Hydrogenation of molecular cyclic diborane4 compounds featuring B-B bonds and olefinic or aromatic bridges: a quantum chemical study.

Hydrogenation reactions starting with di- or oligonuclear boron compounds featuring direct B-B bonds with the B atoms in the formal oxidation state +II are analyzed with the aid of ab initio quantum chemical (RI-MP2) calculations. The products of these reactions are B(III) hydrides which might be useful starting reagents for stoichiometric hydrogenation reactions and possibly in special cases also for hydrogen storage. Several different isomers of these B(III) hydrides featuring either terminal or bridging H atoms were considered. The results are compared to hydrogenation reactions of related molecules.

Electron density controlled carbamate ligand binding mode: towards a better understanding of metalloenzyme activity.

The first structurally characterized mononuclear biscarbamate complex of Zn with eta1-coordinated carbamate ligands can be prepared by reaction between [EtZn(O2CN(iBu)2)]4 and a guanidine base. Usage of a weaker base leads to eta2-coordinated complexes.

Repeated dihydrogen elimination from amidine adducts of group 13 element hydrides: an evaluation of the reaction pathways.

Dinuclear eta2,micro2-bonded amidinate complexes to group 13 element hydrides are of potential interest for applications in the field of hydrogen storage. In this work repeated dihydrogen elimination starting with amidine-stabilized boron, aluminum, and gallium hydrides is discussed on the basis of quantum chemical calculations which give useful information about the thermodynamic properties of these reactions and the possible reaction pathways in dependence of the chosen amidine derivative. It will be shown that, in agreement to recent experimental work, the thermodynamic properties are greatly influenced by the nature of the substituents bonded to the amidine. The amidine stabilized hydrides first eliminate dihydrogen in an intramolecular process leading to mononuclear amidinate complexes. These complexes could dimerize, if the amidine carries not too bulky organic groups, to give dinuclear complexes featuring two eta2,micro2-coordinated amidinate ligands. Further dihydrogen elimination leads to the generation of a dinuclear species with two group 13 elements (E) in the formal oxidation state +II and direct E-E bonding. Finally, elimination of another H2 for E = B possibly gives amidinate complexes featuring a double bond between two boron atoms in the formal oxidation state +I.

Low-lying electronic states of the Ti2 dimer: electronic absorption spectroscopy in rare gas matrices in concert with quantum chemical calculations.

Absorption spectra were measured for Ti2 in Ne and Ar matrices. The spectra give evidence for several electronic transitions in the region between 4000 and 10 000 cm(-1) and provide important information about some excited electronic states of Ti2 in proximity to the ground state. The vibrational fine structure measured for these transitions allowed to calculate the force constants and the anharmonicity of the potential energy curves of the excited states, and to estimate changes in the internuclear Ti-Ti distances relative to the electronic ground state. The quantum chemical studies confirm the previously suggested (3)Delta(g) state as the ground state of Ti2. The equilibrium bond distance is calculated to be 195.4 pm. The calculated harmonic frequency of 432 cm(-1) is in good agreement with the experimental value of 407.0 cm(-1). With the aid of the calculations it was possible to assign the experimentally observed transitions in the region between 4000 and 10 000 cm(-1) to the 1 (3)Pi(u)<--(3)Delta(g), 1 (3)Phi(u)<--(3)Delta(g), 2 (3)Pi(u)<--(3)Delta(g), 2 (3)Phi(u)<--(3)Delta(g), and (3)Delta(u)<--(3)Delta(g) excitations (in the order of increasing energy). The calculated relative energies and harmonic frequencies are in pleasing agreement with the experimentally obtained values, with deviations of less than 5% and 2%, respectively. The bond distances estimated on the basis of the experimental spectra tally satisfactorily with the predictions of our calculations.

Some chemical properties of monochlorogallane: decomposition to gallium(I) trichlorogallate(III), Ga(+)[GaCl3H](-), and other reactions.

Thermal decomposition of monochlorogallane, [H2GaCl]n, at ambient temperatures releases H2 and results in the formation of gallium(I) species, including the new compound Ga[GaHCl3], which has been characterized crystallographically at 100 K (monoclinic P2(1)/n, a = 5.730(1), b = 6.787(1), c = 14.508(1) A, beta = 97.902(5) degrees ) and by its Raman spectrum. The gallane suffers symmetrical cleavage of the Ga(mu-Cl)2Ga bridge in its reaction with NMe3 but unsymmetrical cleavage, giving [H2Ga(NH3)2](+)Cl(-), in its reaction with NH3. Ethene inserts into the Ga-H bonds to form first [Et(H)GaCl]2 and then [Et2GaCl]2.

Reactions of aluminum, gallium, and indium (M) atoms with phosphine: generation and characterization of the species M.PH3, HMPH2, and H2MPH.

Upon deposition of Al, Ga, or In atoms (M) together with phosphine in a solid argon matrix, metal atom complexes M.PH3 are formed. Photolysis of the matrices at lambda = 436 nm results in the tautomerization of the adduct species to the insertion products HMPH2 and H2MPH. In addition, PH is formed from the reactions with Ga and In, with HMPH2 being its most likely precursor. Further photolysis into the absorption maximum of HMPH2 near 550 nm results in decomposition of HMPH2 with partial re-formation of the adduct M.PH3 and further buildup of PH. H2MPH is photostable under these conditions but suffers decomposition under the action of UV light (200 < or = lambda < or = 400 nm). All the molecules have been identified by their IR spectra, the assignments being attested by the effects of deuteration and also by comparison either with the vibrational properties anticipated by density functional theory (DFT) calculations or with those of known, related molecules. The resulting analysis is elaborated for the light it sheds on the structures and properties of the new molecules and on the mechanisms of the reactions affording, or disposing of, them.