Iron(II)-alkoxide and -aryloxide complexes of a tris(thioether)borate ligand: synthesis, molecular structures, and implications on the origin of instability of their iron(II)-catecholate counterpart.

The phenyltris[(tert-butylthio)methyl]borate ligand, [PhTt], has been studied extensively as a platform for coordination, organometallic, and bioinorganic chemistry, especially with 3d metals. While [PhTt]Co(3,5-DBCatH) (3,5-DBCatH is 3,5-di-tert-butylcatecholate), a Co-monoanionic catecholate complex, was successfully isolated to model the active site of cobalt(II)-substituted homoprotocatechuate 2,3-dioxygenase (Co-HPCD) [Wang et al. (2019).

Synthesis and Reactivity Studies of a Series of Nickel(II) Arylchalcogenolates.

Two series of high-spin nickel complexes, [Tp]Ni(EAr) (E = O, Se, Te; Ar = CH) and [Tp]Ni(SeCH-4-X) (X = H, Cl, Me, OMe), were prepared by metathetical reaction of the nickel(II) halide precursor with sodium salts of the corresponding chalcogen, NaEAr. X-ray crystallographic characterization and spectroscopic studies have established the geometric and electronic structures of these complexes. The observed spectroscopic and structural characteristics reveal distinct trends in accordance with the variation of the identity of the arylchalcogenolate and substituent.

Molecular and Electronic Structures and Single-Molecule Magnet Behavior of Tris(thioether)-Iron Complexes Containing Redox-Active α-Diimine Ligands.

Incorporating radical ligands into metal complexes is one of the emerging trends in the design of single-molecule magnets (SMMs). While significant effort has been expended to generate multinuclear transition metal-based SMMs with bridging radical ligands, less attention has been paid to mononuclear transition metal-radical SMMs. Herein, we describe the first α-diiminato radical-containing mononuclear transition metal SMM, namely, [κ-PhTt]Fe(AdNCHCHNAd) (), and its analogue [κ-PhTt]Fe(CyNCHCHNCy) () (PhTt = phenyltris(butylthiomethyl)borate, Ad = adamantyl, and Cy = cyclohexyl).

Electronic, Magnetic, and Redox Properties and O Reactivity of Iron(II) and Nickel(II) o-Semiquinonate Complexes of a Tris(thioether) Ligand: Uncovering the Intradiol Cleaving Reactivity of an Iron(II) o-Semiquinonate Complex.

The iron(II) semiquinonate character within the iron(III) catecholate species has been proposed by numerous studies to account for the O reactivity of intradiol catechol dioxygenases, but a well-characterized iron(II) semiquinonate species that exhibits intradiol cleaving reactivity has not yet been reported. In this study, a detailed electronic structure description of the first iron(II) o-semiquinonate complex, [PhTt]Fe(phenSQ) [PhTt = phenyltris(tert-butylthiomethyl)borate; phenSQ = 9,10-phenanthrenesemiquinonate; Wang et al. Chem.

Steric and electronic factor comparisons in hydrotris(3-phenylpyrazolyl)borate nickel(II) aryloxides.

Hydrotris(pyrazolyl)borate (Tp) ligands, also known as scorpionates, are potent tridentate donors that effectively bind metal ions in a face-capping array. Hydrotris(3-phenylpyrazolyl)borate enforces a tetrahedral environment on Ni to model metalloenzymes. The syntheses and structural characterizations of a number of [hydrotris(3-phenylpyrazolyl)borato]nickel(II) aryloxides were performed to provide insight into the environment of the model active site; these compounds are chlorido[hydrotris(3-phenylpyrazolyl-κN)borato](3-phenyl-1H-pyrazole-κN)nickel(II) chloroform monosolvate, [Ni(CHBN)Cl(CHN)]·CHCl, (2), [hydrotris(3-phenylpyrazolyl-κN)borato](phenolato-κO)nickel(II), [Ni(CHBN)(CHO)], (3), (2,6-dimethylphenolato-κO)[hydrotris(3-phenylpyrazolyl-κN)borato]nickel(II) [Ni(CHBN)(CHO)], (4), (4-tert-butylphenolato-κO)[hydrotris(3-phenylpyrazolyl-κN)borato]nickel(II), [Ni(CHBN)(CHO)], (5), and [hydrotris(3-phenylpyrazolyl-κN)borato](phenolato-κO)(tetrahydrofuran-κO)nickel(II) tetrahydrofuran monosolvate, [Ni(CHBN)(CHO)(CHO)]·CHO, (6).

