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Inorganics
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First-Row Transition Metal Complexes
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First-Row Transition Metal Complexes

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

Deadline for manuscript submissions: closed (31 December 2019) | Viewed by 62959

Special Issue Editor

Dr. John C. Gordon

E-Mail Website
Guest Editor
Inorganic, Isotope and Actinide Chemistry Group (C-IIAC), Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Interests: inorganic and organometallic chemistry; catalysis; chemistry for sustainable and renewable energy applications
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

First row transition metals and their complexes are ubiquitous in chemistry and biochemistry and are technologically useful as well. Many living organisms contain enzymes that are comprised of metal complexes; for example, nitrogenases, responsible for the reduction of nitrogen (N2) to ammonia (NH3), utilize iron (Fe) as part of their molecular machinery. Coordination complexes are also widely used in industrial settings. Molecules such as metal phthalocyanines (e.g., copper (Cu)) find use as dyes and pigments. Metal complex formation itself is used as a technique for extracting metals from ores (e.g., nickel (Ni, Co)). The production of commercially important polymers relies on the use of coordination or organometallic complexes of metals such as titanium (Ti) or chromium (Cr), while metals can be separated from each other by differences in the solubilities of their resultant metal complexes with various ligands. This Special Issue of Inorganics highlights various chemistries of first row transition metal complexes and the relevance that these molecules have with respect to our daily lives.

Prof. Dr. John C. Gordon
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • first row transition metal
  • catalysis
  • polymers
  • materials
  • separations
  • complexation
  • ligand

Published Papers (10 papers)

