The structures and interconversion pathway between the [Cu2(μ-η2:η2-O2)]2+ and [Cu2(μ-O)2]2+ isomers of model systems with three ammonia ligands per copper center are investigated using both density functional theory with a B3LYP functional (B3LYP-DFT) and multiconfigurational perturbation theory (CASSCF/CASPT2). Both methods lead to thoroughly different results for the relative energy of both isomers. The CASPT2 results reveal an intrinsic stabilization of the [Cu2(μ-O)2]2+ isomer, thus indicating that the presence of a [Cu2(μ-η2:η2-O2)]2+ core in the respiratory proteins must be brought back to the presence of bulky capping ligands and/or to external effects caused by solvents and counterions. Both isomers are found to be diamagnetic. For the [Cu2(μ-η2:η2-O2)]2+ isomer an antiferromagnetic coupling constant, −2J, of 4209 cm-1 is calculated at the CASPT2 level. On the other hand, in the [Cu2(μ-O)2]2+ isomer, the lowest 3B u state is calculated at 9316 cm-1, but is found to correspond instead to an oxygen π* → σ* excitation.

Stabilization of the central atom in an oxidation state of zero through coordination of neutral ligands is a common bonding motif in transition-metal chemistry. However, the stabilization of main-group elements in an oxidation state of zero by neutral ligands is rare. Herein, we report that the transamination reaction of the DAMPY ligand system (DAMPY=2,6-[ArNH-CH2 ]2 (NC5 H3 ) (Ar=C6 H3 -2,6-iPr2 )) with Sn[N(SiMe3 )2 ]2 produces the DIMPYSn complex (DIMPY=(2,6-[ArNCH]2 (NC5 H3 )) with the Sn atom in a formal oxidation state of zero. This is the first example of a tin compound stabilized in a formal oxidation state of zero by only one donor molecule. Furthermore, three related low-valent Sn(II) complexes, including a [DIMPYSn(II) Cl](+) [SnCl3 ](-) ion pair, a bisstannylene DAMPY{Sn(II) [N(SiMe3 )2 ]2 }2 , and the enamine complex MeDIMPYSn(II) , were isolated. Experimental results and the conclusions drawn are also supported by theoretical studies at the density functional level of theory and (119) Sn Mössbauer spectroscopy.

The synthesis and characterization of a series of heavier group 14 element (Ge, Sn, and Pb) carbene homologues based on the electronically modified, 2,6-dimesityl substituted terphenyl ligands Ar # -3,5-i Pr 2 , Ar # -4-SiMe 3 , and Ar # -4-Cl (Ar # -3,5-i Pr 2 = C 6 H 2 -2,6-Mes 2 -3,5-i Pr 2 ; Ar # -4-Cl = C 6 H 2 -2,6-Mes 2 -4-Cl; Ar # -4-SiMe 3 = C 6 H 2 -2,6-Mes 2 -4-SiMe 3 ; Mes = C 6 H 2 -2,4,6-Me 3 ) are presented. The consequences of introducing electron withdrawing and -releasing substituents on the solid state structures of the newly synthesized germylenes, stannylenes, and plumbylenes as well as their Mossbauer, NMR and UV−vis spectroscopic properties are presented and discussed in the context of a second order Jahn−Teller type mixing of frontier orbitals with appropriate symmetry. Experimental findings were supported by DFT calculations. More electron withdrawing ligands lead to a bonding situation with higher contribution of p-orbitals from the central heavier group 14 element in σ-bonding toward the ligands and thus increased s-electron character of the lone pair. Furthermore, this results in an increase in the energy separation between the frontier orbitals. Experimentally, these changes are manifested in narrower bending angles at the heavy tetrel atoms and hypsochromic in their UV−vis spectra. In contrast, derivatives of more electron rich m-terphenyl ligands are characterized by a smaller HOMO− LUMO gap and wider interligand angles.

The Al(Fe)Cl3-catalyzed rearrangement of monocyclic permethylated oligosilanes was investigated for different isomers in the range of Me14Si7 to Me28Si14. The reactions of the smaller isomers (Me14Si7 to Me20Si10) resulted in the selective formation of single compounds. In contrast to this, the rearrangements of isomers Me22Si11, Me24Si12, Me26Si13, and Me28Si14 yielded mixtures of isomers. Several of the obtained compounds could be characterized unambiguously by single crystal structure analysis. On the basis of these data and careful analysis of 29Si NMR data we conclude that in all cases cyclopentasilanes were formed as the final products.

