Conversion of Magnus salt into diamminedichloroplatinum(II) isomers in aqueous solution

The conditions inducing conversion of Magnus salt into diamminedichloroplatinum(II) isomers were studied. Syntheses of cis-diamminedichloroplatinum(II) and trans-diamminedichloroplatinum(II), which are used to prepare potassium or ammonium amminetrichloroplatinate(II), are described. The identity and structure of diamminedichloroplatinum(II) isomers were verified by elemental analysis, X-ray powder diffraction, and IR and UV spectroscopy. A workflow for preparing potassium or ammonium amminetrichloroplatinate(II) from diamminedichloroplatinum(II) isomers was developed. This workflow appreciably increases the product yield due to the return of unused Magnus salt to the main synthesis flow.     

A study of the reactions of methionine- and histidine-containing peptides with palladium(II) complexes: The key role of steric crowding on palladium(II) in the selective cleavage of the peptide bond

¹H NMR spectroscopy was applied to study the reactions of palladium(II) complexes, cis-[Pd(dpa)Cl₂] and cis-[Pd(dpa)(H₂O)₂]²⁺ (dpa is 2,2′-dipyridylamine acting as a bidentate ligand) with the dipeptides methionylglycine (Met-Gly) and histidylglycine (His-Gly), and the N-acetylated derivatives of these dipeptides, MeCOMet-Gly and MeCOHis-Gly. All reactions were carried out in the pH range 2.0–2.5 with equimolar amounts of the palladium(II) complex and the peptide at two different temperatures, 25 and 60 °C. In the reactions of cis-[Pd(dpa)Cl₂] and cis-[Pd(dpa)(H₂O)₂]²⁺ with Met-Gly and His-Gly, no hydrolysis of the peptide bond was observed. The final product in these reactions was the [Pd(dpa)₂]²⁺ complex. The square-planar structure of this complex was confirmed by X-ray analysis. The reaction of the cis-[Pd(dpa)(H₂O)₂]²⁺ complex with the MeCOHis-Gly and MeCOMet-Gly peptides under the previously mentioned experimental conditions was remarkably selective in the cleavage of the amide bond involving the carboxylic group of methionine in the side chain. The modes of coordination of cis-[Pd(dpa)Cl₂] and cis-[Pd(dpa)(H₂O)₂]²⁺ in the reactions with the non-acetylated peptides and the total steric inhibition of the hydrolytic reaction between cis-[Pd(dpa)(H₂O)₂]²⁺ and MeCOHis-Gly can be attributed to the steric bulk of the palladium(II) complex. This finding should be taken into consideration in designing new palladium(II) complexes for the regioselective cleavage of peptides and proteins.     

Intermolecular stacking of a tetranuclear cyclic Pt(II) complex: NMR characterization and X-ray crystal structure of cis-trans-cis-trans tetra[μ-2,6-diethynyl-4-nitroaniline-bis(tri(p-tolyl)phosphine)platinum(II)]

The synthesis and characterization of a tetranuclear Pt complex, cis-trans-cis-trans tetra[μ-2,6-diethynyl-4-nitroaniline-bis(tri(p-tolyl)phosphine) platinum(II)], namely [L₂Pt-DENA]₄ with L = tri-p-tolylphosphine, is reported. The complex was obtained by the dehydrohalogenative condensation of 2,6-diethynyl-4-nitroaniline (DENA) with cis-[dichlorobis(tri(p-tolyl)phosphine)platinum(II)]. The single crystal structure determination of [L₂Pt-DENA]₄ indicated the formation of a neutral molecular cycle with four alternating platinum units in cis and trans configurations, all bridged with DENA spacers with the presence of solvent (toluene) crystallization molecules. A twisted tetranuclear cyclic feature was identified. The formation of intermolecular stacks of the tetranuclear complex in solution was assessed by means of nuclear Overhauser enhancement spectroscopy (NOESY) and rotating frame Overhauser effect spectroscopy (ROESY) characterizations.     

