Bis(alkyl) scandium and yttrium complexes coordinated by an amidopyridinate ligand: Synthesis, characterization and catalytic performance in isoprene polymerization, hydroelementation and carbon dioxide hydrosilylation

Article abstract of DOI:10.1039/c9dt04338a

New neutral bis(alkyl) Sc and Y complexes [N,N^py,N^-]Ln(CH₂SiMe₃)₂(THF)_n [n = 0, Ln = Sc (1_Sc), Y (1_Y); n = 1, Ln = Y (1_Y^THF)] stabilized by a tridentate monoanionic amidopyridinate ligand were straightforwardly prepared by alkane elimination, upon mixing ligand [N,N^py,N^-]H and metal precursor Ln(CH₂SiMe₃)₃(THF)₂ in toluene at 0 °C. Depending on the work-up conditions, yttrium bis(alkyl)s were isolated as either a pentacoordinate Lewis base free complex [N,N^py,N^-]Y(CH₂SiMe₃)₂ (1_Y) or as a hexacoordinate THF adduct [N,N^py,N^-]Y(CH₂SiMe₃)₂THF (1_Y^THF). For the smaller Sc ion the only solvent-free complex [N,N^py,N^-]Y(CH₂SiMe₃)₂ (1_Sc) was isolated as a pentacoordinate species irrespective of the reaction/work-up/crystallization conditions applied. Complexes 1_Ln (Ln = Y, Sc) and 1_Y^THF were scrutinized as pre-catalysts in ternary catalytic systems Ln/borate/AlⁱBu₃ (borate = [HNMe₂Ph][B(C₆F₅)₄] or [Ph₃C][B(C₆F₅)₄]), applied to isoprene (IP) polymerization, providing moderate activity albeit high selectivity with predominant formation of 1,4-cis polyisoprene (up to 99%). The same complexes proved to be effcient catalysts also for the intermolecular hydrolelementation of styrene with various EH sustrates (pyrrolidine, morpholine, Ph₂PH, PhPH₂, PhSH) affording linear anti-Markovnikov addition products exclusively. After a preliminary activation by B(C₆F₅)₃, selected bis(alkyl) complexes from this series have been finally used as valuable pre-catalysts for the CO₂ hydrosylilation to CH₄ in the presence of organosilanes as reducing agents (PhMe₂SiH, PhSiH₃, Et₂MeSiH).

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Bis(alkyl) scandium and yttrium complexes
coordinated by an amidopyridinate ligand:
synthesis, characterization and catalytic
performance in isoprene polymerization,
hydroelementation and carbon dioxide
hydrosilylation†
Cite this: DOI: 10.1039/c9dt04338a
c
G. A. Gurina, a A. A. Kissel,a,b D. M. Lyubov, a L. Luconi, c A. Rossin,
G. Tuci, c A. V. Cherkasov, a K. A. Lyssenko,a A. S. Shavyrin,a A. M. Ob’edkov,a
a,b
G. Giambastiani
*
c,d,e and A. A. Trifonov
*
New neutral bis(alkyl) Sc and Y complexes [N,Npy,N−]Ln(CH2SiMe3)2(THF)n [n = 0, Ln = Sc (1Sc), Y (1Y); n =
1, Ln = Y (1YTHF)] stabilized by a tridentate monoanionic amidopyridinate ligand were straightforwardly
prepared by alkane elimination, upon mixing ligand [N,Npy,N−]H and metal precursor Ln(CH2SiMe3)3(THF)2
in toluene at 0 °C. Depending on the work-up conditions, yttrium bis(alkyl)s were isolated as either a pen-
tacoordinate Lewis base free complex [N,Npy,N−]Y(CH2SiMe3)2 (1Y) or as a hexacoordinate THF adduct
[N,Npy,N−]Y(CH2SiMe3)2THF (1YTHF). For the smaller Sc ion the only solvent-free complex [N,Npy,N−]Y
(CH2SiMe3)2 (1Sc) was isolated as a pentacoordinate species irrespective of the reaction/work-up/crystalli-
THF
zation conditions applied. Complexes 1Ln (Ln = Y, Sc) and 1Y
were scrutinized as pre-catalysts in
ternary catalytic systems Ln/borate/AliBu3 (borate = [HNMe2Ph][B(C6F5)4] or [Ph3C][B(C6F5)4]), applied to
isoprene (IP) polymerization, providing moderate activity albeit high selectivity with predominant for-
mation of 1,4-cis polyisoprene (up to 99%). The same complexes proved to be effcient catalysts also for
the intermolecular hydrolelementation of styrene with various EH sustrates (pyrrolidine, morpholine,
Ph2PH, PhPH2, PhSH) affording linear anti-Markovnikov addition products exclusively. After a preliminary
activation by B(C6F5)3, selected bis(alkyl) complexes from this series have been finally used as valuable
pre-catalysts for the CO2 hydrosylilation to CH4 in the presence of organosilanes as reducing agents
(PhMe2SiH, PhSiH3, Et2MeSiH).
Received 8th November 2019,
Accepted 3rd December 2019
DOI: 10.1039/c9dt04338a
rsc.li/dalton
reactivity1–9 which enables hardly implementable transform-
ations such as activation of generally inert sp3- and sp2-hybri-
Introduction
Rare-earth bis(alkyl) complexes have received a great deal of dized C–H bonds of hydrocarbons.10–14 Extensive research
attention in the last decades because of their unique efforts have revealed the great potentiality of rare-earth metal
alkyl derivatives as catalysts (or pre-catalysts) for a variety of
hydroelementation reactions of multiple C–C bonds (hydro-
reaction;15–21
intra-
and
inter-molecular
aInstitute of Organometallic Chemistry of Russian Academy of Sciences,
Tropinina str. 49, GSP-445, 603950 Nizhny Novgorod, Russia. E-mail: trif@iomc.ras.ru
bInstitute of Organoelement Compounds of Russian Academy of Sciences,
Vavilova str. 28, 119334 Moscow, Russia
cInstitute of Chemistry of OrganoMetallic Compounds, ICCOM-CNR and Consorzio
INSTM, Via Madonna del Piano, 10-50019, Sesto F.no, Florence, Italy
dInstitute of Chemistry and Processes for Energy, Environment and Health (ICPEES),
UMR 7515 CNRS – University of Strasbourg (UdS), 25, rue Becquerel,
67087 Strasbourg Cedex 02, France. E-mail: giambastiani@unistra.fr
eKazan Federal University, 420008 Kazan, Russian Federation
silylation
hydroamination,15,22–28 hydrophosphination;29 hydrobenzyla-
tion and hydroarylation).30–35 In addition, cationic mono
(alkyl) rare-earth complexes36,37 have emerged as valuable can-
didates for promoting the catalytic homo- and co-polymeriz-
ation of olefins and dienes36–63 thus providing an important
boost to the development of the field.
The relatively large ion size of rare-earth metals, their elec-
tropositivity along with the limited covalent nature of metal–
ligand bonding in these coordination compounds play a deci-
sive role in controlling both stability and chemical reactivity of
†Electronic supplementary information (ESI) available. CCDC 1956756–1956758.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c9dt04338a
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these species. Hence, the design and synthesis of tailored hydrosilylation process compared to related catalysts from the
ancillary ligands suitable for coordination to rare-earth ions, state-of-the-art.
the isolation of the corresponding alkyl species and the inves-
A comprehensive overview of all catalytic issues with the
tigation of their complex structure–reactivity relationship are newly synthesized organolanthanides complexes has been
currently one of the main trends in organo-rare-earth chem- detailed afterwards.
istry. This fundamental study is important to gain insights on
the fine tuning of their reactivity as homogeneous catalysts.
The paper describes the synthesis and characterization of
Results and discussion
three neutral bis(alkyl)-organolanthanide complexes sup-
ported by a tridentate {N,N,N−} monoanionic amidopyridinate
Synthesis and characterization of bis(alkyl) complexes 1Sc, 1Y
THF
and 1Y
ligand and their high versatility in catalysis. Indeed, these
coordination compounds have been scrutinized as catalysts or
catalyst precursors in a variety of highly challenging transform-
ations. As a first trial, [N,Npy,N−]Ln(CH2SiMe3)2(THF)n [n = 0,
Ln = Sc (1Sc), Y (1Y); n = 1, Ln = Y (1YTHF)] were tested as pre-cat-
alysts for the stereospecific polymerization of 1,3-conjugated
dienes. We focused on the isoprene (IP) polymerization, one of
the most investigated and industrially relevant processes for
the preparation of polyisoprenes (PIPs) with controlled
microstructures.41,42,44,49–52,64–71 All catalytic systems showed
fairly good activity in the process with a prevalent cis-
1,4 monomer enchainment in the polymers microstructure,
irrespective to the nature of the rare-earth ion at work. With
the aim of widening the catalysts scope, the bis(alkyl) organo-
lanthanide complexes from this series have also been tested as
catalysts for the intermolecular styrene hydro-elementation
reaction in the presence of a variety of nucleophiles. Synthesis
of phosphorus-, nitrogen- and sulfur-containing organic mole-
cules from unsaturated compounds certainly covers one of the
THF
Bis(alkyl) scandium and yttrium derivatives 1Sc, 1Y and 1Y
coordinated by the tridentate κ3{N,N,N−} amidopyridinate
ligand 1 were straightforwardly synthesized through alkane
elimination from an equimolar mixture of ligand 1 and the
tris(alkyl) metal precursor of choice [Ln(CH2SiMe3)3(THF)2;
Ln = Sc, Y] (Scheme 1).
Complexes 1Y, 1YTHF and 1Sc were isolated as highly air- and
moisture-sensitive brownish-red (1Y, 1YTHF) or dark red (1Sc)
crystals in 79, 74 and 83% yields, respectively. Depending on
the hydrocarbon solvent used [toluene (i) vs. hexane (ii)],
different coordination compounds have been isolated using
Y(CH2SiMe)3(THF)2 as metal precursor. Indeed, the slow crys-
tallization from cold toluene gave the pentacoordinate
complex 1Y, while no crystals were obtained from pure cold
hexane. Crystals suitable for X-ray diffraction analysis could
only be obtained upon addition of few drops of THF
(hexane : THF = 4 : 1 ca.) as to afford the hexacoordinated THF-
adduct 1YTHF. As for the scandium complex, the only solvent-
free complex 1Sc was isolated as a pentacoordinate species irre-
spective to the applied reaction/crystallization conditions.
