Synthesis of Homo-Metallic Heavier Analogues of Cyclobutene and the Cyclobutadiene Dianion.

The reduction of the boryl-substituted Sn bromide {(HCDippN) B}Sn(IPrMe)Br with 1.5 equivalents of potassium graphite leads to the generation of the cyclic tetratin tetraboryl system K [Sn {B(NDippCH) } ], a homo-metallic heavier analogue of the cyclobutadiene dianion. This system is non-aromatic as determined by Nucleus Independent Chemical Shift Calculations (NICS(0)=-0.28, NICS(1)=-3.17), with the primary contributing resonance structures shown by Natural Resonance Theory (NRT) to involve a Sn=Sn double bond and 1,2-localized negative charges. Abstraction of the K cations or oxidation leads to contraction or cleavage of the Sn unit, respectively, while protonation generates the neutral dihydride 1,2-Sn {B(NDippCH) } H (a heavier homologue of cyclobutene) in a manner consistent with the predicted charge distribution in the [Sn {B(NDippCH) } ] dianion.