New Titanium Complexes and Their Use in Hydroamination and Hydroaminoalkylation Reactions

Article abstract of DOI:10.1002/ejic.201900586

The synthesis of three new sterically crowded titanium complexes which all possess an identical formamidinato ligand, two dimethylamido ligands and in addition, a 2-aminopyridinato ligand that contains either an N-methyl, an N-phenyl, or an N-cyclohexyl substituent is presented. All new complexes are easily accessible from a common titanium mono(formamidinate) precursor and correspondingly N-substituted 2-aminopyridines. Furthermore, the new complexes are used as catalysts for selected hydroamination and hydroaminoalkylation reactions and finally, the catalytic performance of the new catalysts is compared with the performance of the titanium mono(formamidinate) precursor.

Full text of DOI:10.1002/ejic.201900586

A Journal of
Accepted Article
Title: New Titanium Complexes and Their Use in Hydroamination and
Hydroaminoalkylation Reactions
Authors: Jens Bielefeld, Ekaterina Kurochkina, Marc Schmidtmann,
and Sven Doye
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201900586
Link to VoR: http://dx.doi.org/10.1002/ejic.201900586

European Journal of Inorganic Chemistry
10.1002/ejic.201900586
FULL PAPER
New Titanium Complexes and Their Use in Hydroamination and
Hydroaminoalkylation Reactions
[
a]
[a]
[a]
[a]
Jens Bielefeld, Ekaterina Kurochkina, Marc Schmidtmann, and Sven Doye*
[
8]
Abstract: The synthesis of three new sterically crowded titanium
complexes which all possess an identical formamidinato ligand, two
dimethylamido ligands and in addition, a 2-aminopyridinato ligand
that contains either an N-methyl, an N-phenyl, or an N-cyclohexyl
substituent is presented. All new complexes are easily accessible
chelating aminopyridinato ligand. In this context, it must be
mentioned that our decision to focus on this type of ligands was
based on the fact that aminopyridinato titanium complexes have
already been used as highly active and selective catalysts for
hydroaminoalkylation reactions of alkenes, styrenes and 1,3-
[
9]
from
a
common titanium mono(formamidinate) precursor and
butadienes. Furthermore, it was expected that a sterically more
congested titanium center would generally lead to a stronger
preference for the formation of branched hydroaminoalkylation
correspondingly N-substituted 2-aminopyridines. Furthermore, the
new complexes are used as catalysts for selected hydroamination
and hydroaminoalkylation reactions and finally, the catalytic
performance of the new catalysts is compared with the performance
of the titanium mono(formamidinate) precursor.
[
6,7]
products.
However, while all these expectations are based on
the assumption that the catalytically active species are
monomeric it should be mentioned that hyroaminoalkylation
reactions with dimeric catalytic species have also been
[
10]
proposed.
Introduction
[
1]
Eisen´s titanium mono(formamidinate) complex 1 (Scheme 1)
has previously been reported as highly active
catalyst that converts secondary
a
[
2-5]
hydroaminoalkylation
amines and simple 1-alkenes (R
1
=
alkyl) into branched
hydroaminoalkylation products with high selectivity while on the
1
other hand, corresponding reactions of styrenes (R = aryl)
usually give mixtures of a branched and a linear product. From a
[6]
mechanistic point of view, it is generally accepted that the
catalytically active species of hydroaminoalkylation reactions are
[
7]
titanaaziridines (Scheme 1) possessing two spectator ligands
which do not participate in the catalytic reaction but determine
the activity as well as the selectivity of the catalyst. The fact that
the regioselectivity-determining step of the catalytic cycle is the
insertion of the alkene substrate into the titanium carbon bond of
the titanaaziridine suggests that increasing steric hindrance
around the titanium center should favor the formation of
branched hydroaminoalkylation products. Interestingly, in the
case of mono(formamidinate) catalyst 1, the expected
catalytically active species would be titanaaziridine 2 (Scheme
Scheme 1. Hydroaminoalkylation of alkenes catalyzed by the titanium
mono(formamidinate) complex 1.
Results and Discussion
1
) which bears one formamidinato ligand and an additional
2
ligand L [L = NMe
2
or N(R )Me] as the spectator ligands.
