonded with methanide
carbons were omitted for clarity. Selected angles [deg].4:
C(1)-La(1)-C(22) 116.4(2), C(1)-La(1)-Arcentre 103.0(2),
C(22)-La(1)-Arcentre 138.5(2). 5: C(1)-Nd(1)-C(22)
116.15(6), C(1)-Nd(1)-Arcentre 102.64(6), C(22)-Nd(1)-
Arcentre 138.52(6).
10bb,
%
1
2
3
4
5
6
7
8
B(C6F5)3 picoline
HNB
TB
B(C6F5)3 picoline
B(C6F5)3 picoline
B(C6F5)3 lutidine
80 94
72 89
72 97
80 95
1
1
1
2
3
1
1
2
picoline
picoline
80
0
80 85
80 80
80 81
72 90
72
72
72
72
80 95
80 98
80 92
80 89
93/7
TB
lutidine
90/10
90/10
88/12
B(C6F5)3 lutidine
B(C6F5)3 lutidine
B(C6F5)3 lutidine
B(C6F5)3 picoline
—
—
—
—
—
—
9
3
Catalytic activity of complexes 1-5 in
hydroarylation and hydrobenzylation of C=C
bonds with substituted pyridines.
10
11
12
13
14
15
16
0
0
0
0
—
—
1
1
4
4
5
4
picoline
lutidine
picoline
lutidine
picoline
lutidine
Pyridine moieties are among the most important
heterocyclic units included into myriads of natural
products, drugs, functional materials and present
valuable building blocks for modern organic
synthesis.[20] Addition of aryl C(sp2)-H and benzylic
C(sp3)-H bonds of alkylpyridines across multiple C-C
bonds is the most straightforward and atom-
economical way for the synthesis of substituted
pyridines.[21] To date these catalytic transformations
were successfully performed using transition[22] and
90/10
5/95
17
d)
a)Reactions were carried out with 1 mmol of alkylpyridine
and 0.85 mmol of styrene in neat substrates, T(oC) = 80.
b)[B] = Borate, HNB = [Me2NHPh][B(C6F5)4], TB =
[Ph3C][B(C6F5)4]. c) Yields were determined by 1H NMR in
CDCl3. d)Reaction was carried out with 0.75 mmol of
lutidine and 1.6 mmol of styrene
alkali[23] metals complexes and the achievements are
25]
summarized in a series of reviews.[2d,
Hou
6
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10.1002/adsc.202000782
Advanced Synthesis & Catalysis
Similarly to the half-sandwich bis(alkyl) Y and Sc bond can be used for further functionalization. This is
complexes[24a-c] 1-3 in the absence of cationizing in contrast with the scandium-catalyzed polyaddition
agents proved to be inert in catalysis of these of dimethoxyarenes to norbornadiene leading to the
transformations even at 80 °C. However, complexes 1 formation of alternating copolymers.[27]
and 2 as a part of binary catalytic systems
Table 3. Addition of C(sp2)-H bonds of α-substituted
[Ln]/[Borate] performed high catalytic activity in
styrene hydroarylation and hydrobenzylation with α-
pyridines to various olefins catalysed by 4.a)
picoline and 2,6-lutidine. Nearly quantitative
conversions were reached in 72-80 h. The reactions
were found to be highly regioselective affording
exclusively the anti-Markovnikov addition products
for both α-picoline and 2,6-lutidine with no indication
for the formation of other regioisomers. Moreover, in
the reaction of styrene with 2,6-lutidine, where
alkylation of both methyl groups is possible, high
chemoselectivity was observed. At the initial
substrate ratio 1:1 up to 90% of the monoaddition
product was formed (Table 2, entry 6-9). When 2.2
equivalents of styrene were used the alkylation took
place at both methyl groups to give 2,6-bis(3-
phenylpropyl)pyridine 10aa in 95% yield (Table 2,
entry 17). When α-picoline was used as a substrate
only styrene hydroarylation was observed while the
Me-group remained intact. Our trials to involve the
C(sp3)-H bonds into the reaction by applying an
excess of styrene were unsuccessful. As before, only
C(sp2)-H bonds were subjected to activation, and the
excess styrene polymerized.
