A new method for modification of CN-palladacycles

Article abstract of DOI:10.1007/s11172-006-0079-4

The reaction of benzylaminate CN-palladacycle with chlorine dioxide was found to produce the 3-chlorine-substituted analog through the formal insertion of chlorine into the Pd-C bond followed by repeated ortho-palladation of the modified ligand. The structure of the resulting dimeric complex was confirmed by X-ray diffraction study of its triphenylphosphine derivative. A comparison of the ¹H NMR spectra of the phosphine adducts of the starting and chlorinated complexes shows high conformational stability of the new palladacycle. Advantages of the new route to conformational stabilization of labile palladacycles are discussed.

Full text of DOI:10.1007/s11172-006-0079-4

Russian Chemical Bulletin, International Edition, Vol. 54, No. 9, pp. 2073—2082, September, 2005
2073
A new method for modification of CNꢀpalladacycles*
V. V. Dunina,aꢀ O. N. Gorunova,b Yu. K. Grishin,a L. G. Kuz´mina,c
A. V. Churakov,c A. V. Kuchin,d and J. A. K. Howarde
aDepartment of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 932 8846. Eꢀmail: dunina@org.chem.msu.ru
bInstitute of Physiologically Active Compounds, Russian Academy of Sciences,
1 Severnyi proezd, 142432 Chernogolovka, Moscow region, Russian Federation.
Eꢀmail: o.gorunova@org.chem.msu.ru
cN. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
31 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 952 1279. Eꢀmail: churakov@igic.ras.ru
dInstitute of Chemistry, Komi Science Center, Ural Branch of the Russian Academy of Sciences,
48 ul. Pervomaiskaya, 167610 Syktyvkar, Russian Federation.
Fax: +7 (821) 242 2264. Eꢀmail: kutchin@chemi.komisc.ru
eDepartment of Chemistry, University of Durham,
South Road, Durham DH1 3LE, UK.
Fax: +44 (0191) 374 3745. Eꢀmail: j.a.k.howard@durham.ac.uk
The reaction of benzylaminate CNꢀpalladacycle with chlorine dioxide was found to proꢀ
duce the 3ꢀchlorineꢀsubstituted analog through the formal insertion of chlorine into the Pd—C
bond followed by repeated orthoꢀpalladation of the modified ligand. The structure of the
resulting dimeric complex was confirmed by Xꢀray diffraction study of its triphenylphosphine
derivative. A comparison of the 1H NMR spectra of the phosphine adducts of the starting and
chlorinated complexes shows high conformational stability of the new palladacycle. Advanꢀ
tages of the new route to conformational stabilization of labile palladacycles are discussed.
Key words: palladacycles, chlorination, chlorine dioxide, Xꢀray diffraction analysis, conꢀ
formation of palladacycles, histograms.
The reactions of cyclopalladated complexes (CPCs)
at the Pd—C bond are of interest as an elegant approach
to the regioselective organic synthesis.1,2 Although there
are numerous publications concerning this problem, studꢀ
ies of oxidation of palladacycles (formal insertion of oxyꢀ
gen into the Pd—C bond) are rather scarce. Organic
peracids,3—9 lead(IV) acetate,10 tertꢀbutyl hydroperoxꢀ
ide,11,12 molybdenum peroxides,13,14 or iodosoarenes15,16
are used as oxidizing agents in these reactions, whereas
simpler oxidants (for example, H2O2) are unsuitable for
this purpose.6 The efficiency of these processes often
strongly depends on the structure of palladacycle. In some
cases, oxidation can be achieved only in the presence of a
catalyst.11,12 Until recently, the range of substrates has
been limited to cyclopalladated derivatives of achiral
ligands, such as azoarenes,5,6,8,9,15—17 tertiary benzylꢀ
amines,4,11—14 and aliphatic ketone oximes.10
Two factors have stimulated our studies in this area.
First, oxidation of chiral palladacycles could provide a
new route to the synthesis of optically active amino
alcohols, which are known to be efficient ligands in
enantioselective catalysis.18—20 Second, it is of interest to
perform this reaction with the use of simpler and readily
available oxidants. We decided to use chlorine dioxide21
as a cheap commercially available reagent, which often
allows one to perform highly selective oxidation of both
organic22—26 and mainꢀgroup organometallic compounds
(B, Al, and Mg).27,28 Reactions with chlorine dioxide
result predominantly in oxidation of substrates. However,
several examples of the formation of mixtures of the oxiꢀ
dation and chlorination products of organic substrates
were documented.29—34 In this connection, it was necesꢀ
sary to elucidate the features of the behavior of this reꢀ
agent with respect to palladacycles.
In the present study, we examined the reactions of the
simplest chiral CNꢀpalladacycle, viz., the N,Nꢀdimethylꢀ
αꢀmethylbenzylamine derivative, with chlorine dioxide.
* Dedicated to Academician N. S. Zefirov on the occasion of his
70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2010—2019, September, 2005.
1066ꢀ5285/05/5409ꢀ2073 © 2005 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 54, No. 9, September, 2005
Dunina et al.
The preliminary results of our study have been presented
at a conference.35
expected to form a chloroꢀbridged dimeric palladium(II)
complex, viz., either a coordination compound with
N,Oꢀchelated aminophenoxide (2) or a cyclometallated
complex with chlorinated CNꢀpalladacycle (3)
(Scheme 2).
Results and Discussion
The reactions of palladacycles with oxidants generally
lead to the formal insertion of oxygen into the Pd—C
bond giving rise to hydroxy,3—6,8,9,11,12,14—16 alkoxy,13,14
or acyloxy derivatives10,36,37 of the starting substrates isoꢀ
lated as free ligands or their complexes with palladium(II).
