Ferrocene—Beauty and Function - American Chemical Society

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FerroceneBeauty and Function

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metalation of a chiral ferrocenylphosphonic diamide yields triphenyl tin derivatives in high diastereomeric purity according to a protocol by Jurkschat. The cycloaddition chemistry of ferrocenyl-substituted anthracenes is explored by Nikitin and McGlinchey. Herrmann and Kühn insightfully illustrate how ferrocenecarboxylates can be combined with quadruply bonded dimolybdenum units to generate polymolybdenum triangles and squares. Owing to the favorable redox properties, a large fraction of the contributions is devoted to electron transfer between ferrocene units or between ferrocene and other redox centers both intra- and intermolecularly and to applications of such switchable systems. In a detailed review on oligoferrocenylsubstituted five-membered heterocycles Lang and co-workers demonstrate that electron-rich heterocycles and the 2,5substitution pattern promote electron transfer between ferrocene/ferrocenium units. Electronic communication within naphthalene-bridged iron sandwich complexes has been demonstrated by Wolf et al. using a plethora of spectroscopic methods. Redox-interacting di- and triferrocenylsilanes are prepared and covalently bound to platinum oxide surfaces by Casado and Alonso. Electronic coupling in oligopyrroles with ferrocenyl termini is observable up to the dipyrrole bridge, as demonstrated by Lang. Binuclear iron−copper systems using dppf and copper(I) investigated by Sarkar reveal iron-based oxidations and ligand-based reductions. Kaim and co-workers present a tetranuclear Fe2Cu2 redox system that shows weakly interacting ferrocene units via a Cu−N−N−Cu linkage. Electron transfer is intimately coupled to proton transfer in a valence-tautomeric ferrocenium−phenolate radical, as shown by Heinze et al. Electronic coupling between two different peripheral electrophores, ferrocene and tetrathiafulvalene, across a bis-acetylide ruthenium organometallic bridge has been demonstrated by Barrière. The characteristic charge resonance transitions of oxidized, unsymmetrically substituted 1,1′-biferrocenylenes place these cations into class III mixedvalence systems according to Schmittel and co-workers. Aminomethyl-substituted ferrocenesavailable by selective reductive amination of formylferrocenesreveal distinct oxidations of the amine and ferrocene redox units, as shown by Hierso. Torriero and Bond disclose mechanistic details of the homogeneous catalytic oxidation of organic amines in the presence of electrochemically generated ferrocenium ions as catalysts. The redox properties of dendrimers constructed by ionic bonds are highlighted in an article by Astruc et al. The ability of linear and branched ferrocenes to exhibit novel charge transport properties is exemplified by Albrecht and Long. A bis(tryptophan) derivative of ferrocene undergoes thermal- and redox-controlled supramolecular rearrangements, as showcased by the group of Kraatz. Due to the electronically isolated ferrocene unit in cross-conjugated 1,1-bis(alkynyl)-2-ferrocenylethenes, these systems are suggested by Hartl, Kaupp, and Low

