Tetracarbonyl Complexes Research Articles

Intramolecularly O,N,O-Coordinated Tin(II) Salts: Syntheses, Structures, Cyclization, and Transition Metal Complexation.

We report the syntheses of tin(II) salts of the types [L1SnX]SnX3 [L1=2,6-{(i-PrO)2(O)P}2C5H3N: 1, X=Cl; 2, X=Br], [L2SnCl]SnCl3 [L2=2-{(i-PrO)Ph(O)P}-6-{(i-PrO)2(O)P}C5H3N: 3], [L3SnX]SnX3 [L3=2,6-{MeO(O)C}2C5H3N: 4, X=Cl; 5, X=Br], [L4SnX]SnX3 [L4=2,6-{Et2N(O)C}2C5H3N: 6, X=Cl; 7, X=Br]. These compounds were obtained by addition of SnX2 to the corresponding ligand inducing autoionization of the respective tin(II) halide. The thermal stability of 1, 3, and 4 was elucidated, giving, under ester cleavage and cyclisation, the tin(II) derivatives 8-12. The reaction of [L1SnCl]SnCl3 (1) with W(CO)4(thf)2 afforded the tungsten tetracarbonyl complex [{L1SnCl}{SnCl3}W(CO)4] (13), representing the first example in which a tin(II) stannate anion and a tin(II) stannylium cation simultaneously coordinate to a transition metal centre. The compounds were characterized by single crystal X-ray diffraction analyses and in part by elemental analyses, IR and NMR spectroscopy, electrospray ionization mass spectrometry. DFT calculations accompany the experimental work.

Water Splitting Reaction Mechanism on Transition Metal (Fe-Cu) Sulphide and Selenide Clusters-А DFT Study.

The tetracarbonyl complexes of transition metal chalcogenides M2X2(CO)4, where M = Fe, Co, Ni, Cu and X = S, Se, are examined by density functional theory (DFT). The M2X2 core is cyclic with either planar or non-planar geometry. As a sulfide, it is present in natural enzymes and has a selective redox capacity. The reduced forms of the selenide and sulfide complexes are relevant to the hydrogen evolution reaction (HER) and they provide different positions of hydride ligand binding: (i) at a chalcogenide site, (ii) at a particular cation site and (iii) in a midway position forming equal bonds to both cation sites. The full pathway of water decomposition to molecular hydrogen and oxygen is traced by transition state theory. The iron and cobalt complexes, cobalt selenide, in particular, provide lower energy barriers in HER as compared to the nickel and copper complexes. In the oxygen evolution reaction (OER), cobalt and iron selenide tetracarbonyls provide a low energy barrier via OOH* intermediate. All of the intermediate species possess favorable excitation transitions in the visible light spectrum, as evidenced by TD-DFT calculations and they allow photoactivation. In conclusion, cobalt and iron selenide tetracarbonyl complexes emerge as promising photocatalysts in water splitting.

The Best of Both Worlds: Combining the Power of MICs and WCAs To Generate Stable and Crystalline CrI -Tetracarbonyl Complexes with π-Accepting Ligands.

Invited for the cover of this issue are Biprajit Sarkar and co-workers at the University of Stuttgart and University of Freiburg. In the image, the solar flare represents the non-innocence (fluorine-specific interactions) of the counterion, and the black hole at the metal center illustrates the oxidation/electron deficiency of the Cr-center, while the electron "gets lost" in the space (oxidation agent). Read the full text of the article at 10.1002/chem.202301205.

Front Cover: The Best of Both Worlds: Combining the Power of MICs and WCAs To Generate Stable and Crystalline CrI‐Tetracarbonyl Complexes with π‐Accepting Ligands (Chem. Eur. J. 50/2023)

Front Cover: The Best of Both Worlds: Combining the Power of MICs and WCAs To Generate Stable and Crystalline Cr^I‐Tetracarbonyl Complexes with <i>π</i>‐Accepting Ligands (Chem. Eur. J. 50/2023)

The Best of Both Worlds: Combining the Power of MICs and WCAs To Generate Stable and Crystalline CrI -Tetracarbonyl Complexes with π-Accepting Ligands.

