Chelate Silylene–Silyl Ligand Can Boost Rhodium-Catalyzed C?H Bond Functionalization Reactions

Article abstract of DOI:10.1002/chem.201803089

The first N-heterocyclic silylene (NHSi)–silane scaffold LSi?R?Si(H)Mes₂ (1) (L=PhC(NtBu)₂; R=1,12-xanthendiyl spacer; Mes=2,4,6-Me₃C₆H₂) was synthesized and used to form the unique rhodium(III) complex (LSi?R?SiMes₂)Rh(H)Cl 2 through its reaction with 0.5 molar equivalents of [Rh(coe)₂Cl]₂ (coe=cyclooctene). An X-ray diffraction analysis revealed that 2 has a (Si^IISi^IV)Rh(H)Cl core with three short Rh???H?C contacts with Me groups of the ligand 1, which cause a distorted pentagonal bipyramidal coordination of the Rh center. Unexpectedly, the reaction of 2 with tBuONa gives the new bis(silyl)hydridorhodium(III) complex 4. Due to the strong donor ability of the chelate Si^II–Si^IV ligand, 2 and 4 can act as highly efficient pre-catalysts in the Rh-mediated selective C?H functionalization of 2-phenylpyridines with C?C unsaturated organic substrates under mild reaction conditions.

Full text of DOI:10.1002/chem.201803089

A Journal of
Accepted Article
Title: A Chelate Silylene-Silyl Ligand Can Boost Rhodium-Catalyzed C-
H Bond Functionalizations
Authors: Matthias Driess, Zhenbo Mo, Arseni Kostenko, Yupeng Zhou,
and Shenglai Yao
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To be cited as: Chem. Eur. J. 10.1002/chem.201803089
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10.1002/chem.201803089
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COMMUNICATION
A Chelate Silylene-Silyl Ligand Can Boost Rhodium-Catalyzed C-H
Bond Functionalizations
Zhenbo Mo,+ Arseni Kostenko,+ Yu-Peng Zhou, Shenglai Yao, and Matthias Driess*
silicon-based donors prompted us to investigate whether the presence of
a silylene and silyl donor in a chelate ligand can boost metal-mediated
catalytic transformations of organic substrates. To the best of our
knowledge, an intramolecular silylene-silyl ligand remained elusive as
yet. Inspired by the ability of the 9,9-dimethylxanthene backbone which
enabled the synthesis of an intramolecular silylene borane[5] and a
versatile coordination chemistry of the xanthsil ligands developed by
Tobita et al.,[6] we attempted the realization of a silyl-functionalized
silylene ligand scaffold featuring the 9,9-dimethylxanthene backbone
(Chart 1, right).
Abstract: The first N-heterocyclic silylene (NHSi)-silane scaffold LSi-R-
Si(H)Mes2 1 (L = PhC(NtBu)2; -R- = 1,12-xanthendiyl spacer; Mes = 2,4,6-
Me3C6H2) was synthesized and used to form the unique rhodium(III) complex
(LSi-R-SiMes2)Rh(H)Cl 2 through its reaction with 0.5 molar equivalents of
[Rh(coe)2Cl]2 (coe = cyclooctene). An X-ray diffraction analysis revealed
that 2 has a (SiIISiIV)Rh(H)Cl core with three short Rh···H-C contacts with
Me groups of the ligand 1, which cause a distorted pentagonal-bipyramidal
coordination of the Rh center. Unexpectedly, the reaction of 2 with tBuONa
yields the novel bis(silyl)hydridorhodium(III) complex 4. Due to the strong
donor ability of the chelate SiII-SiIV ligand, 2 and 4 can act as highly efficient
pre-catalysts in the Rh-mediated selective C-H functionalization of 2-
phenylpyridines with C-C-unsaturated organic substrates under mild
reaction conditions. A DFT-derived mechanism for the model alkylation
reaction of 2-phenylpyridine with ethylene using the pre-catalyst 2 is
presented.
