Oxidative Substitution Reaction Research Articles

Coordination of Ligands That Contain Thiocarbonyl, Carbonyl, or Thiolate Functionalities to Complex Fragments of Palladium in Various Oxidation States

AbstractTwo phosphine ligands of [Pd(PPh3)4] were substituted by π(CS) coordination of 4‐bromodithiobenzoic acid methyl ester resulting in complex 1. The same ester, after alkylation, afforded the dicationic complex bis(μ‐methanethiolato)tetrakis(triphenylphosphine)dipalladium(2+) bis(tetrafluoroborate) (2) from the same palladium source. A related thiolato‐bridged complex, bis(μ‐methanethiolato)bis(1‐methylpyridin‐2(1H)‐ylidene)bis(triphenylphosphine)dipalladium(2+) bis(tetrafluoroborate) (4) and the trinuclear cluster tris(μ‐methanethiolato)tris(triphenylphosphine)tripalladium(+)(3PdPd) (5) resulted from treatment of a known cationic pyridinylidene complex with MeSLi. The double oxidative substitution reaction of [Pd(PPh3)4] with 1,5‐dichloro‐9,10‐anthraquinone afforded trans‐dichloro[μ‐(9,10‐dihydro‐9,10‐dioxoanthracene‐1,5‐diyl)]tetrakis(triphenylphosphine)dipalladium (6). Some of these complexes could be fully characterized by 1H‐, 13C‐, and 31P‐NMR spectroscopy, mass spectrometry, and elemental analysis. The crystal and molecular structures of all of them, and of trans‐bis(1,3‐dihydro‐1,3‐dimethyl‐2H‐imidazol‐2‐ylidene)diiodopalladium (3), were determined by single‐crystal X‐ray diffraction.

Synthesis and Characterization of New Pentacoordinate Iron‐Based Aryloxide Complexes

AbstractHeterobimetallic lithium–iron coordination compounds are interesting targets for several reasons: they can be used as precursors for mixed metal oxides, as catalysts, for example, for ring‐opening polymerization reactions or to study oxidation/reduction processes. Finally their magnetic properties are also of interest. New heterobimetallic aryloxide complexes, namely [(thf)4Li3Fe(OPh)3(O2C6H4)Cl]2 (1), [{(thf)3Li3Fe(OPh)5Cl}3]n (2), and [(thf)3Li3Fe(OPh)6]2 (3), have been synthesized and characterized by single‐crystal X‐ray diffraction. While compounds 1 and 3 were synthesized by an oxidative substitution reaction, compound 2 was directly obtained from the FeIII salt. These compounds are accessible by both synthetic pathways. Additionally, in compound 1, the phenoxy ligand was catalytically oxidized to ortho‐catechol, which was incorporated into the structure of 1 as a ligand that coordinates strongly to iron. All compounds feature the FeIII ion with a trigonal, bipyramidal environment, with coordination number 5.

Regiospecific Cyclometalation of Diphenyl(2‐substituted phenyl)phosphane with Methyltetrakis(trimethylphosphane)cobalt(I)

AbstractThe pre‐chelate molecules 2‐(diphenylphosphanyl)‐N,N‐dimethylaniline, [2‐(diphenylphosphanyl)benzyl]dimethylamine, 1‐(diphenylphosphanyl)‐2‐ethylbenzene, 1‐(diphenylphosphanyl)‐2‐isopropylbenzene, and 2‐(diphenylphosphanyl)benzonitrile, in a reaction with [CoMe(PMe3)4], eliminate methane to afford the selectively 6‐ortho‐metalated complexes 1−5 that contain four‐membered metallacycles. The molecular structure of 3 shows a tbp‐coordinated cobalt atom, with axial C and PMe3 donor groups. Metalation in the aliphatic side‐chain occurs with 2‐(diphenylphosphanyl)toluene, giving complex 6 that contains a five‐membered metallacycle. Benzyldiphenylphosphane is selectively ortho‐metalated in the benzyl group, affording 7. As shown by the molecular structures, complex 7 is a true ligand isomer of 6. Substitution of a trimethylphosphane group in compounds 4 and 6 by ethene gives the pentacoordinate complexes 8 and 9, respectively. The ethene ligand is π‐coordinated in the equatorial plane of a trigonal bipyramid. Under 1 bar of CO, complex 6 forms monocarbonyl complex 10. Carbonylation of complexes 3 and 4 proceeds by insertion of CO into the Co−C bond under ring expansion, affording the aroylcobalt complexes 11 and 12, respectively. Complex 6 reacts with iodomethane in an oxidative substitution reaction yielding a structurally characterized octahedral complex mer‐13, which eliminates a methyl group in THF at 20 °C to form a pentacoordinate cobalt(II) complex 14. Complex 3 oxidatively adds iodomethane in a stereoselective cis addition to give the cobalt(III) complex mer‐15, which retains its four‐membered metallacycle and the CoCH3 group. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Radical cation mechanism of aromatic halogenation by halogens or iodine chloride in 1,1,1,3,3,3-hexafluoropropan-2-ol

