Synthesis And Catalytic Properties Of Mixed Diacyl Titanate Complexes

The combination of binary acid system consisting of Lewis acid and Br???nsted acid has a great potential to tune the activity and the selectivity of some classic organic condensation reactions. In order to improve the selectivity of the binary acid catalytic systems, in this paper, we designed a class of mixed bis-carboxylate titanocene complexes which are highly selective catalytic systems. We utilized a direct reaction of salicylate titanocene chelate and other aromatic carboxylic acids to efficiently synthysize a series of novel titanocene complexes. It successfully introduced two different carboxylate ligands into stable organometallic Lewis acid precursors and obtained unreported mixed bis-carboxylate titanocene complexes. The discovery of mixed bis-carboxylate titanocene complexes not only enriched the species of titanocene complexes, but also expanded the application of metallocene catalysts in organic reactions. Through the study of their catalytic performance experiments, it reveals that the mixed bis-carboxylate titanocene complexes bearing two different Br???nsted acid ligands have the good catalytic activity and high selectivity. The main research results are as follows:?1? We developed a atom-economy method to successfully synthesized air-stable mixed bis-carboxylate titanocene complexes. These complexes are Cp2Ti[??¹-OOC-C₆H₄-2-OH???¹-OOCC6H5?] ?1?, Cp2Ti[??¹-OOC-C₆H₄-2-OH???¹-OO-CC₆H₄-4-F?] ?2? and Cp₂Ti[??¹-OOC-C₆H₄-2-OH???¹-OOC-3-C₄H₃S?] ?3?. The mixed bis-carboxylate titanocene complexes were fully characterized by FT-IR, NMR, elemental analysis, TG and X-ray diffraction analysis, defining the structure and properties of these complexes. In addition, the synthesis of mixed bis-carboxylate titanocene complexes avoid using expensive silver salts, and our raw materials is cheap and easy to operate, and they could be prepared in a large scale.?2? We investigated the catalytic efficiency of mixed bis-carboxylate titanocene complexes in three-component Mannich reaction of aromatic aldehyde, aromatic amine and cyclohexanone. The experimental results showed that mixed bis-carboxylate titanocene catalytic system not only showed high catalytic activity, but also obtained decent diastereoselectivity in Mannich reaction under mild conditions. The catalytic system have also been successfully to expand various substituted aromatic aldehyde and aromatic amine. In eight products, the catalytic effects were all ideal. The yields were 81-98% and the diastereomer ratios were12:88-1:99.?3? We have developed titanocene catalytic systems which tuned by carboxylate ligands and selectively catalyzed Cross-aldol reaction of aromatic aldehyde and cyclohexanone. These titanocene catalytic systems contained mixed bis-carboxylate titanocene complexes and another binary acid titanocene catalyst which bearing the same carboxylate ligands. The catalytic species are mono- and double-Cross-aldol reactions, respectively. The mixed bis-carboxylate titanocene complexes and the same binary acid titanocene catalyst showed different activation to the substrate. The mixed bis-carboxylate titanocene complexes selectively obtained double Cross-aldol products under optimized conditions and afforded 85-98% yield. The o-aminophenol ligand assisted titanocene catalyst selectively promoted the synthesis of mono-Cross-aldol products, and the yield reached 72-86%. These results revealed that the different carboxylate ligands have significantly different fine-tuning effect on the Lewis acidity of metal Ti center, thus realized the effectively selective reaction.