Neutral and Cationic Bis-Chelate Monoorganosilicon(IV) Complexes of 1-Hydroxy-2-pyridinone

A series of spirocyclic monoorganosilicon compounds of the form RSi(OPO)2Cl [R = phenyl (1); p-tolyl (2); benzyl (3); Me (4); tBu (5); thexyl (6)] (OPO = 1-oxo-2-pyridinone) was synthesized and characterized by 1H , 13C, and 29Si NMR spectroscopy, X-ray crystallography, and elemental analysis. In the solid state, complexes 1, 2, and 3 are neutral and possess cis-OPO ligands in an octahedral arrangement, and complexes 4, 5, and 6 are cationic and possess effectively trans­-OPO ligands in nearly ideal square pyramidal geometries along the Berry-pseudorotation coordinate. In 4-6, chloride dissociation is attributed to the additive effect of multiple intermolecular C—H∙∙∙Cl interactions in their crystals. In DMSO-d6 solution, compounds 1-6 form cationic hexacoordinate DMSO adducts with trans-OPO ligands, all of which undergo dynamic isomerization with energy barriers of ~18-19 kcal/mol. Compounds with better leaving groups, (p-tolyl)Si(OPO)2X [X = I (7); X = triflate (8)], exhibit identical solution NMR spectra as 2, supporting anion dissociation in each. The fluoride derivatives RSi(OPO)2F [R = benzyl (9); Me (10)] exhibit hexacoordinate geometries with cis­-OPO ligands in the solid state and exhibit dynamic isomerization in solution. Overall, these studies indicate, in both the solid and solution states, that the trans-OPO ligand arrangement is favored when anions are dissociated and a cis­-OPO ligand arrangement when anions are coordinated

Chelation and Stereodynamic Equilibria in Neutral Hypercoordinate Organosilicon Complexes of 1-Hydroxy-2-pyridinone

A series of neutral organosilicon compounds, R3Si(OPO) [R = Me (1), Et (2), Ph (3)], cis-R2Si(OPO)2 [R = Me (4), Et (5), iPr (6), tBu (7), Ph (9)], (CH2)3Si(OPO)2 (8), and cis-R2Si(OPO)Cl [R = Me (10), Et (11)] (OPO = 1-oxo-2-pyridinone) have been prepared and fully characterized. X-ray crystallographic analyses show 1 to be tetracoordinate, 3, 7, and 10 to be pentacoordinate, and 4, 5, 6, 8, and 9 to be hexacoordinate. In the hexacoordinate structures, a mixture of diastereomers is observed in the form of C/N site disorder in each OPO ligand. Variable-temperature 13C and 29Si NMR studies indicate reversible Si←OC bond dissociation occurring in all pentacoordinate and hexacoordinate complexes to a varying degree with greater tendency toward dissociation in hydrogen-bonding donor solvents. Significant weakening of the dative Si←OC bond in 3 is observed in the co-crystallized adduct solvate, 3·Ph3SiOH·½C5H12, providing structural evidence for the decrease in coordination number of the OPO ligand by hydrogen-bonding donors. In the hexacoordinate complexes, increasing steric bulk of ancillary ligands also was found to promote dissociation. 1H and 13C VT-NMR studies of 4, 6, 8, and 9 indicate stereoisomerization equilibria concurrent with Si←OC bond dissociation proposed to occur through trigonal bipyramidal intermediates.

A second polymorph of [1,2-bis­(di-tert-butyl­phosphino)ethane]dichlorido­platinum(II)

The title complex, [PtCl2(C18H40P2)], contains a PtII center in an approximately square-planar geometry [cis angle range = 88.09 (3)–91.39 (3)°; twist angle = 1.19 (5)°]. The Pt—P bond lengths of 2.2536 (8) and 2.2513 (8) Å and the Pt—Cl bond lengths of 2.3750 (8) and 2.3588 (8) Å are normal. This crystal form is a polymorph of a structure reported previously [Harada, Kai, Yasuoka & Kasai (1976 ▶). Bull. Chem. Soc. Jpn, 49, 3472–3477]

[2,2′-Bis(diphenyl­phosphan­yl)-1,1′-binaphthyl-κ2 P,P′]chlorido(4-methyl­phenyl­sulfon­yl-κS)palladium(II) dichloro­methane tris­olvate monohydrate