Here we present stable and crystalline chromium(I) tetracarbonyl complexes with pyridyl-MIC (MIC=mesoionic carbene) ligands and weakly coordinating anions (WCA=[Al(ORF )4 ]- , RF =C(CF3 )3 and BArF =[B(ArF )4 ]- , ArF =3,5-(CF3 )2 C6 H3 ). The complexes were fully characterized via crystallographic, spectroscopic and theoretical methods. The influence of counter anions on the IR and EPR spectroscopic properties of the CrI complexes was investigated, and the electronic innocence versus non-innocence of WCAs was probed. These are the first examples of stable and crystalline [Cr(CO)4 ]+ complexes with a chelating accepting ligand, and the data presented here are of relevance for both the photochemical and the electrochemical properties of these classes of compounds.

Bonding and Reactivity of a Diborabutadiene Fe Complex Synthesized by Boron–Boron Bond Activation

Though precious-metal multiboryl complexes feature prominently in catalytic C–H borylation schemes, the corresponding first-row transition multiboryl species have been comparatively underexplored. We set out to explore the iron coordination chemistry of phenylene-bridged diboryl chelates by targeting oxidative addition of strained cyclic diboron reagents. Under UV photolysis, Fe(CO)5 reacts with a four-membered 1,2-diboracycle via B–B bond cleavage to afford an Fe complex that is most consistent with a 1,4-dibora-1,3-butadiene Fe(0) tricarbonyl complex rather than the target diboryl Fe(II) tetracarbonyl complex. The unsaturated phenylene linker is essential for favoring this bonding arrangement. The Fe tricarbonyl product readily undergoes ligand substitution of CO by PMe3 and PMe2Ph to form diboryl iron dicarbonyl phosphine complexes. All three Fe complexes were characterized by IR and NMR spectroscopy, single-crystal X-ray diffraction, high-resolution mass spectrometry, and cyclic voltammetry, which allow for comparisons to be drawn between foundational Fe tricarbonyl diene complexes and their diboradiene analogues.

A comparative study of biradicaloids as ligands in iron tetracarbonyl complexes

A comparative study of biradicaloids as ligands in iron tetracarbonyl complexes

Group 6 (Cr, Mo, W) and Group 7 (Mn, Re) bipyridyl tetracarbonyl complex for electrochemical CO2 conversion: DFT and DLPNO-CCSD(T) study for effects of the central metal on redox potential, thermodynamics, and kinetics

To reveal the effects of central metal on the catalytic efficiency, we estimated the thermodynamics and kinetics of CO2 reduction by Group 6 and Group 7 metal bpy tetracarbonyl complexes using DLPNO-CCSD(T) method. The applied potential V1 required for the formation of the two-electron reduced species of the metal bpy tetracarbonyl complex is greater than the applied potential V2 required for the formation of the two-electron reduced species of the metal bpy tricarbonyl complex, and for each applied potential, the effect of the central metal on the reaction process was investigated. At applied potential V1, CO2 binding to metal center was the rate-limiting step in CO2 reduction by the Group 6 complex, while the second proton transfer was the rate-limiting step for CO2 reduction by the Group 7 complex. At applied potential V2, the rate-limiting step was the dissociation of the CO ligand from the central metal, except for Cr.

Heterometallic phosphinidene-bridged complexes derived from the phosphanyl complexes syn-[MCp(PHR*)(CO)2] (M = Mo, W; R* = 2,4,6-C6H2tBu3)

The title phosphanyl complexes were prepared upon photolysis of equimolar mixtures of dimers [M2Cp2(CO)6] and PH2R* (R* = 2,4,6-C6H2tBu3). They were converted into the corresponding chlorophosphanyl derivatives syn-[MCp(PClR*)(CO)2] upon reaction with CCl4, while its deprotonation (M = Mo) yielded the phosphinidene Li[MoCp(PR*)(CO)2]. These mononuclear precursors were tested for the synthesis of heterometallic PR*-bridged derivatives by following three synthetic strategies. Photochemical reactions between phosphanyl complexes and dimers [M´2(CO)2n] or [M´2Cp2(CO)2n] (M’ = Mn, Re, Fe, Ru, Co) gave binuclear derivatives of types [MM´Cpx(μ-PR*)(CO)n+2] and [MoM´Cpx(μ-PR*)(CO)n+1] (x = 1,2), but yields were very poor except for the WRe complexes. Combinations with Co, Mn, and Re were best made through reaction between carbonylates [M’(CO)n]− and chlorophosphanyl complexes, to give respectively the pentacarbonyl [MoCoCp(μ-PR*)(CO)5] and the heptacarbonyls [MM´Cp(μ-PR*)(CO)7] (MM’ = MoRe, MoMn, WMn). The latter were easily decarbonylated thermally to give hexacarbonyls [MM´Cp(μ-PR*)(CO)6], which display heterometallic single bonds and short M−P distances of ca. 2.27 Å formulated as double M=P bonds, and rearranged upon thermal or photochemical activation to give the hydride-phosphanyl derivatives [MM´Cp(μ-H){μ-P(CH2CMe2)C6H2tBu2}(CO)6]. This process was suppressed in the photochemical reactions by using a THF/NCMe (10:1) mixture as solvent, but then the acetonitrile complexes [MoM´Cp(μ-PR*)(CO)5(1κ-NCMe)] were formed. Combinations with Fe and Ru were best prepared by reacting Li[MoCp(PR*)(CO)2] with halide complexes [MXCp(CO)2], to give the tetracarbonyls [MoM´Cp2(μ-PR*)(CO)4] (M’ = Fe, Ru), a method also useful to prepare the gold complex [MoAuCp(μ-PR*)(CO)2{P(p-tol)3}] upon reaction with [AuCl{P(p-tol)3}]. The above tetracarbonyl complexes were decarbonylated photochemically to give the metal-metal bound tricarbonyls [MoM´Cp2(μ-PR*)(CO)3].

