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Piano stool complexes have been studied over many years and found widespread applications in organic synthesis, catalysis, materials and drug development. We now report the first examples of quantitative chiroptical molecular recognition of chiral compounds through click‐like η6‐arene coordination with readily available half sandwich complexes. This conceptually new approach to chirality sensing is based on irreversible acetonitrile displacement of [Cp*Ru(CH3CN)3]PF6 by an aromatic target molecule, a process that is fast and complete within a few minutes at room temperature. The metal coordination coincides with characteristic circular dichroism inductions that can be easily correlated to the absolute configuration and enantiomeric ratio of the bound molecule. A relay assay that decouples the determination of the enantiomeric composition and of the total sample amount by a practical CD/UV measurement protocol was developed and successfully tested. The introduction of piano stool complexes to the chiroptical sensing realm is mechanistically unique and extends the scope of currently known methods with small‐molecule probes that require the presence of amino, alcohol, carboxylate or other privileged functional groups for binding of the target compound. A broad application range including pharmaceutically relevant multifunctional molecules and the use in chromatography‐free asymmetric reaction analysis are also demonstrated. [ABSTRACT FROM AUTHOR]

Piano stool complexes have been studied over many years and found widespread applications in organic synthesis, catalysis, materials and drug development. We now report the first examples of quantitative chiroptical molecular recognition of chiral compounds through click‐like η6‐arene coordination with readily available half sandwich complexes. This conceptually new approach to chirality sensing is based on irreversible acetonitrile displacement of [Cp*Ru(CH3CN)3]PF6 by an aromatic target molecule, a process that is fast and complete within a few minutes at room temperature. The metal coordination coincides with characteristic circular dichroism inductions that can be easily correlated to the absolute configuration and enantiomeric ratio of the bound molecule. A relay assay that decouples the determination of the enantiomeric composition and of the total sample amount by a practical CD/UV measurement protocol was developed and successfully tested. The introduction of piano stool complexes to the chiroptical sensing realm is mechanistically unique and extends the scope of currently known methods with small‐molecule probes that require the presence of amino, alcohol, carboxylate or other privileged functional groups for binding of the target compound. A broad application range including pharmaceutically relevant multifunctional molecules and the use in chromatography‐free asymmetric reaction analysis are also demonstrated. [ABSTRACT FROM AUTHOR]

NO and H2S serve as signaling molecules in biology with intertwined reactivity. HSNO and HSSNO with their conjugate bases −SNO and −SSNO form in the reaction of H2S with NO as well as S‐nitrosothiols (RSNO) and nitrite (NO2−) that serve as NO reservoirs. While HSNO and HSSNO are elusive, their conjugate bases form isolable zinc complexes Ph,MeTpZn(SNO) and Ph,MeTpZn(SSNO) supported by tris(pyrazolyl)borate ligands. Reaction of Na(15‐C‐5)SSNO with Ph,MeTpZn(ClO4) provides Ph,MeTpZn(SSNO) that undergoes S‐atom removal by PEt3 to give Ph,MeTpZn(SNO) and S=PEt3. Unexpectedly stable at room temperature, these Zn‐SNO and Zn‐SSNO complexes release NO upon heating. Ph,MeTpZn(SNO) and Ph,MeTpZn(SSNO) quickly react with acidic thiols such as C6F5SH to form N2O and NO, respectively. Increasing the thiol basicity in p‐substituted aromatic thiols 4−XArSH in the reaction with Ph,MeTpZn(SNO) turns on competing S‐nitrosation to form Ph,MeTpZn‐SH and RSNO, the latter a known precursor for NO. [ABSTRACT FROM AUTHOR]

NO and H2S serve as signaling molecules in biology with intertwined reactivity. HSNO and HSSNO with their conjugate bases −SNO and −SSNO form in the reaction of H2S with NO as well as S‐nitrosothiols (RSNO) and nitrite (NO2−) that serve as NO reservoirs. While HSNO and HSSNO are elusive, their conjugate bases form isolable zinc complexes Ph,MeTpZn(SNO) and Ph,MeTpZn(SSNO) supported by tris(pyrazolyl)borate ligands. Reaction of Na(15‐C‐5)SSNO with Ph,MeTpZn(ClO4) provides Ph,MeTpZn(SSNO) that undergoes S‐atom removal by PEt3 to give Ph,MeTpZn(SNO) and S=PEt3. Unexpectedly stable at room temperature, these Zn‐SNO and Zn‐SSNO complexes release NO upon heating. Ph,MeTpZn(SNO) and Ph,MeTpZn(SSNO) quickly react with acidic thiols such as C6F5SH to form N2O and NO, respectively. Increasing the thiol basicity in p‐substituted aromatic thiols 4−XArSH in the reaction with Ph,MeTpZn(SNO) turns on competing S‐nitrosation to form Ph,MeTpZn‐SH and RSNO, the latter a known precursor for NO. [ABSTRACT FROM AUTHOR]

A wide range of natural biomolecules and pharmaceuticals are nitrogen rich heterocycles. Though preparation of fused multi-ring systems typically requires multiple synthetic steps, 13-imino-7,13-dihydro-6H-quinazolino[3,4-a]quinazolin-6-one (IDQQ) was serendipitously obtained in one step from commercially available phenylic precursors. Single crystal X-ray diffraction, 1H-NMR and density functional theory calculations (DFT/B3LYP/6-31G(d,p)) were used in combination to unambiguously assign the major tautomer present in the monoclinic crystals. IDQQ appears to be the product of a thermodynamically-driven solution rearrangement of a key intermediate, 1,3-bis(o-cyanophenyl)urea. This type of cyclization may be an efficient method for the formation of other related heterocycles. [ABSTRACT FROM AUTHOR]

The whole mol­ecule of the title compound, C20H14O6, is generated by mirror symmetry, the mirror bis­ecting the central benzene ring. The carbonate groups adopt an s-cis-s-cis conformation, with torsion angles of 58.7 (2) and 116.32 (15)°. The crystal structure of 1,3-phenyl­ene bis­(phenyl carbonate) contains no strong hydrogen bonds, though weak C—H...O and offset π–π inter­actions are observed, forming layers parallel to the ac plane. [ABSTRACT FROM AUTHOR]