Although these reactions are performed with either chloroꢀ
bridged dimeric CPCs4—6,10—12,14,15 or chloride forms of
their mononuclear derivatives,3,8,9,13,16 the insertion of
chlorine into the Pd—C bond of the palladacycle is genꢀ
erally not observed. However, the reactions of chlorides
of benzylaminate CNꢀ and CNNꢀpalladacycles with moꢀ
lybdenum peroxide was demonstrated14 (GLC analysis)
to give (along with standard hydroxy or alkoxy derivaꢀ
tives) alternative chlorination products. For example,
oxidation of the pyridine adduct of orthoꢀpalladated
N,Nꢀdimethylꢀαꢀmethylbenzylamine in methanol afꢀ
forded a chlorination product in trace amounts (4%), but
its yield was increased to 22% when the reaction was
performed in dichloromethane and it was further increased
to 61% in the presence of an excess of chloride ions
(3.2 equiv. of [Et3NBn]Cl).14
Scheme 2
Taking into account these results and the known feaꢀ
tures of the reactivity of chlorine dioxide, we considered
the following two possible pathways of its reactions with
palladacycles at the Pd—C bonds: hydroxylation and chloꢀ
rination (Scheme 1), the former process being assumed as
a more probable pathway.
Initially, we used racemic µꢀchloride dimer 1 in studꢀ
ies of the reaction of CPC with chlorine dioxide. The
reaction was carried out under mild conditions, at room
temperature in a twoꢀphase dichloromethane—water sysꢀ
tem with the use of a stoichiometric amount of ClO2 (as a
~0.05 M aqueous solution) in the absence of light to avoid
radical decomposition of the reagent.41 A chlorinated
complex was isolated in moderate yield (46%) by chroꢀ
matography. In addition, a complex mixture of unidentiꢀ
fied oxidation products was formed.
Scheme 1
Some experimental data provide evidence that chloriꢀ
nation rather than oxidation is the major process under
these conditions. The resulting lightꢀyellow complex difꢀ
fers in the color from known brightꢀred aminophenoxide
analogs 2.12 In addition, the elemental composition of
this complex differs substantially from the calculated comꢀ
position of dimer 2 (by more than 2% of the carbon conꢀ
tent). Both characteristics are quite consistent with those
expected for structure 3, which is a chlorinated analog of
the starting CPC 1. Both alternative reaction products
would be expected to have dinuclear structures. Hence,
with the aim of confirming the structure of the comꢀ
plex by spectroscopy, it was transformed into a monoꢀ
nuclear phosphine derivative with hypothetical strucꢀ
ture 4 using the standard chlorideꢀbridge cleavage reacꢀ
tion (Scheme 3).
Oxidation of chloroꢀbridged dimeric CPCs generꢀ
ally affords dinuclear coordination compounds with
N,Oꢀchelated aminophenoxides of the general formula
[{(κ2ꢀN∩O)Pd(µꢀCl)}2] as primary products.5,11,12,15,16
Monochlorination products are sometimes isolated (withꢀ
out demetallation) as free ligands in reactions of palladaꢀ
cycles with gaseous chlorine.38,39 However, repeated
cyclopalladation of the modified ligand, which occurs
through the intermediate formation of new µꢀchloride
dinuclear CPC, was observed in some cases.17,40 Accordꢀ
ing to these results, whatever the pathway may be, the
reaction of complex 1 with chlorine dioxide would be

Modification of CNꢀpalladacycle
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 9, September, 2005
2075
Scheme 3
Fig. 2. Chiral conformations of the fiveꢀmembered αꢀmethylꢀ
benzylaminate CNꢀpalladacycle, λ(S) and δ(S).
1
mental section) are also consistent with the vicinal arꢀ
rangement of these protons.
The H NMR spectrum of phosphine complex 4 also
confirms its cyclopalladated structure and the presence of
a substituent in the phenylene fragment. The retention of
the Pd—C bond in mononuclear complex 4 (and, conseꢀ
quently, in the starting dimer 3) is evidenced primarily by
upfield shifts (under the influence of anisotropy of the
PPh rings) of the signals for two aromatic protons, H(6)
and H(5), nearest to this bond (to δ 6.21 and 6.29, respecꢀ
tively; Fig. 1) compared to those in the spectra of
trialkylphosphine derivatives of orthoꢀpalladated comꢀ
plexes. In the latter spectra, the proton H(6) generally
gives a signal at δ 7.0—7.6.42 These shifts of the signals are
consistent with the transꢀ(P,N) geometry of phosphine
adduct 4. The observed spinꢀspin coupling constant beꢀ
The presence of the chlorine atom at position 3 of the
phenylene fragment is evidenced by small shifts of the
signals for the aromatic protons in the 1H NMR spectrum
of complex 4 compared to those observed for analog 5: ∆δ
for the protons H(4), H(5), and H(6) are –0.03, –0.09,
and –0.13, respectively, which agree well with the known
increments for the chlorine atom in monosubstituted benꢀ
zenes (from –0.02 to –0.06 ppm), but they are approxiꢀ
mately an order of magnitude smaller than those exꢀ
pected for oxygenꢀcontaining substituents (from –0.4 to
–0.5 ppm for OH).46
The fact that the chlorine atom is in the immediate
vicinity of the side chain of the benzylaminate ligand is
indirectly confirmed by the downfield shifts of the signals
for the protons of the αꢀCH and αꢀMe groups compared
tween the proton H(6) and the phosphorus nucleus (JH,P
=
6.2 Hz) (coupling occurs partially through space) also
confirms the cyclopalladated structure of complex 4 and
its transꢀ(P,N) configuration.
1
to their positions in the H NMR spectrum of triphenylꢀ
phosphineꢀcontaining compound 5 derived from dimer 1
(∆δ 0.2 and 0.13, respectively).
