EPR STUDY OF ELECTRON-TRANSFER AND GROUP-TRANSFER IN ORGANOPLATINUM(II) AND ORGANOPLATINUM(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 PtMe2, PtMe4 and PtMes(2) (Mes = mesityl) can be reversibly reduced to parama gnetic compounds, formulated as platinum(II) or (IV) species bound by radical anion ligands (R-DAB(.-)). EPR studies in fluid and frozen sol ution support this assignment; however, the metal contribution to the singly occupied MO is higher for the paramagnetic Pt-II species than f or the Pt-IV systems. Comparison with related radical complexes of the main group and transition element series reveals that even the organo platinum(Iv) compounds exhibit a relatively high degree of ligand-to-m etal spin transfer as evident from small H-1(CH) and large N-14 and Pt -195 EPR hyperfine coupling constants. The tetramethylplatinum(IV) com plexes are photoreactive; a platinum-containing primary dissociation p roduct from platinum-carbon sigma bond homolysis has been detected by EPR spectroscopy using Bu-t-NO as a spin trap reagent during irradiati on. Group transfer reactivity has also been noted for radical anions w here the conversion [(R-DAB)PtMe2](.-) --> [(R-DAB)PtMe4](.-) could be monitored by EPR spectroscopy.