New routes to fluorocarbon-containing phosphines

Routes to sterically demanding organofluorine-containing phosphines are described, and the stereoelectronic properties and chemistry of the resulting new ligands investigated. The synthesis of Cy2P(CF=CF2), 3, has been accomplished. The nucleophilic substitution of Ph2P(CF=CF2) with tBuLi produces the (Z)-isomer, Ph2P(Z-CF=CF(tBu)), 5-(Z), predominantly, which has been shown to be less electron-withdrawing than Ph2P(CF=CF2), and similar in size to 3. The bis-trifluoropropynyl substituted phosphine PhP(tfp)2, 7, has been prepared, and its reaction with tBuLi investigated. This results in the formation of three previously unknown species, the gem¬-difluorocyclopropenyl-containing compound, PhtBuP(dfcp), 8, (Z)-Ph2P(CH=C(t¬Bu)CF3), 9, and PhtBuP(tfp), 10. The nucleophilic substitution occurs preferentially at the phosphorus centre, as shown by the reaction with one equivalent of tBuLi at -60°C, where compounds 9 and 10 are formed. A new route to perfluoroalkyl-containing phosphines has been discovered. The addition of a perfluoroalkyl iodide to Ph2PSiMe3 results in the formation of six new phosphines, and has been shown to be extendable to partially fluorinated systems. The route can also be applied to iPr2PSiMe3, and to the chiral phosphine PhMePSiMe3. Three examples, Ph2PRf (Rf = CF(CF3)2, 15, (sC4F¬9), 18, (cyc-C6F11), 19), have been produced on a preparative scale. The reaction of the bis-trimethylsilyl phenyl phosphine with (CF3)2CFI has been investigated, though it does not result in the production of the bis-perfluoroalkyl-substituted phosphine, instead the previously unknown P-chiral compound, PhP(H)CF(CF3)2, 27 is formed. Mechanistic studies have indicated that Ph2P-PPh2 is the intermediate, and that there is no evidence of a radical mechanism. There is no reaction between Me2(S)P-P(S)Me2 and (CF3)2CFI, though there is when Me2P-P(S)Me2 is used, suggesting that the lone pair of the intermediate diphosphine is necessary for the reaction to proceed. This has resulted in the formation of the new compound, Me2PCF(CF3)2, 28. The chemistry of the perfluoroalkyl-containing phosphines has been investigated; they do not quaternise, but are oxidatively sensitive. The phosphorus(V) selenides of 15, 18, and 19 have been prepared, and based on their 1JPSe coupling constants, the perfluoroalkyl-groups impart a greater electron-withdrawing effect than perfluorovinyl, trifluoropropynyl, or alkoxy fragments. The oxidation of 15 and 18 with XeF2 has also been accomplished, and shown to yield the corresponding F2PPh2Rf compounds. The molybdenum(0) pentacarbonyl complexes of 3, 7, and 15 have been synthesised and perfluoroalkyl-groups have again been shown to be more electron-withdrawing than perfluorovinyl and trifluoropropynyl groups by comparison of v(CO) values. The gold(I) chloride complexes of Ph2PCF3, 15, and 18 and the platinum(II) dichloride complexes of 3 and 15 have been prepared, and the size of these ligands has been estimated from the crystal structures. Compound 18 has been shown to be the largest of these compounds, with a cone angle of 187°.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Vibrational spectra, assignments and normal coordinate analyses for crystalline zirconium tetrachloride and tetrabromide

Raman and far-IR spectra have been obtained of crystalline ZrCl4 and ZrBr4. The observed frequencies have been interpreted on the basis of the C2h symmetry of the Bravais unit cell and have been subjected to a normal coordinate analysis. The interpretation and results are satisfactorily in accord with the X-ray structure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24546/1/0000826.pd

The reductive activation of CO2 across a Ti═Ti double bond: synthetic, structural, and mechanistic studies

[Image: see text] The reactivity of the bis(pentalene)dititanium double-sandwich compound Ti(2)Pn(†)(2) (1) (Pn(†) = 1,4-{Si(i)Pr(3)}(2)C(8)H(4)) with CO(2) is investigated in detail using spectroscopic, X-ray crystallographic, and computational studies. When the CO(2) reaction is performed at −78 °C, the 1:1 adduct 4 is formed, and low-temperature spectroscopic measurements are consistent with a CO(2) molecule bound symmetrically to the two Ti centers in a μ:η(2),η(2) binding mode, a structure also indicated by theory. Upon warming to room temperature the coordinated CO(2) is quantitatively reduced over a period of minutes to give the bis(oxo)-bridged dimer 2 and the dicarbonyl complex 3. In situ NMR studies indicated that this decomposition proceeds in a stepwise process via monooxo (5) and monocarbonyl (7) double-sandwich complexes, which have been independently synthesized and structurally characterized. 5 is thermally unstable with respect to a μ-O dimer in which the Ti–Ti bond has been cleaved and one pentalene ligand binds in an η(8) fashion to each of the formally Ti(III) centers. The molecular structure of 7 shows a “side-on” bound carbonyl ligand. Bonding of the double-sandwich species Ti(2)Pn(2) (Pn = C(8)H(6)) to other fragments has been investigated by density functional theory calculations and fragment analysis, providing insight into the CO(2) reaction pathway consistent with the experimentally observed intermediates. A key step in the proposed mechanism is disproportionation of a mono(oxo) di-Ti(III) species to yield di-Ti(II) and di-Ti(IV) products. 1 forms a structurally characterized, thermally stable CS(2) adduct 8 that shows symmetrical binding to the Ti(2) unit and supports the formulation of 4. The reaction of 1 with COS forms a thermally unstable complex 9 that undergoes scission to give mono(μ-S) mono(CO) species 10. Ph(3)PS is an effective sulfur transfer agent for 1, enabling the synthesis of mono(μ-S) complex 11 with a double-sandwich structure and bis(μ-S) dimer 12 in which the Ti–Ti bond has been cleaved

