Neutral Three Membered 2 Aromatic Beryllacycle having hole

The electronic structure, bonding, and reactivity of three-membered cyclic beryllium compounds BeR (R=C2H2 (1), C-2(CH3)(2) (2)) were studied at the M06/def2-TZVPP//BP86/def2-TZVPP level of theory. The molecular orbital analysis shows that BeR is a 2 pi electron aromatic system with a sigma-hole on the beryllium atom. EDA-NOCV analysis has been carried out with Be and R in their different electronic state as fragments at the BP86/TZ2P level of theory. The results reveal the preference for three bonding situations, (a) charge-separated interaction where anionic acetylenic fragment R- forms one electron sharing and one donor-acceptor sigma-interaction and one donor-acceptor pi interaction with Be+ having 2s(0)2p(x)(0)2p(y)(1)2p(z)(0) electronic configuration (A), (b) charge separated interaction where anionic acetylenic fragment R- forms one electron sharing and one donor-acceptor sigma-interaction and one donor-acceptor pi interaction with Be+ having 2s(1)2p(x)(0)2p(y)(0)2p(z)(0) electronic configuration (B), and (c) neutral acetylenic fragment forms two electron sharing sigma bonds and one donor-acceptor pi bond with beryllium having 2s(1)2p(x)(0)2p(y)(1)2p(z)(0) electronic configuration (C). BeR compounds show high proton affinity and hydride affinity. The reactivity was studied in detail with different ligands CO, NHC, cAAC, and PMe3. The reaction energy for the formation of adducts is exothermic and follows the order of cAAC>NHC>PMe3>CO.