Palladium-catalyzed activation of E-E and C-E bonds in diaryl dichalcogenides (E = S, Se) under microwave irradiation conditions

Article abstract of DOI:10.1007/s11172-005-0292-6

The first example of palladium-catalyzed stereoselective addition of diphenyl disulfide and diphenyl diselenide to the triple bond of terminal alkynes under microwave irradiation conditions is described. It was found that both the element-element (E-E) and carbon-element bonds can be activated in the catalytic system studied. The products of both reactions were isolated in quantitative yields. According to quantum-chemical calculations, the reaction mechanism involves the oxidative addition of the E-E bond to Pd⁰. Depending on the microwave power and reaction conditions, the next stage is either the reaction with alkyne or the carbon-element bond activation. The product of the oxidative addition of Ph₂Se₂ to Pd ⁰, namely, dinuclear complex [Pd₂(SePh) ₄(PPh_{3 2}], was detected by ³¹P{ ¹H}NMR spectroscopy directly in the Ph₂Se ₂/PPh₃ melt formed under microwave irradiation conditions.

Full text of DOI:10.1007/s11172-005-0292-6

576
Russian Chemical Bulletin, International Edition, Vol. 54, No. 3, pp. 576—587, March, 2005
Palladiumꢀcatalyzed activation of E—E and C—E bonds
in diaryl dichalcogenides (E = S, Se) under microwave irradiation conditions
a
b
V. P. Ananikov,a N. V. Orlov, and I. P. Beletskaya
ꢀ
ꢀ
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Eꢀmail: val@ioc.ac.ru
bDepartment of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119899 Moscow, Russian Federation.
Fax: +7 (095) 939 3618. Eꢀmail: beletska@org.chem.msu.ru
The first example of palladiumꢀcatalyzed stereoselective addition of diphenyl disulfide
and diphenyl diselenide to the triple bond of terminal alkynes under microwave irradiation
conditions is described. It was found that both the element—element (E—E) and carꢀ
bon—element bonds can be activated in the catalytic system studied. The products of both
reactions were isolated in quantitative yields. According to quantumꢀchemical calculations,
the reaction mechanism involves the oxidative addition of the E—E bond to Pd0. Depending on
the microwave power and reaction conditions, the next stage is either the reaction with alkyne
or the carbon—element bond activation. The product of the oxidative addition of Ph2Se2
to Pd0, namely, dinuclear complex [Pd2(SePh)4(PPh3)2], was detected by 31P{1H} NMR
spectroscopy directly in the Ph2Se2/PPh3 melt formed under microwave irradiation conꢀ
ditions.
Key words: palladium complexes, catalysis, microwave irradiation, diaryl dichalcogenides,
element—element bond activation, carbon—element bond activation, alkynes, vinyl sulfides,
vinyl selenides, quantumꢀchemical calculations.
The development of cheap and environmentally
metal to give a Pd(EAr)2(PPh3)2 complex, which then
undergoes dimerization into a dinuclear complex
Pd2(EAr)4(PPh3)2. The structures of the dinuclear comꢀ
plexes were established by Xꢀray analysis13—16 and their
identification under the catalytic reaction conditions
was done by NMR spectroscopy.7,8,11,12 Achievement
of a nearly 100% yield of the reaction product,
Zꢀ(ArE)HC=C(ArE)R, requires an excess of the ligand
(PPh3/[Pd] > 6), which precludes polymerization of the
catalyst and formation of insoluble palladiumꢀcontaining
polymer [Pd(EAr)2]n inactive in this reaction.9,10 Studies
of the catalytic reaction in solution revealed no E—C
bond cleavage under the action of palladium complexes.
friendly methods of synthesis is the leading trend in modꢀ
ern metal complex catalysis. One of the most promising
methods for solving these problems is to carry out cataꢀ
lytic reactions in the absence of a solvent under microꢀ
wave irradiation conditions.1—6 Recently, we have perꢀ
formed the addition of diaryl dichalcogenides to alkynes
in Ar2E2/PPh3 melt under solventꢀfree conditions; the
process was catalyzed by palladium complexes.7,8 Conꢀ
ducting a reaction under solventꢀfree conditions offers
such advantages as shortening of reaction time, high staꢀ
bility of the catalyst and possibility of its recycling, and
significant simplification of the isolation and purification
of the reaction product.7,8
In the present work, we report palladiumꢀcatalyzed
addition of diaryl dichalcogenides Ar2E2 (E = S (1a),
Se (1b)) to alkynes R—C≡CH (2a—d) in melt under miꢀ
crowave irradiation conditions. Activation of not only the
E—E but also the E—C bond in the systems under study
was revealed.
Palladiumꢀcatalyzed addition of Ar2E2 to alkynes alꢀ
lows a highly stereoselective formation of two new C—E
bonds in a single reaction step.9—12 The catalytic cycle
begins with the oxidative addition of ArE—EAr to the
Experimental
NMR spectra were recorded on a Bruker DRXꢀ500 specꢀ
trometer operating at 500.1, 202.5, 125.8, and 95.4 MHz for 1H,
31P, 13C and, 77Se nuclei, respectively. All measurements were
carried out at room temperature. 1H and 13C NMR chemical
shifts are reported relative to the corresponding solvent signals
used as internal references; external references for heteroꢀ
nuclear experiments were 85% H3PO4/H2O (δ(31P) 0.0) and
Se2Ph2/CDCl3 (δ(77Se) 463.0).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 569—580, March, 2005.
1066ꢀ5285/05/5403ꢀ0576 © 2005 Springer Science+Business Media, Inc.

