Neutral Ti complexes as catalysts for the hydroamination of alkynes and alkenes: Do the labile ligands change the catalytic activity?

Article abstract of DOI:10.1002/ejoc.200800471

A detailed comparison between three four-coordinate Ti complexes featuring the general bidentate ligand [η⁵-(C₅H ₄)-SiMe₂-NtBu]^2- and two ligands X (NMe ₂, Me, Cl) as catalyst precursors (I-III) for the intermolecular hydroamination of alkynes and the intramolecular hydroamination of alkenes is presented. The results strongly suggest that the catalytically active species are only identical for reactions performed with the bis(dimethylamido) complex I or the dimethyl complex II. Under the reaction conditions, the labile ligands X are proteolytically removed by the reacting amine to form catalytically active imido or amido complexes, together with dimethylamine or methane. Although both catalyst precursors can be used successfully for many substrate combinations, the preparative and kinetic studies clearly indicate that dimethylamine, which is formed from the bis(dimethylamido) catalyst precursor I and the reacting amine, is able to convert the catalytically active imido or amido complexes back into the catalyst precursor and therefore inhibits the reactions. As a consequence, the bis(dimethylamido) catalyst precursor I shows a poorer catalytic performance than the corresponding dimethyl complex II. Additionally, it is shown that the dichloro complex III is only a suitable catalyst precursor for selected hydroamination reactions. Corresponding reactions that are more difficult to achieve - such as reactions of diarylalkynes or amino alkenes - do not work efficiently with this complex. A possible explanation for this observation is the finding that the dichloro catalyst precursor III is obviously converted into a different catalytically active species. This can happen if the [η⁵-(C₅H₄)-SiMe₂-NtBu]-ligand system of the catalyst precursor is being destroyed and removed from the Ti center under the reaction conditions. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800471

FULL PAPER
DOI: 10.1002/ejoc.200800471
Neutral Ti Complexes as Catalysts for the Hydroamination of Alkynes and
Alkenes: Do the Labile Ligands Change the Catalytic Activity?
Kerstin Gräbe,[a] Frauke Pohlki,[b] and Sven Doye*[a]
Keywords: Alkynes / Amines / Hydroamination / Homogeneous catalysis / Titanium
A detailed comparison between three four-coordinate Ti
complexes featuring the general bidentate ligand [η5-(C5H4)-
SiMe2-NtBu]2– and two ligands X (NMe2, Me, Cl) as catalyst
the catalyst precursor and therefore inhibits the reactions. As
a consequence, the bis(dimethylamido) catalyst precursor I
shows a poorer catalytic performance than the corresponding
precursors (I–III) for the intermolecular hydroamination of al- dimethyl complex II. Additionally, it is shown that the
kynes and the intramolecular hydroamination of alkenes is
presented. The results strongly suggest that the catalytically
active species are only identical for reactions performed with
the bis(dimethylamido) complex I or the dimethyl complex
II. Under the reaction conditions, the labile ligands X are
dichloro complex III is only a suitable catalyst precursor for
selected hydroamination reactions. Corresponding reactions
that are more difficult to achieve – such as reactions of di-
arylalkynes or amino alkenes – do not work efficiently with
this complex. A possible explanation for this observation is
proteolytically removed by the reacting amine to form cata- the finding that the dichloro catalyst precursor III is obvi-
lytically active imido or amido complexes, together with di-
methylamine or methane. Although both catalyst precursors
can be used successfully for many substrate combinations,
the preparative and kinetic studies clearly indicate that di-
methylamine, which is formed from the bis(dimethylamido)
catalyst precursor I and the reacting amine, is able to convert
the catalytically active imido or amido complexes back into
ously converted into a different catalytically active species.
This can happen if the [η5-(C5H4)-SiMe2-NtBu]-ligand sys-
tem of the catalyst precursor is being destroyed and removed
from the Ti center under the reaction conditions.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
other hand, one can argue that the generation of the imido
complex also results in the formation of two equivalents of
HX, which can interfere with the catalytic system and slow
down the reaction. One possible scenario is that HX present
in the reaction mixture converts the imido complex V back
into the catalytically inactive amido complex IV–X, or even
back into the catalyst precursor, and therefore inhibits the
reaction. Consequently, the catalytic performance will be
directly influenced by the ability of HX to undergo an ad-
dition reaction to the electrophilic imido complex V. In this
context, it must be noted that Marks and co-workers have
recently suggested that a Zr-chloride complex with a struc-
ture comparable to IV–Cl can mediate intramolecular hy-
droamination reactions of alkenes and alkynes through a σ-
bond insertion reaction of the alkene or the alkyne into the
Zr–N single bond.[4] Consequently, the Ti-amido complex
IV–X can also be regarded as a possible catalytically active
species of the hydroamination reactions. However, even in
this case, the formation of IV–X from the catalyst precursor
and the amine substrate generates one equivalent of HX,
which can interfere with the catalytic system (e.g., the HX
can inhibit the hydroamination by converting IV–X back
into the catalyst precursor). Consequently, the ability of HX
to react with amido complex IV–X can also directly influ-
ence the catalytic performance.
Introduction
The Ti-catalyzed hydroamination of alkynes[1] has at-
tracted much attention during the past few years. Extensive
mechanistic investigations are consistent with a catalytic cy-
cle that involves three-coordinate Ti-imido complexes (e.g.,
V, Scheme 1) as catalytically active species.[2] Although
some examples in which the corresponding Ti-imido com-
plexes have been directly used as hydroamination catalysts
are known,[3] most reports describe the use of four-coordi-
nate Ti complexes bearing two labile ligands X (Me, NMe2,
or Cl) as catalyst precursors (e.g. I–III). For these catalytic
systems, it is assumed that in the presence of a primary
amine the labile ligands X are proteolytically removed to
form the catalytically active imido complex V, together with
two equivalents of HX (methane, dimethylamine, or HCl).
In principle, variation of the labile ligands X should not
alter the catalytically active species and therefore should not
result in significant changes in the catalytic activity. On the
[a] Institut für Reine und Angewandte Chemie, Universität
Oldenburg,
Carl-von-Ossietzky-Str. 9–11, 26111 Oldenburg, Germany
Fax: +49-441-798-3329
E-mail: doye@uni-oldenburg.de
[b] Current address: Abbott GmbH & Co. KG,
Knollstrasse, 67061 Ludwigshafen, Germany
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K. Gräbe, F. Pohlki, S. Doye
FULL PAPER
imine with NaBH3CN and ZnCl2 in methanol, the second-
ary amines 8–13 were isolated. As can be seen from Table 1,
the dichloro complex III was only able to catalyze a single
transformation of diphenylacetylene (1). However, the yield
for the addition of oct-1-ylamine (7) to 1 is only 19% (En-
try 18).
