Zeise's Dimer Research Articles

Unusual Transformations of Strain-Heightened Oxetanes.

Oxetanes are important motifs for drug discovery and are valuable templates in organic synthesis. Much of their use as synthetic intermediates exploits their inherent strain, often resulting in chain extensions at the expense of the heterocycle. Modifications on the carbon alpha to the oxygen of oxetanes, such as the C═O of β-lactones, extend the modes of reactivity. Nevertheless, the outcomes are still largely predictable. On the other hand, other alpha modifications, such as a ═CH2, a spiro-oxiranyl moiety, or a spiro-cyclopropyl group, increase strain and open pathways not available to simple oxetanes or β-lactones. Methods in generating 2-methyleneoxetanes, 1,5-dioxaspiro[3.2]hexanes, and 4-oxaspiro[2.3]hexanes have been developed by us and others. To date, reactions of these systems have sometimes been predictable, but often the outcomes have been unexpected. This has provided fertile ground for thinking about what controls reactivity and what other reaction pathways might be accessible to these strain-heightened oxetanes.This Account summarizes the published literature on the most straightforward approaches to 2-methyleneoxetanes, dioxaspirohexanes, and oxaspirohexanes and on their reactivity. In contrast to simple oxetanes, reactions of 2-methyleneoxetanes with nucleophiles at C4 release an enolate rather than an alkoxide. Also, 2-methyleneoxetanes can be converted to homopropargyl alcohols or undergo a silicon accelerated isomerization/electrocyclic ring opening, processes accessible only because of the exocyclic double bond. In addition, oxetane oxocarbenium ions, derived from protonation of the enol ether, can react with nucleophiles to provide 2,2-disubstituted oxetanes. Oxaspirohexanes are readily prepared by Simmons-Smith cyclopropanation of 2-methyleneoxetanes. These unusual systems undergo a variety of substituent dependent rearrangements in the presence of the Lewis acid BF3·Et2O. In addition, upon treatment with Zeise's dimer, oxaspirohexanes are transformed to synthetically useful 3-methylenetetrahydrofurans. Dioxaspirohexanes are easily accessed by dimethyldioxirane oxidation of 2-methyleneoxetanes. Predictably, dioxaspirohexanes react with many nucleophiles to give α-functionalized-β'-hydroxy ketones. Unexpectedly, 2,2-disubstituted oxetanes can also be selectively produced. This latter pathway has led to further unusual transformations, illuminating computational studies, and novel routes to biologically relevant molecules.

Effectiveness of the bimetallic catalytic center over the monometallic one for catalyzing the rearrangement of cyclopropanated bicyclic derivatives

Report shows that the cyclopropanated pentacyclic and pyran derivatives undergo ring opening reaction to form monocyclic compounds under the catalysis of Zeise's salt. Present study on the mechanism of the rearrangement reaction by density functional theory shows that this reaction prefers the involvement of two metal atoms, provided by the Zeise's dimer to generate the product. Moreover an external water molecule or alcohol is required to generate the end product. The reduced activation barrier of the reaction pathway, catalyzed by two metal atoms, explains the occurrence of the rearrangement reaction at ambient condition.

Theoretical Study on the Mechanism of Rearrangement Reactions of Bicyclic Derivatives of Cyclopropane to Monocyclic Derivatives under the Catalysis of Pt-Salt

In this paper, the mechanistic studies on the isomerization of hydroxyl and silyl derivatives of bicyclic cyclopropanes under the catalytic action of Zeise’s salt have been reported. The catalytic activity of both the monomeric and the dimeric forms of Zeise’s salt has been studied by applying the high-level quantum mechanical method. Results from this investigation reveal that the reaction goes favorably under the catalysis of the dimeric form of Zeise’s salt. The calculated activation barrier for the catalytic process using Zeise’s dimer reveals that the rearrangement occurs with an activation barrier of 19–25 kcal mol–1. Depending on the nature of substituents present on the substrate, formation of various products has been explained. This study also includes the heteronuclear counter part of Zeise’s dimer where one of the Pt-metals is replaced by palladium (Pd) and nickel (Ni) successively. The calculated activation barrier using these heteronuclear catalysts is found to be close enough to that calculated for the catalytic pathway using Zeise’s dimer.

