Acyclic Diaminocarbene Research Articles

Tuning the luminescence of transition metal complexes with acyclic diaminocarbene ligands

Organometallics featuring acyclic diaminocarbene ligands have recently emerged as powerful emitters for use in electroluminescent technologies.

Synthesis and Contemporary Applications of Platinum Group Metals Complexes with Acyclic Diaminocarbene Ligands (Review)

Synthesis and Contemporary Applications of Platinum Group Metals Complexes with Acyclic Diaminocarbene Ligands (Review)

Protic Ferrocenyl Acyclic Diamino Carbene Gold(I) Complexes

AbstractTwo mononuclear protic ferrocenyl acyclic diamino carbene gold(I) complexes AuCl[C(NHFc)(NR2)] were prepared by nucleophilic attack of diethylamine (R = Et) and diisopropylamine (R = iPr) at the ferrocenyl substituted isocyanide complex chlorido(isocyanoferrocene)gold(I) AuCl(CN−Fc). In the solid state, the multifunctional protic carbene gold(I) complexes display intermolecular aurophilic interactions or intermolecular NH⋅⋅⋅Cl hydrogen bonding in addition to intramolecular non‐classical NH⋅⋅⋅Fe hydrogen bonds. Oxidation of the AuCl[C(NHFc)(NR2)] complexes initially takes place at the iron centres giving highly coloured ferrocenium ions, which subsequently likely undergo electron transfer from gold(I) to iron(III) yielding putative EPR‐active gold(II) species.

An Acyclic Diaminocarbene Complex of Platinum Formed by Desulfurization of 1,3‐Bis(3‐methylpyridin‐2‐yl)thiourea

AbstractThe reaction of the ambidentate ligand 1,3‐bis(3‐methylpyridin‐2‐yl)thiourea (1) with [PtCl2(dmso)2] in dichloromethane led to formation of a poorly soluble compound 2, characterized as a conventional chelate complex [PtCl2(1)]=2. Reaction in methanol resulted in desulfurization to produce a fluorescing cationic diaminocarbene−platinum(II) complex 3, the structure of which was elucidated by X‐ray crystallography, mass spectrometry and NMR. Experimental findings were supported by DFT calculations.

Highly Sterically Encumbered Gold Acyclic Diaminocarbene Complexes: Overriding Electronic Control in Regiodivergent Gold Catalysis

Two series of sterically encumbered gold(I) acyclic diaminocarbene (ADC) complexes were prepared by reaction of mono- and dialkylamines with gold-bound 2-mesitylphenyl isocyanide (monomesityl serie...

Predicting Excited-State and Luminescence Properties of a Cyclometalated Iridium(III) Complex: Quantum Mechanics/Molecular Mechanics Study

The excited-state and luminescence properties of a cyclometalated Ir(III) complex with two C∧N ligands (C∧N = 2-(2,4-difluorophenyl)pyridine, F2ppy) and one acyclic diamino carbene (ADC) ancillary ...

Luminescent cyclometalated platinum(ii) complexes with acyclic diaminocarbene ligands: structural, photophysical and biological properties.

