Reversible Electrochemical Lithium-Ion Insertion into the Rhenium Cluster Chalcogenide-Halide Re6Se8Cl2.

The cluster-based material Re6Se8Cl2 is a two-dimensional ternary material with cluster-cluster bonding across the a and b axes capable of multiple electron transfer accompanied by ion insertion across the c axis. The Li/Re6Se8Cl2 system showed reversible electron transfer from 1 to 3 electron equivalents (ee) at high current densities (88 mA/g). Upon cycling to 4 ee, there was evidence of capacity degradation over 50 cycles associated with the formation of an organic solid-electrolyte interface (between 1.45 and 1 V vs Li/Li+). This investigation highlights the ability of cluster-based materials with two-dimensional cluster bonding to be used in applications such as energy storage, showing structural stability and high rate capability.

Small molecule activation of nitriles coordinated to the [Re6Se8]2+ core: formation of oxazine, oxazoline and carboxamide complexes.

Novel oxazine, oxazoline and carboxamide cluster complexes were prepared when different nucleophilic oxygen species reacted with nitriles coordinated to the Lewis acidic [Re6Se8]2+ cluster core. Reaction of ICH2CH2O- (generated in situ) with [Re6Se8(PEt3)5(NCR)]A2 (1A2 (R = Me) and 2A2 (R = Ph) where A = BF4-), leads to the formation of [Re6Se8(PEt3)5(2-methyloxazoline)]2+ (32+) and [Re6Se8(PEt3)5(2-phenyloxazoline)]2+ (42+). Similarly, reaction of BrCH2CH2CH2O- with the same nitrile complexes, 1A2 and 2A2 (where A = BF4- or SbF6-) leads to the corresponding oxazine complexes, [Re6Se8(PEt3)5(2-methyloxazine)]2+ (52+) and [Re6Se8(PEt3)5(2-phenyloxazine)]2+ (62+). In addition, reaction of 2(BF4)2 with KOH leads to the formation of the carboxamide complex, [Re6Se8(PEt3)5(phenylcarboxamide)](BF4) (7(BF4)). The neutral oxazine and oxazoline ligands can be removed using either heat or UV irradiation; UV irradiation was found to be more efficient at ligand removal as indicated by the shorter reaction times. The relative coordination strength of the neutral N-donor ligands was determined by these reaction times. X-ray structure determinations of 5(BF4)2 and 7(BF4) are also reported.

Crystal structure of octa-µ3-selenido-(p-toluene-sulfonato-κO)penta-kis-(tri-ethyl-phosphane-κP)-octa-hedro-hexa-rhenium(III) p-toluene-sulfonate di-chloro-methane disolvate.

The title compound, [Re6Se8{O3SC6H4(CH3)}{P(C2H5)3}5](CH3C6H4SO3)·2CH2Cl2, contains the face-capped hexa-nuclear [Re6(µ3-Se)8](2+) cluster core. The [Re6Se8](2+) cluster core displays a non-crystallographic center of symmetry and is bonded through the Re(III) atoms to five tri-ethyl-phosphane ligands and one p-toluene-sulfonate ligand. One p-toluene-sulfonate counter-ion and two di-chloro-methane solvent mol-ecules are also present in the asymmetric unit. One of the ethyl chains of one triethylphos-phane ligand and one of the CH2Cl2 solvent molecules are disordered over two sets of sites (occupancy ratios 0.65:0.35 and 0.5:0.5, respectively). The Re-O(sulfon-ate) bond length of 2.123 (5) Šis similar to other Re-O bond lengths of hexa-nuclear rhenium chalcogenide clusters containing other O-donor ligands such as dimethyl sulfoxide (DMSO), di-methyl-formamide (DMF) and hydroxide.

Organometallic rhenium(III) chalcogenide clusters: coordination of N-heterocyclic carbenes.

The preparation of rhenium based octahedral clusters containing N-heterocyclic carbenes is described. These represent the first examples of [M6(µ3-Q)8](n+) or [M6(µ3-X)8](n+) clusters to contain a carbene ligand of any type (NHC, Fischer or Schrock). Surprisingly, the NHC ligands attenuate their luminescent properties.

Octa-µ3-selenido-penta-kis-(tri-ethyl-phos-phane-κP)(tri-methyl-aceto-nitrile-κN)-octa-hedro-hexa-rhenium(III) bis-(hexa-fluorido-anti-monate) tri-methyl-aceto-nitrile monosolvate.