Activation of E—E and E—C bonds
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
577
To carry out reactions under microwave irradiation condiꢀ
tions, a domestic microwave oven was used, with a 100% power
corresponding to 900 W.
Table 2. Reactions of diphenyl disulfide (1a) and diphenyl
diselenide (1b) with phosphorusꢀcontaining compounds 4 under
microwave irradiation conditionsa
Catalytic addition of diaryl dichalcogenides to alkynes (synꢀ
thesis of compounds 3a—h). A mixture of Ar2E2 (0.5 mmol) and
PPh3 (0.1 mmol for E = S and 0.2 mmol for E = Se) in a tube
was heated in the microwave oven at a power of 450 W until the
formation of a homogeneous melt. Then, 0.01 mmol of Pd(OAc)2
(2 mol.%) was added to the melt and the mixture was shaken
until complete dissolution of the salt and formation of a homoꢀ
geneous dark brown melt. Alkyne (0.75 mmol) was added to the
melt and the reaction mixture was placed in the microwave
oven. The reaction was carried out in a tube with a screw cup at
a microwave power of 450 W for 15 min (E = S) and at 180 W for
100 min (E = Se). After completion of the reaction, the nonꢀ
consumed alkyne was distilled off on a rotary evaporator. Chloꢀ
roform (5 mL) was added to the mixture obtained and preꢀ
adsorption on L40/100 silica gel was carried out. The product
was purified by flash chromatography on L5/40 silica gel (with a
hexane—chloroform mixture as an eluent) and dried in vacuo.
The product yields are listed in Table 1. The structures of the
products were established by 1H, 13C, and 77Se NMR spectroꢀ
scopy based on the published data.7—12 The stereochemistry of
the products was established by 2D NOESY and COSYꢀLR
NMR spectroscopy.
Catalytic reactions of diaryl dichalcogenides with triaryl(triꢀ
alkyl)phosphines, triaryl(trialkyl) phosphites, and bidentate phosꢀ
phines. A mixture of Ar2E2 (0.5 mmol) and PR´3 (0.5 mmol) in a
tube was heated in the microwave oven at a power of 450 W until
the formation of a homogeneous melt. Then, 0.01 mmol of
Pd(OAc)2 (2 mol.%) was added to the melt and the mixture was
shaken until complete dissolution of the salt and formation of a
homogeneous dark brown melt. The reaction was conducted in
a tube with a screw cup at a microwave power in the range
450—900 W for 5 to 15 min. The structures of products obtained
were established by 1H and 31P{1H} NMR spectroscopy. The
product yields are listed in Table 2.
Entry Ph2E2
4
Yield b (%)
5
6
1
2
3
4
5
6
7
8
9
1b
1a
1b
1a
1b
1b
1b
1b
1b
PPh3
PPh3
PPh3
PPh3
5b, 10
5a, 5
6b, 10
6a, 5
5b, 96 (92)
5a, 53
5c, 66
6b, 96 (94)
6a, 53
6b, 66
PBu3
P(OBun)3
P(OPh)3
DPPE
DPPB
5d, 23
5e, 86
5f, 97
6b, 23
6b, 86
6b, 97c
6b, 97c
5g, 96
a The reaction was carried out in a tube with a screw cup conꢀ
taining 0.5 mmol of Ph2E2 and 0.5 mmol of PR´3 at a microwave
power of 900 W for 15 min. Entries 1 and 2 were performed
without catalyst and entries 3—9 were performed with 2 mol.%
Pd(OAc)2 as a catalyst.
b Determined by NMR spectroscopy with respect to the initial
amount of Ph2E2; the isolated yield is given in parentheses (see
Experimental).
c A mixture of monoselenide and diselenide of the bidentate
phosphine.
Isolation of Ph2Se and Se=PPh3. After completion of the
reactions (see above), chloroform (5 mL) was added to the melt
and preꢀadsorption on L40/100 silica gel was carried out. Prodꢀ
ucts were purified by flash chromatography on L5/40 silica gel
(with a hexane—ethyl acetate mixture as eluent) and dried
in vacuo. The structures of the products were established by H
and 31P{1H} NMR spectroscopy. The yields were 94% (Ph2Se)
and 92% (Se=PPh3).
1
Calculation Procedure
Table 1. Yields in addition reactions of diphenyl disulfide (1a)
and diphenyl diselenide (1b) to alkynes R—C≡CH (2a—d)*
Geometry optimization and energy calculations were perꢀ
formed using the B3LYP hybrid potential17—19 and the Lanl2dz
basis set20—23 augmented with polarization dꢀfunctions for the
C, P, S, and Se atoms.24,25 The character of the stationary
points located was checked by calculating the eigenvalues of the
Hessian matrix (intermediates were characterized by real freꢀ
quencies and transition states were characterized by one imagiꢀ
nary frequency). The character of the most important transition
states was verified by the IRC calculations. The thermodynamic
functions were calculated according to the "harmonic oscillaꢀ
tor—rigid rotator" model. All calculations were performed using
the GAUSSIANꢀ03 suite of programs.26 The molecular strucꢀ
tures and vibrations were visualized using the MOLDEN graphic
package.27
To reduce the computational cost, calculations were perꢀ
formed for a number of model reactions in which the phosphine
ligand is simulated by the PH3 group and the phenyl substituents
are simulated by Me groups. Earlier, numerous quantumꢀchemiꢀ
cal studies of various catalytic reactions showed28—30 that such
model systems provide a correct qualitative description of major
trends.
Entry Ph2E2 Alkyne
R
Product
Yield** (%)
1
2
3
4
5
6
7
8
1a
1b
1a
1b
1a
1b
1a
1b
2a
2a
2b
2b
2c
2c
2d
2d
nꢀC5H11
nꢀC5H11
3a
3b
3c
3d
3e
3f
99 (85)
99 (86)
99 (82)
99 (85)
99 (92)
99 (97)
97 (80)
96 (79)
(СН2)2ОН
(СН2)2ОН
СН2ОMe
СН2ОMe
СН2NMe2
СН2NMe2
3g
3h
* The reaction was carried out in a hermetically closed tube
containing 0.5 mmol of Ph2E2, 0.75 mmol of alkyne, 2 mol.% of
Pd(OAc)2, and PPh3 (20 mol.% for E = S and 40 mol.% for
E = Se) at a microwave power of 180 W for 100 min for the
diphenyl diselenide addition and at 450 W for 15 min for the
diphenyl disulfide addition.
** Determined by NMR spectroscopy with respect to the initial
amount of Ph2E2; the isolated yield is given in parentheses (see
Experimental).

