Description: This article discusses 3-center-4-electron bonding. Abstract: Na/Hg reduction of (silox)2Cl2Mo=NtBu (3) afforded C2h [(silox)2Mo=NtBu]2(μ-Hg) (12-Hg), which consists of two distorted trigonal monoprisms with Hg at the each apex (d(MoHg) = 2.6810(5)Å). Calculations reveal 3c4e bonding in the linear MoHgMo linkage that renders 12-Hg susceptible to nucleophilic cleavage. Exposure to PMe3 and pyridine rapidly (<5 min) affords (silox)2(tBuN)MoLn (L = PMe3, n = 1 (1-PMe3); py, n = 2 (1-py2)), while poorer nucleophiles (L = C2H4, 2-butyne) yield adducts (e.g., 1-C2H4 and 1-C2Me2) after prolonged heating. The HOMO and LUMO of 12-Hg are "stretched" π and π* orbitals from which four states arise: 1Ag (GS), 3Bu, 1Bu, and 1Ag. ∆E = E(1Bu) - E(3Bu) = 2K, where K is the exchange energy. Magnetic studies indicate E(3Bu) - E(1Ag) ≈ 550 cm-1 (calcd 1744 cm-1), and a UV-vis absorption at 10 000 cm-1 is assigned to 1Ag → 1Bu, permitting K to be evaluated as 4725 cm-1. With the π → π* transition in Schrock's [Mo(NAr)(CH2tBu)(OC6F5)]2 (4) assigned at 528 nm, this estimation places its π-bond energy as {E(π2 → π-1 → π*1 in 4) - E(1Ag → 1Bu in 12-Hg)} + E(1Ag → 3Bu in 12-Hg) = 27 kcal/mol.

Description: This article discusses Abraham model correlations for solute partitioning into o-xylene, m-xylene and p-xylene from both water and the gas phase. Abstract: Experimental data have been compiled from the publisher literature on the partition coefficients of solutes and vapors into o-xylene, m-xylene and p-xylene at 298 K. The logarithms of the water-to-xylene partition coefficients, log P, and gas-to-xylene partition coefficients, log K, were correlated with the Abraham solvation parameter model. The derived mathematical expressions described the observed log P and log K data for the three xylene isomers to within average deviations of 0.14 log units or less.

Description: This article discusses accurate enthalpies of formation of alkali and alkaline earth metal oxides and hydroxides. Abstract: Computing the enthalpies of formation for alkali metal and alkaline earth metal oxides (MₓO) and hydroxides [M(OH)n] using the Gaussian-n (Gn) and Weismann-n (Wn) ab initio model chemistries is difficult due to an improper treatment of core-valence electron correlation effects. Using a new model chemistry called the correlation consistent Composite Approach (ccCA), enthalpies of formation were determined for eight different alkali/alkaline earth metal oxides and hydroxides. Unlike the Gn and Wn model chemistries, which must be modified to properly account for core-valence electron correlation, the standard implementations of the ccCA provide acceptable results, and all enthalpies of formation obtained with the ccCA are within the accepted range of recommended values.

Description: This article discusses the activation of carbon-hydrogen bonds. Abstract: Recent reports of 1,2-addition of C-H bonds across Ru-X(X = amido, hydroxo) bonds of TpRu-(PMe₃)X fragments {Tp = hydridotris(pyrazolyl)borate} suggest opportunities for the development of new catalytic cycles for hydrocarbon functionalization. In order to enhance understanding of these transformations, computational examinations of the efficacy of model d6 transition metal complexes of the form [(Tab)M-(PH3)2X]q (Tab = tris-azo-borate; X = OH, NH2; q = -1 to +2; M = Tc(I), Re(I), Ru(II), Co(III), Ir(III), Ni(IV) Pt(IV) for the activation of benzene C-H bonds, as well as the potential for their incorporation into catalytic functionalization cycles, are presented. For the benzene C-H activation reaction steps, kite-shaped transition states were located and found to have relatively little metal-hydrogen interaction. The C-H activation process is best described as a metal-mediated proton transfer in which the metal center and ligand X function as an activating electrophile and intramolecular base, respectively. While the metal plays a primary role in controlling the kinetics and thermodynamics of the reaction coordinate for C-H activation/functionalization, the ligand X also influences the energetics. On the basis of three thermodynamic criteria characterizing salient energetic aspects of the proposed catalytic cycle and the detailed ...

Description: This article discusses the application of the correlation consistent composite approach (ccCA). Abstract: The correlation consistent composite approach (ccCA) has been applied to the G3/05 training set of 51 energetic properties for the atoms and molecules that contain the 4p elements, Ga-Kr. When atomic and molecular first-order spin orbit coupling corrections are added to open shell atoms and molecules, the ccCA has a mean absolute deviation from experiment (MAD) of 0.95 kcal mol-1, an improvement of 0.10 kcal mol-1 over G3 and G3X model chemistries. The performance of the ccCA on third-row-containing atoms and molecules is, therefore, commensurate in accuracy with previous studies on lighter main group elements H-Ar. While the typical methods used to compute theoretical molecular spin orbit corrections may go against the spirit of "black box" model chemistries, such corrections may be necessary for molecules containing heavy elements such as Ga-Kr. For example, when second-order spin orbit corrections are added to the atomic and molecular energies, the ccCA MAD is reduced to 0.88 kcal mol-1.