Hydrogen Peroxide Coordination to Cobalt(II) Facilitated by Second‐Sphere Hydrogen Bonding

M(H₂O₂) adducts have been postulated as intermediates in biological and industrial processes; however, only one observable M(H₂O₂) adduct has been reported, where M is redox‐inactive zinc. Herein, direct solution‐phase detection of an M(H₂O₂) adduct with a redox‐active metal, cobalt(II), is described. This Co^II(H₂O₂) compound is made observable by incorporating second‐sphere hydrogen‐bonding interactions between bound H₂O₂ and the supporting ligand, a trianionic trisulfonamido ligand. Thermodynamics of H₂O₂ binding and decay kinetics of the Co^II(H₂O₂) species are described, as well as the reaction of this Co^II(H₂O₂) species with Group 2 cations.     

Tellurium Chloride Complexes in Nonaqueous Solutions

Tellurium(IV) complexes (R₄N)₂[TeCl₆] (T6), (R₄N)[TeCl₅] (T5), and (R₄N)[TeCl₄OH] (T4), where (R₄N)⁺ is tetrabutyl, tetraoctyl, and trialkyl benzyl ammonium cations, were synthesized. Tellurium distribution between aqueous HCl solutions and trialkyl benzyl ammonium chloride solution in caprylic acid was studied. The ¹²⁵Te NMR spectra of aqueous HCl solutions of tellurium have a single averaged peak, whose chemical shift (CS) depends on the acid concentration. ¹²⁵Te NMR spectroscopy has shown that the T4 complex in nonaqueous solutions is kinetically inert and the ligand exchange with the T6 and T5 complexes is retarded. In contrast, the T5 and T6 complexes, when simultaneously present in nonaqueous solutions, rapidly exchange ligands. ¹²⁵Te NMR, IR, Raman, and UV spectroscopic studies have shown that under standard conditions, the reaction (Bu₄N)[TeCl₅]+Bu₄NCl = (Bu₄N)₂[TeCl₆] G⁰ = -19.1(1 ± 0.3) kJ/mol and H⁰ = -6.5(1 ± 0.2) kJ/mol) takes place in methylene chloride solution. The symmetry groups of the synthesized complexes in the solid state and CSs for tellurium solutions (0.2 gatom/liter Te) in methylene chloride were determined: O_h and –58 ppm for T6; C_4v and +75 ppm for T5; and C_3v and +54 ppm for T4 (CS = 0 for a 0.2 mol/liter TeO₂ solution in 11.4 mol/liter HCl).     

Synthesis and Coordination Ability of a Donor-Stabilised Bis-Phosphinidene

Chelating phosphines have long been a mainstay as efficient directing ligands in transition-metal catalysis. Low-valent derivatives, namely chelating phosphinidenes, are to date unknown, and could lead to chelating complexes containing more than one metal centre due to the intrisic capacity of phosphinidenes to bind two metal fragments at one P-centre. Here we describe the synthesis of the first such chelating bis-phosphinidene ligand, XantP₂ ( 2 ), generated by the reduction of a diphosphino xanthene derivative, Xant(PH₂)₂ ( 1 ) with ^iPrNHC (^iPrNHC=[:C{N(iPr)C(H)}₂]). Initial studies have shown that this novel chelating ligand can act as a bidentate ligand towards element dihalides (i.e. FeCl₂, ZnI₂, GeCl₂, SnBr₂), forming cationic complexes with the tetryl elements. In contrast, XantP₂ demonstrates an ability to bind multiple metal centres in the reaction with CuCl, leading to a cationic Cu₃P₃ ring complex, with Cu centres bridged by phosphinidene arms. Density Functional Theory calculations show that 2 indeed holds 4 lone pairs of electrons, shedding further light on the coordination capacity for this novel ligand class through observation of directionality and hybridisation of these electron pairs.     

Coordination Patterns of the Diphenyl-Phosphinodithioato Ligand in Tellurium Compounds

Abstract.

Solid state monomeric structures with monometallic biconnective (bidentate) diphenylphosphinodithioato groups were found in Ph₂Te(S₂PPh₂)₂ (1) or [Ph₃Te][S₂PPh₂] (2), while in the polymeric associations [Te₂(S₂PPh₂)₂]_n (3) and [PhTeS(S)PPh₂]_n (4) bimetallic biconnective (bridging) and monodentate biconnective (bridging) patterns were established by X-ray diffractometry. [Te(S₂PPh₂)₃]₂ (5) exhibits an unusual dimeric structure, with both monometallic biconnective and bimetallic triconnective ligand units.     

Structurally Defined Allyl Compounds of Main Group Metals: Coordination and Reactivity

Organometallic allyl compounds are important as allylation reagents in organic synthesis, as polymerization catalysts, and as volatile metal precursors in material science. Whereas the allyl chemistry of synthetically relevant transition metals such as palladium and of the lanthanoids is well‐established, that of main group metals has been lagging behind. Recent progress on allyl complexes of Groups 1, 2, and 12–16 now provides a more complete picture. This is based on a fundamental understanding of metal–allyl bonding interactions in solution and in the solid state. Furthermore, reactivity trends have been rationalized and new types of allyl‐specific reactivity patterns have been uncovered. Key features include 1) the exploitation of the different types of metal–allyl bonding (highly ionic to predominantly covalent), 2) the use of synergistic effects in heterobimetallic compounds, and 3) the adjustment of Lewis acidity by variation of the charge of allyl compounds.     

