Dinuclear N-heterocyclic carbene copper(I) complexes

TLDR: In this article, the synthesis and structural properties of dinuclear copper(I)−NHC complexes are presented, where the authors present a summary of all information available on such species.

About: This article is published in Coordination Chemistry Reviews.The article was published on 2018-01-15 and is currently open access. It has received 28 citations till now.

Figures

Table 1. Comparison of the bond lengths and angles of [{Cu(SIPr)}2(μ-F)]OTf (5) and [{Cu(SIPr)}2(μ-F)]BF4 (8) [17,18].

Table 2. Cu-Cu distances (Å) of the dinuclear copper complexes presented in this review.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Dinuclear n-heterocyclic carbene copper(i) complexes" ?

Contrarily to the parent phosphine complexes, in which the presence of species of higher nuclearity is well established, fewer examples of such copper ( I ) -NHC species are reported and, interestingly, their number is growing. The aim of this review is to present a summary of the synthesis and structural properties of dinuclear copper ( I ) -NHC complexes. It is their hope that by centralizing all information available on such species, future efforts aimed at exploiting their full potential can be facilitated. 

Q2. What is the main characteristic of these complexes?

The main characteristic of these complexes is the six-membered ring formed by the two copper atoms and the four nitrogen of the bridging triazolate. 

Q3. What is the effect of reacting 30 with neutral ligands?

Reacting 30 with additional neutral ligands, such as phosphines or tert-butylisonitrile, results in a migratory insertion of the CAAC ligand into the Cu-H bond instead of the expected mononuclear tricoordinated copper hydride species. 

Q4. What is the description of dinuclear species?

At the moment, dinuclear species are the best candidates among polynuclear copper(I)-NHC compounds for the development of transformations in which the two metal centers cooperate, resulting in an enhancement of the catalytic activity. 

Q5. Why did the authors use a more flexible ligand?

The authors attributed this increased stability to the steric bulk and rigidity of the CAAC ligand used; the same reaction using a more flexible and smaller ligand did not yield the corresponding dimer. 

Q6. What is the chemistry of bis-(NHC)-based complexes?

A natural extension of the chemistry of bis-(NHC)-based complexes is the synthesis of polycarbene ligands, possessing three or more NHCs, which can be divided into open chain ligands or macrocyclic ligands (Scheme 35). 

Q7. What is the twisted angle of the imidazolium units?

The two imidazolium units are twisted of 44.9(11)°, calculated by N(1)-C(1)-C(7)-N(3) torsional angle, thus minimizing any π-bond overlap with the metal center. 

Q8. What is the trigonal-planar geometry of the copper atoms?

Both species are dimeric, possessing a slightly distorted trigonal-planar geometry around each metal center due to the lack of N-coordination of the ligand. 

Q9. What is the role of dinuclear complexes in the formation of alkynes?

Such dinuclear complexes have become attractive entities enabling the study of their role in established reactions but more excitingly will surely facilitate the discovery and development of novel transformations. 

Q10. How is the pyridine atom coordinated to the NCN ligand?

Each copper atom was shown to be coordinated to one NHC of the NCN ligand and to one bromine in an almost linear fashion with CNHC-Cu-Cl angles of 176.1(2)° and 166.1(2)°. 

Q11. What is the atomic distance between the pyridine and the metal centers?

In all species, the nitrogen atoms of the pyridine are directed towards the metal centers and their distances, ranging from 2.4220(18) Å to 2.8298(18) Å, reveal a weak interaction between these two atoms. 

Q12. What is the -acceptor character of copper?

This could be ascribed to the π-acceptor character of olefins and alkynes which reduces the electron density on the metal center.