Reactivity of Terminal Electrophilic Phosphinidene Complexes:  Synthesis of the First Rhenium Phosphinidene, [Re(CO)<INF>5</INF>(η<SUP>1</SUP>-PN<SUP>i</SUP><SUP></SUP>Pr<INF>2</INF>)][AlCl<INF>4</INF>], and Novel Reactions with Azobenzene

The first terminal rhenium phosphinidene complex, [Re(CO)<INF>5</INF>(η¹-PNⁱPr<INF>2</INF>)][AlCl<INF>4</INF>], has been synthesized by chloride abstraction from [Re(CO)<INF>5</INF>{P(Cl)(NⁱPr<INF>2</INF>)}]. The electrophilic character of the terminal phosphinidene ligand is demonstrated by phosphine addition at the unsaturated phosphorus center and by novel reactions with azobenzene, PhN&dbd;NPh, which generate, via C−H activation and P−N and P−C bond formation, coordinated benzodiazaphosphole ligands. The cations [Re(CO)<INF>5</INF>P(PPh<INF>3</INF>)NⁱPr<INF>2</INF>]⁺ and [Re(CO)<INF>5</INF>{P(PhNNHC<INF>6</INF>H<INF>4</INF>)NⁱPr<INF>2</INF>}]⁺ have been crystallographically characterized as their AlCl<INF>4</INF>^- salts. The corresponding late-metal terminal phosphinidene complexes [Co(CO)<INF>3</INF>(PR<INF>3</INF>)(η¹-PNⁱPr<INF>2</INF>)][AlCl<INF>4</INF>] (R = Ph, Et) also afford coordinated benzodiazaphospholes via reaction with PhN&dbd;NPh.