Single-electron transmetalation is recognized as an enabling technology for the mild transfer of alkyl groups to transition metal catalysts in cross-coupling reactions. Hypercoordinate silicates represent a new and improved class of radical precursors because of their low oxidation potentials and the innocuous byproducts generated upon oxidation. Herein, we report the cross-coupling of secondary and primary ammonium alkylsilicates with (hetero)aryl bromides in good to excellent yields. The base-free conditions have exceptional protic group tolerance on both partners, permitting the cross-coupling of unprotected primary and secondary amines.

http://pubs.acs.org/doi/pdf/10.1021/jacs.5b10963

Base-Free Photoredox/Nickel Dual-Catalytic Cross-Coupling of Ammonium Alkylsilicates

Organometalloid compositions of silicon and boron permit rapid, high-yielding, one-step radiolabeling of a covalently linked protein ligand (biotin) under aqueous conditions to give the corresponding alkyltetrafluorosilicates and aryltrifluoroborate salts. Biotin was chosen as a test ligand for protein targeting because of its quantitative interaction with avidin, which in turn allowed us to calculate fluoridation yields that approach 80-100%. The silicate was found to be moderately stable to hydrolysis, whereas the borate appears to be so stable that its hydrolytic decomposition was not readily measured. With the stability of both compounds ascertained, this work describes a novel and robust radiolabeling method that may find use in the development of positron emission tomography radiopharmaceuticals.

Arylfluoroborates and alkylfluorosilicates as potential PET imaging agents: high-yielding aqueous biomolecular 18F-labeling.

Freestanding nanosheets (see Figure) with the thickness of a single molecule and lateral dimensions in the micrometer range have been obtained by the release of self-assembled monolayers from the underlying surface by dissolution of the substrate or by scission of the anchor group-substrate bonds. The self-assembled monolayers are composed of biphenyl units that are crosslinked by electron irradiation.

Freestanding Nanosheets from Crosslinked Biphenyl Self‐Assembled Monolayers

Publisher Summary The chemistry of zwitterionic pentacoordinate silicon compounds is developed systematically. These compounds contain a silicate moiety with five covalent siliconelement bonds and an onium group. This chapter discusses a completely different class of pentacoordinate silicon compounds: zwitterionic λ 5 Si -silicates. These molecular compounds contain a pentacoordinate silicon atom and a tetracoordinate nitrogen atom. The syntheses, structures, and properties of compounds of zwitterionic λ 5 Si -silicates are discussed. The zwitterionic λ 5 Si -silicates are high-melting crystalline solids that are almost insoluble in nonpolar organic solvents and exhibit poor solubility in polar organic solvents. The crystals of these compounds consist of highly polar molecular building blocks that undergo intermolecular dipolar interactions. Different methods are used for their syntheses, some of these methods involving remarkable Si-C cleavage reactions. The products isolated directly from the reaction mixtures are well-crystallized solids, suitable for characterization by single-crystal X-ray diffraction and solid-state nuclear magnetic resonance (NMR) spectroscopy. The zwitterions are neutral molecules and are chiral, with a chiral λ 5 Si -silicates skeleton. Zwitterionic compounds are characterized by unique properties that arise from the charge separation in these molecules.

Zwitterionic pentacoordinate silicon compounds

Switching between penta- and hexacoordination with salen-silicon-complexes

Molecular λ5-silicates: Synthesis, structure and properties of zwitterionic λ5-organospirosilicates and λ5-organofluorosilicates

The zwitterionic A5-spirosilicates bis[1,2-benzenediolato(2–)][(morpholinio)methyl]silicate (1), bis[2,3-naphthalenediolato(2–)][(morpholinio)methyl]silicate (2; isolated as 2 • CH3CN), bis[1,2-benzenediolato(2–)][3-(morpholinio)propyl]silicate (3) and bis[2,3-naphthalenediolato(2 –)][3-(morpholinio)propyl]silicate (4; isolated as 4·1/2CH3CN) have been synthesized by various methods including Si – C bond cleavage reactions. The crystal structures of 2 • CH3CN and 4 · 1/2 CH3CN have been determined. 1,2 • CH3CN, 3 and 4 · 1/2 CH3CN have also been characterized by solution-state (1H, 13C, 29Si) and solid-state NMR spectroscopy (29Si CP/MAS). The pentacoordinate silicon atoms of the zwitterions 1-4 are surrounded by four oxygen atoms and one carbon atom. In the crystal, the coordination polyhedra around the silicon atoms of 2 • CH3CN (two crystallographically independent zwitterions and two crystallographically independent acetonitrile molecules) can be described as nearly ideal trigonal bipyramids, with the carbon atoms occupying equatorial sites. The crystal structure of 2 • CH3CN is considerably influenced by intermolecular N – H···N hydrogen bonds between the zwitterions and the acetonitrile molecules. The coordination polyhedron observed for the silicon atom in the crystal of 4 · 1/2 CH3CN can be described as a distorted square pyramid, with the carbon atom in the apical position. The crystal structure of 4 · 1/2 CH3CN is considerably governed by intermolecular N –H···O hydrogen bonds between the zwitterions which form infinite chains in the crystal. The 29Si chemical shifts (δ = – 75,5 to – 85,8) observed for 1,2 • CH3CN, 3 and 4 · 1/2 CH3CN in solution ([D6]DMSO) and in the crystal are typical of pentacoordinate silicon of the type SiO4C. For all compounds very similar 29Si chemical shifts have been observed for the solution and solid state [⊿(δ29Si) ≤ 0,9] indicating that the zwitterions 1-4 do also exist in solution.

