Organometallic chemistry on periodic mesoporous organosilicas: generation of surface-confined zinc and yttrium centres

Periodic mesoporous ethylenesilicas with hexagonal P6mm and cubic Fm3m/Pm3n symmetry were prepared by using divalent surfactant C(16-3-1) and binary surfactant mixtures C(18-3-1) and C18TABr as structure-directing agents, respectively, under basic conditions. A tetramethyldisilazane-based surface silylation was carried out under mild conditions affording hybrid materials SiHMe2@PMOMCM-41], SiHMe2@PMOKIT-5] and SiHMe2@PMOSBA-1], corresponding to silanol group populations of ca. 1.46, 0.67 and 1.63 mmol g(-1), respectively. New molecular zinc precursor compounds ZnN(SiHMe2)2]2 and EtZn(OSiHtBu2) were synthesized via salt metathesis and alkane elimination procedures from ZnCl2 and LiNSiH(CH3)2]2, HOSiHtBu2 and ZnEt2, respectively. Organozinc and organoyttrium complexes were reacted with the surface silanol groups according to a heterogeneously performed silylamide route, aswell as an alkane elimination reaction, yielding ZnN(SiHMe2)2]@PMOMCM-41], ZnN(SiHMe2)2]@PMOKIT-5], ZnN(SiHMe2)2]@PMOSBA-1], ZnN(SiMe3)2]@PMOMCM-41], ZnN(SiMe3)2]@PMOKIT-5], ZnN(SiMe3)2]@PMOSBA-1], YN(SiHMe2)2]x(THF)y@PMOMCM-41], YN(SiHMe2)2]x(THF)y@PMOKIT-5], YN(SiHMe2)2]x(THF)y@PMOSBA-1] and Zn(OSiHtBu2)@PMOMCM-41]. The metal loading mainly depended on the surface silanol group population, size and shape of metal-coordinated ligand, and reaction time as shown for Zn contents in the range of 4.2 to 10.6 wt%. In addition, a preferred N(SiHMe2)2/OC6H2tBu2-2,6-Me-4 ligand exchangeability was found for the large yttrium surface centres. The parent and functionalized materials were characterized by powder X-ray diffraction, elemental analysis, N2 physisorption, FTIR, 13C CP and 1H MAS NMR spectroscopy.