Selective Metallacyclization and Crystallographic Characterization of Structurally Related Platina-annulenes

The synthesis and characterization of seven platina-annulenes and their dehydrobenzoannulene (DBA) analogues are reported. Assembly of these macrocycles is accomplished via Sn transmetalation or amine-mediated oxidative addition with stoichiometric PtCl2(PR3)2, containing different phosphine ligands, and CuI. In contrast to previously reported DBA cyclization methodology, incorporation of a doubly σ-bonded Pt complex into the annulene backbone resulted in selective metallacyclization dependent on competing factors of ligand identity, PtCl2(PR3)2 isomer, and reaction conditions. Sn transmetalation conditions provided the most selective metallacyclization control and prevented PtCl2(PR3)2 isomerization during cyclization.