SYNTHESIS, PROPERTIES, AND X-RAY STRUCTURES OF THE LANTHANIDE ETA-6-ARENE-BRIDGED ARYLOXIDE DIMERS LN2(O-2,6-I-PR2C6H3)6 AND THEIR LEWIS BASE ADDUCTS LN(O-2,6-I-PR2C6H3)3(THF)2 (LN=PR, ND, SM, GD, ER, YB, LU)

Reaction of 3 equiv of 2,6-diisopropylphenol with Ln[N(SiMe3)2]3 (Ln = Nd, Sm, Er) in refluxing toluene and subsequent crystallization yield pale blue (Nd), deep yellow (Sm), or light pink (Er) crystals of the tris(aryloxide) complexes Ln2(O-2,6-i-Pr2C6H3)6 (Ln = Nd (1), Sm (2), Er (3)) in good yield. X-ray crystallographic studies of 1 and 2 reveal centrosymmetric, dimeric units bridged by eta6-pi-arene interactions of a unique aryloxide ligand. Ln-O bond lengths average 2.122(9) (1, Nd) and 2.101(6) angstrom (2, Sm) for terminal ligands and 2.211(8) (1) and 2.198(5) angstrom (2) for bridging aryloxide ligands. Eta6-Arene bridges hold the dimeric units together with an average Ln-C distance of 3.035 angstrom for 1 and 2.986 and 3.016 angstrom for the two independent molecules in the asymmetric unit of 2. Compounds 1-3 react with THF in toluene solution to give the THF bisadducts Ln(O-2,6-i-Pr2C6H3)3(THF)2 (Ln = Nd (4), Sm (5), Er (6)) in essentially quantitative yield. In a related fashion, Lu(O-2,6-i-Pr2C6H3)3(THF)2 (7) was prepared following the reaction of Lu[N(SiMe3)2]3 with 3 equiv of diisopropylphenol in the presence of THF. The anhydrous trichlorides of Sm, Pr, Gd, and Yb react with 3 equiv of potassium 2,6-diisopropylphenoxide in THF solution to give the 5-coordinate THF bisadducts Ln(O-2,6-i-Pr2C6H3)3(THF)2 (Ln = Sm (5), Pr (8), Gd (9), Yb (10)). X-ray crystal structures have been obtained for Ln(O-2,6-i-Pr2C6H3)3(THF)2 (Ln = Er (6), Lu (7), Pr (8), Gd(9)), The four compounds are isostructural, and the molecular structure consists of a distorted trigonal bipyramidal lanthanide metal center with two axial THF and three equatorial aryloxide ligands. Ln-O distances for the aryloxide ligands average 2.078 (6, Er), 2.044 (7, Lu), 2.172 (8, Pr), and 2.130 (9, Gd) while Ln-O distances for the THF ligands average 2.346 (6), 2.296 (7), 2.482 (8), and 2.394 angstrom (9). Solution H-1 and C-13 NMR data, together with solution IR data, strongly support the proposal that the pi-arene-bridged dimeric structures of 1-3 are maintained in both benzene and toluene solutions at room temperature. Crystal data for 1 (at -162-degrees-C): monoclinic space group P2(1)/a, a = 9.536(2) angstrom, b = 21.219(6) angstrom, c = 17.162(5) angstrom, beta = 104.43(1)-degrees, V = 3363.0 angstrom3, Z = 2, d(calc) = 1.335 g cm-3, R(F) = 0.0518, R(w)(F) = 0.0522. Crystal data for 2 (at -70-degrees-C): monoclinic space group P2(1)/c, a = 9.555(2) angstrom, b = 21.301(2) angstrom, c = 33.220(4) angstrom, beta = 91.50(3)-degrees, V = 6759 angstrom3, Z = 2 (2 molecules per asymmetric unit), d(calc) = 1.341 g cm-3, R(F) = 0.0447, R(w)(F) = 0.0640. Crystal data for 6 (at -170-degrees-C): monoclinic space group P2(1), a = 9.693(1) angstrom, b = 19.141(3) angstrom, c = 12.083(l) angstrom, beta = 109.48(1)-degrees, V = 2113.50 angstrom3, d(calc) = 1.325 g cm-3, Z = 2, R(F) = 0.047, R(w)(F) = 0.063. Crystal data for 7 (at -70-degrees-C): monoclinic space group P2(1), a = 9.632(1) angstrom, b = 19.269(2) angstrom, c = 12.164(1) angstrom, beta = 109.52(1)-degrees, V = 2127.9 angstrom3, d(calc) = 1.328 g cm-3, Z = 2, R(f) = 0.021, R(w)(F) = 0.031. Crystal data for 8 (at -70-degrees-C): monoclinic space group P2(1), a = 9.857(2) k, b = 19.408(4) angstrom, c = 12.085(3) angstrom, beta = 109.81(2)-degrees, V = 2175.1 angstrom3, d(calc) = 1.247 g cm-3, Z = 2, R(F) = 0.045, R(w)(F) = 0.061. Crystal data for 9 (at -70-degrees-C): monoclinic space group P2(1), a = 9.755(1) angstrom, b = 19.377(2) angstrom, c = 12.184(1) angstrom, beta = 109.65(1)-degrees, V = 2168.1 angstrom3, d(calc) = 1.276 g cm-3, Z = 2, R(F) = 0.054, R(F) = 0.073.