The nucleophilic reaction of AgF with perfluoro-2-butine in acetonitrile solvent affords the volatile trans-perfluoro (1-methylpropenyl) silver Ag [CF3-CF = C (CF3)], a white solid isolated by sublimation at 150 ° C / 0.05 Torr [[i]] According to the authors, this was the first known example of perfluorvinyl silver compounds.
The reaction proceeds as follows:
AgF + CF3-C≡C-CF3 => Ag[trans-CF3CF = C (CF3)]
Synthesis: 0.100 mol AgF, 0.110 mol CF3C = CCF3 and 100 ml CH3CN sealed in a glass ampoule were shaken for 36 h at ~25 ° C, AgF and CF3C≡CCF3 dissolved to form a clear solution and a small amount of black precipitate. The solution was decanted and distilled at 0.05 Torr yielding (after removal of CH3CN) 23.4 g of white crystalline sublimate (collected mainly at 150°C) and 0.4 g of a silver-containing residue. During decantation and distillation, 0.026 mol (gas volume) of CF3C≡CCF3 contaminated with CF3CH = CFCF3 and CH3CN was collected in a cold trap.
Unlike 1-methylpropenyl silver, which decomposes at room temperature, trans-perfluoro (1-methylpropenyl) silver is a thermally stable compound and has been isolated by vacuum sublimation at temperatures up to 175 ° C. Its properties are as follows: At 176-177 ° C, the molten ampoule melted with a small percentage of a hole to form a silver mirror (180 ° C). Its structure was confirmed by the preparation method, cleavage reactions, NMR (19F), and absorption spectra. The degree of aggregation was determined not in the solution but from the mass spectrum of the crystalline material where the peak corresponding to the tetramer Ag(CF3CF = C-CF3)4 was found. Only the trans isomer appeared to be soluble in donor aprotic solvents such as ethers and nitriles. Reacts with oxygen (probably via CF3-CF = C (CF3)· free radical) and in the acetonitrile solution with water and HCl, forming CF3-CF = CH-CF3. The compound reacts to 85% with bromine. By-products - black Ag2O or silver halide are falling off immediately after mixing the reagents. Perfluoro (1-methylpropenyl) silver also reacts with CH3I forming trans-CF3-CF = C (CH3) CF3 and AgI after ~ 24 hours of shaking. With excess of copper bromide, Ag[CF3CF=C(CF3)] reacts forming dimerization product CF3-CF = C (CF3) -C (CF3) = CF-CF3 and trans-CF3-CF = CBr-CF3.
The high thermal stability and volatility of perfluoro- (1-methylpropenyl) silver, possible also for other perfluorocarbon Ag compounds bound via sp2 carbon, can be used for its application as MOCVD precursor of Ag-contaning compounds.
[i] W.T.Miller, R.H. Snider, R.J.Hummel, "Perfluoro-1-methylpropenyl-silver", J.Amer.Chem.Soc, 1969, 91, 6532.
Perfluoroprop-2-enyl silver Ag[C(CF3)=CF2], a lower homologue of perfluoro (1-methylpropenyl) silver CF3-CF = C (Ag) -CF3, was synthesized from tetrafluorene and isolated in 66% yield by vacuum sublimation to 160-180 ° C [4]. The reaction (in acetonitrile as solvent) proceeds as follows:
CF2 = C = CF2 + AgF → CF2 = C (Ag) -CF3
The structure of perfluoroprop-2-enyl silver was confirmed by elemental analysis, IR and 19F NMR spectroscopy. It decomposes thermally at 300-350 ° C forming dimerization product CF2 = C (CF3) -C (CF3) = CF2 (56%). At room temperature (20 ° C) the following reactions occur: with water forming CF2 = CH-CF3 (99%), with Br2 acetonitrile forming CF2 = CBr-CF3 (88%), with MeI forming CF2 = C (Me) CF3 (95%) , with Me3SiCl forming CF2 = C (SiMe3) CF3 (99%).
The crystal structure of perfluoro- (1-methyl-1-propenyl) silver precursor was determined, the compound appeared to be a tetramer,
cinsisting of flat square of silver atoms, where each edge is linked by a trans-perfluoro (1-methyl-1-propenyl) ligand bridge. Mean distances and angles between atoms and crystallographic data were determined.[i]
[i] P.M. Jeffries, S.R. Wilson, G.S. Girolami, J. Organomet. Chem., 1993, Vol.449, Iss 1-2, pp.203-209. “Crystal Structure of (CF3CF=CAgCF3)4 and Its Use as a Chemical Vapor Deposition Precursors for Silver Films”
Metallic silver films were deposited by CVD for superconducting wire applications. The best Ag layers were obtained using perfluoro-1-methylpropenyl silver Ag[CF3-CF=C (CF3)] tetramer [Ag(CF3CF = C(CF3)]4 (or Ag(PF)). The CVD process was optimized using thermodynamic calculations performed using a modified SOLGASMIX-PV computer program. With Ag(PF) as precursor, high quality silver films at low temperatures and pressures were obtained. The fibrous wire having a silver barrier layer and a top layer of YBa2Cu3Ox exhibited superconductivity at 72 K. [[i]]
Silver films using
a perfluoro- (1-methyl-1-propenyl) silver were deposited at 275 ° C and 10-4 Torr pressure; Ag films had only traces of F and O and no C contamination. The main organic by-products were trans-CF3-CF = CH-CF3 (50%) and CF3C≡CCF3 (40%). It is assumed
that metallic silver was formed by the elimination of CF3C≡CCF3 from trans- (CF3CF = CAgCF3) 4 forming silver (I) fluoride, which is defluorinated to form metallic siver.
[i] M.J. Shapiro, W.J. Lackey, J.A. Hanigofsky, D.N. Hill, W.B. Carter, E.K. Barefield, J. Alloys Comp., 1992, Vol.187, Iss.2, pp.331-349, “Chemical Vapor Deposition of Silver Films for Superconducting Wire Applications”