Tetrahydrofuran-Mediated Stereoselective Radical C-C Bond Formation in Dicobalthexacarbonyl-Propargyl Complexes
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- 作者：Gagik G. Melikyan ; Ferdinand Villena ; Arthur Florut ; Steve Sepanian ; Hagop Sarkissian ; Aaron Rowe ; Pogban Toure ; Dutt Mehta ; Nolan Christian ; Steven Myer ; David Miller ; Stephanie Scanlon ; Maria Porazi
- 刊名：Organometallics
- 出版年：2006
- 出版时间：September 11, 2006
- 年：2006
- 卷：25
- 期：19
- 页码：4680 - 4690
- 全文大小：173K
- 年卷期：v.25,no.19(September 11, 2006)
- ISSN：1520-6041
文摘
An extensive study on the mechanism of novel tetrahydrofuran (THF)-mediated coupling of Co2(CO)6-complexed propargyl alcohols and cations was carried out. On the basis of the stoichiometry ofthe process, the measurement of the kinetic isotope effect (KIE) in the competitive and noncompetitivesettings (THF-d0 and THF-d8), ligand substitution experiments with 13CO, kinetic studies with modelcompounds-Co2(CO)6-complexed 1-phenyl-2-propyne (6), tetrahydrothiophene, cobalt-alkyne anchoredtetrahydropyran (THP, 21)-and ab initio calculations, the mechanism of the reaction was proposed. Itincludes a reversible coordination of two THF molecules with an 
-cationic center in a 
-bonded propargylmoiety, followed by a single-electron transfer from the THF-sandwiched cobalt complex toward anelectron-deficient propargyl cation. Although used in a 2-fold excess, THF acts as a catalyst, altering,both electronically and structurally, the requisite Co2(CO)6-complexed cations and breaking away fromthe organometallic scaffold, upon radical generation, in a chemically unchanged form. By triggeringdisproportionation between cobalt-complexed propargyl cations, THF acts in an unusual capacity of aradical mediator, previously being known in organic chemistry as a Lewis donor and donor of H atomsand hydride ions. The novel process that provides a facile entry to d,l-3,4-diphenyl-1,5-hexadiyne can beexpanded toward stereo-, chemo-, and regioselective synthesis of polysubstituted d,l-3,4-diaryl-1,5-alkadiynes otherwise hardly accessible.
-cationic center in a -bonded propargylmoiety, followed by a single-electron transfer from the THF-sandwiched cobalt complex toward anelectron-deficient propargyl cation. Although used in a 2-fold excess, THF acts as a catalyst, altering,both electronically and structurally, the requisite Co2(CO)6-complexed cations and breaking away fromthe organometallic scaffold, upon radical generation, in a chemically unchanged form. By triggeringdisproportionation between cobalt-complexed propargyl cations, THF acts in an unusual capacity of aradical mediator, previously being known in organic chemistry as a Lewis donor and donor of H atomsand hydride ions. The novel process that provides a facile entry to d,l-3,4-diphenyl-1,5-hexadiyne can beexpanded toward stereo-, chemo-, and regioselective synthesis of polysubstituted d,l-3,4-diaryl-1,5-alkadiynes otherwise hardly accessible.