Palladium-catalyzed vinylation of cyclohexenes using a directing-group strategy

Palladium-promoted vinylation of cyclohexenes via employment of a directing-group strategy to yield the coupled vinyl cyclohexenes with excellent regio- and stereoselectivity was studied. Typically, reaction of 2-(cyclohex-2-en-1-yl)-N-tosylacetamide ( 1a ) with (Z)-styryl bromides ( 2 ) gave cis-2-[(E)-styryl]cyclopent-3-en-1-yl-N-tosylacetamides in good to excellent yields. It is noticed that (Z)-styryl moiety was inverted into (E)-form in products. Unfortunately, (E)-styryl bromide substrates were not suitable for this reaction under the condition investigated. Further studies on norbornene system, we found that palladium-catalyzed reaction of endo-N-tosylbicyclo[2.2.1]hept-5-ene-2-carboxamide ( 6 ) with styryl bromides gave the Aza-Heck type products.     

Regiospecific Syntheses of Sulfoxides and Sulfones of the (Z)-Configuration

A convenient synthesis for varions (Z)-1-alkanesulfinyl-2-phenylethenes has been developed. This involves addition of different sodium thiolates to phenylacetylene in ethanol, and oxidation of the resulting (Z)-1-alkanesulfenyl-2-phenylethenes [(Z)-styryl alkyl thioethers] with sodium metaperiodate supported on acidic alumina. The corresponding sulfones can be obtained by oxidation of these (Z)-styryl alkyl thioethers with hydrogen peroxide in glycial acetic acid, or, alternatively by reduction of the β-iodostyrylsulfones with zinc in acetic acid. These β-iodostyrylsulfones were obtained by addition of the corresponding sulfonyl iodides to phenylacetylene under the catalytic action of cupric chloride and triethylaminium chloride.     

Reactions of Elemental Phosphorus and Phosphine with Electrophiles in Superbasic Systems: XV. Phosphorylation of Allyl Halides with Elemental Phosphorus

Elemental phosphorus (red or white) reacts with allyl chloride and allyl bromide in a two-phase system aqueous KOH-organic solvent to form tertiary symmetrical and mixed phosphine oxides among which tris(prop-2-enyl)-, bis(prop-2-enyl)[(E)-prop-1-enyl]-, bis(prop-2-enyl)[(Z)-prop-1-enyl]-, (prop-2-enyl)[(E)-prop-1-enyl][(Z)-prop-1-enyl]-, bis[(E)-prop-1-enyl](prop-2-enyl)-, bis[(Z)-prop-1-enyl](prop-2-enyl)-, tris-[(E)-prop-1-enyl]-, and bis[(E)-prop-1-enyl][(Z)-prop-1-enyl]phosphine oxides were identified. The conditions (room temperature, 60% aqueous KOH-dioxane) allowing preparation from white phosphorus and allyl bromide of tris(prop-2-enyl)- and bis(prop-2-enyl)[(E)-prop-1-enyl]phosphine oxides as major products in the total yield of up to 96% were found.     

Pt(II) and Pd(II) Complexes with (2-Bromo-1-phenylvinyl)diphenylphosphine and Tris(Z-styryl)phosphine

Methods were developed for selective synthesis of geometric isomers of Pt(II) and Pd(II) complexes with (2-bromo-1-phenylvinyl)diphenylphosphine and tris(Z-styryl)phosphine.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 5, 2005, pp. 734–737.Original Russian Text Copyright © 2005 by Reznikov, Savin, Krivchun, Skvortsov, Sukhov, Malysheva.     

Reactions and spectroscopic studies of Group 6 metal carbonyls with pyrazinecarboxamide and certain phosphine ligands

Substitution reactions of phosphine ligands, triphenylphosphine (PPh₃), tri(m-chlorophenyl)phosphine (m-ClPPh₃), tri(p-methoxyphenyl)phosphine (p-MeOPPh₃) and tri(benzyl)phosphine (PBz₃) with [M(CO)₄(PCA)] (M?=?Cr, Mo and W, PCA?=?pyrazinecarboxamide) were found to be dependent on the type of metal and phosphine ligand. The complexes were characterized by elemental analysis, mass spectrometry, and IR and ¹H NMR spectroscopy. UV–vis spectra of the complexes in different solvents showed bands due to metal-to-ligand charge transfer.     

