Band 42, Heft 4

The mixed chloro-bromo complexes [RuCl n Br 6-n ] 2- , n = 1-5, have been separated for the first time by ion exchange chromatography on diethylaminoethylcellulose. Due to the stronger trans-effect of Br compared with Cl, on treatment of [RuBr 6 ] 2- with Cl - in the presence of Br 2 nearly pure cis/fac-isomers,and by reaction of [RuCl 6 ] 2- withBr - /Br 2 nearly purer tranS/mer-isomersforn = 2,3,4 are formed. The vibrational spectra of the mixed ligand complexes are completely assigned according to point groups D 4h , C 4v , C 3v and C 2v , respectively. The bands are observed in the characteristic regions: ν(RuCl): 340-270 > ν(RuBr): 245-190 > δ(ClRuCl) ≥ δ(ClRubr) ≥ δ(BrRuBr): 125-90 > νʟ: < 100 cm -1 . The lower stability of the hexahalogeno complexes of Ru(IV), 4d, compared with the homologous complexes of Os(IV), 5d, is confirmed by a decrease of the force field constants by approximately 15%.

Bis(triorganylstannyl)chalcogenides (O, S, Se) have been studied by 119 Sn NMR in solution. In most cases the magnitude of the geminal coupling constants 2 J(SnSn) are indicative of a bent arrangement SnXSn (X = O, S, Se). The exception is bis(tri-tert-butylstannyl)oxide for which the linear structure S n - O - S n as determined by X-ray diffraction in the solid state is preserved in solution. The trend of the coupling constants 2 J(SnSn) depending on X and on the bond angle SnXSn suggests that 2 J(SnOSn) > 0 and 2 J(SnSSn), 2 J(SnSeSn) <0. The X-ray diffraction study of bis(tribenzylstannyl)sulfide shows a bent arrangement (∢SnSSn 105.52(14)°) in contrast to the corresponding oxide.

Based upon the experimentally known but yet unexplained very different reactivities of the two isoelectronic and isolobal intermediates Pt(PMe 3 ) 2 and Pt(PEt 3 ) 2 , the electronic structure and bonding capability of such 14 electron fragments as a function of their geometry (P-Pt-P angle α, determined by the phosphane cone angle) are investigated using molecular orbital calculations. A decrease of the P-Pt -P angle leads to an exceptionally pronounced energy ascent of the b 2 -HOMO of Pt(PR 3 ) 2 species, which, as a consequence, might lead to unusual reactivity patterns and bonding capabilities of 1,3-diphosphaplatinacyclobutane fragments, for which an extreme electronic situation is enforced by steric constraints. Dichloro[η 2 -bis(di-r-butylphosphino) methane]platinum(II), Pt(dtbpm)Cl 2 , is synthesized as a potential precursor of Pt(dtbpm), in order to allow experimental investigations of this taylor made four-membered ring chelate complex of Pt(0). The crystal and molecular structure of Pt(dtbpm)Cl 2 · 2 CHCl 3 has been determined by X-ray diffraction.

[N(PPh 3 ) 2 ][VCl 3 (N 3 S 2 )]·C 7 H 8 is formed by the reaction of VCl 2 (N 3 S 2 ) with excess PPh 3 in CH 2 C1 2 and subsequent treatment of the reaction mixture with toluene, as well as by the reaction of VCl 2 (N 3 S 2 ) with [N(PPh 3 ) 2 ]Cl in CH 2 Cl 2 in the presence of toluene. The compound forms red crystals, which have been characterized by IR spectroscopy. The crystal structure was determined by X-ray diffraction (1433 observed, independent reflexions, R = 0.070). Crystal data: mono-clinic, space group Cc, Z = 4, a = 994.1, b = 2148.0, c = 2055.2 pm, β = 90.03°. The compound consists of [N(PPh 3 ) 2 ] ⊕ cations and [VCl 3 (N 3 S 2 )] ⊖ anions, in which the vanadium atom is five-coordinated by threee chlorine atoms and two nitrogen atoms, and is part of a planar VN 3 S 2 ring.

