N-Heterocyclic Carbene Complexes of Copper, Nickel, and Cobalt

The emergence of N-heterocyclic carbenes as ligands across the Periodic Table had an impact on various aspects of the coordination, organometallic, and catalytic chemistry of the 3d metals, including Cu, Ni, and Co, both from the fundamental viewpoint but also in applications, including catalysis, photophysics, bioorganometallic chemistry, materials, etc. In this review, the emergence, development, and state of the art in these three areas are described in detail.

Tetradecanuclear and Octadecanuclear Gold(I) Sulfido Clusters: Synthesis, Structures, and Luminescent Selective Tracking of Lysosomes in Living Cells

Reactions of the phosphanyl-gold(I) precursor [(AuCl)₂(bdppmapy)] (1; bdppmapy = N,N-bis(diphenylphosphanylmethyl)-2-aminopyridine) with Na₂S in a 1:1 or 1:2 molar ratio gave rise to one tetradecanuclear and one octanuclear Au(I) sulfido cluster, [Au₁₄S₆(bdppmapy)₅]Cl₂ (2) and [Au₁₈S₈(bdppmapy)₆]Cl₂ (3), respectively. The former displays a new structural framework in gold cluster chemistry. Compounds 2 and 3 showed strong green luminescence and were employed as excellent imaging probes to selectively light up the lysosomes of living cells. Their long-term tracking of lysosomes can be achieved for up to 36 h, while tracking with commercial Lyso-Tracker Red under the same conditions was limited to 3 h. Our work demonstrated the possibility of constructing novel gold(I) sulfido clusters supported by special P-N hybrid ligands and the potential application of these clusters as long-term selective trackers of lysosomes in bioimaging.

Cu(i), Ag(i), Ni(ii), Cr(iii) and Ir(i) complexes with tritopic NimineCNHCNamine pincer ligands and catalytic ethylene oligomerization

Potentially pincer-type tritopic N^imineC^NHCN^amine ligands with a variable length of the spacer connecting N^imidazole to the amine donor are evaluated.

A hierarchically-assembled Fe–MoS2/Ni3S2/nickel foam electrocatalyst for efficient water splitting

Hierarchically-assembled Fe–MoS₂/Ni₃S₂/NF demonstrates excellent HER, OER and full water splitting catalytic performances in an alkaline electrolyte.

Reversible dielectric switching behavior of a 1D coordination polymer induced by photo and thermal irradiation

Switchable dielectric relaxation is achieved through photocycloaddition/reversion within a 1D coordination polymer on thermal and photo irradiation.

Stereoselective Solid-State Synthesis of Substituted Cyclobutanes Assisted by Pseudorotaxane-like MOFs

Regioselective photodimerization of trans-4-styrylpyridine (4-spy) derivatives is performed using pseudorotaxane-like Zn-based metal organic frameworks MOFs as templates. The formation of rctt-HT (head-to-tail) dimers is achieved by confining pairs of coordinated 4-spy derivative ligands within hexagonal windows and then irradiating them with UV light. It is also possible to achieve a photodimerization reaction where two different substituted 4-spy ligands are included in such a MOF material. The ether bond formation is employed to protect the sensitive -OH group of HO-spy and the methyl group of CH₃ O-spy is subsequently removed after the formation of cyclobutane derivative in the CH₃ O-spy-based MOF. Introducing substituents at the 2- or 3-position of the phenyl group of 4-spy does not significantly affect the rate of the dimerization process except in the case of the strongly electron-withdrawing nitro group where the rate is significantly decreased. These results are in striking contrast to the mixtures of photoproducts and low yields obtained by untemplated photodimerization in organic solvents.

Perturbing the spin crossover transition activation energies in Fe(H2B(pz)2)2(bipy) with zwitterionic additions

A thermal component to the soft x-ray induced spin crossover transition exists in the switching of a spin crossover compound (complex [Fe{H₂B(pz)₂}₂(bipy)] (pz  =  pyrazol-1-yl, bipy  =  2,2'-bipyridine) combined with the dipolar molecular additives (zwitterionic p-benzoquinonemonoimine C₆H₂([Formula: see text])₂([Formula: see text])₂). The addition of the zwitterionic molecule locks the Fe(II) complex in a largely low spin state configuration over an unusually broad temperature range that includes temperatures well above the thermal spin crossover temperature of 160 K. It is demonstrated here that the process of exciting the [Fe{H₂B(pz)₂}₂(bipy)] moiety, in the presence of with C₆H₂([Formula: see text])₂([Formula: see text])₂, to an electronic state characteristic of the high spin state though incident x-ray fluences, has a thermal activation energies are determined to 14-18 meV for a range of mixing ratios from 1:2 to 1:10. Those activation energies are also significantly reduced as compared to values of 60-80 meV found for nanometer thin films of [Fe{H₂B(pz)₂}₂(bipy)] on SiO₂.

