Acyclic Diaminocarbene Research Articles

Acyclic Diaminocarbene Platinum(IV) Complexes Synthesized by the Oxidative Addition of MeI and I<sub>2</sub>

The oxidative addition of methyl iodide or molecular iodine to the bis(С,N-chelate) deprotonated diaminocarbene platinum(II) complexes [Pt{C(N(H)Ar)(NC(N(H)Ph)N(Ph)}2] (Ar = C6H3-2,6-Me2 (Xyl), C6H2-2,4,6-Me3 (Mes), and C6H4-4-Me (pTol)) affords the corresponding platinum(IV) derivatives in a yield of 89–99%. The addition of CF3CO2H is accompanied by the protonation of the nitrogen atoms of the diaminocarbene fragment to form the cationic complexes [[PtI(X)-{C(N(H)Ar)(NC(N(H)Ph)N(Ph)}2]CF3CO2H (X = Me, I). The structures of the compounds are determined by elemental analysis; high resolution mass spectrometry with electrospray ionization (ESI HRMS); IR spectroscopy; 1H, 13C{1H}, 19F{1H}, and 195Pt{1H} NMR spectroscopy; 2D NMR spectroscopy (1H,1Н COSY, 1H,1Н NOESY, 1H,13C HSQC, 1H,13C HMBC, 1H,15N HSQC, 1H,15N HMBC), and X-ray diffraction (XRD) and thermogravimetric analyses. The synthesized platinum(IV) complexes are thermally stable to 200–260°C and are electroneutral molecules with the octahedral coordination sphere formed by two deprotonated diaminocarbene C,N-chelate substituents and iodine and methyl or two iodine atoms localized in the apical positions.

Luminescent Cyclometalated Platinum Acyclic Diaminocarbene Complexes as PhOLED Dopants

Luminescent Cyclometalated Platinum Acyclic Diaminocarbene Complexes as PhOLED Dopants

Exploring the Pt → ligand back‐donation through the rotational barrier of an acyclic diaminocarbene

The importance of the Dewar‐Chatt‐Duncanson model for inorganic chemists cannot be overstated. It provides a simple yet robust framework for understanding metal‐ligand bonding in terms of σ‐donation and π‐back‐donation. Some years ago, a publication (Chem. Eur. J. 2015, 21, 2467) introduced a method to effectively correlate experimental NMR data with back‐donation, using [LAu(ADC)]+/0 complexes (ADC = acyclic diaminocarbene) as case study. Here, we theoretically expand the same method to [L(PH3)(ADC)PtCl]+/0 complexes, to verify whether the method is general and to gain deeper insights into the influence of L on Pt‐ADC bonding, especially in the trans position. Such insights hold potential for guiding rational catalyst design strategies.

Metal-(Acyclic Diaminocarbene) Complexes Demonstrate Nanomolar Antiproliferative Activity against Triple-Negative Breast Cancer.

Invited for the cover of this issue are Tatiyana Serebryanskaya, Mikhail Kinzhalov and co-workers at St. Petersburg State University, the Research Institute for Physical Chemical Problems, Belarusian State University, Togliatti State University and Blokhin National Medical Research Center of Oncology. The image depicts the shield of Pallas Athena with the structure of a palladium carbene complex that protects against triple-negative breast cancer. Read the full text of the article at 10.1002/chem.202400101.

Front Cover: Metal‐(Acyclic Diaminocarbene) Complexes Demonstrate Nanomolar Antiproliferative Activity against Triple‐Negative Breast Cancer (Chem. Eur. J. 28/2024)

Front Cover: Metal‐(Acyclic Diaminocarbene) Complexes Demonstrate Nanomolar Antiproliferative Activity against Triple‐Negative Breast Cancer (Chem. Eur. J. 28/2024)

Phosphorescent Cyclometalated Palladium(II) and Platinum(II) Complexes Derived from Diaminocarbene Precursors.

