2‐(2′‐Pyridyl)‐4,6‐diphenylphosphinine versus 2‐(2′‐Pyridyl)‐4,6‐diphenylpyridine: Synthesis,Characterization, and Reactivity of Cationic RhIII and IrIII Complexes Based on Aromatic Phosphorus Heterocycles

The bidentate P,N hybrid ligand 1 allows access for the first time to novel cationic phosphinine‐based Rh^III and Ir^III complexes, broadening significantly the scope of low‐coordinate aromatic phosphorus heterocycles for potential applications. The coordination chemistry of 1 towards Rh^III and Ir^III was investigated and compared with the analogous 2,2′‐bipyridine derivative, 2‐(2′‐pyridyl)‐4,6‐diphenylpyridine ( 2 ), which showed significant differences. The molecular structures of [RhCl(Cp*)( 1 )]Cl and [IrCl(Cp*)( 1 )]Cl (Cp*=pentamethylcyclopentadienyl) were determined by means of X‐ray diffraction and confirm the mononuclear nature of the λ³‐phosphinine–Rh^III and Ir^III complexes. In contrast, a different reactivity and coordination behavior was found for the nitrogen analogue 2 , especially towards Rh^III as a bimetallic ion pair [RhCl(Cp*)( 2 )]⁺[RhCl₃(Cp*)]^? is formed rather than a mononuclear coordination compound. [RhCl(Cp*)( 1 )]Cl and [IrCl(Cp*)( 1 )]Cl react with water regio‐ and diastereoselectively at the external P?C double bond, leading exclusively to the anti‐addition products [MCl(Cp*)( 1 H ? OH)]Cl as confirmed by X‐ray crystal‐structure determination.     

meso‐(2‐Pyridyl)‐boron(III)‐subporphyrin: Perimeter Iridium(III) Coordination

Peripherally metalated porphyrinoids are promising functional π‐systems displaying characteristic optical, electronic, and catalytic properties. In this work, 5‐(2‐pyridyl)‐ and 5,10,15‐tri(2‐pyridyl)‐B^III‐subporphyrins were prepared and used to produce cyclometalated subporphyrins by reactions with [Cp*IrCl₂]₂, which proceeded through an efficient C?H activation to give the corresponding mono‐ and tri‐Ir^III complexes, respectively. While the mono‐Ir^III complex was obtained as a diastereomeric mixture, a C₃‐symmetric tri‐Ir^III complex with the three Cp*‐units all at the concave side was predominantly obtained in a high yield of 90 %, which displays weak NIR phosphorescence even at room temperature in degassed CH₂Cl₂, differently from the mono‐Ir^III complexes.     

Iridium(III)‐Catalyzed Intermolecular C(sp3)−H Insertion Reaction of Quinoid Carbene: A Radical Mechanism

Described herein is an Ir^III/porphyrin‐catalyzed intermolecular C(sp³)?H insertion reaction of a quinoid carbene (QC). The reaction was designed by harnessing the hydrogen‐atom transfer (HAT) reactivity of a metal‐QC species with aliphatic substrates followed by a radical rebound process to afford C?H arylation products. This methodology is efficient for the arylation of activated hydrocarbons such as 1,4‐cyclohexadienes (down to 40 min reaction time, up to 99 % yield, up to 1.0 g scale). It features unique regioselectivity, which is mainly governed by steric effects, as the insertion into primary C?H bonds is favored over secondary and/or tertiary C?H bonds in the substituted cyclohexene substrates. Mechanistic studies revealed a radical mechanism for the reaction.     

Group 9 Metal Complexes of meso‐Aryl‐Substituted Rubyrin

The metalation of meso‐tetrakis(pentafluorophenyl)‐substituted [26]rubyrin has been explored with Group 9 metal salts (Rh^I, Co^II, Ir^III), affording a Hückel aromatic [26]rubyrin–bis‐Rh^I complex with a highly curved gable‐like structure, a Hückel antiaromatic [24]rubyrin–bis‐Co^II complex that displays intramolecular antiferromagnetic coupling between the two Co^II ions (J=?4.5 cm^?1), and two Cp*‐capped Ir^III complexes; in one, the iridium metal sits on the [26]rubyrin frame with two Ir?N bonds, whereas the other has an additional Ir?C bond, although both Ir^III complexes display moderate aromatic character. This work demonstrates characteristic metalation abilities of this [26]rubyrin toward Group 9 metals.     

