Hydrophosphination with cationic primary phosphine iron complexes: synthesis of P-chiral functionalized phosphines

The synthesis of P-chiral secondary phosphines, characterized by phosphorus and side chain chirality, has been realized via insertion of various organic multiple bond systems into the PH-bond of the primary phosphine complexes {C5R5(OC)2Fe[P(R′)H2]}BF4 (R=H, Me; R′=alkyl, aryl). In the case of acetylenedicarboxylic acid dimethylester a double hydrophosphination is observed, leading diastereospecifically to the dinuclear complexes {C5R5(OC)2Fe{P(H)(R′)[C(H)(CO2Me)]}}2(BF4)2 (R=H, Me; R′=t-Bu, 2-py), bearing four stereogenic centers. The use of p-benzoquinone gives access to secondary 2,5-bis(hydroxy)aryl phosphine ligands, suitable for further derivatizations. α-Hydroxyalkyl phosphine iron complexes can be obtained by hydrophosphination of aldehydes and ketones. Transformation into highly functionalized tertiary phosphine complexes is performed by a further hydrophosphination step using the alkenes H2CCHX (X=CN, 2-py), diazoacetic ethylester, p-benzoquinone or ethylisocyanate, respectively, in special cases formation of functionalized azaphospholane ligands is observed. Release of the phosphines from the metal is achieved by photoinduced ligand exchange. In addition, primary phosphine iron complexes {C5H5(diphos)Fe[P(R)H2]}BF4 (diphos=DIOP, CHIRAPHOS) bearing chiral bis(phosphine) ligands have been used to provide the stereocontrol of the hydrophosphination process.