Ligand migrations during the formation of some palladium-rhodium heterodinuclear complexes

A new Pd(I)-Rh(II) heterodinuclear complex, trans-(NC)(2)-(CH3O)(3)PRh(mu-dppm)(2)PdCl (2a), was prepared by treatment of [(cod)RhCl](2) with (CH3O)(3)P and trans-(NC)(2)Pd(dppm)(2) (1) (dppm = bis(diphenylphosphino)methane, cod = 1,5-cyclooctadiene) and characterized by P-31 NMR spectroscopy and single-crystal X-ray structure determination. The single crystal of complex 2a is triclinic; its space group <P(1)over bar>(No.2); a = 15.684(6), b = 16.059(5), c = 12.274(4) Angstrom, alpha = 94.43(3), beta = 106.55(3), gamma = 87.86(3)degrees. The Rh-Pd bond distance is 2.7835(5) Angstrom. The molecular structure of this complex suggests that its formation reaction includes: (i) ligand migrations of the Cl- from the Rh center to the Pd center and the two CN- groups from the Pd center to Rh center; (ii) the intermetallic one-electron transfer indicated by the alteration from Rh(I) and Pd(II) to Rh(II) and Pd(I) respectively; (iii) the Pd(I)-Rh(II) bond formation by pairing one electron from Rh(II) with one electron from Pd(I). The differences of chemical shifts of the phosphorus atoms coordinated to the Pd center in the Pd-Ag complexes and the Pd-Rh complexes are discussed.