Oxidative Addition Reactions Research Articles

Halogen-Exchange Reactions of Iminophosphonamido-Chlorosilylenes with Alkali Halides: Convenient Synthesis of Heavier Halosilylenes.

Halogen-substituted silylenes are an important building block for synthesizing silicon-based low-valent and multiple-bond species. However, the number of reports on heavier halosilylenes that contain bromine and iodine is still limited. Here, we present a convenient synthesis for bromo- and iodosilylenes supported by an iminophosphonamide ligand. The heavier halosilylenes [Ph2P(tBuN)2]SiX (2: X = Br, 3: X = I) were successfully synthesized via the halogen-exchange reaction of chlorosilylene 1 with alkali halides in THF. As a demonstration of the reactivity of 2 and 3, oxidative addition reactions of 2 and 3 with elemental selenium in C6D6 afforded the corresponding bromo- (5) or iodosilylene-selone (6) as colorless crystals. The molecular structures of 2, 3, 5, and 6 were fully characterized by spectroscopic means and single-crystal X-ray diffraction analysis. Furthermore, the effects of the halogen atom on the electronic state of halosilylenes 1-3 and halosilylene-selones 4-6 were investigated using density functional theory (DFT) calculations.

Kinetic Study of the Oxidative Addition Reaction between Methyl Iodide and [Rh(imino-β-diketonato)(CO)(PPh)3] Complexes, Utilizing UV–Vis, IR Spectrophotometry, NMR Spectroscopy and DFT Calculations

The oxidative addition of methyl iodide to [Rh(β-diketonato)(CO)(PPh)3] complexes, as modal catalysts of the first step during the Monsanto process, are well-studied. The β-diketonato ligand is a bidentate (BID) ligand that bonds, through two O donor atoms (O,O-BID ligand), to rhodium. Imino-β-diketones are similar to β-diketones, though the donor atoms are N and O, referred to as an N,O-BID ligand. In this study, the oxidative addition of methyl iodide to [Rh(imino-β-diketonato)(CO)(PPh)3] complexes, as observed on UV–Vis spectrophotometry, IR spectrophotometry and NMR spectrometry, are presented. Experimentally, one isomer of [Rh(CH3COCHCNPhCH3)(CO)(PPh3)] and two isomers of [Rh(CH3COCHCNHCH3)(CO)(PPh3)] are observed—in agreement with density functional theory (DFT) calculations. Experimentally the [Rh(CH3COCHCNPhCH3)(CO)(PPh3)] + CH3I reaction proceeds through one reaction step, with a rhodium(III)-alkyl as the final reaction product. However, the [Rh(CH3COCHCNHCH3)(CO)(PPh3)] + CH3I reaction proceeds through two reaction steps, with a rhodium(III)-acyl as the final reaction product. DFT calculations of all the possible reaction products and transition states agree with experimental findings. Due to the smaller electronegativity of N, compared to O, the oxidative addition reaction rate of CH3I to the two [Rh(imino-β-diketonato)(CO)(PPh)3] complexes of this study was 7–11 times faster than the oxidative addition reaction rate of CH3I to [Rh(CH3COCHCOCH3)(CO)(PPh3)].

In Situ Monitoring of Transmetallation in Electric Potential-Promoted Oxidative Coupling in a Single-Molecule Junction

In Situ Monitoring of Transmetallation in Electric Potential-Promoted Oxidative Coupling in a Single-Molecule Junction

Star-shaped Pd(II) and Pt(II) complexes containing C3-symmetric conjugated thiophenes: Synthesis, characterization, and chemical reactions with organic unsaturated molecules

Triple oxidative addition reactions of [M0(styrene)(PMe3)2] (M = Pd/Pt) with C3-symmetric star-shaped molecules containing 1-, 3-, and 5-thiophene-substituted benzene, in 1:0.3 ratio, afforded new Pd(II) and Pt(II) trinuclear complexes in suitable yields. Analogous trinuclear complexes were formed by similar reactions of thiophenyl halide derivatives containing triazine or triphenylamine cores. Alternatively, a trinuclear Pd(II) complex was obtained by oxidative addition of a Pd(0) complex (synthesized from allyl(cyclopentadienyl) palladium(II), [(η5-C5H5)Pd(η3-C3H5)] with PEt3. Sonogashira-type coupling between trinuclear Pt(II) halides (containing C3-symmetric conjugated thiophenes) and alkynes, in the presence of cuprous halide and diethylamine, afforded alkynyl-containing trinuclear Pt(II) complexes with extended π-conjugation. Insertion reactions of organic isocyanides (CN-R) with trinuclear Pd(II) complexes yielded trinuclear Pd(II) imidoyl complexes by insertion of CN-R into Pd-carbon (thiophene) bonds. Reactions of trinuclear Pt(II) halides with Ag(OCOCF3) and NaN3 formed pseudohalogen-containing Pt(II) complexes.

