Regioselective, stereoselective, and conformationally controlled synthesis of (η4-tetraarylcyclobutadiene)(η5-carbomethoxycyclopentadienyl)cobalt metallocenes

Doyle J Cassar; Elisabeth Nagaradja; David C D Butler; Didier Villemin; Christopher J Richards

doi:10.1021/ol203415r

Regioselective, stereoselective, and conformationally controlled synthesis of (η4-tetraarylcyclobutadiene)(η5-carbomethoxycyclopentadienyl)cobalt metallocenes

Org Lett. 2012 Feb 3;14(3):894-7. doi: 10.1021/ol203415r. Epub 2012 Jan 24.

Authors

Doyle J Cassar¹, Elisabeth Nagaradja, David C D Butler, Didier Villemin, Christopher J Richards

Affiliation

¹ School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, United Kingdom.

PMID: 22272556
DOI: 10.1021/ol203415r

Abstract

The Friedel-Crafts reaction of (η(4)-tetraphenylcyclobutadiene)(η(5)-carbomethoxycyclopentadienyl)cobalt with acid chlorides/aluminum chloride resulted exclusively in para-phenyl acylation. Both monoacylated (1.1 equiv of RCOCl/AlCl(3)) and tetraacylated products (>4 equiv of RCOCl/AlCl(3)) were synthesized. Reaction of PhCC(o-RC(6)H(4)) (R = Me, i-Pr) with Na(C(5)H(4)CO(2)Me) and CoCl(PPh(3))(3) gave predominantly (η(4)-1,3-diaryl-2,4-diphenylcyclobutadiene)(η(5)-carbomethoxycyclopentadienyl)cobalt metallocenes (1,3-[trans] vs 1,2-[cis] selectivity up to 6:1). Conformational control of Friedel-Crafts reactions on the major isomers gave exclusively para-acylation of the unsubstituted phenyl groups.