Novel Tetrapodal Molecules and Reticular Polyamides Based on Tetraphenylmethane
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Research Collection Journal Article Novel tetrapodal molecules and reticular polyamides based on tetraphenylmethane Author(s): Lorenzi, Gian P.; Manessis, Andreas; Tirelli, Nicola C.; Gramlich, Volker Publication Date: 1997 Permanent Link: https://doi.org/10.3929/ethz-b-000423050 Originally published in: Structural Chemistry 8(6), http://doi.org/10.1007/BF02311702 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Structural Chemistry, Vol. 8, No. 6, 1997 Novel Tetrapodal Molecules and Reticular Polyamides Based on Tetraphenylmethane Gian P. Lorenzi, 1'3 Andreas Manessis, 1 Nicola C. Tirelli, 1 and Volker Gramlich 2 Received March 4, 1997; revised May 26, 1997; accepted June 8, 1997 A series of tetrapodal derivatives of tetraphenylmethane were synthesized and characterized. Crys- tals obtained from tetrakis(4-acetamidophenyl)methane (lc) and from tetrakis[4-(4-aminobenza- mido)phenyl]methane (2b) were analyzed by X-ray diffraction. The analyses pointed to the crystal packing problems faced by molecules of this kind by showing that the crystals, with composition lc'2DMF'2H20 and 2b'2DMSO, respectively, contained cocrystallized solvent molecules. The solvent molecules were found in both cases to be held in place by H bonds; in the case of 2b.2DMSO they occupied channels running along the b axis. Tetrakis(4-aminophenyl)methane (lb) was used in polycondensation reactions with terephthalic acid, under modified Yamazaki conditions, to produce rigid aromatic polyamide networks. The networks were obtained as gels encompassing the whole volume of the reaction mixture. The volume of the gels did not vary noticeably upon changing the solvent (1-methyl-2-pyrrolidone) with less polar solvents, but the gels collapsed upon drying. No crystallinity was observed. KEY WORDS: Tetraphenylmethane derivatives; tetrapodal molecule's crystal structure; rigid polyamides; porous networks. INTRODUCTION potential of tetrapodal organic molecules is still to be assessed. These considerations and our interest in stiff Tetrapodal [1] organic molecules exhibiting four aromatic polyamides [16] have led us to initiate a study identical stiff chains projecting from a common core to- of tetrapodal derivatives of tetraphenylmethane (1) of ward the vertices of a tetrahedron have attracted recent attention as possible reinforcing agents [1, 2] in blends with other polymers, as monomers of four-armed star polymers [3, 4], and, in particular, as potential [5, 6] or actual [7-13] building blocks of three-dimensionally (3D) ordered, highly porous rigid networks. These net- works, which can originate through self-assembling [7- formula and to try to use monomers of this kind to pre- 13], or, in principle, through polymerization [5-8, 14, pare rigid polyamide networks. In this paper we de- 15], are interesting especially for possible applications scribe the syntheses of the derivatives with n = 0, R = in molecular separations and in catalysis. Work in all NHCOCH 3 (lc), n = 1, R = NO2, NH 2, or NHCOCH3 these fields, however, is only just beginning and the full (2a, 2b, and 2e), and n = 2, R = H, NO2, or NH 2 (3, 3a, and 3b), present the crystal packing characteristics of crystals obtained from lc and 2b, and report on some t Institut fiir Polymere, ETH-Zentrum, CH-8092 Ziirich, Switzerland. results of polycondensation reactions that we have car- 2Laboratorium fiir Kristallographie, ETH-Zentrum, CH-8092 Ziirich, Switzerland. ded out using lb and terephthalic acid as 3Correspondence should be directed to Gian P. Lorenzi, Institut fiir monomers. Part of this work has already been commu- Polymere, ETH-Zentrum, CH-8092 Ziirich, Switzerland. nicated in preliminary form [17]. 435 10404)400/97/1200-0435512.50/0 1997 Plenum PublishingCorporation 436 Lorenzi, Manessis, Tirelli, and Gramlich 4 lb I C NH -CO NO 2 2a ~b o ----Ira,. C ~)-N H-CO-'~'-NH- CO -~'- NH~"J4 3a 3b Scheme 1. Synthesis of the tetrapodal compounds. RESULTS AND DISCUSSION sible to grow such crystals. The molecular conforma- tions found for lc and 2b are illustrated in Figs. 1 and Tetrapodal Compounds 2, respectively. The configuration of the central carbons is not exactly tetrahedral. In the case of lc there are Syntheses around the central carbons six different bond angles Tetrakis(4-aminophenyl)methane (lb) [18] was the yarying from 101.9 ~ to 115.0~ in the case of 2b, where starting material. Acylation with 4-nitrobenzoyl chlo- the central carbons lie on a twofold crystallographic axis, ride and catalytic reduction--with hydrazine hydrate there are around them four different bond angles and [19]--of the resulting tetranitro compound (2a) were they range from 105.0 ~ to 112.0 ~ Similar distortions used to obtain 