2
During initial attempts to replace one of the NMe -ligands of 1 by
Because the latter ligand L offers a promising possibility to
further fine-tune the performance of the catalytic system, we
recently decided to synthesize a number of derivatives of 1 in
aminopyridinato ligands it was found that the synthesis of
corresponding complexes could easily be achieved from 1 and
sterically less demanding aminopyridnes such as N-methyl-2-
aminopyridine, N-phenyl-2-aminopyridine, or N-cyclohexyl-2-
aminopyridine (Scheme 2). In all these cases, the
aminopyridines were simply added to a suspension of 1 in n-
hexane and after stirring at room temperature for 18 hours, the
desired new titanium complexes 3-5 could be isolated in yields
between 42 % and 97 % by simple filtration. Subsequently,
crystals of 3-5 suitable for X-ray single-crystal analysis could be
obtained by recrystallization from toluene. On the other hand,
corresponding reactions with sterically more demanding N-tert-
butyl-2-aminopyridine or 2,6-di(phenylamino)pyridine failed
because in these cases, the formamidinato ligand of 1 did not
2
which one of the NMe -ligands is selectively replaced by a
[
a]
M. Sc. J. Bielefeld, M. Sc. E. Kurochkina, Dr. M. Schmidtmann, Prof.
Dr. S. Doye
Institut für Chemie
Universität Oldenburg
Carl-von-Ossietzky-Straße 9-11, 26129 Oldenburg (Germany)
E-mail: doye@uni-oldenburg.de
Homepage: https://uol.de/oc-doye/
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Inorganic Chemistry
10.1002/ejic.201900586
FULL PAPER
[
11]
Figure 1. New complex 3
bearing one N-methyl-2-aminopyridinato ligand.
stay bonded to the titanium center and as a result, N,N'-bis(2,6-
diisopropylphenyl)formamidine precipitated from the reaction
mixtures.
Hydrogen atoms are omitted for clarity. Selected bond lenghts (Å) and angles
°): Ti−N1 2.2530(7), Ti−N2 2.1887(6), Ti−N3 2.0420(8), Ti−N4 2.2951(10),
Ti−N5 1.9135(7), Ti−N6 1.9077(9), N1−Ti−N3 98.02(3), N1−Ti−N4 89.83(3),
N5−Ti−N6 96.62(4).
(
Scheme 2. Synthesis of new titanium complexes from 1 and 2-aminopyridines.
As can be seen from Figures 1-3, the solid state structures of 3-
5
reveal similarly distorted octahedral geometries around the
titanium centers. The three complexes 3, 4 and 5 are not only
very similar to each other in terms of Ti−N bond lengths and
angles, but also correlate to the already known structure of their
precursor 1. In the case of 1, the distances between the
formamidine nitrogen atoms and the titanium center were
reported to be 2.1847 Å and 2.2926 Å while for the three
remaining dimethylamido ligands an average Ti−N distance of
[
11]
[
1]
Figure 2. New complex 4
Hydrogen atoms are omitted for clarity. Selected bond lenghts (Å) and angles
°): Ti−N1 2.2619(8), Ti−N2 2.1695(6), Ti−N3 2.0676(7), Ti−N4 2.2866(8),
bearing one N-phenyl-2-aminopyridinato ligand.
1.9073 Å was found. For the complexes 3 and 5, a slight tilt of
the formamidinato ligand compared to 1 is observed [Ti−N1 is
shorter by 0.031 Å (3) / 0.011 Å (5); Ti−N2 is longer by 0.004 Å
(
Ti−N5 1.9050(7), Ti−N6 1.9060(8), N1−Ti−N3 98.78(3), N1−Ti−N4 88.16(3),
(
3) / 0.010 Å (5)]. For complex 4, both Ti−N bond lengths are
slightly shorter compared to 1 [∆(Ti−N1) = 0.031 Å, ∆(Ti−N2) =
0.015 Å], which hints at a significant electronic influence of the
N5−Ti−N6 101.75(3).

phenyl substituent of the aminopyridinato ligand. Finally, it can
be mentioned that for the new complexes 3-5, the Ti−N bond
lengths of the dimethylamido ligands are not significantly
changed compared to 1.
[
11]
Figure 3. New complex 5
bearing one N-cyclohexyl-2-aminopyridinato
ligand. Hydrogen atoms are omitted for clarity. Selected bond lenghts (Å) and
angles (°): Ti−N1 2.2812(8), Ti−N2 2.1944(7), Ti−N3 2.0374(7), Ti−N4
2.2496(9), Ti−N5 1.9211(9), Ti−N6 1.9111(9), N1−Ti−N3 100.00(3), N1−Ti−N4
87.14(3), N5−Ti−N6 99.32(4).
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European Journal of Inorganic Chemistry
10.1002/ejic.201900586
FULL PAPER
With sufficient quantities of 3-5 in hand, we then used the new
complexes as catalysts for the hydroaminoalkylation of styrene
with N-methylaniline (Table 1, entries 1-4) and compared the
corresponding results with the outcome of a control experiment
performed with catalyst 1. All reactions were performed under
identical conditions with a catalyst loading of 10 mol% at 140 °C
in n-hexane in sealed Schlenk tubes. First of all, it could be
confirmed that as mentioned above, complex 1 is a highly active
catalyst that delivers the regioisomeric hydroaminoalkylation
products 6a and 6b in excellent combined yield of 92 % (Table 1,
entry 1). On the other hand, only a modest regioselectivity of
Table 1. Hydroaminoalkylation of alkenes.
