Hybrid thiophosphoryl-benzothiazole palladium SCN-pincer complexes: Synthesis and effect of structure modifications on catalytic performance in the suzuki cross-coupling

Article abstract of DOI:10.1021/om101012r

The novel hybrid pincer-type ligands 3, 6, 9, and 11, bearing, as donating sites, a thiophosphoryl group and an imine moiety of the benzothiazole ring bound either directly to the central benzene core or attached to the latter one via O or NHlinkers, unde

Full text of DOI:10.1021/om101012r

ARTICLE
pubs.acs.org/Organometallics
Hybrid ThiophosphorylꢀBenzothiazole Palladium SCN-Pincer
Complexes: Synthesis and Effect of Structure Modifications on
Catalytic Performance in the Suzuki Cross-Coupling
Vladimir A. Kozlov,† Diana V. Aleksanyan,† Yulia V. Nelyubina,† Konstantin A. Lyssenko,†
Pavel V. Petrovskii,† Andrei A. Vasil’ev,‡ and Irina L. Odinets*,†
†A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilova Street, Moscow 119991, Russia
‡N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky Prospect, 119991 Moscow, Russia
S Supporting Information
b
ABSTRACT: The novel hybrid pincer-type ligands 3, 6, 9, and
11, bearing, as donating sites, a thiophosphoryl group and an
imine moiety of the benzothiazole ring bound either directly to
the central benzene core or attached to the latter one via O or
NH linkers, undergo direct cyclopalladation at the C(2) position
of the central benzene core in reaction with (PhCN)2PdCl2
(MeCN or PhCN as a solvent, 80ꢀ120 °C) to afford 5,5- and
5,6-membered κ3-SCN-palladium pincer complexes 12ꢀ15 in
good to high yields. Direct cycloplatination with the related platinum precursor was successful only in the case of N-[3-(1,3-
benzothiazol-2-yl)phenyl]-P,P-diphenylthiophosphinic acid amide 9. The Pd(II) complexes 12ꢀ15 were found to be highly active
(pre)catalysts for the Suzuki cross-coupling of a range of electronically varied aryl bromides with phenylboronic acid. The most
active complex, 14a, also promoted efficiently the coupling of chloroacetophenone, ranking among the best pincer complexes
suggested for this reaction.
’ INTRODUCTION
could avoid the use of any additional ligand. Noteworthy, the best
results for coupling of chloroarenes were achieved (but mainly
the Heck reaction) just with phosphorus-containing pincer
complexes or with palladacycles modified by carbenes. That
was related to the extra stability provided by these ligands toward
the low-ligated catalytically active Pd(0) species involved in
catalytic cycle.5 A literature survey has revealed a few pincer
palladium complexes IꢀVIII (Figure 1) that displayed catalytic
activity when aryl chlorides were used as substrates.6b,e,f,7ꢀ11
Concerning the structures of these palladacycles, one may note
that most of them bear at least one P(III)-donating moiety
(phosphinite, aminophosphine, or phosphine). A high catalytic
efficiency of the only divergent NCN complex VII6f apparently
stems from the hemilabile coordination of the ligand that
facilitates generation of active Pd(0) species.
Directed by our interest in unsymmetrical pincer complexes
with organothiophosphorus ligands, we have elaborated several
palladium pincer systems and thoroughly explored their catalytic
performance in the Suzuki reaction as an appropriate activity
evaluation benchmark (Figure 2). Thus, starting from 5,5-
membered SCS0 thiocarbamoylꢀthiophosphoryl palladacycles
IX12 we showed in principle an ability of pincer complexes with a
PdS coordinating arm to promote the Suzuki cross-coupling of
Palladium-catalyzed cross-coupling reactions have greatly im-
proved the possibilities for chemists to create sophisticated
chemicals, and it is not surprising that the Nobel Prize in
Chemistry in 2010 was awarded to R. F. Heck, E. Negishi, and
A. Suzuki, who developed this area of organic synthesis. Never-
theless, among a plethora of palladium-catalyzed cross-couplings
the Suzuki reaction, which represents the coupling of an aryl
halide with an organoboron reactant and is perceived to be one of
the most powerful methods for CarylꢀCaryl bond construction,
occupies a special place.1,2 An utmost interest that this reaction
has acquired for both academic and industrial purposes is
explained by easy handling of the boron precursors (stability
and nontoxicity), relatively mild reaction conditions, tolerance to
a wide range of functionalities, and facility of workup. One of the
main challenges in this reaction still pertains to the use of less
reactive but cheaper and available aryl chlorides instead of
bromo- and iodoarenes, relatively easily introduced to this
cross-coupling under the catalytic action of a wide range of
organopalladium species. According to the literature data, very
good results for the coupling of chloroarenes were achieved using
different monopalladacycles or, more precisely, their adducts
with trivalent phosphorus derivatives.3 In this respect, applica-
tion of pincer complexes (including nonsymmetrical ones),4ꢀ6 i.e.,
those having two fused metallacycles resulting from stabilization
of a metalꢀcarbon bond by two ancillary coordinating arms,
Received: October 25, 2010
Published: May 04, 2011
r
2011 American Chemical Society
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bromoarenes with phenylboronic acid. Further developed hybrid
palladium pincer complexes XꢀXII13ꢀ15 with two fused metal-
lacyles of unequal sizes were found to be more active than
compounds IX. At the same time, SCN palladacycles XII bearing
two coordination sites of completely different nature with a soft
sulfur and hard nitrogen donor atoms appeared to have the
highest catalytic activity in this range and even promoted the
Suzuki cross-coupling of aryl chlorides with PhB(OH)2, although
the yield of a biphenyl product was only about 20%.15
and (amino)phosphine (IIIꢀV)-based pincer complexes, espe-
cially as organothiophosphorus(V) derivatives are much easier to
handle.
Herein, we report on the convenient synthetic approach to a
series of novel hybrid pincer ligands having thiophosphoryl and
benzothiazole coordinating arms that are either directly bound to
the central benzene ring or connected with it via an additional
linker and their 5,5- and 5,6-memebered palladium SCN-pincer
complexes. These complexes were proved to be excellent
(pre)catalysts for the Suzuki cross-coupling of aryl bromides
and showed, to the best of our knowledge, second-place activity
among pincer complexes in the reaction with activated aryl
chlorides implied in terms of a combination of the reaction time,
conversion, and catalyst loading. Some mechanistic aspects of the
catalytic processes are discussed.
Encouraged by these preliminary findings, we intended to
design a new hybrid pincer system of SCN type combining a
thiophosphoryl moiety with a bulky imine functionality, incor-
porated, for example, into a benzothiazole fragment. The choice
of such heterocyclic moiety was dictated in particular by a
convenient synthetic transformation of previously elaborated
hybrid thioamide ligands, e.g., as those in complexes IX and
XI, or their precursors into the corresponding benzothiazole
derivatives via oxidative cyclization. Moreover, monocyclic ben-
zothiazole-based palladium complexes were shown to possess
high catalytic activity in various chemical processes, including
Heck vinylation of aryl iodides,16 and, in addition, a symmetrical
NCN-pincer platinum complex with a (bis)benzothiazolylbenzene
ligand exhibited valuable luminescent properties.17 Moreover,
adjusting the position of additional linkers between the donor
groups and a central benzene core could result in hybrid 5,6-
membered pincer complexes with either an imine- or thiopho-
sphoryl-containing six-membered metallacycle. Such a structure
variation would provide the possibility of deeper insight into the
influence of structural modifications on the catalytic activity of
SCN-pincer complexes. Of particular interest is the opportunity
to estimate whether OꢀPdS and NHꢀPdS derivatives could
compete with the above-mentioned phosphinite (I, II, VI, VIII)-
’ RESULTS AND DISCUSSION
Synthesis of Ligands. The first ligand of this series with
thiophosphoryl and benzothiazole coordinating arms directly
bound to the central benzene ring was obtained by the oxidative
cyclization18 of secondary N-arylthioamides 1 or 2 (previously
used in the synthesis of complex IX12), having either a phos-
phoryl or a thiophosphoryl group, under the action of potassium
ferricyanide in aqueous sodium hydroxide (the Jacobson
synthesis). Evidently, harnessing of the phosphoryl-substituted
thioamide 1 (X = O, method A) as a precursor in the synthesis of
3 required one more thionation step, whereas its S,S-analogue 2
(X = S, method B) provided the desired ligand in 54% yield in
only one step while retaining the PdS moiety (Scheme 1).
To obtain the pincer ligands with a thiophosphoryl arm
“elongated” with ꢀOꢀ and ꢀNHꢀ bridges, we devised a
synthetic approach based on thiophosphorylation of meta-ben-
zothiazole-substituted phenol and aniline as suitable precursors,
respectively. Therefore, the oxidative cyclization of 3-methoxy-
N-phenylbenzenecarbothioamide 414 with K3[Fe(CN)6] fol-
lowed by demethylation afforded phenol predecessor 5, while
the one-pot condensation of 3-nitrobenzoic acid chloride gen-
erated in situ and aminothiophenol followed by reduction of the
Scheme 1. Synthesis of 2-[3-(Diphenylthiophosphoryl)-
phenyl]-1,3-benzothiazole, 3
Figure 1. Pincer complexes promoting the Suzuki cross-coupling of
chloroarenes with phenylboronic acid.
Figure 2. Hybrid pincer complexes with a thiophosphoryl coordinating arm promoting the Suzuki cross-coupling of bromoarenes with
phenylboronic acid.
