New catalytic system for S-S and Se-Se bond addition to alkynes based on phosphite ligands

Article abstract of DOI:10.1021/om049082g

A new catalytic system for the Ar₂E₂ (E = S, Se) addition to terminal alkynes (HC≡C-R) has been developed to synthesize bis-element-substituted alkenes Z-H(ArE)C=C(EAr)R with high stereoselectivity and yields. Utilizing phosphite ligand P(OiPr)₃ allowed solving two major problems of this catalytic reaction: (1) prevent catalyst polymerization and (2) simplify product purification procedures. Key intermediates-trans- [Pd(SPh)₂(P(OiPr)₃)₂] and trans-[Pd ₂(SPh)₄(P(OiPr)₃)₂] - were synthesized by S-S oxidative addition reaction to Pd(0) and studied by X-ray analysis. The equilibrium between the mononuclear and dinuclear complexes in solution was established by ³¹P NMR spectroscopy. In addition to the advantages in the synthetic procedure, the isolation of the stable palladium complexes with phosphite ligand made possible a detailed mechanistic study of the catalytic reaction.

Full text of DOI:10.1021/om049082g

Organometallics 2005, 24, 1275-1283
1275
New Catalytic System for S-S and Se-Se Bond Addition
to Alkynes Based on Phosphite Ligands
Valentine P. Ananikov,*,† Michael A. Kabeshov,†,‡ Irina P. Beletskaya,*,‡
Vicktor N. Khrustalev,§ and Mikhail Yu. Antipin§
Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospect 47,
Moscow, 119991, Russia, Chemistry Department, Lomonosov Moscow State University,
Vorob’evy Gory, Moscow, 119899, Russia, and Nesmeyanov Institute of Organoelement
Compounds, Russian Academy of Sciences, Vavilov Street 28, Moscow, 119991, Russia
Received November 25, 2004
A new catalytic system for the Ar2E2 (E ) S, Se) addition to terminal alkynes (HCtC-R)
has been developed to synthesize bis-element-substituted alkenes Z-H(ArE)CdC(EAr)R with
high stereoselectivity and yields. Utilizing phosphite ligand P(OiPr)3 allowed solving two
major problems of this catalytic reaction: (1) prevent catalyst polymerization and (2) simplify
product purification procedures. Key intermediatesstrans-[Pd(SPh)2(P(OiPr)3)2] and trans-
[Pd2(SPh)4(P(OiPr)3)2]swere synthesized by S-S oxidative addition reaction to Pd(0) and
studied by X-ray analysis. The equilibrium between the mononuclear and dinuclear complexes
in solution was established by 31P NMR spectroscopy. In addition to the advantages in the
synthetic procedure, the isolation of the stable palladium complexes with phosphite ligand
made possible a detailed mechanistic study of the catalytic reaction.
Scheme 1
1. Introduction
Transition metal catalyzed element-element bond
addition to alkynes provides an efficient methodology
for introducing two carbon-element bonds with high
atom efficiency and selectivity.1 The appropriate choice
of catalyst and ligand are the key factors to achieve high
efficiency and selectivity in the addition process. Very
promising results were achieved using phosphite ligands
P(OR)3, which have several important advantages over
traditionally utilized phosphines PR3.2
The well-known reaction of palladium-catalyzed S-S
and Se-Se bond addition to alkynes leads to Z-substi-
tuted alkenes 2 with excellent stereoselectivity (Scheme
1).3 The products of the reaction, bis-sulfur- and bis-
seleno-substituted alkenes (2), are of much importance
for organic synthesis, for coordination chemistry as
bidentante ligands, and for microelectronics as precur-
sors of new optical materials.4
An in-depth mechanistic study has shown that the
catalytic reaction of S-S and Se-Se bond addition to
alkynes involves intermediate dinuclear palladium com-
plexes [Pd2(ArE)4L2].5 Such complexes have been iso-
lated after the oxidative addition of Ar2E2 to PdL4 or
substitution reaction of the chloride ligands in PdCl2L2
by ArE-.6 The choice of the ligand L was of crucial
importance for performing the catalytic reaction. To
achieve good yield in the catalytic reaction, an excess
of triphenylphosphine ligand (L ) PPh3) was used;5
otherwise rapid catalyst deactivation took place due to
insoluble polymer [Pd(ArE)2]n formation.3b,7 In addition
to the polymerization problem, an excess of PPh3 in
* To whom correspondence should be addressed. (V.P.A.) E-mail:
val@ioc.ac.ru. Fax: +007 (095) 1355328. (I.P.B.) E-mail: beletska@
org.chem.msu.ru. Fax: +007 (095) 9393618.
(4) (a) Patai, S., Rappoport, Z., Eds. The Chemistry of Organic
Selenium and Tellurium Compounds; John Wiley & Sons: New York,
1986-1987; Vols. 1-2. (b) Clemenson, P. I. Coord. Chem. Rev. 1990,
106, 171. (c) Wirth, T., Ed. Organoselenium Chemistry: Modern
Developments in Organic Synthesis; Springer-Verlag: Berlin, 2000. (d)
Kondo, T.; Mitsudo, T. Chem. Rev. 2000, 100, 3205. (e) Zyk, N. V.;
Beloglazkina, E. K.; Belova, M. A.; Dubinina, N. S. Russ. Chem. Rev.
2003, 72, 769.
† Zelinsky Institute of Organic Chemistry.
‡ Lomonosov Moscow State University.
§ Nesmeyanov Institute of Organoelement Compounds.
(1) (a) Togni, A., Grutzmacher, H., Eds. Catalytic Heterofunction-
alization; Wiley-VCH: Weinheim, 2001. (b) Beletskaya, I.; Moberg, C.
Chem. Rev. 1999, 99, 3435. (c) Beller, M.; Seayad, J.; Tillack, A.; Jiao,
H. Angew. Chem., Int. Ed. 2004, 43, 3368.
(2) (a) Duursma, A.; Lefort, L.; Boogers, J. A.; de Vries, A. H.; de
Vries, J. G.; Minnaard, A. J. Org. Biomol. Chem. 2004, 2, 1682. (b)
Schuppan, J.; Minnaard, A. J.; Feringa, B. L. Chem. Commun. 2004,
7, 792. (c) Reetz, M. T.; Mehler, G.; Meiswinkel, A. Tetrahedron:
Asymmetry 2004, 15 (14), 2165. (d) Reetz, M. T.; Goossen, L. J.;
Meiswinkel, A.; Paetzold, J.; Jensen, J. F. Org. Lett. 2003, 5 (17), 3099.
(e) Reetz, M. T.; Moulin, D.; Gosberg, A. Org. Lett. 2001, 3 (25), 4083.
(f) Reetz, M. T.; Sell, T. Tetrahedron Lett. 2000, 41, 6333. (g) Leeuwen,
P. W. N. M. Appl. Catal. A: Gen. 2001, 212, 61.
(5) (a) Ananikov, V. P.; Beletskaya, I. P.; Aleksandrov, G. G.;
Eremenko, I. L. Organometallics 2003, 22, 1414. (b) Ananikov, V. P.;
Kabeshov, M. A.; Beletskaya, I. P.; Aleksandrov, G. G.; Eremenko, I.
L. J. Organomet. Chem. 2003, 687, 451. (c) Ananikov, V. P.; Beletskaya,
I. P. Org. Biomol. Chem. 2004, 2, 284.
(6) (a) Oilunkaniemi, R.; Laitinen, R. S.; Ahlgren, M. J. Organomet.