Metal-mediated self-assembly of isocyanides and methyl 4-aminopyrimidine-5-carboxylate leads to luminescent PdII and PtII complexes featuring C,N-cyclometalated acyclic diaminocarbene (ADC) ligands. The solid-state luminescent properties of these diaminocarbene derivatives are attributed to their triplet-state metal/metal-to-ligand charge-transfer (3MMLCT) nature, which is driven by attractive intermolecular M···M interactions further reinforced by the intramolecular π-π interactions even in the structure of the Pd compound, which is the first Pd-ADC phosphor reported.

Metal-(Acyclic Diaminocarbene) Complexes Demonstrate Nanomolar Antiproliferative Activity against Triple-Negative Breast Cancer.

Hydrolytically stable PdII and PtII complexes supported by acyclic diaminocarbene ligands represent a novel class of structural organometallic anticancer agents exhibiting nanomolar antiproliferative activity in a panel of cancer cell lines (IC50 0.07-0.81 μM) and up to 300-fold selectivity for cancer cells over normal primary fibroblasts. The lead drug candidate was 300 times more potent than cisplatin in vitro and showed higher efficacy in reducing the growth of aggressive MDA-MB-231 xenograft tumors in mice.

Synthesis and reactivity of air stable Ni(II) complexes with isocyanides and dialkyldithiophosphate ligands: acyclic diaminocarbene formation.

A library of new neutral and cationic Ni(II) complexes containing isocyanide ligands and mono- or dialkyl-dithiophosphate have been easily prepared and fully characterized. The synthesis of the neutral complexes unfolds through the alkyl transfer from one alkyldithiophosphate leaving group coordinated to the Ni(II) complex. The alkyl transfer is controlled by steric factors and is highly solvent-dependent. These complexes shown to constitute excellent precursors to obtain new families of air stable Ni(II)-based acyclic diaminocarbene complexes (Ni(II)-ADCs) by nucleophilic attack with various alkyl-substituted amines. Remarkably, the ADC is only produced at one of the isocyanide ligands, keeping the other isocyanide unreacted. This was subsequently exploited to prepare the unprecedented neutral and cationic dinuclear Ni(II) complexes containing a bridging bis-carbene ligand using piperazine.

Addition Polymerization of 3,3-Disubstituted Cyclopropenes in the Presence of a Palladium Complex Containing an Acyclic Diaminocarbene Ligand

Addition Polymerization of 3,3-Disubstituted Cyclopropenes in the Presence of a Palladium Complex Containing an Acyclic Diaminocarbene Ligand

Luminescent Platinum Complexes with π-Extended Aryl Acetylide Ligands Supported by Isocyanides or Acyclic Diaminocarbenes.

In this work, we present a series of luminescent platinum acetylide complexes with acetylides that are electronically modified and/or π-extended. Six isocyanide-supported complexes with the general formula cis-[Pt(CNAr)2(C≡CR)2] and six acyclic diaminocarbene (ADC) complexes of the form trans-[Pt(ADC)2(C≡CR)2], all using the same five acetylide ligands, are described. The compounds are characterized by multinuclear NMR, FT-IR, and single-crystal X-ray diffraction. In most cases, the phosphorescence arises from an acetylide-centered 3(π → π*) excited state, although in one of the isocyanide compounds there is evidence for a charge-transfer excited state. The photoluminescence wavelength depends strongly on the substitution pattern and extent of the π conjugation on the acetylide, with maxima spanning the range of ca. 460-540 nm. Most photoluminescence lifetimes are long, beyond 50 μs, and quantum yields are low to moderate, 0.043-0.27. The photoluminescence quantum yields and lifetimes in these compounds do not systematically improve in the ADC complexes compared to the isocyanide versions, suggesting the neutral ligand σ-donor character does not play a large role in the excited-state dynamics when the triplet excited state is delocalized over a large π system.