The presence of a substituent in the phenylene fragꢀ
ment is evident from the fact that the 1H NMR spectrum
of complex 4 shows only three wellꢀ
resolved signals in the aromatic proꢀ
ton resonance region (δ 6.1—6.9, see
Fig. 1) instead of four signals charꢀ
acteristic of benzylaminate palladaꢀ
cycles containing the unsubstituted
Ph ring,43—45 including the closest
Conformational stabilization of the new palladacycle
is the most important consequence of the appearance of
the chlorine atom adjacent to the side chain of the
benzylaminate ligand. Spectroscopic and structural studꢀ
ies of chiral cyclopalladated derivatives of benzylamines
showed that their simplest representative (present in
dimer 1 and its phosphine adduct 5) is conformationally
labile47—50 and exists in solution as an equilibrium mixꢀ
ture of two conformers* (Fig. 2).
analog 5. The multiplicities of the
resonance lines of three aromatic
To the contrary, the 1ꢀnaphthylꢀ48,51,52 and αꢀtertꢀbuꢀ
tylꢀsubstituted43—45 analogs of compound 1 are conforꢀ
mationally stable and exist predominantly in one λ(S)
conformation, in which a substituent in the αꢀbenzyl poꢀ
sition of the side chain is in an axial orientation. This
property of palladacycles is to a large extent responsible
for their efficiency in chiral recognition.53
protons in the spectrum of complex 4 (see Fig. 1) and the
1H—1H and 1H—31P coupling constants (see the Experiꢀ
To estimate the influence of the chlorine atom at poꢀ
sition 3 of the phenylene fragment on the conformation
of the palladacycle, we performed repeated 1H NMR specꢀ
troscopic study of PPh3 adduct 5.54,55 A comparison of
the spectroscopic characteristics of phosphine complex 4
and its analog 5 shows that the new palladacycle exists
H(5)
H(4)
H(6)
6.8
6.6
6.4
δ
1
Fig. 1. Fragment of the H NMR spectrum of phosphine comꢀ
plex 4 in the region of resonance of the protons of the palladated
phenylene ring.
* Hereinafter, the conformational analysis of racemic complexes
was performed for the (S) enantiomer.

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Russ.Chem.Bull., Int.Ed., Vol. 54, No. 9, September, 2005
Dunina et al.
predominantly in the λ(S) conformation in which the
αꢀMe group in the side chain is in an axial orientation. The
efficiency of spinꢀspin coupling between the αꢀmethine
proton and 31P of the phosphine ligand generally serves
as the main criterion for estimating the conformational
state of this type of palladacycles. According to the prinꢀ
ciples of NMR spectroscopy,46,56 this parameter is deterꢀ
mined primarily by the degree of coplanarity of the
chain consisting of four bonds separating these nuclei
(1H—C—N—Pd—31P). The range of possible variations
of this parameter can be determined as follows. The values
(4JH,P = 6—8 Hz) for PPh3 derivatives of orthoꢀpalladated
benzaldimines with the αꢀmethine proton in a strictly
equatorial orientation can serve as the upper limit of this
range.57 From general considerations,56 this upper limit is
somewhat overestimated due to the presence of the double
bond in the chain of bonds separating the interacting
nuclei (1H—C=N—Pd—31P). The lower limit of this range
(4JH,P = 0 Hz) is determined by the absence of signs of
αꢀCH...31P spinꢀspin coupling for the quasiꢀaxial methine
proton in the spectra of phosphine adducts of αꢀunꢀ
substituted benzylaminate palladacycles.58—60 The conꢀ
This is also evidence that one NMe group in 3ꢀchloroꢀ
substituted complex 4 is in a more equatorial orientation,
whereas another NMe group is in a more axial orientaꢀ
tion. Therefore, the spectroscopic data are indicative of
substantial conformational stabilization of the palladacycle
as a result of the appearance of the chlorine atom at
position 3 of the aromatic ring.
The structure of new dimeric cyclopalladated comꢀ
plex 3 was confirmed by Xꢀray diffraction analysis of its
triphenylphosphine derivative 4. To estimate the influꢀ
ence of the chlorine atom in the phenylene ring on the
conformation of the palladacycle, we carried out Xꢀray
diffraction analysis of its unsubstituted analog 5. The moꢀ
lecular structures of racemic complexes 4 and 5 are shown
in Fig. 3. Selected bond lengths, bond angles, and torsion
C(4)
C(5)
C(34)
a
Cl(2)
C(33)
C(6)
C(25)
C(26)
C(24)
C(23)
C(3)
C(2)
C(32)
C(35)
C(1)
C(9)
4
C(31)
stant JH,P = 6.3 Hz for the αꢀCH proton in complex 4,
C(7)
C(8)
which is close to the upper limit of this range, indicates
that this proton is in a nearly equatorial position. This
corresponds to the quasiꢀaxial orientation of the αꢀMe
group at the carbon stereocenter in the λ(S) conformation
(see Fig. 2, a). For comparison, it should be noted that
C(36)
C(22) C(21)
P(1)
C(16)
Pd(1)
N(1)
C(11)
C(12)
C(13)
C(10)
4
the constant JH,P for the αꢀmethine proton decreases to
Cl(1)
4.7 Hz in the spectrum of complex 5 containing no subꢀ
stituents at position 3, which indicates that the palladaꢀ
cycle exists as an equilibrium mixture of two conformers,
λ(S) and δ(S), in comparable amounts.
C(15)
C(14)
The shift of the equilibrium between two conformers,
viz., δ(S) and λ(S), of the palladacycle in adduct 4 toward
one of these conformers can be additionally confirmed by
the following facts. The signals for the protons of two
diastereotopic NMe groups are shifted in the opposite
directions compared to their positions in the spectrum of
analog 5 containing the unsubstituted phenylene ring.