Dinuclear Olefin and Alkyne Complexes of Platinum(II)

AbstractBis(olefin) complexes of Zeise's dimer type – [{PtCl2(cis‐MeHC=CHMe)}2] (2) or [{PtCl2(c‐Hex)}2] (3, c‐Hex = cyclohexene) – were prepared by treatment of K2[PtCl4] in the presence of SnCl2 or K[PtCl3(cis‐MeHC=CHMe)] with the corresponding olefin. Zeise's dimer, [{PtCl2(H2C=CH2)}2] (1), was found to react in chloroform or dichloromethane with the internal alkynes RC≡CtBu (R = Me, tBu), provided that the cleaved‐off ethene was removed, to yield bis(alkyne) complexes of Zeise's dimer type [{PtCl2(RC≡CtBu)}2] (R = Me, 11; tBu, 12). Without removal of the ethene, mononuclear mixed ethene/alkyne complexes cis‐[PtCl2(H2C=CH2)(RC≡CtBu)] (R = Me, 8; tBu, 9) and cis‐[PtCl2(H2C=CH2)2] (10) were formed. Analogous reactions with alkynes RC≡CR′ bearing sterically less demanding substituents (R, R′ = Me, Et, nPr, Ph) led to (cyclobutadiene)platinum(II) complexes [PtCl2(C4R2R′2)] (R/R′ = Me/Me 4; Et/Et 5; Me/nPr 6) and [PtCl2(C4Me2Ph2)] (7). Furthermore, use of acetone (instead of CHCl3/CH2Cl2) as solvent in the reactions between 1 and sterically undemanding substituted alkynes resulted in bridge cleavage of Zeise's dimer (1) and in aldol addition and condensation reactions, thereby confirming why Chatt et al. in his analogous classical experiments (1961) observed only decomposition. Complexes 2–7 and 11/12 were isolated in pure states and fully characterized by elemental analysis, NMR spectroscopy, and X‐ray diffraction measurements (2, 11, 12). For the dinuclear bis(olefin) (1–3) and bis(alkyne) complexes (11, 12) solvent‐dependent equilibria between the transoid and cisoid isomers were observed, and these could even be ascertained crystallographically for complex [{PtCl2(tBuC≡CtBu)}2] (12), which crystallized both as the transoid isomer 12a and as the cisoid isomer 12b·CHCl3. Furthermore, consistent with DFT calculations, NMR measurements provided evidence of fast rotation and of hindered rotation of olefin and alkyne ligands, respectively, resulting in conformational isomers in 8 and 11.

Platinum‐Catalyzed Synthesis of β‐Keto Tetrahydropyrans and Cyclic Dienolethers

A platinum upgrade: Zeise's dimer [{Cl2Pt(CH2CH2)}2] catalyzes the activation of linear propargylic alcohols and esters. Depending on the presence of a suitably placed alcohol group proximal or distal to the propargylic center, a cyclo-reorganization occurs that delivers either valuable β-keto tetrahydropyrans (from propargylic alcohols), or cyclic dienolethers (from propargylic esters).

ChemInform Abstract: Synthesis, Characterization, and Properties of Ethylene-Coordinated Complexes of β-Platinum(II) Ketones.

The reaction of siloxycyclopropanes with Zeise's dimer ([Pt(C 2 H 4 )Cl 2 ] 2 ) in CHCl 3 yields ethylene-coordinated β-platinum ketones of which the structure has been determined by X-ray diffraction methods, showing a chloride-bridged dimeric structure

Platinum‐Catalyzed Regioselective Formation of β‐Alkoxy Ketones from Internal Alkynes

AbstractA catalytic amount of Zeise's dimer and 15‐crown‐5 were combined to effectively promote the regioselective formation of β‐alkoxy ketones from 2‐(homopropargyloxy)ethanols in dimethoxyethane. The desired products were obtained in 59–98 % yields with up to 17:1 exo/endo regioselectivity. The methodology allows access to β‐hydroxy ketones as an aldol reaction alternative.

Au(I)- and Pt(II)-Catalyzed Cycloetherification of ω-Hydroxy Propargylic Esters

Depending on the nature of the metal catalyst, omega-hydroxy propargylic acetates choose between alternative cycloetherification manifolds to produce functionalized heterocycles in high yields. AuCl catalyzes the formation of oxacyclic enol acetates, whereas [Cl(2)Pt(CH(2)CH(2))]2 (Zeise's dimer) will induce a propargylic substitution via an unprecedented S(N)2'-type allenic substitution from within a chelated square planar cationic Pt(II) complex.

