UNUSUAL RATE ENHANCEMENT IN THE RHCL(PPH(3))(3)-CATALYZED HYDROSILYLATION BY ORGANOSILANES HAVING 2 SI-H GROUPS AT APPROPRIATE DISTANCES - MECHANISTIC ASPECTS
UNUSUAL RATE ENHANCEMENT IN THE RHCL(PPH(3))(3)-CATALYZED HYDROSILYLATION BY ORGANOSILANES HAVING 2 SI-H GROUPS AT APPROPRIATE DISTANCES - MECHANISTIC ASPECTS
复制标题
DOI：
10.1021/om00006a036
复制
发表时间：
1995-06-01
期刊：
影响因子：
2.8
通讯作者：
ITOH, K
中科院分区：
文献类型：
--
作者：
NAGASHIMA, H;TATEBE, K;ITOH, K
在两个系列的实验中研究了RhCl（PPh（3））（3）催化的羰基化合物与某些α，ω-双官能有机硅烷的硅氢化反应中观察到的不寻常的速率增强。首先，用Me（2）HSi（CH 2）（n）SiHMe（2）[1（n = 1），2（n = 2），3（n = 3），和4（n = 4）]，R（2）HSi（CH 2）（2）SiHPh（2）[8（R = Me）和9（R = Ph）]，和1，2-[Me（2）HSi（CH 2）（n）][Me（2）Hsi（CH 2）n '] C6 H4 [5（n = n' = 0）、6（n = 0，n' = 1）和7（n = n' = 1）]进行了研究，以了解这两个紧密间隔的Si-H基团的速率加速。这些双官能有机硅烷中的5种，2、3和5-7，与丙酮的反应异常迅速，并且导致在室温下在几个小时内它们的Si-H键中的仅一个选择性转化为Si-OiPr基团。它们剩余的Si-H键的反应与用单官能有机硅烷如EtMe（2）SiH和PhMe（2）SiH的氢化硅烷化一样慢;在室温下1天后转化率低于25%。丙酮与1或4的反应速率与EtMe（2）SiH或PhMe（2）SiH的反应速率相似。这些结果表明，在那些双官能有机硅烷中，其中两个紧密间隔的Si-H基团通过2-4个碳单元连接，发生了大的速率增强。与单官能有机硅烷相比，在50 ℃下在8或9的氢化硅烷化中观察到类似的速率增强，并导致一个Si-H基团选择性转化为Si-OiPr部分。产物的分析揭示了在与5的反应中参与甲基的再分配。不对称双官能有机硅烷6或8的氢化硅烷化得到两种异构体的1：1混合物。在第二种方法中，8或9与RhCl（PPh（3））（3）的化学计量反应通过H-1和P-31 NMR光谱进行了研究。所得产物取决于所用溶剂;在CDCl_3中，Rh（III）I氧化加合物R（2）（1）HSi（CH_2CH_2）R（2）（2）Si-RhHCl（PPh（3））（2）（R（1），R（2）= Me或Ph），具有三角双锥结构，在顶端位置有两个PPh（3）配体，而在甲苯-d δ中得到的反应混合物的光谱表明形成了Rh（V）-双氧化加合物R（2）（1）Si（CH_2CH_2）R（2）（2）Si-RhH_3（PPh（3））（2）。由于丙酮与2或8的催化氢化硅烷化反应在甲苯-d δ中进行，而在CDCl 3中不进行，因此Rh（V）-双氧化加合物可能在酮与双官能有机硅烷的一端的快速氢化硅烷化中起重要作用。这些实验结果使我们能够讨论两个可能的机制，涉及disilametallacyclic中间体的速率增强的两个紧密间隔的Si-H基团。
Unusual rate enhancement observed in the RhCl(PPh(3))(3)-catalyzed hydrosilylation of carbonyl compounds with certain alpha,omega-bifunctional organosilanes was studied in two series of experiments. First, the reactions with Me(2)HSi(CH2)(n)SiHMe(2)[1(n = 1), 2 (n = 2), 3 (n 3), and 4 (n = 4)], R(2)HSi(CH2)(2)SiHPh(2) [8 (R = Me) and 9 (R = Ph)], and 1,2-[Me(2)HSi(CH2)(n)][Me(2)Hsi(CH2)n']C6H4 [5 (n = n' = 0), 6 (n = 0, n' = 1), and 7 (n = n' = 1)] were investigated in order to understand the rate acceleration by these two closely spaced Si-H groups. The reactions of five of these bifunctional organosilanes, 2, 3, and 5-7, with acetone were unusually rapid and resulted in selective conversion of only one of their Si-H bonds to a Si-OiPr group within several hours at room temperature. The reaction of their remaining Si-H bonds was as slow as the hydrosilylation with monofunctional organosilanes such as EtMe(2)SiH and PhMe(2)SiH; the conversion was below 25% after 1 day at room temperature. The rate of the reaction of acetone with 1 or 4 was similar to that of EtMe(2)SiH or PhMe(2)SiH. These results suggest that the large enhancement in rate occurred in those bifunctional organosilanes in which two closely spaced Si-H groups were connected by 2-4 carbon units. Similar rate enhancement, compared with monofunctional organosilanes, was observed at 50 degrees C in the hydrosilylation of 8 or 9 and led to the selective conversion of one Si-H group to a Si-OiPr moiety. Analysis of the products revealed involvement of redistribution of methyl groups in the reaction with 5. Hydrosilylation of unsymmetrical bifunctional organosilanes, 6 or 8, gave a 1:1 mixture of two isomers. In the second approach, the stoichiometric reaction of 8 or 9 with RhCl(PPh(3))(3) was studied by H-1 and P-31 NMR spectroscopy. The product obtained was dependent on the solvent used; in CDCl3, Rh(III)I oxidative adducts, R(2)(1)HSi(CH2CH2)R(2)(2)Si-RhHCl(PPh(3))(2) (R(1), R(2) = Me or Ph), having a trigonal bipyramidal structure with two PPh(3) ligands at the apical positions were obtained, whereas the spectra of such reaction mixtures obtained in toluene-d delta suggested the formation of Rh(V)-double oxidative adducts, R(2)(1)Si(CH2CH2)R(2)(2)Si-RhH3(PPh(3))(2). Since the catalytic hydrosilylation of acetone with 2 or 8 proceeded in toluene-d delta, but did not in CDCl3, it is likely that the Rh(V)-double oxidative adducts play an important role in the rapid hydrosilylation of ketones with one end of the bifunctional organosilanes. These experimental results allow us to discuss two probable mechanisms involving disilametallacyclic intermediates for the rate enhancement by the two closely spaced Si-H groups.