New cationic rhodium-amine complexes and their implication in the catalytic anti-Markovnikov oxidative amination of styrenes

Article abstract of DOI:10.1016/S0022-328X(98)00745-1

The oxidative anti-Markovnikov amination of styrenes catalyzed by cationic rhodium complexes provides a new access to enamines. As catalyst precursors [Rh(cod)(amine)₂]⁺ complexes have been identified and characterized for the first

Full text of DOI:10.1016/S0022-328X(98)00745-1

Journal of Organometallic Chemistry 566 (1998) 277–285
New cationic rhodium–amine complexes and their implication in the
catalytic anti-Markovnikov oxidative amination of styrenes
Matthias Beller *, Harald Trauthwein, Martin Eichberger, Claudia Breindl, Thomas E. M u¨ ller,
Alexander Zapf
Anorganisch-chemisches Institut der Technischen Uni6ersit a¨ t M u¨ nchen Lichtenbergstraße 4, D-85747 Garching, Germany
Received 13 May 1998
Abstract
The oxidative anti-Markovnikov amination of styrenes catalyzed by cationic rhodium complexes provides a new access to
+
enamines. As catalyst precursors [Rh(cod)(amine)2] complexes have been identified and characterized for the first time by X-ray
crystallography and NMR. While piperazine, N-methylpiperazine, and thiomorpholine form 1:1 Rh–amine complexes, non-
chelating amines such as piperidine and diethylamine form 1:2 Rh–amine complexes. The easier dissociation of the amine ligand
explains why monodentate amines give good yields of the corresponding enamines in contrast to bidentate amines. © 1998
Elsevier Science S.A. All rights reserved.
Keywords: Amines; Amination of olefins; Anti-Markovnikov reaction; Catalysis; Oxidation; Rhodium complexes
In general the linear anti-Markovnikov products are
1. Introduction
more interesting for industrial applications. Unfortu-
nately, so far no transition metal catalyzed process is
known for anti-Markovnikov aminations of neutral
terminal olefins [3]. Thus, this type of reaction has been
named as one of the ten most important goals for
future catalytic processes [4].
Recently, we have developed a new intermolecular
oxidative amination of aromatic olefins to give enam-
ines in good yields (Scheme 2) [5]. Thereby simple
monoamines like piperidine or diethylamine are con-
verted in the presence of cationic rhodium–phosphine
complexes as in situ catalysts to the corresponding
The catalytic construction of carbon–nitrogen bonds
to selectively produce amines is of fundamental impor-
tance in organic synthesis. Particularly interesting are
catalytic aminations of olefins [1] to give primary, sec-
ondary or tertiary amines due to the atom efficiency of
the process and the availability of starting materials [2].
In regards to the regioselectivity of the process it is
interesting to note that Markovnikov as well as anti-
Markovnikov products can be produced (Scheme 1).
ꢀ
-enamine in good yields. A further equivalent of the
aromatic olefin is concurrently reduced to a substituted
ethylbenzene. This reaction is remarkable for several
reasons: it is one of the rare examples of a catalytic
intermolecular oxidative amination reaction of olefins,
[6] and it provides the enamine for the first time with
excellent anti-Markovnikov regioselectivity (\99:1).
The mechanism of the reaction can follow two alter-
native pathways as depicted in Scheme 3. On the one
Scheme 1. Hydroamination of olefins.
*
Corresponding author. Tel.: +49 89 28913096; fax: +49 89
8913473; e-mail: mbeller@arthur.anorg.chemie.tu-muenchen.de
2
0
022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00745-1

278
M. Beller et al. / Journal of Organometallic Chemistry 566 (1998) 277–285
Scheme 2. Anti-Markovnikov oxidative amination of styrene.
hand, an up to now unidentified Rh complex acti-
vates the olefin by complexation, thus the olefin is
prone to a nucleophilic attack of the amine. The
resulting aminoalkylrhodium species eliminates the
enamine and the rhodium dihydride complex hydro-
genates a second olefin to yield the catalytically
active species. On the other hand activation of the
amine by an oxidative addition to give an amido-
hydridorhodium complex [7] may also take place.
Insertion of the olefin into the Rh–N bond and subse-
quent i-hydride elimination leads (similar to the previ-
ous cycle) to an enamine and a rhodium dihydride
complex.
Scheme 3. Possible catalytic cycles of the anti-Markovnikov oxidative
amination.
In order to gain more insight into this new catalytic
reaction as well as taking a further step in the develop-
2. Results and discussion
ment of
a
general anti-Markovnikov amination
methodology, it is necessary to approach the actual
catalytically active rhodium species by isolating and
characterizing intermediates of the oxidative amination
2.1. Variation of the amine in the oxidati6e amination
of styrene
The regioselective oxidative amination of styrenes by
secondary amines permits the effective synthesis of
valuable enamines. In order to investigate the scope
and limitations of the amine compound for the
rhodium catalyzed oxidative amination we tested either
monoamines, which possess only one functional group
as well as amines with two coordinating groups within
the molecule, such as piperazine (Table 1).
reaction.
Cationic [Rh(amine) (olefin) ]
+
(x+y=4) or
(x+y+z=4)
x
y
+
[Rh(amine) (olefin) (phosphine) ]
x y z
complexes are supposed to play an important role in
the formation of the active species, which is unknown
up to now. Thus we were interested in the prepara-
tion of a series of cationic [Rh(amine) (olefin) ]+ (x+
y=4) complexes and comparing the structural
data of these complexes with results from catalysis.
