Transition-Metal Complexes with Bidentate Ligands Spanning trans-Positions. II. Preparation and properties of complexes trans-[MX2(1)] (M = Ni,Pd and Pt; X = Cl,Br and I; 1 = 2, 11-Bis(diphenylphosphinomethyl)benzo[c]phenanthrene)

It is shown that the ligand 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene ( 1 ) reacts with nickel(II), palladium(II) and platinum(II) substrates giving either exclusively, or predominantly, mononuclear complexes of the type trans-[MX₂( 1 )] in which the organic ligand spans trans-positions. It is further shown that the spectroscopic properties which are mainly associated with metal and donor atoms in complexes of this type are closely related to those of the corresponding square planar complexes of the type trans-[MX₂(Ph₂PCH₂Ph)₂].     

Receptors for organochlorine pesticides based on calixarenes

The water soluble 4-sulfocalix[n]arenes (with n?=?4,6,8) have been investigated as potential synthetic receptors for cyclodiene organochlorine pesticides. Steady state fluorescence experiments in ethanol solution have shown that only the cavitands with n equal to 6 and 8 form complexes, of comparable stability, with heptachlor. Electrochemical data, obtained in water solution, confirmed the ability of 4-sulfocalix[6]arene to bind the heptachlor, unlike the smaller calixarene. Moreover, a significant increase in the stability constant is observed in water solutions. This stability is caused by the sterical hindrance of pesticides with respect to the cavity dimension of the calixarene. This results in a selective interaction of this molecule with other organochlorine pesticides. Binding experiments, carried out with endosulfan have shown that, despite of chemical similarity, 4-sulfocalix[6]arene and 4-sulfocalix[8]arene behave in a very different way: the former is unable to bind this pesticide, while the latter shows a binding constant of 4.7?×?10⁵ with endosulfan. To investigate the molecular features of the interactions, molecular dynamic simulations of 4-sulfocalix[6]arene in presence of heptachlor in water solution have been performed. These simulations show that different configurations of heptachlor inside the calixarene cavity are equally populated and easily interconverting, suggesting that a non specific hydrophobic interaction plays a key role in the complex stability. These studies have permitted to individuate versatile synthetic receptors for organochlorine pesticides.     

Acetalization and Transacetalization Reactions Catalyzed by Ruthenium,Rhodium, and Iridium Complexes with {2‐{{Bis[3‐(trifluoromethyl)phenyl]phosphino}methyl}‐2‐methylpropane‐ 1,3‐diyl}bis[bis[3‐(trifluoromethyl)phenyl]phosphine] (MeC[CH2P(m‐CF3C6H4)2]3)

The complexes [RhCl_(3−n)(MeCN)_n(CF₃triphos)](CF₃SO₃)_n (n=1, 2; CF₃triphos=MeC[CH₂P(m‐CF₃C₆H₄)₂]₃) and [M(MeCN)₃ (CF₃triphos)](CF₃SO₃)_n (M=Ru, n=2; M=Ir, n=3) are catalyst precursors for some typical acetalization and transacetalization reactions. The activity of these complexes is higher than those of the corresponding species containing the parent ligand MeC[CH₂P(C₆H₅)₂]₃(Htriphos). Also the complexes [MCl₃(tripod)] (tripod=Htriphos and CF₃triphos) are active catalysts for the above reactions. The complex [RhCl₂(MeCN)(CF₃triphos)](CF₃SO₃) catalyzes the acetalization of benzophenone.     

Platinum-promoted cyclization reactions of amino-olefins : I. The cyclization of 4-aminopentene and related compounds

Olefinic amines of the ytpe CH₂CH(CH₂)_nNHR undergo cyclization in acidic aqueous solution at 60°C in the presence of PtCl₄^2?. The PtCl₄^2? is regenerated at the end of the cyclization so that the reaction may be considered as catalytic. Both pyrrolidines and piperidines may be formed although the former are favored.     

Densely-packed self-assembled monolayers on gold surfaces from a conformationally constrained helical hexapeptide

A novel hexapeptide was functionalized at the N-terminus by a lipoyl group for binding to gold substrates. Owing to the high content of α-aminoisobutyric acid residues, the peptide adopts a rigid helical conformation despite the shortness of its main chain. Binding of the peptide to gold was investigated by quartz crystal microbalance, cyclic voltammetry, X-ray photoelectron spectroscopy, and scanning tunneling microscopy under ultra-high vacuum conditions. Scanning tunneling microscopy experiments revealed that the peculiar self-assembly properties of this short helical peptide determine the complex morphology of the monolayer, showing ‘stripes’, i.e. peptide aggregates horizontally layered on the gold surface, and ‘holes’, i.e. Au vacancy islands coated by the peptide monolayer.     

Rapid crack growth in a thermoelastic solid under mixed-mode thermomechanical loading

A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed.