Coordination chemistry, reactivities, and stereoelectronic properties of chelating phosphine ligands containing thioamide substituents

Article abstract of DOI:10.1039/b007970g

The intramolecular exo-cycloaddition reaction between N,N-dimethylthioacrylamide and 3,4-dimethyl-1-phenylphosphole in the presence of a perchloratopalladium template containing ortho-metallated (S)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary gave the corresponding thioamide-substituted P-chiral phosphanorbornene stereospecifically in 6 d. The exo-cycloadduct coordinated to the palladium template as a bidentate chelate via its phosphorus and thioamide-sulfur donor atoms. The corresponding intermolecular endo-cycloaddition reaction using the analogous chloropalladium template containing the same ortho-metallated naphthylamine auxiliary produced a pair of separable diastereomeric endo-cycloadducts in 60 d. Both the endo-cycloadducts coordinated to the palladium template as monodentates via their phosphorus donor atoms and their thioamide functions were not involved in the metal complexation. The faster rate observed in the exo-cycloaddition reaction is attributed to the electronic polarization and hence the activation of N,N-dimethylthioacrylamide via thioamide-S coordination. Optically active thioamide-substituted phosphanorbornenes could be liberated from these product complexes by treatment with aqueous cyanide. For comparison purposes, the novel ligand Ph₂PC(S)NMe₂ was prepared. This short-chain ligand displaced acetonitrile and monodentate phosphine ligands on Pd^II to form stable 4-membered P-S chelates. The C=S bond in these sterically hindered chelates are unreactive toward cycloaddition reaction with the phosphole cyclic diene. The thioamido (S)C-N bonds in this series of P-S palladium(II) chelates were found to be significantly shorter than those reported for organic thioamides and their non-chelating counterparts in the endo-cycloadducts, thus indicating that nitrogen in the thioamide function contributed electronically to the stability of the Pd→S bonds. The Royal Society of Chemistry 2001.

Full text of DOI:10.1039/b007970g

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Coordination chemistry, reactivities, and stereoelectronic properties
of chelating phosphine ligands containing thioamide substituents
Pak-Hing Leung,* Ying Qin, Guosen He, K. F. Mok and Jagadese J. Vittal
Department of Chemistry, National University of Singapore, Kent Ridge, Singapore 119260
Received 3rd October 2000, Accepted 28th November 2000
First published as an Advance Article on the web 15th January 2001
The intramolecular exo-cycloaddition reaction between N,N-dimethylthioacrylamide and 3,4-dimethyl-1-
phenylphosphole in the presence of a perchloratopalladium template containing ortho-metallated
(S)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary gave the corresponding thioamide-substituted
P-chiral phosphanorbornene stereospecifically in 6 d. The exo-cycloadduct coordinated to the palladium
template as a bidentate chelate via its phosphorus and thioamide-sulfur donor atoms. The corresponding
intermolecular endo-cycloaddition reaction using the analogous chloropalladium template containing
the same ortho-metallated naphthylamine auxiliary produced a pair of separable diastereomeric endo-
cycloadducts in 60 d. Both the endo-cycloadducts coordinated to the palladium template as monodentates via
their phosphorus donor atoms and their thioamide functions were not involved in the metal complexation. The
faster rate observed in the exo-cycloaddition reaction is attributed to the electronic polarization and hence the
activation of N,N-dimethylthioacrylamide via thioamide-S coordination. Optically active thioamide-substituted
phosphanorbornenes could be liberated from these product complexes by treatment with aqueous cyanide. For
comparison purposes, the novel ligand Ph2PC(S)NMe2 was prepared. This short-chain ligand displaced acetonitrile
and monodentate phosphine ligands on PdII to form stable 4-membered P–S chelates. The C᎐S bond in these
᎐
sterically hindered chelates are unreactive toward cycloaddition reaction with the phosphole cyclic diene. The
thioamido (S)C–N bonds in this series of P–S palladium() chelates were found to be significantly shorter than those
reported for organic thioamides and their non-chelating counterparts in the endo-cycloadducts, thus indicating that
nitrogen in the thioamide function contributed electronically to the stability of the Pd→S bonds.
