No abstract

Iridium complexes relevant to the catalytic enantioselective hydrogenation of 2-methyl-6-ethylphenyl-1'-methyl-2'-methoxyethylimine (MEA-imine, 1) in the Syngenta Metolachlor (3) process were prepared and characterized. Reaction of the diphosphane (S)-1-[(R)-2-(diphenylphosphanyl)ferrocenyl]ethyldi(3,5-xylyl)phosphane ((S)-(R)-Xyliphos, (S)-(R)-4) with [Ir(2)(micro-Cl)(2)(cod)(2)] (cod=1,5-cyclooctadiene) afforded [Ir(Cl)(cod)[(S)-(R)-4]] (7), which reacted with AgBF(4) to form [Ir(cod)[(S)-(R)-4]]BF(4) (8). Complexes 7 and 8 reacted with iodide to yield [Ir(I)(cod)[(S)-(R)-4]] (9). When 9 was treated with one and two equivalents of HBF(4), two isomers of the cationic Ir(III) iodo hydrido complex [Ir(I)(H)(cod)[(S)-(R)-4]]BF(4) were solated (10 and 11, respectively). Complex 9 was oxidized with one equivalent of I(2) to give the iodo-bridged dinuclear species [Ir(2)I(2)(micro-I)(3)[(S)-(R)-4](2))]I (12). [Ir(2)(micro-Cl)(2)(coe)(4)] (coe=cyclooctene) reacted with (S)-(R)-4 to yield the chloro-bridged dinuclear complex [Ir(2)(micro-Cl)(2)[(S)-(R)-4](2)] (13). Complexes 7-12 were structurally characterized by single-crystal X-ray diffraction and tested as single-component catalyst precursors for enantioselective hydrogenation of MEA-imine. Complex 10 and dinuclear complex 12 gave the best catalytic results. Efforts were also directed at isolating substrate- or product-catalyst adducts: Treatment of 8 with 2,6-dimethylphenyl-1'-methyl-2'-methoxyethylimine (DMA-imine, 14, a model for 1) under H(2) allowed four isomers of [Ir(H)(2)[(S)-(R)-4](14)]BF(4) (18-21) to be isolated. These analytically pure isomers were fully characterized by 2D NMR techniques. X-ray structural analysis of an Ir(I)-imine adduct, namely, [Ir(C(2)H(4))(2)(14)]BF(4) (25), which was prepared by reacting [IrCl(C(2)H(4))(4)] with [Ag(14)(2)]BF(4) (16), confirmed the kappa(2) coordination mode of imine 14.

N-Dichlorophosphanyldibenzo[b,f]azepine (6) reacted with (−)-2,3-O-isopropylidene-d-threitol, (R)-taddol, (R,R)-diethyltartrate, (R,R)-diethyltartrate, (S)-binaphthol, α,α-diphenyl-l-prolinol, and (S)-proline to form the corresponding chiral P-alkene ligands 7−12. These ligands were then used to synthesize dinuclear chloro-bridged Rh(I) complexes 13−18 with the general formula [Rh(μ-Cl)(P-alkene)]2. It was shown by X-ray diffraction analyses that these P-alkenes indeed act as bidentate ligands for Rh(I). Furthermore, the crystal structures revealed a change in the hybridization state of the dibenzazepine N atom, passing from sp2 in the free ligand to sp3 when coordinated to Rh in a bidentate fashion, thus modifying the bite angle of the ligands. The Rh complexes 16 and 18, bearing the (S)-binaphthol-derived ligand 10 and the α,α-diphenyl-l-prolinol-derived ligand 12, respectively, were shown to be active and enantioselective catalysts for the 1,4 addition of arylboronic acids to enones. At 80 °C turnover numbers of up to 61 and enantiomeric excesses of up to 92% were observed.

A chiral iridium(I) diphosphine complex efficiently catalyses the unprecedented ortho-alkylation of phenol with norbornene in the absence of solvent leading to the formation of one and two C-C bonds.