Using 293 K diffractometer intensity data, the crystal structures of (NH 4 ) 2 SeBr 6 (1) and [H 3 N(CH 2 ) 3 NH 3 ]SeBr 6 (2) have been determined by single crystal X-ray technique and refined to a final R w of 0.049 and 0.040, respectively. The dark red crystals of 1 are cubic (space group Fm3m) with a = 10.478(2) Å and Z = 4. This structure contains SeBe 6 2- octahedra (point symmetry m3̄m, distance Se-Br: 2.577(2) Å in an antifluorite type arrangement of cations and anions. In contrast, the SeBr fi 2-ion in 2 is statically distorted (approximate point symmetry 3m, distance Se-Br min. 2,547(2), max. 2.595(2) Å. The dark red crystals are orthorhombic (space group Pnma) with a = 17.795(3), b = 7.5037(6), c = 10.476(1) Å and Z = 4. The results agree with the rules for the appearance of a static/dynamic stereochemical effect of the lone pair electrons given for TeX 6 2- (X = Cl, Br, I) species (W. Abriel, Acta Crystallogr. B 42, 449 (1986)). Consequently these rules can be extended considering SeX 6 2- as well. Basic structural data for all compounds containing AX 6 2- ions (A = Se, Te; X = Cl, Br, I) known to date are given including the ⊿-values (R. D. Shannon, Acta Crystallogr. A 32, 751 (1976)) as a measure for the distortion of the octahedral anion.

The reaction of tris(ethene)nickel(0) with stoichiometric amounts of bis(dimethylphos-phino)methane (dmpm) in ether at low temperature affords the yellow crystalline, dinuclear complexes (dmpm)Ni 2 (C 2 H 4 ) 4 (1) and (dmpm) 2 Ni 2 (C 2 H 4 ) 2 (2). 2 reacts with ethyne to yield (dmpm) 2 Ni 2 (C 2 H 2 ) 2 (3). When 2 is treated with CO at -40 °C the primary product is (dmpm) 2 Ni 2 (CO) 2 (μ-CO) (4). At 20 °C 4 is converted by additional CO into (dmpm) 2 Ni 2 (CO) 4 (5), which has already been characterized as the reaction product of Ni(CO) 4 with dmpm. In compounds 1-5 the bidentate dmpm acts as a bridging and not as a chelating ligand. The structures of complexes 1-4 were assigned on the basis of their 13 C and 31 P NMR spectra.

Coordination of substitutionally inert [Ru(bpy) 2 ] 2+ fragments (bpy: 2,2′-bipyridine) to the a-iminoketone chelate ligands pyrazine-2-dimethylcarboxamide (4) and 4,7-phenanthroline-5,6-dione (5) yields the complexes [(N,O-4)Ru(bpy) 2 ] 2⊕ , [(O,O′-5 ⊖ )Ru(bpy) 2 ] ⊕ and {(N,O; N′,O′-5)[Ru(bpy) 2 ] 2 } 4⊕ which exhibit a rich electrochemistry. The distinctly different electronic structures of the complexes are evident from the ESR behaviour of paramagnetic intermediates: N.O-coordinated complexes have the unpaired electron residing in the ligand n system upon reduction, albeit with g<2 for the binuclear complex of 5. The paramagnetic O,O′-coordinated mononuclear complex with 5 has its redox potentials shifted positively relative to that of the binuclear system. These results are particularly noteworthy because 4 and 5 can be regarded as model compounds for the flavin and methoxatin dehydrogenase cofactors.

Bis((-)-strychninium)hexasulfide has been synthesized from (-)-strychnine and (NH 4 ) 2 S 5 in ethanolic solution at 0 °C. It is monoclinic, S. G. C2, with a = 34.21(1) Å, b = 7.59(2) Å, c = 7.74(1) Å, β = 103.0(1)°. As expected, the S 6 2- -anions occur as unbranched zig-zag-chains. Surprisingly, they do not show the common helical all-trans-conformation but the all-cis-conformation. The cations and the anions are linked by hydrogen bridges, running from the terminal sulfur atoms of the polysulfide dianions to the protonated nitrogen atoms of the monoprotonated (-)-strychnine molecules.

The complex (1) was obtained by reduction of FeCl 2 [P(CH 2 CH 2 CH 2 PMe 2 ) 3 ] with lithium dust in tetrahydrofuran at room temperature. Although an equilibrium of 1 with its iron(0) tautomer Fe[P(CH 2 CH 2 CH 2 PMe 2 ) 3 ] could not be detected by NMR spectroscopy, the coordinatively unsaturated 16e-fragment could be trapped by ligands favouring low oxidation states: trimethyl phosphite reacted with 1 to give Fe[P(OMe) 3 ][P(CH 2 CH 2 CH 2 PMe 2 ) 3 ] (2), whereas carbon monoxide was observed to add to the metal(O) species to yield a mixture of Fe(CO)[P(CH 2 CH 2 CH 2 PMe 2 ) 3 ] (3) and -(CH 2 ) 3 -PMe 2 (4). 1 was completely unreactive towards dihydrogen and dinitrogen, not, however, towards carbon dioxide, which was found to insert into both the Fe-H and Fe-C bond producing (5). Methyl and benzyl iodide interacted with 1 to give the iodo derivative (6). The reaction of 1 with methanol lead to FeH 2 [P(CH 2 CH 2 CH 2 PMe 2 ) 3 ] (7).

