Following growth doping technique, highly luminescent (quantum yield > 50%) Mn-doped ZnS nanocrystals are synthesized via colloidal synthetic technique. The dopant emission has been optimized with varying reaction parameters and found the ratio of Zn to S as well as the percentage of introduced dopant in the reaction mixture are key factors for controlling the intensity. The method is simple, hassle free, and can be scalable to gram level without hindering the quality of nanocrystals. These nanocrystals retain their emission during various ligand exchange processes and aqueous dispersion.

Three biomimetic iron(II) α-hydroxy acid complexes, [(Tp(Ph2))Fe(II)(mandelate)(H2O)] (1), [(Tp(Ph2))Fe(II)(benzilate)] (2), and [(Tp(Ph2))Fe(II)(HMP)] (3), together with two iron(II) α-methoxy acid complexes, [(Tp(Ph2))Fe(II)(MPA)] (4) and [(Tp(Ph2))Fe(II)(MMP)] (5) (where HMP = 2-hydroxy-2-methylpropanoate, MPA = 2-methoxy-2-phenylacetate, and MMP = 2-methoxy-2-methylpropanoate), of a facial tridentate ligand Tp(Ph2) [where Tp(Ph2) = hydrotris(3,5-diphenylpyrazole-1-yl)borate] were isolated and characterized to study the mechanism of dioxygen activation at the iron(II) centers. Single-crystal X-ray structural analyses of 1, 2, and 5 were performed to assess the binding mode of an α-hydroxy/methoxy acid anion to the iron(II) center. While the iron(II) α-methoxy acid complexes are unreactive toward dioxygen, the iron(II) α-hydroxy acid complexes undergo oxidative decarboxylation, implying the importance of the hydroxyl group in the activation of dioxygen. In the reaction with dioxygen, the iron(II) α-hydroxy acid complexes form iron(III) phenolate complexes of a modified ligand (Tp(Ph2)*), where the ortho position of one of the phenyl rings of Tp(Ph2) gets hydroxylated. The iron(II) mandelate complex (1), upon decarboxylation of mandelate, affords a mixture of benzaldehyde (67%), benzoic acid (20%), and benzyl alcohol (10%). On the other hand, complexes 2 and 3 react with dioxygen to form benzophenone and acetone, respectively. The intramolecular ligand hydroxylation gets inhibited in the presence of external intercepting agents. Reactions of 1 and 2 with dioxygen in the presence of an excess amount of alkenes result in the formation of the corresponding cis-diols in good yield. The incorporation of both oxygen atoms of dioxygen into the diol products is confirmed by (18)O-labeling studies. On the basis of reactivity and mechanistic studies, the generation of a nucleophilic iron-oxygen intermediate upon decarboxylation of the coordinated α-hydroxy acids is proposed as the active oxidant. The novel iron-oxygen intermediate oxidizes various substrates like sulfide, fluorene, toluene, ethylbenzene, and benzaldehyde. The oxidant oxidizes benzaldehyde to benzoic acid and also participates in the Cannizzaro reaction.

O2‐dependent transformation: An iron(II)‐benzilate complex of a tridentate N3 donor ligand reacts with O2 to undergo oxidative decarboxylation. Cyclohexene is selectively converted into cis‐cyclohexane‐1,2‐diol in the reaction.