Unfortunately, apart from pyridine or nitrile ligands
rhodium amine complexes are not very well investi-
gated [8]. Up to now secondary amine groups were
only used as one coordination side in chelating lig-
x
y
While monodentate amines like piperidine and di-
ethylamine provide good yields of the corresponding
enamine, bidentate amines like piperazine and its
derivatives or thiomorpholin react very sluggishly or
even not at all under our previously optimized reaction
conditions (one equivalent amine, four equivalents
styrene, THF reflux, 2.5 mol% [Rh(cod) ]BF , 5 mol%
ands
with
further
donor
centers,
e.g.
2-
2
4
(
aminoalkyl)pyridines, which resulted in the formation
PPh ). As a consequence, the coordination chemistry of
3
of either ion pairs, dimers, tetra- or pentacoordinated
complexes [9,10]. Apart from the ammonia complex
+
Table 1
[
Rh(cod)(NH ) ]
[11] there is to the best of our
3
2
a
Oxidative amination of styrene with various amines
knowledge no structural characterization of cationic
diolefin–rhodium complexes with primary or secondary
amines as ligands [12].
Due to this lack of knowledge, we present here
our initial studies on stoichiometric reactions of the
cationic bis(cyclooctadienyl)rhodium complex with var-
ious secondary aliphatic amines. The resulting rhodium
species are pre-catalysts forming the catalytic active
species in the oxidative anti-Markovnikov amination
reaction.
Amine
Enamine (%)
Ethylbenzene (%)
Piperidine
55
40
B1
B1
4
57
54
B1
B1
5
Diethylamine
Thiomorpholine
Piperazine
N-Methyl-piperazine
a
2
.5 mol% Rh catalyst relative to amine, styrene: amine=4:1, 20 h
reflux in THF.
The yields of enamine and ethylbenzene are referred to amine.

M. Beller et al. / Journal of Organometallic Chemistry 566 (1998) 277–285
279
the cod ligand. The N–H proton signal is located at
.93 ppm and the triplet at 1.50 ppm corresponds to the
2
methyl group of the diethylamine ligand. A quite simi-
1
lar pattern in the H-NMR is observed for the pipe-
ridine complex 2.
Suitable crystals for X-ray diffraction were obtained
by diffusing pentane in a solution of 2 in THF. The
crystals contain discrete molecules, separated by normal
+
Scheme 4. Preparation of cationic [Rh(cod)(amine)2]
with monodentate amines.
complexes
van der Waals distances. An ORTEP drawing of the
+
cationic complex [Rh(cod)(piperidine)2]
is shown in
these two kinds of amines, monodentate and bidentate,
with cationic rhodium centers has to be different.
Fig. 1, and a selection of intraatomic distances are
given in Table 3.
The rhodium atom has a square planar coordination
geometry of cod and two amines with the two pipe-
ridine molecules being cis to each other. Rhodium
nitrogen bond lengths (Rh–N11=2.159(4), Rh–
2
2
.2. Cationic rhodium–amine complexes
.2.1. Monodentate amine ligands
The starting point of our investigation was the obser-
˚
N21=2.186(4) A) are longer than those in the corre-
vation that the reaction mixture, the orange colored
Rh(cod) ]BF complex which is insoluble in THF im-
sponding ammonia complex [Rh(cod)(NH ) ]PF
3
2
6
˚
[
(between 2.114(4) and 2.134(4) A) [11] where the
rhodium centre is coordinated by a dibenzo crown
ether in a second sphere. Surprisingly, in the neutral
complex RhCl(C H )(piperidine) [15] Rh–N bond
2
4
mediately dissolves by adding a surplus of monodentate
amine. Spectroscopic studies of the resulting clear yel-
1
low solution by means of in situ H-NMR spectroscopy
2
4
2
˚
reveal that the yellow color is due to the formation of
lengths are even shorter (2.087(3) and 2.111(3) A, re-
spectively). The angle between the two piperidine nitro-
gens N11–Rh–N21 in 2 is 90.1(1)° which indicates that
there is no steric strain around rhodium. Each of the
nitrogens are in a tetrahedral environment with N–H
forming hydrogen bonds with the fluorine atoms of the
counterion (N11–H11···F1=3.08, N21–H21…F3=
+
a cationic [Rh(cod)(NHR ) ] complex which arises
2
2
due to displacement of one cod ligand by two amines
13].
In isolating the cationic [Rh(cod)(NHR ) ] complex
[
+
2
2
this route proved to be inconvenient as the replaced cod
ligand causes side-reactions and cod is not easily sepa-
rated from the product. Hence, as an alternative syn-
thesis the reaction of an equimolar mixture of
˚
3.29 A).
[
RhL Cl] (L=olefin) and AgX (X=BF , CF SO ) [14]
2.2.2. Bidentate amine ligands
2
2
4
3
3
was tested. Thereby [Rh(cod)Cl] was dissolved in THF
We synthesized and isolated according to the above
mentioned procedure, i.e. treatment of [Rh(cod)Cl]2
with AgX and subsequent addition of bidentate amine,
several cationic cod–rhodium complexes with cyclic
amine ligands which possess an additional donor atom
in the ring. With piperazine as amine complex 3 was
obtained, with N-methylpiperazine complex 4a and 4b,
and with thiomorpholine complex 5 was obtained. All
prepared complexes 1–5 are air and moisture stable.
However, for a prolonged time they are best stored
under an argon atmosphere (Scheme 5).
2
and treated with AgBF . After filtration of AgCl 2.2
4
equivalents of piperidine or diethylamine were added at
0°C to the mixture and a yellow precipitate was ob-
tained in nearly quantitative yield (Scheme 4) (Table 2).
The IR spectra of all compounds, recorded in KBr
pellets, showed a characteristic decrease in the amine
−
1
(
N–H) stretching frequency of Dw ca. 100–150 cm
compared to the free amine suggesting that coordina-
tion of the amine occurs to the rhodium center. The
−
1
strong absorption bands at ca. 1000 cm
can be
assigned to the BF ion indicating a cationic species.
