Syntheses and Structures of Arenethiolato Cobalt(II) Complexes Containing Acylamino Groups: Steric Effects of Bulky Ligands on Coordination and Geometry.

Bulky thiolato ligands have been developed for creating biomimetic model complexes of active sites in metalloenzymes. Herein, we report a series of di--substituted arenethiolato ligands containing bulky acylamino groups (RCONH; R = -Bu-, (4--BuCH)C-,{3,5-(MeCH)CH}C-, and {3,5-(MeSi)CH}C-) that were developed for biomimetics. Bulky hydrophobic substituents generate a hydrophobic space around the coordinating sulfur atom through the NHCO bond.

Stability Enhancement of a π-Stacked Helical Structure Using Substituents of an Amino Acid Side Chain: Helix Formation via a Nucleation-Elongation Mechanism.

Molecular design involving the incorporation of an α-amino acid residue into the side chain or main chain of a polymer is often used to stabilize artificial molecular architectures through intramolecular hydrogen bonding. However, this molecular design strategy rarely considers the importance of interactions between substituents at the α-position of amino acid moieties, as found in nature. Herein, we report the synthesis of a novel series of π-stacked helical poly(quinolylene-2,3-methylene) with amino acid derivatives bearing different substituents at the α-position.

Conformational Switch of Arylopeptide: Helix-Helix Transition Based on Side Chain Solvation.

Controlling the structural transition between well-defined architectures found in living system is essential in polymer chemistry as well as material science. Herein, the reversible conformational switch of a non-natural polypeptide with an aromatic ring (2,6-naphthalene spacer) on its peptide backbone, referred to as an arylopeptide, between two distinct well-defined helical structures (extended 3 -helix and contracted 4 -helix) using side chain solvation is demonstrated. The folding selectivity of the arylopeptide and found that the affinity between the solvent and side chains is an essential factor for determining the global structure is investigated.

Construction of Helically Stacked π-Electron Systems in Poly(quinolylene-2,3-methylene) Stabilized by Intramolecular Hydrogen Bonds.

π-Stacked polymers, which consist of layered π-electron systems in a polymer, can be expected to be used in molecular electronic devices. However, the construction of a stable π-stacked structure in a polymer is considerably challenging because it requires sophisticated designs and precise synthetic methods. Herein, we present a novel π-stacked architecture based on poly(quinolylene-2,3-methylene) bearing alanine derivatives as the side chain, obtained through the living cyclo-copolymerization of an o-allenylaryl isocyanide.

Folding control of a non-natural glycopeptide using saccharide-coded structural information for polypeptides.

We synthesized "glyco-arylopeptides", whose folding structure significantly changes depending on the kind of saccharide in their side chain. The saccharide moiety interacts with the main chain via hydrogen bonding, and the non-natural polypeptides form two well-defined architectures-(P)-3- and (M)-4-helices-depending on the length of the saccharide chains and even the configuration of a single stereo-genic center in the epimers.

Crystal-to-Crystal Isomerization via Drastic Intramolecular Ligand Exchange: Vapochromism of a Bis(arenethiolato)cobalt(II) Complex Containing Bulky Acylamino Groups.

Crystal-to-crystal transitions normally avoid drastic configurational changes that result in loss of crystallinity. A cobalt(II) complex, containing two unsymmetrically disubstituted arenethiolato ligands with bulky acylamino (ArCCONH, Ar = 4-BuCH) and BuCONH groups, showed crystal-to-crystal configurational isomerization accompanied by vapochromism. Recrystallization using THF/-hexane afforded green crystals (isomer ) containing one -hexane molecule per asymmetric unit.

Living Cyclocopolymerization through Alternating Insertion of Isocyanide and Allene via Controlling the Reactivity of the Propagation Species: Detailed Mechanistic Investigation.

Living cyclocopolymerization through the alternating insertion of an isocyanide and allene into palladium-carbon bond was developed based on the controlling the reactivity of the propagation species using bidentate ligands. We revealed that the rate of the presented cyclocopolymerization was depended on the ligands of Pd-initiator. When the palladium-methyl complexes having appropriate cis-chelating ligand, such as 1,3-bis(diphenylphosphino)propane (dppp), were used as initiator, the cyclocopolymerization of bifunctional aryl isocyanides () that contain both isocyano and allenyl moieties polymerized to afford poly(quinolylene-2,3-methylene)s with controlled molecular weight and narrow molecular weight distributions.

Zigzag-Helix Transformation of Expanded Polyvaline Induced by Racemization.

Biological macromolecules are essentially homochiral. For example, proteins mostly consist of l-amino acids. What happens when a chiral molecule meets itself in a mirror? For expanded polyvaline, zigzag-helix transformation occurs.

Side-Chain-Driven Dual Structural System of Poly-Arylopeptide: Selective Helical Formation Derived from Aromatic Ring Flips on the Backbone.