Indeed, the smaller scandium ion size did not show any modi-
fication of the complex coordination sphere as a function of
the crystallization solvent used (toluene vs. hexane/THF).
major
domains
of
organolanthanides
in
catalysis.
Hydroelementation (or hydrofunctionalization) consists in the
formal and metal-mediated addition of an E–H bond (E = P, N,
S) on a carbon–carbon multiple bond. It represents a highly
efficient, sustainable and environmentally friendly methodology
for the preparation of organic commodities. In this context, the
choice of a tailored catalyst allows for the control of the regio-,
chemo- and stereo-selectivity of the addition products.
Finally, to further extend the application range of these
species, selected complexes from this series have been
employed as pre-catalysts for CO2 activation and its sub-
sequent hydrosilylation to methane (CH4). Cationic early-tran-
sition-metal complexes have already been scrutinized as active
catalysts for the process in combination with a variety of
hydrosilanes. Matsuo and Kawaguchi reported firstly on the
use of ZrIV dialkyl phenoxide complexes in combination with
B(C6F5)3 as a strong Lewis acid for the tandem CO2 hydrosilyl-
ation to CH4.72 Since their seminal work, other transition
metal complexes73–75 and organolanthanides76,77 have been
exploited for the tandem transformation. In particular, we
have recently described the tandem hydrosilylation catalysis
with a new class of group-IV coordination compounds stabil-
ized by a tridentate κ3{N−,N,N−} ligand, using B(C6F5)3 as acti-
vator/co-catalyst.78 With TOF values up to twice than those
claimed for the benchmark dialkyl phenoxide ZrIV-complex,
our κ3{N−,N,N−}ZrIV species was found to rank among the
THF
Scheme 1 Synthesis of bis(alkyl) complexes 1Ln (Ln = Sc, Y) and 1Y
.
(i) Toluene, °C; (ii) hexane, 0 °C followed by hexane/THF re-
0
systems with the highest catalytic performance in the tandem crystallization.
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All isolated compounds have shown excellent stability in
dry and degassed benzene-d6 solution at ambient temperature
with no apparent decomposition per weeks. It should be
noticed that related yttrium bis(alkyl) coordination com-
pounds formerly reported by us and featured by benzothiazole
substituted amidopyridinate κ3{N,N,N−} ligands underwent
rapid ligand C–S bond cleavage upon treatment with THF, to
give compounds with original and unexpected coordination
environments.79 At odds with benzothiazole substituted κ3{N,
N,N−} ligands, no traces of new species due to the imidazole
ring-opening were observed either with 1Y or 1YTHF, even after
keeping the latter under harsh conditions for prolonged times
(benzene-d6 at 60 °C for 24 h). The higher chemical stability of
the benzoimidazole ligand is ascribed to the relatively higher
energy required for the C–N bond cleavage (72.9 kcal mol−1
,
305 kJ mol−1) compared to that required for breaking the C–S
1
bond (61.9 kcal mol−1, 259 kJ mol−1).80 The H NMR spectra
recorded for all complexes show largely superimposable
regions with well distinct set of signals (see Experimental
section for NMR details and Fig. S1, S3, and S5†). In particular,
Fig. 1 Molecular structure of 1Sc. Thermal ellipsoids are drawn at the
30% probability level. Hydrogen atoms are omitted for clarity.
the methylene protons at the two residual –CH2SiMe3 frag-
THF
ments in 1Sc and 1Y and 1Y
are diastereotopic and appear
as two doublets (1Sc δH = 0.31 and 0.65 ppm, 2JHH = 11.3 Hz; 1Y
δH = −0.10 and 0.13 ppm, 2JHH = 10.7 Hz; 1YTHF δH = −0.67 and
−0.60 ppm, 2JHH = 10.7 Hz). Carbons from the same methylene
fragments give rise to a slightly broadened singlet in 13C{1H}
NMR spectrum of 1Sc at δC = 39.1 ppm, while doublets are
1
THF
given for 1Y (δC = 34.0 ppm, JYC = 38.5 Hz) and 1Y
(δC =
1
26.7 ppm, JYC = 33.7 Hz), respectively (see Experimental
section for NMR details and Fig. S2, S4, and S6†).
Notably, the presence of a coordinated electron donating
THF
THF molecule in 1Y
causes a significant modification of
the 1H and 13C NMR chemical shifts.
Indeed, the above-mentioned methylene fragments on
THF
1Y
are significantly shifted with respect to its THF-free (1Y)
Fig. 2 Molecular structure of 1Y. Thermal ellipsoids are drawn at the
30% probability level. Hydrogen atoms are omitted for clarity.
counterpart. 2D 1H–89Y MHQC correlation spectra reveal the
same trend for the chemical shifts of 89Y nuclei in the two
coordination compounds 1Y and 1YTHF. As spectra on Fig. S7
show (see the ESI†), 89Y in 1Y
is markedly shifted to upper provided in Table S1 (see ESI†). Five-coordinated complexes
THF
field (singlet at 801 ppm) compared to its THF-free counterpart 1Sc and 1Y crystallize in monoclinic P21/c and C2/c space
1Y (singlet at 1033 ppm). Finally, trimethylsilyl groups of alkyl groups in a distorted square-pyramidal coordination geome-
ligands, pyridine-amido bridging methylene fragments and try,81 in the form of solvates with 1 and 121 molecules of
THF
N–CH2–O moieties of the N-protecting groups give rise sharp toluene, respectively. Complex 1Y
crystallizes in the triclinic
singlets in the 1H and 13C{1H} NMR spectra {[Si(CH3)3: δH
0.01 ppm and δC = 3.6 ppm for 1Sc; δH = 0.07 ppm and δC
=
=
]
P1 space group as a distorted hexacoordinated compound, sol-
vated with 12 molecule of hexane. For all complexes, the amido-
pyridinate ligand acts as tridentate κ3{N,N,N−} monoanionic
species with one covalently linked amido nitrogen and two
coordinative N-donor sites to the rare-earth metal ion. Similar
coordination environments have already been reported in the
literature for related bis(alkyl) organolanthanides79 and group-
ˉ
THF
3.7 ppm for 1Y; δH = −0.25 ppm and δC = 3.7 ppm for 1Y
[Py–CH2–N: δH = 4.92 ppm and δC = 64.9 ppm for 1Sc; δH
4.97 ppm and δC = 65.5 ppm for 1Y; δH = 5.00 ppm and δC
66.0 ppm for 1YTHF] [N–CH2–O: δH = 4.82 ppm and δC
73.1 ppm for 1Sc; δH = 4.79 ppm and δC = 72.9 ppm for 1Y; δH
=
=
=
=
5.10 ppm and δC = 72.8 ppm for 1YTHF]}. The solid-state struc- IV transition metal complexes.78
THF
tures of complexes 1Sc, 1Y and 1Y
have been obtained
The different radii of the two metal ions as well as their
through single crystal X-ray diffraction analysis and a perspec- different coordination number are found to affect the geome-
tive view of each molecule is given in Fig. 1–3. Table 1 sum- try of the metal-amidopyridinate fragment. Thus, in 1Sc the
marizes selected bond lengths and angles of all structures amidopyridinate ligand is nearly planar with a dihedral angle
while all the main crystal and structural refinement data are between the benzoimidazolyl and pyridyl planes of 8.0(2)°. The
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However, the values fall in the typical range given for
related five- and six-coordinate yttrium bis(alkyl) species con-
taining tridentate κ3{N,N,N−} monoanionic amidopyridinate
ligands.79
Study of the catalytic performance of complexes 1Sc, 1Y and
THF
1Y
Isoprene polymerization tests. The stereospecific diene
polymerization is an area of catalysis where organolanthanides
have largely been employed with success, demonstrating all
their inherent potentiality. On this regard, the bis(alkyl) com-
THF
pounds 1Sc, 1Y and 1Y
have been initially scrutinized 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 on the control of
the ultimate catalyst performance as well as on the microstruc-
ture of the resulting polymers. As Table 2 shows, neutral bis
(alkyl) complexes 1Sc, 1Y and 1YTHF as well as their binary mix-
Fig. 3 Molecular structure of 1YTHF. Thermal ellipsoids are drawn at the
30% probability level. Hydrogen atoms and THF molecule (except for
the coordinating O(2) atom are omitted for clarity.
tures 1Ln/borate [borate
=
[Ph3C][B(C6F5)4] (TB) or
[PhNHMe2][B(C6F5)4] (HNB)] or 1Ln/AliBu3 did not show any
appreciable activity in the process even at temperature higher
than ambient (Table 2, entries 1–3). On the other hand,
ternary mixtures 1Ln/borate/AliBu3 (1 : 1 : 10 molar ratio) sud-
denly trigger the isoprene polymerization with fairly good cata-
lytic activity and selectivity depending from the catalyst/activa-
tor system used (vide infra). In the case of 1Sc, its catalytic per-
formance was found to be independent from the choice of the
borate co-reagent in the ternary mixture (TB vs. HNB) with an
almost complete isoprene conversion (1000 eq. vs. cat.) after
6 h on run (Table 2, entries 4–7). At odds with 1Sc, the yttrium
counterpart 1Y showed a marked dependence of its catalytic
performance from the nature of activator used in the tertiary
mixture. Indeed, when HNB was used as activator a marked
slowdown of the catalyst’ performance was observed with a
monomer conversion close to quantitative (96%) only after 18
reaction hours (Table 2, entry 8). This result is in clear-cut con-
trast with the faster and quantitative monomer conversion
achieved with the 1Y/TB/AliBu3 tertiary system at work (Table 2,
entry 9). Indeed, the latter ranks among the most performing
complexes of this series reported so far in the literature and
applied to IP polymerization. The worse performance of the
tertiary 1Y/HNB/AliBu3 system is attributed to the evolution of
the nucleophilic N,N-dimethyl aniline side-product whose sub-
sequent and detrimental competition with isoprene for the
coordination to the electrophilic metal ion offers a reasonable
explanation to the observed reaction slowdown.87,88 Notably,
such a borate effect on the catalyst’s performance was found to
Table 1 Selected bond distances (Å) and angles (°) for complexes 1Sc
,
THF
1
Y and 1Y
THF
1Y ·12C6H14
1Sc·MeC6H5
1Y·112MeC6H5
Ln–C(29)
Ln–C(33)
Ln–N(1)
Ln–N(2)
Ln–N(3)
Ln–O(1)
N(1)–C(1)
C(1)–C(2)
N(2)–C(2)
N(2)–C(6)
C(6)–C(7)
N(3)–C(7)
2.250(3)
2.226(3)
2.081(2)
2.284(2)
2.303(2)
—
2.396(3)
2.424(3)
2.240(2)
2.452(2)
2.456(2)
—
1.447(4)
1.506(4)
1.335(4)
1.363(4)
1.477(4)
1.329(4)
1.398(4)
68.18(8)
65.72(8)
106.74(2)
108.9(2)
111.7(2)
132.6(2)
99.9(2)
2.463(2)
2.475(2)
2.267(2)
2.486(2)
2.485(2)
2.441(2)
1.443(3)
1.495(3)
1.334(3)
1.362(3)
1.473(3)
1.318(3)
1.388(3)
67.71(6)
64.57(6)
110.99(7)
115.22(7)
102.58(7)
109.19(7)
80.69(7)
80.45(7)
1.448(3)
1.493(3)
1.331(3)
1.362(3)
1.468(4)
1.328(3)
1.390(3)
72.79(8)
68.94(7)
105.57(9)
110.35(9)
132.46(9)
108.77(9)
93.47(9)
90.90(9)
N(3)–C(8)
N(1)–Ln(1)–N(2)
N(2)–Ln(1)–N(3)
N(1)–Ln(1)–C(29)
N(1)–Ln(1)–C(33)
N(2)–Ln(1)–C(29)
N(2)–Ln(1)–C(33)
N(3)–Ln(1)–C(29)
N(3)–Ln(1)–C(33)
94.5(2)
ScIII ion deviates of only 0.3 Å from the plane intercepted by
the {N,N,N−} tridentate ligand. The bigger metal ion size (YIII
vs. ScIII) increases the dihedral angle between the benzoimida-
zolyl and pyridyl planes, with values up to 18.6(2)° and 13.5(2)°
for 1Y and 1YTHF, respectively.