[
c]
Entry
R
Catalyst (mol%)
Yield [%]
Regioselectivity [a/b]
[a]
[d]
[d]
[d]
[d]
[e]
[e]
[e]
[e]
1
Ph
1 (10)
3 (10)
4 (10)
5 (10)
1 (2.5)
3 (2.5)
4 (2.5)
5 (2.5)
92
21
63
49
84
73
83
82
77:23
60:40
60:40
60:40
98:2
[
a]
a]
2
3
4
5
6
7
8
Ph
[
Ph
77:23 in favor of the branched product 6a was achieved with this
[a]
[b]
Ph
catalyst. Unfortunately, this severe drawback could not be
overcome by the use of the sterically more crowded new
catalysts 3-5 which all delivered mixtures of the regioisomeric
products 6a and 6b in a worse ratio of only 60:40. In addition,
catalysts 3-5 turned out to be significantly less active than 1 and
as a result, only reduced combined yields between 21 % and
n-C
n-C
n-C
n-C
6
H
6
H
6
H
6
H
13
13
13
13
[
[
b]
b]
98:2
97:3
[b]
97:3
[
a] Reaction conditions: N-methylaniline (214 mg, 2.0 mmol), styrene (312 mg,
.0 mmol), catalyst (10 mol%, 0.2 mmol), n-hexane (1 mL), 140 °C, 96 h. [b]
3
6
3 % were obtained with these catalysts. A possible explanation
Reaction conditions: N-methylaniline (21 mg, 0.2 mmol), 1-octene (31 mg, 0.3
mmol), catalyst (2.5 mol%, 0.005 mmol), toluene (0.1 mL), 140 °C, 96 h. [c]
The regioselectivity a/b was determined by GC-analysis prior to
chromatography. [d] Isolated yield of 6a + 6b. [e] Isolated yield of 7a.
for the latter observation could be the sterically more demanding
bidentate nature of the aminopyridinato ligands of 3-5 compared
to the relatively small monodentate dimethylamido ligand of 1
because additional steric hindrance of the catalytically active
species could slow down one or even more steps in the catalytic
cycle of the overall hydroaminoalkylation reaction. In this context,
it should be mentioned again that the catalytically active species
is expected to be a titanaaziridine of type 2 (Scheme 1) with
ligand L being a small dimethylamido or a bulky aminopyridinato
ligand. The decreased regioselectivity observed with 3-5
suggests that the expected simple effect of an increased steric
hindrance around the titanium center, which should favor the
formation of branched hydroaminoalkylation products, must be
overcompensated by an additional effect. In this context, it
should be mentioned that titanium catalysts possessing only
aminopyridinato ligands have already been reported to
preferably convert styrenes into linear hydroaminoalkylation
Because sterically more demanding titanium catalysts were
often found to offer significant advantages over sterically less
[12,13]
hindered catalysts in hydroamination reactions of alkynes,
we then turned our attention towards a corresponding reaction.
In this context, it must also be mentioned that Schafer and
Kempe et al. have already identified
a titanium mono-
[14]
aminopyridinato complex as a good hydroamination catalyst.
During our study, 1-phenylpropyne was reacted with para-
toluidine (Table 2) in the presence of 4 mol% of one of the
catalysts at temperatures of 60 °C or 80 °C and subsequently, in
each case, the initially formed imines were directly reduced with
3 2
mixtures of NaBH CN and ZnCl to give the regioisomeric
secondary amines 8a and 8b. With regard to the latter reaction
step, it should be mentioned that the only purpose of the
reduction was to facilitate the work-up procedure and the final
isolation of the products.
[
9]
products. During additional hydroaminoalkylation experiments
performed with 1-octene as an example of an alkyl-substituted
1-alkene (Table 1, entries 5-8) it was then found that in this case,
the performance of the catalysts 1, 3, 4, and 5 does not differ
significantly. In particular, the excellent regioselectivities of the
reactions in favor of the branched hydroaminoalkylation product
Table 2. Hydroamination of 1-phenylpropyne and subsequent imine reduction.
7a remain almost unchanged and as a result, only 7a could be
isolated in pure form from these experiments in good yields.