Catalytic asymmetric hetero-Diels–Alder route to a key intermediate for the synthesis of calyxin L

A catalytic asymmetric formal synthesis of diarylheptanoid natural product calyxin L has been achieved by incorporating an enantio- and diastereoselective hetero-Diels–Alder (HDA) reaction, a Suzuki–Miyaura coupling, and a stereocontrolled catalytic hydrogenation of 2,4,6-trisubstituted dihydropyran as the key steps. The HDA reaction between 4-(4-benzyloxyphenyl)-2-triethylsilyloxy-1,3-butadiene and (4-benzenesulfonyloxyphenyl)propynal catalyzed by dirhodium(II) tetrakis[(R)-3-(benzene-fused-phthalimido)-2-piperidinonate], Rh₂(R-BPTPI)₄, provided cis-2,6-disubstituted tetrahydropyran-4-one in 91% yield with 91% ee.     

X-ray study of the molecular structure of α-mercury and α-platinummercury derivatives of l-menthyl phenylacetate

The molecular structures of the L-menthyl ester of S-α-bromomercuriphenyl-acetic acid, diastereomer II, [α]²⁰_D ?18°, and of the related L-menthyl ester of α-bromobis(triphenylphosphine)platinummeruriphenylacetic acid, VI, have been investigated by the X-ray method. Insertion of L₂Pt carbenoid appears to occur into the HgBr bond in II and two phosphine ligands in the product VI occupy cis positions in a planar square around the platinum atom. The HgPt distance is 2.50 Å; there is intermolecular HgBr coordination in II, the distance being 3.23 Å.     

Mixed metal PtxMyLz complexes of L = 1-methyluracil and 1-methylthymine: Preparation and spectroscopic studies

The reactions of cis-(NH₃)₂PtL₂ (L = 1-MeT or 1-MeU, the anions of 1-methylthymine or 1-methyluracil respectively) in water with various salts of Fe(II), Fe(III), Co(II), Ni(II), Cu(II) or Ag(I) have produced 14 new heteronuclear complexes of the general types: cis-[(NH₃)₂PtL₂ML₂Pt(NH₃)₂]X_n·mH₂O or cis-(NH₃)₂PtL₂MX_n·mH₂O, and also with silver(I) perchlorate a complex of stoichiometry cis-{(NH₃)₂Pt(1-MeU)₂}₂· 3AgClO₄·6H₂O. Comparisons are made with previously reported heteronuclear species derived from cis-(NH₃)₂PtL₂ and factors influencing the type of heteronuclear complex formed are discussed, particularly the versatility of binding patterns with Ag(I). A tetranuclear structure is suggested for the compound of stoichiometry cis-(NH₃)₂Pt(1-MeU)₂·FeSO₄·3H₂O involving iron(II) ions linked by sulphate bridges. The electronic spectra of the trinuclear complexes cis-[(NH₃)₂Pt(1-MeU)₂M(1-MeU)₂Pt(NH₃)₂] (NO₃)₂·mH₂O (M = Fe, Co or Ni) are reported. They show that the trans-MO₄Pt₂ geometry results in a very severely trans-elongated ligand field about the central metal ion, M. This conclusion is supported by the Mössbauer spectrum in the case of the iron(II) complex. The X- and Q-band EPR spectra of the Fe(III) analogue are also reported.     

The Fourier transform Raman spectra of a series of platinum(II), palladium(II) and gold(III) square-planar complexes

The Fourier transform Raman spectra of solid samples and some D₂O solutions, of complexes of formula K_nMX₄, M = Pt(II), Pd(II), and Au(III); X = Cl and Br are reported. It was found that the spectra of the tetrabromides contain more bands than the corresponding tetrachlorides; this indication that the two halides have different crystal structures is discussed. Fourier transform Raman spectra of M(NH₃)₄Cl₂ M = Pt(II), and Pd(II), trans- and cis-Pt(NH₃)₂Cl₂ (i.e. the pharmaceutical product “cis-platin”), and trans-Pd(NH₃)₂X₂, X = Cl and Br are also reported here and the significance of the spectra discussed. Although many of these spectra have been reported earlier the quality of the new Fourier transform data is superior to that in the literature.     