Chem. 1999, 587, 200. (b) Oilunkaniemi, R.; Laitinen, R. S.; Ahlgren,
M. J. Organomet. Chem. 2001, 623, 168. (c) Zanella, R.; Ros, R.;
Graziani, M. Inorg. Chem. 1973, 12, 2736. (d) Nakanishi, I.; Tanaka,
S.; Matsumoto, K.; Ooi, S. Acta Crystallogr., Sect. C 1994, C50, 58.
(7) Dey, S.; Jain, V. K.; Varghese, B. J. Organomet. Chem. 2001,
623, 48.
(3) (a) Kuniyasu, H.; Ogawa, A.; Miyazaki, S.; Ryu, I.; Kambe, N.;
Sonoda, N. J. Am. Chem. Soc. 1991, 113, 9796. (b) Ogawa, A. J.
Organomet. Chem. 2000, 611, 463.
10.1021/om049082g CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/15/2005

1276 Organometallics, Vol. 24, No. 6, 2005
Ananikov et al.
Table 1. Ligand Dependence Study in the
Palladium-Catalyzed Ph2S2 Addition to
3-Butyn-1-ola
reaction (entries 1-3; Table 3). We found that the
[Pd]/P(OiPr)3 ratio should be at least 1/6 to perform
the catalytic process under homogeneous conditions.
With the lower amount of the ligand, an insoluble
brown precipitate of the polymeric palladium complex
[Pd(PhS)2]n is formed (see related discussion for the
phosphine ligands3b,5). The [Pd]/P(OiPr)3 ratio of 1/10
was sufficient for the reactions of the S-S and Se-Se
addition with high yields. Further increase of the ligand
amount does not influence the product yield. The
observed ligand dependence is in contrast with the
common framework of the catalytic E-E bond addition
reactions (E ) B, Si, Sn, etc.).1 Excess of the ligand
retards alkyne coordination to the metal complex, thus
blocking the catalytic reaction. In our case even with a
large excess of the ligand an excellent product yield was
obtained (entry 5; Table 3).
Readily available Pd(OAc)2 may also be utilized in the
catalytic reaction; however it requires a larger excess
of the ligand, which in part acts as a reducing agent
converting Pd(II) precursor to the catalytically active
Pd(0) complex (entries 6, 7; Table 3). In this case the
formation of the oxide, OdP(OR)3, has been detected by
31P NMR.
We have found that toluene and THF are the best
solvents for this reaction, giving 85-89% yield after 3
h (entries 1, 2; Table 4). Surprisingly, even hexane (or
petroleum ether) may be used as a solvent, leading to
61% product yield after 3 h (entry 3, Table 4). Increasing
the reaction time to 15 h resulted in quantitative yields
(95-98%) in toluene, THF, and hexane. Among the
studied solvents toluene is a better choice to perform
the reactions at higher temperature. In CHCl3 and
CH3CN an insoluble brown precipitate was formed, in
contrast to homogeneous solutions observed in the other
studied cases (Table 4). Due to catalyst precipitation,
rather poor product yields were obtained in CHCl3 and
CH3CN solutions (entries 4, 5; Table 4).
In the optimized conditionss3 mol % of the Pd
catalyst, 30 mol % of the P(OiPr)3 ligand in toluene
solution at 100 °Csthe catalytic reaction was carried
out with very good yields for several alkynes and
dichalcogenides (Table 5). Quantitative NMR yields and
high isolated yields were achieved in the S-S and
Se-Se bond addition to hexyne-1 and heptyne-1 (entries
1-5; Table 5). A simplified purification procedure with
flash chromatography performed very well for all of
these products. In the same conditions the addition of
Ph2S2 to heptadiyne-1,6 involves both triple bonds (entry
6; Table 5). The catalytic system based on the phosphite
ligand is tolerant of the functional groups in the alkyne
molecule (R ) OH, OMe, NMe2), which have no influ-
ence on the product yield (entries 7-9; Table 5). In all
of the cases above high stereoselectivity of the addition
reaction was observed, as confirmed by 2D NOESY
experiments (entries 1-9; Table 5).
entry
ligand
yield,b %
1
2
3
4
5
6
7
8
9
PPh3
90
88
15
2
P(p-FC6H4)3
PCy3
PBu3
DPPB
2
DPPE
0
4
99
99
P(OPh)3
P(OBu)3
P(OiPr)3
a The reactions were carried out in toluene at 80 °C for 15 h
with 1.5 mol % of Pd2dba3 and 30 mol % of the ligand. b Deter-
mined by NMR.
some cases caused significant difficulties during the
product separation and purification stage.
In the present article we report a new catalytic system
for the S-S and Se-Se bond addition to alkynes
catalyzed by palladium complexes with phosphite ligands.
Both problems of the studied addition reactionscatalyst
polymerization and product purificationshave been
solved using phosphite ligands. The methodology has
several advantages, since phosphite ligands are readily
available and cheaper than corresponding phosphines.
2. Results and Discussion
Using the model reaction of Ph2S2 addition to 3-butyn-
1-ol (R ) CH2CH2OH; Scheme 1) we have investigated
the catalytic activity of the palladium complexes with
various mono- and bidentante phosphine and phosphite
ligands (Table 1). The catalytic reaction with PPh3
studied earlier3,5 was used for comparison (entry 1;
Table 1). Introducing fluorine in trans-position of the
phenyl ring slightly decreases the yield of the addition
reaction (entry 2; Table 1). The electron-donating tri-
alkylphosphines performed rather poorly (entries 3, 4;
Table 1). The reaction did not take place with bidentante
ligands DPPB and DPPE (entries 5, 6; Table 1). Only a
small amount of product was observed with P(OPh)3
(entry 8; Table 1). Surprisingly, excellent results were
achieved with trialkyl phosphite ligands (entries 9, 10;
Table 1).
Using P(OAlk)3 instead of PPh3 slightly increased the
NMR yield of the addition reaction and greatly in-
creased the isolated yields. In addition, the product
separation procedure was significantly simplified (Table
2). This is especially important in the case of the Ph2E2
addition to nonpolar alkynes (without heteroatoms),
because it is rather difficult to separate these products
from the PPh3 ligand using chromatography on silica.
High NMR yields of the Ph2S2 and Ph2Se2 addition to
hexyne-1 were found for both ligands; however isolated
yields of 60-62% and 91-92% were found for PPh3 and
P(OiPr)3, respectively (Table 2). For the phosphite
ligand simple flash chromatography performed very well
and allowed the product of >98% purity to be isolated
(determined by 1H and 13C NMR). The kinetic measure-
ments have indicated that catalytic S-S bond addition
to hexyne-1 using PPh3 and P(OiPr)3 ligands requires
approximately the same time.8
Arylacetylenes are rather difficult substrates to achieve
high stereoselectivity in the S-S and Se-Se bond
addition. In this case the noncatalytic side-reaction
leading to the E-isomer takes place and decreases the
(8) Catalytic reaction with PPh3 ligand is faster than catalytic
reaction with P(OiPr)3 ligand. Particularly, after 60 min of the reaction
89% and 72% product yields were detected for L ) PPh3 and P(OiPr)3,
respectively. Quantitative yields were observed in both cases after 100
min of reaction. See supporting Figure S1 for details.
