C2-Symmetric Fluorous Diamino-Dialkoxide Complexes of Early Transition Metals

Abstract

Coordination of the new fluorous diamino-dialkoxy tetradentate ligands [OC(CF3)2CH2N(Me)(CH2)nN(Me)C(CF3)2O]2- (n = 2, [ON2NO]2-; n = 3, [ON3NO]2-) onto group 3 and group 4 metals has been studied. The diamino-diols [ONnNO]H2 (n = 2, 1a; n = 3, 1b), prepared by ring-opening of with the corresponding secondary diamine, react cleanly with Ti(OiPr)4 to yield quantitatively the dialkoxy complexes [ONnNO]Ti(OiPr)2 (n = 2, 2a; n = 3, 2b). The chloride displacement reaction between TiCl4 and 1a in the presence of NEt3 leads to the dichlorotitanium complex [ON2NO]TiCl2 (3). Alkane elimination and amine elimination reactions provide efficient routes to the zirconium and yttrium complexes [ON2NO]Zr(CH2Ph)2 (4), [ON2NO]Y(N(SiHMe2)2)(THF) (5), and [ON2NO]Y(CH2SiMe3)(THF) (6). X-ray crystallographic analyses show that in the solid state 3 and 4 adopt a distorted octahedral structure with a trans-O, cis-N, cis-X ligand (X = Cl, CH2Ph). Solution NMR data for 2−4 are consistent with this C2-symmetric structure. Variable-temperature NMR studies establish that 4 undergoes inversion of metal configuration (i.e., Λ/Δ isomerization, racemization) on the NMR time scale at elevated temperatures (ΔG⧧(racemization) = 17.0(1) kcal/mol). An X-ray crystallographic analysis reveals that 6 adopts in the solid state a seven-coordinate, distorted structure due to Y···F coordination to one of the four CF3 substituents (Y−F = 2.806(2) Å). In contrast, NMR studies show that 6 adopts a C2-symmetric structure in solution analogous to those of 2−4, while 5 features a C1-symmetric structure.