Dititanium complexes of preorganized binucleating bis(amidinates)

Four different dianionic bis(amidinate) ligands ((iPr)L(DBF)(2)(-), (tBu,Et)L(DBF)(2)(-), (iPr)L(Xan)(2)(-), (tBu,Et)L(Xan)(2)(-)) featuring rigid dibenzofuran (DBF) and 9,9-dimethylxanthene (Xan) backbones have been used to prepare several new dititanium complexes. Reaction of the free-base bis(amidines) (LH(2)) with 2 equiv of Ti(NMe(2))(4) forms the hexaamido derivatives (iPr)L(DBF)Ti(2)(NMe(2))(6) (1), (tBu,Et)L(DBF)Ti(2)(NMe(2))(6) (2), (iPr)L(Xan)Ti(2)(NMe(2))(6) (3), and (tBu,Et)L(Xan)Ti(2)(NMe(2))(6) (4) in good yields. Compound 4, which features an unsymmetrically substituted bis(amidinate) ligand, was isolated as an 8:1 mixture of rotational diastereomers with C(2) and C(s)() symmetry, respectively. The two diastereomers interconvert upon heating, and at equilibrium the C(2) isomer is preferred thermodynamically by 0.2 kcal/mol. Compound 3 reacts with excess Me(3)SiCl in toluene to form the mixed amido-chloride derivative (iPr)L(Xan)Ti(2)(NMe(2))(2)Cl(4) (5) in low-moderate yield. Alternatively, 5 is also prepared by reaction of (iPr)L(Xan)H(2) with 2 equiv of Ti(NMe(2))(2)Cl(2) in good yield. Compound 3 reacts with CO(2) to form the red carbamate derivative (iPr)L(Xan)Ti(2)(NMe(2))(4)(O(2)CNMe(2))(2) (6) in moderate yield. Infrared data for 6 indicates bidentate coordination of the carbamate ligands. Metathesis reaction of (iPr)L(Xan)Li(2) with 2 equiv of CpTiCl(3) affords (iPr)L(Xan)Ti(2)Cp(2)Cl(4) (7) in moderate yield. Reduction of 7 with 1% Na amalgam in toluene solution affords the paramagnetic dititanium(III) complex (iPr)L(Xan)Ti(2)Cp(2)Cl(2) (8) in good yield. Structural studies reveal that 8 features two bridging chloride ligands. Reaction of the free-base bis(amidines) with 2 equiv of CpTiMe(3) forms the red sigma-alkyl derivatives (iPr)L(DBF)Ti(2)Cp(2)Me(4) (9), (tBu,Et)L(DBF)Ti(2)Cp(2)Me(4) (10), and (iPr)L(Xan)Ti(2)Cp(2)Me(4) (11) in good yields. Structural data are presented for compounds 4, 5, 8, and 9.     

Synthesis of monomeric Fe(II) and Ru(II) complexes of tetradentate phosphines

rac-Bis[{(diphenylphosphino)ethyl}-phenylphosphino]methane (DPPEPM) reacts with iron(II) and ruthenium(II) halides to generate complexes with folded DPPEPM coordination. The paramagnetic, five-coordinate Fe(DPPEPM)Cl(2) (1) in CD(2)Cl(2) features a tridentate binding mode as established by (31)P{(1)H} NMR spectroscopy. Crystal structure analysis of the analogous bromo complex, Fe(DPPEPM)Br(2) (2) revealed a pseudo-octahedral, cis-α geometry at iron with DPPEPM coordinated in a tetradentate fashion. However, in CD(2)Cl(2) solution, the coordination of DPPEPM in 2 is similar to that of 1 in that one of the external phosphorus atoms is dissociated resulting in a mixture of three tridentate complexes. The chloro ruthenium complex cis-Ru(κ(4)-DPPEPM)Cl(2) (3) is obtained from rac-DPPEPM and either [RuCl(2)(COD)](2) [COD = 1,5-cyclooctadiene] or RuCl(2)(PPh(3))(4). The structure of 3 in both the solid state and in CD(2)Cl(2) solution features a folded κ(4)-DPPEPM. This binding mode was also observed in cis-[Fe(κ(4)-DPPEPM)(CH(3)CN)(2)](CF(3)SO(3))(2) (4). Addition of an excess of CO to a methanolic solution of 1 results in the replacement of one of the chloride ions by CO to yield cis-[Fe(κ(4)-DPPEPM)Cl(CO)](Cl) (5). The same reaction in CH(2)Cl(2) produces a mixture of 5 and [Fe(κ(3)-DPPEPM)Cl(2)(CO)] (6) in which one of the internal phosphines has been substituted by CO. Complexes 2, 3, 4, and 5 appear to be the first structurally characterized monometallic complexes of κ(4)-DPPEPM.     

