Grafting of bulky rare earth metal complexes onto mesoporous silica MCM-41

Heteroleptic yttrium bis(dimethylsilyl)amide complexes featuring chelating N,N'-bis(3,5-di-tert-butylsalicylidene)ethane-1,2-diamine (H2L1) and trans- 1,2-bis(2,4,6-triisopropylbenzenesulfonamido)cyclohexane (H2L2) ligands wer e immobilized on mesoporous silica MCM-41 according to a heterogeneously pe rformed silylamide route. FTIR Spectroscopy revealed a novel grafting seque nce involving amine elimination and subsequent metal siloxide formation and surface silylation. Nitrogen adsorption/desorption isotherms of the result ing hybrid materials obtained at 77.4 K indicated peculiarities of the immo bilization process such as the presence of differently modified mesopores. According to preliminary catalytic investigations, the hybrid materials exh ibit promising catalytic activity in a hetero Diels-Alder reaction (Danishe fsky transformation). Molecular model complexes were synthesized via amine elimination reactions with triphenylsilanol and fully characterized by mean s of spectroscopy (FTIR, H-1, C-13, Si-29 NMR). Mononuclear [YL1(OSiPh3)(th f)(CH3CN)] adopts a slightly distorted pentagonal bipyramidal geometry in t he solid state, with the (planar) L-1 and acetonitrile ligands located in t he equatorial plane.