Stabilized Carbenium Ions as Latent,Z‐type Ligands

Controlling the reactivity of transition metals using secondary, σ‐accepting ligands is an active area of investigation that is impacting molecular catalysis. Herein we describe the phosphine gold complexes [(o‐Ph₂P(C₆H₄)Acr)AuCl]⁺ ([ 3 ]⁺; Acr=9‐N‐methylacridinium) and [(o‐Ph₂P(C₆H₄)Xan)AuCl]⁺ ([ 4 ]⁺; Xan=9‐xanthylium) where the electrophilic carbenium moiety is juxtaposed with the metal atom. While only weak interactions occur between the gold atom and the carbenium moiety of these complexes, the more Lewis acidic complex [ 4 ]⁺ readily reacts with chloride to afford a trivalent phosphine gold dichloride derivative ( 7 ) in which the metal atom is covalently bound to the former carbocationic center. This anion‐induced Au^I/Au^III oxidation is accompanied by a conversion of the Lewis acidic carbocationic center in [ 4 ]⁺ into an X‐type ligand in 7 . We conclude that the carbenium moiety of this complex acts as a latent Z‐type ligand poised to increase the Lewis acidity of the gold center, a notion supported by the carbophilic reactivity of these complexes.     

Stabilized Carbenium Ions as Latent,Z‐type Ligands

Controlling the reactivity of transition metals using secondary, σ‐accepting ligands is an active area of investigation that is impacting molecular catalysis. Herein we describe the phosphine gold complexes [(o‐Ph₂P(C₆H₄)Acr)AuCl]⁺ ([ 3 ]⁺; Acr=9‐N‐methylacridinium) and [(o‐Ph₂P(C₆H₄)Xan)AuCl]⁺ ([ 4 ]⁺; Xan=9‐xanthylium) where the electrophilic carbenium moiety is juxtaposed with the metal atom. While only weak interactions occur between the gold atom and the carbenium moiety of these complexes, the more Lewis acidic complex [ 4 ]⁺ readily reacts with chloride to afford a trivalent phosphine gold dichloride derivative ( 7 ) in which the metal atom is covalently bound to the former carbocationic center. This anion‐induced Au^I/Au^III oxidation is accompanied by a conversion of the Lewis acidic carbocationic center in [ 4 ]⁺ into an X‐type ligand in 7 . We conclude that the carbenium moiety of this complex acts as a latent Z‐type ligand poised to increase the Lewis acidity of the gold center, a notion supported by the carbophilic reactivity of these complexes.     

Front Cover: Steric Influence on the Constitution of Beryllium Phosphine Complexes (Eur. J. Inorg. Chem. 29/2023)

The phosphine complexes of beryllium chloride, bromide and iodide, [(PMe₂Ph)₂BeX₂], [(PMePh₂)₂BeX₂] and [(PPh₃)BeX₂]₂ (X=Cl, Br, I) were prepared and characterised with multinuclear NMR spectroscopy. Additionally the molecular structure of dinuclear [(PPh₃)BeCl₂]₂ was determined with single crystal X-ray diffraction techniques. The threshold cone angle of the phosphines, below which two ligands can coordinate to the beryllium dihalide fragments, is between 136° and 145°. Halide-chloride exchange in dichloromethane is observed for [(PPh₃)BeBr₂]₂ and [(PPh₃)BeI₂]₂, which leads to the formation of [(PPh₃)BeCl₂]₂. Due to the relatively low Lewis basicity of PPh₃, it almost exclusively acts as a spectator ligand with only little formation of phosphonium cations.     

Redox and Anion Exchange Chemistry of a Stibine–Nickel Complex: Writing the L,X, Z Ligand Alphabet with a Single Element

According to the covalent bond classification (CBC) method, two‐electron donors are defined as L‐type ligands, one‐electron donors as X‐type ligands, and two‐electron acceptors as Z‐type ligands. These three ligand functions are usually associated to the nature of the ligating atom, with phosphine, alkyl, and borane groups being prototypical examples of L‐, X‐ and Z‐ligands, respectively. A new SbNi platform is reported in which the ligating Sb atom can assume all three CBC ligand functions. Using both experimental and computational data, it is shown that PhICl₂ oxidation of (o‐(Ph₂P)C₆H₄)₃SbNi(PPh₃) ( 1 ) into [(o‐(Ph₂P)C₆H₄)₃ClSb]NiCl ( 2 ) is accompanied by a conversion of the stibine L‐type ligand of 1 into a stiboranyl X‐type ligand in 2 . Furthermore, the reaction of 2 with the catecholate dianion in the presence of cyclohexyl isocyanide results in the formation of [(o‐(Ph₂P)C₆H₄)₃(o‐O₂C₆H₄Sb)]Ni(CNCy) ( 4 ), a complex featuring a nickel atom coordinated by a Lewis acidic, Z‐type, stiborane ligand.     

