Towards the upgrading of fermentation broths to advanced biofuels: a water tolerant catalyst for the conversion of ethanol to isobutanol

The conversion of methanol/ethanol mixtures to isobutanol with the pre-catalyst trans-[RuCl2(dppm)2] (1) is tolerant to the addition of water to the system, achieving an isobutanol yield of 36% at 78% selectivity with water concentrations typical of that of a crude fermentation broth.</p

Catalytic conversion of methanol/ethanol to isobutanol – a highly selective route to an advanced biofuel

Catalysts based on ruthenium diphosphine complexes convert methanol/ethanol mixtures to the advanced biofuel isobutanol, with extremely high selectivity (>99%) at good (>75%) conversion via a Guerbet-type mechanism

Homogeneous Ethanol to Butanol Catalysis - Guerbet Renewed

The catalytic conversion of (bio)ethanol into butanol is an attractive route to upgrade the modest fuel characteristics of this widely available bioderived substrate into a molecule that has properties much closer to conventional gasoline. The Guerbet reaction, known for more than 100 years, provides an ideal mechanism for this transformation. However, despite the apparently simple nature of this reaction for ethanol, it provides formidable challenges, especially in terms of achieving high selectivity. There have been advances in both heterogeneous and homogeneous catalysis in this regard, and this Perspective focuses on the very recent reports of homogeneous catalysts that describe encouraging results in terms of achieving high selectivity, mechanistic understanding, and widening scope

Rhenium Complexes Bearing Tridentate and Bidentate Phosphinoamine Ligands in the Production of Biofuel Alcohols via the Guerbet Reaction

We report a variety of rhenium complexes supported by bidentate and tridentate phosphinoamine ligands and their use in the formation of the advanced biofuel isobutanol from methanol and ethanol. Rhenium pincer complexes 1–3 are effective catalysts for this process, with 2 giving isobutanol in 35% yields, with 97% selectivity in the liquid fraction, over 16 h with catalyst loadings as low as 0.07 mol %. However, these catalysts show poorer overall selectivity, with the formation of a significant amount of carboxylate salt solid byproduct also being observed. Production of the active catalyst 1d has been followed by 31P NMR spectroscopy, and the importance of the presence of base and elevated temperatures to catalyst activation has been established. Complexes supported by diphosphine ligands are inactive for Guerbet chemistry; however, complexes supported by bidentate phosphinoamine ligands show greater selectivity for isobutanol formation over carboxylate salts. The novel complex 7 was able to produce isobutanol in 28% yield over 17 h. The importance of the N–H moiety to the catalytic performance has also been established, giving further weight to the hypothesis that these catalysts operate via a cooperative mechanism

Manganese diphosphine and phosphinoamine complexes are effective catalysts for the production of biofuel alcohols via the Guerbet reaction

We report a variety of manganese-based catalysts containing both chelating diphosphine (bis(diphenylphosphino)methane (dppm: 1, 2, and 7) or 1,2-bis(diphenylphosphino)ethane (dppe: 3)), and mixed-donor phosphinoamine (2-(diphenylphosphino)ethylamine (dppea: 4–6)) ligands for the upgrading of ethanol and methanol to the advanced biofuel isobutanol. These catalysts show moderate selectivity up to 74% along with turnover numbers greater than 100 over 90 h, with catalyst 2 supported by dppm demonstrating superior performance. The positive effect of substituting the ligand backbone was also displayed with a catalyst supported by C-phenyl-substituted dppm (8) having markedly improved performance compared to the parent dppm catalysts. Catalysts supported by the phosphinoamine ligand dppea are also active for the upgrading of ethanol to n-butanol. These results show that so-called PNP-pincer ligands are not a prerequisite for the use of manganese catalysts in Guerbet chemistry and that simple chelates can be used effectively

Backbone-functionalised ruthenium diphosphine complexes for catalytic upgrading of ethanol and methanol to iso-butanol †

Efficient catalysts for Guerbet-type ethanol/methanol upgrading to iso-butanol have been developed via Michael addition of a variety of amines to ruthenium-coordinated dppen (1,1-bis(diphenylphosphino)ethylene). All catalysts produce over 50% iso-butanol yield with >90% selectivity in 2 h with catalyst 1 showing the best activity (74% yield after this time). The selectivity and turnover number approach 100% and 1000 respectively using catalyst 6. The presence of uncoordinated functionalised donor groups in these complexes results in a more stable catalyst compared to unfunctionalised analogues

Direct bromination of keggin fragments to give [PW9O28Br6]3−: a polyoxotungstate with a hexabrominated face

Direct halogenations of polyoxometalates [NaPW11O39]6− and [PW9O34]9− led to [PW9O28Br6]3−, a molecular metal oxide with a fully brominated face (see picture). This methodology creates new opportunities for systematic chemistry at polyoxometalate surfaces

Bis(tetra­butyl­ammonium) [mu]-oxalato-bis­[dibromidodioxidotungstate(VI)]

The title compound, (C16H36N)2[W2Br4(C2O4)O4], has a centrosymmetric dinuclear anion in which two tungsten(VI) centres, with distorted octa­hedral coordination, are bridged by an oxalate dianion, forming two five-membered chelate rings. All atoms of the complex anion, except for the Br atoms, lie essentially in a plane