A dinuclear phosphite rhodium(I) complex obtained by syngas treatment of a Rh/hydroxy phosphonite olefin hydroformylation precatalyst.

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.

Synthesis of C2-Symmetric Diphosphormonoamidites and Their Use as Ligands in Rh-Catalyzed Hydroformylation: Relationships between Activity and Hydrolysis Stability.

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.

On the ambiguity of the reaction rate constants in multivariate curve resolution for reversible first-order reaction systems.

If for a chemical reaction with a known reaction mechanism the concentration profiles are accessible only for certain species, e.g. only for the main product, then often the reaction rate constants cannot uniquely be determined from the concentration data. This is a well-known fact which includes the so-called slow-fast ambiguity. This work combines the question of unique or non-unique reaction rate constants with factor analytic methods of chemometrics. The idea is to reduce the rotational ambiguity of pure component factorizations by considering only those concentration factors which are possible solutions of the kinetic equations for a properly adapted set of reaction rate constants. The resulting set of reaction rate constants corresponds to those solutions of the rate equations which appear as feasible factors in a pure component factorization. The new analysis of the ambiguity of reaction rate constants extends recent research activities on the Area of Feasible Solutions (AFS). The consistency with a given chemical reaction scheme is shown to be a valuable tool in order to reduce the AFS. The new methods are applied to model and experimental data.

In Situ FTIR and NMR Spectroscopic Investigations on Ruthenium-Based Catalysts for Alkene Hydroformylation.

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.

A multiresolution approach for the convergence acceleration of multivariate curve resolution methods.

Modern computerized spectroscopic instrumentation can result in high volumes of spectroscopic data. Such accurate measurements rise special computational challenges for multivariate curve resolution techniques since pure component factorizations are often solved via constrained minimization problems. The computational costs for these calculations rapidly grow with an increased time or frequency resolution of the spectral measurements. The key idea of this paper is to define for the given high-dimensional spectroscopic data a sequence of coarsened subproblems with reduced resolutions. The multiresolution algorithm first computes a pure component factorization for the coarsest problem with the lowest resolution. Then the factorization results are used as initial values for the next problem with a higher resolution. Good initial values result in a fast solution on the next refined level. This procedure is repeated and finally a factorization is determined for the highest level of resolution. The described multiresolution approach allows a considerable convergence acceleration. The computational procedure is analyzed and is tested for experimental spectroscopic data from the rhodium-catalyzed hydroformylation together with various soft and hard models.

An operando FTIR spectroscopic and kinetic study of carbon monoxide pressure influence on rhodium-catalyzed olefin hydroformylation.

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.

Development of a ruthenium/phosphite catalyst system for domino hydroformylation-reduction of olefins with carbon dioxide.

An efficient domino ruthenium-catalyzed reverse water-gas-shift (RWGS)-hydroformylation-reduction reaction of olefins to alcohols is reported. Key to success is the use of specific bulky phosphite ligands and triruthenium dodecacarbonyl as the catalyst. Compared to the known ruthenium/chloride system, the new catalyst allows for a more efficient hydrohydroxymethylation of terminal and internal olefins with carbon dioxide at lower temperature. Unwanted hydrogenation of the substrate is prevented. Preliminary mechanism investigations uncovered the homogeneous nature of the active catalyst and the influence of the ligand and additive in individual steps of the reaction sequence.

Carbonylation of the simplest persistent diaminocarbene.

The reactions of the acyclic diaminocarbenes (Me2N)2C and (Ph2N)(iPr2N)C with CO proceed in a 2 : 1 stoichiometric ratio, affording unprecedented betainic oxyallyl species of type [(R2N)2C]2CO.

Carbon-yl{3,3'-di-tert-butyl-5,5'-dimeth-oxy-2,2'-bis-[(4,4,5,5-tetra-methyl-1,3,2-dioxaphospho-lan-2-yl)-oxy]biphenyl-κ(2) P,P'}hydrido(triphenyl-phosphane-κP)rhodium(I) diethyl ether tris-olvate.

In the title compound, [RhH(C74H68O8P2)(C18H15P)(CO)]·3C4H10O, the CHP3 coordination set at the Rh(I) ion is arranged in a distorted trigonal-bipyramidal geometry with the P atoms adopting equatorial coordination sites and the C atom of the carbonyl ligand as well as the H atom adopting the axial sites. The asymmetric unit contains two very similar mol-ecules of the rhodium complex, two half-occupied diethyl ether mol-ecules and further diethyl ether solvent mol-ecules which could not be modelled successfully. Therefore contributions of the latter were removed from the diffraction data using the SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148-155].

Exploring between the extremes: conversion-dependent kinetics of phosphite-modified hydroformylation catalysis.

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.

Dicarbonyl-{3,3'-di-tert-butyl-5,5'-di-meth-oxy-2,2'-bis-[(4,4,5,5-tetra-phenyl-1,3,2-dioxa-phospho-lan-2-yl)-oxy-κP]biphen-yl}hydridorhodium(I) diethyl ether monosolvate.

In the title compound, [Rh(C(74)H(68)O(8)P(2))H(CO)(2)]·C(4)H(10)O, the C(2)HP(2) coordination set at the Rh(I) ion is arranged in a distorted trigonal-planar geometry with one P atom of the diphosphite mol-ecule and the H atom adopting the axial coordination sites.

{2-[Bis(2,4-di-tert-butyl-phen-oxy)phosphan-yloxy-κP]-3,5-di-tert-butyl-phenyl-κC}[(1,2,5,6-η)-cyclo-octa-1,5-diene]rhodium(I) toluene monosolvate.

The reaction of (η(3)-all-yl)[(1,2,5,6-η)-cyclo-octa-1,5-diene]rhodium(I) with tris-(2,4-di-tert-butyl-phen-yl)phosphite in toluene produces the title compound, [Rh(C(42)H(62)O(3)P)(C(8)H(12))]·C(7)H(8), by spontaneous metallation at one of the nonsubstituted phenyl ortho-C atoms of the phosphite mol-ecule. The coordination geometry at the Rh(I) ion is distorted square-planar. The toluene solvent mol-ecule is disordered over two different orientations, with site-occupation factors of 0.810 (2) and 0.190 (2).

Heteroatom-substituted secondary phosphine oxides (HASPOs) as decomposition products and preligands in rhodium-catalysed hydroformylation.

O,O'-3,3'-Di-tert-butyl-5,5'-dimethoxy-1,1'-biphenyl-2,2'-diyl phosphonate (1) is the hydrolysis product of several mono- and bis-phosphites used as ligands in industrial hydroformylation and other catalytic reactions. As a result of a tautomeric equilibrium, this pentavalent heteroatom-substituted phosphine oxide (HASPO) can rearrange to the corresponding trivalent phosphorus compound. The latter is able to react with typical rhodium-containing precursors frequently used for the generation of catalysts. The resulting species were characterised by NMR spectroscopy and X-ray structure analysis. Proof is given that a rhodium complex of 1 forms an active hydroformylation catalyst. Moreover, 1 can add to aldehydes, which are generated as products in the hydroformylation. Thus a broad range of subsequent reactions can be associated with the degradation of the original phosphite ligands, which has a strong influence on the overall outcome of the hydroformylation reaction.

Diastereoisomeric bisphosphite ligands in the hydroformylation of octenes: rhodium catalysis and HP-NMR investigations.

Diastereoisomeric hydroformylation catalysts show differences for the catalyst preformation pathway and a strongly reduced n-octene hydroformylation activity for the (S,S,R)-isomer.