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

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. H₂ activation with polyaromatic diones and B­(C₆F₅)₃ leads to radical formation in good yields. These radicals are robust; they do not decompose on silica gel or react with O₂ and are stable at 35 °C under N₂ 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_<i>n</i>H₈O₂B­(C₆F₅)₂^• (<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 P­(<i>t</i>-Bu)₃ affords the zwitterion 3-(<i>t</i>-Bu)₃PC₁₄H₇O₂B­(C₆F₅)₂ (<b>5</b>) in addition to the salt [HP­(<i>t</i>-Bu)₃]­[C₁₄H₈O₂B­(C₆F₅)₂] (<b>6</b>). In contrast, the reaction of <b>1</b> with PPh₃ proceeds to give two regioisomeric zwitterions, 1-(Ph₃P)­C₁₄H₇O₂B­(C₆F₅)₂ (<b>7a</b>) and 3-(Ph₃P)­C₁₄H₇O₂B­(C₆F₅)₂ (<b>7b</b>), as well as the related boronic ester C₁₄H₈O₂B­(C₆F₅) (<b>2</b>). In a similar fashion, <b>3</b> reacted with PPh₃ to give 3-(Ph₃P)­C₁₆H₇O₂B­(C₆F₅)₂ (<b>8a</b>), 1-(Ph₃P)­C₁₆H₇O₂B­(C₆F₅)₂ (<b>8b</b>), and boronic ester C₁₆H₈O₂B­(C₆F₅) (<b>4</b>). Reactions of secondary phosphines Ph₂PH and <i>t</i>Bu₂PH with <b>3</b> yield 3-(R₂PH)­C₁₆H₇O₂B­(C₆F₅)₂ (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)­C₁₄H₇O₂B­(C₆F₅)₂ (<b>11</b>) and [IMesH]­[C₁₄H₈O₂B­(C₆F₅)₂] (<b>12</b>), while the reactions with quinuclidine and DMAP afforded the species 3-(C₇H₁₃N)­C₁₄H₇O₂B­(C₆F₅)₂ (<b>13</b>) and [H­(NC₇H₁₃)₂]­[C₁₄H₈O₂B­(C₆F₅)₂] (<b>14</b>), and the salt [9,10-(DMAP)₂C₁₄H₈O₂B­(C₆F₅)₂]­[C₁₄H₈O₂B­(C₆F₅)₂] (<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