Organo- f-element thermochemistry. Actinide-ligand bond disruption enthalpies in tris(indenyl)actinide hydrocarbyls

Abstract

Thorium- and uranium-ligand bond disruption enthalpies ( D(AnR)) have been obtained for the series of complexes Ind 3AnR, where Ind  C 9H 7 or 1-C 2H 5C 9H 6, An  Th or U, R = an alkyl group. All the new compounds have been characterised by microanalysis and spectroscopy. The thermodynamic data were determined by oxygen-free batch-titration, solution calorimetry from the enthalpies of solution of the organo- f-element complexes in toluene and from the subsequent enthalpies of alcoholysis with 2,2,2-trifluoroethanol. D(An) gas values obtained (95% of confidence) were as follows: (C 9H 7) 3ThCH 2Si(CH 3) 3, (397 ± 7) kJ mol −1; (C 9H 7) 3ThCH 3, (371 ± 6) kJ mol −1; (1-C 2H 5C 9H 6) 3ThCH 3, (365 ± 5) kJ mol −1; (C 9H 7) 3ThCH(CH 3) 2, (357 ± 8) kJ mol −1; (C 9H 7) 3UCH 3, (351 ± 2) kJ mol −1; (1-C 2H 5C 9H 6) 3UCH 3, (350 ± 4) kJ mol −1 and (C 9H 7) 3ThCH 2C 6H 5, (342 ± 9) kJ mol −1. These bond disruption enthalpies parallel, but are significantly larger than, those for the identical R functionalities in the (C 5H 5) 3ThR series. For corresponding Th/U pairs, the differénce { D(ThR) − D(UR)} is ca. 20 kJ mol −1.