Synchrotron-based Nickel Mössbauer Spectroscopy.

We used a novel experimental setup to conduct the first synchrotron-based (61)Ni Mössbauer spectroscopy measurements in the energy domain on Ni coordination complexes and metalloproteins. A representative set of samples was chosen to demonstrate the potential of this approach. (61)NiCr2O4 was examined as a case with strong Zeeman splittings.

Acetate and acetamide complexes of [Ni(Me4[12]aneN4)]PF6: a tale of two ligands.

Although there are many examples of acetate complexes, acetamide complexes are virtually unknown. A side-by-side comparison in (acetato-κ(2)O,O')(1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane-κ(4)N)nickel(II) hexafluoridophosphate, [Ni(C2H3O2)(C12H28N4)]PF6, (1), and (acetamidato-κ(2)O,O')(1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane-κ(4)N)nickel(II) hexafluoridophosphate, [Ni(C2H4NO)(C12H28N4)]PF6, (2), shows the steric equivalence between these two ligands, suggesting that acetamide could be considered as a viable acetate replacement for electronic tuning.

Five-coordinate M(II)-semiquinonate (M = Fe, Mn, Co) complexes: reactivity models of the catechol dioxygenases.

A series of five-coordinate M(II)-semiquinonate (M = Fe, Mn, Co) complexes were synthesized and characterized, including the first example of a mononuclear Fe(II)-semiquinonate. Intermediates were observed in the reactions of M(II)-phenSQ (M = Fe, Co) with O2. Evidence for the relevance of these intermediates to the intradiol catechol dioxygenases was obtained by characterization of the oxidized semiquinone-derived product, muconic anhydride, resulting from the reaction of [PhTt(tBu)]Co(II)(3,5-DBSQ) with O2.

C-H activation by a diselenido dinickel(II) complex.

Addition of selenium to the nickel(I) complex, [Ni(Me4[12]aneN4)(CO)]PF6, effects a redox reaction leading to the diselenido dinickel(II) complex, {[(Ni(Me4[12]aneN4)]2(Se2)}(PF6)2, in 70% crystalline yield. The product's structure features a μ-η(2):η(2)-Se2 ligand with Se-Se bond length of 2.379(13) Å.

Coordination chemistry of poly(thioether)borate ligands.

This review traces the development and application of the tris(thioether)borate ligands, tripodal ligands with highly polarizable thioether donors. Areas of emphasis include the basic coordination chemistry of the mid-to-late first row transition metals (Fe, Ni, Co, Cu), and the role of the thioether substituent in directing complex formation, the modeling of zinc thiolate protein active sites, high-spin organo-iron and organo-cobalt chemistry, the preparation of monovalent complexes of Fe, Co and Ni, and dioxygen and sulfur activation by monovalent nickel complexes.

Spectroscopic and computational studies of a series of high-spin Ni(II) thiolate complexes.

The electronic structures of a series of high-spin Ni(II)-thiolate complexes of the form [PhTt(tBu)]Ni(SR) (R = CPh(3), 2; C(6)F(5), 3; C(6)H(5), 4; PhTt(tBu) = phenyltris((tert-butylthio)methyl)borate) have been characterized using a combined spectroscopic and computational approach. Resonance Raman (rR) spectroscopic data reveal that the nu(Ni-SR) vibrational feature occurs between 404 and 436 cm(-1) in these species. The corresponding rR excitation profiles display a striking de-enhancement behavior because of interference effects involving energetically proximate electronic excited states.

