The synthesis and electrochemistry of some high-oxidation-state rhenium complexes containing the tris(3,5-dimethylpyrazolyl) hydroborato ligand and a heterobimetallic complex containing both rhenium and molybdenum centres

Abstract

[ReL *O 3] ( 1) [L * = HB(3,5-Me 2C 3N 2 H) 3] is readily prepared by reaction of Re 2O 7 with KL * in THF. Complex 1 is reduced by triphenylphosphine in the presence of excess Me 3SiCl in THF at room temperature to give [ReL *O(OH)Cl] ( 2). This reaction yields an inseparable mixture of 2 and [ReL *OCl 2] ( 3) when carried out under reflux. Reaction of 2 with an excess of thiophenol, 2-methoxythiophenol, 4-nitrothiophenol, 4-hydroxythiophenol or 4-aminothiophenol in THF in the presence of triethylamine affords the thiophenolato derivatives [ReL *O(OH)SAr)] [Ar = C 6H 5 ( 4), C 6H 4-2-OCH 3 ( 5), C 6H 4-4-NO 2 ( 6), C 6H 4-4-OH ( 7) or C 6H 4-4-NH 2 ( 8), respectively]. Reaction of a mixture of 2 and 3 with an excess of thiophenol in toluene in the presence of triethylamine yields both 4 and [ReL *O(SC 6H 5) 2] ( 9). A heterobimetallic complex, [ReL *O(OH){SC 6H 4-4-O}Mo(NO)L *Cl] ( 10), is formed when 7 is reacted with [Mo(NO)L *Cl 2] in toluene in the presence of triethylamine. The new rhenium(V) complexes 2 and 4–10 undergo both reduction and oxidation processes which are in many cases reversible or quasi-reversible.