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By means of metal-atom ligand-vapor cocondensation as well as via wet chemical methods (lithiation and follow-up reaction) the first organostannyl substituted bis(arene)metal complexes (R3Sn-eta(6)-C6H5)(2)M have been prepared: 15 (R = Me, M = V), 16 (R = Ph, M = V). 13 (R = Me, M = V), 17 (R = Ph, M = Cr). Despite the bulkiness of the Ph3Sn groups the geometry of the central sandwich unit in 17 deviates only marginally from that of the parent complex (C6H6)(2)Cr (2) The triclinic unit cell of 17 (space group: P (1) over bar; a = 9.414(4), b = 9.877(5), c = 11.012(13) Angstrom; alpha = 83.51(7), beta = 87.95(7), gamma = 72.67(4)degrees) contains one independent molecule. Perturbation of the electronic structure of the bis(arene)metal unit by organostannyl groups appears to be minute because EPR spectra of the M(d(5)) species fail to reveal deviations from axial symmetry The potentials for reversible oxidation of the Me3Sn-substituted complexes 13 and 15 differ insignificantly (anodic shifts less than or equal to 20 mV) from those of the parent species 1 and 2; reductions are irreversible in both cases. More sizeable anodic shifts are observed for the Ph3Sn-derivatives 16 and 17; here as well, only the redox pairs 0/+ are reversible. The resistance of the neutral complexes to protic media contrasts to ready hydrodestannylation of the complex cations. By way of metal exchange, employing n-butyl lithium, 13 affords (Li-eta(6)-C6H5)(2)Cr strictly 1,1'-disubstituted and devoid of auxiliary base.

Mono-and digerma[n]metallocyclophanes (n = 1, 2) [(eta(6),eta(6)'-dimethyldiphenylgermane)M] (M = Cr, 17; V, 18(.)), [(eta(6),eta(6)'-tetraphenylgermane)M] (M = Cr, 20; V, 21(.)), and [(1,1,2,2-tetramethyl-1,2-di-eta(6),eta(6)'-phenyldigermane)Cr] (24) were synthesized by means of lithiation and subsequent reaction with dichlorodimethylgermane or dichlorodiphenylgermane. Metal-ligand cocondensation of bromodimethylphenylgermane with chromium atoms followed by reductive coupling with lithium naphthalide gave the digermane complex 24. Additionally, the nonbridged derivatives [bis(trimethylgermyl-eta(6)-benzene)M] (M = Cr, 10d; V, 11(.)), [(trimethylgermyl-eta(6)-benzene)(eta(6)-benzene)Cr] (10m), and [bis(triphenylgermyl-eta(6)-benzene)M] (M = Cr, 14; V, 15(.)) were prepared and characterized by H-1- and C-13-NMR (10m, 10d, 14, 17, 20), cyclic voltammetry (CV) (10d, 11(.), 14, 15(.), 18(.), 21(.), 24), and EPR spectroscopy (10d(.+) 11(.), 14(.+), 15(.), 18(.), 21(.), 24(.+)). Crystals of 20 were subjected to a structure determination by X-ray diffraction, which disclosed a bending of the sandwich axis from linearity by 14.4 degrees. The strain exerted on the coordinated benzene ring forces a pyramidal structure on the ipso-C leading to a markedly shielded C-13-NMR resonance. An EPR spectroscopic investigation of the vanadium derivatives reveals an increasing metal to ligand spin delocalization and the appearance of orthorhombic g and A tensors on bending the sandwich axis. While the redox potentials are virtually unaffected, when passing from the unstrained vanadium complexes 11(.) and 15(.) to the germa[1]vanadocyclophanes 18(.) and 21(.), the transient monocationic species of the latter are destabilized dramatically. No evidence of ring-opening polymerization was observed on heating 18(.) to 165 degrees C. Instead, metal-ligand cleavage occurs.

This paper reports on the computer-aided reaction pathway analysis for hydrocracking and hydrogenation of NMBB over Mo and Fe catalysts.

The catalytic effects of several molybdenum-, cobalt-, and iron-containing compounds have been examined in the reactions of dibenzothiophene (DBT) with hydrogen under conditions related to coal liquefaction. The metal compounds are candidate catalyst precursors for direct coal liquefaction. The reactions were carried out in batch microautoclave reactors at 400 degrees C for 30 min with 6.9 MPa (cold) hydrogen pressure and tridecane solvent. A metal loading of 0.5 mol % resulted in low conversion and only hydrogenation. Addition of sulfur in a 4:1 molar ratio led only to a minor increase in conversion and hydrodesulfurization. The use of a higher boiling solvent (octadecane vs tridecane) was beneficial in providing increased conversion, hydrodesulfurization, and hydrogenation. An increase in metal compound loading to 36.2 mol % led to a dramatic increase in conversion, hydrodesulfurization, and hydrocracking. Molybdenum hexacarbonyl at 36 mol % loading, with added sulfur at 6:1 ratio and octadecane solvent, gave 100% conversion of dibenzothiophene to other products with 100% hydrodesulfurization. Ammonium tetrathiomolybdate and molybdenum(III) chloride are less active under similar conditions. A cobalt-molybdenum thiocubane complex gave unexpectedly low conversions. iron and cobalt carbonyls also provided very low conversions, even with added sulfur.