Synthesis, Spectroscopic Characterization, and Structural Studies of Bis(&mgr;-sulfido)bis[{O,O-dialkyl (alkylene) dithiophosphato}oxomolybdenum(V)] Complexes. Crystal Structures of Mo(2)O(2)S(2)[S(2)P(OEt)(2)](2), Mo(2)O(2)S(2)[S(2)P(OEt)(2)](2).2NC(5)H(5), and Mo(2)O(3)[S(2)P(OPh)(2)](4)

A series of new complexes, Mo(2)O(2)S(2)[S(2)P(OR)(2)](2) (where R = Et, n-Pr, i-Pr) and Mo(2)O(2)S(2)[S(2)POGO](2) (where G = -CH(2)CMe(2)CH(2)-, -CMe(2)CMe(2)-) have been prepared by the dropwise addition of an ethanolic solution of the ammonium or sodium salt of the appropriate O,O-dialkyl or -alkylene dithiophosphoric acid, or the acid itself, to a hot aqueous solution of molybdenum(V) pentachloride. The complexes were also formed by heating solutions of Mo(2)O(3)[S(2)P(OR)(2)](4) or Mo(2)O(3)[S(2)POGO](4) species in glacial acetic acid. The Mo(2)O(2)S(2)[S(2)P(OR)(2)](2) and Mo(2)O(2)S(2)[S(2)POGO](2) compounds were characterized by elemental analyses, (1)H, (13)C, and (31)P NMR, and infrared and Raman spectroscopy, as were the 1:2 adducts formed on reaction with pyridine. The crystal structures of Mo(2)O(2)S(2)[S(2)P(OEt(2))](2), Mo(2)O(2)S(2)[S(2)P(OEt)(2)](2).2NC(5)H(5), and Mo(2)O(3)[S(2)P(OPh)(2)](4) were determined. Mo(2)O(2)S(2)[S(2)P(OEt)(2)](2) (1) crystallizes in space group C2/c, No. 15, with cell parameters a = 15.644(3) ?, b = 8.339(2) ?, c = 18.269(4) ?, beta = 103.70(2) degrees, V = 2315.4(8) ?(3), Z = 4, R = 0.0439, and R(w) = 0.0353. Mo(2)O(2)S(2)[S(2)P(OEt)(2)](2).2NC(5)H(5) (6) crystallizes in space group P&onemacr;, No. 2, with the cell parameters a = 12.663(4) ?,b = 14.291(5) ?, c = 9.349(3) ?, alpha = 100.04(3) degrees, beta = 100.67(3) degrees, gamma = 73.03(3) degrees V = 1557(1) ?(3), Z = 2, R = 0.0593, and R(w) = 0.0535. Mo(2)O(3)[S(2)P(OPh)(2)](4) (8) crystallizes in space group P2(1)/n, No. 14, with cell parameters a = 15.206(2)?, b = 10.655(3)?, c = 19.406(3)?, beta = 111.67(1) degrees, V = 2921(1)?(3), Z = 2, R = 0.0518, R(w) = 0.0425. The immediate environment about the molybdenum atoms in 1 is essentially square pyramidal if the Mo-Mo interaction is ignored. The vacant positions in the square pyramids are occupied by two pyridine molecules in 6, resulting in an octahedral environment with very long Mo-N bonds. The terminal oxygen atoms in both 1 and 6 are in the syn conformation. In 8, which also has a distorted octahedral environment about molybdenum, two of the dithiophosphate groups are bidentate as in 1 and 6, but the two others have one normal Mo-S bond and one unusually long Mo-S bond.     

New developments and directions in the area of elastomers and rubberlike elasticity

There are number of important developments in the area of elastomeric polymers, including (i) network chains of controlled stiffness, (ii) model elastomers (including dangling-chain networks), (iii) fluorosiloxane elastomers, (iv) new thermoplastic elastomers, (v) other new elastomers, (v) bimodal network chain-length distributions, (vi) cross linking in solution or in a state of deformation, and (vii) gel collapse. Interesting elastomeric composites include those with (i) in-situ generated ceramic-like particles, (ii) ellipsoidal fillers, (iii) clay-like layered fillers, (iv) polyhedral oligomeric silsesquioxane (POSS) particles, (v) porous fillers, (vi) elastomeric domains modifying ceramics, and (vii) controlled interfaces. New characterization techniques are being developed for elastomers, and there have been new developments in elasticity theory and in elastomer processing. Some examples of societal aspects of relevance are (i) synthesis of elastomers in environmentally-friendly solvents, (ii) biosynthesis, (iii), recyclability, (iv) improved adhesion to tire cords, and (v) better barrier properties in anti-terrorism clothing. Educational topics include curriculum development, and mobile laboratories for elastomer experiments and demonstrations.     

Frustrated beta-chloride elimination. Selective arene alkylation by alpha-chloronorbornene catalyzed by electrophilic metallocenium ion pairs

