Copper(I), Silver(I), and Gold(I) Ethylene Complexes of Fluorinated and Boron-Methylated Bis- and Tris(pyridyl)borate Chelators
Brandon T. Watson, Mukundam Vanga, Anurag Noonikara‐Poyil, Alvaro Muñoz‐Castro, H. V. Rasika Dias
Abstract
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 4 ][MeBF 3 ]. These N-based ligands permitted the isolation of group 11 metal–ethylene complexes [MeB(6-(CF 3 )Py) 3 ]M(C 2 H 4 ) and [Me 2 B(6-(CF 3 )Py) 2 ]M(C 2 H 4 ) (M = Cu, Ag, Au). The gold complexes display the largest coordination-induced upfield shifts of the ethylene 13 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 3 )Py) 3 ]M(C 2 H 4 ) adopt the rare κ 2 coordination mode rather than the typical κ 3 coordination mode of facial capping tridentate ligands. Computational analyses indicate that κ 2 coordination mode is favored over the κ 3 -mode in these coinage metal–ethylene complexes and point to the effects CF 3 -substituents have on κ 2 /κ 3 -energy difference. The M–C and M–N bond distances of [MeB(6-(CF 3 )Py) 3 ]M(C 2 H 4 ) follow the trend expected based on covalent radii of M(I) ions. The calculated ethylene–M interaction energy of κ 2 -[MeB(6-(CF 3 )Py) 3 ]M(C 2 H 4 ) indicated that the gold(I) forms the strongest interaction with ethylene. A comparison to the related poly(pyrazolyl)borates is also presented.