Regioselective, Stereoselective, and Conformationally Controlled Synthesis of (畏4-Tetraarylcyclobutadiene)(畏5-carbomethoxycyclopentadienyl)cobalt Metallocenes
文摘
The Friedel鈥揅rafts reaction of (畏4-tetraphenylcyclobutadiene)(畏5-carbomethoxycyclopentadienyl)cobalt with acid chlorides/aluminum chloride resulted exclusively in para-phenyl acylation. Both monoacylated (1.1 equiv of RCOCl/AlCl3) and tetraacylated products (>4 equiv of RCOCl/AlCl3) were synthesized. Reaction of PhCC(o-RC6H4) (R = Me, i-Pr) with Na(C5H4CO2Me) and CoCl(PPh3)3 gave predominantly (畏4-1,3-diaryl-2,4-diphenylcyclobutadiene)(畏5-carbomethoxycyclopentadienyl)cobalt metallocenes (1,3-[trans] vs 1,2-[cis] selectivity up to 6:1). Conformational control of Friedel鈥揅rafts reactions on the major isomers gave exclusively para-acylation of the unsubstituted phenyl groups.