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This review article presents a comprehensive analysis of metal complexes featuring ortho‐aminophenol based non‐innocent ligands in various oxidation states, including dianion/o‐amidophenolate, monoanion/o‐iminosemiquinonato, and o‐iminoquinonato forms. We focus extensively on the reactivity and catalytic properties of these metal complexes, offering insights into their potential applications and behavior in different chemical environments. The ligands are meticulously categorized based on their denticity, providing a clear framework for understanding their coordination chemistry. Correspondingly, the metal complexes are systematically organized according to the sequence of ligands, ensuring a coherent and logical presentation of the data. The structural approach not only highlights the intricate relationships between ligands and metal centers but also facilitates a deeper understanding of their roles in various catalytic processes. [ABSTRACT FROM AUTHOR]

Spin-crossover (SCO) and single-ion magnets (SIMs), or their mixed SCO-SIM derivatives, are a convenient solution in the evolution from molecular magnetism toward molecular spintronics and quantum computing. Herein, we report on the current trends and future directions on the use of mononuclear six-coordinate CoII SCO-SIM complexes with potential opto-, electro-, or chemo-active 2,6-pyridinediimine (PDI)- and 2,2′:6′,2′-terpyridine (TERPY)-type ligands as archetypical examples of multifunctional and multiresponsive magnetic devices for applications in molecular spintronics and quantum computing technologies. This unique class of spin-crossover cobalt(II) molecular nanomagnets is particularly well suited for addressing and scaling on different supports, like metal molecular junctions or carbon nanomaterials (CNMs) and metal–organic frameworks (MOFs) or metal-covalent organic frameworks (MCOFs), in order to measure the single-molecule electron transport and quantum coherence properties, which are two major challenges in single-molecule spintronics (SMS) and quantum information processing (QIP). [ABSTRACT FROM AUTHOR]

We report on the synthesis and characterization of a series of (mostly) air‐stable diorganyl bis(pyridylimino) isoindolide (BPI) aluminum complexes and their chemistry upon visible‐light excitation. The redox non‐innocent BPI pincer ligand allows for efficient charge transfer homolytic processes of the title compounds. This makes them a universal platform for the generation of carbon‐centered radicals. The photo‐induced homolytic cleavage of the Al−C bonds was investigated by means of stationary and transient UV/Vis spectroscopy, spin trapping experiments, as well as EPR and NMR spectroscopy. The experimental findings were supported by quantum chemical calculations. Reactivity studies enabled the utilization of the aluminum complexes as reactants in tin‐free Giese‐type reactions and carbonyl alkylations under ambient conditions, which both indicated radical‐polar crossover behavior. A deeper understanding of the physical fundamentals and photochemical process was provided, furnishing in turn a new strategy to control the reactivity of bench‐stable aluminum organometallics. [ABSTRACT FROM AUTHOR]

Cobalt(III) corroles are the most commonly studied types of metallocorroles, yet the details of their electronic structure, ground spin states and place of redox events are not always straightforward. Corroles are redox active, potentially non‐innocent ligands, and it has been found through various experimental and computational techniques, that the innocent or non‐innocent behavior is modulated by the apical ligands bound to the cobalt center. In this work, we aim to analyze the effect of corrole substituents and number and type of apical ligands on the electronic structure of cobalt corroles through density functional and wavefunction theories, and to determine the relative energies between closed‐ and open‐shell states. We further perform preliminary analyses on the place of electron abstraction upon oxidation and on the effect of the corrole and apical ligands on the cobalt ligand field splittings. We find that both ligand field and electron‐donating or withdrawing effects determine the relative energies of open‐shell and closed shell singlet states. [ABSTRACT FROM AUTHOR]

Non‐innocent ligands (NILs) like bis(pyridylimino)isoindolide (BPI) play crucial roles in coordination chemistry, biosciences, catalysis and material sciences. Investigating the isolated redox states of NILs is inevitable for understanding their redox‐activity and fine‐tuning the properties of corresponding metal complexes. The limited number of fundamental studies on the coordination behavior and redox chemistry of reduced BPI species is suggested to hamper further applications of the title compounds. This work describes for the first time the isolation of alkali metal complexes of BPI and Me2BPI in three different oxidation states and their characterization by means of NMR or EPR spectroscopy, DFT calculations, and SC‐XRD studies. The latter revealed the connection between bond orders in the ligand scaffold and its oxidation state. The paramagnetic compound Me2BPI‐K2 was isolated as a coordination copolymer with 18‐crown‐6, which enabled the characterization of the dianionic BPI radical. Furthermore, the so‐far unknown trianionic state of BPI was reported by the isolation of BPI‐K3. This divulges an unprecedented bis(amidinato)isoindolide coordination mode. [ABSTRACT FROM AUTHOR]

We report a facile synthetic method for accessing rare T‐shaped Ni0 species, stabilised by low‐coordinate cationic germylene and stannylene ligands which behave as Z‐type ligands toward Ni0. An in‐depth computational analysis indicates significant Nid→Ep donation (E=Ge, Sn), with essentially no E→Ni donation. The tetrylene ligand's Lewis acidity can be modulated in situ through the addition of a donor ligand, which selectively binds at the Lewis acidic tetrylene site. This switches this binding centre from a Z‐type to a classical L‐type ligand, with a concomitant geometry switch at Ni0 from T‐shaped to trigonal planar. Exploring the effects of this geometry switch in catalysis, isolated T‐shaped complexes 3 a–c and 4 a–c are capable of the hydrogenation of alkenes under mild conditions, whilst the closely related trigonal planar and tetrahedral Ni0 complexes 5, D, and E, which feature L‐type chloro‐ or cationic‐tetrylene ligands, are inactive under these conditions. Further, addition of small amounts of N‐bases to the catalytic systems involving T‐shaped complexes significantly reduces turnover rates, giving evidence for the in situ modulation of ligand electronics for catalytic switching. [ABSTRACT FROM AUTHOR]

