Synthesis and characterization of the monomeric gallium monoamides tert-Bu2GaN(R)SiPh3 (R = tert-Bu, 1-adamantyl), Trip2MN(H)Dipp (M = Al, Ga; Trip = 2,4,6-iso-Pr3C6H2; Dipp = 2,6-iso-Pr2C6H3), and Trip2GaNPh2

Diarylpnictogenyldialkylalanes─Synthesis, Structures, Bonding Analysis, and CO2 Capture

Several new diphenylamino- and diphenylphosphanyldialkylalanes are reported, which were characterized in solution and in the solid state, assisted by in-depth bonding analysis within the DFT framework. In the case of bulky alkyl substituents on the aluminum atom, the species are stable in their monomeric form and were structurally characterized by single crystal X-ray diffraction, expanding the relatively small field of monomeric pnictogenylalanes. In the case of oligomeric diphenylpnictogenyldimethylalanes, their reactivity toward different σ-donor ligands was studied, and several examples of monomeric adducts could be structurally characterized, including the first cyclic(alkyl)(amino)carbene complexes. The reactivity of these CAAC complexes, their oligomeric precursors, and an unstabilized monomeric aminoalane toward CO₂ was probed, leading to different insertion products that could be characterized. Additionally, the mechanism was elucidated by DFT calculations.

Extremely bulky amide ligands in main group chemistry

The development of extremely sterically demanding, monodentate amide ligands facilitates the isolation of main group species with new and highly reactive coordination modes. An outstanding feature of these ligands is the ability to tune their steric demands. Reactivity investigations highlight the potential for small molecule activation chemistry and catalysis for these compounds.

Pi Bonding and Negative Hyperconjugation in Mono-, Di-, and Triaminoborane, -alane, -gallane, and -indane

A systematic quantum chemical investigation of mono-, di-, and triaminoborane, -alane, -gallane, and -indane is carried out to determine quantitatively the effects of pi bonding and negative hyperconjugation on structures, energetics, and rotational barriers in these systems. Pi bonding plays a significant role in the aminoborane compounds, but becomes rapidly less significant in the aminoalanes, -gallanes, and -indanes. For each main-group metal X investigated, X-N rotational barriers are found to be essentially equal depending only on the number of remaining in-plane amino groups. The contribution of negative hyperconjugation to reducing rotational barriers, as assessed from natural bond orbital (NBO) delocalization energies, is independent of the pyramidalization of the out-of-plane amino group, and is also dependent only on the number of rotated groups. Optimized tris[bis(trimethylsilyl)amino]-substituted structures of boron, aluminum, gallium, and indium are found to compare quite well with available experimental structural data, and exhibit X-N torsion angles that are independent of the central metal atom.

Gallium and indium hydrazides. Molecular and electronic structure of In[N(SiMe3)NMe2]3 and related compounds

Gallium and indium hydrazides, Ga[N(SiMe(3))NMe(2)](3) (1) and In[N(SiMe(3))NMe(2)](3) (2), were synthesized from the reactions of metal chlorides and Li[N(SiMe(3))NMe(2)]. Single crystal X-ray crystallographic analysis revealed that compound 2 was monomeric with trigonal planar geometries on the indium and the indium-bonded nitrogen atoms. The average In[bond]N distance of 2.078(3) A and the N[bond]In[bond]N[bond]N dihedral angles did not provide clear structural evidence of In[bond]N pi-bonding. The electronic absorption spectra of the indium hydrazido complex revealed transitions at significantly lower energies compared to those observed in the tris(amido) compounds, In[N(SiMe(3))(2)](3) (3) and In[N((t)Bu)(SiMe(3))](3) (4). The absorptions of the indium and gallium compounds were attributed to ligand-metal charge transfer transitions. Trends in the electronic transitions for compounds 2 and 3 calculated at the time-dependent density functional and configuration interaction including single excitations levels, both using a minimal basis set, were consistent with the experimental data, and Mulliken charge analyses support the assignment to ligand-to-metal charge transfer transitions. These calculations also demonstrated the presence of pi-bonding between the In and N p-orbitals, and an analogy is drawn to the frontier molecular orbitals of trimethylenemethane. The low-lying spectroscopic transition in 2, and thus its yellow color, results from mixing of the lone pair electrons on the beta-nitrogens of the hydrazido ligands with the HOMO of the InN(3) core.

