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The formation of hydrido rhodium(I) complexes of the type [HRh(CO)3L] and [HRh(CO)2L2] from [Rh(acac)(CO)2]/L (L: bulky monophosphite ligand) requires a ligand‐to‐rhodium ratio [L]/[Rh] > 10 to prevent the possible partial generation of [Rh6(CO)16] under typical hydroformylation conditions. Significant fractions of formed [Rh6(CO)16] at lower ratios of [L]/[Rh] can be reactivated towards the hydrido complexes after the addition of the monophosphite ligand in the presence of synthesis gas. It was also found that [Rh6(CO)16] can be transformed by treatment with an excess of monophosphite ligand under inert gas to form a mononuclear complex of the type [L`Rh(CO)L] with an ortho‐metallated ligand. [ABSTRACT FROM AUTHOR]

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Copyright of Nachrichten aus der Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A hydroxy phosphonite was found to be unstable during the catalyst preformation routine applied towards a rhodium olefin hydroformylation catalyst. C—P bond cleavage occurred when the phosphonite was reacted with [(acac)Rh(1,5‐COD)] (acac is acetyl acetate and 1,5‐COD is cycloocta‐1,5‐diene) at 80 °C and 20 bar of CO/H2. As a result, a nearly planar six‐membered ring structure consisting of two rhodium(I) cations and two bridging phosphorous acid diester anions was formed, namely bis[μ‐(4,8‐di‐tert‐butyl‐2,10‐dimethoxydibenzo[d,f][1,3,2]dioxaphosphepin‐6‐yl)oxy]‐1:2κ2P:O;1:2κ2O:P‐bis{[6‐([1,1′‐biphenyl]‐2‐yloxy)‐4,8‐di‐tert‐butyl‐2,10‐dimethoxydibenzo[d,f][1,3,2]dioxaphosphepine‐κP]carbonylrhodium(I)} toluene tetrasolvate, [Rh2(C22H28O5P)2(C34H37O5P)2(CO)2]·4C7H8. Further coordination of phosphite and of carbonyl groups resulted in 16‐electron rhodium centres. The crystal structure of a rhodium complex containing fragments and rearrangement products of a hydroxy phosphonite is described. [ABSTRACT FROM AUTHOR]

The racemization tendency of acyclic P‐chirogenic phosphanes is investigated experimentally and theoretically. Results of these investigations are important for the construction and use of P‐chirogenic ligands and organocatalysts frequently used in asymmetric syntheses. Proof is given that triaryl phosphanes undergo easier racemization than compounds in which the phosphorus atom is linked to alkyl substituents. Interestingly, bulky ortho aryl substituents have only a marginal effect, whereas P‐naphthyl rings destabilize the compound. [ABSTRACT FROM AUTHOR]

The highly chemoselective hydrogenation of neral affording citronellal is described. The reaction has been conducted with homogeneous rhodium complexes. Among the set of ancillary diphosphane ligands tested, Xantphos was found to be superior. The relevant precatalyst has been generated from neutral metal sources such as Rh(acac)(CO)2 or the carbon monoxide-free rhodium source Rh(acac)(cod) in the absence of any base. A high activity and chemoselectivity in favor of the desired citronellal is achieved at 0.1 MPa and room temperature. Under the same conditions, geranial is also reduced to citronellal. The addition of carbon monoxide to the hydrogen stream as used in an industrial process is not necessary. [ABSTRACT FROM AUTHOR]

A series of diphosphoramidites has been synthetized with a piperazine, homopiperazine, and an acyclic 1,2-diamine unit in the backbone. New compounds were tested alongside related N-acyl phosphoramidites as ligands in the Rh-catalyzed hydroformylation of n-octenes to investigate their influence on the activity and regioselectivity. A subsequent study of their hydrolysis stability revealed that the most stable ligands induced the highest activity in the catalytic reaction. [ABSTRACT FROM AUTHOR]

Homogeneous ruthenium complexes modified by imidazole-substituted monophosphines as catalysts for various highly efficient hydroformylation reactions were characterized by in situ IR spectroscopy under reaction conditions and NMR spectroscopy. A proper protocol for the preformation reaction from [Ru3(CO)12] is decisive to prevent the formation of inactive ligand-modified polynuclear complexes. During catalysis, ligand-modified mononuclear ruthenium(0) carbonyls were detected as resting states. Changes in the ligand structure have a crucial impact on the coordination behavior of the ligand and consequently on the catalytic performance. The substitution of CO by a nitrogen atom of the imidazolyl moiety in the ligand is not a general feature, but it takes place when structural prerequisites of the ligand are fulfilled. [ABSTRACT FROM AUTHOR]

