Synthesis and catalytic properties of palladium(II) complexes with P,π-chelating ferrocene phosphinoallyl ligands and their non-tethered analogues

Hybrid phosphines usually combine a phosphine moiety with another heteroatom secondary donor group in their structures while compounds equipped with hydrocarbyl π-donor moieties remain uncommon. This contribution reports the synthesis and structural characterization of the first P/π-allyl-chelating complexes that were obtained using the structurally flexible and redox-active ferrocene unit as the scaffold, viz. [PdCl(R2PfcCHCHCH2-η3:κP)] (1R; R = Ph and cyclohexyl (Cy); fc = ferrocene-1,1'-diyl). These compounds were synthesized from the respective phosphinoferrocene carboxaldehydes R2PfcCHO via reaction with vinylmagnesium bromide to generate 1-(phosphinoferrocenyl)allyl alcohols, which were subsequently acetylated. The resulting allyl acetates reacted smoothly with [Pd2(dba)3]/[Et3NH]Cl (dba = dibenzylideneacetone) to produce the target compounds. Complexes 1R and their nontethered analogues [PdCl(η3-C3H5)(FcPR2-κP)] (5R; Fc = ferrocenyl) were evaluated as pre-catalysts for the Pd-catalysed allylic amination of cinnamyl acetate with aliphatic amines and Suzuki-Miyaura-type cross-coupling of 4-tolylboronic acid with benzoyl chloride. In these reactions, better results were achieved with compounds 5R (particularly with 5Ph), presumably because they form more stable LPd(0)-type catalysts.

Engaging Alkenes in Metallaphotoredox: A Triple Catalytic, Radical Sorting Approach to Olefin-Alcohol Cross-Coupling

Metallaphotoredox cross-coupling is a well-established strategy for generating clinically privileged aliphatic scaffolds via single-electron reactivity. Correspondingly, expanding metallaphotoredox to encompass new C(sp3)-coupling partners could provide entry to a novel, medicinally relevant chemical space. In particular, alkenes are abundant, bench-stable, and capable of versatile C(sp3)-radical reactivity via metal-hydride hydrogen atom transfer (MHAT), although metallaphotoredox methodologies invoking this strategy remain underdeveloped. Importantly, merging MHAT activation with metallaphotoredox could enable the cross-coupling of olefins with feedstock partners such as alcohols, which undergo facile open-shell activation via photocatalysis. Herein, we report the first C(sp3)-C(sp3) coupling of MHAT-activated alkenes with alcohols by performing deoxygenative hydroalkylation via triple cocatalysis. Through synergistic Ir photoredox, Mn MHAT, and Ni radical sorting pathways, this branch-selective protocol pairs diverse olefins and methanol or primary alcohols with remarkable functional group tolerance to enable the rapid construction of complex aliphatic frameworks.

Redox-neutral zinc-catalyzed cascade [1,4]-H shift/annulation of diaziridines with donor-acceptor aziridines

The coupling of diaziridines with donor-acceptor aziridines (DAAs) has been achieved using Zn-catalysis to furnish imidazopyrazole-4,4-dicarboxylates via [1,4]-hydride shift. The use of Zn-catalysis, [1,4]-hydride shift, natural product modification and a late-stage molecular docking study are important practical features.

Nickel-Catalyzed Reductive Alkyne Hydrocyanation Enabled by Malononitrile and a Formaldehyde Additive

The development of a nickel-catalyzed reductive alkyne hydrocyanation is described using 2-methyl-2-phenylmalononitrile (MPMN), a C-bound electrophilic transnitrilation reagent. Reproducibility issues led to the detection of oxidized hemiaminal impurities within N,N-dimethylacetamide. These impurities release formaldehyde in situ, which was ultimately identified as a critical reaction additive. A range of diaryl and aryl-alkyl alkynes underwent hydrocyanation. Mechanistic experiments revealed that formaldehyde and MPMN undergo a Ni-catalyzed reductive coupling of two π-components, leading to the controlled release of glycolonitrile as the active cyanating agent.

Catalytic Asymmetric Ring-Opening Reactions of Unstrained Heterocycles Using Cobalt Vinylidenes

Cobalt catalysts promote highly enantioselective ring-opening reactions of 2,5-dihydrofurans using vinylidenes. The products are acyclic organozinc compounds that can be functionalized with an electrophile. The proposed mechanism involves the generation of a cobalt vinylidene species that adds to the alkene by a [2+2]-cycloaddition pathway. Ring-opening then occurs via outer-sphere β-O elimination assisted by coordination of a ZnX2 Lewis acid to the alkoxide leaving group. DFT models reveal that competing inner-sphere syn β-H and β-O elimination pathways are suppressed by the geometric constraints of the metallacycle intermediate. These models rationalize the observed stereochemical outcome of the reaction.

