Development of Enantioselective Carboalumination of Alkenes and Alkynes Catalyzed by Rare-Erath Metal Catalysts

2021 Fiscal Year Annual Research Report

• Project/Area Number: 21F21334
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: 侯 召民 国立研究開発法人理化学研究所, 開拓研究本部, 主任研究員 (10261158)
• Co-Investigator(Kenkyū-buntansha): WANG HAO 国立研究開発法人理化学研究所, 開拓研究本部, 外国人特別研究員
• Project Period (FY): 2021-11-18 – 2024-03-31
• Keywords: rare-earth catalysts / carboalumination / asymmetric synthesis / polymerization

Outline of Annual Research Achievements

Organoaluminums are an important class of organometallics reagents, especially enantio-enriched organoaluminums have many potential applications. Thus, the development of enantioselective carboalumination of alkenes and alkynes is interesting. Our purpose is to explore the use of chiral half-sandwich rare-earth complexes to achieve regio- and enantioselective carboaluminations. This work involves the following subjects: (1) Design and synthesis of new chiral half-sandwich rare-earth catalysts. (2) Rare-earth-catalyzed regio- and enantioselective carboalumination of alkenes. Moreover, (3) Investigating hetero-atom-assisted olefin polymerizations involving a closely related reaction mechanism to that of the present carboalumination reactions is also our research interests.
At the first stage, a series of racemic half-sandwich rare-earth dialkyl complexes were synthesized in this fiscal year. As we have previously reported, these catalysts show unique reactivities towards terminal olefins bearing a tethered heteroatom group, not only in carboalumination but also in some other reactions, such as hetero-atom-assisted olefin polymerizations. Thus, we examined a new type olefin polymerizations involving a heteroatom assisted ring-closure process before starting the studies on the enantioselective carboalumination. We have synthesized several monomer substrates bearing two terminal olefin units and one oxygen atom connected by several different (in structure, length, etc) tethers. Currently, the polymerization of these substrates is being examined under various conditions.

Current Status of Research Progress

3: Progress in research has been slightly delayed.

Reason

Initially, the experimental works for this research subject were scheduled to begin in November 2021 in our laboratory at RIKEN. However, due to restrictions on entry into Japan imposed by the Japanese government for preventing the spread of the COVID-19 infection, the start of our experiments in RIKEN has been delayed by a few months, and the progress of the research has been delayed accordingly. For these reasons, this year, we have only synthesized some fundamental rare-earth catalysts and olefin substrates necessary for this research and only conducted some preliminary experiments. As a result, we could not obtain significant results. We will carry out this research as quickly as possible in the next fiscal year based on our initial plans.

Strategy for Future Research Activity

A series of chiral half-sandwich rare-earth complexes with chiral Cp ligands will be synthesized by the reactions of trialkyl rare-earth complexes and neutral chiral cyclopentadiene (Cp) ligands. These types of catalysts have previously been prepared in our group, but several new types of chiral Cp ligands with 1,1-spirobiindane, ferrocene, and planar backbones will be newly designed. Then, based on our previous work, methylaluminations of silyloxy-substituted alkenes by these new chiral half-sandwich rare-earth catalysts will be explored, which can afford the enantioenriched alkylalane species with high enantioselectivity. The resulting alkylalanes can be trapped by electrophiles such as iodine, formaldehyde, and iodobenzene by meansof Negishi cross-coupling reactions or by Cu-catalyzed allyllation to afford stereodefined tetrasubstituted alkenes. Meanwhile, novel heteroatom-assisted olefin polymerization will be investigated furthermore with newly designed and synthesized monomers.