Air-stable Organometallic Complexes: Synthesis, Characterization And Catalytic Application

Organometallic Lewis acid plays an important role in organic synthesis and chemical engineering. However, The traditional lewis acid and partial organometallic Lewis acid has suffered from one or more disadvantages:（1） air- or moisture-sensitive, low stability;（2） Lower Lewis acidity and poor catalytic activity;（3） poor chemical selectivity and stereoselectivity;（4） high toxicity and serious pollution of the environment;（5） some of organometallic complexes are too expansive to use in wide application. Thus, how to design and synthesis of stable, highly catalytic efficient, cheaper and green organometallic Lewis acid is the key issue for the researchers.Based on the shortcomings of above organometallic Lewis acid chemistry, by incorporation of larger electronic-withdrawing group to metallocence and organoantimony central metal atoms, seven air-stable organometallic Lewis acid catalysts were synthesized and characterized by NMR, Elemental analysis, X-ray single crystal diffraction, TG-DSC technologies and acidity measurements, etc. to demonstrate their structure, composition and physical or chemical properties. Moreover, their applications in construction of carbon-carbon bond and carbon-heteroatom bond formation were also investigated. Some innovative results and conclusions were obtained as follows:（1） Cp₂TiCl₂（1a） was adopted as starting materials, b y incorporation of larger electronic-withdrawing and weaker lipophobicity perfluorobutane（bezene） group ion to replace the chloride in Cp₂TiCl₂, two air-stable and water-tolerant mononuclear titanocene perfluorobutane（bezene）sulfonate complexes Cp₂Ti（OH₂）₂（OSO₂C₄F₉）·H₂O·THF（2a·H₂O·THF）and Cp₂Ti（OH）₂₂（OSO）₂C₆F₅)（3a） were synthesized. They were stable in the open air for three months and remain as yellow powders, and their structures had no the change. By measurements of TG-DSC, conductivity, solubility and acidity, the results showed that two complexes have high thermostability and high solubility in polar organic solvent and strong acidity, which was stronger than that of Sc（OTf）₃. Based on their excellent properties, we investigated their catalytic activities by carbon-carbon bond formation reaction, such as the Strecker reaction, Mannich reaction, Mukaiyama-aldol reaction, allylation, Friedel-Crafts acylation and aza-Friedel-Crafts reaction. The results showed that these complexes had high catalytic activities for above reaction. In addition, two catalysts could be reused more five times.（2） Cp₂ZrCl₂（1b） was adopted as starting materials, b y incorporation of larger electronic-withdrawing perfluorobutane group ion to replace the chloride in Cp₂ZrCl₂, an air-stable and water-tolerant zirconocene complex Cp₂Zr（H₂O）₂（OSO₂C₄F₉）₂（2b） was synthesized. It was stable in the open air for a year and remains as white powders, and the structure had not changed. The complex has high thermostability and high solubility in polar organic solvent and strong acidity. Based on Cp₂Zr（H₂O）₂（OSO₂C₄F₉）₂（2b）, we developed a versatile and green method for synthesis of α-amino phosphonate by the reaction of aldehydes/ketones, amines and diethyl phosphate. Moreover, the complex could be applied for synthesis of Nheterocyclic compounds, such as benzimidazoles, benzodiazepines, dihydropyrimidinones and dihydropyridines. The complex showed high catalytic activity for these reaction. In addition, the catalyst could be reused more than five times.（3） Cp₂HfCl₂（1b） was adopted as starting materials, by incorporation of larger electronic-withdrawing perfluorobutane（bezene） group ion to place the chloride in Cp₂HfCl₂, two air-stable and water-tolerant binuclear hafnocene perfluorobutane（bezene）sulfonate complexes [{CpHf（OH₂）3}₂（μ₂-OH）₂][OSO₂C₄F9]₄·4H₂O·2THF（2c·4H₂O·2THF） and [{Cp Hf（OH2₃}）2（μ）2-OH)₂] [OSO₂C)₆F₅]₄·6H₂O（3c·6H₂O） were synthesized. The single crystal X-ray analysis showed the anions were packed around the complex cation in such a way that their oxygen atoms point towards the H₂O ligands. The perfluoroalkyl group sides of the anion, on the other hand, were clustered together to form the hydrophobic domains. Two complexes have high air-stability, and high thermostability and high solubility in polar organic solvent and strong acidity. we investigated their catalytic activities by carbon-carbon bond formation reaction, such as the Mukaiyama-aldol reaction, Mukaiyama-Michael addition reaction, Michael addition reaction and Mannich reaction. The results showed these complexes have high catalytic activities for above reaction. In addition, two catalysts c ould be reused more than five times.（4） Ph₃SbCl₂（1d） was adopted as starting materials, by incorporation of larger electronic-withdrawing perfluorobezene（octane） group ion to replace the chloride in Ph₃SbCl₂. Two air-stable and water-tolerant binuclear triphenylantimony perfluorobezene（octane）sulfonate complexes [（Ph₃Sb）₂O]（OSO₂C₆F₅）₂（2d） and [（Ph₃SbOH₂）₂O]+ [OSO₂C₈F₁₇]-2（3d） were synthesized. X-ray single crystal diffraction showed the complex 2d was covalent, and 3d was ionic. Two complexes have high air-stability, and high thermostability and high solubility in polar organic solvent and strong acidity. Moreover, these complexes showed high catalytic act ivity for the Michael addition and allylation. In addition, two catalysts can be reused more than five times.（5） A highly efficient and regioselective synthesis of ketones from a wide range of alkynes was described in silver-containing aqueous emulsion, which was self-assembled by silver perfluorooctanesulfonate, perfluorooctanesulfonic acid and water. The reaction was conducted under convenient conditions with broad substrate scope, including a variety of aromatic and aliphatic terminal alkynes and intern al alkynes. Furthermore, the air- and light-stable silver catalytic microemulsion could be reused for 4 times with minimal change in catalytic efficiency. Based on silver-containing microemulsion as a high-efficient and recyclable catalytic system for hydration of alkynes, it should find broad catalytic applications in organic synthesis...