Syntheses, Geometric and Electronic Structures of Inorganic Cumulenes
Jianqin Tang, Chenyang Hu, Agamemnon E. Crumpton, Maximilian Dietz, Debotra Sarkar, Liam P. Griffin, José M. Goicoechea, Simon Aldridge
Abstract
High Resolution Image Download MS PowerPoint Slide Molecular chains of two-coordinate carbon atoms (cumulenes) have long been targeted, due to interest in the electronic structure and applications of extended π-systems, and their relationship to the carbon allotrope, carbyne. While formal (isoelectronic) B═N for C═C substitution has been employed in two-dimensional (2-D) materials, unsaturated one-dimensional all-inorganic “molecular wires” are unknown. Here, we report high-yielding synthetic approaches to heterocumulenes containing a five-atom BNBNB chain, the geometric structure of which can be modified by choice of end group. The diamido-capped system is bent at the 2-/4-positions, and natural resonance theory calculations reveal significant contributions from B═N(:)–B≡N–B resonance forms featuring a lone pair at N (consistent with observed N-centered nucleophilicity). Molecular modification to generate a linear system best described by a B═N═B═N═B resonance structure involves chemical transformation of the capping groups (using B(C 5 F 5 ) 3 ) to enhance their π-acidity and conjugate the N-lone pairs.