Diels-Alder reactions of highly pyramidalized tricyclo[3.3.0.0]oct-1(5)-ene derivatives: further chemistry of pentacyclo[6.4.0.0.0.0]dodeca-5,8,11-triene

A study of the trapping of highly pyramidalized tricyclo[3.3.0.0^3,7]oct-1(5)-ene derivatives (generated from a 1,2-diiodo precursor on reaction with t-BuLi, 0.45% sodium amalgam and molten sodium) with different dienes (11,12-dimethylene-9,10-dihydro-9,10-ethanoanthracene, 1,3-diphenylisobenzofuran, 2,5-dimethylfuran and furan) is presented. Byproducts from the trapping of pentacyclo[6.4.0.0^2,10.0^3,7.0^4,9]dodeca-5,8,11-triene with 1,3-diphenylisobenzofuran have been synthesized and fully characterized, including an X-ray diffraction analysis. Also, the above triene has been cross coupled with 3,7-dimethyltricyclo[3.3.0.0^3,7]oct-1(5)ene to give a tetrasecododecahedratetraene derivative.     

The mechanism of the addition of tetrachloromethane to oct-1-ene catalysed by [Mo2(CO)6(η-Cp)2]

A study of the reaction of CCl₄ with oct-1-ene in the presence of catalytic amounts of [Mo₂(CO)₆(η-Cp)₂] has shown that in the early stages it proceeds by a redox-catalysed mechanism. However, gradual decomposition of the catalyst leads to the intervention of a radical chain pathway.     

A highly pyramidalized cage alkene formed via the double Diels-Alder cycloaddition of syn-4,5,13,14-bis(dehydro)octafluoroparacyclophane to anthracene

[reaction: see text] A double Diels-Alder reaction of the formal syn-bis(dehydro)octafluoroparacyclophane with anthracene leads to formation of a novel cage compound that contains a highly pyramidal double bond. The measures of pyramidality of this double bond constitute what appear to be the highest combined values of psi and phi (34.3 degrees and 33.5 degrees, respectively) yet reported to have been determined by X-ray crystallography. This cage compound, although stable indefinitely as a crystalline compound in air, exhibits the high reactivity with both triplet and singlet O2 in solution that is characteristic of such highly pyramidal pi systems.     

Evidence for a reactive (alkene)peroxoiridium(III) intermediate in the oxidation of an alkene complex with O2

An (alkene)peroxoiridium(III) complex, [Ir(L)(cod)(O(2))] [where LH = PhN=C(NMe(2))NHPh and cod = 1,5-cyclooctadiene], was identified as an intermediate in the reaction of the Ir(I) precursor [Ir(L)(cod)] with O(2) and characterized by spectroscopic methods. Decay of the intermediate and further reaction with 1,5-cyclooctadiene produced 4-cycloocten-1-one.     

The mechanism of alkene addition to a nickel bis(dithiolene) complex: the role of the reduced metal complex

The binding of an alkene by Ni(tfd)(2) [tfd = S(2)C(2)(CF(3))(2)] is one of the most intriguing ligand-based reactions. In the presence of the anionic, reduced metal complex, the primary product is an interligand adduct, while in the absence of the anion, dihydrodithiins and metal complex decomposition products are preferred. New kinetic (global analysis) and computational (DFT) data explain the crucial role of the anion in suppressing decomposition and catalyzing the formation of the interligand product through a dimetallic complex that appears to catalyze alkene addition across the Ni-S bond, leading to a lower barrier for the interligand adduct.     

