Olefin Insertion Versus Cross-Coupling in trans-[Pd(Ar)X(AsPh3)2] Complexes (X = I, F, CF3) Treated with a Phosphine-EWOlefin Ligand to Induce Ar–X Coupling

Producción CientíficaAddition of the coupling promoter PEWO ligand 1-(Ph2P),2-(CH═CH–C(O)Ph)C6F4 (PhPEWO-F) to precursors with the displaceable AsPh3 ligand trans-[PdXAr(AsPh3)2] (X = I, F, CF3) fails to induce the pursued Ar–F or Ar–CF3 coupling and results in formation of products of olefin insertion into the Pd–Ar bond for X = I, CF3, and in Ar–Ar coupling for X = F. In the course of the processes, trans-[PdXAr(PhPEWO-F)(AsPh3)] intermediates are observed for X = I, F, CF3, with P-coordinated PhPEWO-F monodentate ligands and a dangling olefin group. For X = I, CF3, subsequent insertion of the double bond into the Pd–Ar bond and O-coordination gives rise to complexes with a P,C,O-pincer system. The observed insertion rates suggest that the limiting step toward insertion is the trans to cis isomerization, while insertion itself is very fast. This is supported by the fast insertion observed when PhPEWO-F is added to cis-[Pd(CF3)Ar(3-F-py)2]. The insertion mechanism in PhPEWO-F resembles the initial phase of the dearomative rearrangement mechanism reported for PdArBrL (L = dialkyl biaryl phosphine).Ministerio de Economía, Industria y Competitividad (Projects CTQ2014-52796-P, CTQ2016-80913-P, and CTQ2014-52974-REDC)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA256U13

Topological Measure Locating the Effective Crossover between Segregation and Integration in a Modular Network

We introduce an easily computable topological measure which locates the effective crossover between segregation and integration in a modular network. Segregation corresponds to the degree of network modularity, while integration is expressed in terms of the algebraic connectivity of an associated hyper-graph. The rigorous treatment of the simplified case of cliques of equal size that are gradually rewired until they become completely merged, allows us to show that this topological crossover can be made to coincide with a dynamical crossover from cluster to global synchronization of a system of coupled phase oscillators. The dynamical crossover is signaled by a peak in the product of the measures of intra-cluster and global synchronization, which we propose as a dynamical measure of complexity. This quantity is much easier to compute than the entropy (of the average frequencies of the oscillators), and displays a behavior which closely mimics that of the dynamical complexity index based on the latter. The proposed toplogical measure simultaneously provides information on the dynamical behavior, sheds light on the interplay between modularity vs total integration and shows how this affects the capability of the network to perform both local and distributed dynamical tasks

440 MHz radar observations of plasma turbulence in the auroral lower ionosphere

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989.Includes bibliographical references (p. 274-287).by Carlos F. del Pozo.Ph.D

QCD

We discuss QCD studies that will be possible at LEP2. We examine both experimental and theoretical aspects of jets, fragmentation functions, multiplicities and particle spectra.Comment: 44 pages, Latex, epsfig, 18 figures, to appear on the Report of the Workshop on Physics at LEP2, CERN 96-01, vol. 1, 199