ReH3 (PPh3 )4 ] - A Key Compound in the Rhenium Hydride Chemistry.

Abstract

The chemistry of the rhenium trihydrido complex [ReH3 (PPh3 )4 ] (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 [TcH3 (PPh3 )4 ] having a capped-octahedral coordination sphere. The PPh3 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 PMe3 or PBu3 give the mono-substituted complexes [ReH3 (PPh3 )3 (PMe3 )] (2) and [ReH3 (PPh3 )3 (PBu3 )] (3) under retention of the apical PPh3 ligand and substitution of one of the basal PPh3 ligands. The stability of the phosphine trihydride complexes decreases in the order PPh3 >PMe3 >PBu3 . Treatment of [ReH3 (PPh3 )4 ] with trityl hexafluorophosphate in CH3 CN does not result in a hydride abstraction, but gives the tetrahydrido cation [ReH4 (NCCH3 )(PPh3 )3 ]+ (4), while reactions with nitriles give unstable azavinylidene complexes of the composition [ReH2 (PPh3 )3 (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 [ReH2 (PPh3 )3 (NC(H)CH3 )] (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 [ReH5 (PPh3 )3 ] were isolated from reactions of 1 with HOC6 H3 (CH3 )2 and thiourea after prolonged heating in toluene and characterized by IR spectroscopy and X-ray diffraction.