Complexation of 1,3-Dihydro-l.3-diborapentafulvene Derivatives with Fe(C0)3 Fragments: Syntheses, Crystal and Electronic Structure of p-(q4: ~5-1.3-Dihydr~-l,3-diborapentafulvene)-bis(tricarbonyliron) Complexes Reactions of the 1,3-diborapentafulvene derivatives 1 a -c B,C = C unit. The latter resembles the interaction of Fe(CO), with (CO),Fe(C,H,,), lead to the violet dinuclear complexes with trimethylenernethane. An MO calculation indicates that 3a ~ c, which possess a slipped triple-decker structure. The X-the formation of 3 occurs by distortion of 1 . Fe(C0)3; the slipray structure analyses of 3b,c reveal that one Fe(C0)3 group page of Fe(C0)3 from $ to q4 bonding is followed by q5 cois pentahapto-coordinated to the 1,3-diborole frame of ordination of the second Fe(C0)3 group. CzBzC = C, whereas the other interacts with the Y-shaped Die 1,3-Dihydro-3,3-diborapentafulven-Derivate la'*2) 1 b3) und lc4) wirken mittels der endo-und exocyclischen Doppelbindung als 4-e-Donoren in Metallkomplexen. Durch Umsetzung von la,c rnit (C0)3Fe(CsH14)2 im Molverhaltnis l : l entstehen die Tricarbonyleisenkomplexe 2a2), 2c4', deren exocyclische C6-Atome der C = C-Doppelbindung stark entschirmt sind (I3C-NMR 2a: 6 = 230.5, 2c: