Requerimientos básicos

Coordinatively-unsaturated 16-electron osmium sulfonamide complexes can be prepared from their corresponding metal-arene dimer and diamine ligand in the presence of a base, in under an hour. Structural modifications are readily introduced, by substitution of various groups at the sulfonamide or chiral phenyl groups, or by arene chain extension. Though coordinatively-unsaturated, complexes 2-10 were found to be highly stable in both air and in both PBS and DMSO solutions. Crystallographic data were obtained for p-cymene (2) and biphenyl (7) complexes, and were found to be similar to the Ru catalyst to which they are related (Table 3.7).

Upon treatment of complex 1 with formic acid as a hydride source, an osmium-hydride intermediate was observed by 1_{H-NMR, evidence for the postulated transfer}

hydrogenation mechanism. All osmium catalysts exhibited higher turnover frequencies for the reduction of acetophenone than the ruthenium sulphonamide 11, under identical conditions. The osmium catalysts demonstrated good tolerance of electron donating and withdrawing substituents on acetophenone-derived ketone substrates, maintaining high conversion and enantioselectivity. The structure of a novel dichlorido osmium complex (1) was elucidated, which was shown to be equally as useful as a catalyst as the 16-electron active catalyst. DFT calculations highlight the similarity between the Os series, and that substitution on complexes 3-6 and 9-10

appears to only cause localised effects.

The complexes would benefit from future investigation into scope of the catalytic reactions; including more challenging substrates (such as imines and aliphatic ketones) or exploration of tolerance towards forcing reaction conditions (i.e. increased temperature, lower catalyst loading). Overall, Os sulfonamide complexes offer a

3.6

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Chapter 4

Contrasting biological activities of