A Robust, Divalent, Phosphaza-bicyclo[2.2.2]octane Connector Provides Access to Cage-Dense Inorganic Polymers and Networks

While
polymers containing chain or ring motifs in their backbone
are ubiquitous, those containing well-defined molecular cages are
very rare and essentially unknown for the inorganic elements. We report
that a rigid and dinucleophilic cage (PNSiMe3)2(NMe)6, which is chemically robust and accessible on a
multi-gram scale from commercial precursors, serves as a linear and
divalent connector that forms cage-dense inorganic materials. Reaction
of the cage with various ditopic P­(III) dihalide comonomers proceeded
via Me3SiCl elimination to give high molecular weight (30 000–70 000
g mol–1), solution-processable polymers that form
free-standing films. The end groups of the polymers could be tuned
to engender orthogonal reactivity and form block copolymers. Networked
cage-dense materials could be accessed by using PCl3 as
a tritopic P­(III) linker. Detailed mechanistic studies implicate a
stepwise polycondensation that proceeds via phosphino–phosphonium
ion intermediates, prior to Me3SiCl loss. Thus, metathesis
between the dinucleophilic cage and polyhalides represents a general
strategy to making cage-dense polymers, setting the stage for systematically
understanding the consequences of the three-dimensional microstructure
on macroscopic material properties.