Coal liquefaction may involve cleavage of methylene, dimethylene and ether bridges connecting polycyclic aromatic units and the reactions of various oxygen functional groups. Here in this quarterly, we report on the effects of dispersed Mo catalysts and H{sub 2}O addition on hydrogenation and C-C bond hydrocracking of 4-(1- naphthylmethyl)bibenzyl, abbreviated as NMBB. Recent research in this laboratory has demonstrated a strong synergistic effect between a dispersed Mo sulfide catalyst and water in low-severity coal liquefaction reaction. This finding prompted us to examine the effects of dispersed Mo catalysts and H{sub 2}O addition on hydrogenation and C-C bond hydrocracking of 4-(1-naphthylmethyl)bibenzyl, NMBB. Batch studied in microautoclave reactors at 350 and 400{degrees}C for 30 min revealed that active catalysts can be generated in situ from either ammonium tetrathiomolybdate (ATTM) or Mo(CO){sub 6} under the reaction conditions (350 or 400{degrees}C, 30 min), with the main catalysis of the latter for NMBB hydrogenation, but the former for C-C bond cleavage. Water may have strong promoting effect on NMBB conversion in catalytic runs, depending on the conditions. At 350{degrees}C a 50% increase in NMBB conversion was observed upon H{sub 2}O addition to the run using ATTM (1 wt % Mo) as catalyst. However, at 400{degrees}C no major difference in conversion or product distribution was found. Runs of NMBB at 350{degrees}C using Mo(CO){sub 6} lead to tetrahydro-NMBB-derivatives and few cleavage products. Water added to Mo(CO){sub 6} suppressed hydrogenation. The combination of Mo(CO){sub 6} and S lead to almost complete conversion of NMBB. A run with Mo(CO){sub 6}/S/H{sub 2}O gave similar results. It appears that water can increase NMBB conversion with ATTM at 350{degrees}C but decreased conversion for runs at 400{degrees}C. Also contained in this report is mechanistic discussion for hydrocracking and hydrogenation of NMBB.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMetal .pi. complexes of benzene derivatives. 47. Zircona[1]metallocyclophanes: synthesis, properties, and structure of (tBu-.eta.5-C5H4)2Zr(.eta.1-1,.eta.1-1')(.eta.6-C6H5)2V and its chromium analogChristoph Elschenbroich, Eckhardt Schmidt, Bernhard Metz, and Klaus HarmsCite this: Organometallics 1995, 14, 9, 4043–4045Publication Date (Print):September 1, 1995Publication History Published online1 May 2002Published inissue 1 September 1995https://pubs.acs.org/doi/10.1021/om00009a005https://doi.org/10.1021/om00009a005research-articleACS PublicationsRequest reuse permissionsArticle Views97Altmetric-Citations41LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

This chapter discusses the activity and selectivity of iron (Fe) catalysts from organometallic and inorganic precursors for the hydrocracking of 4-(1-naphthylmethyl) bibenzyl. Some iron-containing catalysts have higher activity in the sulfur-free form. Adding sulfur to Fe precursors with Cp-ligands decreased the activity of the resulting catalyst. A positive correlation between sulfur addition and increased activity is seen, but a reversed trend between Fe cluster size and hydrocracking conversion is also observed for carbonyl-type Fe precursors. The activity and selectivity of Fe catalysts for 4-(naphthylmethyl)bibenzyl conversion depends strongly on the type of ligand environment, the oxidation state, and the number of intermetal bonds in the molecular precursor.

The 1,4-Dihydropyridine-bislactone 4 is obtained from nifedipine by the Young method. The pyridinium compound 3 and the brominated 1,4-dihydropyridine monolactones 5 and 6 are isolated from this reaction as by-products. 4 is characterized by redox and photo-chemical reactions. The half-wave potentials of the dihydropyridines and pyridines are determinated.

