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Molecular Redox-Switches by Ligand Exchange.

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tor. CCDC. 12 Union Road. Cambridge CB2 1% UK (fax: int. code
.; [nm] (c [ # - ' c m - ' ] ) = 222 (11200). 344 (625). 'HNMR (300MHz, CD,CN):
+(1223) 336-033; e-mail: techedia chemcrys.cam.ac.uk).
6 = 2.19 ( s . YH). 5.48 (s, 6H), 6.70 (t. 3H), 7.69 (d, 3H), 8.12 (d, 3Hj. 13C NMR
(75 MHz. CD,CN): d =13.0 (CH,), 51.6 (CH,). 100.6 (C2,4.6), 109.2 (C1,3,5),
[I21 The structure i s held together by a complex network of hydrogen bonds be109.6 (C4). 135.1 (CS), 140.7 (C3). Alternatively, zinc chloride (2 equiv) and
tween the tetrachlorozincate anion and three water solvate molecules, one of
hydrochloric acid were added to the above filtrate, which, over a period of weeks,
which is disordered over two sites.
furnished yellow crystals of the ZnCI:- salt of 5, which were suitable for single
[13] R. J. Restivo, G. Ferguson, D. J. O'Sullivan. F. J. Lalor, Inor,?. Chem. 1975, 14,
3046 - 3052.
crystal X-ray structure analysis. C,H,N anal. calcd. for C,,H,,N,RuZnCI,-2H,O:
C 35.79. H 4.00. N 11.92; found: C 35.60, H 3.91. N 11.83
I141 D. Carmona, J. Ferrer, L. A. Oro, M. C. Apreda, C. Foces-Foces. F. H. Cano,
J. Elguero, M. L. Jimeno, J Chem. SOC.Dulton Trans. 1990. 1463-1476.
6: a ) 2.4,6-TrimethylphenoI (2 equiv), 2-bromopyridine (1 equiv) and potassium
1151 G. C. Martin, G. J. Palenik, J. M. Boncella, lnorg. Chem. 1990,29,2027-2030.
carbonate (1 equiv) were heated, with stirring, at 220-230'C for 8 hours. The
[16] W. Luginbuhl, P. Zbinden, P. A. Pittet. T. Armbruster. H.-B. Biirgi, A. E.
resulting mixture was extracted repeatedly with diethyl ether, and the extracts comMerbach. A. Ludi, Innrg. Chem. 1991, 30,2350-2355.
bined and washed with aqueous sodium hydroxide Removal of the solvent under
[17] S. Bhambri, D. A Tocher, Pol.yhedron 1996, 15, 2763-70.
reduced pressure yielded 2,4,6-trimethy1(2-pyridoxy)benzenein 62% yield. b) A
[181 In acetonitrile 5 showed only a series of irreversible reductions starting
mixture of 2.4.6-trimethyl(2-pyridoxy)benzene (I equiv), paraformaldehyde
at -0.91 V (vs. SCE) and no observable oxidation process within the solvent
(4 equiv), and 40% hydrobromic acid was heated at reflux in acetic acid for 14 days;
limits. Ru(+benzenej complexes with tridentate nitrogen Iigands behave simadditional hydrobromic acid was added to the reaction mixture every second day.
ilarly [6]. We thank Dr. A. J. Downard for these measuremcnts.
The resulting solution was poured into water, and the solid filtered and recrystal[19] M. Stebler-Rothlisberger. A. Ludi, PoLvhedron 1986. 5. 1217-1221.
lized from petroleum ether to give 3,5-bis(bromomethyl)-2,4.6-trimethy1(2-pyri[20] A. W. van der Made, R. H. van der Made. J Org. Chem. 1993,58. 1262- 1263.
doxy)benzene in 29 % yield. M.p. = 160-161 'C. C.H,N anal. calcd. for
I211 A. J. Downard, G. E. Honey, P. J. Steel. lnorg. Chem 1991. 30. 3733-3737,
C,,H,,Br,NO. C4X.15, H 4.29, N 3.51; found: C48.57, H 4.28. N3.44. 'HNMR
and references therein.