We report a facile synthetic method for accessing rare T‐shaped Ni0 species, stabilised by low‐coordinate cationic germylene and stannylene ligands which behave as Z‐type ligands toward Ni0. An in‐depth computational analysis indicates significant Nid→Ep donation (E=Ge, Sn), with essentially no E→Ni donation. The tetrylene ligand's Lewis acidity can be modulated in situ through the addition of a donor ligand, which selectively binds at the Lewis acidic tetrylene site. This switches this binding centre from a Z‐type to a classical L‐type ligand, with a concomitant geometry switch at Ni0 from T‐shaped to trigonal planar. Exploring the effects of this geometry switch in catalysis, isolated T‐shaped complexes 3 a–c and 4 a–c are capable of the hydrogenation of alkenes under mild conditions, whilst the closely related trigonal planar and tetrahedral Ni0 complexes 5, D, and E, which feature L‐type chloro‐ or cationic‐tetrylene ligands, are inactive under these conditions. Further, addition of small amounts of N‐bases to the catalytic systems involving T‐shaped complexes significantly reduces turnover rates, giving evidence for the in situ modulation of ligand electronics for catalytic switching. [ABSTRACT FROM AUTHOR]

We present herein the synthesis of a nearly square‐pyramidal chlorophosphorane supported by the tetradentate bis(amidophenolate) ligand, N,N′‐bis(3,5‐di‐tert‐butyl‐2‐phenoxy)‐1,2‐phenylenediamide. After chloride abstraction the resulting phosphonium cation efficiently promotes the disproportionation of 1,2‐diphenylhydrazine to aniline and azobenzene. Mechanistic studies, spectroscopic analyses and theoretical calculations suggest that this unprecedented reactivity mode for PV‐centres is induced by the high electrophilicity at the cationic PV‐center, which originates from the geometry constraints imposed by the rigid pincer ligand, combined with the ability of the o‐amidophenolate moieties to act as electron reservoir. This study illustrates the promising role of cooperativity between redox‐active ligands and phosphorus for the design of organocatalysts able to promote redox processes. [ABSTRACT FROM AUTHOR]

Herein, we report two newly synthesized salen‐type ligands, 2,3‐bis((3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)thio)maleonitrile (H2L1) and 2,3‐bis((3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)amino)malenonitrile (H4L2), bearing different coordination sites (sulfur vs amine) at maleonitrile tethered moiety to investigate metal mediated non‐innocence chemistry of these ligands. Upon metallation, ligand H2L1 did not yield simple metal‐ligand complex, rather ligand was split into two organic fragments, dithiolene moiety (mnt)2− and phenol moiety via C−S bond cleavage wherein (mnt)2− formed a stable metal complex [M(mnt)2]2−. The C−S bond cleavage was interpreted in terms of strong p(π) ... d(π) interaction between metal and dithiolene moiety in H2L1 ligand that invoked the intramolecular rearrangement facilitating C−S bond cleavage. Interestingly, the phenol moiety further transformed to either unprecedented 2,4‐di‐tert‐butyl‐6‐methylenecyclohexa‐2,4‐dienone (i. e. spiro compound; 5) or 2,4‐di‐tert‐butyl‐6‐(hydroxymethyl)phenol (6) depending on the temperature of reaction and type of metal ion used which was further predicted using DFT calculation. On the other hand, combined experimental and DFT studies explained that upon metallation, ligand H4L2 yielded non‐cleavage [M(H2L2)] (3 for M=Cu(II) and 4 for M=Ni(II)) complex, which slowly oxidized at −NH−CH2‐(amine) region to −N=CH− (imine) in H2L2 ligand under aerobic environment via C−H bond activation, yielding [CuII(L3)] (1) (or [NiII(L3)] (2) complex (H2L3=oxidatively dehydrogenated product of H4L2 ligand. [ABSTRACT FROM AUTHOR]

High‐resolution X‐ray diffraction experiments, theoretical calculations and atom‐specific X‐ray absorption experiments were used to investigate two nickel complexes, (MePh3P)2[NiII(bdtCl2)2]·2(CH3)2SO [complex (1)] and (MePh3P)[NiIII(bdtCl2)2] [complex (2)]. Combining the techniques of nickel K‐ and sulfur K‐edge X‐ray absorption spectroscopy with high‐resolution X‐ray charge density modeling, together with theoretical calculations, the actual oxidation states of the central Ni atoms in these two complexes are investigated. Ni ions in two complexes are clearly in different oxidation states: the Ni ion of complex (1) is formally NiII; that of complex (2) should be formally NiIII, yet it is best described as a combination of Ni2+ and Ni3+, due to the involvement of the non‐innocent ligand in the Ni—L bond. A detailed description of Ni—S bond character (σ,π) is presented. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of complexes [Fe2(CO)4(κ2‐phen)(μ‐xdt)] (phen=1,10‐phenanthroline; xdt=pdt (1), adtiPr (2)) in MeCN‐[Bu4N][PF6] 0.2 m is described as a two‐reduction process. DFT calculations show that 1 and its monoreduced form 1− display metal‐ and phenanthroline‐centered frontier orbitals (LUMO and SOMO) indicating the non‐innocence of the phenanthroline ligand. Two energetically close geometries were found for the doubly reduced species suggesting an intriguing influence of the phenanthroline ligand leading to the cleavage of a Fe−S bond as proposed generally for this type of complex or retaining the electron density and avoiding Fe−S cleavage. Extension of calculations to other complexes with edt, adtiPr bridge and even virtual species [Fe2(CO)4(κ2‐phen)(μ‐adtR)] (R=CH(CF3)2, H) or [Fe2(CO)4(κ2‐phen)(μ‐pdtR)] (R=CH(CF3)2, iPr) showed that the relative stability between both two‐electron‐reduced isomers depends on the nature of the bridge and the possibility to establish a remote anagostic interaction between the iron center {Fe(CO)3} and the group carried by the bridged‐head atom of the dithiolate group. [ABSTRACT FROM AUTHOR]

