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

We have analyzed the rate of C(sp(2))-C(sp(2)) reductive elimination from nickel(II) bis(2,4,6-trifluorophenyl)complexes (P-P)Ni(2,4,6-C6H2F3)(2) containing either MeOBiPhep (3a) or amacrocyclic bisphosphine ligand (3b-3e) as a function of force applied to the biaryl backbone of theseligands through intramolecular tension generated by a molecular forceprobe. Nickel complexes 3 were isolated in 22-60%yield from the reaction of bisphosphine with the bis(tetrahydrofuranyl)complex (THF)(2)Ni(2,4,6-C6H2F3)(2) followed by chromatography. Thermolysis of complexes 3 in C6D6 at 68 & DEG;C leads to first-orderdecay through >3 half-lives to the form 2,2 & PRIME;,4,4 & PRIME;,6,6 & PRIME;-hexafluoro-biphenylas the exclusive fluorine-containing product in & GE;93% yield.Whereas compressive forces up to -65 pN have no significanteffect on the rate of reductive elimination, extension forces increasethe rate of reductive elimination by a factor of 3 over an & SIM;230pN range of restoring forces relative to the strain-free MeOBiphepcomplex. The rate response of reductive elimination from nickel(II)bis(trifluorophenyl) complexes as a function of extension force issimilar to the previously reported 2.8-fold increase in the rate ofreductive elimination from platinum diaryl complexes (P-P)Pt(4-C6H4NMe2)(2) over the same rangeof forces.