578
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Ananikov et al.
The catalytic cycle involving mononuclear and dinuclear
palladium complexes was calculated for reactions (1) and (2),
respectively:
spectroscopic data, the addition of Ph2S2 proceeds with
an almost 100% yield (see Table 3, entry 3), in contrast to
the addition of Ph2Se2 where the product yield was
only 40% (see Table 3, entry 4). In the reaction with
compound 1a, the melt remains homogeneous. The reacꢀ
tion with compound 1b is accompanied by the formation
of a dark brown residue of [Pd(SePh)2]n polymer, which
indicates a deficiency of the ligand. An increase in the
amount of triphenylphosphine leads to an increase in the
yield of compound 3b to 85%, which, however, does
not reach a quantitative level (see Table 3, entry 5).
PH3 + MeSeSeMe + Pd(SeMe)2(PH3)2
Se=PH3 + MeSeMe + Pd(SeMe)2(PH3)2, (1)
PH3 + MeSeSeMe + Pd2(SeMe)4(PH3)2
Se=PH3 + MeSeMe + Pd2(SeMe)4(PH3)2. (2)
Results and Discussion
1
Microwaveꢀassisted addition of diaryl dichalcogenides
1 to alkynes 2 was studied taking the model reactions of
diphenyl disulfide (1a) and diphenyl diselenide (1b) with
heptꢀ1ꢀyne (R = C5H11). The reactions were conducted
under solventꢀfree conditions in the presence of Pd(OAc)2
(2 mol.%) and triphenylphosphine (20—40 mol.%) as a
ligand (Scheme 1).
31P{1H} and H NMR analyses of the reaction mixture
revealed a transformation of PPh3 into Se=PPh3 (see
Table 3, entries 4 and 5) and the formation of Ph2Se in a
Ph2Se : Se=PPh3 ratio of 1 : 1 (entries 4 and 5).
Thus, the microwaveꢀassisted addition of dichalcoꢀ
genides to alkynes (see Scheme 1) is accompanied by a
side reaction of Ph2E2 (1) with PPh3 (4) resulting in
E=PPh3 (5) (Scheme 2). A specific feature of the side
reaction is the cleavage of the E—C bond, which has not
earlier been observed in the thermal reactions where only
palladiumꢀcatalyzed activation of the E—E bond occurred
(see Scheme 1). The side reaction is catalyzed by pallaꢀ
dium complexes (cf. entries 2 and 5 in Table 3), being
much more characteristic of compound 1b (cf. entries 3
and 4 in Table 3). In the addition of Ph2Se2 to heptꢀ1ꢀ
yne, nearly 40% of the ligand added is converted into
Se=PPh3 (see Table 3, entries 4 and 5). A dramatic deꢀ
crease in the yield of the product 3b in the presence of a
small excess of PPh3 (see Table 3, entry 4) is due to the
fact that a decrease in the amount of ligand is followed by
fast deactivation of the catalyst owing to formation of an
insoluble polymer, [Pd(SePh)2]n.
Scheme 1
E = S (1a, 3a,c,e,g), Se (1b, 3b,d,f,h);
R = nꢀC5H11 (2a, 3a,b), CH2CH2OH (2b, 3c,d),
CH2OMe (2c, 3e,f), CH2NMe2 (2d, 3g,h);
L = PPh3, P(OBun)3, P(OPh)3 etc.
Microwave heating leads to formation of a dark brown
melt. In the absence of palladium complexes, no reaction
1
occurs (Table 3, entries 1 and 2). According to H NMR
Table 3. Addition of diphenyl disulfide (1a) and diphenyl
diselenide (1b) to heptꢀ1ꢀyne under microwave irradiation conꢀ
ditions*
Scheme 2
Entry Ph2E2
Catalyst
(mol.%)
Product
Yield** (%)
E=PPh3
3
The side reaction was studied under alkyneꢀfree conꢀ
ditions using a large number of phosphorusꢀcontaining
compounds (see Scheme 2 and Table 2). Products 5 and 6
are formed in high yields only in the presence of catalytic
amounts of palladium complexes (see Table 2, cf. enꢀ
tries 1, 2 and 3, 4). Compound 1b is converted into dipheꢀ
nyl selenide 6b in quantitative yield (see Table 2, entry 3).
Diphenyl disulfide (1a) is much less reactive (see Table 2,
entry 4). Compound 1b reacts with tributylphosphine,
tributyl phosphite, and triphenyl phosphite (see Table 2,
entries 5—7) under microwave irradiation conditions. The
low yield of compound 5 in the reaction with tributyl
phosphite is due to a noncatalytic side reaction similar to
the Arbuzov rearrangement, which was confirmed by
1
2
3
1a
1b
1a
PPh3 (20)
PPh3 (40)
Pd(OAc)2 (2),
PPh3 (20)
Pd(OAc)2 (2),
PPh3 (20)
—
—
3a
0
0
98
0
0
1 (5)
4
5
1b
1b
3b
3b
40
85
9 (45)
Pd(OAc)2 (2),
PPh3 (40)
15 (37)
* The reaction was conducted in a tube with a screw cup conꢀ
taining 0.5 mmol of Ph2E2 and 0.75 mmol of heptꢀ1ꢀyne at a
microwave power 900 W for 5 min.
** Determined by NMR spectroscopy with respect to the initial
amount of Ph2E2; the conversion of PPh3 calculated with reꢀ
spect to the initial amount of ligand is given in parentheses.

