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

Abstract

Bis(ferrocenyl)-substituted allenylidene complexes, [(CO) 5M C C CFc 2] ( 1a– c, Fc = (C 5H 4)Fe(C 5H 5), M = Cr ( a), Mo ( b), W ( c)) were obtained by sequential reaction of Fc 2C O with Me 3Si–C CH, KF/MeOH, n-BuLi, and [(CO) 5M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO) 5Cr C C C(Fc)R] (R = Ph, NMe 2), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HC CC(Fc)(Ph)OH with [(CO) 5Cr(THF)] followed by desoxygenation with Cl 2C O, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO) 5Cr C(OR)CH C(NMe 2)Fc], and (c) replacement of OMe in [(CO) 5Cr C C C(OMe)NMe 2] by Fc. Complex 1a was also formed when the mono(ferrocenyl)allenylidene complex [(CO) 5Cr C C C(Fc)NMe 2] was treated first with Li[Fc] and the resulting adduct then with SiO 2. The replacement route (c) was also applied to the synthesis of an allenylidene complex ( 7a) with a C C spacer in between the ferrocenyl unit and C γ of the allenylidene ligand, [(CO) 5Cr C C C(NMe 2)-C CFc]. The related complex containing a CH CH spacer ( 9a) was prepared by condensation of [(CO) 5Cr C C C(Me)NMe 2] with formylferrocene in the presence of NEt 3. The bis(ferrocenyl)-substituted allenylidene complexes 1a– c added HNMe 2 across the C α–C β bond to give alkenyl(dimethylamino)carbene complexes and reacted with diethylaminopropyne by regioselective insertion of the C C bond into the C β–C γ bond to afford alkenyl(diethylamino)allenylidene complexes, [(CO) 5M C C C(NEt 2)CMe CFc 2]. The structures of 5a, 7a, and 9a were established by X-ray diffraction studies.