"True" inorganic heterocycles: structures and stability of group 13-15 analogues of benzene and their dimers

Group 13-15 inorganic analogues of benzene, [HMYH](3) (M = B, Al, Ga; Y = N, P, As), mixed heterocycles of the type [BAlGaNPAs]H(6) and their dimers have been theoretically examined at the B3LYP/TZVP level of theory. Six different isomers have been structurally characterized for the mixed compounds [BAlGaNPAs]H(6). B-N bonding strongly (about approximately 90-100 kJ mol(-)(1)) stabilizes the mixed heterocycles, followed by the preference of the Al-N bonded structures over Ga-N bonded ( approximately 30-40 kJ mol(-1)), while B-P bonding is slightly (5-10 kJ mol(-1)) more favorable compared to B-As. Thus, the bonding pattern is predicted to be the most stable, followed by the core. Processes of [HMYH](3) formation from donor-acceptor complexes H(3)MYH(3) are predicted to be thermodynamically favorable for all MY combinations. Dimerization reactions of the coordinationally unsaturated [HMYH](3) heterocycles yielding hexamer clusters [HMYH](6) are found to be exothermic, with the exception of borazine, for which, as for benzene, dimerization is strongly endothermic due to the aromaticity of C(6)H(6) and [HBNH](3). Despite the high endothermicity of [HBNH](3) dimerization, the B-N bond formation is the driving force of the dimerization of mixed species [BAlGaNPAs]H(6). The dimerization enthalpies of [BAlGaNPAs]H(6) may be both exo- and endothermic, depending on the bonding pattern of the isomers. A complete set of mean MY bond energies in four- and six-membered cycles of [HMYH](6) was derived. The MY energies were found to be transferable quantities and may serve for a qualitative prediction of the relative stability of different isomers of mixed cluster compounds. [BAlGaNPAs](2)H(12) clusters are promising synthetic targets, they are expected to serve as single-source precursors for the stoichiometry-controlled CVD processes of the group 13-15 composites. A strategy of their synthesis and the most suitable starting systems have been also predicted.

From "parasitic" association reactions toward the stoichiometry controlled gas phase synthesis of nanoparticles: a theoretically driven challenge for experimentalists

In the present record a model for the gas-phase reactions during the chemical vapor deposition (CVD) processes of group 13-15 materials is presented, based on the results of extensive quantum-chemical modeling. Thermodynamic criteria have been introduced to evaluate the importance of a range of association reactions. For the organometallic and hydride derivatives, association processes are found to be favorable both thermodynamically and kinetically. Formation of high mass association products takes place under CVD conditions, including laser-assisted CVD. Structural and thermodynamic properties of the most important ring and cluster intermediates have been predicted. The stoichiometry-controlled synthesis of the 13-15 ternary alloys and nanoparticles using cluster compounds as single-source precursors is predicted to be viable. The association pathway described may be generalized to the CVD reactions of many binary materials (12-16, 13-16, 13-15, 14-15, 14-16).

Structure, Spectra, and Reaction Energies of the Aluminum-Nitrogen (HAl-NH)(2) and (H(2)Al-NH(2))(2) Rings and the (HAl-NH)(4) Cluster

Rings of four-coordinate aluminum and nitrogen are easily synthesized and well studied, as are clusters of four-coordinate Al and N. Only recently, however, have rings that are derivatives of the model compounds (HAl-NH)(n)() (n = 2, 3) with three-coordinate Al and N been synthesized. Ab initio investigations of the structure, bonding, vibrational spectra, and reaction energies for the three-coordinate ring (HAl-NH)(2), the four-coordinate ring (H(2)Al-NH(2))(2), and the four-coordinate cluster (HAl-NH)(4) are presented. Even in the absence of differences in steric factors, the four-membered ring has longer Al-N bonds than either the six-membered ring or the unassociated aluminum amide, H(2)Al-NH(2). This is due to both rehybridization and pi interactions. Theoretical reaction energies for formation of the (HAl-NH)(4) cluster from the (H(2)Al-NH(2))(2) ring are consistent with intermolecular loss of hydrogen, or the necessity of surface catalysis.

Comparison of pi-Bond Strengths in M-E (M = B, Al, Ga; E = O, N, S) Compounds. Ab Initio Calculation of Rotational Barriers

Results of ab initio calculations of the electronic structure of compounds of the type R(2)MER'(x) and R(2)MEMR'(2) with R = H, Me, M = Al, Ga, and E = O, N, S are reported at the Hartree-Fock level with split-valence, polarization basis sets for all atoms except hydrogen where a split-valence basis set is used. Full optimizations for the equilibrium geometry and partial optimization at constrained rotational transition states have been performed to evaluate the barriers to rotation as a measure of the pi interactions in these compounds. We conclude that, although important for determining the final conformational equilibrium geometries, pi interactions are weak in these compounds as the rotational barriers are smaller than that for ethylene by 1 or 2 orders of magnitude.