The crystal structure of the title compound, [Re6Se8{NCC(CH3)3}(Et3P)5](SbF6)2·NCC(CH3)3, contains a face-capped octa-hedral [Re6(µ3-Se)8](2+) cluster core. The pseudo-centrosymmetric [Re6Se8](2+) cluster core is bonded through the Re atoms to five tri-ethyl-phosphane ligands and one tri-methyl-aceto-nitrile ligand. No significant interactions are observed between the cationic cluster, the SbF6 (-) anions and the trimethylacetonitrile solvent molecule.

Azide alkyne cycloaddition facilitated by hexanuclear rhenium chalcogenide cluster complexes.

Two hexanuclear rhenium clusters containing azide ligands, [Re6Se8(PEt3)5(N3)]BF4 and [Re6Se8(PEt3)4(N3)2], were synthesized from the analogous pyridine complexes and fully characterized. Studies show that [Re6Se8(PEt3)5(N3)]BF4 reacts with activated alkynes, dimethyl acetylenedicarboxylate and methyl 4-hydroxyhex-2-yneoate, to form the triazolate cluster complexes [Re6Se8(PEt3)5(L1 or L2)]BF4 (where L1 = 4,5-bis(methoxycarbonyl)-1,2,3-triazol-2-yl and L2 = 4-methoxycarbonyl-5-(1-propanol)-1,2,3-triazol-2-yl). The bis-triazolato complex, cis-[Re6Se8(PEt3)4(L1)2] was also prepared via a similar reaction starting with cis-[Re6Se8(PEt3)4(N3)2] demonstrating that these clusters can promote two azide moieties to undergo heterocyclic ring formation. The structures of [Re6Se8(PEt3)5(N3)]BF4, [Re6Se8(PEt3)4(N3)2], and [Re6Se8(PEt3)5(L1)](BF4), were determined by single-crystal X-ray diffraction analysis. In addition, studies involving the alkylation of [Re6Se8(PEt3)5(L1)]BF4 with benzyl bromide and methyl iodide are reported.

Preparation of a family of hexanuclear rhenium cluster complexes containing 5-(phenyl)tetrazol-2-yl ligands and alkylation of 5-substituted tetrazolate ligands.

The preparation of two new families of hexanuclear rhenium cluster complexes containing benzonitrile and phenyl-substituted tetrazolate ligands is described. Specifically, we report the preparation of a series of cluster complexes with the formula [Re(6)Se(8)(PEt(3))(5)L](2+) where L = benzonitrile, p-aminobenzonitrile, p-methoxybenzonitrile, p-acetylbenzonitrile, or p-nitrobenzonitrile. All of these complexes undergo a [2 + 3] cycloaddition with N(3)(-) to generate the corresponding [Re(6)Se(8)(PEt(3))(5)(5-(p-X-phenyl)tetrazol-2-yl)](+) (or [Re(6)Se(8)(PEt(3))(5)(2,5-p-X-phenyltetrazolate)](+)) cluster complexes, where X = NH(2), OMe, H, COCH(3), or NO(2). Crystal structure data are reported for three compounds: [Re(6)Se(8)(PEt(3))(5)(p-acetylbenzonitrile)](BF(4))(2)•MeCN, [Re(6)Se(8)(PEt(3))(5)(2,5-phenyltetrazolate)](BF(4))•CH(2)Cl(2), and [Re(6)Se(8)(PEt(3))(5)(2,5-p-aminophenyltetrazolate)](BF(4)). Treatment of [Re(6)Se(8)(PEt(3))(5)(2,5-phenyltetrazolate)](BF(4)) with HBF(4) in CD(3)CN at 100 °C leads to protonation of the tetrazolate ring and formation of [Re(6)Se(8)(PEt(3))(5)(CD(3)CN)](2+). Surprisingly, alkylation of the phenyl and methyl tetrazolate complexes ([Re(6)Se(8)(PEt(3))(5)(2,5-N(4)CPh)](BF(4)) and [Re(6)Se(8)(PEt(3))(5)(1,5-N(4)CMe)](BF(4))) with methyl iodide and benzyl bromide, leads to the formation of mixtures of 1,5- and 2,5-disubstituted tetrazoles.

Substitution of the terminal chloride ligands of [Re(6)S(8)Cl(6)](4-) with triethylphosphine: photophysical and electrochemical properties of a new series of [Re(6)S(8)](2+) based clusters.