In the title compound, [Pd(C7H7O2S)Cl(C44H32P2)]·3CH2Cl2·H2O, the geometry around the metal atom is distorted square planar, with a twist angle between the P—Pd—P and S—Pd—Cl planes of 28.11 (2)°. The two Pd—P bond lengths differ by about 0.04 Å and the biphosphane bite angle is slightly obtuse [92.92 (2)°]. There are three dichloro­methane and one water mol­ecule co-crystallized with the palladium mol­ecule, all with atoms in general positions. Alternating water and palladium mol­ecules form four-membered cyclic units through O—H⋯Cl and O—H⋯O hydrogen bonding. One of the dichloromethane solvent molecules is disordered over two positions in a 0.55:0.45 ratio

Bis(η5-penta­methyl­cyclo­penta­dien­yl)cobalt(II)

The crystal structure of the title compound, deca­methyl­cobaltocene, [Co(C10H15)2], has been determined. High-quality single crystals were grown from a cold saturated hexa­methyl­disiloxane solution. The structure is related to the manganese and iron analogs. The molecule has D 5d symmetry, with the Co atom in a crystallographic 2/m position. The cobalt–centroid(C5) distance is 1.71Å and the centroid(C5)–Co–centroid(C5) angle is 180°, by symmetry

TMEDA in Iron‐Catalyzed Hydromagnesiation: Formation of Iron(II)‐Alkyl Species for Controlled Reduction to Alkene‐Stabilized Iron(0)

N,N,N’,N’‐Tetramethylethylenediamine (TMEDA) has been one of the most prevalent and successful additives used in iron‐catalysis, finding application in reactions as diverse as cross‐coupling, C‐H activation and borylation. However, the role that TMEDA plays in these reactions remains largely undefined. Herein, studying the iron‐catalyzed hydromagnesiation of styrene derivatives using TMEDA has provided molecular‐level insight into the role of TMEDA in achieving effective catalysis. Key is the initial formation of TMEDA‐iron(II) alkyl species which undergo a controlled reduction to selectively form catalytically active styrene‐stabilized iron(0)‐alkyl complexes. While TMEDA is not bound to the catalytically active species, these active iron(0) complexes cannot be accessed in the absence of TMEDA. This mode of action, allowing for controlled reduction and access to iron(0) species, represents a new paradigm for the role of this important reaction additive in iron catalysis

El tercer sector es posa al dia amb la creació d'aplicacions mòbils socials

A series of mononuclear nickel­(II) thiolate complexes (Et₄N)­Ni­(X-pyS)₃ (Et₄N = tetraethylammonium; X = 5-H (<b>1a</b>), 5-Cl (<b>1b</b>), 5-CF₃ (<b>1c</b>), 6-CH₃ (<b>1d</b>); pyS = pyridine-2-thiolate), Ni­(pySH)₄(NO₃)₂ (<b>2</b>), (Et₄N)­Ni­(4,6-Y₂-pymS)₃ (Y = H (<b>3a</b>), CH₃ (<b>3b</b>); pymS = pyrimidine-2-thiolate), and Ni­(4,4′-Z-2,2′-bpy)­(pyS)₂ (Z = H (<b>4a</b>), CH₃ (<b>4b</b>), OCH₃ (<b>4c</b>); bpy = bipyridine) have been synthesized in high yield and characterized. X-ray diffraction studies show that <b>2</b> is square planar, while the other complexes possess tris-chelated distorted-octahedral geometries. All of the complexes are active catalysts for both the photocatalytic and electrocatalytic production of hydrogen in 1/1 EtOH/H₂O. When coupled with fluorescein (Fl) as the photosensitizer (PS) and triethylamine (TEA) as the sacrificial electron donor, these complexes exhibit activity for light-driven hydrogen generation that correlates with ligand electron donor ability. Complex <b>4c</b> achieves over 7300 turnovers of H₂ in 30 h, which is among the highest reported for a molecular noble metal-free system. The initial photochemical step is reductive quenching of Fl* by TEA because of the latter’s greater concentration. When system concentrations are modified so that oxidative quenching of Fl* by catalyst becomes more dominant, system durability increases, with a system lifetime of over 60 h. System variations and cyclic voltammetry experiments are consistent with a CECE mechanism that is common to electrocatalytic and photocatalytic hydrogen production. This mechanism involves initial protonation of the catalyst followed by reduction and then additional protonation and reduction steps to give a key Ni–H^–/N–H⁺ intermediate that forms the H–H bond in the turnover-limiting step of the catalytic cycle. A key to the activity of these catalysts is the reversible dechelation and protonation of the pyridine N atoms, which enable an internal heterocoupling of a metal hydride and an N-bound proton to produce H₂