Reaching Milestones in the Oxygenation Chemistry of Magnesium Alkyls: towards Intimate States of O2 Activation and the First Monomeric Well-Defined Magnesium Alkylperoxide

Despite decades of extensive studies on the reactivity of magnesium alkyls towards O₂, the isolation and structural characterization of discrete products of these reactions still remains a challenge. Although the formation of the most frequently encountered magnesium alkoxides through unstable alkylperoxide intermediates has commonly been accepted, the latter species have been elusive for over 100 years. Probing the oxygenation of a seemingly simple well-defined neo-pentylmagnesium complex stabilized by a β-diketiminate ligand, (^dippBDI)MgCH₂CMe₃, we report on the isolation and structure characterization of both a dimeric magnesium alkoxide [(^dippBDI)Mg(μ-OCH₂CMe₃)]₂ and the first example of monomeric magnesium alkylperoxide [(^dippBDI)Mg(thf)OOCH₂CMe₃] (^dippBDI=[(ArNCMe)₂CH]⁻ and Ar=C₆H₃iPr₂-2,6). The formation of monomeric magnesium alkylperoxide demonstrates a crucial role of an additional Lewis base for stabilizing the most elusive oxygenation products likely due to increasing of the electron density on the metal centre. Moreover, the ¹H NMR studies at −80 °C revealed that the dissociation of a coordinated Lewis base from the solvated complex (^dippBDI)Mg(L)CH₂CMe₃ (where L=thf or 4-methylpyridine) is likely not required prior to the effective attack of an O₂ molecule on the metal centre and the four-coordinate alkylmagnesium complex reacts smoothly with O₂ under these conditions. The results can be expected to aid future engineering of various organomagnesium/O₂-based reaction systems.     

Dicationic Tellurium Analogues of the Classic N‐Heterocyclic Carbene

The synthesis and comprehensive characterization of the first dicationic tellurium analogues of N‐heterocyclic carbenes (NHCs) has been reported, in both the +2 and +4 oxidation states. For the +2 oxidation state, a base‐stabilized form of TeCl₂ is used as the starting material. The dications are isolated by means of halide metathesis and the solid‐state structures confirm the previously calculated diimine bonding arrangement. For Te^IV, a diamine is used in a high‐yielding dehydrohalogen coupling reaction from TeCl₄. The dicationic NHC analogue is isolated in a base‐stabilized form through halide abstraction and subsequent coordination by pyridine.     

Periodicity in Structure,Bonding, and Reactivity for p-Block Complexes of a Geometry Constraining Triamide Ligand

The use of pincer ligands to access non-VSEPR geometries at main-group centers is an emerging strategy for eliciting new stoichiometric and catalytic reactivity. As part of this effort, several different tridentate trianionic substituents have to date been employed at a range of different central elements, providing a patchwork dataset that precludes rigorous structure–function correlation. An analysis of periodic trends in structure (solid, solution, and computation), bonding, and reactivity based on systematic variation of the central element (P, As, Sb, or Bi) with retention of a single tridentate triamide substituent is reported herein. In this homologous series, the central element can adopt either a bent or planar geometry. The tendency to adopt planar geometries increases descending the group with the phosphorus triamide ( 1 ) and its arsenic congener ( 2 ) exhibiting bent conformations, and the antimony ( 3 ) and bismuth ( 4 ) analogues exhibiting a predominantly planar structure in solution. This trend has been rationalized using an energy decomposition analysis. A rare phase-dependent dynamic covalent dimerization was observed for 3 and the associated thermodynamic parameters were established quantitatively. Planar geometries were found to engender lower LUMO energies and smaller band gaps than bent ones, resulting in different reactivity patterns. These results provide a benchmark dataset to guide further research in this rapidly emerging area.     

Trifluoromethyl Derivatives of Benzooxatellurole

Replacement of the iodine atom in an iodine (III) CF₃‐transfer reagent with a Te‐aryl moiety was accomplished in a three‐step synthetic sequence. Three compounds of this type have been prepared, two of which were characterized by X‐ray diffraction. Single crystal structures were also obtained for three related Te(IV) compounds unreported so far ( 4a , 4b , 6b ). Comparison with the iodine (III) analogues indicate a large degree of structural similarity, however these species display an interesting decomposition pathway under thermal conditions. In addition to the expected Te?CF₃ bond cleavage, C?F bond cleavage is also observed, unlike in the case of iodine (III) compounds.     

