RHODIUM CARBONYL CLUSTER CHEMISTRY UNDER HIGH PRESSURE OF CARBON MONOXIDE AND HYDROGEN. VII. CONVERSION OF 3- INTO OTHER HIGH NUCLEARITY CLUSTERS: NEW HIGH-YIELD SYNTHESES FOR 3- AND 2-

Article abstract of DOI:10.1016/S0022-328X(00)86104-5

The interconversions of ^3-, ^3-, and ^4- have been studied under high pressure of an equimolar mixture of carbon monoxide and hydrogen (12-15 atm; 140-160 deg C).The three clusters can be selectively prepared from identical reaction mixtures (Rh(CO)2acac, CsPhCO2, in glyme solvent) using different contact times.A new synthesis for ^3- by exposing this solution for less than 0.5 hours to reaction conditions was discovered in this way.This procedure allows the preparation of 5-20 g of the cluster, isolated as the bis(triphenylphosphine) iminium salt with a 95percent yield in a 8-hour working period.The fragmentation of ^3- to Rh2(CO)8 and the aggregation of this dimer with the initial cluster is suggested to form ^3-.Conversion of ^3- into ^4- or ^2- occurs subsequently by reaction with carbon monoxide and hydrogen, or by treatment with trifluoromethane sulfonic acid; ^3- has also been converted into ^3- by reaction with formaldehyde in the presence of hydrogen (67 atm, 125 deg C).The oxidative aggregation of two large clusters to yield an even larger species is promoted by protonic acids: ^3- and CF3SO3H react to give ^2-.The effects of the cations on the redox aggregation-fragmentation reactions of the clusters have been noted for the first time during these studies.