L
O
R
Si
tBu
Si
N
SiMes2
N
L
tBu
Ph
or
bi- tridentate silyl
work
this
ligands
N-heterocyclic
=
silylene-silyl ligation
L
phosphine, pyridine, quinoline,
Ligands can play a decisive role in determining the nature of the active
site of catalysts through stabilizing specific oxidation states of metal
centers, and defining the size and shape of the catalytic entity.[1] In the
wide variety of ligands, strongly electron-donating ligands are among
the favorites in the chemists’ ligand arsenal. Such ligands can facilitate
oxidative addition steps of substrates through enhanced nucleophilicity
of the metal center in homogeneous catalysis.[1] In this context, silyl
ligands are of particular interest due to their strong σ-donor ability,
which generate electron-rich metal sites and concomitantly labilize trans
substituents.[2] Thus far, monoanionic silyl ligands that feature pendant
donor groups (Chart 1, left) such as phosphine,[3b] pyridine,[3c]
and
olefin,
N-heterocyclic carbene
Chart 1. Examples of silyl-functionalized chelate ligands.
C-H bond coordination to a TM center is considered to be a central event
in TM-mediated C-H bond activation and functionalization.
[7, 8]
Important recent advances include the studies of σ-alkane complexes in
solutions by time-resolved infrared spectroscopy or in situ NMR
spectroscopy, and characterization of σ-alkane, agostic, and anagostic
complexes in the solid states by X-ray diffraction techniques.[7,9] TM
agostic and anagostic complexes have been considered as possible
candidates for catalytic C-H bond functionalization, olefin
polymerization, hydrocyclization and more.[10] However, the application
of such well-defined TM complexes as (pre)catalyst is scarce. [7]
Herein we report the synthesis and characterization of the first chelate
silylene silane LSi-R-SiHMes2 1 bearing the 9,9-dimethylxanthene
spacer and its unexpected ligation properties towards rhodium.
Oxidative addition of RhI in [RhCl(coe)]2 into the Si-H bond of 1 leads
to a pentagonal-bipyramidal RhIII site in (LSi-R-SiMes2)Rh(H)Cl 2
featuring one agostic and two anagostic interactions. Remarkably, 2
exhibits a high catalytic efficiency and selectivity in alkylation of 2-
phenylpyridine with norbornene via C-H bond activation under mild
reaction conditions. In addition, the selective alkenylation of 2-
phenylpyridine with diphenylacetylene could also be achieved. The high
activity of 2 surpasses those of previously known rhodium analogues
bearing phosphine, NHC, and bis(NHSi) ligands, respectively. DFT
calculations revealed that the NHSi-silyl ligand might be the key for the
unique performance of the Rh-mediated C-H bond functionalization.
quinoline,[3c]
olefin,[3d] and N-heterocyclic carbenes (NHCs)
moieties,[3e,f] have been developed and applied in transition-metal (TM)
mediated activation of inert bonds (i.e., H-H, N-H, C-H, N≡N) in
catalysis.[3] N-Heterocyclic silylenes (NHSis), the heavy analogues of
NHCs, represent a new type of stronger σ-donors than NHCs and
phosphines that have already been demonstrated to be effective in
homogeneous catalysis.[4] Thus, the unique electronic properties of all
[*]
Dr. Z. Mo,[+] Dr. A. Kostenko,[+] Y. P. Zhou, Dr. S. Yao, and Prof.
Dr. M. Driess
Technische Universität Berlin, Department of Chemistry:
Metalorganics and Inorganic Materials, Sekr. C2
Strasse des 17. Juni 135, 10623 Berlin, Germany
E-mail: matthias.driess@tu-berlin.de
[+]
These authors contributed equally to this work.
[**]
We are grateful to the Cluster of Excellence UniCat (EXC 314-2)
for financial support (sponsored by the Deutsche
Forschungsgemeinschaft and administered by the TU Berlin). Z.
M. and A.K. gratefully acknowledge the Alexander von Humboldt
Foundation for a postdoctoral fellowship. Y.P.Z. wishes to thank
the Berlin International Graduate School of Natural Sciences and
Engineering (BIG-NSE) for financial support.
