Palladium-catalyzed cyclization of 6-aminohex-1-yne

Article abstract of DOI:10.1021/om010524n

Mechanistic details and limiting factors for the palladium-catalyzed addition of amines to alkynes (hydroamination) were studied, using the cyclization of 6-aminohex-1-yne to 2-methyl-1,2-dehydropiperidine as a specific example. The complex [Pd(Triphos)](CF₃SO₃)₂ showed the highest catalytic activity of a series of structurally and electronically distinct palladium complexes. Several methods, such as calorimetry and in situ IR and NMR spectroscopy, were used to obtain evidence for a possible reaction cycle. It seems likely that (i) the substrate initially coordinates via the amine group and (ii) an intermediate is formed which is the product of a nucleophilic attack of the amine on a coordinated alkyne. Addition of an acid to the reaction mixture led to a strong increase in the reaction rate, probably by accelerating protolytic cleavage of the palladium-carbon bond in the intermediate complex.

Full text of DOI:10.1021/om010524n

4384
Organometallics 2001, 20, 4384-4393
P a lla d iu m -Ca ta lyzed Cycliza tion of 6-Am in oh ex-1-yn e
Thomas E. Mu¨ller,*,† Michael Berger,‡ Manja Grosche,§
Eberhardt Herdtweck,§ and Franz P. Schmidtchen‡
Lehrstuhl fu¨r Technische Chemie II, Technische Universita¨t Mu¨nchen, Lichtenbergstrasse 4,
85747 Garching, Germany, Lehrstuhl fu¨r Organische Chemie und Biochemie, Technische
Universita¨t Mu¨nchen, Lichtenbergstrasse 4, 85747 Garching, Germany, and Anorganisch
Chemisches Institut, Technische Universita¨t Mu¨nchen, Lichtenbergstrasse 4, 85747 Garching,
Germany
Received J une 15, 2001
Mechanistic details and limiting factors for the palladium-catalyzed addition of amines
to alkynes (hydroamination) were studied, using the cyclization of 6-aminohex-1-yne to
2-methyl-1,2-dehydropiperidine as a specific example. The complex [Pd(Triphos)](CF3SO3)2
showed the highest catalytic activity of a series of structurally and electronically distinct
palladium complexes. Several methods, such as calorimetry and in situ IR and NMR
spectroscopy, were used to obtain evidence for a possible reaction cycle. It seems likely that
(i) the substrate initially coordinates via the amine group and (ii) an intermediate is formed
which is the product of a nucleophilic attack of the amine on a coordinated alkyne. Addition
of an acid to the reaction mixture led to a strong increase in the reaction rate, probably by
accelerating protolytic cleavage of the palladium-carbon bond in the intermediate complex.
In tr od u ction
interest for industrial applications. From the pioneering
work of Reppe it is known that group 12 elements,
especially cadmium and mercury, can catalyze the
addition of secondary amines to acetylene to give the
corresponding enamines.21-23 More recently, a number
of structurally different late transition metal complexes
were found to be good catalysts for the intra- and
intermolecular addition of amines to alkynes.24-27 Ex-
Catalytic C-N forming processes are of fundamental
importance in organic chemistry. However, the direct
addition of N-H bonds across the unsaturated carbon-
carbon bond in alkenes or alkynes (hydroamination)
remains challenging.1 The industrial potential of hy-
droamination reactions is high, and tert-butylamine is
produced on a large scale from ammonia and isobutene.2
The catalyst employed in the commercial process is a
zeolite which acts as a solid acid and activates the
alkene by protonation. Therefore, the method is limited
to alkenes that form a stable carbenium ion. Alternative
approaches for hydroamination catalysts are based on
activation of the amine group with group 1 metal
bases3-7 and group 3 to 4 metal complexes.8-13 Catalysis
by late transition metals14-20 would be of particular
amples are the cyclization of o-alkynylanilines to indoles
28,29
with PdCl2
and of 1-aminoalk-n-ynes to pyrrolines
(n ) 3, 4) or 1,2-dehydropiperidines (n ) 5) with
NaAuCl4‚2H2O30 or [Ni(CO)2(PPh3)2].31
The purpose of this study is to explore the potential
of palladium complexes as hydroamination catalysts and
to provide evidence for a possible reaction mechanism.
The investigation is focused on palladium complexes,
(16) Beller, M.; Trauthwein, H.; Eichberger, M.; Breindl, C.; Mu¨ller,
T. E. Eur. J . Inorg. Chem. 1999, 1121.
* Corresponding author. E-mail: thomas.mueller@ch.tum.de. Tel:
+49-89-289.13538. Fax: +49-89-289-13544.
(17) Beller, M.; Trauthwein, H.; Eichberger, M.; Breindl, C.; Herwig,
J .; Mu¨ller, T. E.; Thiel, O. R. Chem. Eur. J . 1999, 5, 1306.
(18) Brunet, J .-J . Gazz. Chim. Ital. 1997, 127, 111.
(19) Dorta, R.; Egli, P.; Zu¨rcher, F.; Togni, A. J . Am. Chem. Soc.
1997, 119, 10857.
† Lehrstuhl fu¨r Technische Chemie II.
‡ Lehrstuhl fu¨r Organische Chemie und Biochemie.
§ Anorganisch Chemisches Institut.
(1) Mu¨ller, T. E.; Beller, M. Chem. Rev. 1998, 98, 675.
(2) Hoelderich, W. F.; Heitmann, G. Catal. Today 1997, 38, 227.
(3) Beller, M.; Breindl, C. Tetrahedron 1998, 54, 6359.
(4) Pez, G. P.; Galle, J . E. Pure Appl. Chem. 1985, 57, 1917.
(5) Lehmkuhl, H.; Reinehr, D. J . Organomet. Chem. 1973, 55, 215.
(6) Narita, T.; Imai, N.; Tsuruta, T. Bull. Chem. Soc. J ap. 1973, 46,
1242.
(7) Narita, T.; Yamaguchi, T.; Tsuruta, T. Bull. Chem. Soc. J pn.
1973, 46, 3825.
(8) Roesky, P. W.; Stern, C. L.; Marks, T. J . Organometallics 1997,
16, 4705.
(20) Kawatsura, M.; Hartwig, J . F. J . Am. Chem. Soc. 2000, 122,
9546.
(21) Reppe, W. Liebigs Ann. Chem. 1956, 601, 128.
(22) HOUBEN-WEYL: Methoden der organischen Chemie; Georg
Thieme Verlag: Stuttgart, 1955; Vol. IV/2, pp 406-410; 1957; Vol. XI/
1, pp 297-310; 1993; E15, pp 624-628.
(23) Heider, M.; Henkelmann, J .; Ruehl, T. EP 0 646 571 Al, 1994;
DE 43 33 237 A1, 1993.
(24) Mu¨ller, T. E.; Grosche, M.; Herdtweck, E.; Pleier, A.-K.; Walter,
E.; Yan, Y.-K. Organometallics 2000, 19, 170.
(25) Tokunaga, M.; Eckert, M.; Wakatsuki, Y. Angew. Chem., Int.
Ed. 1999, 38, 3222.
(26) Burling, S.; Field, L. D.; Messerle, B. A. Organometallics 2000,
19, 87.
(9) Molander, G. A.; Dowdy, E. D. J . Org. Chem. 1998, 63, 8983.
(10) Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J . Organo-
metallics 1999, 18, 2568.
(11) Gilbert, A. T.; Davis, B. L.; Emge, T. J .; Broene, R. D.
Organometallics 1999, 18, 2125.
(12) Bu¨rgstein, M. R.; Berberich, H.; Roesky, P. W. Organometallics
1998, 17, 1452.
(13) Li, Y.; Marks, T. J . J . Am. Chem. Soc. 1998, 120, 1757.
(14) Seligson, A. L.; Trogler, W. C. Organometallics 1993, 12, 744.
(15) Ambu¨ehl, J .; Pregosin, P. S.; Venanzi, L. M.; Consiglio, G.;
Bachechi, F.; Zambonelli, L. J . Organomet. Chem. 1979, 181, 255.
(27) Uchimaru, Y. J . Chem. Soc., Chem. Commun. 1999, 1133.
(28) Cacchi, S.; Carnicelli, V.; Marinelli, F. J . Organomet. Chem.
