Metal template promoted hydroamination of ethynylphosphines and aniline. Asymmetric synthesis, coordination chemistry, and the imine-enamine tautomerism of P-chiral iminophosphines

Article abstract of DOI:10.1021/om010333k

In the presence of the organopalladium template containing the orthometalated (S)-(1-(dimethylamino)ethyl)naphthylene auxiliary, both diphenyl(phenylethynyl)phosphine and di(phenylethynyl)phenylphosphine were reactive toward the novel hydroamination reaction with aniline to give the corresponding bidentate iminophosphines in high yields. These novel P-N ligands exhibited an interesting imine-enamine tautomerism in solution. Spectroscopic studies confirmed that the uncoordinated ligands adopted the stable imino form but could be transformed to the enamino form upon complexation with palladium. The relative stability of the imino and enamino chelates is sensitive to the substituents on the phosphorus donor atoms. When di(phenylethynyl)phenylphosphine was used as the starting material, the hydroamination reaction gave a 4:1 mixture of the chelating diastereomeric P-chiral iminophosphine on the chiral template. These diastereomeric complexes could be separated efficiently via silica gel column chromatography. A pair of novel and enantiomerically pure P-chiral iminophosphines was obtained in high yields from the separated diastereomeric template complexes by treatment with KCN.

Full text of DOI:10.1021/om010333k

3918
Organometallics 2001, 20, 3918-3926
Meta l Tem p la te P r om oted Hyd r oa m in a tion of
Eth yn ylp h osp h in es a n d An ilin e. Asym m etr ic Syn th esis,
Coor d in a tion Ch em istr y, a n d th e Im in e-En a m in e
Ta u tom er ism of P -Ch ir a l Im in op h osp h in es
Xueming Liu, K. F. Mok, and Pak-Hing Leung*
Department of Chemistry, National University of Singapore, Kent Ridge, Singapore 119260
Received April 23, 2001
In the presence of the organopalladium template containing the orthometalated (S)-(1-
(dimethylamino)ethyl)naphthylene auxiliary, both diphenyl(phenylethynyl)phosphine and
di(phenylethynyl)phenylphosphine were reactive toward the novel hydroamination reaction
with aniline to give the corresponding bidentate iminophosphines in high yields. These novel
P-N ligands exhibited an interesting imine-enamine tautomerism in solution. Spectroscopic
studies confirmed that the uncoordinated ligands adopted the stable imino form but could
be transformed to the enamino form upon complexation with palladium. The relative stability
of the imino and enamino chelates is sensitive to the substituents on the phosphorus donor
atoms. When di(phenylethynyl)phenylphosphine was used as the starting material, the
hydroamination reaction gave a 4:1 mixture of the chelating diastereomeric P-chiral
iminophosphine on the chiral template. These diastereomeric complexes could be separated
efficiently via silica gel column chromatography. A pair of novel and enantiomerically pure
P-chiral iminophosphines was obtained in high yields from the separated diastereomeric
template complexes by treatment with KCN.
In tr od u ction
bidentate ligands in coordination chemistry. In M-P-
CtCR complexes, the carbon-carbon triple bonds are
polarized, with the carbons attached to the phosphorus
being partially negatively charged.5 We therefore believe
that this electronic induction effect on the M-P-C≡CR
triple bond would render coordinated phosphinoalkynes
susceptible to electrophilic and nucleophilic reactions.
In this paper, we present the first examples of the
palladium template activated intermolecular hydroami-
nation between aniline and ethynylphosphines. Chelat-
ing iminophosphine ligands were generated efficiently
from these hydroamination reactions. It is noteworthy
that iminophosphines are important ligands, as they are
potential catalyst supporters.6
Organometallic complexes containing η1-M-CtCR
alkynyl ligands are important starting materials for the
synthesis of carbocyclic and heterocyclic compounds.1
In many organoalkynyl complexes, the carbon-carbon
triple bonds are chemically reactive and are able to
undergo electrophilic additions, Diels-Alder reaction,
and cycloalkenation processes. Similar reactivities are
observed with the carbon-phosphorus triple bonds in
phospha-alkyne η1-M-PtCR derivatives.2 On the other
hand, the carbon-carbon triple bond in coordinated
phosphinoalkynes has been reported to undergo P-C
bond cleavages, insertion, and coupling reactions.3
Furthermore, phosphinoalkynes can be activated by
metal complexation toward nucleophilic attack by water,
ethanol, hydrogen halides, and diphenylphosphine.4
Phosphinoalkynes function typically as monodentate or
Resu lts a n d Discu ssion
Hyd r oa m in a tion of th e Ach ir a l Dip h en yl(p h e-
n yleth yn yl)p h osp h in e. The achiral diphenyl(phenyl-
ethynyl)phosphine was selected as the model compound
for the subsequent asymmetric hydroamination reac-
tion. No reaction between the free Ph2PCtCPh and
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10.1021/om010333k CCC: $20.00 © 2001 American Chemical Society
Publication on Web 08/08/2001

Hydroamination of Ethynylphosphines and Aniline
Organometallics, Vol. 20, No. 18, 2001 3919
Sch em e 1
aniline was observed in the absence of a transition metal
ion. However, the hydroamination reaction proceeded
smoothly when both Ph2PCtCPh and aniline were
coordinated onto the same metal template. We found
the dimeric complex (Sc)-1 to be an efficient template
for this intramolecular coupling reaction. As illustrated
in Scheme 1, the reaction initially involved the re-
giospecific coordination of the phosphinoalkyne ligand
onto the orthometalated naphthylamine complex to form
the monomeric chloro complex (Sc)-2. The regiospecific-
ity is due to the distinct electronic directing effects
originating from the σ-donating nitrogen and the π-ac-
cepting aromatic carbon of the orthopalladated naph-
thylamine ring. Furthermore, it has been well estab-
lished that the chloro ligands in this class of organopal-
ladium complexes are thermodynamically and kinet-
ically stable and cannot be displaced efficiently by most
other monodentate ligands, including phosphines and
aniline.7 Indeed, there was no reaction observed be-
tween aniline and the chloro complex (Sc)-2. Evidently,
the coordinated phosphino alkyne ligand in (Sc)-2 is not
chemically reactive toward free aniline. Thus it was
necessary to remove the chloro ligand in (Sc)-2 by the
treatment with silver perchlorate in order to allow the
coordination of aniline onto the metal.8 The intramo-
lecular hydroamination reaction was subsequently car-
ried out at 100 °C in toluene for 10 h to give the desired
iminophosphine complex (Sc)-3 as pale yellow prisms
(56%), mp > 200 °C (dec), [R]D -193° (c 0.5 CH2Cl2).
The 31P NMR spectrum of (Sc)-3 in CDCl3 exhibited a
singlet signal at δ 48.8. A single crystal X-ray structural
analysis of the highly crystalline cationic complex (Sc)-3
was achieved (Figure 1). Selected bond distances and
angles are given in Table 1. The X-ray structural
analysis of (Sc)-3 establishes unambiguously that the
desired iminophosphine P-N chelate was formed re-
giospecifically on the palladium template. The N(2)-
C(15) [1.293(4) Å] and C(15)-C(16) [1.492(5) Å] dis-
tances are typical for CdN and C-C bonds, respectively.
