CCC型钳形铑配合物的反应性

The reactivities of novel rhodium CCC-type pincer complexes

钳形金属配合物因其独特的结构、性质和应用引起了化学家的广泛关注.然而该类配合物大部分都是以2~3个杂原子(基团)与金属原子配位.只有极少数例子同时具有3个碳原子与金属配位(CCC钳形金属配合物).这是由于该类配合物具有3个金属-碳共价键,通常会具有较高的反应活性.我们对一类新颖的CCC型钳形铑配合物:铑碳龙配合物的反应性开展了深入的研究,发现这类铑配合物能与二氧化锰反应,得到氧化产物和开环产物;也能与叠氮三甲基硅烷和二苯基膦发生亲核反应,实现了氮和磷对铑卡宾的插入反应,分别得到氮、磷插入到金属杂环中的扩环产物:CCN型和CCP型铑配合物.这些研究拓展了碳基钳形金属配合物(以碳为主要配位原子的螯合物)的反应化学,并为碳基铑配合物在催化上的应用打下基础.

Pincer complexes have attracted chemists’attention because of their unique structures,properties,and catalytic applications.Among these pincer complexes,most of them are based on heteroatoms,such as nitrogen,oxygen,phosphorus,sulfur and so on.Few examples that three carbon atoms coordinate to metal(CCC-type pincer)have been reported due to their highly active reactivities.Recently,our group reported a series of novel metal bridgehead fused-ring organometallics,named carbolong complexes.Carbolong complexes are special pincer complexes which are metal bridgehead polycyclic frameworks featuring a conjugate carbon chain(at least 7 carbons and we call these carbon chains carbolong ligand)coordinated to a metal atom via at least three metal-carbonσbonds and note that the d orbital of metal atom in cooperation withπconjugation is a particular characteristic in carbolong complexes.In cooperation with metal,carbolong complexes exhibit numerous distinctive properties different form typical aromatics,such as mixed aromaticity,broad absorption from the UV to the visible and near-infrared region,and excellent photothermal effects,indicating their potential applications in materials science and biomedicine.The reported carbolong complexes were mostly based on osmium,limited their application development.Thanks to the efficient method we developed very recently,the rhodium carbolong complexes,rhodapentalenes were synthesized successfully,which displayed unique intrinsic aromaticity and diverse reactivities.As a novel CCC-type rhodium pincer complexes,the reactivities of rhodapentalenes were rarely investigated.In this report,we investigated the reactivities of two novel rhodium CCC-type pincer complexes.The results showed rhodium carbolong complex 1 could be oxidized by activated Mn O2 and led to complexes 3 and 4,which were confirmed by NMR spectra and single crystal X-ray analysis.Complex 3 was an oxidation product and originated from the oxidation of hydroxy in CCC-type pincer ligand of complex1.However,complex 4 formed through an acid promoted ring-opening reaction.Meanwhile,acid promoted ring-opening reaction could also occur in complex 3,leading to complex 5.Whereas the cis-1,3-diene moiety in complex 5 was unstable in thermodynamics,thus it would isomerize to trans-1,3-diene and transformed to complex 6,which was obtained from the crystallization process.Due to the special structure of complex 5,the isomerization could occur easily by proton migration rather than configuration inversion of sp2 carbon.In addition,rhodapentalene 2 could react with azidotrimethylsilane,leading to CCN-type pincer complex 7 at ambient conditions.In this reaction,he ring expansion reaction of rhodapentalene occurred by a nitrogen insertion,as a result,the insertion of nitrogen to rhodium carbene by azidotrimethylsilane and the transformation of a CCC-pincer complex to a CCN-pincer complex is realized for the first time.Besides,rhodapentalene 2 could react with diphenylphosphine and resulted in CCP-type pincer complex 8.Similar ring expansion reaction of rhodapentalene took place by inserting a diphenylphosphine group.In particular,the sp2 carbon coordinated to rhodium in the other five-membered ring was protonated to sp3 carbon.Further,deuterium labeling reactions were preformed and revealed that the proton originated from diphenylphosphine.Thus,we proposed a proton migration mechanism through a metal-hydride intermediate in this reaction.The reaction realized the insertion of phosphine to rhodium carbene by diphenylphosphine and the transformation of a CCC-pincer complex to a CCP-pincer complex for the first time.The dearomatization reactions of rhodapentalene were realized by this facile method.In summary,these results revealed the diverse and unique reactivities of CCC-type rhodium pincer complexes and offered a convenient method to modify offered CCC-type rhodium pincer complexes.It also laid a good foundation for developing new rhodium pincer catalyzed reactions.