Cyclopentadienyl 1,2- and 1,3-Disubstituted Cobalt Sandwich Compounds {η5-[MeOC(O)]2C5H3} Co(η4-C4Ph4): Precursors for Sterically Hindered Bidentate Chiral and Achiral Ligands

Reaction of the sodium cyclopentadienyl Na­{C5H4[C­(O)­OMe]} with methyl chloroformate, ClC­(O)­OMe, in a 2:1 molar ratio was found to result in a mixture of sodium salts of 1,2- and 1,3-dicarbomethoxycyclopentadienyls. This mixture, on refluxing in toluene with CoCl­(PPh3)3 and diphenylacetylene, resulted in the formation of cyclopentadienyl 1,3- and 1,2-diester derived cobalt sandwich compounds {η5-[MeOC­(O)]2C5H3}­Co­(η4-C4Ph4) (1, 2) in 85% yield. 1,3- and 1,2-diesters 1 and 2 were converted to the dicarboxylic acids 3 and 4 by refluxing with aqueous KOH in ethanol. The diacyl chloride of 4 was generated in situ by the reaction of 4 with oxalyl chloride and this, on further reaction with ferrocene under Friedel–Crafts conditions, yielded the novel bis-metallocenyl acenequinone 5, having both the iron and cobalt sandwich units in the same compound. The dicarboxylic acid 3 on reaction with oxalyl chloride followed by (S)-2-amino-3-methyl-1-butanol, triethylamine, and mesyl chloride was converted to the novel 1,3-bis­(oxazoline) cyclopentadienyl-derived bidentate chiral complex [η5-1,3-(4-iPr-2-Ox)2C5H3]­Co­(η4-C4Ph4) (6; Ox = oxazolinyl). Reaction of 6 with Pd­(OAc)2 in acetic acid at 95 °C resulted in the formation of the chiral palladium complex 7. The utility of this palladium complex as a chiral catalyst for the asymmetric rearrangement of trichloroacetimidates to trichloroacetamides has been evaluated.