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Using visible light conditions, we have developed a green protocol to prepare copper oxide‐doped graphitic carbon nitride (Cu2O@g‐C3N4) photocatalysts with varied ratios of g‐C3N4 nanosheets to copper oxide‐dopant (0.1 %, 0.5 %, 0.7 %, and 5 % respectively) and characterized through various physicochemical techniques. These photo‐responsive catalysts were used for the 1,4 radical oxidative addition of trans crotonaldehyde into β‐hydroxybutyric acid (BA) as a major product, utilizing 30 % hydrogen peroxide as an oxidant and a white LED (Light Emitting Diode) source. Under the innoculous eco‐friendly stipulations, Cu2O@g‐C3N4 (5 %) exclusively promoted the aforementioned reaction leading to 99.85 % trans crotonaldehyde conversion with 66.57 %, 24.1 %, and 9.1 % selectivity for β‐hydroxybutyric acid, crotonic acid and subsequent radical synthesis, respectively. [ABSTRACT FROM AUTHOR]

The complexes of first-row transition metals can undergo elementary reactions by multiple pathways due to their propensity to undergo both one- and two-electron redox steps. Classic and recent studies of the oxidative addition of aryl halides to Ni(0)-a common step in widely practised cross-coupling processes-have yielded contradictory conclusions about stepwise, radical versus concerted mechanisms, but such information is crucial to the design of catalysts based on earth-abundant metals. Here we show that the oxidative addition of aryl halides to Ni(0) ligated by monophosphines occurs by both mechanisms and delineate how the branching of radical and non-radical pathways depends on the electronic properties of both the ligand and reactant arene as well as the identity of the halide. The one-electron pathway occurs by outer-sphere electron transfer to form an aryl radical rather than the often-proposed halogen atom transfer.

Two‐electron oxidative addition is one of the most important elementary reactions for d‐block transition metals but it is uncommon for f‐block elements. Here, we report the first examples of intermolecular oxidative addition of E−H (E=C, N) bonds to uranium(II) centers. The transient U(II) species was formed in‐situ by reducing a heterometallic cluster featuring U(IV)‐Pd(0) bonds with potassium‐graphite (KC8). Oxidative addition of C−H or N−H bonds to the U(II) centers was observed when this transient U(II) species was treated with benzene, carbazole or 1‐adamantylamine, respectively. The U(II) centers could also react with tetracene, biphenylene or N2O, leading to the formation of arene reduced U(IV) products and uranyl(VI) species via two‐ or four‐electron processes. This study demonstrates that the intermolecular two‐electron oxidative addition reactions are viable for actinide elements. [ABSTRACT FROM AUTHOR]

The oxidative addition of methyl iodide or molecular iodine to the bis(С,N-chelate) deprotonated diaminocarbene platinum(II) complexes [Pt{C(N(H)Ar)(NC(N(H)Ph)N(Ph)}2] (Ar = C6H3-2,6-Me2 (Xyl), C6H2-2,4,6-Me3 (Mes), and C6H4-4-Me (pTol)) affords the corresponding platinum(IV) derivatives in a yield of 89–99%. The addition of CF3CO2H is accompanied by the protonation of the nitrogen atoms of the diaminocarbene fragment to form the cationic complexes [PtI(X)-{C(N(H)Ar)(NC-(N(H)Ph)N(Ph)}2]CF3CO2H (X = Me, I). The structures of the compounds are determined by elemental analysis; high resolution mass spectrometry with electrospray ionization (ESI HRMS); IR spectroscopy; 1H, 13C{1H}, 19F{1H}, and 195Pt{1H} NMR spectroscopy; 2D NMR spectroscopy (1H,1Н COSY, 1H,1Н NOESY, 1H,13C HSQC, 1H,13C HMBC, 1H,15N HSQC, 1H,15N HMBC), and X-ray diffraction (XRD) and thermogravimetric analyses. The synthesized platinum(IV) complexes are thermally stable to 200–260°C and are electroneutral molecules with the octahedral coordination sphere formed by two deprotonated diaminocarbene C,N‑chelate substituents and iodine and methyl or two iodine atoms localized in the apical positions. [ABSTRACT FROM AUTHOR]

