Synthesis of P-bridged, planar bis(NHC) BCl₃ adducts

Planar P^V- or P^III-bridged bis(NHCs), which have only been employed in transition metal complex chemistry so far, were subjected to BCl₃-containing solutions targeting the corresponding bis(NHC) BCl₃ adducts. While the P(O)NEt₂-bridged bis(NHC) showed the expected adduct formation, the PNEt₂-bridged bis(NHC) reacted not only at the carbene moiety but also at the P-NEt₂ functional group. The latter enabled access to the first 1,4-diphosphinine bis(NHC) main group adduct; its formation and properties were investigated by DFT calculations. Through the same route, a 1,4-diphosphinine bis(imidazolium) scaffold was generated and explored theoretically and experimentally. The new 1,4-diphosphinines are shown to possess high global aromaticity and a unique P-centred reactivity, allowing the formation of hitherto inaccessible [4 + 2]-cycloaddition products, thus suggesting potential new applications compared to previously known 1,4-diphosphinine derivatives.