Table 1. Intermolecular hydroamination of diphenylacetylene (1)
with various amines 2–7 in the presence of the catalysts I–III.
Scheme 1. Possible catalyst precursors I–III for the hydroamination
of alkynes.
The suggested possibility of inhibition of the hydroamin-
ation through some reaction between HX and catalytically
active Ti-imido or Ti-amido complexes leads to the assump-
tion that the efficiency of the catalytic reaction should de-
crease with increasing ability of HX to react with the imido
or amido complex. Of the three possibilities – methane, di-
methylamine, and HCl – the last two are known to undergo
facile addition reactions with Ti-imido complexes,[5]
whereas the corresponding C–H activation of methane is
far more difficult to achieve.[6] Since a corresponding reac-
tivity trend would also be expected for Ti-amido complexes
of type IV–X, our prediction was that the dimethyl complex
II should show the best catalytic performance. In addition,
HCl must be considered far more reactive towards imido or
amido Ti complexes than dimethylamine, and so the
dichloro complex III would be expected to be the worst
hydroamination catalyst. Furthermore, and regardless of
the mechanistic details, it is also possible that the HX
formed from the catalyst precursor might react with other
intermediates of the catalytic cycle and therefore influence
the rate and the selectivity of the hydroamination. Ad-
ditionally, the induction period needed for the conversion
of the catalyst precursor into the imido complex V or the
amido complex IV–X would be expected to be strongly in-
fluenced by the stabilities of the Ti–X bonds.[7]
Interestingly, no corresponding study comparing the ac-
tivities of catalyst precursors that differ only in the natures
of the labile ligands X has yet been reported. In this publi-
cation we describe a detailed comparison of the three hy-
droamination catalysts I, II, and III (Scheme 1), featuring
the common bidentate ligand [η5-(C5H4)-SiMe2-NtBu]2– to-
gether with labile dimethylamido, methyl, or chloro li-
gands,[8] respectively.
[a] Reaction conditions: 1) alkyne
1
(2.40 mmol), amine
(2.64 mmol), catalyst (0.12 mmol, 5 mol-%), toluene (1.0 mL),
105 °C, 24 h; 2) NaBH3CN (4.80 mmol), ZnCl2 (2.40 mmol),
MeOH (10 mL), 25 °C, 24 h. Yields refer to isolated pure com-
pounds.
Results and Discussion
Initial hydroamination reactions were performed with di-
phenylacetylene (1) and p-toluidine (2), o-toluidine (3), tert-
butylamine (4), cyclopentylamine (5), benzylamine (6), or
oct-1-ylamine (7). All experiments were run at 105 °C for
On the other hand, the reactions of the sterically de-
24 h in the presence of 5 mol-% of one of the catalysts I, manding amines 2–5 in the presence of the bis(dimethyl-
II, or III. After subsequent reduction of the initially formed amido) complex I or the dimethyl complex II resulted in
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Labile Ligands and Catalytic Activity of Neutral Ti Complexes
the formation of the desired products 8–11 in very good to yield of 93%. These results clearly show that no H+-cata-
excellent yields. Although the yields obtained with these lyzed process is operative when the dichloro complex III is
two catalysts do not differ dramatically, it is worth men- used as the catalyst precursor. This last result also suggests
tioning that a slightly better result is always obtained with that the presence of a non-nucleophilic base slightly acceler-
the dimethyl complex II. A much stronger difference be- ates the catalytic reaction. Another interesting point is the
tween I and II was observed when the sterically less hin- fact that the hydroamination of 14 with 2 takes place with
dered benzylamine (6) was employed (Entries 13, 14). In a surprisingly low regioselectivity of only 93:7 when the
this case, the dimethyl complex II gave a much better yield dichloro complex III is used [91:9 in the presence of 1,8-
of the product 12 (95%) than the bis(dimethylamido) com- bis(dimethylamino)naphthalene]. In comparison, the anti-
plex I (11%). However, in this context it must be noted that Markovnikov regioisomer is formed almost exclusively
sterically less demanding amines such as benzylamine (6) (99:1) in the presence of catalysts I and II. The best yield
have often been recognized as poor substrates for Ti-cata- (96%, Entry 4) was again obtained with the dimethyl com-
lyzed intermolecular hydroamination reactions of alkynes.[9] plex II.
Obviously, the bis(dimethylamido) complex I is far more
sensitive than the dimethyl complex II to the negative influ-
ence caused by this amine. Surprisingly, and in contrast
with the results obtained with benzylamine (6), no big dif-
Table 2. Intermolecular hydroamination of 1-phenylpropyne (14)
with p-toluidine (2) in the presence of the catalysts I–III.
ference between I and II was observed when oct-1-ylamine
(7) was used as the amine (Entries 16, 17). Furthermore, it
must be noted that in this case a slightly improved yield is
obtained with catalyst precursor I.
One possible explanation for the lack of activity of the
dichloro catalyst precursor III in addition reactions of the
amines 2–6 to diphenylacetylene (1) would be a lack of for-
Entry
Catalyst Yield (15a+15b) [%][a]
Ratio (15a/15b)[b]
mation of the catalytically active species under the reaction
conditions. Consequently, the catalytic hydroamination of
the alkyne 1 would not be able to take place. In order to
verify this assumption, we turned our attention towards the
reaction between 1-phenylpropyne (14) and p-toluidine (2,
Table 2). Surprisingly, we found that the dichloro complex
III does catalyze the addition of p-toluidine (2) to 1-phenyl-
propyne (14) with high efficiency (Entry 7, 82% yield). First
of all, this result clearly shows that the dichloro complex III
is converted into a catalytically active species under these
reaction conditions when p-toluidine (2) is used as the
amine. However, the fact that the corresponding reaction
with diphenylacetylene (1, Table 1, Entry 3) does not give
the desired hydroamination product suggests that the gener-
ated catalytically active species does not undergo any fur-
ther reaction with this alkyne while it does react with 1-
phenylpropyne (14). This interpretation is in agreement
with the well established fact that 1-phenylpropyne (14) is
1
I
I
91
87
66
96
85
59
82
93
99:1
99:1
99:1
99:1
99:1
98:2
93:7
91:9
2[c]
3[d]
4
I
II
II
II
III
III
5[c]
6[d]
7
8[e]
[a] Reaction conditions: 1) alkyne 14 (2.40 mmol), amine
2
(2.64 mmol), catalyst (0.12 mmol, 5 mol-%), toluene (1.0 mL),
105 °C, 24 h; 2) NaBH3CN (4.80 mmol), ZnCl2 (2.40 mmol),
MeOH (10 mL), 25 °C, 24 h. Yields refer to isolated pure com-
pounds. [b] Determined by GC prior to chromatography. [c] Reac-
tion performed in the presence of 10 mol-% of pyrrolidine. [d] Re-
action performed in the presence of 25 mol-% of pyrrolidine. [e] Re-
action performed in the presence of 10 mol-% of 1,8-bis(dimethyla-
mino)naphthalene.
