Ferrocenyl-substituted allenylidene complexes of chromium, molybdenum and tungsten: Synthesis, structure and reactivity

Bis(ferrocenyl)-substituted allenylidene complexes, [(CO)5Mdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashCFc2] (1a–c, Fc = (C5H4)Fe(C5H5), M = Cr (a), Mo (b), W (c)) were obtained by sequential reaction of Fc2Cdouble bond; length as m-dashO with Me3Si–Ctriple bond; length of mdashCH, KF/MeOH, n-BuLi, and [(CO)5M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO)5Crdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(Fc)R] (R = Ph, NMe2), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HCtriple bond; length of mdashCC(Fc)(Ph)OH with [(CO)5Cr(THF)] followed by desoxygenation with Cl2Cdouble bond; length as m-dashO, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO)5Crdouble bond; length as m-dashC(OR)CHdouble bond; length as m-dashC(NMe2)Fc], and (c) replacement of OMe in [(CO)5Crdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(OMe)NMe2] by Fc. Complex 1a was also formed when the mono(ferrocenyl)allenylidene complex [(CO)5Crdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(Fc)NMe2] was treated first with Li[Fc] and the resulting adduct then with SiO2. The replacement route (c) was also applied to the synthesis of an allenylidene complex (7a) with a Ctriple bond; length of mdashC spacer in between the ferrocenyl unit and Cγ of the allenylidene ligand, [(CO)5Crdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(NMe2)-Ctriple bond; length of mdashCFc]. The related complex containing a CHdouble bond; length as m-dashCH spacer (9a) was prepared by condensation of [(CO)5Crdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(Me)NMe2] with formylferrocene in the presence of NEt3. The bis(ferrocenyl)-substituted allenylidene complexes 1a–c added HNMe2 across the Cα–Cβ bond to give alkenyl(dimethylamino)carbene complexes and reacted with diethylaminopropyne by regioselective insertion of the Ctriple bond; length of mdashC bond into the Cβ–Cγ bond to afford alkenyl(diethylamino)allenylidene complexes, [(CO)5Mdouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashC(NEt2)CMedouble bond; length as m-dashCFc2]. The structures of 5a, 7a, and 9a were established by X-ray diffraction studies.