Synthesis and reactivity of a chlorinated 1,8-bis(diarylmethylium)naphthalenediyl dication

[Reaction: see text] 1,8-Bis(bis(p-chlorophenyl)methylium)naphthalenediyl dication has been prepared by treatment of the corresponding diol with a mixture of [HBF4]aq and (CF3CO)2O. The proximity of the methylium centers leads to strong electrostatic repulsions that are exacerbated by the electron-withdrawing p-chloro substituents. As indicated by cyclic voltammetry, this dication is the strongest oxidant of the 1,8-bis(methylium)naphthalenediyl series. It undergoes a reductive chlorination with chloride and reacts with bromide or iodide to afford the corresponding acenaphthenes.     

Alkylated trimethylene-bridged bis(p-phenylenediamines)

One and two electron oxidation of N,N',N',N'-tetramethyl-1,5,12,16-tetraaza[5,5]paracyclophane (Me3C), a bis-trimethylene bridged bis-p-phenylene diamine (PD), and its ethyl and isopropyl analogues are discussed. The monocation and dication are both stable, as demonstrated by optical studies that show they are in equilibrium in solution, with an especially small difference in first and second oxidation potentials for Me3C in MeCN (+23 to -20 mV, measured by simulation of the optical spectrum and of the cyclic voltammogram, respectively). The monocations have charge localized in one PD unit and show a Hush-type mixed valence transition between their PD0 and PD.+ groups. The dications Me3C2+ and Et3C2+ have optical spectra that appear to show large splittings between their PD.+ groups and have a weak ESR spectrum, and 1H NMR data show that the former is a ground-state singlet. iPr3C2+ has a very different optical spectrum and exhibits a triplet ESR spectrum at 120 K. X-ray crystal structures show that for Me3C0 the N(CH2)3N units on each side are in doubly anti (aa) conformations that put the aryl rings as far apart as possible, but Me3C2+ has doubly gg N(CH2)3N trimethylene bridges and both N,N and C,C distances between the PD.+ groups that are significantly below van der Walls contact. In contrast, iPr3C0 is in a doubly ag conformation, and its diradical dication is suggested to be a triplet because it does not attain the doubly gg conformation.     

Acyclic catena-diphosphinodiphosphonium dications [R3P-PR'-PR'-PR3]2+ or bisphosphine-diphosphenium complexes [R3PPR'-PR'PR3]2+: synthesis by reductive P-P coupling of [R3P-PR'Cl]+ and phosphine ligand exchange

The acyclic tetraphosphorus dication [Ph3P-PPh-PPh-PPh3]2+ has been formed by the reductive coupling of [Ph3P-PPhCl]+, providing a new synthetic method for the systematic development of catena-phosphorus cations. Ligand exchange (Ph3P for Me3P) gives [Me3P-PPh-PPh-PMe3]2+, implicating these dications as bisphosphine-diphosphenium complexes.     

An unprecedented type of linear metallocene with an f-element

The dication [(C5Me5)2U(NCMe)5]2+ was obtained by dissolving (C5Me5)2UI2 in acetonitrile or by treating (C5Me5)2UMe2 with HNEt3BPh4 in acetonitrile. The crystal structure revealed that the cyclopentadienyl rings are parallel and equidistant to the plane defined by the metal center and nitrogen atoms of the five MeCN ligands. Fifty years after the discovery of ferrocene, this compound represents a unique example of linear metallocene with auxiliary ligands in the equatorial girdle; it is also the first linear sandwich complex of an f-element.     

