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Tetrasubstituted-Cyclobutadienepalladium Halides
Full text linkTitle: Tetrasubstituted-Cyclobutadienepalladium Halides, Author: David F. Pollock, Location: ThodeDiphenylacetylenes, RC2R, (R=C6H5, p-ClC6H4 , p-CH3C6H4 , p-CH3OC6H4) reacted with
palladium (II) complexes to give [R4C4OEtPdC1]2 , or
[R4C4 (PdCl2)nI2 and R6C6. Hydrogen halides converted
[R4C4OEtPdCl]2 to [R4C4PdX2]2. Particularly significant were the reactions in
which a cyclobutadiene (R4C4) was transferred from
palladium or nickel onto other metals. A very interesting
reaction was the unprecedented ligand exchange. (R4C4PdX2)2 + 2(R'3P)2NiX2 -> (R4C4NiX2)2 + 2(R'3P)2PdX2 R'OH reacted with [R4C4PdX2]2 (except R=p-CH3OC6H4) to
give exo[R4C4OR'PdX]2 and acids reversed this reaction.
Some complexes [R4C4PdC5H5]+ were also made by ligand
transfer of the cyclopentadienyl ligand onto palladium. 1 H.N.M.R. studies of compounds derived from p,p'-disubstituted diphenylacetylenes showed that the phenyl
region of the spectrum could be used to determine if
the compound possessed the symmetry of a cyclobutadiene
compound.ThesisDoctor of Philosophy (PhD
Studies on Cyclobutadiene-Metal Complexes
Full text link Reaction of tetraphenylcyclobutadienepalladium halides, [(Ph4C4)PdX2]2, with [(C5H5)M(CO)3]2 (M=Mo or W) gave complexes of the type (Ph4C4)(C5H5)M(CO)X (M=Mo, X=Cl, Br or M=W, X=Br). Conversely, reaction of [(R4C4)PdBr2]2 (R=C6H5, p-CH3C6H4) with [(C5H5)Fe(CO)2]2 or (C5H5)Fe(Co)2Br led not to the expected transfer of the cyclobutadiene ring group onto iron, but to complexes of the type [(R4C4)M(C5H5)]+ FeBr4- (M=Pd or Ni). These were converted into the diamagnetic bromides. [(R4C4)M(C5H5)]+ Br- which, on treatment with sodium methoxide, gave the cyclobutenyl complexes (R4C4OMe)M(C5H5) of palladium and nickel. The complexes (R4C4)Co(Co)2X (R=C6H5, p-CH3C6H4, X=halogen) have been prepared by ligand-transfer reactions from [(R4C4)PdX2]2. The reactions of (R4C4)Co(CO)2X show considerable similarity to those of (C5H5)Fe(CO)2X, and evidence for a very strong metal-ring bond in the cobalt complex is
presented. Reaction of (R4C4)Co(CO)2Br with C6F5Li gave the very stable
(R4C4Co(CO)2C6F5. With aromatic hydrocarbons in the presence of AlCl3, (R4C4)Co(CO)2Br gave the stable [(R4C4)Co(π-Arene)]+; cycloheptatriene also reacted with (R4C4)Co(CO)2Br in the absence or a catalyst to give [(R4C4)Co(C7H8)]+. Nucleophilic attack occurred readily at the C7H8 ring in [(R4C4)Co(C7H8)]+ and less readily at the benzene ring in [(R4C4)Co(C6H6)]+ to give (R4C4)Co(cycloheptadienyl) and the (R4C4)Co(cyclohexadienyl)
complexes, respectively. The order of susceptibility of π-complexed ligands in metal d^8 complexes towards nucleophilic attack, cycloheptatriene> benzene> (R4C4)> cyclopentadienyl, is proposed. A novel method for effecting hydride abstraction is reported. Aniline in [(Ph4C4)Co(π-Aniline)]+ is less basic than aniline itself by approximately 1.5 pK units.ThesisDoctor of Philosophy (PhD
Reactions of Some Rhodium and lridium Hydrides
No full textReactions of the complexes [C₅Me₅MCl₂]₂ (M=Rh and Ir) with alcoholic base gave the bridged hydrides (C₅Me₅M)₂HCl₃. The hydrides reacted readily at room temperature with cyclic and acyclic diolefins to give π-allylic complexes, the cyn- isomers being the ones obtained when a choice was available. When both terminal and internal double bonds were present, addition of M-H occurred preferentially to the terminal double bond. The allylic complexes showed varying degrees of stability towards reductive elimination (by lossof HCl) and the formation of 1,3-diene complexes. Allyis with only syn-substituents were stable towards diene complex formation. Those with an additional C-2 methyl substituent were less stable and the diene complexes could be obtained under moderately drastic conditions, presumably via G-allyl intermediates. Allyls with an anti-methyl or -methylene substituent underwent reductive elimination of HCI to give diene complexes spontaneously and these reactions were accelerated by the presence of triethylamine. Kinetic studies on these hydride-diene reactions indicated that the reactions were first-order with respect to the hydride and independent of the nature and concentration of the diene. Except for 2,5-dimethyl-2,4-hexadiene, all dienes studied reacted at the same rate with the same hydride. The deuterides (C₅Me₅M)₂DCl₃ did not show any significant kinetic isotope effect. These results suggested that the rate-determining step of these hydride-diene reactions was the cleaving of the chloride bridge to create a vacant site. Mechanisms for the formation and decompositions of the allyls are proposed. Reactions of [C₅Me₅MCl₂]₂ with dibenzylideneacetone, allyl cyanide and some β-diketones are described.Doctor of Philosophy (PhD