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Research

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15 pages, 1695 KiB  
Article
Accessing Low-Valent Titanium CCC-NHC Complexes: Toward Nitrogen Fixation
by Sriloy Dey and T. Keith Hollis
Inorganics 2021, 9(2), 15; https://doi.org/10.3390/inorganics9020015 - 08 Feb 2021
Cited by 35 | Viewed by 2967
Abstract
The dramatic expansion of the earth’s population can be directly correlated with the Haber–Bosch process for nitrogen fixation becoming widely available after World War II. The ready availability of artificial fertilizer derived thereof dramatically improved food supplies world-wide. Recently, artificial nitrogen fixation surpassed [...] Read more.
The dramatic expansion of the earth’s population can be directly correlated with the Haber–Bosch process for nitrogen fixation becoming widely available after World War II. The ready availability of artificial fertilizer derived thereof dramatically improved food supplies world-wide. Recently, artificial nitrogen fixation surpassed the natural process. The Haber–Bosch process is extremely energy and green-house gas intensive due to its high-temperature and H2 demands. Many low valent Ti(II) complexes of N2 are known. We report herein a preliminary investigation of the low-valent chemistry of Ti with the CCC-NHC ligand architecture. These CCC-NHC pincer Ti(IV) complexes are readily reduced with KC8 or Mg powder. Preliminary results indicate very different reactivity patterns with alkynes and phosphines for this ligand architecture versus prior ligands. Successful reduction to an intact low-valent (CCC-NHC)Ti complex was confirmed by re-oxidation with PhICl2. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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22 pages, 4491 KiB  
Article
Reduction of 2,2′-Bipyridine by Quasi-Linear 3d-Metal(I) Silylamides—A Structural and Spectroscopic Study
by Igor Müller, Christian Schneider, Clemens Pietzonka, Florian Kraus and C. Gunnar Werncke
Inorganics 2019, 7(10), 117; https://doi.org/10.3390/inorganics7100117 - 25 Sep 2019
Cited by 18 | Viewed by 4382
Abstract
Quasi-linear anionic 3d-metal(I) silylamides are a new and promising class of molecules. Due to their highly negative reduction potential we wanted to test their capability to reduce substrates under coordination of their monoanionic radicaloid form. In a proof of principle study, we present [...] Read more.
Quasi-linear anionic 3d-metal(I) silylamides are a new and promising class of molecules. Due to their highly negative reduction potential we wanted to test their capability to reduce substrates under coordination of their monoanionic radicaloid form. In a proof of principle study, we present the results of the reaction of metal(I) silylamides of chromium to cobalt with 2,2′-bipyridine (bipy), the redox non-innocence and reducibility of which was already established. In the course of these studies complexes of the type K{18-crown-6}[M(hmds)2(bipy)] (hmds = –N(SiMe3)2) were obtained. These compounds were isolated and thoroughly characterized to confirm the electron transfer onto the bipyridine ligand, which now acts as a radical monoanion. For comparison of the structural changes of the bipyridine ligand, the analogous zinc complexes were also synthesized. Overall our results indicate that anionic metal(I) silylamides are capable of reducing and ligate substrates, even when the electrochemical reduction potential of the latter is by up to 1 V higher. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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19 pages, 7067 KiB  
Article
A Comparative Study of the Catalytic Behaviour of Alkoxy-1,3,5-Triazapentadiene Copper(II) Complexes in Cyclohexane Oxidation
by Oksana V. Nesterova, Maximilian N. Kopylovich and Dmytro S. Nesterov
Inorganics 2019, 7(7), 82; https://doi.org/10.3390/inorganics7070082 - 29 Jun 2019
Cited by 9 | Viewed by 3251
Abstract
The mononuclear copper complexes [Cu{NH=C(OR)NC(OR)=NH}2] with alkoxy-1,3,5-triazapentadiene ligands that have different substituents (R = Me (1), Et (2), nPr (3), iPr (4), CH2CH2OCH3 (5)) [...] Read more.
The mononuclear copper complexes [Cu{NH=C(OR)NC(OR)=NH}2] with alkoxy-1,3,5-triazapentadiene ligands that have different substituents (R = Me (1), Et (2), nPr (3), iPr (4), CH2CH2OCH3 (5)) were prepared, characterized (including the single crystal X-ray analysis of 3) and studied as catalysts in the mild oxidation of alkanes with H2O2 as an oxidant, pyridine as a promoting agent and cyclohexane as a main model substrate. The complex 4 showed the highest activity with a yield of products up to 18.5% and turnover frequency (TOF) up to 41 h−1. Cyclohexyl hydroperoxide was the main reaction product in all cases. Selectivity parameters in the oxidation of substituted cyclohexanes and adamantane disclosed a dominant free radical reaction mechanism with hydroxyl radicals as C–H-attacking species. The main overoxidation product was 6-hydroxyhexanoic acid, suggesting the presence of a secondary reaction mechanism of a different type. All complexes undergo gradual alteration of their structures in acetonitrile solutions to produce catalytically-active intermediates, as evidenced by UV/Vis spectroscopy and kinetic studies. Complex 4, having tertiary C–H bonds in its iPr substituents, showed the fastest alteration rate, which can be significantly suppressed by using the CD3CN solvent instead of CH3CN one. The observed process was associated to an autocatalytic oxidation of the alkoxy-1,3,5-triazapentadiene ligand. The deuterated complex 4-d32 was prepared and showed higher stability under the same conditions. The complexes 1 and 4 showed different reactivity in the formation of H218O from 18O2 in acetonitrile solutions. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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19 pages, 4401 KiB  