Bonding in complexes of bis(pentalene)di-titanium, Ti2(C8H6)2

Bonding in the bis(pentalene)di-titanium ‘double-sandwich’ species Ti2Pn2 (Pn = C8H6) and its interaction with other fragments have been investigated by xdensity functional calculations and fragment analysis. Ti2Pn2 with C2v symmetry has two metal-metal bonds and a low-lying metal based empty orbital, all three frontier orbitals having a1 symmetry. The latter may be regarded as being derived by symmetric combinations of the classic three frontier orbitals of two bent bis(cyclopentadienyl) metal fragments. Electrochemical studies on Ti2Pn†2 (Pn† = C8H4{SiiPr3-1,4}2) reveal a one-electron oxidation, and the formally mixed-valence Ti(II)-Ti(III) cationic complex [Ti2Pn†2][B(C6F5)4] has been structurally characterised. Theory indicates an S = ½ ground state electronic configuration for the latter, confirmed by EPR spectroscopy and SQUID magnetometry. Carbon dioxide binds symmetrically to Ti2Pn2 preserving C2v symmetry, as does carbon disulfide. The dominant interaction in Ti2Pn2CO2 is σ donation into the LUMO of bent CO2 and donation from the O atoms to Ti2Pn2 is minimal, whereas in Ti2Pn2CS2 there is significant interaction with the S atoms. The bridging O atom in the mono(oxo) species Ti2Pn2O, however, employs all three O 2p orbitals in binding and competes strongly with Pn, leading to weaker binding of the carbocyclic ligand, and the sulfur analog Ti2Pn2S behaves similarly. Ti2Pn2 is also capable of binding one, two and three molecules of carbon monoxide. The bonding demands of a single CO molecule are incompatible with symmetric binding and an asymmetric structure is found. The dicarbonyl adduct Ti2Pn2(CO)2 has Cs symmetry with the Ti2Pn2 unit acting as two MCp2 fragments. Synthetic studies show, that in the presence of excess CO a tricarbonyl complex Ti2Pn†2(CO)3 is formed, which optimises to an asymmetric structure with two terminal CO ligands and one semi-bridging. Low temperature 13C NMR spectroscopy reveals a rapid dynamic exchange between the two bound CO sites and free CO

Solvent- and anion-dependent rearrangement of fluorinated carbene ligands provides access to fluorinated alkenes

The construction of fluorocarbene ligands within the coordination sphere of transition metal complexes using sequential nucleophilic and electrophilic addition to a vinylidene complex is described. Reaction of [Ru(η5-C5H5)(dppe)([double bond, length as m-dash]C[double bond, length as m-dash]CPhF)][N(SO2Ph)2] with [NMe4]F results in nucleophilic attack of fluoride at the metal-bound carbon of the vinylidene ligand to give alkenyl complex [Ru(η5-C5H5)(dppe)(-CF[double bond, length as m-dash]CFPh)]. Subsequent eletrophilic fluorination with N-fluorobenzenesulfonimide (NFSI) results in the formation of the fluorinated carbene complex [Ru(η5-C5H5)(dppe)([double bond, length as m-dash]CF-CHFPh)][N(SO2Ph)2]. The fluorocarbene complexes undergo rearrangement to liberate free fluorinated alkenes, a process governed by the choice of solvent and anion, representing a new metal-mediated route to fluorinated alkenes from alkynes

Palladium–mediated organofluorine chemistry

Producción CientíficaThe substitution of fluorine for hydrogen in a molecule may result in profound changes in its properties and behaviour. Fluorine does not introduce special steric constraints since the F atom has a small size. However, the changes in bond polarity and the possibility of forming hydrogen bonds with other hydrogen donor fragments in the same or other molecules, may change the solubility and physical properties of the fluorinated compound when compared to the non-fluorinated one. Fluorine forms strong bonds to other elements and this ensures a good chemical stability. Altogether, fluorinated compounds are very attractive in materials chemistry and in medicinal chemistry, where many biologically active molecules and pharmaceuticals do contain fluorine in their structure and this has been shown to be essential for their activityJunta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA256U13

Filling a niche in “ligand space” with bulky, electron-poor phosphorus (III) alkoxides

The chemistry of phosphorus(III) ligands, which are of key importance in coordination chemistry, organometallic chemistry and catalysis, is dominated by relatively electron-rich species. Many of the electron-poor P(III) ligands that are readily available have relatively small steric profiles. As such, there is a significant gap in “ligand space” where more sterically bulky, electron-poor P(III) ligands are needed. This contribution discusses the coordination chemistry, steric and electronic properties of P(III) ligands bearing highly fluorinated alkoxide groups of the general form PRn(ORF)3-n, where R = Ph, RF = C(H)(CF3)2 and C(CF3)3; n = 1-3. These ligands are simple to synthesize and a range of experimental and theoretical methods suggest that their steric and electronic properties can be “tuned” by modification of their substituents, making them excellent candidates for large, electron-poor ligands