Dinuclear neodymium and lanthanum bis(2,6-diisopropylphenyl) phosphate complexes bearing a hydroxide ligand: Catalytic activity of the nd complex in 1,3-diene polymerization

The reactions of K[(2,6-ⁱPr₂C₆H₃-O)₂POO] either with LaCl₃(H₂O)₇ or with Nd(NO₃)₃(H₂O)₆ in a 3:1 molar ratio, followed by vacuum drying and recrystallization from alkanes, have led to the formation of diaquapentakis[bis(2,6-diisopropylphenyl) phosphato]-μ-hydroxido-dilanthanum hexane disolvate, [La₂(C₂₄H₃₄O₄P)₅(OH)(H₂O)₂]·2C₆H₁₄, (1)·2(hexane), and tetraaquatetrakis[bis(2,6-diisopropylphenyl) phosphato]-μ-hydroxido-dineodymium bis(2,6-diisopropylphenyl) phosphate heptane disolvate, [Nd₂(C₂₄H₃₄O₄P)₄(OH)(H₂O)₄]·2C₆H₁₄, (2)·2(heptane). The compounds crystalize in the P2₁/n and P\overline{1} space groups, respectively. The diaryl-substituted organophosphate ligand exhibits three different coordination modes, viz. κ² O,O′-terminal [in (1) and (2)], κO-terminal [in (1)] and μ₂-κ¹ O:κ¹ O′-bridging [in (1) and (2)]. Binuclear structures (1) and (2) are similar and have the same unique Ln₂(μ-OH)(μ-OPO)₂ core. The structure of (2) consists of an [Nd₂{(2,6-ⁱPr₂C₆H₃-O)₂POO}₄(OH)(H₂O)₄]⁺ cation and a [(2,6-ⁱPr₂C₆H₃-O)₂POO]⁻ anion, which are bound via four intermolecular O—H...O hydrogen bonds. The molecular structure of (1) displays two O—H...O hydrogen bonds between OH/H₂O ligands and a κ¹ O-terminal organophosphate ligand, which resembles, to some extent, the `free' [(2,6-ⁱPr₂C₆H₃-O)₂POO]⁻ anion in (2). NMR studies have shown that the formation of (1) undoubtedly occurs due to intramolecular hydrolysis during vacuum drying of the aqueous La tris(phosphate) complex. Catalytic experiments have demonstrated that the presence of the coordinated hydroxide anion and water molecules in precatalyst (2) substantially lowered the catalytic activity of the system prepared from (2) in butadiene and isoprene polymerization compared to the catalytic system based on the neodymium tris[bis(2,6-diisopropylphenyl) phosphate] complex, which contains neither OH nor H₂O ligands.