Alan P. Sylwester

Studies of the thermal and photochemical lability of olefin complexes of rhodium(I) to form Rh and Rh2O3

Abstract Thermogravimetric analyses of the series of compounds [L 2 RhCl] 2 , where L 2 = 1,5-COD, NBD and (C 2 H 4 ) 2 under air, nitrogen and 7%H 2 in N 2 atmospheres reveal that thermal decomposition behavior depends on the nature of the olefin ligand and the composition of the atmosphere. Under a 7% H 2 in N 2 atmosphere, the onset of thermal decomposition of these species occurs in the following order: L 2 = (C 2 H 4 ) 2 , 91°C; NBD, 143°C; 1,5-COD, 212°C. Under a nitrogen atmosphere, [L 2 RhCl] 2 , L 2  NBD and (C 2 H 4 ) 2 , undergo weight loss consistent with loss of one or more olefin ligands, then formation of Rh metal at higher temperatures. In contrast, [(1,5-COD)RhCl] 2 formed Rh metal directly. In air, thermal decomposition generally resulted in formation of crystalline Rh metal followed by oxidation above 500°C to form crystalline Rh 2 O 3 , except for [(C 2 H 4 ) 2 RhCl] 2 , which gave Rh 2 O 3 directly. The Rh and Rh 2 O 3 powders were analyzed by powder X-ray diffraction. In some experiments, a weight loss consistent with formation of “RhCl” was observed. However, as a result of the crystalline Rh present, it is proposed that disproportionation to Rh and RhCl 3 may have occurred. The compound [(C 2 H 4 ) 2 Rh(OEt)] 2 . H 2 O is photolabile and undergoes decomposition on exposure to UV radiation to give crystalline, 2 nm sized Rh metal particles as determined by TEM, EDS and electron diffraction.