Surprisingly, when yttrium complex 3 was used
instead the large counterparts (La and Nd) neither
reaction of α-picoline with styrene nor polymerization
of styrene were detected. Curiously, despite the lower
reactivity of C(sp3)-H bond vs C(sp2)-H the system
[(p-tBu-C6H4)2CH]3Y/B(C6F5)3 enables benzylic
alkylation of 2,6-lutidine with styrene in 90 % yield
(Entry 9, Table 2). The nature of the borate obviously
does not affect strongly the catalytic performance of
the binary systems. Zwitterionic complexes 4 and 5
performed activities similar to those of the systems
[Ln]/[Borate], which may be explained by the
dissociation of contact ion pairs of cationic alkyl
complexes in the presence of a large excess of the
pyridine component nullifying the influence of the
counterion (Table 2, entry 14-17).
Complex 4 was selected as pre-catalyst to examine
its applicability in the reactions of other substrates.
Complex 4 proved to be highly active in the reactions
of 2-ethylpyridine and 2-phenylpyridine with styrene
a)Reactions were carried out with 1 mmol of alkylpyridine
and norbornadiene. It is noteworthy that alkylation of
and 0.85 mmol of olefin in neat substrates, T(oC) = 80.
2-phenylpyridine proceeds at the ortho- position of
Isolated yield after column chromatography. c)Reactions
the pyridine unit (no signs of alkylation of the phenyl
were carried out with 1 mmol of pyridine and 1 mmol of
moiety were observed) in contrast with late transition
isoprene.
b)
metal-catalyzed reactions.[26] In addition, the
alkylation of 2-phenylpyridine with styrene and
norbornadiene proceeds faster, in comparison with its
Styrenes bearing electron-donating groups (Me,
alkyl substituted analogues due to electron-
tBu) in para-positions of phenyl rings react
withdrawing nature of phenyl, which may accelerate
sluggishly and the target products are obtained in
the substrate metalation stage (Table 3, entry 3,6).
moderate yields (Table 3, entry 7,8). On the contrary,
Additions of C(sp2)-H bonds of 2-methyl, 2-ethyl and
the substrates with electron-withdrawing (F, Cl)
2-phenylpyridine to norbornadiene afford only the
substituents under similar conditions undergo rapid
monoaddition products even in the presence of a two-
polymerization.
fold molar excess of pyridines. The remaining double
7
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10.1002/adsc.202000782
Advanced Synthesis & Catalysis
Table 4. Addition of benzylic C(sp3)-H bonds of 2,6-
lutidine to various olefins catalysed by 4.a)
pyridine and its benzoannulated analogue quinoline
do not react with olefins under analogous conditions.
Styrenes substituted in the ortho position also do not
undergo the hydroarylation reaction.
Complex 4 also proved to be highly active in
catalysis of a challenging transformation -addition of
benzylic C(sp3)-H bonds of 2,6-lutidine to various
olefins (Table 4). The reaction of equimolar amounts
of 2,6-lutidine with styrene and norbornadiene lead to
monoaddition products in 90 and 74% yields
respectively. The reactions between 2,6-lutidine and 3
equivalents of styrene and norbornadiene allow for
the preparation of the dialkylation products in 93%
and 98% yields upon isolation (Table 4, entry 2, 4).
Para-substituted styrenes bearing either electron-
donating (Me, tBu) or electron-withdrawing (F, Cl)
substituents can not be involved in the addition
reactions; instead, they rapidly polymerize.
Interestingly, complex 4 allows for realization of
hardly feasible transformations: addition of 2,6-
lutidine to 1,1-disubstituted and internal C=C bonds.
The reactions with α-Me-styrene, cis- and trans-
o
stilbene were carried out at 100 C and afforded the
monoaddition products with high chemoselectivity in
70 and 55 % yields respectively.
