Force-Modulated C-C Reductive Elimination from Nickel Bis(polyfluorophenyl) Complexes

We have analyzed the rate of C(sp2)-C(sp2) reductive elimination from nickel(II) bis(2,4,6-trifluorophenyl) complexes (P-P)Ni(2,4,6-C6H2F3)2 containing either MeOBiPhep (3a) or a macrocyclic bisphosphine ligand (3b-3e) as a function of force applied to the biaryl backbone of these ligands through intramolecular tension generated by a molecular force probe. Nickel complexes 3 were isolated in 22-60% yield from the reaction of bisphosphine with the bis(tetrahydrofuranyl) complex (THF)2Ni(2,4,6-C6H2F3)2 followed by chromatography. Thermolysis of complexes 3 in C6D6 at 68 °C leads to first-order decay through >3 half-lives to the form 2,2′,4,4′,6,6′-hexafluorobiphenyl as the exclusive fluorine-containing product in ≥93% yield. Whereas compressive forces up to −65 pN have no significant effect on the rate of reductive elimination, extension forces increase the rate of reductive elimination by a factor of 3 over an ∼230 pN range of restoring forces relative to the strain-free MeOBiphep complex. The rate response of reductive elimination from nickel(II) bis(trifluorophenyl) complexes as a function of extension force is similar to the previously reported 2.8-fold increase in the rate of reductive elimination from platinum diaryl complexes (P-P)Pt(4-C6H4NMe2)2 over the same range of forces.

Duke Scholars

Author Stephen L Craig Chemistry

Author Ross A. Widenhoefer Chemistry