Palladium‐Catalysed, Directed CH Coupling with Organometallics

Exploring the mechanism of the Pd-catalyzed spirocyclization reaction: a combined DFT and experimental study

The mechanism of the palladium-catalyzed spirocyclization of acrylamides has been investigated by density functional theory and experimental studies. The results support a mechanistic pathway that proceeds via oxidative addition, intramolecular carbopalladation, C-H bond activation, and migratory insertion sequence. The M06L/def2-TZVPP//BP86/6-31G(d,p)/LANL2DZ level of theory used and the inclusion of solvent effects provide results in good agreement with the experimental data. The C-H bond activation step proceeds via a concerted outer-sphere metallation deprotonation mechanism that explains the absence of a measurable kinetic isotopic effect. The subsequent intermolecular migratory insertion of arynes is significantly faster than the insertion of internal alkynes. Furthermore, the regioselectivities calculated in the case of unsymmetrical reactants are remarkably close to the experimental values. Evaluation of the potential energy surfaces for specific substrates provides an explanation for the lack of product formation observed experimentally. Finally, the computational and experimental analyses of potential side reactions are also presented and support the initially proposed mechanism.

Recent developments in palladium-catalysed non-directed coupling of (hetero)arene C–H bonds with C–Z (Z = B, Si, Sn, S, N, C, H) bonds in bi(hetero)aryl synthesis

This review article describes the palladium-catalysed non-directed coupling of (hetero)arene C–H bonds with C_(Ar)–Z (Z = B, Si, Sn, S, N, C, H) bonds for facile bi(hetero)aryl synthesis in the past 10 years.

Pd-Catalyzed C–H aziridination of 3,3,5,5-tetrasubstituted piperazin-2-ones

Pd-Catalysed C–H aziridination of 3,3,5,5-tetrasubsituted piperazin-2-ones catalysed by succinic acid. The mechanistic role of the acid is investigated through kinetics experiments.

Iridium-catalysed arylation of C-H bonds enabled by oxidatively induced reductive elimination

Direct arylation of C-H bonds is in principle a powerful way of preparing value-added molecules that contain carbon-aryl fragments. Unfortunately, currently available synthetic methods are not sufficiently effective to be practical alternatives to conventional cross-coupling reactions. We propose that the main problem lies in the late portion of the catalytic cycle where reductive elimination gives the desired carbon-aryl bond. Accordingly, we have developed a strategy where the Ir(III) centre of the key intermediate is first oxidized to Ir(IV). Density functional theory calculations indicate that the barrier to reductive elimination is reduced by nearly 19 kcal mol^-1 for this oxidized complex compared with that of its Ir(III) counterpart. Various experiments confirm this prediction, affording a new methodology capable of directly arylating C-H bonds at room temperature with a broad substrate scope and in good yields. This work highlights how the oxidation states of intermediates can be targeted deliberately to catalyse an otherwise impossible reaction.

Synthesis, Structure, and Redox Properties of a trans-Diaqua Ru Complex That Reaches Seven-Coordination at High Oxidation States

In this work we have prepared and characterized two Ru complexes that contain the pentadenatate tda^2- ligand (tda^2- = [2,2':6',2″-terpyridine]-6,6″-dicarboxylate) that occupies the equatorial positions and two monodentate ligands aqua and/or dmso that occupy the axial positons: [trans-Ru^III(tda-κ-N³O)(OH₂^ax)₂]⁺, 3^III(OH₂)₂⁺, and [Ru^II(tda-κ-N³O)(dmso)(OH₂^ax)], 4^II. The latter is a useful synthetic intermediate for the preparation of Ru-tda complexes with different axial ligands. The two complexes have been characterized in the solid state by single-crystal XRD and by elemental analysis. In solution, complex 4^II has been characterized by NMR spectroscopy as well as the one-electron reduction of complex 3^III(OH₂)₂⁺. The electrochemical properties of 3^III(OH₂)₂⁺ and 4^II have been assessed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Complex 3^III(OH₂)₂⁺ shows the presence of four redox waves that are assigned to the VI/V, V/IV, IV/III, and III/II redox couples. The variation of the redox potentials is analyzed as a function of pH and is graphically presented as a Pourbaix diagram. Finally, the redox potentials displayed by both 3^III(OH₂)₂⁺ and 4^II are compared to related complexes previously reported in the literature and rationalized on the basis of the electron donating or withdrawing capacity of the auxiliary ligands as well as with regard to their ability to undergo seven-coordination at high oxidation states.

