Complexes with heterocyclic nitrogen ligands—III. Cationic rhodium(I) derivatives and applications in catalysis

Cationic rhodium(I) complexes containing 4,4′-disubstituted 2,2′-bipyridines: A systematic variation on electron density over the metal centre

“…It is surprising that the selectivity of this reaction shows little dependence on the ligand, as we have demonstrated that employing the system [(l-acetato)(1,5-cyclooctadien)rhodium(I)]/PR 3 the selectivity depends strongly on the donation ability of PR 3 : the more donating the ancillary, the greater the chemoselectivity for hydroformylation and the diasteroselectivity for 8 are. These complexes have a very similar behaviour to the unpromoted system where the complex [(l-acetato)(1,5-cyclooctadien)rhodium(I)] readily generate [Rh(CO) 3 H] under hydroformylation conditions [21].…”

“…A preliminary evaluation on the catalytic behaviour of this series of complexes on camphene hydroformylation showed that the catalytic activity decreases with the increase of the Rh-bipy bond strength. The selectivity on b-pinene hydroformylation indicates that most of the catalytic activity is carried out by [Rh(CO) 3 H] which is formed in situ from the bipy complexes under the rather harsh reaction conditions employed. Nevertheless, this series of complexes is promising for basic catalytic and electrocatalytic studies as there is a great variation on electron density in the metal centre with virtually no variation in its steric environment.…”

“…On the other hand, for the substituents containing electron-donating groups (CH 3 O, CH 3 ), the conversion of the substrate is slower and the turnover rate is lower. These results suggest that the bipyridine complexes are acting as a precursor for [Rh(CO) 3 H], which carries the fastest catalytic cycle and even at low concentration can account for the observed product distribution. In other words, the complexes containing bipyridines, have low activity compared to [Rh(CO) 3 H].…”

“…These results suggest that the bipyridine complexes are acting as a precursor for [Rh(CO) 3 H], which carries the fastest catalytic cycle and even at low concentration can account for the observed product distribution. In other words, the complexes containing bipyridines, have low activity compared to [Rh(CO) 3 H]. Differences in turnover rates observed for camphene hydroformylation may be related to the ability of the complex to deliver the true catalyst: the stronger the X 2 -bipy-Rh bound, the slower the formation of [Rh(CO) 3 H] is, and, as a consequence, the turnover frequency will be lower.…”

“…Cationic rhodium(I) complexes have long been acknowledged as catalysts precursors for many reactions such as hydrogenation [1] or transfer hydrogenation [2] of double-bonds, water gas shift reaction [3], amination [4], hydroamination [5], hydroformylation [6][7][8], among others. Although phosphorus ligands are more widely used for these reactions, in many instances nitrogen-donors such as 2,2 0 -bipyridines have been successfully employed [9][10][11][12][13][14][15][16][17][18][19][20].…”

Cationic rhodium(I) complexes containing 4,4′-disubstituted 2,2′-bipyridines: A systematic variation on electron density over the metal centre

“…It is surprising that the selectivity of this reaction shows little dependence on the ligand, as we have demonstrated that employing the system [(l-acetato)(1,5-cyclooctadien)rhodium(I)]/PR 3 the selectivity depends strongly on the donation ability of PR 3 : the more donating the ancillary, the greater the chemoselectivity for hydroformylation and the diasteroselectivity for 8 are. These complexes have a very similar behaviour to the unpromoted system where the complex [(l-acetato)(1,5-cyclooctadien)rhodium(I)] readily generate [Rh(CO) 3 H] under hydroformylation conditions [21].…”

“…A preliminary evaluation on the catalytic behaviour of this series of complexes on camphene hydroformylation showed that the catalytic activity decreases with the increase of the Rh-bipy bond strength. The selectivity on b-pinene hydroformylation indicates that most of the catalytic activity is carried out by [Rh(CO) 3 H] which is formed in situ from the bipy complexes under the rather harsh reaction conditions employed. Nevertheless, this series of complexes is promising for basic catalytic and electrocatalytic studies as there is a great variation on electron density in the metal centre with virtually no variation in its steric environment.…”

“…On the other hand, for the substituents containing electron-donating groups (CH 3 O, CH 3 ), the conversion of the substrate is slower and the turnover rate is lower. These results suggest that the bipyridine complexes are acting as a precursor for [Rh(CO) 3 H], which carries the fastest catalytic cycle and even at low concentration can account for the observed product distribution. In other words, the complexes containing bipyridines, have low activity compared to [Rh(CO) 3 H].…”

“…These results suggest that the bipyridine complexes are acting as a precursor for [Rh(CO) 3 H], which carries the fastest catalytic cycle and even at low concentration can account for the observed product distribution. In other words, the complexes containing bipyridines, have low activity compared to [Rh(CO) 3 H]. Differences in turnover rates observed for camphene hydroformylation may be related to the ability of the complex to deliver the true catalyst: the stronger the X 2 -bipy-Rh bound, the slower the formation of [Rh(CO) 3 H] is, and, as a consequence, the turnover frequency will be lower.…”

“…Cationic rhodium(I) complexes have long been acknowledged as catalysts precursors for many reactions such as hydrogenation [1] or transfer hydrogenation [2] of double-bonds, water gas shift reaction [3], amination [4], hydroamination [5], hydroformylation [6][7][8], among others. Although phosphorus ligands are more widely used for these reactions, in many instances nitrogen-donors such as 2,2 0 -bipyridines have been successfully employed [9][10][11][12][13][14][15][16][17][18][19][20].…”