Syntheses, reactivity and DFT studies of group 2 and group 12 metal complexes of tris(pyrazolyl)methanides featuring "free" pyramidal carbanions

Reactions of HC(Me2pz)3 with Grignard reagents, dialkyl magnesium compounds and dimethylzinc are reported, together with a DFT study on some of the aspects of this chemistry. Reactions of HC(Me2pz)3 with MeMgX (X=Cl or Br) gave the half-sandwich zwitterionic compounds [Mg((Me)Tpmd)X] (X=Cl (2) or Br (3); (Me)Tpmd(-)=[C(Me2pz)3](-)). Addition of HCl to 2 gave the structurally characterised half-sandwich compound [Mg{HC(Me2pz)3}Cl2(thf)] (4). The zwitterionic sandwich compound [Mg(MeTpmd)2] (5) formed in low yields in the reaction of MeMgX with HC(Me2pz)3 but was readily prepared from HC(Me2pz)3 and either MgnBu2 or MgPh2. The structurally characterised compound 5 contains two "naked" sp3-hybridised carbanions fully separated from the dicationic metal centre. Only by using MgPh2 as starting material could the half-sandwich compound [Mg(MeTpmd)Ph(thf)] (6) be isolated. The zwitterionic sandwich compound 5 reacted with HOTf (OTf(-)=[O3SCF3](-)) to form the dication [Mg{HC(Me2pz)3}2]2+ (7(2+)), which was structurally characterised. Pulsed field gradient spin-echo (PGSE) diffusion NMR spectroscopy revealed both compounds to be intact in solution. In contrast to the magnesium counterparts, HC(Me2pz)3 reacted only slowly with ZnMe2 (and not at all with ZnPh2) to form the half-sandwich zwitterion [Zn(MeTpmd)Me] (8), which contains a cationic methylzinc moiety separated from a single sp3-hybridised carbanion. Density functional calculations on the zwitterions [M(MeTpmd)Me] and [M(MeTpmd)2] (M=Mg, Zn) revealed that the HOMO in each case is a (Me)Tpmd-based carbanion lone pair. The kappa 1C isomers of [M(MeTpmd)Me] were calculated to be considerably less stable than their kappa 3N-bound counterparts, with the largest gain in energy for Mg due to the greater ease of electron transfer from metal to the (Me)Tpmd apical carbon atom on formation of the zwitterion. Moreover, the computed M-C bond dissociation enthalpies of the kappa 1C isomers of [M(MeTpmd)Me] are considerably higher than expected by simple extrapolation from the corresponding computed H-C bond dissociation enthalpy.     

The preparation and characterisation of hetero- and homobimetallic complexes containing bridging naphthalene-1,8-dithiolato ligands

Homo- and heterobimetallic complexes of the form [(PPh(3))(2)(mu(2)-1,8-S(2)-nap){ML(n)}] (in which (1,8-S(2)-nap)=naphtho-1,8-dithiolate and {ML(n)}={PtCl(2)} (1), {PtClMe} (2), {PtClPh} (3), {PtMe(2)} (4), {PtIMe(3)} (5) and {Mo(CO)(4)} (6)) were obtained by the addition of [PtCl(2)(NCPh)(2)], [PtClMe(cod)] (cod=1,5-cyclooctadiene), [PtClPh(cod)], [PtMe(2)(cod)], [{PtIMe(3)}(4)] and [Mo(CO)(4)(nbd)] (nbd=norbornadiene), respectively, to [Pt(PPh(3))(2)(1,8-S(2)-nap)]. Synthesis of cationic complexes was achieved by the addition of one or two equivalents of a halide abstractor, Ag[BF(4)] or Ag[ClO(4)], to [{Pt(mu-Cl)(mu-eta(2):eta(1)-C(3)H(5))}(4)], [{Pd(mu-Cl)(eta(3)-C(3)H(5))}(2)], [{IrCl(mu-Cl)(eta(5)-C(5)Me(5))}(2)] (in which C(5)Me(5)=Cp*=1,2,3,4,5-pentamethylcyclopentadienyl), [{RhCl(mu-Cl)(eta(5)-C(5)Me(5))}(2)], [PtCl(2)(PMe(2)Ph)(2)] and [{Rh(mu-Cl)(cod)}(2)] to give the appropriate coordinatively unsaturated species that, upon treatment with [(PPh(3))(2)Pt(1,8-S(2)-nap)], gave complexes of the form [(PPh(3))(2)(mu(2)-1,8-S(2)-nap){ML(n)}][X] (in which {ML(n)}[X]={Pt(eta(3)-C(3)H(5))}[ClO(4)] (7), {Pd(eta(3)-C(3)H(5))}[ClO(4)] (8), {IrCl(eta(5)-C(5)Me(5))}[ClO(4)] (9), {RhCl(eta(5)-C(5)Me(5))}[BF(4)] (10), {Pt(PMe(2)Ph)(2)}[ClO(4)](2) (11), {Rh(cod)}[ClO(4)] (12); the carbonyl complex {Rh(CO)(2)}[ClO(4)] (13) was formed by bubbling gaseous CO through a solution of 12. In all cases the naphtho-1,8-dithiolate ligand acts as a bridge between two metal centres to give a four-membered PtMS(2) ring (M=transition metal). All compounds were characterised spectroscopically. The X-ray structures of 5, 6, 7, 8, 10 and 12 reveal a binuclear PtMS(2) core with PtM distances ranging from 2.9630(8)-3.438(1) A for 8 and 5, respectively. The napS(2) mean plane is tilted with respect to the PtP(2)S(2) coordination plane, with dihedral angles in the range 49.7-76.1 degrees and the degree of tilting being related to the PtM distance and the coordination number of M. The sum of the Pt(1)coordination plane/napS(2) angle, a, and the Pt(1)coordination plane/M(2)coordination plane angle, b, a+b, is close to 120 degrees in nearly all cases. This suggests that electronic effects play a significant role in these binuclear systems.     