(300 MHz. CDCI,): 6 = 2.18 ( s , 6H), 2.47 (s. 3H), 4.59 (s, 4H). 6.90 (d. 1 H). 6.95
(1, 1 H), 7.69 (t, 1 H). 8 11 (d, 1 H). I3C NMR (75 MHz, CDCI,): 6 =12.79, 14.92,
29.71. 109.96, 117.84. 131 73, 133.52. 134.26. 139 56, 147.75, 148.53, 162.95. c) A
mixture of 3,5-bis(bromomethyl)-2,4.6-trimethyl(2-pyridoxy)benzene(1 equiv)
pyrazole (2 equiv) and tetrabutylammonium hydroxide was heated at reflux in benzeneiaqueous sodium hydroxide for 18 hours. The benzene layer was then separated, dried (sodium sulhte), and concentrated under reduced pressure to give a crude
product. which was rccrysta!lized from petroleum ether to give the pyridoxybenzene
6 as a colorless solid in 58% yield. M.p. =127"C. C,H.N anal. calcd. for
C,,H,,N,O: C 70.76. H 6.21. N 18.75; found: C 70.51. H 6.05, N 18.66 ' H N M R
(300 MHz. CDCI,): d = 2 15 (s, 6 H ) , 2.27 (s. 3H). 5.43 (s, 4H). 6.20 (t, 2H). 6.94
(d,1H),6.95(t,lH).7.09(d,2H),7.53(d,2H).7.70(t.lH),8.10(d,1H).'3C
NMR (75 MHz, CDCI,): 6 =13.24, 15.58, 50.42, 105.33, 110.07, 117.86. 127.85,
Christophe Canevet, Jacqueline Libman, and
131.36, 132.52. 135.55, 139.22. 139.53, 147.67. 148.88, 162.88.
Molecular Redox-Switches by Ligand
Exchange**
Abraham Shanzer*
Received: April 19, 1996 [29053IE]
German version: Angew. Chem. 1996. 108. 2818-2820
Keywords: arenes . chelate ligands
- ruthenium compounds
[l] A. Shaver in Comprdiensive Coordinurion Chemistry. Vol. 2 (Eds.: G. Wilkinson, R. D. Gillard, J A McCleverty). Pergamon, Oxford, 1987, p. 245.
121 S. Trofimenko, Prog. lnorg. Clrem. 1986, 34. 115-210; Chem. Rev. 1993, 93,
943-980: G Parkin. A h . Inorg. Chem. 1995.42.291 -393; N. Kitajima, W. B.
Tolman. Prog. Inorg Chem. 1995, 43. 419-531.
[3] S. Trofimenko. .I. An?. Chem. Sor. 1967,#9, 3170-3177.6288-6294.
[4] P. K. Byers. A. J. Canty, R. T. Honeyman, Adv. Orgunomef. Chem. 1992, 34,
1 -65; T. Astley. J. M. Gulbis. M. A. Hitchman. E. R. T. Tiekink, J Chem. Sor.
Dalton 7run.s. 1995. 509-515: D. L. Reger, J. E. Collins, R. Layland. R. D.
Adams. lnorg C h m . 1996, 35. 1372- 1376, and references therein.
[5] M. A. Bennett, M. 1. Bruce. T. W. Matheson in Comprehensive Orgunometatlir
Chemi.>-/rr.&I. 4 (Eds.: G. Wilkinson. F. G. A. Stone, E. W. Abel). Pergamon,
Oxford, 1982. p. 691: M. A. Bennett in Comprehensive OrganomefuNit Chemrslry 11, Vol. 7 (Eds.: E. W. Abel. F. G. A. Stone, G. Wilkinson), Pergamon,
Oxford. 199.5. p. 549.
[6] 2. Shirin, R. Mukherjee, J. F. Richardson, R. M Buchanan, J Chem. SOC.
Dulton 7ians. 1994, 465 -469. and references therein.
[7] We propose the name coelenterand for this type of ligand and coelenterate for
its metal complex. after the animal phylum Ccelenterata. from the Greek for
"hollow stomach" We thank Dr. J. A. Gerrard for suggesting this name.
[Sl C. M. Hartshorn. P. J. Steel, Inorg. Chem., in press.
[Y] C. M . Hartshorn. P. J. Steel, Aust. J. Chem. 1995. 48, 1587-1599.
[lo] We thank Prof. D. A. House for this useful suggestion.
