C O MMU N I C A T I O N S
than or similar to the usual value for palladium foil (2.76 Å). This
bond feature is also compatible with the formation of nanopar-
ticles.1
Next, the palladium(0)-catalyzed cross-coupling reaction of aryl
halides and arylboronic acids (Suzuki coupling), an important
synthetic method, is studied. The reaction of STO species (OA1)
and (OA1′) with potassium fluoride in more than equivalent
amounts (see the Supporting Information) to the STO intermediate
addition to the 284.6 eV as in LDH-Cl. The m/z values of (ST2)
are observed at 43 and 44 amu, which correspond to OAc and CO
respectively. The reaction of STO intermediate (ST2) with tribu-
tyltin hydride provides STO intermediate PhPdSnBu (ST3), which
2
,
7,18
3
is isolated and well characterized by XPS and TGA-MS. The high-
resolution narrow scans of STO species (ST3) for Sn and Pd (II)
show 3d5/2 lines at 485.7 and 336.9 eV and 3d3/2 lines at 494.1 and
339.4 eV, respectively, which indicate the presence of a Pd-Sn
bond. No residuum of the earlier STO intermediate (ST2) is
observed, which clearly indicates the complete conversion. The
deconvoluted C 1s XPS spectrum of (ST3) displays four lines at
284.2, 285.0, 286.3, and 288.7 eV. The m/z values observed in the
TGA-MS are 15, 26, 29, 43, 51, 54, 56, 57, and 77 amu, which
6 4
gives only the surface transient species MeOC H PdF (SZ2) and
PhPdF (SZ2′), respectively (Scheme 1). When potassium fluoride
is used in 0.5 M equivalent, the unreacted STO intermediates (OA1)
and (OA1′) are also detected.
The XPS narrow scans of Pd in (SZ2) and (SZ2′) show a shift
in the binding energy of ∼3 eV, which is attributed to the highly
electronegative fluoride (F 1s line at 685.3 eV) and clearly indicates
the presence of a Pd-F bond.19 The m/z values for (SZ2) and (SZ2′)
in the TGA-MS are 15, 19, 31, 76, 107 amu and 19, 51, 77 amu,
correspond to Me, C
2
H
2
6
, C
2
H
5
, C
3
H
7
, C
4
H
3
, C
4
H
6
, C
4
H
8
, C
4
H
9
,
and C
H
6 5
, respectively.1 On heating the STO species (ST3) at 50
°C in NMP solvent gives tributylarylstannane (Supporting Informa-
tion), which reinforces the structure of STO intermediate as
described.
which correspond to Me, F, OMe, C
6 4 6 4 4 3
H , MeOC H and F, C H ,
, respectively.16 Further, the reaction of STO intermediate
The formation of only one STO intermediate in all the coupling
reactions during their reaction sequences and the excellent isolated
yields of each of the coupling product (isolated yields 85-95% of
the theoretical yield, see the Supporting Information) from the
corresponding supported complexes, HK2, SZ3, SG2, and ST3
establish that these supported complexes are the key intermediates
of the coupling reactions. This demonstrates the evolution of the
single-site heterogeneous catalyst by transfer of molecular orga-
nometallic chemistry to surface organometallic chemistry that is
responsible for high order of activity.12
C H
6 5
(
SZ2) and (SZ2′) with phenylboronic acid affords tricoordinated
surface transient organometallic species MeOC PhPdB(OH)
SZ3) and PhPhPdB(OH) (SZ3′), respectively, which are isolated
H
6 4
2
(
2
and characterized by XPS and TGA-MS. Along with the charac-
teristic XPS binding energy peaks for Pd (II) (337.5 and 342.3 eV),
both the STO intermediates (SZ3) and (SZ3′) exhibit B 1s peak at
92.6 eV, which is assigned to Pd-B.20 The deconvoluted O 1s
1
XPS spectrum of (SZ3) and (SZ3′) displays one extra line at 532.6
21
eV, which is attributed to B(OH)
2
.
There is no remnant of the
Acknowledgment. S.M. thanks the CSIR, India, for the award
of SRF. We also thank Prof. M. Beller and Prof. K. Kaneda for
prereviewing our manuscript.
Supporting Information Available: Full characterization of all
surface transition organometallic intermediates with detailed experi-
mental procedures (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
earlier STO intermediates detected, which indicates complete con-
version. The observed evolved gas fragments for (SZ3) and (SZ3′),
when subjected to TGA-MS, are 15, 17, 19, 26, 31, 45, 51 and
4
5, 51, 77 amu, respectively, and correspond to Me, OH, F, C
, respectively.16 On
OMe, B(OH) , C and B(OH) , C , C
heating, both the transient species (SZ3) and (SZ3′) at 100 °C in
,4-dioxane/water solvent system give 4-methoxybiphenyl and bi-
2 2
H ,
2
4
H
3
2
H
4 3
6 5
H
1
phenyl, respectively (see the Supporting Information), which
reinforces the structure of transient intermediate species as indicated
above.
References
(
1) Tietze, L. F.; Kettschau, G.; Heuschert, U.; Nordmann, G. Chem.-Eur.