towards the intermolecular [4 ϩ 2] endo-cycloaddition.2,3 For
Introduction
example, when (Sc)-1 was treated with N,N-dimethylacrylamide
Ever since the discovery of the Grignard reaction much atten-
at room temperature for 32 d the corresponding intermolecular
tion has been focused on the application of metals and metal
cycloaddition reaction occurred and the two possible endo-
ions in organic synthesis.1 The importance of these classic
cycloadducts were obtained as a separable 1:3 diastereomeric
inorganic materials in synthetic chemistry has been well
mixture. The slow reaction rate has been attributed to the
recognized. Numerous excellent achievements in the field of
inherent low dienophilicities of N,N-dimethylacrylamide.3 On
metals and metal complex promoted and catalysed reactions
have indeed changed profoundly the strategic thinking of
the other hand, when the kinetically and thermodynamically
stable chloro ligand in (Sc)-1 was replaced by a kinetically labile
synthetic chemists. Recently, we have been interested in the
palladium template syntheses of a series of functionalized
chiral phosphanorbornenes via [4 ϩ 2] cycloaddition reac-
tions.2,3 These asymmetric syntheses involve both the metal
activation of 3,4-dimethyl-1-phenylphosphole (DMPP) as the
cyclic diene and the subsequent stereochemically controlled
formation of carbon–carbon bonds with various dienophiles in
the presence of a highly efficient chiral ortho-palladated naph-
thylamine template. In most of these syntheses the endo- and
the exo-cycloaddition reaction pathways can effectively be
controlled by manipulating the number of template sites
available for these intra- and inter-molecular Diels–Alder
reactions. In this paper we report the template synthesis and
coordination chemistry of the first optically active thioamide-
substituted phosphanorbornenes. Unlike most documented
P–S heterobidentates which contain thiolato or thioether
sulfur donors, examples of neutral phosphine ligands contain-
perchlorate the potential donor atoms in the dienophiles were
able to interact with the palladium template and adopt the
alternative intra-molecular exo-cycloaddition pathway. Thus
when N,N-dimethylacrylamide was treated with (Sc)-2 for 3 d
under similar conditions to those employed in the endo-
cycloaddition process the corresponding optically pure P–O
chelating exo-cycloadduct was obtained quantitatively. The
dramatic acceleration observed in the exo-cycloaddition
process had been attributed to electronic activation of the
dienophile via amido-O coordination to the readily available
template site on (Sc)-2. In view of these drastic stereoelectronic
template effects associated with N,N-dimethylacrylamide, we
were interested to analyse the analogous exo- and endo-
cycloaddition reactions involving N,N-dimethylthioacrylamide
ing thiocarbonyl C᎐S sulfur donors are rare.4 This is some-
᎐
what surprising as thiocarbonyl compounds are well developed
by organic chemists and transition metal complexes contain-
ing simple thiocarbonyl–S donor atoms have long been
reported.5,6
We have recently reported that the coordinated DMPP in the
chiral chloro complex (Sc)-1 reacts as a typical cyclic diene
DOI: 10.1039/b007970g
J. Chem. Soc., Dalton Trans., 2001, 309–314
This journal is © The Royal Society of Chemistry 2001
309

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Table 1 Selected bond lengths (Å) and angles (Њ) for complex (Sc,Sp)-3
where the amido-oxygen is replaced by a sulfur atom. It is well
known that sulfur exhibits a lower electronegativity than
oxygen in organic chemistry. Therefore, N,N-dimethylthioacryl-
amide itself is expected to be a weaker dienophile than
N,N-dimethylacrylamide. Compared with oxygen, however, sul-
fur generally shows higher affinities to the soft palladium()
ion. Thus it is possible that the stronger sulfur–palladium
coordination would further activate the reactivity of the
thioamide-substituted dienophile in the metal-template
promoted exo-cycloaddition reaction.
Molecule I
Molecule II
Pd(1)–P(1)
Pd(1)–Cl(1)
Pd(1)–Cl(1)
Pd(1)–N(1)
P(1)–C(15)
P(1)–C(18)
C(16)–C(17)
C(19)–C(20)
C(20)–C(21)
S(1)–C(21)
N(3)–C(21)
2.224(1)
2.401(1)
2.014(3)
2.152(3)
1.842(4)
1.845(4)
1.331(5)
1.537(5)
1.528(6)
1.687(4)
1.326(5)
Pd(2)–P(2)
Pd(2)–Cl(2)
Pd(2)–C(41)
Pd(2)–N(2)
P(2)–C(55)
P(2)–C(58)
C(56)–C(57)
C(59)–C(60)
C(60)–C(61)
S(2)–C(61)
N(4)–C(61)
2.227(1)
2.395(1)
2.008(4)
2.149(3)
1.853(4)
1.853(3)
1.332(5)
1.552(5)
1.520(6)
1.671(4)
1.344(6)
Results and discussion
Metal template promoted cycloaddition of DMPP with
N,N-dimethylthioacrylamide
N(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–C(1)
N(1)–Pd(1)–P(1)
Cl(1)–Pd(1)–C(1)
Cl(1)–Pd(1)–P(1)
C(1)–Pd(1)–P(1)
C(15)–P(1)–C(18)
C(20)–C(21)–N(3)
C(20)–C(21)–S(1)
N(3)–C(21)–S(1)
95.5(1)
80.9(1)
173.4(1)
176.1(1)
91.1(1)
92.5(1)
81.4(2)
117.4(4)
121.5(3)
121.0(3)
N(2)–Pd(2)–Cl(2)
N(2)–Pd(2)–C(41)
N(2)–Pd(2)–P(2)
Cl(2)–Pd(2)–C(41)
Cl(2)–Pd(2)–P(2)
C(41)–Pd(2)–P(2)
C(55)–P(2)–C(58)
C(60)–C(61)–N(4)
C(60)–C(61)–S(2)
N(4)–C(61)–S(2)
95.4(1)
81.0(1)
171.5(1)
175.4(1)
89.5(1)
94.5(1)
80.7(2)
116.5(4)
122.1(3)
121.4(3)
N,N-Dimethylthioacrylamide was prepared from the corre-
sponding N,N-dimethylacrylamide using the standard
Lawesson’s Reagent as the thionation reagent.5 As expected,
the thioamide-substituted dienophile is clearly less reactive than
N,N-dimethylacrylamide in the intermolecular endo-cyclo-
addition reaction with DMPP. The reaction between the thio-
amide substituted dienophile and (Sc)-1 at room temperature in
dichloromethane was found to be complete in 60 d (Scheme 1).
