Fascinating chemistry of metal clusters and carbon clusters (fullerenes)

Investigations of a variety of transition metal clusters by means of high-energy spectroscopies including BIS show the occurrence of a metal-insulator transition with decrease in the cluster size. The chemical reactivity of the clusters also varies significantly with the size. Among the many fascinating properties of the fullerenes C60 and C70, a noteworthy one is the interaction between metal clusters and fullerenes. Phase transitions of fullerenes involving orientational disorder and pressure-induced decrease in the band gap of C60 are other novel features of interest.

Organometallic chemistry of diphosphazanes. Part 7. Platinum(II), palladium-(o), -(I) and -(II) complexes of RN[P(OPh)2]2(R = Me or Ph)

The reactions of [MCl2(cod)](M = Pd or Pt, cod = cycloocta-1,5-diene) with RN[P(OPh)2]2[R = Me (L1) or Ph (L2)] afford the chelate complexes [MCl2L1] and [MCl2L2]. The dinuclear palladium(O) complex, [Pd2L13] has been synthesized by starting from [Pd2(dba)3](dba = dibenzylideneacetone). Redox condensation of [Pd2(dba)3] and [PdCl2(PhCN)2] in the presence of the diphosphazane ligands gives the dinuclear palladium(I) complexes [Pd2Cl2L12] and [Pd2Cl2L22]. The structures of the complexes have been deduced from 1H and 31P NMR spectroscopic data. Single-crystal X-ray diffraction studies confirm the structures of [Pd2L13] and [Pd2Cl2L22].

Organometallic chemistry of diphosphazanes *1: VIII. Synthesis, spectroscopic studies and crystal structure of fac-[Mo(CO)3(MeCN)Ph2PN(iPr)P(Ph)(DMP)], and its reactions with tertiary phosphines

The reaction of fac-[Mo(CO)3(MeCN)3] with the unsymmetrical diphosphazane Ph2PN(iPr)P(Ph)(DMP) (L) gives the complex fac-[Mo(CO)3(MeCN)(L)] (2) in almost quantitative yield. The structure of the complex has been determined by an X-ray diffraction study. The compound reacts with PR3 (where R = Ph, OPh) to give fac-[Mo(CO)3(PR3)(L)] (3a, 4a), which undergoes an intramolecular isomerization to afford mer-[Mo(CO)3(PR3)(L)] (3b, 4b). Synthesis of cis-[Mo(CO)4(L)] (1) and fac-[MO(CO)3L] (2a) and their spectroscopic data are also reported.

Surface Chemistry of Thiobacillus ferrooxidans Relevant to Adhesion on Mineral Surfaces

Thiobacillus ferrooxidans cells grown on sulfur, pyrite, and chalcopyrite exhibit greater hydrophobicity than ferrous ion-grown cells. The isoelectric points of sulfur-, pyrite-, and chalcopyrite-grown cells were observed to be at a pH higher than that for ferrous ion-grown cells. Microbe-mineral interactions result in change in the surface chemistry of the organism as well as that of the minerals with which it has interacted. Sulfur, pyrite, and chalcopyrite after interaction with T. ferrooxidans exhibited a significant shift in their isoelectric points from the initial values exhibited by uninteracted minerals. With antibodies raised against sulfur-grown T. ferrooxidans, pyrite- and chalcopyrite-grown cells showed immunoreactivity, whereas ferrous ion-grown cells failed to do so. Fourier transform infrared spectroscopy of sulfur-grown cells suggested that a proteinaceous new cell surface appendage synthesized in mineral-grown cells brings about adhesion to the solid mineral substrates. Such an appendage was found to be absent in ferrous ion-grown cells as it is not required during growth in liquid substrates.