Tertiary Alkylative Suzuki–Miyaura Couplings

AbstractSuzuki–Miyaura coupling is an extremely useful way to construct Csp2–Csp2 carbon bonds. On the other hand, Csp2–Csp3 coupling reactions do not work well, and tert-alkylative Suzuki–Miyaura coupling is particularly challenging due to problematic oxidative addition and β-hydride elimination side reactions. In this short review, we will introduce recent examples of tert-alkylative Suzuki–Miyaura couplings with tert-alkyl electrophiles or -boron reagents. The review will mainly focus on catalyst and product structures and on the proposed mechanisms.1 Introduction2 Ni-Catalyzed tert-Alkylative Couplings3 Pd-Catalyzed tert-Alkylative Couplings4 Fe-Catalyzed tert-Alkylative Couplings5 tert-Alkylative Couplings with 1-Alkenyl Borons6 tert-Alkylative Couplings under Photoirradiation7 Stereospecific tert-Alkylative Couplings8 Conclusion

Structurally characterised intermediate of the oxidative addition of a heteroleptic germylene to gallanediyle.

Bond activation reactions using main group metal complexes are gaining increasing interest. We report on reactions of LGa (L = HC[C(Me)N(Ar)]2, Ar = Dipp = 2,6-i-Pr2C6H3,) with heteroleptic tetrylenes L'ECl (E = Ge, Sn; L' = N(SiMe3)Ar), yielding the donor-acceptor complex LGa-Sn(Cl)L' (1) or the oxidative addition product L(Cl)GaGeL' (3). The reaction with DMPGeCl (DMP = 2,6-Mes2C6H3, Mes = 2,4,6-Me3C6H2) yielded LGa(μ-Cl)GeDMP (2), which represents an intermediate of the oxidative addition reaction. 1-3 were characterized by NMR and IR spectroscopy as well as by single crystal X-ray diffraction (sc-XRD), while their electronic nature was analyzed by quantum chemical calculations.

Investigations into a change of aryl group on the cytotoxicity and anti-leishmanial activity of a series of tris-aryl Sb(V) pentafluoropropionates

Five tris-arylantimony bis(pentafluoropropionates) of the general formula Ar3Sb[OC(O)CF2CF3]2 with Ar = Ph (1), m-Tol, (2) p-Tol (3), C6H4F-4 (4), C6H3-OMe-2-Br-5 (5) have been synthesized by an oxidative addition reaction. Four of them (1–3, 5) are structurally novel. All structures were analytically characterized by X-ray diffraction, IR, 1H, 13C and 19F NMR spectroscopy. The solid-state structures determined by X-ray diffraction analysis have shown that the antimony centre has a typical trigonal–bipyramidal geometry with carboxylic oxygen atoms in axial positions and carbon atoms of aryl groups in the equatorial plane. All complexes have been screened for their anti-leishmanial activity and cytotoxicity towards mammalian macrophages. IC50 values are found in the ranges of 2.32–28.7 μM for the promastigote assay, and 5.14–41.6 μM for the macrophages. Two complexes with the selectivity indices SI = 2.49 (2) and 3.75 (5) have been assessed for their anti-amastigote activity. The percentage infection values of 10.00 % ± 2.25 (2) and 27.50 % ± 2.94 (5) are obtained, showcasing the need for further investigations into a change in aryl group and the structure activity relationships it presents.

Oxidative Addition of a Hypervalent Iodine Compound to Cycloplatinated(II) Complexes for the C-O Bond Construction: Effect of Cyclometalated Ligands.

The complex [PtMe(Obpy)(OAc)2(H2O)], 2a, Obpy = 2,2'-bipyridine N-oxide, is prepared through the reaction of [PtMe(Obpy)(SMe2)], 1a, by 1 equiv of PhI(OAc)2 via an oxidative addition (OA) reaction. Pt(IV) complex 2a attends the process of C-O bond reductive elimination (RE) reaction to form methyl acetate and corresponding Pt(II) complex [Pt(Obpy)(OAc)(H2O)], 3a. The kinetic of OA and RE reactions are investigated by means of different spectroscopies. The obtained results show that the reaction rates of OA step of 1a are faster than its analogous complex [PtMe(ppy)(SMe2)], 1b, ppy = 2-phenylpyridine. The density functional theory (DFT) calculations signify that the OA reaction initiated by a nucleophilic attack of the platinum(II) central atom of 1b on the iodine(III) atom while it had commenced by a nucleophilic substitution reaction of coordinated SMe2 in 1a with a carbonyl oxygen atom of PhI(OAc)2. Our calculation revealed that the key step for 1a is an acetate transfer from the I(III) to Pt(II) through a formation of square pyramidal iodonium complex. This can be attributed to the more electron-withdrawing character of Obpy ligand than to ppy which reduces the nucleophilicity of Pt atom in 1a. Furthermore, 2a with electron-withdrawing Obpy ligand prone to C-O bond formation faster than complex [PtMe(ppy)(OAc)2(H2O)], 2b, with an electron-rich ppy ligand which conforms to the anticipation that REs occur faster on electron-poor metal centers.

