Supramolecular metallocalixarene chemistry: Linking metallocalixarenes through imiclo bridges

Article abstract of DOI:10.1039/a801808a

The synthesis and structures of two novel extended-array metallocalixarenes, derived from the ring-opening of imido-molybdenum precursors, are described.

Full text of DOI:10.1039/a801808a

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Supramolecular metallocalixarene chemistry: linking metallocalixarenes
through imido bridges
Vernon C. Gibson,*a† Carl Redshaw,a William Cleggb and Mark R. J. Elsegoodb
a Department of Chemistry, Imperial College, South Kensington, London, UK SW7 2AY
b Department of Chemistry, University of Newcastle upon Tyne, Newcastle upon Tyne, UK NE1 7RU
The synthesis and structures of two novel extended-array
metallocalixarenes, derived from the ring-opening of imido–
molybdenum precursors, are described.
release the para-bridged dianiline. Crystals suitable for X-ray
diffraction§ were grown from acetonitrile at room temperature.
The molecular structure is shown in Fig. 1(a) and selected bond
lengths and angles are given in the caption. Each molybdenum
possesses a pseudo-octahedral geometry similar to that found in
the monometallocalix[4]arene analogue of 1.5 The molybde-
num atoms are displaced from the O4 mean planes towards the
imido nitrogens of the bridging ligand by 0.246 and 0.247 Å.
The molecule has approximate C2 symmetry, the rotation axis
running through the C(13) atom. Significantly, the metallocal-
ixarenes are organised in a ‘cup-to-cup’ arrangement which
gives rise to a calixarene ‘socket’ [Fig. 1(b)], thus offering the
potential for hosting guest molecules in the cooperatively
aligned calixarene cavities.
In an extension of this work, we then targetted metallocalix-
arene species with pendant amino functionalities which we
envisaged would allow the linking of metallocalixarene units
via, for example, amide bonds. Treatment of the chelating
bis(imido)molybdenum complex {Mo(OBut)2[(2-NC6H4)2-
CH2CH2]} 3 with H4L (one equivalent) in toluene affords, after
work-up, the monoimido calixarene complex {[Mo(N-
CMe)L][2-NC6H4CH2CH2C6H4NH2-2A]} 4 in which the imido
ligand contains a ‘free’ amino functionality (Scheme 1).
Complex 4 is presumed to form via loss of two tert-butanol
ligands followed by transfer of two protons to one of the imido
ligands to release the pendant amino group.5 The IR spectrum of
4 has a strong n(N–H) stretch at 3165 cm21, indicative of an
The ability of calixarenes to act as receptors for a variety of
guest molecules is a feature of central importance to their
chemistry.1 The development of supramolecular structures
incorporating calixarenes offers an opportunity to extend
calixarene host–guest interactions to two- and possibly three-
dimensional lattices. Although supramolecular structures have
been seen as a result of guest–host interactions,2 and metal–oxo
bridges,3 clear methodologies for covalently linking metal-
localixarenes have not, to our knowledge, been described. Here,
we report the synthesis and solid state structures of two novel
metallocalixarenes derived from the ring-opening of imido–
molybdenum precursors. In one case the metallocalixarenes are
linked by hydrogen bonding between pendant amino groups and
in the other by a covalent linkage between imido ligands that
gives rise to a two-dimensional array of ‘cup-to-cup’ metal-
localixarene units.
Treatment of the tetraimido dimolybdenum complex 14 with
two molar equivalents of H4L (H4L = calix[4]arene) in
refluxing toluene affords, after work-up, the bridged complex
{[Mo(NCMe)L]2[3,5-Pri2-4-NC6H2)2CH2]} 2 according to
Scheme 1.‡ Complex 2 is presumed to form via initial
displacement of two chloride ligands (per molybdenum),
followed by proton transfer to one of the imido ligands to
Scheme 1
Chem. Commun., 1998
1969

