Cationic Trans Research Articles

Catalytic oxygen evolution from hydrogen peroxide by trans-[Co(en)2Cl2]@InBTB metal-organic framework catalytic system.

The diethylammonium counter-cations of the [Et2NH2]3[In3(BTB)4] metal–organic framework (InBTB MOF, BTB = 1,3,5-benzenetribenzoate) with an anionic framework can be effectively exchanged with cationic trans-[Co(en)2Cl2]+ complex ions through a simple cation-exchange process. The heterogenized trans-[Co(en)2Cl2]+-encapsulated InBTB MOF (trans-[Co(en)2Cl2]@InBTB) catalytic system maintained the activity of the captured trans-[Co(en)2Cl2]+ complex ion for hydrogen peroxide decomposition in aqueous solution under mild reaction conditions. The captured trans-[Co(en)2Cl2]+ complex also exhibited trans–cis isomerization to produce either cis-[Co(en)2Cl2]@InBTB or cis-[Co(en)2(H2O)Cl]@InBTB based on IR spectroscopic investigation. The trans-[Co(en)2Cl2]@InBTB catalytic system showed high recyclability for oxygen evolution from hydrogen peroxide. The catalytic ability of trans-[Co(en)2Cl2]@InBTB was maintained up to seven times of recycling.

Phenylaminyl Cations in the Liquid and Gas-Phase Phototransformation of Protonated Azobenzene

Data on the spectroscopy of photoexcitation of trans-to-cis isomerization and fragmentation of protonated trans-azobenzene (ABH+) in an inert gas atmosphere are analyzed. Results from gas-phase isomerization are compared to ones from a liquid-phase reaction in aqueous sulfuric acid that results in the formation of cyclic benzo[c]cinnoline. There is no cyclization upon gas-phase trans-to-cis isomerization in a rarefied nitrogen medium at T = 300 K, due to the high rate of inverse cis-to-trans isomerization. It is shown that transformations in both phases proceed with the participation of phenylaminyl type cations trans- and cis-ABH+, which are chromogens. Photofragmentation of trans-ABH+ in an atmosphere of cryogenically cooled helium (T = 40 K) proceeds with the formation of fragment phenyl and phenyl diazonium cations and the participation of phenyl amine cations. Mechanisms of photofragmentation are proposed, including intermediate acts with the participation of H atoms formed by dissociation of the NH group. A fast attack of H atoms along the phenyl ring bonded to the NH group results in the breaking of the C–N bond, eliminating the possibility of trans-to-cis isomerization in a cryogenic helium atmosphere.

CNN pincer ruthenium complexes for efficient transfer hydrogenation of biomass-derived carbonyl compounds.

The ligand HCNNOMe (6-(4-methoxyphenyl)-2-aminomethylpyridine) is easily prepared from the commercially available 6-(4-methoxyphenyl)pyridine-2-carbaldehyde by the reaction of hydroxylamine and hydrogenation (H2, 1 atm) with Pd/C. The pincer complexes cis-[RuCl(CNNOMe)(PPh3)2] (1) and [RuCl(CNNOMe)(PP)] (PP = dppb, 2; and dppf, 3) are synthesized from [RuCl2(PPh3)3], HCNNOMe and PP (for 2 and 3) in 2-propanol with NEt3 at reflux and are isolated in 85-93% yield. Carbonylation of 1 (CO, 1 atm) gives [RuCl(CNNOMe)(CO)(PPh3)] (4) (79% yield) which cleanly reacts with Na[BArf4] and PCy3, affording the cationic trans-[Ru(CNNOMe)(CO)(PCy3)(PPh3)][BArf4] (5) (92% yield). These robust pincer complexes display remarkably high catalytic activity in the transfer hydrogenation (TH) of lignocellulosic biomass carbonyl compounds, using 2-propanol at reflux in a basic medium (NaOiPr or K2CO3). Thus, furfural, 5-(hydroxymethyl)furfural and Cyrene are reduced to the corresponding alcohols with 2 and 3, at S/C in the range of 10 000-100 000, within minutes or hours (TOF up to 1 500 000 h-1). The monocarbonyl complex 5 was found to be extremely active in the TH of cinnamaldehyde, vanillin derivatives and ethyl levulinate at S/C in the range of 10 000-50 000. Vanillyl alcohol is also obtained by the TH of vanillin with 5 (S/C = 500) in 2-propanol in the presence of K2CO3.