Although bidentate cyclic amines like piperazines are
known to act as chelating ligands, especially for transi-
tion metals like Cu, Ni, Pt [16] no cationic Rh complex
with cyclic chelating diamines has been described to the
best of our knowledge.
4
Elemental analysis and mass spectroscopy revealed that
in the case of 1 and 2 (diethylamine and piperidine as
amine ligands) two amine molecules coordinate to the
1
rhodium center, which is confirmed by H-NMR. The
proton NMR of 1 shows one signal at 3.85 ppm for the
olefinic cod protons and two signals at 2.38 and 1.78
IR spectroscopic studies show a characteristic de-
crease in the amine (N–H) stretching frequency of
complexes 3–5. This indicates a coordination of the
amine on the rhodium center. However, by the presence
of two coordinating sides these bidentate amine
molecules react as chelating ligands. This is confirmed
by the rhodium–cod–amine ratio of 1:1:1 shown by
elementary analysis and mass spectroscopy.
ppm for the aliphatic cod protons. The h-CH group in
2
the ethyl group of the diethylamine ligand gives two
different multiplets at 2.75 and 2.56 ppm indicating a
chemical inequivalence for the two geminal protons.
This can be explained by a hindered rotation of the
Rh–N and the N–C bond due to the steric demand of

280
M. Beller et al. / Journal of Organometallic Chemistry 566 (1998) 277–285
Table 2
Yields, analytical results and N–H vibration frequencies of the cationic rhodium compounds 1–5 compared to the free amine in CCl4
No Complex
Yield (%) C calc. C found H calc. H found N calc. N found w(N–H) complex {free amine} (cm−1)
1
2
3
[Rh(cod)(HN(C H )) ]BF 91
43.0
2.6
46.1
6.0
37.5
8.1
7.7
7.3
7.3
5.8
6.3
6.1
6.0
5.7
7.3
3181
2
5
2
4
4
{3278}
3251, 3186
{3346}
3259
[Rh(cod)(HNC H ) ]BF
4
83
93
5
10 2
4
[Rh(cod)(HNC H NH)]
4
8
BF4
3
37.5
8.1
5.8
5.8
7.3
7.3
4
4
5
a
[Rh(cod)(HNC H NCH )] 82
BF4
3304, 3193
{3349}
4
8
3
3
35.4
8.1
5.8
5.3
7.3
6.1
b
[Rh(cod)(HNC H NCH )] 75
4
8
3
OTf
[Rh(cod)(HNC H S)]BF
4
3
5.5
35.9
5.8
5.2
5.3
5.2
6.2
3.5
3.4
88
3278
{3358}
4
8
3
Due to the norbornan-like structure of these chelat-
ing hexacyclic amines complexes, whereby the nitrogen
atoms act as bridgehead atoms and the rhodium atom
effect to the different interactions of the non-coordinat-
−
−
ing anions BF
(4a) and CF
SO
(4b) with the amine
4
3
3
proton via the hydrogen bonds.
13
as a bridge, [17] a splitting of the CH ring protons of
The C-NMR of 4a and 4b also show a splitting of
signals which is caused by the different substitution of
the nitrogen atoms. Hence, two different signals appear
for the olefinic and aliphatic carbon atoms of the cod
ligand as well as for the carbon atoms in the ethylen
bridge of the N-methylpiperazine ligand.
2
1
the coordinated amine is observed in the H-NMR
spectra of 3, 4, and 5. This non-equivalence of the exo
and endo protons of the amine CH groups gives a
2
further indication that the cyclic amine behaves as a
bidentate ligand. In regards to 4 and 5 the non-equiva-
lence of the amine CH2 groups is clearly observed.
Interestingly, in case of the N-methylpiperazine
rhodium complex the methyl group even changes the
chemical surrounding of the olefinic cod protons result-
ing in two different signals (Fig. 2). The exact assigne-
ment of Fig. 2 was performed by means of a HMQC
experiment.
The chelating structure of the bidentate amine ligand
was corroborated by X-ray diffraction studies of 4b.
Suitable crystals were obtained by diffusing diethylether
in a solution (CH Cl ) of 4b. The molecular structure of
2 2
+
the cation [Rh(cod)(N-methylpiperazine)] 4b is shown
in Fig. 3. The rhodium atom is in a distorted square
planar surrounding, ligated by both nitrogen atoms of
one N-methylpiperazine molecule. The rhodium–nitro-
gen bonds observed in 4b (Rh–N11=2.091(2), Rh–
1
A comparison of the H-NMR spectra of 4a and 4b
reveals, that the chemical shift of the N–H signal is
different (4a: 4.34) and (4b: 4.96 ppm). We ascribe this
˚
N21=2.133(2) A) are significantly shorter than those
in 2 and comparable to those in [Rh(cod)(NH ) ]PF
3
2
6
and RhCl(C H )(piperidine) (vice supra) (Table 4).
2
4
2
The N(11)–Rh–N(21) angle is only 70.56(7)°. Conse-
quently, the angles between the cod double bonds, the
rhodium, and the nitrogens are larger than 90°. Because
Table 3
Selected bond distances in 2
˚
Bond length (A)
Rh–N11
Rh–N21
Rh–C1
Rh–C2
Rh–C5
Rh–C6
C1–C2
C5–C6
2.159(4)
2.186(4)
2.113(5)
2.121(6)
2.161(5)
2.155(6)
1.38(1)
1.38(1)
Fig. 1. Molecular structure of 2. N11–Rh–N21=90.08(14)°.

