Alexey Y. Timoshkin

Iron Bispentazole Fe(η5-N5)2, a Theoretically Predicted High-Energy Compound: Structure, Bonding Analysis, Metal–Ligand Bond Strength and a Comparison with the Isoelectronic Ferrocene

Quantum-chemical calculations with gradient-corrected (B3LYP) density functional theory have been carried out for iron bispentazole and ferrocene. The calculations predict that Fe(eta5-N5)2 is a strongly bonded complex which has D5d symmetry. The theoretically predicted total bond energy that yields Fe in the 5D ground state and two pentazole ligands is Do = 109.0 kcal mol(-1), which is only 29 kcal mol(-1) less than the calculated bond energy of ferrocene (Do = 138.0 kcal mol(-1); experimental: 158 +/- 2 kcal mol(-1)). The compound Fe(eta5-N5)2 is 260.5 kcal mol(-1) higher in energy than the experimentally known isomer Fe(N2)5, but the bond energy of the latter (Do = 33.7 kcal mol(-1)) is much less. The energy decomposition analyses of Fe(eta5-N5)2 and ferrocene show that the two compounds have similar bonding situations. The metal-ligand bonds are roughly half ionic and half covalent. The covalent bonding comes mainly from (e1g) eta5-N5- --> Fe2+ pi-donation. The previously suggested MO correlation diagram for ferrocene is nicely recovered by the Kohn-Sham orbitals. The calculated vibrational frequencies and IR intensities are reported.

Do solid-state structures reflect Lewis acidity trends of heavier group 13 trihalides? Experimental and theoretical case study.

Lewis acidity trends of aluminum and gallium halides have been considered on the basis of joint X-ray and density functional theory studies. Structures of complexes of heavier group 13 element trihalides MX(3) (M = Al, Ga; X = Cl, Br, I) with monodentate nitrogen-containing donors Py, pip, and NEt(3) as well as the structure of the AlCl(3)·PPh(3) adduct have been established for the first time by X-ray diffraction studies. Extensive theoretical studies (B3LYP/TZVP level of theory) of structurally characterized complexes between MX(3) and nitrogen-, phosphorus-, arsenic-, and oxygen-containing donor ligands have allowed us to establish the Lewis acidity trends Al > Ga, Cl ≈ Br > I. Analysis of the experimental and theoretical results points out that the solid state masks the Lewis acidity trend of aluminum halides. The difference in the Al-N bond distances between AlCl(3)·D and AlBr(3)·D complexes in the gas phase is small, while in the condensed phase, shorter Al-N distances for AlBr(3)·D complexes are observed with 9-fluorenone, mdta, and NEt(3) donors. The model based on intermolecular (H···X) interactions in solid adducts is proposed to explain this phenomenon. Thus, the donor-acceptor bond distance in the solid complexes cannot always be used as a criterion of Lewis acidity.

Stepwise Expansion of a Cp* Ring at Pentelidene Complexes and Stereoselective Formation of Triphosphines†

Stepwise opening and final removal of the η1-bound Cp* substituents in the bridged pentelidene complexes [Cp*E{W(CO)5}2] (E=P, As) occurs by the reaction with primary phosphines. Not only novel diphospha- and arsaphosphanorbornenes are obtained, but also diastereomerically pure complexed triphosphines. All reaction steps were monitored by NMR spectroscopy, and compounds structurally characterized.

Lewis-Säure/Base-stabilisiertes Phosphanylalan und -gallan

Weder synthetisiert noch in Matrix nachgewiesen wurden bislang die Stammverbindungen des Phosphanylalans bzw. -gallans vom Typ A. Durch H2-Eliminierungsreaktionen zwischen [(CO)5WPH3] und H3ENMe3 (E=Al, Ga) konnten nunmehr erstmals Lewis-Saure/Base-stabilisierte Komplexe des Typs B synthetisiert werden. Umfassende Dichtefunktionalrechnungen an den Aluminiumverbindungen belegen die hohe Stabilitat der Komplexe vom Typ B.

An end-on-coordinated As4 tetrahedron.

One time only: The reaction of [Cp*Ru(dppe)Cl] with the potent As4 transfer reagent [Ag(η(2)-As4)2](+)[pftb](-) leads to [Cp*Ru(dppe)(η(1)-As4)](+)[pftb](-) with an unprecedented end-on-coordinated As4 tetrahedron. Reaction with a second cationic ruthenium complex fragment does not lead to a second end-on coordination but to the cleavage of one basal As-As bond. This behavior, which differs from its phosphorus analogues, is rationalized by DFT calculations.

Relative energies of the C2H2S2 isomers 1,2-dithiete and dithioglyoxal: Peculiar basis set dependencies of density functional theory and ab initio methods

Ab initio calculations at the levels of Hartree–Fock (HF), second order Moller–Plesset perturbation theory (MP2), coupled-cluster theory with singles, doubles, and estimated triple excitations [CCSD(T)], and density functional theory (DFT) using the functionals B3LYP and B3PW91 of the relative energies of the C2H2S2 isomers 1,2-dithiete (2a), and dithioglyoxal (2b) show a peculiar dependence of the results on the f-type polarization functions. The ab initio calculations with 6-31G(nd) basis sets with n=1–3 incorrectly predict that 2a is higher in energy than 2b. The relative energies at the MP2 and CCSD(T) levels change by more than 6 kcal/mol in favor of 2a if the basis set is augmented by one set of f functions. The DFT calculations also give a higher stability of 2a relative to 2b if f functions are included in the basis sets, but the change in the relative energy is only ∼2 kcal/mol. The large change in the relative energies which are calculated at MP2 and CCSD(T) are mainly due to the functions at su...

