Crystal structure of (piperidine-1-carbo-di-thio-ato-κ(2) S,S)[2-(pyridin-2-yl)phenyl-κ(2) C (1),N]palladium(II).

The title compound, [Pd(C11H8N)(C6H10NS2)], crystallizes with three similar and discrete mol-ecules in the asymmetric unit. The CNS2 donor set defines a distorted square-planar geometry around the Pd(II) atom, with very small deviations from planarity. The bidentate nature of the ligands gives fairly large deviations from the ideal 90° angles; the C-Pd-N angles are all around 81° and the S-Pd-S angles are around 75°. Mol-ecules pack via dispersion inter-actions.

Fast and reversible insertion of carbon dioxide into zirconocene-alkoxide bonds. A mechanistic study.

In two consecutive equilibria the compound (Cp*)2Zr(OMe)2 undergoes insertion of CO2 to form the mono- and bis-hemicarbonates. Both equilibria are exothermic but entropically disfavoured. Magnetisation transfer experiments gave kinetic data for the first equilibrium showing that the rate of insertion is overall second order with a rate constant of 3.20 ± 0.12 M(-1) s(-1), which is substantially higher than those reported for other early transition metal alkoxides, which are currently the best homogeneous catalysts for dimethyl carbonate formation from methanol and CO2. Activation parameters for the insertion reaction point to a highly ordered transition state and we interpret that as there being a substantial interaction between the CO2 and the metal during the C-O bond formation. This is supported by DFT calculations showing the lateral attack by CO2 to have the lowest energy transition state.

Allotwinning in a molecular crystal: (1R,3S)-dimethyl 2-oxocyclohexane-1,3-dicarboxylate.

Two polytypic modifications of (1R,3S)-dimethyl 2-oxocyclohexane-1,3-dicarboxylate intergrow to form allotwins. One phase shows monoclinic symmetry, Cc, while the other is orthorhombic Pmc21. The structures may be considered as two different modes of superstructure ordering of an underlying, disordered structure. Considered in the same metrically orthorhombic unit cell a = 37.8883, b = 4.7233, c = 11.6835 Å, the two can be conveniently distinguished by their non-standard centering, Cc being represented as Xc with the centering vectors (0 0 0); (½ 0 ½); (» ½ ¾); (¾ ½ »); and Pmc21 as Xmc21 with the centering vectors (0 0 0); (½ 0 0). The difference between the allotwin domains lies only in the relationship between next-nearest neighbors along the stacking direction 100 and hence the conformations and packing efficiencies are identical for both phases and all three domains. The stacking sequences for the two phases correspond to ABAB for the orthorhombic stacking and ABA'B'/AB'A'B for the two (equivalent) monoclinic stackings. The monoclinic phase dominates comprising ca 80% of the total volume. Within the monoclinic phase, the ratio between the two possible orientations is highly unbalanced (6:1) indicating relatively large domains. The allotwinning detected in this sample may appear exotic in molecular compounds, but we suggest that the rarity of such examples in the literature is a reflection of the paucity of software that can identify and handle such cases. It is easy to overlook the possibility that a complex diffraction pattern originates from allotwinning and assume that normal mono-component twinning is the cause. The underlying mechanism in this case is the formation of two-dimensional layers of molecules that allow for two equivalent, but in terms of absolute geometry, different, ways of stacking.

Towards longer-lived metal-to-ligand charge transfer states of iron(II) complexes: an N-heterocyclic carbene approach.

A 9 ps (3)MLCT lifetime was achieved by a Fe(II) complex based on C(NHC)^N(py)^C(NHC) pincer ligands. This is the longest known so far for any kind of complexes of this abundant metal, and increased by almost two orders of magnitude compared to the reference Fe(II) bis-terpyridine complex.

Catalysis via homolytic substitutions with C-O and Ti-O bonds: oxidative additions and reductive eliminations in single electron steps.

In a combined theoretical and experimental study, an efficient catalytic reaction featuring epoxide opening and tetrahydrofuran formation through homolytic substitution reactions at C-O and Ti-O bonds was devised. The performance of these two key steps of the catalytic cycle was studied and could be adjusted by modifying the electronic properties of the catalysts through introduction of electron-donating or -withdrawing substituents to the titanocene catalysts. By regarding both steps as single electron versions of oxidative addition and reductive elimination, a mechanism-based platform for the design of catalysts and reagents for electron transfer reactions evolved that opens broad perspectives for further investigations.