STERICALLY ENCUMBERED FUNCTIONAL-GROUPS - AN INVESTIGATION OF ENDO VERSUS EXO PHOSPHORYL COMPLEXATION USING H-1 AND P-31 NMR

The synthesis of phosphine oxide bifunctional macrocycles 1-4 is reported. Additionally, the X-ray crystal structures for exo-exo diyne 1 and endo-exo hosts 2 and 4 are presented. Assignment of the two phosphorus signals in the 31P NMR spectra of 2 and 4 and the aromatic proton signals in the 1H NMR spectra of 2 and 4 is reported. The complexation behavior of macrocycles 1-4 and precyclophane 8 with a variety of neutral organic guests and Ph2SnCl2 is investigated by using 1H and 31P NMR as investigative instrumental probes. Initial endo complexation is the preferred mechanism in the 1:2 complexation of 2 with guests, while initial exo complexation is preferred for the complexation of 4 with guests. 2 forms 1:2 complexes with pentafluorophenol, 2,6-dimethyl-4-nitrophenol, and acetic acid via initial exo complexation. Association constants determined from these experiments reveal that the exo phosphoryl binding site in 4 is higher than those in the other reported phosphine oxides. An X-ray crystal structure of the 1:1 complex of 4 with diphenyltin dichloride was obtained to explore this anomaly, and it is reported. © 1990, American Chemical Society. All rights reserved.