New supporting ligands in actinide chemistry: tetramethyltetraazaannulene complexes with thorium and uranium

• Published in: Dalton transactions : an international journal of inorganic chemistry 2017-10, Vol.46 (4), p.13768-13782
• Main Authors: Hohloch, Stephan, Garner, Mary E, Parker, Bernard F, Arnold, John
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c7dt02682j

We report the synthesis, characterization, and preliminary reactivity of new heteroleptic thorium and uranium complexes supported by the macrocyclic TMTAA ligand (TMTAA = Tetramethyl-tetra-aza-annulene). The dihalide complexes Th(TMTAA)Cl 2 (THF) 2 ( 1 ), [UCl 2 (TMTAA)] 2 ( 2 ) and U(TMTAA)I 2 ( 3 ) are further functionalized to the Cp* derivatives ThCp*(TMTAA)Cl ( 4 ), UCp*(TMTAA)Cl ( 5 ) and UCp*(TMTAA)I ( 6 ) (Cp* = pentamethylcyclopentadienide). Compounds 4-6 are also obtained through a one-pot reaction from standard thorium( iv ) and uranium( iv ) starting materials, Li 2 TMTAA and KCp*. Complexes 1-6 function as valuable starting materials for salt metathesis chemistry. Treatment of precursors 4 or 5 with trimethylsilylmethyllithium (LiCH 2 TMS) results in the new actinide TMTAA alkyl complexes ThCp*(TMTAA)(CH 2 TMS) ( 7 ) and UCp*(TMTAA)(CH 2 TMTS) ( 8 ), respectively. The TMTAA-derived alkyl complexes ( 7 and 8 ) show unexpected stability and are stable for several weeks at room temperature in solution and in the solid-state. Additionally, double substitution of the halide ligands in 1-3 shows a strong dependence on the nucleophile used. While weaker nucleophiles, such as amides, and more sterically demanding nucleophiles, such as Cp (Cp = cyclopenadienide), favour the formation of bis-TMTAA "sandwich" complexes [An(TMTAA) 2 ] (An = Th ( 9 ) and An = U ( 10 )), the use of oxygen-functionalized ligands like the ODipp anion (Dipp = diisopropylphenyl) results in the formation of the doubly substituted species Th(ODipp) 2 TMTAA ( 11 ) and U(ODipp) 2 TMTAA ( 12 ). We also describe the divergent reactivity of the TMTAA ligand towards uranium( iii ). Unlike the syntheses of actinide( iv ) TMTAA complexes, the synthesis of a uranium( iii ) TMTAA was not successful and only uranium( iv ) species could be obtained. We report the synthesis, characterization, and preliminary reactivity of new heteroleptic thorium and uranium complexes supported by the macrocyclic TMTAA ligand (TMTAA = Tetramethyl-tetra-aza-annulene).