Aryl Isocyanides Research Articles

Long Excited-State Lifetimes in Three-Coordinate Copper(I) Complexes via Triplet-Triplet Energy Transfer to Pyrene-Decorated Isocyanides.

There has been much effort to improve excited-state lifetimes in photosensitizers based on earth-abundant first-row transition metals. Copper(I) complexes have gained significant attention in this field, and in most cases, sterically driven approaches are used to optimize their lifetimes. This study presents a series of three-coordinate copper(I) complexes (Cu1-Cu3) where the excited-state lifetime is extended by triplet-triplet energy transfer. The heteroleptic compounds feature a cyclohexyl-substituted β-diketiminate (CyNacNacMe) paired with aryl isocyanide ligands, giving the general formula Cu(CyNacNacMe)(CN-Ar) (CN-dmp = 2,6-dimethylphenyl isocyanide for Cu1; CN-pyr = 1-pyrenyl isocyanide for Cu2; CN-dmp-pyr = 2,6-dimethyl-4-(1-pyrenyl)phenyl isocyanide for Cu3). The nature, energies, and dynamics of the low-energy triplet excited states are assessed with a combination of photoluminescence measurements at room temperature and 77 K, ultrafast transient absorption (UFTA) spectroscopy, and DFT calculations. The complexes with the pyrene-decorated isocyanides (Cu2 and Cu3) exhibit extended excited-state lifetimes resulting from triplet-triplet energy transfer (TTET) between the short-lived charge-transfer excited state (3CT) and the long-lived pyrene-centered triplet state (3pyr). This TTET process is irreversible in Cu3, producing exclusively the 3pyr state, and in Cu2, the 3CT and 3pyr states are nearly isoenergetic, enabling reversible TTET and long-lived 3CT luminescence. The improved photophysical properties in Cu2 and Cu3 result in improvements in activity for both photocatalytic stilbene E/Z isomerization via triplet energy transfer and photoredox transformations involving hydrodebromination and C-O bond activation. These results illustrate that the extended excited-state lifetimes achieved through TTET result in newly conceived photosynthetically relevant earth-abundant transition metal complexes.

Sterically Encumbered Aryl Isocyanides Extend Excited-State Lifetimes and Improve the Photocatalytic Performance of Three-Coordinate Copper(I) β-Diketiminate Charge-Transfer Chromophores

Sterically Encumbered Aryl Isocyanides Extend Excited-State Lifetimes and Improve the Photocatalytic Performance of Three-Coordinate Copper(I) β-Diketiminate Charge-Transfer Chromophores

Synthesis of 2,4-Dicyanoalkylated Benzoxazines through the Radical-Mediated Cascade Cyclization of Isocyanides with AIBN under Metal- and Additive-Free Conditions.

A general and novel method for the radical cascade cyclization of aryl isocyanides with AIBN has been described. This strategy provides straightforward access to various 2,4-dicyanoalkylated benzoxazines in moderate to good yields under metal- and additive-free conditions. The reaction can apply to a gram scale and tolerate diverse functional groups. 2,4-Dicyanoalkylated benzoxazine derivatives feature a large Stokes shift and intramolecular charge transfer properties.

Reductive Retrocyclization of a Mangana(II)cyclopentasilane to Form Manganese(0) Bis(η2-disilene) Complexes.

Ligand-exchange reactions on a mangana(II)cyclopentasilane complex that contains two THF ligands with aryl isocyanides led to the formation of manganese(0) bis(η2-disilene) complexes via a retrocyclization. In stark contrast, ligand-exchange reactions with CNtBu, an N-heterocyclic carbene, or pyridine-based ligands furnished manganese(II) complexes wherein the manganacyclopentasilane framework remained intact. The thermolysis of the obtained bis(η2-disilene) complex in the presence of mesityl isocyanide led to the formation of a cyclotetrasilane via the formal dimerization of the two η2-disilene moieties. The insertion of a mesityl isocyanide into the Mn-Siβ bond results in the formation of a manganese(II) complex supported by a [SiCSi]-type tridentate ligand scaffold.