Diverse evolution of [[Ph(2)P(CH(2))(n)PPh(2)]Pt(mu-S)(2)Pt[Ph(2)P(CH(2))(n)PPh(2)]] (n = 2, 3) metalloligands in CH(2)Cl(2)

The nucleophilicity of the [Pt(2)S(2)] core in [[Ph(2)P(CH(2))(n)PPh(2)]Pt(mu-S)(2)Pt[Ph(2)P(CH(2))(n)PPh(2)]] (n = 3, dppp (1); n = 2, dppe (2)) metalloligands toward the CH(2)Cl(2) solvent has been thoroughly studied. Complex 1, which has been obtained and characterized by X-ray diffraction, is structurally related to 2 and consists of dinuclear molecules with a hinged [Pt(2)S(2)] central ring. The reaction of 1 and 2 with CH(2)Cl(2) has been followed by means of (31)P, (1)H, and (13)C NMR, electrospray ionization mass spectrometry, and X-ray data. Although both reactions proceed at different rates, the first steps are common and lead to a mixture of the corresponding mononuclear complexes [Pt[Ph(2)P(CH(2))(n)PPh(2)](S(2)CH(2))], n = 3 (7), 2 (8), and [Pt[Ph(2)P(CH(2))(n)PPh(2)]Cl(2)], n = 3 (9), 2 (10). Theoretical calculations give support to the proposed pathway for the disintegration process of the [Pt(2)S(2)] ring. Only in the case of 1, the reaction proceeds further yielding [Pt(2)(dppp)(2)[mu-(SCH(2)SCH(2)S)-S,S']]Cl(2) (11). To confirm the sequence of the reactions leading from 1 and 2 to the final products 9 and 11 or 8 and 10, respectively, complexes 7, 8, and 11 have been synthesized and structurally characterized. Additional experiments have allowed elucidation of the reaction mechanism involved from 7 to 11, and thus, the origin of the CH(2) groups that participate in the expansion of the (SCH(2)S)(2-) ligand in 7 to afford the bridging (SCH(2)SCH(2)S)(2-) ligand in 11 has been established. The X-ray structure of 11 is totally unprecedented and consists of a hinged [(dppp)Pt(mu-S)(2)Pt(dppp)] core capped by a CH(2)SCH(2) fragment.     

Extended X-ray absorption fine structure (EXAFS) characterisation of the hydroformylation of oct-1-ene by dilute Rh-PEt3 catalysts in supercritical carbon dioxide

Dilute EXAFS characterisation has been used to elucidate species involved during the course of the 3 mM Rh-catalysed hydroformylation of oct-1-ene in scCO(2); significant metal clustering occurs with a Rh:P ratio of 1:1 but at a 1:3 ratio, metal clustering is not detected, with the presence of monomer species only.     

Thermodynamics of the complex formation of copper(II) with L-phenylalanine in aqueous ethanol solutions

Constants of the acid dissociation and complexation of L-phenylalanine (HPhe) with copper(II) ions are determined by potentiometry in aqueous ethanol solutions containing 0 to 0.7 molar fraction of alcohol. Changes in the Gibbs energy for the transfer from water to a binary solvent of L-phenylalanine, Phe^? anion, and [CuPhe]⁺ complex are calculated. It is found that the weakening of solvation of the ligand donor groups in solvents with high ethanol contents is accompanied by an increase in the stability of [CuPhe]⁺ complex.     

Thermal decomposition of the [Pt(NH3)4]2+ complex in NaX zeolite

The effect of the calcination procedure on the decomposition of the [Pt(NH₃)₄]²⁺ complex in a cesium-containing NaX zeolite was studied by thermal decomposition accompanied by mass spectrometry and diffuse reflectance spectroscopy, as well as electron paramagnetic resonance and infrared spectroscopy. The decomposition of the complex took place in two steps. Under oxygen, the [Pt(NH₃)₄]²⁺ complex was first converted into the [Pt(NH₃)₂]²⁺ complex in the first step, with predominant nitrogen release. In the second step, corresponding to the decomposition of the remaining two amine ligands, NO was also formed and adsorbed. Oxygen paramagnetic species were also observed. Under He, the decomposition also occurred in two steps with H₂ release.     

