Weil-defined regioselective iminopyridine rhodium catalysts for anti-Markovnikov addition of aromatic primary amines to 1-qctyne

Article abstract of DOI:10.1002/adsc.200800786

A series of cationic rhodium(I) complexes of the type [Rh(N-N)(COD)] [BPh₄], containing the following iminopyridine-based bidentate nitrogen donor ligands (N-N): 2,6-diisopropyl-/V-[1-(pyridin-2-yl)ethylidene] aniline (dipea, 1), 2,6-dimethyl-i

Full text of DOI:10.1002/adsc.200800786

FULL PAPERS
DOI: 10.1002/adsc.200800786
Well-Defined Regioselective Iminopyridine Rhodium Catalysts
for Anti-Markovnikov Addition of Aromatic Primary Amines to
1-Octyne
Carlos Alonso-Moreno,a,* Fernando Carrillo-Hermosilla,a
Javier Romero-Fernꢀndez,a Ana M. Rodrꢁguez,a Antonio Otero,a,*
and Antonio AntiÇoloa
a
Departamento de Quꢁmica Inorgꢀnica, Orgꢀnica y Bioquꢁmica, Facultad de Ciencias Quꢁmicas, Universidad de Castilla-La
Mancha, Campus Universitario de Ciudad Real, 13071 Ciudad Real, Spain
Fax : (+34)-26-295-318; phone: (+34)-26-295-326; e-mail: Antonio.Otero@uclm.es
Received: December 18, 2008; Revised: March 26, 2009
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200800786.
Abstract: A series of cationic rhodium(I) complexes these cationic rhodium(I) catalysts occurred in an
of the type [RhACHTUNGTRENNUNG(N-N)ACHTUNRTGEG(NNNU COD)]ACHTNUGRTNEN[UGN BPh4], containing the anti-Markovnikov fashion. The rhodium complexes
following iminopyridine-based bidentate nitrogen catalyzed the regioselective formation of the E-
donor ligands (N-N): 2,6-diisopropyl-N-[1-(pyridin-2- isomer of the corresponding imine, without the for-
yl)ethylidene]aniline (dipea, 1), 2,6-dimethyl-N-[1- mation of the Z-isomer or the Markovnikov product.
(pyridin-2-yl)ethylidene]aniline (dmpea, 2), 2,4,6-tri- These compounds are also presented as efficient re-
methyl-N-[1-(pyridin-2-yl)ethylidene]aniline (tmpea, gioselective catalysts for the hydroamination of ani-
3) and 2,6-diisopropyl-N-[1-(4-methylpyridin-2-yl)- lines in the presence of air and/or water.
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Introduction
group compatibility. Recent advances have been
made using lanthanide and early and late transition
À
C N bond forming reactions are of considerable in- metal catalysts; however, a general catalyst for the
terest in both synthetic organic and industrial chemis- coupling of alkenes or alkynes to amines is still an un-
try due to the importance of amines and their deriva- resolved problem. The efficient hydroamination of
tives in almost all areas of chemistry. The catalytic aliphatic alkenes is not yet possible and remains one
coupling of amines with either alkenes or alkynes by of the most important challenges in catalysis research.
hydroamination is an area that has attracted intense In contrast, alkynes are generally more reactive in hy-
research effort.[1] Hydroamination processes must be droamination reactions.[3] A wide variety of catalysts
regarded as highly desirable transformations in organ- have successfully been employed in the catalytic cycli-
ic chemistry, since the starting materials (alkenes, al- zation of aminoalkynes, although intermolecular ami-
kynes and allenes) are inexpensive and readily avail- nation reactions with alkynes are much more difficult.
able and the products are important bulk and fine Pioneering work was carried out by Barluenga et al.,
chemicals, biologically interesting compounds, or ver- who employed mercury and thallium salts for the
satile synthetic intermediates (amines, imines, enam- Markovnikov hydroamination of alkynes with ani-
ines). More specifically, imines are commonly em- lines.[4] In general, a wide variety of metals, including
À
ployed in C C bond formations, such as Mannich re- early and late transition metals or lanthanides, have
actions and aza-Diels–Alder cycloadditions.[2]
been employed in catalytic intermolecular hydroami-
An ideal catalytic coupling would combine high nation of terminal alkynes to yield Markovnikov
TOF (turnover frequency) and broad functional products.[5] In contrast, the hydroamination of termi-
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Carlos Alonso-Moreno et al.
FULL PAPERS
Scheme 1. Synthesis of compounds 1–4.
nal alkynes in an anti-Markovnikov fashion is rare. NaBPh4 to give the cationic rhodium complexes 1–4
Eisen et al. reported an anti-Markovnikov hydroami- (Scheme 1). All of the complexes are quite air stable
nation of terminal alkynes with primary amines using in the solid state and in solutions in organic solvents
an organouranium complex.[6] Some titanium deriva- such as acetone, MeOH or CH2Cl2.