Conformer-specific photoionization and conformational stabilities of isobutanal revealed by one-photon mass-analyzed threshold ionization (MATI) spectroscopy.

Isobutanal is an aliphatic aldehyde which has been extensively studied as an important intermediate in isomerization reactions as well as in astrochemically relevant models in the interstellar medium. Herein, we report on the conformer-specific photoionization and conformational stabilities of isobutanal utilizing one-photon mass-analyzed threshold ionization (MATI) spectroscopy with vacuum ultraviolet (VUV) pulses. The conformational population of isobutanal under different supersonic expansion conditions was explored to identify the conformers, from which their intrinsic photoionizations can be directly elucidated by measuring the VUV-MATI spectrum corresponding to each conformer. The observed MATI spectra could be analyzed through Franck-Condon simulations at the B3LYP/cc-pVTZ level for the isobutanal conformers, trans and gauche, for which the adiabatic ionization energies were precisely determined to be 78 133 ± 3 cm-1 (9.6873 ± 0.0004 eV) and 78 557 ± 3 cm-1 (9.7398 ± 0.0004 eV), respectively. Notably, only the gauche conformer undergoes a unique geometrical change upon ionization, resulting in the progression of the CHO torsional mode in the MATI spectra. Consequently, we determined the conformational stabilities of isobutanal by conformer-specific photoionization, given that the gauche is more stable than the trans by 162 ± 50 cm-1 in the neutral ground state, while the cationic gauche is less stable than the cationic trans by 262 ± 50 cm-1.

Formation of a Trifluorophosphane Platinum(II) Complex by P-F Bond Activation of Phosphorus Pentafluoride with a Pt0 Complex.

The reaction of PF5 with [(Cy3 P)2 Pt] gave the PF3 complex trans-[(Cy3 P)2 PtF(PF3 )][PF6 ], which was characterized by single-crystal X-ray diffraction, multinuclear NMR spectroscopy, and elemental analysis. To the best of our knowledge, this reaction is the first example of the oxidative addition of a P-F bond to a transition metal and is a rare example of an activation of a main-group-element-fluorine bond by a metal. Relativistic DFT calculations showed that the formation of the Lewis pair [(Cy3 P)2 Pt→PF5 ], which was not observed even at low temperatures, represents the initial step of the reaction. From this key intermediate, the cation trans-[(Cy3 P)2 PtF(PF3 )]+ was furnished by a two-step mechanism involving, successively, a second and a third PF5 molecule.

Rapid Markovnikov addition of HCl to a pendant alkyne: evidence for a quinoidal cumulene

Reaction of cis-[RuCl2(dppm)2]BF4 with TlBF4 and 1,4-diethynyl-benzenes results in the formation of the vinylidene cations trans-[Ru([double bond, length as m-dash]C[double bond, length as m-dash]CH-C6H2-2,5-R2-4-C[triple bond, length as m-dash]CH)Cl(dppm)2](+) (R = H, Me). Subsequent reaction with [N(n)Bu4]Cl results in nucleophilic attack at the coordinated organic ligand, but not at the expected metal-bound carbon atom. Instead, trans-[Ru(C[triple bond, length as m-dash]C-C6H2-2,5-R2-4-CCl[double bond, length as m-dash]CH2)Cl(dppm)2] was generated which, when coupled with DFT calculations, provides evidence for an intermediate quinoidal cumulene complex.

Solid-phase room-temperature decomposition of a complex salt trans-[Rh(γ-Pic) 4Cl 2]MnO 4

Permanganate salt of the complex cation trans-[Rh(γ-Pic) 4Cl 2] + (γ-Pic = γ-picoline) was synthesized. The unusual decomposition reaction of the salt was studied at room temperature. This process has been found to conserve the γ-picoline ligands in cation untouched. A number of transformations in anionic part of salt have been observed. Metallic products of the salt thermal decomposition have been studied.