Article
Pyridine-2,6-Dicarboxylic Acid Esters (pydicR2) as O,N,O-Pincer Ligands in CuII Complexes
by Katharina Butsch, Aaron Sandleben, Maryam Heydari Dokoohaki, Amin Reza Zolghadr and Axel Klein
Inorganics 2019, 7(4), 53; https://doi.org/10.3390/inorganics7040053 - 14 Apr 2019
Cited by 14 | Viewed by 5856
Abstract
The pyridine-2,6-carboxylic esters pydicR2 with R = Me or Ph form the unprecedented mononuclear CuII complexes [Cu(pydicR2)Cl3]− in one-pot reactions starting from pyridine-2,6-carboxychloride pydicCl2, CuII chloride, and NEt3 in MeOH or PhOH [...] Read more.
The pyridine-2,6-carboxylic esters pydicR2 with R = Me or Ph form the unprecedented mononuclear CuII complexes [Cu(pydicR2)Cl3]− in one-pot reactions starting from pyridine-2,6-carboxychloride pydicCl2, CuII chloride, and NEt3 in MeOH or PhOH solution under non-aqueous conditions. The triethylammonium salts (HNEt3)[Cu(pydicR2)Cl3] were isolated. The methyl derivative could be crystallized to allow a XRD structure determination. Both structures were optimized using DFT calculations in various surroundings ranging from gas phase and the non-coordinating solvent CH2Cl2 to the weakly coordinating acetone and well-coordinating solvents acetonitrile (MeCN) or dimethylformamide (DMF), while detailed calculation showed the charge distribution, dipole moments, and HOMO–LUMO gap energies changing upon solvation. According to these calculations, the ion pairs and the anionic CuII complexes were stable, which shows only Cu–Cl bond elongation and weakening of the charge transfer between the anionic complex and the cation as solvents become polar. Synthesis attempts in the presence of water yielded the CuII complexes [Cu(pydic)(OH2)2]n and [Cu(OH2)6][{Cu(pydic)}2(µ-Cl)2], which results from pydicCl2 hydrolysis. Alternatively, the new pydic(IPh)2 (IPh = 2-iodo-phenyl) ester ligand was synthesized and reacted with anhydrous CuCl2, which yields the new binuclear complex [{Cu(pydic(IPh)2)Cl}2(µ-Cl)2]. EPR spectroscopy of the solid compounds reveals typical axial spectra in line with the observed and DFT calculated geometries. Cyclic voltammetry and UV–vis absorption spectroscopy in solution are in line with un-dissociated complex species [Cu(pydicR2)Cl3]−. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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12 pages, 3302 KiB  
Article
Synthesis and Reactivity of Mn–CF3 Complexes
by Alex L. Daniels, Jason G. Da Gama, Racquel Edjoc, Bulat M. Gabidullin and R. Tom Baker
Inorganics 2019, 7(1), 3; https://doi.org/10.3390/inorganics7010003 - 06 Jan 2019
Cited by 5 | Viewed by 4019
Abstract
The synthesis, characterization and reactivity of several bi- and tridentate, N-ligated manganese carbonyl trifluoromethyl complexes are presented. These complexes exhibit elongated Mn–CCF3 bonds (versus Mn(CF3)(CO)5), suggesting a lability that could be utilized for the transfer or insertion of [...] Read more.
The synthesis, characterization and reactivity of several bi- and tridentate, N-ligated manganese carbonyl trifluoromethyl complexes are presented. These complexes exhibit elongated Mn–CCF3 bonds (versus Mn(CF3)(CO)5), suggesting a lability that could be utilized for the transfer or insertion of the CF3 functional group into organic substrates. Unlike their Mn–X congeners (X = Cl, Br), these Mn–CF3 complexes exhibit a preference for hard donor ancillary ligands, thus enabling the synthesis of 4 N-ligated Mn–CF3 complexes including a mixed-donor tridentate complex using an NNS Schiff base ([2-(methylthio)-N-(1-(pyridin-2-yl)ethylidene)aniline]). Although we have not yet identified efficient CF3 transfer reactions, fluoride abstraction from the Mn–CF3 complexes using trimethylsilyl triflate affords the first stable Mn fluorocarbenes as evidenced by 19F NMR spectroscopy. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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17 pages, 2722 KiB  
Article
Imidazo-Phenanthroline Ligands as a Convenient Modular Platform for the Preparation of Heteroleptic Cu(I) Photosensitizers
by Marie-Ann Schmid, Martin Rentschler, Wolfgang Frey, Stefanie Tschierlei and Michael Karnahl
Inorganics 2018, 6(4), 134; https://doi.org/10.3390/inorganics6040134 - 12 Dec 2018
Cited by 20 | Viewed by 5311
Abstract
The capture and storage of solar energy is a promising option to overcome current energy issues. To put such systems into practice, molecular photosensitizers should be based on abundant metals and possess a strong absorption capability for visible light. Therefore, a systematic series [...] Read more.