These results are in good agreement with the well-established
reactivity of alkyl-substituted 1-alkenes which are known to
generally deliver branched hydroaminoalkylation products with
excellent regioselectivities in the presence of early transition
[
2]
metal catalysts. In addition, the fact that alkyl-substituted
[a]
[b]
Entry
Catalyst
T [°C]
Yield [%]
Regioselectivity [8a/8b]
[
2]
alkenes react more smoothly than styrenes
possibility to run the hydroaminoalkylation reactions of 1-octene
with a reduced catalyst loading of only 2.5 mol%.
offered the
1
2
3
4
5
6
7
8
1
60
80
60
80
60
80
60
80
78
90
52
87
50
88
28
85
97:3
95:5
3
4
5
> 99:1
98:2
> 99:1
> 99:1
> 99:1
> 99:1
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European Journal of Inorganic Chemistry
10.1002/ejic.201900586
FULL PAPER
phenyl)-(1 %-vinyl)polysiloxane) with
a
flame ionization detector.
[
a] Reaction conditions: 1) 1-phenylpropyne (279 mg, 2.4 mmol), p-toluidine
283 mg, 2.6 mmol), catalyst (4 mol%, 0.1 mmol), toluene (1 mL), 60 or 80 °C,
Regioselectivities were determined by the ratio of the corresponding GC
(
[
1]
areas. Catalyst 1 was synthesized from cheap and readily available
2
2
8
4 h; 2) sodium cyanoborohydride (302 mg, 4.8 mmol), zinc chloride (327 mg,
.4 mmol), methanol (10 mL), room temperature, 20 h. Isolated yield of 8a +
b. [b] The regioselectivity 8a/8b was determined by GC-analysis prior to
[
15]
starting materials according to a literature procedure.
Complex 3: An oven-dried Schlenk flask equipped with a stopcock and a
magnetic stirring bar was transferred into a nitrogen-filled glovebox and
chromatography.
charged with
1 (3.00 g, 5.5 mmol), n-hexane (60.0 mL), and
As can be seen from Table 2, mono(formamidinate) complex 1
again turned out to be the most active catalyst. However, while
this advantage of 1 over the new catalysts 3-5 was most
2-(methylamino)pyridine (627 mg, 5.8 mmol). After stirring the mixture at
room temperature overnight, the crude product was filtered off, washed
with cold n-hexane and was obtained as an orange solid (2.56 g, 4.2
mmol, 76 %). For x-ray analysis, the product was recrystallized from
significant at
a
reaction temperature of 60 °C, the
toluene (300 mg in 1 mL, +4 ºC for 48 h, sealed in a glass ampoule) and
hydroamination reactions performed at 80 °C delivered the
products 8a and 8b in comparable combined yields between
1
obtained as red-orange crystals (rods). H NMR (CDCl
3
, 500 MHz): δ =
0
3
7
.89-1.10 (m, 12 H), 1.10-1.29 (m, 12 H), 3.18 (s, 12 H), 3.20 (s, 3 H),
85 % and 90 % with all four catalysts. Interestingly, with regard
.46 (br. s, 4 H), 6.09 (d, J = 8.6 Hz, 1 H), 6.31 (t, J = 6.9 Hz, 1 H), 7.08-
.14 (m, 6 H), 7.36-7.39 (m, 1 H), 7.74 (s, 1 H), 7.93 (d, J = 4.5 Hz, 1 H)
to selectivity, the use of the new catalysts 3-5 offers the
advantage of an improved regioselectivity. For example, at
13
ppm. C NMR (CDCl , DEPT, 125 MHz): δ = 23.8 (CH ), 26.2 (CH ),
3
3
3
80 °C, the regioisomeric products 8a and 8b were obtained in a
3 3
27.4 (CH), 34.8 (CH ), 47.3 (CH ), 100.9 (CH), 109.1 (CH), 123.4 (CH),
ratio of only 95:5 with catalyst 1 (Table 2, entry 2) while the
sterically mostly crowded new catalysts 4 and 5 gave almost
perfect regioselectivities of more than 99:1 (Table 2, entries 6
and 7).
124.1 (CH), 138.3 (CH), 144.2 (C), 144.4 (CH), 145.5 (C), 166.0 (CH),
1
1
1
67.5 (C) ppm. IR (neat, KBr): 1/λ = 3062, 2965, 2856, 2803, 2763, 2665,
601, 1544, 1473, 1449, 1325, 1283, 1261, 1236, 1188, 1149, 1107,
047, 946 cm . MS (ESI+): m/z (%) = 613.4 (<1) [M+Li] , 365.5 (100)
1
+
+
[
[
2,6-diisopropylphenyl-NH
2
-CH=N-2,6-diisopropylphenyl] ,
176.1
(5)
+
+
2,6-diisopropylphenyl-NH] . HRMS (ESI+): calc. ([C35
H
54
N
6
TiLi] )
613.4044; found 613.4046.