Redox and Anion Exchange Chemistry of a Stibine–Nickel Complex: Writing the L,X, Z Ligand Alphabet with a Single Element

According to the covalent bond classification (CBC) method, two‐electron donors are defined as L‐type ligands, one‐electron donors as X‐type ligands, and two‐electron acceptors as Z‐type ligands. These three ligand functions are usually associated to the nature of the ligating atom, with phosphine, alkyl, and borane groups being prototypical examples of L‐, X‐ and Z‐ligands, respectively. A new SbNi platform is reported in which the ligating Sb atom can assume all three CBC ligand functions. Using both experimental and computational data, it is shown that PhICl₂ oxidation of (o‐(Ph₂P)C₆H₄)₃SbNi(PPh₃) ( 1 ) into [(o‐(Ph₂P)C₆H₄)₃ClSb]NiCl ( 2 ) is accompanied by a conversion of the stibine L‐type ligand of 1 into a stiboranyl X‐type ligand in 2 . Furthermore, the reaction of 2 with the catecholate dianion in the presence of cyclohexyl isocyanide results in the formation of [(o‐(Ph₂P)C₆H₄)₃(o‐O₂C₆H₄Sb)]Ni(CNCy) ( 4 ), a complex featuring a nickel atom coordinated by a Lewis acidic, Z‐type, stiborane ligand.     

Synthesis,characterization, cytotoxicity and computational studies of new phosphine‐ and carbodithioate‐based palladium(II) complexes

In quest of new metallo‐pharmaceuticals with enhanced anticancer activity, four new phosphine‐ and carbodithioate‐based Pd(II) complexes of the type [(R)CS₂Pd(PR₃)Cl] (where R = 4‐(2‐hydroxyethyl)piperazine ( 1 , 2 ), dibenzyl ( 3 , 4 ); PR₃ = diphenyl(p ‐tolyl)phosphine ( 1 , 3 ), tris(4‐tolyl)phosphine ( 2 , 4 )) were synthesized and characterized using elemental analysis, Fourier transform infrared and NMR (¹H, ¹³C and ³¹P) spectroscopies and single‐crystal X‐ray diffraction. The X‐ray diffraction data confirmed the pseudo square‐planar geometry ensuring bidentate coordination mode of carbodithioate ligands. Anticancer activity of the synthesized complexes and their ligands was assessed against human lung (A549), breast (MCF‐7) and prostate (PC3) carcinoma cells using MTT assay. All the tested compounds showed activity in micromolar range. In many cases, the cytotoxicity of the synthesized complexes was higher than or comparable to that of the standard drugs cisplatin and doxorubicin. Complex 3 emerged as the most promising compound with the lowest IC₅₀ values of 4.83, 3.72 and 5.11 μM for A549, MCF‐7 and PC3 carcinoma cell lines, respectively. DNA binding studies were also carried out using UV–visible spectroscopy. We extended our investigations to explore the mechanism of anticancer activity using in silico tools. Based on the mechanism of action of standard drugs used, extensive docking studies were carried out on the three different biomolecular targets.     

Conversion of trans‐Diboran(4)yl Platinum Complexes into Their cis‐Bisboryl Analogues

The diboran(4)yl trans‐[(iPr₃P)₂Pt(Br){B(NMe₂)B(NMe₂)Br}] ( 1 ) is readily converted into its cis‐bisboryl analogues 2 and 3 by reaction with the chelating bisphosphines 1,2‐bis(dicyclohexylphosphino)ethane (dcpe) and 1,1‐bis(dicyclohexylphosphino)methane (dcpm), respectively. A plausible mechanism of this transformation consists of a sequence of reductive diborane(4) elimination and subsequent reoxidative addition of its B? B bond to the low‐valent platinum centers. Thus, the forced cis configuration of the phosphine ligands induces a change in the preferred reaction site of the diborane(4) with respect to oxidative addition. The reactions proceed with high selectivities, and the cis‐bisboryl complexes 2 and 3 were isolated in moderate yields (55 and 46 %). Moreover, their identity was clearly verified by NMR spectroscopy and X‐ray diffraction studies.     

