Interaction between a Transition-Metal Fluoride and a Transition-Metal Hydride: Water-Mediated Hydrofluoric Acid Evolution Following Fluoride Solvation

The reaction between the nickel­(II) PCP pincer fluoride complex (^<i>t</i>BuPCP)­Ni­(F) [^<i>t</i>BuPCP = 2,6-C₆H₃(CH₂P^<i>t</i>Bu₂)₂] and the tungsten­(II) carbonyl hydride CpW­(H)­(CO)₃ (Cp = η⁵-C₅H₅^–) leads to hydrofluoric acid evolution and formation of the bimetallic isocarbonylic species [CpW­(CO)₂(μ-κ,C:κ,O-CO)···Ni­(^<i>t</i>BuPCP)]. The process has been monitored through multinuclear (¹⁹F, ³¹P­{¹H}, ¹H) variable-temperature NMR spectroscopy, collecting ¹⁹F <i>T</i>₁ data values for a fluoride ligand bound to a transition metal. The extremely short relaxation time (minimum value of 13 ms at 193 K) is ascribed to the large chemical shift anisotropy of the Ni–F bond (688 ppm). The in-depth NMR analysis has revealed that the fluoride–hydride interaction is not direct but water-mediated, at odds with what was previously observed for the “hydride–hydride” case (^<i>t</i>BuPCP)­Ni­(H)/CpW­(H)­(CO)₃. Kinetic measurements have unveiled that the first step of the overall mechanism is thought to be solvation of the fluoride ligand (as a result of Ni–F···H₂O hydrogen bonding), while further reaction of the solvated fluoride with CpW­(H)­(CO)₃ is extremely slow and competes with the side reaction of fluoride replacement by a water molecule on the nickel center to form the [(^<i>t</i>BuPCP)­Ni­(H₂O)]⁺ <i>aquo</i> species. Finally, density functional theory analysis of the solvation process through a discrete + continuum model has been accomplished, at the M06//6-31+G­(d,p) level of theory, to support the mechanistic hypothesis