I l l ] Crystal structure analysis of C2,H,,N,Ru-ZnCI;3H20:
M , =722.75, triclinic. space group Pi, u =10.330(2), h =11.557(3), c =12.835(3),&,
a =I14 86(2). a = 102.61(2). ;' = 93.59(2)", V =1336.0(5) A', F(000) =728,
p,,,,,(Z = 2) = 1.797 gcm-'. p = 1.90 mm-', approximate crystal dimensions
0.40 x 0.29 x 0.06 mm. 2U,,, = 5 0 , radiation Mo,, (1. = 0.71073 A), w scans,
T = - 85 C. 4303 measured data, 4078 unique data. Lp corrections, no absorption correction, Patterson/Fourier (SHELXS). full-matrix least-squares
refinement on F 2 with all data (SHELXL93). 338 parameters, H atoms in
calculated positions, conformational orientation of methyl hydrogens deduced
from circular Fourier syntheses, residual electron density < 1.6 e k ' .
GOF = 0.92. wR(al1 data) = 0.156. conventional R value 12571 data with
I > 2o(l)] = 0.061. Crystallographic data (excluding structure factors) for the
structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-179-115.
Copies of the data can be obtained free ofcharge on application to the DirecAnpi%
Clreiit IU. Ed. Gtgl. 1996. 35. No. 22
The increasing interest in molecule-based technologies[" is
stimulating extensive research on the synthesis of task-oriented
molecules such as molecular wires,123'I diodes,14. 51 light converters,I6I and switches." - 141 Recently, several molecular switches
have been introduced that respond to external triggers such as
photons, protons, and electrons. Examples include photochromic materials that undergo reversible, light-induced cyclizations,[' 'I rotaxanes in which macrocyclic structures shuttle
between two stations on a rodlike molecule,['2] catenates in
which redox processes of a guest ion promote swinging motions
of two rings relative to each other," and triple-stranded helices
that undergo electron-induced translocation of an iron atom
between neighboring
Here we introduce a novel redox-switch that interconverts between two distinct states by
ligand exchange. At the heart of this switch is a molecule that
possesses two sets of ion-binding groups: one set of "hard" and
one set of "soft" ligating groups. The two sets are anchored o n
a calix[ll]arene ring["I in a n alternating fashion, such that they
can form either a "hard" o r a "soft" ion-binding cavity; one
cavity is formed at the exclusion of the other. Calix[4]arene was
selected as the anchor since it directs both sets of ion-binding
groups to the same face of the ring and allows either set to
converge by means of a rocking motion. When loaded with Fe"',
the "hard" binding groups, hydroxamates, converge to embrace
the "hard" metal ion, while the soft groups diverge. Upon reduction, the ligand rearranges to engulf Fe" with its "soft"
[*] Prof. A. Shanzer, C. Canevet, Dr. J. Libman
Weizmann Institute of Science
Department of Organic Chemistry
Rehovot 76100 (Israel)
Fax: Int. code f8934-4142
e-mail: coshanzr@weizmann.weimann.ac 11
[**I This work was financially supported by the Israel Academy of Sciences and
Humanities and by the Minerva Foundation. We thank Dr. S . J. Harris, Dublin
University, Ireland. for sharing his knowledge of calix[/l]arene chemistry. The
French- Israeli I'Arc-en-ciel Program is acknowledged.
VCH Verlagsgesellsrhafi mbH, 0-69451 Weinheim. 1996
0570-083319613522-2657$ i5.00+ .25/0
2657
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bipyridyl groups (Fig. l),while the "hard" groups diverge. Subsequent oxidation reverses this process. The distinctly different
spectroscopic characteristics of this switch in its two states enables ready monitoring of the switching process in real time, as
it turns from orange into pink upon reduction.
Fig. 1. Schematic representation of the redox-switch
The mixed-ligand binders 3 and 5 and the reference binders 1,
2, and 4 were prepared from calix[4]arene by a series of steps
shown in Figure 2. The structures of the compounds were established by 'H NMR, FT IR and, FAB MS, and their cone conformations were confirmed by the large chemical shift difference
of the anchors' methylene bridges" 51 (A6 (Ar-CH,H,-Ar) =
0.88, 0.96, 0.72, 1.02, and 1.10, for ligands 1, 2, 3, 4, and 5,
respectively).
