Copper(I), Silver(I), and Gold(I) Ethylene Complexes of Fluorinated and Boron-Methylated Bis- and Tris(pyridyl)borate Chelators.

Bis- and tris-pyridyl borate ligands containing pyridyl donor arms, a methylated boron cap, and a fluorine-lined coordination pocket have been prepared and utilized in coinage metal chemistry. The tris(pyridyl)borate ligand has been synthesized using a convenient boron source, [NBu][MeBF]. These N-based ligands permitted the isolation of group 11 metal-ethylene complexes [MeB(6-(CF)Py)]M(CH) and [MeB(6-(CF)Py)]M(CH) (M = Cu, Ag, Au). The gold complexes display the largest coordination-induced upfield shifts of the ethylene C resonance relative to that of the free ethylene in their NMR spectra, while the silver complexes show the smallest shift. Solid-state structures of five of these metal-ethylene complexes as well as the related free ligands were established by X-ray crystallography. Surprisingly, all three [MeB(6-(CF)Py)]M(CH) adopt the rare κ coordination mode rather than the typical κ coordination mode of facial capping tridentate ligands. Computational analyses indicate that κ coordination mode is favored over the κ-mode in these coinage metal-ethylene complexes and point to the effects CF-substituents have on κ/κ-energy difference. The M-C and M-N bond distances of [MeB(6-(CF)Py)]M(CH) follow the trend expected based on covalent radii of M(I) ions. The calculated ethylene-M interaction energy of κ-[MeB(6-(CF)Py)]M(CH) indicated that the gold(I) forms the strongest interaction with ethylene. A comparison to the related poly(pyrazolyl)borates is also presented.