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Scheme 2. Synthesis of Thiophosphoryloxy- and Thiophosphorylamino-Substituted SCN-Pincer Ligands 6 and 9 with Ben-
zothiazole Moieties
Scheme 3. Synthesis of 2-[3-(Diphenylthiophosphoryl)-
phenoxy]-1,3-benzothiazole, 11
nitro group with tin(II) chloride provided the corresponding
aniline 8 (Scheme 2). Further (thio)phosphorylations under
appropriate conditions depending on the substrate nature gave
the desired ligands 6 and 9 in good yields.
Figure 3. General view of ligand 3 in a representation of atoms by
thermal ellipsoids (p = 50%).
Finally, to introduce an oxygen bridge between the benzothia-
zole heterocycle and benzene core, the reaction of the sodium
salt of thiophosphoryl-substituted phenol 1013 with 2-chloro-
benzothiazole was used (Scheme 3).
relative to the benzene core: in ligand 3 it deviates in the same
direction as the PdS group (the pseudotorsion angle SPCS0 is
99.0(1)°) with an angle between the benzothiazole ring and
central benzene core of 7.5(1)°, while in the above thiopho-
sphorylꢀthioamide analogues these groups deviate in opposite
directions from the benzene core.
Synthesis and Characterization of Pincer Complexes. In
reaction with (PhCN)2PdCl2, ligands 3, 6, 9, and 11 underwent
direct cyclopalladation at the C(2) position of the central
benzene ring, providing the corresponding 5,5- or 5,6-membered
SCN-pincer complexes 12ꢀ15 in good to high yields (60ꢀ89%)
(Scheme 4). The most reactive thiophosphorylamino-substi-
tuted derivative, 9, afforded palladacycle 14a in 89% yield upon
refluxing in acetonitrile for 2 h. At the same time, substantially
higher temperature (heating in benzonitrile at 120 °C for 1ꢀ3 h)
was required to accomplish cyclopalladation of the other ligands
3, 6, and 11. In attempting to perform cycloplatination of the
synthesized compounds with the related platinum precursor, we
managed to obtain only complex 14b having a NH-PdS
coordination arm, with a yield not exceeding 40%.
The structures of the ligands obtained were unambiguously
confirmed by multinuclear NMR (31P, H, 13C) and IR spec-
1
troscopy data. Thus, the 31P NMR spectra of 3 and 11 show
singlet signals at ca. 42 ppm characteristic for phosphine sulfides,
while the phosphorus resonances for 6 and 9 are observed at 83
and 53 ppm, respectively, i.e., the regions typical for the signals of
P atoms of thiophosphoryloxy and thiophosphorylamino groups.
The presence of several phenyl rings in the molecules of
compounds 3, 6, 9, and 11 complicates the interpretation of
1
the H NMR spectra in the region of aromatic proton signals;
however, all the carbon resonances in the 13C NMR spectra can
be easily identified (see Experimental Section). Moreover, in the
IR spectra of all the ligands one may note the absorption bands at
628ꢀ649 cmꢀ1 corresponding to the PdS bond stretching
vibrations. The molecular structure of compound 3 was also
elucidated by X-ray diffraction analysis (Figure 3). According to
the results, the geometric parameters of the thiophosphorylben-
zene moiety in 3 are very close to those in 3-diphenylthio-
phosphoryloxy(amino)benzoic acid thioamides, i.e., free ligands
of complexes XI.14 The major difference in their molecular
geometries concerns the disposition of the CꢀS functionality
Complexes 12ꢀ15 are yellow crystalline solids, air and
moisture stable in the solid state. Moreover, palladium
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Scheme 4. Synthesis of SCN-Pincer Complexes 12ꢀ15 Having Thiophosphoryl and Benzothiazole Coordinating Arms
thiophosphorylꢀbenzothiazole pincer complexes are character-
ized with rather high thermal stability and do not undergo
decomposition up to ∼250 °C, while the decomposition point
for platinum complex 14b is essentially lower (180 °C).
The structures of the complexes obtained were assigned on the
basis of 31P, 1H, and 13C NMR and IR spectroscopy. The signals
of phosphorus atoms of 12 and 15 in the 31P NMR spectra
appeared to be strongly deshielded (Δδ = 22 and 15 ppm,
respectively) upon complexation of phosphine sulfide moieties.
Similarly, the phosphorus resonances of OPS and NHPS groups
in 13 and 14 are shifted by ∼7 ppm compared to the signals of
free ligands, indicating the coordination of the metal ion by these
fragments, although the direction of shifting is opposite to that of
12 and 15. The integral intensities of the proton signals in the 1H
Figure 4. General view of complex 12 in a representation of atoms by
NMR spectra of 12ꢀ15 are reduced by 1H, confirming the
occurrence of metalation. In the 13C NMR spectra of 14a, the
signal of the C2 atom, at which the metalation occurred, is
characterized with the greatest downfield shift (16 ppm) and an
thermal ellipsoids (p = 50%). The interatomic distances PdꢀX (Å) are
Pd(1)ꢀN(1) 2.0970(19), Pd(1)ꢀC(2) 1.968(2), Pd(1)ꢀCl(1)
2.3986(6), Pd(1)ꢀS(1) 2.2930(6).
3
increase in JCP (by ∼2 Hz), although the resonances of other
carbon atoms (e.g., C1 and C7) are also indicative of the complex
formation (see Experimental Section). A lower frequency shift of
the absorption bands corresponding to ν(PdS) compared to
those of the free ligands provides additional evidence for the
coordination of the metal ion by these groups.
Furthermore, the structures of complexes 12 (crystallosolvate
with 0.5 CH2Cl2), 13, and 15 (crystallosolvate with CH2Cl2)
3
were unambiguously confirmed by the single-crystal X-ray
diffraction study. In all cases, the palladium atom appeared to
be bonded with the nitrogen atom of the benzothiazole moiety
(Figures 4ꢀ6); such a behavior has been already reported for the
Pt(II) pincer complexes of bis(benzothiazolyl)benzene.17
The geometrical parameters of the palladacycles involving the
PS and NC functionalities are different, although lie within the
ranges observed earlier for similar systems.12,14,15 In particular,
the five-membered NC ring (5NC) in 12 is planar within 0.02 Å,
like those in the above-mentioned platinum complex with bis-
(benzothiazolyl)benzene;17 a similar ring in 13 is a flattened
envelope with the C(2) atom deviating by 0.16(1) Å. The
conformation of the 5PS palladacycles in 12 and 15 is an
envelope with the S(1) atom deviating by 0.58(1) and 0.89(1)
Å, respectively. For comparison, this deviation in the case of
Figure 5. General view of complex 13 in a representation of atoms by
thermal ellipsoids (p = 50%). The interatomic distances PdꢀX (Å) are
Pd(1)ꢀN(1) 2.0780(13), Pd(1)ꢀC(2) 2.0187(16), Pd(1)ꢀCl(1)
2.3987(5), Pd(1)ꢀS(1) 2.2879(5).
SCS0-pincer complexes IX12 is 0.24ꢀ0.28 Å. The six-membered
rings in 13 and 15 are in a half-chair (PS cycle with the S(1) and
P(1) atoms deviating by 0.38(1) and ꢀ0.53(1) Å) or a twist (NC
cycle with the N(1) and C(7) atoms deviating by 0.92(1) and
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0.69(1) Å) conformation, respectively. It should be mentioned
that in the palladium complex with a similar (pyridine-based)
6NC fragment19 the corresponding N and C atoms deviate by
0.97ꢀ0.98 and 0.73ꢀ0.79 Å, whereas in the case of the aliphatic
NC substituent these deviations are even more pronounced (see,
e.g., ref 20). Therefore, the benzothiazole group makes the
corresponding NC palladacycle moiety less flexible, although
affecting only slightly the binding with the second functionality.
The latter is also reflected in the coordination polyhedron of the
palladium atom. In all cases, the Pd(1) atom is characterized by a
distorted square-planar configuration with folding along the
The supramolecular organizations of complexes 12, 13, and 15
are completely different, partly owing to the presence of solvated
dichloromethane in the crystals of 12 and 15. Thus, pincer
molecules in 12 form infinite chains via rather strong S(1) S(2)
3 3 3
interaction (S S 3.299(2) Å). These associates are held together
3 3 3
by a weaker π π interaction between the benzothiazole moiety
and the benzene core (C C 3.389(3) Å) and a number of
3 3 3
3 3 3
CꢀH Cl and CꢀH π contacts. There is also a very weak
3 3 3
3 3 3
3 3 3
CꢀH Pd contact (Pd C 3.569(2) Å) involving the dichlor-
3 3 3
omethane molecule. The molecules of complex 13 are assembled
into a 3D framework by means of CꢀH π, CꢀH S, and
3 3 3
3 3 3
S(1) N(1) line. The C(2)Pd(1)Cl(1) angles, dihedral angles
CꢀH Cl interactions. In 15, in addition to these three types of
3 3 3
3 3 3
between the Pd(1)C(2)S(1)N(1) and Pd(1)Cl(1)S(1)N(1)
planes, and deviations of the chlorine atoms—the parameters
describing this distortion of the square-planar configuration—
vary in the narrow ranges of 171.3(1)ꢀ176.3(1)°, 3.7(1)ꢀ
10.2 (1)°, and 0.15(1)ꢀ0.43(1) Å, respectively; these values
are typical for 5,5- and 5,6-membered pincer palladium
complexes.12,14,15
contacts, CdS Cl (S Cl 3.357(2) Å) and π π (the
3 3 3
3 3 3
3 3 3
smallest C C distance between two benzothiazole cycles is
3 3 3
3.345(3) Å) interactions are observed between the molecules of
the complex. The latter are assembled with the solvate dichloro-
methane molecules by Cl(dichloromethane) π(benzothiazole)
3 3 3
(Cl S 3.309(2) Å), CꢀH π, and CꢀH Cl contacts.
