Photochemistry of tris(dimethylpyrazolyl)-boratorhodium dicarbonyl and bis(dimethylpyrazolyl)-boratorhodium dicarbonyl complexes in low temperature media at 12–298 K: some insights into CH activation processes

Abstract

IR and electronic spectroscopic evidence, including a study of 13CO enrichment pathways, is presented to show that photolysis of tris (dimethylpyrazolyl)-boratorhodium dicarbonyl and bis(dimethylpyrazolyl)-boratorhodium dicarbonyl complexes in argon and methane matrices at ca. 12 K produces CO loss and ligand dechelation products. No evidence was found for photochemical CH bond activation in methane matrices but the facile tridentate α bidentate interconversion for tris(dimethylpyrazolyl)-boratorhodium dicarbonyl provides support for the proposal that such a process could be the key step in the highly efficient CH photoactivation reaction of this complex at 298 K. In dinitrogen matrices the new CO loss products reacted to form monodinitrogen complexes. In an attempt to investigate whether additional thermal energy is needed for the photoactivation processes, the tris(dimethylpyrazolyl)-boratorhodium dicarbonyl and bis(dimethylpyrazolyl)-boratorhodium dicarbonyl complexes were photolysed in perfluorokerosine and Nujol mulls which could be warmed from ca. 12 K to 298 K. No CH bond photoactivation was observed in Nujol mulls at 12 K or 77 K but at 298 K photoactivation of Nujol by tris(dimethylpyrazolyl)-boratorhodium dicarbonyl was observed, i.e. there appears to be a thermal contribution to the photochemical CH activation process for this particular complex. The results of the low temperature studies are related to photochemical reactions observed in solutions at 298 K.