Solvent‐Free Lanthanoid Complexes Derived From Chelation‐Supported Organoamide Ligands

Treatment of LnCl3 with three molar equivalents of LiL [(L = N-(2-methoxyphenyl)-N-(trimethylsilyl)amide (L1) or N-(2-phenoxyphenyl)-N-(trimethylsilyl)amide (L2)], generated in situ from LH and nBuLi, or with the isolated lithium complex [Li(L1)(OEt2)]2 (for Ln = Yb) in THF afforded the solvent-free homoleptic complexes [Ln(L)3] [Ln = Yb (1a), Er (1b), Sm (1c), Pr (1d), Nd (1e), L = L1; Ln = Yb (2a), Y (2b), Sm (2c), Nd (2d), La (2e), L = L2). With a 2:1 LiL (generated in situ) to LnCl3 molar ratio, the solvent-free heteroleptic complexes [Ln(L)2(μ-Cl)]2 were obtained for L = N,N-dimethyl-N′-trimethylsilylethane-1,2-diaminate (en′) [Ln = Yb (3a), Er (3b), Sm (3c), Nd (3d), La (3e)], but not for L1 or L2, which gave [Ln(L)3] [Ln = Yb (1a), Nd (1e), L = L1; Ln = Yb (2a), Nd (2d), La (2e), L = L2]. However, treatment of LnCl3 with two molar equivalents of the isolated crystalline lithium salt [Li(L1)(OEt2)]2 in THF gave, for the heavier lanthanoids, the solvent-free heteroleptic complexes [Ln(L1)2(μ-Cl)]2 [Ln = Yb (4a), Er (4b), Tb (4c)], although the homoleptic complex [Nd(L1)3] (1e) was obtained for Nd. In contrast, similar reactions of isolated [Li(L2)(DME)] with LnCl3 yielded the heteroleptic species [Ln(L2)2(μ-Cl)]2 only for Ln = Nd [5a·(PhMe)2]. At either end of the Ln series, the homoleptic [Ln(L2)3] complexes [Ln = Yb(2a), La (2e)] were obtained. Single crystal X-ray analyses of 1e or 2a−2e (as their PhMe or C5H9Me solvates) showed these complexes to be monomeric and six-coordinate (mer isomer), whereas the heteroleptic complexes 4a−4c, 5a were found to be dimeric with bridging chloride atoms. Two chelating [L1]− or [L2]− units [trans O(Me/Ph) and cis amido groups] are bound to each lanthanoid centre completing a six-coordinate very distorted octahedral environment. The X-ray structure of [Li(L1)(OEt2)]2 revealed a dimeric structure with each lithium four-coordinate and surrounded by one diethyl ether, two bridging amide nitrogens and a methoxy oxygen in a distorted tetrahedral array. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)