Expedient (3+3)-annulation of in situ generated azaoxyallyl cations with diaziridines

Efficient annulation of in situ formed azaoxyallyl cations using a base has been accomplished with diaziridines to provide 1,2,4-triazines at room temperature. The substrate scope, scale up, functional group tolerance and transition-metal free reaction conditions are the important practical features.

Metal-Catalyst-Controlled Divergent Synthesis of γ-Butyrolactones via Intramolecular Coupling of Epoxides with Alcohols

A metal-controlled divergent protocol for the synthesis of α- and β-substituted γ-butyrolactones was developed through intramolecular coupling of epoxides with alcohols. This method provides an efficient and practicable way to afford γ-butyrolactones with good efficiency, excellent regioselectivity, and broad substrate scope.

Structure-Reactivity Relationships of Buchwald-Type Phosphines in Nickel-Catalyzed Cross-Couplings

The dialkyl-ortho-biaryl class of phosphines, commonly known as Buchwald-type ligands, are among the most important phosphines in Pd-catalyzed cross-coupling. These ligands have also been successfully applied to several synthetically valuable Ni-catalyzed cross-coupling methodologies and, as demonstrated in this work, are top performing ligands in Ni-catalyzed Suzuki Miyaura Coupling (SMC) and C-N coupling reactions, even outperforming commonly employed bisphosphines like dppf in many circumstances. However, little is known about their structure-reactivity relationships (SRRs) with Ni, and limited examples of well-defined, catalytically relevant Ni complexes with Buchwald-type ligands exist. In this work, we report the analysis of Buchwald-type phosphine SRRs in four representative Ni-catalyzed cross-coupling reactions. Our study was guided by data-driven classification analysis, which together with mechanistic organometallic studies of structurally characterized Ni(0), Ni(I), and Ni(II) complexes allowed us to rationalize reactivity patterns in catalysis. Overall, we expect that this study will serve as a platform for further exploration of this ligand class in organonickel chemistry as well as in the development of new Ni-catalyzed cross-coupling methodologies.

Nickel-catalyzed cross-coupling of epoxides with aryltriflates: rapid and regioselective construction of aryl ketones

Aryl ketones are one of the most important classes of organic compounds, and widely present in various pharmacological compounds, biologically active molecules and functional materials. Presented herein is a facile synthetic method for the construction of ketones via Ni-catalyzed cross coupling of epoxides with aryltriflates. A range of easily accessible epoxides can be highly regioselectively converted to the corresponding aryl ketones with good yields in a redox neutral fashion.

Direct and Selective Electrocarboxylation of Styrene Oxides with CO2 for Accessing β-Hydroxy Acids

Highly selective and direct electroreductive ring-opening carboxylation of epoxides with CO2 in an undivided cell is reported. This reaction shows broad substrate scopes within styrene oxides under mild conditions, providing practical and scalable access to important synthetic intermediate β-hydroxy acids. Mechanistic studies show that CO2 functions not only as a carboxylative reagent in this reaction but also as a promoter to enable efficient and chemoselective transformation of epoxides under additive-free electrochemical conditions. Cathodically generated α-radical and α-carbanion intermediates lead to the regioselective formation of α-carboxylation products.

Metal-catalyzed reactions of organic nitriles and boronic acids to access diverse functionality

The nitrile or cyano (-CN) group is one of the most appreciated and effective functional groups in organic synthesis, having a polar unsaturated C-N triple bond. Despite sufficient stability and being intrinsically inert, the nitrile group can be easily transformed into many other functional groups, such as amines, carboxylic acids, ketones, etc. which makes it a vital group in organic synthesis. On the other hand, despite several boronic acids having a low level of genotoxicity, they have found wide applicability in the field of organic synthesis, especially in transition metal-catalyzed cross-coupling reactions. Recently, transition-metal-catalyzed cascade additions or addition/cyclization processes of boronic acids to the nitrile group open up exciting and useful strategies to prepare a variety of functional molecules through the formation of C-C, C-N and CO bonds. Boronic acids can be added to the cyano functionality through catalytic carbometallation or through a radical cascade process to provide newer pathways for the rapid construction of various important acyclic ketones or amides, carbamidines, carbocycles and N,O-heterocycles. The present review focuses on various transition-metal-catalyzed additions of boronic acids via carbometallation or radical cascade processes using the cyano group as an acceptor.

