The Cobalt cyclo-P4 Sandwich Complex and Its Role in the Formation of Polyphosphorus Compounds.

Abstract

A synthetic approach to the sandwich complex [Cp′′′Co(η4‐P4)] (2) containing a cyclo‐P4 ligand as an end‐deck was developed. Complex 2 is the missing homologue in the series of first‐row cyclo‐Pn sandwich complexes, and shows a unique tendency to dimerize in solution to form two isomeric P8 complexes [(Cp′′′Co)2(μ,η4:η2:η1‐P8)] (3 and 4). Reactivity studies indicate that 2 and 3 react with further [Cp′′′Co] fragments to give [(Cp′′′Co)2(μ,η2:η2‐P2)2] (5) and [(Cp′′′Co)3P8] (6), respectively. Furthermore, complexes 2, 3, and 4 thermally decompose forming 5, 6, and the P12 complex [(Cp′′′Co)3P12] (7). DFT calculations on the P4 activation process suggest a η3‐P4 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.