Conformation-Associated C···dz2-PtII Tetrel Bonding: The Case of Cyclometallated Platinum(II) Complex with 4-Cyanopyridyl Urea Ligand

The nucleophilic addition of 3-(4-cyanopyridin-2-yl)-1,1-dimethylurea (1) to cis-[Pt(CNXyl)2Cl2] (2) gave a new cyclometallated compound 3. It was characterized by NMR spectroscopy (1H, 13C, 195Pt) and high-resolution mass spectrometry, as well as crystallized to obtain two crystalline forms (3 and 3·2MeCN), whose structures were determined by X-ray diffraction. In the crystalline structure of 3, two conformers (3A and 3B) were identified, while the structure 3·2MeCN had only one conformer 3A. The conformers differed by orientation of the N,N-dimethylcarbamoyl moiety relative to the metallacycle plane. In both crystals 3 and 3·2MeCN, the molecules of the Pt(II) complex are associated into supramolecular dimers, either {3A}2 or {3B}2, via stacking interactions between the planes of two metal centers, which are additionally supported by hydrogen bonding. The theoretical consideration, utilizing a number of computational approaches, demonstrates that the C···dz2(Pt) interaction makes a significant contribution in the total stacking forces in the geometrically optimized dimer [3A]2 and reveals the dz2(Pt)→π*(PyCN) charge transfer (CT). The presence of such CT process allowed for marking the C···Pt contact as a new example of a rare studied phenomenon, namely, tetrel bonding, in which the metal site acts as a Lewis base (an acceptor of noncovalent interaction).

Photoinduced Platinum-Catalyzed Reductive Allylation of α-Diketones with Allylic Carbonates

A unique process for the photoinduced platinum-catalyzed reductive allylation of α-diketones with allylic carbonates has been developed. This allylation reaction was found to proceed selectively at the more electron-deficient carbonyl group of the diketone to afford an α-keto homoallylic alcohol. Such products could be further derivatized by transformation of the remaining carbonyl group. A mechanistic investigation suggests that a ketyl radical generated in response to photoirradiation reacts with a (π-allyl)platinum complex to form a C-C bond.

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.

Isocyanide-Based Multicomponent Reactions Promoted by Visible Light Photoredox Catalysis

Isocyanide-based multicomponent reactions claim a one century-old history of flourishing developments. On the other hand, the enormous impact of recent progresses in visible light photocatalysis has boosted the identification of new straightforward and green approaches to both new and known chemical entities. In this context, the application of visible light photocatalytic conditions to multicomponent processes has been promoting key stimulating advancements. Spanning from radical-polar crossover pathways, to photoinduced and self-catalyzed transformations, to reactions involving the generation of imidoyl radical species, the present literature analysis would provide a general and critical overview about the potentialities and challenges of exploiting isocyanides in visible light photocatalytic multicomponent reactions.

Bulky NHC–Cobalt Complex-Catalyzed Highly Markovnikov-Selective Hydrosilylation of Alkynes

The hydrosilylation of alkynes is one of the most attractive and, at the same time, most challenging catalytic transformations, usually demanding the use of noble transition metals. We describe a catalytic system, based on cobalt(0) complex and bulky N-heterocyclic carbene (NHC) ligands, permitting the highly effective hydrosilylation of a broad scope of alkynes and silanes. The application of bulky NHC ligands allowed a decrease in the amount of cobalt necessary for an effective reaction run to 2.5 mol% and provided excellent selectivity towards challenging α-vinylsilanes. The developed method tolerates a number of substituted aryl, alkyl, and silyl acetylenes. Moreover, it is suitable for both tertiary and secondary silanes. Our findings confirm that steric hindrance around the metal center can effectively increase the activity of a catalyst and ensure better selectivity than those of analogous complexes bearing smaller ligands.

Palladium(II) and Platinum(II) Deprotonated Diaminocarbene Complexes Based on N-(2-Pyridyl)ureas with Oxadiazole Periphery

Metal mediated coupling of isocyanides with substituted N-(pyridine-2-yl) ureas was first used to incorporate privileged biological motifs into platinum metal complexes. We synthesized two palladium(II) and two platinum(II) cyclometallated species with oxadiazole cores. The compounds were isolated in good yields (61–73%) and characterized by high-resolution mass spectrometry and 1H, 13C, and 195Pt NMR spectroscopies. The structures of three complexes were additionally elucidated by X-ray diffraction analysis. These complexes indeed showed cytotoxic activity. The species bearing the 1,3,4-oxadiazole moiety exhibit more potency than the ones with the 1,2,4-oxadiazole ring. Particularly, the cytotoxic effect of both 1,3,4-oxadiazole-based complexes towards T98G cells significantly exceeds the common antitumor metal-drug cisplatin.

Coupling of Thiazole-2-Amines with Isocyanide Ligands in bis-(Isocyanide) Platinum Complex: A New Type of Reactivity

The treatment of cis-[PtCl2(XylNC)2] with thiazol-2-amines in a 2:1 ratio leads to a regioisomeric mixture of two binuclear complexes. These regioisomers are products of kinetic and thermodynamic control capable of regioisomerization. When the same reaction is carried out with a 5-fold excess of thiazol-2-amine, the nucleophile is able to react with the in situ-formed binuclear platinum(II) complexes, yielding a new type of bis-carbene platinum species. All new isolated compounds were characterized by 1H, 13C{1H}, and 195Pt{1H} NMR spectroscopy, high-resolution ESI-MS, and single-crystal X-ray diffraction.

