Bernhard Walfort

A New Class of Dianionic Sulfur-Ylides: Alkylenediazasulfites

The compounds [[(thf)Li2-[H2CS(NtBu)2]]2] (1) and [((thf)Li2[(Et)-(Me)CS(NtBu)2])2] (2) can be synthesized in a two-step reaction. Firstly addition of an alkyllithium to sulfur diimide gives the diazaalkylsulfinate [RS(NtBu)2] (R =Me, sBu). In a second step the alpha-carbon atom in R is metalated with one equivalent of methyllithium to give the S-ylides. This new class of compounds can be rationalized as sulfite analogues, in which two oxygen atoms are each isoelectronically replaced by a NtBu group and the remaining oxygen atom is replaced by a CR2 group. Similar to Coreys S-ylides (R2(O)S+-CR2) and Wittigs phosphonium ylides (R3P+ - -CR2), these molecules contain a positively charged sulfur atom next to a carbanionic center. Therefore nucleophilic addition reactions of the carbon atom are feasible. The reaction of a sulfur diimide with the anionic carbon center in [H2CS-(NtBu)2]2- gives the intermediate alkylbis(diazasulfinate) [(tBuN)2SCH2S(NtBu)2]2-. The acidity of the hydrogen atoms at the bridging CH2 group is high enough to give, upon deprotonation, the [(tBuN)2SCHS(NtBu)2]3- trianion in [[(thf)Li3[(tBuN)2SCHS(NtBu)2]]2] (3). In [(Et)(Me)CS(NtBu)2]2 the nucleophilic carbon atom is sterically hindered and transimidation instead of deprotonation is observed. In a complex redox process [(thf)6Li6S((NtBu)3S]2] is recovered. The two new classes of compounds broaden the rich coordination chemistry of the triazasulfites by the introduction of a hard carbon center.

Molecular paneling of rac-1,1′-bi-2-naphthol/∼ate (BINOL/BINOLAT): hydrogen-bonded assembly of [M(NH3)4 or 6]2+ complexes (M = Ni, Zn, Cd) in cavities of {[BINOLAT]2−(BINOL)2}-strands

The naphthyl-paneled cavities in the {[BINOLAT]2−(BINOL)2}-host strands in the structures of [M(NH3)n]2+[BINOLAT]2−(BINOL)2 accommodate the [M(NH3)n]2+-guest cation through second-sphere N–H⋯O hydrogen bonding irrespective of the size (M = Ni or Cd, n= 6) or coordination polyhedron (tetrahedron for M = Zn, n= 4 or octahedron for M = Ni, Cd).

Electrochromics by intramolecular redox switching of single bonds

Compounds of the general structure presented in Scheme 1 are proposed as electrochromic systems (ESs) in which reversible electron transfer is associated with breaking or forming of single bonds. In contrast to classical ESs, both redox states represent closed-shell systems. Whereas type OL/CS (Open form − Long-wavelength absorption/Closed form − Short-wavelength absorption) has already been demonstrated, this paper presents examples of the OS/CL type, in which the long-wavelength absorption is displayed by the ring-closed form. Bis(azines) RED-8, RED-13, RED-16, and RED-17, as well as the bis(amines) RED-22, RED-23, and RED-24 were prepared and characterized by their cyclic voltammograms (CV) and spectroelectrograms (SE). Except for the case of RED-24, the reversible overall transfer of two electrons is connected to switching of a single C−C or N−N bond. This reaction is not restricted to an entropically favorable transannular reaction (OX-82+, OX-162+, and OX-172+) but also occurs with the formation of five- (OX-132+ and OX-232+) and certain six-membered rings (OX-222+). These results suggest that the OS/CL general structure type should allow broad variation both in redox potentials and in ranges of color, similarly to the OL/CS type. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthese von [cis-(bipy)Pt(CCPh)2]AgFBF3 und dessen Reaktionsverhalten gegenüber Lewis-Basen; die Festkörperstruktur von cis-(bipy)Pt(CCPh)2 und [(bipy)Pt(CCPh)(PPh3)]BF4