The use of cyclopentadienyl ligands in organometallic chemistry and catalysis is ubiquitous, mostly due to their robust spectator role. Nonetheless, increasing examples of non‐innocent behaviour are being documented. Here, we provide evidence for reversible intramolecular C−H activation at one methyl terminus of C5Me5 in [(η‐C5Me5)Rh(PMe3)2] to form a new Rh−H bond, a process so far restricted to early transition metals. Experimental evidence was acquired from bimetallic rhodium/gold structures in which the gold center binds either to the rhodium atom or to the activated Cp* ring. Reversibility of the C−H activation event regenerates the RhI and AuI monometallic precursors, whose cooperative reactivity towards polar E−H bonds (E=O, N), including the N−H bonds in ammonia, can be understood in terms of bimetallic frustration. [ABSTRACT FROM AUTHOR]

The use of cyclopentadienyl ligands in organometallic chemistry and catalysis is ubiquitous, mostly due to their robust spectator role. Nonetheless, increasing examples of non‐innocent behaviour are being documented. Here, we provide evidence for reversible intramolecular C−H activation at one methyl terminus of C5Me5 in [(η‐C5Me5)Rh(PMe3)2] to form a new Rh−H bond, a process so far restricted to early transition metals. Experimental evidence was acquired from bimetallic rhodium/gold structures in which the gold center binds either to the rhodium atom or to the activated Cp* ring. Reversibility of the C−H activation event regenerates the RhI and AuI monometallic precursors, whose cooperative reactivity towards polar E−H bonds (E=O, N), including the N−H bonds in ammonia, can be understood in terms of bimetallic frustration. [ABSTRACT FROM AUTHOR]

Platinum(IV) complexes are extensively studied for their activity against cancer cells as potential substitutes for the widely used platinum(II) drugs. PtIV complexes are kinetically inert and need to be reduced to PtII species to play their pharmacological action, thus acting as prodrugs. The mechanism of the reduction step inside the cell is however still largely unknown. Gas‐phase activation of deprotonated platinum(IV) prodrugs was found to generate products in which platinum has a formal +3 oxidation state. IR multiple photon dissociation spectroscopy is thus used to obtain structural information helping to define the nature of both the platinum atom and the ligands. In particular, comparison of calculations at DFT, MP2 and CCSD levels with experimental results demonstrates that the localization of the radical is about equally shared between the dxz orbital of platinum and the pz of nitrogen on the amino group, the latter acting as a non‐innocent ligand. [ABSTRACT FROM AUTHOR]

Platinum(IV) complexes are extensively studied for their activity against cancer cells as potential substitutes for the widely used platinum(II) drugs. PtIV complexes are kinetically inert and need to be reduced to PtII species to play their pharmacological action, thus acting as prodrugs. The mechanism of the reduction step inside the cell is however still largely unknown. Gas‐phase activation of deprotonated platinum(IV) prodrugs was found to generate products in which platinum has a formal +3 oxidation state. IR multiple photon dissociation spectroscopy is thus used to obtain structural information helping to define the nature of both the platinum atom and the ligands. In particular, comparison of calculations at DFT, MP2 and CCSD levels with experimental results demonstrates that the localization of the radical is about equally shared between the dxz orbital of platinum and the pz of nitrogen on the amino group, the latter acting as a non‐innocent ligand. [ABSTRACT FROM AUTHOR]

The diphosphine, N‐heterocyclic phosphenium/phosphido (NHP+)/(NHP–)‐containing ligand (PPP+/–) has been coordinated to rhodium to study the coordination chemistry of group 9 metals and NHP+/– fragments. Addition of the chlorophosphine ligand PPClP to [Rh(COD)Cl]2 produces the complex (PPClP)RhCl (2), which can be reduced to form (PPP)Rh(PMePh2) (3), the asymmetric dimer [(PPP)Rh]2 (4), and the asymmetric dimer [(PPP)Rh(CNtBu)]2 (5). Analysis of the solid‐state structures and computational studies have provided insight into the electronic structure and bonding in 3–5, revealing that the NHP+/– fragments in 3, 4, and 5 are best described using an NHP–/RhI description. Both 3 and 5 were found to be reactive towards the S–H bond of thiophenol, generating (PPP)RhSPh (6) and (PPP)Rh(SPh)(CNtBu) (7), respectively. [ABSTRACT FROM AUTHOR]

The first example of ferrocene analogues with two transition‐metal metallole ligands of the general formula (η5‐C4R4M)2Fe in a sandwich structure are reported. Specifically, dinickelaferrocene 2, a type of dimetallametallocene, is efficiently synthesized from the reaction of dilithionickelole 1 with FeBr2 or FeCl2, presumably via a redox process, and is subjected to detailed experimental (single‐crystal X‐ray structural analysis, ICP‐OES, magnetometry, 57Fe Mössbauer, XPS) and theoretical (MOs, CDA, NICS, ICSS, and AICD) characterizations. Unlike ferrocene and its Cp ligands, the aromaticity of dinickelaferrocene and its nickelole ligands is accomplished by electron back‐donation from the Fe 3d orbitals to the π* orbitals of nickelole. Taken together, this work describes a new class of metallaferrocene sandwich complexes and provides a novel approach to effect aromaticity that will contribute to further development of metallocene chemistry. [ABSTRACT FROM AUTHOR]

The first example of ferrocene analogues with two transition‐metal metallole ligands of the general formula (η5‐C4R4M)2Fe in a sandwich structure are reported. Specifically, dinickelaferrocene 2, a type of dimetallametallocene, is efficiently synthesized from the reaction of dilithionickelole 1 with FeBr2 or FeCl2, presumably via a redox process, and is subjected to detailed experimental (single‐crystal X‐ray structural analysis, ICP‐OES, magnetometry, 57Fe Mössbauer, XPS) and theoretical (MOs, CDA, NICS, ICSS, and AICD) characterizations. Unlike ferrocene and its Cp ligands, the aromaticity of dinickelaferrocene and its nickelole ligands is accomplished by electron back‐donation from the Fe 3d orbitals to the π* orbitals of nickelole. Taken together, this work describes a new class of metallaferrocene sandwich complexes and provides a novel approach to effect aromaticity that will contribute to further development of metallocene chemistry. [ABSTRACT FROM AUTHOR]

