[ReH 3 (PPh 3 ) 4 ] - A Key Compound in the Rhenium Hydride Chemistry.

The chemistry of the rhenium trihydrido complex [ReH (PPh ) ] (1) has been reinvestigated. An improved synthesis and the solid-state structure of the compound as well as several reactions are reported. The solid-state structure of 1 is similar to that of [TcH (PPh ) ] having a capped-octahedral coordination sphere. The PPh ligands surround the Re atom in a trigonal-pyramidal mode with a short apical Re-P bond (2.300(2) Å) and three longer basal bonds (2.429(2)-2.449(2) Å). Reactions of 1 with monodentate phosphines such as PMe or PBu give the mono-substituted complexes [ReH (PPh ) (PMe )] (2) and [ReH (PPh ) (PBu )] (3) under retention of the apical PPh ligand and substitution of one of the basal PPh ligands. The stability of the phosphine trihydride complexes decreases in the order PPh >PMe >PBu . Treatment of [ReH (PPh ) ] with trityl hexafluorophosphate in CH CN does not result in a hydride abstraction, but gives the tetrahydrido cation [ReH (NCCH )(PPh ) ] (4), while reactions with nitriles give unstable azavinylidene complexes of the composition [ReH (PPh ) (NC(H)R)] (5). They are formed by an insertion of the nitrile into a Re-H bond. The solid-state structure of the methyl derivative [ReH (PPh ) (NC(H)CH )] (5 a) was determined showing a linear Re-N-C unit with rhenium-nitrogen and nitrogen-carbon double bonds, while the N=CH-C bond is clearly bent with an angle of 124°. Two previously unknown polymorphs of [ReH (PPh ) ] were isolated from reactions of 1 with HOC H (CH ) and thiourea after prolonged heating in toluene and characterized by IR spectroscopy and X-ray diffraction.