Synthesis and Thermal Rearrangement of Tetramethyldisilane-bridged Bis(cyclopentadienyl) Diiron Complexes with Bis(phosphine)Substitution

Photolysis of [Me2SiSiMe2)[C5H4Fe(CO2)]2with a series of bis(phosphine)ligands Ph2P(CH2)n PPh2(n=1-4) leads to the formation of the corresponding diiron complexes with intramolecular and intermolecular bis(phosphine) substitution.When these complexes were heated in refluxing xylene.only in the complexes with intermolecular bis(phosphine )substitution the thermal rearrangement reaction occurred.     

NMR studies of dynamic behavior of dialkyl(acetylacetonato)bis(tertiary phosphine)cobalt(III) and related complexes in solution

The ¹H, ³¹P and ¹³C NMR spectra of cis-dialkyl(acetylacetonato)bis(tertiary phosphine)cobalt(III) complexes were obtained in several solvents. These complexes have an octahedral configuration with trans tertiary phosphine ligands. The coordinated tertiary phosphine ligands are partly dissociated in solution. One of the phosphine ligands in CoR₂(acac)(PR₃′)₂ can be readily displaced with pyridine bases to give pyridine-coordinated complexes. From observation of the ¹H and ³¹P NMR spectra several kinetic and thermodynamic data for exchange reactions and displacement reactions of tertiary phosphines were obtained.     

Synthesis of aurocyanide and auricyanide complexes of phosphines,phosphine sulfides and phosphine selenides,and their characterization by IR,far-IR,UV solution,and solid-state NMR spectroscopic methods

A series of aurocyanide and auricyanide complexes of phosphines, phosphine sulfides, and phosphine selenides were synthesized. These new complexes have the general formula [L _n Au(CN) _m ], where L could be Cy₃P, (2-CN-Et)₃P, Me₃PS, Et₃PS, Ph₃PS, Me₃PSe, or Ph₃PSe. Auricyanide was reacted with L at 1?:?2 ratio. Products were characterized using elemental analysis, melting point, UV, IR, far-IR solution, and solid-state NMR spectroscopy. Phosphine ligands cause gold(III) reduction to gold(I); less redox tendency was found for phosphine sulfides and phosphine selenides. Tri-coordinate complexes [L₂AuCN] were produced from phosphine ligands with gold-tetracyanide. IR and UV spectroscopic methods were used to identify gold oxidation state in the synthesized complexes.     

Sulfur-containing alkenes—A new class of chelating ligands: Synthesis,coordination to palladium,and structure of the resulting complexes

Stable 1,2-disulfanylalkene palladium complexes [(RS-CH=CR′-SR)PdCl₂] were synthesized in 85–94% yield by reaction of palladium(II) chloride with sulfur-containing ligands RS-CH=C(R′)-SR (analogs of dithiolate ligands). The structure of the complexes was studied by NMR spectroscopy and quantum-chemical methods. The binding energy in palladium complexes with bis(arylsulfanyl)- and bis(alkylsulfanyl)alkenes was estimated (DFT) at 50 and 56 kcal/mol, respectively. Variation of substituents on the sulfur atoms is a convenient tool for fine tuning of the ligand properties and controlling the strength of the complex. The bite angle of the ligands does not depend on the substituent nature and is 88–89°, which is typical of square-planar complexes. According to the bite angle, the examined ligands are analogs of well known bidentate phosphine ligands, but the former are more labile since the corresponding binding energy is lower by 36 kcal/mol.     

Synthesis,characterization, and biological activity studies on (E)-N′-[2-hydroxy-1,2-di(pyridin-2-yl)ethylidine]aroyl hydrazides and their copper(II) complexes

