Intramolecular Al/P Frustrated Lewis Pairs Based on an Indoline Backbone─Two Reaction Sites for Small Molecule Activation and Hydrodefluorination

High Resolution Image Download MS PowerPoint Slide The synthesis of compounds of the type Ph 2 P(Ind)AlX 2 (with Ind = indoline and X = Cl, I, Me, and C 6 F 5 ) is reported. They can be accessed starting from the 7-diphenylphosphino indoline via deprotonation and subsequent salt metathesis or via in situ deprotonation using precursors with basic ligands. While in the case of X = Me, X-ray crystallographic and solution studies confirmed that the connectivity and configuration are as envisaged, the latter was only true in the case of X = C 6 F 5 for the solid state. In solution, ligand scrambling was observed, as was for the representatives with X = I and Cl, which unlike the organometallic derivatives were found to have a dimeric structure. The dimers in solution are partly forming the scrambled compounds [Ph 2 P(Ind)] 2 AlX. However, upon contact with donors (D), all compounds were found to react as Ph 2 P(Ind)AlX 2, forming Ph 2 P(Ind)AlX 2 (D). The reactivities of the representatives with X = Me and C 6 F 5 were investigated, showing that diazo compound Ph 2 CN 2 can be activated in the Al/P reaction space, while CO 2 reacts with the aluminum-amide unit to give carbamates. The Al–N units can also be used to perform the dehydrofluorination of fluorocyclohexane. Subsequent investigations showed that achieving this reaction with alanes requires a fine balance and cooperation between a sufficiently Lewis-acidic aluminum center and a basic ligand.