tives have also been applied for anti-Markovnikov
alkyne hydroamination, although the use of bulky pri- represents
mary amines was required in these cases.[7] Schafer
dene]aniline (dipea, 1), 2,6-dimethyl-N-[1-(pyridin-2-
et al. used bis(amidate)titanium complexes as highly yl)ethylidene]aniline (dmpea, 2), 2,4,6-trimethyl-N-[1-
regioselective catalysts for the anti-Markovnikov hy- (pyridin-2-yl)ethylidene]aniline (tmpea, 3) and 2,6-di-
The products [Rh
ACHTUNGTRENU(GNN N-N)ACHTUNREGT(GNNUN COD)]ACHTUNGTREN[NUGN BPh4] where (N-N)
2,6-diisopropyl-N-[1-(pyridin-2-yl)ethyli-
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
droamination of terminal alkynes with a wide range
ACHTUNGTRENiNUNG sopropyl-N-[1-(4-methylpyridin-2-yl)ethylidene]ani-
of primary amines.[8] Recently, Fukumoto et al. de- line] (dipmpea, 4) were isolated as purple crystalline
scribed the first catalytic system that allows both pri- solids and were fully characterized by spectroscopy,
mary and secondary amines to react with terminal al- elemental analysis and, in the cases of 1, 3 and 4, X-
kynes to give anti-Markovnikov products.[9]
ray crystallographic studies. The NMR characteristics
The work described here concerns our initial ap- of the complexes are consistent with those reported
À
proach to develop effective methods for C N bond for related Pd(II) complexes containing these types of
1
formation. The importance of steric protection in late ligands.[10] The H NMR spectra of compounds 1–4 in
metal-catalyzed chemistry stimulated our interest in acetone-d6 contained resonances at relatively high fre-
the synthesis of bulky iminopyridine-rhodium com- quency and these are assigned to protons of the pyrid-
1
plexes. We envisaged that the use of these bulky com- yl ring. H NMR spectroscopy also provided some in-
pounds as catalysts for hydroamination reactions formation about the behaviour of the aryl susbtituents
might by suitable to achieve better control over the in the iminopyridine ligand.[11] In compounds 1 and 4
regioselectivity of the reaction. The work described the isopropyl groups became magnetically non-equiv-
here involved the synthesis and full characterization alent and this change can be attributed to hindered
of novel cationic rhodium complexes of the type rotation of the aryl rings. Solutions of compounds 1–4
1
[Rh
(N-N)
E
G
nopyridine-based ligands with different levels of steric spectra in the temperature range between 310 and
congestion, the regioselective intermolecular hydro- 183 K. At 273 K only one broad signal is observed for
ACHTUNGTRENNUNG
of air or water has in such reactions.
four resonances shows Rh coupling, which indicates
that the Rh carbon bonds remain intact. Dissociation
À
À
of the Rh N
tion about the intact Rh N
N
À
Results and Discussion
count for this process, although other mechanisms
Iminopyridine ligands were conveniently prepared by cannot be ruled out.
condensation of the appropriate amine and ketone.[10]
Complexes 1·CH2Cl2,
Complexation of the ligand to Rh(I) was achieved by 4·0.25C4H10O·CH2Cl2 were characterized by single-
reaction of the ligand with [RhCl(COD)2] in MeOH crystal X-ray diffraction studies. Selected bond
at room temperature, followed by the addition of
3·2CH2Cl2
and
AHCTUNGTRENNUNG
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Regioselective Iminopyridine Rhodium Catalysts for Anti-Markovnikov Addition
FULL PAPERS
Figure 1. ORTEP plots for the structures of complexes 1, 3 and 4. Thermal ellipsoids are given at the 30% probability level.
lengths and angles, and crystallographic details are the coordination plane is partly controlled by the
collected in the Supporting Information.
imino aryl susbtituents.The geometry around the Rh
A convenient view of the molecules is shown in atom is almost identical in all three compounds. The
À
À
Figure 1 along with the numbering systems used in values of the chelating angles N Rh N are compara-
the crystallographic study. Complexes 3·2CH2Cl2 and ble in the three compounds and reflect the small bite
4·0.25C4H10O·CH2Cl2 crystallize in the triclinic P sizes of the ligands.[11,13]
¯
space group and compound 1·CH2Cl2 crystallizes in
Following the pioneering work carried out by Bar-
the monoclinic P21/n space group. All complexes have luenga et al. on the Markovnikov hydroamination of
a monomeric structure in the solid state and the com- alkynes with anilines,[4] intermolecular hydroamina-
pounds have a square planar geometry with the rhodi- tions have been achieved with catalysts of the alkali
um centre coordinated by a chelating iminopyridine metals,[14] early transition metals,[15] lanthanides and
ligand and by the COD group. As in related systems, actinides.[6,16] The applicability and efficiency of these
À
the plane of the N aryl group lies approximately per- various types of catalysts are still limited due to their
pendicular to the metal coordination plane.[12] In this sensitivity to air, humidity and functional groups. In
conformation the two ortho-alkyl groups are located 1999 Wakatsuki et al. introduced a Ru3(CO)12/acid
in positions that are expected to influence the reactiv- catalyst system that predominantly allowed the con-
ity in associative processes. As a consequence of this version of anilines with terminal phenylacetylenes to
orientation, the free space available at the rhodium in give the corresponding branched imines.[17] However,
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Carlos Alonso-Moreno et al.
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Table 1. Rhodium-catalyzed hydroamination of 1-octyne with 2,4,6-trimethylaniline. Reactions performed in an NMR tube
at 508C with acetone-d6 as the solvent.
Entry
Catalyst
1-Octyne/2,4,6-trimethylaniline
Conversion [%]
Time [h]
TOF Nt25% [hÀ1]
1
2
3
4
5
6
7
8
1 (1.5 mol%)
2 (1.5 mol%)
3 (1.5 mol%)
4 (1.5 mol%)
1 (1.5 mol%)
1 (1.5 mol%)
1 (1.5 mol%)
1 (1.5 mol%)
1 (2.5 mol%)
1 (3.5 mol%)
1 (1.5 mol%)
1 (1.5 mol%)
2
2
2
63
55
70
71
27
63
63
30
63
63
63
63
16
75
40
43
72
16
16
97
24
28
16
16
1.32
0.20
0.53
0.46
0.11
2.64
1.32
0.10
0.21
0.13
1.32
1.32
2
2[a]
1
0.5
2[b]
2
9
10
11
12
2
2[c]
2[d]
[a]
Reaction at room temperature.
3 mol% PCy3.
Reaction exposed to the air.
