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4 M afforded TOF’s of 37 and 29 h−1, respectively. This was partially explained by the decrease
in reaction temperature as a result of the lower base concentration (79°C with the 6 M and
76°C with the 4 M).
It was also revealed that [Ru(H)2 (PiPr3)2(CO)2] catalyses the reaction with practically the same
efficiency (TOF = 50 h−1), leaving some speculations as to whether this is the real catalyst.
Moreover, mechanistic investigations suggest that the CO moiety of [Ru(salbinapht)(CO)
(PiPr3)] plays an active role during the catalytic cycle by reacting with hydroxide and thus
forming formic acid and H2. This might open for the possibility that a similar mechanism
might (partially) take place with the Beller and Milstein systems.
Other metal complexes have also been shown to conduct MeOH reforming by AAD, spe-
cifically iron [16, 24], manganese [25], and iridium [26–28]. Several of them are comprised of
PNPiPr pincer ligand complexes, such as the iron-based compounds shown in Figure 11. Beller
initially showed that borohydride coordinated species afforded a TOF2h of 644 h−1 when using
a 4.5 ppm catalyst loading in a 9:1 (v/v) MeOH/H2O mixture containing 8.0 M KOH and stir-
ring at 91°C [24]. A long-term experiment allowed for a TON46h of 9834.
When comparing this result using the iron-based catalyst with the TOF values obtained when
using the ruthenium-based congener, the latter is superior with respect to catalyst activity
and longevity. Nevertheless, showcasing the feasibility of conducting MeOH reforming using
a non-noble metal catalyst is an important step towards applicability, which these findings
therefore represent.
Bernskoetter, Hazari, and Holthausen improved the iron-based MeOH reforming by exchang-
ing the borohydride with a formate, dissolving minute amounts of MeOH and H2O in EtOAc,
Figure 10. Reek catalyst for MeOH reforming. Best result: TOF = 55 h−1.
Figure 9. Milstein PNN ruthenium catalyst for MeOH reforming. Best results: TOF = 45 h−1. TON = 29,000. Yield = 82%.
Reusable system.
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Buch Advanced Chemical Kinetics"
Advanced Chemical Kinetics
- Titel
- Advanced Chemical Kinetics
- Autor
- Muhammad Akhyar Farrukh
- Herausgeber
- InTech
- Ort
- Rijeka
- Datum
- 2018
- Sprache
- englisch
- Lizenz
- CC BY 4.0
- ISBN
- 978-953-51-3816-7
- Abmessungen
- 18.0 x 26.0 cm
- Seiten
- 226
- Schlagwörter
- Engineering and Technology, Chemistry, Physical Chemistry, Chemical Kinetics
- Kategorien
- Naturwissenschaften Chemie