Complex salts trans-[Rh(β-Pic)4Cl2]X (X = Cl−, ReO 4 − , and ClO 4 − ): Synthesis, crystal structures, and thermal properties

Three novel complex salts containing the cation trans-[Rh(β-Pic)4Cl2]+ with the anions Cl− (I), ReO 4 − (II), and ClO 4 − (III) were obtained and characterized by elemental analysis, X-ray diffraction, NMR spectroscopy, and IR spectroscopy. The complex trans-[Rh(β-Pic)4Cl2]ReO4 crystallizes from DMF as a solvate in which solvent molecules fill the channels formed by the cations and anions. The thermal properties of complexes I, II, and II · DMF were examined by DTA. Final and some intermediate products of the thermolysis were isolated and characterized by physicochemical methods.

Preparation, Characterization, and Structural Systematics of Diphosphane and Diarsane Complexes of Indium(III) Halides

The ligands o-C6H4(PMe2)2 and o-C6H4(AsMe2)2 (L-L) react with anhydrous InX3 (X = Cl, Br, or I) in a 2:1 InX3/ligand ratio to form [InX2(L-L)][InX4] containing distorted tetrahedral cations, established by X-ray crystal structures for L-L = o-C6H4(PMe2)2 (X = Br or I) and o-C6H4(AsMe2)2 (X = I). IR, Raman, and multinuclear NMR ((1)H, (31)P, (115)In) spectroscopy show that these are the only species present in solution in chlorocarbons and in the bulk solids. The products from reactions in a 1:1 or 1:2 molar ratio are more diverse and include the halide-bridged dimers [In2Cl6{o-C6H4(PMe2)2}2] and [In2X6{o-C6H4(AsMe2)2}2] (X = Cl or Br) and the distorted octahedral cation trans-[InBr2{o-C6H4(PMe2)2}2][InBr4]. The neutral complexes partially rearrange in chlorocarbon solution, with multinuclear NMR spectroscopy revealing [InX4](-) among other species. The iodo complexes trans-[InI2(L-L)2][InI4(L-L)] contain rare examples of six-coordinate anions, as authenticated by an X-ray crystal structure for L-L = o-C6H4(PMe2)2. Two species of formula [In2Cl5(L-L)2]n[InCl4]n (L-L = o-C6H4(PMe2)2 and o-C6H4(AsMe2)2) were identified crystallographically and contain polymeric cations with six-coordinate indium centers bonded to one chelating L-L and a terminal chlorine, linked by alternating single and double chlorine bridges into chains. The complicated chemistry of InX3 with these two rigid chelates is contrasted with that of the flexible diphosphane Et2P(CH2)2PEt2, which forms [In2Cl6{Et2P(CH2)2PEt2}2], and with more sterically demanding o-C6H4(PPh2)2 (Sigl et al. Eur. J. Inorg. Chem. 1998, 203-210). The results also contrasted with those found for GaX3 with the same ligands (Cheng et al. Inorg. Chem. 2007, 46, 7215-7223).

Palladium Catalysts for Norbornene Polymerization. A Study by NMR and Calorimetric Methods

Neutral trans-[Pd(C6F5)XL2] (X = Cl, Br) and cationic trans-[Pd(C6F5)L2(NCMe)]BF4 (L = SbPh3, AsPh3, As(C6Cl2F3)Ph2, AsCyPh2, AsMePh2, PPh3) complexes have been studied and tested for norbornene (NB) polymerization and copolymerization with 5-norbornene-2-carboxaldehyde (NB-CHO). The neutral complexes are almost inactive and produce only small amounts of oligomers, but the cationic complexes with arsines and stibines are very good for palladium-catalyzed norbornene polymerization. External coordinating molecules (e.g., ligands or monomers with O-donor groups) compete with the olefin function for the coordination sites on Pd and inhibit the reaction. In spite of this, copolymerization of norbornene and 5-norbornene-2-carboxaldehyde could be achieved, with lower yields and higher incorporations of the functionalized norbornene as the NB:NB-CHO ratio decreases. The complex with the fluorinated arsine AsPh2(C6Cl2F3) is the most active catalyst and allows for easy spectroscopic study of the reacting systems by 19F NMR. Calorimetry provides straightforward monitoring and detection of activation and deactivation processes in polymerization reactions that give insoluble products and cannot be followed by NMR spectroscopy.