Synthesis of gold(I) diaminocarbene complexes by the addition of amines across coordinated isocyanoferrocene

Gold(I) acyclic diaminocarbene complexes of the [AuCl{C(NHFc)(NR2)}] type (Fc = ferrocenyl) were conveniently synthesized by a one-pot procedure. In this method, 1 equiv. of isocyanoferrocene (FcNC) and an excess of primary or secondary amines R2NH (dimethylamine, morpholine, methylamine, cyclohexylamine, and p-toluidine) are sequentially added to [AuCl(SMe2)] as a gold source in dichloromethane. The stepwise synthesis, in which [AuCl(FcNC)] is the isolated intermediate, worked equally well but generated lower overall yields due to compound loss during the two purification steps. The approach was further extended to synthesize the corresponding cationic biscarbene complexes [Au{C(NHFc)(NR2)}2]Cl simply by using 2 equiv. of FcNC during the “first” reaction step. The compounds form conformational isomers in solution that differ by the orientation of substituents at the carbene units. Based on DFT calculations, these isomers exhibit similar energies (energy difference ≤ 5 kcal mol–1). The crystal structures revealed symmetrical carbene units and the dominant role of the N-H⋅⋅⋅Cl interactions in the crystal assemblies in all cases, which also control the tendency for a particular conformation in the solid state.

Acyclic diaminocarbenes (ADCs) and their catalytic activity in metal catalysed organic transformation reactions

Abstract Acyclic diaminocarbenes (ADCs)–Metal complex having strong donor ability and thermal stability led to extensive usability across every area of inorganic and organometallic chemistry. The unique properties of acyclic diaminocarbenes (ADCs) provide certain advantages over other carbene ligands and have the potential to make a great impact in catalysis. Further, the straightforward synthesis of M–ADCs (metal bound acyclic diaminocarbenes) complexes via metal-mediated reaction provides a wide range of well-defined metal carbene catalysts, which might inspire more researchers to devise unsymmetrically substituted, chiral, and novel acyclic carbene compounds. Although the above synthetic route is limited to a few late transition metals, but have great opportunities to expand the scope of this method. The application of M–ADCs complexes as a catalyst for several organic transformation reactions such as various cross-coupling reactions and asymmetric synthesis like hydroarylation, hydroazidation, hydroamination, cyclization and addition reactions which have shown comparable or even higher activities than the analogous M–NHCs based on all the reports presented. Recent findings of donor ability of several ADC ligands would be useful in fine-tuning the electronic properties, and then a catalyst with a certain combination of donicity and steric requirement could open new doors in catalytic reactivity. Thus, the objective of this review is to assess the recent growths that have been made in designing novel and chiral ADCs ligands and synthesizing ADCs–Metal complexes and to highlight catalytic activities of metal acyclic diaminocarbene complexes for cross-coupling reactions.

Substituent-Dependent Azide Addition to Isocyanides Generates Strongly Luminescent Iridium Complexes.

Ligand-centered functionalization reactions offer diverse strategies to prepare luminescent organometallic compounds. These compounds can have unique structures that are not accessible via traditional coordination chemistry and can possess enhanced or unusual photophysical properties. Here we show that bis-cyclometalated iridium bis-isocyanide complexes (1) react with azide (N3-) to form novel luminescent structures. The fate of the reaction with azide is determined primarily by the substituent on the aryl isocyanide. Those with electron-withdrawing substituents (CF3 or NO2) react with 1 equiv of azide followed by N2 extrusion, forming aryl cyanamido products (2). With electron-donating groups on the aryl isocyanide the reactivity is more diverse, and three outcomes are possible. In two cases, the isocyanide and azide undergo a [3 + 2] cycloaddition to form a C-bound tetrazolato structure (3). In three other cases, 2 equiv of azide are involved in the formation of a previously unobserved structure, where a tetrazolato and aryl cyanamido couple and rearrange to form a chelating ligand comprised of an N-bound tetrazolato and an acyclic diaminocarbene (4). Finally, a bimetallic aryl cyanamido complex (5) is isolated in one case. All compounds are luminescent, some with exceptional photoluminescence quantum yields as high as 0.81 in solution for sky-blue emission, and 0.87 for yellow emission and 0.65 for orange-red emission in polymer films.