Reductive Retrocyclization of a Mangana(II)cyclopentasilane to Form Manganese(0) Bis(η2‐disilene) Complexes

AbstractLigand‐exchange reactions on a mangana(II)cyclopentasilane complex that contains two THF ligands with aryl isocyanides led to the formation of manganese(0) bis(η2‐disilene) complexes via a retrocyclization. In stark contrast, ligand‐exchange reactions with CNtBu, an N‐heterocyclic carbene, or pyridine‐based ligands furnished manganese(II) complexes wherein the manganacyclopentasilane framework remained intact. The thermolysis of the obtained bis(η2‐disilene) complex in the presence of mesityl isocyanide led to the formation of a cyclotetrasilane via the formal dimerization of the two η2‐disilene moieties. The insertion of a mesityl isocyanide into the Mn−Siβ bond results in the formation of a manganese(II) complex supported by a [SiCSi]‐type tridentate ligand scaffold.

Substituent exchange between an imino(silyl)silylene and aryl isocyanides

Substituent exchange between an imino(silyl)silylene and aryl isocyanides

Cyanation with isocyanides: recent advances and perspectives.

Cyanation has attracted considerable attention in organic synthesis because nitriles are key structural motifs in numerous important dyes, agrochemicals, natural products and drug molecules. As the fourth generation of cyanating reagents, isocyanides occupy a prominent place in the synthesis of nitriles due to their favorable stability, easy operability and high reactivity. In recent years, three types of cyanation with isocyanides have been established: the cleavage of the C-NC bond of tertiary alkyl isocyanides (Type I), the rearrangement of aryl isocyanides with azides (Type II), and the reductive cyanation of ketones with α-acidic isocyanides (Type III). This review focuses on advances in cyanation with isocyanides with an emphasis on reaction scope, limitations and mechanisms, which could reveal their remarkable value and superiority for accessing various nitriles. In addition, the future development prospects of this specific field are also introduced. We believe that this feature article will serve as a comprehensive tool to navigate cyanation with isocyanides across the vast area of synthetic chemistry.

Yb/Si frustrated Lewis pairs with a labile naphthalenyl bridge.

The first examples of RE/Si FLPs (RE: rare-earth metal, FLPs: frustrated Lewis pairs), namely Yb/Si FLPs were synthesized, where Yb⋯Si distances are in the range of 3.55 to 3.72 Å. These FLPs react with triphenylphosphine sulfide and aryl isocyanide to produce novel silylyne group transfer products through dissociation of naphthalene.

Construction of Unique Spiro[dibenzo[a,f]azulene-6,2'-indenes] via Unprecedented Annulation of ortho-C-H Bond of Benzylidene Group.

The domino reaction of alkyl and aryl isocyanides with two molecules of 2-arylidene-1,3-indanediones in acetonitrile at 80 °C resulted in unique functionalized spiro[dibenzo[a,f]azulene-6,2'-indenes] in good yields, in which the two 2-arylidene-1,3-indanediones acted as different building blocks to construct the polycyclic system. More importantly, the unprecedented anticipation of the ortho-position of benzylidene group to form a novel dibenzo[a,f]azulene ring through a formal [5 + 2] cycloaddition process was first observed. On the other hand, DABCO-promoted reaction of the isocyanides with two molecules of 2-arylidene-1,3-indanediones in acetonitrile at 80 °C afforded functionalized spiro[cyclopenta[a]-indene-2,2'-indene] derivatives.

Asymmetric Polymerization-Induced Crystallization-Driven Self-Assembly of Helical, Rod-Coil Poly(aryl isocyanide) Block Copolymers