The reaction between aromatic compounds ArH and halogenating agents, viz. iodine chloride, chlorine, bromine, iodine, N-bromosuccinimide and N-chlorosuccinimide, in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) has been investigated. EPR spectroscopy established that these reagents produced persistent radical cations ArH˙+ from ArH with Erev(ArH˙+/ArH) up to 1.6, 1.3, 1.4, 1.1, 1.5 and 1.2 V vs. Ag/AgCl, respectively. Cyclic voltammetry of the halogenating species shows that no effect of complexation with halide ion is observed in HFP, as expected from its capacity to drastically attenuate nucleophilic reactivity, and that the cathodic peak potentials Epc (referenced to the internal ferricinium/ferrocene redox couple) are significantly or remarkably higher in HFP than in acetonitrile. For N-bromosuccinimide, the difference amounts to almost 1 V.The persistency of the radical cations in HFP is such that the kinetics of reactions between a halogenating agent, such as iodine chloride or bromine, and ArH, such as 1,4-dimethoxybenzene [Erev(ArH˙+/ArH) = 1.50 V vs. Ag/AgCl] or 1,4-dimethoxy-2,3-dimethylbenzene [Erev(ArH˙+/ArH) = 1.16 V], have been studied at room temperature over periods of hours. The initial concentration of the radical cation corresponds to yields in the range of 40–100%, depending on the reaction conditions. It is thus possible to establish that the radical cation decays via two pathways, one being the well known oxidative substitution reaction with halide ion. The second mechanism involves halogen atom transfer from the halogenating agent (Cl atom from ICl, Br atom from bromine). In the case of the radical cation of 1,4-dimethoxy-2,3-dimethylbenzene reacting with bromide ion or bromine, the latter reaction is >102 times faster.

Oligomeric flavanoids. Part 8. The first profisetinidins and proguibourtinidins based on C-8 substituted (–)-fisetinidol units and relatedC-ring isomerized analogues

Structural examination of the phenolic metabolites of Colophospermum mopane reveals the presence of the first profisetinidins and proguibourtinidins based on C-8 substituted (–)-fisetinidol units i.e. the (4α,8)-bis-(–)-fisetinidol (1), (+)-epifisetinidol-(4α,8)-(–)-fisetinidol (3), and the (+)-guibourtinidol-(4α,8)-(–)-fisetinidol (5). They are accompanied by the related functionalized tetrahydropyrano[2,3-h]chromenes (9), (11), (13), (15), and (17), and by a 2,4-diaryl-6-(2,-benzopyranyl)chroman (19), the first C-ring isomerized analogue derived from a B-ring coupled profisetinidin. Efforts towards the synthesis of the (4,8)-bis-fisetinidols from 6-bromo-(–)-fisetinidol and the appropriate flavan-3,4-diol, lead to the biaryl type biflavanoids (33) and (35). Their genesis is explained in terms of an oxidative substitution reaction initiated by bromonium ion.

ChemInform Abstract: Oxidative Substitution Reaction of Olefinic Tin Compounds with Lead Tetraacetate.

AbstractThe stannylmethyl ethers (I) are oxidatively demetalated with lead tetraacetate (II) to form the acetoxymethyl ethers (III).

Oxidative Substitution Reaction of Olefinic Tin Compounds with Lead Tetraacetate

Abstract The oxidative substitution reaction of olefinic tin compounds with lead tetraacetate(LTA) was investigated. The oxidation is highly regioselective and gave a dipole inversed product (acetate) in good yield.

Oxidative substitution reactions of organotin compounds with lead tetra-acetate

A new oxidative substitution reaction where an organotin group is replaced by an acetoxy group has been investigated; this reaction has been successfully applied to the synthesis of 4-ylidenebutenolides.

Oxidative substitution reaction of the osmochrome Os(OEP)[P(OMe) 3] 2 in chlorinated solvents

Steady state photolysis of Os(OEP)[P(OMe) 3] 2, where OEP is octaethylporphine, in the chlorinated solvents CH 2Cl 2, CHCl 3 and CCl 4 at 365 and 405 nm and at 22 °C results in the formation of an osmium(IV) porphyrin identified as Os(OEP)Cl 2. The reaction is described as an oxidative substitution reaction. The rate of formation of the photolysis product increases as the solvent varies in the order CH 2Cl 2 < CHCl 3 < CCl 4 (in the ratio 1:8:120). The quantum yield of product formation is 0.004 and 1.4 in CH 2Cl 2 and CCl 4 respectively. A possible mechanism involving radicals is suggested and is discussed in terms of the experimental observations.