Host-guest chemistry in a urea matrix:: Catalytic and selective oxidation of triorganosilanes to the corresponding silanols by methyltrioxorhenium and the urea/hydrogen peroxide adduct
Host-guest chemistry in a urea matrix:: Catalytic and selective oxidation of triorganosilanes to the corresponding silanols by methyltrioxorhenium and the urea/hydrogen peroxide adduct
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DOI：
10.1021/ja9826542
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发表时间：
1999-03-17
影响因子：
15
通讯作者：
Weichold, O
中科院分区：
文献类型：
--
作者：
Adam, W;Mitchell, CM;Weichold, O
甲基三氧化铼（MTO）催化硅烷氧化为硅烷醇，具有较高的转化率和优异的选择性，有利于硅烷醇的生成（无二硅氧烷产物）。提出这种新型Si-H氧化发生在螺旋脲通道中，其中脲基质用作硅烷底物、H2 O2氧源和作为客体的MTO金属催化剂的主体。在这种受限的环境中，金属催化剂被稳定以防止分解，并且这提高了更高的转化率，同时由于空间原因避免了硅烷醇缩合成其二硅氧烷。光学活性硅烷（S）-（α-Np）PhMeSiH的氧化以优异的产率在构型保持的情况下进行。迄今为止，没有报道用于制备光学活性硅烷醇的催化Si-H氧插入。与（+）-（alpha-Np）PhMeSiH的二环氧乙烷氧化为（+）-（alpha-Np）PhMeSiOH的立体选择性类似，提出了这种新型Si-H氧化的协同螺型过渡态结构。因此，通过用MTO/UHP体系催化和选择性氧化硅烷为硅烷醇，提供了一种有价值的制备硅烷醇的合成方法。
The oxidation of silanes to silanols, catalyzed by methyltrioxorhenium (MTO), proceeds in high conversions and excellent selectivities in favor of the silanol (no disiloxane product) when the urea/hydrogen peroxide adduct (UHP) is used as oxygen source instead of 85% aqueous H2O2 It is proposed that this novel Si-H oxidation takes place in the helical urea channels, in which the urea matrix serves as host for the silane substrate, the H2O2 oxygen source, and the MTO metal catalyst as guests. In this confined environment, the metal catalyst is stabilized against decomposition, and this enhances higher conversions while condensation of the silanol to its disiloxane is avoided for steric reasons. The oxidation.of the optically active silane (S)-(alpha-Np)PhMeSiH proceeds with retention of configuration in excellent yield. To date, no catalytic Si-H oxygen insertion has been reported for the preparation of optically active silanols. In analogy with the stereoselectivity in the dioxirane oxidation of (+)-(alpha-Np)PhMeSiH to (+)-(alpha-Np)PhMeSiOH, a concerted spiro-type transition-state structure is proposed for this novel Si-H oxidation. Herewith, a valuable synthetic,method for the preparation of silanols has been made available through catalytic and selective oxidation of silanes to silanols by the MTO/UHP system.