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The ability to form robust, optoelectronically responsive, and mechanically tunable hydrogels using facile processing is desirable for sensing, biomedical, and light-harvesting applications. We demonstrate that such a hydrogel can be formed using aqueous complexation between one conjugated and one nonconjugated polyelectrolyte. We show that the rheological properties of the hydrogel can be tuned using the regioregularity of the conjugated polyelectrolyte (CPE) backbone, leading to significantly different mesoscale gel morphologies. We also find that the exciton dynamics in the long-time limit reflect differences in the underlying electronic connectivity of the hydrogels as a function CPE regioregularity. The influence of excess small ions on the hydrogel structure and the exciton dynamics similarly depends on the regioregularity in a significant way. Finally, electrical impedance measurements lead us to infer that these hydrogels can act as mixed ionic/electronic conductors. We believe that such gels possess an attractive combination of physical-chemical properties that can be leveraged in multiple applications.

The reaction of realgar with [Cp′2MH3] in boiling toluene gave [Cp′2M2As2S6] (Cp′ = t-BuC5H4; M = Nb: 1; Ta: 2), while [Cp2WH2] (Cp = C5H5) reacted with As4S4 to give [Cp2W(H)(η1-As5S2)] (6). The structures were determined by X-ray crystallography. Compounds 1 and 2 are dimers in which two Cp′M units are symmetrically bridged by a μ,η2:2-AsS3 ligand, a sulfide ligand and a heteroallylic μ,η2:2-AsS2 ligand. The structure of 6 belongs to the type of bent metallocenes in which tungsten is surrounded tetrahedrally by two Cp ligands, a crystallographically found hydride atom and the new As5S2 cage. The reaction of 1 with W(CO)5THF gave [Cp′2Nb2As2S6·W(CO)5] (3) and [Cp′2Nb2As2S6W(CO)3·W(CO)5] (4). Compound 3 is a monoadduct of 1 bearing the W(CO)5 fragment at the As atom of the AsS3 ligand. The structure of 4 contains a distorted cubane-like Nb2WS4As cluster with an integrated W(CO)3 unit. A similar cluster 5 containing a CuI fragment instead of W(CO)3 was prepared from 1 and CuI. The structure is completed by an attached As4S3 cage, the As3 basis of which is oriented towards iodide. Electrochemical investigations of 1, 3, and 4 shows for each compound quasi-reversible one-electron reductions with E1/2 = −0.73 V (1), −0.55 V (3) and −0.67 V (4), respectively.

Reaction of solutions of [ Cp ∗ Cp ∗ = η 5 -C 5 Me 5 ) in CH 2 Cl 2 with solutions of CuHal (Hal = Cl, Br, I) in CH 3 CN gave after slow diffusion the novel coordination polymers [ Cp 2 ∗ Mo 2 P 2 S 3 (CuCl) 4 ] ( 2 ), [ Cp 2 ∗ Mo 2 P 2 S 3 (CuBr) 3 ] ( 3 ) and [ Cp 2 ∗ Mo 2 P 2 S 3 (CuI) 3 ] ( 4 ). The products were characterized by elemental analysis, 31 P magic angle spinning (MAS) NMR spectroscopy and single-crystal X-ray crystallography. The solid-state structures of 2 and 3 are composed of two-dimensional polymeric networks, whereas that of 4 contains parallel stacks of one-dimensional ribbons. In all cases the planar cyclo -P 2 S 3 middle deck of the organometallic building block 1 provides one or two P atoms of the PS dumbbells along with the singly bridging sulfur atom as coordination sites for the various copper halide subunits. The assignment of P atoms follows from the correlation of 31 P MAS NMR spectra with X-ray crystallographic data. In all compounds the distribution of main group atoms in the cyclo -P 2 S 3 middle deck is different from that previously found in the starting material 1 .

The molecular structure of [Cp*2Mo2P2S3] (1; Cp* = η5-C5Me5) has been reinvestigated. In DFT studies a series of various positional isomers A−E have been calculated for the model complex [(C5H5)2Mo2P2S3]. The energetically favored isomer [Cp*2Mo2(μ,η2:2-PS)2(μ-S)] (1B) reacts with W(CO)5THF to give [Cp*2Mo2P2S3·W(CO)5] (2). X-ray diffraction analysis of 2 confirms the presence of two η2:2-PS dumbbells and one singly bridging sulfur ligand, the W(CO)5 fragment being coordinated at one of the P atoms. Arrangement B is also found in the structure of the diadduct [Cp°2Mo2P2S3{W(CO)5}2] (3; Cp° = t-BuMe2C5H2), which is more stable than its Cp* analogue. 31P solid-state MAS NMR spectroscopic studies of 1 and 2 confirm the existence of only one isomer, but reveal disorder phenomena in the solid state within the cyclo-P2S3 middle deck. Addition of excess W(CO)5THF to 1 proceeds via elusive [Cp*2Mo2P2S3{W(CO)5}2] to give the cluster [{Cp*2Mo2W(CO)3(μ2,η2:2-PS)(μ3,η1:1:2-PS)(μ3-S)}{W(CO)5}2] (5). The molecular stru...