M. Beller et al. / Journal of Organometallic Chemistry 566 (1998) 277–285
281
+
Scheme 5. Preparation of cationic [Rh(cod)(amine)] complexes with
bidentate amines.
of the larger steric requirement of N–Me the angles
N14–Rh–C6 and N14–Rh–C5 (102.0(1) and
101.7(1)°, respectively) are larger than the correspond-
ing angles of N–H (N11–Rh–Cl=98.4(1), N11–Rh–
C2=98.1(1)°). Again hydrogen bonds between the
N–H group and the counterion (N11–H11···O2=3.05
Fig. 3. Molecular structure of 4b. N11–Rh–N14=70.56(7)°.
˚
A) are observed.
4
a,b are still soluble in the reaction mixture (solvent
THF), however the formation of a stable chelating
ligand system blocks vacant coordination sites on the
rhodium center, slowing down dramatically the rate of
the reaction (Table 5).
2
.3. Catalytic acti6ity of cationic rhodium olefin–amine
complexes
With regard to mechanistic investigations we were
interested in testing the catalytic activity of the new
cationic Rh–amine complexes 1–5 in the anti-
Markovnikov amination of styrene (Scheme 2). Com-
plexes 3 and 5 are insoluble under the typical reaction
conditions, thus no conversion was observed. However,
even the use of complex 3 in the presence and absence
of triphenylphosphine in DMAc as solvent showed no
reactivity. In case of N-methylpiperazine complexes
We compared the catalytic activity of 2 with our
previously used in situ catalyst mixture ([Rh(cod) BF /2
2
4
+
PPh ). While the [Rh(cod)(piperidine) ] complex (2)
3
2
itself is only marginally active (yield enamine=8%;
TON=3), in the presence of triphenylphosphine the
complex is as active as the in situ catalyst mixture
(
yield=45%; TON=18 vs yield=55%; TON=22). In
order to understand the influence of added
triphenylphosphine we performed in situ NMR studies
of 2 in the presence of triphenylphosphine in CDCl3.
We varied the ratio of triphenylphosphine to 2 using
1
13
0
.5, 1, 2, and 4. Surprisingly the H- and C-NMR
spectra reveal that both the cod and piperidine ligands
are displaced by adding 0.5 equivalents of
31
triphenylphosphine. The P-NMR spectrum of this
reaction mixture shows at least three doublets, indicat-
ing the presence of several species of different Rh–
phosphine complexes. One of the doublets can be
associated with the [Rh(cod)(PPh ) ]BF complex [18].
3
2
4
Table 4
Selected bond distances in 4b
˚
Bond length (A)
Rh–N11
Rh–N14
Rh–C1
Rh–C2
Rh–C5
Rh–C6
C1–C2
C5–C6
2.091(2)
2.133(2)
2.111(2)
2.110(2)
2.125(2)
2.124(2)
1.375(4)
1.375(4)
Fig. 2. 1H-NMR of [Rh(cod)(N-methylpiperazine)]CF SO .
3
3

282
M. Beller et al. / Journal of Organometallic Chemistry 566 (1998) 277–285
Table 5
Regioselective oxidative amination of styrenea
served due to blocking of vacant coordination sites
on the metal center.
Amine
Catalyst
Solvent
DMAc
DMAc
Enamine Ethylbenzene
Piperidine
Piperazine
[Rh(cod)2]
23
40
4. Experimental details
BF /2 PPh3
4
[Rh(cod)2]
B1
B1
4
.1. General procedures
BF /2 PPh3
4
Piperazine
Di-n-ethy-
lamine
Diethylamine 1/2 PPh3
Piperidine
Piperidine
3/2 PPh3
1
DMAc
THF
B1
B1
B1
B1
All reactions involving organometallic compounds
were carried out with the use of vacuum line, Schlenk
and syringe techniques. All solvents were dried and
distilled prior to use, according to standard proce-
THF
THF
THF
31
8
45
28
8
49
2
2/2 PPh3
dures. Amines were distilled from CaH , silver salts
2
a
and other chemicals were purchased from Fluka and
Aldrich and used as received. Samples of [Rh(cod)Cl]2
2
.5 mol% Rh catalyst relative to amine, styrene: amine=4:1, 20 h
reflux in THF.
The yields of enamine and ethylbenzene are referred to amine.
[
19], and [Rh(cod) ]BF4 [18] were prepared as de-
2
scribed in the appropriate reference.
1
13
31
H-, C-, and P-NMR spectra were recorded on
1
13
a Jeol-GX 400 spectrometer. H- and C- chemical
shifts are reported in ppm relative to TMS. P- spec-
tra were referenced to 85% H PO . IR spectra were
31
By increasing the amount of triphenylphosphine in
the reaction mixture the concentration of free cod
and amine is increased, as well as the number of
3
4
obtained on a Perkin Elmer 1600 spectrometer. Mass
spectroscopic analysis was performed on a Finnigan
MAT 311A by using the Fast Atom Bombardment or
Field Desorption method. The elemental analyses
were carried out by the Microanalytical Laboratory
of the Technische Universit a¨ t M u¨ nchen.
GC spectra for analysis of catalytic reactions were
recorded with a HP 6890 gas chromatograph using a
HP-1 capillary column. Yields were determined by us-
ing hexadecane as internal standard.
3
1
peaks in P-NMR spectra. The presence of more
than two equivalents of triphenylphosphine as well as
31
free phosphine was observed in the P-NMR spectra.