1994, 475, 289.
(29) Arcadi, A.; Cacchi, S.; Marinelli, F. Tetrahedron Lett. 1989, 30,
2581.
(30) Fukuda, Y.; Utimoto, K.; Nozaki, H. Heterocycles 1987, 25, 297.
(31) Campi, E. M.; J ackson, W. R. J . Organomet. Chem. 1996, 523,
205.
10.1021/om010524n CCC: $20.00 © 2001 American Chemical Society
Publication on Web 09/11/2001

Pd-Catalyzed Cyclization of 6-Aminohex-1-yne
Organometallics, Vol. 20, No. 21, 2001 4385
Sch em e 1. P a lla d iu m Com p lexes Syn th esized for Th is Stu d y
as the ligand sphere allows one to tune the catalytic
properties of the metal center and enables the use of a
variety of analytic tools for studying the reaction in and
ex situ. Aiming at accelerating the rate of reaction, the
limiting factors and, in particular, the rate-determining
step and a possible resting state of the catalyst will be
discussed.
Hindered rotation around the N-(CHMePh) bond would
render the phosphorus atoms in III diastereotopic and
hence nonequivalent.
However, closer inspection of the 13C{1H} NMR
spectrum of III revealed 12 lines between 11.3 and 68.7
ppm in the region of aliphatic carbon atoms. The chiral
center in the monomeric molecule would lead to only
six inequivalent carbon atoms. Coupling to the 31P
nuclei is generally weak and would only be observed for
the carbon atoms associated with the ethylene bridges,
but not for the CHMePh group. The features in the
13C{1H} NMR spectrum can, however, be rationalized
assuming the formation of a dimer according to eq 1.
Molecular modeling showed that, because of steric
limitations, the two 1-phenylethyl groups in the dimer
can only be positioned trans to each other. As racemi-
cally pure phosphine was used, no center of symmetry
can be present in the molecule. Thus, the two pairs of
carbon atoms associated with the ethylene bridges are
in a different environment and give rise to eight lines
in the aliphatic carbon region. The two 1-phenylethyl
groups give rise to a further four lines in the aliphatic
carbon region, accounting for the total 12 lines in the
13C{1H} NMR spectrum of III. Further, the two PPh2
groups attached to one palladium atom are in a differ-
ent, but very similar environment in the dimer, giving
rise to the higher order 31P{1H} NMR spectrum.
Resu lts a n d Discu ssion
Syn th esis of P a lla d iu m Com p lexes. A series of
closely related palladium complexes were synthesized
to study the influence of the coordination sphere on the
catalytic activity. The palladium complexes I-V as
shown in Scheme 1 were prepared from [PdCl2(COD)]
by displacement of the COD ligand by the corresponding
phosphine ligand followed by halide abstraction with
AgCF3SO3, AgNO3, or AgCH3CO2. The complexes were
fully characterized by multinuclear NMR, IR, FAB-MS,
and elemental analysis. For [Pd(Triphos)](CF3SO3)2 (I,
Triphos ) bis(2-diphenylphosphinoethyl)phenylphos-
phine), [Pd(PPN)](CF3SO3)2 (II, PPN ) N,N-dimethyl-
1-[1′,2-bis(diphenylphosphino)ferrocenyl]ethylamine), [Pd-
(PP)](NO3)2 (IV, PP ) 1,1′-bis(diphenylphosphino)-
ferrocene), and [Pd(Triphos)](CH3CO2)2 (V) the data
were fully consistent with the structural formula given.
However, a comparison of the 31P{1H} NMR spectra
of compound I and [Pd(PNP)](CF3SO3)2 (III, PNP )
R-N,N-bis(2-diphenylphosphinoethyl)-1-phenylethyl-
amine) showed a different nature for the two complexes.
In the spectrum of compound I, signals at 116.7 and
52.7 ppm in a 1:2 ratio could be assigned to the PPh
and the two PPh2 groups positioned trans to each other,
respectively. The spectrum of III showed a complex
multiplet centered at 42.7 ppm. The chemical shift
indicates that the two PPh2 groups in III were also
arranged trans to each other. However, the higher order
spectrum shows that the two PPh2 groups were in a
similar, but not equal environment. Simulation of the
spectrum with gNMR32 gave δ(31P1) ) 42.0(0.5) ppm,
δ(31P2) ) 43.4(0.5) ppm and a coupling constant
J (31P1,31P2) ) -91.8(12.4) ppm. The features of the 31P
NMR spectrum of III can in principle be explained by
the presence of the chiral center in the molecule.
A single-crystal X-ray analysis of I was performed to
(32) gNMR, 1995-1999; IvorySoft, Version 4.1.0, 14. J une 1999.
determine the steric requirements of the tridentate

4386 Organometallics, Vol. 20, No. 21, 2001
Mu¨ller et al.
2.126(7) Å).34 The bond lengths from palladium to P1
and P3, which are opposite to each other, are signifi-
cantly longer than Pd-P2, clearly demonstrating the
trans-influence of phosphorus.35 Two ethylene bridges
connect P2 with P1 and P3, respectively, to form two
five-membered metallacycles with a nearly perfect
envelope configuration. The angles P1-Pd-P2 (82.38-
(2)°), P2-Pd-P3 (83.92(2)°), and P1-Pd-P3 (164.14-
(2)°) are significantly smaller than 90° and 180°, re-
spectively, indicating that steric strain is present in the
metallacycles. The angles O1-Pd-P1 (99.88(6)°) and
O1-Pd-P3 (94.36(6)°) are consequently larger than 90°,
leaving additional space for coordination of the anion.
A search of the Cambridge Crystallographic Data-
-
base36 returned eight entries where CF3SO3 coordi-
nates to a palladium(II) center (Table 2). The Pd-O
bond distance in I‚CHCl3 (2.134(2) Å) is shorter than
in those complexes where a C-ligand is situated trans
(range Pd-O ) 2.126(5)-2.271(7) Å, entries 1-5) and
comparable to those complexes where a P-ligand is trans
(range Pd-O ) 2.118(2)-2.159(3) Å, entries 6-8). The
relatively short Pd-O distance in I‚CHCl3 indicates a
relatively strong Pd-O bond. As the counterion has to
be displaced during catalysis, a large influence of the
anion on the catalytic activity is expected. The S-O
bond distance associated with the coordinated oxygen
(S1-O1 ) 1.457(2) Å) is significantly longer than the
remaining S-O bonds (S1-O2 ) 1.427(2), S1-O3 )
1.421(2) Å). At the same time the angle O-S-CF3 is
smaller for the coordinated oxygen atom (O1-S1-C35
) 99.0(1)°), relative to the uncoordinated oxygen atoms
(O2-S1-C35 ) 104.6(1)°, O3-S1-C35 ) 105.3(1)°).
However, the difference is too small to account for
localized S-O and SdO bonds.
Ca ta lytic Activity of th e P a lla d iu m Ca ta lysts.
The activity of complexes I-V as catalysts for the direct
addition of amines to alkynes was compared for the
cyclization of 6-aminohex-1-yne (1). The cyclization of
1 first generates 2-methylene-piperidine (2) with an
exocyclic double bond (eq 2). Subsequent 1,3-hydrogen
shift occurs in situ and converts the enamine to the
more stable isomeric imine 2-methyl-1,2-dehydropip-
eridine (3).
F igu r e 1. ORTEP50 representation of the monocationic
part of compound I‚CHCl3 in the solid state. Thermal
ellipsoids are at the 50% probability level. Hydrogen atoms
are omitted for clarity.
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for I‚CHCl3
Pd-P1
Pd-P2
Pd-P3
Pd-O1
P1-C1
P1-C5
P1-C11
P2-C2
P2-C3
P2-C17
P3-C4
P3-C23
P3-C29
S1-O1
S1-O2
S1-O3
C1- C2
C3-C4
2.3375(6)
2.2003(6)
2.3480(6)
2.134(2)
1.856(3)
1.813(3)
1.805(2)
1.814(3)
1.814(3)
1.813(3)
1.836(3)
1.811(3)
1.812(3)
1.457(2)
1.427(2)
1.421(2)
1.531(4)
1.533(4)
P1-Pd-P2
P1-Pd-P3
P1-Pd-O1
P2-Pd-P3
P2-Pd-O1
P3-Pd-O1
Pd-P1-C1
Pd-P1-C5
Pd-P1-C11
Pd-P2-C2
Pd-P2-C3
Pd-P2-C17
Pd-P3-C4
Pd-P3-C23
Pd-P3-C29
Pd-O1-S
82.38(2)
164.14(2)
99.88(6)
83.92(2)
175.48(7)
94.36(6)
108.56(10)
109.79(8)
117.58(9)
109.70(10)
110.37(9)
109.45(8)
106.85(9)
110.11(10)
119.89(10)
135.82(12)
99.00(13)
104.63(13)
105.34(14)
O1-S1-C35
O2-S1-C35
O3-S1-C35
phosphine ligand and to investigate the nature of the
interaction between the anion and the palladium center.