The reaction of [ Cp 2 ∗ Nb ( Te 2 H ) ] (Cp∗ = η5-C5Me5) with [Pd(DBA)2] (DBA = dibenzylidenacetone) and dppm (bis(diphenylphosphanyl)methane) gave the new tetratelluropalladate cluster [ ( Cp 2 ∗ Nb ) 2 PdTe 4 ] (1), which has been characterised by means of elemental analysis, FD-MS and X-ray crystallography. The structure of compound 1 contains a planar PdTe4 rectangle to which two niobocene groups are coordinated. DFT calculations on the hypothetical [PdTe4]2− anion and comparison of the results with those of the W and Ni homologues show that the planar arrangement of Te ligands in 1 is due to the intrinsic property of the central Pd atom.

The reaction of Cp* 2 NbBH 4 (Cp* = η 5 -C 5 Me 5 ) with Ru 3 (CO) 1 2 gave a mixture of compounds, from which only [Cp* 2 Nb(CO) 2 ] 2 -[Ru 6 (CO) 1 6 C] (1) could be characterized by spectroscopic and crystallographic methods. 1 1 B NMR spectroscopy proved that interstitial boron may be present in other Ru 6 clusters, but these compounds did not crystallize. The reaction of Cp* 2 NbBH 4 with Co 2 (CO) 8 gave among others the salts [Cp* 2 Nb(CO) 2 ] 2 [Co 6 (CO) 1 5 C] (4) and [Cp* 2 Nb(CO) 2 ] 3 [Co 1 3 (CO) 2 4 C 2 ] (5), which were examined by X-ray diffraction studies. The true nature of the interstitial atoms in 5 was deduced from electrochemical investigations, which reveal similar redox properties as for the already known [Co 1 3 (CO) 2 4 C 2 ] 3 - anion.

The reaction of the cluster salts [Cp* 2 Nb(CO) 2 ] n [Co 1 1 Te 7 (CO) 1 0 ] (Cp* = C 5 Me 5 ; n = 1, 2) with excess PMe 2 Ph gave the neutral, dark brown clusters [Co 1 1 Te 7 (CO) 6 (PMe 2 Ph) 4 ] (5) and [Co 1 1 Te 7 (CO) 5 (PMe 2 Ph) 5 ] (6) with 147 metal valence electrons. The new compounds were characterized by IR spectroscopy, elemental analyses, and mass spectrometry. The molecular structure of 6 was determined by X+ray crystallography. Like its precursor anion, it consists of a pentagonal-prismatic [Co 1 1 Te 7 ] core, but with a ligand sphere composed of five CO and five PMe 2 Ph ligands. Detailed electrochemical studies of both reactions reveal that a stepwise substitution of CO ligands in the initial cluster anions takes place leading to intermediate [Co 1 1 Te 7 (CO) 1 0 - m (PMe 2 Ph) m ] n - ions (m = 1 - 5; n = 1, 2). Each of these intermediates is distinguished by at least one oxidation and two reduction waves, giving rise to a total of 21 redox couples and 27 electroactive species. The electron sponge character of the new compounds is particularly pronounced in 5, which exhibits charges n between + 1 and - 4 corresponding to metal valence electron counts of between 146 and 151.

The reaction of [Cp*2NbCl2] (Cp*=η5-C5Me5) with KOH or Ba(OH)2·8H2O in THF was investigated under slightly modified conditions. In addition to the known complex [Cp*2Nb(O)H] (1), the new compound [Cp*2Nb(O)OH] (2) was formed. The reaction of 2 with PhNCS gave yellow [Cp*2Nb(O){SC(O)NHPh}] (3), while PhNCO formed yellow [Cp*2Nb(O){OC(O)NHPh}] (4). Complexes 3 and 4 were analytically and spectroscopically characterized. X-ray diffraction analyses of both compounds show that they contain either η1-S-thiocarbamato (3) or η1-O-carbamato ligand (4) along with a terminal NbO group. The reaction of 1 with one equivalent of PhNCO mainly gave orange [Cp*2NbH{OC(O)NPh}] (5) along with some 4. The molecular structure of 5 contains a niobocene unit comprising η2-N,O-carbamato chelate, which formally is a [2+2] cycloaddition product of the NbO group and the heterocumulene. A hydride ligand completes the coordination sphere around Nb. Reaction of 1 with excess PhNCO gave a mixture of heterocycles (PhNCO)2 (6) and (PhNCO)3 (7) in the approximate ratio 3:2. By contrast, the reaction of [Cp*2Nb(O)OMe] with PhNCO in molar ratios from 1:3 to 1:100 gave nearly pure triphenylisocyanurate 7.

