RESUMO
The reaction of potassium 2,5-bis[N-(2,6-diisopropylphenyl)iminomethyl]pyrrolyl [(dip(2)-pyr)K] with the borohydrides of the larger rare-earth metals, [Ln(BH(4))(3)(thf)(3)] (Ln=La, Nd), afforded the expected products [Ln(BH(4))(2)(dip(2)-pyr)(thf)(2)]. As usual, the trisborohydrides reacted like pseudohalide compounds forming KBH(4) as a by-product. To compare the reactivity with the analogous halides, the dimeric neodymium complex [NdCl(2)(dip(2)-pyr)(thf)](2) was prepared by reaction of [(dip(2)-pyr)K] with anhydrous NdCl(3). Reaction of [(dip(2)-pyr)K] with the borohydrides of the smaller rare-earth metals, [Sc(BH(4))(3)(thf)(2)] and [Lu(BH(4))(3)(thf)(3)], resulted in a redox reaction of the BH(4) (-) group with one of the Schiff base functions of the ligand. In the resulting products, [Ln(BH(4)){(dip)(dip-BH(3))-pyr}(thf)(2)] (Ln=Sc, Lu), a dinegatively charged ligand with a new amido function, a Schiff base, and the pyrrolyl function is bound to the metal atom. The by-product of the reaction of the BH(4) (-) anion with the Schiff base function (a BH(3) molecule) is trapped in a unique reaction mode in the coordination sphere of the metal complex. The BH(3) molecule coordinates in an eta(2) fashion to the metal atom. The rare-earth-metal atoms are surrounded by the eta(2)-coordinated BH(3) molecule, the eta(3)-coordinated BH(4) (-) anion, two THF molecules, and the nitrogen atoms from the Schiff base and the pyrrolyl function. All new compounds were characterized by single-crystal X-ray diffraction. Low-temperature X-ray diffraction data at 6 K were collected to locate the hydrogen atoms of [Lu(BH(4)){(dip)(dip-BH(3))-pyr}(thf)(2)]. The (DIP(2)-pyr)(-) borohydride and chloride complexes of neodymium, [Nd(BH(4))(2)(dip(2)-pyr)(thf)(2)] and [NdCl(2)(dip(2)-pyr)(thf)](2), were also used as Ziegler-Natta catalysts for the polymerization of 1,3-butadiene to yield poly(cis-1,4-butadiene). Very high activities and good cis selectivities were observed by using each of these complexes as a catalyst in the presence of various cocatalyst mixtures.
RESUMO
The first cyclodiphosph(III)azane complexes of the rare-earth elements have been synthesized. Reactions of the lithium salt cis-[(tBuNP)(2)(tBuN)(2){Li(thf)}(2)] with anhydrous yttrium trichloride or the heavier lanthanide trichlorides resulted in the corresponding cyclodiphosph(III)azane complexes [Li(thf)(4)][{(tBuNP)(2)(tBuN)(2)}LnCl(2)] (Ln=Y (1 a), Ho (1 b), Er (1 c)). The single-crystal X-ray structures showed that compounds 1 a-c consisted of ion pairs composed of a [Li(thf)(4)](+) cation and a C(2v) symmetric [{(tBuNP)(2)(tBuN)(2)}LnCl(2)](-) anion. By treating cis-[(tBuNP)(2)(tBuN)(2){Li(thf)}(2)] with anhydrous SmCl(3) in THF, the trimetallic complex [{(tBuNP)(2)(tBuN)(2)}SmCl(3)Li(2)(thf)(4)] (2) was obtained. The influence of the ionic radii of the lanthanides can be seen in the single-crystal X-ray structure of compound 2, which forms a six-membered Cl-Li-Cl-Li-Cl-Sm metallacycle. The ring adopts a boat conformation in which one chlorine atom and the samarium atom are displaced from the Cl(2)Li(2) least-square plane. Heating of the metalate complexes in toluene resulted in the extrusion of lithium chloride and the formation of the neutral dimeric metal chloride complexes of the composition [(tBuNP)(2)(tBuN)(2)LnCl(thf)](2) (Ln=Y (3 a), La (3 b) Nd (3 c), Sm (3 d)). Furthermore, treating 1 a with KNPh(2) resulted in a lithium metalate complex of the composition [Li(thf)(4)][{(tBuNP)(2)(tBuN)(2)}Y(NPh(2))(2)] (4). The coordination mode of the {(tBuNP)(2)(tBuN)(2)}(2-) ligand in 4 is different to that observed in 1 a-c, 2, and 3 a-d; instead of a symmetric eta(2) coordination of the ligand, a heterocubane-type structure is observed in the solid state. The complex [(tBuNP)(2)(tBuN)(2)NdCl(thf)] (3 c) was used as a Ziegler-Natta catalyst for the polymerization of 1,3-butadiene to poly-cis-1,4-butadiene. The observed activities of the Ziegler-Natta catalyst strongly depended upon the nature of the cocatalyst; in some case very high turnover rates and a cis selectivity of 93-94 % were observed.
