THERMAL EXCHANGE-REACTIONS OF (ETA(5)-C5R5)MN(CO)(2)(L-W) COMPOUNDS (L-W = WEAKLY-BOUND LIGAND) IN SUPERCRITICAL-FLUID SOLUTION AND THE ISOLATION OF (ETA(5)-C5R5)MN(CO)(2)(ETA(2)-H-2) USING HIGH-PRESSURE FLOW AND SEMIFLOW REACTORS

Supercritical fluids offer unrivaled opportunities for manipulating co mpounds with labile ligands, This paper reports a study of ligand-exch ange reactions in supercritical solution aimed at evaluating compounds as precursors for the thermal synthesis of CpMn(CO)(2)(eta(2)-H-2) in supercritical CO2 (scCO(2)), A series of (eta(5)-C5R5)Mn(CO)(2)(L-w) compounds have been prepared, where L-w is a weakly-bound ligand (i.e. , (PrCN)-Pr-n, eta(2)-H2C=CHOEt (EVE), and eta(2)-H-SiEt3), and their reactions with C2H4, N-2, and H-2 have been studied in supercritical s olution, This is the first time that the EVE ligand has been used with the (eta(5)-C5R5)Mn(CO)(2) moiety. We describe flow and semiflow reac tors for carrying out these thermal reactions in supercritical solutio n, Both of these reactors exploit rapid expansion of the supercritical fluid to enable these labile complexes to be isolated from supercriti cal solution without loss of the labile ligand. The reaction of CpMn( CO)(2)(eta(2)-HSiEt3) with H-2 is found to be the best route for the t hermal synthesis of CpMn(CO)(2)(eta(2)-H-2), both in terms of purity and convenience. There are clear opportunities for scale-up, We find t hat exchange between these ligands is so facile that conditions in sup ercritical solution can be varied sufficiently to favor the interchang e between almost any pair of the labile ligands, This ease of intercha nge has important implications for homogeneous catalysis in supercriti cal solution.