Supporting information for this article is given via a link at the end
of the document.
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10.1002/chem.201803089
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COMMUNICATION
1
sBuLi
RT
Figure 1. Molecular structure (left) and selected distances (Å) of 2: Rh1-Si2 2.2273(7),
Rh1-Si3 2.3289(6), Rh1-Cl4 2.4060(6), Rh1-H10 1.45(3).
1) equiv.
-
-78
Et
°C
3 h
2O,
O
tBu
Cl
Si
O
Si
N
Si
HMes
tBu
1
2
equiv.
2)
N
N
Br
SiHMes2
In order to shed more light into the electronic structure and bonding
pattern of 2, quantum chemical calculations were performed. Based on
the experimentally determined structure of 2, a constrained optimization
of only the hydrogen atoms was carried out at the RI-ZORA-B3LYP-
D3/def2-TZVP level of theory. The constrainedly optimized geometry
is only 0.9 kcal mol-1 higher in energy than the fully optimized one which
is in excellent agreement with the experimentally obtained metric data
(see Supporting Information). The constrainedly optimized geometry
was used for further quantum chemical analyses.
Interestingly, the short distance of 2.634 Å between Rh1 and the mesityl
carbon C28 atom implies the presence of an agostic interaction between
Rh and the C28-H hydrogen atom. The agostic M-H-C interactions
imply relatively short M-H distances of ~1.8–2.3 Å and small M-H-C
bond angles of ~90–140°.[11] Thus, the Rh1-H14 distance of 2.018 Å and
the Rh1-C28-H14 angle of 111.32˚ (Table 1) fall in the common
geometric range of agostic M-H interactions. In fact, the ‘Quantum
Theory of Atoms in Molecules’ (QTAIM) molecular graph (Figure 1a)
displays a bond critical point (BCP) between the H14 and the Rh1 with
electron density ρ = 0.046 e Bohr-3 and the Laplacian ∇2ρ = 0.15 e Bohr-
5 (Table 1) that are typical of those detected for agostic interactions.[12]
The NBO second order perturbation analysis reveals a significant
amount of donor-acceptor interactions that are responsible for the Rh1-
H14 bonding with the major donations from σ(C-H) to σ*(Rh-Si2) (E(2)
= 9.1 kcal mol-1), from σ (Rh-H10) to σ*(C-H) to (E(2) = 4.7 kcal mol-1)
and from the σ(Rh-Si3) and σ(Rh-H10) to the extra-valence-shell
orbitals of H14 (E(2) = 7.0, 6.4) kcal mol-1.
tBu
N
1
tBu
Ph
Ph
12 h
-
-78
RT, Et
2O,
°C
toluene
RT, 1 h
1/
Cl]2
2[Rh(coe)2
Ph
tBu
C6D6
N
Norbornene
60 °C, 24 h
60%
Mes
Si
N
tBu
Si
O
H
Cl
Cl
tBu
Mes
RhIII
RhIII
1/2
O
O
Si
H
Si
N
RhIII
N
tBu
tBu
Si
Si
Mes
N
Ph
H
N
Cl
tBu
H
Ph
2
3
Scheme 1. Synthesis of the silylene-silane 1 and its reaction with [Rh(coe)Cl]2 to give
the RhIII complex 2. coe = cyclooctene.
The silylene-silane 1 is accessible from the corresponding bromosilane
precursor via its lithiation and subsequent salt metathesis reaction with
one molar equivalent of N,N′-di-tert-butyl(phenylamidinato)-
chlorosilylene. It can be isolated as a pale yellow solid in 70% yields in
hexane solutions at 0 °C. Its 29Si NMR spectrum features a signal at δ =
13.9 ppm for the silylene group and at δ = -41.1 ppm assignable to the
silyl group. The molecular structure of 1 was confirmed by a single-
crystal X-ray diffraction analysis (see Fig. S14 in SI), revealing a Si-Si
distance of 4.255(1) Å.
