Diastereomerism in palladium(II) allyl complexes of P,P-, P,S- and S,S-donor ligands, Ph2P(E)N(R)P(E′)Ph2 [R=CHMe2 or (S)-*CHMePh; E=E′=lone pair or S]: Solution behaviour, X-ray crystal structure and catalytic allylic alkylation reactions

Article abstract of DOI:10.1016/S0022-328X(03)00227-4

The reactions of achiral homodonor diphosphazane ligands, Ph₂P(E)N(CHMe₂)P(E′)Ph₂ [E=E′=lone pair (1) or S (2)] with the chloro bridged palladium dimers, [Pd(η³-1,3-R′-R″-C₃ H₃)(μ-Cl)]₂ (R′, R″=H, Me or Ph) in the presence of NH₄PF₆ give cationic η³-allyl palladium complexes, [Pd(η³-1,3-R′-R″-C₃H₃) (L-L′)]. Each of these complexes exists as single species in solution except the 1,3-dimethyl allyl complex, which exists as two isomers (syn/syn- and syn/anti-) in solution. Analogous allyl palladium complexes derived from the chiral homodonor diphosphazane ligand, Ph₂PN((S)-*CHMePh)PPh₂ (3) exist as a single species when the allyl moiety is symmetrical (R′=R″=H or Ph) but a 1:1 mixture of two different face-coordinated diastereomers if the allyl moiety is unsymmetrically substituted (R′≠R″). The 1,3-dimethyl-allyl complex, [Pd(η³-1,3-Me₂-C₃H₃) {Ph₂PN((S)-*CHMePh)PPh₂-k²P,P}] PF₆ (20) exists as a mixture of two isomers. The major isomer (20a) has the syn/syn -allylic arrangement while the minor isomer (20b) has the syn/anti configuration. These isomers (20a and 20b) equilibrate in solution via a syn-anti isomerisation pathway. Achiral and chiral heterodonor monosulphide ligands, Ph₂P(S)N(R) PPh₂ [R=CHMe₂ (4), (S)-*CHMePh(5)] give rise to allyl palladium complexes which exist as several isomers in solution. The presence of a chiral centre in the ligand 5 enables the observation of two NMR distinguishable face-coordinated diastereomers for its allyl complexes. However, the solid state structure of [Pd(η³-C₃H₅){Ph₂P(S) N((S)-*CHMePh)PPh₂-k² P,S}]PF₆ (27) shows the presence of only one diastereomer. Two-dimensional (2D) phase sensitive ¹H-¹H NOESY and ROESY measurements indicate that the monosulphide complexes undergo exchange by the opening of the η³-allyl group selectively at the trans position with respect to the greater π-acceptor phosphorus centre to generate a η¹-bonded intermediate. Preliminary studies on the use of the ligands 1-5 for catalytic allylic alkylation reactions of an unsymmetrically substituted substrate, (E)-1-phenyl-2-propenyl-acetate are reported.

Full text of DOI:10.1016/S0022-328X(03)00227-4

Journal of Organometallic Chemistry 676 (2003) 22Á37
/
www.elsevier.com/locate/jorganchem
Diastereomerism in palladium(II) allyl complexes of P,P-, P,S- and
S,S-donor ligands, Ph2P(E)N(R)P(E?)Ph2 [RꢀCHMe2 or (S)-
lone pair or S]: solution behaviour, X-ray crystal
/
*CHMePh; Eꢀ
/
E?ꢀ
/
structure and catalytic allylic alkylation reactionsꢀ
Swadhin K. Mandal a, G.A. Nagana Gowda b, Setharampattu S. Krishnamurthy a,*,
Chong Zheng c, Shoujian Li c, Narayan S. Hosmane c
a Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India
b Sophisticated Instruments Facility, Indian Institute of Science, Bangalore 560012, India
c Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA
Received 29 June 2002; received in revised form 24 February 2003; accepted 24 February 2003
Abstract
The reactions of achiral homodonor diphosphazane ligands, Ph2P(E)N(CHMe2)P(E?)Ph2 [Eꢀ
chloro bridged palladium dimers, [Pd(h3-1,3-R?-Rƒꢀ
C3H3)(m-Cl)]2 (R?, RƒꢀH, Me or Ph) in the presence of NH4PF6 give cationic
h3-allyl palladium complexes, [Pd(h3-1,3-R?-Rƒꢀ
C3H3)(L-L?)]. Each of these complexes exists as single species in solution except the
/
E?ꢀ/lone pair (1) or S (2)] with the
/
/
/
1,3-dimethyl allyl complex, which exists as two isomers (syn/syn- and syn/anti-) in solution. Analogous allyl palladium complexes
derived from the chiral homodonor diphosphazane ligand, Ph2PN((S)-*CHMePh)PPh2 (3) exist as a single species when the allyl
moiety is symmetrical (R?ꢀ
unsymmetrically substituted (R?"
k2P,P}]PF6 (20) exists as a mixture of two isomers. The major isomer (20a) has the syn/syn-allylic arrangement while the minor
isomer (20b) has the syn/anti configuration. These isomers (20a and 20b) equilibrate in solution via a syn Áanti isomerisation
pathway. Achiral and chiral heterodonor monosulphide ligands, Ph2P(S)N(R)PPh2 [RꢀCHMe2 (4), (S)-*CHMePh(5)] give rise to
/
Rƒꢀ
/
H or Ph) but a 1:1 mixture of two different face-coordinated diastereomers if the allyl moiety is
/
Rƒ). The 1,3-dimethylÁ C3H3){Ph2PN((S)-*CHMePh)PPh2-
/
allyl complex, [Pd(h3-1,3-Me2ꢀ
/
/
/
allyl palladium complexes which exist as several isomers in solution. The presence of a chiral centre in the ligand 5 enables the
observation of two NMR distinguishable face-coordinated diastereomers for its allyl complexes. However, the solid state structure
of [Pd(h3-C3H5){Ph2P(S)N((S)-*CHMePh)PPh2-k2P,S}]PF6 (27) shows the presence of only one diastereomer. Two-dimensional
1
(2D) phase sensitive Hꢀ
/
1H NOESY and ROESY measurements indicate that the monosulphide complexes undergo exchange by
the opening of the h3-allyl group selectively at the trans position with respect to the greater p-acceptor phosphorus centre to
generate a h1-bonded intermediate. Preliminary studies on the use of the ligands 1Á
/5 for catalytic allylic alkylation reactions of an
unsymmetrically substituted substrate, (E)-1-phenyl-2-propenyl-acetate are reported.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Palladium; Allyl complexes; P ligands; S ligands; Stereodynamics by NMR spectroscopy; Allylic alkylation
1. Introduction
versatile methodology for Cꢀ
Enantioselective allylic substitution reactions have been
the subject of considerable interest in recent years [1Á3].
A key intermediate in these reactions is a cationic
complex, [Pd(h3-allyl)(auxiliary ligand)]ꢁ. The exact
mechanism by which the catalyst imprints its chirality
upon the product remains unclear; however, the nature
of the auxiliary ligand such as its electronic and steric
properties, shape and depth of the chiral pocket created
/
C bond formation [1,2].
Palladium catalysed nucleophilic substitution reac-
tions of allylic substrates constitute a highly useful and
/
ꢀ Organometallic chemistry of diphosphazanes, part 18. For Part
17, see ref [12(b)].
* Corresponding author. Fax: ꢁ
E-mail address: sskrish@ipc.iisc.ernet.in (S.S. Krishnamurthy).
/91-80-360-0683/1552.
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00227-4