Both factorssnature and amount of the ligandsneed
to be optimized to achieve high yield in the catalytic

S-S and Se-Se Bond Addition to Alkynes
Organometallics, Vol. 24, No. 6, 2005 1277
Table 2. Isolated and NMR Yields of the Products of the Ph2S2 and Ph2Se2 Addition to Hexyne-1 in the
Palladium-Catalyzed Reaction with Different Ligands (L)a
a The reaction was carried out in toluene at 80 °C for 15 h with 1.5 mol % of Pd2dba3 and 30 mol % of the ligand. b Using flash
chromatography, see Experimental Part for details.
Table 3. Yields of the Ph2S2 Addition to Hexyne-1
Depending on the Nature of the Palladium
Complex and Amount of Liganda
[Pd(SPh)2(P(OiPr)3)2] complexes were obtained (Scheme
2; E ) S, Ar ) Ph, R ) iPr). Regular workup of the
reaction mixture (see Experimental Part for details)
followed by crystallization from hexane gave pure
crystals of trans-[Pd(EAr)2(P(OiPr)3)2] in 85% isolated
yield. The structure of the complex has been determined
by X-ray analysis (Figure 2). Exactly the same com-
plexes were synthesized using Pd2(dba)3 precursor
entry
[Pd]
P(OiPr)3/[Pd] ratio
yield,b %
1
2
3
4
5
6
7
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
Pd(OAc)2
Pd(OAc)2
2
4
31
82
97
99
99
28
99
6
10
30
6
1
instead of Pd(OAc)2, as confirmed by 31P{1H} and H
15
NMR.
a The reaction was carried out in toluene at 100 °C for 3 h with
1.5 mol % of Pd2dba3 or 3 mol % of Pd(OAc)2. b Determined by
NMR.
Most likely cis-[Pd(SPh)2(P(OiPr)3)2], 3, is formed
first after the oxidative addition reaction, followed by
isomerization to thermodynamically more stable trans-
[Pd(SPh)2(P(OiPr)3)2], 4 (Scheme 2).
Table 4. Effect of Solvent in the
Palladium-Catalyzed Ph2S2 Addition to Hexyne-1a
Dissolving pure crystals of trans-[Pd(EAr)2(P(OiPr)3)2],
4, in benzene and recording the 31P{1H} NMR spectrum
showed five resonances: δ ) 98.8, 101.2, 102.7, 110.5,
138.7 ppm. The low-field resonance at 138.7 ppm
corresponds to the free ligand P(OiPr)3. The resonances
at δ ) 102.7 and 110.5 ppm correspond to 3 and 4 (see
above). The remaining signals correspond to two new
palladium complexes that were formed upon dissocia-
tion of the P(OiPr)3. This suggests the formation of
dinuclear complexes 5 and 6 (δ ) 98.8, 101.2 ppm) as
the products of the ligand dissociation reaction. The
following ratio was determined by 31P{1H} NMR upon
dissolving 4 in benzene: (3+4)/(5+6)/P(O-iPr)3 ) 1/1/1.
Adding an excess of P(OiPr)3 to this solution resulted
in the disappearance of the signals at δ ) 98.8, 101.2
ppm (5 and 6) and increasing intensity of the signals
at δ ) 102.7, 110.5 ppm (3 and 4).
The pure dinuclear complex trans-[Pd2(EAr)4-
(P(OiPr)3)2], 5, was obtained after removing excess
P(OiPr)3 from complex 4 by flash chromatography. The
structure of the complex has been unambiguously
determined by X-ray analysis (Figure 1). A solution of
the pure dinuclear complexes in C6D6 exhibits two
singlets in the 31P{1H} NMR spectrum at δ ) 98.8 and
101.2 ppm in 8/1 ratio (5 and 6). In the 1H NMR
spectrum two sets of resonances were also observed with
the same 8/1 ratio. As identified by the integration of
the 1H NMR spectrum, each complex (5 and 6) contains
four SPh and two P(OiPr)3 groups, which clearly cor-
respond to the dinuclear structure. Adding P(O-iPr)3 to
the solution of 5 resulted in the appearance of the
signals corresponding to 3 and 4 (δ(31P) ) 102.7, 110.5
ppm). The concentration of the mononuclear complexes
increased upon increasing the excess of the ligand.
When the ratio between the complex and the free ligand
was >30, only the mononuclear complexes were detected
by 31P{1H} NMR.
entry
solvent
yield,b %
1
2
3
4
5
toluene
THF
hexane
CHCl3
CH3CN
85
89
61
14
5
a The reaction was carried out in a sealed tube at 80 °C for 3 h
with 3 mol % of Pd(OAc)2 and 45 mol % of P(O-iPr)3. b Determined
by NMR.
overall selectivity of the addition reaction.1,3,5 Particu-
larly, in Pd-catalyzed Ph2Se2 addition to phenylacety-
lene with PPh3 ligand a noncatalytic pathway makes a
major contribution to the reaction (Z/E ) 1/4).9 However,
in the palladium-catalyzed reaction with the P(OiPr)3
ligand the stereoselectivity was greatly improved by
dramatically decreasing the contribution of the non-
catalytic pathway: Z/E > 10/1 (entries 10-12; Table 5).
Therefore, not only the isolated yield but also the
stereoselectivity of the reaction can be improved using
the catalytic system developed in the present study.
The mechanistic study of the catalytic system has
been started with reaction of Ph2S2 and palladium
complex in the presence of the excess of ligand. Heating
Pd(OAc)2, Ph2S2, and P(OiPr)3 (1/2/12 ratio) in benzene
at 70 °C for 2 h resulted in a dark brown homogeneous
solution without insoluble species. Two new resonances
were detected in the 31P{1H} NMR spectrum, δ ) 102.7
and 110.5 ppm, indicating that two different transition
metal complexes were formed. Two sets of signals were
also found in the 1H NMR spectrum. The integration of
the proton signals showed that for each complex the
ratio SPh/P(OiPr)3 ) 1 is maintained, thus suggesting
that mononuclear trans-[Pd(SPh)2(P(OiPr)3)2] and cis-
(9) Ananikov, V. P.; Beletskaya, I. P. Russ. Chem. Bull. 2003, 52,
811.

1278 Organometallics, Vol. 24, No. 6, 2005
Ananikov et al.
Table 5. Scope of the S-S and Se-Se Bond Addition to Alkynes Catalyzed by Palladium Complexes with
Phosphite Liganda
a See the Experimental Part for detailed description of the synthetic procedure. b NMR and isolated yields (in parentheses). c The ratio
alkyne/Ph2S2 ) 1.0/2.5 was used.
The experiments with 4 and 5 clearly confirm that in
solution the mono- and dinuclear complexes are in
equilibrium and the observed ratio of the complexes
depends on the amount of the free ligand. Using NMR

S-S and Se-Se Bond Addition to Alkynes
Organometallics, Vol. 24, No. 6, 2005 1279
Scheme 2
spectroscopy the equilibrium constant of dinuclear
complex dissociation to mononuclear form has been
measured, K ) (0.066 ( 0.007) M at 30 °C.
Figure 2. Molecular structure of mononuclear complex
trans-[Pd(SPh)2(P(O-iPr)3)2], 4.
It should be emphasized that the nature of the Pd
complexes with trialkyl phosphite ligands (mono- or
dinuclear) can be easily determined by the analysis of
3-5 days. The mononuclear complexes 3 and 4 are more
stable at room temperature than dinuclear ones; how-
ever they quickly decompose upon heating at 70-80 °C
(1-2 h). Decomposition of both mono- and dinuclear
complexes is accompanied with insoluble dark brown
precipitate formation, corresponding to the polymer
[Pd(EAr)2]n (7). If an excess of the P(OiPr)3 ligand was
added to the solutions, the complexes did not decompose
in a noticeable manner neither at room temperature nor
upon heating (80 °C, 10 h). Therefore, ligand excess
suppresses polymerization and stabilizes the complexes
in solution.