β‐Diketonates, such as acetylacetonate, are amongst the most common bidentate ligands towards elements across the entire periodic table and are considered wholly redox‐inactive in their complexes. Herein we show that complexation of 1,1,1,5,5,5‐hexafluoroacetylacetonate (hfac−) to CrII spontaneously affords CrIII and a reduced β‐diketonate radical ligand scaffold, as evidenced by crystallographic analysis, magnetic measurements, optical spectroscopy, reactivity studies, and DFT calculations. The possibility of harnessing β‐diketonates as electron reservoirs opens up possibilities for new metal–ligand concerted reactivity in the ubiquitous β‐diketonate coordination chemistry. [ABSTRACT FROM AUTHOR]

Ruthenium complexes containing catecholamines and catechol as ligands with general formula [Ru(NH3)4(catecholamine)]Cl, where "catecholamine" is isoproterenol (in complex 1), dopamine (in complex 2), noradrenaline (in complex 3), catechol (in complex 4), or adrenaline (in complex 5), were synthesized. The complexes were characterized by vibrational and NMR spectroscopies, mass spectrometry, cyclic voltammetry, and spectroeletrochemistry. The electronic and electrochemical features were analyzed in terms of the electronic density, which is affected by ruthenium complexation and different substituent groups on the aromatic ring. Resonance Raman spectra displayed bands assigned to the Ru(II)-semiquinone stretching frequencies, which agreed with the charge transfer band. Theoretical calculations helped to evaluate the metal-non-innocent ligand orbital mixing. All the results suggested that Ru(II)-semiquinone complexes are formed, and that the unpaired electron is delocalized between the metal ion and the non-innocent ligand. [ABSTRACT FROM AUTHOR]

A titanium(IV) alkoxido complex, (dpp‐bian)Ti(OBn)2 (2), as well as alkoxido chlorido complexes (dpp‐bian)TiCl(OCH2CH2OMe) (3) and (dpp‐bian)TiCl2OBn (4), were synthesized from the titanium(IV) dichloride precursor [(dpp‐bian)TiCl2]2 (1) by exchange with corresponding sodium salts (comps. 2 and 3) or by the alcoholysis with BnOH (comp. 4). The compounds 2–4 were fully characterized by elemental analysis, NMR or EPR, and IR spectroscopy. Molecular structures of the metal complexes in the solid state have been determined by single‐crystal XRD analysis. Compounds 2–4 were tested as catalysts in the ROP of L‐lactide in a toluene medium. Whereas complexes 2 and 3 produce cyclic PLAs with broad dispersities and unpredictable molecular weights, complex 4 acts as an efficient ROP catalyst which polymerizes the monomer in a highly controllable manner. It produces BnO‐capped PLAs with narrow molecular weight distributions as well as linear dependence of Mns on monomer conversion. [ABSTRACT FROM AUTHOR]

Herein, we present the realization of a class of unprecedented aromatic structures 2: metalla‐aromatics with two independent and perpendicular aromatic rings spiro‐fused by a transition‐metal spiro atom, of which their corresponding organic analogues are impossible. Tetralithio spiro manganacycles 2 are readily synthesized from 1,4‐dilithio‐1,3‐butadienes 1 and MnCl2 in the presence of lithium. The aromaticity of 2 is supported by experimental measurements (X‐ray structural analysis, NMR) and theoretical analyses (NICS, ACID, MOs). The spiro atom Mn in 2 uses its 3dxz and 3dxy orbitals to form the two perpendicular manganacycles, which are two independent 6π aromatic systems. Theoretical analyses reveal that the Li cations play an indispensable role in governing their geometric and electronic structures and hence their aromaticity. Therefore, this work contributes not only to enrich the concept of aromaticity, but also to deepen the understanding of the fundamental chemical bonding. [ABSTRACT FROM AUTHOR]

Controlled ligand‐based redox‐activity and chemical non‐innocence are rapidly gaining importance for selective (catalytic) processes. This Concept aims to provide an overview of the progress regarding ligand‐to‐substrate single‐electron transfer as a relatively new mode of operation to exploit ligand‐centered reactivity and catalysis based thereon. Deposit or withdrawal? Controlled ligand‐based redox activity and chemical non‐innocence are rapidly gaining importance for selective (catalytic) processes. This Concept aims to provide an overview of the progress regarding ligand‐to‐substrate single‐electron transfer as a relatively new mode of operation to exploit ligand‐centered reactivity and catalysis based thereon. [ABSTRACT FROM AUTHOR]

Storage of electricity produced intermittently by renewable energy sources is a societal issue. Besides the use of batteries and supercapacitors, conversion of excess electricity into chemical energy is also actively investigated. The conversion of CO2 to fuel or fuel precursors is an option that requires the use of a catalyst to overcome the high activation energy barrier. Of molecular catalysts, metal complexes with polypyridyl ligands are well represented, among which the [Cp*Rh(bpy)Cl]+ and [M(bpy)(CO)3X] (M = Re, Mn) complexes. As redox non‐innocent ligand, the bipyridine ligand is generally involved in the reduction mechanisms. It is thus tempting to replace it by other redox non‐innocent ligands such as vacant polyoxometalates (POMs). We have thus prepared [α‐H2PW11O39{RhIIICp*(OH2)}]3– which is closely related to [Cp*RhIII(bpy)Cl]+ by substitution of the monovacant [PW11O39]7– Keggin‐type POM for the bipyridine ligand. Its activity towards CO2 reduction has been assessed in acetonitrile in the presence of water. Compared to [Cp*Rh(bpy)Cl]+ that produces formate selectively over CO and H2, the POM derived catalyst favors proton reduction over CO2 reduction. [α‐H2PW11O39{RhIIICp*(OH2)}]3– was prepared by reaction between the monovacant Keggin‐type [α‐H2PW11O39]5– and [Cp*Rh(CH3CN)3]2+. It is closely related to the CO2 reduction electrocatalyst [Cp*RhIII(bpy)Cl]+ by changing the bpy ligand by the polyoxometalate, both acting as redox non‐innocent bidentate ligands. The selectivity of the CO2 reduction was altered from the production of formate to dihydrogen. [ABSTRACT FROM AUTHOR]