Mono or bis(tetrazole–thiolato) Pd(II) or Pt(II) complexes were obtained from the reactions of dialkyl Pd(II) or Pt(II) complexes with organic tetrazole–thiones (1-aryl- or 1-alkyl-1H-tetrazole-5-thiones) via deprotonation. In contrast, equimolar reactions of zerovalent Pt(0) or Pd(0) complexes with organic tetrazole–thiones afforded hydrido or bis(tetrazole–thiolato) Pt(II) and Pd(II) complexes, and cyclometallated Pt(II) or Pd(II) complexes bearing a tetrazole–thiolato moiety via oxidative addition, depending on the organic substituents on the tetrazole–thiones. In particular, variable (time and temperature)-dependent 1H-NMR spectra of the hydrido Pt(II) tetrazole–thiolates reveal an upfield shift of the hydride signal, suggesting N,S-coordination behavior of the tetrazole–thiolato ligand. Additionally, the N-CH2 signal corresponds to the six-membered ring of platinacycle or palladacycle exhibiting geminal coupling with multiple protons and PR3 ligands; these coupling values were further determined using 1H{31P} experiments. Finally, treatment of the alkyl Pd(II) tetrazole–thiolate or Pd(II) bis(tetrazole–thiolates) with organic tert-butyl isocyanide, thiophenol, and organic halides caused the selective insertion of the isocyanide into the Pd–C bond or deprotonation to afford a Pd(II) disulfide complex and substitution to afford new organic tetrazolyl sulfides. [ABSTRACT FROM AUTHOR]

The step that cleaves the carbon-halogen bond in copper-catalyzed cross-coupling reactions remains ill defined because of the multiple redox manifolds available to copper and the instability of the high-valent copper product formed. We report the oxidative addition of α-haloacetonitrile to ionic and neutral copper(I) complexes to form previously elusive but here fully characterized copper(III) complexes. The stability of these complexes stems from the strong Cu-CF3 bond and the high barrier for C(CF3)-C(CH2CN) bond-forming reductive elimination. The mechanistic studies we performed suggest that oxidative addition to ionic and neutral copper(I) complexes proceeds by means of two different pathways: an SN2-type substitution to the ionic complex and a halogen-atom transfer to the neutral complex. We observed a pronounced ligand acceleration of the oxidative addition, which correlates with that observed in the copper-catalyzed couplings of azoles, amines, or alkynes with alkyl electrophiles.

While the oxidative addition of Ni(I) to aryl iodides has been commonly proposed in catalytic methods, an in-depth mechanistic understanding of this fundamental process is still lacking. Herein, we describe a detailed mechanistic study of the oxidative addition process using electroanalytical and statistical modeling techniques. Electroanalytical techniques allowed rapid measurement of the oxidative addition rates for a diverse set of aryl iodide substrates and four classes of catalytically relevant complexes (Ni(MeBPy), Ni(MePhen), Ni(Terpy), and Ni(BPP)). With >200 experimental rate measurements, we were able to identify essential electronic and steric factors impacting the rate of oxidative addition through multivariate linear regression models. This has led to a classification of oxidative addition mechanisms, either through a three-center concerted or halogen-atom abstraction pathway based on the ligand type. A global heat map of predicted oxidative addition rates was created and shown applicable to a better understanding of the reaction outcome in a case study of a Ni-catalyzed coupling reaction.

The dinickel(I) complex Ni2(tBuPONNOPONNO), featuring a planar macrocyclic diphosphoranide ligand tBuPONNOPONNO, offers a unique architectural platform for observing bimetallic elementary reactions. Oxidative addition reactions of alkyl halides produce dinickel(II) complexes of the type Ni2(μ‐R)(μ‐X)(tBuPONNOPONNO). However, when R=Et β‐hydride elimination is observed to form a dinickel monohydride, with the rate dependent on the nature of X. DFT studies suggest a new mechanism for bimetallic β‐hydride elimination, where the rate dependence arises from the steric pressure imposed by the X group on the opposing trans face of the dinickel macrocycle. This work enhances understanding of bimetallic elementary reactions, particularly β‐hydride elimination, which have not been well‐explored for dinuclear systems. [ABSTRACT FROM AUTHOR]