The reactions of [Cp#2NbBH4] (1) [Cp# = C5Me5 (Cp*) or C5Me4Et] and [Cp′2TaH3] (Cp′ = tBuC5H4) with elemental selenium give complexes of the general composition [Cp2MSe2H]. These exist in three isomeric forms, A–C, depending on the metal and the chalcogen. [Cp#2NbSe2H] (2) incorporates the novel η2-Se2H ligand (C), which is labile when exposed to light. Solutions of 2(Cp*) can be converted into [Cp*2NbSe2H] (3), which exists in two isomeric forms A or B, along with [Cp*2NbSe3H] (4) and [Cp*2NbO2H] (5). [Cp′2Ta(η2-Se2)H] (6) is the only isomer found for the Ta system. Se abstraction by means of P(OEt)3 gives [Cp′2Ta(=Se)H] (7). Complex 7 can be reduced with Na/Hg and subsequently hydrolysed to give [Cp′2Ta(SeH)H2] (8), which has also been observed during the formation of 6. Coordination of [W(CO)5THF] at the Se lone pair of 7 affords the heterobimetallic complex 9. All compounds have been characterized by means of 1H- and, in some cases, 77Se-NMR spectroscopy. Products 8 and 9 have also been subjected to X-ray diffraction analysis.

Reaction of Cp*2NbCl2 (Cp*=η5-C5Me5) with KOH or Ba(OH)2·8H2O in THF forms the complexes Cp*2Nb(O)X (X=Cl: 2, H: 3). The ratio of 2 and 3 depends on the stoichiometry. If NaOMe is added or MeOH in solution Cp*2Nb(O)OMe 4 is formed in good yields. Reactivity studies with 3 and 4 show that the NbO as well as the Nb–X unit behave as chemically active sites. Protonation of 3 or 4 with HBF4 is followed by an attack of fluoride (from BF4− anion) to give [Cp*2Nb(OH)F]BF4 6 and [Cp*2NbF2]BF4 7. In contrast the reaction of 3 or 4 with HCO2H results in an exchange of X− by formate to give Cp*2Nb(O)OC(O)H 8. The crystal structures of 6 and 8 are reported. Electrochemical investigations of 2–4 and 7, 8 reveal reaction pathways for the transformation of 1 into 3.

Irradiation of Cp 2 ∗ Nb(η 2 S 2 )H (Cp ∗ = C 5 Me 5 ) 1a in the presence of Fe(CO) 5 gives the CO-free complex [Cp 2 ∗ NbS 2 ] 2 Fe 2a . The core of 2a contains an FeS 4 tetrahedron which is ligated by two niobocene ligands as shown by X-ray diffraction analysis. In the reaction of 1a or Cp 2 x Nb(η 2 S 2 )H (CP x = C 5 Me 4 Et) 1b with Co 2 (CO) 8 , compounds 3a and 3b of the same type are formed. Electrochemical studies of 2a and 3a,b show that they undergo three reversible 1e − steps. The oxidation of 3b exerts a considerable influence on its absorption spectrum. A qualitative EHMO analysis is in agreement with a strong delocalisation of electron density over the whole NbS 2 MS 2 Nb system.

Completely reduced Cp 2 ∗ NbCl 2 (Cp ∗ = η 5 -C 5 Me 5 ) solutions (two equipvalents of NaHg) which were previously supposed to contain two isomers A and B of decamethylniobocene react with sulfur to give products 1–4 . Their 1 H and 13 C NMR spectroscopy investigations allow for the first time a clear assignment of the structures of A and B . As 1 and 2 are identical with the previously reported Cp ∗ 2 Nb(η-S 2 )L derivatives (L = H ( 1 ), SH ( 2 )) a bent niobocene structure follows for isomer A . Products 3 and 4 are in agreement with structures involving a η 1 :η 5 -tetramethylfulvene ligand which in the case of 4 is slightly modified by sulfur insertion into the CH 2 Nb bond. Thus the structure of isomer B may be derived from bent niobecene by a hydride migration from one CH 3 group to Nb.

