Pyrrole Denitrogenation and Fragmentation of Tetramethylethylenediamine Promoted by a NbII Cluster

Abstract

A nitrogen center was abstracted from a pyrrolyl ring to form the dinuclear nitrido- and dienyl-bridged complex 1 during the reaction of [{(tmeda)Nb Cl} (μ-Cl) Li(tmeda)] with the lithium salt of 2,5-dimethylpyrrole (tmeda=N,N,N',N'-tetramethylethylenediamine). A second product from this reaction is the amido-carbene-hydride niobium complex 2, which likewise forms under C-N bond cleavage.

Tantalum Complexes of Diphenyldipyrrolide Dianion: Partial Hydrogenation of a Phenyl Ring

“…Among low-valent early transition metals, niobium and tantalum occupy a special place. The few derivatives reported in the literature are able to perform a wide variety of reactions, including pyridine ring-opening, pyrrole denitrogenation, C−N bond cleavage, C−H bond oxidative addition, etc. In addition, the low oxidation state and the electron-rich electronic configuration enable other features such as cluster formation and metal−metal interactions …”

Tri- and Tetravalent and Mixed-Valence Niobium Complexes Supported by a Tripodal Tripyrrolylmethane Trianion

“…A crucial role in this respect is played by the nature of the ancillary ligand around the Nb starting material (TMEDA versus DME) and by the nature of the alkali-metal cation employed (K versus Li). Similar to other transformations involving low-valent niobium, these reactions involve the participation of several metal centers in a complex redox pattern. Further studies to fully exploit the potential of this ligand system will be carried out by increasing the steric hindrance of the tripodal system to prevent encapsulation of the metal center.…”

“…The preeminent features of this ligand can be summarized as (1) the ability to cap a dimetallic unit with an unusual bridging mode and stabilize the trivalent state of Nb, (2) an apparent inertness to reactivity of the trivalent Nb center, and (3) the ability to support formation of Nb−Nb bonds with and without participation of ligand orbitals in the formation of the Nb−Nb MO's. The possibility of coordinating one of the three pyrrolyl rings in a π -bonding fashion is probably the key for understanding the versatility of this ligand and its ability to prevent destructive reactivity patterns such as ring opening, ,8b-f C−N cleavage, ,, and denitrogenation reactions . The trianion also supports the regular pyramidal bonding mode.…”

“…In this paper we describe the results of the reaction of low-valent niobium salts with a novel tripodal tripyrrolyl trianion. The study was prompted by the observation of the ability of pyrrolide anions to be involved at the same time in both the reactivity and stabilization of the metal center via formation of π-bonded complexes . Conversely, polypyrrole anions have recently proven to be more resistant to strongly reducing metals, to have an enhanced tendency toward π-donation, and to support clusterification reactions and even dinitrogen fixation/activation.…”

Intramolecular dealkylation of chelating diamines with Ru(ii) complexes

“…4 Despite the importance of these reactions in terms of their potential applications, only few reports have appeared in the literature in the past few years. Those involved the rupture of C-N single bond of aniline 5 and the ring-opening of pyridine 6 and pyrrol 7 rings by complexes containing highly reactive trivalent Group 5 metals (Nb and Ta), the cleavage of the allylic-N bond of allylamines by Ru, 8a Ni, 8b and Rh 8c complexes or the C-N bond scissions of aliphatic amines by Ru and Os carbonyl clusters. 9 To the best of our knowledge, no examples appear in the literature regarding the N-dealkylation of tertiary chelating diamines by a transition metal complex.…”