Conformational equilibrium of N,N-disubstituted 5-phenyl-1,3,5-diazaphosphorinanes and their derivatives

Conformational analysis of 1,3,6,2-dioxazaphosphocanes and 1,3,6,2-dioxazasilocanes

“…At the same time, rare cases when the single conformation of the heteroring is different, for example, distorted boat!boat in the case of di-p-tolyl derivatives of 1,5,3,7-diazadiphosphocane, are not excluded [14]. As previously noted, replacement of p-tolyl by benzyl groups on phosphorus restores the crown conformation [15].…”

“…The crown conformation was found for the cis isomers of 2,6-dimethyl-1,3,2,6-dioxadiphosphocanes with P=S and P=Se groups, whereas the preferred conformation of the trans isomers is boat!chair (X-ray analysis and NMR spectroscopy [9,10]). The eight-membered heteroring with four phosphorus and four sulfur atoms (RPS) 4 , too, has the crown conformation [11]. The NMR spectra of 1,3,6,2-dioxazasilocanes were almost simultaneously studied by Kupce et al [12] and Hegyes et al [13], who concluded that the eight-membered ring in these compounds has the boat!chair and/or chair!…”

“…Prerequisite for such interactions is that the heteroring conformation allows proximity of the heteroatoms to each other. Fairly scarce data are available in the literature, concerning the structure of 1,3,2-dioxaphosphocanes [133] or diphosphocanes with P3C bonds [4,5]. Hence, an almost ideal crown was found in 1,3,5,7-tetraphenyl-1,5,3,7-diazadiphosphocane with two trivalent phosphorus atoms on the opposite ends of the eightmembered ring [4].…”

“…Fairly scarce data are available in the literature, concerning the structure of 1,3,2-dioxaphosphocanes [133] or diphosphocanes with P3C bonds [4,5]. Hence, an almost ideal crown was found in 1,3,5,7-tetraphenyl-1,5,3,7-diazadiphosphocane with two trivalent phosphorus atoms on the opposite ends of the eightmembered ring [4]. This molecule preserves the same conformation in benzene solutions [5], unlike the corresponding derivative of four-coordinate phosphorus [5] that has the distorted boat!boat conformation in crystal (according to X-ray data) and prefers the crown conformation in solution.…”

“…chair (crown) conformation [12], or a conformation intermediate between crown and boat!boat [13]. Introduction of one more nitrogen atom in the eightmembered ring as in 1,5-di-p-tolyl-3,7-diphenyl-1,5,3l 5 ,7l 5 -diazadiphosphocane 3,7-disulfide makes the cycle to assume the distorted boat!boat conformation [14], but substitution of benzyl for p-tolyl substituents on phosporus atoms restores the crown conformation of the eight-membered heteroring. This conclusion was made on the basis of the X-ray structural analysis of these compounds [14,15].…”