Hydrogen Bond and Ligand Dissociation Dynamics in
Fluoride Sensing of Re(I)–Polypyridyl Complex
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Abstract
Hydrogen bonding interaction plays
an essential role in the early
phases of molecular recognition and colorimetric sensing of various
anions in aprotic media. In this work, the host–guest interaction
between <i>fac</i>-[Re(CO)<sub>3</sub>Cl(L)] with L = 4-([2,2′-bipyridin]-4-yl)phenol
and fluoride ions is investigated for the hydrogen bond dynamics and
the changing local coordination environment. The stoichiometric studies
using <sup>1</sup>H NMR and ESI-MS spectroscopies have shown that
proton transfer in the H-bonded phenol–fluoride complex activates
the dissociation of the CO ligand in the Re(I) center. The phenol-to-phenolate
conversion during formation of HF<sub>2</sub><sup>–</sup> ion
induces nucleophilic lability of the CO ligand which is probed by
intraligand charge transfer (ILCT) and ligand-to-metal charge transfer
(LMCT) transitions in transient absorption spectroscopy. After photoexcitation,
phenol–phenoxide conversion rapidly equilibrates in 280 fs
time scale and the ensuing excited state [Re<sup>II</sup>(bpy•<sup>–</sup>phenolate¯) (CO)<sub>3</sub>Cl]* undergoes
CO dissociation in the ultrafast time scale of ∼3 ps. A concerted
mechanism of hydrogen cleavage and coordination change is established
in anion sensing studies of the rhenium complex