Sawhorse-type ruthenium complexes with triazolopyrimidine ligands - what do they represent in terms of cytotoxic and CORM compounds?

Three sawhorse-type ruthenium(I) complexes containing purine analogs such as triazolopyrimidines of the general formula [Ru2(CO)4(μ-OOCCH3)2(L)2], where L is 1,2,4-triazolo[1,5-a]pyrimidine (tp for 1), 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp for 2) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp for 3), have been synthesized and characterized by elemental analysis, infrared analysis, multinuclear magnetic resonance spectroscopic techniques (1H, 13C, 15N), and single-crystal X-ray diffraction (for 1 and 2). By assay with myoglobin, the photo-activated CO-releasing molecule (PhotoCORM) character of (1-3) has been confirmed, thus indicating the possibility of use in CO-based therapies. The importance of UV-induced modification has been investigated in the context of anticancer properties. Complexes (1) and (2) have been thoroughly screened for their in vitro cytotoxicity against various cancer cell lines: MCF-7 (breast cancer), HeLa (cervical cancer) and C32 (melanoma), as well as L929 normal fibroblasts in the dark and presence of UV-A light (365 nm). The results were compared with those for cisplatin and two reference ruthenium complexes, namely NAMI-A and KP1019. The most hydrophilic [Ru2(CO)4(μ-OOCCH3)2(tp)2] (1) (log P = -1.12) was found to be more cytotoxic than (2), despite the lower cellular uptake measured by ICP-MS toward HeLa cells. Importantly, photo-induced stimulation of cells with (1) resulted in a lower decrease in the viability of L929 normal cells (IC50 = 154.7 ± 6.5 μM) in comparison with HeLa cancer cells (IC50 = 66.7 ± 3.4 μM). The photo-induced stimulation of (1) and (2) increases ROS generation, and their anticancer activity may be a partially ROS-dependent phenomenon.

Mechanistic Study of Tungsten Bipyridyl Tetracarbonyl Electrocatalysts for CO2 Fixation: Exploring the Roles of Explicit Proton Sources and Substituent Effects.

Tungsten bipyridyl tetracarbonyl complexes were shown to reduce CO2 to CO in acetonitrile [Chem. Sci., 2014, 5, 1894-1900]. Here, we employ density functional theory (DFT) calculations to investigate the electronic structure and reactivity of a series of tungsten electrocatalysts, [W(bpy-R)(CO)4] (where R = H, CH3, tBu, OCH3, CF3, and CN), for the CO2 reduction reaction (CO2RR). Our proposed mechanism suggests that initial reduction of the starting material by two electrons is required to access the active catalyst upon CO dissociation, which is slightly endergonic, consistent with the slow product release observed experimentally. The doubly reduced species, which has a closed-shell singlet ground state, can bind CO2 via an η2-CO2 binding mode to yield the metallocarboxylate intermediate. Based on the energy span model, CO2 addition is the TOF-determining transition state (TDTS) in the presence of water as the proton source. Different substituents at the 4,4'-positions of the bipyridine ligand in [W(bpy-R)(CO)4] (R = H, CH3, tBu, OCH3, CF3, and CN) were considered to comprehend the substituent effects for CO2RR. DFT results show that electron-withdrawing substituents, such as CN and CF3, do not yield efficient CO2 reduction catalysts due to the necessity of forming high energy intermediates for the protonation steps, resulting in low TOFs and high overpotentials. Among electron-donating groups, the parent compound and tert-butyl substituted complex are the most active catalysts for CO2RR due to higher TOFs at low overpotentials. Overall, based on the energy span model and theoretical Tafel plots, our computational approach provides quantitative information for designing CO2 reduction electrocatalysts.