Fig. 1 The molecular structure and the absolute stereochemistry of
complex (Sc,Sp)-3.
Scheme 1
phosphorus. Both the sulfur and the nitrogen atoms in the thio-
amide function are not involved in metal complexation. The
absolute configurations of the four newly generated stereogenic
centres at P(1), C(15), C(18) and C(20) are S, R, S and S,
respectively, with the thioamide functional group orientated in
the endo position at C(20). The minor diastereomer (Sc,Rp)-3
could not be induced to crystallize.
However, under similar conditions the corresponding cyclo-
addition reaction with acrylamide required only 30 d for com-
pletion. Interestingly, the stereoselectivities observed with the
two dienophiles in these endo-cycloaddition processes were
similar. The 31P NMR spectra of the crude thio-substituted
cycloadducts in CDCl3 exhibited two sharp singlets at δ 121.6
and 123.1 in the ratio of 3:1. No other 31P NMR signals were
recorded in the low field region thus indicating that only two
diastereomeric phosphanorbornenes were formed in the
cycloaddition reaction. The major diastereomer (Sc,Sp)-3 could
be isolated from the product mixture by silica-gel column
chromatography in 39% yield. The pale yellow complex crystal-
lized from dichloromethane–diethyl ether as bright yellow
prisms with α Ϫ60Њ (589 nm, d-chloroform). The diastereomer
crystallizes as a pair of crystallographically independent mole-
cules [I and II] in the asymmetric unit cell. However, the two
molecules have the same absolute stereochemistry and molecu-
lar connectivity and differ only in the rotational angles along
the P–Pd bonds. For clarity, only one molecule of (Sc,Sp)-3 [I] is
depicted in Fig. 1. Selected bond lengths and bond angles
of both molecules are give in Table 1. The X-ray analysis
confirms that the chiral phosphanorbornene coordinates to
the palladium template as a monodentate ligand solely via its
Relative to the rate observed in the endo-cycloaddition reac-
tion, the exo-cycloaddition reaction between complex (Sc)-2
and N,N-dimethylthioacrylamide under similar conditions may
be regarded as a fast process. The chiral template promoted
intramolecular cycloaddition was monitored by 31P NMR
spectrscopy and found to be complete in 6 d. Furthermore, a
high stereoselectivity was observed as, prior to purification, the
31P NMR spectrum of the crude cycloadducts in CDCl3
recorded only one sharp singlet at δ 109.7 with no other signals
in this low field region. The spectrum thus indicated that only
one cycloadduct was formed stereospecifically in this cyclo-
addition reaction. The cationic complex 4 was subsequently
crystallized from acetone as pale yellow prisms in 58% yield, α
ϩ221.5Њ (589 nm, dichloromethane). The X-ray structural
analysis confirmed that this sole cycloadduct is (Sc,Rp)-4 as
depicted in Scheme 1 and the exo-thioamide substituted phos-
phanorbornene is coordinated to the chiral palladium as a
bidentate chelate via the bridgehead phosphorus and the
310
J. Chem. Soc., Dalton Trans., 2001, 309–314

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Table 2 Selected bond lengths (Å) and angles (Њ) for the cationic
complex (Sc,Rp)-4
processes involving (Sc)-2 occurred ca. 10 times faster than
the corresponding intermolecular endo-Diels–Alder reaction.
However, it was expected that the strong sulfur–palladium bond
would produce a more dramatic electronic polarizing effect on
the thioamide-substituted dienophile. Apparently, this elec-
tronic polarization effect was transmitted predominantly to
the amido-nitrogen atom rather than to the reacting vinylic
Pd–P(16)
Pd–C(1)
2.203(1)
2.017(4)
2.382(1)
2.172(3)
1.854(4)
1.840(4)
C(24)–C(25)
C(26)–C(27)
C(27)–C(28)
C(27)–C(31)
C(31)–S(35)
C(31)–N(32)
1.333(6)
1.552(5)
1.571(6)
1.517(5)
1.711(4)
1.309(6)
Pd–S(35)
Pd–N(12)
P(16)–C(23)
P(16)–C(26)
C᎐C bond. This interesting electronic divergence made the
᎐
exo-cycloaddition with N,N-dimethylthioacrylamide proceed
at a slower rate than that involving N,N-dimethylacrylamide,
despite the fact that the S→Pd bond is more stable than the
O→Pd bond.
