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

Abstract

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@PMO[MCM-41], SiHMe₂@PMO[KIT-5] and SiHMe₂@PMO[SBA-1], corresponding to silanol group populations of ca. 1.46, 0.67 and 1.63 mmol g⁻¹, respectively. New molecular zinc precursor compounds Zn[N(SiHMe₂)₂]₂ and EtZn(OSiH^tBu₂) were synthesized via salt metathesis and alkane elimination procedures from ZnCl₂ and LiN[SiH(CH₃)₂]₂, HOSiH^tBu₂ 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 Zn[N(SiHMe₂)₂]@PMO[MCM-41], Zn[N(SiHMe₂)₂]@PMO[KIT-5], Zn[N(SiHMe₂)₂]@PMO[SBA-1], Zn[N(SiMe₃)₂]@PMO[MCM-41], Zn[N(SiMe₃)₂]@PMO[KIT-5], Zn[N(SiMe₃)₂]@PMO[SBA-1], Y[N(SiHMe₂)₂]_x(THF)_y@PMO[MCM-41], Y[N(SiHMe₂)₂]_x(THF)_y@PMO[KIT-5], Y[N(SiHMe₂)₂]_x(THF)_y@PMO[SBA-1] and Zn(OSiH^tBu₂)@PMO[MCM-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/OC₆H₂^tBu₂-2,6-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.