Selective Formation and Unusual Reactivity of Tetraarsabicyclo[1.1.0]butane Complexes

The selective formation of the dinuclear butterfly complexes [{Cp′′′Fe(CO) 2 } 2 (μ,η 1:1 ‐E 4 )] (E=P ( 1 a ), As ( 1 b )) and [{Cp*Cr(CO) 3 } 2 (μ,η 1:1 ‐E 4 )] (E=P ( 2 a ), As ( 2 b )) as new representatives of this rare class of compounds was found by reaction of E 4 with the corresponding dimeric carbonyl complexes. Complexes 1 b and 2 b are the first As 4 butterfly compounds with a bridging coordination mode. Moreover, first studies regarding the reactivity of 1 b and 2 b are presented, revealing the formation of the unprecedented As 8 cuneane complexes [{Cp′′′Fe(CO) 2 } 2 {Cp′′′Fe(CO)} 2 (μ 4 ,η 1:1:2:2 ‐As 8 )] ( 3 b ) and [{Cp*Cr(CO) 3 } 4 (μ 4 ,η 1:1:1:1 ‐As 8 )] ( 4 ). The compounds are fully characterized by NMR and IR spectroscopy as well as by X‐ray structure analysis. In addition, DFT calculations give insight into the transformation pathway from the E 4 butterfly to the corresponding cuneane structural motif.