Spectroscopic and computational studies of a mu-eta(2):eta(2)-disulfido-bridged dinickel(II) species, [{(PhTt(tBu))Ni}(2)(mu-eta(2):eta(2)-S(2))]: comparison of side-on disulfido and peroxo bonding in (Ni(II))(2) and (Cu(II))(2) species.

In this study, a combined spectroscopic and computational approach has been employed to generate a detailed description of the electronic structure of a binuclear side-on disulfido (Ni(II))(2) complex, [{(PhTt(tBu))Ni}(2)(mu-eta(2):eta(2)-S(2))] (1, where PhTt(tBu) = phenyltris[(tert-butylthio)methyl]borate). The disulfido-to-Ni(II) charge-transfer transitions that dominate the electronic absorption spectrum have been assigned on the basis of time-dependent density functional theory (DFT) calculations. Resonance Raman spectroscopic studies of 1 have revealed that the S-S stretching mode occurs at 446 cm(-1), indicating that the S-S bond is weaker in 1 than in the analogous mu-eta(2):eta(2)-S(2) dicopper species.

Spectroscopic and computational studies of a trans-mu-1,2-disulfido-bridged dinickel species, [{(tmc)Ni}(2)(S(2))](OTf)(2): comparison of end-on disulfido and peroxo bonding in (Ni(II))(2) and (Cu(II))(2) species.

A powerful means of enhancing our understanding of the structures and functions of enzymes that contain nickel-sulfur bonds, such as Ni superoxide dismutase, acetyl-coenzyme A synthase/carbon monoxide dehydrogenase, [NiFe] hydrogenase, and methyl-CoM reductase, involves the investigation of model compounds with similar structural and/or electronic properties. In this study, we have characterized a trans-mu-1,2-disulfido-bridged dinickel(II) species, [{(tmc)Ni}(2)(S(2))](2+) (1, tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) by using electronic absorption, magnetic circular dichroism (MCD), and resonance Raman (rR) spectroscopic techniques, as well as density functional theory (DFT) and time-dependent DFT computational methods. Our computational results, validated on the basis of the experimental MCD data and previously reported (1)H NMR spectra, reveal that 1 is best described as containing two antiferromagnetically coupled high-spin Ni(II) centers.

A Series of Cyanide-Bridged Binuclear Complexes.

A series of cyanide-bridged binuclear complexes, ('S(3)')Ni-CN-M[Tp(tBu)] ('S(3)' = bis(2-mercaptophenyl)sulfide, Tp(tBu) = hydrotris(3-tert-butylpyrazolyl)borate, M = Fe (2-Fe), Co (2-Co), Ni (2-Ni), Zn (2-Zn)) was prepared by the coupling of K[('S(3)')Ni(CN)] with [Tp(tBu)]MX. The isostructural series of complexes was structurally and spectroscopically characterized. A similar coupling strategy was used to synthesize the anionic copper(I) analogue, Et4N{('S3')Ni-CN-Cu[Tp(tBu)]}, 2-Cu.

Synthetic analogs for evaluating the influence of N-H...S hydrogen bonds on the formation of thioester in acetyl coenzyme A synthase.

A series of square planar methylnickel(II) complexes, (dppe)Ni(Me)(SAr) (dppe = 1,2-bis(diphenylphosphino)ethane); 2. Ar = phenyl; 3. Ar = pentafluorophenyl; 4.

A high-spin organometallic Fe-S compound: structural and Mössbauer spectroscopic studies of [phenyltris((tert-butylthio)methyl)borate]Fe(Me).

The synthesis and structure of the pseudotetrahedral, sulfur-rich, high-spin organoiron(II) [phenyltris((tert-butylthio)methyl)borate]Fe(Me), [PhTt(tBu)]Fe(Me), 1, are reported. Low-temperature Mössbauer spectroscopic studies reveal an isomer shift of delta = 0.60(3) mm/s and DeltaE(Q) = 0.

