Reactivity of diacetylplatinum(II) complexes: oxidative addition of alkyl halides and crystal structures of acetyl platinum(IV) complexes

Diacetylplatinum(II) complexes [Pt(COMe)₂(N^N)] (N^N = bpy, 3a; 4,4′-t-Bu₂-bpy, 3b) were found to undergo oxidative addition reactions with organyl halides. The reaction of 3a with methyl iodide and propargyl bromide led to the formation of the cis addition products (OC-6-34)-[Pt(COMe)₂(R)X(bpy)] (R = Me, X = I, 4a; CH₂C≡CH, X = Br, 4k). Analogous reactions of 3a with ethyl iodide, benzyl bromide, and substituted benzyl bromides, 3-(bromomethyl)pyridine, 2-(bromomethyl)thiophene, allyl bromide, and cyclohex-2-enyl bromide led to exclusive formation of the trans addition products (OC-6-43)-[Pt(COMe)₂(R)X(bpy)] (X = I, R = Et, 4b; X = Br, R = CH₂C₆H₅, 4c; CH₂C₆H₄(o-Br), 4d; CH₂C₆H₄(p-COOH), 4e; CH₂-3-py (3-pyridylmethyl), 4f; CH₂-2-tp (2-thiophenylmethyl), 4g; CH₂CH=CH₂, 4h; c-hex-2-enyl (cyclohex-2-enyl), 4i). All complexes 4 were characterized by microanalysis, ¹H and ¹³C NMR and IR spectroscopy. Additionally, complexes 4a, 4f, and 4g were characterized by single-crystal X-ray diffraction analyses. Reactions of 3a and 3b with o-, m- and p-bis(bromomethyl)benzene, respectively, led to the formation of dinuclear platinum(IV) complexes [{Pt(COMe)₂Br(N^N)}₂-{μ-(CH₂)₂C₆H₄}] (5). These complexes were characterized by microanalysis, IR spectroscopy, and depending on their solubility by ¹H and ¹³C NMR spectroscopy, too. A single-crystal X-ray diffraction analysis of complex [{Pt(COMe)₂Br(bpy)}₂{μ-m-(CH₂)₂C₆H₄}] (5b) confirmed its dinuclear composition. The solid-state structures of 4a, 4f, 4g, and 5b are discussed in terms of C–H···O and O–H···O hydrogen bonds as well as π–π stacking between aromatic rings.     

Oxidative addition of n-alkyl halides to diimine-dialkylplatinum(II) complexes: a closer look at the kinetic behaviors

The n-alkyl halides, RX, were oxidatively added to the platina(II)cyclopentane complexes [Pt[(CH2)4](NN)], in which NN = bpy (2,2'-bipyridyl) or phen (1,10-phenanthroline), to give the platinum(IV) complexes [PtRX[(CH2)4](NN)], R = Et and X = Br or I; R = nBu and X = I, 1-3. The same reactions with the analogous dimethyl complex [PtMe2(bpy)] gave the expected platinum(IV) complexes [PtRXMe2(bpy)], R = Et or nPr and X = Br or I; R = nBu and X = I, 4-8. Kinetics of the reactions in benzene and acetone was studied using UV-vis spectrophotometery and a common S(N)2 mechanism was suggested for each case. The platina(ii)cyclopentane complexes reacted faster than the corresponding dimethyl analogs by a factor of 2-3. This is described as being due to a lower positive charge, calculated by density functional theory (DFT), on the platinum atom of [Pt[(CH)2)4](bpy)] compared with that on the platinum atom of the dimethyl analog [PtMe2(bpy)]. The values of DeltaDeltaS(double dagger) = DeltaS(double dagger)(acetone) - DeltaS(double dagger)(benzene) were found to be either positive or negative in different reactions and this is related to the solvation of the corresponding alkyl halide. It is suggested that in these reactions of RX reagents, for a given X, the electronic effects of the R group are mainly responsible for the change in the rates of the reactions and the bulkiness of the group is far less important.     

Studies of the reactions of platinum halo complexes with tin(II) halides

The reaction of a dichloromethane solution of a mixture of cis,trans-[PtCl₂(SMe₂)₂] with a tetrahydrofuran solution of SnBr₂ resulted in oxidation of platinum(II) with halogen exchange producing cis,trans-[PtBr₄(SMe₂)₂]. Reaction of a mixture of cis,trans-[PtCl₂(SEt₂)₂], potassium tetrachloroplatinate(II) or potassium hexachloroplatinate(IV) with SnBr₂ in hydrochloric acid solution resulted in formation of predominantly anionic five-coordinate trichlorostannyl platinum(II) complexes. Reaction of potassium tetrabromoplatinate(II) with SnCl₂ in hydrobromic acid in the presence of tetraphenylphosphonium bromide affords cis-[PPh₄]₂[PtBr₂(SnBr₃)₂]. The insertion of SnCl₂ into Pt–Cl bond of platinum(II) complexes cis-[PtCl₂(L₂)] {L₂ = (PPh₃)₂; (PMe₃)₂; {P(OMe)₃}₂; dppm (bis(diphenylphosphino)methane); dppa (bis(diphenylphosphino)amine); and dppe (1,2-bis(diphenylphosphino)ethane)} is described.     