The kinetic stability provided by the sterically demanding {SiNDipp}2− dianion (SiNDipp = {CH2SiMe2NDipp}2; Dipp = 2,6-i-Pr2C6H3) is intrinsic to the isolation of not only the group 1 alumanyl reagents ([{SiNDipp}AlM]2; M = K, Rb, Cs) but also facilitates the completely selective oxidative addition of a C-H bond of 1,2-C2B10H12 to the aluminium centre. In each case, the resultant compounds comprise a four-coordinate o-carboranyl (hydrido)aluminate anion, [(SiNDipp)Al(H)(1,2-C2B10H11)]−, in which the carboranyl cage is bonded to aluminium by an Al-C σ bond. Although the anions further assemble as extended network structures based on Al-H∙∙∙M, B-H∙∙∙M, and C-H∙∙∙M interactions, each structure is unique due to the significant variation in M+ ionic radius as group 1 is descended. The potassium derivative crystallises as a one-dimensional polymer, its rubidium analogue is a dimer due to the polyhapto-sequestration of a molecule of benzene solvent within the alkali metal coordination sphere, and the caesium species is a two-dimensional assembly of hexameric aggregates. [ABSTRACT FROM AUTHOR]

We report a study of solvent effects on the rate, selectivity, and mechanism of (hetero)aryl (pseudo)halide oxidative addition to Pd(PCy3)2 as an exemplar of L2Pd(0) species. First, 2‐chloro‐3‐aminopyridine is observed to undergo faster oxidative addition in toluene compared to more polar solvents, which is not consistent with the trend we observe with many other 2‐halopyridines. We attribute this to solvent basicity hydrogen bonding between solvent and substrate. Greater hydrogen bond donation from the substrate leads to a more electron‐rich aromatic system, and therefore slower oxidative addition. We demonstrate how this affects rate and site‐selectivity for hydrogen bond donating substrates. Second, electron‐deficient multihalogenated pyridines exhibit improved site‐selectivity in polar solvents, which we attribute to different C−X sites undergoing oxidative addition by two different mechanisms. The C−X site that favours the more polar nucleophilic displacement transition state is preferred over the site that favours a less‐polar 3‐centered transition state. Finally, (hetero)aryl triflates consistently undergo faster oxidative addition in more polar solvents, which we attribute to highly polar nucleophilic displacement transition states. This leads to improved site‐selectivity for C−OTf oxidative addition, even in the presence of highly reactive 2‐pyridyl halides. [ABSTRACT FROM AUTHOR]

Quantitative molecular structure‐reactivity models are useful for generating predictions to guide synthesis design, and in formulating and testing mechanistic hypotheses. We report an expanded multivariate linear regression (MLR) model for the rate of (hetero)aryl (pseudo)halide oxidative addition to L2Pd(0), here exemplified by Pd(PCy3)2. This builds on a prior model from our group, with additional substrate classes (aryl chlorides and iodides) and reaction solvents (THF, toluene, THF/DMF mixture). Overall solvent effects across the entire substrate set are minimal under these conditions, enabling a unified MLR model without introduction of new molecular descriptors beyond the original five. Examining the mechanistic origin of the two molecular electrostatic potential (ESP) descriptors led to generation of a simpler, four descriptor model that is suitable for aryl halides, but not for 2‐halopyridines. Using this model we identified a mechanistic outlier, 2‐pyridyl triflate, which undergoes a nucleophilic displacement oxidative addition that does not involve the adjacent nitrogen atom. Finally, we discuss the relationship between C−X bond strength and oxidative addition rates, and compare the intrinsic bond strength index (IBSI) to bond dissociation enthalpy (BDE) as a bond strength descriptor. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculation has been used to reveal palladium‐catalyzed mode of diaziridinone ring activation. Our theoretical studies found that oxidative addition of di‐tert‐butyldiaziridinone to Pd(II) can give a high valent Pd(IV) intermediate, along with the cleavage of N─N bond in di‐tert‐butyldiaziridinone through a concerted three‐membered‐cyclic transition state. Subsequent transformations via reductive elimination and β‐N elimination give the desired indolo[3,2‐b]indole product. The competitive activation modes such as metathesis and migratory insertion can be excluded in our selected model reaction. The rate‐determining step of this reaction is the oxidative addition of di‐tert‐butyldiaziridinone step. Distortion‐interaction analysis was conducted to reveal that the oxidative addition mode of di‐tert‐butyldiaziridinone is superior to the metathesis mode due to the lower interaction energy. [ABSTRACT FROM AUTHOR]

