Chiral Olefins as Steering Ligands:  Syntheses of C₁-Symmetric Dibenzo[a,e]cyclooctenes (Rdbcot)

A simple three-step synthesis of chiral dibenzo[ a, e ]cyclooctenes (dbcot) starting from commercially available dibenzosuberenone was developed. These compounds give highly stable and robust rhodium(I) and iridium(I) diene complexes of the type [M( R dbcot)(L 1 )(L 2 )] (M = Rh, Ir; L 1, L 2 = MeCN, Cl, diamine, chloride). The complex [Rh(( R )- Ph dbcot)(( R )-(+)-1,1‘-binaphthyl-2,2‘-diamine)] + OTf - could be obtained in enantiomerically pure form and catalyzes the enantioselective 1,2-addition of PhB(OH) 2 to α, β-unsaturated ketones with good activity and acceptable enantiomeric excess (62%). The iridium complex [Ir( Ph dbcot)(MeCN) 2 ] + OTf - catalyzes the hydrogenation of dimethylitaconate with good activity, while the rhodium complexes are almost inactive. Likewise, the complex [Ir( Ph dbcot)(H 2 NCH 2 CH 2 NH 2 )] + OTf - serves as a rather efficient catalyst precursor with an activity 4 orders of magnitude higher than for the analogous rhodium complex. These experiments further establish the use of dienes as steering ligands in catalysis.