Single-site polymerization catalysts generated in situ via activation of Cp*MMe(3) (Cp* = C(5)Me(5); M = Ti, Zr), (CGC)MMe(2) (CGC = C(5)Me(4)SiMe(2)NBu(t)(); M = Ti, Zr), and Cp(2)ZrMe(2) with Ph(3)C(+)B(C(6)F(5))(4)(-) catalyze alkylation of aromatic molecules (benzene, toluene) with alpha-chloronorbornene at room temperature, to regioselectively afford the 1:1 addition products exo-1-chloro-2-arylnorbornane (aryl = C(6)H(5) (1a), C(6)H(4)CH(3) (1b)) in good yields. Analogous deuterium-labeled products exo-1-chloro-2-aryl-d(n)-norbornane-7-d(1) (aryl-d(n) = C(6)D(5) (1a-d(6)), C(6)D(4)CD(3) (1b-d(8))) are obtained via catalytic arylation of alpha-chloronorbornene in either benzene-d(6) or toluene-d(8). Isolated ion-pair complexes such as (CGC)ZrMe(toluene)(+)B(C(6)F(5))(4)(-) and Cp(2)ThMe(+)B(C(6)F(5))(4)(-) also catalyze the reaction of alpha-chloronorbornene in toluene-d(8) to give 1b-d(8) in good yields, respectively. Small quantities of the corresponding bis(1-chloronorbornyl)aromatics 2 are also obtained from preparative-scale reactions. These reactions exhibit turnover frequencies exceeding 120 h(-1) (for the Cp*TiMe(3)/Ph(3)C(+)B(C(6)F(5))(4)(-)-catalyzed system), and chlorine-free products are not observed. Compounds 1 and 2 were characterized by (1)H, (2)H, (13)C, and 2D NMR, GC-MS, and elemental analysis. The aryl group exo-stereochemistry in 1a and 1b is established using (1)H-(1)H COSY, (1)H-(13)C HMBC, and (1)H-(1)H NOESY NMR, and is further corroborated by X-ray analysis of the product 1,4-bis(exo-1-chloro-2-norbornyl)benzene (2a). Control experiments and reactivity studies on each component step suggest a mechanism involving participitation of the metal electrophiles in the catalytic cycle.     

Reaction of Cl atoms with C6F13CH2OH, C6F13CHO, and C3F7CHO

The Cl atom initiated oxidation of C(6)F(13)CH(2)OH, C(6)F(13)CHO, and C(3)F(7)CHO was investigated at 298 K and 1000 mbar pressure of air in a photoreactor using in situ Fourier transform infrared (FTIR) analysis. The rate coefficient for the reaction Cl + C(6)F(13)CH(2)OH (reaction 2) was measured using a relative method: k(2) = (6.5 +/- 0.8) x 10(-13) cm(3) molecule(-1) s(-1). C(6)F(13)CHO was detected as the major primary product, while CO and CF(2)O were found to be the major secondary products. A fitting procedure applied to the concentration-time profiles of C(6)F(13)CHO provided a production yield of (1.0 +/- 0.2) for this aldehyde in reaction 2, and the rate coefficient for the reaction Cl + C(6)F(13)CHO (reaction 4) was k(4) = (2.8 +/- 0.7) x 10(-12) cm(3) molecule(-1) s(-1). A high CO yield observed in the oxidation of C(6)F(13)CH(2)OH, (52 +/- 1)%, is attributed to the Cl atom initiated oxidation of C(6)F(13)CHO. High CO yields, (61 +/- 2)% and (85 +/- 5)%, were also measured in the Cl atom initiated oxidation of C(3)F(7)CHO in air and nitrogen, respectively. These high CO yields suggest the occurrence of a decomposition reaction of the perfluoroacyl, C(6)F(13)CO, and C(3)F(7)CO radicals to form CO which will compete with the combination reaction of these radicals with oxygen to form perfluoroacyl peroxy radicals in the presence of air. The latter radicals C(n)F(2)(n)(+1)CO(O)(2) (n = 6-12), through their reaction with HO(2) radicals, are currently considered as a possible source of persistent perfluorocarboxylic acids which have been detected in the environment. The consequences of the present results would be a reduction of the strength of this potential source of carboxylic acids in the atmosphere.     

Half-sandwich titanium(IV) complexes with Kläui's tripod ligand

Treatment of [Ti(O-i-Pr)(2)Cl(2)] with NaL(OEt) (L(OEt)(-) = [CpCo[P(O)(OEt)(2)](3)](-), Cp = eta(5)-C(5)H(5)) afforded [L(OEt)Ti(O-i-Pr)(2)Cl] that reacted with HCl in ether to give [L(OEt)TiCl(3)] (1). The average Ti-O and Ti-Cl distances in 1 are 1.975 and 2.293 A, respectively. Reaction of titanyl sulfate with NaL(OEt) in water followed by addition of HBF(4) afforded [L(OEt)TiF(3)] (2), the Ti-O and Ti-F distances of which are 2.020(2) and 1.792(2) A, respectively. The Zr(IV) analogue [L(OEt)ZrF(3)] (3) was prepared similarly from zirconyl nitrate, NaL(Oet), and HBF(4) in water. The Zr-O and average Zr-F distances in 3 are 2.139(2) and 1.938(2) A, respectively. Treatment of 1 with tetrachlorocatechol (H(2)Cl(4)cat) afforded [L(OEt)Ti(Cl(4)cat)Cl] (4). The average Ti-O(P), Ti-O(C), and Ti-Cl distances in 4 are 1.972, 1.926, and 2.334 A, respectively. Hydrolysis of 4 in the presence of Et(3)N yielded the mu-oxo dimer [(L(OEt))(2)Ti(2)(Cl(4)cat)(2)(mu-O)] (5). The average Ti-O(P), Ti-O(C), and Ti-O(Ti) distances in 5 are 2.027, 1.926, and 1.7977(9) A. Treatment of 1 with 1,1'-binaphthol (BINOLH(2)) in the presence of Et(3)N afforded [(L(OEt))(2)Ti(2)(mu-O)(2)(mu-BINOL)] x 2BINOLH(2) (6.2BINOLH(2)). Complex 1 is capable of catalyzing ring opening of epoxides with Me(3)SiN(3) under solvent-free conditions presumably via a Ti-azide intermediate.     

