Guido J. Reiss

Microwave-assisted Kumada-type cross-coupling reactions of iodinated carba-closo-dodecaborate anions.

The microwave-assisted Pd-catalyzed Kumada-type cross-coupling reaction of iodinated carba-closo-dodecaborate anions requires smaller amounts of Grignard reagent and catalyst and results in higher yields in much shorter reaction times in comparison to a reaction with conventional heat transfer. 12-Ph(3)P-closo-1-CB(11)H(11) was identified as the side product of the cross-coupling reactions that use [PdCl(2)(PPh(3))(2)]. The inner salt, which is the first example for a {closo-1-CB(11)} cluster with a B-P bond, was selectively synthesized via a related microwave-assisted cross-coupling protocol and characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. In addition, the crystal structures of the tetraethyl ammonium salts of [12-Ph-closo-1-CB(11)H(11)](-), [12-(4-MeOC(6)H(4))-closo-1-CB(11)H(11)](-), and [12-(H(2)C═(Me)CC≡C)-closo-1-CB(11)H(11)](-) are described.

The Coordination Chemistry of cis-3, 5-Diaminopiperidine and Substituted Derivatives

An efficient and convenient method for the preparation of cis-3,5-diaminopiperidine (dapi) has been established and the coordination chemistry of this ligand with CoII, CoIII, NiII, CuII, ZnII, and CdII has been investigated in the solid state and in aqueous solution. Potentiometric measurements revealed a generally high stability for the bis complexes of the divalent cations with maximum stability for NiII (log beta2 = 21.2, beta2 = [M(dapi)2][M](-1)[dapi](-2), 25 degrees C, mu = 0.1 mol dm(-3)). Cyclic voltammetry established quasi-reversible formation of [Ni(dapi)2]3+ with a redox potential of 0.91 V (versus NHE) for the Ni(II/III) couple. [Co(dapi)2]3+ was prepared by aerial oxidation of the corresponding CoII precursor. The two isomers trans-[Co(dapi)2]3+ (1(3+), 26%) and cis-[Co(dapi)2]3+ (2(3+), 74%), have been separated and isolated as solid Cl- and CF3SO3- salts. In a non-aqueous medium 1(3+) and 2(3+) reacted with paraformaldehyde and NEt3 to give the methylidene-imino derivatives 3(3+) and 4(3+), in which the two piperidine rings are bridged by two or one N-CH2-O-CH2-N bridges, respectively. Crystal structure analyses were performed for H3dapi[ZnCl4]Cl, 1Cl3 x 2H2O, 2Cl3 x H2O, 3[ZnCl4]Cl, 4[ZnCl4]Cl, [Ni(dapi)2]Cl2 x H2O, [Cu(dapi)2](NO3)2, [Cu(dapi)Cl2], [(dapi)ClCd-(mu2-Cl)2-CdCl(dapi)], and [Co(dapi)(NO2)(CO3)]. The stability of [M(II)(dapi)]2+ and [M(II)(dapi)2]2+ complexes in aqueous solution, particularly the remarkably high tendency of [M(dapi)]2+ to undergo coordinative disproportionation is discussed in terms of the specific steric requirements of this ligand. Molecular mechanics calculations have been performed to analyze the different types of strain in these complexes. A variety of alkylated derivatives of dapi have been prepared by reductive alkylation with formaldehyde, benzaldehyde, salicylaldehyde, and pyridine-2-carbaldehyde. The NiII complexes of the pentadentate N3,N5-bis(2-pyridinylmethyl)-cis-3,5-diaminopiperidine (py2dapi) and the hexadentate N3,N5,1-tris(2-pyridinylmethyl)-cis-3,5-diaminopiperidine (py3dapi) have been isolated as crystalline ClO4- salts [Ni(py2dapi)Cl]ClO4 and [Ni(py3dapi)](ClO4)2 x H2O and characterized by crystal structure analyses.

Carba-closo-dodecaborate Anions with Two Functional Groups: [1-R-12-HC≡C-closo-1-CB11H10]− (R = CN, NC, CO2H, C(O)NH2, NHC(O)H)

