THE BENZODIPHOSPHAALKENE LIGAND AND ITS PD-II AND PT-II COMPLEXES - THEIR SYNTHESIS, STRUCTURE, AND AN ESR STUDY OF THEIR REDUCTION PRODUCTS

The new diphosphaalkene 1,3-bis[2-(2,4,6-tri-tert-butylphenyl)phosphanediylmethyl]benzeneL has been synthesized. Due to the presence of two P double bond C bonds three isomers (EE, EZ, ZZ) were observed by P-31 NMR, and the crystal structures of two of them could be determined (EE, ZZ). The electrochemical behavior of L has been studied by cyclic voltametry: a quasi-reversible reduction occurs at -1.89 V/SCE and corresponds to the formation of a radical anion which has been studied by ESR at variable temperature. The experimental P-31 and H-1 hyperfine constants are consistent with free rotation about the P double bond C and C-phosphaalkene-C-benzene bonds at room temperature and agree with ab initio predictions. One of the isomers of L forms complexes with palladium(II) and platinum(III) ions. The crystal structures show that L is orthometalated and acts as a terdentate Ligand by coordinating the metal with each phosphorus atom. These complexes are electrochemically reduced between -0.92 and -1.29 V, and the resulting paramagnetic species are studied by ESR in liquid and frozen solutions. This reduction process was shown to be a ligand-centered process, an appreciable part of the unpaired electron is localized on each of the phosphaalkene carbons (20%) and phosphorus atoms (5%).