The reactivity of the racemic N-heterocyclic stannylene [{MeHCN(tBu)}Sn] (1) with the chalcogenide elements O2, S, Se, and Te has been investigated. In the case of the reaction of 1 with molecular oxygen, the cyclic tristannoxane complex [{MeHCN(tBu)}2Sn(μ-O)]3 (3) was isolated and characterised. NMR studies (1H, 13C, and 119Sn) show the formation of D3- and C2- symmetric assemblies. The reaction of 1 with S, Se, and Te, respectively, yielded the cyclo-distannachalcogenide complexes, [{MeHCN(tBu)}2Sn(μ-E)]3 (4: E = S, 5: E = Se, 6: E = Te), again with multinuclear NMR studies proving the formation of C2- and Cs-symmetric assemblies. Single crystal X-ray diffraction studies have been used to elucidate the molecular structures of the products of oxidative addition, 3, 4, 5, and 6. [ABSTRACT FROM AUTHOR]

Despite the progress made in the field of synthetic organic photocatalysis over the past decade, the use of higher wavelengths, especially those in the deep-red portion of the electromagnetic spectrum, remains comparatively rare. We have previously disclosed that a well-defined N,C,N -pincer bismuthinidene ( 1a ) can undergo formal oxidative addition into a wide range of aryl electrophiles upon absorption of low-energy red light. In this study, we map out the photophysical dynamics of 1a and glean insights into the nature of the excited state responsible for the activation of aryl electrophiles. Transient absorption and emission techniques reveal that, upon irradiation with red light, the complex undergoes a direct S 0 → S 1 metal-to-ligand charge transfer (MLCT) transition, followed by rapid intersystem crossing (ISC) to a highly reducing emissive triplet state (-2.61 V vs Fc +/0 in MeCN). The low dissipative losses incurred during ISC (∼6% of the incident light energy) help rationalize the ability of the bismuthinidene to convert low-energy light into useful chemical energy. Spectroelectrochemical and computational data support a charge-separated excited-state structure with radical-anion character on the ligand and radical-cation character on bismuth. Kinetic studies and competition experiments afford insights into the mechanism of oxidative addition into aryl iodides; concerted and inner-sphere processes from the triplet excited state are ruled out, with the data strongly supporting a pathway that proceeds via outer-sphere dissociative electron transfer.

A series of dibenzobismepinyl (C 14 H 10 Bi) substituted transition metal complexes of the type [(C 14 H 10 Bi)M(CO) x (L)] (M=Mn, Co, Fe) was prepared in salt elimination reactions from a halobismepine and sodium metallates. Irradiation of these complexes with visible light has been investigated, aiming at the elimination of one carbonyl ligand and the concomitant coordination of the bismepine's olefin moiety to the transition metal center. The resulting complexes of the type [{κ 2 C,κ 1 Bi-(C 14 H 10 )Bi}M(CO) x-1 (L)] (M=Co, Fe) have been isolated and fully characterized. When two dibenzobismepinyl units are positioned in the coordination sphere of an iron carbonyl complex fragment, reductive elimination/oxidative addition events of the dibismuthane (C 14 H 10 Bi) 2 have been shown to be relevant. The analytical techniques applied in this work include (heteronuclear) NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction analysis, UV/Vis spectroscopy, IR spectroscopy and (TD)-DFT calculations., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