So far no complex has been isolated from this mix-
ture. These observations provide significant evidence
that at least three coordination sites on the metal
center must be easily accessible in order to observe
significant catalysis, otherwise no oxidative amination
takes place. Furthermore it is clear that various
rhodium-olefin-amine-phosphine
present in solution, thus it has not been possible until
now to identify a single active catalyst species.
complexes
are
4
.2. [(1,2,5,6-p)-1,5-Cyclooctadien]bis(diethyl-
amine)rhodium(I) tetrafluoroborate (1)
A total of 100 mg (0.20 mmol) [Rh(cod)Cl] and 80
2
mg (0.41 mmol) AgBF were dissolved under nitrogen
4
3
. Conclusion
in 2 ml THF and stirred for 10 min. The clear or-
ange solution was filtered off the white AgCl and
cooled to 0°C. Then 66 mg (0.90 mmol) diethylamine
was added under stirring and after 5 min a yellow
precipitate was obtained, which was washed twice
with THF and three times with pentane. After drying
In conclusion we were able to isolate and to syn-
thesize a series of cationic rhodium complexes with
olefin and secondary amine ligands for the first time.
A systematic structural investigation by NMR and
X-ray reveals that the bidentate N-methylpiperazine
in 4b is bound more tightly to rhodium than the two
piperidine molecules in 2. This gives an explanation
1
in vacuo 1 was obtained in a 91% yield. H-NMR
(400 MHz, CDCl , 20°C): l=3.86 [s, 4H, CH(cod)],
3
3
3
2.92 [t, J
=6.7 Hz, 2H, NH], 2.75 [sext, JH–H=
6.7 Hz, 4H, N–CH ], 2.55 [septd, 4H, JH–H=6.7
Hz, N–CH2], 2.40 [d,
CH (cod)], 1.78 [d, JH–H=8.5 Hz, 4H, CH (cod),
1.50 [t, JH–H=7.1 Hz, 12H, CH ]. C-NMR (100
MHz, CDCl , 20°C): l=81.1 [d, JRh–C=12.9 Hz,
H–H
3
for the lower catalytic activity of 4b. Cationic
2
+
3
[Rh(cod)(amine)] complexes prepared by reaction of
JH–H=11.1 Hz, 4H,
+
3
[Rh(cod)2] with amines play an important role as
2
2
3
13
pre-catalysts in the formation of the catalytic active
species in the rhodium catalyzed anti-Markovnikov
amination of styrene. In the presence of
triphenylphosphine these complexes show similar cata-
lytic activity compared to in situ catalyst mixtures. In
case of piperazine, 4-thiomorpholine, and N-
methylpiperazine inhibition of the catalysis is ob-
3
3
3
CH(cod)], 47.0 [CH –N], 30.1 [CH (cod)], 14.9
2
2
−
1
[CH –N]. IR(KBr): w(cm )=3181 s, 2960 s, 2929 s,
3
2867 m, 2829 m, 1654 w, 1374 m 1145 s, 1066 ss,
1040 ss, 821 m. MS (FAB) m/z (%): 284.3
+
[Rh(cod)(HNEt )] .
2

M. Beller et al. / Journal of Organometallic Chemistry 566 (1998) 277–285
283
4
.3. [(1,2,5,6-p)-1,5-Cyclooctadien]bis(piperidine)
added under stirring, after 5 min a yellow precipitate
was obtained, which was washed twice with THF and
rhodium(I) tetrafluoroborate (2)
three times with pentane. After drying in vacuo, 4a was
1
A total of 100 mg (0.20 mmol) [Rh(cod)Cl] and 80
obtained in an 82% yield. H-NMR (400 MHz, CDCl ,
2
3
3
mg (0.41 mmol) AgBF were dissolved under nitrogen
20°C): l=4.46 [d, J
=2.5 Hz, 2H, CH(cod)], 4.34
[s, 1H, NH], 4.01 [d, JH–H=2.5 Hz, 2H, CH(cod)],
3.55–3.52 [m, 2H, CHH–NH], 3.48–3.42 [m, 2H,
4
H–H
3
in 2 ml THF and stirred for 10 min. The clear orange
solution was filtered off the white AgCl and cooled to
0°C. Then 78 mg (0.90 mmol) were added under stirring
CHH–N–CH ], 2.92–2.88 [m, 2H, CHH–NH], 2.60–
3
and after 5 min a yellow precipitate was obtained,
which was washed twice with THF and three times with
2.54 [m, 2H, CHH–NCH ], 2.41 [m, 4H, CH (cod)],
3
2
3
2.33 [s, 3H, CH ], 1.86 [d, JH–H=9.0 Hz, 4H,
3
13
pentane. After drying in vacuo, 2 was obtained in a
CH (cod)]. C-NMR (100 MHz, CDCl , 20°C): l=
2 3
1
Rh–C
1
1
8
3% yield. H-NMR (400 MHz, CD Cl , 20°C): l=
82.8 [d, J
=12.5 Hz, CH(cod)], 81.1 [d, JRh–C=
2
2
3
.95 [s, 4H, CH(cod)], 3.10 [s, 4H, N–CH ], 2.70 [s,
112.4 Hz, CH(cod)], 55.0 [CH –N–CH ], 45.5
2
2 3
3
NH], 2.52 [s, 4H, N–CH ], 2.40 [d, JH–H=11.1 Hz,
4
[CH –N], 45.3 [CH –NH] 30.5 [CH (cod)], 30.4
3 2 2
2
3
−1
H, CH (cod)], 1.78 [d, J
=8.5 Hz, 4H, CH (cod),
[CH (cod)]. IR (KBr): w(cm )=3304 s, 3193 s, 3011
2
H–H
2
2
1
.76 [s, 4H, meta-CH ], 1.64 [m, 6H, meta-CH , para-
w, 2935 s, 2878 s, 2838 m, 2789 m, 1468 m, 1453 m,
1432 m, 1146 ss, 1060 ss, 1000 ss, 959 s, 833 m. MS
2
2
13
CH2], 1.42 [s, 2H, para-CH2]. C-NMR (100 MHz,
CD Cl , 20°C): l=81.5 [d,
CH(cod)], 49.4 [CH –N], 29.8 [CH (cod)], 25.8 [meta-
CH ], 23.4 [para-CH ]. IR (KBr): w(cm )=3251 m,
1
JRh–C=12.5 Hz,
(FD,
CH Cl ),
m/z
(%):
311
[Rh(cod)(N-
2
2
2
2
+
methylpiperazine)] .
