1- Hexen transfer hydrogenation

Transfer hydrogenation of dienes to monoenes 1,5-Cyclooctadiene is selectively reduced to cyclooctene by transfer hydrogenation with isopropanol catalyzed by this metal carbonyl cluster. The first step is isomerization to conjugated diene isomers. 1,5-Hexadiene is reduced under these conditions to frms-3-hexene (19%), os-2-hexene (21%), trans-2-, and cw-3-hexene (56%). Ru3(CO)i2, Os3(CO)12, and Ir4(CO)i2 catalyze isomerization of 1,5-cyclooctadiene, but are less active than Rh6(CO)i6 for transfer hydrogenation. 

This is the case as shown in Table 1, runs 4,5, provided that basic sites are free from adsorbed H20 and C02 (compare runs 3 and 4, Table 1). Notably, once again the ratio hexan-3-one/hexen-3-ols appears unaffected by the catalyst precursor and/or pretreatment (runs 3,4, Table 1). These observations suggest that in the transfer hydrogenation of 4-hexen-3-one, the substrate is coordinated on a weak acid site while propan-2-ol must be coordinated on an adjacent surface basic site [7,24]. This is confirmed by the lack of reduction products observed over Mg(OH)2 and MgCl2 (runs 8,9, Table 1). 

Examples of a-olefins include 1-pentene, 1-hexene, 1-octene, etc. A suitable catalyst is titanium trichloride with diethylaluminum chloride as co-catalyst. Hydrogen is a chain transfer agent. 

Procedure. Hexene (Phillips Petroleum, pure grade, 99% ) was dried over sodium and filtered through a layer of A1203 (Merck, Aktivitatsstufe I) to remove peroxides. The alkene was dissolved in benzene (Baker analyzed) dried over sodium, and the reaction mixture was transferred to the reactor. The complex was placed in the jar and the system was closed. To remove all air dissolved in the liquid phase, the system was evacuated and flushed with hydrogen purified for possible 02 by passing a deoxo catalyst (palladium), under a pressure of 10 atm, and then passing a molecular sieve to remove H20 3 to 5 times under stirring. Adjustments permitted stabilization of the pressure in 1-2 min where the reaction rate was to be measured. 

Hydrogen transfer reduction of 4-hexen-3-one catalyzed by doped MgO catalysts.3... 

The formation of 5-hexenal (reaction 18) is believed to be an intramolecular rearrangement since the addition of oxygen does not cause its suppression. At least in a methyl substituted cyclohexanone the analogous process has been shown to occur by the transfer of a hydrogen atom from the beta position to the carbonyl group before the fission of the six-membered carbocyclic ring (29) as only one of the two possible isomeric heptenals is formed. 

HYDROGEN TRANSFER INDEX (HTI1 TEST In this test, 0.5 /xL pulses of 1-hexene feed were carried from a heated sampling valve into a fixed-catalyst bed in a stainless steel reactor by a nitrogen carrier stream at 800 mL/min. (at STP). The catalyst was -250 mesh and diluted with alumina of the same mesh size plus 80-100 mesh acid-washed Alundum. Reactor pressure was controlled by an Annin valve. The effluent stream went to the injector splitter of a gas chromatograph. The reactor conditions included a catalyst temperature of 221°C and 3.45 MPa total pressure. 

Relative hydrogen transfer activity can be determined using an HTI test (11), where the index is a measure of the degree of saturation in the reaction product. The test determines the product ratio of 3-methylpentenes to 3-methylpentane derived from a 1-hexene feed. While the branched products come mainly from oligomerization followed by cracking, the results should be relevant here as well. The higher the index, the lower the relative hydrogen transfer activity. 

Hexene Polymerization Polymerization of 1-hexene (and also propylene) by the Kaminsky catalyst [(Cp2ZrCl2/(MeAlO) /toluene] differs fundamentally from that of ethylene in that beta hydrogen elimination is the only detectable chain transfer mechanism. Insertion of 1-hexene into the Zr-C bond in Cp2ZrCH3+ produces Cp2ZrCH2CH(CH3)C4H9+. The electron donating... 

Formation of 1,1-diacetates—e,g., ethylidene diacetate from ethylene or hexylidene diacetate from hexene—by simple acetate displacement of palladium (Reaction 16) is a much more satisfactory reaction scheme than any previously proposed. On the other hand, accounting for 1,2-diol type products is diflBcult by this scheme, necessitating a reverse hydrogen transfer to form a two-carbon insertion product intermediate. This type... 

As seen from Table 12.2.2, the main pyrolysis products of poly(l-hexene-sulfone) are SO2 and 1-hexene. However, some other fragment molecules are generated by various types of reactions such as hydrogen transfer, cyclization, etc. Typical examples are 2-ethylthiophene, 3-ethylthiophene, and 2,5-dibutylthiophene. 

Catalytic hydrogen transfer from a hydrogen donor molecule to an unsaturated substrate sometimes presents advantages over hydrogenation by molecular hydrogen. This type of reaction can be catalyzed by a number of ruthenium or rhodium catalysts. Cycloocta-1,5-diene and hexa-1,5-diene can be selectively reduced to cyclooctene and a mixture of hexenes, respectively, by Rh6(CO)16 via hydrogen transfer from isopropanol.The reaction proceeds at 145°C and a CO pressure of 45 bar. For cycloocta-1,5-diene... 

The reflux for 4 h of 1-hexene with Fe(CO)5 yields a mixture of all possible straight chain hexenes in approximately their thermodynamic equilibrium concentration. One possible mechanism is allylic hydrogen transfer analogous to the PdCl2 isomerization. Allyl alcohol on treatment with Fe(CO)s undergoes rearrangement to propionaldehyde, undoubtedly via a ir-allyl hydride as shown by deuterium labeling studies ... 

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