A. Klein et al., EPR STUDY OF ELECTRON-TRANSFER AND GROUP-TRANSFER IN ORGANOPLATINUM(II) AND ORGANOPLATINUM(IV) COMPOUNDS, Perkin transactions. 2, (12), 1997, pp. 2573-2577
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.