Dehydrogenation acceptorless

Alan Goldman developed much improved catalysts and also obtained detailed mechanistic information in the 1990s [35, 36]. An unexpected variant developed by Saito, by our own group and most extensively by Goldman, was acceptorless dehydrogenation. It turned out that the reaction could be driven by reflux because the hydrogen was continuously pumped out of the solvent by the reflux action [37-39]. 

The stability of ( uPCP)IrHn at high temperature was exploited to give rates and turnover numbers for acceptorless dehydrogenation greater than those achieved with any previous catalysts [21]. 

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.

The catalyst 18 has also been immobilized on a silica sol gel and applied in the same acceptorless dehydrogenation reaction, resulting in a slower reaction although with a clear advantage in recyclabihty and stabilization compared to the... 

The effect of a hydroxyl unit at the axial position of a [Ru-Ru] core, placed through the agency of a naphthyridyl-functionalized NHC, is examined for catalytic acceptorless dehydrogenation to aldehyde and subsequent coupling with amine to form exclusively imine products... 

By replacing the phenyl backbone of the PCP ligand by a cyclohexyl backbone, the Wendt group succeeded in the synthesis of the aliphatic iridium complex (PCyP)Ir(H)(Cl), 9 (Fig. 6) [48]. The catalytic activity of this complex activated with NaO Bu was found to be very low (TONs up to 50) for the transfer dehydrogenation of COA by TBE (1 1) at 200°C due to fast decomposition of the active species. By decreasing the temperamre to 120°C with the use of a ratio COA/TBE of 24 1 at 120°C, TONs up to 200 have been achieved. The acceptorless dehydrogenation of COA was also carried out at 150°C giving low TONs ( 5). 

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

Figure 9.12 Transfer dehydrogenation and acceptorless dehydrogenation of alkanes catalyzed by complexes 47. (According to Chianese [16a].)...

Prospective Substrates and Oxidation Agents Acceptorless Dehydrogenative Oxidations Oxidative Desymmetrizations... 

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. ... 

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. ... 

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. 

---