1H NMR studies using a cationic complex with a pyridine‐di‐imidazolylidene pincer ligand of formula [Rh(CNC)(CO)]+ revealed that this compound showed high binding affinity with coronene in CH2Cl2. The interaction between coronene and the planar RhI complex is established by means of π‐stacking interactions. This interaction has a strong impact on the electron‐donating strength of the pincer CNC ligand, which is increased significantly, as demonstrated by the shifting of the ν(CO) stretching bands to lower frequencies. The addition of coronene increases the reaction rate of the nucleophilic attack of methyl iodide on the rhodium (I) pincer complex, and also has a positive effect on the performance of the complex as a catalyst in the cycloisomerization of 4‐pentynoic acid. These findings highlight the importance of supramolecular interactions for tuning the reactivity and catalytic activity of square‐planar metal complexes. [ABSTRACT FROM AUTHOR]

The coordination of secondary phosphine oxides (SPO) was shown to efficiently promote the activation of C(sp2)−I bonds by gold, as long as a base is added (NEt3, K2CO3). These transformations stand as a new type of chelation‐assisted oxidative addition to gold. The role of the base and the influence of the electronic properties of the P‐ligand were analyzed computationally. Accordingly, the oxidative addition was found to be dominated by Au→(Ar−I) backdonation. In this case, gold behaves similarly to palladium, suggesting that the inverse electron flow reported previously (with prevailing (Ar−I)→Au donation, resulting in faster reactions of electron‐enriched substrates) is a specific feature of electron‐deficient cationic gold(I) complexes. The reaction gives straightforward access to (P=O,C)‐cyclometallated Au(III) complexes. The possibility to chemically derivatize the SPO moiety at Au(III) was substantiated by protonation and silylation reactions. [ABSTRACT FROM AUTHOR]

Experimental and theoretical techniques were used to investigate the mechanism of pyridine C-H activation by diarylboryl/bis(phosphine) PBP pincer complexes of Ir. The critical intermediate (PBP)IrCO ( 4 ) contains a three-coordinate, Ir-bound boron that retains Lewis acidity in the perpendicular direction. Coordination of pyridine to this boron center in 4 leads to fast insertion of Ir into the 2-CH bond of pyridine, providing a different topology of direction than the conventional directed C-H activation where both the directing group coordination and C-H activation happen at the same metal center. Beyond this critical sequence, the system possesses significant complexity in terms of possible isomers and pathways, which have been thoroughly explored. Kinetic and thermodynamic preferences for the activation of differently substituted pyridines were also investigated. In experimental work, the key intermediate 4 is accessed via elimination of benzene from a phenyl/hydride containing precursor (PB Ph P)IrHCO ( 3 ). Density functional theory (DFT) investigations of the mechanism of benzene loss from 3 revealed the possibility of a genuinely new type of mechanism, whereby the Ph-H bond is made in a concerted process that is best described as C-H reductive elimination from boron, assisted by the transition metal (TMARE). For Ir, this pathway was predicted to be competitive with the more conventional pathways involving C-H reductive elimination from Ir, but still higher in energy barrier. However, for the Rh analog 3-Rh , TMARE was calculated to be the preferred pathway for benzene loss and this prediction was experimentally corroborated through the study of reaction rates and the kinetic isotope effect.

Controlled oxidation of NHB-stabilized disilyne (NHB)Si ≡ Si(NHB) ( 1 , NHB = [ArN(CMe) 2 NAr]B, Ar = 2,6- i Pr 2 C 6 H 3 ) with one equivalent of trimethylamine N-oxide (Me 3 N + ─O - ) in dry n -hexane gave oxo-bridged bis-silepin 2 in high yields. DFT calculations disclosed that silepin 2 is only more stable by 13.4 kcal/mol than the corresponding oxo-bridged bis-silylene intermediate 2' (NHB)Si(μ-O)Si(NHB), and 2 was very likely to be formed by the insertion of the two divalent Si atoms into the pendant aryl rings in bis-silylene intermediate 2' . The two silicon atoms in bis-silepin 2 could undergo formal reductive-elimination of the aryl rings and sequential oxidative-insertion reactions with small molecules and organic substrates. Treatment of 2 with H 2 O, S 8 , and P 4 at 60 °C yielded compounds 3 - 5 via reductive-elimination of the aryl rings, followed by the sequential oxidative-addition of these molecules at the two Si(II) centers. Similarly, reactions of 2 with PhSiH 3 , a diphenylalkyne, pyridines, 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe 4 ), Ph 2 CO, and thiophene yielded the corresponding polycyclic bis-silanes 6 - 12 via reductive-elimination and oxidative-addition of C-H, Si-H, C≡C, and aromatic C═C, C-S, and C═N bonds at the two Si atoms. These novel reactions indicated the pronounced bis-silylene reactivity of bis-silepin 2 , consistent with the low-energy barrier for the interconversion between 2 and 2' , as disclosed by DFT calculations.