The Ln–C (2.226(3) and 2.250(3) Å) and Ln–N (Sc–Namido
2.081(2); Sc–Npy 2.284(2), Sc–Nimidazol 2.303(2) Å) distances in
1Sc proved to be in a good agreement with the distances
measured in the related Sc bis(alkyl) complexes with various
κ3{N,N,N} tridentate ligands.52,70,82–86 As expected, in the six-co-
ordinated 1YTHF complex, Y–C (2.475(2) and 2.463(2) Å) and Y–N
(Y–Namido 2.267(2), Y–Npy 2.486(2), Y–Nimidazol 2.485(2) Å) bond
distances are slightly longer compared to those measured for
the pentacoordinate 1Y (Y–C 2.424(3) and 2.396(3) Å, Y–Namido
2.240(2), Y–Npy 2.452(2), Y–Nimidazol 2.456(2) Å).
be less pronounced in the case of the THF-containing species
THF
1Y
(Table 2, entries 10–13). Indeed, a quantitative isoprene
conversion was achieved with the 1YTHF/borate/AliBu3 tertiary
system after 6 and 7 hours with TB and HNB as activator,
respectively (Table 2, entries 11 and 13). If a more sterically
THF
crowded metal coordination sphere (1Y
vs. 1Y) results into
an appreciable drop of the catalyst turn-over-frequency (TOF)
(Table 2, entries 9 vs. 12), the presence of a THF molecule co-
ordinated to the metal ion partially prevents the competitive/
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Table 2 Isoprene polymerization data and polymer characterizationa
Microstructurec (%)
Activ./AliBu3 (eq.)
t [h]
Yieldb [%]
TOF
trans-1,4
cis-1,4
3,4-Motif
Mnd [10−4
]
Mw/Mn
d
Entry
Cat.
1e
2e
3e
4
5
6
7
8
9
10
11
12
13
1Ln
1Ln
1Ln
1Sc
1Sc
1Sc
1Sc
1Y
1YTHF
1YTHF
1YTHF
1YTHF
1Y
—/—
TB or HNB/—
—/(10)
HNB/(10)
HNB/(10)
TB/(10)
TB/(10)
HNB/(10)
TB/(10)
HNB/(10)
HNB/(10)
TB/(10)
6
6
6
5
6
5
6
18
2
6
0
0
0
89
>99
92
>99
96
92
94
>99
92
—
—
—
178.0
—
184.0
—
53.3
460.0
156.7
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
n.d.
24.8
n.d.
12.1
9.8
—
—
—
—
—
—
n.d.
75.2
n.d.
87.9
90.2
92.4
n.d.
75.9
n.d.
98.0
n.d.
6.1
n.d.
5.2
9.8
11.1
n.d.
5.2
n.d.
11.3
n.d.
1.16
n.d.
1.17
1.97
2.13
n.d.
2.14
n.d.
2.81
7.6
n.d.
24.1
n.d.
2.0
7
5
6
184.0
—
TB/(10)
>99
a Polymerization conditions: Temp = rt (20–22 °C); toluene (3.5 mL); 10 mmol of IP [IP]; 10 μmol of catalyst [cat.] (1Ln); [cat.] : [IP] = 1 : 1000; activa-
tors: 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{1H} NMR spectroscopy in CDCl3 at rt. d Determined by GPC in THF at 40 °C against a polystyrene standard.
e Polymerization runs performed at either rt (20–22 °C) or 50 °C.
poisoning effect raising from the nucleophilic N,N-dimethyl probe molecule to be used in combination with amines, phos-
aniline by-product (Table 2, entries 8 vs. 11). As for the compo- phines and thiols. Organolanthanides are known to catalyse
sition of produced polyisoprenes (PIPs), 1Sc provides samples these efficient and atom-saving processes for the production of
featured by narrow molecular weight distribution (Mw/Mn) heteroatom-containing compounds through the formal
regardless the nature of the cationizing agent used in the addition of an E–H bond (E = N, P, S) to multiple C–C bonds.29
mixture (Table 2, entries 5 and 7). On the other hand, both The catalytic tests on intermolecular styrene hydroelementa-
yttrium systems gave polymers with relatively broader mole- tions were run under solvent-free conditions, using neat sub-
cular weight distribution (Mw/Mn = 1.97–2.81). In terms of strate mixtures in the presence of 2 mol% of each bis(alkyl)
polymer microstructures, all TB and HNB activated complexes pre-catalysts at 70 °C ([styrene]/[E–H]/[Ln] = 50/50/1). As a pre-
from this series display similar microstructures, prevalently liminary screening, each catalytic run was conventionally
1
made of 1,4-cis units and 3,4-motif as determined via H and carried out for 48 h without any optimization of the reaction
13C{1H} NMR spectroscopy (see Fig. S8–S15†). No 1,4-trans time. Scheme 2 outlines the hydroelementation processes
units were observed in all synthesized and isolated PIPs. The investigated with the 1Ln from this catalysts series while
catalytic systems based on yttrium provided 1,4-cis selectivity Table 3 lists the corresponding conversions and (whenever
as higher as 98% as a function of the yttrium precursor and applicable) process selectivity.
the activator used. 1YTHF/borate/AliBu3 have shown the highest
All bis(alkyl) pre-catalysts from the synthesized series
differences on the microstructure of the produced PIPs turned out to be suitable candidates to mediate these reactions
depending on the borate used. While TB gave a PIP with the under relatively mild conditions, showing complete regio-
1,4-cis selectivity that was among the highest given for this selectivity with the generation of the unique anti-Markovnikov
class of compounds (98%), the use of HNB as activator trans- addition product regardless of the nature of the E–H reagent
lated into a polymer with a 1,4-cis selectivity lying around 76%. chosen. As for the intermolecular hydroamination, pyrrolidine
The pentacoordinate 1Y afforded PIPs with similar contents of
1,4-cis units and irrespective to the nature of the activator used
(Table 2, entries 8 and 9). Finally, 1Sc displayed lower 1,4-cis
stereospecificity in the isolated PIPs. Indeed, a 1,4-cis content
ranged from 75.2 to 87.9% as a function of the activator used
in the ternary system (Table 2, entries 5 and 7).
Hydroelementation runs for intermolecular C–N, C–S and C–P
bond forming reactions
To widen the application range of the newly synthesized orga-
nolanthanides, all complexes from this series were tested as
pre-catalysts for the intermolecular C–N, C–S and C–P bond
Scheme 2 General scheme for the styrene hydroelementation cata-
lyzed by complexes 1Ln with a series of E–H (E = N, P, S) reagents.
forming reactions on unsaturated hydrocarbons (hydroelemen-
Reaction conditions: Neat reagents, ([styrene]/[EH]/[Ln]
= 50/50/1),
tation process).29 For these trials, styrene was selected as the 70 °C, 48 h.
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a
Table 3 Styrene hydroelementation catalyzed by complexes 1Ln
always predominant (from 78–84%) (Table 3, entries 7–9).
With both phosphines, the reactions catalysed by 1Y and 1Y
provided, after 48 h at 70 °C, quantitative styrene conversions
(Table 3, entries 8, 9 and 11, 12) whereas a slightly lower
activity was given with the 1Sc complex at work (Table 3,
entries 7 and 10).
THF
Selectivity
Entry
Cat.
E–H
Conv.b (%)
Mono-/Di-hydroelem.b
1
2
3
4
5
6
1Sc
(CH2)4NH
(CH2)4NH
(CH2)4NH
O(CH2)4NH
O(CH2)4NH
O(CH2)4NH
63
76
44
—
37
33
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
1YTHF
1Y
As a last hydroelementation trial, complexes 1Sc, 1Y and
1Sc
THF
1YTHF
1Y
were scrutinized as catalysts for the intermolecular
1Y
styrene hydrothiolation using thiophenol (PhSH) and cyclohex-
anethiol (CySH) as probe reagent molecules. As Table 3 shows,
all complexes catalyzed the PhSH-styrene hydrothiolation in
regioselective fashion (anti-Markovnikov addition) with from
excellent to quantitative yields (Table 3, entries 13–15).
Notably, no catalytic activity was observed when the same reac-
tions were carried out with the aliphatic thiol (CySH) (Table 3,
entries 16–18). Such a different behavior can be tentatively
ascribed to the absence of π–π interactions between either
styrene (or the conjugated ligand framework in 1Ln) and the
reagent. Indeed, such supramolecular interactions can be
likely invoked to justify the excellent hydrothiolation perform-
ance measured with aromatic PhSH compared to the total
7
8
9
10
11
12
1Sc
PhPH2
PhPH2
PhPH2
Ph2PH
Ph2PH
Ph2PH
95
99
99
90
99
99
78/22
84/16
81/19
n.a.
n.a.
n.a.
