Phoenix

A novel chiral coordination polymer, [Cu­(C₆H₅CH­(OH)­COO)­(μ-C₆H₅CH­(OH)­COO)] (<b>1</b>-L and <b>1</b>-D), was synthesized through a reaction of copper acetate with l-mandelic acid at room temperature. Although previously reported copper mandelate prepared by hydrothermal reaction was a centrosymmetric coordination polymer because of the racemization of mandelic acid, the current coordination polymer shows noncentrosymmetry and a completely different structure from that previously reported. The X-ray crystallography for <b>1</b>-L revealed that the copper center of the compound showed a highly distorted octahedral structure bridged by a chiral mandelate ligand in the unusual coordination mode to construct a one-dimensional (1D) zigzag chain structure. These 1D chains interdigitated each other to give a layered structure as a result of the formation of multiple aromatic interactions and hydrogen bonds between hydroxyl and carboxylate moieties at mandelate ligands. The coordination polymer <b>1</b>-L belongs to the noncentrosymmetric space group of C2 to show piezoelectric properties and second harmonic generation (SHG) activity

Synthesis and Protonation of N‑Heterocyclic-Carbene-Supported Dinitrogen Complexes of Molybdenum(0)

The N-heterocyclic-carbene-supported dinitrogen (N₂) complexes of molybdenum(0) <i>trans</i>-Mo­(N₂)₂(L^R)₄ (L^R = 1,3-R₂-4,5-dimethyl­imidazol-2-ylidene; <b>2a</b>: R = Me, <b>2b</b>: R = Et) and <i>mer</i>-Mo­(N₂)₃(L^R)₃ (<b>3</b>: R = ⁱPr) were synthesized from MoCl₄(THF)₂ and KC₈ in the presence of L^R under an atmosphere of N₂. In agreement with the characteristically strong σ-donation from the N-heterocyclic carbenes to molybdenum, complexes <b>2a</b>, <b>2b</b>, and <b>3</b> exhibited lower N–N stretching frequencies in their IR spectra and displayed longer N–N as well as shorter Mo–N bond lengths in their molecular structures relative to corresponding phosphine analogues. Although protonation of the molybdenum-bound N₂ ligands in these phosphine complexes with H₂O is unprecedented, it was accomplished for <b>2a</b>, <b>2b</b>, and <b>3</b> under concomitant release of ammonia

Synthesis of V/Fe/S Clusters Using Vanadium(III) Thiolate Complexes Bearing a Phenoxide-Based Tridentate Ligand

Vanadium­(III) thiolate complexes carrying a phenoxide-based tridentate ligand were prepared from the reactions of V­(NMe₂)₄ with the protonated forms of tridentate ligands (H₂­(O,P,O) = bis­(3,5-di-<i>tert</i>-butyl-2-hydroxy­phenyl)­phenylphosphine or H₂(O,O,O) = bis­(3,5-di-<i>tert</i>-butyl-2-hydroxy­phenyl)­phenyl­phosphine­oxide) and thiols (HSR; R = mesityl (Mes), 2,4,6-<i>ⁱ</i>Pr₃C₆H₂ (Tip)). The vanadium–thiolate complexes were subjected to the V/Fe/S cluster synthesis via treatment with an Fe­(II) thiolate complex [(TipS)­Fe]₂­(μ-SDmp)₂ (<b>4</b>, Dmp = 2,6-(mesityl)₂­C₆H₃) and elemental sulfur in toluene, leading to the formation of two new V/Fe/S clusters. One is an edge-bridged double-cubane-type [VFe₃S₄]-[VFe₃S₄] cluster [(O,P,O)­VFe₃S₄­(SDmp)­(HNMe₂)]₂ (<b>5</b>) having face-capping tridentate (O,P,O) ligands on vanadium atoms. The other is a [VFe₃S₄-Fe] cluster [(μ-O,O,O)­VFe₃S₄­(SDmp)­(STip)­Fe­(μ-SDmp)] (<b>6</b>), the core of which consists of a cubane-type [VFe₃S₄] unit and an external iron atom. The external iron is bound to an SDmp ligand and two oxygen atoms of the tridentate (O,O,O) ligand. Cluster <b>6</b> is structurally relevant to the active site of nickel-dependent CO dehydrogenase, and their common structural features include a cubane-type unit with a heterometal, one more iron atom besides the cubane unit, and a bridging ligand between the external iron and the heterometal of the cubane unit

N‑Heterocyclic Carbene Complexes of Three- and Four-Coordinate Fe(I)