The C-terminal tetrapeptide Gly-Pro-Ala-Thr of TMV coat protein was linked to poly- (L-lysine) of 37,300 and 80,000 daltons and to human serum albumin using different ratios of tetrapeptide to carrier. The new hydrazidosuccinyl HSc cross-linker effected the specific amino terminal attachment of the tetrapeptide by azide coupling. The synthetic peptide and its conjugates were controlled by various methods including 13 C NMR and CD. Using a conjugate containing 74 tetrapeptide residues linked to poly(L-lysine) of 80,000 daltons for screening of monoclonal antibody by ELISA, 5.8 fmol of peptide were detectable. The serological and biological properties of the monoclonal antibody were assayed by indirect ELISA and by quantitative determination of virus neutralization. This neutralization could be reversed by the poly(L-lysine)-tetrapeptide conjugate but not by the free tetrapeptide.

Stabilization of RPSR′, Manganese Complexes, X-Ray Stabilization of a RPSR′ function is possible by its incorporation into the mono-and binuclear manganese complexes, t-BuP[Mn(CO) 5 ]SPh (3b) and (μ-CH 3 PSPh)(μ-SPh)Mn 2 (CO) 8 (4a), re-spectively. Formation of 4a is accomplished via the precursors 3a and PhSMn(CO) 5 (5), which are both unstable. 3a, b and 5 are formed by reaction of RP(Cl)SPh (la, b) [R = CH 3 (a), t-Bu (b)] with [Mn(CO) 5 ] - (2). 4a crystallizes in the orthorhombic space group Pbca with Z = 8.

Thyrotropin-Releasing Hormone (TRH), Copper(II) Ion Complexes The copper(II) complexes of the thyrotropin-releasing hormone (L-pyroglutamyl-L-histidyl-L-prolinamide, TRH) in 3 M LiCl-water solutions were investigated as a function of pH by circular dichroism, absorption, and electron spin resonance spectroscopy. It was concluded that a simple ML (IN) complex of copper(II)-TRH is formed over the pH range 4.0-4.5, while 2N and 3N complexes are present in the solutions of pH 4.4-6.0. From pH 6.1 to 9.8 an ML 2 (4N) complex is formed and this species is the only complex found over the pH range 6.5-8.5. At pH values above 9.0 a 3N species is formed in addition to a 2N complex which is present in the solutions of pH 11.3. These observations are controversial to former reports. TRH [1-2] was synthesized using the fully Adpoc (adamantyl-isopropyloxycarbonyl)-protected histidine. From the synthesis the advantages of the Adpoc group, cleavable under extreme mild acidolytic conditions, become obvious.

A new tryptophan-containing peptide alkaloid, “discarin-K”, has been isolated from Discaria febrifuga, a shrub growing in Brazil, Argentina and Uruguay. Its structure has been determined as 1 on the basis of spectral studies. Another peptide alkaloid, franganin, was also isolated from the same plant and its 1 H NMR and 13 C NMR have been studied using COSY-45, 2 D-J resolved and DEPT techniques.

2-tert-Butyl-4-methyl-2,4-dihydropyrrolo[3,4-b]indole (4a) has been prepared via selective reduction of 2-rm-butyl-4-methyl-2,4-dihydropyrrolo[3,4-b]indol-l(2H)-one or -3(2H)-one 5 and 6 with diisobutylaluminiumhydride. The same precursors 5 and 6 can be transformed into 2-tert-butyl-4-methyl-2,4-dihydropyrrolo[3,4-b]indoles (4b) and (4c) bearing a methoxy group in 1- or 3-position via a two step procedure consisting in O-alkylation and CH-deprotonation. NMR Investigations afford an insight into the structure of the stable tricyclic hetarenes.

Azomethines and vinylenes, containing azobenzene, stilbene or 1,2-di(2-thienyl)ethylene moieties as central groups with additional thiophene systems has been synthesized and charac-terized by their elemental analyses, IR and 1 H NMR spectra and studied in relation to their liquid crystalline properties by DTA analysis and visually by their textures microscoping under polarized light. The liquid crystalline properties of these compounds and some related compounds described in literature are compared and the geometrical elements of their structures are discussed.