3 3 3
3 3 3
3 3 3
Catalytic Studies. Similar to the other palladium pincer
complexes IXꢀXII with hybrid thiophosphorylated ligands,
complexes 12ꢀ15 were tested as (pre)catalysts for the
SuzukiꢀMiyaura cross-coupling of aryl halides with phenyl-
boronic acid. For correct comparison of the catalytic activities
of complexes both within the present series and with IXꢀXII,
all the experiments were carried out under the same condi-
tions—heating in DMF at 120 °C using K3PO4 as a base—the
system suggested for the symmetrical SCS-pincer com-
plex having sulfide coordinating arms3c and successfully
adopted for SCS0 and SCN thiophosphoryl-based pallada-
cycles IXꢀXII.
Several aryl halides were efficiently subjected to the coupling
reaction, and the results are summarized in Table 1. For each
particular complex (12, 13, 14a, 15), the normal dependence on
the electronic properties of the substituent R (R = C(O)Me,
OMe, NMe2) at the aryl bromide was observed.21
For a set period of time (5 h), all the palladacycles under
investigation afforded the complete conversion of easy-to-couple
substrate 4-bromoacetophenone, being used in 1 mol %, and the
catalyst loading could be diminished to 0.1 and 0.01 mol %
Figure 6. General view of complex 15 in a representation of atoms by
thermal ellipsoids (p = 50%). The interatomic distances PdꢀX (Å) are
Pd(1)ꢀN(1) 2.0644(13), Pd(1)ꢀC(2) 1.9858(16), Pd(1)ꢀCl(1)
2.3946(4), Pd(1)ꢀS(1) 2.3154(4).
Table 1. ThiophosphorylꢀBenzothiazole Pincer Palladium Complex-Catalyzed Suzuki Cross-Couplings
Pd cat./conversion, %a
entry
aryl halide
cat load. (mol %)
12
100
13
100
14a
100
15
100
1
4-bromoacetophenone
4-bromoacetophenone
4-bromoacetophenone
4-bromoanisole
1
2
0.1
0.01
1
100
74
97
92(88)
77
61
2
100
95.5
98.5
100(92)
92
100
100
99
100
3
100
4
61(55)
81(62)
92(84)
40
5
4-bromoanisole
0.1
0.01
1
99.5(86)
98
6
4-bromoanisole
7
4-bromo-N,N-dimethylaniline
4-bromo-N,N-dimethylaniline
4-chloroacetophenone
2-chloroacetophenone
39
53
8
0.1
0.1
0.1
26
53
32
9
0
25
93
49
10
0
13
29
3
a Yields in brackets refer to the reactions performed with Bu4NBr additive.
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Figure 7. Plots of conversion vs time for the couplings of 4-bromoacetophenone (a) (cat. loading 0.01 mol %) and 4-bromoanisole (b) (cat. loading 0.1
mol %) catalyzed by complexes 12ꢀ15.
Figure 8. Catalytic activity of SCS0 and SCN thiophosphoryl-containing pincer palladium complexes in the cross-coupling of 4-bromoanisole and
phenylboronic acid.
retaining the close yields (Table 1, entries 1ꢀ3). Nevertheless,
further reduction in the catalyst amount (to 0.001 mol %) led to a
drop in the conversion to only several percent. Good to excellent
yields (77ꢀ98%) were achieved for the coupling of 4-bromoa-
nisole at a very low (0.01 mol %) catalyst loading (Table 1,
entries 4ꢀ6), although its further reduction afforded no cou-
pling. In reaction with the less active 4-bromo-N,N-dimethylani-
line, the yields of the corresponding biaryl product for a catalyst
loading of 1 mol % ranged from 39% to 61%, which is reasonably
good for such an electronically deactivated substrate (Table 1,
entry 7). However, upon a 10-fold reduction of the catalyst
amount, a moderate level of conversion (53%) was retained only
for complex 14a, appearing to be the most active one, while 5,5-
membered SCN palladacycle 12 was almost inactive (Table 1,
entry 8). Note that in some cases the activity at the lower catalyst
loading of 0.1ꢀ0.01 mol % was somewhat higher than that when
1 mol % of a catalyst was used. Apparently, if the complexes serve
as a reservoir of catalytically active Pd(0) particles, at high level of
catalyst loading these colloid particles may stick together
(Ostwald ripening), resulting in a decrease in their effective
surface area and thereby catalytic activity. In any case, the activity
passes the maximum at 0.1ꢀ0.01 mol % loading and later on
steeply decreases. The maximum position depends on the ligand
structure and starting substrate, and, for example, for complex 15
the activity in the coupling of 4-bromoanisole increased with a
decrease of the catalyst loading. In general, in couplings of
bromoarenes under these conditions no pronounced difference
was observed in the catalytic performances of complexes 13, 14a,
and 15, with 5- and 6-membered fused metallacycles, whereas
their 5,5-membered counterpart 12 was somewhat less active,
excluding the reaction with 4-bromoanisole, in which activity of
complex 12 was higher than that of complex 15.
The kinetic studies performed for coupling of 4-bromoaceto-
phenone (catalyst loading of 0.01 mol %, Figure 7a) revealed
that complex 14a was more active than the other thiophos-
phorylꢀbenzothiazole palladacycles and provided >90% conver-
sion for 2 h (for complete conversion 3 h was required). The 5,6-
membered O-bridged complexes 13 and 15 possessed an activity
similar to each other and gave similar conversion levels of >90%
already in ∼4 h. At the same time, in the reaction catalyzed by
complex 12, slightly higher conversion was observed over 1 h
compared with those provided by complexes 13 and 15, but in
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Table 2. Pincer Complexes Catalyzing the Suzuki Cross-
Coupling of 4-Chloroacetophenone
biaryl product went down practically to zero as the amount of the
aforesaid complexes (IXꢀXI) was decreased to 0.01 mol %. At
the same time, SCN-pincer complexes 12ꢀ15, with a benzothia-
zole ring, afforded almost complete conversion of 4-bromoani-
sole even when used at 0.01 mol %, substantially surpassing in
activity the other pincer complexes with a thiophosphoryl
coordinating arm.
Moreover, SCN palladium complex 14a efficiently promoted
the Suzuki cross-coupling of 4-chloroacetophenone with phe-
nylboronic acid, providing 93% conversion at 0.1 mol % catalyst
loading (Table 1, entry 9). The other 5,6-membered thiopho-
sphorylꢀbenzothiazole palladacycles 13 and 15 also manifested
activity in this reaction but were inferior to complex 14a, and the
yields of the biphenyl product did not exceed 50% (entry 9).
Employing complexes 13, 14a, and 15, poor yields were achieved
in the reactions of more sterically hindered 2-chloroacetophe-
none (entry 10). It should be emphasized that complex 12,
having two five-membered metallacycles, showed no activity for
the coupling of these aryl chlorides.
conversion, time,
cat. (load.)
reaction conditions
%
h
ref
Ia (0.1 mol %)
II (1 mol %)
III (2 mol %)
THF, K2CO3, 130 °C
dioxane, CsF, 130 °C
H2O, K2CO3, 150 °C
67
74
77
92
88
58
99
89
93
18
27
4
1.5
18
18
12
20
5
7
8
9
10
11
6e
6f
IV (0.01 mol %) toluene, K3PO4, 100 °C
Va (0.1 mol %) toluene, K2CO3, 110 °C
VI (1 mol %)
VII (1 mol %)
dioxane, Cs2CO3, 100 °C
DMF, K3PO4, 130 °C
VIIIb (1 mol %) dioxane, Cs2CO3, 100 °C
14a (0.1 mol %) DMF, K3PO4, 120 °C
6b
this study
a 4-Chloronitrobenzene was used as a substrate. b Chlorobenzene was
used as a substrate.
time the level of activity became lower. This fact may be
explained by the similar induction periods for these three
complexes, which nevertheless provided different catalytically
active species. The corresponding kinetic experiments in the case
of 4-bromoanisole (catalyst loading of 0.1 mol % was chosen to
provide higher conversions, Figure 7b) have revealed comparable
kinetic traces for complexes 12, 13, and 14a, with insignificantly
higher catalytic activity of the latter one, while complex 15 stood
out against a general tendency of its analogues and demonstrated
lower catalytic efficacy and an increased induction period.
Evidently, in this case the release of catalytically active species
is rather slow. Indeed, as may be seen from Table 1 (entries
4ꢀ6), the catalytic activity of 15 increases as the catalyst loading
is gradually reduced from 1 to 0.01 mol %. Such (pre)catalyst
behavior may be associated with the Ostwald ripening of
catalytically active Pd(0) colloid particles at higher concentra-
tions of a complex, leading in turn to their growth and decrease in
their surface area, which may cause a drop in the total catalytic
activity (see above).
To compare the catalytic activities of a panel of thiophosphoryl-
based pincer complexes of different types, Figure 8 outlines the
results obtained for the model cross-coupling reaction of 4-bro-
moanisole using the most catalytically active representatives
among each series of palladacycles IXꢀXII and 12ꢀ15 (the data
correspond to the reactions performed over 5 h). Note that
reactions promoted by complexes IX, X, and XII were performed
in the presence of tetrabutylammonium bromide, a salt known to
stabilize palladium nanoparticles,10 and in the absence of Bu4NBr
an approximately 10ꢀ15% decrease in the yield of the final biaryl
product was observed. In contrast, Bu4NBr slightly inhibited the
reaction with participation of thiophosphorylꢀthiocarbamoyl-
and thiophosphorylꢀbenzothiazole-based pincer complexes
XI14 and 12ꢀ15 (Table 1, entries 4ꢀ6 for the representative
complex 15), respectively.
