Generation of Well-Defined Pairs of Silylamine on Highly Dehydroxylated SBA-15: Application to the Surface Organometallic Chemistry of Zirconium

Abstract

Design of a new well-defined surface organometallic species [O-(=Si–NH)2Zr(IV)Np2] has been obtained by reaction of tetraneopentyl zirconium (ZrNp4) on SBA-15 surface displaying mainly silylamine pairs [O-(=Si–NH2)2]. These surface species have been achieved by an ammonia treatment of a highly dehydroxylated SBA-15 at 1000°C (SBA-151000). This support is known to contain mainly strained reactive siloxane bridges (≡Si-O-Si≡)[1] along with a small amount of isolated plus germinal silanols =Si(OH)2. Chemisorption of ammonia occurs primarily by opening these siloxane bridges[2] to generate silanol/silylamine pairs [O-(=Si–NH2)(=SiOH)] followed by substitution of the remaining silanol. Further treatment using hexamethyldisilazane (HMDS) results in the protection of the isolated remaining silanol groups by formation of ≡Si-O-SiMe3 and =Si(OSiMe3)2 but leaves ≡SiNH2 untouched. After reaction of this functionalized surface with ZrNp4, this latter displays mainly a bi-podal zirconium neopentyl organometallic complex [O-(=Si–NH)2Zr(IV)Np2] which has been fully characterized by diverse methods such as infrared transmission spectroscopy, magic angle spinning solid state nuclear magnetic resonance, surface elemental analysis, small angle X-ray powder diffraction (XRD), nitrogen adsorption and energy filtered transmission electron microscopy (EFTEM). These different characterization tools unambiguously prove that the zirconium organometallic complex reacts mostly with silylamine pairs to give a bi-podal zirconium bis-neopentyl complex, uniformly distributed into the channels of SBA-151000. Therefore this new material opens a new promising research area in Surface Organometallic Chemistry which, so far, was dealing mainly with O containing surface. It is expected that vicinal amine functions may play a very different role as compared with classical inorganic supports. Given the importance in the last decades of N containing ligands in catalysis, one may expect important prospects…