Sets of variously protected purpurosamine/2-epi-purpurosamine-type glycosyl donors (O-acetates) and sannamine-type glycosyl acceptors were coupled as racemates and pure enantiomers, according to a modified Koenigs-Knorr procedure with TMSOTf as promotor. The α anomers isolated from the respective mixtures of glycosides (yields varying between 51% and 91%, α:β anomeric ratios between 1.5:1 and 13:1, α:α′ diastereomeric ratios between 1:1 and 1:1.5) were transformed through standard protection/deprotection and glycidation measures into 6′-des(N-methyl)sannamycins A (1, 1′, 2, 2′) and B (37, 37′), 2′-epi-6′-des(N-methyl)sannamycins (3, 3′), the enantiomeric sannamycins A and B (ent-4)/ (ent-40), the diastereomers (ent-4′)/(ent-40′), and the enantiomeric 2′-epi-sannamycin A (ent-5)/(ent-β-5). For one of the fluorinated glycosides (α-26′), featuring a somewhat unusual aglycon conformation, an X-ray structural analysis was performed. In explorative biological tests, the naturally configurated glycosides 1 and 3 showed limited, 2 a rather broad activity against a number of pathogenic microorganisms. Yet, none of the glycosides with non-natural configuration was found to be active.

Along an established scheme, 1,2:3,4-dianhydrodeoxy-epi-inositol (3) — readily available from benzene — has been applied to expeditious syntheses of suitably protected, fluorinated, and epimerized aminoglycoside building blocks related to sannamine (rac-14a, rac-16a, rac-18a, rac-31a) and sporamine (rac-21a, rac-23a, rac-26a, rac-34a). By separation of diastereomers formed with (+)-(1-phenylethyl)amine (14c/ 14′c; 16c/16'c) or with (-)-camphanic acid (14e/14'e) and by enzymatic hydrolysis (rac-14b) access is gained to enantiopure glycosyl acceptors.

The reaction of Cp + 2 NbBH 4 with sulfur gives two isomers of composition Cp + 2 NbS 2 H ( 3 , 4 ) and Cp + 2 NbS 3 H ( 5 ). The structures of 3 – 5 have been investigated by IR and 1 H NMR spectroscopic means. X-Ray diffraction analyses have been performed on 3 and 4 . These investigations demonstrate that 3 and 4 are niobocene derivatives, in which either a η 2 -S 2 2− -ligand and a hydride ( 3 ) or a S 2− and a SH − ligand ( 4 ) are attached to the Nb center. Complex 3 can be transformed thermally into 4 by a SS bond rupture, followed by the insertion of sulfur into the NbH bond. The polynuclear compounds Cp + 3 Nb 3 S 7 ( 6 ) and Cp + 3 Nb 3 S 12 ( 7 ) can be formed by the reaction of 3 with S 8 . The role of polysulfide intermediates is discussed.

Along an established scheme, 1,2:3,4-dianhydrodeoxy-epi-inositol (3) — readily available from benzene — has been applied to expeditious syntheses of suitably protected, fluorinated, and epimerized aminoglycoside building blocks related to sannamine (rac-14a, rac-16a, rac-18a, rac-31a) and sporamine (rac-21a, rac-23a, rac-26a, rac-34a). By separation of diastereomers formed with (+)-(1-phenylethyl)amine (14c/ 14′c; 16c/16'c) or with (-)-camphanic acid (14e/14'e) and by enzymatic hydrolysis (rac-14b) access is gained to enantiopure glycosyl acceptors.

NbCl 5 reacts with NaBH 4 and LiCp + (Cp + = EtMe 4 C 5 ) dependent on the stoichiometry and temperature to give Cp + 2 NbCl 2 ( 1 ), Cp + 2 Nb 2 Cl 2 (B 2 H 6 ) ( 2 ), Cp + 2 NbBH 4 ( 3a ) and Cp + 2 Nb 2 (B 2 H 6 ) 2 ( 4a ). With a large excess of NaBH 4 , Cp + 2 NbCl 2 gives 2 at 25°C, which reacts further with NaBH 4 to give 4a . The synthesis of the deep violet, very stable 4a can be generalised by using C 5 Me 5 Li and t BuC 5 H 4 Li, respectively. Compounds 1–4 are characterised by means of IR, 1 H, and heteroatom NMR spectra. An X-ray structure analysis was carried out with 4a . Whereas 1 and 3 are analogous to already known complexes, in 2 and 4a the B 2 H 6 dianion (which is not stable in the free state) is present as a bridging ligand, oriented perpendicularly with respect to the NbNb axis. So far, the highest nuclear magnetic 93 Nb shielding has been observed for compounds 4 , extending the range of Imown δ( 93 Nb) values by 2500 ppm. The temperature dependence of the linewidths of both the 11 B and the 93 Nb NMR signals of 4c allows evaluation of the magnitude of J ( 93 Nb 11 B) = 50 ± 10 Hz.

