Probing the Dynamic Features of Bis(aminocyclopentadienyl) and Bis(aminoindenyl) Zirconium Complexes

Abstract

Treatment of 3-phenylcyclopent-2-enone (1) with either morpholine or pyrrolidine in the presence of 3 Å molecular sieves yielded the corresponding cyclopentadienamines 2a and 2b. Subsequent deprotonation with n-butyllithium followed by the reaction with zirconium tetrachloride led to the formation of the amino-substituted bent metallocenes 4a and 4b. Crystallization furnished the isomerically pure complex meso-bis(phenyl-3-pyrrolidinylcyclopentadienyl)zirconium dichloride (meso-4b), which was characterized by X-ray diffraction. Complex meso-4b exhibits a C(Cp)-N bond length of 1.349(3) Å. A rotational barrier of ∆G q (CN-rot) (248 K) ) 12.1 ( 0.2 kcal mol -1 was measured for meso-4b in solution by dynamic 600 MHz 1 H NMR spectroscopy. Similar treatment of 2-indanone with morpholine, followed by deprotonation and reaction with ZrCl 4 , gave bis(2-morpholinoindenyl)ZrCl 2 (7a), which was also characterized by an X-ray crystal structure analysis (the indenyl-C2/12-N bond lengths are 1.349(5)/1.381(5) Å). Two rotational processes were subsequently frozen out on the 600 MHz 1 H NMR time scale upon decreasing the temperature from ambient to give a C-N rotational barrier of ∆G q (CN-rot) (268 K) ) 12.9 ( 0.2 kcal mol -1 and an activation energy of the rotation about the zirconium-Cp(indenyl) vector of ∆G q (Ind-rot) (178 K) ) 7.6 ( 0.5 kcal mol -1 . In solution and in the solid state only a single C 2 -symmetric metallocene rotamer of 7a was detected. The same is found for bis(2-pyrrolidinoindenyl)ZrCl 2 (7b). By dynamic 1 H NMR spectroscopy the two rotational activation barriers of complex 7b were determined as ∆G q (CN-rot) (338 K) ) 16.4 ( 0.2 kcal mol -1 and ∆G q (Ind-rot) (198 K) ) 9.1 ( 0.5 kcal mol -1 .

Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

“…In a similar fashion, the methyl signal at δ ϭ 0.34 ppm and the methine signals at δ ϭ 6.84 and 5.83 ppm show considerable broadening at 218Ϫ188 K, and split into two resonances below 178 K. Finally, at 173 K a 6.3 Hz 3 J coupling was observed for the methine protons of the six-membered ring. Similar splitting was observed for most of the 13 C NMR signals of 51 recorded at 173 K. Analogous to the amino-substituted zirconocenes 12 and 13 described by Erker and co-workers, and discussed earlier in this microreview (vide supra), [44] the signal splitting indicates a single C 2 -symmetric bent-metallocene conformation that is detected when the equilibration of 51 with its nonsuperimposable mirror image becomes frozen on the NMR time scale (Scheme 17). [111] The calculated activation barrier for 51,…”

“…[40,44,49,52] For 2-(dimethylamino)indene, the synthesis of both dimethylsilylene- [38] and ethylene-bridged [39] bis(indenyl) analogues 18 and 19 in good yields (59 and 77%, respectively) has been described that employs standard deprotonation/ alkylation and deprotonation/silylation procedures in THF or diethyl ether solution (Scheme 1). The synthesis of 3-aminoindenes by enamine reaction of 1-indanone with secondary amines has also been reported.…”

“…[38Ϫ40, 44,45] In terms of metallation yield, toluene appears to be the preferred solvent. The bis(2-dimethylami-Scheme 1.…”

“…For the complexes 12 and 13, a detailed 600 MHz 1 H NMR spectroscopic study in [D 8 ]toluene by Erker and co-workers reveals two different dynamic processes, which freeze on the NMR timescale when the monitoring temperature is lowered (Scheme 4). [44] For complex 12, a CϪN rotational barrier of ∆G ‡ (CN-rot) (338 K) ϭ 16.4 Ϯ 0.2 kcal·mol Ϫ1 and an activation energy for the rotation about the zirconiumϪCp(indenyl) vector of ∆G ‡ (Ind-rot) (198 K) ϭ 9.1 Ϯ 0.5 kcal·mol Ϫ1 was determined. For the 2-morpholinoindenyl complex 13, the corresponding values were measured as ∆G ‡ (CN-rot) (268 K) ϭ 12.9 Ϯ 0.2 kcal·mol Ϫ1 and ∆G ‡ (Ind-rot) (178 K) ϭ 7.6 Ϯ 0.5 kcal·mol…”

Synthesis, Characterization, and Catalytic Properties of ansa‐Zirconocenes [Zr{1‐Me2Si(3‐η5‐C9H5R)2}Cl2] (R = Me, nPr, nBu, and Bz)

“…[15][16][17][18][19][20] The angles between some relevant planes are collected in Table 2 along with the geometrical parameters described in Figure 3 for compounds meso-9, rac-10, and the unsubstituted parent rac-[Zr{1-Me 2 Si(η 5 -C 9 H 6 ) 2 }Cl 2 ]. [12] As usual for bent metallocenes, the overall coordination environment is best described by the set of parameters depicted in Figure 3, which describes the metal accessibility.…”