Addition of FeCl, t o a buffered solution of the mixed-Iigand
binder 3 resulted in the formation of the bishydroxamate complex Fell'-3, as indicated by its UV/Vis spectrum (2-,,, ( E ) =
464 nm (1900)).r'61 Subsequent addition of ascorbic acid caused
the appearance of new, bathochromically displaced maxima
( E ) = 494 (3000), 526 nm (3000)), characteristic for the
Fe"- bipyridyl complex Fe1'-3.[' Addition of ammonium persulfate reversed this process (Fig. 3 ) . The identity of the reduced
form of the switch, Fe"-3, was confirmed by comparison with
the same complex prepared directly by reaction of 3 with FeCI,
under argon. Independent characterization of each state of
the switch was achieved by FABMS, which confirmed the
presence of 1 :1 ca1ixarene:iron complexes without contamination of higher oligomers (see Experimental Procedure). Moreover, the stability of binder 3 to the reduction and oxidation
procedures applied was demonstrated by thin layer chromatography.
These redox processes are most likely to occur intramolecularly, as the half life of the reduction processes was found to be
shorter ( r L , 2 = 30 min) than that for the complexation of solvated Fe" ions to the mixed-iigand binder 3 under the same conditions ( t ,12 > 2 h) .['*I Considering the coordinative requirements
of iron, it is plausible that each set of ligating groups on the
calixarene binds the guest ion in a cisoid, square-planar arrangement, which is completed by two buffer molecules to form an
octahedral coordination environment (Fig. 1). The redox processes of the guest ions are consequently accompanied by a
rearrangement in which the two sets of ligating chains exchange
positions.
The closely related calixI4larene binder 5, in which the
bipyridyl residues had been attached to the 6-positions rather
than 5-positions, failed to form uniquely defined Fell1- hydroxamate and Fell- bipyridyl complexes. Binder 5 yielded mixedligand complexes as indicated by the UV/Vis spectra of Fe"'-5
and Fe"-5, and therefore failed to function as switch. The different behaviors of 5 and 3 can readily be rationalized by
molecular models. In 5 the two sets of ligands lie in the same
imaginary plane above the calixarene ring and may therefore
bind the guest ions simultaneously. In switch 3 the two sets of
ligands lie in different planes, prohibiting simultaneous coordination.
Because this switch is amphiphilic it is eminently suited
for incorporation into airlwater or iipid/water interface^.^"]
4
2
I
1 ) BrCH2CON(OTHP)CH3
2) TFA
1) BrCH2CON(OBn)CH3
2) H2
I
I
1) BrCHz CON( OTHP)CH3
2) TFA
I
2
2
5
1
Fig. 2. Synthetic scheme for the preparation of the mixed-ligand binders 3 and 5. the hydroxamate I . and the bipyridyl derivatives 2 and 4 that serve as reference compounds.
THP = tetrdhydropyran. TFA = trifluoroacetic acid.
3
2658
$> VCH ~ ~ . i . r l ~ ~ ~ . r ~ ~ , ~ : lmhH,
l , r ~ r hD-6Y3jl
uft
Wc~;nlw;in,I Y Y 6
(1.570-0833 96 3512-2658 S IS.(JO+ .25:0
Auec% C/ic,rn In1 Ed Eud 1496 35 No
22
~
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-~
substituted calix[4]arene. Deprotection by treatment with trifluoroacetic acxd. neutralization with diethylaminomethyl polystyrene. and chromalugraphic purification
yielded switch 3 in 20% yield. M.p. 213-215 C ; 'H NMR (400 MHL CDCI,.
25 C. TMS): 6 =8.68.8.65. 8.26, 8.12, 7.91. 7.79. 7.41 (d. \. d. d. t, d. and m.
respectively, each 2H. pyH). 7.05 and 6.97 (each s. each 4 H . ArH). 5.22 and 4.49
(each s. each 4H. CH,). 3.83 and 3 1 1 (each d. each 4 H, Ar-CH,H,-Ar. A6 = 0.72.
J,,,.,,= I 2 Hz). 3.73 (J, 6 H, CH,), 1.14 and 1.07 (each s. each IXH. IBu): IR (CDCl,). = 1653 c m - l (C=O): FAB-MS: m!:' 1181.7 [ ( M Niil'].