Because our preparative studies did not so far clearly
far more reactive than diphenylacetylene (1) in Ti-catalyzed support the prediction that the catalytic efficiency should
intermolecular hydroaminations.[10] Consequently, one can decrease from the dimethyl complex II through the bis(di-
assume that the dichloro complex III is only a suitable hy- methylamido) complex I to the dichloro complex III, we
droamination catalyst for alkynes that are known to display performed additional kinetic investigations to compare the
improved reactivity in hydroamination reactions, such as 1- catalysts I, II, and III directly. For this purpose, we per-
alkyl-2-arylalkynes and terminal alkynes (vide infra). The formed hydroamination reactions of 1-phenylpropyne (14)
possibility that the reaction in the presence of the catalyst- with p-toluidine (2) under identical reaction conditions with
precursor III might take place through a simple H+-cata- constant catalyst concentrations (5 mol-%). Monitoring of
1
lyzed addition[11] of p-toluidine (7) to 1-phenylpropyne (12) the alkyne concentration by H NMR spectroscopy (Fig-
was ruled out at the start by a control experiment per- ure 1) revealed that the reaction catalyzed by II is indeed
formed under identical conditions with 10 mol-% p-tolu- significantly faster than identical reactions catalyzed by I or
idine hydrochloride instead of 5 mol-% III. In this case, no III. Furthermore, a significant induction period was ob-
hydroamination reaction was observed. Furthermore, an served in the case of the dichloro complex III. As expected,
experiment performed with 5 mol-% III and 10 mol-% 1,8- analysis of the kinetic data showed that all reactions are
bis(dimethylamino)naphthalene (proton sponge, Entry 8) first-order in the concentration of alkyne 14 (Figure 2).
gave the desired hydroamination product in an improved However, the calculated rate constants show that the di-
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K. Gräbe, F. Pohlki, S. Doye
FULL PAPER
methyl complex II is approximately 1.5 times more active (vide supra), in which no catalyst precursor could be ob-
1
than the corresponding bis(dimethylamido) complex I and served by either 29Si, H, or 13C NMR spectroscopy. This
7 times more active than the dichloro complex III.
interpretation also explains the finding of Schafer et al.[12]
that preformed Ti- and Zr-imido complexes show improved
catalytic activities in relation to corresponding bis(dimethy-
lamido) complexes. While the NMR studies suggest that for
reactions performed in the presence of I or II the catalyti-
cally active species are identical, this seems not to be the
case when the dichloro precursor III is employed. A dif-
ferent signal at δ = 20.8 ppm was observed by in situ 29Si
NMR (27% conversion, 3 h reaction time) when III was
used as the catalyst precursor (23 mol-%), and correspond-
1
ing differences were also observed by H and 13C NMR
spectroscopy. A possible explanation could be that under
these reaction conditions the [η5-(C5H4)-SiMe2-NtBu] li-
gand system is destroyed and removed from the Ti center.
Consequently, at the moment, we are not sure whether the
chloro ligands, or parts of the [η5-(C5H4)-SiMe2-NtBu] li-
gand system, or both represent the labile ligands that are
exchanged by the reacting amine. This unexpected result
makes it impossible to compare the catalytic performance
of the dichloro catalyst precursor III directly with that of I
or II because obviously different catalytically active species
are involved. From a mechanistic point of view, it is also
worth mentioning that no free [(C5H5)-SiMe2-NHtBu] li-
gand was observed during any of the NMR studies.
Figure 1. Plot of c(14)/c0(14) vs. t for the catalysts I (᭡), II (᭿),
and III (o).
In order to verify the assumption that the dimethylamine
formed from the catalyst precursor I and amine 2 under the
reaction conditions is responsible for the decreased activity
of catalyst precursor I, we performed additional hydroa-
mination reactions of 1-phenylpropyne (14) with p-toluidine
(2) in the presence of pyrrolidine. This amine, which was
selected as an example of a more nucleophilic secondary
amine, is believed to inhibit the hydroamination reaction
because it can convert catalytically active imido or amido
complexes into inactive bisamides of type I. First of all, it
can be seen from Table 2 (Entries 4–6) that the presence of
10 or 25 mol-% pyrrolidine significantly inhibits the hydro-
Figure 2. First-order plot {–ln [c(14)/c0(14)] vs. t} for the catalysts
I (᭡), II (᭿), and III (o).
However, more detailed in situ NMR studies revealed a amination reaction performed in the presence of the di-
number of additional pieces of mechanistic information. methyl catalyst precursor II. While the regioselectivity of
During a hydroamination of 14 with 2 performed in the the reaction is not significantly changed by the additive, the
presence of 22 mol-% of the dimethyl catalyst precursor II yield of the isolated product 15a drops from 96% in the
at 90 °C in C6D6, a single species was observed by in situ absence of pyrrolidine through 85% in the presence of
29Si NMR (65% conversion, 45 min reaction time) at δ = 10 mol-% pyrrolidine to only 59% when 25 mol-% pyrroli-
17.4 ppm (relative to the signal of TMS at δ = 0.00 ppm). dine is present. The fact that corresponding behavior is also
When the bis(dimethylamido) complex I (23 mol-%) was observed for the bis(dimethylamido) complex I (Entries 1–
employed, the same signal at δ = 17.4 ppm was observed 3) strongly supports the idea that nucleophilic secondary
(70% conversion, 2 h reaction time) along with an ad- amines such as pyrrolidine or dimethylamine can convert
ditional signal at 5.9 ppm for the catalyst precursor I, a the catalytically active species into inactive Ti complexes
finding in agreement with corresponding in situ 1H and 13
C
when they are present in the reaction mixture. Conse-
NMR spectra. In addition, free dimethylamine was ob- quently, their presence slows down the catalytic reaction.
served in the 1H (δ =2.14 ppm) and 13C NMR (δ Since dimethylamine is always formed during reactions that
=38.7 ppm) spectra. These observations strongly support employ the bis(dimethylamido) complex I as the catalyst
the idea that the dimethylamine formed during the reaction precursor, the decreased efficiency of I relative to the di-
converts the catalytically active imido or amido species methyl complex II can easily be understood.
back into the catalyst precursor I and therefore inhibits the
The suggestion that the dichloro complex III, regardless
catalytic reaction. Consequently, the reaction performed in of the structure of the catalytically active species, is only a
the presence of I is slower than that in the presence of II suitable hydroamination catalyst for alkynes that are known
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Labile Ligands and Catalytic Activity of Neutral Ti Complexes
to possess improved reactivity in hydroamination reactions Table 3. Intermolecular hydroamination reaction of oct-1-yne (16)
with various amines (2–6) in the presence of the catalysts I–III.