A noticeable feature of the square-planar complex is the
F igu r e 1. Molecular structure and absolute stereochem-
istry of the cationic complex (Sc)-3. Thermal ellipsoids
enclose 50% probability levels.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for th e Tem p la te Com p lex (Sc)-3
Pd(1)-C(1)
Pd(1)-N(2)
N(2)-C(15)
C(15)-C(16)
P(1)-C(16)
2.001(3)
2.206(3)
1.293(4)
1.492(5)
1.841(4)
Pd(1)-N(1)
Pd(1)-P(1)
N(2)-C(23)
C(15)-C(17)
P(1)-C(29)
2.164(2)
2.217(1)
1.439(4)
1.490(4)
1.817(3)
C(1)-Pd(1)-N(1)
C(1)-Pd(1)-P(1)
N(1)-Pd(1)-P(1)
P(1)-C(16)-C(15)
C(15)-N(2)-C(23)
Pd(1)-P(1)-C(16)
Pd(1)-P(1)-C(35)
80.4(1)
96.4(1)
C(1)-Pd(1)-N(2)
N(1)-Pd(1)-N(2)
N(2)-Pd(1)-P(1)
C(16)-C(15)-N(2)
C(15)-N(2)-Pd(1)
Pd(1)-P(1)-C(29)
Pd(1)-N(2)-C(23)
175.4(1)
104.2(1)
79.1(1)
117.7(3)
119.6(2)
113.8(1)
119.7(2)
174.7(1)
108.7(2)
120.7(3)
100.7(1)
122.2(1)
marked expansion in the N(1)-Pd(1)-N(2) angle to
104.2(1)°. This is clearly a consequence of the steric
repulsion between the substituents on the two neigh-
boring nitrogen donor atoms.9
1
The H NMR spectrum of (Sc)-3 in CDCl3 exhibited
two characteristic doublet of doublet (dd) signals for the
two nonequivalent prochiral PCH2 protons at δ 3.87
(2J PH ) 14.3 Hz, 2J HH ) 16.7 Hz) and δ 5.42 (2J PH ) 9.8
Hz, 2J HH ) 16.7 Hz). These dd signals are useful handles
in the spectroscopic investigation of the imine-enamine
tautomerism process, which takes place within the
chelating iminophosphine ligand in complex (Sc)-3.
Interestingly, the dd signal at δ 5.42 disappeared almost
immediately upon adding D2O into an NMR sample of
(Sc)-3. At the same time, the other dd signal at δ 3.87
became a simple doublet (2J PH ) 14.3 Hz). Eventually
the simplified doublet at δ 3.87 diminished in intensity
after the NMR mixture was allowed to stand for 1 h.
This simple spectroscopic experiment thus revealed that
in CDCl3 the bidentate ligand indeed undergoes rapid
imine-enamine tautomerism, as C-H protons in the
imino form are generally inert to D2O exchange, whereas
(7) Kerr, P. G.; Leung, P. H.; Wild, S. B. J . Am. Chem. Soc. 1987,
109, 4321. Dunina, V. V.; Golovan, E. B.; Gulyukina, N. S.; Buyevich,
A. V. Tetrahedron: Asymmetry 1995, 6, 2731. Hockless, D. C, R.;
Gugger, P. A.; Leung, P. H.; Mayadunne, R. C.; Pabel, M.; Wild, S. B.
Tetrahedron 1997, 53, 4083. He, G.; Loh, S. K.; Vittal, J . J .; Mok, K.
F.; Leung, P. H. Organometallics 1998, 17, 3931.
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Inorg. Chem. 1986, 25, 3392. Chooi, S. Y. M.; Hor, T. S. A.; Leung, P.
H.; Mok, K. F. Inorg. Chem. 1992, 31, 1494. Leung, P. H.; Quek, G.
H.; Lang, H.; Liu, A. M.; Mok, K. F.; White, A. J . P.; Williams, D. J .;
Rees, N. H.; McFarlane, W. J . Chem. Soc., Dalton Trans. 1998, 1639.
Song, Y.; Vittal, J . J .; Chan, S. H.; Leung, P. H. Organometallics 1999,
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2000, 19, 3722.
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D. J . Tetrahedron: Asymmetry 1996, 7, 45.

3920 Organometallics, Vol. 20, No. 18, 2001
Liu et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) of th e Dich lor o Com p lex 4
Pd(1)-Cl(1)
Pd(1)-N(1)
N(1)-C(2)
P(1)-C(1)
P(1)-C(21)
2.363(1)
2.074(3)
1.294(4)
1.826(3)
1.817(3)
Pd(1)-Cl(2)
Pd(1)-P(1)
C(1)-C(2)
P(1)-C(15)
N(1)-C(9)
2.288(1)
2.197(1)
1.501(4)
1.797(3)
1.458(4)
Cl(1)-Pd(1)-N(1)
Cl(1)-Pd(1)-Cl(2)
N(1)-Pd(1)-Cl(2)
P(1)-C(1)-C(2)
C(2)-N(1)-C(9)
Pd(1)-P(1)-C(1)
Pd(1)-P(1)-C(21)
94.1(1)
Cl(1)-Pd(1)-P(1)
N(1)-Pd(1)-P(1)
P(1)-Pd(1)-Cl(2)
C(1)-C(2)-N(1)
C(2)-N(1)-Pd(1)
Pd(1)-P(1)-C(15)
Pd(1)-N(1)-C(9)
174.0(1)
80.0(1)
93.3(1)
117.7(3)
118.9(2)
124.5(1)
120.1(2)
92.6(1)
172.6(1)
105.1(2)
121.3(3)
97.5(1)
111.1(1)
acute being associated with the five-membered chelate
ring. The two Pd-Cl bond distances [2.288(1) and 2.363-
(1) Å] differ significantly, with the bond trans to the
phosphorus being noticeably enlarged from normal,
reflecting the stronger electronic trans influence of the
phosphorus versus nitrogen.12 Similar to (Sc)-3, 1H NMR
studies revealed that the imino-substituted phosphine
ligand in the dichloro complex exists predominately in
its imino form, although the imine-enamine tautom-
erism process was found to take place rapidly in
solution.
F igu r e 2. Molecular structure of the dichloro complex 4.
The liberation of the iminophosphine ligand from the
dichloro complex 4 was achieved by treatment of the
complex with potassium cyanide. Thus the free ligand
5 was obtained as an air-stable solid in 65.2% yield. The
31P NMR spectrum of 5 in CDCl3 exhibits a singlet
resonance at δ -13.1. The 1H NMR spectrum of the
ligand in the same solvent exhibited the characteristic
doublet at δ 3.55 (2J PH ) 2.0 Hz) for the two equivalent
PCH2 protons. This doublet signal was not affected by
the D2O exchange experiment. The spectroscopic analy-
sis thus revealed that, in CDCl3 the iminophosphine
ligand 5 exists exclusively in its imino form and does
not transform into the corresponding enamino counter-
part in solution. Apparently the rapid imine-enamine
tautomeric equilibriums observed in the chelating imi-
nophosphine ligands in both complexes (Sc)- 3 and 4
were triggered by the metal complexation.
Asym m et r ic Hyd r oa m in a t ion of t h e P r och ir a l
Di(p h en yleth yn yl)p h en ylp h osp h in e: Syn th esis of
a P a ir of Dia ster eom er ic Com p lexes Con ta in in g
th e P -Ch ir al Im in oph osph in es (Sc,Rp)-7 an d (Sc,Sp)-
7. The above hydroamination reaction has been modified
successfully for the asymmetric synthesis of a pair of
P-chiral iminophosphines by using the prochiral phos-
phinoalkyne PhP(CtCPh)2 as the starting material
(Scheme 2). Thus, upon the removal of chloro ligand in
(Sc)-6 by silver perchlorate, the coupling reaction pro-
ceeded smoothly at room temperature. The reaction was
monitored by 31P NMR spectroscopy and was found to
be complete in 16 h. The 31P NMR spectrum of the
reaction mixture in CDCl3 exhibited two sharp singlets
at δ 15.1 and 17.3 with relative intensities of 4:1.