The paper describes three methods for the preparation of methoxysiloxide complexes, a rare class of complexes of relevance to room temperature vulcanization (RTV) of polysiloxanes. The salt metathesis reaction involves the use of the recently described reagent NaOSi(OMe)2Me with various metal chlorides to give Cp*2Ti[OSi(OMe)2Me](OMe), (Me,MeN2N)NiOSi(OMe)2Me, (IPr)CuOSi(OMe)2Me, and (triphos)CoOSi(OMe)2Me (Cp* = C5Me5, triphos = Me(CH2PPh2)3). Several attempted reactions gave methoxide complexes instead, a pathway that is attributed to the intermediacy of κ2-OSi(OMe)2Me species. The diol Cp*2Zr(OH)2 reacts with excess (MeO)3SiMe to give Cp*2Zr[OSi(OMe)2Me]2. In contrast the less nucleophilic Cp*2Ti(OH)2 was unreactive. The third route to methoxysiloxide complexes involves the reaction of Cp*2M(O)(py) with (MeO)3SiMe to give Cp*2M[OSi(OMe)2Me](OMe) in nearly quantitative yield (M = Ti, Zr). The structures of Cp*2Ti[OSi(OMe)2Me](OMe), Cp*2Zr[OSi(OMe)2Me](OMe), (IPr)CuOSi(OMe)2Me, and (triphos)CoOSi(OMe)2Me were confirmed by single crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

A new 2:1 co-crystal of piroxicam and gentisic acid [systematic name: 4-hydroxy-1,1-dioxo-N-(pyridin-2-yl)-2H-1λ6,2-benzothiazine-3-carboxamide-2-(4-oxido-1,1-dioxo-2H-1λ6,2-benzothiazine-3-amido)pyridin-1-ium-2,5-dihydroxybenzoic acid, 2C15H13N3O4S⋅C7H6O4] has been synthesized using a microfluidic platform and initially identified using Raman spectroscopy. In the co-crystal, one piroxicam molecule is in its neutral form and an intramolecular O--H⋯O hydrogen bond is observed. The other piroxicam molecule is zwitterionic (proton transfer from the OH group to the pyridine N atom) and two intramolecular N--H⋯O hydrogen bonds occur. The gentisic acid molecule shows whole-molecule disorder over two sets of sites in a 0.809 (2):0.191 (2) ratio. In the crystal, extensive hydrogen bonding between the components forms layers propagating in the ab plane. [ABSTRACT FROM AUTHOR]

We report a new class of frustrated Lewis pairs (FLPs) by the hydroboration of bulky isocyanates iPr2ArNCO (iPr2Ar=2,6- iPr2C6H3) and Ph2tBuArNCO (Ph2tBuAr=2,6-Ph2-4- tBuC6H2) with Piers' borane (HB(C6F5)2). While hydroboration of smaller isocyanates such as iPr2ArNCO leads to isocyanate-N/B FLP adducts, hydroboration of the bulkier Ph2tBuArNCO allows isolation of the substrate-free aminoborane with a short, covalent N−B bond. This confused FLP reversibly binds unsaturated substrates such as isocyanates and isocyanides, suggesting the intermediacy of a 'normal' FLP along the reaction pathway, supported by high-level DFT studies and variable-temperature NMR spectroscopy. These results underscore the possibility of FLP behavior in systems that possess no obvious frustrated Lewis acid-base interaction. [ABSTRACT FROM AUTHOR]

Hydrogen bonding between urea functionalities is a common structural motif employed in crystal-engineering studies. Crystallization of 1,3-bis(3-fluorophenyl)urea, C13H10F2N2O, from many solvents yielded concomitant mixtures of at least two polymorphs. In the monoclinic form, one-dimensional chains of hydrogen-bonded urea molecules align in an antiparallel orientation, as is typical of many diphenylureas. In the orthorhombic form, one-dimensional chains of hydrogen-bonded urea molecules have a parallel orientation rarely observed in symmetrically substituted diphenylureas. [ABSTRACT FROM AUTHOR]

Derivatives of 4-hydroxypyrimidine are an important class of biomolecules. These compounds can undergo keto-enol tautomerization in solution, though a search of the Cambridge Structural Database shows a strong bias toward the 3 H-keto tautomer in the solid state. Recrystallization of 2-amino-5,6-dimethyl-4-hydroxypyrimidine, C6H9N3O, from aqueous solution yielded triclinic crystals of the 1 H-keto tautomer, denoted form (I). Though not apparent in the X-ray data, the IR spectrum suggests that small amounts of the 4-hydroxy tautomer are also present in the crystal. Monoclinic crystals of form (II), comprised of a 1:1 ratio of both the 1 H-keto and the 3 H-keto tautomers, were obtained from aqueous solutions containing uric acid. Forms (I) and (II) exhibit one-dimensional and three-dimensional hydrogen-bonding motifs, respectively. [ABSTRACT FROM AUTHOR]

2,6-Diaminopyridine (26-DAP, C5H7N3) is a common intermediate in the synthesis of aromatic azo chromophores, which are widespread in the dyes and pigments industry. Sublimation of commercial 26-DAP powder yielded a new polymorph, denoted Form II, which grew as colorless orthorhombic needles. Recrystallization from acetone or toluene also yielded Form II as the major phase. Thermal analysis shows that Form II is a less stable polymorph and it converts upon heating at 335 K to the previously reported Form I. [ABSTRACT FROM AUTHOR]

A series of fifteen tetravalent thorium phases were prepared. The compounds were isolated from acidic aqueous nitrate solutions using protonated nitrogen heterocycles of varying hydrogen-bond donation strength. Structural analysis via single crystal X-ray diffraction showed that the structures are built from pentanitrato, [Th(NO3)5(H2O)2]1−, and hexanitrato, [Th(NO3)6]2−, molecular units, with the latter being far more prevalent in the solid state. The vibrational properties of the compounds were examined using Raman and IR spectroscopy; the spectra are dominated by stretches characteristic of nitrate and the organic ions. The relative energetics of nitrate complexation was examined using electronic structure theory. These results confirmed that there are clear thermodynamic sinks for the penta- and hexanitrato structural units that were observed experimentally. Additionally, electrostatic surface potentials (ESPs) were calculated in an effort to better understand the counterion stabilization of the complexes. The ESP surfaces showed that the position of the water and nitrate molecules and the coordination geometry of the metal complex had a clear effect on the polarizability of the two structural motifs. Despite limited speciation of the Th–nitrate structural units, the compounds exhibit rich supramolecular chemistry resulting from hydrogen bonding of the Th complexes with the organic N–H donors and π–π stacking interactions from the protonated N-heterocycles. [ABSTRACT FROM AUTHOR]