A methodology for producing dual structural systems of macromolecules, which involves flipping the unsymmetrical aromatic rings on the main chain is presented. Previously, we reported a non-natural polypeptide containing an aromatic ring on the peptide backbone, called a poly "". Herein, we used 2,6-naphthalene rings as axially unsymmetrical spacers, which has two geometrical isomers, and , to create dual structural properties.

Crystal Structures of Expanded Poly(l-leucine) Isomers Containing Bis(pyridine)silver(I) Moieties: Precise Formation of Secondary Structure Depending on the Side Chain.

Precise construction of a three-dimensional molecular structure is key for functional macromolecules, such as enzymes or proteins. Previously, a new concept, "expanded poly(α-amino acid)s" containing rigid spacers, was proposed for strategic construction of chiral helices. Herein, expanded poly(l-leucine) isomers containing bis(pyridine)silver(I) moieties were synthesized, and their crystal structures were determined by X-ray analysis.

One-pot synthesis of imidazolinium salts via the ring opening of tetrahydrofuran.

A new one-pot synthesis of C2-hydroxypropyl-substituted imidazolinium salts via the ring opening of tetrahydrofuran (THF) with N,N'-disubstituted diamines has been developed. Preliminary studies of the reaction mechanism suggest the CO-promoted oxidative ring opening of THF followed by Hg(ii)-mediated oxidation of an imidazolidine intermediate. These novel C2-substituted imidazolinium salts have shown to be active catalysts for the aza-Diels-Alder reactions.

Snapshot of Oxidation of Thiolate by Diiodine: Stabilization of Intermediate by NH···S Hydrogen Bonds.

Ordinary thiolate (RS) reacts with diiodine (I) to afford an intermediate sulfenyl iodide (RSI) by releasing I; RSI is readily converted to disulfide (RSSR) by a disproportionation reaction. In the case of thiolate ArS containing very bulky acylamino groups forming NH···S hydrogen bonds, the crystal of the intermediate, [ArS-I-I], was obtained under usual conditions, and the structure was determined by X-ray diffraction analysis. The results show that the intramolecular NH···S hydrogen bonds stabilized the intermediate [ArS-I-I], consistent with theoretical calculations.

Comparative studies on the contribution of NHS hydrogen bonds in tungsten and molybdenum benzenedithiolate complexes.

A series of monooxotungsten(iv) and dioxotungsten(vi) benzenedithiolates, (NEt)[WO(1,2-S-3-RCONHCH)] (1-W; R = CH (a), t-Bu (b), or CF (c)) and (NEt)[WO(1,2-S-3-RCONHCH)] (2-W), were synthesized and compared with the corresponding molybdenum analogues. Single crystals of trans-1b-W were successfully obtained, and the crystal structure was determined by X-ray analysis although 1b-Mo could not be crystallized. The NHS hydrogen bonds shifted the potential of the W(iv/v) redox couple to more positive values, and the strength of the hydrogen bond and the positive shift value were strongly correlated.

Correction: Significant differences of monooxotungsten(IV) and dioxotungsten(VI) benzenedithiolates containing two intramolecular NH···S hydrogen bonds from molybdenum analogues.

Correction for 'Significant differences of monooxotungsten(IV) and dioxotungsten(VI) benzenedithiolates containing two intramolecular NH···S hydrogen bonds from molybdenum analogues' by Taka-aki Okamura et al., Dalton Trans., 2015, 44, 18090-18100.

Significant differences of monooxotungsten(IV) and dioxotungsten(VI) benzenedithiolates containing two intramolecular NHS hydrogen bonds from molybdenum analogues.

A monooxotungsten(iv) benzenedithiolate complex containing two intramolecular NHS hydrogen bonds, (NEt4)2[W(IV)O(1,2-S2-3-t-BuNHCOC6H3)2] (1-W), was synthesized via a ligand-exchange reaction between a new starting complex, (NEt4)2[W(IV)O(SC6F5)4], and a partially deprotonated dithiol. When dithiol was used in solution, the oxo ligand was protonated and removed to afford (NEt4)2[W(IV)(1,2-S2-3-t-BuNHCOC6H3)3]. The trans isomer, trans-1-W, was crystallized, and the molecular structure was determined via X-ray analysis.

Modeling of the hydrophobic microenvironment of water-soluble molybdoenzymes in an aqueous micellar solution.

A toluene-soluble molybdenum(vi) complex containing a bulky hydrophobic substituent, (Et4N)2[Mo(VI)O2{1,2-S2-3,6-(RCONH)2C6H2}2] (R = (4-(t)BuC6H4)3C), was dissolved in the hydrophobic core of a micelle in an aqueous medium and catalyzed the biomimetic reduction of an amine N-oxide by an NADH analog. The kinetic isotope effect of solvent water clearly indicates that water molecules are essential for catalysis and are involved in the rate-determining step.

Enantio- and diastereoselective asymmetric allylic alkylation catalyzed by a planar-chiral cyclopentadienyl ruthenium complex.

