Synthesis and characterization of bis(imino)pyridine complexes of divalent Mg and Zn

Abstract

Phenyl-bis(imino)pyridine (PhI2P) complexes, (PhI2P)ZnCl2 (1), (PhI2P−)ZnCl (2) and (PhI2P−)Zn(py)Cl (3) were obtained with the I2P ligand in both the neutral and the one-electron reduced state. In all examples, the metal ion is Zn(II). Metrical parameters obtained from solid state structures of 2 and 3 indicate that the PhI2P− ligand exists as a radical which is supported at the carbon atom of the imino donor, and this electronic state is also apparent in the analogous one-electron reduced ligand Al(III) complex, (PhI2P−)AlCl2 (4), that we prepared for comparison. We were unable to obtain PhI2P Mg complexes, and so the more electron rich methyl-substituted bis(imino)pyridine ligand, MeI2P, was investigated. Reaction of two-electron reduced MeI2P with MgCl2 and Mg(OTf)2 did afford the two-electron reduced ligand complexes [(MeI2P2−)Mg(THF)]2(μ-MgCl2) (5) and (MeI2P2−)Mg(THF)2 (6), respectively (MeI2P = 2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenylamine). Complex 5 crystallizes as a trinuclear Mg complex consisting of two (MeI2P2−)Mg moieties bridged by MgCl2 and the (MeI2P2−) ligand is symmetric across the pyridine ring, but is not planar. In contrast, the (MeI2P2−) ligand in 6 is asymmetric across the pyridine ring and all atoms in the ligand are coplanar. Cyclic voltammetry measurements reveal that in complexes, 1, 4, 5, 6, the I2P0, I2P−, and I2P2− ligand charge states are accessible electrochemically.

Electrocatalytic Hydrogen Production by an Aluminum(III) Complex: Ligand‐Based Proton and Electron Transfer

“…[12] We now focus on ligand reactivity only,and report herein that the analogous aluminum chloride complex [( Ph I 2 P 2À )Al-(THF)Cl] (1,S cheme 2) [13] promotes H 2 production from protons in the presence of an applied reducing potential. We also discuss [( Ph I 2 P 1À )AlCl 2 ]( 2), [14] where the After addition of two equivalents of 2,6-lutidinium acid (lutH + )t oasolution of 1,t wo reduction events were observed, namely at À0.95 Va nd À1.20 V, and the anodic shift of these events compared with reduction of 1 (À1.55 V) is consistent with the additional positive charge on the complex resulting from protonation of the ligand (Figure 1a). With excess lutH + ,the current density increased to j c /j p = 10; this result suggested that ac atalytic event had occurred ( Figure 2a).…”

“…[12] We now focus on ligand reactivity only,and report herein that the analogous aluminum chloride complex [( Ph I 2 P 2À )Al-(THF)Cl] (1,S cheme 2) [13] promotes H 2 production from protons in the presence of an applied reducing potential. We also discuss [( Ph I 2 P 1À )AlCl 2 ]( 2), [14] where the Ph I 2 Pl igand is reduced by only one electron.…”

“…( Ph I 2 P 2À )Al(THF)Cl (1), [13] and ( Ph I 2 P 1À )AlCl 2 (2). [14] Ar = 2,6-diisopropylphenyl. [*] E. J.…”

Oxalate-templated synthesis of di-zinc macrocycles

“…Redox activity of mononuclear Zn(II) complexes in redox-active environments has been investigated, [13,14] including recent electrochemical characterization of bis(imino)pyridine Zn(II) complexes and isolation of the reduced bis(imino)pyridine Zn(II) complexes by Berben and coworkers. [15] We wanted to find out whether our complexes, featuring two bis(imino)pyridine units bridged by a [Zn 2 (oxalate)] bridge, also demonstrate reduction events associated with redox-active ligands. Second, we were interested in discovering whether oxalate can be removed from our complexes via oxidation.…”

“…The electrochemical features observed in the cyclic voltammogram are assigned to the redox-active nature of the bis(ketimino)pyridine ligands bound to the redox-inactive zinc. [15] Interestingly, Berben and coworkers have also observed two redox events at the mononuclear bis(imino)pyridine zinc complex with the first event being irreversible due to chloride loss. In our case, the first event is reversible, likely due to the rigid…”