Near-infrared spectroscopy of LiNH3: first observation of the electronic spectrum

Electronic spectra of LiNH(3) and its partially and fully deuterated analogues are reported for the first time. The spectra have been recorded in the near-infrared and are consistent with two electronic transitions in close proximity, the ?(2)E-X(2)A(1) and B(2)A(1)-X(2)A(1) systems. Vibrational structure is seen in both systems, with the Li-N-H bending vibration (ν(6)) dominant in the ?(2)E-X(2)A(1) system and the Li-N stretch (ν(3)) in the B(2)A(1)-X(2)A(1) system. The prominence of the 6(0)(1) band in the ?(2)E-X(2)A(1) spectrum is attributed to Herzberg-Teller coupling. The proximity of the B(2)A(1) state, which lies a little more than 200 cm(-1) above the ?(2)E state, is likely to be the primary contributor to this strong vibronic coupling.     

Head-to-head (HH) and head-to-tail (HT) conformers of cis-bis guanine ligands bound to the [Re(CO)3]+ core

We have prepared four complexes of the type [Re(guanine)(2)(X)(CO)(3)] (guanine = 9-methylguanine or 7-methylguanine, X = H(2)O or Br) in order to understand the factors determining the orientation of coordinated purine ligands around the [Re(CO)(3)](+) core. The 9-methylguanine ligand (9-MeG) was chosen as the simplest N(9) derivatized guanine, and 7-methylguanine (7-MeG) was chosen because metal binding to N(9) does not impose steric hindrance. Two types of structures have been elucidated by X-ray crystallography, an HH (head-to-head) and HT (head-to-tail) conformer for each of the guanines. All complexes crystallize in monoclinic space groups: [Re(9-MeG)(2)(H(2)O)(CO)(3)]ClO(4) (2) in P2(1)/n with a = 12.3307(10) A, b = 16.2620(14) A, c = 13.7171(11) A, and beta = 105.525(9) degrees, V = 2650.2(4) A(3), with the two bases in HT orientation and its conformer [Re(9-MeG)(2)(H(2)O)(CO)(3)]Br (3) in P2(1)/n with a = 15.626(13) A, b = 9.5269(5) A, c = 15.4078(13) A, and beta = 76.951(1) degrees, V = 2234.5(3) A(3), and the two bases in an HH orientation. Similarly, [Re(7-MeG)(2)(H(2)O)(CO)(3)]ClO(4) (4) crystallizes in P2(1)/c with a = 13.0708(9) A, b = 15.4082(7) A, c = 14.316(9) A, and beta = 117.236(7) degrees, V = 2563.5(3) A(3), and exhibits an HT orientation and [ReBr(7-MeG)(2)(CO)(3)] (5) in P2/c with a = 17.5117(9) A, b = 9.8842(7) A, c = 15.3539(1) A, and beta = 100.824(7) degrees, V = 2610.3(3) A(3), and shows an HH orientation. When crystals of any of these complex pairs are dissolved in D(2)O, the (1)H NMR spectrum shows a single peak for the H(8) resonance of the respective coordinated purine indicating a rapid equilibrium between HH and HT conformations in solution. DFT calculations simulating the rotation of one ligand around its Re-N bond showed energetic barriers of less than 8.7 kcal/mol. We find no hypochromic effect in the Raman spectrum of 3, which showed base stacking in the solid state. Neither steric interactions nor hydrogen bonding are important in determining the orientation of the ligands in the coordination sphere.     

Photoionization-induced water migration in the amide group of trans-acetanilide-(H2O)1 in the gas phase

IR-dip spectra of trans-acetanilide-water 1:1 cluster, AA-(H(2)O)(1), have been measured for the S(0) and D(0) state in the gas phase. Two structural isomers, where a water molecule binds to the NH group or the CO group of AA, AA(NH)-(H(2)O)(1) and AA(CO)-(H(2)O)(1), are identified in the S(0) state. One-color resonance-enhanced two-photon ionization, (1 + 1) RE2PI, of AA(NH)-(H(2)O)(1) via the S(1)-S(0) origin generates [AA(NH)-(H(2)O)(1)](+) in the D(0) state, however, photoionization of [AA(CO)-(H(2)O)(1)] does not produce [AA(CO)-(H(2)O)(1)](+), leading to [AA(NH)-(H(2)O)(1)](+). This observation explicitly indicates that the water molecule in [AA-(H(2)O)(1)](+) migrates from the CO group to the NH group in the D(0) state. The reorganization of the charge distribution from the neutral to the D(0) state of AA induces the repulsive force between the water molecule and the CO group of AA(+), which is the trigger of the water migration in [AA-(H(2)O)(1)](+).     

