Metathesis chemistry of inorganic cumulenes driven by B–O bond formation

The reaction chemistry of an unprecedented 'inorganic cumulene' - featuring a five-atom BNBNB chain - towards C[double bond, length as m-dash]O (and related) multiple bonds is disclosed. In marked contrast to related all-carbon systems, the intrinsic polarity of the BNBNB chain (featuring electron-rich nitrogen and electron-deficient boron centres) enables metathesis chemistry with electrophilic heteroallenes such as CO₂ and with organic carbonyl compounds. Transfer of the borylimide unit to [CO], [CS], [PP{(NDippCH₂)₂}] and [C(H)Ph] moieties generates (boryl)N[double bond, length as m-dash]C[double bond, length as m-dash]X systems (X = O, S, PP{(NDippCH₂)₂}, C(H)Ph), driven thermodynamically by B-O bond formation. Pairwise exchange of O and {(HCDippN)₂}BN fragments occurs <i>via</i> consecutive [2+2] cyclo-addition/cyclo-reversion steps. An isolable complex of stoichiometry K[(boryl)NB(O)OC(H)Ph], formed <i>via</i> [2+2] cycloaddition to [(boryl)N[double bond, length as m-dash]B[double bond, length as m-dash]O]^- can be shown to be an intermediate in the formation of (boryl)N[double bond, length as m-dash]C(H)Ph, and provides corroborating evidence for a DFT-calculated mechanism proceeding <i>via</i> a 'bora-Wittig' mechanism.