Small molecule activation of nitriles coordinated to the [Re6Se8]2+ core: formation of oxazine, oxazoline and carboxamide complexes

Abstract

Novel oxazine, oxazoline and carboxamide cluster complexes were prepared when different nucleophilic oxygen species reacted with nitriles coordinated to the Lewis acidic [Re₆Se₈]²⁺ cluster core. Reaction of ICH₂CH₂O⁻ (generated in situ) with [Re₆Se₈(PEt₃)₅(NCR)]A₂ (1A₂ (R = Me) and 2A₂ (R = Ph) where A = BF₄⁻), leads to the formation of [Re₆Se₈(PEt₃)₅(2-methyloxazoline)]²⁺ (3²⁺) and [Re₆Se₈(PEt₃)₅(2-phenyloxazoline)]²⁺ (4²⁺). Similarly, reaction of BrCH₂CH₂CH₂O⁻ with the same nitrile complexes, 1A₂ and 2A₂ (where A = BF₄⁻ or SbF₆⁻) leads to the corresponding oxazine complexes, [Re₆Se₈(PEt₃)₅(2-methyloxazine)]²⁺ (5²⁺) and [Re₆Se₈(PEt₃)₅(2-phenyloxazine)]²⁺ (6²⁺). In addition, reaction of 2(BF₄)₂ with KOH leads to the formation of the carboxamide complex, [Re₆Se₈(PEt₃)₅(phenylcarboxamide)](BF₄) (7(BF₄)). The neutral oxazine and oxazoline ligands can be removed using either heat or UV irradiation; UV irradiation was found to be more efficient at ligand removal as indicated by the shorter reaction times. The relative coordination strength of the neutral N-donor ligands was determined by these reaction times. X-ray structure determinations of 5(BF₄)₂ and 7(BF₄) are also reported.