Synthesis, characterization and X-ray structure of trans-[(nitro)bis(ethylenediamine)( p-nitrobenzoato) cobalt(III)] [p-nitrobenzoate·p-nitrobenzoic acid

The complex salt trans-bis(ethylenediamine)dinitrocobalt(III) nitrate reacts with p-nitrobenzoic acid in a mixture of water and ethanol to give orange crystals of the novel salt trans-[(nitro) bis(ethylenediamine)( p-nitrobenzoato)cobalt(III)][p-nitrobenzoate·p-nitrobenzoic acid], [Co(en)2(NO2)(4-NO2C6H4CO2)][4-NO2C6H4CO2)·4-NO2C6H4CO2H]. It has been characterized by elemental analysis, spectroscopic techniques and its structure has been determined by single crystal X-ray diffraction methods. The salt is triclinic, space group P with a = 9.5061(9), b = 9.6367(8), c = 16.2781(14) Å, α = 91.66(1), β = 92.91(1), γ = 105.03(1)°, Z = 2, V = 1437.0(2) Å3. The complex consists of trans-[Co(en)2NO2(4-NO2C6H4CO2)]+ cations and hydrogen bonded [4-NO2C6H4CO2·4-NO2C6H4CO2H]– anions. The structure is stabilized by additional hydrogen bonds between cations and anions resulting in a unique acid salt containing the cation trans-[Co(en)2NO2(4-NO2C6H4CO2)]+.

Stereochemical Control of Iron(II) Complexes Containing a Diphosphine Ligand with a Pendant Nitrogen Base

A series of cis and trans Fe(II) complexes containing the diphosphine ligand PNP (where PNP is bis((diethylphosphino)methyl)methylamine) have been prepared and isolated. These include cis-[Fe(PNP)2(CH3CN)2](BF4)2 (3), cis-[Fe(PNP)2(CH3CN)(CO)](BF4)2 (4), trans-[Fe(PNP)(dmpm)(CH3CN)2](BF4)2 (5), trans-Fe(PNP)(dmpm)Cl2 (6), trans-[Fe(PNP)(dmpm)(CO)Cl]2[FeCl4] (7), trans-HFe(PNP)(dmpm)Cl (8), and trans-[HFe(PNP)(dmpm)(CH3CN)]BPh4 (9) (where dmpm is bis(dimethylphosphino)methane). In addition, the cations trans-[HFe(PNP)(dmpm)(CO)]+ (10) and trans-[(H2)Fe(PNP)(dmpm)(H)]+ (11) have been observed in solution. These complexes all possess a pendant base that bridges the two phosphorus atoms of the PNP ligand. A cis geometry is observed for those complexes containing two PNP ligands, whereas a trans geometry is observed for the complexes containing one PNP ligand and one dmpm ligand. The molecular structures of cis-[Fe(PNP)2(CH3CN)(CO)](BPh4)2 and trans-[HFe(PNP)(dmpm)(CH3CN)]BPh4 have been confirmed by X-ray diffraction studies. Protonation of 5, 7, and 10 occurs at the nitrogen atom of the PNP ligand, and pKa values are reported for the corresponding protonated complexes. The formation of the dihydrogen complex [trans-[(H2)Fe(PNP)(dmpm)(H)]+ and the protonated PNHP complex trans-[HFe(PNHP)(dmpm)(CO)]2+ demonstrate that intramolecular heterolytic cleavage of the dihydrogen ligand can be controlled by varying the nature of the ligand trans to the incipient dihydrogen ligand.

Group 14 triple-decker cations

The triple-decker cations trans-[(Cp*Sn)(2)(mu-eta(5):eta(5)-Cp*)](+) and trans-[(Cp*Pb)(2)(mu-eta(5):eta(5)-Cp*)](+) have been prepared and structurally characterized as their [B(C(6)F(5))(4)](-) salts from the reactions of [Cp*M][B(C(6)F(5))(4)](M = Sn, Pb) with the appropriate decamethylmetallocene. Both triple-decker cations adopt a cisoid arrangement of terminal Cp* groups, whereas the two known triple-decker main-group anions possess a transoid arrangement of terminal Cp groups. The reason for this conformational difference has been probed on the basis of DFT calculations.

Pyrrolyl substituted allenylidene complexes of ruthenium.