Oxidative addition of Ph2TeCl2 to a dimethylplatinum(II) complex: effects of secondary bonding in the platinum-tellurium products

In the first example of oxidative addition of tellurium-halide bonds to a transition-metal complex, Ph(2)TeCl(2) reacts with [PtMe(2)(bu(2)bpy)], 1, bu(2)bpy = 4,4'-di-tert-butyl-2,2'-bipyridine, to give an organoplatinum(IV) complex that can be formulated as an ionic diphenyl telluride complex [PtClMe(2)(TePh(2))(bu(2)bpy)]Cl or as a neutral chlorodiphenyltelluryl complex [PtClMe(2)(TePh(2)Cl)(bu(2)bpy)]; the complex contains an unusually long Te...Cl bond length of 3.43 A. The weakly bound chloride ligand is easily removed by reaction with AgO(3)SCF(3) to give the cationic complex [PtClMe(2)(TePh(2))(bu(2)bpy)](CF(3)SO(3)) in which the triflate anion is not coordinated to tellurium. This complex reacts with a second 1 equiv of AgO(3)SCF(3) to give the aqua complex [PtMe(2)(OH(2))(TePh(2)..O(3)SCF(3))(bu(2)bpy)](CF(3)SO(3)), in which a triflate anion forms secondary bonds with both the aqua and TePh(2) ligands. In these platinum(IV) complexes, the magnitude of the coupling constant (1)J(PtTe) is strongly influenced by the presence of the weakly bonded Te...X groups.     

Cobalamin reduction by dithionite. Evidence for the formation of a six-coordinate cobalamin(II) complex

Evidence for the formation of a unique, six-coordinate cobalamin(II) complex with the anion-radical SO(2)(-) during the reduction of aquacobalamin(III) by sodium dithionite, was obtained from spectrophotometric and EPR measurements. The pK(a) value of the weakly coordinated dimethylbenzimidazole group was found to be 4.8 ± 0.1 at 25 °C.     

Snapshot of the palladium(II)-catalyzed oxidative biaryl bond formation by X-ray analysis of the intermediate diaryl palladium(II) complex

Pd(II) caught in the act: The diaryl Pd(II) intermediate of a Pd(II)-catalyzed oxidative biaryl bond formation proceeding via a double C-H bond activation has been isolated and fully characterized, including an X-ray crystal structure analysis. Stabilization due to chelation by adjacent pivaloyloxy and acetyl groups has allowed the isolation of this long-sought crucial intermediate. On gentle warming, the complex is transformed into a carbazole product, and the catalytically active Pd(II) species is regenerated by oxidation with Cu(II).     

Kinetics and mechanism of styrene hydroalkoxycarbonylation catalyzed by the complex PdCl2(Ph3P)2 in the presence of butanol

The single-factor experiment method was used to study the kinetics of styrene hydrobutoxycarbonylation catalyzed by the complex PdG₂(Ph₃P)₂ in dioxane (383 K, [BuOH] = 1–8 mol/1). The rates of accumulation of the regioisomeric reaction products as empirical functions of CO pressure and concentrations of styrene, triphenylphosphine, and the catalyst were found. The acyl complex (PhC₂H₄CO)PdCl(Ph₃P)₂ was isolated from the reaction mixture. The assumed intermediate of an alcoholate mechanism, the (BuOOC)PdCl(Ph₃P)₂ complex, is not formed by the reaction of PdCl₂(Ph₃P)₂ with CO and butanol. The set of data generally corresponds to a hydride mechanism of styrene hydrocarboxylation, which includes three key intermediates HPdCIL_2-n(CO)_n (n= 0–2). A change in the solvation properties of the reaction medium due to the replacement of water by butanol affects the kinetic scheme of the process.     

