Synthesis of mono-amidinate-ligated rare-earth-metal bis(silylamide) complexes and their reactivity with [Ph3C][B(C6F5)4], AlMe3 and isoprene.

Amine elimination of rare-earth-metal tris(silylamide) complexes LnN(SiHMe(2))(2)(THF)(x) (Ln = Sc, x = 1; Ln = Y, x = 2) with 1 equiv. of the amidines [PhC(N-2,6-R(2)C(6)H(3))(2)]H afforded a series of neutral mono(amidinate) rare-earth-metal bis(silylamide) complexes [PhC(N-2,6-R(2)C(6)H(3))(2)]LnN(SiHMe(2))(2)(THF)(y) (R = Me, Ln = Sc, y = 0 (1); R = Me, Ln = Y, y = 1 (2); R = (i)Pr, Ln = Y, y = 1 (3)). Treatment of 1-3 with 1 equiv. of [Ph(3)C][B(C(6)F(5))(4)] in THF generated the corresponding cationic amidinate rare-earth-metal mono(silylamide) complexes [{PhC(N-2,6-R(2)C(6)H(3))(2)}Ln{N(SiHMe(2))(2)}(THF)(3)][B(C(6)F(5))(4)] (R = Me, Ln = Sc (4), Y (5); R = (i)Pr, Ln = Y (6)). When 1-3 were first activated with 1 equiv. of [Ph(3)C][B(C(6)F(5))(4)] in toluene, then treatment with THF gave the unexpected cationic amidinate rare-earth-metal amide complexes [{PhC(N-2,6-R(2)C(6)H(3))(2)}LnN{SiHMe(2)}{SiMe(2)N(SiHMe(2))(2)}(THF)(n)][B(C(6)F(5))(4)] (R = Me, Ln = Sc, n = 2 (7); R = Me, Ln = Y, n = 4 (8); R = (i)Pr, Ln = Y, n = 2 (9)). The reaction of 1-3 with excess AlMe(3) produced the heterometallic Ln/Al methyl complexes [PhC(N-2,6-R(2)C(6)H(3))(2)]Ln(μ-Me)(2)AlMe(2) (R = Me, Ln = Sc (10), Y (11); R = (i)Pr, Ln = Y (12)). All these complexes were well-characterized by elemental analysis, NMR spectroscopy and FT-IR spectroscopy. 2, 6 and 11 were further structurally authenticated by X-ray crystallography. The binary catalyst system of 1/[Ph(3)C][B(C(6)F(5))(4)] in toluene showed activity toward 3,4-selective polymerization of isoprene, whilst the tertiary catalyst systems of 1-3/[Ph(3)C][B(C(6)F(5))(4)]/AlMe(3) were highly active for cis-1,4-selective polymerization of isoprene.