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The NHC-stabilised diboryne (B\(_2\)(SIDep)\(_2\); SIDep=1,3-bis(2,6-diethylphenyl)imidazolin-2-ylidene) undergoes a high-yielding P−P bond activation with tetraethyldiphosphine at room temperature to form a B\(_2\)P\(_2\) heterocycle via a diphosphoryldiborene by 1,2-diphosphination. The heterocycle can be oxidised to a radical cation and a dication, respectively, depending on the oxidant used and its counterion. Starting from the planar, neutral 1,3-bis(alkylidene)-1,3-diborata-2,4-diphosphoniocyclobutane, each oxidation step leads to decreased B−B distances and loss of planarity by cationisation. X-ray analyses in conjunction with DFT and CASSCF/NEVPT2 calculations reveal closed-shell singlet, butterfly-shaped structures for the NHC-stabilised dicationic B\(_2\)P\(_2\) rings, with their diradicaloid, planar-ring isomers lying close in energy.
The reductive coupling of an N-heterocyclic carbene (NHC) stabilized (dibromo)vinylborane yields a 1,2-divinyl- diborene, which, although isoelectronic to a 1,3,5-triene, displays no extended p conjugation because of twisting of the C\(_2\)B\(_2\)C\(_2\) chain. While this divinyldiborene coordinates to copper(I) and platinum(0) in an η\(^2\)-B\(_2\) and η\(^4\)-C\(_2\)B\(_2\) fashion, respectively, it undergoes a complex rearrangement to an η\(^4\)-1,3-diborete upon complexation with nickel(0).