Hydroalkylation of Aryl Alkenes with Organohalides Catalyzed by Molybdenum Oxido Based Lewis Pairs

Article abstract of DOI:10.1002/adsc.202000425

Three molybdenum(VI) dioxido complexes [MoO₂(L)₂] bearing Schiff base ligands were reacted with B(C₆F₅)₃ to afford the corresponding adducts [MoO{OB(C₆F₅)₃}(L)₂], which were fully characterized. They exhibit Frustrated Lewis-Pairs reactivity when reacting with silanes. Especially, the [MoO{OB(C₆F₅)₃}(L)₂] complex with L=2,4-dimethyl-6-((phenylimino)methyl)phenol proved to be active as catalyst for the hydroalkylation of aryl alkenes with organohalides and for the Atom-Transfer Radical Addition (ATRA) of organohalides to aliphatic alkenes. A series of gem-dichloride and gem-dibromide compounds with potential for further derivatization were synthesized from simple alkenes and organohalides, like chloroform or bromoform, using low catalyst loading. (Figure presented.).

Full text of DOI:10.1002/adsc.202000425

Title: Hydroalkylation of Aryl Alkenes with Organohalides Catalyzed by
Molybdenum-Oxido Based Lewis Pairs
Authors: Niklas Zwettler, Antoine Dupe, Sumea Klokic, Angela
Milinkovic, Dado Rodic, Simon Walg, Dmytro Neshchadin,
Ferdinand Belaj, and Nadia Mösch-Zanetti
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.202000425
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.202((will be filled in by the editorial staff))
Hydroalkylation of Aryl Alkenes with Organohalides Catalyzed
by Molybdenum-Oxido Based Lewis Pairs
Niklas Zwettler,a Antoine Dupé,a Sumea Klokić,a Angela Milinković,a Dado Rodić,a
Simon Walg,a Dmytro Neshchadin,b Ferdinand Belaja and Nadia C. Mösch-Zanettia*
a
Institute of Chemistry, University of Graz, Schubertstrasse 1, 8010 Graz, Austria
Institute for Physical and Theoretical Chemistry, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria
b
E-Mail: nadia.moesch@uni-graz.at
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract. Three molybdenum(VI) dioxido complexes A series of gem-dichloride and gem-dibromide compounds
[MoO2(L)2] bearing Schiff-base ligands were reacted with with potential for further derivatization were synthesized
B(C6F5)3 to afford the corresponding adducts from simple alkenes and organohalides, like chloroform or
[(L)2Mo(O)OB(C6F5)3], which were fully characterized. bromoform, using low catalyst loading.
They exhibit Frustrated Lewis-Pairs reactivity when
reacting
with
silanes.
Especially,
the
Keywords: C-C coupling; Frustrated Lewis pairs;
[(L)2Mo(O)OB(C6F5)3] complex with L = 2,4-dimethyl-6-
((phenylimino)methyl)phenol proved to be active as catalyst
for the hydroalkylation of aryl alkenes with organohalides
and for the Atom-Transfer Radical Addition (ATRA) of
organohalides to aliphatic alkenes.
Hydroalkylation; Molybdenum-oxido complexes; Silanes
Introduction
Since the discovery of their exceptional reactivity by
Stephan and Erker,[1,2] Frustrated Lewis Pairs (FLP)
became a tool of choice as catalysts for many chemical
transformations, especially in the field of Small
Molecules Activation.[2,3] FLP are Lewis acid-base
pairs that form no or a poor bond between them, for
example by deliberately introducing steric hindrance.
Among the numerous examples of activation of
unreactive molecules by FLP developed over the past
ten years, splitting of H2 for metal-free hydrogenation
of imines,[4] carbonyls,[5] alkenes[6] or alkynes,[7] as
Scheme 1. Top: Lewis adduct formation and frustrated
Lewis pair; bottom: Lewis adduct formation between M=O
and B(C6F5)3.
[8]
well as functionalization of CO2 are the most
prominent examples. In FLP, the role of the Lewis acid
is often played by tris(pentafluorophenyl)borane
B(C6F5)3, due to its high electrophilicity and steric
demand. Besides, B(C6F5)3 is itself a good catalyst for
Inspired by these reports, our group became
interested in investigating the influence of bulky Lewis
acids on oxygen activation and oxidative properties of
our previously published molybdenum dioxido and
oxido-imido complexes.[15-18] We recently reported the
synthesis of a molybdenum oxido-imido complex that
reacted with B(C6F5)3 under formation of an adduct
having FLP-like properties.[19] With this molybdenum-
oxido based Lewis pair, heterolytic cleavage of
silicon-hydrogen bonds was demonstrated, leading to
cationic Mo(VI) species of the formula
[Mo(OSiR3)(NtBu)L2] [HB(C6F5)3] that were isolated
and fully characterized. Ultimately, it was shown that
such FLP-like adducts could catalyze the
several
reactions,
especially
hydrosilylation
reactions.[9,10] Recently, the concept of FLP was
extended to transition metal compounds, where they
act as the Lewis acid or base, allowing for further
reactivity not observed with main group frustrated
Lewis pairs.[11] In particular, transition metals
complexes bearing an oxido ligand could be used as
the Lewis base in combination with a Lewis acid such
as B(C6F5)3, leading to new reactivity for the
complexes, as reported by the group of Schrock[12] and
the group of Ison (Scheme 1).[13,14]
1
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
hydrosilylation of benzaldehyde via insertion of the
substrate into the boron-hydrogen bond of the borate.
In this paper, we further investigate the reactivity of
these FLP-like adducts of B(C6F5)3 with molybdenum
oxido complexes towards alkenes. We found that an
unexpected addition of halides to the alkenes takes
place in presence of catalytic amounts of the metal
FLP and silanes. The addition of organohalides to
alkenes is known as Atom-Transfer Radical Addition
(ATRA) or Kharasch Addition, named after Morris
Kharasch, who studied the reaction of HBr, CHCl3 and
CCl4 with unsymmetrical alkenes in presence of
peroxide.[20] The reaction starts with formation of a
radical species from the organohalide, generally CX4
or CHX3, in presence of an initiator or a transition-
metal catalyst (Scheme 2). The generated •CX3 or
•CHX2 radical can then react with the alkene, leading
to an anti-Markovnikov addition intermediate, which
can subsequently combine with the other radical •X
from the organohalide to afford the final product.
Alternatively, the radical intermediate can react with
one or several equivalents of the initial alkene to afford
a polymer. In this case, the reaction is called Atom-
Transfer Radical Polymerization (ATRP). In a third
outcome, the addition intermediate, when sufficiently
reactive, can react with a hydrogen donor to lead to the
corresponding hydroalkylation product. Such
hydroalkylation may also be referred to as a Giese
addition.[21]
ATRA reactions are nowadays broadly used for the
synthesis of halogenated functionalized molecules.[22]
Ruthenium[23] or copper[24] catalysts bearing ligands
that could photo- or thermo-initiate the formation of
the radical are usually needed to perform ATRA
reactions, but examples using molybdenum complexes
were also reported.[25,26] The molybdenum dioxido-
B(C6F5)3 compounds presented in this paper can not
only catalyze the ATRA reaction when aliphatic
alkenes are used as substrates, but more importantly
the hydroalkylation of aryl alkenes since these ones
form more reactive intermediates. Hence, simple
organohalides like chloroform or bromoform reacted
with a variety of alkenes that were reduced forming
new gem-dichloride and gem-dibromide compounds
that are of interest for further reactivity and
functionalization.