At this point, a comparison in terms of catalytic efficiency can
be performed between the most active complex of this study, 14a,
and the other pincer complexes known to catalyze the Suzuki
cross-coupling of aryl chlorides with phenylboronic acid
(Table 2). A few points should be taken into consideration. To
promote the reaction of activated chloroacetophenone (or
another activated aryl chloride, 4-chloronitrobenzene) using
pincer complexes IꢀVIII and 14a, high temperatures
(100ꢀ150 °C) were required in all cases. The reaction times,
in that range of temperature, varied in a wide range (1.5ꢀ27 h),
although generally exceeded 12 h. The typical catalyst loading
was fairly high, 1ꢀ2 mol %. Hence, considering the data of
Table 2 one can conclude that from the standpoint of the catalyst
loading (0.1 mol %), reaction time (5 h), and conversion (93%),
complex 14a ranks second among all pincer palladacycles
catalyzing the Suzuki cross-coupling of activated aryl chlorides
reported to date.
According to the 31P NMR monitoring of a complex's destiny
after the catalytic cycle (representative reaction was the coupling
of 4-bromoacetophenone and phenylboronic acid at 1 mol %
catalyst loading), palladacycles 12ꢀ15 undergo at least partial
decomposition over the process. Thus, in the case of a catalytic
31
system based on complex 12, the P NMR spectrum of the
reaction mixture demonstrated two singlets at ca. 30 and 26
ppm in a 4:1 ratio. Presumably, they pertain to the metalated
(30 ppm) and nonmetalated (26 ppm) phosphoryl-containing
derivatives (e.g., the chemical shift of the intermediate 2-
[3-(diphenylphosphoryl)phenyl]-1,3-benzothiazole is equal to
26.87 ppm) that may result from the oxidation of the PdS group
and thermally induced demetalation of the starting complex
under the reaction conditions. Note that both these signals were
observed also in the spectrum of the reaction mixture comprised
of 4-bromoacetophenone, K3PO4, and 1 mol % 12 in the absence
of phenylboronic acid, after heating in DMF for 30 min and,
therefore, may be formed under the action of a base. The 31P
NMR spectrum of the reaction catalyzed by complex 13 showed
solely the signals at 25.8 and 15.2 ppm in a 1.5:1 ratio, which were
assigned to the products of OꢀP bond hydrolysis and PdS
group oxidation, i.e., Ph2P(S)OH and Ph2P(O)OH.22 This
allows one to assume the decomposition of the ligand structure.
The phosphorus spectra registered after the reactions catalyzed
by pincer complexes 14a and 15 demonstrated signals with
chemical shifts being very close to those of free ligands (at 50.6
As is easy to see, 5,5-membered SCS0 thiocarbamoylꢀthio-
phosphoryl pincer complex IX did not provide a complete
conversion of this particular substrate, even being used at 3
mol %. Showing the best catalytic activity among bis-
(thiophosphorylated) derivatives X, the complex bearing diethyl-
amino groups at the phosphorus atom of the OꢀPdS moiety
displayed the same level of activity even when used at 1 mol %.
However, its activity decreased to 68% as the catalyst loading was
reduced to 0.1 mol %, while 5,6-membered SCS0 complex XI as
well as SCN palladacyle XII, based on thiophosphoryl-
oxyꢀbenzaldoxime, retained a high level of activity even at a
low catalyst loading (0.1 mol %). Nevertheless, the yields of the
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Figure 9. Temperature-varied plots of conversion vs time for the catalytic system based on complex 14a (0.1 mol %) (coupling of 4-bromoaceto-
phenone (a) and 4-bromoanisole (b) with PhB(OH)2).
Scheme 5. Suppositional Way of Generation of Pd(0)
Species
(0.001 mol %) is also in good agreement with the proposal of the
Pd(0) nature of true catalysts.24
The kinetic studies performed with the representative complex
14a (0.1 mol %) at different temperatures (the temperature was
gradually reduced by 10 degrees from 120 to 90 °C) using both
4-bromoacetophenone and 4-bromoanisole as a starting sub-
strate (Figure 9) revealed that the system under consideration is
characterized by sigmoidal kinetics, and an induction period,
necessary for the starting pincer complex to generate catalytically
active species, becomes especially apparent below 100 °C. This
strongly indicates that pincer complex 14a serves as a (pre)-
catalyst rather than a true catalyst. Furthermore, in addition to
the above-mentioned kinetic experiments, these data indicated
that at this catalyst loading complete conversion in reaction with
4-bromoacetophenone at 120 °C was achieved in only 0.5 h.
Moreover, the lack of activity of complexes 12ꢀ14 in the
presence of excess of Hg(0), which has no poisoning effect on
molecular homogeneous organometallic complexes containing
metals in high oxidation states that are tightly bound by
protective ligands,25,26 provides additional evidence that these
systems are susceptible to decomposition under reaction condi-
tions to form soluble Pd(0) species, as shown in Figure 10 for the
representative reaction catalyzed by complex 14a. In brief, when
Hg(0) was added to the reaction mixtures at time 0 or 20 min, the
reaction stopped at the conversion level of 2% and 38ꢀ42%, 2%
and 63ꢀ66%, 5% and 58ꢀ64%, and 1% and 55% (three to four
measurements up to t = 4 h) for the catalytic systems based on
complexes 12, 13, 14a, and 15, respectively.
Figure 10. Conversion of 4-bromoacetophenone as a function of time
in the Suzuki coupling with 0.1 mol % of complex 14a in the presence of
Hg(0).
and 43.0 ppm, respectively), hence suggesting the rupture of the
PdꢀC bonds.
Furthermore, we detected the downfield shifted signals at 58.3,
62.2, and 94.7 ppm in the 31P NMR spectra of the reaction
mixtures after a catalytic process for palladacycles 12, 15, and
14a, respectively. The first two values fall within the region
typical for the metalated PdS-coordinated derivatives (which
may also possess monopalladacyclic nature), while the latter one
is likely to correspond to the pincer-type complex with a P(III)
coordinating arm (compare, e.g., with the phosphorus resonance
of PCN-pincer complex III9 at 91.3 ppm).
Note that in the catalysis of cross-coupling reactions for the
pincer systems, both symmetric and unsymmetrical, two alter-
native mechanisms including Pd(II)/Pd(0) and Pd(II)/Pd-
(IV)23 catalytic cycles were suggested. The decomposition of
palladacycles 12ꢀ15 over the catalytic cycle in combination with
the observation of palladium black formation (particularly but
not exclusively in the case of complex 13) allow proposing that
they serve as precatalysts of zerovalent low-ligated palladium, and
the described catalytic transformations apparently include a
Pd(0)ꢀPd(II) catalytic cycle. The abrupt decrease in the cata-
lytic efficiency of these complexes at very low concentrations
But how can such active species be generated? The 31P NMR
spectrum of the reaction mixture containing only 4-bromoace-
tophenone (i.e., those free of phenylboronic acid and K3PO4)
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and complex 14a (1 mol %) revealed no changes in the chemical
shift of the latter one after heating for 30 min. Therefore,
complexes 13ꢀ15 apparently generate the catalytically active
Pd(0) species by the reductive elimination of the ortho-metalated
species with an aryl group introduced by phenylboronic acid
(Scheme 5). In this case, the signals observed in the 31P NMR
spectra of the reaction mixtures after complete catalytic cycle
with chemical shifts close to those of free ligands may relate to the
products 17 of the reductive elimination of LꢀPdꢀPh inter-
mediates 16, which differ from the starting ligands 9 and 11 by an
additional phenyl ring at the C2 position of the central benzene
core. It should be noted that such a mechanism of the formation
of catalytically active species in the Suzuki cross-coupling pro-
moted by palladacycles has already been suggested in the
literature for both CN- and CP-monopalldacycles3d,27 and 5,5-
membered symmetrical PCP-pincer complexes,26 where the
product of transmetalation, i.e., the LꢀPdꢀPh complex, was
isolated and structurally characterized. Nevertheless, in the latter
case the experimental results in total were indicative of a
Pd(II)ꢀPd(IV) catalytic cycle, and no further reductive elimina-
tion with liberation of biaryls was observed. In the case of SCN-
pincer complexes 12ꢀ14 the hemilabile coordination may
facilitate such reductive elimination by more feasible, than in
the case of strongly bound P(III) moieties, decoordination of
weakly bonded ancillary arms in order to achieve ortho-mutual
disposition of two leaving phenyl fragments. Indeed, according to
the 31P NMR monitoring, heating of complex 15 with 3 equiv of
phenylboronic acid and 4.5 equiv of K3PO4 in DMF at 120 °C for
1 h leads to the main two components that answer to the
phosphorus signals at 57.5 and 43.0 ppm. The first one obviously
corresponds to the unreacted starting pincer complex, while the
second one is unambiguously not the free ligand (proven by the
addition of compound 11 as an internal standard) and is
tentatively assigned to the biaryl 17.27
Despite all the data supporting the Pd(II)/Pd(0) catalytic
cycle for complexes 12ꢀ15, at least for 5,5-membered complex
12 the alternative Pd(II)/Pd(IV) mechanism cannot be entirely
disclaimed as a minor parallel process. First of all, unlike the other
SCN thiophosphorylꢀbenzothiazole pincer complexes, it does
not contain a rather weakly bonded six-membered metallacycle
to make feasible the reductive elimination of intermediate 16.
