Remarkable effects of counter ions on scandium ion-promoted electron transfer reactions

Scandium ion-promoted electron transfer reactions of p-benzoquinone are remarkably accelerated when tetrakis(pentafluorophenyl)borate anion is used instead of trifluoromethanesulfonate anion as the counter anion of scandium ion. Only a catalytic amount of scandium borate salt (Sc[B (C6F5)4]3) accelerates significantly the Diels–Alder reaction of 9,10-dimethylanthracene with p-benzoquinone, which proceeds via Sc3+-promoted electron transfer from the anthracene to p-benzoquinone.