Scheme 2. ATRA (Kharasch addition), ATRP and hydroalkylation of alkenes with organohalides.
organic solvents and reliable NMR spectroscopy data
Results and Discussion
could be only obtained using DMSO. For this complex,
only one set of signals is clearly visible, while
formation of a second isomer might be the cause of the
other broad signals (see SI). As confirmed by X-ray
crystallography, one of the two isomers for each
complex has nitrogen atoms of both ligands trans to
the oxido group (N,N isomer), whereas the N,O isomer
forms as well but did not crystallized in our attempts.
The three complexes are slightly sensitive towards
moisture and only partially soluble in acetonitrile.
Synthesis of Dioxido Complexes. Three molybdenum
dioxido complexes bearing iminophenolate ligands
with different steric and electronic properties were
synthesized in order to study their reaction with
B(C6F5)3 (Scheme 3). Complex [MoO2(L1)2] (1) was
synthesized following
a
previously published
procedure[16] and complexes [MoO2(L2)2] (2) and
[MoO2(L3)2] (3) were synthesized using similar
protocols: two equiv of ligands HL2[27] or HL3[28]
were reacted with one equiv of [MoO2Cl2] in presence
of excess NEt3 in an appropriate solvent using Schlenk
techniques. After filtration and purification, the three
molybdenum dioxido complexes were isolated as
orange or yellow solids in good yields (65%-78%,
Scheme 3). As reported for 1 in our previous
Synthesis of Molybdenum-Oxido Lewis Adducts. In
a similar procedure to a previous publication,[19]
addition of one equiv of the Lewis acid B(C6F5)3 to the
yellow suspension of the molybdenum(VI) dioxido
precursors 1-3 in pentane led to an immediate color
change to deep red and subsequent formation of the
Lewis adducts [MoO{OB(C6F5)3}(L)2] (L1-L3, 4-6)
as deep red crystalline precipitates. Compounds 4-6
were isolated as red to dark red solids in very good
yields after purification (Scheme 3).
publication,[16] complex
2 exhibits a dynamic
isomerism in solution, reflected by two distinct sets of
resonances with different intensity in the H and 19F
NMR spectra. Complex 3 is very poorly soluble in
1
2
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
Scheme 3. Synthesis of molybdenum dioxido complexes 1-3 and molybdenum oxido Lewis adducts 4-6.
Compounds 4-6 are highly sensitive to moisture
and soluble in most polar organic solvents, but only
sparingly soluble in benzene and toluene. Like
previous observations for the related oxido imido
borane adduct,[19] NMR spectroscopy reveals that
compounds 4-6 exist as single isomers in solution,
which is in contrast to the isomeric equilibrium
observed for the dioxido molybdenum complexes 1-3.
Molecular Structures. The molecular structures of
complexes 1-3 and 4-6 were determined by single
crystal X-ray diffraction analyses. The molecular
views of complexes 1-3 are shown in Figure 1 and of
4-6 in Figure 2. Selected bond lengths and angles are
shown in Table 1 and full crystallographic details are
provided in the supporting information. The dioxido
complexes 1-3 show similar structures, as already
reported for 1[16] and for other published molybdenum
dioxido complexes.[15,18] As reported for similar oxido-
imido complexes forming Lewis adducts,[19] the
Mo=O bond that interact with B(C6F5)3 in 4-6 becomes
elongated in comparison to the parent dioxido
complexes 1-3. Thus, the Mo-N bond trans to the
oxido-borane moiety is shortened for all three
compounds when compared with Mo-N bond from
dioxido complexes. Overall, the structures of
compounds 4-6 are similar in terms of bond lengths,
with the Mo1-O2 bond ranging from 1.783(2) Å in 5
to 1.7900(10) Å in 4 and the O2-B1 bond ranging from
1.530(2) Å in 4 to 1.5371(15) Å in 6. The major
difference between complex 4 and 5-6 is the angle B1-
O2-Mo1 being larger in the case of 4 [159.08(9)°]
compared to 155.8(2)° for 5 and 153.13(8)° for 6, due
to the presence of tert-butyl and phenyl groups at the
ligand.
1
The H NMR spectra features two distinct signal sets
for the ligands, indicating coordination at only one
Mo=O moiety. The coordination of the Lewis acid is
confirmed by a new set of signals corresponding to the
meta, ortho and para fluorines of B(C6F5)3, observable
in 19F NMR spectroscopy. Especially, the pronounced
shift of the para-F resonance (-158.8 ppm, C6D6)
compared to free borane (-142.3 ppm, C6D6) is
characteristic of such coordination.[14,19] The para-F
shift is less pronounced in both adducts 5 (-148.2 ppm,
C6D6) and 6 (-157.6 ppm, C6D6). Due to the
quadrupolar nature of 11B nucleus, 11B NMR
spectroscopy gave no meaningful data for the
complexes 4-6, but IR spectroscopy was used to
confirm Mo=O-B coordination, with a characteristic
strong signal at around 980 cm-1 for each complex.[19]
3
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
Figure 1. Molecular views (50% probability level) of 1-3 (from left to right); hydrogen atoms as well as solvent molecules
are omitted for clarity. For disordered fragments, only atoms with the higher site occupation factors are depicted.
Figure 2. Molecular views (50% probability level) of 4-6 (from top to bottom); hydrogen atoms as well as solvent molecules
are omitted for clarity. For disordered fragments, only atoms with the higher site occupation factors are depicted.
O2-B1
O1-Mo1-O2
O11-Mo1-O21 160.52(5)
1.530(2)
104.47(5)
1.535(4)
103.85(10) 104.37(4)
157.21(9) 157.99(4)
1.5371(15)
Table 1. Selected bond lengths [Å] and angles [°] for
complexes 1-3 and 4-6.
1
2
3
O1-Mo1-N17
O2-Mo1-N27
N17-Mo1-N27 79.02(4)
B1-O2-Mo1 159.08(9)
163.63(5)
169.59(4)
165.94(10) 159.94(4)
171.60(10) 169.94(4)
Mo1-O1
Mo1-O2
1.6983(15) 1.6989(17) 1.705(4)
1.6984(13) 1.7048(17) 1.712(3)
1.9608(13) 1.9404(16) 1.950(3)
1.9409(13) 1.9412(16) 1.946(4)
82.21(9)
155.8(2)
74.80(3)
153.13(8)
Mo1-O11
Mo1-O21
Mo1-N17
Mo1-N27
O1-Mo1-O2
O11-Mo1-O21 152.82(5)
O1-Mo1-N17
O2-Mo1-N27
Reactivity in ATRA and Hydroalkylation of
alkenes. During initial attempts to use complex 4 as
catalyst in olefin hydrosilylation with phenylsilane, we
noticed unexpected reactivity upon use of CHCl3 as
reaction solvent. Thus, using styrene as substrate, we
did not observe the hydrosilylated product, but it was
rather converted to 3,3-dichloropropyl benzene (7a)
and to 1,3,3-trichloropropylbenzene (7a’) (Scheme 4).
This unexpected observation prompted us to
investigate the generalizability and scope of this
reaction in terms of catalyst, olefinic substrate,
organohalide and silane. In this reaction, 1,3,3-
trichloropropylbenzene (7a’) is formed by addition of
chloroform to styrene, representing an ATRA reaction,
which does typically require no silane nor borane.
