The structures and reactivity of NHC-supported copper(i) triphenylgermyls

Deprotonation of triphenyl germane with NHC-supported copper alkoxides afforded four novel (NHC)CuGePh3 complexes. Of these, (IPr)CuGePh3 (IPr = :C{N(2,6-iPr2C6H3)CH}2) was selected for further investigation. Analysis by EDA-NOCV indicates it to be a germyl nucleophile and its σ-bond metathesis reaction with a range of p-block halides confirmed it to be a convenient source of [Ph3Ge]-. The Cu-Ge bond of (IPr)CuGePh3 underwent π-bond insertions with tBuNCS, CS2, and PhNCO to furnish a series of germyl substituted carboxylate derivatives, (IPr)CuXC(Y)GePh3 (X = S, NPh; Y = S, NtBu, O), which were structurally characterised. (IPr)CuGePh3 inserted phenyl acetylene, providing both the Markovnikov and anti-Markovnikov products. The (NHC)CuGePh3 compounds were validated as catalytic intermediates; addition of 10 mol% of NHC-copper(i) alkoxide to a mixture of triphenyl germane and a tin(iv) alkoxide resulted in a tin/germanium cross coupling with concomitant formation of alcohol. Moreover, a catalytic hydrogermylation of Michael acceptors was developed with Ph3GeH adding to 7 activated alkenes in good conversions and yields in the presence of 10 mol% of NHC-copper(i) alkoxide. In all cases, this reaction provided the β-germylated substrate implicating nucleophilicity at germanium.

Synthesis, structure and photophysical properties of two tetranuclear copper(I) iodide complexes based on acetylpyridine and diphosphine mixed ligands

Two copper(I) iodide tetramers, namely, [μ₂-1,3-bis(diphenylphosphanyl)propane-κ²P:P']di-μ₃-iodido-di-μ₂-iodido-[1-(pyridin-3-yl)ethan-1-one-κN]tetracopper(I) dichloromethane disolvate, [Cu₄I₄(C₆H₇NO)₂(C₂₇H₂₆P₂)₂]·2CH₂Cl₂ (CuL³), and [μ₂-1,3-bis(diphenylphosphanyl)propane-κ²P:P']di-μ₃-iodido-di-μ₂-iodido-[1-(pyridin-4-yl)ethan-1-one-κN]tetracopper(I), [Cu₄I₄(C₆H₇NO)₂(C₂₇H₂₆P₂)₂] (CuL⁴), have been synthesized from reactions of CuI, 1,3-bis(diphenylphosphanyl)propane (dppp) and 3- or 4-acetylpyridine (3/4-acepy). The complexes were characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction (XRD), powder XRD and photoluminescence spectroscopy. Both complexes possess a stair-step [Cu₄I₄] cluster structure with a crystallographic inversion centre located in the middle of a Cu₂I₂ ring (Z' = 1/2). The dppp ligands each adopt a bidentate coordination mode that bridges two Cu^I centres on one side of the [Cu₄I₄] cluster and the acepy ligands act as terminal ligands. The solid-state samples of similar complexes show highly efficiency thermally activated delayed fluorescence (TADF) at room temperature. At ambient temperature, both CuL³ and CuL⁴ exhibit photoluminescence, with a maximum emission in the region 560-580 nm and with short emissive decay times, but only phosphorescence was observed at 77 K. The narrow gaps between the higher lying singlet state and the triplet state, ΔE(S₁ - T₁), also confirm the presence of TADF. Structure analysis and consideration of photoluminescence indicates that the position of the acetyl group on the heterocyclic ligand has an obvious influence on the structural arrangement, on intermolecular interactions and on the observed photophysical properties.

Mononuclear Cu Complexes Based on Nitrogen Heterocyclic Carbene: A Comprehensive Review

During the last decade, organometallic, coordination, and catalytic chemistry of the three-dimensional metals such as copper (Cu) has been greatly affected by the emergence of nitrogen heterocyclic carbene (NHC) complexes. The NHCs, and in particular the mononuclear Cu^I-based ones, have been proven vastly useful in several applications such as in biosynthesis, catalysis, photochemistry, etc. This review tries to thoroughly describe a series of mononuclear Cu^I NHC complexes and their subcategories such as heteroleptics, and bidentate and tridentate heteroatom complexes, and give some detailed insights on their development, emergence, and applications. A brief outlook is also disclosed to enable other researchers to further develop a platform for future advances and studies in the field of Cu^I-based NHCs.

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.

A two-coordinate Ni(i) silyl complex: CO2 insertion and oxidatively-induced silyl migrations

Synthesis of the first open-shell two-coordinate silyl complex and its oxidatively-induced silyl rearrangements.