Organometallic chemistry of diphosphazanes. Part IX: Syntheses and spectroscopic studies of molybdenum and tungsten tetracarbonyl complexes of unsymmetrical diphosphazanes

The unsymmetrical diphosphazanes X2PN(Pr(i))PYY'(1a-1h) {X = Ph, YY' = O2 C6H4 (1a) or YY' = O2C12H8 (1b); X = Ph, Y = Ph, Y' = OC6H4Me-4 (1c), OC6H4Br-4 (1d), OC6H3Me2-3,5 (1e), OC5H4N-2 (1f), N2C3HMe2-3,5 (1g) or Cl (1h)} react with [M(CO)4(NHC5H10)2] (M = Mo, W) to yield the cis-chelate complexes [M(CO)4{X2PN(Pr(i)) PYY'}] {M = Mo (2a-2h); M = W (3-f,3-g)}. These complexes have been characterized by H-1, P-31 and C-13 NMR and IR spectroscopic studies.

Organometallic chemistry of diphosphazanes .13. Palladium complexes of unsymmetrical diphosphazanes Ph(2)PN(Pr-i)PYY'

Unsymmetrical diphosphazanes Ph(2)PN(Pr-i)PYY' [YY' = O2C12H8 (L(1)), O2C20H12 (L(2)); Y = Ph and Y' = OC6H4Br-4 (L(3)), OC(6)H(4)Me-4 (L(4)), OC(6)H(3)Me(2)-3,5 (L(5)), N(2)C(3)HMe(2)-3,5 (L(6))] react with cis-[PdCl2(COD)] (COD = cycloocta-1,5-diene) giving the chelate complexes of the type cis-[PdCl2{eta(2)-Ph(2)PN(Pr-i)PYY'}] [YY' = O2C12H8 (1), O2C20H12 (2), Y = Ph and Y' = OC6H4Br-4 (3), OC(6)H(4)Me-4 (4), OC(6)H(3)Me(2)-3,5 (5), N(2)C(3)HMe(2)-3,5 (6)]. The P-N bond in 3 and 5 undergoes a facile cleavage in methanol solution to give cis-[PdCl2{eta(1)Ph(2)P(OMe)}{eta(1)-PhP(NHPri)(Y')}] [Y' = OC6H4Br-4 (7), OC(6)H(3)Me(2)-3,5 (8)]. Reactions of Pd-2(dba)(3) . CHCl3 (dba = dibenzylideneacetone) with the diphosphazanes Ph(2)PN(Pr-i)PPhY' [Y' = OC(6)H(4)Me-4 (L(4)), N(2)C(3)HMe(2)-3,5 (L(6)), N2C3H3 (L(7))] in the presence of MeI yields cis-[PdI2{eta(2)-Ph(2)PN(Pr-i)PPhMe}] (9); the P-O or P-N(pyrazolyl) bond of the starting ligands is cleaved and a p-C(Me) bond is formed. An analogous oxidative addition reaction in the presence of Ph(2)PN(Pr-i)PPh(2) (L(8)) yields cis-[PdI(Me)(eta(2)-L(8))] (10) and cis-[PdI2(eta 2-L(8))] (11). The structures of 8 and 9 have been determined by X-ray diffraction. Copyright (C) 1996 Elsevier Science Ltd

Organometallic Chemistry of Diphosphazanes. 11. Reactions of fac-[Mo(CO)3(MeCN){.eta.2-Ph2PN(Pri)PPh(DMP)}] (DMP = 3,5-Dimethyl-1-Pyrazolyl) with Diphosphazanes and Diphosphinoalkanes and Oxidative Addition with Iodine