Homogeneous Hydrogenation and Isomerisation of Olefins catalysed by Pentamethylcyclopentadienyl-rhodium and -iridium complexes
No full textThe catalytic activity of a series of pentamethylcyclopentadienyl-rhodium and -iridium complexes was explored to determine which catalytic species were significant. The halide complexes [M(C₅Me₅)x₂]₂ ((=Cl, Br, I) were inactive and required the presence of base as co-catalyst for the homogeneous hydrogenation of olefins. As a part of this investigation, a number of new mono-ρ-hydrido [(M(C₅Me₅))₂HX₃], di-ρ-hydrido [Ir(C₅Me₅)HX]₂, and related complexes were isolated and successfully synthesised and characterised. The hydrido complexes [(M(C₅Me₅))₂HX₃] and [lr(C₅Me₅)HX]₂ catalysed the hydrogenation of olefins in the absence of base at 1 atm and ambient temperature. However, they did show some co-catalysis by base and the effect of base on catalytic activity of [M(C₅Me₅)Cl₂]₂, [(M(C₅Me₅))₂HCl₃] and [Ir(C₅Me₅)HCl]₂ was carefully examined. The iridium complexes showed some deactivation on addition of excess triethylamine due to the formation of the caralytically inactive cationic complex [(Ir(C₅Me₅))₂H₃]. No such deactivation and formation of cationic complex was observed for the rhodium system. In general iridium complexes were better catalysts than rhodium ones. The hydrogenation appeared to be favoured by polar and weakly coordinating solvents, particularly isopropanol. A premliminary study of the mechanism of the reactions catalysed by these complexes indicated that the mono-μ-hyrdrio complexes reacted mainly as dimers and dichlorides and di-μ-hydrido complex [Ir(C₅Me₅)HCl]₂ reacted predominantly as monomer; mechanisms are presented to account for these observations. The hydrido complexes [(M(C₅Me₅))₂(D)HCl₃] and [Ir(C₅Me₅)HCl]₂ were also active catalysts for the isomerisation of olefins. During the isomerisation of 4-methylcyclohexene by [(Ir(C₅Me₅))₂DCl₃], appearance of a high field hydride resonance was observed and these reactions are explained in terms of a hydride addition-elimination mechanism. ecies "cre stgnific.ant. The hal ide c~~lexes pl(CSMeS)xzlz ( =. Cl, B ",I) ~e.re ina~tiv,e'and ,required the presence, of base as co~cata1.yst forth'hC!':JQeneous 'hydroQen~ -.' .,'I ,~a' part of thls investi~ation.a numb!J-r 0t, ne\~ oono-~-hydrido_[(M(~SI~e5) i ZHX 3]. d;"-;,-hydr,ido [I~(C5Me5)HX]Z" and'Tflated complexes \~ere"isola~e:1 and s,uccessfull y syntheslsed ~ni1 .c~aracteris:d. . .'.Thehydrido comple~es ['M!Cs~es~)zHX3] and [l~(c5r~e's)HX}L cthe hydrogenation of olefins in t~e absence of base at 1 atm and a~bient_"temperature. However. they did show some co-catalysis by bas~ and ~heeffect Of, !and:[lr(C5~leS)HC.1]2wascarefully, exar.1ined. The iridium compl,,1.'!?s sho','led'. some deactivation. on addit~on of ~xC:~ss trtethYl,ar.line due to t~o~!"'.ationof thecatalytlC-:lly InactIve catlon'\ccomple~ [(!r(CS~1e5)12Hp'\""'iu-- .such deactivation,and formation of cationic complex was observed for theI'hod i urn .sys tem. "In general iridium compleJones. The hydrogenation appea'red to be favoured 'by polar 'and weakly co-I ,ordinating sOflvents. partic:ul.arl y isopropanol: ' I.l,.- A prel.,jminary stud/of the ;,echaniS!:1of the reactlons catalysedl' ,'} by these ccmplexes indicated that the mono-~-hydrido complexes reacted mainly as ,dimers and dichlorides ~nd di-u-,hydridocomplex [Ir(CSf.leS)HC1]Z. \ ' 'reacted predominantly 4S monomer; mec~anisms are. pres~nted to dCco~nt forthese observations, !. (0).'- The hydrido complexes [(H(CSMeS)i ZHC13] and [lr(.CSMeS)HC1]Z 4'e.also active catafysts for the isomerisation of olefins, .During the isom- . . ~eri sa ti on of 4-methylcyc Iohexene by ['(l r( CSfi,eS)) ZOeI3], a ppeari\nce of ahi gh fi el d hydride resonance was observed and thes,e re&c t ions are ~xp I ai nedin" terms of a hydride addition~eliminationinechanism.Doctor of Philosophy (PhD
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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