Organic Chemistry from an Inorganic Perspective: The Serendipitous Discovery of New Chemistry by Attempting the Impossible

A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Chemistry and Physics, College of Science, Health and Engineering, La Trobe University, Victoria, Australia.<br

[Ag]₂[B₁₂Cl₁₂] as a Catalyst in PhICl₂ Mediated Chlorination

The weakly coordinating dianion [B12Cl12]2− originates from a family of carboranes typically reserved for application in coordination chemistry. Herein, we show that its readily accessible Ag(I) salt, [Ag]2[B12Cl12], can be used as a catalyst in the PhICl2 mediated chlorination of arenes, alkenes, and alkynes. The promising activity displayed by [Ag]2[B12Cl12] over a variety of commercially available Ag(I) sources merits its incorporation to the toolkit of commonly screened silver catalysts in synthesis.</p

Lewis acid activation of Weiss' reagents ([PhI(Pyr)2]²⁺) with boranes and isolation of [PhI(4-DMAP)]²⁺

Abstraction of a pyridine ligand from Weiss' reagent ([PhI(Pyr)2]2+) using BF3-Et2O was found to activate Weiss' reagent towards electrophilic aromatic substitution reactions. The activated species can be isolated when 4-DMAP is used as the pyridine ligand and was determined to be [PhI(4-DMAP)]2+ in solution. The isolated cation was reactive in electrophilic aromatic substitution reactions towards mesitylene, xylene and toluene that Weiss' reagent itself does not react with.</p

PhI(OTf)2 Does Not Exist (Yet)

PhI(OTf) has been used for the past 30 years as a strong I(III) oxidant for organic and inorganic transformations. It has been reported to be generated in situ from the reactions of either PhI(OAc) or PhI=O with two equivalents of trimethylsilyl trifluoromethanesulfonate (TMS-OTf). In this report it is shown that neither of these reactions generate a solution with spectroscopic data consistent with PhI(OTf) , with supporting theoretical calculations, and thus this compound should not be invoked as the species acting as the oxidant for transformations that have been associated with its use.</p

PhI(OTf)2 Does Not Exist (Yet)

PhI(OTf) has been used for the past 30 years as a strong I(III) oxidant for organic and inorganic transformations. It has been reported to be generated in situ from the reactions of either PhI(OAc) or PhI=O with two equivalents of trimethylsilyl trifluoromethanesulfonate (TMS-OTf). In this report it is shown that neither of these reactions generate a solution with spectroscopic data consistent with PhI(OTf) , with supporting theoretical calculations, and thus this compound should not be invoked as the species acting as the oxidant for transformations that have been associated with its use.</p

PhICl₂ is activated by chloride ions

A study on the potential activating role of pyridine in the electrophilic chlorination of anisole by PhICl2 has led to the discovery that soluble sources of chloride ions activate PhICl2 in the reaction at catalytic loadings, greatly increasing the rate of chlorination. It is further shown that presence of chloride increases the rate of decomposition of PhICl2 into PhI and Cl2. The specific mechanism by which chloride induces electrophilic chlorination and decomposition of PhICl2 remains an open question.</p

On the activation of PhICl₂ with pyridine

It has been previously proposed that pyridines can activate PhICl2 by displacing a chloride and forming the [PhI(Pyr)(Cl)]+ cation as a reactive intermediate. Here we show that pyridine does not displace chloride, but rather forms a weak complex with the iodine via halogen bonding along the C-I bond axis. This interaction is interrogated by NMR, structural, charge density, and theoretical investigations, which all indicate that pyridine does not activate PhICl2 as proposed.</p