Density functional theory (DFT) calculations were carried out to investigate the stability and aromaticity of metallapentalocyclobutadienes. The results reveal unexpected higher stabilisation achieved with a 3d ruthenium fragment compared to the 4d osmium counterpart. Moreover, direct 1–3 metal–carbon bonding in the metallabutadiene unit of these two complexes is negligible.
Antiaromatic species are substantially less thermodynamically stable than aromatic moieties. Herein, we report the stabilization of two classical antiaromatic frameworks, cyclobutadiene and pentalene, by introducing one metal fragment through the first [2+2] cycloaddition reaction of a late-transition-metal carbyne with alkynes. Experimental observations and theoretical calculations reveal that the metal fragment decreases the antiaromaticity in cyclobutadiene and pentalene simultaneously, leading to air- and moisture-stable products.
Anti-aromatic compounds, as well as small cyclic alkynes or carbynes, are particularly challenging synthetic goals. The combination of their destabilizing features hinders attempts to prepare molecules such as pentalyne, an 8π-electron anti-aromatic bicycle with extremely high ring strain. Here we describe the facile synthesis of osmapentalyne derivatives that are thermally viable, despite containing the smallest angles observed so far at a carbyne carbon.