N-heterocyclic carbene complexes of three- and four-coordinate Fe­(I), [Fe­(L^R)₄]­[PF₆] (L^R = 1,3-R₂-4,5-dimethylimidazol-2-ylidene, R = Me (<b>2</b>), Et (<b>3</b>), ⁱPr (<b>4</b>)) and [Fe­(L^Mes)₂(THF)]­[PF₆] (<b>5</b>) (L^Mes = 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene), were synthesized from successive reactions of [Fe­(toluene)₂]­[PF₆]₂ with 1 equiv of KC₈ and L^R (4 equiv for R = Me, Et, ⁱPr; 2 equiv for R = Mes). The coordination geometry of the iron atom in these complexes varies depending on the nature of the R group in L^R: a tetrahedral geometry was observed for <b>2</b>, a square-planar one for <b>3</b> and <b>4</b>, and a three-coordinate T-shaped one for <b>5</b>. In solution, <b>4</b> releases L^iPr ligand(s), while the L^R ligands of the other Fe­(I) complexes remain firmly bound. Tetrahedral <b>2</b> and T-shaped <b>5</b> contain a high-spin (<i>S</i> = ³/₂) Fe­(I) center, whereas square-planar <b>3</b> and <b>4</b> contain Fe­(I) in the low-spin state (<i>S</i> = ¹/₂)

Synthesis and Protonation of N‑Heterocyclic-Carbene-Supported Dinitrogen Complexes of Molybdenum(0)

The N-heterocyclic-carbene-supported dinitrogen (N₂) complexes of molybdenum(0) <i>trans</i>-Mo­(N₂)₂(L^R)₄ (L^R = 1,3-R₂-4,5-dimethyl­imidazol-2-ylidene; <b>2a</b>: R = Me, <b>2b</b>: R = Et) and <i>mer</i>-Mo­(N₂)₃(L^R)₃ (<b>3</b>: R = ⁱPr) were synthesized from MoCl₄(THF)₂ and KC₈ in the presence of L^R under an atmosphere of N₂. In agreement with the characteristically strong σ-donation from the N-heterocyclic carbenes to molybdenum, complexes <b>2a</b>, <b>2b</b>, and <b>3</b> exhibited lower N–N stretching frequencies in their IR spectra and displayed longer N–N as well as shorter Mo–N bond lengths in their molecular structures relative to corresponding phosphine analogues. Although protonation of the molybdenum-bound N₂ ligands in these phosphine complexes with H₂O is unprecedented, it was accomplished for <b>2a</b>, <b>2b</b>, and <b>3</b> under concomitant release of ammonia

N‑Heterocyclic Carbene Complexes of Three- and Four-Coordinate Fe(I)

N-heterocyclic carbene complexes of three- and four-coordinate Fe­(I), [Fe­(L^R)₄]­[PF₆] (L^R = 1,3-R₂-4,5-dimethylimidazol-2-ylidene, R = Me (<b>2</b>), Et (<b>3</b>), ⁱPr (<b>4</b>)) and [Fe­(L^Mes)₂(THF)]­[PF₆] (<b>5</b>) (L^Mes = 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene), were synthesized from successive reactions of [Fe­(toluene)₂]­[PF₆]₂ with 1 equiv of KC₈ and L^R (4 equiv for R = Me, Et, ⁱPr; 2 equiv for R = Mes). The coordination geometry of the iron atom in these complexes varies depending on the nature of the R group in L^R: a tetrahedral geometry was observed for <b>2</b>, a square-planar one for <b>3</b> and <b>4</b>, and a three-coordinate T-shaped one for <b>5</b>. In solution, <b>4</b> releases L^iPr ligand(s), while the L^R ligands of the other Fe­(I) complexes remain firmly bound. Tetrahedral <b>2</b> and T-shaped <b>5</b> contain a high-spin (<i>S</i> = ³/₂) Fe­(I) center, whereas square-planar <b>3</b> and <b>4</b> contain Fe­(I) in the low-spin state (<i>S</i> = ¹/₂)

Oxido-Bridged Di-, Tri-, and Tetra-Nuclear Iron Complexes Bearing Bis(trimethylsilyl)amide and Thiolate Ligands

