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

► Cyclic alkylaminosilylenes have rather large ΔES-T, ΔEHOMO-LUMO, and υmin > 100 cm−1. ► Significant energy barriers prevent these sextet silylene from rearrangement to their corresponding full valence octet isomers. ► They show rather high heats of hydrogenation through isodesmic reactions. ► They do not dimerize because of high energy barriers. ► Their nucleophilicity and electrophilicity are similar to stable silylenes reported.