(vide supra) was verified in a number of transformations of
the terminal alkyne oct-1-yne (16, Table 3). As predicted,
all amines tested (2–6) underwent successful hydroamina-
tions of 16 in the presence of 5 mol-% of the dichloro com-
plex III. However, with two exceptions (Entries 9 and 15),
better yields were usually obtained with the bis(dimethyla-
mido) complex I or the dimethyl complex II. Of these two
catalysts, the dimethyl complex II again turned out to be
Entry R (amine)
Catalyst Product Yield (a+b) [%][a] Ratio (a/b)[b]
the more active one. Another interesting point is the fact
that the use of complexes I and II led to identical regioselec-
tivities (within experimental error) for reactions of amines
2–5, behavior consistent with the idea that identical catalyti-
cally active species are present in reactions performed with
I or II. Again, significant mechanistic changes obviously do
not take place when the labile ligands are exchanged from
methyl to dimethylamido groups (and vice versa). In con-
trast, hydroamination reactions with p-toluidine (2, En-
tries 1–3) or cyclopentylamine (5, Entries 10–12) performed
in the presence of the dichloro complex III were found to
take place with significantly changed regioselectivities. This
observation, which had already been made in the case of
reactions of 1-phenylpropyne (14, Table 2), strongly sup-
ports the results of the NMR studies, which suggest that
the catalytically active species formed from III is different
from the other two catalyst precursors. Interestingly, and in
contrast with the reactions of 1-phenylpropyne (14,
Table 2), in this case the reactions of oct-1-yne (16) take
place with improved regioselectivity. In addition, identical
(and excellent) regioselectivities were observed with all three
catalysts in reactions employing o-toluidine (3, Entries 4–
6) or tert-butylamine (4, Entries 7–9). In general, all these
observations are in agreement with the well established fact
that Ti-catalyzed hydroamination reactions of terminal
alkyl alkynes with arylamines are Markovnikov-selective
(Entries 1–6) and the corresponding reactions with alk-
ylamines (Entries 7–12) are anti-Markovnikov-selec-
tive.[9c,13] In both cases, better regioselectivities are obtained
with sterically more demanding amines.
Surprisingly, the results obtained with benzylamine (6,
Entries 13–15) do not show the same trend. Although all
yields are low and all regioselectivities are close to a ratio
of 1:1, the bis(dimethylamido) complex I and the dimethyl
complex II obviously do not give the same regioselectivity.
However, this small difference in regioselectivity is in agree-
ment with the difference in yield observed in hydroamin-
ation reactions of diphenylacetylene (1) with benzylamine
(6, Table 1, Entries 13, 14). A possible explanation for both
findings is that the dimethylamine generated from the
bis(dimethylamido) complex I is able to interfere signifi-
cantly with the catalytic system in reactions of benzylamine.
This possibility can be understood in view of the fact that
benzylamine (6) is known to be a poor substrate for Ti-
catalyzed intermolecular hydroamination reactions of al-
kynes.[6] Consequently, one can imagine that at some stage
of the catalytic cycle the dimethylamine is able to compete
with benzylamine and therefore influences not only the effi-
ciency, but also the selectivity, of the process.
1
2
3
4
5
6
7
8
pTol (2)
I
II
III
I
II
III
I
II
III
I
II
III
I
17a/b
18a/b
19a/b
20a/b
21a/b
92
95
45
80
94
90
65
81
91
79
99
51
31
42
49
17:83
17:83
3:97
Ͻ 1:99
Ͻ 1:99
Ͻ 1:99
Ͼ 99:1
Ͼ 99:1
Ͼ 99:1
65:35
oTol (3)
tBu (4)
9
10
11
12
13
14
15
cyclopentyl (5)
Bn (6)
66:34
82:18
57:43
43:57
II
III
48:52
[a] Reaction conditions: 1) alkyne 16 (2.40 mmol), amine
(2.64 mmol), catalyst (0.12 mmol, 5 mol-%), toluene (1.0 mL),
105 °C, 24 h; 2) NaBH3CN (4.80 mmol), ZnCl2 (2.40 mmol),
MeOH (10 mL), 25 °C, 24 h. Yields refer to isolated pure com-
pounds. It was not possible to recover any unreacted alkyne. [b] De-
termined by GC prior to chromatography.
Finally, we turned our attention towards the intramolec-
ular hydroamination of amino alkene 22 (Table 4). Since
only a few neutral Ti catalysts for this difficult transforma-
tion have been identified,[14] it is not very surprising that in
this case the dichloro complex III does not show any cata-
lytic activity. On the other hand, the bis(dimethylamido)
complex I and the dimethyl complex II both do catalyze the
hydroamination/cyclization of 22. Again, however, a better
yield is obtained with the dimethyl complex II.
Table 4. Intramolecular hydroamination of 1-amino-2,2-di-
phenylpent-4-ene (22) in the presence of the catalysts I–III.
Entry
Catalyst
Yield (23) [%][a]
Recovered 22 [%]
1
2
3
I
II
26
74
–
72
16
100
III
[a] Reaction conditions: 1) amino alkene 22 (2.40 mmol), catalyst
(0.12 mmol, 5 mol-%), toluene (1.0 mL), 105 °C, 24 h. Yields refer
to isolated pure compounds.
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K. Gräbe, F. Pohlki, S. Doye
FULL PAPER
ing spectrometers: Bruker Avance DPX 300, Bruker Avance
DRX 500. All H NMR spectra are reported in δ units (ppm) rela-
Conclusions
1
tive to the signal of TMS at δ = 0.00 ppm. All 13C NMR spectra
are reported in δ units (ppm) relative to the central line of the
triplet for CDCl3 at δ = 77.0 ppm or C6D6 at δ = 128.0 ppm. NMR
spectroscopic data recorded for kinetic studies are reported in δ
units (ppm) relative to the signal of ferrocene (internal standard)
at δ = 4.00 ppm. Infrared spectra were recorded on a Bruker Ten-
sor 27 spectrometer by an attenuated total reflection (ATR)
method. Mass spectra were recorded on a Finnigan MAT 95 spec-
trometer (EI with an ionization potential of 70 eV or CI with isobu-
tane as ionization gas). Elemental analyses were carried out on a
Euro EA 3000 machine. GC analyses were performed on a Shim-
adzu GC-2010 gas chromatograph fitted with a flame ionization
detector. PE: light petroleum ether, b.p. 40–60 °C.
