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

Coordination of the new fluorous diamino-dialkoxy tetradentate ligands [OC(CF 3 ) 2 CH 2 N(Me)(CH 2 ) n N(Me)C(CF 3 ) 2 O] 2 - ( n = 2, [ON 2 NO] 2 -; n = 3, [ON 3 NO] 2 - ) onto group 3 and group 4 metals has been studied. The diamino-diols [ON n NO]H 2 ( n = 2, 1a; n = 3, 1b ), prepared by ring-opening of with the corresponding secondary diamine, react cleanly with Ti(O i Pr) 4 to yield quantitatively the dialkoxy complexes [ON n NO]Ti(O i Pr) 2 ( n = 2, 2a; n = 3, 2b ). The chloride displacement reaction between TiCl 4 and 1a in the presence of NEt 3 leads to the dichlorotitanium complex [ON 2 NO]TiCl 2 ( 3 ). Alkane elimination and amine elimination reactions provide efficient routes to the zirconium and yttrium complexes [ON 2 NO]Zr(CH 2 Ph) 2 ( 4 ), [ON 2 NO]Y(N(SiHMe 2 ) 2 )(THF) ( 5 ), and [ON 2 NO]Y(CH 2 SiMe 3 )(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, CH 2 Ph). Solution NMR data for 2 − 4 are consistent with this C 2 -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 (Δ G ⧧ (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 CF 3 substituents (Y−F = 2.806(2) Å). In contrast, NMR studies show that 6 adopts a C 2 -symmetric structure in solution analogous to those of 2 − 4, while 5 features a C 1 -symmetric structure.