We propose large-core correlation-consistent pseudopotential basis sets for the heavy p-block elements Ga-Kr and In-Xe. The basis sets are of cc-pVTZ and cc-pVQZ quality, and have been optimized for use with the large-core (valence-electrons only) Stuttgart-Dresden-Bonn relativistic pseudopotentials.Validation calculations on a variety of third-row and fourth-row diatomics suggest them to be comparable in quality to the all-electron cc-pVTZ and cc-pVQZ basis sets for lighter elements. Especially the SDB-cc-pVQZ basis set in conjunction with a core polarization potential (CPP) yields excellent agreement with experiment for compounds of the later heavy p-block elements.For accurate calculations on Ga (and, to a lesser extent, Ge) compounds, explicit treatment of 13 valence electrons appears to be desirable, while it seems inevitable for In compounds. For Ga and Ge, we propose correlation consistent basis sets extended for (3d) correlation. For accurate calculations on organometallic complexes of interest to homogenous catalysis, we recommend a combination of the standard cc-pVTZ basis set for first-and second-row elements, the presently derived SDB-cc-pVTZ basis set for heavier p-block elements, and for transition metals, the small-core [6s5p3d] Stuttgart-Dresden 1 basis set-RECP combination supplemented by (2f 1g) functions with exponents given in the Appendix to the present paper.

In this theoretical study on the Heck reaction we explore the feasibility of an alternative pathway that involves a PdII/PdIV redox system. Usually, the catalytic cycle is formulated based on a Pd0/PdII mechanism. We performed quantum chemical calculations using density functional theory on a model system that consisted of diphosphinoethane (DPE) as a bidentate ligand and the substrates ethylene and phenyl iodide to compare both mechanisms. Accordingly, the PdII/PdIV mechanism is most likely to occur in the equatorial plane of an octahedral PdIV complex. The energy profiles of both reaction pathways under consideration are largely parallel. A major difference is found for the oxidative addition of the C-I bond to the palladium centre. This is a rate-determining step of the PdII/PdIV mechanism, while it is facile for a Pd0 catalyst. The calculations show that intermediate ligand detachment and reattachment is necessary in the course of the oxidative addition to PdII. Therefore, we expect the PdII/PdIV mechanism to be only feasible if a weakly coordinating ligand is present.

A theoretical study of the oxidative addition of C-C vs C-H bonds to a rhodium(I) complex with PCP-type ligands has been carried out. Special attention has been paid to the effect of different bulky substituents at the phosphorus atoms of the chelate ligand. Therefore, B3LYP/lanl2dz+p//B3LYP/lanl2dz and ONIOM-(B3LYP/lanl2dz+p:B3LYP/lanl2dz)//ONIOM(B3LYP/lanl2dz:HF/lanl1mb) methods have been utilized. According to the calculations, C-H activation is always the kinetically favored process (∆∆E q 20 kJ‚mol -1 ), though the C-C activation product is more stable (∆∆E 20 kJ‚mol -1 ). C-H addition is a reversible process; the product of the C-H activation can interconvert to the C-C activation product via an intermediate structure. Bulky substituents are found to increase the barrier for C-H activation relative to that for C-C activation. With additional ligands (e.g., phosphines), hexacoordinate complexes are formed. This is more favorable for the C-C activation products. Our calculations show that the activation reaction proceeds via complexes with a pentacoordinated rhodium atom. Thus, in the presence of donor ligands, the activation reaction is inhibited.

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Core correlation and scalar relativistic contributions to the atomization energy of 120 first- and second-row molecules have been determined using coupled cluster and averaged coupled-pair functional methods and the MTsmall core correlation basis set. These results are used to parametrize an improved version of a previously proposed bond order scheme for estimating contributions to atomization energies. The resulting model, which requires negligible computational effort, reproduces the computed core correlation contributions with 88%–94% average accuracy (depending on the type of molecule), and the scalar relativistic contribution with 82%–89% accuracy. This permits high-accuracy thermochemical calculations at greatly reduced computational cost.