As mentioned above, treatment of 1 with 0.5 molar equivalent of
[Rh(coe)2Cl]2 (coe = cyclooctene) in toluene at room temperature leads
to (LSi-R-SiMes2)Rh(H)Cl 2 as orange crystals in 64% yields. The
diagnostic resonance in the 1H NMR spectrum at δ = -16.6 ppm with the
JRh-H coupling constant of 27.6 Hz indicates the formation of a RhH
Table 1. Calculated parameters of the Rh1 agostic and anagostic interactions.
H
r(Rh1-H)
Å
α(Rh-H-C)
(deg)
ρ (e Bohr-
∇2ρ (e Bohr-
3
5
)
)
1
H14
2.018
111.32
0.046
0.010
0.012
0.15
0.03
0.03
moiety. Variable temperature H NMR measurements show that the o-
H43C
H49C
2.825
2.702
129.59
136.11
CH3 (mesityl group) proton resonance signal at δ = 2.84 ppm at 298 K
splits into four peaks at 213 K, which might be due to the restricted
rotation of the mesityl groups at low temperatures. Two 29Si NMR
resonances are observed at δ = 33.3 (SiII) and 2.36 (SiIV) ppm with JRh-H
coupling constants of 110.1 and 35.8 Hz, respectively. The solid-state
structure of 2 shows a (SiIISiIV)Rh(H)Cl core with Rh-SiII and Rh-SiIV
distances of 2.2273(7) and 2.3289(6) Å, respectively. Complex 2 is
formally a 14e complex without interaction between the Rh and O.
Heating of a C6D6 solution of 2 at 60 °C in the presence of norbornene
as a hydrogen acceptor leads to the formation of the chloride-bridged
RhIII dimer 3 via intramolecular C-H bond activation.
Figure 2. (a) QTAIM molecular graph of 2 focusing on the Rh-H interactions at
B3LYP/def2-TZVP level of theory, based on constrained optimization of hydrogen
atoms of the X-ray structure of 2 at RI-ZORA-B3LYP-D3/def2-TZVP level of theory.
BCPs are shown in orange. (b) The pentagonal-bipyramidal geometry of 2. The
pentagonal plane is highlighted with blue lines.
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Furthermore, QTAIM calculations show two additional BCPs associated
with the Rh1-H43C and Rh1-H49C contacts (Figure 1a) with ρ = 0.010
e Bohr-3, ∇2ρ = 0.03 e Bohr-5 and ρ = 0.012 e Bohr-3, ∇2ρ = 0.03 e Bohr-5,
respectively. With r(Rh1-H43C) = 2.825 Å, α(Rh1-H43C-C43) =
129.59° and r(Rh1-H49C) = 2.825 Å, α(Rh1-H49C-C49) = 136.11°
(Table 1), these contacts fall in the range of anagostic interactions that
are characterized by relatively long M-H distances of ~2.3–2.9 Å and
large M–H–C bond angles of ~110–170°.[11] The NBO analysis shows
only weak donor acceptor interactions that comprise the Rh1-H43C and
Rh1-H49C contacts with total E(2) of 13.2 and 3.5 kcal mol-1,
respectively (see the full description in Supporting Information).
With its four substituents (Si3, Si4, Cl and H10), one agostic (H14) and
two anagostic (H43C, H49C) interactions, the Rh center in 2 adopts a
distorted pentagonal-bipyramidal geometry, with H10, Si3, H49C, Cl
and H43C lying in the pentagonal plane and H13, Si2 in the axial
positions (Figure 1b). The readiness of 2 to interact with C-H bonds in
agostic and anagostic manners can promote reactions that involve C-H
bond activation as discussed below.
NHSi ligands (Table 2) was compared. In fact, 2 proved to be an efficient
pre-catalyst for alkylation of 2-phenylpyridine with norbornene in the
presence of tBuONa as an additive at 60 °C, affording the corresponding
ortho-monoalkylated product in 84% yield after 24 hours (Table 1, entry
1). In sharp contrast, the analogous reactions applying Rh(PPh3)3Cl or
the combination of [Rh(coe)2Cl]2 with different ligands such as PPh3,
and IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) as pre-
catalysts furnished the desired product in much lower yields at 60 °C
(Table 1, entries 2-5).