2.3896(16) 2.395(2)
2.3898(15) 2.358(2)
2.407(4)
2.382(4)
105.22(7)
105.97(9)
154.66(7)
167.87(8)
167.74(8)
81.84(7)
104.04(18)
154.52(14)
167.46(16)
165.53(15)
77.19(14)
169.72(6)
170.77(6)
N17-Mo1-N27 86.27(5)
4
5
6
Mo1-O1
Mo1-O2
Mo1-O11
Mo1-O21
Mo1-N17
Mo1-N27
1.6909(11) 1.680(2)
1.7900(10) 1.783(2)
1.9008(10) 1.8937(19) 1.9121(9)
1.9229(10) 1.922(2)
2.3569(12) 2.381(3)
2.2967(13) 2.312(3)
1.6892(9)
1.7839(8)
1.9072(9)
2.3950(10)
2.3084(10)
4
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
Such catalytic transformation was already reported to
be catalyzed by molybdenum(VI) complexes in
presence of triethylamine using CCl4 as
organohalide.[26] We envisioned that formation of 3,3-
dichloropropyl benzene (7a) most likely occurs due to
the presence of silane (vide infra).
7a in 91% yield and 7a’ in 9% yield using 1 mol%
catalyst 4 with 2 equiv PhSiH3 after 2 h at 50 °C (entry
1). Using 1 equiv PhSiH3 also afforded 7a with almost
complete conversion of the substrate, albeit slower
(entry 2). Blank and control experiments revealed no
conversion of styrene in absence of complex 4 (entry
3), in absence of silane or in absence of borane (using
the dioxido complex 1, entry 4). The latter was
corroborated
using
commercially
available
[MoO2(acac)2], with which also no reactivity was
observed (entry 5). Furthermore, while the use of
B(C6F5)3 did lead to a partial consumption of styrene,
no formation of the chlorinated products was observed.
Instead, using B(C6F5)3 led to a mixture of unidentified
products accompanied by small quantities of the
hydrosilylation product (entry 6). It is also interesting
to note that the use of the two other borane adducts 5
or 6, or the presence of [MoO2(acac)2] and B(C6F5)3
together in the reaction mixture, although showing
slow conversion of styrene, lead to no formation or in
a small amount of chlorinated products (entry 7 to 9).
Scheme 4. Observed catalytic transformation of styrene into
3,3-dichloropropyl
benzene
(7a)
and
1,3,3-
trichloropropylbenzene (7a’).
With this knowledge at hand, we performed a series
of experiments in order to evaluate which of the
components of the reaction shown in Scheme 4 are
needed for the catalytic conversion. The results are
summarized in Table 2. Styrene was fully converted to
Table 2. Control experiments for the addition of CHCl3 to styrene in presence of silane.
Catalyst
(1 mol%)
Selectivity for
7a (%)
Selectivity for
7a’ (%)
Entry
PhSiH3 (equiv) Reaction time
Conversion (%)
1
2
3
4
5
6
7
8
2
2 h
2 h / 5 h
20 h
20 h
20 h
20 h
2 h / 20 h
2 h / 20 h
> 98
95 / > 98
0
0
0
5
91
77 / 80
0
0
0
0
0 / 7
0 / 0
9
4
4
none
1
[MoO2(acac)2]
B(C6F5)3
5
6
1
2
2
2
2
2
2
2
23 / 16
0
0
0
0
0 / 2
0 / 0
56 / 95
11 / 61
[MoO2(acac)2]
+ B(C6F5)3
9
20 h
83
0
0
General conditions: 1 or 2 equiv PhSiH3, 50 °C, 0.5 mL CHCl3 as solvent. Conversion of styrene as determined by GC-MS
and selectivity as determined by 1H NMR spectroscopy.
Table 3. Solvent screening for the addition of CHCl3 to
styrene in presence of silane.
Thus, exclusively the combination of the oxido-adduct
4 with silane as shown in Scheme 4 leads to catalytic
hydroalkylation of styrene.
With catalyst 4, reaction optimization in toluene
with varying amounts of CHCl3 was performed
revealing optimal conversion and selectivity for 7a
with 5 equiv of chloroform (Table 3, entries 2 – 4).
Solvent screening with 5 equiv of CHCl3 showed 93%
conversion of styrene in chlorobenzene were after 2 h
(entry 5), while no consumption of styrene took place
in acetonitrile as it coordinates to B(C6F5)3 (entry 6).
As the selectivity toward formation of 3,3-
dichloropropyl benzene is very high in chlorobenzene,
where only the ATRA product was observed as a side
product, the latter was used as preferred solvent for the
reaction.
Select. Select.
Conv.
(%)
Equiv
Entry Solvent
for 7a for 7a’
CHCl3
(%)
(%)
1
2
3
4
5
6
CHCl3
Tol.
Tol.
Tol.
PhCl
MeCN
-
> 98
0
60
77
93
0
91
0
73
75
92
0
9
0
0
7
8
0
1
2
5
5
5
General conditions: 1 mol% cat 4, 2 equiv PhSiH3, 50 °C,
2 h. Conversion of styrene as determined by GC-MS and
selectivity as determined by 1H NMR spectroscopy.
5
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
In order to evaluate the scope of applicable chlorinated
substrates, styrene was reacted with various
organochlorides and organobromides. Results are
summarized in Table 4. Chloroform and carbon
tetrachloride react straightforward with styrene using
leading to 100% conversion and almost selective
formation of the hydroalkylation product after only 1
hour (Table 4, entry 4). Despite full conversion of
styrene after 3 h, the reaction with carbon tetrabromide
resulted in only a small amount of brominated product,
possibly due to the instability of CBr4 (Table 4, entry
5). Bulkier CHI3 or substituted organohalides such as
MeCCl3, PhCCl3, NCCCl3 or diethyl bromomalonate
did not react under the reaction conditions (entry 6 to
10). Dichloromethane proved unreactive as well (entry
3).
1
mol% of 4, affording the corresponding
hydroalkylation products with good selectivity (Table
4, entry 1 and 2).
It is noteworthy that the main side product in these
reactions is the ATRA product, where the vicinal
carbon of the aryl group is substituted by a chlorine
atom. Bromoform is the most reactive organohalide,
Table 4. Hydroalkylation of styrene with different organohalides catalyzed by 4 in presence of phenylsilane.
Selectivity for
Conversion (%) hydroalkylation
product (%)
Cat. loading
(mol%)
Entry
R-CXxHy
solvent
Time (h)
1
2
3
4
5
6
7
8
CHCl3
CCl4
CH2Cl2
CHBr3
CBr4
-
2
1
1
1
1
1
1
2
2
1
2
> 98
100
0
100
100
0
0
0
0
0
91
70
0
> 98
25
0
0
0
0
0
PhCl
-
20
20
1
PhCl
PhCl
PhCl
PhCl
PhCl
toluene
PhCl
3
CHI3
20
20
20
20
20
MeCCl3
PhCCl3
NCCCl3
(EtO2C)2CHBr
9
10
General conditions: 2 equiv PhSiH3, 50 °C, 0.5 mL solvent. Conversion of styrene as determined by GC-MS and selectivity
as determined by 1H NMR spectroscopy.
