Hydroformylation spectroscopic studies

The monosulfonated PPh derivative, Ph2P(m-C6H4S03K) (DPM) and its rhodium complex, HRh(CO)(DPM)3 have been synthesized and characterized by IR and NMR spectroscopic techniques. The data showed that the structure was similar to [HRh(CO)(PPh3)3]. The catalytic activity and selectivity of [HRh(CO)(DPM)3] in styrene hydroformylation were studied in biphasic catalytic systems.420 421 Rh1 complexes [Rh(acac)(CO)(PR3)] with tpa (131), cyep (132), (126), ompp (133), pmpp (134), tmpp (135), PPh2(pyl), PPh(pyl)2, and P(pyl)3 were characterized with NMR and IR spectra. Complexes with (131), (132), and (126) were catalysts for hydrogenation of C—C and C—O bonds, isomerization of alkenes, and hydroformylation of alkenes.422 Asymmetric hydroformylation of styrene was performed using as catalyst precursor [Rh(//-0 Me)(COD)]2 associated with sodium salts of m-sulfonated diarylphosphines.423... 

A method for observing intermediates directly in the reaction cycle is in situ IR spectroscopy under reaction conditions. As early as 1975, Penninger published a contribution concerning in situ IR spectroscopic studies of cobalt carbonyl modified by tri-u-butylphosphine as a hydroformylation catalyst [58] at relatively low catalyst concentrations of 2 mmoll-1. The observed carbonyl... 

To verify the homogeneous nature of Rh-3-SILP catalysts, as previously suggested based on IR and NMR spectroscopic studies, [30] kinetic experiments have also been conducted with the catalyst. Here, a continuous fixed-bed reactor setup equipped with online gas-chromatography, described elsewhere in detail, [31] was applied. The general rate law for the hydroformylation of propene was assumed ... 

Studies of stoichiometric hydroformylation, spectroscopic identification, isolation, and transformation of intermediates provided valuable information of the understanding of the catalytic reaction. Despite the complexity of the process, important conclusions were also drawn from kinetic studies. 

In situ IR spectroscopic studies have been carried out on the C02(C0)8 plus PBu"-based catalytic system with ethylene or n-octene as the olefins. Unlike in the case of Co2(CO)8, where HCo(CO)4 and Co(CO)4(COR) may be observed, in the presence of PBu", no Co(CO)3(PBu3)(COR) or Co(CO)3(PBu3))(R) types of complexes could be seen. This presumably is because of low concentrations of such intermediates under operating conditions. The mechanism of hydroformylation is assumed to be similar to the one shown in Fig. 5.7. Very little direct mechanistic evidence at a molecular level is available on the aldehyde hydrogenation reaction. 

In the face of these confusing results, Stanley and co-workers decided to initiate an extensive series of in situ spectroscopic studies to understand what was occurring under hydroformylation conditions with the neutral and dicationic precursor complexes rac-1 and rac-4, why they give such dramatically different catalytic results, in marked contrast to mononuclear hydroformylation catalyst. In a recent book on catalysis by di- and polynuclear metal complexes, edited by R. D. Adams and F. A. Cotton, George G. Stanley gives a detailed account of this fascinating story which reads as exciting as a detective novel. [12]... 

King RB, King AD Jr, Iqbal MZ (1979) ALkybhodium tetracarbonyl derivatives as catalytic intermediates in homogeneous hydroformylation reactions. An infrared spectroscopic study. J Am Chem Soc 101(17) 4893-4896... 

Garland M, Bor G (1989) Infrared spectroscopic studies on metal carbrniyl compounds. 24. Observation of the infrared spectrum of an acyirhodium tetracarbonyl during the hydroformylation of olefins with rhodium-containing catalyst preciusors. friOTg Chem 28(3) 410-413... 

The hydroformylation of 1-octene and the i-octenes was performed with the precursor [Pt(sixantphos)Cl2]. For the internal alkenes, selective tandem isomeriza-tion/hydroformylation toward n-nonanal was observed. In situ UV-Vis spectroscopic studies revealed rapid formation of the corresponding Pt-stannate complex upon reaction with SnCl2, whereas high-pressure in situ IR spectroscopy showed the formation of a Pt—CO species and a short-lived Pt— H species under syngas, as well as a rapid evolution of aldehyde product upon addition of 1-octene to the preformed catalyst in the IR autoclave [73]. 

Chiral diphosphites based on (2R,3R)-butane-2,3-diol, (2R,4R)-pentane-2,4-diol, (25, 5S)-hexane-2,5-diol, (lS -diphenylpropane-hS-diol, and tV-benzyltartarimide as chiral bridges have been used in the Rh-catalyzed asymmetric hydroformylation of styrene. Enantioselectivities up to 76%, at 50% conversion, have been obtained with stable hydridorhodium diphosphite catalysts. The solution structures of [RhH(L)(CO)2] complexes have been studied NMR and IR spectroscopic data revealed fluxional behavior. Depending on the structure of the bridge, the diphosphite adopts equatorial-equatorial or equatorial-axial coordination to the rhodium. The structure and the stability of the catalysts play a role in the asymmetric induction.218... 

In this review, we will discuss the use of in situ spectroscopic techniques, in combination with kinetic and isotopic labeling studies, to obtain a detailed mechanistic insight of the rhodium catalyzed hydroformylation. 

The synergistic effect often observed in bimetallic systems was further explored by Garland and coworkers. The hydroformylation of 3,3-dimethylbut-l-ene to form 4,4-dimethylpentanal in >95% selectivity at room temperature with [Rli4(CO)i2]-[Mn2(CO)io/HMn(CO)5] as catalyst coprecursors was investigated using in situ PT-IR spectroscopic techniques and kinetic studies revealing evidence of a bimetallic catalytic binuclear elimination reaction (CBER). 

Corroles are tetrapyrrole macrocycles that are closely related to porphyrins, with one carbon atom less in the onter periphery and one NH proton more in their inner core. They may also be considered as the aromatic version (identical skeleton) of the only partially conjugated corrin, the cobalt-coordinating ligand in Vitamin B. Two potential application of corroles are in tumor detection and their use in photovoltaic devices. Selective snbstitntion of corroles via nitration, hydroformylation, and chlorosulfonation for the gallinm were studied in detail and the respective mechanistic pathways and spectroscopic data were reported, (an example is shown in Fignre 27). Overall, over 139 varions corroles were synthesized and the effect of various metal complexation pertaining to their selective reactivity examined. ... 

In situ FT-IR and NMR studies on rac-1, however, revealed the catalytically active species to be a dicationic Rh(+II)-Rh(+II) complex The dicationic percursor rac-[Rh2(CO)4(7/ 7/ -L)] + (rac-8), which generates under hydroformylation conditions the same active species and gives identical spectroscopic results as rac-1, was shown to react, under CO atmosphere, with carbon monoxide to give rac-[Rh2(CO)6(i/ t/ -L)]2 (rac-9). Under syn gas (CO/H2) atmosphere, rac-9 takes up molecular hydrogen to give, with elimination of CO (and presumably through the intermediacy of uncharacterized species rac-10 and rac-11), a complex which... 

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