Pyrrolyl and indolyl substituted allenylidene complexes of ruthenium have been prepared from the trapping of cationic trans-[Cl(dppm)(2)Ru=C=C=C=CH(2)](+) with various pyrroles or N-methylindole. The reaction is rationalized as involving regioselective attack of the organometallic electrophile on the electron-rich heterocycle followed by proton migration to the terminal =CH(2) entity of the intermediate butenynyl substituted sigma-complex. Pyrrolyl substituted allenylidene complexes have spectroscopic and electrochemical properties intermediate between those of amino and aryl substituted congeners and can thus be regarded as vinylogous aminoallenylidene complexes. We present spectroscopic evidence that the pyrrole pi-system is efficiently incorporated into the metallabutatriene chromophore including resonance Raman spectroscopy. According to our results, the respective frontier orbitals are delocalized across the entire ClRuC(3)(pyrrolyl) entity which defies any classification of the individual redox events as metal or ligand centered redox processes. This issue has been specifically addressed by spectroelectrochemistry. The structure of the 1-methylindole-3-yl complex has been determined by X-ray crystallography. Bond parameters along the ruthenium-allenylidene chain are intermediate between those of amino and aryl substituted congeners and support our conclusions drawn from the spectroscopic results. While still electron rich, pyrrolyl substituted allenylidene complexes are easily deprotonated to their conjugate bases, which are substituted butenynyl complexes. This has been exemplified with the tetrahydroindole derived complex 3f.

Organometallic complexes for nonlinear optics. 30.1 electrochromic linear and nonlinear optical properties of alkynylbis(diphosphine)ruthenium complexes.

A combination of cyclic voltammetry, UV-vis-NIR spectroelectrochemistry, time-dependent density functional theory (TD-DFT), and Z-scan measurements employing a modified optically transparent thin-layer electrochemical (OTTLE) cell has been used to identify and assign intense transitions of metal alkynyl complexes at technologically important wavelengths in the oxidized state and to utilize these transitions to demonstrate a facile electrochromic switching of optical nonlinearity. Cyclic voltammetric data for the ruthenium(II) complexes trans-[RuXY(dppe)(2)] [dppe = 1,2-bis(diphenylphosphino)ethane, X = Cl, Y = Cl (1), Ctbd1;CPh (2), 4-Ctbd1;CC(6)H(4)Ctbd1;CPh (3); X = Ctbd1;CPh, Y = Ctbd1;CPh (4), 4-Ctbd1;CC(6)H(4)Ctbd1;CPh (5)] show a quasi-reversible oxidation at 0.50-0.60 V (with respect to ferrocene/ferrocenium 0.56 V), which is assigned to the Ru(II/III) couple. The ruthenium(III) complex cations trans-[RuXY(dppe)(2)](+) were obtained by the in situ oxidation of complexes 1-5 using an OTTLE cell. The UV-vis-NIR optical spectra of 1(+)-5(+) contain a low-energy band in the near-IR region ( approximately 8000-16 000 cm(-)(1)), in contrast to 1-5, which are optically transparent at wavelengths < 22 000 cm(-)(1). TD-DFT calculations have been applied to model systems trans-[RuXY(PH(3))(4)] [X = Cl, Y = Cl, Ctbd1;CPh, or 4-Ctbd1;CC(6)H(4)Ctbd1;CPh; X = Ctbd1;CPh, Y = Ctbd1;CPh or 4-Ctbd1;CC(6)H(4)Ctbd1;CPh] to rationalize the optical spectra of 1-5 and 1(+)-5(+). The important low-energy bands in the electronic spectra of 1(+)-5(+) are assigned to the promotion of an electron from either a chloride p orbital or an ethynyl p orbital to the partially occupied HOMO. These absorption bands have been utilized to demonstrate a facile switching of cubic nonlinear optical (NLO) properties at 12 500 cm(-)(1) (corresponding to the wavelength of maximum transmission in biological materials such as tissue) using the OTTLE cell, the first electrochromic switching of molecular nonlinear refraction and absorption, and the first switching of optical nonlinearity using an electrochemical cell.