Hou and co-workers has explored in detail the
mechanism of addition of aromatic and benzylic CH
bonds of substituted pyridines to olefins and dienes
catalyzed by cationic half-sandwich aminobenzyl Sc
and Y complexes.24a-c We assume that in the case of
the systems 1-3/borane and complexes 4 and 5 in
general the reaction proceeds according to a similar
mechanism. We are currently investigating the
reaction mechanism, as well as the products of the
interaction of cationic complexes with pyridine and
olefin substrates.
Conclusion
Here we report on the simple and cheap approach
which allows for the synthesis of highly thermally
stable homoleptic tris(benzhydryl) complexes of large
rare-earth metals in high yields. Bulkiness of
benzhydryl ligands and their η4-coordination mode
results in the formation of base-free homoleptic
hydrocarbyl species of large lanthanides. Complexes
1-3 demonstrated exceptional for organolanthanides
thermostability. Reactions of 1 and 2 with B(C6F5)3
afford the rare examples of base-free cationic alkyl
complexes [(p-tBu-C6H4)2CH]2Ln[(p-tBu-C6H4)2CHB
(C6F5)3]. Complexes 1-3 after treatment with
organoboranes (1:1) as well as complexes 4 and 5
perform excellent activity in catalysis of addition of
aromatic C(sp2)-H and benzylic C(sp3)-H bonds of
substituted pyridines to C=C bonds of various
substrates. Complex 4 allows for realization of hardly
feasible transformations: addition of 2,6-lutidine to
1,1-disubstituted and internal C=C bonds. The
reactions with α-Me-styrene, cis- and trans-stilbene
were carried out at 100 oC and afforded the
monoaddition products with high chemoselectivity in
a)Reactions were carried out with 1.5 mmol of 2,6-lutidine
and 0.85 mmol of olefin in neat substrates, T(oC) = 80.
b)Isolated yield after column chromatography. c)Reaction
was carried out with 1 mmol of 2,6-lutidine and 3 mmol of
olefin. d)Reaction was carried out with 1 mmol of 2,6-
lutidine and 3 mmol of olefin at 100 oC in the presence of 4
mol % 4.
Complex 4 is also applicable for addition of the
C(sp2)-H bonds of α-picoline and 2-phenylpyridine to
isoprene with exceptional selectivity for double-
insertion products 8i and 8j, even when an equimolar
amount of isoprene was used (Table 3, entry 11-12).
This fact strongly contrasts with the results obtained
with Sc[24a] and Zr[22e] complexes, where no selectivity
was observed and both double- and mono-insertion
products were formed. Unfortunately, unsubstituted
8
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10.1002/adsc.202000782
Advanced Synthesis & Catalysis
(m), 562 (s), 550 (m). Anal. Calcd for C63H78La (974.22 g
mol-1) C, 77.67; H, 8.07; La 14.26. Found C, 77.35; H,
7.84; La 14.31.
70 and 55 % yields respectively. This is the first
example
of
olefin
hydroarylation
and
hydrobenzylation catalyzed by cationic homoalkyl
rare-earth complexes.
Synthesis of [(p-tBu-C6H4)2CH]3Nd (2). The synthetic
protocol analogous to that for 1 was applied. (p-tBu-
C6H4)2CH2 (1.90 g, 6.80 mmol) and n-BuNa (0.60 g, 7.40
mmol). The reaction of [(p-tBu-C6H4)2CH]Na with NdCl3
Experimental Section
o
(0.57 g, 2.30 mmol) was carried out in toluene at 100 C.
Complex 2 was obtained as brown crystals by slow
concentration of mother liquour. The yield was 1.63 g (72
%). IR (KBr): 1597 (s), 1499(s), 1364(m), 1314 (w), 1300
(m), 1267 (s), 1182 (s), 1111 (m), 1020 (m), 825 (s), 816
(s), 702 (m), 675 (s), 559 (s). Anal. Calcd for C63H78Nd
(979.56 g mol-1) C, 77.25; H, 8.03; Nd 14.74. Found C,
76.91; H, 8.31; Nd 14.98.