Merging strain-release and copper catalysis: the selective ring-opening cross-coupling of 1,2-oxazetidines with boronic acids

An unprecedented ring-opening cross-coupling of 1,2-oxazetidines with readily available arylboronic acids is achieved for the first time by copper catalysis. Unlike the known electrophilic oxygen reactivity in coupling with organometallic reagents, 1,2-oxazetidines were utilized as formaldimine precursors in this protocol. Remarkable features of this reaction include simple operation, inexpensive catalyst, broad scope and high regioselectivity, delivering a wide array of aminomethylation products. The practicality of this reaction was validated in the one-step downstream transformation of the obtained products into synthetically important molecules and late-stage modification of bioactive acids.

Facile synthesis of amides via acceptorless dehydrogenative coupling of aryl epoxides and amines

The synthesis of amides is significant in a wide variety of academic and industrial fields. We report here a new reaction, namely acceptorless dehydrogenative coupling of epoxides and amines to form amides catalyzed by ruthenium pincer complexes. Various aryl epoxides and amines smoothly convert into the desired amides in high yields with the generation of H₂ gas as the only byproduct. Control experiments indicate that amides are generated kinetically faster than side products, possibly because of the facile activation of epoxides by metal–ligand cooperation, as supported by the observation of a ruthenium-enolate species. No alcohol or free aldehyde are involved. A mechanism is proposed involving a dual role of the catalyst, which is responsible for the high yield and selectivity of the new reaction.

We report the ruthenium pincer complex catalyzed acceptorless dehydrogenative coupling of epoxides and amines to form amides. The reaction offers a facile and atom economical two-step strategy for transforming alkenes into amides.

Nickel-Catalyzed Decarboxylative Coupling of Redox-Active Esters with Aliphatic Aldehydes

The addition of alkyl fragments to aliphatic aldehydes is a highly desirable transformation for fragment couplings, yet existing methods come with operational challenges related to the basicity and instability of the nucleophilic reagents commonly employed. We report herein that nickel catalysis using a readily available bioxazoline (BiOx) ligand can catalyze the reductive coupling of redox-active esters with aliphatic aldehydes using zinc metal as the reducing agent to deliver silyl-protected secondary alcohols. This protocol is operationally simple, proceeds under mild conditions, and tolerates a variety of functional groups. Initial mechanistic studies suggest a radical chain pathway. Additionally, alkyl tosylates and epoxides are suitable alkyl precursors to this transformation providing a versatile suite of catalytic reactions for the functionalization of aliphatic aldehydes.

Univariate classification of phosphine ligation state and reactivity in cross-coupling catalysis

[Figure: see text].

Cu-Catalyzed Cross-Coupling of Benzylboronic Esters and Epoxides

A reaction between epoxides and benzylboronic acid pinacol esters is described. CuI was found to be an effective catalyst of this transformation upon activation of the benzylboronic ester with an alkyllithium reagent. The reaction was very efficient and a variety of substituted epoxides were found to be good substrates with good regioselectivity for substitution at the less substituted side of the epoxide. A reaction using an enantioenriched secondary benzylboronic ester was found to not be stereospecific.

Ni/Photoredox-Catalyzed Enantioselective Cross-Electrophile Coupling of Styrene Oxides with Aryl Iodides

A Ni/photoredox-catalyzed enantioselective reductive coupling of styrene oxides and aryl iodides is reported. This reaction affords access to enantioenriched 2,2-diarylalcohols from racemic epoxides via a stereoconvergent mechanism. Multivariate linear regression (MVLR) analysis with 29 bioxazoline (BiOx) and biimidazoline (BiIm) ligands revealed that enantioselectivity correlates with electronic properties of the ligands, with more electron-donating ligands affording higher ee's. Experimental and computational mechanistic studies were conducted, lending support to the hypothesis that reductive elimination is enantiodetermining and the electronic character of the ligands influences the enantioselectivity by altering the position of the transition state structure along the reaction coordinate. This study demonstrates the benefits of utilizing statistical modeling as a platform for mechanistic understanding and provides new insight into an emerging class of chiral ligands for stereoconvergent Ni and Ni/photoredox cross-coupling.