The use of fac-[Mo(CO)(3)(MeCN)(eta(2)-L(1))] (1a) {L(1) = Ph(2)PN(Pr-i)PPh(DMP)}(2) as a precursor to metalloligands and bimetallic, heterotrimetallic, and heptacoordinated complexes is reported. The reaction of 1a with diphosphazane, dppa, or a diphosphinoalkane such as dppm or dppe yields the fac-eta(1)-diphosphine substituted metalloligands, fac-[Mo(CO)(3)(eta(2)-L(1))(eta(1)-PXP)] {PXP = dppa (2), dppm (3), and dppe (4)}. These undergo isomerization to yield the corresponding mer-diphosphine complexes (5-7). Oxidation of the uncoordinated phosphorus atom of the mer-eta(1)-dppm-substituted complex eventually provides mer-[Mo(CO)(3)-(eta(2)-L(1)){eta(1)-Ph(2)PCH(2)P(O)Ph(2)}](8). The structure of the latter complex has been confirmed by single crystal X-ray diffraction {triclinic system, P ($) over bar 1; a = 11.994(3), b = 14.807(2), c = 15.855(3) Angstrom; alpha = 114.24(1), beta = 91.35(2), and gamma = 98.95(1)degrees; Z = 2, 4014 data (F-0 > 5 sigma(F-0)), R = 0.066, R(W) = 0.069}. Treatment of the dppe metalloligand 7 with [PtCl2(COD)] yields the heterotrimetallic complex cis-[PtCl2{mer-[Mo(CO)(3)(eta(2)-L(1))(eta(1)-dppe]}(2)] (9). Attempts to prepare a related trimetallic complex with the dppm-containing metalloligand were unsuccessful; only the tetracarbonyl complex cis-[Mo(CO)(4)(eta(2)-L(1))] (1b) and cis-[PtCl2(eta(2)-dppm)] were obtained. Reaction of la with dppe in the ratio 2:1 yields the mer-mer dinuclear complex [{mer-[Mo(CO)(3)(eta(2)-L(1))]}(2)(mu-dppe)] (10) bridged by dppe. Oxidation of 1a with iodine yields the Mo(II) heptacoordinated complex [MoI2(CO)(2)(eta(3)-L(1))] (11) with tridentate PPN coordination. The same Mo(II) complex 11 is also obtained by the direct oxidation of the tetracarbonyl complex cis-[Mo(CO)(4)(eta(2)-L(1))] (1b) with iodine. The structure of 11 has been confirmed by X-ray diffraction studies {monoclinic system, Cc; a = 10.471(2), b = 19.305(3), c = 17.325(3) Angstrom; beta = 95.47(2)degrees; Z = 4, 3153 data (F-0 > 5 sigma(F-0)), R = 0.049, R(W) = 0.051}. This complex exhibits an unusual capped-trigonal prismatic geometry around the metal. A similar heptacoordinated complex 12 with a chiral diphosphazane ligand {L(3) = (S,R)-P(h)2PN-(*CHMePh)*PPh(DMP)} has also been synthesized.

Organometallic chemistry of diphosphazanes. Rhodium(I) complexes of RN(PX2)2 (R = C6H5; X = OC6H5, OC6H4Br?p, R = CH3; X = OC6H5)

Reactions of [Rh(COD)Cl](2) with the ligand RN(PX(2))(2) (1: R=C6H5; X=OC6H5) give mono- or disubstituted complexes of the type [Rh-2(COD)Cl-2{eta(2)-C6H5N(P(OC6H5)(2))(2)}-] or [RhCl{eta(2)-C6H5N(P(OC6H5)(2))(2)}](2), depending on the reaction conditions. Reaction of 1 with [Rh(CO)(2)Cl](2) gives the symmetric binuclear complex, [Rh(CO)Cl{mu-C6H5N(P(OC6H5)(2))(2)}], whereas the same reaction with 2 (R=CH3; X=OC6H5) leads to the formation of an asymmetric complex of the type [Rh(CO)(mu-CO)Cl{mu-CH3N(P(OC6H5)(2))(2)}] containing both terminal and bridging CO groups. Interestingly the reaction of 3 (R=C6H5, X = OC6H4Br-p) with either [Rh(COD)Cl](2) or [Rh(CO)(2)Cl](2) leads only to the formation of the chlorine bridged binuclear complex, [RhCl{eta(2)-C6H5N(P(OC6H4Br-p)(2))(2)}](2). The structural elucidation of the complexes was carried out by elemental analyses, IR and P-31 NMR spectroscopic data.