We report the synthesis, characterization, and electronic structure studies of a series of thorium(IV) and uranium(IV) bis‐tetramethyltetraazaannulene complexes. These sandwich complexes show remarkable stability towards air and moisture, even at elevated temperatures. Electrochemical studies show the uranium complex to be stable in three different oxidation states; isolation of the oxidized species reveals a rare case of a non‐innocent tetramethyltetraazaannulene (TMTAA) ligand. Heavy and Guilty: Thorium(IV) and uranium(IV) bis‐tetramethyltetraazaannulene (TMTAA) complexes were synthesized and characterized. Electrochemical studies show the uranium complex to be stable in three different oxidation states; isolation of the oxidized species reveals a non‐innocent TMTAA ligand. [ABSTRACT FROM AUTHOR]

Abstract: A dinuclear CoII complex, [Co2(tphz)(tpy)2]n+ (n=4, 3 or 2; tphz: tetrapyridophenazine; tpy: terpyridine), has been assembled using the redox‐active and strongly complexing tphz bridging ligand. The magnetic properties of this complex can be tuned from spin‐crossover with T1/2≈470 K for the pristine compound (n=4) to single‐molecule magnet with an ST=5/2 spin ground state when once reduced (n=3) to finally a diamagnetic species when twice reduced (n=2). The two successive and reversible reductions are concomitant with an increase of the spin delocalization within the complex, promoting remarkably large magnetic exchange couplings and high‐spin species even at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: A newly developed dihydrazonopyrrole ligand and corresponding Ni complexes have been synthesized and thoroughly characterized. Electrochemical studies and chemical reactivity tests show that these complexes can reversibly store both electrons and protons, or equivalently H‐atoms, via ligand‐based events. The stored H‐atom equivalent can be transferred to small molecules such as acetonitrile or oxygen. Furthermore, this series of complexes can adopt a variety of different coordination modes. In addition to one e− reactivity, the two e− electrophilic oxidation of phosphines is also demonstrated. Taken together, these results show that dihydrazonopyrrole complexes represent a geometrically and electronically flexible scaffold for controlling the flow of both electrons and protons. [ABSTRACT FROM AUTHOR]

Phosphasalen ligands can be viewed as the phosphorus analogues of salen, in which the imine functions were replaced by iminophosphoranes (P=N). Their divergent stereoelectronic properties compared to salen, namely larger electron‐donation, higher flexibility, and larger steric hindrance due to the presence of two substituents on the tetrahedral phosphorus atoms, were exploited in coordination chemistry and catalysis. They were proven to be able to stabilize metals in unusual oxidation states; square planar copper(III) and nickel(III) complexes were isolated. Because of the redox non‐innocent character of these ligands, the electronic structure of the one‐electron oxidized complexes was studied in depth to determine the metallic vs. ligand contribution in the overall delocalization. In addition, the catalytic activity of different phosphasalen complexes was proven for the ring opening polymerization of lactide, and rare‐earth phosphasalen complexes were shown to be powerful, rapid, controlled, and stereoselective initiators. Importantly, the stereochemical outcome of the reaction can be tuned by changing the ligand structure or the metal. In particular, efficient iso‐selective initiators were developed. [ABSTRACT FROM AUTHOR]

Abstract: Recently it was reported that copper bicarbonate/carbonate complexes are good electro‐catalysts for water oxidation. However, the results did not enable a decision whether the active oxidant is a CuIII or a CuIV complex. Kinetic analysis of pulse radiolysis measurements coupled with DFT calculations point out that CuIII(CO3)n3−2n complexes are the active intermediates in the electrolysis of CuII(CO3)n2−2n solution. The results enable the evaluation of E°[(CuIII/II(CO3)n)aq]≈1.42 V versus NHE at pH 8.4. This redox potential is in accord with the electrochemical report. As opposed to literature suggestions for water oxidation, the present results rule out single‐electron transfer from CuIII(CO3)n3−2n to yield hydroxyl radicals. Significant charge transfer from the coordinated carbonate to CuIII results in the formation of C2O62− by means of a second‐order reaction of CuIII(CO3)n3−2n. The results point out that carbonate stabilizes transition‐metal cations at high oxidation states, not only as a good sigma donor, but also as a non‐innocent ligand. [ABSTRACT FROM AUTHOR]

Non-innocent ligands render the determination of the electronic structure in metal complexes difficult. As such, a combination of experimental techniques and quantum chemistry are required to correctly elucidate them. This paper deals with the one-electron oxidation of copper(II) and nickel(II) complexes featuring a phosphasalen ligand (Psalen), which differs from salen analogues by the presence of iminophosphorane groups (P=N) instead of imines. Various experimental techniques (X-ray diffraction, cyclic voltammetry, NMR, EPR, and UV/Vis spectroscopies, and magnetic measurements) as well as quantum chemical calculations were used to define the electronic structure of the oxidized complexes. These can be modified by a small change in the ligand structure, that is, the replacement of a tert-butyl group by a methoxy on the phenoxide ring. The different techniques have allowed quantifying the amount of spin density located on the metal center and on the Psalen ligands. All complexes were found to possess a multi-configurational ground state, in which the ratio of the +II versus +III oxidation state of the metal center, and therefore the phenolate versus phenoxyl radical ligand character, varies upon the substituents. The tert-butyl group favors a strong localization on the metal center whereas with the methoxy group the metallic configurations decrease and the ligand configurations increase. The importance of the geometrical considerations compared with the electronic substituent effect is highlighted by the differences observed between the solid-state (EPR, magnetic measurements) and solution characterizations (EPR and NMR data). [ABSTRACT FROM AUTHOR]