Cobalt Catalyst Determines Regioselectivity in Ring Opening of Epoxides with Aryl Halides

Ring-opening of epoxides furnishing either linear or branched products belongs to the group of classic transformations in organic synthesis. However, the regioselective cross-electrophile coupling of aryl epoxides with aryl halides still represents a key challenge. Herein, we report that the vitamin B₁₂/Ni dual-catalytic system allows for the selective synthesis of linear products under blue-light irradiation, thus complementing methodologies that give access to branched alcohols. Experimental and theoretical studies corroborate the proposed mechanism involving alkylcobalamin as an intermediate in this reaction.

Metal-catalysed C-Het (F, O, S, N) and C-C bond arylation

The formation of C-aryl bonds has been the focus of intensive research over the last decades for the construction of complex molecules from simple, readily available feedstocks. Traditionally, these strategies involve the coupling of organohalides (I, Br, Cl) with organometallic reagents (Mg, Zn, B, Si, Sn,…) such as Kumada-Corriu, Negishi, Suzuki-Miyaura, Hiyama and Sonogashira cross-couplings. More recently, alternative methods have provided access to these products by reactions with less reactive C-Het (F, O, S, N) and C-C bonds. Compared to traditional methods, the direct cleavage and arylation of these chemical bonds, the essential link in accessible feedstocks, has become increasingly important from the viewpoint of step-economy and functional-group compatibility. This comprehensive review aims to outline the development and advances of this topic, which was organized into (1) C-F bond arylation, (2) C-O bond arylation, (3) C-S bond arylation, (4) C-N bond arylation, and (5) C-C bond arylation. Substantial attention has been paid to the strategies and mechanistic investigations. We hope that this review can trigger chemists to discover more efficient methodologies to access arylation products by cleavage of these C-Het and C-C bonds.

The transition-metal-catalyzed stereoselective ring-expansion of vinylaziridines and vinyloxiranes

The transition-metal-aided stereoselective construction of sp3-carbon-rich heterocyclic scaffolds using strained-ring systems has received considerable attention in recent years due to the prominent presence of these scaffolds in myriad natural products, bioactive molecules, and pharmaceutical components. In this area, the catalytic ring-enlargement of vinylaziridines and vinyloxiranes plays a predominant role when synthesizing high sp3-content biorelevant heterocyclic compounds. This article aims to portray recent advancements in the ring-expansion of vinylaziridines and vinyloxiranes for accessing densely functionalized stereoselective heterocycles that have been developed over the past five years, with an emphasis on the substrate scopes and mechanistic insights into the key methodologies, and it is arranged based on the transition metals used and the ring sizes of the heterocyclic scaffolds.

Ranking Ligands by Their Ability to Ease (C6F5)2NiIIL → Ni0L + (C6F5)2 Coupling versus Hydrolysis: Outstanding Activity of PEWO Ligands

The Ni^II literature complex cis-[Ni(C₆F₅)₂(THF)₂] is a synthon of cis-Ni(C₆F₅)₂ that allows us to establish a protocol to measure and compare the ligand effect on the Ni^II → Ni⁰ reductive elimination step (coupling), often critical in catalytic processes. Several ligands of different types were submitted to this Ni-meter comparison: bipyridines, chelating diphosphines, monodentate phosphines, PR₂(biaryl) phosphines, and PEWO ligands (phosphines with one potentially chelate electron-withdrawing olefin). Extremely different C₆F₅-C₆F₅ coupling rates, ranging from totally inactive (producing stable complexes at room temperature) to those inducing almost instantaneous coupling at 25 °C, were found for the different ligands tested. The PR₂(biaryl) ligands, very efficient for coupling in Pd, are slow and inefficient in Ni, and the reason for this difference is examined. In contrast, PEWO type ligands are amazingly efficient and provide the lowest coupling barriers ever observed for Ni^II complexes; they yield up to 96% C₆F₅-C₆F₅ coupling in 5 min at 25 °C (the rest is C₆F₅H) and 100% coupling with no hydrolysis in 8 h at -22 to -53 °C.

Palladium-Catalyzed Tandem C-C Activation/Cyclization Induced by Carbopalladation of Functionalized Nitriles: Synthesis of Benzo Dipyrromethenes

A palladium-catalyzed carbon-carbon bond activation-initiated reaction of 2-(3-phenyloxiran-2-yl)benzonitriles with arylboronic acids is reported. Multiple chemical bonds were cleavaged and reconstructed via β-carbon elimination in this reaction, enabling the construction of valuable benzo-fused dipyrromethenes that are difficult to prepare by other methods. Additionally, a series of benzannulated boron dipyrromethenes are synthesized and show practical significance in terms of expanding the applications and types of fluorescent materials. The proposed mechanism is supported by preliminary mechanistic experiments.