The fact that the reaction with CCl4 lead mainly to
formation of the hydroalkylation product is a proof
that the silane is the source of the hydrogen atom
added to the double bond. In order to confirm this, an
experiment using CDCl3 as the organohalide in the
hydroalkylation of styrene was performed, then the 1H
NMR spectrum in CDCl3 of the obtained product was
compared to the one when CHCl3 is used in C6D6
(Figure 3).
Disappearance of the triplet signal at 5.2 ppm could be
observed and the integration for the two signals
corresponding to the two CH2 groups remained the
same, indicating that the CDCl2 moiety is incorporated
to the product and no C-H bond from the organohalide
is cleaved during the reaction. This 1H NMR
spectroscopy study of the reaction of styrene with
CHCl3 in C6D6 in presence of PhSiH3 and 4 confirmed
the formation of PhSiH2Cl and PhSiHCl2 as side-
products from the reaction. Furthermore, the
hydroalkylation of styrene takes place and affords 7a
not only with phenylsilane but also with secondary and
tertiary silanes, albeit slower (Table 5).
The observation of two different products in the
here described system is in contrast to a classical
ATRA, where the halide of the organohalide is
incorporated to the alkene substrate. Since the ATRA
and the hydroalkylation reactions involve formation of
radical species, we investigated if indeed our catalytic
reaction proceeds in a similar fashion. Addition of the
free radical-scavenger galvinoxyl to the typical
reaction mixture for the hydroalkylation of styrene (1
mol% 4, 2 equiv PhSiH3, 5 equiv CHBr3) shut down
the reactivity and styrene remained intact, providing
evidence that the organohalide is added to the alkene
1
Figure 3. H NMR spectra of hydroalkylation of styrene
1
via formation of radical species. Furthermore, a H
using CDCl3 (top) or CHCl3 in C6D6 (bottom) as the
organohalide.
NMR spectroscopy study of the reaction of PhSiH3
6
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
with CHCl3 in C6D6 in presence of 4, without substrate,
confirmed the formation of radical species (Figure 4).
In these conditions, PhSiH3 reacts with CHCl3 to form
a mixture of PhSiH2Cl, PhSiHCl2, CH2Cl2 and CH3Cl,
similar to the chlorination of hydrosilanes reported by
Chulsky and Dobrovetsky.[10]
this intermediate might not be the catalytically active
species, this result shows that reduction of the
molybdenum center occurs during the reaction. The
reactivity of complexes 5 and 6 was also tested without
substrate to see if this chlorination of PhSiH3 takes
places. We observed the same formation of PhSiH2Cl
and CH2Cl2, but only in trace amounts and the reaction
is slower than for 4. This lack of reactivity of PhSiH3
with CHCl3, after reacting with the FLP adducts 5 or
6, could be explained by the presence of electron-
withdrawing substituents at the ligands. The Mo(V)
intermediate arising from the reaction of PhSiH3 with
5 or 6 would be stable enough to react with the radical
species or other molecules present in the mixture,
leading to deactivation of the catalyst, while for
complex 4, the Mo(V) intermediate is probably a
transient species, allowing reaction of H2PhSi• with
CHCl3. These results led us to consider a plausible
mechanism for the reaction similar to the mechanism
reported by Hell et al. for the silyl radical-mediated
activation of sulfamoyl chlorides (Scheme 5).[21d]
Table 5. Silane screening for the addition of CHCl3 to
styrene in toluene.
Select. Select.
Conv.
Silane
Time
2 h
for 7a for 7a’
(%)
(%)
(%)
96 /
> 98
76 /
> 98
1
2
PhSiH3
77
4 / 0
0 / 0
2 h /
20 h
2 h /
20 h
72 /
> 98
PhMeSiH2
Et3SiH
3
4
0 / 51
0 / 88
0 / 0
0
PhMe2SiH 20 h
44
0
General conditions: 1 mol% cat 4, 2 equiv Silane, 5 equiv
CHCl3, 50 °C in toluene. Conversion of styrene as
determined by GC-MS and selectivity as determined by 1H
NMR spectroscopy.
When the reaction is run with a stoichiometric
amount of galvinoxyl, the 1H NMR spectrum showed
no exchange between PhSiH3 and CHCl3. This
indicates that PhSiH3 reacts with the organohalide in
presence of borane adduct 4 generating a radical
species. This exchange reaction with PhSiH3 is very
fast for CHBr3, but surprisingly does not proceed when
using CHI3.
Scheme 5. Plausible mechanism for the hydroalkylation or
ATRA of an alkene with an organohalide in presence of 4
and PhSiH3.
In the proposed mechanism, PhSiH3 react at first with
the FLP complex 4 to form the corresponding Lewis
Pair I, that undergoes Single Electron-Transfer (SET)
to activate another PhSiH3 molecule, leading to the
radical H2PhSi• II, a Mo(V) intermediate III and a free
proton. H2PhSi• then abstracts a halogen atom of the
organohalide, forming the side-product PhSiH2X and
the radical •CHX2 IV. This radical adds to the alkene,
forming a new reactive radical intermediate V. The
catalytic cycle is closed by recombination of this
radical with HB(C6F5), affording the final product VI,
and a SET regenerating the Mo(VI) complex 4. In the
case of aliphatic alkenes, the radical intermediate V is
less reactive and has time to react with the
organohalide, leading to ATRA product VII.
As reactions with bromoform lead exclusively to the
hydroalkylation product, the experiments to extent the
scope of the olefinic substrates as summarized in Table
6 were performed using CHBr3 as the organohalide.
The most striking observation concerns the substrate
structure, where a phenyl group adjacent to the double
bond led to quick conversion into the hydroalkylation
1
Figure 4. H NMR Spectra in C6D6 of the chlorination of
PhSiH3 with CHCl3 in presence of 4 without radical
scavenger.
Besides, an EPR measurement of the reaction of
complex 4 with 1 equiv PhSiH3 in C6D6 without
substrate or organohalide was performed and showed
that the reaction led to formation of a Mo(V)
intermediate (see Supporting Information). Although
7
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
product
(3,3-dibromo
derivatives).
Aliphatic
7f in 42% and 41% yield, respectively (entry 7 and 8).
Substrates that possess an aryl group adjacent to an
internal double bond, such as prop-1-en-1-ylbenzene
react with CHBr3 to afford the hydroalkylation
products 7g-i, albeit requiring longer reaction time and
higher catalyst loading (entry 9-11). We also
investigated the influence of substituents at the aryl
group onto the activity of the catalyst. Using 1-bromo-
4-vinylbenzene or 1-(tert-butyl)-4-vinylbenzene as
substrate lead to excellent isolated yields, 90% for both
products 7j and 7k, after 3 h using 1 mol% catalyst
(entry 12-13). Having a methoxy group trans to the
vinyl functionality lead to formation of numerous side
products by reaction with the silane. No halogenation
product was observed in the case of 1-methoxy-4-
vinylbenzene, and the hydroalkylation product 7l of
the reaction with trans-anethole appears to involve
etherification of the anethole (entry 14 and 15).
