Nandi A, Martin JML. Heavy-Atom Tunneling in the Covalent/Dative Bond Complexation of Cyclo[18]carbon-Piperidine.
J Phys Chem B 2022;
126:1799-1804. [PMID:
35180344 PMCID:
PMC8900127 DOI:
10.1021/acs.jpcb.2c00218]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Recent quantum chemical
computations demonstrated the electron-acceptance
behavior of this highly reactive cyclo[18]carbon (C18)
ring with piperidine (pip). The C18–pip complexation
exhibited a double-well potential along the N–C reaction coordinate,
forming a van der Waals (vdW) adduct and a more stable, strong covalent/dative
bond (DB) complex by overcoming a low activation barrier. By means
of direct dynamical computations using canonical variational transition
state theory (CVT), including the small-curvature tunneling (SCT),
we show the conspicuous role of heavy atom quantum mechanical tunneling
(QMT) in the transformation of vdW to DB complex in the solvent phase
near absolute zero. Below 50 K, the reaction is entirely driven by
QMT, while at 30 K, the QMT rate is too rapid (kT ∼ 0.02 s–1), corresponding to a
half-life time of 38 s, indicating that the vdW adduct will have a
fleeting existence. We also explored the QMT rates of other cyclo[n]carbon–pip systems. This study sheds light on the
decisive role of QMT in the covalent/DB formation of the C18–pip complex at cryogenic temperatures.
Collapse