Surface organometallic chemistry on zeolites: control of the pore opening of mordenite by grafting of thermally stable GeBu3 fragments

GeBu₄ reacts at 250°C with the external silanols of two different mordenites (Si/Al = 11 or 40) to give the surface organometallic complex SiOGeBu₃ 1 which has been characterized by ¹³C CP-MAS NMR; 1 is able to discriminate sterically different alkanes such as n-hexane, 2-methyl-pentane, 2,3-dimethyl butane, 2,2,4-trimethyl pentane. Such discrimination is parallel to that already observed for SiOSnBu₃ grafted on the same mordenites. Interestingly and in contrast to the behaviour of the grafted tin complex, 1 even after treatment at 400°C is still able to separate n-hexane from isooctane, a property ascribed to a steric molecular control of the Ge(Bu)₃ fragment which has an exceptional thermal stability.