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.
Keywords: cobalt; diphosphete complexes; phosphaalkynes; silver; weakly coordinating anions.
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