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Probing the Association of Frustrated Phosphine–Borane Lewis Pairs in Solution by NMR Spectroscopy

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journal contribution
posted on 08.01.2014, 00:00 by Luca Rocchigiani, Gianluca Ciancaleoni, Cristiano Zuccaccia, Alceo Macchioni
19F,1H HOESY, diffusion, and temperature-dependent 19F and 1H NMR studies allowed us to unequivocally probe the association between the frustrated PR3/B­(C6F5)3 (1, R = CMe3; 2, R = 2,4,6-Me3C6H2) Lewis pairs in aromatic solvents. No preferential orientation is favored, as deduced by combining 19F,1H HOESY and DFT results, suggesting association via weak dispersion rather than residual acid/base interactions. The association process is slightly endoergonic [K = 0.5 M–1, ΔG0(298 K) = +0.4 kcal/mol for 2], as derived from diffusion NMR measurements.