Homologation of Methanol in Fe(CO) 5 -NMe 3 -MeOH Solution

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1 Homologation of Methanol in Fe(CO) 5 -NMe 3 -MeOH Solution Accidental discovery in the study of hydrogenation of CO _ with HFe(CO) 4 _ HFe(CO) 4 as a nucleophile Methylammonium ion as a methyl carrier No higher alcohol production due its S N 2 mechanism (CH 3 >> C 2 H 5 >C 3 H 7 ) paralleling steric requirements at alkyl, whereas the conventional HCo(CO) 4 catalyst is believed to follow an S N 1 mechanism with C 3 H 7 > C 2 H 5 > CH 3 paralleling carbonium ion stabilities 35

2 A system that uses an inorganic base HCO 2 _ as the base; no amine Mn(CO) 5 _ as the nucleophile HCO 2 CH 3 as the methyl carrier Methyl formate is about as effective as tetramethyammonium ion as a methyl carrier in the catalytic process. Thus, at 200 o C in n-methylpyrrolidone solution: for (CO) 5 Mn - + NMe + 4, k(s N 2) = 2.7 x 10-3 for (CO) 5 Mn - + CH 3 O 2 CH, k(s N 2) = 2.4 x

3 Improved heterobimetallic system Precursor (mmol) Reaction Time (hrs) * C 2 H 5 OH (mmol) CH 4 (mmol) Fe(CO) 5 (16.0) Mn 2 (CO) 10 (11.5) Fe(CO) 5 (16.0) Mn 2 (CO) 10 (11.5) Fe(CO) 5 (16.0) Re 2 (CO) 10 (8.0) * In methanol solution containing N-methylpiperidine (320 mmol) at 200 o C and 3:1 CO/H 2 (300 atm): total volume = 160 ml 37

4 Results and Conclusions Due to important differences in catalysis mechanism, the metal carbonyl/base approach described here leads to much higher alcohol selectivity than the earlier HCo(CO) 4 method first reported by Wender. The metal carbonyl/base approach uses properties common in metal carbonyl chemistry; thus, there are many opportunities for improvement. In contrast, the high acidity of HCo(CO) 4 required for it to function in homologation is rare for a hydride that can be produced reversibly from dihydrogen. The heterobimetallic Fe(CO) 5 /Mn 2 (CO) 10 and Fe(CO) 5 /Re 2 (CO) 10 systems show interesting synergistic and inhibitory effects that need to be explored. 38

5 Future activities Test proposed mechanism for the heterobimetallic enhancement. Use operando methods to look for mixed-metallic intermediates like (CO) 5 Mn-Fe(CO) 4 H. Explore the ionic fluid, Li/KO 2 CH eutectic, to: (1) improve carbonylation/hydrogenation selectivity, (2) replace the amine, and (3) improve product separation Use operando methods to probe solvation effects, selectivies, kinetics, and key equilibria in this medium In accord with the lower pk a values of its corresponding acid, ~0 for HCo(CO) 4 (compared with 4.4 for H 2 Fe(CO) 4 and 7.1 for HMn(CO) 5 ), one would anticipate that (CO) 4 Co - would be a poorer nucleophile. However, based on the use of cobalt (and rhodium) carbonyls in the hydroformylation of olefins (where carbonylation/hydrogenation selectivity is a key issue) the (CO) 4 Co - or (CO) 4 Rh - anions would be expected to improve ethanol/methane selectivity in this reaction. Use of phosphines would improve their nucleophilicities and low pressure stabilities. We will test these strategies. 39

6 Argonne s Operando Toroid NMR Devices Toroid Cavity Imager Uses ml Be-Cu ( psi tensile strength) gold-plated Be-Cu, or Ti-Al ( psi tensile strength) pressure vessels. Tested at psi. Operates at 7500 psi at 250 o C. Can be equipped with an NMR magnet-driven magnetic stirrer. 40

7 Potential mechanism for the heterobimetallic effect Might be analogous to the Co 2 (CO) 8 catalyzed hydrogenation of Mn 2 (CO) 10 in supercritical CO 2 Is isoelectronic Fe 2 (CO) 8-2 catalyzing the hydrogenation of Mn 2 (CO) 10 in the heterobimetallic ethanol synthesis? Proposed intermediate: 41

8 Chemically Selective Radial Imaging ) Water 2) Isopropanol 3) Acetone 4) Water 5) Isopropanol d = 1.0 mm Woelk, Klingler, and Rathke J. Magn. Reson. A 105, (1993) r Chemical Shift Δr = 0.8 mm 42

9 Near Electrode NMR Imager Potentiostat In situ formation of ion s 10 micrometer resolution Multinuclear NMR: 7 Li, 19 F Working Electrode Counter Electrode Toroid Cavity Working Electrode Chemical Shift Radial Position (1/r) NMR Spectrometer 200 μm US Patent

10 Substitution of Fossil fuels with Biofuels To be a viable substitute, an alternative fuel should have a net energy gain over the energy sources used to produce it, be economically competitive with it, be producible in sufficient quantities to make a meaningful impact on energy demands, and have superior environmental benefits over the fossil fuel it displaces. Therefore, it is necessary to analyze each biofuel industry, including farms and production facilities, as though it were an island economy. It is a net energy exporter only if the energy value of the biofuel and Its co-products exceeds that of all direct and indirect energy inputs. 44

11 NEB of corn grain ethanol and soybean biodiesel production Hill, Jason et al. Proc. Natl. Acad. Sci. (2006) USA 103,

12 Coil vs. Cavity Solenoid Coil Helmholtz Coil Toroid Coil Toroid Cavity Toroid Cavity Confined RF Magnetic Flux RF Magnetic Field / Gradient Radial Electric Field 46

13 Homogeneous Catalytic CO Hydrogenation Reaction at 220 o C and 300 atm of CO/H 2 in benzene Accidental discovery in the study of ydrogenation of benzene with HCo(CO) 4 The first demonstrably homogeneous CO hydrogenation catalyst Proved to be mononuclear when conventional wisdom required multiple metal centers This mechanism generally accepted for Co, Rh, and Ru complex catalysts CO 47

14 Mechanism The rate law is: d[c 2 H 5 OH]/dt = k (2) [(CH 3 ) 4 N + ][HFe(CO) 4 - ] The rate determining step is: (CH 3 ) 4 N + + HFe(CO) 4 - = CH 3 FeH(CO) 4 + (CH 3 ) 3 N For the bimolecular reaction of A + B: 48

15 Temperature dependence 49

16 Methyl Transfer between Mn(CO) 5 - and NMe 4 + in NMP NMP = N-methyl-2-pyrrolidinone 50

17 Problems What is the mechanism of the heterobimetallic rate/selectivity enhancement and inhibition? Can inorganic bases be used? How can metal carbonyl contamination of the product be avoided? How can the ethanol/methane selectivity be improved? How can the pressure requirements be lowered? How can the rates be improved? How can the catalyst stability be improved? 51