Octahedral non-heme oxo and non-oxo Fe(IV) complexes: an experimental/theoretical comparison

Electron-transfer series are described for three ferric complexes of the pentadentate ligand 4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane-1-acetate (Me(3)cyclam-acetate) with axial chloride, fluoride, and azide ligands. These complexes can all be reduced coulometrically to their Fe(II) analogs and oxidized reversibly to the corresponding Fe(IV) species. The Fe(II), Fe(III), and Fe(IV) species have been studied spectroscopically and their UV-vis, M?ssbauer, EPR, and IR spectra are presented. The fluoro species [(Me(3)cyclam-acetate)FeF](n+) (n = 0, 1, 2) have been studied computationally using density functional theory (DFT), and the electronic structure of the Fe(IV) dication [(Me(3)cyclam-acetate)FeF](2+) is compared with that of the isoelectronic Fe(IV) oxo cation [(Me(3)cyclam-acetate)FeO](+); the different properties of the two species are mainly due to the significantly covalent Fe=O pi bonds in the latter.     

Can the hexamethylhydrazinium dication [Me(3)N-NMe(3)](2+) be prepared?

The long sought hexamethylhydrazinium(2+) dication, Me(3)N-NMe(3)(2+), calculationally unstable towards "coulombic explosion" because of formal positive charges on adjacent N atoms, can be synthesized and isolated as a CHB(11)Cl(11)(-) carborane salt.     

The pummerer and the thio-claisen–type rearrangements of naphtho[1,8-bc]-1,5-dithiocin monooxide and N-p-tosylsulfilimine

Naphtho[1,8-bc]-1,5-dithiocin N-p-tosylsulfilimine ( 8 ) and monosulfoxide ( 9 ) were prepared. On treatment with conc. H₂SO₄, both the sulfilimine ( 8 ) and sulfoxide ( 9 ) gave the dithia dication which was converted to the sulfoxide by hydrolysis. The H–D exchange reaction of ( 8 ) took place highly regioselectively to afford the monodeuterated ( 8–D ) at the a-position of the N-tosyl group. The Pummerer rearrangement reaction of monooxide ( 9 ) with acetic anhydride gave the a-acetoxy derivative by the dication ( 10b ), while a new thio-Claisen rearrangement of sulfilimine ( 8 ) t-BuOK in CH₂Cl₂ gave 2-allyl-naphtho[1,8-bc]-1,5-dithiole. © John Wiley & Sons, Inc.     