Coinage metal complexes of NHC-stabilized silyliumylidene ions

The first coinage metal complexes (M = Cu, Ag, Au) of an N-heterocyclic carbene-stabilized silyliumylidene ion are reported.

[(18-C-6)K][(N≡C)CuI-SiMe2Ph], a Potassium Silylcyanocuprate as a Catalyst Model for Silylation Reactions with Silylboranes: Syntheses, Structures, and Catalytic Properties

Cu^I-catalyzed silylation reactions involving silylboranes (in particular, pinB-SiMe₂Ph (1)) as silyl sources have recently gained considerable attention. One of the most efficient and versatile and yet simplest catalyst systems consists of CuCN/NaOMe; however, nothing is known about the catalytically relevant species. Using an NHC-based model catalyst, copper silyl complexes of the type [(NHC)Cu-SiMe₂Ph] have been established to be crucial species in these catalytic processes. The well-defined and spectroscopically and structurally characterized complex [(18-C-6)K][NC-Cu-OtBu] (2), as a model for the catalytic system, CuCN/NaOMe, shows comparable catalytic activity toward established, exemplary substrates (aldehydes, imines, α,β-unsaturated carbonyls) and in extension allows the efficient silylation of ketones. In addition, a number of peculiarities of the catalytic reaction are readily rationalized on the basis of the mechanistic insight already established using [(NHC)Cu-SiMe₂Ph] as a model catalyst. Analogously to the NHC model system, the reaction of 2 with the silylborane 1 furnishes the silylcyanocuprate [(18-C-6)K][NC-Cu-SiMe₂Ph] (3) as a potential crucial intermediate in these silylation reactions also suggesting mechanistic similarities between (NHC)Cu- and CuCN/NaOMe-based catalyst systems. Moreover, 3 and [(NHC)Cu-SiMe₂Ph] complexes also share structurally distinctive features. In the solid state 3 either exists as a linear, two-coordinated copper complex or, depending on the conditions of crystallization, forms binuclear μ-silyl bridged dimers exhibiting very short Cu···Cu distances. Both structural motifs are also known for [(NHC)Cu-SiR₃] complexes. These findings give an initial insight into the versatile structural chemistry of certain silylcyanocuprates; in particular, the finding of dinuclear silylcuprates gives rise to the question whether these dimeric species are of mechanistic relevance for the catalytic processes. However, all peculiarities of the investigated catalytic reaction can readily be rationalized on the basis of the mechanistic details established using (NHC)Cu model complexes.

[(NHC)Cu(I)-ER3] Complexes (ER3 = SiMe2Ph, SiPh3, SnMe3): From Linear, Mononuclear Complexes to Polynuclear Complexes with Ultrashort Cu(I)···Cu(I) Distances

A series of complexes of the type [(NHC)Cu-ER3] (NHC = IDipp, IMes, ItBu, Me2IMe, and ER3 = SiMe2Ph, SiPh3, SnMe3) and [(NHC)Cu-R'] (NHC = IDipp, Me2IMe and R' = Ph, C≡CPh) was synthesized in good yields by the reaction of the corresponding [(NHC)Cu-OtBu] complex with the respective silylborane pinB-ER3 (pin = OCMe2CMe2O; ER3 = SiMe2Ph, SiPh3), the stannylborane ((C2H4)(iPrN)2)B-SnMe3, or a boronic acid ester pinB-R' (R' = Ph, C≡CPh). Solid structures of all complexes were systematically studied by X-ray diffraction analysis. The solid state structures of the complexes [(NHC)Cu-ER3] show a dependence of the structural motif from the steric properties of the NHC ligand. The sterically demanding NHC ligands (IDipp, IMes, ItBu) lead to monomeric, linear complexes [(NHC)Cu-ER3], while with the less demanding Me2IMe ligand, polynuclear, μ-ER3-bridged complexes with ultrashort Cu···Cu distances are observed. For the related complexes [(NHC)Cu-R'] no analogous complexes with bridging anionic ligands are realized. Instead, irrespective of the NHC ligand, linear coordinated copper complexes of different types are formed. (29)Si heteronuclear solution NMR spectroscopic data on [(NHC)Cu(I)-SiR3] exhibit distinctly different chemical shifts for the (in the solid state) monomeric and dimeric complexes suggesting different structure types also in solution. This agrees well with the observation of a trinuclear complex [(Me2IMe)Cu-SnMe3]3 both in the solid state and in solution. Initial catalytic studies suggest that [(NHC)Cu-OtBu] complexes (NHC = ItBu, Me2IMe) are, in addition to the established [(IDipp)Cu-OtBu] complex, efficient precatalysts for the silylation of aldehydes and α,β-unsaturated ketones with pinB-SiMe2Ph.