However, reaction with 4-vinylbenzonitrile or 2-
vinylpyridine did not lead to conversion of the
substrate, possibly because of the interaction of the
donor atom with the borane moiety (entry 16).
substrates with terminal double bonds reacted much
slower and formed the ATRA product (1,3,3-tribromo
derivatives) exclusively (Scheme 6). The reaction of
cyclooctene with CHBr3, although showing
conversion of the substrate, did not lead to formation
of brominated product. However, reaction of
cyclooctene with CCl4 in chlorobenzene using 1 mol%
of catalyst 4 shows full conversion of the substrate to
a mixture of 1,2- and 1,4-addition products, as reported
in previous publications (Table 6, entry 3).[29]
Scheme 6. Different outcome of the reaction of various
alkenes with CHBr3 in presence of catalyst 4 and
phenylsilane.
Formation of the ATRA product as side product was
also observed for styrene when using CCl4 or CHCl3,
but it is interesting to see that these ATRA products
can react in the reaction conditions to form the
hydroalkylation product (entry 4). Furthermore,
alkenes with a phenyl substituent proved to be
significantly more reactive if terminal rather than
internal. Hence, aryl-substituted alkenes such as
styrene, 1,1-diphenylethene or α-methylstyrene react
quickly with CHBr3 with low catalyst loading to afford
Conclusion
In summary, we synthesized and characterized a
molybdenum-oxido Frustrated Lewis Pair adduct
[L2Mo(O)OB(C6F5)3]
(L
=
2,4-dimethyl-6-
((phenylimino)methyl)phenol) which is able to react
with phenylsilane to catalyze the hydroalkylation of
various aryl alkenes with organohalides and the ATRA
of organohalides to aliphatic alkenes. Examples of
such catalytic hydroalkylation of alkene using simple
chlorine and bromine derivatives, like bromoform, are
scarce. This catalytic system leads to formation of
gem-dichloride and gem-dibromide derivatives in very
good yields using low catalyst loadings.
the
corresponding
hydroalkylation
products
7a-d in excellent isolated yields (entry 1, 2, 5 and 6).
On the other hand, reaction of 1-octene or 4-phenyl-1-
butene with bromoform using 2 mol% of complex 4 in
presence of phenylsilane lead to the isolation of
Kharasch
addition
products
(3,5,5-
tribromopentyl)benzene 7e and 1,3,3-tribromononane
Table 6. Products scope of the reaction of various alkenes with organohalides in presence of catalyst 4 and phenylsilane.
Catalyst 4
Substrate /
Conversion (%)
Entry
1
Organohalide
CHCl3
Product / Isolated yield (%)
loading
(mol%)
Time (h)
2
7a, 86
(GC)
> 98
> 98
100
1
1
1
2
3
CHBr3
CCl4
7b, 86
3
2
General conditions: 1 mmol substrate, 2 equiv PhSiH3, 5 equiv organohalide, 50 °C in chlorobenzene. Conversion of
substrate as determined by GC-MS.
8
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
Table 6 (cont). Products scope of the reaction of various alkenes with organohalides in presence of catalyst 4 and
phenylsilane.
4
5
6
79
CHCl3
CHBr3
CHBr3
7a, 79
7c, 90
7d, 96
1
1
2
20
1
100
100
1
7
57
CHBr3
7e, 42
2
24
8
46
95
36
71
CHBr3
CHBr3
CHBr3
CHBr3
7f, 41
7g, 76
7h, 18
7i, 46
2
3
2
1
24
24
24
24
9
10
11
12
13
100
100
CHBr3
CHBr3
7j, 90
1
1
3
3
7k, 90
7l, 18
14
15
100
100
CHBr3
CHBr3
2
1
5
unidentified
24
9
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
16
0
CHBr3
-
1
24
General conditions: 1 mmol substrate, 2 equiv PhSiH3, 5 equiv organohalide, 50 °C in chlorobenzene. Conversion of
substrate as determined by GC-MS.
10
This article is protected by copyright. All rights reserved.

10.1002/adsc.202000425
Advanced Synthesis & Catalysis
Synthesis of Complex 4 [Mo{OB(C6F5)3}O(L1)2]. A
solution of B(C6F5)3 (1 equiv, 0.068 g, 0.13 mmol) in dry
pentane (2 mL) was added to a suspension of complex 1 (1
equiv, 0.1 g, 0.13 mmol) in the same solvent (3 mL). The
addition was accompanied by an immediate color change of
the suspension from yellow to dark red. The reaction mixture
was subsequently stirred at room temperature for 6 h,
whereupon a large quantity of a dark red precipitate had
formed. The precipitate was subsequently filtered off,
washed thoroughly with cold pentane (3x 5 mL) and dried
in vacuo to yield complex 4 as a dark red solid (0.153 g,
91%). Single crystals suitable for X-ray diffraction analysis
were obtained via vapor diffusion of pentane into a saturated
Experimental Section
General Informations. If not otherwise noted, reactions
were carried out under N2 atmosphere, using standard
Schlenk-techniques or a N2-filled glovebox. The substrates
were purchased from commercial sources and used as
received. Solvents were purified via a Pure-Solv MD-4-EN
solvent purification system from Innovative Technology,
Inc. CHCl3, CCl4 and chlorobenzene were purchased from
commercial sources and distilled prior to use. The complex
[MoO2(L1)2],[16] the Schiff base ligands HL2[27] and HL3[28]
[30]
1
as well as B(C6F5)3
were synthesized according to
toluene solution of 4 at room temperature. H NMR (300
1
previously published literature. The H, 11B, 13C and 19F
NMR spectra were recorded on a Bruker Optics instrument
at 300/96/75/282 MHz. Peaks are denoted as singlet (s)
doublet (d), doublet of doublets (dd), triplet (t), quartet (q)
and multiplet (m), broad peaks are denoted (br) and all peaks
are referenced to the solvent residual signal. Shifts in 11B and
19F NMR spectra are referenced to external standards
(BF3·Et2O and CFCl3, respectively). Used solvents and peak
assignment are mentioned at the specific data sets. GC–MS
analyses were performed with an Agilent 7890A GC system
with an Agilent 19091J-433 column coupled to a 5975C
inert XL EI/CI mass selective detector (MSD). IR spectra
were measured as solid samples on a Bruker Alpha-P
Diamond FTIR-ATR spectrometer. Elemental analyses
were carried out using a Heraeus Vario Elementar automatic
analyzer at the Institute of Inorganic Chemistry at the
University of Technology in Graz.
MHz, C6D6): δ = 7.76 (s, 1H, CH=N), 7.56 (d+s, 2H,
ArH+CH=N), 7.44 (d, 1H, ArH), 6.95-6.82 (m, 5H, Ph),
6.78 (d, 1H, ArH), 6.75 (d, 1H, ArH), 6.62-6.50 (m, 5H, Ph),
1.23 (s, 9H, tert-Bu), 1.10 (s, 9H, tert-Bu), 1.06 (s, 9H, tert-
Bu), 1.03 (s, 9H, tert-Bu). 13C NMR (75 MHz, C6D6): δ =
171.64, 169.14 (C=N), 159.36, 155.36 (Ar-O), 152.46,
151.20 (q-C), 149.97, 146.81 (C6F5), 146.48, 145.18 (q-C),
141.84 (C6F5), 139.35, 139.17 (q-C), 135.74 (C6F5), 133.06,
132.92 130.48, 129.89 (ArH), 128.84, 128.73, 127.36,
127.24, 124.04, 123.65 (Ph), 123.46, 121.69 (q-C), 35.46,
35.22, 34.50, 34.36 (q-tert-Bu), 31.21, 31.16, 30.74, 29.56
(tert-Bu). 19F NMR (282 MHz, C6D6): δ = -130.25 (dd, 6F,
o-F), -158.78 (t, 3F, p-F), -165.03 (m, 6F, m-F). 11B NMR
(96 MHz, C6D6): δ = 5.49. IR (ATR, cm-1): υ = 2962 (m, C-
H), 1606 (w, C=N), 1514 (m), 1467 (s), 1235 (m), 1094 (s),
977 (s), 880 (s), 843 (s), 765 (s), 555 (s, Mo-O). Anal. calcd
for C60H52BF15MoN2O4: C, 57.34; H, 4.17; N, 2.23; Found:
C, 57.14; H, 4.08; N, 2.23.
