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Issue 7, 2021

Ambiphilic boryl groups in a neutral Ni(ii) complex: a new activation mode of H2

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Abstract

The concept of metal–ligand cooperation opens new avenues for the design of catalytic systems that may offer alternative reactivity patterns to the existing ones. Investigations of this concept with ligands bearing a boron center in their skeleton established mechanistic pathways for the activation of small molecules in which the boron atom usually performs as an electrophile. Here, we show how this electrophilic behavior can be modified by the ligand trans to the boron center, evincing its ambiphilic nature. Treatment of diphosphinoboryl (PBP) nickel–methyl complex 1 with bis(catecholato)diboron (B2Cat2) allows for the synthesis of nickel(II) bis-boryl complex 3 that promotes the clean and reversible heterolytic cleavage of dihydrogen leading to the formation of dihydroborate nickel complex 4. Density functional theory analysis of this reaction revealed that the heterolytic activation of H2 is facilitated by the cooperation of both boryl moieties and the metal atom in a concerted mechanism that involves a Ni(II)/Ni(0)/Ni(II) process. Contrary to 1, the boron atom from the PBP ligand in 3 behaves as a nucleophile, accepting a formally protic hydrogen, whereas the catecholboryl moiety acts as an electrophile, receiving the attack from the hydride-like fragment. This manifests the dramatic change in the electronic properties of a ligand by tuning the substituent trans to it and constitutes an unprecedented cooperative mechanism that involves two boryl ligands in the same molecule operating differently, one as a Lewis acid and the other one as a Lewis base, in cooperation with the metal. In addition, reactivity towards different nucleophiles such as amines or ammonia confirmed the electrophilic nature of the Bcat moiety, allowing the formation of aminoboranes.

Graphical abstract: Ambiphilic boryl groups in a neutral Ni(ii) complex: a new activation mode of H2

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Article information


Submitted
02 Nov 2020
Accepted
21 Dec 2020
First published
22 Dec 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2021,12, 2540-2548
Article type
Edge Article

Ambiphilic boryl groups in a neutral Ni(II) complex: a new activation mode of H2

P. Ríos, J. Borge, F. Fernández de Córdova, G. Sciortino, A. Lledós and A. Rodríguez, Chem. Sci., 2021, 12, 2540 DOI: 10.1039/D0SC06014C

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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