In summary, we have presented a comparison of three
four-coordinate Ti complexes featuring the common biden-
tate ligand [η5-(C5H4)-SiMe2-NtBu]2– together with two li-
gands X (NMe2, Me, Cl) as catalyst precursors I–III for the
intermolecular hydroamination of alkynes and the intramo-
lecular hydroamination of alkenes. Our results strongly sug-
gest that for reactions performed with the bis(dimethyl-
amido) complex I or the dimethyl complex II, the catalyti-
cally active species are identical. Under the reaction condi-
tions, the ligands X are proteolytically removed by the re-
acting amine to form catalytically active imido or amido
complexes, together with dimethylamine or methane. Both
catalyst precursors can be used successfully for many sub-
strate combinations. However, the preparative and kinetic
studies clearly indicate that the dimethylamine formed from
the bis(dimethylamido) catalyst precursor I and the reacting
amine is able to convert the catalytically active imido or
amido complexes back into the catalyst precursor and
therefore inhibits the reactions. As a consequence, the
bis(dimethylamido) catalyst precursor I shows a worse cata-
lytic performance than the corresponding dimethyl complex
II. On the other hand, the dichloro complex III is only a
suitable catalyst precursor for selected reactions that are
known to proceed smoothly. Hydroamination reactions that
are more difficult to achieve, such as reactions of diarylal-
kynes or amino alkenes, do not work efficiently with this
complex. A possible explanation for this observation is the
finding that the dichloro catalyst precursor III is converted
into a different catalytically active species. This can happen
if the [η5-(C5H4)-SiMe2-NtBu] ligand system of the catalyst
Intermolecular Hydroamination of Alkynes. General Procedure: A
Schlenk tube fitted with a Teflon stopcock and a magnetic stirring
bar was transferred into a nitrogen-filled glovebox and charged
with the alkyne (2.40 mmol), the amine (2.64 mmol), the catalyst
(0.12 mmol, 5 mol-%), and toluene (1.0 mL). The tube was then
sealed, and the resulting mixture was heated to 105 °C for 24 h.
After the mixture had been cooled to room temperature,
NaBH3CN (302 mg, 4.80 mmol), ZnCl2 (328 mg, 2.40 mmol), and
MeOH (10 mL) were added. After this mixture had been stirred at
25 °C for 20 h, CH2Cl2 (50 mL) and saturated Na2CO3 solution
(20 mL) were added. The resulting mixture was filtered, and the
solid residue was washed with CH2Cl2 (50 mL). After extraction,
the organic layer was separated. The aqueous layer was extracted
with CH2Cl2 (6ϫ50 mL), and the combined organic layers were
dried with MgSO4. After concentration under vacuum, the crude
product was purified by flash chromatography (SiO2).
(1,2-Diphenylethyl)-p-tolylamine (8):[9c] The general procedure was
used to synthesize 8 from diphenylacetylene (1, 428 mg, 2.40 mmol)
precursor is destroyed and removed from the Ti center un- and p-toluidine (2, 282 mg, 2.64 mmol). After chromatography
(PE/EtOAc, 40:1), 8 (631 mg, 2.20 mmol, 92%, catalyst: II) was
obtained as a yellow oil. H NMR (500 MHz, CDCl3): δ = 2.15 (s,
der the reaction conditions.
1
3 H), 3.00 (dd, J = 8.3, 14.0 Hz, 1 H), 3.12 (dd, J = 5.6, 14.0 Hz,
1 H), 4.02 (br. s, 1 H), 4.55 (dd, J = 5.7, 8.1 Hz, 1 H), 6.37 (d, J =
8.3 Hz, 2 H), 6.85 (d, J = 8.2 Hz, 2 H), 7.11 (d, J = 7.1 Hz, 2 H),
7.20–7.37 (m, 8 H) ppm. 13C NMR (125 MHz, DEPT, CDCl3): δ
= 20.3 (CH3), 45.2 (CH2), 59.5 (CH), 113.8 (CH), 126.5 (CH),
126.7 (CH), 127.0 (CH), 128.5 (CH), 128.5 (CH), 129.2 (CH), 129.5
(CH), 137.8 (C), 143.6 (C), 145.0 (C) ppm.
Experimental Section
General Remarks: All reactions were performed under nitrogen in
oven-dried Schlenk tubes (Duran glassware, 100 mL, Ø 30 mm) fit-
ted with Teflon stopcocks and containing magnetic stirring bars
(15ϫ4.5 mm). The catalysts I–III[8] and 1-amino-2,2-diphenylpent-
4-ene (22)[15] were synthesized by literature procedures. [D6]Ben-
zene was distilled from molten sodium. Toluene (toluene extra dry
with molecular sieves), and methanol (methanol extra dry with mo-
lecular sieves) were purchased from Acros Organics. Prior to use,
the volatile amines (3–7) and oct-1-yne (14) were purified and dried
by distillation (20 cm Vigreux column) from CaH2 on molecular
sieves at ambient pressure under an inert atmosphere. Diphenylace-
tylene (1) and p-toluidine (2) were purified by kugelrohr distil-
lation. All alkynes, amines, and catalysts were stored in a nitrogen-
filled glovebox (M. Braun, Unilab). All other reagents were pur-
chased from commercial sources and were used without further
purification. Unless otherwise noted, yields refer to isolated yields
of pure compounds as gauged by thin layer chromatography (TLC)
and 1H and 13C NMR spectroscopy. All products were charac-
terized by 1H NMR, 13C NMR and infrared (IR) spectroscopy and
mass spectrometry (MS). Additional characterization data were ob-
tained by CHN elemental analysis and/or high-resolution mass
spectrometry (HRMS). NMR spectra were recorded on the follow-
(1,2-Diphenylethyl)-o-tolylamine (9): The general procedure was
used to synthesize 9 from diphenylacetylene (1, 428 mg, 2.40 mmol)
and o-toluidine (3, 282 mg, 2.64 mmol). After chromatography
(PE/EtOAc, 20:1), 9 (646 mg, 2.25 mmol, 94%, catalyst: II) was
obtained as a colorless solid. 1H NMR (500 MHz, CDCl3): δ =
2.03 (s, 3 H), 3.00 (dd, J = 8.8, 13.9 Hz, 1 H), 3.20 (dd, J = 5.2,
13.9 Hz, 1 H), 3.99 (br. s, 1 H), 4.58 (dd, J = 5.2, 8.7 Hz, 1 H),
6.28 (d, J = 8.0 Hz, 1 H), 6.56 (t, J = 7.3 Hz, 1 H), 6.89 (t, J =
7.4 Hz, 1 H), 6.97 (d, J = 7.3 Hz, 1 H), 7.16 (d, J = 7.0 Hz, 1 H),
7.21–7.37 (m, 9 H) ppm. 13C NMR (125 MHz, DEPT, CDCl3): δ
= 17.4 (CH3), 45.6 (CH2), 59.3 (CH), 111.3 (CH), 117.0 (CH),
122.2 (C), 126.3 (CH), 126.8 (CH), 126.9 (CH), 127.0 (CH), 128.6
(CH), 128.6 (CH), 129.2 (CH), 129.8 (CH), 137.8 (C), 143.7 (C),
145.3 (C) ppm. IR (neat): ν = 3413, 3022, 2915, 2839, 1607, 1588,
˜
1510, 1453, 1322, 1266, 749, 698 cm–1. MS (CI, 25 °C): m/z (%) =
288 (100) [M + H]+, 196 (22) [M – C7H7]+. HRMS (CI): calcd.
