Wikipedia
Tetramesityldiiron
Tetramesityldiiron is an organoiron compound with the formula Fe(CH(CH)). It is a red, air-sensitive solid that is used as a precursor to other iron complexes. It adopts a centrosymmetric structure. The complex is a Lewis acid, forming monomeric adducts, e.g. Fe(CH(CH)) pyridine. The complex is prepared by treating ferrous halides with the Grignard reagent formed from mesityl bromide:
2 FeCl + 4 BrMgCH(CH) → Fe(CH(CH)) + 2 MgBr