The Suzuki–Miyaura Cross‐Coupling as the Key Step in the Synthesis of 2‐Aminobiphenyls and 2,2'‐Diaminobiphenyls: Application in the Synthesis of Schiff Base Complexes of Zn

Abstract

2‐Nitrophenylboronic acids serve as interesting starting materials for the construction of biphenyl‐ and terphenyl‐based amines if subjected to the Suzuki–Miyaura reaction. Unfortunately, these boronic acids suffer from low reactivity in Suzuki reactions, alongside their low stability in the presence of Pd. Herein, a general method for the construction of 2‐nitro‐substituted bi‐ and terphenyls is presented, with special emphasis on the synthesis of 2‐amino‐2'‐nitrobi‐ and terphenyls. Comparisons are made with other boronic acids that have some of the aforementioned issues. Finally, the application of the obtained 2‐amino‐2'‐nitrobi‐ and terphenyls as starting materials for the synthesis of bi‐ and terphenyl based di‐ and triamines is encountered for, with emphasis on the use of these amines as precursors for Schiff base ligands. In addition, the synthesis of some Zn complexes of these ligands is presented.

The Reactivity of Multidentate Schiff Base Ligands Derived from Bi‐ and Terphenyl Polyamines towards M(II) (M=Ni, Cu, Zn, Cd) and M(III) (M=Co, Y, Lu)

“…In the minor component, the 1 H NMR resonances of the protons of discussion were observed at significantly lower ppm values; δ 7.27, δ 7.00, δ 6.82 and δ 5.16 respectively, being closer to what is expected for an aromatic amine of this kind. [17] The 15 N NMR resonance of the NH 2 nitrogen of the major component was observed at a lower ppm value than the corresponding resonance of the minor component (δ À 326.9 and δ À 317.2 respectively) (Figure 12). This can be seen as an indication that the major component in [D 6 ]DMSO actually is the NH 2 -coordinated complex depicted to the left in Scheme 9.…”

“…In addition, the ZnÀ NH 2 bond in 1b-ZnÀ NH 2 was of similar length as the ZnÀ O(DMSO) bond in a related Zn complex previously reported by us. [17] As [D 6 ]DMSO is susceptible to break up dimeric pentacoordinated Zn Schiff base complexes and form monomeric pentacoordinated DMSOligated complexes, the same may occur for 1b-ZnÀ NH 2 . However, since the nature of the pentacoordination for the latter is predominantly intramolecular, DMSO ligation would be less favorable compared to dimers where the pentacoordination at Zn is a result of an intermolecular process.…”

“…In a recent publication we reported the synthesis of biphenyland terphenyl triamines using the Suzuki-Miyaura reaction of bromoanilines and an ortho-nitro-substituted arylboronic acid as the key step. [17] Some of these triamines (5, 6, and 7, Scheme 1) were subjected to typical synthesis conditions for formation of Schiff bases giving access to ligands 1a-d, 2a-c and 3 (Scheme 1).…”

“…From NMR studies of complexes 2a-Zn and 3-Zn, the behavior in solution was largely analogous to what has earlier been reported for Zn complexes of biphenyl-and terphenyl-based tetradentate N 2 O 2 ligands. [14,17] No evidence was found for the coordination of the third salicylaldimine group to Zn. For complex 1a-Zn, 1 H NMR studies were somewhat less straightforward.…”

“…For 1a-Zn and 2a-Zn, the ZnÀ μ-O bond distances were similar to what has been reported for a related dimeric Zn complex in literature. [17] The ZnÀ O-Scheme 6. Suggested dynamic behavior of the naphthol-derived complex 1d-Zn in CDCl 3 .…”