Toward unsaturated stannylenes Y₂ZSn: And related compounds with triplet electronic ground states

A new series of unsaturated stannylenes is studied computationally. The singlet and triplet states of acyclic and cyclic stannylenes are fully optimized using the B3LYP, BHLYP, OPBE, and M06 functionals. The basis sets used are of double-ξ plus polarization quality with additional s- and p-type diffuse functions denoted DZP++. All cyclic and most acyclic stannylenes have been found to have triplet ground states. The most favored triplet state is that for the NHC (NMeCHCHNMe)SnSn: system, where the triplet state lies ∼20 kcal mol^-1 below the singlet. The saturated cyclic systems are expected to be easier to synthesize, but the unsaturated cyclic counterparts have larger singlet-triplet splittings. A preparative outline based on retro-synthetic routes is briefly described.