Dizinc Alkoxides and Amides Supported by Binucleating Bis(amidoamine) Ligands

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 (MeLH2) with 2 equiv of EtZn(OiPr) forms the dizinc bis(alkoxide) MeLZn2(OiPr)2 (1), which was isolated in 76% yield. Similarly, MeLH2 reacts cleanly with EtZn(OPh) and
EtZn(OCHPh2) to form MeLZn2(OPh)2 (2) and MeLZn2(OCHPh2)2 (3), respectively. The solid-state structures of 1 and
2 feature puckered [Zn2(μ-OR)2]2+ cores, with short intermetal separations (2.81−2.88 Å). Overall, the molecules
have approximate (noncrystallographic) C2v symmetry. The use of the more-hindered iPr-substituted ligand N,N‘-bis(2-diisopropylaminoethyl)dibenzofuran-4,6-diamine (iPrLH2) to prepare zinc alkoxides gave similar results. Thus,
reaction of iPrLH2 with 2 equiv of EtZn(OPh), EtZn(OMe), EtZn(OCHPh2), and EtZn(OCH2Ph) forms iPrLZn2(OPh)2
(4), iPrLZn2(OMe)2 (5), iPrLZn2(OCHPh2)2 (6), and iPrLZn2(OCH2Ph)2 (7), respectively (isolated yields 48−63%). At
70 °C, C6D6 solutions of 6 undergo β-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 MeLZn2(OiPr)(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 MeLZn2Ph2 (9) reacts with 1 equiv of tert-butylamine to form the protonolysis product MeLZn2(Ph)(NHtBu)
(10) in 66% isolated yield. The solid-state structure of 10 (two independent molecules) reveals a somewhat asymmetric [Zn2(μ-Ph)(μ-NHtBu)]2+ core with short Zn−Zn separations [2.6761(5) and 2.6518(5) Å]. 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 ΔG⧧ = 12.7(1) kcal·mol-1 (−27 °C). At 75 °C, toluene solutions of MeLH2 react with 2 equiv of EtZnNHtBu to form the dizinc bis(amido) product MeLZn2(NHtBu)2 (11) in 46% isolated yield. The solid-state structure of
11 (two independent molecules) features a puckered and fairly symmetric [Zn2(μ-NHtBu)2]2+ core with short intermetal
separations [2.775(1), 2.760(1) Å].