Rendering classical hydrophilic enantiopure Werner salts [M(en)(3)](n+) nX(-) lipophilic (M/n = Cr/3, Co/3, Rh/3, Ir/3, Pt/4); new chiral hydrogen bond donor catalysts and enantioselectivities as a function of metal and charge

摘要

Known hydrophilic halide salts of the title compounds are converted to new lipophilic BArf- (B(3,5=C6H3(CF3)(2))(4)(-)) salts. These are isolated as hydrates (Lambda- or Delta-[M(en)(3)](n+) nBAr(f)(-)center dot zH(2)O; z = 17-9) and characterized by NMR (acetone-d(6)) and microanalyses. Thermal stabilities are probed by capillary thermolyses and TGA and DSC measurements (onset of dehydration 71-151 degrees C). In the presence of tertiary amines, they are effective catalysts for enantioselective Michael type carbon-carbon or carbon-nitrogen bond forming additions of 1,3-dicarbonyl compounds (acceptors: trans-beta-nitrostyrene, di-tert-butylazodicarboxylate, 2-cyclopenten-1-one; average ee = 33%, 52%, 17%). Effects of the metal and charge upon enantioselectivities are analyzed. A number of properties appear to correlate to the NH Bronsted acidity order ([Pt(en)(3)](4+) > [Cr(en)(3)](3+) > [Co(en)(3)](3+) > [Rh(en)(3)](3+) > [Ir(en)(3)](3+)).