The capture and storage of solar energy is a promising option to overcome current energy issues. To put such systems into practice, molecular photosensitizers should be based on abundant metals and possess a strong absorption capability for visible light. Therefore, a systematic series of four novel heteroleptic Cu(I) complexes of the type [(P^P)Cu(N^N)]+ (with P^P = xantphos and N^N = different diimine ligands) has been prepared. As an essential feature, these copper photosensitizers contain an imidazole moiety at the backbone of the diimine ligand, which increases the aromatic π-system compared to phenanthroline type ligands. Moreover, 2-(4-bromophenyl)-1-phenyl-1H-imidazo-[4,5-f][1,10]phenanthroline was used as a starting point and modular platform for gradually extended diimine ligands. Suzuki cross-coupling was applied to introduce different kind of substituents in the back of this ligand. Afterwards, a combination of NMR spectroscopy, mass spectrometry, X-ray analysis, cyclic voltammetry, UV/vis and emission spectroscopy was used to investigate the structural, electrochemical and photophysical properties of these compounds. As a result, a reversible reduction, strongly increased extinction coefficients and significantly redshifted absorption maxima (>20 nm) were found compared to traditional Cu(I) photosensitizers without an imidazo moiety. Moreover, these compounds show a bright emission in the solid state. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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11 pages, 6232 KiB  
Article
Room Temperature Ni(II) Catalyzed Hydrophosphination and Cyclotrimerization of Alkynes
by Ruth L. Webster
Inorganics 2018, 6(4), 120; https://doi.org/10.3390/inorganics6040120 - 02 Nov 2018
Cited by 12 | Viewed by 4472
Abstract
The catalytic activity of nickel complexes in hydrophosphination involving secondary phosphines is not a commonly studied transformation. Beyond a small number of stand-out examples, many reports in the literature focus on the use of simple nickel salts. β-Diketiminates have been proven to be [...] Read more.
The catalytic activity of nickel complexes in hydrophosphination involving secondary phosphines is not a commonly studied transformation. Beyond a small number of stand-out examples, many reports in the literature focus on the use of simple nickel salts. β-Diketiminates have been proven to be incredibly effective ligands for catalysis using a range of metal centers. This synthetic study investigates the catalytic ability of a Ni(II) β-diketiminate complex in the hydrophosphination of alkenes and alkynes, with a serendipitous discovery of its ability to effect alkyne cyclotrimerization and phosphine dehydrocoupling. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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18 pages, 3827 KiB  
Article
[2 × 2] Molecular Grids of Ni(II) and Zn(II) with Redox-Active 1,4-Pyrazine-Bis(thiosemicarbazone) Ligands
by Natalia Arefyeva, Aaron Sandleben, Alexander Krest, Ulrich Baumann, Mathias Schäfer, Maxim Kempf and Axel Klein
Inorganics 2018, 6(2), 51; https://doi.org/10.3390/inorganics6020051 - 21 May 2018
Cited by 7 | Viewed by 4601
Abstract
Tetranuclear complexes [M4(LR)4] with M = Ni(II) or Zn(II), with a [2 × 2] grid-type structure, were assembled in good yields and purity from the easily accessible but unprecedented pyrazine-bridged bis(thiosemicarbazone) protoligands (ligand precursors) H2L [...] Read more.
Tetranuclear complexes [M4(LR)4] with M = Ni(II) or Zn(II), with a [2 × 2] grid-type structure, were assembled in good yields and purity from the easily accessible but unprecedented pyrazine-bridged bis(thiosemicarbazone) protoligands (ligand precursors) H2LR (1,4-pyrazine-2,5-bis(R-carbaldehyde-thiosemicarbazone); R = Me, Et, iPr, or Ph). The complexes were characterised in solution by NMR, MS, IR, and UV-Vis absorption spectroscopy and (spectro)electrochemical methods. HR-MS spectra unequivocally reveal that the tetranuclear species are very stable in solution and any measurements represent these species. Only at higher temperatures (fragmentation in solution: MS and in the solid: TG-DTA) or upon the addition of protons (acidic UV-Vis titrations) can the tetrameric entities be decomposed. Single crystal XRD measurement remained preliminary. Rapid loss of co-crystallised solvent molecules within the [2 × 2] grid-type structures resulted in crystals of very poor quality, but the results were qualitatively in line with spectroscopy, electrochemistry, and quantum chemical (DFT) calculations. IR and NMR spectroscopy point clearly to a thiolate coordination of dianionic (deprotonated) ligands. The electrochemistry reveals four electronically coupled and reversible one-electron reductions centred largely at the pyrazine bridges. EPR and UV-Vis spectroelectrochemical measurements in combination with DFT calculation support the assignment. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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Review