Rare examples of trinuclear [Ni–N2–M–N2–Ni] core (M = Ca, Mg) with linear bridged dinitrogen ligands are reported in this work. The reduction of [iPr2NN]Ni(μ-Br)2Li(thf)2 (1) (iPr2NN = 2,4-bis-(2,6-diisopropylphenylimido)pentyl) with elemental Mg or Ca in THF under an atmosphere of dinitrogen yields the complex {iPr2NNNi(μ-N2)}2M (thf)4 (M = Mg, complex 2 and M = Ca, complex 3). The bridging end-on (μ-N2)2M(thf)4 moiety connects the two [iPr2NNNi]− nickelate fragments. A combination of X-ray crystallography, solution and solid-state spectroscopy have been applied to characterize complexes 2 and 3, and DFT studies have been used to help explain the bonding and electronic structure in these unique Ni–N2–Mg and Ni–N2–Ca complexes. [ABSTRACT FROM AUTHOR]

We report herein three new modes of reactivity between arylazides N3Ar with a bulky copper(I) β-diketiminate. Addition of N3ArX3 (ArX3=2,4,6-X3C6H2; X=Cl or Me) to [iPr2NN]Cu(NCMe) results in triazenido complexes from azide attack on the β-diketiminato backbone. Reaction of [iPr2NN]Cu(NCMe) with bulkier azides N3Ar leads to terminal nitrenes [iPr2NN]Cu]=NAr that dimerize via formation of a C−C bond at the arylnitrene p-position to give the dicopper(II) diketimide 4 (Ar=2,6-iPr2C6H3) or undergo nitrile insertion to give diazametallocyclobutene 8 (Ar=4-Ph-2,6-iPr2C6H2). Importantly, reactivity studies reveal both 4 and 8 to be 'masked' forms of the terminal nitrenes [iPr2NN]Cu=NAr that undergo nitrene group transfer to PMe3, tBuNC, and even into a benzylic sp3 C−H bond of ethylbenzene. [ABSTRACT FROM AUTHOR]

We report herein three new modes of reactivity between arylazides N3Ar with a bulky copper(I) β-diketiminate. Addition of N3ArX3 (ArX3=2,4,6-X3C6H2; X=Cl or Me) to [iPr2NN]Cu(NCMe) results in triazenido complexes from azide attack on the β-diketiminato backbone. Reaction of [iPr2NN]Cu(NCMe) with bulkier azides N3Ar leads to terminal nitrenes [iPr2NN]Cu]=NAr that dimerize via formation of a C−C bond at the arylnitrene p-position to give the dicopper(II) diketimide 4 (Ar=2,6-iPr2C6H3) or undergo nitrile insertion to give diazametallocyclobutene 8 (Ar=4-Ph-2,6-iPr2C6H2). Importantly, reactivity studies reveal both 4 and 8 to be 'masked' forms of the terminal nitrenes [iPr2NN]Cu=NAr that undergo nitrene group transfer to PMe3, tBuNC, and even into a benzylic sp3 C−H bond of ethylbenzene. [ABSTRACT FROM AUTHOR]

Five novel BiIII-thiophenemonocarboxylate (BiIII-TMC) compounds containing pyridinium cations have been synthesized from room-temperature reactions of bismuth precursors with 2-thiophenecarboxylic acid (HTMC) and pyridine in water. The structures have been determined by single-crystal Xray diffraction, and two of the compounds have been further characterized by Raman spectroscopy and thermogravimetric analysis. The solid-state structures of the compounds are built from anionic BiIII building units that vary in nuclearity, overall connectivity, and dimensionality. When using bismuth nitrate at a relatively low metal/ligand ratio, Hpy[Bi(TMC)4(HTMC)] (1) is formed, which consists of mononuclear units charge-balanced by second coordination sphere pyridinium cations. With increasing metal/ligand ratios, and by consequence, increasing nitrate concentration, nitrate and carboxylate-bridged chains of [Bi2(TMC)3(NO3)]- units in Hpy[Bi2(TMC)6(NO3)] (2), and nitratebridged [Bi2(TMC)3(NO3)2]2- dimers in Hpy[Bi(TMC)3(NO3)] (3) are isolated. Starting from Bi2O3, polymorphs (Hpy)2[Bi2(TMC)8] (4) and (Hpy)2[Bi2(TMC)8] (5) are formed, both of which contain bismuth centers bridged by carboxylate groups to form dimeric units that are charge-balanced by pyridinium cations. Presented herein is a discussion of the synthetic conditions over which 1-5 were isolated, and their solid-state structural chemistry. The thermal stability of 1 and 3, and the spectroscopic characterization of the compounds, are also reported. [ABSTRACT FROM AUTHOR]

Nitrite (NO2-) and nitroso compounds (E-NO, E = RS, RO, and R2N) in mammalian plasma and cells serve important roles in nitric oxide (NO) dependent as well as NO independent signaling. Employing an electron deficient β-diketiminato copper(II) nitrito complex [Cl2NNF6]Cu(?2-O2N)oTHF, thiols mediate reduction of nitrite to NO. In contrast to NO generation upon reaction of thiols at iron nitrite species, at copper this conversion proceeds through nucleophilic attack of thiol RSH on the bound nitrite in [CuII](?2-O2N) that leads to S-nitrosation to give the S-nitrosothiol RSNO and copper(II) hydroxide [CuII]-OH. This nitrosation pathway is general and results in the nitrosation of the amine Ph2NH and alcohol tBuOH to give Ph2NNO and tBuONO, respectively. NO formation from thiols occurs from the reaction of RSNO and a copper(II) thiolate [CuII]-SR intermediate formed upon reaction of an additional equiv thiol with [CuII]-OH. [ABSTRACT FROM AUTHOR]

Radical salts and charge-transfer complexes (CTCs) containing tetracyanoquinodimethane (TCNQ) display electrical conductivity, which has led to the development of many TCNQ derivatives with enhanced electron-accepting properties that are applicable toward organic electronics. To expand the family of TCNQ derivatives, we report the synthesis and structures of 11,11,12,12-tetracyano-2,6-diiodo-9,10-anthraquinodimethane (abbreviated as DITCAQ), C20H6I2N4, and its charge-transfer complexes with various electron donors, namely DITCAQ-anthracene (2/1), C20H6I2N4·0.5C14H10, (I), DITCAQ-pyrene (2/1), C20H6I2N4·0.5C16H10, (II), and DITCAQ-tetrathiafulvalene (2/1), C20H6I2N4·0.5C6H4S4, (III). The molecular structure of DITCAQ consists of a 2,6-diiodo-9,10-dihydroanthracene moiety with two malononitrile substituents. DITCAQ possesses a saddle shape, since the malononitrile groups bend significantly up out of the plane of the central ring and the two benzene rings bend down out of the same plane. π-π interactions between DITCAQ and the electron-donor molecules control the degree of charge transfer in cocrystals (I), (II), and (III), which is reflected in both the dihedral angles between the terminal benzene ring and the central ring on the DITCAQ motifs, and their corresponding IR spectra. [ABSTRACT FROM AUTHOR]

