Coordination chemistry of α-ω-di(pyridyl-imine) ligands containing flexible linkers with copper(I)

Abstract

Copper(I) complexes of a series of six potentially tetradentate bis(pyridylimine) ligands were prepared, where the pyridylimine groups were separated by different linking units [in L1, CH2CH2CH2(SiMe2O)20SiMe2CH2CH2CH2; in L2, CH2CH2CH2SiMe2OSiMe2CH2CH2CH2; in L3, CH2CH2; in L4, CH2(CH2)4CH2; in L5, CH2(CH2)7CH2; in L6, CH2CH2CH2OCH2CH2OCH2CH2OCH2CH2CH2]. The solubilities of L1, L2 and [Cu(L2)](PF6) in supercritical carbon dioxide were determined. The coordination chemistry of L1–L2 with CuI was studied by UV/Vis, multinuclear NMR and IR spectroscopy, MALDI-TOF and ESI mass spectrometries and elemental analysis. These data suggested that [1+1] complexes had formed. Dicopper complexes of L3–L6 were prepared for comparison, and [Cu2(L5)2](PF6)2 characterized by single-crystal X-ray diffraction analysis. Close methylene C–H···π interactions are observed within the structure. PGSE NMR spectroscopy was used to determine the hydrodynamic radii of the species in solution and comparison of these data with computational models for the complexes was made. Freezing point depression measurements afforded molecular weights for solution-state species in agreement with the formulations proposed via NMR and mass spectrometric data. There is no evidence to support linear metallopolymer formation but data suggest that [2+2] and [1+1] metallomacrocyles were formed, with siloxane linking groups encouraging the formation of [1+1] species. Solid-state NMR spectroscopic data on [Cu(L1)](PF6) indicate the presence of two different environments for the PF6– anions.