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28 pages, 3424 KiB  
Review
The First-Row Transition Metals in the Periodic Table of Medicine
by Cameron Van Cleave and Debbie C. Crans
Inorganics 2019, 7(9), 111; https://doi.org/10.3390/inorganics7090111 - 06 Sep 2019
Cited by 32 | Viewed by 17134
Abstract
In this manuscript, we describe medical applications of each first-row transition metal including nutritional, pharmaceutical, and diagnostic applications. The 10 first-row transition metals in particular are found to have many applications since there five essential elements among them. We summarize the aqueous chemistry [...] Read more.
In this manuscript, we describe medical applications of each first-row transition metal including nutritional, pharmaceutical, and diagnostic applications. The 10 first-row transition metals in particular are found to have many applications since there five essential elements among them. We summarize the aqueous chemistry of each element to illustrate that these fundamental properties are linked to medical applications and will dictate some of nature’s solutions to the needs of cells. The five essential trace elements—iron, copper, zinc, manganese, and cobalt—represent four redox active elements and one redox inactive element. Since electron transfer is a critical process that must happen for life, it is therefore not surprising that four of the essential trace elements are involved in such processes, whereas the one non-redox active element is found to have important roles as a secondary messenger.. Perhaps surprising is the fact that scandium, titanium, vanadium, chromium, and nickel have many applications, covering the entire range of benefits including controlling pathogen growth, pharmaceutical and diagnostic applications, including benefits such as nutritional additives and hardware production of key medical devices. Some patterns emerge in the summary of biological function andmedical roles that can be attributed to small differences in the first-row transition metals. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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37 pages, 6274 KiB  
Review
Ddpd as Expanded Terpyridine: Dramatic Effects of Symmetry and Electronic Properties in First Row Transition Metal Complexes
by Christoph Förster, Matthias Dorn, Thomas Reuter, Sven Otto, Güllü Davarci, Tobias Reich, Luca Carrella, Eva Rentschler and Katja Heinze
Inorganics 2018, 6(3), 86; https://doi.org/10.3390/inorganics6030086 - 27 Aug 2018
Cited by 39 | Viewed by 9321
Abstract
The 2,2′:6′:2″-terpyridine ligand has literally shaped the coordination chemistry of transition metal complexes in a plethora of fields. Expansion of the ligand bite by amine functionalities between the pyridine units in the tridentate N,N’-dimethyl-N,N’-dipyridine-2-yl-pyridine-2,6-diamine ligand (ddpd) [...] Read more.
The 2,2′:6′:2″-terpyridine ligand has literally shaped the coordination chemistry of transition metal complexes in a plethora of fields. Expansion of the ligand bite by amine functionalities between the pyridine units in the tridentate N,N’-dimethyl-N,N’-dipyridine-2-yl-pyridine-2,6-diamine ligand (ddpd) modifies the properties of corresponding transition metal complexes, comprising redox chemistry, molecular dynamics, magnetism and luminescence. The origins of these differences between ddpd and tpy complexes will be elucidated and comprehensively summarized with respect to first row transition metal complexes with d2–d10 electron configurations. Emerging applications of these ddpd complexes complementary to those of the well-known terpyridine ligand will be highlighted. Full article
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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