双羰基双膦合铂(O)配合物的合成及其与卤代烃的氧化加成反应

本文报道一种合成标题配合物Pt(diphos)(CO)2的简便方法及其与碳-卤键的氧化加成反应. 在一氧公碳气氛存在下用NaBH4还原[Pt(diphos)Cl2]可“原位"得到[Pt(diphos)(CO)2]的THF溶液, 能与卤代烃发生氧化加成反应, 并用^1H NMR和^3^1PNMR谱进行了研究. 氧化加成反应按自由基非链式机理进行, 加成产物[Pt(diphos)X2]之一[Pt(d(i-Pr)pe)I2]经过分子结构测定, 反应能力与卤代烃和双膦螯合配体的电子性质有关.     

Oxidative addition in the coupling of alkylgold(I) with alkyl halides

MeAu(PPh₃) reacts with MeI to afford C₂H₆ and I(PPh₃)Au by a multi-step mechanism involving: (i) oxidative addition to form an intermediate Me₂AuI(PPh₃) species, which (ii), undergoes iodide-methyl exchange with another MeAu(PPh₃) species to afford Me₃Au(PPh₃), followed by (iii), reductive elimination of C₂H₆ and reformation of MeAu(PPh₃). The more reactive trime thylphosphine derivative also readily undergoes (i) oxidative addition and (ii) methyl exchange. However, Me₃Au(PMe₃) is more stable than the PPh₃ analog and does not undergo (iii) reductive elimination. Instead, it is involved in (iv), a further very slow reaction with IAu(PMe₃) and MeI to afford Me₂ AuI(PMe₃) in high yields. C₂H₅Au(PPh₃) specifically affords n-C₄H₁₀ at 0° in MeI. Reactions of other alkylgold(I) complexes with alkyl halides are also reported, and fit into a general mechanistic pattern desribed by reactions (i) – (iv).     

Controlling the oxidative addition of aryl halides to Au(I)

By means of density functional theory calculations, we computationally analyze the physical factors governing the oxidative addition of aryl halides to gold(I) complexes. Using the activation strain model of chemical reactivity, it is found that the strain energy associated with the bending of the gold(I) complex plays a key role in controlling the activation barrier of the process. A systematic study on how the reaction barrier depends on the nature of the aryl halide, ligand, and counteranion allows us to identify the best combination of gold(I) complex and aryl halide to achieve a feasible (i.e., low barrier) oxidative addition to gold(I), a process considered as kinetically sluggish so far. © 2014 Wiley Periodicals, Inc.     

Iron(II) complexes with functionalized amine-pyrazolyl tripodal ligands in the cross-coupling of aryl Grignard with alkyl halides

Structurally distinctive Fe(II) complexes with furan, thiophene and pyridine functionalized amine-pyrazolyl tripodal hybrid ligands have been synthesized and crystallographically characterized. The tether substituent at the central amine plays an active role in determining the coordination mode of the ligand and the metal geometry. All complexes are catalytically active towards cross-coupling of aryl Grignard reagents with primary and secondary alkyl halides with β-hydrogen under ambient conditions. ESI-MS spectra analysis revealed the ligand-stabilised Fe(II) and Mg(II) species.     

Reactivity of diacetylplatinum(II) complexes: Oxidative addition of halogens and hydrogen halides

Diacetylplatinum(II) complexes [Pt(COMe)₂()] ( = bpy, 3a; 4,4′-t-Bu₂-bpy, 3b), obtained by the reaction of [Pt(COMe)₂X(H)()] with NaOH in CH₂Cl₂/H₂O, were found to undergo oxidative addition reactions with halogens (Br₂, I₂) yielding the platinum(IV) complexes (trans, OC-6-13)/(cis, OC-6-32) [Pt(COMe)₂X₂()] ( = bpy, X = Br, 4a/4b; I, 4c/4d;  = 4,4′-t-Bu₂-bpy, X = Br, 4e/4f; I, 4g/4h). The diastereoselectivity of the reactions proved to be strongly dependent on the solvent. The oxidative addition of (SCN)₂ resulted in the formation of (OC-6-13)-[Pt(COMe)₂(SCN)₂()] ( = bpy, 4i; 4,4′-t-Bu₂-bpy, 4j). In a reaction the reverse of their formation, the diacetylplatinum(II) complexes 3 underwent oxidative addition with anhydrous HX (X = Cl, Br, I), prepared in situ from Me₃SiX/H₂O, yielding diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)₂X(H)()] ( = bpy, X = Cl, 5a; Br, 5b; I, 5c;  = 4,4′-t-Bu₂-bpy, X = Cl, 5d; Br, 5e; I, 5f). Furthermore, diacetyldihaloplatinum complexes 4 were found to undergo reductive elimination reactions in boiling methanol yielding acetylplatinum(II) complexes [Pt(COMe)X()] ( = bpy, X = Br, 6b; I, 6c;  = 4,4′-t-Bu₂-bpy, X = Br, 6e; I, 6f). All complexes were characterized by microanalysis, IR and ¹H and ¹³C NMR spectroscopy. Additionally, the bis(thiocyanato) complex 4j was characterized by single-crystal X-ray diffraction analysis.     