1YTHF
1Y
1Sc
1YTHF
1Y
13
14
15
16
17
18
1Sc
PhSH
PhSH
PhSH
CySH
CySH
CySH
95
99
99
0
0
0
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
1YTHF
1Y
1Sc
1YTHF
1Y
a Reaction conditions: Temp = 70 °C; neat reagents, [styrene]/[E–H]/
[Ln] = 50/50/1 = 0.5 mmol/0.5 mmol/10 µmol, 48 h. b Determined by
1H and 13C{1H} NMR or 31P{1H} spectroscopy in CDCl3. n.a. = not absence of reactivity in the presence of the aliphatic counter-
applicable.
parts (i.e. CySH). On this basis, it seems reasonable to postu-
late the existence of similar interactions to justify the perform-
ance of 1Ln in all other hydroelementation processes carried
and morpholine were selected as benchmark reagents for the out with aromatic reagents.
1Ln mediated addition to styrene. As Table 3 shows, complex
1Y was the most active from this series with styrene conver-
sions of 76% and 37% for the pyrrolidine and morpholine
adducts, respectively (Table 3, entries 2 and 5). Conversions
Tandem catalytic CO2 hydrosilylation to methane (CH4) with
1Sc* and 1Y*
The deoxygenative CO2 reduction to CH4 in the presence of
hydrosilanes is known to proceed through two successive
(tandem) catalytic cycles where the initial CO2 activation at the
electrophilic metal ion of the cationized catalyst is supposed to
initiate the process (Scheme 3). B(C6F5)3 is well-known to acti-
vate hydrosilanes for the carbonyl89,90 and carboxyl90 reduction
as well as for the cleavage of aryl and alkyl ethers91 but the
higher thermodynamic stability of CO2 and its subsequent
chemical inertness make mandatory the carbon dioxide pre-
activation at an electrophilic metal ion (Scheme 3, A) thus
allowing the first kinetically sluggish hydrosilylation step to
measured under identical conditions but in the presence of
THF
the six-coordinated 1Y
were affected by the more crowded
metal coordination sphere. Indeed, the presence of a THF
molecule coordinated to the metal ion was supposed to limit
the regular uptake of the substrate to the catalyst active site. As
a result, hydroamination adducts with pyrrolidine and mor-
pholine were formed in only 44% and 33% yield, respectively
(Table 3, entries 3 and 6). The 1Sc showed lower catalytic per-
formance compared to its yttrium pentacoordinate counter-
part. Indeed, it afforded 63% styrene conversion in the pyrroli-
dine adduct (Table 3, entry 1) whereas it did not show any
appreciable catalytic activity when morpholine was employed
as reagent. 1Sc was completely inactive for the intermolecular
hydroamination using morpholine as reagent thus confirming
THF
the following catalysts’ trend in the process: 1Y > 1Y
⋙ 1Sc.
All catalysts were also investigated in the hydrophosphination
reaction using phenylphosphine (PhPH2) and diphenyl-
phosphine (Ph2PH) as probe reagents for the addition to
styrene. Similarly to hydroamination reactions, all catalyzed
reactions with the two phosphines resulted into regioselective
anti-Markovnikov addition products only. However, when
PhPH2 was used as reagent the chemoselectivity (mono- vs. di-
hydrophosphination reaction) turned out to be moderate.
Indeed, with all complexes from this series the combination of
styrene with PhPH2 in equimolar amount afforded mixtures of
Scheme 3 Proposed mechanistic scheme for the tandem CO2 hydro-
silylation catalysis using a model R3SiH hydrosylane as reductant and the
secondary and tertiary phosphines with the former being Lewis acid B(C6F5)3 as catalyst and hydrosilanes activator.
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occur.72,78 A metal-silylformate intermediate (not shown in the
scheme) is supposed to undergo an additional hydrosilylation
step to give the silylacetal species (B) that formally closes the
cycle of metal-mediated transformations.92–94 Afterwards, the
borane–silane pair allows the process to be completed as a
metal-free process till CH4 production (Scheme 3).
Overall, the strong Lewis acid B(C6F5)3 acts as an activator
for the cationization of the bis(alkyl) catalyst precursor and
activates the silane in the hydrosilylation steps.72,78 The iso-
lation and quantification of siloxane by-products is conven-
tionally used to evaluate the catalyst performance.
Preliminary and qualitative catalytic hydrosilylation runs
were carried out in a J Young NMR tube where a benzene-d6
mixture of 1Y and B(C6F5)3 (1 : 1.5 eq. with PhMe2SiH; 1 : 1.1
eq. with PhSiH3) was treated with various hydrosilanes before
being pressurized with isotopically enriched 13CO2 (99 atom%
13C, 1 atm). All catalytic trials were systematically monitored by
1H, 13C{1H} and 13C NMR spectroscopy mainly with respect to
distinctive signals attributed to CO2, CH4 and possible inter-
mediates of the tandem hydrosilylation process. The B(C6F5)3
addition to a solution of 1Y let to the almost immediate for-
mation of a semisolid, not crystalline precipitate along with a
solution color change from deep violet to dark brown. If the
generation of a solid precipitate was somehow indicative of the
occurred complex cationization, all our attempts to character-
Fig. 4 1H and 13C{1H} NMR spectra (400 MHz, C6D6, 298 K) recorded at
variable time for the 13CO2 hydrosilylation reaction, using Ph(CH3)2SiH
as reductant. Conditions: r.t., 1Y* (6 µmol, 1.2 mol%); (Y/B = 1/1.5). Green
insets refer to 13C NMR spectra.
1
ize the activated complex 1Y* failed.95 Indeed, H and 13C{1H}
NMR spectra recorded on 1Y* gave only broad and undistinc-
tive signals not suitable for a complete sample characteriz-
ation. Furthermore, the activation of 1Y in more polar deute-
rated solvents resulted in the complete material decompo- 1.02 ppm whose attribution to methane and dimethylphenyl
sition with the rapid formation of intractable sticky solids.95 silylether, respectively, was unambiguously done on the basis
Finally, the addition of a silane to 1Y* did not change the solu- of literature precedents. An additional proof of evidence for
tion/suspension color or the semisolid nature of the precipi- the above given peak assignment finally come from the dis-
tate. Indeed, the H NMR spectrum of each 1Y*/silane mixture tinctive H coupled 13C NMR patterns of both signals: 13CH4
1
1
1
(recorded prior to its pressurization with 13CO2) showed all dis- (δ = −4.29 ppm, quint, JHC = 125 Hz) and [Ph(CH3)2Si]2O (δ =
tinctive and sharp signals of the unreacted silane as the back- 1.02 ppm, quart, 1JHC = 117 Hz) (green insets).
ground of a noisy sample baseline. The final 1Y*/silane
A careful analysis of 13C{1H} and 13C NMR spectra recorded
mixture pressurization step with 13CO2 (1 atm) was found to at different reaction times have also shown the appearance
1
trigger almost immediately the hydrosilylation process. When of a new signal at δ = 84.9 ppm (t, JCH = 162.0 Hz, 13CH2)
PhMe2SiH was selected as reducing agent, 1Y* catalysed the that was ascribed to the transient formation of the bis(silyl)
complete 13CO2 deoxygenative hydrosilylation to CH4 in about acetal (PhMe2SiO)2 13CH2 intermediate (Fig. 4B). A similar
6 h along with the stoichiometric formation of the dimethyl- reaction scheme was followed in the case of PhSiH3 as redu-
phenyl silylether [Ph(CH3)2Si]2O as the unique reaction side- cing agent. According to other literature precedents, the reac-
product. The reaction course was systematically monitored by tion kinetics was markedly affected by the choice of the
1H and 13C{1H} NMR spectroscopy till the complete 13CO2 con- hydrosilanes used. As a result, in the case of PhSiH3 an
sumption. As Fig. 4A shows, the H NMR spectra recorded at almost complete 13CO2 consumption was observed for pro-
1
different reaction times indicate a progressive disappearance longed reaction times only (>90 h). For the present issue, the
of the silane resonances along with the grow up of new reaction path was even easier to be followed by 13C{1H} NMR
high-field and distinctive signals attributed to 13CH4 (δH
=
spectroscopy as CH4 was the unique reaction product. No
1
0.16 ppm, d, JHC = 125 Hz) and dimethylphenyl silylether other appreciable silane signals were observed spectroscopi-
(δH = 0.32 ppm, s) as hydrosilylation by-product, respectively. cally. Indeed, PhSiH3 hydrosilylation was expected to give sil-
The 13CH4 formation was also followed by 13C{1H} NMR and sesquioxane polymers of general formula (PhSiO1.5 n
)
as
13C NMR spectroscopy till the complete disappearance of the unique silane by-products (Fig. S10†). All these data taken
13CO2 singlet at 124.5 ppm (Fig. 4B).
together provided evidence of the ability of the organo-
In addition, the formation of 13CH4 was double checked by lanthanides from this series to catalyze the tandem hydro-
the appearance of two sharp singlets at δ = −4.29 and silylation reaction.
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To complete the study and to provide a more accurate and when the same reaction was carried out in the presence of a
quantitative analysis of the reaction products and the catalysts borane excess (Y : B = 1 : 1.5 instead of 1 : 1.1), (PhMe2Si)2O was
turnover, 1Y and 1Sc were scrutinized as precursors for the the only silane side-product (>95 mol% of the staring A) iso-
tandem hydrosilylation in a batch reactor using various hydro- lated already after 4 h. Under these optimized conditions, cata-
silanes as reducing agents. To this aim, a Teflon-lined 20 mL lyst TOF was nearly doubled (Table 4, entries 3 vs. 1). Overall,
stainless-steel reactor, equipped with a magnetic stirrer bar, it can be inferred that a large excess of borane in the mixture
was charged with a toluene solution of the pre-catalyst under had beneficial effects on the hydrosilylation kinetics. If 1Y*
inert atmosphere, hence B(C6F5)3 and a selected silane (A, B or was formed almost immediately and quantitatively upon the
C, see Table 4) were added in sequence prior to the reactor treatment of its neutral counterpart with 1.1 eq. of B(C6F5)3 (as
pressurization with CO2 (1 atm at room temperature). witnessed by the rapid precipitation of 1Y* and disappearance
Afterwards, all crude reaction mixtures were sampled and ana- of distinctive 1H NMR signals of 1Y from the reaction mixture),
lysed via GC-MS before removing all solvents and volatiles the excess of borane was found to foster the silane activation
under vacuum. Except for reactions with PhSiH3 (B) as redu- and reduction kinetics of the last metal-free hydrosilylation
cing agent, all other dried mixtures obtained upon reaction steps mainly [from the bis(silyl)acetal intermediate (B) to
1
with hydrosilanes A and C were monitored via H NMR spec- methane via
a
methoxy–silane intermediate (C), see
troscopy as to provide the molar fraction of each silane Scheme 3]. When PhSiH3 (B) was employed as hydrosilylating
product or intermediate generated throughout the catalytic agent (1.35 eq. vs. CO2), 1Sc* showed slightly better catalytic
run. Catalysts turnover number (TON) and turnover frequency performance of its 1Y* counterpart (Table 4, entries 6 vs. 5)
(TOF) were finally determined from the weight of isolated under identical conditions (Ln : B = 1 : 1.1). Anyway, the cata-
siloxanes (or silsesquioxane polymers in the case of B as reduc- lytic outcomes recorded with B as reductant were in line with
tant) and values were expressed as Si–H bonds reacted per the more sluggish kinetics already observed in J Young NMR
mmol of catalyst (TON) per hour (TOF). Table 4, lists all main tube experiments using isotopically enriched 13CO2.
