Milton Orchin

ON THE MECHANISM OF THE OXO REACTION

Abstract The “oxo” o r hydroformylation reaction is a remarkable reaction on many accounts. Total annual world production of alcohols via the 0x0 reaction is now in excess of five billion pounds; thus there continues to be much interest in the technology of the reaction. The single alcohol produced in largest amount via the 0x0 process is 2-ethylhexanol, a product of the condensation of butyraldehyde, which in turn results from the hydroformylation of propylene. Although the commercial OxO reaction has been practised for more than 25 years, there has been thus far little technological change in the manufacturing process. (Only recently have modifications been introduced on a laboratory scale that have resulted in some fundamental technological changes. These developments are reviewed elsewhere in this issue.)

The preparation and properties of some cis-platinum(II) carbonylphosphine complexes, PtX2(CO)(PR3)

Abstract A series of substituted platinum(II) carbonyl complexes, cis -[PtX 2 (CO)(PR 3 )] has been prepared. The effects of various X and R groups on the carbonyl stretching frequency and the dipole moment are discussed. A modified general procedure for the preparation of dimeric platinum(II) complexes. [Pt 2 Cl 4 (PR 3 ) 2 ] has been developed.

Hydroformylation of formaldehyde

Abstract The reaction between hydridotetracarbonylcobalt and monomeric formaldehyde at 0°C in the presence of 1 atm of carbon monoxide leads to stoichiometric hydroformylation with the formation of glycolaldehyde in high yield.

The stoichiometric hydrogenation of 1,1-diphenylethylene with hydridocobalt tetracarbonyl; differences from the hydroformylation reaction

Abstract The kinetics of the stoichiometric hydrogenation of 1,1-diphenylethylene with HCo(CO) 4 is cleanly second order, permitting a determination of the activation parameters. The rate is unaffected by the atmosphere over the reaction and is enhanced by substituting DCo(CO) 4 for HCo(CO) 4 . These results contrast sharply with those secured in the hydroformylation of 1-alkenes and thus dual mechanistic pathways are available for the reaction of HCo(CO) 4 with unsaturated systems. It is very possible that the stoichiometric hydrogenation of 1,1-diphenylethylene involves a geminate free radical pair but definitive proof is still lacking.

Transient species of importance in the stoichiometric hydroformylation reaction I. Evidence for HCo(CO)3 by matrix isolation

Abstract Spectra of HCo(CO) 4 in a low temperature argon matrix show a weak band at 2018 cm −1 . On irradiation, this band grows rapidly and additional bands (previously too weak to be readily observable) appear at 2025 and 485 cm −1 . These three bands are assigned to HCo(CO) 3 , a coordinatively unsaturated species persistently proposed as an intermediate in the hydroformylation reaction but not previously characterized.

The Homogeneous Catalytic Isomerization of Olefins by Transition Metal Complexes

Publisher Summary This chapter discusses the homogeneous catalytic isomerization of olefins by transition metal complexes. Transition metal hydrides play a key role in the catalytic homogeneous isomerization of olefins. The pure hydrides, such as HCo(CO) 4 can function as the catalyst or transition metals complexed to stabilizing ligands can function as catalysts. The catalysis almost certainly proceeds through hydride intermediates in many cases. The most attractive mechanism for olefin isomerization consists of initial complexing between olefin and metal, addition of H–M across the double bond to generate a σ carbon-metal bond, and then elimination of H–M in the opposite direction with eventual release of the isomerized olefin. The evidence for such a mechanism is compelling, especially with the heavier transition metals. However, when some σ-alkyl metals of cobalt and iron have been treated with olefins under conditions appropriate for isomerization, no transfer of the metal to the olefin occurred.

Radical hydroformylation and hydrogenation of cyclopropenes with HCo(CO)4 and HMn(CO)5

Abstract The results of a study of the reactions of HCo(CO)4 and HMn(CO)5 with a variety of a substituted cyclopropenes are consistent with the formation of the intermediate caged radical pairs; recombination in the cage of the radical pair leads to hydroformylation, and cage escape leads to hydrogenation. Steric factors play an important role in determining rates as well as the stereochemistry of the products.

The preparation and reactions of the azides of fac-Mn(CO)3(P-P)N3. The X-ray crystal structures of fac-[Mn(CO)3(P-P)(OH2)]BF4, fac-Mn(CO)3(P-P)() [(P-P)=dppe and depe], and fac-[Mn(CO)3(depe)(PPh3)]BF4

Abstract A simple three-step, high-yield synthesis of the titled azides from Mn2(CO)10 and P-P is described involving the intermediate aqua complexes, fac-[Mn(CO)3(P-P)(H2O)]BF4, 3a,b. The aqua ligand is very labile; it is easily exchanged for D2O, PPh3, and NO2−. Crystal structures of the two titled aqua complexes and fac-[Mn(CO)3(depe)(PPh3)]BF4, 6a, are reported. The aqua complexes react instantaneously with aqueous NaN3 to give quantitative yields of the corresponding covalent azides which undergo the expected 1,3-dipolar additions with CF3CN to give the corresponding tetrazoles whose crystal structures are also reported.

Olefin reactions with HMn(CO)5: Product selectivity by micelle sequestering

Abstract The reaction of HMn(CO)5 with certain cyclopropenes when carried out in a detergent medium gives a different mixture of hydroformylated and hydrogenated products than is obtained when the same reaction is carried out in a homogeneous medium. These results are consistent with the intermediacy of caged geminate radical pairs whose escape from the cage is retarded by micelle sequestering.

Membrane-supported rhodium hydroformylation catalysts

Abstract Films prepared from THF solutions containing cellulose acetate, [HRh(CO)(PPh3)3] and PPh3 were tested for catalytic activity in the vapor phase hydroformylation of ethylene and propylene: RCH=CH2+CO+H2→RCH2CH2CHO. The reaction proceeded smoothly at 800 ton- and 80 °C. Turnover rates were about 25 mol propanai per mol Rh per h. No loss of PPh3 or Rh from the film was observed even after long periods of reaction. The excess PPh3 seemed to stabilize the catalytic activity of the film but concentrations beyond 10 molar produced no further improvement. The turnover rate with the films was equal to or even slightly higher than that obtained under similar conditions using a homogeneous solution of [HRh(CO)PPh3] in 2-methylmaphthalene solvent. The turnover rate for propylene to C-4 aldehydes was about an order of magnitude smaller than that for ethylene to propanal. Films prepared from poly(phenylsulfone) were also active catalysts. The ratio of n/iso C-4 aldehydes with this support was about 20. In the absence of oxygen the catalyst system retained its activity for more than 13 days but no attempt was made to test for longer lifetimes. The use of polymeric films or membranes as a support for the rhodium catalysis of the hydroformylation reaction thus appears to hold considerable promise.