金属有机化学：Insertion and elimination.ppt

Less common elimination reactions b-elimination from alkoxides of late transition metals is easy: The hydride often decomposes to H+ and reduced metal:alcohols easily reduce late transition metals. Also, the aldehyde could be decarbonylated to yield metal carbonyls. For early transition metals, the insertion is highly exothermicand irreversible. Insertion and elimination * * 三个可能的反应机理，CO直接插入；甲基转移；CO转移插入 * 首先排除机理I * 机理2和3都可能 * 实验结果表明cis:trans=2：1；有部分*CO释放 * 插入和消除都改变了金属中心的电子数，但是没有改变金属中的价态 * 1,1插入，pi配体增加了价态 * CO插入很少放热；得到的酰基配体需要进一步反应被消耗掉；被消耗掉的过程一般是比较快的。CO不会聚合，而CN会聚合 * 1.配体大比较拥挤；2lewis酸促进反应 * 1.有利于插入反应的是金属中心有吸电子基；2.较早的过渡金属；3.炔比烯更容易反应 * 插入和消除反应速率比 * Insertion and elimination Insertion reactions 插入反应的发生必备条件： If at a metal centre you have a s-bound group (hydride, alkyl, aryl) a ligand containing a p-system (olefin, alkyne, CO) the s-bound group can migrate to the p-system. Insertion and elimination * Insertion in MeMn(CO)5 Insertion and elimination * 3 Insertion in MeMn(CO)5 Insertion and elimination 首先排除哪个反应机理？？ * Insertion in MeMn(CO)5 Insertion and elimination * Insertion in MeMn(CO)5 Insertion and elimination * Insertion in MeMn(CO)5 Insertion and elimination HOMO LUMO insertionTS agostic h2-acyl CO adduct CO 计算结果也表明CH3迁移路径能量最低 * Insertion reactions The s-bound group migrates to the p-system. But if you only see the result, it looks like the p-system has inserted into the M-X bond, hence the name insertion. To emphasize that it is actually (mostly) the X group that moves, we use the term migratory insertion. The reverse of insertion is called elimination. Insertion reduces the electron count, elimination increases it. Neither insertion nor elimination causes a change in oxidation state. Insertion and elimination * 1,1 insertions In a 1,1-insertion, metal and X group move to the same atom of the inserting substrate. The metal-bound substrate atom increases its valence. CO, isonitriles (RNC) and SO2 often undergo 1,1-insertion. Insertion and elimination * I