Accordingly, two stereochemically nonequivalent prod-
ucts were generated in this reaction. The mixture could
Thermal ellipsoids enclose 50% probability levels.
N-H protons in the enamino form are prone to the
exchange. It is important to note that the 31P NMR
spectrum of the same sample recorded the original
singlet signal at δ 48.8 throughout the course of D2O
exchange. Thus the P-N chelate in (Sc)-3 exists pre-
dominately in its imino form in solution. To date, there
are several examples of monodentate N-imino donor
atoms that undergo such a dynamic imine-enamine
tautomerism in organopalladium complexes.10 However,
the imine-enamine tautomerism observed in complex
(Sc)-3 is the first example that such a dynamic process
could occur within a bidentate metal chelate. Such
tautomeric processes may affect the electronic properties
of these unsaturated ligands.11
The naphthylamine ligand on the template complex
(Sc)-3 could be removed chemoselectively by treatment
with concentrated HCl. Thus the achiral dichloro com-
plex 4 was obtained as yellow prisms in 88% yield, mp
> 200 °C (dec). The 31P NMR spectrum of 4 in CDCl3
exhibited a singlet at δ 46.1. A single-crystal X-ray
structural analysis of 4 confirmed that while the ortho-
metalated naphthylamine ligand could be efficiently
removed by concentrated HCl, the iminophosphine P-N
chelate remained unchanged in this acid treatment
(Figure 2). Selected bond distances and angles are given
in Table 2. In contrast to (Sc)-3, no major interchelate
repulsion exists within the dichloro complex and the
geometry at palladium is regular planar with cis angles
ranging between 80.8(1)° and 94.1(1)°, with the most
(10) O’Connor, J . M.; Uhrhammer, R.; Rheingold, A. L.; Roddick,
D. M. J . Am. Chem. Soc. 1991, 113, 4530. Al´ıas, F. M.; Belderra´ın, T.
R.; Paneque, M.; Poveda, M. L.; Carmona, E. Organometallics 1997,
16, 301. Al´ıas, F. M.; Belderra´ın, T. R.; Paneque, M.; Poveda, M. L.;
Carmona, E. Organometallics 1998, 17, 5620. Veya, P.; Floriani, C.;
Chiesi-Villa, A.; Rizzoli, L. Organometallics 1993, 12, 4899.
(11) Casey, C. P.; Czerwinski, C. J .; Fusie, K. A.; Hayashi, R. K. J .
Am. Chem. Soc. 1997, 119, 3971. De los Rios, I.; J ime´nez Tenorio, M.;
Puerta, M. C.; Valerga, P. J . Am. Chem. Soc. 1997, 119, 6529.
Wakatsuki, Y.; Koga, N.; Werner, H.; Morkuma, K. J . Am. Chem. Soc.
1997, 119, 360.
(12) For examples, see: Leung, P.-H.; Siah, S.-Y.; White, A. J . P.;
Williams, D. J . J . Chem. Soc., Dalton Trans. 1998, 893. Leung, P.-H.;
He, G. S.; Lang, H. F.; Liu, A. M.; Loh, S.-K.; Selvaratnam, S.; Mok,
K. F.; White, A. J . P.; Williams, D. J . Tetrahedron 2000, 56, 7. Leung,
P.-H.; Loh, S. K.; Mok, K. F.; White, A. J . P.; Williams, D. J . Chem.
Commun. 1996, 591. Leung, P.-H.; Lang, H. F.; White, A. J . P.;
Williams, D. J . Tetrahedron: Asymmetry 1998, 9, 2961.

Hydroamination of Ethynylphosphines and Aniline
Organometallics, Vol. 20, No. 18, 2001 3921
F igu r e 3. Numbering scheme of the diastereomeric com-
plex 7 for the ROESY NMR studies.
F igu r e 4. Absolute conformation of the PdCN ring and
the staggered orientation of its C(11) and N(12) substitu-
ents.
Sch em e 2
these NMR analyses, the well-established stereochem-
ical features of the orthometalated (S)-naphthylamine
unit within the diastereomeric complexes 7 are used as
the internal stereochemical references. Due to the
repulsive interaction between Me(11) and the proximal
H(8) naphthylene proton, Me(11) invariably takes up
the axial position in the stable five-membered organo-
palladium ring which adopts the static λ absolute
conformation (Figure 4). This axial Me(11) group projects
perpendicularly below the square-plane. On the other
hand, the prochiral N-Me groups attached to the orga-
nopalladium ring are locked by the rigid λ ring confor-
mation into the nonequivalent axial and equatorial
positions. The axial NMe group projects perpendicularly
above the square-plane, while the equatorial NMe group
protrudes somewhat below the plane and toward the
adjacent nitrogen donor in the P-N ring. Similarly, the
rigid organometallic ring also locks the H(2) naphthyl-
ene proton in the position slightly above the plane and
close to the phosphorus donor atom. With reference to
the unique structural feature of the auxiliary, appropri-
ate interchelate NOE interactions between the naph-
thylamine auxiliary and the iminophosphine chelates
would allow the assignment of the absolute stereochem-
istry of the P-N chelates.
Ster eoch em ica l Con sid er a tion s of th e Dia ster -
eom er ic Com p lexes. On the basis of the absolute
chirality of the phosphorus center and the absolute
conformation of the iminophosphine P-N ring, the
above asymmetric hydroamination reaction may gener-
ate up to four stereoisomeric products. Figure 5 shows
the absolute stereochemistries of the four isomers. The
absolute configuration at the stereogenic phosphorus
centers of isomer A and B is R. They differ in their five-
membered P-N ring conformation in that the P-N ring
conformation in isomer A is δ, but in isomer B it is λ.
Similarly, isomers C and D are conformers with the
same S absolute configuration at the stereogenic phos-
phorus centers. A Dreiding model study indicated that
in isomers A and C, the δ-iminophosphine rings dispose
their N-Ph substituents in sterically unfavorable posi-
tions whereby they suffer from severe interchelate
repulsions between their neighboring equatorial-NMe
groups. On the other hand, these neighboring N-
substituents in isomers B and D are located in sterically
favorable staggered orientations. Similarly, the equa-
torially disposed P-substituents in both isomers A and
C interact somewhat unfavorably with the protruding
H(2) proton from the naphthylamine auxiliaries. Ac-
cordingly, isomers A and C are sterically unfavorable
and the two diastereomeric products are likely to be
isomers B and D. Nevertheless, the four isomers are
stereochemically distinct molecules and should be readily
identified by 2D-ROESY NMR spectroscopy.
be separated efficiently by silica gel column chromatog-
raphy. The major isomer was obtained as yellow solids
in 56% yield, [R]D -266.1° (CH2Cl2), and the minor
isomer was isolated in similar form in 15% yield, [R]D
+62.5° (CH2Cl2). Both isomeric complexes showed simi-
lar elemental analysis results. Furthermore, their ES-
MS spectral patterns were identical with their molec-
ular weights recorded at the same 708.9 (M+) position.