Activation of E—E and E—C bonds
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
579
31P NMR spectroscopy (see Table 2, entry 6). Comꢀ
pound 1b also reacts with chelateꢀforming phosphines,
namely, bis(diphenylphosphino)ethane (DPPE) and
bis(diphenylphosphino)butane (DPPB) (see Table 2, enꢀ
tries 8 and 9).
When carried out under optimized conditions, the adꢀ
ditions of diphenyl diselenide and diphenyl disulfide to
various alkynes at 180 and 450 W, respectively, gave nearly
100% yields of the corresponding products (see Table 1)
with high stereoselectivity (Z/E > 97/3). The configuraꢀ
tion of the double bond in the reaction products was
established by the 2D COSYꢀLR and NOESY NMR
methods. The yields of the reaction products isolated by
flash chromatography were 79—97%. The addition of
diphenyl disulfide to alkynes can be performed at a miꢀ
crowave power of 900 W for 5 min and at 180 W for
100 min.
In spite of the longer reaction time, the lower microꢀ
wave power is more preferable because of the higher
stereoselectivity of the reaction achieved in this case. High
microwave power and long heating time lead to the forꢀ
mation of the Eꢀisomer of the product (up to 10—20%)
due to the double bond isomerization or noncatalytic adꢀ
dition of diaryl dichalcogenides to alkynes by a radical
mechanism.
In order to compare conventional heating and microꢀ
waveꢀassisted heating, we additionally studied the reacꢀ
tions of PPh3 with compounds 1a,b (see Scheme 2) in a
thermostated oil bath with magnetic stirring. The nonꢀ
catalytic reaction does not proceed in toluene upon heatꢀ
ing and in melt under solventꢀfree conditions (Table 5,
entries 1—3). The addition of palladium acetate (2 mol.%)
followed by heating of the melt at 140 °C for 30 min leads
to a 85% yield of the reaction product of 1b and PPh3;
further heating of the melt leads to a virtually quantitative
yield of the products (see Table 5, entries 6 and 7). The
halfꢀconversion time determined from kinetic measureꢀ
ments was 17 min. At temperatures below 140 °C, the
product yields were very low (see Table 5, entries 4 and 5).
Microwaveꢀassisted catalytic reactions of phosphines
with diaryl dichalcogenides can be used for synthetic purꢀ
poses to obtain products 5 and 6. Both products, Ph2Se
and Se=PPh3, were isolated by flash chromatography in
92 and 94% yields, respectively (see Table 2, entry 3).
As expected, the yields of product 3b in the catalytic
addition of Ph2Se2 to heptꢀ1ꢀyne (see Scheme 1) carried
out with different ligands were far from 100% (78% with
L = P(OBun)3, 53% with L = P(OPh)3, and only trace
amounts of product 3b were detected in the reaction with
the chelateꢀforming ligand, DPPE). Similar results were
obtained in studies of conventional thermal reactions in
toluene and benzene with chelateꢀforming ligands.7—12
By varying the microwave power, we succeeded in
preparing product 3b in virtually 100% yield (Table 4).
A decrease in the microwave power causes slowing down
of the side reaction of PPh3 with Ph2Se2, which leads to a
decrease in the yields of compounds 5b and 6b and to an
increase in the yield of product 3b (see Table 4, enꢀ
tries 4—6). In particular, at a microwave power of 180 W
the reaction proceeds with a nearly 100% yield (Table 4,
entry 6). As the microwave power decreases, the catalytic
reaction also slows down, which requires an increase in
the reaction time to 100 min.
The yield of product 3a in the catalytic reaction of
Ph2S2 with heptꢀ1ꢀyne is independent of microwave power
(see Table 4, entries 1—3), because in this case the side
reaction (ligand conversion) proceeds much more slowly.
The catalytic reaction is completed in 5 min and provides
an almost 100% yield of product 3a (see Table 4).
Table 5. Reactions of diphenyl disulfide (1a) and diphenyl
diselenide (1b) with triphenylphosphine under conventional
heating conditions*
Table 4. Effect of microwave power on product yields in the
addition reactions of diphenyl disulfide (1a) and diphenyl
diselenide (1b) to heptꢀ1ꢀyne*
Entry Ph2E2 Solvent T/°C t/min Pd(OAc)2 Yield** (%)
(mol.%)
5
6
Entry Ph2E2
Power
/W
t/min
Yield** (%)
1
2
3
4
5
6
7
8
1b Toluene 100
120
120
180
120
120
30
—
—
—
2
2
2
0
0
2
11
4
85
94
0
0
0
2
11
4
85
94
0
3
5
6
1b
1b
—
—
100
140
1
2
3
4
5
6
1a
1a
1a
1b
1b
1b
900
450
180
900
450
180
5
10
100
5
10
100
98
97
99
39
68
99
1
0
0
10
14
1
1
0
0
10
14
1
1b Toluene 100
1b
1b
1b
1a
—
—
—
—
100
140
140
140
60
30
2
2
* Reactions were carried out in a tube with a screw cup containꢀ
ing 0.5 mmol of Ph2E2, 0.75 mmol of heptꢀ1ꢀyne, 2 mol.%
Pd(OAc)2, and 20 mol.% of PPh3.
** Determined by NMR spectroscopy with respect to the initial
amount of Ph2E2.
* Reactions were carried out in a tube with a screw cup containꢀ
ing 0.5 mmol of Ph2E2 and 0.5 mmol of PR´3. The tubes were
placed in a thermostatted oil bath with magnetic stirring.
** Determined by NMR spectroscopy with respect to the initial
amount of Ph2E2.

