Stable organopalladium(II) and organoruthenium(II) complexes with spin-labeled phosphine ligands

Palladium(II) and ruthenium(II) complexes containing aminoxyl radical-substituted triphenylphosphine ligands are reported. The novel spin-labeled phosphine ligands [(p-(4,4,5,5,-tetramethylimidazolinyl-1-oxyl-3-oxide)phenyl)diphenylphosphine] (1) and [(p-(N-oxyl-tert-butylamino-2-)phenyl)diphenylphosphine] (2) react with PdCl2 to yield trans-Pd[1](2)Cl-2 and trans-Pd[2](2)Cl-2 (complexes 3 and 4, respectively), which show exchange-coupled EPR spectra. This through-space, intramolecular coupling provides a method of determining the number of radical phosphines coordinated to the Pd(II) center. Systems with only one coordinated phosphine show EPR spectra typical of the ligand. Phosphine 2 reacts with [(eta(3)-C3H5)PdCl](2) and [(eta(6)-p-cymene)RuCl2](2) to form the mononuclear metal phosphine adducts (eta(3)-C3H5)Pd[2]Cl (5) and (eta(6)-p-cymene)Ru[2]Cl-2 (6). All complexes show broad, shifted H-1 NMR spectra, and magnetic susceptibility measurements confirm the presence of one (complexes 5, 6) or two (complexes 3, 4) radicals per complex accordingly. The X-ray crystal structures of Pd[2](2)Cl-2 and (eta(3)-C3H5)Pd[2]Cl are also reported. Complexes 5 and 6 are unusual examples of stable organometallic systems with peripheral free radicals, i.e., spin-labeled organometallics.