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The selective separation of toxic heavy metals such as uranyl can be accomplished using ligands with stereognostic hydrogen bonding interactions to the uranyl oxo group, as proposed by Raymond and co-workers (T. S. Franczyk, K. R. Czerwinski and K. N. Raymond, J. Am. Chem. Soc., 1992, 114, 8138-8146). Recently, several ligands possessing this weak interaction have been proposed involving the hydrogen bonding of NH and OH based moieties with uranyl oxygen. We herein report the structurally and spectroscopically characterized CH?O hydrogen bonding using a sterically bulky amide based ligand. In conjunction with experiments, electronic structure calculations are carried out to understand the structure, binding and the strength of the CH?O hydrogen bonding interactions. This weak interaction is mainly due to the steric effect caused by a bulky substituent around the donor group which has direct relevance in designing novel ligands in nuclear waste management processes. Although the kinetics are very slow, the ligand is also highly selective to uranyl in the presence of other interfering ions such as lanthanides.

From the temperature dependence of NMR spectra, two separate conformational processes can be distinguished and studied in N,N-diisopropylneopentylamine.A high-barrier inversion/ rotation process involves eclipsing of t-butyl and isopropyl groups, while a rotation process with a lower barrier involves lesser eclipsing interactions.Molecular mechanics calculations help illustrate the ground state conformations involved.Barriers are smaller when the neopentyl group is replaced by less branched primary alkyl groups.

Sterically hindered tertiary amines 7,8,14,17 are synthesized by reaction of the iminium salts 3,4, and 16 with Grignard compounds 5,12 or alkyllithium compounds 11,13.Hindered guanidines 24 are prepared from chloroformamidinium 22 or (dichloromethane)iminium salts 26 and primary amines 23.The pKa values of the amines 7,8,17, and guanidines 24 are measured, and their alkylation with methyl fluorosulfonate (31) is studied.