The homoleptic compounds [U(salan-R2)2] (R = Me (1), tBu (2)) were prepared in high yield by salt-metathesis reactions between UI4(L)2 (L = Et2O, PhCN) and 2 equiv of [K2(salan-R2)] in THF. In contrast, the reaction of the tetradentate ligands salan-R2 with UI3(THF)4 leads to disproportionation of the metal and to mixtures of U(IV) [U(salan-R2)2] and [U(salan-R2)I2] complexes, depending on the ligand to M ratio. The reaction of K 2salan-Me2 ligand with U(IV) iodide and chloride salts always leads to mixtures of the homoleptic bis-ligand complex [U(salan-Me 2)2] and heteroleptic complexes [U(salan-Me 2)X2] in different organic solvents. The structure of the heteroleptic complex [U(salan-Me2)I2(CH3CN)] (4) was determined by X-ray studies. Heteroleptic U(IV) and Th(IV) chloride complexes were obtained in good yield using the bulky salan-tBu 2 ligand. The new complexes [U(salan-tBu 2)Cl2(bipy)] (5) and [Th(salan-tBu 2)Cl2(bipy)] (8) were crystallographically characterized. The salan-tBu2 halide complexes of U(IV) and Th(IV) revealed good precursors for the synthesis of stable dialkyl complexes. The six-coordinated alkyl complexes [Th(salan-tBu2)(CH 2SiMe3)2] (9) and [U(salan-tBu 2)(CH2SiMe3)2] (10) were prepared by addition of LiCH2SiMe3 to the chloride precursor in toluene, and their solution and solid-state structures (for 9) were determined by NMR and X-ray studies. These complexes are stable for days at room temperature. Preliminary reactivity studies show that CO2 inserts into the An-C bond to afford a mixture of carboxylate products. In the presence of traces of LiCl, crystals of the dimeric insertion product [Th 2Cl(salan-tBu2)2(μ- η1:η1-O2CCH2SiMe 3)2(μ-η1:η2-O 2CCH2SiMe3)] (11) were isolated. The structure shows that CO2 insertion occurs in both alkyl groups and that the resulting carboxylate is easily displaced by a chloride anion. © 2012 American Chemical Society.