A new synthesis of bis(triphenyl-λ(5)-phosphanylidene)ammonium fluoride ((Ph3PNPPh3)F, abbreviated as (PNP)F), is described. The title compound has been fully characterized by multinuclear NMR spectroscopy, vibrational spectroscopy, elemental analysis and single crystal and powder X-ray diffraction for the first time. In the solid state (PNP)F exists as a covalent molecular compound, in which the fluoride ion is asymmetrically bonded to the two phosphorus atoms of the [PNP](+) cation. The phosphorus-fluorine bond with 181.98(13) pm is surprisingly long and the longest P-F bond in any phosphorane. (PNP)F can be assumed to be a very good source of reactive fluoride. To investigate the fluoride ion donating properties, (PNP)F was reacted with a range of different fluoromethylsilanes Me(n)SiF(4-n) (n = 0-4). Reactions of (PNP)F with the fluoromethylsilanes were performed in aceto- or propionitrile and in 1,2-dimethoxyethane under inert conditions. The resulting hypervalent fluoromethylsilicates [Me(n)SiF(5-n)](-) (n = 0-3) were fully characterized by multinuclear NMR and vibrational spectroscopy and single crystal X-ray diffraction. From the reaction of (PNP)F with Me4Si in acetonitrile, the starting materials were recovered unchanged. To aid the understanding of the experimental results the fluoride ion affinities (FIA) for these silanes have been calculated by DFT calculations on the PBE0/def2-TZVPP level of theory. The fluoride ion affinity in the series of Me(n)SiF(4-n) (n = 0-4) decreases with the number of methyl groups and is too low for Me4Si to bind a fluoride ion under these reaction conditions.
While hydrogen bridging is very common in boron chemistry, halogen bridging is rather rare. The simplest halogen-bridged boron compounds are the [B2X7](-) anions (X = F, Cl, Br, I), of which only [B2F7](-) has been reported to exist experimentally. In this paper a detailed theoretical and synthetic study on the [B2X7](-) anions is presented. The structures of [B2X7](-) anions have been calculated at the MP2/def2-TZVPP level of theory, and their local minima have been shown to be of C2 symmetry in all cases. The bonding situation varies significantly between the different anions. While in [B2F7](-) the bonding is mainly governed by electrostatics, the charge is almost equally distributed over all atoms in [B2I7](-) and additional weak iodine···iodine interactions are observed. This was shown by an atoms in molecules (AIM) analysis. The thermodynamic stability of the [B2X7](-) anions was estimated in all phases (gas, solution, and solid state) based on quantum-chemical calculations and estimations of the lattice enthalpies using a volume-based approach. In the gas phase the formation of [B2X7](-) anions from [BX4](-) and BX3 is favored in accord with the high Lewis acidity of the BX3 molecules. In solution and in the solid state only [B2F7](-) is stable against dissociation. The other three anions are borderline cases, which might be detectable under favorable conditions. However, experimental attempts to identify [B2X7](-) (X = Cl, Br, I) anions in solution by (11)B NMR spectroscopy and to prepare stable [PNP][B2X7] salts failed.
The title crystal structure is a new triclinic polymorph of [(Ph3P)2N]Cl·(B(OH)3) or C36H30NP2
+·Cl−·BH3O3. The crystal structure of the orthorhombic polymorph was reported by [Andrews et al. (1983 ▶). Acta Cryst. C39, 880–882]. In the crystal, the [(Ph3P)2N]+ cations have no significant contacts to the chloride ions nor to the boric acid molecules. This is indicated by the P—N—P angle of 137.28 (8)°, which is in the expected range for a free [(Ph3P)2N]+ cation. The boric acid molecules form inversion dimers via pairs of O—H⋯O hydrogen bonds, and each boric acid molecule forms two additional O—H⋯Cl hydrogen bonds to one chloride anion. These entities fill channels, created by the [(Ph3P)2N]+ cations, along the c-axis direction.
This article reviews the literature reported during 2011 on gold and silver coordination and organometallic chemistry, focusing on synthetic applications (catalysis, coupling reactions, transmetallation), photochemical properties, biochemical studies as well as compounds with unique structural features. Gold and silver nanomaterials, self-assembled monolayers on Au surfaces as well as other metallic compounds (alloys) of gold and silver are not included.
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