Four new cyclometalated Pt(ii) complexes bearing acyclic diaminocarbene (ADC) ligands, [Pt(C^N)Cl{C(NHXyl)(NHR)}] [C^N = 2,6-difluorophenylpyridine (dfppy), phenylquinoline (pq); R = Pr 3a, 4a, CH2Ph 3b, 4b], were prepared by the nucleophilic attack on the isocyanide [Pt(C^N)Cl(CNXyl)] (C^N = dfppy 1, pq 2) by the corresponding amine RNH2 (R = Pr, CH2Ph). Complexes 3 show in their 1H NMR spectra in CDCl3 a notable concentration dependence, with a clear variation of the δH (NHXyl) signal, suggesting an assembling process implying donor-acceptor NHXylCl bonding, also supported by 1D-PGSE (Pulse Field Gradient Spin Echo) and 2D-DOSY (Diffusion Ordered Spectroscopy) NMR experiments in solution and X-ray diffraction studies. The intermolecular interactions in compounds 3a and 3b were studied by using Hirshfeld surface analysis and Non-Covalent Interaction (NCI) methods on their X-ray structures. Their photophysical properties were investigated by absorption and emission spectroscopies and also by TD-DFT calculations performed on 3a and 4b. These complexes show green (3) or orange (4) phosphorescence, attributed to a mixed 3IL/3MLCT excited state. The carbene ligand does not affect the emission maxima but it produces an increase of the quantum yields in relation to the isocyanide in the precursors. In fluid solutions, the emission is not concentration-dependent, but the complexes may show aggregation induced emission as detailed for complexes 3a and 4a. In addition, cytotoxicity studies in the human cell lines A549 (lung carcinoma) and HeLa (cervix carcinoma) showed good activity for these complexes and 3a, 3b and 4a exhibit a strong effect on DNA electrophoretic mobility. To the best of our knowledge, compounds 3 and 4 represent the first examples of cycloplatinated complexes bearing acyclic diamino carbenes with antiproliferative properties.

Efficient Deep Blue Platinum Acetylide Phosphors with Acyclic Diaminocarbene Ligands.

Here we report five blue-phosphorescent platinum bis-phenylacetylide complexes with an investigation of their photophysical and electrochemical attributes. Three of the complexes (1-3) are of the general formula cis-Pt(CNR)2 (C≡CPh)2 , in which CNR is a variably substituted isocyanide and C≡CPh is phenylacetylide. These isocyanide complexes serve as precursors for complexes of the general formula cis-Pt(CNR)(ADC)(C≡CPh)2 (4 and 5), in which ADC is an acyclic diaminocarbene installed by amine nucleophilic addition to one of the isocyanides. All of the complexes exhibit deep blue phosphorescence with λmax ∼430 nm in poly(methyl methacrylate) (PMMA) thin films. Whereas isocyanide complexes 1-3 exhibit modest photoluminescence quantum yields (ΦPL ), incorporation of one acyclic diaminocarbene ligand results in a three-fold to 16-fold increase in ΦPL while still maintaining an identical deep blue color profile.

Stereoelectronic Profiling of Acyclic Diamino Carbenes (ADCs).

A library of 14 heterobis(carbene) complexes of the general formula [Au(iPr2-bimy)(ADC)]BF4 (7-20) containing the N-heterocyclic carbene reporter iPr2-bimy and various protic acyclic diaminocarbenes (ADCs) have been prepared to estimate their stereoelectronic properties by 13C NMR spectroscopy and percentage buried volume (%Vbur) determinations. Their preparation was achieved by nucleophilic attack of five secondary amines on six mixed NHC/isocyanide complexes of the type [Au(iPr2-bimy)(CN-R)]BF4 (1-6). Analyses of the iPr2-bimy carbene signals reveal that protic ADCs are stronger donors than classical and expanded-ring NHCs. On the other hand, they are weaker donating compared to NHCs with reduced-heteroatom stabilization. Moreover, stereoelectronic fine-tuning of these ligands is possible by a diverse range of substituents originating from the employed isocyanides and amines.

Phosphorescent Iridium(III) Complexes with Acyclic Diaminocarbene Ligands as Chemosensors for Mercury.

A new application for bis(cyclometalated) iridium(III) species containing ancillary acyclic diaminocarbene ligands, viz. for sensing of mercury(II) ions, is disclosed. A family of bis(cyclometalated) iridium(III) species supported by both parent isocyanide and acyclic diaminocarbene ligands was prepared, and their electrochemical and photophysical properties were evaluated, revealing efficient blue-green phosphorescence in solution with quantum yields of up to 55%. We uncovered that the photophysical properties of these complexes are dramatically altered by the presence of metal ions and that the complex [Ir(ppy)2(CN){C(NH2)(NHC6H4-4-X)}] with an ADC ligand reacts selectively with Hg2+ ions, enabling its use for sensing of mercury(II) ions in solution. The limit of detection was as low as 2.63 × 10-7 M, and additional mechanistic studies indicated the formation of an unusual dinuclear iridium(III) cyclometalated intermediate, bridged by a mercury dicyano fragment as a driving force of mercury sensing.

