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 his 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.