(C21H22N) 288.1752; found: 288.1752. C21H21N (287.4): calcd. C
87.76, H 7.36, N 4.87; found C 87.50, H 7.28, N 4.76.
4820
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 4815–4823

Labile Ligands and Catalytic Activity of Neutral Ti Complexes
tert-Butyl(1,2-diphenylethyl)amine (10):[9c] The general procedure
was used to synthesize 10 from diphenylacetylene (1, 428 mg,
Amines 17a/17b: The general procedure was used to synthesize
amines 17a and 17b from oct-1-yne (16, 264 mg, 2.40 mmol) and
2.40 mmol) and tert-butylamine (4, 193 mg, 2.64 mmol). After p-toluidine (2, 282 mg, 2.64 mmol). After chromatography (PE/
chromatography (PE/EtOAc, 20:1Ǟ5:1), 10 (576 mg, 2.28 mmol,
95%, catalyst: II) was obtained as a bright yellow oil. 1H NMR
(500 MHz, CDCl3): δ = 0.83 (s, 9 H), 1.33 (br. s, 1 H), 2.70 (dd, J
= 9.0, 13.4 Hz, 1 H), 2.91 (dd, J = 5.5, 13.5 Hz, 1 H), 3.98 (dd, J
= 5.6, 8.8 Hz, 1 H), 7.13 (d, J = 7.6 Hz, 2 H), 7.19 (d, J = 7.3 Hz,
2 H), 7.23–7.29 (m, 4 H), 7.38 (d, J = 7.8 Hz, 2 H) ppm. 13C NMR
(125 MHz, DEPT, CDCl3): δ = 29.9 (CH3), 47.2 (CH2), 51.1 (C),
EtOAc, 20:1), a mixture of 17a and 17b (500 mg, 2.28 mmol, 95%,
catalyst: II) was obtained as an orange oil. The 17a/17b ratio was
determined by GC as 17:83 (catalyst: II). 1H NMR (500 MHz,
CDCl3, mixture of 17a and 17b): δ = 0.88 (t, J = 6.5 Hz, 3 H), 0.88
(t, J = 7.1 Hz, 3 H), 1.15 (d, J = 6.3 Hz, 3 H), 1.20–1.70 (m), 2.22
(s, 3 H), 3.08 (t, J = 7.1 Hz, 2 H), 3.27 (br. s, 1 H), 3.43 (sext, J =
6.2 Hz, 1 H), 6.49–6.55 (m, 2 H), 6.94–7.00 (m 2 H) ppm. 13C
59.2 (CH), 126.3 (CH), 126.4 (CH), 127.1 (CH), 128.1 (CH), 128.3 NMR (125 MHz, DEPT, CDCl3, mixture of 17a and 17b): δ = 14.1
(CH), 129.3 (CH), 139.3 (C), 147.5 (C) ppm.
(CH3), 20.3 (CH3), 20.8 (CH3), 22.6 (CH2), 26.1 (CH2), 27.2 (CH2),
29.3 (CH2), 29.4 (CH2), 29.4 (CH2), 29.6 (CH2), 31.9 (CH2), 37.2
(CH2), 44.5 (CH2), 48.9 (CH), 113.0 (CH), 113.5 (CH), 129.7 (CH),
Cyclopentyl(1,2-diphenylethyl)amine (11):[9c] The general procedure
was used to synthesize 11 from diphenylacetylene (1, 428 mg,
2.40 mmol) and cyclopentylamine (5, 225 mg, 2.64 mmol). After
chromatography (PE/EtOAc, 20:1), 11 (596 mg, 2.25 mmol, 94%,
catalyst: II) was obtained as a yellow oil. 1H NMR (500 MHz,
CDCl3): δ = 1.05–1.71 (m, 9 H), 2.75–2.95 (m, 3 H), 3.92 (t, J =
7.9 Hz, 1 H), 7.11 (d, J = 7.1 Hz, 2 H), 7.13–7.33 (m, 8 H) ppm.
13C NMR (125 MHz, DEPT, CDCl3): δ = 23.6 (CH2), 32.3 (CH2),
33.7 (CH2), 45.4 (CH2), 57.3 (CH), 63.2 (CH), 126.2 (CH), 126.9
(CH), 127.4 (CH), 128.2 (CH), 128.3 (CH), 129.2 (CH), 139.0 (C),
144.1 (C) ppm.
129.7 (CH) ppm. IR (neat, mixture of 17a and 17b): ν = 3406,
˜
2956, 2924, 2855, 1619, 1518, 1457, 1376, 1317, 1301, 1250, 1182,
805 cm–1. MS (CI, 25 °C, mixture of 17a and 17b): m/z = 220 (100)
[M + H]+. HRMS (CI, mixture of 17a and 17b): calcd. (C15H26N)
220.2066; found 220.2065. C15H25N (219.4, mixture of 17a and
17b): calcd. C 82.13, H 11.49, N 6.38; found C 82.53, H 11.89, N
6.83.
