The Parent Diarsene HAs=AsH as Side‐on Bound Ligand in an Iron Carbonyl Complex

The terminal diarsene HAs=AsH ligand attracts special interest concerning its bonding relation in comparison to its isolable relative, ethene. Herein, by the methanolysis of {Fe(CO)₄}As(SiMe₃)₃] ( 1 ) the synthesis of {Fe(CO)₄}(η²‐As₂H₂)] ( 2 ) is reported, containing a parent diarsene as unprecedented side‐on coordinated ligand. Following this synthetic route, also the D‐labeled complex {Fe(CO)₄}(η²‐As₂D₂)] ( 2D ) could be isolated. The electronic structure and bonding situation of 2 was elucidated by DFT calculations revealing that 2 is best described as an olefin‐like complex. Moreover, the reactivity of 2 towards the Lewis acids {M(CO)₅}(thf)] (M=Cr, W) was investigated, leading to the complexes Fe(CO)₄AsHW(CO)₅]₂ ( 3 ) and {Fe(CO)₄}₂AsH{Cr(CO)₅}] ( 4 ), respectively.