Conclusions
Complex 4: An oven-dried Schlenk flask equipped with a stopcock and a
magnetic stirring bar was transferred into a nitrogen-filled glovebox and
charged with 1 (1.09 g, 2.0 mmol), N-phenyl-2-aminopyridine (340 mg,
In summary, we have presented the synthesis of three new
sterically crowded titanium complexes which all possess an
identical formamidinato ligand, two dimethylamido ligands and in
addition, a 2-aminopyridinato ligand that contains either an N-
methyl, an N-phenyl, or an N-cyclohexyl substituent. All new
complexes were easily formed at room temperature from
2.0 mmol), and n-hexane (9.0 mL). The solution was stirred at room
temperature overnight. The product was isolated by filtration (1.30 g, 1.94
mmol, 97 %) and obtained as an orange solid. For x-ray analysis, a
sample of the product was recrystallized from toluene (300 mg in 1 mL,
+
4 °C for 48 h, sealed in a glass ampoule) and obtained as red-orange
1
Eisen´s titanium mono(formamidinate) complex
1
and
3
crystals (blocks). H NMR (CDCl , 500 MHz): δ = 0.92-1.14 (m, 12 H),
correspondingly N-substituted 2-aminopyridines. Although the
solid state structures of the new complexes are very similar to
each other, their catalytic performance in hydroamination and
hydroaminoalkylation reactions slightly differs. Most importantly,
the best regioselectivities for the intermolecular hydroamination
of 1-phenylpropyne with para-toluidine could be achieved with
the sterically mostly crowded new catalysts. Overall, we have
presented a very simple and cheap method for the derivatization
of a catalyst which might prove useful for altering the selectivity
of other highly active catalysts in the future, whenever
dimethylamido spectator ligands are present in the catalyst.
1.14-1.34 (m, 12 H), 3.19 (s, 12 H), 3.50 (br. s, 4 H), 6.34 (d, J = 8.6 Hz,
1 H), 6.38 (t, J = 5.8 Hz, 1 H), 7.02-7.08 (m, 3 H), 7.10-7.18 (m, 6 H),
13
7
(
(
.27-7.31 (m, 3 H), 7.79 (s, 1 H), 8.03 (d, J = 3.2 Hz, 1 H) ppm. C NMR
CDCl , DEPT, 125 MHz): δ = 23.7 (CH ), 26.4 (CH ), 27.5 (CH), 47.9
CH ), 103.7 (CH), 110.3 (CH), 123.1 (CH), 123.4 (CH), 124.3 (CH),
24.5 (CH), 129.0 (CH), 138.4 (CH), 144.1 (C), 144.5 (CH), 145.5 (C),
3
3
3
3
1
1
3
1
48.7 (C), 165.9 (C), 166.3 (CH) ppm. IR (neat, KBr): 1/λ = 3335, 3306,
025, 2963, 2855, 2809, 2762, 1666, 1600, 1565, 1493, 1451, 1369,
318, 1230, 1189, 1150, 942 cm
1
.
Elemental composition: calc.
56 6
(C40H N Ti) C 71.84, H 8.44, N 12.57; found C 71.83, H 9.40, N 12.61.
Complex 5: An oven-dried Schlenk flask equipped with a stopcock and a
magnetic stirring bar was transferred into a nitrogen-filled glovebox and
charged with 1 (1.17 g, 2.2 mmol), toluene (2.2 mL), and N-cyclohexyl-2-
aminopyridine (380 mg, 2.2 mmol). After stirring the mixture at room
temperature overnight, the product was isolated by filtration (627 mg, 0.9
mmol, 42 %) as an orange solid. For x-ray analysis, the product was
recrystallized from toluene (300 mg in 1 mL, +4 °C for 48 h, sealed in a
Experimental Section
General information: For all syntheses of titanium complexes and their
use in catalytic reactions, solvents were dried by refluxing over sodium
and degassed. NMR spectra were recorded on a Bruker Fourier 300,
1
glass ampoule) and obtained as red-orange crystals (plates). H NMR
(
CDCl
3
, 500 MHz): δ = 0.81-1.34 (m, 27 H), 1.56 (q, J = 10.2 Hz, 2 H),
.64 (d, J = 12.8 Hz, 1 H), 1.79 (t, J = 15.0 Hz, 4 H), 3.22 (s, 12 H), 3.33-
.50 (m, 5 H), 6.18-6.24 (m, 2 H), 7.06-7.14 (m, 6 H), 7.26-7.30 (m, 1 H),
1
Bruker Avance DRX 500 or Bruker Avance III 500 MHz. H NMR spectra
1
3
7
=
6
1
13
are referenced to the solvent (7.26 ppm for CDCl
referenced to the solvent (77.16 ppm for CDCl or 128.06 ppm for C
3
). C NMR spectra are
).
