Ultrashort metal-metal distances and extreme bond orders

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Three aspects have been investigated during the first period of support.1. The reactivity of Cr-Cr quintuple bondsStable molecules that contain extremely high bond orders (bond orders > 4) were found only recently. Thus, it is now possible to investigate their reactivity and by doing so we are enabled to understand such bonds better. Our contributions dominate the state of the art in the field of Cr-Cr quintuple bond reactivity worldwide.2. Ultra-short metal-metal distancesRecently, after 30 years of silence new records in terms of short metal-metal distances were obtained with chromium complexes having a formal quintuple bond. Rational ligand design is the key. Work carried our by us determines the state of the art in that field. During the first period of support, we could isolate a compound with a metal-metal distance similar to that of the longest C-C bond (1.706 and 1.704 Å, respectively).3. Bond orders > 4 for molybdenum and tungstenMolybdenum and tungsten complexes are better suited to form high (effective) bond orders. Accordingly, we aimed for transferring the chromium chemistry towards molybdenum and eventually towards tungsten. The state of the art for molybdenum is meanwhile determined by the Tsai group. Tungsten compounds are unknown. We could find an access to such compounds in the first period of support.The following aims have been defined for the second period of researchA. Finalization of the quintuple bond reactivity studiesB. Investigation of the reactivity of the primary activation productsMany products obtained by reacting substrates (or elements) with Cr-Cr quintuple bonds are themselves rather reactive organometallic compounds. Their reactivity especially in catalytic reactions is proposed to be investigated.C. Tungsten complexes with quintuple or sixtuple bondsTungsten complexes having bond orders > 4 are subject of the second period of support. Theoretical work on the instable M2 molecules (M = Cr, Mo and W), species that could only be isolated in an inert matrix, gave effective bond orders of six for Mo2 and W2. Cr2 is characterized by a strong size mismatch of the relevant s- and d-orbitals. Thus, only weakly binding interactions are partially possible. They lead to a low effective bond order. We plan to find an access to W complexes having quintuple (and/or sixtuple) bonds.D. Investigations of the reactivity of tungsten compounds having unusual high bond orders