Mason R. Haneline

Carbon-carbon coupling of C(sp3)-F bonds using alumenium catalysis.

Dialkylalumenium cation equivalents coupled with the hexabromocarborane anion function as efficient and long-lived catalysts for alkylation of aliphatic C-F bonds (alkylative defluorination or AlkDF) by alkylaluminum compounds. Only C(sp(3))-F bonds undergo AlkDF; C(sp(2))-F bonds are unaffected. Examples of compounds undergoing AlkDF include monofluoroalkanes, gem-difluorocyclopentane, and compounds containing a CF(3) group attached to either an aryl or an alkyl substituent. Conversion of C-F bonds to C-Me bonds is accomplished with high fidelity using Me(3)Al as the stoichiometric reagent. In reactions with Et(3)Al, hydrodefluorination of the C-F bonds is competitive with alkylation, indicative presumably of competitive hydride vs alkyl transfer from Et(3)Al. In a trialkylaluminum reagent, 1.1-1.4 alkyl groups per Al can be used to replace C-F bonds. Organoaluminum compounds efficiently remove water from the reaction mixture, obviating the need for rigorously dry solvents. Some organoaluminum compounds, especially methylaluminoxane, are capable of AlkDF with more reactive substrates, but catalysis by alumenium offers an advantage over the uncatalyzed C-F activation in terms of both increased rate and, in some cases, a dramatically increased selectivity.

Group IV Imino-Semiquinone Complexes Obtained by Oxidative Addition of Halogens

An isostructural series of titanium, zirconium, and hafnium complexes, M[ap] 2L 2 (M = Ti, Zr, Hf; L = THF, pyridine), of the redox-active 4,6-di- tert-butyl-2- tert-butylamidophenolate ligand ([ap] (2-)) have been prepared. The zirconium and hafnium derivatives react readily with halogen oxidants such as XeF 2, PhICl 2, and Br 2, leading to products in which one-electron oxidation of each [ap] (2-) ligand accompanies halide addition to the metal center. Iodine proved to be too weak of an oxidant to yield the corresponding oxidative addition product, and under no conditions could halogen oxidative addition products be obtained for titanium. According to X-ray crystallographic studies, the zirconium and hafnium oxidation products are best formulated as MX 2[isq.] 2 ([isq.] (-) = 4,6-di- tert-butyl-2- tert-butylimino-semiquinonate; M = Zr, Hf; X = F, Cl, Br) species, in which the molecule is symmetric with each redox-active ligand in the semiquinone oxidation state. Temperature-dependent magnetization measurements suggest a singlet ( S = 0) ground-state for the diradical complexes with a thermally accessible triplet ( S = 1) excited state. Solution electron paramagnetic resonance (EPR) spectra are consistent with this assignment, showing both Delta m s = 1 and Delta m s = 2 transitions for the antiferromagnetically coupled electrons.

Methyl substituted benzene adducts of trimeric perfluoro-o-phenylene mercury

Trimeric perfluoro-ortho-phenylene mercury (1) dissolves in substituted benzenes including toluene, ortho-xylene, meta-xylene, para-xylene and is sparingly soluble in mesitylene. The 199Hg NMR resonance of 1 in toluene, ortho-xylene, meta-xylene, and para-xylene appears at δ −1051.8, −1053.5, −1051.4 and −1059.1 ppm, respectively. These resonances are slightly upfield from the resonance observed for 1 in CH2Cl2 (δ −1045.2 ppm) and possibly indicates the solvation of the mercury centres by molecules of arenes. Slow evaporation of solutions of 1 in toluene, ortho-xylene, meta-xylene, para-xylene and mesitylene affords 1·toluene (2), 1·ortho-xylene (3), 1·meta-xylene (4), 1·para-xylene (5) and 1·mesitylene (6), respectively, as crystalline complexes. These adducts have been characterized by elemental analysis and X-ray crystallography. Thermogravimetric analyses indicate that 2–5 begin to lose the coordinated arene at a temperature below 50 °C; however, in the case of 6 loss begins around 91 °C. The structures of 2, 4 and 5 reveals the existence of binary stacks in which the aromatic core of the benzenes approaches the mercury centres of 1. In the case of 3 and 6, the aromatic molecule appears preferentially bound to one of the two proximal molecules of 1. Hence, 3 and 6 are best described as discrete 1 ∶ 1 complexes. In 2–6, the resulting Hg⋯Caromatic distances are in the range 3.2–3.5 A and are within the sum of the van der Waals radii. They reflect the presence of secondary polyhapto π-interactions occurring between the electron-rich aromatic molecules and the acidic mercury centres.

Nanoelectrospray MS and MS-MS investigation of two polydendate Lewis acids, (C6F4Hg)3 and o-C6F4(HgCl)2, characterization and halide binding selectivity

Abstract The coordination of halide anions by two polyfunctional Lewis acids, namely trimeric perfluoro- ortho -phenylene mercury ( 1 ) and 1,2-bis(chloromercurio)tetrafluorobenzene ( 2 ) has been monitored by negative ion nanoelectrospray mass spectrometry using a hybrid quadrupole time-of-flight instrument. Experiments carried out on compound 1 in the presence of halide anions show the formation of the anionic complexes, [ 1 ·X] − and [( 1 ) 2 ·X] − . The latter are likely to exhibit a bridged structure in which the halide anion is sandwiched by two molecules of 1 . In order to determine the anion binding selectivity of 1 , relative affinity measurements were carried out and reveal the following order: I − >Br − >Cl − >F − . After normalization of the halide binding affinities to that of iodide, the following values could be obtained: I − 100%, Br − 9.5±1.6%, Cl − 2.4±1.5%, and F − 0.3±0.1% indicating that 1 is ∼10× less likely to bind bromide, ∼40× less likely to bind chloride, and ∼400× less likely to bind fluoride than iodide. Two fragmentation methods, namely nozzle-skimmer fragmentation and CID MS–MS, were used to further characterize the anionic complexes of 1 . Experiments carried out on 2 in the presence of different halides gave widely varied results. With excess chloride, the anionic complex [ 2 ·Cl] − is formed. In the presence of excess bromide, 2 is converted into 1,2-bis(bromomercurio)tetrafluorobenzene ( 3 ) and detected as the bromide complex [ 3 ·Br] − . With excess iodide, 2 undergoes a condensation reaction to form 1 , which is detected as the iodide complex [ 1 ·I] − .

Polymorphism of Trimeric Perfluoro-ortho-phenylene Mercury, [Hg(o-C6F4)]3

Three new modifications of trimeric perfluoro-ortho-phenylene mercury (2) have been investigated by single crystal X-ray diffraction. In each of these modifications, the molecules of 2 form extended stacks. Within each stack, the successive molecules are parallel and separated by approximately 3.3 - 3.4 Å. The packing observed in the different structures is rationalized on the basis of secondary mercury-π interactions, mercuriophilic interactions and electrostatic interactions. Altogether, little preference is given for one particular type of interaction. The packing appears to be dominated by non-directional van der Waals interactions between molecules of 2 which are largely aromatic and whose overall polarizability is magnified by relativistic effects at the mercury(II) centers.