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

The versatile coordination behavior of the P4 butterfly complex [{Cp′′′Fe(CO)2}2(μ,η1:1-P4)] (1, Cp′′′=η5-C5H2tBu3) towards different iron(II) compounds is presented. The reaction of 1 with [FeBr2⋅dme] (dme=dimethoxyethane) leads to the chelate complex [{Cp′′′Fe(CO)2}2(μ3,η1:1:2-P4){FeBr2}] (2), whereas, in the reaction with [Fe(CH3CN)6][PF6]2, an unprecedented rearrangement of the P4 butterfly structural motif leads to the cyclo-P4 moiety in {(Cp′′′Fe(CO)2)2(μ3,η1:1:4-P4)}2Fe][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(μ3,η1:1:2-P4){Cp′′′Fe(CO)}][PF6] (4) and [{Cp′′′Fe(CO)2}2(μ3,η1:1:4-P4){Cp′′′Fe}][PF6] (5), give insight into the stepwise activation of the P4 butterfly moiety in 1.