A Critical Review of Electronic Effects in Enediamido and α‐Diimino Complexes of the Group 4 Metals

Abstract

. The M-DAD metallacycle is generally either planar or folded at the N···N vector, the latter arrangement being observed when the number of co-ligands is reduced and hence there is insufficient saturation at the metal. The conformation also depends on the relative electron population of DAD, which is a noninnocent ligand and exists as a continuum between the neutral and dianionic resonance forms. Herein some theoretical concepts, that have

The 1,4-diazabutadiene/1,2-enediamido non-innocent ligand system in the formation of iridaheteroaromatic compounds: Spectroelectrochemistry and electronic structure

“…It is noteworthy that the ''Arduengo carbene" as prototypical N-heterocyclic carbene (NHC) displays a similar CC and CN bond length sequence [52] as compound 2 (which is unusual in that it contains a late transition metal associated with an enediamido(2À) ligand). All other reported enediamido chelates involve either early transition metals [36], specially zirconium [53], hafnium [54], tantalum [55], or chromium [56,57], or main group element atoms [34,38,[58][59][60][61][62].…”

“…1,4-Diazabutadienes [28][29][30] are among the most conspicuous non-innocent ligands [31][32][33], being able to coordinate also as 1,2-enediamido(2À) ligands [21,[34][35][36][37][38] or as radical anion complex intermediates (RNCHCHNR) Å- [29,33,[39][40][41][42][43][44][45].…”

Electronic and Geometric Structures of Paramagnetic Diazadiene Complexes of Lithium and Sodium

“…The corresponding data obtained from the DFT calculations show a C−C bond length of 1.43 Å and a C−N bond length of 1.34 Å, both of which are in good agreement with the experimental data. These structural data are indicative of the radical character of the ligand among the several possible coordination modes of the DAD ligands (see Scheme ) . The calculated Li−N bond length of 1.90 Å is significantly shorter than the experimental value of 2.032(5) Å.…”

“…Important practical applications of metal diazadiene complexes include homogeneous catalysis, C−H bond activation, materials science, and the synthesis of single‐molecule magnets . A unique electronic property of 1,4‐diaza‐1,3‐dienes is that they are redox non‐innocent and can undergo one‐ and two‐electron reduction steps to afford the corresponding radical anions and the enediamide dianions, respectively, as shown in Scheme …”

“…The so‐far‐reported EPR spectroscopy results on DAD complexes have mostly indicated that the unpaired electron is delocalized over the DAD backbone, and therefore, a dominant ligand‐centered character with small g and A anisotropies is generated. However, there are other cases that report weak or rather strong delocalization into metal centers in addition to the DAD backbone …”