Acyclic diaminocarbene-based Thiele, Chichibabin, and Müller hydrocarbons.

Thiele, Chichibabin and Müller hydrocarbons are considered as classical Kekulé diradicaloids. Herein we report the synthesis and characterization of acyclic diaminocarbene (ADC)-based Thiele, Chichibabin, and Müller hydrocarbons. The calculated singlet–triplet energy gaps are ΔES–T = −27.96, −3.70, −0.37 kcal mol−1, respectively, and gradually decrease with the increasing length of the π-conjugated spacer (p-phenylene vs. p,p′-biphenylene vs. p,p′′-terphenylene) between the two ADC-scaffolds. In agreement with the calculations, we also experimentally observed the enhancement of paramagnetic diradical character as a function of the length of the π-conjugated spacer. ADC-based Thiele's hydrocarbon is EPR silent and exhibits very well resolved NMR spectra, whereas ADC-based Müller's hydrocarbon displays EPR signals and featureless NMR spectra at room temperature. The spacer also has a strong influence on the UV-Vis-NIR spectra of these compounds. Considering that our methodology is modular, these results provide a convenient platform for the synthesis of an electronically modified new class of carbon-centered Kekulé diradicaloids.

Theoretical study on reaction mechanism of synthesis of iridium complexes having cyclometalated acyclic diaminocarbene ancillary ligands.

DFT calculations at the M06-2X level were performed to explore the reaction mechanism for the synthesis of the new cyclometalated iridium(III) complexes with acyclic diaminocarbene ancillary ligands. The solvent effects of the reaction systems have been considered by a single-point energy calculation using the SMD model in the experimental conditions of CH2Cl2 solvent. The calculated results show that the reaction consists of two main steps: the first step is the hydrogen transfer between the two N atoms, and the next step is the closed-loop process of the Ir atom and the aromatic ring ortho to release the HCl molecule. The reaction has a relatively low activation free energy of 17.1-23.2kcalmol-1, indicating that it is easy to occur under the experimental conditions of Na et al. At the same time, it was found that the aryl para-CF3 substituent has higher reactivity than the corresponding reactant of the NO2 substituent.

Platinum(II)-mediated aminonitrone–isocyanide interplay: A new route to acyclic diaminocarbene complexes

The complex cis-[PtCl2(Me2SO)2] (1) reacts with 1equiv. of C-4-trifluoromethylphenyl-N-methylaminonitrone(2) to give the product [PtCl(Me2SO){ON(Me)C(4-CF3C6H4)NH}] (3; 75%). Treatment of 3 with an excess cyclohexyl isocyanide, CyNC, leads to the acyclic diaminocarbene complex [PtCl(CNCy){N(Me)C(4-CF3C6H4)NC(=NHCy)}] (4; 28%). The latter exhibits solid-state phosphorescence with an emission maximum at 600 nm and 23% quantum yield. Complexes 3 and 4 were characterized by HRESI+-MS, FTIR, 1H and 13C{1H} NMR spectroscopic techniques. The complex 4 was additionally characterized by X-ray diffraction; short PtPt contacts (3.2360(5)Å) were observed in the crystal structure. These non-covalent interactions have an attractive nature and their estimated strength is 4.6–5.6 kcal/mol.

