Beryllepin, C₆H₆Be, and “Beryllium‐Inserted Benzenes,” C₆H₆Be_n, n = 2–6: A Density Functional Computational Investigation

Abstract

The seven‐membered beryllium‐containing heterocycle beryllepin, C6H6Be, has been examined computationally at the B3LYP/6‐311++G** density functional level of theory. Beryllepin is best described as a planar singlet heterocyclic conjugated triene with marginal aromatic character containing a C–Be–C moiety forced to be nonlinear (∠C‐Be‐C = 146.25°) by the cyclic constraints of the seven‐membered ring. The molecule can be considered to be derived from a benzene‐like system in which a neutral beryllium atom has been inserted between two adjacent carbon atoms. The 11 other possible “beryllium‐inserted benzenes,” C6H6Ben, n = 2–6, have also been investigated. Only two of these heterocyclic systems, the eight‐membered 1,4‐diberyllocin and the nine‐membered 1,4,7‐triberyllonin, were found to be stable, singlet‐ground‐state systems, albeit with little aromatic character. Of the remaining nine beryllium‐inserted benzenes, with the exception of the 11‐membered ring containing five beryllium atoms and the 12‐membered ring containing six beryllium atoms, which were calculated to exist as a ground state pentet and septet, respectively, all were calculated to be ground state triplet systems.

Magnesepin, 1,4‐dimagnesocin, 1,4,7‐trimagnesonin, and their C6H6Mgn, n=1‐3, isomers: A density functional computational investigation

“…Magnesepin ( 1 ) optimized from both planar and nonplanar initial trial geometries to a planar singlet molecule exhibiting significant C–C bond alternation (Figure ) with essentially C 2v symmetry. The ∠C–Mg–C was calculated to be 131.1°, which is slightly larger than the 128.6° angle expected for a regular heptagon, yet smaller than the 146.2° angle calculated for beryllepin . The Mg–C distances in 1 are 203.9 pm.…”

“…The ∠C-Mg-C was calculated to be 131.1°, which is slightly larger than the 128.6° angle expected for a regular heptagon, yet smaller than the 146.2° angle calculated for beryllepin. [1] The Mg-C distances in 1 are 203.9 pm. Reports of the crystal structures of molecules containing Mg-C bonds indicate that these distances are somewhat shorter than expected (although no direct comparisons to experimental data for magnesium-containing heterocycles are available).…”

“…Recently, the density functional investigation of the structures and properties of the 12 possible “beryllium‐inserted benzenes” found that three of the heterocycles were stable ground‐state singlet systems: beryllepin, 1,4‐diberyllocin, and 1,4,7‐triberyllonin (Figure ). Of these three molecules, beryllepin was calculated to exhibit marginal aromatic character based on nucleus‐independent chemical shift (NICS) data; the larger molecules were predicted to exhibit little or no aromatic character.…”

Triberyllium cluster sandwich complexes: A density functional investigation

“…Recently [1], the structures and properties of the twelve so-called "beryllium-inserted benzenes" -heterocyclic molecules theoretically produced by successive insertions of beryllium atoms between adjacent carbon atoms in a benzene moiety -were determined at the B3LYP/6-311++G** level of density functional theory. Only three of the twelve possible monocyclic molecules were found to be stable ground state singlet molecules: beryllepin, 1,4diberyllocin, and 1,4,7-triberyllonin.…”

“…Only three of the twelve possible monocyclic molecules were found to be stable ground state singlet molecules: beryllepin, 1,4diberyllocin, and 1,4,7-triberyllonin. The largest of the molecules that were investigated, the twelve-membered monocyclic system 1, was determined to be a ground state septet system, but also exhibited a low-lying pentet state [1].…”