Donor-stabilized monomeric pentelylalanes and gallanes: beyond the steric bulk

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During the last decade mixed Group 13/15 compounds attracted significant attention as precursors for functional materials, inorganic polymers or as hydrogen storage materials. Current studies focused in particular on N/B- and P/B-systems and although synthetic procedures for the heavier analogs have been developed, they remain underrepresented and such derivatives still bear bulky organo-substituents. The parent compounds of the type H2EMH2 (M = Group 13 element, E = Group 15 element) are isoelectronic with ethane, have not been isolated yet and were only be described by computational studies. In this respect, the Scheer group succeeded in the isolation of the monomeric parent compound of the phosphanylalanes and -gallanes (OC)5W·H2PMH2·NMe3 (M = Al, Ga) by applying Lewis acid(LA)/base(LB) stabilization and achieved the first controlled oligomerization reactions of those compounds. The present project is focused on the fine tuning of the electronic and steric properties of the starting materials and the reaction conditions (temperature, solvent and others) to control the H2 elimination process for such compounds with the ultimate goal to obtain the most condensed, H-free cage compounds and mixed Group 13/15 chain composites. The selective substitution by special organic moieties on the pentel atom will lead to reactive precursors for the fabrication of novel soluble, mixed Group 13/15 oligomeric/polymeric materials. Furthermore, the synthesis of the only donor-stabilized (LB) compounds of the type H2EMH2·LB (E = P, As, Sb; M = Al, Ga) is a central goal of the project via a novel salt metathesis route from LB·MH2I or by a LA abstraction method from LA·H2PMH2·LB (M = Al, Ga) by appropriate LBs. Strong donors like carbenes with a high steric demand are promising LBs to generate the only by a LB stabilized parent compounds for the first time. Moreover, the yet unknown only by a LA stabilized parent compound of the type LA·H2PMH2 will be synthesized within this project. The research on these different types of compounds will be accompanied and complemented by extensive gas phase and thermal investigations as well as by additionally DFT calculations. In particular, compounds of the type H2PMH2·LB (M = Al, Ga), with LBs with negligible volatility - like sterically congested N-heterocyclic carbenes or cyclic(alkyl)(amino)carbenes - are expected to liberate H2PMH2 into the gas phase or into the argon matrix and allow its detection for the very first time.