Stabilities and Limitations in the Reactivity of Phosphorus Ylide‐Based Aluminum– and Gallium–Carbon Ambiphiles: A Combined Experimental and Computational Approach

The unexpected reactivity and stability limits of phosphorus ylide-based aluminum– and gallium–carbon ambiphiles are described. While the previously published t-butyl-substituted compound (2-{AltBu2}-C6H4)Ph2PCMe2 (1tBu) reacts reversibly with NH3 at room temperature (RT) with cleavage of a NH bond, the reaction with MeNH2 is much less favorable and proceeds irreversibly only at 90 °C. All other title compounds 1R with R = Me, Et, Mes, and C6F5 decompose in the presence of NH3. The decomposition of 1Et in the presence of ammonia can be well followed by nuclear magnetic resonance (NMR) spectroscopy. All title compounds remain stable in the presence of t-BuNH2 and Et2NH. In addition, an unexpected reactivity is found in the reaction of 1R and the gallium analogues 2R with isocyanates. Instead of yielding the expected ring-expansion products, the title compounds catalyze the trimerization of isocyanates. Also the reactivity toward MeOH and H2O is presented. Quantum chemical calculations show that activation of the OH bonds should be feasible at RT. Experimental findings, however, only show the decomposition of 1tBu in the corresponding reactions. ... mehrNevertheless, the cleavage of the OH bond is feasible and affords the activation products 7 and 8 starting from the ammonia activation product 3.