Suitable crystals of I.CHCl3 were grown by slow evapo-
ration of a chloroform solution of complex I. A perspec-
tive view of the complex is shown in Figure 1; selected
bond lengths and angles are given in Table 1. The
phosphine is coordinated in a tridentate fashion to the
palladium center. The anticipated vacant coordination
site trans to the PPh phosphorus atom is occupied by
an oxygen atom (O1) of one trifluoromethanesulfonate
anion. Thus, the geometry is based on the normal
square-planar geometry of PdII centers. The rms devia-
tion of all five fitted atoms defining the coordination
plane (Pd, P1-P3, O1) amounts to 0.122(1) Å. The
palladium-phosphorus and palladium-oxygen dis-
tances are Pd-P1 ) 2.3375(6), Pd-P2 ) 2.2003(6), Pd-
P3 ) 2.3480(6), and Pd-O1 ) 2.134(2) Å. These
distances are within the range of two similar palladium
complexes with a square-planar PdII(OP3) coordination
geometry [Pd(Triphos)](acac-F6)2 (Pd-O ) 2.110(5) Å)33
and the related [Pd(Triphos)](CF3SO3)2‚C6H6 (Pd-O )
The catalytic activity of the complexes I-V ranges
from 5.6(6) to 243(14) molSub‚(molCat‚h)-1 (Figure 2). The
(33) Siedle, A. R.; Newmark, R. A.; Pignolet, L. H. J . Am. Chem.
Soc. 1981, 103, 4947.
(34) Aizawa, S.-I.; Yagyu, T.; Kato, K.; Funahashi, S. Anal. Sci. 1995,
11, 557.
(35) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.
(36) 3d Search and research Using the Cambridge Structural
Database (1/2000, 215403 entries): Allen, F. H.; Kennard, O. Chem.
Des. Autom. News 1993, 8, 1 and 31-37.

Pd-Catalyzed Cyclization of 6-Aminohex-1-yne
Organometallics, Vol. 20, No. 21, 2001 4387
Ta ble 2. 3D Sea r ch a n d Resea r ch Usin g th e Ca m br id ge Str u ctu r a l Da ta ba se36
entry
1
complexa
CSD-name
d(Pd-O) [Å]
d(SdO) [Å]
trans Pd-C
2.21(1)
2.16(1)
[Pd((CC5H5)C(CH3)2CH2)(PMe3)(CF3SO3)]51
BIXFET
1.43436
1.42936
1.441(8)
1.45636
1.453(4)
1.440(5)
2
3
4
5
[Pd(CO(CH2)2NEt2)(NHEt2)(CF3SO3)]52
[Pd(COD)(CH3)(CF3SO3)]53
FMSEPD
GOSKEE
RUNCOS
ZOQLAS
2.271(7)
2.126(5)
2.184(4)
2.147(5)
trans Pd-P
2.126(7)
2.159(3)
2.118(2)
2.118(2)
2.134(2)
[Pd(C14H27N2)(PEt3)2(CF3SO3)] (at 143 K)54
[Pd(C24H29O12)py2(CF3SO3)] (at 173 K)55
34
6
7
8
[Pd(Triphos)(CF3SO3)](CF3SO3)‚C6H6
RIDPOJ
YOSVOR
ZAGDAM
1.441(9)
1.469(4)
1.46136
1.46136
1.457(2)
[Pd(DPPP)(H2O)(CF3SO3)](CF3SO3)56
57
[Pd2(DPPP)2(C8H4N2)(CF3SO3)2](CF3SO3)2
9
I‚CHCl3
a
(CC5H5)C(CH3)2CH2, 2-(benzene-1,1-diyl)-2-methyl-propyl; CO(CH2)2NEt2, 3-(diethylamino)propanoyl; C14H27N2, 2-p-tolylazido-5-
methylphenyl; C24H29O12, cis,cis-1,2,3,4-tetrakis(methoxycarbonyl)-4-(2,3,4-trimethoxy-6-ethoxymethylphenyl)buta-1,3-dienyl; py, pyridyl;
DPPP, 1,3-bis(diphenylphosphino)propane; C8H4N2, µ2-1,4-dicyanobenzene-N,N′.
F igu r e 2. Time concentration diagram for the formation of 3 from 1 using the complexes I-V as catalysts. * The rate of
reaction is given in molSub‚molCat-1‚h-1 for t f 0.
differences in activity can be rationalized in part on the
basis of the significant structural and electronic differ-
ences of these complexes. The highest activity was
observed for I, whereas the lowest activity was observed
for V. As the palladium cation has the same ligand
sphere in the two complexes, the different activity must
The activity of IV, containing a bidentate phosphine,
was only slightly higher than that of V and much lower
than of I. In contrast, II, with an additional amine group
attached to one of the Cp rings, had a much higher
catalytic activity than IV, but lower than I. The low
activity of complex IV cannot fully be explained by the
less favorable NO3- anion. The low activity also seems
to be due to the ligand sphere, i.e., the bidentate
phosphine. In contrast, tridentate ligands such as the
phosphines in complexes I and II seem to be especially
favorable. Substitution of a ligand cis to the empty
coordination site has little electronic effect on the orbital
involved in bonding of the substrate. The lower activity
of II relative to I could be due to the different nature of
the substituents attached to the coordinating atoms. The
phenyl groups of the triphos ligand in I leave a narrow
wedge which is favorable for approach of an unpolar
substrate molecule, whereas the NMe2 group in II is
more polar and, thus, less favorable.
-
-
be due to the different anion (CF3SO3 and CH3CO2
,
respectively). In this respect, it was observed before that
basic anions such as acetate lead to a low catalytic
activity of late transition metal complexes in hydroami-
nation reactions, whereas anions derived from sulfonic
acids lead to an especially high activity.24
Formal replacement of the PPh group opposite the
empty coordination site in I by a N(CHMePh) moiety
gives complex III, which had an intermediate catalytic
activity. The monomeric and the dimeric forms of III
probably have similar catalytic activities, as the free
coordination sites are in very similar environments and
their number remains the same. The lower activity of
III shows that a nitrogen ligand opposite the empty
coordination site is less favorable than a phosphine
ligand. It seems likely that this results from the strong
trans effect37 of the phosphine ligand, which weakens
bonding of the substrate, the product, or an intermedi-
ate species to the metal center.
Mech a n istic Stu d ies. Substrate 1 can coordinate to
the palladium center either via the amine or via the
alkyne group (Scheme 2). To differentiate between the
two bonding modes, the complex formation constant
between I and 1 was determined using titration calo-
rimetry (ITC). A solution of 1 in CHCl3 was added
incrementally to a solution of I in CHCl3 and the heat
(37) Basolo, F.; Pearson, R. G. Prog. Inorg. Chem. 1962, 4, 381.

4388 Organometallics, Vol. 20, No. 21, 2001
Mu¨ller et al.
F igu r e 3. Infrared spectra of in situ 1:1 mixtures of [Pd(Triphos)](CF3SO3)2 (I) and various ligands. To facilitate analysis,
the spectrum of I was subtracted from each of the infrared spectra obtained for mixtures a -d .
2929 cm-1) was subtracted from each of the spectra
Sch em e 2. Equ ilibr iu m betw een Coor d in a tion of
1 to th e P a lla d iu m Cen ter in I via th e Am in e Lon e
obtained for a -d . The C-H stretching region proved
suitable for an assignment and interpretation of the
signals (Figure 3).
