| Research Abstract |
1. [M(hfac)_2] (M=Pt, Pd) reacted with [18-crown-6/K] (X=Cl, Br, I,No_2, NO_3 NCO etc.) or [Ph_4P] X (X=Cl, Br, I) in CH_2Cl_2 to give a variety of products. The reaction proceeds successively as follows, 5-coordinate complex [MX(hfac)_2]^-, [MX(hfac)(hfac-O)]^-, [MX_2(hfac)]^-, and[MX_4]^<2-> or [M_2(mu-X)_2X_4]^<-2>. When a basicity of X is weak, [MX(hfac)(hfac-C^3)]^-, containing M-C bond, was produced. In the transition state of the M-C bond formation, hfac^- ion should attack the metal atom in [MX_2(hfac)]^- ; electrostatically and sterically unfavorable path. [Ph_4P][MX(hfac)_2] (X=Cl, Br, I) was isolated as red crystals. A distorted square pyramidal structure with halide ligand in the basal plane was determined by single crystal X-ray analysis. The temperature-variable NMR spectra were explained by two independent dynamic motions in solution ; a site exchange between apical-O and X-cis-O (Path A), and a site exchange between apical-O and X-trans-O (Path B). A ratio of the exchange rates of each path is dependent on the kind of the halide ; k_A>k_B (Cl), k_B>>k_A (Br, I). k_A is in the order, Cl>I,but k_B is in the reverse order, I>Br>Cl. The rate of the cis-trans isomerization is predicted as in the order, Cl>Br>I.
2. Reaction of [Pd(hfac)_2] with monoximes gave new Pd(II) complex with one hfac-O,O' and one hfac-oxime-C,N-chelate, in which a C-O bond was formed between the C^3-bonded hfac and the N-bonded monoxime. The structure was determined by an X-ray analyzes and NMR spectra. A precursor complex, [Pd(hfac)(oxime)_2](hfac), was detected by NMR at low termperature.
3. First acac (3-) complex with Pt(II) was prepared by the reaction of [Pt(acac)_2] and PPh_3 in MeOH.Multi-nuclear NMR spectra revealed the eta^3 : C,O-binding structure. M-C bond formation was deduced to follow "ionic reaction mechanism, ", since a methyl proton abstraction by an acac^- anion in the outer sphere from acac (2-) ligand seems to be a key step.
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