Bis(amido)cyclodiphosph(III)azane Complexes of Yttrium and the Lanthanides

Abstract

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.