Rey Planells A, Espinosa Ferao A. Accurate Ring Strain Energies of Unsaturated Three-Membered Heterocycles with One Group 13-16 Element.
Inorg Chem 2022;
61:6459-6468. [PMID:
35442022 PMCID:
PMC9066411 DOI:
10.1021/acs.inorgchem.2c00067]
[Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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High-quality ring
strain energy (RSE) data for 1H-unsaturated (CH)2X parent rings, where X is a group 13–16
element, are reported in addition to the 2H-isomers
of the pnictogenirene rings. RSE data are obtained from appropriate
homosdesmotic reactions and calculated at the DLPNO-CCSD(T)/def2-TZVPP//B3LYP-D3/def2-TZVP(ecp)
level. 1H-Tallirene and 1H-plumbirene
have unique donor–acceptor structures between an acetylene
π(CC) orbital and an empty p orbital of a metallylene subunit
(a Dewar–Chatt–Duncanson description) and therefore
cannot be described as proper rings but as pseudocyclic structures.
Also, 1H-indirene and 1H-oxirene
lack ring critical points and constitute borderline cases of pseudorings.
1H-Unsaturated rings exhibit enhanced RSE compared
to their saturated homologues. The mechanism of ring strain relaxation
by increasing the s character in the lone pair (LP) of group 15–16
elements is remarkable and increases on descending the groups. Furthermore,
RSE is affected by the aromatic character of group 13 rings and certain
aromatic or antiaromatic character in group 14 or 15–16 rings,
respectively, which tend to vanish on descending the group as shown
by NICS(1) values. 2H-Unsaturated rings were found
only for group 15 elements (although only 2H-azirine
shows a proper cyclic structure) and displayed lower RSE (higher stability)
than the corresponding 1H-isomers.
Accurate ring strain energies (RSE) are
calculated for three-membered
1H-unsaturated rings containing a 13−16 group
element and group 15 2H-isomers. The presence or
absence of lone pairs at the heteroatom and the existence of intrinsic
or residual (anti)aromaticity were shown to affect the RSE.
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