Günter Mattern

Beiträge zur chemie der halogensilan-addukte: XXN. Über die ionisierung der SiCl-Bindung. Temperaturabhängige ubergänge zwischen penta- und tetrakoordinierten SiCl-Verbindungen. Die kristall- und molekülstruktur von chloro-dimethyl-(3,4,7,8-tetrahydro-2H,6H-pyrimido[1,2-a]pyrimidin-1-ylmethyl-C1,N9)-silicium☆☆☆

1,3,4,6,7,8-hexahydro-1-trimethylsilyl-2H-pyrimido[1,2-a]pyrimidin (TMSTBD) (BSiMe3) reacts with chloromethyl(methyl)chlorosilanes to give (BCH2SiMenCl3-n) (n = 2, 1, 0) (5–7) and with 1-chloroethyltrichlorosilane togive (BCHCH3SiCl3) (8). Their solid-state and solution structures have been determined by X-ray crystallography (5), IR, 29Si, 13C and 1H NMR spectroscope. The presence of the strong base B causes interesting changes of coordination at Si of 5 and 6 when compared with 1 and 2 that contain a weaker base B. All compounds are pentacoordinated in the solid-state, and 7 and 8 also in solution. The latter do not differ from their counterpart 3 containing a weak base B. On the other hand, the pentacoordinated solid-state structure of 5 is more strongly distorted towards tetracoordination at Si and ionization of the SiCl bond than 1, as shown e.g. by the remarkably long SiCl bond (2.679 A). Solution data are consistent with the same pattern for the dissolved compounds. An increasing extent of tetracoordination at Si and ionization of the SiCl bond is observed for 5 and 6 when compared with 1 and 2. A shift to tetracoordination and SiCl ionization has been observed for the first time for a dichlorosubstituted silane (6). The extent of penta- or tetracoordination at Si is temperature and solvent dependent. Increase of temperature causes a shift to pentacoordination and vice versa (entropy effect). The effect of different solvents on the extent of penta- or tetracoordination at Si (ionization of the SiCl bond) can be correlated with their acceptor numbers (AN).

Bis(2,3-naphthalindiolato)[2-(pyrrolidinio)ethyl]silicat: Synthese und strukturelle charakterisierung eines zwitterionischen λ5-spirosilicates

The zwitterionic spirocyclic bis(2,3-naphthalenediolato)[2-(pyrrolidinio)ethyl]silicate [(C10H6O2)2-SiCH2CH2(H)NC4H8, 3] was synthesized and its structure characterized (single crystal X-ray structural analysis; 1H, 13C and 29Si NMR studies of solutions in DMSO). 3 was obtained by reaction of cyclohexylmethoxyphenyl(2-pyrrolidinoethyl)silane [C6H11(CH3O)Si(C6H5)CH2CH2NC4H8, 4] with 2,3-dihydroxynaphthalene [C10H6(OH)2] in acetonitrile at room temperature (isolated as 3·CH3CN, yield 81%). The formation of 3 involves two unusual SiC cleavage reactions (cleavage of SiC6H5 and SiC6H11 under mild reaction conditions). In addition, 3 was prepared by reaction of 2,3-dihydroxynaphthalene with dimethoxyphenyl(2-pyrrolidinoethyl)silane [C6H5(CH3O)2SiCH2CH2NC4H8, 5] and trimethoxy(2-pyrrolidinoethyl)silane [(CH3O)3SiCH2CH2NC4H8, 6], respectively (isolated as 3·CH3CN; yields 83 and 86%, respectively). 3·CH3CN crystallizes in the space group Pbca with a = 8.877(2) A, b = 22.823(4) A, c = 24.597(4) A, and Z = 8 (R = 0.0592, Rw = 0.0529). The pentacoordinated Si atom of 3·CH3CN is surrounded by its ligands in a nearly ideal square-pyramidal fashion (four basal O atoms and one apical C atom). The CH3CN molecule does not coordinate to the Si atom.

The absolute configuration of dichapetalin A

Abstract The absolute configuration of dichapetalin A, [(4 α ,6′ α ,7 α ,17 α ,20 S ,23 R ,24 E )-2′,3′,5′,6′-tetrahydro-7,23,26-trihydroxy-6′-phenyl-13,30-cyclo-29-nordammara-2,11,24-tri-eno [4,3-c]pyran-21-oic acid γ-lactone], the major cytotoxic constituent from Dichapetalum madagascariense has been established to be 4 R ,5 R ,7 R ,8 R ,9 R ,10 S ,13 R ,14 S ,17 S ,20 S ,23 R ,6′ S .

Neuartige zwitterionische λ5-Spirosilicate: Synthese und Kristallstruktur von Bis[l,2-benzoldiolato(2 – )][2-(dimethylammonio)phenyl]silicat sowie Synthese von Bis[2,3-naphthalindiolato(2 – )][2-(dimethylammonio)phenyl]silicat-Hemiacetonitril-Solvat / Novel Zwitterionic λ5-Spirosilicates: Synthesis and Crystal Structure of Bis[1,2-benzenediolato(2–)][2-(dimethylammonio)phenyl]silicate and Synthesis of Bis[2,3-naphthalenediolato(2–)][2-(dimethylammonio)phenyl]silicate Hemiacetonitrile Solvate

The zwitterionic λ5-spirosilicates bis[1,2-benzenediolato(2–)][2-(dimethylammonio)-phenyl]silicate (4) and bis [2,3-naphthalenediolato(2–)][2-(dimethylammonio)phenyl]silicate (5; isolated as 5 · ½CH3CN) were synthesized and the crystal structure of 4 was studied by X-ray diffraction. 4 was prepared by reaction of [2-(dimethylamino)phenyl]trimethoxysilane (7) or bis[2-(dimethylamino)phenyl]dimethoxysilane (8) with 1,2-dihydroxybenzene in acetonitrile at room temperature. 5 was synthesized analogously by reaction of 7 or 8 with 2,3-dihydroxynaphthalene. The silanes 7 and 8 were obtained by reaction of tetramethoxysilane (6) with [2-(dimethylamino)phenyl]lithium. The reactions 8 → 4 and 8 → 5 involve a remarkable Si–C cleavage leading to the formation of (dimethylamino)benzene. The pentacoordinate silicon atoms of 4 and 5 are surrounded by four oxygen atoms and one sp2 hybridized carbon atom. The coordination polyhedron of 4 can be described as a distorted square pyramid, the carbon atom being in the apical position (the structure is distorted by 69,1 % from the trigonal bipyramid towards the square pyramid). In the crystal, 4 forms an intramolecular N-H···O hydrogen bond.

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

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.