General Procedures. All reactions were performed under
a dry argon or nitrogen atmosphere using standard Schlenk
techniques or under nitrogen atmosphere in a MBraun
glovebox, unless indicated. Dry, oxygen-free solvents were
used throughout. After being dried over KOH, THF was
purified by distillation from sodium/benzophenone ketyl,
hexane and toluene by distillation from sodium/potassium
alloy prior to use. Petroleum ether (PE) and ethylacetate
(EA) were purified by single distillation. Benzene-d6, THF-
d8 and toluene-d8 were heated at reflux over Na/K alloy,
vacuum-transferred, and stored over 4 Å molecular sieves
in a nitrogen-filled glovebox. [p-tBuC6H4]2CH2,[28] n-
BuNa,[29] LnCl3,[30] LnCl3(THF)3.5, and YI3(THF)3.5[31] were
obtained according to literature procedures. B(C6F5)3 was
donated by Synor Ltd. and used without additional
purification. tBuONa was purchased from Aldrich. 2-
methylpyridine, 2-ethylpyridine, 2-phenylpyridine, styrene,
Synthesis of [(p-tBu-C6H4)2CH]3Y (3). The synthetic
protocol analogous to that for 1 and 2 was applied. (p-tBu-
C6H4)2CH2 (2.00g, 7.10 mmol) and n-BuNa (0.63 g, 7.80
mmol) were used in the synthesis. The reaction of [(p-tBu-
C6H4)2CH]Na with YI3(THF)3.5 (1.68 g, 2.36 mmol) was
carried out in toluene at 60 oC within 20 min. Toluene was
removed in vacuum, the solid residue was dried thoroughly
o
in vacuum at 100 C for 1 h and was extracted twice with
toluene (210 mL). 3 was isolated as bright-orange crystals
in 75 % yield (1.42 g).1H NMR (400 MHz, toluene-d8, 293
K): δ 7.26 (d, 12H, m-CH, C6H4, 3JHH = 8.3 Hz), 6.29 (br s,
12H, o-CH, C6H4), 2.62 (s, 3 H, CH-benzhydryl), 1.39 (s,
54 H, tBu). 13C{1H} NMR (100 MHz, toluene-d8, 293 K):
δ 142.99 (s, ipso-C), 137.09 (s, ipso-C), 125.13 (s, m-CH,
C6H4), 119.53 (br.s, o-CH, C6H4), 76.54 (s, CH-
benzhydryl), 34.08 (s, C(CH3)3), 31.42 (s, CH3). IR
(KBr):1601 (s), 1495 (m), 1377 (s), 1316 (w), 1300(m),
1262 (m), 1184 (s), 1111 (m), 1020 (w), 962 (w), 916 (w),
825 (s), 808 (s), 677 (s), 630 (w), 557 (s). Anal. Calcd for
C63H78Y (924.22 g mol-1) C, 81.87; H, 8.51; Y 9.62. Found
C, 81.44; H, 8.27; Y 9.39.
p-tBu-styrene,
p-Me-styrene,
norbornadiene,
2,6-
dimethylpyridine, α-Me-styrene, cys-stilbene, isoprene
were purchased from Aldrich, dried over CaH2, vacuum-
transferred, degassed by two freeze-pump-thaw cycles and
kept in a glovebox. Silica gel column chromatography was
performed with Merck Silica Gel 60 (0.040-0.063 mm).
NMR spectra were recorded on a Bruker DPX 200 or
Bruker Avance DRX 400 spectrometers. Chemical shifts
were reported in δ units with references to the residual
solvent resonance of the deuterated solvents for proton and
carbon chemical shifts. IR spectra were recorded as Nujol
mullsor KBr plates on FSM 1201 and Bruker Vertex 70
instruments. The N, C, H elemental analyses were carried
out in the microanalytical laboratory of the IOMC by
means of a Carlo Erba Model 1106 elemental analyzer with
an accepted tolerance of 0.4 unit on carbon (C), hydrogen
(H), and nitrogen (N). Lanthanide metal analysis was
carried out by complexonometric titration.[32] A “Polaris Q
GC/MS” spectrometer was used for GS/MS analysis.
