Product Distribution of Steady-State and Pulsed Electrochemical Regeneration of 1,4-NADH and Integration with Enzymatic Reaction.

The direct electrochemical reduction of nicotinamide adenine dinucleotide (NAD+) results in various products, complicating the regeneration of the crucial 1,4-NADH cofactor for enzymatic reactions. Previous research primarily focused on steady-state polarization to examine potential impacts on product selectivity. However, this study explores the influence of dynamic conditions on the selectivity of NAD+ reduction products by comparing two dynamic profiles with steady-state conditions. Our findings reveal that the main products, including 1,4-NADH, several dimers, and ADP-ribose, remained consistent across all conditions. A minor by-product, 1,6-NADH, was also identified. The product distribution varied depending on the experimental conditions (steady state vs. dynamic) and the concentration of NAD+, with higher concentrations and overpotentials promoting dimerization. The optimal yield of 1,4-NADH was achieved under steady-state conditions with low overpotential and NAD+ concentrations. While dynamic conditions enhanced the 1,4-NADH yield at shorter reaction times, they also resulted in a significant amount of unidentified products. Furthermore, this study assessed the potential of using pulsed electrochemical regeneration of 1,4-NADH with enoate reductase (XenB) for cyclohexenone reduction.

Synthesis and Structural Characterization of p-Carboranylamidine Derivatives.

In this contribution, the first amidinate and amidine derivatives of p-carborane are described. Double lithiation of p-carborane (1) with n-butyllithium followed by treatment with 1,3-diorganocarbodiimides, R-N=C=N-R (R = iPr, Cy (= cyclohexyl)), in DME or THF afforded the new p-carboranylamidinate salts p-C2H10B10[C(NiPr)2Li(DME)]2 (2) and p-C2H10B10[C(NCy)2Li(THF)2]2 (3). Subsequent treatment of 2 and 3 with 2 equiv. of chlorotrimethylsilane (Me3SiCl) provided the silylated neutral bis(amidine) derivatives p-C2H10B10[C{iPrN(SiMe3)}(=NiPr)]2 (4) and p-C2H10B10[C{CyN(SiMe3)}(=NCy)]2 (5). The new compounds 3 and 4 have been structurally characterized by single-crystal X-ray diffraction. The lithium carboranylamidinate 3 comprises a rare trigonal planar coordination geometry around the lithium ions.

Small compound - big colors: synthesis and structural investigation of brightly colored alkaline earth metal 1,3-dimethylviolurates.

A series of brightly colored alkaline earth metal 1,3-dimethylviolurates M(Me2Vio)2 have been prepared and fully characterized. The title compounds AE(Me2Vio)2·nH2O (AE = Mg, n = 6 (3); AE = Ca, n = 8 (4), AE = Sr, n = 6 (5); AE = Ba, n = 4 (6)) were obtained by neutralizing 1,3-dimethylvioluric acid monohydrate (=H(Me2Vio)·H2O; 2) with 0.5 equiv. of the corresponding metal dihydroxides AE(OH)2. The hair-like appearance of the Sr derivative 5 prevented the growth of single-crystals. This problem could be solved by crystallizing the crown ether derivative Sr(Me2Vio)2(18-crown-6) (5a). The isolated salts exhibit intense colors ranging from red to purple. Various attempts to prepare the beryllium derivative Be(Me2Vio)2 failed. Instead, work-up of the reaction mixtures provided pink crystals of a new modification of 2 formulated as [H3O][Me2Vio] (2b) as shown by an X-ray diffraction study. An unexpected oxidation reaction of the barium salt Ba(Me2Vio)2 led to formation of the novel mixed-anion salt Ba(Me2Vio)(Me2NO2Barb)·2H2O (8, Me2NO2Barb- = 1,3-dimethyl-5-nitrobarbiturate anion). Compound 8 could also be synthesized deliberately by treatment of Ba(OH)2 with a 1 : 1 mixture of 2 and 1,3-dimethyl-5-nitrobarbituric acid (7, =H(Me2NO2Barb)·H2O). All new compounds were fully characterized by their IR, Raman, NMR (1H, 13C{1H}) and UV-vis spectra as well as elemental analyses. Single-crystal X-ray diffraction studies revealed that the solid-state structures of compounds 3, 4, 5a and 6 are governed by the typical coordination behavior of the alkaline-earth metals, i.e. increasing coordination numbers and a decreasing degree of hydration when going from Mg to Ba. The dimensions of the structures range from hydrogen-bonded ions (3) over monomeric, neutral complex molecules (4, 5a), to polymeric networks (6). The successful isolation of the mixed-anion barium salt 8 adds a new facet to the coordination chemistry of violurate and related ligands.