Similar to ref 26, in this case a further scenario may comprise the
reaction with ArBr to give Pd(IV) species followed by catalyst
recovery after elimination of biaryl. The partial retaining of
catalytic activity in the Hg(0) poisoning experiment could be a
reasonable argument for this hypothesis. Furthermore, it cannot
be completely excluded that Hg(0) interferes with catalysis in a
way other than killing the true heterogeneous catalyst.
having a thiophosphoryl group and a benzothiazole imine moiety
as coordination sites. Direct cyclometalation of these ligands
afforded 5,5- and 5,6-membered pincer palladium complexes and
a 5,6-membered pincer platinum one in the case of the ligand
having a thiophosphorylamino moiety. The palladacycles derived
were proved to be excellent (pre)catalysts for the Suzuki cross-
coupling of electronically varied bromoarenes, while 5,6-mem-
bered pincer complex 14a, with a thiophosphorylamino group,
also efficiently promoted the reaction with chloroacetophenone,
ranking among the best pincer (pre)catalysts suggested for this
reaction.
’ EXPERIMENTAL SECTION
If not noted otherwise, all manipulations were carried out without taking
precautions to exclude air and moisture. Benzene was distilled over
sodium/benzophenone ketyl, and acetonitrile was distilled from P2O5.
3-(Diphenylphosphoryl)-N-phenylbenzamide,12 3-(diphenylphosphoryl)-
N-phenylbenzenecarbothioamide, 1,28 3-(diphenylthiophosphoryl)-N-
phenylbenzenecarbothioamide, 2,12 3-methoxy-N-phenylbenzenecar-
bothioamide, 4,14 2-(3-methoxyphenyl)-1,3-benzothiazole,18 3-amino-N-
phenylbenzamide,29 Ph2P(S)Cl,30 3-(diphenylthiophosphoryl)phenol,
10,13 2-(3-nitrophenyl)benzothiazole, and the corresponding amino deri-
vative 8 (for both compounds see ref 31) were obtained according to
literature procedures. All other chemicals and solvents were used as
purchased.
NMR spectra were recorded on Bruker Avance-300 and Bruker
Avance-400 spectrometers, and the chemical shifts (δ) were internally
referenced by the residual solvent signals relative to tetramethylsilane
(1H and 13C) or externally to H3PO4 (31P). The 13C NMR spectra were
registered using the JMODECHO mode; the signals for the C atoms
bearing odd and even numbers of protons have opposite polarities. The
numeration for carbon atoms of the central benzene ring in the
descriptions of the 13C spectral data is in agreement with IUPAC
nomenclature used for the ligand 3. The same principle of numbering
was used to describe the solid-state molecular structures characterized by
X-ray crystallography.
Flash chromatography was carried out using Merck silica gel 60
(230ꢀ400 mesh ASTM). IR spectra were recorded on a Magna-IR750
Fourier spectrometer (Nicolet), resolution 2 cmꢀ1, 128 scans. The
assignment of absorption bands in the IR spectra was made according to
ref 32. Melting points were determined with a MPA 120 EZ-Melt
automated melting point apparatus and are uncorrected.
Synthesis of Ligands. 2-[3-(Diphenylthiophosphoryl)phenyl]-
1,3-benzothiazole, 3. Method A. To a suspension of 3-(diphenyl-
phosphoryl)-N-phenylbenzenecarbothioamide (1) (1.8 g, 4.4 mmol)
in 1 mL of ethanol was added a 30% aqueous solution of NaOH
(3.3 mL). Then the mixture was diluted with water to reach a final
concentration of NaOH of 10%. Aliquots of this mixture (0.5 mL) were
added at one-minute intervals to a stirred solution of K3[Fe(CN)6]
(5.73 g, 17.4 mmol) in water (20 mL) at 80 °C. The reaction mixture
was heated at 80 °C for 30 min. After cooling to room temperature, the
resulting precipitate was filtered, rinsed with water, and dried in vacuo to
afford 1.2 g of 2-[3-(diphenylphosphoryl)phenyl]-1,3-benzothiazole as a
white, crystalline solid. Yield: 67%. Mp: 165.0ꢀ167.1 °C (benzene). 31P
In conclusion it should be noted that the main disparity in the
activities of complexes tested consists in the performances of 5,5-
membered complex 12 and its counterparts 13ꢀ15. Obviously,
the lower activity of compound 12 may be explained by its higher
stability, leading to a slower generation of the catalytically active
species. In this respect, the hemilabile properties of pincer
complexes 13ꢀ15, having five- and rather weakly bonded six-
membered fused metallacycles, apparently serve as a factor for
their higher activity.
1
NMR (121.49 MHz, CDCl3): δ 26.87 ppm. H NMR (300.13 MHz,
CDCl3): δ 7.37ꢀ7.77 (m, 14H), 7.91 (d, 1H, H(C6), 3JHH = 7.8 Hz),
8.07 (d, 1H, H(C12), 3JHH = 8.2 Hz), 8.35 (d, 1H, H(C9), 3JHH = 7.8
3
Hz), 8.41 (d, 1H, H(C2), JHP = 12.3 Hz). Anal. Calcd for
C25H18NOPS: C, 72.98; H, 4.40; N, 3.40. Found: C, 73.14; H, 4.39;
N, 3.27.
A mixture of the above 2-[3-(diphenylphosphoryl)phenyl]-1,3-ben-
zothiazole (0.65 g, 1.6 mmol) and the Lawesson reagent (2,4-bis-
(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-dithione, 0.32 g,
’ CONCLUSIONS
To summarize the results presented, we have elaborated the
synthetic approaches to novel types of NCS-pincer ligands
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0.8 mmol) was refluxed in xylene (20 mL) for 12 h. After cooling to
room temperature, the mixture was washed with a 20% aqueous solution
of Na2CO3 and water. The organic layer was separated, dried over
anhydrous Na2SO4, and evaporated to dryness. The resulting residue
was recrystallized from EtOAc to give 0.4 g of 3 as a white solid. Yield:
59%. Mp: 173.1ꢀ174.2 °C (EtOAc). 31P NMR (161.98 MHz, DMSO-
d6): δ 42.35 ppm. 1H NMR (DMSO-d6): δ 7.47ꢀ7.51 (m, 1H),
8.0 Hz), 8.17 (d, 1H, H(C9), 3JHH = 7.6 Hz), 8.29ꢀ8.31 (m, 1H), 8.51
(d, 1H, H(C2), 3JHP = 14.1 Hz). 13C{1H} NMR (75.47 MHz, CDCl3/
DMSO-d6): δ 121.89 (s, C9), 122.98 (s, C12), 125.49 (s, C11), 126.40
(s, C10), 128.58 (d, m-C in P(S)Ph2, 3JCP = 12.6 Hz), 129.37 (d, C2,
2JCP = 12.1 Hz), 130.15 (d, C5, 3JCP = 15.9 Hz), 130.21 (s, C6), 131.68
(d, o-C in P(S)Ph2, 2JCP = 10.4 Hz), 131.75 (s, p-C in P(S)Ph2), 131.84
(d, ipso-C in P(S)Ph2, 1JCP = 85.1 Hz), 133.41 (d, C1, 3JCP = 12.6 Hz),
133.78 (d, C4, 2JCP = 9.9 Hz), 134.01 (d, C3, 1JCP = 84.0 Hz), 134.48
(s, C13), 153.40 (s, C8), 165.73 (s, C7). IR (KBr, ν/cmꢀ1): 495(w),
515(s), 614(m), 628(m) (ν(PdS)), 641(m), 659(m), 680(m), 696(s),
714(s), 725(m), 742(m), 754(m), 787(w), 999(m), 1098(s), 1234(w),
1312(m), 1409(m), 1435(s), 1457(w), 1478(m), 1507(w) (ν(CdN)),
1585(w), 1700(w), 3051(w). Anal. Calcd for C25H18NPS2: C, 70.23; H,
4.24; N, 3.28. Found: C, 70.19; H, 4.17; N, 3.23.
Method B. Analogous to the first stage of method A, the reaction of
3-(diphenylthiophosphoryl)-N-phenylbenzenecarbothioamide (2) (1.5
g, 3.5 mmol) with K3[Fe(CN)6] (4.6 g,14.0 mmol) led to compound 3
(0.8 g, 54% yield).
3-(1,3-Benzothiazol-2-yl)phenol, 5. A mixture of 2-(3-methoxy-
phenyl)-1,3-benzothiazole (2.2 g, 9.1 mmol) and pyridine hydrochloride
(3.2 g, 27.7 mmol) was heated under stirring at 180ꢀ190 °C (oil bath)
for 3 h. After cooling to room temperature, the reaction mixture was
diluted with CH2Cl2, washed with water, and dried over anhydrous
Na2SO4. After separation of Na2SO4, the filtrate was half-evaporated to
afford precipitation of the crude product, which then was recrystallized
from CHCl3. Yield: 1.2 g (58%). Mp: 161.9ꢀ164.2 °C (compare with
161ꢀ163 °C in ref 33).
