Phosphine oxide functionalised with two bipyridine subunits: a novel ligand for the engineering of sterically hindered complexes

Abstract

Ligand L, containing two 6-methyl-6′-methyl-yl-2,2′-bipyridine moieties linked by a “PhPO” spacer, has been prepared. Subsequent complexation with [Cu(CH₃CN)₄](BF₄) led to a unique complex of formula [CuL](BF₄). The molecular structure has been determined by X-ray crystallography in the solid state and NMR studies in solution. The complex displays an intense absorption band in the visible wavelength range with maxima at 418 and 509 nm, and is oxidised reversibly at +0.66 V (ΔE_p  = 80 mV) to the corresponding Cu(II) species, while two successive reductions of the coordinated bipyridine fragments occur at −1.60 (ΔE_p  = 66) and −1.84 V (ΔE_p  = 70 mV) s. SCE. Direct spectrophotometric titrations with global analysis allowed us to elicit stability constants for the emergent complex and to highlight the formation of a dinuclear complex in the presence of excess copper.