S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á
/
37
23
by a chiral auxiliary ligand and ligand bite angle play a
significant role in catalysis [3,4]. Several donor atom
combinations such as P,P- [5], N,N- [6], P,N- [3], N,S-
[7] and P,S- [8] bidentate ligand systems have been
successfully tested for the enantioselective allylic alkyla-
tion using the 1,3-symmetrically substituted substrates
as model systems. The use of a chiral auxiliary ligand
can make the h3-allyl intermediate to exist as diaster-
eomers, which can exhibit a complex dynamic behaviour
in solution. The interconversion among the various
diastereomers in solution makes the prediction of the
outcome of the allylic substitution often difficult. The
situation becomes more complicated when both the
auxiliary ligands and the allyl moiety are unsymmetrical
as this would lead to the formation of various geome-
trical isomers along with different allylic arrangements.
As a part of our ongoing research [9,10] on the
organometallic chemistry of diphosphazane ligands
[11], we have recently reported our investigations on
the palladium allyl chemistry of 3,5-dimethylpyrazolyl
substituted diphosphazanes Ph2PN(R)PPh(N2C3HMe2-
2.2. Palladium allyl complexes with achiral homodonor
ligands, Ph2P(E)N(CHMe2)P(E?)Ph2 (1, 2)
The allyl palladium complexes (7Á
the achiral homodonor ligands Ph2P(E)N(CH-
Me2)P(E?)Ph2 [EꢀE?ꢀlone pair (1) or EꢀE?ꢀS (2)]
/
16) derived from
/
/
/
/
(shown in Scheme 1) exist as a single species in each case
except in the case of the 1,3-dimethyl allyl derivative (10)
of ligand 1 (see Fig. 1). The 31P{1H}-NMR spectra of
the complexes (7, 10a, 11, 12, 15 and 16) bearing
symmetrical allyl moieties (R?ꢀRƒ) show a singlet.
/
The phosphorus chemical shifts lie downfield as com-
pared to that of the free ligand 1 and the magnitude of
coordination shift, Dd[Ddꢀ
gand)] is in the range 9Á1.6 ppm. On the other hand, the
phosphorus chemical shifts for the complexes (12Á16)
derived from the disulphide ligand 2 are close to that of
the free ligand. The Dd values lie in the range ꢂ0.1 to ꢂ
allyl
/
d (complex)*/d (free li-
/
/
/
/
2.8 ppm except in the case of the 1-phenylÁ
/
complex, 14 for which the 31P{1H}-NMR spectrum is
of the AX type with one of the phosphorus nuclei
showing a Dd of ꢂ9.2 ppm. The low Dd values
/
3,5) (RꢀCHMe2 or (S)-*CHMePh) and the monosul-
/
observed for the allyl palladium complexes of the
disulphide ligand 2, are not surprising as the coordina-
tion to the metal centre would not significantly affect the
chemical environment of the phosphorus centres which
are not directly bonded to palladium.
phide Ph2P(S)N(CHMe2)PPh(N2C3HMe2-3,5) [12]. In
this paper, we report the synthesis, characterisation and
dynamic behaviour of cationic palladium(II) allyl com-
plexes containing the ligands Ph2P(E)N(R)P(E?)Ph2
[Rꢀ
E?ꢀS (2); Rꢀ
RꢀCHMe2, Eꢀ
*CHMePh, EꢀS, E?ꢀ
/
CHMe2, Eꢀ
(S)-*CHMePh, Eꢀ
S, E?ꢀlone pair (4); Rꢀ
lone pair (5)]. The purpose of
/
E?ꢀ
/
lone pair (1); Rꢀ
E?ꢀlone pair (3);
(S)-
/
CHMe2, Eꢀ
/
The allylic proton resonances are assigned on the
/
/
/
/
basis of a 1Hꢀ
sets of magnetically equivalent allylic protons for the
/
1H COSY experiment, which shows three
/
/
/
/
/
/
complexes having unsubstituted allyl group (R?ꢀRƒꢀ
/
/
this investigation is to identify the source of diastereo-
merism in palladium allyl complexes of this type of
ligands on the basis of a systematic variation of both the
allyl moieties and auxiliary ligands and to study the
various stereodynamic processes in solution besides
investigating the utility of these ligands in palladium
catalysed alkylation reactions.
H). The two syn protons give rise to a signal at a lower
field as compared to that for the two anti proton
resonances (see Table 1). The incorporation of a
substituent in the allyl part (R?"Rƒ) leads to non-
/
equivalence of the phosphorus and the proton nuclei as
1
reflected in the 13C, 31P and H-NMR spectra of the
complexes 8, 9, 13 and 14. The substituted allyl moiety
can have different arrangements [13] (syn or anti with
respect to the central allyl proton, Hc) as shown in
Scheme 2.
2. Results and discussion
The syn-arrangement in all the mono-substituted allyl
complexes of ligands 1 and 2 is established by perform-
ing 1Hꢀ
allylÁ
to the central allyl proton Hc revealing a syn-configura-
tion of the allylÁmethyl group with respect to the central
/
1H NOESY experiments. For example, the
/methyl protons show a strong NOE cross-peak
2.1. Synthesis
The cationic allyl complexes of general formula,
/
[Pd(h3-1,3-R?-Rƒꢀ
/
C3H3)(1Á
from the reactions of the chlorobridged palladium allyl
dimer, [Pd2Cl2(h3-1,3-R?-Rƒꢀ
C3H3)2] (6) with the ap-
propriate ligands (1Á5) in the presence of NH4PF6 in
/
5)]PF6 (7Á
/
31) are prepared
allyl proton Hc. The 1,3-dimethyl allyl complex 10 exists
as two isomers in solution. The major isomer 10a is
assigned the syn/syn-arrangement and the minor isomer
the syn/anti-arrangement of the allyl substituents (see
/
/
acetone (Scheme 1). All these complexes have been
characterised by NMR spectral data and elemental
analyses. The salient features of the spectroscopic data
and dynamic behaviour are discussed below.
Fig. 1). The isomer 10b is present to an extent B5%.
However, the 1,3-diphenyl analogues of ligand 1 and 2
exist as a single species having the syn/syn-arrangement
/
of the allylÁphenyl groups which is expected from the
/

24
S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á37
/
Scheme 1.
Fig. 1. The h3-allyl palladium complexes [Pd(h3-1,3-R?-Rƒ-C3H3){Ph2P(E)N(CHMe2)P(E?)Ph2-k2P,P or S,S}]PF6 (Eꢀ
with homodonor ligands 1Á3.
/
E?ꢀ
/
lone pair or S; 7Á21)
/
/

S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á
/
37
25
Table 1
Selected 1H-NMR data a for complexes 7Á
/
21 (only allyl protons are listed)
b
?
?
Ha
Complex
Hs
Ha
Hs
Hc
CH3
7
4.59 m
4.34 br
3.82 m
3.30 m
3.10 br t (10.2) c,d
3.82 e
Á
Á/
Á/
Á/
/
Á
/
5.68 m
5.69 m
6.29 m
Á
/
8
4.34 e
1.76 dt (12.6) d (6.4) c
9
10a
5.25 dt (13.0) c (5.0) d
4.12 m
Á/
Á/
Á/
Á/
Á/
Á/
Á/
5.68 t (12.4) c
5.55 m
1.72 dt (13.2) d (6.4) c
1.73 e and 0.93 m
10b
11
5.20 br
4.40 br
5.63 dt (12.8) c (9.2) d
Á/
Á/
Á/
Á/
Á/
Á/
Á/
Á/
6.59 t (12.8) c
5.20 m
Á/
Á/
12
13
4.23 br
3.99 br s
4.23 br
2.79 br
3.66 br s
2.90 br
Á/
2.63 br s
4.49 br
4.95 m
1.36 br s
14
15
5.64 m
Á/
Á/
Á/
Á/
Á/
3.52 br s
4.64 br
4.80 t (11.6) c
6.06 t (11.7) c
5.65 m
1.37 br s
16
17
Á/
Á/
4.51 br
4.31 m
4.42 m
3.23 m
2.97 t (12.4) c,d
3.46 m
Á/
18a and 18b
19a and 19b
4.22 m
5.31 dt (12.7) c (5.0) d
5.57 m
6.21 m
1.67 m
Á/
Á/
Á/
20a
20b
21
Á/
Á/
Á/
Á/
Á/
Á/
4.08 m
4.45
5.48 m
5.64 t (11.1) c
5.46
1.82 m and 1.73 m
1.78 and 0.89
5.11
Á/
6.58 t (12.8) c
Á/
Abbreviations: br, broad; br s, broad singlet; t, triplet; br t, broad triplet; dt, doublet of triplets; m, multiplet.
a
1
The H-NMR spectra were recorded in CDCl3 at 25 8C. Hs and Ha are syn and anti allyl protons, respectively attached to unsubstituted allyl
?
terminus. Hs and Ha are syn and anti allyl protons, respectively at the substituted allyl terminus. Coupling constants in Hz are given in parenthesis.
?
b
Allyl CH3 protons.
3J(H,H).
J(P,H).
Overlapped with signal arising from other allyl proton.
c
d
e
gives rise to a signal in the 13C-NMR spectrum at a
chemical shift value which is down field compared to the
chemical shift value for unsubstituted allyl terminus
(Ct). The same trend is observed in the 13C chemical
shifts of the allyl carbon nuclei for the complexes (12Á
/
16)
formed
by
the
disulphide
ligand,
Ph2P(S)N(CHMe2)P(S)Ph2 (2). However, the allyl 13C
signals for these complexes are singlets indicating that
3
the J(P,C) coupling is close to zero.
Scheme 2.
2.3. Palladium allyl complexes with the chiral homodonor
ligand, Ph2PN((S)-*CHMePh)PPh2 (3)
higher steric demand of the allylÁ
anti allylic position.
/phenyl group at the
The allylic carbon nuclei are assigned by recourse to a
13Cꢀ1H COSY experiment with the help of pre-assigned
proton chemical shifts. The central allyl carbon reso-
The various isomers observed for the palladium allyl
complexes of the chiral homodonor ligand Ph2PN((S)-
*CHMePh)PPh2 (3) are shown in Fig. 1. Incorporation
of chirality in the ligand backbone does not alter nature
of the allyl complexes of 3 as compared to those of its
achiral analogue 1 if one considers the symmetrical allyl
/
2
nance appears as a triplet with a low J(P,C) value (Â
/
9.0 Hz) for the complexes bearing ligand 1 (see Table 2).
The resonances arising from the two terminal allyl
carbon nuclei in the allyl complexes 7, 10 and 11 bearing
derivatives (R?ꢀRƒ). Thus, only a single species is
/
symmetrical allyl moiety appear as a triplet [2J(P,C)ꢀ
/
observed in the NMR spectra for the allyl complexes
17 and 21 containing a symmetrical allyl group. How-
ca. 30 Hz] at a relatively higher field compared to those
of the central allyl carbon resonances. For the mono-
substituted allyl derivatives (8 and 9) of ligand 1, two
sets of terminal 13C resonances (doublet of doublets in
each case owing to coupling to two different phosphorus
nuclei) are observed. As expected, the 2J(P,C) involving
the allyl 13C nuclei in the trans position to phosphorus is
larger than the 2J(P,C) involving the 13C nuclei in the cis
ever, asymmetry in the allyl part (R?"Rƒ) causes the
/
complexes (18 and 19) to exist as a 1:1 mixture of two
1
isomers. The H-NMR spectrum does not distinguish
the two isomers. However, the 13C-NMR and 31P-NMR
spectra (see Table 2) reveal the presence of two isomers.
The 31Pꢀ
/
31P COSY spectrum of complex 18 reveals four
doublets arising from the two isomers. The 13C-NMR
spectrum of complexes 18 or 19 exhibits four different
?
position [14]. The substituted allyl carbon terminus (Ct )