Cyclometalated Mono‐ and Dinuclear IrIII Complexes with “Click”‐Derived Triazoles and Mesoionic Carbenes

Orthometalation at Ir^III centers is usually facile, and such orthometalated complexes often display intriguing electronic and catalytic properties. By using a central phenyl ring as C?H activation sites, we present here mono‐ and dinuclear Ir^III complexes with “click”‐derived 1,2,3‐triazole and 1,2,3‐triazol‐5‐ylidene ligands, in which the wingtip phenyl groups in the aforementioned ligands are additionally orthometalated and bind as carbanionic donors to the Ir^III centers. Structural characterization of the complexes reveal a piano stool‐type of coordination around the metal centers with the “click”‐derived ligands bound either with C^N or C^C donor sets to the Ir^III centers. Furthermore, whereas bond localization is observed within the 1,2,3‐triazole ligands, a more delocalized situation is found in their 1,2,3‐triazol‐5‐ylidene counterparts. All complexes were subjected to catalytic tests for the transfer hydrogenation of benzaldehyde and acetophenone. The dinuclear complexes turned out to be more active than their mononuclear counterparts. We present here the first examples of stable, isomer‐pure, dinuclear cyclometalated Ir^III complexes with poly‐mesoionic‐carbene ligands.     

Iridium‐Catalyzed β‐Alkynylation of Aliphatic Oximes as Masked Carbonyl Compounds and Alcohols

An Ir‐catalyzed C(sp³)?H alkynylation of aliphatic ketones, aldehydes, and alcohols was achieved by using the corresponding oxime derivatives and a Ir^III catalyst. This general reaction is selective towards primary C(sp³)?H bonds and can be used for the late‐stage C?H alkynylation of complex molecules.     

Rhodium(III)‐ and Iridium(III)‐Catalyzed C7 Alkylation of Indolines with Diazo Compounds

A Rh^III‐catalyzed procedure for the C7‐selective C?H alkylation of various indolines with α‐diazo compounds at room temperature is reported. The advantages of this process are: 1) simple, mild, and pH‐neutral reaction conditions, 2) broad substrate scope, 3) complete regioselectivity, 4) no need for an external oxidant, and 5) N₂ as the sole byproduct. Furthermore, alkylation and bis‐alkylation of carbazoles at the C1 and C8 positions have also been developed. More significantly, for the first time, a successful Ir^III‐catalyzed intermolecular insertion of arene C?H bonds into α‐diazo compounds is reported.     

Reactions of Pyridyl‐Functionalized,Chelating λ3‐Phosphinines in the Coordination Environment of RhIII and IrIII

Rh^III and Ir^III complexes based on the λ³‐P,N hybrid ligand 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine ( 1 ) react selectively at the P?C double bond to chiral coordination compounds of the type [( 1 H ? OH)Cp*MCl]Cl ( 2 , 3 ), which can be deprotonated with triethylamine to eliminate HCl. By using different bases, the pK_a value of the P? OH group could be estimated. Whereas [( 1 H ? O)Cp*IrCl] ( 4 ) is formed quantitatively upon treatment with NEt₃, the corresponding rhodium compound [( 1 H ? O)Cp*RhCl] ( 5 ) undergoes tautomerization upon formation of the λ⁵σ⁴‐phosphinine rhodium(III) complex [( 1? OH)Cp*RhCl] ( 6 ) as confirmed by single‐crystal X‐ray diffraction. Blocking the acidic P? OH functionality in 3 by introducing a P? OCH₃ substituent leads directly to the λ⁵σ⁴‐phosphinine iridium(III) complex ( 8 ) upon elimination of HCl. These new transformations in the coordination environment of Rh^III and Ir^III provide an easy and general access to new transition‐metal complexes containing λ⁵σ⁴‐phosphinine ligands.     

