Diaryliodonium salts (Ar2IX) have emerged as versatile multi-purpose reagents with desirable properties such as easy accessibility, low toxicity and applicability under mild and metal-free reaction conditions. Despite displaying broad utility in arylations of both carbon and heteroatom nucleophiles, the overall sustainability of these protocols is compromised by featuring poor atom economy due to the formation of stochiometric iodoarene byproducts. In this thesis, this imperative drawback was addressed by development of a novel class of diaryliodonium salts with unprecedented reactivity that prevents the formation of iodoarene waste by incorporating both aryl groups as well as the iodine-component into the final products. The first project concerns the development and design of ortho-fluorinated iodonium salts, where updated synthetic protocols were established to attain extensive salt scopes with diverse functionalities. The unique design of these reagents unveiled a cascade reaction whereby heteroatom-diarylated products were formed through concomitant nucleophilic aromatic substitution and intramolecular aryl transfer. The second project focuses on the applications of the ortho-fluorinated salts in diarylations of aliphatic amines, anilines, ammonia and water to attain industrially important diaryl- and triaryl amines as well as diaryl ethers (>100 examples). This atom-efficient methodology allows for transfer of two different aryl groups in a single step under mild and metal-free conditions, giving structurally diverse multi-arene products that would otherwise require expensive and time-consuming multi-step synthesis. The third project explores the potent combination of the diarylation strategy with the structural diversification of secondary aliphatic amines in the preparation of densely functionalized diarylamines. Cyclic amines constitute essential cornerstones in drug discovery and incorporation of such valuable moieties in Ar2IX reagents is of considerable interest. By further exploiting the SNAr reactivity of the ortho-fluorinated diaryliodonium salts, a previously inaccessible class of amino-functionalized Ar2IX were prepared by reactions with cyclic amines. These N-functionalized reagents were utilized in a one-pot sequential arylation/ring opening pathway, where intramolecular arylation afforded diarylammonium salts in situ, which upon reaction with external nucleophiles underwent deconstructive C­-N functionalizations. The methodology enables atom- and step-economical access to value-added diarylamines with versatile functionalities at both the C- and N- terminal. The final project emphasizes the applicability of the diarylated products as versatile building blocks in various downstream functionalizations. The retention of the iodine-component enables diversification by a range of transition metal-catalysed cross-couplings, delivering products with increased structural complexity. The significance of the diarylation methodology was further demonstrated in the three-step synthesis of the drug molecule NMP-7. Two protocols were developed for transformation of the ortho-iododiaryl ethers into oxygen-bridged cyclic diaryliodonium salts and acyclic aryloxy salts. The synthetic utility of these unexplored Ar2IX reagents was demonstrated in metal-free, chemoselective functionalizations of common nucleophiles.