Titanium(IV) Catecholate‐Grafted Mesoporous Silica KIT‐6: Probing Sequential and Convergent Immobilization Approaches

Abstract

Molecular TiIV catecholates were obtained as dimeric complexes from protonolysis reactions of Ti(NMe2)4 with pyrocatechol (H2CAT), 4‐tert‐butylcatechol (H2CATtBu‐4), 3,5‐di‐tert‐butylcatechol (H2CATtBu2–3,5), 2,3‐dihydroxynaphthalene (H2DHN) and 3,6‐di‐tert‐butylcatechol (H2CATtBu2–3,6). The heteroleptic monocatecholate amide complexes were characterized by X‐ray structure analysis but only [Ti(CAT)(NMe2)2]2 and [Ti(DHN)(NMe2)2]2 were obtained as pure compounds. The solid‐state structures revealed TiIV centers bridged by two catecholato ligands adopting a [κ2(O,µ‐O′)] coordination mode except for complex [Ti(CATtBu2–3,6)(NMe2)2] featuring one bridging catecholato and one bridging amido ligand. Heteroleptic complex [Ti(DHN)(NMe2)2]2 was grafted onto large‐pore periodic mesoporous silica KIT‐6 (convergent approach) and the resulting TiIV surface species compared with the established sequential approach, i.e., grafting of Ti(NMe2)4 onto the KIT‐6 material and subsequent ligand exchange with H2DHN. Dimeric complex [Ti(DHN)(NMe2)2]2 proved to be sufficiently reactive for a direct grafting yielding the same dominant surface species as obtained according to the sequential approach, as revealed by nitrogen physisorption, elemental analysis, and DRIFT/13C CP MAS spectroscopy.