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

五配位配合物[PtX（hfac）_2]^-（X = Cl、Br或I，hfac =六氟乙酰丙酮）具有畸变四方锥结构，在溶液中可迅速进行配位交换。从温度变化的NMR，假设两个独立的路径;顶端O-供体攻击X-顺式位置或X-反式位置。通过比较各反应速率数据，得到了卤代配体的顺反效应。对这些分子内位点交换过程进行了从头计算。过渡态能量分析表明，卤代配体的顺式效应顺序为Cl > Br > I，反式效应顺序为I > Br > Cl，这与实验结果一致。在[Pt（hfac）_2]中，以C-、N-或O-为给体制备类似的五配位配合物，结果在羰基碳上产生了加合物配合阴离子。NHR加合物络合物是羰基化合物和伯胺之间的亚胺形成反应的中间体的良好模型。这种加合物实际上产生了席夫碱络合物。但在另一种反应条件下，NHR解离并攻击Pt（II），得到取代产物。NHR加合物活化溶剂分子中的C-H或O-H键以形成C-供体或O-供体加合物。新形成的C-C键非常弱，因为C-供体加合物容易释放溶剂分子。C-供体也与MeOH中的OMe交换。如此弱的C-C键是非常新颖的。

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.