Ring Expansions of Nonpolar Polyphosphorus Rings

The reaction of the phosphinidene complex [Cp*P{W(CO) 5 } 2 ] ( 1 a ) (Cp*=C 5 Me 5 ) with the anionic cyclo ‐P n ligand complex [(η 3 ‐P 3 )Nb(ODipp) 3 ] − ( 2 , Dipp=2,6‐diisopropylphenyl) resulted in the formation of [{W(CO) 5 } 2 {μ 3 ,η 3:1:1 ‐P 4 Cp*}Nb(ODipp) 3 ] − ( 3 ), which represents an unprecedented example of a ring expansion of a polyphosphorus‐ligand complex initiated by a phosphinidene complex. Furthermore, the reaction of the pnictinidene complexes [Cp*E{W(CO) 5 } 2 ] (E=P:  1 a , As:  1 b ) with the neutral complex [Cp′′′Co(η 4 ‐P 4 )] (Cp′′′=1,2,4‐ t Bu 3 C 5 H 2 ) led to a cyclo ‐P 4 E ring (E=P, As) through the insertion of the pentel atom into the cyclo ‐P 4 ligand. Starting from 1 a , the two isomers [Cp′′′Co(μ 3 ,η 4:1:1 ‐P 5 Cp*){W(CO) 5 } 2 ] ( 5 a , b ), and from 1 b , the three isomers [Cp′′′Co(μ 3 ,η 4:1:1 ‐AsP 4 Cp*){W(CO) 5 } 2 ] ( 6 a – c ) with unprecedented cyclo ‐P 4 E ligands (E=P, As) were isolated. The complexes 6 a – c represent unique examples of ring expansions which lead to new mixed five‐membered cyclo ‐P 4 As ligands. The possible reaction pathways for the formation of 5 a , b and 6 a – c were investigated by a combination of temperature‐dependent 31 P{ 1 H} NMR studies and DFT calculations.