2
2
−
1
2
2
3
1
186 s, 2941 s, 2923 s, 2859 m, 2824 m, 1654 m, 1457 m
4
.6. [(1,2,5,6-p)-1,5-Cyclooctadien]-
095 ss, 1090 ss, 1054 ss, 1040 ss, 871 s. MS (FD,
(N,N%-p)-N-methylpiperazinerhodium(I) triflate (4b)
+
CH Cl ), m/z (%): 381.6 [Rh(cod)(piperidine) ] .
2
2
2
A total of 100 mg (0.20 mmol) [Rh(cod)Cl] and 105
2
4.4. [(1,2,5,6-p)-1,5-Cyclooctadien]-
mg (0.41 mmol) AgOSO CF was dissolved under ni-
2 3
(
N,N%-p)-piperazinerhodium(I) tetrafluoroborate (3)
trogen in 2 ml THF and stirred for 10 min. The clear
orange solution was filtered off the white AgCl and
cooled to 0°C. Then 45 mg (0.45 mmol) N-methylpiper-
azine was added under stirring, after 5 min a yellow
precipitate was obtained, which was washed twice with
THF and three times with pentane. After drying in
A total of 100 mg (0.20 mmol) [Rh(cod)Cl] and 80
2
mg (0.41 mmol) AgBF were dissolved under nitrogen
in 2 ml THF and stirred for 10 min. The clear orange
solution was filtered off the white AgCl and cooled to
4
1
0
°C. Then 39 mg (0.45 mmol) piperazine was added
vacuo, 4b was obtained in a 75% yield. H-NMR (400
under stirring and after 5 min a yellow precipitate was
obtained, which was washed twice with THF and three
times with pentane. After drying in vacuo, complex 3
was obtained in a 93% yield.
MHz, CDCl , 20°C): l=4.96 [s, 1H, NH], 4.45 [s, 2H,
CH(cod)], 4.01 [s, 2H, CH(cod)], 3.52–3.47 [m, 2H,
3
CHH–NH], 3.43–3.37 [m, 2H, CHH–NCH ], 2.82–
3
2.78 [m, 2H, CHH–NH], 2.60–2.54 [m, 2H, CHH–
NCH ], 2.46–2.32 [m, 4H, CH (cod)], 2.33 [s, 3H,
1
H-NMR (400 MHz, CD NO , 20°C): l=4.40 [s,
3
3
2
3
2
3
3 2
13
4
2
H, CH(cod)], 3.63 [d, 4H, JH–H=6.0 Hz, N–CH2],
CH ], 1.83 [d, JH–H=9.0 Hz, 4H, CH (cod)]. C-
NMR (100 MHz, CDCl , 20°C): l=82.8 [d, JRh–C=
12.5 Hz, CH(cod)], 81.1 [d, JRh–C=112.4 Hz,
3
1
.90 [d, JH–H=6.5 Hz, 4H, N–CH ], 2.38 [s, 4H,
2
3
3
l
CH (cod)], 1.78 [d, JH–H=8.0 Hz, 4H, CH (cod)].
2
2
1
1
3
C-NMR (100 MHz, CD NO , 20°C): l=81.8 [d,
CH(cod)], 55.0 [CH –N–CH ], 45.5 [CH –N], 45.3
3
2
2
3
3
JRh–C=12.3 Hz, CH(cod)], 46.7 [CH –N], 31.6
[CH –NH] 30.5 [CH (cod)], 30.4 [CH (cod)].
2 2 2
2
−
1
[
CH (cod)]. IR (KBr): w(cm )=3279 s, 3259 s, 2945
2
s, 2880 m, 2834 m, 1125 s, 1084 ss, 878 s. MS (FD,
4
.7. [(1,2,5,6-p)-1,5-Cyclooctadien]-
+
CH Cl ), m/z (%): 297 [Rh(cod)(piperazine)] .
2
2
(N,S-p)-thiomorpholinerhodium(I) tetrafluoroborate (5)
4.5. [(1,2,5,6-p)-1,5-Cyclooctadien]-
A total of 100 mg (0.20 mmol) [Rh(cod)Cl] and 80
2
(N,N%-p)-N-methylpiperazinerhodium(I)
mg (0.41 mmol) AgBF was dissolved under nitrogen in
4
tetrafluoroborate (4a)
2 ml THF and stirred for 10 min. The clear orange
solution was filtered off the white AgCl and cooled to
0°C. Then 48 mg (0.45 mmol) 4-thiomorpholine was
added under stirring, after 5 min a yellow precipitate
was obtained, which was washed twice with THF and
three times with pentane. After drying in vacuo, 5 was
obtained in an 88% yield.