It is noteworthy that optically active phosphanorbornenes
endo-(Rp)-5 and exo-(Sp)-5 could be liberated by treatment of
(Sc,Sp)-3 and (Sc,Rp)-4, respectively, with aqueous potassium
cyanide (Scheme 2). The apparent inversion of configuration
N(12)–Pd–S(35)
N(12)–Pd–C(1)
N(12)–Pd–P(16) 166.8(1)
S(35)–Pd–C(1)
S(35)–Pd–P(16)
C(31)–S(35)–Pd
93.8(1)
80.6(1)
C(1)–Pd–P(16)
93.4(1)
81.3(2)
117.9(4)
122.9(3)
119.2(3)
101.0(2)
C(23)–P(16)–C(26)
C(27)–C(31)–N(32)
C(27)–C(31)–S(35)
N(32)–C(31)–S(35)
C(27)–C(26)–P(16)
172.3(1)
93.2(1)
107.5(1)
Fig. 2 The molecular structure and absolute stereochemistry of the
cation in complex (Sc,Rp)-4.
Scheme 2
thioamide-sulfur donor atoms (Fig. 2). The absolute configur-
ations of the four new chiral centres at P(16), C(23), C(26) and
C(27) are R, R, S and S, respectively, with the thioamide func-
tional group orientated in the exo position at C(27). It is note-
that takes place at the phosphorus stereogenic centres when the
phosphanorbornenes are liberated from the metal is merely the
consequence of the Cahn–Ingold–Prelog (CIP) sequence rules.7
These liberated ligands are highly air-sensitive and configura-
tionally unstable. Hence they must be recomplexed to selected
metal ions within 30 min.
worthy that the C᎐S bond in (S ,R )-4 [1.711(4) Å, Table 2] is
᎐
c
p
notably longer than that observed in monodentate complex
(Sc,Sp)-3 [1.687(4) Å in molecule I and 1.671(4) Å in II]. The
lengthening of the C᎐S bond in the S-bonded complex is an
᎐
indication of the weakening of the double bond character via
coordination. Interestingly, however, the thioamido C(31)–
N(32) distance [1.309(6) Å] in the bidentate complex (Sc,Rp)-4
is clearly shorter than those observed in the endo complex
(Sc,Sp)-3 [1.326(5) Å in molecule I and 1.344(6) Å in II]. The
shortening of the thioamido (S)C–N bond together with the
Coordination chemistry and reactivity of diphenylphosphino-
N,N-dimethylthioamide
The isolation and the structural investigation of complex
(Sc,Rp)-4 suggest that, due to the electronic properties of the
thioamide function, chelating agents containing phosphorus
and amido-sulfur donor atoms are powerful sequesterers for
palladium(). To investigate further the full potential of this
class of P–S metal complexation and the reactivities of the
lengthening of the C᎐S bond in (S ,R )-4 suggests that the all
᎐
c
p
three S᎐C–N atoms of the thioamide group contribute elec-
᎐
tronically to the S→Pd coordination. It is noted that the previ-
ously reported oxygen-substituted amidophosphanorbornene
palladium complexes exhibit similar, but less dramatic, coordin-
amido C᎐S bonding, the thioamide-substituted phosphine 6
᎐
was prepared (Scheme 3). This ligand was designed with the
intention of examining the electronic contribution of the amido
group towards metal complexation and the reactivity of the
ation effects on the amido group.3 For example, the C᎐O dis-
᎐
tance in the exo-bidentate-P, O complex is 1.252(7) Å, which is
slightly longer than that recorded for the two monodentate-P
endo-diastereomers [1.220(5) and 1.237(8) Å, respectively].3
Consistent with the thioamide analogues, the amido (O)C–N
distance in the reported P–O chelate is 1.321(7) Å which is
somewhat shorter than that recorded for the two diastereomeric
non-chelating endo-counterparts [1.335(6) and 1.353(9) Å,
respectively].3 In analysing the changes in the bond distances, it
appears that the nitrogen atom in the thioamide chelate is
significantly more sensitive to coordination effects than its
counterpart in the previously reported amido-P,O complex.
As with the accelerated exo-cycloaddition reaction observed
with N,N-dimethylacrylamide, the thioamide-substituted
dienophile evidently can be activated via metal complexation.
With both dienophiles, the intramolecular exo-cycloaddition
C᎐S towards the cycloaddition reaction. It has been established
᎐
that C᎐S bonds in thioamides are able to undergo a hetero Diels–
᎐
Alder reaction.8 Furthermore, the thiocarbonyl function in 6 is
located at the vinylic position with respect to the phosphorus
donor atom. We have reported that the C᎐C bonds in coordin-
᎐
ated vinylphosphines are able to function as dienophiles toward
cycloaddition reaction with DMPP.9 In reactivity consider-
ations, however, the formation of a stable P–S chelation may
deter the dienophilicity of 6 as the C᎐S bond becomes part of a
᎐
chelate ring. In steric considerations, on the other hand, the
sterically unfavorable 4-membered ring may be kinetically labile
and thus allow the C᎐S bond to undergo the coupling reaction.
