[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 CH3CN 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 HOC6H3(CH3)2 and thiourea after prolonged heating in toluene and characterized by IR spectroscopy and X‐ray diffraction.