Metal-Induced B–H Activation in Three-Component Reactions: 16-Electron Complex CpCo(S2C2B10H10), Ethyl Diazoacetate, and Alkynes

The three-component reactions of the 16-electron half-sandwich complex CpCo(S2C2B10H10) (Cp = cyclopentadienyl) (1) with ethyl diazoacetate (EDA) and alkynes R1≡R2 (R1 = Ph, R2 = H; R1 = CO2Me, R2 = H; R1 = R2 = CO2Me; R1 = Fc, R2 = H) at ambient temperature lead to compounds CpCo(S2C2B10H9)(CH2CO2Et) (CHCO2Et)(R1═R2) (2–5), CpCo(S2C2B10H9)(CH2CO2Et)(R2–R1–CHCO2Et) (6–9), CpCo(S2C2B10H9)(CH2CO2Et)(CH(Ph)C═CHCO2Et) (10), and CpCo(S2C2B10H9)(CH2CO2Et)(CH(Fc)–CH–CCO2Et) (11). In 2–5, one alkyne is stereoselectively inserted into the Co–B bond, one EDA molecule is used to form a sulfide ylide, and the second EDA molecule is inserted into one Co–S bond to form a three-membered metallacyclic ring. At ambient temperature 2–5 undergo rearrangement to 6–9 through migratory insertion of the inserted EDA. Different from 2–5, in 10 phenylacetylene is inserted into the Co–B bond at the terminal carbon and the terminal carbon is coupled with one EDA to afford a six-membered metallacyclic ring with the C═O coordination ...