The downfield shift of one of these signals (∆δ +0.08)
indicates that this proton approaches the coordination
plane, e.g., to an anisotropy region of the chloride ligand
bound to palladium, whereas the signal of another NMe
group is shifted upfield (∆δ –0.12), which is associated
with the fact that it moves away from the Pd—Cl bond.
These shifts are quite significant taking into account the
statistical factor. The conclusion that the palladacycle in
adduct 4 exists predominantly in one of two possible conꢀ
formations is also confirmed by the fact that the differꢀ
ence between the coupling constants between the protons
of two NMe groups and the phosphorus nucleus in the
1H NMR spectrum of 4 (4JH,P = 3.6 and 1.7 Hz) is almost
twice as large as that for analog 5 containing the unꢀ
substituted phenylene fragment (4JH,P = 3.1 and 2.1 Hz).
C(4)
C(5)
C(6)
b
C(3)
C(15)
C(16)
C(34)
C(14)
C(33)
C(2)
C(7)
C(35)
C(1)
C(9)
N(1)
C(36)
C(32)
C(31)
C(13)
C(11)
C(12)
C(8)
P(1)
Pd(1)
C(21)
C(26)
C(10)
C(22)
Cl(1)
C(23)
C(25)
C(24)
Fig. 3. Molecular structure and the atomic numbering scheme
for the (S) enantiomers of triphenylphosphine complexes 4 (a)
and 5 (b).

Modification of CNꢀpalladacycle
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 9, September, 2005
2077
Table 3. Selected torsion angles in the structures of comꢀ
plexes 4 and 5
angles are given in Tables 1, 2, and 3, respectively. Phosꢀ
phine adduct 4 crystallizes in the chiral space group
P212121, and the unit cell contains four molecules of 4 of
an (S) configuration. Analog 5 crystallizes in the nonꢀ
Angle
τ/deg
Complex 4
Complex 5
Table 1. Selected bond lengths in the structures of comꢀ
plexes 4 and 5
Parameters of palladacycle
C(1)—Pd(1)—N(1)—C(7)
Pd(1)—N(1)—C(7)—C(2)
C(1)—C(2)—C(7)—N(1)
Pd(1)—C(1)—C(2)—C(7)
N(1)—Pd(1)—C(1)—C(2)
C(1)—C(2)—C(3)—Cl(2)
–38.54(0.12)
44.75(0.17)
–30.18(0.23)
–3.06(0.22)
23.42(0.14)
36.34(16)
–45.1(2)
34.2(3)
–3.3(3)
–18.88(17)
—
Bond
d/Å
Complex 4
Complex 5
Pd(1)—P(1)
Pd(1)—Cl(1)
Pd(1)—C(1)
Pd(1)—N(1)
P(1)—C(21)
P(1)—C(11)
P(1)—C(31)
N(1)—C(9)
N(1)—C(10)
N(1)—C(7)
C(1)—C(2)
C(2)—C(7)
C(7)—C(8)
C(7)—H(7)
Cl(2)—C(3)
2.2606(5)
2.3814(4)
2.007(2)
2.158(2)
1.817(2)
1.822(2)
1.832(2)
1.490(3)
1.495(2)
1.503(3)
1.412(3)
1.514(3)
1.521(3)
0.98(2)
2.2474(6)
2.4052(6)
1.998(2)
2.160(2)
1.828(2)
1.818(2)
1.828(2)
1.490(4)
1.479(4)
1.512(3)
1.414(3)
1.507(4)
1.518(4)
1.03(3)
–173.85(0.14)
Orientations of substituents in palladacycle
C(1)—Pd(1)—N(1)—C(9)
78.26(0.13)
–80.01(18)
158.9(2)
–87.4(3)
C(1)—Pd(1)—N(1)—C(10) –160.73(0.18)
C(1)—C(2)—C(7)—C(8)
91.30(0.22)
Orientation of PPh rings
C(1)—Pd(1)—P(1)—C(11)
C(1)—Pd(1)—P(1)—C(21)
C(1)—Pd(1)—P(1)—C(31)
153.12(0.09)
–86.64(0.09)
35.04(0.09)
82.76(10)
–158.64(10)
–40.83(11)
centrosymmetric space group Pbca, and the unit cell conꢀ
tains eight molecules of (S) and (R) configurations in an
equal ratio.
1.762(2)
Xꢀray diffraction data unambiguously confirmed the
cyclopalladated structure of complex 4 and the presence
of the chlorine atom in the phenylene fragment of the
benzylaminate ligand in the ortho position with respect to
the side chain (see Fig. 3, a).