Synthesis of [(p-tBu-C6H4)2CH]2La{(C6F5)3BCH(p-tBu-
C6H4)2} (4). 1 (2.00 g, 2.00 mmol) was dissolved in
benzene (25 mL) and B(C6F5)3 (1.00 g, 2.00 mmol) was
added with vigorous stirring at RT, the solution instantly
turned dark red. Slow concentration (28 h) of the resulting
solution afforded 4 as dark red prisms in 89% yield (2.65
1
g). H NMR (400 MHz, toluene-d8, 293 K):δ 7.42 (br s,
3
4H, m-CH, C6H4), 6.82 (d, 8H, m-CH, C6H4 , JHH = 6.9
Synthesis of [(p-tBu-C6H4)2CH]3La (1). (p-tBu-
C6H4)2CH2 (3.00 g, 10.70 mmol) was dissolved in THF (15
mL), the solution was cooled to -78 °C, and n-BuNa (0.94
g, 11.70 mmol) was added to the solution under vigorous
stirring. The resulting red solution was stirred at this
temperature for 3 h, then brought to room temperature, and
left for 5 h. THF was removed in vacuum and the red solid
residue of [(p-tBu-C6H4)2CH]Na was dried in vacuo for 1 h
at 50 oC. LaCl3(THF)3.5 was obtained by stirring a
suspension of LaCl3 (0.875 g, 3.50 mmol) in THF for 3
days at RT. [(p-tBu-C6H4)2CH]Na was suspended in
toluene (15 mL) and slowly added to the dry LaCl3(THF)3.5
powder at room temperature. The reaction mixture was
Hz), 6.29 (br s, 4H, o-CH, C6H4), 5.72 (br s, 8H, o-CH,
C6H4), 3.84 (br s, 1H, CHB), 3.15 (s, 2H, CHLa), 1.31 (br
s, 36H, tBu), 1.15 (br. s, 18H, tBu). 11B{1H} (128 MHz,
toluene-d8, 293 K) δ -10.6.19F NMR (376.5 MHz, toluene-
3
d8, 293 K): δ-126.2 (6F, s; o-C6F5), -163.9 (3F, t, J=18.6
Hz; p-C6F5), -166.8 (6F, s; m-C6F5).IR (KBr): 1642 (s),
1603 (s), 1514 (s), 1377 (m), 1364 (m), 1267 (s), 1200 (w),
1179 (m), 1155 (w), 1080 (s), 1018 (m), 974 (s), 881 (m),
823 (s), 808 (m), 793 (m), 766 (m), 760 (m), 693 (m), 673
(s), 609 (w), 600 (m), 563 (s). Anal. Calcd for
C81H78BF15La (1486.21 g mol-1) C, 65.46; H, 5.29; La 9.35.
Found C, 65.11; H, 5.02; La 9.10.
o
heated at 100 С for 1 h. The solution was centrifuged, the
Synthesis of [(p-tBu-C6H4)2CH]2Nd{(C6F5)3BCH(p-tBu-
C6H4)2} (5). 2 (1.5 g, 1.53 mmol) was dissolved in benzene
(20 mL) and B(C6F5)3 (0.78 g, 1.53 mmol) was added with
vigorous stirring at RT, the solution instantly turned black.
