Synthesis of metallasiloxanes of group 13-15 and their application in catalysis

973 Program [2012CB821704]; National Nature Science Foundation of China [91027014, 20972129]; National Key Lab Foundation for PCOSS [20923004]; Innovative Research Team Program [IRT1036]Herein we report on the synthesis, characterization and catalytic application of metallasiloxanes of group 13-15. Reactions of R(Me)Si(OH)(2) (R = N(SiMe3)-2,6-iPr(2)C(6)H(3)) (A) with Bi(NEt2)(3), Sb(NEt2)(3), Ge[N(SiMe3)(2)](2) and AlMe3 afforded [R(Me)SiO2BiNEt2](2) (1), [R(Me)SiO2SbOSi(OH)(Me)R](2) (2), [R(Me)SiO2](3)(GeH)(2) (3), and [R(Me)SiO2AlMe(THF)](2) (4), respectively. Reactions of RSi(OH)(3) (B) with Bi(NEt2)(3) and AlMe3 produced complexes (RSiO3Bi)(4) (5) and (RSiO3)(2)[AlMe(THF)](3) (6). Compounds 1-6 have been characterized by IR and NMR spectroscopy, single crystal X-ray structure and elemental analysis. Each of the compounds 1, 2 and 4 features an eight-membered ring of composition Si2O4Bi2, Si2O4Sb2 and Si2O4Al2, while 3 and 6 exhibit a bicyclic structure with the respective skeletons of Si3O6Ge2 and Si2O6Al3. Compound 5 has a cubic core of Si4O12Bi4. Compounds 1-6 exhibit very good catalytic activity in the addition reaction of trimethylsilyl cyanide (TMSCN) with benzaldehyde. Compound 5 was found to be the best catalyst and its activity was probed in the reactions of TMSCN with a number of aldehydes and ketones

Synthesis, characterization and oxygen atom transfer reactivity of a pair of Mo(iv)O- and Mo(vi)O2-enedithiolate complexes – a look at both ends of the catalytic transformation

Two new molybdenum complexes (Bu4N)2[MoIVO(ntdt)2] (1) and (Ph4P)2[MoVIO2(ntdt)2] (2) (ntdt = 2-naphthyl-1,4-dithiolate) were synthesized using asymmetric dithiolene precursors and were characterized as structural models for the active site of arsenite oxidase, a molybdopterin bearing enzyme. The ligand was obtained readily by a two-step synthesis starting from 2-bromo-2′-acetonapthone. Complexes 1 and 2 were obtained by reaction of the resulting 4-naphthyl-1,3-dithiol-2-one with metal precursors trans-[MoO2(CN)4]4- and cis-[MoO2(NCS)4]2- respectively. Notably and to the best of our knowledge, this work constitutes the first utilization of the latter in dithiolene chemistry. 1 and 2 were characterized by NMR and IR spectroscopy, by cyclic voltammetry, mass spectrometry, elemental analysis and in case of 1 by single-crystal X-ray diffraction. The molecular structure of compound 1 exhibits the less common cis isomeric form (i.e. the naphthyl groups of the 2-naphthyl-1,4-dithiolate ligands are located on the same side of the MoS4 square base). Structural, spectroscopic and electrochemical data are discussed in context. The catalytic oxo-transfer properties of 1 and 2 were investigated by oxo-transfer reactions from DMSO to PPh3 with varied catalyst:PPh3 ratios. Interestingly, the oxygen atom transfer reaction from DMSO to PPh3 starting from compound 2 was found to be more efficient under the given conditions than when the reduced catalyst 1 was employed as initial species. The two catalytic systems are discussed and compared in terms of their reactivity

A crystallographic and Mo K-edge XAS study of molybdenum oxo bis-, mono-, and non-dithiolene complexes : first-sphere coordination geometry and noninnocence of ligands