Formation of Homo- and Heteronuclear Platinum(II) and Palladium(II) Carbene Complexes in the Reactions of Coordinated Isocyanides with Aminothiazaheterocycles

The reaction of 5-(trifluoromethyl)-1,3,4-thiadiazol-2-amine with cis-dichlorobis(2,6-dimethylphenyl isocyanide)platinum(II) (cis-[PtCl₂(CNXyl)₂], Xyl = 2,6-Me₂C₆H₃) gave platinum(II) monocarbene complex whose deprotonation with an organic base generated a nucleophilic species capable of reacting with palladium(II) and platinum(II) bis(isocyanide) complexes to afford homo- and heteronuclear isocyanide/carbene structures.     

cis-Bis(7-methylnaphth-1-yl)bis(triphenylphosphan)platin(II)

From the reaction of cis-dichlorobis(triphenylphosphane)platinum(II) with the lithium compound obtained as the bromination product of 2-methylnaphthalene cis-bis(7-methylnaphth-1-yl)bis(triphenylphosphane)platinum(II) (6), has been isolated. The unexpected formation of 6 has been explained.     

Thermal decomposition of trans-chloro(2-allylphenyl)bis(triethylphospine)nickel(II)

Thermolysis of trans-chloro(2-allylphenyl)bis(triethylphosphine)nickel(II), I, in tetrachloroethylene has afforded indene as the major hydrocarbon product along with lesser amounts of allylbenzene and trans-β-methylstyrene. Organonickel products were trans-chloro(trichlorovinyl)bis(triethylphosphine)nickel(II), II, chloro[2-(trans-propenyl)phenyl]bis(triethylphosphine)nickel(II), III, and trans-dichlorobis(triethylphosphine)nickel(II). Compound III was the major product from thermolysis of I in benzene. Chloro[2-(cis-propenyl)phenyl]bis(triethylphosphine)nickel(II), IV, and III could be synthesized independently by treatment of chloro-2-(cis-propenyl)benzene and chloro-2-(trans-propenyl)benzene, respectively, with nickel acetylacetonate and triethylaluminium in the presence of triethylphosphine. Thermolysis of I in benzene containing allylbenzene led to the formation of trans-β-methylstyrene. The thermolysis of I in benzene in the presence of cis-1,4-hexadiene caused the skeletal rearrangement of the diene to trans-2-methyl-1,3-pentadiene. A catalyst derived from ethylenebis(triphenylphosphine)nickel(0) and hydrogen chloride isomerized allylbenzene to trans-β-methylstyrene.     

Synthesis,characterization and antimicrobial studies on cis-platinum(II) complexes of 5-nitrosouracil derivatives

Two complexes were obtained during the reactions of 6-amino-1-methyl-5-nitrosouracil (AMNU) and 6-methylamino-1-benzyl-5-nitrosouracil (MABNU) with cis-diaquadiamineplatinum(II) nitrate complex, cis-[Pt(NH₃)₂(H₂O)₂](NO₃)₂. The complexes were isolated in good yields as powdery precipitates. They were characterized through their elemental analysis, infrared, UV–vis, and ¹H NMR spectroscopies as well as thermal analyses. The obtained results indicated that, pyrimidine bases substitute easily aqua ligands and interact with Pt(II) ions as a monodentate ligand in the neutral and ionic form for the ligands AMNU and MABNU, respectively. The exocyclic oxygen atoms are the most probable binding site. Square planar structures, cis-form, were proposed in both cases. The free ligands, and their Pt(II) complexes were screened for their antimicrobial activities.     

Quantum-chemical study of the effect of butadiene interaction with anionic active sites on the polymer microstructure

The electronic and geometric structure of the models for prereaction complexes of the anionic active sites for polymerization of butadiene have been calculated using a modified CNDO method: C₄H₄Li-cis-C₄H₆(I), C₄H₇Li-trans-C₄H₆(II), (C₄H₇Li)₂-cis-C₄H₆(III) and (C₄H₇Li)₂-trans-C₄H₆. The configuration of complexes I and II resulting from the total energy minimization points to the preferential C₄H₆ attack on the α-C atom of the monomeric active site (AS) leading to 1,4-units in polybutadiene. A more pronounced complexation effect observed with I as compared to II was taken into account when interpreting data on the preferential formation of cis-1,4-structure within macromolecules. The structure of models III and IV and also a decrease in the difference of the energy of interaction with C₄H₆ incorporated in these models, as compared to models I and II, indicate a decrease in the 1,4-cis-units content with increasing initiator concentration. Based on results of the present study, an evaluation was also made of the effect of the interaction between the living macromolecule aggregates and diene on the dissociation processes.     