N,N'-ethylenebis(pyridoxylideneiminato) and N,N'-ethylenebis(pyridoxylaminato): synthesis, characterization, potentiometric, spectroscopic, and DFT studies of their vanadium(IV) and vanadium(V) complexes

The Schiff base N,N'-ethylenebis(pyridoxylideneiminato) (H(2)pyr(2)en, 1) was synthesized by reaction of pyridoxal with ethylenediamine; reduction of H(2)pyr(2)en with NaBH(4) yielded the reduced Schiff base N,N'-ethylenebis(pyridoxylaminato) (H(2)Rpyr(2)en, 2); their crystal structures were determined by X-ray diffraction. The totally protonated forms of 1 and 2 correspond to H(6)L(4+), and all protonation constants were determined by pH-potentiometric and (1)H NMR titrations. Several vanadium(IV) and vanadium(V) complexes of these and other related ligands were prepared and characterized in solution and in the solid state. The X-ray crystal structure of [V(V)O(2)(HRpyr(2)en)] shows the metal in a distorted octahedral geometry, with the ligand coordinated through the N-amine and O-phenolato moieties, with one of the pyridine-N atoms protonated. Crystals of [(V(V)O(2))(2)(pyren)(2)].2 H(2)O were obtained from solutions containing H(2)pyr(2)en and oxovanadium(IV), where Hpyren is the "half" Schiff base of pyridoxal and ethylenediamine. The complexation of V(IV)O(2+) and V(V)O(2) (+) with H(2)pyr(2)en, H(2)Rpyr(2)en and pyridoxamine in aqueous solution were studied by pH-potentiometry, UV/Vis absorption spectrophotometry, as well as by EPR spectroscopy for the V(IV)O systems and (1)H and (51)V NMR spectroscopy for the V(V)O(2) systems. Very significant differences in the metal-binding abilities of the ligands were found. Both 1 and 2 act as tetradentate ligands. H(2)Rpyr(2)en is stable to hydrolysis and several isomers form in solution, namely cis-trans type complexes with V(IV)O, and alpha-cis- and beta-cis-type complexes with V(V)O(2). The pyridinium-N atoms of the pyridoxal rings do not take part in the coordination but are involved in acid-base reactions that affect the number, type, and relative amount of the isomers of the V(IV)O-H(2)Rpyr(2)en and V(V)O(2)-H(2)Rpyr(2)en complexes present in solution. DFT calculations were carried out and support the formation and identification of the isomers detected by EPR or NMR spectroscopy, and the strong equatorial and axial binding of the O-phenolato in V(IV)O and V(V)O(2) complexes. Moreover, the DFT calculations done for the [V(IV)O(H(2)Rpyr(2)en)] system indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds.     

C76 fullerene chlorides and cage transformations. Structural and theoretical study

Chlorination of the D(2)-C(76) fullerene under various conditions is studied in detail. It is found that, in addition to the previously known C(76)Cl(18) and C(76)Cl(34), a number of intermediate chlorides are formed, with all molecules falling into two structural types. The first type is observed in the C(76)Cl(18)-C(76)Cl(28) range, whereas further chlorination provides the C(76)Cl(30)-C(76)Cl(34) compounds of the second type exhibiting a major change in the addition motif. We also present a detailed theoretical rationalization of the previously observed skeletal rearrangement in the D(2)-C(76) that affords the non-IPR (18917)C(76)Cl(24) compound.     

Reactivity investigation of dinuclear vanadium(IV,V)-citrate complexes in aqueous solutions. A closer look into aqueous vanadium-citrate interconversions

Well-known vanadium(IV)- and vanadium(V)-citrate complexes have been employed in transformations involving vanadium redox as well as nonredox processes. The employed complexes include K(2)[V(2)O(4)(C(6)H(6)O(7))(2)] x 4H(2)O, K(4)[V(2)O(4)(C(6)H(5)O(7))(2)] x 5.6H(2)O, K(2)[V(2)O(2)(O(2))(2)(C(6)H(6)O(7))(2)] x 2H(2)O, K(4)[V(2)O(2)(C(6)H(4)O(7))(2)] x 6H(2)O, K(3)[V(2)O(2)(C(6)H(4)O(7))(C(6)H(5)O(7))] x 7H(2)O, (NH(4))(4)[V(2)O(2)(C(6)H(4)O(7))(2)] x 2H(2)O, and (NH(4))(6)[V(2)O(4)(C(6)H(4)O(7))(2)] x 6H(2)O. Reactions toward hydrogen peroxide at different vanadium(IV,V):H(2)O(2) ratios were crucial in delineating the routes leading to the interconversion of the various species. Equally important thermal transformations were critical in showing the linkage between pairs of dinuclear vanadium-citrate peroxo as well as nonperoxo complexes, for which the important vanadium(V)-assisted oxidative decarboxylation, leading to reduction of vanadium(V) to vanadium(IV), seemed to be a plausible pathway in place for all the cases examined. FT-IR spectroscopy and X-ray crystallography were instrumental in the identification of the arising products of all investigated reactions. Collectively, the data support the existence of chemical links between different and various structural forms of dinuclear vanadium(IV,V)-citrate complexes in aqueous media. Furthermore, in corroboration of past studies, the examined interconversions lend credence to the notion that the involved species are active participants in the respective aqueous distributions of the metal ion in the presence of the physiological ligand citrate. The concomitant significance of structure-specific species relating to soluble and potentially bioavailable forms of vanadium is mentioned.     