P e n t y l p y r i d i n i u m T r i b r o m i d eAbstract: The synthesis and characterization of the room temperature ionic liquid pentylpyridinium tribromide (2) is described. Tribromide 2 was used as a vapor pressure free bromine analogue for the bromination of ketones, aromatics, alkenes, and alkynes. The brominations were carried out in the absence of organic solvents and in most cases the only extraction solvent needed was water. Selectivities and reactivities were shown to be superior to current protocols. The spent reagent pentylpyridinium bromide (1) was easily recycled.Key words: pentylpyridinium tribromide, room temperature ionic liquid, solvent-free brominations Bromine is widely used for the functionalization of organic and inorganic substrates. However, bromine is a hazardous chemical that is difficult to manipulate due to its toxicity and high vapor pressure. Half a century ago, Djerassi and Scholz introduced the pyridinium hydrobromide perbromide (PHP) salt as an alternative, readily weighable, and selective ketone brominating agent. 1 PHP proved also useful for the bromination of alkenes 2 and aromatics, 3 as catalyst for aziridinations, 4 and for the stereoselective alkene bromination in water suspension. 5 On the other hand, alkylpyridinium salts are well-documented and commercially available room temperature ionic liquids (RTIL's). The combination of an alkylpyridinium cation with the tribromide anion should therefore lead to a RTIL bromine analogue. Brominations in classic RTIL media, such as [BMI]PF 6 , which replace environmentally problematic chlorinated solvents, have been recently demonstrated. 6 We disclose here the synthesis, full characterization, and reactivity of pentylpyridinium tribromide (2), a proton free RTIL bromine analogue that does not have any measurable vapor pressure. Furthermore, 2 is a rare example of a RTIL which integrates the function of solvent and reagent. 7Adding molecular bromine dropwise under mechanical stirring to powdered pentylpyridinium bromide (1) 8 exothermically formed the red liquid pentylpyridinium tribromide (2) 9 (Equation 1) which displayed a density of 1.79 g cm -3 and a viscosity of h 35-500 = 0.038 Pa s at 25 °C (constant over a shear velocity range between 35 s -1 and 500 s -1 ). 10 The UV-Vis spectrum showed a characteristic absorption at l = 268 nm (e = 1.14 × 10 4 L mol -1 cm -1 ). The conductivity of the neat RTIL 2 was k = 8.09 mS cm -1 .Excess bromine was likewise readily absorbed by 2. However, under high vacuum the excess was efficiently removed leaving pure 2. Even after prolonged heating at 70°C under vacuum (<10 -2 mmHg), 2 was recovered unaltered without loss of bromine. The ionic nature of 2 thus effectively eliminates any noxious residual bromine vapor pressure. 11 RTIL 2 is hydrophobic forming two phases with water contrasting the highly hydrophilic and hygroscopic character of salt 1. Likewise, it forms two phases with CHCl 3 , alkanes, aromatic solvents, and ethers. RTIL 2 also showed an extended shelf life of at least 3 month...

The dibenzo[b,f ]azepinate (DBAP) complexes (DBAP)Li•(THF) 3 , (DBAP) 2 Mg•(THF) 2 , and (DBAP) 2 Ca•(THF) 3 could be isolated as highly air-sensitive compounds in yields of 93%, 72%, and 48%, respectively. Crystal structures of these THF adducts reveal monomeric complexes in which the degree of ring puckering depends on the nature of the metal. The most extreme deviation from planarity is found for the most covalent bound metal, Mg, but in all cases no interaction between the metal and the azepine CC bond is observed. The THF-free complex [(DBAP) 2 Mg] 2 , which could be obtained in 77% yield, crystallizes as an unusual dimer with three bridging and one terminal DBAP ligand. The bridging DBAP ligands are highly bent and span a cavity in which a Mg 2+ ion is bound through three alkene−Mg interactions with an average Mg•••C distance of 2.794(3) Å. Theoretical calculations support these contacts. A combination of AIM and NPA analyses shows polarization of the alkene π-electron density toward the metal (vertical polarization) but also demonstrates a polarization of electron density toward the C atom closest to Mg (horizontal polarization). Such metal−alkene interactions and implicit CC bond polarization are key features in main group metal catalyzed alkene conversions.

The reactivity of the dinuclear Ir(I) complexes cis-and trans-[Ir 2 (µ-Cl) toward O-H and C-H bonds has been studied (1 was previously shown to be a catalyst precursor for the asymmetric addition of aniline to norbornene, via N-H activation). Compound 1 undergoes clean oxidative addition of water in toluene, affording a mixture of two isomeric, dinuclear hydroxo-bridged Ir(III) complexes. Isomerization to a single product, syn-trans-[((R)-(S)-PPFPPh 2 ) 2 Ir 2 Cl 2 (H) 2 (µ-OH) 2 ] (3), takes place upon dissolution in THF. syn-trans-3 has been characterized by X-ray diffraction. Reaction of 1 with 2,6-dimethylaniline affords the corresponding sp 3 C-H activation product 5, the crystal structure of which has been determined. Both oxidative addition reactions are (partly) reversible at high temperature.

Abstract:The direct electro-reduction of CO 2 to functional molecules like ethene is a highly desirable variant of CO 2 utilization. The formation of, for example, ethene from CO 2 is a multistep electrochemical process going through various intermediates. As these intermediates are organic species, the CO 2 reducing electro-catalyst has to be competent for a variety of organic functional group transformations to yield the final product. In this work, the activity of an in situ-grown nano-structured copper catalyst towards a variety of organic functional group conversions was studied. The model reagents were selected from the product spectrum of actual CO 2 reduction reaction (CO 2 RR) experiments and from proposals in the literature. The CO 2 bulk electrolysis benchmark was conducted at 170 mAcm −2 current density with up to 43% Faradaic Efficiency (FE) for ethene and 23% FE for ethanol simultaneously. To assure relevance for application-oriented conditions, the reactivity screening was conducted at elevated current densities and, thus, overpotentials. The found reactivity pattern was then also transferred to the CO reduction reaction (CORR) under benchmark conditions yielding additional insights. The results suggest that at high current density/high overpotential conditions, also other ethene formation pathways apart from acetaldehyde reduction such as CH 2 dimerization are present. A new suggestion for a high current density mechanism will be presented, which is in agreement with the experimental observations and the found activity pattern of copper cathodes toward organic functional group conversion.