Table 2. Selected bond angles in the structures of comꢀ
plexes 4 and 5
Angle
ω/deg
As can be seen from Tables 1 and 2, the geometric
parameters of molecule 4 are rather similar to those of
molecule 5. The Pd—C, Pd—N, Pd—P, and Pd—Cl bond
lengths in complexes 4 and 5 fall in the ranges typical of
triphenylphosphine adducts of fiveꢀmembered αꢀarylꢀ
alkylaminate palladacycles. Both complexes have slightly
tetrahedrally distorted squareꢀplanar structures. The angles
between the {NPdC}/{PPdCl} planes are 7.55(8) and
13.04°, respectively.* In both complexes, the coordinaꢀ
tion environment of the palladium(II) atom has the
transꢀ(P,N) geometry characteristic of this type of comꢀ
pounds. In both complexes, the distance between the aroꢀ
matic proton H(6), which is the nearest one to the site of
metallation, and the phosphorus atom of the auxiliary
ligand is shortened (2.98(2) and 3.03(3) Å, respectively)
and is smaller than or close to the sum of the van der
Waals radii of these atoms (~3.0 Å).61 This confirms that
Complex 4
Complex 5
C(1)—Pd(1)—N(1)
C(1)—Pd(1)—P(1)
N(1)—Pd(1)—P(1)
C(1)—Pd(1)—Cl(1)
N(1)—Pd(1)—Cl(1)
P(1)—Pd(1)—Cl(1)
C(21)—P(1)—Pd(1)
C(11)—P(1)—Pd(1)
C(31)—P(1)—Pd(1)
C(9)—N(1)—C(10)
C(9)—N(1)—C(7)
C(10)—N(1)—C(7)
C(9)—N(1)—Pd(1)
C(10)—N(1)—Pd(1)
C(7)—N(1)—Pd(1)
C(2)—C(1)—Pd(1)
C(1)—C(2)—C(7)
N(1)—C(7)—C(2)
N(1)—C(7)—C(8)
C(2)—C(7)—C(8)
N(1)—C(7)—H(7)
C(2)—C(7)—H(7)
C(21)—P(1)—C(11)
C(21)—P(1)—C(31)
C(11)—P(1)—C(31)
80.57(7)
91.95(5)
169.62(5)
172.28(6)
92.25(4)
95.53(2)
114.20(7)
113.32(7)
112.00(7)
106.7(2)
110.1(2)
110.6(2)
108.4(1)
117.6(1)
103.4(1)
111.6(1)
117.6(2)
106.5(2)
111.9(2)
110.1(2)
108.00(1)
107.00(1)
105.05(9)
106.90(9)
104.63(9)
80.32(9)
94.60(7)
170.47(6)
168.22(7)
94.16(6)
92.25(2)
111.80(8)
111.88(7)
118.95(8)
107.1(2)
108.5(2)
111.6(2)
110.2(2)
114.9(2)
104.4(2)
113.0(2)
117.2(2)
105.5(2)
111.9(2)
111.3(2)
—
1
the throughꢀspace H(6)...31P interaction can occur. The
orientation of the PPh ring nearest to the H(6) atom with
respect to this atom is consistent with the effects, which
1
are observed in the H NMR spectra and are associated
with anisotropy of the aromatic rings of the auxiliary
ligand. In the structures of complexes 4 and 5, the disꢀ
—
105.9(1)
101.5(1)
105.6(1)
* Hereinafter, the first and second parameters refer to comꢀ
plexes 4 and 5, respectively.

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Dunina et al.
Number of structures
tance between the H(6) atom and the center of the nearꢀ
est PPh ring is 3.31 and 3.59 Å, respectively.
14
12
10
8
A comparison of the conformational features of two
palladacycles in two maximum similar complexes in the
crystalline state is of most interest. Both palladacycles
adopt a twisted envelop conformation with the nitrogen
atom deviating from the mean plane through the other
four atoms. The angles between the {PdNC(7)} and
{PdC(1)C(2)C(7)} planes in the structures of complexes
4 and 5 have similar values (46.0(1) and 44.7(1)°, respecꢀ
tively). Both palladacycles are also characterized by apꢀ
proximately the same degree of nonplanarity, which is
described by the averaged absolute values of the intraꢀ
chelate torsion angles of 28.0 and 27.6°, respectively. Both
palladacycles adopt the λ(S) conformation as evidenced
from the negative values of the C(1)—Pd—N—C(7) torꢀ
sion angles (–38.5(1) and –36.3(2)°, respectively; see
Table 3). Quantitative differences are observed only in the
orientation of the substituents in the side chain of the
benzylaminate palladacycles. A comparison of the angles
between the corresponding bonds and the normal to the
mean coordination plane (mcpl) shows that the position
of the N—Meeq bond in the chlorinated palladacycle of
adduct 4 is somewhat closer to equatorial (69.2 and 62.9°),
the orientations of the axial N—Meax bond being almost
the same in both complexes (angles are 4.0 and 4.5°). This
is consistent with the aboveꢀmentioned difference in the
spectroscopic parameters of two complexes.
It is not surprising that the λ(S) conformation of the
starting (nonchlorinated) palladacycle in complex 5 is
stabilized in the crystal lattice taking into account its flexꢀ
ibility. Among an extensive series of crystallographiꢀ
cally characterized derivatives of αꢀmethylbenzylaminate
palladacycle containing chiral or achiral additional
ligands, we can find complexes containing palladacycles
either in the λ(S) or δ(S) conformation, depending on the
requirements imposed by either an auxiliary ligand or the
crystal lattice. This is quite evident from the distribution
histogram of the inclination angles of the Cα—C(Me)
bond with respect to the normal to mcpl presented in
Fig. 4. The histogram was constructed using the data on
αꢀmethylbenzylaminate palladacycles of type A1 and their
2ꢀnaphthyl analogs of type A2, which contain no substituꢀ
ents at position 3 of the metallated phenylene ring, taken
from the Cambridge Structural Database (CSD).*
Cα—Meax
Cα—Meeq
6
4
2
0
10
30
50
70
Angle/deg
Fig. 4. Distribution histogram of the angles between the
Cα—C(Me) bond and the normal to mcpl for derivatives
of αꢀmethylbenzylaminate and αꢀ(2ꢀnaphthyl)ethylaminate
palladacycles of type A containing no substituents at the
C(3) atom of the metallated phenylene fragment (64 entries,
103 fragments).
Of 103 nonequivalent palladacycles of type A, only
68 palladacycles adopt the λ(S) conformation with the
axial αꢀMe group (angles between the Cα—C(Me) bond
and the normal to mcpl vary in the range of ~0—40°). In
other 35 fragments comprising oneꢀthird of all data, the
metallacycle adopts the opposite δ(S) conformation with
the equatorial αꢀMe group (angles are ~50—90°). This
statistics is quite consistent with the aboveꢀgiven NMR
data for complex 5.
