Examining the Generality of Metal–Ligand Cooperativity Across a Series of First-Row Transition Metals: Capture, Bond Activation, and Stabilization

Abstract

We outline the generality and requirements for cooperative N 2 H 4 capture, N−N bond scission, and amido stabilization across a series of first-row transition metal complexes bearing a pyridine(dipyrazole) ligand. This ligand contains a pair of flexibly tethered trialkylborane Lewis acids that enable hydrazine capture and M−NH 2 stabilization. While the Lewis acids are required to bind N 2 H 4 , the identity of the metal dictates whether N−N bond scission can occur. The redox properties of the M(II) bis(amidoborane) series of complexes were investigated and reveal that ligand-based events prevail; oxidation results in the generation of a transiently formed aminyl radical, while reduction occurs at the redox-active pyridine(dipyrazole) ligand.

Bis-Ferrocenyl-Pyridinediimine Trinuclear Mixed-Valent Complexes with Metal-Binding Dependent Electronic Coupling: Synthesis, Structures, and Redox-Spectroscopic Characterization

“…Furthermore, a cationic Fe­(III) can generate local electric field gradients and polarize substrates, ferrocenium LMCT states have been shown to be useful in photocatalysis, and it is known to act as a Lewis acid catalyst . Addition of Lewis acids in the secondary coordination sphere is an attractive strategy in bond activation . Furthermore, the acceptor orbital in charge transfer transitions for the neutral complexes (see theory section) features a similar ligand centered LUMO that is one of the occupied frontier orbitals in highly reduced PDI structures .…”

“…56 Addition of Lewis acids in the secondary coordination sphere is an attractive strategy in bond activation. 57 Furthermore, the acceptor orbital in charge transfer transitions for the neutral complexes (see theory section) features a similar ligand centered LUMO that is one of the occupied frontier orbitals in highly reduced PDI structures. 44b Based on these interesting excited states, we suggest that an internal electron donor could function as a photoreductant in lieu of aggressive reductants such as NaEt 3 BH or Na(Hg).…”

A Bidentate Ligand Featuring Ditopic Lewis Acids in the Second Sphere for Selective Substrate Capture and Activation

“… Selected examples of known ditopic boranes, [11, 12b, 14, 15e] and design strategy outlining the ditopic ligand used in this work from prior work using a bidentate ligand with single second‐sphere Lewis acid, [9a–c] and a tridentate ligand with two Lewis acids [4, 9d, e] …”

Group 13 ion coordination to pyridyl models NAD+ reduction potentials

“…[12][13][14][15] Coordination compounds of pz 2 P are reported largely with transition element ions and focus on the metal-centred reaction chemistry. [16][17][18][19] Herein, we compare the redox inert ions Al III , Ga III and Zn II which can promote pyridyl centred redox chemistry as in NAD + . 20,21 We demonstrate that these redox inert d 0 or d 10 ions affect pyridyl electronic structure similarly to N-alkylation of pyridyl (Chart 1).…”