Synthesis and characterization of cationic iodonium macrocycles

A synthetic strategy for the high-yield preparation of iodonium containing macrocycles such as rhomboids, a square, and a pentagon is described, with the long-term objective of preparing iodonium compounds for potential molecular electronics applications. Two cationic rhomboid shaped molecules were prepared for the first time (55-70%) by the treatment of compounds 11 and 12a or 12b with Me3SiOTf. The reaction of dication 8 with 6 in the presence of Me3SiOTf gave an iodonium containing molecular square in 70% yield. In addition, a pentagon-shaped macromolecule was prepared in 60% yield. These iodonium-containing charged macromolecules were characterized by multinuclear NMR, mass spectrometry, and physical means.     

General pathway for a convenient one-pot synthesis of trifluoromethyl-containing 2-amino-7-alkyl(aryl/heteroaryl)-1,8-naphthyridines and fused cycloalkane analogues

A convenient and general method for the synthesis in 26-73% yields of a new series of 7-alkyl(aryl/heteroaryl)-2-amino-5-trifluoromethyl-1,8-naphthyridines from direct cyclocondensation reactions of 4-alkoxy-1,1,1-trifluoroalk-3-en-2-ones [CF?C(O)CH=C(R1)OR, where R1 = H, Me, Ph, 4-MePh, 4-OMePh, 4-FPh, 4-BrPh, 4-NO?Ph, 2-furyl, 2-thienyl and R = Me, Et] with 2,6-diaminopyridine (2,6-DAP), under mild conditions, is described. Another synthetic route also allowed the synthesis of 2-amino-5-trifluoromethyl-cycloalka[b][1,8]naphthyridines in 33-36% yields, from direct or indirect cyclo-condensation reactions of five-, six- and seven-membered 2-trifluoroacetyl-1-methoxy-cycloalkenes with 2,6-DAP.     

Key factors determining the course of methyl iodide oxidative addition to diamidonaphthalene-bridged diiridium(I) and dirhodium(I) complexes

The course of methyl iodide oxidative addition to various nucleophilic complexes, [Ir2(mu-1,8-(NH)2naphth)(CO)2(PiPr3)2] (1), [IrRh(mu-1,8-(NH)2naphth)(CO)2(PiPr3)2] (2), and [Rh2(mu-1,8-(NH)2naphth)(CO)2(PR3)2] (R = iPr, 3; Ph, 4; p-tolyl, 5; Me, 6), has been investigated. The CH3I addition to complex 1 readily affords the diiridium(II) complex [Ir2(mu-1,8-(NH)2naphth)I(CH3)(CO)2(PiPr3)2] (7), which undergoes slow rearrangement to give a thermodynamically stable stereoisomer, 8. The reaction of the Ir-Rh complex 2 gives the ionic compound [IrRh(mu-1,8-(NH)2naphth)(CH3)(CO)2(PiPr3)2]I (10). The dirhodium compounds, 3-5, undergo one-center additions to yield acyl complexes of the formula (Rh2(mu-1,8-(NH)2naphth)I(COCH3)(CO)(PR3)2] (R = iPr, 12; Ph, 13; p-tolyl, 14). The structure of 12 has been determined by X-ray diffraction. Further reactions of these Rh(III)-Rh(I) acyl derivatives with CH3I are productive only for the p-tolylphosphine derivative, which affords the bis-acyl complex [Rh2(mu-1,8-(NH)2naphth)(CH3CO)2I2(P(p-tolyl)3)2] (15). The reaction of the PMe3 derivative, 6, allows the isolation of the bis-methyl complex [Rh2(mu-1,8-(NH)2naphth)(mu-I)(CH3)2(CO)2(PMe3)2]I (16a), which emanates from a double one-center addition. Upon reaction with methyl triflate, the starting materials, 1, 2, 3, and 6, give the isostructural cationic methyl complexes 9, 11, 17, and 18, respectively. The behavior of these cationic methyl compounds toward CH3I, CH3OSO2CF3, and tetrabutylamonium iodide is consistent with the role of these species as intermediates in the SN2 addition of CH3I. Compounds 18 and 17 react with an excess of methyl triflate to give [Rh2(mu-1,8-(NH)2naphth)(mu-OSO2CF3)(CH3)2(CO)2(PMe3)2][CF3SO3] (19) and [Rh2(mu-1,8-(NH)2naphth)(OSO2CF3)(COCH3)(CH3)(CO)(PiPr3)2][CF3SO3] (20), respectively. Upon treatment with acetonitrile, complexes 17 and 18 give the isostructural cationic acyl complexes [Rh2(mu-1,8-(NH)2naphth)(COCH3)(NCCH3)(CO)(PR3)2][CF3SO3] (R = iPr, 21; Me, 22). A kinetic study of the reaction leading to 21 shows that formation of these complexes involves a slow insertion step followed by the fast coordination of the acetonitrile. The variety of reactions found in this system can be rationalized in terms of three alternative reaction pathways, which are determined by the effectiveness of the interactions between the two metal centers of the dinuclear complex and by the steric constraints due to the phosphine ligands.     