4 : In it procedure a n a l o ~ o u sto that used for 2. tetru-~c~rf-butylcalix[4]arene
I151
(0.20 g. 0.31 mmol) was treated with 6-bromomethyl-6-meth?l-2,2'-bipyridine
[2!]
(0.43 g, 1.6 mmol) and anhydrous potassium carbonate (0.20 8. 1.4 mmol) i n anhydrous D M F (IOmL) to yield 4 (0.17 g, 55% yield). M.p. 108 110 C , ' H N M R
(400 MHz.CDC1,.25 C.TMS):6 = 8 34.X.20.7.73-7.62.7.15(d.t.m,d.2H,4H.
4 H . 2H. respectiwly, pyH), 7.34 (s. 2H. OH). 7 08 and 6 x 2 (each s. each 4 H .
ArH),5.26(~.4H.CH,).4.37and3.35(eachd,each4H.Ar-CH,H,,-Ar.A~~
=1.02,
Ja," = 13 Hz). 2.65 (s. 6 H . CH,). 1.30 and 0.95 (each s. each 18 H. iBu); FAB-MS:
f71'::
1013.5 [ ( M + H)'].
5 : In a procedure analogous to that used for 3. calixarene 4 (0.35 g. 0.35 mmok) was
treated with BrCH,CON(OTHP)Me (1.25 g. 5.0 mmol). porasslum iodide (0.50 g.
3.0 mmol). and sodium hydride (60 mg, 2.0 mmol). in anhydrous T H F (25 mL) to
provide 200 mg (45% yield) of the protected product. Deprotection by treatment
with TFA yielded binder 5 in 40% yield. M.p. > 300'C, ' H NMR (400 MHz.
CDCI,. 25 C. TMS): 6 = 8.19, 7.90. 7.74. 7.67. 7.56, and 7.17 (d. t. d. t. d. and d.
respectively. each 2 H . pyH). 7.03 and 6.94 (each s, each 4 H , ArH). 5.15 and 4.45
+
0.0
I
.
~
.
.-.
.
-A_
A_c_
.
.
.
A
300
280
- ,.--
320
Alnm ---+
(eachs.each4H,CH,).4.17and3.07(eachd.each4H.Ar-CH,H,-Ar.A6=1.10.
=12 Hz). 3.57 and 2.59 (each s. each 6 H , CH,). 1.15 and 1.04 (each s. each
18H. tBu). IR (CDCI,): i'=1654cm-' (C=O). FAB-MS: ~ 7 ) : :
1209.6
[(M+ Na)'].
Fe1"-3: 1 .O mL of a solution of 3 (1.2 mM in CF,CH,OH) was diluted with 1.0 mL
of CH,OH. and 1.2 mL of a solution of FeCI, (0.90 mM in CH,OH) and 0.80 m L
of2-(N-morpholino)ethanesuIfonicacid (MES) (0.10 M in H,O) were added. The
A!nm
-
Fig. 3 UV (top) m d Vis (bottom) absorption spectra of Feiii-3(-- - --) and FeIl-3
(- .
-) (0 77 mv). ('hmges in the Vis spectrum (bottom) of Feiii-3after treatment
with ascorbic acid iit several time intervals (----). and final Vis (bottom) and UV
(top) spcctrii after subsequent treatment with ammonium persulFate (....).
These options are under current consideration as is the
possibility of disrupting the orientation of organized assemblies
by the pronounced conforinational changes of these switches.
E.\rpc.rinicwtitl Proc~c~ilurr.
1 : To a solution of tt.trn-rrrr-butylcalix[4]arene[15] (0 25 g. 0.38 mmol) in anhydrous DMSO (10 ml.) was added BrCH,CON(OBn)Me (0.40 g. 1.5 mmol) and
anhydrous potassium carbonate (0.25 g, 1.8 mmol) The reaction mixture was
stirred for 2 d ;it ainbicnt temperature and poured into 10% aq. HCI (40 mL). The
precipitate was remobed by filtration and washed twice with water. Chromatographic purilication pi-ovided protected 1. which was hydrogenated at atmospheric
pressure in thc prerence of Pd!C to yield 1 (0.15 g. 40%). M p. 208-213 C:
'H NMR (400 MHz. CDCI,. 25 'C. TMS)- 0 =7.03 and 6.93 (each s. each 4 H .