580
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Ananikov et al.
No reaction of disulfide 1a with PPh3 occurred even at
140 °C (see Table 5, entry 8). Thus, microwave heating
allows the temperatures above 140 °C to be achieved rapꢀ
idly, which substantially accelerates the formation of prodꢀ
ucts 5 and 6 (cf. Tables 2 and 5).
In previous studies13—16 of the mechanism of convenꢀ
tional thermal reaction it was established that the oxidaꢀ
tive addition of compounds Ph2E2 (E = S, Se) to Pd0/PPh3
results in complexes [Pd(EPh)2(PPh3)2], which can unꢀ
dergo dimerization into [Pd2(EPh)4(PPh3)2] dinuclear
complexes under the reaction conditions. Recently,7,8 we
have shown that dinuclear complexes are also formed in a
melt under solventꢀfree conditions. To establish the strucꢀ
ture of the intermediates formed under microwave irraꢀ
diation conditions, we performed a special NMR study.
A Ph2Se2/PPh3 mixture was melted by exposure to microꢀ
wave irradiation directly in the NMR tube, Pd(OAc)2 was
added to the melt, and the mixture was heated in the
microwave oven (450 W) for 2 min. The 31P{1H} NMR
spectrum of the reaction mixture exhibited the signals at
δ 34.7, 27.0, 25.6, 24.6, 21.2, 16.7, and –4.6. The sigꢀ
nals at δ 34.7, 24.6, and –4.6 correspond to Se=PPh3,
O=PPh3, and PPh3, respectively. The signals at δ 27.0
and 25.6 can be assigned to dinuclear complexes,
transꢀ[Pd2(SePh)4(PPh3)2] and cisꢀ[Pd2(SePh)4(PPh3)2],
respectively. The structures of related complexes were
established13—16 by Xꢀray analysis and NMR spectrosꢀ
copy. The signals at δ 21.2 and 16.7 can be attributed to
mononuclear complexes, transꢀ[Pd(SePh)2(PPh3)2] and
cisꢀ[Pd(SePh)2(PPh3)2], respectively, but unambiguous
proof of the structures of these complexes based on the
31P NMR spectrum is impossible. Thus, our 31P{1H} NMR
study revealed the formation of the same intermediate
dinuclear complexes in melt under microwave irradiation
conditions as those formed in conventional thermal reacꢀ
tions.7,8
Fig. 1. Potential energy surface calculated for the oxidative adꢀ
dition reaction of Se—Se and Se—C bonds to palladium comꢀ
plexes.
bond also involves the oxidative addition to Pd0. To clarify
the issue, we carried out a density functional quantumꢀ
chemical study of the reaction of Me2Se2 with PH3 (see
Scheme 2) with the B3LYP density functional method
and the Lanl2dz(d) basis set (the model system was deꢀ
scribed in the Experimental).
Quantumꢀchemical calculations showed that both oxiꢀ
dative addition reactions begin with preꢀcoordination of
the diselenide to the palladium atom (Scheme 3, Fig. 1
and 2) and formation of intermediate II. Both reactions
have threeꢀcenter transition states, IIIꢀTS and VꢀTS, in
which two new bonds with the metal atom are formed
simultaneously with cleavage of the Se—Se or C—Se bond
(see Fig. 1). The transition state VꢀTS was more "late" in
character compared to IIIꢀTS, as is evident from the
Pd—Se bond lengths equal to 2.431 and 2.538 Å, respecꢀ
tively (see Fig. 2). The calculated geometric parameters are
in good agreement with the energy characteristics. The
oxidative addition of the Se—Se bond to the palladium
complex (II → IIIꢀTS → IV) is characterized by an actiꢀ
vation barrier, ∆E≠, of 8.4 kcal mol–1 and an energy gain,
∆E, of –5.1 kcal mol–1. The oxidative addition of the
C—Se bond to the palladium complex (II → VꢀTS → VI)
is characterized by a much higher activation barrier
A commonly accepted mechanism of the element—elꢀ
ement bond activation in palladiumꢀcatalyzed addition to
alkynes begins with oxidative addition of the E—E bond
to Pd0. It is logical to assume that activation of the C—E
∆E≠ = 25.9 kcal mol–1 and energy loss ∆E = 5.2 kcal mol–1
.
Scheme 3

Activation of E—E and E—C bonds
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
581
P
Se
P
Se
2.538
C
C
C
2.365
2.412
2.521
Pd
Se
Pd
C
2.693
P
Se
P
C
P
Se
Se
C
P
P
IIIꢀTS
IV
2.327
2.351
2.547
1.988
2.402
2.366
Pd
Pd
P
Se
Se
P
2.306
P
C
C
2.098
Pd
C
2.270
C
2.437
2.414
2.350
2.437
Pd
Se
C
I
II
Se
2.431
Se
2.519
P
P
Se
C
VꢀTS
VI
Fig. 2. Molecular structures of compounds I—VI optimized by the B3LYP/Lanl2dz(d) method.
The reaction products, namely, complexes IV and VI,
have a square planar structure (see Fig. 2) typical of PdII.
Complex IV is 10.3 kcal mol–1 more stable than comꢀ
plex VI.
In this case, the oxidative addition of the C—Se bond
can be considered as hardly probable compared to the
oxidative addition of the Se—Se bond. This means that
cleavage of the selenium—carbon bond and formation of
a new selenium—phosphorus bond occurs in the next
reaction step and involves palladium(II) chalcogenide
complexes.
A
comparison of the Pd—P bond lengths in
Fig. 3. Potential energy surface of 1,3ꢀ and 1,2ꢀshifts of the
Me group involving mononuclear palladium complexes.
transꢀposition relative to the Me group and SeCH3 fragꢀ
ments (see Fig. 2) gives the following order of the trans inꢀ
fluence of the ligands is as follows: CH3 > SeCH3.
In recent studies13—16 of the oxidative addition reꢀ
action in solution, it was shown that the initially
formed complex Pd(EAr)2L2 undergoes dimerization
into a dinuclear complex Pd2(EAr)4L2. Therefore, in orꢀ
der to clarify the reaction mechanism, we performed
quantumꢀchemical calculations of both complexes, viz.,
mononuclear Pd(SeCH3)2(PH3)2, and dinuclear
Pd2(SeCH3)4(PH3)2.
The calculated pathways of formation of compounds
SeMe2 (X) and Se=PH3 (XI) involving mononuclear palꢀ
ladium complexes are shown in Scheme 4 and in Fig. 3.
Scheme 4