Rubidium and Cesium Enediamide Complexes Derived from Bulky 1,4-Diazadienes.

The first rubidium and cesium enediamide complexes based on bulky 1,4-diaza-1,3-diene ligands (DADs) have been prepared by metalation of either 1,4-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (1, = H2DADDipp) or 1,4-bis(2,6-diisopropylphenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene (2, = Me2DADDipp) with an excess of Rb or Cs metals in coordinating solvents such as tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME). All new complexes were fully characterized by spectroscopic and analytical methods as well as single-crystal X-ray diffraction studies.

Catenated and spirocyclic polychalcogenides from potassium carbonate and elemental chalcogens.

The reaction of potassium carbonate with elemental sulfur or selenium in acetone in the presence of [PPN]Cl (PPN = (Ph3P)2N) produces catena-[S12]2-, the longest structurally characterised polysulfide dianion, or spiro-[Se11]2- as ion-separated [PPN]+ salts.

An unsymmetrical dinuclear scandium complex comprising salophen ligands [H2salophen = N,N'-bis-(salicyl-idene)-1,2-phenyl-enedi-amine].

Treatment of scandium nitrate tetra-hydrate with the tetra-dentate ligand H2salophen [N,N'-bis-(salicyl-idene)-1,2-phenyl-enedi-amine] afforded the yellow dinuclear complex Sc(NO3)2(µ-salophen)Sc(salophen)(EtOH) or [Sc2(C20H14N2O2)2(NO3)2(C2H6O)] (systematic name: (ethanol-κO)bis-(nitrato-κ2 O,O'){µ-2,2'-[1,2-phenyl-enebis(nitrilo-methanylyl-idene)]diphenolato-κ4 N,N',O,O':κ2 O,O'}{2,2'-[1,2-phenyl-enebis(nitrilo-methanylyl-idene)]diphenolato-κ4 O,N,N',O'}discandium). In this compound, one salophen ligand displays a bridging coordination via the two oxygen atoms, while the other salophen ligand is attached to only one Sc center. This arrangement is stabilized by a hydrogen-bonded EtOH co-ligand, and by π-π stacking inter-actions between the two salophen ligands.

Formation and structural characterization of a potassium amidino-guanidinate.

The first potassium amidino-guanidinate complex, catena-poly[[bis-(µ-1-amidinato-N,N',N'',N'''-tetra-iso-propyl-guanidinato-κ5 N 1:N 1,N 2:N 2,N 4)dipotassium]-µ-1,2-di-meth-oxy-ethane-κ2 O:O'], [K2(C14H32N4)2(C4H10O2)] n or [{ i PrN= CHN( i Pr)N(N i Pr)2K}2(µ-DME)] n where DME is 1,2-di-meth-oxy-ethane, has been synthesized and structurally characterized. The title compound was isolated in 76% yield from a reaction of N,N'-diiso-propyl-carbodi-imide with potassium hydride in DME. The single-crystal X-ray structure determination of the title compound revealed a polymeric chain structure comprising cage-like dimeric units, with the amidino-guanidinate ligand displaying a mixed σ-/π-coordination mode.

Synthesis and structural characterization of four di-chlorido-bis-(cyclo-propyl-alkynyl-amidine)-metal complexes.

