Pseudo-Enantiomeric Paraphaeolactones and Their Biosynthetic Derivatives from Paraphaeosphaeria sp. KT4192: A Proposition of a Favorskii Rearrangement for Their Biosynthesis.

Paraphaeolactones A1, A2, B1, and B2 (1-4, respectively), known arthropsadiol D (5), massariphenone (6) and its positional isomer 7, and massarilactones E (8) and G (9) were isolated from the culture broth of Paraphaeosphaeria sp. KT4192. Although the structural resemblance between 1 and 2 implies that these comprised a diastereomeric pair at the C-2 stereogenic center, electronic circular dichroism (ECD) spectral analyses revealed that they were pseudo-enantiomers possessing the common (2R)-configuration. Paraphaeolactones B1 and B2 (3 and 4) were the derivatives of 2, which equipped the 3-(1-hydroxy-2-oxopropyl)-4-methylcatechol moiety via an acetal bond at C-10. The relative configurations of their acetal carbons were elucidated by NOE experiments, and those of C-8' were deduced independently by ECD spectral analysis. The present study disclosed that 1-5, 8, and 9 contain a methylcyclohexene substructure with the same absolute configuration. This prompted us to reinvestigate the absolute configurations of known structurally related fungal metabolites, allowing us to conclude that the methylcyclohexene moieties of these natural products have the same absolute configuration despite the variety of configurations of other stereogenic centers. The plausible biosynthetic routes for 1-9 are discussed on the basis of the above conclusion. We propose a Favorskii rearrangement as the key transformation for biosyntheses of 1-4.

Synthesis, Structural Characterization, and Guest Exchange Properties of Hydrogen-Bonded Organic Frameworks Based on Bis(benzimidazole)ZnCl2 Complexes.

Hydrogen-bonded organic frameworks (HOFs) based on coordination compounds constitute a developing class of interesting porous materials. Herein, we report on the synthesis, crystal structures, and guest exchange properties of four HOFs based on zinc dichlorido complexes that bear a bis(benzimidazolyl)methane ligand (bis(benzimidazole)ZnCl2). The porous structures of these bis(benzimidazole)ZnCl2-based HOFs are characterized predominantly by intermolecular N-H···Cl hydrogen bonds in conjunction with π-π interactions. One of these HOFs was found to exchange guest molecules via single-crystal-to-single-crystal transformations with or without structural change. A single-crystal X-ray diffraction study revealed that the guest exchange accompanied by a structural change is induced by the cleavage of the N-H···Cl hydrogen bonds between the bis(benzimidazole)ZnCl2 complexes, followed by the formation of alternate hydrogen bonds with guest molecules. This result suggests that the use of weaker N-H···Cl hydrogen bonds than those typically used for the construction of HOFs (e.g., carboxylic acid dimers, N-heterocycles, and charge-assisted moieties) may represent a convenient strategy to synthesize flexible HOFs.

Nonaqueous capillary gel electrophoretic analysis of metal nanoclusters in polymeric-DMSO-Li+ systems.

In this study, we investigated a combination of nonaqueous CE with capillary gel electrophoresis to achieve highly efficient analysis of metal nanoclusters. In the nonaqueous capillary gel electrophoresis (NACGE), PVA and hydroxypropyl methylcellulose were dissolved in DMSO. In addition, to enhance the entanglement of the polymer chains, Li+ ions were also added. By employing the PVA-DMSO-Li+ solution, we studied the effects of the molecular weight, the degree of hydrolysis, and the concentration of the polymers and Li+ on the separation. As a result, good separations of standard mononuclear metal complexes and tetrairon nanoclusters were achieved by NACGE.

Synthesis, Structures, and Solution Dynamics of Titanium and Zirconium Complexes Carrying a Bis(indolyl) and Two Diethylamido Ligands.

Indolyl is the anionic species obtained from the deprotonation of the N-H group of indole. Group 4 transition-metal complexes that carry indolyl-based polydentate ligands represent promising homogeneous catalysts for, e.g., olefin polymerization, hydroamination, and nitrogen-fixation reactions due to the weak π-donation and electron-withdrawing properties, as well as the low basicity of indolyl. In this study, we systematically investigated the synthesis and structures of titanium and zirconium complexes that carry deprotonated 2,2'-bis(indolyl)methane ligands (henceforth: bis(indolyl) ligands) and two diethylamido ligands. We found that the coordination geometry of the indolyl nitrogen atom in such bis(indolyl) ligands is affected by the steric impact of the substituents attached to the central aromatic ring. Moreover, we examined the dynamics of such bis(indolyl) ligands in solution for the corresponding zirconium complexes, and the mechanism was discussed in conjunction with DFT calculations. The results of this study suggest that bis(indolyl) ligands may also serve as coordinatively flexible ancillary ligands, and indicate the feasibility of an expansion from bis(indolyl) to bis(indolyl)-donor ligands.

Redox-responsive recombination of carbon-carbon bonds on flexible tetrairon cores.

When a brown powder of 2a was dissolved in acetonitrile, 2a was converted to 2b. Equilibrium was reached at a 74:26 molar ratio within 1 week at 303 K. The isomerization proceeds through a cubane-like transition state, in which recombination of a carbon-carbon bond occurs.

Recombination of an Fe-Si-P linkage to an Fe-P-Si linkage through an isolable intermediate phosphasilaferracyclopropane.

