Direct carbon-13 nuclear magnetic resonance study of boron trifluoride and boron trichloride complexes with ethers
A direct, low-temperature, 13C n.m.r. study of the boron trifluoride and boron trichloride complexes with several ethers has been completed. At ca.–100°, ligand exchange is slow enough to permit the observation of separate signals for bulk and co-ordinated ether molecules. The chemical shift changes induced by complex formation reflect inductive and steric effects. Doublet patterns were observed for the signals of co-ordinated ethyl s-butyl, ethyl t-butyl, and di-isopentyl ether. The most reasonable interpretation of this result appears to be hindered rotation about the O–R bond in the complex.