Christian Boehme

N-Heterocyclic Carbene, Silylene, and Germylene Complexes of MCl (M = Cu, Ag, Au). A Theoretical Study1

Quantum chemical calculations at the MP2 level of theory using relativistic ECPs with large valence basis sets for the metals are reported for the complexes of CuCl, AgCl, and AuCl with the N-heterocyclic carbene imidazol-2-ylidene 1 and the related silylene 2 and germylene 3. The metal−ligand bond dissociation energies are predicted at CCSD(T). The metal−carbene bonds are very strong. The strongest bond is predicted for 1-AuCl, which has a bond strength De = 82.8 kcal/mol. Even the silylene and germylene complexes have substantial bond energies between 37.4 and 64.1 kcal/mol for 2 and between 29.9 and 49.4 kcal/mol for 3. The trend of the bond energies for the metal fragments is AuCl > CuCl > AgCl, and for the ligands it is 1 > 2 > 3. The metal−ligand bonds have a strong ionic character which comes from the Coulomb attraction between the positively charged metal atom and the σ-electron pair of the donor atom. The covalent part of the bonding shows little π-back-bonding from the metal to the ligand. The a...

Chemical bonding in mononuclear transition metal complexes with Group 13 diyl ligands ER (E=BTl): Part X: Theoretical studies of inorganic compounds☆

Abstract Recent advances in the synthesis of stable transition metal complexes with terminal BR, AlR, GaR and InR ligands where R is mostly but not always a π-donor ligand, gave rise to speculation about metal–ligand binding interactions. In response to this, theoretical studies have been carried out, which focus on the nature of the chemical bond in transition metal complexes with terminal Group 13 diyl ligands ER (E=BTl). Some of these investigations were made in cooperation with experimental work which reported new stable complexes. The theoretical work made predictions about the geometries and bond energies of the complexes. The bonding situation of the TMER bonds, which has been controversial in the literature, has also been examined. The review summarizes the results and the progress in the understanding of the nature of the TMER bonds which has been gained in recent theoretical work. Previous discussions focused on the importance of RE→TM σ donation and particularly the RE←TM π-backdonation. The analysis of the bonding situations revealed that the π-backdonation may indeed become as important as RE→TM σ donation, but the total covalent TMER bond order is always less than 1. The most important conclusion which arises from these theoretical studies is that the TMER bonding interactions are largely ionic, and that the covalent donor–acceptor interactions play a less important role. This makes the discussion whether the TMER bond should be considered as a single or triple bond irrelevant.

The Nature of the Gallium–Iron Bond in [Ar*GaFe(CO)4]

Gallium–iron bonds in the model compounds [(C6H5)GaFe(CO)4] (1 a) and [CpGaFe(CO)4] (2 a) were analyzed using the CDA partitioning scheme. The Ga−Fe bonds are largely ionic. There is a substantially higher degree of Ga←Fe π backbonding in 1 a than in 2 a. Gallium becomes stabilized in 1 a mainly by Ga←Fe backdonation, whereas Ga←Cp backdonation stabilizes Ga in 2 a.

Do Perchlorate and Triflate Anions Bind to the Uranyl Cation in an Acidic Aqueous Medium? A Combined EXAFS and Quantum Mechanical Investigation

Structural properties of uranyl cations in acidic aqueous perchlorate and triflate solutions were investigated using uranium LIII -edge extended X-ray absorption fine-structure spectroscopy (EXAFS) in conjunction with quantum mechanical calculations of gas-phase model complexes. EXAFS spectra were measured in aqueous solutions of up to 10 M triflic and 11.5 M perchloric acid, as well as mixtures of perchloric acid and sodium perchlorate. In no case is the perchlorate anion coordinated to UO2(2+). The number of equatorial water molecules bound to UO2(2+) is always about five. In the case of the 10 M CF3SO3H solution, an inner-sphere complexation of the triflate is observed with a U-S radial distance of 3.62 Å. These results are in qualitative agreement with quantum mechanical calculations of model uranyl complexes, according to which the interaction energies of anions follow the order perchlorate

Übergangsmetallsubstituierte Gallane: Synthese, Struktur und Bindungsverhältnisse von [(CO)4CoGaEt2(NC7H13)], [(PMe3)(CO)3CoGaCl2(NMe3)], [(CO)4CoGaCl3]K und [(CO)5MnGaEt2(NC7H13)]