The reactions of 3d transition metal atoms with N 2 O, producing the metal oxide and N 2 , have been studied by means of density functional theory and the coupled cluster method CCSD(T). The importance of charge transfer in the reaction mechanism has been investigated. For Sc, Ti, and V, the transition state is very reagentlike, and almost no charge transfer occurs. On the other hand, charge transfer from the metal 4s orbital into the N 2 O LUMO becomes more important when moving to the right in the 3d series. The reactions with Sc, Ti, and V proceed almost without energy barriers, whereas for Mn, Fe barriers around 9 kcal/mol are calculated. For transition metal atoms with a 3d n 4s 2 ground-state configuration, a correlation is found between the activation barriers and the binding energy of the formed metal oxide. The 3d n+1 4s 1 configuration gives rise to a higher reactivity than the 3d n 4s 2 configuration.

Reactions of 1,2-dipotassiotetrakis(trimethylsilyl)disilane with group 4 metallocene dichlorides lead to the formation of the respective metallocene 1,1,2,2-tetrakis(trimethylsilyl)disilene complexes. While the disilene titanocene complex could be structurally characterized, the zirconocene and hafnocene compounds, which are believed to possess some degree of bis-[bis(trimethylsilyl)silylene] character, can only be isolated in substance as the respective trimethylphosphane adducts. Analogous metallocene 1,1,2,2-tetrakis(trimethylsilyl)digermene complexes and a tetrakis(trimethylsilyl)silagermene complex were prepared. Instead of metallocene 1,1,2,2-tetrakis(trimethylsilyl)distannene complexes, four-membered rings composed of a metallocene and three bis(trimethylsilyl)stannylene units were obtained.

Reaction of the magnesium transmetalation product of a 1,2-dipotassiodisilane with hafnocene dichloride gives a disilene hafnocene complex. X-ray crystallography of the respective trimethylphosphane adduct provides structural proof for this assignment.

The conformations of dodecamethylcyclohexasilane Si6Me12 and undecamethylcyclohexasilane Si6Me11H have been investigated by ab initio calculations employing the B3LYP density functional with a 6-31+G(d) basis set. Local minima as well as transition structures were calculated with imposed symmetry constraints. For Si6Me12, three unique minima, which correspond to the chair, twist and boat conformations were located with relative zero-point-vibration-corrected energies of 0.0, 7.8 and 11.4 kJ mol(-1). A half-chair conformation with four coplanar silicon atoms connects the chair and twisted minima via an energy barrier of 16.0 and 8.2 kJ mol(-1), respectively. A second transition structure with a barrier of 3.9/0.3 kJ mol(-1) connects the twist with the boat structure. Solution Raman spectra of Si6(CH3)12 and Si6(CD3)12 fully corroborate these results. Below -40 degrees C, the symmetric SiSi ring breathing vibration is a single line, which develops a shoulder (originating from the twist conformer) at longer wavelengths whose intensity increases with increasing temperature. From a Van't Hoff plot, the chair/twist enthalpy difference is 6.6+/-1.5 kJ mol(-1) for Si6(CH3)12 and 6.0+/-1.5 kJ mol(-1) for Si6(CD3)12, which is in reasonable agreement with the ab initio results. Due to the low barrier, the boat conformation cannot be observed, because either the lowest torsional vibration level lies above it or a rapid interconversion between the twist and boat conformations occurs, resulting in averaged Raman spectra. For Si6Me11H, six local minima were located. The chair with the hydrogen atom in the axial position (axial chair) is the global minimum, followed by the equatorial chair (+1.9 kJ mol(-1)) and the three twist conformers (+5.3, +8.0 and +8.1 kJ mol(-1)). The highest local minimum (+11.9 kJ mol(-1)) is a C(s) symmetric boat with the hydrogen atom in the equatorial position. Two possible pathways for the chair-to-chair interconversion with barriers of 13.9 and 14.5 kJ mol(-1) have been investigated. The solution Raman spectra in the SiSi ring breathing region clearly show that below -50 degrees C only the axial and equatorial chairs are present, with an experimental deltaH-value of 0.46 kJ mol(-1). With increasing temperature a shoulder develops which is attributed to the combined twist conformers. The experimental deltaH-value is 6.9 kJ mol(-1), in good agreement with the ab initio results. Due to the low interconversion barriers, the various twist conformers cannot be detected separately.