Zwitterionische Bis[vic-arendiolato(2 –)] [(morpholinio)alkyl]silicate: Synthese sowie strukturelle Charakterisierung in Lösung und im Kristall / Zwitterionic Bis[vic-arenediolato(2 –)] [(morpholinio)alkyl]silicates: Synthesis and Structural Characterization in Solution and in the Crystal

Reactions of dimethoxy(methyl)(pyrrolidinomethyl)silane [Me(MeO) 2 SiCH 2 NC 4 H 8 , NC 4 H 8 =pyrrolidino] and methoxy(methyl)phenyl(pyrrolidinomethyl)silane [MePh(MeO)SiCH 2 NC 4 H 8 ] with hydrogen fluoride at 0 o C in ethanol/hydrofluoric acid yielded trifluoro(methyl)pyrrolidiniomethyl)silicate [F 3 Si(Me)CH 2 N(H)C 4 H 8 (9), N(H)C 4 H 8 =pyrrolidinio] (yield 90% and 89%, respectively).

/pdf/syntheses-x-ray-crystal-structure-analyses-and-solid-state-2kv0i92an6.pdf

Syntheses, x-ray crystal structure analyses, and solid-state NMR studies of some zwitterionic organofluorosilicates

Treatment of Si(OMe)4 with three molar equivalents of 1,2-C6H4(OH)2 (= 1,2-dihydroxybenzene) and two molar equivalents of HO(CH2)nNMe2 (n = 2, 3) in acetonitrile at room temperature yields the λ6Si-silicates (HO(CH2)nNMe2H)2(SiL3) (5: n = 2; 6: n = 3; L2 = 1,2-C6H4(O)22 (= benzene-1,2-diolato(2))). The analogous λ6Ge-germanates (HO(CH2)nNMe2H)2(GeL3) (7: n = 2; 8: n = 3) were synthesized analogously starting from Ge(OMe)4. Compounds 5·2CH3CN and 6-8 were structurally characterized by single-crystal X-ray diffraction. In addition, aqueous solutions of the Si/Ge analogs 5/7 and 6/8 were studied by NMR spectroscopy. The title compounds may be regarded as model systems for the transport and storage of silicon in biological systems and as tools to investigate biosilification.Key words: hexacoordinate silicon, hexacoordinate germanium, silicon biochemistry

Di((hydroxyalkyl)dimethylammonium) tris(benzene- 1,2-diolato(2-))silicates and their germanium analogs: syntheses, crystal structure analyses, and NMR studies

On the Existence of Zwitterionic λ5-(Ammonioorganyl)tetrafluorosilicates: Synthesis and Crystal and Molecular Structure of Tetrafluoro(pyrrolidiniomethyl)silicate



The zwitterionic tetrafluoro(pyrrolidiniomethyl)silicate (6) was synthesized by the reaction of trimethoxy(pyrrolidinomethyl)silane (7) with hydrogen fluoride in ethanol/hydro-fluoric acid (yield 83%). 6 crystallizes in the space group P1/c with two crystallographically distinct molecules in the asymmetric unit. In both molecules the pentacoordinate silicon atom is surrounded by four fluorine atoms and one carbon atom, the latter being in an equatorial position. The coordination polyhedron of the silicon atoms can be described as a slightly distorted trigonal bipyramid. The zwitterionic structure was also proved for dissolved 6 (solution in CD3CN, NMR-spectroscopic studies).

Zur Existenz zwitterionischer λ5-(Ammonioorganyl)tetrafluorosilicate: Synthese sowie Kristall- und Molekülstruktur von Tetrafluoro(pyrrolidiniomethyl)silicat

Joachim Becht

Papers

Molecular λ5-silicates: Synthesis, structure and properties of zwitterionic λ5-organospirosilicates and λ5-organofluorosilicates

Zwitterionische Bis[vic-arendiolato(2 –)] [(morpholinio)alkyl]silicate: Synthese sowie strukturelle Charakterisierung in Lösung und im Kristall / Zwitterionic Bis[vic-arenediolato(2 –)] [(morpholinio)alkyl]silicates: Synthesis and Structural Characterization in Solution and in the Crystal

Syntheses, x-ray crystal structure analyses, and solid-state NMR studies of some zwitterionic organofluorosilicates

Di((hydroxyalkyl)dimethylammonium) tris(benzene- 1,2-diolato(2-))silicates and their germanium analogs: syntheses, crystal structure analyses, and NMR studies

Zur Existenz zwitterionischer λ5-(Ammonioorganyl)tetrafluorosilicate: Synthese sowie Kristall- und Molekülstruktur von Tetrafluoro(pyrrolidiniomethyl)silicat