Lower main-group element complexes with a soft scorpionate ligand: the structural influence of stereochemically active lone pairs

The syntheses and structures of complexes of the fifth period elements indium and antimony, and the sixth period element bismuth with the soft scorpionate ligand, hydrotris(methimazolyl)borate (Tm(Me)) are reported. A considerable variety of structural motifs were obtained by reaction of the main-group element halide and NaTm(Me). The indium(III) complexes took the form [In(kappa(3)-Tm(Me))(2)](+). This motif could not, however, be isolated for antimony(III), the dominant product being [Sb(kappa(3)-Tm(Me))(kappa(1)-Tm(Me))X] (X = Br, I). An iodo-bridged species [Sb(kappa(3)-Tm(Me))I(mu(2)-I)](2), analogous to a previously reported bismuth complex, was also isolated. Reaction of antimony(III) acetate with NaTm(Me) results in a remarkable species in which three different ligand binding modes are observed. In each antimony complex the influence of the nonbonded electron pair is observed in the structure. Bismuth halides form complexes analogous to those of antimony, with directional lone pairs, but in addition, reaction of Bi(NO(3))(3) with NaTm(Me) results in a complex with a regular S(6) coordination sphere and a nonstereochemically active lone pair. Comparisons are drawn with known Tm(Me) complexes of As, Sn, and Bi in which the stereochemical influence of the lone pairs is negligible and with Tm(Me) complexes of Te and Bi in which the lone pairs are stereochemically active. This study highlights the ability of Tm(Me) to coordinate in a variety of modes as dictated by the metal centre with no adverse effects on the stability of the complexes formed.     

碲的形态分析进展

综述了近年来国内外碲的无机、有机形态分析进展。因碲在环境样品中的含量低、分散,存在形式较多,建立快速、准确的碲形态分析方法是值得进一步探讨的问题。     

A Germanium(II) Cation with [1+1] Coordination

Breaking the molecular symmetry by protonation of germylene 1 is the key step in the synthesis of the germyliumylidene 2 , which is stabilized by an intramolecular interaction with a distant imido group.

     

Interpnictogen Cations: Exploring New Vistas in Coordination Chemistry

Pnictine derivatives can behave as both 2e^? donors (Lewis bases) and 2e^? acceptors (Lewis acids). As prototypical ligands in the coordination chemistry of transition metals, amines and phosphines also form complexes with p‐block Lewis acids, including a variety of pnictogen‐centered acceptors. The inherent Lewis acidity of pnictogen centers can be enhanced by the introduction of a cationic charge, and this feature has been exploited in recent years in the development of compounds resulting from coordinate Pn–Pn and Pn–Pn′ interactions. These compounds offer the unusual opportunity for homoatomic coordinate bonding and the development of complexes that possess a lone pair of electrons at the acceptor center. This Review presents new directions in the systematic extension of coordination chemistry from the transition series into the p‐block.     

Coordination modes of 2-mercapto-1,3-benzothiazolate in gallium and indium complexes

2-Mercapto-1,3-benzothiazole (mbztH) may act as a chelating or bridging ligand. In this study, reactions of mbztH with Me₃Ga and Me₃In were examined. The products were characterized by NMR spectroscopy, elemental analyses, melting point, and molecular weight determinations. Formation of mononuclear chelating complexes Me₂M(mbzt) (M = Ga, In) was observed in solutions. Crystallization of Me₂M(mbzt) yielded uncommon non-symmetrical dinuclear complexes Me₄M₂(mbzt)₂, in which one metal is bonded to two sulfurs and the other to two nitrogens.     

NHC→SiCl4: An Ambivalent Carbene‐Transfer Reagent

The addition of BCl₃ to the carbene‐transfer reagent NHC→SiCl₄ (NHC=1,3‐dimethylimidazolidin‐2‐ylidene) gave the tetra‐ and pentacoordinate trichlorosilicon(IV) cations [(NHC)SiCl₃]⁺ and [(NHC)₂SiCl₃]⁺ with tetrachloroborate as counterion. This is in contrast to previous reactions, in which NHC→SiCl₄ served as a transfer reagent for the NHC ligand. The addition of BF₃ ? OEt₂, on the other hand, gave NHC→BF₃ as the product of NHC transfer. In addition, the highly Lewis acidic bis(pentafluoroethyl)silane (C₂F₅)₂SiCl₂ was treated with NHC→SiCl₄. In acetonitrile, the cationic silicon(IV) complexes [(NHC)SiCl₃]⁺ and [(NHC)₂SiCl₃]⁺ were detected with [(C₂F₅)SiCl₃]^? as counterion. A similar result was already reported for the reaction of NHC→SiCl₄ with (C₂F₅)₂SiH₂, which gave [(NHC)₂SiCl₂H][(C₂F₅)SiCl₃]. If the reaction medium was changed to dichloromethane, the products of carbene transfer, NHC→Si(C₂F₅)₂Cl₂ and NHC→Si(C₂F₅)₂ClH, respectively, were obtained instead. The formation of the latter species is a result of chloride/hydride metathesis. These compounds may serve as valuable precursors for electron‐poor silylenes. Furthermore, the reactivity of NHC→SiCl₄ towards phosphines is discussed. The carbene complex NHC→PCl₃ shows similar reactivity to NHC→SiCl₄, and may even serve as a carbene‐transfer reagent as well.