582
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Ananikov et al.
Se—С = 1.986
Se
P
P
2.534
2.595
P
P
Se
Se
Se
C
2.767
2.359
2.414
2.365
2.322
2.373
2.331
2.521
2.489
2.439
2.473
2.432
2.463
Pd
Se
Pd
Se
VIIꢀTS
C
Pd
Pd
C
2.605
C
2.698
2.376
P
P
C
C
P
Se
P
P
Se—С 1.971
IX
IV
VIII
+
Se
1.975
Pd—P = 2.415
Se(1)—С(1) = 2.914
Pd—С(1) = 2.193
Se(1)—С(1) = 3.088
Pd—С(1) = 2.153
Pd—P = 2.418
P
C
C
2.540
P
Se(1)
Se(1)
2.431
C
Se(1)
X
P
2.394
2.433
2.497
C(1)
Se2Me2
C(1)
Pd
Pd
Pd
Pd—P = 2.446
2.517
C
C
Se
2.118
P
P
Se(2)
Pd—Se(2) = 2.493
Se(2)—С(1) = 3.367
Se(2)
Pd—Se(2) = 2.488
Se(2)—С(1) = 3.319
P
P
C(1)
Pd—C(1) = 2.269
Se(2)—С(1) = 2.645
Se(2)
Pd—P = 2.478
XI
Pd—P = 2.502
XIIꢀTS
XIII
XIVꢀTS
IV + X
Fig. 4. Molecular structures of compounds VIIꢀTS—XI optimized by the B3LYP/Lanl2dz(d) method.
The optimized molecular structures are presented in Fig. 4.
We calculated this transformation assuming two different
routes. One of them involves 1,3ꢀtransfer of Me group via
transition state VIIꢀTS in which the lengths of the broken
and newly formed C—Se bonds are 2.767 and 2.605 Å,
respectively (see Fig. 4). Motion along the reaction coorꢀ
dinate toward product VIII is accompanied by the formaꢀ
tion of new carbon—selenium and phosphorus—selenium
bonds, the oxidation state of the metal being decreased
from PdII to Pd0 (see Scheme 4). Ligand substitution
in VIII leads to formation of complex IX. The catalytic
cycle is completed after dissociation of XI and oxidative
addition of the diselenide to Pd(PH3)2.
An alternative reaction pathway involves two consecuꢀ
tive 1,2ꢀshifts of the Me group via transition states XIIꢀTS
and XIVꢀTS (see Scheme 4) with the lengths of the broꢀ
ken and newly formed C—Se bonds of 2.914 and 2.645 Å,
respectively (see Fig. 4). In this case, the C—Se bond
activation involves the oxidative addition resulting in
a fiveꢀcoordinate complex of PdIV (compound XIII).
Shortening of the Pd=Se(1) bond to 2.433 Å compared to
the Pd—Se(2) bond (2.488 Å) is evidence for the formaꢀ
tion of a multiple palladium—selenium bond (see Fig. 4).
Complex XIII cannot be considered as a stable intermeꢀ
diate owing to very low barrier to the reverse reaction
XIII → XIIꢀTS → IV (the energies of XIII and XIIꢀTS
are 50.37 and 50.44 kcal mol–1, respectively). The barꢀ
riers to reaction involving VIIꢀTS and XIVꢀTS are
54.7 kcal mol–1. Thus, for mononuclear palladium
complexes both pathways (1,3ꢀshift or two consecutive
1,2ꢀshifts) can make equal contributions to the formation
of the reaction product.
According to our calculations, activation of the carꢀ
bon—chalcogen bond in dinuclear palladium complexes
can also be a multipath process and follow alternative
routes involving 1,3ꢀ and 1,2ꢀshifts of the Me groups.
Consider transfer of a Me group by a 1,3ꢀshift (Scheme 5,
Fig. 5 and 6). In dinuclear complex XV, the process can
involve transfer of a Me group (1) from the bridging to
the terminal selenium atom (XV → XVIꢀTS → XVII),
(2) from the terminal to the bridging selenium atom
(XV → XVIIIꢀTS → XIX), and (3) between the bridging
selenium atoms (XV → XXꢀTS → XXI). The calculated
activation energies for the first and second reactions are
51.4 and 63.5 kcal mol–1, respectively. We failed to locate
the transition state XXꢀTS, because in this case geometry
optimization led to the transition state of the 1,2ꢀshift of
the Me group (see below). It is noteworthy that the interꢀ
Fig. 5. Potential energy surface of 1,3ꢀshifts of the Me group
involving dinuclear palladium complexes.

Activation of E—E and E—C bonds
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
583
Scheme 5
C
C
C
C
Se
P
P
Se
Se
Pd
Se
Pd
2.575
Pd
Pd
2.492
Se
2.544
2.440
2.480
2.508
Se
C
P
C
Se
2.785
P
Se
2.700
C
C
C
Se
P
C
2.324
2.519
XVIꢀTS
XVII
Se
Pd
C
Pd
C
C
C
2.522
Se
P
P
Se
Se
2.552
Se
Se
Pd
P
Se
Pd
Pd
C
Pd
2.446
Se
2.427
2.581
Se
2.562
2.618
XV
Se
2.466
Se
P
C
P
C
2.491
2.903
C
XIX
C
C
XVIIIꢀTS
P
Se
Se
2.531
2.495
2.488
Pd
2.557
Pd
2.502
C
2.575
Se
P
Se
C
C
XXI
Fig. 6. Molecular structures of compounds XV—XXI optimized by the B3LYP/Lanl2dz(d) method.

584
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Ananikov et al.
Scheme 6
mediate complex with the bridging Se ligand (XXI) is
15 kcal mol–1 more stable then the complex with the
terminal Se ligand (XIX).
in the dinuclear palladium complexes (Scheme 6; Figs 7
and 8). Two transition states, XXIIꢀTS and XXIVꢀTS,
correspond to the Me group transfer from the bridging
selenium atom to the palladium atom and one transition
state, XXVIꢀTS, corresponds to the Me group transfer
from the terminal selenium atom to the Pd atom. In the
lastꢀmentioned case, the motion along the reaction coorꢀ
dinate is accompanied by formation of a selenium—phosꢀ
phorus bond, which results in complex XXVIII. A similar
A comparison of the lengths of the cleaved and newly
formed C—Se bonds in XVIꢀTS (2.785 and 2.700 Å, reꢀ
spectively) and XVIIIꢀTS (2.903 and 2.491 Å, respecꢀ
tively) suggests that the transition state XVIIIꢀTS is more
"late" than XVIꢀTS (see Fig. 6). This is in excellent agreeꢀ
ment with the higher activation energy obtained for
XVIIIꢀTS (see Scheme 5 and Fig. 5). The bonds between
palladium atoms and the bridging Se ligand in XVII (2.480
and 2.508 Å; see Fig. 6) are shorter than the correspondꢀ
ing bonds for the SeMe ligand in XV (2.519 and 2.552 Å;
see Fig. 6) but longer than the Pd=Se bond in XIII
(2.433 Å; see Fig. 4). The lengths of the bonds beꢀ
tween palladium atoms and the SeMe2 bridging ligand in
XIX (2.562 and 2.581 Å; see Fig. 6) are intermediate
between the lengths of the bonds of the SeMe bridging
ligand in XV (2.519 and 2.552 Å; see Fig. 6) and the
Pd—SeMe2 bond length in VIII (2.698 Å; see Fig. 4).
This is an indication of electron density delocalization on
the palladium atoms in the dinuclear complexes XVII
and XIX.
Three different transition states were located in quanꢀ
tumꢀchemical calculations of 1,2ꢀshifts of the Me groups
Fig. 7. Potential energy surface of 1,2ꢀshifts of the Me group
involving dinuclear palladium complexes.

