Structural depolymerization of titanium(IV) fluoride - the basis of formation fluoride complexes of titanium(IV)

Structural depolymerization of titanium(IV) fluoride: basis for the formation of titanium(IV) fluoride complexes

Synthesis of 3-substituted (azido, acylthio, chloro or fluoro)-2,3-dideoxy-D- erythro-pentoses and 3-methyl-3-substituted-2,3-dideoxy-D- erythro-pentoses

The compounds (NH4)4Li2A3F18 and NH4NaAF6 (A = Ge or Ti) were studied thermogravimetrically. These fluoro complexes are thermolyzed in the range 230–450°C. Measurements on a differential scanning microcalorimeter revealed reversible phase transitions in NH4NaAF6 at T 1 = 126°C and T 2 = 111°C.

A significant amount of information regarding the synthesis, reactivity, and catalytic activity of titanium fluoride complexes is available in the literature. However, the reports are mostly nonsystematic and spread over a large number of specific journals. An attempt is made to collect and organize all available information. Emphasis is given on work published after 1990 with links to the previous reviews, but earlier work is also included if no systematic report was done before.Published synthetic methods to access titanium fluoride complexes are covered in the present review, as well as the properties and reactivity of titanium fluoride complexes. In particular, the behavior of TiF4 in non-aqueous solvents, as well as the interaction of TiF4 with neutral and charged ligands in non-aqueous solvents is reviewed. All published tetrafluoride complexes TiF4L2 (L – neutral ligand) are presented. Mixed chloro and fluoro titanium complexes supported by neutral ligands, their preparation, and isomerism are surveyed. DFT calculations were performed to estimate the relative basicities of molecular ligands in titanium fluoride complexes as well as the relative stability of fluoride bridged titanium complexes.The reactivity of heterometallic titanium–alkali metal, titanium–alkaline earth metal fluoride complexes, the interaction of titanium fluoride complexes with silicon substrates, and the reactivity of titanium complexes toward organofluorine compounds are presented later in the review.Titanium fluoride complexes have found numerous applications in organic synthesis, and in many cases, the fluoride complex shows better performance than do complexes supported by other types of ligands. Organotitanium fluoride complexes show antitumor activity, and their values of cytotoxicity are comparable to that of the “gold standard” cisplatin.

Negatively charged titanium and zirconium complexes with α-hydroxy carboxylic acids and fluorides can be exhausted on the positively charged wool fibre in acid conditions, the result being a significant improvement in the natural flame-resistance of wool that is fast to washing and dry-cleaning. The complexes with carboxylic acids are exhausted on the wool fibre at the boil, whereas the fluoride complexes can be effectively exhausted at lower temperatures. The fluoride complexes can also be applied by a pad-batch-rinse-dry technique. Titanium complexes are more effective than the zirconium ones, probably because of better penetration of the fibre with the smaller titanium complexes. However, titanium complexes cause yellowing of wool, which increases with light exposure. Zirconium complexes do not affect the shade of wool and are fast to light.

Chlorosulfites prepared in situ using thionyl chloride react with nitrile complexes of titanium (IV) fluoride to give a one-pot conversion of alcohols into amides. For the first time, amides are obtained from cyclic alcohols with stereoretention. Critical to the design of these new Ti(IV) reactions has been the use of little explored Ti(IV) nitrile complexes which are thought to chelate chlorosulfites in the transition state to create a carbocation that is rapidly captured by the nitrile nucleophile via a front-side attack mechanism.

The cationic titanium fluoride containing complexes [fac-TiF3(MeCN)3][SbF6].MeCN (1), [trans-TiF2(15-Crown-5)][SbF6]2(2) and [trans-TiF2(18-Crown-6)][SbF6]2(2), were prepared by the reaction of TiF4, the molecular ligand and SbF5 in MeCN. Complexes 1-3 were characterized by X-ray single crystal analysis, elemental analysis, IR, NMR and mass spectroscopy. Titanium tetrafluoride reacts with the SbF5 in SO2 with the formation of fac-[TiF3(SO2)3]+, detected by 19F NMR. Application of the volume-based approach to thermodynamics (VBT) offers a means, for the first time, of exploring the energetics surrounding these materials and in the thermodynamic section a discussion of this new approach is provided. It emerges that the basis of the thermodynamic driving force of formation of [TiF3L3][SbF6](s) salts, that enforces the unfavourable [DeltaH degrees =+ 237 (+/-20) kJ mol(-1)] fluoride ion transfer from the Lewis acid TiF4(s) to SbF5(l) to give the hypothetical [TiF3]+[SbF6]-(s), is the higher Ti-L (L = ligand) bond energy in the cationic complexes [TiF3L3]+ as compared to that in the molecular adducts TiF4L2(s) and SbF5L(s) so giving rise to larger enthalpies of complexation of [TiF3]+(g) by 3L(g) compared to those for complexation of TiF4(g) by 2L(g) and SbF5(g) by 1L(g). Formation of the trans-[TiF2(15-Crown-5)]2+ and trans-[TiF2(18-Crown-6)]2+ is accounted for the stabilization of [TiF2]2+ cation by the five donor acceptor Ti-O contacts and the accompanying positive charge delocalization. Cationic titanium(IV) complexes fac-[TiF3MeCN)3-nLn]+(n= 0-3) and cis-[TiF318-Crown-6)]+, trans-[TiF2(Crown)]2+(Crown = 15-Crown-5 and 18-Crown-6) were obtained in MeCN solution by the reaction of fac-[TiF3(MeCN)3]+ and L = Et2, THF, H2 or crown ethers. Complexes fac-[TiF3(MeCN)3-nLn][SbF6] L = Et2, THF, H2O, crown ethers are unstable in MeCN solution and slowly decompose giving molecular complexes cis-TiF4L2, cis-TiF4(Crown), SbF5L, titanium oxofluoride and alkoxide complexes. The structure of the fac-[TiF3(MeCN)3]+ is similar to the fac-[TiCl3(MeCN)3]+ and the complexes trans-[TiF2L]2+ L = 15-Crown-5, 18-Crown-6 have very similar geometries to that of trans-[TiCl2(15-Crown-5)]+ showing that the essential features of coordination are the same for the cationic titanium chloride and fluoride complexes with MeCN and 15-Crown-5, 18-Crown-6.

