PENTAMETHYLCYCLOPENTADIENYLBIS(ETHENE)IRO N - A 17E HALFSANDWICH COMPLEX WITH EASILY DISPLACEABLE ETHENE LIGANDS

The new room temperature stable halfsandwich complex Cp()Fe(tmeda)Cl (2) has been synthesized by the 1:1 reaction of FeCl2(thf)(1.5) with L iCp() in a mixture of THF and TMEDA at -30 degrees C. 2 is an ideal s tarting material for the synthesis of a wide range of new iron complex es. Treatment of 2 with lithium sand in THF in the presence of COD or ethene followed by the addition of TMEDA yields the ferrates [Li(tmeda )(x)][Cp()Fe(cod)] (3) or [Li(tmeda)][Cp(*)Fe(C2H4)(2)] (4). By delit hiation with dichloroethane, 3 and 4 can be transformed into the novel 17e iron complexes Cp()Fe(cod) (5) and Cp(*)Fe(C2H4)(2) (6). 6 is ex tremely labile. Since the ethene ligands can be easily displaced, the title compound is a synthetically valuable source of the Cp()Fe fragm ent. Whereas the photochemically generated 17e dicarbonyl species CpFe (CO)(2) rapidly recombines to give the dimer [CpFe(CO)(2)](2), the iso electronic 6 is stable in ethene saturated pentane for several days at 0 degrees C. Without the stabilizing effect of ethene (in pure pentan e or under vacuum), 6 loses ethene to give the dinuclear complex ((CPF e)-Fe-)(2)(C2H4)(2) (8) irreversibly. The structure of 8 has been cha racterized by X-ray analysis.