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

Abstract

The pro‐ligand HNacNac‐dibenzofuran‐Br precursor, LH, was synthesized by the condensation of H2N‐dibenzofuran‐Br 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.