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Fig. 1 Molecular structure of 2 without H atoms: (a) showing the atom
labelling; (b) the crystal packing diagram showing the ‘cup-to-cup’
alignment of the metallocalixarene units. Selected bond lengths (Å) and
angles (°): Mo(1)–N(1) 1.735(5), Mo(1)–O(1) 1.936(5), Mo(1)–O(2)
1.941(4), Mo(1)–O(3) 1.936(5), Mo(1)–O(4) 1.949(5), Mo(1)–N(3)
2.304(6), Mo(2)–N(2) 1.716(5), Mo(2)–O(5) 1.948(5), Mo(2)–O(6)
1.942(4), Mo(2)–O(7) 1.920(4), Mo(2)–O(8) 1.953(5); Mo(1)–N(1)–C(1)
176.7(5), Mo(2)–N(2)–C(14) 178.8(5), C(4)–C(13)–C(17) 112.2(5) (a
colour version is provided at: http://www.rsc.org./suppdata/cc/1998/1969.
Fig. 2 Molecular structure of 4 without hydrogen atoms: (a) showing the
atom labelling; (b) showing the intermolecular interactions between
adjacent metallocalixarene units. Selected bond lengths (Å) and angles (°):
Mo(1)–N(1) 1.729(2), Mo(1)–O(1) 1.9419(18), Mo(1)–O(2) 1.9334(16),
Mo(1)–O(3) 1.9323(18), Mo(1)–O(4) 1.9713(16), Mo(1)–N(3) 2.326(2);
Mo(1)–N(1)–C(1) 171.60(19).
mm21 (Mo-Ka, l = 0.71073 Å), T = 160 K. 51852 Reflections were
measured on a Siemens SMART CCD area-detector diffractometer and
corrected for absorption. The structure was solved by direct methods and
refined by full-matrix least-squares on F2 values of all 16446 unique data
(Rint = 0.1135) with restraints on disordered substituents and solvent
uncoordinated NH2 group, together with a strong n(C–N)
stretch at 1287 cm21. The structure was confirmed by an X-ray
crystallographic study and is shown in Fig. 2(a). Each of the two
aromatic rings of the imido ligand interact weakly with two
aromatic carbons on an adjacent imido ligand [C(5)···C(12A)
3.449, C(6)···C(13A) 3.561 Å], and there is a hydrogen-bonding
interaction between one of the amine hydrogens and a
calixarene oxygen atom [O(4)···H(2AA) 2.188 Å] [Fig. 2(b)].
The complexes described here represent the first steps
towards the covalent linking of metallocalixarene units and the
development of tailored supramolecular metallocalixarene
arrays.
molecules; RA = {S[w(Fo 2 Fc2)2]/S[w(Fo2)2]}1/2 = 0.2589 for all data,
2
2
conventional R = 0.0779 on F values of 11304 reflections with Fo
>
2s(Fo2); goodness of fit = 1.086 on F2 for 1432 parameters and 423
restraints. Largest peak in final difference map 1.224 e Å23 ( > 3.2 Å from
all atoms, possibly further unresolved disordered solvent). Programs:
Siemens SMART (control), SAINT (integration), SHELXTL and local
programs.
Crystal data for 4: C60H69MoN3O4, M = 992.12, triclinic, space group
¯
P1, a = 12.5913(8), (b) = 14.5121(9), c = 14.5797(8) Å, a = 81.253(2),
b = 84.564(2), g = 84.657(2)°, U = 2612.9(3) Å3, Z = 2, Dc = 1.261
g cm23, m = 0.300 mm21 (Mo-Ka, l = 0.71073 Å), T = 160 K. 16442
The Engineering and Physical Sciences Research Council is
thanked for financial aupport.
Reflections were measured as for
2 yielding 11367 unique data
(Rint = 0.0193). The structure was solved by Patterson synthesis and refined
as for 2 with restraints on one disordered tert-butyl group; RA = 0.1004 for
Notes and References
2
all data, R = 0.0412 on F values of 9626 reflections with Fo > 2s(Fo2);
goodness of fit = 1.061 on F2 for 658 parameters and 139 restraints. Largest
† E-mail: v.gibson@ic.ac.uk
‡ Satisfactory elemental analyses have been obtained on 2 and 4. Selected
spectroscopic data for 2: 1H NMR (CDCl3, 300 MHz, 298 K) d 7.12 (m,
peak in final difference map 0.686 e Å23. CCDC 182/971.
3
2
20H, aromatic H), 4.68 [spt, 4H, JHH 6.8, CH(CH3)2], 4.43 (d, 8H, JHH
12.2, CH2), 4.26 (s, 2H, ArCH2Ar), 3.23 (d, 8H, 2JHH 12.2, CH2), 1.53 [d,
1 Calixarenes by C. D. Gutsche, Royal Society of Chemistry, Cambridge,
1989.
2 A. Zanotti-Gerosa, E. Solari, L. Giannini, C. Floriani, A. Chiesi-Villa and
C. Rizzoli, Chem. Commun., 1996, 119; J. A. Acho, T. Ren, J. W. Yuu
and S. J. Lippard, Inorg. Chem., 1995, 34, 5226.
3 B. Xu and T. M. Swager, J. Am. Chem. Soc., 1993, 115, 1159.
4 V. C. Gibson, C. Redshaw, W. Clegg, M. R. J. Elsegood, U. Siemeling
and T. Turk, J. Chem. Soc., Dalton Trans., 1996, 4513.
5 V. C. Gibson, C. Redshaw, W. Clegg and M. R. J. Elsegood,
J. Chem. Soc., Chem. Commun., 1995, 2371.
3
24H, JHH 6.8 Hz, (CH3)2CH], 1.21 [m, 72H, (CH3)3C], 20.08 (s, 6H,
MeCN). For 4: 1H NMR (CDCl3, 300 MHz, 298 K) d 8.05–6.50
(overlapping m, 16H, aromatic H), 4.42 (d, 4H, 2JHH 12.2, CH2calix), 3.95
2
2
(br s, 2H, NH2), 3.67 (t, 2H, JHH 7.4, ArCH2), 3.36 (t, 2H, JHH 7.4,
ArCH2), 3.32 (d, 4H, 2JHH 12.2 Hz, CH2calix), 2.03 (s, 3H, MeCN), 1.21 [s,
36H, (CH3)2CH], 20.08 (s, 3H, MeCN).
§ Crystal data for 2·2C5H12: C117H144Mo2N4O8·2C5H12, M = 2070.5,
monoclinic, space group I2/a (non-standard setting of C2/c avoiding large
b
angle),
a = 34.891(2), b = 16.2235(11), c = 45.318(3) Å,
b = 101.303(2)°, U = 25155(3) Å3, Z = 8, Dc = 1.093 g cm23, m = 0.251
Received in Basel, Switzerland, 5th March 1998; 8/01808A
1970
Chem. Commun., 1998