For comparison, another histogram (Fig. 5) repreꢀ
sents the distribution of the inclination angles of the
Me group at the αꢀC* stereocenter for diverse derivaꢀ
tives of modified αꢀmethylbenzylaminate palladacycles
containing a particular substituent at position 3 of
the metallated phenylene fragment. This set of comꢀ
pounds includes cyclopalladated derivatives of αꢀ(1ꢀnaphꢀ
thyl)ethylamines (B1 type), αꢀ(9ꢀphenanthryl)ethylamine
(B2 type), and α,2,5ꢀtrimethylbenzylamine (B3 type). In
these types of complexes, palladacycles are characterized
by high conformational stability in solutions. As expected,
essentially all data for these complexes fall within a narꢀ
row range of inclination angles of the bond with the axial
αꢀMe group (~0—28°) corresponding to the λ(S) conꢀ
formation of palladacycles. The only exception is the
fiveꢀcoordinate derivative of N,Nꢀdimethylꢀαꢀ(1ꢀnaphꢀ
thyl)ethylaminate palladacycle of type B1 containing the
macrocyclic diiminodiarsine ligand, for which this paꢀ
rameter increases to ~46 or ~68° depending on the
chosen base of the polyhedron.
* The CSD Version 5.25 (August 2004 Release) was used.

Modification of CNꢀpalladacycle
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 9, September, 2005
2079
Number of structures
18
tertiary benzylamine followed by its repeated cycloꢀ
palladation (Scheme 4).
Scheme 4
16
14
12
10
8
Cα—Meax
6
4
2
0
10
30
50
Angle/deg
Fig. 5. Distribution histogram of the angles between the
Cα—C(Me) bond and the normal to mcpl for derivatives of
αꢀ(1ꢀnaphthyl)ethylaminate and other palladacycles of type B
containing a substituent at the C(3) atom of the metallated
phenylene fragment (74 entries, 99 fragments).
The preliminary results of experiments with an opꢀ
tically active cyclopalladated derivative of prochiral
benzhydrylamine confirm this scheme.62 This pathway is
quite consistent with the known precedents of the formaꢀ
tion of mixtures of polychlorinated azobenzenes through
repeated cyclopalladation of the ligands modified in preꢀ
vious steps. The latter process provides the basis for a
procedure of catalytic chlorination of azobenzene in the
presence of palladium(II) chloride.17,40
Second, an important result is that the reaction with
chlorine dioxide produces new CPC rather than a free
modified ligand or its coordination compound with pallaꢀ
dium. This reaction opens a new way for conformational
stabilization of the readily available optically active (but
dynamically labile) αꢀmethylbenzylaminate palladacycle
due to steric control by the bulky chlorine atom located in
the vicinity of the side chain. This is of importance for the
chiral recognition ability of palladacycle. For compariꢀ
son, it should be noted that the known procedure for the
synthesis of orthoꢀchloroꢀsubstituted (S)ꢀαꢀmethylbenzylꢀ
amine (through Nꢀsilylation of primary amine, orthoꢀliꢀ
thiation, and subsequent chlorination with hexachloroetꢀ
hane)63 involves many steps and is very laborious (total
yield of 56%). An alternative approach to conformational
stabilization of αꢀmethylbenzylaminate palladacycles
based on a structural modification of the starting ligands,
which has been recently developed,64,65 is also more comꢀ
plicated. This approach requires the separation of enantiꢀ
omers either at the stage of racemic primary amine (for
example, in the case of the replacement of the Ph ring
with the 9ꢀphenanthryl fragment in CPC of type B2)65 or
at the stage of a cyclopalladated complex prepared from
The above results deserve detailed consideration in
two aspects.
First, we found that the cheap and commercially availꢀ
able reagent chlorine dioxide acts as a regioselective chloꢀ
rinating agent rather than as an oxidant with respect to
palladacycles. Since the direct replacement of the hydroꢀ
gen atom at position 3 of the aromatic ring seems to be
improbable because of both electronic and steric factors,
it is reasonable to assume that the process involves chloriꢀ
nation at the Pd—C bond to give orthoꢀchloroꢀsubstituted

2080
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 9, September, 2005
Dunina et al.
culated (%): C, 57.31; H, 4.81; N, 2.38. 31P NMR (CDCl3), δ:
this amine (in the case of the insertion of 2,5ꢀdimethyl
3
+37.96. 1H NMR (CDCl3), δ: 4.02 (dq, 1 H, αꢀCH, JH,H
=
groups into the Ph ring in CPC of type B3).64
3
3
6.3 Hz, JH,P = 6.3 Hz); 1.93 (d, 3 H, αꢀMe, JH,H = 6.3 Hz);
2.73 (d, 3 H, NMeax
,
3JH,P = 1.7 Hz); 2.85 (d, 3 H, NMeeq
,
Experimental
3JH,P = 3.6 Hz); 6.21 (ddd, 1 H, H(6), J5,6 = 7.7 Hz,
3
4J4,6 =1.0 Hz, JH,P = 6.2 Hz); 6.29 (t, 1 H, H(5), J5,4 = J5,6
≈
3
3
7.7 Hz); 6.80 (dd, 1 H, H(4), 3J4,5 = 7.7 Hz, 4J4,6 = 1.0 Hz); 7.35
(m, 6 H, Hm, PPh3); 7.41 (m, 3 H, Hp, PPh3); 7.70 (m, 6 H, Hо,
PPh3, 3JH,P = 11.3 Hz).
The 1H and 31P{1H} NMR spectra were recorded on a Varian
VXRꢀ400 spectrometer (400 and 169.1 MHz, respectively) in
CDCl3 at room temperature. The chemical shifts in the 1H NMR
spectra were determined relative to the internal standard (Me4Si),
and the chemical shifts in the 31P NMR spectra were measured
relative to the external standard (H3PO4). The assignment of the
signals was made using the homonuclear 1Hꢀ1H spinꢀspin
decoupling technique The melting point was measured using the
melting point indicator EMꢀMGU No. 49 in a sealed capillary
tube. The course of the reactions was monitored and the purities
of the compounds were checked by TLC on Silufol UVꢀ254.
