Observations on reaction pathways of dicobalt octacarbonyl with alkynyl amines

Treatments of a bis(diphenylphosphino)methylene (dppm) bridged dicobalt complex, Co2(CO)6(dppm) (4), with propargylamine and 4-ethynylaniline at 25 °C for 24 h gave [(dppm)Co2(CO)4(μ-HCtriple bond; length of mdashCCH2NH2)] (5) and [(dppm)Co2(CO)4(μ-HCtriple bond; length of mdashCC6H4NH2)] (6), respectively. Interestingly, only alkynyl amines bridged dicobalt complexes were obtained rather than the previously observed coupling products. The results are in acceptance with the proposed mechanism which describes the formation of the coupling products {[Co2(CO)6(μ-HCtriple bond; length of mdashC–)]–CH2NH}2Cdouble bond; length as m-dashO (1) and {[Co2(CO)6(μ-HCtriple bond; length of mdashC–)]–C6H4Ndouble bond; length as m-dash}2 (2) from the reaction of Co2(CO)8 with propargylamine and 4-ethynylaniline, respectively. Similar results were attained for the reactions of 4 with propioamide and 1-ethynylcyclohexylamine at 25 °C for 24 h which yielded [(dppm)Co2(CO)4(μ-HCtriple bond; length of mdashCC(double bond; length as m-dashO)NH2)] (7) and [(dppm)Co2(CO)4(μ-HCtriple bond; length of mdashCC6H10NH2)] (8), respectively. Reaction of 1-ethynylcyclohexylamine with one molar equivalent of Co2(CO)8 in THF at 25 °C for 15 min gave an alkyne bridged dicobalt complex, [Co2(CO)6(μ-HCtriple bond; length of mdashCC6H10NH2)] (9). Direct treatment of 3-ethynlaniline with one molar equivalent of Co2(CO)8 in THF at 25 °C for 1 h gave an alkyne bridged dicobalt complex, [Co2(CO)6(μ-HCtriple bond; length of mdashCC6H4NH2)] (11) and an azobenzene derivative, {[Co2(CO)6(μ-HCtriple bond; length of mdashC)]C6H4Ndouble bond; length as m-dash}2 (10). Further treatments of 8, 9, and 11 with one molar equivalent of Sanger’s reagent, 2,4-dinitrofluorobenzene, in THF at25 °C for 48 h gave [(dppm)Co2(CO)4(μ-HCtriple bond; length of mdashCC6H10NHC6H3(NO2)2)] (13), [Co2(CO)6(μ-HCtriple bond; length of mdashCC6H10NHC6H3(NO2)2)] (14), and [Co2(CO)6(μ-HCtriple bond; length of mdashCC6H4NHC6H3(NO2)2)] (15), respectively.