Hence it can be deduced that they are diastereomeric
products (Sc,Rp)-7 and (Sc,Sp)-7. The two complexes have
similar molecular connectivities but, as desired, differ
in the absolute chiralities at their stereogenic phospho-
rus donors. Both isomers are chemically stable and
readily soluble in organic solvents. However, they could
not be induced to form single crystals suitable for X-ray
structure analysis. Accordingly, it was necessary to
determine the absolute stereochemistry of these iso-
meric hydroamination products by the 2D rotating
1
frame nuclear Overhauser enhancement (ROESY) H
NMR technique.13 We have previously applied this
reliable 2D NMR technique for the assignments of the
absolute stereochemistry in a series of coordinated
P-chiral phosphines containing the same orthometalated
naphthylamine auxiliary.
Assign m en ts of Absolu te Ster eoch em istr y in th e
Dia ster eom er ic Com p lexes. Th e Ch ir a l Au xilia r y
a n d In ter n a l Ster eoch em ica l Refer en ces. Figure 3
shows the numbering scheme of the diastereomeric
complexes 7 used in the 2D ROESY NMR analysis. In
(13) Bookham, J . L.; McFarlane, W. J . Chem. Soc., Chem. Commun.
1993, 1352. Aw, B.-H.; Selvaratnam, S.; Leung, P. H.; Rees, N. H.;
McFarlane, W. Tetrahedron: Asymmetry 1996, 7, 1753. Aw, B.-H.; Hor,
A. T. S.; Selvaratnam, S.; Mok, K. F.; White, A. J . P.; Williams, D. J .;
Rees, N. H.; McFarlare, W.; Leung, P.-H. Inorg. Chem. 1997, 36, 2138.
Lang, H. F.; Leung, P. H.; Rees, N. H.; McFarlane, W. Inorg. Chim.
Acta 1999, 284, 99.

3922 Organometallics, Vol. 20, No. 18, 2001
Liu et al.
Ta ble 3. Selected 31P a n d 1H NMR Sp ectr a Ch em ica l Sh ift Va lu es of (Sc)-3, (Sc,Rp )-7, a n d (Sc,Sp )-7 in CDCl3
(cou p lin g con sta n ts in Hz a r e given in p a r en th eses)
(Sc)-3
(Sc,Rp)-7
(Sc,Sp)-7
31P
CHMe
49.8 s
2.06 d
15.1 s
2.08 d
17.3 s
2.02 d
(3J HH ) 6.4)
2.09 d
(3J HH ) 6.4)
2.08 d
(3J HH ) 6.4)
2.00 d
NMe(eq)
NMe(ax)
CHMe
(4J PH ) 4.0)
2.41 d
(4J PH ) 3.6)
2.37 d
(4J PH ) 2.8)
2.48 (d)
(4J PH )1.6)
4.21 qn
(4J PH ) 2.0)
4.20 qn
(4J PH ) 2.0)
4.23 qn
(3J HH )4J PH ) 6.4)
3.87 dd
(3J HH ) 4J PH ) 6.4)
3.83 dd
(3J HH ) 4J PH ) 6.4)
3.83 dd
CHH(eq)
CHH(ax)
Np-H(2)
Np-H(3)
o-PPh
(2J HH ) 14.3, J PH ) 16.7)
(2J HH )2J PH ) 16.5)
5.13 dd
(2J HH ) 16.9, J PH ) 14.9)
2
2
5.42 dd
5.27 dd
(2J HH ) 16.7, J PH ) 9.8)
(2J HH ) 16.5, J PH ) 8.9)
(2J HH ) 16.9, J PH ) 12.8)
2
2
2
6.88 dd
7.08 dd
signal not discernible
signal not discernible
8.27 dd
(3J HH )8.4, J PH ) 6.9)
(3J HH ) 4J PH ) 8.2)
7.18 d
4
7.06 d
(3J HH ) 8.4)
8.19 dd
(3J HH ) 8.2)
8.05 dd
(3J HH ) 6.9, J PH ) 11.8)
(3J HH ) 7.8, J PH ) 14.6)
(3J HH ) 7.8, J PH ) 13.8)
3
3
3
F igu r e 5. The four possible conformations of (Sc,Rp)-7 and
(Sc,Sp)-7.
Ster eoch em ica l An a lysis of Dia ster eom er s by 2D
ROESY NMR Sp ectr oscop y. Selected 31P and 1H
NMR data of the two diastereomeric complexes 7 are
given in Table 3. Selected data of the model complex
(Sc)-3 are included in the table for comparison purposes.
F igu r e 6. Two-dimensional 1H ROESY NMR spectrum of
complex (Sc,Rp)-7 in CDCl3. All off-diagonal peaks are of
negative intensity. Selected NOE contacts: A, H11-Me12-
(eq); B, Me11-H11; C, H11-Me12(ax); D, Me12(ax)-Me12-
(eq); E, H11-H8; F, Me11-H8; G, Me11-o-PPh; H, H2-
o-PPh; I, Me12(eq)-Ph13; J, Me12(eq)-Ph14; K, Me12(ax)-
Ph14; L, Me12(ax)-Ph13; M, H15(ax)-H15(eq); N, H15(eq)-
o-Ph14; O, H15(eq)-Ph14; P, H15(ax)-o-Ph14; Q, H15(ax)-
Ph14; R, H15(ax)-o-PPh.
1
These NMR assignments are based on a series of H,
31P,1H{31P}, and 2D 1H-ROESY NMR studies of the
complexes. Figures 6 and 7 show the 2D 1H-1H ROESY
NMR spectra of the major and the minor hydroamina-
tion products, respectively. In both spectra, the char-
acteristic NOE patterns within the orthometalated (S)-
naphthylamine ring are clearly recorded. For example,
strong NOE signals (A-C) are observed for the expected
proximities between H(11) and the three methyl groups
on N(12) and C(11). The driving forces for Me(11) to
assume the axial position, i.e., the H(8)-H(11) (E) and
H(8)-Me(11) (F) repulsive interactions, are clearly
reflected in the spectrum. No interaction between Me11
and NMe(ax) is observed. Consistent with the exclusive
adoption of the λ ring conformation by the (S)-naphthy-
lamine auxiliary, Me(11) interacts only with one neigh-
boring NMe group, i.e., NMe(eq). In the δ conformation,
this CMe group would interact with both NMe groups.
In Figure 6, the 2D ROESY NMR spectrum of the
major product shows a long-range interchelate NOE
interaction between the o-PPh protons and the Me(11)
(signal G). This NOE signal thus indicates that these
two groups are located on the same side below the

Hydroamination of Ethynylphosphines and Aniline
Organometallics, Vol. 20, No. 18, 2001 3923
Sch em e 3
from the asymmetric hydroamination reaction is com-
plex (Sc,Rp)-7.
Similarly, the 2D ROESY NMR studies of the minor
hydroamination product confirm that the complex is
(Sc,Sp)-7. As seen in Figure 7, there is no NOE interac-
tion between Me(11) and o-PPh. The absence of this
NOE signal suggests that the two groups are located
at different sides of the square plane. This information
allows the assignment of the S absolute configuration
at the phosphorus stereogenic center in the minor
isomer. Another major difference between the two
ROESY spectra is that, in Figure 7, the o-PPh protons
do not interact with the axially orientated PCH proton,
but a strong interaction is observed with the equatori-
ally disposed PCH proton (signal M). This clearly
indicates that the o-PPh and the axial PCH are on
opposite sides of the plane. This NOE interaction, taken
in conjunction with the fact that both NMe groups of
the chiral auxiliary interact with the imino N-Ph group
(signals H and J ), confirms that the P-N ring of the
minor isomer also adopts the λ absolute conformation.