1
the H spectra, since the resonances of the aromatic
(SPh) and aliphatic (iPr) protons are clearly resolved.
This was not possible for the catalytic system with
triphenylphosphine studied earlier, since the SPh sig-
nals strongly overlap with the ligand signals (PPh3).
The dinuclear complexes 5 and 6 slowly decompose
in benzene at room temperature; the corresponding
signals in 31P{1H} and 1H NMR spectra disappeared in
According to the literature data, the structure of
palladium complexes with EAr ligands (PdnLx(EAr)y, E
) S, Se; n ) 1, 2) strongly depends on the nature of L.
With trialkylphosphines (L ) PBu3) the mononuclear
complex trans-[Pd(SePh)2(PBu3)2] was isolated.10 Tri-
phenylphosphine (L ) PPh3) facilitates dinuclear com-
plex formation, as was found for trans-[Pd2(SePh)4-
(PPh3)2]6b and trans-[Pd2(SPh)4(PPh3)2].6d It is the unique
feature of P(OR)3 ligands that allows both complexes
to be isolated. To the best of our knowledge, this study
is the first example where both mono- and dinuclear
complexes have been isolated and the equilibrium
between these complexes in solution was established.
The molecular structures and the numbering of the
atoms of 5 and 4 are shown in Figure 1 and Figure 2.
Selected bond distances and angles are listed in Tables
6 and 7.
The Pd atoms in the dinuclear complex 5 show
expectedly a slightly distorted square-planar coordina-
tion geometry. The sums of the four bond angles around
the metal atoms are 359.5° and 360.1°, in agreement
with the virtually planar coordination.
The two square-planar coordination spheres in di-
nuclear Pd(II) complexes can adopt either a coplanar
or hinged arrangement (Scheme 3).
Complex 5 exhibits the hinged arrangement (see
Figure 1b), which seems to be a less common feature in
Figure 1. Molecular structure of dinuclear complex trans-
[Pd2(SPh)4(P(O-iPr)3)2], 5.
(10) Alyea, E. C.; Ferguson, G.; Kannan, S. Polyhedron 1998, 17,
2231.

1280 Organometallics, Vol. 24, No. 6, 2005
Ananikov et al.
Table 6. Selected Bond Lengths [Å] and Angles
[deg] for 5
Scheme 3
Pd(1)-S(1)
Pd(1)-S(2)
Pd(1)-S(3)
Pd(1)-P(1)
Pd(2)-S(1)
Pd(2)-S(2)
Pd(2)-S(4)
Pd(2)-P(2)
S(1)-C(1)
S(2)-C(7)
S(3)-C(13)
S(4)-C(19)
2.380(2)
2.396(2)
2.305(3)
2.208(3)
2.298(2)
2.384(2)
2.354(3)
2.254(2)
1.729(7)
1.775(7)
1.678(7)
1.714(8)
P(1)-O(1)
P(1)-O(2)
P(1)-O(3)
P(2)-O(4)
P(2)-O(5)
P(2)-O(6)
O(1)-C(25)
O(2)-C(28)
O(3)-C(31)
O(4)-C(34)
O(5)-C(37)
O(6)-C(40)
1.581(7)
1.602(6)
1.592(6)
1.573(7)
1.583(5)
1.561(6)
1.456(9)
1.440(8)
1.469(10)
1.467(10)
1.473(9)
1.489(11)
by the geometrical requirements of the ligands. Complex
5 is the first dinuclear Pd(II) compound with the hinged
arrangement of nonchelating ligands. The fold angle
between the two neighboring PdL4 coordination planes
is 166.0°.
S(1)-Pd(1)-S(2)
S(1)-Pd(1)-S(3)
S(2)-Pd(1)-S(3)
P(1)-Pd(1)-S(1)
P(1)-Pd(1)-S(2)
P(1)-Pd(1)-S(3)
S(1)-Pd(2)-S(2)
S(1)-Pd(2)-S(4)
S(2)-Pd(2)-S(4)
P(2)-Pd(2)-S(1)
P(2)-Pd(2)-S(2)
P(2)-Pd(2)-S(4)
Pd(1)-S(1)-Pd(2)
Pd(1)-S(2)-Pd(2)
C(1)-S(1)-Pd(1)
C(1)-S(1)-Pd(2)
C(7)-S(2)-Pd(1)
C(7)-S(2)-Pd(2)
81.57(7)
94.88(8)
O(1)-P(1)-O(2)
O(1)-P(1)-O(3)
106.4(3)
100.2(3)
99.8(4)
The bridging phenylthiolato ligands in 5 are not
equidistant from the two palladium atoms. The Pd-S
bond lengths are noticeably different (2.298(2)-
2.396(2) Å, Table 6) and practically cover the range of
values known for analogous compounds (2.283(6)-
2.3887(7) Å).6,11,13 The differences in the Pd-S bond
lengths can be attributed to the relative effects of the
trans influence as well as to the steric effects.
The Pd-P distances in 5 (2.208(3) and 2.254(2) Å,
Table 6) are within the range 2.1837(8)-2.281(5) Å of
Pd-P distances observed in previously investigated
Pd(II) complexes with P(OR)3 ligands.14 The differences
in the bond lengths can again be explained by the effects
of relative trans influence.
The phenyl groups bound to terminal and bridging
sulfur atoms have the syn conformation relative to the
Pd2S2 ring, respectively. The Pd‚‚‚Pd length of 3.503(1)
Å seems too long to be assigned as any direct metal-
metal interaction.
The Pd atom in mononuclear complex 4 lies in an
inversion center, and the coordination geometry is thus
required to be trans and strictly planar. The planar
coordination is not exactly square, as the crystallo-
graphically unique P(1)-Pd(1)-S(1) angle is 85.61(3)°.
