Chalcogenophosphinites with a Cyclic Oligosilane Backbone

Abstract

A structurally authenticated series of chalcogenophosphinites, R2P(ChPh) (Ch = S, Se, Te), supported by a compact tetrasilaphosphacyclopentane backbone, is presented. The parent secondary phosphane is obtained in two scalable steps from a dichlorohexasilane via substitution with 2.0 eq. NaPH2 and intramolecular ring-closure driven by PH3 elimination. Selective deprotonation furnishes lithium and potassium phosphides that serve as versatile entry points to functionalization. Reaction of the parent phosphane with PhChChPh (Ch = S, Se) yields the thio- and selenophosphinites, whereas employing the potassium phosphide delivers the full S/Se/Te series in higher yields and provides access to the tellurium derivative that is not accessible from the secondary phosphane. Across the series, 31P NMR shifts move markedly upfield in a nonlinear fashion (S → Se → Te), and UV/vis spectra exhibit progressive bathochromism; both trends are reproduced by DFT/TD-DFT and traced to HOMO–LUMO gap narrowing together with increasing polarizability and heavy-atom effects down the group. Single-crystal X-ray data reveal systematic lengthening of P-Ch bonds and widening of Si–P–Ch angles. Together, these results provide a sterically constant platform that enables direct S/Se/Te comparison and illuminates periodic trends in neutral chalcogenophosphinites stabilized by an oligosilane backbone.