Selective borane reduction of phosphinoferrocene carbaldehydes to phosphinoalcohol-borane adducts. The coordination behaviour of 1-(diphenylphosphino)-1 '-(methoxymethyl)ferrocene, a new ferrocene O,P-hybrid donor prepared from such an adduct
Abstract
The reduction of ferrocene phosphino-aldehydes, R2PfcCHO (R = Ph, 2; Cy, 3; fc = ferrocene-1,1'-diyl, Cy = cyclohexyl) and (S-p)-[Fe(eta(5)-C5H3-1-CHO-2-PPh2)(eta(5)-C5H5)] ((Sp)-4), with BH3*THF or BH3*SMe2 in THF at 0 degrees C selectively afforded the corresponding phosphinoalcohol-borane adducts, R2PfcCH2OH*BH3 (R = Ph, 5; Cy, 6) and (Sp)-[Fe(eta(5)-C5H3-1-CH2OH-2-PPh2)(eta(5)-C5H5)]*BH3 ((Sp)-7), in quantitative yields. In contrast, the reactions performed at elevated temperatures favoured the formation of methyl derivatives (e. g., Ph2PfcCH3*BH3 (8)) resulting from overreduction (deoxygenation).
The crystal structures of 3, 5, (Sp)-7, 8 and Cy2PfcBr (9) have been determined by single-crystal X-ray diffraction analysis. The crystal assemblies of adducts 5 and (Sp)-7 are built up by means of C-H...O contacts, O-H...HB dihydrogen bonds and other soft interactions but, surprisingly, not via the conventional O-H...O hydrogen bonds.
Adduct 5 was smoothly deprotected to give the corresponding free phosphine, Ph2PfcCH2OH (1), and was further used for the preparation of a hybrid phosphinoether ligand, Ph2PfcCH2OMe (11). The latter compound was studied as a donor for Group 8-10 metal ions and for Cu(I).