15 research outputs found
Rhodium(I)-Catalyzed Intermolecular Hydroacylation of α-Keto Amides and Isatins with Non-Chelating Aldehydes.
The application of the bidentate, electron-rich bisphosphine ligand, 1,3-bis(dicyclohexyl)phosphine-propane (dcpp), in rhodium(I)-catalyzed intermolecular ketone hydroacylation is herein described. Isatins and α-keto amides are shown to undergo hydroacylation with a variety of non-chelating linear and branched aliphatic aldehydes. Also reported is the synthesis of new bidentate chiral phosphine ligands, and their application in hydroacylation is discussed
Recommended from our members
Rhodium(I)-Catalyzed Intermolecular Hydroacylation of α-Keto Amides and Isatins with Non-Chelating Aldehydes.
The application of the bidentate, electron-rich bisphosphine ligand, 1,3-bis(dicyclohexyl)phosphine-propane (dcpp), in rhodium(I)-catalyzed intermolecular ketone hydroacylation is herein described. Isatins and α-keto amides are shown to undergo hydroacylation with a variety of non-chelating linear and branched aliphatic aldehydes. Also reported is the synthesis of new bidentate chiral phosphine ligands, and their application in hydroacylation is discussed
Stable Borocyclic Radicals via Frustrated Lewis Pair Hydrogenations
The
synthesis and isolation of stable main group radicals remains
an ongoing challenge. Here we report the application of frustrated
Lewis pair chemistry to the synthesis of boron-containing radicals.
H<sub>2</sub> activation with polyaromatic diones and BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> leads to radical formation in good yields.
These radicals are robust; they do not decompose on silica gel or
react with O<sub>2</sub> and are stable at 35 °C under N<sub>2</sub> indefinitely. The mechanism of formation is explored experimentally,
with support from DFT calculations. EPR and UV/vis spectroscopy as
well as cyclic voltammetry data are provided, and the radicals are
shown to react with cobaltocenes in one-electron chemical reductions
to their corresponding borate anions
Hydrogen Activation by an Aromatic Triphosphabenzene
Aromatic hydrogenation is a challenging transformation typically requiring alkali or transition metal reagents and/or harsh conditions to facilitate the process. In sharp contrast, the aromatic heterocycle 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene is shown to be reduced under 4 atm of H-2 to give [3.1.0]bicylo reduction products, with the structure of the major isomer being confirmed by X-ray crystallography. NMR studies show this reaction proceeds via a reversible 1,4-H-2 addition to generate an intermediate species, which undergoes an irreversible suprafacial hydride shift concurrent with P P bond formation to give the isolated products. Further, para-hydrogen experiments confirmed the addition of H-2 to triphosphabenzene is a bimolecular process. Density functional theory (DFT) calculations show that facile distortion of the planar triphosphabenzene toward a boat-conformation provides a suprafacial combination of vacant acceptor and donor orbitals that permits this direct and uncatalyzed reduction of the aromatic molecule.</p
Optical and electronic properties of air-stable organoboron compounds with strongly electron-accepting bis(fluoromesityl)boryl groups
Three compounds with phenyl (1), 4-tert-butylphenyl (2) and 4-N,N-diphenylaminophenyl (3) groups attached to bis(fluoromesityl)boryl ((FMes)2B) through B–C bonds have been prepared. The restricted rotation about the B–C bonds of boron-bonded aryl rings in solution has been studied by variable-temperature 19F NMR spectroscopy, and through-space F–F coupling has been observed for 3 at low temperature. Steric congestion inhibits binding of 1 by Lewis bases DABCO and tBu3P and the activation of H2 in their presence. Photophysical and electrochemical studies have been carried out on 2, 3, and an analogue of 3 containing a bis(mesityl)boryl ((Mes)2B) group, namely 4. Both 2 and 3 show bright emission in nonpolar solvents and in the solid-state, very strong electron-accepting ability as measured by cyclic voltammetry, and good air-stability. In addition, 2 displayed unusually long-lived emission (τ = 2.47 s) in 2-MeTHF at 77 K. The much stronger acceptor strength of (FMes)2B than (Mes)2B leads to significantly red-shifted emission in solution and the solid state, stronger emission solvatochromism, and significantly lower reduction potentials. Theoretical calculations confirm that 2 and 3 tend to form highly twisted excited states with good conjugation between one FMes group and the boron atom, which correlate well with their blue-shifted solid-state emissions and low kr values in solution