A systematic substitution of the terminal chlorides coordinated to the hexanuclear cluster [Re(6)S(8)Cl(6)](4-) has been conducted. The following complexes: [Re(6)S(8)(PEt(3))Cl(5)](3-) (1), cis- (cis-2) and trans-[Re(6)S(8)(PEt(3))(2)Cl(4)](2-) (trans-2), mer- (mer-3) and fac-[Re(6)S(8)(PEt(3))(3)Cl(3)](-) (fac-3), and cis- (cis-4) and trans-[Re(6)S(8)(PEt(3))(4)Cl(2)] (trans-4) were synthesized and fully characterized. Compared to the substitution of the halide ligands of the related [Re(6)S(8)Br(6)](4-) and [Re(6)Se(8)I(6)](3-) clusters, the chloride ligands are slower to substitute which allowed us to prepare the first monophosphine cluster (1). In addition, the synthesis of fac-3 was optimized by using cis-2 as the starting material, which led to a significant increase in the overall yield of this isomer. Notably, we observed evidence of phosphine isomerization taking place during the preparation of the facial isomer; this was unexpected based on the relatively inert nature of the Re-P bond. The structures of Bu(4)N(+) salts of trans-2, mer-3, and fac-3 were determined using X-ray crystallography. All compounds display luminescent behavior. A study of the photophysical properties of these complexes includes measurement of the excited state lifetimes (which ranged from 4.1-7.1 µs), the emission quantum yields, the rates of radiative and non-radiative decay, and the rate of quenching with O(2). Quenching studies verify the triplet state nature of the excited state.

Beta-amino alcohol derived beta-hydroxy- and beta-(o-diphenylphosphino)benzoyloxy(o-diphenylphosphino)benzamides: an ester-amide ligand structural model for the palladium-catalyzed allylic alkylation reaction.

A commercially available collection of beta-amino alcohols have been converted to their corresponding beta-hydroxy- and beta-(o-diphenylphosphino)benzoyloxy(o-diphenylphosphino)benzamides 11a-f and 12a-f and have been employed in the Tsuji-Trost asymmetric alkylation reaction with 1,3-diphenylpropenyl acetate. With the exception of ligands 11b and 11f, the beta-hydroxybenzoyloxy(o-diphenylphosphino)benzamide ligands 11a-f primarily afforded the (R)-enantiomer of the product. In contrast, the bis(phosphine) ligands 12a-f consistently afforded the (S)-enantiomer. The best ligand (12c) was derived from cis-(1R,2S)-2-amino-1,2-diphenyl-1-ethanol, and when applied in the asymmetric allylic alkylation reaction, it yielded the product in an enantiomeric ratio of 97.8.22 favoring the (S)-enantiomer. A computational study was conducted on the conformation that this ligand might adopt in the palladium-catalyzed alkylation reaction as compared to that of the Trost ligand 1a.

Synthesis and study of hexanuclear molybdenum clusters containing thiolate ligands.

Four hexanuclear molybdenum chloride cluster complexes containing terminal thiolate ligands have been synthesized and fully characterized. (Bu 4N) 2[Mo 6Cl 8(SEt) 6] was prepared by reacting Na 2[Mo 6Cl 8(OMe) 6] with an excess of ethanethiol in refluxing tetrahydrofuran. (PPN) 2[Mo 6Cl 8(SBu) 6], (Bu 4N) 2[Mo 6Cl 8(SBn) 6], and (Bu 4N) 2[Mo 6Cl 8(SNC 8H 6) 6] (C 8H 6NS (-) = 3-indolylthiolate) were subsequently prepared in the reaction of [Mo 6Cl 8(SEt) 6] (2-) with an excess of HSR (R = Bu, Bn or 3-indolyl). Single crystal X-ray diffraction analyses were performed on two of these complexes: (PPN) 2[Mo 6Cl 8(SEt) 6].Et 2O, crystallizes in the triclinic space group P1 with a = 12.3894(11), b = 13.7651(12), c = 15.0974(13), alpha = 103.975(2), beta = 99.690(2), gamma = 98.062(2), and Z = 1; (PPh 3Me) 2[Mo 6Cl 8(SBn) 6].2NO 2CH 3, also crystallizes in the P1 space group with a = 12.1574(16), b = 13.4441(17), c = 14.2132(18), alpha = 89.654(2), beta = 88.365(2), gamma = 71.179(2), and Z = 1. Our studies demonstrate that [Mo 6Cl 8(SEt) 6] (2-) displays luminescent properties and that the same complex undergoes substitution reactions with different thiols, as well as reaction with electrophilic reagents such as MeI.