Retraction of “Improved Visible Photocatalytic Activity on Titania Modified with −O–Pd–Cl Species Assisted by Oxidative Addition Reaction of Pd0”

Retraction of “Improved Visible Photocatalytic Activity on Titania Modified with −O–Pd–Cl Species Assisted by Oxidative Addition Reaction of Pd⁰”

Platinum(II)‐mediated disulfide/thiolate interconversion in organic disulfides: Density functional theory thermodynamic study

AbstractWe present a complete Density Functional Theory (DFT) study of the thermodynamics of the reactions of disulfides (l‐cystine, cystamine, dl‐homocystine, and 3,3′‐dithiodipropionic acid) with Pt(II) ions in aqueous media. SMD solvation model was fitted to take into account the solvation effects of the medium. DFT calculations predict the oxidative addition reaction with the formation of thiolate complexes of Pt(IV)—[PtCl4(S‐R)2] which is consistent with experimental data. We propose a theoretical model that rationalizes the experimental data on Pt(II) interactions with homological disulfides. The role of explicit solvation in reactions is also investigated. We propose that the stability of S,S′‐binuclear disulfide complexes correlates with the redistribution of charges on sulfur atoms. We compared MN15 and PBE0 functionals for the calculation of equilibrium constants.

Oxidative Addition Reactions of Low‐Valent Gallium Compounds with Primary Phosphanes

AbstractOxidative addition reactions of (Dipp2NacNac)Ga with the primary silylphosphanes R2R'Si‐PH2 in toluene led to the phospha‐gallanes (Dipp2NacNac)GaH(PHSiR2R’); R=R’=Me (1), R=Me, R’=Thex (2), R=R’=iPr (3) and R=Ph, R’=tBu (4). The same reaction starting from the diphosphane iPr2Si(PH2)2 yields the digallane {(Dipp2NacNac)GaH(PH)}2(SiiPr2) (5 a). In contrast, reaction with the hypersilylphosphane resulted in the elimination of (Me3Si)3SiH and formation of the diphospha‐gallane (Dipp2NacNac)Ga(PH2)(PHSi(SiMe3)3) (6). The primary organo‐phosphane tBuPH2 shows a similar reaction behavior in toluene though both the di‐ and monophospha‐gallanes (Dipp2NacNac)GaX(PHtBu) (7 a: X=PH2, 7 b: X=H) occur. In a row of used solvents, only pyridine led selective to the formation of 7 b thus we tested the influence of this solvent on the reaction of iPr2Si(PH2)2 with only one equivalent (Dipp2NacNac)Ga which yields the compound (Dipp2NacNac)GaH(PHSiiPr2PH2) (5 b). Additionally, a derivative of compound 3, (Dipp2NacNac)GaCl(PHSiiPr3) (8), with an Cl atom bond to gallium instead of a hydrogen was obtained by the reaction of (Dipp2NacNac)GaCl2 with iPr3SiPHLi.

Photochemical C(sp)-C(sp2) Bond Activation in Phosphaalkynes: A New Route to Reactive Terminal Cyaphido Complexes LnM-C≡P.

The photochemical activation of the C(sp)-C(sp2) bond in Pt(0)-η2-aryl-phosphaalkyne complexes leads selectively to coordination compounds of the type LnPt(aryl)(C≡P). The oxidative addition reaction is a novel, clean, and atom-economic route for the synthesis of reactive terminal Pt(II)-cyaphido complexes, which can undergo [3 + 2] cycloaddition reactions with organic azides, yielding the corresponding Pt(II)-triazaphospholato complexes. The C-C bond cleavage reaction is thermodynamically uphill. Upon heating, the reverse and quantitative reductive elimination toward the Pt(0)-phosphaalkyne-π-complex is observed.

