Rhodium

and, Luis A. Oro; Carmona, Daniel

doi:10.1002/9783527619382.ch1

Cited by 13 publications

(10 citation statements)

References 145 publications

(53 reference statements)

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“…In the case of the rhodium catalyst the experimental data point to a dihydride active species and a classical “substrate mechanism” (Scheme ); this is in agreement with the saturation kinetics observed with respect to substrate concentration, the close to first-order dependence on the hydrogen pressure, and a wealth of knowledge on rhodium-catalyzed hydrogenation reactions …”

Section: Resultssupporting

confidence: 81%

Selective Hydrogenation of Cinnamaldehyde and Other α,β-Unsaturated Substrates Catalyzed by Rhodium and Ruthenium Complexes

et al. 2009

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The complexes [Rh(PhBP 3 )(cod)] ( 1) and [{Ru(PhBP 3 )(µ-Cl)} 2 ] (8), containing the tripodal phosphanoborate ligand [PhB(CH 2 PPh 2 ) 3 ] -, are efficient catalysts for the selective hydrogenation of cinnamaldehyde to the corresponding allyl alcohol. Complex 8 is one of the most efficient catalysts reported to date for this reaction, in terms of activity (TOF 527 h -1 ) and selectivity (g97%) under mild reaction conditions (6.8 atm H 2 , 75 °C). The rhodium system also displays good catalytic features in the hydrogenation of cinnamaldehyde (TOF 219 h -1 ), particularly a high selectivity (81%) for this metal in the reduction of the CdO bond. Crotonaldehyde can also be reduced, although the selectivities are not as high as for cinnamaldehyde; 2-cyclohexenone is rapidly and specifically reduced to cyclohexanone by both catalysts. The ruthenium catalyst 8 operates via heterolytic activation of hydrogen, involving monohydride intermediates and possibly ionic hydrogen transfer, while the rhodium complex 1 involves oxidative addition of dihydrogen to form dihydride intermediates and follows a substrate route. Indeed, complex 1 reacts with hydrogen in acetonitrile to give the dihydride complex [Rh(PhBP 3 )(H) 2 (NCMe)] (3), while protonation of one of the phosphane arms of the ligand occurs on treatment of complex 1 with HBF 4 to give the cationic species [Rh{PhB(PH)P 2 }(cod)]BF 4 . The hydride ligands in 3 are easily removed as molecular hydrogen by reaction with CO under atmospheric pressure to give the rhodium(I) complex [Rh(PhBP 3 )(CO) 2 ]. In this reaction, the replacement of acetonitrile by CO takes place previously to the elimination of hydrogen, which indicates that substrates can coordinate to the metal in 3 by replacement of the labile acetonitrile ligand. Under an atmosphere of argon, complex 3 reacts with chloroform to give an equimolecular mixture of the cis and trans isomers of [{Rh(PhBP 3 )(H)(µ-Cl)} 2 ] and, eventually, complex [Rh(PhBP 3 )Cl 2 ] in one day.

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Section: Resultssupporting

confidence: 81%

Selective Hydrogenation of Cinnamaldehyde and Other α,β-Unsaturated Substrates Catalyzed by Rhodium and Ruthenium Complexes

et al. 2009

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“…It is well documented that cyclooctadiene can be hydrogenated to cyclooctane (COA) and liberated from rhodium bisphosphine cations. , Similarly, it was expected that the addition of H 2 to complex 7 would release COA and form a Rh dihydride complex, as had been observed in the reaction of the NBD analogue 2 with H 2 . In fact, the reaction of 7 with H 2 led to complex 8 , which has a different structure, as described below.…”

Section: Resultsmentioning

confidence: 94%

Synthesis, Characterization, and Reactivity of Arene-Stabilized Rhodium Complexes

O’Connor¹,

Kaminsky

Heinekey

et al. 2011

Organometallics

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The synthesis and characterization of (COD)Rh(I) and (NBD)Rh(I) (COD = cyclooctadiene; NBD = norbornadiene) chloride complexes containing the 2-(dicyclohexylphosphino)biphenyl (PCy 2 -biPh) ligand are reported. Abstraction of the halide with Na(BAr F ) 4 yields cationic Rh(I) complexes [(NBD)Rh(PCy 2 biPh)][B(Ar F ) 4 ] (2) and [(COD)Rh(PCy 2 biPh)][B(Ar F ) 4 ] ( 7) (Ar F = 3,5-bis(trifluoromethyl)phenyl). In complex 2, the pendent arene of the ligand is coordinated in an η 2 -fashion to rhodium. Complex 7 exists in two configurations that were characterized by low-temperature NMR spectroscopy. One structure is analogous to 2 with η 2 -coordination of the arene, and the other exhibits η 6 -coordination. These structures interconvert on the NMR time scale at room temperature. Addition of H 2 to complex 2 yields the Rh(III) dihydride complex [(PCy 2 biPh)RhH 2 ][B(Ar F ) 4 ] (5), while the addition of H 2 to 7 generates the Rh(I) olefin complex [(COE)Rh(PCy 2 biPh)][B(Ar F ) 4 ] (8). In both 5 and 8, the pendent arene of the ligand is bound η 6 to Rh. Benzene hydrogenation to cyclohexane using 2 as a catalyst precursor is described. Poisoning experiments indicate that heterogeneous rhodium is likely to be the active catalyst in this arene hydrogenation reaction.

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“…Subsequently, Repo and co-workers designed a linked amine-hydroborane FLP ( 1 ) for the selective cis-hydrogenation of internal alkynes . This reaction proceeds via a hydroboration–H 2 cleavage–protodeboronation mechanism (Figure ), which bears a clear analogy to the classic inner-sphere TM hydrogenation mechanism. , This catalyst displays a high degree of chemoselectivity toward internal alkynes, as upon hydroboration with an olefin and subsequent H 2 splitting, catalyst degradation via loss of C 6 F 5 H was more favorable than alkane release. A similar reaction has also been realized via a hydridoborane/silica-supported phosphine FLP .…”

Section: Metallomimetic Boron In Interelement Cooperative Reactivity...mentioning

confidence: 70%

Metallomimetic Chemistry of Boron

2019

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The study of main-group molecules that behave and react similarly to transition metal (TM) complexes has attracted significant interest in the recent decades. Most notably, the attractive idea of eliminating the all-too-often rare and costly metals from catalysis has motivated efforts to develop main-group-element-mediated reactions. Main-group elements, however, lack the electronic flexibility of many TM complexes that arise from combinations of empty and filled d-orbitals and that seem ideally suited to bind and activate many substrates. In this Review, we look at boron, an element which, despite its non-metal nature, low atomic weight, and relative redox staticity has achieved great milestones in terms of TM-like reactivity. We show how in inter-element cooperative systems, diboron molecules and hypovalent complexes, the fifth element can acquire a truly metallomimetic character. As we discuss, this character is particularly strikingly demonstrated by the reactivity of boron-based molecules with H2, CO, alkynes, alkenes and even with N2.

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Rhodium

Cited by 13 publications

References 145 publications

Selective Hydrogenation of Cinnamaldehyde and Other α,β-Unsaturated Substrates Catalyzed by Rhodium and Ruthenium Complexes

Selective Hydrogenation of Cinnamaldehyde and Other α,β-Unsaturated Substrates Catalyzed by Rhodium and Ruthenium Complexes

Synthesis, Characterization, and Reactivity of Arene-Stabilized Rhodium Complexes

Metallomimetic Chemistry of Boron

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