[b]
[c]
[d]
Mixture of acetone-d6/D2O 9/1 as solvent.
only one example was given for the hydroamination and 2,4,5-trimethylaniline (1:0.5) in acetone-d6 and
of the aliphatic compound 1-octyne with aniline, the reaction mixture was heated at 508C. All of the
which gave the corresponding product in 63% yield. complexes tested catalyzed the intermolecular hydro-
Alternative methods that employed titanium com- amination regioselectively to give the E-isomer,
plexes were developed by Ackermann,[18] Doye,[7c,d] through anti-Markovnikov addition, with varying de-
and Odom[19]. It is noteworthy that all of these ap- grees of efficiency (Table 1, entries 1–4). After 16–
proaches involved reaction temperatures of about 43 h, compounds 1, 3 and 4 had promoted a maximum
1008C and that non-activated aliphatic alkynes have conversion of near 70% (Table 1, entries 1, 3 and 4)
only given low to moderate yields to date. Late transi- while compound 2 needed 75 h (Table 1, entry 2).
tion metal complexes have the advantage of a low ox- Compound 1 was significantly more effective than the
ophility and better functional group tolerance. Rhodi- other catalysts. The substituents on the ligand proved
um or iridium complexes have previously been re- to be an important feature for catalyst activity. The
ported to catalyze intermolecular hydroamina- presence of a more electron-donating alkyl group in
tions.[9,20] Iminopyridines constitute a broad family of the aryl ring seems to improve the efficiency of the
chelating dinitrogen ligands whose coordination catalyst in the hydroamination reaction. Imine 5 was
chemistry has been used in palladium and nickel cat- obtained in moderate to high yields and with excel-
alysis, particularly in olefin polymerization.[11,21] The lent selectivity. Two potential mechanisms for the rho-
results of these studies motivated us to study com- dium catalyst in intermolecular hydroamination reac-
plexes 1–4 as suitable active catalysts in intermolecu- tion of 1-octyne with 2,4,6-trimethylaniline are out-
lar hydroamination reactions. The initial experiments lined in Figure 2: Path A involves activation of the C-
involving the hydroamination of alkynes were per- C multiple bond by coordination to a Lewis acidic
formed under previously described standard reactions metal centre, which renders the alkyne susceptible to
conditions.[20a] The most stable imine was obtained by nucleophilic attack by the lone electron pair of the
hydroamination of the alkyne followed by tautomeri- amine nitrogen atom. Subsequent protolytic cleavage
zation of the resultant enamine.
of the metal-carbon bond provides the enamine prod-
Complexes 1–4 were tested as catalysts in intermo- uct, which desorbs from the coordination sphere of
lecular hydroamination reactions; 1.5 mol% of the the metal. The resulting enamine isomerizes to the
rhodium complex was added to a mixture of 1-octyne corresponding imine. On the other hand, an amine ac-
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Regioselective Iminopyridine Rhodium Catalysts for Anti-Markovnikov Addition
FULL PAPERS
Figure 2. Proposed mechanisms for the hydroamination reaction of 1-octyne with 2,4,6-trimethylaniline in the presence of a
cationic rhodium catalyst 1–4.
tivation pathway cannot be excluded (Path B). This to the alkyne/amine ratio, the yields did not increase
pathway might be effective for the couple Rh(I)/ on using an excess of either amine or alkyne (Table 1,
RhACHTUNGTRENNUNG
(III).[20c,d,22] Oxidative addition of the amine pro- entries 6 and 7).
vides a hydrido-amido complex. Subsequently, the
In 2001 Beller et al.[20a] reported the efficient con-
À
alkyne inserts into the M N bond. Reductive elimina- version of aliphatic alkynes with anilines by means of
tion of the product regenerates the active low-valent a commercially available rhodium catalyst. However,
metal species and generates the enamine product, the addition of a phosphine is a prerequisite for a suc-
which tautomerizes to the more stable imine.
cessful reaction since in the absence of phosphine the
Oligomerization of the alkyne was observed as a product is only formed in very low yields. In order to
side reaction. It is important to note that the use of a improve the activities obtained in our experiments,
lower reaction temperature can be a decisive factor in we attempted to achieve the hydroamination reaction
the activity (Table 1, entry 5) but did not appreciably of 1-octyne and 2,4,6-trimethylaniline with compound
influence in the production of oligomers. With respect 1 as the catalyst in the presence of PCy3. Appreciable
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Carlos Alonso-Moreno et al.
Table 2. [RhACHTUNGTRENNUNG(dipea)ACHTUNGTRENNUNG(COD)]ACTHUNGTRENNNGU
[BPh4] 1 (1.5 mol%) catalyzed hydroamination of 1-octyne with aromatic primary amines.[a]
FULL PAPERS
Entry
Amine
Conversion [%]
Time [h]
TOF Nt25% [hÀ1]
1
2
3
4
5
6
7
8
9
2,4,6-trimethylaniline
aniline
2,6-diisopropylaniline
2-bromoaniline
4-bromoaniline
4-tert-butylaniline
4-methylaniline
63
25
50
50
31
42
42
70
40
16
4
96
2
7
2.5
8
1.32
2.08
0.17
8.3
1.49
5.6
1.73
2.98
0.27
2,6-di-tert-butylaniline
2,6-dimethylaniline
8
50
[a]
Reactions were run in an NMR tube at 508C with acetone-d6 as solvent and a ratio 1-octyne/amine of 2.
improvement in the activity was not observed after
ACHTUNGTRENaNUNG niline, we decided to expand the scope of the sub-
the test (Table 1, entry 8). Compounds 1–4 are pre- strate with a series of different substitution patterns
sented as convenient catalysts for hydroamination re- in the aniline (Table 2). The results obtained with 1 as
actions without the need to use an external base and a catalyst in the hydroamination reactions of 1-octyne
these reactions give moderate to good yields.