Reactions of Boron-Derived Radicals with Nucleophiles
Reactions of phenanthrenedione- and pyrenedione-derived borocyclic
radicals, C<sub><i>n</i></sub>H<sub>8</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub><sup>•</sup> (<i>n</i> = 14 (<b>1</b>), 16 (<b>3</b>)), with a variety
of nucleophiles have been studied. Reaction of <b>1</b> with
PÂ(<i>t</i>-Bu)<sub>3</sub> affords the zwitterion 3-(<i>t</i>-Bu)<sub>3</sub>PC<sub>14</sub>H<sub>7</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> (<b>5</b>) in addition
to the salt [HPÂ(<i>t</i>-Bu)<sub>3</sub>]Â[C<sub>14</sub>H<sub>8</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>] (<b>6</b>). In contrast, the reaction of <b>1</b> with
PPh<sub>3</sub> proceeds to give two regioisomeric zwitterions, 1-(Ph<sub>3</sub>P)ÂC<sub>14</sub>H<sub>7</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> (<b>7a</b>) and 3-(Ph<sub>3</sub>P)ÂC<sub>14</sub>H<sub>7</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> (<b>7b</b>), as well as the related boronic ester C<sub>14</sub>H<sub>8</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>) (<b>2</b>). In a similar fashion, <b>3</b> reacted with PPh<sub>3</sub> to give 3-(Ph<sub>3</sub>P)ÂC<sub>16</sub>H<sub>7</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> (<b>8a</b>), 1-(Ph<sub>3</sub>P)ÂC<sub>16</sub>H<sub>7</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> (<b>8b</b>), and boronic
ester C<sub>16</sub>H<sub>8</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>) (<b>4</b>). Reactions of secondary phosphines Ph<sub>2</sub>PH and <i>t</i>Bu<sub>2</sub>PH with <b>3</b> yield 3-(R<sub>2</sub>PH)ÂC<sub>16</sub>H<sub>7</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> (R = Ph (<b>9</b>), <i>t-</i>Bu (<b>10</b>)). The reaction of <b>1</b> with N-heterocyclic carbene IMes afforded 3-(IMes)ÂC<sub>14</sub>H<sub>7</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> (<b>11</b>) and [IMesH]Â[C<sub>14</sub>H<sub>8</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>] (<b>12</b>), while the reactions with quinuclidine and DMAP afforded the species
3-(C<sub>7</sub>H<sub>13</sub>N)ÂC<sub>14</sub>H<sub>7</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> (<b>13</b>) and [HÂ(NC<sub>7</sub>H<sub>13</sub>)<sub>2</sub>]Â[C<sub>14</sub>H<sub>8</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>] (<b>14</b>), and the salt [9,10-(DMAP)<sub>2</sub>C<sub>14</sub>H<sub>8</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>]Â[C<sub>14</sub>H<sub>8</sub>O<sub>2</sub>BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>] (<b>15</b>), respectively. These products have been fully
characterized, and the mechanism for the formation of these products
is considered in the light of DFT calculations
An Improved Method for the Synthesis of <i>F</i>-BODIPYs from Dipyrrins and Bis(dipyrrin)s
An improved methodology for the synthesis of <i>F-</i>BODIPYs from dipyrrins and bis(dipyrrin)s is reported. This strategy employs lithium salts of dipyrrins as intermediates that are then treated with only 1 equiv of boron trifluoride diethyletherate to obtain the corresponding <i>F-</i>BODIPYs. This scalable route to <i>F</i>-BODIPYs renders high yields with a facile purification process involving merely filtration of the reaction mixture through Celite in many cases
An Improved Method for the Synthesis of <i>F</i>-BODIPYs from Dipyrrins and Bis(dipyrrin)s
An improved methodology for the synthesis of <i>F-</i>BODIPYs from dipyrrins and bis(dipyrrin)s is reported. This strategy employs lithium salts of dipyrrins as intermediates that are then treated with only 1 equiv of boron trifluoride diethyletherate to obtain the corresponding <i>F-</i>BODIPYs. This scalable route to <i>F</i>-BODIPYs renders high yields with a facile purification process involving merely filtration of the reaction mixture through Celite in many cases
An Improved Method for the Synthesis of <i>F</i>-BODIPYs from Dipyrrins and Bis(dipyrrin)s
An improved methodology for the synthesis of <i>F-</i>BODIPYs from dipyrrins and bis(dipyrrin)s is reported. This strategy employs lithium salts of dipyrrins as intermediates that are then treated with only 1 equiv of boron trifluoride diethyletherate to obtain the corresponding <i>F-</i>BODIPYs. This scalable route to <i>F</i>-BODIPYs renders high yields with a facile purification process involving merely filtration of the reaction mixture through Celite in many cases