Synthesis and X-ray crystal structures of the samarium mono(pentamethylcyclopentadienyl) aryloxide complexes (η-C5Me5)Sm(O-2,6-t-Bu2C6H3)2(THF) and [(η-C5Me5)Sm(O-2,6-i-Pr2C6H3)3Li(THF)].: Differences in metathesis chemistry of 2,6-di-iso-propylphenoxide and 2,6-di-tert-butylphenoxide ligands

The reaction of SmCl3 with three equivalents of KO-2,6-t-Bu2C6H3 in THF produces the tris(aryloxide) complex Sm(OAr)(3),(THF) (Ar = 2,6-t-Bu2C6H3, 1). Complex 1 undergoes clean metathesis reaction with one equivalent of LiC5Me5 to form the mono(pentamethylcyclopentadienyl) aryloxide derivative (eta-C5Me5)Sm(OAr)(2)(THF) (2). In contrast, an analogous reaction of LiC5Me5 with the 2,6-di-iso-propylphenoxide complex Sm(OAr*)(3)(THF)(2)(Ar* = 2,6-i-Pr2C6H3, 3) leads to overall addition of the alkali metal reagent, and isolation of the lithium-containing 'ate' complex [(eta-C5Me5)Sm(OAr*)(mu-OAr*)(2)Li(THF)] (4). Compounds 2 and 4 have been subjected to single-crystal X-ray diffraction studies. Complex 2 features a three-legged piano-stool geometry, with Sm-O distances to the aryloxide ligands of 2.133(6) and 2.188(6) Angstrom, and a Sm-O(THF) distance of 2.435(7) Angstrom. Complex 4 also exhibits a three-legged piano-stool geometry, with two of the aryloxide oxygen atoms coordinated to a lithium metal center. A THF ligand completes the coordination sphere of the lithium. The Sm-O bond lengths to the lithium-coordinated aryloxide oxygens (2.250(6) and 2.247(5) Angstrom) are longer than the distance to the terminal aryloxide (Sm-O = 2.144(6) Angstrom). The Li-O distances range from 1.876(17) to 1.945(18) Angstrom. (C) 1999 Elsevier Science S.A. All rights reserved.