Recently, our group reported the synthesis of the corresponding
chelating bis(NHSi)xanthene ligand, which is a strikingly efficient
ligand in nickel-catalyzed hydrogenation of olefins.[8b] However, under
similar reaction conditions, the combination of [Rh(coe)2Cl]2 with
bis(NHSi)xanthene ligand was ineffective in promoting C-H bond
alkylation (Table 1, entry 6). We assume that the higher catalytic activity
of 2 stems from the more effective donor ability of the NHSi-silyl ligand.
This strong effect of the ligand scaffold 1 in alternation of the catalytic
activity of the Rh catalyst points to the nature of the active catalytic
species in the C-H bond alkylation. High-valent late transition metals,
that are known to be highly active in catalytic functionalization by C-H
bond activation such as PdII, RhIII, IrIII and RuII typically react via an
electrophilic pathway that requires a catalyst to be rather electron-poor.16
In contrast, similar metal sites in lower oxidation state such as RhI and
IrI typically react via oxidative addition with C–H bonds, which is
facilitated through the presence of strong donor ligands that increase the
electron-density at the metal center (e.g., phosphines or NHCs).16 Thus,
the catalytic activity through the presence of the strong σ-donor NHSi-
silyl ligand 1 is a key factor to achieve the good performance of the
rhodium catalyst for the alkylation of 2-phenylpyridine and may
indicates that the active catalyst contains low-valent RhI.
Furthermore, we probed the influence of the additive (base) and solvent
on the reaction progress. Without addition of tBuONa, 2 is incapable of
promoting C-H bond alkylation. As we discuss below, the addition of a
base may facilitates the formation of the catalytically active RhI species.
The different performance of 2 in C6D6 and THF suggests the
importance of the nature of solvent in stabilizing the catalytic
intermediates. In THF, the reaction proceeds with lower yields, i.e. 25%
vs. 84% in toluene (Table 2, Entry 1 and 8). This observation is also
concurrent with the conclusion that the active catalytic species is RhI that
operates via oxidative addition into C-H bond, rather than RhIII operating
in a electrophilic pathway. Control experiments showed the addition of
mercury does not affect the reaction yield in accordance with a
homogenously catalyzed process.[17]
Encouraged by the high catalytic activity of 2 in alkylation of 2-
phenylpyridine, we examined its ability with other substituted
arylpyridines; it turned out that the corresponding monoalkylated
products are produced in good yields of 80-86% (Scheme S1). In
addition to the reactions with norbornene, selective alkenylation of 2-
phenylpyridine with diphenylacetylene could also be achieved,
affording an ortho-monoalkenylated product in 82% yields. To our
delight, a pyrazole group can also serve as a directing group to produce
monoalkenylated and monoalkylated products but in somewhat lower
yields.
Table 2. Catalytic performance of various Rh complexes in the alkylation of 2-
phenylpyridine with norbornene.[a]
cat.
5.0 mol%
N
N
5.0 mol% additive
+
solvent
60 °C
24 h
yield[b]
Entry
catalyst
solvent
additive
tBuONa
-
1
2
2
C6D6
C6D6
84
<5
Cl
Rh(PPh)3
-
-
3[c]
4
C6D6
nd
35
Cl]2/PPh3
[Rh(coe)2
[Rh(coe)2
[Rh(coe)2
D6
D6
Cl]2/IPr
Cl]2/IPr
C6
tBuONa
-
C6
C6
C6
15
nd
5
D6
D6
Cl]2/NHSi
[Rh(coe)2
6
7
-
nd
25
2
tBuONa
d8-THF
2
8
tBuONa/Hg
-
80
85
9[d]
10
C6D6
2
4
D6
C6
[a]
Reaction conditions: Rh complexes (5 mol%), 2-phenylpyridine (0.1 mmol),
[b]
and norbornene (0.2 mmol) in 0.5 mL solvent.
