Synthesis, variable temperature NMR investigations and solid state characterisation of novel octafluorofluorene compounds

The preparation of a number of new 9-substituted octafluorofluorene derivatives, solution NMR studies, and the first examples of solid state structures of octafluorofluorenes [1,2,3,4,5,6,7,8-octafluorofluorene, C13H2F8, 1; 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenylfluorene, C19HF13, 8; 1,1′,2,2′,3,3′,4,4′,5,5′,6,6′,7,7′,8,8′-hexadecafluoro-9,9′-bifluorenyl, C26H2F16, 11] are reported. Variable temperature 19F NMR investigations have been performed on the 9-aryl substituted compounds 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenyl-9-hydroxyfluorene, C19HF13O, 4, 1,2,3,4,5,6,7,8-octafluoro-9-(nonafluoro-4′-biphenylyl)-9-hydroxyfluorene, C25HF17O, 5, and 8, and the energetic barriers to rotation of the aryl have been determined. A lower rotational barrier is observed for compound 4 with respect to compound 8, while 5 does not show fluxional behaviour below 338 K. The results of the variable temperature experiments performed on 8 have been rationalized by 2D NMR studies, and compared to the solid state data resulting from the X-ray structural analysis

The chemistry of Niobium and Tantalum halides, MX5, with haloacetic acids and their related anhydrides: anhydride C–H bond activation promoted by MF5

Niobium and tantalum pentahalides, MX5 (1), react with acetic acid and halo-substituted acetic acids, in 1:1 ratio, to give the dinuclear complexes [MX4(μ-OOCMe)]2 [M = Nb, X = Cl, 2a; M = Ta, X = Cl, 2b; Br, 2c] and [MCl4(μ-OOCR)]2 [M = Nb, R = CH2Cl, 4a; CHCl2, 4c; CCl3, 4e; CF3, 4g; CHBr2, 4i; CH2I, 4j; M = Ta, R = CH2Cl, 4b; CHCl2, 4d; CCl3, 4f; CF3, 4h]. The solid state structures of 2b and 4e have been ascertained by X-ray diffraction studies. The reactions of 1 with acetic anhydride and halo-substituted acetic anhydrides result in C–O bond activation and afford 2 and 4, respectively, with concomitant formation of acetyl halides. Moreover, the complexes MCl5[OC(Cl)Me] [M = Nb, 3a; M = Ta, 3b] have been detected in significant amounts within the mixtures of the reactions of MCl5 with acetic anhydride. TaI5 is unreactive, at room temperature, towards both MeCOOH and (MeCO)2O. MF5 react with RCOOH (R = Me, CH2Cl) in 1:1 molar ratio, to afford the ionic compounds [MF4(RCOOH)2][MF6], 5a–d, in high yields. The additions of (RCO)2O (R = Me, CH2Cl) to MF5 give 5, suggesting that anhydride C–H and C–O bonds activation is operative during the course of these reactions

Back-Donation in High-Valent d0 Metal Complexes: Does It Exist? the Case of NbV

In the last years, some N-heterocyclic carbene (NHC) complexes of high-valent d0 transition-metal halides have been structurally characterized, showing a significant short distance between the carbene carbon and the cis-halide ligands (Clax). Some authors attributed this arrangement to a halide â\u86\u92 Ccarbene unusual "back-donation", whereas, according to others, the M-carbene bond is purely Ï\u83. More, in general, the ability of d0 metal centers to provide back-donation to suitable ligands is still debated, and detailed bond analyses for this class of systems are missing in the literature. In this contribution, we analyze in detail the NbV-L bond within neutral, cationic, and anionic derivatives of NbCl5, with L = NHC, CO, CNH, and CN-. In [NbVCl6-x(NHC)x]x-1 complexes, with NHC being either a model carbene (1,3-dimethylimidazol-2-ylidene, IMe) or a realistic one [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, IPr], we demonstrate that the metal center is really capable of back-donation to the carbene ligand by a charge flux that involves the chloride in the trans position and, directly, the metal. In this case, a direct interaction between Clax and Ccarbene can be excluded, while if different Ï\u80-acceptor ligands, such as CO or CNH, are used (instead of NHC), the direct Clax â\u86\u92 L interligand interaction becomes predominant

