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 -C5 H2t Bu3 ) 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(CH3 CN)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 )}2 Fe][PF6 ]2 (3). Complex 3 represents the first fully characterized "carbon-free" sandwich complex containing cyclo-P4 R2 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.