Synthesis of new heteroleptic strontium complexes

Synthesis of Mononuclear Strontium Complexes with Polyether and β-Diketonato Ligands

Strontium β-diketonate complexes were synthesized by the substitution reaction of the bis(trimethylsilyl) amide of Sr(btsa)₂·2DME with an ethereal group and β-diketonate ligands. The compounds [Sr(tmge)(btsa)]₂ (1), [Sr(tod)(btsa)]₂ (2), Sr(tmgeH)(tfac)₂ (3), Sr(tmgeH)(acac)₂ (4), Sr(tmgeH)(tmhd)₂ (5), Sr(todH)(tfac)₂ (6), Sr(todH)(acac)₂ (7), Sr(todH)(tmhd)₂ (8), Sr(todH)(hfac)₂ (9), Sr(dmts)(hfac)₂ (10), [Sr(mee)(tmhd)₂]₂ (11), and Sr(dts)(hfac)₂·DME (12) were obtained and analyzed by various techniques, including FT-IR, NMR, TGA (thermogravimetric analyses), and elemental analysis. Complexes 1, 3, 8, 9, 10, 11, and 12 were further structurally confirmed by single-crystal X-ray crystallography, where complexes 1 and 11 showed dimeric structures with μ₂-O bonds of ethereal groups or tmhd ligands, and complexes 3, 8, 9, 10, and 12 displayed monomeric structures. Interestingly, compounds 10 and 12, which preceded trimethylsilylation of the coordinating ethereal alcohols such as tmhgeH and meeH in the presence of HMDS as by-products due to highly increasing acidity of them, originated from electron-withdrawing two hfac ligands.

Heteroleptic strontium complexes stabilized by donor-functionalized alkoxide and β-diketonate ligands

Heteroleptic complexes of strontium () were prepared by employing β-diketonates and donor-functionalized alkoxides as coordinating ligands. The results illustrate the effect of alkoxide substituent groups on the overall structures of the complexes. The presence of a terminal methoxy group in the alkoxide ligands leads to the formation of trimeric complexes , whereas the substituents on the amine nitrogen prove to have less influence in determining the structure. The attempts to increase steric bulkiness of the aminoalkoxide ligands by introducing ethyl groups on the amine nitrogen and to the alkoxy carbon did not lead to a structural change from the dimeric form in but resulted in structurally interesting strontium complexes. In trimeric complexes , the three strontium atoms were held together by two μ3-O bonds using alkoxide oxygen atoms and two μ2-O bonds using a combination of alkoxide and β-diketonate ligand oxygens. The strontium metal centers in these complexes exhibit seven-coordination states in and , whereas exhibits one six-coordinated and two seven-coordinated strontium metals in its structure. All of the complexes were characterized using FT-NMR, FT-IR, elemental analyses, and thermogravimetric (TG) analyses.