Studies on the Reaction of Iron(II) with NO in a Noncoordinating Ionic Liquid.

In an earlier study we investigated the reaction of iron(II) chloride with NO in a strongly coordinating ionic liquid 1-ethyl-3-methylimidazolium dicyanamide [emim][dca] and showed that the actual reactive species in solution was [Fe(II)(dca)5Cl](4-). For the present report we investigated in detail how this reaction could proceed in a noncoordinating ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate [emim][OTf]. The donor ability of OTf(-) is much lower than that of dca(-), such that the solubility of FeCl2 in [emim][OTf] strongly depended on other donors like water or chloride ions present or added to the ionic liquid. On increasing the chloride concentration in [emim][OTf], the tetrachloridoferrate complex [emim]2[FeCl4] was formed, as verified by X-ray crystallography. This complex undergoes reversible binding of NO, for which the UV-vis spectral characteristics of the green-brown nitrosyl product resembled that found for the corresponding nitrosyl complexes formed in water and [emim][dca] as solvents. A detailed analysis of the spectra revealed that the {Fe-NO}(7) species has Fe(II)-NO(•) character in contrast to Fe(III)-NO(-) as found for the other solvents. The formation constant, however, is much higher than in [emim][dca], lying closer to the value found for water as solvent. Surprisingly, the Mössbauer spectrum found in [emim][OTf] is very unusual and unsimilar to that found in water and [emim][dca] as solvents, pointing at a different electron density distribution between Fe and NO in {Fe-NO}.7 First, the high isomer shift points to the presence of iron(II) species in solution, thus indicating that upon NO binding no oxidation to iron(III) occurs. Second, the negligible quadrupole splitting suggests a high local symmetry around the iron center. The nitrosyl product is suggested to be [Fe(II)Cl3NO](-), which is supported by electron paramagnetic resonance (EPR) and IR measurements. The nature of the Fe(II) complexes formed in [emim][OTf] depends on the additives required to dissolve FeCl2 in this ionic liquid.

Why do cationic hydridoiridium(III) complexes with beta-aminophosphane ligands favour the transfer hydrogenation of ketones over the direct "H2-hydrogenation"?--A computational approach.

Density functional theory and ab initio molecular orbital calculations show that the observed inability of cationic hydridoiridium(III) complexes with beta-aminophosphane ligands to catalyse the direct hydrogenation of carbonyl compounds with dihydrogen ("H2-hydrogenation") in contrast to their ruthenium(II) equivalents is due to the inability of H2 to displace a coordinated solvent molecule from an intermediate hydrido complex.

syn-Tri-mu-chlorido-bis{[(R,R)/(S,S)-2,2'-bis(diphenylphosphino)-1,1'-biphenyl]hydridoiridium(III)} tetrafluoridoborate dichloromethane disolvate.

In the structure of the title compound, [Ir(2)Cl(3)H(2)(C(36)H(28)P(2))(2)]BF(4) x 2 CH(2)Cl(2), the bimetallic cation features a confacial bioctahedral structure that is held together by three bridging chloride ions and is very close to C(2) symmetric. The hydrides are in a syn orientation (trans to the same halide bridge), and the chelating bis(phosphine) atropisomers display a racemic (R,R)/(S,S) configuration. Because of the high trans-bond-weakening influence of the hydride ligands, the Ir-Cl bonds trans to Ir-H [2.5262 (7) and 2.5365 (7) A] are significantly longer than those opposite the Ir-P linkages [2.4287 (7)-2.4672 (8) A]. The Ir-P distances vary between 2.2464 (9) and 2.2565 (8) A. This study illustrates the usefulness of sterically demanding biaryl-based P(2) ligands in the synthesis of halide-bridged Ir(2) complexes, which are valuable precursors of versatile catalysts for homogeneous C=O hydrogenation.

The impact of different chelating leaving groups on the substitution kinetics of mononuclear Pt(II)(1,2-trans-R,R-diaminocyclohexane)(X-Y) complexes.

A set of three oxaliplatin derivatives containing 1,2-trans-R,R-diaminocyclohexane (dach) as a spectator ligand and different chelating leaving groups X-Y, viz., [Pt(dach)(O,O-cyclobutane-1,1-dicarboxylate)], or Pt(dach)(CBDCA), [Pt(dach)(N,O-glycine)]+, or Pt(dach)(gly), and [Pt(dach)(N,S-methionine)]+, or Pt(dach)(L-Met), where L-Met is L-methionine, were synthesized and the crystal structure of Pt(dach)(gly) was determined by X-ray diffraction. The effect of the leaving group on the reactivity of the resulting Pt(II) complexes was studied for the nucleophiles thiourea, glutathione (GSH) and L-Met under pseudo-first-order conditions as a function of nucleophile concentration and temperature, using UV-vis spectrophotometric techniques. 1H NMR spectroscopy was used to follow the substitution of the leaving group by guanosine 5'-monophosphate (5'-GMP2-) under second-order conditions. The rate constants indicate for all reactions a direct substitution of the X-Y chelate by the selected nucleophiles, thereby showing that the nature of the chelate, viz., O-O (CBDCA2-), N-O (glycine) or S-N (L-Met), respectively, plays an important role in the kinetic and mechanistic behavior of the Pt(II) complex. The k1 values for the reaction with thiourea, L-Met, GSH and 5'-GMP2- were found to be as follows (10(3) k1, 37.5 degrees C, M(-1) s(-1)): Pt(dach)(CBDCA) 61 +/- 2, 21.6 +/- 0.1, 23 +/- 1, 0.352 +/- 0.002; Pt(dach)(gly) 82 +/- 3, 6.2 +/- 0.2, 37 +/- 1, 1.77 +/- 0.01; Pt(dach)(L-Met) (thiourea, GSH) 62 +/- 2, 24 +/- 1. The activation parameters for all reactions studied suggest an associative substitution mechanism.