Transition-Metal-Free Stereospecific Oxidative Annulative Coupling of Indolines with Aziridines

Tandem C-N bond formation for the oxidative annulation of indolines with aziridines is accomplished employing the combination of DDQ and NaOCl at ambient conditions. Optically active aziridine can be coupled with high enantiomeric purity (>99% ee). The substrate scope, stereocontrol with the enantioenriched substrate, and scale-up are the important practical advantages.

Regioselective Cross-Electrophile Coupling of Epoxides and (Hetero)aryl Iodides via Ni/Ti/Photoredox Catalysis

A cross-electrophile coupling reaction of epoxides and (hetero)aryl iodides that operates via the merger of three catalytic cycles involving a Ni-, Ti-, and organic photoredox catalyst has been developed. Three distinct classes of epoxides, styrene oxides, cyclic epoxides, and terminal aliphatic epoxides, all undergo coupling in moderate to good yield and high regioselectivity with the use of three different nitrogen-based ligands for Ni under otherwise identical reaction conditions. The mild reaction conditions accommodate a broad scope of abundant and complex coupling partners. Mechanistic studies suggest that when styrene oxides are employed radical intermediates are involved via Ti-radical ring-opening of the epoxide. Conversely, for terminal aliphatic epoxides, involvement of an iodohydrin intermediate enables the formation of the unexpected linear product.

Expedient iron-catalyzed stereospecific synthesis of triazines via cycloaddition of aziridines with diaziridines

Iron-catalyzed stereospecific [3+3]-annulation of aziridines with diaziridines is described to furnish [1,2,4]-triazines in high yield at room temperature. The use of an inexpensive iron salt catalyst, substrate scope and enantiomeric purity are the important practical features.

Covalent Organic Framework as a Heterogeneous Ligand for the Regioselective Oxidative Heck Reaction

A simple imine-based covalent organic framework (COF) as heterogeneous ligand for Pd^II-promoted Heck reaction is reported. Good regioselectivity for a wide range of electronically unbiased olefins is obtained (linear/branched >100:1 in most cases). Related tests and density functional theory calculations are used to explore the reason underlying the high selectivity. This research opens a route for COF as an intriguing platform to control regioselectivity catalysis.

Palladium-catalysed regio- and stereoselective arylative substitution of γ,δ-epoxy-α,β-unsaturated esters and amides by sodium tetraaryl borates

The palladium-catalysed reaction of γ,δ-epoxy-α,β-unsaturated esters or amides with NaBAr₄reagents proceeded regio- and stereoselectively to produce aryl-substituted homoallyl alcohols.

Base-free Ni-catalyzed Suzuki-type cross-coupling reactions of epoxides with boronic acids

A Ni-catalyzed Suzuki-type cross-coupling of boronic acids with epoxides without an exogenous base and with broad substrate scope has been developed.

Palladium-catalyzed tandem reaction of epoxynitriles with arylboronic acids in aqueous medium: divergent synthesis of furans and pyrroles

A palladium-catalyzed controllable divergent synthesis of furans and pyrroles through a cascade reaction of epoxynitriles with arylboronic acids has been developed in the aqueous phase.

Bimetallic Radical Redox-Relay Catalysis for the Isomerization of Epoxides to Allylic Alcohols

Organic radicals are generally short-lived intermediates with exceptionally high reactivity. Strategically, achieving synthetically useful transformations mediated by organic radicals requires both efficient initiation and selective termination events. Here, we report a new catalytic strategy, namely, bimetallic radical redox-relay, in the regio- and stereoselective rearrangement of epoxides to allylic alcohols. This approach exploits the rich redox chemistry of Ti and Co complexes and merges reductive epoxide ring opening (initiation) with hydrogen atom transfer (termination). Critically, upon effecting key bond-forming and -breaking events, Ti and Co catalysts undergo proton transfer/electron transfer with one another to achieve turnover, thus constituting a truly synergistic dual catalytic system.