Ethylene tri-/tetramerization catalysts supported by diphosphinoindole ligands

A new class of diphosphinoindole ligands have been developed. Upon activation with MMAO-3A, Cr catalysts supported by these bisphosphine ligands are active for ethylene tri-/tetramerization. The best result was achieved by using the bisphosphine ligand containing a phenyl group at C3 position of indole, giving a high activity of up to 364 kg/(g Cr/h) with a total selectivity of up to 72% toward 1-hexene (23.5%) and 1-octene (48.4%). A representative chromium tetracarbonyl complex was synthesized and structurally characterized by single-crystal X-ray diffraction.

Electrochemically Driven Reduction of Carbon Dioxide Mediated by Mono‐Reduced Mo‐Diimine Tetracarbonyl Complexes: Electrochemical, Spectroelectrochemical and Theoretical Studies

AbstractThe activation of carbon dioxide by three different Mo‐diimine complexes [Mo(CO)4(L)] (L=bipyridine (bpy), 1,10‐phenantroline (phen) or pyridylindolizine (py‐indz)) has been investigated by electrochemistry and spectroelectrochemistry. Under an inert atmosphere, monoreduction of the complexes is ligand‐centered and leads to tetracarbonyl [Mo(CO)4(L)].− species, whereas double reduction induces CO release. Under CO2, [Mo(CO)4(L)] complexes undergo unexpected coupled chemical‐electrochemical reactions at the first reduction step, leading to the formation of reduced CO2 derivatives. The experimental results obtained from IR, NIR and UV‐Vis spectroelectrochemistry, as well as DFT calculations, demonstrate an electron‐transfer reaction whose rate is ligand‐dependent.

Synthesis and characterization of cationic manganese–carbonyl complexes bearing imidazol(in)ium-2-dithiocarboxylate ligands

Four cationic manganese–tetracarbonyl complexes with the generic formula [Mn(CO)4(S2C·NHC)]PF6 that featured chelating imidazol(in)ium-2-dithiocarboxylate ligands derived from common N-heterocyclic carbenes bearing mesityl or 2,6-diisopropylphenyl substituents on their nitrogen atoms were readily synthesized by reacting the corresponding [MnBr(CO)3(S2C·NHC)] precursors with silver hexafluorophosphate in dichloromethane at room temperature in the presence or absence of added carbon monoxide. All the products were fully characterized by various analytical techniques and their most striking features on IR, NMR, and XRD spectroscopies were compared with those exhibited by related compounds. Their fragmentation in the gas phase was probed by using advanced mass spectrometry techniques. Upon CID, a clean decarbonylation of the parent [Mn(CO)4(S2C·NHC)]+ cations led to the formation of [Mn(CO)3(S2C·NHC)]+, [MnO2(S2C·NHC)]+, and [Mn(OH2)(S2C·NHC)]+ species.

Ethylene oligomerisation chromium catalysts with unsymmetrical PCNP ligands.

Chromium(iii) complexes of chelating diphosphines, with PNP or PCNCP backbones, are excellent catalysts for ethylene tetra- and/or trimerisations. A missing link within this ligand series are unsymmetric chelating diphosphines based on a PCNP scaffold. New bidentate PCNP ligands of the type Ph2PCH2N(R)PPh2 (R = 1-naphthyl or 5-quinoline groups, 2a-d) have been synthesised and shown to be extremely effective ligands for ethylene tri-/tetramerisations. Three representative tetracarbonyl Cr0 complexes bearing a single PN(R)P (5), PCN(R)P (6), or PCN(R)CP (7) diphosphine (R = 1-naphthyl) have been prepared from Cr(CO)4(η4-nbd) (nbd = norbornadiene). Furthermore we report a single crystal X-ray diffraction study of these compounds and discuss their structural parameters.

Photochemical conversion of CO2 to CO by a Re complex: theoretical insights into the formation of CO and HCO3 - from an experimentally detected monoalkyl carbonate complex.