Di-μ-chlorido-bis[chlorido(η2-ethene)platinum(II)

Zeise's dimer, [Pt2Cl4(C2H4)2)], consists of two independent dimeric mol­ecules in the unit cell, one of which is crystallographically centrosymmetric. All Pt atoms are essentially square planar with bridging and trans terminal chloride groups. The eth­ene groups are orthogonal to the mol­ecular square plane. In the non-centrosymmetric mol­ecule, the two square planes subtend an angle of 160.10 (13)° at the bridging Cl atoms. The crystal structure exhibits layers of molecules running approximately parallel to the (001) face, with a layer of the centrosymmetric dimer stacked directly between two layers of the non-centro­symmetric mol­ecules [Pt⋯Pt = 4.053 (1) and 4.090 (1) A]. Within this stack, the eth­ene groups of the central mol­ecule are located betwen two terminal chloride groups of the adjacent mol­ecules. Adjacent three-layer sandwiches are staggered from each other so that stacking occurs for only one square plane, disrupting any further inter­action by one Pt atom but allowing a weaker Pt⋯Pt inter­action [4.249 (1) A]. The non-centrosymmetric mol­ecule layer exhibits a weak hydrogen bond between a terminal chloride and an ethene H atom of an adjacent mol­ecule.

Synthesis of Platinacyclobutanes Bearing Biological Components for Targeted, Cisplatin Prodrugs

A new series of platinacyclobutanes with attached biomolecules have been prepared. Biological components include thymidine, cholesterol, glucose, and proline, all of which have been coupled to cyclopropylmethanol and then reacted with platinum(II), in the form of Zeise's dimer, to give the respective platinacycle.

Regiospecific Hydration of γ-Hydroxy-α,β-acetylenic Esters: A Novel Asymmetric Synthesis of Tetronic Acids

[reaction: see text] The optically active gamma-hydroxy-alpha,beta-acetylenic esters are obtained from the enantioselective reaction of methyl propiolate with both aliphatic and aromatic aldehydes. These compounds can undergo regiospecific hydration in the presence of Zeise's dimer, [PtCl(2)(C(2)H(4))](2), to generate the optically active tetronic acids.

Opening the [4 + 2 + 2] cycloadducts of bicyclo[2.2.1]hepta-2,5-dienes (norbornadienes) to cis-fused bicyclo[5.3.0]decanes.

Tetracyclo[5.4.0.0.(2,4)0(3,7)]undec-9-enes, prepared by the transition-metal-catalyzed [4 + 2 + 2] homo-Diels-Alder reactions of norbornadiene and 1,3-butadienes, can be opened using either acid-promoted or Zeise's dimer-mediated cyclopropane ring cleavage, ultimately leading to cis-fused bicyclo[5.3.0]decanes (perhydroazulenes). Stereoselective functionalization of the olefin unit in the tetracycloundecenes to an alcohol or diol prior to ring opening is tolerated by the Zeise's dimer ([Pt(C(2)H(4))Cl(2)](2)) catalyst to yield highly functionalized bicyclo[5.3.0]decanes, which form the core structure of numerous sesquiterpenes.

Platinum-Catalyzed Ring Opening of 1,2-Cyclopropanated Sugars withO-Nucleophiles. Convenient Synthesis of 2-C-Branched Carbohydrates

A new reaction is described catalyzed by Zeise's dimer that allows for ring opening of 1,2-cyclopropanated sugars with O-nucleophiles to give 2-C-branched carbohydrates. A number of O-nucleophiles can participate in the ring opening including alcohols, phenols, and water. A wide range of alcohols has been employed giving 2-C-branched glycosides ranging from simple methyl glycosides to more complex disaccharides. A very high diastereoselectivity is obtained at the newly formed C-1 stereocenter. The α-glycoside, favored by the anomeric effect, is always the major product in the ring opening with alcohols regardless of the stereochemistry of the starting cyclopropane. When electron-rich phenols are employed as O-nucleophiles, rearrangement to the glycosyl arene has been observed. In general, the ring opening occurs readily with unsubstituted sugar cyclopropanes to give 2-C-methyl carbohydrates. However, cyclopropanes with ester or alkyl substituents are significantly less reactive and some even completely in...

