Reaction of [Pt(1,5-C₈H₁₂)Cl₂] with Li₂(C₈H₈) in diethyl ether in the presence of excess of 1,5-C₈H₁₂ gives the white crystalline complex [Pt(1,5-C₈H₁₂)₂] in good yield. A similar reaction of [Pd(1,5-C₈H₁₂)Cl₂] in the presence of propene affords [Pd(1.5-C₈H₁₂)₂]. stable below ambient temperatures. The reaction of [M(1,5-C₈H₁₂)Cl₂](M = Pd or Pt) with Li₂(C₈H₈) and excess of bicyclo[2.2.1]heptene gives, respectively, tris(bicyclo[2.2.1]heptene)- palladium and -platinum. These complexes are also obtained by displacement of cyclo-octa-1,5-diene from [M(1,5-C₈H₁₂)₂](M = Pd or Pt) by bicyclo[2.2.1]heptene. Related displacement reactions with trans-cyclo-octene and ethylene afford, respectively, tris(trans-cyclo-octene)palladium, tris(trans-cyclo-octene)platinum. tris(ethylene)palladium, and tris(ethylene)platinum. The ethylene complexes are highly volatile, and can be isolated as crystalline species, although they readily deposit the metals. The structural identity of tris(bicyclo-[2.2.1]heptene)platinum has been established by analysis of single-crystal X-ray data recorded on a four-circle diffractometer both at room temperature and at 190 K. The complex is orthorhombic, space group P2₁2₁2₁. Z= 4, a= 5.717(1), b= 10.735(4), c= 28.749(12)Å, at 300 K: at 190 K a= 5.598(6), b= 10.775(16), c= 28.562(40)Å. Full-matrix least-squares refinement, using 1 781 reflections, has converged to R 0.056 (R′ 0.066)(190 K data). The molecule has a trigonal-planar structure in which the maximum deviation from planarity is 0.03 Å.