Assembly of the triangular, organic radical-bridged complexes Cp*6Ln3(μ3-HAN) (Cp*=pentamethylcyclopentadienyl; Ln=Gd, Tb, Dy; HAN=hexaazatrinaphthylene) proceeds through the reaction of Cp*2Ln(BPh4) with HAN under strongly reducing conditions. Significantly, magnetic susceptibility measurements of these complexes support effective magnetic coupling of all three LnIII centers through the HAN3−. radical ligand. Thorough investigation of the DyIII congener through both ac susceptibility and dc magnetic relaxation measurements reveals slow relaxation of the magnetization, with an effective thermal relaxation barrier of Ueff=51 cm−1. Magnetic coupling in the DyIII complex enables a large remnant magnetization at temperatures up to 3.0 K in the magnetic hysteresis measurements and hysteresis loops that are open at zero-field up to 3.5 K. [ABSTRACT FROM AUTHOR]

The synthesis of the divinylamido PNP nickel(II) complex [NiBr{N(CHCHP tBu2)2}] is reported. This compound exhibits reversible, ligand-centered oxidation and protonation reactions. The resulting pincer chemical non-innocence can be utilized for benzylic C−H hydrogen atom abstraction. The thermochemistry and kinetics of hydrogen atom transfer were examined. [ABSTRACT FROM AUTHOR]

Copper(II) chloride complexes with nitrogen-containing ligands (amines, amides, heterocycles) were studied as catalysts of selective oxidation of thiols to disulfides. This process has an important biochemical analogue – the formation of disulfide bridge in proteins [Wang C, Wesener SR, Zhang H, Cheng Y-Q. An FAD-dependent pyridine nucleotide-disulfide oxidoreductase is involved in disulfide bond formation in FK228 anticancer depsipeptide. Chem and Biol. 2009;16:585–593]; which affects their activity [Zhang L, Chou CP, Moo-Young M. Disulfide bond formation and its impact on the biological activity and stability of recombinant therapeutic proteins produced by Escherichia coli expression system. Biotech Adv. 2011;29:923–929]. Also, thiol oxidation is an important process of oil sweetening. The search for effective and stable catalysts for this reaction is still topical [Ganguly SK, Das G, Kumar S, Sain B, Garg MO. Mechanistic kinetics of catalytic oxidation of 1-butanethiol in light oil sweetening. Catal Tod. 2012;198:246–251]. This article describes a mechanistic study of thiol oxidation and non-innocent ligands transformations during this reaction. The studied ligands are capable of oxidizing thiols, the reaction being followed by reoxidation of the reduced forms of the ligands with air oxygen. The oxidative activity of the ligand correlates with catalyst activity for thiol oxidation. [ABSTRACT FROM PUBLISHER]

Owing to their unique topologies and abilities to self-assemble into a variety of extended and aggregated structures, the binary platinum carbonyl clusters [Pt3(CO)6] n2− ('Chini clusters') continue to draw significant interest. Herein, we report the isolation and structural characterization of the trinuclear electron-transfer series [Pt3(μ-CO)3(CNArDipp2)3] n− ( n=0, 1, 2), which represents a unique set of monomeric Pt3 clusters supported by π-acidic ligands. Spectroscopic, computational, and synthetic investigations demonstrate that the highest-occupied molecular orbitals of the mono- and dianionic clusters consist of a combined π*-framework of the CO and CNArDipp2 ligands, with negligible Pt character. Accordingly, this study provides precedent for an ensemble of carbonyl and isocyanide ligands to function in a redox non-innocent manner. [ABSTRACT FROM AUTHOR]

Biomimetic diiron complexes bearing redox non-innocent ligands are discussed in this review. The complexes are synthesized to model the active site of [FeFe] hydrogenase in order to elucidate the catalytic mechanism of H2 evolution and design superior artificial catalysts. Employment of the redox active ligands serves an important factor to modulate electronic structure of the Fe2 core as the similar functionality exerted by the [4Fe4S] cofactor within the H-cluster. Different types of redox active ligands are summarized. The influence of their ligation is observable in spectroscopy as well as cyclic voltammetry, and studied by theoretical calculation. [ABSTRACT FROM AUTHOR]

Reducing hexaazatrinaphthylene (HAN) with potassium in the presence of 18-c-6 produces [{K(18-c-6)}HAN], which contains the S=1/2 radical [HAN].−. The [HAN].− radical can be transferred to the cobalt(II) amide [Co{N(SiMe3)2}2], forming [K(18-c-6)][(HAN){Co(N′′)2}3]; magnetic measurements on this compound reveal an S=4 spin system with strong cobalt-ligand antiferromagnetic exchange and J≈−290 cm−1 (−2 J formalism). In contrast, the CoII centres in the unreduced analogue [(HAN){Co(N′′)2}3] are weakly coupled (J≈−4.4 cm−1). The finding that [HAN].− can be synthesized as a stable salt and transferred to cobalt introduces potential new routes to magnetic materials based on strongly coupled, triangular HAN building blocks. [ABSTRACT FROM AUTHOR]

