Surface Organometallic Chemistry on Oxides, on Zeolites and on Metals

Abstract

New concepts are slowly emerging from the overlap between organometallic chemistry and surface science. In particular the rules of molecular chemistry seem to apply quite well when organometallic complexes (mononuclear, polynuclear; transition metals, main group elements, lanthanides or actinides) react with a surface (oxide, zeolite, zerovalent metal). In the case of oxides it is thus possible to classify those surfaces by their chemical properties (e.g. acid-base, redox a.s.o.). Well defined surface organometallic fragments can also be prepared via organometallic complexes at the surface of oxides, zeolites and metals; it is thus possible to study on those fragments the real “elementary steps” of heterogeneous catalysis (oxidative addition, reductive elimination, insertion, C-C coupling, etc.). By means of supported heteropolynuclear complexes it is now possible to prepare bimetallic particles having the same composition as that of the starting complexes, a useful approach for the synthesis of tailor made catalysts. By means of organometallics it is possible to control the external pore size of zeolites and introduce a new approach of shape selectivation where the molecular steric control can be adjusted by the size of the organometallic fragment. Reaction of organometallics of main group elements with group VIII metals is a way to prepare well defined alloys of known composition which exhibit highly chemoselective properties in heterogeneous catalysis. It is also possible to graft organometallic fragments at the surface of metal particles and obtain a new generation of modified metallic catalysts extremely selective in a variety of catalytic reactions and which are already in practice in industry.