ArH).4.82(s.4H.CH,).4.26and3.3X(eachd.each4H.Ar-CH,H,-Ar.Ab
= 0.88.
J&,,,= 13 HL). 3.40 Is. 6 H . CH,). 1.25 and 1.06 (each s. each 18H. IBu); IR
(CDC'I,): i. = lh57cm ( C = O ) . FAB MS: m!:: 845.4 ( ( M t Na)'].
2 . To a solution of teti-a-r~~~i-butylcalix[4]arene
[15] (0.50 g. 0.77 mmol) in anhydrous D M F (20 rnL) was added fi-bromomethyl-2._7'-bipyridine I201 (1.0g.
4.0 mmol) and a n h y d r o u potassium carbonate (0.50 g. 3.6 mmol). The reaction
mixture was stirred lor 20 h at 70 C, cooled. and poured into water (100 m L ) The
precipitate H ~ S colkcted by filtration. Chromatography provided pure 2
(0.24g. 30(!4,). M p. 161 163 C . ' H NMR (400 MHz. CDCI,. 25 C. TMS):
6 = 8.88. X 60. 8.47. X.39. 8.18. 7.71, 7.27- 7.13 (d. md. dd. td, dd. dt. and m.
respectively. t . x h 2H. pyH). 7 13 (s. 2H. O H ) , 7.05 and 6.81 (each s, each 4 H .
ArH). 5.18 1. 4 H . C H ? ] 4.24and
.
3.2X(each d. each4H. Ar-CH,H,-Ar. A& = 0.96.
JA." = 1 3 H i ) . 1 2 9 a n d (1.96 (each s. each 18H. rBu): FAB-MS: i m z : 985.7
((hl H)+].
3: Bisbipyridine 2 (0.21 g.O.21 mrnol) in anhydrous T H F (20 mL) was treated with
BrCH,CON(OTHP)Me (0.84 g. 3.3 mmol), potassium iodide (0.31 g. 1.9 mmol).
and sodium hydride (37 mg. 1.2 mmol). and heated at reflux overnight. The product
wiis filtered a n d chrom;iiographed to provlde 70 mg (25% yield) of protected tetra-
+
pH \yas adjusted to 6.2 with NaOH (1.0 "i in H,O). FAB-MS: n 7 1 1 : 1213.4
[(M+ Fez"- 2 H + ) ]
F&3: A procedure analogous to that used for Feii'-3was applied. exccpt a solution
of FeCl, was used and the experiments were conducted under .irgon
Redox reactions. 3.0 mL of a solution of Fefi'-3 (as prepared ithove) was treated
with 30 pL of a solution of ascorbic acid (0.20 M in H,O) and the reduction process
was monitored at regular time intervals by recording the Vis spectra. The reduced
solution was subjected to FAB-MS: w z : 1215 2 [ ( M + Fe")]; n7/z: 1237 1
[ ( M + Fe" + Na')]. 2.0 mL of the resulting mixture was then oxidized by trealment with 26 pL of a solution of ammonium persulfate (0.40 M in H,O) at 70 'C for
5 min. Oxidation was indicated by the conversion of the pink color of the mixture
to the original orange color. and by its UV!Vis spectra.
Received: April 19, 1996
Revised version: July 26. 1996 [Z 9057 IE]
German version. Angew. Chrwr. 1996. 108, 2842 - 2845
Keywords: calixarenes * iron compounds * molecular switches
redox reactions
*
[I] F. L. Carter. Moleculur Ekecrronir.D P W ~11S. Dekker. New York. 1987.
[2] M. D. Ward. Chem. Sac. Re&,.1995, 121-133.
131 V. Grosshenny. A. Harriman. R. Ziessel. Angew Chrm. 1995. 107. 121 1 - 1214;
Angen. Chefn.Inf. E d EngI. 1995, 34. 1100-1102.
[4] A. Aviram, M. A. Ratner. Chrm. Phys. L e f t . 1974, 29, 277- 283.