Disubstituted carba-closo-dodecaborate anions with one functional group bonded to the cluster carbon atom and one ethynyl group bonded to the antipodal boron atom were synthesized from easily accessible {closo-1-CB11} clusters. [Et4N][1-NC-12-HC≡C-closo-1-CB11H10] ([Et4N]4b) was prepared starting from Cs[12-Et3SiC≡C-closo-1-CB11H11] (Cs1c) via salts of the anions [1-HO(O)C-12-HC≡C-closo-1-CB11H10](-) (2b) and [1-H2N(O)C-12-HC≡C-closo-1-CB11H10](-) (3b). In a similar reaction sequence [Et4N][1-CN-12-HC≡C-closo-1-CB11H10] ([Et4N]7b) was obtained from Cs[1-H2N-12-HC≡C-closo-1-CB11H10] (Cs5b) by formamidation to yield [Et4N][1-H(O)CHN-12-HC≡C-closo-1-CB11H10] ([Et4N]6b) and successive dehydration. In addition, the synthesis of the isonitrile [Et4N][1-CN-closo-1-CB11H11] ([Et4N]7a) is presented. The {closo-1-CB11} derivatives were characterized by multinuclear NMR as well as vibrational spectroscopy, mass spectrometry, and elemental analysis. The crystal structures of [Et4N][1-HO(O)C-12-HC≡C-closo-1-CB11H10] ([Et4N]2b), [Et4N][1-H2N(O)C-12-HC≡C-closo-1-CB11H10] ([Et4N]3b), [Et4N][1-NC-12-HC≡C-closo-1-CB11H10] ([Et4N]4b), [Et4N][1-H(O)CHN-12-HC≡C-closo-1-CB11H10] ([Et4N]6b), [Et4N][1-CN-12-HC≡C-closo-1-CB11H10] ([Et4N]7b), and K[1-H(O)CHN-closo-1-CB11H11] ([Et4N]6a) were determined. The transmission of electronic effects through the carba-closo-dodecaboron cage was studied based on (13)C NMR spectroscopic data, by results derived from density functional theory calculations, and by a comparison to the data of related benzene and bicyclo[2.2.2]octane derivatives.

The Coordination Chemistry ofcis-3,4-Diaminopyrrolidine and Related Polyamines

cis-3,4-Diaminopyrrolidine (cis-dap), trans-3,4-diaminopyrrolidine (trans-dap), cis-1,2-cyclopentanediamine (cis-cptn), and trans-1,2-cyclopentanediamine (trans-cptn) have been prepared in multigram quantities. The complexation of these ligands and of 3-aminopyrrolidine (ampy) with NiII, CuII, ZnII, and CdII has been studied in solution by means of potentiometric and spectrophotometric titrations. The complexes of the triamines cis-dap and trans-dap show a pronounced tendency to form protonated species such as [MII(HL)]3+, [MII(HL)2]4+, and [MII(HL)L]3+, indicative of a bidentate coordination mode of the ligand L. The UV/Vis spectra of the corresponding CuII complexes further confirmed bidentate coordination with trans-CuN4 geometry. The overall stabilities of the bis complexes [ML2]2+ decrease in the order cis-cptn > cis-dap > trans-cptn > ampy > trans-dap. The considerably lower stabilities of the ampy complexes as compared to the corresponding cis-dap complexes indicate metal binding to the two primary amino groups of the latter ligand. This was supported by molecular mechanics calculations (CuII and CoIII complexes) and confirmed by single-crystal X-ray diffraction studies of [Pt(Hcis-dap)Cl4]Cl·H2O, [Pd(Hcis-dap)2](ClO4)4·2H2O, and [Cu(Hcis-dap)2(OH2)2](SO4)2·3.5H2O − 2x H+ + x Cu2+ with 0.01 ⩽ x ⩽ 0.11. For the diamine ligands, coordination through the two exocyclic amino groups or through one exocyclic and one endocyclic amino group was established from the X-ray structure analyses of [Ni(cis-cptn)2](ClO4)2 and [Cu(3R-ampy)(3S-ampy)](ClO4)2, respectively. The crystal structure determination of [Co(cis-dap)(tach)][ZnCl4]Cl·C2H5OH (tach = cis-1,3,5-cyclohexanetriamine) revealed tridentate, facial coordination of cis-dap in this particular complex. However, the structural parameters of the [Co(cis-dap)(tach)]3+ moiety indicate significant strain for this coordination mode. The coordinating properties of the ligand cis-dap are compared with those of other aliphatic and alicyclic triamines.

(Dimethyl­phosphor­yl)methanaminium chloride

The crystal structure of the title salt, C3H11NOP+·Cl−, is primarily built from centrosymmetric dimers of two cations, connected head-to-tail by two charge-supported strong N—H⋯O hydrogen bonds, with a graph-set descriptor R 2 2(10). The chloride counter-anions connect these dimeric cationic units into chains along the a-axis direction.