Evaluation of benzthiazolidine-based formamidinium salts for the synthesis of penem-type β-lactams by uncatalysed carbonylation of acyclic diaminocarbenes

Abstract The reaction of [iPr2N=CHCl]Cl with 2-phenylbenzthiazolidine (Ph-BtzH) and subsequent anion metathesis afforded the formamidinium salt [(Ph-Btz)CH(NiPr2)][PF6] ([1aH][PF6]). The reaction of [1aH][PF6] with (Me3Si)2NNa in the presence of grey selenium furnished the selenourea derivative 1aSe as trapping product of the acyclic diaminocarbene 1a. In the absence of selenium, a 2H-1,4-benzothiazine derivative (2) was obtained, which is an isomer of 1a, whose formation is plausibly initiated by deprotonation of [1aH]+ not at the cationic N2CH unit, but at the neighbouring PhCH position. CO was ineffective as trapping reagent for 1a. [1aH][PF6], 1aSe and 2 have been structurally characterised by X-ray diffraction.

Cover Feature: Stable and Persistent Acyclic Diaminocarbenes with Cycloalkyl Substituents and Their Transformation to β‐Lactams by Uncatalysed Carbonylation with CO (Chem. Eur. J. 6/2019)

Cover Feature: Stable and Persistent Acyclic Diaminocarbenes with Cycloalkyl Substituents and Their Transformation to β‐Lactams by Uncatalysed Carbonylation with CO (Chem. Eur. J. 6/2019)

Palladium Acyclic Diaminocarbene (ADC) Triflate Complexes as Effective Precatalysts for the Hiyama Alkynylation/Cyclization Reaction Yielding Benzofuran Compounds: Probing the Influence of the Triflate Co‐Ligand in the One‐Pot Tandem Reaction

AbstractPalladium acyclic diaminocarbene (ADC) complexes of the type cis‐[(R1NH)(R2)methylidene]Pd(OCOCF3)2(CNR1) [R1 = 2,4,6‐(CH3)3C6H2: R2 = NC4H8 (1); NC5H10 (2)] have been synthesized and structurally characterized. These 1 and 2 complexes are effective precatalysts for the one‐pot tandem Hiyama alkynylation/cyclization reaction producing benzofuran compounds and, quite interestingly, higher yields of ca. 33−52 % were observed for the aryl triethoxysilylalkyne substrates as compared to that of ca. 15−21 % for the aliphatic triethoxysilylalkyne substrates. The 1 and 2 complexes were conveniently prepared by the salt metathesis reaction of the chloro derivatives with AgOCOCF3 in excellent yields (ca. 84−94 %) under ambient conditions.

The reaction of a particularly electrophilic acyclic diaminocarbene with carbon monoxide: formation of β- and γ-lactams

Abstract The reaction of carbon monoxide with the acyclic diaminocarbene iPr2N–C–TMP (TMP=2,2,6,6-tetramethylpiperidino), generated in situ from the formamidinium salt [(iPr2N)CH(TMP)][PF6] and NaN(SiMe3)2, unexpectedly afforded a mixture of β- and γ-lactams.

Cleavage of acyclic diaminocarbene ligands at an iridium(iii) center. Recognition of a new reactivity mode for carbene ligands.

Reaction of [Ir(μ-Cl)(ppy)2]2 (1) with 4 equivs of CNC6H4X (X = F 2a, Cl 2b, Br 2c, I 2d) in the presence of 2 equivs of AgOTf in dichloromethane at 20-25 °C furnished the bisisocyanide complexes [Ir(ppy)2(CNC6H4X)2](OTf) ([3a-d](OTf); 72-87%). Reaction of [3a-d](OTf) with an excess of gaseous ammonia at room temperature gave the bisdiaminocarbene species [Ir(ppy)2{C(NH2)NHC6H4X}2](OTf) [5a-d](OTf) (73-83%); the two-step addition proceeds through an intermediate formation of appropriate monocarbene complexes [4a-d](OTf). Further reaction of [5a-d](OTf) with an excess of gaseous ammonia at 50 °C led to the cleavage of one diaminocarbene ligand to the cyanide ligand in [Ir(ppy)2(CN){C(NH2)NHC6H4X}] (6a-d) and this transformation is accompanied with the elimination of a substituted aniline. Treatment of [5a-d](OTf) with N(CH2CH2OH)3 at 50 °C resulted in the cleavage of the diaminocarbene ligand to the isocyanide and uncomplexed NH3; isocyanide remains bound to the iridium(iii) center in [Ir(ppy)2{C(NH2)NHC6H4X}(CNC6H4X)](OTf) (4a-d). All isolated compounds were characterized by elemental analyses (C, H, N), molar conductivity measurements, TG/DTA, HRESI+/--MS, FTIR, 1D (1H, 13C{1H}, 19F{1H}) and 2D (1H,1H-COSY, 1H,13C-HMQC/1H,13C-HSQC, 1H,13C-HMBC) NMR, and also by X-ray diffraction (for the bisisocyanide 3, the diaminocarbene/isocyanide 4, the bisdiaminocarbene 5, and the diaminocarbene/cyanide 6 type complexes).

