Effects of α-mono heteroatoms (N vs. P), and β-conjugation on cyclic silylenes

Following the quest for stable silylenes, we have found high thermodynamic and kinetic viabilities for a series of novel cyclic alkylaminosilylenes [CAASs: including 1 N – 4 N )] over their corresponding cyclic alkylphosphinosilylenes (CAPSs: 1 P – 4 P , respectively), at ab initio and DFT levels, coupled with appropriate isodesmic reactions. Among silylenes scrutinized, 4 N immerged the most promising for its higher singlet–triplet energy difference (Δ E S–T ), wider band gap (Δ E HOMO–LUMO ), higher heat of hydrogenation (Δ E H ), significant resistance to dimerization and resistance to rearrangement to its full valence octet isomer, etc. Unsaturation destabilized 2 N , 3 N , and 3 P through cross conjugation.