Amine 18b:[16] The general procedure was used to synthesize amine
18b from oct-1-yne (16, 264 mg, 2.40 mmol) and o-toluidine (3,
282 mg, 2.64 mmol). After chromatography (PE/EtOAc, 40:1), 18b
(494 mg, 2.25 mmol, 94%, catalyst: II) was obtained as a colorless
oil. 1H NMR (500 MHz, CDCl3): δ = 0.88 (t, J = 6.5 Hz, 3 H),
1.20 (d, J = 6.2 Hz, 3 H), 1.24–1.71 (m, 10 H), 2.11 (s, 3 H), 3.29
(br. s, 1 H), 3.50 (sext, J = 6.0 Hz, 1 H), 6.60 (t, J = 7.5 Hz, 2 H),
7.03 (d, J = 7.2 Hz, 1 H), 7.10 (t, J = 7.8 Hz, 1 H) ppm. 13C NMR
(125 MHz, DEPT, CDCl3): δ = 14.1 (CH3), 17.6 (CH3), 21.0 (CH3),
22.6 (CH2), 26.2 (CH2), 29.4 (CH2), 31.9 (CH2), 37.3 (CH2), 48.3
(CH), 110.0 (CH), 116.2 (CH), 121.6 (C), 127.1 (CH), 130.2 (CH),
145.6 (C) ppm.
Benzyl(1,2-diphenylethyl)amine (12):[9c] The general procedure was
used to synthesize 12 from diphenylacetylene (1, 428 mg,
2.40 mmol) and benzylamine (6, 282 mg, 2.64 mmol). After
chromatography (PE/EtOAc, 5:1), 12 (654 mg, 2.28 mmol, 95%,
1
catalyst: II) was obtained as a colorless oil. H NMR (500 MHz,
CDCl3): δ = 1.68 (br. s, 1 H), 2.89 (dd, J = 8.6, 13.5 Hz, 1 H), 2.96
(dd, J = 5.5, 13.5 Hz, 1 H), 3.46 (d, J = 13.6 Hz, 1 H), 3.65 (d, J
= 13.6 Hz, 1 H), 3.88 (dd, J = 5.6, 8.6 Hz, 1 H), 7.08–7.14 (m, 4 H),
7.15–7.29 (m, 7 H), 7.30–7.38 (m, 4 H) ppm. 13C NMR (125 MHz,
DEPT, CDCl3): δ = 45.3 (CH2), 51.4 (CH2), 63.6 (CH), 126.3 (CH),
126.7 (CH), 127.1 (CH), 127.4 (CH), 127.9 (CH), 128.2 (CH), 128.3
(CH), 128.4 (CH), 129.3 (CH), 138.8 (C), 140.5 (C), 143.7 (C) ppm.
Amine 19a: The general procedure was used to synthesize amine
19a from oct-1-yne (16, 264 mg, 2.40 mmol) and tert-butylamine
(4, 193 mg, 2.64 mmol). After chromatography (EtOAc, + 5% 7 
NH3 in MeOH), 19a (361 mg, 1.95 mmol, 81%, catalyst: II) was
(1,2-Diphenylethyl)octylamine (13): The general procedure was used
to synthesize 13 from diphenylacetylene (1, 428 mg, 2.40 mmol)
and oct-1-ylamine (7, 341 mg, 2.64 mmol). After chromatography
(PE/EtOAc, 40:1 to EtOAc), 13 (426 mg, 1.38 mmol, 58%, catalyst:
II) was obtained as a bright yellow oil. 1H NMR (500 MHz,
CDCl3): δ = 0.86 (t, J = 7.1 Hz, 3 H), 1.05–1.40 (m, 12 H), 1.81
(br. s, 1 H), 2.30–2.43 (m, 2 H), 2.84–2.96 (m, 2 H), 3.83 (dd, J =
6.0, 8.1 Hz, 1 H), 7.08–7.32 (m, 10 H) ppm. 13C NMR (125 MHz,
DEPT, CDCl3): δ = 14.0 (CH3), 22.6 (CH2), 27.1 (CH2), 29.2
(CH2), 29.3 (CH2), 29.8 (CH2), 31.7 (CH2), 45.4 (CH2), 47.6 (CH2),
64.8 (CH), 126.2 (CH), 126.9 (CH), 127.2 (CH), 128.2 (CH), 128.3
1
obtained as a bright yellow oil. H NMR (500 MHz, CDCl3): δ =
0.88 (t, J = 6.7 Hz, 3 H), 1.09 (s, 9 H), 1.19–1.37 (m, 10 H), 1.38–
1.50 (m, 2 H), 2.53 (t, J = 7.3 Hz, 2 H) ppm. 13C NMR (125 MHz,
DEPT, CDCl3): δ = 14.1 (CH3), 22.7 (CH2), 27.6 (CH2), 29.1
(CH3), 29.3 (CH2), 29.6 (CH2), 31.1 (CH2), 31.9 (CH2), 42.6 (CH2),
50.2 (C) ppm. IR (neat): ν = 2957, 2924, 2854, 1465, 1387, 1360,
˜
1231, 1132, 1097, 1020, 692 cm–1. MS (CI, 25 °C): m/z (%) = 186
(100) [M + H]+. HRMS (CI): calcd. (C12H28N) 186.2222; found
186.2222. No correct CHN elemental analysis could be obtained
because of the viscosity of the product.
(CH), 129.2 (CH), 138.9 (C), 143.8 (C) ppm. IR (neat): ν = 3027,
˜
2924, 2853, 1602, 1494, 1454, 1115, 1070, 1029, 908, 757, 732, 698,
627 cm–1. MS (EI, 25 °C): m/z (%) = 309 (1) [M]+, 218 (100) [M –
C7H7], 181 (4) [M – C8H18N].