Stable and Persistent Acyclic Diaminocarbenes with Cycloalkyl Substituents and Their Transformation to β-Lactams by Uncatalysed Carbonylation with CO.

Four new acyclic diaminocarbenes (ADACs), viz. [(cyclo-Cn H2n-1 )2 N]2 C (n=5-7) and iPr2 N-C-N(cyclo-C6 H11 )2 , were synthesised by reacting the corresponding formamidinium hexafluorophosphates with NaN(SiMe3 )2 . Their nucleophilicities and electrophilicities were respectively judged from the 1 JCH values determined for the N2 CH unit of the corresponding formamidinium cations and from the 77 Se NMR chemical shifts of the selenourea derivatives obtained from the reaction of elemental selenium with the corresponding ADACs. An ambiphilic profile essentially identical to that of the "Alder carbene" (iPr2 N)2 C was found in each case. Similar to the latter carbene, the new ADACs undergo a well-defined thermal decomposition by β-fragmentation, affording an alkene and a formamidine. The stabilities of [(cyclo-Cn H2n-1 )2 N]2 C depend strongly on the value of n, following the order 6>5>7, with the latter congener being too unstable for isolation. [(cyclo-C6 H11 )2 N]2 C shows no thermal decomposition at room temperature in solution and is thus significantly more stable than (iPr2 N)2 C. The stability of iPr2 N-C-N(cyclo-C6 H11 )2 is intermediate between that of (iPr2 N)2 C and [(cyclo-C6 H11 )2 N]2 C, its β-fragmentation selectively affording propene and iPrN=CH-N(cyclo-C6 H11 )2 . [(cyclo-Cn H2n-1 )2 N]2 C (n=5-7) react readily with CO under mild conditions, selectively affording trisubstituted spirocyclic β-lactam derivatives with an antimicrobial activity spectrum similar to that of penicillin G.

Syntheses and Structures of a Series of Acyclic Diaminocarbene Palladium(II) Complexes Derived from 3,4-Diaryl-1H-pyrrol-2,5-diimines and Bisisocyanide Palladium(II) Complexes

Reactions of 3,4-diaryl-1H-pyrrol-2,5-diimines with various bisisocyanide palladium(II) complexes were studied. The coupling proceeds with one isocyanide ligand to accomplish the acyclic diaminocarbene complexes. The structure of generated diaminocarbene complexes depends on bulkiness of isocyanide ligand in the bisisocyanide complexes of palladium(II). The imino-group of 3,4-diaryl-1H-pyrrol-2,5-diimine reacts with one isocyanide ligand of cis-[PdCl2(CN–R)2] (R = i-Pr, Cy, t-Bu, Bn), and the nitrogen atom of the pyrrole ring is coordinated to the palladium center as the second isocyanide ligand remains intact. In the case of cis-[PdCl2(CN–R)2] (R = 2-acyloxyphenyl, 2-sulfonyloxyphenyl), one isocyanide ligand is displaced from the coordination sphere. Structural features of the prepared diaminocarbene complexes have been studied by molecular spectroscopy techniques, cyclic voltammetry, single-crystal X-ray diffraction, and DFT calculations. The photophysical properties of the obtained acyclic diaminocarbe...