6
D
6
13
3
.75 (s, 1 H), 7.92 (br. s, 1 H) ppm. C NMR (C
23.9 (CH ), 26.3 (CH ), 26.8 (CH ), 27.7 (CH), 33.4 (CH
0.3 (CH), 103.7 (CH), 108.4 (CH), 123.9 (CH), 124.9 (CH), 138.2 (CH),
44.0 (C), 144.6 (CH), 146.1 (C), 167.0 (C), 167.3 (CH) ppm. IR (neat,
6 6
D , DEPT, 125 MHz): δ
Infrared spectra were recorded on a Bruker Vector 22 spectrometer. MS
and HRMS analyses were performed on a Waters Q-TOF Premier (ESI+,
TOF). GC analyses were performed on a Shimadzu GC-2010 gas
3
2
2
2
), 48.6 (CH ),
3
chromatograph (column: FS-SE-54-CB-0.25, length
= 29 m, inner
KBr): 1/λ = 3263, 3060, 3023, 2972, 2933, 2866, 2807, 2760, 1667, 1594,
540, 1463, 1435, 1312, 1291, 1266, 1190, 1156, 1131, 1112, 1043, 996,
diameter = 0.32 mm, film thickness = 0.25 μm, (94 %-methyl)-(5 %-
1
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European Journal of Inorganic Chemistry
10.1002/ejic.201900586
FULL PAPER
1
9
45, 897, 824 cm . Elemental composition: calc. (C40
62 6
H N Ti) C 71.19,
H), 3.49 (br. s., 1 H), 3.86-3.89 (m, 1 H), 6.71 (d, J = 8.2 Hz, 2 H), 7.16 (d,
13
H 9.26, N 12.45; found C 70.66, H 9.80, N 12.37.
J = 8.0 Hz, 2 H), 7.32-7.37 (m, 3 H), 7.44 (t, J = 7.4 Hz, 2 H) ppm.
NMR (CDCl , DEPT, 125 MHz): δ = 20.3 (CH ), 20.5 (CH ), 42.4 (CH
49.7 (CH), 113.7 (CH), 126.3 (CH), 126.4 (C), 128.4 (CH), 129.6 (CH),
C
3
3
3
2
),
[
5]
Hydroaminoalkylation of styrene:
equipped with a Teflon stopcock and a magnetic stirring bar was
transferred into a nitrogen-filled glovebox and charged with the catalyst
An oven-dried Schlenk tube
129.9 (CH), 138.7 (C), 145.0 (C) ppm.
[
16] 1
(
10 mol%) and n-hexane (0.5 mL). N-Methylaniline (214 mg, 2.0 mmol),
8b:
3
H NMR (CDCl , 500 MHz): δ = 0.95 (t, J = 7.4 Hz, 3 H), 1.76-1.89
styrene (312 mg, 3.0 mmol), and n-hexane (0.5 mL) were added. The
tube was sealed and the mixture was heated to 140 °C for 96 h. The
mixture was cooled to room temperature and methylene chloride (40 mL)
(m, 2 H), 2.18 (s, 3 H), 4.20 (t, J = 6.7 Hz, 1 H), 6.44 (d, J = 8.4 Hz, 2 H),
6.89 (d, J = 8.1 Hz, 2 H), 7.19-7.23 (m, 1 H), 7.25-7.27 (m, 1 H), 7.28-
13
3 3
7.36 (m, 4 H) ppm. C NMR (CDCl , DEPT, 125 MHz): δ = 10.9 (CH ),
was added. The products were purified by flash chromatography (SiO
light petroleum ether/EtOAc = 20/1) and were isolated as yellow oils.
2
,
20.5 (CH ), 31.8 (CH ), 60.2 (CH), 113.5 (CH), 126.4 (CH), 126.7 (C),
126.9 (CH), 128.6 (CH), 129.7 (CH), 144.3 (C), 145.4 (C) ppm.
3
2
[
5] 1
6
3
a: H NMR (CDCl , 500 MHz): δ = 1.27 (d, J = 7.0 Hz, 3 H), 2.99 (sext,
J = 6.9 Hz, 1 H), 3.17 (dd, J = 12.4 Hz, 8.2 Hz, 1 H), 3.27 (dd, J = 12.4
Hz, 6.3 Hz, 1 H), 3.49 (br. s., 1 H), 6.49-6.51 (m, 2 H), 6.64 (t, J = 7.3 Hz,
Acknowledgments
1
H), 7.11 (t, J = 7.4 Hz, 1 H), 7.16-7.19 (m, 3 H), 7.25-7.28 (m, 2 H) ppm.
13
We thank the Deutsche Forschungsgemeinschaft for financial
support of our research as well as Francesco Fabbretti for his
help recording HRMS analyses.
C NMR (CDCl
CH ), 113.0 (CH), 117.3 (CH), 126.7 (CH), 127.3 (CH), 128.7 (CH),
29.3 (CH), 144.6 (C), 148.2 (C) ppm.