The reaction of the differently substituted cyclopentadienyl complexes L 2 M 2 (CO) 4 with sulfur is investigated with respect to the ligand L (etmcp = ethyltetramethylcyclopentadienyl, tbcp = t-butylcyclopentadienyl, ipcp = isopropylcyclopentadienyl) and the metal M (Cr, Mo, W). For M  Cr the only isolated product is etmcp 2 Cr 2 S 5 . For M  Mo three isomers A , D , E of composition L 2 MO 2 S 4 (L  ipcp, etmcp) are formed whereas only two isomers ( A , D ) exist for L  tbcp. Only two isomers ( D , E ) of composition L 2 W 2 S 4 are formed in the system L 2 W 2 (CO) 4 /S 8 , a further product is L 2 W 2 (CO) 2 S 3 for L  etmcp. Structural characterisation of all compounds was achieved by IR, 1 H, and 95 Mo NMR spectroscopy, whereas the structures of syn -etmcp 2 M 2 (μ-S) 2 S 2 (M  Mo, W) were determined by X-ray crystallography, the result of which allows the correction of a previous structure assignment. It is further shown that a thermal equilibrium exists between L 2 Mo 2 (μ, ν 2 -S 2 )(μ-S) 2 ( A ) and syn -L 2 Mo 2 (μ-S) 2 S 2 ( D ) which depends strongly on the ligands.

Extended investigations of the reaction sequence [Cp′2Nb(Te2)H]/CH3Li/[Co2(CO)8] (Cp′ = tBuC5H4) led to the identification of Lin[3] {3 = [Co9Te6(CO)8]; n = 1, 2} salts through their transformation with [PPN]Cl into [PPN]n[3] (PPN = Ph3PNPPh3). These compounds form in the solid state columnar ([PPN][3]) or undulated 2D ([PPN]2[3]) supramolecular networks. Electrochemical studies of [Cp*2Nb(CO)2][3] (Cp* = C5Me5) or [Na(THF)6][3] revealed the presence of the redox couples [3]–/[3]2–/[3]3–/[3]4–/[3]5– regardless of the nature of the cation, whereas in the anodic part oxidative degradation of the cluster takes place. This behavior is in agreement with the observation that [3]– containing salts form with PPh3AuCl or dppe decomposition products like [(PPh3)2Au][CoCl3PPh3] or [Co(CO)2dppe]2(μ-Te). A neutral cluster comprising the Co@Co8(μ4-Te)6 core formed in the reaction of [Cp*2Nb(CO)2][Co11Te7(CO)10] with PPh3AuCl, which gave [Co9Te6(CO)4(PPh3)4] (4) after oxidative cluster degradation and CO substitution. 4 was characterized by X-ray crystallography. DFT calculations carried out on all members of the [3]n (n = +1 to –5) family and on related species indicate that there is no significant Jahn–Teller distortion (and therefore no connectivity change) for any of the considered electron counts. Magnetic investigations on [PPN][3] show that the ground state of [3]– is a spin triplet with spins interacting antiferromagnetically in a 1D space.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The novel cluster anion [Co(11)Te(5)(CO)15]- ([3]-) has been isolated and structurally characterized as part of the salt [Cp*(2)Nb(CO)2][3] (Cp* = C(5)Me(5)). The cobalt-centered Co10 pentagonal prism is surrounded by a shell of two mu5-Te, three mu4-Te ligands, and 15 CO groups in terminal, symmetrical, and sigma-semibridging bonding modes. The hybrid carbonyl-telluride character of the ligand shell is reflected in the solid state by a one-dimensional assembly of polyhedral prisms along a backbone of [Cp*(2)Nb(CO)2]+ cations. Electrochemical studies reveal the presence of four redox couples of [3]n (n = -1 to -5). The electronic structures of various metal-centered and empty pentagonal-prismatic (PP) M10 clusters (M = Co, Ni) are calculated and compared to those of pentagonal-antiprismatic (PA) M10 structures. Closed-shells of 152 and 156 metal valence electrons, respectively, are found to determine the electronic structures and chemical properties of these geometries. From these considerations, magnetic properties have been predicted. They have been verified for the [Co(11)Te(7)(CO)10]- cluster anion, which exhibits a singlet-triplet gap of 0.318 kcal/mol.

