Intramolecular Al/P Frustrated Lewis Pairs Based on an Indoline Backbone─Two Reaction Sites for Small Molecule
Sanjay Biswas1, Siad Wolff1, Beatrice Cula1
1Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489 Berlin, Germany.
None:
The synthesis of compounds of the type Ph2P(Ind)AlX2 (with Ind = indoline and X = Cl, I, Me, and C6F5) 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 = C6F5 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 [Ph2P(Ind)]2AlX. However, upon contact with donors (D), all compounds were found to react as Ph2P(Ind)AlX2, forming Ph2P(Ind)AlX2(D). The reactivities of the representatives with X = Me and C6F5 were investigated, showing that diazo compound Ph2CN2 can be activated in the Al/P reaction space, while CO2 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.
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