Facile access to methyl tantalum derivatives by unprecedented phosphorus—methyl bond cleavage of dimethylphenylphosphane

Reactions of the paramagnetic pentacoordinated TaBr₃(PhPMe₂)₂ adduct with strong bases, (RLi (R = Me, Bu) or 1,8-bis(dimethylamino)naphthalene) have been found to give methyltantalum(IV) derivatives as a result of PMe bond cleavage.     

Nanostructured columnar and cubic liquid-crystalline assemblies consisting of unconventional rigid mesogens based on triphenylmethanes

Liquid-crystalline (LC) molecules of unconventional shapes that form columnar and micellar cubic structures have been synthesized using triarylmethyl moieties as building blocks. The molecules have bowl- and dumbbell-shape. Despite the rigidity and bulkiness of the triarylmethyl moieties, the molecules form columnar and micellar cubic LC phases. The bowl-shaped molecules containing one triarylmethyl moiety show LC phases. The LC temperature ranges of the dumbbell-shaped molecules containing two triarylmethyl moieties connected by rigid rods are wider than those of bowl-shaped molecules containing one triarylmethyl moiety. The UV-vis spectroscopy of the dumbbell-shaped molecules having a terphenyl moiety reveals that the terphenyl moieties aggregate in the mesophase.     

Proton sponge phosphines: electrospray-active ligands

Attachment of a proton sponge to a phosphine ligand renders neutral complexes of the ligand highly amenable to analysis by electrospray ionisation mass spectrometry (ESI-MS). The ligand 1,8-bis(dimethylamino)naphthyldiphenylphosphine (3) is extremely efficient and highly selective in forming exclusively [M + H]+ ions, which may be detected at very low concentration. Ionisation efficiency of 3 in the presence of H+ approached 100%. The bis-substituted ligand bis{1,8-bis(dimethylamino)naphthyl}phenylphosphine (4) was also prepared and characterised, as were Fe(CO)4- (5c), Mn(eta5-C5H4Me)(CO)2- (6) and W(CO)5- (7) complexes of 3. Compounds 3, 3.HBr.EtOH, 4 and 5c were all structurally characterised.     

Platinum complexes of naphthalene-1,8-dichalcogen and related polyaromatic hydrocarbon ligands

Platinum bisphosphine complexes bearing dichalcogen-derivatised naphthalene, acenaphthene or phenanthrene ligands have been prepared by either oxidative addition to zero-valent platinum species or from [PtCl(2)(PPhR(2))] (R=Ph or Me) and the disodium or dilithium salts of the parent disulfur, diselenide or mixed S/Se species. The parent naphthalene, acenaphthene and phenanthrene chalcogen compounds were treated with either [Pt(PPh(3))(4)] or [Pt(C(2)H(4))(PMe(3))(2)] (prepared in situ from [PtCl(2)(PMe(3))(2)], ethene and sodium naphthalide or super hydride [LiBEt(3)H]) to give the appropriate platinum(II) species. The dilithium salts of 1,8-E(2)-naphthalene (E=S or Se) prepared in situ by reduction of the E-E bond with [LiBEt(3)H] were treated with [PtCl(2)(PPh(3))(2)] to give [Pt(1,8-E(2)-nap)(PPh(3))(2)]. The tetraoxides [Pt(1,8-(S(O)(2))(2)-nap)(PR(3))(2)] (PR(3)=PPh(3) or PMe(2)Ph) were prepared in a similar metathetical manner from the appropriate [PtCl(2)(PR(3))] complexes and the disodium salt of naphthalene 1,8-disulfinic acid (1,8-(S(O)ONa)(2)-nap). The X-ray structures of selected examples reveal bidentate coordination with the naphthalene-E(2) unit hinged (111-137 degrees) with respect to the coordination plane. The naphthalene ring suffers significant distortion from planarity.     