Polymerization-induced crystallization-driven self-assembly (PI-CDSA) is combined, for the first time, with helical, rod-coil block copolymer (BCP) self-assembly to enable scalable and controllable in situ synthesis of chiral nanostructures of variable shape, size, and dimensionality. Herein, we report newly developed asymmetric PI-CDSA (A-PI-CDSA) methodologies in the synthesis and in situ self-assembly of chiral, rod-coil BCPs composed of poly(aryl isocyanide) (PAIC) rigid-rod and poly(ethylene glycol) (PEG) random-coil components. Using PEG-based nickel(II) macroinitiators, the construction of PAIC-BCP nanostructures with variable chiral morphologies is accomplished at solids contents ranging 5.0-10 wt %. At low core-to-corona ratios for PAIC-BCPs, we demonstrate the scalable formation of chiral one-dimensional (1D) nanofibers via "living" A-PI-CDSA whose contour lengths can be tuned through alterations to unimer-to-1D seed particle ratio. At high core-to-corona ratios, A-PI-CDSA was implemented for the rapid fabrication of molecularly thin, uniform hexagonal nanosheets via spontaneous nucleation and growth aided by vortex agitation. Investigations into 2D seeded, living A-PI-CDSA revealed a brand-new paradigm in the context of CDSA where hierarchically chiral, M helical spirangle morphologies (i.e., hexagonal helicoids) are size-tuned in three dimensions (i.e., heights and areas) via alterations to unimer-to-seed ratio. These unique nanostructures are formed in situ at scalable solids contents up to 10 wt % via rapid crystallization about screw dislocation defect sites in an enantioselective fashion. The liquid crystalline nature of PAIC blocks dictates the hierarchical assembly of these BCPs, with chirality translated across length scales and in multiple dimensions affording large amplifications in chiroptical activity with g-factors reaching -0.030 for spirangle nanostructures.

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.

Phenylimido complexes of rhenium: fluorine substituents provide protection, reactivity, and solubility.

Reactions of [Re(NPhF)Cl3(PPh3)2] ({NPhF}2- = p-fluorophenylimide) with a variety of alkyl and aryl isocyanides have been studied. Different reactivity patterns and products have been obtained depending on the steric and electronic properties of the individual ligands. This involves the formation of 1 : 1 and 1 : 2 exchange products of Re(V) with the general formulae mer-[Re(NPhF)Cl3(PPh3)(isocyanide)] and cis- or trans-[Re(NPhF)Cl3(isocyanide)2]. The stability of the obtained products is correlated with the substitution pattern of the isocyanide ligands. The products have been studied by single-crystal X-ray diffraction and spectroscopic methods, including IR and multinuclear NMR spectroscopy as well as mass spectrometry. The use of partially fluorinated starting materials and ligands allows the modulation of the solubilities of the starting materials and the products as well as the monitoring of the reactions by means of 19F NMR. The attachment of the CF3 or F substituent on the isocyanides gives control over the steric bulk and the electronic properties of the ligands and, thus, their reactivity.

Polymerization of Aryl Polyisocyanides Catalyzed by N-Heterocyclic Carbene-Ligated Scandium Trialkyl Complex

Polyisocyanide has attracted continuous attention because of its stable helical rod structure and its wide application, it has a unique π-conjugated system in which the carbon-nitrogen double bond in each unit is twisted along the polymeric backbone to form a helical configuration. In this paper, a series of aryl isocyanides polymers are prepared using N-heterocyclic carbene-ligated scandium trialkyl complex 1 (IPr)Sc(CH2SiMe3)3 as the catalyst and 2 equiv. [Ph3C][B(C6F5)4] as the co-catalyst. The catalyst can convert 96% of 100 equiv. monomer in 5 minutes and the activity of the polymerization can reach 329 kg of polymer molSc-1 h-1. Two optically active polymers are obtained by using chiral monomers, they show strong CD signal at 364 nm and the two signals are opposite.

Urea Synthesis from Isocyanides and O-Benzoyl Hydroxylamines Catalyzed by a Copper Salt

In the presence of CuOAc, a series of unsymmetric ureas can be generated in moderate to good yields under mild reaction conditions (10 mol% of CuOAc, 2 equiv t-BuONa or PhONa, 30 °C), using aryl isocyanides and O-benzoyl hydroxylamines as the readily accessible starting materials. The reactions might undergo a cascade process involving isocyanide insertion into the N-O bond and Mumm-type rearrangement. This work represents a rare example of isocyanide insertion into N-O bonds, which would extend isocyanide insertion chemistry.

Zn‐Mediated Reductive Addition of Isocyanides with Unactivated Tertiary Alkyl Oxalates

AbstractA facile and efficient method is presented for the synthesis of 6‐alkylated phenanthridine, possessing hindered quaternary carbon centers, by Zn‐mediated reductive trapping of tertiary alkyl radicals with both electron‐rich and electron‐deficient aryl isocyanides using nickel as a promoter. Bench‐stable and operation‐friendly tertiary alkyl oxalates derived from abundant tertiary alkyl alcohols were first used as radical precursors for the alkylation of isocyanobiphenyl species. This reaction displays excellent functional group tolerance and broad substrate scope, allowing access to desired products in good to excellent yields.