Synthesis of Complex 2 [MoO2(L2)2]. [MoO Cl ] (1 equiv,
0.12 g, 0.60 mmol) was added to a solution2 of2 HL2 (2.1
equiv, 0.56 g, 1.26 mmol) and NEt3 (2.4 equiv, 0.2 mL, 1.43
mmol) in acetonitrile (5 mL) under stirring. The addition
was accompanied by a color change from bright yellow to
orange-red. The reaction mixture was subsequently stirred
overnight at room temperature, whereupon a yellow
precipitate had formed. The precipitate was filtered off,
washed with cold acetonitrile (3x2 mL) and dried in vacuo
to obtain complex 2 as bright yellow solid (0.394 g, 65%).1H
NMR (300 MHz, C6D6): δ = 7.61 (d, 2H, ArH), 7.60 (s, 2H,
CH=N), 7.53 (br s, 2H, Ph), 7.34 (br s, 4H, ArH), 7.06 (d,
Synthesis of Complex 5 [Mo{OB(C6F5)3}O(L2)2]. A
solution of B(C6F5)3 (1 equiv, 0.025 g, 0.05 mmol) in dry
pentane (1 mL) was added to a suspension of complex 2 (1
equiv, 0.05 g, 0.05 mmol) in the same solvent (2 mL). The
addition was accompanied by an immediate color change of
the suspension from yellow to deep red and by the formation
of a dark red precipitate. The reaction mixture was
subsequently stirred at room temperature for 6 h, the
precipitate was filtered off, washed thoroughly with cold
pentane (3x 5 mL) and dried in vacuo to yield complex 5 as
a dark red-brownish solid (0.063 g, 84%). Single crystals
suitable for X-ray diffraction analysis were obtained from a
saturated pentane solution of 5 at -35 °C. 1H NMR (300 MHz,
C6D6): δ =7.58 (d, 2H, ArH), 7.54 s, 2H, CH=N), 7.51 (br s,
2H, Ph), 7.26 (br s, 4H, Ph), 7.03 (d, 2H, ArH), 1.26 (s, 18H,
tert-Bu), 0.91 (s, 18H, tert-Bu). 13C NMR (75 MHz, C6D6,
C6F5 obscured): δ = 171.99 (C=N), 159.22 (Ar-O), 153.85,
145.45, 139.63 (q-C), 134.05 (ArH), 133.07 (q, 1JC-F = 33.9
Hz, CF3), 130.98 (ArH), 124.90 (q-C), 123.53 (br, 2 Ph),
121.28 (q-C), 121.16 (Ph), 35.09, 34.55 (q-tert-Bu), 31.13,
29.33 (tert-Bu). 19F NMR (282 MHz, C6D6): δ = -62.81 (s,
12F, CF3), -132.31 (d, 6F, o-F), -148.23 (br s, 3F, p-F),
-161.03 (m, 6F, m-F). 11B NMR (96 MHz, C6D6): δ = IR
(ATR, cm-1): υ = 2962 (m, C-H), 1596 (w, C=N), 1517 (m),
1467 (s), 1365 (s), 1278 (m), 1176 (m), 1141 (s), 1094 (s),
978 (s), 880 (s), 847 (s), 762 (m), 682 (s), 560 (s, Mo-O).
Anal. calcd for C64H48BF27MoN2O4·0.5C5H12: C, 51.04; H,
3.48; N, 1.79; Found: C, 50.99; H, 3.84; N, 1.75.
2H, ArH), 1.31 (s, 18H, tert-Bu), 1.07 (s, 18H, tert-Bu). 13
C
NMR (75 MHz, C6D6): δ = 171.30 (C=N), 161.08 (Ar-O),
154.53, 143.47, 139.85 (q-C), 133.01, 132.57 (CF3), 130.54
(ArH), 125.14 (q-C), 123.50 (br, 2x Ph), 121.52 (br, Ph),
121.06 (q-C), 35.20, 34.47, 31.35, 29.24 (tert-Bu). 19F NMR
(282 MHz, C6D6): δ = -62.75 (s, 6F, CF3). IR (ATR, cm-1):
υ = 2960 (m), 1598 (s, C=N), 1475 (s), 1364 (s), 1276 (s),
1179 (s), 1134 (s), 935 (m), 916 (m), 893 (s, Mo=O), 847 (s),
682 (m), 555 (m, Mo-O). Anal. calcd for C46H48F12MoN2O4:
C, 54.34; H, 4.76; N, 2.76; Found: C, 54.21; H, 4.97; N, 2.72.
Synthesis of Complex 3 [MoO2(L3)2]. [MoO Cl2] (1 equiv,
0.52 g, 2.63 mmol) was suspended in acetoni2trile (20 mL),
whereupon HL3 (2.1 equiv, 1.40 g, 5.26 mmol) and NEt3
(2.4 equiv, 0.88 mL, 6.31 mmol) were added under stirring.
The addition was accompanied by a color change from
bright yellow to deep red. The reaction mixture was
subsequently stirred overnight at room temperature,
whereupon a beige precipitate had formed. The precipitate
was filtered off, washed with cold acetonitrile (3x15 mL)
and pentane (2x 10 mL) and dried in vacuo to obtain 3 as
bright yellow solid (1.34 g, 78%). Single crystals of 3
suitable for X-ray diffraction analysis were obtained via
slow evaporation from a concentrated solution of 3 in
Synthesis of Complex 6 [Mo{OB(C6F5)3}O(L3)2]. A
solution of B(C6F5)3 (1 equiv, 0.2 g, 0.39 mmol) in dry
pentane (10 mL) was added to a suspension of complex 3 (1
equiv, 0.26 g, 0.39 mmol) in the same solvent (10 mL). The
addition was accompanied by an immediate color change
from yellow to deep red and by the formation of a red
precipitate. The reaction mixture was subsequently stirred at
room temperature overnight, the precipitate was filtered off,
washed thrice with cold pentane (3x 10 mL) and dried in
vacuo to yield 6 as a brick red solid (0.35 g, 76%). Single
crystals suitable for X-ray diffraction analysis were obtained
from a concentrated benzene solution of 6 at room
temperature or a concentrated toluene solution at -35 °C. 1H
NMR (300 MHz, CD2Cl2): δ = 8.24 (s, 1H, CH=N), 8.09 (s,
1H, CH=N), 7.40-7.35 (m, 2H, ArH), 7.27-7.07 (br m, 10H,
Ph), 6.72-6.69 (m, 2H, ArH). 13C NMR (75 MHz, CD2Cl2):
δ = 166.71, 166.46, 153.10, 152.40, 150.38, 150.06, 146.77,
1
dichloromethane layered with n-heptane. H NMR (300
MHz, (CD3)2SO): δ = 8.51 (s, 2H, CH=N), 7.88-7.11 (m,
14H, ArH+Ph). 13C NMR (300 MHz, (CD3)2SO): δ = 167.41,
152.88, 150.33, 134.10, 132.71, 132.26, 130.72, 129.65,
128.81, 128.32, 126.66, 124.70, 123.90, 123.32, 123.06,
122.58, 121.53. IR (ATR, cm-1): υ = 1613 (s, C=N), 1444 (s),
1375 (m), 1279 (s), 1177 (s), 916 (s), 900 (s, Mo=O), 873
(s), 857 (s), 783 (s), 733 (s), 699 (s), 608 (s), 543 (s, Mo-O),
509 (s), 483 (s), 463 (s). Anal. calcd for
C26H16Cl4MoN2O4·0.2C5H12: C, 48.21; H, 2.76; N, 4.16;
Found: C, 48.48; H, 2.80; N, 4.16.