argon atmosphere. The reaction mixture was refluxed for 5 h and, after
addition of sulfur (0.22 g, 6.9 mmol), continued to reflux for a further 7
h. After cooling to room temperature, the resultant mixture was filtered;
the filtrate was washed with 5% aq. HCl and water, dried over Na2SO4,
and evaporated to dryness. The resulting residue was recrystallized from
benzene to afford 1.93 g of 9 as a white solid. Mp: 169.4ꢀ172.4 °C
(C6H6). Yield: 52%. 31P{1H} NMR (161.98 MHz, CDCl3): δ 52.61
ppm. 1H NMR (400.13 MHz, CDCl3): δ 5.22 (d, 1H, NH, 3JHP = 6.0
Hz), 7.13ꢀ7.15 (m, 1H, HAr), 7.22ꢀ7.25 (m, 1H, HAr), 7.35ꢀ7.38 (m,
1H, HAr), 7.45ꢀ7.55 (m, 7H, HAr), 7.60 (d, 1H, H(C6), 3JHH = 7.4 Hz),
7.65 (br s, 1H, H(C2)), 7.86 (d, 1H, H(C12), 3JHH = 7.9 Hz), 8.00ꢀ8.06
(m, 5H, o-H in P(S)Ph2þH(C9)). 13C{1H} NMR (75.47 MHz,
7.54ꢀ7.69 (m, 7H), 7.73ꢀ7.78 (m, 6H), 8.08 (d, 1H, H(C12), 3JHH
=
3
CDCl3): δ 117.80 (d, C2, JCP = 7.6 Hz), 120.76 (s, C6), 120.91 (d,
3
C4, JCP = 6.2 Hz), 121.48 (s, C9), 122.81 (s, C12), 125.21
3
(s, C11), 126.30 (s, C10), 128.64 (d, m-C in P(S)Ph2, JCP = 13.1
Hz), 129.59 (s, C5), 131.45 (d, o-C in P(S)Ph2, 2JCP = 11.8 Hz), 131.11
(d,
p-C in P(S)Ph2, 4JCP = 2.1 Hz), 133.04 (d, ipso-C in P(S)Ph2, 1JCP = 103.8
Hz), 133.73 (s, C13), 134.55 (s, C1), 140.99 (s, C3), 153.09 (s, C8),
167.83 (s, C7). IR (KBr, ν/cmꢀ1): 483(w), 510(m), 613(m) and
629(m) (both ν(PdS)), 690(m), 717(s), 753(m), 936(s), 1018(w),
1105(m), 1197(w), 1260(w), 1279(w), 1304(m), 1372(w), 1437(s),
1463(m), 1486(s), 1510(m) (ν(CdN)), 1589(m), 1606(m), 2922(w),
3055(w), 3201(m). Anal. Calcd for C25H19N2PS2: C, 67.85; H, 4.32; N,
6.33. Found: C, 67.69; H, 4.25; N, 6.21.
2-[3-(Diphenylthiophosphoryl)phenoxy]-1,3-benzothiazole, 11. A
mixture of 2-chloro-1,3-benzothiazole (0.7 g, 4 mmol) and sodium
phenolate prepared from 3-(diphenylthiophosphoryl)phenol 10 (0.6 g,
1.9 mmol) and a 60% dispersion of NaH in mineral oil (0.09 g, 1.9
mmol) in 15 mL of xylene was refluxed for 20 h and allowed to cool.
After evaporation of the reaction mixture, the resulting residue was
dissolved in Et2O and filtered. The ether filtrate was evaporated
to dryness, and the resulting residue was recrystallized from a
EtOAcꢀhexane mixture (1:2) to give 0.56 g of 11 as a white, crystalline
solid. Yield: 65%. Mp: 127.3ꢀ129.8 °C (EtOAcꢀhexane (1:2)). 31P
NMR (161.98 MHz, DMSO-d6): δ 41.87 ppm. 1H NMR (DMSO-d6):
δ 7.35 (m, 1H), 7.45 (m, 1H), 7.57ꢀ7.76 (m, 15H), 7.97 (d, 1H,
O-[3-(1,3-Benzothiazol-2-yl)phenyl]diphenylthiophosphinate, 6. A
solution of Ph2P(S)Cl (0.9 g, 3.6 mmol) in benzene (5 mL) was slowly
added dropwise to a mixture of 5 (0.8 g, 3.6 mmol) and Et3N (0.5 mL,
3.6 mmol) in 20 mL of C6H6. The resulting reaction mixture was stirred
at 60 °C for 2 h and left overnight. The reaction mixture was filtered, and
the filtrate was evaporated to dryness, crystallized from diethyl ether,
purified by flash chromatography (eluent CH2Cl2), and recrystallized
from EtOAc to give 1.3 g of 7 as a white solid. Yield: 83%. Mp:
148.4ꢀ149.6 °C (EtOAc). 31P{1H} NMR (121.49 MHz, CDCl3): δ
82.98 ppm. 1H NMR (300.13 MHz, CDCl3): δ 7.19 (d, 1H, 3JHH = 8.0
Hz), 7.32ꢀ7.40 (m, 2H), 7.45ꢀ7.55 (m, 7H), 7.77 (d, 1H, H(C2),
4JHP = 1.8 Hz), 7.83ꢀ7.89 (m, 2H), 7.97ꢀ8.05 (m, 5H). 13C{1H} NMR
(100.61 MHz, CDCl3): δ 120.67 (d, C2, 3JCP = 5.1 Hz), 121.46 (s, C9),
123.15 (s, C12), 123.71 (d, C5, 4JCP = 1.1 Hz), 123.79 (d, C4, 3JCP = 4.7
3
H(C9), JHH = 8.0 Hz). 13C{1H} NMR (100.61 MHz, CDCl3): δ
121.24 (s, C9), 121.64 (s, C12), 123.44 (d, C6, 4JCP = 2.6 Hz), 124.11
(d, C2, 2JCP = 11.7 Hz), 124.21 (s, C11), 126.23 (s, C10), 128.52 (d, m-C
in P(S)Ph2, 3JCP = 12.7 Hz), 129.62 (d, C4, 2JCP = 10.1 Hz), 130.08 (d, C5,
3JCP = 14.0 Hz), 131.66 (d, p-C in P(S)Ph2, 4JCP = 2.9 Hz), 132.14 (d,
o-C in P(S)Ph2, 2JCP = 10.8 Hz), 132.19 (s, C13), 132.24 (d, C3, 1JCP
=
85.7 Hz), 135.37 (d, ipso-C in P(S)Ph2, 1JCP = 84.1 Hz), 148.65 (s, C8),
3
154.21 (d, C1, JCP = 16.6 Hz), 170.80 (s, C7). IR (KBr, ν/cmꢀ1):
515(m), 633(w) and 649(m) (both ν(PdS)), 693(m), 717(m),
751(m), 764(w), 1098(m), 1210(m), 1229(s), 1247(m), 1411(m),
1439(s), 1529(s) (ν(CdN)), 1580(w), 1599(w), 3054(w). Anal. Calcd
for C25H18NOPS2: C, 67.70; H, 4.09; N, 3.16. Found: C, 67.05; H, 3.93;
N, 2.83.
Synthesis of Pincer Complexes. General Procedure (complexes
12, 13, and 15). A solution of (PhCN)2PdCl2 (77 mg, 0.2 mmol) and
the corresponding ligand 3, 6, or 11 (0.2 mmol) in 4 mL of benzonitrile
was heated at 120 °C for 3, 2, and 1 h, respectively, and allowed to
cool. The resulting mixture was dilutedwithCH2Cl2 (12 mL) and filtered.
After evaporation of dichloromethane, 15 mL of diethyl ether was added.
The desired precipitated product was collected by filtration, washed with
Et2O (15 mL), and dried in air. When the compound 11 was used as a
starting ligand, to precipitate the desired pincer product, diethyl ether
was added directly to the benzonitrile reaction mixture.
Hz), 125.18 (s, C11), 126.19 (s, C10), 128.44 (d, m-C in P(S)Ph2, 3JCP
=
13.4 Hz), 129.73 (s, C6), 131.26 (d, o-C in P(S)Ph2, 2JCP = 11.6 Hz),
132.11 (d, p-C in P(S)Ph2, 4JCP = 3.3 Hz), 133.79 (d, ipso-C in P(S)Ph2,
1JCP = 110.8 Hz), 134.79 (s, C13), 134.90 (s, C1), 150.88 (d, C3, 2JCP
=
8.4 Hz), 153.80 (s, C8), 166.63 (s, C7). IR (KBr, ν/cmꢀ1): 491(m),
506(s), 640(m) (ν(PdS)), 687(m), 717(m), 728(s), 757(m), 791(m),
846(m), 857(m), 893(m), 910(s), 1107(m), 1161(m), 1174(m)
1238(m), 1254(m), 1313(w), 1436(s), 1463(w), 1505(m)
(ν(CdN)), 1580(m), 1605(w), 3028(w), 3051(w), 3064(w). Anal.
Calcd for C25H18NOPS2: C, 67.70; H, 4.09; N, 3.16. Found: C, 67.71;
H, 4.09; N, 3.21.
