A quest for stable bicyclic carbenes with one, two, and three carbenic centers at theoretical level

The effects of halogen substituents on structure, stability, and electronic properties of bicyclo[1.1.1]pentanylene at density functional theory

“…The calculated ΔE s-t values via B3LYP/6-311++G** and MRMP2/def2-SVP level theories show similar trends for (1-15) carbenes (Table 6). All bicyclic carbenes (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) = 37.36 kcal/mol) with three carbenic centers. The order of thermodynamic stability based on the absolute values of ΔE s-t in kcal/mol is carbenes with three carbenic centers (11-15) > one carbenic center (1-5) > two carbenic centers (6-10) (Table 6).…”

“…All structures are optimized without any symmetry constraint, at B3LYP level of theory as the method of choice in the present work, in common with other papers on carbenes (using 6-311++G** [1][2][3] at the GAMESS software package [30][31][32] ). This basis set is employed for C, H, F, Cl, and Br atoms, while the valence double-zeta LANL2DZ basis set with effective core potential (ECP) of Hay and Wadt is used for I atom.…”

“…[31,34,35] The natural bond orbital (NBO) population analysis on optimized carbenes are accomplished at the same level. [1][2][3] The vibrational frequency computations are applied to characterize the nature of stationary points as minimum (NIMAG = 0) or transition state (NIMAG = 1) [36][37][38][39][40] on the potential energy surface for restricted singlet and (unrestricted triplet) carbenes at the (U)B3LYP/6-311++G** level of theory. In addition, the singlet-triplet energy gaps (ΔE s-t ) and the energy difference of HOMO and LUMO (ΔΕ HOMO-LUMO ) are obtained, at 298.15 K and 1.0 atm.…”

“…Carbenes, in a Lewis sense, have two electrons not involved in bonding (singlet (s) or triplet state (t)) and two non-bonding orbitals into which to place those electrons. [1][2][3][4][5][6][7][8][9][10] The electronic structure and stability of a carbene are affected by the mesomeric or inductive effects of substituents attached to the carbenic center. [11][12][13][14][15] Goddard and coworkers have suggested certain simple, empirically corrected computational approaches to estimate s-t gaps, particularly for halo-substituted carbenes.…”

“…Also, they are applied in catalysis, photophysics, bioorganometallic chemistry, and so on. [29] Following our quest for stable cyclic compounds divalent group 14 atoms, [1][2][3] here, density functional theory (DFT) calculations are employed to form a systematic investigation on the effects of halogen substituents on the stability (ΔE s-t ), band gap (ΔΕ HOMO-LUMO ), nucleophilicity (N), electrophilicity (ω), and proton affinity (ΔE PA ) (Tables 1-8).…”