P/O ligand systems: Facile synthesis, structure, and catalytic tests of 2'-phosphanyl-1,1'-biphenyl-2-ols and 2'-phosphanyl-1,1'-binaphthyl-2-ols

A facile synthesis of 2'-phosphanyl-1,1'-biphenyl- and 2'-phosphanyl-1,1'-binaphthyl-2-ols and their silyl ethers has been developed, consisting of electron-transfer-catalyzed ring-opening of dibenzofuran and dinaphthofuran, respectively, subsequent reaction with chlorophosphanes, and work-up with acetic acid or ClSiMe3. Studies of the molecular and crystal structures reveal the presence of P ... H-O bridging bonds in the more basic tBuPhP derivative and a nearly perpendicular arrangement of the aryl planes in the biphenyl derivatives. The barrier to rotation of the aryl planes about the C-C axis was determined by NMR in the case of the P-asymmetric derivative 3d, using the appearance of diastereoisomers by atropisomerism and P-asymmetry. Comparative screening tests of the title compounds, phosphanylphenols and phosphanylnaphthols in homogeneous Rh-catalyzed reactions demonstrate catalytic activity in hydroformylation reactions and superior properties of the biphenyl- and binaphthgl-2-ol derivatives in relation to other P-O ligands.