It is noteworthy that, with this λ ring conformation, the
P-Ph group in complex (Sc,Sp)-7 is orientated in the axial
position. Model studies indicated that, however, the
P-Ph group at this axial position suffers from consider-
able steric constraints due to the phenyl ring which is
attached to C(14). In contrast, the λ ring conformation
allows the P-Ph group in the major (Sc,Rp)-7 isomer to
occupy a sterically more favorable equatorial position.
We believe that this is indeed the major discriminating
effect on the relative populations of the two diastereo-
meric hydroamination products.
Im in e-E n a m in e Ta u t om er ic E q u ilib r iu m of
(Sc,Rp )-7 a n d (Sc,Sp )-7. Similar to the model complexes
containing the PPh2 moiety, both P-chiral template
complexes undergo the tautomerism process in solution.
Indeed, they are significantly more potent to adopt their
enamine forms than the model complexes. In dichloro-
menthane, (Sc,Rp)- and (Sc,Sp)-7 transformed quantita-
tively into their enamino counterparts (Sc,Rp)- and
(Sc,Sp)-8, respectively within one week (Scheme 3). Both
pure enamino complexes (Sc,Rp)- and (Sc,Sp)-8 were
isolated as light yellow solids in quantitative yields.
Similar to their imino counterparts, however, the enam-
ino complexes could not be induced to crystallize for
structural analysis. The ES-MS spectra of both the
enamino complexes and their imino parent compounds
show similar molecular ion isotopic distribution pat-
terns, which agree with the theoretical calculation.
F igu r e 7. Two-dimensional 1H ROESY NMR spectrum of
complex (Sc,Sp)-7 in CDCl3. All off-diagonal peaks are of
negative intensity. Selected NOE contacts: A, H11-Me12-
(eq); B, Me11-H11; C, H11-Me12(ax); D, Me12(ax)-Me12-
(eq); E, H11-H8; F, Me11-H8; G, Me12(eq)-Ph14; H,
Me12(eq)-Ph13; I, Me12(ax)-Ph14; J , Me12(ax)-Ph13; K,
H15(ax)-H15(eq); L, H15(eq)-Ph14; M, H15(eq)-o-PPh;
N, H15(ax)-Ph14.
square plane. Accordingly, the absolute configuration
at the phosphorus center is R. Furthermore, the regio-
chemistry of the two asymmetric bidentate chelates can
be confirmed by the NOE interaction (signal H) between
the o-PPh protons and the adjacent naphthylene proton
H(2). Consistent with their regioarrangements, the NMe
groups in the chiral auxiliary show NOE interaction
signals with the imino N-Ph group and the phenyl
group attached to C(14) (signals I-L). Within the
iminophosphine chelate, the two nonequivalent PCH2
protons show the expected strong NOE interaction with
each other (signal M). Both PCH2 protons interact with
the neighboring phenyl group attached to C(14) (signals
N-Q). Most importantly, the axially oriented PCH
proton shows a strong NOE interaction with the o-PPh
protons (signal R). This NOE signal thus confirms that
the iminophosphine ring adopts the λ absolute confor-
mation, i.e., isomer B (Figure 5). The λ rather than δ
conformation adopted by the P-N ring is indeed in
agreement with our earlier findings from the model
studies. The intense interchelate repulsions between the
equatorially disposed NMe group of the naphthylamine
auxiliary and the N-Ph group of the imino donor indeed
deter the adoption of the δ conformation by the P-N
ring, as depicted in isomer A of Figure 5. In isomer B,
these N-substituents are oriented in the favorable
staggered orientation. The above spectroscopic studies
confirm unambiguously that the major product obtained

3924 Organometallics, Vol. 20, No. 18, 2001
Liu et al.
Ta ble 4. Selected 31P a n d 1H NMR Sp ectr a Ch em ica l Sh ift Va lu es of (Sc,Rp )-8 a n d (Sc,Sp )-8 in CDCl3
(cou p lin g con sta n ts in Hz a r e given in p a r en th eses)
(Sc, Rp)-8
(Sc,Sp)-8
31P
CHMe
-7.6 s
-6.2 s
2.00 d
2.02 d
(3J HH ) 6.0)
2.98 d
(3J HH ) 6.0)
2.96 d
NMe(eq)
NMe(ax)
CHMe
CdCH
NH
4J PH ) 3.6)
2.72 d
(4J PH ) 4.0)
2.82 d
(4J PH ) 1.6)
4.32 qn
(4J PH ) 1.6)
4.30 qn
(3J HH )4J PH ) 6.0)
(3J HH )4J PH ) 6.0)
5.45 dd
5.20 dd
(2J PH ) 18.1, J HH ) 3.2)
(2J PH ) 18.5, J HH ) 3.0)
4
4
5.92 dd
561 dd
(3J PH ) 16.9,4J HH ) 3.2)
8.29 ddd
(3J PH ) 18.3,4J HH ) 3.0)
o-PPh
8.17 ddd
(3J HH ) 7.6,3J PH ) 12.5, J HH ) 1.6)
(3J HH ) 7.6, J PH ) 12.8, J HH ) 2.0)
4
3
4
Sch em e 4
Sch em e 5
Interestingly, both the enamino complexes are thermo-
dynamically more stable than their parent imino coun-
terparts. The reverse isomerization was not observed
when the enamino complexes were dissolved in solution.
Selected NMR data of the diastereomeric enamino
complexes are given in Table 4.
the same iminophosphine (Sp)-9 was obtained when the
enamino complex (Sc,Rp)-8 was treated with aqueous
KCN. The enantiomeric iminophosphine, (Rp)-9, with
[R]D - 105.3° (CH2Cl2), could be liberated from either
(Sc,Sp)-7 or (Sc,Sp)-8 in similar yields. The enantiomeri-
cally pure ligands are stable in the solid state. In
solution however, they are sensitive to air and racemize
slowly under ambient conditions.
The optical purity of the liberated 9 was established
by the recomplexation of the liberated ligand to the
enantiomeric complexes (Rc)- and (Sc)-10 (Scheme 5).
Interestingly, only the enamino forms of complexes were
regenerated in these complexation reactions. Thus,
when (SP)-9 was treated with (Sc)-10, the 31P NMR
spectrum of the crude product in CDCl3 exhibited a sole
singlet at δ -7.6. When the same ligand was treated
with (Rc)-10, however, the 31P NMR spectrum did not
show any signal at δ -7.6. Instead, a new singlet was
recorded at δ -6.2. This is consistent with the formation
of (Rc,Rp)-8, as the same signal was observed for (Sc,Sp)-
8. In the absence of external chiral environment, enan-
tiomers show the same NMR signals.
Liber a tion of th e P -Ch ir a l Im in op h osp h in es
(Rp )- a n d (Sp )-9. The liberation of the enantiomerically
pure P-chiral iminophosphines from (Sc,Rp)- and (Sc-
,Sp)-7 was achieved by separate treatments of the
diastereomers with aqueous KCN (Scheme 4). Thus
(Sp)-9 was liberated from (Sc,Rp)-7 as an air-stable pale
yellow solid in 68% yield, [R]D + 105.3° (CH2Cl2). It
should be noted that the apparent inversion of config-
uration that takes place at the phosphorus stereogenic
center when the P-chiral iminophosphine is liberated
from the complex is merely a consequence of the Cahn-
Ingold-Prelog (CIP) sequence rule.14 The 31P NMR
spectrum of the liberated ligand in CDCl3 exhibited a
sole singlet at δ -21.7. The 300 MHz 1H NMR spectrum
of (Sp)-9 in the same solvent showed two simple doublets
at δ 5.80 and 5.83 (2J HH ) 9.6 Hz) for the two non-
equivalent PCH2 protons. Interestingly, these PCH2
resonance signals did not diminish when the NMR
sample was treated with D2O for one week. The D2O
exchange experiment does reveal that, without metal
complexation, (Sp)-9 adopts the thermodynamically
stable imino form. This finding clearly reveals that, once
again, the imine-enamine tautomerisms oberved in the
chelating iminophosphine complexes were indeed trig-
gered by the metal complexation. It is noteworthy that
In conclusion, the present study provides a novel and
effective way to synthesize enantiomerically pure P-
chiral iminophosphine ligands, which show interesting
dynamic properties and coordination chemistry. We are
currently investigating further synthetic applications of
this novel asymmetric hydroamination reaction.
