Transition Metal‐Substituted Arsaalkenes, II. Synthesis, Structure and Reactivity of the Arsaalkenes RAs=C(NMe 2 ) 2 [R = Me 3 Si, (η 5 ‐C 5 Me 5 )(CO) 2 Fe] and the 1,2‐Dihydroarsete (η 5 ‐C 5 Me 5 )(CO) 2 ‐Fe

Reaction of equimolar amounts of thiuronium salt [(Me 2 N) 2 C‐SMe]I ( 1 , with LiAs(SiMe 3 ) 2 · 2 THF ( 2 ) afforded arsaalkene Me 3 SiAs=C(NMe 2 ) 2 ( 3 ). Combination of 3 with (η 5 ‐C 5 Me 5 )(CO) 2 FeBr led to the formation of (η 5 ‐C 5 Me 5 )(CO) 2 ‐FeAs=C(NMe 2 ) 2 ( 4 ). Reaction of the latter with dimethyl fumarate gave the 1,2‐dihydroarsete (η 5 ‐C 5 Me 5 )(CO) 2 ‐Fe ( 6 ). Compounds 3, 4 , and 6 were characterized by means of spectroscopy (IR, 1 H, 13 C{ 1 H}, 29 Si{ 1 H} NMR and mass spectrometry). The molecular structures of 4 and 6 were determined by X‐ray diffraction analysis.