Tetraaminoperylenes: their efficient synthesis and physical properties

Trimethylsilylation of 1,8-diaminonaphthalene gave 1,8-bis(trimethylsilylamino)naphthalene (1 a), which was in turn lithiated with two molar equivalents of n-butyllithium to give the tris(thf)-solvated dilithium diamide [1,8-[(Me(3)SiN)Li(thf)](2)C(10)H(6)](thf) (2 a). Metal exchange of 2 a with TlCl was carried out in two steps, via the previously characterized mixed-metal amide [1-[(Me(3)SiN)Li(thf)(2)]-8-[(Me(3)SiN)Tl]C(10)H(6)], to give the dithallium diamide [1,8-[(Me(3)SiN)Tl](2)C(10)H(6)] (3 a). Thermolysis of 3 a cleanly gave a 1:1 mixture of the 4,9-bis(trimethylsilylamino)perylenequinone-3,10-bis(trimethylsilylimine) (4 a) and 1 a. By this route, a whole series of silylated homologues of 4 a was obtained in good yields, while the same method proved to be inefficient for the synthesis of the alkyl-substituted analogues. Compound 4 a and its tert-butyldimethylsilyl derivative 4 d were reduced with sodium amalgam to give, after protonation, the corresponding 3,4,9,10-tetraaminoperylenes 7 a and 7 d. Cyclic voltammetry showed two reversible, closely spaced reduction waves (E(red 1)=-1.39, E(red 2)=-1.59 V versus SCE) corresponding to this conversion. The perylenes 7 a and 7 d are thought to be the primary products in the reaction cascade leading to the perylene derivatives, involving the thermal demetalation of the thallium amides, possibly via Tl(II)bond;Tl(II) intermediates, first to give 7 a and its analogues. The final oxidation of the tetraaminoperylenes by one molar equivalent of 3 a and analogous thallium amides gave the quinoidal derivatives such as 4 a and 4 d, a step that could be studied by direct reaction of the isolated species. The UV/Vis absorption spectra of the 4,9-bis(silylamino)perylenequinone-3,10-bis(silylimines) are characterized by a long-wavelength absorption band with a pronounced vibrational structure (lambda(max)=639 nm, lg epsilon =4.53) attributed to a pi*<--pi and a pi*<--n absorption band at 454 nm (lg epsilon 4.83), along with intense absorption in the UV region. A weak red emission with a rather low quantum yield (Phi(fl)=0.001, lambda(max)=660 nm) is observed upon irradiation of a sample; the lifetime of the emission is only 66 ps. The low emission quantum yield is attributed to the *pi<--n transition of the amino perylene, which induces strong spin-orbit coupling, leading to a large triplet yield. The triplet state was probed by transient absorption spectroscopy and found to have a lifetime of 200 ns in air, and 1100 ns in argon-flushed solution. Treatment of 4 a with a stoichiometric amount of KF in methanol/water under phase-transfer conditions (with the cryptand [C 222]) gave an almost quantitative yield of the parent compound 4,9-diaminoperylenequinone-3,10-diimine (8). Treatment of 8 with two molar equivalents of the ruthenium complex [Ru(bpy)(2)(acetone)(2)](PF(6))(2), generated in situ, yielded the blue dinuclear ruthenium complex [(bpy)(4)Ru(2)[mu(2)-N,N':N",N"'-[[4,9-(NH(2))(2)-3,10-(NH)(2)]C(20)H(8)]]](PF(6))(4) (9), the redox properties of which were studied by cyclic voltammetry. The difference in the potentials of the two one-electron redox steps (225 mV) indicates strong coupling of the metal centers through the 4,9-diaminoperylenquinone-3,10-dimine bridging ligand and corresponds to a comproportionation constant K(c) of 6.3 x 10(3). The UV/Vis absorption spectrum of the mixed valent form, which is stable in air, has a characteristic intervalence charge-transfer (IVCT) band in the near infrared at 930 nm (lg epsilon =3.95), from which an electronic coupling parameter J of 760 cm(-1) could be estimated, placing compound 9 at the borderline between the class II and class III cases in the Robin-Day classification.     