Advancing our understanding of the minor actinides (Am, Cm) versus lanthanides is key for developing advanced nuclear-fuel cycles. Herein, we describe the preparation of (NBu4)Am[S2P( tBu2C12H6)]4 and two isomorphous lanthanide complexes, namely one with a similar ionic radius (i.e., NdIII) and an isoelectronic one (EuIII). The results include the first measurement of an Am−S bond length, with a mean value of 2.921(9) Å, by single-crystal X-ray diffraction. Comparison with the EuIII and NdIII complexes revealed subtle electronic differences between the complexes of AmIII and the lanthanides. [ABSTRACT FROM AUTHOR]

Advancing our understanding of the minor actinides (Am, Cm) versus lanthanides is key for developing advanced nuclear-fuel cycles. Herein, we describe the preparation of (NBu4)Am[S2P( tBu2C12H6)]4 and two isomorphous lanthanide complexes, namely one with a similar ionic radius (i.e., NdIII) and an isoelectronic one (EuIII). The results include the first measurement of an Am−S bond length, with a mean value of 2.921(9) Å, by single-crystal X-ray diffraction. Comparison with the EuIII and NdIII complexes revealed subtle electronic differences between the complexes of AmIII and the lanthanides. [ABSTRACT FROM AUTHOR]

The syntheses of M(ii) (M = Mn, Fe, Co) complexes bearing the tris(5-cycloaminoazafulvene-2-methyl)amine (H3N(afaCy)3) ligand in its datively coordinated, tautomeric form is reported. The metal–azafulvene complexes [N(afaCy)3M](OTf)2 are generated in high yields, featuring a secondary coordination sphere composed of amino moieties from the ligand platform. To investigate the ability of the hydrogen bonding network to support hydrogen-bond accepting, coordinating anions, pseudohalide derivatives, [N(afaCy)3MX](OTf) (X = NCS−, NCO−, N3−) were synthesized by exposure of [N(afaCy)3M](OTf)2 to an equivalent of the corresponding salt, [(nBu)4N](X). Structural characterization of the products reveals two isomorphs of the desired species. One complex features a single hydrogen bonding interaction with the pseudohalide, while the second compound has two H-bonds from the secondary coordination sphere to the coordinated anion. These complexes showcase the structural and electron flexibility of the ligand platform, presenting a scaffold capable of accessing a different number of hydrogen bonds for stabilizing a given moiety. [ABSTRACT FROM AUTHOR]

Four heteroleptic bismuth-organic phases bearing 2,2′;6′,2′′-terpyridine (terpy) and 2-thenoyltrifluoroacetone (TTA) of the general formula [BiXy(TTA)3−y(terpy)], where X = NO3 (2), Cl (3), Br (4), Br2 (5), were synthesized at room temperature. A minor phase, [Bi2(terpy)2(MeO)2(NO3)4] (1), formed in the same reaction as 2, and was manually separated to afford a phase pure sample of 2. The structures were determined through single crystal X-ray diffraction, and further characterized via powder X-ray diffraction, Raman spectroscopy, and thermogravimetric analysis. The structures of 2–5 are built from discrete monomeric units, whereas 1 contains dimeric complexes. Significant π–π stacking and halide–π interactions are observed in the solid-state structures. Europium-doped phases of 2–5 were synthesized through addition of an aliquot of a europium nitrate or europium chloride solution to the initial reaction solution. For comparison, [EuNO3(TTA)2(terpy)]·0.3MeOH (6), which is isostructural to 2, was synthesized. Photophysical measurements were carried out for each of the lanthanide containing phases, and quantum yield and lifetime values were determined for the visible-light emitters. The synthesis, structural chemistry, and spectroscopic properties of the phases are presented. [ABSTRACT FROM AUTHOR]

The nucleobase derivative 5‐aminouracil (AUr, C4H5N3O2) is of interest for its biological activity, yet the solid state structure of this compound has remained elusive owing to its propensity to crystallize as aggregates of microcrystalline particles. Here we report the first single‐crystal structure of AUr determined from synchrotron x‐ray diffraction data. An early crystal structure prediction effort, which assumed that AUr was rigid in the isolated molecule optimized conformation, provided several poor matches to the simulated PXRD pattern. Revisiting these crystal structures, by periodic electronic level modelling (PBE‐TS optimization) gave more realistic relative lattice energies, but a good match to the experimental powder pattern required using the experimental cell parameters. PXRD and Raman spectroscopy suggest that phase impurities may be present in the bulk crystallization product, though the identity of alternative polymorphs could not be confirmed on the basis of the data available. [ABSTRACT FROM AUTHOR]

Aqueous reactions of thorium chloride and furanmono‐ and dicarboxylate ligands including 2‐furoate (2FA), 3‐furoate (3FA), and 2,5‐furandicarboxylate (2,5FDC) yielded four Th(IV) phases that exhibit diverse structural chemistry ranging from isolated molecular units to 3D topologies. [Th(2FA)4]n (Th‐1) and [Th(3FA)4]n (Th‐2) consist of isostructural ligand bridged 1D chains. The compounds exhibit wide stability, forming at temperatures of 20–120 °C and pH ca. 1–4. Using the bifunctional ligand 2,5FDC a stark difference is observed; Th2(2,5FDC)4(H2O)10·2H2O (Th‐3) is built from relatively rare ligand‐bridged molecular complexes. Th‐3 similarly exhibits broad synthetic stability, forming over 20–100 °C and pH 1.8–6. At higher temperatures; however, [Th(2,5FDC)2(H2O)2]n (Th‐4), which adopts an extended 3D network is observed. The structures were determined by single‐crystal X‐ray diffraction and further characterized via Raman and IR spectroscopy as well as thermogravimetric analysis. Overall, the work highlights the role of organic ligands in the stabilization of unique Th structural units. [ABSTRACT FROM AUTHOR]

