Dynamics of intramolecular carbenic rearrangements

Abstract

Abstract

Dynamic supramolecular polymers built from cucurbit[n]urils and viologens

“…Basics of viologen insertion in cucurbiturils 1,1-Di(hydrocarbyl)-4,4 ′ -bipyridinium salts, best known as viologens (V 2+ ), 8 exhibit unique redox and chemical behaviors which have proved highly valuable to the construction of functional molecular materials, 9 including for applications in organic electronics, organic batteries and for the development of molecular machines. Viologen derivatives are for instance commonly used as electron-poor components in donor-acceptor type host-guest complexes, as seen in the work of Stoddart's group on 'blue-box'-based rotaxanes and catenanes.…”

“…From a thermodynamic point of view, the exceptionally high affinity of CB[n]s for positively charged organic guests in water is attributed to a combination of factors including the desolvation of the guest, the ejection of 'high energy' water molecules trapped inside CB[n]s prior to encapsulation, and ion-dipole interactions between the carbonyl functions at the cavity portal and any positively charged parts of the guest. In most cases only one guest can be fitted within the cavity of the smallest CB[n] (n = 5, 6, 7) while the larger cavity of CB [8] can potentially accommodate two or even three guests. [30][31][32][33][34][35] Most efforts in the field of supramolecular chemistry have focused on CB [8], on account of its ability to accommodate two -conjugated guests tightly interacting inside the barrel-shaped cavity in the form of cofacial charge transfer complexes.…”

“…In most cases only one guest can be fitted within the cavity of the smallest CB[n] (n = 5, 6, 7) while the larger cavity of CB [8] can potentially accommodate two or even three guests. [30][31][32][33][34][35] Most efforts in the field of supramolecular chemistry have focused on CB [8], on account of its ability to accommodate two -conjugated guests tightly interacting inside the barrel-shaped cavity in the form of cofacial charge transfer complexes. 36 The opportunities are more limited for the smallest analogs CB [5], CB [6] and CB [7], whose inner cavities only allow hosting single guests.…”

“…The size, structure and symmetry of viologen derivatives, together with their dicationic nature, make them perfect guests for CB [7] or CB [8], forming very stable caviplexes ( Fig. 1(a)) with binding constants as high as 5 × 10 4 mol −1 L with CB[7] and 1.1 × 10 5 mol −1 L with CB [8] in water at 25 ∘ C. 38,39 The major driving force for the formation of such caviplexes seems to be strong ion-dipole interactions between the cavitand oculi and the positive charges of the guest. CB [8] can even accommodate two viologen cation radicals to yield the dicationic 1:2 caviplex depicted in Fig.…”

Constrained Carbenes

“…[17,113d,160-162] In fact, the C-H insertion product 70 was observed even at T = 11 K and was likely formed by QM tunneling. [161,163] Scheme 18. (tert-Butyl)chlorocarbene (67) mostly undergoes 1,3-CH insertion.…”