Synthesis of the new, cubane-like W3S4Co cluster core. Completion of the homologous series [(eta5-Cp')3M3S4Co(CO)] (M = Cr, Mo, W).

Reaction between the cluster salts [(eta(5)-Cp')(3)M(3)S(4)][pts] (M = Mo, W; Cp' = methylcyclopentadienyl; pts = p-toluenesulfonate) and [Co(2)(CO)(8)] yielded the electroneutral clusters [(eta(5)-Cp')(3)M(3)S(4)Co(CO)]. The molecular structure of [(eta(5)-Cp')(3)W(3)S(4)Co(CO)] was determined by single-crystal X-ray diffraction methods. The unprecedented 60 electron W(3)S(4)Co cluster completes a homologous series of heterobimetallic clusters, [(eta(5)-Cp')(3)M(3)S(4)Co(CO)] (M = Cr, Mo, W), containing a cubane-like core motif.

Cyclometalated analogues of platinum terpyridine complexes: kinetic study of the strong sigma-donor cis and trans effects of carbon in the presence of a pi-acceptor ligand backbone.

The substitution kinetics of the complexes [Pt(N-N-C)Cl] (N-N-CH = 6-phenyl-2,2'-bipyridine), [Pt(N-C-N)Cl] (N-CH-N = 1,3-di(2-pyridyl)benzene), and [Pt(N-N-N)Cl]Cl (N-N-N = 2,2':6',2' '-terpyridine) with the nucleophiles Br(-), I(-), and, for the first two complexes, also thiourea, N,N-dimethylthiourea, and N,N,N',N'-tetramethylthiourea, have been studied in methanol as solvent. In case of the thioureas, the activation parameters DeltaH, DeltaS, and DeltaV were also determined from the temperature and pressure dependence of the reactions. Two crystal structures of [Pt(N-N-C)Cl] were determined (yellow and red polymorphs); the intense red color of the latter polymorph results from Pt-Pt interactions (Pt-Pt distance = 3.366 A). The data enable an analysis of the cis and trans effects and the influence of the strong sigma-donor carbon in the presence of an electron withdrawing pi-acceptor ligand backbone. The results indicate that the intrinsic reactivity is enhanced greatly by the labilizing effect of the trans carbon donor, but the nucleophilic discrimination is dramatically reduced due to the decrease in electrophilicity on the metal center. However, although the electron withdrawing pi-acceptor effect is partly counteracted by the sigma-donor effect, the complex still benefits from a higher nucleophilic discrimination than in the comparable Pt(II) trans carbon donor complexes, where no or fewer pi-acceptors are present. In the case of the cis carbon donor complex, the intrinsic reactivity remains unchanged, but the nucleophilic discrimination is reduced and leads to a reduced reactivity of the [Pt(N-N-C)Cl] complex in comparison to [Pt(N-N-N)Cl]Cl. On the basis of these results, a more detailed treatment of the nature of the cis effect is offered.

6-(2-Hydroxybenzoyl)-5-(pyrrol-2-yl)-3H-pyrrolizine.

The title compound, 2-hydroxyphenyl 5-(pyrrol-2-yl)-3H-pyrrolizin-6-yl ketone, C(18)H(14)N(2)O(2), was isolated from the base-catalyzed 1:2 condensation of 2-hydroxyacetophenone with pyrrole-2-carbaldehyde. The pyrrole N-H and hydroxybenzoyl O-H groups are hydrogen bonded to the benzoyl O atom. The allylic C=C double bond of the 3H-pyrrolizine system is located between ring positions 1 and 2, the C atom at position 3 (adjacent to the N atom) being single bonded.

A complete family of isostructural cluster compounds with cubane-like M(3)S(4)M' cores (M = Mo, W; M' = Ni, Pd, Pt): comparative crystallography and electrochemistry.

By reaction of the geometrically incomplete cubane-like clusters [(eta(5)-Cp')(3)Mo(3)S(4))][pts] and [(eta(5)-Cp')(3)W(3)S(4)][pts] (Cp' = methylcyclopentadienyl; pts = p-toluenesulfonate) with group 10 alkene complexes, three new heterobimetallic clusters with cubane-like cluster cores were isolated: [(eta(5)-Cp')(3)W(3)S(4)M'(PPh(3))][pts] ([5][pts], M' = Pd; [6][pts], M' = Pt); [(eta(5)-Cp')(3)Mo(3)S(4)Ni(AsPh(3))][pts] ([7][pts]). The compounds [5][pts]-[7][pts] are completing the extensive series of clusters [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] (M = Mo, W; M' = Ni, Pd, Pt; E = P, As) which allows the consequences of replacing a single type of atom on structural and NMR and UV/vis spectroscopic as well as electrochemical properties to be determined. Single-crystal X-ray structure determinations of [5][pts]-[7][pts] revealed that [5][pts] was not isomorphous to the other members of the series [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] due to distinctly different cell parameters, which in the molecular structure of [5](+) is reflected in a slightly different orientation of the PPh(3) ligand. Electrochemical measurements on the series showed that the Mo-based clusters were more difficult to oxidize than their W-based analogues. The Pd-containing clusters underwent two-electron oxidation processes, whereas the Ni- and Pt-containing clusters underwent two separated one-electron oxidation processes.