Pyridine‐2(1H)‐thione as a Bifunctional Nucleophile in Reaction with PdII and PtII Aryl Isocyanide Complexes

AbstractA method for obtaining C,S‐cyclometalated deprotonated diaminocarbene complexes via the addition of a bifunctional N,S‐nucleophile's endocyclic nitrogen atom to a coordinated isocyanide has been extended to the reactions with pyridine‐2(1H)‐thione. The coupling of PdII‐ and PtII‐bis(arylisocyanide) complexes with pyridine‐2(1H)‐thione leads to the formation of mononuclear C,S‐cyclometalated deprotonated diaminocarbene complexes in 90–96 % yield. The reaction proceeds via the initial coordination of the thione sulfur atom to the metal center followed by the intramolecular nucleophilic addition of the heterocyclic nitrogen atom to the metal‐ligated isocyanide carbon. Using an excess of pyridine‐2(1H)‐thione in this reaction leads to the formation of a mono‐C,S‐cyclometalated complex with a pendant mercaptopyridine ligand which is involved in the reversible intramolecular nucleophilic addition of the pyridine nitrogen to the isocyano carbon. The obtained complexes were characterized by elemental analysis, mass spectrometry, IR and NMR spectroscopies, and single‐crystal X‐ray diffraction.

Combining cycloaddition reactions for the one-pot synthesis of novel xanthoquinone dyes

Xanthoquinones, as a new class of quinone dyes comprising the xanthone and quinone subunits have been synthesized. An elusive aminofurochromone as an electron-rich diene was generated in situ from the corresponding chromone-3-carbaldehyde and alkyl or aryl isocyanide via a formal [4 + 1] cycloaddition reaction, then engaged by p-quinone partner (1,4-benzoquinone or 1,4-naphthoquinone) as an electron-deficient dienophile to afford the desired novel xanthoquinone dye via a [4 + 2] cycloaddition/ring opening/dehydrative aromatization sequence.

Stimuli-responsive and core cross-linked micelles developed by NiCCo-PISA of helical poly(aryl isocyanide)s.

We report the synthesis of redox- and pH-sensitive block copolymer micelles that contain chiral cores composed of helical poly(aryl isocyanide)s. Pentafluorophenyl (PFP) ester-containing micelles synthesised via nickel-catalysed coordination polymerisation-induced self-assembly (NiCCo-PISA) of helical poly(aryl isocyanide) amphiphilic diblock copolymers are modified post-polymerisation with various diamines to introduce cross-links and/or achieve stimulus-sensitive nanostructures. The successful introduction of the diamines is confirmed by Fourier-transform infrared spectroscopy (FT-IR), while the stabilisation effect of the cross-linking is explored by dynamic light scattering (DLS). The retention of the helicity of the core-forming polymer block is verified by circular dichroism (CD) spectroscopy and the stimuli-responsiveness of the nanoparticles towards a reducing agent (l-glutathione, GSH) and pH is evaluated by following the change in the size of the nanoparticles by DLS. These stimuli-responsive nanoparticles could find use in applications such as drug delivery, nanosensors or biological imaging.

Rationally designed conjugated microporous polymers for efficient photocatalytic chemical transformations of isocyanides

Click-based conjugated microporous polymers have been rationally designed and prepared for efficient N–H insertion like reaction of aryl isocyanides and photosynthesis of thiocarbamates.

Neutral isocyanide-templated assembly of pillar[5]arene [2] and [3]pseudorotaxanes.

Unprecedented pillar[5]arene-isocyanide pseudorotaxane complexes are reported. Extensive 1H-NMR experiments reveal remarkably strong binding affinities of alkyl diisocyanide guests (Ka > 105 M-1 in CDCl3) by pillar[5]arenes. Characterised by multinuclear 1H and 13C-NMR spectroscopy and single-crystal X-ray diffraction, it is demonstrated that pillar[5]arenes are capable of encapsulating a series of alkyl diisocyanides wherein either [2]- or [3]pseudorotaxanes can be formed by varying the alkyl chain length. Moreover, electron-deficient aryl isocyanides, are demonstrated to form inclusion complexes within the cavities of pillar[5]arenes stabilised by multiple C-H⋯π interactions.