The Lewis Base Stabilized Parent Arsanylborane H2AsBH2⋅NMe3

Exclusively hydrogen-substituted arsanylboranes: The synthesis of the unprecedented Lewis base stabilized monomeric parent compound of the arsanylborane H2AsBH2⋅NMe3 was achieved in a one-pot reaction in high yield and purity. The analogous phosphanylborane was synthesized in a similar manner. A series of different reactions was performed on H2AsBH2⋅NMe3 to show its broad reactivity pattern.

The Oligomerization of Phosphinoborane by Titanium Complexes

Among inorganic monomers that are interesting for polymerization reactions to obtain inorganic polymers, ammonia–borane is currently in the focus of interest owing to its high hydrogen content. The metal-induced polymerization is widely studied, and recently some progress was achieved for the recycling of the oligomerized material. Compared to organic analogues, the 14-valence electron (VE) monomer H3NBH3 can be regarded as an ethane analogue. Following this comparison, the corresponding BN congener of ethylene would be the 12 VE species aminoborane (NH2BH2), which was only proposed to be a transient on the way to further oligomerization. In contrast, the parent pair of heavier homologue H3PBH3 is very labile even at low temperatures, and it dissociates. However, Denis et al. described dehydrocondensation of both components at higher temperatures (90 8C) catalyzed by B(C6F5)3 to give a polymer of the presumed composition [H2P BH2]n. It is ambiguous whether monomeric phosphinoborane is an intermediate of such a reaction. Thus some time ago we have been focused and finally succeeded on the synthesis of the Lewis basestabilized parent phosphinoborane PH2BH2NMe3. [8] It is a potential precursor compound for the unknown phosphinoborane PH2BH2, for which a defined synthetic approach does not exist, even by matrix-isolation techniques. Initial investigations for its use in polymerization reactions show spontaneous polymerization by elimination of the base, resulting in a material with a high ceramic yield. In contrast, Manners et al. could show alkane-analogous phosphine–boranes of the type RPH2BH3 to polymerize by using Rh catalysts or {Cp2Ti} in stoichiometric reactions. [11] The question thus arises as to whether the ethylene-analogous phosphinoborane PH2BH2NMe3 can be used to monitor its oligomerization process, and if so, can a stepwise aggregation be achieved. Herein, we report first snapshots of the early transition-metal-supported oligomerization of this parent phosphinoborane. For the oligomerization, a defined {Cp2Ti} source was needed, and we chose [Cp2Ti(btmsa)] (btmsa = bis(trimethylsilyl)acetylene) for which a clean elimination of the acetylene is known. The reaction of the parent phosphinoborane PH2BH2NMe3 with [Cp2Ti(btmsa)] depends on the reaction conditions, such as stoichiometry and temperature (Scheme 1). The resulting dinuclear (2), trinuclear (3), and

A theoretical approach to the single-source precursor concept: quantum chemical modeling of gas-phase reactions

Abstract Results of extensive quantum-chemical modeling of the gas-phase reactions during CVD of group 13–15 materials are discussed in the light of single-source precursor concept. Two quantitative parameters (donor–acceptor bond dissociation enthalpy and elimination reaction enthalpy) are introduced as criteria for the classification of potential candidates for the single-source precursors. Hydrogen-containing molecules are predicted to have higher importance as precursors for the stoichiometry-controlled CVD processes. Importance of the ring and cluster single-source precursors in the CVD of doped metal nitrides is emphasized. In contrast, P, As-containing precursors with metal-halide bonds are predicted to be inefficient.

Donor-acceptor complexes of borazines.

Donor-acceptor complexes of borazine (BZ) and its substituted derivatives with Lewis acids (A = MCl(3), MBr(3); M = B, Al, Ga) and Lewis bases (D = NH(3), Py) have been theoretically studied at the B3LYP/TZVP level of theory. The calculations showed that complexes with Lewis bases only are unstable with respect to dissociation into their components, while complexes with Lewis acids only (such as aluminum and gallium trihalides) are stable. It was shown that formation of ternary D→BZ→A complexes may be achieved by subsequent introduction of the Lewis acid (acceptor A) and the Lewis base (donor D) to borazine. The nature of substituents in the borazine ring, their number, and position were shown to have only minor influence on the stability of ternary D→BZ→A complexes due to the compensation effect. Much weaker acceptor properties of borazine are explained in terms of large endothermic pyramidalization energy of the boron center in the borazine ring. In contrast to borazine, binary complexes of the isoelectronic benzene were predicted to be weakly bound even in the case of very strong Lewis acids; ternary DA complexes of benzene were predicted to be unbound. The donor-acceptor complex formation was predicted to significantly reduce both the endothermicity (by 70-95 kJ mol(-1)) and the activation energy (by 40-70 kJ mol(-1)) for the borazine hydrogenation. Thus, activation of the borazine ring by Lewis acids may be a facile way for the hydrogenation of borazines and polyborazines.