SOME ASPECTS OF CATALYTIC SYNTHESES IN RHODIUM CHEMISTRY

Substttutrons at coba!t(IlI), rhodrum(III) and urdmm(II1) centres m polar medra, lake water, are m genera! much slower than those for other oxtdatton states of the partrcular meta! Work m polar medra naturally mvolves complexes of tire more polar ltgands, such as ammoma or ammo acrds. It has been known for some time that consrderable rate en- hancements, often useful synthettcally, may be achieved through the addrtron of a redoa reagent, and the ovldatton states (for complexes contammg essentrally a-bonding hgands hke Cl- or NH3) most commonly mvoked to rattonahse tlus findmg are shown m Table 1 The critical factor in catalysts by one electron reducmg agents at cobalt(II1) 1s the for- matron of a cobalt(I1) specres, followed by a (usually) rate-determmmg electron transfer from tlus or a derivative to a cobalt(II1) congener Srmrlar features underhe the catalysrs of reactions of chrommm(II1) by the relatively maccessrble chrommm(I1) The entirely drfferent relations between oxldatron states for rhodrum (or rrrdrum) as opposed to cobalt result m this one-electron reductive meclranism bemg non-catalytic* and rt 1s the purpose of tlus present note to comment on the alternative way m wluch substrtuttons at rhodtum(IiI) are catalysed