26
S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á37
/
Table 2
The 13C-NMR (the allyl carbon nuclei only are listed) and 31P{1H}-NMR data a for h3-allyl palladium complexes 7Á
/21
Complex
13C-NMR (d)
31P{1H}-NMR (d)
b
?
Ct
Ct
Cc
CH3
7
69.0 t (20.6) c,d
Á
/
123.9 t (8.5)
123.8 t (9.1)
118.5 t (9.3)
Á
/
60.9 s
8
63.8 dd (31.7) c (9.7) d
65.4 dd (33.0) c (8.2) d
89.8 dd (32.6) c (10.3) d
92.3 dd (32.2) c (10.6) d
18.6 s
57.8 d (90.3), 61.6 d
58.3 d (107.1), 63.3 d
64.4 s
9
10a
Á/
Á
(ꢂ
/
84.4 t (21.7) c,d
125.3 t (9.0)
e
18.5 s
e
/
e
e
10b
11
/
)
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
)
65.4 br s, 63.8 br s
62.6 s
Á/
88.3 t (26.6) c,d
113.3 t (11.0)
114.9 s
Á/
Á/
12
13
68.6 s
63.8 s
Á/
67.2 s
88.2 s
89.2 br s
82.9 s
115.0 s
109.0 s
18.0 s
67.4 br s, 66.2 br s
67.3 br s, 58.3 br s
65.2 s
14
15
64.3 br s
Á/
(ꢂ)
Á/
Á/
e
Á/
Á/
116.4 s
127.8 s
124.0 t (9.2)
/
16
17
104.6 s
64.7 s
66.l s
69.3 t (23.7) c,d
Á/
18a and 18b
64.3 dd (34.0) c (8.5) d and 64.9 89.9 dd (34.0) c (10.7) d and 90.7 124.5 m and
19.4 d (4.1) and 66.7 d (94.7), 69.5 d and
19.2 d (4.2)
dd (33.7) c (9.0) d
dd (33.6) c (10.0) d
124.5 f
66.1 d (95.2), 69.4 d
64.9 d (112.9), 69.8 d and
68.4 d (109.3), 69.4 d
19a and 19b
66.0 dd (32.9) c (8.4) d and 65.4 92.3 dd (31.2) c (10.5) d and 93.0 119.0 t (9.8) and
Á/
dd (32.8) c (7.6) d
dd (31.2) c (10.6) d
118.5 t (9.1)
125.3 t (10.0)
20a
Á/
84.93 dd (28.6) c (15.3) d and
18.7 br s and 18.4 70.9 br s, 70.7 br s
br s
83.7 dd (27.5) c (16.0) d
e
e
e
e
20b
21
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
Á/
/
)
71.4 br s, 70.2 br s
68.7 d (123.4), 66.6 d
Á/
89.3 dd (30.7) c (10.9) d and 88.2 113.3 t (10.3)
dd (30.8) c (11.8) d
Abbreviations: s, singlet; br s, broad singlet; d, doublet; dd, doublet of doublets; t, triplet.
a
2
The 13C-NMR and 31P{1H}-NMR spectra were recorded in CDCl3 at 258 C. The coupling constants in Hz {2J(C,P) and J(P,P)} are given in
?
parenthesis. Ct is the unsubstitutcd terminal allyl carbon. Ct is the substituted terminal allyl carbon. Cc is central allyl carbon.
b
Allyl-methyl carbon.
2J(P,C)trans
c
.
d
e
f
2J(P,C)cis
The signal could not be observed.
Overlapped with signal arising from other isomer.
.
sets of doublet of doublets for the terminal allyl carbon
nuclei arising from the two isomers in each case. The
allyl complexes of ligand 3. This feature is also reflected
in the 1H-NMR spectrum of the syn/syn-isomer 20a
chemical shift values for allyl carbon resonances of 17Á
/
revealing two different allylÁ
/
methyl groups. The phase
1H NOESY and ROESY spectra of com-
1
21 are listed in Table 2. Similarity in the chemical shift
values of different allylic protons for the two isomers
suggests that they posses very closely related structures.
Thus each of the complexes 18 and 19 may be regarded
as a pair of diastereomers arising from two different
allyl face coordination to the palladium centre.
sensitive Hꢀ
/
plex 20 lead us to conclude that there is a dynamic
process equilibrating the two isomers (20a and 20b) in
solution. The conversion of a syn/syn-isomer to the syn/
anti-isomer is well-known process (termed as syn Á
isomerisation) in palladium allyl chemistry [2a,3a,15].
The anti allylÁmethyl protons of the syn/anti-isomer
(20b) show exchange cross-peaks with allylÁmethyl
/
anti
/
As observed for the 1,3-dimethylÁallyl palladium
/
/
complex (10) of Ph2PN(CHMe2)PPh2 (1), the 1,3-
dimethyl allyl palladium complex (20) of the ligand
Ph2PN((S)-*CHMePh)PPh2 (3) exists as a mixture of
two isomers which may be assigned the syn/syn- and
syn/anti-configurations of the allyl moiety. Of these, the
syn/syn-isomer (20a) is the major one. The analogous
1,3-diphenyl allyl complex (21) of ligand 3 exists as a
single isomer (syn/syn-) in solution. Unlike the spectra
observed for the complexes of the achiral ligands 1 and
2, the 31P-NMR spectra of the 1,3-disubstituted syn/syn-
allyl isomers (20a and 21) feature an AB spin system.
The 13C-NMR spectra show two different terminal allyl
carbon resonances. The presence of an asymmetric
centre in the ligand backbone destroys the molecular
symmetry even in the case of symmetrically substituted
protons of both methyl groups of the syn/syn-isomer
(20a). This result can be explained by postulating an h1-
allyl intermediate, which is formed by the opening of the
h3-allyl group at either of the allyl termini. Thus the
opening of the allyl moiety is not selective with respect
to any one of the allyl termini.
2.4. Palladium allyl complexes of the achiral heterodonor
diphosphazane monosulphide ligand,
Ph2P(S)N(CHMe2)PPh2 (4) and dynamic behaviour in
solution
The structures of the allyl palladium complexes
formed by 4 are formulated as shown in Fig. 2 on the