Deliberate hydrolysis of lithium cyclo-propyl-alkynylamidinates, Li[c-C3H5-C≡C(NR')2] [R' = i Pr, Cy = cyclo-hex-yl)], afforded the hitherto unknown neutral cyclo-propyl-alkynyl-amidine derivatives c-C3H5-C≡C-C(NR')(NHR') [R' = i Pr (1), Cy (2)]. Subsequent reactions of 1 or 2 with metal(II) chlorides, MCl2 (M = Mn, Fe, Co), provided the title complexes di-chlorido-bis-(3-cyclo-propyl-N,N'-diisopropyl-prop-2-ynamidine)-manganese(II), [MnCl2(C12H20N2)2], (3), di-chlorido-bis-(3-cyclo-propyl-N,N'-diisopropyl-prop-2-ynamidine)-iron(II), [FeCl2(C12H20N2)2], (4), di-chlorido-bis-(N,N'-di-cyclo-hexyl-3-cyclo-propyl-prop-2-ynamidine)-iron(II), [FeCl2(C18H28N2)2], (5), and di-chlorido-bis-(N,N'-di-cyclo-hexyl-3-cyclo-propyl-prop-2-ynamidine)-cobalt(II), [CoCl2(C18H28N2)2], (6), or more generally MCl2[c-C3H5-C≡C-C(NR')(NHR')]2 [R' = i Pr, M = Mn (3), Fe (4); R' = Cy, M = Fe (5), Co (6)] in moderate yields (30-39%). Besides their spectroscopic data (IR and MS) and elemental analyses, all complexes 3-6 were structurally characterized. The two isopropyl-substituted complexes 3 and 4 are isotypic, and so are the cyclo-hexyl-substituted complexes 5 and 6. In all cases, the central metal atom is coordinated by two Cl atoms and two N atoms in a distorted-tetra-hedral fashion, and the structure is supported by intra-molecular N-H⋯Cl hydrogen bonds.

The "Wanderlust" of Me3Si groups in rare-earth triple-decker complexes: a combined experimental and computational study.

The migration of Me3Si groups ("Wanderlust") in rare-earth triple-decker sandwich complexes of the type Ln2(COT'')3 (COT'' = bis(trimethylsilyl)cyclooctatetraenyl) has been elucidated by a combined experimental and computational study. For the first time, two isomers of a Ln2(COT'')3 triple-decker have been isolated and characterized in the case of Y2(COT'')3.

Three new types of transition metal carboranylamidinate complexes.

Three new types of transition metal carboranylamidinate complexes are reported. The tetranuclear Mn(ii) complex Mn4Cl6[(o-C2B10H10)C(NiPr)(NHiPr)]2(THF)4·THF (2) was prepared by treatment of anhydrous MnCl2 with Li[(o-C2B10H10)C(NiPr)(NHiPr)] ([double bond, length as m-dash]Li[HLiPr]) in THF, while the analogous reaction with FeCl2 afforded ionic [Li(DME)3][FeCl2{(o-C2B10H10)C(NiPr)(NHiPr)}] (3). The dinuclear Mo(ii) complex Mo2[(o-C2B10H10)C(NiPr)(NHiPr)]2(OAc)2·2THF (4), obtained from Mo2(OAc)4 and 2 equiv. of Li[HLiPr], represents the first example of a M-M multiple bond stabilized by carboranylamidinate ligands. All title compounds were structurally characterized by single-crystal X-ray diffraction. The M-M bonding in compound 4 has been further elucidated through Complete Active Space Self Consistent Field (CASSCF) calculations.

Formation and structural characterization of a europium(II) mono(scorpionate) complex and a sterically crowded pyraza-bole.

The reaction of EuI2(THF)2 with potassium hydro-tris-(3,5-diiso-propyl-pyrazol-yl)borate (K[HB(3,5- iPr2pz)3] (= KTp iPr2, pz = pyrazol-yl) in a molar ratio of 1:1.5 resulted in extensive ligand fragmentation and formation of the europium(II) mono(scorpionate) complex bis-(3,5-diisopropyl-1H-pyrazole)[hydro-tris-(3,5-diiso-propyl-pyrazol-yl)borato]iodido-europium(II), [Eu(C27H46BN6)I(C9H16N2)2] or (Tp iPr2)(3,5- iPr2pzH)2EuIII, 1, in high yield (78%). As a typical by-product, small amounts of the sterically crowded pyraza-bole derivative trans-4,8-bis-(3,5-diiso-propyl-pyrazol-1-yl)-1,3,5,7-tetra-iso-propyl-pyraza-bole, C36H62B2H8 or trans-{(3,5- iPr2pz)HB(µ-3,5- iPr2pz)}2, 2, were formed. Both title compounds have been structurally characterized through single-crystal X-ray diffraction. In 1, two isopropyl groups are each disordered over two orientations with occupancy ratios of 0.574 (10):0.426 (10) and 0.719 (16):0.281 (16). In 2, one isopropyl group is similarly disordered, occupancy ratio 0.649 (9):0.351 (9).

