Formation of N-bridgehead 1,2,5-thiadiazolium and selenadiazolium rings through an intramolecular cyclisation reaction

Treatment of N-lithiopyridylketimide derivatives Li[R(C=N)py] (R=Ph, py) with ECl(2) (E=S, Se) affords the fused thiadiazolium and selenadiazolium salts [RC(6)H(4)N(2)E]Cl [1]Cl and [2]Cl containing a bridgehead N atom through intramolecular coordination.     

Use of decoupling to reduce the radiated noise generated by panels

Four types of sources that induce on a panel four different responses are considered. The differences show up also in the way the responses radiate to the far field. A decoupling device in a form of a layer is placed adjacent to the top surface of the panel. The decoupling layer modifies the radiated fields that the sources generate. The modifications in terms of radiation reduction factors and levels are defined. These factors and levels are analyzed for two kinds of decoupling layers. The first is a compliant coating and the second is a layer of a mixture of gas and fluid. The compliant coating may induce on the fluid a velocity field that is different from that of the panel. The mixture of gas and fluid introduces a surface impedance discontinuity between the top surface of the panel and the top surface of the layer, the top surface being in contact with the semi-infinite fluid above the panel.     

The Synthesis of Cystine Peptides by Iodine Oxidation of S-Trityl-cysteine and S-Acetamidomethyl-cysteine Peptides

Previously reported studies of the iodine oxidation of S-trityl-cysteine peptides and S-acetamidomethyl-cysteine peptides, leading directly to cystine peptides, have been extended. Detailed investigations have been made of the reactivities of the S-trityl and the S-acetamidomethyl group towards iodine in various solvents. In chloroform, methylene chloride, trifluoroethanol, and hexafluoroisopropyl alcohol the differences in the reaction rates of the two groups have been found to be extremely large, allowing the selective conversion of the tritylthio groups to disulfides in the presence of the S-acetamidomethyl derivatives. In a second group of solvents, consisting of methanol, acetic acid, dioxane, and mixtures of these solvents with water, simultaneous iodine oxidation of S-trityl- and S-acetamidomethyl-cysteine peptides leads to a preferential combination of these two residues, resulting in predominantly asymmetrical cystine derivatives. - The suitability of the two sulfur-protecting groups in the synthesis of cyclic cystine peptides has been assessed. - Possible reaction mechanisms are discussed. - The scope and limitations of iodine oxidation in peptide synthesis have been studied. The applicability of the method has been demonstrated in the preparation of the open-chain asymmetrical cystine peptide 5 , the protected somatostatin derivative 17 , and the A(1–13) segment 19 of human insulin, previously employed in the total synthesis of this hormone.     

Synthesis and structures of M[N(TePPri2)2-Te,Te']n (n = 2, M = Zn, Cd, Hg; n = 3, M = Sb, Bi): the first ditelluroimidodiphosphinato p- and d-block metal complexes

Reactions of Na[N(TePPri2)2] with the appropriate metal halide produce the air-stable complexes M[N(TePPri2)2-Te,Te']n (n = 2, M = Zn, Cd, Hg; n = 3, M = Sb, Bi), which adopt distorted tetrahedral (M = Zn, Cd, Hg) and octahedral (M = Sb, Bi) structures, respectively.     

Macrocyclic gold(I) complexes and [2]catenanes containing carbonyl functionalized diacetylide ligands

The carbonyl derivatized bis(alkyne) O=C(4-C₆H₄OCH₂CCH)₂ was converted into the imine derivatives RN=C(4-C₆H₄OCH₂CCH)₂ [R=OH, NHC(O)NH₂, NHC₆H₃-2,4-(NO₂)₂] and into the 4-bromomethyl-1,3-dioxolane derivative BrCH₂C₂H₃O₂C(4-C₆H₄OCH₂CCH)₂. The alkyne units in these compounds react with [AuCl(SMe₂)] in the presence of base to form the corresponding digold(I) diacetylide complexes, that exist as insoluble oligomers or polymers. They reacted with the diphosphines Ph₂PZPPh₂ [Z=CC, trans-HC=CH and (CH₂)_n, n=3–5] to give macrocyclic gold(I) complexes of the type [Au₂(μ-LL)(μ-PP)], where LL is the diacetylide and PP the diphosphine ligand. The ability of these macrocyclic complexes to self-assemble to [2]catenanes has been studied. The ketone and imine derivatives do not form [2]catenanes because the orientation of the aryl groups is unfavorable, but the 1,3-dioxolane derivatives may catenate if the ring size is optimum.     

Macrocyclic and lantern complexes of palladium(II) with bis(amidopyridine) ligands: synthesis, structure, and host-guest chemistry

The reactions of [PdCl2(NCPh)2] in a 1:1 ratio with the bis(amidopyridine) ligands LL=C6H3(5-R)(1,3-CONH-3-C5H4N)2 with R=H (1a) or R=t-Bu (1b) give the corresponding neutral dipalladium(II) macrocycles trans,trans-[Pd2Cl4(mu-LL)2], 2a and 2b, which crystallize from dimethylformamide with one or two solvent molecules as macrocycle guests. The reaction of [PdCl2(NCPh)2] with LL in a 1:2 ratio gave the cationic lantern complex [Pd2(mu-LL)4]Cl4, 3c (LL=1b), and the reaction in the presence of AgO2CCF3 gave the corresponding trifluoroacetate salts [Pd2(mu-LL)4](CF3CO2)4, 3a (LL=1a) and 3b (LL=1b). These lantern complexes exhibit a remarkable host-guest chemistry, as they can encapsulate cations, anions, and water molecules by interaction of the guest with either the electrophilic NH or the nucleophilic C=O substituents of the amide groups, which can be directed toward the center of the lantern through easy conformational change. The structures of several of these host-guest complexes were determined, and it was found that the cavity size and shape vary according to the ligand conformation, with Pd...Pd separations in the range from 9.45 to 11.95 A. Supramolecular ordering of the lanterns was observed in the solid state, through either hydrogen bonding or secondary bonding to the cationic palladium(II) centers. The selective inclusion by the lantern complexes of alkali metal ions in the sequence Na+ > K+ > Li+ was observed by ESI-MS.     

Tetraphosphinitoresorcinarene complexes: dynamic clusters with silver(I) and copper(I) halides

Silver(I) and copper(I) halide derivatives of several tetrakis(diphenylphosphinito)resorcinarene ligands are reported. The complexes [resorcinarene(O(2)CR)(4)(OPPh(2))(4)(M(5)X(5))], with resorcinarene = (PhCH(2)CH(2)CHC(6)H(2))(4), R = C(6)H(11), 4-C(6)H(4)Me, C(4)H(3)S, OCH(2)CCH, or OCH(2)Ph, M = Ag, X = Cl, Br, or I, M = Cu, and X = Cl or I, contain a crownlike [P(4)M(5)X(5)] metal halide cluster. These crown clusters were found to be dynamic in solution, as studied by variable-temperature NMR, and easily fragment to give the corresponding complexes containing [P(4)M(4)X(5)](-) and [P(4)M(2)(micro-X)](+) units. Reaction of pentasilver crown clusters with triflic acid gave the corresponding disilver complexes [resorcinarene(O(2)CR)(4)(OPPh(2))(4)]Ag(2)(micro-Cl)]]CF(3)SO(3). Thus, these resorcinarene-based ligands act as a platform for the easy and reversible assembly of copper(I) and silver(I) clusters with novel structures.