From Organometallics to Supercharged Supramolecular Systems

In 1995, the diffusion coefficients of a series of polycyclics and their respective dianions as well as corannulene (64) and its tetraanion (64 ) were measured in [DgjTHF solutions [58a]. Upon the formation of the charged species, a large decrease in the diffusion coefficients was observed and, partially, assigned to the increased solvation ofthe charged systems in the [DgjTHF solutions. However, some of the systems showed too large a decrease of their diffusion coefficients upon 

However, one of the most intriguing examples in this field, which also demonstrates the power of diffusion NMR to characterize supramolecular systems obtained by self aggregation, is the assignment of the different species that prevail in solution following the reduction of 2,5,8,ll-tetra-tert-butylcycloocta[l,2,3,4-def-,5,6,7,8]bis-biphenylene (65) to its respective tetraanions [59]. In this sample, different species were observed and only diffusion NMR provided a proof, in conjunction with 2-D NOESY, that the different molecular species are indeed different helically-stacked anionic aggregates of 65. When NMR diffusion measurements were performed on the obtained solution, four different diffusion coefficients were found for the mixture. These coefficients that were assigned to the monomer, dimer, trimer and tetramer of 65 (Fig. 6.24). Based on Eq. (6.16)  

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