Reactions of the dimeric cobalt complex [(L−Co)2] ( 1, L=[(2,6- iPr2C6H3)NC(Me)]2) with polyarenes afforded a series of mononuclear and dinuclear complexes: [LCo(η4-anthracene)] ( 2), [LCo(μ-η4:η4-naphthalene)CoL] ( 3), and [LCo(μ-η4:η4-phenanthrene)CoL] ( 4). The pyrene complexes [{Na2(Et2O)2}{LCo(μ-η3:η3-pyrene)CoL}] ( 5) and [{Na2(Et2O)3}{LCo(η3-pyrene)}] ( 6) were obtained by treating precursor 1 with pyrene followed by reduction with Na metal. These complexes contain three potential redox active centers: the cobalt metal and both α-diimine and polyarene ligands. Through a combination of X-ray crystallography, EPR spectroscopy, magnetic susceptibility measurement, and DFT computations, the electronic configurations of these complexes were studied. It was determined that complexes 2- 4 have a high-spin CoI center coupled with a radical α-diimine ligand and a neutral polyarene ligand. Whereas, the ligand L in complexes 5 and 6 has been further reduced to the dianion, the cobalt remains in a formal (I) oxidation state, and the pyrene molecule is either neutral or monoanionic. [ABSTRACT FROM AUTHOR]

Brownish gray microcrystalline powders of Ba3[Rh(CN)3] were synthesized from pellets of mixtures of Ba2N, rhodium, NaCN, and graphite at 1070 K in an argon atmosphere. Synchrotron powder diffraction data at 293(1) K revealed the crystal structure of the compound [ P63/ m, a = 9.23266(7) Å, c = 5.81612(6) Å] is isostructural to Ba3[Co(CN)3] and Ba3[Ir(CN)3]. The trigonal-planar complex [Rh(CN)3]6- is surrounded by nine Ba2+ cations forming a tri-capped trigonal prism. Compared to typical cyano ligands, the C-N bond is long [1.21(5) Å] and the vibrational frequencies are low (IR 1674 cm-1, Raman 1728 cm-1). [ABSTRACT FROM AUTHOR]

An unprecedented catalytic pathway for oxa-Michael addition reactions of alcohols to unsaturated nitriles has been revealed using a PNN pincer ruthenium catalyst with a dearomatized pyridine backbone. The isolation of a catalytically competent Ru-dieneamido complex from the reaction between the Ru catalyst and pentenenitrile in combination with DFT calculations supports a mechanism in which activation of the nitrile through metal-ligand cooperativity is a key step. The nitrile-derived Ru-N moiety is sufficiently Brønsted basic to activate the alcohol and initiate conjugate addition of the alkoxide to the α,β-unsaturated fragment. This reaction proceeds in a concerted manner and involves a six-membered transition state. These features allow the reaction to proceed at ambient temperature in the absence of external base. [ABSTRACT FROM AUTHOR]

Non-Innocent ligand complexes of aluminum are described in this Concept article, beginning with a discussion of their synthesis, and then structural and electronic characterization. The main focus concerns the ability of the ligands in these complexes to mediate proton transfer reactions. As examples, aluminum-ligand cooperation in the activation of polar bonds is described, as is the importance of hydrogen bonding to stabilization of a transition state for β-hydride abstraction. Taken together these reactions enable catalytic processes such as the dehydrogenation of formic acid. [ABSTRACT FROM AUTHOR]

A non-innocent ligand, H4L [ABSTRACT FROM AUTHOR]

A functionalized β-dialdimine was prepared, bearing a 3,3-dimethylindoleninyl group at the meso-position and two N-phenolic groups. The structure contains three labile protons, which can be lost or migrate through tautomerism to provide an N2O2 coordination core. A number of divalent and trivalent metal ions (CuII, NiII, CoII/III, and MnIII) were accommodated inside the core, forming a series of intensely colored products consisting of a tricyclic MN2O2 chelate. In the resulting divalent metal complexes, the dialdimine ligand is deprotonated only at the two phenolic oxygen atoms and is thus dianionic, whereas in the trivalent metal complexes, the dialdiminato ligand is triply deprotonated. The copper and nickel complexes adopt square-planar geometries, whereas in the trivalent cobalt and manganese complexes, two neutral ancillary ligands complete an octahedral geometry around the metal center. In each case, the denticity of the diimino-diiminato ligand is four. The electrochemical oxidation of the copper and nickel complexes was studied by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

The compounds [RuII(bmaa-)(bpy)2](PF6) [ 1(PF6)], [RuII(bmaa-)(Cym)Cl] ( 2), and [RuII(bmaa-)(Cym)(py)](PF6) [ 3(PF6)] [bmaa- = N, N′-bis(4-methoxyphenyl)acetamidinato, bpy = 2,2'-bipyridine, Cym = p-cymene, py = pyridine] were studied spectroelectrochemically (EPR, UV/Vis) to reveal metal-centered oxidation for 1+ but bmaa--based oxidation to yield amidinyl ligands in 2+ and 32+. [ABSTRACT FROM AUTHOR]

The synthesis of a ruthenium carbene complex based on a sulfonyl-substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal-carbon interaction can be tuned between a RuC single bond with additional electrostatic interactions and a RuC double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non-polar bonds (OH, HH) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non-innocent ligand supporting the bond activation as nucleophilic center in the 1,2-addition across the metal-carbon double bond. This metal-ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis. [ABSTRACT FROM AUTHOR]

Photochemical activation of [(PNNH)Rh(N3)] (PNNH=6-di-(tert-butyl)phosphinomethyl-2,2'-bipyridine) complex 2 produced the paramagnetic (S=1/2), [(PNN)Rh= NC-Rh(PNN)] complex 3 (PNN-=methylene-deprotonated PNNH), which could be crystallographically characterized. Spectroscopic investigation of 3 indicates a predominant nitridyl radical (CN2-) character, which was confirmed computationally. Complex 3 reacts selectively with CO, producing two equivalents of [(PNN)RhI(CO)] complex 4, presumably by nitridyl radical N,N-coupling. [ABSTRACT FROM AUTHOR]

