Special Issue "Binuclear Complexes"

A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Coordination Chemistry".

Deadline for manuscript submissions: closed (30 April 2019)

Special Issue Editor

Guest Editor
Prof. Dr. Philippe Schollhammer

Université de Bretagne Occidentale, Laboratoire de Chimie, Electrochimie et Photochimie Moléculaires, Brest, France
Website | E-Mail
Interests: inorganic molecular chemistry; coordination; organometallic and bioorganometallic chemistry; biomimetism; bimetallic activation; hydrogenases and nitrogenase models; activation of small molecules; synthesis and reactivity; inorganic and organometallic electrochemistry and electrocatalysts

Special Issue Information

Dear Colleagues,

Binuclear complexes of transition metals have attracted the interest of a great number of chemists for several decades in their quest for new homogeneous catalysts, as well as in mimicking, with simple molecular models, the active sites of metalloenzymes or the surfaces of heterogeneous catalysts. The research on functional bimetallic catalysts has, in particular, found inspiration in the functions of metalloenzymes which are often based on polymetallic activation. As an example, an outstanding bioorganometallic chemistry has been extensively developed in the last few years for reproducing the activity of [FeFe]- or [NiFe]-hydrogenases in the hope of obtaining efficient electrocatalysts for an alternative free-noble metal production of H2. Currently, the activation of small molecules using dinuclear complexes, based on non-noble metals, is a modern challenge that offers promising perspectives. The attractiveness of such systems lies in the expected cooperative bimetallic activation that two proximate metal centers may afford, and in their ability to induce transformations of substrates that are different from those observed with catalysts having a single-metal center. Moreover, coordinatively-unsaturated dinuclear compounds, featuring metal–metal multiple bonds provide original templates, as well as electron-reservoirs for multisite activation.

This Special Issue aims to highlight recent developments in bimetallic complex topics, covering their syntheses, characterization, and stoichiometric reactivity or catalytic activity for novel activation modes of substrates, as well as electrochemical and theoretical studies.

Prof. Dr. Philippe Schollhammer
Guest Editor

Manuscript Submission Information

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Keywords

  • dinuclear complexes
  • bimetallic activation
  • activation of small molecules
  • synthesis and reactivity
  • catalytic activity
  • mechanism determination
  • structure-reactivity relation-ship

Published Papers (10 papers)

