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 1N–4N)] over their corresponding cyclic alkylphosphinosilylenes (CAPSs: 1P–4P, respectively), at ab initio and DFT levels, coupled with appropriate isodesmic reactions. Among silylenes scrutinized, 4N immerged the most promising for its higher singlet–triplet energy difference (ΔES–T), wider band gap (ΔEHOMO–LUMO), higher heat of hydrogenation (ΔEH), significant resistance to dimerization and resistance to rearrangement to its full valence octet isomer, etc. Unsaturation destabilized 2N, 3N, and 3P through cross conjugation.