᎐
We have previously reported a series of kinetically labile
palladium() complexes containing thiophosphine chelates.10
J. Chem. Soc., Dalton Trans., 2001, 309–314
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Table 3 Selected bond lengths (Å) and angles (Њ) for complex 7
the steric repulsion between the projecting NMe group and the
PPh rings. The C᎐S bond distance [1.705(3) Å] is comparable
᎐
Pd(1)–P(1)
Pd(1)–S(1)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
2.209(1)
2.290(1)
2.329(1)
2.376(1)
C(1)–S(1)
C(1)–P(1)
C(1)–N(1)
C(2)–N(1)
1.705(3)
1.838(2)
1.298(3)
1.466(3)
with that recorded for (Sc,Rp)-4. However, the N–C distance
[1.298(3) Å] in the amido function of 7 is clearly shorter than
those observed in organic thioamides6 and in both (Sc,Sp)-3 and
(Sc,Rp)-4. The short N(1)–C(1) distance once again reaffirmed
clearly that the amido-nitrogen atom, although not directly
attached to palladium, is electronically involved in the metal–
thioamide sulfur coordination. Furthermore, the S→Pd bond
in the 4-membered chelate was found to be kinetically stable
as no cycloaddition reaction occurred between 7 and DMPP,
despite the strong reaction conditions that were used.
S(1)–Pd(1)–Cl(1)
S(1)–Pd(1)–Cl(2)
S(1)–Pd(1)–P(1)
Cl(1)–Pd(1)–P(1)
Cl(2)–Pd(1)–P(1)
Cl(2)–Pd(1)–Cl(1)
169.7(1)
95.0(1)
75.2(1)
94.6(1)
170.1(1)
95.3(1)
C(1)–P(1)–Pd(1)
C(1)–S(1)–Pd(1)
S(1)–C(1)–N(1)
S(1)–C(1)–P(1)
N(1)–C(1)–P(1)
C(1)–N(1)–C(2)
91.1(1)
91.9(1)
126.1(2)
101.5(1)
132.3(2)
120.2(2)
Interestingly, the thioamido-substituted phosphine 6 was
found to displace DMPP from (Sc)-2 to give the cationic com-
plex (Sc)-8 regiospecifically in quantitative yield, α Ϫ60.0Њ (589
nm, dichloromethane). The 31P NMR spectrum of (Sc)-8 in
CDCl3 showed a singlet at δ 8.4. Once again, the 4-member ring
and the C᎐S bond in this cationic complex were found to be
᎐
stable and unreactive. Attempts to prepare complex 9 from
the cycloaddition reaction between DMPP and (Sc)-8 were
unsuccessful. In all these attempts, (Sc)-8 remained unchanged
even though strong reaction conditions were used. The P–S
chelate was also found to be stable under strong acidic condi-
tions. Thus, when (Sc)-8 was treated with concentrated HCl
only the ortho-metallated naphthylamine auxiliary was removed
chemoselectively to give the dichloro complex 7 in quantitative
yield.
Fig. 3 The molecular structure of the dichloro complex 7.
In this work the formation of the non-chelating endo-
cycloadduct (Sc,Sp)-3 indicates that the thioamide functional
group in N,N-dimethylthioacrylamide may not be a sufficiently
strong donor system to form stable monodentate complexes
with palladium(). The solid state structural features and the
reactivities of (Sc,Rp)-4 and 7, however, clearly illustrate that
with the assistance of a phosphorus donor the nitrogen atom in
the thioamide function plays an important role to the kinetic
and thermodynamic stabilities of the thioamido P–S bidentate
chelates.
Experimental
Reactions involving air-sensitive compounds were performed
under a positive pressure of purified nitrogen. For NMR,
proton spectra were recorded at 500.14 MHz and 31P spectra
at 202.46 MHz on Bruker ACF 300 and AMX500 NMR
spectrometers. Molar conductivities were measured with a
Horiba ES-12 conductivity meter for 10Ϫ3 M solutions of the
complexes at 25 ЊC. Elemental analyses were performed by
the Elemental Analysis Laboratory of the Department of
Chemistry at the National University of Singapore.
Scheme 3
The phosphine ligand 6 was obtained as a stable yellow solid
from the reaction between sodium diphenylphosphide and
dimethylthiocarbamoyl chloride in THF. The 31P NMR spec-
trum of 6 in CDCl3 exhibited a sharp singlet at δ 18.4. In the
absence of other strong donor atoms, the thioamide-substituted
ligand is able to form a P–S chelate with PdII. Thus when 6 was
treated with [Pd(MeCN)2Cl2] in dichloromethane the dichloro
complex 7 was formed immediately. The 31P NMR spectrum of
the crude product in CDCl3 exhibited only one sharp singlet at
δ Ϫ29.6. The neutral complex was subsequently crystallized
from dichloromethane–diethyl ether as yellow prisms. The
molecular structure and the coordination chemistry of 7 were
studied by X-ray structural analysis (Fig. 3). Selected bond
lengths and bond angles are given in Table 3. The X-ray analysis
revealed that the short-chain thioamido-phosphine ligand was
indeed coordinated to palladium() as a bidentate chelate via its
phosphorus and sulfur donor atoms to form a 4-membered
ring. The geometry at palladium is distorted square planar with
angles at palladium in the range 75.2(1)–95.3(1)Њ. The C(1)–
S(1)–Pd(1) and C(1)–P(1)–Pd(1) angles [91.9(1) and 91.1(1)Њ,
respectively] within the 4-member chelate ring are acute. The
N(1)–C(1)–P(1) angle [132.3(2)Њ] is enlarged, presumably due to
N,N-Dimethylthioacrylamide5 and the chiral complexes (Sc)-
1 and (Sc)-22,3 were obtained as previously described.
