Rotaxanes compartmental

The next step is shown in Scheme 9.19 prerotaxane 232+(PF6 )2, 3,5-di-r-butylbenzaldehyde 1818 and (diethyl-3,3 -dimethyl-4,4 -dipyrryl-2,2 )methane 2423 (molar ratio 1 4 10) are mixed and stirred in dichloromethane, in the presence of trifluoroacetic acid (3 1) for 17 h. Subsequently, a large excess of p-chloranil (30 1) is added in order to oxidize the intermediate porphyrinogens and the reaction mixture is heated under reflux for 1.5 h. After work-up and chromatographic separation, three porphyrins are isolated the etio-por-phyrin 24, the desired Cu(I) [2]-rotaxane 252+(PF6 )2 and the compartmental bis-copper(I) [3]-rotaxane 264+(PF6")4. Copper(I) [2]-rotaxane 252+(PF6")2 is isolated in 25% yield (Scheme 9.19). 

Figure 2.29. Schematic representation of the principle of transition-metal-templated synthesis of [3]-rotaxanes and compartmental [5]-rotaxanes from macrocyclic chelate (A), metal cation (black disk) and open chelate (B). The latter bears functions X at its extremities, which will be used for anchoring or constmcting the stoppers (represented as diamonds), (i) Threading step ( ) stoppering step.

Figure 2.30. Copper(I)-templated synthesis of Cu(I)-complexed [3]-rotaxane 86 and compartmental [5]-rotaxane 87, bearing free-base porphyrins as stoppers.

The prerotaxane obtained (147) (1 equiv.) was then reacted with dipyrrylmethane (141) (10 equiv), 3,5-di-tert-butylbenzaldehyde (132) (8 equiv.) in dichloromethane solution acidified with trifluoroacetic acid, affording, after oxidation of the porphyrinogen intermediates by excess chloranil (133), bis-copper(l)-complexed [3]-rotax-ane (148) in 35% yield (Figure 53). Remarkably, a copper(l)-complexed [5]-rotaxane (149) could be isolated from the reaction mixture, in 8% yield. We shall discuss the formation of this compartmental rotaxane in the last section. The free-base... 

Figure 54 Schematic representation of the formation of compartmentai [3]- and [5]-rotaxanes (136) and (149). (i) Condensation of two pre([2]-rotaxane) units (A) to afford compartmentaJ [3]-rotaxane (C) (iii) condensation of two pre([3J-rotaxane) units (B) to afford compartmental [5]-rotaxane (D) [59, 117].

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