Efficient production of high value added materials via selective hydroformylation of difficult substrates like internal alkenes and butadiene.

Aldehydes are important intermediates for the preparation of a large variety of fine- and bulk-chemicals. Applications of these compounds are found in the pharmaceutical industry, aroma and flavour industry, and in the production of agrochemicals and detergents. Many of these products are currently prepared via stoichiometric reactions which often results in large amounts of chemical waste. There is an increasing demand for new production methods based on mild and selective reactions with a very high atom efficiency , thus reducing the chemical waste problem. The rhodium catalysed hydroformylation of alkenes is an example of such a mild and clean process for the production of high-quality aldehydes, using only CO and H2 as reagents and therefore producing no waste products at all.In this project we will develop a new generally applicable catalyst system capable of converting both internal alkenes and conjugated dienes into high value-added aldehydes and / or esters. Atom economic and clean hydroformylation technology of butadiene to the intermediate 1,6-hexanedial would create a major contribution to the sustainable production of polyamides. Many industries and academic researchers, however, have studied the rhodium-catalyzed hydroformylation of butadiene, but generally the reported selectivity for the desired product 1,6-hexanedial is very low. This is caused by the formation of deleterious Rh allyl and enolate complexes, which can be suppressed by simultaneous activation of both alkene functions using properly designed bimetallic catalysts.Therefore, we will develop well-defined tetraphosphine ligand systems for the formation of bimetallic complexes capable of activating otherwise unreactive substrates by mutual interactions with functional groups by both metals. Starting point will be a successful class of bidentate ligands, already developed by the PI, which will be modified in such a way that they can be bridged straightforwardly by condensation with diacids. The resulting tetraphosphines will provide novel bimetallic complexes that will be applied in the hydroformylation of conjugated dienes. In a later stage the novel ligands systems will be explored in different reactions like palladium catalyzed alkoxycarbonylation of dienes. The exact ligand structures can be optimized by subtle changes in steric, electronic and bite-angle properties. In another approach we will aim at coupling of two different ligand backbones which opens the possibility of the formation of heterobimetallic complexes. Differences in the structure of the ligand backbone will have impact on the complexation constants of different transition metals. It is anticipated that this can be employed to influence the preferential coordination of one transition metal over another. It will be investigated if this will lead to the selective formation of heterobimetallic complexes based on rhodium and palladium without interference of homometallic binuclear compounds. We will explore the use of these rhodium palladium heterobimetallic complexes as catalyst for one-pot hydroformylation / methoxycarbonylation of dienes. The formation of these alpha,omega-aldehyde esters via a two-step process has been investigated intensively by DSM/DuPont.The design of the new chiral catalysts will be supported by fundamental spectroscopic (including kinetic) studies of the catalytic species present under actual reaction conditions. HP-NMR will be used to study the structure of the bimetallic complexes under static conditions. The effect of the metal-metal distance on the interaction with bifunctional substrates will be investigated. HP-IR will be used to study these complexes under actual catalytic conditions.