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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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Trichloro-oxomolybdenum(v) reacts with Schiff bases H2L in the presence of base, with the diiithium salt L12L, or with the bis(trimethylsily1) derivative L(SiMe,), [L = salen, salpn, salphen, 3-MeO-salen, 3-MeO-salphen, 3-Me0salpn, or 2,2'-bi(2,3-dihydrobenzothiazolyl) (H,bzt)] to give the complexes [MoCI(O)L]. E.s.r., and i.r. spectral data suggest that the complex with L = salen [ethylenebis(salicylideneiminato)] exists as a mixture of cis and trans isomers. but with L = salpn [propane-l,3-diylbis(salicylideneiminato)] or salphen [o-phenylenebis-(salicylideneiminato)] solely in the trans and cis configurations, respectively. On heating under reflux in air, the [ MoCl(0) L] complexes are oxidised to [ MoO,L]. CKELATING Schiff-base ligands have been the subject of row transition metals have been investigated.ly2 Less many studies, and in particular complexes with first-information is available on complexes of the early Science and Technology, Manchester M60 1 OD heavy transition-metal ions and we report here some of 2 S. Yamada, Co-ordination Chem. Rev., 1966, 1, 415. plexes of such ligands. Previously, reactions of 1 540 cm-l indicating that the Schiff-base ligands do not bridge via oxygen in the complexes.11J2 All the complexes showed a strong absorption in the 930-960 cm-l 8 V. A. Kogan, 0. A. Osipov, V. I. Minkin, and V. P. Sokolov, Russ. J . Inorg. Chem., 1965, 10, 45.