Ten square-based pyramidal molybdenum complexes with different sulfur donor ligands, that is, a variety of dithiolenes and sulfides, were prepared, which mimic coordination motifs of the molybdenum cofactors of molybdenum-dependent oxidoreductases. The model compounds were investigated by Mo K-edge X-ray absorption spectroscopy (XAS) and (with one exception) their molecular structures were analyzed by X-ray diffraction to derive detailed information on bond lengths and geometries of the first coordination shell of molybdenum. Only small variations in Mo=O and Mo-S bond lengths and their respective coordination angles were observed for all complexes including those containing Mo(CO) 2 or Mo(μ-S)2Mo motifs. XAS analysis (edge energy) revealed higher relative oxidation levels in the molybdenum ion in compounds with innocent sulfur-based ligands relative to those in dithiolene complexes, which are known to exhibit noninnocence, that is, donation of substantial electron density from ligand to metal. In addition, longer average Mo-S and Mo=O bonds and consequently lower ν(Mo=O) stretching frequencies in the IR spectra were observed for complexes with dithiolene-derived ligands. The results emphasize that the noninnocent character of the dithiolene ligand influences the electronic structure of the model compounds, but does not significantly affect their metal coordination geometry, which is largely determined by the Mo(IV) or (V) ion itself. The latter conclusion also holds for the molybdenum site geometries in the oxidized MoVI cofactor of DMSO reductase and the reduced MoIV cofactor of arsenite oxidase. The innocent behavior of the dithiolene molybdopterin ligands observed in the enzymes is likely to be related to cofactor-protein interactions

Stable Silaimines with Three- and Four-Coordinate Silicon Atoms

Samuel PP, Azhakar R, Ghadwal R, et al. Stable Silaimines with Three- and Four-Coordinate Silicon Atoms. Inorganic Chemistry. 2012;51(20):11049-11054.The reactions of silylenes with organic azides are quite diverse, depending on the substituents of the silylene center and on the nature of the azide employed. Elusive silaimine with three-coordinate silicon atom L1SiN(2,6-Triip2-C6H3) (5) {L1 = CH[(C═CH2)(CMe)(2,6-iPr2C6H3N)2] and Triip = 2,4,6-triisopropylphenyl} was synthesized by treatment of the silylene L1Si (1) with a sterically demanding 2,6-bis(2,4,6-triisopropylphenyl)phenyl azide (2,6-Triip2C6H3N3). The reaction of Lewis base-stabilized dichlorosilylene L2SiCl2 (2) {L2 = 1,3-bis(2,6-iPr2C6H3)imidazol-2-ylidene} with Ph3SiN3 afforded four-coordinate silaimine L2(Cl2)SiNSiPh3 (6). Treatment of 2,6-Triip2C6H3N3 with L3SiCl (3) (L3 = PhC(NtBu)2) yielded silaimine L3(Cl)SiN(2,6-Triip2-C6H3) (7) possessing a four-coordinate silicon atom. The reactions of L3SiN(SiMe3)2 (4) with adamantyl and trimethylsilyl azide furnished silaimine compounds with a four-coordinate silicon atom L3(N(Ad)SiMe3)SiN(SiMe3) (8) (Ad = adamantyl) and L3(N(SiMe3)2)SiN(SiMe3) (9). Compound 8 was formed by migration of one of the SiMe3 groups. Compounds 5–9 are stable under inert atmosphere and were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray studies

Organobismuth(III) and Dibismuthine Complexes Bearing N,N′-Disubstituted 1,8-Diaminonaphthalene Ligand: Synthesis, Structure, and Reactivity

The organobismuth­(III) and dibismuthine complexes bearing N,N′-disubstituted 1,8-diaminonaphthalene ligand were prepared. The reaction of LBiNMe₂ (<b>1</b>) [L = 1,8-(NSiMe₃)₂C₁₀H₆] with ClSiMe₃ results in the elimination of Me₃SiNMe₂, while PhCCH, Cp*H, and PhOH proceed via HNMe₂ elimination and provide the complexes of LBiCl (<b>2</b>), LBiCCPh (<b>3</b>), LBiCp*­(<b>4</b>), and LBiOPh (<b>5</b>), respectively. Reaction of <b>1</b> with AlMe₃ in <i>n</i>-hexane yields LBiMe (<b>6</b>). Compound <b>1</b> reacts with diisopropylcarbodiimide and phenyl isocyanate under insertion at the Bi–NMe₂ bond to give the addition products LBi­(N-<i>i</i>Pr)₂CNMe₂ (<b>7</b>) and LBiN­(Ph)­C­(O)­NMe₂ (<b>8</b>). The reactions of <b>1</b> with sulfur and PhSiH₃ result in the formation of LBi–S–BiL (<b>9</b>) and LBi–BiL (<b>10</b>), respectively. Compounds <b>2</b>–<b>10</b> were characterized by elemental analysis, ¹H, ¹³C, and ²⁹Si NMR spectroscopy, and X-ray crystallographic studies