Novel Complexes trans(Cl)-[Os(bpy)(CO)(CH3CN)Cl2]n (n = 0, +1; bpy = 2,2′-Bipyridine): Photo- and Electrochemical Syntheses and Comparative Study of Their Bonding and Redox Properties

Photoirradiation of the complex trans(Cl)-[Os(bpy)(CO)2Cl2] in acetonitrile with λ ⩾ 320 nm light gives rise to substitution of a CO ligand, with the formation of trans(Cl)-[Os(bpy)(CO)(CH3CN)Cl2]. The bonding properties and redox reactions of the novel photoproduct were thoroughly investigated by several methods such as nanosecond time-resolved UV/Vis absorption and resonance Raman spectroscopy, cyclic voltammetry, and IR and UV/Vis spectroelectrochemistry. Its one-electron electrochemical oxidation in acetonitrile produces the stable cation trans(Cl)-[Os(bpy)(CO)(CH3CN)Cl2]+. This complex is also formed as the major product during one-electron oxidation of the dicarbonyl precursor trans(Cl)-[Os(bpy)(CO)2Cl2] in acetonitrile at room temperature. By contrast, the initial dicarbonyl oxidation product trans(Cl)-[Os(bpy)(CO)2Cl2]+ remains stable in dry noncoordinating dichloromethane and in butyronitrile at low temperatures. The CO-loss reactivity of trans(Cl)-[Os(bpy)(CO)2Cl2], induced by the partial oxidation of the formally osmium(II) centre, is dramatically lower compared to the corresponding ruthenium(II) complex due to the stronger Os−CO bonds. Replacement of one CO or Cl ligand in trans(Cl)-[Os(bpy)(CO)2Cl2] by a stronger σ-donor CH3CN or isopropoxycarbonyl [−C(O)OiPr] ligands strengthens the Os−CO bond(s) and results in photostable derivatives. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis and molecular structure of four-coordinate neutral and cationic diphenylcarbenerhodium(I) complexes

Abstract Neutral diphenylcarbenerhodium(I) complexes of the general composition trans -[RhX(CPh 2 )(P i Pr 3 ) 2 ] (X=F ( 3 ), OCN ( 4 ), CF 3 CO 2 ( 5 ), PhCO 2 ( 6 ), CF 3 SO 3 ( 7 )) were prepared from the chloro or bromo precursors trans -[RhCl(CPh 2 )(P i Pr 3 ) 2 ] ( 1 ) and trans -[RhBr(CPh 2 )(P i Pr 3 ) 2 ] ( 2 ) by salt metathesis in acetone and isolated in excellent yields. While treatment of 1 with Tl(acac[F 6 ]) afforded the substitution product trans -[Rh(κ 1 -acac[F 6 ])(CPh 2 )(P i Pr 3 ) 2 ] ( 8 ), the corresponding reaction of 1 with Tl(acac) gave the chelate compound [Rh(κ 2 -acac)(CPh 2 )(P i Pr 3 )] ( 9 ) with only one phosphine ligand attached to the metal center. In acetone solution, the triflato complex 7 is in equilibrium with the cation trans -[Rh{OC(CH 3 ) 2 }(CPh 2 )(P i Pr 3 ) 2 ] + which after addition of NaBAr F 4 precipitates as the BAr F 4 salt 11 . The starting material 1 as well as the bis(triphenylphosphine) and bis(triisopropylstibine) analogues 14 and 15 react with pyridine or acetonitrile in the presence of KPF 6 to yield the cationic complexes trans -[Rh(py)(CPh 2 )(PPh 3 ) 2 ]PF 6 ( 16 ) and trans -[Rh(CH 3 CN)(CPh 2 )(L) 2 ]PF 6 (L=P i Pr 3 ( 17 ), Sb i Pr 3 ( 18 )). The BAr F 4 salt of the cation trans -[Rh(CH 3 CN)(CPh 2 )(Sb i Pr 3 ) 2 ] + ( 19 ) was characterized by X-ray crystallography. Compounds 11 , 16 – 19 and the bis(pyridine) derivative cis -[Rh(CPh 2 )(NC 5 H 5 ) 2 (P i Pr 3 )]PF 6 ( 12 ) are the first representatives of four-coordinate cationic diphenylcarbenerhodium(I) complexes.

