Coordination mode of cyclohex-1-enylolonium cation and bridging pyridyl derivatives as gem-diol chelates to rhenium(I) and (VII)

Abstract

Rhenium(I) and (VII) complexes with cyclohex-1-enylolonium cation and bridging pyridyl derivatives are reported. Additionally, the CO-bridged pyridyl and their related compounds have shown interesting behaviour in their reactivity towards compounds containing two amino groups. The unusual cationic compound: (2,6-diaza-cyclohex-1-enylolonium)2-aza-benzoate (H₂den), was isolated from the reaction mixture of 1,2-di(pyridin-2-yl)ethane-1,2-dione with propane-1,3-diamine in methanol. The latter ligand: H₂den, was used in the synthesis of rhenium(I) complex in its reaction with [Re(CO)₅Cl] that gave rise to novel rhenium(I) complex fac-[Re(CO)₃(Hhdm)] (1). The surprising aspect in the formation of (1) is the modification of H₂den which was stabilized into a coordinated six-membered pyrimidine ring, 1,4,5,6-tetrahydropyrimidin-2-yl)di(pyridin-2-yl)methanol (H₂hdm) chelate. The derived ligand acts as a tridentate monoanionic N₂,O-donor ligand towards the fac-[Re(CO)₃]⁺ core. Surprisingly, the 2-aza-benzoate counter-ion that was present in the used ligand is not displayed in the crystal structure of complex 1, and might have been stabilized into 2-aza-benzoic acid (picolinic acid). The reaction of the potential tridentate N₂,O-donor ligand 2,2′-dipyridylketone (dpk) with trans-[ReOI₂(OEt)(PPh₃)₂] led to the isolation of [ReO₃(dpk·OH)] (2). The ligand H₂den and the rhenium complexes were spectroscopically characterized, and the structures of H₂den, 1 and 2 were established by X-ray diffraction.