Energy Decomposition Analysis Coupled with Natural Orbitals for Chemical Valence and Nucleus-Independent Chemical Shift Analysis of Bonding, Stability, and Aromaticity of Functionalized Fulvenes: A Bonding Insight.

ABSTRACT: The Donor base ligand-stabilized cyclopentadienyl-carbene compounds L-C₅H₄ (L = H₂C, aAAC; (CO₂Me)₂C, Py; aNHC, NHC, PPh₃; SNHC; aAAC = acyclic alkyl(amino) carbene, aNHC = acyclic N-hetero cyclic carbene, NHC = cyclic N-hetero cyclic carbene, SNHC = saturated N-hetero cyclic carbene, Py = pyridine) (1a-1d, 2a-2c, 3) have been theoretically investigated by energy decomposition analysis coupled with natural orbitals for chemical valence calculation. Among all these compounds, aNHC=C₅H₄ (2a) and Ph₃P=C₅H₄ (2c) had been reported five decades ago. The bonding analysis of compounds with the general formula L=C₅H₄ (1a-1d) [L = (H₂C, aAAC, (CO₂Me)₂C, Py] showed that they possess one electron-sharing σ bond and electron-sharing π bond between L and C₅H₄ neutral fragments in their triplet states as expected. Interestingly, the bonding scenarios have completely changed for L = aNHC, NHC, PPh₃, SNHC. The aNHC analogue (2a) prefers to form one electron-sharing σ bond (C_L-C_C5H4) and dative π bond (C_L ← C_C5H4) between cationic (aNHC)⁺ and anionic C₅H₄ ^- fragments in their doublet states. Similar bonding scenarios have been observed for NHC (2b) and PPh₃ (2c) (P_L-C_C5H4, P_L ← C_C5H4) analogues. In contrast, the SNHC and C₅H₄ neutral fragments of SNHC=C₅H₄ (3) prefer to form a dative σ bond (C_SNHC → C_C5H4) and a dative π bond (C_SNHC ← C_C5H4) in their singlet states. The pyridine analogue 1d is quite different from 2c from the bonding and aromaticity point of view. The nucleus-independent chemical shifts of all the abovementioned species (1-3) corresponding to aromaticity have been computed using the gauge-independent atomic orbital approach.

SUBMITTER: Gorantla SMNVT 

PROVIDER: S-EPMC8296031 | biostudies-literature |

REPOSITORIES: biostudies-literature