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Kinetic and mechanistic studies have been performed on the cobaloxime-mediated catalytic chain transfer polymerization (CCTP) of tert-butyl methacrylate (t-BMA) and dimethyl itaconate (DMI) in order to further elucidate the role of monomer substituents in the hydrogen-abstraction reaction. The studies on t-BMA, which include a pulsed-laser polymerization study for the determination of the propagation rate coefficient, are inconclusive insofar that they cannot unambiguously distinguish between possible monomer viscosity effects and direct steric interactions between the substituents at the radical center and the cobalt catalyst in the hydrogen-abstraction reaction. Studies on the CCTP of DMI included ¹H, ¹³C, COSY, NOESY, HMQC, and HMBC NMR studies of a mixture of DMI oligomers, which showed that the hydrogen abstraction occurs preferentially from the α substituent of the radical center rather than from the backbone yielding predominantly E isomers. The low chain transfer rate coefficient for DMI is conceivably caused by steric hindrances as a result of the large substituents.

Reactions of Cp2W2Ir2(CO)10 (1) with n equivalents of PPh3 and PMe3 (n = 1, 2) proceed in dichloromethane at room temperature to afford the clusters Cp2W2Ir2(μ-CO)3(CO)7-n(PPh3)n (n = 1 (2), 2 (3)) and Cp2W2Ir2(μ-CO)3(CO)7-n(PMe3)n (n = 1 (4), 2 (5)), respectively, in reasonable yields (38−63%). These products exhibit ligand fluxionality in solution, resolvable at low temperature into the constituent interconverting isomers. A structural study of one isomer of 2, namely 2a, reveals that the three edges of a WIr2 face of the tetrahedral core are spanned by bridging carbonyls and that the iridium-bound PPh3 ligates axially and the tungsten-bound cyclopentadienyl ligands coordinate apically and axially with respect to the plane of bridging carbonyls. Information from this crystal structure and ¹³C and ³¹P NMR spectral data have been employed to assign coordination geometries for the isomers of 2−5. NMR studies included development and use of 2D triple-resonance experiments with carbonyl cluster complexes; these ¹H−³¹P−¹³C correlation experiments, designed to elucidate P−C coupling networks involving phosphorus and carbonyl ligands (a “HPCO experiment”), benefit from the sensitivity enhancement gained from using proton detection. All the isomers of clusters 2−5 contain a carbonyl-bridged WIr2 basal plane and an apical tungsten atom; ligands can be approximately coplanar (radial) to the basal plane or below the plane (axial). The configuration of 2a (axial phosphine, axial Cp, apical Cp), as assigned by NMR spectroscopy, is consistent with the structural determination. A second configuration (2b, 4b:  axial phosphine, axial Cp, apical Cp) is the only one identified (within the temperature range 183−293 K) for the PMe3-substituted cluster 4. Two isomers, both with radial phosphine, axial phosphine, axial Cp, apical Cp configurations, have been identified for 5, namely 5a and 5b; it is likely that isomers of 3 adopt the same configurations. The WIr2-bridged form is seen exclusively across the isomers, indicating that the presence of two electropositive tungsten atoms may be polarizing the electron distribution toward the iridiums, although steric factors may also be involved.

AbstractThe endemic New World eucheiloid complex is distinguished from the other complexes (thyreopteroid, eurycoleoid, somotrichoid, and pericaloid) of pericaline Lebiini by securiform labial palpomere 3, serrate-setose margins of the pronotum, and flattened stylomere 2 of the ovipositor. The geographical range of eucheiloids extends from northern Argentina to southernmost United States (Brownsville, Texas). All taxa are believed to be arboreal. A key distinguishes among the three genera and 16 species, and each taxon is characterized in terms of structural features, habitat, and geographical distribution. The genera are: Hansus, new genus (generitype?H. reichardti, new species); InnaPutzeys (generitype?Inna punctataPutzeys = Polystichus boyeri(Solier)); and EucheilaDejean (generitype?Euchyla flavilabris(Dejean)). Seven new species and one new subspecies are described: Hansus reichardti(type locality?Guyana, EssequiboR.. Morrabali Ck.); Inna palpalis, I. atrata arbor, and I. inpa(type locality?Brazil, Amazonas, near Manaus); I. purpurea(type locality?Brazil, Amazonas, 60 km n. Manaus); I. splendens(type locality?Venezuela, Aragua, Rancho Grande); Eucheila adisi(type locality?Brazil, Amazonas, 60 km n. Manaus); and E. cordova(type locality?M?xico, Veracruz, Cordova). The following new synonymies of specific names are proposed (valid names listed first): Inna costulataChaudoir, 1872 = I. granulataChaudoir, 1872; Inna boyeri(Solier, 1835) = I. punctataPutzeys, 1863, and I. texanaSchaeffer, 1910. A reconstructed phylogeny of the eucheiloids, based on analysis of 60 character states included in 33 characters, shows that Hansusis sister group of the ancestral stock of Inna+ Eucheila. Evolutionary modifications have affected principally body size, head and mouthparts (feeding and associated adaptations), reproductive structures, and features of the body surface thought to be associated with avoidance of predators (concealment and flash coloration). Diversification may also have involved differentiation by habitat (type of forest occupied). The principal theater of evolution has been tropical South America, with incursions both southward and northward. Middle America has been invaded by five lineages, probably during Cenozoic time, from Middle Tertiary to the Quaternary. Of these lineages, three are represented in Middle America by endemic species: E. cordova, I. planipennisBates, and I. nevermanniLiebke. Two lineages are represented by species whose ranges extend northward from South America: I. costulataChaudoir and I. boyeri(Solier).