Hexamethylphosphorus triamide: A chloride-for-dimethylamido, Me2N−, exchange reagent

The reaction of P(NMe2)3 with WCl6 produces [ClP(NMe2)3][WCl4(NMe2)2], [ClP(NMe2)3][2], through apparent Cl−-for-NMe2− exchange. A six-coordinate [Cl5W–PCl(NMe2)3] metallophosphorane species is proposed as a probable intermediate in this ligand exchange reaction. A similar reaction with NbCl5 results in a more complex product, [NbCl4(NHMe2)(η2-N(Me)–C(H)–P(NMe2)3)], 3, in which Cl−-for-NMe2− exchange is attended by additional reactions that include C–H activation and cyclometallation of an NMe2− ligand, H+ transfer to NMe2− to form a dimethylamine ligand, and adduct formation between exogenous P(NMe2)3 and the formyliminium carbon resulting from cyclometallation. Structural characterization of [ClP(NMe2)3][2] reveals a cis disposition of NMe2− ligands that are oriented at 63.2° relative to one another and an appreciable lengthening of the W–Cl bonds trans to the NMe2− ligands (2.4615[4] Å) as compared to those that are cis (2.3918[4] Å). The structure of 3 is distorted pentagonal bipyramidal with the formyliminium carbon and nitrogen atoms arranged slightly above and below by ∼0.37 Å the equatorial plane. The potential synthetic utility of P(NMe2)3 as an alternative to the classical method of delivery of dialkylamido ligands via LiNR2 is discussed.

Graphical abstractThe reaction of WVICl6 with P(NMe2)3 forms [ClP(NMe2)3][cis-WVCl4(NMe2)2] through a Cl−-for-NMe2− exchange mechanism that likely involves a metallophosphorane intermediate. Reactivity appears limited to two ligand exchanges and is attended by one-electron reduction of tungsten. A more complex product, [NbCl4(NHMe2)(η2-N(Me)–C(H)–P(NMe2)3], results from the reaction between NbVCl5 and P(NMe2)3.Figure optionsDownload full-size imageDownload as PowerPoint slide