The valuable use of fluorocarbons as refrigerants and foam-blowing agents and components of agrochemicals and pharmaceuticals has increased the demand for new synthetic routes to fluorinated chemicals. Since pioneering studies by Stone et al. in 1961 showed formation of perfluoroferracyclopentane from tetrafluoroethylene (TFE, CF2=CF2) and Fe(CO)5, the synthesis of fluorometallacycles has been explored most widely for nickel. In this work, our combined experimental-computational study investigates the effects of ancillary ligands (L) and the nature of the fluoroalkene (FA) on the oxidative cyclization at Ni(0). DFT calculations show lower activation barriers for L2Ni(FA)2 [vs. LNi(FA)2], and for TFE vs. CH2=CF2. Most remarkable, however, is the dramatic increase in the L-Ni-L angle (ca. 145°) during conversion of the bis(olefin) complex to metallacycle (Figure 1). As a result, reactions with wide bite-angle bis(phosphines) such as DPEphos and Bisbi allow for the observation of an intermediate metallacycle prior to formation of the stable square planar metallacycle.

Mechanism of perfluoronickelacyclopentane formation: Effects of ancillary ligand bite angle

ACS Spring Meeting 2021

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