are summarized in Table 2 (entries 1–9). The imines
In order to assess the influence of the catalyst con- 5–13 were obtained as single products (see isolated
centration on the outcome of the reaction, different yields in the Experimental Section). Electron-donat-
concentrations of catalyst 1 were used, while the con- ing and electron-withdrawing susbtituents on the ani-
centrations 1-octyne and amine were kept constant line ring are tolerated. The conversion levels and the
(Table 1, entries 1, 9 and 10). A decrease in the turn- yields in these reactions were found to vary from
over frequency was observed on increasing the cata- moderate to high and in all cases the isomer with E
lyst concentration. This observation could be indica- stereochemistry was obtained as the only product. To
tive of the formation of a less reactive ion aggregate make sure that the structure determination of the
in solution.
imine was correct, we synthesized as example the E-
The results shown in entry 11 (Table 1) represent a imine 5 from the corresponding aldehyde and primary
catalyst assay in which purification of solvents and ex- amine.[23] The spectral data of (E)-2,4,6-trimethyl-N-
clusion of air were not performed. It can be seen that octylideneaniline compare well with those of com-
catalyst 1 did not lose activity in this assay, showing it pound 5, proving the isolation of the E-isomer of the
to be an efficient catalyst for hydroamination reaction imine products. Unfortunately, the scope of the reac-
in the presence of air. As special purifications or ex- tion is strongly limited to aliphatic terminal alkynes
clusion of water were not required (Table 1, entry 11), and primary amines. In the case of phenylacetylene or
catalyst 1 was evaluated with deuterated water as a 2-octyne, rapid oligomerization occurred and this re-
co-solvent (Table 1, entry 12). Changes in efficiency sulted in very low product yields. Concerning the use
were not observed under these conditions.
of secundary amines, no reaction was observed when
Encouraged by the performance of complex 1 in N-methylaniline, morpholine or piperidine were used
the hydroamination of 1-octyne with 2,4,6-trimethyl- as substrates.
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Regioselective Iminopyridine Rhodium Catalysts for Anti-Markovnikov Addition
FULL PAPERS
Conclusions
X-Ray Crystallographic Structure Determination for
Complexes 1·CH2Cl2, 3·2CH2Cl2 and
In conclusion, a rhodium catalyst stabilized by a che- 4·0.25C4H10O·CH2Cl2
lating iminopyridine ligand has been prepared that
Single crystals were mounted on a glass fibre and trans-
had not previously been reported to catalyze the in-
termolecular hydroamination of alkynes in an anti-
Markovnikov fashion to yield the corresponding
imine derivatives. Therefore, compounds 1–4 were
able to catalyze the selective formation of the E-
isomer. Further studies examining thoroughly the
effect of changes to the substituents of the ligand
framework on the catalysis behaviour of the com-
plexes are underway.
ferred to a Bruker X8 APEX II CCD-based diffractometer
equipped with a graphite monochromated Mo-Ka radiation
source (l=0.71073 ꢃ). Data were integrated using
SAINT[24] and an absorption correction was performed with
the program SADABS.[25] The software package SHELXTL
version 6.12[26] was used for space group determination,
structure solution and refinement by full-matrix least-
squares methods based on F2. All non-hydrogen atoms were
refined with anisotropic thermal parameters. Hydrogen
atoms were placed using a “riding model” and included in
the refinement at calculated positions.
CCDC 713863, 713864 and 713865 contain the supplemen-
tary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
Experimental Section
General Procedures
All manipulations were performed under nitrogen using
standard Schlenk techniques. [RhClACTHNUTRGENUG(N COD)]2 and MeOH
Synthesis of Rhodium Complexes
were used as purchased (Aldrich). Liquid amines were dis-
tilled from CaH2. Alkynes were degassed, flushed with ni-
trogen, and stored over molecular sieves (4 ꢃ). Iminiopyri-
dine ligands were obtained by standard literature meth-
ods.[10] Deuterated solvents were stored over activated 4 ꢃ
molecular sieves and degassed by several freeze-thaw cycles.
Microanalyses were carried out with a Perkin–Elmer 2400
[Rh
solution of dipea [2,6-diisopropyl-N-(1-(pyridin-2-yl)ethyl-
idene)aniline] (0.37 g, 1.20 mmol) in CH3OH (10 mL) was
added dropwise by cannula under N2 to a solution of [RhCl-
(COD)]2 (0.30 g, 0.60 mmol) in CH3OH (20 mL). The solu-
tion became dark purple and the mixture was stirred for 1
hour. After this time, solution of NaBPh4 (0.41 g,
ACHTUNGRTEN(GNUN dipea)ACHTUNGTREG(NNUN COD)]CAHTNUGTERN[NUNG BPh4] (1): In a 250-mL Schlenk tube, a
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
1
CHN analyzer. H and 13C NMR spectra were recorded on a
a
Varian Mercury FT-300 spectrometer and referenced to the
residual deuterated solvent. The NOESY-1D, g-HSQC,
DEPT, COSY spectra were recorded on a Varian Inova FT-
500 spectrometer with the following acquisition parameters:
irradiation time 2 s and number of scans 256, using standard
Varian-FT software. Two-dimensional NMR spectra were
acquired using standard Varian-FT software and processed
using an IPC-Sun computer. The imine product structures
were confirmed by GC-MS analyses at ꢄLaboratorio Espec-
trometrꢁa Masas y Cromatografꢁaꢅ, University of Cꢆrdoba
(Spain).