Cationic rhodium(I) complexes containing 4,4′-disubstituted 2,2′-bipyridines: A systematic variation on electron density over the metal centre

“…It is surprising that the selectivity of this reaction shows little dependence on the ligand, as we have demonstrated that employing the system [(l-acetato)(1,5-cyclooctadien)rhodium(I)]/PR 3 the selectivity depends strongly on the donation ability of PR 3 : the more donating the ancillary, the greater the chemoselectivity for hydroformylation and the diasteroselectivity for 8 are. These complexes have a very similar behaviour to the unpromoted system where the complex [(l-acetato)(1,5-cyclooctadien)rhodium(I)] readily generate [Rh(CO) 3 H] under hydroformylation conditions [21].…”

“…A preliminary evaluation on the catalytic behaviour of this series of complexes on camphene hydroformylation showed that the catalytic activity decreases with the increase of the Rh-bipy bond strength. The selectivity on b-pinene hydroformylation indicates that most of the catalytic activity is carried out by [Rh(CO) 3 H] which is formed in situ from the bipy complexes under the rather harsh reaction conditions employed. Nevertheless, this series of complexes is promising for basic catalytic and electrocatalytic studies as there is a great variation on electron density in the metal centre with virtually no variation in its steric environment.…”

“…On the other hand, for the substituents containing electron-donating groups (CH 3 O, CH 3 ), the conversion of the substrate is slower and the turnover rate is lower. These results suggest that the bipyridine complexes are acting as a precursor for [Rh(CO) 3 H], which carries the fastest catalytic cycle and even at low concentration can account for the observed product distribution. In other words, the complexes containing bipyridines, have low activity compared to [Rh(CO) 3 H].…”

“…These results suggest that the bipyridine complexes are acting as a precursor for [Rh(CO) 3 H], which carries the fastest catalytic cycle and even at low concentration can account for the observed product distribution. In other words, the complexes containing bipyridines, have low activity compared to [Rh(CO) 3 H]. Differences in turnover rates observed for camphene hydroformylation may be related to the ability of the complex to deliver the true catalyst: the stronger the X 2 -bipy-Rh bound, the slower the formation of [Rh(CO) 3 H] is, and, as a consequence, the turnover frequency will be lower.…”

“…Cationic rhodium(I) complexes have long been acknowledged as catalysts precursors for many reactions such as hydrogenation [1] or transfer hydrogenation [2] of double-bonds, water gas shift reaction [3], amination [4], hydroamination [5], hydroformylation [6][7][8], among others. Although phosphorus ligands are more widely used for these reactions, in many instances nitrogen-donors such as 2,2 0 -bipyridines have been successfully employed [9][10][11][12][13][14][15][16][17][18][19][20].…”

Cationic rhodium(I) complexes containing 4,4′-disubstituted 2,2′-bipyridines: A systematic variation on electron density over the metal centre

“…It is surprising that the selectivity of this reaction shows little dependence on the ligand, as we have demonstrated that employing the system [(l-acetato)(1,5-cyclooctadien)rhodium(I)]/PR 3 the selectivity depends strongly on the donation ability of PR 3 : the more donating the ancillary, the greater the chemoselectivity for hydroformylation and the diasteroselectivity for 8 are. These complexes have a very similar behaviour to the unpromoted system where the complex [(l-acetato)(1,5-cyclooctadien)rhodium(I)] readily generate [Rh(CO) 3 H] under hydroformylation conditions [21].…”

“…A preliminary evaluation on the catalytic behaviour of this series of complexes on camphene hydroformylation showed that the catalytic activity decreases with the increase of the Rh-bipy bond strength. The selectivity on b-pinene hydroformylation indicates that most of the catalytic activity is carried out by [Rh(CO) 3 H] which is formed in situ from the bipy complexes under the rather harsh reaction conditions employed. Nevertheless, this series of complexes is promising for basic catalytic and electrocatalytic studies as there is a great variation on electron density in the metal centre with virtually no variation in its steric environment.…”

“…On the other hand, for the substituents containing electron-donating groups (CH 3 O, CH 3 ), the conversion of the substrate is slower and the turnover rate is lower. These results suggest that the bipyridine complexes are acting as a precursor for [Rh(CO) 3 H], which carries the fastest catalytic cycle and even at low concentration can account for the observed product distribution. In other words, the complexes containing bipyridines, have low activity compared to [Rh(CO) 3 H].…”

“…These results suggest that the bipyridine complexes are acting as a precursor for [Rh(CO) 3 H], which carries the fastest catalytic cycle and even at low concentration can account for the observed product distribution. In other words, the complexes containing bipyridines, have low activity compared to [Rh(CO) 3 H]. Differences in turnover rates observed for camphene hydroformylation may be related to the ability of the complex to deliver the true catalyst: the stronger the X 2 -bipy-Rh bound, the slower the formation of [Rh(CO) 3 H] is, and, as a consequence, the turnover frequency will be lower.…”

“…Cationic rhodium(I) complexes have long been acknowledged as catalysts precursors for many reactions such as hydrogenation [1] or transfer hydrogenation [2] of double-bonds, water gas shift reaction [3], amination [4], hydroamination [5], hydroformylation [6][7][8], among others. Although phosphorus ligands are more widely used for these reactions, in many instances nitrogen-donors such as 2,2 0 -bipyridines have been successfully employed [9][10][11][12][13][14][15][16][17][18][19][20].…”