The bis-phenyltin-substituted, lone-pair-containing tungstoarsenate [(C(6)h(5)Sn)(2)as(2)W(19)O(67)(H(2)O)](8)(-)

The bis-phenyltin-substituted, lone-pair-containing tungstoarsenate [(C(6)H(5)Sn)(2)As(2)W(19)O(67)(H(2)O)](8)(-) (1) has been synthesized and characterized by multinuclear NMR, IR, and elemental analysis. Single-crystal X-ray analysis was carried out on (NH(4))(7)Na[(C(6)H(5)Sn)(2)As(2)W(19)O(67)(H(2)O)].17.5H(2)O (NH(4)(-1), which crystallizes in the monoclinic system, space group P2(1)/c, with a = 18.3127(17) A, b = 24.403(2) A, c = 22.965(2) A, beta = 106.223(2) degrees, and Z = 4. Polyanion 1 consists of two B-alpha-(As(III)W(9)O(33)) Keggin moieties linked via a WO(H(2)O) fragment and two SnC(6)H(5) groups leading to a sandwich-type structure with nominal C(2)(v) symmetry. Polyanion 1 is stable in solution as indicated by the expected 6-line pattern (4:4:4:4:2:1) in (183)W NMR and the expected (119)Sn, (13)C, and (1)H NMR spectra. Synthesis of 1 was accomplished by reaction of C(6)H(5)SnCl(3) and K(14)[As(2)W(19)O(67)(H(2)O)] in a 2:1 molar ratio in aqueous acidic medium (pH 2). In the solid-state structure of NH(4)(-1, neighboring polyanions are weakly bound via W-O-Na bonds leading to chains which interact with each other via the phenyl rings resulting in a 2-D assembly.     

A feasibility study on the use of Li(4)V(3)O(8) as a high capacity cathode material for lithium-ion batteries

Li(4)V(3)O(8) materials have been prepared by chemical lithiation by Li(2)S of spherical Li(1.1)V(3)O(8) precursor materials obtained by a spray-drying technique. The over-lithiated vanadates were characterised physically by using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and electrochemically using galvanostatic charge-discharge and cyclic voltammetry measurements in both the half-cell (vs. Li metal) and full-cell (vs. graphite) systems. The Li(4)V(3)O(8) materials are stable in air for up to 5 h, with almost no capacity drop for the samples stored under air. However, prolonged exposure to air will severely change the composition of the Li(4)V(3)O(8) materials, resulting in both Li(1.1)V(3)O(8) and Li(2)CO(3). The electrochemical performance of these over-lithiated vanadates was found to be very sensitive to the conductive additive (carbon black) content in the cathode. When sufficient carbon black is added, the Li(4)V(3)O(8) cathode exhibits good cycling behaviour and excellent rate capabilities, matching those of the Li(1.1)V(3)O(8) precursor material, that is, retaining an average charge capacity of 205 mAh g(-1) at 2800 mA g(-1) (8C rate; 1C rate means full charge or discharge of a battery in one hour), when cycled in the potential range of 2.0-4.0 V versus Li metal. When applied in a non-optimised full cell system (vs. graphite), the Li(4)V(3)O(8) cathode showed promising cycling behaviour, retaining a charge capacity (Li(+) extraction) above 130 mAh g(-1) beyond 50 cycles, when cycled in the voltage range of 1.6-4.0 V, at a specific current of 117 mA g(-1) (C/3 rate).     

Synthesis and reactivity of the aquation product of the antitumor complex trans-[Ru(III)Cl4(indazole)2]-

Aquation of the investigational anticancer drug trans-[Ru(III)Cl4(Hind)2](-) (1, KP1019) results in the formation of mer,trans-[Ru(III)Cl3(Hind)2(H2O)] (2), which was isolated in high yield (85%) and characterized by spectroscopic methods and X-ray crystallography. Dissolution of 2 in acetone, led to its dimerization into [Ru(III)2(mu-Cl)2Cl4(Hind)4] x 2 (Me)2CO (3) in 79% yield, with release of two water molecules. Complex 2 reacts readily with nucleophilic organic molecules, viz., methanol or dimethyl sulfide, at room temperature by replacement of the aqua ligand to give mer,trans-[Ru(III)Cl3(Hind)2(MeOH)] (4) and mer,trans-[Ru(III)Cl3(Hind)2(Me2S)] (5) in 58 and 64% yield, respectively. By reaction of 2 with DMSO at room temperature or dimethyl sulfide at elevated temperatures trans,trans,trans-[Ru(II)Cl2(Hind)2(Me2S)2] (6) and trans,trans,trans-[Ru(II)Cl2(Hind)2(S-DMSO)2] (7) were prepared in 64 and 75% yield, respectively. Dissolution of 2 in acetonitrile or benzonitrile gave rise to mer,trans-[Ru(III)Cl3(Hind)(HNC(Me)ind)] (8a), mer,trans-[Ru(III)Cl3(Hind)(HNC(Ph)ind)] (8b), and trans,trans-[Ru(III)Cl2(HNC(Me)ind)2]Cl (9) in 67, 50, and 23% yield, respectively, upon metal-assisted iminoacylation of indazole, which is unprecedented for ruthenium(III). Furthermore, complex 2 reacts with the DNA-model bases 9-methyladenine (9-meade) and N6,N6-dimethyladenine (6-me2ade) to yield mer,trans-[Ru(III)Cl3(Hind)2(9-meade)] (10) and mer,trans-[Ru(III)Cl3(Hind)2(6-me2ade)] (11) with the purine bases bound to the Ru(III) center via N7 and N3, respectively. Complex 11 represents the first ruthenium complex in which the coordination of the purine ligand N6,N6-dimethyladenine occurs via N3. In addition, the polymer [Na(EtOAc)2Ru(III)(mu-Cl)4(Hind)2]n (12) was crystallized from ethyl acetate/diethyl ether solutions of Na[trans-Ru(III)Cl4(Hind)2] x 1.5 H2O (1a). The reported complexes were characterized by elemental analysis, IR and UV-vis spectroscopy, ESI mass spectrometry, cyclic voltammetry, and X-ray crystallography. Electrochemical investigations give insight into the mechanistic details of the solvolytic behavior of complex 2. The lability of the aqua ligand in 2 suggests that this complex is a potential active species responsible for the high antitumor activity of trans-[Ru(III)Cl4(Hind)2](-).     

