EPR study of electron transfer and group transfer in organoplatinum(II) and (IV) compounds

Chelate complexes between the 1,4-diazabuta-1,3-diene ligands RN=CH-CH=NR = R-DAB (R = alkyl, aryl) and the organoplatinum fragments PtMe(2), PtMe(4) and PtMes(2) (Mes = mesityl) can be reversibly reduced to paramagnetic compounds, formulated as platinum(II) or (IV) species bound by radical anion ligands (R-DAB(.-)). EPR studies in fluid and frozen solution support this assignment; however, the metal contribution to the singly occupied MO is higher for the paramagnetic Pt(II) species than for the Pt(IV) systems. Comparison with related radical complexes of the main group and transition element series reveals that even the organoplatinum(Iv) compounds exhibit a relatively high degree of ligand-to-metal spin transfer as evident from small (1)H(CH) and large (14)N and (195)Pt EPR hyperfine coupling constants. The tetramethylplatinum(IV) complexes are photoreactive; a platinum-containing primary dissociation product from platinum-carbon sigma bond homolysis has been detected by EPR spectroscopy using Bu(t)-NO as a spin trap reagent during irradiation. Group transfer reactivity has also been noted for radical anions where the conversion [(R-DAB)PtMe(2)](.-) --> [(R-DAB)PtMe(4)](.-) could be monitored by EPR spectroscopy.