The title compounds la-3c were prepared by stereoselective reduction of the respective dibromides. Pyrolysis gave allylic bromides (8, 9, 11) as primary and dienes (10, 12) as secondary products. Product ratios were independent of the stereochemistry of the starting materials. No differences of the rearrangement rates of the stereoisomers were observed in gas phase reactions of the derivatives of bicyclo[6.1.0]- and bicyclo[8.1.0]alkanes. With the larger bicyclo[10.1.0] derivatives, however, distinct differences in the thermal stability of cis-trans-isomers4c/5c or 2c/3c were found in condensed phase.

In the radiolysis of N 2 O/O 2 (4:1 )-saturated aqueous solutions of diisopropyl ether(10 -3 moldm -3 ), OH radicals abstract H-atoms, thereby producing radicals at C(2) (1 ≈ 78%) and to a lesser extent at C(l) (2 ≈ 22%) which are converted by oxygen into the corresponding peroxyl radicals 3 and 4. Some O 2 radicals are formed by the reaction of radiolytically produced H atoms with oxygen. Methyl radicals formed in the course of the bimolecular decay of 3 and 4 give rise to methylperoxyl radicals 5. At high dose rate as delivered by 2.8 MeV electron pulses the products (G values in parentheses) are: isopropyl acetate (2.6), acetone (1.1), isopropanol (1.1), 2-isopropoxypropanal (1.4, estimated), formaldehyde (2.0), organic hydroperoxides (0.4), organic acids (0.5) and hydrogen peroxide (1.9). At low dose rates (≤ 0.39 Gy s -1 ) G(acetone) is considerably increased and is no longer balanced by an equivalent yield of isopropanol. This is thought to be due to an intramolecular H-abstraction of radical 3. Pulse radiolysis studies revealed that 3, 4 and 5 decay by second order kinetics. At the early stages the bimolecular decay is faster (2k ≈ 6 × 10 7 dm 3 mol -1 s -1 ) than toward the end (2k ≈ 2 × 10 7 dm 3 moI -1 s -1 ) . It is suggested that the faster decay at the beginning is due to a preponderance of termination by the primary peroxyl radical 4 with the tertiary peroxyl radical 3 while at later stages termination is mainly governed by the reaction of 3-1-3 which produces 5. The rate constants k(5 + 3) and k(5 + 5) are very likely much higher than 2k(3 + 3), hence 2k(3 + 3 ) < 2 × 10 7 dm 3 mol -1 s -1 . In O 2 -saturated solutions O 2 plays a considerable role in the termination reactions, and organic hydroperoxides which are unimportant in N 2 O/O 2 -saturated solutions at high dose rates are now the major products.

The ratio of isomeric enaminones, obtained by acylation of enamines with acid chlorides in the presence of triethylamine, depends on the possibility of forming isomeric enoles of the inter-mediate cyclobutanone adducts.

The isotypic compounds SrPt 4 P 6 , SrPt 4 As 6 and BaPt 4 As 6 were found to crystallize with a Pyrite-type derivative structure (monoclinic, C2/c, Z = 4) in which one Sr or Ba atom per formula unit occupies the position of a P 2 or As 2 pair. BaPt 2 P 3 forms another Pyrite-type related structure (monoclinic, P2 1 /c, Z = 4) built up by Ba 2 Pt and Pt 3 P 6 layers. All crystal structures were refined from four-circle diffractometer data, the lattice constants are: SrPt 4 P 6 : a = 825.2(1) pm, b = 798.4(1) pm, c = 1142.8(1) pm, β = 90.74(2)°; SrPt 4 As 6 : a = 858.2(1) pm, b = 832.1(1) pm, c = 1194.5(1) pm, β = 91.00(2)°; BaPt 4 As 6 : a = 868.8(1) pm, b = 833.3(1) pm, c = 1197.1(1) pm, β = 90.81(2)°; BaPt 2 P 3 a = 835.2(1) pm, b = 577.6(1) pm, c = 1157.4(1) pm, β = 106.73(2)°.

Amino Sugars, Triflate Displacement, Amino Acids Novel one step syntheses of a new class of phar-macologically interesting 6-amino-6-deoxy sugars are described. The reaction sequence consists of esterifying 1,2:3,4-di-O-isopropylidene-α-D-galac-topyranose with trifluoromethanesulfonic anhydride and reacting the resulting triflate with a variety of suitably protected naturally occurring amino acids. The difficulties which, sometime, are encountered during displacement reactions in carbohydrates are absent.