Synthesis and electrochemical study of the first tetrazolate hexanuclear rhenium cluster complex.

The linkage isomers [Re(6)Se(8)(PEt(3))(5)(1,5-MeN(4)C)](+) and [Re(6)Se(8)(PEt(3))(5)(2,5-MeN(4)C)](+) were generated upon reaction of tetrabutylammonium azide with the corresponding acetonitrile complex, [Re(6)Se(8)(PEt(3))(5)(NCCH(3))](2+); these are the first (tetrazolato)rhenium complexes reported to date.

Polycyclooctatetraeneoxy alkane polyanionic polyradicals.

The room temperature potassium reduction of 1,2,3-triscyclooctatetraeneoxypropane, in hexamethylphosphoramide (HMPA), yields an anion radical, which disproportionates so strongly to the dianion diradical that the anion radical cannot be observed via EPR. The dianion diradical has one unpaired electron in a primary and one in a secondary ring system, and it can be readily reduced to the corresponding trianion triradical. An analogous reduction of 1,2,3,4-tetrakiscyclooctatetraeneoxybutane does produce an observable anion radical, but it also is readily reduced to the system corresponding to one electron per eight-membered ring (the tetraanion tetraradical). These results and those obtained from systems containing two cyclooctatetraene (COT) moieties are explained in terms of the geometry changes COT undergoes upon one-electron reduction, the interactions between reduced and adjacent unreduced ring systems, and the electron- electron repulsion present in the polyanion polyradicals.

New riches in carbaporphyrin chemistry: silver and gold organometallic complexes of benzocarbaporphyrins.

The NH-N-NH-N core of the porphyrin system represents one of the best studied and most versatile platforms for coordination chemistry. However, the replacement of one or more of the interior nitrogens with carbon atoms would be expected to diminish the ability of these systems to form metallo derivatives considerably. Despite this expectation, carbaporphyrinoid systems have been shown to form stable organometallic derivatives. Although azuliporphyrins and benziporphyrins act as dianionic ligands, benzocarbaporphyrins are trianionic ligands. Treatment of five different meso unsubstituted benzocarbaporphyrins and two different meso tetraarylbenzocarbaporphyrins with excess silver(I) acetate afforded 65-97% yields of the corresponding silver(III) organometallic derivatives. The insertion of silver metal was confirmed by mass spectrometry and X-ray crystallography. The UV-vis spectra showed a strong Soret band at wavelengths between 437 and 451 nm, together with a series of Q-type bands at longer wavelengths. The new metallo carbaporphyrins demonstrate the presence of a strong diatropic ring current in their proton NMR spectra, and carbon-13 NMR spectroscopy indicates that the derivatives retain a plane of symmetry. The reaction of meso tetraaryl carbaporphyrins with gold(III) acetate afforded the related gold(III) complexes, and these also showed strongly porphyrin-like aromatic characteristics. The UV-vis spectra for the gold complexes again showed a strong Soret band between 437-439 nm, but a secondary band near 400 nm is somewhat intensified for the gold species compared to the spectra for the related silver(III) meso tetrasubstituted carbaporphyrins. The ring currents observed for the gold(III) complexes by proton NMR spectroscopy were comparable to those of the silver(III) derivatives, implying that both series have similar macrocyclic conformations. Cyclic voltammetry was performed on two different carbaporphyrins, their silver(III) derivatives, and a gold(III) complex. The silver complexes display a reversible cathodic wave that is assigned to the Ag(III/II) couple. However, the gold porphyrinoid gave a value for the reductive wave that could be due to a gold(III/II) couple or a ligand-based process.

Organometallic chemistry of azuliporphyrins: synthesis, spectroscopy, electrochemistry, and structural characterization of nickel(II), palladium(II), and platinum(II) complexes of azuliporphyrins.