11
This article is protected by copyright. All rights reserved.

10.1002/adsc.202000425
Advanced Synthesis & Catalysis
141.95, 139.32, 138.47, 137.54, 136.08, 135.88, 135.57, 1.84 (m, 2H,-CH2), 1.30 (bs, 8H, -CH2), 0.89 (t, 3H, 1JC-H
132.57, 132.29, 129.76, 129.52, 128.90, 128.50, 128.04, 6.6 Hz, -CH3).
=
126.15, 125.98, 123.83, 123.41, 123.02, 122.38. 19F NMR Analytical
data
for
(3,3-dibromo-2-
trans-β-
(282 MHz, CD2Cl2): δ = -132.0 (d, 6F, o-F), -158.97 (t, 3F, methylpropyl)benzene 7g. Using 0.118
g
p-F), -164.93 (m, 6F, m-F). 11B NMR (96 MHz, C6D6): δ = methylstyrene as substrate, 7g was isolated in 76% yield
5.71. IR (ATR, cm-1): υ = 1610 (m, C=N), 1546 (m), 1465 (0.22 g). 1H NMR (300 MHz, CDCl3): δ = 7.36-7.20 (m, 5H,
1
(s), 1446 (s), 1269 (s), 1093 (s), 976 (s), 882 (s), 790 (s), 732 ArH), 5.73 (d, 1H, JC-H = 2.6 Hz,-CHBr2), 2.88-2.81 (dd,
1
1
(m), 701 (m), 671 (m), 609(m), 551 (s, Mo-O), 520 (m). 1H, JC-H = 13.7, 7.3 Hz, -CH2), 2.63 (dd, 1H, JC-H = 13.7,
Anal. calcd for C44H16BCl4F15MoN2O4: C, 45.16; H, 1.38; N, 7.3 Hz, -CH2), 2.44-2.32 (m, 1H,-CHMe), 1.20 (d, 3H, 1JC-H
2.39; Found: C, 45.07; H, 1.42; N, 2.58.
= 6.5 Hz, -CH3). 13C NMR (75 MHz, CDCl3): δ = 138.85,
129.17, 128.78, 126.73, 54.53, 46.83, 40.62, 16.58.
Analytical
data
for
(3,3-dibromopropane-1,2-
Procedure for Catalytic Runs. All catalytic experiments
for determination of conversion using Gas Chromatography
were performed under inert conditions (N2 atmosphere,
exclusion of moisture) in Mininert® reaction vessels. In a
typical experiment, an aliquot of a chlorobenzene stock
solution of the respective catalyst was added to 0.5 mL of
chlorobenzene containing 0.1 mmol of the substrate, two
equivalent of silane and five equivalents of the respective
halide. 0.1 mmol of mesitylene was used as internal standard.
Samples for GC-MS measurements were withdrawn at given
time intervals with a microliter syringe (10 µL), quenched
with Na2CO3 and diluted by a factor of 50 with HPLC grade
ethyl acetate. A 0 h sample was withdrawn before addition
of the silane. All catalytic experiments for determination of
isolated yields of products 7a-7l were performed under inert
conditions using Schlenk techniques. 0.01-0.03 mmol of the
catalyst was weighted in the glovebox in a Schlenk flask and
dissolved in 5 mL chlorobenzene, then 1 mmol of the
substrate, 2 mmol PhSiH3 and 5 mmol of the respective
halide were added. After stirring at 50 °C for the
corresponding reaction time, the reaction was quenched with
aqueous sodium carbonate, the solvent and volatiles were
removed under vacuum, the residue re-dissolved in
dichloromethane and filtered over a plug of silica. Isolated
yields were obtained by purifying the products using column
chromatography over silica with a Biotage Isolera Four
equipment, using cyclohexane / Ethyl Acetate mixtures
(10:1) as the eluent.
diyl)dibenzene 7h. Using 0.18 g cis-stilbene as substrate, 7h
1
was isolated in 18% yield (0.064 g). H NMR (300 MHz,
1
CDCl3): δ = 7.41-7.10 (m, 10H, ArH), 5.85 (d, 1H, JC-H
=
4.5 Hz, -CHBr2), 3.60-3.56 (m, 1H, -CHPh), 3.48-3.41 (m,
1H, -CH2), 3.17-3.10 (m, 1H, -CH2). 13C NMR (75 MHz,
CDCl3): δ = 138.61, 138.58, 129.40, 129.16, 128.61, 128.31,
128.01, 126.65, 58.14, 51.64, 38.87.
Analytical
data
for
2-(dibromomethyl)-1,2,3,4-
tetrahydronaphthalene 7i. Using 0.13
g
1,2-
dihydronaphtalene as substrate, 7i was isolated in 46% yield
1
(0.14 g). H NMR (300 MHz, CDCl3): δ = 7.14-7.12 (m, 4H,
1
ArH), 5.87 (d, 1H, JC-H = 4.2 Hz, -CHBr2), 3.12-2.82 (m,
4H, -CH2), 2.45-2.32 (m, 1H, CH2), 2.21-2.12 (m, 1H, CH2),
1.80-1.65 (m, 1H, CH). 13C NMR (75 MHz, CDCl3): δ =
135.87, 134.79, 129.38, 128.83, 126.16, 126.09, 53.12,
46.18, 32.97, 28.92, 27.60.
Analytical
data
for
1-(tert-butyl)-4-(3,3-
4-tert-
dibromopropyl)benzene 7j. Using 0.16
g
butylstyrene as substrate, 7j was isolated in 90% yield (0.3
g). 1H NMR (300 MHz, CDCl3): δ = 7.35-7.32 (m, 2H, Ar),
7.16-7.13 (m, 2H, Ar), 5.60 (t, 1H, 1JC-H = 6.4 Hz, -CHBr2),
2.86-2.81 (m, 2H, CH2), 2.73-2.66 (m, 2H, CH2), 1.32 (s, 9H,
tert-Bu). 13C NMR (75 MHz, CDCl3): δ = 149.56, 136.11,
128.35, 125.73, 46.90, 45.57, 34.58, 33.70, 31.51.
Analytical
data
for
1-bromo-4-(3,3-
4-
dibromopropyl)benzene 7k. Using 0.183
g
bromostyrene as substrate, 7k was isolated in 90% yield
(0.32 g). 1H NMR (300 MHz, CDCl3): δ = 7.45-7.42 (m, 2H,
Analytical data for (3,3-dichloropropyl)benzene 7a.