Iron(II)-α-hydroxy acid complexes of a tripodal N4 ligand undergo oxidative decarboxylation upon exposure to O 2 and mimic the aliphatic C1-C2 cleavage step catalyzed by CloR.The large majority of nonheme iron enzymes that cleave C-C bonds are catechol dioxygenases, which take advantage of the electron-rich nature of the aromatic substrates to initiate O 2 activation. 1 There are now related enzymes that cleave aliphatic C-C bonds, but a different O 2 activation mechanism is required because of the difference in the substrates. 2 A recently characterized example is 2-hydroxyethylphosphonate (HEP) dioxygenase (HEPD) that catalyzes the cleavage of the HEP C1-C2 bond to form hydroxymethylphosphonate and formate. 2, 3 The nonheme iron center is bound to a 2-His-1-carboxylate facial triad4 , 5 and the substrate binds in a bidentate manner to the iron via the 2-OH and phosphonate groups. 3 Another example is CloR, an enzyme involved in the biosynthesis of clorobiocin, 6 an aminocoumarin antibiotic that targets bacterial DNA gyrase. 7,8 Clorobiocin has a 3DMA-4HB moiety (Scheme 1) that derives from 3DMA-4HPP via two consecutive oxidative decarboxylation steps catalyzed by CloR. Of interest to this work is the novel C1-C2 bond cleavage of 3DMA-4HMA in the second step. By analogy to HEPD, the mandelate substrate may bind in a bidentate fashion to the iron to intiate the O 2 activation mechanism. This notion is tested with model complexes in this study.There are only two reports on the iron (II)-α-hydroxycarboxylate complexes,9 , 10 and no biomimetic iron(II) complexes that use O 2 for the selective oxidative decarboxylation of mandelic acid to benzoic acid. Thus, to develop an understanding of the reaction catalyzed by CloR, we have initiated the syntheses of a series of iron(II)-α-hydroxy acid complexes and associated reactivity studies. We report herein the structure of [(6-Me 3 -TPA) Fe II (mandelate)] + (1, 6-Me 3 -TPA = tris-[(6-methyl-2-pyridyl)methyl]amine) and its reaction with dioxygen as well as those of other iron(II)-α-hydroxy acid complexes of the same tetradentate ligand.The reaction of Fe(ClO 4 ) 2 ·6H 2 O, 6-Me 3 -TPA ligand, mandelic acid and triethylamine in methanol yields a light yellow iron(II) complex [(6-Me 3 -TPA)Fe II (mandelate)] + (1) with a This journal is

A series of iron(II) benzilate complexes (1-7) with general formula [(L)Fe(benzilate)] have been isolated and characterized to study the effect of supporting ligand (L) on the reactivity of metal-based oxidant generated in the reaction with dioxygen. Five tripodal N ligands (tris(2-pyridylmethyl)amine (TPA in 1), tris(6-methyl-2-pyridylmethyl)amine (6-Me-TPA in 2), N,N-dimethyl-N,N-bis(2-pyridylmethyl)ethane-1,2-diamine (iso-BPMEN in 3), N,N-dimethyl-N,N-bis(6-methyl-2-pyridylmethyl)ethane-1,2-diamine (6-Me-iso-BPMEN in 4), and tris(2-benzimidazolylmethyl)amine (TBimA in 7)) along with two linear tetradentate amine ligands (N,N-dimethyl-N,N-bis(2-pyridylmethyl)ethane-1,2-diamine (BPMEN in 5) and N,N-dimethyl-N,N-bis(6-methyl-2-pyridylmethyl)ethane-1,2-diamine (6-Me-BPMEN in 6)) were employed in the study. Single-crystal X-ray structural studies reveal that each of the complex cations of 1-3 and 5 contains a mononuclear six-coordinate iron(II) center coordinated by a monoanionic benzilate, whereas complex 7 contains a mononuclear five-coordinate iron(II) center. Benzilate binds to the iron center in a monodentate fashion via one of the carboxylate oxygens in 1 and 7, but it coordinates in a bidentate chelating mode through carboxylate oxygen and neutral hydroxy oxygen in 2, 3, and 5. All of the iron(II) complexes react with dioxygen to exhibit quantitative decarboxylation of benzilic acid to benzophenone. In the decarboxylation pathway, dioxygen becomes reduced on the iron center and the resulting iron-oxygen oxidant shows versatile reactivity. The oxidants are nucleophilic in nature and oxidize sulfide to sulfoxide and sulfone. Furthermore, complexes 2 and 4-6 react with alkenes to produce cis-diols in moderate yields with the incorporation of both the oxygen atoms of dioxygen. The oxygen atoms of the nucleophilic oxidants do not exchange with water. On the basis of interception studies, nucleophilic iron(II) hydroperoxides are proposed to generate in situ in the reaction pathways. The difference in reactivity of the complexes toward external substrates could be attributed to the geometry of the O-derived iron-oxygen oxidant. DFT calculations suggest that, among all possible geometries and spin states, high-spin side-on iron(II) hydroperoxides are energetically favorable for the complexes of 6-Me-TPA, 6-Me-iso-BPMEN, BPMEN, and 6-Me-BPMEN ligands, while high spin end-on iron(II) hydroperoxides are favorable for the complexes of TPA, iso-BPMEN, and TBimA ligands.

