Ethyl 1-benzyl-1,2,3,3a,4,10b-hexa-hydro-pyrrolo-[2',3':3,4]pyrrolo-[1,2-a]benzimidazole-2-carboxyl-ate.

The title mol-ecule, C(22)H(23)N(3)O(2), was obtained via an intra-molecular cyclo-addition of an azomethine ylide and an alkene tethered by a benzimidazole unit. The benzoimidazole unit is essentially planar, with an r.m.s. deviation of 0.0087 Å from the nine constituent atoms. It has a cis fusion of the two pyrrolidine rings as well as a cis ester appendage. The two pyrrolidine rings rings have envelope conformations. The crystal packing is stabilized by aromatic π-π stacking of parallel benzimidazole ring systems, with a centroid-to-centroid distance of 3.518 (6) Å. Weak inter-molecular C-H⋯O contacts may also play a role in the stability of the packing

A pendant proton shuttle on [Fe4N(CO)12]- alters product selectivity in formate vs. H2 production via the hydride [H-Fe4N(CO)12].

Proton relays are known to increase reaction rates for H2 evolution and lower overpotentials in electrocatalytic reactions. In this report we describe two electrocatalysts, [Fe4N(CO)11(PPh3)]- (1-) which has no proton relay, and hydroxyl-containing [Fe4N(CO)11(Ph2P(CH2)2OH)]- (2-). Solid state structures indicate that these phosphine-substituted clusters are direct analogs of [Fe4N(CO)12]- where one CO ligand has been replaced by a phosphine. We show that the proton relay changes the selectivity of reactions: CO2 is reduced selectively to formate by 1- in the absence of a relay, and protons are reduced to H2 under a CO2 atmosphere by 2-. These results implicate a hydride intermediate in the mechanism of the reactions and demonstrate the importance of controlling proton delivery to control product selectivity. Thermochemical measurements performed using infrared spectroelectrochemistry provided pKa and hydricity values for [HFe4N(CO)11(PPh3)]-, which are 23.7, and 45.5 kcal mol-1, respectively. The pKa of the hydroxyl group in 2- was determined to fall between 29 and 41, and this suggests that the proximity of the proton relay to the active catalytic site plays a significant role in the product selectivity observed, since the acidity alone does not account for the observed results. More generally, this work emphasizes the importance of substrate delivery kinetics in determining the selectivity of CO2 reduction reactions that proceed through metal-hydride intermediates

Miniaturization of Chemical Analysis Systems – A Look into Next Century's Technology or Just a Fashionable Craze?

Miniaturization of already existing techniques in on-line analytical chemistry is an alternative to compound-selective chemical sensors. Theory points in the direction of higher efficiency, faster analysis time, and lower reagent consumption. Micromachining, a well known photolithographic technique for structures in the micrometer range, is introduced and documented with structures as examples for flow injection analysis, electrophoresis, and a detector cell

Ethyl 1-benzyl-1,2,3,3a,4,10b-hexa-hydro-pyrrolo-[2',3':3,4]pyrrolo-[1,2-a]benzimidazole-2-carboxyl-ate.

The title mol-ecule, C(22)H(23)N(3)O(2), was obtained via an intra-molecular cyclo-addition of an azomethine ylide and an alkene tethered by a benzimidazole unit. The benzoimidazole unit is essentially planar, with an r.m.s. deviation of 0.0087 Å from the nine constituent atoms. It has a cis fusion of the two pyrrolidine rings as well as a cis ester appendage. The two pyrrolidine rings rings have envelope conformations. The crystal packing is stabilized by aromatic π-π stacking of parallel benzimidazole ring systems, with a centroid-to-centroid distance of 3.518 (6) Å. Weak inter-molecular C-H⋯O contacts may also play a role in the stability of the packing

H+/AuPPh3+ exchange for the hydride complexes CpMoH(CO)(2)(L) (L=PMe3, PPh3, CO). Formation and structure of [Cp(CO)(2)(PMe3)Mo(AuPPh3)(2)](+)[BF4](-)

International audienceThe reaction of CpMoH(CO)2L with AuPPh3+BF4- in THF at −40 °C proceeds directly to the MoAu2 cluster compounds [CpMo(CO)2L(AuPPh3)2]+BF4- (L = PMe3 (1), PPh3 (2)) with release of protons. A 1:1 reaction leaves 50% of the starting hydride unreacted. At lower temperature, however, the formation of a [CpMo(CO)2(PMe3)(μ-H)(AuPPh3)]+ intermediate is observed. This compound evolves to the cation of 1 and CpMoH(CO)2(PMe3) upon warming and is deprotonated by 2,6-lutidine to afford CpMo(CO)2(PMe3)(AuPPh3). The X-ray structure of 1 can be described as a four-legged piano stool with the PMe3 and the “η2-(AuPPh3)2” ligands occupying relative trans positions. [Cp(CO)2(PMe3)Mo(AuPPh3)2]+[BF4]- (Mr = 1298.41):  monoclinic, space group P21/n, a = 18.1457(13) Å, b = 9.7811(7) Å, c = 26.096(2) Å, β = 105.086(5)°, V = 4472.0(5) Å3, Z = 4. The reaction of CpMoH(CO)2(PMe3) with 3 equiv of AuPPh3+ affords a MoAu3 cluster, [CpMo(CO)2(PMe3)(AuPPh3)3]2+ (3), in good yields under kinetically controlled conditions. Under thermodynamically controlled conditions, 3 dissociates extensively into 1 and free AuPPh3+. It is proposed that the hydride ligand helps build higher nuclearity Mo−Au clusters. The difference in reaction pathways for the interaction of AuPPh3+ with CpMoH(CO)2L when L = PR3 or CO and for the interaction of CpMoH(CO)2(PMe3) with E+ when E = H, Ph3C or AuPPh3 is discussed. The lower acidity and greater aurophilicity of the [CpMo(CO)2L(μ-H)(AuPPh3)]+ intermediate when L = PMe3 favor attack by AuPPh3+ before deprotonation