Visible Light-Induced Transition Metal Catalysis

In recent years, visible light-induced transition metal catalysis has emerged as a new paradigm in organic photocatalysis, which has led to the discovery of unprecedented transformations as well as the improvement of known reactions. In this subfield of photocatalysis, a transition metal complex serves a double duty by harvesting photon energy and then enabling bond forming/breaking events mostly via a single catalytic cycle, thus contrasting the established dual photocatalysis in which an exogenous photosensitizer is employed. In addition, this approach often synergistically combines catalyst-substrate interaction with photoinduced process, a feature that is uncommon in conventional photoredox chemistry. This Review describes the early development and recent advances of this emerging field.

Experimental and Computational Tuning of Metalla-N-Heterocyclic Carbenes at Palladium(II) and Platinum(II) Centers

Palladium(II) and platinum(II) complexes featuring metalla-N-heterocyclic carbenes (7–12) were synthesised via metal-mediated coupling between equimolar cis-[MCl2(CNR)2] (R = 2,6-Me2C6H3 (Xyl), 2,4,6-Me3C6H3 (Mes)] and 2-aminopyridine or 2-aminopyrazine. Thiocyanate complexes 13–18 with...

Deprotonated diaminocarbene platinum complexes for thermoresponsive luminescent silicone materials: both catalysts and luminophores

C,N-Chelate deprotonated diaminocarbene platinum(II) complexes were synthesized by coupling coordinated isocyanides and azinyl-substituted ureas. The complexes act as catalysts of α,ω-divinylpolydimethylsiloxane and poly(dimethylsiloxane-co-methylhydrosiloxane) hydrosilylation cross-linking. Silicone rubbers obtained with (aminoisoquinoline)-containing complex 3d exhibit temperature-responsive luminescence. Their emission changes irreversibly when heated from 80-100 °C (green radiation) to 120 °C or more (blue radiation).

Metal-free photocatalytic hydrosilylation of olefins in the presence of photoinitiators

Photocatalytic hydrosilylation of olefins.

Visible-light-induced silylation: an update

This review summarizes the recent findings and developments in the emerging area of photocatalytic silylation with literature coverage mainly extending from 2014 to February 2021.

PdII- and PtII-mediated coupling of aryl isocyanides with N-heterocyclic thiones

A Pd^II- and Pt^II-mediated reaction of aryl isocyanides with N-heterocyclic thiones results in a previously undescribed type of regioselectivity for ambident nucleophile addition to coordinated isocyanides.

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 λ_max ∼430 nm in poly(methyl methacrylate) (PMMA) thin films. Whereas isocyanide complexes 1-3 exhibit modest photoluminescence quantum yields (Φ_PL ), incorporation of one acyclic diaminocarbene ligand results in a three-fold to 16-fold increase in Φ_PL while still maintaining an identical deep blue color profile.

(Isocyano group)⋯lone pair interactions involving coordinated isocyanides: experimental, theoretical and CSD studies

Both carbon and nitrogen centers in the coordinated isocyano group are capable of acting as a π-hole donor toward lone pairs.

Water soluble palladium(ii) and platinum(ii) acyclic diaminocarbene complexes: solution behavior, DNA binding, and antiproliferative activity

Water soluble Pd(ii) and Pt(ii)–ADC species synthesized via the metal-mediated coupling of isocyanides and 1,2-diaminobenzene have demonstrated antitumor potential.

Recent Advances on Visible Light Metal-Based Photocatalysts for Polymerization under Low Light Intensity

In recent years, polymerization processes activated by light have attracted a great deal of interest due to the wide range of applications in which this polymerization technique is involved. Parallel to the traditional industrial applications ranging from inks, adhesives, and coatings, the development of high-tech applications such as nanotechnology and 3D-printing have given a revival of interest to this polymerization technique known for decades. To initiate a photochemical polymerization, the key element is the molecule capable to interact with light, i.e., the photoinitiator and more generally the photoinitiating system, as a combination of several components is often required to create the reactive species responsible for the polymerization process. With the aim of reducing the photoinitiator content while optimizing the polymerization yield and/or the polymerization speed, photocatalytic systems have been developed, enabling the photosensitizer to be regenerated during the polymerization process. In this review, an overview of the photocatalytic systems developed for polymerizations carried out under a low light intensity and visible light is provided. Over the years, a wide range of organometallic photocatalysts has been proposed, addressing both the polymerization efficiency and/or the toxicity, as well as environmental issues.

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

A new reactivity mode for acyclic diaminocarbene ligands, viz. competitive cleavage of either C–NH₂ or C–NHR bonds in the aminocarbene fragment, is recognized.

Silyl radical initiated radical cascade addition/cyclization: synthesis of silyl functionalized 4H-pyrido[4,3,2-gh]phenanthridin-5(6H)-ones

A cyclization cascade initiated by the addition of a silyl radical to an electron-deficient carbon-carbon double bond of N-arylacrylamides, followed by intramolecular cyano group insertion and homolytic aromatic substitution has been reported. In the presence of di-lauroyl peroxide (LPO), under metal-free conditions, several readily available hydrosilanes were successfully used as the source of silyl radicals and a series of silyl functionalized 4H-pyrido[4,3,2-gh]phenanthridin-5(6H)-ones were obtained in moderate to good yields.