Three bismuth(III)-organic compounds, [Bi4Cl8(PDC)2(phen)4]·2MeCN (1), [BiCl3(phen)2] (2), and [Bi2Cl6(terpy)2] (3), were prepared from solvothermal reactions of bismuth chloride, 2,6-pyridinedicarboxylic acid (H2PDC), and 1,10-phenanthroline (phen) or 2,2′;6′,2′′-terpyridine (terpy). The structures were determined through single crystal X-ray diffraction and the compounds were further characterized via powder X-ray diffraction, Raman and infrared spectroscopy, and thermogravimetric analysis. The photoluminescence properties of the solid-state materials were assessed using steady state and time-dependent techniques to obtain excitation and emission profiles as well as lifetimes. The compounds exhibit visible emission ranging from the yellow-green to orange region upon UV excitation. Theoretical quantum mechanical calculations aimed at elucidating the observed emissive behavior show that the transitions can be assigned as predominantly ligand-to-ligand and ligand-to-metal charge transfer transitions. The solid-state structural chemistry, spectroscopic properties, and luminescence behavior of the bismuth compounds are presented herein. [ABSTRACT FROM AUTHOR]

S‐Nitrosothiols (RSNOs) serve as air‐stable reservoirs for nitric oxide in biology. While copper enzymes promote NO release from RSNOs by serving as Lewis acids for intramolecular electron‐transfer, redox‐innocent Lewis acids separate these two functions to reveal the effect of coordination on structure and reactivity. The synthetic Lewis acid B(C6F5)3 coordinates to the RSNO oxygen atom, leading to profound changes in the RSNO electronic structure and reactivity. Although RSNOs possess relatively negative reduction potentials, B(C6F5)3 coordination increases their reduction potential by over 1 V into the physiologically accessible +0.1 V vs. NHE. Outer‐sphere chemical reduction gives the Lewis acid stabilized hyponitrite dianion trans‐[LA‐O‐N=N‐O‐LA]2− [LA=B(C6F5)3], which releases N2O upon acidification. Mechanistic and computational studies support initial reduction to the [RSNO‐B(C6F5)3] radical anion, which is susceptible to N−N coupling prior to loss of RSSR. [ABSTRACT FROM AUTHOR]

S‐Nitrosothiols (RSNOs) serve as air‐stable reservoirs for nitric oxide in biology. While copper enzymes promote NO release from RSNOs by serving as Lewis acids for intramolecular electron‐transfer, redox‐innocent Lewis acids separate these two functions to reveal the effect of coordination on structure and reactivity. The synthetic Lewis acid B(C6F5)3 coordinates to the RSNO oxygen atom, leading to profound changes in the RSNO electronic structure and reactivity. Although RSNOs possess relatively negative reduction potentials, B(C6F5)3 coordination increases their reduction potential by over 1 V into the physiologically accessible +0.1 V vs. NHE. Outer‐sphere chemical reduction gives the Lewis acid stabilized hyponitrite dianion trans‐[LA‐O‐N=N‐O‐LA]2− [LA=B(C6F5)3], which releases N2O upon acidification. Mechanistic and computational studies support initial reduction to the [RSNO‐B(C6F5)3] radical anion, which is susceptible to N−N coupling prior to loss of RSSR. [ABSTRACT FROM AUTHOR]

Uranium(IV) complexation by 2‐furoic acid (2‐FA) was examined to better understand the effects of ligand identity and reaction conditions on species formation and stability. Five compounds were isolated: [UCl2(2‐FA)2(H2O)2]n (1), [U4Cl10O2(THF)6(2‐FA)2]⋅2 THF (2), [U6O4(OH)4(H2O)3(2‐FA)12]⋅7 THF⋅H2O (3), [U6O4(OH)4(H2O)2(2‐FA)12]⋅8.76 H2O (4), and [U38Cl42O54(OH)2(H2O)20]⋅m H2O⋅n THF (5). The structures were determined by single‐crystal X‐ray diffraction and further characterized by Raman, IR, and optical absorption spectroscopy. The thermal stability and magnetic behavior of the compounds were also examined. Variations in the synthetic conditions led to notable differences in the structural units observed in the solid state. At low H2O/THF ratios, a tetranuclear oxo‐bridged [U4O2] core was isolated. Aging of this solution resulted in the formation a U38 oxo cluster capped by chloro and water ligands. However, at increasing water concentrations only hexanuclear units were observed. In all cases, at temperatures of 100–120 °C, UO2 nanoparticles formed. [ABSTRACT FROM AUTHOR]

Nitrate and nitrite anions have multifaceted impacts on the environment and human health. We herein report selective recognition of nitrite over nitrate anion inside the cavity of bimetallic azacryptates having p-xylyl spacers. This work reveals a number of binding interactions which play pivotal roles in nitrite anion recognition by rigid metal cryptates. [ABSTRACT FROM AUTHOR]

Undirected C(sp3)−H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C−H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C−H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C−H bonds over tertiary and benzylic C−H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C−H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N3. Mechanistic and DFT studies indicate that C−H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ2‐N,O‐NC(O)Ar) to provide carbon‐based radicals R. and copper(II)amide intermediates [CuII]‐NHC(O)Ar that subsequently capture radicals R. to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C−H amidation selectivity in the absence of directing groups. [ABSTRACT FROM AUTHOR]

Undirected C(sp3)−H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C−H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C−H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C−H bonds over tertiary and benzylic C−H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C−H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N3. Mechanistic and DFT studies indicate that C−H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ2‐N,O‐NC(O)Ar) to provide carbon‐based radicals R. and copper(II)amide intermediates [CuII]‐NHC(O)Ar that subsequently capture radicals R. to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C−H amidation selectivity in the absence of directing groups. Swimming against the tide: A new β‐diketiminate CuI catalyst system has been developed for C−H amidation with aroyl azides via copper nitrene intermediates. Owing to their steric bulk they target stronger, more accessible primary and secondary C−H bonds in the presence of weaker, hindered tertiary C−H bonds. [ABSTRACT FROM AUTHOR]