endo-Cycloaddition reaction: isolation of chloro{(S)-1-[1-
(dimethylamino)ethyl]-2-naphthyl-C 2,N}{(1ꢀ,4ꢀ,5ꢁ,7S)-5-
(N,N-dimethylthiocarbamoyl)-2,3-dimethyl-7-phenyl-7-
phosphabicyclo[2.2.1]hept-2-ene-P7}palladium(II) (Sc,Sp)-3
A mixture of complex (Sc)-2 (0.20 g, 0.38 mmol) and N,N-
dimethylthioacrylamide (0.21 g, 1.9 mmol) in dichloroethane
(30 cm3) was stirred for 60 d at room temperature. The solvent
was removed under reduced pressure to give a black residue.
This material was chromatographed on a silica column (50 g,
Merck, 40–63 µm) giving the diastereomeric neutral complexes
(Sc,Rp)-3 and (Sc,Sp)-3 in 22 and 39% yield, respectively. Com-
plex (Sc,Sp)-3 could be crystallized from dichloromethane–
diethyl ether as pale yellow prisms, mp 209–210 ЊC (decomp.)
(Found: C, 57.7; H, 5.8; N, 4.4; S, 4.8. Calc. for C31H38-
ClN2PPdS: C, 57.9; H, 5.9; N, 4.4; S, 5.0%). α Ϫ60.0Њ (589 nm,
c 0.1 g per 100 cm3, CDCl3). 1H NMR (CDCl3): δ 1.28 (s, 3 H,
3
C᎐CMe), 1.83 (s, 3 H, C᎐CMe), 1.92 (d, 3 H, JHH = 6.0,
᎐
᎐
312
J. Chem. Soc., Dalton Trans., 2001, 309–314

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Table 4 Crystallographic data for complexes (Sc,Sp)-3, (Sc,Rp)-4 and 7
(Sc,Sp)-3
(Sc,Rp)-4
7
Formula
M
Space group
Crystal system
C31H38ClN2PPdSؒ0.5Et2O
680.57
P212121
C31H38ClN2O4PPdS
707.51
P212121
C15H16Cl2NPPdS
450.62
P21/n
Orthorhombic
Orthorhombic
Monoclinic
a/Å
b/Å
c/Å
12.5862(4)
22.6849(7)
23.3035(7)
10.7346(2)
14.3998(3)
20.3434(2)
10.1583(2)
12.3121
14.4431
98.122(1)
1788.28(5)
4
β/Њ
V/Å3
6653.5(4)
8
3144.60(9)
4
Z
T/K
293(2)
0.71073
7.75
293(2)
0.71073
8.31
293(2)
0.71073
15.34
λ/Å
µ/cmϪ1
R1 (obs. data)
wR2 (obs. data)
0.0362
0.0716
0.0379
0.0891
0.0291
0.0618
CHMe), 2.36–2.43 (m, 1 H, CH(exo)H(endo)), 2.56 (s, 3 H, NMe),
tion of sodium diphenylphosphide, that had previously been
prepared from diphenylphosphine (1.1 g, 5.9 mmol) and
sodium foil (0.14 g, 5.9 mmol) in the same solvent. After the
addition the reaction mixture was stirred at room temperature
for 8 h. At this stage the solvent was removed under reduced
pressure and the residue treated with water (3 × 30 cm3). The
product was extracted with dichloromethane and subsequently
chromatographed on a silica column with dichloromethane–
hexane (7:3). Pure ligand 6 was thus obtained as yellow crystals
(0.88 g, 55%), mp 108–110 ЊC (decomp.) (Found: C, 65.7; H,
6.1; N, 4.8; S, 12.1. Calc. for C15H16NPS: C, 65.9; H, 5.9; N, 5.1;
4
2.86 (d, 3 H, JPH = 2.8, NMe), 3.00–3.16 (m, 2 H, CH(exo)
-
H
(endo) ϩ PCH), 3.47 (s, 3H, C(S)NMe), 3.67 (bs, 1 H, PCH),
3
3.76 (s, 3H, C(S)NMe), 4.28 (qn, 1 H, JHH = 4JPH = 6.2,
3
CHMe), 4.80–4.84 (m, 1 H, C(S)CH), 7.08 (dd, 1 H, JHH
=
4
8.4, JPH = 6.4 Hz, naphthyl Hγ) and 7.33–7.96 (m, 10 H,
aromatics). 31P-{H} NMR (CDCl3): δ 121.6 (s, 1P). Complex
(Sc,Rp)-3 could not be induced to crystallize in all solvent
systems attempted.
exo-Cycloaddition reaction: isolation of {(S)-1-[1-(dimethyl-
amino)ethyl]-2-naphthyl-C2,N}{(1ꢀ,4ꢀ,5ꢀ,7R)-5-(N,N-dimethyl-
thiocarbamoyl)-2,3-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]-
hept-2-ene-P7,S}palladium(II) perchlorate, (Sc,Rp)-4
1
4
S, 11.7%). H NMR (CDCl3): δ 3.39 (d, 3 H, JPH = 1.2 Hz,
NMe), 3.54 (s, 3 H, NMe) and 7.03–7.69 (m, 10 H, aromatics).
