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(SiMe(3))(3)] (1) the synthesis of [{Fe(CO)(4)}(η(2)‐As(2)H(2))] (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)}(η(2)‐As(2)D(2))] (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)(4)AsHW(CO)(5)](2) (3) and [{Fe(CO)(4)}(2)AsH{Cr(CO)(5)}] (4), respectively.