Synthesis and reactivity of the aquation product of the antitumor complex trans-[Ru(III)Cl4(indazole)2]-

Aquation of the investigational anticancer drug trans-[Ru(III)Cl4(Hind)2](-) (1, KP1019) results in the formation of mer,trans-[Ru(III)Cl3(Hind)2(H2O)] (2), which was isolated in high yield (85%) and characterized by spectroscopic methods and X-ray crystallography. Dissolution of 2 in acetone, led to its dimerization into [Ru(III)2(mu-Cl)2Cl4(Hind)4] x 2 (Me)2CO (3) in 79% yield, with release of two water molecules. Complex 2 reacts readily with nucleophilic organic molecules, viz., methanol or dimethyl sulfide, at room temperature by replacement of the aqua ligand to give mer,trans-[Ru(III)Cl3(Hind)2(MeOH)] (4) and mer,trans-[Ru(III)Cl3(Hind)2(Me2S)] (5) in 58 and 64% yield, respectively. By reaction of 2 with DMSO at room temperature or dimethyl sulfide at elevated temperatures trans,trans,trans-[Ru(II)Cl2(Hind)2(Me2S)2] (6) and trans,trans,trans-[Ru(II)Cl2(Hind)2(S-DMSO)2] (7) were prepared in 64 and 75% yield, respectively. Dissolution of 2 in acetonitrile or benzonitrile gave rise to mer,trans-[Ru(III)Cl3(Hind)(HNC(Me)ind)] (8a), mer,trans-[Ru(III)Cl3(Hind)(HNC(Ph)ind)] (8b), and trans,trans-[Ru(III)Cl2(HNC(Me)ind)2]Cl (9) in 67, 50, and 23% yield, respectively, upon metal-assisted iminoacylation of indazole, which is unprecedented for ruthenium(III). Furthermore, complex 2 reacts with the DNA-model bases 9-methyladenine (9-meade) and N6,N6-dimethyladenine (6-me2ade) to yield mer,trans-[Ru(III)Cl3(Hind)2(9-meade)] (10) and mer,trans-[Ru(III)Cl3(Hind)2(6-me2ade)] (11) with the purine bases bound to the Ru(III) center via N7 and N3, respectively. Complex 11 represents the first ruthenium complex in which the coordination of the purine ligand N6,N6-dimethyladenine occurs via N3. In addition, the polymer [Na(EtOAc)2Ru(III)(mu-Cl)4(Hind)2]n (12) was crystallized from ethyl acetate/diethyl ether solutions of Na[trans-Ru(III)Cl4(Hind)2] x 1.5 H2O (1a). The reported complexes were characterized by elemental analysis, IR and UV-vis spectroscopy, ESI mass spectrometry, cyclic voltammetry, and X-ray crystallography. Electrochemical investigations give insight into the mechanistic details of the solvolytic behavior of complex 2. The lability of the aqua ligand in 2 suggests that this complex is a potential active species responsible for the high antitumor activity of trans-[Ru(III)Cl4(Hind)2](-).     

Mechanism for the formation and structure of the iodoplatination product of propargyl acid in the Pt(IV)-I−-H2O system

Propargyl alcohol in aqueous Pt(IV) iodide solutions at 10–15°C gives the product of the addition of Pt^IV and iodide to the triple bond, isolated as Pt^IV(CH=Cl-CH₂OH)₂I₂(CH₃OH). The vinyl ligands in this complex are in cis position. The complex decomposes at 80°C to give E,E-2,5-diiodo-2,4-hexadiene-1,6-diol and PtI₂. The E, E structure of the diene indicates trans addition of Pt^IV and I^– to the alkyne in the iodoplatination steps.L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg St., 340114 Donetsk, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 4, pp. 234–237, July–August, 1996. Original article submitted October 17, 1995.     

A diplatinum complex containing one bridging and two chelating dppm ligands. The X-ray structure analysis of [Pt2 (dppm)3] [PF6]2 (dppm = Ph2CH2PPh2)

The dinuclear platinum(I) complex [Pt₂(dppm)₃][PF₆]₂ unexpectedly contains a PtPt bond, one bridging and two chelating dppm ligands, in marked contrast to the related zerovalent platinum compound [Pt₂(dppm)₃].