3 3
, JMOD, 125 MHz): δ = 19.8 (CH ), 39.2 (CH), 50.9
(
2
1
[
5] 1
6
3
b: H NMR (CDCl , 500 MHz): δ = 1.91 (pent, J = 7.2 Hz, 2 H), 2.70 (t,
Keywords: alkenes • alkynes • hydroamination •
J = 7.4 Hz, 2 H), 3.10 (t, J = 7.0 Hz, 2 H), 3.54 (br. s, 1 H), 6.54 (d, J =
.7 Hz, 2 H), 6.67 (t, J = 7.3 Hz, 1 H), 7.12-7.19 (m, 5 H), 7.25-7.28 (m, 2
hydroaminoalkylation • titanium
7
13
H) ppm. C NMR (CDCl
3
, JMOD, 125 MHz): δ = 31.1 (CH
), 112.8 (CH), 117.3 (CH), 126.0 (CH), 128.5 (CH), 128.5 (CH),
29.3 (CH), 141.8 (C), 148.4 (C) ppm.
2 2
), 33.5 (CH ),
[
[
1]
2]
T. Elkin, N. V. Kulkarni, B. Tumanskii, M. Botoshansky, L. J. W. Shimon,
M. S. Eisen, Organometallics 2013, 32, 6337-6352.
43.5 (CH
2
1
For reviews on hydroaminoalkylation reactions of alkenes, see: a) E.
Chong, P. Garcia, L. L. Schafer, Synthesis 2014, 46, 2884-2896; b) J.
Hannedouche, E. Schulz, Organometallics 2018, 37, 4313-4326; c) P.
M. Edwards, L. L. Schafer, Chem. Commun. 2018, 54, 12543-12560.
For selected examples of late transition metal-catalyzed
hydroaminoalkylation reactions of alkenes, see: a) A. T. Tran, J.-Q. Yu,
Angew. Chem. 2017, 129, 10666-10670; Angew. Chem. Int. Ed. 2017,
[
9b]
Hydroaminoalkylation of 1-octene:
An oven-dried 1 mL-ampoule
was transferred into a nitrogen-filled glovebox and charged with the
catalyst (2.5 mol%). N-Methylaniline (21 mg, 0.2 mmol), 1-octene (31 mg,
[3]
0.3 mmol), and toluene (0.1 mL) were added. The ampoule was sealed
and the mixture was heated to 140 °C for 96 h. The mixture was cooled
to room temperature and methylene chloride (5 mL) was added. The
56, 10530-10534; b) M. Spettel, R. Pollice, M. Schnürch, Org. Lett.
2017, 19, 4287-4290; c) S. M. Thullen, T. Rovis, J. Am. Chem. Soc.
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4201-4203; e) M. Schinkel, L. Wang, K. Bielefeld, L. Ackermann, Org.
product was purified by flash chromatography (SiO
ether/EtOAc = 20/1) and was isolated as colorless oil.
2
, light petroleum
[
9b] 1
7a:
3
H NMR (CDCl , 500 MHz): δ = 0.91 (t, J = 7.0 Hz, 3 H), 0.99 (d, J
Lett. 2014, 16, 1876-1879; f) A. A. Kulago, B. F. Van Steijvoort, E. A.
Mitchell, L. Meerpoel, B. U. W. Maes, Adv. Synth. Catal. 2014, 356,
=
6.7 Hz, 3 H), 1.17-1.49 (m, 10 H), 1.76 (oct, J = 6.6 Hz, 1 H), 2.91 (dd,
J = 12.2 Hz, 7.3 Hz, 1 H), 3.08 (dd, J = 12.2 Hz, 5.9 Hz, 1 H), 3.94 (br. s,
1610-1618.
1
2
H), 6.64 (d, J = 7.9 Hz, 2 H), 6.71 (t, J = 7.3 Hz, 1 H), 7.19 (t, J = 8.3 Hz,
[4]
For examples of group 5 metal catalysts for hydroaminoalkylation
reactions of alkenes, see: R. C. DiPucchio, S.-C. Rosca, G. Athavan, L.
L. Schafer, ChemCatChem 2019, 11, DOI: 10.1002/cctc.201900398
and references cited therein.
13
H) ppm. C NMR (CDCl
3
, JMOD, 125 MHz): δ = 14.2 (CH
), 29.7 (CH ), 32.0 (CH ), 33.0 (CH), 34.9
), 113.0 (CH), 117.3 (CH), 129.4 (CH), 148.5 (C) ppm.
3
), 18.2
(CH
CH
3
), 22.8 (CH
), 50.7 (CH
2
), 27.1 (CH
2
2
2
(
2
2
[5]
[6]
[7]
J. Dörfler, T. Preuß, C. Brahms, D. Scheuer, S. Doye, Dalton Trans.
Hydroamination of 1-phenylpropyne and subsequent imine
2
015, 44, 12149-12168.