catalytic outcomes recorded in the reduction process with
Hence, catalysts’ TOFs resulted markedly lower compared
both activated organolanthanides in the presence of various to those obtained with silane A (Table 4, entries 5 vs. 1 and 6
hydrosilanes. With Ph(CH3)2SiH (A), 1Y* showed higher per- vs. 2). Finally, Et2MeSiH (C) was selected as a more sterically
formance compared to its scandium (1Sc*) counterpart with a demanding reducing agent [compared to Ph(CH3)2SiH] with
TOF value of 26 and a calculated methane yield as high as the final aim at studying the 1Ln* sensitivity to the hindrance
66% (Table 4, entries 1 vs. 2). In the case of 1Y*, we have also around the Si–H bond. As Table 4, entry 7 shows, after 40 h
observed an almost complete dimethyl–phenyl silane (4.1 eq. reaction with 1Y*, only 31 mol% of Et2MeSiH were reacted of
vs. CO2) consumption (<3% residue) after 8 h. Nevertheless, which more than 90% to give the (Et2MeSiO)2CH2 intermedi-
the reaction course was incomplete as a 66 : 34 mixture of ate. With 1Sc* the mol of Si–H bonds reacted were even lower
(PhMe2Si)2O and the intermediate (PhMe2SiO)2CH2, respect- (24 mol% after 40 h; Table 4, entry 8) although the % of
ively, was obtained after the reaction work-up. Noteworthy, (Et2MeSi)2O in the mixture (hence CH4 produced) was slightly
a
Table 4 CO2 hydrosilylation by 1Y* and 1Sc
*
Entry
1
Cat. 1Ln/B
Silaneb
A
Time (h)
8
Si-Byproducts
mmolc
TONd
207
TOFe
26
CH4 f yield (%)
1Y*
(PhMe2Si)2O
(PhMe2SiO)2CH2
(PhMe2Si)2O
(PhMe2SiO)2CH2
(PhMe2Si)2O
(PhMe2Si)2O
2.18
1.13
1.30
0.86
3.24
2.46
2.16
3.24
0.10
0.95
0.14
0.68
2.56
0.35
2.30
0.52
65.7
—
39.1
—
97.5
74.1
65.0
97.6
3.1
—
4.1
—
77.3
—
2
1Sc
*
A
8
135
17
3g
4g
5
6
7
1Y*
A
A
B
B
C
4
4
72
72
40
202
154
135
202
66
50
38
1.9
2.8
1.6
1Sc
*
1Y*
(PhSiO1.5 n
)
1Sc
*
(PhSiO1.5 n
)
1Y*
(Et2MeSi)2O
(Et2MeSiO)2CH2
(Et2MeSi)2O
(Et2MeSiO)2CH2
(Et2MeSi)2O
(Et2MeSiO)2CH2
(Et2MeSi)2O
8
1Sc
*
C
C
C
40
40
40
51
182
176
1.3
4.5
4.4
9g
10g
1Y*
1Sc
*
69.3
—
(Et2MeSiO)2CH2
a Reaction conditions: Catalyst precursor (16 µmol, 0.44 mol% per Si–H bond), B(C6F5)3 (17.6 µmol, M/B = 1/1.1, 0.48 mol% per Si–H bond), CO2
(1 atm, 295 K, 20 mL, 0.83 mmol), toluene (2.5 mL), 295 K. b Silanes: (A) PhMe2SiH (3.40 mmol); (B) PhSiH3 (1.12 mmol); (C) Et2MeSiH
(3.40 mmol). c mmol of silane side-products given as mmol of reacted Si–H bond. In case of mixtures, the relative molar fractions have been
determined from by 1H NMR spectra recorded on the crude mixture after evaporation of all solvents and volatiles and bulb-to-bulb distillation/
purification. d TON calculated on the basis of Si–H reacted per mmol of catalyst. e TOF calculated as TON h−1
silane/4)/(mmol of CO2)] × 100. g With 24 µmol of B(C6F5)3 (M/B = 1/1.5, 0.70 mol% per Si–H bond).
.
f Calculated as: [(mmol of reacted
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higher (17%) compared to the yttrium-catalyzed reaction. As in a dry-box filled with nitrogen. THF, toluene and hexane
for the case of reductant A, also with C the use of an excess of were purified by distillation from sodium/triglyme benzophe-
B(C6F5)3 had beneficial effects on the catalysts performance. none ketyl and stored over CaH2. Benzene-d6 was dried over
Indeed, when a Ln : B ratio increased from 1 : 1.1 to 1 : 1.5, sodium/benzophenone ketyl and condensed in vacuo prior to
96
methane production (% yield) grow up remarkably, irrespective use. Tris(alkyl) precursors Ln(CH2SiMe3)3(THF)2
and the
to the nature of the activated organolanthanide complex at ligand [N,Npy,N−]H (1) were prepared according to previously
work (Table 4, entries 10 vs. 8 and 9 vs. 7). Overall, more steri- published procedures. PhMe2SiH, Ph3SiH and Et2MeSiH were
cally crowded Si–H bonds translated into sluggish process purchased from Aldrich Chemical Co. Inc. and used as
rates and catalytic performance very close each other, regard- received. [Ph3C][B(C6F5)4] and [HNMe2Ph][B(C6F5)4] were
less of the nature of the metal ion employed in the process. At obtained from Synor Ltd, while tris-(pentafluorophenyl)borane
the same time, the use of a larger borane excess triggered posi- [B(C6F5)3] was obtained from Strem Chemicals Inc. and it was
tively both the rate of the metal-assisted and metal-free sublimed at 70 °C under (static) high reduced pressure prior to
reduction steps in the tandem hydrosilylation process. In spite be used in catalysis. 1H and 13C{1H} and 2D (COSY H,H;
of the general process feasibility, the best catalytic perform- HETCOR H,C) NMR spectra were recorded on a Bruker Avance
1
ance obtained with 1Ln* in the tandem CO2 hydrosilylation III-400 spectrometer (400.13 and 100.61 MHz for H and 13C,
reaction is appreciably lower than that of the benchmark respectively). Chemical shifts are reported in ppm relative to
κ3{N−,N,N−}MIV(CH2Ph)2/B(C6F5)3 (MIV = Zr, Hf) system under TMS and peaks are referenced to the chemical shifts of
the same hydrosilylation conditions and whatever the nature residual solvent resonances (1H and 13C). The C, H, N elemen-
of the hydrosilylating reagents used.78
tal analyses are conducted in the microanalytical laboratory of
IMOC. Lanthanide metal analysis was carried out by complexo-
metric titration.97
Synthesis of 1Sc. A solution of 1 (0.108 g; 0.39 mmol) in
toluene (10 mL) was added at 0 °C to a solution of Sc
Conclusions
In conclusion, a new class of bis(alkyl) Sc and Y complexes (CH2SiMe3)3(THF)2 (0.176 g; 0.39 mmol) in toluene (5 mL).
[N,Npy,N−]Ln(CH2SiMe3)2(THF)n coordinated by
tridentate The reaction mixture was stirred at 0 °C for 1 h and was
a
monoanionic amidopyridinate ligand have been synthesised and allowed to warm to room temperature, the volatiles were
completely characterized. At odds with bis(alkyl) species pre- removed in vacuum. The crude products were re-dissolved in
viously reported by some of us and containing benzothiazolyl fresh toluene (5 mL) and stored at −30 °C for 48 h till the for-
substituted amidopyridinate frameworks,79 [N,Npy,N−]Ln mation of the dark red microcrystals of 1Sc. The mother liquor
(CH2SiMe3)2(THF)n systems from this series with a N-protected was decanted from the product, the crystals were washed with
imidazolate group proved to be robust and thermally stable com- cold toluene and dried in vacuum for 10 min. Dark red crystals
1
pounds. They do not undergo intramolecular rearrangements of complex 1Sc were isolated in 83% yield (0.244 g). H NMR
through heteroaromatic ring opening paths. The organolantha- (400 MHz, C6D6, 293 K): 0.01 (s, 18H, CH2Si(CH3)3), 0.31 (d,
2
nides were finally scrutinized as catalysts or catalyst precursors in 2JHH = 11.3 Hz, 2H, CH2SiMe3), 0.65 (d, JHH = 11.3 Hz, 2H,
3
a relatively wide variety of challenging catalytic transformations. CH2SiMe3), 0.83 (t, JHH = 7.0 Hz, 3H, CH3CH2O), 1.43 (d,
3
Indeed, they have successfully been employed as either effective 3JHH = 6.9 Hz, 6H, CH(CH3)2), 1.71 (d, JHH = 6.9 Hz, 6H, CH
3
polymerization pre-catalysts for the cis-1,4 stereo-enriched polyi- (CH3)2), 3.05 (q, JHH = 7.0 Hz, 2H, CH3CH2O), 4.34 (sept,
soprene (PIP) production as well as good catalyst candidates for 3JHH = 6.9 Hz, 2H, CH(CH3)2), 4.82 (s, 2H, CH2OEt), 4.92 (s, 2H,
3
3
the anti-Markovnikov intermolecular addition of a variety of E–H CH2NAr), 6.43 (d, JHH = 8.0 Hz, 1H, CH Ar), 6.82 (t, JHH
=
containing molecules (E = N, S, P) to a model unsaturated CvC 7.9 Hz, 1H, CH Ar), 6.88 (d, 3JHH = 8.3 Hz, 1H, CH Ar), 7.09 (m,
bond substrate. Finally, selected rare-earth compounds from this 1H, CH Ar, overlaps with solvate toluene), 7.25 (t, JHH = 7.8
3
3
3
series have also been investigated as valuable catalyst precursors Hz, 1H, CH Ar), 7.36 (dd, JHH = 8.7 Hz, JHH = 6.2 Hz, 1H,
for the tandem CO2 hydrosilylation to CH4 in the presence of a CH Ar), 7.42 (m, 2H, CH Ar), 7.54 (d, 3JHH = 7.7 Hz, 1H, CH Ar),
series of organosilanes as reducing agents (PhMe2SiH, PhSiH3, 8.71 (d, JHH = 8.2 Hz, 1H, CH Ar) ppm. 13C{1H} NMR
3
Et2MeSiH) and the strong Lewis acid B(C6F5)3 as catalyst and (100 MHz, C6D6, 293 K): 3.6 (s, CH2Si(CH3)3), 14.7 (s,
silane(s)-activator. Overall, these catalytic outcomes highlight the CH3CH2O), 24.7 (s, CH(CH3)2), 27.8 (s, CH(CH3)2), 28.0 (s,
high versatility of bis(alkyl)organolanthanides in catalysis and CH(CH3)2), 39.1 (br s, ScCH2SiMe3), 65.0 (s, CH2NAr), 65.4 (s,
open new horizons for their future exploitation in processes at CH3CH2O), 73.1 (s, CH2OEt), 109.6 (s, CH Ar), 119.4 (s, CH Ar),
the heart of renewable energy technology.