Die ubergangsmetallsubsituierten Gallane [(CO)5MnGaEt2(NC7H13)] (1), [(PMe3)(CO)3CoGaCl2 · (NMe3)] (2), [(CO)4CoGaEt2(NC7H13)] (3) und [(CO)4CoGaCl3]K (4) wurden durch Reaktion der Carbonylmetallate [(CO)nM] (Na/K) mit den Galliumchloriden ClGaEt2(NC7H13), Cl3Ga(NMe3) bzw. GaCl3 erhalten. Die Einkristallstrukturbestimmungen ergaben fur 1: Raumgruppe P21/c (I.T.-Nr.: 14); Z = 4; a = 1425,4(2) pm, b = 1007,4(1) pm, c = 1429,9(3) pm; β = 113,92(1)°; 2: Raumgruppe P21/m (I.T.-Nr.: 11); Z = 2; a = 746,1(1) pm, b = 1131,2(1) pm, c = 1061,5(1) pm; β = 101,87(1)°; 3: Raumgruppe P21/c (I.T.-Nr.: 14); Z = 8; a = 1405,9(2) pm, b = 1786.2(2) pm, c = 1430,9(2) pm; β = 91,47(1)°; 4: Raumgruppe P21/c; Z = 4; a = 1185,7(1) pm, b = 895,4(1) pm, c = 1144,7(3) pm; β = 106,47(2)°. Anhand der Modellverbindungen [{L′(CO)3Co}GaX2L] (L′ = CO, PH3; L = NH3, X = H, Cl) wurden die polaren σ(Co–Ga)-Bindungen und die Substituenteneffekte auf die Bindungslange auf der Basis quantenchemischer Dichtefunktionalrechnungen (DFT) charakterisiert. Transition Metal substituted Gallanes: Synthesis and X-Ray Structures of [(CO)4CoGaEt2(NC7H13)], [(PMe3)(CO)3CoGaCl2(NMe3)], [(CO)4CoGaCl3]K, and [(CO)5MnGaEt2(NC7H13)] The transition metal substituted gallanes [(CO)5MnGaEt2(NC7H13)] (1), [(PMe3)(CO)3CoGaCl2 · (NMe3)] (2), [(CO)4CoGaEt2(NC7H13)] (3), and [(CO)4CoGaCl3]K (4) were obtained by the reaction of the potassium/sodium salts of the manganese- and cobaltcarbonylmetallates with the chlorogallium species ClGaEt2(NC7H13), Cl3Ga(NMe3), and GaCl3. The structures were established by single crystal X-ray analysis 1: space group P21/c (I.T.-No.: 14); Z = 4; a = 1425.4(2) pm, b = 1007.4(1) pm, c = 1429.9(3) pm; β = 113.92(1)°; 2: space group P21/m (I.T.-No.: 11); Z = 2; a = 746.1(1) pm, b = 1131.2(1) pm, c = 1061.5(1) pm; β = 101.87(1)°; 3: space group P21/c (I.T.-No.: 14); Z = 8; a = 1405.9(2) pm, b = 1786.2(2) pm, c = 1430.9(2) pm; β = 91.47(1)°; 4: space group P21/c; Z = 4; a = 1185.7(1) pm, b = 895.4(1) pm, c = 1144.7(3) pm; β = 106.47(2)°. The model compounds [{L′(CO)3Co}GaX2L] (L′ = CO, PH3; L = NH3, X = H, Cl) with polar σ(Co–Ga) bonds and the effect of the substituent on the bond length are characterized with DFT-calculations.

The electronic structure of transition metal compounds

Publisher Summary This chapter addresses a particular problem of transition metal chemistry: the bonding between a transition metal and a main group metal. Recently, transition metal carbonyl complexes of AlI- and Ga1-fragments—for example, [(CO)5Cr-Ga(C2H5)L2] (L2 = tmeda), [(CO)4Fe-A1Cp*], and [(CO)5W-AlClL2] (L2 = tmeda) could be synthesized and characterized by X-ray analysis. The position of the v(CO)-IR-bands has been taken as indication against the extreme description of the complexes as contact ion pairs. The overall structures suggest an interpretation of the interaction between the transition metal and the main group metal as a donor–acceptor bond. The study of the compounds [(CO)5W-XCln(NH3)m]x– discussed in the chapter gives a thorough description of the bonding between a main group metal and a transition metal for a wide range of main group elements. The MP2 optimized geometry of model system [(CO)5W-AlCl(NH3)2] is in agreement with the X-ray structure of the recently synthesized [(CO)5W-A1C1L2] (L2 = tmeda). The analysis of the electronic structure using the natural bond orbital (NBO) analysis and the newly developed charge decomposition analysis (CDA) clearly shows that the free electron pair of aluminum forms a donor bond to tungsten and, therefore, [(CO)5W-A1CI(NH3)2] is best understood as a donor–acceptor complex.