Synthesis and thermal reactivity of organoscandium and yttrium complexes of sterically less bulky salicylaldiminato ligands

Scandium and yttrium bis(ligand) mono(alkyl) complexes, of N-phenyl (L1) N-2-isopropylphenyl (L2) and N-mesityl (L3) substituted orthotert-butylsalicylaldiminato ligands were prepared by alkane elimination from [M(CH2SiMe2R)3(THF)2](R = Me, Ph) and two equivalents of proteo ligand (HL). The resulting [L2M(THF)n(CH2SiMe2R)](n= 0-2, L = L1(1), L2(2), L3(3)) complexes are thermally unstable, decomposing rapidly between -20 and 20 °C. In order to gain insight in to ligand features necessary to impart thermal stability in early transition metal organometallic chemistry, the decomposition pathways of 1-3 have been investigated and compared with more sterically congested N-2,6-diisopropylphenyl substituted analogues. Compounds 1 and 2 decompose rapidly and cleanly at room temperature by 1,3-migration of the entire CH2SiMe2R group to the aldimine carbon. By contrast, L3 mono(alkyls)3 decompose cleanly by metallation of an ortho-C6H2Me3 group. In the case of yttrium, the metallated alkyl undergoes subsequent 1,3-migration to the aldimine carbon, forming a five-membered C4N-ring.