Sandwich Complexes of the As42-Aromatic Ring with Some Transition Metals

The equilibrium geometries, energies, harmonic vibrational frequencies, and nuc- leus independent chemical shifts (NICS) of the new type sandwich structures [As4MAs4]n- (M = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt; n = 0, 1 or 2) are investigated at the B3LYP level.All the [As4MAs4]n- species adopt staggered (D4d) conformations as their stable structures and eclipsed (D4h) conformations as their transition states, and once the sandwich complexes are formed, the As42- square properties remain unchanged.The NICS calculation confirms that the complexes of Fe, Co, and Ni are aromatic with negative NICS values, and those of Ru, Rh, and Ir exhibit slight aromaticity, while those of Pd, Os, and Pt show slight antiaromaticity.     

Doping of Zinc Oxide with Selected First Row Transition Metals for Photocatalytic Applications

ZnO doped with Cr, Mn, Fe, Co, Ni and Cu was prepared by homogeneous hydrolysis of sulfates with urea. The samples were annealed at various temperatures and characterized by X‐ray powder diffraction, UV/VIS reflectance spectroscopy, BET (Brunauer‐Emmet‐Teller) surface area and porosity measurements. The photocatalytic activity of the samples was evaluated by measuring the degradation of an organic dye Reactive Black 5. The morphology of the samples was determined by scanning electron microscopy and atomic force microscopy. For the Cu‐doped ZnO sample, EPR spectra were obtained. All samples annealed at 800°C contained hexagonal ZnO. In the VIS region, the best photocatalytic performance had the ZnO samples doped with Cr, Fe and Cu.     

Methyl Complexes of the Transition Metals

Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition‐metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition‐metal complexes containing M?CH₃ fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last five years. After a panoramic overview on M?CH₃ compounds of Groups 3 to 11, which includes the most recent landmark findings in this area, two further sections are dedicated to methyl‐bridged complexes and reactivity.     

Complex Formation Between Hydroxy Naphthol Blue and First Row Transition Metal Cyanide Complexes

Abstract

It has been found that cyanide complexes of first row transition metal elements exhibit enhanced binding to hydroxy naphthol blue (HNB) relative to the binding of corresponding aquo-ions. HNB forms a 2:1 complex with Fe³⁺ and Cu²⁺ cyanides, and 1:1 complexes with all other transition metal cyanide complexes studied; formation constants have been calculated from the spectrophotometric data in each case. It is possible to use HNB as a spectrophotometric reagent for transition metal cyanide complexes, lower limits of detection being determined for each complex.     

Nitrido Complexes of Transition Metals

In the past decade new syntheses and numerous structural determinations have enlivened studies in the still relatively young field of nitrido-transition-metal complexes. Aside from the terminal function of the nitrido ligand M?N:, this group also occurs as linear μ₂-bridging ligand in symmetric and asymmetric coordination; examples are known with almost right-angled bridge function; and, finally, it also functions as μ₃-bridging ligand. Accordingly, the fresh impulses given to synthetic chemistry by nitrido complexes are also many-sided: such complexes are used, inter alia, for the preparation of phosphaniminato and thionitrosyl complexes as well as for the synthesis of metallaheterocycles of the type MN₃S₂ and MN₃P₂ with delocalized π-systems. In technetium chemistry complexes with terminal nitrido group are employed as radiopharmaceuticals, and, owing to the strong trans influence of the M?N: group, nitrido complexes of molybdenum are suitable as catalysts in olefin metathesis. Finally, nitrido complexes are also of wide interest in theoretical studies.     

