Heterogeneous or homogeneous catalysis? Mechanistic studies of the rhodium-catalyzed dehydrocoupling of amine-borane and phosphine-borane adducts

被引:265
作者
Jaska, CA [1 ]
Manners, I [1 ]
机构
[1] Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada
关键词
D O I
10.1021/ja0478431
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
In depth, comparative studies on the catalytic dehydrocoupling of the amine-borane adduct (Me2NHBH3)-B-. (to form [Me2N-BH2](2)) and the phosphine-borane adduct (Ph2PHBH3)-B-. (to form Ph2PH-BH2-PPh2-BH3) with a variety of Rh (pre)catalysts such as [{Rh(1,5-cod)(mu-Cl)}(2)], Rh/Al2O3, Rh-colloid/[Oct(4)N]Cl, and [Rh(1,5-cod)(2)]OTf have been performed in order to determine whether the dehydrocoupling proceeds by a homogeneous or heterogeneous mechanism. The results obtained suggest that the catalytic dehydrocoupling of (Me2NHBH3)-B-. is heterogeneous in nature involving Rh(0) colloids, while that of (Ph2PHBH3)-B-. proceeds by a homogeneous mechanism even when starting with Rh(0) precursors such as Rh/Al2O3. The catalytic dehydrocoupling reactions are thought to proceed by different mechanisms due to a combination of factors such as (i) the greater reducing strength of amine-borane adducts, (ii) the increased ease of dissociation of phosphine-borane adducts, and (iii) phosphine ligation and/or poisoning of active catalytic sites on metal colloids.
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页码:9776 / 9785
页数:10
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