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Non-innocent ligands

Berben, L.A.; de Bruin, B.; Heyduk, A.F.

Published in:Chemical Communications

DOI:10.1039/c4cc90480j

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Citation for published version (APA):Berben, L. A., de Bruin, B., & Heyduk, A. F. (2015). Non-innocent ligands. Chemical Communications, 51(9),1553-1554. https://doi.org/10.1039/c4cc90480j

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Download date: 22 Mar 2020

This journal is©The Royal Society of Chemistry 2015 Chem. Commun., 2015, 51, 1553--1554 | 1553

Cite this:Chem. Commun., 2015,

51, 1553

Non-innocent ligands

Louise A. Berben,a Bas de Bruinbc and Alan F. Heydukd

Redox reactions, bond-making and bond-breaking events and hydrogen bondinginteractions all play an important role inchemical transformations. Hence, it is notsurprising that reactive and redox-activeligands constitute a vibrant area of researchin coordination and organometallicchemistry. We deliberately entitled thisthemed issue of Chemical Communications‘‘Non-Innocent Ligands’’ to encompass alarge and broad class of ligands that are

either redox-active (‘‘redox non-innocent’’)or actively involved in bond-making or-breaking processes (‘‘chemically non-innocent’’ or ‘‘cooperative’’). In general, all(ancillary) ligands are important: they keepa reactive metal ion in solution, stabilizespecific metal oxidation states, and can beused to tune the reactivity of a metal bydefining the steric and electronic propertiesof the complex as a whole. In addition tothese important features, redox-active and

a Department of Chemistry, University of California,

Davis, CA 95616, USA.

E-mail: laberben@ucdavis.edub Universiteit van Amsterdam, Faculty of Science, van ’t

Hoff Institute for Molecular Sciences, Department of

Homogeneous Catalysis, Postbus 94720, 1090 GS

Amsterdam, The Netherlands.

E-mail: B.deBruin@uva.nlc Science Park 904, 1098 XH Amsterdam, The

Netherlands.d Department of Chemistry, University of California,

Irvine, CA 92697, USA. E-mail: aheyduk@uci.edu

Louise A. Berben

Louise A. Berben is an Associate Professor inthe Department of Chemistry at the Uni-versity of California, Davis. Her currentresearch focuses on ligand-mediated protonand electron-transfer reactions of aluminumcomplexes, and on developing iron-basedelectrocatalysts for the reduction of CO2.

Bas de Bruin

Bas de Bruin is full professor in the Van ’tHoff Institute for Molecular Sciences (HIMS)at the University of Amsterdam (UvA). He isinvolved in various research activities,including radical organometallic chemistry,EPR spectroscopy, olefin oxygenation, polymersynthesis, mechanistic studies and computa-tional catalysis, with a focus on thedevelopment of new (bio-inspired) catalytictransformations.

Alan F. Heyduk

Alan F. Heyduk is a Professor of Chemistry atthe University of California, Irvine. Hisresearch program is focused on the use ofredox-active ligands in transition metalcoordination complexes for a variety ofapplications including small-molecule activa-tion, electrocatalysis, and solar energyconversion.

DOI: 10.1039/c4cc90480j

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1554 | Chem. Commun., 2015, 51, 1553--1554 This journal is©The Royal Society of Chemistry 2015

cooperative ligands offer even more featuresby actively participating in redox reac-tions and bond-breaking and bond-making processes.

Based upon the enthusiastic responsesfrom authors contributing to this themedissue of Chemical Communications on‘‘Non-Innocent Ligands’’, we are confi-dent that interest in this area of researchcontinues to grow. This collection bringstogether research communications thatspan the Periodic Table, including com-plexes of main group, transition metal,lanthanide, and actinide ions with non-innocent ligands. The fundamentalchemical questions addressed in thesearticles are similarly broad, ranging fromthe synthesis of new molecules, to discus-sions of structure and bonding, to theinvestigation of stoichiometric and cata-lytic reaction chemistry.

