associative, A, exchange mechanism. The reactivity of CO exchange follows the increasing trans effect of the halogens (Cl < Br << I), and this is observed on both metal centers. For the same halogen, the rhodium complex is more reactive than the iridium complex. This reactivity difference between rhodium and iridium is less marked for chloride (1.5: 1) than for iodide (8.6:1) at 298 K.
顺式[[M(CO)2X2]-上的CO交换,其中M = Ir(X = Cl,la; X = Br,1b; X = I,1c)和M = Rh(X = Cl,2a; X = Br,2b; X = I,2c)在
二氯甲烷中研究。随温度变化,进行交换反应[顺式-[M(CO)2X2]-+ 2 * CO处于顺式-[M(* CO)2X2]-+ 2CO(交换常数:kobs)],使用自制的高压NMR蓝宝石管测量
一氧化碳的浓度(最高6 MPa)。对于CO和顺式-[M(CO)2 X 2]-浓度,反应都是一级反应。六个复合物的二阶速率常数k2(298)(= kobs)[CO]),焓ΔH*和激活熵deltaS *分别为:la,(1.08 + /-0.01)x 10(3)L mol(-1)s(-1),15.37 +/- 0.3 kJ mol(-1),-135.3 +/- 1 J mol(-1)K(-1) ; 1b,(12