The complexes were preparatively isolated by dry column chroꢀ
matography66 on silica gel Silpearl. The solvents were purified
by standard methods: chloroform and dichloromethane were
passed through a column with neutral Al2O3 (Brockmann acꢀ
tivity II, L 40/250) and distilled; benzene was refluxed over
sodium metal and distilled; acetone (special purity grade) and
hexane were distilled.
(R,S)ꢀChloroꢀ[2ꢀ(1ꢀdimethylaminoethyl)phenylꢀC,N ](triꢀ
phenylphosphineꢀP)palladium(II) (5) was synthesized according
to the method described earlier for the (S) enantiomer.55 After
chromatographic purification on a column (h = 2.5 cm, d =
2.5 cm, elution with diethyl ether—hexane mixtures with a poꢀ
larity gradient from 1 : 3 to 5 : 1), complex 5 was isolated as an
amorphous lightꢀyellow powder in 84% yield, m.p. (with
decomp.) 205—207 °C; Rf 0.53 (benzene—acetone, 5 : 1).
3
1H NMR (CDCl3), δ: 3.82 (dq, 1 H, αꢀCH, JH,H = 6.5 Hz,
3
3JH,P = 4.7 Hz); 1.80 (d, 3 H, αꢀMe, JH,H = 6.5 Hz); 2.85 (d,
3 H, NMeax, , =
3JH,P = 2.1 Hz); 2.77 (d, 3 H, NMeeq 3JH,P
3
4
3.1 Hz); 6.34 (ddd, 1 H, H(6), J6,5 = 7.5 Hz, J6,4 = 1.3 Hz,
JH,P = 6.2 Hz); 6.38 (dt, 1 H, H(5), 3J5,4 = 3J5,6 ≈ 7.5 Hz); 6.83
(ddd, 1 H, H(4), 3J4,5 = 3J4,3 ≈ 7.5 Hz, 4J4,6 = 1.3 Hz); 7.00 (dd,
Commercial chlorine dioxide as an aqueous solution
(3 g L–1) was used without additional purification; its concenꢀ
tration was determined by titration according to a known
method.67 Triphenylphosphine was twice recrystallized from a
benzene—hexane mixture. The racemic dimer of diꢀµꢀchloroꢀ
bis{2ꢀ(1ꢀdimethylaminoethyl)phenylꢀC,N}dipalladium(II) (1)
was synthesized according to a known procedure.54
Table 4. Crystallographic data, details of Xꢀray data collection,
and characteristics of structure refinement of complexes 4 and 5
Parameter
4
5
Molecular formula
Molecular weight
Temperature
Crystal system
Space group
a/Å
b/Å
c/Å
V/Å3
C28H28Cl2N1P1Pd1 C28H29Cl1N1P1Pd1
586.78
120(2)
552.34
95(2)
(R,S)ꢀDiꢀµꢀchlorobis[3ꢀchloroꢀ2ꢀ(1ꢀdimethylaminoꢀ
ethyl)phenylꢀC,N ]dipalladium(II) (3). An aqueous ClO2 solution
(15.8 mL) was added to a solution of complex 1 (0.1000 g,
0.172 mmol) in dichloromethane (5 mL), after which the color
of the organic layer changed from yellow to red. The reaction
mixture was stirred at room temperature for 18 h in the dark.
The organic layer was separated and washed with water
(2×3 mL). The aqueous fraction was extracted with CH2Cl2
(4 mL). The combined organic extracts were concentrated to
dryness. After chromatographic purification on a column
(h = 4 cm, d = 2.5 cm, hexane and benzene as the eluents)
complex 3 was isolated as an amorphous lightꢀyellow powder in
a yield of 0.0538 g (46%), m.p. (with decomp.) 241—243 °C;
Rf 0.77 (benzene—acetone, 25 : 1). Found (%): C, 37.40; H, 4.33;
N, 4.21. C20H26Cl4N2Pd2. Calculated (%): C, 37.01; H, 4.04;
N, 4.32. 1H NMR (CDCl3), δ: 3.80 (m, 1 H, αꢀCH); 1.81 (d,
Orthorhombic
P212121
Orthorhombic
Pbca
7.7195(1)
16.4007(3)
20.7317(3)
2624.74(7)
4
11.5040(8)
17.167(1)
25.160(2)
4968.9(6)
8
Z
dcalc/g cm–3
1.485
1.477
µ/mm–1
0.988
0.935
F(000)
1192
2256
θ Scan range/deg
Ranges of indices
1.58—27.50
–9 ≤ h ≤ 10
–21 ≤ k ≤ 17
–26 ≤ l ≤ 25
18405/5997
1.62—28.00
–15 ≤ h ≤ 15
–24 ≤ k ≤ 23
–34 ≤ l ≤ 35
50930/6000
Number of measured/
independent
3
3 H, αꢀMe, JH,H = 6.0 Hz); 2.61 and 2.91 (both s, 3 H each,
3
NMe); 7.05 (m, 1 H, H(6)); 6.80 (t, 1 H, H(5), J5,4 = 7.9 Hz,
reflections
3J5,6 = 7.9 Hz); 6.96 (d, 1 H, H(4), 3J4,5 = 7.9 Hz, 4J4,6 = 0.8 Hz).