The reactivity of niobium and tantalum pentahalides with imines

The reactivity of NbCl5, NbF5 and TaCl5 with a selection of commercial imines was investigated for the first time by using dichloromethane as reaction medium. NbCl5 reacted with Ph2C=NH, in 1:2 molar ratio, affording [Ph2C=NH2][NbCl5(N=CPh2)], 1, in 55% yield, as result of imine self-protonation. The iminium salt [PhCH=NHtBu][NbCl6], 2, was isolated in 52% yield from NbCl5 and PhCH=NtBu (1:1 molar ratio), while a low yield of [tBu2C=NH2][NbCl6], 3, was identified from NbCl5/tBu2C=NH. The 1:1 reactions of NbF5 with Ph2C=NH and PhCH=NtBu were accompanied by electron interchange and led to the isolation of the salts [Ph2C=NH2][NbF6], 4, and [PhCH=NHtBu][NbF6], 5, respectively, in ca. 50% yields. Few crystals of [Ph2C=NH2]2[Ta2Cl10O], 6, were recovered from TaCl5/Ph2C=NH, the anion being probably generated by the action of adventitious water. Compounds 1-6 were characterized by elemental analysis, IR and NMR spectroscopy. The structures of 1, 4 and 6 were ascertained by X-ray diffraction studies

Arene ruthenium (II) complexes with phosphorous ligands as possible anticancer agents

Ruthenium(II) complexes of formula [Ru(?6-arene)Cl2(PTA)] (RAPTA) are potential anticancer drugs with notable antimetastatic and antiangiogenic activity, which are now pointing to clinical trials. Following the great interest aroused by these compounds, a variety of RAPTA derivatives, obtained by chloride substitution and/or containing functionalized arene ligands, and complexes resembling the RAPTA structure but bearing different phosphorous ligands have been synthesized and evaluated for their anticancer activity. An overview of all of these biologically relevant complexes will be given, with particular reference to the anticancer behaviour exhibited by the compounds and the possible relationship with structural aspects

Activation reactions of 1,1-dialkoxoalkanes and unsaturated O-donors by titanium tetrafluoride

The reactivity of TiF4 with a variety of non cyclic 1,1-dialkoxoalkanes [CH2(OR)(2), R = Me, Et, Me2C(OMe)(2), MeCH(OEt)(2), ClCH2CH(OEt)(2), CH(OMe)(3), PhC CCH(OEt)(2)], 1,3-dioxolane, N2CHCO2Et and 1,2-epoxybutane has been investigated. Activation, including fragmentation and/or rearrangement of the organic moiety, has been observed at room temperature in some cases; it generally occurs unselectively via C-O bond fission and the formation of new C-O, C-H and C-C bonds. Small differences in the structure of the organic substrate may determine significant differences in the reactivity with TiF4

The reactivity of MoCl5 with molecules containing the alcohol functionality

The 1:1 M reaction of MoCl5 with Cl(CH2)2OH, in dichloromethane at room temperature, proceeded with chlorine–oxygen interchange and HCl release to give MoOCl3 in 65% yield. The analogous reactions involving iPrOH, MeOH, L-menthol and H2O gave impure MoOCl3. MoCl5 reacted with Me2N(CH2)2OH in 1:1 M ratio affording the 2-chloroammonium salt [Me2NH(CH2)2Cl]2[Mo2O2Cl8], 1. The reaction of MoCl5 with MeO(CH2)2OH afforded a mixture of [Mo(O(CH2)2OMe)2Cl2][Mo2O2Cl7], 2a, and [Mo(O(CH2)2OMe)2Cl2][MoOCl4], 2b. The products 1, 2a and 2b were characterized by analytical and spectroscopic techniques, and by X-ray diffractometry. The X-ray structure of 2b shows weak anion–anion interactions, therefore 2b might be alternatively viewed as a [Mo2O2Cl8]2- salt

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