Dizirconium complexes supported by preorganized binucleating bis(amidinates)

作者：Hagadorn JR^*; McNevin MJ; Wiedenfeld G; Shoemaker R

来源：Organometallics, 2003, 22(23): 4818-4824.

DOI：10.1021/om034063c

Several new dizirconium complexes have been prepared using preorganized bis(amidinate) ligands featuring rigid 9,9-dimethylxanthene backbones. Reaction of the bis(amidine) (LXanH12)-L-iPr with 2 equiv of Zr(NMe2)(4) forms the hexa(amido) derivative (LXanZr2)-L-iPr(NMe2)(6) (1) in good yield. In a similar reaction, the unsymmetrical bis(amidine) (LXanH2)-L-tBu,Et reacts with Zr(NMe2)(4) to form (LXanZr2)-L-tBu,Et(NMe2)(6) (2) as a 9:1 mixture Of C-2- and C-s-symmetrical rotational diastereomers. At elevated temperatures the two diastereomers interconvert, and the C-2-form is slightly preferred thermodynamically (ca. 0.3 kcal/mol). Metathesis reaction of (LXanLi2)-L-iPr with 2 equiv of CpZrCl3 affords the mixed amidinate-cyclopentadienyl anion derivative (LXanZr2Cp2Cl4)-L-iPr (3) in good yield. Solutions of 3 are readily converted to the sigma-alkyl derivatives (LXanZr2Cp2Me4)-L-iPr (4) and (LXanZr2Cp2)-L-iPr(CH2SiMe3)(4) (5) by treatment with dialkyl-magnesium and organolithium reagents. At slightly elevated temperatures, solutions of 5 react with H-2 to form yellow tetrahydride (LXanZr2Cp2H4)-L-iPr (6). The solid-state structure of 6 reveals that three of the four hydrido ligands bridge the two metal centers, resulting in a short intermetal separation of 3.1050(6) Angstrom. In solution, 6 undergoes a rapid fluxional process (observed by H-1 NMR spectroscopy) that exchanges the four hydrides. At low temperature, three distinct hydrides can be observed, which is consistent with either a dibridged structure or a tribridged species undergoing rapid exchange of the terminal hydride with only one Of the three bridging hydrides.

• 出版日期2003-11-10