Research Highlights

Eliminating nonradiativedecay in Cu(I) emitters: > 99%quantum efficiency and microsecond lifetime

OLED 2.0: Organic Light Emitting Diodes (OLED) are traditionally made using luminescent complexes of heavy metals such as iridium, platinum, and ruthenium. Achieving comparable performance from copper, an earth-abundant metal, requires overcoming weak spin-orbit coupling, as well as limiting high reorganization energies. In a recent report in Science, however, Jesse Peltier (left) from the Bertrand group at UCSD and Rasha Hamze (right) from the Thompson group at USC, thoroughly explored two-coordinate copper complexes that sandwich the metal between an amide ligand and a cyclic (alkyl)(amino)carbene ligand (CAAC) and measured a nearly perfect luminescence efficiency. They used this property to produce a prototype blue organic light-emitting diode.

Science 2019, 363, 601.

DOI: 10.1126/science.aav2865

A Crystalline Doubly Oxidized Carbene

The chemistry of carbon is governed by the octet rule, which refers to its tendency to have eight electrons in its valence shell. However, a few exceptions do exist. The trityl radical (Ph₃C∙) and carbocation (Ph₃C+) possess seven and six valence electrons, respectively. Carbenes (R₂C:), two-coordinate octet-defying species, formally possess six valence electrons. Can we undress the carbene further by removing its non-bonding electrons? As published in Nature and highlighted in C&EN, we have synthesized a crystalline doubly oxidized carbene (R₂C²⁺) formally possessing just four valence electrons.

Nature 2023, 1.

DOI: 10.1038/s41586-023-06539-x

C&EN 2023,

Link

Ambiphilic Carbene Mimicks Transition-Metal Catalysts in the Activation of Carbon Monoxide

The activation and catalytic transformation of carbon monoxide by transition metals is well known. However, within the realm of organocatalysis the former behavior is rare while the latter is entirely unknown - until now. As published in JACS and highlighted in Synfacts, we have succesfully demonstrated a metal-free, carbene-catalyzed carbonylation with CO. Insights from this discovery will pave the way for further developments in metal-free catalysis.

Synfacts 2021, 17, 0088.

DOI: 10.1055/s-0040-1706092

JACS 2020, 142, 18336–18340.

DOI: 10.1021/jacs.0c09938.

$Tandem copper hydride-Lewis Pair catalysed reduction of carbon dioxide to formate with dihydrogen Atmospheric CO2 levels are rising at an alarming rate and require novel catalytic methodologies to transform this greenhouse gas into useful organic products like formic acid. We just reported, in Nature Catalysis, the development of a synergistic tandem copper(I)-hydride/classical Lewis pair catalyst system capable of reducing CO2 to formate using H2 as the reductant. During our investigation, we discovered that true FLPs are unable to perform as co-catalysts in this transformation Nature Catalysis 2018, 1, 743-747. DOI: 10.1038/s41929-018-0140-3 a crystalline monosubstituted carbene No one would have expected that in the last 30 years, stable disubstituted carbenes would extended their reach beyond organic and organometallic chemistry, to find applications in material and even medicinal science. Despite these advances, our recent report in Nature Chemistry details the synthesis and characterization of the simplest monosubstituted aminomethylene carbene, a species which represents the missing link between stable disubstituted carbenes and the transient parent methylene carbene. Nature Chemistry2018, online. DOI: 10.1038/s41557-018-0153-1 a stable singlet phosphinidene Since the development of the first stable carbene, many attempted syntheses of non-carbon based analogues have been attempted. Our group synthesized the first stable nitrene in 2012, which prompted us to turn our attention to the heavier group 15 homologue, namely, a phosphinidene. Utilizing the stabilizing ability of phosphorus and immense steric bulk on the flanking nitrogen atoms, we were able to synthesize a phosphorus stabilized phosphinidene, or (phosphino)phosphinidene, which is isolable and stable at room temperature. Chem 2016, 1, 147-153. DOI: 10.1016/j.chempr.2016.04.001 Isolation of Copper Click Chemistry Intermediates The copper-catalyzed 1,3-dipolar cycloaddition of an azide to a terminal alkyne (CuAAC) is one of the most popular chemical transformations. The isolation of both a previously postulated π,σ-bis(copper) acetylide and a hitherto never-mentioned bis(metallated) triazole complex is reported. We also demonstrate that although mono- and bis-copper complexes promote the CuAAC reaction, the dinuclear species are involved in the kinetically favored pathway. Science Advances 2015, 1, e1500304. DOI: 10.1126/sciadv.1500304 A stable nitrene Nitrogen atoms form strong, relatively unreactive triple bonds with themselves (in L2) and with carbon (in cyanides and nitriles). In contrast, binding to transition metals often leaves an otherwise naked nitrogen center more prone to reactivity. A phosphorus atom can support an otherwise uncoordinated nitrogen atom. This organic moiety acts more like a metal than a light element. Although this compound, the first stable organic nitrene, can be isolated at room temperature and characterized by X-ray diffraction, it can also be used as a nitrogen transfer agent to unsaturated carbon compounds. Science 2012, 337, 1526-1528 DOI: 10.1126/science.1226022 An anti-Bredt N-Heterocyclic Carbene Placing one of the adjacent nitrogen atoms of an NHC in the bridgehead position of a bicyclic scaffold prevents the donation of its lone pair. Thus, the π-electron accepting properties of the carbene center are enhanced, while the strong σ-electron donating properties of classical NHCs are retained. Angew. Chem. Int. Ed. 2012, 51, 6172-6175. DOI: 10.1002/anie.201202137 Tricoordinated boron atoms can be Lewis bases In textbooks, tricoordinated boron compounds are typical Lewis acids. Flanked by stable singlet carbenes, boron becomes a Lewis base as shown by its reactivity. Science 2011, 333, 610-613. DOI: 10.1126/science.1207573 Mesoionic carbenes-Ru complexes are powerful latent olefin-metathesis catalysts Addition of a Brønsted acid to a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) results in protonolysis of the Ru–MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicated a rate-determining protonation step in the generation of the metathesis-active species. The activity of the NHC/MIC catalyst was found to exceed those of current commercial ruthenium catalysts. J. Am. Chem. Soc. 2011, 133,8498-8501. DOI: 10.1021/ja203070r Mesoionic Carbenes: perfectly stable as free species Only a small range of complexes featuring mesoionic carbenes (MICs, also termed abnormal NHCs or aNHCs) were known. For this reason these compounds were seen as curiosities with limited potential as ligands . We show that many MICs are indeed perfectly stable and can be isolated at room temperature. Moreover, a large variety of substitution patterns can be tolerated without precluding the isolation of the corresponding MIC. Angew. Chem. Int. Ed. 2010, 49, 4759-4762. DOI: 10.1002/anie.201001864 Science 2009, 326, 556-559. DOI: 10.1126/science.1178206$

UCSD-CNRS joint chemistry lab - UMI 3555

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e-mail : guybertrand@ucsd.edu

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