(PNSiMe₃)₄(NMe)₆: A Robust Tetravalent Phosphaza‐adamantane Scaffold for Molecular and Macromolecular Construction**

Abstract

Tetraarylmethanes and adamantanes are important rigid covalent connectors that play a four‐way scaffolding role in molecular and materials chemistry. We report the synthesis of a new tetravalent phosphaza‐adamantane cage, (PNSiMe3)4(NMe)6 (2), that shows high thermal, air, and redox stability due to its geometry. It nevertheless participates in covalent four‐fold functionalization reactions along its periphery. The combination of a robust core and reactive corona makes 2 a convenient inorganic scaffold upon which tetrahedral molecular and macromolecular chemistry can be constructed. This potential is demonstrated by the synthesis of a tetrakis(bis(phosphine)iminium) ion (in compound 3) and the first all P/N poly(phosphazene) network (5).

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

“…The robustness of 3 may be due to the rigid nature of the cage, which makes any degradation reactions involving structural rearrangements more challenging. 31 Reactivity of 3 as a Linear Divalent Scaffold. The facile and scalable synthesis of 3 coupled with its robustness suggests that this compound could be a practical scaffolding molecule if covalent metathesis chemistry involving the Si−N bonds is realized.…”

“…Finally, 3 is also air-stable – solutions exposed to ambient air (50–70% atmospheric humidity) show less than 5% decomposition over the course of 7 days. The robustness of 3 may be due to the rigid nature of the cage, which makes any degradation reactions involving structural rearrangements more challenging …”

“…We attribute these differing degrees of air stability to the relative basicity of the P(III) linker environments in each case: electron-rich alkylphosphines are better bases than aryl phosphines, resulting in faster degradation of Poly Hex films when exposed to air and moisture. 31 P NMR spectra of Poly Hex taken after exposure to ambient air show 1 J P-H coupling consistent with protonation at the linker environment (Figure S168). A preliminary examination of the thermal characteristics of the polymers was carried out by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).…”

“…Variable temperature NMR spectroscopy showed no change in the signal broadness upon cooling to 238 K in CD 3 CN (Figure S163). Solid-state 31 P Magic Angle Spinning (MAS) NMR revealed a spectrum that aligned closely with the solution state 31 P NMR spectrum (Figure S164), suggesting that the broad signals observed in solution are not due to fluxional behavior, but rather due to the presence of polymeric material.…”

“…Recently we showed that polyvalent phosphorus-nitrogen cages can serve as rigid inorganic connectors from which functional groups can be extended at well-defined angles. Specifically, an all-PN analogue of adamantanes was reported as a new tetrahedral and tetranucleophilic connector for covalent chemistry (Figure d, I ) . The added value of such inorganic cages comes from the presence of a convenient 31 P NMR spectroscopy handle, complementary sizing to existing hydrocarbon cages, the presence of several lone pairs for coordination or redox chemistry, and their exceptional stability in some cases.…”