Efficient blue-phosphorescent trans-bis(acyclic diaminocarbene) platinum(ii) acetylide complexes.

The lack of efficient and robust deep-blue phosphorescent metal complexes remains a significant challenge in the context of electroluminescent color displays. The emissive triplet states of blue phosphors are deactivated by low-lying metal-centered (3MC) states, which can be ameliorated by increasing the σ-donating ability of the supporting ligands. Here we unveil a synthetic strategy to access blue-phosphorescent complexes with two supporting acyclic diaminocarbenes (ADCs), known to be even stronger σ-donors than N-heterocyclic carbenes (NHCs). This new class of platinum complexes has excellent photoluminescence quantum yields, with four of six complexes affording deep-blue emission. Experimental and computational analyses are consistent with a pronounced destabilization of the 3MC states by the ADCs.

Cyclometalated platinum(II) complexes with acyclic diaminocarbene ligands for OLED application.

A novel series of cyclometalated platinum(II) complexes bearing acyclic diaminocarbene (ADC) ancillary ligands were designed and prepared. Their photophysical properties were systematically studied through experimental and theoretical investigations. All complexes exhibit green phosphorescence with a quantum efficiency of up to 45% in 2 wt% doped PMMA film at room temperature. The complexes are used as light-emitting dopants for organic light-emitting diode (OLED) fabrication. The devices displayed a green emission with a maximum current efficiency of 2.9 cd A-1 and a luminance of 2700 cd m-2. These results show that these cyclometalated platinum(II) complexes can be used as efficient green emitting components of OLED devices.

Synthesis of Addition Poly(5-methyl-2-norbornene) in the Presence of Palladium Complexes Containing Acyclic Diaminocarbene Ligands

Synthesis of Addition Poly(5-methyl-2-norbornene) in the Presence of Palladium Complexes Containing Acyclic Diaminocarbene Ligands

Current Developments of N-Heterocyclic Carbene Au(I)/Au(III) Complexes toward Cancer Treatment.

Since their first discovery, N-heterocyclic carbenes have had a significant impact on organometallic chemistry. Due to their nature as strong σ-donor and π-acceptor ligands, they are exceptionally well suited to stabilize Au(I) and Au(III) complexes in biological environments. Over the last decade, the development of rationally designed NHCAu(I/III) complexes to specifically target DNA has led to a new “gold rush” in bioinorganic chemistry. This review aims to summarize the latest advances of NHCAu(I/III) complexes that are able to interact with DNA. Furthermore, the latest advancements on acyclic diamino carbene gold complexes with anticancer activity are presented as these typically overlooked NHC alternatives offer great additional design possibilities in the toolbox of carbene-stabilized gold complexes for targeted therapy.

New phosphorus-containing polycycles with a spiroamine group

Aim. To synthesize hexahydrospiro[cyclopropane-1,10’-pyrido[1,2-c]quinazoline] and 2-λ5-benzo[f][1,4,2]diazaphosphepine derivatives – new N-P containing heterocyclic compounds with the 6-azaspiro[2.5]octane fragment.Results and discussion. A new analog of the powerful electrophilic reagent – “Alder dimer” ‒ was obtained from the interaction of triflic anhydride and spiro(4-cyclopropane) piperidinyl formamide, and further used to synthesize new Nʹ-PV- and PIII-substituted Νʹ-phenyl, Νʹʹ-hexahydro(azaspiro)octylformamidinium salts – precursors of acyclic N-phosphorylated diamino carbenes with a spiroamine group. It has been shown that acyclic N-phosphorylated diaminocarbenes are transient species affording various products. The structure of the final product is primarily determined by nature of the phosphorus-bearing substituent, namely a phosphoryl or phosphino-group. N-PV-substituted carbene undergoes a 1,2-phosphorus shift with the formation of (selenophosphoryl)formamidine in a high yield. For N-PIII-substituted carbene a compatible 1,3-H shift also occurs with the formation of an intermediate azomethine ylide converted into a new heterocyclic system – hexahydrospirocyclopropane -1,10’-pyrido[1,2-c]quinazoline. Under the action of acid an unexpected further expansion of the 6-member ring occurs with the formation of a diazepine derivative.Experimental part. The reaction of Alder reagent with N-PV-seleno phosphoryl arylamides afforded N-phosphorus substituted formamidinium salts, which are easily reduced to PIII analogues. In addition to the corresponding formamidines, the new N-phosphorylated spiroamine-containing polycyclic system was isolated from the reaction mixture formed by the deprotonation of such salts with a strong non-nucleophilic base.Conclusions. The Alder reagent approach allows synthesizing precursors of acyclic formamidine carbenes with the spiroamine group. Such carbenes are unstable. By converting these compounds N-PIII-substituted tetrahydropyrimidine and diazaphosphepine derivatives with the 6-azaspiro[2.5]octane fragment have been obtained for the first time.

