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. 2022 Nov 21;27(22):8069.
doi: 10.3390/molecules27228069.

Stabilizing Halogen-Bonded Complex between Metallic Anion and Iodide

Fei Ying  1 , Xu Yuan  2   3 , Xinxing Zhang  2   3 , Jing Xie  1
Affiliations

Stabilizing Halogen-Bonded Complex between Metallic Anion and Iodide

Fei Ying et al. Molecules. .

Abstract

Halogen bonds (XBs) between metal anions and halides have seldom been reported because metal anions are reactive for XB donors. The pyramidal-shaped Mn(CO)5- anion is a candidate metallic XB acceptor with a ligand-protected metal core that maintains the negative charge and an open site to accept XB donors. Herein, Mn(CO)5- is prepared by electrospray ionization, and its reaction with CH3I in gas phase is studied using mass spectrometry and density functional theory (DFT) calculation. The product observed experimentally at m/z = 337 is assigned as [IMn(CO)4(OCCH3)]-, which is formed by successive nucleophilic substitution and reductive elimination, instead of the halogen-bonded complex (XC) CH3-I···Mn(CO)5-, because the I···Mn interaction is weak within XC and it could be a transient species. Inspiringly, DFT calculations predict that replacing CH3I with CF3I can strengthen the halogen bonding within the XC due to the electro-withdrawing ability of F. More importantly, in so doing, the nucleophilic substitution barrier can be raised significantly, ~30 kcal/mol, thus leaving the system trapping within the XC region. In brief, the combination of a passivating metal core and the introduction of an electro-withdrawing group to the halide can enable strong halogen bonding between metallic anion and iodide.

Keywords: halogen bond; metallic anion; nucleophilic substitution reaction; quantum chemistry calculation; reductive elimination.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Calculated (a) structure and Mulliken charge, (b) electrostatic potential map in e/Bohr3, and (c) HOMO of Mn(CO)5− anion. The M06-2X/aug-cc-pVTZ level of theory is used [23,24,25,26]. Color code: C, grey; O, red; Mn, purple.
Figure 2
Figure 2
Mass spectrometric results. (a) A typical mass spectrum showing the reaction products between Mn(CO)5− and CH3I; (b) CID mass spectrum of [Mn(CO)5(CH3I)]− at m/z 337 taken with the MS3 mode. The nominal applied CID voltage is 5 V.
Scheme 1
Scheme 1
Potential energy profile of Mn(CO)5− reacting with CR3I. The captions in black are for R = H, and the captions in blue are for R = F. Zero-point corrected energies (in kcal/mol) are given relative to the total energy of isolated R3CI and Mn(CO)5−.
Figure 3
Figure 3
Structures of selected stationary points on the PES of Mn(CO)5− reacting with CH3I. The bond distances (Å) in black are for CH3I, and those in blue are for CF3I.
Figure 4
Figure 4
Donor and acceptor natural bond orbitals (NBOs) of halogen-bonded complex CF3−I···Mn(CO)5− to illustrate the charge transfer interaction between I and Mn.
See this image and copyright information in PMC

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