Aminovinylboranes can act as h2 (via the C:C bond) and as h4 ligands (via C:C and B:N group) in iron carbonyl complexes. From bromo(dimethylamino)vinylborane and (dimethylamino)methylvinylborane and Fe2(CO)9 [h2-bromo(dimethylamino)vinylborane]tetracarbonyliron (I) and tetracarbonyl[h2-(dimethylamino)methylvinylborane]iron (II), resp., are formed in the absence of light. The h2 coordination via the C:C group in I is proved by an x-ray structure anal. The C2BN frame is trans-arranged. By the action of light, I and II are transferred into the very unstable tetrahapto complexes [h4-bromo(dimethylamino)vinylborane]tricarbonyliron and tricarbonyl[h4-(dimethylamino)methylvinylborane]iron, which can only be investigated in soln. Using tert-butyl(dimethylamino)vinylborane the reaction leads, even in the absence of light, directly to [h4-tert-butyl(dimethylamino)vinylborane)tricarbonyliron, a compd. likewise easily unstable. The transition of the h2 into the h4 complexes can be followed IR and 11B NMR spectroscopically.