ince ferrocene was independently discovered in 1951 by Kealy, Pauson, and Miller, the impact of this breakthrough and pioneering work has been enormous. It opened new areas of chemistry, deepened our understanding of structure, bonding, and reactivity, and hence paved the way for the burgeoning field of organometallic chemistry itself. Ferrocene and ferrocene-based molecules are not mere trophy molecules for the shelf; rather, the synthesis of this sandwich system in all its flavors, its versatile reaction chemistry, structural features, attendant mechanistic and theoretical studies, its use in homogeneous catalysis, especially in stereoselective and asymmetric transformations, in electrochemistry, particularly in electron-transfer processes, as new materials including polymer chemistry, as fuel additives, as anticancer reagents, in bioorganometallic chemistry, etc. has contributed to the rapid growth and hence rapidly moving frontiers of this family of compounds during the last 60+ years. The special issue FerroceneBeauty and Function highlights all of these topics and confirms the sustained key role of ferrocene in organometallic chemistry. The cover art for this issue is intended to convey the strong excitement and enthusiasm for ferrocene and ferrocene-based molecules of all the contributors of this special issue, although the number, quality, and diversity of the contributions are challenging to combine in a single artistic rendering. We tried, however, to graphically illustrate some major topics addressed in this issue. Synthetic advances in the field of ferrocene chemistry ranging from basic substitution reactions to stereoselective transformations and polymer synthesis are reported by several groups. A review article by Lang gives an overview of methodologies developed so far for the synthesis of planar chiral ferrocences. Gasser and co-workers report a threecomponent reaction of aminomethyl ferrocenes, amines, and elemental sulfur to give thioamides. Applying the ferrocene diamine scaffold to generate a chelating bis(phosphinoamide) ligand system has been shown by Fryzuk to effectively prevent ligand redistribution in scandium hydride complexes. Zakrzewski obtained monoalkenylated ferrocenes using electron-poor alkenes and Pd(OAc)2/4,5-diazafluoren-9-one as catalyst in an aerobic dehydrogenative Heck alkenylation of ferrocene. Butenschön discloses an anionic thia-Fries rearrangement of electron-rich ferrocenyl triflates to ferrocenoles. Half-open ferrocenes with edge-bridged open indenyl ligands are presented by Tamm and co-workers. Walter reports the synthesis, reactivity, and electronic structure of sterically encumbered diazaferrocenes. Jäkle presents a new route to planar chiral Lewis acid base pairs by borylation of stannyl(pyridyl) and mercurio(pyridyl) ferrocenes disclosing different (stereochemical) mechanisms. Tamm and co-workers provide the ferrocene community with an efficient and simple method for the preparation of 1,1′-ferrocenedicarboxylic acid and various 1,1′-disubstituted ferrocenes derived therefrom. AB and AB2 block copolymers consisting of redox-active poly(vinylferrocene) and biodegradable poly(L-lactide) have been crafted by Frey and Gallei. A diastereoselective ortho © 2013 American Chemical Society

Special Issue: Ferrocene - Beauty and Function Published: October 28, 2013 5623

dx.doi.org/10.1021/om400962w | Organometallics 2013, 32, 5623−5625

Organometallics

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metallic proton sponges and (b) tridentate ligands toward metal centers with Fe→M dative bonds. Ferrocene−bridge− acceptor chromophores with second-order nonlinear optical properties are studied using TD-DFT methods by Barlow et al. Cucurbiturils have attracted great attention in supramolecular chemistry, and Kaifer illustrates how 1,1′-bis(alkylammonium)ferrocenes afford pseudorotaxanes with the ferrocenyl residue in the host cavity. In our opinion, the wealth and diversity of these excellent and stimulating contributions to this “old” but groundbreaking and frontier-crossing field are astounding. When organizing such a special issue, it is inevitable that there will always be some authors missing who are experts in the field of ferrocene chemistry. Nevertheless, the idea of presenting an overall picture of the importance of ferrocene and ferrocene-based compounds in organometallic chemistry as outlined above has clearly been accomplished by the contributors who have participated. We sincerely wish to thank all those who have helped bring this special issue to fruitionthe authors, the reviewers, the editors, and the production personnel, all of whom have critically evaluated and improved the content. We hope that the readers of Organometallics will find this selection interesting and stimulating in terms of further advancing the field and expanding the scope of applications of arguably the most beautiful and versatile organometallic moleculeferrocene.