A general and highly chemo- and regioselective synthesis of ketones from olefins by domino hydroformylation/aldol condensation/hydrogenation reaction has been developed. A variety of olefins are efficiently converted into various ketones in good to excellent yields and regioselectivities in the presence of a specific rhodium phosphine/base-acid catalyst system. [ABSTRACT FROM AUTHOR]

The influence of carbon monoxide concentration on the kinetics of the hydroformylation of 3,3-dimethyl-1-butene with a phosphite-modified rhodium catalyst has been studied for the pressure range p(CO)=0.20-3.83 MPa. Highly resolved time-dependent concentration profiles of the organometallic intermediates were derived from IR spectroscopic data collected in situ for the entire olefin-conversion range. The dynamics of the catalyst and organic components are described by enzyme-type kinetics with competitive and uncompetitive inhibition reactions involving carbon monoxide taken into account. Saturation of the alkyl-rhodium intermediates with carbon monoxide as a cosubstrate occurs between 1.5 and 2 MPa of carbon monoxide pressure, which brings about a convergence of aldehyde regioselectivity. Hydrogenolysis of the acyl intermediate is fast at 30 °C and low pressure of p(CO)=0.2 MPa, but is of minus first order with respect to the solution concentration of carbon monoxide. Resting 18-electron hydrido and acyl complexes that correspond to early and late rate-determining states, respectively, coexist as long as the conversion of the substrate is not complete. [ABSTRACT FROM AUTHOR]

Metal (Co, Rh, Pt/Sn)-catalyzed homogeneous hydroformylation reactions produce aldehydes, acetals, and alcohols, respectively, which are important aroma compounds that are used as ingredients in numerous perfumes, flavors, and foodstuffs. Indeed, not only the products, but also several olefins that are used as starting material have a pleasant scent. In this review, different methods for hydroformylation reactions are discusses, together with the typical aroma properties of the educts and products. We will show that hydroformylation is one of the most attractive synthetic methods in this area. Interestingly, its value seems to be rather underestimated and a re-evaluation may be necessary. [ABSTRACT FROM AUTHOR]

The preparation of racemic or enantioenriched propane-1,2-diol from dilactides, oligolactides, or poly- L-lactic acid (PLLA) is described. The transformation is carried out as tandem reactions in MeOH, covering hydrolysis and subsequent hydrogenation by using copper chromite as a catalyst. The starting material present undesired side products of the PLLA synthesis or PLLA waste. [ABSTRACT FROM AUTHOR]

The multicomponent factorization of multivariate data often results in nonunique solutions. The so-called rotational ambiguity paraphrases the existence of multiple solutions that can be represented by the area of feasible solutions (AFS). The AFS is a bounded set that may consist of isolated subsets. The numerical computation of the AFS is well understood for two-component systems and is an expensive numerical process for three-component systems. In this paper, a new fast and accurate algorithm is suggested that is based on the inflation of polygons. Starting with an initial triangle located in a topologically connected subset of the AFS, an automatic extrusion algorithm is used to form a sequence of growing polygons that approximate the AFS from the interior. The polygon inflation algorithm can be generalized to systems with more than three components. The efficiency of this algorithm is demonstrated for a model problem including noise and a multicomponent chemical reaction system. Further, the method is compared with the recent triangle-boundary-enclosing scheme of Golshan, Abdollahi, and Maeder (Anal. Chem. 2011, 83, 836-841). Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Multivariate curve resolution techniques are powerful tools to extract from sequences of spectra of a chemical reaction system the number of independent chemical components, their associated spectra, and the concentration profiles in time. Usually, these solutions are not unique because of the so-called rotational ambiguity. In the present work, we reduce the non-uniqueness by enforcing the consistency of the computed concentration profiles with a given kinetic model. Traditionally, the kinetic modeling is realized in a separate step, which follows the multivariate curve resolution procedure. In contrast to this, we consider a hybrid approach that combines the model-free curve resolution technique with the model-based kinetic modeling in an overall optimization. For a two-component model problem, the range of possible solutions is analyzed, and its reduction to a single, unique solution by means of the hybrid kinetic modeling is shown. The algorithm reduces the rotational ambiguity and improves the quality of the kinetic fitting. Numerical results are also presented for a multi-component catalytic reaction system that obeys the Michaelis-Menten kinetics. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The kinetics of the hydroformylation of 3,3-dimethyl-1-butene with a rhodium monophosphite catalyst has been studied in detail. Time-dependent concentration profiles covering the entire olefin conversion range were derived from in situ high-pressure FTIR spectroscopic data for both, pure organic components and catalytic intermediates. These profiles fit to Michaelis-Menten-type kinetics with competitive and uncompetitive side reactions involved. The characteristics found for the influence of the hydrogen concentration verify that the pre-equilibrium towards the catalyst substrate complex is not established. It has been proven experimentally that the hydrogenolysis of the intermediate acyl complex remains rate limiting even at high conversions when the rhodium hydride is the predominant resting state and the reaction is nearly of first order with respect to the olefin. Results from in situ FTIR and high-pressure (HP) NMR spectroscopy and from DFT calculations support the coordination of only one phosphite ligand in the dominating intermediates and a preferred axial position of the phosphite in the electronically saturated, trigonal bipyramidal (tbp)-structured acyl rhodium complex. [ABSTRACT FROM AUTHOR]

