Rhodium computational study

Most Pauson-Khand reactions have been conducted with an alkene, an alk5me, and CO. However, PKRs have been developed with aUenynes (Scheme 17.36). Narasaka reported the first example of an intramolecular allenyne PKR catalyzed by an iron complex, and Brum-mond has extensively studied the allenic Pauson-Khand reaction. These reactions have been catalyzed by the combination of Mo(CO) and DMSO or by [Rh(CO)2Cl]2, and several examples are shown in Equations 17.77 and 17.78. - The reactions in Equations 17.77 and 17.78 illustrate the different regiochemistry of the products from reactions catalyzed by molybde num and rhodium. Computational studies indicate that different geometries of octahedral Mo(0), and square-planar Rh(I) species account for the different regioselectivities. ... 

A thorough computational study of this process has been carried out using B3LYP/ONIOM calculations.31 The rate-determining step is found to be the formation of the rhodium hydride intermediate. The barrier for this step is smaller for the minor complex than for the major one. Additional details on this study can be found at ... 

Status of the Computational Study of Rhodium-Complex-Catalyzed Enantioselective Hydrogenation... 

Abstract The applications of hybrid DFT/molecular mechanics (DFT/MM) methods to the study of reactions catalyzed by transition metal complexes are reviewed. Special attention is given to the processes that have been studied in more detail, such as olefin polymerization, rhodium hydrogenation of alkenes, osmium dihydroxylation of alkenes and hydroformylation by rhodium catalysts. DFT/MM methods are shown, by comparison with experiment and with full quantum mechanics calculations, to allow a reasonably accurate computational study of experimentally relevant problems which otherwise would be out of reach for theoretical chemistry. 

One computational study see Molecular Orbital Theory) has appeared using RhCl(PH3)2 to model the rhodium-catalyzed hydroboration of ethylene see Hydroboration Catalysis). Both associative and dissociative pathways were examined (equation 47). In the associative path, three possible... 

Abstract Computational methods are an indispensible tool for the study of metal-organic reaction mechanisms. A particularly fruitful area is that of transition metal-catalyzed hydrogenations, including enantioselective versions that are extensively used at both the laboratory and the industrial scale. This review covers computational studies of rhodium-, ruthenium-, and iridium-catalyzed hydrogenation of enamides, acrylamides, carbonyls, and unactivated olefins. The evolution of the mechanistic models and the relationship of the computational studies to experimental studies are discussed. 

This chapter provides an overview of the current state of the understanding of the mechanism of hydrogenations of double bonds catalyzed by the most commonly used transition metals, rhodium, iridium, and ruthenium. The focus of the review will be on recent computational studies, but older computational work and experimental investigations will be discussed in context. Where appropriate, open questions and mechanistic controversies will be addressed. 

On the other hand, the dirhodium bridge caged within a lantern structure is thought to be essential to the success of dirhodium complexes in which two rhodium atoms are surrounded by four ligands in a nominal symmetry. Both computational studies and characterization of dirhodium car-benoid intermediates suggested that the intermediate adopts a Rh—Rh=C framework. In another word, two rhodium atoms are bound to one carbene center, and the bonding scenario obeys the three-center orbital paradigm. As such, metal carbenoids derived from chiral Rh complexes and donor/ acceptor diazo compounds are routinely utilized. 

A few studies of isolated metal-silyl complexes and ttie computational study of rhodium-sUyl complexes illustrate the insertion of olefins into metal-silicon bonds. Wrighton studied the photochemical reaction of iron-silyl complexes witti ettiylene (Scheme 9.13). Photolysis of Cp FefCOl fSiMej) in the presence of ettiylene forms Cp Fe(CO)(CjHJ(SiMej). This complex appears to insert ethylene, but ttie 16-electron insertion product is unstable and forms the corresponding vinylsilane and iron hydride complexes as products. Photolysis of Cp Fe(CO)j(SiMe3) in the presence of ethylene and CO forms ttie p-silylaDcyl complex containing two CO ligands. 

Gridnev, I. D. Liu, Y. Imamoto, T. Mechanism of asymmetric hydrogenation of P-dehydroamino acids catalyzed by rhodium complexes Large-scale experimental and computational study. ACS Catal. 2014,4,203-219. 

Abstract The application of QM/MM methods to the study of the reaction mechanisms involved in chemo-, regio-, and enantio- selective processes has been a very productive area of research in the last two decades. This review summarizes basic general ideas in both QM/MM methods and the computational study of selectivity and presents selected results on the study of three of the most representative examples of these applications rhodium-catalyzed hydrogenation, rhodium-catalyzed hydroformylation, and copper-catalyzed cyclopropanation. 

Many rhodium(II) complexes are excellent catalysts for metal-carbenoid-mediated enantioselective C-H insertion reactions [101]. In 2002, computational studies by Nakamura and co-workers suggested the dirhodium tetracarboxylate catalyzed diazo compounds insertion reaction to alkanes C-H bonds proceed through a three-centered hydride-transfer-like transition state (Fig. 25) [102]. Only one rhodium atom of the catalyst is involved in the formation of rhodium carbene intermediate, while the other rhodium atom served as a mobile ligand, which enhanced the electrophilicity of the first one and facilitate the cleavage of rhodium-carbon bond. In this case, the metal-metal bond constitutes a special example of Lewis acid activation of Lewis acidic transition-metal catalyst. 

I) A, respectively]—compounds that are thought to possess modest residual B—H interactions." The degree of activation of the B—H bond in 48 can be further put in context when compared with the half-sandwich rhodium systems reported by Flartwig and coworkers. Thus, the short B—H contacts determined in Cp Rli(Bpin)2(H)2 (51) and Cp Rh(Bpin)3(H) (52) (<1.70 A), for example, are indicative of the retention of structurally (and chemically) more significant B—H interactions, an assertion given further weight by computational studies." ... 

Extensive spectroscopic and other evidences are available for all the three catalytic cycles. For the Co-based catalytic cycle, good kinetic, spectroscopic, and structural data on model complexes exist. For rhodium-catalyzed carbonylation, oxidative addition is found to be the rate-determining step. In contrast, for iridium-catalyzed carbonylation, insertion of CO is the rate-determining step. Thus kinetic measurements show that for 4.13 the insertion reaction is about 700 times faster than that for 4.11. Computational studies, as mentioned earlier (see 3.5), are also in agreement with the kinetic data. 

Rhodium complexes, formed in situ with [Rh(COD)2]BF4 and monodentate chiral spiro phosphite and phosphine ligands, catalyse the AH of both (Z)- and (E)-P-arylenamides with up to 97% ee. A library of 19 chiral binol-monophosphite ligands containing a phthalic acid secondary bis-amide group has been synthesized and screened for use in stereocontrol of rhodium-catalysed hydrogenation of several prochiral dehydroamino esters and enamides. Spectroscopic and computational studies... 

Tye JW, Hartwig IF (2009) Computational studies of the relative rates for migratory insertions of alkcmes into square-planar, methyl, -amido, and -hydroxo complexes of rhodium. J Am Chem Soc 131(41) 14703-14712... 

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