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 -tri-tert-butylphenyl)phosphanediylmethyl]benz eneL 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 cr ystal structures of two of them could be determined (EE, ZZ). The elec trochemical behavior of L has been studied by cyclic voltametry: a qua si-reversible reduction occurs at -1.89 V/SCE and corresponds to the f ormation of a radical anion which has been studied by ESR at variable temperature. The experimental P-31 and H-1 hyperfine constants are con sistent with free rotation about the P double bond C and C-phosphaalke ne-C-benzene bonds at room temperature and agree with ab initio predic tions. One of the isomers of L forms complexes with palladium(II) and platinum(III) ions. The crystal structures show that L is orthometalat ed and acts as a terdentate Ligand by coordinating the metal with each phosphorus atom. These complexes are electrochemically reduced betwee n -0.92 and -1.29 V, and the resulting paramagnetic species are studie d by ESR in liquid and frozen solutions. This reduction process was sh own to be a ligand-centered process, an appreciable part of the unpair ed electron is localized on each of the phosphaalkene carbons (20%) an d phosphorus atoms (5%).