The Importance of Ligand-Induced Backdonation in the Stabilization of Square Planar d10 Nickel π-Complexes

The electronic nature of Ni π-complexes is underexplored even though these complexes have been widely postulated as intermediates in organometallic chemistry. Herein, the geometric and electronic structure of a series of nickel π-complexes, Ni(dtbpe)(X) (dtbpe=1,2-bis(di-tert-butyl)phosphinoethane; X=alkene or carbonyl containing π-ligands), is probed using a combination of ³¹ P NMR, Ni K-edge XAS, Ni K_β XES, and DFT calculations. These complexes are best described as square planar d¹⁰ complexes with π-backbonding acting as the dominant contributor to M-L bonding to the π-ligand. The degree of backbonding correlates with ² J_PP from NMR and the energy of the Ni 1s→4p_z pre-edge in the Ni K-edge XAS data, and is determined by the energy of the π*_ip ligand acceptor orbital. Thus, unactivated olefinic ligands tend to be poor π-acids whereas ketones, aldehydes, and esters allow for greater backbonding. However, backbonding is still significant even in cases in which metal contributions are minor. In such cases, backbonding is dominated by charge donation from the diphosphine, which allows for strong backdonation, although the metal centre retains a formal d¹⁰ electronic configuration. This ligand-induced backbonding can be formally described as a 3-centre-4-electron (3c-4e) interaction, in which the nickel centre mediates charge transfer from the phosphine σ-donors to the π*_ip ligand acceptor orbital. The implications of this bonding motif are described with respect to both structure and reactivity.

Base-Promoted, Remote C-H Activation at a Cationic (η5-C5Me5)Ir(III) Center Involving Reversible C-C Bond Formation of Bound C5Me5

C–H bond activation at cationic [(η⁵-C₅Me₅)Ir(PMe₂Ar′)] centers is described, where PMe₂Ar′ are the terphenyl phosphine ligands PMe₂Ar^Xyl₂ and PMe₂Ar^Dipp₂. Different pathways are defined for the conversion of the five-coordinate complexes [(η⁵-C₅Me₅)IrCl(PMe₂Ar′)]⁺, 2(Xyl)⁺ and 2(Dipp)⁺, into the corresponding pseudoallyls 3(Xyl)⁺ and 3(Dipp)⁺. In the absence of an external Brønsted base, electrophilic, remote ζ C–H activation takes place, for which the participation of dicationic species, [(η⁵-C₅Me₅)Ir(PMe₂Ar′)]²⁺, is proposed. When NEt₃ is present, the PMe₂Ar^Dipp₂ system is shown to proceed via 4(Dipp)⁺ as an intermediate en route to the thermodynamic, isomeric product 3(Dipp)⁺. This complex interconversion involves a non-innocent C₅Me₅ ligand, which participates in C–H and C–C bond formation and cleavage. Remarkably, the conversion of 4(Dipp)⁺ to 3(Dipp)⁺ also proceeds in the solid state.

Direct oxidative dearomatization of indoles: access to structurally diverse 2,2-disubstituted indolin-3-ones

Described is an efficient oxidative dearomatization of indoles with TEMPO oxoammonium salt and a broad range of nucleophiles.

Palladium-mediated intramolecular dearomatization of ligated dialkylterphenyl phosphines

Thermal dearomative rearrangement of coordinated dialkylterphenyl phosphines mediated by Pd(II).

Direct experimental evaluation of ligand-induced backbonding in nickel metallacyclic complexes

The details of ligand-induced backbonding in nickel diphosphine π complexes are explored using nickel L-edge (3d←2p) X-ray absorption spectroscopy as a means of quantifying the degree of backbonding derived from direct Ni 3d donation into the π ligand. It is observed that backbonding into weakly π acidic ligands such as alkenes and arenes is dominated by contributions from the diphosphine ligand via σ-donation, leading to activated metallacycles with a Ni(0) d10 metal centre. With more strongly π acidic ligands, however, metal contributions to backbonding increase substantially leading to a more electron-deficient metal centre that is best described as having a Ni(i) spectroscopic oxidation state.

Bimolecular oxidative C–H alkynylation of α-substituted isochromans

The first bimolecular oxidative C–H functionalization of secondary benzylic ethers for tertiary ether synthesis has been established in high efficiency.

Recent advances in well-defined, late transition metal complexes that make and/or break C-N, C-O and C-S bonds

Chemical transformations that result in either the formation or cleavage of carbon-heteroatom bonds are among the most important processes in the chemical sciences. Herein, we present a review on the reactivity of well-defined, late-transition metal complexes that result in the making and breaking of C-N, C-O and C-S bonds via fundamental organometallic reactions, i.e. oxidative addition, reductive elimination, insertion and elimination reactions. When appropriate, emphasis is placed on structural and spectroscopic characterization techniques, as well as mechanistic data.