Alcohols dehydrogenation, acceptorless

The isoelectronic [Ru -Ru ] complexes are relatively more accessible, and such complexes are proving to be useful for a range of chemical reactions. This article collects the chemistry at sites trans to the [Ru-Ru] single bond. The C-H activation, C-C bond formation, acceptorless alcohol dehydrogenation, cyclo-propanation, carbenoid C-H insertion, and C-H amination reactions are covered. Reactivity studies at axial sites on [Ru-Ru] multiply bonded systems are also included because of their direct relevance in catalytic chemistry. The purpose of this article is to highlight the recent progress on the axial-site chemistry on [Ru -Ru ] platforms with intent to infuse interests for further development. 

Substitution of noble metals in catalysts for cheap and abundant materials is of obvious importance, and many works concern the preparation and study of the latter systems. Thus, cobalt(II) alkyl complexes of aliphatic PNP pincer ligands (Fig. 12) are active precatalysts for the hydrogenation of ketones and the acceptorless dehydrogenation of alcohols under mild conditions in this case the alcohol dehydrogenation likely proceeds through a cobalt(I)/(III) redox cycle. ... 

Zeng G, Sakaki S, Fujita K, Sano H, Yamaguchi R. Efficient catalyst for acceptorless alcohol dehydrogenation interplay of theoretical and experimental studies. HCS Catal. 2014 4(3) 1010-1020. 

Zhang G, Hanson SK. Cobalt-catalyzed acceptorless alcohol dehydrogenation synthesis of imines from alcohob and amines. Org Lett. 2013 15 650-653. 

Figure 3.17 Acceptorless dehydrogenation of alcohols by Gelman s Ir-PCP-pincer complex.

Scheme 8.18 Acceptorless dehydrogenation of alcohols catalysed by dibenzobarrelene based iridium complexes.

Friedrich, A. Schneider, S. Acceptorless dehydrogenation of alcohols Perspectives for synthesis and H2 storage. ChemCatChem 2009,1, 72-73. 

Structurally related PCP-pincer Ir complexes (Fig. 10) were synthesized by straightforward [4+2] cycloaddition and employed as catalysts in the acceptorless dehydrogenation of alcohols. Such complexes can be easily modified with a functional sidearm that is capable of interacting with the catalytic site, thus making them suitable candidates for catalytic studies involving ligand-metal cooperation. The H2 formation involves an intramolecular cooperation between the structurally remote functionality and the metal center. ... 

Figure 12 Cobalt(ll) complex with a PNP pincer ligand as a catalyst precursor for acceptorless dehydrogenation of alcohols." " ...

In general, the iron catalysts seem to be very promising, and interesting works on Fe-catalyzed acceptorless dehydrogenations of alcohols appear... 

Ti02-supported Co NPs are also catalyticaUy active in the acceptorless dehydrogenation of various aUphatic secondary alcohols to the corresponding ketones. ... 

The acceptorless dehydrogenation can be used not only for simple transformation of alcohols to the corresponding ketones or aldehydes or for... 

Ru(II) hydride complexes based on electron-rich PNP and PNN ligands of the type depicted on Fig. 13 (which can undergo aromatization/ dearomatization steps) efficiently and selectively catalyze the acceptorless dehydrogenation of primary alcohols to esters and H2 with high TONs... 

Song H, Kang B, Hong SH. Fe-catalyzed acceptorless dehydrogenation of secondary benzyKc alcohols. ACS Catal. 2014 4 2889-2895. 

Yi J, Miller JT, Zemlyanov DY. A reusable imsupported rhenium nanocrystalline catalyst for acceptorless dehydrogenation of alcohols through y-C-H activation. Angew Chem Int Ed Engl. 2014 53 833-836. 

Shimizu K, Kon K, Seto M, Shimura K, Yamazaki H, Kondo JN. Heterogeneous cobalt catalysts for the acceptorless dehydrogenation of alcohols. Green Chem. 2013 15 418-424. 

Li F, Sun C, Wang N. Catalytic acceptorless dehydrogenative coupling of aryUiydrazines and alcohols for the synthesis of aryUiydrazones. J Org Chem. 2014 79 8031-8039. 

Moromi SK, Siddiki HSMA, Ali MA, Kon K, Shimizu K. Acceptorless dehydrogenative coupling of primary alcohols to esters by heterogeneous Pt catalysts. Catal Sd Technol. 2014 4 3631-3635. 

Symmetrical pyrazines may be accessed by the dimerisation of vicinal amino alcohols (Scheme 12.35). Milstein discovered that a ruthenium PNP pincer complex catalyses the acceptorless dehydrogenation of amino alcohols in toluene at reflux, likely inducing double condensation to a dihy-dropyrazine which may undergo an additional dehydrogenation to provide the observed products. A similar Ru-PNN pincer complex, possessing a hemi-labile amine arm, was found to catalyse the conversion of amino alcohols to diketopiperazines (see Section 12.2.2)... 

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