Braunstein, Pierre; Kormann, Hans-Peter; Meyer-Zaika, Wolfgang; Pugin, Raphael; Schmid, Gunter:

Strategies for the anchoring of metal complexes, clusters, and colloids inside nanoporous alumina membranes.

In: Chemistry--A European Journal, Jg. 6 (2000) ; Nr. 24, S. 4637-4646
ISSN: 0947-6539
Zeitschriftenaufsatz / Fach: Chemie
Abstract:
Two complementary strategies are presented for the anchoring of mol. Pd complexes, of Co or Pt clusters or of Au colloids inside the nanopores of alumina membranes. The first consists in the one-step condensation of an alkoxysilyl functional group carried by the metal complex with the hydroxy groups covering the surface of the membrane pores. Thus, using the short-bite alkoxysilyl-functionalized diphosphine ligands (Ph2P)2N(CH2)3Si(OMe)3 (1) and (Ph2P)2N(CH2)4SiMe2(OMe) (2) derived from (Ph2P)2NH (dppa) (dppa = bis(diphenylphosphanyl)amine), the Pd complexes [Pd(dmba){k2-P,P-(Ph2P)2N(CH2)3Si(OMe)3}] Cl (3) and [Pd(dmba){k2-P,P-(Ph2P)2N(CH2)4SiMe2(OMe)}]Cl (4) (dmbaH = dimethyl(benzyl)amine), resp., were tethered to the pore walls. After controlled thermal treatment, confined and highly dispersed Pd nanoparticles were formed and characterized by TEM. This method could not be applied to the Co cluster [Co4(CO)8(m-dppa){m-P,P-(Ph2P)2N(CH2)4SiMe2(OMe)}] (7) owing to its too limited soly. However, its anchoring was achieved by using the second method which consisted of first derivatizing the pore walls with 1 or 2. The covalent attachment of the diphosphine ligands provides a mol. anchor that allows subsequent reaction with the cluster [Co4(CO)10(m-dppa)] (6) to generate anchored 7 and this step was monitored by UV/visible spectroscopy. In addn., the presence of carbonyl ligands in the cluster provides for the first time a very sensitive spectroscopic probe in the IR region which confirms both cluster incorporation and the retaining of its mol. nature inside the membrane. The presence of the bridging dppa ligand in 6 provides addnl. stabilization and accounts for the selectivity of the procedure. Using this method, Pt clusters (diam. .apprx.2 nm) and Au colloids (diam. .apprx.13 nm) were immobilized after passing their soln. through the functionalized membrane pores. The resulting membranes were characterized by TEM which demonstrated the efficiency of the complexation and showed the high dispersion of the metal loading. The successful application of these methods demonstrated that nanoporous alumina membranes are not only unique supports to incorporate metal complexes, clusters, or colloids but can also be regarded as functional matrixes or microreactors, thus opening new fields for applications.