FLOW REACTORS FOR PREPARATIVE CHEMISTRY IN SUPERCRITICAL-FLUID SOLUTION - SOLVENT-FREE SYNTHESIS AND ISOLATION OF CR(CO)(5)(C2H4) AND (ETA(5)-C5H5)MN(CO)(2)(ETA(2)-H-2)

We describe the use of supercritical flow reactors as a new but relatively straightforward approach to carrying out reaction chemistry in high-pressure fluids (<350 bar). Two photochemical flow reactors are described in detail, one reactor for the synthesis of Cr(CO)(5)(C2H4) from the reaction of Cr(CO)(6) with supercritical C2H4 (scC(2)H(4)), the other reactor for the generation of CpMn(CO)(2)(eta(2)-H-2) from CpMn(CO)(3) and H-2 in supercritical CO2 (scCO(2)). Both compounds are isolated by rapid expansion of the supercritical solution. This is the first time that either compound has been isolated as a solid, and both are found to be not nearly as labile as had been anticipated, Indeed, CpMn(CO)(2)(eta(2)-H-2) is one of the simplest dihydrogen compounds so far to have been isolated, yet it is one of the more robust compounds, taking 2 h to react with moderately high pressures of CO or C2H4. Other reactions involving scC(2)H(6) as the fluid or N-2 as the reactant (e.g., to form CpMn(CO)(2)N-2) are described briefly. So far, the reactions have been carried out on a modest scale, ca. 20-40 mg per h, but this is more a limitation of the photochemistry rather than of the reactors themselves. All reactions are carried out without the use of any conventional organic solvents.