as templates for electrochemically gated quantum interference transistors. The wettability of surfaces modified with poly(vinylferrocene) or poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate) is affected by the oxidation state of the ferrocene units, as shown by Gallei. Rüffer establishes that the oxidation of ferrocenyl units can play a crucial role in fine-tuning magnetic superexchange interactions in bis(oxamato) copper systems. In an effort directed at nanoscopic electrochromes, Astruc has decorated various rigid scaffolds with bi(ferrocenyl) substituents and examined the effect on a number of physical properties as the iron units are successively oxidized. Bioorganometallic chemistry and medical applications of ferrocene derivatives are exemplified by a wealth of contributions. The review of Braga focuses on medicinal ferrocenes with cytotoxic activity, classifying them into functionalized ferrocenes, heterobimetallic complexes with ferrocene ancillary ligands, and supramolecular architectures which act as ferrocene delivery systems. In their study Zakrzewski et al. suggest that biotin can serve as a biological vector delivering cytotoxic ferrocenyl moieties to cancer cells. Top and Jaouen report the synthesis and characterization of a new family of organometallic suberamides with antiproliferative activities against triple-negative MDA-MB-231 and hormonedependent MCF-7 breast cancer cell lines. Kowalski presents syntheses and biological studies of uracil−ferrocene derivatives showing activity against cancer cells and several bacterial strains. Improved antimycobacterial activities are demonstrated by Biot and Kumar for ferrocene-linked isatins. Oxindolecontaining ferrocenes inhibit kinases at submicromolar concentrations, as demonstrated by Spencer. A novel ferrocenyl-substituted heteroscorpionato NNO ligand with potential as part of an active site model of nonheme iron oxygenase is featured in an article by Burzlaff. Ferrocenecontaining phosphines have been converted to mercapto gold derivatives by Gimeno, and biological assays establish an impressive level of antitumor activity. Ferrocenyl-containg ligands are widely used in catalytic and sensing applications: Štěpnička has employed novel phosphinoferrocene carboxamides as ligands in palladium-catalyzed Suzuki−Miyaura cross-coupling reactions in dioxane and in pure water. Bimetallic catalysis promoted by bispalladacycles connected by a flexible ferrocene unit is demonstrated by Miehlich and Peters. Hey-Hawkins has designed chiral ferrocene-based ligands for grafting onto silica surfaces. Anion sensing and detection of Hg2+ by electrochemical and optical means is achieved using ferrocene-substituted triazoles by Tarraga and Molina. Jurkschat and Jouikov narrate a detailed study of crown ether substituted tin-containing ferrocenophanes for complexation of lithium chloride. Unusual bonding situations such as those found in strained ferrocenophanes or metal−metal interactions such as those found in bimetallic complexes are discussed in several contributions, often with a strong theoretical background. Manners’ review summarizes recent advances in the field of strained ferrocenophanes, focusing on their preparation, structural characterization, electronic structure, and unusual reactivity. Nataro et al. have found weak iron−metal interactions in 1,1′-bis(di-tert-butylphoshino)ferrocene complexes with platinum and palladium, as corroborated by X-ray diffraction and DFT calculations. Diaconescu has systematically analyzed the electronic properties of 1,1′-diamidoferrocene uranium adducts as a function of oxidation state. Siemeling highlights ferrocene-bridged bis(guanidines) as (a) organo-

Katja Heinze,* Guest Editor

Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University, Mainz, Germany

Heinrich Lang,* Guest Editor

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Institute of Chemistry, Technische Universität Chemnitz, Chemnitz, Germany

AUTHOR INFORMATION

Corresponding Authors

*E-mail for K.H.: [email protected]. *E-mail for H.L.: [email protected]. Notes

Views expressed in this editorial are those of the authors and not necessarily the views of the ACS. The authors declare no competing financial interest. Biographies

Katja Heinze is professor of organometallic and bioinorganic chemistry at the Johannes Gutenberg University of Mainz, Germany. After receiving a diploma degree (1995) and a Ph.D. degree (1998) from the University of Heidelberg (G. Huttner), she went for a postdoctoral stay to the University of Zurich, Zurich, Switzerland (1999). She was 5624

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Organometallics

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appointed Privatdozent in 2004 at the University of Heidelberg and Full Professor in 2008 at the Johannes Gutenberg University of Mainz. She received the Lieseberg award of the Faculty of Chemistry and Earth Sciences, University of Heidelberg (2002), a Heisenberg fellowship from the Deutsche Forschungsgemeinschaft (2004), and a Hengstberger Award of the University of Heidelberg (2007). Currently she serves as vice spokesperson of the International Research Training Group 1404 - Self-organized Materials for Optoelectronics and as vice chair of the Institute of Inorganic and Analytical Chemistry, University of Mainz. Since 2011 she has served as a member of the International Advisory Board of Organometallics.

Heinrich Lang studied chemistry at the University of Constance, where he graduated in Chemistry (Diploma, 1982; Ph.D., 1985) under the supervision of G. Huttner. Afterward he spent two years as a postdoctoral fellow (DFG) at MIT with D. Seyferth. He joined the Faculty at the Ruprecht-Karls-University of Heidelberg in 1988, where he received his Habilitation in 1992. From 1992 until 1996 he held the position of a Privatdozent as a Heisenberg fellow (DFG) at the same university. Since 1996 he has been a full professor (holding the Chair of Inorganic Chemistry) at TU Chemnitz. A call to TU Kaiserslautern in 2003 was declined. He is a member of scientific and editorial advisory boards and has published 570 peer-reviewed papers and received many honors and awards. Since 2012 he has been vice president of TU Chemnitz for Research and Young Scientists. His research interests are in organometallic and metal−organic chemistry, electron transfer studies, inkjet printing, gas-phase deposition, spray coating of conductive/semiconductive patterns/layers, and homogeneous catalysis. He is also interested in topics such as hybrid materials and nanomaterials, including metal and metal oxide nanoparticles and their embedding in polymers, and is researching the field of photovoltaics.

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