Switching of global minima of novel germylenic reactive intermediates via halogens (X): C2GeH2 vs. C2GeHX at ab initio and DFT levels

Halogen switching of azacarbenes C2NH ground states at ab initio and DFT levels

“…These results appear consistent with those of C 3 HX carbenes, C 2 SiHX silylenes, and C 2 GeHX germylenes [1m, 6,7]. The 1 s-X species with a nitrogen atom attached to a divalent carbon and with expected aromatic character is close to the first isolated carbenes, with imidazol-2-ylidene structure, reported by Arduengo and coworker [36].…”

“…This is consistent with the analogues cyclic carbenes, while is in contrast to the analogues cyclic silylenes and/or germylenes [1m, 6,7]. This phenomenon can be rationalized by considering the electronic structures and hybridizations of the atoms attached to the divalent centers [7]. For instance, in the cyclic structures 1 s-X and 1 t-X , as well as the acyclic structures 3 s-X and 3 t-X , the strictly localized NBO of the σ molecular orbitals have significant p character for the divalent centers (C 1 ).…”

“…All divalent angles C 3 C 1 N of the singlet states (1 s-X ) are smaller than those of their corresponding triplet states, 1 t-X . This is consistent with the analogues cyclic carbenes, while is in contrast to the analogues cyclic silylenes and/or germylenes [1m, 6,7]. This phenomenon can be rationalized by considering the electronic structures and hybridizations of the atoms attached to the divalent centers [7].…”

“…Among all the halogenated C 2 NX azacarbenes, the lowest energy minima appear to be singlet 3 s-X , whereas for C 2 NH analogues the lowest energy minimum is triplet 3 t-H . These results are in clear contrast to the C 3 HX, C 2 SiHX, and C 2 GeHX, where singlet cyclic aromatic 1 s-H was more stable than its corresponding triplet 3 t-H [1m, 6,7]. Resonance-stabilizing effects of the cyano group (CN) along with inductive and/or resonance effects of halogens in both singlet and triplet states of structure 3 can justify this trend of stability (Fig.…”

“…The effect of electron-donating and electronwithdrawing substituents, including amino, cyano, and methoxy groups, on C 2 NH carbenes indicated that only electron-donating substituents switch the multiplicities of their corresponding carbenes [5]. It has been predicted recently that halogens can switch the global minima of C 2 SiHX silylenes [6] and C 2 GeHX germylenes [7]. However, up to date no attempt has been made to account for how halogens influence the stability and multiplicity of C 2 NH carbenes.…”