(R,S)ꢀChloroꢀ[(3ꢀchloroꢀ2ꢀ(1ꢀdimethylaminoethyl)phenylꢀ
C,N ](triphenylphosphineꢀP)palladium(II) (4). An excess of PPh3
(0.0181 g, 0.0679 mmol) was added to a solution of complex 3
(0.0201 g, 0.0309 mmol) in benzene (2 mL). The reaction mixꢀ
ture was stirred at room temperature for 30 min and concenꢀ
trated to dryness. After chromatographic purification on a colꢀ
umn (h = 4 cm, d = 2.5 cm, hexane, benzene, and benꢀ
zene—acetone, 20 : 1, as the eluents), complex 4 was isolated as
an amorphous almost colorless powder in a yield of 0.0328 g
(90%), m.p. 205—208 °C; Rf 0.24 (benzene—acetone, 20 : 1).
Found (%): C, 56.93; H, 4.65; N, 2.16. C28H28Cl2NPPd. Calꢀ
Rint
0.0258
410
0.0717
406
Number of parameters
in refinement
R1 (I ≥ 2σ(I ))
wR2 (based on
all reflections)
Goodnessꢀofꢀfit on F 2
Flack parameter
Residual electron
density
0.0193
0.0465
0.0347
0.0769
1.040
–0.03(1)
0.468/–0.305
1.205
—
0.509/–0.626
(max/min)/e Å–3

Modification of CNꢀpalladacycle
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 9, September, 2005
2081
3
4
1 H, H(3), J3,4 = 7.5 Hz, J3,5 = 1.3 Hz); 7.35 (m, 6 H, Hm,
14. P. L. Alsters, J. Boersma, and G. van Koten, Organometalꢀ
lics, 1993, 12, 1629.
3
PPh3); 7.42 (m, 3 H, Hp, PPh3); 7.73 (m, 6 H, Hо, JH,P
=
11.4 Hz, PPh3).
15. R. Bhawmick, H. Biswas, P. Bandyopadhyay, and
A. Chakravorty, J. Organomet. Chem., 1995, 498, 81.
16. K. Kamaraj and D. Bandyopadhyay, Organometallics, 1999,
18, 438.
17. D. R. Fahey, J. Organomet. Chem., 1970, 27, 283.
18. H. B. Kagan, in Asymmertic Synthesis, Ed. J. D. Morrison,
Academic Press, Inc., London, 1985, 5, 1.
19. V. V. Dunina and I. P. Beletskaya, Zh. Org. Khim., 1992, 28,
2369 [Russ. J. Org. Chem., 1992, 28 (Engl. Transl.)].
20. S. T. Handy, Current Organic Chemistry, 2000, 4, 363.
21. R. P. Wayne, G. Poulet, P. Biggs, J. P. Burrows, R. A. Cox,
P. J. Crutzen, G. D. Hayman, M. E. Jenkin, G. Le Bras,
G. K. Moortgat, U. Platt, and R. N. Schindler, Atmos.
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23. A. V. Kuchin, S. A. Rubtsova, L. P. Karmanova, S. N.
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24. A. V. Kuchin, S. A. Rubtsova, I. V. Loginova, and S. N.
Subbotina, Zh. Org. Khim., 2000, 36, 1819 [Russ. J. Org.
Chem., 2000, 36 (Engl. Transl.)].
25. A. V. Kuchin, S. A. Rubtsova, and I. V. Loginova, Izv. Akad.
Nauk, Ser. Khim., 2001, 413 [Russ. Chem. Bull., Int. Ed.,
2001, 50, 432].
26. O. M. Lezina, S. A. Rubtsova, and A. V. Kuchin, Izv. Akad.
Nauk, Ser. Khim., 2003, 1779 [Russ. Chem. Bull., Int. Ed.,
2003, 52, 1877].
27. A. V. Kuchin and L. L. Frolova, Izv. Akad. Nauk, Ser. Khim.,
2000, 1658 [Russ. Chem. Bull., Int. Ed., 2000, 49, 1647].
28. A. V. Kuchin, I. A. Dvornikova, and I. Yu. Nalimova, Izv.
Akad. Nauk, Ser. Khim., 1999, 2025 [Russ. Chem. Bull., 1999,
48 (Engl. Transl.)].
29. U. Glabisz, J. Chem. Soc., Sect. A, 1966, 211.
30. J. Jalowiczor, Zesz. Nauk. Politech. Szczecin., Chem.,
1968, 8, 105.
31. B. O. Lindgren and B. Ericsson, Acta Chem. Scand., 1969,
23, 3451.
32. W. J. Masschelein, Chlorine Dioxide: Chemistry and Environꢀ
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Arbor Publishers, Inc., 1979, 418 p.
Xꢀray diffraction study. Crystals of complexes 4 and 5 suitꢀ
able for Xꢀray diffraction study were grown by slow crystallizaꢀ
tion from benzene—dichloromethane—hexane and chloroform—
heptane—hexane solvent systems, respectively. Xꢀray diffracꢀ
tion data sets were collected on a Bruker SMART diffractometer
(MoKα radiation, λ = 0.71073 Å, graphite monochromator).
Crystallographic data, details of Xꢀray data collection, and charꢀ
acteristics of structure refinement for complexes 4 and 5 are
given in Table 4. Absorption corrections were applied based
on the intensities of equivalent reflections. The structures
were solved by direct methods (SHELXSꢀ86).68 All nonꢀ
hydrogen atoms were refined by the fullꢀmatrix leastꢀsquares
method against F2 with anisotropic displacement parameters
(SHELXLꢀ97).69 The hydrogen atoms in both structures were
located from difference Fourier maps and refined isotropically.
The crystallographic data for the structures of compounds 4
and 5 were deposited with the Cambridge Structural Database
(refcodes BANMAF and XOZPAD, respectively).
This study was financially supported by the Council
on Grants of the President of the Russian Federation
(Program for State Support of Young Scientists, Grant
MKꢀ3697.2004.3), the Russian Science Support Founꢀ
dation, the Russian Foundation for Basic Research
(Project No. 04ꢀ03ꢀ32986), and the NATO (Grant
PST.CLG.979757).
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Received April 4, 2005;
in revised form June 14, 2005