A total of 100 mg (0.20 mmol) [Rh(cod)Cl] and 80
mg (0.41 mmol) AgBF was dissolved under nitrogen in
2
4
2
ml THF and stirred for 10 min. The clear orange
solution was filtered off the white AgCl and cooled to
°C. Then 45 mg (0.45 mmol) N-methylpiperazine was
0

284
M. Beller et al. / Journal of Organometallic Chemistry 566 (1998) 277–285
1
Table 6
H-NMR (400 MHz, CD NO , 20°C): l=4.87 [s,
3
2
Crystal data and data collection for 2
2
H, CH(cod)], 4.67 [s, 2H, CH(cod)], 3.59 [m, 2H,
CHH–NH], 3.38 [m, 2H, CHH–S], 3.05–2.93 [m, 4H,
Empirical formula
Habit
Unit cell dimensions
C H BF N ORh
22 42 4 2
Colorless rectangular parallelepiped
3
CHHNH, CHHS], 2.42 [d, JH–H=9.9 Hz, 4H,
3
˚
˚
˚
CH (cod)], 2.07 [d, J
=10.2 Hz, 4H, CH (cod)].
a=11.0228(4) A, h=90°
2
H–H
2
1
1
3
b=11.8312(5) A, i=90°
C-NMR (100 MHz, CD NO , 20°C): l=81.7 [d,
JRh–C=12.3 Hz, CH(cod)], 48.0 [CH –N], 30.5
3
2
c=18.9404(6) A, k=90°
2
3
˚
V (A )
2457.0(2)
4
−
1
[
CH (cod)], 28.8 [CH –S]. IR (KBr): w(cm )=3278 s,
2 2
Z
2939 m, 2924 m, 2882 s, 2834 m, 1311 m, 1434 s, 1056
˚
Wavelength (A)
1.54184, Cu–K , Graphite
h
ss, 1019 ss, 872 s. MS (FD, CH Cl ), m/z (%): 314
monochromator
193(2)
2
2
+
Temperature (K)
Space group
Crystal size (mm )
Absorption correction
Diffractometer
[Rh(cod)(thiomorpholine)] .
P2 2 2 , Orthorhombic
1
1 1
3
0.23×0.23×0.20
None, v=60.2 cm
CAD4 (Enraf Nonius)
q/2q-scan
4.41
4.8. General procedure for the oxidati6e amination of
−1
styrene
Measurement method
qmin
Catalytic reactions: 0.11 mmol of catalyst and 0.22
qmax
67.92
mmol of PPh were suspended under argon in 10 ml
3
h
k
l
−13BhB0
−14BkB14
0B1B22
4628
THF or DMAc. Subsequently, 4.40 mmol of amine and
17.6 mmol of styrene were added at room temperature
(
r.t.). The mixture was heated to reflux for 20 h and
Reflections collected
Independent reflections
4287
analyzed by GCMS. The yield was determined by gas
chromatography using hexadecane as internal standard.
Isolation of amine products was performed according
to [5].
Final R indices [I\2|(I)] R =0.0384, wR =0.0940
1
2
R indices (all data)
R =0.0428, wR =0.1012
1 2
computer, and for all subsequent calculations the
STRUX-V package was used [20]. No correction of
intensity or absorption was applied. The structure was
solved by direct and Fourier methods. The refinements
were carried out by full matrix least-squares with
isotropic and then with anisotropic thermal parameters
4
.9. X-ray crystallographic analysis of 2
Details are given in Table 6. Suitable single crystals
were obtained by slow diffusion of pentane in a THF
solution of 2 at r.t. A systematic search in reciprocal
space using an Enraf Nonius CAD4 diffractometer
showed that crystals of 2 belong to the orthorhombic
system. The resulting data set was transferred to a DEC
Table 7
3000 AXP computer, and for all subsequent calcula-
Crystal data and data collection for 4b
tions the STRUX-V package was used [20]. No correc-
tion of intensity or absorption was applied. The
structure was solved by direct and Fourier methods.
The refinements were carried out by full matrix least-
squares with isotropic and then with anisotropic ther-
mal parameters in the last cycles for all non-hydrogen
atoms. All hydrogen atoms were found and positions
were refined with the following restraints: C–H dis-
tances at C12, C14, C16, C22, and C26 were fixed (0.99
Empirical formula
Habit
Unit cell dimensions
C H F N O RhS
14 24 3 2 3
Yellow square plates
˚
a=13.5985(7) A, h=90°
˚
b=9.1768(3) A, i=103.729(5)°
˚
c=14.4497(7) A, k=90°
˚
3
V (A )
1751.67(14)
4
Z
˚
Wavelength (A)
0.71073, Mo–K , Graphite
h
monochromator
193(2)
Temperature (K)
Space group
Crystal size (mm )
˚
A). All hydrogen atoms in THF were put in their
geometrically calculated positions and refined ‘riding’
on the corresponding carbon atoms.
P2 /n, Monoclinic
1
3
0.25×0.25×0.10
None, v=11.4 (cm−1)
IPDS (STOE&CIE)
q/2q)-scan
2.65
Absorption correction
Diffractometer
Measurement method
qmin
4.10. X-ray crystallographic analysis of 4b
qmax
27.72
Details are given in Table 7. Suitable single crystals
h
k
l
−17BhB16
−8BkB11
−18B1B18
8584
were obtained by slow diffusion of diethylether in a
methylene chloride of 4b solution at r.t. A systematic
search in reciprocal space using an STOE&CIE IPDS
diffractometer showed that crystals of 4b belong to the
monoclinic system. The resulting data set was trans-
ferred to a DEC 3000 AXP and a Micro-VAX 3100
Reflections collected
Independent reflections
Final R indices [I\2|(I)] R =0.0247, wR =0.0582
R indices (all data)
3695
1
2
R =0.0332, wR =0.0611
1 2

M. Beller et al. / Journal of Organometallic Chemistry 566 (1998) 277–285
285
L.S. Hegedus, Angew. Chem. Int. Ed. Engl. 27 (1988) 1113. (e)
A.L. Casalnuovo, J.L. Calabrese, D. Milstein, J. Am. Chem.
Soc. 110 (1988) 6738. (f) D. Steinborn, B. Thies, I. Wagner, R.
Taube, Z. Chem. 29 (1989) 333. (g) M.R. Gagn e´ , C.L. Stern, T.J.
Marks, J. Am. Chem. Soc. 114 (1992) 275. (h) R.C. Larock, T.R.