1.20 mmol) in CH3OH (20 mL) was added to the mixture. A
dark purple precipitate was observed. The solid was filtered
off and recrystallized from CH2Cl2/Et2O (8/2) at À268C to
give compound 1 as purple crystals suitable for X-ray dif-
fraction; yield: 0.45 g (93%). Anal. calcd. for C51H56BN2Rh:
C 75.56, H 6.96, N 3.46; found: C 74.98, H 6.64, N, 3.79;
1H NMR (300 MHz, acetone-d6, 297 K): d=8.29 (m, 1H,
H3-py), 8.26 (m, 1H, H6-py), 8.06 (m, 1H, H5-py), 7.82 (m,
1H, H4-py), 7.41 (m, 2H, m-Ar), 6.94 (m, 1H, p-Ar), 7.34,
6.77, 6.92 (3 m, 20H, phenyl rings), 4.18 (bs, 4H, H1’,2’,5’,6’-
COD), 3.23 [m, 2H, CH(Me)2], 2.48, 2.06 (m, 4H,
H3’,4’,7’,8’-COD), 2.05 (s, 3H, (Me)C=N), 1.47, 1.14 [2d, 6H
3
each, J=7 Hz, CH(Me)2]; 13C NMR (300 MHz, acetone-d6,
General Procedure for Hydroamination Reactions in
NMR Tube Scale
297 K): d=206.3 (C=N), 142.4 (C3-py), 140.1 (C6-py), 131.0
(C5-py), 129.3 (p-Ar), 128.9 (C4-py), 125.3 (m-Ar), 122.2,
125.9, 136.9 (phenyl rings), 88.1 (C1’,2’,5’,6’-COD), 30.1, 29.8
(C3’,4’,7’,8’-COD), 29.7 [CH(Me)2], 28.7 [(Me)C=N], 25.2,
23.6 [CH(Me)2].
Catalytic reactions were performed on a small scale in an
NMR tube fitted with a concentric Teflon valve. Reactions
were performed in the NMR spectrometer with 0.5 mmol of
aromatic primary amine, 1 mmol of 1-octyne and 1.5 mol%
of cationic rhodium complex in approximately 0.6 mL of
acetone-d6 at 508C under nitrogen. The conversion of the
starting material to product was determined by integration
of the product resonances relative to the substrate peaks in
[Rh
ACHTUNGTREN(UNGN dmpea)ACHTUNTRGEG(NNUN COD)]ACUTHNGTRENNUNG
carried out in an identical manner to 1. [RhClACHTUNGTRENNUNG
(0.30 g, 0.60 mmol), dmpea [2,6-dimethyl-N-(1-(pyridin-2-
yl)ethylidene)aniline] (0.27 g, 1.20 mmol) and NaBPh4
(0.41 g, 1.20 mmol); yield: 0.41 g (91%). Anal. calcd. for
C47H48BN2Rh: C 74.81, H 6.41, N 3.71; found: C 75.10, H
6.34, N 3.57; 1H NMR (300 MHz, acetone-d6, 297 K): d=
8.34 (m, 1H, H3-py), 8.29 (m, 1H, H6-py), 8.13 (m, 1H, H5-
py), 7.88 (m, 1H, H4-py), 7.24 (m, 2H, m-Ar), 7.21 (m, 1H,
p-Ar), 7.33, 6.77, 6.92 (3 m, 20H, phenyl rings), 4.18 (bs,
4H, H1’,2’,5’,6’-COD), 2.49, 2.08 (2 m, 4H each, H3’,4’,7’,8’-
COD), 2.34 (s, 6H, o-Me-Ar), 2.05 [s, 3H, (Me)C=N];
13C NMR (300 MHz, acetone-d6, 297 K): d=206.3 (C=N),
143.8 (C3-py), 143.4 (C6-py), 132.0 (C5-py), 129.8 (p-Ar),
1
the H NMR spectrum. The TOF (turnover frequency) (Nt/
h) was calculated as the number of moles of product/mole
of catalyst/hour and was calculated at the point of 25% con-
version of substrate to product.
Adv. Synth. Catal. 2009, 351, 881 – 890
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asc.wiley-vch.de
887

Carlos Alonso-Moreno et al.
FULL PAPERS
129.3 (C4-py), 126.3 (m-Ar), 122.2, 125.9, 136.9 (phenyl
rings), 88.3 (C1’,2’,5’,6’-COD), 30.4, 30.2 (C3’,4’,7’,8’-COD),
30.3 [(Me)C=N], 19.2 (o-Me-Ar).
1H NMR (300 MHz, acetone-d6, 297 K): d=7.40 (m, 1H,
H8), 7.21 (m, 2H, H11,13), 6.69 (m, 1H, H12), 6.51 (m, 2H,
H10,14), 2.20–2.06 (m, 6H, H5,6,7), 1.62–1.29 (m, 6H,
H2,3,4), 0.92 (m, 3H, H1); 13C NMR (75 MHz, acetone-d6,
508C): d=163.4 (C8), 145.1 (C9), 133.4 (C11,13), 125.6
(C12), 117.0 (C10,14), 28.1 (C5), 26.4 (C4), 25.3 (C6), 19.3
(C7), 14.8 (C2,3), 10.4 (C1); MS: m/z (%)=203 (M+, 31), 77
(78), 132 (100).
