Synthesis of multiply bonded main-group compounds for small molecule activation reactions

Amines play an important role in a variety of industries, including in agriculture and the pharmaceutical sector. Although amines can be easily synthesised on a laboratory scale, these synthetic protocols are often unattractive to industry, usually due to safety concerns with precursors or atom inefficient methodologies. By contrast, hydroamination (the addition of ammonia across an unsaturated substrate, such as an alkene or alkyne) is an attractive process for the synthesis of value-added chemicals such as fertilisers in an sustainable fashion. Despite the attractive nature of this process, ammonia is a challenging substrate, and to date there are no known catalysts which can use it as a feedstock. Transition metal catalysts typically fail in effecting hydroamination because of their propensity to form Werner complexes with ammonia which precludes N-H bond activation. In contrast, main-group systems are an attractive alternative to transition metals as they are more Earth-abundant and less likely to form unreactive ammonia adducts, but their catalytic behaviour is less well explored. Clearly, the development of a viable hydroamination catalyst is an important step towards reducing the cost and waste of amine synthesis. Recently, the Goicoechea group has synthesised novel species containing P-Ga double bonds (known as phosphagallenes). Their ability to act as a frustrated Lewis pair (FLP) and activate a variety of N-H bonds, including that of ammonia has also been demonstrated; these join the approximately dozen examples of single-site N-H bond activation using main-group systems. The goal of this project is to exploit this unusual reactivity in cooperative catalysis with transition metals, paving the way for the synthesis of amine substrates from inexpensive and widely available ammonia feedstocks. The project aims to synthesise novel species containing group 13/15 element multiple bonds and to study the behaviour of such compounds in small-molecule activation reactions, with a particular focus on amines. Further, the project will probe the viability of these novel compounds in catalytic hydroamination reactions of unsaturated species, such as alkenes and alkynes. Traditionally, small-molecule activation is largely limited to transition metals. Although these elements have widespread application in catalysis, this does not extend to the catalytic hydroamination of ammonia; only a single example based on Au(I) is presently known. By contrast, a number of main-group compounds have been shown to stoichiometrically activate ammonia, but catalysis with main-group systems is limited to the alkaline-earth metals and only with more substituted amines. The aim of this project is to exploit the novel behaviour of phosphagallenes in catalytic hydroamination. This project falls within the EPSRC Catalysis research area, which directly contributes to the Manufacturing the Future and Physical Sciences research themes.