Electronic Consequences of Ligand Substitution at Heterometal Centers in Polyoxovanadium Clusters: Controlling the Redox Properties through Heterometal Coordination Number

The rational control of the electrochemical properties of polyoxovanadate‐alkoxide clusters is dependent on understanding the influence of various synthetic modifications on the overall redox processes of these systems. In this work, the electronic consequences of ligand substitution at the heteroion in a heterometal‐functionalized cluster was examined. The redox properties of [V$_{5}$O$_{6}$(OCH$_{3}$)$_{12}$FeCl] (1‐[V$_{5}$FeCl] ) and [V$_{5}$O$_{6}$(OCH$_{3}$)$_{12}$Fe]X (2‐[V5Fe]X ; X=ClO$_{4}$, OTf) were compared in order to assess the effects of changing the coordination environment around the iron center on the electrochemical properties of the cluster. Coordination of a chloride anion to iron leads to an anodic shift in redox events. Theoretical modelling of the electronic structure of these heterometal‐functionalized clusters reveals that differences in the redox profiles of 1‐[V$_{5}$FeCl] and 2‐[V$_{5}$Fe]X arise from changes in the number of ligands surrounding the iron center (e.g., 6‐coordinate vs. 5‐coordinate). Specifically, binding of the chloride to the sixth coordination site appears to change the orbital interaction between the iron and the delocalized electronic structure of the mixed‐valent polyoxovanadate core. Tuning the heterometal coordination environment can therefore be used to modulate the redox properties of the whole cluster

Oxidized and reduced [2Fe-2S] clusters from an iron(I) synthon

© 2015 SBIC. Abstract Synthetic [2Fe-2S] clusters are often used to elucidate ligand effects on the reduction potentials and spectroscopy of natural electron-transfer sites, which can have anionic Cys ligands or neutral His ligands. Current synthetic routes to [2Fe-2S] clusters are limited in their feasibility with a range of supporting ligands. Here, we report a new synthetic route to synthetic [2Fe-2S] clusters, through oxidation of an iron(I) source with elemental sulfur. This method yields a neutral diketiminate-supported [2Fe-2S] cluster in the diiron(III)-oxidized form. The oxidized [2Fe-2S] cluster can be reduced to a mixed valent iron(II)-iron(III) compound. Both the diferric and reduced mixed valent clusters are characterized using X-ray crystallography, Mössbauer spectroscopy, EPR spectroscopy and cyclic voltammetry. The reduced compound is particularly interesting because its X-ray crystal structure shows a difference in Fe-S bond lengths to one of the iron atoms, consistent with valence localization. The valence localization is also evident from Mössbauer spectroscopy

Efficient Bimolecular Mechanism of Photochemical Hydrogen Production Using Halogenated Boron-Dipyrromethene (Bodipy) Dyes and a Bis(dimethylglyoxime) Cobalt(III) Complex

A series of Boron-­dipyrromethene (Bodipy) dyes were used as photosensitizers for photochemical hydrogen production in conjunction with [CoIII(dmgH)2pyCl] (where dmgH = dimethylglyoximate, py = pyridine) as the catalyst and triethanolamine (TEOA) as the sacrificial electron donor. The Bodipy dyes are fully characterized by electrochemistry, x-­‐ray crystallography, quantum chemistry calculations, femtosecond transient absorption and time-­‐resolved fluorescence, as well as in long-­‐term hydrogen production assays. Consistent with other recent reports, only systems containing halogenated chromophores were active for hydrogen production, as the long-­‐lived triplet state is necessary for efficient bimolecular electron transfer. Here, it is shown that the photostability of the system improves with Bodipy dyes containing a mesityl group versus a phenyl group, which is attributed to increased electron donating character of the mesityl substituent. Unlike previous reports, the optimal ratio of chromophore to catalyst is established and shown to be 20:1, at which point this bimolecular dye/catalyst system performs 3-­‐4 times better than similar chemically linked systems. We also show that the hydrogen production drops dramatically with excess catalyst concentration. The maximum turnover number of ~700 (with respect to chromophore) is obtained under the following conditions: 1.0 × 10­‐4 M [Co(dmgH)2pyCl], 5.0 × 10-6 M Bodipy dye with iodine and mesityl substituents, 1:1 v:v (10% aqueous TEOA):MeCN (adjusted to pH 7), and irradiation by light with λ \u3e 410 nm for 30 h. This system, containing discrete chromophore and catalyst, is more active than similar linked Bodipy – Co(dmg)2 dyads recently published, which, in conjunction with our other measurements, suggests that the nominal dyads actually function bimolecularly