Reactions between the 1,3-diphosphete complex [Cp'''Co(η⁴ -P₂ C₂ tBu₂ )] (1) and Ag[Al{OC(CF₃ )₃ }₄ ] (Ag[pftb]) were carried out under different conditions. In CH₂ Cl₂ , the unprecedented 1,2-diphosphete isomerization product [Ag₂ {Cp'''Co(μ,η⁴ :η¹ :η¹ -1,2-P₂ C₂ tBu₂ )}₂ {Cp'''Co(μ,η⁴ :η¹ -1,2-P₂ C₂ tBu₂ )}₂ ]⋅2[pftb] (2) could be isolated. In diffusion experiments of 1 in n-hexane with Ag[pftb] in CH₂ Cl₂ , the triphosphacobaltocenium complex [Cp'''Co(η⁵ -P₃ C₂ tBu₂ )][pftb] (4) and the phosphirenylium complex [Cp'''Co(η³ -PC₂ tBu₂ )][pftb] (5) were obtained, showing a ring expansion and a ring contraction, respectively, under mild conditions. Moreover, addition of pyridine to the Ag complex 2 led to the new 1,2-diphosphete complex [Cp'''Co(η⁴ -1,2-P₂ C₂ tBu₂ )] (3). Compound 3 is also formed by thermolysis of 1, making it a promising method for this type of isomerization. 1,2-Diphosphete complexes like 3 are thermodynamically more stable but also synthetically more elusive than their 1,3-isomer counterparts.

Veronika Heinl

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