Alkyl complexes of palladium(II) with trimethylphosphine and 1,2-bis-(dimethylphosphino)ethane ligands

A number of neutral, mononuclear dialkylpalladium(II) tertiary phosphine complexes of geneal formula cis or trans-PdR₂(PMe₃)₂ and cis-PdR₂ (dmpe) [dmpe = 1,2-bis(dimethylphosphino)ethane], R = Me, CH₂Ph, CH₂CMe₂Ph, CH₂SiMe₃ have been obtained by interaction of magnesium reagents with palladium(II) acetate or trans-Pd(O₂CMe)₂(PMe₃)₂.     

Strukturuntersuchungen an mono- und bis-alkoxy(triphenylsilyl)-carben-komplexen des rheniums

Steric and electronic influences on bond lengths and angles at the carbene carbon atoms of cis-Re₂(CO)₉C(OR)SiPh₃ (I: R = CH₃, II, R = C₂H₅) and cis,trans-Re₂(CO)₈[C(OEt)SiPh₃]₂ (III) are discussed based on their structural analyses. I (ReRe 305.2(1) pm; ReC(carbene) 209(2) pm) and II (two independent molecules; ReRe 305.0(3) and 305.2(4) pm; ReC (carbene) 208(5) and 210(5) pm) differ by the cis and trans positions of the alkyl groups at the partial C(carbene)O double bonds. The change in configuration affects the bond angles at the carbene carbon. In III the carbene ligands are bonded to different rhenium atoms; cis to one Re atom and trans to the other Re atom (ReRe bond 309.1(2) pm). The ReC(carbene length of the trans- carbene ligand is significantly shorter (185(3) pm) than that of the cis-carbene ligand (208(3) pm).     

Oxidative addition of N-halosuccinimides to palladium(0): the discovery of neutral palladium(II) imidate complexes, which enhance Stille coupling of allylic and benzylic halides

The Stille coupling of organostannanes and organohalides, mediated by air and moisture stable palladium(II) phosphine complexes containing succinimide or phthalimide (imidate) ligands, has been investigated. An efficient synthetic route to several palladium(II) complexes containing succinimide and phthalimide ligands, has been developed. cis-Bromobis(triphenylphosphine)(N-succinimide)palladium(II) [(Ph₃P)₂Pd(N-Succ)Br] is shown to mediate the Stille coupling of allylic and benzylic halides with alkenyl, aryl and allyl stannanes. In competition experiments between 4-nitrobromobenzene and benzyl bromide with a cis-stannylvinyl ester, (Ph₃P)₂Pd(N-Succ)Br preferentially cross-couples benzyl bromide, whereas with other commonly employed precatalysts 4-nitrobromobenzene undergoes preferential cross-coupling. Furthermore, preferential reaction of deactivated benzyl bromides over activated benzyl bromides is observed for the first time. The type of halide and presence of a succinimide ligand are essential for effective Stille coupling. The type of phosphine ligand is also shown to alter the catalytic activity of palladium(II) succinimide complexes.     

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 S_N2 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.     

Preparation of cis-bis-acetylene-bis(pentafluorophenyl)-palladium(II) and -platinum(II) complexes,crystal structure of cis-[Pt(C6F5)2 (PhCCPh)2]

Treatment of cis-[M(C₆F₅)₂(THF)₂] (M = Pd, Pt; THF = tetrahydrofuran) with PhCCPh has given the novel bis-acetylene-palladium(II) and -platinum(II) complexes cis-[M(C₆F₅)₂(PhCCPh)₂]; these are stable even though there seems to be no significant π-back bonding according to the X-ray structure of the platinum complex.     

