Coordination chemistry and catalysis of new ligands

Research project P 14089 Coordination Chemistry and Catalysis of New Ligands Peter BRÜGGELLER 11.10.1999 In the last few years several new ligands have been developed in our laboratory and the production of further ligands is planned. The new compounds are designed to fulfil the requirements of a catalytic application. In the case of Pd(II) the flexibility and stereochemical demands of cis,trans,cis-1,2,3,4-tetrakis(diphenyl- phosphino)cyclobutane (dppcb) are very interesting in view of the possible application as catalysts for the alternating copolymerization of ethene and carbon monoxide. The goal of this research could be to find an even better catalyst than used in the industry for the moment. With respect to Ru(II) complexes of dppcb a very interesting question has to be answered by future experiments. Is the photochemical behaviour of a recently obtained complex a consequence of superexchange? The interest in these compounds stems from chromophore- quencher assemblies, new dyes for use as sensitizers, and hydrodesulfurization. In the case of Rh(I) it will be a great challenge to find other examples of dppcb dimers showing mechanical coupling, to understand when and why this .. I effect occurs, and to use it in a possible catalytic application. A Pt(II) species containing cis-1,2- bis(diphenylphosphino)ethene (cis-dppen) and O2- has been produced and is the first example of a class of compounds. Interest in the area of Pt .hydroxo and oxo chemistry has been driven by the antitumor activity of cis- platin and surface-bound oxygen species. For Hg(II) it is planned to study the different modes of coordination of Angeli`s salt and the stabilization of other small groups of atoms. Furthermore, the Cu(I) coordination chemistry of dppcb and the derivation of dppcb will be investigated. Most of the investigations will be carried out using the scientific equipment at the Chemical Departments of the University of Innsbruck. The project is planned for three years. ATS 120.000,-- material costs are expected. The employment of two co-workers would be very desirable.

Tertiary phosphines are excellent ligating agents to metal ions and transition metals in a variety of oxidation states and , thus are important constituents of compounds for catalysis, structure-bonding relationships, and spectroscopic studies. The compability of phosphorus ligands with other organic finctional groups has extended their importance and synthetic scope. Especially the growth in polyphosphine chemistry results from their use in catalysis, organic synthesis, and solid-state materials. The bis(bidentate) phosphine cis, trans, cis-1,2,3,4- tetrakis(diphenylphosphino)cyclobutane (dppcb) has been prepared only recently in our laboratory. It is designed as a spacer having two bidentate sets of coordination environments to incorporate different molecular components and has been successfully applied to the alternating copolymerization of carbon monoxide and ethene representing an important example of catalytic C-C bond formation. Though nobody knows which catalytic system is actually used in industry and the cost of the new ligand could be prohibitive when compared with the "so-called" commercial ligand, the response of the industry to these new catalysts containing dppcb has been exemplary: the world company Shell financed a protecting patent. The search for further novel di- and tetraphosphine-modified palladium catalysts has been successful. The alkoxycarbonylation of olefins belongs to a family of industrially relevant carbonylation reactions that are efficiently catalysed by homogeneous palladium complexes. In the case of styrene, carbonylation in methanol in the presence of palladium initiators may yield as many as six different types of products spanning from alternating polyketones, esters, ketones, to aldehydes. This investigation has allowed a partial optimization of the process so as to abtain the largely predominant formation of either methyl cinnamate (highest selectivity 99 %) or dimethyl phenylsuccinate (highest selectivity 88 %). Methyl cinnamate is an important building block for the production of pharmaceuticals, fragrances, light-sensitive and current-conducting materials, and agrochemicals. From an environmental point of view, mercury(II) is very important. Therefore, a careful study of the coordination behavior of dppcb with mercury(II) is of great interest. Investigation of the coordination chemistry of HgII is complicated by the tolerance for many different coordination numbers and coordination geometries, where coordination to a metal ion with favourable NMR properties provides an additional means for characterizing the dynamics of complexes in solution and correlating solution state spectra with solid state structures. However, polydentate donor ligands like dppcb restrict the number of accessible structures. The use of chelating agents for the coordination of HgII is important, since the initial step of the Hg-C bond cleavage process is the induction of higher coordination numbers by nature`s mercury detoxification catalysts. Furthermore, evidence for new classes of metal-binding motifs in enzymes, transcription factors, and regulatory proteins underscores the need for structural insights about local HgII coordinations. A completely unexpected photochemical reactivity of ruthenium(II) polypyridine complexes induced by dppcb has been observed. Ruthenium(II) polypyridine complexes represent interesting possibilities as components in photochemical and electrochemical devices and potential chemotherapeutics. In this connection dinuclear RuII complexes bridged by bis(bidentate) ligands have received much attention. In the case of polyphosphine ligands the large stereochemical control of the ligand and the added electron density on the metal atom, contribute to electron rich coordination sites. A replacement of the four MeCN ligands by different groups could lead to asymmetrical ligand environments, which have been found to be important for photoinduced electron and energy transfer.