Light‐driven metallo‐organic catalysis: Intramolecular photoelectron transfer in the heterodinuclear complex 1 facilitates the photocatalytic production of hydrogen and the selective hydrogenation of tolane to give cis‐stilbene. All three well‐coordinated parts of the supramolecular system are essential: the (tbbpy)2Ru fragment as a photoactive unit, the redox‐active bridging ligand as an electron relay and storage site, and the palladium as a catalytically active center.

Two N-heterocyclic carbene ligands at once may be one too many, at least if you intend to have highly active ruthenium catalysts for olefin metathesis. Density functional calculations recommend the replacement of the second carbene ligand in the successful ROMP catalysts 1 by coordinatively more labile ligands as in 2 or 3. In both cases, the catalytic activity is greatly improved.

Hydroformylation regioselectivities of rhodium-phosphine ligand systems are calculated according to a perspicuous formula that connects the regioselectivity of one phosphine coordination mode to the relative energies of the corresponding transition states of olefin insertion. If only one coordination mode is preferredswhich may be fulfilled by bidentate chelating ligandssthe formula quantifies the experimentally observed regioselectivities. To determine the relative transition-state energies, a combined QM/MM method with frozen reaction centers was applied and is discussed in detail. Tendencies in regioselectivites of four systems with the bidentate chelating ligands DIPHOS 4, BISBI 5, NAPHOS 6, and the monodentate reference ligand triphenylphosphine (TPP) could be reproduced for the first time. As has been demonstrated previously, our method is also useful for the explanation of hydroformylation stereoselectivities.

In this theoretical study on rhodium-catalysed hydroformylation we examine an unmodified hydridorhodium(I) carbonyl system a together with three variants modified by the model phosphane ligands PF3 (system b), PH3 (system c) and PMe3 (system d), which show increasing basicity on the Tolman chi parameter scale. The olefinic substrate for all systems is ethene. Based on the dissociative hydroformylation mechanism, static and dynamic quantum-mechanical approaches are made for preequilibria and the whole catalytic cycle. Agreement with experimental results was achieved with regard to the predominance of phosphane monocoordination in systems b-d, different sensitivity of unmodified and modified systems towards hydrogen pressure and the early location of the rate-determining step. Neither the catalytic cycle as a whole nor olefin insertion as an important selectivity-determining step gives a clear picture of activity differences among a-d. However, the crucial first catalytic step, association of ethene to the active species [HRhL3] (L=CO, PR3), may play the key role in the experimentally observed higher activity of a and systems with less basic phosphane ligands modelled by b.