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†
The reduction of ferrocene phosphino-aldehydes, R2PfcCHO (R = Ph, 2; Cy, 3; fc = ferrocene-1,1′-diyl, Cy = cyclohexyl) and (Sp)-[Fe(η5-C5H3-1-CHO-2-PPh2)(η5-C5H5)] ((Sp)-4), with BH3·THF or BH3·SMe2 in THF at 0 °C selectively afforded the corresponding phosphinoalcohol–borane adducts, R2PfcCH2OH·BH3 (R = Ph, 5; Cy, 6) and (Sp)-[Fe(η5-C5H3-1-CH2OH-2-PPh2)(η5-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), whereupon the following complexes were isolated and structurally characterised: [(η6-p-cymene)RuCl2(11-κP)] (12*), [(η6-p-cymene)RuCl(11-κP)(MeCN)][SbF6] (13*), [RhCl(cod)(11-κP)] (cod = η2:η2-cycloocta-1,5-diene; 14), trans-[PdCl2(11-κP)2] (trans-15*), [PdCl(μ-Cl)(11-κP)]2 (16*), cis- and trans-[PtCl2(11-κP)2] (cis-17 and trans-17*), and [Cu(CF3SO3-κO)(11-κP)(H2O)] (18) (the asterisk indicates that the crystal structure was determined). In all these compounds, ligand 11 behaves as a P-monodentate donor while its ether group remains uncoordinated. This probably reflects structural flexibility of 11 resulting from the presence of the methylene linker and also distinguishes 11 from its known, non-spaced analogue Ph2PfcOMe.