Four azuliporphyrins, two meso-unsubstituted and two meso-tetraaryl substituted, were investigated in the synthesis of novel organometallic compounds. The meso-unsubstituted or "etio" series azuliporphyrins 8 reacted with nickel(II) acetate, palladium(II) acetate, and platinum(II) chloride in DMF to give the corresponding chelates 14-16, where the metal cation lies within the macrocyclic cavity and binds to all three nitrogens and the internal carbon atom. The newly available meso-tetraarylazuliporphyrins 13 similarly afforded the corresponding nickel(II), palladium(II), and platinum(II) complexes, 17-19, respectively. The new organometallic complexes are stable nonpolar compounds and were fully characterized spectroscopically and by mass spectrometry. The UV-vis data indicate that these complexes, in common with the parent azuliporphyrin system 8, do not possess porphyrin-type aromaticity. However, electron donation from the azulene unit can give rise to dipolar resonance contributors that provide a degree of carbaporphyrin-type aromatic character. The platinum(II) azuliporphyrins 16 gave noteworthy proton NMR spectra where the meso-protons showed satellite peaks due to transannular coupling to platinum-195. The pyrrolic protons of the platinum(II) meso-tetraarylazuliporphyrin 19b also showed similar satellite peaks due to coupling from the platinum-195 isotope. The electrochemistry of free base tetraphenylazuliporphyrin 13a and the related nickel(II) and palladium(II) complexes was investigated using cyclic voltammetry, and these data indicate that metal coordination improves the reversibility of the ligand-based oxidations. Nickel(II) azuliporphyrin 14a and palladium(II) tetrakis(4-chlorophenyl)azuliporphyrin 18b were also structurally characterized by X-ray crystallography. The macrocyclic core of the palladium(II) complex 18b was significantly more planar than the nickel(II) derivative 14b, and this difference was attributed to the better size match between the azuliporphyrin cavity and the larger palladium(II) ion. The straightforward synthesis of metalloazuliporphyrins under mild conditions, and their interesting spectroscopic, electrochemical, and structural features, demonstrates that the azuliporphyrin system holds great promise as a platform for organometallic chemistry.

Silver(III) carbaporphyrins: the first organometallic complexes of true carbaporphyrins.

Reaction of carbaporphyrins 1 with silver(I) acetate in methanol-CH(2)Cl(2) gave excellent yields of the related silver(III) complexes 6. These nonpolar organometallic compounds retain fully aromatic properties as judged by UV-vis and NMR spectroscopy and were further characterized by X-ray crystallography and cyclic voltammetry.

Conjugated macrocycles related to the porphyrins. 21. Synthesis, spectroscopy, electrochemistry, and structural characterization of carbaporphyrins.

The "3 + 1" variant of the MacDonald condensation has been shown to be an excellent methodology for synthesizing carbaporphyrins. In particular, 1,3-indenedicarbaldehyde condenses with tripyrranes in the presence of TFA to give, following oxidation with DDQ, a series of benzocarbaporphyrins in excellent yields. Triformylcyclopentadienes also afford carbaporphyrin products, albeit in low yields ranging from 5 to 8%. These hybrid bridged annulene structures have porphyrin-like electronic absorption spectra with strong Soret bands near 420 nm and a series of Q-bands through the visible region. The proton NMR spectrum confirms the presence of a strong diamagnetic ring current, and the meso-protons show up at 10 ppm, while the internal CH is shielded to approximately -7 ppm. Carbaporphyrins undergo reversible protonation with TFA. Initial addition of acid affords a monocation, although mixtures of protonated species are observed in the presence of moderate concentrations of TFA. However, in the presence of 50% TFA a C-protonated dication is generated. The dications relocate the pi-delocalization pathway through the benzo moiety of benzocarbaporphyrins, and these therefore represent bridged benzo[18]annulenes, although they nevertheless retain powerful macrocyclic ring currents. Carbaporphyrins with fused acenaphthylene and phenanthrene rings have been prepared, and the former demonstrated significantly larger bathochromic shifts in UV-vis spectroscopy that parallel previous observations for acenaphthoporphyrins. A diphenyl-substituted benzocarbaporphyrin 19b was also characterized by X-ray crystallography, and these data show that the macrocycle is reasonably planar although the indene subunit is tilted out of the mean macrocyclic plane by 15.5 degrees. The structural data indicates that the preferred tautomer in the solid state has the two NH's flanking the pyrrolene unit in agreement with previous spectroscopic and theoretical studies. Cyclic voltammetry for carbaporphyrin 19a was more complex than for true porphyrins, showing five anodic waves and two quasi-reversible reductive couples.