P a ir or via th e Alk yn e π-System
Solution a showed an intense broad signal ranging
from 3300 to 2850 cm-1 and signals at 3307 and 2941
cm-1 with a lower intensity. The signal at 3307 cm-1 is
easily assigned to the alkyne νst(tCH) by comparison
with the spectrum of d . No change in the frequency
relative to the parent heptyne was observed, whereas
a decrease in intensity and a slight broadening indicates
weak interaction of the CtCH moiety. A solution of
hexylamine in CDCl3 did not show a signal that could
be assigned to νst(NH), whereas in CD3CN it was
observed as a weak band at 3385 cm-1. Upon coordina-
tion of hexylamine to I (CDCl3, c) three additional broad
signals appeared at 3302, 3225, and 3143 cm-1, which
were assigned to the NH protons, indicating that the
amine group strongly interacts with the palladium
center. The signals due to coordinated amine were not
detected for solution a so that simple coordination of
the amine group to the palladium can be excluded. The
broad signal and a decrease of the intensity of the
alkyne signal in mixture a relative to mixture d indicate
that both functionalities may be involved in the interac-
tion of I and 1. Presumably, the amine is coordinated
to the palladium center via the NH2 group and the
alkyne moiety is involved in a weak interaction as, for
example, hydrogen bonding.38 A mixture of product
molecule 3 and I (b) showed a completely different IR
spectrum and clearly cannot account for the observa-
tions in a .
generated upon mixing the solutions was measured.
Close to a molar ratio of 1/I ) 1, the heat developed
dropped to zero. For the complex formation, a reaction
enthalpy ∆H° ) -71.0(7) kJ ‚mol-1 and an equilibrium
constant K ) 4.2(1.4) × 106 mol‚dm-3 were calculated.
For the complexation of hexylamine (formally replacing
CtCH in 1 by C2H5) to I a very similar ∆H° ) -69.8(7)
kJ ‚mol-1 and a slightly smaller equilibrium constant K
) 1.1(0.3) × 106 mol‚dm-3 were determined. In contrast,
no heat evolution was detected when a solution of
heptyne (formally replacing NH2 in 1 by CH3) was added
to a solution of I.
The similar complex formation constant of 1 and
hexylamine indicates that, during catalysis, the initial
interaction of 1 with the palladium center occurs via
coordination of the nitrogen lone pair to the palladium
center. The low heat flow observed for coordination of
heptyne is due to either a very small complex formation
constant, i.e., a weak coordination of π(CtC) to the
palladium center, or a very small ∆H° of the reaction.
The coordination of the substrate to the palladium
center was also studied with IR spectroscopy. For this
purpose, a solution of I in CDCl3 was prepared, 1 equiv
of 1 added, and the mixture (a ) immediately analyzed
by IR spectroscopy. For comparison reasons, the corre-
sponding spectra of solutions containing (b) a mixture
of I and 3, (c) a mixture of I and hexylamine, and (d ) a
mixture of I and heptyne were also measured. To
facilitate the analysis, the spectrum of the parent
complex I (signals due to νst(CH) at 3063, 2965, and
To identify the palladium species present during
catalysis, a 100-fold excess of 1 was added to a solution
of I in CDCl3 and a 31P{1H} NMR spectrum of the
mixture taken. Only two signals were detected at 102.8
and 45.2 ppm, which are assigned to the PPh moiety
and the two PPh2 groups of a new palladium complex
VI. To identify this complex, a series of comparison
samples was prepared and a 31P{1H} NMR spectrum of
each mixture taken (Table 3). The spectrum of a mixture
of I and 1 equiv of 1 (entry 2) showed intense signals at
(38) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond; Oxford
University Press: Oxford, 1999.

Pd-Catalyzed Cyclization of 6-Aminohex-1-yne
Organometallics, Vol. 20, No. 21, 2001 4389
Ta ble 3. 31P {1H} NMR Sign a ls Obser ved for Mixtu r es of [P d (Tr ip h os)]X2 (X ) CF 3SO3-, CH3CO2-) a n d
Va r iou s Liga n d sc
entry
ligand for [Pd(Triphos)](CF3SO3)2
δ(P1) [ppm]
δ(P2/3) [ppm]
assignment
1
2
s
116.7
116.7
109.5
102.7
102.8a
116.7
109.5
116.8
108.7
116.7
112.7
102.9
112.6
103.0
116.7
112.3
52.7
52.7
53.9
45.2
45.2a
52.7
53.8
53.0
53.9
52.5
47.5
45.3
47.5
45.3
52.7
47.2
[Pd]--O3SCF3
[Pd]--O3SCF3
[Pd]-NC6H11
1 equiv of HtC(CH2)4NH2 (1)
+
[Pd]--CdC-NR3+
[Pd]--CdC-NR3
[Pd]--O3SCF3
[Pd]-NC6H11
3
4
100 equiv of HCtC(CH2)4NH2 (1)
1 equiv of NC6H11 (3)
5
6
1 equiv of H2N(CH2)5CH3
[Pd]--O3SCF3
[Pd]-NH2Hex
[Pd]--O3SCF3
[Pd]-NEt3
(1) 1 equiv of HCtC(CH2)4CH3
(2) 1 equiv of NEt3
+
[Pd]--CdC-NR3
7
(1) 1 equiv of NEt3
[Pd]-NEt3
[Pd]--CdC-NR3
+
(2) 1 equiv of HCtC(CH2)4CH3
1 equiv of HCtC(CH2)4CH3
1 equiv of NEt3
8
9
[Pd]--O3SCF3
[Pd]-NEt3
entry
ligand for [Pd(Triphos)](CH3CO2)2
δ(P1) [ppm]
δ(P2/3) [ppm]
assignment
10
11
12
s
112.8
112.8
112.8
47.4
47.4
47.3
[Pd]--O2CCH3
[Pd]--O2CCH3
[Pd]--O2CCH3
1 equiv of HCtC(CH2)4NH2 (1)
100 equiv of HCtC(CH2)4NH2 (1)
b
b
+
102.7
45.3
[Pd]--CdC-NR3
102.8 t (J (31P,31P) ) 17.7 Hz); 45.2 d (J (31P,31P) ) 17.8 Hz). 102.7 t (J (31P,31P) ) 17.8 Hz); 45.3 d (J (31P,31P) ) 14.9 Hz). c The
a
b
chemical shift of the main component in each reaction mixture is given in bold; [Pd] denotes [Pd(Triphos)]2+
.
109.5 and 53.9 ppm. These can be assigned to formation
of the cyclization product 3 and its coordination to the
palladium center (see entry 4). Additional weaker
signals at 116.7/52.7 and 102.7/45.2 ppm can be as-
signed to the parent palladium complex I and the
unknown intermediate VI, respectively. Coordination
of hexylamine to I gave rise to a pair of signals at 108.7/
53.9 ppm (entry 5), while addition of heptyne to I did
not give a shift of the 31P signals relative to I (entry 8),
indicating no or only weak coordination of the alkyne
moiety to palladium.
signals in the spectrum of VII are readily assigned to
the parent palladium complex and coordination of NEt3
to palladium. To prove that the formation of intermedi-
ate VII is an equilibrium reaction, the order of adding
the ligands was reversed, adding first triethylamine and
subsequently heptyne (entry 7). In this mixture complex
VII was observed in about the same concentration as
before, confirming that its formation is an equilibrium
reaction.
The chemical shift of the signals in the 31P NMR
spectrum of the mixture of hexylamine and I indicates
that the amine is coordinated via the lone pair to the
palladium. It can be excluded that the amine is oxida-
tively added to the palladium center in stoichiometric
quantities, as this would give rise to a large shift of the
31P NMR signals. However, this does not preclude
oxidative addition in the catalytic cycle.