Expedient one-pot synthesis of indolo[3,2-c]isoquinolines via a base-promoted N-alkylation/tandem cyclization

A transition metal-free, one-pot protocol has been developed for the synthesis of 11H-indolo[3,2-c]isoquinolin-5-amines via the atom economical annulation of ethyl (2-cyanophenyl)carbamates and 2-cyanobenzyl bromides. This method proceeds via sequential N-alkylation and base-promoted cyclization. Optimization data, substrate scope, mechanistic insights, and photoluminescence properties are discussed

Terphenyl Substituted Derivatives of Manganese(II): Distorted Geometries and Resistance to Elimination

Reaction of Li(THF)Ar′MnI 2 2 (Ar′ = C 6H 3-2,6-(C 6H 2-2,6- iPr 3) 2) with LiAr′, LiCCR (R = tBu or Ph), or (C 6H 2-2,4,6- iPr 3)MgBr(THF) 2 afforded the diaryl MnAr′ 2 (1), the alkynyl salts Ar′Mn(CC tBu) 4Li(THF) 3 (2) and Ar′Mn(CCPh) 3Li 3(THF)(Et 2O) 2(μ 3-I) (3), and the manganate salt Li(THF)Ar′Mn(μ-I)(C 6H 2-2,4,6- iPr 3) (4), respectively. Complex 4 reacted with one equivalent of (C 6H 2-2,4,6- iPr 3)MgBr(THF) 2 to afford the homoleptic dimer Mn(C 6H 2-2,4,6- iPr 3)(μ-C 6H 2-2,4,6- iPr 3) 2 (5), which resulted from the displacement of the bulkier Ar′ ligand in preference to the halogen. The reaction of the more crowded Li(THF) Ar*MnI 2 2 (Ar* = C 6H 3-2,6-(C 6H 2-2,4,6- iPr 3) 2) with Li tBu gave complex Ar*Mn tBu (6). Complex 1 is a rare monomeric homoleptic two-coordinate diaryl Mn(ii) complex; while 6 displays no tendency to eliminate β-hydrogens from the tBu group because of the stabilization supplied by Ar*. Compounds 2 and 3 have cubane frameworks, which are constructed from a manganese, three carbons from three acetylide ligands, three lithiums, each coordinated by a donor, plus either a carbon from a further acetylide ligand (2) or an iodide (3). The Mn(ii) atom in 4 has an unusual distorted T-shaped geometry while the dimeric 5 features trigonal planar manganese coordination. The chloride substituted complex Li 2(THF) 3Ar′MnCl 2 2 (7), which has a structure very similar to that of Li(THF)Ar′MnI 2 2, was also prepared for use as a possible starting material. However, its generally lower solubility rendered it less useful than the iodo salt. Complexes 1-7 were characterized by X-ray crystallography and UV-vis spectroscopy. Magnetic studies of 2-4 and 6 showed that they have 3d 5 high-spin configurations. © The Royal Society of Chemistry 2010

Spin-state Crossover with Structural Changes in a Cobalt(II) Organometallic Species: Low-coordinate, First Row, Heteroleptic Amido Transition Metal Aryls. Synthesis and Characterization of Ar′MN(H)Ar# (M = Mn, Fe, Co) (Ar′ = C₆H₃-2,6-(C₆H₃-2,6-ⁱPr₂)₂, Ar# = C₆H₃-2,6-(C₆H₂-2,4,6-Me₃)₂)

The synthesis and characterization of the monomeric aryl transition metal amido complexes Ar′MN(H)Ar# (Ar′ = C6H3-2,6-(C6H3-2,6-iPr2)2, Ar# = C6H3-2,6-(C6H2-2,4,6-Me3)2, M = Mn (1), Fe (2), Co(3a, b)) are reported. The compounds were characterized by X-ray crystallography, electronic and infrared spectroscopy, and magnetic measurements. At about 90 K the complexes 1 and 2 possess quasi-two coordinate geometry with a weak, secondary, M---C interaction involving a flanking aryl ring from an amido group. In contrast, at the same temperature, their cobalt analogue 3a features a strong Co-η6-flanking ring interaction to give an effectively higher coordination geometry. Magnetic studies of 1−3a showed that 1 and 2 have high spin configurations, whereas the cobalt species 3a has a low-spin configuration (S = 1/2). However, 3a undergoes a spin crossover to a high spin (S = 3/2) state 3b near 229 K. An X-ray structural determination above the crossover temperature at 240 K showed that the low temperature structure of 3a had changed to 3b which involves a weak secondary M---C interaction analogous to those in 1 and 2. The complexes 1−3 are very rare examples of heteroleptic quasi-two coordinate open shell transition metal complexes