Synthesis and structural characterization of Group 4 metallocene complexes that contain remote carboxamide functionalites at their Cp-side chains

摘要

Treatment of the levulinic acid amides CH_3COCH_2CH_2CONR_2 7 [-NR_2 = NMe_2 (a), NEt_2 (b), pyrrolidino (c)] with cyclopentadiene in the presence of excess pyrrolidine gave the corresponding pentafulvene derivatives 8(a-c). Their subsequent reaction with [Me_2CuLi] followed by hydrolysis furnished the corresponding C-methylated cyclopentadienes 9(a-c), each obtained as a mixture of isomers (9-A and 9-B). Deprotonation of the cyclopentadiene units in these compounds was achieved by treatment with ltihium diisopropylamide (LDA) to yield the substituted lithium cyclopentadienide reagents [(C_5H_4)-CMe_2CH_2CH_2CONR_2]Li(10a-c), that were resistant to intramolecular cyclization under the applied reaction conditions. The transmetalation reaction of 10a with FeCl_2 funished the ferrocene derivative [(C_5H_4)-CMe_2CH_2CH_2CONMe_2]_2Fe (11a). Treatment of 10a-c with CpTiCl_3 gave the Group 4 bent metallocene complexes Cp[(C_5H_4)-CMe_2CH_2CH_2CONR_2]TiCl_2 (12a-c). Similarly, the reaction of 10b with CpZrl_3 led to formation of the complex Cp[(C_5H_4)CMe_2CH_2CH_2CONEt_2]ZrCl_2 (13b). Treatment of 12a with Meerwein's reagent [(Et_3O~+)(BF_4~-)] resulted in chloride abstraction with formation of the metallocene cation complex 16 (with BF_4~- anion), in which, contrary to the 16-electron systems 12 and 13, the carboxamido oxygen atom intramolecularly coordinates to the electron deficient Group 4 metal cation. The organic reagents 8a and 9a as well as the transition metal complexes 11a, 13b, and 16[BF_4~-] were characterized by X-ray crystal structure analyses.