A rare example of a mononuclear complex [(bpy)2Ru(L1−H)](ClO4), 1(ClO4) and dinuclear complexes [(bpy)2Ru( μ-L1−2H)Ru(bpy)2](ClO4)2, 2(ClO4)2, [(bpy)2Ru( μ-L2−2H)Ru(bpy)2](ClO4)2, 3(ClO4)2, and [(bpy)2Ru( μ-L3−2H)Ru(bpy)2](ClO4)2, 4(ClO4)2 (bpy=2,2′-bipyridine, L1=2,5-di-(isopropyl-amino)-1,4-benzoquinone, L2=2,5-di-(benzyl-amino)-1,4-benzoquinone, and L3=2,5-di-[2,4,6-(trimethyl)-anilino]-1,4-benzoquinone) with the symmetrically substituted p-quinone ligands, L, are reported. Bond-length analysis within the potentially bridging ligands in both the mono- and dinuclear complexes shows a localization of bonds, and binding to the metal centers through a phenolate-type 'O−' and an immine/imminium-type neutral 'N' donor. For the mononuclear complex 1(ClO4), this facilitates strong intermolecular hydrogen bonding and leads to the imminium-type character of the noncoordinated nitrogen atom. The dinuclear complexes display two oxidation and several reduction steps in acetonitrile solutions. In contrast, the mononuclear complex 1+ exhibits just one oxidation and several reduction steps. The redox processes of 11+ are strongly dependent on the solvent. The one-electron oxidized forms 23+, 33+, and 43+ of the dinuclear complexes exhibit strong absorptions in the NIR region. Weak NIR absorption bands are observed for the one-electron reduced forms of all complexes. A combination of structural data, electrochemistry, UV/Vis/NIR/EPR spectroelectrochemistry, and DFT calculations is used to elucidate the electronic structures of the complexes. Our DFT results indicate that the electronic natures of the various redox states of the complexes in vacuum differ greatly from those in a solvent continuum. We show here the tuning possibilities that arise upon substituting [O] for the isoelectronic [NR] groups in such quinone ligands. [ABSTRACT FROM AUTHOR]

The complexes [{(tmpa)CoII}2(μ-L1)2−]2+ ( 12+) and [{(tmpa)CoII}2(μ-L2)2−]2+ ( 22+), with tmpa=tris(2-pyridylmethyl)amine, H2L1=2,5-di-[2-(methoxy)-anilino]-1,4-benzoquinone, and H2L2=2,5-di-[2-(trifluoromethyl)-anilino]-1,4-benzoquinone, were synthesized and characterized. Structural analysis of 22+ revealed a distorted octahedral coordination around the cobalt centers, and cobalt-ligand bond lengths that match with high-spin CoII centers. Superconducting quantum interference device (SQUID) magnetometric studies on 12+ and 22+ are consistent with the presence of two weakly exchange-coupled high-spin cobalt(II) ions, for which the nature of the coupling appears to depend on the substituents on the bridging ligand, being antiferromagnetic for 12+ and ferromagnetic for 22+. Both complexes exhibit several one-electron redox steps, and these were investigated with cyclic voltammetry and UV/Vis/near-IR spectroelectrochemistry. For 12+, it was possible to chemically isolate the pure forms of both the one-electron oxidized mixed-valent 13+ and the two-electron oxidized isovalent 14+ forms, and characterize them structurally as well as magnetically. This series thus provided an opportunity to investigate the effect of reversible electron transfers on the total spin-state of the molecule. In contrast to 22+, for 14+ the metal-ligand distances and the distances within the quinonoid ligand point to the existence of two low-spin CoIII centers, thus showing the innocence of the quintessential non-innocent ligands L. Magnetic data corroborate these observations by showing the decrease of the magnetic moment by roughly half (neglecting spin exchange effects) on oxidizing the molecules with one electron, and the disappearance of a paramagnetic response upon two-electron oxidation, which confirms the change in spin state associated with the electron-transfer steps. [ABSTRACT FROM AUTHOR]

This review summarizes our current understanding of the geometric and electronic structures of ferrous and ferric heme-nitrosyls, which are of key importance for the biological functions and transformations of NO. In-depth correlations are made between these properties and the reactivities of these species. Here, a focus is put on the discoveries that have been made in the last 10 years, but previous findings are also included as necessary. Besides this, ferrous heme-nitroxyl complexes are also considered, which have become of increasing interest recently due to their roles as intermediates in NO and multiheme nitrite reductases, and because of the potential role of HNO as a signaling molecule in mammals. In recent years, computational methods have received more attention as a means of investigating enzyme reaction mechanisms, and some important findings from these theoretical studies are also highlighted in this chapter. [ABSTRACT FROM AUTHOR]

A comprehensive overview is presented of the biologically relevant coordination chemistry of nitrosyls and its biochemical consequences. Representative classes of metal nitrosyls are introduced along with the structural and bonding aspects that may have consequences for the biological functioning of these complexes. Next, the biological targets and functions of nitrogen (II) oxide are discussed. Up-to-date biochemical applications of metal nitrosyls are reviewed. [ABSTRACT FROM AUTHOR]

This review provides a historical introduction to nitrosyl complexes. In the 1960s and 1970s, the renaissance of coordination chemistry led to the detailed study of nitrosyl complexes, and the emerging of new spectroscopic and structural techniques were used to define the metrics of nitric oxide when coordinated to transition metals and established that unlike CO and CN-, NO adopted alternative geometries. The development of theoretical models to account for this geometric ambivalence was initially based on semiempirical molecular orbital calculations in the early 1970s. Subsequently more accurate and sophisticated calculations have deepened our understanding of the bonding in transition metal-nitrosyl complexes. The discovery in the 1980s of the key importance of these complexes as models for the biological functions and transformations of NO encouraged these studies. NO is produced in vivo by the nitric oxide synthase (NOS) family of enzymes and plays a key role in the nerve-signal transreduction, vasodilation, blood clotting, and immune response by white blood cells. In these biological processes, the coordination of nitric oxide to metal centres is crucial, and therefore, their detailed study is essential for an understanding of nitric oxide's functions at the molecular level. [ABSTRACT FROM AUTHOR]