[S] A. S. Martin, J. R Sambles. G. J. Ashwell. P h u . Re,,. Lett. 1993. 70,218-221
161 B Alpha. V Balzani. J.-M. Lehn, S. Perathoner, N Sabbatini. A n . p n . Chem.
1987. 99, 1310--1311; Aiigm Ckin. In,. Ed. Etig/. 1987. 26. 1266-1268
[7] M. R. Wasielewski, M. P. ONeill, D. Gosztola, M. P. Niemc7yk. W. A. Svec.
P f m , App!. Chmi. 1992. 64. 1319- 1325.
Rev. 1995, 24, 197-202.
[8] L. Fabbrizzi. A. Poggi, C1ii.m. SCJC.
191 R. A. Bissell. A P. de Silva. H. Q. N. Gunaratne, P. L. M. Lynch. G. E. M.
Maguire. K. R. A. S. Sandanayake, Chrfn. SOC.Rev. 1992, 21. 187-195.
[lo] P. Giitlich, A. Hauser, H. Sptering, Angeil-. Chern. 1994. 106. 2109 -2141,
AnReir-. Chetri. In!. E d €rig(. 1994. 33, 2024-2054.
[l 11 S. L Gilat. S. H. Kawai. J.-M. Lehn, J. C h w . Sor. Chcn~.Cornrrr. 1993. 14391442.
[12] R. A. Bissell. E. Cordova. A. E. Kaifer, J. F Stoddart. Nufurc 1994.369, 133137.
(131 A. Livoreil. C 0 . Dietrich-Buchccker, JLP. Sauvage. J. A m Chrm So<. 1994,
116.9399-9400.
[14] L. Zelikovitch. J Libman. A. Shanzer, Nature 1995, 374, 790- 792.
[l 51 C. D. Gutsche in Cali.\-urent.s. Monogruph.7 in Stiprumoler.irlur Chrmirtr? (Ed.:
J. F. Stoddart). The Royal Society of Chemistry. Cambridge. 1989.
[16] The observed spectral data are indicative of an Feiii-3-bishydroxamate complex: M Birus. Z. Bradic. N. Kujundzic, M Prjbanic. P C. Wilkins. R . G .
Wilkins, Inorg. Chrni.1985, 24. 3980-3983.
1171 The observed spectral data are indicative of an Fe"J-bipyridine complex, since
the trjs(bipyridyJ)iron(ir) complex derived from the same bipyridyl chro.
mophore exhibits significantly larger extinction coefficients ( 8 2 5000)
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[18] Comparative intermolecular redox experiments with I and 2 could not be
performed because of the preference of 1 to form Fe"'-trishydroxarnate
(L,,, = 428 nm) rather than-bishydroxamate complexes and the tendency of
these complexes to precipitate under analogous reaction conditions.
[19] Y. Ishikawa, T. Kunitake, T. Matsuda. T. Otsuka. S. Shinkai, J. Chrm. Soc.
Chrm. Commun. 1989,136-738.
[20] S-BromomethyI-2,2'-bipyridine was prepared by bromination of S-methyl-2.2'bipyridine with N-bromosuccinimide (NBS), and S-methyI-2,2-bipyridine was
prepared according to a procedure provided by Prof. A. von Zelewsky (University of Fribourg, Switzerland).
[21] 6-Bromornethyl-6-methyl-2.2'-bipyridine
was prepared by bromination of 6.6
dimethyl-2,2'-bipyridine with NBS, and 6.6-dimethyl-2,2'-bipyridine was prepared according to a procedure provided by Prof. J.-M. Lehn (Universite Louis
Pasteur, France).
Hexaaryltellurium, the First Neutral Compounds
Comprising Hexaarylated Elements **
Mao Minoura, Takao Sagami, Kin-ya Akiba," Claudia
Modrakowski, Allexander Sudau, Konrad Seppelt,*
and Stephan Wallenhauer
The rich diversity and practical utility of organotellurium
chemistry['] continues to attract widespread interest, for instance in organic synthesisc2]and in the chemistry of Iow-[~] and
h~pervalent[~l
compounds. Although considerable attention
has been paid to the hypervalency of some tetraaryltellurium
derivatives (TeAr,) over the past forty years,[5, a hexaaryltellurium (TeAr,), with tellurium in its highest oxidation state, has
not been rep~rted.'~]
Only three examples of neutral peralkylated hexavalent compoundsfs1(W(CH,),,r9**'I Re(CH,),,['O. * I
and Te(CH,),['*. 13]) have been published. Here we report the
synthesis and structure of the first neutral hexaarylated cornpounds, namely, TeAr, (Ar = C,H4-4-CF,: 1 a; Ar = C,H,:
1 b), which are thermally extraordinarily stable (up to 300 "C).
