Insertion Reactions on Carbopalladated Benzyne: From Eight- to Nine- and Ten-Membered Palladacycles. Applications to the Synthesis of N-Heterocycles

Rational design of fluorescent chemosensor for Pd2+ based on the formation of cyclopalladated complex

According to the assumption that the formation of C-Pd bond becomes a cyclopalladated complex (CPC), we designed and synthesized two C-N-N pincer ligands of BODIPY appended 2,2'-bipyridine derivatives (BP and BPB). It has been confirmed that the C-Pd bond does exist and plays a crucial role in "on-off" fluorescence behavior. Based on it, a coordination-induced fluorescence quenching sensor for Pd²⁺ was constructed. The results indicated that BP possessed high sensitivity and specificity for Pd²⁺ in solution. The limit of detection (LOD) of BP is determined to be 0.97 nM within a linear range between 1.0 and 50.0 nM, meanwhile, the platinum-group ions demonstrate no interference. The bio-imaging application of BP was investigated and it exhibited a promising vitro test for fluorescent imaging of Pd²⁺ ions in MCF-7 cells. Meanwhile, BPB coated sensor label for Pd²⁺ was set up. The visible color variation was displayed under UV light with increasing concentrations of Pd²⁺. Briefly speaking, fluorescence probes of BP and BPB offer new approaches for Pd²⁺ detection in a lab and on-site test, as well as the vivo imaging. Then, with the aid of (TD)DFT calculation, the internal reason for the optical difference between the two ligands was disclosed. This concept of CPC containing a Pd-C covalent bond provides a promising perspective of coordination fluorescence sensors.

Sequential Insertion of Alkynes, Alkenes, and CO into the Pd–C Bond of ortho-Palladated Primary Phenethylamines: from η3-Allyl Complexes and Enlarged Palladacycles to Functionalized Arylalkylamines

The eight-membered metallacycles arising from the insertion of 1 equiv of alkyne into the Pd–C bond of ortho-metalated homoveratrylamine and phentermine can further react with alkenes to give two different types of mononuclear complexes depending on the nature of the olefin. When terminal alkenes (styrene and ethyl acrylate) are used, a mixture of the anti/syn η³-allyl Pd(II) complexes are isolated, which evolve slowly to the syn isomers by heating the mixtures appropriately. These η³-allyl Pd(II) complexes do not react with CO or weak bases, but when they are treated with a strong base, such as KO^tBu, they afford Pd(0) and the functionalized starting phenethylamines containing a 1,3-butadienyl substituent in an ortho position. When 2-norbornene was used instead of terminal alkenes, the strained olefin inserts into the alkenyl Pd(II) complex to afford a 10-membered norbornyl palladium(II) complex, in which the new C,N-chelate ligand is coordinated to the metal through an additional double bond, occupying three coordination positions. The reactivity of these norbornyl complexes depends on the substituents on the inserted alkenyl fragment, and thus they can further react with (1) KO^tBu, to give Pd(0) and a tetrahydroisoquinoline nucleus containing a tricyclo[3.2.1]octyl ring, or (2) CO and TlOTf, to afford Pd(0) and amino acid derivatives or the corresponding lactones arising from an intramolecular Michael addition of the CO₂H group to the α,β-unsaturated ester moiety. Crystal structures of every type of compound have been determined by X-ray diffraction studies.

Pd-Catalyzed C(sp2)-H Imidoylative Annulation: A General Approach To Construct Dibenzoox(di)azepines

A general method to construct the scaffolds of dibenzooxazepine and dibenzodiazepine, through Pd-catalyzed isocyanide insertion and intramolecular C(sp²)-H activation, has been developed. This is the first example of seven-membered heterocycle formation by C-H imidoylative annulation.

Arynes and Their Precursors from Arylboronic Acids via Catalytic C-H Silylation

A new, operationally simple approach is presented to access arynes and their fluoride-activated precursors based on Ru-catalyzed C-H silylation of arylboronates. Chromatographic purification may be deferred until after aryne capture, rendering the arylboronates de facto precursors. Access to various new arynes and their derivatives is demonstrated, including, for the first time, those based on a 2,3-carbazolyne and 2,3-fluorenyne core, which pave the way for novel derivatizations of motifs relevant to materials chemistry.

Synthesis of spiro-oxoindoles through Pd-catalyzed remote C–H alkylation using α-diazocarbonyl compounds

In this communication we describe a new route to spiro-oxoindole derivatives through a novel Pd-catalyzed cascade process.

Multiple Roles of Isocyanides in Palladium-Catalyzed Imidoylative Couplings: A Mechanistic Study

Kinetic, spectroscopic and computational studies examining a palladium-catalyzed imidoylative coupling highlight the dual role of isocyanides as both substrates and ligands for this class of transformations. The synthesis of secondary amides from aryl halides and water is presented as a case study. The kinetics of the oxidative addition of ArI with RNC-ligated Pd⁰ species have been studied and the resulting imidoyl complex [(ArC=NR)Pd(CNR)₂ I] (Ar=4-F-C₆ H₄ , R=tBu) has been isolated and characterized by X-ray diffraction. The unprecedented ability of this RNC-ligated imidoyl-Pd complex to undergo reductive elimination at room temperature to give the amide in the presence of water and an F^- /HF buffer is demonstrated. Its behavior in solution has also been characterized, revealing an unexpected strong tendency to give cationic complexes, and notably [(ArC=NR)Pd(CNR)₃ ]⁺ with excess isocyanide and [(ArC=NR)Pd(PP^ )(CNR)]⁺ with bidentate phosphines (PP^ ). These species may be responsible for catalyst deactivation and side-reactions. Ab initio calculations performed at the DFT level allowed us to rationalize the multiple roles of RNC in the different steps of the catalytic cycle.

