Cyclic Three-, Four-, Five-, and Six-Coordinate Nitrogen-Containing Phosphorus Compounds Varying in Ring Size from Five- to Ten-Membered. P-N Donor Action(1).

Abstract

New nitrogen-containing phosphorus compounds 1 and 3-5 were prepared by the reaction of a nitrogen-containing phenol with PhPCl(2). Hydrolysis of 1 gave an acyclic anionic phosphinate hydrogen bonded to an ammonium component (2). Use of a nitrogen-containing diol with P(OPh)(3) resulted in oxidative addition to give hexacoordinate pentaoxyphosphorus compound 6 exhibiting P-N donor action. X-ray analyses performed on all six phosphorus compounds revealed a variety of geometries extending from three- to six-coordinate with ring sizes varying from five- to ten-membered. The structure of 3 is displaced toward a trigonal bipyramid (TBP) as a result of weak P-N donor action. As a consequence of N-C bond cleavage, 1 forms as a bicyclic phosphorane with the nitrogen atom located at an equatorial site of a TBP. In the formation of the tetracoordinate cyclic phosphinate 5, a P-C bond is formed at the expense of O-C bond cleavage of the reactant diol. (1)H and (31)P NMR spectra indicated that the basic coordination structures were retained in solution. It is concluded that the more elusive donor action found for nitrogen relative to sulfur and oxygen is a consequence of bond cleavage reactions. However, with sufficient phosphorus electrophilicity in higher valent states, P-N donor action is achievable as found in the pentaoxyphosphorane (6) in this study while more modest donor action takes place in the lower coordinate state present in 3.