S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á
/
37
27
basis of NMR studies. The 31P{1H}-NMR spectra of the
complexes 22Á26 feature an AX spin system; the ꢀ
P(S)Ph2 and the ꢀPPh2 chemical shifts are assigned
the values 75Á81 and 91Á98 ppm respectively based on
the magnitude of Dd. The coordinated phosphorus (ꢀ
The phase sensitive 1Hꢀ
spectra of complex 22 reveal that the allylic protons Hs
?
and Ha trans to the sulphur atom exchange with each
other while no such exchange is observed among the
allylic protons Ha and Hs trans to the coordinated
phosphorus atom. The exchange result is summarised in
Scheme 3. The observation can be rationalised by
/
1H NOESY and ROESY
?
/
/
/
/
/
/
PPh2) chemical shift lies very much downfield as
compared to that of the free ligand, 4 and the magnitude
assuming that syn Áanti isomerisation occurs by the
/
of Dd is 34Á
of Dd for the non-coordinated phosphorus [ꢀ
lies in the range 9Á14 ppm. The diphosphazane mono-
sulphide ligand Ph2P(S)N(CHMe2)PPh2 (4) breaks the
allylic symmetry in complex 22 having the unsubstituted
1
allyl moiety. The H-NMR spectrum of 22 reveals five
/
44 ppm. On the other hand, the magnitude
opening of the h3-allyl group selectively at the trans
position with respect to the higher p-acceptor phospho-
rus centre to give a s-bonded intermediate. The opening
of the h3-allyl group is thus controlled electronically
[16,17]. Because of the greater p-acceptor character of
the phosphorus centre compared to that of sulphur, the
/P(S)Ph2]
/
distinct allylic protons and they are assigned on the basis
1
of a Hꢀ
/
1H COSY experiment. The syn allylic proton
Hs, trans to the coordinated phosphorus centre gives
metalÁcarbon bond trans to phosphorus is weakened
/
and hence it preferentially opens up to give the s-
bonded intermediate as shown in Scheme 3. This type of
electronic control over the interconversion process is
well known in the case of allyl palladium complexes of
P,S-, P,N- and P,O- bidentate heterodonor ligands
rise to a signal at 4.76 ppm which is downfield to the
?
resonance (3.93 ppm) arising from the syn proton Hs,
which is trans to the sulphur atom. The chemical shifts
?
of the anti allylic protons (Ha and Ha) follow the same
[14b,17,18]. The syn Áanti isomerisation process in 22
/
trend (see Table 3). The allyl carbon resonances in the
13C-NMR spectrum of 22 are assigned on the basis of a
allows the shifting of the metal coordination from one
face of the allyl moiety to the other but the achiral
nature of the ligand 4 does not result in the formation of
any NMR distinguishable diastereomeric pair.
The incorporation of a substituent on the allyl moiety
in complexes 23 and 24 introduces an additional
possibility that the substituent can lie at the trans or
cis position with respect to the coordinating phosphorus
13Cꢀ
/
1H HSQC experiment with the help of pre-assigned
allylic proton chemical shifts. The terminal allylic
carbon (Ct) trans to the coordinated phosphorus centre
gives rise to a doublet at a lower field region as
?
compared to the terminal allyl carbon resonance (Ct )
trans to the sulphur atom.
atom. Thus the 1-methylÁ
mixture of four isomers as revealed by its 31P- and H-
NMR spectra. A detailed NMR study (13C, 1Hꢀ1H
DQF COSY, NOESY and ROESY) shows that the
allylÁmethyl group is syn to the central allyl proton and
/
allyl complex 23 exists as a
1
/
/
located at the trans position with respect to the
coordinated phosphorus centre in the major isomer
23a; in other words, the major isomer has the syn,
trans-orientation of the allyl moiety. The isomer 23b is
assigned the syn, cis-configuration. The 13C-NMR
spectra of these isomers provide support for these
assignments (see Table 4). One of the terminal allyl
carbon nuclei in isomer 23a gives rise to a doublet at
96.0 ppm with 2J(P,C)ꢀ
31.7 Hz. This resonance is
/
assigned to the substituted allyl carbon terminus trans
to the coordinated phosphorus centre. The unsubsti-
tuted allyl carbon in 23a gives rise to a singlet at a
relatively higher field (62.7 ppm) which can be assigned
to the allyl carbon terminus trans to the sulphur atom,
On the other hand, 23b exhibits a singlet at a lower field
(86.1 ppm) and a doublet at relatively higher field (70.4
2
ppm) with a value of J(P,C)ꢀ
/
30.9 Hz. This reverse
trend in 13C-NMR spectrum clearly points to the cis
disposition of the allylÁmethyl group with respect to the
/
coordinated phosphorus centre in complex 23b (see
Table 4). The resonances arising from the third and
fourth isomers (23c and 23d respectively) could not be
Fig. 2. The h3-allyl palladium complexes (22Á
metrical diphosphazane ligand, Ph2P(S)N(CHMe2)PPh2 (4).
/
26) of achiral unsym-

Table 3
Selected 1H-NMR data a for complexes 22Á
/31 (only allyl protons are listed)
b
c
?
?
Ha
Complex
HS
Ha
Hs
Hc
CH3
CH3
22
23a
4.76 br t (6.0) d,e
3.41 dd (12.3) d (11.4) c
4.42 m
3.93 br d (6.0) d
3.67 br d (5.7) d
2.77 d (12.3) d
5.50 m
5.37 m
Á
/
Á
Á/
/
Á/
2.59 br d (11.6) d
1.94 dd (10.7) c
(6.2) d
23b
23c
23d
24a
24b
25a
4.52 t (75) d,e
4.61 t
5.73 m
3.22 t (12.2) d,e
3.59 br d
Á/
3.79 m
5.27 m
5.39 f
5.19 m
Á/
1.17 dd (9.1) e (6.2) d
0.40 t
4.75 m
3.59 f
5.37 f
Á/
Á
/
Á/
3.03 br d
4.82 f
5.10 d (11.9) d
3.60
1.17 f
Á/
Á/
Á/
Á
/
5.37 t (12.1) d,e
3.59 t (12.0) d,e
4.23 m
6.11 m
6.05 m
5.20 t (12.0)d
Á/
Á/
4.82 f
Á/
Á/
Á/
1.88 dd (10.0)e
(6.0)d
1.22 dd (8.8)e (6.8)d
25b
25c
Á/
4.63 m
4.47 m
Á/
5.27 f
5.03 br t (6.0) d
6.42 t (12.3) d
1.91 f
1.10 f
0.45 t (6.8) d,c
1.15 f
5.45 m
Á/
Á/
Á/
4.14 m
4.95 d (12.1) d
26
27a and
27b
Á/
5.60 t (12.2) d,e
Á/
Á/
Á/
Á/
4.81 m and 4.81 f
3.45 m and 3.45 f
3.95 br d (6.8) d and 3.83 2.71 d (13.0) d and 2.82 d 5.50 m and 5.50 f
br d (6.8) d
(12.3) d
28a and
28b
Á/
4.44 m and 4.44 f
3.73 d (5.8) d and 3.62 d 2.55 d (12.7) dand 2.66 d 5.35 m and 5.35 f
1.99 m and
1.97 f
Á/
(5.9) d
(12.3) d
3.75 f and 3.89 m
28c and
28d
4.59 t (7.5) d,e and 4.66 3.24 t (12.7) d,e and 3.29 t
t (8.5) d,e
3.88 f and 3.79 f
Á/
5.26 m and 5.23 m
5.17 f and 5.19 f
Á/
1.10 dd (9.1) e (6.2) d and 0.97 dd
(9.1) c (6.1) d
0.43 t and 0.35 t
(12.7) d,e
3.02 br d and 3.14 br
28e and
28f
4.73 m and 4.67 f
3.93 and 3.80 br d
Á/
Á/
29a and
29b
Á/
5.25 m and 5.25 f
3.52 m and 3.52 f
4.28 m and 4.28 f
5.43 m and 5.43 f
2.94 d (11.8) d and 2.86 d 6.01 m and 6.01 f
Á/
Á/
(12.1) d
29c and
29d
4.80 m and 4.75 m
Á/
4.75 d (11.9) d and 4.64 d 5.87 m and 5.87 f
(12.2) d
Á/
Á/
30a and
30b
Á/
Á/
3.49 m and 3.65 m
5.22 m and 5.20 f
1.94 m and
1.94 f
1.09 m and 0.91 m
31a and
31b
Á/
Á/
4.75 d (12.0) d and 4.89 d 6.62 t (12.3) d and 6.56
(11.9) d t (12.3) d
Á/
Á/
Abbreviations: br, broad; s, singlet; d, doublet; br d, broad doublet; dd, doublet of doublets; t, triplet; m, multiplet.
a
The 1H-NMR spectra were recorded in CDCl3 at 25 8C for all the complexes except for 24 and 31 in which cases a 1:1 mixture of CDCl3 and DMSO-d6; was used. Coupling constants in Hz are
?
given in parenthesis. Hs and Ha are the syn and anti allylic protons trans to the coordinated phosphorus atom, respectively. Hs and Ha are the syn and anti allylic protons trans to the sulphur atom,
?
respectively.
b
Allyl CH3 trans to the coordinated phosphorus centre.
Allyl CH3 trans to the sulphur atom.
3J(H,H).
J(P,H).
Overlapped with signal arising from other allyl or ligand proton.
c
d
e
f