Highly chemoselective ruthenium(ii)-catalyzed direct arylation of cyclic and N,N-dialkyl benzamides with aryl silanes

The ruthenium(ii)-catalyzed oxidative cross-coupling of C(sp2)-H bonds with organosilanes has been accomplished for the first time. This novel protocol enlists challenging cyclic and N,N-dialkyl benzamides as weakly-coordinating substrates to achieve highly regioselective C(sp2)-H arylation as a proof-of-concept, taking advantage of the attractive features of organosilanes as coupling partners. This innovative method is characterized by very high chemoselectivity, installing halide functional groups (I, Br, Cl) that are incompatible with Ru(ii)-carboxylate systems employing halides as cross-coupling partners, while obviating the need for sensitive organometallic reagents and cryogenic temperatures typical to the classic directed-ortho-metallation (DoM) techniques, employing benzamides to afford bioactive structural motifs.

Rhodium(iii)-catalyzed directed C–H benzylation and allylation of indoles with organosilicon reagents

Rhodium(iii)-catalyzed C2-benzylation and allylation of indoles with organosilicon reagents via chelation-assisted C–H activation has been developed.

An approach to spirooxindoles via palladium-catalyzed remote C–H activation and dual alkylation with CH2Br2

An approach for the synthesis of spirooxindoles has been developed via palladium-catalyzed remote C–H functionalization with CH₂Br₂.

Pd-Catalyzed regioselective intramolecular dehydrogenative C-5 cross coupling in anN-substituted pyrrole-azole system

A C5-selective intramolecular dehydrogenative cross coupling inN-substituted pyrrole-azoles in the presence of a reactive C2 position is achieved.

Ruthenium(ii)-catalyzed ortho-C–H arylation of diverse N-heterocycles with aryl silanes by exploiting solvent-controlled N-coordination

We report the first method for the direct, regioselective Ru(ii)-catalyzed oxidative arylation of C–H bonds in diverse N-heterocycles with aryl silanes by exploiting solvent-controlled N-coordination.

Ruthenium(0)-Catalyzed C-H Arylation of Aromatic Imines under Neutral Conditions: Access to Biaryl Aldehydes

The first ruthenium(0)-catalyzed C-H bond arylation of aromatic imines with arylboronates under neutral conditions is reported. This versatile method provides rapid access to a wide range of biaryl aldehydes that are difficult to assemble using traditional methods with high atom economy. A new hydrogen acceptor for Ru(0) arylation has been identified. This atom-economical strategy has potential for an array of direct applications in Ru(0)-catalyzed C-H bond arylations using removable directing groups. An indole synthesis by a sequential one-pot, multiple C-H activation protocol is reported.

Pd(OAc)2-catalysed regioselective alkoxylation of aryl (β-carbolin-1-yl)methanones via β-carboline directed ortho-C(sp(2))-H activation of an aryl ring

Synthesis of (2-alkoxyphenyl)(9H-pyrido[3,4-b]indol-1-yl)methanone via Pd(OAc)2-catalyzed regioselective alkoxylation of aryl (β-carbolin-1-yl) methanones employing β-carboline directed ortho-C(sp(2))-H activation of an aryl ring under oxidative conditions is described.

Palladium catalyzed C–H bond acetoxylation: isoxazolinyl as a directing group

Pd(OAc)₂-catalyzed acetoxylations of 3-aryl or 3-alkyl groups mounted on a 2-isoxazoline ring were studied. Substituent effect on reactivity and regioselectivity was examined. The acetoxylation was applied to the synthesis of useful intermediates.

Ruthenium-catalyzed direct arylations with aryl chlorides

Aryl chlorides are readily available at lower cost than the corresponding bromides and iodides, but are much more challenging as substrates in metal-catalyzed cross-couplings.

[RuCl2(η6-p-cymene)] complexes bearing phosphinous acid ligands: preparation, application in C–H bond functionalization and mechanistic investigations

A series of [RuCl₂(η⁶-p-cymene)] complexes bearing phosphinous acid (PA) ligands have been straightforwardly prepared from the dimer [RuCl₂(p-cymene)]₂ and secondary phosphine oxides (SPOs) and fully characterized.

Amino acid-promoted C–H alkylation with alkylboronic acids using a removable directing group

Palladium-catalyzed C–H alkylation reaction with alkylboronic acids has been developed using a removable pyridyldiisopropylsilyl directing group.

[N,P]-pyrrole PdCl2complexes catalyzed the formation of dibenzo-α-pyrone and lactam analogues

Catalytic applications on direct intramolecular arylation was developed using a new family of palladium complexes that includes [N,P] ligands based on the pyrrole ring with α-phosphine and phosphole units.

Ruthenium(0)-catalyzed hydroarylation of alkynes via ketone-directed C–H functionalization using in situ-generated ruthenium complexes

Ketone-directed Ru(0)-catalyzed hydroarylation of alkynes enabled byin situgeneration of a Ru(0) catalyst from an air-stable, inexpensive and user-friendly Ru(ii) precatalyst is reported.

Palladium(ii)-catalyzed hydroxy-involved enolate-type efficient C–C functionalization of hydroxynaphthoquinones at room temperature

A simple, mild, efficient and scalable strategy has been developed for synthesizing hydroxynaphthoquinones via a Pd-catalyzed hydroxy-involved enolate-type reaction.