Activation of E—E and E—C bonds
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
585
Se—Se = 2.402
Pd—C = 2.118
Se
2.787
Se
C
Se
P
P
Se
2.938
P
C
Pd—C = 2.347
Se—C = 2.467
Pd—Se = 2.685
Pd
Pd
Pd
Pd
P
Se
Se
Se
C
Se
C
C
C
XXIII
XXIIꢀTS
C
Se
C
C
P
Se
Se
Se
P
2.4C30
Pd
2.492
C
Se
C
P
2.496
Pd—C = 2.118
2.324
2.519
Se
Pd
Se
Pd—C = 2.239
Se—C = 2.692
2.436
Pd
Se
Pd
Pd
P
2.522
Pd
Se
C
Se
C
2.552
Se
P
C
C
P
Se
XXIVꢀTS
XXV
C
XV
C
C
C
Se
C
Se
P
Se
P
P
Se
C
2.079
2.592
Pd
Pd
Pd
Pd—C = 2.138
Se—C = 3.187
Pd
C
2.422
P
Se
Se
C
Se
Se
C
XXVIꢀTS
XXVIII
Fig. 8. Molecular structures of compounds XXIIꢀTS—XXVIII optimized by the B3LYP/Lanl2dz(d) method.
process was also found for mononuclear palladium comꢀ
plexes (see above). The reaction leading to intermediate
XXV is hardly probable due to the lower barrier to the
reverse reaction (XXV → XXIVꢀTS → XV). It is noteworꢀ
thy that the calculated activation barrier to cleavage of
the Se—C bond via transition state XXIIꢀTS is only
for the systems XIX and XXI, the structures of these metal
complexes can be described in terms of various resonance
structures (Scheme 7). The highest relative stability is
characteristic of the intermediates which (1) contain no
terminal Se ligands, (2) contain no bridging SeMe2
ligands, and (3) contain a minimum number of the resoꢀ
nance structures with PdIV. Combination of these three
features gives the following series of the relative stability
of metal complexes: XVII > XXI, XXIII > XIX, XXV (see
Schemes 5 and 6 and Figs 5 and 7).
Based on the geometric parameters, the resonance
structure with two PdII atoms contributes largely to the
stabilization of complex XXIII. The Se—Se bond in comꢀ
plex XXIII (see Fig. 8) is only slightly longer than in free
diselenide (2.402 Å vs. 2.366 Å), being equal to the bond
length of coordinated diselenide in intermediate II (see
Fig. 2).
33.6 kcal mol–1
.
Among the three transition states of 1,2ꢀshifts of the
Me group in dinuclear complexes, the geometry of transiꢀ
tion state XXVIꢀTS has the strongest similarity to that of
the transition state XIIꢀTS in the mononuclear complex
(see Figs 2 and 8). These transition states are characterꢀ
ized by similar activation barriers (51.2 and
50.4 kcal mol–1, respectively). It is noteworthy that in
both cases we deal with the Me group shift from the
terminal SeMe ligand to the palladium atom. The activaꢀ
tion barriers to the cleavage of the selenium—carbon bond
calculated for the Me group shift from the bridging
SeMe ligand to the palladium atom are lower (33.6 and
39.6 kcal mol–1; see Fig. 7). Thus, here we deal with a
pronounced stabilization effect, which takes place in
dinuclear palladium complexes.
Thus, additional stabilization of intermediates of the
Se—C bond activation reaction in dinuclear palladium
complexes is possible owing to electron density delocalꢀ
ization over the bridging ligands and to contribution of
different resonance structures, which is impossible in the
case of mononuclear complexes.
The relative stabilities of the intermediates XVII, XIX,
XXI, XXIII, and XXV (see Schemes 5 and 6 and Figs 5
and 7) vary over a wide range (5—38 kcal mol–1). Except
Geometry optimization of the transition state of the
reaction of selenium—phosphorus bond formation involvꢀ

586
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Ananikov et al.
Scheme 7
Note. Donorꢀacceptor bonds are denoted by dashed lines.
Table 6. Relative energies of stationary points I—XXVIII obꢀ
tained from B3LYP/Lanl2dz(d) calculations*
ing cisꢀarranged Se and PH3 ligands in complexes XVII,
XIX, XXI, XXIII, XXV led to compound XI. A similar
reaction was discussed above for mononuclear complexes.
Therefore, the reactions of dinuclear palladium complexes
also result in products X and XI.
Stationary
points
∆E
∆H
Stationary
points
∆E
∆H
I
II
IIIꢀTS
IV
VꢀTS
VI
VIIꢀTS
VIII
IX + X
IV + XI + X
XIIꢀTS
XIII
0.0
0.0
XV
XVIꢀTS
XVII
XVIIIꢀTS
XIX
XXI
XXIIꢀTS
XXIII
XXIVꢀTS
XXV
XXVIꢀTS
XXVIII
0.0
51.4 49.8
5.4 5.3
0.0
The results obtained in our calculations revealed the
possibility of Se—C bond activation in both mononuclear
and dinuclear palladium complexes. The lowest activaꢀ
tion barrier was obtained for the C—Se bond cleavage via
–5.6 –4.6
2.8 3.0
–10.7 –9.1
20.3 19.7
63.5 62.1
37.6 37.7
22.5 22.4
33.6 32.0
25.5 24.6
39.6 38.2
38.3 37.6
51.2 50.1
27.5 27.1
transition state XXIIꢀTS (∆E≠ = 33.6 kcal mol–1) in
.
–0.4
0.5
dinuclear complexes. This is consistent with modern conꢀ
cepts of involvement of such complexes in the reactions
with alkynes in this system and is in agreement with the
available experimental data.
The results of quantumꢀchemical calculations were
discussed in terms of ∆E (see Schemes 3—6 and
Figs 1, 3, 5, and 7). The results of calculations of the
potential energy surface ∆H are listed in Table 6. It was
found that the ∆E and ∆H values differ only slightly from
one another, which confirms reliability of conclusions
drawn.
54.7 53.4
12.4 12.7
14.4 15.0
8.3
9.6
50.4 49.0
50.4 49.5
54.7 53.2
XIVꢀTS
* The energies of the stationary points II—XIVꢀTS were calcuꢀ
lated relative to the energy of the stationary point I and the
energies of the stationary points XVIꢀTS—XXVIII were calcuꢀ
lated relative to the energy of the stationary point XV.