121.5 (s, CH Ar), 123.5 (s, CH Ar), 124.4 (s, CH Ar), 124.7 (s,
CH Ar), 125.8 (s, CH Ar), 126.0 (s, CH Ar), 136.3 (s, C Ar), 137.9
(s, C Ar), 139.7 (s, CH Ar), 143.2 (s, C Ar), 146.8 (s, C Ar), 150.8 (s,
C Ar), 152.0 (s, C Ar), 168.8 (s, C Ar) ppm. Elemental analysis cal-
culated for C36H55N4OScSi2·(C7H8) (753.11 g mol−1): C, 68.58;
H, 8.43; N, 7.44; Sc, 5.97. Found: C 68.75, H 8.67, N 7.22, Sc 5.71.
Synthesis of 1Y. A solution of 1 (0.235 g; 0.54 mmol) in
Experimental section
General details and considerations
All air- and/or moisture-sensitive reactions were performed
under inert atmosphere using standard Schlenk-type vessels or toluene (10 mL) was added to
a
solution of
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Y(CH2SiMe3)3(THF)2 (0.265 g; 0.54 mmol) in toluene (10 mL) (d, 3JHH = 7.8 Hz, 1H, CH Ar), 8.21 (d, 3JHH = 8.0 Hz, 1H, CH Ar)
at 0 °C. The reaction mixture was stirred for 1 h and was ppm. 13C{1H} NMR (100 MHz, C6D6, 293 K): 3.9 (s, CH2Si
allowed to warm to room temperature. The volatiles were (CH3)3), 14.4 (s, CH3CH2O), 24.9 (s, CH(CH3)2), 25.3 (br s,
1
removed in vacuum and the crude products were re-dissolved β-CH2, THF), 26.7 (br d, JYC = 33.7 Hz, YCH2SiMe3), 27.2 (s,
in fresh toluene (10 mL) and stored at −20 °C for 48 h till the CH(CH3)2), 27.3 (s, CH(CH3)2), 64.9 (s, CH3CH2O), 66.0 (d,
formation of dark red crystals. The mother liquor was dec- 2JYC = 2.5 Hz, CH2NAr), 68.1 (br s, α-CH2, THF), 72.8 (s,
anted, the product was washed with cold toluene and dried in OCH2N), 109.6 (s, CH Ar), 120.6 (s, CH Ar), 123.3 (s, CH Ar),
vacuum for 10 min. Dark red crystals of complex 1Y were iso- 123.6 (s, CH Ar), 123.8 (s, CH Ar), 124.7 (s, CH Ar), 125.3 (s, CH
1
lated in 79% yield (0.337 g). H NMR (400 MHz, C6D6, 293 K): Ar), 125.4 (s, CH Ar), 136.4 (s, C Ar), 137.9 (s, CH Ar), 144.1 (s,
2
2
−0.10 (dd, JHH = 10.7 Hz, JYH = 2.3 Hz, 2H, CH2SiMe3), 0.07 C Ar), 147.2 (s, C Ar) 150.9 (s, C Ar), 151.3 (s, C Ar), 169.3 (s, C
2
(s, 18H, CH2Si(CH3)3), 0.13 (br d, JHH = 10.7 Hz, YH splitting Ar) ppm. The 2D Y–H g-HMQC NMR spectrum was set with
3
not observed, 2H, CH2SiMe3), 0.82 (t, JHH = 6.8 Hz, 3H, hsqcetgp pulse program, delay D1 = 1.5 s, cnst2 = 200, GPZ2 =
3
CH3CH2O), 1.44 (d, JHH = 6.6 Hz, 6H, CH(CH3)2), 1.68 (d, 14% (400; 19.6 MHz, 293 K, C6D6): −0.68; 800.9 (Y-CH2SiMe3),
3
3JHH = 6.6 Hz, 6H, CH(CH3)2), 3.03 (q, JHH = 6.8 Hz, 2H, −0.60; 801 (Y-CH2SiMe3), −0.25; 801 (Y-CH2Si(CH3)3), 5.00;
3
CH3CH2O), 4.28 (sept, JHH = 6.6 Hz, 2H, CH(CH3)2), 4.78 (s, 801 (Y-NCH2Pyr) ppm. Elemental analysis calculated for
3
2H, CH2OEt), 4.97 (s, 2H, CH2NAr), 6.49 (d, JHH = 7.5 Hz, 1H, C40H63N4O2Si2Y (777.03 g mol−1): C 61.83, H 8.17, N 7.21, Y
CH Ar), 6.84 (m, 2H, CH Ar), 7.16 (m, 1H, CH Ar overlaps with 11.44. Found: C 62.13, H 8.09, N 7.38, Y 11.23.
C6D6), 7.20 (t, 3JHH = 7.6 Hz, 1H, CH Ar), 7.32 (d, 3JHH = 8.1 Hz,
3
3
Polymerization of isoprene
1H, CH Ar), 7.39 (d, JHH = 7.2 Hz, 2H, CH Ar), 7.62 (d, JHH
7.3 Hz, 1H, CH Ar), 8.56 (d, 3JHH = 8.1 Hz, 1H, CH Ar) ppm. 13
=
C
All polymerization tests were conducted under a nitrogen atmo-
{1H} NMR (100 MHz, C6D6, 293 K): 3.7 (s, CH2Si(CH3)3), 14.4 sphere. In a typical procedure, 10 μmol of the selected catalyst
(s, CH3CH2O), 24.8 (s, CH(CH3)2), 27.4 (s, CH(CH3)2), 27.7 (s, precursor (1Sc, 1Y and 1YTHF) was dissolved in toluene (3 mL)
1
CH(CH3)2), 34.0 (d, JYC = 38.5 Hz, CH2SiMe3), 65.1 (s, and treated with a solution of the proper activator {10 μmol;
1
CH3CH2O), 65.5 (d, JYC = 2.5 Hz, CH2NAr), 72.9 (s, CH2OEt), [CPh3][B(C6F5)4] or [HNMe2Ph][B(C6F5)4]} in toluene (2 mL). 10
109.5 (s, CH Ar), 119.7 (s, CH Ar), 120.6 (s, CH Ar), 123.6 (s, CH equiv. of AliBu3 (0.1 mL, 100 μmol, 1.0 M in toluene) were added
Ar), 123.9 (s, CH Ar), 124.0 (s, CH Ar), 125.6 (s, CH Ar), 125.8 and the reaction mixture was stirred for 2 min; then 1 mL
(s, CH Ar), 135.8 (s, C Ar), 138.2 (s, CH Ar), 139.3 (s, C Ar), (10 mmol) of isoprene was added via syringe at room tempera-
143.2 (s, C Ar), 146.8 (s, C Ar), 149.6 (s, C Ar), 152.6 (s, C Ar), ture. The reaction mixture was stirred for 2–18 h. Afterwards,
169.4 (s, C Ar) ppm. The 2D Y–H g-HMQC NMR spectrum was polymerization was stopped by quenching the mixture with an
set with hsqcetgp pulse program, delay D1 = 1.5 s, cnst2 = 200, excess of methanol (20 mL) and dried under vacuum at ambient
GPZ2 = 14% (400; 19.6 MHz, C6D6, 293 K): −0.11; 1033 temperature to a constant weight. The polymer microstructures
(Y-CH2SiMe3), 0.06; 1033 (Y-CH2Si(CH3)3), 0.13; 1033 were determined by 1H and 13C{1H} NMR spectroscopy in CDCl3
(Y-CH2SiMe3), 4.97; 1033 (Y-NCH2Ar) ppm. Elemental analysis at r.t. GPC of polyisoprenes was performed in THF at 20 °C. The
calculated for C36H55N4OSi2Y·(C7H8) (797.06 g mol−1): C, average molecular masses (Mn) and polydispersity (Mw/Mn) of
64.80; H, 7.97; N, 7.03; Y, 11.15. Found: C 64.95, H 8.13, N the polymers were calculated with reference to a universal cali-
7.09, Y 10.93.
bration against polysterene standards.
Synthesis of 1YTHF. A solution of 1 (0.205 g; 0.46 mmol) in
General procedure for hydroelementation reactions
hexane (15 mL) was added to
a
solution of
Y(CH2SiMe3)3(THF)2 (0.230 g; 0.46 mmol) in hexane (15 mL) at In typical hydrophosphination, hydroamination or hydrothio-
THF
0 °C. The reaction mixture was stirred for 1 h, then it was lation experiments, the complexes 1Sc, 1Y and 1Y
(10 μmol)
allowed to warm to room temperature and the volatiles were were loaded in tube in the glovebox, then at first styrene
removed in vacuum. The crude products were re-dissolved in (0.5 mmol; 50 equiv.) was added at ambient temperature and
hexane/THF mixture (4/1, 10 mL) and the solution was stored then E–H substrate was added (0.5 mmol, 50 equiv.). The reac-
at −30 °C for 12 h. The mother liquor was decanted and the tion mixture was heated at 70 °C for a definite time in a pre-
crystals were washed with cold hexane and dried in vacuum heated oil bath. After the desired reaction time, CDCl3 was
THF
for 10 min. Dark red crystals of complex 1Y
were isolated in added to the reaction mixture, and the 1H and 31P{1H} (for
74% yield (0.267 g; 0.34 mmol). 1H NMR (400 MHz, C6D6, hydrophosphination) or 13C{1H} (for hydroamination and
2
2
293 K): −0.68 (dd, JHH = 10.7 Hz, JYH = 2.0 Hz, 2H, hydrothiolation) NMR spectra were recorded. Conversion was
2
2
CH2SiMe3), −0.60 (dd, JHH = 10.7 Hz, JYH = 2.8 Hz, 2H, determined by integrating the remaining substrates and the
3
CH2SiMe3), −0.25 (s, 18H, CH2Si(CH3)3), 0.90 (t, JHH = 6.9 Hz, newly formed addition product in the 1H spectra as well as the
3
3H, CH3CH2O), 1.35 (br s, 4H, β-CH2, THF), 1.47 (d, JHH = 6.8 remaining and newly formed phosphines in the 31P{1H}.
