Bifunctional Perfluoroaryl Boranes: Synthesis and Coordination Chemistry with Neutral Lewis Base Donors

A practical synthetic route for the preparation of the known bifunctional perfluoroaryldiborane C6F4-1,2-[B(C6F5)2]2, 1, and the new diborane C6F4-1,2-[B(C12F8)]2, 2, that circumvents the use of toxic mercury
reagents has been developed. Key intermediates and 2 have been fully characterized in solution and the
solid state. Solution and structural investigations of their MeCN and THF adducts have shown that 2 is
a superior Lewis acid to 1, primarily owing to the reduction in steric pressure afforded by the planar
9-borafluorene rings in 2 versus the freely rotating set of pentafluorophenyl rings in 1. The two compounds
bind Lewis bases via differing coordination modes, as demonstrated by the solid-state structures of the
Lewis base adducts 1·MeCN, 2·THF, and 2·MeCN. Solution studies suggest that bis Lewis base adducts
are also accessible; the structures of two examples (1·(MeCN)2 and 2·(THF)2) have been determined,
and their role in the dynamic solution behavior of these systems is discussed.