Novel Bi- and trinuclear gallium halides and hydrides with acyclic and bicyclic guanidinate substituents: Synthesis and reactivity

摘要

We report on the synthesis and characterization of new molecular Ga halides and hydrides with acyclic guanidinate substituents with bicyclic guanidinate substituents. Acyclic guanidinates were found to adopt terminal bonding modes like in the dimeric Ga~(II) compound [(iPr_2N)C(NiPr) _2GaI]_2. In contrast, bicyclic guanidinates prefer bridging bonding modes. Hence, the reaction between Me_3N?GaH_3 and htbo (1,4,6-triazabicyclo[3.3.0]oct-4-ene) affords the binuclear Ga ~(III) hydride [H_2Ga(μ-tbo)]_2. This new hydride turned out to be unstable in solution at 25 °C, dihydrogen is slowly eliminated. In the solid state, however, the hydride is stable up to 80 °C. The thermodynamic properties of this and similar dehydrogenation reactions were studied my means of quantum chemical calculations. With Ga_2H _5(μ_3-O)(μ-tbn)_2 and Ga_2H _5(μ_3-O)(μ-hpp)_2, two new hydrides were synthesized which can be regarded as the first hydrolysis intermediates of binuclear Ga hydrides with bridging guanidinate substituents. Reaction between Me_3N?GaH_3 and the bicyclic guanidine htbo affords a new binuclear Ga hydride which eliminates further H_2 already at room temp. in solution. In the presence of H_2O trinuclear Ga hydrides are formed.