This work was undertaken to determine why the vinyl and allyl esters of unsaturated fatty acids polymerize slowly and incompletely. It was found that the polymerization rate decreases as the degree of unsaturation in the fatty ester increases. The esters of the dienoic fatty acids polymerize very slowly, and the degree of polymerization is low. It makes little difference in the polymerization rate whether the double bonds are conjugated or separated by a methylene group. The retardation of polymerization and low degree of polymerization are explained by the reaction of radical initiators and polymer chains with the unsaturation in the fatty acid molecule. These reactions give new radicals which react by radical combination, thereby either robbing the system of initiator radicals or terminating polymer chains. wish to express our appreciation to Dr. J. W. Opie, who did the initial work on this problem, and to hlr. H. hl. Boyd for carrying out the spectral analyses.

complex, occurs within the potential limits of an aqueous solution.(The H-, notation in the formula indicates the number of amidate nitrogens coordinated to the palladium.) Flow electrolysis of pale yellow 1 at 1.35 V vs. Ag/AgCl produces a pink species, 2. The CV behavior of 2 is very similar to that of 1. Typically, flow electrolysis of 1-2 mM solutions of 1 proceeds with >90% yield.The oxidized species, 2, in 0.050 M chloroacetate buffer, pH 3.0, with 0.10 M NaCl undergoes an absorbance loss of only 15% in 1 h when protected from room light. The products of the thermal decay in aqueous solution are palladium(I1) species, as determined by UV-vis spectroscopy. In acetonitrile the stability of 2 is excellent, with <1% loss in 1 h when protected from room light.The following experimental facts indicate oxidation of 1 occurs at the metal center and that 2 is formally a palladium(1V) species.1. Reaction of 2 with the two-electron reductant iodide to give 13or with the one-electron reductant [Cu(H-,Aib3)]-to give C U ( H -~A~~, ) shows that 2 is 2 equiv more oxidized than 1. 2. In aquwus solution 2 is EPR silent at 77 K but NMR active at room temperature, consistent with the metal-centered oxidation of d8 palladium(I1) to d6 palladium(1V). A comparison of the 'H N M R spectral data for H2Aib3+, 1, and 2 in Table I suggests a metal-center4 oxidation with a more electron-withdrawing metal coordinated to the ligand in 2 than in 1.3. The chemical oxidation of 1 to 2 with Oxone (2KHSO5-K-HS04-K2S04) and the subsequent reduction of 2 to 1 with NHIOH yields 1 in 95% yield. Thus, the conversion of 1 to 2 is reversible. Ligand-centered oxidation of 1 by Oxone in an aqueous solution with subsequent reduction would be expected to give a muchlower yield of 1.4. The electronic spectral data for 2 collected in Table I show charge-transfer bands (presumably ligand-to-metal charge transfer (LMCT)) at longer wavelengths than those for 1, as expected for an increase in the oxidation state of the central metal.5. Visible radiation photoreduces the central metal in 2. Divalent 1 is not subject to decomposition by visible radiation.Photoactivity appears to be a general characteristic of high-valent m e t a l a~d a t e complexes since Cu(H2Aib,)l3 and Ni(H2Aib3)% complexes are also photoactive for LMCT band irradation.The electronic spectral data for 2 under varying medium conditions as presented in Table I suggest axial halide coordination at low pH and axial hydroxide coordination at neutral pH. That is, the 243-nm LMCT shifts to 266 nm when the medium is changed from 0,lO M NaCl to 0.10 M NaBr; also, at pH 7 the spectrum is independent of the presence or absence of chloride. Since palladium(1V) is a d6 metal ion, an octahedral coordination geometry is expected. Thus we suggest a structure for 2 is [Pd-(H2Aib,)X2]-where X = C1-, Br-, or OHdepending on medium conditions.x 2 Because of our success in the ready preparation of 2 without an excess of strong oxidant, we are able to begin investigation of the scope of reactivity of the palla...

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