Synthesis and Ligand Properties of 1-Phosphaethenyl-2-phosphanylferrocenes

(S)-1-Phosphaethenyl-2-diarylphosphanylferrocenes with planar chirality (Fc(CHPMes*)PAr2: PAr2 = PPh2 (3a), P(1-naphthyl)Ph (3b)) are prepared in high yields from optically active 2-phosphanylferrocenecarboxaldehydes by the phospha-Peterson reactions with Mes*P(Li)SiMe3 in THF. The stereochemistry of 3b is determined by X-ray diffraction analysis. Compounds 3a and 3b readily react with [PtMe2(μ-SMe2)]2 in Et2O to afford dimethyl complexes with bidentate coordination of these ligands (PtMe2(L): L = 3a (4a), 3b (4b)). The X-ray structure of 4b reveals almost identical trans-influence of the phosphaethenyl and phosphanyl groups, showing comparable σ-donating abilities of those components. Treatment of 3a and 3b with [Pd(η3-allyl)(μ-Cl)]2 in CH2Cl2 in the presence of AgOTf forms the corresponding π-allyl complexes [Pd(η3-allyl)(L)]OTf (L = 3a (5a), 3b (5b)), respectively, which are mixtures of diastereomers with endo- and exo-oriented π-allyl ligands. Complex 5a catalyzes hydroamination of 1,3-cyclohexadiene with aniline in toluene in the presence of 5 Å molecular sieves at room temperature, giving N-cyclohexen-3-ylaniline in 84% yield.