Phosphasilaferracycle [Cp*(CO)Fe{kappa(2)Si,P-SiMe(2)PPh(2)}], prepared upon irradiation of [Cp*(CO)(2)FeSiMe(2)PPh(2)], was converted to [Cp*(CO)(2)FeP(Ph)SiMe(2)Ph] under mild conditions. The unusual recombination of the iron, silicon, and phosphorus cores could be achieved through a sequence of 1,2- and 1,3-group migrations in an FeSiP system.

Regioselective silylphosphination of methyl vinyl ketone with complexes containing cyclic and linear iron-silicon-phosphorus reacting sites.

Treatment of Cp*(CO)Fe{kappa2(Si,P)-SiMe2PPh2} with methyl vinyl ketone gave a 1,2-addition product, Cp*(CO)Fe{kappa2(Si,P)-SiMe2OCMe(CH=CH2)PPh2}. A linear-type Cp*(CO)2FeSiMe2PPh2 also reacted with the ketone to yield a 1,4-addition product, Cp*(CO)2Fe{kappa1(Si)-SiMe2OC(Me=CHCH2PPh2}, which was further converted to a seven-membered metallacycle, Cp*(CO)Fe{kappa2(Si,P)-SiMe2OC(Me)=CHCH2PPh2}, upon photolysis.

Stepwise bromination of two acetylene molecules on a butterfly-type tetrairon core and reactivity of the resulting bromoacetylene fragment toward nucleophiles.

Treatment of the acetylene-coordinated tetrairon cluster, [(eta5-C5H4Me)4Fe4(HCCH)2]+, with N-bromosuccinimide led to stepwise bromination of two acetylene ligands to form [(eta5-C5H4Me)4Fe4(HCCBr)(HCCH)]+, [(eta5-C5H4Me)4Fe4(HCCBr)2]+, [(eta5-C5H4Me)4Fe4(BrCCBr)(HCCBr)]+, and [(eta5-C5H4Me)4Fe4(BrCCBr)2]+. The reactivity of the bromoacetylene fragment in [(eta5-C5H4Me)4Fe4(HCCBr)(HCCH)]+ toward water, pyridine, and ZnMe2 was also investigated.

Reversible cleavage and recombination of an acetylenic carbon-carbon bond on a tetrairon cluster coupled with a two-electron redox reaction.

Two-electron reduction of [(eta5-C5H4Me)4Fe4(mu3-CH)2(mu3-CO)2](PF6)2 (1) results in the coupling of two methylidyne ligands to form (eta5-C5H4Me)4Fe4(HCCH)(mu3-CO)2 (2), the two-electron oxidation of which reproduces 1. Structures of 1 and 2 were determined by X-ray diffraction analysis.

Phosphasilaferracyclopropane: an activator of small molecules having polarized single, double, and aromatic unsaturated bonds.

Irradiation of Cp*(CO)2FeSiMe2PPh2 resulted in the formation of phosphasilaferracyclopropane 2, which readily reacted with small organic molecules with polarized bonds to yield 3-5.

Insertion of pyridine into an iron-silicon bond: structure of the product Cp*(CO)Fe[eta3(C,C,C)-C5H5NSiMe2NPh2].

Heating a toluene solution of Cp*(CO)(C5H5N)FeSiMe2NPh2 led to insertion of pyridine into the iron-silicon bond to form Cp*(CO)Fe[eta3(C,C,C)-C5H5NSiMe2NPh2].

Synthesis and structures of one- and two-electron oxidized forms of bis(acetylene)tetrairon clusters Cp'(4)Fe(4)(HCCH)(2) (Cp' = Cp, eta5-C(5)H(4)Me).

Air-oxidation of Cp'(4)Fe(4)(HCCH)(2) (Cp' = Cp (1a), C(5)H(4)Me (1b)) in an NH(4)PF(6)/CH(3)CN solution afforded the one-electron oxidized clusters [Cp'(4)Fe(4)(HCCH)(2)](PF(6)). Oxidation of 1a with excess AgBF(4) in THF afforded [1a](BF(4)), while that of 1b with excess AgBF(4) gave [1b](BF(4))(2). The X-ray crystal structure analysis of [1a](BF(4)) revealed that the monocationic cluster retains the butterfly-type Fe(4)(mu4-eta(2):eta(2):eta(1):eta(1)-HCCH)(2) framework similar to that of the neutral cluster. The average Fe-Fe bond length is shorter by 0.029 A than that in the neutral cluster. Electrochemical oxidation of 1a and 1b in 0.1 M NH(4)PF(6)/CH(3)CN solution at +0.30 and +0.25 V versus Ag/10 mM AgNO(3), respectively, afforded the two-electron oxidized clusters [1a](PF(6))(2) and [1b](PF(6))(2). The X-ray crystal structure analysis for [1b](BF(4))(2) shows that the butterfly-type cluster core is retained but shrinks more of those of neutral and monocationic clusters. The four Fe-Fe bonds in [1b](BF(4))(2) are unequivalent: one Fe-Fe bond (2.397(1) A) is apparently shorter than the others (2.439(2)-2.461(2) A).

Formation of Isomeric Tetrathiotungstate Clusters [{Cp*Ru(CO)}2 (WS4 ){W(CO)4 }] by the Reaction of [Cp*2 Ru2 S4 ] with [W(CO)3 (MeCN)3 ].

Thermal and photochemical interconversion occurs between the isomeric pair of tetrathiotungstate [WS4 ]2- clusters 1 and 2, which were formed by thermolysis of [Cp*2 Ru2 S4 ] and [W(CO)3 (MeCN)3 ] [Eq. (1)] and then structurally characterized. During synthesis, a dramatic redistribution of ligands between the Ru and W atoms takes place without the loss of any CO and S ligands.