Metal鈥揕igand Cooperation by Aromatization鈥揇earomatization: A New Paradigm in Bond Activation and 鈥淕reen鈥?Catalysis
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- 作者：Chidambaram Gunanathan ; David Milstein
- 刊名：Accounts of Chemical Research
- 出版年：2011
- 出版时间：August 16, 2011
- 年：2011
- 卷：44
- 期：8
- 页码：588-602
- 全文大小：1564K
- 年卷期：v.44,no.8(August 16, 2011)
- ISSN：1520-4898
文摘
In view of global concerns regarding the environment and sustainable energy resources, there is a strong need for the discovery of new, green catalytic reactions. For this purpose, fresh approaches to catalytic design are desirable. In recent years, complexes based on 鈥渃ooperating鈥?ligands have exhibited remarkable catalytic activity. These ligands cooperate with the metal center by undergoing reversible structural changes in the processes of substrate activation and product formation.
We have discovered a new mode of metal鈥搇igand cooperation, involving aromatization鈥揹earomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidation state, and so far the activation of H鈥揌, C鈥揌 (sp2 and sp3), O鈥揌, and N鈥揌 bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process, which involves consecutive thermal liberation of H2 and light-induced liberation of O2, using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex. An acridine pincer complex displays unique 鈥渓ong-range鈥?metal鈥搇igand cooperation in the activation of H2 and in reaction with ammonia.
In this Account, we begin by providing an overview of the metal鈥搇igand cooperation based on aromatization鈥揹earomatization processes. We then describe a range of novel catalytic reactions that we developed guided by these new modes of metal鈥搇igand cooperation. These reactions include the following: (1) acceptorless dehydrogenation of secondary alcohols to ketones, (2) acceptorless dehydrogenative coupling of alcohols to esters, (3) acylation of secondary alcohols by esters with dihydrogen liberation, (4) direct coupling of alcohols and amines to form amides and polyamides with liberation of dihydrogen, (5) coupling of esters and amines to form amides with H2 liberation, (6) selective synthesis of imines from alcohols and amines, (6) facile catalytic hydrogenolysis of esters to alcohols, (7) hydrogenolysis of amides to alcohols and amines, (8) hydrogenation of ketones to secondary alcohols under mild hydrogen pressures, (9) direct conversion of alcohols to acetals and dihydrogen, and (10) selective synthesis of primary amines directly from alcohols and ammonia. These reactions are efficient, proceed under neutral conditions, and produce no waste, the only byproduct being molecular hydrogen and/or water, providing a foundation for new, highly atom economical, green synthetic processes.
We have discovered a new mode of metal鈥搇igand cooperation, involving aromatization鈥揹earomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidation state, and so far the activation of H鈥揌, C鈥揌 (sp2 and sp3), O鈥揌, and N鈥揌 bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process, which involves consecutive thermal liberation of H2 and light-induced liberation of O2, using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex. An acridine pincer complex displays unique 鈥渓ong-range鈥?metal鈥搇igand cooperation in the activation of H2 and in reaction with ammonia.
In this Account, we begin by providing an overview of the metal鈥搇igand cooperation based on aromatization鈥揹earomatization processes. We then describe a range of novel catalytic reactions that we developed guided by these new modes of metal鈥搇igand cooperation. These reactions include the following: (1) acceptorless dehydrogenation of secondary alcohols to ketones, (2) acceptorless dehydrogenative coupling of alcohols to esters, (3) acylation of secondary alcohols by esters with dihydrogen liberation, (4) direct coupling of alcohols and amines to form amides and polyamides with liberation of dihydrogen, (5) coupling of esters and amines to form amides with H2 liberation, (6) selective synthesis of imines from alcohols and amines, (6) facile catalytic hydrogenolysis of esters to alcohols, (7) hydrogenolysis of amides to alcohols and amines, (8) hydrogenation of ketones to secondary alcohols under mild hydrogen pressures, (9) direct conversion of alcohols to acetals and dihydrogen, and (10) selective synthesis of primary amines directly from alcohols and ammonia. These reactions are efficient, proceed under neutral conditions, and produce no waste, the only byproduct being molecular hydrogen and/or water, providing a foundation for new, highly atom economical, green synthetic processes.