Molecular “Iron Maidens”: Ultrashort Nonbonded Contacts in Cyclophanes and Other Crowded Molecules

Abstract

Ultrashort nonbonded interactions involving aromatic rings should be the sole province of cyclophane chemists, but it is not always so. In this review, the structures, syntheses, and properties of molecules exhibiting the closest nonbonded contacts of various atoms and functional groups with the faces of aromatic rings are discussed and illustrated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Dreifach‐verbrückte Diphosphane mit von innen nach außen invertierender Konfiguration

“…Der erste könnte durch 1,3,5-Cyclophane, die ausreichend lange verbrückende Ketten enthalten, realisiert werden. [20] Der letztere zeichnet sich durch eine Spezies mit vier Brücken-ketten aus, von denen zwei durch den von den beiden übrigen Ketten gebildeten makrocyclischen Ring hindurchschwingen können und damit eine Isomerisierung bewirken. Darüber hinaus gibt es viele dreifach-verbrückte Diamine, wobei allerdings in/out-Isomere vorzugsweise durch pyramidale Inversion am Stickstoff ineinander umgewandelt werden, was der viel niedrigeren Energiebarriere geschuldet ist.…”

Dibridgehead Diphosphines that Turn Themselves Inside Out

“…The former could operate in the case of 1,3,5-cyclophanes with sufficient bridge lengths. [20] Type VIII structures have four bridges, with isomerization involving pulling two of them through the macrocycle defined by the remaining two. Many dibridgehead diamines exist, but in/out isomers preferentially interconvert through pyramidal inversion at the nitrogen atom, because of the much lower energy barriers.…”

Fluorine in a C−F Bond as the Key to Cage Formation

“…[1] Our particular stratagem is to place fluorine,a sp art of aCÀFbond, within an "open door" cage precursor whereby it is pointed directly at, and could interact at close range with, ap rominent organic functional group.T he resulting interaction would thus effectively shut the "door" to the cage. One possibility is to capture it within acage,orelse to make it part of the structure of the cage itself.I nf act, the cages of particular interest to us are not of the "encapsulating" form, in which the cage totally surrounds an entrapped entity.…”