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

The chemistry of the rhenium trihydrido complex [ReH 3 (PPh 3 ) 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 [TcH 3 (PPh 3 ) 4 ] having a capped-octahedral coordination sphere. The PPh 3 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 3 or PBu 3 give the mono-substituted complexes [ReH 3 (PPh 3 ) 3 (PMe 3 )] (2) and [ReH 3 (PPh 3 ) 3 (PBu 3 )] (3) under retention of the apical PPh 3 ligand and substitution of one of the basal PPh 3 ligands. The stability of the phosphine trihydride complexes decreases in the order PPh 3 >PMe 3 >PBu 3 . Treatment of [ReH 3 (PPh 3 ) 4 ] with trityl hexafluorophosphate in CH 3 CN does not result in a hydride abstraction, but gives the tetrahydrido cation [ReH 4 (NCCH 3 )(PPh 3 ) 3 ] + (4), while reactions with nitriles give unstable azavinylidene complexes of the composition [ReH 2 (PPh 3 ) 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 [ReH 2 (PPh 3 ) 3 (NC(H)CH 3 )] (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 5 (PPh 3 ) 3 ] were isolated from reactions of 1 with HOC 6 H 3 (CH 3 ) 2 and thiourea after prolonged heating in toluene and characterized by IR spectroscopy and X-ray diffraction.