摘要
以金属-烯酮中间体(L_2XM=C=O),作为在钯络合物催化剂上,乙炔羰化和双羰化配位催化机理的单元反应模型,其中反馈键组分可近似地用“Pauling”三电子键来描述。在L_2XM^xC^x=O分子中,定域在M—C两个原子上的两个自旋平行电子,相当于形成一个“增价结构”来提供C_2H_2的配位活化或氧化加成。对[Pd(CO)SnCl_3·Cl_2]^(-1)(A)和[Pd-(CO)Cl_3]^(-1)(B)模拟物的MOs能级及电荷分布的量化计算结果表明:(1)Pd—C键的强度被削弱;(2)模拟物(A)羰基碳原子带上较多正电荷,故容易发生RO^-亲核进攻反应。乙炔与钯络合物配位后,通过π-σ重排,其分子对称性由C_2v变化到Cs,导致前沿轨道能级下降,且LUMO由原来弱反键(C_2v)趋向于非键(Cs)。非键轨道可允许增加一对电子仍保持络合物的稳定。因此,Cs构型中心离子的配位可超越Tolman的16—18价电子规律。
The mechanism of elementary reactions of acetylene carbonylation and di-carbonylation based on suggesting the metal-carbene-ketone [M-C(sp)-M-C (sp2)] as intermediate has been studied. The metal-carbene with partial double bond may consist of a o-donation and a n-feedback interaction, the latter can be described approximately by a 'Pauling 3-electron bond'. The two unpairedelectrons with parallel spin remained are available for partially sharing and abound atom A-Y substrate to provide an 'increased valence structure',thatleads to the oxidative addition as well as the inserted reaction. The focal point of this study is the mechanism of elementary reactions of acetylene carbonylation and oxidative dicarbonylation over Pd catalytic systems under mild reaction conditions. The catalytic kinetics of these two reactions is examined, and the active complexes are suggested to be L2Pd(Cl)SnCl3 and C(CO)2Pd2X432-respectively. The possible reaction mechanisms are proposed, and partially demonstrated with simulators CPd(CO)SnCl3.Cl2]-1 and CPd(CO)Cls]-1 via quantum chemical (Xa) calculations.
基金
国家自然科学基金