Yield is based on 2-
phenylpyridine determined by 1H NMR using ferrocene as internal standard. [c]
0.05 mmol [Rh(coe)2Cl]2 and 0.03 mmol PPh3 were used, nd (not detectable).
[d]
40 mmol Hg was added. IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-
ylidene), NHSi = bis(NHSi)xanthene ligand, see ref.8b.
Since the pioneering work of Murai and coworkers,[13] TM-mediated C-
H bond functionalization has become a useful method in natural product
and drug synthesis driven by the ubiquity of C-H bonds.[14] However,
most of the known systems generally need high temperature and strong
oxidants as additives.[15] The strongly electron donating NHSi-silyl
ligand scaffold present in 2 prompted us to study whether C-H bond
activation steps and subsequent functionalization could be achieved
under milder reaction conditions. Choosing 2-phenylpyridine and
norbornene as standard substrates the catalytic alkylation competency of
2 with other related rhodium complexes bearing phosphine, NHC, and
In order to shed light on the mechanism for the C-H bond
functionalization with 2, stoichiometric reactions of 2 with tBuONa were
carried out. The reaction of 2 with tBuONa in THF occurred immediately
at room temperature with the formation of the bis(silyl)HRhIII complex
4 in 65% isolated yields (Scheme 2).[19] The 1H NMR spectrum of 4 in
C6D6 displays six sets of singlets for the methyl of mesityl groups due to
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10.1002/chem.201803089
Chemistry - A European Journal
COMMUNICATION
the restricted rotation of the mesityl groups. The 29Si NMR spectrum of
4 reveals two resonance signals at δ = 9.1 and 2.9 ppm, one at lower-
field (δ = 9.1 ppm) is downfield shifted compared with that of 2. A
single-crystal X-ray diffraction analysis reveals that the central
structural motive of 4 features a distorted tetrahedral (SiIISiIV)Rh(H)N
core with Rh-SiIV distances of 2.3131(8) and 2.2273(8) Å, respectively,
(see Figure S16).
[2] a) T. D. Tilley, The Chemistry of Organic Silicon Compounds, Vol. 1
(Eds.: S. Patai, Z. Rappoport,), Wiley, New York, 1989, pp. 1415-
1477; b) J. Y. Corey, Chem. Rev. 2016, 116, 11291-11435.
[3] a) For a recent review on silyl ligands see: M. Simon, F. Breher,
Dalton Trans. 2017, 46, 7976-7997; b) For a recent review on PSiP-
complexes see: L. Turculet, PSiP Transition-metal pincer complexes:
synthesis, bond activation, and catalysis, of pincer and pincer-type
complexes, chapter 6, in Applications in Organic Synthesis and
Catalysis, (Eds. K. J. Szabó, O.F. Wendt), Wiley-VCH, Weinheim,
2014; c) For a recent review on NSiN-complexes see: F. J. Fernández-
Alvarez, R. Lalrempuia, L. A. Oro, Coord. Chem. Rev. 2017, 350, 49-
60; d) D. Ostendorf, C. Landis, H. Grützmacher, Angew. Chem. 2006,
118, 5293-5297; Angew. Chem. Int. Ed. 2006, 45, 5169-5173; e) Z.
Mo, Y. Liu, L. Deng, Angew. Chem. 2013, 125, 11045-11049; Angew.
Chem. Int. Ed. 2013, 52, 10845-10849; f) J. Sun, L. Luo, Y. Luo, L.
Deng, Angew. Chem. 2017, 129, 2764-2768; Angew. Chem. Int. Ed.
