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(CO)Cl, and CpFe(CO)[PhP[(C(5)Me(4))(2)]]Me. For comparison purposes, derivatives of the related phospholane ligand PhP[Me(2)C(4)H(6)] have also been investigated, including Ph[Me(2)C(4)H(6)]PS, IrPh[Me(2)C(4)H(6)](CO)Cl, IrPh[Me(2)C(4)H(6)](CO)Me, IrPPh[Me(2)C(4)H(6)](Cl), and Pd[P[Me(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, PhP[Me(2)C(4)H(6)].