Immobilization of copper complexes with (1,10-phenanthrolinyl)phosphonates on titania supports for sustainable catalysis

Abstract

Different strategies for the immobilization of copper complexes with 1,10-phenanthroline (phen) using the phosphonate anchoring group were investigated to prepare robust and porous heterogeneous catalysts. Homoleptic and heteroleptic copper(I) complexes with phen bearing the bis(trimethylsiloxy)phosphoryl anchoring group (Pphen-Si) at different positions of the phen backbone were prepared and covalently incorporated into titania (TiO₂) xerogels by using the sol–gel process or grafted onto the surface of mesoporous TiO₂ (S_BET = 650 m² g⁻¹). Copper(I) bis(Pphen-Si) complexes were the only complexes that were successfully anchored onto the TiO₂ surface because the heterogenization was often accompanied by the undesirable dissociation of copper complexes. Hybrid materials based on copper(I) chelates with one phen ligand were obtained following a two-step procedure involving the immobilization of Pphen-Si chelators and their successive complexation with copper(I) ions. Porous material, Cu/6b/SM/A, displaying a BET surface area of 243 m² g⁻¹ and bearing 0.57 mmol g⁻¹ of the complex was synthesized according to this approach. Excellent catalytic performance of the reusable Cu/6b/SM/A material in the Sonogashira-type coupling and the Huisgen 1,3-dipolar cycloaddition was also demonstrated. This solid represents the first example of mesoporous TiO₂-supported transition metal catalysts.