Synthetic and reactivity studies of some asymmetric dinuclear platinum(II) monohydrido-bridged cations. The neutron diffraction structure of [(Pet3)2(Ph)Pt(μ-H)PtH(PEt3)2][BPh4

The complexes [(PEt3)2(Ar)Pt(μ-H)PtH(PEt3)2][BPh4] (Ar=Ph,2,4-Me2C6H3, 2,4,6-Me3C6H22) were prepared and characterized. Multinuclear, multidimensional NMR studies of these complexes show that, in solution, (i) they exist in rapidly intercoverting conformers which retainn the bent Pt(μ-H)PtH moieties found in the solid state, (ii) the coordination at each platinum atom is square planar, (iii) the two coordination planes are perpendicular to each other and (iv) the aryl group is perpendicular to the coordination plane of the platinum atom to which it is bonded. The complex [PEt3)2Pt(μ-H)PtH(PEt3)2][BPh4] does not react with C2H4 and CH2:CH·CO2Me. At −60°C or above, [(PEt3)2(Ph)Pt(μ-H)PtH(PEt3)2)][BPh4] reacts with CO giving the platinum(II) cations trans-[PtX(CO)(PEt3)2](Ph)∗ (X=H and Ph), and [PtH(PEt3)3]+ and the platinum(0) carbonyl cluster [Pt4(μ-CO)3)4]. The cluster structure of I(PEt3)2(Ph)·Pt(μ-H)PtH(PEt3)2][BPh4, obtained by neutron diffraction, shows that the Pt-H-Pt bond angle in this cation is 125(1)° indicating that the interaction between these three atoms is weak.

Triplet and radical ion properties of (E)-1-styrylpyrene and (E)-3-styrylchrysene

The photophysical and photochemical features of trans isomers of 1-styrylpyrene (StPy) and 3-styrylchrysene (StCh) have been studied in benzene and acetonitrile solution at room temperature, and in 2-methyltetrahydrofuran (MTHF) at low temperatures. The major deactivation process of the excited trans singlet state (1trans*) is fluorescence, (fluorescence quantum yield, ϕF= 0.7–0.9), whereas singlet → triplet (S1→ T1) intersystem crossing is inefficient (as is trans→cis photoisomerization of StPy). Quenching of the 1trans* state by diethylaniline (DEA) leads to an exciplex fluorescence in benzene. Fluorescence quenching by 4-bromodimethylaniline (via the external heavy-atom effect) enhances the formation of the trans triplet configuration (3trans*). In acetonitrile, the radical anion (trans˙–) of the two 1,2-diarylethenes was observed by optical and conductometric detection in the presence of DEA. Photoionization with a low quantum yield (ϕPI= 0.007–0.015) was observed in neat acetonitrile. The properties of the radical cation (trans˙+) were studied after photoinduced electron transfer from 1trans* to 1,4-dicyanobenzene (DCNB). The effect of temperature on the yield and decay kinetics of 3trans* was analysed for StCh in MTHF and a mechanism is proposed for the trans→cis photoisomerization via an upper excited triplet state.

Synthesis and characterization of phenylimidorhenium(V) compounds containing polypyridyl ligands. Crystal structures of mer-[Re(NPh)Cl3(bipy)], trans-[Re(NPh)(OEt)(bipy)2][PF6]2and trans-[Re(NPh)Cl2(terpy)]PF6(bipy = 2,2′-bipyridine, terpy = 2,2′:6′,2″-terpyridine)

The reaction between mer-[Re(O)Cl3(L–L)][L–L = 2,2′-bipyridine (bipy) or 4,4′-dimethyl-2,2′-bipyridine] and aniline in refluxing o-xylene gave phenylimido compounds formulated as mer-[Re(NPh)Cl3(L–L). These compounds do not react with an alcohol (ROH) to form alkoxyimido compounds of the type cis-[Re(NPh)(OR)Cl2(L–L), but in the presence of an excess of the polypyridyl ligand, salts of the cation trans-[Re(NPh)(OEt)(L–L)2]2+ were obtained. When salts of trans-[Re(NPh)(OEt)(L–L)2]2+ were dissolved in MeCN solutions containing a few drops of concentrated hydrochloric acid rapid reaction occurred that resulted in the isolation of mer-[Re(NPh)Cl3(L–L)]. The salt trans-[Re(NPh)Cl2(terpy)]PF6 was prepared from the reaction between mer-trans-[Re(NPh)Cl3(PPh3)2], and 2,2′:6′2″-terpyridine (terpy) in refluxing ethanol. The spectroscopic and electrochemical properties of these compounds were investigated and the structures of mer-[Re(NPh)Cl3(bipy)], trans-[Re(NPh)(OEt)(bipy)2][PF6]2 and trans-[Re(NPh)Cl2(terpy)]PF6 determined by X-ray crystallography.