NMR spectroscopic investigations on the successive implementation of nickel and zinc ions to a NacNac-dibenzofuran-Br ligand precursor

The ligand precursor HNacNac-dibenzofuran-Br, LH, was synthesized by the condensation of 6-bromo-4-dibenzofuranamine and 4-(N-(mesityl)amino)pent-3-en-2-one with the aim of preparing heterodinuclear nickel/zinc complexes in two successive steps. Reacting LH with Zn(HMDS)2, Zn(C6F5)2 and Zn(C2H5)2 led to the respective X-Zn-NacNac-dibenzofuran-Br complexes (X=HMDS (2), C6F5 (3), Et (4)). However, in case of 2 and 3 the subsequent treatment with Ni(COD)2/TMEDA did not lead to any conversion, probably as the steric bulk imposed by the NacNac-Zn-X entities was too high. 4 did react with Ni(COD)2/TMEDA, likely in the envisaged manner, but apparently the targeted product complex Et-Zn-NacNac-dibenzofuran-Ni(TMEDA)Br, once formed, immediately reacts further via a Negishi coupling reaction, so that Br-Zn-NacNac-dibenzofuran-Et (5) is formed. The reaction of 4 with triethylammonium bromide led to the formation of the Br-Zn-NacNac-dibenzofuran-Br (6) complex that could be reacted with Ni(COD)2/TMEDA successfully. All attempts to purify the product led to Zn(NacNac-dibenzofuran-Ni(TMEDA)Br)2, which is insoluble in THF and thus drives a dismutation reaction. image