Construction of a low-valent thiolate-bridged dicobalt platform and its reactivity toward hydrogen activation and evolution

Low-valence transition metallic complexes have drawn longstanding attention due to their high reactivity toward catalytic transformation of various small molecules.Among these known complexes,the low-valence metal centres are commonly stabilized by neutral bulky ligands with strong electron-donating capacity.However,low-valence bimetallic complexes supported by anionic sulfur and cyclopentadienyl ligands are still difficult to obtain in high isolated yield.Herein,we report the synthesis and characteri-zation of two scarce thiolate-bridged Co^(I)Co^(II)and Co^(I)Co^(I)complexes bearing sterically demanding ligands through two stepwise one-electron reduction processes.Interestingly,the Co^(I)Co^(II)complex can facilely promote the homolytic cleavage of dihydrogen across the short Co−Co metallic bond to give a Co^(II)Co III dihydride bridged complex,which is capable of serving as a competent hydrogen atom transfer agent.Moreover,the anionic Co^(I)Co^(I)complex can trigger a stepwise hydrogen generation cycle involving several isolated and structurally well-characterized intermediates.

Synthesis,characterization and reactivity of thiolate-bridged cobalt-iron and ruthenium-iron complexes

Thiolate-bridged hetero-bimetallic complexes[Cp^(*)M(MeCN)N_(2)S_(2)FeCl][PF_(6)](2,M=Ru;3,M=Co,Cp^(*)=η^(5)-C_(5)Me_(5),N_(2)S_(2)=N,N'-dimethyl-3,6-diazanonane-1,8-dithiolate)were prepared by self-assembly of dimer[N_(2)S_(2)Fe]2 with mononuclear precursor[Cp^(*)Ru(MeCN)_(3)][PF_(6)]or[Cp^(*)Co(MeCN)_(3)][PF_(6)]_(2)in the presence of CHCl_(3)as a chloride donor.Complexes 2 and 3 exhibit obviously different redox behaviors investigated by cyclic voltammetry and spin density distributions supported by DFT calculations.Notably,iron-cobalt complex 3 possesses versatile reactivities that cannot be achieved for complex 2.In the presence of CoCp_(2),complex 3 can undergo one-electron reduction to generate a stable formally Co^(II)Fe^(II)complex[Cp^(*)CoN_(2)S_(2)FeCl](4).Besides,the terminal chloride on the iron center in 3 can be removed by dehalogenation agent AgPF_(6)or exchanged with azide to afford the corresponding complexes[Cp^(*)Co(MeCN)N_(2)S_(2)Fe(MeCN)][PF_(6)]_(2)(5)and[Cp^(*)Co(MeCN)N_(2)S_(2)Fe(N_(3))][PF_(6)](6).In addition,complexes 2,3 and 4 show distinct catalytic reactivity toward the disproportionation of hydrazine into ammonia.These results may be helpful to understand the vital role of the heterometal in some catalytic transformations promoted by heteromultinuclear complexes.