| 16471998 |
Hlavinka ML, McNevin MJ, Shoemaker R, Hagadorn JR: Dizinc alkoxides and amides supported by binucleating bis (amidoamine) ligands. Inorg Chem. 2006 Feb 20;45(4):1815-22.
Several new dizinc complexes that are supported by dianionic bis (amidoamine) ligands are reported. Reaction of N,N'-bis (2-dimethylaminoethyl) dibenzofuran-4,6-diamine ((Me) LH (2)) with 2 equiv of EtZn (O (i) Pr) forms the dizinc bis (alkoxide) (Me) LZn2 (O (i) Pr) 2 (1), which was isolated in 76% yield. Similarly, (Me) LH2 reacts cleanly with EtZn (OPh) and EtZn (OCHPh2) to form (Me) LZn2 (OPh) 2 (2) and (Me) LZn2 (OCHPh2) 2 (3), respectively. The solid-state structures of 1 and 2 feature puckered [Zn2 (mu-OR) 2] 2+ cores, with short intermetal separations (2.81-2.88 Angstroms). Overall, the molecules have approximate (noncrystallographic) C2v symmetry. The use of the more-hindered (i) Pr-substituted ligand N,N'-bis (2-diisopropylaminoethyl) dibenzofuran-4,6-diamine (i (Pr) LH2) to prepare zinc alkoxides gave similar results. Thus, reaction of i (Pr) LH2 with 2 equiv of EtZn (OPh), EtZn (OMe), EtZn (OCHPh2), and EtZn (OCH2Ph) forms i (Pr) LZn2 (OPh) 2 (4), i (Pr) LZn2 (OMe) 2 (5), i (Pr) LZn2 (OCHPh2) 2 (6), and i (Pr) LZn2 (OCH2Ph) 2 (7), respectively (isolated yields 48-63%). At 70 degrees C, C6D6 solutions of 6 undergo beta-hydride transfer with 2 equiv of benzaldehyde to form 7 and benzophenone in quantitative yield (according to 1H NMR spectroscopy). Benzene solutions of 1 react with 1 equiv of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf) to form (Me) LZn2 (O (i) Pr)(OTf) (8) in 70% isolated yield. In the solid state, 8 features a bridging alkoxide donor as well as a 1,3-bridging triflate group. The previously reported dinuclear organozinc species (Me) LZn2Ph2 (9) reacts with 1 equiv of tert-butylamine to form the protonolysis product (Me) LZn2 (Ph)(NH (t) Bu) (10) in 66% isolated yield. The solid-state structure of 10 (two independent molecules) reveals a somewhat asymmetric [Zn2 (mu-Ph)(mu-NH (t) Bu)] 2+ core with short Zn-Zn separations [2.6761 (5) and 2.6518 (5) Angstroms]. In CD2Cl2 solution, the Ph bridge of 10 undergoes rapid reversible cleavage. Cleavage of this bridging interaction followed by rotation about the Zn-Ph bond and re-formation of the bridging interaction results in exchange of the inequivalent ortho (and meta) protons of the phenyl ligand. Variable-temperature 1H NMR spectroscopic data indicate that this exchange occurs with DeltaG = 12.7 (1) kcal.mol (-1) (-27 degrees C). At 75 degrees C, toluene solutions of (Me) LH2 react with 2 equiv of EtZnNH (t) Bu to form the dizinc bis (amido) product (Me) LZn2 (NH (t) Bu) 2 (11) in 46% isolated yield. The solid-state structure of 11 (two independent molecules) features a puckered and fairly symmetric [Zn2 (mu-NH (t) Bu) 2] 2+ core with short intermetal separations [2.775 (1), 2.760 (1) Angstroms]. |
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