Several of the articles contained in thisissue focus on special reactivity gained bythe combination of a metal center with aredox-active ligand. The Feature Article byGallo and coworkers (DOI: 10.1039/C4CC03016H) provides an overview of theapplication of organic azides for the inter-molecular amination of sp3 and sp2 C–Hbonds. Bart and coworkers (DOI: 10.1039/C4CC03355H) present an oxidative additionreaction mediated by a U(IV) center wherebond-forming occurs at the metal and redoxchanges occur on the tridentate redox-activeligand. In the work by Szostak and Proctorand coworkers (DOI: 10.1039/C4CC03216K),coordination of Sm(III) to a b-hydroxy acidleads to formation of a C–O bond in thechemically non-innocent ligand, wherethe O originates from water. The depen-dence of Cu-mediated nitrene transfer andH-atom abstraction reactions on spin state

is described in a communication by Rayand coworkers (DOI: 10.1039/C4CC03754E).Ligand-based oxidation state changes alsoplay a role in metal–ligand bond formationin a series of Cr–azide complexes presentedby Smith and coworkers (DOI: 10.1039/C4CC04545A). Murr and Fensterbank andcoworkers (DOI: 10.1039/C4CC04487H)utilize a Cu complex of a redox-activeimino semiquinonate ligand to manifestumpolung reactivity by coaxing a CF3

+

source to deliver a CF3�. Hicks and

coworkers (DOI: 10.1039/C4CC04863F)show that the redox-active verdazylligand in combination with Pd can affectredox transformations, while Kuwataand Ikariya (DOI: 10.1039/C4CC04457F)describe Ir, Fe, Pd, and Ru complexes ofbidentate and tridentate donor ligandsin which proton transfer reactivity isfacilitated by heterocyclic N atoms. Electro-chemically driven C–C bond formationbetween benzylhalide substrates is featuredin a contribution by Sarkar et al. (DOI: 10.1039/C4CC03309D), using Co complexesof redox-active o-iminoquinones as thecatalyst.

A second group of the featured articlesfocuses on the structural and electronicproperties that can be obtained using non-innocent ligands. Chang and Otten (DOI:10.1039/C4CC03244F) describe the transme-tallation of redox-active formazanate ligandsfrom zinc to boron, and explore the redox-activity of the resulting boron complexes.Burger and coworkers (DOI: 10.1039/C4CC03624G) describe the formation ofbridging nitride complexes of iridium,which are based on the well-known, redox-active pyridine-2,6-diimine ligand. Theopoldand coworkers (DOI: 10.1039/C4CC03332A)investigate the structure and spectroscopic

properties of [Cr(a-diimine)3]n+ complexesin the redox-states n = 0, 1, 2. Similarly,Cipressi and Brown (DOI: 10.1039/C4CC03404J) probed geometrical distor-tions of Os & Ru complexes induced byredox changes at a-diimine ligands. Thegroup of Fedushkin (DOI: 10.1039/C4CC04019H) developed a new redox-active metallo-carbenoid ligand derivedfrom the redox-active diimine dpp-bianand coordinated it to molybdenum.Holland and coworkers (DOI: 10.1039/C4CC05495D) show that even the simplepyridine ligand can be redox-active,accepting up to two electrons from low-valent iron ions. Ghosh, Bendix andcoworkers (DOI: 10.1039/C4CC02548B)report the synthesis of bis-aryl–platinumcomplexes with one-electron oxidizedcorrole ligands, and chart the structuraland spectroscopic properties of the oxi-dized corrole ligands.

From these contributions it is readilyapparent that the field of non-innocentligands is blossoming into a diverse andexciting area of research. The field hasmatured from a collection of spectroscopiccuriosities to a dynamic and fast-movingenterprise that impacts other mainstreamresearch in the fields of catalysis, chemicalbiology and materials science, while conti-nuing to develop fundamental understand-ing of electronic structure in coordinationcomplexes. We anticipate that the workpresented here is merely the tip of theiceberg when it comes to the chemistryof non-innocent ligand platforms, andwe look forward to many more dis-coveries and revelations that the contri-butions collected in this themed issuewill inspire from the readership ofChemical Communications.

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