S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á
/
37
29
Scheme 3.
seen in the 13C-NMR spectrum owing to their relative
low concentrations (B5%). However, their structures
Unlike the case observed for complex 23, the 1-
phenylÁallyl derivative 24 exists as a mixture of two
/
/
1
can be deduced on the basis of the Hꢀ
/
1H COSY and
NOESY spectra as the anti, cis- (23c) and anti, trans-
isomers in the ratio l.4:1, The major isomer 24a is
assigned the syn, trans configuration and the minor
isomer 24b the syn, cis-configuration on the basis of
1
(23d) isomers (see Fig. 2). The H chemical shifts are
1
1
listed in Table 3. The most abundant isomers 23a and
1H
13C, H, 31P(1H}, Hꢀ
/
1H COSY and NOESY spectra.
1
1
23b contain the syn allylÁ
/
methyl group as the Hꢀ
/
The Hꢀ
/
1H COSY and NOESY spectra reveal that the
isomers 24a and 24b possess the syn-allylic arrangement
COSY spectrum reveals that the central allyl proton of
23a or 23b couples strongly to two anti allylic protons
of the phenylÁallyl group. The chemical shifts and
/
and weakly to one syn allylic proton. The allylÁ
/methyl
coupling constants observed in the 13C-NMR spectrum
of 24 (see Table 4) show that the major isomer 24a
protons (trans to the coordinated phosphorus centre) of
23a resonate at 1.94 ppm which is relatively at a lower
contains the allylÁ
with respect to the coordinated phosphorus and the
minor isomer 24b has a cis disposition of the allylÁ
/phenyl group at the trans position
field compared to the allylÁ
sulphur atom) of isomer 23b. The allylÁ
/
methyl protons (trans to the
methyl protons
/
/
of isomer 23b resonate at 1.17 ppm. This trend in
chemical shifts arises from the different electronic effects
of the two different donor centres (phosphorus and
sulphur) bonded to palladium and supports the assign-
ment of 23a as the syn, trans- and 23b as the syn, cis-
phenyl group with respect to the coordinated phospho-
rus centre. The absence of any anti-isomer in this case is
not surprising because of the higher steric demand of the
larger allylÁ
/
phenyl group compared to the allylÁmethyl
/
group at the anti-allylic position. The major component
for both the complexes 23 and 24 is the syn, trans-
isomer. The preference for the syn, trans-isomer can be
understood in terms of the higher trans influence of the
phosphorus centre so that the electron releasing sub-
stituent (Me or Ph) preferably occupies the trans-
position.
isomer respectively. The relative low abundance (B5%)
/
of minor isomers 23c and 23d and overlap of several
allylic proton resonances with those of major isomers
(23a and 23b) make their assignment difficult. However,
a careful look at the 1Hꢀ
the allylÁ
proton at 4.75 ppm in isomer 23c while in isomer 23d the
allylÁmethyl protons at 1.17 ppm couples with a proton
at 5.73 ppm. The high field resonances at 0.40 and 4.75
ppm in 23c are assigned to the anti allylÁmethyl protons
and syn proton (Hs) respectively trans to sulphur; hence
23c is the anti, cis-isomer (the anti allylÁmethyl group
/
1H COSY spectrum shows that
/methyl protons at 0.40 ppm couples with a
The phase sensitive 1Hꢀ
/
1H NOESY (shown in Fig. 3)
/
and ROESY spectra of complex 23 reveal two types of
stereodynamic processes in solution. The major ex-
change process is the one between syn and anti protons
of the isomer 23a at the trans position to the sulphur
/
?
/
atom and is similar to the selective syn Áanti isomerisa-
/
in 23c is cis to the coordinated phosphorus centre; see
Fig. 2). On the basis of the trends observed in the
chemical shifts of the allyl protons in P,S-coordinated
palladium allyl complexes (see above), the resonances at
tion observed for the unsubstituted allyl complex 22.
The isomer 23a at the same time exchanges with the syn,
cis-isomer 23b. The exchange behaviour (shown in
Scheme 4) suggests a cis-trans isomerisation between
1.17 and 5.73 ppm are assigned to the anti allylÁ
protons and syn proton (Hs) of 23d respectively (the anti
allylÁmethyl group in 23d is trans to the coordinated
phosphorus centre; see Fig. 2).
/methyl
23a and 23b via a rotation around the Pdꢀ
/
C(sp3) bond
in the s-bonded intermediate ‘A’. On the other hand,
the isomer 23b exchanges with the anti, cis-isomer 23c,
/
which may he explained by considering a syn Áanti
/

30
S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á37
/
Table 4
The 13C-NMR (the allyl carbon nuclei are only listed) and 31P{1H}-NMR data a for the, h3-allyl palladium complexes (22Á
/
31)
Complex
13C-NMR
31P{1H}-NMR
b
?
Ct
Ct
Cc
CH3
PA
Px
22
75.3 dd (32.6) c (4.0) d
96.0 d (31.7) c
68.2 d (4.5) d
62.7 br s
86.1 br s
121.0 d (7.0)
119.9 d (6.2)
120.1 d (7.0)
Á
/
78.7 d (90.3)
76.5 d (72.7)
80.9 d (90.4)
77.2 d (80.9)
77.3 d (89.6)
76.5 d (72.6)
80.9 d (90.4)
93.7 d
93.6 d
97.4 d
92.7 d
93.3 d
93.6 d
93.4 d
94.6 d
23a
23b
23c
23d
24a
24b
25a
18.5 br s
18.2 br s
70.4 d (30.9) c
e
e
e
e
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
/
)
(ꢂ)
(ꢂ)
Á/
/
e
e
e
e
/
(ꢂ
/)
(ꢂ
/)
(ꢂ
/)
96.1 d (29.4) c
71.1 d (32.9) c
92.0 d (26.8) c
63.5 s
87.3 d (5.8) d
80.4 br s
114.5 d (6.9)
114.2 d (6.7)
121.0 d (6.5)
Á/
18.4 d (4.9) and 76.4 d (80.9)
18.2 br s
e
e
e
e
25b
25c
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
(ꢂ
Á/
/
)
75.9 d (78.1)
78.3 d (97.9)
78.0 d (76.2)
78.1 d (81.6) and
78.1 f
93.0 d
93.0 f
91.7 d
e
e
e
e
(ꢂ
/)
(ꢂ
/)
(ꢂ
/)
/
)
26
27a and
27b
94.0 d (26.0) c
83.6 br s
109.1 d (7.0)
121.0 d (6.5) and
120.8 d (6.4)
75.2 dd (16.0) c (3.1) d and 75.5 68.5 d (4.2) d and
Á/
90.0 d and
90.5 d
90.4 d 90.1 d
dd (16.0) c (3.3) d
68.6 d (4.5) d
28a and
28b
95.6 d (29.7) c and 95.3 (30.3) c
62.6 s and 62.1 br s 119.5 br s and 119.1 18.4 s and 18.6 s 76.5 d (59.6) and
br s
119.7 br s and
76.8 d (60.2)
17.6 s and 17.5 s 80.2 d (70.3) and
79.7 d (69.1)
28c and
28d
69.8 d (32.8) c and 70.1 d (32.4) c 86.7 br s and
85.7 br s
92.8 d and
(92.4) d
89.3 d and
90.0 f
119.6 f
e
e
e
e
28e and
28f
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
/
)
78.9 d (67.4) and
79.0 d (64.1)
29a and
29b
96.0 d (29.9) c and 95.6 d (28.7) c 64.8 br s and 64.8 f 114.1 d (6.7) and
114.4 d (6.8)
Á/
74.1 d (71.2) and
74.0 d (70.4)
87.7 d and
87.0 d
29c and
29d
71.7 d (26.2) cand 71.4 d (28.9) c 88.7 br s and
88.0 br s
114.7 d (5.4) and
113.7 d (5.9)
120.9 d (6.2) and
Á
/
78.1 d (84.2) and
77.7 d (83.4)
17.9 s,17.7 s and 75.2 d (82.2) and
90.4 d and
91.5 d
30a and
30b
91.7 d (30.6) cand 92.0 d (29.3) c 80.0 d (6.0) d and
80.1 d (4.7) d
89.2 d and
88.9 d
120.8 d (6.6)
e
18.4 br s
e
/
75.2 f
e
e
30c and
30d
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
/)
(ꢂ
)
77.4 d (77.1) and
77.9 d (81.8)
73.9 d (86.1) and
74.5 d (88.2)
76.5 d (76.0) and
76.3 d (75.8)
86.8 d and
85.9 d
e
e
e
e
30e and
30f
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
/
)
(ꢂ
/
)
90.8 d and
90.0 d
31a and
31b
93.3 d (29.1) c and 92.9 d (31.6) c 83.9 s and 83.9 f
108.9 d (4.2) and
108.6 d (4.6)
Á/
92.5 d and
91.9 d
Abbreviations: s, singlet; br s, broad singlet; d, doublet; dd, doublet of doublets.
a
The 13C and 31P{1H}-NMR were recorded in CDCl3 at 25 8C except for 24 and 31 in which cases a 1:1 mixture of CDCl3 and DMSO-d6 was
used. The coupling constants {2J(C,P) and 2J(P,P)} in Hz are given in parenthesis. Ct is terminal allyl carbon trans to the coordinated phosphorus
?
center. Ct is terminal allyl carbon cis to the coordinated phosphorus center. Cc is central allyl carbon. PA is ꢀ
/
Ph2P(S) phosphorus and PX is ꢀPPh2
/
phosphorus.
b
Allyl-methyl carbon.
2J(P,C)trans
c
d
e
f
.
2J(P,C)cis
The signal could not be observed.
Overlapped with signal arising from other isomer.
.
isomerisation. The isomer 23d does not show exchange
with any of the other isomers (23aÁ23c).
2.5. Palladium allyl complexes of chiral heterodonor
diphosphazane monosulphide ligand, Ph2P(S)N((S)-
*CHMePh)PPh2 (5): the effect of chirality
/
The 1,3-dimethyl allyl complex 25 exists as a mixture
of three isomers in the ratio 9:1.5:1. The major isomer
25a is assigned the syn/syn-allylic arrangement while the
minor isomers 25b and 25c are assigned the anti/syn-
allylic arrangements (the anti allylmethyl group is trans
to the sulphur atom) and syn/anti-isomer (the anti
The structures assigned to the allyl palladium com-
plexes (27Á31) formed by the chiral diphosphazane
/
monosulphide Ph2P(S)N((S)-*CHMePh)PPh2 (5) on
the basis of NMR spectral data are shown in Fig. 4.
The NMR spectra become more complicated as there is
an additional possibility of face-coordinated diastereo-
meric pairs that can exist in the case of a chiral
heterodonor ligand 5. Thus the number of isomers
observed in the NMR spectra is doubled for ligand 5
allylÁmethyl group is trans to the coordinated phos-
/
phorus centre) respectively. These isomeric configura-
tions are shown in Fig. 2. The 1,3-diphenyl allyl complex
(26) bearing the larger phenyl groups exists as a single
species with the syn/syn-allylic arrangement.