On the other hand, VI could be the result of an
intramolecular nucleophilic attack (eq 3). In this respect,
it is known that a nucleophilic attack of an amine on
coordinated alkenes or alkynes is possible.39 To test this
hypothesis, 1 equiv of heptyne and 1 equiv of NEt3 were
added in succession to a solution of I. Complex VII
formed in situ according to eq 440 and gave rise to a pair
of signals in the 31P{1H} NMR spectrum at exactly the
same chemical shift as the unknown intermediate VI
(entry 6). Thus, the direct environment of the palladium
center must be very similar in both intermediates and
is assigned the moiety [(Triphos)Pd2+rCH-dCR-
NR′3+] with R ) alkyl, R′ ) H, alkyl. The groups R and
R′ are different in VI and VII, but the distance of 4 and
5 bonds to the phosphorus nuclei is too big to have an
effect on their chemical shift. Additional low-intensity
To investigate why V has a much lower activity in
the cyclization of 1, the same sequence of 31P{1H} NMR
experiments was performed with this complex. For all
samples, except when 100 equiv of 1 was added to V,
only the 31P signals due to the parent complex V were
observed. For the latter mixture, a pair of signals at
102.7/45.3 ppm was noticed (entry 12). The chemical
shift was equal to the shift observed for VI and VII and
(39) Akermark, B.; Ba¨ckvall, J .-E.; Zetterberg, K. Acta Chem. Scand.
B 1982, 36, 577.
(40) For a related platinum complex see: Ambu¨ehl, J .; Pregosin, P.
S.; Venanzi, L. M.; Ughetto, G.; Zambonelli, L. Angew. Chem., Int. Ed.
Engl. 1975, 44, 369.

4390 Organometallics, Vol. 20, No. 21, 2001
Sch em e 3. Rea ction Mech a n ism P r op osed for th e Cycliza tion of 1
Mu¨ller et al.
indicates the formation of the same cationic intermedi-
ate. Thus, even strong donor ligands such as NEt3 are
unable to displace the acetate ion from its coordination
to the palladium center. A large excess of 1 is required
to shift the equilibrium toward displacement of the
acetate ion from the primary coordination sphere. Thus,
in addition to the basic nature of the acetate ion
mentioned before, its ability to strongly coordinate to
the palladium center could explain the low catalytic
activity of V.
A likely reaction sequence for the addition of amines
to alkynes catalyzed by palladium is shown in Scheme
3, using as a specific example the cyclization of 1. Initial
coordination of substrate 1 to the palladium center
occurs via the amine. The complex isomerizes so that
the alkyne group becomes coordinated to the metal
center. This renders the π-system susceptible to a
nucleophilic attack of the nitrogen lone pair which gives
the 2-ammonio alken-1-yl complex VI. Protolytic cleav-
age of the metal-carbon bond leads to desorption of 2
and regenerates the catalyst. Subsequently, the enam-
ine 2 isomerizes in situ to the more stable imine 3. This
reaction sequence is proposed based on the observations
described above and reports that zinc(II) salts were also
good catalysts for the cyclization of aminoalkynes.24 For
the latter, an alternative mechanism, where the amine
is added oxidatively to the zinc center, is not possible.41
For palladium, the tridentate phosphine ligands used
in this study inevitably make the oxidative addition of
H-N (or other H-X) more difficult in comparison with
bi- or monodentate ligands. Accordingly, the mechanism
proposed is not necessarily applicable to hydroamination
reactions involving palladium complexes with bi- and
monodentate ligands as encountered in other organic
syntheses.16,17,42
F igu r e 4. Initial rate of reaction for the cyclization of
6-aminohex-1-yne (1) using the catalyst [Pd(Triphos)](CF3-
SO3)2 (I) in the presence of CF3SO3H or LiNiPr2 as
cocatalyst.
the catalytic cycle, or the subsequent step, protolytic
cleavage of the palladium-carbon bond, is the rate-
limiting step. If the latter hypothesis were valid, a
higher concentration of protons in the catalytic mixture
should accelerate the reaction. Therefore, trifluo-
romethane sulfonic acid was added to the catalytic
mixture. With addition of 1 equiv of CF3SO3H relative
to palladium, the rate of reaction doubled from 243(14)
to 435(15) (Figure 4). When higher concentrations of
CF3SO3H were employed, the rate of reaction increased
further; however, the increase in rate was less. For a
mixture of 1:I:CF3SO3H ) 100:1:100 the reaction was
complete within 5 min and the rate of reaction could
only be estimated (ca. 1800 molSub‚(molCat‚h)-1). In
contrast, even small amounts of a base (here LiNiPr2)
inhibited the reaction completely.
These observations confirm the hypothesis that com-
plex VI occurs in a high concentration because protolytic
cleavage of the palladium-carbon bond is a slow step
in the catalytic cycle. It seems likely that the acid leads
to faster protonation of the alkenyl-carbon in VI and
thus facilitates formation of enamine 2 (Scheme 3, A).
Rate-limiting cleavage of the metal-carbon bond was
Complex VI was identified as the palladium species
that occurs in the highest concentration during the
palladium-catalyzed cyclization of 1. Two explanations
for the high concentration seem likely: Complex VI
could be a resting state and not be directly involved in
(41) Mu¨ller, T. E.; Pleier, A.-K. J . Chem. Soc., Dalton Trans. 1998,
4, 583.
(42) Hahn, C.; Spiegler, M.; Herdtweck, E.; Taube, R. Eur. J . Inorg.
Chem. 1999, 435.

Pd-Catalyzed Cyclization of 6-Aminohex-1-yne
Organometallics, Vol. 20, No. 21, 2001 4391
25% CW-400 + 2.5% KOH on Chrom-W-AW) column. Infrared
spectra were obtained on a Perkin-Elmer 2000 FT-IR spec-
trometer from solutions in CDCl3 or KBr disks. Mass spectro-
scopic analyses were performed on a Finnigan MAT 311A by
the fast atom bombardment (FAB) method. Elemental analy-
ses were performed by the Microanalytical Laboratory of the
Technische Universita¨t Mu¨nchen. Isothermal titration calo-
rimetry was performed using a MCS-J TC instrument (Micro-
cal, MA) and applying corrections obtained from blind titra-
tions to account for the heats of dilution.
P r ep a r a tion s. [P d (Tr ip h os)](CF 3SO3)2 (I). The complex
[PdCl2(COD)] (40 mg, 0.14 mmol) was dissolved in CH2Cl2 (10
cm3), and a solution of bis(2-diphenylphosphinoethyl)phe-
nylphosphine (Triphos, 75 mg, 0.14 mmol) in CH2Cl2 (5 cm3)
added. The volatiles were removed in vacuo, the residue of
[PdCl(Triphos)]Cl was redissolved in CH2Cl2 (10 cm3), a
solution of AgCF3SO3 (72 mg, 0.28 mmol) in CH3CN (2 cm3)
was added, and the mixture was stirred at room temperature
overnight. A white precipitate formed, which was removed by
filtration, and the volume of the filtrate was reduced in a
partial vacuum. Addition of Et2O yielded a light yellow solid,
which was recrystallized from CH2Cl2/pentane and dried in
vacuo.
also predicted in a recent theoretical study on hy-
droamination reactions.43 However, in the cyclization
of 1 the protons could also be involved in two further
steps of the catalytic cycle (Scheme 3, B and C).
(i) The substrate initially coordinates via the amine
lone pair rather than the alkyne group. Isomerization
and coordination of the alkyne is necessary prior to the
nucleophilic attack. Reversible protonation of the amine
group shifts the equilibriumswhich is on the side of the
aminestoward coordination of the alkyne.
(ii) Protons catalyze the isomerization of enamines to
the corresponding imines. Thus, in the cyclization of 1
the concentration of free intermediate 2 will be lower
in acidic conditions. If desorption of 2 from the pal-
ladium center is slow, addition of an acid will lead to a
faster desorption of the product and acceleration of the
overall process.
Con clu sion s
The activity of palladium complexes for the cyclization
of 6-aminohex-1-yne (1) to 2-methyl-1,2-dehydropiperi-
dine (3) was investigated. The highest activity in the
series of complexes studied was observed for [Pd-
(Triphos)](CF3SO3)2 (I). Initial coordination of 1 to the
palladium center probably occurs via the amine group.
