Andreas Sundermann

Isoelectronic Arduengo-type carbene analogues with the Group IIIa elements boron, aluminum, gallium, and indium

While Arduengo-type carbenes are now well established for the Group IVa elements carbon, silicon and germanium, they are experimentally unknown for the isoelectronic anions with the Group IIIa elements boron, aluminum, gallium, and indium. In the present quantum chemical investigations, the bonding features of this class of compounds are explored. As a result, they are predicted to be stable species with sizeable singlet-triplet energy separations and electron affinities. Hence, they may be considered as valid targets for experimental investigations. An analysis of the electron density distribution in the case of boron and aluminum reveals a strongly polar B-N bond for the former, and a half Al-N bond with positive charge at the aluminum, emphasizing the donor-acceptor formulation for the latter.

Do Divalent [{HC(CR′NR′′)2}E] Compounds Contain E(I) or E(III) (E = B, Al, Ga, In)? On the Correspondence of Formal Oxidation Numbers, Lewis Structures, and Reactivity

Very recently, carbene-analogous aluminum and gallium compounds have been obtained in beautiful synthetic work giving rise to interesting theoretical questions in the framework of qualitative MO theory. We analyze the concept of oxidation numbers and the stabilities of these [{HC(CR′NR′′)2}E] compounds, 1(E), with E being boron, aluminum, gallium, and indium. Population analyses and the electron localization function are used as analytical tools for the elucidation of the electronic density distribution. Singlet-triplet splitting energies, and model reactions probing donor and acceptor properties of the atom E, yield criteria for the reactivity of the cyclic molecules. It is demonstrated that a unique class of Lewis structures can be selected from the large number of chemically reasonable Lewis structures in order to achieve a sufficiently good mapping of the quantum chemical results on simple chemical concepts. The analysis yields that 1(E), where E = In, is expected to have similar properties as the experimentally known compounds 1(Al) and 1(Ga), while the boron homologue is expected to be highly reactive, such that its synthesis appears to be difficult. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

A study of some unusual hydrides: BeH2, BeH+6 and SH6

Standard ab initio methods are used to characterize some types of hydride, BeH2, BeH+2 and SH6, which have not been studied extensively either experimentally or theoretically. BeH+2 is an example where the equilibrium structure of an AB2 system exhibits symmetry breaking, i.e., the two AB bonds are different lengths. The SH6 molecule is not yet known experimentally. Though thermodynamically unstable, it is predicted to be kinetically stable, since the barrier to dissociation is found to be more than 200 kJ mol-1. If it could be synthesized, it could become a potentially valuable hydrogen carrier system.

On the Bonding Properties of Diphosphanylmethanide Complexes with the Group‐14 Elements Silicon, Germanium, Tin, and Lead in Their Divalent Oxidation States

The mono- and bidentate chelation of the main-group elements silicon, germanium, tin, and lead through the phosphorus atoms of the diphosphanylmethanide ligand has been studied by means of quantum chemical methods. In accord with experimental investigations, the species are found to adopt a psi-tbp conformation of high flexibility. The various distortional modes causing the axial and equatorial positions to become equivalent have also been investigated. In addition, the bonding situations in the electronically related bis(diamino)- and the higher element homologue bis(diarsanyl)methanide ligand systems have been studied. The bonding situation in the hitherto experimentally unknown bis(diamino)methanide Ligands is predicted to be similar to that in bis(amidinate) complexes. An analysis of the electron distributions (natural bond orbital population analysis) in these compounds reveals that the central main-group element is positively charged and weakly chelated by the surrounding ligands.

NH-Phosphanylamido- and PH-Phosphoraneiminato Transition-Metal Complexes: Syntheses, Structures and Computational Studies

Reactions of aminobis(diorganylamino)phosphanes (R2N)2PNH2 (R = iPr (a), Cy (b)) with Cp2MCl2 (M = Ti, Zr, Hf), CpTiCl3, and TiCl4 lead to the formation of the transition-metal complexes (R2N)2PN(H)MCp2Cl (M = Ti (1b), Zr (2a,b), Hf (3a,b)) (R2N)2P(H)NTiCpCl2 (8a,b), and (R2N)2P(H)NTiCl3 (10a,b), respectively. The influence of electronic effects of the metal fragment on the resulting equilibrium between the (NH)-phosphanylamido and the tautomeric (PH)-iminophosphorane form is presented in detail. Computational studies unambiguously confirm the experimental results. The molecular structures of 2a, 3a, and 8b have been determined by single-crystal X-ray diffraction.