The deviations from the square-planar geometry are
imposed by the steric hindrances of the ligands. The
Pd-S distance of 2.3526(8) Å (Table 6) is similar to
those observed in other mononuclear Pd(II)-phenylthi-
173.47(11) O(2)-P(1)-O(3)
174.85(7)
96.60(9)
O(4)-P(2)-Pd(2)
O(5)-P(2)-Pd(2)
108.0(3)
115.9(2)
119.6(3)
107.5(3)
103.1(3)
101.5(4)
125.5(5)
121.3(5)
126.4(5)
122.3(5)
121.0(5)
123.8(5)
123.1(5)
118.3(6)
123.1(6)
117.4(6)
86.48(10) O(6)-P(2)-Pd(2)
83.54(7)
178.09(8)
94.70(9)
95.92(8)
172.03(8)
O(4)-P(2)-O(5)
O(4)-P(2)-O(6)
O(5)-P(2)-O(6)
C(25)-O(1)-P(1)
C(28)-O(2)-P(1)
85.93(10) C(31)-O(3)-P(1)
96.96(6)
94.24(8)
108.4(3)
109.9(3)
110.8(3)
106.5(2)
C(34)-O(4)-P(2)
C(37)-O(5)-P(2)
C(40)-O(6)-P(2)
C(2)-C(1)-S(1)
C(6)-C(1)-S(1)
C(8)-C(7)-S(2)
C(12)-C(7)-S(2)
C(14)-C(13)-S(3) 122.2(6)
C(18)-C(13)-S(3) 118.5(6)
C(20)-C(19)-S(4) 122.5(6)
C(24)-C(19)-S(4) 119.6(7)
C(13)-S(3)-Pd(1) 107.9(3)
C(19)-S(4)-Pd(2) 112.3(3)
O(1)-P(1)-Pd(1)
O(2)-P(1)-Pd(1)
O(3)-P(1)-Pd(1)
111.1(3)
118.4(2)
118.8(2)
Table 7. Selected Bond Lengths [Å] and Angles
[deg] for 4
Pd(1)-S(1)
Pd(1)-P(1)
S(1)-C(1)
P(1)-O(1)
P(1)-O(2)
2.3526(8)
2.3050(9)
1.771(3)
1.595(2)
1.602(2)
P(1)-O(3)
O(1)-C(7)
O(2)-C(10)
O(3)-C(13)
1.579(2)
1.451(4)
1.473(4)
1.469(4)
P(1)-Pd(1)-S(1)
C(1)-S(1)-Pd(1)
O(1)-P(1)-O(2)
O(1)-P(1)-O(3)
O(2)-P(1)-O(3)
O(1)-P(1)-Pd(1) 114.97(10) C(6)-C(1)-S(1)
O(2)-P(1)-Pd(1) 118.82(8)
85.61(3)
108.76(11) C(7)-O(1)-P(1)
O(3)-P(1)-Pd(1) 112.64(8)
127.1(2)
101.00(12) C(10)-O(2)-P(1) 121.7(2)
100.54(12) C(13)-O(3)-P(1) 124.2(2)
106.73(12) C(2)-C(1)-S(1)
117.7(3)
123.7(3)
(13) (a) Wei, G.; Liu, H. Acta Crystallogr., Sect. C 1990, 46, 2457.
(b) Pasquali, M.; Marchetti, F.; Leoni, P.; Beringhelli, T.; D’Alfonso,
G. Gazz. Chim. Ital. 1993, 123, 659. (c) Singhal, A.; Jain, V. K.;
Varghese, V.; Tiekink, E. R. T. Inorg. Chim. Acta 1999, 285, 190. (d)
Lobana, T. S.; Verma, R.; Hundal, G.; Castineiras, A. Polyhedron 2000,
19, 899. (e) Guzei, I. A.; Maisela, L. L.; Darkwa, J. Acta Crystallogr.,
Sect. C 2000, 56, 564. (f) Benefiel, A.; Roundhill, D. M.; Fultz, W. C.;
Rheingold, A. L. Inorg. Chem. 1984, 23, 3316. (g) Real, J.; Prat, E.;
Polo, A.; Alvarez-Larena, A.; Piniella, J. F. Inorg. Chem. Commun.
2000, 3, 221. (h) Maisela, L. L.; Crouch, A. M.; Darkwa, J.; Guzei, I.
A. Polyhedron 2001, 20, 3189. (i) Cerrada, E.; Falvello, L. R.; Hurst-
house, M. B.; Laguna, M.; Luquin, A.; Pozo-Gonzalo, C. Eur. J. Inorg.
Chem. 2002, 826. (j) Gomez-Benitez, V.; Hernandez-Ortega, S.; Morales-
Morales, D. Inorg. Chim. Acta 2003, 346, 256. (k) Sanchez, G.;
Momblona, F.; Sanchez, M.; Perez, J.; Lopez, G.; Casabo, J.; Molins,
E.; Miravitlles, C. Eur. J. Inorg. Chem. 1998, 1199.
(14) (a) Huttner, G.; Jibril, I. Angew. Chem., Int. Ed. Engl. 1984,
23, 740. (b) Espinet, P.; Garcia, G.; Herrero, F. J.; Jeannin, Y.; Philoche-
Levisalles, M. Inorg. Chem. 1989, 28, 4207. (c) Espinet, P.; Alonso, M.
Y.; Garcia-Herbosa, G.; Ramos, J. M.; Jeannin, Y.; Philoche-Levisalles,
M. Inorg. Chem. 1992, 31, 2501. (d) Gavrilov, K. N.; Mikhel’, I. S.;
Lyssenko, K. A.; Antipin, M. Yu.; Timofeeva, G. I.; Polosukhin, A. I.;
Korostylev, A. V. Russ. J. Inorg. Chem. 1997, 42, 520. (e) Bohm, A.;
Schreiner, B.; Steiner, N.; Urban, R.; Sunkel, K.; Polborn, K.; Beck,
W. Z. Naturforsch., B: Chem. Sci. 1998, 53, 191. (f) Gavrilov, K. N.;
Korostylev, A. V.; Bondarev, O. G.; Petrovskii, P. V.; Lyssenko, K. A.;
Polosukhin, A. I.; Davankov, V. A. Russ. Chem. Bull. 2000, 50, 533.
(g) Korostylev, A. V.; Bondarev, O. G.; Kovalevsky, A. Y.; Petrovskii,
P. V.; Davankov, V. A.; Gavrilov, K. N. Inorg. Chim. Acta 2001, 312,
117.
dinuclear palladium centers involving bridging chalco-
gen donors than the coplanar arrangement.6,11 More-
over, until now the hinged arrangement was observed
only in complexes in which the bridging ligands were
coordinated to Pd atoms in a chelate fashion.12 The
hinged arrangement in these compounds is determined
(11) (a) Fenn, R. H.; Segrott, G. R. J. Chem. Soc. A 1970, 3197. (b)
Fenn, R. H.; Segrott, G. R. J. Chem. Soc., Dalton Trans. 1972, 330. (c)
Padilla, E. M.; Golen, J. A.; Richmann, P. N.; Jensen, C. M. Polyhedron
1991, 10, 1343. (d) Guangming, L.; Sihai, L.; Tan, A. L.; Yip, W.-H.;
Mak, C. W.; Hor, T. S. A. J. Chem. Soc., Dalton Trans. 1996, 4315. (e)
Cao, R.; Hong, M.; Jiang, F.; Kang, B.; Xie, X.; Liu, H. Polyhedron 1996,
15, 2661.
(12) (a) Roundhill, D. M.; Roundhill, S. G. N.; Beaulieu, W. B.;
Bagchi, U. Inorg. Chem. 1980, 19, 3365. (b) Albinati, A.; Herrmann,
J.; Pregosin, P. S. Inorg. Chim. Acta 1997, 264, 33. (c) Ford, S.; Khanna,
P. K.; Morley, C. P.; di Vaira, M. J. Chem. Soc., Dalton. Trans. 1999,
791. (d) Brugat, N.; Polo, A.; Alvarez-Larena, A.; Piniella, J. F.; Real,
J. Inorg. Chem. 1999, 38, 4829. (e) Hauptman, E.; Fagan, P. J.;
Marshall, W. Organometallics 1999, 18, 2061. (f) Zhang, Q.; Slawin,
A. M. Z.; Woollins, J. D. J. Chem. Soc., Dalton. Trans. 2001, 3598. (g)
Dervisi, A.; Jenkins, R. L.; Malik, K. M. A.; Hursthouse, M. B.; Coles,
S. J. Chem. Soc., Dalton Trans. 2003, 1133.

S-S and Se-Se Bond Addition to Alkynes
Organometallics, Vol. 24, No. 6, 2005 1281
Scheme 4
Figure 3. Yield of 2 vs time in the reaction of hexyne-1
with complex 4 at different [Pd]/P(O-iPr)3 ratios (see
Experimental Part for details).
olato complexes such as Pd(SPh)2(dppe) (2.3486(7)
Å),13a Pd(SPh)2(PHCy2)2 (2.336(2) and 2.338(2) Å),13b
Pd(SC6F5)2(dppe)2 (2.354(1) and 2.361(1) Å),13c
Pd(SPy-2)2(dppe)2 (2.333(2) and 2.382(2) Å),13d or
Pd(SPh)2(dippf) (2.3703(7) and 2.3887(7) Å),13e and the
Pd(1)-S(1)-C(1) angle shows the almost ideal tetrahe-
dral value of 108.76(11)°. The Pd(1)-P(1) distance of
2.3050(9) Å is considerably longer than those in previ-
ously investigated Pd(II)-tertiary tri(alkyl)phosphito
complexes.14 The tri(isopropyl)phosphito groups are
staggered with respect to each other.