Anellated Lactones from Bay-K-8644 and Dihydropyridine By-Products in the Hantzsch Synthesis Bay-K-8644 ( 1 ) reacts with pyridiniumbromide perbromide (PBPB) to yield the anellated 1,4-dihydropyridine (DHP) lactone 7 and the pyridinium compound 8 , whose irradiation with UV A-light leads to the 3-pyridinoles 10 and 11 . The monolactone 12 , the bislactone 13 and the dibromomethyl derivative 14 can be isolated from the diester-1,4-DHP 2 with PBPB. The 1,2-DHP 4 , isomeric to 1 , with PBPB only gives the oxidation product 17 , while the diester-1,2-DHP 5 leads to the pyridine (Py) 18 as well as to the anellated 1,2-DHP-lactones 19 and 24, 25 is obtained from 24 by solvolysis. All DHPs are dehydrogenated to the corresponding pyridines. The half-wave potentials of the DHP/Py system are determined by anodic oxidation and relationships to structural parameters are discussed. The 1,4-DHP 13 is formed in a two electronic reaction from the pyridine lactone 16 by polarographic assay, which is proven by preparative cathodic reduction.

The nitro compounds 1 and 2 have been reduced to the phenylhydroxylamines 3 and 4 and transformed into the benzhydroxamic acids 5 and 6. From the reduction of the 1,2-dihydropyridine 2 the 2,6-methano-1,5-benzodiazocine 10 could be isolated as a by-product. All dihydropyridines are characterized by their half-wave potentials, their retention times obtained by hplc and spectrometric methods.

Reaction of Nifedipine with Pyridinium Bromide Perbromide The 1,4-Dihydropyridine-bislactone 4 is obtained from nifedipine by the Young method. The pyridinium compound 3 and the brominated 1,4-dihydropyridine monolactones 5 and 6 are isolated from this reaction as byproducts. 4 is characterized by redox and photo-chemical reactions. The half-wave potentials of the dihydropyridines and pyridines are determinated.

Das zu dem Calciumantagonisten Nifedipin isomere 1,2‐Dihydropyridin 3 reagiert mit Pyridiniumbromidperbromid (PBPB) zum korrespondierenden Pyridin 4 und dem Dihydropyridinlacton 5 als Nebenprodukt. Lichtexposition von 5 führt zum Nitrosopyridin 8 , Oxidation zum Nitropyridin 12. 12 läßt sich besser auf dem alternativen Weg über das N ‐Oxid von 4 , Boekelheide ‐Umlagerung und Lactonisierung darstellen. Durch Reduktionsverfahren können aus 12 die cyclische Hydroxamsäure 13 und das Lactam 14 erhalten werden.

Die möglichen Nebenprodukte bei der Hantzsch ‐Synthese des Calcium‐Agonisten Bay‐K‐8644 (1), die symmetrischen 1,4‐Dihydropyridine (DHP) 2 und 3, die 1,2‐DHP 12, die Tetrahydropyrimidine (THPM) 16, das Hydrobenzamid 18 und das Amarin 19 werden dargestellt. Als neuer Verbindungstyp wird das Nitroalkyl‐Aldimin 13 isoliert. Durch Dehydrierung werden die zu erwartenden Metabolite, die Pyridine 9 und 14 und das Pyrimidin 17 gewonnen. Die Nitroverbindungen 1, 9c und 12a werden mit Zink zu den Aminopyridinen 10 und 15 reduziert. 1 reagiert in MeOH mit UV A‐Licht zu den 3‐Pyridinolen 11a und b; aus 3 wird unter gleichen Bedingungen das 5‐Nitro‐3‐pyridinol 11c erhalten. Elektrochemische Untersuchungen beweisen, daβ die 1,4‐DHP stabiler sind als die 1,2‐DHP. Halbstufenpotential‐Struktur‐Beziehungen bei anodischen Oxidationen von DHP und THPM sowie bei kathodischen Reduktionen von Nitroverbindungen werden analysiert.

Die Nitroverbindungen 1 und 2 wurden zu den Phenylhydroxylaminen 3 und 4 reduziert und zu den Benzhydroxamsäuren 5 und 6 umgesetzt. Als Neben‐produkt der Reduktion des 1,2‐Dihydropyridins 2 wurde das 2,6‐Methano‐1,5‐benzodiazocin 10 isoliert. Alle Dihydropyridine werden durch ihre Halbstufenpotentiale, die durch HPLC ermittelten Retentionszeiten und spektrometrische Methoden charakterisiert.

The 1,2-dihydropyridine 3, isomeric to the calcium antagonist nifedipine, reacts with pyridiniumbromideperbromide (PBPB) to yield the corresponding pyridine 4 and the dihydropyridine-lactone 5 as a by-product. 5 is extremely sensitive to light giving the nitrosopyridine 8, while oxidation leads to the nitropyridine 12. 12 is better accessible by the alternative route via the N-oxide of 4, Boekelheide rearrangement and lactonization. The cyclic hydroxamic acid 13 and the lactame 14 were obtained from 12 by reductive processes.