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.