N-[3-(1,3-Benzothiazol-2-yl)phenyl]-P,P-diphenylthiophosphinic
Acid Amide, 9. A solution of Ph2PCl (1.3 g, 5.9 mmol) in 15 mL of
benzene was slowly dropwise added to a suspension of 8 (1.3 g, 5.8
mmol) and pyridine (0.55 mL, 5.8 mmol) in 35 mL of C6H6 under an
[2-(1,3-Benzothiazol-2-yl)-6-(diphenylthiophosphoryl)phenyl]-
palladium Chloride, 12. Yield: 80%. Mp: >295 °C (dec). 31P{1H}
NMR (161.98 MHz, DMSO-d6): δ 64.17 ppm. 1H NMR (400.13 MHz,
DMSO-d6): δ 7.37ꢀ7.42 (m, 1H), 7.78ꢀ7.64 (m, 3H), 7.69ꢀ7.72 (m,
2929
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ARTICLE
Table 3. Crystal Data and Structure Refinement Parameters for 3, 12, 13, and 15
3
12 0.5CH2Cl2
13
15 0.5CH2Cl2
3
3
empirical formula
C25H18NPS2
427.49
C51H36Cl4N2P2Pd2S4
1221.60
triclinic
P1
C25H17ClNOPPdS2
584.34
C26H19Cl3NOPPdS2
669.26
fw
cryst syst
space group
Z
triclinic
P1
monoclinic
P21/n
triclinic
P1
2
2
4
2
a, Å
7.1960(8)
11.8679(13)
13.0523(15)
107.189(3)
101.533(2)
100.036(2)
1010.5(2)
1.405
9.6828(6)
11.1434(6)
12.3807(7)
71.5290(10)
82.3750(11)
69.1980(10)
1184.15(12)
1.713
9.9749(9)
20.4107(19)
11.6540(11)
8.8770(4)
11.9311(5)
13.0779(5)
84.7270(11)
79.5330(10)
71.3160(10)
1289.44(9)
1.724
b, Å
c, Å
R, deg
β, deg
γ, deg
V, Å3
108.592(2)
2248.9(4)
1.726
Dcalc (g cmꢀ1
)
linear absorption, μ, cmꢀ1
3.55
12.69
12.21
12.77
F(000)
444
610
1168
668
2θmax, deg
58
56
58
58
reflns measd
12 072
13 105
26 543
5979
15 418
indep reflns
5349
5685
6816
obsd reflns [with I > 2σ(I)]
4131
4982
5145
6180
params
262
293
289
316
R1
0.0392
0.0277
0.0210
0.0527
1.003
0.0225
wR2
0.0995
0.0678
0.0509
GOF
1.004
1.008
1.010
ΔFmax/ΔFmin, e Åꢀ3
0.451/ꢀ0.264
1.481/ꢀ0.986
0.508/ꢀ0.504
0.568/ꢀ1.018
4H, m-H in P(S)Ph2), 7.78ꢀ7.81 (m, 2H, p-H in P(S)Ph2), 7.87 (dd,
4H, o-H in P(S)Ph2, 3JHH = 7.6 Hz, 3JHP = 13.6 Hz), 8.00 (d, 1H, H(C6),
{2-(1,3-Benzothiazol-2-yl)-6-[(diphenylthiophosphoryl)amino]-
phenyl}palladium Chloride, 14a. A solution of (PhCN)2PdCl2 (46
mg, 0.120 mmol) in 5 mL of acetonitrile was slowly dropwise added to a
suspension of ligand 9 (0.120 mmol) in 5 mL of CH3CN. The stirred
reaction mixture was refluxed for 2 h. After cooling to room temperature,
the resulting precipitate was filtered, washed with CH3CN (7 mL) and
Et2O (15 mL), and dried in vacuo to give 62 mg of 14a as a yellow solid.
Yield: 89%. Mp: >268 °C (dec). 31P{1H} NMR (121.49 MHz, DMSO-
d6): δ 45.21 ppm. 1H NMR (300.13 MHz, DMSO-d6): δ 7.06 (d, 1H,
3
3JHH = 7.3 Hz), 8.27 (d, 1H, H(C12), JHH = 7.8 Hz), 9.47 (d, 1H,
H(C9) 3JHH = 8.1 Hz). IR (KBr, ν/cmꢀ1): 518(s), 601(m) (ν(PdS)),
618 (w), 692(m), 704(m), 718(m), 732(m), 748(m), 761(s), 996(w),
1038(m), 1101(m), 1272(w), 1319(w), 1394(m), 1415(m), 1434(m),
1475(w), 1511(w), 1546(m) (ν(CdN)), 1600(w), 2852(w), 2926(w),
3043(w), 3061(w). Anal. Calcd for C25H17ClNPPdS2 0.67CH2Cl2: C,
3
49.32; H, 2.96; N, 2.24. Found: C, 49.27; H, 2.91; N, 2.24.
H(C4), 3JHH = 7.8 Hz), 7.18 (m, 1H, H(C5)), 7.34 (d, 1H, H(C6), 3JHH
=
{2-(1,3-Benzothiazol-2-yl)-6-[(diphenylthiophosphoryl)oxy]phenyl}-
palladium Chloride, 13. Yield: 75%. Mp: >275 °C (dec). 31P{1H}
NMR (161.98 MHz, DMSO-d6): δ 75.22 ppm.1H NMR (400.13 MHz,
DMSO-d6): δ 7.34 (m, 2H), 7.50ꢀ7.60 (m, 3H), 7.65ꢀ7.70 (m, 4H),
7.3 Hz), 7.44ꢀ7.54 (m, 2H, H(C10)þH(C11)), 7.64ꢀ7.74 (m, 6H,
p- and m-H in P(S)Ph2), 7.81ꢀ7.88 (m, 4H, o-H in P(S)Ph2), 8.12 (d,
1H, H(C12), 3JHH = 7.5 Hz), 9.22 (d, 1H, NH, 2JHP = 5.7 Hz), 9.49 (d,
1H, H(C9), 3JHH = 8.0 Hz). 13C{1H} NMR (125.76 MHz, DMSO-d6):
δ 120.32 (s, C9), 121.91 (d, C4, 3JCP = 9.6 Hz), 122.38 (s, C6), 123.02
(s, C12), 125.57 (s, C11), 126.39 (s, C5), 126.50 (s, C10), 128.55 (d,
7.75ꢀ7.77 (m, 2H), 8.06 (dd, 4H, o-H in P(S)Ph2, 3JHH = 7.4 Hz, 3JHP
=
3
13.8 Hz), 8.19 (d, 1H, H(C12), JHH = 7.6 Hz), 9.58 (d, 1H, H(C9),
3JHH = 8.5 Hz). IR (KBr, ν/cmꢀ1): 492(m), 515(m), 633(m)
(ν(PdS)), 692(s), 719(s), 756(s), 782(w), 798(w), 952(s), 962(m),
1106(s), 1119(s), 1164(m), 1198(s), 1270(m), 1298(m), 1412(m),
1435(m), 1446(w), 1457(w), 1488(w) (ν(CdN)), 1580(w), 2854(w),
2925(w), 3081(w), 3438(w). Anal. Calcd for C25H17ClNOPPdS2: C,
51.38; H, 2.93; N, 2.40. Found: C, 51.10; H, 2.73; N, 2.34.
ipso-C in P(S)Ph2, 1JCP = 99.8 Hz), 128.99 (d, m-C in P(S)Ph2, 3JCP
=
11.5 Hz), 130.53 (s, C13), 131.83 (d, o-C in P(S)Ph2, 2JCP = 11.5 Hz),
133.19 (d, p-C in P(S)Ph2, 4JCP = 3.8 Hz), 134.34 (d, C2, 3JCP = 9.6 Hz),
141.99 (s, C1), 142.14 (s, C3), 150.65 (s, C8), 178.13 (s, C7). IR
(KBr, ν/cmꢀ1): 512(m), 606(m) (ν(PdS)), 623(m), 690(m), 710(s),
724(m), 754(m), 760(m), 951(m), 1115(m), 1273(m), 1303(m), 1373(s),
1427(m), 1435(m), 1458(m), 1491(w) (ν(CdN)), 1575(w), 2922(w),
3095(w), 3142(m), 3430(w). Anal. Calcd for C25H18ClN2PPdS2:
C, 51.47; H, 3.11; N, 4.80. Found: C, 51.34; H, 3.13; N, 4.91.
[2-(1,3-Benzothiazol-2-yloxy)-6-(diphenylthiophosphoryl)phenyl]-
palladium Chloride, 15. Yield: 60%. Mp: >249 °C (dec). 31P{1H}
NMR (121.49 MHz, DMSO-d6): δ 56.87 ppm. 1H NMR (300.13 MHz,
DMSO-d6): δ 7.04ꢀ7.10 (m, 1H), 7.30ꢀ7.35 (m, 1H), 7.40ꢀ7.46 (m,
3H), 7.67ꢀ7.86 (m, 10H), 8.01ꢀ8.04 (m, 1H), 8.61ꢀ8.63 (m, 1H). IR
(KBr, ν/cmꢀ1): 517(s), 562(m), 607(m) and 623(w) (both ν(PdS)),
671(m), 692(s), 707(s), 720(m), 755(s), 996(w), 1059(w), 1107(m),
1147(w), 1159(m), 1192(m), 1234(m), 1272(s), 1289(s), 1400(m),
1437(m), 1448(m), 1458(w), 1515(m) (ν(CdN)), 1560(w), 1593(w),
2856(w), 2925(w), 3040(w), 3432(w). Anal. Calcd for C25H17ClNOPPdS2:
C, 51.38; H, 2.93; N, 2.40. Found: C, 51.11; H, 2.88; N, 2.35.
{2-(1,3-Benzothiazol-2-yl)-6-[(diphenylthiophosphoryl)amino]-
phenyl}platinum Chloride, 14b. A solution of (PhCN)2PtCl2 (53 mg,
0.112 mmol) and ligand 9 (50 mg, 0.112 mmol) in 15 mL of CH3CN
was refluxed for 20 h. The resulting precipitate was filtered and
recrystallized from a DMSOꢀEt2O (1:3) mixture to give 29 mg of 14b
as a yellow, crystalline solid. Yield: 38%. Mp: >180 °C (dec). 31P{1H}
NMR (121.49 MHz, DMSO-d6): δ 42.09(2JPPt= 65.7 Hz) ppm. 1H NMR
2930
dx.doi.org/10.1021/om101012r |Organometallics 2011, 30, 2920–2932

Organometallics
ARTICLE
(300.13 MHz, DMSO-d6): δ 7.06 (d, 1H, HC(4), 3JHH = 7.5 Hz), 7.20 (m,
(2) For some recent advances in application of Suzuki cross-
coupling, see: (a) Molander, G. A.; Gormisky, P. E.; Sandrock, D. L.
