Evidence for new surface organotin and germanium complexes with functional groups grafted at the surface of Pt and Rh

Abstract

It has been previously demonstrated that reaction of organometallic compounds with group VIII metallic surfaces can lead to grafted organometallic fragments with well defined structures. The presence of remaining alkyl groups on the catalytic surface was demonstrated by various physical and chemical techniques (EXAFS, Magnetic measurements, I.R. spectroscopy, Mössbauer, Thermoreduction, etc.). Surface organometallic complexes with an average formula M s [M′R x ] y (M=Rh, Pt, Ni; M′=Sn, Ge, Si, Se; R=Me, Et, Bu) were proposed. The impact of the presence of these alkyl groups on the selectivity and activity for various catalytic reactions is a subject of important investigations. In this work, we demonstrate that organometallic fragments with functional groups can also be grafted on a platinum or rhodium surface. We will describe the synthesis of R x M′R 4− x f (M′=Sn or Ge; R=H or Bu and R f=(CH 2) 3OH, (CH 2) 3OMe, (CH 2) 3O(CH 2) 2O(CH 2) 2OMe, or (CH 2) 4OH) and the kinetics of the reaction under atmospheric pressure of hydrogen with the silica supported platinum or rhodium catalysts. In every case, the hydrogenolysis of the organometallic complexes is not total and some organometallic fragments with functional groups remain on the surface. With R f=(CH 2) 3OH, M=Rh, M′=Sn, on average, the grafted organometallic fragment can be formulated as: Rh s [SnBu 0.4R 0.4 f] y /SiO 2. With R f=(CH 2) 3O(CH 2) 2O(CH 2) 2OMe, M=Rh, Pt, M′=Sn, on average, the grafted organometallic fragment can be formulated as: Pt s [SnBu 0.6R 0.5 f] 0.43/SiO 2 or Rh s[SnR 0.6 f] 0.6/SiO 2. With (CH 2) 3OMe, M=Rh, Pt, M′=Sn, there is formation of a grafted organometallic fragment which can be formulated on average as: Rh s [H x SnR 0.9 f] 0.9/SiO 2 and Pt s [H x SnR 1.2 f] 0.9/SiO 2. With R f=(CH 2) 4OH, M=Rh, Pt, M′=Ge, an average formula can be obtained as: Pt s [Ge(H) x R 1 f] 0.6/SiO 2, Rh s [Ge(H) x R 0.9 f] 0.6/SiO 2. Catalytic properties of these new material is under investigation.