The reaction of the isolated mononuclear complex 4
with alkynes (R ) nBu, CH2OMe, CH2NMe2) resulted
in the quantitative formation of the corresponding
products 2 (>90% yield after 3 h at 80 °C in toluene).
In the same conditions the reaction of the dinuclear
complex 5 with alkynes gave only 30-40% of 2 and
insoluble polymeric species. The quantitative yield of 2
was obtained only if two or more equivalents of P(OiPr)3
were added to the solution. Therefore, the role of the
ligand excess is to prevent palladium complex polym-
erization. It should be noted that in all cases the
reactions of the isolated palladium complexes with
alkynes lead to the same product as the corresponding
catalytic reaction does (2).
After studying the stoichiometric reactions and es-
tablishing the structure of the palladium complexes we
have investigated the catalytic reaction. Using 31P and
1H NMR monitoring of the catalytic reaction complexes
3-6 were detected in solution with the ratio (3+4)/(5+6)
) 10/1, therefore confirming intermediate formation of
these complexes under the catalytic conditions. Finally,
to prove this assumption, we have performed the
catalytic reactions using the isolated mono- and di-
nuclear complexes (4 and 5) as the catalysts. Exactly
the same yields and stereoselectivity were obtained in
these catalytic reactions as compared to the Pd(OAc)2/
P(OiPr)3 and Pd2(dba)3/P(OiPr)3 catalytic systems.
The mechanism of E-E bond addition to alkynes
involves the following stages: (1) oxidative addition, (2)
ligand dissociation and alkyne coordination to form the
π-complex (8), (3) alkyne insertion into the M-E bond
(9), and (4) C-E reductive elimination releasing the
final product 2 (Scheme 4). In many cases it was
reported that an excess of the ligand retards alkyne
coordination and blocks the catalytic cycle.1 In the
studied case excellent yields were obtained only with
an excess of the ligand, which is rather unusual
behavior.
To reveal the mechanism of the reaction, we have
studied the reactions of isolated palladium chalcogenide
complexes with hexyne-1 at different P(O-iPr)3 ligand
concentrations (Figure 3). It was found that the excess
of the ligand in solution decreases the rate of the product
2 formation in the reaction of the palladium complex
with alkyne (Pd/L ratios of 1/10, 1/20, and 1/30 were
used; see Figure 3). This finding is in agreement with
the catalytic reaction mechanism (Scheme 4). Increasing
ligand concentration decreases the observed rate of the
product 2 formation, since coordination vacancy is
needed to bind alkyne and facilitate insertion to the
M-E bond.
According to the performed study, an excess of phos-
phite ligands retards alkyne coordination to the metal
complex (8) and decreases the rate of the product
formation (Figure 3). However, an excess of the ligand
is of vital importance to prevent catalyst deactivation
via the insoluble polymer (7) formation. The ratio [Pd]/
[L] ) 1/10 seems to be a good compromise to achieve
high yields in reasonable reaction time (Table 5).
According to the 31P NMR, both types of complexes
(mononuclear and dinuclear) are present under catalytic
conditions. Neither complex 8 nor 9 was detected in the
NMR monitoring of the stoichiometric or catalytic
reactions. Therefore, for the moment it is difficult to find
out whether dinuclear (5+6) or mononuclear (3+4)
complexes make major contributions to the product
formation under catalytic conditions. For simplicity only
the mononuclear complexes are shown in Scheme 4,
assuming that dinuclear complexes may react in the
same way. A detailed investigation of this problem will
be undertaken in our future studies.
3. Conclusions
It was shown that Pd complexes with trialkyl phos-
phite ligands are very efficient catalysts for the addition
reactions of Ar2E2 (E ) S, Se) to terminal alkynes. The
reaction catalyzed by Pd(0)-P(OR)3 has many advan-
tages in comparison with Pd(0)-PR3, since phosphite
ligands are readily available and can be easily removed
from the reaction mixture upon completing the catalytic
process.
Both mononuclear and dinuclear complexes were
detected in solution after oxidative addition of the E-E
bond to palladium. The relative concentration of the
complexes depends on the amount of the ligand in

1282 Organometallics, Vol. 24, No. 6, 2005
Ananikov et al.
CH3), 1.22 (m, 2H, γ-CH2), 1.46 (qw, 2H, â-CH2), 2.22 (tr, 2H,
R-CH2), 6.82 (s, 1H, HCd), 7.02 (m, 4H, Ar), 7.54 (m, 4H, Ar);
13C{1H} NMR (126 MHz; CDCl3; δ, ppm) 13.7, 21.8, 31.0, 39.4,
solution. The complexes were isolated and fully char-
acterized by NMR and X-ray diffraction studies, and it
was shown that in solution the complexes are in
equilibrium with each other.
The stoichiometric reactions of the isolated palladium
complexes with alkynes lead to the same product as the
catalytic reaction. It was found that increasing the
concentration of the phosphite ligand in solution de-
creases the rate of the product formation, but increases
the product yield by suppressing catalyst polymeriza-
tion.
3
116.3 (Ar,3J(C-F) ) 11 Hz), 116.5 J(C-F) ) 11 Hz, 123.8,
125.6, 127.3, 135.1 2J(C-F) ) 60 Hz, 135.2 2J(C-F) ) 60 Hz,
136.8, 162.5 1J(C-F) ) 248 Hz, 162.6 1J(C-F) ) 248 Hz; mass
spectrum (EI) m/z 432 (M+, 70) Anal. Calcd for C18H18F2Se2:
C, 50.25; H, 4.22. Found: C, 50.46; H, 4.32.
Z-HC(S-Ph)dC(S-Ph)-RCH2 CH2 CH2 CH2CH3 (2e): yel-
low oil; 1H NMR (500 MHz; CDCl3; δ, ppm) 0.83 (tr, 3H, CH3),
1.21 (m, 4H, γ-CH2, δ-CH2), 1.50 (qw, 2H, â-CH2), 2.24 (tr, 2H,
R-CH2), 6.57 (s, 1H, HCd), 7.20-7.33 (m, 6H, Ar), 7.37 (d, 2H,
Ar), 7.42 (d, 2H, Ar); 13C{1H} NMR (126 MHz; CDCl3; δ, ppm)
13.9, 22.3, 28.1, 30.9, 37.0, 126.6, 126.7, 128.8, 128.9, 129.0,
129.6 130.4, 133.8, 134.3, 135.8; mass spectrum (EI) m/z 314
(M+, 70). Anal. Calcd for C19H22S2: C, 72.56; H, 7.05. Found:
C, 72.58; H, 7.50.
â
γ
δ
Exploring the potential of phosphite ligands in the
catalytic carbon-element bond formation reactions and
further mechanistic details are the subjects of ongoing
studies.
