Synthesis and Structural Characterization of PhP[(C5Me4)2], a Monodentate Chiral Phosphine Derived from Intramolecular C−C Coupling of Tetramethylcyclopentadienyl Groups:  An Evaluation of Steric and Electronic Properties

The chiral monodentate phosphine PhP[(C5Me4)2] is readily obtained by oxidation of the lithium complex Li2[PhP(C5Me4)2] with I2, which couples the two cyclopentadienyl groups to form a five-membered heterocyclic ring. The steric and electronic properties of PhP[(C5Me4)2] have been evaluated by X-ray diffraction and IR spectroscopic studies on a variety of derivatives, including Ph[(C5Me4)2]PE (E = S, Se), Cp*MCl4{P[(C5Me4)2]Ph} (M = Mo, Ta), Ir{P[(C5Me4)2]Ph}2(CO)Cl, and CpFe(CO){PhP[(C5Me4)2]}Me. For comparison purposes, derivatives of the related phospholane ligand PhP[Me2C4H6] have also been investigated, including Ph[Me2C4H6]PS, Ir{Ph[Me2C4H6]}2(CO)Cl, Ir{Ph[Me2C4H6]}2(CO)Me, Ir{PPh[Me2C4H6]}(COD)(Cl), and Pd{P[Me2C4H6]Ph}[η2-C6H4C(H)(Me)NMe2]Cl. The steric and electronic properties of PhP[(C5Me4)2] are determined to be intermediate between those of PPh2Me and PPh3. Thus, the crystallographic cone angles increase in the sequence PPh2Me (134.5°) < PhP[(C5Me4)2] (140.2°) < PPh3 (148.2°), while the electron donating abilities decrease in the sequence PPh2Me > PhP[(C5Me4)2] > PPh3. Finally, PhP[(C5Me4)2] has a smaller cone angle and is less electron donating than the structurally similar phosphine, PhP[Me2C4H6].