Lewis Base Stabilized Group 14 Metalylenes

The chemistry of stable metalylenes (the heavier group 14 element analogues of carbenes) is an intriguing target of main group chemistry due to their synthetic potential and industrial application. In the present study, we report on the utilization of an abnormal N-heterocyclic carbene (aNHC) and a cyclic alkyl-amino carbene (cAAC) as a Lewis base for the syntheses of compounds aNHC·SiCl₂ (<b>3</b>), aNHC·SnCl₂ (<b>4</b>), and cAAC·SnCl₂ (<b>5</b>). The synthesis of silylene <b>3</b> involved the ligand-substitution reaction between NHC·SiCl₂ and an aNHC. However, compounds <b>4</b> and <b>5</b> were synthesized by the reactions of aNHC and cAAC with SnCl₂ in the molar ratio of 1:1. Compounds <b>3</b>–<b>5</b> are well-characterized with various spectroscopic methods and single-crystal X-ray structural analysis

Lewis Base Stabilized Group 14 Metalylenes

The chemistry of stable metalylenes (the heavier group 14 element analogues of carbenes) is an intriguing target of main group chemistry due to their synthetic potential and industrial application. In the present study, we report on the utilization of an abnormal N-heterocyclic carbene (aNHC) and a cyclic alkyl-amino carbene (cAAC) as a Lewis base for the syntheses of compounds aNHC·SiCl₂ (<b>3</b>), aNHC·SnCl₂ (<b>4</b>), and cAAC·SnCl₂ (<b>5</b>). The synthesis of silylene <b>3</b> involved the ligand-substitution reaction between NHC·SiCl₂ and an aNHC. However, compounds <b>4</b> and <b>5</b> were synthesized by the reactions of aNHC and cAAC with SnCl₂ in the molar ratio of 1:1. Compounds <b>3</b>–<b>5</b> are well-characterized with various spectroscopic methods and single-crystal X-ray structural analysis

Aspherical-Atom modeling of coordination compounds by single-crystal X-ray diffraction allows the correct metal atom to be identified

Single-crystal X-ray diffraction (XRD) is often considered the gold standard in analytical chemistry, as it allows element identification as well as determination of atom connectivity and the solid-state structure of completely unknown samples. Element assignment is based on the number of electrons of an atom, so that a distinction of neighboring heavier elements in the periodic table by XRD is often difficult. A computationally efficient procedure for aspherical-atom least-squares refinement of conventional diffraction data of organometallic compounds is proposed. The iterative procedure is conceptually similar to Hirshfeld-atom refinement (Acta Crystallogr. Sect. A­ 2008, 64, 383–393; IUCrJ. 2014, 1,61–79), but it relies on tabulated invariom scattering factors (Acta Crystallogr. Sect. B­ 2013, 69, 91–104) and the Hansen/Coppens multipole model; disordered structures can be handled as well. Five linear-coordinate 3d metal complexes, for which the wrong element is found if standard independent-atom model scattering factors are relied upon, are studied, and it is shown that only aspherical-atom scattering factors allow a reliable assignment. The influence of anomalous dispersion in identifying the correct element is investigated and discussed

Synthetic Access to a Hydrocarbon-Soluble Trifluorinated Ge(II) Compound and its Sn(II) Congener

Trifluorinated germanium anions attracted attention of theoretical chemists already in the late 1990s to predict their physical and chemical properties. However these species were not synthesized in the laboratory, although substantial evidence for their existence was obtained from the mass spectrometry of GeF₄. The present study shows that controlled fluorination of LMNMe₂ (L = PhC­(N^<i>t</i>Bu)₂, M = Ge, Sn) using HF·pyridine in toluene leads to the formation of [LH₂]⁺[MF₃]⁻ under elimination of HNMe₂. The products contain the trifluorinated Ge­(II) and Sn­(II) anionic species which are stabilized by interionic H···F bonds. The new compounds were characterized by single crystal X-ray structural analysis, NMR spectroscopy, and elemental analysis