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Research

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Open AccessArticle
Reactive Heterobimetallic Complex Combining Divalent Ytterbium and Dimethyl Nickel Fragments
Received: 8 March 2019 / Revised: 29 March 2019 / Accepted: 17 April 2019 / Published: 26 April 2019
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Abstract
This article presented the synthesis and characterization of original heterobimetallic species combining a divalent lanthanide fragment and a divalent nickel center bridged by the bipyrimidine ligand, a redox-active ligand. X-ray crystal structures were obtained for the Ni monomer (bipym)NiMe2, 1, [...] Read more.
This article presented the synthesis and characterization of original heterobimetallic species combining a divalent lanthanide fragment and a divalent nickel center bridged by the bipyrimidine ligand, a redox-active ligand. X-ray crystal structures were obtained for the Ni monomer (bipym)NiMe2, 1, as well as the heterobimetallic dimer compounds, Cp*2Yb(bipym)NiMe2, 2, along with 1H solution NMR, solid-state magnetic data, and DFT calculations only for 1. The reactivity with CO was investigated on both compounds and the stoichiometric acetone formation is discussed based on kinetic and mechanistic studies. The key role of the lanthanide fragment was demonstrated by the relatively slow CO migratory insertion step, which indicated the stability of the intermediate. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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Open AccessArticle
Electrochemical and Computational Insights into the Reduction of [Fe2(CO)6{µ-(SCH2)2GeMe2}] Hydrogenase H-Cluster Mimic
Received: 8 February 2019 / Revised: 25 March 2019 / Accepted: 26 March 2019 / Published: 10 April 2019
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Abstract
The electrochemical reduction of the complex [Fe2(CO)6{µ-(SCH2)2GeMe2}] (1) under N2 and CO is reported applying cyclic voltammetry. Reduction of complex 1 in CO saturated solutions prevents the possible [...] Read more.
The electrochemical reduction of the complex [Fe2(CO)6{µ-(SCH2)2GeMe2}] (1) under N2 and CO is reported applying cyclic voltammetry. Reduction of complex 1 in CO saturated solutions prevents the possible release of CO from the dianion 12−, while the latter reacts with additional CO forming a spectroscopically uncharacterized product P1. This product undergoes a reversible redox process at E1/2 = −0.70 V (0.2 V∙s−1). In this report, the structure of the neutral complex 1, isomers of dianionic form of 1, and P1 are described applying DFT computations. Furthermore, we propose reaction pathways for H2 production on the basis of the cyclic voltammetry of complex 1 in presence of the strong acid CF3SO3H. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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Open AccessArticle
Understanding Factors that Control the Structural (Dis)Assembly of Sulphur-Bridged Bimetallic Sites
Received: 19 February 2019 / Revised: 13 March 2019 / Accepted: 13 March 2019 / Published: 27 March 2019
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Abstract
Bimetallic structures of the general type [M2(µ-S)2] are omnipresent in nature, for biological function [M2(µ-S)2] sites interconvert between electronically distinct, but isostructural, forms. Different from structure-function relationships, the current understanding of the mechanism of formation [...] Read more.
Bimetallic structures of the general type [M2(µ-S)2] are omnipresent in nature, for biological function [M2(µ-S)2] sites interconvert between electronically distinct, but isostructural, forms. Different from structure-function relationships, the current understanding of the mechanism of formation and persistence of [M2(µ-S)2] sites is poorly developed. This work reports on bimetallic model compounds of nickel that interconvert between functional structures [Ni2(µ-S)2]+/2+ and isomeric congeners [2{κ-S–Ni}]2+/+, S = Aryl-S, in which the nickel ions are geometrically independent. Interconversion of the two sets of structures was studied quantitatively by UV–VIS absorption spectroscopy and cyclic voltammetry. Assembly of the [Ni2(µ-S)2]+ core from [2{κ-S–Ni}]+ is thermodynamically and kinetically highly preferred over the disassembly of [Ni2(µ-S)2]2+ into [2{κ-S–Ni}]2+. Labile Ni-η2/3-bonding to aromatic π-systems of the primary thiophenol ligand is critical for modeling (dis)assembly processes. A phosphine coligand mimics the role of anionic donors present in natural sites that saturate metal coordination. Three parameters have been identified as critical for structure formation and persistence. These are, first, the stereoelectronic properties of the metals ions, second, the steric demand of the coligand, and, third, the properties of the dative bond between nickel and coligand. The energies of transition states connecting functional and precursor forms have been found to depend on these parameters. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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Open AccessArticle
Electronic Communication between Dithiolato-Bridged Diiron Carbonyl and S-Bridged Redox-Active Centres
Received: 31 January 2019 / Revised: 1 March 2019 / Accepted: 2 March 2019 / Published: 8 March 2019
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Abstract
The catalytic potential of linked redox centres is exemplified by the catalytic site of [FeFe]-hydrogenases, which feature a diiron subsite linked by a cysteinyl S atom to a 4Fe4S cube. The investigation of systems possessing similarly-linked redox sites is important because it provides [...] Read more.