J. 2001, 7, 368.
The Sonogashira coupling of aryl halides with terminal acetylenes
is also a useful coupling reaction. The reaction of surface transient
species (OA1′) with phenylacetylene gives STO intermediate
PhPdCtCPh (SG2), which was isolated and well characterized by
XPS and TGA-MS (Scheme 1). The XPS narrow scan of STO
intermediate (SG2) for Pd (II) 3d shows a 3d5/2 line at 337.5 eV
and 3d3/2 line at 341.8 eV. The high-resolution XPS scan of STO
intermediate (SG2) for C 1s exhibits five lines on deconvolution
at 284.4, 285.3, 286.5, 288.1, and 289.1 eV, in contrast to the two
(2) Nicolaou, K. C.; Sorensen, E. J. Classics in Total Synthesis; VCH: New
York, 1996; Chapter 31. These authors refer to the Heck reaction as “one
of the true ‘power tools’ of contemporary organic synthesis” (p 566).
(
(
(
(
3) Badar, R. R.; Baumeister, P.; Blaser, H.-U. Chimia 1996, 50, 99.
4) Alcazar-Roman, L. M.; Hartwig, J. F. Organometallics 2002, 21, 491.
5) Aliprantis, A. O.; Canary, J. W. J. Am. Chem. Soc. 1994, 116, 6985.
6) Aramendia, M. A.; Lafont, F. J. Org. Chem. 1999, 64, 3592.
(7) Brown, J. M.; Hii, K. K. Angew. Chem., Int. Ed. Engl. 1996, 35, 657.
(
8) Amatore, C.; Jutand, A.; M’Barki, M. A. Organometallics 1992, 11, 3009.
9) Hii, K. K.; Claridge, T. D. W.; Brown, J. M. Angew. Chem., Int. Ed.
Engl. 1997, 36, 984.
(
(
10) Fitton, P.; Johnson, M. P.; McKeon, J. E. Chem. Commun. 1968, 6.
11) Coperet, C.; Chabanas, M.; Saint-Arroman, R. P.; Basset, J. M. Angew.
Chem., Int. Ed. 2003, 42, 156.
(12) Choudary, B. M.; Madhi, S.; Chowdari, N. S.; Kantam, M. L.; Sreedhar,
B. J. Am. Chem. Soc. 2002, 124, 14127.
(13) Details are described in Supporting Information.
(14) Moulder, J. F.; Stickle, W. F.; Sobol, P. E.; Bomden, K. D. Handbook of
X-ray Photoelectron Spectroscopy; Perkin-Elmer: Eden Prairie, MN, 1992.
(15) Raemaekers, K. G. H.; Bart, J. C. J. Thermochim. Acta 1997, 295, 1.
16) The m/z values (TGA-MS) of the final products are not detected, which
suggests that the mass fragments are the pyrolysis products of the
respective STO intermediates.
(
lines present in the LDH-PhPdCl, which clearly indicates the
presence of Pd-CtCPh bond.22 The m/z values obtained from
TGA-MS are 51 and 77 amu correspond to C
4
H
3
and C
6
H
5
,
respectively.16 The transient species (SG2) on heating at 80 °C with
THF/water solvent system gives diphenylacetylene (see the Sup-
porting Information), which strengthens the assigned structure of
STO intermediate as described above.
(
Another widely used coupling reaction is the Stille-type coupling
of aryl halides with trialkyltin reagents (see the Supporting
Information). The reaction of surface transient species (OA1′) with
potassium acetate gives surface transient species PhPdOAc (ST2)
(17) Guillemot, D.; Polisset-Thfoin, M.; Fraissard, J. J. Phys. Chem. B 1997,
01, 8243.
1
(
18) Burch, R. In Catalysis; Bond, G. C., Webb, G., Eds.; Royal Society of
Chemistry: London, 1986; Vol. 7, p 161 and references therein.
19) Tressaud, A.; Khairoun, S.; Touhara, H.; Watanabe, N. Z. Anorg. Allg.
Chem. 1986, 540, 291.
(
(Scheme 1). The XPS narrow scans for the STO intermediate (ST2)
(20) Stranick, M. A.; Houalla, M.; Hercules, D. M. J. Catal. 1987, 104, 396.
(
21) Nefedov, V. I.; Gati, D.; Dzhurinskii, B. F.; Sergushin, N. P.; Salyn, Y.
exhibits Pd (II) 3d5/2 line at 337.2 eV and 3d3/2 line at 341.3 eV
and O 1s at 531.1 and 532.0 eV; the former is attributed to impurity
and the latter to Pd-O bond.23 The deconvoluted C 1s XPS
V. Zh. Neorg. Khim. 1975, 20, 2307.
(22) Brant, P.; Benner, L. S.; Balch, A. L. Inorg. Chem. 1979, 18, 3422.
(23) Kim, K. S.; Gossman, A. F.; Winograd, N. Anal. Chem. 1974, 46, 197.
spectrum of the (ST2) displays two lines at 285.0 and 288.9 eV, in
JA038270F
J. AM. CHEM. SOC.
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