Three bismuth-2,5-thiophenedicarboxylates (Bi-TDC) and two europium-2,5-thiophenedicarboxylates (Eu-TDC) were synthesized under ambient conditions. The structures were determined through single crystal X-ray diffraction, and three of the phases were further characterized by powder X-ray diffraction, Raman spectroscopy, and thermogravimetric analysis. Reactions of bismuth nitrate, 2,5-thiophenedicarboxylate, and pyridine in an acidic solution of acetic acid and ethanol yield Hpy[Bi(TDC)2(H2O)]·1.5H2O (1), whereas reactions in a water/ethanol mixture produce a minor phase, [Hpy]3 [Bi2(TDC)4(HTDC) (H2O)]·xH2O (2) along with a major product, (Hpy)2[Bi(TDC)2(HTDC)]·0.36H2O (3). The structures of 1-3 are all built from anionic Bi-TDC chains that are further bridged through additional TDC linkages into interpenetrated 2D sheets. Addition of an aqueous lanthanide solution to the reaction mixtures that yielded 1 and 2-3 resulted in the formation of doped phases, Hpy[Bi1-xLnx(TDC)2(H2O)]·1.5H2O (Bi1-xLnx-1), where Ln = Nd, Sm, Eu, Tb, Dy, and Yb, and (Hpy)2[Bi0.99Eu0.01 (TDC)2(HTDC)]·0.36H2O (Bi0.99Eu0.01-3). Using europium nitrate rather than the bismuth precursor resulted in the formation of two homometallic europium based phases, [Eu(TDC)(NO3)(H2O)]n (4) and [Eu2(TDC)3(H2O)9]·5H2O (5), which adopt an extended 3D network and an interpenetrated 2D structure, respectively. Photophysical measurements were carried out for 1 and the lanthanide containing phases and quantum yield and lifetime values were determined for the visible light emitters. Herein, the structural chemistry, spectroscopic properties, and luminescence of the bismuth phases, their lanthanide doped analogs, and the europium compounds are presented. [ABSTRACT FROM AUTHOR]

Abstract: A bismuth‐organic compound containing 2,2′:6′2“‐terpyridine (terpy) and 2‐thiophenecarboxylate (TC), of the general formula (terpy)Bi(κ2‐TC)3⋅0.47 H2O (BiOM‐1), has been synthesized under hydrothermal conditions. Addition of a lanthanide nitrate solution to the reaction mixture led to statistical replacement of the bismuth centers, and yielded isomorphous lanthanide containing compounds Bi1−xLnxOM‐1 (Ln=Nd, Sm, Eu, Tb, Dy, Er, and Yb) that showed bismuth and/or ligand sensitized lanthanide‐centered emission, and the first example of NIR emission from a lanthanide doped BiOM. The structure was determined by single‐crystal X‐ray diffraction, and the level and uniformity of lanthanide ion incorporation into the bismuth host was determined by ICP‐OES and electron microprobe analysis. For the visible emitters, lifetime data and quantum yields are presented. A high efficiency of sensitization was calculated for the europium analog (50.1 %), showing significant improvement over previously reported europium thiophenecarboxylates. These novel materials may provide strategies to address concerns over the long‐term sustainability of the rare earth elements, especially relating to optical devices. [ABSTRACT FROM AUTHOR]

Well-defined metal nanocrystals play important roles in various fields, such as catalysis, medicine, and nanotechnology. They are often synthesized through kinetically controlled process in colloidal systems that contain metal precursors and surfactant molecules. The chemical functionality of surfactants as coordinating ligands to metal ions however remains a largely unsolved problem in this process. Understanding the metal-ligand complexation and its effect on formation kinetics at the molecular level is challenging but essential to the synthesis design of colloidal nanocrystals. Herein we report that spontaneous ligand replacement and anion exchange control the form of coordinated Pt-ligand intermediates in the system of platinum acetylacetonate [Pt(acac)2], primary aliphatic amine, and carboxylic acid ligands. The formed intermediates govern the formation mode of Pt nanocrystals, leading to either a pseudo two-step or a one-step mechanism by switching on or off an autocatalytic surface growth. This finding shows the importance of metal-ligand complexation at the prenucleation stage and represents a critical step forward for the designed synthesis of nanocrystal-based materials. [ABSTRACT FROM AUTHOR]

The preparation of a lanthanide series, with the exception of promethium, incorporating 2,2′:6′,2′′-terpyridine (terpy) and 2-thiophenecarboxylate (TC) functionality has been achieved via hydrothermal reaction conditions. The structures of the crystalline products were determined using single crystal X-ray diffraction and bulk purity was confirmed via powder X-ray diffraction and elemental analysis. The series is comprised of four structure types wherein the effects of the lanthanide contraction are manifested in changes in the coordination number and nuclearity of the complexes. From lanthanum through holmium an isomorphous series of symmetric dimers of the general formula [Ln2(terpy)2(TC)4(μ-TC)2(H2O)2]·nH2O (Ln-1, Ln = La–Ho, excluding Pm) was isolated. Using holmium oxide resulted in the formation of Ho-1 whereas use of the holmium chloride precursor resulted in the formation of [Ho2(terpy)2(TC)3(μ-TC)2(H2O)2]TC (Ho-2), that consists of an asymmetric dimer. Beyond Ho, Er–Lu were found to form compounds of the general formula [Ln(terpy)(TC)3(H2O)], the structures of which consist of monomeric units. While Er adopts Er-3, Tm–Lu adopt another structure type (Ln-4, where Ln = Tm, Yb, and Lu), the latter arising from differences in intramolecular hydrogen bonding interactions as well as π–π stacking interactions. The luminescent behaviour of the solid samples was examined and showed ligand-sensitized metal-based visible (Sm, Eu Tb, Dy) and NIR (Nd, Sm, and Yb) emission, with lifetimes up to hundreds of microseconds for select samples. Quantum yields of the visible light emitters have been measured and are additionally presented. [ABSTRACT FROM AUTHOR]

A series of 14 lanthanide compounds bearing 2-thiophenecarboxylate (TC) have been prepared under aqueous conditions and structurally characterized. Single crystal X-ray diffraction studies reveal a full isomorphous series across the 4f block of the general formula [(Ln(TC)3(H2O)2)·(HPy·TC)] n , (Ln = La (La-1) - Lu (Lu-1), excluding Pm), with observable contraction of the cell volume and average metal-oxygen bond distances occurring when moving from lanthanum to lutetium. The 8-coordinate Ln metal centers are bound to two water molecules as well as six oxygen atoms from one bidentate and four bridging TC units that link LnO8 structural units into 1D chains. One lattice stabilizing pyridinium and one outer coordination sphere TC anion are present per formula unit. Reaction optimization provided moderate to high yields of the title products; a lanthanum byproduct [La(TC)3(HTC)2] n (La-2) was formed by performing the reaction at reduced temperature, or alternatively, successive grinding of La-1 in ethanol resulted in partial conversion to La-2. Solid-state fluorescence studies show ligand sensitized metal-based emission for Eu(III), Tb(III), and Dy(III) in the visible region, and Nd(III) and Er(III) in the NIR. Color tuning was easily achieved by varying europium:terbium metal ratios in the reaction mixtures. [ABSTRACT FROM AUTHOR]

