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

A synthetic approach to the sandwich complex [CpCo((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 [(CpCo)(2)(,(4):(2):(1)-P-8)] (3 and 4). Reactivity studies indicate that 2 and 3 react with further [CpCo] fragments to give [(CpCo)(2)(,(2):(2)-P-2)(2)] (5) and [(CpCo)(3)P-8] (6), respectively. Furthermore, complexes 2, 3, and 4 thermally decompose forming 5, 6, and the P-12 complex [(CpCo)(3)P-12] (7). DFT calculations on the P-4 activation process suggest a (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