A series of di-, tri-, and tetra-nuclear iron-oxido clusters with bis­(trimethylsilyl)­amide and thiolate ligands were synthesized from the reactions of Fe­{N­(SiMe₃)₂}₂ (<b>1</b>) with 1 equiv of thiol HSR (R = C₆H₅ (Ph), 4-^tBuC₆H₄, 2,6-Ph₂C₆H₃ (Dpp), 2,4,6-ⁱPr₃C₆H₂ (Tip)) and subsequent treatment with O₂. The trinuclear clusters [{(Me₃Si)₂N}­Fe]₃(μ₃-O)­{μ-S­(4-RC₆H₄)}₃ (R = H (<b>3a</b>), ^tBu (<b>3b</b>)) were obtained from the reactions of <b>1</b> with HSPh or HS­(4-^tBuC₆H₄) and O₂, while we isolated a tetranuclear cluster [{(Me₃Si)₂N}₂Fe₂(μ-SDpp)]₂(μ₃-O)₂ (<b>4</b>) as crystals from an analogous reaction with HSDpp. Treatment of a tertrahydrofuran (THF) solution of <b>1</b> with HSTip and O₂ resulted in the formation of a dinuclear complex [{(Me₃Si)₂N}­(TipS)­(THF)­Fe]₂(μ-O) (<b>5</b>). The molecular structures of these complexes have been determined by X-ray crystallographic analysis

Interconversion between [Fe₄S₄] and [Fe₂S₂] Clusters Bearing Amide Ligands

Structural conversion of [Fe₄S₄] clusters into [Fe₂S₂] clusters has been suggested to be a fundamental process for some O₂-sensing proteins. While the formation of [Fe₂S₂] clusters from synthetic [Fe₄S₄] clusters has been unprecedented, an all-ferric [Fe₄S₄]⁴⁺ cluster Fe₄S₄{N­(SiMe₃)₂}₄ (<b>1</b>) was found to split in the presence of pyridines, giving [Fe₂S₂] clusters Fe₂S₂­{N­(SiMe₃)₂}₂(L)₂ (<b>2</b>, L = pyridines). The structural conversion between [Fe₄S₄] and [Fe₂S₂] clusters appeared to be reversible, and the thermodynamic parameters for the equilibrium reactions between <b>1</b> + L and <b>2</b> were determined. Assembly of two [Fe₂S₂] clusters was also induced by chemical reductions of Fe₂S₂­{N­(SiMe₃)₂}₂(Py)₂ (Py = pyridine), and the resultant [Fe₄S₄] clusters [<b>1</b>]⁻ and [<b>1</b>]^2– were found to split into two [Fe₂S₂] clusters by oxidation with [Cp₂Fe]⁺ in the presence of pyridine

Catalytic Generation of Borenium Ions by Cooperative B–H Bond Activation: The Elusive Direct Electrophilic Borylation of Nitrogen Heterocycles with Pinacolborane

The B–H bond of typical boranes is heterolytically split by the polar Ru–S bond of a tethered ruthenium­(II) thiolate complex, affording a ruthenium­(II) hydride and borenium ions with a dative interaction with the sulfur atom. These stable adducts were spectroscopically characterized, and in one case, the B–H bond activation step was crystallographically verified, a snapshot of the σ-bond metathesis. The borenium ions derived from 9-borabicyclo[3.3.1]­nonane dimer [(9-BBN)₂], pinacolborane (pinBH), and catecholborane (catBH) allowed for electrophilic aromatic substitution of indoles. The unprecedented electrophilic borylation with the pinB cation was further elaborated for various nitrogen heterocycles

Dinuclear Iron(0) Complexes of N‑Heterocyclic Carbenes

The synthesis, structures, and reactivity of dinuclear Fe⁰ complexes of N-heterocyclic carbenes (NHCs, denoted as L) are reported. The NHC adducts of ferric chloride (L)­FeCl₃ were prepared from the reactions of FeCl₃ with L in toluene. The reduction of (L)­FeCl₃ with KC₈ resulted in the formation of the dinuclear Fe⁰ complexes Fe₂{μ-η¹(C):η⁶(arene)-L}₂ (<b>2a</b>, L = 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene (IMes); <b>2b</b>, L = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene (IPr)), in which NHC ligands bridge two iron atoms using one of the arene rings as an η⁶ ligand. Their magnetic properties are different: <b>2a</b> is paramagnetic and <b>2b</b> is diamagnetic. The dinuclear complexes <b>2a</b>,<b>b</b> serve as precursors for monomeric (NHC)­Fe⁰ species, and treatment of <b>2a</b>,<b>b</b> with 1 atm of CO led to the formation of (L)­Fe­(CO)₄. Complex <b>2a</b> was found to react with 1-azidoadamantane, giving rise to the dinuclear tetrazene complex (IMes)­Fe­(μ-NAd)₂Fe­(AdNNNNAd) (<b>4</b>)