Chelating and bridging bis(diphenylphosphino)aniline complexes of copper(I)

The ligand bis(diphenylphosphino)aniline (dppan) has been shown to be a versatile ligand sporting different coordination modes and geometries as dictated by copper(I) and the counter ion. The molecular structures of its Cu(I) complexes were characterized by X-ray crystallography. The ligand was found in a chelating mode and monomeric complexes were formed when the ligand to copper ratio was 2:1 and the anion was non-coordinating. However, with thiocyanate as the counter anion, the ligand was found to adopt two different modes, with one ligand chelating and the other acting as a monodentate ligand. With CuX (X = Cl, Br), dppan formed a tetrameric complex when the ligand and metal were reacted in the ratio of 1:1. But reactions containing ligand and metal in the ratios of 1:2 or 2:1, resulted in the formation of a mixture of species in solution. Crystallization however, led to the isolation of the tetrameric complex. Variable temperature 31P{1H} NMR spectra of the isolated tetramers did not show the presence of chelated structures in solution. Tetra-alkylammonium salts were added to solutions of various complexes of dppan and studied by 31P{1H} NMR to probe the effect of anions on the stability of complexes in solution. The Cu–dppan complexes were robust and did not interconvert with other structures in solution unlike the bis(diphenylphosphino)isopropylamine complexes.

Several copper(I) complexes of bis(diphenylphosphino)aniline have been synthesized and characterized. The structure of the complexes are dependant on the anion as in the case of complexes formed by bis(diphenylphosphino)isopropyl amine. However, they are different in their solution behavior. The thiocyante ion forces an interesting monodentate mode for the ligand.Figure optionsDownload as PowerPoint slideHighlights
► Crystallographic characterization of copper(I) complexes with the short bite bis(diphenylphosphino)aniline.
► Role of counterion in determining structures shown to be important.
► Structures of complexes are stable in solution in contrast with a closely related ligand system with an aliphatic substituent on the N.
► Counterintuitive Cu–Cu bond distances in polynuclear halogen bridged systems.