PHOSPHORADAMANTANES ET ANALOGUES TRICYCLIQUES PHOSPHORES

Rigid PN cages as 3-dimensional building blocks for crystalline or amorphous networked materials

Three-dimensional covalent connectors are valuable synthons for accessing crystalline or amorphous networks. Currently, fused polycyclic alkanes are employed as connectors in this context. We debut phosphorus-nitrogen (PN) cages as new 3-dimensional (3-D) inorganic connectors that yield crystalline and amorphous networks, including examples with gas porosity. We show that the high tunability of PN cages accelerates network diversification and the presence of a responsive 31P NMR spectroscopic handle provides structural insight. Collectively, this work unlocks a new and convenient 3-D synthon for reticular chemistry.

N-Bridged Acyclic Trimeric Poly-Cyclodiphosphazanes: Highly Tuneable Cyclodiphosphazane Building Blocks

We have synthesized a completely new family of acyclic trimeric cyclodiphosphazane compounds comprising NH, Nⁱ Pr, N^t Bu and NPh bridging groups. In addition, the first NH-bridged acyclic dimeric cyclophosphazane has been produced. The trimeric species display highly tuneable characteristics so that the distance between the terminal N(H)R moieties can be readily modulated by the steric bulk present in the bridging groups (ranging from ≈6 to ≈10 Å). Moreover, these species exhibit pronounced topological changes when a weak non-bonding NH⋅⋅⋅π aryl interaction is introduced. Finally, the NH-bridged chloride binding affinities have been calculated and benchmarked along with the existing experimental data available for monomeric cyclodiphosphazanes. Our results underscore these species as promising hydrogen bond donors for supramolecular host-guest applications.

The First Synthesis of the Sterically Encumbered Adamantoid Phosphazane P4 (N(t) Bu)6 : Enabled by Mechanochemistry

All reported attempts to synthesize the tert-butyl-substituted adamantoid phosph(III)azane P4 (N(t) Bu)6 have failed, leading to the classification of this molecule as inaccessible and a literature example of steric control in chemistry of phosphorus-nitrogen compounds. We now demonstrate that this structure is readily accessible by a solvent-free mechanochemical milling approach, highlighting the importance of mechanochemical reaction environments in evaluating chemical reactivity.

Suggestion of a "twist" mechanism in the oligomerisation of a dimeric phospha(III)zane: insights into the selection of adamantoid and macrocyclic alternatives

The reaction of the dimeric phospha(III)zane [ClP(mu-Npy)]2 (1) (py = 2-pyridyl) with pyNHLi (2:1 equivalents, respectively) in THF/Et3N leads to rapid formation of the bicyclic nona-phospha(III)zane [[ClP(Npy)2]2-[P2(Npy)]] (2). This novel rearrangement can be rationalised by a mechanism involving "twisting (or swivelling)" of the central P(mu-Npy)P fragment of the presumed intermediate [[ClP(mu-Npy)2P]2(mu-Npy)] (3), a process that provides a fundamental mechanistic relationship between the majority of previously reported imidophosphospha(III)zanes. This process is fundamentally reliant on relief from ring strain on going from the four-membered ring units of 3 to the six-membered units of 2. The rearrangement observed for 1 is suppressed on steric grounds by Me-substitution of the pyridine ring at the 6-position, the dimeric phosphazane [ClP(mu-N-6-Me-py)]2 (4) (6-Me-py = 6-methyl-2-pyridyl) being formed almost exclusively in the 1:1 reaction of PCl3 with 6-Me-pyNHLi. The syntheses and X-ray structures of 1, 2 and 4 are reported, together with 31P NMR spectroscopic and DFT calculational studies of the conversion of models of 1 into 2. The combined studies pinpoint relief from ring strain as the key factor dictating the rearrangement.