Inorg. Chem. 2006, 45, 5266−5268
Unexpected PtII Migration between the Calixarene Oxygen Atoms
Natalie Kotzen, Israel Goldberg, Sofia Lipstman, and Arkadi Vigalok*
School of Chemistry, The Raymond and BeVerly Sackler Faculty of Exact Sciences,
Tel AViV UniVersity, Tel AViV 69978, Israel
Received April 11, 2006
Scheme 1
Reaction between the 1,3-bis(trimethylsilyl) ether of calix[4]arene
and platinum(II) difluoro complexes unexpectedly results in the
formation of the 1,2-bridging platinum(II) calixarene complex, which,
upon treatment with 2 equiv of acyl chloride, reinstates the 1,3-
disubstitution pattern in the calixarene moiety.
While the coordination of metal ions to the oxygen atoms
of the calixarene scaffolds has been extensively studied
interested in investigating the reactivity of platinum(II)
difluoro complex dpppPtF2 (dppp ) 1,3-diphenylphosphi-
nopropane) 2a8 with 1,3-bis(trimethylsilyl) calixarene ether,
1. The reaction between the two compounds in benzene at
room temperature overnight resulted in the formation of
TMS-F (as observed by 19F NMR spectroscopy) and a new
Pt complex 3a (Scheme 1), which showed a single resonance
in the 31P NMR spectrum at -8.35 ppm (JPtP ) 3492.6 Hz).
The same product was also observed when the reaction was
performed in chloroform.
Surprisingly, the 1H NMR spectrum of the new compound
showed an asymmetric pattern for the bridging CH2 groups,
inconsistent with the expected 1,3-coordination mode. Six
sets of doublets were observed in this spectrum for the CH2
groups. One of these signals appeared at 6.50 ppm, a very
low field resonance for this group. The phenolic H atoms
showed a sharp singlet at 10.40 ppm,5a again far downfield
from the value expected for the disubstituted calixarene
molecule. Single crystals of 3a were obtained, upon slow
evaporation of its CH2Cl2/pentane solution, and subjected
to X-ray analysis.9 The structure of 3a (Figure 1) revealed
that the Pt center had indeed replaced both silyl groups in 1.
However, an unprecedented concomitant metal migration to
during the last 2 decades, nearly all of these studies involved
highly oxophilic early and middle-row transition metals.1,2
In the absence of a pendant soft donor ligand,3 coordination
of the Pt group metals to the oxygen atoms competes with
the more favorable η6 coordination to the calixarene aromatic
rings.4 Such competition was recently exemplified by Ishii
and co-workers, who demonstrated that a Rh center can be
coordinated to the lower calix[4]arene (calixarene) rim only
after one of the metal ions is attached to the phenoxide
aromatic ring.5 To circumvent this problem, we thought of
utilizing a strategy that directs a late transition metal toward
oxygen atoms of the lower rim. Silyl-protected calixarene
molecules6 appear to be a suitable starting point because the
protective groups can easily be removed by reaction with
the fluoride ion. As late-transition-metal fluoro complexes
can serve as sources of highly active fluoride ions,7 we were
* To whom correspondence should be addressed. E-mail: avigal@
post.tau.ac.il.
(1) For general references, see: (a) Calixarenes ReVisited; Gutsche, C.
D., Ed.; Springer: New York, 1998. (b) Bohmer, V. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 713. (c) Ikeda, A.; Shinkai, S. Chem. ReV.
1997, 97, 1713. (d) Ludwig, R. Fresenius’ J. Anal. Chem. 2000, 367,
103.
(2) For reviews on transition-metal calixarene chemistry, see: (a) Wieser,
C.; Dieleman, C. B.; Matt, D. Coord. Chem. ReV. 1997, 165, 93. (b)
Harvey, P. D. Coord. Chem. ReV. 2002, 233-234, 289. (c) Petrella,
A. J.; Raston, C. L. J. Organomet. Chem. 2004, 689, 4125. (d) Sliwa,
W. Croat. Chem. Acta 2002, 75, 131. (e) Floriani, C.; Floriani-Moro,
R. AdV. Oranomet. Chem. 2001, 47, 167.
(3) Jeunesse, C.; Armspach, D.; Matt, D. Chem. Commun. 2005, 5603.
(4) Staffilani, M.; Hancock, K. S. B.; Steed, J. W.; Holman, K. T.; Atwood,
J. L.; Junega, R. K.; Burkhalter, R. S. J. Am. Chem. Soc. 1997, 119,
6324.
(8) Yahav, A.; Goldberg, I.; Vigalok, A. J. Am. Chem. Soc. 2003, 125,
13634.
(9) X-ray structure data for 3a: C71H80O4P2Pt‚CH2Cl2, M ) 1339.31, 0.25
× 0.25 × 0.15 mm3, monoclinic, space group P21/c, a ) 21.0646(3)
Å, b ) 12.6317(2) Å, c ) 24.6998(5) Å, â ) 94.8104(6)°, V )
6549.02(19) Å3, Z ) 4, Nonius Kappa CCD, Mo KR radiation (λ )
0.710 73 Å), graphite monochromator, T ) 110(2) K, 15 672 collected
reflections, and 11 587 unique reflections (Rint ) 0.0530). The structure
was determined by direct methods (SIR-97) and refined anisotropically
by least squares on F 2 data (SHELXL-97; 746 parameters with no
restraints). R1 ) 0.0475, wR2 ) 0.0753 for 11 587 data with I >
2σ(I), and R1 ) 0.1106, wR2 ) 0.1249 for all unique data. One of
the t-Bu groups is rotationally disordered and modeled so. The CH2-
Cl2 solvent located inside the calix suffers also from a significant
positional/orientational disorder, which however could not be resolved.
(5) (a) Ishii, Y.; Onaka, K.-I.; Hirakawa, H.; Shiramizu, K. Chem.
Commun. 2002, 1150. (b) A late transition metal was incorporated
inside the calixarene cavity in a bimetallic system: Iwasa, K.; Kochi,
T.; Ishii, Y. Angew. Chem., Int. Ed. 2003, 42, 3658.
(6) Anwander, R.; Eppinger, J.; Nagl, I.; Scherer, W.; Tafipolsky, M.;
Sirsch, P. Inorg. Chem. 2000, 39, 4713.
(7) Grushin, V. V. Angew. Chem., Int. Ed. 1998, 37, 994.
5266 Inorganic Chemistry, Vol. 45, No. 14, 2006
10.1021/ic0606126 CCC: $33.50
© 2006 American Chemical Society
Published on Web 06/09/2006