S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á
/
37
31
Fig. 3. The phase sensitive 1Hꢀ
/
1H NOESY (400 MHz, CDCl3, 25 8C) spectrum of [Pd(h3-1-Me-C3H4){Ph2P(S)N(CHMe2)PPh2-k2P,S}]PF6 (23)
23c.
revealing various exchange cross-peaks between the allyl isomers 23aÁ
/
Scheme 4.

32
S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á37
/
as compared to the complexes containing ligand 4. For
example, the unsubstituted-allyl complex 27 exists as a
1:1 mixture of two isomers 27a and 27b as shown by its
31P- and 13C-NMR spectra (see Table 4). The phase
experiment. The structures of the two minor isomers 28e
1
and 28f are deduced on the basis of their H-(Table 3)
and 31P-NMR spectra (Table 4).
The 1,3-dimethyl complex 30 exists as three diaster-
eomeric pairs as shown by its 31P-NMR spectrum. The
major diastereomeric pair 30a and 30b (present to an
extent of 90%) possesses the syn/syn-allylic arrange-
ment. The other two diastereomeric pairs are syn/anti-
sensitive 1Hꢀ
/
1H NOESY and ROESY spectra show that
the two isomers undergo exchange with each other in a
similar way as that observed for complex 22. The two
isomers (27a and 27b) thus can be assigned as a pair of
diastereomers that are formed by different allyl face
coordination to the palladium centre. The introduction
of one chiral centre in the ligand backbone thus converts
the enantiomeric pair (observed for complex 22 bearing
the achiral ligand 4) into a NMR distinguishable
diastereomeric pair. Such a result has been previously
reported by Lanza et al. [19] for the palladium allyl
complexes of chiral N,N- and S,S-donor dithioxamide
ligands. The mono-substituted allyl derivatives 28 and
29 exist in solution as six and four isomers respectively.
(30c and 30d; the anti allylÁ
coordinated phosphorus atom) and anti/syn-isomers
(30e and 30f; the anti allylÁmethyl group is trans to
/methyl group is trans to the
/
the sulphur atom). The 1,3-diphenyl allyl complex 31
exists as two face-coordinated diastereomers in 1:1 ratio
having the syn/syn-allylic arrangement.
3. Solid state structure of the complex [Pd(h3-
C3H5){Ph2P(S)N((S)-*CHMePh)PPh2-k2P,S}]PF6
(27)
A detailed NMR study on the 1-methylÁallyl complex
/
28 reveals that the two major isomers 28a and 28b
constitute a diastereomeric pair having syn, trans-
geometry. The isomers 28c and 28d constitute another
pair of diastereomers having syn, cis-geometry. The
isomers 28e and 28f constitute the third diastereomeric
pair with anti, cis-allylic configuration (see Fig. 4). The
13C-NMR resonances (see Table 4) for the four isomers
A crystallographic study has been carried out for the
complex 27. The solid state structure consists of only
one diastereomer shown in Fig. 5, The coordination
geometry around the metal is distorted square planar;
the P(2)ꢀ
94.6(8)8 and 67.5(5)8, respectively. The Pdꢀ
bond distances are in the expected range observed for
/
Pd(1)ꢀ
/
S(1) and C(1)ꢀ
/
Pd(1)ꢀ
/
C(3) angles are
/
C and Pdꢀ
/
S
(28aÁ
/
28d) are assigned on the basis of a 13Cꢀ
/
1H HSQC
Fig. 4. The h3-allyl palladium complexes (27Á
31) of chiral unsymmetrical diphosphazane ligand, Ph2P(S)N((S)-*CHMePh)PPh2 (5).
/