The catalytic potential of linked redox centres is exemplified by the catalytic site of [FeFe]-hydrogenases, which feature a diiron subsite linked by a cysteinyl S atom to a 4Fe4S cube. The investigation of systems possessing similarly-linked redox sites is important because it provides a context for understanding the biological system and the rational design of abiological catalysts. The structural, electrochemical and spectroscopic properties of Fe2(CO)5(CH3C(CH2S)2CH2SPhNO2, I-bzNO2 and the aniline analogue, I-bzNH2, are described and IR spectroelectrochemical studies have allowed investigation of the reduction products and their reactions with CO and protons. These measurements have allowed identification of the nitrobenzenyl radical anion, quantification of the shifts of the (CO) bands on ligand-based reduction compared with NO2/NH2 exchange and protonation of the pendent ligand. The strength of thioether coordination is related to the electronic effects, where competitive binding studies with CO show that CO/thioether exchange can be initiated by redox processes of the pendent ligand. Stoichiometric multi electron/proton transfer reactions of I-bzNO2 localised on nitrobenzene reductions occur at mild potentials and a metal-centred reduction in the presence of protons does not lead to significant electrocatalytic proton reduction. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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Open AccessArticle
Dinuclear Gold Complexes Supported by Wide Bite Angle Diphosphines for Preorganization-Induced Selective Dual-Gold Catalysis
Received: 29 January 2019 / Revised: 14 February 2019 / Accepted: 20 February 2019 / Published: 26 February 2019
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Abstract
The synthesis, reactivity, and potential of well-defined dinuclear gold complexes as precursors for dual-gold catalysis is explored. Using the preorganizing abilities of well-known wide bite angle diphosphine ligands, DBFPhos and DPEPhos, dinuclear Au(I)–Au(I) complexes 1 and 2 are used as precursors to form [...] Read more.
The synthesis, reactivity, and potential of well-defined dinuclear gold complexes as precursors for dual-gold catalysis is explored. Using the preorganizing abilities of well-known wide bite angle diphosphine ligands, DBFPhos and DPEPhos, dinuclear Au(I)–Au(I) complexes 1 and 2 are used as precursors to form well-defined monocationic species with either a chlorido- or acetylido-ligand bridging the two gold centers. These compounds are active catalysts for the dual-gold heterocycloaddition of a urea-functionalized alkyne, and the preorganization of both Au-centers affords efficient σ,π-activation of the substrate, even at high dilution, significantly outperforming benchmark mononuclear catalysts. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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Open AccessArticle
Synthesis, Structures and Chemistry of the Metallaboranes of Group 4–9 with M2B5 Core Having a Cross Cluster M–M Bond
Received: 29 January 2019 / Revised: 13 February 2019 / Accepted: 14 February 2019 / Published: 26 February 2019
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Abstract
In an attempt to expand the library of M2B5 bicapped trigonal-bipyramidal clusters with different transition metals, we explored the chemistry of [Cp*WCl4] with metal carbonyls that enabled us to isolate a series of mixed-metal tungstaboranes with an M [...] Read more.
In an attempt to expand the library of M2B5 bicapped trigonal-bipyramidal clusters with different transition metals, we explored the chemistry of [Cp*WCl4] with metal carbonyls that enabled us to isolate a series of mixed-metal tungstaboranes with an M2{B4M’} {M = W; M’ = Cr(CO)4, Mo(CO)4, W(CO)4} core. The reaction of in situ generated intermediate, obtained from the low temperature reaction of [Cp*WCl4] with an excess of [LiBH4·thf], followed by thermolysis with [M(CO)5·thf] (M = Cr, Mo and W) led to the isolation of the tungstaboranes [(Cp*W)2B4H8M(CO)4], 13 (1: M = Cr; 2: M = Mo; 3: M = W). In an attempt to replace one of the BH—vertices in M2B5 with other group metal carbonyls, we performed the reaction with [Fe2(CO)9] that led to the isolation of [(Cp*W)2B4H8Fe(CO)3], 4, where Fe(CO)3 replaces a {BH} core unit instead of the {BH} capped vertex. Further, the reaction of [Cp*MoCl4] and [Cr(CO)5·thf] yielded the mixed-metal molybdaborane cluster [(Cp*Mo)2B4H8Cr(CO)4], 5, thereby completing the series with the missing chromium analogue. With 56 cluster valence electrons (cve), all the compounds obey the cluster electron counting rules. Compounds 15 are analogues to the parent [(Cp*M)2B5H9] (M= Mo and W) that seem to have generated by the replacement of one {BH} vertex from [(Cp*W)2B5H9] or [(Cp*Mo)2B5H9] (in case of 5). All of the compounds have been characterized by various spectroscopic analyses and single crystal X-ray diffraction studies. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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Open AccessArticle
Syntheses, Structures, and Catalytic Hydrocarbon Oxidation Properties of N-Heterocycle-Sulfonated Schiff Base Copper(II) Complexes
Received: 16 October 2018 / Revised: 3 January 2019 / Accepted: 31 January 2019 / Published: 6 February 2019
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Abstract
Reaction of the o-[(o-hydroxyphenyl)methylideneamino]benzenesulfonic acid (H2L) (1) with CuCl2·2H2O in the presence of pyridine (py) leads to [Cu(L)(py)(EtOH)] (2) which, upon further reaction with 2,2’-bipyridine (bipy), pyrazine (pyr), or piperazine [...] Read more.
