Solvent‐Polarity‐Induced Assembly of Calixarene‐Capped Titanium‐Oxo Clusters with Catalytic Activity in the Oxygenation of Sulfides

Abstract

Four calixarene-coordinated titanium-oxo clusters, namely, [Ti 4 (C6A) 2 (μ 3 -O) 2 (DMF) 2 ] (CIAC-258), [Ti 8 (H 3 C6A) 4 (C 6 H 5 PO 3 ) 8 (μ 2 -O) 4 ] 4À (CIAC-259), [Ti 6 (TC4A) 3 (μ 2 -O) 3 (OiPr) 6 ] (CIAC-260) and [Ti 6 (H 2 TC4A) 4 (C 6 H 5 PO 3 ) 4 (μ 2 -O) 5 (DMF) 2 ] 2À (CIAC-261) were obtained, which feature sandwich-like, windmill-like, triangular, and tetrahedral structures, respectively. The polarity of the solvent determines the involvement of the auxiliary ligand phenylphosphonic acid in the formation of the products and their structures. Compounds CIAC-258 and CIAC-261 exhibit good catalytic performance in the selective oxidation of sulfides to sulfoxides with H 2 O 2 as the oxidant, which can be attributed to the Ti active sites coordinated by exchangeable DMF molecules. Moreover, density functional theory (DFT) calculations revealed that the Ti-hydroperoxo species formed by the interaction of the Ti active site in CIAC-258 or CIAC-261 and H 2 O 2 is the most likely catalytic active component during the catalytic sulfoxidation process.

Auxiliary Carboxylate-Induced Assembly of Calix[6]arene-Polyoxotitanate Hybrid Systems with Photocatalytic Activity in the Oxidation of Sulfides

“…The potential catalytic pathways are discussed as follows. Numerous studies have demonstrated that the Ti–peroxo species, formed by the combination of the Ti active site and H 2 O 2 , are responsible for the catalytic oxidation process. , As illustrated in the stacking diagram of the Ti 2 -SA cluster (Figure S5), a substantial number of Ti-OR units are extended outside rather than encapsulated by the calixarene. The labile −OR groups on the cluster surface can dissociate and expose the active Ti 4+ ions, which can then combine with H 2 O 2 to generate peroxo–Ti species.…”

“…15−21 They are multidentate-capable and versatile ligands, making them one of the most attractive options as protective ligands in TOCs. Recently, our group and others have investigated the coordination chemistry of calix[8]arene, 22−26 calix [4]arene, 27,28 and thiacalix [4]arene, 29,30 with Ti(IV), synthesizing a series of calixarene-stabilized TOCs with aesthetically appealing structures. These molecules display intriguing topologies, and their structures can be regulated by the addition of auxiliary ligands.…”

“…Calix­[n]­arenes are large ring molecules composed of multiple phenol units bridged by methylene (−CH 2 −), sulfur (−S−), or sulfonyl (−SO 2 −) in the ortho-position, considered the third generation of supramolecules with hollow cavity structures. − They are multidentate-capable and versatile ligands, making them one of the most attractive options as protective ligands in TOCs. Recently, our group and others have investigated the coordination chemistry of calix[8]­arene, − calix[4]­arene, , and thiacalix[4]­arene, , with Ti­(IV), synthesizing a series of calixarene-stabilized TOCs with aesthetically appealing structures. These molecules display intriguing topologies, and their structures can be regulated by the addition of auxiliary ligands.…”

Solvent-polarity-controlled assembly of polynuclear titanium-calixarene complexes: constructing isolated {Ti7}, {Ti13}, {Ti24} and {Tb2Ti13} clusters

“…12 For instance, a conical calix [4]arene or thiacalix [4] arene molecule tends to bind with titanium atoms via two to four phenolic oxygen atoms to form a shuttlecock-like secondary building unit (Scheme 1a-c). [19][20][21] A conical calix [6] arene molecule has two sets of three pendant phenolato oxygen atoms, each chelating a Ti ion, forming a bi-nuclear Ti 2 -C6A motif (Scheme 1e). 22,23 The calix [6]arene molecule with an inverted biconical configuration also provides two binding sites for titanium chelation, either endo-or exo-to the cavity.…”