(14) Cahn, R. S.; Ingold, C. K.; Prelog, V. Angew. Chem., Int. Ed.
Engl. 1966, 5, 385.

Hydroamination of Ethynylphosphines and Aniline
Organometallics, Vol. 20, No. 18, 2001 3925
3
suppressed by D2O, CHH), 4.21 (qn, 1H, J HH
)
4J PH ) 6.4
Exp er im en ta l Section
2
2
Hz, CHMe), 5.42 (dd, 1H, J PH ) 9.8 Hz, J HH ) 16.7 Hz,
3
4
Reactions involving air-sensitive compounds were performed
under a positive pressure of purified nitrogen. NMR spectra
were recorded at 25 °C on Bruker ACF300 and AMX500
spectrometers. The phase-sensitive ROESY NMR experiments
were acquired into a 1024 × 512 matrix with a 250 ms spin
locking time and a spin lock field strength such that γB1/2π )
5000 Hz and then transformed into 1024 × 1024 points using
a sine bell weighting function in both dimensions. Electrospray
mass spectroscopic experiments were recorded on a Finnigan
TSQ 7000 triple stage quadropole mass spectrometer by
positive electrospray ionization. Optical rotations were mea-
sured on the specified solution in a 1 dm cell at 25 °C with a
Perkin-Elmer 341 polarimeter. Elemental analyses were per-
formed by the Elemental Analysis Laboratory of the Depart-
ment of Chemistry at the National University of Singapore.
The phosphinoalkynes were prepared by the literature
methods.15 The enantiomerically pure form of the dimeric
palladium complex (Sc)-1 and the cationic bis(acetonitrile)
complexes (Rc)- and (Sc)-10 were prepared as previously
described.16
suppressed by D2O, CHH), 6.88 (dd, 1H, J HH ) 8.4 Hz, J PH
3
) 6.9 Hz, H2), 7.06 (d, 1H, J HH ) 8.4 Hz, H3), 6.98-7.76 (m,
3
3
22H, aromatics) 8.19 (dd, 2H, J HH ) 6.9 Hz, J PH ) 11.8 Hz,
o-PPh).
Rem ova l of th e Na p h th yla m in e Au xilia r y. Isola tion
of Dich or o{1,2-d ip h en yl-3-d ip h en ylp h osp h in o-1-a za -1-
p r op en e-N1,P 3′}p a lla d iu m (II), 4. A dichloromethane solu-
tion (5 mL) of the hyroamination product (Sc)-3 (0.2 g) was
treated with concentrated HCl (5 mL) at room temperature
for 1 h. The mixture was then diluted with dichloromethane
(50 mL), washed with water, and dried (MgSO4). Removal of
the solvent gave a yellow solid, which readily recrystallized
from dichloromethane-diethyl ether to give 4 as yellow
crystals: 0.13 g (88% yield); mp > 220 °C (dec). Anal. Calcd
for C26H22Cl2NPPd: C, 56.1; H, 4.0; N, 2.5. Found: C, 55.8;
H, 4.0; N, 2.8. 31P NMR (CDCl3): δ 46.1 (s). H NMR (CDCl3):
1
δ 4.52 (d, 2H, 2J PH ) 13.3 Hz, suppressed by D2O, CH2), 6.91-
3
3
7.59 (m, 18H, aromatics), 7.96 (dd, 2H, J HH ) 7.2 Hz, J PH
13.3 Hz, o-PPh).
)
Liber a tion of th e Im in op h osp h in e Liga n d . Isola tion
of 1,2-Dip h en yl-3-d ip h en ylp h osp h in o-1-a za -1-p r op en e, 5.
A dichloromethane solution of the dichloro complex (0.1 g) was
treated with potassium cyanide (0.2 g) in water (2 mL). The
reaction mixture was stirred vigorously at room temperature
for 0.5 h. The organic layer was separated, washed with water,
and dried (MgSO4). Removal of the solvent under high vacuum
gave the iminophosphine ligand 5 as an air-stable solid, 44
mg (65% yield). Anal. Calcd for C26H22NP: C, 82.3; H, 5.8; N,
3.7. Found: C, 82.3; H, 5.5; N, 4.0. 31P NMR (CDCl3): δ -13.1
(s). 1H NMR (CDCl3): δ 3.55 (d, 2H, 2J PH ) 2.0 Hz, CH2), 6.37
(d, 2H, 3J HH ) 8.2 Hz, m-NPh), 6.10-7.50 (m, 16H, aromatics),
Ca u tion ! All the cationic complexes described were isolated
as perchlorate salts and should be handled as potentially
explosive compounds.
[SP -4-4-(S)-Ch lor o[1-[1-(d im eth yla m in o)eth yl]-2-n a p h -
th a len yl-C,N][d ip h en ylp h en yleth yn ylp h osp h in e-P ]p a l-
la d iu m (II), (Sc)-2. A mixture of the dimeric complex (Sc)-1
(3.75 g) and diphenyl(phenylethynyl)phosphine (3.16 g) in
dichloromethane (50 mL) was stirred at room temperature for
0.5 h. The solution was concentrated to give a yellow residue.
Crystallization of the crude product from dichloromethane-
diethyl ether gave the complex (Sc)-2 as pale yellow crystals:
6.3 g (91% yield); mp > 200 °C (dec); [R]D +81.8° (c 0.3, CH2-
Cl2). Anal. Calcd for C34H31ClNPPd: C, 65.2; H, 5.0; N, 2.2.
Found: C, 65.4; H, 5.0; N, 2.2. 31P NMR (CDCl3): δ 11.6 (s).
3
7.83 (d, 2H, J HH ) 8.2 Hz, o-NPh).
[SP -4-4-(S)-Ch lor o[1-[1-(d im eth yla m in o)eth yl]-2-n a p h -
th a len yl-C,N][d i(p h en yleth yn yl)p h en ylp h osp h in e-P ]p a l-
la d iu m (II), (Sc)-6. A mixture of the dimeric complex (Sc)-1
(2.0 g) and di(phenylethynyl)phenylphosphine (1.9 g) in dichlo-
romethane (50 mL) was stirred at room temperature for 0.5
h. Removal of the solvent gave (Sc)-6 as a yellow residue, 3.9
g (100%); mp > 200 °C (dec); [R]D +78.6° (c 0.3, CH2Cl2). 31P
3
1H NMR (CDCl3): δ 2.05 (d, 3H, J HH ) 6.4 Hz, CHMe), 2.73
4
4
(d, 3H, J PH(trans) ) 1.6 Hz, NMe), 2.95 (d, 3H, J PH(trans) ) 3.6
3
Hz, NMe), 4.35 (qn, 1H, J HH ) 4J PH ) 6.4 Hz, CHMe), 7.22-
3
3
7.73 (m, 20H, aromatics), 7.80 (dd, 2H, J HH ) 6.8 Hz, J PH
)
3
3
12.8 Hz, o-PPh), 8.19 (dd, 2H, J HH ) 7.7 Hz, J PH ) 13.3 Hz,
o-PPh′ ).