Reaction of the o-[(o-hydroxyphenyl)methylideneamino]benzenesulfonic acid (H2L) (1) with CuCl2·2H2O in the presence of pyridine (py) leads to [Cu(L)(py)(EtOH)] (2) which, upon further reaction with 2,2’-bipyridine (bipy), pyrazine (pyr), or piperazine (pip), forms [Cu(L)(bipy)]·MeOH (3), [Cu2(L)2(μ-pyr)(MeOH)2] (4), or [Cu2(L)2(μ-pip)(MeOH)2] (5), respectively. The Schiff base (1) and the metal complexes (25) are stabilized by a number of non-covalent interactions to form interesting H-bonded multidimensional polymeric networks (except 3), such as zigzag 1D chain (in 1), linear 1D chain (in 2), hacksaw double chain 1D (in 4) and 2D motifs (in 5). These copper(II) complexes (25) catalyze the peroxidative oxidation of cyclic hydrocarbons (cyclooctane, cyclohexane, and cyclohexene) to the corresponding products (alcohol and ketone from alkane; alcohols, ketone, and epoxide from alkene), under mild conditions. For the oxidation of cyclooctane with hydrogen peroxide as oxidant, used as a model reaction, the best yields were generally achieved for complex 3 in the absence of any promoter (20%) or in the presence of py or HNO3 (26% or 30%, respectively), whereas 2 displayed the highest catalytic activity in the presence of HNO3 (35%). While the catalytic reactions were significantly faster with py, the best product yields were achieved with the acidic additive. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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Open AccessArticle
Trapping of an Heterometallic Unsaturated Hydride: Structure and Properties of the Ammonia Complex [MoMnCp(μ-H)(μ-PPh2)(CO)5(NH3)]
Inorganics 2018, 6(4), 125; https://doi.org/10.3390/inorganics6040125
Received: 15 October 2018 / Revised: 9 November 2018 / Accepted: 15 November 2018 / Published: 24 November 2018
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Abstract
Complexes displaying multiple bonds between different metal atoms have considerable synthetic potential because of the combination of the high electronic and coordinative unsaturation associated to multiple bonds with the intrinsic polarity of heterometallic bonds but their number is scarce and its chemistry has [...] Read more.
Complexes displaying multiple bonds between different metal atoms have considerable synthetic potential because of the combination of the high electronic and coordinative unsaturation associated to multiple bonds with the intrinsic polarity of heterometallic bonds but their number is scarce and its chemistry has been relatively little explored. In a preliminary study, our attempted synthesis of the unsaturated hydrides [MoMCp(μ-H)(μ-PR2)(CO)5] from anions [MoMCp(μ-PR2)(CO)5] and (NH4)PF6 yielded instead the ammonia complexes [MoMCp(μ-H)(μ-PR2)(CO)5(NH3)] (M = Mn, R = Ph; M = Re, R = Cy). We have now examined the structure and behaviour of the MoMn complex (Mo–Mn = 3.087(3) Å) and found that it easily dissociates NH3 (this requiring some 40 kJ/mol, according to DFT calculations), to yield the undetectable unsaturated hydride [MoMnCp(μ-H)(μ-PPh2)(CO)5] (computed Mo–Mn = 2.796 Å), the latter readily adding simple donors L such as CNR (R = Xyl, p-C6H4OMe) and P(OMe)3, to give the corresponding electron-precise derivatives [MoMnCp(μ-H)(μ-PPh2)(CO)5(L)]. Thus the ammonia complex eventually behaves as a synthetic equivalent of the unsaturated hydride [MoMnCp(μ-H)(μ-PPh2)(CO)5]. The isocyanide derivatives retained the stereochemistry of the parent complex (Mo–Mn = 3.0770(4) Å when R = Xyl) but a carbonyl rearrangement takes place in the reaction with phosphite to leave the entering ligand trans to the PPh2 group, a position more favoured on steric grounds. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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Open AccessArticle
Hydrogenase Biomimetics with Redox-Active Ligands: Synthesis, Structure, and Electrocatalytic Studies on [Fe2(CO)42-dppn)(µ-edt)] (edt = Ethanedithiolate; dppn = 1,8-bis(Diphenylphosphino)Naphthalene)
Inorganics 2018, 6(4), 122; https://doi.org/10.3390/inorganics6040122
Received: 28 August 2018 / Revised: 5 November 2018 / Accepted: 9 November 2018 / Published: 20 November 2018
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Abstract
Addition of the bulky redox-active diphosphine 1,8-bis(diphenylphosphino)naphthalene (dppn) to [Fe2(CO)6(µ-edt)] (1) (edt = 1,2-ethanedithiolate) affords [Fe2(CO)42-dppn)(µ-edt)] (3) as the major product, together with small amounts of a P–C bond [...] Read more.
Addition of the bulky redox-active diphosphine 1,8-bis(diphenylphosphino)naphthalene (dppn) to [Fe2(CO)6(µ-edt)] (1) (edt = 1,2-ethanedithiolate) affords [Fe2(CO)42-dppn)(µ-edt)] (3) as the major product, together with small amounts of a P–C bond cleavage product [Fe2(CO)51-PPh2(1-C10H7)}(µ-edt)] (2). The redox properties of 3 have been examined by cyclic voltammetry and it has been tested as a proton-reduction catalyst. It undergoes a reversible reduction at E1/2 = −2.18 V and exhibits two overlapping reversible oxidations at E1/2 = −0.08 V and E1/2 = 0.04 V. DFT calculations show that while the Highest Occupied Molecular Orbital (HOMO) is metal-centred (Fe–Fe σ-bonding), the Lowest Unoccupied Molecular Orbital (LUMO) is primarily ligand-based, but also contains an antibonding Fe–Fe contribution, highlighting the redox-active nature of the diphosphine. It is readily protonated upon addition of strong acids and catalyzes the electrochemical reduction of protons at Ep = −2.00 V in the presence of CF3CO2H. The catalytic current indicates that it is one of the most efficient diiron electrocatalysts for the reduction of protons, albeit operating at quite a negative potential. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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Review