Z-HC(S-Ph)dC(S-Ph)CH2OCH3 (2g): yellow oil; 1H NMR
(500 MHz; CDCl3; δ, ppm) 3.28 (s, 3H, CH3), 3.95 (s, 2H, CH2),
6.98 (s, 1H, HCd), 7.20-7.35 (m, 6H, Ar), 7.40 (d, 2H, Ar),
7.43 (d, 2H, Ar); 13C{1H} NMR (126 MHz; CDCl3; δ, ppm) 57.9,
74.4, 126.8, 127.1, 127.2, 129.0, 129.1, 130.0 130.2, 133.3,
134.4, 134.9; mass spectrum (EI) m/z 288 (M+, 70). Anal. Calcd
for C16H16OS2: C, 66.63; H, 5.59. Found: C, 66.48; H, 5.99
Z-HC(Se-Ph)dC(Se-Ph)C6H4NH2 (2l): yellow oil; 1H NMR
(500 MHz; CDCl3; δ, ppm) 3.60 (br s, 2H, NH2), 6.49 (ddd, 1H),
6.82 (tr, 1H), 6.90 (ddd, 1H), 6.98 (tr, 1H), 7.10-7.18 (m, 3H),
7.29 (m, 3H), 7.36 (dd, 2H), 7.56 (s, 1H, HCd), 7.59 (m, 2H);
13C{1H} NMR (126 MHz; CDCl3; δ, ppm) 114.1, 114.6, 118.0,
126.5, 127.8, 129.1, 129.2, 129.4, 130.6, 130.7, 131.1, 131.4,
133.2, 136.2, 141.7, 146.0; mass spectrum (EI) m/z 431 (M+,
20). Anal. Calcd for C20H17NSe2: C, 55.96; H, 3.99; N, 3.26.
Found: C, 55.96; H, 3.99; N, 3.05.
4. Experimental Part
4.1. General Comments. The synthetic work was carried
out under argon atmosphere. Solvents were purged with argon
before use. All NMR measurements were performed using a
three-channel Bruker DRX500 spectrometer operating at
500.1, 202.5, 125.8, and 95.4 MHz for 1H, 31P, 13C, and 77Se
nuclei, respectively. The spectra were processed on a Silicon
Graphics workstation using the XWINMR 3.0 software pack-
age. All 2D spectra were recorded using an inverse triple
resonance probehead with an active shielded Z-gradient coil.
1H and 13C chemical shifts are reported relative to the
corresponding solvent signals used as internal reference,
external 85% H3PO4/H2O (δ ) 0.0 ppm) was used for 31P, and
Ph2Se2/CDCl3 (δ ) 463.0 ppm) was used for 77Se. See the
previous study for a detailed description of the 2D experi-
ments.5
4.2. General Synthetic Procedure. (i) Pd2dba3 as Cata-
lyst Precursor. Under argon Ar2E2 (4.0 × 10-4 mol), Pd2dba3
(5.6 mg, 6.1 × 10-6 mol), P(OiPr)3 (25 mg, 1.2 × 10-4 mol),
and the alkyne (6.1 × 10-4 mol) were dissolved in 0.6 mL of
degassed toluene. The reaction was performed in a sealed tube
for 3 h at 100 °C. The mixture remained homogeneous during
the reaction without noticeable catalyst polymerization.
(ii) Pd(OAc)2 as Catalyst Precursor. Under argon Ar2E2
(4.0 × 10-4 mol), Pd(OAc)2 (2.7 mg, 1.2 × 10-5 mol), P(OiPr)3
(30 mg, 2.4 × 10-4 mol), and the alkyne (6.1 × 10-4 mol) were
dissolved in 0.6 mL of degassed toluene. The reaction was
performed in a sealed tube for 3 h at 100 °C. The mixture
remained homogeneous during the reaction without noticeable
catalyst polymerization.
Z-HC(S-Ph)dC(SPh)(3-C9H6N) (2m): yellow oil; 1H NMR
(500 MHz; CDCl3; δ, ppm) 7.00 (tr, 1H), 7.10 (tr, 2H), 7.24 (d,
2H), 7.26 (d, 1H), 7.32 (tr, 2H), 7.39 (s, 1H, HCd), 7.39 (tr,
1H), 7.47 (d, 2H), 7.55 (tr, 1H), 7.65 (d, 1H), 7.95 (d, 1H), 8.17
(d, 1H), 9.07 (d, 1H); 13C{1H} NMR (126 MHz; CDCl3; δ, ppm)
126.2, 126.3, 126.8, 127.5, 127.8, 127.9, 128.6, 129.0, 129.0,
129.2, 129.3, 130.6, 131.5, 132.8, 133.7, 134.6, 138.8, 147.1,
148.9; mass spectrum (EI) m/z 371 (M+, 70). Anal. Calcd for
C23H17NS2: C, 74.36; H, 4,61; N, 3.77. Found: C, 74.09, H,
4.80; N, 3,43.
4.3. Synthesis of the Mononuclear Complex trans-
[Pd(SPh)2(P(OiPr)3)2] (4). Pd(OAc)2 (0.200 g, 0.89 mmol),
Ph2S2 (0.389 g, 1.78 mmol), P(OiPr)3 (2.23 g, 10.7 mmol), and
10 mL of benzene were placed into a 50 mL round-bottom
flask. The mixture was stirred at room temperature for 20 min
until a homogeneous reddish-brown solution was formed. The
solution was stirred for 2 h at 70 °C. The solvent was removed
on a rotary evaporator, giving the crude product as a dark
brown oil. The oil was dissolved in a minimum amount of
hexane and kept at -20 °C overnight. Brown crystals were
washed with 2 mL of cold hexane and dried under vacuum.
Yield: 0.561 g (85%). Anal. Calcd for C30H52O6P2PdS2: C,
48.61; H, 7.07; S, 8.65; Pd, 14.36; P, 8.36. Found: C, 48.81; H,
7.22; S, 8.71; Pd, 14.40; P, 8.38. 31P{1H} NMR (202 MHz; C6D6;
(iii) Product Separation and Purification. After com-
pleting the reaction the solvent was evaporated on a rotary
evaporator and the product was purified by flash chromatog-
raphy on silica L5/40 with hexane/ethyl acetate gradient
elution. After drying in a vacuum the pure products were
obtained as a light oil. The yields are given in Table 5. The
products 2a, 2b, 2f, 2h, 2i, 2j, and 2k were identified according
to the published data.3,5,9 The data for the other compounds
are given below. In all cases the structure of the products was
1
δ, ppm) 102.7; H NMR (500 MHz; C6D6; δ, ppm; J, Hz) 7.82
confirmed with H, 13C, and 77Se NMR. The stereochemistry
1
(m, 4H, Ph), 7.03 (m, 4H, Ph), 6.88 (m, 2H, Ph), 4.95 (m, 6H,
CH), 1.10 (d, J ) 6.0, 36H, CH3).
was determined using 2D NOESY and COSY-LR experiments.
