Experimental and theoretical investigations into the mechanisms of haliranium ion π-ligand exchange reactions with cyclic alkenes in the gas phase.

Autor: Brydon SC; School of Chemistry and Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Parkville, Victoria 3010, Australia. brydons@student.unimelb.edu.au., da Silva G; Chemical Engineering, The University of Melbourne, Parkville, Victoria 3010, Australia., O'Hair RAJ; School of Chemistry and Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Parkville, Victoria 3010, Australia. brydons@student.unimelb.edu.au., White JM; School of Chemistry and Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Parkville, Victoria 3010, Australia. brydons@student.unimelb.edu.au.
Jazyk: angličtina
Zdroj: Physical chemistry chemical physics : PCCP [Phys Chem Chem Phys] 2021 Nov 24; Vol. 23 (45), pp. 25572-25589. Date of Electronic Publication: 2021 Nov 24.
DOI: 10.1039/d1cp04494j
Abstrakt: Haliranium ions are intermediates often involved in complex cyclisations, where their structure allows for control over stereospecific outcomes. Extending previous studies into their structure and reactivity in the gas phase, this work focuses on the bimolecular reactivity of ethyl bromiranium and iodiranium ions with cyclic alkenes. The products observed via mass spectrometry were broadly attributed to either addition by cyclohexene at the iranium carbon or attack at the heteroatom to undergo associative π-ligand exchange. The model proposed was supported by both kinetic experiments and DFT calculations, where the rate of parent ion consumption proceeded at the collision rate (Br: k 2 = 1.25 × 10 -9 and I: k 2 = 1.28 × 10 -9 cm 3 molecule -1 s -1 ) with the subsequent partitioning dependent on the relative stability of the initial intermediates and the relatively large barriers present in the addition pathway. Exploration of the effect of cycloalkene ring strain on the iodiranium ion reactivity was conducted with a series of crossover experiments with 50 : 50 mixtures of either cyclohexene or cis -cyclooctene and styrene, where the outcomes were dependent on the competing ring strain relief gained by reaction with each neutral. The nature of the exchange transition state was determined to be pseudocoarctate following both natural bond orbital (NBO) and anisotropy of the induced current density (ACID) analysis.
Databáze: MEDLINE
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