sigma vs. π bonding in organoactinides and possibilities of CO coordination to actinides

Results of studies of the coordination of sigma-methyl and π-cyclopentadienyl (Cp) groups to iron and uranium are reported. The discussion focuses on the 3d64s04p0 Fe(II) and 5f06d07s0790 U(VI) electron counts with the charge on the hypothetical molecules set at +1 for FECp and +5 for UCp. Changes in overlap population were studied as a function of the M-Cp and M-CH3 (M=metal) separation, and the observed results are explained on the basis of the nature of the M-Cp and M-CH3 bonds. The small U-Cp overlap population were explained by assuming that the weak π bond of the U-Cp carries very weak covalent character while covalency of the Fe-Cp bond is substantial. The U-CH3 sigma bond is strongly covalent. From the analysis of the character of the bonding of actinides to Cp and CH3, synthesis of actinide compounds with neutral π ligands such as olefins dienes, etc. is seen as very difficult while the possibility of neutral sigma ligand bonding with actinides seems highly possible. The most likely possibility of complex formation is coordination with CO