A Molecular Knot with Twelve Amide Groups—One-Step Synthesis, Crystal Structure, Chirality

Abstract

Molecular knots are a little known class of substances. [1] Hitherto only some of the (historically first) phenanthroline type (Dietrich-Buchecker and Sauvage, 1989), [2] of the nucleic-acid type (Seeman, 1992), [3] and of the crown/quat type (Stoddart et al., 1997) [4] have been synthesized. We report here on probably the simplest synthesis of a new molecular trefoil knot in 20 % yield, which proceeds under self-organization. Besides a 96-membered araliphatic skeleton this knot only includes twelve CONH groups.In the course of the synthesis [5] of higher [n]catenanes [1] Ð with more than two interlacing wheelsÐwe planned to prepare larger amounts of macrocycle 4, [6] which should be favorable as a (ditopic) concave (host) template in the synthesis of [2]-and [3]catenanes. [7] For this purpose we treated the proven substrates 2,6-pyridinedicarboxylic acid dichloride 1 and diamine 2 [6] under dilution conditions (concentration 10 À3 mm) [5] in dichloromethane together with the auxiliary base triethylamine. This reaction gave besides 3 (yield 15 %) and 4 (yield 23 %) a colorless product in 20 % yield which had a molecular weight of m/z 2718.6 (MALDI-TOF-/FAB-MS), a melting point of > 325 8C, and an R f value [1] a) the ten CH 3 COO À groups, assigned as lattice constituents, was strongly indicated by elemental analysis and IR spectroscopy, but it was not possible to locate these groups crystallographically due to a disorder problem. It cannot be excluded that these groups are (at least partially) coordinated to the {(Mo)Mo 5 } pentagons, where many orientations are possible. The denomination ªKeplerateº, used in this paper for an anionic species, should be also used for neutral species when the topology of the system is in accordance with the definition (see ref.[1b]). [3] Crystal structure analysis of 2: H 492 C 24 Mo 102 O 534 ; M 19 114.06 g mol À1 , space group C2/c, a 44.586(1), b 26.365(1), c 44.565(1) , b 104.21(1)8, V 50 782 3 , Z 4, 1 2.500 g cm À3 , m 2.550 mm À1 , F(000) 36 768, crystal size 0.20 Â 0.08 Â 0.06 mm 3 . Crystals of 2 were removed from the mother liquor and immediately measured at 183(2) K on a Bruker axs SMART diffractometer (three-circle goniometer with a 1 K CCD detector, Mo Ka radiation, graphite monochromator; hemisphere of data collection at 0.38 wide w scans over three runs of 606, 435, and 230 frames (f 08, 888, 1808) from a 5.00 cm-distant detector). A total of 148 391 reflections (1.54 < V < 26.998) were collected, of which 54 698 unique reflections (R(int) 0.0811) were used. An empirical absorption correction on the basis of symmetry-equivalent reflections was performed with the SADABS program. The structure was solved and refined with the SHELXS-97 and SHELXL-97 programs (G. M. Sheldrick, University of Göttingen, 1997) to R 0.0713 for 23 929 reflections with I > 2s(I) and a max./ min. residual electron density of 2.816/ À 3.078 e À3 . Structure graphics were produced with the DIAMOND 2.1 program (K. Brandenburg, Crystal Impact GbR, 1999). Due to disorder, not all positions of the...

A synthetic molecular pentafoil knot

“…Although other syntheses of trefoil knots have been reported [15][16][17][18][19][20][21][22] (as have composites of trefoil knots 23 and other molecular topologies such as catenanes [24][25][26][27][28] and Borromean links 29 ), higher-order molecular knots remain elusive. Here, we report on the synthesis of a molecular pentafoil knot that combines the use of metal helicates to create crossover points 30 , anion template assembly to form a cyclic array of the correct size [31][32][33] , and the joining of the metal complexes by reversible imine bond formation 34-37 aided by the gauche effect 38 to make the continuous 160-atom-long covalent backbone of the most complex non-DNA molecular knot prepared to date.…”

Molekulare Knoten

“…[72,73] Angewandte Chemie Aufsätze dass die Verbindung tatsächlich ein Kleeblattknoten (22)war (Schema 7, oben). [82] Später wurde erfolgreich eine Racematspaltung der Knoten-Enantiomere durchgeführt. [83] Diese Episode zeigt, was füre ine wichtige Rolle die Rçntgen-strukturanalyse in der eindeutigen Identifizierung einer bestimmten molekularen Topologie spielen kann.…”

“…[82] Ein Netzwerk aus Wasserstoffbrücken (gestrichelte Linien) richtet die Bausteine zur Bildung des Knotens aus. Schema 8.…”

Templated Synthesis of Interlocked Molecules

“…Upon electrochemical stimulation, the [2]rotaxane 32 displays bistable switching behavior in which the macrocyclic lactam ring moves from the succinamide station to the naphthalimide station. Furthermore, by using similar synthetic strategies described above, other amide-based [2]catenanes [113][114][115][116] and amide-based [2]rotaxanes [117] have also been reported.…”