A Highly Active Bifunctional Iridium Complex with an Alcohol/Alkoxide‐Tethered N‐Heterocyclic Carbene for Alkylation of Amines with Alcohols

A series of new iridium(III) complexes containing bidentate N‐heterocyclic carbenes (NHC) functionalized with an alcohol or ether group (NHC? OR, R=H, Me) were prepared. The complexes catalyzed the alkylation of anilines with alcohols as latent electrophiles. In particular, biscationic Ir^III complexes of the type [Cp*(NHC‐OH)Ir(MeCN)]²⁺2[BF₄^?] afforded higher‐order amine products with very high efficiency; up to >99 % yield using a 1:1 ratio of reactants and 1–2.5 mol % of Ir, in short reaction times (2–16 h) and under base‐free conditions. Quantitative yields were also obtained at 50 °C, although longer reaction times (48–60 h) were needed. A large variety of aromatic amines have been alkylated with primary and secondary alcohols. The reactivity of structurally related iridium(III) complexes was also compared to obtain insights into the mechanism and into the structure of possible catalytic intermediates. The Ir^III complexes were stable towards oxygen and moisture, and were characterized by NMR, HRMS, single‐crystal X‐ray diffraction, and elemental analyses.     

Highly Stereoselective Cobalt(III)‐Catalyzed Three‐Component C−H Bond Addition Cascade

A highly stereoselective three‐component C(sp²)?H bond addition across alkene and polarized π‐bonds is reported for which Co^III catalysis was shown to be much more effective than Rh^III. The reaction proceeds at ambient temperature with both aryl and alkyl enones employed as efficient coupling partners. Moreover, the reaction exhibits extremely broad scope with respect to the aldehyde input; electron rich and poor aromatic, alkenyl, and branched and unbranched alkyl aldehydes all couple in good yield and with high diastereoselectivity. Multiple directing groups participate in this transformation, including pyrazole, pyridine, and imine functional groups. Both aromatic and alkenyl C(sp²)?H bonds undergo the three‐component addition cascade, and the alkenyl addition product can readily be converted into diastereomerically pure five‐membered lactones. Additionally, the first asymmetric reactions with Co^III‐catalyzed C?H functionalization are demonstrated with three‐component C?H bond addition cascades employing N‐tert‐butanesulfinyl imines. These examples represent the first transition metal catalyzed C?H bond additions to N‐tert‐butanesulfinyl imines, which are versatile and extensively used intermediates for the asymmetric synthesis of amines.     

[FeIII(F20‐tpp)Cl] Is an Effective Catalyst for Nitrene Transfer Reactions and Amination of Saturated Hydrocarbons with Sulfonyl and Aryl Azides as Nitrogen Source under Thermal and Microwave‐Assisted Conditions

[Fe^III(F₂₀‐tpp)Cl] (F₂₀‐tpp=meso‐tetrakis(pentafluorophenyl)porphyrinato dianion) is an effective catalyst for imido/nitrene insertion reactions using sulfonyl and aryl azides as nitrogen source. Under thermal conditions, aziridination of aryl and alkyl alkenes (16 examples, 60–95 % yields), sulfimidation of sulfides (11 examples, 76–96 % yields), allylic amidation/amination of α‐methylstyrenes (15 examples, 68–83 % yields), and amination of saturated C? H bonds including that of cycloalkanes and adamantane (eight examples, 64–80 % yields) can be accomplished by using 2 mol % [Fe^III(F₂₀‐tpp)Cl] as catalyst. Under microwave irradiation conditions, the reaction time of aziridination (four examples), allylic amination (five examples), sulfimidation (two examples), and amination of saturated C? H bonds (three examples) can be reduced by up to 16‐fold (24–48 versus 1.5–6 h) without significantly affecting the product yield and substrate conversion.     

IrIII‐Catalyzed One‐Pot Cascade Synthesis of Pentacyclic‐Fused Carbazoles from Indoles and Diazoes

A highly efficient Ir^III‐catalyzed cascade cyclization of indoles and diazoes giving access to unique pentacyclic‐fused carbazoles has been developed. This novel strategy expanded the application scope of coupling partners to take diazo compounds as a C2 source, and two new cycles, three new C?C and one new C?N bonds were formed in one‐pot.     

