Metal–Metal Interactions in C₃-Symmetric Diiron Imido Complexes Linked by Phosphinoamide Ligands

Abstract

The tris(phosphinoamide)-bridged Fe(II)Fe(II) diiron complex Fe(μ-(i)PrNPPh2)3Fe(η(2)-(i)PrNPPh2) (1) can be reduced in the absence or presence of PMe3 to generate the mixed-valence Fe(II)Fe(I) complexes Fe(μ-(i)PrNPPh2)3Fe(PPh2NH(i)Pr) (2) or Fe(μ-(i)PrNPPh2)3Fe(PMe3) (3), respectively. Following a typical oxidative group transfer procedure, treatment of 2 or 3 with organic azides generates the mixed-valent Fe(II)Fe(III) imido complexes Fe((i)PrNPPh2)3Fe≡NR (R = (t)Bu (4), Ad (5), 2,4,6-trimethylphenyl (6)). These complexes represent the first examples of first-row bimetallic complexes featuring both metal-ligand multiple bonds and metal-metal bonds. The reduced complexes 2 and 3 and imido complexes 4-6 have been characterized via X-ray crystallography, Mössbauer spectroscopy, cyclic voltammetry, and SQUID magnetometry, and a theoretical description of the bonding within these diiron complexes has been obtained using computational methods. The effect of the metal-metal interaction on the electronic structure and bonding in diiron imido complexes 4-6 is discussed in the context of similar monometallic iron imido complexes.

Unprecedented Five‐Coordinate Iron(IV) Imides Generate Divergent Spin States Based on the Imide R‐Groups

“…In addition to Que's example, a couple of other notable exceptions stand out in potential higher‐coordination environments. Thomas and co‐workers have described a dimeric iron imide complex with an iron–iron bond, while Peters and Moret reported an iron imide with a hemi‐labile borane trans to the imide, which they described as pseudotetrahedral while in the imide conformation …”

Synthesis of Iron and Cobalt Complexes of a Ferrocene-Linked Diphosphinoamide Ligand and Characterization of a Weak Iron–Cobalt Interaction

“…Complex 3 displays C i symmetry where the inversion center of the molecular structure sits in the middle of an elongated sixmembered heterocyclic ring composed of two Fe(II) centers and two phosphinoamide moieties. The bridging phosphinoamides in 3, (N1−P1 ≈ 1.67 Å), are similar to other iron N-Aryl phosphinoamides complexes, 46 all of which are longer than typical N-alkyl substituted phosphinoamides, 46 Other examples of trigonal planar iron phosphinoamide complexes have been reported by the Thomas group 46,55 and in all cases the N−P axes are perpendicular to the donor atom plane.…”

Homo- and heteroleptic group 4 2-(diphenylphosphino)pyrrolide complexes: Synthesis, coordination chemistry and solution state dynamics

“…Unlike traditional tetragonal bimetallics, trigonal systems with weaker ligand fields should promote more favorable metal-metal bonding interactions. Systematic analysis of different metal pairs and ligand donor sets has allowed Lu and Thomas example, metal-metal bonding with the first row transition metals is typically best when metals and coordination environments are similar, and becomes weaker (ultimately leading to the inability to form d-and p-bonds) as the metals and/or their coordination environments become more disparate [47][48][49][50][51][52][53][54][55][56]. In the case of first row late transition metals paired with heavier second and third row early metals, multiple bonding is possible, although highly polarized [21].…”