基于过渡金属亚乙烯基中间体的炔烃转化

过渡金属亚乙烯基LnM=C=CRR’是一类特殊的不饱和卡宾配合物，具有和卡宾相似的化学性质，又因含有额外的碳-碳双键而表现出比卡宾配合物更丰富的反应性，而且也易于通过端基炔与过渡金属反应得到，因此，在包含端基炔的催化反应中有着重要应用。然而也存在一些需解决的问题，例如，目前端基炔醇、炔胺内环异构化的研究多数还主要集中于五、六元含氧或含氮杂环的合成，适用于中环杂环合成的催化体系还很缺乏。另外，虽然最近发现的非末端炔烃也可通过1,2-碳迁移重排成亚乙烯基为发展这类配合物的催化性质提供了新契机，但这些研究还刚起步。本项目拟针对这些问题开展基于过渡金属亚乙烯基中间体的炔烃转化研究，包括: 合成新的亚乙烯基配合物并考察其反应性质；发展炔醇、炔胺经亚乙烯基中间体的环异构化催化反应；发展双碳取代基的非末端炔通过1,2-碳迁移异构化成亚乙烯基的反应；探索亚乙烯基金属-碳双键的新反应性质，开发新催化反应。

Transition-metal carbene complexes LnM=CRR’ are an important class of organometallic complexes, which display rich chemical and catalytic properties. Closely related to carbene complexes are metal vinylidene complexes (LnM=C=CRR’). These complexes are interesting because they are expected to have even richer chemistry due to the presence of additionl C=C functionalities. In addition, as they can be easily obtained from the reactions of terminal alkynes with coordinatively unsaturated complexes or complexes with labile ligands, they can mediate organometallic and catalytic reactions involving terminal alkynes. Therefore, the development of catalytic reactions through vinylidene intermediates is attracting considerable current interest. In fact, many catalytic reactions along this line have been developed over the past decades. However, there are also several previously unresolved problems. For example, there have been growing efforts in the endo cycloisomerization of alkynyl alcohols or alkynamine to endo-cyclic enol ethers or cyclic enamines through metal vinylidene intermediates. However, it appears that most of the studies so far mainly focus on the methodologies for the synthesis of five- and six-membered oxacycles and azacycles. In contrast, the development of new efficient catalysts for the selective synthesis of the larger seven- and eight-membered heterocycles remains a challenging objective. In addition, the recent discovery on the rearrangement of carbon-disubstitued internal alkyne into vinylidene via 1,2-carbon migration on the transition-metal coordination sphere provdied a new oppotunity for the developement of organometallic chemistry of vinylidene and its application in catalytic reactions. However, these research are still rather underdeveloped. The studies on the reactivities of metal vinylidene species (either the preformed complexes or the species in situ generated from the reaction) may help to develop new catalytic reactions. This proposal mainly focuses on the chemistry and catalytic properties of vinylidene complexes. The main objectives of the proposed research are (i) to prepare new metal complexes and investigate their stoichiometric reactivity towards alkynes (including terminal or internal alkynes) so that new vinylidene complexes or the new metal complexes formed via vinylidene intermediate can be synthesized, (ii) to develope new efficient catalysts for the selective synthesis of medium size seven- and eight-membered heterocycles via cycloisomerization of alkynols or alkynamine/ynamides via vinylidene intermediates, (iii) to unravel the factors that affect the isomerization of carbon-disubstitued internal alkyne into vinylidene via 1,2-carbon migration; (iv) to explore new reactivity of vinylidene complexes and develope new catalytic reactions.