Slow concentration (28 h) of the resulting solution affords
cationic complex 5 in the form of black prisms in 94%
yield (2.14 g). IR (KBr): 1642 (s), 1605 (s), 1511 (s), 1264
(s), 1189 (m), 1078 (s), 1017 (s), 977 (s), 862 (m), 832 (m),
792 (s), 761 (s), 696 (s) 670 (m), 611 (w), 595 (w), 574 (s),
548 (m). Anal. Calcd for C81H78BF15Nd (1491.54 g mol-1)
C, 65.23; H, 5.27; Nd 9.67. Found C, 65.05; H, 5.00; Nd
9.80.
precipitate of NaCl was separated, extracted with toluene
(10 mL). The toluene extracts were combined, and slow
concentration of the mother liqueur afforded 1 as bright-
yellow crystals in 86 % yield (3.00 g). 1H NMR (400 MHz,
C6D6, 293 K): δ 7.30 (d, 12H, m-CH, C6H4, 3JHH = 8.0 Hz),
6.09 (br. s, 12H, o-CH, C6H4), 2.49 (s, 3H, CH-
benzhydryl), 1.41 (s, 54H, tBu). 13C{1H} NMR (100 MHz,
C6D6, 293 K): δ 142.98 (br. s, ipso-C), 136.52 (s, ipso-C),
125.28 (s, m-CH, C6H4), 118. 84 (br s, o-CH, C6H4), 84.87
1
(s, CH-benzhydryl), 34.11 (s, C(CH3)3), 31.60 (s, CH3). H
NMR (400 MHz, toluene-d8, 203 K): δ 7.55 (d, 3H, m-CH,
3
3
C6H4, JHH = 7.2 Hz), 7.32 (d, 3H, m-CH, C6H4, JHH = 7.4
Hz), 7.22 (d, 6H, m-CH, C6H4, 3JHH = 8.0 Hz), 6.75 (d, 3H,
o-CH, C6H4, 3JHH = 9.0 Hz), 6.43 (d, 6H, o-CH, C6H4, 3JHH
= 5.8 Hz), 4.72 (d, 3H, o-CH, C6H4,3JHH = 6.7 Hz), 2.42 (s,
3H, CH-benzhydryl), 1.57 (s, 27H, tBu), 1.40 (s, 27H,
tBu). IR (KBr): 1595 (s), 1501 (s), 1304 (m), 1264 (s),
1182 (s), 1109 (s), 1020 (m), 931 (w), 822 (s), 700 (s), 667
A typical procedure for catalytic alkylation of
pyridines. In a typical reaction with neat substrates the
pre-catalyst, complex 4 (20 mg, 0.02 mmol) was dissolved
in alkylpyridine (1 mmol) in Schlenk tube, and left at room
temperature for 1 h. After this, olefin (0.85 mmol) was
9
This article is protected by copyright. All rights reserved.

10.1002/adsc.202000782
Advanced Synthesis & Catalysis
added using microsyringes in the glovebox. The Schlenk
tube was taken out of the glovebox, evacuated and sealed.
The mixture was heated at 80 °C in an oil bath for the
desired reaction time. Then the mixture was cooled to
room temperature and purified directly by silica gel
column chromatography (PE/EA=10/1) to afford an
alkylation product. Spectroscopic data are consistent to
that reported in the literature for known products [24a, c]
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X-ray crystallography. The X-ray data for 1-5 were
collected with Bruker Smart Apex (1), Bruker D8 Quest (3)
and Rigaku OD Xcalibur (2, 4, 5) diffractometers (MoKα-
radiation, ω-scans technique, λꢀ=ꢀ0.71073ꢀÅ, T = 100 K)
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and were refined by full-matrix least squares on F2 for all
data using SHELX[35]. SADABS[36] and scaling algorithms
implemented in CrysAlisPro were used to perform
absorption corrections. All non-hydrogen atoms and
hydrogen atoms of methanide carbons and ortho-carbon
atoms coordinated to metal cations 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).
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The crystallographic data and structures refinement
details are given in Table S1. CCDC-2011373 (1),
2011374(2), 2011375 (3), 2011376 (4) and 2011377 (5)
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
The Russian Foundation for Basic Research (Project No. 18-33-
20165) is acknowledged for the financial support of this work.
The X-ray study of 1-5 has been carried out in the framework of
the Russian state assignment using the equipment of The
Analytical Center of IOMC RAS.
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FULL PAPER
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13
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