Synthesis of Planar Chiral Cobalt Metallocenes by Microwave-Assisted Diastereoselective Complexation

Ether- and ester-linked diynes were readily synthesized in two steps by starting from secondary terminal propargylic alcohols. On either heat- or microwave-assisted reaction of the diynes with cyclopentadienylcobalt dicarbonyl, new planar chiral (η⁵-cyclopentadienone)(η⁵-cyclopentadienyl)cobalt metallocenes were formed with diastereomeric ratios of up to 5:1. For both the ether and ester series the identity of the major isomer was established by X-ray crystallography. The complexation method was shown to be applicable to the synthesis of scalemic planar chiral metallocenes. Preliminary investigations were carried out to transform the new complexes into other functionalized cobalt metallocenes.