Darstellung von PdCl2-komplexen substituierter cis,cis-cycloocta-1,5-diene aussachtringen und den entsprechenden substituierten cis-1,2-divinylcyclobutanen. cis,trans-zuordnung 3,4-,3,7- und 3,8-disubstituierter cis,cis-cycloocta-1,5-diene

cis-1,2-Divinylcyclobutanes are transformed with dibenzonitrilepalladium(II) chloride into the corresponding cis,cis-cycloocta-1,5-diene-PdCl₂ complexes. When e.g. the 3-methyl-cis,cis-cycloocta-1,5-diene-PdCl₂ complex is prepared using trans- or cis-3-methyl-cis-1,2-divinylcyclobutane or the corresponding eight-membered ring. two PdCl₂ complexes with the methyl group in the equatorial or axial position are formed in different percentages. With the aid of ¹H NMR spectroscopy the cis- or trans-configurations of 3,4-, 3,7- or 3,8-disubstituted cis,cis-cycloocta-1,5-dienes can be determined unambiguously in PdCl₂ complexes.     

Synthesis of eleven-membered carbocycles via a homo-Cope type of five-carbon ring expansion reaction utilized β-(hydroxymethyl)allylsilane

Eleven-membered carbocycles were synthesized from six-membered compounds fitted with a β-(hydroxymethyl)allylsilane unit via the title reaction. Namely, trans- and cis-(E)-2-(trimethylsilylmethyl)-3-(2-vinylcyclohex-1-yl)prop-2-en-1-ol were treated with Tf₂O in CH₂Cl₂ in the presence of 2,6-lutidine to afford (1E)-3-methylenecycloundeca-1,6-diene in good yield. The geometry of the product was shown to depend upon the trans- and cis-substitution pattern on the cyclohexane ring of the substrates; i.e. trans-isomer afforded (6E)-product exclusively and cis-isomer afforded the mixture of (6E)- and (6Z)-product in 1:2 ratio. The (Z)-substrate with respect to allylsilane moiety afforded the same ring expansion product, however, the yield was lower than the reaction with the (E)-substrate. The substrates bearing t-butyl or benzyloxy substituents on the cyclohexane ring also afforded the product analogously, indicating that the reaction depends upon the conformation of the substrate. On the other hand, the substrate bearing isopropenyl group instead of a simple vinyl group did not afford the ring expansion product but produced bicyclo[5.4.0]undecane via the ene reaction.     

Reactivity of cyclopalladated compounds: VIII. Synthesis of cyclometallated compounds with an oxygen as the donor atom. Crystal and molecular structure of (8-methylquinoline-C,N)-(1-methoxynaphthalene-8-C,O)palladium(II)

Treatment of 1-methoxynaphthalene (MXNH) with n-butyllithium in a diethyl ether/n-hexane solution gives 1-methoxynaphthalene-8-lithium (MXNLi) in 30% yield as an insoluble material. This compound reacts with PdCl₂(SEt₂)₂ to give bis(1-methoxynaphthalene-8-C,O)palladium(II) (I)_and with PtCl₂(SEt₂)₂ to give cis- and trans-(1-methoxynaphthalene-8-C,O)(1-methoxynaphthalene-8-C)(diethylsulfide)platinum(II) (II), which are non-rigid molecules in solution. With the cyclopalladated dimers [{$\text{Pd(CN}$)Cl₂}₂], MXNLi gives the palladobicyclic compounds: ($\text{N∩C)P}$$\text{d(C∩O}$) (III). An X-ray diffraction study of compound IIIa where N∩N = 8-methylquinoline-C,N reveals the planarity of the molecule, shows that it has a cis configuration with respect to the PdC bonds, and confirms that the oxygen atom of MXN is bonded to palladium: PdO 2.236(4) Å. The geometry of IIIa is maintained in solution, whereas the corresponding compounds IIIb and IIIc in which N∩C is benzo[h]quinoline-9-C,N and N,N-dimethyl-1-naphthylamine-8-C,N, respectively, appear to be mixtures of cis and trans isomers in solution. With PMe₂Ph I and II give trans-Pd(MXN)₂(PMe₂Ph)₂ and cis-Pt(MNX)₂(PMe₂Ph)₂, respectively, in which the methoxynaphthalene is bound to the metals via the 8-carbon of the naphthalene ring. Only one phosphine ligand adds to compounds IIIb and IIIc with displacement of the O → Pd bond. One carbon monoxide ligand can be added to the platinum compound II to give Pt(MXN)₂(SEt₂)CO which in solution exists as two isomers in equilibrium.