COMMUNICATIONS
The mixture was then cooled to 788C and sequentially treated with
methyl pyruvate 5 (0.25 mmol) containing methyl-1-naphthoate (internal
standard) and ketene thioacetal 4 (0.30 mmol). After transferring the
Schlenk tube into an ice bath, samples were taken at time intervals and
filtered through a short (2 cm) silica gel plug,[19] and the conversion and the
6/7 ratio were determined by GLC.[16] When conversion was complete, the
reaction mixture was filtered under an inert atmosphere, and the filtrate
containing 6 and 7 was hydrolyzed as described.[16] Yield and ee of 7 were
determined by 1H NMR spectroscopy and HPLC (Chiralcel OD-H,
0.5 mLmin 1, hexane/2-propanol 99:1), respectively.
Self-Assembly of Pyramidal Tetrapalladium
Complexes with a Halide at the Apex**
Â
Camino Bartolome, Raquel de Blas, Pablo Espinet,*
Â
Â
Ä
Jose M. Martín-Alvarez, and Fernando Villafane
Compared to the ubiquitous presence of m1-X and m2-X
ligands (X halide), and the frequent m3-X coordination
(often involved in cubane-like structures), higher coordina-
tion numbers for halide ligands in discrete molecules are
much less common.[1] A coordination number four (m4-X) is
rare. Apart from a few scattered cases found in polynuclear V,
Mn, Zn, or Sb compounds,[2] the examples known seem to
concentrate on d10 CuI,[3] AgI, or HgII complexes.
The recovered complex 3 ´ Cu(OTf)2 was washed with dry CH2Cl2 and dried
under vacuum. The MS could be mechanically removed at this stage.
Recycle runs were carried out according to the general procedure,
beginning with the addition of the initial amount of Cu(OTf)2 (entries 4 ±
8) or skipping this step (entries 9 ± 10).
Received: December 6, 2000 [Z16236]
The group of Hawthorne[4] has reported a number of such
structures based on [12]mercuracarborand-4 macrocycles
containing four Hg atoms defining a square plane. These
electrophilic Hg atoms can bind one halide in an almost
square-planar (for X Cl) or square-pyramidal (for X I)
fashion, depending on the size of the halide. Removal of the
halide guest regenerates the free host. On the other hand, the
group of Puddephatt has reported the inclusion of halides in
electrophilic bowl-shaped calix(4)arene complexes of CuI or
AgI, where the geometry imposed by the calixarene host can
stabilize either m3- or m4-binding modes of the halide, depend-
ing on the size of the latter.[5] The mercury macrocycles cited
above, as well as other similar ones containing three or five
mercury atoms, can even take a second halide to give
bipyramidal structures with one halide at each apex.[6] In all
these cases the hosting electrophilic metal centers are d10 ions
which are involved in a macrocyclic structure which exists
independently of the presence of the m4-binding halide. We
present here a case of self-assembly of d8 metal centers and
halides around a pyramidal halide to give tetrapalladium
complexes. Unlike the cases reported by Hawthorne and
Puddephat, in our case the metallamacrocycle owes its
formation to the halide acting as a template.
[1] a) Comprehensive Asymmetric Catalysis (Eds.: E. N. Jacobsen, A.
Pfaltz, H. Yamamoto), Springer, Berlin, 1999; b) Transition Metals for
Organic Synthesis (Eds.: M. Beller, C. Bolm), Wiley-VCH, Weinheim,
1998.
[2] Chiral Catalyst Immobilization and Recycling (Eds.: D. E. De Vos,
I. F. J. Vankelecom, P. A. Jacobs), Wiley-VCH, Weinheim, 2000.
[3] a) S. J. Shuttleworth, S. M. Allin, P. K. Sharma, Synthesis 1997, 1217 ±
1239; b) P. Hodge, Chem. Soc. Rev. 1997, 26, 417 ± 424.
[4] a) Q. H. Fan, C. Y. Ren, C. H. Yeung, W. H. Hu, A. S. C. Chen, J. Am.
Chem. Soc. 1999, 121, 7407 ± 7408; b) ref. [2], chap. 9.
[5] a) P. Salvadori, D. Pini, A. Petri, Synlett 1999, 1181 ± 1190; b) C. Bolm,
G. Arne, Eur. J. Org. Chem. 1998, 1, 21 ± 27; c) L. Canali, E. Cowan, H.
Deleuze, C. L. Gibson, D. Sherrington, J. Chem. Soc. Perkin Trans. 1
2000, 2055 ± 2066; d) T. S. Reger, K. D. Janda, J. Am. Chem. Soc. 2000,
122, 6929 ± 6934; e) ref. [2], chap. 10.