2b and these two reactions were repeated also have been observed with tetraphenylmethane [21] to obtain 3b (Scheme 1). An obstacle to the extension and with Cui[tetrakis(4-cyanophenyl)methane]BF4 of this simple procedure to the synthesis of even higher xC6HsNO2 [8]. All amide groups have the Z-configu- tetrapodal oligomers was posed by the rapid decrease in ration. The arms of the central carbons of le--all con- solubility accompanying the lengthening of the arms. 3b formationally different, albeit slightly--reach at the out- was poorly soluble, and its solutions tended to gel upon standing. The IH NMR spectra of this compound in DMSO-d6 showed split signals of variable, concentra- C(8) tion-dependent relative intensity, and revealed inter- C(5) CIS'") molecular NOE effects indicating aggregation. Interest- C(6) .~.,,~ ~ C(8") ingly, split IH NMR signals have been also observed by others for an aramid dendrimer of comparable size in the same solvent; the interpretation, however, has been O(~ '" different [20]. The exact nature of the aggregates formed by 3b was not investigated. C15') ~ ,.,p. ~,~ .... ,.~ .,r,, ") N" Crystal Structures The tetrapodal structure and the potential for non- covalent interactions of the new molecules synthesized provided strong motivation for a study of their crystal C~ ~ C(8") packing behavior. Attempts to obtain crystals suitable for X-ray analysis were made with every product, but O' only in the cases of lc and 2b, using solutions in DMF/ Fig. 1. ORTEP plot [22] (50% probability ellipsoids) of lc in crystals nitrobenzene and DMSO/HzO, respectively, was it pos- of le'2DMF'2H20, with the atom numbering. Novel Tetrapodal Molecules Based on Tetraphenylmethane 437 CIIO') C(12} respectively, the tetrapodal molecules held the solvent N(2') ,~.~ C(9" C(13~ N{2) molecules using hydrogen-bonding (Figs. 3 and 4). In the case of 2b.2DMSO it is the N(1) that is connected to the oxygen of the solvent [N(1)...O(DMSO), 2.86 0(1') C~(13,)~C(4,1 C3, ) C(3) C(7)1~~r O81 ~{9) ~,]. In these crystals (Fig. 4) the tetrapodal molecules interact not only through hydrogen-bonding c,l 'Zo,4, IN(2)...O(1'), 2.94 A,], but also in the way of a 7r,~r interaction through a cofacial pairing of the p-amino- benzamido rings C(8')-C(13'). An interesting feature of the crystals of 2b.2DMSO is that the enclathrated DMSO molecules are located in channels running par- allel to the b axis (Fig. 4). No attempts were made to obtain solvent-free crystals with empty pores, but a con- trol X-ray analysis was carried out on crystals that had remained in air at ambient temperature for more than 2 years. The analysis showed that the crystal structure had Fig. 2. ORTEP plot [22] (50% probability ellipsoids) of 2b in crys- tals of 2b'2DMSO, with the atom numbering. not changed and that the enclathrated DMSO molecules were still present. Reticular Aramids ermost nonhydrogen atom a length of 8.08-8.12 A_. Those of 2b--identical in pairs--measure 12.12 and Polycondensations of a tetrapodal monomer with a 12.14 A,, respectively. Not surprisingly, since a loose stiff bifunctional comonomer afford a convenient way crystal packing of the tetrapodal molecules was antici- for obtaining rigid networks with evenly spaced, tetra- pated, the X-ray analyses showed that the crystals ob- hedral branch points (Fig. 5). The networks can be tained contained cocrystallized solvent molecules. highly porous materials with windows and cavities--all The analyses also indicated that in the clathrates, identical in the case of ideal 3D-ordered networks--of with composition lc'2DMF-2H20 and 2b-2DMSO, very large size. In the aramid networks obtained, as in / ~ // " Fig. 3. A section through the crystal structure of le.2DMF.2H20. Only half the depth of the unit-cell contents, in the direction of the c axis, is shown. The hydrogen bonds are indicated by dashed lines; O, nitrogen; ~, oxygen. Note that there is no direct hydrogen bond between lc and DMF. 438 Lorenzi, Manessis, Tireili, and Gramlich Fig. 4. Perspectiveview of 2b" 2DMSO down the center of the unit cell in the direction of the b axis. The view shows four channels with the DMSO molecules. The paired rings at the center of the cell are the rings C(8')-C(13') (Fig. 2). The dashed lines are hydrogen bonds between N(I) and O(DMSO) and between N(2) and O(1') [N(2') and O(1), not re- garded as hydrogen-bonded,come as close as 3.00 .~ to each other], this work, from lb and terephthalic acid, having a dis- synthesized in the present work in that they were ob- tance of about 19 ,~, between branch points, more than tained from nontetrapodal and generally less than tetra- 80 % of the volume could be free. Highly porous, rigid functional monomers and in that their branch points were aramid networks, including even some with identical only trifunctional.