Why do Pt(PR3)2 complexes catalyze the alkyne diboration reaction, but their palladium analogues do not?: A density functional study
Why do Pt(PR3)2 complexes catalyze the alkyne diboration reaction, but their palladium analogues do not?: A density functional study
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DOI：
10.1021/om970277g
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发表时间：
1998-02-16
期刊：
影响因子：
2.8
通讯作者：
Morokuma, K
中科院分区：
文献类型：
--
作者：
Cui, Q;Musaev, DG;Morokuma, K
采用B3 LYP杂化密度泛函方法对Pd（0）催化的炔二硼化反应机理进行了理论研究。已经发现，该反应通过与Pt（0）催化的二硼化反应相同的机理进行，并且涉及以下步骤：（i）乙硼烷R2 B-BR 2与Pd（0）络合物的配位，（ii）B-B键与Pd的氧化加成，（iii）一个膦配体的解离，（iv）乙炔的配位，（v）乙炔插入Pd-B键之一中，（vi）伴随膦配体的再配位的所得络合物的异构化，和（vii）烯基-二硼产物的还原消除。然而，Pd（0）配合物不能催化炔二硼化反应，而其Pt（0）类似物可以。发现这种差异的主要原因是B-B键与M（PH 3）的氧化加成过程（2）该步骤发生在M = Pt时，活化势垒为14.0 kcal/mol，并且是放热的，但它不发生在NI = Pd时，其中加成产物由于非常小的反向势垒而不稳定。Pd（0）的这种不活泼性的起源是d（10）-->sd（9）促进能，这对于具有sd（9）基态的Pt（0）是不需要的。
The B3LYP hybrid density functional method has been applied to study theoretically the mechanism of the Pd(0)-catalyzed alkyne diboration reaction. It has been found that this reaction proceeds via the same mechanism as the Pt(0)-catalyzed diboration reaction and involves the following steps: (i) coordination of diborane R2B-BR2 to the Pd(0) complex, (ii) oxidative addition of the B-B bond to Pd, (iii) dissociation of one phosphine ligand, (iv) coordination of acetylene, (v) insertion of acetylene into one of the Pd-B bonds, (vi) isomerization of the resultant complex accompanied by recoordination of a phosphine ligand, and (vii) reductive elimination of the alkenyl-diboron products. However, the Pd(0) complex cannot catalyze the alkyne diboration reaction, while its Pt(0) analogue can. The main reason for this difference is found to be in the oxidative addition process of the B-B bond to M(PH3)(2) This step takes place for M = Pt with a 14.0 kcal/mol activation barrier and is exothermic, but it does not take place for NI = Pd, where the addition product is not stable due to a very small reverse barrier. The origin of this inactivity of Pd(0) is the d(10)-->sd(9) promotion energy, which is not required for Pt(0) with the sd(9) ground state.