First we succeeded in preparing l a (13.5% yield based on
tellurium) by a one-pot reaction of LiC,H,-4-CF3 (ArLi) and
TeCI, in the molar ratio 4: 1, TeAr, (2a, 28.1 %) was also
formed. The reaction of a stoichiometric quantity (6: 1 ) or excess
of ArLi with TeCI, did not produce 1 a.
The reaction sequence is obviously multistep (Scheme 1 ) and
has not been studied in detail. However, the key step seems to
involve a disproportionation reaction between TeAr, (3) and
CI,TeAr, (4), which are formed in situ, to afford Cl,TeAr, ( 5 )
and TeAr, (2). TeAr, (1 a) is most likely formed by the succeeding reaction of 5 with ArLi during warming of the reaction
mixture to room temperature. Unfortunately, Te(C,H,), (1 b)
was obtained only in low yield (ca. 0.5%) in the above-mentioned one-pot process. We could, however, prepare 1 b by reaction of F,Te(C,H,), (6) with phenyllithium (PhLi). Following
our experience with 1 a, we successfully treated 6 with PhLi at
room temperature['41 for several hours (1 b, 7.1 %). Difluoride
['I
I*'[
2TeCI4 + 8 A r b ------+
-8LiCI
TeCI, + 4ArLi
TeCI,
+ 2ArLi
TeAr6 + TeAra
-4LiCI
-2LicI
=-
1
2
TeAr,
3
C12TeAr2
4
3
+
5
+ 2ArLi
4
------+
disproporiionalion
2
+ ClzTeAr,
5
-2LicI +
1
Scheme 1. Probable course of the synthesis of 1.
6 was prepared as described in Ref. [7a] from XeF, and
Te(C,H,), ,[5"1andthe cis-configuration was established by a
single crystal structure determination."
Compounds 1 a and 1 b are both thermally extremely stable,
colorless solids and are not light sensitive, unlike tetraorganotellurium corn pound^.^^*^^ Crystals of l a and l b were obtained
from chloroform. Molecular structures of both TeAr, were determined by X-ray crystallographic analysis (Figs. 1 and 2) .[I6]
Fig. 1. ORTEP drawing of the structure of l a (thermal ellipsoids represent 50%
probability). Selected bond lengths [A] and bond angles I"]: Tel-C1 2.229(4),
Tel-C8 2.240(2), Tel-CIS 2.226(4); Cl-Tel-C8 88.9(1), C1-Tel-CIS 91.4(2),
C8-Tel -C15 88.8(1).
Prof. Dr. K.-y. Akiba, Dr. M. Minoura, T. Sagami
Department of Chemistry, Faculty of Science, Hiroshima University
1-3-1 Kagamiyama, Higashi-Hiroshima 739 (Japan)
Fax: Int. code +(824)24-0723
e-mail: akibatz sci.hiroshima-u.ac.jp
Prof. Dr. K. Seppelt. C. Modrakowski, A. Sudau, Dr. S. Wallenhauer
lnstitut fuer Anorganische und Analytische Chemie der
Freien Universitat
D-14195 Berlin (Germany)
Fax: Int. code +(30)838-2424
e-mail : seppelt(R:chemie.fu-berlin.de
Financial support from the Ministry of Education. Science. Culture, and
Sports, Japan, the Deutsche Forschungsgemeinschaft, and the Fonds der
Chemischen Industrie is gratefully acknowledged.
2660
VCH Ver/ugsgese//stltuftmbH, 0-69451 Wemheim, 1996
Fig. 2. ORTEP drawing of the structure of I b (thermal ellipsoids represent 50%
probability). Selected bond lengths [A] and bond angles I"]: Tel-C11 2.228(1),
Tel-C21 2.228(1). TelLC31 2.227(1): CIl-Tel-C21 90.63(5), Cll-Tel-C31
90.33(5). C21 -Tel -C31 90.34(5).
0570-0X33/9613522-2660S 15.00
+ .2S10
Anyew. Chem. Int Ed. E n d 19%. 35. No. 22
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