Trifluorophosphine Complexes of Transition Metals

The present paper deals with a new class of inorganic coordination compounds, the first member of which, tetrakis(trifluorophosphine)nickel(0), was discovered in 1951. Not only have the neutral metal(0) trifluorophosphines been prepared, but also a number of their derivatives (trifluorophosphinemetal hydrides and trifluorophosphinemetallates, as well as nitrosyl, carbonyl, halogeno, and aromatic trifluorophosphine complexes). These compounds have been characterized by their chemical behavior and by spectroscopic and magnetochemical studies. Trifluorophosphine has the strongest π-acceptor properties of all neutral ligands, and is therefore particularly suitable for the stabilization of unusually low oxidation states (zero and negative) of transition metals.     

New Cyclosiloxanolate Cluster Complexes of Transition Metals

New cyclosiloxanolate transition metal cluster complex derivatives were prepared. PhSiO₂K reacted with NiX₂ (X₂ = Cl₂ or acac) to give K₂{[η⁶−(PhSiO₂)₆]₂[μ₃−(OH)]₂Ni₄K₄}, a mixed group 1–group 10 metal complex. PhSiO₂Na reacted with Ni(NH₃)₆I₂ to give Na{[η⁶−(PhSiO₂)₆]₂Ni₆(μ₆−I)} as the first example of “encapsulated” I⁻ ion in siloxanolate complexes. The macrocyclic Na₄{[η¹²−(PhSiO₂)₁₂]Cu₄} complex reacted with η⁶−(1,3,5−C₇H₈)Cr(CO)₃ to give the heterobimetallic adduct Na₄{[η¹²−(PhSiO₂)₁₂]Cu₄}· [Cr(CO)₃]₃ as one of the rare examples of heterobimetallic complexes with different oxidation numbers of the metals. The copper derivative {[η⁶−(PhSiO₂)₆]₂Cu₆(n−BuOH)₅} reacted in MeOH/CHCl₃ (1:6) with Et₄NCN to give the hexanuclear complex {[η⁶−(PhSiO₂)₆]₂Cu₆(η²−C₃H₅N₂O₂)₂}, containing 2-amino-2-oxoetanimidic acid methyl ester monoanion ligands, product of an unexpected C–C coupling reaction. This latter complex was characterized also by X-ray diffraction crystal and molecular structure determination. This paper is dedicated to the 70th birthday of Professor Dr. Gunter Schmid (Essen), pioneer of large cluster chemistry, known to friends as GOLD-Schmid, because of his famous discovery of the Au₅₅ cluster. The Authors are proud to be within his many friends.     

Electrochemical Arylation of N-Containing Chelate and Macrocyclic Complexes of Transition Metals with the Aid of Diphenyliodonium Salts

A new method of electrochemical arylation of complexes of transition metals (Fe, Co, Ni) with N-containing chelate and macrocyclic (dimethylglyoximate, porphyrin, etc.) ligands employs diphenyliodonium salts as arylating agents and permits the synthesis of compounds containing functional groups that are easily reduceable or sensitive to the action of organometallic compounds. A homogeneous redox catalysis (mediator 1,5-dinitroanthraquinone-9,10) reduces the reaction potential to –0.45 V (Ag/AgCl/KCl), thus substantially decreasing the contribution of side processes.     

Syntheses and Crystal Structures of the First Row Transition Metals with 1,6-Bis(2'-pyridyl)-2,5-dithiahexane

Six first row transition metal complexes with 1,6-bis(2′-pyridyl)-2,5-dithiahexane(Py_2S_2), namely, MnPy_2S_2Cl_2(1), FePy_2S_2Cl_2(2), Co Py_2S_2Cl(3), CoPy_2S_2(SCN)_2(4), NiPy_2S_2(SCN)_2(5) and NiPy_2S_2(N_3)_2(6), have been synthesized. A mixture of MCl_2·x H_2O(M = Mn, Co) in MeOH(FeCl_2·4H_2O in MeCN) and the stoichiometric amount of Py_2S_2 was stirred for 4 h at room temperature, then these aiming products 1, 2 and 3 could be obtained by purification. A mixture of MPy_2S_2Cl_2(M = Co, Ni) in MeOH and two equivalents of KSCN or NaN_3 was stirred for 4 h at room temperature. After that, complexes 4, 5 and 6 could be got by purifying. For 1, 2, 3, 4 and 5, the metal centers are hexa-coordinated in a similar distorted octahedral geometry and the crystal structures have the same space group Pbcn. The crystal structure of compound 6 belongs to monoclinic with space group P21/c. The coordinated atoms around M(Ⅱ) are two pyridyl N atoms(N(1) and N(2)), two thioether S atoms(S(1) and S(2)) and two chloride ions(Cl(1) and Cl(2)) in compounds 1, 2, and 3, but in 4, 5, and 6, two chloride ions(Cl(1) and Cl(2)) are replaced by another two N atoms from N_3~– or NCS~–.     

