5 coordinate complex as a model for the reaction of the square planar complex

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The 5-coordinate complex, [PtX(hfac)_2]^- (X = Cl, Br or I, hfac = hexafluoroacetyl acetonate), has a distorted square pyramidal structure and exchanges the coordination sites quickly in solution. From the temperature-variable NMR, two independent paths were supposed ; an apical O-donor assaults an X-cis position or an X-trans position. The cis and trans effects of halide ligand were obtained by comparing the each rate data. Ab initio calculations of these intra molecular site exchange process were performed. The transition state energies of possible paths show that the order of the cis effect of halide ligand as, Cl > Br > I, and the trans effect as, I > Br > Cl, which is in accordance with the experimental results. The attempt to prepare similar 5-coordinate complexes with C-, N-, or O-donor resulted in producing the adducts complex anion on a carbonyl carbon in [Pt(hfac)_2]. An NHR adduct complex is a good model of the intermediate of the imine formation reaction between the carbonyl compound and the primary amine. This adduct actually produced a Schiff base complex. But in another reaction conditions, NHR dissociates and assaults Pt(II) to give the substituted products. The NHR adduct activates the C-H or O-H bond in solvent molecule to form the C-donor or O-donor adduct. The newly formed C-C bond is very weak since the C-donor adduct easily liberates the solvent molecule. Also the C-donor exchanges with the OMe in MeOH. Such a weak C-C bond is very novel.