Bi- and tricyclic penta- and hexacoordinated phosphoranes with varying ring sizes: synthesis, structures, and reactivity

Abstract

New tricyclic hexacoordinated phosphoranes 1-6 with internal N→P coordination containing ring sizes varying from five to eight membered have been synthesized by oxidative addition of a quinone or a diol to a cyclic phosphite. The bicyclic phosphorane (NC₉H₆O)P(O₂(3,5-t-Bu)₂C₆H₂)((O-2,4-(t-Bu)₂C₆H₂)₂CH₂).½H₂O (7.½H₂O) has been synthesized by adding the 3,5-di-tert-butyl-o-benzoquinone to the cyclic phosphite. The compound (NC₉H₆O)P(2,2'-OC₆H₄C₆H₄O)₂ (6) results from a novel ring exchange reaction of a phosphorinane by a phosphepin in two ways: (a) by treating (OCH₂CMe₂CH₂O)P((OC₉H₆N) with 2,2'-biphenol/N-chlorodiisopropylamine and (b) by treating (Et₂N)P(OCH₂CMe₂CH₂O)(2,2'-OC₆H₄C₆H₄O) with 8-hydroxyquinoline. Treatment of the aminophosphorane (Et₂N)P(OCH₂CMe₂CH₂O)(O₂C₁₄H₈) with 2,4,6-trimethylbenzoic acid led to the unique ester (OCH₂CMe₂CH₂O)P(O){OC₁₄H₈O(C(O)-2,4,6-Me₃C₆H₂)} (10). ³¹P NMR data for the new compounds are discussed with respect to the differing ring sizes and coordination number on phosphorus. X-ray analysis shows hexacoordination in 2, 4, and 6 with an N→P bond and pentacoordination in 7 without an N→P bond. The coordinating nitrogen is trans to an oxygen of the six-membered ring in 2 and of the seven-membered ring in 4. The eight-membered ring in 7 spans a diequatorial position in a trigonal bipyramidal arrangement.