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A new tridentate N ligand (TMGtach) consisting of cis,cis-1,3,5-triaminocyclohexane (tach) and three N,N,N',N'-tetramethylguanidino (TMG) groups has been developed to prepare copper complexes with a tetrahedral geometry and a labile coordination site. Treatment of the ligand with CuX (X = Cl and Br) gave copper(II)-halide complexes, [Cu(TMGtach)Cl] (2) and [Cu(TMGtach)Br] (2), the structures of which have been determined by X-ray crystallographic analysis. The complexes exhibit a four-coordinate structure with C symmetry, where the labile halide ligand (X) occupies a position on the trigonal axis. 2 was converted to a methoxido-copper(II) complex [Cu(TMGtach)(OMe)](OTf) (2), also having a similar four-coordinate geometry, by treating it with an equimolar amount of tetrabutylammonium hydroxide in methanol. The methoxido-complex 2 was further converted to the corresponding phenolato-copper(II) (2) and thiophenolato-copper(II) (2) complexes by ligand exchange reactions with the neutral phenol and thiophenol derivatives, respectively. The electronic structures of the copper(II) complexes with different axial ligands are discussed on the basis of EPR spectroscopy and DFT calculations.

Two molecular copper­(II) complexes, (NMe4)2[CuII(L1)] (1) and (NMe4)2[CuII(L2)] (2), ligated by a N2O2 donor set of ligands [L1 = N,N′-(1,2-phenylene)­bis­(2-hydroxy-2-methylpropanamide), and L2 = N,N′-(4,5-dimethyl-1,2-phenylene)­bis­(2-hydroxy-2-methylpropanamide)] have been synthesized and thoroughly characterized. An electrochemical study of 1 in a carbonate buffer at pH 9.2 revealed a reversible copper-centered redox couple at 0.51 V, followed by two ligand-based oxidation events at 1.02 and 1.25 V, and catalytic water oxidation at an onset potential of 1.28 V (overpotential of 580 mV). The electron-rich nature of the ligand likely supports access to high-valent copper species on the CV time scale. The results of the theoretical electronic structure investigation were quite consistent with the observed stepwise ligand-centered oxidation process. A constant potential electrolysis experiment with 1 reveals a catalytic current density of >2.4 mA cm–2 for 3 h. A one-electron-oxidized species of 1, (NMe4)­[CuIII(L1)] (3), was isolated and characterized. Complex 2, on the contrary, revealed copper and ligand oxidation peaks at 0.505, 0.90, and 1.06 V, followed by an onset water oxidation (WO) at 1.26 V (overpotential of 560 mV). The findings show that the ligand-based oxidation reactions strongly depend upon the ligand’s electronic substitution; however, such effects on the copper-centered redox couple and catalytic WO are minimal. The energetically favorable mechanism has been established through the theoretical calculation of stepwise reaction energies, which nicely explains the experimentally observed electron transfer events. Furthermore, as revealed by the theoretical calculations, the O–O bond formation process occurs through a water nucleophilic attack mechanism with an easily accessible reaction barrier. This study demonstrates the importance of redox-active ligands in the development of molecular late-transition-metal electrocatalysts for WO reactions.