Isomerization and coordination of the alkyne group
enables the subsequent nucleophilic attack of the amine
lone pair on the CC π-system. This leads to the 2-am-
monioalken-1-yl complex VI, which was the predomi-
nant palladium species (>99%) in the catalytic mixture,
as shown by 31P NMR spectroscopy. The high concen-
tration of the complex indicates that the subsequent
step, protolytic cleavage of the Pd-C bond in VI, is rate
limiting. Addition of trifluoromethanesulfonic acid to the
catalytic mixture drastically accelerated the overall
reaction. Thus, protons act as cocatalysts in the pal-
ladium-catalyzed addition of the amine N-H bond to
the CC triple bond in 1. In summary, it seems likely
that the key step of the reaction is the coordination of
the triple bond to the metal center, which enables
nucleophilic attack of the free electron pair on nitrogen
on the CC π-system. The findings presented in this
study are in excellent agreement with a recent theoreti-
cal study on the molecular background of hydroamina-
tion reactions.43
Yield: 0.11 g, 85%. Found: C, 46.2; H, 3.5. Calcd for
C
36H33F6O6P3PdS2: C, 46.2; H, 3.5. 31P{1H} NMR (CDCl3): δ
116.7 (s, 1P, PPh), 52.7 (s, 2P, PPh2). 13C{1H} NMR (CDCl3):
134.7 to 123.9 (mm, Ph), 29.8 (d, 1J (13C, 31P) 35 Hz, CH2), 28.4
1
(t, 1/3J (13C, 31P) 17 Hz, CH2). H NMR (CDCl3): 8.19 (dd, 2H,
Ph), 7.74-7.48 (mm, 23H, Ph), 3.37 (sept, 2H, CHa), 3.11 (dd,
3
2J (1H, 31P) 55 Hz, J (1H, 31P) 15 Hz, CHa′), 3.00 (m, 2H, CHb),
2.25 (b, 2H, CHb′). IR: 3058 (m), 2965 (w), 2920 (w), 1485 (m),
1437 (s), 1324 (m), 1266 (vs), 1158 (s), 1105 (s), 1030 (vs), 999
(m), 830 (m), 747 (m), 725 (m), 709 (m), 690 (m), 637 (vs), 572
(m) cm-1. m/z (FAB): 789 (M+ - CF3SO3), 640 (M+ - 2CF3-
SO3).
[P d (P P N)](CF 3SO3)2 (II). The complex [PdCl2(COD)] (52
mg, 0.18 mmol) was dissolved in CH2Cl2 (10 cm3) and a solution
of N,N-dimethyl-1-[1′,2-bis(diphenylphosphino)ferrocenyl]-
ethylamine (PPN, 0.11 g, 0.18 mmol) in CH2Cl2 (5 cm3) added.
The volatiles were removed in vacuo, the residue redissolved
in CH2Cl2, a solution of AgCF3SO3 (93 mg, 0.36 mmol) in CH3-
CN (5 cm3) added, and the mixture stirred for 1 h. The mixture
was filtered and the volume of the filtrate reduced in a partial
vacuum. The product was precipitated with Et2O, recrystal-
lized from CH2Cl2/pentane, and dried in vacuo.
Yield: 0.13 g, 70% black microcrystals. Found: C, 44.4; H,
3.7; N, 1.5. Calcd for C41H38Cl2F6FeNO6P2PdS2: C, 44.2; H,
3.4; N, 1.3. 31P{1H} NMR (CD3CN/CD3NO2): 54.2 (s), 48.9 (s).
1H NMR (CD3CN): 7.7-7.3 (mm, 25H, Ph), 4.2 (m, 7H, Cp),
2.7 (m, 6H, NMe2), 1.7 (m, 3H, Me). IR: 3058 (w), 1481 (w),
1437 (s), 1279 (vs), 1256 (vs), 1166 (vs), 1120 (w), 1098 (m),
1030 (vs), 998 (w) cm-1. m/z (FAB): 881 (M+ - CF3SO3).
[P d (P NP )](CF 3SO3)2‚CH3CN (III). The complex [PdCl2-
(COD)] (0.13 g, 0.46 mmol) was dissolved in CH2Cl2 (25 cm3),
and a solution of R(+)-N,N-bis(2-diphenylphosphinoethyl)-1-
phenylethylamine (PNP, 0.25 g, 0.46 mmol) in CH2Cl2 (10 cm3)
was added. The volatiles were removed in vacuo, the residue
redissolved in CH2Cl2, a solution of AgCF3SO3 (0.12 g, 0.46
mmol) in CH3CN (5 cm3) added, and the mixture stirred for 1
h. The latter part of the procedure was repeated adding a
solution of AgCF3SO3 (0.12 g, 0.46 mmol) in CH3CN (5 cm3)
and stirring the mixture for 1 h. The mixture was then filtered
and the volume of the filtrate reduced in a partial vacuum.
The product was precipitated with Et2O, recrystallized from
CH2Cl2/pentane, and dried in vacuo.
Exp er im en ta l Section
Ma ter ia ls a n d Meth od s. All reactions involving air- and/
or water-sensitive compounds were performed using standard
Schlenk techniques. Solvents were obtained dry from Aldrich.
Catalysts and other chemicals not described in the Experi-
mental Section were purchased from Aldrich, Fluka, or Strem
and used as received. The compounds 6-aminohex-1-yne (1),41
[Pd(PP)](NO3)2 (IV),41 and [Pd(Triphos)](CH3CO2)2 (V) 24 were
prepared as described in the respective reference.
P h ysica l a n d An a lytica l Meth od s. 1H, 13C{1H}, and 31P-
{1H} NMR spectra were recorded on a Bruker AM 400 and
referenced in ppm relative to the solvent shift44 or tetrameth-
ylsilane. GC analyses were performed on a HP 5730A gas
chromatograph equipped with a Supelco Amine (3m × 1/8 S.S.,
Yield: 0.37 g, 85% yellow powder. Found: C, 48.4; H, 4.1;
N, 2.4. Calcd for C40H40F6N2O6P2PdS2: C, 48.5; H, 4.1; N, 2.8.
31P{1H} NMR (CD3CN): 42.0(0.5), 43.4(0.5), J (31P,31P) ) -91.8-
(12.4). 19F NMR (CD3CN): -16.5 (s). 13C{1H} NMR (CD3CN):
137.7-129.5 (mm, Ph), 68.6 (s), 67.8 (s), 63.6 (s), 58.9 (s), 39.5
(s), 31.1 (s), 29.6 (s), 24.5 (s), 23.6 (s), 14.3 (s), 13.2 (s), 11.3
(43) Senn, H. M.; Blo¨chl, P. E.; Togni, A. J . Am. Chem. Soc. 2000,
122, 4098.
(44) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J . Org. Chem. 1997,
62, 7512.

4392 Organometallics, Vol. 20, No. 21, 2001
Ta ble 4. Cr ysta llogr a p h ic Da ta for I‚CHCl3
Mu¨ller et al.
factors for all atoms and anomalous dispersion corrections for
the non-hydrogen atoms were taken from International Tables
for Crystallography.49 All other calculations (including ORTEP
graphics) were done with the program PLATON.50 Calculations
were performed on a PC workstation (Intel Pentium II)
running LINUX.
chem formula
fw
C35H33F3O3P3PdS, CF3O3S, CHCl3
1058.46
color/shape
cryst size (mm)
cryst syst
space group
a (Å)
yellow/fragment
0.28 × 0.25 × 0.15
monoclinic
P21/ n (No. 14)
10.0166(1)
26.7427(5)
16.6381(3)
104.373(1)
4317.4(1)
Ca ta lysis. In a typical procedure, a mixture of [Pd(Triphos)]-
(CF3SO3)2 (3.3 mg, 3.5 µmol) and toluene (10 cm3) was heated
at reflux and the reaction started by addition of 6-aminohex-
1-yne41 (1) (40 mm3, 0.35 mmol). At regular intervals, small
samples were taken and analyzed by gas chromatography. For
the experiments given in Figure 2 3.3 mg of [Pd(Triphos)](CF3-
SO3)2, 3.6 mg of [Pd(PPN)](CF3SO3)2, 3.3 mg of [Pd(PNP)](CF3-
SO3)2, 3.0 mg of [Pd(PP)](CF3SO3)2, and 2.7 mg of [Pd(Triphos)]-
(CH3CO2)2 were used. For the experiments given in Figure 4,
the same amounts (3.3 mg of [Pd(Triphos)](CF3SO3)2, 40 mm3
of 6-aminohex-1-yne, and 15 cm3 of toluene) were used, and
the cocatalyst trifluoromethanesulfonic acid (3.5, 18, 35, 176,
351 µmol) or LiNiPr2 (3.5, 18, 35, 176, 351 µmol) was added to
the catalytic mixture within 2 min of the reaction being
started.
