Diastereo- and enantioselective synthesis of organometallic bis(helicene)s by a combination of C-H activation and dynamic isomerization

Homochiral and heterochiral cis-bis-cycloplatinated-[6]helicene derivatives 1 b^{1, 2}, as representative examples of platina[6]helicenes that share a common platinum center, have been prepared. A diastereo- and enantioselective synthesis, which combines CH activation and dynamic isomerization from heterochiral structure 1b² into homochiral structure 1b¹, is also described. Overall, this isomerization process results in the transfer of chiral information from one helicene moiety to the other one. The chiroptical properties of homochiral (P)- and (M)-1b¹ were greatly modified upon oxidation into their corresponding (P)- and (M)-diiodo-Pt^IV complexes (5). The changes were also analyzed by performing theoretical calculations. C-H activation in the synthesis of organometallic helicenes is further demonstrated by the preparation of cis-bis-cycloplatinated-[8]helicene 1 c.