Rearrangement of a P4 Butterfly Complex-The Formation of a Homoleptic Phosphorus-Iron Sandwich Complex

The versatile coordination behavior of the P-4 butterfly complex [{Cp' Fe(CO)(2)}(2)(mu,eta(1:1)-P-4)] (1, Cp'''=eta(5)-C(5)H(2)tBu(3)) towards different iron(II) compounds is presented. The reaction of 1 with [FeBr2 center dot dme] (dme = dimethoxyethane) leads to the chelate complex [{Cp''' Fe(CO)(2)}(2)(mu(3), eta(1:1:2)-P-4){FeBr2}] (2), whereas, in the reaction with [Fe(CH3CN)(6)][PF6](2), an unprecedented rearrangement of the P-4 butterfly structural motif leads to the cyclo-P-4 moiety in {(Cp'''Fe(CO)(2))(2)(mu(3),eta(1:1:4)-P-4)}(2)Fe][PF6](2) (3). Complex 3 represents the first fully characterized carbon-free sandwich complex containing cyclo-P4R2 ligands in a homoleptic-like iron-phosphorus-containing molecule. Alternatively, 2 can be transformed into 3 by halogen abstraction and subsequent coordination of 1. The additional isolated side products, [{Cp'''Fe(CO)(2)}(2)(mu(3),eta(1:1:2)-P-4){Cp'''Fe(CO)}][PF6] (4) and [{Cp'''Fe(CO)(2)}(2)(mu(3),eta(1:1:4)-P-4){Cp'''Fe}][PF6] (5), give insight into the stepwise activation of the P-4 butterfly moiety in 1.