3
Hz, 6H, CH(CH3)2), 1.56 (d, JHH = 6.8 Hz, 6H, CH(CH3)2), 3.24
(q, JHH = 6.9 Hz, 2H, CH3CH2O), 3.55 (br. s, 4H, α-CH2, THF),
4.33 (sept, JHH = 6.8 Hz, 2H, CH(CH3)2), 5.00 (s, 2H, CH2NAr),
5.10 (s, 2H, CH2OEt), 6.58 (d, JHH = 7.9 Hz, 1H, CH Ar), 7.00 A 3 mL J Young NMR tube was charged under nitrogen atmo-
(m, 2H, CH Ar), 7.23 (m, 2H, CH Ar), 7.31 (m, 3H, CH Ar), 7.99 sphere with a pre-catalyst solution of 1Y (6.0 μmol, in C6D6
3
General procedure for NMR tube scale reduction of isotopically
enriched 13CO2 with hydrosilanes catalyzed by 1Y/B(C6F5)3
3
3
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0.4 mL; 1.2 mol% vs. PhMe2SiH or 1.5 mol% vs. PhSiH3). groups). The crystallographic data and structures refinement
Afterwards, a solution of B(C6F5)3 (9 μmol or 6.6 μmol) in dry details for 1Sc, 1Y and 1YTHF are given in Table S1 (ESI).† CCDC
and degassed C6D6 (0.4 mL) and the proper hydrosilane (4.08 1956756 (1Sc), 1956757 (1Y) and 1956758 (1YTHF)† contains the
eq. of PhMe2SiH vs. 13CO2; 1.35 eq. of PhSiH3 vs. 13CO2) were supplementary crystallographic data for this paper.
rapidly added in sequence. The tube underwent three succes-
sive evacuation/refilling cycles with 13CO2 and it was finally
charged with a positive 13CO2 pressure of 1 atm (ca. 124 μmol). Conflicts of interest
The reaction course was followed via 1H, 13C and 13C{1H} NMR
There are no conflicts to declare.
at variable times.
General procedure for the reduction of CO2 with hydrosilane
catalyzed by 1Sc(1Y)/B(C6F5)3
Acknowledgements
A 20 mL stainless-steel reactor, equipped with a magnetic
stirrer bar, was charged under an inert atmosphere with a
toluene solution of the precatalyst (1Sc or 1Y) in dry and
degassed toluene (1.5 mL). The reactor was sealed, then
B(C6F5)3 (1.1 or 1.5 equiv. with respect to the metal in 1 mL of
toluene) and neat hydrosilane (3.40 mmol for A and C or
1.13 mmol for B) were added by syringe in sequence. The
system was submitted immediately to successive evacuation/
refilling cycles (three cycles) with CO2 before it was charged
with a positive pressure of CO2 (1 atm, 20 mL, 0.83 mmol).
After the first addition (precatalyst), the mixture was main-
tained under stirring for 2 min before it was treated with the
hydrosilane. The final mixture was then maintained under stir-
ring at RT for the desired time. Afterwards, the reactor was
opened and its contents were transferred into a glass flask
before all volatiles were removed under reduced pressure. The
composition of each crude mixture and relative molar fractions
This work was financially supported by the Russian Science
Foundation (grant 17-73-20262). The X-ray studies of 1Sc, 1Y
THF
and 1Y
have been carried out in the framework of the
Russian state assignment using the equipment of the
Analytical Center of the G. A. Razuvaev Institute of
Organometallic Chemistry, RAS. G. G. thanks the TRAINER
project (Catalysts for Transition to Renewable Energy Future)
of the “Make our Planet Great Again” program (Ref. ANR-17-
MPGA-0017) for support. The Italian team would also like to
thank the Italian MIUR through the PRIN 2017 Project Multi-e
(20179337R7) “Multielectron transfer for the conversion of
small molecules: an enabling technology for the chemical use
of renewable energy” for financial support to this work.
Notes and references
1
of all compounds were followed by using GC-MS and H NMR
1 M. Zimmermann and R. Anwander, Chem. Rev., 2010, 110,
6194–6259.
2 N. Marques, A. Sella and J. Takats, Chem. Rev., 2002, 102,
2137–2160.
3 S. A. Cotton, Coord. Chem. Rev., 1997, 160, 93–127.
4 W. E. Piers and D. J. H. Emslie, Coord. Chem. Rev., 2002,
233–234, 131–155.
analysis. After solvent removal, all crude residues from reac-
tions with hydrosilanes A and C were distilled by using a bulb-
to-bulb distillation system (Kugelrohr) to give (R3SiO)2CH2
and/or (R3Si)2O as inseparable colorless oils that were analyzed
1
by using H NMR spectroscopy in C6D6. For the reactions with
PhSiH3 (B) solvent evaporation gave organosilicon compounds
of the general formula (PhSiO1.5 n
)
as an offwhite viscous oil
5 A. A. Trifonov, Russ. Chem. Rev., 2007, 76, 1122–1144.
6 A. A. Trifonov and D. M. Lyubov, Coord. Chem. Rev., 2017,
340, 10–61.
7 A. A. Trifonov, Coord. Chem. Rev., 2010, 254, 1327–1347.
8 M. Nishiura and Z. Hou, Nat. Chem., 2010, 2, 257–268.
9 M. Nishiura, F. Guo and Z. Hou, Acc. Chem. Res., 2015, 48,
2209–2220.
that was washed thoroughly with pentane and dried under
vacuum to constant weight. The TON and TOF were measured
experimentally from the isolated Si byproducts (siloxanes) and
expressed conventionally as Si–H bonds reacted per mmol of
catalyst (TON) per hour (TOF).
X-Ray crystallography
10 P. L. Watson and G. W. Parshall, Acc. Chem. Res., 1985, 18,
51–56.
THF
The X-ray data for 1Sc, 1Y and 1Y
were collected on Bruker
Apex II (1Sc, 1YTHF; T = 120 K) and Bruker Smart Apex (1Y; T =
100 K) diffractometers (MoKα-radiation, ω-scans technique, λ =
0.71073Å) using Smart and APEX2 98 software packages. The
structures were solved by direct methods and were refined by
full-matrix least squares on F2 for all data using SHELX.99
11 K. R. D. Johnson and P. G. Hayes, Chem. Soc. Rev., 2013,
42, 1947–1960.
12 H. Tsurugi, K. Yamamoto, H. Nagae, H. Kaneko and
K. Mashima, Dalton Trans., 2014, 43, 2331–2343.
13 P. L. Arnold, M. W. McMullon, J. Rieb and F. E. Kühn,
Angew. Chem., Int. Ed., 2015, 54, 82–100.
14 J. Oyamada, M. Nishiura and Z. Hou, Angew. Chem., Int.
Ed., 2011, 50, 10720–10723.
15 A. G. Trambitas, T. K. Panda, J. Jenter, P. W. Roesky,
C. Daniliuc, C. G. Hrib, P. G. Jones and M. Tamm, Inorg.
Chem., 2010, 49, 2435–2446.
SADABS100 was used to perform absorption corrections. All
THF
non-hydrogen atoms in 1Sc, 1Y and 1Y
were found from
Fourier syntheses of electron density and were refined aniso-
tropically. All hydrogen atoms were placed in calculated posi-
tions and were refined in the “riding” model with U(H)iso
=
1.2Ueq of their parent atoms (U(H)iso = 1.5Ueq for methyl
This journal is © The Royal Society of Chemistry 2019
Dalton Trans.

View Article Online
Paper
Dalton Transactions
16 M. Ohashi, M. Konkol, I. Del Rosal, R. Poteau, L. Maron
and J. Okuda, J. Am. Chem. Soc., 2008, 130, 6920–6921.
17 D. S. Levine, T. D. Tilley and R. A. Andersen, Chem.
Commun., 2017, 53, 11881–11884.
18 S. Ge, A. Meetsma and B. Hessen, Organometallics, 2008,
27, 3131–3135.
19 B. R. Elvidge, S. Arndt, T. P. Spaniol and J. Okuda, Dalton
Trans., 2006, 7, 890–901.
20 G. A. Molander and J. A. C. Romero, Chem. Rev., 2002,
102, 2161–2186.
21 G. Zhan, H.-L. Teng, Y. Luo, S.-J. Lou, M. Nishiura and
Z. Hou, Angew. Chem., Int. Ed., 2018, 57, 12342–12346.
22 X. Xu, Y. Chen, J. Feng, G. Zou and J. Sun,
Organometallics, 2010, 29, 549–553.
23 N. K. Hangaly, A. R. Petrov, K. A. Rufanov, K. Harms,
M. Elfferding and J. Sundermeyer, Organometallics, 2011,
30, 4544–4554.
43 K. Lv and D. Cui, Organometallics, 2010, 29, 2987–2993.
44 L. Wang, D. Cui, Z. Hou, W. Li and Y. Li, Organometallics,
2011, 30, 760–767.
45 Y. Luo, S. Fan, J. Yang, J. Fang and P. Xu, Dalton Trans.,
2011, 40, 3053–3059.
46 D. Robert, E. Abinet, T. P. Spaniol and J. Okuda, Chem. –
Eur. J., 2009, 15, 11937–11947.
47 G. Du, Y. Wei, L. Ai, Y. Chen, Q. Xu, X. Liu, S. Zhang,
Z. Hou and X. Li, Organometallics, 2011, 30, 160–170.
48 S. Li, D. Cui, D. Li and Z. Hou, Organometallics, 2009, 28,
4814–4822.
