FLUORINATED TRIS(PYRAZOLYL)BORATES AND SILVER(I) COMPLEXES OF GROUP 14 LIGANDS

Abstract

This review presents an overview of fluorinated tris(pyrazolyl)borate ligands and their role in the development of silver adducts containing group 14 ligands. Tris(pyrazolyl)borates bearing fluorocarbon substituents are sterically somewhat similar but electronically very different from their hydrocarbon counterparts. They have weakly donating nitrogen sites. Fluorinated hydridotris(pyrazolyl)borates also have less reducing B-H groups. These mono-anionic, nitrogen-based donors are ideal supporting ligands to stabilize silver complexes bearing labile donors. For example, fluorinated tris(pyrazolyl)borates have enabled the isolation of thermally stable Ag(I)-CO, Ag(I)-ethylene, and Ag(I)-acetylene adducts. Compounds with unsupported Ag(I)-Ge(II) and Ag(I)-Sn(II) bonds have also been synthesized. Most of these contain easily removable halide groups and silver atoms in the same molecule, but do not show the silver-halide metathesis. Fluorinated tris(pyrazolyl)borate ligands without the problematic B-H moiety have been reported. They afford silver-tris(pyrazolyl) borates with higher solution stability. The κ3-coordination mode is the most common for tris(pyrazolyl)borates but κ2-bonded tris(pyrazolyl)borate silver adducts are also known. Some silver adducts of fluorinated tris(pyrazolyl)borates are excellent tris(pyrazolyl)borato ligand transfer agents, promising homogeneous catalysts and effective antimicrobial agents.