[Rh
ACHTUNGTRENNUNG(tmpea)ACHTUNGTRENNUNG(COD)]ACUTHNGTRENNNUG
ried out in an identical manner to 1. [RhClACHTUNGTRENNNUG
0.60 mmol), tmpea [2,4,6-trimethyl-N-(1-(pyridin-2-yl)ethyli-
dene)aniline] (0.29 g, 1.20 mmol) and NaBPh4 (0.41 g,
1.20 mmol); yield: 0.42 g (94%); anal. calcd. for
C48H50BN2Rh: C 75.00, H 6.56, N 3.64; found: C 75.21, H
6.39, N 3.73; 1H NMR (300 MHz, acetone-d6, 297 K): d=
8.30 (m, 1H, H3-py), 8.28 (m, 1H, H6-py), 8.10 (m, 1H, H5-
py), 7.84 (m, 1H, H4-py), 7.05 (m, 2H, m-Ar), 7.34, 6.77,
6.92 (3 m, 20H, phenyl rings), 4.13 (bs, 4H, H1’,2’,5’,6’-
COD), 2.48, 2.06 (2 m, 4H each, H3’,4’,7’,8’COD), 2.30 (s,
3H, p-Me-Ar), 2.28 (s, 6H, o-Me-Ar), 2.05 [s, 3H, (Me)C=
N]; 13C NMR (300 MHz, acetone-d6, 297 K): d=206.3 (C=
N), 141.8 (C3-py), 139.9 (C6-py), 130.3 (C5-py), 128.7 (C4-
py), 125.3 (m-Ar), 121.6, 125.4, 136.4 (phenyl rings), 87.5
(C1’,2’,5’,6’-COD), 30.5, 30.1 (C3’,4’,7’,8’-COD), 30.2
[(Me)C=N], 20.2 (p-Me-Ar), 17.4 (o-Me-Ar).
(E)-2,6-Diisopropyl-N-octylideneaniline (7): The synthesis
of 7 was carried out in an identical manner to 5. 1-Octyne
(0.55 g, 5.0 mmol), [RhACTHUNGTREN(NNUG dipea)ACHNUTRTGEN(NGUN COD)]CAHTNUGTREN[NUGN BPh4] 1 (1.5 mol%)
and 2,6-diisopropylaniline (0.72 g, 2.5 mmol). Fractional dis-
tillation afforded 6 as a colourless oil; yield: 48%; bp 86–
1
878C/0.1–0.2 mbar; H NMR (300 MHz, acetone-d6, 297 K):
3
d=7.40 (m, 1H, H8), 7.08 (t, 1H, JH,H =7.6 Hz, H12), 6.99
(m, 2H, 3JH,H =7.6 Hz, H11,13), 2.69 [m, 2H, CH
ACHTUNGTRENNUNG
[d, 12H, 3JH,H =6.6 Hz, CH
ACTHNUGTRNEG(UN CH3)2], 1.53–1.10 (m, 6H,
H2,3,4), 0.92 (m, 3H, H1); 13C NMR (75 MHz, acetone-d6,
297 K): d=163.4 (C8), 147.1 (C9), 122.8 (C11,13), 119.9
[Rh
ACHTUNGTRENNUNG(dipmpea)ACHTUNGTRENNUNG(COD)]ACUTHNGTRENNNUG
(C12), 31.6 (C5), 29.3 (C4), 27.9 (C6), 26.4 [CHACHTNUGTRNEG(UN CH3)2], 22.7
carried out in an identical manner to 1. [RhClACHTUNGTRENNUNG
(C7), 22.3 [CHACTHUNTRGNE(UNG CH3)2], 18.6 (C3), 18.3 (C2), 14.8 (C1); MS:
(0.30 g, 0.60 mmol), dipmpea [2,6-diisopropyl-N-(1-(5-meth-
ylpyridin-2-yl)ethylidene)aniline] (0.35 g, 1.20 mmol) and
NaBPh4 (0.41 g, 1.20 mmol); yield: 0.46 g (94%); anal. calcd.
for C52H58BN2Rh: C 75.73, H 7.09, N 3.40; found: C 75.61,
m/z (%)=287 (M+, 28), 216 (100), 161 (70).
(E)-2-Bromo-N-octylideneaniline (8): The synthesis of 8
was carried out in an identical manner to 5. 1-Octyne
(0.55 g, 5.0 mmol), [RhACTHUNGTREN(NNUG dipea)ACHNUTRTGEN(NGUN COD)]CAHTNUGTREN[NUGN BPh4] 1 (1.5 mol%)
1
H 6.89, N 3.13; H NMR (300 MHz, acetone-d6, 297 K): d=
and 2-Bromoaniline (0.71 g, 2.5 mmol). Fractional distilla-
tion afforded 6 as a colourless oil; yield: 49%; bp 86–878C/
0.1–0.2 mbar; 1H NMR (300 MHz, acetone-d6, 297 K): d=
7.42 (m, 1H, H8), 7.33, 7.29, 6.93, 6.84 (4 m, 1H each, H11–
14), 2.81 (m, 2H, H7), 2.20–2.06 (m, 4H, H6,5), 1.50–1.00
(m, 6H, H4,3,2), 0.92 (m, 3H, H1); 13C NMR (75 MHz, ace-
tone-d6, 297 K): d=162.2 (C8), 145.9 (C9), 142.1 (C13),
136.2 (C12), 129.3 (C11), 119.1 (C10), 31.9 (C4), 28.5 (C5),
28.3 (C6), 22.5 (C7), 19.9 (C2,3), 17.1 (C1); MS: m/z (%)=
281 (M+, 21), 209 (100), 154 (44).
8.20 (m, 1H, H3-py), 7.94 (m, 1H, H6-py), 7.70 (m, 1H, H5-
py), 7.34 (m, 1H, p-Ar), 6.90 (m, 2H, m-Ar), 7.34, 6.77, 6.92
(3 m, 20H, phenyl rings), 4.13 (bs, 4H, H1’,2’,5’,6-COD),
2.47, 2.07 (2 m, 4H each, H3’,4’,7’,8’-COD), 3.23 [m, 2H,
3
CH(Me)2], 2.60 (s, 3H, Me-Ar), 1.48, 1.14 [2d, 6H each, J=
7 Hz, CH(Me)2], 2.05 [s, 3H, (Me)C=N], 13C NMR
(300 MHz, acetone-d6, 297 K): d=206.3 (C=N), 149.4 (C3-
py), 139.5 (C6-py), 130.6 (C5-py), 129.5 (p-Ar), 128.8 (C4-
py), 125.4 (m-Ar), 121.6, 124.8, 136.5 (phenyl rings), 87.8
(C1’,2’,5’,6’-COD), 30.3, 29.9 (C3’,4’,7’,8’-COD), 29.4
[CH(Me)2], 28.7 [(Me)C=N], 24.6, 23.0 [CH(Me)2], 20.9
(Me-py).