Synthesis and esterolytic chemistry of some (dialkylamino) pyridine-functionalized micellar aggregates. Evidence of catalytic turnover

Four new (dialkylamino)pyridine-functionalized surfactants have been synthesized. Micelles were generated either from the surfactant alone in aqueous buffer (pH 8.5 or 9.0) or by comicellization in 1 x 10(-3)-1 x 10(-4) M aqueous micellar cetyltrimethylammonium bromide (CTABr) solution at pH 8.5 or 9.0. Such aggregates were used to cleave p-nitrophenyl alkanoates or p-nitrophenyl diphenylphosphate. The nucleophilic reagents and the second-order ''catalytic'' rate constants toward esterolysis of the substrate p-nitrophenyl octanoate (at 25 degrees C, pH 9.0) were [cat.] = 1 x 10(-4) M, [CTABr] = 1 x 10(-3) M, and k(cat.) = 440.13 M(-1) s(-1) for 1b, [cat.] = 5 x 10(-4) M, [CTABr] = 5 x 10(-4) M, and k(cat.) = 30.8 M(-1) s(-1) for 1c, [cat.] = 5 x 10(-4) M, [CTABr] = 5 x 10(-3) M, and k(cat.) = 183.64 M(-1) s(-1) for 2a, and [cat.] = 3 x 10(-4) M and k(cat.) = 54.1 M(-1) s(-1) for 2b. The catalytic systems, especially 1b/CTABr and 2a/CTABr, also conferred significantly greater reactivity toward the esters derived from alkanoic acids of moderate chain length (C-6-C-10) during hydrolytic cleavages relative to their shorter and longer counterparts. Importantly, the catalytic systems comprising the coaggregates of either neutral 1b and CTABr (1:10) or anionic 2a and CTABr (1:10) conformed to the Michaelis-Menten kinetic scheme and demonstrated turnover behavior in the presence of excess substrate.

The chemistry of a non-natural product: Troger's base

Troger's base was the first amine to be resolved where the chirality was solely due to very high inversion barrier around nitrogen atom(s). Though the molecule was known over a century, work done during the past one decade has shown that Troger's base and its analogues could be used as chiral solvating agents, DNA-binding ligands and for the construction of biomimetic molecular receptors and clathrate hosts, Asymmetric synthesis of Troger's base analogues has also been achieved recently, Because of the rigid, 'V'-shaped chiral nature of this molecule, there is a growing interest for use of this unit in the design of potential host systems, This review article focuses on the chemistry of Troger's base along with the possible future utilities.

Chemistry of dihydrogen complexes containing only phosphorus co-ligands

A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)(2)Ru(eta(2)-H-2)(L)][BF4](2) (dppm = Ph2PCH2PPh2; L = phosphite) have been prepared by protonating the precursor hydride complexes cis-[(dPPM)(2)Ru(H)(L)][BF4] using HBF4.Et2O. The precursor hydride complexes have been obtained from trans-[(dppm)(2)Ru(H)(L)][BF4][(L = phospfiite) via a rare acid-catalysed isomerization reaction in six coordinate species. The trans-[(dppm)(2)Ru(H)(L)][BF4] complexes (L = phosphine) upon protonation gave the isomerized derivatives, however, further addition of acid resulted in a five-coordinate species, [(dppm)(2)RuCl](+) presumably via an intermediate phosphine dihydrogen complex. The electronic as well as the steric properties of the co-ligands seem to strongly influence the structure-reactivity behaviour of this series of complexes.

Chemistry of tetrathiomolybdate: Applications in organic synthesis

The utility of tetrathiomolybdate in a variety of organic transformations is presented in this account. The sulfur transfer ability of tetrathiomolybdate is exploited in the synthesis of organic disulfides under mild reaction conditions. The induced internal redox reactions associated with tetrathiomolybdate have been thoroughly exploited in developing various methodologies, which include the reduction of organic azides, synthesis of diselenides, cyclic imines, thioamides, and thiolactams. In addition, novel deprotection strategies using tetrathiomolybdate have been developed to cleave the propargyl and propargyloxy carbonyl (POC) protecting groups. Tetrathiomolybdate mediated tandem sulfur transfer-reduction-Michael reactions have been applied to the synthesis of sulfur containing bicyclic systems. Furthermore, the reactions in the solid state and the reactions in water medium assisted by tetrathiomolybdate have greatly simplified the synthesis of organic disulfides.