S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á
/
37
33
compared to that trans to sulphur is consistent with the
proposed mechanism (Scheme 3) involving selective
opening of the allyl terminus, which is trans to
phosphorus. The five-membered chelate ring adopts a
non-planar conformation as shown by the distance
calculations from the mean plane defined by S(1),
Pd(1) and P(2) atoms; N(1) is almost coplanar with
˚
this plane (the deviation is only 0.03 A with respect to
˚
this plane) whereas P(1) lies at a distance of 0.81 A from
P(2) plane. Two phenyl groups on P(2)
the S(1)ꢀ
/
Pd(l)ꢀ
/
arc not symmetrically placed with respect to the
coordination plane formed by S(1), Pd(1) and P(2)
atoms. The dihedral angle between S(1)ꢀ
and C(25)ꢀC(24)ꢀC(29) is 52.78 revealing a pseudo-
equatorial arrangement of this phenyl group with
respect to the S(1)ꢀPd(1)ꢀP(2) plane. On the other
hand, the dihedral angle between the planes formed by
C(31) is 73.98; hence
/
Pd(1)ꢀ/P(2)
/
/
/
/
S(1)ꢀ
/
Pd(1)ꢀ
/
P(2) and C(35)ꢀ
/
C(30)ꢀ
/
this phenyl group may be considered as having a
pseudo-axial arrangement.
Fig. 5. The molecular structure of [Pd(h3-C3H5){Ph2P(S)N((S)-
*CHMePh)PPh2-k2P,S}]PF6 (27) (The hydrogen atoms and hexa-
˚
fluorophosphate anion are not shown.). Selected bond distances (A)
and angles (8) are; Pd(1)ꢀ
Pd(1)ꢀC(3)ꢀ2.192(1); Pd(1)ꢀ
P(1)ꢀS(1)ꢀ1.992(3); P(1)ꢀN(1)ꢀ
P(2)ꢀPd(1)ꢀS(1)ꢀ94.6(8); C(1)ꢀPd(1)ꢀ
P(2)ꢀ165.5(3); C(1)ꢀPd(1)ꢀS(1)ꢀ165.6(4);
110.2(4).
/
C(1)ꢀ
P(2)ꢀ
1.685(7); P(2)ꢀ
C(3)ꢀ67.5(5); C(3)ꢀ
P(l)ꢀN(1)ꢀ
/
2.060(1); Pd(1)ꢀ
/
C(2)ꢀ
S(1)ꢀ
N(1)ꢀ
/
2.082(2);
/
/
/
/
2.285(2); Pd(1)ꢀ
/
/
2.375(2);
4. Catalytic studies
/
/
/
/
/
/
l.741(8);
Pd(1)ꢀ
P(2)ꢀ
/
/
/
/
/
/
/
/
The palladium catalysed allylic alkylation with (E)-1-
phenyl-2-propenyl acetate (I) is investigated to study the
regio-selectivity in these systems (Scheme 5) using
dimethyl malonate as the nucleophile [21]. Catalytic
precursors are generated in situ from [Pd(h3-C3H5)(m-
C)]2 (1 mol%) and the appropriate ligands (2.5 mol%).
The use of an unsymmetrical substrate such as (I) in
allylic alkylation would afford a mixture of linear and
branched regioisomer (II) and (III), respectively depend-
ing on the nucleophilic attack at one or the other
/
/
/
/
/
/
/
Pd(II) allyl compounds of other P,S-chelate ligands [8b].
The PꢀNꢀP angle is 110.2(4)8 which is smaller than that
observed [124.3(2)8] for the free ligand 5 [20]. The Pꢀ
distances do not change significantly as compared to
those for the free ligand whereas the PꢀS distance
/
/
/
N
/
˚
increases by 0.04 A. The two terminal allyl carbon
atoms are not coplanar with the coordination plane
formed by S(1), Pd(1) and P(2) atoms; the distances of
1
terminal allyl carbon centres (Scheme 5). The H-NMR
˚
C(1) and C(3) from this plane are 0.23 and 0.17 A
C allyl bond lengths are
significantly different from one another; the carbon
spectrum of the reaction mixture shows complete
conversion of the substrate in 24 h at 25 8C and the
ratio of linear and branched isomer is shown in Table 5
for various diphosphazane ligands. The results indicate
that the nucleophilic substitution takes place predomi-
nantly at the unsubstituted terminus of the substrate.
The steric effect of the substituent seems to play an
important role in determining the regio-selectivity of the
nucleophilic attack.
respectively. The terminal Pdꢀ
/
atom trans to phosphorus displays the expected longer
˚
2.192(1) A], as compared to its
distance [Pd(1)ꢀ
/
C(3)ꢀ
/
˚
partner trans to sulphur [Pd(1)ꢀ
/
C(1)ꢀ2.060(1) A]. This
/
is a reflection of the higher trans influence [8b,16] of the
phosphorus donor centre. This elongation of Pd-term-
inal allyl carbon bond length trans to phosphorus as
Scheme 5.

34
S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á37
/
Table 5
Results of allylic alkylation reactions of an unsymmetrically substituted substrate (E)-1-phenyl-2-propenyl acetate using diphosphazane ligands 1Á5
/
Entry
Diphosphazane ligand (L)
Linear product (II) (%) a
Branched product (III) (%) a
(1)
(2)
(3)
(4)
(5)
Ph2PN(CHMe2)PPh2(1)
96
96
97
95
96
4
4
3
5
4
Ph2P(S)N(CHMe2)P(S)Ph2 (2)
Ph2PN((S)-*CHMePh)PPh2 (3)
Ph2P(S)N(CHMe2)PPh2(4)
Ph2P(S)N((S)-*CHMePh)PPh2 (5)
a
The relative percentages of the alkylated products are determined from the 1H-NMR spectrum of the reaction mixture.
5. Summary and conclusions
the possibility that the palladium allyl complexes can
exist as a pair of different face-coordinated diastereo-
mers. Diastereomerism is observed for the allyl com-
plexes bearing the homodonor chiral ligand, Ph2PN((S)-
*CHMePh)PPh2 (3) only when the allyl moiety is
unsymmetrical. NMR studies on the fluxional behaviour
The
diphosphazane
ligands
of
the
type
Ph2P(E)N(R)P(E?)Ph2 (1Á/5) exhibit diverse palladium
allyl chemistry including various fluxional processes in
solution. The symmetrical ligands Ph2PN(CHMe2)PPh2
(1) and Ph2P(S)N(CHMe2)P(S)Ph2 (2) effectively form
only one allyl palladium complex in solution because the
achiral nature of these ligands does not permit the
differentiation of the two enantiomers arising from the
coordination of the two faces of the allyl moiety to the
metal by means of NMR spectroscopy. However, the
presence of syn/anti-isomer in the case of complex,
of the complex [Pd(h3-1,3-Me2ꢀ
/
C3H3){Ph2PN((S)-
*CHMePh)PPh2-k2P,P}]PF6 (20) show that the open-
ing of the,h3-allyl group to form a s-bonded inter-
mediate is not selective as the ligand Ph2PN((S)-
*CHMePh)PPh2 consists of identical donating atoms.
Allyl palladium complexes of the achiral heterodonor
P,S-ligand, Ph2P(S)N(CHMe2)PPh2 (4) exhibit geome-
trical isomerism when the allyl moiety is unsymmetri-
(Pd(h3 -1,3-Me2 ꢀ
k2P,P}]PF6 (10) does indicate that these allyl palladium
complexes (7Á16) are fluxional in solution. Incorpora-
/
C3 H3 ){Ph2 PN(CHMe2 )PPh2 -
cally substituted (R?"Rƒ). The incorporation of a chiral
/
/
centre in the P,S-ligand increases the number of possible
isomers as the allyl face-coordination can lead to
tion of a chiral centre in the ligand backbone introduces
Table 6
Yield, melting point and elemental analysis data for h3-ally palladium complexes 7Á
31
/
Compound
Yield (%)
M.p. (8C) a
Elemental analysis b
C
H
N (%)
7
79
68
83
81
83
89
87
81
85
69
68
61
67
77
90
76
85
91
78
79
78
181Á
185Á
178Á
188Á
I82Á
165Á
150Á
174Á
181Á
145Á
174Á
178Á
168Á
170Á
194Á
193Á
191Á
214Á
158Á
175Á
219Á
/
183
188
180
190
50.9(50.0)
51.2(50.8)
53.9(54.3)
51.4(51.4)
57.8(57.8)
46.8(46.0)
45.6(46.7)
48.1(47.3)
54.0(53.9)
54.2(53.8)
52.7(54.3)
56.7(57.4)
62.1(60.4)
48.5(47.9)
48.5(48.6)
52.3(52.2)
49.3(49.3)
54.3(55.8)
51.2(51.6)
52.0(52.2)
58.1(58.4)
4.9(4.4)
4.9(4.6)
4.7(4.5)
4.4(4.8)
4.8(4.6)
4.2(4.1)
4.6(4.3)
4.5(4.4)
4.5(4.3)
4.6(4.4)
4.5(4.5)
4.4(4.4)
4.7(4.5)
4.5(4.3)
4.4(4.4)
4.1(4.4)
4.6(4.6)
4.5(4.4)
4.2(4.2)
4.3(4.4)
4.5(4.4)
1.7(1.9)
1.8(1.9)
1.6(1.8)
1.9(1.9)
1.6(1.6)
1.8(1.8)
1.5(1.8)
1.7(1.7)
1.3(1.5)
1.6(1.8)
1.7(1.8)
1.5(1.6)
1.4(1.5)
1.9(1.9)
1.8(1.8)
1.7(1.7)
1.9(1.8)
1.7(1.6)
1.6(1.7)
1.6(1.7)
1.1(1.5)
8
/
9
/
10
11
12
13
15
16
17
18
19
21
22
23
24
25
26
27
28
31
/
/184
/
167
152
176
184
147
176
180
170
172
196
195
194
216
160
178
221
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
The complexes 14, 20, 29 and 30 could not be isolated in pure form.
a
With decomposition.
Calculated values are in parentheses.
b

