The reactions of [Cp*Co(μ-Cl)]2 with various aryl
lithium reagents (ArLi) were performed with a view to access bridging
diaryl dicobalt(II) complexes. Treatment of [Cp*Co(μ-Cl)]2 with 1 equiv of ArLi provided bridging aryl Co(II) complexes
with the formula [(Cp*Co)2(μ-Cl)(μ-Ar)] (Ar = C6H5
–, 1; p-CH3C6H4
–, 2). With 2 equiv of C6H5Li or p-CH3C6H4Li, the reaction provided triple-decker dicobalt(I) complexes
[(Cp*Co)2-μ-(η4:η4-biphenyl)] (3) and [(Cp*Co)2-μ-(η4:η4-dimethyl-biphenyl)] (4).
The biphenyl ligands in 3 and 4 underwent
dissociation resulting in formation of the more stable triple-decker
tricobalt complexes [(Cp*Co)3-μ-(η4:η4:η4-biphenyl)] (5) and [(Cp*Co)3-μ-(η4:η4:η4-dimethyl-biphenyl)] (6),
respectively. The bridging diaryl complex [(Cp*Co)2(μ-η1:η1-Ar)2] was proposed as the
intermediate in the formation of triple-decker dicobalt(I) complexes
through the reductive coupling of the aryl ligand, because the diaryl
cobalt(II) complex[(Cp*Co)2-μ-(o-CH3C6H4)2] (7) is stabilized by increased steric hindrance at the o-position of the aryl ligand.
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