Structure and Reactivity of Organopalladium Complexes Bearing Unusual Oxidation State of Pd

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The aim of this project is i) to synthesize a number of organopalladium complexes having a formal oxidation state of Pd(I) or Pd(IV), ii) to elucidate their molecular and electronic structures, and iii) to explore some reactivities characteristic of such structures.The principal findings obtained follow.1) Transformations proceeding through Pd(IV) complexesPI-Allyl complex containing the chloromethyl group at 2-position of the allyl framework, [Pd(CH_2C(CH_2Cl)CH_2)(C_5H_5)] afforded C-C bond formation product, [Pd(CH_2C(CH_2G_5H_5)CH_2)Cl] via a Pd(IV)-metallacycle [Pd(CH_2C(=CH_2)CH_2)(C_5H_5)] ^+. Other than the C_5H_5 ligand, the SPh group of [Pd(CH_2C(CH_2CL)CH_2)SPh] also enabled an analogous transformation via the Pd(IV) intermediate, giving rise to [Pd(CH_2C(CH_2SPh)CH_2)CI].2) Synthesis and structure of Pd(I) complexesA general method of synthesizing Pd(I)-Pd(I) dinuclear complexes has been developed by making use of coupling between Pd(0) and Pd(II) species with butadiene playing a template role. Thus, employing some ligands on Pd(II) (Cl, Br, I) and diene ligands led to selective synthesis of anionic, [Pd_2X_3(diene)], neutral, [Pd_2X_2(PPh_3)(diene)], and cationic, [Pd_2X(PPh_3)_2(diene)] ^+ dinuclear complexes. X-Ray structure determinations confirmed the s-trans bridging diene ligand. The diene ligands so coordinating included anionic dienolate. The structure determination also revealed unusually long Pd-Pd distance (3.19 A) in [Pd_2(PPh_3) _2(diene) _2] ^<2+>, a value much longer than the previously reported Pd-Pd length (-2.83 A). MO calculations indicated that such elongated Pd-Pd length is attributed to back donation of electron densities from the Pd-Pd bond to LUMO of the diene. The unusual dicationic dipalladium complex reacted with acetonitrile or acetylene to result. in liberation of two or one diene molecule, respectively.