Uranium(IV) bis(amido), imido and bis(acetylide) complexes: synthesis, molecular structure, solution dynamics and interconversion reactions

Reactions of [UMe2(C5Me5)2] with primary aromatic or aliphatic amines led to the rapid formation of monomeric uranium(IV) complexes [U(C5Me5)2(NHR)2](R = 2,6-dimethylphenyl 1, Et 2 or But3). The compounds were characterized by standard techniques and for 1, by X-ray diffraction. In co-ordinating solvents like tetrahydrofuran (thf) compound 1 reacted intramolecularly releasing one primary amine and forming the imidouranium(IV)[U(C5Me5)2{N(C6H3Me2-2,6)}]·thf 4, whereas in non-co-ordinating solvents the base-free [U(C5Me5)2{N(C6H3Me2-2,6)}]5 was obtained. The thf in 4 was found not to be in equilibrium with bulk solvents, and different proton chemical shifts for the adducted base were observed as a function of temperature following a Curie–Weiss behaviour. σ-Bond metathesis reactions of the bis(amido) and/or imido complexes with terminal alkynes produced the bis(acetylide) complexes [U(C5Me5)2(CCR)2](R = Ph 6 or But7) active species for the regioselective oligomerization of terminal alkynes, which can be prepared also from the reaction of [UMe2(C5Me5)2] with 2 equivalents of the corresponding terminal alkyne. Reactivity studies show the possible interconversion among these bis(amido), imido and bis(acetylide) complexes.

Bis(3-aza­niumylpyridin-1-ium) hexa­chloridostannate(IV) dichloride

The asymmetric unit of the title compound, (C5H8N2)2[SnCl6]Cl2, consists of one 3-azaniumylpyridin-1-ium dication and one chloride ion in a general position and a hexachloridostannate(IV) dianion lying about a centre of inversion. The [SnCl6]2− anion exhibits almost perfect octahedral geometry. The 3-azaniumylpyridin-1-ium and chloride ions are connected via medium–strong charge-supported N—H⋯Cl hydrogen bonds, forming undulating layers in the (110) plane. The [SnCl6]2− ions are located between these layers and occupy cavities formed by two facing layer puckers.

Pseudosymmetric fac-di­aqua­trichlorido[(di­methyl­phosphor­yl)methanaminium-κO]manganese(II)

In the title compound, [Mn(C3H11NOP)Cl3(H2O)2], the MnII metal center has a distorted octahedral geometry, coordinated by the three chloride ligands showing a facial arrangement. Two water molecules and the O-coordinated dpmaH cation [dpmaH = (dimethylphosphoryl)methanaminium] complete the coordination sphere. Each complex molecule is connected to its neighbours by O—H⋯Cl and N—H⋯Cl hydrogen bonds. Two of the chloride ligands and the two water ligands form a hydrogen-bonded polymeric sheet in the ab plane. Furthermore, these planes are connected to adjacent planes by hydrogen bonds from the aminium function of cationic dpmaH ligand. A pseudo-mirror plane perpendicular to the b axis in the chiral space group P21 is observed together with inversion twinning [ratio = 0.864 (5):0.136 (5)].

Bis(diisopropyl­ammonium) hexa­chlorido­stannate(IV)

The title compound, (C6H16N)2[SnCl6], crystallizes with one diisopropylammonium cation lying on a general position and the hexachloridostannate(IV) anion about a centre of inversion. The [SnCl6]2− anion undergoes a slight distortion from octahedral symmetry as the result of the formation of four unforked charge-supported N—H⋯Cl hydrogen bonds. The hydrogen bonds between the cations and anions form layers perpendicular to [101]. These layers are built by 24-membered rings which can be classified with an R 8 8(24) graph-set descriptor. According to this hydrogen-bonding motif, the title compound is isostructural with (C6H16N)2[IrCl6].

α-Aminoxy Oligopeptides: Synthesis, Secondary Structure, and Cytotoxicity of a New Class of Anticancer Foldamers

α-Aminoxy peptides are peptidomimetic foldamers with high proteolytic and conformational stability. To gain an improved synthetic access to α-aminoxy oligopeptides we used a straightforward combination of solution- and solid-phase-supported methods and obtained oligomers that showed a remarkable anticancer activity against a panel of cancer cell lines. We solved the first X-ray crystal structure of an α-aminoxy peptide with multiple turns around the helical axis. The crystal structure revealed a right-handed 28 -helical conformation with precisely two residues per turn and a helical pitch of 5.8 Å. By 2D ROESY experiments, molecular dynamics simulations, and CD spectroscopy we were able to identify the 28 -helix as the predominant conformation in organic solvents. In aqueous solution, the α-aminoxy peptides exist in the 28 -helical conformation at acidic pH, but exhibit remarkable changes in the secondary structure with increasing pH. The most cytotoxic α-aminoxy peptides have an increased propensity to take up a 28 -helical conformation in the presence of a model membrane. This indicates a correlation between the 28 -helical conformation and the membranolytic activity observed in mode of action studies, thereby providing novel insights in the folding properties and the biological activity of α-aminoxy peptides.