New synthetic routes to tris(pentaalkylcyclopentadienyl)lanthanide complexes including the X ray crystal structure of (C(5)Me(4)Et)(3)Sm

The synthetic chemistry leading to tris(pentamethylcyclopentadienyl)samarium complexes has been examined to determine why some routes fail and to develop routes superior to the first synthesis from (C(5)Me(5))(2)Sm and 1,3,5,7-cyclooctatetraene (COT). (C(5)Me(5))(2)Sm(THF) fails as a reagent since (C(5)Me(5))(3)Sm reacts with any THF present to form the ring-opened product (C(5)Me(5))(2)Sm[O(CH2)(4)C(5)Me(5)](THF). However, (C(5)Me(5))(2)Sm(OEt(2)) reacts cleanly with COT to form (C(5)Me(5))(3)Sm and (C(5)Me(5))Sm(C8H8). A more efficient synthesis involves the reaction of (C(5)Me(5))(2)Sm(OEt(2)) with (C(5)Me(5))(2)Pb which generates (C(5)Me(5))(3)Sm in >90% yield. This route has been used to synthesize the more sterically crowded tris(pentaalkylcyclopentadienyl) complex (C(5)Me(4)Et)(3)Sm, which shows that the limit of steric crowding in this class has not yet been realized. X-ray crystallographic study of(C(5)Me(4)Et)(3)Sm revealed a trigonal planar arrangement of ring centroids around samarium with an average Sm-C(C(5)Me(5)) distance of 2.834 Angstrom. Two ethyl groups point toward samarium with a minimum Sm-C distance of 3.620-(13) Angstrom.