Triethanolamine (TEOA) has been used for the photocatalytic reduction of CO2, and the experimental studies have demonstrated that the TEOA increases the catalytic efficiency. In addition, the formation of a carbonate complex has been confirmed in the Re photocatalytic system where DMF and TEOA are used as solvents. In this study, we survey the reaction pathways of the photocatalytic conversions of CO2 to CO + H2O and CO2 to CO + HCO3− by fac-Re(bpy)(CO)3Br in the presence of TEOA using density functional theory (DFT) and domain-based local pair natural orbital coupled cluster approach, DLPNO-CCSD(T). Under light irradiation, the solvent-coordinated Re complex is first reduced to form a monoalkyl carbonate complex in the doublet pathway. This doublet pathway is kinetically advantageous over the singlet pathway. To reduce carbon dioxide, the Re complex needs to be reduced by two electrons. The second electron reduction occurs after the monoalkyl carbonate complex is protonated. The second reduction involves the dissociation of the monoalkyl carbonate ligand, and the dissociated ligand recombines the Re center via carbon to generate Re–COOH species, which further reacts with CO2 to generate tetracarbonyl complex and HCO3−. The two-electron reduced ligand-free Re complex converts CO2 to CO and H2O. The pathways leading to H2O formation have lower barriers than the pathways leading to HCO3− formation, but their portion of formation must depend on proton concentration.

Highly Active Manganese-Based CO2 Reduction Catalysts with Bulky NHC Ligands: A Mechanistic Study.

Because of the strong σ-donor and weak π-acceptor of the N-heterocyclic carbene (NHC), Mn-NHC complexes were found to be active for the reduction of CO2 to CO with high activity. However, some NHC-based manganese complexes showed low catalytic activity and required very negative potentials. We report herein that complex fac-[MnI(bis-MesNHC)(CO)3Br] [1; bis-MesNHC = 3,3-bis(2,4,6-trimethylphenyl)-(1,1'-diimidazolin-2,2'-diylidene)methane] could catalyze the electrochemical reduction of CO2 to CO with high activity (TOFmax = 3180 ± 6 s-1) at a less negative potential. Due to the introduction of the bulky Mes groups, a one-electron-reduced intermediate {[Mn0(bis-MesNHC)(CO)3]0 (2•)} was isolated as a packed "dimer" and crystallographically characterized. Stopped-flow Fourier-transform infrared spectroscopy was used to prove the direct reaction between doubly reduced intermediate fac-[Mn(bis-MesNHC)(CO)3]- and CO2; the tetracarbonyl Mn complex [Mn+(bis-MesNHC)(CO)4]+ ([2-CO]+) was captured, and its further reduction proposed as the rate-limiting step.

Thermal Dehydrogenation of Dimethylamine Borane Catalyzed by a Bifunctional Rhenium Complex

The reaction of a bidentate pyrrole based rhenium tetracarbonyl complex with dimethylamine borane at room temperature results in rapid dehydrogenation. Hydrogen generation was detected at temperatu...

Synthesis, Structure, and Bonding Analysis of Tin(II) Dihalide and Cyclopentadienyltin(II) Halide (Alkyl)(amino)carbene Complexes

Tin(II) dibromide, 2b, and cyclopentadienyltin(II) chloride, 2c, and cyclopentadienyltin(II) bromide, 2d, were reacted with cyclic (alkyl)(amino)carbene (cAAC), 1, to give the corresponding complexes cAAC·SnBr2, 3b, cAAC·SnCpCl, 3c, and cAAC·SnCpBr, 3d, which were studied in solution and in the solid state. Although isolatable as crystalline solids, 3c,d exist in a heteroleptic/homoleptic equilibrium with other tin(II) species, in solution. In addition, the coordination chemistry of 3b was investigated and the corresponding iron tetracarbonyl complex, 5, could be isolated and structurally characterized. Furthermore, the mechanism of the equilibrium reaction observed for 3c,d in solution, as well as the chemical bonding nature of all cAAC complexes were investigated by quantum-chemical calculations within the DFT framework.

Intermolecular C–H⋯O and n → π* and short intramolecular σ → π* interactions in the molybdenum(0) tetracarbonyl complex of a very twisted 14-membered tetraazaannulene macrocyclic ligand: structural and computational studies

An interesting intermolecular n → π* interaction supported an intermolecular C–H⋯O interaction in a molybdenum tetracarbonyl complex of a substituted dibenzo-tetraazaannulene complex to consolidate the crystal packing in the solid state.