Hightower, L.A. Hasvold, K.P. Peterson, J. Org. Chem. 61
in the last cycles for all non-hydrogen atoms. Hydrogen
atoms at C3, C4, C7, and C8 were put in their geomet-
rically calculated positions and refined ‘riding’ on the
corresponding carbon atoms.
(
1996) 3584.
[
[
[
3] C.M. Jensen, W.C. Trogler, Science 233 (1986) 1069.
4] Chem. Engl. News, 31 May (1993) 23.
5] (a) M. Beller, M. Eichberger, H. Trauthwein, Angew. Chem. 109
5
. Summary
Cationic diolefin-rhodium-amine complexes have
(
1997) 2306; M. Beller, M. Eichberger, H. Trauthwein, Angew.
been identified and characterized by X-ray for the first
time. They play an important role in the catalytic
regioselective anti-Markovnikov oxidative amination of
styrenes.
Chem. Int. Ed. Engl. 36 (1997) 2225. (b) M. Beller, M. Eich-
berger, H. Trauthwein in: F.E. Herkes (Ed.), Catalysis in Or-
ganic Synthesis, Marcel Dekker, 1998, (in print).
[
[
6] J.-J. Brunet, D. Neibecker, K. Philippot, Tetrahedron Lett. 34
(
1993) 3877.
7] For an excellent review see: H.E. Bryndza, W. Tam, Chem. Rev.
8 (1988) 1163.
[8] (a) M. Green, T.A. Kuc, S.H. Taylor, J. Chem. Soc. (A) (1971)
334. (b) G. Mestroni, A. Camus, G. Zassinovich, J. Organomet.
8
Acknowledgements
2
Chem. 65 (1974) 119. (c) R. Uson, L.A. Oro, J.A. Cuchi, M.A.
Garralda, J. Organomet. Chem. 116 (1976) C35. (d) B. Denise,
G. Pannetier, J. Organomet. Chem. 63 (1973) 423. (e) H. Brun-
ner, A.F.M.M. Ranman, Chem. Ber. 117 (1984) 710.
We are grateful to the Fonds der Chemischen Indus-
trie for a doctoral scholarship to H. Trauthwein, to the
Studienstiftung des deutschen Volkes and the Max-
Buchner Forschungsstiftung for doctoral scholarships
to A. Zapf, and Degussa AG and Hereaus AG for a
[9] (a) M.A. Garralda, R. Hern a´ ndez, L. Ibarlucea, M.I. Arriotua,
M.K Urtiaga, Inorg. Chim. Acta 232 (1995) 9. (b) E. Anzuela,
M.A. Garralda, R. Hern a´ ndez, L. Ibarlucea, E. Pinilla, M.A.
Monge, Inorg. Chim. Acta 185 (1991) 211.
generous loan of RhCl . T.E. M u¨ ller gratefully ac-
3
knowledges the Liebig-Stipendium granted by the Fond
der Chemischen Industrie. We are also indebted to Dr
Eberhardt Herdtweck (T.U. M u¨ nchen) for taking the
X-ray data as well as Dr J u¨ rgen Herwig and Professor
Dr Klaus K u¨ hlein (both Hoechst AG) for helpful
discussions.
[
[
10] P. Pertici, F. D’Arata, C. Rosini, J. Organomet. Chem. 515
(
1996) 163.
11] H.M. Colquhoun, S.M. Doughty, J.F. Stoddart, A.M.Z. Slawm,
D.J. Williams, J. Chem. Soc. Dalton Trans. (1986) 1639.
12] C. Hahn, J. Sieler, R. Taube, Chem. Ber. 130 (1997) 939.
13] B. Denise, G. Pannetier, J. Organomet. Chem. 161 (1978) 171.
14] R.R. Schrock, J.A. Osborn, J. Am. Chem. Soc. 93 (1971) 3089.
15] D. Selent, D. Scharfenberg-Pfeiffer, G. Reck, R. Taube, J.
Organomet. Chem. 415 (1991) 417.
[
[
[
[
References
[16] (a) P.J. Hendra, D.B. Powell, J. Chem. Soc. (1960) 5105. (b)
W.K. Musker, M.S. Hussain, Inorg. Chem. 8 (1969) 528. (c)
L.K. Singh, S. Mitra, J. Chem. Soc. Dalton Trans. (1987) 2089.
[17] A.J. Blake, G. Reid, M. Schr o¨ der, Polyhedron 9 (1990) 2925.
[18] (a) R.R. Schrock, J.A. Osborn, J. Am. Chem. Soc. 93 (1971)
3089. (b) J. Sanders, J. Chem. Soc. (A) (1971) 2991. (c) L.M.
Haines, Inorg. Chem. 10 (1971) 1685.
[19] G. Giordano, R.H. Crabtree, Inorg. Synth. 19 (1979) 218.
[20] G. Artus, W. Scherer, T. Priermeier, E. Herdtweck, T.U.
M u¨ nchen, 1994.
[
1] For recent reviews see (a) T. M u¨ ller, M. Beller, Chem. Rev. 98
1998) 675. (b) R. Taube in: B. Cornils, W.A. Herrmann (Eds.),
(
Applied Homogeneous Catalysis with Organometallic Com-
pounds, VCH, Weinheim, 1996, p. 507.
[
2] (a) D.R. Coulson, Tetrahedron Lett. (1971) 429. (b) D.R. Coul-
son (Du Pont), US 3.758.586 (1973), (Chem. Abstr. 79 (1973)
1
25808g). (c) D. Steinborn, R. Taube, Z. Chem. 26 (1986) 349.
(d) L.S. Hegedus, Angew. Chem. Int. Ed. Engl. 100 (1988) 1147;
.