A Systematic Survey of the Reactivity of Chlorinated N2P2, NP3 and P4 Ring Systems

Abstract The reactivity of the four‐membered NP3 ring system [RN(μ‐PCl)2PR] (R=Mes*=2,4,6‐tri‐tert‐butylphenyl) towards Lewis acids, Lewis bases, and reducing agents was investigated. Comparisons with the literature‐known, analogous cyclic compounds [ClP(μ‐NR)]2 (R=Ter=2,6‐dimesitylphenyl) and [ClP(μ‐PR)]2 (R=Mes*) are drawn, to obtain a better systematic understanding of the reactivity of cyclic NP species. Apart from experimental results, DFT computations are discussed to further the insight into bonding and electronic structure of these compounds.


Mes*NPCl + DMAP
To understand the origin of the signal at 109.7 ppm in the 31 P NMR spectrum in Figure S5, Mes*NPCl (which is formally obtained by cycloreversion of the NP3 ring system 2) was treated with DMAP:  According to the analytical data, a weak 1:1 adduct between Mes*NPCl and DMAP is formed. The 31 P NMR signal is somewhat broadened, indicating dynamic exchange.
However, the resonance does not correspond exactly to the signal observed in Figure   S5. While this might be attributed to concentration effects, it hampers an unequivocal assignment of the signal in question.
Some of the red crystals were re-dissolved to obtain a 31 P NMR spectrum. Due to the small amounts and instability of the compound, we were unable to record a spectrum S33 of a pure sample. The 31 P NMR signals were assigned on the basis of calculated data and spectrum simulation.  Table 2 in the manuscript.

S34
To obtain a better insight into the reaction sequence, in situ 31 P NMR spectra were recorded after mixing the two reactants.

NMR data of [Mes*2NP3Cl][GaCl4] (6)
When investigating the theoretical structure of the azatriphosphenium cation of 6, it became clear that there are two possible minimum structures with similar energy.
Both structures differ in the arrangement of one Mes* substituent (rotation about a P-C single bond). Thus, it can be expected that the system is highly dynamic in solution and a fast exchange between both isomers is observed in the NMR spectrum. Consequently, the predicted 31 P NMR shifts were calculated as a weighted average of both isomers using a Boltzmann distribution at 203 K (Table S8).

Isomers of P5H3
In total, eight different structures of P5H3 were considered ( Figure S16). For more details on electronic energies, see Table S9.