Chemistry of Transition Metal Fluoride Complexes

ABSTRACT

Metal fluoride complexes that are extremely sensitive to air and water have been characterized by liquid injection field desorption/ionization (LIFDI) mass spectrometry. Dilute solutions of fluoride complexes of nickel, rhodium, titanium, zirconium, hafnium and ruthenium in toluene and tetrahydrofuran were examined by LIFDI methods on a time-of-flight mass spectrometer. All the spectra of nickel, titanium zirconium and hafnium complexes exhibited the molecular ion as base peak. The ruthenium and rhodium complexes showed loss of HF from the molecular ion as base peaks but the molecular ions were easily detected.
Two new nickel fluoride complexes are formed by C-F activation reactions with 2,3,5,6-tetrafluoro-4-dimethylaminopyridine and 2,3,5,6-tetrafluoro-4-methoxypyridine yielding 3,5,6-trifluoro-4-dimethylaminopyridine nickel fluoride and 3,5,6-trifluoro-4-methoxypyridine nickel fluoride, respectively. The crystal structure of 3,5,6-trifluoro-4-dimethylaminopyridine nickel fluoride shows typical square planar coordination at nickel with an Ni-F distance of 1.8521(9) Å. pentamethylcyclopentadienyl metal difluoride (metal = Ti, Zr, Hf) complexes were synthesized from the reaction corresponding metal dichloride with NaF. N,N-dimethylethylene-1,2-diamine metal difluoride complexes (metal = Zn, Co, Ni) were synthesized from the reaction of metal difluoride with N,N-dimethylethylene-1,2-diamine. Ruthenium difluoride complexes were prepared from the reaction of ruthenium bis bifluoride complexes with TMAF. The compounds were characterized by multinuclear NMR spectroscopy and LIFDI mass spectrometry.
The nickel monofluoride complexes do not provide useful mass spectra by EI or ESI methods. Only the difluoride complexes of titanium, zirconium, hafnium, ruthenium, zinc, cobalt and nickel species showed evidence of the fluoride ligands in the ESI spectra. Collision induced dissociation (CID) was used to investigate the fragmentation pattern of the ions formed in the ESI mass spectrum. It was observed that the ligand attached to the metal has an effect on the fragmentation pattern of complex and the presence of phosphine strengthens the metal fluoride bond.
A modified quadrupole mass spectrometer was used to carry out gas phase ion molecule (I-M) reaction of metal ions with liquid and gaseous neutral molecule. Transition metal fluoride complexes did not show evidence of I-M reactions while Re and Mn tricarbonyl complexes have shown 100% conversion to the product.
The decay pathway of multiply charged anions (MCAs) of Ti and Zr was also investigated and it was found that these ions decay through ionic fragmentation rather than electron detachment.
Hydrogen bonding of pentamethyl cyclopentadienyl difluoride complexes of Ti and Zr with indole and 1,1,1,3,3,3 hexafluoroisopropanol was studied using fluorine NMR spectroscopy. Change in entropy and change in enthalpy were calculated from the equilibrium constant values (K) using Van’t Hoff’s equation.