We report asymmetric allylic alkylation of allylic chloride with β-diketones as the prochiral carbon nucleophiles using a planar-chiral Cp'Ru catalyst. The reaction proceeds under mild conditions; the resulting chiral products containing vicinal tertiary stereocenters are obtained with high regio-, diastereo-, and enantioselectivities. These chiral products can then be transformed into a chiral diol by controlling the four stereocentres.

Synthesis and structures of soluble magnesium and zinc carboxylates containing intramolecular NH···O hydrogen bonds in nonpolar solvents.

Readily soluble magnesium and zinc carboxylates [M(Ln)2(H2O)4] (MLn2) (M = Mg, Zn; L1 = O2C-2-Ar3CCONH-6-n-BuCONHC6H3; L2 = O2C-2-Ar3CCONHC6H4; Ar = 4-t-BuC6H4) containing intramolecular NH···O hydrogen bonds in nonpolar solvents were synthesized and their molecular structures were determined by X-ray analysis. The complexes were crystallized in the trans or cis configuration. The M–O bond distances were dependent on the mode of the hydrogen bonds.

Efficient uptake of dimethyl sulfoxide by the desoxomolybdenum(IV) dithiolate complex containing bulky hydrophobic groups.

A desoxomolybdenum(IV) complex containing bulky hydrophobic groups and NH···S hydrogen bonds, (Et4N)[Mo(IV)(OSi(t)BuPh2)(1,2-S2-3,6-{(4-(t)BuC6H4)3CCONH}2C6H2)2], was synthesized. This complex promotes the oxygen-atom-transfer (OAT) reaction of DMSO by efficient uptake of the substrate into the active center. The clean OAT reaction of Me3NO is also achieved.

Regulation of the hydrolytic activity of Mg²⁺-dependent phosphatase models by intramolecular NH···O hydrogen bonds.

Magnesium-dependent phosphatase models containing intramolecular NH···O hydrogen bonds were synthesized and structurally characterized by X-ray analysis. The Mg-O bond distances varied with the mode of the hydrogen bonds. (1)H NMR spectra in nonpolar solvents revealed that the acidity of the coordinated water molecule was regulated by the hydrogen bonds.

Behavior of anionic molybdenum(IV, VI) and tungsten(IV, VI) complexes containing bulky hydrophobic dithiolate ligands and intramolecular NH···S hydrogen bonds in nonpolar solvents.

Molybdenum(IV, VI) and tungsten(IV, VI) complexes, (Et4N)2[M(IV)O{1,2-S2-3,6-(RCONH)2C6H2}2] and (Et4N)2[M(VI)O2{1,2-S2-3,6-(RCONH)2C6H2}2] (M = Mo, W; R = (4-(t)BuC6H4)3C), with bulky hydrophobic dithiolate ligands containing NH···S hydrogen bonds were synthesized. These complexes are soluble in nonpolar solvents like toluene, which allows the detection of unsymmetrical coordination structures and elusive intermolecular interactions in solution. The (1)H NMR spectra of the complexes in toluene-d8 revealed an unsymmetrical coordination structure, and proximity of the counterions to the anion moiety was suggested at low temperatures.

Zinc(II) and cadmium(II) metal-organic frameworks with 4-imidazole containing tripodal ligand: sorption and anion exchange properties.

The use of a 4-imidazole containing tripodal ligand 1,3,5-tri(1H-imidazol-4-yl)benzene (H3L) enabled isolation of two three-dimensional (3D) porous metal-organic frameworks (MOFs) [Zn(HL)] · solvent (1) and [Cd(H3L)2](ClO4)2 · 10.5H2O (2) featuring 4,4- and 3,6-connected nets related to the structures of ecl and pyrite, respectively. Framework 1 has 3D channels based on Zn-Im(-) (Im(-) = imidazolate) moieties due to partial deprotonation of the 1H-imidazol-4-yl groups of H3L while porous framework 2 is constructed by the coordination of neutral H3L ligands with Cd(II).

Structural modulation of silver complexes and their distinctive catalytic properties.

A family of silver(I) complexes, [Ag2(L)2(OOCCF3)2] (1), [Ag(L)0.5(OOCCF3)] (2), [Ag(L)2](OOCCF3)(H2O)2 (3), was obtained by reactions of 4,4'-di(2-oxazolinyl)biphenyl (L) and AgOOCCF3 in different reaction media. Compound 1 has a 1D chain structure with alternative connections between the Ag(I) and L ligand.

Contribution of intramolecular NH···O hydrogen bonds to magnesium-carboxylate bonds.

A series of magnesium carboxylate complexes containing intramolecular NH···O hydrogen bonds were synthesized. Their molecular structures were determined by X-ray analysis. A direct NH···O hydrogen bond to the coordinated oxygen atom elongated the Mg-O bond, while a hydrogen bond to the carbonyl group shortened the Mg-O bond.