Synthesis, Structures, and Reactivity of (R6-acen)ZrR'2 and (R6-acen)Zr(R')+ Complexes (R = H, F; R' = CH2CMe3, CH2Ph)

Abstract

The synthesis, structures, and reactivity of neutral and cationic Zr(IV) alkyl complexes incorporating acen and hexafluoroacen ligands are described. Alkane elimination reactions of H2(R6-acen) (6a, R = F; 6b, R = H) and ZrR'4 afford (R6-acen)ZrR'2 (11a, R = F, R' = CH2CMe3; 11b, R = H, R' = CH2CMe3; 12, R = F, R' = CH2Ph) in high yield. 11a has been characterized by X-ray diffraction: space group P1̅, a = 12.280(3) Å, b = 12.731(3) Å, c = 8.825(3) Å, α = 96.66(2)°, β= 97.21(2)°, γ = 76.68(2)°, V = 1327(1) Å3, Z = 2, R = 0.042, Rw= 0.049. 11a adopts a trigonal prismatic structure with a twisted F6-acen ligand and a large angle (129.9(2)°) between the neopentyl groups. Solution NMR data for 11a,b and 12 are in accord with similar structures. The reaction of 11a,b with [HNMe2Ph][B(C6F5)4] yields cationic amine adducts [(R6-acen)Zr(CH2CMe3)(NMe2Ph)][B(C6F5)4] (13a, R = F; 13b, R = H). Similarly, the reaction of 11a with [HNEt2Ph][B(C6F5)4] yields [(F6-acen)Zr(CH2-CMe3)(NEt2Ph)][B(C6F5)4] (14). However, the reaction of 11a with [HNMePh2][B(C6F5)4] in benzene yields the base-free complex [(F6-acen)Zr(CH2CMe3)][B(C6F5)4] (15). Complex 14 decomposes in CH2Cl2 to [NEt2Ph(CH2Cl)][B(C6F5)4] (18), an unusual chloride-bridged dinuclear cation [{(F6-acen)Zr(CH2CMe3)}2(μ-Cl)][B(C6F5)4] (19), and free NEt2Ph in 1:1:1.3 ratio. It is proposed that this reaction proceeds via nucleophilic attack of NEt2Ph on the CH2Cl2 ligand of an intermediate (F6-acen)Zr(CH2CMe3)(CH2Cl2)+ solvent adduct (formed by NEt2Ph dissociation from 14), followed by trapping of the resulting (F6-acen)Zr(CH2CMe3)-Cl (17) by a second equivalent of 14. 13a is stable toward this process because the amine does not dissociate extensively. Direct chloride abstraction from CH2Cl2 is not observed; base-free 15 is very stable in CH2Cl2. 13a has been characterized by X-ray diffraction: space group = C2/c, a = 39.707(4) Å, b = 11.226(1) Å, c = 30.045(3) Å, β = 126.667(9)°, V= 10742.6(22) Å3, Z = 8, R = 0.0608, Rw= 0.0880. The (F6-acen)Zr(CH2CMe3)(NMe2Ph)+ cation of 13a adopts a distorted octahedral structure with a more planar F6-acen ligand (vs that in 11a) and a large angle (144.7(2)°) between the neopentyl and amine ligands. 13a and 15 react with Lewis bases to yield [(F6-acen)Zr(CH2CMe3)(L)n][B(C6F5)4] adducts (n = 1, PMe2Ph (22); n = 2, L = PMe3 (21), CH3CN (24)). 13a inserts CO, yielding a η2-acyl cation [(F6-acen)Zr{η2-C(═O)CH2CMe3}(NME2Ph)][B(C6F5)4] (25, two isomers). 13a also reacts with 2 equiv of benzophenone to yield an alkoxide ketone complex [(F6-acen)Zr(OCPh2CH2CMe3)-(O═CPh2)][B(C6F5)4] (26). Neither 13a nor 15 reacts with ethylene or 2-butyne in the absence of Al cocatalysts. © 1995, American Chemical Society. All rights reserved.