Alkyl Coordination in meso-(ONO)2- Supported Uranium(IV) Complexes

A series of U(IV) complexes bearing alkyl and chloride ligands in the trans configuration was synthesized and characterized. Starting with the diastereopure U(IV) trans-dichloride complex meso-((ONO)-O-tBu2P)UCl2(dtbpy) (1, (ONO)-O-tBu2P = 2,6-bis((di-tert-butylphosphino)methanolato)pyridine), four distinct alkyl groups were employed to prepare ((ONO)-O-tBu2P)U(R)Cl(dtbpy), where R = (trimethylsilyl)methyl (neosilyl), 2a, R = 2,2-dimethyl propyl (neopentyl), 2b, and R = 2-methyl-2-phenyl propyl (neophyl), 2c. Alkylation occurs with specificity but generates a predominant species and a minor species corresponding to anti/syn regioisomers relative to the P-tBu2 groups of the ligand. For synthesis using R = methyl, the dimethyl complex ((ONO)-O-tBu2P)U(Me)(2)(dtbpy), 2d, was prepared; the addition of 1 equiv of MeLi produced a mixture of products. Complexes 2a-2d were characterized using single crystal X-ray diffraction (SC-XRD), UV-vis-nIR, and H-1 and P-31 NMR spectroscopies.