Scandium-Mediated Formation of a Bis(tetrahydropentalene).

The reactivity of Li[Sc(COT'')2 ] (1; COT''=1,4-bis(trimethylsilyl)cyclooctatetraenyl) towards CoCl2 is considerably different from that of related lanthanide triple-decker sandwich complexes. In addition to the expected triple-decker complex Sc2 (COT'')3 (2), the complex Sc2 {µ-BTHP}(COT'')2 (3) is formed, which comprises the novel BTHP2- ligand (BTHP2- =bis(3,5-bis(trimethylsilyl)-1,3a,6,6a-tetrahydropentalene-1-yl)diide or bis(2,7-bis(trimethylsilyl)bicyclo[3.3.0]octa-2,7-dien-4-yl)diide, C16 H10 (SiMe3 )42- ). The formation of 3 is likely facilitated by the fact that scandium prefers η8 ,η3  coordination rather than highly symmetric η8 ,η8  coordination, and the η3 -coordinated COT'' ligand in 1 is activated owing to a loss of aromaticity. Acid hydrolysis of 3 leads to air-stable H2 BTHP (4).

Synthesis and structural study of new metallasilsesquioxanes of potassium and uranium.

The first metallasilsesquioxanes comprising potassium and uranium have been synthesized and structurally characterized by single-crystal X-ray diffraction. (Cy7Si7O12)2K6(DME)4 (2; Cy = cyclohexyl) is a centrosymmetric dimer, in which the two silsesquioxide ligands are interconnected by µ3- and µ4-bridging siloxide moieties. (Cy7Si7O12)2UVI (3) represents the first metallasilsesquioxane complex of an actinide element, featuring a U atom that is coordinated by two tridentate silsesquioxide ligands in a distorted octahedral fashion. The different structural effects of the large metal atomic radii are discussed.

Crystal structures of two ytterbium(III) complexes comprising alkynylamidinate ligands.

Two ytterbium(III) complexes comprising alkynylamidinate ligands, namely bis-(η5-cyclo-penta-dien-yl)(3-cyclo-propyl-N,N'-diiso-propyl-propynamidinato-κ2N,N')ytterbium(III), [Yb(C5H5)2(C12H19N2)] or Cp2Yb[( i Pr2N)2C-C≡C-c-C3H5] (1) and tris-(3-phenyl-N,N'-di-cyclo-hexyl-propynamidinato-κ2N,N')ytterbium(III), [Yb(C21H27N2)3] or Yb[(CyN)2C-C≡C-Ph]3 (Cy = cyclo-hex-yl) (2) have been synthesized and structurally characterized. Both complexes are monomers; for complex 2, the contribution to the scattering from highly disordered toluene solvent molecules in these voids was removed with the SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9-18] in PLATON. The stated crystal data for Mr, µ etc. do not take these into account.

Formation and structure of the first metal complexes comprising amidino-guanidinate ligands.

The first metal complexes comprising amidino-guanidinate ligands have been prepared and structurally characterized, namely bis-[µ-N,N',N'',N'''-tetraisopropyl-1-(1-butyl-amidinato)guanidinato-κ3N1,N2:N2]bis-[(tetra-hydro-furan)lithium], [Li2(C18H37N4)2(C4H8O)2], (2), and [bis-(tetra-hydro-furan)-lithium]-di-µ-chlorido-{(N,N'-di-cyclo-hexyl-1-butyl-amidinato-κ2N1,N2)[N,N',N'',N'''-tetra-cyclo-hexyl-1-(1-butyl-amidinato)guanidinato-κ2N1,N2]holmate(III)}, [HoLiCl2(C4H8O)2(C17H31N2)(C30H53N4)], (3). The novel lithium amidino-guanidinate precursors Li[ n BuC(=NR)(NR)C(NR)2] [1: R = Cy (cyclo-hex-yl), 2: R = i Pr) were obtained by treatment of N,N'-diorganocarbodi-imides, R-N=C=N-R (R = i Pr, Cy), with 0.5 equivalents of n-butyl-lithium under well-defined reaction conditions. An X-ray diffraction study of 2 revealed a ladder-type dimeric structure in the solid state. Reaction of anhydrous holmium(III) chloride with in situ-prepared 2 afforded the unexpected holmium 'ate' complex [ n BuC(=NCy)(NCy)C(NCy)2]Ho[ n BuC(NCy)2](µ-Cl)2Li(THF)2 (3) in 71% yield. An X-ray crystal structure determination of 3 showed that this complex contains both an amidinate ligand and the new amidino-guanidinate ligand.

