Bis[hydrazido(2-)] and related complexes of molybdenum(VI): towards alkene-metathesis catalysts based on hydrazido(2-) ligation

Abstract

The complex [Mo(NBu ^t ) ₂ Cl ₂ (dme)] (dme = 1,2-dimethoxyethane) underwent an imide-ligand exchange reaction with an excess of 1,1-diphenylhydrazine hydrochloride in refluxing dme to give the bis[hydrazido(2-)] complex [MoCl ₂ (NNPh ₂ ) ₂ (dme)] 1. Reaction of 1 with an excess of PMe ₃ in CH ₂ Cl ₂ gave [MoCl ₂ (NNPh ₂ ) ₂ (PMe ₃ ) ₂ ] 2. Treatment of Na ₂ [MoO ₄ ] with 2 molar equivalents of Ph ₂ NNH ₂ ·HCl in the presence of NEt ₃ and SiMe ₃ Cl in refluxing dme afforded the salt [NHEt ₃ ][MoCl ₄ (NNPh ₂ )(NHNPh ₂ )] 3. The crystal structures of 1–3 have been determined; all possess octahedral geometries with unidentate hydrazido groups. The hydrazido(2-) Mo–N bond distances vary from 1.749(2) and 1.771(2) Å in 1, to 1.793(3) in 2 and 1.748(2) Å in 3, with no simple correlation with the Mo–N _α –N _β angle. The anionic component of 3 contains a bent hydrazide(1-) ligand (Mo–N–N 136.0°) and a linear hydrazido(2-) group (Mo–N–N 174.4°).