Group 3 dialkyl complexes with tetradentate (L, L, N, O; L = N, O, S) monoanionic ligands: Synthesis and reactivity
Marinescu, SC; Agapie, T; Day, MW; Bercaw, JE
Tripodal, tetradentate phenols, (LCH(2))(2)NCH(2)-C(6)H(2)-3,5-(CMe(3))(2)-2-OH (L = CH(2)OCH(3) (1), CH(2)NEt(2) (2), 2-C(5)H(4)N (3), CH(2)SCMe(3) (5), CH(2)NMe(2) (6)), were synthesized, and metalations were performed via alkane elimination from yttrium and scandium trialkyl complexes to generate the corresponding dialkyl complexes [(LCH(2)CH(2))(2)NCH(2)-C(6)H(2)-3,5-(CMe(3))(2)-2-O]MR(2) (M = Y, L = OCH(3), R = CH(2)SiMe(2)Ph (7a); M = Y, L = NEt(2), R = CH(2)SiMe(2)Ph (7b); M = Sc, L = OCH(3), R = CH(2)SiMe(2)Ph (8a); M = Sc, L = SCMe(3), R = CH(2)SiMe(2)Ph (8b); M = Y, L = OCH(3), R = CH(2)SiMe(3) (9); M = Sc, L = OCH(3), R = CH(2)SiMe(3) (10)). X-ray crystallographic studies show that 7a,b and 8a adopt, in the solid state, mononuclear structures of C(1) symmetry. The (1)H NMR spectra of these dialkyl complexes in benzene-d(6) at high temperatures reveal exchange processes involving the ether groups and the alkyl groups. The dynamic behavior of species 7a, 8a, and 10 in toluene-d(8) was investigated by variable-temperature (1)H NMR spectroscopy. The activation parameters of the fluxional processes for 7a, 8a, and 10 were determined by line-shape and Eyring analyses (for 7a, Delta H = 7.3 +/- 0.3 kcal/mol and Delta S = -16 +/- 1.4 cal/(mol K); for 8a, Delta H = 9.9 +/- 0.5 kcal/mol and Delta S = -15.3 +/- 1.8 cal/ (mol K); for 10, Delta H = 10.8 +/- 0.6 kcal/mol and Delta S = -11.4 +/- 1.9 cal/(mol K)). These data establish that the dialkyl complexes 7a, 8a, and 10 undergo a nondissociative exchange process. The scandium dialkyl complex [(C(5)H(4)N-2-CH(2))(2)NCH(2)-C(6)H(2)-3,5-(CMe(3))(2)-2-O]Sc(CH(2)SiMe(2)Ph)(2) (11) was found to undergo clean activation of a C-H bond of a methylene linking a pyridine to the central nitrogen donor. This process follows first-order kinetics (k = [2.8(3)] x 10(-4) s(-1) at 0 degrees C). The yttrium dialkyl complexes 7a and 9 react with 1 equiv of [PhNHMe(2)](+)[B(C(6)F(5))(4)](-) in chlorobenzene-d(5), to generate a solution that slowly polymerizes ethylene. Compounds 7-10 also polymerize ethylene with low activity upon activation with MAO.