[kriggy]

Im reading this paper about chan-lam reaction (J. Am. Chem. Soc. 2017, 139, 4769−4779). Authors say that  BPin esters are usualy not reactive or give lower yields compared to free boronic acids. Reason is that the pinacol chelates the copper and renders it inactive or lowers the activity. That was confirmed in other paper by the same group (J. Org. Chem. 2016, 81, 3942−3950). However, in the second paper they say that "A mixed MeCN/EtOH solvent system was found to enable effective C−N bond formation using aryl amines while EtOH is not required for the coupling of alkyl amines."
They say that the ethanol helps to dissociate the Cu dimer but why the monomer is not then coordinated by the pinacol ? I mean it is chelator of sorts so the Cu-Pin should be more stable than Cu-EtOH?
Or maybe to rephrase my question:
How addition of methanol stops the chelation of Cu by pinacol? Even if the Cu-methanol complex forms faster then the Cu-pinacole should prevail (chelating efect) because the reaction goes for 24hrs (seems quite a while)