Investigating the non-classical M-H2 bonding in OsClH3(PPh3)3

Dihydrogen ligation to metal centers results in a wide range of metal-hydrogen interactions. Compounds containing non-classical dihydrogen ligands in which the H–H contacts are significantly longer than the 0.74 Å distance found in solid H2 are classified as Kubas-like compounds, stretched dihydrogen ligands, or compressed dihydrides, depending on the H–H contact length. Compounds containing stretched dihydrogen and compressed dihydride ligands are somewhat rare. Developing a more complete understanding of the metal-hydrogen and hydrogen-hydrogen interactions in these species may provide insights into the mechanisms for the oxidative addition reaction and hydrogen storage. Here, we use diffraction and inelastic neutron scattering (INS) measurements, paired with both molecular and solid-state density functional theory (DFT), to fully characterize the nature of the metal-hydrogen and hydrogen-hydrogen interactions in a previously reported compound, OsClH3(PPh3)3. In that report, the H–H distance was measured as 1.48(2) Å by single-crystal neutron diffraction and was described as a “stretched” dihydrogen. The INS-generated phonon density of states is well described by the DFT calculations, including those normal modes dominated by the vibrational motions of the three Os-ligated hydrogen atoms. The resulting calculated electron charge density landscape indicates that there is no remnant bonding character between the Os-ligated hydrogen atoms in the compound. Based on these findings, we update the understanding of the metal-hydrogen bonding in this complex and reclassify it as a compressed dihydride. As such, OsClH3(PPh3)3 represents a rare example of a non-classical compressed dihydride species.

Reactivity of a Dinuclear PdI Complex [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2] with PPh3: Implications for Cross-Coupling Catalysis Using the Ubiquitous Pd(OAc)2/nPPh3 Catalyst System.

[PdI2(μ-PPh2)(μ2-OAc)(PPh3)2] is the reduction product of PdII(OAc)2(PPh3)2, generated by reaction of ‘Pd(OAc)2’ with two equivalents of PPh3. Here, we report that the reaction of [PdI2(μ-PPh2)(μ2-OAc)(PPh3)2] with PPh3 results in a nuanced disproportionation reaction, forming [Pd0(PPh3)3] and a phosphinito-bridged PdI-dinuclear complex, namely [PdI2(μ-PPh2){κ2-P,O-μ-P(O)Ph2}(κ-PPh3)2]. The latter complex is proposed to form by abstraction of an oxygen atom from an acetate ligand at Pd. A mechanism for the formal reduction of a putative PdII disproportionation species to the observed PdI complex is postulated. Upon reaction of the mixture of [Pd0(PPh)3] and [PdI2(μ-PPh2){κ2-P,O-μ-P(O)Ph2}(κ-PPh3)2] with 2-bromopyridine, the former Pd0 complex undergoes a fast oxidative addition reaction, while the latter dinuclear PdI complex converts slowly to a tripalladium cluster, of the type [Pd3(μ-X)(μ-PPh2)2(PPh3)3]X, with an overall 4/3 oxidation state per Pd. Our findings reveal complexity associated with the precatalyst activation step for the ubiquitous ‘Pd(OAc)2’/nPPh3 catalyst system, with implications for cross-coupling catalysis.

Synthesis of Unsymmetrical 1,4-Dicarbonyl Compounds by Photocatalytic Oxidative Radical Additions.

Herein we report a photocatalytic oxidative radical addition reaction for the synthesis of unsymmetrical 1,4-dicarbonyl compounds. This reaction utilizes a desulfurization process to generate electrophilic radicals, which add to α-halogenated alkenes and undergo further oxidation to deliver 1,4-dicarbonyl compounds. This mild and highly efficient method provides a valuable alternative to known strategies.

Heterolytic Oxidative Addition of sp2 and sp3 C-H Bonds by Metal-Ligand Cooperation with an Electron-Deficient Cyclopentadienone Iridium Complex.

Oxidative addition reactions of C-H bonds that generate metal-carbon-bond-containing reactive intermediates have played essential roles in the field of organometallic chemistry. Herein, we prepared a cyclopentadienone iridium(I) complex 1 designed for oxidative C-H bond additions. The complex cleaves the various sp2 and sp3 C-H bonds including those in hexane and methane as inferred from their H/D exchange reactions. The hydroxycyclopentadienyl(nitromethyl)iridium(III) complex 2 was formed when the complex was treated with nitromethane, which highlights this elementary metal-ligand cooperative C-H bond oxidative addition reaction. Mechanistic investigations suggested the C-H bond cleavage is mediated by polar functional groups in substrates or another iridium complex. We found that ligands that are more electron-deficient lead to more favorable reactions, in sharp contrast to classical metal-centered oxidative additions. This trend is in good agreement with the proposed mechanism, in which C-H bond cleavage is accompanied by two-electron transfer from the metal center to the cyclopentadienone ligand. The complex was further applied to catalytic transfer-dehydrogenation of tetrahydrofuran (THF).

