PROTONATION AT THE AROMATIC RING VS AT THE CARBONYL GROUP OF LANTHANIDE-DIARYL KETONE DIANION SPECIES BY ARYL ALCOHOLS - FORMATION, STRUCTURAL CHARACTERIZATION, AND REACTIVITY OF LANTHANIDE ARYLOXIDE, MIXED ARYLOXIDE/ALKOXIDE, AND ARYLOXIDE/ENOLATE COMPLEXES

Reaction of the ytterbium-benzophenone dianion complex [Yb(mu-eta(1), eta(2)-OCPh(2))(HMPA)(2)](2) (1), which was formed by reaction of Yb metal with benzophenone in THF/HMPA, with 2,6-di-tert-butyl-4-methylphenol, yielded the ytterbium(II) aryloxide complex Yb(OAr)(2)(HMPA)(2) (2, Ar = C6H2-(t)Bu(2)2,6-Me-4) as a major product (80%) and the ytterbium(III) enolate complex Yb(OC(=CCH-CHCH2CH=CH)Ph)(2)(OAr)(HPPA)(2)(3, Ar = C6H2-(t)Bu(2)-2,6-Me-4) as a minor one (ca. 5% yield). In contrast, the similar reaction of samarium benzophenone dianion species with ArOH (Ar = C6H2-(t)Bu(2)-2,6-Me-4 or C6H3-(t)Bu(2)-2,6) gave the samarium(III) enolate complex Sm(OC(=CCH=CHCH2CH=CH)Ph)(2)(OAr)(HMPA)(2) (4a, Ar = C6H2-(t)Bu(2)-2,6-Me-4, 60%; 4b, Ar = C6H3-(t)Bu(2)-2,6, 56%) as a major product, while samarium(II) aryloxide analogous to 2 was not obtained. When ArOD (Ar = C6H2-(t)Bu(2)-2,6-Me-4) was used instead of ArOH, the deuterated enolate Sm(OC(=CCH=CHCHDCH=CH)Ph)(2)(OAr)(HMPA)(2) (4c, Ar = C6H2-(t)Bu(2)-2,6-Me-4) was formed. In the reaction with 2,6-(t)Bu(2)-4-Me-C6H2OH, a mixed aryloxide/alkoxide complex Sm(OCKPh2)(OAr)(2)(HMPA)(2) (5a, Ar = C6H2-(t)Bu(2)-2,6-Me-4) was also isolated in ca. 2% yield. When samarium fluorenone dianion species was allowed to react with 2,6-(t)Bu(2)-C6H3OH, the fluorenoxy analogue of 5a, Sm(fluorenoxy)(OAr)(2)(HMPA)(2) (6, Ar = C6H3-(t)Bu(2)-2,6, 64%), was obtained as the only isolable product. Upon heating at 180 degrees C in toluene, 4a,b isomerized into 7a,b Sm(OCHPh(2))(2)(OAr)(HMPA)(2) (7a, Ar = C(6)H(2)(t)Bu(2)-2,6,-Me-4;7b, Ar = C6H3-(t)Bu(2)-2,6). Deuterium labeled experiments indicated that this isomerization was an intramolecular one step 1,5-hydrogen shift process. Reaction of 4a and 7a with 2,6-(t)Bu(2)-C6H3OH yielded the aryloxy exchange products 4b and 7b, respectively, while the reaction of 7a with 2,6-Me(2)-C6H3OH gave the diphenylmethoxy substitution product Sm(OAr)(OAr'')(2)(HMPA)(2) (8, Ar = C6H2-(t)Bu(2)-2,6,-Me-4; Ar'' = C6H3-Me(2)-2,6). The mechanisms of these reactions are discussed. X-ray crystallographic studies reveal that 3, 4a, and 7b are isostructural, and so are 5a and 6. The central metal ions in these complexes are all five-coordinated in a trigonal bipyramid form (highly distorted in the case of 5a and 6) with two HMPA ligands at the apical and three anionic oxygen ligands at the equatorial positions.