Recent developments in the synthesis of chiral phosphorus ligands are summarized. Main emphasis is given to the multitude of protocols for their synthesis starting from compounds of the chiral pool or by using other easily available chiral starting materials. Besides mono- and bidentate P-ligands hybrid ligands bearing N, O, or olefinic groups as second ligating units are addressed. The syntheses of new P-chirogenic ligands, as well as ligands with supramolecular structures are likewise reviewed. In appropriate cases structures of related privileged ligands are given for comparison. When available, the efficiency of the new ligands for metal catalyzed reactions are briefly assessed. [ABSTRACT FROM AUTHOR]

The article discusses a protocol for the homogeneously catalyzed amination of alcohols in water, which can be applied for several synthetic tasks in academic and industrial scale. It describes hydrogen autotransfer or borrowing hydrogen methodology based on a catalytic dehydrogenation/hydrogenation mechanism for which the metal serves as a temporary hydrogen acceptor/donor. The methodology has been used in producing numerous secondary and tertiary amines.

A major problem of multivariate curve resolution methods is the underlying non‐uniqueness of the pure component decompositions. This raises the question how a chemical experiment should be designed so that the solution ambiguity is as small as possible. Changes of the reaction conditions belong to the possible variations whereas for a fixed chemical reaction system, the pure component spectra appear to be unchangeable. The paper investigates and discusses the possibility to design a chemical experiment in a way that minimizes the ambiguity of the factorization. The analysis identifies regions of the spectra that are responsible for a small ambiguity. Certain sources are identified that are responsible for an increased ambiguity by means of an a posteriori analysis. This results in recommendations how to construct spectral measurements incorporating a reduced factorization ambiguity. Furthermore, lower bounds on an unavoidable base level of ambiguity are specified under the constraint of fixed reactants. The problem analysis is accompanied by investigations of several experimental data sets. [ABSTRACT FROM AUTHOR]

Abstract: Borgen plots are low‐dimensional representations of the set of all nonnegative factorizations of spectral data matrices. Classical Borgen plots are limited to nonnegative data and can be constructed for the spectral factor or for the concentration profiles. In the first part of this paper, a simultaneous construction of the two dual Borgen plots is presented, which intensively exploits the underlying duality principles. The second part introduces algorithmic enhancements which make the simultaneous Borgen plot construction possible for noisy experimental data matrices which can contain small negative matrix entries. The new method is tested for FT‐IR spectral data from the Rhodium catalyzed hydroformylation process. The results are compared to those by the FACPACK‐implementation of the polygon inflation method. [ABSTRACT FROM AUTHOR]

A scented trail The cover picture shows two people who have never met in real life: Otto Roelen (1897–1993), the discoverer of the hydroformylation reaction, and Gabrielle Bonheur “Coco” Chanel (1883–1971). Both had completely different lives. He was a cautious scientist who went largely unnoticed, even amongst the community of chemists during his active career. She was the exciting “Grande Dame” of fashion, with the attitude of a liberated and assertive woman. Their paths crossed when Coco, out of several samples developed by her perfumer, opted for sample number 5 (“Chanel No 5”), the sample that happened to contain the highest proportion of linear aldehydes. At this time, in 1922, these aldehydes were extracted from valuable plants. Years later, aldehydes used for this and other famous perfumes can be prepared more easily by hydroformylation with homogeneous catalysts and syngas, as E. V. Gusevskaya, J. Jiménez‐Pinto, and A. Börner describe in their Review on p. 382 ff. [ABSTRACT FROM AUTHOR]

The article proposes a highly efficient protocol for the enantioselective hydroformylation of α-substituted acrylates. It defines hydroformylation as the process of preparing aldehydes by the reaction of olefins with a mixture of carbon monoxide and hydrogen in the presence of a metal catalyst. The principle of regioselective hydroformylation is illustrated. Also described are the P-chirogenic ligands used for asymmetric hydroformylation.

A picture of a disk and musical notes are presented.