Platinum(II)-Substituted Phenylacetylide Complexes Supported by Acyclic Diaminocarbene Ligands.

We introduce phosphorescent platinum aryl acetylide complexes supported by tert-butyl-isocyanide and strongly σ-donating acyclic diaminocarbene (ADC) ligands. The precursor complexes cis-[Pt(CNtBu)2(C≡CAr)2] (4a-4f) are treated with diethylamine, which undergoes nucleophilic addition with one of the isocyanides to form the cis-[Pt(CNtBu)(ADC)(C≡CAr)2] complexes (5a-5f). The new compounds incorporate either electron-donating groups (4-OMe and 4-NMe2) or electron-withdrawing groups [3,5-(OMe)2, 3,5-(CF3)2, 4-CN, and 4-NO2] on the aryl acetylide. Experimental HOMO-LUMO gaps, estimated from cyclic voltammetry, span the range of 2.68-3.61 eV and are in most cases smaller than the unsubstituted parent complex, as corroborated by DFT. In the ADC complexes, peak photoluminescence wavelengths span the range of 428 nm (2a, unsubstituted phenylacetylide) to 525 nm (5f, 4-NO2-substituted), with the substituents inducing a red shift in all cases. The phosphorescence E0,0 values and electrochemical HOMO-LUMO gaps are loosely correlated, showing that both can be reduced by either electron-donating or electron-withdrawing substituents on the aryl acetylides. The photoluminescence quantum yields in the ADC complexes are between 0.044 and 0.31 and the lifetimes are between 4.8 and 14 μs, a factor of 1.8-10× higher (for ΦPL) and 1.2-3.6× longer (for τ) than the respective isocyanide precursor (ΦPL = 0.014-0.12, τ = 2.8-8.2 μs).

Reactivity of Diamines in Acyclic Diamino Carbene Gold Complexes.

Acyclic diamino carbenes (ADCs) are interesting alternatives to their more widely studied N-heterocyclic carbene counterparts, particularly due to their greater synthetic accessibility and properties such as increased sigma donation and structural flexibility. ADC gold complexes are typically obtained through the reaction of equimolar amounts of primary/secondary amines on gold-coordinated isocyanide ligands. As such, the reaction of diamine nucleophiles to isocyanide gold complexes was expected to lead to bis-ADC gold compounds with potential applications in catalysis or as novel precursors for gold nanomaterials. However, the reaction of primary diamines with two equivalents of isocyanide gold chlorides resulted in only one of the amine groups reacting with the isocyanide carbon. The resulting ADC gold complexes bearing free amines dimerized via coordination of the amine to the partner gold atom, resulting in cyclic, dimeric gold complexes. In contrast, when secondary diamines were used, both amines reacted with an isocyanide carbon, leading to the expected bis-ADC gold complexes. Density functional theory calculations were performed to elucidate the differences in the reactivities between primary and secondary diamines. It was found that the primary amines were associated with higher reaction barriers than the secondary amines and hence slower reaction rates, with the formation of the second carbenes in the bis-ADC compounds being inhibitingly slow. It was also found that diamines have a unique reactivity due to the second amine serving as an internal proton shuttle.