Five different types of η(8)-cyclooctatetraenyl-lanthanide half-sandwich complexes from one ligand set, including a "giant neodymium wheel".

The lithium-cyclopropylethynylamidinates Li[c-C3H5-C[triple bond, length as m-dash]C-C(NR)2] (1a: R = (i)Pr, 1b: R = cyclohexyl (Cy)) have been used as precursors for the preparation of five new series of half-sandwich complexes. These complexes contain the large flat cyclooctatetraenyl ligand (C8H8(2-), commonly abbreviated as COT), and were isolated as solvated, unsolvated and inverse sandwich complexes. Treatment of the halide precursors [(COT)Pr(µ-Cl)(THF)2]2 with 1b and [(COT)Nd(µ-Cl)(THF)2]2 with 1a and 1b in THF in a 1 : 2 molar ratio, respectively, afforded (COT)Ln[µ-c-C3H5-C[triple bond, length as m-dash]C-C(NR)2]2Li(L) (2: Ln = Pr, R = Cy, L = Et2O; 3: Ln = Nd, R = (i)Pr, L = THF; 4: Ln = Nd, R = Cy, L = THF). Treatment of the dimeric cerium(iii) bis(cyclopropylethynylamidinate) complexes [{c-C3H5-C[triple bond, length as m-dash]C-C(NR)2}2Ce(µ-Cl)(THF)]2 (5: R = (i)Pr; 6: R = Cy) in situ with K2C8H8 in a 1 : 1 molar ratio in THF at room temperature afforded the inverse-sandwich complexes (µ-η(8):η(8)-COT)[Ce{c-C3H5-C[triple bond, length as m-dash]C-C(NR)2}2]2 (7: R = (i)Pr; 8: R = Cy). This reaction represents a new method for encapsulation of a planar (C8H8)(2-) ring in lanthanide complexes containing amidinate ligands in the outer decks. Novel unsolvated dinuclear lanthanide half-sandwich complexes were prepared by using the precursors 1a, 1b and COT(2-). Unlike the complexes 2-4, the reaction of [(COT)Pr(µ-Cl)(THF)2]2 with 1a afforded the unsolvated centrosymmetric complex [(COT)Pr(µ-c-C3H5-C[triple bond, length as m-dash]C-C(N(i)Pr)2)]2 (9). These dimeric structures could be also accessed by reaction of LnCl3 (Ln = Ce or Nd) with 1a or 1b and K2COT in a 1 : 1 : 1 molar ratio as a one-pot reaction to give novel [(COT)Ln(µ-c-C3H5-C[triple bond, length as m-dash]C-C(NR)2)]2 complexes (10: Ln = Ce, R = (i)Pr; 11: Ln = Ce, R = Cy; 12: Ln = Nd, R = (i)Pr). Similar treatment of HoCl3 with 1a or 1b and K2COT as three-component reactions in a 1 : 1 : 1 molar ratio afforded the solvated half-sandwich complexes (COT)Ho(c-C3H5-C[triple bond, length as m-dash]C-C(NR)2)(THF) (13: R = (i)Pr; 14: R = Cy). A unique multidecker sandwich complex [(µ-η(8):η(8)-COT){Nd(c-C3H5-C[triple bond, length as m-dash]C-C(NCy)2)(µ-Cl)}2]4 (15) was prepared by reaction of anhydrous NdCl3 with K2COT and 1b in a one-pot reaction. The solid state structure of 15 revealed the presence of an unprecedented macrocyclic sandwich compound ("giant neodymium wheel") consisting of four COT rings sandwiched between eight Nd(3+) ions, and each Nd(3+) ion is bonded to one amidinate ligand and bridged by two chlorine atoms with the neighbouring Nd(3+) ion.

