Free and Polymer-Bound Tricyclic Azaphosphatranes HP(RNCH2CH2)3N+: Procatalysts in Dehydrohalogenations and Debrominations with NaH

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Abstract
The commercially available nonionic base P(CH3NCH2CH2)3N (1a) was shown earlier to be superior to DBU as a stoichiometric reagent for the conversion of primary and secondary alkyl halides to alkenes (Arumugam, S.; Verkade, J. G. J. Org. Chem. 1997, 62, 4827). The precursor cation HP(CH3NCH2CH2)3N+ (2) to 1a, which is more stable and less expensive, is reported herein to be an efficient procatalyst for these reactions and also for the debromination of vicinal dibromides using NaH as a relatively inexpensive stoichiometric hydride source in CH3CN at room temperature. In dehydrohalogenations requiring more than ca. 10 h, the CH2CN- ion also acts as a base. By itself, NaH does not function well or at all under the same conditions. A catalytic cycle is proposed in which hydride deprotonates cation 2 liberating catalytic 1a. The cations HP(HNCH2CH2)3N+ (3) and HP[N(polymer)CH2CH2]N(CH2CH2NH)2+ (4) are also shown to function as procatalysts for the efficient dehydrohalogenation of RX and for the debromination of vicinal dibromides. The preparation of the heterogeneous procatalyst 4(OTf) is also described.

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