Fluoride ion capture from water with a cationic borane

The reaction of the [Li(THF)4]+ salt of dimesityl-1,8-naphthalenediylborate with [Me2NCH2]I affords a borane (1-(Mes2B)-8-(Me2NCH2)-C10H6) which can be converted into a cationic borane [3]+ ([1-(Mes2B)-8-(Me3NCH2)-C10H6]+) by methylation with MeOTf. This cationic borane promptly complexes fluoride to afford the corresponding zwitterionic ammonium/fluoroborate 3-F (1-(Mes2FB)-8-(Me3NCH2)-C10H6). Cation [3]+ fails to react with chloride, bromide, and iodide indicating that fluoride complexation is selective. Structural, spectroscopic, and computational studies carried out on 3-F show the existence of an unusual C-H...F-B hydrogen bond. Remarkably, [3]+ captures fluoride from water under biphasic conditions (H2O/CHCl3) to form 3-F. The high fluoride affinity of [3]+ can be correlated to the Coulombic forces which stabilize the B-F bond against heterolysis.     

Reaction of the 1,8-bis(diphenylmethylium)naphthalenediyl dication with fluoride: formation of a cation containing a C-F-->C bridge

Treatment of 1,8-bis(diphenylhydroxymethyl)naphthalene with a mixture of [HBF(4)](aq) and (CF(3)CO)(2)O affords the corresponding dication, 1,8-bis(diphenylmethylium)naphthalenediyl (1(2+)), which was isolated as the [BF4]- salt. This dication has been fully characterized, and its structure has been studied computationally. The (13)C NMR resonance of the methylium centers appears at 207.7 ppm. As indicated by an X-ray single-crystal analysis, the vicinal methylium centers are separated by 3.112(4) A. Dication (1(2+)) reacts with fluoride to afford [1-F]+ which has been isolated as the [BF4]- salt. The fluorine atom of [1-F](+) is connected to one of the former methylium centers through a typical C-F bond of 1.424(2) A and forms a long interaction of 2.444(2) A with the other methylium center. While the structure of [1-F]+ can be largely accounted for by considering a simple methylium formulation, density functional calculations followed by an Atom In Molecules analysis as well as a calculation of the Boys localized orbitals indicate that the long C-F interaction of 2.444(2) A corresponds to a dative bond. Hence, formulation of [1-F]+ as an unsymmetrical fluoronium must also be considered. As indicated by 1H NMR spectroscopy, the structure of this ion is fluxional; the fluorine atom oscillates between the former methylium centers with apparent activation parameters of DeltaH++ = 52(+/-3) kJ mol(-1) and DeltaS++ = -18(+/-9) J K(-1) mol(-1) as derived from line shape analysis. This dynamic process, which has also been studied theoretically by B3LYP density functional theory and M?ller-Plesset second-order perturbation theory methods, involves symmetrical fluoronium ions as low-energy transition states.     

Electrochemical and EPR studies of the corannulene ruthenium(II) sandwich complex [(eta6-C6Me6)Ru(eta6-C20H10)](SbF6)(2)

The dication [(eta6-C6Me6)Ru(eta6-C20H10)]2+ in propylene carbonate solution exhibits a sequence of reduction processes that is either metal-centered [Ru(II)/Ru(I)/Ru(0)] or ligand-centered. The marginally stable Ru(I) monocation [(eta6-C6Me6)Ru(eta6-C20H10)]+ has been characterized by EPR spectroscopy. The electrochemistry of C20H10 and EPR features of its stable monoanion [C20H10]- have also been revisited.