Identification and characterization of intermediates in the formation of the cyclobutadiene linked dimeric cobalt sandwich compound [(𝜂5-RCp)Co(𝜂4-C4Ph3)]2 [R = H, CH3C(O)O]

Journal of Chemical Sciences

Anil J Elias1¹  Nem Singh¹ 

[1] Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India$$

关键词: Cyclobutadiene;    cobalt sandwich;    mechanism;    dimer;    unsymmetrical.;   

DOI  :  

来源: Indian Academy of Sciences

【 摘 要 】

The synthesis of novel cyclobutadiene linked dimers of [𝜂5-RCp]Co(𝜂4-C4Ph4) was reported recently from a three-component reaction of 1,4-diphenylbutadiyne, diphenylacetylene and [𝜂5-RCp]Co(PPh3)2 [R = H or MeOC(O)]. The chiral bis oxazoline derivative of this dimer was found to form cobalt oxazolinyl palladacycles which were excellent chiral catalysts for the Overman-Claisen rearrangement of trichloroacetimidates, similar to the well-known COP catalysts. In this paper, we report reactions carried out for identifying the intermediates in the formation of the dimeric sandwich compound {[𝜂5-MeOC(O)Cp]Co(𝜂4-C4Ph3)}2 (1). On varying the stoichiometric ratio of the reactants of the three component reaction, two new cobalt sandwich compounds [𝜂5-MeOC(O)Cp]Co[𝜂4-C4Ph3(C≡CPh)] (2) and [𝜂5-MeOC(O)Cp]Co[𝜂4-C4-Ph2(C≡CPh)2] (3) were found to form as viscous oily liquids. The identity of 2 was ascertained by oxidizing its alkyne moiety to yield crystalline [𝜂5-MeOC(O)Cp]Co{𝜂4-C4Ph3[C(O)-C(O)Ph]} (4) which was structurally characterized. Further, the role of phenylethynyl derived monomeric sandwich compound 2 as a precursor to the dimeric compound 1 was established by reacting 2 with diphenylacetylene and CpCo(COD) which yielded the first example of an unsymmetrical cyclobutadiene linked dimeric cobalt sandwich compound {𝜂5-[MeOC(O)Cp]Co(𝜂4-C4Ph3)}[(𝜂5-Cp)Co(𝜂4-C4Ph3)] (5) which was also structurally characterized.

【 授权许可】

Unknown