Z-HC(S-C6H4CH3)dC(S-C6H4CH3)-RCH2âCH2γCH2CH3
4.4. Synthesis of the Dinuclear Complex trans-
[Pd2(SPh)4(P(OiPr)3)2] (5). Pd(OAc)2 (0.200 g, 0.89 mmol),
Ph2S2 (0.389 g, 1.78 mmol), P(OiPr)3 (2.23 g, 10.7 mmol), and
10 mL of benzene were placed into a 50 mL round-bottom
flask. The mixture was stirred at room temperature for 20 min
until a homogeneous reddish-brown solution was formed. The
solution was stirred for 2 h at 70 °C. The solvent was removed
on a rotary evaporator, giving the crude product as a dark
brown oil. The oil was preadsorbed on 3 g of silica L40/100
stirring with 10 mL of CHCl3. The solvent was evaporated
followed by the flash chromatography on silica L5/40 with
1
(2c): yellow oil; H NMR (500 MHz; CDCl3; δ, ppm) 0.83 (tr,
3H, CH3), 1.22 (m, 2H, γ-CH2), 1.48 (qw, 2H, â-CH2), 2.22 (tr,
2H, R-CH2), 2.33 (s, 3H, CH3-Ar), 2.34 (s, 3H, CH3-Ar), 6.48
(s, 1H, HCd), 7.12 (m, 4H, Ar), 7.32 (m, 4H, Ar); 13C{1H} NMR
(126 MHz; CDCl3; δ, ppm) 13.7, 20.9, 21.0, 21.8, 30.6, 36.5,
128.6, 129.6, 129.7 130.0, 130.1, 131.0, 132.4, 134.2, 136.8,
136.8; mass spectrum (EI) m/z 328 (M+, 80). Anal. Calcd for
C20H24S2: C, 73.12; H, 7.36. Found: C, 73.14; H, 7.56.
Z-HC(Se-C6H4-F)dC(Se-C6H4-F)-RCH2 CH2 CH2CH3 (2d):
â
γ
yellow oil; 1H NMR (500 MHz; CDCl3; δ, ppm) 0.82 (tr, 3H,

S-S and Se-Se Bond Addition to Alkynes
Organometallics, Vol. 24, No. 6, 2005 1283
Table 8. Crystallographic Data for 5 and 4
hexane/ethyl acetate gradient elution. X-ray quality dark
brown crystals were obtained after crystallization from
hexane (20 h, -20 °C). Yield: 0.327 g (69%). Anal. Calcd for
C42H62O6P2Pd2S4: C, 47.32; H, 5.86; P, 5.81; Pd, 19.97; S, 12.03.
Found: C, 48.07; H, 5.89; P, 5.80; Pd, 19.92; S, 12.17. 1H NMR
(500 MHz; C6D6; δ, ppm; J, Hz) 8.13 (m, 4H, Ph), 7.98 (m, 4H,
Ph), 7.09 (m, 4H, Ph), 6.96 (m, 8H, Ph), 4.95 (m, 6H, CH), 1.04
(d, J ) 6.1, 36H, CH3); 31P{1H} NMR (202 MHz; C6D6; δ, ppm)
98.8.
4.5. Kinetic Measurements of the Alkyne Reaction
with Complex 4 at Different Ligand Concentrations.
Complex 4 (4.44 × 10-2 mmol, 0.033 g), 0.010 mL of hexyne-1
(8.88 × 10-2 mmol), and 0.3 mL of C6D6 were placed into each
of the three NMR tubes and purged with argon. P(OiPr)3s
0.101 mL (0.44 mmol), 0.201 mL (0.89 mmol), and 0.302 mL
(1.33 mmol)swas added to the NMR tubes, maintaining
[Pd]/P(OiPr)3 ratios of 1/10, 1/20, and 1/30, respectively. The
necessary amount of C6D6 was added to each of the NMR tubes
to increase the total solution volume to 0.7 mL. The NMR tubes
were purged with argon and sealed. The reactions were carried
out at 70 °C and monitored with 1H NMR. The dependence of
the product 2a yield versus time is shown in Figure 3.
4.6. Reactions of Palladium Complexes with Alkynes.
The same as above; see the text for the [Pd]/P(OiPr)3 ratio and
other details.
4.7. X-ray Structure Determinations. Data were col-
lected on a Bruker three-circle diffractometer equipped with
a SMART 1000 CCD detector (for 5) and Syntex P21 automated
four-circle diffractometer (for 4); in the case of 5 data were
corrected for absorption.15 For details see Table 8. The
structures were solved by direct methods and refined for all
data by full-matrix least-squares methods on F2 with aniso-
tropic thermal parameters for non-hydrogen atoms. The
refinement of the Flack parameter for compound 5, which was
equal to 0.32(4), indicates that the absolute structure in this
case cannot be determined unambiguously due to the specific
centrosymmetric arrangement of heavy atoms Pd and P. The
hydrogen atoms were placed in calculated positions and refined
in the riding model with fixed thermal parameters. All
calculations were carried out by use of the SHELXTL PLUS
(PC Version 5.10) program.16
5
4
empirical formula
fw
C
42H62O6P2S4Pd2
C
30H52O6P2S2Pd
1065.90
120(2)
741.18
173(2)
temp (K)
cryst size (mm)
cryst syst
space group
a (Å)
0.30 × 0.28 × 0.21 0.50 × 0.40 × 0.30
monoclinic
Pc
monoclinic
P21/c
14.6763(19)
14.9844(19)
11.8916(15)
113.396(2)
2400.1(5)
2
12.274(3)
12.865(3)
13.011(3)
112.62(3)
1896.5(7)
2
b (Å)
c (Å)
â (deg)
V (Å3)
Z
dc (g cm-3
F(000)
)
1.475
1.298
1096
776
µ (mm-1
)
1.032
0.719
θ range (deg)
index range
1.51 to 27.00
-18 e h e 18
-19 e k e 19
-15e l e 15
22 257
2.40 to 26.05
-9 e h e 15
-15 e k e 15
-16 e l e 14
6821
no. of rflns collected
no. of unique rflns
no. of rflns with
I > 2σ(I)
R1; wR2 (I > 2σ(I))
R1; wR2 (all data)
10 394
9028
3725
3091
0.0611; 0.1442
0.0698; 0.1526
0.0416; 0.1013
0.0532; 0.1093
3725/0/187
no. of data/restraints/ 10394/2/506
params
GOF on F2
0.999
0.001
1.069
0.001
max. shift/error
absolute struct param 0.32(4)
largest diff peak/
hole (e Å-3
abs corr Tmax; Tmin
1.880/-1.538
1.233/-0.710
)
0.812; 0.747
none
(Grant for Young Scientists MD-2384.2004.3), the Rus-
sian Federation of Basic Research (Project No.04-03-
32501), and the Chemistry and Material Science Branch
of the Russian Academy of Sciences (Program: “Theo-
retical and experimental investigations of the nature
of chemical bonding and mechanisms of the most
important chemical reactions and processes”). The X-ray
study was performed in the frame of the Russian
Federation President program in support of the scien-
tific schools (Project No. SS-1060.2003.3).
Crystallographic data for 5 and 4 have been deposited with
the Cambridge Crystallographic Data Center, CCDC No.
253771 and No. 253772, respectively, and may be obtained free
of charge from the Director, CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax: +44 1223 336033; e-mail: deposit@
ccdc.cam.ac.uk or www.ccdc.cam.ac.uk).
Supporting Information Available: Kinetic measure-
ments of the catalytic reaction with PPh3 and P(OiPr)3 ligands.
Tables of atom coordinates, bond lengths and angles, torsion
angles, and anisotropic displacement parameters for 5 and 4.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. The work was carried out with
partial support by President of Russian Federation
(15) Sheldrick, G. M. SADABS, V2.01, Bruker/Siemens Area Detec-
tor Absorption Correction Program; Bruker AXS: Madison, WI, 1998.
(16) Sheldrick, G. M. SHELXTL, V5.10; Bruker AXS Inc.: Madison,
WI, 1997.
OM049082G