Structural evidence for the arc-shaped topology of hetero[5]polynorbornanes

Molecular tweezers with a rotationally restricted linker and freely rotating porphyrin moieties

“…The favourable properties of fused [n]polynorbornyl scaffolds in molecular receptors, particularly with respect to host preorganisation, are reported in the literature by a number of research groups including those of Warrener and Butler, 7,[31][32][33][34][35][36][37][38][39] Paddon-Row, [40][41][42][43] Johnston, 19,[44][45][46] Pfeffer, [47][48][49][50][51][52][53] Clever, 47,50,54 and Margetić. [55][56][57][58] Importantly, tweezers 1 and 2 share a freely rotating phenyl diimide core inserted within the otherwise rigid polycyclic linker, a feature which allows unhindered adjustment of the interporphyrin distance, to potentially allow the binding of guests of different lengths. However, because all conformations are readily accessible, the possibility of 1 assuming an anti-conformation arises, thereby decreasing the proportion of the syn-conformation and the formation of syn-1 bis-porphyrin:guest complexes.…”

To Cooperate or Not: The Role of Central Functionality in Bisthiourea [6]polynorbornane Hosts

“…Bridged bisnorbornene units are excellent substrates for twin Alkene + Cyclobutene Epoxide (ACE) 1,3‐dipolar cycloaddition reactions and by heating 4a , 4b or 4c with two equivalents of the known cyclobutane epoxide 6 the corresponding diboc‐protected [6]polynorbornane frameworks 7a – 7c were accessed in good yield (65, 76 and 71 % respectively). A one‐pot procedure involving deprotection then reaction of the resulting amines with 4‐fluorophenylisothiocyanate gave the bisthiourea hosts 8a – 8c in good yield (77, 74 and 73 % respectively).…”

“…Fused [ n ]polynorbornane scaffolds are highly preorganised molecular frameworks and as such have been incorporated as rigid components in a variety of larger molecular architectures . The synthetic methodology allows the user to design and construct the requisite scaffold in the intended three‐dimensional shape.…”

Tetra-porphyrin molecular tweezers: two binding sites linked via a polycyclic scaffold and rotating phenyl diimide core

“…11), which appear at different chemical shifts due to the influence of the 7-oxanorbornane in these linear systems. 25,26,30 There is some evidence of facial differentiation within the porphyrin macrocycles in the 1 H NMR spectrum of the freebase tetra-porphyrin tweezer 2 (see S24 †). While the β-pyrrole resonance appears as a singlet, there is slight splitting/desymmetrisation within some of the meso-phenyl resonances, and the linking meso-phenyl resonances are somewhat broad (see S24 †).…”

“…More recent examples include those by the groups of Johnston, 21,22 Pfeffer, 23,24 and Margetić. [25][26][27] Molecular modelling by Warrener 28,29 and Johnston, 30 and experimental evidence by Margetić 26 has shown that the inclusion of certain modules provides either linearity or curvature to the polycyclic scaffold. Importantly, a number of studies by several research groups has identified that polycyclic backbones are characterised by a higher degree of rigidity when only consisting of fused bridged polycyclic rings, with non-bridged cyclohexane(ene) rings and fused aromatic rings increasing flexibility.…”