Amines 20a/20b: The general procedure was used to synthesize the
amines 20a and 20b from oct-1-yne (16, 264 mg, 2.40 mmol) and
cyclopentylamine (5, 225 mg, 2.64 mmol). After chromatography
(EtOAc, + 5% 7  NH3 in MeOH), a mixture of 20a and 20b
(468 mg, 2.38 mmol, 99%, catalyst: II) was obtained as a yellow
oil. The 20a/20b ratio was determined by GC to be 66:34 (catalyst:
II). 1H NMR (500 MHz, CDCl3, mixture of 20a and 20b): δ = 0.88
(t, J = 6.7 Hz, 3 H), 0.88 (t, J = 6.7 Hz, 3 H), 1.02 (d, J = 6.3 Hz,
(1-Methyl-2-phenylethyl)-p-tolylamine (15a):[9c] The general pro-
cedure was used to synthesize 15a from 1-phenylpropyne (14,
279 mg, 2.40 mmol) and p-toluidine (2, 281 mg, 2.64 mmol). After
chromatography (PE/EtOAc, 40:1), 15a (490 mg, 2.18 mmol, 91%,
catalyst: II) was obtained as a yellow oil. 1H NMR (500 MHz,
CDCl3): δ = 1.16 (d, J = 6.5 Hz, 3 H), 2.25 (s, 3 H), 2.69 (dd, J = 3 H), 1.18–1.95 (m), 2.56 (t, J = 7.3 Hz, 2 H), 2.65 (sext, J = 6.0 Hz,
7.5, 13.5 Hz, 1 H), 2.94 (dd, J = 4.5, 13.0 Hz, 1 H), 3.45 (br. s, 1 1 H), 3.04 (quint, J = 6.9 Hz, 1 H), 3.15 (quint, J = 7.0 Hz, 1
H), 3.74 (sext, J = 6.5 Hz, 1 H), 6.57 (d, J = 8.5 Hz, 2 H), 7.01 (d, H) ppm. 13C NMR (125 MHz, DEPT, CDCl3, mixture of 20a and
J = 8.5 Hz, 2 H), 7.17–7.24 (m, 3 H), 7.30 (t, J = 7.0 Hz, 2 H) ppm.
20b): δ = 14.1 (CH3), 20.8 (CH3), 22.7 (CH2), 23.9 (CH2), 24.1
(CH2), 26.1 (CH2), 27.5 (CH2), 29.1 (CH2), 29.3 (CH2), 29.6 (CH2),
13C NMR (125 MHz, DEPT, CDCl3): δ = 20.2 (CH3), 20.4 (CH3),
42.3 (CH2), 49.7 (CH), 113.7 (CH), 126.2 (C), 126.5 (C), 128.2 30.5 (CH2), 31.9 (CH2), 31.9 (CH2), 33.3 (CH2), 33.4 (CH2), 33.9
(CH), 129.5 (CH), 129.8 (CH), 138.7 (C), 144.9 (C) ppm. (CH2), 37.6 (CH2), 48.9 (CH2), 51.4 (CH), 57.0 (CH), 60.0
Eur. J. Org. Chem. 2008, 4815–4823
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4821

K. Gräbe, F. Pohlki, S. Doye
FULL PAPER
(CH) ppm. IR (neat, mixture of 20a and 20b): ν = 2954, 2923, 2854,
˜
1681, 1456, 1375, 1134, 722 cm–1. MS (CI, 25 °C, mixture of 20a
and 20b): m/z (%) = 198 (100) [M + H]+. HRMS (CI, mixture of
20a and 20b): calcd. (C13H28N) 198.2222; found 198.2222. No cor-
rect CHN elemental analysis could be obtained, because of the
viscosity of the product mixture.
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Amines 21a/21b:[16,17] The general procedure was used to synthesize
amines 21a and 21b from oct-1-yne (16, 264 mg, 2.40 mmol) and
benzylamine (6, 282 mg, 2.64 mmol). After chromatography (PE/
EtOAc, 2:1), a mixture of amines 21a and 21b (222 mg, 1.01 mmol,
42%, catalyst: II) was obtained as a colorless oil. The 21a/21b ratio
was determined by GC to be 43:57 (catalyst: II). 1H NMR
(500 MHz, CDCl3, mixture of 21a and 21b): δ = 0.88 (t, J = 5.5 Hz,
3 H), 0.88 (t, J = 5.5 Hz, 3 H), 1.08 (d, J = 6.2 Hz, 3 H), 1.18–1.55
(m), 2.62 (t, J = 7.2 Hz, 2 H), 2.67 (sext, J = 5.8 Hz, 1 H), 3.73 (d,
J = 13.0 Hz, 1 H), 3.79 (s, 2 H), 3.83 (d, J = 12.9 Hz, 1 H), 7.20–
7.35 (m) ppm. 13C NMR (125 MHz, DEPT, CDCl3, mixture of 21a
and 21b): δ = 14.1 (CH3), 20.4 (CH3), 22.7 (CH2), 26.0 (CH2), 27.4
(CH2), 29.3 (CH2), 29.5 (CH2), 30.1 (CH2), 31.8 (CH2), 37.1 (CH2),
49.6 (CH2), 51.4 (CH2), 52.5 (CH), 54.1 (CH2), 126.8 (CH), 126.8
(CH), 128.1 (CH), 128.4 (CH), 140.6 (C), 141.0 (C) ppm.
[2]
[3]
[4]
[5]
2-Methyl-4,4-diphenylpyrrolidine (23):[12,14b–14d,14g–14k] A Schlenk tube
fitted with a Teflon stopcock and containing a magnetic stirring
bar was transferred into a nitrogen-filled glovebox and charged
with 1-amino-2,2-diphenylpent-4-ene (22, 570 mg, 2.40 mmol), the
catalyst (0.12 mmol, 5 mol-%), and toluene (1.0 mL). The tube was
then sealed, and the resulting mixture was heated to 105 °C for 24
h. After the mixture had been cooled to room temperature, the
product was directly isolated by flash chromatography (SiO2, PE/
EtOAc, 1:2) to give 23 (422 mg, 1.78 mmol, 74%, catalyst: II) as a
colorless oil. 1H NMR (500 MHz, CDCl3): δ = 1.21 (d, J = 6.5 Hz,
3 H), 2.04 (dd, J = 9.1, 12.7 Hz, 2 H), 2.21 (br. s, 1 H), 2.74 (ddd,
J = 0.8, 6.7, 12.7 Hz, 1 H), 3.32–3.43 (m, 1 H), 3.47 (d, J = 11.4 Hz,
1 H), 3.68 (d, J = 11.6 Hz, 1 H), 7.12–7.19 (m, 2 H), 7.20–7.33 (m,
8 H) ppm. 13C NMR (125 MHz, DEPT, CDCl3): δ = 22.3 (CH3),
47.1 (CH2), 53.1 (CH), 57.3 (C), 57.9 (CH2), 126.0 (CH), 127.0
(CH), 127.0 (CH), 128.3 (CH), 128.3 (CH), 147.1 (C), 147.8
(C) ppm.
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alkyne 14 was determined by H NMR spectroscopy. For this pur-
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Acknowledgments
We thank the Deutsche Forschungsgemeinschaft (DFG) and the
Fonds der Chemischen Industrie for financial support of our re-
search.
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 4815–4823

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Received: May 13, 2008
Published Online: August 27, 2008
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Eur. J. Org. Chem. 2008, 4815–4823
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www.eurjoc.org
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