Revisiting the Molecular Roots of a Ubiquitously Successful Synthesis: Nickel(0) Nanoparticles by Reduction of [Ni(acetylacetonate)₂]

Abstract

The widely used preparation of Ni(0) nanoparticles from [Ni(acac)(2)] (acac=acetylacetonate) and oleylamine, often considered to be a thermolysis or a radical reaction, was analyzed anew by using a combination of DFT modeling and designed mechanistic experiments. Firstly, the reaction was followed up by using TGA to evaluate the energy barrier of the limiting step. Secondly, all the byproducts were identified using NMR spectroscopy, mass spectrometry, FTIR, and X-ray crystallography. These methods allowed us to depict both main and side-reaction pathways. Lastly, DFT modeling was utilized to assess the validity of this new scheme by identifying the limiting steps and evaluating the corresponding energy barriers. The oleylamine was shown to reduce the [Ni(acac)(2)] complex not through a one-electron radical mechanism, as often stated, but as an hydride donor through a two-electron chemical reduction route. This finding has strong consequences not only for the design of further nanoparticles syntheses that use long-chain amine as a reactant, but also for advanced understanding of catalytic reactions for which these nanoparticles can be employed.

Synthesis and Structural Evolution of Nickel-Cobalt Nanoparticles Under H2and CO2

“…At the end of this first step, the solution contained Ni(0) NPs mostly stabilized by TOP ligands . It also contained excess TOP, as well as by‐products derived from oleylamine, as extensively described elsewhere …”

Ultrathin Europium Oxide Nanoplatelets: “Hidden” Parameters and Controlled Synthesis, Unusual Crystal Structure, and Photoluminescence Properties

“…Such an attempt has been reported by Mezailles and co-workers in the case of a very simple system (thermal decomposition of nickel acetylacetonate in pure OAm). 40 Even in that particular case, drastic experimental simplifications were necessary.…”

Mechanistic Investigations of the Synthesis of Size‐Tunable Ni Nanoparticles by Reduction of Simple NiII Diamide Precursors

“…The reduction of [Ni(acac) 2 ] by oleylamine was shown to produce imine through a β‐H transfer from an amido moiety to the acac ligand (Scheme ) . We postulated that a similar β‐H transfer from one amido to the other could occur and, therefore, analyzed the crude mixture after Ni 0 NP synthesis by using mass spectrometry (see the Supporting Information).…”

“… a) Mechanism of reduction of [Ni(acac) 2 ] to Ni NPs, and b) proposed mechanism of reduction of M II dioleylamide species to M 0 NPs …”

“…The reduction of 1 by oleylamine has been shown, through both calculations and experiment, to proceed through a Ni II species with one acac ligand, one primary amide ligand, and one amine ligand (Scheme a). Most importantly, the formation of water and the reduction of Ni II to Ni 0 are two independent steps.…”