REACTIONS OF CATECHOLBORANE WITH WILKINSON CATALYST - IMPLICATIONS FOR TRANSITION METAL-CATALYZED HYDROBORATIONS OF ALKENES
REACTIONS OF CATECHOLBORANE WITH WILKINSON CATALYST - IMPLICATIONS FOR TRANSITION METAL-CATALYZED HYDROBORATIONS OF ALKENES
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DOI：
10.1021/ja00050a015
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发表时间：
1992-11-18
影响因子：
15
通讯作者：
CALABRESE, JC
中科院分区：
文献类型：
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作者：
BURGESS, K;VANDERDONK, WA;CALABRESE, JC
儿茶酚硼烷 (HBO2C6H4) 与 RhCl(PPh3)3 (1) 的反应会产生多种产物，具体取决于 B/Rh 比例、溶剂和温度。与催化烯烃硼氢化反应特别相关的是 HBO2C6H4 降解为 B2(O2C6H4)3/'BH3' 和二氢化物 RhH2Cl(PPh3)3 (3)。通过X射线衍射测定，3的分子结构具有子午膦配体和顺式氢化物。由 PPh3 原位加成到 [Rh(mu-Cl)(COD)]2 (COD = 1,5-环辛二烯) 形成的催化剂体系与 Wilkinson 催化剂有根本的不同。 RhCl(COD)(PPh3) 最初形成，但与 PPh3 的反应很慢。在氧化后处理之前，通过多核核磁共振波谱监测使用威尔金森催化剂和儿茶酚硼烷进行的催化硼氢化反应，结果表明烷基硼烷是与一些位阻烯烃形成的。例如，对于 2-甲基丁-2-烯 (24)，我们观察到通过将“BH3”添加到 24 中形成大量的二异戊基硼烷 (CHMeCHMe2)2。然而，当向催化剂体系中添加过量的 PPh3 时，会以高产率形成所需的烷基硼酸酯。 RhCl(PPh3)3 的部分氧化对产物（和 D 标记）分布有显着影响。对 DBO2C6H4 催化加成到烯丙基硅醚 CH2=C(Me)CRR'(OSitBuMe2) (R, R' = H, Me) 的详细研究表明，只有在新制备的 Wilkinson 催化剂中或在氧化催化剂中添加过量 PPh3 时，才会在伯醇产物中与硼键合的碳上掺入氘。使用新制备的 Wilkinson 催化剂，将 H-2（或 D2）添加到这些底物中是一个显着的竞争反应，并且还观察到乙烯基硼酸酯的明显催化形成。后者可能是通过将烯烃插入 Rh-B 键，然后消除 β-氢化物而产生的。随后将H-2(DH或D2)原位添加至这些乙烯基硼酸酯中，为α-氘并入所得伯醇中提供了另一种解释。
Reactions of catecholborane (HBO2C6H4) with RhCl(PPh3)3 (1) yield a variety of products depending on the B/Rh ratio, solvent, and temperature. Of particular relevance to catalyzed alkene hydroboration is degradation of HBO2C6H4 to B2(O2C6H4)3/'BH3' and the dihydride RhH2Cl(PPh3)3 (3). The molecular structure of 3, determined by X-ray diffraction, has meridional phosphine ligands and cis hydrides. Catalyst systems formed from in situ addition of PPh3 to [Rh(mu-Cl)(COD)]2 (COD = 1,5-cyclooctadiene) are fundamentally different from Wilkinson's catalyst; RhCl(COD)(PPh3) forms initially, but the reaction of this with PPh3 is slow. Monitoring catalyzed hydroborations using Wilkinson's catalyst and catecholborane by multinuclear NMR spectroscopy, prior to oxidative workup, showed that alkylboranes were formed with some sterically hindered alkenes. With 2-methylbut-2-ene (24), for example, we observed significant quantities of disiamylborane, (CHMeCHMe2)2, form via addition of 'BH3' to 24. When excess PPh3 was added to the catalyst systems, however, the desired alkylboronate ester was formed in high yield. Partial oxidation of RhCl(PPh3)3 had a significant effect on product (and D-label) distributions. Detailed investigations of catalyzed additions of DBO2C6H4 to allylic silyl ethers CH2=C(Me)CRR'(OSitBuMe2) (R, R' = H, Me) demonstrated that deuterium incorporation at the carbon bonded to boron in the primary alcohol product occurs only with freshly prepared Wilkinson's catalyst or when excess PPh3 is added to the oxidized catalyst. With freshly prepared Wilkinson's catalyst, addition of H-2 (or D2) to these substrates is a significant competing reaction and appreciable catalytic formation of vinylboronate esters is also observed. The latter presumably arise via insertion of alkene into a Rh-B bond, followed by beta-hydride elimination. Subsequent in situ addition Of H-2 (DH or D2) to these vinylboronate esters provides an alternative explanation to alpha-deuterium incorporation into the resulting primary alcohols.