The Cobalt cyclo‐P(4) Sandwich Complex and Its Role in the Formation of Polyphosphorus Compounds

A synthetic approach to the sandwich complex [Cp′′′Co(η(4)‐P(4))] (2) containing a cyclo‐P(4) ligand as an end‐deck was developed. Complex 2 is the missing homologue in the series of first‐row cyclo‐P(n) sandwich complexes, and shows a unique tendency to dimerize in solution to form two isomeric P(8) complexes [(Cp′′′Co)(2)(μ,η(4):η(2):η(1)‐P(8))] (3 and 4). Reactivity studies indicate that 2 and 3 react with further [Cp′′′Co] fragments to give [(Cp′′′Co)(2)(μ,η(2):η(2)‐P(2))(2)] (5) and [(Cp′′′Co)(3)P(8)] (6), respectively. Furthermore, complexes 2, 3, and 4 thermally decompose forming 5, 6, and the P(12) complex [(Cp′′′Co)(3)P(12)] (7). DFT calculations on the P(4) activation process suggest a η(3)‐P(4) Co complex as the key intermediate in the synthesis of 2 as well as in the formation of larger polyphosphorus complexes via a unique oligomerization pathway.