The crystal structures of two new bimetallic uranyl-transition metal compounds with diglycolic acid [or 2-(carboxymethoxy)acetic acid] have been hydrothermally synthesized and structurally characterized via single-crystal X-ray diffraction. The compounds, namely catena-poly[[[tetraaquamanganese(II)]-μ-2,2′-oxydiacetato-[dioxidouranium(VI)]-μ-2,2′-oxydiacetato] dihydrate], {[MnU(C4H4O5)2O2(H2O)4]·2H2O} n, and catena-poly[[[tetraaquacobalt(II)]-μ-2,2′-oxydiacetato-[dioxidouranium(VI)]-μ-2,2′-oxydiacetato] dihydrate], {[CoU(C4H4O5)2O2(H2O)4]·2H2O} n, both crystallize in the triclinic space group P. These compounds form one-dimensional chains via alternating uranyl and transition metal building units. The chains then assemble into three-dimensional supramolecular networks through several hydrogen bonds between water molecules and diglycolate ligands. Luminescence measurements were conducted and no uranyl emission was observed in either compound. [ABSTRACT FROM AUTHOR]

Copper(II) aryl species are proposed key intermediates in Cu-catalyzed cross-coupling reactions. Novel three-coordinate copper(II) aryls [CuII]-C6F5 supported by ancillary β-diketiminate ligands form in reactions between copper(II) alkoxides [CuII]-O t Bu and B(C6F5)3. Crystallographic, spectroscopic, and DFT studies reveal geometric and electronic structures of these Cu(II) organometallic complexes. Reaction of [CuII]-C6F5 with the free radical NO(g) results in C-N bond formation to give [Cu](η²-ONC6F5). Remarkably, addition of the phenolate anion PhO- to [CuII]-C6F5 directly affords diaryl ether PhO-C6F5 with concomitant generation of the copper(I) species [CuI](solvent) and {[CuI]-C6F5}-. Experimental and computational analysis supports redox disproportionation between [CuII]-C6F5 and {[CuII](C6F5)(OPh)}- to give {[CuI]-C6F5}- and [CuIII](C6F5)(OPh) unstable toward reductive elimination to [CuI](solvent) and PhO-C6F5. [ABSTRACT FROM AUTHOR]

Supramolecular crystalline assembly constitutes a rational approach to bioengineer intracellular structures. Here, biocrystals of clofazimine (CFZ) that form in vivo within macrophages were measured to have marked curvature. Isolated crystals, however, showed reduced curvature suggesting that intracellular forces bend these drug crystals. Consistent with the ability of biocrystals to elastically deform, the inherent crystal structure of the principal molecular component of the biocrystals-the hydrochloride salt of CFZ (CFZ-HCl)-has a corrugated packing along the (001) face and weak dispersive bonding in multiple directions. These characteristics were previously found to be linked to the elasticity of other organic crystals. Internal stress in bent CFZ-HCl led to photoelastic effects on the azimuthal orientation of polarized light transmittance. We propose that elastic, intracellular crystals can serve as templates to construct functional microdevices with different applications. [ABSTRACT FROM AUTHOR]

Supramolecular crystalline assembly constitutes a rational approach to bioengineer intracellular structures. Here, biocrystals of clofazimine (CFZ) that form in vivo within macrophages were measured to have marked curvature. Isolated crystals, however, showed reduced curvature suggesting that intracellular forces bend these drug crystals. Consistent with the ability of biocrystals to elastically deform, the inherent crystal structure of the principal molecular component of the biocrystals-the hydrochloride salt of CFZ (CFZ-HCl)-has a corrugated packing along the (001) face and weak dispersive bonding in multiple directions. These characteristics were previously found to be linked to the elasticity of other organic crystals. Internal stress in bent CFZ-HCl led to photoelastic effects on the azimuthal orientation of polarized light transmittance. We propose that elastic, intracellular crystals can serve as templates to construct functional microdevices with different applications. [ABSTRACT FROM AUTHOR]

Nitric oxide is a vital signaling molecule that controls blood flow and oxygenation and nitrite serves as an important reservoir for nitric oxide in biology. While copper containing enzymes are known to reduce nitrite to nitric oxide, herein we report a new pathway to release nitric oxide via oxygen atom transfer from nitrite at a copper(ii) site. [ABSTRACT FROM AUTHOR]

A variety of acyl protected phenols AcOAr participate in sp3C-H etherification of substrates R-H to give alkyl aryl ethers R-OAr employingtBuOOtBu as oxidant with copper(I) β-diketiminato catalysts [CuI]. Although 1°, 2°, and 3° C-H bonds may be functionalized, selectivity studies reveal a preference for the construction of hindered, 3° C-OAr bonds. Mechanistic studies indicate that β-diketiminato copper(II) phenolates [CuII]-OAr play a key role in this C-O bond forming reaction, formed via transesterification of AcOAr with [CuII]-OtBu intermediates generated upon reaction of [CuI] withtBuOOtBu. [ABSTRACT FROM AUTHOR]

We report a new class of frustrated Lewis pairs (FLPs) by the hydroboration of bulky isocyanates iPr2ArNCO (iPr2Ar=2,6- iPr2C6H3) and Ph2tBuArNCO (Ph2tBuAr=2,6-Ph2-4- tBuC6H2) with Piers' borane (HB(C6F5)2). While hydroboration of smaller isocyanates such as iPr2ArNCO leads to isocyanate-N/B FLP adducts, hydroboration of the bulkier Ph2tBuArNCO allows isolation of the substrate-free aminoborane with a short, covalent N−B bond. This confused FLP reversibly binds unsaturated substrates such as isocyanates and isocyanides, suggesting the intermediacy of a 'normal' FLP along the reaction pathway, supported by high-level DFT studies and variable-temperature NMR spectroscopy. These results underscore the possibility of FLP behavior in systems that possess no obvious frustrated Lewis acid-base interaction. [ABSTRACT FROM AUTHOR]

