Secondary Interactions in Phosphane-Functionalized Group 4 Cycloheptatrienyl-Cyclopentadienyl Sandwich Complexes

Phosphane-functionalized cycloheptatrienyl-cyclopentadienyl Group 4 metal complexes of the type [(eta(7)-C7H7)M(eta(5)-C5H4PR2)] (M = Ti (9); M = Zr (10); M = Hf (11); R = Ph (a), R = iPr (b)) have been prepared by the reduction of [eta(5)-C5H4PR2)TiCl3] or [(eta(5)-C5H4PR2)(2)MCl2] (M = Zr, Hf) with magnesium in the presence of cycloheptatriene (C7H8). In the solid state, the Ti complex 9a and the complex 11b are monomeric, whereas 10a, 10b, and 11a form dimers, in which the sandwich units are linked by long Zr-P or Hf-P bonds. Density-functional theory (DFT) calculations indicate that the metal-phosphane interaction is weak, and accordingly, both the Ti complex 9b and the Zr complex 10b act as monodentate phosphane ligands upon reaction with [{(cod)RhCl}(2)] (cod =eta(4)-1,5-cyclooctadiene). The X-ray crystal structures of [(cod)Rh(9b)Cl] (12) and [(cod)Rh(10b)Cl] (13) reveal that only the latter exhibits a secondary intramolecular Cl-metal interaction. The complex [(10b)(2)Pd] (14) was obtained by reaction of [(eta(5)-C5H5)Pd(eta(3)-C3H5)] with two equivalents of 10b. The solid-state structure of 14 reveals a T-shaped Pd-0 center with a long Pd-Zr bond of 2.9709(3) angstrom, which can be interpreted as a weak noncovalent Pd-0 -> Zr+IV bond, as indicated by the calculated relaxed force constant of 5.68 N m(-1).