Platinum-Catalyzed Hydrosilylation of 2,2-Divinyladamantane

Only partial dihydrosilylation of 2,2-divinyladamantane with triethylsilane (Et3SiH) mediated by a platinum(II) complex is observed in refluxing benzene after several days, while monosilylation occurs at room temperature within minutes. Steric effects may explain the longer reaction times. On the other hand, 2,2-divinyladamantane reacts with bis(hydrosilane) species in the presence of Zeise's dimer [Pt2Cl4(CH2CH2)2] to give disilacyclic compounds (double terminal addition) via an intramolecular process or acyclic compounds via an intermolecular process in high yields depending on nature, structure, and type of disilane used. Using o-bis(dimethylsilyl)benzene as the disilane, an unprecedented partial hydrogenation of 2,2-divinyladamantane catalyzed by a mononuclear platinum catalyst is observed.

Metal-Catalyzed [4 + 2 + 2] Cycloadditions: Cycloadducts of Substituted Norbornadienes and Their Opening with Zeise's Dimer

Metal-Catalyzed [4 + 2 + 2] Cycloadditions: Cycloadducts of Substituted Norbornadienes and Their Opening with Zeise's Dimer

A facile, high-yield synthesis of [Pt2(PR3)2(µ-Cl)2Cl2

Contrary to previous reports, Zeise's dimer, [Pt2(η2-C2H4)2(µ-Cl)2Cl2], reacts with tertiary phosphines in refluxing toluene or tetrachloroethane to give high yields of the phosphine-substituted analogues [Pt2(PR3)2(µ-Cl)2Cl2][PR3= PMe3, PMe2Ph, PEt2Ph, P(C6H11)2Ph, PMePh2, P(C6H11)Ph2 or PPh3]. A wide range of examples has been synthesised and fully characterised by 31P-{1H} and 195Pt-{1H} spectroscopy.

Pressure tuning IR and micro-raman spectra of solid zeiseߣs salt, kp[pt(η-C2H4)Cl4], and the related dimer, [Pt(η-C2H4)Cl2]2

Pressure-tuning vibrational spectroscopy using diamond-anvil cells is now well established as a useful technique for investigating the phase-transition behavior of inorganic and organic solids. Much of our recent research has been focused on organotransition metal compounds, especially metal carbonyls. The pressure dependences (dv/dP) of the v(CO) modes provide important information on the extent of #- backbonding between the metals and the carbonyl groups. We have now extended these high-presure studies to other #-acceptor ligands, including olefins. We report here the results of a high-pressure IR and micro-Raman spectroscopic investigation of the ethylene complexes, K[Pt(η-C2H4)C13] (Zeise's salt) and the related dimeric species, [Pt(η-C2H4)C12]2- We were interested in examining the effect of high pressures on the Dewar-Chatt-Ducanson σ-/π-bonding description of the platinum-ethylene bonding. There is still considerable controversy over the relative σ- and π-contributions to the overall bonding in such metal-olefin complexes.Micro-Raman spectra of solid K[Pt(η-C2H4)C13] were obtained at room temperature for the low-energy region (500-180 cm-1) at varying pressures up to 33 kbar with the aid of a diamond-anvil cell. Similarly, pressure-tuning IR spectra were measured for Zeise's salt (3080-480 cm-1; 32 kbar) and Zeise's dimer (4000-480 cm-1; 28 kbar) up to the pressures indicated.

Room temperature isomerization of siloxycyclopropanes to silyl ethers of 2-methylenealkanols catalyzed by Zeise's dimer

Room temperature isomerization of siloxycyclopropanes to silyl ethers of 2-methylenealkanols catalyzed by Zeise's dimer

Carbon-13 shielding tensors of Zeise's salt and Zeise's dimer

The 13C cross-polarization magic angle spinning NMR spectra of crystalline Zeise's salt, K[PtCl3(η2-C2H4)], and Zeise's dimer, trans-[{PtCl2(η2-C2H4)}2], have been recorded at room temperature. The 13C chemical shift tensors have been determined. The values of the tensor elements are compared to those of the free ethylene ligand and are discussed in terms of the bonding.

Synthesis, characterization, and properties of ethylene-coordinated complexes of .beta.-platinum(II) ketones

The reaction of siloxycyclopropanes with Zeise's dimer ([Pt(C 2 H 4 )Cl 2 ] 2 ) in CHCl 3 yields ethylene-coordinated β-platinum ketones of which the structure has been determined by X-ray diffraction methods, showing a chloride-bridged dimeric structure