Linear CuI2 Pd0 , CuI Pd02 , and AgI2 Pd0 Metal Chains Supported by Rigid N,N'-Diphosphanyl N-Heterocyclic Carbene Ligands and Metallophilic Interactions

Selective copper(I) to palladium(0) transmetallation of P-donors from the rigid N,N'-diphosphanyl-imidazol-2-ylidene C₃ H₂ [NP(tBu)₂ ]₂ (PC^NHC P) was observed when known [Cu₃ (μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₃ was reacted with [Pd(PPh₃ )₄ ]. When 1.2 equivalents of [Pd(PPh₃ )₄ ] was used, the product [Cu₂ Pd(μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₂ (2(OTf)₂ ) was obtained, which features a Cu^I -Cu^I -Pd⁰ chain and appears to be the first linear heterotrinuclear complex with d¹⁰ -d¹⁰ interactions between Pd⁰ and Cu^I . When the Cu₃ precursor was reacted with 3.0 equivalents of [Pd(PPh₃ )₄ ], the complex [CuPd₂ (μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₂ (3(OTf)₂ ) was obtained, which, on the basis of magnetic measurements, DFT calculations, and computed nuclear shieldings, was formulated as containing a Pd⁰ -Cu^I -Pd⁰ chain with an electron hole delocalized over the whole cation, including the metal chain. Similarly, selective transmetallation of the P-donors in [Ag₃ (μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₃ from silver to palladium (originating from [Pd(PPh₃ )₄ ]) gave the linear chain [Ag₂ Pd(μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₂ (5(OTf)₂ ), which on the basis of NMR spectroscopy comprises an Ag^I -Ag^I -Pd⁰ metal core. However, X-ray diffraction data collected on various samples of 5(OTf)₂ were modeled with 50:50 metal disorder at the terminal positions, corresponding to a (Ag^I /Pd⁰ )-Ag^I -(Ag^I /Pd⁰ ) formulation. Upon standing in solution, 5(OTf)₂ transformed to 6(OTf)₂ , the regioisomer of 5(OTf)₂ in which the Pd center has migrated to the central position of an Ag^I -Pd⁰ -Ag^I chain. Prolonged standing in CH₂ Cl₂ or by reaction with [PtCl₂ (NCMe)₂ ] converts complex 6(OTf)₂ to the Ag^I /Pd^II complex [Ag₂ PdCl₂ (μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₂ (7(OTf)₂ ). The structural data of 2(OTf)₂ , 3(OTf)₂ , and 7(OTf)₂ establish significant heterometallophilic interactions.

Metal complexes with oxygen-functionalized NHC ligands: synthesis and applications

Ligand design has met with considerable success with both categories of hybrid ligands, which are characterized by chemically different donor groups, and of N-heterocyclic carbenes (NHCs). Their spectacular development and diversity are attracting worldwide interest and offers almost unlimited diversity and potential in e.g. coordination/organometallic main group and transition metal chemistry, catalysis, medicinal chemistry and materials science. This review aims at providing a comprehensive update on a specific class of ligands that has enjoyed much attention in the past few years, at the intersection between the two categories mentioned above, that of hybrid NHC ligands in which the functionality associated with the carbene donor is of the oxygen-donor type. For each type of oxygen-donor present in such chelating (Section 1) or bridging (Section 2) hybrid ligands, we will examine the synthesis, structures and reactivity of their metal complexes and their applications, with a special focus on homogeneous catalysis (Section 3). Thus, hydrogenation, C-H bond activation, C-C, C-N, C-O bond formation, hydrolysis of silanes, oligomerization, polymerization, metathesis, hydrosilylation, C-C bond cleavage, acceptorless dehydrogenation, dehalogenation/hydrogen transfer, oxidation and reduction reactions will be successively presented in a tabular manner, to facilitate an overview and a rapid identification of the relevant publications describing which metals associated with a given oxygen functionality are most suitable. The literature coverage includes the year 2015.

Reactivity of a dearomatised pincer CoIIBr complex with PNCNHC donors: alkylation and Si–H bond activation via metal–ligand cooperation

Whereas [Co(^CyP*N_aC^NHC)Br] (1) with dearomatised pincer ^CyP*N_aC^NHC affords the Co^II–alkyl complex 3, uncommon silane reduction yields the Co^I complex 4.

A tritopic carbanionic N-heterocyclic dicarbene and its homo- and heterometallic coinage metal complexes

Homo (Au₃)- and heterotrinuclear coinage metal complexes (Au₂Ag and Au₂Cu) ligated by the first tritopic dicarbanionic NHC have been prepared by deprotonation of ditopic NHC digold complexes.

Tritopic NHC Precursors: Unusual Nickel Reactivity and Ethylene Insertion into a C(sp3 )-H Bond

The imidazolium chloride [C₃ H₃ N(C₃ H₆ NMe₂ )N{C(Me)(=NDipp)}]Cl (1; Dipp=2,6-diisopropyl phenyl), a potential precursor to a tritopic N^imine C^NHC N^amine pincer-type ligand, reacted with [Ni(cod)₂ ] to give the Ni^I -Ni^I complex 2, which contains a rare cod-derived η³ -allyl-type bridging ligand. The implied intermediate formation of a nickel hydride through oxidative addition of the imidazolium C-H bond did not occur with the symmetrical imidazolium chloride [C₃ H₃ N₂ {C(Me)(=NDipp)}₂ ]Cl (3). Instead, a Ni-C(sp³ ) bond was formed, leading to the neutral N^imine CHN^imine pincer-type complex Ni[C₃ H₃ N₂ {C(Me)(=NDipp)}₂ ]Cl (4). Theoretical studies showed that this highly unusual feature in nickel NHC chemistry is due to steric constraints induced by the N substituents, which prevent Ni-H bond formation. Remarkably, ethylene inserted into the C(sp³ )-H bond of 4 without nickel hydride formation, thus suggesting new pathways for the alkylation of non-activated C-H bonds.