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Open AccessReview
Bond Forming Reactions Involving Isocyanides at Diiron Complexes
Received: 28 January 2019 / Revised: 12 February 2019 / Accepted: 14 February 2019 / Published: 26 February 2019
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Abstract
The versatility of isocyanides (CNR) in organic chemistry has been tremendously enhanced by continuous advancement in transition metal catalysis. On the other hand, the urgent need for new and more sustainable synthetic strategies based on abundant and environmental-friendly metals are shifting the focus [...] Read more.
The versatility of isocyanides (CNR) in organic chemistry has been tremendously enhanced by continuous advancement in transition metal catalysis. On the other hand, the urgent need for new and more sustainable synthetic strategies based on abundant and environmental-friendly metals are shifting the focus towards iron-assisted or iron-catalyzed reactions. Diiron complexes, taking advantage of peculiar activation modes and reaction profiles associated with multisite coordination, have the potential to compensate the lower activity of Fe compared to other transition metals, in order to activate CNR ligands. A number of reactions reported in the literature shows that diiron organometallic complexes can effectively assist and promote most of the “classic” isocyanide transformations, including CNR conversion into carbyne and carbene ligands, CNR insertion, and coupling reactions with other active molecular fragments in a cascade sequence. The aim is to evidence the potential offered by diiron coordination of isocyanides for the development of new and more sustainable synthetic strategies for the construction of complex molecular architectures. Full article
(This article belongs to the Special Issue Binuclear Complexes)
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