Structure determination of a bis[4-(di-n-butylamino)phenyl](pyridin-3-yl)borane tetramer highlighting a unique geometric conformation of the core 16-membered ring

Abstract

The tetramer of bis(4-di-n-butylaminophenyl)(pyridin-3-yl)borane [systematic name: 2λ4,4λ4,6λ4,8λ4-tetrabora-1,3,5,7(1,3)-tetrapyridinacyclooctaphane-11,31,51,71-tetrakis(ylium)], C132H192B4N12, was synthesized unexpectedly and crystallized. Its structure contains an unusual 16-membered ring core made up of four (pyridin-3-yl)borane groups. The ring adopts a conformation with pseudo-S 4 symmetry that is very different from the two other reported examples of this ring system. Density functional theory (DFT) computations indicate that the stability of the three reported ring conformations is dependent on the substituents on the B atoms, and that the pseudo-S 4 geometry observed in the bis(4-dibutylaminophenyl)(pyridin-3-yl)borane tetramer becomes significantly more stable when phenyl or 2,6-dimethylphenyl groups are attached to the boron centers.

Electrostatically Enhanced 3- and 4-Pyridyl Borate Salt Nucleophiles and Bases

“…A benchtop stable crystalline solid corresponding to a cyclic tetramer, however, was isolated in low yield from potassium 3pyridyltrifluoroborate (eq 1). 30 Conversions of the potassium salts of 1F − , 1t-Bu − , 2F − , 2t-Bu − , 2OMe − , and 2OMe2 − to their tetrabutylammonium (Bu 4 N + ) and tetraarylphosphonium (Ar 4 P + ) derivatives 31 were accomplished via ion metathesis. For the latter species, the solubilities of KCl and KBr in water but not CH 2 Cl 2 were exploited using biphasic conditions to afford the products in near-quantitative yields.…”