Activation of E—E and E—C bonds
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
587
9. H. Kuniyasu, A. Ogawa, S.ꢀI. Miyazaki, I. Ryu, N. Kambe,
and N. Sonoda, J. Am. Chem. Soc., 1991, 113, 9796.
10. A. Ogawa, J. Organomet. Chem., 2000, 611, 463.
11. V. P. Ananikov, M. A. Kabeshov, I. P. Beletskaya, G. G.
Aleksandrov, and I. L. Eremenko, J. Organomet. Chem., 2003,
687, 451.
12. V. P. Ananikov, I. P. Beletskaya, G. G. Aleksandrov, and
I. L. Eremenko, Organometallics, 2003, 22, 1414.
13. R. Oilunkaniemi, R. S. Laitinen, and M. Ahlgren,
J. Organomet. Chem., 2001, 623, 168.
14. R. Oilunkaniemi, R. S. Laitinen, and M. Ahlgren,
J. Organomet. Chem., 1999, 587, 200.
15. I. Nakanishi, S. Tanaka, K. Matsumoto, and S. Ooi, Acta
Crystallogr., Sect. C., 1994, 50, 58.
16. M. S. HannuꢀKuure, K. Paldán, R. Oilunkaniemi, R. S.
Laitinen, and M. Ahlgren, J. Organomet. Chem., 2003,
687, 538.
*
*
*
Thus, in the present work we realized for the first time
a catalytic element—element bond activation followed by
the addition to alkynes under microwave irratiation conꢀ
ditions. It was shown that the reaction in Ph2S2/PPh3
melt proceeds as palladiumꢀcatalyzed stereoselective adꢀ
dition of diphenyl disulfide to the triple bond, resulting in
nearly 100% yields of Zꢀ(PhS)HC=C(SPh)R. The reacꢀ
tion involving diphenyl diselenide depends on the microꢀ
wave power. At low microwave power, a palladiumꢀcataꢀ
lyzed stereoselective synthesis of Zꢀ(PhSe)HC=C(SePh)R
similar to the reaction involving diphenyl disulfide proꢀ
ceeds in the Ph2Se2/PPh3 melt. At a higher microwave
power, a previously unknown catalytic reaction of diꢀ
phenyl diselenide with triphenylphosphine resulting in
Se=PPh3 and Ph2Se proceeds in the system under study.
A similar chemical transformation is also characteristic of
other phosphine and phosphite ligands.
Oxidative addition of Ph2Se2 to Pd0 in Ph2Se2/PPh3
melt under microwave irradiation conditions results in
[Pd2(SePh)4(PPh3)2] dinuclear complexes detected by
31P{1H} NMR spectroscopy.
According to the results of quantumꢀchemical calcuꢀ
lations, both mononuclear and dinuclear palladium comꢀ
plexes can catalyze the Se—C bond cleavage reaction.
The reactions involving dinuclear complexes can proceed
with smaller energy requirements, which is due to stabiliꢀ
zation of the bridging selenium ligands.
17. A. D. Becke, Phys. Rev. A, 1988, 38, 3098.
18. C. Lee, W. Yang, and R. G. Parr, Phys. Rev. B, 1988, 37, 785.
19. A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
20. P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 270.
21. W. R. Wadt and P. J. Hay, J. Chem. Phys., 1985, 82, 284.
22. P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299.
23. T. H. Dunning, Jr. and P. J. Hay, in Modern Theoretical
Chemistry, Ed. H. F. Schaefer, III, Vol. 3, Plenum, New
York, 1976, 1.
24. R. Ditchfield, W. J. Hehre, and J. A. Pople, J. Chem. Phys.,
1971, 54, 724.
25. G. Orlova and J. D. Goddard, J. Phys. Chem. A, 1999,
103, 6825.
26. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr.,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross,
C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth,
P. Salvador, J. J. Dannenberg, V. G. Zakrzewski,
S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman,
J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski,
B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A.
AlꢀLaham, C. Y. Peng, A. Nanayakkara, M. Challacombe,
P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong,
C. Gonzalez, and J. A. Pople, Gaussian 03, Rev. C. 1,
Gaussian, Inc., Pittsburgh (PA), 2003.
This work was financially supported by the Russian
Federation Presidential Foundation (Grant for Young
Scientists MDꢀ2384.2004.3), the Russian Foundation for
Basic Research (Project No. 04ꢀ03ꢀ32501), and the
Chemistry and Materials Science Division of the Russian
Academy of Sciences (in the framework of the Program
No. 1 "Theoretical and experimental investigations of the
nature of chemical bonding and mechanisms of the most
important chemical reactions and processes").
References
1. M. Larhed, C. Moberg, and A. Hallberg, Acc. Chem. Res.,
2002, 35, 717.
2. K. Tanaka and F. Toda, Chem. Rev., 2000, 100, 1025.
3. R. S. Varma, Pure Appl. Chem., 2001, 73, 193.
4. J. O. Metzger, Angew. Chem., Int. Ed. Engl., 1998, 37, 2975.
5. A. Loupy, A. Petit, J. Hamelin, F. TexierꢀBoullet,
P. Jacquault, and D. Mathe, Synthesis, 1998, 1213.
6. I. V. Tselinskii, A. A. Astrat´ev, and A. S. Brykov, Zh. Obshch.
Khim., 1996, 66, 1699 [Russ. J. Gen. Chem., 1996, 66 (Engl.
Transl.)].
27. G. Schaftenaar and J. H. Noordik, J. Comput.ꢀAided Mol.
Des., 2000, 14, 123.
28. A. Dedieu, Chem. Rev., 2000, 100, 543.
29. D. G. Musaev and K. Morokuma, Top. Catal., 1999, 7, 107.
30. N. Koga and K. Morokuma, Chem. Rev., 1991, 91, 823.
7. V. P. Ananikov and I. P. Beletskaya, Org. Biomol. Chem.,
2004, 2, 284.
8. V. P. Ananikov and I. P. Beletskaya, Izv. Akad. Nauk. Ser.
Khim., 2004, 534 [Russ. Chem. Bull., Int. Ed., 2004, 53, 561].
Received December 10, 2004;
in revised form February 16, 2005