31P-{H} NMR (CDCl3): δ 18.4 (s, 1P). 13C-{H} NMR (CDCl3):
3
δ 43.6 (d, JPC = 22.7, NMe), 44.8 (s, NMe), 128.4–134.8 (m,
A mixture of the perchlorato complex (Sc)-2 (0.66 g, 1.1 mmol)
and N,N-dimethylthioacrylamide (0.64 g, 5.58 mmol) in
dichloroethane (50 cm3) was stirred for 6 d at room temper-
ature. The solvent was removed under reduced pressure to give
a yellow residue. This material was crystallized from acetone as
pale yellow prisms (0.39 g, 58%), mp 219–223 ЊC (decomp.)
(Found: C, 52.3; H, 5.4; N, 4.1; S, 4.2. Calc. for C31H38-
ClN2O4PPdS: C, 52.6; H, 5.4; N, 4.0; S, 4.5%). α ϩ221.5Њ (589
aromatics) and 208.5 (d, 1JPC = 30.3 Hz, S᎐C).
᎐
Dichloro{N,N-dimethyl(diphenylphosphino)thioformamide-
S,P}palladium(II), 7. A solution of [Pd(MeCN)2Cl2] (0.08 g, 0.2
mmol) in dichloromethane (30 cm3) was treated with the thio-
amide ligand 6 (0.06 g, 0.2 mmol) in the same solvent for 30
min. The dichloro complex 7 was filtered off and washed with
diethyl ether. It was subsequently crystallized from acetone–
diethyl ether as pale yellow prisms (0.07 g, 71%), mp 220–
221 ЊC (decomp.) (Found: C, 39.7; H, 3.4; N, 3.4; S, 6.7. Calc.
for C15H16Cl2NPPdS: C, 40.0; H, 3.6; N, 3.1; S, 7.1%). 1H NMR
(CD2Cl2): δ 3.20 (s, 3 H, NMe), 3.45 (s, 3 H, NMe) and 7.62–
7.96 (m, 10 H, aromatics). 31P-{H} NMR (CD2Cl2): δ Ϫ29.6
(s, 1P).
nm, c 0.5 g per 100 cm3, CH2Cl2). 1H NMR (CDCl3): δ 1.51 (s, 3
3
H, C᎐CMe), 1.78 (d, 3 H, JHH = 6.0, CHMe), 1.96 (s, 3 H,
᎐
C᎐CMe), 2.44–2.66 (m, 1 H, CH(exo)H(endo)), 2.56 (s, 3 H, NMe),
᎐
4
2.70–2.79 (m, 2 H, CH(exo)H(endo)) 2.87 (d, 3 H, JPH = 3.3,
NMe), 3.05 (s, 1 H, PCH), 3.56–3,69 (m, 2H, C(S)CH ϩ PCH),
3.71 (s, 3H, C(S)NMe), 3.74 (s, 3H, C(S)NMe), 4.31 (qn,
3
1 H, JHH = 4JPH = 6.0 Hz, CHMe) and 7.07–7.67 (m, 11 H,
aromatics). 31P-{H} NMR (CDCl3): δ 109.7 (s, 1P).
{(S)-1-[1-(dimethylamino)ethyl]-2-naphthyl-C2,N}{N,N-
dimethyl(diphenylphosphino)thioformamide-S,P}palladium(II),
(Sc)-8. A mixture of the perchlorato complex (Sc)-2 (0.31 g, 0.52
mmol) and 6 (0.05 g, 0.17 mmol) in dichloroethane (20 cm3) was
stirred for 4 d at room temperature. The mother liquor was
concentrated under reduced pressure to give a yellow solid (0.03
g, 20%), mp 168–169 ЊC (decomp.). α Ϫ60Њ (589 nm, c 0.5 g per
100 cm3, CH2Cl2). ΛM = 22 ΩϪ1 cm2 molϪ1 (CH2Cl2). 1H NMR
Liberation of (1ꢀ,4ꢀ,5ꢁ,7S)-5-(N,N-dimethylthiocarbamoyl)-
2,3-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-2-ene, endo-
(Rp)-5
A solution of complex (Sc,Sp)-3 (0.41 g, 0.06 mmol) in
dichloromethane (10 cm3) was stirred for 2 h with an excess of
potassium cyanide (0.42 g, 6.4 mmol) in water (1 cm3). The
organic layer was separated, washed consecutively with water
and dilute sulfuric acid (to remove the naphthylamine auxiliary)
and finally dried over MgSO4. Removal of the solvent left a
viscous oil (0.01 g, 51%). α Ϫ15.0Њ (589 nm, c 0.5 g per 100 cm3,
CH2Cl2). 31P-{H} NMR (CDCl3): δ 120.2 (s, 1P). The bidentate
ligand exo-(Sp)-5 was similarly liberated from (Sc,Rp)-4. α
ϩ114.0Њ (589 nm, c 0.5 g per 100 cm3, CH2Cl2). 31P-{H} NMR
(CDCl3): δ 98.8 (s, 1P).