1
NMR (CDCl3): δ -19.5 (s). H NMR (CDCl3): δ 2.05 (d, 3H,
3J HH ) 6.4 Hz, CHMe), 2.78 (d, 3H, J PH(trans) ) 2.0 Hz, NMe),
4
Hyd r oa m in a tion Rea ction of th e Ach ir a l Dip h en yl-
(p h en yleth yn yl)p h osp h in e. Syn th esis of {(S)-1-[1-(Di-
m eth yla m in o)eth yl]n a p h th yl-C,N}{1,2-d ip h en yl-3-d ip h e-
n ylp h osp h in o-1-a za -1-p r op en e-N1,P 3′}p a lla d iu m (II) P er -
ch lor a te, (Sc)-3. A solution of the chloro complex (Sc)-2 (0.5
g) in dichloromethane (20 mL) was treated with silver per-
chlorate (0.3 g) in water (1 mL) for 30 min. The mixture was
then filtered through Celite, washed with water, and dried
(MgSO4), and the solvent was removed under reduced pres-
sure. The resulting perchlorato complex was dissolved in
toluene (50 mL) and treated with aniline (0.37 g). The mixture
was then heated at 100 °C for 10 h. Removal of the solvent
gave the crude hydroamination product as a black residue.
Subsequent purification of the crude product by silica gel
column chromatography (ethyl acetate-hexane, 1:1) gave pure
(S)-3 as a pale yellow solid. The product was recrystallized
from dichloromethane-diethyl ether as pale yellow crystals:
0.35 g (56% yield); mp > 200 °C (dec); [R]D -193.2° (c 0.3, CH2-
Cl2). Anal. Calcd for C40H38ClN2O4PPd: C, 61.3; H, 4.9; N, 3.6.
Found: C, 61.2; H, 5.3; N, 3.5. 31P NMR (CDCl3): δ 49.8 (s).
4
3
3.01 (d, 3H, J PH(trans) ) 4.0 Hz, NMe), 4.35 (qn, 1H, J HH
)
4J PH ) 6.4 Hz, CHMe), 7.25-7.73 (m, 22H, aromatics), 8.29
3
3
(dd, 2H, J HH ) 9.6 Hz, J PH ) 14.4 Hz, o-PPh). The complex
decomposed slowly in solution and was used directly without
further purification for the subsequent hydroamination reac-
tion.
Asym m etr ic Hyd r oa m in a tion of th e P r och ir a l Di-
(p h en yleth yn yl)p h en ylp h osp h in e. Syn th esis of {(S)-1-[1-
(Dim eth yla m in o)eth yl]n a p h th yl-C,N}{(3R)-1,2-d ip h en yl-
3-p h e n yl(p h e n yle t h yn yl)p h osp h in o-1-a za -1-p r op e n e -
N1,P 3′}p a lla d iu m (II) P er ch lor a te, (Sc,Rp )-7, a n d {(S)-1-[1-
(Dim eth yla m in o)eth yl]n a p h th yl-C,N}{(3S)-1,2-d ip h en yl-
3-p h e n yl(p h e n yle t h yn yl)p h osp h in o-1-a za -1-p r op e n e -
N1,P 3′}p a lla d iu m (II) P er ch lor a te, (Sc,Sp )-7. A solution of
the chloro complex (Sc)-6 (1 g) in dichloromethane (50 mL) was
treated with silver perchlorate (0.6 g) in water (5 mL) for 30
min. The reaction mixture was filtered through Celite, washed
with water, and dried (MgSO4), and the solvent was removed
under reduced pressure. The crude perchlorato complex was
dissolved in chloroform (100 mL) and treated with excess
aniline (1.4 g) at room temperature for 16 h. Upon completion,
the solvent was removed under reduced pressure. Subsequent
purification by silica gel column chromatography (ethyl acetate/
hexane, 1:1) gave the diastereomeric products (Sc,Rp)-7 and
(Sc,Sp)-7 as yellow solids. (Sc,Rp)-7: 0.7 g (56% yield); mp >
180 °C (dec); [R]D -266.1° (c 0.3, CH2Cl2). Anal. Calcd for
3
1H NMR (CDCl3): δ 2.06 (d, 3H, J HH ) 6.4 Hz, CHMe), 2.09
4
4
(d, 3H, J PH(trans) ) 4.0 Hz, NMe), 2.41 (d, 3H, J PH(trans) ) 1.6
2
2
Hz, NMe), 3.87 (dd, 1H, J PH ) 14.3 Hz, J HH ) 16.7 Hz,
(15) Carty, A. J .; Hota, N. K.; Ng, T. W.; Patel, H. A.; O’Connor, T.
J . Can. J . Chem. 1971, 49, 2707.
(16) Liu, X. M.; Mok, K. F.; Vittal, J . J .; Leung, P. H. Organome-
tallics 2000, 19, 3722. Leung, P. H.; Quek, G. H.; Lang, H.; Liu, A.;
Mok, K. F.; White, A. J . P.; Williams, D. J .; Rees, N. H.; McFarlane,
W. J . Chem. Soc., Dalton Trans. 1998, 1639.
C
42H38N2ClO4PPd: C, 62.5; H, 4.7; N, 3.5. Found: C, 62.4; H,
4.6; N, 3.5. 31P NMR (CDCl3): δ 15.1 (s). H NMR (CDCl3): δ
1

3926 Organometallics, Vol. 20, No. 18, 2001
Liu et al.
Ta ble 5. Cr ysta llogr a p h ic Da ta for Com p lexes
3
4
2.08 (d, 3H, J HH ) 6.4 Hz, CHMe), 2.08 (d, 3H, J PH(trans)
)
4
(Sc)-3 a n d 4
3.6 Hz, NMe), 2.37 (d, 3H, J PH(trans) ) 2.0 Hz, NMe), 3.83 (dd,
2
2
3
4
1H, J PH ) J HH ) 16.5 Hz, CHH), 4.20 (qn, 1H, J HH ) J PH
(Sc)-3
4
2
2
) 6.4 Hz, CHMe), 5.13 (dd, 1H, J HH ) 16.5 Hz, J PH ) 8.9
formula
fw
C40H38N2O4ClPPd C26H22NCl2PPd‚0.5Et2O
3
4
Hz, CHH), 7.08 (dd, 1H, J HH ) J PH ) 8.2 Hz), 7.18 (d, 1H,
783.5
588.7
3J HH ) 8.2 Hz), 7.20-7.73 (m, 22H, aromatics), 8.05 (dd, 2H,
space group
cryst syst
a/Å
P212121
orthorhombic
9.878(1)
18.360(1)
20.699(1)
3754.1(1)
4
Pbca
3
3J HH ) 7.8 Hz, J PH ) 14.6 Hz, o-PPh). (Sc,Sp)-7: 0.2 g (15%
orthorhombic
16.374(1)
17.836(1)
18.212(1)
5318.5(5)
8
yield); mp > 180 °C (dec); [R]D +62.5° (c 0.3, CH2Cl2). Anal.