RhV‐Nitrenoid as a Key Intermediate in RhIII‐Catalyzed Heterocyclization by CH Activation: A Computational Perspective on the Cycloaddition of Benzamide and Diazo Compounds

A mechanistic study of the substituent‐dependent ring formations in Rh^III‐catalyzed C?H activation/cycloaddition of benzamide and diazo compounds was carried out by using DFT calculations. The results indicated that the decomposition of the diazo is facilitated upon the formation of the five‐membered rhodacycle, in which the Rh^III center is more electrophilic. The insertion of carbenoid into Rh?C(phenyl) bond occurs readily and forms a 6‐membered rhodacycle, however, the following C?N bond formation is difficult both kinetically and thermodynamically by reductive elimination from the Rh^III species. Instead, the Rh^V‐nitrenoid intermediate could be formed by migration of the pivalate from N to Rh, which undergoes the heterocyclization much more easily and complementary ring‐formations could be modulated by the nature of the substituent at the α‐carbon. When a vinyl is attached, the stepwise 1,3‐allylic migration occurs prior to the pivalate migration and the 8‐membered ring product will be formed. On the other hand, the pivalate migration becomes more favorable for the phenyl‐contained intermediate because of the difficult 1,3‐allylic migration accompanied by dearomatization, thus the 5‐membered ring product was formed selectively.     

Iridium‐Catalyzed Distal Hydroboration of Aliphatic Internal Alkenes

The regioselective hydroboration of aliphatic internal alkenes remains a great challenge. Reported herein is an iridium‐catalyzed hydroboration of aliphatic internal alkenes, providing distal‐borylated products in good to excellent yields with high regioselectivity (up to 99:1). We also demonstrate that the C?B bond of the distal‐borylated product can be readily converted into other functional groups. DFT calculations indicate that the reaction proceeds through an unexpected Ir^III/Ir^V cycle.     

Iridium(III)‐Catalyzed Regioselective Intermolecular Unactivated Secondary Csp3−H Bond Amidation

For the first time, a highly regioselective intermolecular sulfonylamidation unactivated secondary Csp³?H bond has been achieved using Ir^III catalysts. The introduced N,N’‐bichelating ligand plays a crucial role in enabling iridium–nitrene insertion into a secondary Csp³?H bond via an outer‐sphere pathway. Mechanistic studies and density functional theory (DFT) calculations demonstrated that a two‐electron concerted nitrene insertion was involved in this Csp³?H amidation process. This method tolerates a broad range of linear and branched‐chain N‐alkylamides, and provides efficient access to diverse γ‐sulfonamido‐substituted aliphatic amines.     

Iridium(III)‐Catalyzed CH Amidation of Arylphosphoryls Leading to a P‐Stereogenic Center

Direct C?H amidation of arylphosphoryl compounds has been developed by using an Ir^III catalyst system under mild conditions. A wide range of substrates could be employed with high functional‐group tolerance. This procedure was successfully applied for the first time to the asymmetric reaction giving rise to a P‐chirogenic center with a high diastereomeric ratio of up to 19:1 (90 % de).     

Synthesis,Structure, and Reactivity of Hydridoiridium Complexes Bearing a Pincer‐Type PSiP Ligand