Liquid injection field desorption/ionization of transition metal fluoride complexes

Synthesis and structures of paramagnetic organo titanium fluoride clusters

The standard rate constants of charge transfer (k s) for the Nb(V)/Nb(IV) redox couple in the NaCl-KCl(equimol.)-NaF(10 wt%)-K2NbF7 melt with addition of alkaline Earth metal cations (Mg2+, Ca2+, Sr2+, Ba2+) were determined. It was found that addition of alkaline Earth metal cations resulted in increasing of k s to the certain ratio of Me2+/Nb(V) for the all alkaline Earth metal cations due to substitution of Na+ and K+ cations by Me2+ in the second coordination sphere of niobium complexes that leads to decreasing of niobium fluoride complexes stability. Further addition brought to some decrease of the standard rate constants because the viscosity of melts increasing, which brings to decrease of the diffusion coefficients. The standard rate constants increase with increasing of the ionic potential and reach maximum values for the complexes with outer-sphere magnesium cations. Comparative analysis of the electrochemical behavior of Nb(V)/Nb(IV) and Ti(IV/Ti(III)) redox couples in the NaCl-KCl(equimol.)-NaF(10 wt%) melt without and with addition of alkaline Earth metal cations has been done. It was determined that mechanism of electron transfer from the cathode to niobium and titanium complexes in melts containing alkaline Earth metal cations is the same and has a bridge nature.

Structural chemistry of fluoride and oxofluoride complexes of titanium(IV)

Review: 138 refs.

The aim of the present investigation was study of charge transfer kinetics for the redox couple Ti(IV)/Ti(III) in the (NaCl-KCl)equimol.-NaF(10 wt.%)-K2TiF6 melt and the estimation of the alkali earth metal cations influence on the standard rate constants of charge transfer (ks ) for this redox couple. Method of cyclic voltammetry was employed for the determination of the standard rate constants of charge transfer. The electrochemical redox process: Ti(IV) + e-↔ Ti(III) (1) was classified as quasi-reversible in the range of scan rate 0.75 V s-1≤ν≤2.0 V s-1. The standard rate constants of charge transfer for the reaction (1) were calculated based on the Nicholson’s equation. It was shown, that k s increase with increasing temperature and the temperature dependence of k swas described by the following empirical equation: log k s=(1.505±0,32)–(3364±675)/Т (2) The activation energy of charge transfer calculated from (2) was found equal to (64.41±13) kJ mol-1. Influence of strongly polarizing cations of Mg2+, Ca2+, Sr2+ and Ba2+on the standard rate constants of charge transfer for the redox couple Ti(IV)/Ti(III) was studied. It was determined that addition of alkali earth metal cations resulted in increasing of ks up to the certain mole ratio of Me2+/Ti(IV), which was inversely proportional to ionic potential of cations. Further addition brought some decreasing of the standard rate constants. Increase of ks is connected with substitution of Na+ and K+ cations by strongly polarizing cations in the second coordination sphere of titanium complexes that led to increasing of the bond distance between Ti and F- ligands and decreasing of titanium fluoride complexes strength. Decrease of ks at the definite ratio of components can be explained by increasing of the viscosity melts, which brings to decreasing of the diffusion coefficients. It was established the linear dependence of ks on ionic potential of alkali earth metal cations and the maximum value was obtained for complexes with outer sphere cations of magnesium. The temperature dependences for the maximum values of ks in the melts containing strongly polarizing cations were fitted by empirical equations and the activation energies of charge transfer were calculated. Values of activation energy for systems with strongly polarizing cations are considerably less than activation energy for initial system. Acknowledgments The work was financially supported by Russian Foundation for Basic Research (15-03-02290_a).

Strengths of different Lewis bases in stabilizing titanium fluorides: A theoretical insight

Synthesis and investigation of the stability of Ti(III) β-diketiminato complexes. Structure of the tetrameric non-metallocene titanium fluoride complex (L2) 4Ti 4F 6O 2·2toluene supported by the β-diketiminato ligand