Synthesis and spectroscopic identification of a mu-1,2-disulfidodinickel complex.

Reduction of elemental sulfur by a monovalent nickel precursor leads to a trans-1,2-mu-disulfidodinickel(II) complex assigned based on a combination of advanced spectroscopic methods in conjunction with density functional theory calculations. The disulfido linkage is characterized by an intense optical S --> Ni charge transfer transition at 650 nm, which causes a significant distortion of the Ni(2)S(2) core along an isotope-sensitive v(S-S) mode at 474 cm(-1), as demonstrated by the resonance Raman excitation profile of this vibrational feature.

Influence of ligand electronic effects on the structure of monovalent cobalt complexes.

The syntheses, spectroscopic properties, and structures of the monovalent cobalt complexes, [PhTt (tBu)]Co(L), 1-L {PhTt (tBu) = phenyltris[( tert-butylthio)methyl]borate; L = PPh 3, PMe 3, PEt 3, PMe 2Ph, PMePh 2, P(OPh) 3, CNBu (t)}, are described. Complexes 1-L are prepared via the sodium amalgam reduction of [PhTt (tBu)]CoCl in the presence of L. The complexes display magnetic moments and paramagnetically shifted (1)H NMR spectra consistent with triplet, S = 1, ground states.

Binuclear complexes containing a methylnickel moiety: relevance to organonickel intermediates in acetyl coenzyme A synthase catalysis.

A series of binuclear NiNi complexes supported by a single thiolate bridge and containing a methylnickel moiety have been prepared and fully characterized. The complexes represent structural analogues for the proposed organonickel intermediate in the acetyl coenzyme A synthase catalytic cycle. Variable temperature 31P NMR spectroscopy was used to examine dynamic behavior of the thiolate bridging interaction in two of the derivatives.

New synthetic routes to a disulfidodinickel(II) complex: characterization and reactivity of a Ni2(mu-eta2:eta2-S2) core.

Activation of elemental sulfur by the monovalent nickel complex [PhTt (tBu)]Ni(CO) [PhTt(tBu)=phenyl{tris[(tert-butylmethyl)thio]methyl}borate] generates the disulfidodinickel(II) complex 2. This species is alternatively accessible via thermal decomposition of [PhTt (tBu)]Ni(SCPh3). Spectroscopic, magnetic, and X-ray diffraction studies establish that 2 contains a mu-eta(2):eta(2)-S2 ligand that fosters antiferromagnetic exchange coupling between the Ni (II) ions.

Monovalent iron in a sulfur-rich environment.

A series of low-coordinate, paramagnetic iron complexes in a tris(thioether) ligand environment have been prepared. Reduction of ferrous {[PhTt(tBu)]FeCl}2 [1; PhTt(tBu) = phenyltris((tert-butylthio)methyl)borate] with KC8 in the presence of PR3(R = Me or Et) yields the high-spin, monovalent iron phosphine complexes [PhTt(tBu)]Fe(PR3) (2). These complexes provide entry into other low-valent derivatives via ligand substitution.

Structural, spectroscopic, and electrochemical properties of a series of high-spin thiolatonickel(II) complexes.

A series of high-spin thiolatonickel(II) complexes, [PhTttBu]Ni(SR) (PhTttBu = phenyltris((tert-butylthio)methyl)borate; 2, R = triphenylmethyl; 3, R = pentafluorophenyl; 4, R = phenyl), were synthesized via the reaction of [PhTttBu]Ni(NO3) (1) with thiols (RSH) in the presence of triethylamine. The [PhTttBu]Ni(SR) products were isolated and characterized by various physicochemical measurements including X-ray diffraction analyses. These thiolatonickel(II) complexes have a distorted trigonal pyramidal geometry with somewhat different tau values: 0.