A series of iridium tetrahydride complexes [Ir(H)₄(PSiP‐R)] bearing a tridentate pincer‐type bis(phosphino)silyl ligand ([{2‐(R₂P)C₆H₄}₂MeSi]⁻, PSiP‐R, R=Cy, iPr, or tBu) were synthesized by the reduction of [IrCl(H)(PSiP‐R)] with Me₄N ⋅ BH₄ under argon. The same reaction under a nitrogen atmosphere afforded a rare example of thermally stable iridium(III)–dinitrogen complexes, [Ir(H)₂(N₂)(PSiP‐R)]. Two isomeric dinitrogen complexes were produced, in which the PSiP ligand coordinated to the iridium center in meridional and facial orientations, respectively. Attempted substitution of the dinitrogen ligand in [Ir(H)₂(N₂)(PSiP‐Cy)] with PMe₃ required heating at 150 °C to give the expected [Ir(H)₂(PMe₃)(PSiP‐Cy)] and a trigonal bipyramidal iridium(I)–dinitrogen complex, [Ir(N₂)(PMe₃)(PSiP‐Cy)]. The reaction of [Ir(H)₄(PSiP‐Cy)] with three equivalents of 2‐norbornene (nbe) in benzene afforded [Ir^I(nbe)(PSiP‐Cy)] in a high yield, while a similar reaction of [Ir(H)₄(PSiP‐R)] with an excess of 3,3‐dimethylbutene (tbe) in benzene gave the C H bond activation product, [Ir^III(H)(Ph)(PSiP‐R)], in high yield. The oxidative addition of benzene is reversible; heating [Ir^III(H)(Ph)(PSiP‐Cy)] in the presence of PPh₃ in benzene resulted in reductive elimination of benzene, coordination of PPh₃, and activation of the C H bond of one aromatic ring in PPh₃. [Ir^III(H)(Ph)(PSiP‐R)] catalyzed a direct borylation reaction of the benzene C H bond with bis(pinacolato)diboron. Molecular structures of most of the new complexes in this study were determined by a single‐crystal X‐ray analysis.     

Room‐Temperature Decarboxylative Couplings of α‐Oxocarboxylates with Aryl Halides by Merging Photoredox with Palladium Catalysis

Enabled by merging iridium photoredox catalysis and palladium catalysis, α‐oxocarboxylate salts can be decarboxylatively coupled with aryl halides to generate aromatic ketones and amides at room temperature. DFT calculations suggest that this reaction proceeds through a Pd⁰–Pd^II–Pd^III pathway, in which the Pd^III intermediate is responsible for reoxidizing Ir^II to complete the Ir^III–*Ir^III–Ir^II photoredox cycle.     

Catalytic 1,4‐Rhodium(III) Migration Enables 1,3‐Enynes to Function as One‐Carbon Oxidative Annulation Partners in CH Functionalizations

1,3‐Enynes containing allylic hydrogens cis to the alkyne are shown to act as one‐carbon partners, rather than two‐carbon partners, in various rhodium‐catalyzed oxidative annulations. The mechanism of these unexpected transformations is proposed to occur through double C? H activation, involving a hitherto rare example of the 1,4‐migration of a Rh^III species. This phenomenon is general across a variety of substrates, and provides a diverse range of heterocyclic products.     

Stabilization of High‐Valence Ruthenium with Silicotungstate Ligands: Preparation,Structural Characterization,and Redox Studies of Ruthenium(III)‐Substituted α‐Keggin‐Type Silicotungstates with Pyridine Ligands, [SiW11O39RuIII(Py)]5−

Ruthenium(III)‐substituted α‐Keggin‐type silicotungstates with pyridine‐based ligands, [SiW₁₁O₃₉Ru^III(Py)]^5?, (Py: pyridine ( 1 ), 4‐pyridine‐carboxylic acid ( 2 ), 4,4′‐bipyridine ( 3 ), 4‐pyridine‐acetamide ( 4 ), and 4‐pyridine‐methanol ( 5 )) were prepared by reacting [SiW₁₁O₃₉Ru^III(H₂O)]^5? with the pyridine derivatives in water at 80 °C and then isolated as their hydrated cesium salts. These compounds were characterized using cyclic voltammetry (CV), UV/Vis, IR, and ¹H NMR spectroscopy, elemental analysis, titration, and X‐ray absorption near‐edge structure (XANES) analysis (Ru K‐edge and L₃‐edge). Single‐crystal X‐ray analysis of compounds 2 , 3 , and 4 revealed that Ru^III was incorporated in the α‐Keggin framework and was coordinated by pyridine derivatives through a Ru? N bond. In the solid state, compounds 2 and 3 formed a dimer through π? π interaction of the pyridine moieties, whereas they existed as monomers in solution. CV indicated that the incorporated Ru^III–Py was reversibly oxidized into the Ru^IV–Py derivative and reduced into the Ru^II–Py derivative.