Theoretical Study of Ir-Catalyzed Chemoselective C1–O Reduction of Glucose with Silane

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• 作者：Qi Zhang ; Hai-Zhu Yu ; Yao Fu
• 刊名：Organometallics
• 出版年：2016
• 出版时间：August 8, 2016
• 年：2016
• 卷：35
• 期：15
• 页码：2473-2479
• 全文大小：548K
• 年卷期：0
• ISSN：1520-6041

文摘

Density functional theory (DFT) calculations have been performed to study the mechanism of Ir(III) pincer complex (POCOP)Ir(H)(acetone)⁺ (POCOP = 2,6-bis(dibutylphosphinito)phenyl) catalyzed chemoselective C1–O hydrosilylative reduction of glucose. The mechanisms for reduction of the external and internal C1–O (i.e., C1–O^ext and C1–O^int) on the C1-MeO-substituted glucose (i.e., 1_Me) and C1–Me₂EtSiO-substituted glucose (i.e., 1_Si) have been investigated. The calculation results show that both mechanisms proceed with the first concerted silyl transfer and the subsequent C1–O^ext or C1–O^int bond cleavage and hydride transfer steps. In the hydride transfer step, the Ir-H moiety acts as the hydride source. The C1–O cleavage is the rate-determining step of the overall mechanism. The C1–O^ext reduction is more favorable than C1–O^int reduction for the substrate 1_Me, while the C1–O^int reduction is more favorable for 1_Si. These results are consistent with the recent experimental outcomes. Analyzing the origin of chemoselectivity for the C1–O^ext or C1–O^int cleavage, we found that the more stable precursor of C1–O^ext cleavage and retention of the six-membered-ring structure result in the selective C1–O^ext reduction of 1_Me. Meanwhile, the higher basicity of the alkyl ether O^int atom (in comparison to the silyl ether O^ext atom) and greater steric hindrance in the precursor favor the C1–O^int bond weakening. Therefore, the C1–O^int reduction occurs selectively for 1_Si.