(CDCl3): δ 1.83 (d, 3 H, 3JHH = 6.4, CHMe), 2.96 (d, 3 H, 4JPH
2.0 Hz, NMe), 2.96 (s, 3 H, NMe), 3.06 (d, 3 H, JPH = 4.8,
=
4
NMe), 3.33 (s, 3H C(S)NMe), 3.60 (s, 3H C(S)NMe), 4.47 (qn,
3
3
1 H, JHH = 4JPH 6.0, CHMe), 6.65 (dd, 1 H, JHH = 4JPH = 8.4
Hz, naphthyl Hγ) and 7.15–7.98 (m, 15 H, aromatics). 31P-{H}
NMR (CDCl3): δ 8.4 (s, 1P).
Crystal structure determinations of complexes (Sc,Sp)-3, (Sc,Rp)-
4 and 7
Syntheses
Crystal data for complexes (Sc,Sp)-3, (Sc,Rp)-4 and 7 and a
summary of the crystallographic analyses are given in Table 4.
Diffraction data were collected on a Siemens CCD diffract-
ometer using graphite monochromated Mo-Kα radiation.
N,N-Dimethyl(diphenylphosphino)thioformamide, 6. A solu-
tion of N,N-dimethylthiocarbamoyl chloride (0.73 g, 5.9 mmol)
in THF (30 cm3) was added over a period of 10 min to a solu-
J. Chem. Soc., Dalton Trans., 2001, 309–314
313

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SADABS11 absorption corrections were applied and all non-
hydrogen atoms refined anisotropically, except for those of the
solvent molecule. Hydrogen atoms were introduced at fixed dis-
tances from carbon atoms and assigned fixed thermal param-
eters. All calculations were performed on a Silicon Graphics
workstation using programs provided by Siemens.
CCDC reference number 186/2289.
1998, 17, 3931; Y. C. Song, K. F. Mok, P. H. Leung and S. H. Chan,
Inorg. Chem., 1998, 37, 6399; G. He, Y. Qin, K. F. Mok and
P. H. Leung, Chem. Commun., 2000, 167.
3 P. H. Leung, S. K. Loh, K. F. Mok, A. J. P. White and D. J. Williams,
Chem. Commun., 1996, 591; P. H. Leung, G. He, H. Lang, A. Liu,
S. K. Loh, S. Selvaratnam, K. F. Mok, A. J. P. White and D. J.
Williams, Tetrahedron, 2000, 56, 7.
4 H. P. M. M. Ambrosius, J. Willemse, J. A. Cras, W. P. Bosman and
J. H. Noordik, Inorg. Chem., 1984, 23, 2672; K. H. Yih and
Y. C. Lin, J. Organomet Chem., 1999, 577, 134; T. Q. Ly, A. M. Z.
Slawin and J. D. Woollins, Polyhedron, 1999, 18, 1761.
5 H. Alper and D. A. Brandes, Organometallics, 1991, 10, 2457.
6 F. Duus, in Comprehensive Organic Chemistry, Pergamon, Oxford,
1979, vol. 3, ch. 11.22.
See http://www.rsc.org/suppdata/dt/b0/b007970g/ for crystal-
lographic files in .cif format.
Acknowledgements
We are grateful to the National University of Singapore for
support of this research and PhD research scholarships to
Y. Q. and G. H.
7 R. S. Cahn, C. K. Ingold and V. Prelog, Angew. Chem., Int. Ed. Engl.,
1966, 5, 385.
8 R. Arnaud, P. Y. Chavant, K. Molvinger and Y. Vallee, J. Chem.
Soc., Chem. Commun., 1995, 1897.
9 B. H. Aw, T. S. A. Hor, S. Selvaratnam, K. F. Mok, A. J. P. White,
D. J. Williams, N. H. Rees, W. McFarlane and P. H. Leung,
Inorg. Chem., 1997, 36, 2138; S. Selvaratnam, K. F. Mok, P. H.
Leung, A. J. P. White and D. J. Williams, Inorg. Chem., 1996, 35,
4798; A. M. Liu, K. F. Mok and P. H. Leung, Chem. Commun.,
1997, 2397; P. H. Leung, A. Liu and K. F. Mok, Tetrahedron
Asymmetry, 1999, 10, 1309.
10 P. H. Leung, J. W. L. Martin and S. B. Wild, Inorg. Chem., 1986, 25,
3396.
11 G. M. Sheldrick, SADABS, software for empirical absorption
correction, University of Göttingen, 1996.
References
1 See, for examples, A. F. Noels, M. Graziani and A. J. Hubert,
in Metal Promoted Selectivity in Organic Synthesis, Kluwer,
Dordrecht, 1991; B. Bosnich, in Asymmetric Catalysis, Martinus
Nijhoff Press, Boston, 1986.
2 See, for examples, P. H. Leung, S. Y. Siah, A. J. P. White and
D. J. Williams, J. Chem. Soc., Dalton Trans., 1998, 893; G. He,
S. K. Loh, J. J. Vittal, K. F. Mok and P. H. Leung, Organometallics,
314
J. Chem. Soc., Dalton Trans., 2001, 309–314