49 L. Li, C. Wu, D. Liu, S. Li and D. Cui, Organometallics,
2013, 32, 3203–3209.
50 Y. Pan, T. Xu, G.-W. Yang, K. Jin and X.-B. Lu, Inorg.
Chem., 2013, 52, 2802–2808.
51 W. Rong, D. Liu, H. Zuo, Y. Pan, Z. Jian, S. Li and D. Cui,
Organometallics, 2013, 32, 1166–1175.
24 S. Bambirra, H. Tsurugi, D. van Leusen and B. Hessen,
Dalton Trans., 2006, 1157–1161, DOI: 10.1039/B512135C.
25 T. E. Müller, K. C. Hultzsch, M. Yus, F. Foubelo and
M. Tada, Chem. Rev., 2008, 108, 3795–3892.
26 J. Hannedouche, J. Collin, A. Trifonov and E. Schulz,
J. Organomet. Chem., 2011, 696, 255–262.
27 H.-L. Teng, Y. Luo, M. Nishiura and Z. Hou, J. Am. Chem.
Soc., 2017, 139, 16506–16509.
28 H.-L. Teng, Y. Luo, B. Wang, L. Zhang, M. Nishiura and
Z. Hou, Angew. Chem., Int. Ed., 2016, 55, 15406–15410.
29 A. A. Trifonov, I. V. Basalov and A. A. Kissel, Dalton Trans.,
2016, 45, 19172–19193.
30 B.-T. Guan and Z. Hou, J. Am. Chem. Soc., 2011, 133,
18086–18089.
31 J. Oyamada and Z. Hou, Angew. Chem., Int. Ed., 2012, 51,
12828–12832.
32 B.-T. Guan, B. Wang, M. Nishiura and Z. Hou, Angew.
Chem., Int. Ed., 2013, 52, 4418–4421.
33 G. Song, W. N. O. Wylie and Z. Hou, J. Am. Chem. Soc.,
2014, 136, 12209–12212.
34 X. Shi, M. Nishiura and Z. Hou, J. Am. Chem. Soc., 2016,
138, 6147–6150.
35 Y. Luo, H.-L. Teng, M. Nishiura and Z. Hou, Angew. Chem.,
Int. Ed., 2017, 56, 9207–9210.
36 S. Arndt and J. Okuda, Adv. Synth. Catal., 2005, 347, 339–
354.
37 P. M. Zeimentz, S. Arndt, B. R. Elvidge and J. Okuda,
Chem. Rev., 2006, 106, 2404–2433.
38 S. Arndt and J. Okuda, Chem. Rev., 2002, 102, 1953–1976.
39 A. A. Trifonov, in Olefin Upgrading Catalysis by
Nitrogen-based Metal Complexes, ed. J. Campora and
G. Giambastiani, Springer, Dordrecht, 2011, vol. 34,
pp. 119–152.
52 L. Wang, D. Liu and D. Cui, Organometallics, 2012, 31,
6014–6021.
53 X. Li and Z. Hou, Coord. Chem. Rev., 2008, 252, 1842–1869.
54 M. Nishiura and Z. Hou, Nat. Chem., 2010, 2, 257.
55 M. Zimmermann, O. Nuyken and W. Obrecht, in Advances
in Polymer Science, ed. O. Nuyken, Springer-Verlag, Berlin,
Heidelberg, 2006.
56 L. S. Baugh and J. A. M. Canich, Stereoselective
Polymerization with Single-Site Catalysts, CRC Press/Taylor
& Francis, New York, 2008.
57 Z. Zhang, D. Cui, B. Wang, B. Liu and Y. Yang, in
Molecular Catalysis of Rare-Earth Elements, ed.
P. W. Roesky, Springer Berlin Heidelberg, Berlin,
Heidelberg, 2010, pp. 49–108, DOI: 10.1007/430_2010_16.
58 D. Takeuchi, in Encyclopedia Of Polymer Science and
Technology, John Wiley & Sons, 2013, DOI: 10.1002/
0471440264.pst595.
59 H. Wang, Y. Zhao, M. Nishiura, Y. Yang, G. Luo, Y. Luo
and Z. Hou, J. Am. Chem. Soc., 2019, 141, 12624–12633.
60 H. Wang, Y. Yang, M. Nishiura, Y. Higaki, A. Takahara
and Z. Hou, J. Am. Chem. Soc., 2019, 141, 3249–3257.
61 C. Wang, G. Luo, M. Nishiura, G. Song, A. Yamamoto,
Y. Luo and Z. Hou, Sci. Adv., 2017, 3, e1701011.
62 S. Li, D. Liu, Z. Wang and D. Cui, ACS Catal., 2018, 8,
6086–6093.
63 B. Liu, S. Li, M. Wang and D. Cui, Angew. Chem., Int. Ed.,
2017, 56, 4560–4564.
64 Z. Hou and Y. Wakatsuki, Coord. Chem. Rev., 2002, 231, 1–22.
65 L. Zhang, T. Suzuki, Y. Luo, M. Nishiura and Z. Hou,
Angew. Chem., Int. Ed., 2007, 46, 1909–1913.
66 W. Gao and D. Cui, J. Am. Chem. Soc., 2008, 130, 4984–4991.
67 L. Zhang, M. Nishiura, M. Yuki, Y. Luo and Z. Hou, Angew.
Chem., Int. Ed., 2008, 47, 2642–2645.
40 Z. Hou, Y. Luo and X. Li, J. Organomet. Chem., 2006, 691,
3114–3121.
68 Y. Yang, K. Lu, L. Wang, Y. Wang and D. Cui, Chem.
Commun., 2010, 46, 6150–6152.
41 M. Zimmermann, K. W. Törnroos and R. Anwander,
Angew. Chem., Int. Ed., 2008, 47, 775–778.
69 B. Wang, D. Cui and K. Lv, Macromolecules, 2008, 41,
1983–1988.
42 D. Li, S. Li, D. Cui and X. Zhang, Organometallics, 2010,
29, 2186–2193.
70 H. Liu, J. He, Z. Liu, Z. Lin, G. Du, S. Zhang and X. Li,
Macromolecules, 2013, 46, 3257–3265.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
71 C. Yao, D. Liu, P. Li, C. Wu, S. Li, B. Liu and D. Cui,
Organometallics, 2014, 33, 684–691.
85 E. Lu, J. Chu, Y. Chen, M. V. Borzov and G. Li, Chem.
Commun., 2011, 47, 743–745.
72 T. Matsuo and H. Kawaguchi, J. Am. Chem. Soc., 2006, 128,
12362–12363.
86 P. Zhang, H. Liao, H. Wang, X. Li, F. Yang and S. Zhang,
Organometallics, 2017, 36, 2446–2451.
73 S. J. Mitton and L. Turculet, Chem. – Eur. J., 2012, 18,
15258–15262.
74 Y. Jiang, O. Blacque, T. Fox and H. Berke, J. Am. Chem.
Soc., 2013, 135, 7751–7760.
75 P. Rios, A. Rodriguez and J. Ljpez-Serrano, ACS Catal.,
2016, 5715–5723.
76 A. Berkerfeld, W. E. Piers, M. Parvez, L. Castro, L. Maron
and O. Eisenstein, Chem. Sci., 2013, 4, 2152–2162.
77 F. A. LeBlanc, W. E. Piers and M. Parvez, Angew. Chem.,
Int. Ed., 2014, 53, 789–792.
87 L. Luconi, D. M. Lyubov, A. Rossin, T. A. Glukhova,
A. V. Cherkasov, G. Tuci, G. K. Fukin, A. A. Trifonov and
G. Giambastiani, Organometallics, 2014, 33, 7125–7134.
88 S. Bambirra, A. Meetsma and B. Hessen, Organometallics,
2006, 25, 3486–3495.
89 D. J. Parks, J. M. Blackwell and W. E. Piers, J. Org. Chem.,
2000, 65, 3090–3098.
90 D. J. Parks and W. E. Piers, J. Am. Chem. Soc., 1996, 118,
9440–9441.
91 V. Gevorgyan, M. Rubin, S. Benson, J.-X. Liu and
Y. Yamamoto, J. Org. Chem., 2000, 65, 6179–6186.
92 S. Bontemps, Coord. Chem. Rev., 2016, 308, 117–130.
93 F. J. Fernández-Alvarez, A. M. Aitani and L. A. Oro, Catal.
Sci. Technol., 2014, 4, 611–624.
78 L. Luconi, A. Rossin, G. Tuci, Z. Gafurov, D. M. Lyubov,
A. A. Trifonov, S. Cicchi, H. Ba, C. Pham-Huu,
D. Yakhvarov and G. Giambastiani, ChemCatChem, 2019,
11, 495–510.
79 D. M. Lyubov, L. Luconi, A. Rossin, G. Tuci,
A. V. Cherkasov, G. K. Fukin, G. Giambastiani and
A. A. Trifonov, Chem. – Eur. J., 2014, 20, 3487–3499.
80 C. Gorton and E. Eugene, in Bond Energies, ed. C. Gorton,
Tennessee, Southwestern, 2002, vol. 1.
81 A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and
G. C. Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1394–
1356.
94 M. Cokoja, C. Bruckmeier, B. Rieger, W. A. Herrmann and
F. E. Kuhn, Angew. Chem., Int. Ed., 2011, 50, 8510–8537.
THF
95 Upon treatment with B(C6H5)3, 1Y
behaved similarly.
The cationization process though was slower at the begin-
ning of the reaction, probably because of the more
crowded metal coordination sphere.
96 M. F. Lappert and R. Pearce, J. Chem. Soc., Chem.
Commun., 1973, 126–126.
82 J. Blackwell, C. Lehr, Y. Sun, W. E. Piers, S. D. Pearce-
Batchilder, M. J. Zaworotko and V. G. Young Jr.,
Can. J. Chem., 1997, 75, 702–711.
97 S. J. Lyle and M. M. Rahman, Talanta, 1963, 10, 1177–
1182.
98 Bruker-AXS, 2014.
83 G. Du, Y. Wei, W. Zhang, Y. Dong, Z. Lin, H. He, S. Zhang
and X. Li, Dalton Trans., 2013, 42, 1278–1286.
99 G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem.,
2015, 71, 3–8.
84 W. Gao, D. Cui, X. Liu, Y. Zhang and Y. Mu, 100 L. Krause, R. Herbst-Irmer, G. M. Sheldrick and D. Stalke,
Organometallics, 2008, 27, 5889–5893.
J. Appl. Crystallogr., 2015, 48, 3–10.
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Dalton Trans.