Abstract The synthesis of the heterobimetallic platinum(II)–silver(I) complex {cis-[Pt](CCPh)2}AgFBF3 (3) in which the respective transition metals are bridged by σ- and π-bound phenylacetylides, succeeds by the reaction of cis-[Pt](CCPh)2 {[Pt]=(bipy′)Pt, bipy′=4,4′-dimethyl-2,2′-bipyridine} (1) with equimolar amounts of [AgBF4] (2). The reaction chemistry towards different Lewis-bases L (L=tetrahydrofuran, NR3, PPh3) is reported. Although 3 reacts with L to give coordination adducts of general type [{cis-[Pt](CCPh)2}AgL]BF4 in which the Lewis-base L is datively bound to the silver(I) ion, such a complex could only be isolated and characterised when L resembles PPh3 (4). All other Lewis-bases L are forming reversible adducts, which are only stable, when an excess of L is used. While [{cis-[Pt](CCPh)2}Ag(PPh3)]BF4 (5) is stable in the solid-state, it appeared that in solution it rearranges to produce the mononuclear, ionic platinum(II) complex {[Pt](CCPh) (PPh3)}BF4 (6) along with [AgCCPh] (8). The result of the X-ray structure analysis of 1 and 6 is reported. Complex 1 crystallises in the monoclinic space group C2/c with following cell parameters: a=19.3538(3), b=13.5356(3), c=8.9716(2) A, β=108.540(1)°, V=2228.27(8) A3, Z=4 and δ=1.734 g mol−1. Complex 6 crystallises in the monoclinic space group P21/n with a=9.0321(1), b=22.8014(4), c=15.6304(3) A, β=100.2414(7)°, V=3167.71(9) A3, Z=4 and δ=1.739 g mol−1. In both complexes a square-planar environment around the d8-configurated platinum(II) ion is typical. Each complex features a chelate-bound bipy′ group. To reach the coordination number four, two PhCC ligands (1) or one phenylacetylide and a PPh3 group (6) are σ- or datively bound to the platinum atom.

Vanadium complexes incorporating the β-diketiminato ligand L. Syntheses and structures of LV(OSO2CF3)2 and LVPPh2

The reaction of LLi (where L = N,N′-bis(2-diethylaminoethyl)-2,4-pentanediimine-ate(-1)) with VCl3·3THF yielded LVCl2, which was characterized by EI-MS and elemental analysis. Subsequent reactions of LVCl2 with AgOSO2CF3 and KPPh2 afforded two new complexes, LV(OSO2CF3)2 and LVPPh2 which were characterized by 19F, 31P NMR spectroscopy, EI-MS, elemental analysis, and single crystal X-ray structural analysis.

REGIO-AND STEREOSELECTIVE SYNTHESIS OF THIAZOLE-SUBSTITUTED HISTAMINE AND ADENINE DERIVATIVES BY NUCLEOPHILIC ATTACK AT ALLENYL ISOTHIOCYANATE

The ambident oligonucleophiles histamine and adenine were reacted with allenyl isothiocyanate to yield N-(5-methylthiazol-2-yl) substituted derivatives of the natural products. Whereas histamine led selectively in three clean steps or alternatively in a one-pot procedure to a final product bearing three thiazole units, adenine gave exclusively the mono derivative with a thiazolyl group at N-7. The regio- and stereochemistry of these transformations were proved by single-crystal X-ray analyses of the title compounds.

Methylenetriimidosulfate H2CS(NtBu)32−—The First Dianionic Sulfur(VI) Ylide

Through isoelectronic replacement of the oxygen atoms in SO42- ions by one CH2 and three NtBu groups one arrives formally at the dianion H2 CS(NtBu)32- , which has been isolated for the first time in the form of the sulfur(VI) ylide complex [(tmeda)2 Li2 {CH2 S(NtBu)3 }]. Deprotonation of the S-bonded methyl group in the triimidosulfonate MeS(NtBu)3- ion provides facile access in good yields. Hydrolysis favors the formation of the triimidosulfate [{(tmeda)Li2 [OS(NtBu)3 ]}3 ] and methane, and not, as one might expect, diimidomethylenesulfate and the amine. tmeda=Me2 NCH2 CH2 NMe2 .

[(thf)6Ba6(dmpz)8{(OSiMe2)2O}2] (dmpz = 3,5-dimethylpyrazolate): a molecule with six barium cations in a plane capped by two siloxane dianions and framed by eight dmpz anions

In the synthesis of barium 3,5-dimethylpyrazolate, silicone joint grease and cyclo-(Me2SiO)4 are cleaved and two O(SiMe2O)22− bidentate chelating siloxane anions are coordinated above and below an unprecedented Ba612− layer framed by eight σ/π coordinated pyrazolate anions.

The inverse podant[Li3(NBut)3S}]+ stabilises a single ethylene oxide OCHCH2anion as a high- and low-temperature polymorph of[(thf)3Li3(OCHCH2){(NBut)3S}]

A single ethylene oxide anion derived from the ether cleavage reaction of thf with ButLi is stabilised by the inverse podant [Li3(NBut)3S)]+ to give a high- and a low-temperature polymorph with a considerable difference in conformation and packing.

1-[(4-Chloro­benzoyl)­methyl]-4-(N,N-di­methyl­amino)­pyridinium bromide sesquihydrate and 1-[(4-bromo­benzoyl)­methyl]-4-(N,N-di­methyl­amino)­pyridinium bromide sesquihydrate

The title compounds, C15H16ClN2O+.Br-.1.5H2O and C15H16BrN2O+.Br-.1.5H2O, are isomorphous. The benzene ring is oriented nearly normal to the pyridine ring in both compounds. The molecular packing is mainly influenced by intermolecular O-H...O and O-H...Br interactions, as well as weak intramolecular C-H...O interactions. The H2OBr- units form an extended water-bromide chain, with a bridging water molecule on a twofold axis.