Novel reactions of copper (I) phenoxide with hetero-allenes: a synthetic and structural study.

Abstract

In the present study several novel reactions of copper(I) phenoxide with small molecules like CS?, PhNCS, PhNCO and other heteroallenes have been investigated. The products have been characterised by spectroscopic techniques and X-ray structural analysis. Reaction of copper(I) phenoxides with CS? leads to the formation of tetraphenyl orthocarbonates, C(OAr)?. This is the first report of such a novel reactivity being observed. It is shown that the reaction proceeds via an intermediate tetrameric copper(I) phenoxide species rather than by a simple nucleophilic substitution of phenoxide at CS?. The reactivity of copper(I) phenoxide is further modified in the presence of ancillary ligands. Pure ?-donor nitrogen ligands like NEt? and TMED lead to the formation of thiocarbonates, (ArO)?C=S. In the presence of ?-acceptor ligands like phenanthroline and bipyridyl, a soluble complex is formed and the reaction is monitored spectrophotometrically and it follows first-order kinetics. These results are rationalised based on the formation of an intermediate copper(I) binuclear phenoxide-bridged complex. The reaction of copper(I) phenoxides with other heteroallenes like PhNCO, PhNCS and dicyclohexylcarbodiimide are dependent on the nature of the ancillary ligands, order of addition of the reagents and the nature of the solvents used. In the presence of P(OCH?)? ligand, PhNCS gives a hexanuclear copper(I) complex, [??-SC(=NC?H?)OC?H?]?, as deduced from an X-ray structural study. In contrast, the use of PPh? leads to a monomeric [(PPh?)CuSC(=NC?H?)(OC?H?)] complex, as proposed from spectroscopic data. The characteristic feature of the latter complex is the lability of the PPh? ligand and its ready conversion in CH?CN to the hexanuclear copper(I) complex. The reaction of copper(I) phenoxide with analogous CS? in the presence of PPh? gives a monomeric copper(I) complex, [(PPh?)?Cu(??-S?C:OC?H?)], as confirmed by an X-ray structural study. A mechanism involving an intermediate monomeric copper(I) complex, coordinated by phosphine ligand, is proposed for the formation of these complexes. Theoretical and X-ray structural investigations of three tetraphenyl orthocarbonates are also carried out. The study throws light on the additivity of anomeric interactions and its role in determining the conformation of these compounds.