From a Fluorenyl Substituted Ylide‐Functionalized Phosphine to a Neutral Phosphide via P−C Bond Cleavage

The attempted synthesis of a 9-methylfluorenyl-substituted ylide-functionalized phosphine is reported, which results in the formation of a secondary phosphine by elimination of methylenefluorene. This phosphine features interesting coordination properties which allow the facile formation of zwitterionic bimetallic phosphido complexes through proton shift into the ylide backbone.

Abstract

Bulky ylide-substituted phosphines have recently found application as potent ligands in homogeneous catalysis. The attempted synthesis of the ylide-substituted fluorenylphosphine Y_PhP(Cy)Flu [Y_Ph=Cy₃P(Ph)C; Flu=9-methylfluorenyl] now resulted in the unexpected elimination of 9-methylenefluorene during the deprotonation step of the intermediary α-phosphino phosphonium salt to yield the secondary ylide-substituted phosphine Y_PhP(Cy)H. This phosphine underwent formal H₂ elimination under basic conditions to form a cyclic phosphonium ylide with a P−C−P−C four-membered ring via deprotonation of one cyclohexyl group of the PCy₃ moiety. Upon coordination to transition metals the secondary ylidylphosphine forms a neutral phosphide ligand by shift of the proton into the ylide-backbone and formation of zwitterionic metal complexes.

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