The Redox Properties of Germylenes Stabilized by N‐Donor Ligands

AbstractGermylenes, organic compounds of divalent germanium, are often considered as promising catalytic systems efficient in reactions of oxidative addition and reductive elimination, including SET reactions. However, the systematic studies of their redox properties, allowing for the quantitative evaluation of the levels of frontier molecular orbitals and the stability of single electron transfer products, are extremely limited in number. In this work, a series of germylenes with various types of stabilization: N−Ge−N, (N→)C−Ge−C(←N), N−Ge−N(←N), O−Ge−O(←N) и (N→)O−Ge−O(←N) (“−“ ‐a covalent bond, stabilization is achieved by p‐donation of a lone pair of electrons of N or O, “→” ‐donor‐acceptor bond) were characterized by cyclic voltammetry. The results were compared with UV/Vis spectroscopy data and DFT calculations. All germylenes studied in MeCN and THF with Bu4NPF6 as a supporting electrolyte are chemically irreversibly oxidized in the potential range of 0.5–1.4 V vs. Ag/AgCl. In all cases, as estimated by the quantum chemical calculations, the HOMO remains at the covalently unsaturated germanium center although being significantly redistributed over the molecular system. In turn, electroreduction of germylenes is possible only in the presence of a strong electron‐withdrawing substituent or a pyridine ring depleted in electron density donated to germanium. In both cases, the LUMO is localized exactly on these moieties and is absent on the germanium. Thus, the use of stabilizing groups makes it possible both to improve germylene stability and to fine‐tune their HOMO level that determines their ability to participate in oxidative addition reactions.

The Coordination Chemistry and Clustering of Subvalent Ga+ and In+ upon Addition of σ‐Donor Ligands

AbstractThis review addresses the coordination chemistry (mainly) enabled by using the univalent [M(fluoroarene)2–3]+[Al(ORF)4]−‐salts (M=Ga, In; RF=C(CF3)3) as robust starting materials. In the course of this work, it became clear that the orbital energy of the ns2 (n=4, 5) lone pair in such [:M(L)n]+ cations reacts drastically depending on the quality of the ligand employed. Activation of the lone pair with strong σ‐donor ligands might be used for bond activation and oxidative addition reactions. Yet, unexpectedly, using sterically undemanding and electron rich ligands with limited π‐accepting properties, aggregation to highly charged and rather unusual univalent cluster cations [Mn(L)m]°+ (n=2…5, m=4…6, o=3…5) was observed. An overview and rationalization of these findings is presented here.

The reactivity of N-heterocyclic germylenes and stannylenes based on 9,10-phenanthrendiimines towards metal carbonyls and sulfur

The reactivity of germylene and stannylene based on 9,10-phenanthrenediimine are described. Complexes of nickel and iron carbonyls with a coordinated germylene were obtained in good yields under mild conditions. The abilities of germylene to be involved in oxidative addition reactions with preserving of N-heterocycle were demonstrated in reactions with dithio-bis(tricarbonyliron) and elemental sulfur. All the compounds were characterized structurally by X-ray diffraction analysis.

Photophysical Properties and Kinetic Studies of 2-Vinylpyridine-Based Cycloplatinated(II) Complexes Containing Various Phosphine Ligands.

A series of cycloplatinated(II) complexes with general formula of [PtMe(Vpy)(PR3)], Vpy = 2-vinylpyridine and PR3 = PPh3 (1a); PPh2Me (1b); PPhMe2 (1c), were synthesized and characterized by means of spectroscopic methods. These cycloplatinated(II) complexes were luminescent at room temperature in the yellow–orange region’s structured bands. The PPhMe2 derivative was the strongest emissive among the complexes, and the complex with PPh3 was the weakest one. Similar to many luminescent cycloplatinated(II) complexes, the emission was mainly localized on the Vpy cyclometalated ligand as the main chromophoric moiety. The present cycloplatinated(II) complexes were oxidatively reacted with MeI to yield the corresponding cycloplatinated(IV) complexes. The kinetic studies of the reaction point out to an SN2 mechanism. The complex with PPhMe2 ligand exhibited the fastest oxidative addition reaction due to the most electron-rich Pt(II) center in its structure, whereas the PPh3 derivative showed the slowest one. Interestingly, for the PPhMe2 analog, the trans isomer was stable and could be isolated as both kinetic and thermodynamic product, while the other two underwent trans to cis isomerization.