Synthesis of phthalide derivatives using nickel-catalyzed cyclization of o-haloesters with aldehydes

The reaction of o-bromobenzoate (1 b) with benzaldehyde (2 a) in the presence of [NiBr(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) and zinc powder in THF (24 hours, reflux temperature), afforded 3-phenyl-3H-isobenzofuran-1-one (3 a) in an 86 % yield. Similarly, o-iodobenzoate reacts with 2 a to give 3 a, but in a lower yield (50 %). A series of substituted aromatic and aliphatic aldehydes (2 b, 4-MeC(6)H(4)CHO; 2 c, 4-MeOC(6)H(4)CHO; 2 d, 3-MeOC(6)H(4)CHO; 2 e, 2-MeOC(6)H(4)CHO; 2 f, 4-CNC(6)H(4)CHO; 2 g, 4-(Me)(3)CC(6)H(4)CHO; 2 h, 4-C(6)H(5)C(6)H(4)CHO; 2 i, 4-ClC(6)H(4)CHO; 2 j, 4-CF(3)C(6)H(4)CHO; 2 k, CH(3)(CH(2))(5)CHO; 2 l, CH(3)(CH(2))(2)CHO) also underwent cyclization with o-bromobenzoate (1 b) producing the corresponding phthalide derivatives in moderate to excellent yields and with high chemoselectivity. Like 1 b, methyl 2-bromo-4,5-dimethoxybenzoate (1 c) reacts with tolualdehyde (2 b) to give the corresponding substituted phthalide 3 m in a 71 % yield. The methodology can be further applied to the synthesis of six-membered lactones. The reaction of methyl 2-(2-bromophenyl)acetate (1 d) with benzaldehyde under similar reaction conditions afforded six-membered lactone 3 o in a 68 % yield. A possible catalytic mechanism for this cyclization is also proposed.     

Amidines derived from Pt(IV)-mediated nitrile-amino alcohol coupling and their Zn(II)-catalyzed conversion into oxazolines

The reaction between the platinum(IV) complex trans-[PtCl(4)(EtCN)(2)] and the amino alcohols NH(2)CH(2)CH(2)OH, NH(2)CH(2)CH(Me)OH-(R)-(-), NH(2)CH(Ph)CH(2)OH-(R)-(-), NH(2)CH(Et)CH(2)OH-(R)-(-), NH(2)CH(Et)CH(2)OH-(S)-(+), and NH(2)CH(Pr(n)())CH(2)OH proceeds rapidly at room temperature in CH(2)Cl(2) to furnish the amidine complexes [PtCl(4)(HN=C(Et)NH(arcraise;)OH)(2)] (1-6) in good yield (70-80%). The related reaction between the platinum(II) complex trans-[PtCl(2)(EtCN)(2)] and monoethanolamine in a molar ratio of 1:2 in CH(2)Cl(2) results in the addition of 4 equiv of NH(2)CH(2)CH(2)OH per mole of complex to give [Pt(HN=C(Et)NHCH(2)CH(2)OH)(2)(NH(2)CH(2)CH(2)OH)(2)](2+) (7). Formulation of 1-6 is based upon satisfactory C, H, N elemental analyses, electrospray mass spectrometry, IR spectroscopy, and (1)H, (13)C((1)H), (15)N, and (195)Pt NMR spectroscopies, while the structures of trans-[PtCl(4)((Z)-NH=C(Et)NHCH(2)CH(2)OH)(2)] (1), trans-[PtCl(4)((Z)-NH=C(Et)NHCH(2)CH(Me)OH-(R)-(-))(2)] (2), and trans-[PtCl(4)((Z)-NH=C(Et)NHCH(Et)CH(2)OH-(R)-(-))(2)] (4) were determined by X-ray single-crystal diffraction. The Z-amidine configuration of the ligands is preserved in CDCl(3) solutions as confirmed by gradient-enhanced (15)N,(1)H-HMQC spectroscopy and NOE experiments. The amidines, formed upon Pt(IV)-mediated nitrile-amino alcohol coupling, were liberated from their platinum(IV) complexes 1, 3, and 4 by reaction with Ph(2)PCH(2)CH(2)PPh(2) (dppe) giving free NH=C(Et)NHCHRCH(2)OH (R = H 8, Et 9, Ph 10), with the substituents R of different types, and dppe oxides; the P-containing species were identified by (31)P((1)H) NMR spectroscopy. NOESY spectroscopy indicates that the liberated amidines retained the same configuration relative to the C=N double bond, i.e., syn-(H,Et)-NH=C(Et)NHCHRCH(2)OH. The liberated hydroxo-functionalized amidines 8-10 were converted into oxazolines (11-13) in the presence of a catalytic amount of ZnCl(2). A similar catalytic effect has also been reached using anhydrous MSO(4) (M = Cu, Co, Cd), CdCl(2), and AlCl(3).     

