Synthesis and X-ray structures of new concave pi-prismand hydrocarbon [2.2.1]m,p,p- and [2.2.1]p,p,p-cyclophanes

The synthesis of the smaller analogues of the well-known [2.2.2]p,p,p-cyclo phane (1) pi -prismand were performed via a well-established pyrolysis rout e from the corresponding disulfones. In spite of their smaller size and inc reased rigidity, these cyclophanes showed remarkably similar complexation b ehaviour with Ag+ ions compared to [2.2.2]p,p,p-cyclophane. X-Ray crystal s tructure determinations showed the bis-sulfide 12 (1,10-dithia[3.3.1]m,p,p- cyclophane) to be helically chiral. The single crystal X-ray analysis showe d that the reduction of the ring size from 17-membered hydrocarbon 17 to 16 -membered hydrocarbon 16 has only a slight effect on the size and shape of the cavity. In the Ag+ complex of [2.2.1]m,p,p-cyclophane (18) the interact ion between silver and hydrocarbon is accomplished by the coordination of s ilver to one double bond in two phenyl rings and to only one carbon of the third phenyl ring. However, in the case of [2.2.1]p,p,p-cyclophane-Ag+ trif late (19), silver is bonded to one of the double bonds in each phenyl ring. Similarly to larger [2.2.2]cyclophanes the conformations of the parent [2. 2.1]m,p,p- (16) and [2.2.1]p,p,p-cyclophanes (17) do not change dramaticall y upon the complexation with the Ag+ ion.