Bridge-splitting reactions and far-infrared spectra of diene derivatives of palladium(II) and platinum(II) complexes

Abstract

Bridge-splitting reactions of complexes of the type [M(diene·OCH₃)X]₂(M = Pd^II, Pt^II; diene = cyclo-octa-1,5-diene, dicyclopentadiene; X = Cl, Br) by neutral ligands (L) having nitrogen or phosphorus as donor atoms are reported. For the products [M(diene·OCH₃)LX] two structures are possble, i.e., with L cis to the olefinic double bond (A) or trans to it (B). On the basis of far-i.r. spectra, structure (A) has been attributed to [Pd(diene·OCH₃)(py)Cl] and [Pt(diene·OCH₃)LX](L = pyridine and p-toluidine). Structure (B) has been attributed to [Pt(diene·OCH₃)(PPh₃)X] and to the analogous palladium(II) complexes.

From [M(diene·OCH₃)(py)Cl] the pyridine is displaced by another neutral ligand, whereas the chloride ion is displaced only by an anionic one.

The far-i.r. spectra (500–60 cm.^–1) of the dimers [M(diene·OCH₃)X]₂ are reported and the metal–bridging halogen stretching frequencies are assigned on the basis of a C_i point-group symmetry. ν(M–Cl_bridging) falls in the range 298–216 cm.^–1, ν(M–Br_bridging) 201–148 cm.^–1, and ν(M–I_bridging) 165–122 cm.^–1.