The reaction of tertiary phosphines with (Ph2Se2I2)2--the influence of steric and electronic effects

The reaction of (Ph(2)Se(2)I(2))(2) with a wide variety of tertiary phosphines possessing different steric and electronic properties has been studied, leading in most cases to R(3)PSe(Ph)I adducts; [R(3)P = (p-CH(3)C(6)H(4))(3)P (1), (m-CH(3)C(6)H(4))(3)P (2), (o-OCH(3)C(6)H(4))(3)P (4), Ph(2)MeP (6), Me(2)PhP (7), Me(3)P (8), Cy(3)P (9)]. All of the products formed were characterised by elemental analysis, Raman and multinuclear NMR spectroscopy. Both steric and electronic factors are important in determining the structural motif (CT vs. ionic) observed in the solid-state. In general, highly basic phosphines result in a lengthening of the Se-I interaction, and a preference for an ionic structure. The reaction with (o-CH(3)C(6)H(4))(3)P does not yield a stable R(3)PSe(Ph)I adduct, and instead (o-CH(3)C(6)H(4))(3)PI(2) (3) is formed. The unusually long P-I bond, [2.5523(12) A], and short I-I bond, [3.0724(4) A], exhibited by is a result of the high steric requirements of this phosphine. The similarly bulky (o-SCH(3)C(6)H(4))(3)P yields a mixture of (o-SCH(3)C(6)H(4))(3)PSe(Ph)I (5a) and [(o-SCH(3)C(6)H(4))(3)PSePh]I(3) (5b). The crystal structures of (m-CH(3)C(6)H(4))(3)PSe(Ph)I, 2, (o-CH(3)C(6)H(4))(3)PI(2), 3, [(o-OCH(3)C(6)H(4))(3)PSePh]I.CH(2)Cl(2), 4, [(o-SCH(3)C(6)H(4))(3)PSePh]I(3), 5b, two pseudo-polymorphs of Ph(2)MePSe(Ph)I, 6a/6b, and [Me(3)PSe(Ph)I](2).CH(2)Cl(2), 8, are reported. The R(3)PSe(Ph)I adducts formed exhibit one of four types of behaviour. Type I products, (such as 2) are CT in the solid-state and display fluxionality in solution. Type II products (such as 6a/6b) lie close to the CT/ionic structural borderline, displaying long Se-I bonds, and are more appropriately classified as [R(3)PSePh] (acceptor)/I(-) (donor) CT complexes. Type II complexes ionise in solution to [R(3)PSePh]I. Type III products, such as 8, are ionic in solution, but frequently show cation-anion, or cation-solvent interactions in the solid-state, although these interactions are weak and the linear P-Se-I motif is lost. Type IV products (such as 4) are ionic and feature bulky phosphines. They display no short cation-anion interactions in the solid-state.     

Phase behavior and preparation of mesoporous silica in aqueous mixtures of fluorinated surfactant and hydrophobic fluorinated polymer

The phase behavior and formation of self-assemblies in the ternary water/fluorinated surfactant (C(8)F(17)EO(10))/hydrophobic fluorinated polymer (C(3)F(6)O)(n)COOH system and the application of those assemblies in the preparation of mesostructured silica have been investigated by means of phase study, small angle X-ray scattering, and rheology. Hexagonal (H(1)), bicontinuous cubic (V(1)) with Ia3d symmetry, and polymer rich lamellar (L(alpha)(')) are observed in the ternary diagram. C(8)F(17)EO(10) molecules are dissolved in polymer rich aggregates, whereas (C(3)F(6)O)(n)COOH molecules are practically insoluble in the surfactant lamellar phase due to packing restrictions. Hence, two types of lamellar phases exist: one with surfactant rich (L(alpha)) and the other with polymer rich (L(alpha)(')) in the water/C(8)F(17)EO(10)/(C(3)F(6)O)(n)COOH system. As suggested by rheological measurements, worm-like micelles are present in C(8)F(17)EO(10) aqueous solutions but a rod-sphere transition takes place by solubilization of (C(3)F(6)O)(n)COOH. C(8)F(17)EO(10) acts as a structure directing agent for the preparation of hexagonal mesoporous silica by the precipitation method. The addition of (C(3)F(6)O)(n)COOH induces the formation of larger but disordered pores.