Pre-coordination to a transition metal by the terminal donor groups of a tri-dentate ligand is a common strategy to stabilise elusive groups, to achieve unprecedented bond activation and to develop novel modes of metal–ligand-cooperation for catalysis. In the current manuscript, we demonstrate that the oxidative addition of a central E–H-bond after pre-coordination to the metal centre is disfavoured for metals with d10 electron configuration. For exemplary pincer ligands and metals with d10 electron configuration, quantum chemical calculations suggest a second barrier, which is associated with the rearrangement of the saw-horse structure, obtained after oxidative addition, to the expected square planar geometry for the resulting d8 electron configuration. In the case of PBP-type ligands with a central L2BH2-group (L = R3P) the reaction with Pt0 precursors proceeds via an alternative pathway of activation, which involves the backside attack of a nucleophile to the boron atom, which facilitates the nucleophilic attack of the Pt0 centre and formation of a boryl complex (LBH2). As the corresponding reaction with a PtII precursor leads to B–H- instead of B–L-activation and formation of complex 2 with a L2BH donor, our results show that ligand-stabilized borylenes (L2BH) can in principle be converted to boryls (LBH2) via boronium salts (L2BH2+). [ABSTRACT FROM AUTHOR]

This study demonstrates that the oxidative addition of hypervalent iodine PhICl2 to Au(I) complexes LAuAr follows an unprecedented stepwise mechanism. The energy of the Au(I) dx2−y2 orbital determines the ease of the oxidative addition reaction; the fewer electron-withdrawing substituents present on the Ar ligand, the higher the energy of the dx2−y2 orbital and the easier the oxidative addition. [ABSTRACT FROM AUTHOR]

The rigid-backbone bidentate ligands Indoline-2-carboxylic acid (IndoliH) and Indole-2-carboxylic acid (IndolH) were evaluated for rhodium(I). IndoliH formed [Rh(Indoli)(CO)(PPh3)] (A2), while IndolH yielded the novel dinuclear [Rh1(Indol')(CO)(PPh3)Rh2(CO)(PPh3)2] (B2) complex (Indol' = Indol2−), which were characterized by SCXRD. In B2, the Rh1(I) fragment [Rh1(Indol')(CO)(PPh3)] (bidentate N,O-Indol) exhibits a square-planar geometry, while Rh2(I) shows a 'Vaska'-type trans-[O-Rh2(PPh3)2(CO)] configuration (bridging the carboxylate 'oxo' O atom of Indol2−). The oxidative addition of MeI to A2 and B2 via time-resolved FT-IR, NMR, and UV/Vis analyses indicated only Rh(III)-alkyl species (A3/B3) as products (no migratory insertion). Variable temperature kinetics confirmed an associative mechanism for A2 via an equilibrium-based pathway (ΔH≠ = (21 ± 1) kJ mol−1; ΔS≠ = (−209 ± 4) J K−1mol−1), with a smaller contribution from a reverse reductive elimination/solvent pathway. The dinuclear complex B2 showed the oxidative addition of MeI only at Rh1(I), which formed a Rh(III)-alkyl, but cleaved the bridged Rh2(I) site, yielding trans-[RhI(PPh3)2(I)(CO)] (5B) as a secondary product. A significantly smaller negative activation entropy [ΔH≠ = (73.0 ± 1.2) kJ mol−1; ΔS≠ = (−21 ± 4) J K−1mol−1] via a more complex/potential interchange mechanism (the contribution of ΔS≠ to the Gibbs free energy of activation, ΔG≠, only ±10%) was inferred, contrary to the entropy-driven oxidative addition of MeI to A2 (the contribution of ΔS≠ to ΔG≠ ± 75%). [ABSTRACT FROM AUTHOR]