S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á
/
37
35
different diastereomers. Unlike the case observed for the
Table 7
Crystal data and structure refinement for complex 27
chiral homodonor ligand Ph2PN((S)-*CHMePh)PPh2
(3), the complexes of the heterodonor chiral ligand
Ph2P(S)N((S)-*CHMePh)PPh2 (5) show diastereomer-
ism even when the allyl group is symmetrical and
unsubstituted. The stereodynamic behaviour of the allyl
complexes bearing the P,S-ligands is subject to electro-
nic control; the s-bonded intermediate involved in the
exchange process is formed selectively at the trans
position with respect to the sulphur centre.
Identification code
Empirical formula
Formula weight
Temperature (K)
27
C35H34F6NP3PdS
814.00
293(2)
˚
Wavelength (A)
0.71073
Monoclinic
P21
Crystal system
Space group
Unit cell dimensions
˚
a (A)
9.4449(9)
15.9292(15)
12.5389(12)
109.537(2)
1777.9(3)
2
˚
b (A)
˚
c (A)
b (8)
6. Experimental
3
V (A )
˚
Z
Dcalc (mg mꢂ3
)
1.521
0.773
824
6.1. General comments
Absorption coefficient (mmꢂ1
F(0 0 0)
)
Crystal size (mm3)
0.12ꢃ
23.298
105h 510, ꢂ
135l 512
8121
/0.08ꢃ0.04
/
All reactions and manipulations were carried out
under an atmosphere of dry nitrogen using standard
Schlenk and vacuum-line techniques. The solvents were
purified by standard procedures [22] and distilled under
nitrogen. The chlorobridged palladium allyl dimers
Theta range for data collection 1.72Á
Index ranges
/
ꢂ/
/
/
/175
/
k 5
/
16, ꢂ
/
/
/
Reflections collected
Independent reflections
4685 [Rint
99.6%
ꢀ0.0298]
/
[Pd(h3-C3H5)(m-Cl)]2,
[Pd(h3-1-PhꢀC3H4)(m-C1)]2, [Pd(h3-1,3-Me2ꢀ
Cl)]2 and [Pd(h3-1,3-Ph2ꢀ
C3H3)(m-Cl)]2 were prepared
[Pd(h3-1-Meꢀ
/
C3H4)(m-Cl)]2,
C3H3)(m-
Completeness to uꢀ/23.298
Refinement method
Data/restraints/parameters
Goodness-of-Fit on F2
Full-matrix least-squares on F2
/
/
4685/1/419
1.123
/
as previously described [23]. The diphosphazane ligands
Ph2PN(CHMe2)PPh2 [24], Ph2PN((S)-*CHMePh)PPh2
[9e], Ph2P(S)N(CHMe2)PPh2 [9d] and Ph2P(S)N((S)-
*CHMePh)PPh2 [9a] were prepared by published pro-
cedures. The disulphide ligand, Ph2P(S)N(CHMe2)P-
Final R indices [I ꢀ
/
2s(I)]
R1ꢀ
R1ꢀ
0.03(5)
0.0029(7)
/
0.0528, wR2ꢀ
/
0.1236
R indices (all data)
Absolute structure parameter
Extinction coefficient
/0.0683, wR2ꢀ
/
0.1362
ꢂ
/
Largest difference peak and hole 1.142 and ꢂ0.544
/
ꢂ3
˚
(e A
)
(S)Ph2
was
prepared
by
the
reaction
of
Ph2PN(CHMe2)PPh2 with sulphur in boiling benzene
[25]. The NMR spectra were recorded at 298 K using
Bruker DRX-500 MHz, Bruker AMX-400 MHz, JEOL-
300 MHz and Bruker ACF-200 MHz spectrometers.
Chemical shifts downfield from the reference standard
were assigned positive values. Elemental analyses were
ligand. The yields, melting points and elemental analyses
for these complexes are given in Table 6.
6.3. X-ray structure determination
carried out using a PerkinÁ
The 1H, 13C- and 31P-NMR data for complexes 7Á
given in Tables 1Á4.
/
Elmer 2400 CHN analyser.
Crystal data for complex 27 was collected using
Siemen’s SMART-CCD diffractometer. The crystallo-
graphic data and details of data collection are sum-
marised in Table 7. The structure was solved by Direct
method using the program SIR-97 [26] and refined on F2
values for all unique data by full-matrix least-squares
using SHELXTL [27]. The non-hydrogen atoms were
refined anisotropically. The hydrogen atoms were fixed
at their calculated geometrical positions and refined
isotropically. The validity of the absolute structure was
established by the method of Flack [28].
/31 are
/
6.2. Synthesis of palladium allyl complexes [Pd(h3-
C3H5){Ph2PN(CHMe2)PPh2-k2P,P}]PF6 (7)
A mixture of 0.036 g (0.98ꢃ
C3H5)(m-Cl)]2, 0.033 g (2.02ꢃ
10ꢂ4 mol) of NH4PF6
and 0.090 g (2.10ꢃ
10ꢂ4 mol) of 1 was dissolved in 20
/
10ꢂ4 mol) of [Pd(h3-
/
/
cm3 of acetone. The solution was stirred for 2 h at 25 8C
and the white precipitate formed during the reaction was
filtered off. The resulting colourless filtrate was con-
centrated under reduced pressure to 1.0 cm3 and the
solution was layered by adding 10 cm3 of hexane (B.p
6.4. General procedure for palladium-catalysed allylic
alkylation
40Á
/
60 8C) to yield light yellow micro-crystals of the title
compound. The other allyl palladium complexes, 8Á31
were synthesised by an analogous procedure by varying
/
The ligand (2.5 mol%) and [Pd(h3-C3H5)(m-Cl)]2 (1
mol%) were dissolved in 4 cm3 of degassed (by three
the allyl palladium chloro dimer and the diphosphazane
freezeÁthaw cycles) CH2Cl2. A solution of (E)-1-phenyl-
/

36
S.K. Mandal et al. / Journal of Organometallic Chemistry 676 (2003) 22Á37
/
2-propenyl acetate (I) (one equivalents) in 2 cm3 CH2Cl2
was added followed by dimethyl malonate (two equiva-
lents), bis(trimethyl silyl) acetamide(BSA) (two equiva-
lents) and a catalytic amount of KOAc. The mixture was
stirred at 25 8C for 24 h and the reaction was monitored
by TLC. The ratio of the linear (II) and branched (III)
(c) B.M. Trost, I. Hachiya, J. Am. Chem. Soc. 120 (1998)
1104;
(d) A. Pfaltz, Acc. Chem. Res. 26 (1993) 339.
[7] (a) T. Morimoto, K. Tachibana, K. Achiwa, Synlett (1997)
783;
(b) J.C. Anderson, D.S. James, J.P. Mathias, Tetrahedron:
Asymmetry 9 (1998) 753;
1
(c) J.V. Allen, J.F. Bower, J.M.J. Williams, Tetrahedron: Asym-
metry 5 (1994) 1895;
isomers was determined by H-NMR spectrum of the
reaction mixture.
(d) K. Boog-Wick, P.S. Pregosin, G. Trabesinger, Organometal-
lics 17 (1998) 3254.
[8] (a) D.A. Evans, K.R. Campos, J.S. Tedrow, F.E. Michael, M.R.
Gagne´, J. Org. Chem. 64 (1999) 2994;
7. Supplementary material
(b) D.A. Evans, K.R. Campos, J.S. Tedrow, F.E. Michael, M.R.
Gagne´, J. Am. Chem. Soc. 122 (2000) 7905;
(c) K. Selvakumar, M. Valentini, P.S. Pregosin, A. Albinati,
Organometallics 18 (1999) 4591;
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 188163 for complex 27. Copies
of the information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
(d) A. Albinati, P. Pregosin, K. Wick, Organometallics 15 (1996)
2419.
[9] (a) K. Raghuraman, S.S. Krishnamurthy, M. Nethaji, J. Orga-
nomet. Chem. 669 (2003) 79;
1EZ, UK (Fax: ꢁ44-1223-336033; e-mail: deposit@
/
(b) K. Raghuraman, S.S. Krishnamurthy, M. Nethaji, J. Chem.
Soc. Dalton Trans. (2002) 4289;
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
(c) M. Ganesan, S.S. Krishnamurthy, M. Nethaji, J. Organomet.
Chem. 570 (1998) 247;
(d) R.P.K. Babu, K. Aparna, S.S. Krishnamurthy, M. Nethaji,
Phosphorus, Sulfur, Silicon Relat. Elem. 103 (1995) 39;
(e) R.P.K. Babu, S.S. Krishnamurthy, M. Nethaji, Tetrahedron:
Asymmetry 6 (1995) 427.
Acknowledgements
SKM, GAN and SSK thank the Department of
Science and Technology (DST), New Delhi, India for
financial support.
[10] (a) R.P.K. Babu, S.S. Krishnamurthy, M. Nethaji, Organome-
tallics 14 (1995) 2047;
(b) R.P.K. Babu, S.S. Krishnamurthy, M. Nethaji, Polyhedron 15
(1996) 2689.
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Nixon, J.C.T.R. Burckett St. Laurent, Coord. Chem. Rev. 129
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