The reaction of copper(II) salts with (E)-N-(2-hydroxy-1,2-di(pyridin-2-yl)ethylidene)aroyl hydrazide (H₂L¹, H₂L², H₃L³) or (E)-N-(2-hydroxy-1,2-di(pyridin-2-yl)ethylidene) isonicotinohydrazide (H₂L⁴) afforded the complexes [(L)Cu(H₂O)₃], [(H₂L)Cu(OAc)(H₂O)], [(HL)Cu(OAc)] _n , [(H₂L)Cu(H₂O)](ClO₄)₂ and [(H₂L)Cu(OAc)(H₂O)], where n = 1 or 2 and L is the dinegative ion of the ligands. The ligands and their complexes are characterized by elemental analyses, spectral (IR, NMR, electronic, and ESR) and magnetic studies. The FT-IR indicates that the ligands are neutral or anionic polydentate. The number of the coordinating centers depends on the nature of the metal used and the reaction conditions. The room temperature magnetic moment values, electronic spectra and ESR data indicate square planar, trigonal bipyramidal, square pyramidal, and distorted octahedral ligand fields around copper(II). Thermal decomposition of the complexes was monitored by TG and DTG under N₂ and the thermal decomposition mechanisms are given. The compounds were screened for their antimicrobial activities on some Gram-positive and Gram-negative bacterial species. The free ligands are inactive against all studied bacteria. The complexes have variable activity with the most active [(H₂L)Cu(H₂O)](ClO₄)₂, where H₂L is H₂L¹ or H₂L². The minimum inhibition concentrations for these two complexes were determined. These biological activity results are related to the structures of the compounds.     

Secoiridoid Glycosides from Swertia mileensis

From the MeOH extract of the aerial parts of Swertia mileensis, four new secoiridoid glycosides were isolated, 4′‐O‐[(E)‐caffeoyl]swertiamarin ( 1 ), 4′‐O‐[(Z)‐coumaroyl]swertiamarin ( 7 ), 6′‐O‐[(E)‐coumaroyl]swertiamarin ( 8 ), and 6′‐O‐[(Z)‐coumaroyl]swertiamarin ( 9 ), together with five known compounds. Their structures were elucidated by NMR spectroscopy and tandem mass spectrometry. Detailed HPLC/MS analyses and MS/MS fragmentation pathways are discussed for the identification of the swertiamarin‐derived (E)/(Z) isomers 6 / 7 and 8 / 9 .     

Development of the First P‐Stereogenic PCP Pincer Ligands,Their Metallation by Palladium and Platinum,and Preliminary Catalysis

The potentially tridentate P‐stereogenic [P*CP*] ligands 1,3‐{bis[(tert‐butyl)(phenyl)phosphino]methyl}benzene and 1,3‐{bis[(tert‐butyl)(phenyl) phosphino]methyl}‐2‐bromobenzene have been synthesized as the protected phosphine‐borane adducts. Deprotection with a secondary amine affords the free phosphine ligand which can be metallated by Pd and Pt with standard metal synthons. Two of the resultant [P*CP*] metal complexes have been characterized by X‐ray crystallography. The complexes exhibit a C₂ symmetric environment about the remaining binding site of the square‐planar center, with t‐Bu groups filling two quadrants of the open site. The Pd complexes can be converted by use of a Ag salt to the analogous aquo complex, which is catalytically active in the aldol condensation of methyl 2‐isocyanoacetate and benzaldehyde. Preliminary results and comparisons with previously reported catalysts with more distal C‐stereogenicity are presented.     

Diepoxy[18]annulene(10.0) : (Z,E,Z,E,Z)‐Diepoxy[18]annulen(10.0) – ein hochdynamisches Annulen

Diepoxy[18]annulenes(10.0): ( Z , E , Z , E , Z )‐Diepoxy[18]annulene(10.0) – a Highly Dynamic Annulene The McMurry reaction of (all‐E)‐5,5′‐([2,2′‐bifuran]‐5,5′‐diyl)bis[penta‐2,4‐dienal] ( 13 ) only occurs intramolecularly to give a mixture of the diepoxy[18]annulenes(10.0) 6 and 7 . Tetraepoxy[36]annulene(10.0.10.0) resulting from an intermolecular McMurry reaction is not formed. According to spectroscopic data, 6 is (Z,E,Z,E,Z)‐ and 7 (Z,E,E,Z,E)‐configured. The ¹H‐NMR data confirm that in 6 the (E)‐ethene‐1,2‐diyl bonds (C(11)=C(12) and C(15)=C(16)) rotate around the adjacent σ‐bonds. Beginning at −70°, this rotation freezes, and 6 is becoming a diatropic aromatic ring system. Beside [18]annulene itself, (Z,E,Z,E,Z)‐diepoxy[18]annulene(10.0) 6 is the only hitherto known [18]annulene derivative with dynamic properties.