The reaction of [ Cp 2 ′ Nb ( Te 2 ) H ] ( 1 ) (Cp′ = t -BuC 5 H 4 ) with CH 3 Li in THF was examined by variable temperature 1 H NMR, ESR and mass spectroscopic means. From these methods it is evident that the diamagnetic compounds [ Cp 2 ′ NbH 2 ( TeCH 3 ) ] ( 2 ) and [ Cp 2 ′ Nb ( Te ) CH 3 ] ( 3 ) as well as the paramagnetic compound [ Cp 2 ′ Nb ( TeCH 3 ) 2 ] ( 4 ) form simultaneously. In the subsequent reaction of the intermediate solution with [Co 2 (CO) 8 ] compound 4 was consumed and the compound [ Cp 2 ′ Nb ( μ - TeCH 3 ) 2 Co(CO) 2 ] ( 5 ) formed in good yield. Complex 5 was characterized by IR and variable temperature 1 H NMR spectroscopies. Electrochemical two-electron reduction of 1 leads, in a quasi-reversible process, to products that are not stable in solution.

Science and the National Science Foundation announce the winners and honorable mentions in the categories of photography, illustration, informational graphics, noninteractive multimedia, and interactive multimedia in this year9s Science and Engineering Visualization Challenge. (Read more.)

Reactions of Cp*2Nb(η2-S2)H 1 (Cp*=C5Me5 (a), C5Me4Et (b)) and Cp*2Nb(η2-Se2H) 3 with 0.5 equivalents of M(CO)6 (M=Cr, Mo) in boiling toluene give the CO free complexes [Cp*2NbE2]2M 4–7. X-ray diffraction analyses have been carried out for the Mo complexes 5a (E=S) and 7a (E=Se) showing that the structures contain ME4 tetrahedral cores with two attached niobocene ligands thus forming a nearly linear trimetallic unit. Absorption spectra and electrochemical studies of complexes 4–7 are described. Characteristic of the novel CrSe4 chromophor are four reversible one electron redox steps. Chemical oxidation of 4a and 5a with [(C5H5)2Fe]PF6 gives the salts {[Cp*2NbS2]2M}PF6 (M=Cr, Mo) 10 and 11. A qualitative EHMO analysis provides evidence for a strong delocalisation of electron density over the whole metal–ligand system.

CP(dagger)2NbCl2 (CP(dagger) = 175-C5Me4Et) (1b) was synthesized from NbCl5 and a slight excess of Cp(dagger)Li and NaBH4. Its electrochemical (2 e-, E1/2 = -1.6 V) and chemical reduction (2 equiv of Na/Hg) was studied showing that peralkylation of the Cp ligand facilitates two-electron reduction compared to less substituted CP2NbHal2 derivatives. The reduced solutions of CP*2NbCl2 (CP* = C5Me5) (1a) and of lb were shown by means of EPR spectroscopy to contain two new paramagnetic species 1A,B for which bent niobocene (A(Nb) = 100 G) and fulvene-like structures (A(Nb) = 55 G) are proposed. The high reduction potential of these species led in their reaction with HPF6 to the first stable difluoroniobocene derivative, [CP(dagger)2NbF2]PF6 (2), in good yield. The molecular structures of 2 and a cocrystallizate of 2 and [CP(dagger)2NbCl2]PF6 (3), analyzing as [CP(dagger)2NbCl(Cl,F)]PF6 (4), were studied by X-ray diffraction techniques. Comparison with the structure of 1b shows a marked decrease of the angle Hal-Nb-Hal from 102.3(4)-degrees (2) to 85.2(1)-degrees (1b). Electrochemical 1 e- reduction of 2 gave rise to the formation of CP(dagger)2NbF2, which exhibits a much lower potential (E1/2 = -2.38 V) than other niobocene dihalides. Reaction of 2 with Li2S2 gave CP(dagger)2Nb(eta-S2)F, whereas 3 was reduced by Li2S2 to give 1b.

The cover picture shows an organometallic electron sponge and an elephant-ear sponge in the background (photo by F. and J. Burek, National Marine Sanctuaries). The electronic flexibility of the cobalt-centered cubic [Co9Te6(CO)8]n cluster ([3]n) in the central circle is expressed by differently charged states (n = 1+ to 5–). Starting from the upper left corner of our graphic in a clockwise direction, neutral [Co9Te6(CO)4(PPh3)4], structurally diverse networks of [Ph3PNPPh3][3] and [Ph3PNPPh3]2[3] salts and the core of the [Co9Te3{ν5-Cp′2Nb(CO)Te}3(CO)8] cluster as a pseudo-protonated representative of the [3]3– anion are shown. Details of the structural, electrochemical and theoretical properties of these compounds are described in the article by J. Wachter et al. on page 1959 ff.