Sandwich Compounds of Transition Metals with Cyclopolyenes and Isolobal Boron Analogues

A series of sandwich compounds of transition metals (M=Ni, Fe, Cr) with cyclic hydrocarbon (M(CH)_n) and borane (M(BH₂)_n), ligands (including mixed hydrocarbon/borane sandwiches) has been studied using density functional theory (B3LYP/6‐311+G(df,p)). Multicenter bonding between the central metal atom and basal cycloborane rings provides stabilization to planar cycloborane species. Large negative NICS values allude to aromatic character in the cycloboranes similar to the analogous cyclic hydrocarbons. The ability of cycloborane sandwiches to stabilize attached carbocations, radicals and carbanions is also assessed.     

Novel Cofacial Porphyrin-Based Homo- and Heterotrimetallic Complexes of Transition Metals

We present a straightforward and generally applicable synthesis route for cofacially linked homo- and heterotrimetallic trisporphyin complexes. The protocol encompasses synthesising the first aryl-based, trans-o-phenylene trisporphyrin starting from pyrrole and benzaldehyde with an overall yield of 3.6 %. It also allows investigating the respective cis-isomer as the first conformationally restricted planar-chiral trisporphyrin. The free-base ligand was used in subsequent metalation reactions to afford the corresponding homotrimetallic Mn(III)-, Fe(III)-, Ni(II)-, Cu(II)-, Zn(II)- and Pd(II) complexes – additionally, a small adaptation of the protocol resulted in the defined Ni(II)Fe(III)Ni(II) complex in a total yield of 2.3 %. By monitoring Ni(II) insertion into the empty trimeric ligands, we affirmed that the outer porphyrin rings are filled before the internal ring. The molecular species were characterised by ¹H NMR, UV-Vis, photoluminescence, IR, MS, CID, and high-resolution IMS measurements.     

On the Reactivity of Disilylphosphido Complexes of Transition Metals Towards Acid Chlorides

Abstract

The first phosphaalkenyl complex Cp(CO)₂Fe-P=C (OSiMe₃)(t-Bu) was generated from Cp(CO)₂FeP(SiMe₃)₂ and t-Bu(CO)Cl. In order to test the validity of this synthetic approach, we varied the ring ligand (Cp, C₅Me₅), the metal (Fe, Ru, Os), the main group element (P, As), and the carbonyl chlorides. The diphosphenyl complexes (C₅Me₅)(CO)₂M-P=P-[2,4,6-t-Bu₃C₆H₂] were obtained from (C₅Me₅)(CO)₂M-P(SiMe₃)₂ and the corresponding phosphonous chloride. These metallated diphosphenes are easily converted to diphospho-ureas by treatment with Fe₂(CO)₉.     

第一过渡系金属硅烯配合物的理论研究

以HF/6-311+G^*基组研究了硅烯SiH₂同第一过渡系金属的配合物MSiH₂的分子轨道特征及键解离能.MSiH₂为共平面构型.其中基态的3TiSiH₂和4CoSiH₂带有明显的双键特征.M-Si键具有共价性质.M-Si的键解离能,从Sc到Cu呈现周期性变化,这种变化趋势同M的金属离子激发能之间存在近似的线性关系.