b (Å)
c (Å)
â (deg)
V (Å3)
Z
4
T (K)
123
1.628
0.893
2128
Fcalcd (g cm-3
)
µ (mm-1
F000
)
θ-range (deg)
1.98-25.37
(12, (32, (20
29 015
7850 (all)/0.0312
7182 (obsd)
659
0.0308/0.0352
0.0679/0.0699
1.052/1.052
+0.94 /-0.75
data collected (h,k,l)
no. of reflns collected
no. of indep rflns/Rint
no. of obsd rflns (I>2σ(I))
no. of params refined
R1 (obsd/all)
In Situ IR Exp er im en ts. Mixtu r e a . The complex [Pd-
(triphos)](CF3SO3)2 (7.3 mg, 7.8 × 10-3 mmol) was dissolved
in a solution of 6-aminohex-1-yne (8.8 × 10-4 cm3, 7.8 × 10-3
mmol) in CDCl3 (0.21 cm3) and the IR spectrum taken against
CDCl3 as the background.
wR2 (obsd/all)
GOF (obsd/all)
max/min ∆F (e Å-3
)
(s). 1H NMR (CD3CN): 8.05-7.18 (mm, 25H, Ph), 4.38 (q, 1H,
CH), 4.20 (q, 1H, CHaHb), 3.85 (b, 1H, CHaHb), 3.67 (m, 2H,
CHaHb), 3.41 (m, 2H, CHaHb), 3.20 (m, 1H, CHaHb), 3.01 (m,
1H, CHaHb), 2.20 (s, 3H, CH3CN), 1.63 (d, 3H, CH3). IR: 3057
(m), 2990 (m), 2929 (m), 2328 (m), 2300 (m), 1484 (m), 1455
(m), 1436 (s), 1258 (vs), 1224 (s), 1157 (vs), 1104 (s), 1030 (vs),
997 (s) cm-1. m/z (FAB): 800 (M+ - CF3SO3), 651 (M+ - 2
CF3SO3).
Mixtu r e b. The complex [Pd(triphos)](CF3SO3)2 (7.2 mg, 7.7
× 10-3 mmol) was dissolved in a solution of 2-methyl-1,2-
dehydropiperidine (8.7 × 10-4 cm3, 7.7 × 10-3 mmol) in CDCl3
(0.20 cm3) and the IR spectrum taken against CDCl3 as the
background.
Mixtu r e c. The complex [Pd(triphos)](CF3SO3)2 (7.4 mg, 7.9
× 10-3 mmol) was dissolved in a solution of n-hexylamine (1.0
× 10-3 cm3, 7.9 × 10-3 mmol) in CDCl3 (0.21 cm3), and the IR
spectrum taken against CDCl3 as the background.
X-r a y Str u ctu r e Deter m in a tion of Com p lex I‚CHCl3.
Details of the X-ray experiment, data reduction, and final
structure refinement calculation are summarized in Table 4.
Crystals of complex I‚CHCl3 suitable for X-ray structure
determination were grown by slow evaporation of a saturated
solution of I in chloroform. Preliminary examination and data
collection were carried out on a kappa-CCD system (Nonius
Mach3) equipped with a rotating anode (NONIUS FR591; 50
kV; 60 mA; 3.0 kW) and graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). Data collection was performed at
123 K with an exposure time of 48 s per film (æ- and ω-scan,
oscillation modus, ∆æ/∆ ) 1.0°). A total of 29 015 reflections
were collected.45 After merging, 7850 independent reflections
remained and were used for all calculations. The data were
corrected for Lorentz and polarization effects. Corrections for
absorption and decay effects were not applied. The unit cell
parameters were obtained by full-matrix least-squares refine-
ments of 24 372 reflections with the program Scalepack.46 The
structure was solved by a combination of direct methods and
difference Fourier syntheses.47 All non-hydrogen atoms of the
asymmetric unit were refined with anisotropic thermal dis-
placement parameters. All hydrogen atoms were found in the
difference Fourier map and refined freely with individual
isotropic thermal displacement parameters. Full-matrix least-
Mixtu r e d . The complex [Pd(triphos)](CF3SO3)2 (7.1 mg, 7.6
× 10-3 mmol) was dissolved in a solution of 1-heptyne (1.0 ×
10-3 cm3, 7.6 × 10-3 mmol) in CDCl3 (0.20 cm3) and the IR
spectrum taken against CDCl3 as the background.
In Sit u NMR E xp er im en t s. Mixt u r e 1. The complex
[Pd(triphos)](CF3SO3)2 (5.2 mg, 5.5 × 10-3 mmol) was dissolved
in CDCl3 (0.6 cm3) and H, 13C{1H}, and 31P{1H} NMR spectra
1
taken.
1H NMR (CDCl3): 8.19 (dd, 2H, Ph), 7.74-7.48 (mm, 23H,
Ph), 3.37 (sept, 2H, CHa), 3.11 (dd, 2J (1H, 31P) 55 Hz, 3J (1H,
31P) 15 Hz, CHa′), 3.00 (m, 2H, CHb), 2.25 (b, 2H, CHb′). 13C-
1
{1H} NMR (CDCl3): 134.7 to 123.9 (mm, Ph), 29.8 (d, J (13C,
31P) 35 Hz, CH2), 28.4 (t, 1/3J (13C, 31P) 17 Hz, CH2). 31P{1H}
NMR (CDCl3): δ 116.7 (s, 1P, PPh), 52.7 (s, 2P, PPh2).
Mixtu r e 2. The complex [Pd(triphos)](CF3SO3)2 (5.2 mg, 5.5
× 10-3 mmol) was dissolved in CDCl3 (0.5 cm3), 6-aminohex-
1-yne (6.3 × 10-4 cm3, 5.5 × 10-3 mmol) in CDCl3 (0.1 cm3)
added, and a 31P{1H} NMR spectrum taken.
(49) International Tables for Crystallography, Wilson, A. J . C., Ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C, Tables 6.1.1.4 (pp 500-502), 4.2.6.8 (pp 219-222), and 4.2.4.2 (pp
193-199).
(50) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 1999.
(51) Campora, J .; Lopez, J . A.; Palma, P.; Valerga, P.; Spillner, E.;
Carmona, E. Angew. Chem. 1999, 111, 199.
2
squares refinements were carried out by minimizing ∑w(Fo
- Fc2)2 with the SHELXL-97 weighting scheme and stopped
at maximum shift/err < 0.001.48 Neutral atom scattering
(45) Data Collection Software for Nonius Kappa-CCD, Delft, The
Netherlands, 1997.
(46) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Methods in Enzymology; Carter, W.
C., J r., Sweet, R. M., Eds.; Academic Press: New York, 1996; Vol. 276,
p 307.
(47) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli M. SIR92. J . Appl. Crystallogr. 1994,
27, 435-436.
(48) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨t-
tingen, Germany, 1998.
(52) Anderson, O. P.; Packard, A. B. Inorg. Chem. 1979, 18, 1129.
(53) Burger, P.; Baumeister, J . M. J . Organomet. Chem. 1999, 575,
214.
(54) Vicente, J .; Arcas, A.; Bautista, D.; J ones, P. G. Organometallics
1997, 16, 2127.
(55) Vicente, J .; Abad, J .-A.; Fernandez-de-Bobadilla, R.; J ones, P.
G.; Ramirez de Arellano, M. C. Organometallics 1996, 15, 24.
(56) Stang, P. J .; Cao, D. H.; Poulter, G. T.; Arif, A. M. Organome-
tallics 1995, 14, 1110.
(57) Stang, P. J .; Cao, D. H.; Saito, S.; Arif, A. M. J . Am. Chem.
Soc. 1995, 117, 6273.

Pd-Catalyzed Cyclization of 6-Aminohex-1-yne
Organometallics, Vol. 20, No. 21, 2001 4393
31P{1H} NMR (CDCl3): δ 109.5 (s, 1P, PPh), 53.9 (s, 2P,
PPh2), small signals at 116.7, 102.7, 52.7, and 45.2.
Mixtu r e 3. The complex [Pd(triphos)](CF3SO3)2 (5.2 mg, 5.5
× 10-3 mmol) was dissolved in CDCl3 (0.5 cm3), 6-aminohex-
1-yne (6.3 × 10-2 cm3, 0.55 mmol) in CDCl3 (0.1 cm3) added,
and 1H, 13C{1H}, and 31P{1H} NMR spectra taken.