[6] a) B. Altava, M. I. Burguete, J. M. Fraile, J. I. García, S. V. Luis, J. A.
Mayoral, M. J. Vincent, Angew. Chem. 2000, 112, 1563 ± 1566; Angew.
Chem. Int. Ed. 2000, 39, 1503 ± 1506, and references therein;
b) ref. [2], chap. 11.
[7] A. Mandoli, D. Pini, S. Orlandi, F. Mazzini, P. Salvadori, Tetrahedron:
Asymmetry 1998, 9, 1479 ± 1482.
[8] a) A. K. Ghosh, P. Mathivanan, J. Cappiello, Tetrahedron: Asymmetry
1998, 9, 1 ± 45, and references therein; b) J. Johnson, D. A. Evans, Acc.
Chem. Res. 2000, 33, 325 ± 335 and references therein.
[9] For asymmetric cyclopropanation with structurally related aza-bis-
oxazoline ligands linked to a soluble polymer, see M. Glos, O. Reiser,
Org. Lett. 2000, 14, 2045 ± 2048.
[10] J. M. Fraile, J. I. García, J. A. Mayoral, T. Tarnai, M. A. Harmer, J.
Catal. 1999, 186, 214 ± 221.
[11] C. Langham, S. Taylor, D. Bethell, P. McMorn, P. C. Bulman Page,
D. J. Willock, C. Sly, F. E. Hancock, F. King, G. J. Hutchings, J. Chem.
Soc. Perkin Trans. 2 1999, 5, 1043 ± 1049.
[12] a) D. A. Evans, J. S. Johnson, E. J. Olhava, J. Am. Chem. Soc. 2000,
122, 1635 ± 1649; b) D. A. Evans, E. J. Olhava, J. S. Johnson, J. M.
Janey, Angew. Chem. 1998, 110, 3554 ± 3557; Angew. Chem. Int. Ed.
1998, 37, 3372 ± 3375.
The reaction of precursors of ªPd(Fmes)º (Fmes 2,4,6-
tris(trifluoromethyl)phenyl) such as 1 or 2 (Scheme 1)[7] with
halides QX (the overall ratio of Pd:X is 4:5) in CH2Cl2 affords
high yields of the tetrametallic species Q[Pd4(Fmes)4X5] (3)
(X Cl, Br, I; Q PPh4 or PPN (bis(diphenylphosphane)-
iminium)).[8] The formation of compounds 3 involves the
displacement of MeCN and becomes easier in the order I >
Br> Cl; thus, only for X I is compound 3 readily formed
starting from the MeCN-rich complex 2.
[13] D. A. Evans, G. S. Peterson, G. S. Johnson, D. M. Barnes, K. R.
Campos, K. A. Woerpel, J. Org. Chem. 1998, 63, 4541 ± 4544.
[14] a) D. C. Sherrington, Chem. Commun. 1998, 2275 ± 2286; b) A. Guyot,
M. Bartholin, Prog. Polym. Sci. 1982, 8, 277 ± 332.
Figure 1 shows the crystal structure of the anion in
(PPN)[Pd4(Fmes)4Cl5]. The four Pd atoms display a square-
[15] R. P. Singh, Bull. Soc. Chim. Fr. 1997, 134, 765 ± 768.
[16] D. A. Evans, C. S. Burgey, M. C. Kozlowski, S. W. Tregay, J. Am.
Chem. Soc. 1999, 121, 686 ± 699.
Â
Â
[*] Prof. P. Espinet, C. Bartolome, R. de Blas, J. M. Martín-Alvarez,
Ä
F. Villafane
Â
Departamento de Química Inorganica
Facultad de Ciencias
[17] Control experiments showed that the enantioselectivities for the
formation of
6 and 7 were identical within the experimental
Universidad de Valladolid
47005 Valladolid (Spain)
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uncertainty. Therefore the ee values were routinely determined after
the conversion of 6 to 7 (see Experimental Section).
[18] The heterogeneous nature of the catalytic system was demonstrated
by the fact that removing 3 ´ Cu(OTf)2 by filtration at 30% conversion
completely stopped the reaction.
[**] This work was supported by the DGESIC (Project No. MAT99-0971)
and the JCyL (Project No. VA17/00B). We thank Prof. Odile
Eisenstein for very useful discussions during her stay as Iberdrola
Visiting Professor.
[19] This treatment did not cause desilylation of 6.
Angew. Chem. Int. Ed. 2001, 40, No. 13
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