Synthesis and structural characterization of PHP[(C(5)Me(4))(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(C(5)Me(4))(2)] is readily obtained by oxidation of the lithium complex Li(2)PhP(C(5)Me(4))(2)] with I(2), which couples the two cyclopentadienyl groups to form a five-membered heterocyclic ring. The steric and electronic properties of PhP(C(5)Me(4))(2)] have been evaluated by X-ray diffraction and IR spectroscopic studies on a variety of derivatives, including Ph(C(5)Me(4))(2)]PE (E = S, Se), Cp*MCl(4)P(C(5)Me(4))(2)]Ph] (M = Mo, Ta), IrP(C(5)Me(4))(2)]Ph](2)(CO)Cl, and CpFe(CO)PhP(C(5)Me(4))(2)]]Me. For comparison purposes, derivatives of the related phospholane ligand PhPMe(2)C(4)H(6)] have also been investigated, including PhMe(2)C(4)H(6)]PS, IrPhMe(2)C(4)H(6)]](2)(CO)Cl, IrPhMe(2)C(4)H(6)]](2)(CO)Me, IrPPhMe(2)C(4)H(6)]](COD)(Cl), and PdPMe(2)C(4)H(6)]Ph]eta(2)-C(6)H(4)C(H)(Me)NMe(2)]Cl. The steric and electronic properties of PhP(C(5)Me(4))(2)] are determined to be intermediate between those of PPh(2)Me and PPh(3). Thus, the crystallographic cone angles increase in the sequence PPh(2)Me (134.5 degrees) < PhP(C(5)Me(4))(2)] (140.2 degrees) < PPh(3) (148.2 degrees), while the electron donating abilities decrease in the sequence PPh(2)Me > PhP(C(5)Me(4))(2)] > PPh(3). Finally, PhP(C(5)Me(4))(2)] has a smaller cone angle and is less electron donating than the structurally similar phosphine, PhPMe(2)C(4)H(6)].