1H NMR (CDCl3): δ 2.73 (t, 2H, 1, CH2-N), 2.21 (dt, 2H, 1,
CH2-C+C), 1.96 (t, 1H, 1, HC+C), 2.32 (s, 2H, 1, NH2), 1.58
(q, 4H, 1, CH2-CH2), small signals due to 2, 3, and VI. 13C-
{1H} NMR (CDCl3): δ 84.6 (s, 1, C2), 68.8 (s, 1, C1), 41.7 (s, 1,
C6), 32.6 (s, 1, C5), 26.1 (s, 1, C4), 18.5 (s, 1, C3), small signals
due to 2, 3, and VI. 31P{1H} NMR (CDCl3): δ 102.8 (t, J (31P,
31P) ) 17.7 Hz, 1P, PPh), 45.2 (d, J (31P, 31P) ) 17.8 Hz, 2P,
PPh2).
Mixtu r e 4. The complex [Pd(triphos)](CF3SO3)2 (5.2 mg, 5.5
× 10-3 mmol) was dissolved in CDCl3 (0.5 cm3), 2-methyl-1,2-
dehydropiperidine (6.3 × 10-4 cm3, 5.5 × 10-3 mmol) in CDCl3
(0.1 cm3) added, and a 31P{1H} NMR spectrum taken.
31P{1H} NMR (CDCl3): δ 109.5 (s, 1P, PPh), 53.8 (s, 2P,
PPh2), small signals at 116.7 and 52.7.
× 10-4 cm3, 5.5 × 10-3 mmol) in CDCl3 (0.1 cm3) added, and a
31P{1H} NMR spectrum taken.
31P{1H} NMR (CDCl3): δ 116.7 (s, 1P, PPh), 52.7 (s, 2P,
PPh2).
Mixtu r e 9. The complex [Pd(triphos)](CF3SO3)2 (5.2 mg, 5.5
× 10-3 mmol) was dissolved in CDCl3 (1 cm3), triethylamine
(7.7 × 10-4 cm3, 5.5 × 10-3 mmol) added, and a 31P{1H} NMR
spectrum taken.
31P{1H} NMR (CDCl3): δ 112.3 (s, 1P, PPh), 47.2 (s, 2P,
PPh2).
Mixtu r e 10. The complex [Pd(triphos)](CH3CO2)2 (2.2 mg,
2.9 × 10-3 mmol) was dissolved in CDCl3 (0.6 cm3), and 1H,
13C{1H}, and 31P{1H} NMR spectra were taken.
1H NMR (CDCl3): 8.34 (dd, 2H, Ph), 7.85 (quart, 4H, Ph),
7.70 (quart, 4H, Ph), 7.60-7.44 (mm, 15H, Ph), 5.30 (s, 2H,
CH2Cl2), 4.08 (sept, 2H, CHa), 3.13 (dd, 2J (1H, 31P) 58 Hz, 3J (1H,
31P) 15 Hz, CHa′), 2.75 (m, 2H, CHb), 2.22 (b, 2H, CHb′). 13C-
{1H} NMR (CDCl3): 134.6-125.0 (mm, Ph), 30.3 (td, 1J (13C,
31P) 33 Hz, 2/3J (13C, 31P) 6 Hz, PhP-CH2), 28.6 (dt, 1/3J (13C,
31P) 16 Hz, 2J (13C, 31P) 8 Hz, Ph2P-CH2). 31P{1H} NMR
(CDCl3): δ 112.3 (s, 1P, PPh), 47.2 (s, 2P, PPh2).
Mixtu r e 11. The complex [Pd(triphos)](CH3CO2)2 (2.2 mg,
2.9 × 10-3 mmol) was dissolved in CDCl3 (0.5 cm3), 6-amino-
hex-1-yne (3.3 × 10-4 cm3, 2.9 × 10-3 mmol) in CDCl3 (0.1 cm3)
added, and a 31P{1H} NMR spectrum taken.
31P{1H} NMR (CDCl3): δ 112.8 (s, 1P, PPh), 47.4 (s, 2P,
PPh2).
Mixtu r e 12. The complex [Pd(triphos)](CH3CO2)2 (2.2 mg,
2.9 × 10-3 mmol) was dissolved in CDCl3 (0.5 cm3), 6-amino-
hex-1-yne (3.3 × 10-2 cm3, 0.29 mmol) in CDCl3 (0.1 cm3)
added, and a 31P{1H} NMR spectrum taken.
Mixtu r e 5. The complex [Pd(triphos)](CF3SO3)2 (5.2 mg, 5.5
× 10-3 mmol) was dissolved in CDCl3 (0.5 cm3), n-hexylamine
(7.3 × 10-4 cm3, 5.5 × 10-3 mmol) in CDCl3 (0.1 cm3) added,
and a 31P{1H} NMR spectrum taken.
31P{1H} NMR (CDCl3): δ 108.7 (s, 1P, PPh), 53.9 (s, 2P,
PPh2), small signals at 116.8 and 53.0.
Mixtu r e 6. The complex [Pd(triphos)](CF3SO3)2 (5.2 mg, 5.5
× 10-3 mmol) was dissolved in CDCl3 (1 cm3), hept-1-yne (7.3
× 10-4 cm3, 5.5 × 10-3 mmol) and triethylamine (7.7 × 10-4
1
cm3, 5.5 × 10-3 mmol) were added, and H, 13C{1H}, and 31P-
{1H} NMR spectra were taken.
1H NMR (CDCl3): δ 7.94-7.85 (m, 9H, Ph), 7.46-7.36 (m,
16H, Ph), 3.28 (m, 4H, PCH2), 3.11 (q, J (1H, 1H) ) 7.2 Hz, 6H,
NCH2), 2.20 (m, 4H, PCH2), 2.10 (m, 2H, CH2), 1.94 (s, 1H,
CH), 1.31 (t, J (1H, 1H) ) 7.5 Hz, 9H, NCH3), 1.11 (m, 4H, CH2),
31P{1H} NMR (CDCl3): δ 102.7 (t, J (31P, 31P) ) 17.8 Hz, 1P,
PPh), 45.3 (d, J (31P, 31P) ) 14.9 Hz, 2P, PPh2), small signals
at 112.8 and 47.3.
1
1
0.81 (q, J (1H, H) ) 7.7 Hz, 2H, CH2), 0.67 (t, J (1H, H) ) 7.1
Hz, 3H, CH3). 13C{1H} NMR (CDCl3): δ 132.2-129.5 (mm, Ph),
47.2 (s, NCH2), 31.4 (s, CH2), 30.0 (s, CH2), 22.7 (s, CH2), 21.7
(s, CH2), 14.4 (s, CH3), 9.1 (s, NCH2CH3). 31P{1H} NMR
(CDCl3): δ 102.9 (s, 1P, PPh), 45.3 (s, 2P, PPh2), small signals
at 116.8, 112.7, 52.5, and 47.5.
Ack n ow led gm en t. The financial contribution of the
“Stiftung Stipendien-Fonds des Verbandes der Chemis-
chen Industrie e.V.” and the “Dr.-Ing. Leonhard-Lorenz-
Stiftung” is gratefully acknowledged. Xaver Hecht and
Andreas Marx are thanked for the experimental sup-
port.
Mixtu r e 7. The complex [Pd(triphos)](CF3SO3)2 (5.2 mg, 5.5
× 10-3 mmol) was dissolved in CDCl3 (1 cm3), triethylamine
(7.7 × 10-4 cm3, 5.5 × 10-3 mmol) and hept-1-yne (7.3 × 10-4
cm3, 5.5 × 10-3 mmol) were added, and a 31P{1H} NMR
spectrum was taken.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
and data collection parameters, atomic coordinates, bond
lengths, bond angles, and thermal displacement parameters
for I‚CHCl3 in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
31P{1H} NMR (CDCl3): δ 103.0 (s, 1P, PPh), 45.3 (s, 2P,
PPh2), small signals at 112.6 and 47.5.
Mixtu r e 8. The complex [Pd(triphos)](CF3SO3)2 (5.2 mg, 5.5
× 10-3 mmol) was dissolved in CDCl3 (0.5 cm3), heptyne (7.3
OM010524N