2017, 56, 2720-2724.
tBuONa
thf
RT
O
H
O
H
tBu
tBu
Mes
Mes
O
N
Si
Si
Si
Si
N
tBu
N
RhIII
RhIII
H
N
H
H
tBu
Ph
Ph
Cl
H
H
4
2
[4] a) M. Asay, C. Jones, M. Driess, Chem. Rev. 2011, 111, 354-396; b)
S. Yao, Y. Xiong, M. Driess, Organometallics 2011, 30, 1748-1767;
c) B. Blom, D. Gallego, M. Driess, Inorg. Chem. Front. 2014, 1, 134-
148; d) S. Raoufmoghaddam,Y. Zhou, Y. Wang, M. Driess J.
Organomet. Chem. 2017, 829, 2-10; d) L. Alvarez-Rodriguez, J. A.
Cabeza, P. Garcia-Álvarez, D. Polo, Coord. Chem. Rev. 2015, 300, 1-
28.
Scheme 2. Synthesis of 4 from the reaction of 2 with tBuONa..
One possible rout to complex 4 is outlined in Scheme 2, migration of
imine from silicon to rhodium could be followed by 1,2-shift of tert-
butoxide group from rhodium to silicon. Testing the catalytic
performance of the 4 revealed that it has very similar catalytic activity
to that of 2 in the reaction of 2-phenylpyridine with norbornene. In situ
1H-NMR studies on the catalytic reactions also proved the formation of
4 as an intermediate in the catalytic process. For oxidant free rhodium-
catalyzed C-H bond functionalization, RhI species is always proposed to
be the catalytic active species.[14] We supposed that 4 might undergo Si-
O bond activation, via a tBuOH elimination, to form an olefin stabilized
RhI intermediate A (Scheme S3). Such cleavage reactions of Si-O bonds
of silyl ligands to form silylene complexes were proposed by Ogino,
Tilley, and Braun et al.[19] The routes of formation of the proposed
catalytically active RhI intermediate from 2 and 4 are presented in
Scheme S3. A tentative calculated mechanism of model catalytic
alkenylation reaction of phenylpyridine with ethylene using the RhI
intermediate A is shown in Scheme S4. Attempts to detect these genuine
catalytically active species were hitherto unsuccessful.
[5] Mo, Z.; Szilvási, T.; Zhou, Y.; Yao, S.; Driess, M. Angew. Chem. 2017,
129, 3753-3756; Angew. Chem. Int. Ed. 2017, 56, 3699-3702.
[6]
a) H. Tobita, K. Hasegawa, J. J. Gabrillo Minglana, L.-S. Luh, M.
Okazaki, H. Ogino, Organometallics 1999, 18, 2058-2060; b) M.
Okazaki, N. Yamahira, J. J. G. Minglana, T. Komuro, H. Ogino, H.
Tobita, Organometallics 2008, 27, 918-926; c) T. Komuro, T. Kitano,
N. Yamahira, K. Ohta, S. Okawara, N. Mager, M. Okazaki, H. Tobita,
Organometallics 2016, 35, 1209-1217; d) T. Kitano, T. Komuro, R.
Ono, H. Tobita, Organometallics 2017, 36, 2710-2713.
[7] a) G. J. Kubas, Metal Dihydrogen and σ-Bond Complexes, Springer,
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In summary, the reaction of the first chelate NHSi-silane 1 with
[Rh(coe)2Cl]2 led to the unusual rhodium(III) complex (LSi-R-
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catalytic efficiency under relatively mild reaction conditions. Reactivity
t
investigations on the pre-catalyst 2 towards BuONa furnished the new
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Keywords: N-Heterocyclic Silylene • DFT Calculations • Agostic
Complex • Alkenylation • Atoms in Molecules
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COMMUNICATION
A pentagonal- bipyramidal
rhodium(III) complex
Z. Mo, A. Kostenko, Y.-P.
Zhou, S. Yao, M. Driess *
featuring one agostic and
two anagostic interactions
with a novel SiII-SiIV ligand
has been synthesized,
which can be used as pre-
catalyst for alkenylation
and alkylation of C-H
Page No. – Page No.
A Chelate Silylene-Silyl
Ligand Can Boost the
Rhodium-Catalyzed
C-H Bond
bonds with high catalytic
efficiency under mild
Functionalizations
reaction conditions.
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