Related Experiment Video
Updated: Sep 24, 2025

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
From cyclic amines and acetonitrile to amidine zinc(ii) complexes
Nina Podjed1, Barbara Modec1, María M Alcaide2
1Faculty of Chemistry and Chemical Technology, University of Ljubljana Večna pot 113 1000 Ljubljana Slovenia barbara.modec@fkkt.uni-lj.si.
Abstract:
A seemingly simple combination of [Zn(quin)2(H2O)] (quin- = quinaldinate) and a selected secondary cyclic amine, piperidine (pipe), pyrrolidine (pyro) or morpholine (morph), afforded in acetonitrile a number of products: anionic homoleptic quinaldinate, neutral heteroleptic quinaldinate/amine and quinaldinate/amidine complexes. The piperidine and pyrrolidine systems underwent reaction with acetonitrile to give amidines. The in situ formed piperidinoacetamidine (pipeam) or pyrrolidinoacetamidine (pyroam) coordinated to zinc(ii). Reactions with piperidine led to trans-[Zn(quin)2(pipe)2]·2CH3CN (1), [Zn(quin)2(pipe)]·cis-[Zn(quin)2(pipe)2] (2), pipeH[Zn(quin)3]·CH3CN (3), [Zn(quin)2(pipeam)]·CH3CN (4a), [Zn(quin)2(pipeam)]·2CHCl3 (4b), pipeamH[Zn(quin)3] (5) and pipeamH[Zn(quin)2(CH3COO)]·acetamide (6) (pipeH+ and pipeamH+ denote protonated amine or amidine). By analogy, [Zn(quin)2(pyro)2] (7), pyroH[Zn(quin)3]·CH3CN (8), pyroH[Zn(quin)2Cl] (9), [Zn(quin)2(pyroam)]·CH3CN·0.5pyroam·0.5H2O (10a), [Zn(quin)2(pyroam)]·2CHCl3 (10b), [Zn(quin)2(pyroam)]·CH2Cl2 (10c) and pyroamH[Zn(quin)3] (11) were obtained in the pyrrolidine reactions. The morpholine system allowed isolation of only two novel products, trans-[Zn(quin)2(morph)2] (12) and morphH[Zn(quin)3]·CH3CN (13). Importantly, no amidine could be isolated. Instead, in autoclaves at 105 °C morpholine degraded to ammonia, as confirmed by mass spectrometry of the gas phase. pyroamH[Zn(quin)3] exists in two polymorphs which differ in the binding modes of quinaldinate ligands. In 11triclinic, the metal ion of [Zn(quin)3]- features a five-coordinate environment, whereas that in 11monoclinic is surrounded by six donors. Stabilities of the [Zn(quin)3]- isomers were assessed with DFT calculations. The one with a six-coordinate zinc(ii) ion was found to be more stable than its five-coordinate counterpart. Favorable intermolecular interactions in the solid state stabilize both and reduce the energy difference between them. The calculations show the conversion of the five-coordinate [Zn(quin)3]- into its coordinatively saturated isomer to be an almost barrierless process.
More Related Videos
07:50Efficient Synthesis of All-Carbon Quaternary Centers via the Conjugate Addition of Functionalized Monoorganozinc Bromides
Published on: May 26, 2019
10:14Synthesis and Purification of Iodoaziridines Involving Quantitative Selection of the Optimal Stationary Phase for Chromatography
Published on: May 16, 2014
Related Concept Videos
Preparation of 1° Amines: Azide Synthesis
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum...
Amines to Amides: Acylation of Amines
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary...
Preparation of Amides
The DCC-promoted synthesis of amides begins with the protonation of DCC by carboxylic acid. The protonation makes it a better acceptor. Next, the addition of carboxylate to the protonated carbodiimide gives a reactive acylating agent.
Subsequently, the amine acts as a nucleophile that attacks the acylating agent to form a tetrahedral intermediate. In the...
Acid Halides to Amides: Aminolysis
In the first step of the aminolysis mechanism, the amine attacks the carbonyl carbon of the acyl chloride to form a tetrahedral intermediate. In the second step, the carbonyl group is re-formed with the elimination of a chloride...
Preparation of 1° Amines: Gabriel Synthesis
Strong bases like NaOH or KOH deprotonate the phthalimide to form the corresponding anion, which acts as a nucleophile. Further, the anion attacks an...
1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Mechanism