Zusammenfassung Thermolysis of a mixture of Cp′4Nb2Sn (Cp′ = t-BuC5H4; n = 8, 9) results in the formation of the new niobium polysulfide complexes: Cp′3Nb3S12 (2), Cp′3Nb3S10O (3), Cp′3Nb3S10O (4) and Cp′4Nb4S13 (5). The structures of 2 and 3 have been established by X-ray diffraction studies. The complexes are characterized by an unusual variety of different sulfur ligands (up to five in 2), which is responsible for the absence of any metal-metal interaction.

Both enantiomers of purpurosaminides C (ent-7b, 13a–c), of a 2-azido analogue (ent-16b) and of 2-azido epimers (ent-26b, ent-29b), suitably protected for their direct use as glycosyl donors, are prepared from racemic 3,4-dihydro-2H-pyran-2-carbaldehyde (acrolein dimer, rac-1). The latter has been resolved on a preparative scale through the diastereoisomeric trifluoroacetylated 1′-amines obtained with (1R)- and (1S)-1-phenylethylamine, which allowed the combination of optical resolution with the introduction of the glycosyl 6-amino function.

The methylation reaction of (C 5 Me 5 ) 2 Mo 2 (μ-S 2 )(μ-S) 2 (Ia) leads to two isomers of composition (C 5 Me 5 ) 2 Mo 2 (SMe) 2 S 2 (IV and IVb) which were separated by column chromatography. As an intermediate product of this reaction the iodine-containing adduct (C 5 Me 5 ) 2 Mo 2 S 4 I 2 is formed. All compounds were investigated by means of 1 H and 95 Mo NMR spectroscopy as well as by an X-ray structure analysis in the case of IVa. Thus, the SCH 3 ligands in IV are found to be arranged in a trans position. As a further result a cleavage of the η 2 -disulfur bridge, originally present in Ia, has been found to occur in the second step of the reaction sequence.

Starting from the prochiral dianhydrodeoxy-epi-inositol 9 a highly efficient synthesis for rac-sannamines (1, salts, derivatives) and rac-de-O-methylsannamine (18, salt) has been developed. Key steps are two regiospecific, practically quantitative epoxide opening reactions: intramolecularly in the diepoxyurethanes 11 and intermolecularly in the epoxyurethanes rac-13. With (R)-1-phenyl-ethylamine as potential primary amino group in the second step separation of the corresponding diastereomers (16, 16′) is achieved without significant loss of material. By this route enantiomerically pure (de-O-methyl)sannamines become available in which all functionalities are protected except that to be glycosidated. Attempts for an asymmetric realization of this synthesis resulted in only very small ee(de) values. Aminoglycosid-Antibiotika - Enantiomerenreine Sannamin-Bausteine Ausgehend vom prochiralen Dianhydrodesoxy-epi-inosit 9 wurde eine leistungsfahige Synthese fur enantiomerenreine rac-Sannamine (1, Salze, Derivate) und rac-Des-O-methylsannamin (18, Salz) ausgearbeitet. Essentielle Schritte sind zwei regiospezifische, praktisch quantitative Epoxidoffnungen: Intramolekular in den Diepoxyurethanen 11 und intermolekular in den Epoxyurethanen rac-13. Mit (R)-1-Phenylethylamin als potentieller primarer Aminogruppe im zweiten Schritt gelingt die Diastereomerentrennung (16, 16′) ohne signifikante Verluste. Es werden direkt enantiomerenreine (Des-O-methyl)Sannamin-Derivate gewonnen, in welchen alle Substituenten bis auf die zu glycosidierende OH-Gruppe geschutzt sind. Versuche zur asymmetrischen Durchfuhrung der Synthese brachten nur bescheidene ee(de)-Werte.

The reaction of the cubane cluster (C5Me5)2Cr2Co2(CO)2S4 with PR3 (R = Ph, OMe) resulted in a stepwise substitution of CO ligands by PR3. One of the reaction products, (C5Me5)2Cr2Co2{P(OMe)3}2S4, was characterized by an X-ray diffraction study, confirming that the 60-e core of composition Cr2Co2S4 was retained.

Reaction of the complexes Cp* 2 M 2 (μ-CO) 2 ( M = M ; Cp* = η 5 -C 5 Me 5 ; M = Co, Rh) with elemental sulfur, selenium, or tellurium results in addition of one or two equivalents of the chalcogen to the MM double bond, the outcome is dependent on the reaction conditions and the stoichiometry. Complexes of the type Cp* 2 Rh 2 (CO) 2 E (E = S, Se) and Cp* 2 M 2 (CO) 2 E 2 ( M= Co, Rh; E = Se, Te) have been isolated and characterized spectroscopically. Reaction of excess chalcogen with Cp* 2 M 2 (CO) 2 gives the CO-free diamagnetic compounds Cp* 2 Co 2 S 4 , Cp* 2 Rh 2 S 8 , and Cp* 2 M 2 Se 5 (M = Co, Rh). X-ray diffraction studies have been carried out on Cp* 2 Co 2 Se 5 and Cp* 2 Rh 2 (CO) 2 Se. The latter compound exhibits a Rh 2 Se three-membered cycle with attached anti -oriented Cp* and CO ligands. In the cobalt compound a Se 2− and a Se 4 2− ligand form a nearly planar pseudo five-membered cycle, which bisects the Co–Co axis. All reactions can be interpreted in terms of stepwise addition of chalcogens to the MM double bond with subsequent replacement of carbon monoxide.