J. Org. Chem. 2008, 73, 2052. (b) Tan, Ch. G.; Grass, R. N. Chem.
Commun. 2008, 4297. (c) Davies, C. J.; Gregory, A.; Griffith, P.; Perkins,
T.; Singh, K.; Solan, G. A. Tetrahedron 2008, 64, 9857. (d) Smith, A. E.;
Clapham, K. M.; Batsanov, A. S.; Bryce, M. R.; Tarbit, B. Eur. J. Org.
Chem. 2008, 1458. (e) Roulland, E. Angew. Chem., Int. Ed. 2008,
47, 3762. (f) Kylmala, T.; Kuuloja, N.; Xu, Y.; Rissanen, K.; Franzen,
R. Eur. J. Org. Chem. 2008, 4019. (g) Burzicki, G.; Voisin-Chiret, A. S.;
Sopkovꢀa-de Oliveira Santos, J.; Rault, S. Tetrahedron 2009, 65, 5413. (h)
Grimm, J. B.; Wilson, K. J.; Witter, D. J. J. Org. Chem. 2009, 74, 6390. (i)
Kabri, Y.; Gellis, A.; Vanelle, P. Eur. J. Org. Chem. 2009, 4059. (j) Filatov,
M. A.; Guilard, R.; Harvey, P. D. Org. Lett. 2010, 12, 196. (k) Bergin, E.;
Hughes, D. L.; Richards, Ch. J. Tetrahedron: Asymmetry 2010, 21, 1619.
(l) Knappke, Ch. E. I.; von Wangelin, A. J. Angew. Chem., Int. Ed. 2010,
49, 3568. (m) Liu, T.-P.; Xing, Ch.-H.; Hu, Q.-Sh. Angew. Chem., Int. Ed.
2010, 49, 2909. (n) Afonso, A.; Roses, C.; Planas, M.; Feliu, L. Eur. J. Org.
Chem. 2010, 1461.
(3) (a) Botella, L.; Najera, C. Angew. Chem., Int. Ed. 2002, 41, 179.
(b) Alonso, D. A.; Najera, C.; Pacheco, M. C. J. Org. Chem. 2002,
67, 5588. (c) Zim, D.; Gruber, A. S.; Ebeling, G.; Dupont, J.; Monteiro,
A. L. Org. Lett. 2000, 2, 2881. (d) Bedford, R. B.; Cazin, C. S. J. Chem.
Commun. 2001, 1540. (e) Bedford, R. B.; Cazin, C. S. J.; Hazelwood, S. L.
Angew. Chem., Int. Ed. 2002, 41, 4120. (f) Schnyder, A.; Indolese, A. F.;
Studer, M.; Blaser, H. U. Angew. Chem., Int. Ed. 2002, 41, 3668. (g) Bedford,
R. B.; Hazelwood, S. L.; Limmert, M. E.; Albisson, D. A.; Draper, S. M.;
Scully, P. N.; Coles, S. J.; Hursthouse, M. B. Chem.ꢀEur. J. 2003, 9, 3216. (h)
Navarro, O.; Kelly, R. A.; Nolan, S. P. J. Am. Chem. Soc. 2003, 125, 16194.
(4) For reviews on catalytic properties of pincer complexes, see: (a)
Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750. (b)
Singleton, J. T. Tetrahedron 2003, 59, 1837. (c) van der Boom, M. E.;
Milstein, D. Chem. Rev. 2003, 103, 1759. (d) Morales-Morales, D. Rev. Soc.
Quím. Mꢁex. 2004, 48, 338. (e) Dupont, J.; Consorti, C. S.; Spencer, J. Chem.
Rev. 2005, 105, 2527. (f) Moreno, I.; SanMartin, R.; Ines, B.; Churruca, F.;
Dominguez, E. Inorg. Chim. Acta 2009, 363, 1903. (g) Moreno, I.;
SanMartin, R.; Ines, B.; Herrero, M. T.; Domínguez, E. Curr. Org. Chem.
2009, 13, 878. (h) Morales-Morales, D. Curr. Org. Synth. 2009, 6, 169.
(5) Morales-Morales, D.; Jensen, C. M., Eds. The Chemistry of Pincer
Compounds; Elsevier: New York, 2007.
3
1H, H(C5)), 7.42 (d, 1H, HC(6), JHH = 7.3 Hz), 7.50ꢀ7.62 (m, 2H,
H(C10)þH(C11)), 7.67ꢀ7.80 (m, 6H, p- and m-H in P(S)Ph2), 7.88 (dd,
4H, o-H in P(S)Ph2, 3JHH = 7.3 Hz, 3JHP = 13.7 Hz), 8.18 (d, 1H, H(C12),
3JHH =8.0Hz), 9.22 (d, 1H, NH, 2JHP = 7.5 Hz), 9.73 (d, 1H, H(C9) 3JHH
=
8.2 Hz). IR (KBr, ν/cmꢀ1): 513(m), 605(m) (ν(PdS)), 623(w), 685(m),
710(s), 724(w), 747(m), 753(m), 955(m), 1023(w), 1101(m), 1115(m),
1274(m), 1297(m), 1305(m), 1372(s), 1424(m), 1435(m), 1458(m),
1484(w) (ν(CdN)), 1580(w), 2924(w), 3098(w), 3174(m), 3438(m).
Anal. Calcd for C25H18ClN2PPtS2: C, 44.68; H, 2.70; N, 4.17. Found: C,
44.60; H, 2.87; N, 4.02.
Catalytic Experiments. In a typical experiment a solution of 0.25
mmol of aryl halide, 0.375 mmol of PhB(OH)2, 0.5 mmol of K3PO4, and
the mentioned amount of the corresponding palladium complex (used
as titrated solutions in DMF) in 1 mL of DMF was heated at the
corresponding temperature (ordinarily at 120 °C) for 5 h. For kinetic
experiments the time was varied from 30 min up to 5 h. After cooling, the
reaction mixture was treated with water (3ꢀ4 mL), extracted with benzene,
and analyzed by GC. Hg(0) poisoning experiments were performed
according to ref 34 with 300 equiv of Hg relative to the metal complex.
Hg was added at either t = 0 or 20 min to the reaction mixture.
X-ray Crystallography. Single crystals were grown by recrystalli-
zation of 3 from a CH2Cl2ꢀEtOH (1:3) solution, slow diffusion of
ethanol into a DMSO solution of 12, and slow diffusion of pentane into
CH2Cl2 solutions of 13 and 15. All diffraction data were collected on a
Bruker SMART APEX II CCD diffractometer [λ(Mo KR) = 0.71072 Å,
ω-scans] at 100 K. The substantial redundancy in data allows the
empirical absorption correction to be made with the SADABS program
(Sheldrick, G. M., SADABS; University of Gottingen, 1996) using
multiple measurements of equivalent reflections. The structures were
solved by direct methods and refined by the full-matrix least-squares
technique against F2 in the anisotropicꢀisotropic approximation. All
calculations were performed with the SHELXTL software package
(SHELXTL, version 6.1; Bruker AXS Inc.: Madison, WI, 2005). Crystal
data and structure refinement parameters are listed in Table 3.
’ ASSOCIATED CONTENT
(6) For recent examples of application of pincer complexes for the
SuzukiꢀMiyaura cross-coupling, see: (a) Zhang, B.-Sh.; Wang, Ch.;
Gong, J.-F.; Song, M.-P. J. Organomet. Chem. 2009, 694, 2555. (b) Lipke,
M. C.; Woloszynek, R. A.; Ma, L.; Protasiewicz, J. D. Organometallics
2009, 29, 188. (c) Solano-Prado, M. A.; Estudiante-Negrete, F.; Morales-
Morales, D. Polyhedron 2010, 29, 592. (d) Hurtado, J.; Ibanez, A.; Rojas,
R.; Valderrama, M. Inorg. Chem. Commun. 2010, 13, 1025. (e) Yorke, J.;
Sanford, J.; Decken, A.; Xia, A. Inorg. Chim. Acta 2010, 363, 961. (f) Hao,
X.-Q.; Wang, Y.-N.; Liu, J.-R.; Wang, K.-L.; Gong, J.-F.; Song, M.-P.
J. Organomet. Chem. 2010, 695, 82. (g) Serrano-Becerra, J. M.; Hernꢁan-
dez-Ortega, S.; Morales-Morales, D. Inorg. Chim. Acta 2010, 363, 1306.
(7) Bedford, R. B.; Draper, S. M.; Scully, P. N.; Welch, S. L. New J.
Chem. 2000, 24, 745.
(8) (a) Rosa, G. R.; Ebeling, G.; Dupont, J.; Monteiro, A. L. Synthesis
2003, 18, 2894. (b) Rosa, G. R.; Rosa, C. H.; Rominger, F.; Dupont, J.;
Monteiro, A. L. Inorg. Chim. Acta 2006, 359, 1947.
(9) (a) Ines, B.; SanMartin, R.; Churruca, F.; Dominquez, E.; Urtiga,
M. K.; Arriortua, M. I. Organometallics 2008, 27, 2833. (b) Ines, B.;
Moreno, I.; SanMartin, R.; Dominquez, E. J. Org. Chem. 2008, 73, 8448.
(10) Bolliger, J. L.; Blacque, O.; Frech, C. M. Angew. Chem., Int. Ed.
2007, 46, 6514.
S
Supporting Information. This material is available free
b
of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: odinets@ineos.ac.ru.
’ ACKNOWLEDGMENT
The authors are grateful to the Russian Foundation for Basic
Research (grant 08-03-00508) for financial support.
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2931
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dx.doi.org/10.1021/om101012r |Organometallics 2011, 30, 2920–2932