C-H Activation in Primary 3-Phenylpropylamines: Synthesis of Seven-Membered Palladacycles through Orthometalation. Stoichiometric Preparation of Benzazepinones and Catalytic Synthesis of Ureas

The dimeric cyclometalated complexes [Pd2{κ(2)C,N-C6H4CH2CH2C(R)(Me)NH2-2}2(μ-Cl)2] (R = Me (1a), H (1b)) are prepared by reacting 1,1-dimethyl-3-phenylpropylammonium or 1-methyl-3-phenylpropylammonium triflate with Pd(OAc)2 in a 1:1 molar ratio and subsequent treatment with excess NaCl. The mononuclear derivatives [Pd{κ(2)C,N-C6H4CH2CH2C(R)(Me)NH2-2}Cl(L)] (L = PPh3, R = Me (3a), H (3b); L = 4-picoline (4-pic), R = Me (4a), H (4b)) were prepared from 1a,b by splitting the chloro bridges with the neutral ligands L. A conformational analysis of the mononuclear palladacycles in solution has been carried out. Insertion of CO takes place into the Pd-C bond of complexes 1a,b, affording Pd(0) and the tetrahydro-benzazepinone 5a or 5b, which possesses potential pharmacological interest. Additionally, the triflate salt A or B undergoes catalytic carbonylation with CO to afford the corresponding N,N'-dialkylurea, using Pd(OAc)2/Cu(OAc)2, in boiling acetonitrile. The crystal structures of 3a·(1)/2H2O, 3b, 4b·CHCl3, and 5a were determined by X-ray diffraction studies.

Reactivity towards nitriles, cyanamides, and carbodiimides of palladium complexes derived from benzyl alcohol. Synthesis of a mixed Pd2Ag complex

The chelate complex [Pd(κ(2)-C,O-C6H4CH2O-2)(bpy)] () reacts with acetonitrile, cyanamides, or carbodiimides, in the presence of AgOTf (1 : 5 : 1 molar ratio) and residual water, to form complexes [Pd{κ(2)-C,N-C6H4{CH2OC([double bond, length as m-dash]NX)Y}-2}(bpy)](OTf), where X = H, Y = Me (), NMe2 (), NEt2 (), X = R, Y = NHR (R = (i)Pr (), Tol ()), as a result of the insertion of the unsaturated reagent into the O-Pd bond of and the protonation of one of the N atoms. In the absence of AgOTf the reaction of with TolN[double bond, length as m-dash]C[double bond, length as m-dash]NTol (Tol = p-Tolyl) results in the formation of the neutral complex [Pd{κ(2)-C,N-C6H4{CH2OC([double bond, length as m-dash]NTol)NTol}-2}(bpy)] (). Complexes and can be interconverted by deprotonation ( + KO(t)Bu) or protonation ( + KOTf + HOTf) reactions. When the reaction of with TolN[double bond, length as m-dash]C[double bond, length as m-dash]NTol in the presence of AgOTf is carried out in a 1 : 1 : 1 stoichiometric ratio, or for a short period of time, a mixture of and a mixed heterometallic Ag2Pd complex is obtained ( = [Ag(N-)2](OTf)). Complex is the major product when the AgOTf is added before the carbodiimide, and the reaction is stopped immediately. can also be obtained by reaction of with 0.5 equiv. of AgOTf. When complex [PdI(C6H4CH2OH-2)(bpy)] () reacts with (i)PrN[double bond, length as m-dash]C[double bond, length as m-dash]N(i)Pr in the presence of TlOTf, instead of AgOTf, a ca. 1 : 1 mixture of and [Pd{κ(2)-O,N-OCH2{C6H4{C([double bond, length as m-dash]NH(i)Pr)N(i)Pr}-2}}(bpy)](OTf) () forms. Complex is the result of the insertion of the carbodiimide into the C-Pd bond. Complexes have been extensively characterized by NMR spectroscopy, and the crystal structures of , , and ·2.5CHCl3·0.5Et2O have been determined by X-ray diffraction studies.

Synthesis of biaryls using aryne intermediates

The synthesis of biaryls from benzyne intermediates offers an alternative strategy to conventional metal-catalyzed cross-coupling approaches.

Boryl (Hetero)aryne Precursors as Versatile Arylation Reagents: Synthesis through C-H Activation and Orthogonal Reactivity

(Pinacolato)boryl ortho-silyl(hetero)aryl triflates are presented as a new class of building blocks for arylation. They demonstrate unique versatility by delivering boronate or (hetero)aryne reactivity chemoselectively in a broad range of transformations. This approach enables the unprecedented postfunctionalization of fluoride-activated (hetero)aryne precursors, for example, as substrates in transition-metal catalysis, and offers valuable new possibilities for aryl boronate postfunctionalization without the use of specialized protecting groups.