I. Prochnow, P. Zark, T. Müller, S. Doye, Angew. Chem. 2011, 123,
525-6529; Angew. Chem. Int. Ed. 2011, 50, 6401-6405
[
16]
reduction:
An oven dried Schlenk tube equipped with a Teflon
stopcock and a magnetic stirring bar was transferred into a nitrogen-filled
glovebox and charged with the catalyst (5 mol%), 1-phenylpropyne (279
mg, 2.4 mmol), p-toluidine (283 mg, 2.6 mmol), and toluene (1 mL). The
tube was sealed and the mixture was heated to 60 °C or 80 °C for 24 h.
6
M. Manßen, N. Lauterbach, J. Dörfler, M. Schmidtmann, W. Saak, S.
Doye, R. Beckhaus Angew. Chem. 2015, 127, 4458-4462; Angew.
Chem. Int. Ed. 2015, 54, 4383-4387.
The mixture was cooled to room temperature and then NaBH
mg, 4.8 mmol), anhydrous ZnCl (327 mg, 2.4 mmol), and methanol (10
mL) were added. After the mixture had been stirred at 25 C for 20 h,
methylene chloride (40 mL) and saturated aqueous Na CO -solution (50
mL) were added. The organic layer was separated and the aqueous layer
was extracted with methylene chloride (5 × 20 mL). The combined
3
CN (302
[
[
[
8]
For reviews on aminopyridinato ligands, see: a) R. Kempe, Eur. J. Inorg.
Chem. 2003, 791-803; b) R. Kempe, N. Hoss, T. Irrgang, J. Organomet.
Chem. 2002, 647, 12-20; c) R. Kempe, Z. Anorg. Allg. Chem. 2010, 636,
2
2
3
2135-2147.
9]
a) J. Dörfler, S. Doye, Angew. Chem. 2013, 125, 1851-1854; Angew.
Chem. Int. Ed. 2013, 52, 1806-1809; b) J. Dörfler, T. Preuß, A.
Schischko, M. Schmidtmann, S. Doye, Angew. Chem. 2014, 126, 8052-
organic layers were dried with MgSO
vacuum, the residue was purified by flash chromatography (SiO
petroleum ether/EtOAc = 20/1) to give the products as yellow liquids.
4
and, after concentration under
2
, light
8056; Angew. Chem. Int. Ed. 2014, 53, 7918-7922.
10] J. A. Bexrud, P. Eisenberger, D. C. Leitch, P. P. Payne, L. L. Schafer, J.
Am. Chem. Soc. 2009, 131, 2116-2118.
[
16] 1
8a:
3
H NMR (CDCl , 500 MHz): δ = 1.28 (d, J = 6.3 Hz, 3 H), 2.40 (s, 3
[11] CCDC 1915106 (3), CCDC 1915107 (4), and CCDC 1915109 (5)
contain the supplementary crystallographic data for compounds 3, 4
H), 2.82 (dd, J = 7.3 Hz, 13.3 Hz, 1 H), 3.07 (dd, J = 4.6 Hz, 13.3 Hz, 1
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European Journal of Inorganic Chemistry
10.1002/ejic.201900586
FULL PAPER
and 5. These data can be obtained free of charge from The Cambridge
3389-3391; b) A. Heutling, S. Doye, J. Org. Chem. 2002, 67, 1961-
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
1964.
[
12] For selected reviews on hydroamination reactions, see: a) A. L.
Reznichenko, K. C. Hultzsch, Org. React. 2015, 88, 1-554; b) T. E.
Müller, K. C. Hultzsch, M. Yus, F. Foubelo, M. Tada, Chem. Rev. 2008,
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1
407-1420; d) S. Doye, Synlett 2004,1653-1672.
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7583-7592.
[
2 2 2 2
13] For a comparison between Cp TiMe and Cp* TiMe as catalysts for the
hydroamination of alkynes, see: a) E. Haak, I. Bytschkov, S. Doye,
Angew. Chem. 1999, 111, 3584-3586; Angew. Chem. Int. Ed. 1999, 38,
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European Journal of Inorganic Chemistry
10.1002/ejic.201900586
FULL PAPER
Entry for the Table of Contents
Layout 1:
FULL PAPER
Three new sterically crowded titanium
complexes which all possess an
identical formamidinato ligand, two
dimethylamido ligands and in addition,
a 2-aminopyridinato-ligand that
contains either an N-methyl, an N-
phenyl, or an N-cyclohexyl substituent
are easily accessible from a common
titanium mono(formamidinate)
Alkene Hydroaminoalkylation
J. Bielefeld, E. Kurochkina, M.
Schmidtmann, S. Doye*
Page No. – Page No.
New Titanium Complexes and Their
Use in Hydroamination and
Hydroaminoalkylation Reactions
precursor and correspondingly N-
substituted 2-aminopyridines.
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