The uncoordinated sulphur of the iso-μ(η 1 -S 2 ) ligand in (C 5 Me 5 ) 2 Cr 2 S 5 is easily abstracted by PPh 3 causing formation of (C 5 Me 5 )Cr 2 S 4 , isoelectronic with (C 5 Me 5 ) 2 Mo 2 (μ-S 2 )(μ-S) 2 . From the nature of the products [(C 5 Me 5 ) 2 Cr 2 S 5 H]PF 6 , [(C 5 Me 5 ) 2 Cr 2 S 5 CH 3 ]PF 6 , [(C 5 Me 5 ) 2 Cr 2 S 4 CH 3 ]PF 6 and [C 5 Me 5 ) 2 Mo 2 S 4 CH 3 ]PF 6 formed from these complexes by reaction with CF 3 CO 2 H and CH 3 I a decrease in nucleophilicity is deduced for μ(η 1 -S 2 ) > μ-S > μ(η 2 -S 2 ). The reaction of (C 5 Me 5 ) 2 Mo 2 S 4 with C 5 H 5 (CO) 2 Mn(THF) gives a complex of composition (C 5 Me 5 ) 2 Mo 2 (C 5 H 5 )Mn(CO) 2 S 4 , whereas (C 5 Me 5 ) 2 Cr 2 S 5 gives only the known complexes [C 5 H 5 (CO) 2 Mn] 2 S 2 and [C 5 H 5 (CO) 2 Mn] 2 S together with (C 5 Me 5 ) 2 Cr 2 S 4 . In the reaction with H 2 (150 bar/80°C) (C 5 Me 5 ) 2 Mo 2 S 4 forms (C 5 Me 5 ) 2 Mo 2 S 4 H 2 , in contrast to (C 5 Me 5 ) 2 Cr 2 S 4 and (C 5 Me 5 ) 2 Cr 2 S 5 which give the cubane type cluster (C 5 Me 5 ) 4 Cr 4 S 4 .

From the reaction of (C 5 R 5 ) 2 Mo 2 (CO) 4 (R = H, CH 3 ) with boiling CS 2 the new compounds C 5 R 5 (CO) 3 Mo-Mo(CO) 2 (η 2 -CS 2 )C 5 R 5 , I and II, have been isolated. These deep blue products, fully characterised by their IR, 1 HNMR, 13 C NMR, and mass spectra, contain as a novel structural featur a non-bridging, terminal η 2 -CS 2 ligand.

High pressure carbonylation of Cp(CO)2Mo(CNPh)Mo(NPh)Cp-(Mo-Mo) gives a product that has been shown by an X-ray diffraction study to be a metalla-amidinato complex. This means that the originally present terminal phenylimido ligand inserts into an η2, (σ + π)-bonded isocyanide bridge to form a four-membered heterocycle in which a CP(CO)2Mo unit is coordinated by both N atoms, whereas a Cp(CO)3Mo unit is attached to the central carbon atom. In boiling toluene this process is reversed, with release of CO. A by-product in this reaction is a mononuclear Cp(CO)2Mo-amidinato complex bearing a cyclopentadiene group at the central C atom.

The reaction of Cp★2Mo2(CO)4(MoMo) (Cp★ = η5-C5Me5) with P4S3 in boiling toluene gives the complexes Cp★(CO)2MoP3 (I), Cp★2(CO)4Mo2P2 (II), Cp★2Mo2P2S3 (III), and Cp★2Mo2P4S (IV). The structures of III and IV follow from their 31P NMR spectra as well as from an X-ray diffraction analysis of their corresponding Cr(CO)5 monoadducts (VII and VIII). Characteristic features of the structure of VII are an η2-PS and an η3-P3 ligand in a plane perpendicular to the MoMo axis, which is bisecting. A similar geometry is found for VIII, which, however, contains an η2-S2 and an η3-P2S ligand. Coordination of the Cr(CO)5 fragment to the P2S ligand in III may either occur at an S atom, which then acts as a μ5-bridge (VIII) or at a P atom as manifested by the presence of a PW coupling in the W(CO)5 adduct (VI).