Using 0.1 g 7a’ as substrate, 7a was isolated in 79% yield
(0.067 g). NMR data are supported by previous
publication.[31]
1
Ar), 7.10-7.07 (m, 2H, Ar), 5.58 (t, 1H, JC-H = 6.2 Hz, -
CHBr2), 2.85-2.80 (m, 2H, CH2), 2.70-2.63 (m, 2H, CH2).
13C NMR (75 MHz, CDCl3): δ = 138.18, 131.92, 130.42,
120.52, 46.55, 44.82, 33.64.
1H NMR (300 MHz, CDCl3): δ = 7.34-7.20 (m, 5H, ArH),
5.66 (t, 1H, 1JC-H = 6.1 Hz, -CHCl2), 2.91-2.86 (m, 2H, Ar-
CH2), 2.55-2.48 (m, 2H, -CH2).
Analytical
data
for
4,4'-oxybis((3,3-dibromo-2-
methylpropyl)benzene) 7l. Using 0.148 g anethole as
1
substrate, 7l was isolated in 18% yield (0.107 g). H NMR
Analytical data for (3,3-dibromopropyl)benzene 7b.
Using 0.1 g styrene as substrate, 7b was isolated in 86%
yield (0.23 g). NMR data are supported by previous
publication.[32] 1H NMR (300 MHz, CDCl3): δ = 7.35-7.20
(300 MHz, CDCl3): δ = 7.08-7.05 (m, 4H, ArH), 6.80-6.77
1
(m, 4H, ArH), 5.71 (d, 2H, JC-H = 2.6 Hz, -CHBr2), 2.77-
2.70 (dd, 2H, 1JC-H = 13.8, 7.3 Hz, -CH2), 2.58-2.51 (dd, 2H,
1JC-H = 13.8, 7.3 Hz, -CH2), 2.35-2.23 (m, 2H, -CHMe), 1.17
(d, 6H, 1JC-H = 6.5 Hz, -CH3). 13C NMR (75 MHz, CDCl3):
154.30, 131.01, 130.32, 115.60, 54.60, 46.97, 39.76, 16.48.
ESI-MS (135 V): m/z = 592.8 [M-H]-.
1
(m, 5H, ArH), 5.60 (t, 1H, JC-H = 6.3 Hz, -CHBr2), 2.89-
2.85 (m, 2H, Ar-CH2), 2.74-2.67 (m, 2H, -CH2).
Analytical
data
for
(3,3-dibromopropane-1,1-
diyl)dibenzene 7c. Using 0.18 g 1,1-diphenylethylene as
substrate, 7c was isolated in 90% yield (0.318 g). 1H NMR
(300 MHz, CDCl3): δ = 7.36-7.22 (m, 10H, ArH), 5.30 (t, Crystallographic Data for Complexes 1-6. The X-ray data
1
1
1H, JC-H = 6.9 Hz, -CHBr2), 4.28 (t, 1H, JC-H = 7.7 Hz, collections were performed with a Bruker AXS SMART
Ar2CH), 3.16-3.11 (dd, 2H, 1JC-H = 6.9 Hz, 1JC-H = 7.7 Hz, - APEX-II CCD diffractometer at 100 K with Mo-Kα radiation
CH2). 13C NMR (75 MHz, CDCl3): δ = 142.20, 129.00, ( = 0.71073 Å) from an Incoatec microfocus sealed tube
127.91, 127.07, 51.05, 49.95, 44.38.
equipped with a multilayer monochromator. Absorption
Analytical data for (4,4-dibromobutan-2-yl)benzene 7d. corrections were made semi-empirically from equivalents.
Using 0.118 g α-methylstyrene as substrate, 7d was isolated The structures were solved by direct methods (SHELXS-97)
in 96% yield (0.278 g). 1H NMR (300 MHz, CDCl3): δ = and refined by full-matrix least-squares techniques against
7.35-7.20 (m, 5H, ArH), 5.27-5.22 (m, 1H, -CHBr2), 3.11- F2 (SHELXL-2014/6). A weighting scheme of w =
2.99 (m, 1H, ArCHMe), 2.69-2.63 (m, 2H, -CH2), 1.31 (d, 1/[2(Fo )+(aP)2+bP] where P = (Fo +2Fc2)/3 was used. The
2
2
1
1H, JC-H = 7.0 Hz, -CH3). 13C NMR (75 MHz, CDCl3): absolute configuration of 3 was established by anomalous
144.05, 128.98, 127.13, 126.99, 53.72, 44.72, 39.29, 21.80.
dispersion effects in the diffraction measurements of the
Analytical data for (3,5,5-tribromopentyl)benzene 7e. crystal. The non-hydrogen atoms of 1, 3, 4, and 6 were
Using 0.132 g 4-phenyl-1-butene as substrate, 7e was refined with anisotropic displacement parameters without
isolated in 42% yield (0.16 g). 1H NMR (300 MHz, CDCl3): any constraints. The H atoms of the phenyl rings including
δ = 7.34-7.21 (m, 5H, ArH), 5.93-5.89 (m, 1H, -CHBr2), any adjacent CH=N groups were put at the external bisectors
4.16-4.07 (m, 1H, CHBr), 2.98-2.74 (m, 4H, -CH2), 2.22- of the C–C–C angles at C–H distances of 0.95 Å and
2.13 (m, 2H, -CH2). 13C NMR (75 MHz, CDCl3): 140.34, common isotropic displacement parameters were refined for
128.75, 128.59, 126.48, 53.69, 53.52, 43.35, 40.21, 33.55.
the H atoms of the same ring. The H atoms of the tert-butyl
Analytical data for 1,1,3-tribromononane 7f. Using 0.112 groups were refined with common isotropic displacement
g 1-octene as substrate, 7f was isolated in 41% yield (0.149 parameters for the H atoms of the same group and idealized
g). NMR data are supported by previous publication.[33] 1
NMR (300 MHz, CDCl3): δ = 5.92-5.88 (m, 1H, -CHBr2), around the C–C bonds, and C–H distances of 0.98 Å.
4.16-4.08 (m, 1H, CHBr), 2.84-2.76 (m, 2H, -CH2), 1.89- Crystallographic data for the structures of compounds 1-6
H
geometries with tetrahedral angles, enabling rotations
12
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10.1002/adsc.202000425
Advanced Synthesis & Catalysis
have been deposited with the Cambridge Crystallographic
Data Center (CCDC 1940999 to CCDC 1941004 for 1 to 6).
[12] D. V. Peryshkov, W. P. Forrest, R. R. Schrock, S. J.
Smith, P. Müller, Organometallics 2013, 32, 5256-5259.
[13] a) N. S. Lambic, C. A. Brown, R. D. Sommer, E. A.
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Acknowledgements
Financial support by the Austrian Science Fund (FWF, grant
number P26264) and NAWI Graz is greatly acknowledged.
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FULL PAPER
Hydroalkylation of Aryl Alkenes with
Organohalides Catalyzed by Molybdenum-Oxido
Based Lewis Pairs.
Adv. Synth. Catal. Year, Volume, Page – Page
Niklas Zwettler, Antoine Dupé, Sumea Klokić,
Angela Milinković, Dado Rodić, Simon Walg,
Dmytro Neshchadin, Ferdinand Belaj and Nadia C.
Mösch-Zanetti*
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