Stabilization of molecular lanthanide polysulfides by bulky scorpionate ligands.

Well-defined lanthanide polysulfide complexes containing S4(2-) and S5(2-) ligands, the samarium(iii) pentasulfide complex Sm(Tp(iPr2))(κ(1)-3,5-(i)Pr2Hpz)(S5) and the tetrasulfide-bridged binuclear ytterbium(iii) complex (µ-S4)[Yb(Tp(iPr2))(κ(1)-3,5-(i)Pr2Hpz)(κ(2)-3,5-(i)Pr2pz)]2 (Tp(iPr2) = hydro-tris(3,5-diisopropylpyrazolyl)borate), have been synthesized and structurally characterized by single-crystal X-ray diffraction.

Heterometallic europium disiloxanediolates: synthesis, structural diversity, and photoluminescence properties.

This contribution presents a full account of a structurally diverse class of heterometallic europium disiloxanediolates. The synthetic protocol involves in situ metalation of (HO)SiPh2OSiPh2(OH) (1) with either (n)BuLi or KN(SiMe3)2 followed by treatment with EuCl3 in suitable solvents such as 1,2-dimethoxyethane (DME) or tetrahydrofuran (THF). Reaction of EuCl3 with 2 equiv of (LiO)SiPh2OSiPh2(OLi) in DME afforded the Eu(III) bis(disiloxanediolate) "ate" complex [{(Ph2SiO)2O}2{Li(DME)}3]EuCl2 (2), which upon attempted reduction with Zn gave the tris(disiloxanediolate) [{(Ph2SiO)2O}3{Li(DME)}3]Eu (3). Treatment of EuCl3 with (LiO)SiPh2OSiPh2(OLi) in a molar ratio of 1:2 yielded both the ate complex [{(Ph2SiO)2O}3Li{Li(THF)2}{Li(THF)}]EuCl·Li(THF)3 (4) and the LiCl-free europium(III) complex [{(Ph2SiO)2O}2{Li(THF)2}2]EuCl (5). Compound 5 was found to exhibit a brilliant red triboluminescence. When (KO)SiPh2OSiPh2(OK) was used as starting material in a 3:1 reaction with EuCl3, the Eu(III) tris(disiloxanediolate) [{(Ph2SiO)2O}3{K(DME)}3]Eu (6) was isolated. Attempted ligand transfer between 5 and (DAD(Dipp))2Ba(DME) (DAD(Dipp) = N,N'-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene) afforded the unique mixed-valent Eu(III)/Eu(II) disiloxanediolate cluster [(Ph2SiO)2O]6Eu(II)4Eu(III)2Li4O2Cl2 (7). All new complexes were structurally characterized by X-ray diffraction. Photoluminescence studies were carried out for complex 5 showing an excellent color quality, due to the strong (5)D0→(7)F2 transition, but a weak antenna effect.

Unprecedented formation of polycyclic diazadiborepine derivatives through cage deboronation of m-carborane.

An unprecedented deboronation reaction of icosahedral carboranes is described, in which a BH group of m-carborane is detached from the cage and incorporated into an unusual nido-carborane-anellated diazadiborepine ring system.

Crystal structure of the high-energy-density material guanylurea dipicryl-amide.

The title compound, 1-carbamoylguanidinium bis-(2,4,6-tri-nitro-phen-yl)amide [H2NC(=O)NHC(NH2)2](+)[N{C6H2(NO2)3-2,4,6}2](-) (= guanylurea dipicryl-amide), was prepared as dark-red block-like crystals in 70% yield by salt-metathesis reaction between guanylurea sulfate and sodium dipicryl-amide. In the solid state, the new compound builds up an array of mutually linked guanylurea cations and dipicryl-amide anions. The crystal packing is dominated by an extensive network of N-H⋯O hydrogen bonds, resulting in a high density of 1.795 Mg m(-3), which makes the title compound a potential secondary explosive.