(E)-4-Bromo-N-octylideneaniline (9): The synthesis of 9
was carried out in an identical manner to 5. 1-Octyne
(0.55 g, 5.0 mmol), [RhACTHUNGTREN(NNUG dipea)ACHNUTRTGEN(NGUN COD)]CAHTNUGTREN[NUGN BPh4] 1 (1.5 mol%)
and 4-Bromoaniline (0.65 g, 2.5 mmol). Fractional distilla-
tion afforded 9 as a colourless oil; yield: 28%; bp 85–868C/
0.1–0.2 mbar; 1H NMR (300 MHz, acetone-d6, 297 K): d=
Synthesis of Imine Compounds
(E)-2,4,6-Trimethyl-N-octylideneaniline
(0.55 g, 5.0 mmol) was added dropwise to a solution of the
[Rh(dipea)(COD)][BPh4] 1 (1.5 mol%) and 2,4,6-trimethy-
(5):
1-Octyne
3
7.45 (m, 1H, H8), 7.35 (d, 2H, JH,H =8.4 Hz, H13,11), 6.54
3
(d, 2H, JH,H =8.4 Hz, H14,10), 2.24 (m, 2H, H7), 2.20–2.06
A
R
ACHTUNGTRENNUNG
(m, 4H, H6,5), 1.50–1.00 (m, 6H, H4,3,2), 0.92 (m, 3H, H1);
13C NMR (75 MHz, acetone-d6, 297 K): d=160.2 (C8), 148.9
(C9), 132.4 (C11,13), 122.2 (C10,14), 31.2 (C5), 29.1 (C4),
27.9 (C6), 21.1 (C7), 18.6 (C3), 18.3 (C2), 13.9 (C1). MS:
m/z (%)=281 (M+, 21), 224 (100), 154 (44).
(E)-4-tert-butyl-N-octylideneaniline (10): The synthesis of
10 was carried out in an identical manner to 5. 1-Octyne
laniline (0.34 g, 2.5 mmol) in acetone (30 mL) at room tem-
perature, and the mixture was refluxed for 24 h. Isolation of
the product was done by fractional distillation under
vacuum; yield: 55%; bp 71–728C/0.1–0.2 mbar; 1H NMR
(300 MHz, acetone-d6, 297 K): d=7.40 (m, 1H, H8), 6.81 (s,
2H, H11,13), 2.27 (m, 2H, H7), 2.23 (s, 3H, Me12), 2.17 (m,
2H, H6), 2.06 (m, 2H, H5), 1.93 (s, 6H, Me10,14), 1.29–1.62
(m, 6H, H2,3,4), 0.92 (m, 3H, H1; 13C NMR (75 MHz, ace-
tone-d6, 297 K): d=163.4 (C8), 146.9 (C9), 136.4 (C11,13),
131.2 (C10,14), 128.7 (C12), 31.5 (C5), 28.9 (C4), 28.7 (C6),
22.7 (C7), 18.3 (C3), 18.1 (C2), 22.6 (Me12), 17.3 (Me10,14),
13.8 (C1); MS: m/z (%)=245 (M+, 38), 119 (81), 189 (100).
(E)-N-Octylideneaniline (6): The synthesis of 6 was car-
ried out in an identical manner to 5. 1-Octyne (0.55 g,
(0.55 g, 5.0 mmol), [RhACTHUNGTREN(NNUG dipea)ACHNUTRTGEN(NGUN COD)]CAHTNUGTREN[NUGN BPh4] 1 (1.5 mol%)
and 4-tert-butylaniline (0.64 g, 2.5 mmol). Fractional distilla-
tion afforded 10 as a colourless oil; yield: 40%; bp 87–888C/
0.1–0.2 mbar; 1H NMR (300 MHz, acetone-d6, 297 K): d=
3
7.41 (m, 1H, H8), 7.36 (d, 2H, JH,H =8.1 Hz, H13,11), 6.61
3
(d, 2H, JH,H =8.1 Hz, H14,10), 2.27 (m, 2H, H7), 2.20–2.06
(m, 4H, H6,5), 1.21 (s, 9H, t-Bu12), 1.50–1.00 (m, 6H,
H4,3,2), 0.92 (m, 3H, H1); 13C NMR (75 MHz, acetone-d6,
297 K): d=161.6 (C8), 150.1 (C9), 138.6 (C11,13), 120.9
(C10,14), 31.3 (C5), 31.6 (t-Bu12), 29.3 (C4), 27.9 (C6), 22.5
5.0 mmol), [RhACHTUNGTRENNUNG(dipea)AHCTUNRTEGNN(GUN COD)]ACHTUNGTREN[NUGN BPh4] 1 (1.5 mol%) and ani-
line (0.51 g, 2.5 mmol). Fractional distillation afforded 6 as a
colourless oil; yield: 20%; bp 65–668C/0.1–0.2 mbar;
888
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Adv. Synth. Catal. 2009, 351, 881 – 890

Regioselective Iminopyridine Rhodium Catalysts for Anti-Markovnikov Addition
FULL PAPERS
(C7), 18.5 (C3), 18.3 (C2), 13.8 (C1); MS: m/z (%)=259 References
(M+, 34), 202 (100), 133 (66).