Nitrosobenzene (PhNO) serves as a stable analogue of nitroxyl (HNO), a biologically relevant, redox-active nitric oxide derivative. Capture of nitrosobenzene at the electron-deficient β-diketiminato nickel(I) complex [ iPr2NNF6]Ni results in reduction of the PhNO ligand to a (PhNO)./− species coordinated to a square planar NiII center in [ iPr2NNF6]Ni(η2-ONPh). Ligand centered reduction leads to the (PhNO)2− moiety bound to NiII supported by XAS studies. Systematic investigation of structure-reactivity patterns of (PhNO)./− and (PhNO)2− ligands reveals parallels with superoxo (O2)./− and peroxo (O2)2− ligands, respectively, and forecasts reactivity patterns of the more transient HNO ligand. [ABSTRACT FROM AUTHOR]

Nitrosobenzene (PhNO) serves as a stable analogue of nitroxyl (HNO), a biologically relevant, redox-active nitric oxide derivative. Capture of nitrosobenzene at the electron-deficient β-diketiminato nickel(I) complex [ iPr2NNF6]Ni results in reduction of the PhNO ligand to a (PhNO)./− species coordinated to a square planar NiII center in [ iPr2NNF6]Ni(η2-ONPh). Ligand centered reduction leads to the (PhNO)2− moiety bound to NiII supported by XAS studies. Systematic investigation of structure-reactivity patterns of (PhNO)./− and (PhNO)2− ligands reveals parallels with superoxo (O2)./− and peroxo (O2)2− ligands, respectively, and forecasts reactivity patterns of the more transient HNO ligand. [ABSTRACT FROM AUTHOR]

Low-temperature reaction of the tris(pyrazolyl)borate copper(II) hydroxide [iPr2TpCu]2(μ-OH)2 with triphenylsilane under a dinitrogen atmosphere gives the bridging dinitrogen complex [iPr2TpCu]2(μ-1,2-N2) ( 3). X-ray crystallography reveals an only slightly activated N2 ligand (N-N: 1.111(6) Å) that bridges between two monovalent iPr2TpCu fragments. While DFT studies of mono- and dinuclear copper dinitrogen complexes suggest weak π-backbonding between the d10 CuI centers and the N2 ligand, they reveal a degree of cooperativity in the dinuclear Cu-N2-Cu interaction. Addition of MeCN, CNAr2,6-Me, or O2 to 3 releases N2 with formation of iPr2TpCu(L) (L=NCMe, CNAr2,6-Me2) or [iPr2TpCu]2(μ-η2:η2-O2) ( 1). Addition of triphenylsilane to [iPr2TpCu]2(μ-OH)2 in pentane allows isolation of a key intermediate [iPr2TpCu]2(μ-H) ( 5). Although 5 thermally decays under N2 to give 3, it reduces unsaturated substrates, such as CO and HC≡CPh to HC(O)H and H2C=CHPh, respectively. [ABSTRACT FROM AUTHOR]

Low-temperature reaction of the tris(pyrazolyl)borate copper(II) hydroxide [iPr2TpCu]2(μ-OH)2 with triphenylsilane under a dinitrogen atmosphere gives the bridging dinitrogen complex [iPr2TpCu]2(μ-1,2-N2) ( 3). X-ray crystallography reveals an only slightly activated N2 ligand (N-N: 1.111(6) Å) that bridges between two monovalent iPr2TpCu fragments. While DFT studies of mono- and dinuclear copper dinitrogen complexes suggest weak π-backbonding between the d10 CuI centers and the N2 ligand, they reveal a degree of cooperativity in the dinuclear Cu-N2-Cu interaction. Addition of MeCN, CNAr2,6-Me, or O2 to 3 releases N2 with formation of iPr2TpCu(L) (L=NCMe, CNAr2,6-Me2) or [iPr2TpCu]2(μ-η2:η2-O2) ( 1). Addition of triphenylsilane to [iPr2TpCu]2(μ-OH)2 in pentane allows isolation of a key intermediate [iPr2TpCu]2(μ-H) ( 5). Although 5 thermally decays under N2 to give 3, it reduces unsaturated substrates, such as CO and HC≡CPh to HC(O)H and H2C=CHPh, respectively. [ABSTRACT FROM AUTHOR]

The intermediacy of a reduced nickel--iron hydride in hydrogen evolution catalyzed by Ni--Fe complexes was verified experimentally and computationally. In addition to catalyzing hydrogen evolution, the highly basic and bulky (dppv)Ni(μ-pdt)Fe(CO)(dppv) ([1]°; dppv = cis-C2H2(PPh2)2) and its hydride derivatives have yielded to detailed characterization in terms of spectroscopy, bonding, and reactivity. The protonation of [1]° initially produces unsym-[H1]+, which converts by a first-order pathway to sym-[H1]+. These species have C1 (unsym) and Cs (sym) symmetries, respectively, depending on the stereochemistry of the octahedral Fe site. Both experimental and computational studies show that [H1]+ protonates at sulfur. The S = 1/2 hydride [H1]0 was generated by reduction of [H1]+ with Cp*2Co. Density functional theory (DFT) calculations indicate that [H1]0 is best described as a Ni(I)--Fe(II) derivative with significant spin density on Ni and some delocalization on S and Fe. EPR spectroscopy reveals both kinetic and thermodynamic isomers of [H1]0. Whereas [H1]+ does not evolve H2 upon protonation, treatment of [H1]0 with acids gives H2. The redox state of the "remote" metal (Ni) modulates the hydridic character of the Fe(II)-H center. As supported by DFT calculations, H2 evolution proceeds either directly from [H1]0 and external acid or from protonation of the Fe--H bond in [H1]0 to give a labile dihydrogen complex. Stoichiometric tests indicate that protonation-induced hydrogen evolution from [H1]0 initially produces [1]+, which is reduced by [H1]0. Our results reconcile the required reductive activation of a metal hydride and the resistance of metal hydrides toward reduction. This dichotomy is resolved by reduction of the remote (non-hydride) metal of the bimetallic unit. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a series of cobalt complexes featuring a pincer bis(carbene) ligand of the meta-phenylene-bridged bis-N-heterocyclic carbene (ArCCC, Ar = 2,6-diispropylphenyl or mesityl) are reported. Cleavage of the aryl C–H bond of the ligand was achieved in a one-pot metalation procedure using Co(N(SiMe3)2)2(py)2, an equivalent of exogenous base, and trityl chloride to form the (DIPPCCC)CoCl2py complex. This species could be reduced to the Co(ii) and Co(i)–N2 molecules with the appropriate equivalents of reductant. Subsequent generation of (MesCCC)CoI–III derivatives with the mesityl ligand proceeded in good yields. A suite of characterization techniques and the interconversion between all three oxidation states of the cobalt complexes is described. [ABSTRACT FROM AUTHOR]