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The solution mixture of the dinitrogen complexes Fe(CO)2(PEt3)2(N2) (1a) and [Fe(CO)2(PEt3)2]2(μ-N2) (1b) reacts with methyl or ethyl haloacetates to yield the oxidative addition products Fe(CO)2(PEt3)2(X)CH2COOR (X = Cl, R = Me, 2a; X = Br, R = Me, 2b; X = I, R = Et, 2e). These complexes can be transformed in ether to carbonylhalo-bis(triethylphosphane)[1-((trimethylsilyl)oxy)-2-(alkoxycarbonyl)ethenyl]iron compounds (X = Cl, R = Me, 7a; X = Br, R = Me, 7b; X = I, R = Et, 7c) in the presence of LDA and subsequent trapping of the formed anions with Me3SiCl. When DBU is used as a base and 1 bar CO is applied with otherwise similar reaction conditions as before the transformations of 2a−c take the course of the formation of ester-functionalized ketene compounds E,Z-Fe(CO)2(PEt3)2{η²-(C,O)-[OCCH(COOR)]} (R = Me, 8a; R = Et, 8b) and of dicarbonyl(1-alkoxy-1,3-dioxopropen-3-yl)bis(triethylphosphane)iron derivatives (R = Me, 9a, R = Et, 9b). In the solid state only the Z form of complexes 8 is found. In a comparable manor as for the synthesis of compounds 2, it is possible to obtain Fe(CO)2(PEt3)2(X)(CH2R) (R = OMe, 10a; R = 1,3-dioxolan-2-yl, 10b; R = 2,4,10-trioxoadamantan-3-yl, 10c) species. While 10a does not react, the derivatives 10b,c are converted in the presence of DBU and CO to E,Z mixtures of ketene complexes Fe(CO)2(PEt3)2 [η²(C,O)-(COCHR)] (R = 1,3-dioxolan-2-yl, 13b^E,Z; R = 2,4,10-trioxoadamantan-3-yl, 13c^E,Z). (13b,c)^Z crystallize from solutions. In further attempts comparable to the reactions to 2 and 10, haloorganyliron complexes Fe(CO)2(PEt3)2(X)(CH2Y) (X = Y = Cl, 14a; X = Y = I, 14b; X = I, Y = CH2CN, 14c) could be obtained. All derivatives 14 cannot be transformed to ketene complexes in the presence of DBU and CO. Finally the known complexes Fe(CO)2(I)(PEt3)2(Me, Et) (15a,b) and the new species Fe(CO)2(I)(CH2SiMe3)(PEt3)2 (15c) were attempted to be converted to ketene complexes. By IR spectroscopy it was possible to detect Fe(CO)2(I)(PEt3)2(OCCHR) compounds (R = H, 17a; R = Me, 17b; R = SiMe3, 17c); however, these molecules could not be isolated from the reaction mixtures of the reaction of 15a−c with DBU and CO. 17c was then prepared by an independent route by reacting 1a,b with Me3SiCH&dbd;C&dbd;O. Under these conditions 17c was much more stable. In an exemplary way it was shown that the ketene unit of 17c can be cleanly replaced by CO to afford Fe(CO)3(PEt3)2 (18). The structures of 7a, 8a^Z, 9b, and 14a have been determined by X-ray diffraction studies.