title: Constrained-geometry bisphosphazides derived from 1,8-diazidonaphthalene: synthesis, spectroscopic characteristics, structural features, and theoretical investigations.
abstract: Investigations on the Staudinger reaction between 1,8-diazidonaphthalene and phosphorous(III) building blocks, a key step in the synthesis of superbasic bisphosphazene proton sponges, yielded a set of bisphosphazides with a constrained geometry 1,8-disubstituted naphthalene backbone. This compound class has attracted our interest not only due to their surprisingly high stability, but in particular because of their theoretically predicted basicity in the range of their bisphosphazene analogues that can be referred to the constrained geometry interaction of two highly basic nitrogen atoms. Eleven new bisphosphazides bearing simple P-amino groups as well as P-guanidino substituents, azaphosphatrane moieties, P2 building blocks, or chiral P-amino substituents derived from L-proline are presented. They were studied concerning their spectroscopic properties and partly also their chromophoric and structural features. In the case of the pyrrolidino-substituted TPPN(2N2) (TPPN = 1,8-bis(trispyrrolidinophosphazenyl)naphthalene), the stepwise nitrogen elimination is investigated theoretically and experimentally, which led to the isolation and structural characterization of TPPN(1N2) bearing a phosphazide and a phosphazene functionality in one molecule. Attempts to protonate the obtained bisphosphazides and to prove the computationally predicted pKBH(+) values through NMR titration reactions resulted in their decay, which again was rationalized by theoretical calculations. Altogether we present the so far most extensive spectroscopic, structural and theoretical investigation of constrained geometry bisphosphazides and their Brønsted and Lewis basic properties.
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35032 Marburg (Germany), Fax: (+49) 642128-25711.
authors.forename: Julius F
authors.initials: JF
authors.lastname: Kögel
authors.forename: Nuri C
authors.initials: NC
authors.lastname: Abacılar
authors.forename: Felicia
authors.initials: F
authors.lastname: Weber
authors.forename: Benjamin
authors.initials: B
authors.lastname: Oelkers
authors.forename: Klaus
authors.initials: K
authors.lastname: Harms
authors.forename: Borislav
authors.initials: B
authors.lastname: Kovačević
authors.forename: Jörg
authors.initials: J
authors.lastname: Sundermeyer
keywords: ab initio calculations; basicity; ligands; phosphazenes; reaction mechanisms