High temperature phase chemistry of system Eu-Pd-O

An isothermal section of the phase diagram for the system Eu - Pd - O at 1223 K has been established by equilibration of samples representing 20 different compositions, and phase identification after quenching by optical and scanning electron microscopy, X-ray powder diffraction, and energy dispersive spectroscopy. Three ternary oxides, Eu4PdO7, Eu2PdO4, and Eu2Pd2O5, were identified. Liquid alloys and the intermetallic compounds EuPd2 and EuPd3 were found to be in equilibrium with EuO. The compound EuPd3 was also found to coexist separately with Eu3O4 and Eu2O3. The oxide phase in equilibrium with EuPd5 and Pd rich solid solution was Eu2O3. Based on the phase relations, four solid state cells were designed to measure the Gibbs energies of formation of the three ternary oxides in the temperature range from 925 to 1350 K. Although three cells are sufficient to obtain the properties of the three compounds, the fourth cell was deployed to crosscheck the data. An advanced version of the solid state cell incorporating a buffer electrode with yttria stabilised zirconia solid electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode was used for high temperature thermodynamic measurements. Equations for the standard Gibbs energy of formation of the interoxide compounds from their component binary oxides Eu2O3 with C type structure and PdO have been established. Based on the thermodynamic information, isothermal chemical potential diagrams and isobaric phase diagrams for the system Eu - Pd - O have been developed.

Organometallic chemistry of chiral diphosphazane ligands: Synthesis and structural characterisation

The diphosphazane ligands of the type, (C20H12O2)PN(R)P(E)Y2 (R = CHMe2 or (S)-*CHMePh; E = lone pair or S; Y2 = O2C20H12 or Y = OC6H5 or OC6H4Me-4 or OC6H4OMe-4 or OC6H4But-4 or C6H5) bearing axially chiral 1,1'-binaphthyl-2,2′-dioxy moiety have been synthesised. The structure and absolute configuration of a diastereomeric palladium complex, [PdCl2{ηsu2}-((O2C20H12)PN((S)-*CHMePh)PPh2] has been determined by X-ray crystallography. The reactions of [CpRu(PPh3)2Cl] with various symmetrical and unsymmetrical diphosphazanes of the type, X2PN(R)PYY′ (R = CHMe2 or (S)-*CHMePh; X = C6H5 or X2 = O2C20H12; Y=Y′= C6H5 or Y = C6H5, Y′ = OC6H4Me-4 or OC6H3Me2-3,5 or N2C3HMe2-3,5) yield several diastereomeric neutral or cationic half-sandwich ruthenium complexes which contain a stereogenic metal center. In one case, the absolute configuration of a trichiral ruthenium complex, viz. [Cp*Ruη2-Ph2PN((S)-*CHMePh)*PPh (N2C3HMe2-3,5)Cl] is established by X-ray diffraction. The reactions of Ru3(CO)12 with the diphosphazanes (C20H12O2)PN(R)PY2 (R = CHMe2orMe; Y2=O2C20H12or Y= OC6H5 or OC6H4Me-4 or OC6H4OMe-4 or OC6H4But-4 or C6H5) yield the triruthenium clusters [Ru3(CO)10{η-(O2C20H12)PN(R)PY2}], in which the diphosphazane ligand bridges two metal centres. Palladium allyl chemistry of some of these chiral ligands has been investigated. The structures of isomeric η3-allyl palladium complexes, [Pd(η3-l,3-R′2-C3H3){η2-(rac)-(02C20H12)PN(CHMe2)PY2}](PF6) (R′ = Me or Ph; Y = C6H5 or OC6H5) have been elucidated by high field two-dimensional NMR spectroscopic and X-ray crystallographic studies.