4-Cyanoaniline complexes with transition metal(II) halides

Summary Coordination compounds formed by the interaction of manganese(II), cobalt(II), nickel(II) and copper(II) chloride and bromide with 4-cyanoaniline (4-CA) have been prepared and characterized by molar conductance, magnetic susceptibilities, electronic and i.r. spectral measurements down to 200 cm^–1 in the solid state. The isolated complexes are M(4-CA)₂X₂ except for nickel(II) bromide which is NI(4-CA)₄Br₂. I.r. spectra, indicate that 4-CA, though a potentially bidentate ligand, nevertheless acts only as a terminally aniline (NH₂) bonded monodentate ligand in all the complexes. Tentative stereochemistries of the complexes have been suggested in the solid state.     

Silver-catalyzed coupling reactions of alkyl halides with indenyllithiums

Coupling reactions of tertiary and secondary alkyl halides with indenyllithiums proceeded effectively in the presence of a catalytic amount of silver bromide to provide tertiary- and secondary-alkyl-substituted indene derivatives in good yields.     

Kumada-Corriu reactions of alkyl halides with alkynyl nucleophiles

[reaction: see text] Pd(2)(dba)(3)-Ph(3)P-catalyzed Kumada-Corriu coupling reactions of unactivated alkyl bromides or iodides with an alkynyl nucleophile furnish C(sp)-C(sp)3 bond formation. Alkynyl nucleophiles can be alkynyllithiums or the corresponding Grignard reagents. The superior performance of Ph(3)P ligand over the trialkylphosphine ligands indicates that this cross-coupling reaction may be a reductive-elimination-controlled process.     

Interaction of pyridineplatinum(II) complexes with alkyl sulfoxides

Interaction of pyridineplatinum(II) complexes with dimethyl sulfoxide and diethyl sulfoxide is studied by NMR spectroscopy. The interaction products are pyridinesulfoxide and bissulfoxide platinum(II) complexes. Cis-trans isomerization of the products is observed along with the substitution reaction and determines the final configuration of the complexes.     

Catalysts for cross-coupling reactions with non-activated alkyl halides

Despite the problems inherent to metal-catalyzed cross-coupling reactions with alkyl halides, these reactions have become increasingly important during the last few years. Detailed mechanistic investigations have led to a variety of novel procedures for the selective cross-coupling of non-activated alkyl halides bearing beta hydrogen atoms with a variety of organometallic nucleophiles under mild reaction conditions. This Minireview highlights selected examples of metal-catalyzed coupling methods and is intended to encourage chemists to exploit the potential of these approaches in organic synthesis.     

Metal to ligand group transfer reactions : II. Reactions of some π-allylrhodium(I) complexes with trifluoroacetic acid and alkyl,acyl and trimethyltin halides

Rh(π-C₃H₅)(PF₃)₃ (I), reacts with trifluoroacetic acid to form propene and [Rh(CF₃COO)(PF₃)₂]₂ (II). I reacts with t-butyl bromide to give [RhBr(PF₃)₂]₂ and a mixture of propene and 2-methyl-1-propene and with n-propyl bromide to give propene and [RhBr(PF₃)₂]₂. Rh(π-C₃H₅)(PPh₃)₂ (III), and t-butyl bromide yield propene and 2-methyl-1-propene. In these reactions a mechanism involving β-hydrogen abstraction and hydrogen migration via the metal to carbon is proposed. When III reacts with Me₃SnCl the Me₃Sn—moiety migrates intact to the π-allyl group. I reacts with acetyl chloride to give propene, [RhCl(PF₃)₂]₂ and the carbonyl rhodium complex Rh₂Cl₂(PF₃)₃(CO). II does not apparently undergo phosphine ligand exchange unlike the analogous halogeno-bridged dimers.     

Enthalpy changes in oxidative addition reactions of iodine with monomeric and dimeric rhodium(I) complexes

The heat of reaction for addition of iodine to the planar complexes RhCl(CO)dppe, Rh(dppen)₂⁺, Rh(dppe)₂⁺ and to the dimer Rh₂Cl₂(CO)₂(dppm)₂ has been obtained by a calorimetric method. Iodine forms stronger Rh---I bonds with RhCl(CO)dppe than with the bichelate complexes. The presence of metal-metal interaction in the iodine addition compound of Rh₂Cl₂(CO)₂(dppm)₂ makes a significant contribution to the enthalpy change for the oxidative addition. The stereochemistry of the complexes are discussed on the basis of IR and ³¹P NMR spectra.