TY - JOUR
T1 - Novel α-spirocyclic (alkyl)(amino)carbenes at the theoretical crossroad of flexibility and rigidity
AU - Kassaee, M. Z.
AU - Momenitaheri, Mohammadreza
AU - Shakib, F. A.
AU - Ghambarian, M.
AU - Musavi, S. M.
PY - 2010/2/8
Y1 - 2010/2/8
N2 - Spirocyclic (alkyl)(amino)carbenes (CAACs) with reasonable conformations of cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl substituents in the position α to the carbenic center are investigated at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G*. The singlet-triplet energy separations (ΔEs-t), HOMO-LUMO energy gaps (ΔEHOMO-LUMO), hydrogenation energies (ΔEH), heats of methylene formation (ΔE) as well as philicity indices (N and ω) of these carbenes are compared and contrasted. The highest ΔEs-t is encountered for the cyclopropyl substituted CAAC (54.2 kcal/mol), while the other ones lay in a narrow range of 48.2-51.8 kcal/mol. Assignment of the barriers for ring inversions is carried out in order to probe the "flexible steric bulk" of cyclic substituents, showing negligible differences with those of the unsubstituted rings. The calculated N and ω indices indicate that in contrast to the popular belief, CAACs appear less electrophilic than N-heteorcyclic carbenes (NHCs).
AB - Spirocyclic (alkyl)(amino)carbenes (CAACs) with reasonable conformations of cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl substituents in the position α to the carbenic center are investigated at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G*. The singlet-triplet energy separations (ΔEs-t), HOMO-LUMO energy gaps (ΔEHOMO-LUMO), hydrogenation energies (ΔEH), heats of methylene formation (ΔE) as well as philicity indices (N and ω) of these carbenes are compared and contrasted. The highest ΔEs-t is encountered for the cyclopropyl substituted CAAC (54.2 kcal/mol), while the other ones lay in a narrow range of 48.2-51.8 kcal/mol. Assignment of the barriers for ring inversions is carried out in order to probe the "flexible steric bulk" of cyclic substituents, showing negligible differences with those of the unsubstituted rings. The calculated N and ω indices indicate that in contrast to the popular belief, CAACs appear less electrophilic than N-heteorcyclic carbenes (NHCs).
KW - CAAC
KW - DFT
KW - NHC
KW - Nucleophilicity and electrophilicity
KW - Ring inversion
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U2 - 10.1007/s11224-010-9585-y
DO - 10.1007/s11224-010-9585-y
M3 - Article
AN - SCOPUS:77952291150
SN - 1040-0400
VL - 21
SP - 593
EP - 598
JO - Structural Chemistry
JF - Structural Chemistry
IS - 3
ER -