|Abstract||The work developed in this dissertation consists in the development of new methodologies for the preparation of H-phosphinic acid derivatives and their P-chiral counterparts. Special emphasis is given to the role of H-phosphinates as useful synthons for organophosphorus compounds via tandem processes. A review of the most relevant literature in terms of the preparation methodologies and reactivity of H-phosphinic acid derivatives is provided in Chapter I. The following chapter describes the addition of hypophosphorous compounds to unsaturated substrates in presence of metal-catalysts. The mechanism, regioselectivity on alkynes, and reactivity of substituted alkenes, allenes, allenols, and 1,3-dienes as substrates in a palladium-catalyzed hydrophosphinylation was investigated. A novel alkyne hydrophosphinylation catalyzed by nickel chloride or its hydrate in the absence of added ligand was discovered and exploited in the synthesis of various important organophosphorus compounds.^The third chapter details a tandem esterification - cross-coupling reaction of alkyl phosphinates with aryl, heteroaryl, alkenyl, and benzylic halides and triflates. Thus the reaction of the electrophilic substrate with a hypophosphorous acid salt, in the presence of a silicate, a base and the palladium catalyst provided directly a wide variety of H-phosphinates, which were not accessible previously.In the following chapter, transition metal-catalyzed reactions of hypophosphorous compounds with allylic electrophiles are disclosed. Allylic acetates, benzoates and carbonates undergo an effective cross-coupling in the presence of palladium catalysts where pure H-phosphinic acids can be isolated by a simple acidic work-up or esterified in situ to the corresponding H-phosphinate esters. Chapter V describes a palladium-catalyzed dehydrative allylation of hypophosphorous acid with allylic alcohols, in the absence of additives.^The next chapter focuses on P-H bond activation of H-phosphinates through catalytic allylation and oxidation strategies, which lead to disubstituted phosphinic acid and phosphonic acids, respectively. In the last chapter, desymmetrization strategies to access P-chiral H-phosphinates are reported. Two different avenues are explored: the use of chiral ligands in palladium-catalyzed reactions and the use of chiral auxiliaries by means of esterification of hypophosphorous acid with chiral alcohols, where 8-phenylmenthol provides, in a palladium-catalyzed hydrophosphinylation reaction, our best result with around 70% diastereomeric excess.