(E)-4-Methyl-N-octylideneaniline (11): The synthesis of
11 was carried out in an identical manner to 5. 1-Octyne
(0.55 g, 5.0 mmol), [RhACTHUNGTREN(NNUG dipea)ACHNUTRTGEN(NGUN COD)]CAHTNUGTREN[NUGN BPh4] 1 (1.5 mol%)
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[5] For recent reports on the intermolecular Markovnikov
hydroamination of alkynes, see: a) R.-Y. Lai, K. Sure-
kha, A. Hayashi, F. Ozawa, Y.-H. Liu, S.-M. Peng, S.-T.
Liu, Organometallics 2007, 26, 1062; b) N. Lingaiah,
N. S. Babu, K. M. Reddy, P. S. Prasad, I. Suryanarayana,
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and 4-methylaniline (0.54 g, 2.5 mmol). Fractional distilla-
tion afforded 11 as a colourless oil; yield: 40%; bp 68–698C/
0.1–0.2 mbar; 1H NMR (300 MHz, acetone-d6, 297 K): d=
3
7.44 (m, 1H, H8), 7.10 (d, 2H, JH,H =8.1 Hz, H13,11), 6.59
3
(d, 2H, JH,H =8.1 Hz, H14,10), 2.27 (m, 2H, H7), 2.20–2.06
(m, 4H, H6,5), 2.23 (s, 3H, Me12), 1.50–1.00 (m, 6H,
H4,3,2), 0.92 (m, 3H, H1); 13C NMR (75 MHz, acetone-d6,
297 K): d=161.7 (C8), 152.1 (C9), 135.5 (C11,13), 123.8
(C10,14), 31.6 (C5), 29.3 (C4), 26.6 (Me12), 26.6 (C6), 22.8
(C7), 17.9 (C3), 17.7 (C2), 14.1 (C1); MS: m/z (%)=217
(M+, 13), 160 (100), 91 (63).
(E)-2,6-Di-tert-butyl -N-octylideneaniline (12): The syn-
thesis of 12 was carried out in an identical manner to 5. 1-
Octyne (0.55 g, 5.0 mmol), [RhACHTNUGTREN(NNGU dipea)ACHTUNTRGEG(NNNU COD)]ACHTNGUTREN[UNNG BPh4] 1 (1.5
mol%) and 2,6-di-tert-butylaniline (0.79 g, 2.5 mmol). Frac-
tional distillation afforded 12 as a colourless oil; yield: 66%;
1
bp 100–1028C/0.1–0.2 mbar; H NMR (300 MHz, acetone-d6,
297 K): d=7.41 (m, 1H, H8), 7.14 (t, 1H, 3JH,H =7.6 Hz,
H12), 6.53 (m, 2H, 3JH,H =7.6 Hz, H11,13), 2.21 (m, 2H,
H7), 2.17 (m, 2H, H6), 2.06 (m, 2H, H5), 1.27 (s, 18H, t-
Bu14,10), 1.50–1.10 (m, 6H, H2,3,4), 0.92 (m, 3H, H1);
13C NMR (75 MHz, acetone-d6, 297 K): d=163.4 (C8), 151.2
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1996, 15, 3773.
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18.5 (C2), 14.18 (C1); MS m/z (%)=315 (M+, 19), 272
(100), 189 (55).
(E)-2,6-Dimethyl-N-octylideneaniline (13): The synthesis
of 13 was carried out in an identical manner to 5. 1-Octyne
(0.55 g, 5.0 mmol), [RhACTHUNGTREN(NNUG dipea)ACHNUTRTGEN(NGUN COD)]CAHTNUGTREN[NUGN BPh4] 1 (1.5 mol%)
and 2,6-dimethylaniline (0.58 g, 2.5 mmol). Fractional distil-
lation afforded 13 as a colourless oil; yield: 37%; bp 69–
1
708C/0.1–0.2 mbar; H NMR (300 MHz, acetone-d6, 297 K):
3
d=7.40 (m, 1H, H8), 6.98 (d, 2H, JH,H =7.1 Hz, H11,13),
6.82 (m, 1H, H12), 2.24 (m, 2H, H7), 2.17 (m, 2H, H6), 2.06
(m, 2H, H5), 1.97 (s, 6H, Me14,10), 1.53–1.10 (m, 6H,
H2,3,4), 0.92 (m, 3H, H1); 13C NMR (75 MHz, acetone-d6,
297 K): d=160.4 (C8), 149.8 (C9), 127.6 (C12), 116.9
(C11,13), 31.6 (C5), 29.3 (C4), 27.9 (C6), 22.7 (C7), 18.7
(C3), 18.5 (Me14,10), 18.3 (C2), 13.8 (C1); MS: m/z (%)=
231 (M+, 12), 188 (100), 105 (60).
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Supporting Information
Full crystallographic data for 1, 3 and 4 are available in the
Supporting Information.
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We gratefully acknowledge financial support from the Minis-
terio de Ciencia e Innovaciꢀn, Spain (Grant Nos. Consolider-
Ingenio 2010 ORFEOCSD2007-00006, CTQ2005-08123-
C02–01/BQU, CTQ2006-11845/BQU) and the Junta de Co-
munidades de Castilla-La Mancha, Spain (Grant No. PCI08-
0010).
Adv. Synth. Catal. 2009, 351, 881 – 890
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
889

Carlos Alonso-Moreno et al.
FULL PAPERS
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by combining the aldehyde and 2,4,6-trimethylamine
(5 mmol each) in toluene (5 mL) at 238C, removing the
solvent under vacuum, filtering the toluene solution of
the residue through activated silica gel (0.2 g), and con-
centrating to afford the pure imine.
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