Calcd for C42H38N2ClO4PPd: C, 62.5; H, 4.7; N, 3.5. Found:
b/Å
C, 62.3; H, 4.9; N, 4.0. 31P NMR (CDCl3): δ 17.3 (s). H NMR
1
c/Å
V/Å3
4
(CDCl3): δ 2.00 (d, 3H, J PH(trans) ) 2.8 Hz, NMe), 2.02 (d, 3H,
4
3J HH ) 6.4 Hz, CHMe), 2.48 (d, 3H, J PH(trans) ) 2.0 Hz, NMe),
Z
3.83 (dd, 1H, 2J HH ) 16.9 Hz, 2J PH ) 14.9 Hz, CHH), 4.23 (qn,
T/K
293(2)
1.386
293(2)
1.471
F
cacld/g cm-3
3
4
2
1H, J HH ) J PH ) 6.4 Hz, CHMe), 5.27 (dd, 1H, J HH ) 16.9
λ/Å
0.71073
6.50
-0.03(2)
0.037
0.71073
9.77
Hz, 2J PH ) 12.8 Hz, CHH), 7.14-7.72 (m, 24H, aromatics); 8.27
µ/cm-1
3
(dd, 2H, J HH ) 7.8 Hz,3J PH ) 13.8 Hz, o-PPh).
Flack params
R1 (obs data)a
0.038
0.106
Im in e-En a m in e Ta u tom er ism . Isola tion of {(S)-1-[1-
(Dim eth yla m in o)eth yl]n a p h th yl-C,N}{(3R)-1,2-d ip h en yl-
3-p h e n yl(p h e n yle t h yn yl)p h osp h in o-1-a za -2-p r op e n e -
N1,P 3′}p a lla d iu m (II) P er ch lor a te (Sc,Rp )-8 a n d {(S)-1-[1-
(Dim eth yla m in o)eth yl]n a p h th yl-C,N}{(3S)-1,2-d ip h en yl-
3-p h e n yl(p h e n yle t h yn yl)p h osp h in o-1-a za -2-p r op e n e -
N1,P 3′}palladiu m (II)P er ch lor ate (Sc,Sp)-8.Adichloromethane
solution of (Sc,Rp)-7 (0.1 g) was kept at room temperature for
1 week. The 31P NMR studied indicated that the imino complex
was converted completely into its enamino form. Removal of
the solvent gave the enamino complex (Sc,Rp)-8 as a yellow
solid: 0.1 g (100%), mp > 180 °C (dec); [R]D -185.6° (c 0.3,
CH2Cl2). Anal. Calcd for C42H38N2ClO4PPd: C, 62.5; H, 4.7;
N, 3.5. Found: C, 62.3; H, 5.2; N, 3.1. 31P NMR (CDCl3): δ
wR2 (obs data)b 0.082
a
b
2
R1 ) ∑||Fo| - |Fc||/∑|Fo||.
wR2 ) x{∑[w(Fo - Fc2)2]/
∑[w(Fo2)2]}, w-1 ) σ2(Fo)2 + (aP)2 + bP.
gave the liberated iminophosphine ligand (Sp)-9 as an air-
stable low melting yellow solid: 72 mg (72%); [R]D -105.3° (c
0.3, CH2Cl2). Anal. Calcd for C28H22NP: C, 83.4; H, 5.5; N,
3.5. Found: C, 83.3; H, 5.2; N, 3.8. 31P NMR (CDCl3): δ -21.7.
2
1H NMR (CDCl3): δ 5.80 (d, 1H, J HH ) 9.6, CHH′); δ 5.83 (d,
2
1H, J HH ) 9.6, CHH′); 6.70-8.09 (20H, aromatics). The
enantiomer (Rp)-9, with [R]D +105.3° (c 0.3, CH2Cl2), was
1
obtained similarly from (Sc,Sp)-7. The 31P NMR and H NMR
spectra are identical to those recorded for (Sp)-9.
3
-7.6 (s). 1H NMR (CDCl3): δ 2.00 (d, 3H, J HH ) 6.0 Hz,
Cr yst a l St r u ct u r e Det er m in a t ion of (Sc)-3 a n d 4.
Crystal data for both complexes and a summary of the
crystallographic analyses are given in Table 5. Diffraction data
were collected on a Siemens SMART CCD diffractometer with
Mo KR radiation (graphite monochromator) using ω-scans.
SADABS absorption corrections were applied, and refinements
by full-matrix least-squares were based on SHELXL 93.17 All
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were introduced at fixed distance from carbon atoms
and were assigned fixed thermal parameters.
4
CHMe), 2.72 (d, 3H, J PH(trans) ) 1.6 Hz, NMe), 2.98 (d, 3H,
3
4J PH(trans) ) 3.6 Hz, NMe), 4.32 (qn, 1H, J HH ) 4J PH ) 6.0 Hz,
4
2
CHMe), 5.45 (dd, 1H, J HH ) 3.2 Hz, J PH ) 18.1 Hz, CdCH),
4
3
5.92 (dd, 1H, J HH ) 3.2 Hz, J PH ) 16.9 Hz, NH); 6.83-7.70
(m, 24H, aromatics); 8.29 (ddd, 2H, 3J HH ) 7.6 Hz,3J PH ) 12.5
4
Hz, J HH ) 1.6 Hz, o-PPh). The diastereomeric enamino
complex (Sc,Sp)-8 was obtained similarly from (Sc,Rp)-8: mp
> 180 °C (dec); [R]D +139.2 (c 0.3, CH2Cl2). Anal. Calcd for
C
42H38N2ClO4PPd: C, 62.5; H, 4.7; N, 3.5. Found: C, 62.3; H,
5.2; N, 3.1. 31P NMR (CDCl3): δ -6.2 (s). 1H NMR (CDCl3):
3
4
Ack n ow led gm en t. We are grateful to the National
University of Singapore for the financial support and a
Ph.D. research scholarship for X.M.L.
2.02 (d, 3H, J HH ) 6.0 Hz, CHMe), 2.82 (d, 3H, J PH(trans)
)
4
1.6 Hz, NMe), 2.96 (d, 3H, J PH(trans) ) 4.0 Hz, NMe), 4.30 (qn,
3
4
4
1H, J HH ) J PH ) 6.0 Hz, CHMe), 5.20 (dd, 1H, J HH ) 3.0
2
4
3
Hz, J PH ) 18.5 Hz, CdCH), 5.67 (dd, 1H, J HH ) 3.0 Hz, J PH
) 18.3 Hz, NH); 6.83-7.70 (m, 24H, aromatics); 8.17 (ddd, 2H,
Su p p or tin g In for m a tion Ava ila ble: For (Sc)-3 and 4
tables of crystal data, data collection, solution and refinement,
final positional parameters, bond distances and angles, ther-
mal parameters of non-hydrogen atoms, and calculated hy-
drogen parameters. This material is available free of charge
via the Internet at http://pubs.acs.org.
3J HH ) 7.6 Hz, J HH ) 2.0 Hz, J PH ) 12.8 Hz, o-PPh).
Liber a tion of th e P -Ch ir a l Im in op h osp h in es. Isola tion
of (3S)-1,2-Dip h en yl-3-p h en yl(p h en yleth yn yl)p h osp h in o-
1-a za -1-p r op en e, (Sp )-9. A solution of (Sc,Rp)-7 (0.2 g) in
dichloromethane (20 mL) was stirred vigorously with a satu-
rated aqueous solution of potassium cyanide (0.5 g) for 0.5 h.
The resulting organic layer was separated and washed with
water and dilute HCl followed by water again before being
dried over MgSO4. Removal of solvent under reduced pressure
4
3
OM010333K
(17) Sheldrick, G. M. SHELXL 93, Program for Crystal Structure
Refinement; University of Gottingen: Germany, 1993.