Periodic Mesoporous Organosilica Derivatives Bearing a High Density of Metal Complexes on Pore Surfaces

Abstract

Periodic mesoporous organosilicas (PMOs) synthesized from alkoxysilane precursors bridged with organic moieties, R[Si-(OR') 3 ] n , n ! 2, R = organic group, R' = CH 3 , C 2 H 5 , etc. by surfactant-directed self-assembly are a new class of functional materials that have well-defined nanoporous structures and highly functional organic groups in the silica walls. [1] It is preferable to incorporate organic groups in the pore walls rather than to graft them on the wall surfaces because in the former case the organic groups offer little resistance to the diffusion of molecules and ions in the mesochannels and are quite resistant to leaching. Many PMOs containing bridging organic groups (R) that range from aliphatic and aromatic hydrocarbons to heterocycles and metal complexes have been reported. [2,3] Incorporating metal complexes into PMO frameworks is particularly important because metal complexes possess unique features such as catalytic activity, luminescence emission, redox properties, and excited-state reactivity. [4] PMOs with metal complexes are usually prepared by co-condensation of a metal-complex-bridged alkoxysilane precursor and a large amount (typically over 90 %) of tetraethoxysilane. This is due to general difficulties in producing PMOs from just a precursor with a bulky metal complex because of weak interaction between hydrolyzed precursors and surfactants. [5] An alternative approach is to form metal complexes on a pore surface after synthesis by using bridging organic groups in the framework as metal ligands. Matsuoka and co-workers attached the organometallic fragments {Cr(CO) 3 } and {Mo(CO) 3 } to the phenyl ring of phenylene(Ph)-bridged PMO. [6] Recently, Polarz and co-workers reported the coordination of transition-metal cations to Ph-PMOs functionalized with carboxylic, dithiocarboxylic, acetylacetonate, and amine groups. [7] This approach has the advantage that bulky metal complexes can be densely and selectively integrated on the pore surface of highly ordered PMOs. However, these metal complexes attached to a PMO framework have limited functionalities mainly because of the poor ligand ability of these PMOs.Recently, octahedral d 6 metal complexes such as polypyridine-coordinated ruthenium (Ru II ) and iridium (Ir III ) com-

Nanoceramics: Issues and Opportunities

“…In addition to the well‐known tetraethyl orthosilicate (TEOS), a range of other organosilicon compounds have been used to synthesize PMO's with potentially interesting properties and applications . Figure gives an overview together with the most prominent property of the resulting organosilicon , . The optical properties and the potential of these materials for photocatalysis applications were highlighted at the conference.…”

Bipyridine Periodic Mesoporous Organosilica: A Solid Ligand for the Iridium‐Catalyzed Borylation of CH Bonds

“…2 nm; a relatively large value, as PMOs of this type typically give rise to walls of a few molecular layers. [8,10] In the pore walls the material shows a high degree of ordering as evident by powder X-ray diffraction (Figure 1, b). Five sharp peaks are observed at 2V/8 = 7.5, 15, 23, 31, 38, they can be assigned to a periodic structure of 1.16 nm and the corresponding higher order reflections.…”

“…[8] They thus provide a well-defined immediate environment making them ideal candidates as catalyst supports. Most PMOs prepared for catalytic applications so far rely on monodentate ligands [7e,9] with a few examples describing more elaborate systems such as phenylpyridine [10] or BINAP. [11,12] In homogeneous catalysis, the Ir(I)-catalyzed direct borylation of C À H bonds [13] has been recognized as a mild and versatile reaction generating high value building blocks [14] directly from easily available starting materials.…”

Estudos espectroscópicos de sistemas luminescentes hóspede/hospedeiro

“…1,14,[40][41][42][43] Este problema tem sido abordado através da dispersão destes emissores em matrizes poliméricas, 39,44,45 em argilas multicamadas, 46,47 ou por sol-gel, em processos de auto montagem de micro-e nano-partículas, 27,43,48,49 por dissolução no sol e posterior condensação do material híbrido, 1,43,50 por impregnação úmida em matrizes mesoporosas, [51][52][53][54] ou por processos de funcionalização da matriz e posterior ligação covalente do centro luminescente. 27,33,52,55 Alternativamente, pesquisadores têm se dedicado a modificar os grupos formadores dos corantes ou dos grupos substituintes dos ligantes dos complexos que atuam como espaçadores moleculares, 8,35,56,57 como agentes polimerizantes, 14,58 e/ou como grupos transportadores de carga. 59…”