Cis‐Dioxo‐molybdenum(VI) Complexes with Diaminoguanidinium and Triaminoguanidinium Schiff Bases and Their Catalytic Application for Epoxidation of Cyclohexene

Abstract

AbstractDiaminoguanidinium and triaminoguanidinium Schiff bases of 1,3‐bis(3,5‐di‐tert‐butyl‐2‐hydroxyphenylmethylideneamino)guanidine hydrochloride (H5saldagtBu2 ⋅ HCl) and tris(3,5‐di‐tert‐butyl‐2‐hydroxybenzylidene)‐triaminoguanidinium chloride (H5saltagtBu2 ⋅ HCl) are synthesized. Treatment of H5saldagtBu2 ⋅ HCl with Na2MoO4 ⋅ 2H2O or (NH4)6Mo7O24 ⋅ 4H2O under different molar ratios afforded mono‐ and di‐nuclear molybdenum(VI) complexes of [(MoO2)(MeOH)(H3saldagtBu2)] (1), [(MoO2)2(MeOH)2(HsaldagtBu2)] ⋅ 2DMF (2 ⋅ 2DMF), and [(MoO2)2(HsaldagtBu2)] ⋅ ‐[(MoO2)2(H2O)2(HsaldagtBu2)] (3). Interactions of H5saltagtBu2 ⋅ HCl with Na2MoO4 ⋅ 2H2O or (NH4)6Mo7O24 ⋅ 4H2O under different reaction conditions resulted mono‐, di‐, and tetra‐nuclear molybdenum(VI) complexes of [(MoO2)(MeOH)(H3saltagtBu2)] (4), [(MoO2)(H2O)(H3saltagtBu2)] (5), [(MoO2)2(H2O)(DMF)(HsaltagtBu2)] ⋅ 3DMF (6) (Ref [31]), and [(MoO2)4(DMF)2(HsaltagtBu2)2] ⋅ 2H2O (7 ⋅ 2H2O). Complexes 1–7 were characterized by IR, 1H NMR and UV/vis spectroscopies. Molecular structures of H5saltagtBu2 ⋅ MeOH, 1, 2 ⋅ 2DMF, 3–5 and 7 ⋅ 2H2O are confirmed by single crystal X‐ray diffraction ananlysis, which shows that the diaminoguanidinium and triaminoguanidinium Schiff bases are coordinated to the cis‐{MoO2}2+ moieties via ONN atoms to form five‐ and six‐membered rings, sharing one Mo−N bond. The catalytic properties of these cis‐dioxo‐molybdenum(VI) complexes for epoxidation of cyclohexene were also investigated.