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 PtCl<INF>2</INF>(PR<INF>3</INF>)<INF>2</INF>, 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, PtCl<INF>2</INF>(PR<INF>3</INF>)<INF>2</INF> isomer, and reaction conditions. Sn transmetalation conditions provided the most selective metallacyclization control and prevented PtCl<INF>2</INF>(PR<INF>3</INF>)<INF>2</INF> isomerization during cyclization.