Reactions of Cobalt and Nickel Complexes with Fluoroalkenes and Perfluorobutadiene

Abstract

Organofluorine compounds are highly desirable products owing to the unique physical and chemical properties imparted by fluorine. Fluorocarbons are useful molecules that are used in multiple industries such as refrigeration, agrochemicals, pharmaceuticals, insecticides, high-value fluoropolymers and reagents in catalysis. As ligands, they are privileged in the relative inertness of the C–F bonds and their electrophilicity, which makes them ideal candidates for coordination chemistry with late, electron rich metals. Chapter 2 describes the preparation of new Ni metallacyclopentene complexes with phosphite and bis(phosphine) ligands and investigates the reaction of the latter with Lewis acidic trimethylsilyltriflate, TMSOTf (Tf = SO2CF3). As phosphine ligands react with the perfluoro-butadiene (PFB) substrate, the phosphite complex Ni((2-C4F6)[P(O-i-Pr)3]2 (2-1) was prepared from Ni(cod)2 /2 P(O-i-Pr)3 and excess PFB. Reaction of 2.1 with bis(phosphine) dppe [1,2-bis(diphenylphosphine)ethane] proceeded slowly with release of P(O-i-Pr)3 and formation of electron-rich Ni(2-C4F6)(dppe) (2-2) that undergoes fluoride abstraction using TMSOTf. The major product is proposed to be a dienyl complex resulting from ring contraction and cycloreversion. In Chapter 3 we investigate reactions of fluoroalkenes with cobalt hydrides containing phosphine and phosphite ligands in order to see if their reactivity can be controlled by the ligands’ steric and electronic properties. The four cobalt compounds used were CoH[P(OiPr)3]4 (3-1), CoH[P(O-o-tol)3]n (3-2), CoH(triphos)(CO) (3-3); [triphos = bis(diphenylphosphinoethyl)-phenylphosphine], and CoH(PPh3)3(N2) (3-4). In light of previous reports of tetrafluoroethylene insertion into Co carbonyl hydrides, we were surprised that analogous reactivity was not observed except for 3-4. Instead, reactions with hexafluoropropene gave a mixture of alkene cobalt fluoride and cobalt alkenyl complexes. In Chapter 4 we summarize our contributions to knowledge and compare our results to those from the current state of the art.